(583d) Tuning Single Atom Dopants on Manganese Oxide for Selective Electrocatalytic Olefin Epoxidation

Olefin epoxidation is an essential chemical functionalization reaction for the synthesis of various commercial end products. Current routes of olefin epoxidation involve hazardous reagents and stoichiometric side products, leading to challenges in separation and significant waste streams. Our group previously reported an electrochemical route for olefin epoxidation where manganese oxide nanoparticles catalyzed the direct epoxidation of cyclooctene using water as an oxygen atom source, with a Faradaic efficiency of approximately 30%. While this method provides an environmentally friendly and safe route to make epoxides, its low selectivity and rate must be improved for it to become industrially relevant.

One way to improve the efficiency of heterogeneous catalysts is through the introduction of atomically dispersed metal atoms on the appropriate supporting materials. Single metal centers can be introduced to a substrate that already acts as a catalyst for the target reaction. In this case, it is important to consider the geometric and electronic tuning of the original active sites upon the introduction of heteroatoms to the host catalyst, in addition to their role as additional active sites. In this study, we utilized galvanic replacement reactions to synthesize single-iridium-decorated manganese oxide nanoparticles (Ir_single-MnO_x NPs), which showed a cyclooctene epoxidation current density of 10.5±2.8 mA/cm² and a Faradaic efficiency of 46±4 %. Results from operando X-ray absorption spectroscopy suggest that manganese leaching from the nanoparticles during galvanic replacement introduces lattice vacancies that make the nanoparticles more susceptible to metal oxidation and catalyst reconstruction under an applied anodic potential. Highly electrophilic oxygens induced by adjacent electron-poor metals were possibly responsible for the enhanced electrocatalytic cyclooctene epoxidation performance on Ir_single-MnO_x. Our findings highlight that galvanic replacement reactions can be employed for the mild tuning of metal oxide catalysts by introducing heteroatoms as well as by modifying the structural and electronic properties of the catalyst.