Uncovering Insights to the Reaction Mechanism of the Electrochemical Hydrogenation and Hydrogenolysis of Furanic Species

Abstract

Biomass derived compounds may be used as platform molecules for valorization to value-added products and biofuels. Two such molecules are furfural (FF) and 5-(hydroxymethyl)furfural (HMF). Using electricity as the energy source, FF and HMF can be upgraded by electrochemical hydrogenation and hydrogenolysis (ECH) reactions. The products of interest when FF is used as the starting molecule are the hydrogenation product, furfuryl alcohol (FA), a chemical intermediate, and the hydrogenolysis product, 2-methylfuran (MF), a biofuel. Similarly, HMF undergoes ECH to form 2,5-dihydroxymethylfuran (DHMF), a chemical intermediate, and 2,5-dimethylfuran (DMF), a biofuel. Existing studies probe the effect of electrode, electrolyte, applied potential, and temperature on reaction efficiency and selectivity, however fundamental questions remain about the reaction pathway and kinetics. This study elucidates the reaction pathway of FF and HMF to products through bulk electrolysis ECH.The ECH reactions were carried out via potentiostatic bulk electrolysis in an H-type cell with Cu flag working electrode in acidic electrolyte (0.5M H2SO4). By sampling the electrolyte at various times throughout the reaction, the product distribution with time for the ECH reactions was developed. The concentration of HMF and its products was determined by HPLC and the concentration of FF and its products was determined by GCMS. For 90 minutes of FF ECH, the concentration of both FA and MF increased steadily with reaction time; neither showed signs of further consumption. This observation indicates that FF ECH occurs over two separate, parallel paths to FA and MF. This is further evidenced by the lack of reaction to MF when FA is used as the starting molecule for ECH.