Catalytic activity of vanadium oxides in the oxidation of benzene

Abstract

The catalytic oxidation of benzene over V 2O 5, V 6O 13, V 2O 4, V 7O 13, V 6O 11, V 5O 9, V 4O 7, V 3O 5, and V 2O 3 was investigated at 300–400 °C. Stoichiometric V 2O 5 was catalytically inactive. However, after reduction with C 6H 6 vapor it became active and selective for formation of maleic anhydride. The catalyst was then an intimate mixture of V 2O 4, V 6O 13 with smaller amounts of V 6O 13 and V 4O 9. All the oxides lower than V 2O 5 were active without any pretreatment. The curve showing the initial catalytic activity versus average oxidation number of vanadium in particular oxides exhibited two distinct stronger and weaker maxima corresponding to V 2O 4 and V 4O 7 phases, respectively. In the course of the catalytic reaction the oxides lower than V 2O 4 were slowly oxidized and partially transformed into other phases. The most stable under the conditions of the catalytic reaction were V 2O 4 and V 6O 13 in which vanadium practically did not change its oxidation state. The selectivity with respect to maleic anhydride in the case of the pure oxides was generally low and total degradation of benzene to carbon oxides and water predominated. However, the selectivity could be markedly improved by introducing MoO 3 into solid solution in V 6O 13 or V 2O 4.