Mars Van Krevelen Catalytic Methane Combustion Via Formate Intermediates over Hematite: Atomistic Surface Studies and DFT

Effective methane utilization for either clean power generation or value-added chemical production has been the subject of growing attention worldwide for decades, yet challenges persist mostly in relation to methane activation under mild conditions. Here we report hematite, an earth-abundant material, to be a highly effective and thermally stable catalyst for catalytic methane combustion (CMC) at low temperatures (< 500°C) with a low light-off temperature of 230°C and 100% conversion to CO₂. The performance is comparable to those precious-metal-based catalysts with an incredibly low apparent activation energy of 17.60 kcal·mol^-1. From our theoretical calculations, the active site is found to be a tetrairon center with an antiferromagnetic diiron couple, which is analogous to that of the methane monooxygenase. Isotopic oxygen tracer experiments confirm a Mars van Krevelen redox mechanism where methane pre-activation occurs via lattice oxygen first, followed by a catalytic cycle through a molecular-oxygen-assisted pathway. Surface studies with in situ DRFITS and first-principles DFT calculations reveal the evolution of reaction intermediates from a methoxy CH₃-O-Fe, to a bridging bidentate formate b-HCOO-Fe, to a monodentate formate m-HCOO-Fe before CO₂ is eventually formed as temperature increases.