Electrochemically catalyzed processes have potential to be more energy efficient and selective than traditional thermal catalysis while taking advantage of an increasing supply of renewable electricity. However, while providing a promising opportunity, the field of electrocatalysis is still relatively underexplored compared to traditional catalysis. To successfully employ electrochemically catalyzed processes, we must develop informed models to enable control over the reaction mechanisms and mass transport phenomena which govern them. Here, we explore the electrooxidation of cyclohexene using water as an oxygen source in a biphasic electrochemical cell. The novel cell design (Figure 1) separates the organic reactant from the aqueous electrolyte via a permeable electrode, allowing the reaction to occur at supported triple phase boundary regions between otherwise immiscible phases, while also minimizing the cost of separations downstream. Using this cell design, cyclohexene oxidation activity can be optimized by tuning reaction conditions (i.e. flow rates, electrolyte pH, applied potential) and electrode properties (i.e. catalyst location, electrode hydrophobicity) while monitoring charge passed towards formation of various oxidation products. We compare activities and product distributions for catalysts with varied support materials and binding strengths to oxygen-based surface adsorbates, to tune reaction pathways and subsequent products. Products are analyzed and Faradaic efficiencies are calculated for both the aqueous and organic phases via Gas Chromatography – Mass Spectroscopy and Nuclear Magnetic Resonance, respectively, to detect five major cyclohexene oxidation products. Representative results for a nanoparticulate Mn3O4 catalyst as a function of applied potential are shown in Figure 1. Catalyst materials and surface intermediates are characterized using a range of spectroscopic techniques to identify structure/reactivity relationships for this novel application of direct electrooxidation for chemical synthesis.

Investigating electrochemical oxidation of cyclohexene towards value added chemicals in a unique cell design

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ACS Fall 2022

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