Competition of the Two Reaction Mechanisms of Maleic Anhydride Formation in Vapor-Phase Oxidation of Butadiene over Supported Molybdena Catalysts

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Abstract
Vapor-phase oxidation of butadiene, 2,5-dihydrofuran and furan over supported molybdena catalysts has been investigated with reference to the reaction mechanism and the rate-determining step of maleic anhydride formation from butadiene. Formation of maleic anhydride during the oxidation of butadiene was found to follow two reaction mechanisms, (a) via 2,5-dihydrofuran and furan, and (b) via 2,5-dihydrofuran but not via furan. The energy barrier for the addition of oxygen species to adsorbed butadiene or furan is very high, i.e., 28.9 or 21.9kcal/g-mol, respectively, as compared to that for the oxidative dehydrogenation of the intermediate compounds such as 2,5-dihydrofuran. Formation of 2,5-dihydrofuran is rate-determining in these mechanisms during the oxidation of butadiene to maleic anhydride. The second mechanism plays a more important role in maleic anhydride formation at low temperatures, the role of the first mechanism increasing with a rise in the reaction temperature.