O2 adsorption on MgO(001) surface with oxygen and magnesium vacancies

The adsorption Of O-2 at oxygen vacancy site (F, F+ or F2+ site) and magnesium vacancy site (V, V- or V2- site) has been studied using cluster models embedding in a large array of point charges coupled to density functional method at B3LYP/6-31G ( d) level. The value of point charges is determined by the self-consistent technique. The calculated results indicate that the MgO (00 1) surface with oxygen vacancies has more excellent catalyst structure contributing to the adsorptive-decomposition Of O-2 in comparison with the low-coordinated corner site in the previous study. The adsorption energies for O-2 adsorbed on MgO(001) surface with oxygen vacancies are larger than those on MgO(001) surface with magnesium vacancies. Moreover, the MgO(001) surface with magnesium vacancies hardly exhibits catalytic reactivity toward O-2 decomposition. The Mulliken charge analysis illustrates that, for O-2 adsorption on MgO (001) surface with oxygen vacancies, the electrons are transferred from the substrate to the adsorbed O-2 and occupy the anti-bonding orbital, pi* Of O-2. Thus, the O - O bond strength is weakened. Potential energy curve shows that the energy barrier is considerably decreased for O-2 adsorbed at oxygen vacancy site of MgO(001) surface when compared to that at corner site in our previous study.