Water Vapor Sorption on Mesoporous Gamma-Alumina Prepared by the Selective Leaching Method

Abstract

Water vapor adsorption and desorption properties of mesoporous γ-alumina prepared by the selective leaching method were investigated. The γ-alumina was prepared by selective leaching of amorphous silica from calcined kaolinite and mesopores were formed in the inside of the pseudomorph particles of kaolinite. It showed a very narrow unimodal pore size distribution at a radius of 3 nm. The specific surface area and total pore volume measured at −196°C by the BET method using nitrogen gas as adsorbate were around 240 m2 g-1 and 0.7 ml g-1, respectively. Water vapor sorption isotherm measured at 25°C showed a type IV isotherm and a type H1 hysteresis loop at high partial pressure (P/P0 region. The steep increase of water adsorption by capillary condensation occurred from around P/P0=0.8 whereas that of water desorption by evaporation occurred from around P/P0=0.75. 0These observed P/P0 values shown were in good agreement with those calculated from the Kelvin equation using the pore radius of 3 nm. The maximum adsorption capacity of water vapor was ca. 600 ml g-1 at P/P0 = 0.9 and was larger than that of the commercial γ-alumina. The statistical thickness of water adsorbed on the surface of the samples calculated from the water adsorption and nitrogen adsorption isotherms of this γ-alumina was apparently thinner than that of the commercial γ-alumina and this difference was attributed to the characteristic microtexture of this γ-alumina. The effects of K2O and SiO2 components for the water vapor sorption isotherms of the γ-alumina were also discussed.