Abstract
ZSM-5 zeolite with a typical MFI topological structure was successfully synthesized via a facile hydrothermal method. The prepared ZSM-5 possesses a uniform microporous structure, high crystallinity and moderate strong acid sites. Benefiting from its unique ten-membered ring pore system and tunable acidity, ZSM-5 exhibits excellent catalytic performance in hydrocarbon conversion reactions, including methanol to olefins (MTO), aromatization and isomerization. The results show that well-crystallized ZSM-5 can effectively promote the formation of light hydrocarbons and inhibit the generation of heavy by-products, demonstrating great potential in petrochemical catalysis.
1. Introduction
ZSM-5 is one of the most important MFI-type microporous zeolites widely applied in industrial catalysis. Different from other conventional zeolites, ZSM-5 has a unique intersecting pore structure composed of straight channels and sinusoidal channels, which provides favorable mass transfer channels for reactant and product molecules. In addition, the adjustable silicon-aluminum ratio endows ZSM-5 with controllable Brønsted and Lewis acid sites, which are critical for catalytic cracking, aromatization and organic transformation reactions. Due to its high thermal stability, good shape selectivity and low coking tendency, ZSM-5 has become a core catalyst in modern petroleum refining and fine chemical industries.
2. Experimental Section
ZSM-5 zeolite was synthesized by a conventional hydrothermal crystallization method. Tetrapropylammonium hydroxide (TPAOH) was used as the structure-directing agent, silica sol as the silicon source, and sodium aluminate as the aluminum source. The initial gel molar ratio was set as SiO₂: Al₂O₃: TPAOH: H₂O = 100:1:12:400. After uniform stirring and aging at room temperature, the homogeneous gel was transferred into a Teflon-lined autoclave. Hydrothermal crystallization was carried out at 170 °C for 24 h. After cooling, the product was centrifuged, washed with deionized water to neutral pH, dried at 120 °C, and finally calcined at 550 °C for 4 h to remove the organic template.
3. Results and Discussion
XRD patterns confirm that the synthesized sample presents typical characteristic diffraction peaks of MFI structure without miscellaneous crystal phases, indicating the successful preparation of high-purity ZSM-5 zeolite. SEM images show that the ZSM-5 crystals display regular hexagonal prism morphology with uniform particle size and good dispersion. The pore structure characterization proves that ZSM-5 has a stable microporous system with a pore size of approximately 0.55 nm, which matches the ten-membered ring pore feature of MFI zeolite.
Acid characterization indicates that the prepared ZSM-5 contains moderate strong acid sites and abundant weak acid sites, which can effectively activate carbon–hydrogen bonds during hydrocarbon reactions. Catalytic tests reveal that ZSM-5 exhibits high conversion activity and good light olefin selectivity in methanol conversion. The unique pore shape selectivity suppresses the generation of macromolecular heavy hydrocarbons, while the appropriate acidity reduces carbon deposition, improving the catalytic stability.
