【作者】 杜孟辉（Do Manh Huy）；

【导师】 陈丰秋； 程党国；

【作者基本信息】 浙江大学 ， 工业催化， 2014， 博士

【摘要】 随着人口增长和生活水平的提高,化石资源不断消耗,环境污染,人类健康是全球面临的问题,如何在不断推进人类物质文明进步和社会发展的同时仍保证生态的可持续发展是我们面临的任务和挑战。沸石分子筛由于具有规则的孔道结构,其孔径大小与一般分子相近和表面性质可修饰的特点,已被广泛应用于工业催化、吸附、分离等领域,徽地提高了相关过程的效率,减少了对环境的污染。同时近年来,新型沸石分子筛的设计和制备,如多级孔道、纳米晶体、整体型多级孔及空心球形等,进一步提高了其应用效率,已成为合成新沸石分子筛材料的新趋势。然后,由于人们对沸石分子筛内在生长机理认识仍存在不足,至今虽已有不少合成这些新结构沸石分子筛的方法,但其制备步骤多、外加结构导向剂多,如何简化制备工艺、减少污染是当前沸石分子筛制备领域的研究热点。沸石分子筛生长机理的深入理解对设计及合成性能优异的沸石材料是必不可少的。为了揭示沸石成核及生长机理,本文选择富碱-凝胶作为模型体系,采用SEM和TEM等表征技术结合AFM, XRD,27A1-MAS NMR,氮、氩吸附及因素分析等方法对沸石晶体形成与生长机理进行系统表征。研究表明沸石的成核是在平衡凝胶相中发生的,这些平衡凝胶相为溶解的铝硅根离子沉淀成缩聚初级聚集。晶核在平衡凝胶相中形成可以扩散到液相和平衡凝胶的液-固界面。因此,沸石晶体的形成遵循了一种“液相转变”和“固相转变”的协同生长机理。在液相和平衡凝胶的液-固界面里,在沸石生长的前期,取向聚集起决定作用,而这些聚集的驱动力是在带正电荷的活化Na+与生长的晶体或晶核表面的TO-负电荷之间的静电力。在沸石晶体生长的后期,和并和Ostwald熟化生长占主导地位。尽管小分子和超分子模板剂分别在微孔和介孔分子筛合成方面都非常成功,但由于在介孔材料与沸石相之间存在相分离,通过两种不同模板体系的共组装,将分子筛的微孔引入有序介孔网络是一个富有挑战性的研究课题。本文为了解决上述的问题,提出了一种简单的、碱辅助的双模板新方法。从而成功地制备出二维六方对称的有序介孔MFI沸石。采用该方法也可以制备介孔取向的ZSM-5沸石以及整体型多级孔沸石分子筛。通过纳米沸石分子筛的组装形成多级孔材料是一种克服沸石微孔孔道对大分子扩散及传质限制的有效手段。到目前止,纳米沸石分子筛组装合成方法需要使用至少一种(微孔或介孔)有机结构导向剂,即模板剂。而有机模板剂的使用后又需要用煅烧或溶剂去除,这样不仅增加成本还会造成环境污染。因此,本文依据沸石分子筛的协同生长机理,成功研发了既无有机模板剂又无沸石晶种条件下直接法合成纳米棒组装的沸石晶体及空心球的整体型多级孔MOR沸石的新方法。这种合成方法不但步骤简单,而且完全避免了有机模板剂的使用,对环境友好,并且还可以成功应用于其它整体型多级孔ZSM-5沸石分子筛的合成。为了更好地测定分子筛晶体的结构,认识反应物分子在微孔分子筛中的吸附、扩散和反应规律,大晶粒分子筛的合成一直以来受到广泛关注。目前大晶粒沸石分子筛的合成方法一般是通过采用有毒的氟化物抑制沸石成核来控制晶体缓慢地生长。这样往往需要几天甚至几周的晶化时间,而且产品的晶粒大小往往不均匀。本论文提出了一种既简洁又无氟化物和有机模板剂直接合成均匀大晶粒的GIS、ANA和MOR晶粒沸石分子筛的新方法。此方法通过富碱快速溶解硅铝凝胶到液相可促进成核及晶体生长,这不仅消除了晶化过程的凝胶溶解形成的第二的晶核,还缩短了晶化时间,从而得到了均匀晶粒的沸石分子筛。另外我们发现ANA沸石的大晶体是从GIS型沸石晶体的转变而形成。ANA沸石的晶体生长遵循“液相转变”和“固相转变”的协同机理。具有有序介孔或大孔沸石材料不仅在先进的催化及分离领域,还在如药物、光电子学及其他的纳米技术领域有广阔的应用前途。目前有序介孔沸石分子筛合成方法是模板法。本文提出了一种导向大孔沸石合成的新路线---沸石building block的分解路线。此路线是采用NaOH直接分解晶体生长过程形成的沸石building block,合成的取向有序的大孔MOR和Na-P1沸石具有良好水热稳定。更多还原

【Abstract】 How to promote the economic, social and human development while ensuring ecosystem sustainability are the emerging tasks and challenges we faced. Characterized by a regular channel system of interconnected micropores with molecular dimensions below2nm and tailorability of pore size and surface functional groups, as well as framework stability, zeolites have been widely applied in industry as catalysts, adsorbents and ion exchangers. To meet the growing demand for ecologically sustainable solutions to global issues such as enhancing energy demand, reduction of resources, environmental protection, and human health improvement, new zeolite architectures such as hierarchically porous structures, nanosized crystals, self-standing monoliths, membranes and hollow microspheres have become one of new trends in the synthesis of zeolite materials. Although there have been many routes suitable to obtain the new architectures with novel advanced properties, rational synthesis strategies still remain a great challenge due to unclear understanding their formation mechanism.Understanding of zeolite crystal growth mechanism is essential for designing and producing better zeolite materials with desired physical and chemical properties, but still remains elusive. To uncover the zeolite nucleation and growth mechanisms, we chose a sodium-rich dense hydrogel system, used the synthesis of ZSM-5zeolite monolith mentioned above, as a model system and conducted SEM and TEM studies in combination with AFM, XRD,27Al-MAS NMR, N2and Ar adsorption measures and element analysis of the samples collected at different synthesis times. Experimental findings of zeolite crystal evolution from sodium-rich hydrogel revealed that the zeolite nucleation occurs at the equilibrated gel phase of the condensed primary aggregates precipitated from the dissolved (alumio)silicate species. The nuclei produced from the nucleation could be diffused into the liquid-solid interface of the equilibrated gel phase and the liquid phase. The zeolite growth therefore occurs through a synergistic mechanism of two growth processes:a solution-mediated process and a solid-state transformation. In the liquid phase and the liquid-gel (equilibrated gel) interface, the oriented aggregation governs in early stages of the zeolite growth. The major driving force for the aggregation is electrostatic force between the positively charged active Na+and the negative charges of the (T)O groups on the surface of the nuclei and growing nanocrystals. In the last steps the crystal growth by the coalescence and the Ostwald rule becomes predominant.Although assemblies of molecular and supramolecular templates have proven very successful for fabricating both zeolites and mesoporous molecular sieves, the combination of crystalline zeolite micropores into an ordered mesopore network by cooperative assembly of two different templating systems is challenging because of the phase separation between the mesoporous material and zeolite phases. Here, we designed a simple and general alkali-assisted template strategy which allows to solve this problem. With this strategy, we have successfully synthesized the highly ordered mesoporous zeolite with the2D hexagonal symmetry mesospores and MFI zeolitic framework walls. This strategy also allows to prepare the oriented mesoporous ZSM-5as well as self-standing hierarchical zeolite monoliths composed of the MFI nanosheet. The materials are believed to have promising catalytic activities for organic reactions involving bulky molecules.An efficient way to overcoming the diffusion and mass transfer limitations of the zeolite microporous network system for bulky molecules is to assemble nanosized zeolites into hierarchical materials. The existing strategies for the synthesis of such hierarchical materials require the use of at least one organic structure-directing agent. Designing and developing new more environmentally-friendly and more economical synthesis routes to assemble the nanocrystals into mechanically stable, hierarchical monoliths are thus significantly important for the hierarchical zeolite materials to be applied in heterogeneous catalysis and separation processes on an industrial scale. On the basis of our proposed synergistic mechanism, we designed successfully an organic-template-free, zeolite-seed-free direct route for the first synthesis of self-standing hierarchical zeolite monoliths composed of nanorod assembled mordenite (MOR) zeolites and hollow nanorod MOR zeolite assembled spheres. This route also is used successfully for the synthesis of the self-standing hierarchical ZSM-5zeolite monoliths.In order to effectively utilizezeolite micropores for the special applications as host materials for guest molecules in optical, magnetic, and electronic devices as well as fundamental studies such as precise crystal structure determination and the measurements of intracrystalline adsorption, diffusion and reactivity of guest molecules, the synthesis of large single crystals is required. To date, most existing methods for fabricating large zeolite crystals are based on repressing the zeolite nucleation and controlling the slow growing rate using toxic fluorine species. These require longer crystallization time from days to weeks and difficultly avoids the crystal growth of the second nuclei resulting in the uniformity of the crystals is difficultly obtained. Furthermore the negative effects of the use of fluorine on environment is unavoidably. We have proposed a new simple, rapid, fluorine-free, organic-template-free strategy for the synthesis of the large and uniform crystals of Na-P1(GIS), MOR and analcime (ANA) zeolites. This strategy is based on catalyzing simultaneously both the zeolite nucleation and crystal growth processes by NaOH with a high content. This rout allows saving time and energy consumption and avoiding the use of toxic fluorine species as well as organic templates. In addition, we found that the formation of ANA zeolite is result from the transformation of GIS zeolite and the mechanism of the transformation is the combination of the solid-state and solution-mediated transformations. The mechanism allows us design the hierarchical hollow or yolk@shell structures without template.Zeolite materials with ordered macroporous and/or mesoporous structures hold promise not only for advanced catalysis and separation but also advanced applications such as medicines, photonics, photoelectronics, and other emerging nanotechnologies. The existing methods of synthesis of ordered mesoporous zeolites are based on assembly of structure-directing agents. Here we demonstrated a disassembly route to generating the oriented macropores in zeolite crystals. Our route is based on the direct disassembly of zeolitic building blocks formed during the crystal growth process by NaOH. The orientation of the ordered mesopores in the crystals of fabricated MOR and Na-P1(GIS) zeolites with their good hydrothermal stability could make them interesting material platforms for fundamental studies of the structure-properties correlation and the special applications.更多还原