Mechanistic Changes with Applied Potential in Cu Fouling during Furfural Electrochemical Hydrogenation and Hydrogenolysis

Abstract

CO2 emissions are generated in the chemical industry by factors such as the generation of reactants, including hydrogen, as well as in heating of the reactors. Electrochemical methods can avoid the need for externally provided hydrogen by generating required protons in-situ from the electrolyte, and can be more easily coupled with renewable electricity than their thermocatalytic counterparts. Therefore, to assist in the mitigation of CO2 emissions, electrochemical processes can be used. Furfural is a biomass-derived platform molecule that can be electrochemically reacted to form several species of interest including fine chemicals and fuels. Furfuryl alcohol, the hydrogenation product, is one fine chemical of interest used to make furanic molds or resins. The hydrogenolysis product of furfural, 2-methylfuran, has been identified as a fuel additive. The electrochemical hydrogenation and hydrogenolysis over Cu catalysts in acidic media allows for the parallel production of furfuryl alcohol and 2-methylfuran. During the electrochemical hydrogenation and hydrogenolysis of furfural over Cu in acidic electrolyte, the Cu catalyst will become covered in carbonaceous material with use. This fouling changes with applied potential, with a polymeric material being formed at -560 mV RHE while at -700mV a non-polymeric carbonaceous material is formed on the Cu. In both cases, the fouling leads to deactivation of the catalyst. In this work, Cu metal foils were intentionally fouled to study the mechanisms that led to catalyst fouling to provide insights into possible mitigation techniques.A semi batch reactor was used in which the Cu working electrode was recycled to further foul the catalyst. The catholyte had 200 mM furfural and 0.5 M H2SO4 in a 80:20 vol% water:acetonitrile co-solvent. The Cu electrode was recycled thrice with fresh electrolytes each time. After use at -560 mV RHE a polymer formed on the surface; FTIR of the fouled surface showed consistent spectra as poly(furfuryl alcohol). At -700 mV RHE, no polymer was found, however a carbonaceous layer was found. XPS was used to better distinguish between the carbonaceous fouling that occurred at different applied potentials.