Ag-ZnO Nanoflowers Enable Highly Selective Photocatalytic Conversion of CH4 to CH3OH at Atmospheric Pressure: Unraveling Reactive Interfaces and Intermediate Control

Abstract

At atmospheric pressure, the main challenge in the photocatalytic oxidation of CH₄ to CH₃OH is to absorb and activate the inert C─H bond while preventing excessive oxidation of CH₃OH. In this study, metal-supported ZnO nanoflowers (Ag-ZnO) are designed to produce abundant active interfacial oxygen sites for CH₄ oxidation at atmospheric pressure, with a CH₃OH yield reaching 1300 µmol g_cat ⁻¹ h⁻¹ and the selectivity is 94%. DFT calculation and in situ analysis show that the addition of Ag regulates the electron state density and band center of O, which is beneficial to the adsorption of CH₄, and decreases the dissociation energy barrier of C─H bond at O_L(Lattice oxygen) site. The further selective conversion of ·CH₃ to CH₃OH involves two different pathways: one pathway consists of the oxidation of ·CH₃ by O_L, and the other pathway is the combination of ·CH₃ and ·OH generated from dissolved O₂ (0.28 mm) in water. Notably, in the photochemical flow device, the yield of CH₃OH is increased to 5200 µmol g_cat ⁻¹ h⁻¹ and the selectivity is close to 100%. This work offers valuable insights into reactive interfaces, morphological engineering, and the control of intermediate evolution toward selective conversion of CH₄ to oxygenates at atmospheric pressure.