Asymmetric Cobalt Single-Atom Catalysts with Engineered Hydrophobic Microenvironment: A Reaction-Transport Coupled Strategy for Efficient Methyl Oleate Epoxidation

The depletion of fossil resources and the urgent demand for biodegradable alternatives drive innovations in transforming renewable vegetable oils into high-value chemicals. Despite substantial progress in epoxidized vegetable oils (EVOs) as green alternatives to petrochemicals, this process remains hindered by low activity and/or selectivity. Herein, we present an effective strategy coupling intrinsically active asymmetric single-atom Co-N2-O2 sites with an engineered hydrophobic microenvironment to overcome these challenges in methyl oleate epoxidation, a model reaction for vegetable oil conversion. This rationally designed catalyst achieves a record turnover frequency of 1356 h-1 and 99% selectivity under ambient conditions by using O2 as the terminal oxidant. Mechanistic studies reveal that the asymmetric Co-N2-O2 coordination markedly enhances O2 activation by creating a modulated electronic structure that up-shifts the d-band center of the Co atom, thereby boosting electronic reactivity toward O2 compared to symmetric Co-N4 sites. Crucially, the alkyl anhydride-grafted hydrophobic surface engineers a unique microenvironment that facilitates the partitioning of the lipophilic methyl oleate substrate and creates "oxygen-enriched surfaces" that increase local O2 concentration near the active sites, leading to a more than 3-fold activity enhancement over its hydrophilic counterpart. This performance is achieved by finally realizing a "reaction-transport coupled" mechanism, which synergistically leverages the enhanced O2 activation capability of the asymmetric Co sites with the improved mass transport of reactants conferred by the engineered hydrophobic microenvironment. This work not only provides a scalable and energy-efficient pathway for industrial EVO production but also offers a generalizable molecular engineering paradigm that synergistically integrates active site design─specifically leveraging asymmetric single-atom sites─with microenvironment engineering.