Strongly acidic mesoporous aluminosilicates prepared via hydrothermal restructuring of a crystalline layered silicate

Abstract

We describe the preparation of crystalline as-synthesized aluminosilicate–surfactant mesophases and surfactant-free aluminosilicate mesoporous materials derived from the layered silicate Na-RUB-18, by performing hydrothermal restructuring in the presence of cetyltrimethylammonium (CTA) surfactant molecules. The hydrothermal treatment, at 150 °C for 48 h, with Na-RUB-18 as the silica source and a known amount of aluminium isopropoxide (gel Si/Al ratio 5, 10 or 20) in the presence of cetyltrimethylammonium (CTA) ions generates molecularly ordered aluminosilicate–surfactant mesophases. The transformation from mesophases to mesoporous materials takes place with retention of mesostructures with varying levels of crystallinity depending on the mode of template removal. The highest apparent retention of crystallinity in a surfactant-free mesostructure is achieved at Si/Al ratio = 20 after surfactant removal via solvent extraction in acidified ethanol. The textural properties of the mesoporous materials (surface area in the range of 141–388 m² g⁻¹ and pore volume in the range of 0.12–0.46 cm³ g⁻¹) depend on the mode of surfactant removal and Si/Al ratio. The mesoporous aluminosilicates are strongly acidic with most of the acid sites generated (>80% and typically above 95%) classified as strong sites and exhibit attractive activity as solid acid catalysts.