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.