Nanosize gold catalysts promoted by vanadium oxide supported on titania and zirconia for complete benzene oxidation

The complete benzene oxidation reaction was used to test the reactivity of the Au-V2O5/TiO2 and Au-V2O5/ZrO2 catalytic systems. A strong synergistic e ffect between gold and vanadia was established when molecular oxygen was us ed as an oxidizing agent. This effect was more pronounced for titania than for the zirconia support. In the presence of gold, predominantly polyvanada te structures are formed on the surface which are more active in the reacti on of complete benzene oxidation in comparison with monovanadate species an d bulk V2O5 The deposition of gold leads to a relative lengthening of the V =O bond and to a higher electron delocalization. The B and C parameters cal culated from ESR spectra showed no differences for the fresh and spent gold -containing samples, i.e, the catalytic systems seemed to be "stabilized" u nder the working conditions. The effect of gold on the vanadium oxide reduc ibility, which could be related to the strength of the V-O-support bond, re sults in a considerable lowering of the temperature of the V5+ --> V3+ tran sition. With ozone as the oxidizing agent, an additional lowering of the re action temperature was achieved and very close values of the catalytic acti vity on all investigated samples were registered. Upon oxidation by molecul ar oxygen the oxidant activation takes place on the nanosize gold particles while the vanadium oxide surface species are responsible for the activatio n of benzene. This is in agreement with synergistic effect between the fine ly dispersed gold and the surface vanadium structures. (C) 2001 Elsevier Sc ience B.V. All rights reserved.