Methane, one of the most abundant raw materials from fossil and biogenic sources, constitutes an important feedstock for the synthesis of major energy sources. Because of the highly strong C-H bonds, activation and the further transformation of methane into value-added chemicals is usually performed under extreme conditions, such as high temperatures and high pressures.

To uncover the elementary steps in methane transformation is a challenge. Therefore, the activation of methane under mild conditions has attracted the attention for decades.

Atomic clusters that can be handled under isolated conditions are being actively studied for activation of methane. The positively charged clusters are very reactive with methane than the corresponding negatively charged species, particularly for noble metal free anions.

Recently, a research group at Institute of Chemistry of Chinese Academy of Sciences led by Prof. HE Shenggui reported that the reactivity of molybdenum carbide cluster anions toward methane can be enhanced by the adsorption of a CO molecule. This work was published on Angew. Chem. Int. Ed. 

The isolated Mo₂C₂^– cluster is inert with CH₄ molecule. Mass spectrometry, photoelectron spectroscopy and quantum chemistry calculations demonstrated that Mo₂C₃O^– cluster with the dissociated attached CO molecule is more reactive.

In contrast, Mo₂C₃O^– isomer with the non-dissociated CO molecule is unreactive toward CH₄. The noble-metal-free cluster anions (Mo₂C₃O^–) that can react with CH₄ thermal collision conditions has been reported for the first time. The dissociative adsorption of CO molecule on Mo₂C₂^– cluster can tune down the spin density distribution on one Mo atom, and then the activation of CH₄ is promoted through oxidative addition.