On the intrinsic activity of vanadium centres in the oxidative dehydrogenation of propane over V-Ca-O and V-Mg-O catalysts

The performance of V-Ca-O catalysts for the oxidative dehydrogenation of propane has been studied for the first time, being compared with that of similar V-Mg-O catalysts, and their differences are interpreted in terms of their physico-chemical properties. The VCaO catalyst showed the same initial selectivity to propene as the most selective VMgO composition, but it decreased faster with increasing propane conversion. Vanadium species present in the catalyst surface were different for the two supports: isolated V5+ tetrahedra on CaO and magnesium orthovanadate and pyrovanadate on MgO. The intrinsic activity of isolated vanadium centres in the surface of the V-Ca-O catalyst was more than one order of magnitude higher than that of dimeric or polymeric tetahedral species in the magnesium-containing catalysts.