硅锗酸盐分子筛双四元环(D4R)组装机制研究

Zeolites are widely used in the gas separations, selective sorption, ion exchange, host-guest chemistry and other advanced functional materials. Their superior properties are stronly related to their unique framework structures and compositions. Design and synthesis of new zeolite structures with highly specific chemical and physical properties are a major research theme in inorganic synthesis chemistry. However, their synetheses are based primarily on an empirical "trial-and-erro" method. Therefore, exploring the assembly mechanism of building units in the formation of zeolite frameworks towards to the rational synthesis of novel zeolite materials are of importance and also a big challenge. Recently, a zeolite family of silicogermanates: SU-32 (polymorph A)with helical channels, SU-15 (polymorph B) and a hypothetical polymorph C with multi-dimentional interecting channels, all built by the D4R (double four-membered ring) building unit with different stacking sequence, have been sucessfully synthesized by us. We found that SU-15 and SU-32 often coexisted in the product, which limits their applications. Herein,the pure phase of SU-15 and SU-32 will be respectively prepared under the hydrothermal condition with the help of organic structure-directing agents, seeding and the incorporation of heteroatoms into framework. The relatioship between structure characteristics of these polymorphs and synthetic parameters will be entirely investigated in order to discover the key parameters which play significant roles on the self-assembly of D4R. The aggregation and stacking sequence of D4R in polymorph C will be induced by modifying and optimizing the synthetic parameters according to the above results. Through the combinatorial synthesis approach, the novel silicogermanate zeolites will be synthesized based on the assembly of D4R in the formation of three polymorphs. Eventually, the assembly mechanism of D4R will be proposed. All the samples will be prepared under a hydrothermal condition with the assistance of the computer simulation on the prediction of templates. We believe that a thorough understanding of the relationships between the building units D4Rs in this zeolite family containing both chiral and achiral frameworks and the synthesis methology can lead to new strategies for the design and rational synthesis of zeolites with desired functions and structures.

设计、合成具有新型结构和化学组成的分子筛材料是无机制备化学领域的重要内容。深入研究结构构筑单元在骨架搭建过程中的组装机制，对定向合成新型分子筛材料具有重要意义。本项目选定 SU-15-32硅锗酸盐分子筛家族为研究对象，其结构构筑单元单一，为双四元环(D4R)，多样的堆积连接方式决定该家族中三种多形体(手性SU-32，具有多维交叉孔道的SU-15和预测结构C)结构不同；SU-15和SU-32常以混晶出现在产物中。本项目以计算机模拟筛选模板剂为辅助，在水热条件下(1)利用模板剂导向、晶种诱导和杂原子效应等方法，合成SU-15和SU-32的纯相，揭示影响D4R定向组装的关键导向因素；(2)采用调整、优化合成导向因素，诱导D4R定向组装预测结构C；(3)应用以上D4R组装规律，利用组合合成技术，合成新型硅锗酸盐分子筛结构。对D4R组装规律的深刻认识能够为新型分子筛的开发提供高效合成方法和理论支持。

具有新型结构和化学组成的分子筛材料的定向合成一直是无机制备化学领域的重要研究内容。深入研究合成参数与结构构筑单元在骨架搭建过程中的组装方式间的协同作用规律，对定向合成新型分子筛材料具有重要意义。本项目选定SU-15-32硅锗酸盐分子筛家族为研究对象，采用结构导向剂诱导、晶种诱导、杂原子掺杂、干胶转化法等多种合成策略，重点研究SU-32和多形体C的定向合成，探索合成参数与双四元环D4R组装方式或结构类型的相互作用规律：.1.以二异丙基胺(DIPA)为结构导向剂，调变合成参数可制备纯相SU-15(SOF结构)和SU-32(STW结构)，结果显示多种合成因素（凝胶组成、反应温度和时间）协同作用，可诱导SOF或STW结构的形成，即决定SOF或STW结构形成的关键驱动力不是单一因素。.2.利用计算机模拟辅助筛选结构导向剂，考察其与骨架相互作用对合成规律和产物结构类型的影响。N,N-二乙基乙二胺和N,N'-二乙基乙二胺可定向合成STW结构分子筛，与模拟计算结果较低的骨架作用能相吻合；制得产物不仅骨架组成Si/Ge比高于文献报道，而且非D4R骨架原子位置的Ge占有率下降到12%，但是骨架Si/Ge比不能通过改变投料比进行调变，且无法合成STW纯硅分子筛，说明结构导向剂的种类、形状、尺寸和电荷密度等参数影响Ge原子在骨架组成的比例和位置且必须相互匹配才能得到目标结构。但是有些有机结构导向剂，即使与骨架相互作用能相对合理，理论上可以合成STW或多形体C，但是产物是其他类型(BEC、ITH、AST、ASV、MFI等)或其他骨架组成(FER、UZM-5等)的分子筛结构，可能由于晶化区域考察不全面。以上说明Ge物种和这些有机结构导向剂协同作用可诱导STW结构的生成。.3. 在浓溶胶或水热\溶剂热体系中，采用STW或SOF或具有D4R结构单元的分子筛作为晶种，并不能诱导目标结构的形成，原因是有机结构导向剂对结构的诱导作用远大于晶种释放出的结构碎片的作用。杂原子掺杂可以赋予材料优越的催化性能，但是Cu, Co, B等的引入并不能影响结构类型，如Cu-,Co-STW的制备；而Al源的加入将和Ge物种形成强烈的竞争关系，往往只能得到FER、UZM-5硅铝酸盐等分子筛。.4.尝试干凝胶转化法合成硅锗酸盐分子，结合晶种诱导以及骨架参杂等合成策略，发现结构导向剂和Ge源是生成目标结构的关键因素。