Electron transfer processes at the surface of MoOx/SiO2 catalysts

EPR studies using naturally abundant and Mo-95-enriched molybdenum have sho wn that reduced MoOx/SiO2 catalysts with different dispersion of molybdenum provide a unique opportunity for molecular-level investigations of surface phenomena involved in the bonding to and activation of small molecules by oxide surfaces. Different types of electron transfer (ET) processes accompa nying the activation of O-2 and N2O as well as the reactivity of O- and . C H2OH transients with coadsorbed CH3OH and O-2, respectively, have been iden tified. They include nondissociative and dissociative ET, surface intramole cular ET, and electroprotic transformation (ET coupled with proton transfer ). In the case of methanol dehydrogenation it was found that if the reactio n occurs on the MoOx cluster centers, ET exhibits a complementary character , in contrast to isolated Mo centers where noncomplementary ET accompanied by migration of the hydroxymethyl intermediate is observed.