(133d) Electrification of Furanic Reduction Reactions: Insights into Balancing Desired and Undesired Reactions over Cu in Acid

Efforts to decarbonize the chemical industry have led to interest in renewable feedstock materials, such as biomass derived species, and a desire to couple reactions with intermittent renewable energy sources like solar or wind. Furfural is one biomass derived species that has been identified as a promising building block chemical due to its abundance and array of valorized products that can be formed. Furfural (FF) can be electrochemically reduced via hydrogenation to form furfuryl alcohol (FA), or hydrogenolysis to form 2-methylfuran (MF). FA is used to produce temperature stable resins and molds for foundry industry, and MF has been identified as a high octane fuel or fuel additive.

In acidic solutions on Cu electrodes, the electrochemical hydrogenation and hydrogenolysis reactions proceed in parallel reactions, showing that FA is not an intermediate in the formation of MF. For the selective production of the MF product on Cu electrodes, an acidic electrolyte is necessary, however it has been shown that FA and MF will undergo homogeneous side reactions in the acid leading to undesirable humin formation. At high concentrations of FF with long durations of electrolysis, fouling of Cu catalysts leading to performance drop has been shown as well. Understanding the different pathways to desired and undesired reactions that occur is key in designing catalysts and reactors that can increase the selectivity to desired products and minimize side reactions.

In this work, the characteristics and kinetics of desired and undesired reactions that occur during the electrochemical hydrogenation and hydrogenolysis of furfural on Cu in acidic solutions will be presented. We identified kinetic models for the desired electrochemical reactions towards FA and MF suggesting that they are formed via the non-competitive Langmuir-Hinshelwood mechanism through different intermediates. Undesired reactions occur both at the electrode, in terms of fouling, as well as homogeneously in electrolyte due to acidity. The undesired fouling reactions were found to be potential dependent, showing polymer formation or graphitic coking at moderate and high negative overpotentials, respectively. In solution, the undesired homogeneous reactions consumed FA and MF and were shown to follow first order kinetics with the proton activity and the concentration of FA or MF.