Carbon-supported metal nanoparticles are widely used catalysts that combine chemical and structural diversity with electrical conductivity. Modified carbon materials support catalytic reactions through electronic and acid–base-induced interactions. Here, we applied acid treatment, carbonization of N- and O-precursors, and O2 plasma treatment to carbon prior to addition of palladium (Pd) nanoparticles and studied rates of selective electrocatalytic hydrogenation (ECH) of benzaldehyde to benzyl alcohol. All Pd catalysts enabled the hydrogenation of benzaldehyde to benzyl alcohol by electrocatalysis at room temperature. Rates per mass of catalyst as well as rates normalized to the accessible Pd surface atoms showed direct correlations with the concentration of Brønsted-acid sites of the modified felts and Pd catalysts. Remarkably, the correlation of ECH rates and concentration of acid sites in the Pd catalysts indicates that both metal and acid functionalities are required for an efficient electrocatalytic hydrogenation of the carbonyl group. Brønsted-acid sites in the proximity of the metal particles open a robust new catalytic route for the ECH of benzaldehyde via a proton-coupled electron transfer that is inaccessible if the hydrogenation is performed with H2 only. This insight opens new pathways for selective organic transformations and the low-temperature reductive manipulation of functional groups.
The research described here is part of the Chemical Transformation Initiative at Pacific Northwest National Laboratory (PNNL).
Revised: April 23, 2020 |
Published: January 20, 2020