TY - JOUR
T1 - Mechanistic Effects of Water on the Fe-Catalyzed Hydrodeoxygenation of Phenol. the Role of Brønsted Acid Sites
AU - Hensley, Alyssa J.R.
AU - Wang, Yong
AU - Mei, Donghai
AU - McEwen, Jean Sabin
N1 - Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/3/2
Y1 - 2018/3/2
N2 - 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 Brønsted 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 Brønsted acid sites via surface doping.
AB - 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 Brønsted 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 Brønsted acid sites via surface doping.
KW - Brønsted acid sites
KW - Fe catalyst
KW - density functional theory
KW - hydrodeoxygenation
KW - mechanistic effect of liquid water
KW - phenol
KW - reaction pathways
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U2 - 10.1021/acscatal.7b02576
DO - 10.1021/acscatal.7b02576
M3 - Article
AN - SCOPUS:85042912868
SN - 2155-5435
VL - 8
SP - 2200
EP - 2208
JO - ACS Catalysis
JF - ACS Catalysis
IS - 3
ER -