In a study published in Nature Communications, a research group led by Prof. DENG Dehui, Assoc. Prof. CUI Xiaoju, and Prof. YU Liang from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences has achieved highly efficient photo-driven carbonylation of methane (CH₄) with carbonic oxide (CO) and oxygen (O₂) to acetic acid (CH₃COOH) using a nano-heterostructure catalyst. 

This catalyst features Rh-Zn atomic-pair dual sites confined within a MoS₂ lattice, integrated with TiO₂ nanoparticles. This innovative catalyst enables a CH₃COOH productivity of 152 μmol gcat.^-1 h^-1, and a turnover frequency of 62 h^-1 with a high selectivity of 96.5%.

The direct conversion of CH₄ to high value multi-carbon (C₂₊) oxygenates, such as CH₃COOH, under mild conditions presents a promising pathway for upgrading natural gas to transportable liquid chemicals.

The oxidative carbonylation of CH₄ with CO and O₂ to CH₃COOH under mild conditions is an attractive and environmentally friendly route for CH₄ utilization. However, this process involves complex reactions, including the activation of O₂, efficient CH₄ activation, and controllable C-C coupling. It's therefore a major challenge to achieve CH₄, CO, and O₂ to CH₃COOH with both high catalytic activity and selectivity for mild CH₄ conversion.

Schematic illustration of the photo-driven CH₄ carbonylation with CO and O₂ to CH₃COOH over the RhZn-MoS₂/TiO₂ and the comparison of catalytic activity for different catalysts (Image by LI Yanan and LIU Huan)

In this study, the researchers showed that the active OH species, generated from O₂ photoreduction at the Zn site by proton-coupled electron transfer, promote CH₄ dissociation to CH₃ species. These CH₃ species then easily couple with adsorbed CO at the adjacent Rh site, leading to highly selective CH₃COOH formation. 

Additionally, the dual Rh-Zn atomic-pair sites provide separate catalytic sites for C-H activation and C-C coupling, creating a synergistic effect that overcomes the typical trade-off between activity and selectivity in CH₄ carbonylation.

"Our study opens up a new horizon for the design of efficient catalysts and provides a new pathway for photo-driven CH₄ carbonylation to CH₃COOH," said Prof. DENG.