PROMOTION EFFECTS OF VARIOUS OXIDES ON OXIDATION OF BENZENE OVER VANADIUM PENTOXIDE CATALYSTS

The effect of promoters on the activity and selectivity of the active sites was investigated in the selective oxidation of benzene over vanadium pentoxide catalysts. The activity per surface area is increased by addition of MoO3, WO3, P2O5 and SnO2, but the activity of each redox sites, i.e., turnover frequency (TF), was not. This indicates that the promoters enhanced the activity by increasing the redox sites, such as the surface V = O species. The selectivity to maleic anhydride (MA) was improved by the addition of MoO3, WO3 and P2O5, while it was lowered by SnO2. The effect on the selectivity was discussed in the light of the electronegativity of promoter cations. The additions of MoO3, WO3 and P2O5, of which the cations are more electronegative than V5+, decreased TF of the production of carbon oxides more seriously than that of MA. On the other hand, the addition of less electronegative cation, i.e., Sn4+, increased TF of the production of carbon oxides at the sacrifice of MA.