Electrocatalytic hydrogenation of acetophenone and benzophenone using palladium electrodes

We have studied the electrocatalytic hydrogenation of acetophenone and benzophenone using a) potentiometric titration of adsorbed hydrogen by the organic reactant in excess, b) electrochemical impedance spectroscopy at a potential at the onset of hydrogen evolution and c) electrolysis at constant potential at high adsorbed hydrogen coverage. The rate of reactions between adsorbed hydrogen and adsorbed ketones and the respective alcohols intermediates of hydrogenation have been obtained from the titration curves at different organic reagent concentrations. Both the reaction rate and the charge transfer resistance, Rct, for the H+/Hads reaction follow a concentration dependence that can be interpreted by a Langmuir adsorption isotherm for the organic molecules and also a blockage of the palladium surface for the hydrogen adsorption. From the results of electrolysis at controlled potential under high hydrogen coverage, the faradaic yield and the product distribution, namely 1-phenylethanol, ethylbenzene, diphenylmethanol, diphenylmethane have been obtained.