Journal
INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY
Volume 20, Issue 2, Pages 1081-1089Publisher
WILEY
DOI: 10.1111/ijac.14215
Keywords
activation energy; aluminosilicates; drying; in situ observation; Raman spectroscopy; zeolites
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The local structure of the dry gel before synthesis was evaluated using in situ Raman spectroscopy, and the conformational change of TEA(+) cations and the transformation of silicate building units were observed during the drying process, providing insights into the faster crystallization of zeolite beta.
To investigate faster crystallization of zeolite beta by the dry-gel conversion method, the local structure of the dry gel before synthesis was quantitatively evaluated using in situ Raman spectroscopy during the drying process. The dry gel prepared from Si and Al sources, and tetraethylammonium hydroxide solution was crystallized after several hours by the dry-gel conversion method. The conformational change of TEA(+) cations was observed during the drying process by the deconvolution of the spectrum, and the conformational change was larger than that during the synthesis process. The rate of conformational change was increased with the drying temperature, and the apparent activation energy was estimated to be 68.2 kJ/mol. The generation and transformation of double three-membered silicate rings (D3Rs) and 4-2 type secondary building units (SBUs), which are essential for the crystallization of zeolite beta, were observed during the drying process. The transformation from D3R to 4-2 SBU in the dry gel during drying process could be confirmed quantitatively by the difference of the time variation for the amounts of these silicate building units estimated by in situ observation.
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