Methane is a competitive candidate for producing the liquid fuels and value-added chemicals for its advantage in abundant reserve and low cost. Besides, it is the most stable organic molecule with high C-H bond strength (~440 kJ mol^-1). However, the intermediates after C-H activation are highly reactive and hard to escape from deep mineralization.  

The selective methane activation and its oriented conversion are global challenges. By now, the industry still uses indirect method of methane valorization, which depends on preliminary high-temperature and high-pressure oxidation to produce syngas. The liquid fuels and commodity chemicals are produced through the Fischer-Tropsch process. The entire process is low efficient. 

Recently, Prof. WANG Wenzhong's group at Shanghai Institute of Ceramics of Chinese Academy of Sciences designed Cu modified polymeric carbon nitride and achieved photocatalytic methane-to-ethanol conversion. They also made in-depth explorations in the photocatalytic mechanism. The study was published in Nature Communications. A Chinese invention patent was also granted (201811339733.2). 

Photocatalysis promotes the reactions under the mild conditions by virtue of photoexcitation instead of thermal activation, and it is a promising green alternative for direct methane conversion.  

Given that both the excessive hydroxyl radical from direct H₂O oxidation and the neglect of methane activation on the material will cause deep mineralization, researchers introduced Cu species into polymeric carbon nitride.

They realized photocatalytic anaerobic methane conversion with an ethanol productivity of 106 μmol g^-1 h^-1.

Cu modified polymeric carbon nitride could manage generation and in situ decomposition of H₂O₂ to produce hydroxyl radical, of which Cu species were also active sites for methane adsorption and activation. These features avoided excess hydroxyl radical for overoxidation and facilitated methane conversion.

Moreover, researchers proposed a hypothetic mechanism through a methane-methanol-ethanol pathway. It emphasizes the synergy of Cu species and the adjacent C atom in the polymeric carbon nitride for obtaining C₂ product.

This study demonstrated a strategy to construct a mild condition for methane activation, and broadened the horizon of methane conversion. 

The work was supported by the National Natural Science Foundation.