Abstrakt

Different aspects of quantum chemical modelling of catalytic systems are discussed. Further, the electronic structure of various VnOm clusters representing the vanadium pentoxide (010) surface is studied and the reactivity of different surface oxygen sites with respect to adsorption of hydrogen as well as propylene is examined. Results of ab initio HF and DFT calculations are compared with those of the semiempirical INDO-type method. It is found that the different quantum chemical methods lead to the same qualitative results. Satisfactory convergence in cluster properties is achieved for clusters of ten vanadium atoms. The saturation of dangling bonds by hydrogen atoms does not influence the properties of the oxygen centers significantly. Among different oxygen centers the oxygens bridging two bare vanadium atoms are most negatively charged. Hydrogen binds to all inequivalent oxygen sites with the strongest binding occurring for oxygens bridging two vanadium atoms. INDO cluster studies for propylene adsorption/reaction on V2O5 (010) show that different approaches of the molecule to the surface yield different surface complexes which can then react to form different products.