Selective catalytic reduction of NO over Cu-Al-MCM-41

Abstract

Al-MCM-41 and Cu-Al-MCM-41 were prepared by a modified hydrothermal method. The characterization using XRD, NMR, and N 2 adsorption isotherms revealed that the structure of Al-MCM-41 remained unchanged after the complete exchange of protons for copper ions. Cu-Al-MCM-41 catalysts were studied for the selective catalytic reduction (SCR) of NO by C 3H 6 in the presence of excess oxygen. Particular attention was paid to the influence of both copper content and Si/Al ratio on the nature of the active copper sites and, therefore, on the performance of the catalysts. It was observed that the most active catalyst have ∼ 100 % of copper exchange. For the underexchanged catalyst of the same copper content, it was found that the NO reduction activity decreased with decreasing Si/Al ratio. H 2-TPR and NO-TPD experiments showed that copper is mainly in the form of isolated Cu 2+ ions in Cu-Al-MCM-41 catalysts with copper exchange ⩽ 100 % , whereas at higher copper loadings CuO species are also present. Moreover, when the catalyst Si/Al ratio increases copper is more easily reduced. These results are in agreement with the view accepted in the field of Cu-zeolite catalysts that the isolated Cu 2+ ions are involved in the SCR of NO by propylene.