【作者】 李彩今；

【导师】 肖丰收； 李守贵；

【作者基本信息】 吉林大学 ， 无机化学， 2009， 博士

【摘要】 沸石分子筛的生成机理研究是即有理论意义又有实际意义的重要课题,硅铝酸盐溶液中硅铝酸根的聚合态及它的液相结构的研究是沸石分子筛生成机理中的一个非常关键的环节,然而没有有效的检测方法给硅铝酸根聚合态的研究带来了很大的困难。本论文围绕着硅铝酸盐溶液中硅铝酸根的聚合态及它的液相结构开展了研究。利用29Si-和27Al-NMR研究硅铝酸盐溶液中硅铝酸根的核磁信号并对它进行归属,根据信号峰的特点及其化学位移判断硅铝酸根的聚合态和它的结构,进一步利用硅化学位移的计算公式对硅铝酸根的信号进行归属。利用NaY沸石的导向剂溶液的稳定性,仔细研究导向剂溶液中对NaY沸石的晶化起导向作用的活性结构单元。利用固体高分辨核磁共振技术和紫外拉曼光谱,跟踪检测LTA﹑FAU﹑EMT沸石的晶化过程,并提出沸石的晶化过程的模型。更多还原

【Abstract】 Zeolites such as LTA and NaY have been widely used in many scientific fields due to their outstanding properties of adsorption, ion-exchange and catalysis. Therefore, the development of zeolites with unique function or novel structures has attracted much attention. However, the synthetic mechanism of zeolites was still unclear. Nowadays, design and synthesis of new zeolites based on the intensive understanding of formation mechanism. As a result, there is an urgent call for further investigation of formation mechanism on zeolites.The formation of zeolites usually contains a lot of complex process, for example, the polymerization of silicates anions, polymerization of aluminosilicates anions, formation and transformation of sol, formation of gel, structure directing, growth of zeolites crystal, metaphase transformation and so on. Among these processes, the polymerization states and their structures in liquid phase have been intensively investigated through various techniques. Typically, TMS-GC and ²⁹Si-NMR were considered as powerful characterizations. Because most of zeolites were aluminosilicates, the research on the polymerization and structure of aluminosilicates is very important for the synthesis mechanism on zeolites. However, there are still some problems that should be addressed. （i）, the interaction between silicates with aluminates usually results in the formation of gel products rather than sol products; （ii）, low concentration of aluminosilicate anions in the samples, which is difficult to analyze these species by NMR and other techniques. Due to the above problems, the research on aluminosilicates species is very difficutl yet.In this work, we have used ²⁹Si-and ²⁷Al-NMR to characterize the aluminosilicate solutions. In the previous studies, the description of aluminates in organic and inorganic alkali solutions is unclear. For example, chemical shift of Q1 in TMAS solution is 75.2 ppm, however, the chemical shift of Q1 in sodium silicate is about 70⁷2 ppm. In our results, the intensive signals of chemical shift appear at 75.8 ppm in sodium aluminosilicates solutions, indicating that previous results were not correct. In fact, there is not any significant difference between the NMR signals of aluminium in sodium aluminosilicates and organic alkali solutions. We carefully investigated the change of ²⁷Al-NMR peaks, and find that Q2 signal reveal a much broader peak than other ones, which was explained as the quadrupolar interaction of cyclic aluminosilicates in grades of electric field.Additionally, this work is also to calculate the unknown chemical shift of aluminosilicate anions by using known ones, and it is effective. There are some precious report on chemical shift of cyclic tetramer and double cyclic tetramer of silicates. In addition, the synthesis of single crystal D4R of aluminosilicates was also reported, in which Si chemical shift of Si-Al double cyclic tetramer was obtained. Then we could calculate the chemical shift of Si in the cyclic tetramer of aluminosilicates by using above three factors according to the method reported in Nature. Typically, we got the chemical shift of Si in the cyclic tetramer is -75.27 ppm from calculation. In the experimental results, chemical shift at -75.1 ppm was detected, in good agreement with that from the calculation. Moreover, it is obtained two possibilities for connecting D6R, one is resulted from the connection of three S4R, and another is obtained from the connection of two S6R. The two connections are well consistent with experimental chemical shifts of NaY and EMT zeolite. UV-Raman spectra also confirm the two connections. Therefore, it is suggested the conclusions in the following: a, There are double cyclic hexamers formed by three times of single cyclic tetramers in the crystallization of FAU zeolite, and the highest atom ratio Si/Al is 3; b, There are a lot of double cyclic hexamers formed by two times of single cyclic hexamers in the crystallization of EMT zeolite, and the highest atom ratio Si/Al is 5.We also investigated the seeds solution of NaY zeolites by ²⁹Si-NMR, and find out that there are crystalline nuclei of NaY in the seeds solution, D6R attached FAU cages. The larger nuclei with smaller D6R result in the decrease of seeds solution for crystallization of NaY zeolite.In this thesis, author successfully explain the polymerization of aluminosilicate anions in the solutions, understanding the crystallization process of LTA, FAU, EMT zeolites. This work would become a new methodology for investigating formation mechanism of zeolites.更多还原