CHARACTERIZATION OF SILICA-CONTAINING ALUMINUM HYDROXIDE AND OXIDE AEROGELS

Pure and silica-containing Al hydroxide aerogels were prepared by the supercritical drying method. The samples were later calcined, giving r ise to alumina and Si-Al mixed oxides. The materials were characterize d from the points of view of their bulk and surface structures. The Si -free material before calcination is well-crystallized boehmite that c onverts to gamma-alumina by calcination. The silica-containing hydroxi des are composed of boehmite layers with silicates in the interlayer r egion. The resulting mixed oxides present silica essentially in the bu lk. The surface structure of alumina seems poorly sensitive to silica addition. Surface silanol groups appear only for SiO2 more than 4%. No Bronsted acidity appears. Silica addition allows mixed oxides with hi gher surface areas to be obtained. (C) 1997 Academic Press.