ZSM‑5 Zeolite: Structure, Properties
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ZSM‑5, short for Zeolite Socony Mobil‑5, is a crystalline microporous aluminosilicate zeolite with MFI topology, first invented by Mobil Oil Corporation in 1972. It belongs to the pentasil zeolite family and has become one of the most widely applied heterogeneous catalysts in modern petrochemical and fine chemical industries.
Crystal Structure
ZSM‑5 possesses an interconnected three‑dimensional 10‑membered ring pore system. It contains two sets of elliptical micropores: straight channels with pore size of 0.53 nm × 0.56 nm, and intersecting sinusoidal (zigzag) channels of 0.51 nm × 0.55 nm. The crossing points of these two pore channels form confined reaction cavities, which generate the unique shape‑selective catalysis effect of ZSM‑5. Its unit cell formula can be expressed as \(\ce{Na_{n}Al_{n}Si_{96-n}O_{192}·16H_{2}O}\), where n ranges from 0 to less than 27. The silica‑to‑alumina (Si/Al) ratio is adjustable in a wide range, which is the core parameter to tune its acidity, hydrophilicity and hydrothermal stabilityIZA Struct....
Key Physicochemical Properties
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Tunable acidity: Framework aluminum atoms produce Brønsted acid sites after ion exchange to H‑form. By adjusting Si/Al ratio, the density and strength distribution of acid sites can be precisely controlled, meeting different catalytic reaction requirements.
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Excellent thermal and hydrothermal stability: High‑silica ZSM‑5 maintains stable crystal structure under high temperature and steam atmosphere, suitable for harsh reaction conditions in refinery processes.
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Shape selectivity: The size of 10‑ring pores allows small‑molecule reactants to diffuse in and products to escape, while suppressing bulky by‑products, which greatly improves target product selectivity.
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Hydrophobic surface: High Si/Al ZSM‑5 shows good hydrophobic performance, making it useful for selective adsorption and separation of organic molecules from water‑containing gas or liquid streams.
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Modification potential: Hierarchical ZSM‑5 can be fabricated by desilication, dealumination or template-assisted synthesis to introduce mesopores, shortening diffusion paths and reducing carbon deposition during catalytic cyclesACS Public
