Transformation of layered aluminosilicates and gallosilicates with kanemite structure into mesoporous materials

Layered aluminosilicates and gallosilicates with kanemite structure and var ied Si/M ratios have been prepared and can be transformed into mesoporous m aterials with MCM-41-like structure in an exchange solution of cetyltrimeth ylammonium chloride at pH 11.0-11.7 and 20-80 degrees C or at pH < 9.6 and 80 degrees C. The metal ions in both the layered metallosilicates and the c orresponding mesoporous materials are in a tetrahedral environment. Togethe r with the hydrolysis of the layered aluminosilicates (Al-kanemite) it is s uggested that aluminium is incorporated into the framework of the layered m aterials. The formation of mesoporous materials derived from the layered al uminosilicates is believed to occur through lamellar phases at pH 11.0-11.7 . One characteristic lamellar phase with a basal spacing of ca. 32 Angstrom has been obtained at pH 10.6 at 80 degrees C, which can be partly transfor med into mesoporous materials when the pH of exchange solution is reduced t o a value of between 8.0 and 8.5. The lamellar phase has inorganic layers i n a higher degree of silicate condensation, and is perhaps the reason that it does not form the hexagonal array at higher pH, such as pH 11.7 or 12.0. After removing the surfactant template and sodium ions by extraction with heptane-ethanol containing a small amount of hydrochloric acid, the mesopor ous materials derived from the layered aluminosilcates in the exchange medi um at pH 11.7 and 80 degrees C have Bronsted and Lewis acidity similar to A l-MCM-41. In contrast, no significant acid sites have been detected over th e mesoporous samples obtained at pH < 9.6 and at 80 degrees C.