Synthesis of novel microporous materials based on the elucidation of formation of zeolites in nanolevel

在本研究项目中，利用各种原位表征技术，在原子水平上对沸石前驱体在成核和晶体生长阶段进行了研究。沸石晶体的形成过程被认为是一种反应网络，对于沸石前驱体的澄清，重点讨论了由硅、铝和/或其他金属的氧化物等杂原子组成的环结构的生成以及碱金属在生成过程中的作用。利用高能X射线衍射仪研究了沸石形成过程中铝硅酸盐物种的环状结构。我们可以用这个工具来阐明杂原子对环物种的关键作用和碱金属对环组装的关键作用。结果表明，Al的引入降低了奇数环的比例贡献，而锌的加入促进了三元环的形成。值得注意的是，在晶化到每个沸石相之前，已经确定了反应物铝硅酸盐水凝胶的非晶相中的环数分布。通过小角X射线散射(SAXS)-广角X射线散射(WAXS)原位测量，我们得出结论，在相继成核和生长阶段，溶液水相中存在初级和次级单元和晶体三种颗粒。通过这些探索，我们最终提出了一个完整的沸石晶化过程示意图，并成功地获得了比以往报道的更小的沸石纳米晶。在这种方法中，不需要添加有机添加剂，就可以在较高浓度下实现纳米晶体的结晶，而有机添加剂通常被认为是制备这类纳米晶体不可或缺的试剂。

In this research project, investigation on zeolite precursors during the stages of nucleation and crystal growth is performed at the level of atomic scale by means of various in situ characterization techniques. The formation process of zeolite crystals is recognized here as a kind of reaction network.As for the clarification of zeolite precursors, generation of ring structures which are composed of hetero-atoms such as oxides of Si, Al, and/or other metals, and the roles of alkali metals in the generation were focused on. High-Energy X-Ray Diffraction (HEXRD) is utilized for the investigation of ring structures of aluminosilicate species involved in the formation process of zeolites. We could clarify by the tool the critical roles of hetero-atoms on the ring species and of alkali metals on the assembly of the rings. We could successfully lead the conclusion that introduction of Al into the ring structure decreased the proportional contribution of odd-numbered rings, and the addition of Zn enhanced the formation of three-membered ring. It is noted that the ring number distribution is already determined in the amorphous phase of reactant aluminosilicate hydrogel prior to crystallization to each zeolitic phase. In the successive stage, nucleation and growth, we concluded that three kinds of particles of primary and secondary units and crystal exist in the aqueous phase of solution, by our original contribution using Small Angle X-ray Scattering(SAXS)-Wide Angle X-ray Scattering(WAXS) in situ measurement. We finally proposed a whole schematic process of crystallization of zeolite through these explorations.We also succeeded to obtain much smaller nano-crystal of zeolite than previously reported, owing to the knowledge obtained above. In this method, nano-crystals at higher concentration were achieved to crystallize without addition of organic additives, which are conventionally accepted as an indispensable reagent for such a type of nano-crystal.