Copper Inhibits the Over-Oxidation of Rh during Methane Oxidation Catalyzed by Bimetallic Cation CuRh

Partial oxidation of methane with molecular oxygen to produce hydrogen is a promising strategy for hydrogen generation. However, maintaining catalyst stability remains challenging, as the catalyst is prone to overoxidation by the strong oxidant O₂ during the reaction. Herein, benefiting from state-of-the-art mass spectrometry, we demonstrate that heteronuclear metal cation CuRh⁺ catalyzes the reaction of methane with O₂ at room temperature to yield 2H₂ and CO₂. Comparative studies show that even though the homonuclear Rh₂⁺ system can construct an analogous catalytic cycle, it is more susceptible to overoxidation by O₂, leading to the formation of the undesirable intermediate Rh₂O₃⁺. Cu-doping markedly enhances the antioveroxidation capability of CuRh⁺ to result in the generation of stable and desirable intermediate CuRhO⁺ under an oxygen atmosphere. Density functional theory shows that Cu plays a suppressive role during two steps of the overoxidation reaction. By reducing the electron supply from the metal site to O₂, Cu hampers the initial adsorption step and compels the O-O bond dissociation to rely on orbital reorganization across a large energy gap. This finding not only provides new insights into the unique role of copper in heterogeneous catalysis but also offers a valuable guidance for the rational design of low-cost and stable catalysts for CH₄-to-H₂ under mild conditions.