Synthesis of high surface area Al-containing mesoporous silica from calcined and acid leached kaolinites as the precursors

Al-containing mesoporous silicas were synthesized by hydrothermal treatment of microporous silica prepared by selectively acid leached metakaolinites with Si/Al = 3.9-92.5 mixed with a surfactant of cetyltrimethylammonium bromide (CTABr). The specific surface area of the products increased with higher surfactant/microporous silica (surf/Si) ratio and Si/Al ratio of the microporous silica, reaching about 1400 m²/g at CTABr/Si {greater than or slanted equal to} 0.1 and Si/Al {greater than or slanted equal to} 40. The XRD patterns of these products show a hexagonal (100) peak with the lattice parameter a₀ = 4.2 - 4.3 nm and the N₂ adsorption isotherms show steep increase of adsorption between relative pressure of 0.3 and 0.4. Hexagonal mesoporous microstructure is observed by high resolution TEM. The pore size distributions of the products show a sharp peak at 2.8 nm by the BJH method. The high specific surface area of the present mesoporous samples is attributed to the lower matrix density and surface roughness of mesopore wall. The highest specific surface area of the products reached up to 1420 m²/g and this value is apparently higher than those reported in hexagonal mesoporous silicas. A unique microporous structure of the starting material is thought to be related to achieve such a high specific surface area of the products.