Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
Chem Asian J. 2013 Jul;8(7):1419-27. doi: 10.1002/asia.201300365. Epub 2013 May 13.
Hollow aluminosilicate zeolite beta was successfully synthesized by adding CIT-6, that is, zincosilicate zeolite, which has the same topology as beta, as seeds to the Na-aluminosilicate gel without the need for organic structure-directing agents. One important factor in the successful organic structure-directing agent (OSDA)-free synthesis of hollow beta crystals is the solubility of the seed crystals in alkaline media. CIT-6 was less stable than aluminosilicate zeolite beta in alkaline media and the solubility changed depending on whether the crystals were calcined or not. The hollow beta could be obtained by using the uncalcined CIT-6 seed crystals. The volumes of intra-crystalline voids were tuned by changing the reaction time and the initial gel compositions, such as the SiO2/Al2O3 and Na2O/SiO2 ratios. We estimated that the intra-crystalline voids were formed through the dissolution of the seed crystals, just after the crystal growth of new beta on the outer surface of the seeds. In addition, new crystal growth toward inside of the void was also observed by TEM. On the basis of the characterization data, such as chemical analysis, N2-adsorption/desorption measurements, and TEM observation, a formation mechanism of the intra-crystalline voids is proposed and discussed.
成功地在没有使用有机结构导向剂的条件下，通过向硅铝酸钠凝胶中添加与 β 沸石具有相同拓扑结构的 CIT-6（锌硅沸石）作为晶种来合成中空 β 沸石。成功实现无有机结构导向剂的中空β沸石晶体合成的一个重要因素是晶种在碱性介质中的溶解度。CIT-6 在碱性介质中的稳定性低于β沸石，并且其溶解度取决于晶体是否经过煅烧。可以使用未煅烧的 CIT-6 晶种获得中空β沸石。通过改变反应时间和初始凝胶组成（如 SiO2/Al2O3 和 Na2O/SiO2 比）来调节晶体内部空隙的体积。我们估计，在新的β沸石在晶种的外表面上生长之后，通过晶种的溶解形成了晶体内部的空隙。此外，还通过 TEM 观察到了新的晶体向空隙内部的生长。基于化学分析、N2-吸附/解吸测量和 TEM 观察等表征数据，提出并讨论了晶体内部空隙的形成机制。
