Supported Vanadia Catalysts with Alkali and Alkaline Earth Additives in Oxidative Dehydrogenation of Propane. Part II. V2O5/SiO2 System

Alkali metals (Li, Na, K, Rb) and Ca were introduced to vanadia dispersed on magnesia: the catalysts obtained were characterized by XRD, XPS isopropanol decomposition (a probe of acido-basic properties) and tested in oxidative dehydrogenation of propane, ODH. No vanadia phase was observed by XRD, vanadium being most probably present in the samples as magnesium orthovanadate dispersed on the MgO surface. Low concentration of acidic and high of basic centres have been observed in the catalysts. Selectivity to propene does not exceed 40%, andCO2 is themain product of total oxidation. The presence of the additives leads to: a) decrease of the acidity and increase the basicity, b) decrease of the total activity in ODH, c) decrease in the selectivity to propene (except for the Ca additive). The effect of additives to VMg catalysts is compared with that reported in Part I for VSi catalysts, and reasons for opposite effect of the additives on the selectivity to propene (increase for VSi and decrease for VMg series) are suggested.