Hydrothermally Stable and Regenerable Molybdenum-Zeolite Catalysts for Nonoxidative Conversion of Methane to Dihydrogen and Ethene

Designing Mo-zeolite catalysts that retain structural stability over many reaction–regeneration cycles is a challenge in developing practical methane dehydroaromatization (DHA) routes to produce dihydrogen, ethene, and aromatics. Mo-MFI zeolites typically used for methane DHA irreversibly deactivate during regeneration due to framework dealumination and structural degradation. Here, we synthesize Mo supported on small-pore zeolites (e.g., CHA, AEI, RTH), which are more durable than MFI under hydrothermal aging conditions (>823 K, >2 kPa H2O). Methane DHA forms H2 and ethene at equivalent rates on Mo-CHA and Mo-MFI. Benzene formation rates (per Mo) increase with decreasing crystallite size, indicating that rates are intracrystalline-diffusion limited in CHA frameworks, consistent with density functional theory (DFT) estimates of benzene diffusion barriers in CHA 8-membered ring (8-MR) windows. Initial DHA rates (per Mo) remain invariant on Mo-CHA after successive reaction–regeneration cycles (>10), supported by high-resolution transmission electron microscopy (HRTEM) and quantitative site characterization data showing minimal site or structural degradation on Mo-CHA, in sharp contrast to the systematic decrease in rates and structural degradation observed on Mo-MFI. This work reports materials that can be fully regenerable under potential industrial conditions and provides structure–function relations between catalyst properties and DHA rates, selectivity, and long-term stability.