Electrochemical Hydrogenation, Hydrogenolysis, and Dehydrogenation for Reductive and Oxidative Biomass Upgrading Using 5-Hydroxymethylfurfural as a Model System

Ever increasing energy demands and concerns about the environment necessitate the discovery of methods for producing fuels and chemicals from renewable resources in an environmentally benign manner. Electrochemical biomass conversion is particularly promising due to the abundance of renewable biomass and the advantages of electrochemistry, including the use of renewable electricity to drive chemical reactions without consumption of additional reductants and oxidants. Biomass intermediates are chemically complex and contain multiple functional groups, requiring selective reduction or oxidation for effective biomass conversion. Reductively, controlling the selectivity between hydrogenation and hydrogenolysis is necessary for efficient reduction of oxygenated functional groups to produce desired fuels and chemicals. Oxidatively, selective dehydrogenation of a particular functional group (e.g., alcohol or aldehyde oxidation to carboxylic acid) while preventing complete oxidation to CO2 is required for conversion of biomass to value-added products. In this Perspective, we use biomass-derived 5-hydroxymethylfurfural (HMF) as an especially useful model molecule for discussing recent developments in electrochemical hydrogenation, hydrogenolysis, and dehydrogenation reactions for biomass conversion, as HMF, which contains multiple functional groups, can be transformed into various valuable chemicals by both reductive and oxidative processes. For each reaction, the electrocatalysts, reaction conditions, and mechanisms will be discussed. Through this discussion, this Perspective aims to provide researchers with a foundational understanding of electrochemical hydrogenation, hydrogenolysis, and dehydrogenation reactions that can be applied to a wide variety of organic transformations, including biomass conversion.