A new model for the molecular structure of supported vanadium oxide catalysts

Raman spectroscopy experiments found the V=O stretching frequency for the supported VO4 species to decrease with increasing catalyst temperature. Calculations on the vibrational frequencies of several models using density functional theory show that a consistent description of the experimental data can be obtained if we assume that the VO4 species are anchored to the oxidic surface by one V-O bond only, in contrast to the traditional pyramidal model, which assumes three V-O-support bonds and one V=O. The proposed VO3 structure points away from the surface and consists of one V=O unit and an active oxygen 'molecule' loosely bound to the vanadium atom, a peroxide species. (C) 2004 Elsevier B.V. All rights reserved.