Room-Temperature Methane Oxidation to Formaldehyde Mediated by CoMoO⁺ Gas-Phase Cations

Formaldehyde (HCHO) is a fundamental chemical feedstock with widespread industrial applications. The direct oxidation of methane by oxygen to formaldehyde (CH₄ + 1/2O₂ → H₂ + HCHO) under mild conditions represents an attractive but challenging transformation, as it requires both activation of the inert C-H bonds of CH₄ and suppression of overoxidation to products such as carbon dioxide. In this work, mass spectrometry experiments combined with theoretical calculations reveal that CoMoO⁺ cations can efficiently mediate this transformation at room temperature. The unique electronic structure of CoMoO⁺ facilitates the formation of a crucial CoMoOCH₂⁺ intermediate during the reaction with CH₄ and prevents methanol formation. In the subsequent oxidation reaction, the Mo atom in CoMoO⁺ serves as the active site for O₂ adsorption, and both Mo and Co atoms act as electron donors to activate O₂, leading to the formation of the C-O bond in formaldehyde. This work reports the first gas-phase example of achieving conversion of CH₄ to HCHO and its radical derivatives by O₂ at room temperature using heteronuclear non-noble metal cations. Remarkably, the CoMoOCH₂⁺ cation maintains high reactivity after adsorbing one or two CH₄ molecules. These findings provide new mechanistic insights into selective methane activation and conversion.