Highly Efficient and Selective Photocatalytic Nonoxidative Coupling of Methane to Ethylene over Pd-Zn Synergistic Catalytic Sites.

Photocatalytic nonoxidative coupling of CH₄ to multicarbon (C₂₊) hydrocarbons (e.g., C₂H₄) and H₂ under ambient conditions provides a promising energy-conserving approach for utilization of carbon resource. However, as the methyl intermediates prefer to undergo self-coupling to produce ethane, it is a challenging task to control the selective conversion of CH₄ to higher value-added C₂H₄. Herein, we adopt a synergistic catalysis strategy by integrating Pd-Zn active sites on visible light-responsive defective WO₃ nanosheets for synergizing the adsorption, activation, and dehydrogenation processes in CH₄ to C₂H₄ conversion. Benefiting from the synergy, our model catalyst achieves a remarkable C₂₊ compounds yield of 31.85 μmol·g^-1·h^-1 with an exceptionally high C₂H₄ selectivity of 75.3% and a stoichiometric H₂ evolution. In situ spectroscopic studies reveal that the Zn sites promote the adsorption and activation of CH₄ molecules to generate methyl and methoxy intermediates with the assistance of lattice oxygen, while the Pd sites facilitate the dehydrogenation of methoxy to methylene radicals for producing C₂H₄ and suppress overoxidation. This work demonstrates a strategy for designing efficient photocatalysts toward selective coupling of CH₄ to higher value-added chemicals and highlights the importance of synergistic active sites to the synergy of key steps in catalytic reactions.