Influence of the synthesis additive on the textural and structural characteristics of sol-gel Al2O3-TiO2

Al2O3-TiO2 materials were prepared by the sol-gel. method using different additives (HNO3, NH4OH, and CH3COOH) and their physical properties were evaluated by various techniques. The materials at two compositions (Al/Ti atomic ratios 2 and 25) were synthesized at 278 K and calcined at temperatures from 573 to 1173 K. The solids were characterized by TGA, DTA, XRD, BET, and SEM. The complexing (CH3COOH) and the basic (NH4OH) additives led to solids with high pore volumes and broad pore size distributions. On one hand, very high surface areas (525 m(2)/g for solids calcined at 773 K) were found for samples prepared with CH3COOH. On the other hand, high-temperature stability was obtained with NH4OH addition (200 m(2)/g, for Al2O3-rich samples at 1173 K). HNO3-catalyzed samples showed lower surface areas and pore volumes. Surface areas and sintering behavior were a function of TiO2 content. TiO2-rich samples showed higher surface areas (713 K) than Al2O3-rich oxides, but at more severe conditions they suffered a severe specific area loss. The alumina-rich formulations showed good stability in the whole range of temperatures studied.