INFLUENCE OF THE SOL-GEL PROCESSING METHOD ON THE STRUCTURE AND THE POROUS TEXTURE OF NONDOPED ALUMINAS

Alumina supports for high-temperature catalysts were synthesized by di fferent sol-gel methods, including one xerogel dried by simple evapora tion and two aerogels dried by supercritical drying in CO2 or in alcoh ol. The influence of the gel synthesis technique and the additives use d for gelation on the porous structure of alumina and its evolution du ring heat treatment at 400, 900, and 1200 degrees C was analyzed by X- ray diffraction and by the BET nitrogen adsorption method. Complexatio n with acetic acid at the gel step followed by supercritical drying at low temperature (35 degrees C) caused a retardation of alpha-alumina formation with a significant residual specific surface area after heat ing for 5 h at 1200 degrees C in air, namely 70 m(2)/g. (C) 1997 Acade mic Press.