Spatially Decoupled Reaction-Diffusion Microenvironments in Mordenite Enable Highly Selective Methane-to-Methanol Conversion

The selective oxidation of methane to value-added oxygenates represents a formidable challenge in heterogeneous catalysis, fundamentally limited by the thermodynamic trade-off between activating the reactant and preventing the subsequent overoxidation of fragile products. This vulnerability is deeply tied to the spatial accessibility within the catalytic microenvironment; highly open channels, while facilitating mass transfer, indiscriminately expose the generated products to secondary oxidation. Herein, we develop a site-selective construction strategy to establish spatially decoupled reaction-diffusion microenvironments within mordenite (MOR). By utilizing pyridine as a pore-blocking agent to occupy 12-membered ring (12-MR) channels, we preferentially localize the active Cu species, identified as bent mono-μ-oxo dicopper cores, within the well-defined 8-membered ring (8-MR) side pockets. This architecture induces a profound dual spatial effect. At the reaction level, the 8-MR acts as a nanoscopic kinetic shield by providing a customized local topology that suppresses the reactivity of oxygenated intermediates while retaining sufficient methane activation capability. Crucially, at the mass-transfer level, Cu incorporation into the 12-MR main channels is largely suppressed, allowing these channels to serve as unobstructed diffusion pathways and reducing the probability that desorbed methanol recontacts oxidative Cu sites during outward transport. Furthermore, by eliminating the structural heterogeneity inherent to non-selective synthesis, this spatially defined microenvironment and homogeneous Cu coordination structure enable the elucidation of the intrinsic structure-performance relationship. Under continuous operating conditions, this spatially engineered catalyst exhibits high methanol selectivity and productivity, ranking among the leading Cu-MOR systems for methane-to-methanol conversion. These findings demonstrate that designing a decoupled reaction-diffusion microenvironment can regulate catalytic selectivity beyond electronic-structure modulation, while also offering a generalizable method for the site-selective placement of metal ions within zeolite.