Synergistic Dual-Cocatalyst Strategy of Au and CaCO ₃ on ZnO for Highly Selective Photocatalytic Oxidative Coupling of Methane to Ethane

The photocatalytic oxidative coupling of methane (OCM) to ethane represents a promising route for methane utilization, yet achieving high selectivity remains challenging due to overoxidation. Herein, we report a highly tunable and selective photocatalytic OCM system by constructing a ZnO-supported dual-cocatalyst composed of Au nanoparticles and CaCO 3 . Simply adjusting the CaCO 3 loading enables precise modulation of ethane selectivity across a wide range from 85% to a remarkable 96.4%, underscoring its pivotal role in directing the reaction pathway. Within this synergistic architecture, Au nanoparticles serve as active sites for C–H activation and methyl radical coupling, while CaCO 3 acts as a multifunctional modulator. The CO 3 2– ions in CaCO 3 provide strong Lewis basic sites that stabilize key CH 3 intermediates and strongly adsorb generated CO 2, inhibiting its desorption. This effectively kinetically suppresses the further oxidation of CH 3 intermediates into deep oxidation products like COOH* and CH 2 O*, fundamentally blocking the overoxidation pathway. The 2%Au/0.05CaCO 3 /ZnO catalyst achieves an ethane production rate of 7284.1 μmol·g –1 ·h –1 with 90% selectivity and excellent stability, while studies indicate that increasing the CaCO 3 loading can further enhance the selectivity to approach unity. This work not only reveals a unique kinetic control mechanism of suppressing key overoxidation intermediates by stabilizing the product (CO 2 ) but also establishes a versatile cocatalyst strategy for selective methane conversion in sustainable chemistry.