Structure and activity of silica-supported vanadia catalysts for the oxidation of propylene

Abstract

Two series of silica-supported vanadium oxide catalysts were prepared by adsorption-hydrolysis of VOCl 3 on OH groups of silica and by impregnation with aqueous vanadyl oxalate complex. They were studied and characterised by TG, XRD, TEM, IR, XPS and O 2 chemisorption on partially reduced catalysts at -196°C. This information was correlated with the catalytic activity in the reaction of the oxidation of propylene in the presence of steam. The catalysts, containing 0-8 wt% V 2O 5, were found to contain vanadium oxide in a very high degree of dispersion, mainly as a monolayer. In catalysts prepared by impregnation with vanadyl oxalate, XPS and IR spectra showed that V 4+ species were predominant while the V 5+ species was in the majority when the adsorption-hydrolysis of VOCl 3 procedure was used. Catalyst activity appeared to be related to the presence of reduced vanadium oxide. Possible causes for the selectivity differences between phases in both series of catalysts are discussed.