Effects of synthetic conditions on the textural structure of pseudo-boehmite

Abstract

Mesoporous alumina with pseudo-boehmite phase was prepared by using the cation–anion double hydrolysis method from mixed aqueous solution of aluminum sulfate and sodium aluminate. The effect of synthetic conditions on the crystal structure and textual properties of pseudo-boehmite was investigated, such as synthetic temperature, pH value and the addition of sodium silicate. With the assistance of characterization techniques, such as X-ray diffraction (XRD), N2 adsorption–desorption isotherms (BET) and 27Al magic-angle spinning nuclear magnetic resonance (MAS NMR), the relationship between textural properties of the mesoporous alumina samples and their synthetic conditions was discussed. The results displayed that an increase in synthesis temperature promoted the formation of higher crystalline pseudo-boehmite with the increase of its surface area and pore volume. Pure pseudo-boehmite phase could be obtained in the pH value range from 6.0 to 9.0, while bayerite phase occurred when the pH value was over 10.0. The introduction of sodium silicate could greatly improve the pore volume (1.20cm3/g) and surface area (480.2m2/g) of pseudo-boehmite. Interestingly, pure pseudo-boehmite phase was obtained at very high pH value without formation of bayerite phase when sodium silicate was initially added into the aluminum hydroxide colloid.