The adsorption of toluene on V–Sb oxides. Theoretical aspects

Toluene adsorption reactions on the (1 1 0) surface of VSbO4 have been analyzed following the changes in the electronic structure of the hydrocarbon molecule and metal cation sites of the oxide using the Just Another Extended Hückel Molecular Orbital Program (JAEHMOP) code. The bonding character of these interactions has also been studied in the same theoretical framework. The calculations indicate that the exothermic hydrocarbon parallel interaction on Sb–V sites results in the weakening of one of the C–H bonds of the methyl fragment. This leads to a H-abstraction that involves the participation of a Sb-cation. Both methyl and phenyl fragments decrease their electronic population and so does the V-cation site. Most of these electrons are transferred to other V atoms in the bulk solid. As a result the LUMO of the toluene–oxide system fully populates. The analysis reveals that methyl–Sb bonding interactions mainly involve C2px and H1s orbitals with Sb5s orbital, while non-bonding phenyl–V interactions involve C2px orbitals with V3dx2−y2 orbital. This last interaction facilitates the desorption of the benzyl species after H-abstraction.