The impact of redox properties on the reactivity of V2O5/Al2O3 catalysts

The redox properties of 5 and 15 wt.% V2O5/Al2O3 catalysts calcined at 753 and 973 K were characterized by measuring their composition as a function of image at 748 K using coulometric titration. The redox isotherms showed that the 5 wt.% catalyst calcined at 753 K underwent gradual reduction from V+5 to V+4 at image between 10−4 and 10−19 atm, and stepwise reduction from V+4 to V+3 at a image of 10−24 atm corresponding to a ΔGred of 343 kJ/mol of O2. This sample was also found to exhibit relatively high thermal stability. The redox isotherm for a 15 wt.% catalyst calcined at 753 K was similar to that obtained for a 5 wt.% catalyst. This sample was much less thermally stable, however, and recrystallized upon calcination at 973 K, forming a highly reducible AlVOx species that underwent reduction from V+5 to V+3 in a single step at a image of 10−6 atm at 748 K with a ΔGred of 86 kJ/mol. In spite of the differences in the redox properties, all the catalysts were found to exhibit a similar reactivity for the selective oxidation of methanol. The catalysts also exhibited a similar propane ODH activity except for the 15 wt.% catalyst calcined at 973 K which had a lower activity, was unselective, and produced only CO2.