Demonstrating the electron-proton transfer mechanism of aqueous phase 4-nitrophenol hydrogenation on supported metal catalyst using unbiased electrochemical cells

29 June 2022, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Heterogeneous thermocatalytic hydrogenation is widely believed to occur via co-adsorption of H2 and other reactants, but in aqueous phase an ionic or electrochemical mechanism was also proposed. Herein, we conduct 4-nitrophenol hydrogenation in an unbiased H-cell, where H2 and substrate are separately supplied into two chambers connected by a proton exchange membrane, in comparison with the same reaction in a single-cell in which H2 and 4-nitrophenol are co-fed. Based on the observation of the almost identical hydrogenation performance between the H-cell and the single cell, we conclude that co-adsorption of H2 and 4-nitrophenol is not a prerequisite for hydrogenation in aqueous phase in the tested pH range. Isotope experiments, scavenger test, DFT calculations and reaction kinetics suggest that a coupled electrochemical half-reaction mechanism for 4-nitrophenol hydrogenation in acidic aqueous phase is predominant. Importantly, while H2 oxidation primarily occurs on metal sites, 4-nitrophenol reduction occurs on both metal sites and conductive support, highlighting the non-innocent role of the support if the hydrogenation reaction follows the electron-proton transfer pathway.

Supplementary materials

Title
Description
Actions
Title
Supporting information
Description
Supporting information
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.