NEW PREPARATION METHOD FOR MESOPOROUS GAMMA-ALUMINA BY SELECTIVE LEACHING OF CALCINED KAOLIN MINERALS

Mesoporous gamma-alumina with uniform pore size has been prepared by selective leaching of silica from calcined kaolin minerals, 2SiO(2) . Al2O3 . nH(2)O. A microtexture of very fine spinel-phase grains, consisting of gamma-alumina containing several wt.% of silica, precipitating within an amorphous silica matrix, was obtained by calcining kaolin minerals at around 950 degrees C. Porous gamma-alumina was prepared by selectively dissolving the amorphous silica in KOH solution at temperatures of 25-90 degrees C. The gamma-alumina obtained from kaolinite showed a very narrow unimodal pore size distribution at a radius of around 2-3 nm. The specific surface area was around 270 m(2) g(-1) and the total pore volume was 0.84 ml g(-1). On the other hand, the gamma-alumina obtained from tubular halloysite showed a bimodal pore size distribution at radii of around 2-3 nm and 10-20 nm. The specific surface area was ca. 320 m(2) g(-1) and the total pore volume was 0.69 ml g(-1).