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Phenol is an important model compound to understand the thermocatalytic (TCH) and electrocatalytic hydrogenation (ECH) of biomass to biofuels. Although Pt and Rh are among the most studied catalysts for aqueous-phase phenol hydrogenation, the reason why certain facets are active for ECH and TCH is not fully understood. Herein, we identify the active facet of Pt and Rh catalysts for aqueous-phase hydrogenation of phenol and explain the origin of the size-dependent activity trends of Pt and Rh nanoparticles. Phenol adsorption energies extracted on the active sites of Pt and Rh nanoparticles on carbon by fitting kinetic data show that the active sites adsorb phenol weakly. We predict that the turnover frequencies (TOFs) for the hydrogenation of phenol to cyclohexanone on Pt(111) and Rh(111) terraces are higher than those on (221) stepped facets based on density functional theory modeling and mean-field microkinetic simulations. The higher activities of the (111) terraces are due to lower activation energies and weaker phenol adsorption, preventing high coverages of phenol from inhibiting hydrogen adsorption. We measure that the TOF for ECH of phenol increases as the Rh nanoparticle diameter increases from 2 to 10 nm at 298 K and −0.1 V vs the reversible hydrogen electrode, qualitatively matching prior reports for Pt nanoparticles. The increase in experimental TOFs as Pt and Rh nanoparticle diameters increase is due to a larger fraction of terraces on larger particles. These findings clarify the structure sensitivity and active site of Pt and Rh for the hydrogenation of phenol and will inform the catalyst design for the hydrogenation of bio-oils.
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Enhancing Phenol Adsorption on Hydrophobic Pd/SiO2 to Achieve Faster and More Selective Hydrogenation
The effect of catalyst hydrophobicity on the kinetics of hydrogenation of aqueous phenol was investigated. The hydrophobicity of a Pd/SBA-15 catalyst was altered by synthesizing an organosilane with biphenylene framework linkers. Partitioning of phenol between the aqueous solution and the pores favors the hydrophobic catalyst by an order of magnitude at room temperature, relative to the hydrophilic catalyst. The rate of hydrogenation at 75 °C is higher in the hydrophobic catalyst, as is the selectivity for the partial hydrogenation product, cyclohexanone. Analysis of kinetic profiles measured using operando 13C NMR reveals that the hydrophobic catalyst has a larger apparent (i.e., composite) adsorption constant for phenol, which results in higher phenol surface coverage and, consequently, faster and more selective hydrogenation to cyclohexanone.
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- Award ID(s):
- 1805129
- PAR ID:
- 10461958
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Topics in Catalysis
- Volume:
- 66
- ISSN:
- 1022-5528
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s11244-023-01851-2
