Fundamental Study of the Oxidation of Butane over Vanadyl Pyrophosphate

Article abstract of DOI:10.1021/ja00303a012

The oxidation of butane as catalyzed by β-(VO)2P2O7 was studied as a fuction of the separate catalyst oxidation and reduction steps.The vanadyl pyrophosphate was found to have a reversible oxidation capacity approaching one oxygen molecule per two surface vanadium centers.The reduction reaction of the catalyst surface was found to be first order in butan and the oxidation reaction was found to be first order in oxygen.These two reactions occur in distinct, separate steps, a behavior similar to that exhibited by catalysts which can utilize lattice oxygen from the bulk in oxidation reactions.Pulse studies over the catalyst, involving the use of 2H- and 18O-labeled compounds, revealed a very dynamic surface for β-(VO)2P2O7 at 400 deg C.All oxygen and hydrogen atoms in the surface layer were found to be in fast exchange relative to the time scale of the conversion of butane to maleic anhydride and combustion products.Experiments with deuterium-labeled butane revealed that the rate-controlling step for butane oxidation was the irreversible activation of a methylene carbon-hydrogen bond in butane on the catalyst surface.Vanadium(IV) sites on the catalyst surface are proposed to be responsible for both the chemisorption of oxygen and the activation of butane.The combination of a V(V)<*>V(IV) couple and the dynamic nature of the surface layer are thought to be mechanistically important for the 14-electron oxidation of butane to maleic anhydride.