The behavior of Cu/ZSM-5 in the oxide and reduced form in the presence of NO and methanol
The behavior of Cu/ZSM-5 in the oxide and reduced form in the presence of NO and methanol
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DOI：
10.1016/s0926-860x(99)00444-5
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发表时间：
2000-02
影响因子：
5.5
通讯作者：
M. A. Carvalho;F. B. Passos;M. Schmal
中科院分区：
文献类型：
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作者：
M. A. Carvalho;F. B. Passos;M. Schmal
采用紫外-可见漫反射光谱、CO化学吸附和NO程序升温脱附等手段对Cu/ZSM-5催化剂进行了表征。结果表明，在Cu 2+交换水平是完全的。焙烧后铜离子的氧化数为2+，形成孤立的Cu 2+物种，CuO和（Cu-O-Cu）2+化合物，这取决于预处理条件。结果表明，铜原子呈小团簇状排列，在分子筛骨架中分散良好。结果表明，催化分解NO的活性物种为Cu 2+，Cu 2+可被还原为Cu+，形成Cu+-NO2和Cu+-（NO）2络合物。铜离子状态的依赖性，因此，预处理是重要的NO分解活性，由于形成（Cu-O-Cu）2+氧位物种，作为催化位点的NO分解为N2 O +NO2。甲醇氧化反应的活性和选择性不受预处理温度的影响，但受酸中心分布的影响较大。甲醇对NO还原无活性，因为甲醇不能在NO吸附位点上活化形成对NO还原有活性的物种。
Cu/ZSM-5 catalysts were characterized by DRS UV–Vis IR spectroscopy, CO chemisorption and NO TPD. The results indicated that the exchange level in Cu2+is complete. The oxidation number of copper ions after calcination is 2+, with the formation of isolated Cu2+species, CuO and (Cu–O–Cu)2+compounds, depending on the pretreatment conditions. It was found that copper atoms are arranged as small clusters, well dispersed in the zeolite framework. The results indicated the active species for catalytic decomposition of NO is Cu2+, which can be reduced to Cu+forming Cu+–NO2and Cu+–(NO)2complexes. The dependence of copper ions state and therefore, the pretreatment are important for the NO decomposition activity due to the formation of the (Cu–O–Cu)2+oxocation species, which act as catalytic sites for the disproportionation of NO to N2O+NO2. Methanol oxidation showed that the activity and selectivity are not dependent on pretreatment temperature, but they are markedly influenced by the acid site distribution. Methanol was inactive for NO reduction, since methanol can not be activated on the NO adsorption sites to form species that are active for NO reduction.