Synergy between Brønsted Acid Sites and Cu/Zn Single-Atom Sites in Zeolite for the Direct Oxidation of Methane

The direct oxidation of methane to liquid oxygenates is challenging due to the high C-H bond activation barrier. While metal sites in zeolites are typically considered the primary active centers, this study reveals that Brønsted acid sites (BAS) are indispensable for CH₄ activation. Atomic-level incorporation of Cu and Zn into ZSM-5 tunes Brønsted acid strength and stabilizes the framework, creating a cooperative acid-metal environment that enables a remarkable C1 oxygenates productivity of 41651 μmol gcat.⁻¹ h⁻¹ with nearly 90% selectivity at 70 °C. Through CH₄-DRIFTS, in situ EPR, and DFT calculations, we demonstrate that BAS induce polarization of CH₄, while Cu and Zn activate H₂O₂ to generate •OH and •OOH radicals. The •OH radicals cleave polarized CH₄ to form •CH₃ radicals, which selectively couple with reactive oxygen species to yield CH₃OH and HCOOH. This work highlights the critical acid-metal synergy in metal-zeolite catalysts for efficient CH₄ valorization under mild conditions.