Abstract
Beta zeolite, possessing the BEA topological framework, is a classic microporous aluminosilicate zeolite first synthesized by Mobil Oil Corporation in 1967. Distinct from MFI-type ZSM-5 and FAU-type Y zeolite, Beta zeolite features a unique three-dimensional intersecting 12-membered-ring pore system, combining large pore channels, abundant adjustable acid sites, excellent hydrothermal stability and high specific surface area. Thanks to its balanced mass transfer performance and catalytic activity, Beta zeolite has become a universal catalyst widely applied in petroleum refining, fine chemical synthesis, environmental pollution control and other industrial fields. This paper systematically introduces the crystal structure, core physicochemical properties, modification strategies and mainstream industrial applications of Beta zeolite.
1. Crystal and Pore Structure of BEA Topology
Beta zeolite belongs to the monoclinic crystal system, consisting of two polymorphs (A and B) with random stacking faults inside the crystal lattice, which endows the material with rich structural defects and exchangeable active sites. Its most remarkable structural characteristic is the fully interconnected three-dimensional 12-membered-ring micropore network without large supercages.
Two sets of cross-linked pore channels run through the crystal grain:
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Linear channels along the [001] direction with a pore opening size of 0.66 nm × 0.67 nm;
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Tortuous sinusoidal channels along the [100] direction with a pore opening size of 0.56 nm × 0.56 nm.
The aperture range of Beta zeolite is 0.55–0.67 nm, which fills the performance gap between medium-pore ZSM-5 (10-membered ring, ~0.55 nm) and ultra-large-pore Y zeolite (12-membered ring supercage, ~0.74 nm). The wide and interconnected pore channels greatly reduce mass transfer resistance, allowing macromolecular aromatic hydrocarbons and long-chain alkane molecules to diffuse freely inside the framework.
The framework of Beta zeolite is constructed by SiO₄ and AlO₄ tetrahedrons linked via bridging oxygen atoms. The molar ratio of silica to alumina (SiO₂/Al₂O₃) can be regulated in a wide range from 10 up to 200 for industrial products. Its typical physicochemical parameters include a specific surface area of 500–800 m²/g and pore volume of 0.40–0.55 cm³/g. The complete pore channel structure without enclosed cages enables full ion exchange of sodium ions, ammonium ions and transition metal cations.
2. Core Physicochemical Properties
2.1 Adjustable Acid Sites
The Brønsted acid (B-acid) centers of aluminosilicate zeolites originate from Si–OH–Al bridging hydroxyl groups, while Lewis acid (L-acid) sites derive from extra-framework aluminum and structural defects. For Beta zeolite, silica-alumina ratio directly determines the total acid content: the higher the Si/Al ratio, the fewer framework Al atoms, and the weaker the overall acidity.
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Low Si/Al Beta zeolite (10–25): high total acid amount, abundant strong acid sites, high catalytic activity for cracking and alkylation reactions;
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High Si/Al Beta zeolite (50–200): low acid density, dominated by weak and medium acid sites, strong hydrophobicity, outstanding anti-coking performance and long service life.
Metal modification (Fe, Cu, P, La) and dealumination treatment can further optimize acid strength distribution to match different catalytic reaction demands.
2.2 Superior Thermal and Hydrothermal Stability
Well-crystallized Beta zeolite maintains intact BEA framework above 600 °C. Under industrial hydrothermal aging conditions (500 °C, long-term water vapor exposure), it only suffers slight dealumination without framework collapse. Compared with conventional Y zeolite, high-silicon Beta zeolite shows much stronger resistance to hydrothermal deactivation, supporting long-cycle continuous production and high-temperature regeneration.
2.3 Excellent Ion Exchange Capacity
Without confined supercages, all acid sites and framework aluminum of Beta zeolite are exposed inside open pore channels. Cations can fully access active centers during ion exchange, facilitating the preparation of metal-loaded functional catalysts for denitrification, catalytic combustion and selective oxidation.
