In situ DRIFT studies of alkane adsorption on vanadia supported titania-doped catalysts

Abstract

In-situ DRIFT studies of alkane adsorption (ethane and propane) are performed over well characterized 90Ti-M (M = Si, Al, and W) and 2V90Ti-M catalysts at different temperatures and partial pressures of alkanes. The titania-doped mixed oxide supports are synthesized by the sol-gel method and supported vanadia catalysts are prepared by the incipient wet impregnation method. The supported vanadia catalysts possess only surface vanadia species coordinated with titania and/or silica, alumina and tungsten in the corresponding catalysts. Analysis of the in situ DRIFT spectra of alkane adsorption confirms the formation of various surface oxygenated species, such as ethoxide/isopropoxide, acetaldehyde/ketone, acetate, formate and cyclic anhydride. The alkoxides (ethoxide and isopropoxide) are formed due to the breaking of the CH bond of the parent alkane and are the precursor for the formation of olefins (ethylene and propylene). The unstable alkoxide species are further oxidized to form aldehyde or ketone, respectively. The carboxylates species (acetate and formate) are formed due to further oxidation of acetaldehyde and acetone at high temperatures. Deposition of vanadia suppresses the formation of cyclic anhydride, a precursor for the formation of CO2. In-situ DRIFT studies of propane ODH reaction reveal that isopropoxide is not a readily detectable surface species in the presence of oxygen even at low temperature. However, the carbonate species and propylene are identified during propane ODH reaction. Furthermore, the intensity of overtone VO vibration decreases and shifts from 2030 cm−1 to 2025 cm−1 during alkane adsorption.