Ordered Hexagonal Mesoporous Aluminosilicates with Low Si/Al Ratio: Synthesis, Characterization, and Catalytic Application

Ordered hexagonal mesoporous aluminosilicates with lower Si/Al ratio below 5 have been successfully synthesized via the co-assembly of preformed aluminosilicate precursors with Gemini surfactant [C12H25N+(CH3)(2)(CH2)(6)N+(CH3)(2)C12H25] center dot 2Br(-) as the template. Powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, N-2 adsorption-desorption isotherm measurements, fourier transform infrared spectroscopy, Al-27 nuclear magnetic resonance, thermogravimetric analysis, and temperature-programmed desorption of cyclohexylamine are employed to characterize the resulting samples. The phenol alkylation reaction is carried out to evaluate their catalytic performances. These studies indicate that the sample with a low Si/Al ratio of 3 still retains a highly ordered hexagonal mesoporous structure. And it also possesses the highest acidity of 0.96 mmol among the samples with lower Si/Al ratios below 5 due to its higher specific surface area together with more content of tetrahedrally coordinated Al in the framework. The catalytic tests confirm that the acidity of the samples plays a key role in determining their catalytic performances.