Electron transfer processes at the surface of MoOx/SiO2 catalysts

Abstract

EPR studies using naturally abundant and ⁹⁵Mo-enriched molybdenum have shown that reduced MoO _x /SiO₂catalysts 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 accompanying the activation of O₂and N₂O as well as the reactivity of O^-and ⋅CH₂OH transients with coadsorbed CH₃OH and O₂, respectively, have been identified. They include nondissociative and dissociative ET, surface intramolecular ET, and electroprotic transformation (ET coupled with proton transfer). In the case of methanol dehydrogenation it was found that if the reaction occurs on the MoO _x 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.