Specific surface area and structures of aluminas from fibrillar pseudoboehmite

Abstract

By heating powders of the aluminum monohydroxide fibrillar pseudoboehmite from 200ºC to 1400ºC several high surface area aluminas are prepared and characterized by X-ray diffraction and electron optical methods. Aqueous sols with pseudoboehmite fibrils of different lengths were dried by two methods: at room temperature and spray-dried. The following aluminas were obtained after treatment of the powders at increasing temperatures and having a range of specific surface areas: γ-Al2O3 (470ºC - 770ºC; 179 m²/g - 497 m²/g); δ -Al2O3 (770ºC - 930ºC; 156 m²/g - 230 m²/g); θ-Al2O3 (930ºC - 1050ºC; 11 m²/g - 200 m²/g); α-Al2O3 (1050ºC - 1400ºC; 2 m²/g - 17 m²/g). Spray-dried powders, fired at the same temperature than the ground powders, showed higher specific surface areas. The higher surface area alumina have values of the same order of magnitude of the commercial "ad-cat" aluminas.