A Study of the Catalytic Partial Oxidation of Hydrocarbons. VI. The Effect of Molybdenum Addition to the Vanadium Oxide Catalyst on the Oxidation of Butene to Maleic Anhydride

In the present work, the vapor-phase partial oxidation of cis-2-butene was carried out using V2O5-MoO3 catalysts with different compositions, at 350°C, and at a butene content of 0.65% in air, in order to elucidate the effect of the addition of MoO3 to the V2O5 catalyst on the selectivity and the mechanism for maleic anhydride formation. Two types of catalytic specificities were found, depending upon the Mo content: in the range of less than 20 atom% Mo, the specificity was similar to that of V2O5 alone, while in the range of more than 50 atom% Mo, a different specificity was observed, one which gave 1.2 times the yield of maleic anhydride than did V2O5 alone or the Mo-poor catalysts. The increase in the selectivity of butene to maleic anhydride which occurred when a large amount of MoO3 was doped is considered to be caused by the increase in the selectivity of the C4H4O→MA step, not in that of the C4H8→C4H6 or C4H6→C4H4O step. The selectivity of the side pathway in the C4H8→C4H6step was so great that no satisfactory maleic anhydride yield from butene can be expected by the use of the V2O5-MoO3 catalyst.