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Balance between Reducibility and N2O Adsorption Capacity for the N2O Decomposition: CuxCoy Catalysts as an Example
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Balance between Reducibility and N2O Adsorption Capacity for the N2O Decomposition: CuxCoy Catalysts as an Example
Reducibility 和 N2O 对 N2O 分解的吸附能力：CuxCoy Catalysts as an Example
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环境科学与生态学TOPEI检索SCI升级版 环境科学与生态学1区SCI基础版 环境科学与生态学1区IF 10.8SWJTU A++SWUFE A

  • Shangchao Xiong
    Shangchao Xiong
    State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China
    National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China
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  • Jianjun Chen*
    Jianjun Chen
    State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China
    National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China
    *E-mail: chenjianjun@tsinghua.edu.cn. Phone: +86 010 62771093.
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    Orcidhttp://orcid.org/0000-0003-4730-7803
  • Nan Huang
    Nan Huang
    State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China
    School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China
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  • Shijian Yang
    Shijian Yang
    School of Environment and Civil Engineering, Jiangnan University, Wuxi 214122, PR China
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    Orcidhttp://orcid.org/0000-0002-8275-5225
  • Yue Peng
    Yue Peng
    State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China
    National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China
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    Orcidhttp://orcid.org/0000-0001-5772-3443
  • Junhua Li
    Junhua Li
    State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China
    National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China
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    Orcidhttp://orcid.org/0000-0001-7249-0529
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Environmental Science & Technology

Cite this: Environ. Sci. Technol. 2019, 53, 17, 10379–10386
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https://doi.org/10.1021/acs.est.9b02892
Published August 5, 2019
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Abstract 摘要

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CuxCoy (CuO–Co3O4 mixed oxides) catalysts were prepared via co-precipitation for the N2O decomposition reaction. They exhibited a higher N2O decomposition activity than that of pure CuO and Co3O4 because of the balance of the redox property and N2O adsorption capacity. Co3O4 presented a large number of surface oxygen vacancies, increasing the N2O chemical adsorption as “□–Co–ON2” on the catalyst surface, whereas CuO was dispersed around Co3O4 and presented high reducibility on the interface of Co3O4–CuOx for the N–O break of N2O, healing oxygen vacancies by leaving one oxygen atom in the vacancy. Based on kinetic studies, the rate constant of N2O decomposition was related to the number of surface vacancy sites ([Mn+]) and the rate of N–O break (k3), whereas the rate-determining step is the N–O break. Therefore, the N2O decomposition rate is first order to the N2O concentration. Overall, both the density functional theory calculations and kinetic results indicate that the quantities of adsorption and activation sites derived from the interaction between Co and Cu (dual-function mechanism) were accounted for the excellent N2O decomposition performance of CuxCoy catalysts.
CuxCoy (CuO-Co3O4 混合氧化物）共沉淀制备了用于 N2O 分解反应的催化剂。与纯 CuO 和 Co3O4 因为氧化还原特性和 N2O 吸附能力的平衡。Co3O4 表面存在大量氧空位、增加了催化剂表面的 N2O 化学吸附，表现为"□-Co-ON2"、而 CuO 分散在 Co3O4 周围，并在 Co3O4-CuOx N2O 的 N-O 断裂、通过在空位中保留一个氧原子来修复氧空位。 根据动力学研究、N2O 分解的速率常数与表面空位的数量（[Mn+]）和N-O断裂速率（k3）有关、而决定速率的步骤是 N-O 断裂。因此，N2O 分解速率与 N2O 浓度呈一阶关系。总之、密度泛函理论计算和动力学结果都表明，Co 和 Cu 之间的相互作用（双功能机制）所产生的吸附量和活化位点是 N2CuxCoy 催化剂。

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1. Introduction 1.导言

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Nitrous oxide (N2O) emitted from the production of adipic acid and nitric acid, as well as the processes using nitric acid as an oxidant, contributes to the ozone hole and greenhouse effect. (1,2) Its global warming potential is ∼310 times and ∼31 times higher than that of CO2 and CH4, respectively, and the lifetime of N2O is ∼114 years. (3) Moreover, N2O can deplete the ozone layer by a reaction pathway similar to that of chlorofluorocarbons. Previous studies reported that N2O would be the dominant ozone-depleting substance in the 21st century. (4) Thus, the reduction in anthropogenic N2O emissions is urgently required. Several techniques were proposed to control anthropogenic N2O emissions, whereas the direct catalytic decomposition of N2O is regarded as the most promising alternative technique. (5,6) Retrofitting the existing flue gas treatment process to incorporate this technique is relatively convenient and can minimize the economic demands.
一氧化二氮（N2O ）从己二酸和硝酸的生产过程以及使用硝酸作为氧化剂的过程中排放出来，造成了臭氧空洞和温室效应。(1、2) 其全球变暖潜势分别是 CO2 和 CH4 的 310 倍和 31 倍、而 N2O 的寿命则为∼114 年。(3) 此外，N2O 可以通过与氟氯化碳类似的反应途径消耗臭氧层。先前的研究报告指出，N2O 将成为 21 世纪最主要的臭氧消耗物质。(4) 因此，迫切需要减少人为 N2O 排放。人们提出了几种控制人为 N2O 排放的技术，而直接催化分解 N2O 被认为是最有前途的替代技术。(5,6) 对现有烟气处理工艺进行改造以采用该技术相对方便，并能最大限度地降低经济要求。
A series of noble metals and non-noble metals were used to catalyze the decomposition of N2O. (6) Noble metals (e.g., Rh and Ru) show a satisfactory N2O decomposition performance at low temperature, but their high cost and poor tolerance to various influential factors (e.g., oxygen and water vapor) extremely restrict their widespread applications. (7−9) Iron-based zeolites (especially Fe-ZSM-5) are another type of N2O decomposition catalyst, which attracted great interest because of their tolerance to O2 and H2O. (10,11) The N2O decomposition activity of Fe-ZSM-5 is even promoted by the presence of NO in flue gas. (12) However, the reaction temperature of iron-based zeolites is quite high, and it is difficult to meet the actual flue gas conditions.
一系列贵金属和非贵金属被用来催化 N2O 的分解。(6) 贵金属（如 Rh 和 Ru）在低温下具有令人满意的 N2O 分解性能，但其成本高，对各种影响因素（如氧气和水蒸气）的耐受性差，极大地限制了其广泛应用。(7-9) 铁基沸石（尤其是 Fe-ZSM-5）是另一类 N2O 分解催化剂、由于对 O2 和 H2O 的耐受性，这些催化剂引起了人们的极大兴趣。(10,11) 烟气中的 NO 甚至促进了 Fe-ZSM-5 的 N2O 分解活性。(12) 然而，铁基沸石的反应温度相当高，很难满足实际烟气条件。
Metal oxides, especially transition-metal oxides, are widely researched and employed in the N2O decomposition reaction, which are consequences of their low price, excellent reducibility, and adequate catalytic characteristics. (13,14) Particularly, metal oxides exhibiting the spinel structure are efficient catalysts to decompose N2O. (15) The metal cations in the spinel structure are in the mixed valence state, which frequently consists of divalent and trivalent states. The divalent and trivalent cations in the spinel structure are located in tetrahedral and octahedral coordination centers and are represented as AIIBIII2O4. Because the key step in the N2O decomposition reaction is generally regarded as the charge transfer from the active sites to the antibonding orbital of N2O, spinels can decompose N2O at a relatively low temperature because of their excellent redox property attributed to the divalent and trivalent cations in the spinel structure. (16,17) Given this perspective, metal oxides with the spinel structure were systematically investigated in the decomposition of N2O. (6) Russo et al. investigated several spinel-type catalysts and found that Co-based spinels can provide the most efficient N2O decomposition performance. (18) However, the redox properties of Co-based spinels are not the best among those of spinel catalysts. Consequently, there must exist another crucial property that significantly affects the catalytic performance of N2O decomposition. Many researchers used density functional theory (DFT) methods to calculate the reaction pathway of N2O decomposition and proposed that N2O adsorption is the first step in N2O decomposition. (15,19) The chemical adsorption of N2O generally follows “N–N–O–□”. (20,21) This result suggests that abundant surface oxygen vacancies can contribute to the chemical adsorption of N2O, and this is probably the main reason for the superior N2O decomposition performance of the Co3O4 spinel. Given this perspective, improving the reducibility without blocking oxygen vacancies is the most efficient way to improve the N2O decomposition performance of the Co3O4 spinel. Cu-based catalysts are another type of N2O decomposition catalysts that possess a superior redox property. (22) Combining the advantages of both the Cu-based catalysts and Co3O4 spinel can certainly improve the N2O decomposition performance. Therefore, in this work, a series of CuxCoy (CuO–Co3O4 spinel mixed oxides) catalysts were synthesized to decompose N2O.
金属氧化物，尤其是过渡金属氧化物，因其价格低廉、还原性好、催化性强等特点，在N2O 分解反应中被广泛研究和应用。(13,14) 尤其是尖晶石结构的金属氧化物是分解 N2O 的高效催化剂。(15) 尖晶石结构中的金属阳离子处于混合价态，通常由二价态和三价态组成。尖晶石结构中的二价和三价阳离子位于四面体和八面体配位中心，用 AIIBIII2O4 。由于 N2O 分解反应的关键步骤通常被认为是电荷从活性位点转移到 N2O 的反键轨道、尖晶石能在相对较低的温度下分解 N2O ，这是因为尖晶石结构中的二价和三价阳离子具有出色的氧化还原特性。 (16,17) 从这个角度出发，在分解 N2O 的过程中，对具有尖晶石结构的金属氧化物进行了系统研究。(6) Russo 等人研究了几种尖晶石型催化剂，发现 Co 基尖晶石具有最高效的 N2O 分解性能。(18) 然而，Co 基尖晶石的氧化还原特性并不是尖晶石催化剂中最好的。因此，一定还有另一种关键性质会对 N2O 分解的催化性能产生重大影响。许多研究人员利用密度泛函理论（DFT）方法计算了 N2O 分解的反应途径，并提出了 N2O 吸附是 N2O 分解的第一步。(15,19) N2O 的化学吸附一般遵循 "N-N-O-□"。 (20,21) 这一结果表明，丰富的表面氧空位有助于 N2O 的化学吸附、这可能是 Co3O4 尖晶石具有出色的 N2O 分解性能的主要原因。有鉴于此、从这个角度来看，在不阻塞氧空位的情况下提高还原性是改善 N2Co3O4 尖晶石的氧化分解性能。铜基催化剂是另一种具有优异氧化还原特性的 N2O 分解催化剂。(22) 结合铜基催化剂和 Co3O4 尖晶石无疑可以改善 N2O 的分解性能。 因此，在这项工作中、CuxCoy （CuO-Co3O4 尖晶石混合氧化物）催化剂，用于分解 N2O 。
Kinetic study is an important approach to investigate the key factors of the N2O decomposition reaction. Kapteijn et al. accomplished a comparative kinetic analysis over Co-, Fe-, and Cu-ZSM-5 and found that the effects of O2, NO, and CO were influenced by their partial pressure. (23) Obalová and Fíla established a novel kinetic model over hydrotalcites, which proposes that N2O chemisorption determines the rate of N2O decomposition at low O2 partial pressures, whereas the reaction between active O atoms and N2O is the rate-determining step at high O2 partial pressures. (24) However, kinetic studies of N2O decomposition are rarely reported among recent studies and are even absent from recent reviews. (6,15) Furthermore, a lack of connection between the kinetic model and physicochemical properties exists and greatly limits the design of efficient catalysts for N2O decomposition.
动力学研究是研究 N2O 分解反应关键因素的重要方法。Kapteijn 等人对 Co-、Fe- 和 Cu-ZSM-5 进行了动力学比较分析，发现 O2 、NO 和 CO 的影响受其分压的影响。(23) Obalová 和 Fíla 建立了一种新的氢铝酸盐动力学模型、该模型提出，在低 O2O 化学吸附作用下，N2O 分解的速率决定于低 O2 分压、而在高 O2 分压下，活性 O 原子和 N2O 之间的反应是决定速率的步骤。(24)然而，对 N2O 分解的动力学研究在最近的研究中鲜有报道，甚至在最近的综述中也没有提及。(6,15)此外，动力学模型与物理化学性质之间缺乏联系，极大地限制了 N2O 分解的高效催化剂的设计。
Herein, the N2O decomposition mechanism and the key roles of CuO and Co3O4 spinel in CuxCoy mixed oxides were systematically investigated by a kinetic study combined with DFT, in situ diffuse reflectance Fourier transforms, N2O-temperature program desorption (TPD), H2-TPR and X-ray photoelectron spectroscopy (XPS) studies. The crucial properties of CuxCoy catalysts and the connection between the physicochemical properties and the kinetic study were proposed.
在此、N2O 分解机理以及 CuO 和 Co3O4 尖晶石在 CuxCoy 混合氧化物中的尖晶石、通过动力学研究结合 DFT、原位漫反射傅立叶变换、N2O 温度程序解吸 (TPD)、H2-TPR 和 X 射线光电子能谱 (XPS) 研究，对混合氧化物进行了系统研究。提出了铜xCoy 催化剂的关键性质以及物理化学性质与动力学研究之间的联系。

2. Experimental Section 2.实验部分

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2.1. Catalyst Preparation
2.1.催化剂制备

Co3O4, CuxCoy, and CuO catalysts were prepared via the coprecipitation method. CuxCoy represents Cu1Co2, Cu1.5Co1.5, and Cu2Co1 catalysts, corresponding to molar ratios of Cu to Co of 1:2, 1:1, and 2:1, respectively. Suitable amounts of cupric nitrate and cobaltous sulfate were added to a solution with an excess of sodium hydroxide followed by continuous stirring for 3 h. The suspension was separated by centrifugation and washed with deionized water. The process of centrifugation and washing was repeated five times to remove any residual substances. The obtained particles were dried at 105 °C for 12 h and then calcinated at 500 °C for 3 h in air.
Co3O4、通过共沉淀法制备了 CuxCoy 和 CuO 催化剂。CuxCoy 表示 Cu1Co2、Cu1.5Co1.5 和 Cu2Co1 催化剂，对应的 Cu 与 Co 的摩尔比分别为 1:2、1:1 和 2:1。将适量的硝酸铜和硫酸钴加入到过量氢氧化钠溶液中，然后持续搅拌 3 小时。离心和洗涤过程重复五次，以去除任何残留物质。得到的颗粒在 105 °C 下干燥 12 小时，然后在 500 °C 下空气中煅烧 3 小时。

2.2. Characterization 2.2.特征

The Brunauer–Emmett–Teller (BET) surface area and X-ray diffraction (XRD) data were determined on a physisorption analyzer (BELSORP-max II) and an X-ray diffractometer (Rigaku D/max-2500). The surface analyses [XPS and atomic emission spectroscopy (AES)] were carried out on an XPS microprobe (ESCALAB 250 Xi). TPD of O2 and N2O were both conducted on a chemisorption apparatus (AutoChem II 2920), and N2O-TPD was further analyzed by a mass spectrum (MS, HPR-20 R&D). H2-temperature program reduction (H2-TPR) was also performed on the chemisorption apparatus. After H2-TPR studies, the coefficient between the H2 consumption rate and peak intensity was gotten by the test results of the standard sample (standard CuO). Therefore, the dependences of H2 consumption rates versus 1/T (T = 130–165 °C) were obtained as the initial H2 consumption rates.
在物理吸附分析仪（BELSORP-max II）和 X 射线衍射仪（Rigaku D/max-2500）上测定了布鲁纳-埃美特-泰勒（BET）表面积和 X 射线衍射（XRD）数据。表面分析[XPS 和原子发射光谱（AES）]是在 XPS 微探针（ESCALAB 250 Xi）上进行的。O2 和 N2O 的 TPD 均在化学吸附仪 (AutoChem II 2920) 上进行、而 N2O-TPD 则通过质谱（MS，HPR-20 R&；D).H2 温度程序还原（H2-TPR ）也在化学吸附仪器上进行。H2-TPR 研究结束后，根据标准样品（标准 CuO）的测试结果得出了 H2 消耗率与峰值强度之间的系数。因此、因此，H2 消耗率与 1/T （T = 130-165 °C）得到的初始 H2 消耗率。

2.3. DFT Calculation Details
2.3.DFT 计算细节

Previous experimental data indicated that the Co3O4 spinel mainly exposes the (100) and (111) planes, with only a minor exposure of the (110) plane. (25) Additionally, the (100) plane is more stable than the (110) and (111) planes in a wide range of temperatures. (26) Thus, the (100) plane of the Co3O4 spinel was reconstructed by a [2 × 2] supercell to generate the slab model. For CuO, the (111) plane is regarded as the most stable plane. (27) Therefore, a slab model of the CuO (111) plane was also reconstructed by a [2 × 2] supercell.
以前的实验数据表明，Co3O4 尖晶石主要暴露于 (100) 和 (111) 平面，只有少量暴露于 (110) 平面。(25) 此外，在很宽的温度范围内，(100) 面比 (110) 面和 (111) 面更稳定。(26) 因此、Co3O4 尖晶石的 (100) 平面由 [2 × 2] 超级电池重构，生成板坯模型。对于氧化铜，(111) 平面被认为是最稳定的平面。(27) 因此，CuO（111）面的板坯模型也是通过 [2 × 2] 超级电池重建的。
All calculations were conducted by the Vienna ab initio simulation package (VASP 5.4.4). The Perdew, Burke, and Ernzerhof functional within the generalized gradient approximation plus Hubbard model (GGA + U) was used to calculate the electronic exchange and correlation. The Ueff of Cu and Co in this study were 7.0 and 3.5 eV, respectively. (28,29) The cutoff energy was 500 eV, and a Monkhorst–Pack grid of 2 × 2 × 1 k-points were employed due to the large size of the slab (∼12 Å × 12 Å). The thickness of the slab was ∼8 Å, with a 15 Å vacuum gap. Moreover, all of the slabs were relaxed until the atomic forces were reduced below 0.05 eV/Å.
所有计算均由维也纳原子序数模拟软件包（VASP 5.4.4）进行。使用广义梯度近似加哈伯德模型（GGA + U）中的 Perdew、Burke 和 Ernzerhof 函数计算电子交换和相关性。本研究中铜和钴的 Ueff 分别为 7.0 和 3.5 eV。(28,29) 临界能量为 500 eV，由于板坯尺寸较大（∼12 Å × 12 Å），采用了 2 × 2 × 1 k 点的 Monkhorst-Pack 网格。平板厚度为 ∼8 Å，真空间隙为 15 Å。此外，所有板坯都被放松，直到原子力降低到 0.05 eV/Å 以下。
The adsorption energies of N2O (Ead) were estimated by the following equationwhere E
N2O 的吸附能（Ead）通过下式估算E
surf represents the energy of the clean surface, EN2O denotes the energy of a free N2O molecule in the vacuum, and Esurf+N2O is the energy of N2O adsorbed on the surface. It is noteworthy that a negative value for Ead indicates a stable adsorption.
surf 表示清洁表面的能量、EN2O 表示自由 N2O 分子在真空中的能量、和 Esurf+N2O 是表面吸附的 N2O 的能量。值得注意的是，Ead 的负值表示吸附稳定。

2.4. Activity Test 2.4.活动测试

The catalytic decomposition of N2O was performed in a fixed-bed reactor with 100 mL min–1 of flue gas containing 1000 ppm N2O, 2% O2 (when used), 200 ppm NO (when used), 0.5% H2O (when used), and the balance as N2. The catalyst mass was 100 mg, and the corresponding gas hourly space velocity (GHSV) was 60 000 cm3 g–1 h–1. The N2O concentration at the outlet was monitored online by a MultiGas 2030 Fourier transform infrared continuous gas analyzer.
N2O 的催化分解是在一个固定床反应器中进行的。100 mL min-1 含有 1000 ppm N2O 的烟道气的固定床反应器中进行、2% O2（使用时）、200 ppm NO（使用时）、0.5% H2O（使用时），余量为 N2。催化剂质量为 100 毫克、相应的气体时空速度 (GHSV) 为 60 000 cm3 g-1 h-1。出口处的 N2O 浓度由 MultiGas 2030 傅立叶变换红外连续气体分析仪在线监测。
The steady-state kinetic study of N2O decomposition was also performed in the fixed-bed reactor. The flue gas contained 500–1500 ppm N2O with the balance as N2. An extremely high GHSV of 60 000–6 000 000 cm3 g–1 h–1 was used to ensure that the N2O decomposition was less than 20%, thus, overcoming the diffusion limitation. (30−32)
N2O 分解的稳态动力学研究也在固定床反应器中进行。烟气中含有 500-1500 ppm N2O ，其余为 N2。60 000-6 000 000 cm3 g-1 h-1 来确保 N2O 分解小于 20%、从而克服了扩散限制。(30−32)

3. Results 3.成果

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3.1. Performance of N2O Decomposition
3.1.N2O 分解的性能

The N2O decomposition performance of Co3O4, CuxCoy, and CuO catalysts is shown in Figure 1a. The N2O decomposition activity of Co3O4 was superior to that of CuO. Furthermore, all of the CuxCoy catalysts showed activity superior to that of Co3O4 and CuO. Interestingly, although CuO presented the lowest N2O decomposition activity, high amounts of Cu promoted the performance more significantly. For Cu2Co1, the reaction temperature for full N2O decomposition was ∼375 °C under idealized reaction conditions, which was significantly lower than ∼450 °C for Co3O4 and ∼500 °C for CuO.
The N2O decomposition performance of Co3O4、CuxCoy、Figure 1a 中所示。Co2O 的 N3O4 分解活性优于 CuO。此外、所有的 CuxCoy 催化剂的活性优于 Co3O4 和 CuO。有趣的是，虽然 CuO 的 N2O 分解活性最低，但高含量的 Cu 对性能的促进作用更为显著。对于 Cu2Co1、在理想化反应条件下，N2O 完全分解的反应温度为 ∼375 °C、这明显低于 Co3O4 和 CuO 的 ∼450 °C。

Figure 1 图 1

Figure 1. (a) N2O decomposition performance of the Co3O4, CuxCoy, and CuO catalysts. (b) N2O decomposition performance of Cu2Co1 under different conditions. Reaction conditions: [N2O] = 1000 ppm, [O2] = 2% (when used), [NO] = 200 ppm (when used), [H2O] = 0.5% (when used), catalyst mass = 100 mg, flow rate = 100 mL min–1, and GHSV = 60 000 cm3 g–1 h–1.
图 1。(a) Co3O4 的 N2O 分解性能、CuxCoy 和 CuO 催化剂。(b) Cu2O 在不同条件下的 N2Co1 分解性能。反应条件：[N2O] = 1000 ppm，[O2] = 2%（使用时）、[NO] = 200 ppm（使用时），[H2O] = 0.5%（使用时），催化剂质量 = 100 毫克，流速 = 100 毫升/分钟-1 、和 GHSV = 60 000 cm3 g-1 h-1 。

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Generally, O2, NO, and water vapor exist in flue gas and often interfere with N2O decomposition. (33) The effects of O2, NO, and water vapor on N2O decomposition over Cu2Co1 were investigated (Figure 1b). O2, NO, and water vapor all interfered with the N2O decomposition performance of Cu2Co1 at low temperatures, and the influencing degree increased according to the following sequence: NO < O2 < H2O. These results were also observed in Co3O4, Cu1Co2, and CuO catalysts (shown in Figure S1). Previous studies have shown that NO and H2O have completely different inhibiting mechanisms in the N2O decomposition. H2O prefers to bind with oxygen vacancy sites and then blocks the oxygen transfer, whereas NO shows a competitive oxidation effect, which consumes labile oxygen and decelerates the regeneration of active sites. (34) Further, O2 possibly can inhibit the recombination of residual O during the N2O decomposition reaction, leading to the inhibition of the regeneration of active sites. On the whole, N2O decomposition dramatically decreased from ∼90 to ∼6% at 350 °C when O2, NO, and water vapor coexisted; however, their influencing degrees decreased with increasing temperature. The N2O decomposition of Cu2Co1 in the presence of O2, NO, and H2O increased from ∼6 to ∼95% when the temperature increased from 350 to 450 °C. This result suggests that Cu2Co1 still showed a superior N2O decomposition performance in the simulated flue gas.
一般来说，烟道气中存在 O2 、NO 和水蒸气，它们经常干扰 N2O 的分解。(33) O2, NO、和水蒸气对 N2O 在 Cu2Co1 进行了研究（图1b）。O2, NO、和水蒸气都会干扰 Cu2O 在低温下的分解性能、影响程度按以下顺序增加：NO < O2 < H2O。在 Co3O4 中也观察到了这些结果、Cu1Co2 和 CuO 催化剂（如图 S1所示）。以前的研究表明，NO 和 H2O 对 N2O 分解的抑制机制完全不同。 H2O更喜欢与氧空缺位点结合，然后阻断氧的转移，而 NO 则表现出竞争性氧化作用，它消耗可变氧，减缓活性位点的再生。(34) 更多、O2 可能会在 N2O 分解反应过程中抑制残余 O 的重组，从而导致活性位点的再生受到抑制。总的来说，当 O2 、NO 和水蒸气共存时，350 °C 时 N2O 的分解率从∼90%急剧下降到∼6%，但它们的影响程度随着温度的升高而降低。N2O 分解 Cu2Co1 在 O2、NO 和 H2O 的情况下，当温度从 350 ℃ 升高到 450 ℃ 时，Cu2O 的溶解度从 6 ∼ 95% 增加。这一结果表明，在模拟烟道气中，Cu2Co1 的 N2O 分解性能仍然优越。

3.2. Characterization 3.2.特征

3.2.1. XRD and BET Surface Area
3.2.1.XRD 和 BET 表面积

As shown in Figure S2, the XRD pattern of Co3O4 corresponded well to that of the cubic spinel (JCPDS: #43-1003), and the XRD pattern of CuO was assigned to tenorite (JCPDS: #48-1548). The XRD patterns of the CuxCoy catalysts showed characteristic peaks corresponding to both the Co3O4 and CuO, and the peak positions were nearly unchanged. The crystal sizes and crystal parameters of CuO and Co3O4 clusters in the Co3O4, CuxCoy, and CuO catalysts were calculated on the basis of the XRD patterns, and the results are shown in Table 1. The crystal parameters of Co3O4 clusters of CuxCoy catalysts (a = b = c = ∼0.8097) were all slightly higher than those of pure Co3O4 (a = b = c = 0.8090), meanwhile the crystal parameters of CuO clusters of CuxCoy catalysts were slightly different from those of pure CuO. These results indicate that a small amount of Cu–Co solid solution was generated, whereas most of CuO and Co3O4 existed in a crystal form. The Co3O4 and CuO catalysts exhibited the maximum crystal sizes, whereas the crystal size of Cu2Co1 was the smallest. These results are in accordance with the results of BET surface area. The BET surface area of Cu2Co1 was higher than those of Co3O4, CuO, and other CuxCoy catalysts. Moreover, the BET surface area of CuO was only 8.1 m2 g–1, which was significantly lower than those of the Co3O4 and CuxCoy catalysts. This difference might have been one of the reasons responsible for the poor N2O decomposition performance of CuO.
如图 S2所示、Co3O4 的 XRD 图与立方尖晶石（JCPDS：#43-1003），而 CuO 的 XRD 图样被归类为芒硝（JCPDS：#48-1548）。CuxCoy 催化剂显示出与 Co3O4 和 CuO 相对应的特征峰、的峰位置几乎没有变化。CuO 和 Co3O4 Co3O4 簇、CuxCoy、和 CuO 催化剂的 XRD 图谱进行计算，结果见表1 。 Co3O4 CuxCoy 催化剂（a = b = c = ∼0.8097）都略高于纯 Co3O4 (a = b = c = 0.8090），而 CuxCoy 催化剂的 CuO 簇的晶体参数与纯 CuO 的略有不同。这些结果表明，生成了少量 Cu-Co 固溶体，而大部分 CuO 和 Co3O4 以晶体形式存在。Co3O4 和 CuO 催化剂的晶体尺寸最大、而 Cu2Co1 的晶体尺寸最小。这些结果与 BET 表面积的结果一致。 Cu2Co1 高于 Co3O4、CuO 以及其他 CuxCoy 催化剂。此外，CuO 的 BET 表面积仅为 8.1 m2 g-1 、明显低于 Co3O4 和 CuxCoy 催化剂。这种差异可能是导致 CuO 的 N2O 分解性能较差的原因之一。
Table 1. Crystal Sizes, Crystal Parameters, and BET Surface Areas of the Co3O4, CuxCoy, and CuO Catalysts
表 1.Co3O4 的晶体尺寸、晶体参数和 BET 表面积、CuxCoy 和 CuO 催化剂。
 crystal sizea/nm
晶体尺寸a/nm		crystal parametera/nm
晶体参数a/nm		 
 CuO 氧化铜Co3O4CuO 氧化铜Co3O4BET surface area/m2 g–1
BET 表面积/m2 g-1
Co3O4 21 a = b = c = 0.8090, α = β = γ = 90°
a = b = c = 0.8090，α = β = γ = 90°。		27
Cu1Co22218a = 0.4689, b = 0.3433, c = 0.5137, α = γ = 90°, β = 99.44°
a = 0.4689, b = 0.3433, c = 0.5137, α = γ = 90°, β = 99.44°		a = b = c = 0.8098, α = β = γ = 90°
a = b = c = 0.8098，α = β = γ = 90°。		30
Cu1.5Co1.52417a = 0.4678, b = 0.3446, c = 0.5127, α = γ = 90°, β = 99.47°
a = 0.4678, b = 0.3446, c = 0.5127, α = γ = 90°, β = 99.47°		a = b = c = 0.8097, α = β = γ = 90°
a = b = c = 0.8097，α = β = γ = 90°。		28
Cu2Co11413a = 0.4687, b = 0.3399, c = 0.5104, α = γ = 90°, β = 99.49°
a = 0.4687, b = 0.3399, c = 0.5104, α = γ = 90°, β = 99.49°		a = b = c = 0.8095, α = β = γ = 90°
a = b = c = 0.8095，α = β = γ = 90°。		40
CuO 氧化铜27 a = 0.4687, b = 0.3420, c = 0.5135, α = γ = 90°, β = 99.37°
a = 0.4687, b = 0.3420, c = 0.5135, α = γ = 90°, β = 99.37°		 8.1
a

Calculated from the XRD patterns.


a

根据 XRD 图样计算得出。

3.2.2. Redox Properties 3.2.2.氧化还原特性

The reducibility of active sites (e.g., Cu, (21) Ni, (35) Co, (17) and Fe (36)) would strongly affect the N2O decomposition performance. H2-TPR studies were performed to investigate the enhancement in reducibility of CuxCoy catalysts (Figure 2a). The H2 reduction peaks of the CuxCoy catalysts were similar to those of CuO, which are situated at lower temperatures than those of Co3O4. That result means the reductions of CuO and Co3O4 in CuxCoy catalysts occurred at approximately the same time. Consequently, the data indicate the Cu species in CuxCoy catalysts played a dominant role in the redox reaction, which could promote the reduction of Co species by a charge interaction in the CuxCoy catalysts. (37) Moreover, the H2 reduction peaks and the initial H2 consumption temperature of all of the Cu-containing catalysts seem identical (∼158 °C). To further identify the reducibility of Cu-containing catalysts, the initial H2 consumption rates were determined and are shown in Figure 2b. The initial H2 consumption rate of Cu2Co1 was clearly faster than those of the other Cu-containing materials. This result indicates that Cu2Co1 represented the optimal reducibility, which could facilitate the N2O decomposition of the Cu2Co1 mixed oxide.
活性位点的还原性（如Cu、(21) Ni、(35) Co、(17) 和 Fe (36)）会严重影响 N2O 的分解性能。进行了 H2-TPR 研究，以了解 CuxCoy 催化剂（Figure 2a ）。CuxCoy 催化剂的温度与 CuO 相似、3O4 催化剂的温度较低。这一结果意味着 CuO 和 Co3O4 在 CuxCoy 催化剂中的反应时间大致相同。 因此，数据表明 CuxCoy 催化剂中的 Cu 物种在氧化还原反应中起主导作用、这可以通过 CuxCoy 催化剂中的电荷相互作用促进 Co 物种的还原。(37) 此外、所有含铜催化剂的 H2 还原峰和初始 H2 消耗温度似乎相同（∼158 °C）。为了进一步确定含铜催化剂的还原性，测定了初始 H2 消耗率，如 图 2b 所示。Cu2Co1 的初始 H2 消耗率明显快于其他含铜材料。 这一结果表明，Cu2Co1 代表了最佳还原性、这有助于 Cu2Co1 混合氧化物的 N2O 分解。

Figure 2 图 2

Figure 2. (a) H2-TPR profiles of the Co3O4, CuxCoy, and CuO catalysts. (b) Initial H2 consumption rates of the CuxCoy and CuO catalysts in the H2-TPR study.
图 2。(a) Co2 的 H3O4 的 TPR 曲线、CuxCoy 和 CuO 催化剂。(b) Cu2 和 CuO 催化剂的初始 HxCoy 和 CuO 催化剂的 H2-TPR 研究。

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3.2.3. Surface Analysis 3.2.3.表面分析

Generally, the redox cycles between the Cu2+/Cu and Co+3+/Co2+ play important roles in N2O decomposition. (38) Thus, the ratios of Cu/(Cu + Cu++2+) and Co2+/(Co2+ + Co3+) are crucial to N2O decomposition. (15) The AES and XPS studies were used to determine the surface components of the Co3O4, CuxCoy, and CuO catalysts, and the surface chemical compositions are listed in Table 2. In Figure 3a, the AES spectra of Cu-containing catalysts over the spectral region of the Cu LMM contained features mainly centered at ∼916.0 and ∼918.0 eV, which were assigned to Cu and Cu+2+, respectively. (39,40) Among the Cu-containing samples, the ratios of Cu/(Cu + Cu++2+) for all of the CuxCoy catalysts were higher than those for CuO. This result was further confirmed by the XPS spectra for the Cu 2p3/2 spectral region (shown in Figure S3). Additionally, the Cu 2p3/2 spectral region of pure CuO was situated at higher binding energies, whereas the peaks of Cu 2p3/2 for the CuxCoy catalysts were shifted to lower binding energies. These results imply that the electron cloud of Cu species in the CuxCoy catalysts were altered due to the charge interaction between Cu and Co. Corresponding with the shift in Cu 2p3/2, Figure 3b shows that the Co 2p3/2 spectral region of pristine Co3O4 was also located at higher binding energies, and the peaks moved to lower binding energies as Cu was added, further confirming the existence of the charge interaction between Cu and Co. These results are in accordance with those of the H2-TPR study. The XPS spectra of Co-containing samples for the spectral region of the Co 2p3/2 contained peaks mainly centered at 780.5 and 779.3 eV, which were attributed to Co2+ and Co3+, respectively. The ratios of Co2+/(Co2+ + Co3+) for the CuxCoy catalysts were also higher than that for Co3O4. Overall, part of the metal elements on the surface of the CuxCoy catalysts transformed from high valence states to relatively low valence states, which was mainly due to the charge interaction between Co and Cu. (41) The facilitation of redox cycles between Cu2+/Cu and Co+3+/Co2+ could play an important role in the N2O decomposition performance of the CuxCoy catalysts.
一般来说、Cu2+/Cu 和 Co+3+/Co2+ 在 N2O 分解中发挥重要作用。(38) 因此、Cu/(Cu + Cu++2+) 和 Co2+/(Co2+ + Co3+) 对 N2O 分解至关重要。(15) AES 和 XPS 研究用于确定 Co3O4 的表面成分、CuxCoy、表2中列出了CuO催化剂和CuO催化剂的表面化学成分。在图3a 中，含铜催化剂在 Cu LMM 光谱区的 AES 光谱包含主要以 ∼916.0 和 ∼918.0 eV 的特征，这些特征分别归属于 Cu 和 Cu+2+。 (39,40) 在含铜样品中、++2+) 的比率xCoy催化剂的辐照度均高于 CuO 催化剂。Cu 2p3/2 光谱区的 XPS 光谱进一步证实了这一结果（如图 S3 所示）。此外，纯氧化铜的 Cu 2p3/2 光谱区位于较高的结合能上、而 Cu 2p3/2 的峰xCoy 催化剂被转移到较低的结合能。这些结果表明，由于 Cu 和 Co 之间的电荷相互作用，CuxCoy 催化剂中 Cu 物种的电子云发生了改变。 对应于铜 2p 的移动3/2、图3b显示原始Co的Co 2p3/2光谱区3O4 也位于较高的结合能处、随着 Cu 的加入，峰值移动到较低的结合能处，这进一步证实了 Cu 和 Co 之间存在电荷相互作用。这些结果与 H2-TPR 研究的结果一致。含 Co 样品在 Co 2p3/2 光谱区的 XPS 光谱包含的峰值主要集中在 780.5和 779.3 eV，分别归因于Co2+和Co3+。Co2+/(Co2+ + Co3+）的 CuxCoy 催化剂也高于 Co3O4. 总的来说，CuxCoy 催化剂表面的部分金属元素从高价态转变为相对低价态、这主要是由于 Co 和 Cu 之间的电荷相互作用。(41) Cu2+/Cu 和 Co+3+/Co2+ 可能在 Cu2O 分解性能中发挥重要作用。uid="125">xCoy 催化剂的氧化分解性能。

Figure 3 图 3

Figure 3. (a) AES spectra of the CuxCoy and CuO catalysts for the spectral region of the Cu LMM. (b) XPS spectra of the Co3O4 and CuxCoy catalysts for the spectral region of the Co 2p3/2.
图 3。(a) CuxCoy 和 CuO 催化剂在 Cu LMM 光谱区的 AES 光谱。(b) Co3O4 和 CuxCoy 催化剂的 Co 2p3/2 光谱区。

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Table 2. Surface Chemical Compositions of the Co3O4, CuxCoy, and CuO Catalysts/%
表 2.Co3O4 的表面化学成分、CuxCoy 和 CuO 催化剂/%。
 CuaCob 
 Cu2+Cu+Co3+Co2+O
Co3O4  13.27.779.1
Cu1Co29.83.811.69.565.3
Cu1.5Co1.513.44.710.38.563.1
Cu2Co117.16.98.56.660.9
CuO 氧化铜36.54.8  58.7
a

Calculated from the AES spectra of Cu LMM.


a

根据 Cu LMM 的 AES 光谱计算得出。

b

Obtained from the XPS spectra of Co 2p3/2.


b

从 Co 2p 的 XPS 光谱中获得3/2.

3.2.4. N2O Adsorption Capacities
3.2.4.N2O 吸附能力。

DFT calculations were employed to identify the characteristics of N2O adsorption on the CuxCoy catalysts. Considering that the CuxCoy catalysts were mixed oxides of CuO and Co3O4, the N2O adsorption configurations on their slab models were calculated. A negative value for Ead indicates a stable adsorption in this study. As shown in Figure 4a, N2O could be weakly adsorbed on Cu2+ to form a Cu–ON2 species. The bond length of Cu–O in the Cu–ON2 species was 2.87 Å, and the corresponding N2O adsorption energy (Ead) was only −0.1 eV. N2O could also be weakly adsorbed on a CuO surface with an oxygen vacancy to form a □–Cu–ON2 species (Figure 4b). The bond length of Cu–O in the □–Cu–ON2 species was quite short (2.14 Å), whereas the corresponding Ead was slightly lower than that of the Cu–ON2 species. These results suggest that oxygen vacancies slightly promoted N2O adsorption on CuO, but these adsorption configurations remained very unstable. For Co3O4, N2O could hardly be adsorbed on the complete surface structure (Figure 4c). The Ead of Co–ON2 was even higher than 0. However, the Ead of N2O adsorbed on the Co3O4 surface with an oxygen vacancy (Figure 4d–f) was lower than those of N2O adsorbed on Co3O4 and CuO, which suggests that N2O could be strongly adsorbed on the Co3O4 surface with oxygen vacancies to form the □–Co–ON2 species. Consequently, N2O is more likely to be adsorbed on a Co3O4 surface with oxygen vacancies than on a CuO or CuO–□ surface in the CuxCoy catalysts.
DFT 计算确定了 N2O 在 CuxCoy 催化剂上的 O 吸附。考虑到 CuxCoy 催化剂是 CuO 和 Co3O4 的混合氧化物、计算了 N2O 在其板坯模型上的吸附构型。在本研究中，Ead 的负值表示吸附稳定。如图4a 所示、N2O 可以弱吸附在 Cu2+ 上，形成 Cu-ON2 物种。Cu-ON2 物种中 Cu-O 的键长为 2.87 Å，相应的 N2O 吸附能 (Ead) 仅为 -0.1 eV。 N2O 也可以弱吸附在有氧空位的 CuO 表面，形成 □-Cu-ON2 物种（图4b）。在 □-Cu-ON2 物种中，Cu-O 的键长相当短（2.14 Å），而相应的 Ead 则略低于 Cu-ON2 物种。这些结果表明，氧空位略微促进了 N2O 在 CuO 上的吸附，但这些吸附构型仍然很不稳定。对于 Co3O4、N2O 几乎不能吸附在完整的表面结构上（图4c）。Co-ON2 的Ead 甚至高于 0。 然而、Ead 的 N2O 吸附在 Co3O4 氧空位的表面（Figure 4d-f）低于 N2O 吸附在 Co3O4 和 CuO 上、这表明，N2O 可能会强烈吸附在 Co3O4 表面的氧空位，形成 □-Co-ON2 物种。因此、N2O 更有可能被吸附在 Co3O4 表面的氧空位比在 CuxCoy 催化剂。

Figure 4 图 4

Figure 4. Model structures of N2O adsorbed on: (a) CuO, (b) CuO with an oxygen vacancy, (c) Co3O4, and (d−f) Co3O4 with an oxygen vacancy. The white balls represent N, red balls represent O, blue balls represent Cu, and navy-blue balls represent Co. (g) N2O desorption amounts during N2O-TPD over Co3O4, CuxCoy, and CuO catalysts.
图 4.吸附在 N2O 上的模型结构：(a) CuO，(b) 具有氧空位的 CuO，(c) Co3O4 、和 (d-f) Co3O4 氧空位。白球代表 N，红球代表 O，蓝球代表 Cu，藏青色球代表 Co。(g) N2O 在 N2O-TPD over Co3O4、CuxCoy 和 CuO 催化剂。

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N2O-TPD was performed to determine the capacity of N2O adsorption at 50 °C. In the N2O-TPD study, all of the samples were first treated under a He atmosphere at 400 °C for 1 h and then cooled to 50 °C to adsorb 2% N2O/He for 30 min. Finally, the original N2O-TPD profiles (Figure S4a) were recorded by a thermal conductivity detector (TCD) detector at a heating rate of 10 °C/min, and the detailed desorption species were analyzed by MS (Figures S4b–f). Therefore, the desorption amounts of N2O (Figure 4g), N2 (Figure S4g), and NO (Figure S4h, a byproduct of N2O decomposition) were obtained by the integration of MS spectra. It is worth mentioning that the desorption amounts of O2 generated by N2O decomposition during N2O-TPD could not be obtained because of the influences of adsorbed oxygen and/or the crystal oxygen on/in the catalysts.
Interestingly, although the N2O decomposition performance of Co3O4 was weaker than those of the CuxCoy catalysts, the catalyst showed a relatively high capacity for N2O adsorption. This property is mainly originated from the abundant surface oxygen vacancies of Co3O4 (shown in Figure S5), which could promote the N2O adsorption through a □–Co–ON2 style (shown in Figure 4d–f). The high N2O adsorption capacity was probably responsible for the excellent N2O decomposition performance of Co3O4 and the other Co-based spinels. In contrast, CuO exhibited the worst N2O adsorption capacity, which was mainly due to the unstable Cu–ON2 and □–Cu–ON2 species (shown in Figure 4a,b) and the lowest BET surface area, and therefore, this catalyst showed the poorest N2O decomposition performance. The N2O adsorption capacities of the CuxCoy catalysts increased with the Cu doping amount, which is in excellent accordance with their N2O decomposition performance and O2-TPD profiles (Figure S5). Consequently, the capacity of N2O adsorption played an important role in the N2O decomposition reaction.

4. Discussion

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4.1. Reaction Mechanism and Kinetic Study

Many researchers proposed that the N2O decomposition process can be generally described as (17,19,21,42,43)
(1)
(2)
(3)
First, N2O is adsorbed at an active site on the surface (reaction 1). Then, the adsorbed N2O can decompose to N2 and a residual O atom (reaction 2). Finally, two residual O atoms on the surface can combine to generate O2, and the active sites are regenerated (reaction 3).
Thus far, the rate-limiting step of N2O decomposition was comprehensively discussed using the DFT calculations and experimental study. However, the conclusions were completely inconsistent. (15) Some researchers found that the splitting of N2O (reaction 2) is the rate-determining step, but others considered that the recombination of O2 (reaction 3) determines the N2O decomposition rate. (44−47)
If the rate-determining step is the splitting of N2O (reaction 2), the rate of N2O decomposition can be described as
(4)
where υN2O, k2, and [Mn+–ONN] represent the N2O decomposition rate, kinetic constant of reaction 2, and concentration of adsorbed N2O, respectively.
While the GHSV is extremely high and the gaseous N2O concentration is relatively low, reaction 1 can be simply considered as a reversible reaction. Therefore, the concentration of the adsorbed N2O can be approximately described as
(5)
where K1, [Mn+], and [N2O(g)] represent the equilibrium constant of reaction 1, quantity of active sites, and the concentration of gaseous N2O, respectively.
Combined with eqs 4 and 5, the N2O decomposition rate can de depicted as
(6)
In eq 6, K1 and k2 are only related to the reaction temperature over the same catalyst. Therefore, K1 and k2 can be regarded as constants if the reaction reaches a steady state. Meanwhile, the quantity of active sites (Mn+) can be rapidly regenerated through reaction 3. This action suggests that the quantity of active sites (Mn+) can also be regarded as a constant. Therefore, eq 6 can be simplified to
(7)
(8)
where kN2O denotes the reaction rate constant of the N2O decomposition.
Overall, the N2O decomposition is a first-order reaction when the rate-determining step is the splitting of N2O.
If the recombination of O2 (reaction 3) determines the N2O decomposition rate, then the rate of N2O decomposition can be described as
(9)
where k3 and [M(n+1)+–O–] denote the reaction rate constant of reaction 3 and concentration of M(n+1)+–O–, respectively.
Reactions 1 and 2 can be regarded as opposing reactions while the GHSV is extremely high with a relatively low gaseous N2O concentration, and the recombination of O2 is the rate-determining step. Therefore, eq 5 remains workable in this case, and the concentration of M(n+1)+–O– can be described as
(10)
where K2 represents the equilibrium constant of reaction 2 in this case.
Combining eqs 5, 9, and 10, the rate of N2O decomposition can be formulated as
(11)
(12)
Overall, the N2O decomposition is a second-order reaction when the rate-determining step is the recombination of O2.

4.2. Model Verification

A steady-state kinetic study was performed to judge the rate-limiting step of N2O decomposition. An extremely high GHSV and a relatively low gaseous N2O concentration were employed to satisfy the assumptions of the kinetic equations and to overcome the diffusion limitations. The results of the steady-state kinetic study over the Co3O4, CuxCoy and CuO catalysts are shown in Figure S6. All of the materials showed significant linear relationships between the gaseous N2O concentration and the N2O decomposition rate from 350 to 500 °C, with all lines going through the origin of the coordinates. This result indicates that the N2O decomposition reaction was a first-order reaction in this case, which is in good accordance with eq 7. Therefore, the splitting of N2O (reaction 2), rather than the recombination of O2 (reaction 3), was the rate-determining step of N2O decomposition over the Co3O4, CuxCoy, and CuO catalysts. Because if the recombination of O2 was the rate-determining step, then the reaction order of N2O decomposition would be 2. Thus, the linear regression presented in Figure S6 was performed to obtain the reaction rate constant of N2O decomposition, and the results are shown in Figure 5.

Figure 5

Figure 5. N2O decomposition rate constants of the Co3O4, CuxCoy, and CuO catalysts.

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Hinted by eqs 7 and 8, the reaction rate constant of N2O decomposition (kN2O) positively correlated with the equilibrium constant of N2O adsorption (K1), kinetic constant of N2O splitting (k2), and quantity of active sites (Mn+). Generally, the kinetic constant of N2O splitting (k2) increases with the temperature. Therefore, the N2O decomposition rate of all of the materials increased with the temperature (shown in Figure 5). The kinetic constant of N2O splitting (k2) relates to the redox ability, (21,38) whereas the quantity of active sites (Mn+) mainly relates to the metal cations in a low valence state (e.g., Cu and Co+2+) on the surface. The results of the H2-TPR study (Figure 2) suggest that the sequence of redox ability followed Cu2Co1 > Cu1.5Co1.5 ≈ Cu1Co2 ≈ CuO ≫ Co3O4. The AES and XPS results (Figure 3) demonstrate that the percentages of metal cations in a low valence state on the surface of the CuxCoy catalysts were almost the same, but these percentages were significantly higher than those for CuO and Co3O4. The equilibrium constant of N2O adsorption (K1) is mainly related to the ability to adsorb N2O. The adsorptivity of N2O was determined by N2O-TPD (Figure 4g), and the results show that the adsorptivity of N2O decreased in the following sequence: Cu2Co1 > Co3O4 > Cu1.5Co1.5 > Cu1Co2 > CuO. CuO presented the lowest N2O adsorptivity and redox cyclability, as well as a medium quantity of active sites and redox property. Therefore, the lowest N2O decomposition performance of CuO (shown in Figure 5) mainly resulted from its poor N2O adsorptivity and redox cycling between the Cu2+/Cu. Co+3O4 presented a relatively high N2O adsorptivity as well as a medium quantity of active sites. However, its redox ability was the weakest, which was mainly responsible for the inferior N2O decomposition performance of Co3O4 (shown in Figure 5). For the CuxCoy catalysts, the redox ability derived from CuO, N2O adsorptivity derived from Co3O4, and higher quantities of active sites derived from the charge interaction between Co and Cu were all responsible for the excellent N2O decomposition performance. Meanwhile, these properties in Cu1.5Co1.5 and Cu1Co2 were almost the same, except that the N2O adsorption capacity of Cu1.5Co1.5 was slightly higher than that of Cu1Co2. This result proves that the N2O decomposition performance of Cu1.5Co1.5 was slightly higher than that of Cu1Co2 (shown in Figure 5). Cu2Co1 sustained the highest N2O adsorptivity, redox ability, and quantity of active sites. Consequently, Cu2Co1 showed the optimum performance for N2O decomposition (shown in Figure 5).
Based on the above results and conclusions, the N2O decomposition mechanism over CuxCoy catalysts and the key roles of CuO and Co3O4 in CuxCoy catalysts for N2O decomposition were proposed (Scheme 1). The DFT calculation results suggest that Co3O4 provided abundant surface oxygen vacancies, and thus, served as the major adsorption site of N2O. CuO was dispersed around Co3O4 and provided high reducibility on the interface of Co3O4–CuOx, which promoted the rate-determining step (N–O break) of N2O decomposition and left O in the defect sites. Meanwhile, the charge interaction became stronger with the increasing Cu content and promoted the formation of Cu and Co+2+, which performed as the active sites and adsorption sites, respectively. Finally, the residual O in the defect sites recombined to release O2.

Scheme 1

Scheme 1. Key Roles of CuO and Co3O4 in the CuxCoy Catalysts for N2O Decomposition
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Supporting Information

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.9b02892 .

  • N2O decomposition performances of Co3O4, Cu1Co2, and CuO under different conditions; XRD patterns of the Co3O4, CuxCoy, and CuO catalysts; XPS spectra of the CuxCoy and CuO catalysts for the spectral region of Cu 2p3/2; TCD signals of N2O-TPD profiles over Co3O4, CuxCoy, and CuO catalysts; MS spectra of N2O, O2, NO, and N2 over Co3O4, CuxCoy, and CuO during N2O-TPD; N2 and NO desorption amounts during N2O-TPD over Co3O4, CuxCoy, and CuO catalysts; and dependence of the N2O decomposition rate on the N2O concentration over the Co3O4, CuxCoy, and CuO catalysts at 350–500 °C (PDF)

Balance between Reducibility and N2O Adsorption Capacity for the N2O Decomposition: CuxCoy Catalysts as an Example

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S
1
Supporting Information
Balance
between
R
educibility and N
2
O
A
dsorption
C
apacity for
the N
2
O
D
ecomposition:
Cu
x
Co
y
C
atalysts as an
E
xample
Shangchao Xiong
1, 2
,
Jianjun Chen*
1, 2
, Nan
Huang
1, 3
, Shijian Yang
4
,
Yue Peng
1, 2
, Junhua Li
1, 2
1
State Key Joint Laboratory of Environment Simulation and Pollution Control, School of
Environment, Tsinghua University, Beijing 100084
,
PR China
2
National Engineering Laboratory for Multi Flue Gas
Pollution Control Technology and
Equipment,
Tsinghua University,
Beijing
100084,
PR
China
3
School of Environmental and Biological Engineering, Nanjing University of
Science and
Technology, Nanjing
210094
,
PR China
4
School of Environment and Civil Engineeri
ng, Jiangnan University, Wuxi 214122, PR China
*Corresponding author.
Phone: +86 010 62771093
E
–
mail address:
chenjianjun@tsinghua.edu.cn (Jianjun Chen)
Content including:
7
pages
and
6
figures
S
2
(
a
)
(b)
(
c
)
Fig
ure
S
1.
N
2
O decomposition
performance
s
of
Co
3
O
4
(
a
)
, Cu
1
Co
2
(b)
, and
CuO
(c)
under different
conditions. Reaction conditions: [N
2
O] = 1000 ppm, [O
2
] = 2% (when used), [NO] = 200 ppm
(when used), [H
2
O] = 0.5% (when used), catalyst mass = 100 mg, flow rate = 100 ml min
−1
, and
GHSV=60
,000 cm
3
g
−1
h
−1
.
350
400
450
0
20
40
60
80
100
N
2
O decomposition/%
Temperature/
o
C
no addition
with O
2
with NO
with H
2
O
350
400
450
0
20
40
60
80
100
N
2
O decomposition/%
Temperature/
o
C
no addition
with O
2
with NO
with H
2
O
350
400
450
0
20
40
60
80
100
N
2
O decomposition/%
Temperature/
o
C
no addition
with O
2
with NO
with H
2
O

Terms & Conditions

Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Author
    • Jianjun Chen - State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China;  National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China;  Orcidhttp://orcid.org/0000-0003-4730-7803;  Email: chenjianjun@tsinghua.edu.cn
  • Authors
    • Shangchao Xiong - State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China;  National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China
    • Nan Huang - State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China;  School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, PR China
    • Shijian Yang - School of Environment and Civil Engineering, Jiangnan University, Wuxi 214122, PR China;  Orcidhttp://orcid.org/0000-0002-8275-5225
    • Yue Peng - State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China;  National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China;  Orcidhttp://orcid.org/0000-0001-5772-3443
    • Junhua Li - State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, PR China;  National Engineering Laboratory for Multi Flue Gas Pollution Control Technology and Equipment, Tsinghua University, Beijing 100084, PR China;  Orcidhttp://orcid.org/0000-0001-7249-0529
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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This work was financially supported by the National Key Research and Development Program (2017YFC0210700 and 2017YFC0212804) and the National Natural Science Foundation of China (21876093 and 21777081).

References

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    On the importance of the catalyst redox properties in the N2O decomposition over alumina and ceria supported Rh, Pd and Pt
    Parres-Esclapez, S.; Illan-Gomez, M. J.; Salinas-Martinez de Lecea, C.; Bueno-Lopez, A.
    Applied Catalysis, B: Environmental (2010), 96 (3-4), 370-378CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    Rh, Pd, and Pt supported by γ-Al2O3, pure CeO2, and La- or Pr-doped CeO2 catalyst were tested for N2O decompn., and the effect of CO and O2 in the feed gas was assessed. The catalysts were characterized by Raman spectroscopy, x-ray diffraction, N2 adsorption at -196°, H2 temp.-programmed redn., and transmission electron microscopy. Catalytic activity for N2O decompn. of the noble metals was Rh > Pd > Pt; the support significantly affected activity. For the CeO2-contg. catalyst, a relationship between N2O decompn. capacity and H2 redn. of CeO2 was obsd.: the easier the redn., the higher the catalytic activity. The rate-limiting step of the N2O decompn. mechanism over noble metal/CeO2 catalysts seemed to be redn. of catalytically active sites. For Rh catalysts, CeO2 supports were actively involved in N2O decompn.; all CeO2-based supports improved the catalytic activity of Rh with regard to γ-Al2O3, due to the CeO2 redox properties. Pd catalysts with pure and doped CeO2 supports exhibited similar activity which was higher than Pd/γ-Al2O3. Pt/CeO2 was the most active catalyst among the Pt catalysts, but CeO2 doped with La or Pr had a neg. effect on activity. The most active catalyst among those synthesized in this work was Rh/CeO2(Pr).
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  10. 10
    Rutkowska, M.; Piwowarska, Z.; Micek, E.; Chmielarz, L. Hierarchical Fe-, Cu- and Co-Beta zeolites obtained by mesotemplate-free method. Part I: Synthesis and catalytic activity in N2O decomposition. Microporous Mesoporous Mater. 2015, 209, 54– 65,  DOI: 10.1016/j.micromeso.2014.10.011
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    10
    Hierarchical Fe-, Cu- and Co-Beta zeolites obtained by mesotemplate-free method. Part I: Synthesis and catalytic activity in N2O decomposition
    Rutkowska, M.; Piwowarska, Z.; Micek, E.; Chmielarz, L.
    Microporous and Mesoporous Materials (2015), 209 (), 54-65CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
    Two series of BEA zeolites (Beta and Beta/meso) have been prepd. A first series of the samples was obtained by a conventional aging of parent zeolite gel, while the second series (Beta/meso) was prepd. by mesotemplate-free method. In this method Beta nanoparticles are aggregated under acidic conditions with the formation of micro-mesoporous material. Both series (Beta and Beta/meso) were doped with Fe, Cu and Co by ion-exchange method and tested as catalysts of N2O decompn. The Cu-Beta catalyst was found to be the most active in the process of N2O decompn. conducted in inert gas atm. However, in the process performed under conditions similar to those prevailing in waste gases emitted from nitric acid plants (one of the main sources of N2O emission) higher reaction rate was found for the Cu-Beta/meso catalyst.
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  11. 11
    Jíša, K.; Novakova, J.; Schwarze, M.; Vondrova, A.; Sklenak, S.; Sobalik, Z. Role of the Fe-zeolite structure and iron state in the N2O decomposition: Comparison of Fe-FER, Fe-BEA, and Fe-MFI catalysts. J. Catal. 2009, 262, 27– 34,  DOI: 10.1016/j.jcat.2008.11.025
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    11
    Role of the Fe-zeolite structure and iron state in the N2O decomposition: Comparison of Fe-FER, Fe-BEA, and Fe-MFI catalysts
    Jisa, K.; Novakova, J.; Schwarze, M.; Vondrova, A.; Sklenak, S.; Sobalik, Z.
    Journal of Catalysis (2009), 262 (1), 27-34CODEN: JCTLA5; ISSN:0021-9517. (Elsevier)
    The decompn. of nitrous oxide was compared over Fe-FER, Fe-MFI, and Fe-BEA with well established iron distribution in cationic positions and low amts. of less well-established oxide species. It was evidenced that, despite a comparable content of Fe(II) in the cationic positions, the catalytic activity of Fe-FER greatly exceeds that of Fe-BEA and Fe-MFI. While about one half of the iron sites in Fe-FER (Fe/Al < 0.15) participate in the decompn. of nitrous oxide after activation at 450 °C, the no. of active sites in Fe-BEA or Fe-MFI was much lower, and, accordingly, without acceleration of the reaction by the addn. of NO, these samples exhibit much lower catalytic activity than Fe-FER. This could be likely correlated with the concn. of Fe(II) in positions with a specific spatial iron arrangement at optimal Fe···Fe distances. For that role we propose a local structure with two adjacent β sites, where the Fe···Fe distance would be 7 to 7.5 Å, i.e. comparable to the length of the N2O mol., and provide potential for cooperation of the two iron cations on the N2O mol. splitting. Such arrangement is absent in both the Fe-BEA and Fe-MFI structures.
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  12. 12
    Pirngruber, G.; Pieterse, J. The positive effect of NO on the N2O decomposition activity of Fe-ZSM-5: A combined kinetic and in situ IR spectroscopic study. J. Catal. 2006, 237, 237– 247,  DOI: 10.1016/j.jcat.2005.11.012
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    12
    The positive effect of NO on the N2O decomposition activity of Fe-ZSM-5: A combined kinetic and in situ IR spectroscopic study
    Pirngruber, Gerhard D.; Pieterse, Johannis A. Z.
    Journal of Catalysis (2006), 237 (2), 237-247CODEN: JCTLA5; ISSN:0021-9517. (Elsevier)
    NO-assisted N2O decompn. over four different Fe-ZSM-5 samples prepd. by wet ion exchange (WIE) or chem. vapor deposition (CVD) of FeCl3 was investigated by steady-state kinetics, in situ IR spectroscopy, and transient response methods. Despite their lower iron loading, the samples prepd. by WIE had the highest activity for N2O decompn. in the presence of NO. The in situ IR expts. showed that the most active sample was characterized by a high concn. of adsorbed NO, as well as adsorbed NO2 under reaction conditions. Step response expts. proved that NO2 is an intermediate of the catalytic cycle and functions as intermediate oxygen storage. IR and transient kinetic expts. showed that WIE catalysts behave qual. different in NO-assisted N2O decompn. than CVD catalysts. These differences are discussed in terms of the different structure of the iron species in the two types of samples.
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  13. 13
    Yao, X.; Tang, C.; Gao, F.; Dong, L. Research progress on the catalytic elimination of atmospheric molecular contaminants over supported metal-oxide catalysts. Catal. Sci. Technol. 2014, 4, 2814– 2829,  DOI: 10.1039/c4cy00397g
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    Research progress on the catalytic elimination of atmospheric molecular contaminants over supported metal-oxide catalysts
    Yao, Xiaojiang; Tang, Changjin; Gao, Fei; Dong, Lin
    Catalysis Science & Technology (2014), 4 (9), 2814-2829CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
    A review. Catalytic elimination is an important technique to reduce the emission of atm. mol. contaminants (such as CO, NOx, VOCs, HC, and PM, etc.) efficiently. In this field, the supported metal-oxide catalysts have attracted more and more attention in recent years due to their low cost and excellent catalytic performance. It is well known that catalytic performances are significantly dependent on the supports, surface-dispersed components, and the pretreatment of the catalysts. In this work, we present a brief review and propose some perspectives for supported metal-oxide catalysts according to the above-mentioned three aspects. Meanwhile, this paper covers some interesting results about the prepn. of supported metal-oxide catalysts and the improvement of their catalytic performances for the elimination of atm. mol. contaminants obtained by our research group. Moreover, we propose the concepts of "green integration prepn. (GIP)" and "surface synergetic oxygen vacancy (SSOV)" to understand the relationship between the "compn.-structure-activity" of the supported metal-oxide catalysts, and further clarify the nature of the catalytic reactions.
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    Konsolakis, M.; Sgourakis, M.; Carabineiro, S. A. C. Surface and redox properties of cobalt–ceria binary oxides: On the effect of Co content and pretreatment conditions. Appl. Surf. Sci. 2015, 341, 48– 54,  DOI: 10.1016/j.apsusc.2015.02.188
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    14
    Surface and redox properties of cobalt-ceria binary oxides: On the effect of Co content and pretreatment conditions
    Konsolakis, Michalis; Sgourakis, Michalis; Carabineiro, Sonia A. C.
    Applied Surface Science (2015), 341 (), 48-54CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
    Ceria-based transition metal catalysts have recently received considerable attention both in heterogeneous catalysis and electro-catalysis fields, due to their unique physicochem. characteristics. Their catalytic performance is greatly affected by the surface local chem. and oxygen vacancies. The present study aims at investigating the impact of Co/Ce ratio and pretreatment conditions on the surface and redox properties of cobalt-ceria binary oxides. Co-ceria mixed oxides with different Co content (0, 20, 30, 60, 100 wt.%) were prepd. by impregnation method and characterized by means of N2 adsorption at -196 °C, X-ray diffraction (XRD), H2 temp.-programmed redn. (H2-TPR) and XPS. The results shown the improved reducibility of Co/CeO2 mixed oxides compared to single oxides, due to a synergistic interaction between cobalt and cerium. Oxidn. pretreatment results in a preferential localization of cerium species on the outer surface. In contrast, a uniform distribution of cobalt and cerium species over the entire catalyst surface is obtained by the redn. process, which facilitates the formation of oxygen vacancies though Co3+/Co2+ and Ce3+/Ce4+ redox cycles. Fundamental insights toward tuning the surface chem. of cobalt-ceria binary oxides are provided, paving the way for real-life industrial applications.
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  15. 15
    Konsolakis, M. Recent advances on nitrous oxide (N2O) decomposition over non-noble-metal oxide catalysts: Catalytic performance, mechanistic considerations, and surface chemistry aspects. ACS Catal. 2015, 5, 6397– 6421,  DOI: 10.1021/acscatal.5b01605
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    15
    Recent Advances on Nitrous Oxide (N2O) Decomposition over Non-Noble-Metal Oxide Catalysts: Catalytic Performance, Mechanistic Considerations, and Surface Chemistry Aspects
    Konsolakis, Michalis
    ACS Catalysis (2015), 5 (11), 6397-6421CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    A review; nitrous oxide (N2O) is the largest stratospheric-ozone-depleting substance, being concomitantly the third most potent greenhouse gas. The direct catalytic decompn. of N2O (deN2O process) is one of the most promising remediation technologies for N2O emissions abatement. Although noble metals (NMs)-based catalysts demonstrate satisfactory deN2O performance, their high cost and sensitivity to various effluent stream components (e.g., water vapor, oxygen) limit their widespread industrial applications. Hence, the development of NMs-free catalysts of low cost and satisfactory deN2O performance is of paramount importance. This survey appraises the recent advances, which have been reported since 2000, on N2O decompn. over non-noble-metal oxidic catalysts. Initially, a brief overview of N2O sources, environmental consequences, and remediation technologies is provided. The literature related to the deN2O process over NMs-free metal oxides (MOs) is categorized and critically discussed, as follows: (i) bare oxides, (ii) hexaaluminates, (iii) hydrotalcites, (iv) spinels, (v) perovskites, and (iv) mixed metal oxides not belonging in the above categories. This review covers several aspects with respect to the reaction mechanisms, the structure-activity correlations, the role of various inhibitors (e.g., O2, NO, H2O) as well as the strategies followed to adjust the local surface structure of MOs. Fundamental insights toward fine-tuning of surface chem. of MOs by means of advanced prepn. routes and/or electronic promotion are also provided, paving the way for real-life energy and environmental applications, beyond the deN2O process.
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  16. 16
    Pasha, N.; Lingaiah, N.; Babu, N.; Reddy, P.; Prasad, P. Studies on cesium doped cobalt oxide catalysts for direct N2O decomposition in the presence of oxygen and steam. Catal. Commun. 2008, 10, 132– 136,  DOI: 10.1016/j.catcom.2008.06.006
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    16
    Studies on cesium doped cobalt oxide catalysts for direct N2O decomposition in the presence of oxygen and steam
    Pasha, Nayeem; Lingaiah, N.; Babu, N. Seshu; Reddy, P. Siva Sankar; Prasad, P. S. Sai
    Catalysis Communications (2008), 10 (2), 132-136CODEN: CCAOAC; ISSN:1566-7367. (Elsevier B.V.)
    Bulk cobalt oxide and cesium promoted cobalt oxide catalysts are prepd. and characterized by different spectroscopic techniques. These catalysts are studied for direct N2O decompn. to N2 and O2. Cs addn. to Co3O4 catalysts enhanced the catalytic activity for the decompn. of N2O. The characterization results suggest that the alkali metals weakens the Co-O bond strength and promote early oxygen desorption from the catalyst surface thus leading to high activity. The effect of oxygen and/or steam in the feed stream is also studied and the reasons for low N2O decompn. in presence of water are elucidated.
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  17. 17
    Xue, L.; Zhang, C.; He, H.; Teraoka, Y. Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst. Appl. Catal., B 2007, 75, 167– 174,  DOI: 10.1016/j.apcatb.2007.04.013
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    17
    Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst
    Xue, Li; Zhang, Changbin; He, Hong; Teraoka, Yasutake
    Applied Catalysis, B: Environmental (2007), 75 (3-4), 167-174CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    A series of CeO2 promoted cobalt spinel catalysts were prepd. by the co-pptn. method and tested for the decompn. of nitrous oxide (N2O). Addn. of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decompn. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400° even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The anal. results indicated that the addn. of CeO2 could increase the surface area of Co3O4, and then improve the redn. of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-detg. step of the N2O decompn. over cobalt spinel catalyst. We conclude that these effects, caused by the addn. of CeO2, are responsible for the enhancement of catalytic activity of Co3O4.
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  18. 18
    Russo, N.; Fino, D.; Saracco, G.; Specchia, V. N2O catalytic decomposition over various spinel-type oxides. Catal. Today 2007, 119, 228– 232,  DOI: 10.1016/j.cattod.2006.08.012
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    18
    N2O catalytic decomposition over various spinel-type oxides
    Russo, Nunzio; Fino, Debora; Saracco, Guido; Specchia, Vito
    Catalysis Today (2007), 119 (1-4), 228-232CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)
    Various spinel-type catalysts AB2O4 (where A = Mg, Ca, Mn, Co, Ni, Cu, Cr, Fe, Zn and B = Cr, Fe, Co) were prepd. and characterized by XRD, BET, TEM and FESEM-EDS. The performance of these catalysts towards the decompn. of N2O to N and O was evaluated in a temp. programmed reaction (TPR) app. in the absence and the presence of O. Spinel-type oxides contg. Co at the B site were found to provide the best activity. The half conversion temp. of N2O over the MgCo2O4 catalyst was 440° and 470° in the absence and presence of O, resp. (GHSV =80,000/h). On the grounds of temp. programmed O desorption (TPD) analyses as well as of reactive runs, the prevalent activity of the MgCo2O4 catalyst could be explained by its higher concn. of suprafacial, weakly chemisorbed O species, whose related vacancies contribute actively to N2O catalytic decompn. This indicates the way for the development of new, more active catalysts, possibly capable of delivering at low temps. amts. of these oxygen species even higher than those characteristic of MgCo2O4.
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  19. 19
    Piskorz, W.; Zasada, F.; Stelmachowski, P.; Kotarba, A.; Sojka, Z. DFT modeling of reaction mechanism and ab initio microkinetics of catalytic N2O decomposition over alkaline earth oxides: From molecular orbital picture account to simulation of transient and stationary rate profiles. J. Phys. Chem. C 2013, 117, 18488– 18501,  DOI: 10.1021/jp405459g
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    19
    DFT Modeling of Reaction Mechanism and Ab Initio Microkinetics of Catalytic N2O Decomposition over Alkaline Earth Oxides: From Molecular Orbital Picture Account to Simulation of Transient and Stationary Rate Profiles
    Piskorz, Witold; Zasada, Filip; Stelmachowski, Pawel; Kotarba, Andrzej; Sojka, Zbigniew
    Journal of Physical Chemistry C (2013), 117 (36), 18488-18501CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    A comprehensive mol. modeling of the reaction mechanism, complemented by ab initio microkinetic studies of the catalytic decompn. of N2O on a series of the alk. earth oxides (MgO, CaO, and SrO), was performed. The DFT level of theory was used to study the intimate mechanism of conceivable elementary steps of the deN2O reaction over the terrace sites of the most stable (100) planes. The principal mechanistic events were thoroughly analyzed in terms of the frontier MO picture, and a multiple role of the anionic redox active centers constituted by surface O2-(surf) ions was revealed. The harmonic transition state theory along with the calcd. free enthalpies of activation were used to model the reaction progress with the elementary step resoln. in pulse (transient) and steady state regimes. For modeling the surface diffusion and recombination of the reaction key intermediates (peroxy groups), a Monte Carlo approach was applied to rationalize dioxygen formation along the static and dynamic routes. The developed kinetic scheme was able to reproduce the results of temp.-programmed surface reaction (TPSR) and isothermal steady state expts. with high accuracy without fitting any parameters. On the basis of obtained results, a complete mol. mechanistic description of the deN2O reaction was proposed, resolving definitely the dependence of the particular elementary steps on the strength of anionic redox centers and their Lewis basicity.
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  20. 20
    Piskorz, W.; Zasada, F.; Stelmachowski, P.; Kotarba, A.; Sojka, Z. Decomposition of N2O over the surface of cobalt spinel: A DFT account of reactivity experiments. Catal. Today 2008, 137, 418– 422,  DOI: 10.1016/j.cattod.2008.02.027
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    20
    Decomposition of N2O over the surface of cobalt spinel: A DFT account of reactivity experiments
    Piskorz, Witold; Zasada, Filip; Stelmachowski, Pawel; Kotarba, Andrzej; Sojka, Zbigniew
    Catalysis Today (2008), 137 (2-4), 418-422CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)
    The DFT mol. modeling of N2O decompn. over cobalt spinel (1 0 0) plane was performed using a cluster approach, and applied to rationalize the exptl. reactivity data. The energetics of the postulated elementary steps such as N2O adsorption, N2O activation through dissociative electron or oxygen atom transfer, surface diffusion of resultant oxygen intermediates, and their recombination into O2, was evaluated and discussed. The geometry and electronic structure of the implicated active sites and intermediates were detd. Three different transition states were found for the activation of nitrous oxide mol. In the preferred electron transfer mechanism, involving a monodentate transition state, the N2O activation and the formation of dioxygen are energetically the most demanding steps, whereas the barrier for the oxygen surface diffusion was found to be distinctly smaller. For the oxygen atom transfer the reaction is energetically constraint by the N-O bond-breaking step. The inhibiting effect of co-adsorbed water and oxygen on the particular reaction steps was briefly addressed.
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  21. 21
    Zhou, H.; Huang, Z.; Sun, C.; Qin, F.; Xiong, D.; Shen, W.; Xu, H. Catalytic decomposition of N2O over CuxCe1–xOy mixed oxides. Appl. Catal., B 2012, 125, 492– 498,  DOI: 10.1016/j.apcatb.2012.06.021
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    21
    Catalytic decomposition of N2O over CuxCe1-xOy mixed oxides
    Zhou, Haibo; Huang, Zhen; Sun, Chao; Qin, Feng; Xiong, Desheng; Shen, Wei; Xu, Hualong
    Applied Catalysis, B: Environmental (2012), 125 (), 492-498CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    The catalytic N2O decompn. was investigated over a series of CuxCe1-xOy mixed oxides with different Cu/Ce molar ratios. Effects of synergy over mixed oxides of CeO2 and CuO were obsd. significantly, the catalyst of Cu0.67Ce0.33Oy exhibited the high activity among the Cu-Ce-O mixed oxides for N2O decompn. Characterizations of XRD, N2 adsorption, XPS, and H2-TPR were applied to correlate their properties with the corresponding catalytic performance, and reveal the synergetic effect between CuO and CeO2 for N2O decompn. In situ DRIFTS investigation confirmed the presence of CuI species that was closely related with the activity of CuxCe1-xOy catalyst. The synergy of CuxCe1-xOy promoted the stability and the ability to regenerate the active CuI site.
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  22. 22
    Zabilskiy, M.; Djinović, P.; Tchernychova, E.; Tkachenko, O. P.; Kustov, L. M.; Pintar, A. Nanoshaped CuO/CeO2 materials: Effect of the exposed ceria surfaces on catalytic activity in N2O decomposition reaction. ACS Catal. 2015, 5, 5357– 5365,  DOI: 10.1021/acscatal.5b01044
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    22
    Nanoshaped CuO/CeO2 Materials: Effect of the Exposed Ceria Surfaces on Catalytic Activity in N2O Decomposition Reaction
    Zabilskiy, Maxim; Djinovic, Petar; Tchernychova, Elena; Tkachenko, Olga P.; Kustov, Leonid M.; Pintar, Albin
    ACS Catalysis (2015), 5 (9), 5357-5365CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
    This study reports a thorough investigation of nanosized CuO/CeO2 materials as an efficient catalyst for decompn. of N2O, which is a strong greenhouse gas largely produced by chem. industry. Effect of terminating CeO2 cryst. planes ({100}, {110}, and {111}) on the behavior of CuO dispersed over CeO2 nanocubes, nanorods and polyhedral crystallites was examd. in detail by using a variety of catalyst characterization techniques. The 4 wt % Cu was found as the most advantageous metal loading, whereas higher Cu content resulted in lower dispersion and formation of significantly less active, segregated bulk CuO phase. It was discovered that CuO/CeO2 solids should enable both excessive oxygen mobility on the catalyst surface as well as formation of highly reducible Cu defect sites, in order to ensure high intrinsic activity. Detailed studies further revealed that CeO2 morphol. needs to be tailored to expose {100} and {110} high-energy surface planes, as present in CeO2 nanorods. Oxygen mobility and regeneration of active Cu phase on these surface planes is easier, which in turn facilitates higher catalytic activity through the recombination of surface oxygen atoms and desorption as mol. oxygen that replenishes active sites for subsequent catalytic cycles. As a consequence, CuO supported on CeO2 nanorods demonstrated lower activation energy (87 kJ/mol) in N2O decompn. reaction compared to catalysts based on CeO2 nanocubes (102 kJ/mol) or polyhedral CeO2 (92 kJ/mol).
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  23. 23
    Kapteijn, F.; Marbán, G.; Rodriguez-Mirasol, J.; Moulijn, J. A. Kinetic Analysis of the Decomposition of Nitrous Oxide over ZSM-5 Catalysts. J. Catal. 1997, 167, 256– 265,  DOI: 10.1006/jcat.1997.1581
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    23
    Kinetic analysis of the decomposition of nitrous oxide over ZSM-5 catalysts
    Kapteijn, Freek; Marban, Gregorio; Rodriguez-Mirasol, Jose; Moulijn, Jacob A.
    Journal of Catalysis (1997), 167 (1), 256-265CODEN: JCTLA5; ISSN:0021-9517. (Academic)
    A detailed comparative kinetic anal. has been made of the N2O decompn. over Co-, Fe-, and CuZSM-5. The effect of partial pressure of N2O, O2, CO, and NO, the space time, and temp. have been investigated. The decompn. is first order in N2O over Fe- and CoZSM-5 and has a slightly lower order over the Cu sample. Inhibition of oxygen obsd. for CuZSM-5 is absent for Co and for Fe at the lower temps. N2O destruction is enhanced by CO for all catalysts and by NO for FeZSM-5 only. In the presence of NO, NO2 is produced over Fe- and CoZSM-5. Over CuZSM-5 the enhancement by CO passes through a max. as a function of CO pressure due to the strong adsorption at reduced sites. A detailed kinetic model that accounts quant. for the obsd. dependencies and which deviates from the classical model for oxidic systems is advanced. Ests. of the max. turnover rates for the various model steps range from 10-4 to L s-1.
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  24. 24
    Obalová, L.; Fíla, V. Kinetic analysis of N2O decomposition over calcined hydrotalcites. Appl. Catal., B 2007, 70, 353– 359,  DOI: 10.1016/j.apcatb.2005.11.031
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    24
    Kinetic analysis of N2O decomposition over calcined hydrotalcites
    Obalova, L.; Fila, V.
    Applied Catalysis, B: Environmental (2007), 70 (1-4), 353-359CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    The kinetics of N2O decompn. over a catalyst prepd. by calcination of Co-Mn hydrotalcite was examd. in an integral fixed-bed reactor (V (total vol. flow)/w (catalyst mass) = 12-96 L/gcat-h) at various N2O and O2 initial partial pressures at a temp. range of 330-450°. Kinetic data were evaluated by linear and nonlinear regression methods, and 15 kinetic expressions were tested. Based on the obtained results, a redox model of N2O decompn. was proposed. At low pressures of O2, adsorbed oxygen is formed by the N2O decompn.; the N2O chemisorption is considered as the rate-detg. step. On the contrary, at high O2 pressure it could be assumed that adsorbed oxygen species appear as a result of O2 adsorption and the Eley-Rideal mechanism is the rate-detg. step. N2O decompn. is well described by the 1st rate law at N2O and O2 concns. typical for waste gases.
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  25. 25
    Liu, X.; Qiu, G.; Li, X. Shape-controlled synthesis and properties of uniform spinel cobalt oxide nanocubes. Nanotechnology 2005, 16, 3035– 3040,  DOI: 10.1088/0957-4484/16/12/051
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    25
    Shape-controlled synthesis and properties of uniform spinel cobalt oxide nanocubes
    Liu, Xiaohe; Qiu, Guanzhou; Li, Xingguo
    Nanotechnology (2005), 16 (12), 3035-3040CODEN: NNOTER; ISSN:0957-4484. (Institute of Physics Publishing)
    Inorg. nanoparticles with controlled size and shape seem esp. technol. important due to the strong correlation between these parameters and their magnetic, elec., and catalytic properties. Herein uniform spinel Co oxide (Co3O4) nanocubes can be successfully synthesized on a large scale via a facile hydrothermal synthetic route under mild conditions. The size and shape of final products can be readily tuned in a wide range by tuning process parameters such as hydrothermal time, reaction temp., surfactant, concn., and molar ratios of starting material.
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  26. 26
    Shojaee, K.; Montoya, A.; Haynes, B. S. Insight into oxygen stability and vacancy formation on Co3O4 model slabs. Comput. Mater. Sci. 2013, 72, 15– 25,  DOI: 10.1016/j.commatsci.2013.02.001
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    26
    Insight into oxygen stability and vacancy formation on Co3O4 model slabs
    Shojaee, Kambiz; Montoya, Alejandro; Haynes, Brian S.
    Computational Materials Science (2013), 72 (), 15-25CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)
    Spin-polarised periodic d. functional simulations were used to study the stability of oxygen on Co3O4 slab models with (1 0 0) and (1 1 0) terminations in order to understand better the oxidative properties of Co3O4. We obsd. that the PBE + U method gives binding energies and geometrical parameters similar to those obtained for at. oxygen adsorption at low coverage using the revised version of screened hybrid exchange functional HSE06. Atomic oxygen is most stably bound on a Co3O4(1 1 0)-terminated surface where the oxygen adatom binds above the bridge sites of cobalt atoms with a binding energy of 401 kJ mol-1. On-surface O recombination to O2 leaving a bare slab from the Co3O4(1 1 0) terminations is 116-123 kJ mol-1 more activated than recombination of O on (1 0 0) surfaces. Removal of surface lattice oxygen by an on-surface oxygen producing O2 and leaving a slab with an O vacancy site is at least 65 kJ mol-1 more activated in the (1 1 0) surface than in the (1 0 0) surface.
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  27. 27
    Maimaiti, Y.; Nolan, M.; Elliott, S. D. Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption. Phys. Chem. Chem. Phys. 2014, 16, 3036– 3046,  DOI: 10.1039/c3cp53991a
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    27
    Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption
    Maimaiti, Yasheng; Nolan, Michael; Elliott, Simon D.
    Physical Chemistry Chemical Physics (2014), 16 (7), 3036-3046CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    We studied the redn. of CuO(111) surface using d. functional theory (DFT) with the generalized gradient approxn. cor. for on-site Coulomb interactions (GGA + U) and screened hybrid DFT (HSE06 functional). The surface redn. process by oxygen vacancy formation and H2 adsorption on the CuO(111) surface is investigated as two different redn. mechanisms. It is found that both GGA + U and HSE06 predict the same trend in the relative stability of oxygen vacancies. We found that loss of the subsurface oxygen is initially thermodynamically favorable. As the oxygen vacancy concn. increases, mixt. of subsurface and surface vacancies is energetically preferred over full redn. of the surface or subsurface monolayer. The redn. of Cu2+ to Cu+ is found to be more favorable than that of Cu+ to Cu0 in the most stable vacancy structures at all concns. Consistent with the oxygen vacancy calcns., H2 adsorption occurs initially on under-coordinated surface oxygen. Water mols. are formed upon the adsorption of H2 and this gives a mechanism for H2 redn. of CuO to Cu. Ab initio atomistic thermodn. shows that reducing CuO to metallic Cu at the surface is more energetically difficult than in the bulk so that the surface oxide protects the bulk from redn. Using H2 as the reducing agent, it is found that the CuO surface is reduced to Cu2O at approx. 360 K and that complete redn. from Cu2O to metallic Cu occurs at 780 K.
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  28. 28
    Yang, B.-X.; Ye, L.-P.; Gu, H.-J.; Huang, J.-H.; Li, H.-Y.; Luo, Y. A density functional theory study of CO oxidation on CuO1-x(111). J. Mol. Model. 2015, 21, 195,  DOI: 10.1007/s00894-015-2726-x
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    28
    A density functional theory study of CO oxidation on CuO1-x(111)
    Yang Bing-Xing; Ye Li-Ping; Gu Hui-Jie; Huang Jin-Hua; Li Hui-Ying; Luo Yong
    Journal of molecular modeling (2015), 21 (8), 195 ISSN:.
    The surface structures, CO adsorption, and oxidation-reaction properties of CuO1-x(111) with different reduction degree have been investigated by using density functional theory including on-site Coulomb corrections (DFT + U). Results indicate that the reduction of Cu has a great influence on the adsorption of CO. Electron localization caused by the reduction turns Cu(2+) to Cu(+), which interacts much stronger with CO, and the adsorption strength of CO is related to the electronic interaction with the substrate as well as the structural relaxation. In particular, the electronic interaction is proved to be the decisive factor. The surfaces of CuO1-x(111) with different reduction degree all have good adsorption to CO. With the expansion of the surface reduction degree, the amount of CO that is stably adsorbed on the surface increases, while the number of surface active lattice O decreases. In general, the activity of CO oxidation first rises and then declines.
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    Zasada, F.; Piskorz, W.; Sojka, Z. Cobalt spinel at various redox conditions: DFT+U investigations into the structure and surface thermodynamics of the (100) facet. J. Phys. Chem. C 2015, 119, 19180– 19191,  DOI: 10.1021/acs.jpcc.5b05136
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    29
    Cobalt Spinel at Various Redox Conditions: DFT+U Investigations into the Structure and Surface Thermodynamics of the (100) Facet
    Zasada, Filip; Piskorz, Witold; Sojka, Zbigniew
    Journal of Physical Chemistry C (2015), 119 (33), 19180-19191CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Periodic spin unrestricted DFT-PW91 + U calcns. together with ab initio thermodn. modeling were used to study the structure, defects, and stability of different terminations of the (100) surface of cobalt spinel under various redox conditions imposed by different oxygen partial pressure and temp. Three terminations contg. under-stoichiometric (100)-O, stoichiometric (100)-S, and overstoichiometric (100)-R amt. of cobalt ions were analyzed, and their at. and defect structure, reconstruction, and stability were elucidated. For the most stable (100)-S and (100)-O facets, formation of cationic and anionic vacancies was examd., and a surface redox state diagram of possible spinel (100) terminations in the stoichiometry range from Co2.75O4 to Co3O3.75 was constructed and discussed in detail. The results revealed that the bare (100)-S surface is the most stable at temps. and pressures of typical catalytic processes (T ∼ 200 °C to ∼500 °C, pO2/p° ∼ 0.001 to ∼1). In more reducing conditions (T > 600 °C and pO2/p° < 0.0001), the (100)-S facet is readily reduced by formation of oxygen vacancies, whereas in the oxidizing conditions (T < 200 °C and pO2/p° > 10), coexistence of (100)-S and (100)-O terminations was revealed. Formation of the oxygen vacancies involves redn. of the octahedral trivalent cobalt and is accompanied by migration of the divalent tetrahedral cobalt into empty, interstitial octahedral positions. It was also found that the constituent octahedral Co cation proximal to the interstitial cobalt adopts a low spin configuration in contrast to the distal one that preserves its surface high spin state. In the case of the Co depleted surfaces, the octahedral vacancies are thermodynamically disfavored with respect to the tetrahedral ones in the whole range of the examd. T and pO2 values. The obtained theor. results, supported by TPD-O2 and TG expts., show that the octahedral cobalt ions are directly involved in the redox processes of Co3O4.
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  30. 30
    Xiong, S.; Xiao, X.; Liao, Y.; Dang, H.; Shan, W.; Yang, S. Global kinetic study of NO reduction by NH3 over V2O5-WO3/TiO2: Relationship between the SCR performance and the key factors. Ind. Eng. Chem. Res. 2015, 54, 11011– 11023,  DOI: 10.1021/acs.iecr.5b03044
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    30
    Global Kinetic Study of NO Reduction by NH3 over V2O5-WO3/TiO2: Relationship between the SCR Performance and the Key Factors
    Xiong, Shangchao; Xiao, Xin; Liao, Yong; Dang, Hao; Shan, Wenpo; Yang, Shijian
    Industrial & Engineering Chemistry Research (2015), 54 (44), 11011-11023CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
    The nonselective catalytic redn. (NSCR) reaction and the catalytic oxidn. of NH3 to NO (C-O reaction) simultaneously happened during the selective catalytic redn. (SCR) of NO with NH3 over V2O5-WO3/TiO2, esp. at higher temps. There was an excellent linear relationship between the SCR reaction rate and gaseous NO concn., and the intercept and slope can be used to describe the rate const. of NO redn. through the Langmuir-Hinshelwood mechanism and that through the Eley-Rideal mechanism, resp. However, the NSCR reaction rate was nearly independent of gaseous NO concn., and the reaction order of the C-O reaction with respect to gaseous NO concn. was much less than zero. According to the kinetic study, the relationship of the SCR performance (i.e., SCR activity and N2 selectivity) with the key factors (for example V2O5 content, H2O effect, and reactant concn.) was built, which can be used to predict the SCR performance.
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  31. 31
    Xiong, S.; Weng, J.; Liao, Y.; Li, B.; Zou, S.; Geng, Y.; Xiao, X.; Huang, N.; Yang, S. Alkali metal deactivation on the low temperature selective catalytic reduction of NOx with NH3 over MnOx-CeO2: A mechanism study. J. Phys. Chem. C 2016, 120, 15299– 15309,  DOI: 10.1021/acs.jpcc.6b05175
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    31
    Alkali Metal Deactivation on the Low Temperature Selective Catalytic Reduction of NOx with NH3 over MnOx-CeO2: A Mechanism Study
    Xiong, Shangchao; Weng, Jingxia; Liao, Yong; Li, Bo; Zou, Sijie; Geng, Yang; Xiao, Xin; Huang, Nan; Yang, Shijian
    Journal of Physical Chemistry C (2016), 120 (28), 15299-15309CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Use of MnOx-CeO2 as a low temp. selective redn. (SCR) catalyst to control NOx emissions from coal-fired power generating facilities is extremely restricted due to unrecoverable deactivation by SO2. There is little SO2 in biomass-fired power generating facility flue gas, and alkali metals concns. in flue gas following electrostatic pptn. is very low, so the use of MnOx-CeO2 may be possible to control NOx emissions from biomass-fired power generating facilities. However, a very small amt. of alkali metals exhibited a seriously neg. effect on NO redn. over MnOx-CeO2; NOx conversion and N2 selectivity was obviously decreased. This work assessed the NO redn. mechanism over MnOx-CeO2 and K-MnOx-CeO2 in a transient reaction study; NO redn. kinetic parameters were obtained from the steady-state kinetic study. After comparing kinetic parameters, the mechanism of K deactivation on NO redn. over MnOx-CeO2 was discovered. The decreased SCR activity of MnOx-CeO2 after K deactivation was mainly attributed to the decrease of acid sites and Mn4+ concns. on the catalyst surface; the increase of N2O selectivity was mainly related to the occurrence of N2O formation over K-MnOx-CeO2 through the Langmuir-Hinshelwood mechanism.
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    Wang, D.; Peng, Y.; Xiong, S.-c.; Li, B.; Gan, L.-n.; Lu, C.-m.; Chen, J.-j.; Ma, Y.-l.; Li, J.-h. De-reducibility mechanism of titanium on maghemite catalysts for the SCR reaction: An in situ DRIFTS and quantitative kinetics study. Appl. Catal., B 2018, 221, 556– 564,  DOI: 10.1016/j.apcatb.2017.09.045
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    De-reducibility mechanism of titanium on maghemite catalysts for the SCR reaction: An in situ DRIFTS and quantitative kinetics study
    Wang, Dong; Peng, Yue; Xiong, Shang-chao; Li, Bing; Gan, Li-na; Lu, Chun-mei; Chen, Jian-jun; Ma, Yong-liang; Li, Jun-hua
    Applied Catalysis, B: Environmental (2018), 221 (), 556-564CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    An environmentally benign TiO2-doped maghemite catalyst, γ-Fe95Ti5, was prepd. by pptn. microwave pyrolysis and used to remove NOx. The γ-Fe95Ti5 catalyst exhibited significantly higher activity and better N2 selectivity than pure maghemite, γ-Fe100Ti0. The catalyst selective catalytic redn. (SCR) active window was broadened and water and SO2 resistances were preserved. Ti4+ cations could enter the γ-Fe100Ti0 lattice, forming a partial solid soln. on the catalyst surface, as γ-Fe2-ζTiζO3+ξ. This structure improved the quantity and stability of Lewis and Bronsted acid sites vs. γ-Fe100Ti0. Dopant cations suppressed Fe3+ redn. and the percent of active O on the catalyst surface. These could suppress N2O formation from NH3 oxidn. and NOx redn. By combining diffuse reflectance Fourier transform IR spectroscopy and kinetic methods, the γ-Fe95Ti5 catalyst rate consts. by the Eley-Rideal and Langmuir-Hinshelwood mechanisms increased simultaneously; the rate const. for catalytic oxidn. of NH3 decreased vs. γ-Fe100Ti0.
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    Pérez-Ramírez, J.; Kapteijn, F.; Schöffel, K.; Moulijn, J. A. Formation and control of N2O in nitric acid production. Appl. Catal., B 2003, 44, 117– 151,  DOI: 10.1016/s0926-3373(03)00026-2
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    Formation and control of N2O in nitric acid production. Where do we stand today?
    Perez-Ramirez, J.; Kapteijn, F.; Schoffel, K.; Moulijn, J. A.
    Applied Catalysis, B: Environmental (2003), 44 (2), 117-151CODEN: ACBEE3; ISSN:0926-3373. (Elsevier Science B.V.)
    A review. Nitric acid prodn. represents the largest source of N2O in the chem. industry, with a global annual emission of 400 kt N2O. The high impact of N2O on the environment as greenhouse gas and stratospheric ozone depletor, and the ongoing agreements and prospective regulations calls for the development of efficient and economical systems for N2O mitigation, but no mature com. technol. is yet available. In this review, the current state-of-the-art for N2O control in the nitric acid manuf. is presented. The formation of N2O and the process are analyzed and several options for reducing its emissions are discussed, depending on the position in the process. Primary abatement options deals with modifications in the ammonia oxidn. catalyst, secondary abatement with options between the ammonia converter and the absorber, tertiary abatement with options in the tail-gas upstream of the expander, and quaternary abatement with options in the tail-gas downstream of the expander. The abatement technologies are evaluated based on the tech. advantages and disadvantages, and cost efficiency.
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    Zabilskiy, M.; Djinović, P.; Tchernychova, E.; Pintar, A. N2O decomposition over CuO/CeO2 catalyst: New insights into reaction mechanism and inhibiting action of H2O and NO by operando techniques. Appl. Catal., B 2016, 197, 146– 158,  DOI: 10.1016/j.apcatb.2016.02.024
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    N2O decomposition over CuO/CeO2 catalyst: New insights into reaction mechanism and inhibiting action of H2O and NO by operando techniques
    Zabilskiy, Maxim; Djinovic, Petar; Tchernychova, Elena; Pintar, Albin
    Applied Catalysis, B: Environmental (2016), 197 (), 146-158CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    In this work, a combination of ex situ (STEM-EELS, STEM-EDX, H2-TPR and XPS), in situ (CO-DRIFTS) and operando (DR UV-vis and DRIFTS) approaches was used to probe the active sites and det. the mechanism of N2O decompn. over highly active 4 wt.% Cu/CeO2 catalyst. In addn., reaction pathways of catalyst deactivation in the presence of NO and H2O were identified. The results of operando DR UV-vis spectroscopic tests suggest that [Cu-O-Cu]2+ sites play a crucial role in catalytic N2O decompn. pathway. Due to exposure of {1 0 0} and {1 1 0} high-energy surface planes, nanorod-shaped CeO2 support simultaneously exhibits enhancement of CuO/CeO2 redox properties through the presence of Ce3+/Ce4+ redox pair. Its dominant role of binuclear Cu+ site regeneration through the recombination and desorption of mol. oxygen is accompanied by its minor active participation in direct N2O decompn. NO and H2O have completely different inhibiting action on the N2O decompn. reaction. Water mols. strongly and dissociatively bind to oxygen vacancy sites of CeO2 and block further oxygen transfer as well as regeneration of catalyst active sites. On the other hand, the effect of NO is expressed through competitive oxidn. to NO2, which consumes labile oxygen from CeO2 and decelerates [Cu+ Cu+] active site regeneration.
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    Pasha, N.; Lingaiah, N.; Siva Sankar Reddy, P.; Sai Prasad, P. S. An investigation into the effect of Cs promotion on the catalytic activity of NiO in the direct decomposition of N2O. Catal. Lett. 2007, 118, 64– 68,  DOI: 10.1007/s10562-007-9146-1
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    An investigation into the effect of Cs promotion on the catalytic activity of NiO in the direct decomposition of N2O
    Pasha, Nayeem; Lingaiah, N.; Reddy, P. Siva Sankar; Prasad, P. S. Sai
    Catalysis Letters (2007), 118 (1-2), 64-68CODEN: CALEER; ISSN:1011-372X. (Springer)
    A series of Cs promoted NiO catalysts have been prepd. and tested for direct decompn. of N2O. These catalysts are characterized by BET surface area, X-ray diffraction (XRD), temp. programmed redn. (TPR), temp. programmed desorption of N2O (TPD-N2O) and X-ray photo electron spectroscopy (XPS). The Cs promoted NiO catalysts exhibit higher activity for the decompn. of N2O compared to bulk NiO. The catalyst with Cs/Ni ratio of 0.1 showed highest activity. The enhancement in catalytic activity of the Cs promoted catalysts is attributed to the change in the electronic properties of NiO. The characterization techniques suggest weakening of Ni-O bond thereby the desorption of oxygen becomes more facile during the reaction. The Cs promoted NiO catalyst is effective at low reaction temp. and also in the presence of oxygen and steam in the feed stream.
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    Perezalonso, F.; Meliancabrera, I.; Lopezgranados, M.; Kapteijn, F.; Fierro, J. Synergy of FexCe1–xO2 mixed oxides for N2O decomposition. J. Catal. 2006, 239, 340– 346,  DOI: 10.1016/j.jcat.2006.02.008
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    Bloemen, P. J. H.; van de Vorst, M. T. H.; Johnson, M. T.; Coehoorn, R.; de Jonge, W. J. M. Magnetic layer thickness dependence of the interlayer exchange coupling in (001) Co/Cu/Co. J. Appl. Phys. 1994, 76, 7081– 7083,  DOI: 10.1063/1.358034
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    Magnetic layer thickness dependence of the interlayer exchange coupling in (001) Co/Cu/Co
    Bloemen, P. J. H.; van de Vorst, M. T. H.; Johnson, M. T.; Coehoorn, R.; de Jonge, W. J. M.
    Journal of Applied Physics (1994), 76 (10, Pt. 2), 7081-3CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
    A dependence of the strength of the antiferromagnetic coupling across Cu on the Co layer thickness was obsd. The Co thickness dependence displays two clear peaks consistent with the recently predicted oscillation period of 6.2 Å Co. Apart from the two peaks also several small peaks are visible on a scale of ∼1 monolayer Co. Free-electron calcns. indicate that these rapid variations in strength may result from slight differences between the slopes and starting points of the two Co wedges that were involved in the expt.
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    Konsolakis, M.; Carabineiro, S. A. C.; Papista, E.; Marnellos, G. E.; Tavares, P. B.; Moreira, J. A.; Romaguera-Barcelay, Y.; Figueiredo, J. L. Effect of preparation method on the solid state properties and the deN2O performance of CuO–CeO2 oxides. Catal. Sci. Technol. 2015, 5, 3714– 3727,  DOI: 10.1039/c5cy00343a
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    Effect of preparation method on the solid state properties and the deN2O performance of CuO-CeO2 oxides
    Konsolakis, M.; Carabineiro, S. A. C.; Papista, E.; Marnellos, G. E.; Tavares, P. B.; Moreira, J. Agostinho; Romaguera-Barcelay, Y.; Figueiredo, J. L.
    Catalysis Science & Technology (2015), 5 (7), 3714-3727CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
    The present work aims at investigating the catalytic decompn. of N2O over CuO-CeO2 single or mixed oxides prepd. by different synthesis routes, i.e., impregnation, pptn. and exotemplating. To gain insight into the particular role of CeO2 as well as of CuO-CeO2 interactions, three different types of materials were prepd. and tested for N2O decompn. both in the absence and presence of excess O2: (i) bare CeO2 prepd. by pptn. and exotemplating, (ii) CuO/CeO2 oxides synthesized by the impregnation of CeO2 samples prepd. in (i) with CuO, and iii) single stage CuO-CeO2 mixed oxides synthesized employing the co-pptn. and exotemplating methods. The corresponding com. samples were also examd. for comparison purposes. All materials were characterized by N2 adsorption at -196 °C, X-ray diffraction (XRD), H2 temp.-programmed redn. (H2-TPR), XPS, micro-Raman spectroscopy (micro-Raman) and SEM. The results demonstrated the key role of the prepn. procedure on the direct catalytic decompn. of N2O. Among the bare CeO2 samples, the best performance was obtained with the samples prepd. by the pptn. method, followed by exotemplating, while com. CeO2 showed the lowest performance. All bare oxides demonstrated low N2O conversion, never exceeding 40% at 600 °C. Amongst the CuO-CeO2 oxides, the optimum performance was obsd. for those prepd. by co-pptn., which achieved complete N2O conversion at 550 °C. In the presence of excess oxygen in the feed stream, a slight degrdn. is obsd., with the sequence of deN2O performance remaining unchanged. The superiority of the Cu-Ce mixed oxides prepd. by pptn. compared to all of the other materials can be mainly ascribed to their excellent redox properties, linked to Ce4+/Ce3+ and Cu2+/Cu+ redox pairs. A redox mechanism for the N2O catalytic decompn. is proposed, involving N2O adsorption on Cu+ sites and their regeneration through Cu-ceria interactions.
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    Svintsitskiy, D. A.; Kardash, T. Y.; Stonkus, O. A.; Slavinskaya, E. M.; Stadnichenko, A. I.; Koscheev, S. V.; Chupakhin, A. P.; Boronin, A. I. In situ XRD, XPS, TEM, and TPR study of highly active in CO oxidation CuO nanopowders. J. Phys. Chem. C 2013, 117, 14588– 14599,  DOI: 10.1021/jp403339r
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    39
    In Situ XRD, XPS, TEM, and TPR Study of Highly Active in CO Oxidation CuO Nanopowders
    Svintsitskiy, Dmitry A.; Kardash, Tatyana Yu.; Stonkus, Olga A.; Slavinskaya, Elena M.; Stadnichenko, Andrey I.; Koscheev, Sergei V.; Chupakhin, Alexei P.; Boronin, Andrei I.
    Journal of Physical Chemistry C (2013), 117 (28), 14588-14599CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Copper(II) oxide nanopowders exhibit a high catalytic activity in CO oxidn. at low temps. The combination of in situ XPS, XRD, and HRTEM methods was applied to investigate initial steps of CuO nanoparticles redn., to identify oxygen and copper species and to revealed structural features in the dependence on reducing power of reaction medium. At the oxygen deficient surface of CuO nanopowders the metastable Cu4O3 oxide was formed under the mild reducing conditions -10-5 mbar CO or CO + O2 mixt. with oxygen excess. Destruction of Cu4O3 structures in strong reducing medium (P(CO) ≥ 10-2 mbar) or under UHV conditions resulted in the formation of Cu2O which was epitaxially bounded with initial CuO particle. The reversible bulk redn. of CuO nanopowder to Cu2O at temps. ∼150 °C can be explained by effortless propagation of Cu2O‖CuO epitaxial front inside the nanoparticle. The model of the surface restructuring along the {-111}CuO → {202}Cu4O3 → {111}Cu2O planes under the redn. of CuO nanopowders is proposed. The initial surface of CuO nanopowders is probably distorted and resembles Cu4O3-like structures that facilitates the CuOx ↔ Cu4O3 transition in mild reducing conditions. Such restructuring results in a unique electronic Cu4O3 structure with high oxygen deficiency and low-valence Cu1+ sites stimulating the formation of highly reactive CO and O2 adsorbed species. It was shown that the most active oxygen species on the surface of CuOx is stabilized as O-, which was previously reported in papers by Roberts and Madix in their study of the copper-oxygen systems.
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    Timmermans, B.; Reniers, F.; Hubin, A.; Buess-Herman, C. Chemical effects in the Auger spectrum of copper-oxygen compounds. Appl. Surf. Sci. 1999, 144–145, 54– 58,  DOI: 10.1016/s0169-4332(98)00764-8
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    Chemical effects in the Auger spectrum of copper-oxygen compounds
    Timmermans, B.; Reniers, F.; Hubin, A.; Buess-Herman, C.
    Applied Surface Science (1999), 144-145 (), 54-58CODEN: ASUSEE; ISSN:0169-4332. (Elsevier Science B.V.)
    AES and XPS are 2 powerful techniques for the detn. of the compn. of a surface. The nature of the chem. binding of an element is usually studied by XPS. However, the Auger peaks also contain theor. information about the chem. environment of the elements. As mostly one or 2 valence levels are involved in the emission of the Auger electron, a careful anal. of the Auger lines should allow to reveal the changes in the electron densities in the electronic levels due to a change in the chem. environment. However, for metals (with a high no. of electrons) the chem. effects are mostly weak, hidden or hard to interpret. To try to understand better the nature of the chem. effects in AES of metals, a systematic study of well-defined Cu compds. is performed. Cu, CuO, Cu2O, CuCO3 and Cu acetate std. samples were prepd. and characterized. The Cu LMM lines were analyzed. The energy shifts, change in relative intensities and change in FWHM were studied as a function of increasing O environment. The energy shift and the relative intensities of the Auger peak are good fingerprints of the oxidn. state, and the width of the Cu L3M4.5M4.5 peak can be related to the width of the valence band.
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    Fierro, G.; Lo Jacono, M.; Inversi, M.; Dragone, R.; Porta, P. TPR and XPS study of cobalt-copper mixed oxide catalysts: evidence of a strong Co-Cu interaction. Top. Catal. 2000, 10, 39– 48,  DOI: 10.1023/a:1019151731177
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    TPR and XPS study of cobalt-copper mixed oxide catalysts: evidence of a strong Co-Cu interaction
    Fierro, G.; Lo Jacono, M.; Inversi, M.; Dragone, R.; Porta, P.
    Topics in Catalysis (2000), 10 (1,2), 39-48CODEN: TOCAFI; ISSN:1022-5528. (Baltzer Science Publishers)
    In this work the results of TPR and XPS investigation of CoxOy-CuO mixed oxides in the range of compn. Co:Cu = 100:0-8:92 are reported and compared. The final catalysts were obtained by thermal decompn. in air and N2 at 723 K for 24 h of single-phase cobalt-copper hydroxycarbonates prepd. by copptn. at const. pH. The Co:Cu = 100:0 specimen calcined in air formed the Co2+[Co3+]2O4 (Co3O4) spinel phase. The copper-contg. catalysts (Co:Cu = 85:15-8:92) showed mainly two phases: (i) spinels, like Co2+[Co3+]2O4, Co1-x2+Cux2+[Co3+]2O4 and (ii) pure CuO, the relative amt. of each phase depending on the Co:Cu at. ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co2+, Co3+ and Cu2+ species at the catalyst surface. Moreover, the surface quant. anal. evidenced a cobalt enrichment, in particular for the most dild. cobalt samples. The TPR study showed that the catalyst redn. is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co3O4 and CuO phases and the redn. of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst compn. On the other hand, the Co:Cu = 100:0 specimen calcined in N2 formed, as expected, CoO. The initial addn. of copper resulted in the formation of the Cu+Co3+O2 compd., besides CoO, up to a Co/Cu = 1 at. ratio at which the CuCoO2 phase was the main component. A further addn. of copper led to the formation of CuCoO2 and CuO phases. The XPS results were in good agreement with these findings and the surface quant. anal. revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR anal. confirmed that the redn. of the N2-calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of redn.
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    Grzybek, G.; Stelmachowski, P.; Gudyka, S.; Indyka, P.; Sojka, Z.; Guillén-Hurtado, N.; Rico-Pérez, V.; Bueno-López, A.; Kotarba, A. Strong dispersion effect of cobalt spinel active phase spread over ceria for catalytic N2O decomposition: The role of the interface periphery. Appl. Catal., B 2016, 180, 622– 629,  DOI: 10.1016/j.apcatb.2015.07.027
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    Strong dispersion effect of cobalt spinel active phase spread over ceria for catalytic N2O decomposition: The role of the interface periphery
    Grzybek, G.; Stelmachowski, P.; Gudyka, S.; Indyka, P.; Sojka, Z.; Guillen-Hurtado, N.; Rico-Perez, V.; Bueno-Lopez, A.; Kotarba, A.
    Applied Catalysis, B: Environmental (2016), 180 (), 622-629CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
    A series of Co3O4/CeO2 catalysts with increasing cobalt spinel loading in the range of 1-20 wt.% was prepd. by incipient wetness impregnation of CeO2. The obtained catalysts were thoroughly examd. by XRD, XPS, XRF, RS, TEM/EDX/EELS, TPR and BET techniques. The catalytic tests in deN2O reaction revealed that the 10 wt.% of cobalt spinel in supported system is able to reproduce the activity of bare Co3O4 catalyst. However, it was found that the catalyst with the lowest content of Co3O4 equal to 1 wt.% exhibits the highest apparent reaction rate per mass of the spinel active phase. The obsd. activity was explained basing on the transmission electron microscopy anal. in terms of the dispersion of spinel phase over ceria support. A simple model that accounts for the obsd. strong dispersion effect is proposed. It consists in a two-step mechanism, where N2O is dissocd. on the spinel nanograins and the resultant oxygen species are preferentially recombined at the Co3O4/CeO2 interface periphery.
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    Piskorz, W.; Zasada, F.; Stelmachowski, P.; Diwald, O.; Kotarba, A.; Sojka, Z. Computational and experimental investigations into N2O decomposition over MgO nanocrystals from thorough molecular mechanism to ab initio microkinetics. J. Phys. Chem. C 2011, 115, 22451– 22460,  DOI: 10.1021/jp2070826
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    Computational and Experimental Investigations into N2O Decomposition over MgO Nanocrystals from Thorough Molecular Mechanism to ab initio Microkinetics
    Piskorz, Witold; Zasada, Filip; Stelmachowski, Pawel; Diwald, Oliver; Kotarba, Andrzej; Sojka, Zbigniew
    Journal of Physical Chemistry C (2011), 115 (45), 22451-22460CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    In this article a comprehensive mol. modeling of the reaction mechanism complemented by ab initio microkinetic modeling of the catalytic decompn. of N2O on MgO nanocrystals is discussed. The d. functional level of theory was used to study the mol. mechanism of conceivable elementary steps of the deN2O reaction over the most stable (100) surface, including the effect of surface morphol. It is shown that terrace sites are responsible for steady state reactivity, whereas the more basic and reactive sites located on edges and corners are involved only in the initial stages of the reaction because of poisoning. Detailed anal. of the reaction progress in terms of the energy profiles and the evolution of partial charges and bond orders for each step allowed for an in-depth insight at the at. scale into the nature of the catalytic N2O decompn. over anionic redox active sites constituted by surface O2- ions. The harmonic transition state theory along with the calcd. free enthalpies of activation were used to model the reaction progress in pulse (transient) and steady state regimes as well as to predict the kinetic isotopic effects (KIE) for 15N and 18O labeled reactants. The proposed kinetic scheme was able to reproduce the results of temp.-programmed surface reaction and KIE expts. with high accuracy without fitting of any parameters.
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    Liu, X.; Yang, Z.; Li, Y.; Zhang, F. Theoretical study of N2O decomposition mechanism over binuclear Cu-ZSM-5 zeolites. J. Mol. Catal. A: Chem. 2015, 396, 181– 187,  DOI: 10.1016/j.molcata.2014.09.039
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    Theoretical study of N2O decomposition mechanism over binuclear Cu-ZSM-5 zeolites
    Liu, Xin; Yang, Zuoyin; Li, Yaping; Zhang, Fazhi
    Journal of Molecular Catalysis A: Chemical (2015), 396 (), 181-187CODEN: JMCCF2; ISSN:1381-1169. (Elsevier B.V.)
    The mechanism of N2O decompn. over binuclear Cu-ZSM-5 zeolites is investigated using d. functional theory (DFT). It is found that the activation energy of two N2O mols. dissocn. are 47.19 and 63.89 kcal/mol, and the desorption energy of O2 from Cu2O2 is 14.70 kcal/mol. The DFT results show that the N-O splitting step of N2O mol. controls the whole catalytic cycle, and the binuclear Cu-ZSM-5 has not suffered from O2 inhibition. Moreover, some exptl. work reports O2 inhibition is not obsd. at high Cu loading, which is in agreement with the present calcn. These findings suggest that the catalytic behavior of binuclear Cu-ZSM-5 is different from that of mononuclear. Furthermore, the kinetic anal. confirms the rate-limiting step in the binuclear Cu-ZSM-5 system is the N2O dissocn. step, and the rate const. indicates that high temp. could accelerate the N2O dissocn. These results could allow us to understand the structure of the active sites and reveal the active sites controlling catalytic activity. The DFT calcn. results combined with the kinetic study would provide us a comprehensive understanding on the NOx decompn. mechanism over the Cu-ZSM-5 zeolites.
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    Yamashita, T.; Vannice, A. N2O decomposition over manganese oxides. J. Catal. 1996, 161, 254– 262,  DOI: 10.1006/jcat.1996.0183
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    N2O decomposition over manganese oxides
    Yamashita, Tatsuji; Vannice, Albert
    Journal of Catalysis (1996), 161 (1), 254-262CODEN: JCTLA5; ISSN:0021-9517. (Academic)
    The catalytic decompn. of N2O was studied over four different oxides of manganese-MnO, Mn3O4, Mn2O3, and MnO2. The resp. specific activities were 6.3 × 10-4, 2.5 × 10-3, 4.8 × 10-3, and 8.1 × 10-4 μmol/s·m2 at 623 K and 0.066 atm of N2O. Apparent activation energies fell between 19 and 27 kcal/mol, and the reaction orders with respect to N2O were between 0.74 and 0.89. XRD patterns showed that pretreatment at 773 K under He converted MnO2 into Mn2O3, which gave a specific activity similar to that of the original Mn2O3 sample; therefore, MnO2 was pretreated under pure oxygen at 645 K prior to reaction to retain the bulk MnO2 phase. On the other hand, MnO was oxidized to Mn3O4 during the course of N2O decompn. Thus, Mn2O3 is the phase assocd. with the highest catalytic activity. A detailed kinetic study with the most active Mn2O3 sample found that the reaction order at 648 K with respect to N2O was near 0.8 over a wide pressure range, and the reaction rate was retarded by oxygen. The exptl. data fit a simple Langmuir-Hinshelwood model well and both kinetic and thermodn. parameters could be detd. The activation energy for the rate detg. step- dissocn. of adsorbed N2O into N2(g) and adsorbed oxygen- was 31 kcal/mol. Weak N2O adsorption was indicated by heat of adsorption and entropy of adsorption values of 7 kcal/mol and -9 cal/mol·K, resp., while for O2 adsorption resp. values were 22 kcal/mol and -26 cal/mol·K. Independent Langmuir isotherms for N2O adsorption between 297 and 353 K revealed only reversible adsorption with a heat of adsorption of 5 kcal/mol.
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    Smeets, P.; Sels, B.; Vanteeffelen, R.; Leeman, H.; Hensen, E.; Schoonheydt, R. The catalytic performance of Cu-containing zeolites in N2O decomposition and the influence of O2, NO and H2O on recombination of oxygen. J. Catal. 2008, 256, 183– 191,  DOI: 10.1016/j.jcat.2008.03.008
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    The catalytic performance of Cu-containing zeolites in N2O decomposition and the influence of O2, NO and H2O on recombination of oxygen
    Smeets, Pieter J.; Sels, Bert F.; van Teeffelen, Robert M.; Leeman, Hugo; Hensen, Emiel J. M.; Schoonheydt, Robert A.
    Journal of Catalysis (2008), 256 (2), 183-191CODEN: JCTLA5; ISSN:0021-9517. (Elsevier)
    The catalytic decompn. of N2O was studied over Cu-contg. zeolites with different Cu loadings and framework topologies (MFI, MOR, FER, BEA, and FAU). The influence of NO, O2, and H2O on the rate of N2O decompn. was investigated. A kinetic model was developed based on the relevant elementary reaction steps in the mechanism of N2O decompn. The recombination of oxygen atoms into mol. oxygen is recognized as the rate-limiting step in N2O decompn. The rate of oxygen desorption depends strongly on the Cu loading. At low Cu loadings, migration of oxygen atoms is required for recombinative desorption. NO accelerates oxygen recombination, because it provides an alternative route for oxygen migration via gas-phase NO2. The effect of water differs for Cu-contg. zeolites with high and low Cu loadings. At high Cu loading, the rate is suppressed by competitive adsorption of water on the active sites, resulting in an increase in apparent activation energy. The rate of N2O decompn. is increased substantially for catalysts with a low Cu loading. This is tentatively attributed to water-induced mobility of Cu ions, which facilitates oxygen migration. The effect of water addn. is fully reversible.
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    Wu, L.; Qin, W.; Hu, X.; Ju, S.; Dong, C.; Yang, Y. Decomposition and reduction of N2O on CaS (100) surface: A theoretical account. Surf. Sci. 2015, 632, 83– 87,  DOI: 10.1016/j.susc.2014.09.014
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    Decomposition and reduction of N2O on CaS (100) surface: A theoretical account
    Wu, Lingnan; Qin, Wu; Hu, Xiaoying; Ju, Shaoda; Dong, Changqing; Yang, Yongping
    Surface Science (2015), 632 (), 83-87CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
    The catalytic effect of CaS on N2O decompn. and redn. was investigated using d. functional theory calcns. N2O approached the CaS (100) surface and crossed an energy barrier of 1.228 eV, decompg. into a free N2 mol. and an adsorbed O atom. The generated adsorbed O atom could be removed through two reaction pathways: binding with a neighboring adsorbed O atom into O2 with the barrier energy of 1.877 eV or reacting with another N2O mol. generating an adsorbed O2 with the barrier of 1.863 eV. The removal of the surface adsorbed O atom is the rate-detg. step of the catalytic decompn. of N2O. In comparison with the homogeneous reaction between N2O and CO, CO accelerated the removal of the adsorbed O atom, hence improving the redn. of N2O on CaS (100). Furthermore, while compared with the CaO-catalytic removal of N2O, CaS is not as active as CaO for the decompn. and redn. of N2O. Our study is the first attempt to theor. reveal the mechanism of CaS-catalytic decompn. and redn. of N2O, which provides a better understanding of the nitrogen chem. in the reducing atm. zone of circulating fluidized bed boilers.
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Cite this: Environ. Sci. Technol. 2019, 53, 17, 10379–10386
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  • Abstract

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    Figure 1

    Figure 1. (a) N2O decomposition performance of the Co3O4, CuxCoy, and CuO catalysts. (b) N2O decomposition performance of Cu2Co1 under different conditions. Reaction conditions: [N2O] = 1000 ppm, [O2] = 2% (when used), [NO] = 200 ppm (when used), [H2O] = 0.5% (when used), catalyst mass = 100 mg, flow rate = 100 mL min–1, and GHSV = 60 000 cm3 g–1 h–1.

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    Figure 2

    Figure 2. (a) H2-TPR profiles of the Co3O4, CuxCoy, and CuO catalysts. (b) Initial H2 consumption rates of the CuxCoy and CuO catalysts in the H2-TPR study.

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    Figure 3

    Figure 3. (a) AES spectra of the CuxCoy and CuO catalysts for the spectral region of the Cu LMM. (b) XPS spectra of the Co3O4 and CuxCoy catalysts for the spectral region of the Co 2p3/2.

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    Figure 4

    Figure 4. Model structures of N2O adsorbed on: (a) CuO, (b) CuO with an oxygen vacancy, (c) Co3O4, and (d−f) Co3O4 with an oxygen vacancy. The white balls represent N, red balls represent O, blue balls represent Cu, and navy-blue balls represent Co. (g) N2O desorption amounts during N2O-TPD over Co3O4, CuxCoy, and CuO catalysts.

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    Figure 5

    Figure 5. N2O decomposition rate constants of the Co3O4, CuxCoy, and CuO catalysts.

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    Scheme 1

    Scheme 1. Key Roles of CuO and Co3O4 in the CuxCoy Catalysts for N2O Decomposition
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  • References

    This article references 47 other publications.

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      Zabilskiy, Maxim; Djinovic, Petar; Erjavec, Bostjan; Drazic, Goran; Pintar, Albin
      Applied Catalysis, B: Environmental (2015), 163 (), 113-122CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      High surface area CeO2 nanospheres as an active catalyst support were synthesized using glycothermal approach. Different loadings of copper (4, 6, 10 and 15 wt.%) were supported by wet impregnation method. Prepd. materials were characterized by means of TEM, SEM-EDX, XRD, UV-Vis diffuse reflectance, N2 adsorption/desorption, DRIFT and H2-TPR techniques, and tested for the catalytic reaction of nitrous oxide decompn. The best activity in the N2O degrdn. was found for the sample contg. 10 wt.% of Cu that can be attributed to the highest no. of small CuO clusters on the catalyst surface. Further increase of copper content strongly affects the dispersion and leads to the formation of less active segregated CuO phase, which was confirmed by XRD, UV-Vis and H2-TPR results. Accordingly to UV-Vis examn. and DRIFT anal. using CO as a probe mol., all solids contain Cu+1 ions which play a crucial role in the N2O decompn. mechanism. The synthesized catalysts were also tested in wet or NO contg. atmospheres, where an inhibiting effect takes place and leads to shifting of conversion profiles to higher temp. by 65 and 10 °C, correspondingly. It was found out that the formation of a new, cryst. CuO·3H2O phase occurs in water vapor contg. atm., which can result in catalyst deactivation. However, this effect is fully reversible and the catalyst is able to replenish initial activity in dry atm. Potentiality of CuO/CeO2 materials in catalytic N2O decompn. in industrial processes was confirmed by long-term stability tests performed in the period of 50 h in the presence of inhibiting gas components.
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    4. 4
      Ravishankara, A. R.; Daniel, J. S.; Portmann, R. W. Nitrous oxide (N2O): the dominant ozone-depleting substance emitted in the 21st century. Science 2009, 326, 123– 125,  DOI: 10.1126/science.1176985
      4
      Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century
      Ravishankara, A. R.; Daniel, John S.; Portmann, Robert W.
      Science (Washington, DC, United States) (2009), 326 (5949), 123-125CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)
      By comparing the O3 depletion potential-weighted anthropogenic emissions of N2O with those of other O3-depleting substances, the authors showed N2O emissions are currently the single most important O3-depleting emission; it is expected to remain the largest throughout the 21st century. N2O is unregulated by the Montreal Protocol. Limiting future N2O emissions would enhance recovery of the O3 layer from its depleted state and reduce anthropogenic climate forcing, resulting in a win-win for both O3 and climate.
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    5. 5
      Dandekar, A.; Vannice, M. A. Decomposition and reduction of N2O over copper catalysts. Appl. Catal., B 1999, 22, 179– 200,  DOI: 10.1016/s0926-3373(99)00049-1
      5
      Decomposition and reduction of N2O over copper catalysts
      Dandekar, A.; Vannice, M. A.
      Applied Catalysis, B: Environmental (1999), 22 (3), 179-200CODEN: ACBEE3; ISSN:0926-3373. (Elsevier Science B.V.)
      The kinetics of N2O decompn. was investigated over Cu/C, Cu/Al2O3, Cu/SiO2, and Cu/ZSM-5 catalysts with the intent of monitoring the requirements for achieving stoichiometric catalytic decompn. over Cu and elucidating the role of the support in the catalytic cycle. The very efficient oxygen scavenging capability of C led to higher initial activities and turnover frequencies on Cu/C catalysts compared to Cu/ZSM-5; however, rapid gasification of the carbon support limited the lifetime of these Cu/C catalysts. Very low decompn. activity was exhibited by Cu/Al2O3 and Cu/SiO2 at temps. below 823 K; however, addn. of CO or H2 to the reactor feed stream significantly lowered the temps. required to achieve catalytic N2O redn. With all catalysts, the temp. at which the product ratio in the effluent stream stabilized near the stoichiometric ratio of O2/N2 (or CO2/N2) = 1/2 was found to correspond to that at which O2 either desorbs or is removed by carbon. DRIFT spectra of CO adsorbed at 173 K on these catalysts indicated that both Cu+ and Cu2+ species coexist during the active phase, as expected for a redox mechanism requiring a balance between these two sites. In contrast, spectra of deactivated catalysts indicated that the Cu sites exist predominantly as Cu2+ species, with only a very small Cu+ fraction, thus suggesting that the deactivation obsd. in these catalysts at lower temps. is primarily due to the inability to reduce Cu2+ cations back to a Cu+ state. Different kinetic rate expressions, derived from sequences of elementary steps appropriate for each catalyst, fit the data well for N2O decompn. on Cu/ZSM-5 and Cu/Al2O3 as well as N2O redn. by carbon and CO, and they yielded meaningful values for enthalpies and entropies of adsorption for N2O, O2 and CO.
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    6. 6
      Liu, Z.; He, F.; Ma, L.; Peng, S. Recent advances in catalytic decomposition of N2O on noble metal and metal oxide catalysts. Catal. Surv. Asia 2016, 20, 121– 132,  DOI: 10.1007/s10563-016-9213-y
      6
      Recent Advances in Catalytic Decomposition of N2O on Noble Metal and Metal Oxide Catalysts
      Liu, Zhiming; He, Fang; Ma, Lingling; Peng, Sha
      Catalysis Surveys from Asia (2016), 20 (3), 121-132CODEN: CSAABF; ISSN:1571-1013. (Springer)
      Catalytic decompn. of nitrous oxide (N2O) is one of the most efficient methods for the removal of N2O which is of high greenhouse potential and ozone-depleting property. Recent progress in the decompn. of N2O has been reviewed with the focus on noble meal and metal oxide catalysts. The influence factors, such as catalyst support, prepn. method, alkali metal additives and the reaction conditions (including O2, H2O, SO2, NO and CO2), on the performance of deN2O catalysts have been discussed. Finally, future research direction for the catalytic decompn. of N2O is proposed.
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    7. 7
      Komvokis, V. G.; Marti, M.; Delimitis, A.; Vasalos, I. A.; Triantafyllidis, K. S. Catalytic decomposition of N2O over highly active supported Ru nanoparticles (≤3nm) prepared by chemical reduction with ethylene glycol. Appl. Catal., B 2011, 103, 62– 71,  DOI: 10.1016/j.apcatb.2011.01.009
      7
      Catalytic decomposition of N2O over highly active supported Ru nanoparticles (≤3 nm) prepared by chemical reduction with ethylene glycol
      Komvokis, Vasilis G.; Marti, Maria; Delimitis, Andreas; Vasalos, Iacovos A.; Triantafyllidis, Kostas S.
      Applied Catalysis, B: Environmental (2011), 103 (1-2), 62-71CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      In the present work we studied the N2O decompn. activity of nano-Ru/γ-Al2O3 catalysts prepd. by in situ redn. with ethylene glycol (EG), in comparison to catalysts prepd. via typical incipient wetness procedure. The metal content, particle size, dispersion and redn. characteristics of the supported Ru catalysts were studied by ICP-AES, x-ray diffraction, HRTEM, TPR-H2 and TPD-H2. The EG redn. method favored the formation of almost spherical metallic Ru nanoparticles with the size of 1-3 nm (HRTEM) and dispersion of 70-35% (TPD-H2), at Ru loading levels of 0.4-1%. The impregnated-calcined catalysts exhibited larger Ru nanoparticles (10-80 nm, TEM) with low degree of dispersion (∼10%). The activity of the EG-prepd. catalysts for the decompn. of N2O in oxygen rich feeds and in the absence or presence of NO, H2O, SO2, CO and CO2, was significantly higher compared to that of the impregnated-calcined samples and comparable with that of the most active catalytic systems reported in the literature for the treatment of combustion processes off-gases. The superior activity of the former catalysts, esp. of the sample with low Ru content (0.4 wt. % Ru, 1-2 nm particle size), was attributed both to the high dispersion of Ru (70% dispersion), i.e., the high surface area of Ru metal available for reaction, and to the higher intrinsic activity and lower apparent activation energy of the small supported Ru nanoparticles prepd. by the EG redn. method. The EG-prepd. nano-Ru/γ-Al2O3 catalysts could retain their high N2O decompn. activity (higher than 90%) for long time-onstream by applying intermediate, short term regenerations in reducing atm. at moderate temps. (i.e., 500°); treatment of the partially deactivated catalysts under reducing (H2/He) atm. leads to elimination of Ru(SO4)2 that is usually formed during reaction via redn. of Ru4+ to active Ru metallic phase.
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    8. 8
      Kawi, S.; Liu, S. Y.; Shen, S.-C. Catalytic decomposition and reduction of N2O on Ru/MCM-41 catalyst. Catal. Today 2001, 68, 237– 244,  DOI: 10.1016/s0920-5861(01)00283-8
      8
      Catalytic decomposition and reduction of N2O on Ru/MCM-41 catalyst
      Kawi, S.; Liu, S. Y.; Shen, S.-C.
      Catalysis Today (2001), 68 (1-3), 237-244CODEN: CATTEA; ISSN:0920-5861. (Elsevier Science B.V.)
      Three types of Ru/MCM-41 catalysts were prepd. by impregnating MCM-41 with a surface area of 1200 m2/g and uniform mesoporous size of 27 A, with RuCl3 or Ru(OH)3 or Ru3(CO)12. The catalysts were characterized by surface area and pore size distribution. The state of Ru and its dispersion on MCM-41 surface was studied by XPS and chemisorption, resp. The conversion of N2O to N and O, by catalytic decompn. and redn. reactions, was studied using the synthesized Ru/MCM-41 catalysts. The effects of the amt. of Ru loading, the type of Ru precursor, catalyst pore size, as well as the presence of O, CO, and moisture in the feed stream on the catalyst activities for the catalytic decompn. and redn. of N2O were studied. The results show that the Ru/MCM-41 catalyst prepd. from Ru(OH)3 as the catalyst precursor and with a 5-wt.% Ru loading is promising for the catalytic decompn. and redn. of N2O.
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    9. 9
      Parres-Esclapez, S.; Illán-Gómez, M. J.; de Lecea, C. S.-M.; Bueno-López, A. On the importance of the catalyst redox properties in the N2O decomposition over alumina and ceria supported Rh, Pd and Pt. Appl. Catal., B 2010, 96, 370– 378,  DOI: 10.1016/j.apcatb.2010.02.034
      9
      On the importance of the catalyst redox properties in the N2O decomposition over alumina and ceria supported Rh, Pd and Pt
      Parres-Esclapez, S.; Illan-Gomez, M. J.; Salinas-Martinez de Lecea, C.; Bueno-Lopez, A.
      Applied Catalysis, B: Environmental (2010), 96 (3-4), 370-378CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      Rh, Pd, and Pt supported by γ-Al2O3, pure CeO2, and La- or Pr-doped CeO2 catalyst were tested for N2O decompn., and the effect of CO and O2 in the feed gas was assessed. The catalysts were characterized by Raman spectroscopy, x-ray diffraction, N2 adsorption at -196°, H2 temp.-programmed redn., and transmission electron microscopy. Catalytic activity for N2O decompn. of the noble metals was Rh > Pd > Pt; the support significantly affected activity. For the CeO2-contg. catalyst, a relationship between N2O decompn. capacity and H2 redn. of CeO2 was obsd.: the easier the redn., the higher the catalytic activity. The rate-limiting step of the N2O decompn. mechanism over noble metal/CeO2 catalysts seemed to be redn. of catalytically active sites. For Rh catalysts, CeO2 supports were actively involved in N2O decompn.; all CeO2-based supports improved the catalytic activity of Rh with regard to γ-Al2O3, due to the CeO2 redox properties. Pd catalysts with pure and doped CeO2 supports exhibited similar activity which was higher than Pd/γ-Al2O3. Pt/CeO2 was the most active catalyst among the Pt catalysts, but CeO2 doped with La or Pr had a neg. effect on activity. The most active catalyst among those synthesized in this work was Rh/CeO2(Pr).
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    10. 10
      Rutkowska, M.; Piwowarska, Z.; Micek, E.; Chmielarz, L. Hierarchical Fe-, Cu- and Co-Beta zeolites obtained by mesotemplate-free method. Part I: Synthesis and catalytic activity in N2O decomposition. Microporous Mesoporous Mater. 2015, 209, 54– 65,  DOI: 10.1016/j.micromeso.2014.10.011
      10
      Hierarchical Fe-, Cu- and Co-Beta zeolites obtained by mesotemplate-free method. Part I: Synthesis and catalytic activity in N2O decomposition
      Rutkowska, M.; Piwowarska, Z.; Micek, E.; Chmielarz, L.
      Microporous and Mesoporous Materials (2015), 209 (), 54-65CODEN: MIMMFJ; ISSN:1387-1811. (Elsevier Inc.)
      Two series of BEA zeolites (Beta and Beta/meso) have been prepd. A first series of the samples was obtained by a conventional aging of parent zeolite gel, while the second series (Beta/meso) was prepd. by mesotemplate-free method. In this method Beta nanoparticles are aggregated under acidic conditions with the formation of micro-mesoporous material. Both series (Beta and Beta/meso) were doped with Fe, Cu and Co by ion-exchange method and tested as catalysts of N2O decompn. The Cu-Beta catalyst was found to be the most active in the process of N2O decompn. conducted in inert gas atm. However, in the process performed under conditions similar to those prevailing in waste gases emitted from nitric acid plants (one of the main sources of N2O emission) higher reaction rate was found for the Cu-Beta/meso catalyst.
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    11. 11
      Jíša, K.; Novakova, J.; Schwarze, M.; Vondrova, A.; Sklenak, S.; Sobalik, Z. Role of the Fe-zeolite structure and iron state in the N2O decomposition: Comparison of Fe-FER, Fe-BEA, and Fe-MFI catalysts. J. Catal. 2009, 262, 27– 34,  DOI: 10.1016/j.jcat.2008.11.025
      11
      Role of the Fe-zeolite structure and iron state in the N2O decomposition: Comparison of Fe-FER, Fe-BEA, and Fe-MFI catalysts
      Jisa, K.; Novakova, J.; Schwarze, M.; Vondrova, A.; Sklenak, S.; Sobalik, Z.
      Journal of Catalysis (2009), 262 (1), 27-34CODEN: JCTLA5; ISSN:0021-9517. (Elsevier)
      The decompn. of nitrous oxide was compared over Fe-FER, Fe-MFI, and Fe-BEA with well established iron distribution in cationic positions and low amts. of less well-established oxide species. It was evidenced that, despite a comparable content of Fe(II) in the cationic positions, the catalytic activity of Fe-FER greatly exceeds that of Fe-BEA and Fe-MFI. While about one half of the iron sites in Fe-FER (Fe/Al < 0.15) participate in the decompn. of nitrous oxide after activation at 450 °C, the no. of active sites in Fe-BEA or Fe-MFI was much lower, and, accordingly, without acceleration of the reaction by the addn. of NO, these samples exhibit much lower catalytic activity than Fe-FER. This could be likely correlated with the concn. of Fe(II) in positions with a specific spatial iron arrangement at optimal Fe···Fe distances. For that role we propose a local structure with two adjacent β sites, where the Fe···Fe distance would be 7 to 7.5 Å, i.e. comparable to the length of the N2O mol., and provide potential for cooperation of the two iron cations on the N2O mol. splitting. Such arrangement is absent in both the Fe-BEA and Fe-MFI structures.
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    12. 12
      Pirngruber, G.; Pieterse, J. The positive effect of NO on the N2O decomposition activity of Fe-ZSM-5: A combined kinetic and in situ IR spectroscopic study. J. Catal. 2006, 237, 237– 247,  DOI: 10.1016/j.jcat.2005.11.012
      12
      The positive effect of NO on the N2O decomposition activity of Fe-ZSM-5: A combined kinetic and in situ IR spectroscopic study
      Pirngruber, Gerhard D.; Pieterse, Johannis A. Z.
      Journal of Catalysis (2006), 237 (2), 237-247CODEN: JCTLA5; ISSN:0021-9517. (Elsevier)
      NO-assisted N2O decompn. over four different Fe-ZSM-5 samples prepd. by wet ion exchange (WIE) or chem. vapor deposition (CVD) of FeCl3 was investigated by steady-state kinetics, in situ IR spectroscopy, and transient response methods. Despite their lower iron loading, the samples prepd. by WIE had the highest activity for N2O decompn. in the presence of NO. The in situ IR expts. showed that the most active sample was characterized by a high concn. of adsorbed NO, as well as adsorbed NO2 under reaction conditions. Step response expts. proved that NO2 is an intermediate of the catalytic cycle and functions as intermediate oxygen storage. IR and transient kinetic expts. showed that WIE catalysts behave qual. different in NO-assisted N2O decompn. than CVD catalysts. These differences are discussed in terms of the different structure of the iron species in the two types of samples.
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    13. 13
      Yao, X.; Tang, C.; Gao, F.; Dong, L. Research progress on the catalytic elimination of atmospheric molecular contaminants over supported metal-oxide catalysts. Catal. Sci. Technol. 2014, 4, 2814– 2829,  DOI: 10.1039/c4cy00397g
      13
      Research progress on the catalytic elimination of atmospheric molecular contaminants over supported metal-oxide catalysts
      Yao, Xiaojiang; Tang, Changjin; Gao, Fei; Dong, Lin
      Catalysis Science & Technology (2014), 4 (9), 2814-2829CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
      A review. Catalytic elimination is an important technique to reduce the emission of atm. mol. contaminants (such as CO, NOx, VOCs, HC, and PM, etc.) efficiently. In this field, the supported metal-oxide catalysts have attracted more and more attention in recent years due to their low cost and excellent catalytic performance. It is well known that catalytic performances are significantly dependent on the supports, surface-dispersed components, and the pretreatment of the catalysts. In this work, we present a brief review and propose some perspectives for supported metal-oxide catalysts according to the above-mentioned three aspects. Meanwhile, this paper covers some interesting results about the prepn. of supported metal-oxide catalysts and the improvement of their catalytic performances for the elimination of atm. mol. contaminants obtained by our research group. Moreover, we propose the concepts of "green integration prepn. (GIP)" and "surface synergetic oxygen vacancy (SSOV)" to understand the relationship between the "compn.-structure-activity" of the supported metal-oxide catalysts, and further clarify the nature of the catalytic reactions.
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    14. 14
      Konsolakis, M.; Sgourakis, M.; Carabineiro, S. A. C. Surface and redox properties of cobalt–ceria binary oxides: On the effect of Co content and pretreatment conditions. Appl. Surf. Sci. 2015, 341, 48– 54,  DOI: 10.1016/j.apsusc.2015.02.188
      14
      Surface and redox properties of cobalt-ceria binary oxides: On the effect of Co content and pretreatment conditions
      Konsolakis, Michalis; Sgourakis, Michalis; Carabineiro, Sonia A. C.
      Applied Surface Science (2015), 341 (), 48-54CODEN: ASUSEE; ISSN:0169-4332. (Elsevier B.V.)
      Ceria-based transition metal catalysts have recently received considerable attention both in heterogeneous catalysis and electro-catalysis fields, due to their unique physicochem. characteristics. Their catalytic performance is greatly affected by the surface local chem. and oxygen vacancies. The present study aims at investigating the impact of Co/Ce ratio and pretreatment conditions on the surface and redox properties of cobalt-ceria binary oxides. Co-ceria mixed oxides with different Co content (0, 20, 30, 60, 100 wt.%) were prepd. by impregnation method and characterized by means of N2 adsorption at -196 °C, X-ray diffraction (XRD), H2 temp.-programmed redn. (H2-TPR) and XPS. The results shown the improved reducibility of Co/CeO2 mixed oxides compared to single oxides, due to a synergistic interaction between cobalt and cerium. Oxidn. pretreatment results in a preferential localization of cerium species on the outer surface. In contrast, a uniform distribution of cobalt and cerium species over the entire catalyst surface is obtained by the redn. process, which facilitates the formation of oxygen vacancies though Co3+/Co2+ and Ce3+/Ce4+ redox cycles. Fundamental insights toward tuning the surface chem. of cobalt-ceria binary oxides are provided, paving the way for real-life industrial applications.
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    15. 15
      Konsolakis, M. Recent advances on nitrous oxide (N2O) decomposition over non-noble-metal oxide catalysts: Catalytic performance, mechanistic considerations, and surface chemistry aspects. ACS Catal. 2015, 5, 6397– 6421,  DOI: 10.1021/acscatal.5b01605
      15
      Recent Advances on Nitrous Oxide (N2O) Decomposition over Non-Noble-Metal Oxide Catalysts: Catalytic Performance, Mechanistic Considerations, and Surface Chemistry Aspects
      Konsolakis, Michalis
      ACS Catalysis (2015), 5 (11), 6397-6421CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      A review; nitrous oxide (N2O) is the largest stratospheric-ozone-depleting substance, being concomitantly the third most potent greenhouse gas. The direct catalytic decompn. of N2O (deN2O process) is one of the most promising remediation technologies for N2O emissions abatement. Although noble metals (NMs)-based catalysts demonstrate satisfactory deN2O performance, their high cost and sensitivity to various effluent stream components (e.g., water vapor, oxygen) limit their widespread industrial applications. Hence, the development of NMs-free catalysts of low cost and satisfactory deN2O performance is of paramount importance. This survey appraises the recent advances, which have been reported since 2000, on N2O decompn. over non-noble-metal oxidic catalysts. Initially, a brief overview of N2O sources, environmental consequences, and remediation technologies is provided. The literature related to the deN2O process over NMs-free metal oxides (MOs) is categorized and critically discussed, as follows: (i) bare oxides, (ii) hexaaluminates, (iii) hydrotalcites, (iv) spinels, (v) perovskites, and (iv) mixed metal oxides not belonging in the above categories. This review covers several aspects with respect to the reaction mechanisms, the structure-activity correlations, the role of various inhibitors (e.g., O2, NO, H2O) as well as the strategies followed to adjust the local surface structure of MOs. Fundamental insights toward fine-tuning of surface chem. of MOs by means of advanced prepn. routes and/or electronic promotion are also provided, paving the way for real-life energy and environmental applications, beyond the deN2O process.
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    16. 16
      Pasha, N.; Lingaiah, N.; Babu, N.; Reddy, P.; Prasad, P. Studies on cesium doped cobalt oxide catalysts for direct N2O decomposition in the presence of oxygen and steam. Catal. Commun. 2008, 10, 132– 136,  DOI: 10.1016/j.catcom.2008.06.006
      16
      Studies on cesium doped cobalt oxide catalysts for direct N2O decomposition in the presence of oxygen and steam
      Pasha, Nayeem; Lingaiah, N.; Babu, N. Seshu; Reddy, P. Siva Sankar; Prasad, P. S. Sai
      Catalysis Communications (2008), 10 (2), 132-136CODEN: CCAOAC; ISSN:1566-7367. (Elsevier B.V.)
      Bulk cobalt oxide and cesium promoted cobalt oxide catalysts are prepd. and characterized by different spectroscopic techniques. These catalysts are studied for direct N2O decompn. to N2 and O2. Cs addn. to Co3O4 catalysts enhanced the catalytic activity for the decompn. of N2O. The characterization results suggest that the alkali metals weakens the Co-O bond strength and promote early oxygen desorption from the catalyst surface thus leading to high activity. The effect of oxygen and/or steam in the feed stream is also studied and the reasons for low N2O decompn. in presence of water are elucidated.
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    17. 17
      Xue, L.; Zhang, C.; He, H.; Teraoka, Y. Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst. Appl. Catal., B 2007, 75, 167– 174,  DOI: 10.1016/j.apcatb.2007.04.013
      17
      Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst
      Xue, Li; Zhang, Changbin; He, Hong; Teraoka, Yasutake
      Applied Catalysis, B: Environmental (2007), 75 (3-4), 167-174CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      A series of CeO2 promoted cobalt spinel catalysts were prepd. by the co-pptn. method and tested for the decompn. of nitrous oxide (N2O). Addn. of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decompn. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400° even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The anal. results indicated that the addn. of CeO2 could increase the surface area of Co3O4, and then improve the redn. of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-detg. step of the N2O decompn. over cobalt spinel catalyst. We conclude that these effects, caused by the addn. of CeO2, are responsible for the enhancement of catalytic activity of Co3O4.
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    18. 18
      Russo, N.; Fino, D.; Saracco, G.; Specchia, V. N2O catalytic decomposition over various spinel-type oxides. Catal. Today 2007, 119, 228– 232,  DOI: 10.1016/j.cattod.2006.08.012
      18
      N2O catalytic decomposition over various spinel-type oxides
      Russo, Nunzio; Fino, Debora; Saracco, Guido; Specchia, Vito
      Catalysis Today (2007), 119 (1-4), 228-232CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)
      Various spinel-type catalysts AB2O4 (where A = Mg, Ca, Mn, Co, Ni, Cu, Cr, Fe, Zn and B = Cr, Fe, Co) were prepd. and characterized by XRD, BET, TEM and FESEM-EDS. The performance of these catalysts towards the decompn. of N2O to N and O was evaluated in a temp. programmed reaction (TPR) app. in the absence and the presence of O. Spinel-type oxides contg. Co at the B site were found to provide the best activity. The half conversion temp. of N2O over the MgCo2O4 catalyst was 440° and 470° in the absence and presence of O, resp. (GHSV =80,000/h). On the grounds of temp. programmed O desorption (TPD) analyses as well as of reactive runs, the prevalent activity of the MgCo2O4 catalyst could be explained by its higher concn. of suprafacial, weakly chemisorbed O species, whose related vacancies contribute actively to N2O catalytic decompn. This indicates the way for the development of new, more active catalysts, possibly capable of delivering at low temps. amts. of these oxygen species even higher than those characteristic of MgCo2O4.
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    19. 19
      Piskorz, W.; Zasada, F.; Stelmachowski, P.; Kotarba, A.; Sojka, Z. DFT modeling of reaction mechanism and ab initio microkinetics of catalytic N2O decomposition over alkaline earth oxides: From molecular orbital picture account to simulation of transient and stationary rate profiles. J. Phys. Chem. C 2013, 117, 18488– 18501,  DOI: 10.1021/jp405459g
      19
      DFT Modeling of Reaction Mechanism and Ab Initio Microkinetics of Catalytic N2O Decomposition over Alkaline Earth Oxides: From Molecular Orbital Picture Account to Simulation of Transient and Stationary Rate Profiles
      Piskorz, Witold; Zasada, Filip; Stelmachowski, Pawel; Kotarba, Andrzej; Sojka, Zbigniew
      Journal of Physical Chemistry C (2013), 117 (36), 18488-18501CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      A comprehensive mol. modeling of the reaction mechanism, complemented by ab initio microkinetic studies of the catalytic decompn. of N2O on a series of the alk. earth oxides (MgO, CaO, and SrO), was performed. The DFT level of theory was used to study the intimate mechanism of conceivable elementary steps of the deN2O reaction over the terrace sites of the most stable (100) planes. The principal mechanistic events were thoroughly analyzed in terms of the frontier MO picture, and a multiple role of the anionic redox active centers constituted by surface O2-(surf) ions was revealed. The harmonic transition state theory along with the calcd. free enthalpies of activation were used to model the reaction progress with the elementary step resoln. in pulse (transient) and steady state regimes. For modeling the surface diffusion and recombination of the reaction key intermediates (peroxy groups), a Monte Carlo approach was applied to rationalize dioxygen formation along the static and dynamic routes. The developed kinetic scheme was able to reproduce the results of temp.-programmed surface reaction (TPSR) and isothermal steady state expts. with high accuracy without fitting any parameters. On the basis of obtained results, a complete mol. mechanistic description of the deN2O reaction was proposed, resolving definitely the dependence of the particular elementary steps on the strength of anionic redox centers and their Lewis basicity.
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    20. 20
      Piskorz, W.; Zasada, F.; Stelmachowski, P.; Kotarba, A.; Sojka, Z. Decomposition of N2O over the surface of cobalt spinel: A DFT account of reactivity experiments. Catal. Today 2008, 137, 418– 422,  DOI: 10.1016/j.cattod.2008.02.027
      20
      Decomposition of N2O over the surface of cobalt spinel: A DFT account of reactivity experiments
      Piskorz, Witold; Zasada, Filip; Stelmachowski, Pawel; Kotarba, Andrzej; Sojka, Zbigniew
      Catalysis Today (2008), 137 (2-4), 418-422CODEN: CATTEA; ISSN:0920-5861. (Elsevier B.V.)
      The DFT mol. modeling of N2O decompn. over cobalt spinel (1 0 0) plane was performed using a cluster approach, and applied to rationalize the exptl. reactivity data. The energetics of the postulated elementary steps such as N2O adsorption, N2O activation through dissociative electron or oxygen atom transfer, surface diffusion of resultant oxygen intermediates, and their recombination into O2, was evaluated and discussed. The geometry and electronic structure of the implicated active sites and intermediates were detd. Three different transition states were found for the activation of nitrous oxide mol. In the preferred electron transfer mechanism, involving a monodentate transition state, the N2O activation and the formation of dioxygen are energetically the most demanding steps, whereas the barrier for the oxygen surface diffusion was found to be distinctly smaller. For the oxygen atom transfer the reaction is energetically constraint by the N-O bond-breaking step. The inhibiting effect of co-adsorbed water and oxygen on the particular reaction steps was briefly addressed.
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    21. 21
      Zhou, H.; Huang, Z.; Sun, C.; Qin, F.; Xiong, D.; Shen, W.; Xu, H. Catalytic decomposition of N2O over CuxCe1–xOy mixed oxides. Appl. Catal., B 2012, 125, 492– 498,  DOI: 10.1016/j.apcatb.2012.06.021
      21
      Catalytic decomposition of N2O over CuxCe1-xOy mixed oxides
      Zhou, Haibo; Huang, Zhen; Sun, Chao; Qin, Feng; Xiong, Desheng; Shen, Wei; Xu, Hualong
      Applied Catalysis, B: Environmental (2012), 125 (), 492-498CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      The catalytic N2O decompn. was investigated over a series of CuxCe1-xOy mixed oxides with different Cu/Ce molar ratios. Effects of synergy over mixed oxides of CeO2 and CuO were obsd. significantly, the catalyst of Cu0.67Ce0.33Oy exhibited the high activity among the Cu-Ce-O mixed oxides for N2O decompn. Characterizations of XRD, N2 adsorption, XPS, and H2-TPR were applied to correlate their properties with the corresponding catalytic performance, and reveal the synergetic effect between CuO and CeO2 for N2O decompn. In situ DRIFTS investigation confirmed the presence of CuI species that was closely related with the activity of CuxCe1-xOy catalyst. The synergy of CuxCe1-xOy promoted the stability and the ability to regenerate the active CuI site.
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    22. 22
      Zabilskiy, M.; Djinović, P.; Tchernychova, E.; Tkachenko, O. P.; Kustov, L. M.; Pintar, A. Nanoshaped CuO/CeO2 materials: Effect of the exposed ceria surfaces on catalytic activity in N2O decomposition reaction. ACS Catal. 2015, 5, 5357– 5365,  DOI: 10.1021/acscatal.5b01044
      22
      Nanoshaped CuO/CeO2 Materials: Effect of the Exposed Ceria Surfaces on Catalytic Activity in N2O Decomposition Reaction
      Zabilskiy, Maxim; Djinovic, Petar; Tchernychova, Elena; Tkachenko, Olga P.; Kustov, Leonid M.; Pintar, Albin
      ACS Catalysis (2015), 5 (9), 5357-5365CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)
      This study reports a thorough investigation of nanosized CuO/CeO2 materials as an efficient catalyst for decompn. of N2O, which is a strong greenhouse gas largely produced by chem. industry. Effect of terminating CeO2 cryst. planes ({100}, {110}, and {111}) on the behavior of CuO dispersed over CeO2 nanocubes, nanorods and polyhedral crystallites was examd. in detail by using a variety of catalyst characterization techniques. The 4 wt % Cu was found as the most advantageous metal loading, whereas higher Cu content resulted in lower dispersion and formation of significantly less active, segregated bulk CuO phase. It was discovered that CuO/CeO2 solids should enable both excessive oxygen mobility on the catalyst surface as well as formation of highly reducible Cu defect sites, in order to ensure high intrinsic activity. Detailed studies further revealed that CeO2 morphol. needs to be tailored to expose {100} and {110} high-energy surface planes, as present in CeO2 nanorods. Oxygen mobility and regeneration of active Cu phase on these surface planes is easier, which in turn facilitates higher catalytic activity through the recombination of surface oxygen atoms and desorption as mol. oxygen that replenishes active sites for subsequent catalytic cycles. As a consequence, CuO supported on CeO2 nanorods demonstrated lower activation energy (87 kJ/mol) in N2O decompn. reaction compared to catalysts based on CeO2 nanocubes (102 kJ/mol) or polyhedral CeO2 (92 kJ/mol).
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    23. 23
      Kapteijn, F.; Marbán, G.; Rodriguez-Mirasol, J.; Moulijn, J. A. Kinetic Analysis of the Decomposition of Nitrous Oxide over ZSM-5 Catalysts. J. Catal. 1997, 167, 256– 265,  DOI: 10.1006/jcat.1997.1581
      23
      Kinetic analysis of the decomposition of nitrous oxide over ZSM-5 catalysts
      Kapteijn, Freek; Marban, Gregorio; Rodriguez-Mirasol, Jose; Moulijn, Jacob A.
      Journal of Catalysis (1997), 167 (1), 256-265CODEN: JCTLA5; ISSN:0021-9517. (Academic)
      A detailed comparative kinetic anal. has been made of the N2O decompn. over Co-, Fe-, and CuZSM-5. The effect of partial pressure of N2O, O2, CO, and NO, the space time, and temp. have been investigated. The decompn. is first order in N2O over Fe- and CoZSM-5 and has a slightly lower order over the Cu sample. Inhibition of oxygen obsd. for CuZSM-5 is absent for Co and for Fe at the lower temps. N2O destruction is enhanced by CO for all catalysts and by NO for FeZSM-5 only. In the presence of NO, NO2 is produced over Fe- and CoZSM-5. Over CuZSM-5 the enhancement by CO passes through a max. as a function of CO pressure due to the strong adsorption at reduced sites. A detailed kinetic model that accounts quant. for the obsd. dependencies and which deviates from the classical model for oxidic systems is advanced. Ests. of the max. turnover rates for the various model steps range from 10-4 to L s-1.
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    24. 24
      Obalová, L.; Fíla, V. Kinetic analysis of N2O decomposition over calcined hydrotalcites. Appl. Catal., B 2007, 70, 353– 359,  DOI: 10.1016/j.apcatb.2005.11.031
      24
      Kinetic analysis of N2O decomposition over calcined hydrotalcites
      Obalova, L.; Fila, V.
      Applied Catalysis, B: Environmental (2007), 70 (1-4), 353-359CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      The kinetics of N2O decompn. over a catalyst prepd. by calcination of Co-Mn hydrotalcite was examd. in an integral fixed-bed reactor (V (total vol. flow)/w (catalyst mass) = 12-96 L/gcat-h) at various N2O and O2 initial partial pressures at a temp. range of 330-450°. Kinetic data were evaluated by linear and nonlinear regression methods, and 15 kinetic expressions were tested. Based on the obtained results, a redox model of N2O decompn. was proposed. At low pressures of O2, adsorbed oxygen is formed by the N2O decompn.; the N2O chemisorption is considered as the rate-detg. step. On the contrary, at high O2 pressure it could be assumed that adsorbed oxygen species appear as a result of O2 adsorption and the Eley-Rideal mechanism is the rate-detg. step. N2O decompn. is well described by the 1st rate law at N2O and O2 concns. typical for waste gases.
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    25. 25
      Liu, X.; Qiu, G.; Li, X. Shape-controlled synthesis and properties of uniform spinel cobalt oxide nanocubes. Nanotechnology 2005, 16, 3035– 3040,  DOI: 10.1088/0957-4484/16/12/051
      25
      Shape-controlled synthesis and properties of uniform spinel cobalt oxide nanocubes
      Liu, Xiaohe; Qiu, Guanzhou; Li, Xingguo
      Nanotechnology (2005), 16 (12), 3035-3040CODEN: NNOTER; ISSN:0957-4484. (Institute of Physics Publishing)
      Inorg. nanoparticles with controlled size and shape seem esp. technol. important due to the strong correlation between these parameters and their magnetic, elec., and catalytic properties. Herein uniform spinel Co oxide (Co3O4) nanocubes can be successfully synthesized on a large scale via a facile hydrothermal synthetic route under mild conditions. The size and shape of final products can be readily tuned in a wide range by tuning process parameters such as hydrothermal time, reaction temp., surfactant, concn., and molar ratios of starting material.
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    26. 26
      Shojaee, K.; Montoya, A.; Haynes, B. S. Insight into oxygen stability and vacancy formation on Co3O4 model slabs. Comput. Mater. Sci. 2013, 72, 15– 25,  DOI: 10.1016/j.commatsci.2013.02.001
      26
      Insight into oxygen stability and vacancy formation on Co3O4 model slabs
      Shojaee, Kambiz; Montoya, Alejandro; Haynes, Brian S.
      Computational Materials Science (2013), 72 (), 15-25CODEN: CMMSEM; ISSN:0927-0256. (Elsevier B.V.)
      Spin-polarised periodic d. functional simulations were used to study the stability of oxygen on Co3O4 slab models with (1 0 0) and (1 1 0) terminations in order to understand better the oxidative properties of Co3O4. We obsd. that the PBE + U method gives binding energies and geometrical parameters similar to those obtained for at. oxygen adsorption at low coverage using the revised version of screened hybrid exchange functional HSE06. Atomic oxygen is most stably bound on a Co3O4(1 1 0)-terminated surface where the oxygen adatom binds above the bridge sites of cobalt atoms with a binding energy of 401 kJ mol-1. On-surface O recombination to O2 leaving a bare slab from the Co3O4(1 1 0) terminations is 116-123 kJ mol-1 more activated than recombination of O on (1 0 0) surfaces. Removal of surface lattice oxygen by an on-surface oxygen producing O2 and leaving a slab with an O vacancy site is at least 65 kJ mol-1 more activated in the (1 1 0) surface than in the (1 0 0) surface.
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    27. 27
      Maimaiti, Y.; Nolan, M.; Elliott, S. D. Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption. Phys. Chem. Chem. Phys. 2014, 16, 3036– 3046,  DOI: 10.1039/c3cp53991a
      27
      Reduction mechanisms of the CuO(111) surface through surface oxygen vacancy formation and hydrogen adsorption
      Maimaiti, Yasheng; Nolan, Michael; Elliott, Simon D.
      Physical Chemistry Chemical Physics (2014), 16 (7), 3036-3046CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      We studied the redn. of CuO(111) surface using d. functional theory (DFT) with the generalized gradient approxn. cor. for on-site Coulomb interactions (GGA + U) and screened hybrid DFT (HSE06 functional). The surface redn. process by oxygen vacancy formation and H2 adsorption on the CuO(111) surface is investigated as two different redn. mechanisms. It is found that both GGA + U and HSE06 predict the same trend in the relative stability of oxygen vacancies. We found that loss of the subsurface oxygen is initially thermodynamically favorable. As the oxygen vacancy concn. increases, mixt. of subsurface and surface vacancies is energetically preferred over full redn. of the surface or subsurface monolayer. The redn. of Cu2+ to Cu+ is found to be more favorable than that of Cu+ to Cu0 in the most stable vacancy structures at all concns. Consistent with the oxygen vacancy calcns., H2 adsorption occurs initially on under-coordinated surface oxygen. Water mols. are formed upon the adsorption of H2 and this gives a mechanism for H2 redn. of CuO to Cu. Ab initio atomistic thermodn. shows that reducing CuO to metallic Cu at the surface is more energetically difficult than in the bulk so that the surface oxide protects the bulk from redn. Using H2 as the reducing agent, it is found that the CuO surface is reduced to Cu2O at approx. 360 K and that complete redn. from Cu2O to metallic Cu occurs at 780 K.
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    28. 28
      Yang, B.-X.; Ye, L.-P.; Gu, H.-J.; Huang, J.-H.; Li, H.-Y.; Luo, Y. A density functional theory study of CO oxidation on CuO1-x(111). J. Mol. Model. 2015, 21, 195,  DOI: 10.1007/s00894-015-2726-x
      28
      A density functional theory study of CO oxidation on CuO1-x(111)
      Yang Bing-Xing; Ye Li-Ping; Gu Hui-Jie; Huang Jin-Hua; Li Hui-Ying; Luo Yong
      Journal of molecular modeling (2015), 21 (8), 195 ISSN:.
      The surface structures, CO adsorption, and oxidation-reaction properties of CuO1-x(111) with different reduction degree have been investigated by using density functional theory including on-site Coulomb corrections (DFT + U). Results indicate that the reduction of Cu has a great influence on the adsorption of CO. Electron localization caused by the reduction turns Cu(2+) to Cu(+), which interacts much stronger with CO, and the adsorption strength of CO is related to the electronic interaction with the substrate as well as the structural relaxation. In particular, the electronic interaction is proved to be the decisive factor. The surfaces of CuO1-x(111) with different reduction degree all have good adsorption to CO. With the expansion of the surface reduction degree, the amount of CO that is stably adsorbed on the surface increases, while the number of surface active lattice O decreases. In general, the activity of CO oxidation first rises and then declines.
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    29. 29
      Zasada, F.; Piskorz, W.; Sojka, Z. Cobalt spinel at various redox conditions: DFT+U investigations into the structure and surface thermodynamics of the (100) facet. J. Phys. Chem. C 2015, 119, 19180– 19191,  DOI: 10.1021/acs.jpcc.5b05136
      29
      Cobalt Spinel at Various Redox Conditions: DFT+U Investigations into the Structure and Surface Thermodynamics of the (100) Facet
      Zasada, Filip; Piskorz, Witold; Sojka, Zbigniew
      Journal of Physical Chemistry C (2015), 119 (33), 19180-19191CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Periodic spin unrestricted DFT-PW91 + U calcns. together with ab initio thermodn. modeling were used to study the structure, defects, and stability of different terminations of the (100) surface of cobalt spinel under various redox conditions imposed by different oxygen partial pressure and temp. Three terminations contg. under-stoichiometric (100)-O, stoichiometric (100)-S, and overstoichiometric (100)-R amt. of cobalt ions were analyzed, and their at. and defect structure, reconstruction, and stability were elucidated. For the most stable (100)-S and (100)-O facets, formation of cationic and anionic vacancies was examd., and a surface redox state diagram of possible spinel (100) terminations in the stoichiometry range from Co2.75O4 to Co3O3.75 was constructed and discussed in detail. The results revealed that the bare (100)-S surface is the most stable at temps. and pressures of typical catalytic processes (T ∼ 200 °C to ∼500 °C, pO2/p° ∼ 0.001 to ∼1). In more reducing conditions (T > 600 °C and pO2/p° < 0.0001), the (100)-S facet is readily reduced by formation of oxygen vacancies, whereas in the oxidizing conditions (T < 200 °C and pO2/p° > 10), coexistence of (100)-S and (100)-O terminations was revealed. Formation of the oxygen vacancies involves redn. of the octahedral trivalent cobalt and is accompanied by migration of the divalent tetrahedral cobalt into empty, interstitial octahedral positions. It was also found that the constituent octahedral Co cation proximal to the interstitial cobalt adopts a low spin configuration in contrast to the distal one that preserves its surface high spin state. In the case of the Co depleted surfaces, the octahedral vacancies are thermodynamically disfavored with respect to the tetrahedral ones in the whole range of the examd. T and pO2 values. The obtained theor. results, supported by TPD-O2 and TG expts., show that the octahedral cobalt ions are directly involved in the redox processes of Co3O4.
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    30. 30
      Xiong, S.; Xiao, X.; Liao, Y.; Dang, H.; Shan, W.; Yang, S. Global kinetic study of NO reduction by NH3 over V2O5-WO3/TiO2: Relationship between the SCR performance and the key factors. Ind. Eng. Chem. Res. 2015, 54, 11011– 11023,  DOI: 10.1021/acs.iecr.5b03044
      30
      Global Kinetic Study of NO Reduction by NH3 over V2O5-WO3/TiO2: Relationship between the SCR Performance and the Key Factors
      Xiong, Shangchao; Xiao, Xin; Liao, Yong; Dang, Hao; Shan, Wenpo; Yang, Shijian
      Industrial & Engineering Chemistry Research (2015), 54 (44), 11011-11023CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
      The nonselective catalytic redn. (NSCR) reaction and the catalytic oxidn. of NH3 to NO (C-O reaction) simultaneously happened during the selective catalytic redn. (SCR) of NO with NH3 over V2O5-WO3/TiO2, esp. at higher temps. There was an excellent linear relationship between the SCR reaction rate and gaseous NO concn., and the intercept and slope can be used to describe the rate const. of NO redn. through the Langmuir-Hinshelwood mechanism and that through the Eley-Rideal mechanism, resp. However, the NSCR reaction rate was nearly independent of gaseous NO concn., and the reaction order of the C-O reaction with respect to gaseous NO concn. was much less than zero. According to the kinetic study, the relationship of the SCR performance (i.e., SCR activity and N2 selectivity) with the key factors (for example V2O5 content, H2O effect, and reactant concn.) was built, which can be used to predict the SCR performance.
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    31. 31
      Xiong, S.; Weng, J.; Liao, Y.; Li, B.; Zou, S.; Geng, Y.; Xiao, X.; Huang, N.; Yang, S. Alkali metal deactivation on the low temperature selective catalytic reduction of NOx with NH3 over MnOx-CeO2: A mechanism study. J. Phys. Chem. C 2016, 120, 15299– 15309,  DOI: 10.1021/acs.jpcc.6b05175
      31
      Alkali Metal Deactivation on the Low Temperature Selective Catalytic Reduction of NOx with NH3 over MnOx-CeO2: A Mechanism Study
      Xiong, Shangchao; Weng, Jingxia; Liao, Yong; Li, Bo; Zou, Sijie; Geng, Yang; Xiao, Xin; Huang, Nan; Yang, Shijian
      Journal of Physical Chemistry C (2016), 120 (28), 15299-15309CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Use of MnOx-CeO2 as a low temp. selective redn. (SCR) catalyst to control NOx emissions from coal-fired power generating facilities is extremely restricted due to unrecoverable deactivation by SO2. There is little SO2 in biomass-fired power generating facility flue gas, and alkali metals concns. in flue gas following electrostatic pptn. is very low, so the use of MnOx-CeO2 may be possible to control NOx emissions from biomass-fired power generating facilities. However, a very small amt. of alkali metals exhibited a seriously neg. effect on NO redn. over MnOx-CeO2; NOx conversion and N2 selectivity was obviously decreased. This work assessed the NO redn. mechanism over MnOx-CeO2 and K-MnOx-CeO2 in a transient reaction study; NO redn. kinetic parameters were obtained from the steady-state kinetic study. After comparing kinetic parameters, the mechanism of K deactivation on NO redn. over MnOx-CeO2 was discovered. The decreased SCR activity of MnOx-CeO2 after K deactivation was mainly attributed to the decrease of acid sites and Mn4+ concns. on the catalyst surface; the increase of N2O selectivity was mainly related to the occurrence of N2O formation over K-MnOx-CeO2 through the Langmuir-Hinshelwood mechanism.
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    32. 32
      Wang, D.; Peng, Y.; Xiong, S.-c.; Li, B.; Gan, L.-n.; Lu, C.-m.; Chen, J.-j.; Ma, Y.-l.; Li, J.-h. De-reducibility mechanism of titanium on maghemite catalysts for the SCR reaction: An in situ DRIFTS and quantitative kinetics study. Appl. Catal., B 2018, 221, 556– 564,  DOI: 10.1016/j.apcatb.2017.09.045
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      De-reducibility mechanism of titanium on maghemite catalysts for the SCR reaction: An in situ DRIFTS and quantitative kinetics study
      Wang, Dong; Peng, Yue; Xiong, Shang-chao; Li, Bing; Gan, Li-na; Lu, Chun-mei; Chen, Jian-jun; Ma, Yong-liang; Li, Jun-hua
      Applied Catalysis, B: Environmental (2018), 221 (), 556-564CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      An environmentally benign TiO2-doped maghemite catalyst, γ-Fe95Ti5, was prepd. by pptn. microwave pyrolysis and used to remove NOx. The γ-Fe95Ti5 catalyst exhibited significantly higher activity and better N2 selectivity than pure maghemite, γ-Fe100Ti0. The catalyst selective catalytic redn. (SCR) active window was broadened and water and SO2 resistances were preserved. Ti4+ cations could enter the γ-Fe100Ti0 lattice, forming a partial solid soln. on the catalyst surface, as γ-Fe2-ζTiζO3+ξ. This structure improved the quantity and stability of Lewis and Bronsted acid sites vs. γ-Fe100Ti0. Dopant cations suppressed Fe3+ redn. and the percent of active O on the catalyst surface. These could suppress N2O formation from NH3 oxidn. and NOx redn. By combining diffuse reflectance Fourier transform IR spectroscopy and kinetic methods, the γ-Fe95Ti5 catalyst rate consts. by the Eley-Rideal and Langmuir-Hinshelwood mechanisms increased simultaneously; the rate const. for catalytic oxidn. of NH3 decreased vs. γ-Fe100Ti0.
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    33. 33
      Pérez-Ramírez, J.; Kapteijn, F.; Schöffel, K.; Moulijn, J. A. Formation and control of N2O in nitric acid production. Appl. Catal., B 2003, 44, 117– 151,  DOI: 10.1016/s0926-3373(03)00026-2
      33
      Formation and control of N2O in nitric acid production. Where do we stand today?
      Perez-Ramirez, J.; Kapteijn, F.; Schoffel, K.; Moulijn, J. A.
      Applied Catalysis, B: Environmental (2003), 44 (2), 117-151CODEN: ACBEE3; ISSN:0926-3373. (Elsevier Science B.V.)
      A review. Nitric acid prodn. represents the largest source of N2O in the chem. industry, with a global annual emission of 400 kt N2O. The high impact of N2O on the environment as greenhouse gas and stratospheric ozone depletor, and the ongoing agreements and prospective regulations calls for the development of efficient and economical systems for N2O mitigation, but no mature com. technol. is yet available. In this review, the current state-of-the-art for N2O control in the nitric acid manuf. is presented. The formation of N2O and the process are analyzed and several options for reducing its emissions are discussed, depending on the position in the process. Primary abatement options deals with modifications in the ammonia oxidn. catalyst, secondary abatement with options between the ammonia converter and the absorber, tertiary abatement with options in the tail-gas upstream of the expander, and quaternary abatement with options in the tail-gas downstream of the expander. The abatement technologies are evaluated based on the tech. advantages and disadvantages, and cost efficiency.
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    34. 34
      Zabilskiy, M.; Djinović, P.; Tchernychova, E.; Pintar, A. N2O decomposition over CuO/CeO2 catalyst: New insights into reaction mechanism and inhibiting action of H2O and NO by operando techniques. Appl. Catal., B 2016, 197, 146– 158,  DOI: 10.1016/j.apcatb.2016.02.024
      34
      N2O decomposition over CuO/CeO2 catalyst: New insights into reaction mechanism and inhibiting action of H2O and NO by operando techniques
      Zabilskiy, Maxim; Djinovic, Petar; Tchernychova, Elena; Pintar, Albin
      Applied Catalysis, B: Environmental (2016), 197 (), 146-158CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      In this work, a combination of ex situ (STEM-EELS, STEM-EDX, H2-TPR and XPS), in situ (CO-DRIFTS) and operando (DR UV-vis and DRIFTS) approaches was used to probe the active sites and det. the mechanism of N2O decompn. over highly active 4 wt.% Cu/CeO2 catalyst. In addn., reaction pathways of catalyst deactivation in the presence of NO and H2O were identified. The results of operando DR UV-vis spectroscopic tests suggest that [Cu-O-Cu]2+ sites play a crucial role in catalytic N2O decompn. pathway. Due to exposure of {1 0 0} and {1 1 0} high-energy surface planes, nanorod-shaped CeO2 support simultaneously exhibits enhancement of CuO/CeO2 redox properties through the presence of Ce3+/Ce4+ redox pair. Its dominant role of binuclear Cu+ site regeneration through the recombination and desorption of mol. oxygen is accompanied by its minor active participation in direct N2O decompn. NO and H2O have completely different inhibiting action on the N2O decompn. reaction. Water mols. strongly and dissociatively bind to oxygen vacancy sites of CeO2 and block further oxygen transfer as well as regeneration of catalyst active sites. On the other hand, the effect of NO is expressed through competitive oxidn. to NO2, which consumes labile oxygen from CeO2 and decelerates [Cu+ Cu+] active site regeneration.
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    35. 35
      Pasha, N.; Lingaiah, N.; Siva Sankar Reddy, P.; Sai Prasad, P. S. An investigation into the effect of Cs promotion on the catalytic activity of NiO in the direct decomposition of N2O. Catal. Lett. 2007, 118, 64– 68,  DOI: 10.1007/s10562-007-9146-1
      35
      An investigation into the effect of Cs promotion on the catalytic activity of NiO in the direct decomposition of N2O
      Pasha, Nayeem; Lingaiah, N.; Reddy, P. Siva Sankar; Prasad, P. S. Sai
      Catalysis Letters (2007), 118 (1-2), 64-68CODEN: CALEER; ISSN:1011-372X. (Springer)
      A series of Cs promoted NiO catalysts have been prepd. and tested for direct decompn. of N2O. These catalysts are characterized by BET surface area, X-ray diffraction (XRD), temp. programmed redn. (TPR), temp. programmed desorption of N2O (TPD-N2O) and X-ray photo electron spectroscopy (XPS). The Cs promoted NiO catalysts exhibit higher activity for the decompn. of N2O compared to bulk NiO. The catalyst with Cs/Ni ratio of 0.1 showed highest activity. The enhancement in catalytic activity of the Cs promoted catalysts is attributed to the change in the electronic properties of NiO. The characterization techniques suggest weakening of Ni-O bond thereby the desorption of oxygen becomes more facile during the reaction. The Cs promoted NiO catalyst is effective at low reaction temp. and also in the presence of oxygen and steam in the feed stream.
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    36. 36
      Perezalonso, F.; Meliancabrera, I.; Lopezgranados, M.; Kapteijn, F.; Fierro, J. Synergy of FexCe1–xO2 mixed oxides for N2O decomposition. J. Catal. 2006, 239, 340– 346,  DOI: 10.1016/j.jcat.2006.02.008
      There is no corresponding record for this reference.
    37. 37
      Bloemen, P. J. H.; van de Vorst, M. T. H.; Johnson, M. T.; Coehoorn, R.; de Jonge, W. J. M. Magnetic layer thickness dependence of the interlayer exchange coupling in (001) Co/Cu/Co. J. Appl. Phys. 1994, 76, 7081– 7083,  DOI: 10.1063/1.358034
      37
      Magnetic layer thickness dependence of the interlayer exchange coupling in (001) Co/Cu/Co
      Bloemen, P. J. H.; van de Vorst, M. T. H.; Johnson, M. T.; Coehoorn, R.; de Jonge, W. J. M.
      Journal of Applied Physics (1994), 76 (10, Pt. 2), 7081-3CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
      A dependence of the strength of the antiferromagnetic coupling across Cu on the Co layer thickness was obsd. The Co thickness dependence displays two clear peaks consistent with the recently predicted oscillation period of 6.2 Å Co. Apart from the two peaks also several small peaks are visible on a scale of ∼1 monolayer Co. Free-electron calcns. indicate that these rapid variations in strength may result from slight differences between the slopes and starting points of the two Co wedges that were involved in the expt.
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    38. 38
      Konsolakis, M.; Carabineiro, S. A. C.; Papista, E.; Marnellos, G. E.; Tavares, P. B.; Moreira, J. A.; Romaguera-Barcelay, Y.; Figueiredo, J. L. Effect of preparation method on the solid state properties and the deN2O performance of CuO–CeO2 oxides. Catal. Sci. Technol. 2015, 5, 3714– 3727,  DOI: 10.1039/c5cy00343a
      38
      Effect of preparation method on the solid state properties and the deN2O performance of CuO-CeO2 oxides
      Konsolakis, M.; Carabineiro, S. A. C.; Papista, E.; Marnellos, G. E.; Tavares, P. B.; Moreira, J. Agostinho; Romaguera-Barcelay, Y.; Figueiredo, J. L.
      Catalysis Science & Technology (2015), 5 (7), 3714-3727CODEN: CSTAGD; ISSN:2044-4753. (Royal Society of Chemistry)
      The present work aims at investigating the catalytic decompn. of N2O over CuO-CeO2 single or mixed oxides prepd. by different synthesis routes, i.e., impregnation, pptn. and exotemplating. To gain insight into the particular role of CeO2 as well as of CuO-CeO2 interactions, three different types of materials were prepd. and tested for N2O decompn. both in the absence and presence of excess O2: (i) bare CeO2 prepd. by pptn. and exotemplating, (ii) CuO/CeO2 oxides synthesized by the impregnation of CeO2 samples prepd. in (i) with CuO, and iii) single stage CuO-CeO2 mixed oxides synthesized employing the co-pptn. and exotemplating methods. The corresponding com. samples were also examd. for comparison purposes. All materials were characterized by N2 adsorption at -196 °C, X-ray diffraction (XRD), H2 temp.-programmed redn. (H2-TPR), XPS, micro-Raman spectroscopy (micro-Raman) and SEM. The results demonstrated the key role of the prepn. procedure on the direct catalytic decompn. of N2O. Among the bare CeO2 samples, the best performance was obtained with the samples prepd. by the pptn. method, followed by exotemplating, while com. CeO2 showed the lowest performance. All bare oxides demonstrated low N2O conversion, never exceeding 40% at 600 °C. Amongst the CuO-CeO2 oxides, the optimum performance was obsd. for those prepd. by co-pptn., which achieved complete N2O conversion at 550 °C. In the presence of excess oxygen in the feed stream, a slight degrdn. is obsd., with the sequence of deN2O performance remaining unchanged. The superiority of the Cu-Ce mixed oxides prepd. by pptn. compared to all of the other materials can be mainly ascribed to their excellent redox properties, linked to Ce4+/Ce3+ and Cu2+/Cu+ redox pairs. A redox mechanism for the N2O catalytic decompn. is proposed, involving N2O adsorption on Cu+ sites and their regeneration through Cu-ceria interactions.
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    39. 39
      Svintsitskiy, D. A.; Kardash, T. Y.; Stonkus, O. A.; Slavinskaya, E. M.; Stadnichenko, A. I.; Koscheev, S. V.; Chupakhin, A. P.; Boronin, A. I. In situ XRD, XPS, TEM, and TPR study of highly active in CO oxidation CuO nanopowders. J. Phys. Chem. C 2013, 117, 14588– 14599,  DOI: 10.1021/jp403339r
      39
      In Situ XRD, XPS, TEM, and TPR Study of Highly Active in CO Oxidation CuO Nanopowders
      Svintsitskiy, Dmitry A.; Kardash, Tatyana Yu.; Stonkus, Olga A.; Slavinskaya, Elena M.; Stadnichenko, Andrey I.; Koscheev, Sergei V.; Chupakhin, Alexei P.; Boronin, Andrei I.
      Journal of Physical Chemistry C (2013), 117 (28), 14588-14599CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Copper(II) oxide nanopowders exhibit a high catalytic activity in CO oxidn. at low temps. The combination of in situ XPS, XRD, and HRTEM methods was applied to investigate initial steps of CuO nanoparticles redn., to identify oxygen and copper species and to revealed structural features in the dependence on reducing power of reaction medium. At the oxygen deficient surface of CuO nanopowders the metastable Cu4O3 oxide was formed under the mild reducing conditions -10-5 mbar CO or CO + O2 mixt. with oxygen excess. Destruction of Cu4O3 structures in strong reducing medium (P(CO) ≥ 10-2 mbar) or under UHV conditions resulted in the formation of Cu2O which was epitaxially bounded with initial CuO particle. The reversible bulk redn. of CuO nanopowder to Cu2O at temps. ∼150 °C can be explained by effortless propagation of Cu2O‖CuO epitaxial front inside the nanoparticle. The model of the surface restructuring along the {-111}CuO → {202}Cu4O3 → {111}Cu2O planes under the redn. of CuO nanopowders is proposed. The initial surface of CuO nanopowders is probably distorted and resembles Cu4O3-like structures that facilitates the CuOx ↔ Cu4O3 transition in mild reducing conditions. Such restructuring results in a unique electronic Cu4O3 structure with high oxygen deficiency and low-valence Cu1+ sites stimulating the formation of highly reactive CO and O2 adsorbed species. It was shown that the most active oxygen species on the surface of CuOx is stabilized as O-, which was previously reported in papers by Roberts and Madix in their study of the copper-oxygen systems.
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    40. 40
      Timmermans, B.; Reniers, F.; Hubin, A.; Buess-Herman, C. Chemical effects in the Auger spectrum of copper-oxygen compounds. Appl. Surf. Sci. 1999, 144–145, 54– 58,  DOI: 10.1016/s0169-4332(98)00764-8
      40
      Chemical effects in the Auger spectrum of copper-oxygen compounds
      Timmermans, B.; Reniers, F.; Hubin, A.; Buess-Herman, C.
      Applied Surface Science (1999), 144-145 (), 54-58CODEN: ASUSEE; ISSN:0169-4332. (Elsevier Science B.V.)
      AES and XPS are 2 powerful techniques for the detn. of the compn. of a surface. The nature of the chem. binding of an element is usually studied by XPS. However, the Auger peaks also contain theor. information about the chem. environment of the elements. As mostly one or 2 valence levels are involved in the emission of the Auger electron, a careful anal. of the Auger lines should allow to reveal the changes in the electron densities in the electronic levels due to a change in the chem. environment. However, for metals (with a high no. of electrons) the chem. effects are mostly weak, hidden or hard to interpret. To try to understand better the nature of the chem. effects in AES of metals, a systematic study of well-defined Cu compds. is performed. Cu, CuO, Cu2O, CuCO3 and Cu acetate std. samples were prepd. and characterized. The Cu LMM lines were analyzed. The energy shifts, change in relative intensities and change in FWHM were studied as a function of increasing O environment. The energy shift and the relative intensities of the Auger peak are good fingerprints of the oxidn. state, and the width of the Cu L3M4.5M4.5 peak can be related to the width of the valence band.
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    41. 41
      Fierro, G.; Lo Jacono, M.; Inversi, M.; Dragone, R.; Porta, P. TPR and XPS study of cobalt-copper mixed oxide catalysts: evidence of a strong Co-Cu interaction. Top. Catal. 2000, 10, 39– 48,  DOI: 10.1023/a:1019151731177
      41
      TPR and XPS study of cobalt-copper mixed oxide catalysts: evidence of a strong Co-Cu interaction
      Fierro, G.; Lo Jacono, M.; Inversi, M.; Dragone, R.; Porta, P.
      Topics in Catalysis (2000), 10 (1,2), 39-48CODEN: TOCAFI; ISSN:1022-5528. (Baltzer Science Publishers)
      In this work the results of TPR and XPS investigation of CoxOy-CuO mixed oxides in the range of compn. Co:Cu = 100:0-8:92 are reported and compared. The final catalysts were obtained by thermal decompn. in air and N2 at 723 K for 24 h of single-phase cobalt-copper hydroxycarbonates prepd. by copptn. at const. pH. The Co:Cu = 100:0 specimen calcined in air formed the Co2+[Co3+]2O4 (Co3O4) spinel phase. The copper-contg. catalysts (Co:Cu = 85:15-8:92) showed mainly two phases: (i) spinels, like Co2+[Co3+]2O4, Co1-x2+Cux2+[Co3+]2O4 and (ii) pure CuO, the relative amt. of each phase depending on the Co:Cu at. ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co2+, Co3+ and Cu2+ species at the catalyst surface. Moreover, the surface quant. anal. evidenced a cobalt enrichment, in particular for the most dild. cobalt samples. The TPR study showed that the catalyst redn. is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co3O4 and CuO phases and the redn. of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst compn. On the other hand, the Co:Cu = 100:0 specimen calcined in N2 formed, as expected, CoO. The initial addn. of copper resulted in the formation of the Cu+Co3+O2 compd., besides CoO, up to a Co/Cu = 1 at. ratio at which the CuCoO2 phase was the main component. A further addn. of copper led to the formation of CuCoO2 and CuO phases. The XPS results were in good agreement with these findings and the surface quant. anal. revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR anal. confirmed that the redn. of the N2-calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of redn.
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    42. 42
      Grzybek, G.; Stelmachowski, P.; Gudyka, S.; Indyka, P.; Sojka, Z.; Guillén-Hurtado, N.; Rico-Pérez, V.; Bueno-López, A.; Kotarba, A. Strong dispersion effect of cobalt spinel active phase spread over ceria for catalytic N2O decomposition: The role of the interface periphery. Appl. Catal., B 2016, 180, 622– 629,  DOI: 10.1016/j.apcatb.2015.07.027
      42
      Strong dispersion effect of cobalt spinel active phase spread over ceria for catalytic N2O decomposition: The role of the interface periphery
      Grzybek, G.; Stelmachowski, P.; Gudyka, S.; Indyka, P.; Sojka, Z.; Guillen-Hurtado, N.; Rico-Perez, V.; Bueno-Lopez, A.; Kotarba, A.
      Applied Catalysis, B: Environmental (2016), 180 (), 622-629CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)
      A series of Co3O4/CeO2 catalysts with increasing cobalt spinel loading in the range of 1-20 wt.% was prepd. by incipient wetness impregnation of CeO2. The obtained catalysts were thoroughly examd. by XRD, XPS, XRF, RS, TEM/EDX/EELS, TPR and BET techniques. The catalytic tests in deN2O reaction revealed that the 10 wt.% of cobalt spinel in supported system is able to reproduce the activity of bare Co3O4 catalyst. However, it was found that the catalyst with the lowest content of Co3O4 equal to 1 wt.% exhibits the highest apparent reaction rate per mass of the spinel active phase. The obsd. activity was explained basing on the transmission electron microscopy anal. in terms of the dispersion of spinel phase over ceria support. A simple model that accounts for the obsd. strong dispersion effect is proposed. It consists in a two-step mechanism, where N2O is dissocd. on the spinel nanograins and the resultant oxygen species are preferentially recombined at the Co3O4/CeO2 interface periphery.
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    43. 43
      Piskorz, W.; Zasada, F.; Stelmachowski, P.; Diwald, O.; Kotarba, A.; Sojka, Z. Computational and experimental investigations into N2O decomposition over MgO nanocrystals from thorough molecular mechanism to ab initio microkinetics. J. Phys. Chem. C 2011, 115, 22451– 22460,  DOI: 10.1021/jp2070826
      43
      Computational and Experimental Investigations into N2O Decomposition over MgO Nanocrystals from Thorough Molecular Mechanism to ab initio Microkinetics
      Piskorz, Witold; Zasada, Filip; Stelmachowski, Pawel; Diwald, Oliver; Kotarba, Andrzej; Sojka, Zbigniew
      Journal of Physical Chemistry C (2011), 115 (45), 22451-22460CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      In this article a comprehensive mol. modeling of the reaction mechanism complemented by ab initio microkinetic modeling of the catalytic decompn. of N2O on MgO nanocrystals is discussed. The d. functional level of theory was used to study the mol. mechanism of conceivable elementary steps of the deN2O reaction over the most stable (100) surface, including the effect of surface morphol. It is shown that terrace sites are responsible for steady state reactivity, whereas the more basic and reactive sites located on edges and corners are involved only in the initial stages of the reaction because of poisoning. Detailed anal. of the reaction progress in terms of the energy profiles and the evolution of partial charges and bond orders for each step allowed for an in-depth insight at the at. scale into the nature of the catalytic N2O decompn. over anionic redox active sites constituted by surface O2- ions. The harmonic transition state theory along with the calcd. free enthalpies of activation were used to model the reaction progress in pulse (transient) and steady state regimes as well as to predict the kinetic isotopic effects (KIE) for 15N and 18O labeled reactants. The proposed kinetic scheme was able to reproduce the results of temp.-programmed surface reaction and KIE expts. with high accuracy without fitting of any parameters.
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    44. 44
      Liu, X.; Yang, Z.; Li, Y.; Zhang, F. Theoretical study of N2O decomposition mechanism over binuclear Cu-ZSM-5 zeolites. J. Mol. Catal. A: Chem. 2015, 396, 181– 187,  DOI: 10.1016/j.molcata.2014.09.039
      44
      Theoretical study of N2O decomposition mechanism over binuclear Cu-ZSM-5 zeolites
      Liu, Xin; Yang, Zuoyin; Li, Yaping; Zhang, Fazhi
      Journal of Molecular Catalysis A: Chemical (2015), 396 (), 181-187CODEN: JMCCF2; ISSN:1381-1169. (Elsevier B.V.)
      The mechanism of N2O decompn. over binuclear Cu-ZSM-5 zeolites is investigated using d. functional theory (DFT). It is found that the activation energy of two N2O mols. dissocn. are 47.19 and 63.89 kcal/mol, and the desorption energy of O2 from Cu2O2 is 14.70 kcal/mol. The DFT results show that the N-O splitting step of N2O mol. controls the whole catalytic cycle, and the binuclear Cu-ZSM-5 has not suffered from O2 inhibition. Moreover, some exptl. work reports O2 inhibition is not obsd. at high Cu loading, which is in agreement with the present calcn. These findings suggest that the catalytic behavior of binuclear Cu-ZSM-5 is different from that of mononuclear. Furthermore, the kinetic anal. confirms the rate-limiting step in the binuclear Cu-ZSM-5 system is the N2O dissocn. step, and the rate const. indicates that high temp. could accelerate the N2O dissocn. These results could allow us to understand the structure of the active sites and reveal the active sites controlling catalytic activity. The DFT calcn. results combined with the kinetic study would provide us a comprehensive understanding on the NOx decompn. mechanism over the Cu-ZSM-5 zeolites.
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    45. 45
      Yamashita, T.; Vannice, A. N2O decomposition over manganese oxides. J. Catal. 1996, 161, 254– 262,  DOI: 10.1006/jcat.1996.0183
      45
      N2O decomposition over manganese oxides
      Yamashita, Tatsuji; Vannice, Albert
      Journal of Catalysis (1996), 161 (1), 254-262CODEN: JCTLA5; ISSN:0021-9517. (Academic)
      The catalytic decompn. of N2O was studied over four different oxides of manganese-MnO, Mn3O4, Mn2O3, and MnO2. The resp. specific activities were 6.3 × 10-4, 2.5 × 10-3, 4.8 × 10-3, and 8.1 × 10-4 μmol/s·m2 at 623 K and 0.066 atm of N2O. Apparent activation energies fell between 19 and 27 kcal/mol, and the reaction orders with respect to N2O were between 0.74 and 0.89. XRD patterns showed that pretreatment at 773 K under He converted MnO2 into Mn2O3, which gave a specific activity similar to that of the original Mn2O3 sample; therefore, MnO2 was pretreated under pure oxygen at 645 K prior to reaction to retain the bulk MnO2 phase. On the other hand, MnO was oxidized to Mn3O4 during the course of N2O decompn. Thus, Mn2O3 is the phase assocd. with the highest catalytic activity. A detailed kinetic study with the most active Mn2O3 sample found that the reaction order at 648 K with respect to N2O was near 0.8 over a wide pressure range, and the reaction rate was retarded by oxygen. The exptl. data fit a simple Langmuir-Hinshelwood model well and both kinetic and thermodn. parameters could be detd. The activation energy for the rate detg. step- dissocn. of adsorbed N2O into N2(g) and adsorbed oxygen- was 31 kcal/mol. Weak N2O adsorption was indicated by heat of adsorption and entropy of adsorption values of 7 kcal/mol and -9 cal/mol·K, resp., while for O2 adsorption resp. values were 22 kcal/mol and -26 cal/mol·K. Independent Langmuir isotherms for N2O adsorption between 297 and 353 K revealed only reversible adsorption with a heat of adsorption of 5 kcal/mol.
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    46. 46
      Smeets, P.; Sels, B.; Vanteeffelen, R.; Leeman, H.; Hensen, E.; Schoonheydt, R. The catalytic performance of Cu-containing zeolites in N2O decomposition and the influence of O2, NO and H2O on recombination of oxygen. J. Catal. 2008, 256, 183– 191,  DOI: 10.1016/j.jcat.2008.03.008
      46
      The catalytic performance of Cu-containing zeolites in N2O decomposition and the influence of O2, NO and H2O on recombination of oxygen
      Smeets, Pieter J.; Sels, Bert F.; van Teeffelen, Robert M.; Leeman, Hugo; Hensen, Emiel J. M.; Schoonheydt, Robert A.
      Journal of Catalysis (2008), 256 (2), 183-191CODEN: JCTLA5; ISSN:0021-9517. (Elsevier)
      The catalytic decompn. of N2O was studied over Cu-contg. zeolites with different Cu loadings and framework topologies (MFI, MOR, FER, BEA, and FAU). The influence of NO, O2, and H2O on the rate of N2O decompn. was investigated. A kinetic model was developed based on the relevant elementary reaction steps in the mechanism of N2O decompn. The recombination of oxygen atoms into mol. oxygen is recognized as the rate-limiting step in N2O decompn. The rate of oxygen desorption depends strongly on the Cu loading. At low Cu loadings, migration of oxygen atoms is required for recombinative desorption. NO accelerates oxygen recombination, because it provides an alternative route for oxygen migration via gas-phase NO2. The effect of water differs for Cu-contg. zeolites with high and low Cu loadings. At high Cu loading, the rate is suppressed by competitive adsorption of water on the active sites, resulting in an increase in apparent activation energy. The rate of N2O decompn. is increased substantially for catalysts with a low Cu loading. This is tentatively attributed to water-induced mobility of Cu ions, which facilitates oxygen migration. The effect of water addn. is fully reversible.
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    47. 47
      Wu, L.; Qin, W.; Hu, X.; Ju, S.; Dong, C.; Yang, Y. Decomposition and reduction of N2O on CaS (100) surface: A theoretical account. Surf. Sci. 2015, 632, 83– 87,  DOI: 10.1016/j.susc.2014.09.014
      47
      Decomposition and reduction of N2O on CaS (100) surface: A theoretical account
      Wu, Lingnan; Qin, Wu; Hu, Xiaoying; Ju, Shaoda; Dong, Changqing; Yang, Yongping
      Surface Science (2015), 632 (), 83-87CODEN: SUSCAS; ISSN:0039-6028. (Elsevier B.V.)
      The catalytic effect of CaS on N2O decompn. and redn. was investigated using d. functional theory calcns. N2O approached the CaS (100) surface and crossed an energy barrier of 1.228 eV, decompg. into a free N2 mol. and an adsorbed O atom. The generated adsorbed O atom could be removed through two reaction pathways: binding with a neighboring adsorbed O atom into O2 with the barrier energy of 1.877 eV or reacting with another N2O mol. generating an adsorbed O2 with the barrier of 1.863 eV. The removal of the surface adsorbed O atom is the rate-detg. step of the catalytic decompn. of N2O. In comparison with the homogeneous reaction between N2O and CO, CO accelerated the removal of the adsorbed O atom, hence improving the redn. of N2O on CaS (100). Furthermore, while compared with the CaO-catalytic removal of N2O, CaS is not as active as CaO for the decompn. and redn. of N2O. Our study is the first attempt to theor. reveal the mechanism of CaS-catalytic decompn. and redn. of N2O, which provides a better understanding of the nitrogen chem. in the reducing atm. zone of circulating fluidized bed boilers.
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  • Supporting Information

    Supporting Information

    The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.9b02892.

    • N2O decomposition performances of Co3O4, Cu1Co2, and CuO under different conditions; XRD patterns of the Co3O4, CuxCoy, and CuO catalysts; XPS spectra of the CuxCoy and CuO catalysts for the spectral region of Cu 2p3/2; TCD signals of N2O-TPD profiles over Co3O4, CuxCoy, and CuO catalysts; MS spectra of N2O, O2, NO, and N2 over Co3O4, CuxCoy, and CuO during N2O-TPD; N2 and NO desorption amounts during N2O-TPD over Co3O4, CuxCoy, and CuO catalysts; and dependence of the N2O decomposition rate on the N2O concentration over the Co3O4, CuxCoy, and CuO catalysts at 350–500 °C (PDF)


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