VANADIUM PENTOXIDE .2. QUANTUM-CHEMICAL MODELING

The electronic structure of vanadium pentoxide, V2O5, is discussed bas ed upon the cluster quantum chemical calculations. Satisfactory conver gence in cluster properties is achieved for the cluster of 10 vanadium atoms. No influence of the second layer on the surface properties is found. The results of the adsorption of hydrogen, treated as a probe r eaction to model the first step in the selective oxidation of hydrocar bons at the structurally different oxygen sites, are compared with the adsorption/activation of the propene and toluene molecules at the van adium pentoxide (0 10) surface. Among the different oxygen centers the oxygens bridging two bare vanadium atoms are most negatively charged. Hydrogen binds to all inequivalent oxygen sites with the strongest bi nding occurring for oxygen bridging two bare vanadium atoms. The calcu lations for propene and toluene adsorption/reaction on V2O5 (0 1 0) sh ow that the oxidation into the aldehyde species proceeds through the b inding of the carbon into the bridging oxygen, abstraction of two hydr ogens from the same carbon atom of methyl group and formation of two h ydroxyl groups at the surface. The potential usage of quantum chemical approaches in the description of electronic properties of a catalyst surface and in understanding the mechanism of catalytic reactions (in particular the determination of the reaction pathways) is discussed. I t is shown how modern quantum chemical methods can address questions w hich are relevant in surface science and catalysis.