Ethylene Glycol Partial Aqueous Oxidation on Co3O4 (001) Surfaces: Pathways to Two- and Four-Electron Products in Neutral and Oxidative Conditions

Abstract

The catalytic oxidation of ethylene glycol (EG) on the Co₃O₄ (001) surface is investigated by AIMD simulations in the presence of a water layer for the A- and B- terminations. In addition to the surface structure and composition, the chemical state of the aqueous environment plays a crucial role in the oxidation process. Specifically, it depends on the concentration of surface hydroxyl groups, which can act both as proton donors and acceptors. Reference surfaces, which are generated by bringing the unhydrogenated A- and B-terminated surfaces in contact with a stoichiometric water layer, show some spontaneous water dissociation, which produces a number of surface hydroxyl groups. On such an A-terminated reference surface, the EG molecule is barely reactive. This holds even in a more oxidative state. On the B-terminated surface, EG's decomposition into ethylenedioxy species occurs already in the reference state. Under the more oxidative hydrogen-deficient conditions obtained by removing eight hydrogen atoms, the reaction proceeds to the formation of the two-electron oxidation product glycolaldehyde. Removal of altogether 16 hydrogen atoms facilitates the formation of four-electron oxidation products, such as glycolic acid and glyoxal and the observation of a transient H₂O₂ species, which subsequently evolves to form dioxygen.