Towards the Next Level of Molecular Control in the Sol-Gel Preparation of Mixed Oxides

摘要CTS-9522066本项目探索了使用溶胶-凝胶法制备混合氧化物以获得可预测的结构或织构，并将其应用于酸性催化剂的合成。具体地说，研究了二氧化钛-二氧化硅和氧化铝-二氧化硅；硅前驱体的反应活性明显较慢，这允许预水解用作调节变量。通过改变预水解比，可以得到不同微观结构的凝胶网络。产品性质的表征可以提供均一性与酸度之间的关联。用氮气吸附、X-射线衍射、热分析、吡啶吸附和1-丁烯异构化等手段对复合氧化物的织构、结构和催化性能进行了表征。还研究了双金属醇盐和预制型溶胶等替代前驱体，以及通过共沉淀法制备的混合氧化物。这一努力应该为设计具有特定性质的混合氧化物提供手段。虽然所使用的程序已经很好地确定了，但关于所涉及的变量如何影响产品性能的系统工作还很少。(换句话说，混合氧化物的制备更像是一门艺术，而非科学。)虽然这项工作着眼于催化性能，但如果成功，它显然可以扩展到使用混合氧化物的其他应用，如光波导。***

ABSTRACT CTS-9522066 This project explores the use of sol-gel preparation of mixed oxides to achieve predictable structures or textures and to apply this to the synthesis of acid catalysts. Specifically, titania-silica and alumina-silica are studied; the silicon precursor has significantly slower reactivity and this permits prehydrolysis to be used as a tuning variable. By varying the prehydrolysis ratio, gel networks of various microstructures can be obtained. Characterization of the product properties may provide a correlation of homogeneity with acidity. Nitrogen adsorption, X-ray diffraction, thermal analysis, pyridine adsorption, and 1-butene isomerization are used to characterize the textural, structural, and catalytic properties of the mixed oxides. Alternative precursors such as double metal alkoxides and performed sols are also studied, as are mixed oxides prepared by coprecipitation. This effort should provide the means to design mixed oxides with specific properties. Although the procedures to be used are well established, little systematic work on how the variables involved affect product properties has been done. (In other words, mixed oxide preparation is more "art" than "science".) Although this effort looks at catalytic properties, if successful it would clearly be extendable to other applications using mixed oxides, such as optical waveguides. ***