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

Authors: 
Ruggiero, B. - Presenter, Northwestern University
Notestein, J., Northwestern University
Seitz, L., Northwestern University
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.