Journal
ACS CATALYSIS
Volume 9, Issue 2, Pages 1120-1128Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.8b04039
Keywords
hydrogenation; phenol; platinum; Bronsted-Evans-Polanyi; aqueous phase; hydrogen adsorption; pH effects; molecular dynamics simulations
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Funding
- Washington Research Foundation Innovation Fellowship
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences Division Grant [DE-FG02-96ER14630]
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In aqueous phase, the rates of hydrogenation of aromatic substrates such as phenol on Pt/C and Rh/C are influenced by varying activity of hydronium ions. Decreasing the pH from 8 to 1 increases the rate of hydrogenation of phenol on Pt at 20 bar H-2 and 80 degrees C by 15-fold. This increase is attributed to weakening of the hydrogen binding energy (HBE) on the metal surface with decreasing pH. A weaker HBE at lower pH is also predicted by ab initio molecular dynamics simulations, providing atomistic insight into the impact of electrolyte ion distribution and interfacial solvent reorganization on HBE. The lower HBE results in a decrease in the activation energy for addition of adsorbed H from the metal to the adsorbed organic (with a Bronsted-Evans-Polanyi slope of similar to 1). The kinetic model derived accounts also for the lack of pH dependence at low hydrogen coverages (at 1 bar H-2 on Pt or up to 70 bar H-2 on Rh), when the weakening of the HBE decreases the hydrogen coverage.
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