Adsorption/Oxidation of CH3OH on V2O5. A Theoretical and Experimental Study

Abstract

The adsorption/oxidation of CH3OH on V2O5 was studied in previous work by mass spectrometric analysis of the reaction atmosphere, and by measuring the electrical properties (Hall effect) and total pressure of the system. Such data allowed a reaction pathway to be proposed. In the present work, the variations in the surface oxidation number have been calculated via balances in the C and H atoms in the reaction atmosphere and models of the (010) plane of V2O5 and of CH3OH have also been utilized to find energetically favourable sites for the adsorption of CH3OH and its subsequent oxidation to H2CO. For this purpose, the variation in the total energy of the system was computed by Extended Hückel-type calculations (ASED, Atom Superposition and Electron Delocalization). From such experimental results, it was deduced that the H atoms are removed by the network oxygens and that methanol is adsorbed as the methoxy group. Such removal of H atoms has two consequences: high surface hydroxylation and surface reduction [V(5+) → V(4+)]. In support of these suggestions, the theoretical results have confirmed both the removal of H atoms and methoxy group formation, and have also revealed two possible adsorption sites for CH3OH on V2O5: the terminal oxygens (V=O) and the network bridging oxygens (V-O-V).