Tuning Single-Atom Dopants on Manganese Oxide for Selective Electrocatalytic Cyclooctene Epoxidation

Abstract

Selective and efficient electrocatalysts are imperative for the successful deployment of electrochemistry toward synthetic applications. In this study, we used galvanic replacement reactions to synthesize iridium-decorated manganese oxide nanoparticles, which showed a cyclooctene epoxidation partial 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. This results in an increased presence of electrophilic oxygen atoms on the catalyst surface during reaction conditions, which may contribute to the enhanced electrocatalytic activity toward cyclooctene epoxidation.

Controlling the Hydrophilicity of the Electrochemical Interface to Modulate the Oxygen-Atom Transfer in Electrocatalytic Epoxidation Reactions

“…Herein we study an archetypal anodic oxygenation reaction, the electrocatalytic epoxidation of cyclooctene in ACN/water mixtures (Scheme 1). 27,30 To examine the role played by the surface of the electrocatalyst on the oxygenatom transfer, we aimed for a single surface that can possess, or not, oxygen ligands as a function of cycling conditions. For that, gold was selected as in ACN/water mixtures, gold oxide is formed at potentials less positive than the OER, 55,56 allowing for investigating the epoxidation process both at a metallic surface and at a metal oxide surface.…”

Controlling the Hydrophilicity of the Electrochemical Interface to Modulate the Oxygen-Atom Transfer in Electrocatalytic Epoxidation Reactions

“…13 Among these reactions, electrochemical oxygenation reactions are of particular interest as they allow for the direct and chemoselective functionalization of C-H and C=C bonds forming industrially and pharmaceutically relevant chemical functions such as enones, 14 ketones, [15][16][17][18][19][20][21][22] aldehydes, 16,19,23 lactams, 24 lactones, 25 alcohols 15,21,22,26 and epoxides. 21,22,[27][28][29][30][31][32][33][34][35][36][37][38] The efficient and environmentally friendly preparation of an epoxide moiety is of prime importance as this structure is found in numerous natural products with potential biological activities, [39][40][41] is a versatile building block in organic chemistry 41,42 and plays an important role in industry. 11,43 Electrochemical epoxidation methods currently proceed via the anodic activation of molecular complexes, 20,35,44 thus complicating the isolation of the final product, or via the in situ generation of hazardous oxidants such as Cl2,...…”

“…21,28,32,34,36,38 Recently, an electrocatalytic epoxidation strategy using water as the sole oxygen source and a manganese oxide electrocatalyst to heterogeneously transfer the oxygen to the alkene was proposed to circumvent the aforementioned drawbacks. 27,30 However, little is known regarding the role of the electrocatalyst on the oxygen-atom transfer and more precisely on the parameters governing the selectivity between the oxygen evolution reaction (OER) and the epoxidation, which are pivotal for increasing the efficiency of the later process. In particular, questions arise regarding the exact role of the oxygen ligand at the surface of the electrocatalyst on the oxygen-atom transfer to the alkene.…”

“…Herein we study an archetypal anodic oxygenation reaction, the electrocatalytic epoxidation of cyclooctene in ACN/water mixtures (Scheme 1). 27,30 To examine the role played by the electrocatalyst surface on the oxygen-atom transfer, we aimed for a single surface that can possess, or not, oxygen ligands as a function of cycling conditions. For that, gold was selected as, in ACN/water mixtures, gold oxide is formed at potentials less positive than the OER, 55,56 allowing for investigating the epoxidation process both at a metallic surface and at a metal oxide surface.…”

“…In particular, questions arise regarding the exact role of the oxygen ligand at the surface of the electrocatalyst on the oxygen-atom transfer to the alkene. Indeed, conflicting results exist in the literature, with studies postulating that oxygen ligand is involved in the oxygen transfer 27,29,30,45 and others not. 17,26 For the competing reaction involving water oxidation, i.e.…”