SILICA OBTAINED BY SOL-GEL PROCESSING AND MODIFIED THROUGH INDIUM INCORPORATION

摘要

Silica substrata are materials widely used in heterogeneous catalysis due to their great specific areas, i.e. 200 to 1300 m~2/g, and also because these materials represent inert supports. The sol-gel process has had a great success in the preparation of catalytic materials, since the final physical and chemical properties of the resultant materials can be controlled during the hydrolysis step. When silica is prepared through the sol-gel process, the solid surface maintains a high density of hydroxyls groups even after treatments at very high temperatures. These OH groups can create Broensted sites on the surface as well as the adsorption of some specific molecules, which have a crucial participation in the catalytic reactions. These outstanding characteristics of silica supports are very important for an appropriate dispersion of catalytically active metals. If silica is doped with some elements, this may induce structural changes of the substrate. When an active metal is incorporated to during the sol formation, this allows creating a strong interaction between the metal and support in the final gel material. Over the last years, indium has been recognized as a fine promoter for the development of new materials, so that this element is very useful for catalysis research. Halasz et al. demonstrated the influence of this metal when it was incorporated into zeolitic structures employed for hydrocarbon oxidation. Miro et al. has studied the physico-chemical changes suffered by catalytic supports after indium is incorporated to them through different methods. In the present work, we have combined both silica and indium properties in order to obtain a new material that is synthesized by the sol-gel process. We carried out a physical and chemical characterization of these novel substrata through X- rays diffraction, infrared spectroscopy, thermal analysis, and N_2 sorption at 77 K for surface area determination and pore size. These tests are the first step toward a future application of these SiO_2-In catalytic supports.