Mechanistic Understanding of Methane to Methanol Conversion on Graphene-Stabilized Single-Atom Metal Centers

The functionalization of methane to value-added chemicals, such as methanol, remains as one of the “grand challenges” in the chemical industry due to the energy-demanding C-H activation step. This restricts the extensive utilization of methane despite its vast reserves. A single Fe atom stabilized on N-functionalized graphene has been reported as an efficient catalyst for direct conversion of methane to methanol¹. In this work, we investigate the C-H activation of methane and successive methanol production mechanisms through reaction with H₂O₂, using Density Functional Theory calculations. By elucidating different reaction paths, it is shown that methanol is likely to be produced even at ambient temperatures through a radical formation mechanism. Importantly we demonstrate that the active site is a di-oxo iron center, which is responsible for generating methyl radicals (and the site being hydroxylated). These radicals can react with either the formed hydroxyl on the active site or directly with H₂O₂ from the liquid phase to form methanol. In both cases the active site is regenerated through a H₂O₂ reduction to H₂O step. We demonstrate that the high activity is attributed to a fine balance of keeping the catalyst at an activated oxidized state (oxo-species) rather than the thermodynamically preferred hydroxylated state. Taken together, this work reveals novel mechanisms and catalytic functionalities for converting shale gas (methane) to valued chemicals (methanol), while addressing solvent effects and catalyst stability on the overall catalytic behavior.

[1] X. Cui et al., Chem 4(8), 1902-1910 (2018).