Aqueous-phase aerobic oxidation of ethylene glycol on Co 3 O 4 : a facet specific investigation in alkaline free conditions

Using ab initio molecular dynamics simulations at 393.15 K, a comparative investigation of the Co 3+ terminated (110) and (111) surfaces in alkaline free conditions demonstrates distinct adsorption behaviors, reaction pathways, and overall surface-mediated redox processes. The (110) surface facilitates the selective oxidation of Ethylene glycol (EGLY) to hydroxyaldehyde, a 2-electron product. This pathway proceeds via a bidentately adsorbed EGLY molecule, followed by sequential dehydrogenation and deprotonation events. The surface acts as an electron sink, becoming reduced as its accepts electrons from the oxidizing molecules. In contrast, the (111) surface does not support selective oxidation. Instead, it promotes single deprotonation, leading to the formation of ethylenedioxy intermediates and side products, including molecular hydrogen and surface cobalt oxyhydroxide (Co-OOH). The charge analysis confirms that the (111) surface, while also undergoing partial reduction, remains in a significantly more oxidized state overall. This electron-deficient character drives the decomposition pathways of molecules. The key differentiating factor is the nature of the active sites. The (110) surface provides well-defined, stable Co 3+ sites that stabilize bidentate adsorption and enable C-H activation. The reconstructed (111) surface, with its dynamic Co 2+ and Co 3+ ions, creates adsorption modes that lead to unselective chemistry and surface passivation through oxyhydroxide formation.