PNNL

Abstract

The electrocatalytic reduction of benzaldehyde to benzyl alcohol on Pd supported on a carbon felt was conducted in the aqueous phase using a continuous flow fixed bed reactor at room temperature and atmospheric pressure. Methanol, ethanol, or isopropanol were added to the electrolyte to study the impact of alcohol type and concentration on the rates of benzaldehyde electrocatalytic hydrogenation and H2 evolution, the prevalent side reaction. Whereas the electrocatalytic hydrogenation rates and Faradaic efficiency decreased with increasing alcohol concentrations, the H2 evolution rates remained constant. The impact of the alcohol on hydrogenation was greater as the length of the alcohol’s hydrocarbon chain increased. Increasing the benzaldehyde concentration allows for high electrocatalytic hydrogenation rates, and high Faradaic efficiency. The reaction order increased from ~0.13 to ~0.66 with half-cell potential increasing from -650 mV to -1150 mV (vs. Ag/AgCl). A kinetic analysis reveals that the changes in reaction order are due to changes in benzaldehyde (and H) surface coverages as a function of half-cell cathodic potential. Thus, the results shown here reveal how the performance of the continuous electrocatalytic operation is affected by the electrolyte composition and half-cell cathodic potential.