(384f) Tandem Oxidative Chemical Transformations Using Electrochemically Produced Hydrogen Peroxide

Highly selective oxidizing species for low temperature catalytic reactions are critical for industrial production of chemicals. Electrochemical reduction of oxygen (O₂) to hydrogen peroxide (H₂O₂), an oxidant that solely produces H₂O as a byproduct, paves the way to integrate renewable resources to drive selective oxidation reactions. In contrast to the conventional anthraquinone oxidation process, electrochemical routes to H₂O₂ could also enable distributed facilities. In distributed plants, integrating electrochemical catalysis to synthesize H₂O₂ in tandem with thermochemical catalysis to subsequently utilize H₂O₂, has potential to open new avenues of research and may enhance the economic and environmental attractiveness of using H₂O₂ as a green oxidant.

Herein, we describe the development of combined schemes to electrochemically produce H₂O₂ from O₂ and directly use it in molecularly catalyzed oxidation reactions. Development of tandem electro- and molecular catalytic reactors for chemical production requires active and selective catalytic materials, but also depends on careful tuning of the reaction environment. Using a rotating ring disk electrode, CMK-3 carbon electrocatalyst, and electrolyte pH between 1-6, we found that overpotential was minimized and highest H₂O₂ selectivity was achieved for K₂SO₄ electrolyte compared to other alkali sulfates and acetates.

We next studied the oxidation of cyclohexanol using H₂O₂ solutions representative of those formed during electrochemical reduction of O₂. Following published reports, reactions were carried out in agitated 2-phase mixtures of cyclohexanol and H₂O₂ at 90°C with H₂WO₄ as the catalyst. Oxidation yielded several C₆ oxygenates including cyclohexanone, hexanoic acid, and eventually adipic acid. Under these conditions, conversion rates were approximately first order in H₂O₂ concentration and there was no dependence on sulfate concentration. Interestingly, we found reaction rates increased with added K₂SO₄ electrolyte, which is promising for tandem oxidation schemes. An improved fundamental understanding of this reaction system might enable broader implementation of sustainable pathways for industrial chemical synthesis.