Nitrobenzene was hydrogenated at a H-2-pressure of 0.5...4MPa and a temperature of 310...370K, using Ni/SiO2, and Pt/C as catalysts. During the hydrogenation the catalyst＇s electrochemical potential was kept at a given level by regulation of the nitrobenzene feed (potential controlled hydrogenation). If the substrate concentrations are increased to values about some percent the hydrogenation rate decreases. Reaction instabilities caused by this effect can be reliably avoided by potential controlled substrate supply.