【作者】 史芸；

【导师】 马新宾；

【作者基本信息】 天津大学 ， 化学工艺， 2011， 博士

【摘要】 MCM-41介孔分子筛具有比表面积高、孔道结构规则以及孔径易调节、化学稳定性好、表面易改性等特点,在有机催化领域有广阔的应用前景。过渡金属杂原子介孔分子筛的合成和功能化研究已成为分子筛材料开发的热点。本论文研究了Ti-MCM-41介孔分子筛的合成方法、孔径调变、质子酸改性及其在草酸二甲酯（DMO）与苯酚酯交换合成草酸二苯酯（DPO）反应中的催化性能,深入分析了Ti-MCM-41的结构、物化性质和催化性能间的构效关系。以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯和钛酸四丁酯为原料分别采用水热晶化法和微波辐射法合成了Ti-MCM-41介孔分子筛。通过XRD、低温N2吸附-脱附、TEM、FTIR、DR UV-vis、Py-FTIR、NH₃-TPD、XPS以及ICP-OES等表征技术分析研究了Ti-MCM-41的结构和物化性质,考察了微波辐射条件对分子筛性质的影响。结果表明,Ti-MCM-41分子筛具有长程有序的六方相介孔结构,Ti原子完全进入了分子筛的骨架,且主要以四配位体中心存在。微波辐射法具有合成周期短,产品粒径小、结构有序度高、孔道分布均匀、比表面积高以及活性组分损失少的优点。Ti-MCM-41分子筛对DMO与苯酚酯交换反应表现出良好的催化性能,这与其优良的结构和表面性质紧密相关。首先,分子筛中存在大量的骨架Ti（Ⅳ）中心,为酯交换反应提供了丰富的弱L酸性催化中心;其次,介孔分子筛高比表面积、大孔容的特征结构有利于反应体系的分子扩散,提高了酯交换反应的效率。根据增溶作用机理,添加有机扩孔剂进行Ti-MCM-41分子筛孔径调变。扩孔剂的疏水性和分子构型能够影响表面活性剂胶束的稳定性和溶胀体积,对扩孔效果有重要影响。添加适当的扩孔剂能够在保持Ti-MCM-41分子筛特征介孔结构及表面化学性质的同时有效的扩大其孔道尺寸,显著地提高了其催化酯交换反应的活性。正庚烷的扩孔效果最佳,分子筛平均孔径可由28.6（A|°）扩大至48.3（A|°）。考察了H₂SO₄改性合成S/Ti-MCM-41分子筛的结构和化学性质。由于SO₄^2-中S=O的强电子诱导作用,L酸中心增多,同时增强了L酸中心的吸电子能力,进一步活化了分子筛表面的羟基,生成B酸中心。对S/Ti-MCM-41分子筛的催化活性考察发现,B酸中心对酯交换反应有促进作用,但是同时会导致苯甲醚等副产物的生成。更多还原

【Abstract】 MCM-41 mesoporous molecular sieve has many advantages such as high surface area, periodic hexagonal pore channels, easy adjustability of pore dimension, high chemical stability, and facile modification of surface properties. It has wide applications in catalytic organic chemistry. Synthesis and functionalization of transition-metal-substituted mesoporous molecular sieves have attract much attention in materials field. This dissertation focuses on the effect of synthesis conditions of Ti-MCM-41 mesoporous sieve on catalytic performance for transesterification of dimethyl oxalate （DMO） and phenol. Investigations have been carried out on the prosity regulation and protonic acid modification of Ti-MCM-41 and analysis of its structure-activity relationship.Ti-MCM-41 materials were successfully synthesized through both hydrothermal and microwave irradiation methods, using cetyltrimethylammonium bromide as a template agent, tetraethyoxysilane and tetrabutyl titanate as Si and Ti sources respectively in an alkaline solution. Various characterization techniques, including XRD, N2 adsorption-desorption, TEM, FTIR, UV-vis, Py-FTIR, NH₃-TPD, XPS and ICP-OES were carried out to analyze the textural and physicochemical properties of these Ti-MCM-41 samples, with particular emphasis on the influences of microwave conditions on molecular sieves properties. Ti-MCM-41 molecular sieve possesses a long-range ordered hexagonal structure and titanium has incorporated into the silica framework with Ti species mostly in tetrahedral coordination. Experimental results suggested that the microwave irradiation method could provide a short crystallization period, small particle size of products, high structural order, narrow pore size distribution, large surface area, and little loss of active component. The optimum microwave-irradiation condition was keeping a continuous heating at 120℃for 40 min.The desirable catalytic activities of Ti-MCM-41 molecular sieves could be ascribed to its favorable structure and surface properties. First, the rich inner-framework Ti （Ⅳ） centers could provide plenty of weak L acid sites for the transesterification of DMO and phenol. Secondly, the mesoporous structure with high surface area and large pore volume is beneficial for the molecular diffusion in reaction system, which improves the efficiency of transesterification reaction.According the mechanism of solubilization, the porosity regulation of Ti-MCM-41 by utilizing organic swelling agents was examined. Swelling agents played a key role for pore expansion because its hydrophobic and molecular properties could affect the stability and the swelling volume of surfactant micelles. Addition of swelling agents has been proved to be an effective way for pore expansion of Ti-MCM-41 while the characteristic mesoporous structure and its chemical properties were maintained simultaneously. Thus, the catalytic activity of Ti-MCM-41 molecular sieve was accelerated greatly as its pore size expanded. N-heptane was an optimal swelling agent with which the average pore diameter was expanded form 28.6（A|°） to 48.3 （A|°） .The structure and chemical properties of S/Ti-MCM-41 were also studied intensively. Due to the strong electron inductive effect caused by the S=O bond of SO₄^2-, Lewis acid sites were intensified significantly. Moreover, the surface hydroxyl groups were further activated and formed H⁺, generating Br（o|¨）nsted acid sites. The results of catalytic test of S/Ti-MCM-41 catalysts showed that Br（o|¨）nsted acid sites could promote the transesterification reaction between DMO and phenol, although it would also lead to the formation of by-product anisole.更多还原