Spatially Confined Molybdenum Catalysts in Hollow ZSM-5 Zeolites via Si/Al Ratio-Tailored Desilication-Recrystallization for High-Efficiency Propane Dehydrogenation

Abstract The rational design of highly stable and selective molybdenum-based catalysts for propane dehydrogenation (PDH) remains a major challenge, due to severe intraparticle mass transfer limitations and rapid deactivation driven by active site volatilization and coking. Here, we report a controlled desilication-recrystallization strategy to construct hollow ZSM-5 zeolites with in situ spatially confined Mo species, using Mo-impregnated silicalite-1 as a sacrificial precursor. We systematically investigated the effects of Si/Al ratio (25, 50, and 100) on the structural evolution, physicochemical properties, and PDH catalytic performance of the resulting materials. An optimal Si/Al ratio of 50 yielded well-defined hollow ZSM-5 structures with high mesoporosity (0.59 cm3·g–1) and balanced acidity (B/L = 1.20). The resulting Mo-SZ(50) catalyst exhibited exceptional catalytic performance, achieving 48.4% propane conversion and 76.9% propylene selectivity at 550 °C, and significantly outperformed other catalysts prepared in this work. UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and H2 temperature-programmed reduction (H2-TPR) characterizations further confirmed that the desilication-recrystallization strategy enabled the selective formation of highly active isolated tetrahedrally coordinated Mo6+ species, and the rigid zeolite shell provided robust spatial confinement to inhibit the migration, agglomeration, phase transformation and high-temperature volatilization of Mo species during the reaction. Moreover, consecutive reaction–regeneration cycle tests revealed that the Mo-SZ(50) catalyst possessed outstanding regenerative stability, with nearly full recovery of intrinsic catalytic activity and propylene selectivity achieved after each regeneration process, and no pronounced irreversible deactivation was observed throughout the cyclic operations. During the 100 h continuous PDH operation, Mo-SZ(50) exhibited excellent stability with propylene selectivity maintained above 73%, significantly exceeding that of the conventionally impregnated reference catalyst. The hierarchical hollow structure facilitated mass transfer within the hollow core while the crystalline shell confined the active Mo species, preventing thermal volatilization. This work establishes a promising strategy for developing efficient dehydrogenation catalysts through precise control of spatial confinement and acidic properties.