The influence of Na on benzene hydrogenation over Pt has been investigated. The amount of Na interacting with the Pt catalyst was reversibly changed by electrochemically pumping the Na from B " Al2O3, a solid electrolyte which was both the Pt support and the source of the Na. The kinetics of the reaction are affected in a way that indicates an electronic effect of Na on benzene adsorption. The reaction can be completely inhibited at apparently low coverages of Na relative to the total surface area measured by oxygen chemisorption which may imply that only a small fraction of this surface is active for benzene hydrogenation on Pt/beta " Al2O3.