Kinetics and mechanism of reduction and reoxidation of the alkali metal promoted vanadia-titania catalysts

Kinetics of reduction of the V2O5/TiO2 catalysts has been investigated as a function of reductant pressure, temperature, V2O5 content and the alkali metal (K, Rb) additives. It has been found that reduction is limited by the adsorption of propane at the surface of the vanadium phase. Reoxidation occurs in two stages: a quick surface reaction and a slow process limited by the bulk diffusion through the growing layer of the oxidation product, in agreement with Zhuravlev's model. Addition of promoters hinders the reduction due to the blocking of propane adsorption centres at the surface of the vanadium phase. Implications of the obtained results for the catalytic oxidative dehydrogenation of propane are discussed.