Molecularly ordered layered aluminosilicate-surfactant mesophases and their conversion to hydrothermally stable mesoporous aluminosilicates

We report the first synthesis and characterisation of molecularly ordered aluminosilicate-surfactant mesophases. The layered aluminosilicate-surfactant mesophases, with varying amounts of Al, were prepared via hydrothermal crystallisation of CTAOH/Al,Si/H2O (Si/Al = 10, 25 or 50) systems at 135 °C for 24 days. The structural and molecular ordering in the aluminosilica mesophases before and after calcination was probed by powder XRD, nitrogen sorption analysis and solid state NMR. Silicon-29 MASNMR of the aluminosilica mesophases identified at least four Si environments, which we ascribe to Si atoms bonded to n Al atoms (i.e., Si(nAl) where n = 0, 1, 2 or 3). The proportion of Si atoms linked to at least one Al atom was greater at higher Al content. The Al in the aluminosilica mesophases was entirely incorporated in framework (tetrahedrally coordinated) sites; calcination generated only a small amount of extra-framework (octahedrally coordinated) Al sites. Calcination of the mesophases generated mesoporous aluminosilica materials that have high surface area (400–800 m2/g), pore volume (0.8–1.2 cm3/g) and acidity (0.35–0.61 mmol H+/g). The calcined aluminosilica materials exhibit high hydrothermal stability and retain between 80% and 97% of surface area (depending on Al content) after refluxing in water for 24 h.