Asymmetric Cobalt Single-Atom Catalysts with Engineered Hydrophobic Microenvironment: A Reaction-Transport Coupled...

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.