【作者】 付文华；

【导师】 何鸣元； 王一萌；

【作者基本信息】 华东师范大学 ， 物理化学， 2015， 博士

【摘要】 超微孔材料(孔径大小为1-2 nnm)有望同时解决沸石分子筛孔道内扩散受限和引入介孔后择形性消失或减弱的问题。现有报道的超微孔材料绝大多数具有p6mm或者无序的结构,但三维结构(如Pm3n结构)的孔道内的扩散限制更小。Pm3n结构的孔道由笼状孔和连接“窗口”构成,这种特殊的结构有利于择形催化的发生。传统合成Pm3n结构氧化硅使用不可从市售获取的十六烷基三乙基溴化铵模板剂在强酸性条件下进行。本论文中使用短链模板剂合成Pm3n结构的氧化硅和硅铝材料,目的在于：1)得到孔径更小的(超微孔)材料；2)逐步解决模板剂不可从市售获取的问题；3)避免使用强酸,合成条件更绿色、环保,原料中铝源的利用率更高,主要包括以下结果：1、使用十二烷基三乙基溴化铵(DTEAB)模板剂合成得到了Pm3n结构的超微孔氧化硅和硅铝材料。当合成在弱碱性进行时,SO42-的Hofmeister salting-out阴离子效应有助于减小表面活性剂的堆积参数(g)；当合成在弱酸性条件下进行时,有机固体羧酸的亲疏水性决定了氧化硅的对称结构,其中丙二酸、丁二酸亲水性较好,可以有效降低表面活性剂的堆积参数,因而容易得到Pm3n结构氧化硅。超微孔硅铝材料在环己酮与季戊四醇的缩酮反应中表现出了高于分子筛催化剂的催化活性和较好的稳定性。2、使用市售的十二烷基三甲基溴化铵(C12TMAB)模板剂合成得到了Pm3n结构的超微孔氧化硅和硅铝材料。合成中使用了氨水为碱源(弱碱性合成条件),但需要少量H2SO4水解TEOS,并且利用SO42-的Hofineister salting-out阴离子效应使表面活性剂g参数减小以得到Pm3n结构的氧化硅。超微孔硅铝材料在环己酮与季戊四醇的缩酮反应中表现出了高活性和很好的稳定性；在邻苯二酚与叔丁醇的气相烷基化反应中具有最高的催化活性和目标产物4-叔丁基邻苯二酚(4-TBC)产率。3、为了进一步缩小材料的孔径,使用碳链更短的癸基三甲基溴化铵(C10TMAB)模板剂合成得到了Pm3n结构的超微孔氧化硅和硅铝材料。合成中使用了氨水为碱源(弱碱性合成条件),表面活性剂本身堆积参数较小,SO42-和NH4+的Hofmeister salting-out离子效应也促进了Pm3n结构的生成。在甲缩醛和三聚甲醛缩合制聚甲醛二甲醚(PODEW)的反应中,Pm3n结构的超微孔硅铝材料表现出了高催化活性和最高的目标产物PODE3-8的选择性,体现出了超微孔材料孔道内独特的择形催化。4、除了控制氧化硅的孔径之外,在合成体系中加入羧甲基纤维素钠(CMC)作分散剂还可以控制氧化硅的形貌、颗粒尺寸和粒径分布。在优化的条件下,可以合成得到Pm3n结构的单分散氧化硅纳米颗粒,氧化硅的初级孔尺寸在超微孔价孔的边界上,纳米颗粒尺寸小于100 nm,氧化硅的总孔容在1cm3·g-1以上。更多还原

【Abstract】 Since crystalline microporous zeolites (i.e., those with very small pores) restrict diffusion of large-molecule reactions, and conventional ordered mesoporous materials lose shape selectivity in catalysis, supermicroporous materials with pore diameters in the range of 1-2 nm have become candidates for overcoming the above two drawbacks simultaneously. However, the majority of the supermicroporous materials published in the literature display 2-D hexagonal (p6mm symmetry) or disordered structures. From the point of view of catalysis, a three-dimensional pore system offers more accessible pathways for substrates to diffuse in and out compared to disordered or one-dimensional pore systems. As a result, the synthesis of ordered supermicroporous materials with 3-D structures is of more significance. Structures displaying Pm3n symmetry with spherical and ellipsoidal cages connected by narrower windows are of particular interest. In this thesis, we prepared a set of supermicroporous silicas and aluminosilicates with Pm3n symmetry by using short chain surfactants. The catalytic performance of the supermicroporous aluminosilicates was also investigated. The details of the dissertation include:In Chapter 3, dodecyltriethylammonium bromide (DTEAB) was used as template. Ordered cubic Pm3n supermicroporous silica and aluminosilicate materials were synthesized using sodium silicate as silicon source under alkaline condition. The presence of Hofmeister salting-out anion SO42- helped to stabilize the spherical micelles and provoke the forming of cubic Pm3n structure. A series of aluminosilicates was prepared and the SiO2/Al2O3 molar ratio in products could be achieved as low as 32 with the cubic Pm3n structure well-preserved. Highly ordered supermicroporous silicas and aluminosilicates with cubic Pm3n symmetry could also be prepared in weakly acidic solution of succinic acid and malonic acid for the first time. The polycarboxylic acids acted as auxiliary for fabricating cubic Pm3n structure by reducing the packing parameter of the surfactant. Aluminosilicates could be prepared via the direct-synthesis or post-synthesis approach. Aluminosilicates prepared via the post-synthesis approach preserved the cubic Pm3n structure better than the direct-synthesized ones. What was more, aluminosilicates prepared via the post-synthesis approach showed higher specific area and pore volume and larger pore size. The cubic Pm3n aluminosilicates prepared in our research exhibited much higher reactivity and more pronounced deactivation resistance property in the acetalization of cyclohexanone with pentaerythritol compared to the zeolite catalyst.In Chapter 4, dodecyltrimethylammonium bromide (C12TMAB) was used as template. The synthesis was carried out in the absence of concentrated acid solution or any organic auxiliaries. A small amount of H2SO4 was used to hydrolyze TEOS and the Hofmeister salting-out anion SO42- also played an important role in reducing the packing parameter of the surfactant. The Pm3n symmetry could be well preserved after Al incorporated into the framework and the molar ratio of SiO2/Al2O3 in the aluminosilicates reached as low as 25. The pore size of the cubic Pm3n silicas and aluminosilicates was in the supermicroporous range. For catalytic performance testing, it turned out that compared to zeolite USY-1 and mesoporous C16-AISBA-1 catalyst synthesized in concentrated acid solution, aluminosilicates prepared herein exhibited higher reactivity and more pronounced deactivation resistance property in the acetalization of cyclohexanone with pentaerythritol. Thanks to its supermicroporous open 3-D pore-structure and high ordering, the cubic Pm3n supermicroporous aluminosilicates showed higher yield of 4-t-butyl-catechol in the tert-butylation of catechol reaction compared to other catalysts.In Chapter 5, decyltrimethylammonium bromide (C10TMAB) was used as template. Decyltrimethylammonium has not only shorter chain length but also smaller packing parameter than dodecyltrimethylammonium. As a result, the cubic Pm3n structure could be facilely obtained in the presence of Hofmeister salting-out ions, SO42- and NH4+. The catalytic performance of the cubic Pm3n supermicroporous aluminosilicates was tested by the preparation of polyoxymethylene dimethyl ethers (PODEn). Shape selectivity was observed in the nanopores, whose size is most fit for the size of the target product PODE3.8, of the ordered supermicroporous catalyst. The ordered cubic Pm3n supermicroporous catalyst exhibited a superior PODE3.8 selectivity than zeolites and mesoporous catalysts did.In Chapter 6, we prepared monodispersed silica nanospheres with cubic Pm3n symmetry by using dodecyltrimethylammonium bromide (C12TMAB) as template and sodium carboxymethyl cellulose (CMC) as dispersing agent. By the addition of different amount of CMC, the ordering, particle diameter and particle dispersity of the silica samples could be tuned. The primary pore size was on the boundary between supermicropore and mesopore and the total pore volume of the silica nanospheres exceeded 1 cm3·g-1. CMC acted as dispersing agent in the synthesis and the interaction between CMC and the surfactant was weak. The method we displayed was facile and the yield of the silica was higher than 85%.更多还原