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.