【作者】 王培煜；

【导师】 李建功；

【作者基本信息】 兰州大学 ， 材料物理与化学， 2009， 博士

【摘要】 在有机合成中,钯催化的Heck反应是合成碳—碳键的实用方法,受到人们广泛关注。传统的Heck反应催化剂主要是Pd（OAc）₂、PdCl₂等均相催化剂,尽管这类催化剂活性较高,但它们很难从反应体系中分离和回收再用,高温下稳定性差,这些因素严重影响了Heck反应的工业应用。负载型钯催化剂,因有可能克服这些缺点,而得到了人们的重视。其中,介孔材料负载金属催化剂由于稳定性高、腐蚀性小、易从反应体系中分离回收、可重复使用、具有较高的催化活性和立体选择性,而受到了催化界工作者的关注。SBA-15介孔分子筛是具有较大比表面积、规整孔道结构的新型有序介孔硅材料,在催化和吸附分离等领域具有很好的应用前景。本文旨在将钯颗粒组装在SBA-15介孔分子筛孔道中,制备钯活性组分高度隔离和分散的新型催化剂,掌握钯颗粒在SBA-15介孔分子筛孔中的组装方法,研究SBA-15介孔分子筛中负载钯颗粒的结构特征,探索催化剂的结构与催化活性的关系。首先,利用传统离子交换法制备Pd/SBA-15复合材料。通过调节碱性钯阳离子的pH值,得到具有高达5.21 wt%金属负载量的复合物。金属前驱物的嵌入效率达到65%以上,这种制备方法比较简单、有效。该催化剂在空气中对活性卤代苯Heck反应具有较高的催化活性,高产率生成一系列反式产物,均在1-3 h内完成反应。催化剂的稳定性较好,可循环使用,是活性卤代苯Heck反应的高效催化剂,具有一定的应用前景。利用双氨基修饰法制备具有高负载量的和高分散度的钯负载SBA-15复合材料（Pd-SBA-15）。首先采用表面接枝法,以氨乙基氨丙基三甲氧基硅烷（ATMS）来修饰SBA-15;被修饰过的介孔材料在氯化钯溶液中吸附钯离子,后用水合肼还原钯离子。复合物的钯含量是4.30 wt%,钯的分散度为35%。对复合物中合适的胺基/Pd比率对Heck反应活性及溶液中钯残留的研究,发现N/Pd为2/1时起催化活性最强,钯的残留量较小。通过催化剂的Heck反应,发现这种复合物不仅对于活性卤代苯有很高的催化活性,而且对于溴苯这种活性较差的卤代烃也有较高的催化活性。催化剂通过简单的分离洗涤,可以重复使用多次。对已经重复使用的催化剂表征发现其活性下降是由于在反应过程中钯的损失和反应过程中钯分散度的少许降低（七次使用后的催化剂钯分散度降低为28%）。采用两步法,在表面活性剂存在下先生成钯纳米颗粒,钯颗粒尺寸在6-10 nm之间,然后以包裹了钯颗粒的表面活性剂为模板剂生成介孔SBA-15复合物。对复合物进行表征发现6-10 nm的钯颗粒均匀的分散于介孔材料的孔道中。虽然这种催化剂的钯的分散度不高（17%）,但是其表面积和孔体积较大,其催化活性仍然较高。通过催化剂的Heck反应,发现这种复合物不仅对于活性较大的碘苯,而且在催化剂用量增加下,对于溴苯这种活性较差的卤代烃也有较高的催化活性。对催化剂催化Heck反应的机理进行了探讨,发现催化剂确实为非均相催化剂。采用原位生成法,生成SBA-15-Pd复合物。将厌水性的钯有机物氯仿溶液增溶于介孔材料生成所必需的表面活性剂胶束中,然后将预水解的正硅酸乙酯加入表面活性剂溶液中。水热反应后,将产物过滤、干燥、煅烧,氢气还原后生成单分散的钯颗粒嵌入介孔材料SBA-15孔道中。大于85%的金属前驱物嵌入到介孔材料孔道中。在小的金属嵌入量下（1.46 wt%）,介孔材料的骨架没有被破坏;而在高含量下（3.02 wt%）,介孔材料骨架遭到一定程度的破坏。对小的金属嵌入量的催化剂（1.46wt%）进行表征发现钯颗粒均匀分散于介孔材料孔道中,而且在介孔材料外部没有发现钯颗粒。通过Heck反应,发现这种复合物不仅对于活性较大的碘苯,而且在催化剂用量较少的情况下,对于溴苯这种活性较差的卤代烃也有较高的催化活性。催化剂的可以重复利用很多次。总体比较所制得的催化剂的结构和催化活性发现,影响催化剂活性的因素很多,诸如钯的分散度,催化剂的孔体积和比表面积等。更多还原

【Abstract】 Palladium-catalyzed Heck reactions have received considerable attention in recent years, as they offer a versatile method for the generation of new C-C bonds in organic synthesis. These reactions are normally carried out with the homogeneous palladium catalyst such as Pd（OAc）₂ and PdCl₂. These catalysts have high catalytic activity for Heck reactions; however, they suffer from severe problems related with the separation, recovery, and the instability of the homogeneous catalysts at high temperatures. These problems have so far precluded the wide industrial applications of Heck reactions. These problems can be solved, however, by the use of heterogeneous catalysts made up of supported-palladium catalysts. Among the supported-palladium catalysts, palladium supported on mesoporous silica is a more catalytically active, selective, and stable catalyst. At the same time, they can be easily recycled and have little causticity for equipments. For these reasons, palladium supported on mesoporous silica has always attacted great attention. SBA-15, a kind of mesoporous silica with large surface area and uniform hexagonal channels, has attracted considerable attention due to its potential applications in catalysis and adsorption. In this work, the preparations of well dispersed and isolated Pd nanoparticles in SBA-15 mesoporous silica are described with four different synthesis methods such as ion-exchange method, diamine functional method, two-step method, and in-situ formation method. The formation mechanism and structure characteristics of Pd nanoparticles encapsulated in SBA-15 as well as the relationship between catalysts structure and catalytic activity were investigated.First, Pd nanoparticles supported on mesoporous silica SBA-15 （or Pd/SBA-15 nanocomposites） were prepared by traditional ion-exchange method with cationic Pd precursor in an alkaline solution. The high Pd loading in these nanocomposites can be achieved up to 5.21 wt% by adjusting the pH value of the solution. Using this method higher than 65% of the Pd precursor in the solution was incorporated into the mesoporous SBA-15. Therefore, this method is simple and highly effective for the preparation of Pd nanoparticles encapsulated in SBA-15. The Pd/SBA-15 nanocomposites exhibit excellent catalytic activities for the Heck reactions of actived aryl halide in air. The resulting trans-isomers were obtained in high yield at 1-3 h. The catalyst is stable and can be recycled for many times. Therefore, the catalyst is highly effective and would have a potential in industrial applications. Pd supported on SBA-15 （or Pd-SBA-15） with high Pd loading and high Pd dispersion was prepared by functionalizing SBA-15 with [3-（2-aminoethyl aminopropyl）] trimethoxysilane, grafting palladium ions on the functionalized SBA-15, and reducing palladium ions in the functionalized SBA-15 with hydrazine hydrate. The Pd-SBA-15 nanocomposite has a Pd loading of the 4.30 wt% and a Pd dispersion of 35%. The test of catalytic activity and Pd leaching as a function of N to Pd molar ratio shows the optimum N/Pd molar ratio is 2:1. The catalyst with controlled molar ratio of amino groups to palladium provides excellent catalytic activity for Heck reactions not only for activated aryl halides but also for non-activated aryl halide in air. The recycling reaction shows that the catalyst can be reused many times by simple filtration. The catalyst shows low Pd leaching and a little decrease in metal dispersion （the Pd dispersion of 28% for the used catalyst recovered from the seventh run） during the reaction which cause the little decrease in its catalytic activity during the recycling test.Pd/SBA-15 was prepared by a two-step method using the Pd nanoparticle-copolymer unit as a template. Pd nanoparticles of 6-10 nm in size have been synthesized by formalin reduction and incorporated into mesoporous SBA-15 silica during hydrothermal synthesis. The characterizations of the Pd nanoparticles encapsulated in mesoporous silica （Pd/SBA-15） reveal that the Pd nanoparticles in the range of 6-10 nm are encapsulated within the surfactant micelles during mesoporous silica formation and well dispersed within the mesoporous SBA-15 channels. The catalytic activity of Pd/SBA-15 was investigated in Heck coupling reactions with activated and non-activated aryl substrates. Although the Pd dispersion of Pd/SBA-15 is low （17%）, its surface area and pore volume are high; they also show relatvley high catalytic activity in Heck reactions. The Pd/SBA-15 composites exhibit an excellent catalytic activity for activated iodobenzene. Moreover, they also show high activity for non-activated bromobenzene when more catalyst is used. The mechanism of the heterogeneous Heck reactions was investigated; the catalyst follows a heterogeneous pathway.Palladium-containing SBA-15 （SBA-15-Pd） was synthesized via an in-situ formation approach. In this procedure, hydrophobic Pd（acac）2 chloroform solution was solubilized in the triblock copolymer micelles. Then the prehydrolysised TEOS was mixed with the surfactant solution. After the hydrothermal reaction, the as-synthesized sample was filtrated, dried, and calcinated. The resulting sample （SBA-15-Pd） was obtained by reduction with H₂ gas. A total of above 85% of the Pd precursor is incorporated in the porous host matrix. A 1.46 wt% metal loading is achieved without the loss of pore ordering, while sample with 3.02 wt% loading shows a less ordered structure. Highly dispersed and uniform Pd nanoparticles are confined in the hexagonal channels and no outside large particles are found by the characterizations of SBA-15-Pd （1.46 wt% metal loading）. The SBA-15-Pd nanocomposites exhibit an excellent catalytic activity not only for actived aryl halide but also for non-actived bromo-benzene using less catalyst. They also show high reuse ability in air for the Heck reactions.Comparison with the structure and catalytic activity of all the prepred catalysts, we find there are many factors to affect the catalytic activity of the catalysts such as Pd dispersion, the pore volume and surface area of catalysts.更多还原