Boosting Formic Acid Production in Methane Oxidation by Zeolite Confined Single-Site Rh Catalyst

The selective oxidation of methane to value-added oxygenates remains a long-standing challenge in catalysis, often constrained by poor reactivity (and single-pass methane conversion) and limited product selectivity. In this study, we report a Rh-Beta catalyst featuring atomically dispersed Rh^δ+ species embedded in the aluminosilicate *BEA zeolite matrix that enables highly selective methane oxidation in a CH_4-O_2-CO-H₂O system. This catalyst achieves a remarkable formic acid space-time yield of 210 mol mol_Rh ^-1 h^-1 at 7.84% methane conversion, with formic acid selectivity of 96%-surpassing all previously reported catalyst systems. Mechanistic investigations combining spectroscopy and theory reveal that hydroxyl radicals, generated via acid-promoted water-gas shift and in situ H_2-O₂ reactions, are responsible for methane activation, while the zeolite backbone plays a vital role in stabilizing formaldehyde intermediate and promoting its further oxidation to formic acid product. This work offers a new perspective on the conversion-selectivity relationship in methane oxidation and demonstrates a feasible pathway for the selective functionalization of methane under mild conditions.