Syntheses of aluminosilicate mesostructures with high aluminum content

Ordered aluminosilicate mesostructures having a S/O-2/Al2O3 ratio near 5 were prepared using a surfactant-templated synthesis. The solid structures were analyzed by scanning electron microscopy (SEM), nitrogen sorption to determine pore volume and pore sizes, powder X-ray diffraction (PXRD), thermal desorption of a chemisorbed base to determine strong acid site density, and magic-angle-spinning (MAS) NMR spectroscopy for the Al-27 and Si-29 nuclei. We were successful in synthesizing a mesoporous aluminosilicate having a SiO2/Al2O3 ratio near 5 when the source of the aluminum ion was Al hydroxide and the surfactant was cetyltrimethylammonium cation (C(16)TMA(+)). The uncalcined samples showed only tetrahedral aluminum as confirmed by Al-27 MAS NMR. When the pH of the synthesis gel was 10.5, the mesostructure developed. pore volume of 0.59 cm(3)/g with an average pore diameter of 2.2 nm. The pore volume was less at pH values other then 10.5 (e.g., for pH 12.6 and 8.1, the pore volumes were 0.50 and 0.43 cm(3)/g, respectively). The aluminosilicate mesostructure showed Bronsted and Lewis sites as confirmed by the IR vibrational spectroscopy of chemisorbed pyridine. The mesostructure Bronsted acid site density was 0.36 mu mol H+/m(2)-solid, based on Bronsted acid site titration by isopropylamine temperature-programmed desorption. It was similar to that observed for an amorphous alumina-silica having a SiO2/Al2O3 ratio near 6. However, the mesostructure Bronsted site density per unit mass was much lower than that measured for an acidic Y-faujasite with a SiO2/Al2O3 ratio of 2.75.