Similarity in the reactivity of O –2 and double bond type lattice oxygen as revealed by vapour-phase catalytic oxidation of furan to maleic anhydride

Abstract

Vapour-phase oxidation of furan over titania and molybdena catalysts has been investigated with reference to the oxygen species incorporated into maleic anhydride. The sequence of the amount of O^–₂ formed on titania and molybdena catalysts modified with VA group oxides was found to be P₂O₅ > As₂O₃≫ Sb₂O₃ > Bi₂O₃, which is in agreement with the electronegativity of the added V_A group elements. The rate of maleic anhydride formation over the modified titania showed the same sequence, but the rate over the modified molybdena increased in the following order; Bi₂O₃ > Sb₂O₃ > P₂O₅ > As₂O₃, which is in line with the reactivity of the double bond type lattice oxygen, MoO, in these modified molybdena catalysts. Therefore, it is proposed that O^–₂ or double bond oxygen MoO plays a very important role in the oxidation of furan to maleic anhydride over a titania or molybdena catalyst. This has been supported further by kinetic studies and discussion of these reaction mechanisms, and these oxygen species are shown to be incorporated into the maleic anhydride formed. Thus, the results suggest a similarity in the reactivity of O^–₂ and that of the double bond oxygen in the oxidation of furan.