Influence of Reductive Pretreatments on the Activity and Selectivity of Vanadium-Phosphorus Oxide Catalysts for n-Butane Partial Oxidation

The catalytic activities for -butane conversion to maleic anhydride of two series of vanadium-phosphorus oxide catalysts with phosphorusrvanadium ratios in the range 0.94 to 1.10 and calcined at 773 or 923 K were compared before and after reduction by hydrogen. In almost all cases studied, reduction gave rise to increased conversion, and for catalysts with low phosphorus:vanadium ratios increased selectivity was also noted. When n-butane was contacted with these catalysts In the absence of gas phase oxygen, maleic anhydride and total oxidation products continued to be formed until changes in average oxidation state of vanadium of up to-1.5 were recorded. From considerations of the dynamic state of the catalysts during catalysis, it was concluded that a morphology consisting of oxidized surface layers on a reduced core favors high activities and selectivities for this process.