A molecular mechanics study of the adsorption of ethane and propane on V2O5(001) surfaces with oxygen vacancies

Adsorption geometries and energies of ethane and propane physisorbed on the (001) surface of vanadium pentoxide with oxygen vacancies were determined by a molecular mechanics simulation. Three types of oxygen vacancies, built up by removal of vanadyl oxygen, two-fold and three-fold coordinated oxyge n, respectively, have been modeled as defects. The energetically most favor able adsorption site is on top of a vacancy of two-fold coordinated oxygen for ethane and propane, respectively. The next favorable site for both alka nes is on top of a vacancy of vanadyl oxygen. Due to the generation of a "v an der Waals cage" which traps the hydrocarbon the adsorption on the defect site is favored in comparison with the ideal surface for these two defect types. A vacancy of three-fold coordinated oxygen does not lead to an enhan cement of adsorption and pushes the reactant towards the unperturbed surfac e areas due to the fact, that no energy minimum can be obtained in the vici nity of the defect.