The activity and/or selectivity determining roles of carbonaceous deposits of various kinds and metal-metal oxide interfaces are described in metal-catalyzed hydrogenation and isomerization reactions. The catalysts used were silica-supported Pt, Pd, Ph, Ni and Cu, while a wide range of probe molecules (cyclopropane, 1,1-dimethylcyclopropane, propylcyclobutane, methyloxirane, 2-methyl-2-butene, cyclohexene) were tested, in most cases, in the presence of H-2 or D-2, The properties of catalytic surfaces were studied by infrared spectroscopy and kinetic methods in static or flow reactors. Six treatment or reaction types were applied for learning about surface transformations during or after the reaction. Carbonaceous deposits of various kinds were identified and their reaction influencing properties are analyzed. Metal-metal oxide interfaces are found to be crucial in the hydrogenative ring opening of methyloxirane and the roles of the metal and the metal oxide are elucidated as well.