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