CLUSTER QUANTUM-CHEMICAL STUDY OF THE CHEMISORPTION OF METHANE ON ZINC-OXIDE SURFACE

A quantum-chemical study based on a supermolecular approach and using a modified MINDO/3 method was applied to study the interactions of methane (a) with a ZnO surface containing structural defects i.e., low-coordinated Zn-LC(2+) and O-LC(2-) ions and (b) with dioxygen preadsorbed on various oxygen vacancies of the ZnO surface. The zinc oxide was modelled by a Zn16O16 four-layer molecular cluster. From calculated heats of dissociative adsorption of CH4 on the various pairs of acid-base centres of the ZnO surface it could be derived that only the Zn-2C(2+)-O-3C(2-) pair of centres is responsible for initial activation of methane. The calculations also indicate that for dioxygen, molecular adsorption on the oxygen vacancy centres is more favourable than dissociative adsorption. On the basis of computational results the various channels of methane interaction with zinc oxide, the possibilities of formation of various oxygen vacancies on ZnO and their role in activation of dioxygen and methane molecules are discussed.