On the nature of highly dispersed vanadium oxide catalysts:: effect of the support on the structure of VOx species

The nature of VOx specie supported on TiO2, gamma -Al2O3 and SiO2 is analyzed. The plausibility of different VOx specie (mono, di, pyrovanadates) is evaluated by means of a theoretical study of the extended Huckel (EH) type. Theoretical results are compared with published characterization data and discussion is performed taking account both results. The interaction of VOx with the support and the structure of supported surface vanadia are influenced by the composition of the oxide carrier. On SiO2, only the monovanadate species are formed. On gamma -Al2O3, dimers seem to be the more plausible supported form of VOx. On TiO2, monomers and dimers are present; however, the latter species being the most abundant. (C) 2000 Elsevier Science B.V. All rights reserved.