Promoted TIO2 (anatase)-supported vanadium oxide catalysts. TPR study and activity in oxidation of toluene

Vanadium oxide doped with K, Li, Bi, Sb, Te, U or Mo oxide, supported on TiO2- anatase, was studied by temperature programmed reduction (TPR). The influence of the addition of promoters (up to molar ratio M:V=0.5) to 5 wt.% V2O5/TiO2 catalyst on the TPR profile is presented in correlation with their catalytic activity in the vapor phase oxidation of toluene. All promoters, except Bi2O3, decrease the catalyst reducibility and decrease the rate of the toluene oxidation. A strong negative influence on the activity of the toluene oxidation have K, Li, and Te oxides. However, the presence of all tested promoters in the molar ratio M : V=0.05 has a positive effect on the selectivity of benzoic acid formation. A further increase of this ratio leads to a decrease of the selectivity in the case of U, Mo and mainly K oxides, while with Li, Bi, Sb, and Te oxides, the selectivity remains almost unchanged. No correlation between TPR profiles of doped catalysts and their selectivity was found. The most effective promoter of vanadia catalysts for the benzoic acid production is Sb oxide, possessing a very high selectivity at high conversion of toluene.