K. Samson

Effect of doping of TiO2 support with altervalent ions on physicochemical and catalytic properties in oxidative dehydrogenation of propane of vanadia-titania catalysts

Vanadia phase (one monolayer) was deposited on TiO2 anatase doped with Ca2+, Al3+, Fe3+ and W6+ ions and the catalysts thus obtained (VMeTi) were characterized by XPS, work function technique, decomposition of isopropanol (a probe reaction for acido–basic properties) and tested in oxidative dehydrogenation of propane. The doping of the TiO2 support modifies physicochemical and catalytic properties of the active vanadia phase with respect to the undoped TiO2. The specific activity in the propane oxydehydrogenation decreases in the order: VFeTi>VWTi>VTi>VAlTi>VCaTi (3), whereas the selectivity to propene follows the sequence: VWTi VTi>VFeTi>VAlTi>VCaTi. This implies that the lower is the surface energy barrier for transfer of electrons from the catalyst to the reacting molecules the higher is the selectivity to the partial oxidation product. It is argued that owing to the decrease in this energy barrier the reoxidation step in the catalytic reaction, involving such a transfer: O2+4e→2O2− is fast, thus, preventing the presence of intermediate non-selective electrophilic oxygen species on the surface.

Oxidative dehydrogenation of propane on TiO2-supported chromium and zinc oxides

Oxidative dehydrogenation of propane has been studied on chromium, zinc and zinc-chromium mixed oxides supported on anatase titania. The order of activity and selectivity to propene was CrTi>ZnCrTi>ZnTi. The activity and selectivity to propene did not change markedly with increase in the reaction temperature.

Effect of the rhenium additive to VOx/TiO2 and MoOx/TiO2 catalysts on their properties in oxidative dehydrogenation of propane

VOx/TiO2 and MoOx/TiO2 catalysts with the addition of Re (Re/V or Mo = 0.5) were synthetized and tested in oxidative dehydrogenation of propane and in reduction by propane. XPS measurements showed depletion of the surface in Re. The Re additive does not affect the total conversion of propane, but increases the selectivity to propene. The effect is more pronounced for the MoOx/TiO2 catalyst. The increase in the selectivity to propene is accompanied with the increase in the reducibility of the catalysts.