K/Mo catalysts supported over sol-gel silica-titania mixed oxides in the oxidative dehydrogenation of propane

The use of silica-titania mixed-oxide-supported molybdenum catalysts has be en studied with regard to their activity for the oxidative dehydrogenation of propane. The effect of alkali doping on the catalyst surface characteris tics and, in turn, on the catalytic performance has been examined. The cata lysts used in this study have been synthesized by a "one-pot" sol-gel/copre cipitation technique. The main focus of the work has been characterization of the surface molybdena species, physical-chemical properties of the Si:Tr support, surface acidity, reducibility, adsorption/desorptian behavior, an d surface intermediates present during the reaction. Catalysts were charact erized by BET surface area measurements, X-ray diffraction, laser Raman spe ctroscopy, temperature-programmed reduction, X-ray photoelectron spectrosco py, propane temperature-programmed desorption, and diffuse reflectance infr ared Fourier transform spectroscopy. By varying the K/Mo molar ratio a maxi mum in selectivity and yield of propylene was obtained. The maximum yield o f propylene obtained in dilute feed experiments was similar to 30%. Experim ents with more concentrated feed mixtures were also performed to achieve a higher percentage of propylene (6-7%) in the product stream. (C) 2000 Acade mic Press.