Hydrogenative ring-opening reactions of methyloxirane (MOX) were performed over reduced and preoxidized silica-supported Pt, Pd, Ph, Ni and Cu catalysts in order to study reactions at metal-metal oxide interfaces. A comparison of the activity, as well as ring-opening selectivity data over the reduced and preoxidized surfaces, revealed that MOX adsorbed through the ring oxygen and itself oxidized the metal surfaces. This means that the active sites for its catalytic transformations are ionic species formed in situ at the metal-metal oxide interface.