Adsorption/Oxidation of CHOH on VO. A Theoretical and Experimental Study

Abstract

The adsorption/oxidation of CH 3 OH on V 2 O 5 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 V 2 O 5 and of CH 3 OH have also been utilized to find energetically favourable sites for the adsorption of CH 3 OH and its subsequent oxidation to H 2 CO. 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 CH 3 OH on V 2 O 5 : the terminal oxygens (V=O) and the network bridging oxygens (V-O-V).