Electrocatalytic hydrogenation (ECH) is a promising approach that combines the utilization of renewable electricity with the conversion of biogenic carbon sources storing energy in chemical bonds. Carbonyl groups are one of the most abundant and reactive functionalities of molecules contained in bio-oil. Hence, the stability of the treated bio-oil is improved by reducing the carbonyl content. Recent studies pertaining to ECH of benzaldehyde on different carbon supported metal catalyst demonstrated the superior activity of Pd/C compared to other catalysts (Pt/C, Rh/C, Ni/C) towards hydrogenation of carbonyl functionalities. In the present study we explore the chemistry of aqueous phase hydrogenation of different carbonyl compounds at low temperatures under the influence of electric potentials with an aim to understand the influence of molecular structure on the reaction pathways and selectivity to ECH. Series of aromatic and aliphatic carbonyl compounds have been tested on C-supported Pd. All measurements were conducted in acetate buffer (pH 5) within a cathodic potential range of -0.1 to -0.3V vs RHE. At these reaction conditions the reactivity of aromatic carbonyls is much higher than that of aliphatic ones. Aldehydes and ketones are selectively converted to alcohols, i.e. aromatic rings are unreactive. The H<sub>2</sub> evolution reaction (HER) is the only pathway competing with the hydrogenation of the organics. The ECH rates of aromatic carbonyls, as well as HER rates, increase with increasing cathodic potential and further enhancement of these rates (~ 2 fold) was noted by using acidic electrolyte (pH 2). Thermal catalytic hydrogenation (TCH) of these carbonyl compounds were also studied whit 1 bar H<sub>2</sub> used as the reductant. The rates of ECH were always higher than TCH rates, which points to an electrochemical mechanism dominating the reaction. The kinetic studies as well as plausible elementary steps of carbonyl hydrogenation pathways will be discussed in detail.

Elucidating the reaction networks and mechanisms in electrocatalytic hydrogenation of carbonyl compounds

2019 Spring National Meeting

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