Kinetics of furfural electrochemical hydrogenation and hydrogenolysis in acidic media on copper

Electrochemical processes can be implemented for the valorization of biomass-derived species such as furfural to generate fine chemicals and fuels. The electrochemical hydrogenation and hydrogenolysis (ECH) of furfural (FF) can produce furfuryl alcohol (FA) and 2-methylfuran (MF) as the major products over Cu catalysts in acidic conditions. The production of these species are in competition and the kinetics of these reactions should be studied so that the product distribution can be better controlled. In this work, the competing kinetics of furfural ECH to furfuryl alcohol and 2-methylfuran were studied on Cu in acidic media by using the applied cathodic potential, temperature, and initial concentration of furfural as probes. An increased temperature of the system was shown to promote the MF production in the range tested (15 degrees C and 45 degrees C), however the production of FA was decreased when the temperature was increased from 35 degrees C to 45 degrees C, due to significant promotion of side reactions. By varying the concentration of FF used in bulk electrolysis, we saw that the rates of reaction to FA and MF shift from positive order to zero order, suggesting a Langmuir-Hinshelwood or Eley-Rideal mechanism at -0.56 V vs. RHE and 25 degrees C. An analysis of the reaction mechanisms showed that a non-competitive Langmuir-Hinshelwood mechanism is likely occurring. In addition, we suggest the likely rate limiting steps based on the mechanisms are the first hydrogenation step of FF to C4H3O-CH2O to form FA, and the C-O cleavage of the C4H3O-CHOH intermediate to form MF.

Automated summary

Electrochemical processes can be used to valorize biomass-derived species like furfural to produce fine chemicals and fuels. The competition between furfuryl alcohol and 2-methylfuran in the electrochemical hydrogenation and hydrogenolysis reactions of furfural over Cu catalysts in acidic conditions can be influenced by factors such as temperature and initial furfural concentration. The study suggests that the reaction mechanisms likely involve a non-competitive Langmuir-Hinshelwood mechanism, with the rate limiting steps being the first hydrogenation of furfural to furfuryl alcohol and the C-O cleavage to form 2-methylfuran.