【作者】 余淑媛；

【导师】 何鸣元； 单永奎；

【作者基本信息】 华东师范大学 ， 分析化学， 2004， 博士

【摘要】 多金属含氧簇合物(POM)同时具有酸性、氧化-还原性、“假液相”行为等催化特性，在原子经济反应和环境友好催化方面有着诱人的实用前景。但POM的比面积小、负载后易溶脱，机械强度和热稳定性差是它作为催化剂的致命弱点。介孔分子筛的出现和应用为充分发挥多金属含氧簇合物低温高催化活性、无污染、低腐蚀性的巨大化学工业催化潜能开辟了一条很好的途径。介孔属于纳米尺度范围，为POM纳米粒子的可控组装提供了可能，同时孔材料大的表面积和丰富的羟基，为高度分散和嫁接多金属含氧簇合物也提供了操作平台。但到目前为止，国内外还未见有关利用介孔材料孔道作为微型反应器制备多金属含氧簇合物纳米晶体及其作为催化剂研究的成功例子。这与POM本身的结构、组成特点和制备方法的特殊性以及所选择的载体，组装方法有关。在介孔孔道内将POM以纳米粒子的形式嵌居其中，并研究其催化活性，需要探索多原子簇合物纳米材料新的制备方法，探讨利用介孔作为纳米反应器制备纳米固体B酸，进而开发纳米固体酸高效催化材料，这于绿色化学的发展亦颇有裨益。 本论文利用介孔分子筛的孔作为纳米反应器，结合POM的结构、组成、性质、以及合成上的特点，主要研究将多金属含氧簇合物以纳米晶粒的形式嵌入介孔中的方法和途径。经实验证明真空浸渍和原位晶化法是两个行之有效的组装方法，通过这两种方法，POM能以纳米粒子的形式较好地被组装在介孔的孔道中，与利用常规方法在介孔分子筛上负载POM所得催化材料相比，此类纳米催化剂表现出了更好的酸催化活性。同时，还利用新的溶胶-凝胶(Sol-Gel)方法，在正硅酸乙酯水解的同时，将POM以醚合物的形式加入其中，醚合物水解后POM以纳米晶体的形式被原位包容入硅胶中，也取得很好的效果。除此之外，在文献的基础上，改进已有的两步浸渍在介孔材料上负载多金属含氧簇合物铯盐的方法，在近似固相体系中研磨反应使多金属含氧簇合物铯盐在孔内原位生成并结晶成纳米粒子。最后还研究了利用有机官能团与POM通过化学键的作用锚定到基体TIOZ上的方法，将POM固定在基体表面，由此修饰制备出的催化剂对于在以分子氧为氧化剂，苯一步氧化轻化制苯酚的反应中表现出了很好的催化活性。 具体内容如下:根据POM的结构特点，选用孔径较大的SBA一巧(36nln)作为载体，以其孔道为纳米反应器，采用改进的真空法，利用分子涡轮泵将载体首先进行高真空(10一7Torr)处理，将孔道中的水分子、空气以及其它杂质分子排除以减少POM进驻时的阻力。然后在真空的条件下，利用POM的水溶液或醇溶液浸渍载体，从而大量的POM分子进驻孔道，然后结晶组装成POM的纳米粒子。TEM结果直观地说明POM在孔道中以纳米粒子存在的状态。与此相比，利用较小孔径的分子筛SBA一巧(7 .7nln)作为载体，采用同样方法组装时，由于孔径的限制，POM水合作用的影响，POM在孔道内以单分子的形式存在，难以在孔道内形成纳米晶体。换用介电常数更小的有机溶剂醇类作为介质，发现醇在将POM大量带入孔道内有一定的优势，能在孔道内形成更密集的纳米晶粒。但由于溶剂醇容易使POM还原发生性质变化，在酸性功能方面不及利用水作为介质所组装的催化剂。利用POM合成时中间产物—醚合物组成和性质上的特点，使用原位晶化法，选用孔径较大的介孔分子筛SBA一巧为载体，借用真空浸渍的方法，在真空体系中使分子筛的孔道内充满水，再利用溶剂热的技术将POM醚合物压入分子筛孔道，醚合物遇到孔道中的水随即水解释放出POM，最后在孔道内原位结晶生成POM的纳米粒子。选用孔径较小的SBA一15分子筛，利用原位晶化法也可在介孔孔道内组装入POM纳米粒子。采用改进的501一Gel法，利用HF酸能够催化正硅酸乙醋水解(TEOS)反应使TEOS快速水解和POM醚合物与正硅酸乙酷有较大相混性的原理，使多金属含氧簇合物以纳米晶体的形式镶嵌在硅胶中。对其产物进行了一系列的表征证明:利用这种“包容”的方法制备的材料，与其他负载方法比，主客体之间有更强的相互作用。同时发现改进的溶胶一凝胶法制备的材料具有介孔(由粒子与粒子之间的间隙构成)结构，与常用的溶胶一凝胶法制备的微孔材料有明显差别。4.根据固体中离子迁移的基本规律，改进己有的两步浸渍在介孔材料上负 载多金属含氧簇合物艳盐的方法，在分子筛的孔道中合成Cs盐的纳米粒 子。该组装方法简单，组装后多金属含氧簇合物Cs盐得到了很好的分散， 载体的孔道结构保持了较好的规整性。5.采用TIOZ纳米粒子为基体，通过对表面官能团的功能化，利用嫁接技术， 将POM锚定在基体表面，从而POM在有机溶剂中不易洗脱，具有良好 的稳定性。6.以上纳米固体酸催化剂在苯与十二烯的烷基化和Q一甲基苯乙烯二聚 (AMS)反应中均表现出了催化活性，其中真空浸渍法、原位晶化法制备 的催化剂在反应中表现出了优良的催化活性;两步法组装的多金属含氧簇 合物Cs盐活性相对要低;溶胶一凝胶法制备的催化剂在两种反应中活性相 差较大，表现在催化烷基化反应时活性最低，但能高效催化AMS二聚反 ?更多还原

【Abstract】 Polyoxometalates(POM) are useful materials as acidic and oxidation catalysts for various reactions and have been practically applied in industry. As solid acid catalysts, especially characterized in providing a unique "pseudoliquid phase" reaction environment, POM catalysts should find more and more applications in green/sustainable and atomic economic reactions. However, bulk POM generally exhibit poor catalytic performance due to their low surface area and low stability, their applications have been limited. The mesoporous materials, which have been developed rapidly in recent years, providing nano-scale space for growing nano-scale POM particles and large amounts of-OH group and large surface area for facilitating the modification and dispersion of POM. The concept to assembly nanometer POM crystals with mesoporous materials using the mesopore space as nanoreactor has not been reported so far in literature. For this purpose, the characteristics of structure, composition, properties of POM and the chosen carrier should be further studied in detail. The assembly methods are also the key factor for the materials finally obtained. It is a challenge for the present paper to prepare useful and efficient nano solid Bronsted acid materials utilizing the mesopores of mesoporous molecular sieves as microreactor, and hence to promote the development of green chemistry.The goal of the present work is to find efficient assembly methods of nanometer POM particles in porous materials including mesoporous molecular sieve SBA15 and silica gel. Novel vacuum impregnation and in-situ crystallization methods have been developed to prepare nano POM in the channels of porous materials. Comparing with common impregnation method, the methods developed by the present work show significant superiority. The sol-gel method was also applied to synthesize nano 12-tungstophosphoric acid in the pores of silica gel. Nano Cs-substituted tungstophosphric acid salt was deposited in the pores of SBA-15 by a improved twostep synthesis method. In addition to the above methods, POM was also immobilized onto the surface of TiO2 particle by grafting to prevent POM from leaching in polar solvent media. Meanwhile, the nano POM/ porous materials were tested in acid-catalyzed benzene alkylation with 1-dodecene, cyclic dimmerision of a-methylstyrene (AMS), and in the selective oxidation of benzene to phenol by molecular oxygen.The main contents are as follows:1. Vacuum impregnation method was developed, in which the molecular sieve SBA-15 with a pore size of 36 ran was selected according to the size of the hydrated form of POM. The support was evacuated under high vacuum to remove impurities in the pores of mesoporous molecular sieve, then aqueous or alcoholic 12-tungstophosphoric acid(PW) solution was added, and the adsorption equilibrium was achieved under vacuum. Large numbers of PW molecules diffused into the clear channels of silica and nano PW crystals was formed into the mesopores. When alcohol was used as media, PW could deeply enter inside of the channels more easily because the lower dielectric constant of solvents provided a higher probability for POM anions to diffuse further in the pores with less restriction due to reduced electrostatic interactions with the silica support. However, when alcohol was used as media, the reduction of heteropoly acid to heteropoly blue was a disadvantage for the property of the products.2. In-situ crystallization method was used for the first time in the pores of SBA-15. Heteropoly acid etherate was used tentatively in the present work, which was an intermediate in the synthesis of POM. After filling water in pores by vacuum impregnation, POM etherate was impelled into the channels under hydrothermal condition, then dissociated and crystallized with the help of water finally. Nanometer polyoxometalate clusters was crystallized in-situ inside the channels of mesopores.3. Sol-gel method was improved. POM etherate was used here again. The mainidea of th更多还原