Effects of Applied Potentials and Copper Electrocatalysts on Electrochemical Hydrogenation and Hydrogenolysis of Furfural in Acidic Solution

Furfural (FF) is a C 5 biomass-derived platform chemical obtained from lignocellulose. It can be converted to an industrial adhesive intermediate, furfuryl alcohol (FA), and a promising biofuel candidate, 2-methyl furan (MF) [1]. Liquid phase catalytic hydrogenation and hydrogenolysis (CH) is a widely used manner for biomass conversion. However, it requires large quantities of externally supplied hydrogen gas with high pressure and high temperature [1]. In contrast to CH, electrochemical hydrogenation and hydrogenolysis (ECH) enables biomass conversion at ambient conditions. Also, atomic hydrogen for ECH can be supplied from the aqueous electrolyte. These advantages led to recent studies of electrochemical biomass conversion [2]. From the previous studies for ECH of FF, FA can be obtained at various pH ranges (0 – 13)[2], while MF can be only produced in low pH (0 – 1) solutions. The highest selectivity (c.a. 80%) of MF was shown at pH 0 and 8 o C with a Cu foil electrode[3]. A concurrent reaction during ECH of FF is the hydrogen evolution reaction that undesirably consumes electrons[4], which is in competition with ECH of FF. Moreover, from our previous study, we reported that furanic compounds in acidic electrolytes (pH ≤ 1) participate in homogeneous side reactions, decreasing the mole balance closure[5]. This investigation focuses on the combined effects of reaction conditions, copper electrocatalysts and experimental setup towards selective MF production. This is to improve the conversion of FF, yield of MF and energy efficiency with high mole balance for the selective production of MF in pH 0 solution (0.5 M H 2 SO 4 ). In order to obtain high yield of MF and avoid homogenous side reactions of MF within the acidic solution, vigorous stirring and N 2 gas flowing through the reaction solution was introduced to evaporate volatile MF rapidly. Bare Cu foil and micro-sized Cu electrocatalysts, obtained by electrodeposition, have been used as the electrocatalysts. ECH of FF was run at potentials from - 0.5 to - 0.95 V vs RHE. Vigorous stirring and N 2 gas flowing improved the mole balance and MF yield. Micro-sized Cu electrocatalysts showed higher conversion of FF and yield of MF compared to bare Cu. In addition, conversion of FF and yield of MF increased as applied potential increased, while faradaic efficiency for FA and MF production increased as applied potential decreased. [1] Y. Nakagawa, M. Tamura, K. Tomishige, Catalytic reduction of biomass-derived furanic compounds with hydrogen, ACS Catalysis, 3 (2013) 2655-2668. [2] Y. Kwon, K.J.P. Schouten, J.C. van der Waal, E. de Jong, M.T.M. Koper, Electrocatalytic conversion of furanic compounds, ACS Catalysis, 6 (2016) 6704-6717. [3] P. Nilges, U. Schröder, Electrochemistry for biofuel generation: production of furans by electrocatalytic hydrogenation of furfural, Energy & Environmental Science, 6 (2013) 2925-2931. [4] R. Parsons, The rate of electrolytic hydrogen evolution and the heat of adsorption of hydrogen, Transactions of the Faraday Society, 54 (1958) 1053-1063. [5] S. Jung, E.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 (2016) 6500-6508.