Journal
ACS CATALYSIS
Volume 8, Issue 3, Pages 2200-2208Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.7b02576
Keywords
hydrodeoxygenation; mechanistic effect of liquid water; phenol; Fe catalyst; density functional theory; reaction pathways; Bronsted acid sites
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Funding
- U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program
- DOE [DE-AC05-06OR23100]
- U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Chemical Sciences, Biosciences and Geosciences [DE-SC0014560]
- DOE Office of Science BES [DE-FG02-05ER15712, DE-AC05-RL01830, FWP-47319]
- American Chemical Society Petroleum Research Fund
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A mechanistic understanding of the roles of water is essential for developing highly active and selective catalysts for hydrodeoxygenation (HDO) reactions because water is ubiquitous in such reaction systems. Here we present a study for phenol HDO on Fe catalysts using density functional theory which examines the effect of water on three elementary pathways for phenol HDO using an explicit solvation model. The presence of water is found to significantly decrease activation barriers required by hydrogenation reactions via two pathways. First, proton transfer in the hydrogen bonding network of the liquid water phase is nearly barrierless, which significantly promotes the direct tautomerization of phenol; Second, due to the high degree of oxophilicity on Fe, liquid water molecules are found to be easily dissociated into surface hydroxyl groups that can act as Bronsted acid sites. These sites dramatically promote hydrogenation reactions on the Fe surface. As a result, hydrogen-assisted dehydroxylation becomes the dominant phenol HDO pathway. This work provides fundamental insights into aqueous phase HDO of biomass-derived oxygenates over Fe-based catalysts; e.g., the activity of Fe-based catalysts can be optimized by tuning the surface coverage of Bronsted acid sites via surface doping.
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