Direct oxidative carbonylation of methane to acetic acid via high-valent iron-oxo mediated water activation.

Abstract

Direct conversion of CH₄ into value-added chemicals is impeded by the inert C-H bonds and inefficient C-C coupling. We report a spatially separated Rh-O-Fe active-site architecture that decouples CH₄ and H₂O activation through a high-valent-metal mediated radical mechanism, enabling selective CH₃COOH synthesis. In-situ infrared, operando Mössbauer spectroscopy, and quasi in-situ high-field EPR reveal that O₂ oxidizes Rh and Fe to high valence states. Rh^(III) activates CH₄ to •CH₃, while Fe^(IV) = O dissociates H₂O into •OH through a truncated water-gas shift pathway. •OH rapidly reacts with CO to form •COOH intermediates, which couples with •CH₃ within the zeolite to yield CH₃COOH. This dual-site strategy circumvents kinetic limits of conventional water-gas shift and CO insertion steps. The catalyst achieves 18.2 mmol g_cat^-1 h^-1 CH₃COOH with 92% selectivity and 100-hour stability in continuous operation. This study establishes radical decoupling enabled by high-valent metal sites as a design principle for selective alkane oxidation.