Large surface area mesoporous Al2O3 from kaolin: Methodology and characterization

Facile synthesis of mesoporous Al2O3 from acid-leachates of calcined kaolin was carried out. In the presence of non-ionic or anionic surfactant micelles, mesostructured phases were obtained in aqueous media by hydrolysis and condensation of different inorganic Al reactants including monomeric cations (such as [Al(H2O)6]3+) and/or oligomeric cationic species (such as Keggin Al clusters). X-ray diffraction, differential scanning calorimetry and thermogravimetry, transmission electron microscopy, N2 adsorption–desorption isotherms, and magic angle spinning nuclear magnetic resonance were used to characterize both the raw materials and final products. The results showed that the synthesized mesoporous Al2O3 had a large surface area of ca. 460 m2/g and an average pore diameter of 5.8 nm. A general mechanism for the formation of the mesoporous Al2O3 was proposed based on the unique morphology of the Keggin-type of Al13 polycationic species and their aggregation in aqueous solution.

Research Highlights
► This paper first reports the successful synthesis of mesoporous Al2O3 with large surface area of ca. 460 m2/g from kaolin in the presence of non-ionic or anionic surfactant micelles.
► The porosity of such Al2O3 was monitored and controlled by the hydrolysis and polymerization of Al salts in aqueous solution.
► A general mechanism for the formation of the mesoporous Al2O3 was proposed based on the unique morphology of the Keggin-type of Al13 polycationic species and their aggregation in aqueous solution.