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Research ArticleAugust 7, 2023
研究论文August 7， 2023

Catalytic Activation of Molecular Oxygen Toward Producing Hydroxyl Radicals Controllably for Highly Selective Oxidation of Hydroxyl Compounds under Mild Conditions
在温和条件下催化氧以产生羟基自由基以产生羟基自由基，用于羟基化合物的高选择性氧化
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Xin Liu 刘欣
Xin Liu
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
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Hong Ma* 马宏*
Hong Ma
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
*Email: mahong@dicp.ac.cn
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Meiyun Zhang 张美云
Meiyun Zhang
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
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Penghua Che 车鹏华
Penghua Che
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
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Yang Luo 罗阳
Yang Luo
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
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Shujing Zhang 张淑静
Shujing Zhang
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
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Jie Xu* 徐杰*
Jie Xu
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
*Email: xujie@dicp.ac.cn
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https://orcid.org/0000-0003-2535-094X

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ACS Catalysis

Cite this: ACS Catal. 2023, 13, 16, 11104–11116

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https://doi.org/10.1021/acscatal.3c02736

Published August 7, 2023

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Abstract 抽象

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Hydroxyl radicals (OH^•), as one of the most highly oxidizing oxidants, are difficult to utilize in chemical synthesis since they usually cause unavoidable oxidative damage with CO₂ released. Here, a Co–N–C nanomaterial composed of CoN₄ sites on graphitic carbon nitride was constructed, which fulfills the self-cascade activation of O₂ in water, wherein OH^• is guided to generate in a controlled level and exerts a highly selective oxidation role for efficient synthesis of a variety of organic acids by oxidation of furan alcohols, aromatic alcohols, and fatty alcohols under mild conditions. 5-Hydroxymethylfurfural (HMF) reached >99.9% conversion with 94.2% yield of 2,5-furandicarboxylic acid (FDCA) at 25 °C under atmospheric O₂ pressure. This study allows a promising utility of O₂ in a low energy-consuming way independent of light or electricity.
羟基自由基（OH^•）作为最具高度氧化性的氧化剂之一，很难用于化学合成，因为它们通常会在释放 CO₂ 时造成不可避免的氧化损伤。在这里，构建了一种由石墨氮化碳上的 CoN₄ 位点组成的 Co-N-C 纳米材料，它实现了 O₂ 在水中的自级联活化，其中 OH^• 被引导在受控水平生成并发挥高度选择性的氧化作用，通过氧化呋喃醇高效合成多种有机酸，芳香醇和温和条件下的脂肪醇。在 25 °C 的大气 O₂ 压力下，5-羟甲基糠醛（HMF）的转化率达到 >99.9%，2,5-呋喃二羧酸（FDCA）的产率为 94.2%。这项研究允许 O₂ 以低能耗的方式独立于光或电而具有广阔的用途。

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1. Introduction 1. 引言

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Molecular oxygen (O₂) is well acknowledged as an ideal oxidant for high atomic economic production of oxygen-containing chemicals, and facilitating its utility at a low temperature (25–60 °C) close to that of natural enzymes has always been one of the most difficult pursued goals. (1,2) An attractive strategy is to activate O₂ into reactive oxygen species (ROS) such as hydroxyl radicals (OH^•), superoxide radicals (O₂^•–), hydrogen peroxide (H₂O₂), and singlet oxygen (¹O₂), (3) so as to break the limit of spin forbidden between thermodynamically inert O₂ in the triplet state and organic substrates in the singlet state. (4) OH^•, as one of the most highly oxidizing oxidants and typical electrophilic species from O₂, has high positive redox potential (E⁰(OH^•/OH^–) = 1.90 V, E⁰(OH^• + H⁺/H₂O) = 2.73 V). (5) Such superhigh oxidizing ability is of particular interest as critical reaction conditions are not required to overcome the activation energy barrier but generally leads to ability in breaking chemical bonds, destructing organic structures, sterilizing and damaging cells, etc. (5,6) Typically, OH^• provided by an external source of H₂O₂ (e.g., Fenton’s reagent) is adopted in advanced oxidation processes (AOPs) for wastewater treatment, completely degrading water pollutants into CO₂ without leaving residues. (7) However, the excessively generated OH^• due to the rapid reduction by metallic ions such as Fe²⁺ (8) is difficult to exert a highly selective oxidation role for synthesis application purposes. Although there are some examples of using photo- or electrocatalysts (9,10) as well as noble metal catalysts such as Au NPs, (11,12) to achieve in situ formation of OH^•, it is still a challenge for OH^• to be controllably formed from O₂ under mild conditions if only thermocatalysis is to be relied on. For example, Iglesia et al. revealed that catalytic generation of OH^• on the surface of Mn/Na₂WO₄/SiO₂ could enhance the rate and selectivity for oxidative coupling of methane, but operation at a high thermal induction temperature of 1073 K makes this method merely applicable for gas-phase oxidation. (13) To the best of our knowledge, the utilization of OH^• for thermocatalytic selective oxidation over heterogeneous non-noble metal catalysts at room temperature is very difficult and has not been reported.
分子氧（O₂）是公认的高原子经济生产含氧化学品的理想氧化剂，在接近天然酶的低温（25-60 °C）下促进其效用一直是最困难追求的目标之一。（1,2）一个有吸引力的策略是将 O₂ 活化成活性氧（ROS），例如羟基自由基（OH^•）、超氧自由基（O₂^•–）、过氧化氢（H₂O₂）和单重态氧（¹O₂），（3）以打破三重态的热力学惰性 O₂ 和单重态的有机底物之间的自旋限制。（4） OH^•作为氧化性最强的氧化剂之一，也是O₂的典型亲电物质，具有高正氧化还原电位（E⁰（OH^•/OH^–） = 1.90 V，E⁰（OH^• + H⁺/H₂O） = 2.73 V）。（5）这种超高的氧化能力特别值得关注，因为不需要关键反应条件来克服活化能屏障，但通常会导致破坏化学键、破坏有机结构、消毒和破坏细胞等的能力。（5,6）通常，OH^• 由 H₂O₂ 的外部来源提供（例如 Fenton 试剂）用于废水处理的高级氧化过程（AOP），将水污染物完全降解为 CO₂，而不会留下残留物。（7）然而，由于金属离子如 Fe²⁺（8）的快速还原而产生的过量 OH^• 难以发挥用于合成应用目的的高选择性氧化作用。尽管有一些使用光或电催化剂（9,10）以及贵金属催化剂（如 Au NPs）（11,12）来实现 OH^•的原位形成的例子，但如果仅依靠热催化，在温和的条件下由 O₂ 可控地形成 OH^• 仍然是一个挑战。例如，Iglesia 等人揭示了在 Mn/Na₂WO₄/SiO₂ 表面催化生成 OH^• 可以提高甲烷氧化偶联的速率和选择性，但在 1073 K 的高热感应温度下运行使该方法仅适用于气相氧化。（13）据我们所知，在室温下利用 OH^• 对非均相非贵金属催化剂进行热催化选择性氧化非常困难，尚未报道。

To bridge the high oxidizing ability of OH^• and the synthetic application, the key point is producing OH^• in a controlled manner under mild conditions and avoid its excessive generation during the oxidation process. Recently, the great advancement achieved with certain nanomaterial-based artificial enzymes has encouraged the development in biomimetic activation of O₂ into various ROS. (14,15) It is noteworthy that inspired by the metal coordination structure of natural enzymes, some biomimetic single-atom nanomaterials such as the ZIF-8-derived Zn–N–C can mimic the activity of peroxidase (POD) to facilely yield OH^• from H₂O₂ decomposition at 25 °C, overcoming the disadvantages of native enzymes such as structural vulnerability to damage, narrow pH value scale, etc. (16) By density functional theory (DFT) calculation and activity analysis experiments, the oxidase (OXD)-like activity has been demonstrated to depend largely on the local N coordination environment around the Co sites such as Co–N₄. (17) Even more interestingly, when some peroxidase-like nanomaterials combine with natural oxidases, a cascade catalysis may be created to enable the generation of OH^• via promoting the interconversion among ROS. For example, H₂O₂ could be initially produced from O₂ by using glucose oxidase, and subsequently, H₂O₂ is decomposed into OH^• catalyzed with the CuO-based artificial enzyme. (18) These findings bring new opportunities for the selective generation of OH^• via biomimetic cascade catalysis. Unfortunately, such prominent ability is exploited primarily for disease therapy, antibacterial application, biosensing, fluorescence analysis, degradation of environmental pollutants, etc. (14,15) So far, there is an urgent need to guide the activation of O₂ for the generation of reactivity-controllable OH^• under the inspiration of cascade catalysis and realize the production of important organic chemicals, especially acids, aldehydes, ketones, etc., which are in large demand and with wide applications in modern chemistry. (19−25)
为了平衡 OH^• 的高氧化能力和合成应用，关键是在温和的条件下以受控方式生产 OH^• 并避免在氧化过程中过度产生。最近，某些基于纳米材料的人工酶取得的巨大进步促进了 O₂ 仿生激活成各种 ROS 的发展。（14,15）值得注意的是，受天然酶的金属配位结构的启发，一些仿生单原子纳米材料，如 ZIF-8 衍生的 Zn-N-C，可以模拟过氧化物酶（POD）的活性，在 25 °C 下从 H₂O₂ 分解中轻松产生 OH^•，克服了天然酶的缺点，例如结构易受损伤，窄 pH 值尺度等。（16）通过密度泛函理论（DFT）计算和活性分析实验，已证明氧化酶（OXD）样活性在很大程度上取决于 Co 位点周围的局部 N 配位环境，例如 Co-N₄。（17）更有趣的是，当一些类似过氧化物酶的纳米材料与天然氧化酶结合时，可能会产生级联催化，通过促进 ROS 之间的相互转化来产生 OH^• 。例如，H₂O₂ 最初可以通过使用葡萄糖氧化酶从 O₂ 产生，随后，H₂O₂ 在基于 CuO 的人工酶的催化下分解成 OH^•。（18）这些发现为通过仿生级联催化选择性生成 OH^• 带来了新的机会。不幸的是，这种突出的能力主要用于疾病治疗、抗菌应用、生物传感、荧光分析、环境污染物降解等。（14,15）到目前为止，迫切需要在级联催化的启发下指导 O₂ 的活化以产生反应性可控的 OH^• 并实现重要有机化学品的生产，尤其是酸，醛、酮等，在现代化学中需求量很大，应用广泛。（19−25）

Our laboratory has been conducting a series of studies on catalytic selective oxidations of biomass feedstocks to synthesize chemicals with O₂. (26−30) We proposed a strategy by using hydrogen binding-initiated activation of O–H bonds to realize the highly efficient oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). (27) Although the reaction kinetics was clearly promoted, the dependence of the reaction on temperature still persisted. The activity declined seriously once the temperature is lower than 80 °C, which is consistent with the mostly adopted temperature range of 80–130 °C for non-noble metal catalysts. (31) Besides O–H bonds, the H-elimination of C–H bonds at the hydroxymethyl group is another key factor that influence the oxidation. We noticed in our previously designed biomimetic catalytic system, NHPI/anthraquinone/HY zeolite, that the strong electrophilic species PINO showed remarkable ability in facilitating the cleavage of inert C–H bonds of ethylbenzene by single electron transformation. (32) Considering that OH^• is also a highly electrophilic species and formed from O₂ itself, we speculated that it may act as the ideal ROS toward biomimetic oxidative synthesis. Herein, a single-atom Co–N–C catalyst has been designed to activate O₂ by self-cascade catalysis, wherein OH^• plays the selective oxidation role at a regulated level in water, so as to ensure the biomass-derived platform HMF oxidized with a high yield at 25 °C and atmospheric oxygen pressure. It combines the advantages of enzymatic and thermal catalysis, independent of stoichiometric co-reductants compared to natural enzymes.
我们的实验室一直在进行一系列关于生物质原料催化选择性氧化以合成具有 O₂ 的化学品的研究。（26−30）我们提出了一种策略，通过使用氢结合引发的 O-H 键激活来实现 5-羟甲基糠醛（HMF）高效氧化为 2,5-呋喃二羧酸（FDCA）。（27）尽管反应动力学明显得到促进，但反应对温度的依赖性仍然存在。当温度低于 80 °C 时，活性严重下降，这与非贵金属催化剂主要采用的 80–130 °C 温度范围一致。（31）除了 O-H 键外，羟甲基 C-H 键的 H 消除是影响氧化的另一个关键因素。我们注意到在我们之前设计的仿生催化系统 NHPI/蒽醌/HY 沸石中，强亲电物种 PINO 在促进乙苯惰性 C-H 键裂解方面表现出显着的能力通过单电子转化。（32）考虑到 OH^• 也是一种高度亲电的物质，并且由 O₂ 本身形成，我们推测它可能作为仿生氧化合成的理想 ROS。在此，设计了一种单原子 Co-N-C 催化剂，通过自级联催化活化 O₂，其中 OH^• 在水中发挥调节水平的选择性氧化作用，从而保证生物质衍生平台 HMF 在 25 °C 和大气氧压下以高产率被氧化。它结合了酶和热催化的优点，与天然酶相比，它独立于化学计量共还原剂。

2. Results and Discussion
2. 结果与讨论

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2.1. Design, Characterization, and Biomimetic Catalytic Performance of the Co–N–C Catalyst
2.1. Co-N-C 催化剂的设计、表征和仿生催化性能

We proposed a strategy of activating O₂ into OH^• at a controllable level by mimicking the cascaded catalysis of enzymes, so as to enable Co–N–C to accomplish the biomimetic oxidation synthesis. Scheme 1a illustrates that in the biomimetic catalytic system that uses Co–N–C with O₂ as the oxidant, the concentration of OH^• is reduced to a sufficiently low level and in control throughout the oxidation process, and thus, its oxidative capacity is reduced to a suitable degree since the oxidative capacity is generally positively correlated with the concentration in the oxidized state. On the contrary, using H₂O₂ as an OH^• source will lead to an uncontrollable production of OH^• at a relatively high level, which causes a high oxidative damage effect. By design of a biomimetic Co–N–C system, in situ and continuous generation of OH^• can be fulfilled (Scheme 1b). The Co–N–C catalyst containing CoN₄ sites has exhibited the ability to mimick enzymically cascaded catalysis of oxidase (OXD), superoxide dismutase (SOD), and peroxidase (POD), accomplishing the interconversions among ROS. Three ROS including O₂^•–, H₂O₂, and OH^•, with different oxidative capacities, were generated via cascading steps in sequence. Even at 25 °C, O₂ can be initially activated into O₂^•– in situ and subsequently into H₂O₂, which is further converted into OH^• at a sufficiently low level by adjusting the pH value of the aqueous solution, guaranteeing that OH^• plays a selective oxidation role in the oxidation of hydroxyl compounds, instead of the oxidative degradation effect (Scheme 1c). Considering that HMF is prone to staying in various oxidation stages and forming intermediates with different reactivities, which can be used to evaluate the oxidation ability of ROS in situ generated, the selective oxidation of the biomass platform HMF to FDCA was selected as a model reaction. In addition, the catalytic performance of Co–N–C was evaluated at room temperature (25 °C) and atmospheric pressure with O₂ bubbling to test whether it can achieve excellent performance comparable to that of natural enzymes under such mild conditions.
我们提出了一种通过模拟酶的级联催化在可控水平上将 O₂ 激活成 OH^• 的策略，从而使 Co-N-C 能够完成仿生氧化合成。方案 1a 表明，在使用带有 O₂ 的 Co-N-C 作为氧化剂的仿生催化系统中，OH^• 的浓度降低到足够低的水平并在整个氧化过程中处于受控状态，因此，其氧化能力降低到适当的程度，因为氧化能力通常与氧化状态下的浓度呈正相关。相反，使用 H₂O₂ 作为 OH^• 源会导致 OH^• 在相对较高的水平上无法控制地产生，从而产生很高的氧化损伤效应。通过设计仿生 Co-N-C 系统，可以实现 OH^• 的原位和连续生成（方案 1b）。含有 CoN₄ 位点的 Co-N-C 催化剂表现出模拟氧化酶（OXD）、超氧化物歧化酶（SOD）和过氧化物酶（POD）的酶促级联催化的能力，从而完成 ROS 之间的相互转化。通过级联步骤依次生成具有不同氧化能力的三种 ROS，包括 O₂^•–、H₂、O₂ 和 OH^•。即使在 25 °C 下，O₂ 也可以最初原位活化为 O₂^•–，随后转化为 H₂O₂，通过调节水溶液的 pH 值，在足够低的水平上进一步转化为 OH^•，保证 OH^• 在羟基化合物的氧化中起选择性氧化作用，而不是氧化降解效应（方案 1c）。考虑到 HMF 易停留在各种氧化阶段并形成具有不同反应性的中间体，可用于评价原位生成的 ROS 的氧化能力，因此选择生物质平台 HMF 选择性氧化为 FDCA 作为模型反应。此外，在室温（25 °C）和 O₂ 鼓泡的大气压下评估了 Co-N-C 的催化性能，以测试它在如此温和的条件下是否能达到与天然酶相当的优异性能。

Scheme 1. Comparison of OH^• Generation in Different Systems (a); Design of the Biomimetic System for In Situ and Continuous Generation of OH^• (b); Conversion of RCH₂OH in Different OH^• Generation Systems: Oxidative Degradation of RCH₂OH with Uncontrollable Production of OH^• (c, Left), Selective Oxidation of RCH₂OH with Controllable Production of OH^• (c, Right)
方案 1.不同系统中 OH^• 生成的比较（a）;原位和连续生成 OH 的仿生系统设计^• （b）;RCH₂OH 在不同 OH^• 生成系统中的转化：RCH₂OH 的氧化降解与无法控制的 OH产生^• （c，左），RCH₂OH 的选择性氧化与 OH 的可控产生^• （c，右）

To our delight, the Co–N–C single-atom catalyst (SAC) showed outstanding activity at 25 °C, affording 94.2% yield of FDCA at >99.9% conversion of HMF for 10 h in an aqueous solution when the pH value varied to 12.79 (Table 1, entry 1). It is worth noting that such mild conditions are very intriguing for non-noble metal catalysts achieving high activity proximity to natural oxidase, instead of deep oxidative degradation with C–C and C–O bond breaking. The oxidation time in the Co–N–C system could be shortened by 2–6 times compared with the natural enzymes such as the HMFO enzyme (25 °C, 24 h) (33) and GOase + HLADH enzyme (30 °C, 60 h). (34) In contrast, typical non-SAC cobalt-based catalysts for comparison showed poor activities, including other N-doped carbon-supported cobalt nanocatalysts such as Co/N–C-1, Co/N–C-2, CoO_x@N–C, and CoO_x-N/C, homogeneous biomimetic cobalt complexes (Co(Phen)₂ and CoTPP) containing similar CoN₄ coordination structures, and Co/AC without N-doped carbon structures (Table 1, entries 2–8). To the best of our knowledge, there is no example that can be accomplished at 25 °C by using non-noble metal catalysts for this model reaction, which generally requires at least 80 °C and above and mostly in the pressured O₂ (i.e., 0.3–2.0 MPa) (Figure S1). (31) Moreover, Co–N–C provides a broad range of reaction temperatures (25–60 °C) that can maintain high activity and selectivity simultaneously. By reacting at optimized 60 °C, it could further improve the catalytic efficiency and shorten oxidation time while achieving a high yield of FDCA (98.0%, 5 h). However, when the temperature continued to rise to 120 °C, the FDCA yield decreased to 6.7% with a serious carbon imbalance due to the side reactions. In the subsequent investigations, 60 °C was chosen as the experimental temperature to ensure the accurate progress of the exploration as efficiently as possible.
令我们高兴的是，Co-N-C 单原子催化剂（SAC）在 25 °C 下表现出出色的活性，当 pH 值变化至 12.79 时，在水溶液中 10 小时内 HMF 的 >99.9% 转化率下，FDCA 收率为 94.2%（表 1，条目 1）。值得注意的是，这种温和的条件对于非贵金属催化剂来说非常有趣，因为它在天然氧化酶附近实现了高活性，而不是通过 C-C 和 C-O 键断裂进行深度氧化降解。与天然酶（如 HMFO 酶（25 °C，24 小时）（33）和 GOase + HLADH 酶（30 °C，60 小时））相比，Co-N-C 系统中的氧化时间可以缩短 2-6 倍。（34）相比之下，用于比较的典型非 SAC 钴基催化剂表现出较差的活性，包括其他 N 掺杂碳负载钴纳米催化剂，如 Co/N-C-1、Co/N-C-2、CoO_x@N-C 和 CoO_x-N/C，含有相似 CoN₄ 配位结构的均相仿生钴配合物（Co（Phen）₂ 和 CoTPP），以及不含 N 掺杂碳结构的 Co/AC（表 1，条目 2-8）。据我们所知，在25 °C下使用非贵金属催化剂进行该模型反应尚无示例，该模型反应通常需要至少80 °C及以上的温度，并且主要在加压的O₂（即0.3-2.0 MPa）中（图S1）。（31）此外，Co-N-C 提供广泛的反应温度范围（25–60 °C），可以同时保持高活性和选择性。通过在优化的 60 °C 下反应，它可以进一步提高催化效率并缩短氧化时间，同时实现高 FDCA 收率（98.0%，5 h）。然而，当温度继续升高到 120 °C 时，FDCA 收率下降到 6.7%，副反应导致严重的碳失衡。在随后的调查中，选择 60 °C 作为实验温度，以尽可能高效地保证勘探的准确进行。

Table 1. Comparison of the Catalytic Performance of Cobalt-Based Catalysts for HMF Oxidation at 25 °C^a
表 1.钴基催化剂在 25 °C^a 下催化 HMF 氧化的性能比较

entry 进入	catalyst 催化剂	HMF conv. (mol %) HMF 转化率（mol %）	FDCA yield (mol %) FDCA 产量（mol %）
1	Co–N–C 钴 N- C	>99.9	94.2
2	Co/N–C-1 钴/N-C-1	>99.9	43.2
3	Co/N–C-2 钴/N-C-2	>99.9	15.8
4	CoO_x@N–C	>99.9	45.9
5	CoO_x-N/C CoO_x-N/C	>99.9	22.7
6	Co(Phen)₂ 钴（Phen）₂	49.1	0.6
7	CoTPP CoTPP 协议	41.6	0.1
8	Co/AC Co/AC 公司	51.0	0.1

^{^a}

Reaction conditions: 0.5 mmol HMF, 1.25 mmol NaOH, 0.032 mmol Co in the catalyst, 5 mL of H₂O, 40 mL/min O₂, 25 °C, 10 h. Phen: 1,10-phenanthroline, and TPP: meso-tetraphenylporphyrin.

^{^a}

反应条件：催化剂中加入 0.5 mmol HMF、1.25 mmol NaOH、0.032 mmol Co、5 mL H₂O、40 mL/min O₂、25 °C、10 h。Phen：1,10-菲咯啉和 TPP：内消旋四苯卟啉。

Afterward, the Co–N–C catalyst has been characterized in detail and demonstrated to have atomically dispersed cobalt-coordinated macrocycles along with the nitrogen doping graphitization structure. In the presented transmission electron microscopy (TEM) image (Figure 1a) and aberration-corrected high-angular annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) image (Figure 1i), no metallic cobalt or cobalt oxide nanoparticles were detected on the graphitic carbon sheet structure of Co–N–C, which was consistent with the X-ray diffraction (XRD) pattern (Figure 1m). The diffraction peaks at 25 and 43 degrees corresponded to the (002) and (004) planes of carbon, respectively, indicating a higher degree of graphitization. (27) The energy dispersive X-ray spectroscopy (EDX) analysis revealed that Co, N, and O were homogeneously dispersed on the carbon matrix (Figure 1b–d). As revealed by the X-ray absorption near-edge structure (XANES) analysis, the Co–N–C had almost the same first inflection point (E₀ value) as the CoO sample (Figure 1e), and the valence state of cobalt in Co–N–C was +2. (35) Both the extended X-ray absorption fine structure (EXAFS) spectrum and the wavelet transforms for the EXAFS spectrum showed a Co–N-characteristic signal and no obvious Co–Co and Co–O signals (Figure 1f–g). (35) The EXAFS fitting revealed that one Co atom coordinated with four N atoms, i.e., CoN₄ moiety was formed (Figure S2). The nitrogen content of Co–N–C was as high as 10.7 wt %, and the doped nitrogen species existed in the forms of pyridinic N/pyridinic N–Co, pyrrolic N, graphitic N, and pyridine N-oxide by X-ray photoelectron spectroscopy (XPS) analysis (Figure 1h). (36) The density of Co atoms in Co–N–C was approximately 0.72 Co atoms per nm², which was calculated based on the Brunauer–Emmett–Teller (BET) surface area (641 m²/g) and the cobalt loading (4.3 wt %) of the catalyst. Such high surface area and highly dispersed cobalt atoms were desirable for catalytic applications.
之后，对 Co-N-C 催化剂进行了详细表征，并证明具有原子分散的钴配位大环以及氮掺杂石墨化结构。在所呈现的透射电子显微镜（TEM）图像（图 1a）和像差校正的高角度环形暗场扫描透射电子显微镜（AC HAADF-STEM）图像（图 1i）中，在 Co-N-C 的石墨碳片结构上未检测到金属钴或钴氧化物纳米颗粒，这与 X 射线衍射（XRD）图样一致（图 1m）. 25 度和 43 度处的衍射峰分别对应于碳的（002）和（004）平面，表明石墨化程度较高。（27）能量色散 X 射线光谱（EDX）分析显示，Co、N 和 O 均匀分散在碳基体上（图 1b-d）。正如 X 射线吸收近边缘结构（XANES）分析所揭示的那样，Co-N-C 与 CoO 样品具有几乎相同的第一拐点（E₀ 值）（图 1e），钴在 Co-N-C 中的价态为 +2。（35）扩展 X 射线吸收精细结构（EXAFS）光谱和 EXAFS 光谱的小波变换都显示 Co-N 特征信号，没有明显的 Co-Co 和 Co-O 信号（图 1f-g）。（35） EXAFS 拟合显示一个 Co 原子与四个 N 原子配位，即形成 CoN₄ 部分（图 S2）。Co–N–C 的氮含量高达 10。7 wt %，掺杂的氮种类以吡啶 N/吡啶 N-Co、吡咯 N、石墨 N 和吡啶 N-氧化物的形式存在通过 X 射线光电子能谱（XPS）分析（图 1h）。（36） Co-N-C 中 Co 原子的密度约为 0.72 个 Co 原子/nm²，这是根据 Brunauer-Emmett-Teller （BET）表面积（641 m²/g）和催化剂的钴负载量（4.3 wt %）计算得出的。如此高的表面积和高度分散的钴原子是催化应用的理想选择。

Figure 1. TEM image (a), HAADF STEM image (b), and corresponding EDX maps for the overlapping Co, N, C, and O (c, d) of Co–N–C; normalized XANES spectra (e), EXAFS spectra (f), and wavelet transforms for the EXAFS spectra (g) of Co–N–C and Co foil; N 1s XPS spectrum (h), AC HAADF-STEM image (i) of Co–N–C; TEM images of Co/N–C-1 (j), Co/N–C-2 (k), and Co/AC (l); XRD patterns (m), ratio of the intensity of DMPO-OH^• adducts in the electron spin resonance (ESR) spectra at the reaction times of 20 min (n), and the catalytic performance of HMF oxidation (o) of different Co-based catalysts. Reaction conditions: 0.5 mmol HMF, 1.25 mmol NaOH, 0.032 mmol Co in the catalyst, 5 mL of H₂O, 40 mL/min O₂, 60 °C, and 5 h.
图 1.TEM 图像（a）、HAADF STEM 图像（b）以及 Co-N-C 重叠的 Co、N、C 和 O （c， d）的相应 EDX 图;Co-N-C 和 Co 箔的 EXAFS 光谱（g）的归一化 XANES 光谱（e）、EXAFS 光谱（f）和小波变换;N 1s XPS 谱图（h），Co–N–C 的 AC HAADF-STEM 图像（i）;Co/N-C-1 （j）、Co/N-C-2 （k）和 Co/AC （l）的 TEM 图像;XRD 图谱（m），反应时间为 20 min 时电子自旋共振（ESR）光谱中 DMPO-OH^• 加合物强度的比值（n），以及不同钴基催化剂的 HMF 氧化催化性能（o）。反应条件：催化剂中加入 0.5 mmol HMF、1.25 mmol NaOH、0.032 mmol Co、5 mL H₂O、40 mL/min O₂、60 °C 和 5 h。

Next, the significant effect of the Co–N–C SAC structure on the formation of OH^• has been evidenced by electron spin resonance spectroscopy (ESR) using the trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The relative ability in generating OH^• was determined in terms of comparing the ratio of I and I₀ (I/I₀), where I represents the intensity of the DMPO-OH^• signal and I₀ represents that in the blank experiment (the aqueous solution at a pH value of 12.79), which afforded trace OH^• with a weak signal of DMPO-OH^• without catalysts (Figure S4). Compared to the atomically dispersed CoN₄ sites in Co–N–C, increasing the average size of Co composites in Co/N–C-1 (3.21 nm) and Co/N–C-2 (13.78 nm) led to an obvious decrease in I/I₀ as well as the selectivity of FDCA (Figure 1n,o). In addition to the CoN₄ moiety, the Co/N–C-1 and Co/N–C-2 catalysts also contained Co species in the forms of Co (0) and CoO_x as evidenced by the nanoparticle morphology shown in the TEM images (Figure 1j,k) and the XRD patterns (Figure 1m). For the Co/AC catalyst with large aggregated Co composite nanoparticles (average size of around 100.06 nm) and the N–C catalyst without any Co loaded, the I/I₀ values of DMPO-OH^• were close to 1. There was no CoN₄ moiety existing in Co/AC and N–C catalysts, and both consequently exhibited poor activity for selective oxidation of HMF (Table S1). This obvious distinction in I/I₀ and activities indicated that the OH^• generation was closely related to the atomically dispersed CoN₄ sites. Toxicity experiments on CoN₄ sites were conducted by employing KSCN as the toxic reagent to further verify the facilitation of CoN₄ sites. A significant reduction in the catalytic activity for HMF oxidation over Co–N–C pretreated with KSCN indicated that the highly dispersed CoN₄ sites in Co–N–C were the core of OH^• production and selective oxidation of HMF and those unevenly distributed cobalt nanoparticles do not play a major role.
接下来，Co-N-C SAC 结构对 OH^• 形成的显着影响已通过使用捕获剂 5,5-二甲基-1-吡咯啉 N-氧化物（DMPO）的电子自旋共振光谱（ESR）得到证明。通过比较 I 和 I₀ （I/I₀）的比率来确定产生 OH^• 的相对能力，其中 I 代表 DMPO-OH^• 信号的强度，I₀ 代表在空白实验中（pH 值为 12.79 的水溶液）中的强度，这提供了痕量 OH^• 具有 DMPO-OH^• 弱信号• 没有催化剂（图 S4).与 Co-N-C 中原子分散的 CoN₄ 位点相比，Co/N-C-1 （3.21 nm）和 Co/N-C-2 （13.78 nm）中 Co 复合材料的平均尺寸增加导致 I/I₀ 以及 FDCA 选择性的明显降低（图 1n，o）。除了 CoN₄ 部分外，Co/N-C-1 和 Co/N-C-2 催化剂还含有 Co （0）和 CoO_x 形式的 Co 物质，TEM 图像（图 1j，k）和 XRD 图谱（图 1m）中显示的纳米颗粒形态证明了这一点。对于具有大聚集体 Co 复合纳米颗粒（平均尺寸约为 100.06 nm）的 Co/AC 催化剂和没有任何 Co 负载的 N-C 催化剂，DMPO-OH^• 的 I/I₀ 值接近 1。Co/AC 和 N-C 催化剂中不存在 CoN₄ 部分，因此两者都表现出较差的 HMF 选择性氧化活性（表 S1）。 I/I₀ 和活性的这种明显差异表明 OH^• 生成与原子分散的 CoN₄ 位点密切相关。采用 KSCN 作为毒性试剂对 CoN₄ 位点进行毒性实验，以进一步验证 CoN₄ 位点的便利性。与用 KSCN 预处理的 Co-N-C 相比，HMF 氧化的催化活性显着降低，这表明 Co-N-C 中高度分散的 CoN₄ 位点是 HMF 产生 ^OH• 和选择性氧化的核心，那些分布不均匀的钴纳米颗粒不起主要作用。

For comparison, we continued to check the OH^• level with the classical Fenton system (H₂O₂ + Fe²⁺) and alkaline hydrogen peroxide system (H₂O₂ + OH^–), which are frequently used for oxidative degradation at room temperature. As expected, a rather stronger signal of the DMPO-OH^• adduct has been detected by the ESR analysis, indicating the elevated OH^• concentration. (37) It evidenced OH^• produced from H₂O₂ decomposition in an uncontrollable way, leading to fully oxidative degradation of HMF into CO₂. This observation agreed well with previous studies that the destructive capacity came from the high level of OH^• concentration, which was closely related to the concentration of H₂O₂. (38) Such differences in oxidation product types showed that Co–N–C could activate O₂ and form OH^• in a controlled manner, with properties similar to those of enzymes. This characteristic has not been reported in previous studies, which only found that the CoN₄ structure could facilitate the adsorption of O₂; (39) the specific mechanism needs to be further clarified.
为了进行比较，我们继续检查经典芬顿系统（H₂O₂ + Fe²⁺）和碱性过氧化氢系统（H₂O₂ + OH^–）的 OH^• 水平，它们经常用于室温下的氧化降解。正如预期的那样，ESR 分析检测到 DMPO-OH^• 加合物的信号相当强，表明 OH^• 浓度升高。（37）它证明 H₂O₂ 以不可控的方式分解产生 OH^•，导致 HMF 完全氧化降解为 CO₂。这一观察结果与以前的研究非常吻合，即破坏能力来自高水平的 OH^• 浓度，这与 H₂O₂ 的浓度密切相关。（38）氧化产物类型的这种差异表明，Co-N-C 可以以受控方式激活 O₂ 并形成 OH^•，其性质与酶相似。这个特性在以前的研究中没有报道，只发现 CoN₄ 结构可以促进 O₂ 的吸附;（39）具体机制有待进一步明确。

In light of the unique property, Co–N–C could be considered a new nanomaterial-based artificial enzyme to produce OH^• in situ, via the activation of O₂. By taking advantage of the OH^• with high oxidation ability, the −CH₂OH will be activated under mild conditions and substrates may follow the selective oxidation pathway (Scheme 1c, right), instead of undergoing the oxidative degradation pathway for the cleavage of C–C and C–O bonds and releasing CO₂ caused by the high concentration of OH^• (Scheme 1c, left). It is attractive for Co–N–C simulating enzyme-catalyzed O₂ activation and requires in-depth exploration of specific generation, control, and mechanism.
鉴于其独特的特性，Co-N-C 可以被认为是一种新的基于纳米材料的人工酶，通过激活 O₂ 原位产生 OH^•。通过利用具有高氧化能力的 OH^•，-CH₂OH 将在温和的条件下被激活，底物可以遵循选择性氧化途径（方案 1c，右），而不是经历氧化降解途径以裂解 C-C 和 C-O 键并释放由高浓度 OH^• 引起的 CO₂（方案 1c， left）。它对 Co-N-C 模拟酶催化的 O₂ 活化很有吸引力，需要深入探索特异性生成、控制和机制。

2.2. Self-Cascade Catalysis for the Generation of OH^•
2.2. 用于生成 OH^• 的自级联催化

To distinguish the transformation of ROS via mimicking enzymically cascaded catalysis that ultimately generates OH^•, experiments consisting of three steps were performed under specific conditions (Figure 2a). ROS including O₂^•–, ¹O₂, OH^•, and H₂O₂ were detected by free radical trapping–ESR analysis using specific radical quenchers, in combination with gas chromatography–mass spectrometry (GC–MS) and titration. In step 1, Co–N–C showed activity like OXD in activating O₂ to O₂^•– as trapped by DMPO in toluene (Figure 2b), in which O₂^•– is stabilized enough for measurement purposes but undetectable in water due to the short lifetime. (40) When replacing O₂ with N₂, the six characteristic ESR peaks of the DMPO-O₂^•– adduct disappeared (Figure S6a). When the inhibitor p-benzoquinone (PBQ) was introduced into step 1, O₂^•– was no longer observed (Figure S6b). These results implied the electron transfer from Co–N–C to O₂. It agreed well with previous reports that conjugated N-doped carbon structures were beneficial to the enrichment of electrons on the surface and thus profited the adsorption of O₂ on atomically dispersed CoN₄ sites. (39) The ζ-potential of Co–N–C was measured, which is less than 0, proving the existence of negative charges on the catalyst surface in the aqueous solution. The treatment of Co–N–C with the cationic reagent 3-chloro-2-hydroxypropyltrimethylammonium chloride could shield the surface negative charges, thus leading to a significant decrease in HMF conversion and FDCA selectivity, further indicating that the electron-rich surface of Co–N–C played a crucial role in transferring electrons to O₂. The present biomimetic case was free of co-reductants, such as NADH required by natural oxidases. (41)
为了区分通过模拟最终产生 OH^•的酶级联催化来转化 ROS，在特定条件下进行了由三个步骤组成的实验（图 2a）。使用特异性自由基淬灭剂通过自由基捕获-ESR 分析结合气相色谱-质谱（GC-MS）和滴定法检测 ROS，包括 O₂^•–、1 O₂、^OH^•和 H₂O₂。在第 1 步中，Co-N-C 显示出类似 OXD 的活性，即激活 O₂ 到 O₂^•– 被 DMPO 捕获在甲苯中（图 2b），其中 O₂^•– 足够稳定，可用于测量目的，但由于寿命短，在水中无法检测到。（40）当用 N₂ 代替 O₂ 时，DMPO-O₂^•– 加合物的六个特征 ESR 峰消失了（图 S6a）。当将抑制剂对苯醌（PBQ）引入步骤 1 时，不再观察到 O₂^•– （图 S6b）。这些结果表明电子从 Co-N-C 转移到 O₂。它与以前的报道非常吻合，即共轭 N 掺杂碳结构有利于表面电子的富集，从而有利于 O₂ 在原子分散的 CoN₄ 位点上的吸附。（39）测量了 Co-N-C 的 ζ 电位，小于 0，证明水溶液中催化剂表面存在负电荷。用阳离子试剂 3-氯-2-羟丙基三甲基氯化铵处理 Co-N-C 可以屏蔽表面负电荷，从而导致 HMF 转化率和 FDCA 选择性显着降低，进一步表明 Co-N-C 的富电子表面在将电子转移到 O₂ 中起着至关重要的作用。目前的仿生案例不含共还原剂，例如天然氧化酶所需的 NADH。（41）

Figure 2. Cascade process of OH^• generation by the activation of O₂ and H₂O over Co–N–C (a); ESR spectrum of the DMPO-O₂^•– in the toluene phase of step 1 (b); MS spectrum of triphenylphosphine oxide formed in the water phase of step 2 (c); ESR spectrum of the DMPO-OH^• in the water phase of step 3 (d); and effect of solvents and inhibitors on the generation of ROS (e, f). Reaction conditions: for the detection of H₂O₂ and OH^• in water, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 1 mmol scavenger, 2.5 mL of H₂O, 40 mL/min O₂, and 60 °C and for the detection of O₂^•– in toluene, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 1 mmol scavenger, 2.5 mL of toluene, 0.6 MPa O₂, and 100 °C.
图 2.通过 Co-N-C （a）上 O₂ 和 H₂O 的活化生成 OH^• 的级联过程;DMPO-O 的 ESR 谱₂^•– 在步骤 1 （b）的甲苯相中;在步骤 2 （c）的水相中形成的三苯基氧化膦的 MS 谱图;步骤 3 （d^{）中} DMPO-OH • 在水相中的 ESR 谱图;以及溶剂和抑制剂对 ROS 生成的影响（e， f）。反应条件：用于检测水中的 H₂O₂ 和 OH^•、0.032 mmol Co 的 Co-N-C 溶液、1.25 mmol NaOH、1 mmol 清除剂、2.5 mL 的 H₂O、40 mL/min O₂ 和 60 °C，以及用于检测甲苯中的 O₂^•--0.032 mmol Co 和 Co-N-C 溶液， 1.25 mmol NaOH、1 mmol 清除剂、2.5 mL 甲苯、0.6 MPa O₂ 和 100 °C。

In step 2, specific biphasic experiments have been conducted and revealed that O₂^•– facilely transformed into H₂O₂ when encountering water. To the suspension of toluene in step 1 (containing O₂^•–) was added water to form a two-phase system, and O₂^•– remained in the upper toluene phase, while it was undetectable in the lower aqueous phase as being immediately converted to H₂O₂ after its formation, supported by the typical oxygenated product Ph₃P═O arising from the oxidation of Ph₃P by H₂O₂ (Figure 2c). The chromogenic reaction of KI also confirmed this. After adding the KI solution into the isolated water phase, the aqueous phase changed brown, suggesting that I^– was oxidized to I₂ by H₂O₂ (Figure S8). If PBQ was added into the toluene phase, O₂^•– was inhibited, and the subsequent addition of water would not enable H₂O₂ generation (Figure S9). Such biomimetic activity of Co–N–C may be attributed to the CoN₄ sites and graphitized structure, mimicking the electronic and structural characteristics of natural SOD. The disproportionation of O₂^•– to H₂O₂ could occur as metal–nitrogen sites in the SOD could adsorb O₂^•– and facilitate the electron transfer of O₂^•–. (42) Together, the Co–N–C possessed SOD-like activity to generate H₂O₂ from O₂^•– and H₂O.
在第 2 步中，进行了特定的双相实验，结果表明 O₂^•– 遇到水时很容易转化为 H₂O₂。在步骤 1 中的甲苯悬浮液（含有 O₂^•–）中加入水以形成两相体系，O₂^•– 保留在上层甲苯相中，而它在下层水相中检测不到，因为它在形成后立即转化为 H₂O₂，由典型的含氧产物 Ph 3 P═O 支持，该产物 Ph₃_{P 由}H₂O₂ 氧化产生（图 2KI 的显色反应也证实了这一点。将 KI 溶液加入分离的水相中后，水相变为棕色，表明 I^– 被 H₂O₂ 氧化成 I₂（图 S8）。如果将 PBQ 添加到甲苯相中，O₂^•– 被抑制，随后加水不会使 H₂O₂ 产生（图 S9）。Co-N-C 的这种仿生活性可能归因于 CoN₄ 位点和石墨化结构，模仿天然 SOD 的电子和结构特性。O₂^•– 到 H₂O₂ 的歧化可能是因为 SOD 中的金属-氮位点可以吸附 O₂^•– 并促进 O₂^•–的电子转移。（42） Co-N-C 一起具有类似 SOD 的活性，可从 O₂^•– 和 H₂O 生成 H₂O₂。

Step 3 demonstrated the activity of Co–N–C like POD under the alkaline environment. Once the water phase in step 2 was adjusted from neutral (pH = 7.02) to alkaline (pH = 12.79) by adding NaOH, it could be found that in the aqueous phase in addition to H₂O₂ (slightly decomposed), the OH^• species also appeared as evidenced by the ESR signal of the DMPO-OH^• adduct (Figure 2d). If isopropyl alcohol (IPA), an inhibitor of OH^•, was introduced into the system, the OH^• disappeared, while H₂O₂ remained. Afterward, OH^• could also generate when H₂O₂ was introduced into the aqueous system (containing the Co–N–C catalyst) instead of O₂ bubbling, which verified that OH^• originated from the decomposition of the in situ generated H₂O₂ (Figure S10). Such POD-like behavior in decomposing H₂O₂ into OH^• was also found in some nanomaterial-based artificial enzymes containing the CoN₄ macrocyclic structures. (43) The present Co–N–C system exhibited strong alkaline resistance and was clearly distinguished from common enzymes.
步骤 3 展示了 Co-N-C 样 POD 在碱性环境下的活性。通过添加 NaOH 将步骤 2 中的水相从中性（pH = 7.02）调整为碱性（pH = 12.79）后，可以发现在水相中，除了 H₂O₂（略微分解）外，还出现了 OH^• 物质，DMPO-OH^• 加合物的 ESR 信号证明了这一点（图 2d）。如果将 OH^•抑制剂异丙醇（IPA）引入系统，OH^• 消失，而 H₂O₂ 仍然存在。之后，当 H₂O₂ 被引入水性系统（包含 Co-N-C 催化剂）中时，也会产生 OH^• 而不是 O₂ 鼓泡，这验证了 OH^• 起源于原位生成的 H₂O₂ 的分解（图 S10）。在一些含有 CoN₄ 大环结构的基于纳米材料的人工酶中也发现了这种将 H₂O₂ 分解成 OH^• 的类似 POD 的行为。（43）目前的 Co-N-C 系统表现出很强的耐碱性，与普通酶明显不同。

In addition, when PBQ was added in advance in step 1, followed by the subsequent steps 2 and 3, H₂O₂ and OH^• that should have been generated subsequently could no longer be detected (Figure 2e,f). It suggested that the first step for activation of O₂ to O₂^•– was indispensable for the cascade process. Taken together, the mimicking cascaded catalysis of the OXD, SOD, and POD of the Co–N–C catalyst started with the activation of O₂ to O₂^•–, and O₂^•– subsequently converted into H₂O₂ once the water was present; then, H₂O₂ further converted to OH^• in a basic solution (i.e., pH = 12.79). The source of OH^• was also explored via the OH^• trapping experiment and liquid chromatography quadrupole time-of-flight mass spectrometry (LC–QTOF–MS) analysis by using isotope-labeled ¹⁸O₂, H₂¹⁸O, and D₂O. As shown in Figure 3, when ¹⁸O₂ and H₂¹⁸O were employed, the ¹⁸O-labeled DMPO-¹⁸OH^• was detected as the main adduct in both cases. Replacing H₂O with D₂O, DMPO-OD^• was formed, demonstrating that the source of H in OH^• was from H₂O. These results indicated that OH^• was produced from O₂ and H₂O through Co–N–C. Compared with the conventional enzyme cascade process of O₂ activation via glucose oxidase and peroxidase, (18) this cascade process exhibited higher temperature and pH tolerance and higher efficiency.
此外，当在步骤 1 中预先添加 PBQ 时，随后是后续步骤 2 和 3，本应随后生成的 H₂、O₂ 和 OH^• 无法再检测到（图 2e、f）。它表明 O₂ 到 O₂^•– 激活的第一步对于级联过程是必不可少的。综上所述，Co-N-C 催化剂的 OXD、SOD 和 POD 的模拟级联催化始于 O₂ 到 O₂^•–，而 O₂^•– 随后在水存在后转化为 H₂O₂;然后，H₂O₂ 在碱性溶液（即 pH = 12.79）中进一步转化为 OH^•。还通过 OH^• 捕获实验和液相色谱四极杆飞行时间质谱（LC-QTOF-MS）分析，使用同位素标记的 ¹⁸O₂、H₂¹⁸O 和 D₂O 来探索 OH^• 的来源。如图 3 所示，当使用 ¹⁸O₂ 和 H₂¹⁸O 时，在两种情况下都检测到 ¹⁸O 标记的 DMPO-18 OH^• 作为主要加合物。用 D₂O 代替 H₂O，形成 DMPO-OD^• ，表明 OH^• 中 H 的来源来自 H₂O。这些结果表明，OH^• 是由 O₂ 和 H₂O 通过 Co-N-C 产生的。与通过葡萄糖氧化酶和过氧化物酶激活 O₂ 的常规酶级联过程相比，（18）这种级联过程表现出更高的温度和 pH 耐受性以及更高的效率。

Figure 3. Mass spectra of the OH^• trapping experiments by DMPO in isotope-labeled H₂O and O₂. Reaction conditions: 1.25 mmol NaOH, 0.032 mmol Co in Co–N–C, 5 mL of H₂O, 60 °C, 40 mL/min O₂, and 30 min.
图 3.DMPO 在同位素标记的 H₂O 和 O₂ 中进行 OH^• 捕获实验的质谱。反应条件：1.25 mmol NaOH、0.032 mmol Co in Co–N-C、5 mL H₂O、60 °C、40 mL/min O₂ 和 30 min。

2.3. Identifying the Role of ROS in Selectivity Oxidation of HMF
2.3. 确定 ROS 在 HMF 选择性氧化中的作用

Because O₂^•–, H₂O₂, and OH^• were involved in the self-cascade catalysis for O₂ activation over Co–N–C, it is necessary to identify the oxidation ability of different ROS in the oxidation of HMF. The generation of different types of ROS was performed in different conditions by altering the reaction solvents or pH values. We examined the capacity of O₂^•– by conducting the oxidation of HMF in toluene because the role of O₂^•– is difficult to resolve owing to its instability and extremely short lifetime in water. The Co–N–C revealed no activity at 25 °C and could afford 49.0% yield of 2,5-furandicarboxaldehyde (DFF) as the major oxidation product at 100 °C (Table 2, entry 1). O₂^•– demonstrated that the only ROS involved is suggested to play a role in selectively oxidizing −CH₂OH to −CHO, showing insufficient oxidative capacity to oxidize −CH₂OH to −COOH even at 100 °C. Next, by adding IPA to scavenge OH^• in the Co–N–C + water + OH^– system that pregenerates H₂O₂ and OH^•, H₂O₂ can be maintained as a dominant ROS. Accordingly, FDCA was formed with a yield of 30.5%, accompanied by partially unconverted 5-hydroxymethyl-2-furancarboxylic acid (HMFCA, yield of 35.2%) with a carbon balance of only 66.0% (Table 2, entry 2). H₂O₂ exhibited weak oxidation ability to the oxidation of −CH₂OH to −COOH and was failed to convert HMF in time, resulting in side reactions with carbon imbalance. If OH^• remained in the Co–N–C system, the intermediates DFF and HMFCA with relative higher stability are not detected. The high yield of 94.8% for the oxidative product FDCA confirmed the high oxidative capacity of OH^• (Table 2, entry 3).
由于 O₂^•–、H₂、O₂ 和 OH^• 参与了 Co-N-C 上 O₂ 活化的自级联催化，因此有必要确定不同 ROS 在 HMF 氧化中的氧化能力。通过改变反应溶剂或 pH 值，在不同条件下生成不同类型的 ROS。我们通过传导 HMF 在甲苯中的氧化来检查 O₂^•– 的容量，因为 O₂^•– 的作用由于其不稳定性和在水中的寿命极短而难以解决。Co-N-C 在 25 °C 下没有活性，在 100 °C 下可以得到 49.0% 的 2,5-呋喃二甲醛（DFF）作为主要氧化产物（表 2，条目 1）。O₂^•– 证明唯一涉及的 ROS 被认为在选择性地将 -CH₂OH 氧化为 -CHO 中发挥作用，即使在 100 °C 下也显示出不足的氧化能力，无法将 -CH₂OH 氧化为 -COOH。接下来，通过在预生成 H₂O₂ 和 OH^•的 Co–N–C + 水 ^{+ OH}– 系统中添加 IPA 来清除 OH^•，H₂O₂ 可以保持为占主导地位的 ROS。因此，形成 FDCA，产率为 30.5%，伴有部分未转化的 5-羟甲基-2-呋喃羧酸（HMFCA，产率 35.2%），碳平衡仅为 66.0%（表 2，条目 2）。H₂O₂ 对 -CH₂OH 氧化为 -COOH 表现出弱的氧化能力，并且未能及时转化 HMF，导致与碳不平衡的副反应。如果 OH^• 保留在 Co-N-C 系统中，则不会检测到稳定性相对较高的中间体 DFF 和 HMFCA。氧化产物 FDCA 的 94.8% 的高产量证实了 OH^• 的高氧化能力（表 2，条目 3）。

Table 2. Comparison of the Effect of Different ROS in HMF Oxidation over Co–N–C
表 2.不同 ROS 在 HMF 氧化对 Co-N-C 的影响比较

						yield (%) 产量（%）
entry 进入	solvent 溶剂	base 基础	additive 添加剂	dominant ROS 优势 ROS	conv. (%) 转化率（%）	FDCA	HMFCA	FFCA	DFF
1^a 1^个	toluene 甲苯			O₂^•–	87.1	nd	nd	nd	49.0
2^b 2^乙	water 水	NaOH 氢氧化钠	IPA	H₂O₂	>99.9	30.5	35.2	0.3	nd
3^b 3^乙	water 水	NaOH 氢氧化钠		OH^•	>99.9	94.8	nd	nd	nd

^{^a}

Reaction conditions: 0.5 mmol HMF, 0.032 mmol Co in Co–N–C, 5 mL of toluene, 0.6 MPa O₂, 100 °C, and 10 h.

^{^a}

反应条件：0.5 mmol HMF、0.032 mmol Co in Co–N-C、5 mL 甲苯、0.6 MPa O₂、100 °C 和 10 h。

^{^b}

0.5 mmol HMF, 1.25 mmol NaOH, 0.032 mmol Co in Co–N–C, 1.0 mmol additive, 5 mL of H₂O, 40 mL/min O₂, 60 °C, and 4 h.

^{^b}

0.5 mmol HMF、1.25 mmol NaOH、0.032 mmol Co in Co–N–C、1.0 mmol 添加剂、5 mL H₂O、40 mL/min O₂、60 °C 和 4 h。

Subsequently, the pulse experiments were conducted to explore whether OH^• is the dominant ROS playing the selective oxidation role. With O₂ bubbling, 0.05 mmol HMF was added to the Co–N–C + water + OH^– system at 14 min intervals. The intensity of OH^• was monitored by ESR analysis and exhibited a cyclic change dependent on the addition and consumption of HMF. The OH^• appeared to decrease first and then increase after each addition of HMF (Figure 4a above). By correlating the concentrations of HMF and FDCA with the intensity ratio of OH^•, one could find that the consumption of HMF was basically synchronous with the consumption of OH^• (Figure 4a below), indicating that the selective oxidation of HMF would constantly consume OH^•, resulting in a concentration close to the blank experiment (the intensity ratio consistently remained around 1) when HMF depleted for each addition.
随后，进行脉冲实验，探讨 OH^• 是否是发挥选择性氧化作用的优势 ROS。在 O₂ 鼓泡的情况下，以 14 分钟的间隔向 Co–N–C + 水 + OH^– 系统中加入 0.05 mmol HMF。通过 ESR 分析监测 OH^• 的强度，并表现出取决于 HMF 添加和消耗的循环变化。OH^• 在每次添加 HMF 后似乎先降低，然后增加（上面的图 4a）。通过将 HMF 和 FDCA 的浓度与 OH^•的强度比相关联，可以发现 HMF 的消耗量与 OH^• 的消耗量基本同步（下图 4a），表明 HMF 的选择性氧化会不断消耗 OH^•，导致浓度接近空白实验（强度比始终保持在 1 左右），当 HMF 每次添加耗尽时。

Figure 4. Time curve of the intensity of DMPO-OH^• adducts in the ESR spectra of the Co–N–C system with HMF addition (a, above), the concentrations of HMF and FDCA during the HMF oxidation process in the Co–N–C system (a, below); the high-performance liquid chromatography (HPLC) traces for HMF oxidation in the Co–N–C system (b); the time curve of the intensity of DMPO-OH^• adducts in the ESR spectra of the Co–N–C system without HMF addition (c); the time curve of the intensity of DMPO-OH^• adducts in the ESR spectra of the H₂O₂ + OH^– system with and without HMF addition (d). Reaction conditions: in the Co–N–C system, 1.25 mmol NaOH, 0.032 mmol Co in Co–N–C, 5 mL of H₂O, 40 mL/min O₂, and 60 °C and in the H₂O₂ + OH^– system, 1.25 mmol NaOH, 1 mL of 30 wt % H₂O₂, 4 mL of H₂O, and 60 °C. In these two systems, 0.05 mmol HMF was added in the 11th min, 25th min, 39th min, and 53rd min.
图 4.添加 HMF 后 Co-N-C 系统 ESR 光谱中 DMPO-OH^• 加合物强度的时间曲线（a，上图），Co-N-C 系统中 HMF 氧化过程中 HMF 和 FDCA 的浓度（a，下图）;Co-N-C 系统中 HMF 氧化的高效液相色谱（HPLC）迹线（b）;未添加 HMF 的 Co-N-C 系统的 ESR 光谱中 DMPO-OH^• 加合物强度的时间曲线（c）;H₂O₂ ^{+ OH}– 添加和不添加 HMF 的 ESR 光谱中 DMPO-OH^• 加合物强度的时间曲线（d）。反应条件：在 Co-N-C 系统中，1.25 mmol NaOH、0.032 mmol Co 的 Co-N-C 溶液、5 mL 的 H₂O、40 mL/min O₂ 和 60 °C，以及在 H₂O₂ + OH^– 系统中，1.25 mmol NaOH，1 mL 30 wt % H₂O_2,4 mL H₂O，和 60 °C。在这两个系统中，在第 11 min、第 25 min、第 39 min 和第 53 min 添加 0.05 mmol HMF。

Meanwhile, similar trends were observed for the peaks of HMF and intermediates in the HPLC spectra with each interval addition of HMF (Figure 4b). HMF appeared first and then gradually decreased to exhaustion. During the interval between each two additions of HMF, intermediates HMFCA as well as a small amount of 5-formyl-2-furancarboxylic acid (FFCA) also appeared first and then decreased to zero. FDCA, which accumulated with the addition of HMF, continued to be elevated in its concentration. The intermediates HMFCA and FFCA showed a tendency to rise first and then decreased due to further conversion. When HMF and intermediates were consumed, the OH^• resumed to form and accumulated. When HMF was added again, similar cycles continued to follow, and at the end of each cycle, the level of OH^• still returned close to the initial. If HMF was not added to the Co–N–C + water + OH^– system, the I/I₀ values of DMPO-OH^• increased gradually and remained constant at 2.0 after 90 min, indicating that an equilibrium was reached after a certain time (Figure 4c), and the concentration of OH^• was no longer improved and maintained at a certain concentration. These results indicated that OH^• in the Co–N–C system was produced in situ and continuously, which ensured the highly selective oxidation of hydroxyl compounds to the corresponding carboxylic acids.
同时，在每次间隔添加 HMF 后，HPLC 谱图中 HMF 和中间体的峰也观察到类似的趋势（图 4b）。HMF 首先出现，然后逐渐下降到疲惫。在每添加两次 HMF 的间隔期间，中间体 HMFCA 以及少量 5-甲酰基-2-呋喃羧酸（FFCA）也首先出现，然后减少到零。随着 HMF 的添加而积累的 FDCA 浓度继续升高。中间体 HMFCA 和 FFCA 表现出先上升后下降的趋势，这是由于进一步的转化。当 HMF 和中间体被消耗时，OH^• 恢复形成并积累。当再次添加 HMF 时，类似的循环继续进行，在每个循环结束时，OH^• 的水平仍然恢复到接近初始水平。如果未将 HMF 添加到 Co–N–C + 水 + OH^– 系统中，DMPO-OH^• 的 I/I₀ 值逐渐增加，并在 90 分钟后保持在 2.0 恒定，表明一定时间后达到平衡（图 4c），OH^• 的浓度不再改善并维持在一定浓度。这些结果表明，Co-N-C 系统中的 OH^• 是原位连续产生的，这确保了羟基化合物高度选择性地氧化为相应的羧酸。

When H₂O₂ was directly used instead of O₂ as the oxidant, the intermittent addition of HMF into the H₂O₂ + OH^– system led to a quite different trend in the I/I₀ values of DMPO-OH^•, which decreased during all the pulse experiments, indicating that OH^• only arose from the decomposition of H₂O₂ without the Co–N–C catalyst. If H₂O₂ was fed in one batch and no HMF was added in the H₂O₂ + OH^– system, a large amount of OH^• was immediately generated at high intensity. For example, its I/I₀ value at 15 min was 8.4 times higher than that of the Co–N–C system. The I/I₀ value of DMPO-OH^• gradually decreased with the decomposition of H₂O₂ until exhaustion (Figure 4d). As a result, in the case of intermittent addition of HMF into the H₂O₂ + OH^– system, OH^• at a high level led to the oxidative degradation of HMF into CO₂ without any selective oxidation products (Figure S16). Such oxidative degradation also led to OH^• being quickly consumed within 66 min. This was consistent with the need of continuously replenishing H₂O₂ for the application of the H₂O₂ system in the oxidative degradation. (44) Therefore, a high level of OH^• in the H₂O₂ + OH^– system was not conducive to the selective oxidation.
当直接使用 H₂O₂ 代替 O₂ 作为氧化剂时，HMF 间歇性添加到 H₂O₂ + OH^– 体系中导致 DMPO-OH^•的 I/I₀ 值出现完全不同的趋势，在所有脉冲实验中均有所下降，表明 OH^• 仅由 H₂O₂ 分解产生，没有 Co-N-C 催化剂。如果 H₂O₂ 分批进料，并且在 H₂O₂ + OH^– 系统中未添加 HMF，则立即以高强度产生大量 OH^•。例如，它在 15 min 时的 I/I₀ 值比 Co-N-C 系统的 8.4 倍高。DMPO-OH^• 的 I/I₀ 值随着 H₂O₂ 的分解而逐渐降低，直至耗尽（图 4d）。因此，在将 HMF 间歇性添加到 H₂O₂ + OH^– 系统的情况下，高水平的 OH^• 导致 HMF 氧化降解成 CO₂，而没有任何选择性氧化产物（图 S16）。这种氧化降解也导致 OH^• 在 66 分钟内被迅速消耗。这与不断补充 H₂O₂ 以将 H₂O₂ 系统应用于氧化降解的需求是一致的。（44）因此，H₂O₂ + OH^– 系统中高水平的 OH^• 不利于选择性氧化。

According to the time course of HMF oxidation catalyzed by the Co–N–C catalyst (Figure 5a), the reaction mainly proceeded along the route in which HMF was oxidized to the intermediate HMFCA and then converted to FDCA. The oxidation of −CH₂OH in HMFCA to −COOH is the key step affecting the whole reaction rate. After adding IPA to inhibit the formation of OH^•, the generation rate of FDCA was reduced significantly and so was the conversion rate of HMFCA (Figure 5b), confirming the crucial role of OH^• in the oxidation of −CH₂OH to −COOH. To further verify whether OH^• played a dominant role, the oxidation using HMFCA as a starting substrate was performed (Figure 5c). By addition of IPA, OH^• was inhibited and H₂O₂ remained, and the conversion of HMFCA was greatly reduced with the yield of FDCA decreased from 92.0 to 7.6% (Figure 5d), indicating that OH^• played a major role in the oxidation of −CH₂OH to −COOH. If both H₂O₂ and OH^• were inhibited by PBQ via inhibiting the starting species O₂^•–, it could lead to a further decrease in HMFCA conversion (from >99.9 to 10.9%) with no FDCA yielded, suggesting that H₂O₂ made a weak contribution to the oxidation of −CH₂OH in this key step. Taken together, three ROS with different oxidizing abilities were generated via O₂ activation over the Co–N–C catalyst, and the OH^• produced by mimicking the cascaded catalysis process exhibited the highest oxidizing ability among the three ROS and played the key role in the oxidation of −CH₂OH to −COOH. It was suggested that the OH^• promoted the key step of the conversion of −CH₂OH to −COOH in HMFCA oxidation, so as to enhance the efficiency in production of FDCA with high selectivity.
根据 Co-N-C 催化剂催化的 HMF 氧化的时间进程（图 5a），反应主要沿着 HMF 被氧化成中间体 HMFCA，然后转化为 FDCA 的路线进行。HMFCA 中的 -CH₂OH 氧化为 -COOH 是影响整个反应速率的关键步骤。添加 IPA 抑制 OH^• 的形成后，FDCA 的生成速率显著降低，HMFCA 的转化率也显著降低（图 5b），证实了 OH^• 在 −CH₂OH 氧化为 −COOH 中的关键作用。为了进一步验证 OH^• 是否起主导作用，使用 HMFCA 作为起始底物进行了氧化（图 5c）。通过添加 IPA，OH^• 被抑制，H₂O₂ 仍然存在，HMFCA 的转化率大大降低，FDCA 的产量从 92.0% 下降到 7.6%（图 5d），表明 OH^• 在 -CH₂OH 氧化为 -COOH 中起主要作用。如果 H₂O₂ 和 OH^• 都通过抑制起始物质 O₂^•– 被 PBQ 抑制，则可能导致 HMFCA 转化率进一步降低（从 >99.9% 降低到 10.9%），而没有产生 FDCA，这表明 H₂O₂ 在这个关键步骤中对 -CH₂OH 的氧化贡献微弱。综上所述，通过在 Co-N-C 催化剂上进行 O₂ 活化生成了三种具有不同氧化能力的 ROS，通过模拟级联催化过程产生的 OH^• 在三种 ROS 中表现出最高的氧化能力，并在 -CH₂OH 氧化为 -COOH 中起关键作用。有人提出 OH^• 促进了 HMFCA 氧化中 -CH₂OH 转化为 -COOH 的关键步骤，从而提高了高选择性 FDCA 的生产效率。

Figure 5. Reaction time profile of HMF oxidation over Co–N–C (a) and inhibited by IPA (b) and the reaction time profile of HMFCA oxidation over Co–N–C (c) and inhibited by IPA (d). Reaction conditions: 0.5 mmol HMF or HMFCA, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 5 mL of H₂O, 1.0 mmol IPA, 40 mL/min O₂, and 60 °C.
图 5.HMF 在 Co-N-C （a）上被 IPA 抑制的反应时间曲线，以及 HMFCA 氧化在 Co-N-C 上被（c）和被 IPA 抑制的反应时间曲线（d）。反应条件：0.5 mmol HMF 或 HMFCA、0.032 mmol Co in Co–N–C、1.25 mmol NaOH、5 mL H₂O、1.0 mmol IPA、40 mL/min O₂ 和 60 °C。

2.4. Comparison of the External and In Situ Formed H₂O₂
2.4. 外部形成和原位形成的 H₂O₂ 的比较

The oxidation of HMF was monitored by UV–vis spectroscopy and is presented in Figure 6a,b. In the case of bubbling O₂ in the Co–N–C + water + OH^– system, HMF quickly converted in the initial period and then oxidized into FDCA, as shown by the sharp decrease of absorbance intensity at 284 nm (HMF) and increase at 259 nm (acidic products) versus time. The variations of UV–vis spectra agreed well with the trend in FDCA concentration (Figure 6c) and excellent results (FDCA selectivity of 98.0% and carbon balance of nearly 100%). In the case of the H₂O₂ + OH^– system, HMF was also quickly consumed, but no peaks of acidic products were observed. As demonstrated above, the one-time addition of H₂O₂ immediately formed a large amount of OH^• and led to the complete degradation of HMF to CO₂.
通过紫外-可见光谱法监测 HMF 的氧化，如图 6a、b 所示。在 Co–N–C + 水 + OH^– 系统中冒泡 O₂ 的情况下，HMF 在初始阶段迅速转化，然后氧化成 FDCA，如 284 nm 处吸光度强度（HMF）和 259 nm 处吸光度强度（酸性产物）随时间急剧增加所示。紫外-可见光谱的变化与 FDCA 浓度（图 6c）和优异结果（FDCA 选择性为 98.0%，碳平衡接近 100%）的趋势非常吻合。在 H₂O₂ + OH^– 系统的情况下，HMF 也被迅速消耗，但没有观察到酸性产物的峰值。如上所述，一次性添加 H₂O₂ 立即形成大量 OH^• 并导致 HMF 完全降解为 CO₂。

Figure 6. UV–vis spectra of the HMF oxidation process in the Co–N–C system (a) and H₂O₂ + OH^– system (b); evolution of FDCA concentration in HMF oxidation in the Co–N–C system with O₂ bubbling (A), with H₂O₂ addition 10 times (B), with H₂O₂ addition 1 time (C), and in the H₂O₂ + OH^– system (D) (c); ESR spectra of DMPO-OH^• adducts at the reaction time of 1 min in the Co–N–C system with O₂ bubbling, with H₂O₂ addition 10 times and 1 time and in the H₂O₂ + OH^– system (d). Reaction conditions: 0.5 mmol HMF, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 5 mL of H₂O, 60 °C, and 40 mL/min O₂ (A); 0.1 mL of 30 wt % H₂O₂ was added 10 times at equal intervals (B); 1 mL of 30 wt % H₂O₂ was added 1 time (C); 1 mL of 30 wt % H₂O₂ was added 1 time without Co–N–C addition (D). Reaction conditions of UV–vis monitoring in (a, b) were consistent with those of (A) and (D) in (c), respectively.
图 6.Co-N-C 系统（a）和 H₂O₂ + OH^– 系统（b）中 HMF 氧化过程的紫外-可见光谱;在 Co-N-C 系统中 O₂ 鼓泡（A）、H₂O₂ 添加 10 倍（B）、H₂O₂ 添加 1 倍（C）和 H₂O₂ + OH^– 系统（D）（c）中 HMF 氧化中 FDCA 浓度的演变;DMPO-OH^• 加合物在 Co–N-C 系统中反应时间为 1 min 时的 ESR 光谱，O₂ 鼓泡，H₂O₂ 添加 10 次和 1 次，以及在 H₂O₂ + OH^– 系统（d）中。反应条件：0.5 mmol HMF、0.032 mmol Co in Co–N–C、1.25 mmol NaOH、5 mL H₂O、60 °C 和 40 mL/min O₂ （A）;以相等的间隔添加 0.1 mL 30 wt % H₂O₂ 10 次（B）;添加 1 mL 30 wt % H₂O₂ 1 次（C）;加入 1 mL 30 wt % H₂O₂ 1 次，不添加 Co-N-C （D）。（a、b）中紫外-可见分光光度计监测的反应条件分别与（c）中（A）和（D）的反应条件一致。

It makes us curious about what changes will occur when this H₂O₂ + OH^– system is added by the Co–N–C catalyst, that is, external H₂O₂ is used to provide the OH^• source for HMF oxidation. If the addition of H₂O₂ was changed once to several times to reduce its concentration, would the pathway over the Co–N–C catalyst be changed? Then, we compared the HMF oxidation experiments over Co–N–C with 1 and 10 additions of H₂O₂ for validation (Figure 6c). It was intriguing that when 1 mL of 30 wt % H₂O₂ (8.8 mmol) was added once to replace the O₂ feeding, the Co–N–C + H₂O₂ + OH^– system undergoes selective oxidation in addition to oxidative degradation. As evidenced by ESR (Figure 6d), Co–N–C showed POD-like activity to convert H₂O₂ into OH^•, with the I/I₀ of OH^• at 1.5 in the initial stage of the reaction (1 min). It was higher than that of the O₂ feeding case (1.1), further confirming that the one-time addition of H₂O₂ would lead to the formation of a relatively higher concentration of OH^•, which led to 33.0% of HMF decomposition at 300 min. With the gradual consumption of H₂O₂, the OH^• concentration decreased accordingly, thus exhibiting an insufficient ability to oxidize HMF to FDCA, and FDCA was produced with lower selectivity (33.7%) when HMF was consumed completely. If 0.1 mL of 30 wt % H₂O₂ was added 10 times at equal intervals, the initial intensity of OH^• was lower, with no longer continuous decrease with supplementation of H₂O₂. However, the instantaneous concentration of OH^• was still higher than that of the O₂ feeding case (Figure 6d). Although the FDCA selectivity was increased to 70.9% in this case, there was still 20.6% of the added HMF decomposed in the initial stage of the reaction. Moreover, the carbon balance was not satisfied and only reached 79.4%.
这让我们很好奇，当这个 H₂O₂ + OH^– 系统由 Co-N-C 催化剂添加时会发生什么变化，即使用外部 H₂O₂ 为 HMF 氧化提供 OH^• 源。如果将 H₂O₂ 的添加量改为多次以降低其浓度，Co-N-C 催化剂上的途径会改变吗？然后，我们将 Co-N-C 与 H_{2 O}₂ 的 1 次和 10 次添加进行了 HMF 氧化实验以进行验证（图 6c）。有趣的是，当添加 1 mL 的 30 wt % H₂O₂ （8.8 mmol）以代替 O₂ 进料时，Co-N-C + H₂O₂ + OH^– 系统除了氧化降解外，还会发生选择性氧化。正如 ESR 所证明的（图 6d），Co-N-C 显示出将 H₂O₂ 转化为 OH^•的 POD 样活性，OH^• 的 I/I₀ 在反应的初始阶段（1 分钟）为 1.5。它高于 O₂ 进料情况（1.1），进一步证实了 H₂O₂ 的一次性添加会导致形成相对更高浓度的 OH^•，这导致 300 min 时 HMF 分解 33.0%。随着 H₂O₂ 的逐渐消耗，OH^• 浓度相应降低，从而表现出将 HMF 氧化为 FDCA 的能力不足，当 HMF 完全消耗时，FDCA 的选择性较低（33.7%）。如果为 0.以相等的间隔添加 10 次 30 wt % H₂O₂ 的 1 mL，OH^• 的初始强度较低，添加 H₂O₂ 不再持续降低。然而，OH^• 的瞬时浓度仍然高于 O₂ 进料情况（图 6d）。虽然在这种情况下 FDCA 选择性提高到 70.9%，但在反应的初始阶段仍有 20.6% 的添加 HMF 被分解。此外，碳平衡并未得到满足，仅达到 79.4%。

In the case of adding H₂O₂ at one time, i.e., the H₂O₂ + OH^– system, the I/I₀ of OH^• reached 4.8 in the initial stage of the reaction. It was more than 3 times higher than those of the above-mentioned three cases (Figure 6d, lines A, B, and C). Thus, HMF was degraded rapidly, and the mass spectrum of the gas product confirmed that the main degradation product was CO₂ (Figure S16). These results further suggested that the transformation of ROS (O₂^•– and H₂O₂) in the Co–N–C system could ensure the in situ and continuous generation of OH^• with low concentration, and only in situ controllable production of OH^• was beneficial to the highly selective oxidation of hydroxyl compounds. Reducing the concentration of externally added H₂O₂ is beneficial for selective oxidation but not enough to reduce the oxidative degradation to a sufficiently low extent as in Co–N–C.
在一次加入 H₂O₂ 的情况下，即 H₂O₂ + OH^– 系统，OH^• 的 I/I₀ 在反应的初始阶段达到 4.8。它比上述三种情况高 3 倍以上（图 6d，A、B 和 C 行）。因此，HMF 迅速降解，气体产物的质谱证实主要降解产物是 CO₂（图 S16）。这些结果进一步表明，ROS（O₂^•– 和 H₂O₂）在 Co–N–C 系统中的转化可以保证低浓度 OH^• 的原位连续生成，并且只有原位可控地产生 OH^• 才有利于羟基化合物的高选择性氧化。降低外部添加的 H₂O₂ 的浓度有利于选择性氧化，但不足以将氧化降解降低到足够低的程度，如 Co-N-C。

2.5. Control in OH^• Produces via pH Variation
2.5. OH^{中的控制•} 通过改变 pH 值产生

Obviously, the concentration of OH^• formed in situ was sufficiently low compared to that of the externally added H₂O₂ to ensure selective oxidation rather than oxidative degradation. Further studies found that adjusting the pH value in the Co–N–C system could tune the intensity of the OH^• formed in situ. As shown in Figure 7a, no signal for OH^• appeared in a neutral aqueous solution (pH = 7.02), and HMF was converted slowly with extremely low selectivity for FDCA. When increasing to pH = 8.16 by adding NaHCO₃, weak peaks of the OH^• signal could be observed. As the pH value increased to 13.32 by adding NaOH, the OH^• intensity continuously increased. The results showed that the OH^• formation activity of Co–N–C closely depended on the basic intensity of the aqueous solution. The yield of FDCA and pH value had a volcano curve relationship, in which pH = 12.79 was the best with the highest yield of 98.0% (Figure 7d). This is consistent with the reported studies that inorganic bases such as NaOH, Na₂CO₃, NaHCO₃, etc. were necessary for the oxidation of HMF to FDCA when using non-noble metal catalysts as alkaline conditions could facilitate the dehydrogenation process and prevent the adsorption of FDCA on the catalyst surface. (31) While the highly selective oxidation of HMF under neutral or weakly basic environments could occur on noble metal catalysts. (24,25) NaOH in this Co–N–C system also played an additional role, that is, by adjusting to appropriate alkaline conditions, O₂ was activated to OH^• with a suitable concentration, which could ensure the highly selective oxidation of HMF at room temperature. Clearly, excessive OH^• was not conducive to the selective oxidation due to causing side reactions. In contrast, HMF almost completely decomposed without FDCA formation by using the H₂O₂ + OH^– system with initial OH^• intensity 4 times higher than that of the Co–N–C system at the optimized pH value (12.79). These results verified that the high OH^• concentration was unfavorable for the enhancement of catalytic selectivity. Therefore, regulation of OH^• concentration to the appropriate level could be realized by adjusting the pH value in the Co–N–C system, thus exhibiting the optimal performance of catalytic selective oxidation of hydroxyl compounds.
显然，与外部添加的 H₂O₂ 相比，原位形成的 OH^• 浓度足够低，以确保选择性氧化而不是氧化降解。进一步的研究发现，调整 Co-N-C 系统中的 pH 值可以调节原位形成的 OH^• 的强度。如图 7a 所示，在中性水溶液（pH = 7.02）中没有出现 OH^• 信号，并且 HMF 转化缓慢，对 FDCA 的选择性极低。当通过添加 NaHCO₃ 增加到 pH = 8.16 时，可以观察到 OH^• 信号的弱峰。随着 NaOH 的加入使 pH 值升高到 13.32，OH^• 强度持续增加。结果表明，Co-N-C 的 OH^• 形成活性与水溶液的基本强度密切相关。FDCA 的产量与 pH 值呈火山曲线关系，其中 pH = 12.79 最好，最高产量为 98.0%（图 7d）。这与报道的研究一致，即当使用非贵金属催化剂作为碱性条件时，HMF 氧化成 FDCA 所必需的无机碱如 NaOH、Na₂、CO₃、NaHCO₃ 等可以促进脱氢过程并防止 FDCA 在催化剂表面的吸附。（31）而 HMF 在中性或弱碱性环境中的高选择性氧化可能发生在贵金属催化剂上。（24,25） NaOH 在这个 Co-N-C 体系中还起了额外的作用，即通过调整到适当的碱性条件，O₂ 被活化为具有适当浓度的 OH^• ，这可以保证 HMF 在室温下的高度选择性氧化。显然，过量的 OH^• 由于引起副反应，不利于选择性氧化。相比之下，在最佳 pH 值（4）下，HMF 使用 H₂O₂ + OH^– 系统几乎完全分解，没有形成 FDCA，初始 OH^• 强度比 Co-N-C 系统高 12.79 倍。这些结果验证了高 OH^• 浓度不利于催化选择性的增强。因此，可以通过调节 Co-N-C 系统中的 pH 值来实现将 OH^• 浓度调节到适当的水平，从而表现出羟基化合物催化选择性氧化的最佳性能。

Figure 7. ESR spectra of DMPO-OH^• adducts at the reaction time of 30 min in the H₂O₂ + OH^– system at a pH value of 12.79 and Co–N–C system with different pH values (a); the intensity of the DMPO-OH^• adducts in the ESR spectra (b); Arrhenius plots of HMF oxidation with and without OH^• in the Co–N–C system (c); the product yield in HMF oxidation in the Co–N–C system with different pH values and in the H₂O₂ + OH^– system at a pH value of 12.79 (d); and the schematic illustration of the HMF oxidation with OH^• formation in the Co–N–C system (e). Reaction conditions: 0.5 mmol HMF, 0.032 mmol Co in Co–N–C, 5 mL of H₂O, 60 °C, 40 mL/min O₂, 5 h, at different pH values; ^a0.5 mmol HMF, 1 mL of 30 wt % H₂O₂, 4 mL of H₂O, 60 °C, 5 h, and pH = 12.79.
图 7.DMPO-OH^• 加合物在 pH 值为 12.79 的 H₂O₂ + OH^– 系统和不同 pH 值的 Co-N-C 系统中反应时间为 30 分钟的 ESR 光谱（a）;ESR 光谱中 DMPO-OH^• 加合物的强度（b）;Co-N-C 系统中含和不含 OH^• 的 HMF 氧化的 Arrhenius 图（c）;在不同 pH 值的 Co-N-C 体系和 pH 值为 12.79 的 H₂O₂ + OH^– 体系中 HMF 氧化的产物收率（d）;以及 Co-N-C 系统中 HMF 氧化与 OH^• 形成的示意图（e）。反应条件：0.5 mmol HMF，0.032 mmol Co in Co–N–C，5 mL H₂O，60 °C，40 mL/min O_2,5 h，不同 pH 值;^0.5mmol HMF、1 mL 30 wt % H₂O₂、4 mL H₂O、60 °C、5 h 和 pH = 12.79。

The calculated apparent activation energy (E_a) of HMF oxidation in the Co–N–C system with different pH values was also determined (Figure 7c). Compared with OH^• free in pH = 7.02, the E_a value in pH = 12.79 with OH^• formation was reduced from 58.4 to 25.7 kJ/mol, and lower than that reported for the noble metal catalyst (Pt/C, 29.0 kJ/mol). (45) The controllable production of OH^• with strong oxidizing ability by the activation of O₂ and H₂O over the Co–N–C catalyst contributed to the decrease of the apparent activation energy in the oxidation of hydroxyl compounds.
还确定了不同 pH 值下 Co-N-C 系统中 HMF 氧化的计算表观活化能（E_a）（图 7c）。与 pH = 7.02 中的不含 OH^• 相比，OH^• 形成时 pH = 12.79 时的 E_a 值从 58.4 kJ/mol 降低到 25.7 kJ/mol，低于贵金属催化剂报道的值（Pt/C，29.0 kJ/mol）。（45）通过在 Co-N-C 催化剂上活化 O₂ 和 H₂O 可控地产生具有强氧化能力的 OH^• 有助于降低羟基化合物氧化过程中的表观活化能。

2.6. OH^• Accelerating the H-Abstraction of C–H Bonds
2.6. OH^• 加速 C-H 键的 H 抽象

The oxidation of −CH₂OH groups to −C═O groups often required hydrogen abstraction, i.e., cleavage of two classes of chemical bonds, O–H and C–H. In the conventional OH^• generating systems, the strong electrophilicity of OH^• was employed in the H-atom abstraction of alkanes or aromatics, thus leading to the degradation of them. (5) To explore the relationship between OH^• and hydrogen abstraction in −CH₂OH oxidation in this Co–N–C system, the kinetic isotope effects (KIE) were studied by using model substrates of benzyl alcohol deuterated at the methylene group (PhCD₂OH) and at the hydroxyl group (PhCH₂OD), respectively. As shown in Figure S19 and Table S2, the KIE value (k(PhCH₂OH)/k(PhCH₂OD)) for PhCH₂OD was 1.27, while the PhCD₂OH gave a higher KIE value (k(PhCH₂OH)/k(PhCD₂OH)) of 2.40. These results indicated that the hydrogen abstraction of the C–H bond in the −CH₂OH group was involved in the rate-determining step of the PhCH₂OH oxidation. Then, increasing the OH^• concentration by the enhancement of pH values in the reaction system led to all the values of k(PhCH₂OH), k(PhCD₂OH), and k(PhCH₂OD) increasing. Meanwhile, the KIE value for PhCD₂OH decreased from 2.40 to 1.82 with the increase of the OH^• concentration. In contrast, the KIE value for PhCH₂OD was almost unchanged. Although the acidity of hydroxyl hydrogen is stronger than that of C–H in the −CH₂OH group, the enhancement of alkalinity in the reaction system caused by the pH increase did not lead to the activation of O–H in the PhCH₂OH oxidation process. Therefore, the promoting effect of the enhancement of alkalinity on the breaking of C–H bonds could be ignored. These results indicated that the hydrogen abstraction of C–H bonds could be favored by OH^• at appropriate concentrations during the oxidation of −CH₂OH groups in hydroxyl compounds.
-CH₂OH 基团氧化成 -C═O 基团通常需要提取氢，即裂解两类化学键，O-H 和 C-H。在传统的 OH^• 生成系统中，OH^• 的强亲电性被用于烷烃或芳烃的 H 原子提取，从而导致它们的降解。（5）为了探索该 Co-N-C 系统中 -CH₂OH 氧化中 OH^• 和氢提取之间的关系，分别使用在亚甲基（PhCD₂OH）和羟基（PhCH₂OD）处氘化的苯甲醇的模型底物研究了动力学同位素效应（KIE）。如图 S19 和表 S2 所示，PhCH₂OD 的 KIE 值（k（PhCH₂OH）/k（PhCH₂OD））为 1.27，而 PhCD₂OH 的 KIE 值（k（PhCH₂OH）/k（PhCD₂OH））更高，为 2.40。这些结果表明，−CH₂OH 基团中 C-H 键的氢提取参与了 PhCH₂OH 氧化的速率确定步骤。然后，通过提高反应体系中的 pH 值来增加 OH^• 浓度，导致 k（PhCH₂OH）、k（PhCD₂OH）和 k（PhCH₂OD）的所有值都增加。同时，随着 OH^• 浓度的增加，PhCD₂OH 的 KIE 值从 2.40 降低到 1.82。相比之下，PhCH₂OD 的 KIE 值几乎没有变化。尽管在 −CH₂OH 基团中羟基氢的酸度比 C-H 强，但 pH 值升高引起的反应系统中碱度的增强并不会导致 PhCH₂OH 氧化过程中 O-H 的激活。因此，碱度增强对 C-H 键断裂的促进作用可以忽略不计。这些结果表明，在羟基化合物中 −CH₂OH 基团的氧化过程中，适当浓度的 OH^• 可能有利于 C-H 键的氢提取。

The substrate scope for the biomimetic Co–N–C catalyst was extended to a variety of model hydroxyl compounds, including cellulose-derived furan alcohols, lignin-derived aromatic alcohols, and oil-based aromatic alcohols, with excellent yields (84.1–97.4%) of the corresponding acids obtained (Table 3). In comparison with the previous studies, (31,46−48) the thermal catalytic oxidation of these hydroxyl compounds was usually performed under harsh reaction conditions when employing non-noble metal catalysts for the purpose of acid products. For example, cobalt-based catalysts (Co/GS@C, Co-Co₃O₄@NC, Co₃O₄, etc.) generally required a temperature above 100 °C for the oxidation of typical lignin-derived model aromatic alcohols. In the case of 3,4,5-trimethoxybenzyl alcohol, Co₃O₄ only afforded 16.1% yield of 3,4,5-trimethoxybenzoic acid by catalytic oxidation at 140 °C under 4 MPa O₂. (48) In contrast, the present non-noble Co–N–C catalyst achieved 95.6% yield of 3,4,5-trimethoxybenzoic acid under significantly milder conditions (at 60 °C under the atmospheric pressure of O₂). Considering there were few reports on the non-noble metals catalyzed oxidation of specific fatty alcohols in water, the activity of Co–N–C was tested in the oxidation of 1-butanol. It achieved as high as 79.1% yield of butyric acid, which is not accessible by the reported heterogeneous non-noble catalysts. These results demonstrated the wide generalizability of Co–N–C in the hydroxyl compounds oxidation. The stability and reusability of Co–N–C were also explored. The Co–N–C catalyst could retain its activity for at least four recycling runs, with only a slight reduction of FDCA yield (Figure S20). It is noteworthy that the catalyst could be reused by simply washing with water and soaping in NaOH aqueous solution. While for the majority of the reported N-doped carbon-supported metal-based catalysts for catalytic oxidation, the reduction under H₂ or calcination in inert gas at high temperatures was usually required to restore their activity. (30,49) This difference reflected the excellent stability and reusability of Co–N–C. As discussed above, the in situ and continuously generated OH^• by self-cascade catalysis in the Co–N–C system was conducive to the hydroxyl compounds oxidation via promoting the hydrogen abstraction of C–H bonds in the −CH₂OH groups, thus realizing that the highly selective oxidation of multiple sources of hydroxyl compounds to the corresponding acids could be performed under mild conditions.
仿生 Co-N-C 催化剂的底物范围扩展到各种模型羟基化合物，包括纤维素衍生的呋喃醇、木质素衍生的芳香醇和油基芳香醇，获得的相应酸的产率极高（84.1–97.4%）（表 3）。与以前的研究相比，（31,46−48）当使用非贵金属催化剂生产酸产品时，这些羟基化合物的热催化氧化通常是在恶劣的反应条件下进行的。例如，钴基催化剂（Co/GS@C、Co-Co₃O₄@NC、Co₃O₄ 等）通常需要 100 °C 以上的温度才能氧化典型的木质素衍生的模型芳香醇。在 3,4,5-三甲氧基苯甲醇的情况下，Co₃O₄ 在 140 °C 下在 4 MPa O₂ 下催化氧化，仅得到 3,4,5-三甲氧基苯甲酸的 16.1% 产率。（48）相比之下，目前的非贵金属 Co-N-C 催化剂在明显较温和的条件下（在 O₂ 的大气压下为 60 °C）实现了 3,4,5-三甲氧基苯甲酸的 95.6% 产率。考虑到关于非贵金属催化水中特定脂肪醇氧化的报道很少，因此在 1-丁醇的氧化中测试了 Co-N-C 的活性。它实现了高达 79.1% 的丁酸收率，这是已报道的非均相非贵金属催化剂无法获得的。这些结果表明 Co-N-C 在羟基化合物氧化中的广泛泛化性。还探讨了 Co-N-C 的稳定性和可再利用性。 Co-N-C 催化剂可以保持其活性至少四次回收运行，而 FDCA 收率仅略有降低（图 S20）。值得注意的是，只需用水清洗并在 NaOH 水溶液中皂洗即可重复使用该催化剂。而对于大多数已报道的用于催化氧化的 N 掺杂碳负载金属基催化剂，通常需要在 H₂ 下还原或在高温下在惰性气体中煅烧以恢复其活性。（30,49）这种差异反映了 Co-N-C 出色的稳定性和可重用性。如上所述，在 Co-N-C 系统中通过自级联催化原位和连续生成的 OH^• 通过促进 -CH₂OH 基团中 C-H 键的氢提取，有利于羟基化合物氧化，从而实现多种来源的羟基化合物高度选择性氧化为相应的酸在温和的条件下。

Table 3. Catalytic Oxidation of Various Hydroxyl Compounds over the Co–N–C Catalyst
表 3.各种羟基化合物在 Co-N-C 催化剂上的催化氧化

^{^a}

Reaction condition: 0.5 mmol substrate, 0.022 mmol Co in Co–N–C, 1.0 mmol NaOH, 5 mL of H₂O, 40 mL/min O₂, and 60 °C.

^{^a}

反应条件：0.5 mmol 底物、0.022 mmol Co in Co–N–C、1.0 mmol NaOH、5 mL H₂O、40 mL/min O₂ 和 60 °C。

^{^b}

0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 60 °C.

^{^b}

0.032 mmol Co 的 Co–N–C 溶液，1.25 mmol NaOH，60 °C。

^{^c}

0.016 mmol Co in Co–N–C, 1.25 mmol NaOH, 50 °C.

^{^c}

0.016 mmol Co 的 Co–N–C 溶液，1.25 mmol NaOH，50 °C。

3. Conclusions 3. 结论

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In summary, the Co–N–C catalyst enabled the regulated activation of molecular oxygen into reactivity controllable OH^• via self-cascade catalysis for efficient selective oxidation of a variety of biomass and petroleum-based hydroxyl compounds to organic acids under mild conditions. For the HMF oxidation, the >99.9% conversion of HMF with 94.2% selectivity of FDCA could be obtained at 25 °C under atmospheric pressure, with a high FDCA productivity value (8.1 h^–1). The OH^• with high oxidizing potential could be controllably and continuously generated in situ from O₂ and H₂O with simple pH variation. The high catalytic performance of the Co–N–C catalyst was closely related to its atomically dispersed CoN₄ sites and large conjugated aromatic coordination structures. Moreover, a promotion effect by OH^• in the hydrogen abstraction of the C–H bond in the −CH₂OH group resulted in obviously reduced activation energy. This study provides a promising strategy of regulated activation of molecular oxygen into designed reactive oxygen species for oxidative synthesis of chemicals.
总之，Co-N-C 催化剂能够通过自级联催化将分子氧调节活化为反应性可控的 OH^• ，从而在温和条件下将各种生物质和石油基羟基化合物高效选择性氧化为有机酸。对于 HMF 氧化，在 25 °C 大气压下可以获得 >99.9% 的 HMF 转化率和 94.2% 的 FDCA 选择性，具有较高的 FDCA 生产率值（8.1 h^–1）。具有高氧化电位的 OH^• 可以从 O₂ 和 H₂O 原位受控地连续生成，pH 值变化简单。Co-N-C 催化剂的高催化性能与其原子分散的 CoN₄ 位点和大的共轭芳烃配位结构密切相关。此外，OH^• 在 −CH₂OH 基团中 C-H 键的氢提取中的促进作用导致活化能明显降低。本研究提供了一种很有前途的策略，将分子氧调节活化成设计的活性氧，用于化学品的氧化合成。

Supporting Information 支持信息

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acscatal.3c02736.
支持信息可在 https://pubs.acs.org/doi/10.1021/acscatal.3c02736 免费获取。

Details of experimental procedures and data processing, comparison of Co–N–C and reported non-noble catalysts for HMF oxidation, additional characterization data of Co-based catalysts, ESR spectra of DMPO-radical adducts, UV–vis spectra of KI oxidation, GC spectra of Ph₃P oxidation, mass spectrum of CO₂, reaction time profiles for HMF and HMFCA oxidations, recycling experiments of Co–N–C, kinetics analysis for benzyl alcohol oxidation, and supplementary catalytic evaluation (PDF)
实验程序和数据处理的详细信息，用于 HMF 氧化的 Co-N-C 和已报道的非贵金属催化剂的比较，Co 基催化剂的其他表征数据，DMPO 自由基加合物的 ESR 光谱，KI 氧化的紫外-可见光谱，Ph₃P 氧化的 GC 光谱，CO₂ 的质谱，HMF 和 HMFCA 氧化的反应时间曲线， Co-N-C 回收实验、苯甲醇氧化动力学分析和补充催化评估（PDF）

cs3c02736_si_001.pdf (812.04 kb)
cs3c02736_si_001.pdf （812.04 kb）

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Author Information 作者信息

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Corresponding Authors 通讯作者
- Hong Ma - State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China; Email: mahong@dicp.ac.cn
  Hong 马 - 中国科学院大连化学物理研究所催化国家重点实验室，中国116023连市中山路457号; 电子邮件： mahong@dicp.ac.cn
- Jie Xu - State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China; https://orcid.org/0000-0003-2535-094X; Email: xujie@dicp.ac.cn
  徐杰 - 中国科学院大连化学物理研究所催化国家重点实验室，中国大连116023中山路457号; https://orcid.org/0000-0003-2535-094X; 电子邮件： xujie@dicp.ac.cn
Authors 作者
- Xin Liu - State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China; University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  刘欣 - 中国科学院大连化学物理研究所催化国家重点实验室，中国大连116023中山路 457 号;中国科学院大学，北京 100049
- Meiyun Zhang - State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China; University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  Meiyun Zhang - 中国科学院大连化学物理研究所催化国家重点实验室，中国大连116023中山路457号;中国科学院大学，北京 100049
- Penghua Che - State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
  Penghua Che - 中国科学院大连化学物理研究所催化国家重点实验室，中国大连116023中山路 457 号
- Yang Luo - State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
  罗洋 - 中国科学院大连化学物理研究所催化国家重点实验室，中国116023连市中山路457号
- Shujing Zhang - State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
  张淑静 - 中国科学院大连化学物理研究所催化国家重点实验室，中国大连116023中山路457号
Author Contributions 作者贡献
J.X., H.M., and X.L. designed the research. X.L. performed the catalyst preparation, characterizations, and tests, and completed the paper. M.Z., P.C., Y.L., and S.Z. participated in beneficial discussions. All authors reviewed and commented on the article.
J.X.、H.M. 和 X.L. 设计了这项研究。X.L. 进行了催化剂制备、表征和测试，并完成了论文。M.Z.、P.C.、Y.L. 和 S.Z. 参与了有益的讨论。所有作者都对文章进行了审阅和评论。
Notes 笔记
The authors declare no competing financial interest.
作者声明没有竞争性的经济利益。

Acknowledgments 确认

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This work was supported by the National Natural Science Foundation of China (21790331, 22272172, and 22072149) and the National Key R&D Program of China (2022YFA1504902).
这项工作得到了国家自然科学基金（21790331、22272172 和 22072149）和国家重点研发计划（2022YFA1504902）的支持。

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Li， Qi;Li， Fa-tang
Chemical Engineering Journal（荷兰阿姆斯特丹）（2021 年）， 421 （Part_1）、 129915科登： CMEJAJ; 国际标准书号：1385-8947。（爱思唯尔 BV）
综述。分子氧是最环保的潜在氧化剂，但其禁止旋转的性质限制了它的活化和应用。利用光催化技术将摩尔氧活化为活性氧（ROS）是从能量转移过程和电荷转移过程的活化方法中启动摩尔氧活化性能的可行策略，例如提高系统间交叉的效率，减少非辐射衰变，增强分子氧吸附和电荷 SEPN。效率。介绍了分子氧激活途径分析和 ROS 检测方法的新观点。此外，活性氧在一些氧化反应中的应用，包括 degrdn.对组织污染物、组织合成和肿瘤的光动力疗法进行了总结。最后，简要介绍了结论和挑战。
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Metz, M.; Solomon, E. I. Dioxygen Binding to Deoxyhemocyanin: Electronic Structure and Mechanism of the Spin-Forbidden Two-Electron Reduction of O₂. J. Am. Chem. Soc. 2001, 123, 4938– 4950, DOI: 10.1021/ja004166b
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Dioxygen Binding to Deoxyhemocyanin: Electronic Structure and Mechanism of the Spin-Forbidden Two-Electron Reduction of O2
Metz, Markus; Solomon, Edward I.
Journal of the American Chemical Society (2001), 123 (21), 4938-4950CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Spectroscopically calibrated DFT is used to investigate the reaction coordinate of O2 binding to Hemocyanin (Hc). A reaction path is calcd. in which O2 approaches the binuclear copper site with increasing metal-ligand overlap, which switches the coordination mode from end-on η1-η1, to μ-η1:η2, then to butterfly, and finally to the planar [Cu2(μ-η2:η2O2)] structure. Anal. of the electronic structures during O2 binding reveals that simultaneous two-electron transfer (ET) takes place. At early stages of O2 binding the energy difference between the triplet and the singlet state is reduced by charge transfer (CT), which delocalizes the unpaired electrons and thus lowers the exchange stabilization onto the sepd. copper centers. The electron spins on the copper(II) ions are initially ferromagnetically coupled due to close to orthogonal magnetic orbital pathways through the dioxygen bridging ligand, and a change in the structure of the Cu2O2 core turns on the superexchange coupling between the coppers. This favors the singlet state over the triplet state enabling intersystem crossing. Comparison with mononuclear model complexes indicates that the protein matrix holds the two copper(I) centers in close proximity, which enthalpically and entropically favors O2 binding due to destabilization of the reduced binuclear site. This also allows regulation of the enthalpy by the change of the Cu-Cu distance in deoxyHc, which provides an explanation for the O2 binding cooperativity in Hc. These results are compared to our earlier studies of Hemerythrin (Hr) and a common theme emerges where the spin forbiddeness of O2 binding is overcome through delocalization of unpaired electrons onto the metal centers and the superexchange coupling of the metal centers via a ligand bridge.
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梅茨，M.;所罗门，EI 双氧结合脱氧血蓝蛋白：O₂ 的自旋禁止双电子还原的电子结构和机制。J. Am. Chem. Soc. 2001， 123， 4938– 4950， DOI： 10.1021/ja004166b
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双氧结合与脱氧血蓝蛋白：O2 Metz 自旋禁止双电子还原的电子结构和机制
，Markus;所罗门，爱德华一世。
美国化学会杂志（2001 年）、 123 元（21）、 4938-4950科登： JACSAT公司; 国际标准书号：0002-7863。（美国化学学会）
光谱校准的 DFT 用于研究 O2 与血蓝蛋白（Hc）结合的反应坐标。反应路径是 calcd。其中 O2 以增加金属-配体重叠接近双核铜位点，这将配位模式从末端 η1-η1 切换到 μ-η1：η2，然后切换到蝶形，最后切换到平面 [Cu2（μ-η2：η2O2）] 结构。 O2 结合过程中的电子结构分析显示同时发生双电子转移（ET）。在 O2 结合的早期阶段，三重态和单重态之间的能量差异通过电荷转移（CT）而减小，电荷转移（CT）使未成对的电子离域，从而降低对分离铜中心的交换稳定性。由于通过双氧桥接配体的接近正交磁轨道路径，铜（II）离子上的电子自旋最初是铁磁耦合的，并且 Cu2O2 核心结构的变化会打开铜之间的超交换耦合。这有利于单重态而不是三重态，从而实现系统间交叉。与单核模型复合物的比较表明，蛋白质基质将两个铜（I）中心紧紧地保持在一起，由于还原的双核位点的不稳定，这在焓和熵上有利于 O 2 结合。这也允许通过改变脱氧 Hc 中 Cu-Cu 距离来调节焓，这为 Hc 中的 O2 结合协同性提供了解释。将这些结果与我们早期的 Hemerythrin （Hr）研究进行了比较，出现了一个共同的主题，即通过将不成对的电子离域到金属中心和金属中心通过配体桥的超交换耦合来克服 O2 结合的自旋禁止。
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Gligorovski, S.; Strekowski, R.; Barbati, S.; Vione, D. Environmental Implications of Hydroxyl Radicals (^•OH). Chem. Rev. 2015, 115, 13051– 13092, DOI: 10.1021/cr500310b
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Environmental Implications of Hydroxyl Radicals (•OH)
Gligorovski, Sasho; Strekowski, Rafal; Barbati, Stephane; Vione, Davide
Chemical Reviews (Washington, DC, United States) (2015), 115 (24), 13051-13092CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)
A review concerning the formation, occurrence, reactivity, scavenging, and detection of OH- in natural environmental compartments (natural water and indoor and outdoor atm.) and lab. systems is given. A comprehensive understanding of OH- sources and sinks and their implications in natural water and in the atm. is critically important, including the way surface water irradiated chromophoric dissolved org. matter yields OH- via the H2O2-independent pathway, and including an assessment of the relative importance of gas- vs aq.-phase OH- reactions with many atm. components. Topics discussed include: introduction; OH- formation and scavenging under different conditions (aq. environment, atm., indoor atm.); OH- generation under controlled lab. conditions (aq. phase, gas phase); OH- prodn. and prodn.-detection in the lab. and gaseous and aq. phases; OH- kinetic properties in aq. soln.; OH- reaction mechanisms in aq. soln. and in gas phase; and conclusions and outlook.
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格里戈罗夫斯基，S.;斯特雷科夫斯基，R.;巴巴蒂，S.;维奥内 D. 羟基自由基的环境影响（^•OH）。化学修订版 2015， 115， 13051– 13092， DOI： 10.1021/cr500310b
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羟基自由基的环境影响（•OH）
Gligorovski， Sasho;斯特雷科夫斯基，拉法尔;巴巴蒂，斯蒂芬;Vione， Davide
Chemical Reviews （美国华盛顿特区）（2015 年）， 115 元（24）、 13051-13092科登：克雷; 国际标准书号：0009-2665。（美国化学学会）
综述了自然环境隔室（天然水和室内外 atm）和实验室系统中 OH- 的形成、发生、反应性、清除和检测。全面了解 OH- 源和汇及其在自然水和大气中的影响至关重要，包括地表水照射发色溶解组织物质通过 H2O2 非依赖性途径产生 OH- 的方式，包括评估气体与水溶液相 OH- 反应与许多大气压成分的相对重要性。讨论的主题包括：引言;不同条件下的 OH- 形成和清除（水生环境、大气压、室内大气压）;OH- 在受控实验室下生成。条件（水相、气相）;OH- prodn.以及实验室中的生产检测。以及气相和 AQ 相;水溶液中的 OH- 动力学特性;水溶液和气相中的 OH- 反应机理;以及结论和展望。
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Hou, J.-T.; Zhang, M.; Liu, Y.; Ma, X.; Duan, R.; Cao, X.; Yuan, F.; Liao, Y.-X.; Wang, S.; Ren, W. X. Fluorescent Detectors for Hydroxyl Radical and their Applications in Bioimaging: A Review. Coord. Chem. Rev. 2020, 421, 213457 DOI: 10.1016/j.ccr.2020.213457
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Fluorescent detectors for hydroxyl radical and their applications in bioimaging: A review
Hou, Ji-Ting; Zhang, Man; Liu, Yan; Ma, Xuefei; Duan, Ran; Cao, Xinhua; Yuan, Fengying; Liao, Ye-Xin; Wang, Shan; Xiu Ren, Wen
Coordination Chemistry Reviews (2020), 421 (), 213457CODEN: CCHRAM; ISSN:0010-8545. (Elsevier B.V.)
A review. Among various reactive oxygen species (ROS), hydroxyl radical (·OH) has the strongest oxidizability, which causes damage to a wide array of biomacromols. in the cells, including DNA, lipid, and proteins. Therefore, the over-produced ·OH is verified to be implicated in various oxidative-stress related pathophysiol. processes, such as inflammation, cancer, and cardiovascular disorder. However, the precise pathogenic roles played by this substance have been far from being clearly understood due to its high reactivity, short lifetime, and low concn. in biosystems. Thus, developing highly sensitive and selective detecting tools for monitoring ·OH is of significant importance. This review summarizes the advances that have been made in the last decade in the development of fluorescent sensors for ·OH detection based on small mols. and nanoparticles as well as their diverse biol. applications.
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侯 J.-T.;张 M.;刘 Y.;马，X.;段 R.;曹 X.;袁 F.;廖 Y.-X.;王 S.;任，W. X. 羟基自由基荧光检测器及其在生物成像中的应用：综述。Coord. Chem. Rev. 2020， 421， 213457 DOI： 10.1016/j.ccr.2020.213457
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羟基自由基荧光探测器及其在生物成像中的应用：综述
侯吉婷;张曼;刘燕;马雪飞;段冉;曹新华;袁凤英;廖叶欣;王姗;秀任，温
配位化学评论（2020 年）， 421 （）， 213457科登： CCHRAM; 国际标准书号：0010-8545。（爱思唯尔 BV）
评论。在各种活性氧（ROS）中，羟基自由基（·OH）具有最强的氧化性，可对多种生物大分子造成损害。在细胞中，包括 DNA、脂质和蛋白质。因此，过度生产的 ·OH 被证实与各种氧化应激相关的病理生理学有关。炎症、癌症和心血管疾病等过程。然而，由于其高反应性、短寿命和低浓度，该物质所起的确切致病作用远未得到明确理解。在 Biosystems 中。因此，开发高灵敏度和选择性的检测工具进行监测 ·OH 非常重要。本文总结了过去十年中荧光传感器开发的进展 ·基于小分子的 OH 检测。和纳米颗粒及其各种生物学应用。
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Wang, B.; Su, H.; Zhang, B. Hydrodynamic Cavitation as a Promising Route for Wastewater Treatment–A Review. Chem. Eng. J. 2021, 412, 128685 DOI: 10.1016/j.cej.2021.128685
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Hydrodynamic cavitation as a promising route for wastewater treatment - A review
Wang, Baowei; Su, Huijuan; Zhang, Bo
Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 412 (), 128685CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
A review. As one of the advanced oxidn. processes, the cavitation-based process has become a promising technol. for treating industrial effluents due to the advantages of cost-effectiveness in operation, higher energy efficiencies, and large-scale operation. In hydrodynamic cavitation (HC), cavities are generated as a result of local pressure drops caused by various constrictors or by mech. rotation of the vortex diode and other rotating-type devices. The study on the influence of various geometric parameters of different kinds of HC reactors and the operation conditions is popular among researchers. In the present work, we systematically introduced the formation of HC and the mechanism of degrdn. of pollutants by HC. Further, for various cavitating devices, the influence of various geometrical and operating parameters affecting the cavitation conditions was discussed in detail. Overviews of earlier work based on the different types of HC reactors including venturi, orifice plate, rotating-type HC devices, and vortex diode were elaborated. Moreover, a detailed summary of HC-based hybrid technologies employed in recent work was presented to better show the synergetic index of different processes. Some recommendations for future work have been proposed.
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王 B.;苏，H.;张斌流体动力空化作为废水处理的有前途的路线——综述。化学工程学杂志 2021， 412， 128685 DOI： 10.1016/j.cej.2021.128685
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流体动力空化作为废水处理的有前途的路线 - 综述
王宝伟;苏慧娟;Zhang， Bo
Chemical Engineering Journal （荷兰阿姆斯特丹）（2021 年）， 412 （）， 128685科登： CMEJAJ; 国际标准书号：1385-8947。（爱思唯尔 BV）
评论。作为高级氧化剂之一。工艺中，基于空化的工艺已成为一种很有前途的技术。由于运行成本效益高、能源效率高和大规模运行等优势，用于处理工业废水。在流体动力学空化（HC）中，空腔是由于各种收缩器或机械引起的局部压降而产生的。涡流二极管和其他旋转型器件的旋转。研究不同种类 HC 反应器的各种几何参数和运行条件的影响受到研究人员的欢迎。在这项工作中，我们系统地介绍了 HC 的形成和 degrdn 的机制。HC 的污染物。此外，对于各种空化装置，详细讨论了影响空化条件的各种几何和操作参数的影响。详细阐述了基于不同类型的 HC 反应器的早期工作，包括文丘里管、孔板、旋转式 HC 装置和涡旋二极管。此外，还详细总结了最近工作中采用的基于 HC 的混合技术，以更好地显示不同过程的协同指数。已经为未来的工作提出了一些建议。
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Cheng, C.; Ren, W.; Miao, F.; Chen, X.; Chen, X.; Zhang, H. Generation of FeIV═O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron-N-C Catalyst. Angew. Chem., Int. Ed. 2023, 62, e202218510 DOI: 10.1002/ange.202218510
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Generation of FeIV=O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron-N-C Catalyst
Cheng, Cheng; Ren, Wei; Miao, Fei; Chen, Xuantong; Chen, Xiaoxiao; Zhang, Hui
Angewandte Chemie, International Edition (2023), 62 (10), e202218510CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
GeneratingFeIV=O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the FeIV=O generation pathway and oxidn. behavior remain obscure. Employing an Fe-N-C catalyst with a typical Fe-N4 moiety to activate peroxymonosulfate (PMS), we demonstrate that generating FeIV=O is mediated by an Fe-N-C-PMS* complex-a well-recognized nonradical species for induction of electron-transfer oxidn.-and we detd. that adjacent Fe sites with a specific Fe1-Fe1 distance are required. After the Fe atoms with an Fe1-Fe1 distance <4 S are PMS-satd., Fe-N-C-PMS* formed on Fe sites with an Fe1-Fe1 distance of 4-5 S can coordinate with the adjacent FeII-N4, forming an inter-complex with enhanced charge transfer to produce FeIV=O. FeIV=O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidn. potential.
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程 C.;任， W.;苗， F.;陈 X.;陈 X.;张 H. FeIV═O 的生成及其对单原子铁-N-C 催化剂上 Fenton 类反应的贡献。Angew. Chem.，国际教育 2023， 62， e202218510 DOI： 10.1002/ange.202218510
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FeIV=O 的产生及其对单原子铁-N-C 催化剂上 Fenton 样反应的贡献
Cheng， Cheng;任魏;苗飞;陈轩彤;陈晓晓;Zhang， Hui
Angewandte Chemie，国际版（2023 年）， 62 （10）、编号 e202218510科登： ACIEF5; 国际标准书号：1433-7851。（Wiley-VCH Verlag GmbH & Co. KGaA）
通过 Fenton 样反应在单原子催化剂上生成 FeIV=O 已经用于水处理;然而，FeIV=O 的生成途径和氧化行为仍然不清楚。使用具有典型 Fe-N4 部分的 Fe-N-C 催化剂来激活过氧一硫酸盐（PMS），我们证明了 FeIV=O 的产生是由 Fe-N-C-PMS* 配合物介导的 - 一种公认的用于诱导电子转移氧化的非自由基物质。需要具有特定 Fe1-Fe1 距离的相邻 Fe 位点。在Fe1-Fe1距离为<4 S的Fe原子被PMS-satd.后，在Fe1-Fe1距离为4-5 S的Fe位点上形成的Fe-N-C-PMS*可以与相邻的FeII-N4配位，形成电荷转移增强的复合物，产生FeIV=O。 FeIV=O 使 Fenton 类系统能够以底物特异性、pH 值耐受性和可持续的方式有效地氧化各种污染物，其中其突出贡献体现在单电子氧化率较高的污染物中。潜在。
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Chen, Z.; Zhou, H.; Kong, F.; Wang, M. Piezocatalytic Oxidation of 5-Hydroxymethylfurfural to 5-Formyl-2-Furancarboxylic Acid over Pt Decorated Hydroxyapatite. Appl. Catal., B 2022, 309, 121281 DOI: 10.1016/j.apcatb.2022.121281
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Piezocatalytic oxidation of 5-hydroxymethylfurfural to 5-formyl-2-furancarboxylic acid over Pt decorated hydroxyapatite
Chen, Zhiwei; Zhou, Hongru; Kong, Fanhao; Wang, Min
Applied Catalysis, B: Environmental (2022), 309 (), 121281CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
Selective oxidn. of 5-hydroxymethylfurfural (HMF) to 5-formyl-2-furancarboxylic acid (FFCA) is a crit. reaction for producing value-added chems. from biomass. The challenge for this reaction is to develop an efficient catalytic process that can be conducted under mild conditions. Herein, we first propose piezocatalytic HMF oxidn. using a Pt decorated hydroxyapatite (HAP) piezocatalyst (Pt/HAP). The introduction of Pt on HAP creates an interfacial elec. field. The couple of nonlocal piezoelec. field and localized interfacial elec. field greatly promotes both the bulk and surface charges transfer. Moreover, Pt not only promotes the sepn. of piezo-induced charges but also activates oxygen mols. and org. functional groups of the substrates. Compared with pristine HAP, Pt/HAP exhibits outstanding piezocatalytic activity, which reached 96% HMF conversion and 70% FFCA yield in 2 h under room temp. A wide range of aldehydes and alcs., such as fatty aldehydes, furan aldehydes, fatty alcs., and ethylene glycol, were all oxidized to carboxylic acids. This work provides a novel method on utilizing piezocatalysis for biomass conversion.
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陈 Z.;周， H.;孔，F.;王 M. 5-羟甲基糠醛在 Pt 修饰的羟基磷灰石上压电催化氧化为 5-甲酰基-2-呋喃羧酸。应用加泰罗尼亚， B 2022， 309， 121281 DOI： 10.1016/j.apcatb.2022.121281
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5-羟甲基糠醛在 Pt 修饰的羟基磷灰石上压电催化氧化为 5-甲酰基-2-呋喃羧酸
Chen， Zhiwei;周洪儒;孔凡浩;Wang， Min
Applied Catalysis， B：环境（2022 年）， 309 元（）， 121281科登： ACBEE3; 国际标准书号：0926-3373。（爱思唯尔 BV）
5-羟甲基糠醛（HMF）选择性氧化成 5-甲酰基-2-呋喃羧酸（FFCA）是一种从生物质中生产增值化学品的关键反应。该反应的挑战是开发一种可以在温和条件下进行的有效催化过程。在此，我们首先提出了压电催化 HMF 氧化剂。使用 Pt 修饰的羟基磷灰石（HAP）压电催化剂（Pt/HAP）。 Hap 上 Pt 的引入创造了一个界面电场。这对非本地压电。场和局部界面电场极大地促进了本体电荷和表面电荷转移。此外，Pt 不仅促进了 sepn。压电诱导的电荷，但也激活氧 mols。和组织。底物的功能基团。与原始 HAP 相比，Pt/HAP 表现出优异的压电催化活性，在室温下 2 小时内达到 96% 的 HMF 转化率和 70% 的 FFCA 产率。脂肪醛、呋喃醛、脂肪醛和乙二醇等多种醛类和醇类物质均被氧化成羧酸。这项工作提供了一种利用压电催化进行生物质转化的新方法。
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Liu, Y.; Wang, M.; Zhang, B.; Yan, D.; Xiang, X. Mediating the Oxidizing Capability of Surface-Bound Hydroxyl Radicals Produced by Photoelectrochemical Water Oxidation to Convert Glycerol into Dihydroxyacetone. ACS Catal. 2022, 12, 6946– 6957, DOI: 10.1021/acscatal.2c01319
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Mediating the Oxidizing Capability of Surface-Bound Hydroxyl Radicals Produced by Photoelectrochemical Water Oxidation to Convert Glycerol into Dihydroxyacetone
Liu, Yang; Wang, Miao; Zhang, Bing; Yan, Dongpeng; Xiang, Xu
ACS Catalysis (2022), 12 (12), 6946-6957CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Highly selective oxidn. of a single specific hydroxyl group in glycerol is attractive but challenging because glycerol contains three similar hydroxyl groups. In this work, we developed a ternary photoanode comprising Ag nanoparticle-supported layered double hydroxide (LDH) nanosheets on TiO2 (denoted Ag@LDH@TiO2) for the glycerol selective oxidn. to 1,3-dihydroxyacetone via photoelectrochem. water oxidn. under neutral conditions. It was proved that hydroxyl radicals generated by water oxidn. were the dominating active oxygen species and oxygen atoms in the main oxidn. product came from water. The LDHs and Ag nanoparticles enhanced the selectivity of secondary hydroxyl oxidn., and the Ag nanoparticles further accelerated the corresponding kinetics. The Ag@LDH@TiO2 photoanode exhibited a 1,3-dihydroxyacetone selectivity of 72% at 1.2 V vs reversible hydrogen electrode, which is obviously higher than that of pure TiO2 (23.5%) and surpasses most materials reported thus far. The role of LDHs and Ag nanoparticles in selective oxidn. of glycerol was revealed through detailed spectroscopic and computational studies. Specifically, Fourier transform IR spectroscopy anal. revealed that the middle hydroxyl group is preferentially adsorbed to LDH surfaces, while d. function theory calcns. verified that the surface-bound hydroxyl radicals mediated dehydrogenation barriers of middle carbon of adsorbed glycerol; the Ag nanoparticles promoted the selective adsorption of middle hydroxyl of glycerol, which further induced its selective oxidn.
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Zope, B. N.; Hibbitts, D. D.; Neurock, M.; Davis, R. J. Reactivity of the Gold/Water Interface During Selective Oxidation Catalysis. Science 2010, 330, 74– 78, DOI: 10.1126/science.1195055
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Reactivity of the Gold/Water Interface During Selective Oxidation Catalysis
Zope, Bhushan N.; Hibbitts, David D.; Neurock, Matthew; Davis, Robert J.
Science (Washington, DC, United States) (2010), 330 (6000), 74-78CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
The selective oxidn. of alcs. in aq. phase over supported metal catalysts is facilitated by high-pH conditions. We have studied the mechanism of ethanol and glycerol oxidn. to acids over various supported gold and platinum catalysts. Labeling expts. with 18O2 and H218O demonstrate that oxygen atoms originating from hydroxide ions instead of mol. oxygen are incorporated into the alc. during the oxidn. reaction. D. functional theory calcns. suggest that the reaction path involves both soln.-mediated and metal-catalyzed elementary steps. Mol. oxygen is proposed to participate in the catalytic cycle not by dissocn. to at. oxygen but by regenerating hydroxide ions formed via the catalytic decompn. of a peroxide intermediate.
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Kung, M. C.; Davis, R. J.; Kung, H. H. Understanding Au-Catalyzed Low-Temperature CO Oxidation. J. Phys. Chem. C 2007, 111, 11767– 11775, DOI: 10.1021/jp072102i
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Understanding Au-Catalyzed Low-Temperature CO Oxidation
Kung, Mayfair C.; Davis, Robert J.; Kung, Harold H.
Journal of Physical Chemistry C (2007), 111 (32), 11767-11775CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
A review; the discovery of exceptionally high catalytic activities of small Au particles has initiated intense research activity to understand their origin. In spite of a large vol. of work, the system is far from being fully understood. There are four major issues in Au-catalyzed CO oxidn. that have not been resolved: (1) the importance of the nature of the support on catalyst activity; (2) the Au oxidn. state necessary for high activity; (3) the sensitivity of the activity to the moisture level in the reaction feed; and (4) reasons for the high activity in small Au particle size and for the strong dependence on particle size and specific morphol. The current understanding of these issues based on available exptl. evidence and computational investigations is discussed, as well as aspects that remain unresolved.
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Takanabe, K.; Iglesia, E. Rate and Selectivity Enhancements Mediated by OH Radicals in the Oxidative Coupling of Methane Catalyzed by Mn/Na₂WO₄/SiO₂. Angew. Chem., Int. Ed. 2008, 47, 7689– 7693, DOI: 10.1002/anie.200802608
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Rate and selectivity enhancements mediated by OH radicals in the oxidative coupling of methane catalyzed by Mn/Na2WO4/SiO2
Takanabe, Kazuhiro; Iglesia, Enrique
Angewandte Chemie, International Edition (2008), 47 (40), 7689-7693CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
OH radicals formed by quasi-equilibrated steps on oxide surfaces introduce homogeneous pathways that lead to higher rates and C2 yields in oxidative methane coupling relative to those attained by CH4 activation with chemisorbed oxygen. The reactivity of OH• leads to a weaker influence of the C-H bond energies on the relative rates of H abstraction from CH4, C2H6, and C2H4.
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Jiang, D.; Ni, D.; Rosenkrans, Z. T.; Huang, P.; Yan, X.; Cai, W. Nanozyme: New Horizons for Responsive Biomedical Applications. Chem. Soc. Rev. 2019, 48, 3683– 3704, DOI: 10.1039/C8CS00718G
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Nanozyme: new horizons for responsive biomedical applications
Jiang, Dawei; Ni, Dalong; Rosenkrans, Zachary T.; Huang, Peng; Yan, Xiyun; Cai, Weibo
Chemical Society Reviews (2019), 48 (14), 3683-3704CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
Nanozymes are nanomaterial-based artificial enzymes. By effectively mimicking catalytic sites of natural enzymes or harboring multivalent elements for reactions, nanozyme systems have successfully served as direct surrogates of traditional enzymes for catalysis. With the rapid development and ever-deepening understanding of nanotechnol., nanozymes offer higher catalytic stability, ease of modification and lower manufg. cost than protein enzymes. Addnl., nanozymes possess inherent nanomaterial properties, providing not only a simple substitute of enzymes but also a multimodal platform interfacing complex biol. environments. Recent extensive research has focused on designing various nanozyme systems that are responsive to one or multiple substrates by tailored means. Catalytic activities of nanozymes can be regulated by pH, H2O2 and glutathione concns. and levels of oxygenation in different microenvironments. Moreover, nanozymes can be remotely-controlled via different stimuli, including a magnetic field, light, ultrasound, and heat. Collectively, these factors can be adjusted to maximize the diagnostic and therapeutic efficacies of different diseases in biomedical settings. Therefore, by integrating the catalytic property and inherent nanomaterial nature of nanozyme systems, we anticipate that stimuli-responsive nanozymes will open up new horizons for diagnosis, treatment, and theranostics.
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Wu, J.; Wang, X.; Wang, Q.; Lou, Z.; Li, S.; Zhu, Y.; Qin, L.; Wei, H. Nanomaterials with Enzyme-Like Characteristics (Nanozymes): Next-Generation Artificial Enzymes (II). Chem. Soc. Rev. 2019, 48, 1004– 1076, DOI: 10.1039/C8CS00457A
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Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)
Wu, Jiangjiexing; Wang, Xiaoyu; Wang, Quan; Lou, Zhangping; Li, Sirong; Zhu, Yunyao; Qin, Li; Wei, Hui
Chemical Society Reviews (2019), 48 (4), 1004-1076CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
Nanozymes are nanomaterials with enzyme-like characteristics (Chem. Soc. Rev., 2013, 42, 6060-6093). They have been developed to address the limitations of natural enzymes and conventional artificial enzymes. Along with the significant advances in nanotechnol., biotechnol., catalysis science, and computational design, great progress has been achieved in the field of nanozymes since the publication of the above-mentioned comprehensive review in 2013. To highlight these achievements, this review first discusses the types of nanozymes and their representative nanomaterials, together with the corresponding catalytic mechanisms whenever available. Then, it summarizes various strategies for modulating the activity and selectivity of nanozymes. After that, the broad applications from biomedical anal. and imaging to theranostics and environmental protection are covered. Finally, the current challenges faced by nanozymes are outlined and the future directions for advancing nanozyme research are suggested. The current review can help researchers know well the current status of nanozymes and may catalyze breakthroughs in this field.
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Xu, B.; Wang, H.; Wang, W.; Gao, L.; Li, S.; Pan, X.; Wang, H.; Yang, H.; Meng, X.; Wu, Q.; Zheng, L.; Chen, S.; Shi, X.; Fan, K.; Yan, X.; Liu, H. A Single-Atom Nanozyme for Wound Disinfection Applications. Angew. Chem., Int. Ed. 2019, 58, 4911– 4916, DOI: 10.1002/anie.201813994
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A single-atom nanozyme for wound disinfection applications
Xu, Bolong; Wang, Hui; Wang, Weiwei; Gao, Lizeng; Li, Shanshan; Pan, Xueting; Wang, Hongyu; Yang, Hailong; Meng, Xiangqin; Wu, Qiuwen; Zheng, Lirong; Chen, Shenming; Shi, Xinghua; Fan, Kelong; Yan, Xiyun; Liu, Huiyu
Angewandte Chemie, International Edition (2019), 58 (15), 4911-4916CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Single-atom catalysts (SACs), as homogeneous catalysts, have been widely explored for chem. catalysis. However, few studies focus on the applications of SACs in enzymic catalysis. Herein, we report that a zinc-based zeolitic-imidazolate-framework (ZIF-8)-derived carbon nanomaterial contg. atomically dispersed zinc atoms can serve as a highly efficient single-atom peroxidase mimic. To reveal its structure-activity relationship, the structural evolution of the single-atom nanozyme (SAzyme) was systematically investigated. Furthermore, the coordinatively unsatd. active zinc sites and catalytic mechanism of the SAzyme are disclosed using d. functional theory (DFT) calcns. The SAzyme, with high therapeutic effect and biosafety, shows great promises for wound antibacterial applications.
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Zhu, S.; Li, Z.; Zhang, F.; Liu, F.; Ni, P.; Chen, C.; Jiang, Y.; Lu, Y. Single-Atom Cobalt Catalysts as Highly Efficient Oxidase Mimics for Time-Based Visualization Monitoring the TAC of Skin Care Products. Chem. Eng. J. 2023, 456, 141053 DOI: 10.1016/j.cej.2022.141053
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Single-atom cobalt catalysts as highly efficient oxidase mimics for time-based visualization monitoring the TAC of skin care products
Zhu, Shicheng; Li, Zhe; Zhang, Feifan; Liu, Fangning; Ni, Pengjuan; Chen, Chuanxia; Jiang, Yuanyuan; Lu, Yizhong
Chemical Engineering Journal (Amsterdam, Netherlands) (2023), 456 (), 141053CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
Reactive oxygen species (ROS) are an important cause of oxidative skin aging and can be removed by adding some antioxidant ingredients to skin care products. However, total antioxidant capacity (TAC) assays generally require sophisticated lab. equipment, which greatly limits their daily application. Fortunately, the adoption and development of portable smartphone platforms could promises to solve this challenge. Herein, we report a cobalt single atom-based portable smartphone platform which can realize dynamic-time visualization monitoring the TAC of skin care product. Theor. calcns. and specific exptl. results show that single-atom cobalt catalysts (SA-Co/NC) present excellent oxidase-like activity and can effectively convert dissolved oxygen into strongly oxidizing reactive oxygen species. More interestingly, based on the unique sacrificial inhibition catalytic mechanism of ascorbic acid (AA), it can be combined with a portable smartphone platform to detect the TAC of real samples by fitting a time-color-concn. std. curve and recording the change of color RGB values during the reaction. Compared with the traditional scheme, this scheme is convenient, low cost, and can realize visual detection of mobile terminals. This work provides a new scheme for miniaturization, convenience and home-based of TAC detection.
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Ye, Y.; Xiao, L.; Bin, H.; Zhang, Q.; Nie, T.; Yang, X.; Wu, D.; Cheng, H.; Li, P.; Wang, Q. Oxygen-Tuned Nanozyme Polymerization for the Preparation of Hydrogels with Printable and Antibacterial Properties. J. Mater. Chem. B 2017, 5, 1518– 1524, DOI: 10.1039/C6TB03317B
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Oxygen-tuned nanozyme polymerization for the preparation of hydrogels with printable and antibacterial properties
Ye, Yuemei; Xiao, Linlin; Bin He; Zhang, Qi; Nie, Tao; Yang, Xinrui; Wu, Dongbei; Cheng, Heli; Li, Ping; Wang, Qigang
Journal of Materials Chemistry B: Materials for Biology and Medicine (2017), 5 (7), 1518-1524CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
Nanozymes merge nanotechnol. with biol. and provide a lower cost and higher stability options, compared to that of natural enzymes. However, nanozyme catalyzed polymn. under physiol. conditions is still a big challenge due to heavy oxygen inhibition. In this study, the simple glucose oxidase system can effectively adjust oxygen concn. and generate hydrogen peroxide, which assists in the realization of nanozyme-catalyzed polymn. The nanozyme based hydrogel is printable due to its mild prepn. with gradually increased viscosity. The antibacterial performance is ascribed to the in situ generated hydroxyl radical via the reaction of the bound nanozyme and glucose.
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Mondelli, C.; Gözaydın, G.; Yan, N.; Pérez-Ramírez, J. Biomass Valorisation over Metal-Based Solid Catalysts from Nanoparticles to Single Atoms. Chem. Soc. Rev. 2020, 49, 3764– 3782, DOI: 10.1039/D0CS00130A
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Biomass valorisation over metal-based solid catalysts from nanoparticles to single atoms
Mondelli, Cecilia; Gozaydin, Gokalp; Yan, Ning; Perez-Ramirez, Javier
Chemical Society Reviews (2020), 49 (12), 3764-3782CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
A review. Heterogeneous catalysts are vital to unlock superior efficiency, atom economy, and environmental friendliness in chem. conversions, with the size and speciation of the contained metals often playing a decisive role in the activity, selectivity and stability. This tutorial review analyses the impact of these catalyst parameters on the valorisation of biomass through hydrogenation and hydrodeoxygenation, oxidn., reforming and acid-catalyzed reactions, spanning a broad spectrum of substrates including sugars and platform compds. obtained from (hemi)cellulose and lignin derivs. It outlines multiple examples of classical structure sensitivity on nanoparticle-based materials with significant implications for the product distribution. It also shows how the recently emphasized application of metals in the form of ultrasmall nanoparticles (<2 nm), clusters and single atoms, while fulfilling superior metal utilization and robustness, opens the door to unprecedented electronic and geometric properties. The latter can lead to facilitated activation of reactants as well as boosted selectivity control and synergy between distinct active sites in multifunctional catalysts. Based on the anal. conducted, guidelines for the selection of metals for diverse applications are put forward in terms of chem. identity and structure, and aspects that should be explored in greater depth for further improving the exploitation of metals in this research field and beyond are highlighted.
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Liu, S.-S.; Sun, K.-Q.; Xu, B.-Q. Specific Selectivity of Au-Catalyzed Oxidation of Glycerol and Other C₃-Polyols in Water without the Presence of a Base. ACS Catal. 2014, 4, 2226– 2230, DOI: 10.1021/cs5005568
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Specific Selectivity of Au-Catalyzed Oxidation of Glycerol and Other C3-Polyols in Water without the Presence of a Base
Liu, Shu-Sen; Sun, Ke-Qiang; Xu, Bo-Qing
ACS Catalysis (2014), 4 (7), 2226-2230CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
A big challenge in upgrading bio-oxygenate platform mols. is to develop catalysts for the selective oxidn. of a nonterminal HO-bonded carbon atom in polyols. We report herein the first finding of a specific selectivity of oxide-supported nano-Au catalysts for dihydroxyacetone (DHA) prodn. in glycerol oxidn. in water without NaOH. Though the support nature (Al2O3, TiO2, ZrO2, NiO, and CuO) significantly affects the Au activity, a highly active Au/CuO catalyst offering DHA yields up to 80% at 40-50 °C has been identified. Rich data are provided to clarify that DHA is the only primary product of glycerol oxidn. This propensity of nano-Au for oxidizing the HO-bonded secondary (central) carbon is further verified by comparing the oxidn. of propanediols and propanols. Mol. insight into the reactions is given on the basis of the kinetic isotopic effect study of deuterium on the oxidn. of 2-propanol, uncovering an unanticipated chem. of Au catalysis.
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Zhang, J.; Nagamatsu, S.; Du, J.; Tong, C.; Fang, H.; Deng, D.; Liu, X.; Asakura, K.; Yuan, Y. A Study of FeN_x/C Catalysts for the Selective Oxidation of Unsaturated Alcohols by Molecular Oxygen. J. Catal. 2018, 367, 16– 26, DOI: 10.1016/j.jcat.2018.08.004
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A study of FeNx/C catalysts for the selective oxidation of unsaturated alcohols by molecular oxygen
Zhang, Jinping; Nagamatsu, Shinichi; Du, Junmou; Tong, Chaoli; Fang, Huihuang; Deng, Dehui; Liu, Xi; Asakura, Kiyotaka; Yuan, Youzhu
Journal of Catalysis (2018), 367 (), 16-26CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)
Transition-metal nitrides can exhibit catalytic performance comparable to that of noble metal catalysts in many reactions. However, investigations on the correlation of catalyst structure, performance, and stability are still highly demanded. Here, a series of metal nitrides were prepd. and evaluated for the selective oxidn. of alcs. by mol. oxygen. Among them, FeNx/C-T catalysts (T represents the pyrolysis temp.) display above 95% selectivity to the corresponding aldehydes in the selective oxidn. of unsatd. alcs. The optimized FeNx/C-900 catalyst gives the highest TOF of 7.0 h-1 for the conversion of 5-hydroxymethylfurfural to 2,5-diformylfuran. A combination of characterizations and expts. suggests that Fe-N4 species are the main active sites. In addn., investigate the reasons for the catalyst deactivation and provide an effective approach to regenerating the catalysts. The results indicate that the deactivated catalysts can be regenerated by heat treatment under NH3/N2 after each run. Based on these studies, a plausible reaction mechanism over the FeNx/C catalysts is proposed.
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Tu, C.; Nie, X.; Chen, J. G. Insight into Acetic Acid Synthesis from the Reaction of CH₄ and CO₂. ACS Catal. 2021, 11, 3384– 3401, DOI: 10.1021/acscatal.0c05492
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Insight into Acetic Acid Synthesis from the Reaction of CH4 and CO2
Tu, Chunyan; Nie, Xiaowa; Chen, Jingguang G.
ACS Catalysis (2021), 11 (6), 3384-3401CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
A review. The reaction of CH4 and CO2 to produce acetic acid is an atom-efficient way for using carbon resources and for mitigating CO2 emissions. This article provides a crit. assessment of the progress in this catalytic reaction from the perspective of identifying and constructing the active sites. We elucidate how Cu- and Zn-based catalysts with different structures are used for the activation of CH4 and CO2. The differences in the metal oxidn. state may affect the adsorption of CH4 and CO2 and consequently change the activation barriers for the dissocn. of the C-H bond of CH4 and the C-C coupling reaction. We discuss how the active sites and transition states can be modified by the location of metal sites, the framework environment, and the promotion effect of different acid sites. We also compare different technologies, including catalyst pretreatment, preactivation with CO2, tandem reaction, and plasma-driven catalysis for the CH4 and CO2 conversion. We conclude by identifying opportunities for improving the efficiency of heterogeneous catalysts for this important reaction.
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Thomas, J. M.; Raja, R.; Sankar, G.; Bell, R. G. Molecular Sieve Catalysts for the Regioselective and Shape-Selective Oxyfunctionalization of Alkanes in Air. Acc. Chem. Res. 2001, 34, 191– 200, DOI: 10.1021/ar970020e
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Molecular Sieve Catalysts for the Regioselective and Shape-Selective Oxyfunctionalization of Alkanes in Air
Thomas, John Meurig; Raja, Robert; Sankar, Gopinathan; Bell, Robert G.
Accounts of Chemical Research (2001), 34 (3), 191-200CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
A review with 42 refs. Framework-substituted, mol.-sieve, aluminophosphate, microporous solids are the centerpieces of a new approach to the aerobic oxyfunctionalization of satd. hydrocarbons. The sieves, and the few percent of the AlIII sites within them that are replaced by catalytically active, transition-metal ions in high oxidn. states (CoIII, MnIII, FeIII), are designed so as to allow free access of oxygen in to and out of the interior of these high-area solids. Certain metal-substituted, mol. sieves permit only end-on approach of linear alkanes to the active centers, thereby favoring enhanced reactivity of the terminal Me groups. By optimizing cage dimension, with respect to that of the hydrocarbon reactant, as well as adjusting the av. sepn. of active centers within a cage, and by choosing the sieve with the appropriate pore aperture, highly selective conversions such as n-hexane to hexanoic acid or adipic acid, and cyclohexane to cyclohexanol, cyclohexanone, or adipic acid, may be effected at low temp., heterogeneously in air.
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Wang, Q.; Hou, W.; Li, S.; Xie, J.; Li, J.; Zhou, Y.; Wang, J. Hydrophilic Mesoporous Poly(ionic liquid)-Supported Au–Pd Alloy Nanoparticles towards Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid under Mild Conditions. Green Chem. 2017, 19, 3820– 3830, DOI: 10.1039/C7GC01116D
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Hydrophilic mesoporous poly(ionic liquid)-supported Au-Pd alloy nanoparticles towards aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid under mild conditions
Wang, Qian; Hou, Wei; Li, Shuai; Xie, Jingyan; Li, Jing; Zhou, Yu; Wang, Jun
Green Chemistry (2017), 19 (16), 3820-3830CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
Design of stable high-performance heterogeneous catalysts has become crucial for efficient catalytic conversion of renewable biomass into high value-added chems. Noble metal alloy nanoparticles (NPs) are of great interest due to their unique tunable structures and high activity. In this study, Au-Pd alloy NPs supported on hydrophilic mesoporous poly(ionic liq.) (MPIL) exhibited encouragingly high performance in the aerobic oxidn. of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in water under mild conditions. Nearly complete conversion of HMF is attained at a low temp. of 90° under atm. O2, resulting in 99% FDCA yield and high turnover no. (TON) of up to 350. After reaction, the catalyst can be facilely recovered and reused with stable activity. Surface wettability plays a dominant role in the oxidn. of HMF to FDCA, and synergistic alloy effect accounts for high activity. The results also show that MPILs are a promising support platform to achieve stable and efficient metal NPs through task-specific design of functional monomers.
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Liu, X.; Chen, L.; Xu, H.; Jiang, S.; Zhou, Y.; Wang, J. Straightforward Synthesis of Beta Zeolite Encapsulated Pt Nanoparticles for the Transformation of 5-Hydroxymethyl Furfural into 2,5-Furandicarboxylic Acid. Chin. J. Catal. 2021, 42, 994– 1003, DOI: 10.1016/S1872-2067(20)63720-2
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Straightforward synthesis of beta zeolite encapsulated Pt nanoparticles for the transformation of 5-hydroxymethyl furfural into 2,5-furandicarboxylic acid
Liu, Xiaoling; Chen, Lei; Xu, Hongzhong; Jiang, Shi; Zhou, Yu; Wang, Jun
Chinese Journal of Catalysis (2021), 42 (6), 994-1003CODEN: CJCHCI; ISSN:1872-2067. (Elsevier B.V.)
Encapsulating noble metal nanoparticles (NPs) within the zeolite framework enhances the stability and accessibility of active sites; however, direct synthesis remains a challenge because of the easy pptn. of noble metal species under strong alkali crystn. conditions. Herein, beta zeolite-encapsulated Pt NPs (Pt@Beta) were synthesized via a hydrothermal approach involving an unusual acid hydrolysis preaging step. The ligand-(3-mercaptopropyl)trimethoxysilane-and Pt precursor were cohydrolyzed and cocondensed with a silica source in an initially weak acidic environment to prevent colloidal pptn. by enhancing the interaction between the Pt and silica species. Thus, the resultant 0.2%Pt@Beta was highly active in the transformation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid (FDCA) under atm. O2 conditions by using water as the solvent while stably evincing a high yield (90%) assocd. with a large turnover no. of 176. The excellent catalysis behavior is attributable to the enhanced stability that inhibits Pt leaching and strengthens the intermediates that accelerate the rate-detg. step for the oxidn. of 5-formyl-2-furan carboxylic acid into FDCA.
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Zhang, M.; Ma, H.; Liu, X.; Zhang, S.; Luo, Y.; Gao, J.; Xu, J. Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn–Co Catalyst. ACS Appl. Mater. Interfaces 2022, 14, 18539– 18549, DOI: 10.1021/acsami.2c01858
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Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn-Co Catalyst
Zhang, Meiyun; Ma, Hong; Liu, Xin; Zhang, Shujing; Luo, Yang; Gao, Jin; Xu, Jie
ACS Applied Materials & Interfaces (2022), 14 (16), 18539-18549CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
Activation of mol. oxygen plays a crucial role in natural organisms and the modern chem. industry. Herein, we report a Mn-Co dual-single-atom catalyst that exerts a specific synergy in boosting O2 activation by collaboration between two distinct types of activation sites. Taking the oxidative esterification of the biomass platform 5-hydroxymethylfurfural (HMF) as the model reaction, the activation of O2 is demonstrated through transforming O2 into a reactive superoxide anion radical (O2•-) on Co-N4 sites and, meanwhile, by reversible consumption and supplement of coordinated surface oxygen as a new type of reactive oxygen species (ROS) on N,O-coordinated single-atom Mn sites (Mn-NxOy). EXAFS anal. results show a longer av. Mn-O bond distance at near 2.19 Å, which makes the breaking and formation of surface Mn-O bonds easier to cycle. Control expts. support that such Mn-O bonding conditions could facilitate H-elimination of C-H in HMF. The co-existence of two types of ROS effectively matches the oxidn. of hydroxyl and aldehyde groups, and thus, the overall reaction is boosted in excellent yield of diester (95.8%) with an extremely high carbon balance. This study represents a rare example of taking advantage of the synergy of the diat. catalyst for activating O2 by two types of activation pathways.
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Liu, X.; Luo, Y.; Ma, H.; Zhang, S.; Che, P.; Zhang, M.; Gao, J.; Xu, J. Hydrogen-Binding-Initiated Activation of O–H Bonds on a Nitrogen-Doped Surface for the Catalytic Oxidation of Biomass Hydroxyl Compounds. Angew. Chem., Int. Ed. 2021, 133, 18251– 18258, DOI: 10.1002/ange.202103604
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Sun, Y.; Ma, H.; Jia, X.; Ma, J.; Luo, Y.; Gao, J.; Xu, J. A High-Performance Base-Metal Approach for the Oxidative Esterification of 5-Hydroxymethylfurfural. ChemCatChem 2016, 8, 2907– 2911, DOI: 10.1002/cctc.201600484
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A High-Performance Base-Metal Approach for the Oxidative Esterification of 5-Hydroxymethylfurfural
Sun, Yuxia; Ma, Hong; Jia, Xiuquan; Ma, Jiping; Luo, Yang; Gao, Jin; Xu, Jie
ChemCatChem (2016), 8 (18), 2907-2911CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
Exploring high-performance base-metal approaches for the sustainable prodn. of chems. from biomass is presently attracting immense interest and is truly important to promote their industrialized application. Herein, CoOx-N/C and α-MnO2 were combined as a base-metal catalyst that can achieve high yields of furan-2,5-dimethylcarboxylate (FDMC, 95.6 %) for the catalytic oxidative esterification of 5-hydroxymethylfurfural (HMF) without basic additive. The reaction proceeds through fast conversion of HMF to diformylfuran (DFF) with α-MnO2 and subsequent transformation of DFF to FDMC by CoOx-N/C. Quant. XPS anal. and d. functional theory (DFT) calcns. indicated that the pyridinic-N present in doped carbon could behave as a Lewis base to promote the abstraction of hydrogen for the oxidative esterification reaction. Consequently, CoOx-N/C is a high performance catalyst for the synthesis of FDMC from DFF in a neutral medium.
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Sun, Y.; Ma, H.; Luo, Y.; Zhang, S.; Gao, J.; Xu, J. Activation of Molecular Oxygen Using Durable Cobalt Encapsulated with Nitrogen-Doped Graphitic Carbon Shells for Aerobic Oxidation of Lignin-Derived Alcohols. Chem. - Eur. J. 2018, 24, 4653– 4661, DOI: 10.1002/chem.201705824
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Activation of Molecular Oxygen Using Durable Cobalt Encapsulated with Nitrogen-Doped Graphitic Carbon Shells for Aerobic Oxidation of Lignin-Derived Alcohols
Sun, Yuxia; Ma, Hong; Luo, Yang; Zhang, Shujing; Gao, Jin; Xu, Jie
Chemistry - A European Journal (2018), 24 (18), 4653-4661CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
It has long been a challenge for activating O2 by transition-metal nanocatalysts, which might lose activity due to strong tendency for oxidn. Herein, O2 could be activated by durable encapsulated cobalt nanoparticles (NPs) with N-doped graphitic carbon shells (Co@N-C), but not by encapsulated cobalt NPs with graphitic carbon, exposed cobalt NPs supported on activated carbon, or N-doped carbon. ESR, real-time in situ FTIR spectroscopy, and mass spectrometry measurements demonstrated the generation of the highly active superoxide radical, O2.-. This unique ability enables Co@N-C to afford an excellent catalytic performance in model aerobic oxidn. of monomeric lignin-derived alcs. Further anal. elucidated that encapsulated cobalt and nitrogen-doped graphitic carbon might contribute to the capacity through influencing the electronic properties of outer layers. Moreover, through isolation by N-doped graphitic carbon shells, the inner metallic cobalt NPs are inaccessible in term of either alcs. or oxygenated products, and a distinctive resistance to leaching and agglomeration has been achieved.
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Wang, T.; Ma, H.; Liu, X.; Luo, Y.; Zhang, S.; Sun, Y.; Wang, X.; Gao, J.; Xu, J. Ultrahigh-Content Nitrogen-Doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural. Chem. - Asian J. 2019, 14, 1515– 1522, DOI: 10.1002/asia.201900099
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Ultrahigh-Content Nitrogen-doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural
Wang, Ting; Ma, Hong; Liu, Xin; Luo, Yang; Zhang, Shujing; Sun, Yuxia; Wang, Xinhong; Gao, Jin; Xu, Jie
Chemistry - An Asian Journal (2019), 14 (9), 1515-1522CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)
It is an attractive and challenging topic to endow non-noble metal catalysts with high efficiency via a nitrogen-doping approach. In this study, a nitrogen-doped carbon catalyst with high nitrogen content encapsulating cobalt NPs (CoOx@N-C(g)) was synthesized, and characterized in detail by XRD, HRTEM, N2-physisorption, ICP, CO2-TPD, and XPS techniques. g-C3N4 nanosheets act as nitrogen source and self-sacrificing templates, giving rise to an ultrahigh nitrogen content of 14.0 %, much higher than those using bulk g-C3N4 (4.4 %) via the same synthesis procedures. As a result, CoOx@N-C(g) exhibited the highest performance in the oxidative esterification of biomass-derived platform furfural to methylfuroate under base-free conditions, achieving 95.0 % conversion and 97.1 % selectivity toward methylfuroate under 0.5 MPa O2 at 100 °C for 6 h, far exceeding those of other cobalt-based catalysts. The high efficiency of CoOx@N-C(g) was closely related to its high ratio of pyridinic nitrogen species that may act as Lewis basic sites as well as its capacity for the activation of dioxygen to superoxide radical O2.-.
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Chen, C.; Wang, L.; Zhu, B.; Zhou, Z.; El-Hout, S. I.; Yang, J.; Zhang, J. 2, 5-Furandicarboxylic Acid Production via Catalytic Oxidation of 5-Hydroxymethylfurfural: Catalysts, Processes and Reaction Mechanism. J. Energy Chem. 2021, 54, 528– 554, DOI: 10.1016/j.jechem.2020.05.068
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2,5-Furandicarboxylic acid production via catalytic oxidation of 5-hydroxymethylfurfural: Catalysts, processes and reaction mechanism
Chen, Chunlin; Wang, Lingchen; Zhu, Bin; Zhou, Zhenqiang; El-Hout, Soliman I.; Yang, Jie; Zhang, Jian
Journal of Energy Chemistry (2021), 54 (), 528-554CODEN: JECOFG; ISSN:2095-4956. (Science Press)
Biomass conversion to value-added chems. has received tremendous attention for solving global warming issues and fossil fuel depletion. 5-Hydroxymethylfurfural (HMF) is a key bio-based platform mol. to produce many useful org. chems. by oxidn., hydrogenation, polymn., and ring-opening reactions. Among all derivs., the oxidn. product 2,5-furandicarboxylic acid (FDCA) is a promising alternative to petroleum-based terephthalic acid for the synthesis of biodegradable plastics. This review anal. discusses the recent progress in the thermocatalytic, electrocatalytic, and photocatalytic oxidn. of HMF into FDCA, including catalyst screening, synthesis processes, and reaction mechanism. Rapid fundamental advances may be possible in non-precious metal and metal-free catalysts that are highly efficient under the base-free conditions, and external field-assisted processes like electrochem. or photoelectrochem. cells.
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Yang, G.; Ma, Y.; Xu, J. Biomimetic Catalytic System Driven by Electron Transfer for Selective Oxygenation of Hydrocarbon. J. Am. Chem. Soc. 2004, 126, 10542– 10543, DOI: 10.1021/ja047297b
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Biomimetic Catalytic System Driven by Electron Transfer for Selective Oxygenation of Hydrocarbon
Yang, Guanyu; Ma, Yinfa; Xu, Jie
Journal of the American Chemical Society (2004), 126 (34), 10542-10543CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
A biomimetic system was developed which has a nonmetallic redox center, composed of anthraquinones, N-hydroxyphthalimide, and zeolite HY, for selective hydrocarbon oxidn. by mol. oxygen, a crucial industrial process. Selectivity of 95.8% for acetophenone and 66.2% conversion were accomplished for oxygenation of ethylbenzene at temps. as low as 80°. The redox cycle, driven by one-electron transfer and product orientation by Zeolite HY, opens up the possibility of mimicking bio-oxidn. under mild conditions. The process is a good alternative to use of metallic catalysts that require higher temps. and often show lower selectivity.
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Dijkman, W. P.; Groothuis, D. E.; Fraaije, M. W. Enzyme-Catalyzed Oxidation of 5-Hydroxymethylfurfural to Furan-2, 5-Dicarboxylic Acid. Angew. Chem., Int. Ed. 2014, 53, 6515– 6518, DOI: 10.1002/anie.201402904
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Enzyme-Catalyzed Oxidation of 5-Hydroxymethylfurfural to Furan-2,5-dicarboxylic Acid
Dijkman, Willem P.; Groothuis, Daphne E.; Fraaije, Marco W.
Angewandte Chemie, International Edition (2014), 53 (25), 6515-6518CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
Furan-2,5-dicarboxylic acid (FDCA) is a biobased platform chem. for the prodn. of polymers. In the past few years, numerous multistep chem. routes have been reported on the synthesis of FDCA by oxidn. of 5-hydroxymethylfurfural (HMF). Recently we identified an FAD-dependent enzyme which is active towards HMF and related compds. This oxidase has the remarkable capability of oxidizing [5-(hydroxymethyl)furan-2-yl]methanol to FDCA, a reaction involving four consecutive oxidns. The oxidase can produce FDCA from HMF with high yield at ambient temp. and pressure. Examn. of the underlying mechanism shows that the oxidase acts on alc. groups only and depends on the hydration of aldehydes for the oxidn. reaction required to form FDCA.
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Jia, H. Y.; Zong, M. H.; Zheng, G. W.; Li, N. One-Pot Enzyme Cascade for Controlled Synthesis of Furancarboxylic Acids from 5-Hydroxymethylfurfural by H₂O₂ Internal Recycling. ChemSusChem 2019, 12, 4764– 4768, DOI: 10.1002/cssc.201902199
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One-Pot Enzyme Cascade for Controlled Synthesis of Furancarboxylic Acids from 5-Hydroxymethylfurfural by H2O2 Internal Recycling
Jia, Hao-Yu; Zong, Min-Hua; Zheng, Gao-Wei; Li, Ning
ChemSusChem (2019), 12 (21), 4764-4768CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
Furancarboxylic acids are promising biobased building blocks in pharmaceutical and polymer industries. In this work, dual-enzyme cascade systems composed of galactose oxidase (GOase) and alc. dehydrogenases (ADHs) are constructed for controlled synthesis of 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF), based on the catalytic promiscuity of ADHs. The byproduct H2O2, which is produced in GOase-catalyzed oxidn. of HMF to 2,5-diformylfuran (DFF), is used for horseradish peroxidase (HRP)-mediated regeneration of the oxidized nicotinamide cofactors for subsequent oxidn. of DFF promoted by an ADH, thus implementing H2O2 internal recycling. The desired products FFCA and FDCA are obtained with yields of more than 95 %.
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Liu, W.; Zhang, L.; Yan, W.; Liu, X.; Yang, X.; Miao, S.; Wang, W.; Wang, A.; Zhang, T. Single-Atom Dispersed Co–N–C Catalyst: Structure Identification and Performance for Hydrogenative Coupling of Nitroarenes. Chem. Sci. 2016, 7, 5758– 5764, DOI: 10.1039/C6SC02105K
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Single-atom dispersed Co-N-C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes
Liu, Wengang; Zhang, Leilei; Yan, Wensheng; Liu, Xiaoyan; Yang, Xiaofeng; Miao, Shu; Wang, Wentao; Wang, Aiqin; Zhang, Tao
Chemical Science (2016), 7 (9), 5758-5764CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
Co-N-C catalysts are promising candidates for substituting platinum in electrocatalysis and org. transformations. The heterogeneity of the Co species resulting from high-temp. pyrolysis, however, encumbers the structural identification of active sites. Herein, we report a self-supporting Co-N-C catalyst wherein cobalt is dispersed exclusively as single atoms. By using sub-Ångstrom-resoln. HAADF-STEM in combination with XAFS and DFT calcn., the exact structure of the Co-N-C is identified to be CoN4C8-1-2O2, where the Co center atom is coordinated with four pyridinic N atoms in the graphitic layer, while two oxygen mols. are weakly adsorbed on Co atoms in perpendicular to the Co-N4 plane. This single-atom dispersed Co-N-C catalyst presents excellent performance for the chemoselective hydrogenation of nitroarenes to produce azo compds. under mild reaction conditions.
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Jagadeesh, R. V.; Junge, H.; Pohl, M.-M.; Radnik, Jr.; Brückner, A.; Beller, M. Selective Oxidation of Alcohols to Esters Using Heterogeneous Co₃O₄–N@C Catalysts under Mild Conditions. J. Am. Chem. Soc. 2013, 135, 10776– 10782, DOI: 10.1021/ja403615c
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Selective Oxidation of Alcohols to Esters Using Heterogeneous Co3O4-N@C Catalysts under Mild Conditions
Jagadeesh, Rajenahally V.; Junge, Henrik; Pohl, Marga-Martina; Radnik, Joerg; Brueckner, Angelika; Beller, Matthias
Journal of the American Chemical Society (2013), 135 (29), 10776-10782CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
Novel cobalt-based heterogeneous catalysts have been developed for the direct oxidative esterification of alcs. using mol. oxygen as benign oxidant. Pyrolysis of nitrogen-ligated cobalt(II) acetate supported on com. carbon transforms typical homogeneous complexes to highly active and selective heterogeneous Co3O4-N@C materials. By applying these catalysts in the presence of oxygen, the cross and self-esterification of alcs. to esters proceeds in good to excellent yields.
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Madden, K. P.; Taniguchi, H. The Role of the DMPO-Hydrated Electron Spin Adduct in DMPO-OH^• Spin Trapping. Free Radical Biol. Med. 2001, 30, 1374– 1380, DOI: 10.1016/S0891-5849(01)00540-8
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The role of the DMPO-hydrated electron spin adduct in DMPO-√OH spin trapping
Madden, K. P.; Taniguchi, H.
Free Radical Biology & Medicine (2001), 30 (12), 1374-1380CODEN: FRBMEH; ISSN:0891-5849. (Elsevier Science Inc.)
Time-resolved in situ radiolysis ESR (ESR, equivalently EPR, ESR) studies have shown that the scavenging of radiolytically produced hydroxyl radical in nitrous oxide-satd. aq. solns. contg. 2 mM DMPO is essentially quant. (94% of the theor. yield) at 100 μs after the electron pulse [1]. This result appeared to conflict with earlier results using continuous cobalt-60 γ radiolysis and hydrogen peroxide photolysis, where factors of 35 and 33% were obtained, resp. [2,3]. To investigate this discrepancy, nitrogen-satd. aq. solns. contg. 15 mM DMPO were cobalt-60 γ irradiated (dose rate = 223 Gy/min) for periods of 0.25-6 min, and ESR absorption spectra were obsd. ∼ 30 s after irradn. A rapid, pseudo-first-order termination reaction of the protonated DMPO-hydrated electron adduct (DMPO-H) with DMPO-OH was obsd. for the first time. The rate const. for the reaction of DMPO-H with DMPO-OH is 2.44×102 (± 2.2×101) M-1 s-1. In low-dose radiolysis expts., this reaction lowers the obsd. yield of DMPO-OH to 44% of the radiation-chem. OH radical yield (G = 2.8), in good agreement with the earlier results [2,3]. In the absence of the DMPO-H radical, the DMPO-OH exhibits second-order radical termination kinetics, 2kT = 22 (± 2) M-1 s-1 at initial DMPO-OH concns. ≥ 13 μM, with first-order termination kinetics obsd. at lower concns., in agreement with earlier literature reports [4].
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Yamazaki, I.; Piette, L. H. EPR Spin-Trapping Study on the Oxidizing Species Formed in the Reaction of the Ferrous Ion with Hydrogen Peroxide. J. Am. Chem. Soc. 1991, 113, 7588– 7593, DOI: 10.1021/ja00020a021
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EPR spin-trapping study on the oxidizing species formed in the reaction of the ferrous ion with hydrogen peroxide
Yamazaki, Isao; Piette, Lawrence H.
Journal of the American Chemical Society (1991), 113 (20), 7588-93CODEN: JACSAT; ISSN:0002-7863.
Using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping reagent for HO•, the ratio of rate consts. for the reaction of HO• with HO• scavengers (k) was compared to those for the reaction with DMPO (kDMPO) in a photolysis or a Fenton (FeII-H2O2) system. Assuming that the k/kDMPO ratio measures the extent to which HO• is free in soln. relative to 100% in a photolysis system, it is concluded that HO• formed in the Fenton reaction is not totally free in soln. The extent to which it is not free but bound in some kind of complex, depended upon the type of chelator used and increased in the order FeIIADP < FeII-phosphate = FeIIEDTA < FeIIDETAPAC. There was a remarkable difference in the mode of the Fenton reaction between FeIIDETAPAC and FeIIEDTA, particularly at high FeII concns. (0.1 mM). An ethanol-oxidizing species other than HO•, presumably the ferryl ion was detected in the FeIIEDTA reaction but not in the FeIIDETAPAC reaction. The major oxidizing species in the FeIIEDTA-H2O2 reaction changed from the ferryl ion to HO• as the H2O2 concn. was increased, while it was invariably HO• alone in the FeIIDETAPAC-H2O2 reaction. Benzoate and tert-Bu alc., known as typical HO• scavengers, were shown to react not only with HO• but also with the ferryl ion in the FeIIEDTA reaction. Similar scavenging effects were obsd. with histidine, formate, and mannitol.
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Qi, Y.; Li, J.; Zhang, Y.; Cao, Q.; Si, Y.; Wu, Z.; Akram, M.; Xu, X. Novel Lignin-Based Single Atom Catalysts as Peroxymonosulfate Activator for Pollutants Degradation: Role of Single Cobalt and Electron Transfer Pathway. Appl. Catal., B 2021, 286, 119910 DOI: 10.1016/j.apcatb.2021.119910
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Novel lignin-based single atom catalysts as peroxymonosulfate activator for pollutants degradation: Role of single cobalt and electron transfer pathway
Qi, Yuanfeng; Li, Jing; Zhang, Yanqing; Cao, Qi; Si, Yanmei; Wu, Zhiren; Akram, Muhammad; Xu, Xing
Applied Catalysis, B: Environmental (2021), 286 (), 119910CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
In this work, a facile one-pot pyrolytic strategy was employed to fabricate a nitrogen coordinated Co single-atom catalyst (SA Co-N/C catalyst) by using lignin as carbon sources. The HAADF-STEM images and X-ray absorption spectra (XAS) anal. showed the isolated Co atoms less than 2 Å throughout the entire SA Co-N/C architecture. Results showed that the single-atom Co sites served as the main active sites for naproxen (NPX) degrdn. via peroxymonosulfate (PMS) activation. This was confirmed by the high pos. correlation (R2 = 0.9675) between the rate consts. and Co amts. in all SA Co-N/C catalysts. In particular, the as-prepd. SA Co-N/C catalyst with a very small Co loading (2.45 wt.%) exhibited exceptional high turnover frequency (TOF) value for NPX (4.82 min-1), which is promising for the potential application prospect. Electron transfer was induced by the single-atom Co sites, which was the dominated mechanism for the NPX degrdn.
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Tran, P.; Kopel, J.; Risitic, B.; Marsh, H.; Fralick, J.; Reid, T. Antimicrobial Seleno-Organic Coatings and Compounds Acting Primarily on the Plasma Membrane: A Review. Adv. Redox Res. 2022, 4, 100031 DOI: 10.1016/j.arres.2022.100031
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Antimicrobial seleno-organic coatings and compounds acting primarily on the plasma membrane: A review
Tran, Phat; Kopel, Jonathan; Ristic, Bojana; Marsh, Harrison; Fralick, Joe; Reid, Ted
Advances in Redox Research (2022), 4 (), 100031CODEN: ARRDCD; ISSN:2667-1379. (Elsevier B.V.)
A review. Bacterial infections have been the major cause of disease throughout history. However, some bacteria have evolved to attain multi-drug resistance (MDR) against a wide range of antibiotics. Today, the acquisition and spread of antibiotic resistance among pathogenic bacteria constitute a major threat to modern medicine. One approach to overcoming MDR bacteria has been the use of elemental selenium to generate reactive oxygen species (ROS) which damage the cell membrane and intracellular proteins. In this review, we will discuss the underlying antibacterial mechanisms of selenium-coated devices, selenium conjugated peptides, antibodies, and nanoparticles against MDR bacteria. We conducted a literature review of the characteristics of selenium and recent developments of its utilization as an effective treatment strategy. One of the proposed solns. to this problem was the attachment of elemental selenium to different materials to kill bacteria through the catalytic generation of superoxide radicals. Superoxide anion, along with hydrogen peroxide and hydroxyl radical, are the noxious byproducts of partial oxygen redn. that perform lethal cellular oxidative damage. Due to the short half-life of the superoxide radical (≤1 ms) only bacteria localized near selenium are destroyed. Therefore, due to this antimicrobial mechanism, surface coatings of a plethora of devices contg. elemental selenium have been demonstrated as an effective method against pathogenic and antibiotic resistant bacteria. Furthermore, utilization of selenium conjugated peptides, antibodies, and nanoparticles have been investigated as both antimicrobial and anti-cancer therapeutics.
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Shiibashi, T.; Iida, T. J. D. NADPH and NADH Serve as Electron Donor for the Superoxide-Generating Enzyme in Tilapia (Oreochromis Niloticus) Neutrophils. Dev. Comp. Immunol. 2001, 25, 461– 465, DOI: 10.1016/S0145-305X(01)00005-2
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NADPH and NADH serve as electron donor for the superoxide-generating enzyme in tilapia (Oreochromis niloticus) neutrophils
Shiibashi, T.; Iida, T.
Developmental & Comparative Immunology (2001), 25 (5-6), 461-465CODEN: DCIMDQ; ISSN:0145-305X. (Elsevier Science Ltd.)
NADPH oxidase has been identified as the superoxide-generating enzyme in fish neutrophils. To clarify the electron-donating ability of this enzyme, we examine the requirement of NADPH as the electron donor in superoxide generation in tilapia (Oreochromis niloticus) neutrophils using CLA-dependent chemiluminescence (CL). Phorbol ester-induced CL responses were terminated upon the addn. of a detergent, Renex-30. The addn. of graded amts. of NADPH or NADH restored the CL in a dose-dependent manner. The restoration of CL was completely eliminated by superoxide dismutase, suggesting that the restored CL was due to superoxide generation. NADPH tended to have a greater effect than NADH on the CL responses of tilapia neutrophils.
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Gleason, J. E.; Galaleldeen, A.; Peterson, R. L.; Taylor, A. B.; Holloway, S. P.; Waninger-Saroni, J.; Cormack, B. P.; Cabelli, D. E.; Hart, P. J.; Culotta, V. C. Candida Albicans SOD5 Represents the Prototype of an Unprecedented Class of Cu-only Superoxide Dismutases Required for Pathogen Defense. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 5866– 5871, DOI: 10.1073/pnas.1400137111
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Candida albicans SOD5 represents the prototype of an unprecedented class of Cu-only superoxide dismutases required for pathogen defense
Gleason, Julie E.; Galaleldeen, Ahmad; Peterson, Ryan L.; Taylor, Alexander B.; Holloway, Stephen P.; Waninger-Saroni, Jessica; Cormack, Brendan P.; Cabelli, Diane E.; Hart, P. John; Culotta, Valeria Cizewski
Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (16), 5866-5871CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
Human fungal pathogens Candida albicans and Histoplasma capsulatum have been reported to protect against the oxidative burst of host innate immune cells using a family of extracellular proteins with similarity to Cu/Zn superoxide dismutase 1 (SOD1). Here, the authors report that these mols. are widespread throughout fungi and deviate from canonical SOD1 at the primary, tertiary, and quaternary structural levels. The crystal structure of C. albicans SOD5 revealed that although the β-barrel of Cu/Zn SODs was largely preserved, SOD5 was a monomeric Cu-contg. protein that lacked a Zn-binding site and was missing the electrostatic loop element proposed to promote catalysis through superoxide guidance. Without an electrostatic loop, the Cu site of SOD5 was not recessed and was readily accessible to bulk solvent. Despite these structural deviations, SOD5 had the capacity to disproportionate superoxide with kinetics that approached diffusion limits, similar to those of canonical SOD1. In cultures of C. albicans, SOD5 was secreted in a disulfide-oxidized form and apoprotein pools of secreted SOD5 could readily capture extracellular Cu for rapid induction of enzyme activity. The authors suggest that the unusual attributes of SOD5-like fungal proteins, including the absence of Zn and an open active site that readily captures extracellular Cu, make these SODs well suited to meet challenges in Zn and Cu availability at the host-pathogen interface.
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Jiao, L.; Wu, J.; Zhong, H.; Zhang, Y.; Xu, W.; Wu, Y.; Chen, Y.; Yan, H.; Zhang, Q.; Gu, W. Densely Isolated FeN₄ Sites for Peroxidase Mimicking. ACS Catal. 2020, 10, 6422– 6429, DOI: 10.1021/acscatal.0c01647
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Densely Isolated FeN4 Sites for Peroxidase Mimicking
Jiao, Lei; Wu, Jiabin; Zhong, Hong; Zhang, Yu; Xu, Weiqing; Wu, Yu; Chen, Yifeng; Yan, Hongye; Zhang, Qinghua; Gu, Wenling; Gu, Lin; Beckman, Scott P.; Huang, Liang; Zhu, Chengzhou
ACS Catalysis (2020), 10 (11), 6422-6429CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
Despite the breakthroughs of transition-metal catalysts in enzyme mimicking, fundamental investigation on the design of efficient nanozymes at the at. scale is still required for boosting their intrinsic activities to fill in gaps from enzymes to nanozymes. Herein, we developed a universal salt-template strategy for the fabrication of atomically dispersed Fe atoms on ultrathin nitrogen-doped carbon nanosheets characterized by a dramatically high concn. of 13.5 wt %. The proposed Fe-N-C nanozymes with densely isolated FeN4 sites show high peroxidase-like activities and exhibit a specific activity of 25.33 U/mg, superior to Zn(Co)-N-C nanozymes. Both expts. and theor. anal. revealed that FeN4 sites not only lead to the strong adsorption of H2O2 mols. but also weaken the bonding interaction between single Fe atom and two absorbed hydroxyl groups, lowering the energy barrier of the formation of hydroxyl radicals and therefore boosting their peroxidase-like activities. As expected, utilizing the peroxidase-like activity of Fe-N-C nanozymes, good sensitivity and selectivity for the intracellular H2O2 monitoring were realized. It offers a versatile approach for the construction of densely isolated M-N-C single-atom catalysts and achieves better understanding of single sites for the peroxidase-like catalytic mechanisms.
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Urbański, N. K.; Beręsewicz, A. Generation of ^•OH Initiated by Interaction of Fe²⁺ and Cu⁺ with Dioxygen; Comparison with the Fenton Chemistry. Acta Biochim. Pol. 2000, 47, 951– 962, DOI: 10.18388/abp.2000_3950
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Generation of .OH initiated by interaction of Fe2+ and Cu+ with dioxygen; comparison with the Fenton chemistry
Urbanski, Norbert K.; Beresewicz, Andrzej
Acta Biochimica Polonica (2000), 47 (4), 951-962CODEN: ABPLAF; ISSN:0001-527X. (Polish Biochemical Society)
Iron and copper toxicity has been presumed to involve the formation of hydroxyl radical (.OH) from H2O2 in the Fenton reaction. The aim of this study was to verify that Fe2+-O2 and Cu+-O2 chem. is capable of generating .OH in the quasi physiol. environment of Krebs-Henseleit buffer (KH), and to compare the ability of the Fe2+-O2 system and of the Fenton system (Fe2+ + H2O2) to produce .OH. The addn. of Fe2+ and Cu+ (0-20 μM) to KH resulted in a concn.-dependent increase in .OH formation, as measured by the salicylate method. While Fe3+ and Cu2+ (0-20 μM) did not result in .OH formation, these ions mediated significant .OH prodn. in the presence of a no. of reducing agents. The .OH yield from the reaction mediated by Fe2+ was increased by exogenous Fe3+ and Cu2+ and was prevented by the deoxygenation of the buffer and reduced by superoxide dismutase, catalase, and desferrioxamine. Addn. of 1 μM, 5 μM or 10 μM Fe2+ to a range of H2O2 concns. (the Fenton system) resulted in a H2O2-concn.-dependent rise in .OH formation. For each Fe2+ concn. tested, the .OH yield doubled when the ratio [H2O2]:[Fe2+] was raised from zero to one. In conclusion: (i) Fe2+-O2 and Cu+-O2 chem. is capable of promoting .OH generation in the environment of oxygenated KH, in the absence of pre-existing superoxide and/or H2O2, and possibly through a mechanism initiated by the metal autoxidn.; (ii) The process is enhanced by contaminating Fe3+ and Cu2+; (iii) In the presence of reducing agents also Fe3+ and Cu2+ promote the .OH formation; (iv) Depending on the actual [H2O2]:[Fe2+] ratio, the efficiency of the Fe2+-O2 chem. to generate .OH is greater than or, at best, equal to that of the Fe2+-driven Fenton reaction.
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Chen, C.; Li, X.; Wang, L.; Liang, T.; Wang, L.; Zhang, Y.; Zhang, J. Highly Porous Nitrogen- and Phosphorus-Codoped Graphene: An Outstanding Support for Pd Catalysts to Oxidize 5-Hydroxymethylfurfural into 2, 5-Furandicarboxylic Acid. ACS Sustainable Chem. Eng. 2017, 5, 11300– 11306, DOI: 10.1021/acssuschemeng.7b02049
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Highly Porous Nitrogen- and Phosphorus-Codoped Graphene: An Outstanding Support for Pd Catalysts to Oxidize 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid
Chen, Chunlin; Li, Xingtao; Wang, Lingchen; Liang, Ting; Wang, Lei; Zhang, Yajie; Zhang, Jian
ACS Sustainable Chemistry & Engineering (2017), 5 (12), 11300-11306CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
The oxidn. of 5-hydroxylmethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a sustainable and promising route to bioderived arom. polyesters. So far, the design of catalyst has been restricted by the unclear working mechanism, and thus most of the supported noble metal catalysts cannot provide a remarkable reaction rate under atm. pressures and room temp. Here we report a new mechanistic insight into the structure-performance correlation of graphene-supported Pd catalysts. It is demonstrated that a new kind of highly porous nitrogen- and phosphorus-codoped graphene sheets (HPGSs) will enhance the fraction of surface Pd2+ species, which plays a detg. role to reduce the activation energies of both HMF conversion and FDCA formation. Such a support effect may assist in developing highly active catalysts for FDCA synthesis under mild conditions.
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Senthamarai, T.; Chandrashekhar, V. G.; Rockstroh, N.; Rabeah, J.; Bartling, S.; Jagadeesh, R. V.; Beller, M. A “Universal” Catalyst for Aerobic Oxidations to Synthesize (Hetero)aromatic Aldehydes, Ketones, Esters, Acids, Nitriles, and Amides. Chem 2022, 8, 508– 531, DOI: 10.1016/j.chempr.2021.12.001
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A "universal" catalyst for aerobic oxidations to synthesize (hetero)aromatic aldehydes, ketones, esters, acids, nitriles, and amides
Senthamarai, Thirusangumurugan; Chandrashekhar, Vishwas G.; Rockstroh, Nils; Rabeah, Jabor; Bartling, Stephan; Jagadeesh, Rajenahally V.; Beller, Matthias
Chem (2022), 8 (2), 508-531CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
Here, the prepn. of graphitic layers encapsulated in Co-nanoparticles by pyrolysis of cobalt-piperazine-tartaric acid complex on carbon as a most general oxidn. catalyst was reported. This unique material allows for the synthesis of simple, functionalized, and structurally diverse (hetero)arom. aldehydes, ketones, carboxylic acids, esters, nitriles, and amides from alcs. in excellent yields in the presence of air.
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Xu, D.; Li, J.; Li, B.; Zhao, H.; Zhu, H.; Kou, J.; Zhang, F.; Dong, Z.; Ma, J. Selective Oxidation of Alcohols to High Value-Added Carbonyl Compounds using Air over Co-Co₃O₄@NC Catalysts. Chem. Eng. J. 2022, 434, 134545 DOI: 10.1016/j.cej.2022.134545
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Selective oxidation of alcohols to high value-added carbonyl compounds using air over Co-Co3O4@NC catalysts
Xu, Dan; Li, Jianfeng; Li, Boyang; Zhao, Huacheng; Zhu, Hanghang; Kou, Jinfang; Zhang, Fengwei; Dong, Zhengping; Ma, Jiantai
Chemical Engineering Journal (Amsterdam, Netherlands) (2022), 434 (), 134545CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
The sustainable catalytic transformation of alcs. to high value-added fine chems. is a significant and challenging research topic. Herein, a set of nitrogen-doped carbon encapsulated Co-based catalysts (Co-Co3O4@NC-T) were prepd. by using low-cost dicyandiamide, glyoxal and cobalt nitrate as precursors. The obtained catalysts were utilized for the selective oxidn. of alcs. to high value-added esters and carboxylic acids with air as the oxygen source and displayed wide applicability for the oxidn. of both arom. and aliph. alcs. Based on the controlled expts., the protective effect of N-doped carbon structure and the synergistic effect between Co core and Co3O4 species guaranteed the high reaction conversion and selectivity. Benefitting from heterogeneity and magnetism of the catalyst, it can be easily recycled and reused for long-term stability. Reasonable mechanisms of selective oxidn. reaction were proposed through EPR anal. and controlled expts. The present work provides a facile strategy for potential large-scale prepn. of heterogeneous catalyst for sustainable and green catalytic transformations.
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Mate, V.; Jha, A.; Joshi, U.; Patil, K.; Shirai, M.; Rode, C. Effect of Preparation Parameters on Characterization and Activity of Co₃O₄ Catalyst in Liquid Phase Oxidation of Lignin Model Substrates. Appl. Catal., A 2014, 487, 130– 138, DOI: 10.1016/j.apcata.2014.08.023
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Effect of preparation parameters on characterization and activity of Co3O4 catalyst in liquid phase oxidation of lignin model substrates
Mate, V. R.; Jha, A.; Joshi, U. D.; Patil, K. R.; Shirai, M.; Rode, C. V.
Applied Catalysis, A: General (2014), 487 (), 130-138CODEN: ACAGE4; ISSN:0926-860X. (Elsevier B.V.)
The nano structured spinel cobalt oxide (Co3O4) was prepd. via simple co-pptn. method and its catalytic activity was evaluated for the liq. phase aerobic oxidn. of lignin sub structure compds. such as veratryl alc. Catalyst prepn. parameters influenced its morphol. eventually affecting its oxidn. activity. Thus, nano rod shaped Co3O4 catalyst showed 75% and 38% conversion of veratryl alc. with complete selectivity to veratryl aldehyde in toluene and water, resp., under base free condition. The influence of reaction conditions, such as temp., oxygen pressure and catalyst loading was studied to obtain the optimum product yield and selectivity to the desired product. Furthermore, oxidn. of various sub-structures of lignin model compds. was also studied over the same catalyst which was found to be in the following order: secondary alc. > di-substituted > tri-substituted > mono-substituted > non-substitution. The stability of the catalyst was confirmed by its successful recycle for three times.
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Zhou, H.; Xu, H.; Wang, X.; Liu, Y. Convergent Production of 2,5-Furandicarboxylic Acid from Biomass and CO₂. Green Chem. 2019, 21, 2923– 2927, DOI: 10.1039/C9GC00869A
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Convergent production of 2,5-furandicarboxylic acid from biomass and CO2
Zhou, Hua; Xu, Huanghui; Wang, Xueke; Liu, Yun
Green Chemistry (2019), 21 (11), 2923-2927CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
We report a rationally designed process for complete lignocellulose conversion and CO2 utilization to convergently produce 2,5-furandicarboxylic acid (FDCA) that can be used in bioplastics and resins. The phenolic motif of the lignin structure enables the assembly of metal-lignin hybrids to fabricate a single-atom cobalt over nitrogen-doped carbon (Co SAs/N@C) catalyst. The Co SAs/N@C catalyst exhibits outstanding performances in the transformation of carbohydrate-based hydroxymethylfurfural (HMF) and furfural into FDCA and furoate, resp. Importantly, during the furfural oxidn., Cs2CO3 is used as a base additive, which can also promote the carboxylation of the 5 position C-H of furoate in the subsequent reaction to give the desired FDCA using CO2 as the C1 source.
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Xinying Tan, Shenghe Si, Difei Xiao, Xiaolei Bao, Kepeng Song, Zeyan Wang, Yuanyuan Liu, Zhaoke Zheng, Peng Wang, Ying Dai, Baibiao Huang, Hefeng Cheng. Single Cobalt Atoms Induced Molecular O2 Activation for Enhanced Photocatalytic Biomass Upgrading on ZnIn2S4 Nanosheets. ACS Catalysis 2023, 13 (21) , 14395-14403. https://doi.org/10.1021/acscatal.3c03332

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Cite this: ACS Catal. 2023, 13, 16, 11104–11116
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Abstract 抽象
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Scheme 1 方案 1
Scheme 1. Comparison of OH^• Generation in Different Systems (a); Design of the Biomimetic System for In Situ and Continuous Generation of OH^• (b); Conversion of RCH₂OH in Different OH^• Generation Systems: Oxidative Degradation of RCH₂OH with Uncontrollable Production of OH^• (c, Left), Selective Oxidation of RCH₂OH with Controllable Production of OH^• (c, Right)
方案 1.不同系统中 OH 生成的比较（a）;用于原位和连续生成 OH 的仿生系统设计（b）;RCH₂OH 在不同 OH 生成系统中的转化：RCH₂OH 的氧化降解与 OH 的不可控产生（c，左），RCH₂OH 的选择性氧化与 OH 的可控产生（c，右）
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Figure 1 图 1
Figure 1. TEM image (a), HAADF STEM image (b), and corresponding EDX maps for the overlapping Co, N, C, and O (c, d) of Co–N–C; normalized XANES spectra (e), EXAFS spectra (f), and wavelet transforms for the EXAFS spectra (g) of Co–N–C and Co foil; N 1s XPS spectrum (h), AC HAADF-STEM image (i) of Co–N–C; TEM images of Co/N–C-1 (j), Co/N–C-2 (k), and Co/AC (l); XRD patterns (m), ratio of the intensity of DMPO-OH^• adducts in the electron spin resonance (ESR) spectra at the reaction times of 20 min (n), and the catalytic performance of HMF oxidation (o) of different Co-based catalysts. Reaction conditions: 0.5 mmol HMF, 1.25 mmol NaOH, 0.032 mmol Co in the catalyst, 5 mL of H₂O, 40 mL/min O₂, 60 °C, and 5 h.
图 1.TEM 图像（a）、HAADF STEM 图像（b）以及 Co-N-C 重叠的 Co、N、C 和 O （c， d）的相应 EDX 图;Co-N-C 和 Co 箔的 EXAFS 光谱（g）的归一化 XANES 光谱（e）、EXAFS 光谱（f）和小波变换;N 1s XPS 谱图（h），Co–N–C 的 AC HAADF-STEM 图像（i）;Co/N-C-1 （j）、Co/N-C-2 （k）和 Co/AC （l）的 TEM 图像;XRD 图谱（m），反应时间为 20 min 时电子自旋共振（ESR）光谱中 DMPO-OH 加合物强度的比值（n），以及不同钴基催化剂的 HMF 氧化催化性能（o）。反应条件：催化剂中加入 0.5 mmol HMF、1.25 mmol NaOH、0.032 mmol Co、5 mL H₂O、40 mL/min O₂、60 °C 和 5 h。
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Figure 2 图 2
Figure 2. Cascade process of OH^• generation by the activation of O₂ and H₂O over Co–N–C (a); ESR spectrum of the DMPO-O₂^•– in the toluene phase of step 1 (b); MS spectrum of triphenylphosphine oxide formed in the water phase of step 2 (c); ESR spectrum of the DMPO-OH^• in the water phase of step 3 (d); and effect of solvents and inhibitors on the generation of ROS (e, f). Reaction conditions: for the detection of H₂O₂ and OH^• in water, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 1 mmol scavenger, 2.5 mL of H₂O, 40 mL/min O₂, and 60 °C and for the detection of O₂^•– in toluene, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 1 mmol scavenger, 2.5 mL of toluene, 0.6 MPa O₂, and 100 °C.
图 2.通过 Co-N-C 上 O₂ 和 H₂O 的活化产生 OH 的级联过程（a）;DMPO-O 的 ESR 谱₂^•– 在步骤 1 （b）的甲苯相中;在步骤 2 （c）的水相中形成的三苯基氧化膦的 MS 谱图;步骤 3 （d）水中 DMPO-OH 的 ESR 谱图;以及溶剂和抑制剂对 ROS 生成的影响（e， f）。反应条件：用于检测水中 H₂O₂ 和 OH、0.032 mmol Co 的 Co-N-C 溶液、1.25 mmol NaOH、1 mmol 清除剂、2.5 mL 的 H₂O、40 mL/min O₂ 和 60 °C，以及用于检测甲苯中的 O₂^•--0,0.032 mmol Co 的 Co-N-C 溶液， 1.25 mmol NaOH、1 mmol 清除剂、2.5 mL 甲苯、0.6 MPa O₂ 和 100 °C。
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Figure 3
Figure 3. Mass spectra of the OH^• trapping experiments by DMPO in isotope-labeled H₂O and O₂. Reaction conditions: 1.25 mmol NaOH, 0.032 mmol Co in Co–N–C, 5 mL of H₂O, 60 °C, 40 mL/min O₂, and 30 min.
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Figure 4
Figure 4. Time curve of the intensity of DMPO-OH^• adducts in the ESR spectra of the Co–N–C system with HMF addition (a, above), the concentrations of HMF and FDCA during the HMF oxidation process in the Co–N–C system (a, below); the high-performance liquid chromatography (HPLC) traces for HMF oxidation in the Co–N–C system (b); the time curve of the intensity of DMPO-OH^• adducts in the ESR spectra of the Co–N–C system without HMF addition (c); the time curve of the intensity of DMPO-OH^• adducts in the ESR spectra of the H₂O₂ + OH^– system with and without HMF addition (d). Reaction conditions: in the Co–N–C system, 1.25 mmol NaOH, 0.032 mmol Co in Co–N–C, 5 mL of H₂O, 40 mL/min O₂, and 60 °C and in the H₂O₂ + OH^– system, 1.25 mmol NaOH, 1 mL of 30 wt % H₂O₂, 4 mL of H₂O, and 60 °C. In these two systems, 0.05 mmol HMF was added in the 11th min, 25th min, 39th min, and 53rd min.
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Figure 5
Figure 5. Reaction time profile of HMF oxidation over Co–N–C (a) and inhibited by IPA (b) and the reaction time profile of HMFCA oxidation over Co–N–C (c) and inhibited by IPA (d). Reaction conditions: 0.5 mmol HMF or HMFCA, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 5 mL of H₂O, 1.0 mmol IPA, 40 mL/min O₂, and 60 °C.
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Figure 6
Figure 6. UV–vis spectra of the HMF oxidation process in the Co–N–C system (a) and H₂O₂ + OH^– system (b); evolution of FDCA concentration in HMF oxidation in the Co–N–C system with O₂ bubbling (A), with H₂O₂ addition 10 times (B), with H₂O₂ addition 1 time (C), and in the H₂O₂ + OH^– system (D) (c); ESR spectra of DMPO-OH^• adducts at the reaction time of 1 min in the Co–N–C system with O₂ bubbling, with H₂O₂ addition 10 times and 1 time and in the H₂O₂ + OH^– system (d). Reaction conditions: 0.5 mmol HMF, 0.032 mmol Co in Co–N–C, 1.25 mmol NaOH, 5 mL of H₂O, 60 °C, and 40 mL/min O₂ (A); 0.1 mL of 30 wt % H₂O₂ was added 10 times at equal intervals (B); 1 mL of 30 wt % H₂O₂ was added 1 time (C); 1 mL of 30 wt % H₂O₂ was added 1 time without Co–N–C addition (D). Reaction conditions of UV–vis monitoring in (a, b) were consistent with those of (A) and (D) in (c), respectively.
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Figure 7
Figure 7. ESR spectra of DMPO-OH^• adducts at the reaction time of 30 min in the H₂O₂ + OH^– system at a pH value of 12.79 and Co–N–C system with different pH values (a); the intensity of the DMPO-OH^• adducts in the ESR spectra (b); Arrhenius plots of HMF oxidation with and without OH^• in the Co–N–C system (c); the product yield in HMF oxidation in the Co–N–C system with different pH values and in the H₂O₂ + OH^– system at a pH value of 12.79 (d); and the schematic illustration of the HMF oxidation with OH^• formation in the Co–N–C system (e). Reaction conditions: 0.5 mmol HMF, 0.032 mmol Co in Co–N–C, 5 mL of H₂O, 60 °C, 40 mL/min O₂, 5 h, at different pH values; ^a0.5 mmol HMF, 1 mL of 30 wt % H₂O₂, 4 mL of H₂O, 60 °C, 5 h, and pH = 12.79.
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  Generation of FeIV=O and its Contribution to Fenton-Like Reactions on a Single-Atom Iron-N-C Catalyst
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  GeneratingFeIV=O on single-atom catalysts by Fenton-like reaction has been established for water treatment; however, the FeIV=O generation pathway and oxidn. behavior remain obscure. Employing an Fe-N-C catalyst with a typical Fe-N4 moiety to activate peroxymonosulfate (PMS), we demonstrate that generating FeIV=O is mediated by an Fe-N-C-PMS* complex-a well-recognized nonradical species for induction of electron-transfer oxidn.-and we detd. that adjacent Fe sites with a specific Fe1-Fe1 distance are required. After the Fe atoms with an Fe1-Fe1 distance <4 S are PMS-satd., Fe-N-C-PMS* formed on Fe sites with an Fe1-Fe1 distance of 4-5 S can coordinate with the adjacent FeII-N4, forming an inter-complex with enhanced charge transfer to produce FeIV=O. FeIV=O enables the Fenton-like system to efficiently oxidize various pollutants in a substrate-specific, pH-tolerant, and sustainable manner, where its prominent contribution manifests for pollutants with higher one-electron oxidn. potential.
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  Piezocatalytic oxidation of 5-hydroxymethylfurfural to 5-formyl-2-furancarboxylic acid over Pt decorated hydroxyapatite
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  Selective oxidn. of 5-hydroxymethylfurfural (HMF) to 5-formyl-2-furancarboxylic acid (FFCA) is a crit. reaction for producing value-added chems. from biomass. The challenge for this reaction is to develop an efficient catalytic process that can be conducted under mild conditions. Herein, we first propose piezocatalytic HMF oxidn. using a Pt decorated hydroxyapatite (HAP) piezocatalyst (Pt/HAP). The introduction of Pt on HAP creates an interfacial elec. field. The couple of nonlocal piezoelec. field and localized interfacial elec. field greatly promotes both the bulk and surface charges transfer. Moreover, Pt not only promotes the sepn. of piezo-induced charges but also activates oxygen mols. and org. functional groups of the substrates. Compared with pristine HAP, Pt/HAP exhibits outstanding piezocatalytic activity, which reached 96% HMF conversion and 70% FFCA yield in 2 h under room temp. A wide range of aldehydes and alcs., such as fatty aldehydes, furan aldehydes, fatty alcs., and ethylene glycol, were all oxidized to carboxylic acids. This work provides a novel method on utilizing piezocatalysis for biomass conversion.
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10. 10
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  10
  Mediating the Oxidizing Capability of Surface-Bound Hydroxyl Radicals Produced by Photoelectrochemical Water Oxidation to Convert Glycerol into Dihydroxyacetone
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  ACS Catalysis (2022), 12 (12), 6946-6957CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Highly selective oxidn. of a single specific hydroxyl group in glycerol is attractive but challenging because glycerol contains three similar hydroxyl groups. In this work, we developed a ternary photoanode comprising Ag nanoparticle-supported layered double hydroxide (LDH) nanosheets on TiO2 (denoted Ag@LDH@TiO2) for the glycerol selective oxidn. to 1,3-dihydroxyacetone via photoelectrochem. water oxidn. under neutral conditions. It was proved that hydroxyl radicals generated by water oxidn. were the dominating active oxygen species and oxygen atoms in the main oxidn. product came from water. The LDHs and Ag nanoparticles enhanced the selectivity of secondary hydroxyl oxidn., and the Ag nanoparticles further accelerated the corresponding kinetics. The Ag@LDH@TiO2 photoanode exhibited a 1,3-dihydroxyacetone selectivity of 72% at 1.2 V vs reversible hydrogen electrode, which is obviously higher than that of pure TiO2 (23.5%) and surpasses most materials reported thus far. The role of LDHs and Ag nanoparticles in selective oxidn. of glycerol was revealed through detailed spectroscopic and computational studies. Specifically, Fourier transform IR spectroscopy anal. revealed that the middle hydroxyl group is preferentially adsorbed to LDH surfaces, while d. function theory calcns. verified that the surface-bound hydroxyl radicals mediated dehydrogenation barriers of middle carbon of adsorbed glycerol; the Ag nanoparticles promoted the selective adsorption of middle hydroxyl of glycerol, which further induced its selective oxidn.
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  The selective oxidn. of alcs. in aq. phase over supported metal catalysts is facilitated by high-pH conditions. We have studied the mechanism of ethanol and glycerol oxidn. to acids over various supported gold and platinum catalysts. Labeling expts. with 18O2 and H218O demonstrate that oxygen atoms originating from hydroxide ions instead of mol. oxygen are incorporated into the alc. during the oxidn. reaction. D. functional theory calcns. suggest that the reaction path involves both soln.-mediated and metal-catalyzed elementary steps. Mol. oxygen is proposed to participate in the catalytic cycle not by dissocn. to at. oxygen but by regenerating hydroxide ions formed via the catalytic decompn. of a peroxide intermediate.
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  A review; the discovery of exceptionally high catalytic activities of small Au particles has initiated intense research activity to understand their origin. In spite of a large vol. of work, the system is far from being fully understood. There are four major issues in Au-catalyzed CO oxidn. that have not been resolved: (1) the importance of the nature of the support on catalyst activity; (2) the Au oxidn. state necessary for high activity; (3) the sensitivity of the activity to the moisture level in the reaction feed; and (4) reasons for the high activity in small Au particle size and for the strong dependence on particle size and specific morphol. The current understanding of these issues based on available exptl. evidence and computational investigations is discussed, as well as aspects that remain unresolved.
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  Rate and selectivity enhancements mediated by OH radicals in the oxidative coupling of methane catalyzed by Mn/Na2WO4/SiO2
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  OH radicals formed by quasi-equilibrated steps on oxide surfaces introduce homogeneous pathways that lead to higher rates and C2 yields in oxidative methane coupling relative to those attained by CH4 activation with chemisorbed oxygen. The reactivity of OH• leads to a weaker influence of the C-H bond energies on the relative rates of H abstraction from CH4, C2H6, and C2H4.
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  Jiang, D.; Ni, D.; Rosenkrans, Z. T.; Huang, P.; Yan, X.; Cai, W. Nanozyme: New Horizons for Responsive Biomedical Applications. Chem. Soc. Rev. 2019, 48, 3683– 3704, DOI: 10.1039/C8CS00718G
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  Nanozyme: new horizons for responsive biomedical applications
  Jiang, Dawei; Ni, Dalong; Rosenkrans, Zachary T.; Huang, Peng; Yan, Xiyun; Cai, Weibo
  Chemical Society Reviews (2019), 48 (14), 3683-3704CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  Nanozymes are nanomaterial-based artificial enzymes. By effectively mimicking catalytic sites of natural enzymes or harboring multivalent elements for reactions, nanozyme systems have successfully served as direct surrogates of traditional enzymes for catalysis. With the rapid development and ever-deepening understanding of nanotechnol., nanozymes offer higher catalytic stability, ease of modification and lower manufg. cost than protein enzymes. Addnl., nanozymes possess inherent nanomaterial properties, providing not only a simple substitute of enzymes but also a multimodal platform interfacing complex biol. environments. Recent extensive research has focused on designing various nanozyme systems that are responsive to one or multiple substrates by tailored means. Catalytic activities of nanozymes can be regulated by pH, H2O2 and glutathione concns. and levels of oxygenation in different microenvironments. Moreover, nanozymes can be remotely-controlled via different stimuli, including a magnetic field, light, ultrasound, and heat. Collectively, these factors can be adjusted to maximize the diagnostic and therapeutic efficacies of different diseases in biomedical settings. Therefore, by integrating the catalytic property and inherent nanomaterial nature of nanozyme systems, we anticipate that stimuli-responsive nanozymes will open up new horizons for diagnosis, treatment, and theranostics.
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  Wu, J.; Wang, X.; Wang, Q.; Lou, Z.; Li, S.; Zhu, Y.; Qin, L.; Wei, H. Nanomaterials with Enzyme-Like Characteristics (Nanozymes): Next-Generation Artificial Enzymes (II). Chem. Soc. Rev. 2019, 48, 1004– 1076, DOI: 10.1039/C8CS00457A
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  Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes (II)
  Wu, Jiangjiexing; Wang, Xiaoyu; Wang, Quan; Lou, Zhangping; Li, Sirong; Zhu, Yunyao; Qin, Li; Wei, Hui
  Chemical Society Reviews (2019), 48 (4), 1004-1076CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  Nanozymes are nanomaterials with enzyme-like characteristics (Chem. Soc. Rev., 2013, 42, 6060-6093). They have been developed to address the limitations of natural enzymes and conventional artificial enzymes. Along with the significant advances in nanotechnol., biotechnol., catalysis science, and computational design, great progress has been achieved in the field of nanozymes since the publication of the above-mentioned comprehensive review in 2013. To highlight these achievements, this review first discusses the types of nanozymes and their representative nanomaterials, together with the corresponding catalytic mechanisms whenever available. Then, it summarizes various strategies for modulating the activity and selectivity of nanozymes. After that, the broad applications from biomedical anal. and imaging to theranostics and environmental protection are covered. Finally, the current challenges faced by nanozymes are outlined and the future directions for advancing nanozyme research are suggested. The current review can help researchers know well the current status of nanozymes and may catalyze breakthroughs in this field.
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  Xu, B.; Wang, H.; Wang, W.; Gao, L.; Li, S.; Pan, X.; Wang, H.; Yang, H.; Meng, X.; Wu, Q.; Zheng, L.; Chen, S.; Shi, X.; Fan, K.; Yan, X.; Liu, H. A Single-Atom Nanozyme for Wound Disinfection Applications. Angew. Chem., Int. Ed. 2019, 58, 4911– 4916, DOI: 10.1002/anie.201813994
  16
  A single-atom nanozyme for wound disinfection applications
  Xu, Bolong; Wang, Hui; Wang, Weiwei; Gao, Lizeng; Li, Shanshan; Pan, Xueting; Wang, Hongyu; Yang, Hailong; Meng, Xiangqin; Wu, Qiuwen; Zheng, Lirong; Chen, Shenming; Shi, Xinghua; Fan, Kelong; Yan, Xiyun; Liu, Huiyu
  Angewandte Chemie, International Edition (2019), 58 (15), 4911-4916CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Single-atom catalysts (SACs), as homogeneous catalysts, have been widely explored for chem. catalysis. However, few studies focus on the applications of SACs in enzymic catalysis. Herein, we report that a zinc-based zeolitic-imidazolate-framework (ZIF-8)-derived carbon nanomaterial contg. atomically dispersed zinc atoms can serve as a highly efficient single-atom peroxidase mimic. To reveal its structure-activity relationship, the structural evolution of the single-atom nanozyme (SAzyme) was systematically investigated. Furthermore, the coordinatively unsatd. active zinc sites and catalytic mechanism of the SAzyme are disclosed using d. functional theory (DFT) calcns. The SAzyme, with high therapeutic effect and biosafety, shows great promises for wound antibacterial applications.
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17. 17
  Zhu, S.; Li, Z.; Zhang, F.; Liu, F.; Ni, P.; Chen, C.; Jiang, Y.; Lu, Y. Single-Atom Cobalt Catalysts as Highly Efficient Oxidase Mimics for Time-Based Visualization Monitoring the TAC of Skin Care Products. Chem. Eng. J. 2023, 456, 141053 DOI: 10.1016/j.cej.2022.141053
  17
  Single-atom cobalt catalysts as highly efficient oxidase mimics for time-based visualization monitoring the TAC of skin care products
  Zhu, Shicheng; Li, Zhe; Zhang, Feifan; Liu, Fangning; Ni, Pengjuan; Chen, Chuanxia; Jiang, Yuanyuan; Lu, Yizhong
  Chemical Engineering Journal (Amsterdam, Netherlands) (2023), 456 (), 141053CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
  Reactive oxygen species (ROS) are an important cause of oxidative skin aging and can be removed by adding some antioxidant ingredients to skin care products. However, total antioxidant capacity (TAC) assays generally require sophisticated lab. equipment, which greatly limits their daily application. Fortunately, the adoption and development of portable smartphone platforms could promises to solve this challenge. Herein, we report a cobalt single atom-based portable smartphone platform which can realize dynamic-time visualization monitoring the TAC of skin care product. Theor. calcns. and specific exptl. results show that single-atom cobalt catalysts (SA-Co/NC) present excellent oxidase-like activity and can effectively convert dissolved oxygen into strongly oxidizing reactive oxygen species. More interestingly, based on the unique sacrificial inhibition catalytic mechanism of ascorbic acid (AA), it can be combined with a portable smartphone platform to detect the TAC of real samples by fitting a time-color-concn. std. curve and recording the change of color RGB values during the reaction. Compared with the traditional scheme, this scheme is convenient, low cost, and can realize visual detection of mobile terminals. This work provides a new scheme for miniaturization, convenience and home-based of TAC detection.
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18. 18
  Ye, Y.; Xiao, L.; Bin, H.; Zhang, Q.; Nie, T.; Yang, X.; Wu, D.; Cheng, H.; Li, P.; Wang, Q. Oxygen-Tuned Nanozyme Polymerization for the Preparation of Hydrogels with Printable and Antibacterial Properties. J. Mater. Chem. B 2017, 5, 1518– 1524, DOI: 10.1039/C6TB03317B
  18
  Oxygen-tuned nanozyme polymerization for the preparation of hydrogels with printable and antibacterial properties
  Ye, Yuemei; Xiao, Linlin; Bin He; Zhang, Qi; Nie, Tao; Yang, Xinrui; Wu, Dongbei; Cheng, Heli; Li, Ping; Wang, Qigang
  Journal of Materials Chemistry B: Materials for Biology and Medicine (2017), 5 (7), 1518-1524CODEN: JMCBDV; ISSN:2050-7518. (Royal Society of Chemistry)
  Nanozymes merge nanotechnol. with biol. and provide a lower cost and higher stability options, compared to that of natural enzymes. However, nanozyme catalyzed polymn. under physiol. conditions is still a big challenge due to heavy oxygen inhibition. In this study, the simple glucose oxidase system can effectively adjust oxygen concn. and generate hydrogen peroxide, which assists in the realization of nanozyme-catalyzed polymn. The nanozyme based hydrogel is printable due to its mild prepn. with gradually increased viscosity. The antibacterial performance is ascribed to the in situ generated hydroxyl radical via the reaction of the bound nanozyme and glucose.
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19. 19
  Mondelli, C.; Gözaydın, G.; Yan, N.; Pérez-Ramírez, J. Biomass Valorisation over Metal-Based Solid Catalysts from Nanoparticles to Single Atoms. Chem. Soc. Rev. 2020, 49, 3764– 3782, DOI: 10.1039/D0CS00130A
  19
  Biomass valorisation over metal-based solid catalysts from nanoparticles to single atoms
  Mondelli, Cecilia; Gozaydin, Gokalp; Yan, Ning; Perez-Ramirez, Javier
  Chemical Society Reviews (2020), 49 (12), 3764-3782CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
  A review. Heterogeneous catalysts are vital to unlock superior efficiency, atom economy, and environmental friendliness in chem. conversions, with the size and speciation of the contained metals often playing a decisive role in the activity, selectivity and stability. This tutorial review analyses the impact of these catalyst parameters on the valorisation of biomass through hydrogenation and hydrodeoxygenation, oxidn., reforming and acid-catalyzed reactions, spanning a broad spectrum of substrates including sugars and platform compds. obtained from (hemi)cellulose and lignin derivs. It outlines multiple examples of classical structure sensitivity on nanoparticle-based materials with significant implications for the product distribution. It also shows how the recently emphasized application of metals in the form of ultrasmall nanoparticles (<2 nm), clusters and single atoms, while fulfilling superior metal utilization and robustness, opens the door to unprecedented electronic and geometric properties. The latter can lead to facilitated activation of reactants as well as boosted selectivity control and synergy between distinct active sites in multifunctional catalysts. Based on the anal. conducted, guidelines for the selection of metals for diverse applications are put forward in terms of chem. identity and structure, and aspects that should be explored in greater depth for further improving the exploitation of metals in this research field and beyond are highlighted.
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20. 20
  Liu, S.-S.; Sun, K.-Q.; Xu, B.-Q. Specific Selectivity of Au-Catalyzed Oxidation of Glycerol and Other C₃-Polyols in Water without the Presence of a Base. ACS Catal. 2014, 4, 2226– 2230, DOI: 10.1021/cs5005568
  20
  Specific Selectivity of Au-Catalyzed Oxidation of Glycerol and Other C3-Polyols in Water without the Presence of a Base
  Liu, Shu-Sen; Sun, Ke-Qiang; Xu, Bo-Qing
  ACS Catalysis (2014), 4 (7), 2226-2230CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  A big challenge in upgrading bio-oxygenate platform mols. is to develop catalysts for the selective oxidn. of a nonterminal HO-bonded carbon atom in polyols. We report herein the first finding of a specific selectivity of oxide-supported nano-Au catalysts for dihydroxyacetone (DHA) prodn. in glycerol oxidn. in water without NaOH. Though the support nature (Al2O3, TiO2, ZrO2, NiO, and CuO) significantly affects the Au activity, a highly active Au/CuO catalyst offering DHA yields up to 80% at 40-50 °C has been identified. Rich data are provided to clarify that DHA is the only primary product of glycerol oxidn. This propensity of nano-Au for oxidizing the HO-bonded secondary (central) carbon is further verified by comparing the oxidn. of propanediols and propanols. Mol. insight into the reactions is given on the basis of the kinetic isotopic effect study of deuterium on the oxidn. of 2-propanol, uncovering an unanticipated chem. of Au catalysis.
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21. 21
  Zhang, J.; Nagamatsu, S.; Du, J.; Tong, C.; Fang, H.; Deng, D.; Liu, X.; Asakura, K.; Yuan, Y. A Study of FeN_x/C Catalysts for the Selective Oxidation of Unsaturated Alcohols by Molecular Oxygen. J. Catal. 2018, 367, 16– 26, DOI: 10.1016/j.jcat.2018.08.004
  21
  A study of FeNx/C catalysts for the selective oxidation of unsaturated alcohols by molecular oxygen
  Zhang, Jinping; Nagamatsu, Shinichi; Du, Junmou; Tong, Chaoli; Fang, Huihuang; Deng, Dehui; Liu, Xi; Asakura, Kiyotaka; Yuan, Youzhu
  Journal of Catalysis (2018), 367 (), 16-26CODEN: JCTLA5; ISSN:0021-9517. (Elsevier Inc.)
  Transition-metal nitrides can exhibit catalytic performance comparable to that of noble metal catalysts in many reactions. However, investigations on the correlation of catalyst structure, performance, and stability are still highly demanded. Here, a series of metal nitrides were prepd. and evaluated for the selective oxidn. of alcs. by mol. oxygen. Among them, FeNx/C-T catalysts (T represents the pyrolysis temp.) display above 95% selectivity to the corresponding aldehydes in the selective oxidn. of unsatd. alcs. The optimized FeNx/C-900 catalyst gives the highest TOF of 7.0 h-1 for the conversion of 5-hydroxymethylfurfural to 2,5-diformylfuran. A combination of characterizations and expts. suggests that Fe-N4 species are the main active sites. In addn., investigate the reasons for the catalyst deactivation and provide an effective approach to regenerating the catalysts. The results indicate that the deactivated catalysts can be regenerated by heat treatment under NH3/N2 after each run. Based on these studies, a plausible reaction mechanism over the FeNx/C catalysts is proposed.
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22. 22
  Tu, C.; Nie, X.; Chen, J. G. Insight into Acetic Acid Synthesis from the Reaction of CH₄ and CO₂. ACS Catal. 2021, 11, 3384– 3401, DOI: 10.1021/acscatal.0c05492
  22
  Insight into Acetic Acid Synthesis from the Reaction of CH4 and CO2
  Tu, Chunyan; Nie, Xiaowa; Chen, Jingguang G.
  ACS Catalysis (2021), 11 (6), 3384-3401CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  A review. The reaction of CH4 and CO2 to produce acetic acid is an atom-efficient way for using carbon resources and for mitigating CO2 emissions. This article provides a crit. assessment of the progress in this catalytic reaction from the perspective of identifying and constructing the active sites. We elucidate how Cu- and Zn-based catalysts with different structures are used for the activation of CH4 and CO2. The differences in the metal oxidn. state may affect the adsorption of CH4 and CO2 and consequently change the activation barriers for the dissocn. of the C-H bond of CH4 and the C-C coupling reaction. We discuss how the active sites and transition states can be modified by the location of metal sites, the framework environment, and the promotion effect of different acid sites. We also compare different technologies, including catalyst pretreatment, preactivation with CO2, tandem reaction, and plasma-driven catalysis for the CH4 and CO2 conversion. We conclude by identifying opportunities for improving the efficiency of heterogeneous catalysts for this important reaction.
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23. 23
  Thomas, J. M.; Raja, R.; Sankar, G.; Bell, R. G. Molecular Sieve Catalysts for the Regioselective and Shape-Selective Oxyfunctionalization of Alkanes in Air. Acc. Chem. Res. 2001, 34, 191– 200, DOI: 10.1021/ar970020e
  23
  Molecular Sieve Catalysts for the Regioselective and Shape-Selective Oxyfunctionalization of Alkanes in Air
  Thomas, John Meurig; Raja, Robert; Sankar, Gopinathan; Bell, Robert G.
  Accounts of Chemical Research (2001), 34 (3), 191-200CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)
  A review with 42 refs. Framework-substituted, mol.-sieve, aluminophosphate, microporous solids are the centerpieces of a new approach to the aerobic oxyfunctionalization of satd. hydrocarbons. The sieves, and the few percent of the AlIII sites within them that are replaced by catalytically active, transition-metal ions in high oxidn. states (CoIII, MnIII, FeIII), are designed so as to allow free access of oxygen in to and out of the interior of these high-area solids. Certain metal-substituted, mol. sieves permit only end-on approach of linear alkanes to the active centers, thereby favoring enhanced reactivity of the terminal Me groups. By optimizing cage dimension, with respect to that of the hydrocarbon reactant, as well as adjusting the av. sepn. of active centers within a cage, and by choosing the sieve with the appropriate pore aperture, highly selective conversions such as n-hexane to hexanoic acid or adipic acid, and cyclohexane to cyclohexanol, cyclohexanone, or adipic acid, may be effected at low temp., heterogeneously in air.
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24. 24
  Wang, Q.; Hou, W.; Li, S.; Xie, J.; Li, J.; Zhou, Y.; Wang, J. Hydrophilic Mesoporous Poly(ionic liquid)-Supported Au–Pd Alloy Nanoparticles towards Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid under Mild Conditions. Green Chem. 2017, 19, 3820– 3830, DOI: 10.1039/C7GC01116D
  24
  Hydrophilic mesoporous poly(ionic liquid)-supported Au-Pd alloy nanoparticles towards aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid under mild conditions
  Wang, Qian; Hou, Wei; Li, Shuai; Xie, Jingyan; Li, Jing; Zhou, Yu; Wang, Jun
  Green Chemistry (2017), 19 (16), 3820-3830CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
  Design of stable high-performance heterogeneous catalysts has become crucial for efficient catalytic conversion of renewable biomass into high value-added chems. Noble metal alloy nanoparticles (NPs) are of great interest due to their unique tunable structures and high activity. In this study, Au-Pd alloy NPs supported on hydrophilic mesoporous poly(ionic liq.) (MPIL) exhibited encouragingly high performance in the aerobic oxidn. of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) in water under mild conditions. Nearly complete conversion of HMF is attained at a low temp. of 90° under atm. O2, resulting in 99% FDCA yield and high turnover no. (TON) of up to 350. After reaction, the catalyst can be facilely recovered and reused with stable activity. Surface wettability plays a dominant role in the oxidn. of HMF to FDCA, and synergistic alloy effect accounts for high activity. The results also show that MPILs are a promising support platform to achieve stable and efficient metal NPs through task-specific design of functional monomers.
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25. 25
  Liu, X.; Chen, L.; Xu, H.; Jiang, S.; Zhou, Y.; Wang, J. Straightforward Synthesis of Beta Zeolite Encapsulated Pt Nanoparticles for the Transformation of 5-Hydroxymethyl Furfural into 2,5-Furandicarboxylic Acid. Chin. J. Catal. 2021, 42, 994– 1003, DOI: 10.1016/S1872-2067(20)63720-2
  25
  Straightforward synthesis of beta zeolite encapsulated Pt nanoparticles for the transformation of 5-hydroxymethyl furfural into 2,5-furandicarboxylic acid
  Liu, Xiaoling; Chen, Lei; Xu, Hongzhong; Jiang, Shi; Zhou, Yu; Wang, Jun
  Chinese Journal of Catalysis (2021), 42 (6), 994-1003CODEN: CJCHCI; ISSN:1872-2067. (Elsevier B.V.)
  Encapsulating noble metal nanoparticles (NPs) within the zeolite framework enhances the stability and accessibility of active sites; however, direct synthesis remains a challenge because of the easy pptn. of noble metal species under strong alkali crystn. conditions. Herein, beta zeolite-encapsulated Pt NPs (Pt@Beta) were synthesized via a hydrothermal approach involving an unusual acid hydrolysis preaging step. The ligand-(3-mercaptopropyl)trimethoxysilane-and Pt precursor were cohydrolyzed and cocondensed with a silica source in an initially weak acidic environment to prevent colloidal pptn. by enhancing the interaction between the Pt and silica species. Thus, the resultant 0.2%Pt@Beta was highly active in the transformation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid (FDCA) under atm. O2 conditions by using water as the solvent while stably evincing a high yield (90%) assocd. with a large turnover no. of 176. The excellent catalysis behavior is attributable to the enhanced stability that inhibits Pt leaching and strengthens the intermediates that accelerate the rate-detg. step for the oxidn. of 5-formyl-2-furan carboxylic acid into FDCA.
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26. 26
  Zhang, M.; Ma, H.; Liu, X.; Zhang, S.; Luo, Y.; Gao, J.; Xu, J. Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn–Co Catalyst. ACS Appl. Mater. Interfaces 2022, 14, 18539– 18549, DOI: 10.1021/acsami.2c01858
  26
  Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn-Co Catalyst
  Zhang, Meiyun; Ma, Hong; Liu, Xin; Zhang, Shujing; Luo, Yang; Gao, Jin; Xu, Jie
  ACS Applied Materials & Interfaces (2022), 14 (16), 18539-18549CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
  Activation of mol. oxygen plays a crucial role in natural organisms and the modern chem. industry. Herein, we report a Mn-Co dual-single-atom catalyst that exerts a specific synergy in boosting O2 activation by collaboration between two distinct types of activation sites. Taking the oxidative esterification of the biomass platform 5-hydroxymethylfurfural (HMF) as the model reaction, the activation of O2 is demonstrated through transforming O2 into a reactive superoxide anion radical (O2•-) on Co-N4 sites and, meanwhile, by reversible consumption and supplement of coordinated surface oxygen as a new type of reactive oxygen species (ROS) on N,O-coordinated single-atom Mn sites (Mn-NxOy). EXAFS anal. results show a longer av. Mn-O bond distance at near 2.19 Å, which makes the breaking and formation of surface Mn-O bonds easier to cycle. Control expts. support that such Mn-O bonding conditions could facilitate H-elimination of C-H in HMF. The co-existence of two types of ROS effectively matches the oxidn. of hydroxyl and aldehyde groups, and thus, the overall reaction is boosted in excellent yield of diester (95.8%) with an extremely high carbon balance. This study represents a rare example of taking advantage of the synergy of the diat. catalyst for activating O2 by two types of activation pathways.
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27. 27
  Liu, X.; Luo, Y.; Ma, H.; Zhang, S.; Che, P.; Zhang, M.; Gao, J.; Xu, J. Hydrogen-Binding-Initiated Activation of O–H Bonds on a Nitrogen-Doped Surface for the Catalytic Oxidation of Biomass Hydroxyl Compounds. Angew. Chem., Int. Ed. 2021, 133, 18251– 18258, DOI: 10.1002/ange.202103604
  There is no corresponding record for this reference.
28. 28
  Sun, Y.; Ma, H.; Jia, X.; Ma, J.; Luo, Y.; Gao, J.; Xu, J. A High-Performance Base-Metal Approach for the Oxidative Esterification of 5-Hydroxymethylfurfural. ChemCatChem 2016, 8, 2907– 2911, DOI: 10.1002/cctc.201600484
  28
  A High-Performance Base-Metal Approach for the Oxidative Esterification of 5-Hydroxymethylfurfural
  Sun, Yuxia; Ma, Hong; Jia, Xiuquan; Ma, Jiping; Luo, Yang; Gao, Jin; Xu, Jie
  ChemCatChem (2016), 8 (18), 2907-2911CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Exploring high-performance base-metal approaches for the sustainable prodn. of chems. from biomass is presently attracting immense interest and is truly important to promote their industrialized application. Herein, CoOx-N/C and α-MnO2 were combined as a base-metal catalyst that can achieve high yields of furan-2,5-dimethylcarboxylate (FDMC, 95.6 %) for the catalytic oxidative esterification of 5-hydroxymethylfurfural (HMF) without basic additive. The reaction proceeds through fast conversion of HMF to diformylfuran (DFF) with α-MnO2 and subsequent transformation of DFF to FDMC by CoOx-N/C. Quant. XPS anal. and d. functional theory (DFT) calcns. indicated that the pyridinic-N present in doped carbon could behave as a Lewis base to promote the abstraction of hydrogen for the oxidative esterification reaction. Consequently, CoOx-N/C is a high performance catalyst for the synthesis of FDMC from DFF in a neutral medium.
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29. 29
  Sun, Y.; Ma, H.; Luo, Y.; Zhang, S.; Gao, J.; Xu, J. Activation of Molecular Oxygen Using Durable Cobalt Encapsulated with Nitrogen-Doped Graphitic Carbon Shells for Aerobic Oxidation of Lignin-Derived Alcohols. Chem. - Eur. J. 2018, 24, 4653– 4661, DOI: 10.1002/chem.201705824
  29
  Activation of Molecular Oxygen Using Durable Cobalt Encapsulated with Nitrogen-Doped Graphitic Carbon Shells for Aerobic Oxidation of Lignin-Derived Alcohols
  Sun, Yuxia; Ma, Hong; Luo, Yang; Zhang, Shujing; Gao, Jin; Xu, Jie
  Chemistry - A European Journal (2018), 24 (18), 4653-4661CODEN: CEUJED; ISSN:0947-6539. (Wiley-VCH Verlag GmbH & Co. KGaA)
  It has long been a challenge for activating O2 by transition-metal nanocatalysts, which might lose activity due to strong tendency for oxidn. Herein, O2 could be activated by durable encapsulated cobalt nanoparticles (NPs) with N-doped graphitic carbon shells (Co@N-C), but not by encapsulated cobalt NPs with graphitic carbon, exposed cobalt NPs supported on activated carbon, or N-doped carbon. ESR, real-time in situ FTIR spectroscopy, and mass spectrometry measurements demonstrated the generation of the highly active superoxide radical, O2.-. This unique ability enables Co@N-C to afford an excellent catalytic performance in model aerobic oxidn. of monomeric lignin-derived alcs. Further anal. elucidated that encapsulated cobalt and nitrogen-doped graphitic carbon might contribute to the capacity through influencing the electronic properties of outer layers. Moreover, through isolation by N-doped graphitic carbon shells, the inner metallic cobalt NPs are inaccessible in term of either alcs. or oxygenated products, and a distinctive resistance to leaching and agglomeration has been achieved.
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30. 30
  Wang, T.; Ma, H.; Liu, X.; Luo, Y.; Zhang, S.; Sun, Y.; Wang, X.; Gao, J.; Xu, J. Ultrahigh-Content Nitrogen-Doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural. Chem. - Asian J. 2019, 14, 1515– 1522, DOI: 10.1002/asia.201900099
  30
  Ultrahigh-Content Nitrogen-doped Carbon Encapsulating Cobalt NPs as Catalyst for Oxidative Esterification of Furfural
  Wang, Ting; Ma, Hong; Liu, Xin; Luo, Yang; Zhang, Shujing; Sun, Yuxia; Wang, Xinhong; Gao, Jin; Xu, Jie
  Chemistry - An Asian Journal (2019), 14 (9), 1515-1522CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)
  It is an attractive and challenging topic to endow non-noble metal catalysts with high efficiency via a nitrogen-doping approach. In this study, a nitrogen-doped carbon catalyst with high nitrogen content encapsulating cobalt NPs (CoOx@N-C(g)) was synthesized, and characterized in detail by XRD, HRTEM, N2-physisorption, ICP, CO2-TPD, and XPS techniques. g-C3N4 nanosheets act as nitrogen source and self-sacrificing templates, giving rise to an ultrahigh nitrogen content of 14.0 %, much higher than those using bulk g-C3N4 (4.4 %) via the same synthesis procedures. As a result, CoOx@N-C(g) exhibited the highest performance in the oxidative esterification of biomass-derived platform furfural to methylfuroate under base-free conditions, achieving 95.0 % conversion and 97.1 % selectivity toward methylfuroate under 0.5 MPa O2 at 100 °C for 6 h, far exceeding those of other cobalt-based catalysts. The high efficiency of CoOx@N-C(g) was closely related to its high ratio of pyridinic nitrogen species that may act as Lewis basic sites as well as its capacity for the activation of dioxygen to superoxide radical O2.-.
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31. 31
  Chen, C.; Wang, L.; Zhu, B.; Zhou, Z.; El-Hout, S. I.; Yang, J.; Zhang, J. 2, 5-Furandicarboxylic Acid Production via Catalytic Oxidation of 5-Hydroxymethylfurfural: Catalysts, Processes and Reaction Mechanism. J. Energy Chem. 2021, 54, 528– 554, DOI: 10.1016/j.jechem.2020.05.068
  31
  2,5-Furandicarboxylic acid production via catalytic oxidation of 5-hydroxymethylfurfural: Catalysts, processes and reaction mechanism
  Chen, Chunlin; Wang, Lingchen; Zhu, Bin; Zhou, Zhenqiang; El-Hout, Soliman I.; Yang, Jie; Zhang, Jian
  Journal of Energy Chemistry (2021), 54 (), 528-554CODEN: JECOFG; ISSN:2095-4956. (Science Press)
  Biomass conversion to value-added chems. has received tremendous attention for solving global warming issues and fossil fuel depletion. 5-Hydroxymethylfurfural (HMF) is a key bio-based platform mol. to produce many useful org. chems. by oxidn., hydrogenation, polymn., and ring-opening reactions. Among all derivs., the oxidn. product 2,5-furandicarboxylic acid (FDCA) is a promising alternative to petroleum-based terephthalic acid for the synthesis of biodegradable plastics. This review anal. discusses the recent progress in the thermocatalytic, electrocatalytic, and photocatalytic oxidn. of HMF into FDCA, including catalyst screening, synthesis processes, and reaction mechanism. Rapid fundamental advances may be possible in non-precious metal and metal-free catalysts that are highly efficient under the base-free conditions, and external field-assisted processes like electrochem. or photoelectrochem. cells.
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  https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB38XisFKqtbrE&md5=f4b8fcdc404b97fb731cca91f2154791
32. 32
  Yang, G.; Ma, Y.; Xu, J. Biomimetic Catalytic System Driven by Electron Transfer for Selective Oxygenation of Hydrocarbon. J. Am. Chem. Soc. 2004, 126, 10542– 10543, DOI: 10.1021/ja047297b
  32
  Biomimetic Catalytic System Driven by Electron Transfer for Selective Oxygenation of Hydrocarbon
  Yang, Guanyu; Ma, Yinfa; Xu, Jie
  Journal of the American Chemical Society (2004), 126 (34), 10542-10543CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  A biomimetic system was developed which has a nonmetallic redox center, composed of anthraquinones, N-hydroxyphthalimide, and zeolite HY, for selective hydrocarbon oxidn. by mol. oxygen, a crucial industrial process. Selectivity of 95.8% for acetophenone and 66.2% conversion were accomplished for oxygenation of ethylbenzene at temps. as low as 80°. The redox cycle, driven by one-electron transfer and product orientation by Zeolite HY, opens up the possibility of mimicking bio-oxidn. under mild conditions. The process is a good alternative to use of metallic catalysts that require higher temps. and often show lower selectivity.
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33. 33
  Dijkman, W. P.; Groothuis, D. E.; Fraaije, M. W. Enzyme-Catalyzed Oxidation of 5-Hydroxymethylfurfural to Furan-2, 5-Dicarboxylic Acid. Angew. Chem., Int. Ed. 2014, 53, 6515– 6518, DOI: 10.1002/anie.201402904
  33
  Enzyme-Catalyzed Oxidation of 5-Hydroxymethylfurfural to Furan-2,5-dicarboxylic Acid
  Dijkman, Willem P.; Groothuis, Daphne E.; Fraaije, Marco W.
  Angewandte Chemie, International Edition (2014), 53 (25), 6515-6518CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Furan-2,5-dicarboxylic acid (FDCA) is a biobased platform chem. for the prodn. of polymers. In the past few years, numerous multistep chem. routes have been reported on the synthesis of FDCA by oxidn. of 5-hydroxymethylfurfural (HMF). Recently we identified an FAD-dependent enzyme which is active towards HMF and related compds. This oxidase has the remarkable capability of oxidizing [5-(hydroxymethyl)furan-2-yl]methanol to FDCA, a reaction involving four consecutive oxidns. The oxidase can produce FDCA from HMF with high yield at ambient temp. and pressure. Examn. of the underlying mechanism shows that the oxidase acts on alc. groups only and depends on the hydration of aldehydes for the oxidn. reaction required to form FDCA.
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34. 34
  Jia, H. Y.; Zong, M. H.; Zheng, G. W.; Li, N. One-Pot Enzyme Cascade for Controlled Synthesis of Furancarboxylic Acids from 5-Hydroxymethylfurfural by H₂O₂ Internal Recycling. ChemSusChem 2019, 12, 4764– 4768, DOI: 10.1002/cssc.201902199
  34
  One-Pot Enzyme Cascade for Controlled Synthesis of Furancarboxylic Acids from 5-Hydroxymethylfurfural by H2O2 Internal Recycling
  Jia, Hao-Yu; Zong, Min-Hua; Zheng, Gao-Wei; Li, Ning
  ChemSusChem (2019), 12 (21), 4764-4768CODEN: CHEMIZ; ISSN:1864-5631. (Wiley-VCH Verlag GmbH & Co. KGaA)
  Furancarboxylic acids are promising biobased building blocks in pharmaceutical and polymer industries. In this work, dual-enzyme cascade systems composed of galactose oxidase (GOase) and alc. dehydrogenases (ADHs) are constructed for controlled synthesis of 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF), based on the catalytic promiscuity of ADHs. The byproduct H2O2, which is produced in GOase-catalyzed oxidn. of HMF to 2,5-diformylfuran (DFF), is used for horseradish peroxidase (HRP)-mediated regeneration of the oxidized nicotinamide cofactors for subsequent oxidn. of DFF promoted by an ADH, thus implementing H2O2 internal recycling. The desired products FFCA and FDCA are obtained with yields of more than 95 %.
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35. 35
  Liu, W.; Zhang, L.; Yan, W.; Liu, X.; Yang, X.; Miao, S.; Wang, W.; Wang, A.; Zhang, T. Single-Atom Dispersed Co–N–C Catalyst: Structure Identification and Performance for Hydrogenative Coupling of Nitroarenes. Chem. Sci. 2016, 7, 5758– 5764, DOI: 10.1039/C6SC02105K
  35
  Single-atom dispersed Co-N-C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes
  Liu, Wengang; Zhang, Leilei; Yan, Wensheng; Liu, Xiaoyan; Yang, Xiaofeng; Miao, Shu; Wang, Wentao; Wang, Aiqin; Zhang, Tao
  Chemical Science (2016), 7 (9), 5758-5764CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)
  Co-N-C catalysts are promising candidates for substituting platinum in electrocatalysis and org. transformations. The heterogeneity of the Co species resulting from high-temp. pyrolysis, however, encumbers the structural identification of active sites. Herein, we report a self-supporting Co-N-C catalyst wherein cobalt is dispersed exclusively as single atoms. By using sub-Ångstrom-resoln. HAADF-STEM in combination with XAFS and DFT calcn., the exact structure of the Co-N-C is identified to be CoN4C8-1-2O2, where the Co center atom is coordinated with four pyridinic N atoms in the graphitic layer, while two oxygen mols. are weakly adsorbed on Co atoms in perpendicular to the Co-N4 plane. This single-atom dispersed Co-N-C catalyst presents excellent performance for the chemoselective hydrogenation of nitroarenes to produce azo compds. under mild reaction conditions.
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36. 36
  Jagadeesh, R. V.; Junge, H.; Pohl, M.-M.; Radnik, Jr.; Brückner, A.; Beller, M. Selective Oxidation of Alcohols to Esters Using Heterogeneous Co₃O₄–N@C Catalysts under Mild Conditions. J. Am. Chem. Soc. 2013, 135, 10776– 10782, DOI: 10.1021/ja403615c
  36
  Selective Oxidation of Alcohols to Esters Using Heterogeneous Co3O4-N@C Catalysts under Mild Conditions
  Jagadeesh, Rajenahally V.; Junge, Henrik; Pohl, Marga-Martina; Radnik, Joerg; Brueckner, Angelika; Beller, Matthias
  Journal of the American Chemical Society (2013), 135 (29), 10776-10782CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
  Novel cobalt-based heterogeneous catalysts have been developed for the direct oxidative esterification of alcs. using mol. oxygen as benign oxidant. Pyrolysis of nitrogen-ligated cobalt(II) acetate supported on com. carbon transforms typical homogeneous complexes to highly active and selective heterogeneous Co3O4-N@C materials. By applying these catalysts in the presence of oxygen, the cross and self-esterification of alcs. to esters proceeds in good to excellent yields.
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37. 37
  Madden, K. P.; Taniguchi, H. The Role of the DMPO-Hydrated Electron Spin Adduct in DMPO-OH^• Spin Trapping. Free Radical Biol. Med. 2001, 30, 1374– 1380, DOI: 10.1016/S0891-5849(01)00540-8
  37
  The role of the DMPO-hydrated electron spin adduct in DMPO-√OH spin trapping
  Madden, K. P.; Taniguchi, H.
  Free Radical Biology & Medicine (2001), 30 (12), 1374-1380CODEN: FRBMEH; ISSN:0891-5849. (Elsevier Science Inc.)
  Time-resolved in situ radiolysis ESR (ESR, equivalently EPR, ESR) studies have shown that the scavenging of radiolytically produced hydroxyl radical in nitrous oxide-satd. aq. solns. contg. 2 mM DMPO is essentially quant. (94% of the theor. yield) at 100 μs after the electron pulse [1]. This result appeared to conflict with earlier results using continuous cobalt-60 γ radiolysis and hydrogen peroxide photolysis, where factors of 35 and 33% were obtained, resp. [2,3]. To investigate this discrepancy, nitrogen-satd. aq. solns. contg. 15 mM DMPO were cobalt-60 γ irradiated (dose rate = 223 Gy/min) for periods of 0.25-6 min, and ESR absorption spectra were obsd. ∼ 30 s after irradn. A rapid, pseudo-first-order termination reaction of the protonated DMPO-hydrated electron adduct (DMPO-H) with DMPO-OH was obsd. for the first time. The rate const. for the reaction of DMPO-H with DMPO-OH is 2.44×102 (± 2.2×101) M-1 s-1. In low-dose radiolysis expts., this reaction lowers the obsd. yield of DMPO-OH to 44% of the radiation-chem. OH radical yield (G = 2.8), in good agreement with the earlier results [2,3]. In the absence of the DMPO-H radical, the DMPO-OH exhibits second-order radical termination kinetics, 2kT = 22 (± 2) M-1 s-1 at initial DMPO-OH concns. ≥ 13 μM, with first-order termination kinetics obsd. at lower concns., in agreement with earlier literature reports [4].
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38. 38
  Yamazaki, I.; Piette, L. H. EPR Spin-Trapping Study on the Oxidizing Species Formed in the Reaction of the Ferrous Ion with Hydrogen Peroxide. J. Am. Chem. Soc. 1991, 113, 7588– 7593, DOI: 10.1021/ja00020a021
  38
  EPR spin-trapping study on the oxidizing species formed in the reaction of the ferrous ion with hydrogen peroxide
  Yamazaki, Isao; Piette, Lawrence H.
  Journal of the American Chemical Society (1991), 113 (20), 7588-93CODEN: JACSAT; ISSN:0002-7863.
  Using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping reagent for HO•, the ratio of rate consts. for the reaction of HO• with HO• scavengers (k) was compared to those for the reaction with DMPO (kDMPO) in a photolysis or a Fenton (FeII-H2O2) system. Assuming that the k/kDMPO ratio measures the extent to which HO• is free in soln. relative to 100% in a photolysis system, it is concluded that HO• formed in the Fenton reaction is not totally free in soln. The extent to which it is not free but bound in some kind of complex, depended upon the type of chelator used and increased in the order FeIIADP < FeII-phosphate = FeIIEDTA < FeIIDETAPAC. There was a remarkable difference in the mode of the Fenton reaction between FeIIDETAPAC and FeIIEDTA, particularly at high FeII concns. (0.1 mM). An ethanol-oxidizing species other than HO•, presumably the ferryl ion was detected in the FeIIEDTA reaction but not in the FeIIDETAPAC reaction. The major oxidizing species in the FeIIEDTA-H2O2 reaction changed from the ferryl ion to HO• as the H2O2 concn. was increased, while it was invariably HO• alone in the FeIIDETAPAC-H2O2 reaction. Benzoate and tert-Bu alc., known as typical HO• scavengers, were shown to react not only with HO• but also with the ferryl ion in the FeIIEDTA reaction. Similar scavenging effects were obsd. with histidine, formate, and mannitol.
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39. 39
  Qi, Y.; Li, J.; Zhang, Y.; Cao, Q.; Si, Y.; Wu, Z.; Akram, M.; Xu, X. Novel Lignin-Based Single Atom Catalysts as Peroxymonosulfate Activator for Pollutants Degradation: Role of Single Cobalt and Electron Transfer Pathway. Appl. Catal., B 2021, 286, 119910 DOI: 10.1016/j.apcatb.2021.119910
  39
  Novel lignin-based single atom catalysts as peroxymonosulfate activator for pollutants degradation: Role of single cobalt and electron transfer pathway
  Qi, Yuanfeng; Li, Jing; Zhang, Yanqing; Cao, Qi; Si, Yanmei; Wu, Zhiren; Akram, Muhammad; Xu, Xing
  Applied Catalysis, B: Environmental (2021), 286 (), 119910CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
  In this work, a facile one-pot pyrolytic strategy was employed to fabricate a nitrogen coordinated Co single-atom catalyst (SA Co-N/C catalyst) by using lignin as carbon sources. The HAADF-STEM images and X-ray absorption spectra (XAS) anal. showed the isolated Co atoms less than 2 Å throughout the entire SA Co-N/C architecture. Results showed that the single-atom Co sites served as the main active sites for naproxen (NPX) degrdn. via peroxymonosulfate (PMS) activation. This was confirmed by the high pos. correlation (R2 = 0.9675) between the rate consts. and Co amts. in all SA Co-N/C catalysts. In particular, the as-prepd. SA Co-N/C catalyst with a very small Co loading (2.45 wt.%) exhibited exceptional high turnover frequency (TOF) value for NPX (4.82 min-1), which is promising for the potential application prospect. Electron transfer was induced by the single-atom Co sites, which was the dominated mechanism for the NPX degrdn.
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40. 40
  Tran, P.; Kopel, J.; Risitic, B.; Marsh, H.; Fralick, J.; Reid, T. Antimicrobial Seleno-Organic Coatings and Compounds Acting Primarily on the Plasma Membrane: A Review. Adv. Redox Res. 2022, 4, 100031 DOI: 10.1016/j.arres.2022.100031
  40
  Antimicrobial seleno-organic coatings and compounds acting primarily on the plasma membrane: A review
  Tran, Phat; Kopel, Jonathan; Ristic, Bojana; Marsh, Harrison; Fralick, Joe; Reid, Ted
  Advances in Redox Research (2022), 4 (), 100031CODEN: ARRDCD; ISSN:2667-1379. (Elsevier B.V.)
  A review. Bacterial infections have been the major cause of disease throughout history. However, some bacteria have evolved to attain multi-drug resistance (MDR) against a wide range of antibiotics. Today, the acquisition and spread of antibiotic resistance among pathogenic bacteria constitute a major threat to modern medicine. One approach to overcoming MDR bacteria has been the use of elemental selenium to generate reactive oxygen species (ROS) which damage the cell membrane and intracellular proteins. In this review, we will discuss the underlying antibacterial mechanisms of selenium-coated devices, selenium conjugated peptides, antibodies, and nanoparticles against MDR bacteria. We conducted a literature review of the characteristics of selenium and recent developments of its utilization as an effective treatment strategy. One of the proposed solns. to this problem was the attachment of elemental selenium to different materials to kill bacteria through the catalytic generation of superoxide radicals. Superoxide anion, along with hydrogen peroxide and hydroxyl radical, are the noxious byproducts of partial oxygen redn. that perform lethal cellular oxidative damage. Due to the short half-life of the superoxide radical (≤1 ms) only bacteria localized near selenium are destroyed. Therefore, due to this antimicrobial mechanism, surface coatings of a plethora of devices contg. elemental selenium have been demonstrated as an effective method against pathogenic and antibiotic resistant bacteria. Furthermore, utilization of selenium conjugated peptides, antibodies, and nanoparticles have been investigated as both antimicrobial and anti-cancer therapeutics.
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41. 41
  Shiibashi, T.; Iida, T. J. D. NADPH and NADH Serve as Electron Donor for the Superoxide-Generating Enzyme in Tilapia (Oreochromis Niloticus) Neutrophils. Dev. Comp. Immunol. 2001, 25, 461– 465, DOI: 10.1016/S0145-305X(01)00005-2
  41
  NADPH and NADH serve as electron donor for the superoxide-generating enzyme in tilapia (Oreochromis niloticus) neutrophils
  Shiibashi, T.; Iida, T.
  Developmental & Comparative Immunology (2001), 25 (5-6), 461-465CODEN: DCIMDQ; ISSN:0145-305X. (Elsevier Science Ltd.)
  NADPH oxidase has been identified as the superoxide-generating enzyme in fish neutrophils. To clarify the electron-donating ability of this enzyme, we examine the requirement of NADPH as the electron donor in superoxide generation in tilapia (Oreochromis niloticus) neutrophils using CLA-dependent chemiluminescence (CL). Phorbol ester-induced CL responses were terminated upon the addn. of a detergent, Renex-30. The addn. of graded amts. of NADPH or NADH restored the CL in a dose-dependent manner. The restoration of CL was completely eliminated by superoxide dismutase, suggesting that the restored CL was due to superoxide generation. NADPH tended to have a greater effect than NADH on the CL responses of tilapia neutrophils.
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42. 42
  Gleason, J. E.; Galaleldeen, A.; Peterson, R. L.; Taylor, A. B.; Holloway, S. P.; Waninger-Saroni, J.; Cormack, B. P.; Cabelli, D. E.; Hart, P. J.; Culotta, V. C. Candida Albicans SOD5 Represents the Prototype of an Unprecedented Class of Cu-only Superoxide Dismutases Required for Pathogen Defense. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 5866– 5871, DOI: 10.1073/pnas.1400137111
  42
  Candida albicans SOD5 represents the prototype of an unprecedented class of Cu-only superoxide dismutases required for pathogen defense
  Gleason, Julie E.; Galaleldeen, Ahmad; Peterson, Ryan L.; Taylor, Alexander B.; Holloway, Stephen P.; Waninger-Saroni, Jessica; Cormack, Brendan P.; Cabelli, Diane E.; Hart, P. John; Culotta, Valeria Cizewski
  Proceedings of the National Academy of Sciences of the United States of America (2014), 111 (16), 5866-5871CODEN: PNASA6; ISSN:0027-8424. (National Academy of Sciences)
  Human fungal pathogens Candida albicans and Histoplasma capsulatum have been reported to protect against the oxidative burst of host innate immune cells using a family of extracellular proteins with similarity to Cu/Zn superoxide dismutase 1 (SOD1). Here, the authors report that these mols. are widespread throughout fungi and deviate from canonical SOD1 at the primary, tertiary, and quaternary structural levels. The crystal structure of C. albicans SOD5 revealed that although the β-barrel of Cu/Zn SODs was largely preserved, SOD5 was a monomeric Cu-contg. protein that lacked a Zn-binding site and was missing the electrostatic loop element proposed to promote catalysis through superoxide guidance. Without an electrostatic loop, the Cu site of SOD5 was not recessed and was readily accessible to bulk solvent. Despite these structural deviations, SOD5 had the capacity to disproportionate superoxide with kinetics that approached diffusion limits, similar to those of canonical SOD1. In cultures of C. albicans, SOD5 was secreted in a disulfide-oxidized form and apoprotein pools of secreted SOD5 could readily capture extracellular Cu for rapid induction of enzyme activity. The authors suggest that the unusual attributes of SOD5-like fungal proteins, including the absence of Zn and an open active site that readily captures extracellular Cu, make these SODs well suited to meet challenges in Zn and Cu availability at the host-pathogen interface.
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43. 43
  Jiao, L.; Wu, J.; Zhong, H.; Zhang, Y.; Xu, W.; Wu, Y.; Chen, Y.; Yan, H.; Zhang, Q.; Gu, W. Densely Isolated FeN₄ Sites for Peroxidase Mimicking. ACS Catal. 2020, 10, 6422– 6429, DOI: 10.1021/acscatal.0c01647
  43
  Densely Isolated FeN4 Sites for Peroxidase Mimicking
  Jiao, Lei; Wu, Jiabin; Zhong, Hong; Zhang, Yu; Xu, Weiqing; Wu, Yu; Chen, Yifeng; Yan, Hongye; Zhang, Qinghua; Gu, Wenling; Gu, Lin; Beckman, Scott P.; Huang, Liang; Zhu, Chengzhou
  ACS Catalysis (2020), 10 (11), 6422-6429CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
  Despite the breakthroughs of transition-metal catalysts in enzyme mimicking, fundamental investigation on the design of efficient nanozymes at the at. scale is still required for boosting their intrinsic activities to fill in gaps from enzymes to nanozymes. Herein, we developed a universal salt-template strategy for the fabrication of atomically dispersed Fe atoms on ultrathin nitrogen-doped carbon nanosheets characterized by a dramatically high concn. of 13.5 wt %. The proposed Fe-N-C nanozymes with densely isolated FeN4 sites show high peroxidase-like activities and exhibit a specific activity of 25.33 U/mg, superior to Zn(Co)-N-C nanozymes. Both expts. and theor. anal. revealed that FeN4 sites not only lead to the strong adsorption of H2O2 mols. but also weaken the bonding interaction between single Fe atom and two absorbed hydroxyl groups, lowering the energy barrier of the formation of hydroxyl radicals and therefore boosting their peroxidase-like activities. As expected, utilizing the peroxidase-like activity of Fe-N-C nanozymes, good sensitivity and selectivity for the intracellular H2O2 monitoring were realized. It offers a versatile approach for the construction of densely isolated M-N-C single-atom catalysts and achieves better understanding of single sites for the peroxidase-like catalytic mechanisms.
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44. 44
  Urbański, N. K.; Beręsewicz, A. Generation of ^•OH Initiated by Interaction of Fe²⁺ and Cu⁺ with Dioxygen; Comparison with the Fenton Chemistry. Acta Biochim. Pol. 2000, 47, 951– 962, DOI: 10.18388/abp.2000_3950
  44
  Generation of .OH initiated by interaction of Fe2+ and Cu+ with dioxygen; comparison with the Fenton chemistry
  Urbanski, Norbert K.; Beresewicz, Andrzej
  Acta Biochimica Polonica (2000), 47 (4), 951-962CODEN: ABPLAF; ISSN:0001-527X. (Polish Biochemical Society)
  Iron and copper toxicity has been presumed to involve the formation of hydroxyl radical (.OH) from H2O2 in the Fenton reaction. The aim of this study was to verify that Fe2+-O2 and Cu+-O2 chem. is capable of generating .OH in the quasi physiol. environment of Krebs-Henseleit buffer (KH), and to compare the ability of the Fe2+-O2 system and of the Fenton system (Fe2+ + H2O2) to produce .OH. The addn. of Fe2+ and Cu+ (0-20 μM) to KH resulted in a concn.-dependent increase in .OH formation, as measured by the salicylate method. While Fe3+ and Cu2+ (0-20 μM) did not result in .OH formation, these ions mediated significant .OH prodn. in the presence of a no. of reducing agents. The .OH yield from the reaction mediated by Fe2+ was increased by exogenous Fe3+ and Cu2+ and was prevented by the deoxygenation of the buffer and reduced by superoxide dismutase, catalase, and desferrioxamine. Addn. of 1 μM, 5 μM or 10 μM Fe2+ to a range of H2O2 concns. (the Fenton system) resulted in a H2O2-concn.-dependent rise in .OH formation. For each Fe2+ concn. tested, the .OH yield doubled when the ratio [H2O2]:[Fe2+] was raised from zero to one. In conclusion: (i) Fe2+-O2 and Cu+-O2 chem. is capable of promoting .OH generation in the environment of oxygenated KH, in the absence of pre-existing superoxide and/or H2O2, and possibly through a mechanism initiated by the metal autoxidn.; (ii) The process is enhanced by contaminating Fe3+ and Cu2+; (iii) In the presence of reducing agents also Fe3+ and Cu2+ promote the .OH formation; (iv) Depending on the actual [H2O2]:[Fe2+] ratio, the efficiency of the Fe2+-O2 chem. to generate .OH is greater than or, at best, equal to that of the Fe2+-driven Fenton reaction.
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45. 45
  Chen, C.; Li, X.; Wang, L.; Liang, T.; Wang, L.; Zhang, Y.; Zhang, J. Highly Porous Nitrogen- and Phosphorus-Codoped Graphene: An Outstanding Support for Pd Catalysts to Oxidize 5-Hydroxymethylfurfural into 2, 5-Furandicarboxylic Acid. ACS Sustainable Chem. Eng. 2017, 5, 11300– 11306, DOI: 10.1021/acssuschemeng.7b02049
  45
  Highly Porous Nitrogen- and Phosphorus-Codoped Graphene: An Outstanding Support for Pd Catalysts to Oxidize 5-Hydroxymethylfurfural into 2,5-Furandicarboxylic Acid
  Chen, Chunlin; Li, Xingtao; Wang, Lingchen; Liang, Ting; Wang, Lei; Zhang, Yajie; Zhang, Jian
  ACS Sustainable Chemistry & Engineering (2017), 5 (12), 11300-11306CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)
  The oxidn. of 5-hydroxylmethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) is a sustainable and promising route to bioderived arom. polyesters. So far, the design of catalyst has been restricted by the unclear working mechanism, and thus most of the supported noble metal catalysts cannot provide a remarkable reaction rate under atm. pressures and room temp. Here we report a new mechanistic insight into the structure-performance correlation of graphene-supported Pd catalysts. It is demonstrated that a new kind of highly porous nitrogen- and phosphorus-codoped graphene sheets (HPGSs) will enhance the fraction of surface Pd2+ species, which plays a detg. role to reduce the activation energies of both HMF conversion and FDCA formation. Such a support effect may assist in developing highly active catalysts for FDCA synthesis under mild conditions.
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46. 46
  Senthamarai, T.; Chandrashekhar, V. G.; Rockstroh, N.; Rabeah, J.; Bartling, S.; Jagadeesh, R. V.; Beller, M. A “Universal” Catalyst for Aerobic Oxidations to Synthesize (Hetero)aromatic Aldehydes, Ketones, Esters, Acids, Nitriles, and Amides. Chem 2022, 8, 508– 531, DOI: 10.1016/j.chempr.2021.12.001
  46
  A "universal" catalyst for aerobic oxidations to synthesize (hetero)aromatic aldehydes, ketones, esters, acids, nitriles, and amides
  Senthamarai, Thirusangumurugan; Chandrashekhar, Vishwas G.; Rockstroh, Nils; Rabeah, Jabor; Bartling, Stephan; Jagadeesh, Rajenahally V.; Beller, Matthias
  Chem (2022), 8 (2), 508-531CODEN: CHEMVE; ISSN:2451-9294. (Cell Press)
  Here, the prepn. of graphitic layers encapsulated in Co-nanoparticles by pyrolysis of cobalt-piperazine-tartaric acid complex on carbon as a most general oxidn. catalyst was reported. This unique material allows for the synthesis of simple, functionalized, and structurally diverse (hetero)arom. aldehydes, ketones, carboxylic acids, esters, nitriles, and amides from alcs. in excellent yields in the presence of air.
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47. 47
  Xu, D.; Li, J.; Li, B.; Zhao, H.; Zhu, H.; Kou, J.; Zhang, F.; Dong, Z.; Ma, J. Selective Oxidation of Alcohols to High Value-Added Carbonyl Compounds using Air over Co-Co₃O₄@NC Catalysts. Chem. Eng. J. 2022, 434, 134545 DOI: 10.1016/j.cej.2022.134545
  47
  Selective oxidation of alcohols to high value-added carbonyl compounds using air over Co-Co3O4@NC catalysts
  Xu, Dan; Li, Jianfeng; Li, Boyang; Zhao, Huacheng; Zhu, Hanghang; Kou, Jinfang; Zhang, Fengwei; Dong, Zhengping; Ma, Jiantai
  Chemical Engineering Journal (Amsterdam, Netherlands) (2022), 434 (), 134545CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
  The sustainable catalytic transformation of alcs. to high value-added fine chems. is a significant and challenging research topic. Herein, a set of nitrogen-doped carbon encapsulated Co-based catalysts (Co-Co3O4@NC-T) were prepd. by using low-cost dicyandiamide, glyoxal and cobalt nitrate as precursors. The obtained catalysts were utilized for the selective oxidn. of alcs. to high value-added esters and carboxylic acids with air as the oxygen source and displayed wide applicability for the oxidn. of both arom. and aliph. alcs. Based on the controlled expts., the protective effect of N-doped carbon structure and the synergistic effect between Co core and Co3O4 species guaranteed the high reaction conversion and selectivity. Benefitting from heterogeneity and magnetism of the catalyst, it can be easily recycled and reused for long-term stability. Reasonable mechanisms of selective oxidn. reaction were proposed through EPR anal. and controlled expts. The present work provides a facile strategy for potential large-scale prepn. of heterogeneous catalyst for sustainable and green catalytic transformations.
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48. 48
  Mate, V.; Jha, A.; Joshi, U.; Patil, K.; Shirai, M.; Rode, C. Effect of Preparation Parameters on Characterization and Activity of Co₃O₄ Catalyst in Liquid Phase Oxidation of Lignin Model Substrates. Appl. Catal., A 2014, 487, 130– 138, DOI: 10.1016/j.apcata.2014.08.023
  48
  Effect of preparation parameters on characterization and activity of Co3O4 catalyst in liquid phase oxidation of lignin model substrates
  Mate, V. R.; Jha, A.; Joshi, U. D.; Patil, K. R.; Shirai, M.; Rode, C. V.
  Applied Catalysis, A: General (2014), 487 (), 130-138CODEN: ACAGE4; ISSN:0926-860X. (Elsevier B.V.)
  The nano structured spinel cobalt oxide (Co3O4) was prepd. via simple co-pptn. method and its catalytic activity was evaluated for the liq. phase aerobic oxidn. of lignin sub structure compds. such as veratryl alc. Catalyst prepn. parameters influenced its morphol. eventually affecting its oxidn. activity. Thus, nano rod shaped Co3O4 catalyst showed 75% and 38% conversion of veratryl alc. with complete selectivity to veratryl aldehyde in toluene and water, resp., under base free condition. The influence of reaction conditions, such as temp., oxygen pressure and catalyst loading was studied to obtain the optimum product yield and selectivity to the desired product. Furthermore, oxidn. of various sub-structures of lignin model compds. was also studied over the same catalyst which was found to be in the following order: secondary alc. > di-substituted > tri-substituted > mono-substituted > non-substitution. The stability of the catalyst was confirmed by its successful recycle for three times.
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49. 49
  Zhou, H.; Xu, H.; Wang, X.; Liu, Y. Convergent Production of 2,5-Furandicarboxylic Acid from Biomass and CO₂. Green Chem. 2019, 21, 2923– 2927, DOI: 10.1039/C9GC00869A
  49
  Convergent production of 2,5-furandicarboxylic acid from biomass and CO2
  Zhou, Hua; Xu, Huanghui; Wang, Xueke; Liu, Yun
  Green Chemistry (2019), 21 (11), 2923-2927CODEN: GRCHFJ; ISSN:1463-9262. (Royal Society of Chemistry)
  We report a rationally designed process for complete lignocellulose conversion and CO2 utilization to convergently produce 2,5-furandicarboxylic acid (FDCA) that can be used in bioplastics and resins. The phenolic motif of the lignin structure enables the assembly of metal-lignin hybrids to fabricate a single-atom cobalt over nitrogen-doped carbon (Co SAs/N@C) catalyst. The Co SAs/N@C catalyst exhibits outstanding performances in the transformation of carbohydrate-based hydroxymethylfurfural (HMF) and furfural into FDCA and furoate, resp. Importantly, during the furfural oxidn., Cs2CO3 is used as a base additive, which can also promote the carboxylation of the 5 position C-H of furoate in the subsequent reaction to give the desired FDCA using CO2 as the C1 source.
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Supporting Information
Supporting Information
The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acscatal.3c02736.
- Details of experimental procedures and data processing, comparison of Co–N–C and reported non-noble catalysts for HMF oxidation, additional characterization data of Co-based catalysts, ESR spectra of DMPO-radical adducts, UV–vis spectra of KI oxidation, GC spectra of Ph₃P oxidation, mass spectrum of CO₂, reaction time profiles for HMF and HMFCA oxidations, recycling experiments of Co–N–C, kinetics analysis for benzyl alcohol oxidation, and supplementary catalytic evaluation (PDF)
- cs3c02736_si_001.pdf (812.04 kb)
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STEP 1: 步骤1：

STEP 2: 步骤2：

Scheme 1 方案 1

ACS Catalysis

Abstract 抽象

1. Introduction 1. 引言

2. Results and Discussion2. 结果与讨论

2.1. Design, Characterization, and Biomimetic Catalytic Performance of the Co–N–C Catalyst2.1. Co-N-C 催化剂的设计、表征和仿生催化性能

Scheme 1 方案 1

Figure 1 图 1

2.2. Self-Cascade Catalysis for the Generation of OH•2.2. 用于生成 OH• 的自级联催化

Figure 2 图 2

Figure 3 图 3

2.3. Identifying the Role of ROS in Selectivity Oxidation of HMF2.3. 确定 ROS 在 HMF 选择性氧化中的作用

Figure 4 图 4

Figure 5 图 5

2.4. Comparison of the External and In Situ Formed H2O22.4. 外部形成和原位形成的 H2O2 的比较

Figure 6 图 6

2.5. Control in OH• Produces via pH Variation2.5. OH中的控制• 通过改变 pH 值产生

Figure 7 图 7

2.6. OH• Accelerating the H-Abstraction of C–H Bonds2.6. OH• 加速 C-H 键的 H 抽象

3. Conclusions 3. 结论

Supporting Information 支持信息

Terms & Conditions 条款和条件

Author Information 作者信息

Acknowledgments 确认

References 引用

Cited By

ACS Catalysis ACS 催化

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Citations 引文

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Strongly Electron-Interacting Ru–Ce Pair Sites in RuOx/CeO2–HAP for Efficient Oxidation of MMF to FDCARuOx/CeO 2-HAP 中的强电子相互作用 Ru-ce 对位点用于 MMF 高效氧化为 FDCA

Aerobic Oxidation of 5-Hydroxymethyl-furfural to 2,5-Furandicarboxylic Acid at 20 °C by Optimizing Adsorption on AgPd Alloy Nanoparticle Catalysts通过优化 AgPd 合金纳米颗粒催化剂上的吸附，在 20 °C 下 5-羟甲基糠醛有氧氧化为 2,5-呋喃二羧酸

Theoretical Exploration of the Origin of Alkaline Dependence in the Oxidation of 5-Hydroxymethylfurfural Catalyzed by NiO2HxNiO2Hx 催化的 5-羟甲基糠醛氧化中碱性依赖性来源的理论探索

CoOx-MC (MC = Mesoporous Carbon) for Highly Efficient Oxidation of 5-Hydroxymethylfurfural (5-HMF) to 2,5-Furandicarboxylic Acid (FDCA)CoOx-MC （MC = 介孔碳） 用于 5-羟甲基糠醛 （5-HMF） 高效氧化为 2,5-呋喃二羧酸 （FDCA）

Abstract 抽象

Scheme 1 方案 1

Figure 1 图 1

Figure 2 图 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

References

Supporting Information

Supporting Information

Terms & Conditions

2. Results and Discussion
2. 结果与讨论

2.1. Design, Characterization, and Biomimetic Catalytic Performance of the Co–N–C Catalyst
2.1. Co-N-C 催化剂的设计、表征和仿生催化性能

2.2. Self-Cascade Catalysis for the Generation of OH^•
2.2. 用于生成 OH^• 的自级联催化

2.3. Identifying the Role of ROS in Selectivity Oxidation of HMF
2.3. 确定 ROS 在 HMF 选择性氧化中的作用

2.4. Comparison of the External and In Situ Formed H₂O₂
2.4. 外部形成和原位形成的 H₂O₂ 的比较

2.5. Control in OH^• Produces via pH Variation
2.5. OH^{中的控制•} 通过改变 pH 值产生

2.6. OH^• Accelerating the H-Abstraction of C–H Bonds
2.6. OH^• 加速 C-H 键的 H 抽象

Strongly Electron-Interacting Ru–Ce Pair Sites in RuO_x/CeO₂–HAP for Efficient Oxidation of MMF to FDCA
RuO_x/CeO 2-HAP 中的强电子相互作用 Ru-ce 对位点用于 MMF 高效氧化为 FDCA

Aerobic Oxidation of 5-Hydroxymethyl-furfural to 2,5-Furandicarboxylic Acid at 20 °C by Optimizing Adsorption on AgPd Alloy Nanoparticle Catalysts
通过优化 AgPd 合金纳米颗粒催化剂上的吸附，在 20 °C 下 5-羟甲基糠醛有氧氧化为 2,5-呋喃二羧酸

Theoretical Exploration of the Origin of Alkaline Dependence in the Oxidation of 5-Hydroxymethylfurfural Catalyzed by NiO₂H_x
NiO₂H_x 催化的 5-羟甲基糠醛氧化中碱性依赖性来源的理论探索

CoO_x-MC (MC = Mesoporous Carbon) for Highly Efficient Oxidation of 5-Hydroxymethylfurfural (5-HMF) to 2,5-Furandicarboxylic Acid (FDCA)
CoO_x-MC （MC = 介孔碳）用于 5-羟甲基糠醛（5-HMF）高效氧化为 2,5-呋喃二羧酸（FDCA）