Electrode potential of a dispersed Raney nickel electrode during acetone hydrogenation: Influence of the promoters

Abstract

The hydrogenation of acetone was investigated in basic aqueous solution with (Co, Cr, Cu, Mo, Ti) doped and undoped Raney nickel catalysts. The reaction was carried out under pressure in an autoclave equipped with a reference electrode. The hydrogen consumption and the electrode potential were measured during the course of the reaction. Addition of Cr, Mo or Ti improves the activity in acetone hydrogenation while the activity of Co or Cu promoted catalysts remains similar to that of the undoped nickel. The kinetics obeys a Langmuir-Hinshelwood mechanism. A mathematical model was applied which fits well the experimental kinetic data. It allows the computation of the rate constant and the adsorption equilibrium constants. The metallic catalyst particles behave like a dispersed electrode and an electrochemical double layer is formed at their surface. In the presence of hydrogen alone, the metal potential is determined by the Nernst law for the hydrogen electrode. In the presence of acetone, the measured potential goes to the positive region for several tenths millivolts. The extent of the initial potential shift measured when acetone is introduced in the reactor is experimentally correlated with the physicochemical characteristics of the catalysts and their activities for acetone hydrogenation in the liquid phase.