THE KINETIC SIGNIFICANCE OF V5-BUTANE OXIDATION CATALYZED BY VANADIUMPHOSPHATES( IN N)

Maleic anhydride, a precursor to polyester resins, is made by oxidatio n oi n-butane over vanadium phosphate catalysis. This system is of gen eral interest because it is the only heterogeneously catalyzed, alkane -selective oxidation reaction in commercial use. Time-resolved in situ x-ray absorption spectroscopy shows that when either alpha(1)-VOPO4/S iO2 or (VO)(2)P2O7/SiO2 catalysts are exposed to n-butane, the rate of maleic anhydride formation is proportional to the rate oi decay of V5 + species in the catalyst. Thus V5+ species are kinetically significan t for the production of maleic anhydride and not just for the producti on of by-products. The results also suggest that V5+ species may play a role in the initial hydrogen abstraction from n-butane, the rate-det ermining step in the reaction sequence. V4+ sites appear to be respons ible for by-product formation.