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 VA 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, Mo[double bond, length as m-dash]O, in these modified molybdena catalysts. Therefore, it is proposed that O–2 or double bond oxygen Mo[double bond, length as m-dash]O 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.
