【作者】 陈英；

【导师】 韩金玉；

【作者基本信息】 天津大学 ， 化学工艺， 2008， 博士

【摘要】 介孔氧化硅材料具有规则的孔道结构、纳米范围可调变的孔径、大的比表面,以及表面大量存在的可供修饰的硅羟基等优异的结构特征,在催化、吸附等领域具有广阔的应用前景。酸碱活性位的协同催化作用可以有效改善催化性能与效率,延长催化剂寿命,受到广泛重视。因此,本工作力图开发简便、高效介孔材料酸碱双功能化新方法,将酸碱活性位与介孔硅基体相结合,合成出兼具酸碱协同效应及优异介孔骨架结构的新型酸碱双功能介孔材料。提出制备酸碱双功能化介孔材料的固态离子迁移法,一步完成酸碱活性位的产生与母体模板剂的移除,实现介孔硅材料功能化。该方法采用无溶剂路线,简便、高效。通过该方法成功合成了一系列的酸碱双功能化介孔纳米复合材料MgO-Al2O3–SBA-15 (MA–SBA-15)。表征结果表明,合成的纳米复合材料的介孔骨架结构完好,活性物种能够进入到母体SBA-15的介孔孔道中,并有效的分散到孔道表面,与母体表面的硅醇基团发生作用,形成Si–O–Mg与Si–O–Al共价键。MA–SBA-15样品表面酸性位,包括Lewis酸与Br?nsted酸,与碱性位共存。同时,探讨了功能化过程机理。该酸碱双功能化介孔复合材料在碳酸二甲酯和碳酸二乙酯酯交换合成碳酸甲乙酯过程中显示了较高的活性。利用原位合成法,通过向合成介孔氧化硅(SBA-15)的原料混合物中引入锆盐和镁盐,成功合成了一系列具有酸碱双功能的介孔纳米复合材料MgO-ZrO2–SBA-15(MZ–SBA-15)。表征结果表明,制备的功能化介孔材料具有酸碱性能及完好的介孔骨架结构。采用模板法自组装合成了两种新型纯硅基介孔材料GML-MGE与GMS-MGE,并探讨了不同晶化温度、晶化时间、老化温度、模板剂脱除方式、不同碳链长度的表面活性剂对介孔结构的影响。采用XRD、N2吸附-脱附和FTIR对其进行表征,结果显示其具有介孔结构特征。在此基础上合成了新型功能化的M-MGE介孔材料(M=Al,Mg),并考察了不同镁铝前驱体对介孔结构的影响。表征结果表明活性物种进入了介孔硅的骨架结构并保持了介孔结构特征,活性物种在母体表面分散较好。以十八酸和丙三醇反应生成硬脂酸单甘酯的酯化反应作为探针反应,考察了M-MGE介孔材料的催化性能。结果表明M-MGE介孔材料有较好的酯化反应活性。反应时间10 h,催化剂用量5 wt%,反应温度110℃,十八酸的转化率为52%,硬脂酸单甘酯的选择性达96 %。更多还原

【Abstract】 Ascribing to their excellent textural properties, including highly ordered pore channels, controllable narrow pore size distribution, large surface area, as well as a large amounts of Si-OH, which can facilitate the modification of their surface with metals and organic group, the functionalization of mesoporous silicas have attracted more and more attention. And in many cases, the synergism of the acid-base active centres usually contributes to promote the progress of the reaction, and results in an enhancement of the reaction velocity, in an improvement of the selectivity and in a prolongation of the catalyst life. Therefore, acid-basic bifunctional mesoporous materials, which could combine the advantages of mesoporous structure and acid-basic properties, that is, combining the specific chemical reactivity of the acid-basic groups with attractive structure properties, have generated considerable interest in their application such as shape-selective catalysis, adsorption-separation processes, and other fields. In this work, we attempt to develop new facile and efficient strategies for the acidic-basic bifunctionalization of mesoporous silicas.A new acidic-basic bifunctional approach with high efficiency and facility, named solid state ionics migration, for mesoporous silica was developed. The generation of acid-base active sites and removal of host template were achieved in a single step by this method. A series of acid-base bifunctional mesoporous nanocomposites MgO-Al2O3–SBA-15 (MA–SBA-15) have been successfully synthesized by means of this approach. The characterization results indicated that the resultant bifunctional mesoporous nanocomposites can keep mesoporous framework well, and the guest species can be efficiently introduced into the channel and fully dispersed on the surface of the host. The electric positive Mg2+ and Al3+ can form covalent bonds between the metal ions and the oxygen atoms of the Si-OH groups on the surface of the host during calcination. Hence, the Si–O–Mg and/or Si–O–Al interlinkages can conveniently establish between the mesoporous host and the introduced guests to achieve the bifuctionalization. The results of NH3, CO2-TPD and pyridine adsorption unambiguously indicated the acidic sites, including Lewis and Br?nsted acid sites, and basic sites co-exist on the surface of the mesoporous nanocomposites synthesized by the titled method. And the mechanism and inherent rules of bifuctionalization was also investigated. In addition, the resultant nanocomposite exhibits high activity for the synthesis of ethyl methyl carbonate.By the in-situ grafting method, a series of surface-modified mesoporous silicas, MgO-ZrO2–SBA-15(MZ–SBA-15), endowed with acid-base properties have been firstly successfully synthesized in one pot by the introduction of zirconium and magnesium salts into the initial mixture of synthesizing mesoporous silica (SBA-15). The characterization results indicated the resultant nanocomposites exhibit excellent acid-basic properties with well periodically ordered mesoporous backbone.Two novel mesoporous silica materials, GML-MGE and GMS-MGE, have been firstly synthesized by self-assembly route, and the influence of the crystallization temperature, crystallization time, aging temperature, removal method of template and surfactants with different chain length on mesoporous framework have been investigated. XRD, N2 adsorption-desorption isotherms and FTIR employed to characterize the structure properties of the new mesoporous silica materials, and the results showed that GML-MGE and GMS-MGE possess the typical mesoporous structure properties. Subsequently, the modification of GMS-MGE mesoporous material with metal ions (M-MGE, M=Al,Mg) was performed and the effect of different metal salt precursors on the mesoporous structure was investigated. The characterization results indicated the resultant mesoporous nanocomposites can keep mesoporous structure properties well and the active species can fully disperse on the channel surface of the host. The esterification reation of stearic acid and glycerol was employed as a probe reaction to evaluate the catalytic performance of M-MGE mesoporous material. The results suggested the M-MGE mesoporous material exhibits good performance on this reaction. The conversion of stearic acid reach 52 % and the selectivity of monoglyceric stearate can reach 96 % under the condition: reaction time 10 h, catalyst loading 5 wt %, reaction temperature 110℃.更多还原