Ab initio molecular-orbital study on the adsorption of ethylene and oxygen molecules over vanadium oxide clusters

Abstract

The ab initio Hartree–Fock molecular-orbital method has been used to investigate the electronic structures of a VO₄H₃ cluster as a model for silica-supported vanadium oxide catalysts and the interactions between the cluster and ethylene and/or oxygen molecules. Wavefunctions have been obtained for the singlet ground state and the lowest triplet state formed by irradiation of ultraviolet light. The VO bond in the triplet state is longer by 0.3 Å than that in the ground state. The ethylene molecule is adsorbed in a stable form on the cluster only in the triplet state. The interaction between the cluster and oxygen is repulsive for both the singlet and triplet states. However, the coadsorption of both molecules is found to be stable for the triplet state. These results are consistent with recent experimental data, and the mechanism of electronic interactions is discussed in detail using the molecular-orbital expansion technique.