The behavior of Cu/ZSM-5 in the oxide and reduced form in the presence of NO and methanol

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+-NO2 and Cu+-(NO)(2) complexes. 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. (C) 2000 Elsevier Science B.V. All rights reserved.