ZSM-35, a FER-type molecular sieve with a unique two-dimensional pore system, has attracted significant attention in catalysis due to its excellent shape-selectivity, moderate acidity, and high thermal stability. This article provides a concise overview of ZSM-35, covering its crystal structure, synthesis methods, post-synthesis modifications, and key applications in petrochemical refining, fine chemical synthesis, and environmental remediation.
ZSM-35 (FER-type zeolite) belongs to the orthorhombic crystal system with a chemical formula of Na₂Mg₂[Al₆Si₃₀O₇₂]·18H₂O. Its distinctive pore structure consists of intersecting 10-membered ring (10-MR) channels (0.54 × 0.46 nm) and sinusoidal 8-membered ring (8-MR) channels (0.35 × 0.45 nm), enabling precise molecular sieving and diffusion control. With a Si/Al ratio ranging from 15 to 70, ZSM-35 exhibits adjustable acid strength, making it highly selective for specific catalytic reactions while minimizing side reactions.
The conventional hydrothermal method involves mixing silica (e.g., fumed silica), alumina (e.g., pseudoboehmite), and organic templates (e.g., cyclohexylamine, CHA) under high-temperature (160–180°C) and autogenous pressure conditions. Key parameters include:
Example: A study achieved >95% crystallinity with a Si/Al ratio of 30, CHA/Al₂O₃ = 26, and crystallization at 170°C for 40 h.
To reduce costs, template-free methods using ZSM-35 seeds or inorganic directing agents (e.g., fluoride ions) have been developed. While slightly lower in crystallinity (~90%), these methods are eco-friendly and scalable.
ZSM-35 is a benchmark catalyst for n-butene → isobutene conversion (key for MTBE production), achieving >90% selectivity at 380°C and 1.9 h⁻¹ WHSV due to its 10-MR channel selectivity.
In xylene isomerization and toluene disproportionation, ZSM-35’s moderate acidity reduces coke deposition compared to ZSM-5, extending catalyst lifetime by 30–50%.
