Decene and acetone were hydrogenated over Ni, Pd, Pt, Cu, Ag, and Au catalysts in a polymer electrolyte hydrogen pump (PEHP) reactor. Water was oxidized over a Pt mesh anode and protons were pumped to the catalysts supported on porous carbon cathodes in contact with an organic liquid phase. The protons are reduced at the cathode to adsorbed hydrogen atoms which hydrogenate adsorbed olefins and carbonyl groups by heterogeneous catalysis. At low current density decene hydrogenation over Pd and Pt increased with the current density to the 1/2 power, indicating the surface reaction of adsorbed hydrogen with adsorbed decene was the rate limiting step. At high current density the reaction rate decreased linearly with current density, indicating adsorbed hydrogen inhibited decene adsorption and decene adsorption was the rate limiting step. Decene hydrogenation at 50 degrees C was 100 times slower over Ni, Cu, Ag, and Au catalysts compared to Pd and Pt. Acetone hydrogenation over Pt increased linearly with proton current density and was 10 times slower than decene hydrogenation. Acetone and decene hydrogenation rates at 50 degrees C were almost the same over Cu catalysts. Data were fit with modified Langmuir-Hinshelwood kinetics; the rate limiting steps were identified as the first hydrogen addition to adsorbed decene and the second hydrogen addition to adsorbed acetone.