(157c) Quantum Chemical Insight into Electrochemical Upgrading of Bio-oil

Bio-oil from plant-derived lignin is a renewable source of energy and organic feedstocks that
provides a sustainable alternative to fossil fuels. Pyrolysis of lignocellulosic biomass yields a rich
mixture oxygenated organic species with low energy density and low stability. Recent work suggests
that electrochemical methods are a viable approach of upgrading bio-oil to increase energy density
and to produce value-added chemicals [1,2]. Deconvoluting the network of reactions that occur in
these systems is a vital step toward the design of optimal upgrading processes.
Current work focuses on the electrochemical hydrodeoxygenation of furfural (FF) and 4-
propylphenol (4-PP), two representative constituents of raw bio-oil. In a binary mixture, the presence
of FF has been shown to reduce the hydrogenation activity of 4-PP. Here, we probe the underlying
mechanisms of these competing reactions by density functional theory (DFT) and experimental
electrochemical deposition techniques. The binding energies of FF, 4-PP, and the respective
hydrogenation products, as shown in Scheme 1, are examined comparatively on multiple facets of
single crystal platinum and ruthenium catalysts. With isolated adsorbates, the preferred binding
orientation is determined on each facet of the catalysts considered. Preliminary results suggest that 4-
PP binds more strongly to the surfaces considered, but is competitive with FF, particularly on
Pt(111) and Ru. The adsorption behavior of these molecules is additionally explored experimentally
through blocked hydrogen under potential electrochemical deposition experiments. Here, we predict
aqueous phase heats of adsorption which are correlated to the gas phase for comparison with
computational results. Optimized adsorption configurations for a given molecule and surface were
then utilized to assess the reaction thermodynamics, including the effect of potential bias. The
proposed pathways and potential side reactions of FF that may be inhibitory are evaluated.
Assessment of the binding energies and reaction thermodynamics on multiple catalysts and relevant
facets enable a quantitative analysis of preferential surface reaction to better understand the
experimental outcomes.
Scheme 1. Proposed reaction scheme.
References:
[1] C. H. Lam, C. B. Lowe, Z. Li, K. N. Longe, J. T. Rayburn, M. A. Caldwell, C. E. Houdek, J. B.
Maguire, C. M. Saffron, D. J. Miller and J. E. Jackson, Green Chem., 17, 601–609 (2015). [2] S.
Das, J. E. Anderson, R. De Kleine, T. J. Wallington, J. E. Jackson and C. M. Saffron, Sustainable
Energy Fuels, 6, 2823–2834 (2022).