Tandem Catalysis for Selective Oxidation of Methane to Oxygenates Using Oxygen over PdCu/Zeolite

Selective oxidation of methane to oxygenates with O₂ under mild conditions remains a great challenge. Here we report a ZSM-5 (Z-5) supported PdCu bimetallic catalyst (PdCu/Z-5) for methane conversion to oxygenates by reacting with O₂ in the presence of H₂ at low temperature (120 °C). Benefiting from the co-existence of PdO nanoparticles and Cu single atoms via tandem catalysis, the PdCu/Z-5 catalyst exhibited a high oxygenates yield of 1178 mmol g^-1 _Pd  h^-1 (mmol of oxygenates per gram Pd per hour) and at the same time high oxygenates selectivity of up to 95 %. Control experiments and mechanistic studies revealed that PdO nanoparticles promoted the in situ generation of H₂ O₂ from O₂ and H₂ , while Cu single atoms not only accelerated the activation of H₂ O₂ for the generation of abundant hydroxyl radicals (⋅OH) from H₂ O₂ decomposition, but also enabled the homolytic cleavage of CH₄ by ⋅OH to methyl radicals (⋅CH₃ ). Subsequently, the ⋅OH reacted quickly with the ⋅CH₃ to form CH₃ OH with high selectivity.