NO reduction by propane over monolithic cordierite-based Fe/Al2O3 catalyst: Reaction mechanism and effect of H2O/SO2

Abstract

The selective reduction of NO by C3H8 and the sensitivity to H2O and SO2 have been studied over monolithic cordierite-based Fe/Al2O3 catalysts, which were prepared by the sol–gel and impregnation method. The catalysts were investigated by N2 adsorption, X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques. Results showed that NO reduction was more than 90% in the absence of oxygen at 500°C and in the presence of oxygen at 600°C respectively. In a continues test of 12h at 600°C, 0.02% of SO2 caused an irrecoverable decrease of NO conversion from 94% to 85% and 2.5% of H2O caused a drop of NO conversion from 86% to 56%, while NO conversion totally recovered when H2O was removed. The catalysts lost 15% of the initial activity after a hydrothermal treatment due to the agglomeration of iron oxide nanorods. Sulphidation treatment caused about a loss of 30% of the initial activity because of the deposited SO42− species. In situ study by DRIFTS indicated that coexisting H2O influenced the formation NO2 adspecies and unidentate nitrate, while SO2 slightly inhibited the formation of NO2/NO3− species, but promoted the formation of acetate/formate species during NO reduction by C3H8. Based on the results, a preliminary mechanism was proposed and discussed. The results may help understand the fundamental performance of monolithic cordierite-based Fe/Al2O3 catalysts and provide some reference for SCR-HC catalyst design.