Role of the nature of copper sites in the activity of copper-based catalysts for no conversion

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Abstract
The activities of the copper-based catalysts, Cu2+ /SiO2,Cu2+ /Vycor and Cu2+/ZSM-5, and V2O5/TiO2 for NO conversion to N2 in the presence or absence of NH3 and/or O2 have been investigated. The Cu2+ /ZSM-5 catalyst exhibited the highest activity, even higher than that of V2O5/TiO2. Photoluminescence studies of the dehydrated copper-based catalysts have suggested that the copper ions anchored onto ZSM-5 locate as isolated copper species near Brönsted sites in the zeolite channels while the copper ions anchored onto Vycor and SiO2 locate mainly as copper dimer forms. These results suggest the role of copper ions which are stabilized with near-lying oxygen vacancies created by dehydroxylation of the zeolite, in NO conversion. As a result, it may be concluded that the isolated copper ions near Brönsted sites play a significant role in NO conversion but dimeric or polynuclear copper species are less effective for the reaction.