| Acidic aluminosilicate mesostructures have been synthesized using a surfactant-templated synthesis mechanism. The solid structure was analyzed by scanning electron microscopy, nitrogen sorption, powder X-ray diffraction, thermal analysis, 27Al MAS NMR and 29Si MAS NMR spectroscopy. The solid acidity was characterized by infrared spectroscopy, microcalorimetry and temperature-programmed desorption. It was shown that the surface Bronstedt acid site density of aluminosilicate mesostructures and amorphous aluminosilicate matrices are comparable at same SiO2/Al2O3 ratio. However the Bronstedt acid site density of aluminosilicate mesostructures is much lower than that found in acidic Faujasite Y with similar SiO2/Al2O3 ratio. The strength and the density of the mesostructure acid sites depends on the nature of the Al precursors.; In certain conditions, it was possible to synthesize mesostructures with the same SiO2/Al2O3 ratio as commercial zeolite cracking catalysts. When cetyltrimethylammonium chloride was used as surfactant, these mesostructures afforded a mesopore volume up to 0.59 cc/g and an average pore diameter close to 2.2 nm, compared to ∼0.36 cc/g adsorptive volume and 0.8 nm average pore diameter in acidic Faujasite Y. When the mesostructures were aged in deionized water at 110°C for a week, they developed a surprisingly high mesopore volume. For example, the mesopore volume of an aluminosilicate mesostructure prepared from a hydrogel with a SiO2/Al2O 3∼5 could increase by over 50% after 3 hydrothermal treatments. It is believed that the mesostructures undergo a reconstruction process upon hydrothermal treatment, yielding a solid with improved thermal and hydrothermal stability. For example, after treatment at 750°C for 2 hours in steam, the pore volume of a treated silicate mesostructure was 0.54 cc/g vs. 0.35 cc/g for an untreated mesostructure. These mesostructures are believed to hold great promise for applications in new purification, separation and catalytic processes. |
