1. Introduction
ZSM-5 (Zeolite Socony Mobil-5) is one of the most widely applied synthetic zeolites in modern industrial catalysis. First developed in the 1970s, it belongs to the MFI topological family and possesses a unique pentasil framework structure. Unlike large-pore Y-type and mordenite zeolites suitable for macromolecular reactions or small-pore SAPO/CHA zeolites limited to light olefin screening, ZSM-5 has moderate 10-MR pore size and three-dimensional cross-channel mass transfer system, which perfectly matches the dynamic diameter of light hydrocarbons, aromatic molecules and small organic compounds.
ZSM-5 has an ultra-wide adjustable Si/Al ratio, ranging from low-silicon acidic zeolite to high-silicon hydrophobic zeolite. Its Brønsted and Lewis acid sites can be precisely regulated through synthetic control and post-treatment modification, realizing accurate matching of catalytic activity and reaction selectivity. At present, ZSM-5 is the core catalyst for methanol chemical conversion, light olefin upgrading, aromatic synthesis and oil product upgrading. It also plays an irreplaceable role in VOCs degradation, flue gas purification and new energy catalytic reactions. In this review, the structural superiority, performance regulation methods and full-scale industrial applications of ZSM-5 are comprehensively summarized.
2. Structural and Physicochemical Properties of ZSM-5
2.1 MFI Topological Pore Structure
ZSM-5 has a typical three-dimensional cross-pore system composed of two sets of mutually perpendicular 10-membered ring channels. The straight channels extend along the b-axis, while the sinusoidal zig-zag channels are distributed along the a-axis, forming interconnected pore networks without dead ends. This unique structure greatly improves molecular diffusion efficiency and avoids the pore-blocking deactivation defect of one-dimensional channel zeolites such as ZSM-48 and ZSM-22.
The moderate pore size of ZSM-5 endows it with precise shape-selective effects. It allows free diffusion of light olefins, benzene, toluene and xylene molecules, while restricting the generation and escape of oversized polycyclic aromatic hydrocarbons and heavy carbon precursors, which fundamentally reduces coking rate and improves catalytic stability. Short b-axis ZSM-5 crystals further shorten the intracrystalline diffusion path, significantly enhancing anti-coking performance and long-cycle stability in methanol conversion reactions.
2.2 Core Physicochemical Characteristics
Tunable acidity and wide Si/Al range: ZSM-5 can be synthesized with variable Si/Al ratios from 20 to infinity. Low-silicon ZSM-5 provides abundant strong acid sites for cracking and alkylation reactions, while high-silicon ZSM-5 presents weak acidity and excellent hydrophobicity, suitable for high-selectivity organic synthesis and environmental adsorption catalysis.
Excellent structural stability: The rigid pentasil framework possesses ultra-high thermal stability, resisting structural damage above 800 °C. It also exhibits good hydrothermal stability and can adapt to long-term high-temperature steam reaction and regeneration environments, which is superior to SAPO-34 and partial FAU zeolites.
Adjustable surface properties: Modified ZSM-5 can realize the transformation from hydrophilic to hydrophobic surface, improving water resistance and anti-pollution ability in complex industrial systems.
3. Main Modification Strategies of ZSM-5
3.1 Acid-Base Composite Modification
Alkali treatment selectively dissolves partial framework silicon to construct abundant intracrystalline mesopores, forming hierarchical micro-mesopore structures and effectively solving the diffusion limitation of traditional microporous ZSM-5. Acid washing removes extra-framework aluminum impurities, optimizes the distribution of effective acid sites, eliminates excessive strong acid centers, and suppresses over-cracking and coking side reactions. The composite acid-base modified ZSM-5 achieves the optimal matching of pore structure and acidity.
3.2 Metal and Heteroatom Doping
Transition metals (Ga, Zn, Ni, Cu) and rare earth elements (La, Ce) are widely used for ZSM-5 modification. Zn and Ga doping can adjust the acid strength and promote aromatization reactions, significantly increasing BTX selectivity. Rare earth modification improves framework hydrothermal stability and anti-carbon deposition ability. Phosphorus modification can effectively stabilize framework aluminum and inhibit acid site loss under high-temperature hydrothermal conditions.
3.3 Crystal Morphology and Grain Size Regulation
Nano-sized ZSM-5 and short b-axis ZSM-5 are developed to shorten molecular diffusion paths, reduce intermediate residence time, and slow down coking deactivation. Ultrathin sheet-like ZSM-5 exposes more active crystal planes, improves acid site accessibility, and exhibits excellent catalytic performance in high-selectivity petrochemical reactions.
