Direct Oxidation of Methane to Formaldehyde With Molecular Oxygen Catalyzed by Gold-Tungsten Oxide Cluster Cations.

Catalytic direct oxidation of methane with molecular oxygen can be highly exothermic in thermodynamics. It offers a promising green method for production of value-added chemicals such as formaldehyde (CH₂O), an indispensable feedstock in industry, under mild conditions. However, it faces a long-standing grand challenge due to the intrinsic kinetic inertness of methane. Herein, an active gold-tungsten oxide cluster catalyst, AuWO₂ ⁺, being able to spontaneously catalyze CH₄ + O₂ → CH₂O + H₂O at room temperature has been successfully identified by mass spectrometry, which is distinctly different from the related condensed phase catalysis wherein the photo-excitation of catalysts in the presence of H₂O or H₂ was prerequisite to initiate catalytic reactions. The previously unrecognized mechanisms of direct methane oxidation have been unveiled: the interfacial Au-metal centers can undergo thermal reaction with O₂ to spontaneously generate the active (O···O)-• hole that subsequently works together with Au atom in a relay-manner to easily cleave two C-H bonds of methane directional for CH₂O and H₂O production. This finding lays a solid foundation for future design of better-performing catalysts for direct oxidation of methane (or other molecules) with O₂ without the need of any external energy or co-feeding with alien molecules.