Unveiling the elusive role of tetraethyl orthosilicate hydrolysis in ionic-liquid-templated zeolite synthesis |
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| Authors: | X Li T-H Li W Zhou Y-P Li PH-L Sit Z Wu OJ Curnow KC-W Wu J Choi ACK Yip |
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| Affiliation: | 1. Department of Chemical and Process Engineering, University of Canterbury, Christchurch 8041, New Zealand;2. Department of Chemical Engineering, National Taiwan University, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan;3. School of Energy and Environment, City University of Hong Kong, 999077, Hong Kong, China;4. Schools and State Key Laboratory of Heavy Oil Processing and Key Laboratory of Catalysis of CNPC, China University of Petroleum, Beijing 102249, China;5. School of Physical and Chemical Sciences, University of Canterbury, Christchurch 8041, New Zealand;6. Department of Chemical and Biological Engineering, Korea University, Seoul 02841, Republic of Korea |
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| Abstract: | Despite previous reports showing that crystallization kinetics affects zeolite phase selectivity because zeolites are metastable species in their synthesis solution rather than thermodynamic end points, the critical kinetics-controlling parameter is yet to be determined. This work elucidated the effect of tetraethyl orthosilicate (TEOS) hydrolysis before hydrothermal treatment on the final zeolite phase selectivity in the ionic liquid-templated synthesis of 10-membered ring zeolites (MFI- or TON-type zeolites). The results showed that the dissolved silica concentration in the synthesis solution, which is controlled by varying the TEOS hydrolysis temperature and addition rate, induced heterogeneous nuclear growth. Specifically, in 1-butyl-3-methylimidazolium (BMIM]Br)-directed syntheses, the high and low concentrations of dissolved silica species led to MFI and TON zeolite formation, respectively. The experimental results are supported by silica polymerization modeling using the Reaction Ensemble Monte Carlo method and theoretical calculations on composite building unit formation. The results are valuable for understanding the nucleation mechanism in zeolite crystallization. |
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| Keywords: | Ionic liquids TON MFI TEOS·hydrolysis Zeolites |
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