New preparation method for mesoporous γ-alumina by selective leaching of calcined kaolin minerals

Abstract

Mesoporous γ-alumina with uniform pore size has been prepared by selective leaching of silica from calcined kaolin minerals, 2SiO2·Al2O3·nH2O. A microtexture of very fine spine)-phase grains, consisting of γ-alumina containing several wt.% of silica, precipitating within an amorphous silica matrix, was obtained by calcining kaolin minerals at around 950 °C. Porous γ-alumina was prepared by selectively dissolving the amorphous silica in KOH solution at temperatures of 25–90 °C. The γ-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 m2 g–1 and the total pore volume was 0.84 ml g–1. On the other hand, the γ-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 m2 g–1 and the total pore volume was 0.69 ml g–1