【作者】 李鹏；

【导师】 熊光；

【作者基本信息】 大连理工大学 ， 工业催化， 2013， 博士

【摘要】 介孔-微孔复合分子筛结合了介孔材料的孔道优势和微孔沸石的酸性特点,在大分子催化反应中具有潜在的应用前景。目前该领域的研究主要集中在合成方法的探索和合成材料的应用,对其合成机理研究较少。为达到可控合成的目的,对于更深层次的机理研究是非常必要的。本文以纳米组装法合成Y/MCM-41介微孔分子筛为研究对象,利用UV-Raman光谱并结合XRD、SEM、TEM、FT-IR、XRF、N2吸附、29Si及27Al MAS NMR等表征技术,对其合成机理进行了系统研究。本论文的研究重点由以下几个部分构成：1.作为合成Y/MCM-41分子筛的前驱体,首先对Y型沸石的合成机理进行了研究。在晶化过程中,最初形成的凝胶固相首先发生解聚,向液相中释放活性寡聚态硅物种。液相促进凝胶固相的解聚和解聚出来的活性寡聚态硅物种的传递。活性硅铝物种相互作用后在凝胶固相中生成一种硅铝4元环过渡态物种,最终4元环硅铝物种相互连接形成沸石晶体骨架结构。当体系碱度较高时,硅铝物种聚合度低,品化速度较快,沸石的Si/Al比较低。2.对Y/MCM-41介孔相的形成过程进行了系统研究。结果发现,对于晶化程度较低的Y型沸石合成凝胶,其中存在尚未连接成沸石骨架的无定形4元环硅铝次级结构单元。这种次级结构单元具有较高的电荷密度,较易作为多齿配体与CTAB胶束进行作用。在进行碱度调节前的较高pH值范围内,这种次级结构单元即可与CTAB形成一种介稳态介孔结构。但是,Y型沸石合成凝胶中的的寡聚态硅物种及沸石晶体则不会起到这种作用。当pH值降低至9.3时,寡聚态硅物种与沸石结构单元发生聚合,共同构成了Y/MCM-41的高度有序六方介孔相结构。3.研究结果表明,组装前体的选择与介孔合成过程中pH值的调节对Y/MCM-41的最终结构具有较大影响。在合成过程中的第二阶段,pH值的调低起到了双重作用：1.促进了体系内硅铝物种聚合形成介孔,2.酸的引入使前体中的Y型沸石脱铝,导致晶体受到一定程度的破坏,可降解释放出更多沸石次级结构单元。本实验中首次证实,即使选用含有低结品度Y沸石品体的合成凝胶为硅铝源,同样可以合成出含有沸石结构单元的纯介孔相Y/MCM-41。因此,通过选择不同品化程度的Y型沸石合成凝胶及进行pH值调节可以控制合成具有不同结构的Y/MCM-41型分子筛,如只含有Y型沸石次级结构单元4元环的纯介孔相,含有4元环和6元环次级结构单元的纯介孔相以及Y型沸石与介孔相混合的分子筛。4. Y/MCM-41显示出比普通Al-MCM-41更强的水热稳定性、热稳定性及酸性。具有不同结构与酸性的Y/MCM-41对1,3,5-三异丙苯催化裂化的活性与产物分布不同。可针对不同催化反应需要,可控合成出不同类型的Y/MCM-41分子筛。更多还原

【Abstract】 Meso-microporous molecular sieves have potential applications in the catalytic conversion of large molecules by combining the performances of both microporous and mesoporous molecular sieves. The current research mainly focused on the synthesis and applications of the meso-microporous molecular sieves. However, there are few studies focusing on the synthesis mechanism. In this thesis, the formation mechanism of Y/MCM-41has been investigated by using UV Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (IR), and electron microscopies (SEM and TEM). The main contents can be summarized as follows.1. The formation mechanism of zeolite Y as the precursor for Y/MCM-41has been studied. The solid phase releases oligomeric silicate species to the liquid phase by depolymerization. The liquid phase promotes the depolymerization of the gel by dissolving the oligomeric silicon species, and delivers the active species during the crystallization. The4-membered ring species are formed in the solid phase of the gel at the early stages of crystallization, and then they connect with each other to form the zeolite framework. The higher the alkalinity, the lower polymerization of the aluminosilicate species, the faster the speed of the crystallization and the lower the framework Si/Al ratio are.2. The mesopore formation of Y/MCM-41has been investigated. The4-membered ring species in the zeolite Y synthsis gel promotes the formation of a metastable mesopore structure just after mixing the zeolite precursors with CTAB. This has been ascribed to its high anionic charge density as well as the appropriate multidentate coordination. In contrast, the low-polymerized aluminosilicates and well-crystallized zeolite crystals cannot assemble with CTAB at this stage. Lowering down the pH value to9.3, the oligomeric silicon species polymerize with zeolite Y building units to constitute the highly ordered hexagonal mesoporous phase of Y/MCM-41.3. The precursor structures and the pH adjustment during the formation process affect the final structure of Y/MCM-41. Lowering the pH value down to9.3in the second step has a twofold effect:1. Enhance the polymerization of the amorphous silicate species to form the mesoporous phase;2. Break down the zeolite Y crystal to zeolite building units by dealumination, which leads to the structural change of the precursors. For the first time, it was confirmed that pure mesophase containing zeolite building units can be prepared by using the precursor containing zeolite crystals. Combining the effects of both the precursor structure and the pH adjustment, pure Y/MCM-41mesoporous phase containing4-membered ring building units, pure Y/MCM-41mesoporous phase containing4-membered ring and double6-membered ring building units, and the mixture of zeolite Y and mesoporous phase can be synthesized.4. Compared with Al-MCM-41, Y/MCM-41shows higher hydrothermal/thermal stability and stronger acidity. The catalytic activity of Y/MCM-41was studied by1,3,5-triisopropylbenzene craking reaction. Y/MCM-41with different structure and acidities show different activities and product distributions. Therefore, the catalytic performances can be controlled by using different Y/MCM-41as the catalyst.更多还原