【作者】 田大勇；

【导师】 于吉红； 徐如人；

【作者基本信息】 吉林大学 ， 无机化学， 2009， 博士

【摘要】 分子筛是一类重要的结晶性微孔材料,具有规则的孔道结构和大的比表面积。分子筛晶体的特殊聚集态不仅与分子筛材料在催化、吸附、分离等领域的应用密切相关,而且对分子筛膜、光学器件等复合材料的制备有着重要意义。本论文以磷酸铝分子筛为研究对象,致力于控制磷酸铝分子筛晶体的生长行为,并对其特殊的聚集态进行表征,研究磷酸铝分子筛的晶体生长机制。第一章为绪论,介绍了磷酸铝分子筛的发展历史,特殊聚集态分子筛的研究现状,分子筛晶体的生长机制,无机材料的晶体生长习性,及本论文的选题目的与意义;第二章介绍了过渡金属取代磷酸铝分子筛AlPO4-5的晶貌控制,发现了聚乙二醇分子对AFI分子筛c-轴生长的抑制作用,及杂原子取代对磷酸铝分子筛晶体生长行为的影响,实现了特殊晶貌,如棱柱状、片状、花状Cr-AFI及猕猴桃状Ti-AFI分子筛的可控生长;第三章介绍了溶剂热外延生长法制备Ti-/Cr-AFI核壳材料,实现了Ti-AFI纳米片在Cr-AFI晶体表面的有序外延生长,同时发现由于Cr-AFI不同晶面与Ti-AFI晶体晶格“不匹配度”不同,Ti-AFI在Cr-AFI晶体(100)晶面的生长优先于(001)晶面;第四章介绍了微波辐射条件下混合溶剂体系中AlPO4-5分子筛的晶貌控制,晶体的长径比(c/a)可以实现从1.7到6.3之间的调变,当在体系中加入晶种诱导时,产物晶粒的大小随加入晶种量的增加和诱导时间的延长而明显减小;第五章介绍了梯度酸度SAPO4-34分子筛核壳材料的制备,通过外延生长法制备了具有梯度酸度的SAPO4-34核壳结构,该核壳结构的强酸中心明显低于SAPO4-34分子筛,在MTO反应中相对于SAPO4-34表现出较高的乙烯选择性和较低的丙烷副产物选择性;第六章对本论文的工作做出了总结并进行展望。本论文详细研究和讨论了上述特殊聚集态磷酸铝分子筛材料的合成方法、影响因素、生长机制以及性质等,为设计具有特殊性质和应用前景的先进功能材料提供了实验和理论基础。更多还原

【Abstract】 Zeolites and related microporous materials that have a large surface area and well-defined pore structures are important due to their wide applications in catalysis, ion-exchange, adsorption, chemical separation, and host/guest chemistry. Aluminophosphate molecular sieve (AlPO4-n) is one of the important families of microporous materials. In contrast to the traditionally anionic aluminosilicate zeolite frameworks, their structures are typically built up from strict alternation of AlO4 and PO4 tetrahedra through corner sharing of an oxygen atom to form a neutral open framework. The lattice Al and/or P atoms can be partially replaced by silicon and/or other elements to form frameworks with Br?nsted acid sites as well as catalytically active metal sites. In the recent years, aluminophosphate molecular sieves have also been developed for new applications, such as optics devices and membranes. The morphology control is important for the special property and application of AlPO4-n. And it depends on the better understanding of the growth mechanism of AlPO4-n. Whereas, because of the limit of characterization method, the growth mechanism of AlPO4-n is not well clear. So the growth mechanism research of AlPO4-n faces a big challenge.In this thesis, systematic researches have been done on the preparation of aluminophosphate with special aggregative states. The pEG molecules have been used as a co-solvent to control the crystal growth of transition metal substituted AFI crystals. The results demonstrate that the crystal growth of AFI crystal along c-axis can be significantly inhibited by using pEG molecules as the crystal growth inhibitor. Varying the volume ratio of pEG/H2O, different morphologies of AFI crystals can be obtained, such as prismlike, tabletlike and flowerlike Cr-AFI, and kiwi fruitlike Ti-AFI crystals depending on the type of transition metal ions in the reaction system. Our work suggests that the different isomorphic substitution of metal ions may be responsible for the different growth behavior of Me-AFI crystals with the presence of pEG in the reaction system. The flowerlike and nanosheetlike morphology significantly reduce the length of the [001] pore of Me-AFI crystal, whch is important for the diffusion of guest molecular in the pores of host molecular sieves.Additional, the combination of two single-site heterogeneous catalysts of Cr-AFI and Ti-AFI was achieved for the first time by forming a core-shell composite via solvothermal epitaxial growth. The sheetlike Ti-AFI microcrystals were epitaxially grown on the surface of the pre-synthesized tabletlike Cr-AFI crystals core. The growth process of the Ti-AFI microcrystals on the surface of core of Cr-AFI crystal was detailedly studied by the SEM characterization. The results demonstrate that the Ti-AFI microcrystals nucleate preferentially on the (100) basal face of the Cr-AFI crystals core.The N2 adsorption analysis shows that the channel systems of the core and shell have good communication, which may provide a good mass transport pathway for the catalytic reaction. The core-shell composite of Ti-/Cr-AFI makes it possible to combine two catalytic sites in one catalyst, which may benefit some special catalysis reactions. The morphology control of AlPO4-5 crystal was also investigated by microwave irradiation in mixed-solvents system. The results show that the aspect ratio of the AlPO4-5 (c/a) crystals decreases significantly with the increase of the volume ratio of EG/H2O. Interestingly, the dumbbell shape AlPO4-5 crystals can be obtained when the volume ratio of n-butanol/H2O reaches to 5:1 in the mixed-solvents of n-butanol and H2O. With the addition of the crystal seeds, the size of the AlPO4-5 crystals decreases with the increase of the amount of crystal seeds and the induction time.Based on the understanding of the epitaxial growth mechanism of aluminophosphate molecular sieve, we designed and prepared the SAPO4-34 core-shell material. The N2 adsorption analysis shows that the channel systems of the core and shell have good communication. The NH3-TPD results show that the strong acid sites are fewer in the core-shell composite than that in SAPO4-34, which is caused by the lower Si content in the shell. The catalytic property is evaluated by the MTO reaction. The core-shell material shows good ethylene selectivity and lower propane by-product. The SAPO4-34 core-shell material may provide a new way for the development of new catalyst for MTO reaction.In conclusion, the work of preparing aluminophosphate molecular sieves with special morphology and aggregative states provides new methods and ideas to realize the controlled synthesis of AlPO4-n, and can help us to better understand their growth mechanism.更多还原