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 been studied with regard to their activity for the oxidative dehydrogenation of propane. The effect of alkali doping on the catalyst surface characteristics and, in turn, on the catalytic performance has been examined. The catalysts used in this study have been synthesized by a "one-pot" sol-gel/coprecipitation 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, and surface intermediates present during the reaction. Catalysts were characterized by BET surface area measurements, X-ray diffraction, laser Raman spectroscopy, temperature-programmed reduction, X-ray photoelectron spectroscopy, propane temperature-programmed desorption, and diffuse reflectance infrared Fourier transform spectroscopy. By varying the K/Mo molar ratio a maximum in selectivity and yield of propylene was obtained. The maximum yield of propylene obtained in dilute feed experiments was similar to 30%. Experiments with more concentrated feed mixtures were also performed to achieve a higher percentage of propylene (6-7%) in the product stream. (C) 2000 Academic Press.