The co-conversion of methane and carbon dioxide to value-added chemicals represents an important subject in C1-chemistry from energy and environmental perspectives. However, the reports dealing with the conversion of CH₄ with CO₂ were very limited because it is rather difficult to find an active species that could simultaneously activate the reductive CH₄ and the oxidative CO₂. Design of better-performing catalysts for direct conversion of CH₄ with CO₂ requires fundamental insights into not only the mechanistic details of the bond-forming and bond-breaking processes, but also the nature of crucial intermediates. Atomic clusters are considered as the intermediate matter to bridge atoms and their bulk counterparts that can act as individual active sites of real-life catalysts.
Recently, a research group from Institute of Chemistry, Chinese Academy of Sciences, has prepared and characterized the first dinuclear cluster species, RhVO₃^–, which mediates the co-conversion of CH₄ and CO₂ to oxygenated products, CH3OH and CH₂O, in the temperature range of 393-600 K. The resulting cluster ions RhVO₃CO^– after CH₃OH formation can further desorb the [CO] unit to regenerate the RhVO3– cluster, leading to the successful establishment of a catalytic cycle for methanol production from CH₄ and CO₂ (CH₄ + CO₂ → CH₃OH + CO). The excellent activity of RhVO₃^– cluster is attributed to its optimal structure: a balance of the concurrent bonding of Rh with the oxygen (O) and metal (V) atoms (O-Rh-V) creates a metallic Rh atom that is highly active for selective methane activation while the reductive Rh?V bond can well reduce the CO₂. The molecular-level mechanism of the catalytic CH₃OH formation provides insights into the design of active sites that can mediate the co-conversion of methane with soft oxidant CO₂.
Their work entitled “Direct Conversion of Methane with Carbon Dioxide Mediated by RhVO3^– Cluster Anions” has been published in Angew. Chem. Int. Ed.2019, 58, 17287-17292.
This work was financially supported by the National Natural Science Foundation of China, the Youth Innovation Promotion Association of CAS, and the Beijing Municipal Science & Technology Commission.

The proposed catalytic cycle for the reaction of CH4 + CO2 → CH3OH + CO mediated by the RhVO3^– cluster. (image by YANG Yuan and Dr. ZHAO Yanxia)

Contact:
Prof. HE Shenggui
Institute of Chemistry, Chinese Academy of Sciences 
E-mail: shengguihe@iccas.ac.cn