(513ay) Deconvoluting Electrocatalytic Oxidation Pathways of Furfural Using Theory and Experiments

Driving reactions with electric potential, such as the electro-oxidation of furfural, could be a promising green method for chemical synthesis. Electro-oxidation may offer different reaction paths and selectivity control not offered in chemical oxidation, motivating our mechanistic analysis. We have earlier showed with Density Functional Theory (DFT) calculations that decarboxylation of furoic acid (C-C cleavage) limits the rate of furfural oxidation, which is consistent with high selectivity towards furoic acid at moderate potentials (0.8V-1V-RHE)[1, 2]. On Au/C surfaces, experiments show even more pronounced preference towards furoic acid (FA) over a wider potential range and with higher activity. We calculated the potential dependent free energy profiles for furoic acid formation on both Pt and Au through both carbonyl route or diol routes (Figure 1). Significantly weaker binding of the furanic ring on Au lead to a preferred diol route towards FA formation and faster desorption, leading to even higher activity. We also compared DFT predicted spectra of furoate (deprotonated furoic acid) and Stark rates of intense modes with in-situ spectroscopy (ATR-IR) to determine the orientation of furoate. Calculated and observed spectra along with steady state experiments with varying concentrations showed that the adsorption of furoic acid is potential dependent with a deprotonated furoic acid (furoate) binding in bidentate configuration, eventually blocking the surface at higher potentials. These results can help us to design a better catalyst tuned to be selective towards furoic acid or deeper oxidation products in different potential regimes.

References:

1. Gong, L., Agrawal, N., Roman, A., Holewinski, A., & Janik, M. J. (2019). Density functional theory study of furfural electrochemical oxidation on the Pt (1 1 1) surface. Journal of catalysis, 373, 322-335.
2. Román, A. M., Hasse, J. C., Medlin, J. W., & Holewinski, A. (2019). Elucidating Acidic Electro-Oxidation Pathways of Furfural on Platinum. ACS Catalysis, 9(11), 10305-10316.