Formation of high-silica zeolites from xM2O-yTAABr-Al2O3-zSiO2-3000 H2O gels (M = Li or K and TAA = tetramethyl, tetraethyl, and tetrabutyl)
✍ Scribed by F. Testa; F. Crea; A. Nastro; R. Aiello; R. Mostowicz; J.B. Nagy
- Book ID
- 104290156
- Publisher
- Elsevier Science
- Year
- 1991
- Tongue
- English
- Weight
- 563 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0144-2449
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✦ Synopsis
The role of tetramethyl (TMA)-, tetraethyl (TEA)-, and tetrabutylammonium (TBA) cations are examined, in presence of either lithium or potassium ions, on the rate of formation of various zeolites. In presence of K+ ions and either TEABr or TBABr, the main zeolitic phases are ZSM-5 and ZSM-11, respectively. The induction periods are only slightly influenced, while the crystallization rate increases with increasing tetraalkylammonium (TAA) concentration.
In presence of Li+ ions, the induction period decreases, while the crystallization rate increases with increasing TAA+ ion concentration. Oppositely to TEA+ and TBA+ ions, TMA+ cations influence the induction period, the crystallization rate, and the nature of the zeolites formed. In presence of Li+ ions, ZSM-5 and ZSM-39 are formed only at high TMA+ concentrations.
In presence of K+ ions, ZSM-5 is the main zeolitic phase at low TMA+ concentration, while at high TMA+ concentrations, both ZSM-39 and ZSM-48 are formed. The Li content of the ZSM-5 samples is higher than is the K content. In addition, the Li+ cations are more hydrated when neutralizing the framework (SCO-AI)-negative charges than when being counterions to =SiO-defect groups.