Elucidating Pathways to Electrochemical Reduction of Furfural Via Tailoring Interfacial Environments Toward Selective Production of Valuable Furanic Chemicals

Abstract

Electrochemical reduction of biomass-derived feedstocks holds great promise to produce value-added chemicals or fuels driven by renewable electricity. However, mechanistic understanding of the aldehyde reduction toward valuable products at the electrode/electrolyte interface at the molecular level is still lacking. Herein, we studied the furfural reduction on Pb electrodes in acid conditions and elucidated the detailed pathways toward three key products: furfuryl alcohol (FA), 2-methylfuran (MF), and hydrofuroin. First, by coupling isotopic labeling and electrokinetics, we revealed that protons (H2O and H3O+) plays an important role in the hydrogenation pathway toward FA and MF. In particular, the study of product-selective kinetic isotopic effect of H/D and the surface property-dependent hydrogenation/deuteration pathway strongly impacted the generation of FA but not MF, which can be attributed to their different formation mechanisms: FA is produced from Langmuir-Hinshelwood pathway that need both adsorbed furfural and hydrogen, but MF produced from Eley-Rideal pathway that need proton directly from the electrolyte. Modifying the double layer by cations with large radii, we further correlated the product selectivity (FA and MF) with interfacial environments (local H3O+ and H2O content, etc). Combined methods, including pulsed electrolysis, electron paramagnetic resonance (EPR) spectroscopy, and DFT calculations, further suggested that the formation of hydrofuroin and FA shared one intermediate. Hydrofuroin is produced through the desorption of the intermediate as ketyl radicals followed by its self-coupling in the electrolyte, while FA is generated from further hydrogenation of that intermediate. The acquired into the electrochemical reduction of the aldehyde group in furfural to alcohol, alkyl, and dimer may be extended to other organic compounds with carbonyl group, such as 5-hydromethylfurfural, toward a sustainable electrochemical manufacturing of higher-valued chemicals from biomass feedstock.