【作者】 宋春敏；

【导师】 阎子峰；

【作者基本信息】 中国石油大学 ， 化学工程与技术， 2007， 博士

【摘要】 以MCM-41为代表的介孔分子筛材料在催化裂化、烷基化和异构化等炼油工业重要的催化反应上具有潜在的应用前景,但其较弱的酸性和较差的水热稳定性无法满足这些过程对催化剂酸强度和水热稳定性的要求,故此限制了介孔材料在工业催化领域的应用。最近的研究表明,将沸石纳米簇作为前驱体可直接组装进入介孔分子筛的骨架使其酸性和水热稳定性大幅度提高。基于此,本论文旨在开发从商用的微孔沸石出发制备复合分子筛的合成路线,尝试得到具有较强酸性和较高水热稳定性的介孔分子筛材料,并探索了不同组装路线的组装行为。本论文首先对商用的ZSM-5沸石进行碱处理,得到碱处理的浆液、滤液和滤饼,并考察了碱处理沸石的性能,提出了相应的碱溶机理。然后将浆液、滤液和滤饼分别作为硅铝源考察了不同组装方法的可行性及其相应的组装行为。碱处理ZSM-5沸石的滤液和浆液中含有一些可溶解的纳米级硅铝酸盐碎片和一些具有沸石次级结构单元的纳米晶,因此可以作为前驱体溶液合成复合结构分子筛。而碱处理ZSM-5沸石得到的滤饼为富含超细化颗粒的晶粒,且晶粒粗糙度很高,因此易于附晶生长介孔分子筛,得到的微孔颗粒表面附晶生长的介孔分子筛,具有很好的长程有序度,为六方排列的孔道结构。由碱处理ZSM-5沸石的滤液,与表面活性剂在碱性条件下基于S+I–静电组装路线可得到孔壁含有沸石次级结构单元的介孔分子筛,其结构与常规的MCM-41的六方结构一样,且具有较高的热和水热稳定性,以及较强的酸性,这主要是由于沸石的次级结构单元组装进入了分子筛骨架,并提出了相应的自组装机制。由碱处理浆液与表面活性剂在水热条件下自组装同样可得到复合结构分子筛,但得到的分子筛应为混相,包括孔壁含有ZSM-5沸石次级结构单元的介孔分子筛,微孔颗粒表面附晶生长的介孔分子筛以及不含任何ZSM-5结构单元的纯粹MCM-41。并详细考察了产物分子筛的结构性能、表面形貌、酸性和水热稳定性。考察了主要因素对分子筛性能的影响,表明随碱处理苛刻度增大,可以组装得到与滤液类似的介孔材料,并提出了由浆液自组装复合分子筛的机理。而要得到微孔与介孔性能都适宜的复合分子筛,需选择合适的碱处理条件。本论文还探索了由碱处理ZSM-5沸石的浆液或滤液作为部分硅铝源与单体硅铝源共组装方法的可行性,研究了滤液或浆液和硅酸钠、铝酸纳在表面活性剂体系中的共组装行为,通过控制适宜的碱处理条件可以得到微孔、介孔性能优异的复合分子筛,论证了共组装方法路线的可行性。最后还考察了分子筛的催化性能,对非临氢反应具有较高的异构化选择性,对临氢反应,有较高的裂化选择性。更多还原

【Abstract】 Mesoporous molecular sieves have potential applications in industrially important reactions such as catalytic cracking, alkylation and isomerization. However, the acidity and hydrothermal stability of mesostructured aluminosilicates MCM-41 are less than required for many catalytic applications, which are the main obstacles to applying mesoporous molecular sieves as catalysts or catalyst supports. Recently, the acidity and the hydrothermal stability of mesostructured aluminosilicate are significantly improved by direct assembly of the zeolite precursors. Based on the previous results, new routes to synthesize mesoporous molecular sieves from commercial ZSM-5 zeolite are developed, and the assembly behaviours of zeolite precursors in different routes were investigated in the present work.The commercial ZSM-5 zeolites were treated by the alkaline solutions to obtain slurry or filtrate and filter cake of alkaline dissolution of ZSM-5 zeolite. The mechanism of alkaline dissolution of ZSM-5 zeolite was proposed. And then the assembly behaviours of slurry, filtrate and filter cake of alkali-treated ZSM-5 zeolite as silica-alumina source were studied. The slurry and filtrate of alkaline dissolution of ZSM-5 zeolite, which contain soluble aluminosilicate species with fragments of ZSM-5 zeolite structure, were used for the synthesis of an MCM-41-type mesoporous material. And filter cake of alkali-treated ZSM-5 zeolite contain many small grains, and the surfaces of these grains are very rough. It is feasible to overgrow mesoporous MCM-41 on the rough surfaces of the grains. The obtained samples possess the ordered hexagonal mesoporous structure of MCM-41-type molecular sieves.Mesoporous molecular sieves (denoted as MZ-B) with ordered hexagonal structure have been successfully synthesized by the assembly of the precursors from filtrate of alkali-treated ZSM-5 zeolite with CTMABr surfactant micelles in alkaline media based on S+I– static electricity route. The samples were characterized by XRD, N2 adsorption, IR, SEM, TEM and so on. The synthesized samples exhibit highly hydrothermal stability and strongly acidity compared with conventional MCM-41. It’s indicated that the mesoporous walls of MZ-B samples contain the secondary building units similar to the units in microporous crystal of ZSM-5 zeolite. Furthermore, the mechanism of self-assembly using filtrate of alkali-treated ZSM-5 zeolite as the silica-alumina source was proposed. The composite molecular sieves (denoted as MZ-A) were hydrothermally synthesized using the slurry of alkaline dissolution of ZSM-5 zeolite. The obtained MZ-A samples were composed of the mesoporous molecular sieves with pore walls of secondary building units of ZSM-5 microporous zeolite, mesoporous MCM-41 overgrowth on the rough surfaces of the microporous grains, and normal MCM-41. The structure, morphology, acidity and hydrothermal stability of the composite materials were thoroughly characterized by XRD, N2 adsorption, IR, SEM, TEM, etc. The structures of obtained samples are similar to these from filtrate with the acrid degree of alkaline treatment increased. The mechanism of self-assembly from the slurry of alkali-treated ZSM-5 zeolite was put forward. The properties of obtained composite samples are related with the condition of alkaline treatment of ZSM-5 zeolite.In this work, it was investigated the possibility of the coassembly of the slurry or filtrate of alkali-treated ZSM-5 zeolite and monomeric silicate and aluminate species into mesostructured aluminosilicates. The behaviours of the soluble aluminosilicate species and monomeric silicate-aluminate in current coassembly were elucidated. The results show that the obtained samples possess more ordered hexagonal mesoporous structure as Si/Al ratio increased. The performance of the conversion reactions of n-C12 on composite molecular sieves shows high isomerization selectivity for non-hydrogen process, and good hydrocracking selectivity for catalytic hydrogenation process.更多还原