Specific surface area and structures of aluminas from fibrillar pseudoboehmite

By heating powders of the aluminum monohydroxide fibrillar pseudoboehmite from 200 degrees C to 1400 degrees C 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: gamma-Al2O3 (470 degrees C - 770 degrees C; 179 m(2)/g 497 m(2)/g); delta-Al2O3 (770 degrees C - 930 degrees C; 156 m(2)/g - 230 m(2)/g); theta-Al2O3 (930 degrees C - 1050 degrees C; 11 m(2)/g - 200 m(2)/g); alpha-Al2O3 (1050 degrees C - 1400 degrees C; 2 m(2)/g - 17 m(2)/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.