Nanostructured Electrocatalysts for Triglyceride Hydrogenation.

Abstract

An electrochemical process for the reduction of organic compounds could have a number of advantages over thermochemical reduction, including enhanced separation between reactants and products, lower operating temperatures and pressures, and improved mass transfer of reactants to and from catalyst surfaces. This research investigated the use of noble metal, base metal, transition metal carbide, and carbide-supported metal catalysts for the electrochemical hydrogenation of triglycerides. We report that many of these catalysts, including W2C-supported Pd catalysts, had high rates and/or selectivities for the hydrogenation reaction.

Low activities for certain catalysts were hypothesized to be related to lack of stability in the electrochemical hydrogenation reactor. The solid polymer electrolyte (SPE) used in this study is known to be strongly acidic, which can create a corrosive environment under certain applied potentials. Two techniques, thermogravimetric analysis of the post-reaction membrane electrode assemblies and chronoamperometry in a model SPE cell, were used to characterize catalyst stabilities. It was concluded that the low activities of these base metal and carbide catalysts for triglyceride hydrogenation were due to their incompatibility with the SPE.

This study is among the first to investigate the nature of the hydrogenation mechanism is the context of the SPE reactor. By varying the applied voltage across the SPE reactor, it was found that catalytic activities varied with potential. Linear sweep voltammetry was used with the various catalysts in a model SPE cell, which showed that this dependence was due to the electrochemical nature of the hydrogenation rate determining step. Variations in the hydrogenation activities of the different catalysts were found to correlate with their activities for the hydrogen evolution reaction, suggesting that similar sites are involved in each reaction. With this understanding of the triglyceride hydrogenation mechanism, catalyst formulations could be modified to improve the activities and selectivities for this and related reactions. A preliminary economic analysis indicated that the electrochemical hydrogenation of triglycerides may be economically viable in comparison to the thermochemical process currently used in industry.