Methane, the main component of natural gas, shale gas and combustible ice, has attracted considerable attention worldwide not only in terms of reducing greenhouse gas emissions to protect the environment, but also as an energy resource oriented towards high value-added products. However, it remains a major challenge to simultaneously achieve high activity for the methane conversion and complete selectivity of the oxygenates under mild conditions.

A research group led by Prof. Xiaodong Wang and Prof. Jian Lin from Dalian Institute of Chemical Physics (DICP) of Chinese Academy of Sciences (CAS), in collaboration with Prof. Sen Lin from Fuzhou University, realized that the metal-organic frameworks (MOFs)-supported single-atom catalyst could enhance the selective oxidation of methane.

This study was published in Journal of the American Chemical Society on June 6.

The Ru₁/UiO-66 catalyst directly converts CH₄ to oxygenates with nearly 100% selectivity (Image by Geqian Fang)

There is a trade-off effect between methane activation and oxygenate selectivity on supported transition-metal catalysts for the DSOM reaction even at lower CH₄ conversion, which is mainly due to excessive dissociation of the C-H bond of oxygenates by supported metal species. However, most of the current nanoscale or atomically dispersed metal catalysts show unsatisfactory selectivity, as they are unable to prevent the formation of CO₂ in the presence of ultra-strong oxidant of •OH species. To solve the above challenges, the researchers developed a highly efficient MOFs-supported single-atom Ru catalyst (Ru1/UiO-66) for the DSOM reaction using H₂O₂ as oxidant. It endows nearly 100% selectivity and an excellent turnover frequency of 185.4 h^-1 for the production of oxygenates.

The Ru₁ site is responsible for the activation of CH4 via the resulting Ru1=O* species while the Zr-oxo nodes undertake the formation of oxygenic radical species to produce oxygenates. In particular, the Zr-oxo nodes retrofitted by Ru1 can prune the excess H₂O₂ to inactive O₂ more than •OH species, helping to suppress the over-oxidation of oxygenates.

The above work was supported by National Natural Science Foundation of China, National Key Research and Development Program, Dalian Science Foundation for Distinguished Young Scholars and YLU-DNL Fund. (Text by Geqian Fang)