Zn-Fe pair sites catalyst for highly selective photocatalytic oxidation of methane to formaldehyde

Efficient methane photooxidation into formaldehyde in H₂O under mild conditions lies in C-H bond activation and intermediates coupling. Here, we report a Zn-Fe pair sites (Zn-Fe_x PS) photocatalyst to polarize the CH₄ molecules on Zn⁺-O^-sites and facilitate the coupling of *CH₃ and *OH on Fe sites. Various in situ investigations confirm that the Zn-Fe_0.2 PS promotes the generation of *CH₃ and *OH. The theoretical calculations reveal that the local charge density accumulation on Zn and O atoms significantly strengthens Zn⁺-O^- sites polarization, lowering the energy barrier for *CH₃ formation from 0.87 eV to 0.36 eV. Moreover, a strong d-σ hybridization between *CH₃ and Fe reduces C-H bonds steric hindrance, enhancing the coupling of *CH₃ and *OH. Accordingly, the HCHO productivity over Zn-Fe_0.2 PS reaches 2660.44 μmol·g⁻¹ with a remarkable selectivity of 95.89 %. This study broadens the scope for designing cost-effective photocatalysts to selectively oxidize CH₄ into value-added oxygenates.