Thermochemical Aerobic Oxidation Catalysis in Water Proceeds via Coupled Electrochemical Half-Reactions
<div> <p><b>Heterogeneous aqueous-phase aerobic oxidations are an important emerging class of catalytic transformations, particularly for upgrading next generation bio-derived substrates. The mechanism of these reactions and the precise role of O<sub>2</sub> in particular remains unclear. Herein, we test the hypothesis that thermochemical aerobic oxidation proceeds via two coupled electrochemical half-reactions for oxygen reduction and substrate oxidation. We collect</b><b> electrochemical and thermochemical data on common noble metal catalysts under identical reaction/transport environments, and find that the electrochemical polarization curves of the O<sub>2</sub> reduction and the substrate oxidation half-reaction closely predict the mixed potential of the catalyst measured <i>in operando</i> during thermochemical catalysis across 13 diverse variables spanning </b><b>reaction conditions, catalyst composition, reactant identity, and pH</b><b>. Additionally, we find that driving the oxidation half-reaction reaction electrochemically in the absence of O<sub>2</sub> at the mixed potential leads to very similar rates and selectivities as for the thermochemical reaction in all cases examined. These findings strongly indicate that the role of O<sub>2</sub> in thermochemical aerobic oxidation is solely as an electron scavenger that provides an incipient electrochemical driving force for substrate oxidation. These studies provide a </b><b>quantitative and predictive link between thermochemical and electrochemical catalysis, thereby enabling the rational design of new thermochemical liquid-phase aerobic oxidation schemes by applying the principles of electrochemistry.</b></p> </div> <br>