Selective Oxidation of Light Alkanes on Transition Metal Promoted Vanadyl Pyrophosphate (VPO) Catalysts

摘要

Vanadyl diphosphate (≡vanadyl pyrophosphate) promoted with Bi, Cs, Co and Te was studied as catalyst in the oxidation of propane, n-butane and л-pentane. The additives modified the surface P/V ratio as determined by XPS, and Brpnsted and Lewis acidity, determined by TPD of ammonia and transformation of 2-methyl-3-butyn-2-ol. The specific rate of the oxidation of hydrocarbons correlated with the nucleophilicity of surface oxygen ions. With increase of Lewis acidity the selectivity to maleic anhydride in oxidation of n-butane increased, whereas in oxidation of n-pentane the selectivity to phthalic anhydride increased and that to maleic anhydride decreased. The mechanism is discussed.