Catalytic hydrogenation in the liquid-phase over supported metal catalysts at high hydrogen pressures can be described by the zero order in respect to all components. The reaction mechanism which involves formation of intermediate complexes including hydrogen and organic compound is discussed. The reaction rate in the region of zero orders is determined by the isomerisation rate of these complexes. Experimental data presented indicate that the pre-exponential factor in Arrhenius equation is essentially less then expected from the absolute rate theory. These observations are explained based on the model of an anharmonic oscillator.