A Cu/Al-MCM-41 mesoporous molecular sieve: application in the abatement of no in exhaust gases

Abstract

-Propane oxidation and reduction of NO to N 2 with propane under oxidative conditions on a Cu-Al-MCM-41 mesoporous molecular sieve and Cu-ZSM-5 zeolites were studied. Both types of catalysts were prepared by ion exchange in aqueous solutions of copper acetate and characterised by X-ray diffraction (XRD), nitrogen sorption measurement, diffuse reflectance ultra-violet spectroscopy (DRS-UV), diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS) of the adsorption of CO on Cu + and temperature-programmed reduction with hydrogen (H 2 -TPR). The NO reduction was performed between 200 and 500 o C using a GHSV = 42,000 h -1. H 2 -TPR data showed that in the prepared Cu-Al-MCM-41 all the Cu atoms are on the surface of the mesopores as highly dispersed CuO, which results in a decrease in specific surface area and in mesopore volume. H 2 -TPR together with DRIFTS data provided evidence that in Cu/ZSM-5 catalysts, Cu atoms are found as two different Cu 2+ cations: Cu α 2+ and Cu β 2+, which are located on charge compensation sites, and their thermo-redox properties were different from those of Cu atoms in Cu-Al-MCM-41. The specific activity of the Cu 2+ exchangeable cations in Cu-ZSM-5, irrespective of their nature, was much greater than that of the Cu 2+ in Cu-Al-MCM-41, where they are found as CuO.