Production of hydrocarbon fuels and value-added chemicals from lignin derived phenolic monomers (e.g., guaiacol) requires the selective removal of oxygen rather than the undesired ring saturation during hydrodeoxygenation (HDO) catalysis. On transition metal surfaces, catalytic paths and their selectivity depend strongly on the identity of active site and its environment. For condensed phase catalysis, solvent molecules play critical catalytic roles—they not only solvate and then stabilize/destabilize the intermediates and transition states [1], but also directly participate in catalytic turnovers [2-6]. Despite their obvious manifestation, there is a lack of atomistic descriptions on these interfacial properties and the resulting mechanistic consequences. Furthermore, protic solvents such as water can ionize hydrogen adatoms (H*) [7], generating protons (H+) at the solid-liquid interface, which alters the kinetically relevant paths. Here, we rationalize the kinetic isotopic experiments with density functional theory (DFT) calculations to probe the charge of reactive hydrogen intermediates on Ru surfaces, as these hydrogen species acquire the charge and character of H* and H+. We address the promotional effects of H+ in aromatic ring hydrogenation, which alters the most abundant reactive intermediate (MARI) and subsequently lowers the barrier for Ar-OCH cleavage. Our study shows that, by choosing an appropriate pair of solvent and metal, we can manipulate the charge of the reactive hydrogen species and in turn the HDO reactivity and selectivity towards the desired C-O bond cleavage. As such, by combining a theoretical explicit solvent model and kinetic isotopic measurements, we demonstrate that the presence of water enables proton-shuttling; the atomistic-scale movement of protons and electrons at the solid-liquid interface improves the catalytic HDO performance as well as generally polar bond hydrogenation (e.g. carbonyl conversion to alcohols [2]).

Elucidating the effects of the environment during guaiacol hydrodeoxygenation on Ru

ACS Spring Meeting 2021

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