介孔/大孔 Al2O3-SiO2复合氧化物的制备与表征

 以正硅酸甲酯和硝酸铝为硅和铝的前驱体,以非离子表面活性剂C16EO10为结构导向剂,采用溶胶-凝胶法制备了双孔结构硅铝复合氧化物材料. 扫描电镜和N2吸附/脱附分析表明,材料具有三维连续大孔和骨架介孔的双孔分布结构. 微米范围的连续大孔结构是由于溶胶-凝胶过程中诱发了Spinodal相分离所致,而骨架介孔的形成则可能是由于表面活性剂分子进入凝胶骨架中,起到构建介孔结构的模板作用. 骨架元素分析结果表明,制备过程中添加的铝大部分进入了凝胶骨架中,取代部分硅而形成酸性硅铝复合氧化物. 采用Hammett指示剂法和吡啶吸附红外光谱法分析了材料的表面固体酸性,结果显示,硅铝复合氧化物属于中强酸,酸强度H0在-5.6～-3.0 之间的酸中心数约为0.35 mmol/g, 并且材料表面的L酸位较为丰富, B酸位相对较少.

Preparation and Characterization of Meso/Macroporous Composite Oxides Al2O3-SiO2

Bimodal porous alumina-silica composite oxides were prepared via the sol-gel method using nonionic surfactant C16EO10 as the structure-directing agent. Tetramethoxysilane and aluminum nitrate were used as the silicon and aluminum precursors, respectively. Scanning electron microscopy and N2 adsorption/desorption measurements indicated that the composite oxides possess interconnected macropores and texture mesopores. The micrometer-range interconnected macropores were obtained by freezing the transitional structure of spinodal phase separation in the sol-gel process. The evolution of nanometer-range mesopores in the gel skeletons can possibly be attributed to the supramolecular templating by the nonionic surfactant. Energy dispersive spectroscopy proved that a large part of initially added aluminium was incorporated in the gel network. The Hammett indicator method and infrared spectra showed that the alumina-silica composite oxides were mild strong solid acids, and the amount of acid with acid strength H0 of -5.6 to -3.0 was 0.35 mmol/g. Moreover, these oxides contained abundant Lewis acid sites and less Broensted acid sites.