Kinetically Balanced Relay Catalysis for Efficient Oxidation of Methane to Methanol with O2

Selective oxidation of methane to methanol using molecular oxygen (O2) is a promising route for upgrading abundant methane resources, but is limited by the difficulty of coupling O2 activation with selective C-H functionalization. Herein, we report a relay catalysis strategy that spatially separates CO-assisted O2 activation from H2O2-mediated methane oxidation over a composite catalyst consisting of mordenite-supported Au nanoparticles and isolated Cu sites (Au/H-MOR∥Cu/H-MOR). The optimized relay catalyst achieves a CH3OH productivity of 1765 μmol gcat-1 h-1 with ca. 98% selectivity among liquid oxygenates, substantially outperforming monometallic Au/H-MOR while using less than one-third of the Au amount. Further decreasing the Au amount enhances the CO utilization and noble-metal efficiency, affording an Au-normalized CH3OH productivity of 5000 mmol gAu-1 h-1 and a CO utilization efficiency of 42%. Structural and kinetic studies reveal that Au nanoparticles catalyze CO-assisted O2 reduction in water to generate H2O2, whereas isolated Cu sites promote H2O2 activation and subsequent CH4 oxidation, thereby alleviating the kinetic mismatch between H2O2 generation and utilization. Mechanistic studies demonstrate that CO not only assists O2 activation on Au nanoparticles to generate H2O2 but also promotes H2O2 activation on isolated Cu sites to generate •OH species, thereby accelerating subsequent methane oxidation. This work establishes improved kinetic matching between oxidant generation and utilization as a design principle for selective methane oxidation.