Steric effect of coordinative-saturated monomeric Fe sites enables aerobic oxidation of methane to C₂ hydrocarbons

Iron-containing zeolite catalysts (Fe-zeolites) demonstrate exceptional performance in selective oxidation of methane to C₁ oxygenates, while aerobic C–C coupling to C₂ hydrocarbons has remained elusive. The heterogeneity of Fe species within zeolites, intertwined with kinetically competing over-oxidation processes, engenders ambiguities in determining catalytic pathways, thereby fundamentally impeding rational design of the catalyst. Here, we report that continuous aerobic C–C coupling of methane can be achieved under oxygen-lean conditions over tailored Fe-zeolites. Crucially, the oxygen-lean environment enables clear identification of distinct active-site roles: CO is directly generated on low-coordinated monomeric Fe sites, while C₂ hydrocarbons formation predominantly occurs on coordinatively saturated monomeric Fe sites. Detailed spectroscopic studies and density functional theory (DFT) calculation reveals that steric effect of octahedral-coordinated monomeric Fe³⁺ Lewis acid sites (LAS) compels *CH₃ species to preferentially bind to the Brønsted acid sites (BAS), facilitating C–C coupling and suppressing overoxidation. Furthermore, the Mars–van Krevelen (MvK) mechanism is verified as a feasible pathway for methane-to-ethane conversion. This work elucidates the critical role of Fe site coordination in dictating reaction pathways during oxygen-mediated methane conversion.