(439f) Insights into the Reaction Schemes of Furfural and 5-Hydroxymethylfurfural Reductions in Acidic Media over Copper

Decarbonization can be brought about through electrochemical reactions that use renewable electricity to transform sustainable feedstocks, such as biomass derived species. Biomass derived species are abundant and renewable on much shorter time scales compared to petroleum species, however the technology to upgrade them is much younger. Two biomass derived species of interest for their availability, cost, and status as platform molecules are furfural and 5-hydroxymethylfurfural (HMF). Cu metal catalysts can be used to transform FF into furfuryl alcohol and 2-methylfuran, used for making resins and as a fuel candidate, respectively. Likewise, over Cu, HMF can transform to several reduction products, used as fuels or fine chemicals. One key parameter in the product distribution is the pH of the electrolyte, with a low pH allowing for hydrogenolysis products to be produced.

In this work, the product distributions of FF and HMF were investigated on Cu in acidic media using bulk electrolysis to show the electrochemical pathways that occur in acid. Bulk electrolysis was done using concentrations of the organic substrate between 10 and 120 mM for FF or 50mM for HMF and its derivatives. The electrolyte was acidic with 0.1M or 0.5M H₂SO₄ to allow production of all species of interest. FF has a simpler reaction network than HMF due to having 2 main products as opposed to 4. We were able to model the FF kinetics through an initial rate study of the electrochemical reactions and determine the most likely mechanism, a non-competitive Langmuir-Hinshelwood mechanism [1]. HMF ECH has a more complex reaction network, however we were able to narrow the network down and determined reactions that will not occur electrochemically under our experimental conditions. Spectroscopy was used to investigate further the surface species during electrochemical reduction.

Homogeneous acidic reactions are well documented for FF [2,3], and we showed in this work that they occur within the HMF system as well. We quantified these homogeneous side reactions using capped vials with no electrochemistry occurring to fully describe the kinetics of the FF and HMF electrochemical systems and quantify which products in the reaction scheme are most susceptible to mass losses from side reactions.

[1] May, Andrew S., Steven M. Watt, and Elizabeth J. Biddinger. "Kinetics of furfural electrochemical hydrogenation and hydrogenolysis in acidic media on copper." Reaction Chemistry & Engineering 6, no. 11 (2021): 2075-2086

[2] Jung, Sungyup, and Elizabeth J. Biddinger. "Electrocatalytic hydrogenation and hydrogenolysis of furfural and the impact of homogeneous side reactions of furanic compounds in acidic electrolytes." ACS Sustainable Chemistry & Engineering 4, no. 12 (2016): 6500-6508

[3] Jung, Sungyup, and Elizabeth J. Biddinger. "Controlling competitive side reactions in the electrochemical upgrading of furfural to biofuel." Energy Technology 6, no. 7 (2018): 1370-1379