Directly Oxidizing Ethanol to Glycolic Acid over a Single-Rh-Site Catalyst via Water-Mediated Oxygen Shuttle.

Abstract

Direct oxidation of ethanol to glycolic acid in aqueous solutions under mild conditions offers opportunities for sustainable chemistry. Herein, we report a water-mediated oxygen-shuttle mechanism on S/N/I atoms synergistically coordinated single-Rh-site catalysts (Rh₁/AC-SNI₄₀₀) to enable the direct production of glycolic acid from ethanol oxidation with 93% selectivity in liquid products and a TOF of 250 h^-1 at 160 °C. Comprehensive characterizations including isotope labeling experiments and theoretical calculations reveal that hydroxyl radicals (•OH), generated via O₂/I-triggered H₂O dissociation, insert into C-I bonds to form hydroxyl groups and meanwhile, replace the original OH in ethanol to form C═O, ensuring that all oxygen atoms of glycolic acid directly originate from H₂O. O₂ enters the system through the decomposition and regeneration of HIO intermediates, completing the oxygen-shuttle cycle driven by sustainable regeneration of water. Furthermore, the optimized S/N/I atoms' synergistical coordination enhances electron delocalization around single-Rh sites, substantially reducing the activation barriers of critical reaction steps and outperforming Rh nanoparticles by 16-fold in activity.