Reduction of molecular oxygen on the surface of transition metal complex oxide

Abstract

Ab initio quantum‐chemical calculations have been carried out for the electronic structures of molecular clusters and adsorption complexes to model physical and chemical adsorption of molecular oxygen on the surface of nickel‐cobalt and iron‐cobalt mixed oxides (spinels). The quantum‐chemical calculations were done using the Hartree‐Fock‐Roothan self‐consistent field MO LCAO formalism in the 6–31 basis set of Gaussian functions. It was shown that the value of adsorption energy of hydrogen peroxide influences the mechanism of oxygen reduction: at lower adsorption energies oxygen is reduced by the two‐electron mechanism, which is followed by desorption of the peroxide molecule formed. At higher adsorption energies the reduction of oxygen occurs via the four‐electron mechanism up to water formation. An explanation was proposed that the catalytic reaction of oxygen reduction proceeds on average via a 3.7‐electron mechanism, which is confirmed experimentally.