Selective oxidation over mixed oxide catalysts

Abstract: Since the metal oxide catalysts used in many chemical processes show very high selectivity for the products aimed at, both today and in the future, they play a key role in the environmentally and economically sustainable production of chemical intermediates. Two processes of this sort have been studied in the thesis: the ammoxidation of propane and propene over a Mo-V-Nb-Te-oxide catalyst and the selective oxidation of methanol over vanadium-based catalysts. Since propane is cheaper and more available than propene as a feedstock for the industrial production of acrylonitrile, strong research efforts have been made to find suitable catalysts for it. The work presented here concerns way of improving the performance of the M1 and M2 phases, both of which are selective for acrylonitrile. Dilution of these phases with ?-Al2O3, SiO2 and TiO2 led to the catalysts formed being more dispersed but less active and selective. Partial or complete substitution then of W, Ti and Ce for Mo, V and Te, respectively, in the M2 phase increased both the activity and the selectivity of the Mo-V-Nb-Te-oxide system to acrylonitrile, making it more useful for industrial applications. Use of bulk-phase and supported vanadium-based oxide catalysts in the oxidation of methanol to formaldehyde was studied. The bulk-phase catalysts were found to be preferable to the supported ones since they showed higher selectivity to formaldehyde and lower volatility of the vanadium. However, although the vanadates showed lower volatility of the active metals than a commercial iron molybdate catalyst did, they were less selective to formaldehyde. Thus, they cannot replace the molybdate in industrial applications without increasing the cost of the methanol.