【作者】 刘建红；

【导师】 李瑞丰；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2010， 博士

【摘要】 近年来介孔分子筛的研究热点包括开发新材料、新合成路线和新的应用方向等。与早期报道的M41S类介孔分子筛相比,SBA-15是一种由三嵌段高聚物(PEO-PPO-PEO)导向而成的有序度高、大孔径(2-30nm)、厚壁和具有较好水热稳定性的介孔材料,从被合成以来就逐渐成为介孔材料的一个重要分支。研制介孔SBA-15分子筛与沸石复合、或与大孔复合的多级孔分子筛,采用新合成路线制备具有新结构性能特点的杂原子改性SBA-15,研究SBA-15及改性SBA-15的应用,是目前关于介孔SBA-15分子筛的几个重要的研究方向。通常催化剂在实际应用前都被要求制成一定形状和粒径的颗粒,这是因为材料的形貌和粒径的改变会直接影响到材料的物化性能和实际应用。而在目前关于介孔分子筛研究的文献报道中,膜状和球状是最具有实用意义的两种形貌特征。有很多实例证明,球形颗粒由于其几何优越性,在各种形貌中比表面积最高,接触面积最大,因此开发介孔分子筛的球形材料对于提高SBA-15的功能性和实用性有重要的意义。本文选择球形的杂原子改性SBA-15分子筛作为主要的研究课题,论文内容有两个部分:首先,结合胶体化学、溶胶-凝胶化学、自组装化学、微相分离理论等知识,研究单一介孔的SBA-15微球的合成机理及影响因素,研究介孔SBA-15与大孔复合的多级孔二氧化硅球形单块材料的合成。考虑到一般分子筛样品呈粉体状态,必须经过后处理加工成型或者是模具辅助成型,而本文所得单一孔及多级孔分子筛,都是在合成过程中直接自组装成为球形。对纯硅介孔分子筛的形貌研究则是制备杂原子改性介孔分子筛微球的基础。与之前已经报道的各种非球形形貌的改性杂原子SBA-15不同,在本文第二部分中,采用一步法直接合成具有球形形貌的、高负载效率的改性杂原子SBA-15材料,包括合成一系列分别含铜、铝、锌、铁、锆等金属的杂原子介孔SBA-15微球,合成CuAlZn-SBA-15和Zr-SBA-15两种中空微球,微球大小都在10微米左右。深入探索了杂原子的引入与介孔分子筛形貌特征、结构组成和催化性能之间的关系,研究了介孔SBA-15微球、杂原子介孔SBA-15微球以及杂原子介孔SBA-15中空微球的形成机理和影响因素。具体研究结果如下:(1)关于介孔SBA-15微球的形成机理和影响因素,前人的研究结果并不一致,为了澄清这一问题,本文首先探讨了共表面活性剂、无机酸浓度、无机盐、温度和搅拌条件等因素对介孔SBA-15微球合成过程的影响。结果表明,合成体系的酸度、搅拌条件和静置处理温度对杂原子介孔微球的合成影响最为明显;而共表面活性剂和无机盐的引入对SBA-15微球的形成没有明显地影响;通过对这些影响因素的考察,结合扫描电镜对SBA-15微球形成的观察结果,SBA-15微球的形成可能是由表面活性剂球形胶团与初步水解的硅酸根离子共同生成的球形微晶为种子,与后来水解的硅酸根离子一起在球形胶团模板的诱导下倾向于团聚成球形的溶胶-凝胶球,在水热处理过程中,球体内部自组装得到介孔SBA-15结构。(2)本文以正硅酸丁酯为硅源、三嵌段共聚物P123和少量的OP-10为共模板剂合成了介孔-大孔的二氧化硅单块,宏观形貌为0.2-0.5毫米的大球,内部分布着尺寸达0.5微米的连续大孔孔道,孔壁是规整的SBA-15介孔结构,孔径为4-5纳米。通过对比实验证明,这种多级孔二氧化硅单块大球的形成,需要有带有长链烷基的硅源TBOS和小分子表面活性剂OP-10共同参与才能形成。这种内部含有多级孔结构的二氧化硅大球在大黄素分子的药物吸附试验中,与单一孔结构的SBA-15微球相比效果要好,要比后者更快地达到吸附平衡而且对大分子药物具有更大的吸附贮存容量。(3)本文提出了一种直接合成杂原子介孔SBA-15微球的制备方法,即向SBA-15微球的合成过程中引入杂原子,在水热晶化得到SBA-15初级微晶后,不分离反应体系用氨水调节体系的pH值,再继续水热合成,就直接得到了含杂原子的SBA-15微球。论文合成了多种杂原子SBA-15微球,分别包括Cu、Zn、Fe和Al等(这种杂原子SBA-15微球的制备方法已经申请专利)。以这种方法制备的含铜SBA-15微球为例,铜的引入效率和分散性高于传统合成法和浸渍法,在甲基橙氧化降解反应中的活性比后两种方法制备的催化剂要好,而且活性组分的流失也少。(4) CuAlZn-SBA-15中空微球和Zr-SBA-15中空微球是两种新型的杂原子SBA-15中空微球,尺寸约10微米,壳层厚度达数百纳米甚至1微米。以Zr-SBA-15为例,XRD、ICP、TEM-EDS、UV-vis DRS和FTIR等实验证明部分锆原子进入了骨架,部分锆原子以纳米氧化锆的形式分散在SBA-15的孔道中。用吡啶吸附原位红外来表征杂原子SBA-15中空微球的表面酸性,结果发现,无论是含铜铝锌的SBA-15中空微球,还是含锆的SBA-15中空微球,其表面都是以Lewis酸为主要的酸活性中心,结合NH3-TPD的结果说明这种杂原子SBA-15中空微球的表面上多存在弱酸和中强酸中心,适合于对酸性要求不高的有机反应。(5)杂原子SBA-15中空微球相对于未改性的纯硅SBA-15都表现出明显的酸催化活性:在常压300℃甲醇脱水的醚化反应当中,CuAlZn-SBA-15中空微球的甲醇转化率可以达到60%,二甲醚的选择性100%,Zr-SBA-15中空微球的甲醇转化率可以达到71%,二甲醚的选择性>90%;将Zr-SBA-15中空微球应用于环己酮与乙二醇的缩酮合成反应,反应活性与纯硅SBA-15相比也有了很大的改善,缩酮的产率可以达到69~84%。以Zr-SBA-15系列催化剂为例,研究表明催化活性与催化剂表面酸性和结构参数的变化有直接的关系,随着锆含量的增加,表面酸性增强,反应活性也增加,孔结构参数下降则抑制了反应的顺利进行。更多还原

【Abstract】 During the past ten years, there are several hot focuses about the mesoporous materials such as functionalized hybrid materials and other new mesoporous molecular sieves, bioinspired method and other new synthesis routes, biological medicine and other new applications. Among these materials, SBA-15 is an important mesoporous material due to its regular porous structure (2-30nm) and high hydrothermal stability. It is very significant for the further development of SBA-15 to synthesize the hierarchical porous materials, prepare the modified-SBA-15 materials, and develop the new applications on separation, catalysis, etc.Generally the catalysts are manufactured with special morphology and metered diameter before practical application, because the morphology and diameter of materials can immediately affect the properties and practical applications. Membrane and sphere are two major forms in the previous reports. Spherical catalysts have been affirmed to be advantageous in some reactions owing to the highest surface area among the different shapes. Therefore, the development of spherical mesoporous materials can improve their functionality and practicability in the future. In this presentation, there are two major topics: one is spherical morphology control of mono-porous and hierarchical porous materials, and another is spherical morphology control of modified SBA-15 materials. The originalities of these works are the direct synthesis method. Mono-porous and meso-macroporous silica spheres are directly synthesized without help of special moulds and other post-treatments. Heteroatomic SBA-15 spheres or hollow spheres are also directly synthesized in“one pot”synthesis solution. The following is the detailed experimental results.(1) The key factors and formation mechanism of SBA-15 spheres were not affirmed before this paper. The experimental results suggested: temperature, stirring conditions are the key factors to the synthesis of SBA-15 spheres; co-surfactant, inorganic salts and other factors can not prevent the formation of SBA-15 microspheres, but can affect the perfectness of spherical products; the formation of spherical SBA-15 was dependent on the spherical conglomerations and the polymerizing growth between surfactant micelles and silicate anions.(2) The spherical meso-macroporous silica monoliths with diameter of 0.2-0.5 mm were prepared via a sol-gel method and phase separation mechanism, in which the tetrabutylorthosilicate (TBOS) was used as silicon source. The triblock copolymer (P123) and polyoxyethylene octylphenol ether (OP-10) were used as templates. The results showed that the inner structure had macroporous channels (0.5μm) and mesoporous SBA-15 skeleton (4-5nm). The spherical silica monoliths with meso-macroporous structure demonstrated higher absorption efficiency and capacity for Emodin molecules than the SBA-15 spheres with mono-porous structure.(3) A facile route to synthesize modified SBA-15 spheres was suggested. Typically, SBA-15 synthesis solution was prepared using block polymer globular aggregates as template and tetraethyl orthosilicate (TEOS) as silica source. The heteratoms were directly added to the solution, and then ammonia water was used to adjust pH to the special value. The solid samples were filtered, washed, dried and calcined after hydrothermal treatment. Until now, Cu, Zn, Al, Fe had separately introduced the mesoporous SBA-15 spheres with diameter about 10μm. The spherical heteroatomic SBA-15 materials and the corresponding synthesis methods had been applied to patent’s protection in China. Cu/SBA-15 microspheres via the same method displayed better performance in wet oxide degradation than the catalysts via traditional direct method and impregnation method.(4) CuAlZn-SBA-15 and Zr-SBA-15 hollow spheres were synthesized via the similar direct synthesis method, which showed that the hollow spheres were in ~10 microns diameter and the shell thickness was about 100 nanometers. The metal ammine complexes during the sol-gel process became the key factor in the formation of hollow spheres and dispersion of heteroatoms. The analysis results confirmed that the heteroatoms had been well embedded inside the siliceous matrix and partial nanocrystals appear inside of the pore channels, which can be used to explain the phenomenon that the surface area and orderliness of mesoporous catalysts decrease with the zirconium content. The analysis by in situ pyridine-absorption FI-IR spectra and NH3-TPD curves proved the weak and mid-strong Lewis acidity on the catalysts surface due to the introduction of heteroatoms.(5) The experimental results confirmed that incorporation of metal atoms into the mesoporous structure would supply the siliceous matrix with the new distinct catalytic activity. When the methanol dehydration was used as probe reaction, there was about 60% methanol converted to dimethyl ether while selectivity was 100% on the CuAlZn-SBA-15 hollow spheres. And the methanol conversion was increased to 71% and selectivity of dimethyl ether was >90% on Zr-SBA-15. When the dehydration of cyclohexanone and ethanediol was used as probe reaction, the ketal yield on Zr-SBA-15 hollow spheres were from 69% up to 84%. In comparison, the ketal yield was just about 10% with Si-SBA-15. The reaction performance will increase with the metal content, but the porous properties will be compromised with the increase of metal loading, which was not conducive to the methanol conversion.更多还原