Mechanism of catalytic decomposition of NO by Cu-ZSM-5
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摘要: Cu-ZSM-5催化分解NO具有潜在的应用前景。为揭示NO在Cu-ZSM-5催化剂的催化分解机理，基于密度泛函模拟了NO在Cu-ZSM-5催化剂中短距离Cu+对上的吸附，并提出副产物N2O、NO2辅助催化分解NO的反应路径。计算结果表明，双核铜氧物种是Cu基催化剂的重要活性中心。催化分解NO过程中，副产物NO2在双核铜氧物种上的分解需要的活化能最高（为171.39 kJ/mol），N2O分解需要86.92 kJ/mol的活化能垒，表明NO2在活性位的分解难于N2O的分解。N2、O2的解析分别吸收28.43、100.78 kJ/mol的热量，限速步骤为O2的脱附。NO既作为反应物，同时又是催化过程中Cu-ZSM-5催化剂活性中心实现氧化还原循环的关键还原剂。Abstract: Catalytic decomposition of NO by Cu-ZSM-5 has potential application. In order to reveal the catalytic decomposition mechanism of NO over Cu-ZSM-5, the adsorption of NO over short-range Cu+ pairs in Cu-ZSM-5 was simulated based on density functional theory. The reaction pathways of NO decomposition assisted by the by-products N2O and NO2 were also proposed. The results showed that the double nuclear copper-oxygen species was an important active centre. During the reaction, the highest activation energy (171.39 kJ/mol) was required for the decomposition of the by-product NO2 on the binuclear copper-oxygen species. While that for the decomposition of N2O was 86.92 kJ/mol, suggesting that the decomposition of NO2 was more difficult. The desorption energy of N2 and O2 were 28.43 and 100.78 kJ/mol, respectively. The rate determining step was O2 desorption. NO acted both as a reactant and a key reductant for the redox cycle of the active centre of Cu-ZSM-5 during the process.
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Key words:
- Cu-ZSM-5 /
- catalytic decomposition /
- binuclear copper-oxygen species /
- redox cycle
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图 1 Cu-ZSM-5催化剂模型的侧视图和主视图
Figure 1 Side view and front view of Cu-ZSM-5 catalyst model
图 3 Cu1-ON-NO-Cu2-TS和N2O-Cu-O-Cu优化后的构型及部分参数
Figure 3 Optimized structure and parameters of Cu1-ON-NO-Cu2-TS and N2O-Cu-O-Cu
图 5 Cu-Cu-N2O和Cu-Cu-NNO-TS优化后的构型及参数
Figure 5 Optimized structure and parameters of Cu-Cu-N2O and Cu-Cu-NNO-TS
图 6 Cu-Cu-O--NN和Cu-O-Cu优化后的构型及参数
Figure 6 Optimized structure and parameters of Cu-Cu-O--NN and Cu-O-Cu
图 8 Cu-O-Cu--NO和Cu-O-NO-Cu-TS优化后的构型及部分参数
Figure 8 Optimized structure and parameters of Cu-O-Cu--NO and Cu-O-NO-Cu-TS
图 10 Cu-ONO-Cu和Cu-Cu-NO2优化后的构型及参数
Figure 10 Optimized structure and parameters of Cu-ONO-Cu and Cu-Cu-NO2
图 11 Cu-O-Cu-NO2和Cu-O-Cu-NO2-TS优化后的构型及参数
Figure 11 Optimized structure and parameters of Cu-O-Cu-NO2 and Cu-O-Cu-NO2-TS
图 12 Cu-O-ONO-Cu和Cu-O-O-Cu优化后的构型及参数
Figure 12 Optimized structure and parameters of Cu-O-ONO-Cu and Cu-O-O-Cu
表 1 NO在Cu-ZSM-5上催化分解的能垒
Table 1 Energy barrier for the catalytic decomposition of NO on Cu-ZSM-5
Elementary step Barrier/(kJ·mol−1) Cu-Cu+2NO→Cu-O-Cu+N2O 16.55 Cu-Cu+N2O→Cu-O-Cu+N2 86.92 Cu-O-Cu+NO→Cu-Cu+NO2 86.22 Cu-O-Cu+NO2→Cu-NO3-Cu→Cu-Cu+NO+O2 171.39 
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