(399c) Impact of Phenol on the Electrocatalytic Hydrogenation of Carbonyl Compounds on Metal Catalysts

Impact of phenol on
the electrocatalytic hydrogenation of carbonyl
compounds on metal catalysts

Udishnu Sanyal, Katherine Koh, Laura
Meyer, Jamie Holladay, Oliver Y Gutiérrez, Johannes A. Lercher

Physical and
Computational Sciences Directorate, Pacific Northwest National Laboratory,
Richland WA, United States

*Corresponding author: udishnu.sanyal@pnnl.gov

Electrocatalytic
hydrogenation (ECH) is a promising route for low-temperature bio-oil treatment,
wherein renewable electricity can be used to store hydrogen in hydrocarbon
energy carriers used as transportation fuels.¹ ECH of phenol and benzaldehyde
(model compounds) shows rates and selectivity to hydrogenation that depend on
the metal.² As bio-oil is a mixture of compounds with different
functionalities, development of a sustainable process towards bio-oil
stabilization often requires the fundamental understanding of competitive hydrogenation
pathways in presence of mixtures of model compounds. Thus, the present study
aims to explore the hydrogenation kinetics and reaction pathways of simultaneous
conversion of phenol and aromatic carbonyls on carbon supported metal catalysts.

Under ECH, the H₂
evolution reaction (HER) is the reaction competing with the hydrogenation of
oxygenates. Therefore an important variable to study is the selectivity (Faradaic
efficiency) defined as fraction of total electron used for hydrogenation. All catalysts
tested (Rh/C, Pd/C, Ru/C, Cu/C) were active for benzaldehyde
hydrogenation to benzyl alcohol, however, only Rh/C was active for the
hydrogenation of phenol which yielded cyclohexanone and cyclohexanol
at pH 5, and -0.1 V vs RHE. When phenol was co-feeded
alongside benzaldehyde, no phenol hydrogenation was noted on all catalysts
tested. However, an enhancement in ECH rate of benzaldehyde (~2-4 fold
depending on metal catalyst) was observed in case of Pd/C,
Ru/C and Cu/C. ECH of benzaldehyde was very similar on Rh/C in presence and
absence of phenol. The presence of phenol in the feed increased Faradaic
efficiency in case of Cu/C and decreased it on Ru/C. We hypothesize that phenol,
coadsorbed on the metal, affects the rates of HER but
its acidic nature results in higher hydrogen chemical potential and thus, in an
enhancement in ECH rates. Hydrogenation of benzaldehyde was further investigated
on Pd/C with different phenolic compounds by varying
the pK_a of phenolic moieties. The results
of the detail kinetic studies, the generality of the chemistry for other
carbonyl compounds and the reaction pathways for electrocatalytic
hydrogenation will be addressed in this presentation.   

Reference

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Song,
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68.