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

Layered aluminosilicates and gallosilicates with kanemite structure and varied Si/M ratios have been prepared and can be transformed into mesoporous materials with MCM-41-like structure in an exchange solution of cetyltrimethylammonium chloride at pH 11.0–11.7 and 20–80 °C or at pH < 9.6 and 80 °C. The metal ions in both the layered metallosilicates and the corresponding mesoporous materials are in a tetrahedral environment. Together with the hydrolysis of the layered aluminosilicates (Al-kanemite) it is suggested that aluminium is incorporated into the framework of the layered materials. The formation of mesoporous materials derived from the layered aluminosilicates is believed to occur through lamellar phases at pH 11.0–11.7. One characteristic lamellar phase with a basal spacing of ca. 32 Å has been obtained at pH 10.6 at 80 °C, which can be partly transformed into mesoporous materials when the pH of exchange solution is reduced to a value of between 8.0 and 8.5. The lamellar phase has inorganic layers in 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 mesoporous materials derived from the layered aluminosilcates in the exchange medium at pH 11.7 and 80 °C have Brønsted and Lewis acidity similar to Al-MCM-41. In contrast, no significant acid sites have been detected over the mesoporous samples obtained at pH < 9.6 and at 80 °C.