Aluminum Magadiite: an Acid Solid Layered Material

Aluminum-modified magadiite samples with high concentration of aluminum have been synthesized under hydrothermal conditions by modifying the traditional preparation route of the layered siliceous material. A new synthetic strategy, named aluminum-induced crystallization (AIC) method, was thus developed to introduce different amounts of Al in the siliceous framework. A systematic study of the physicochemical properties and thermal behavior of the produced Al-derived magadiite materials was performed by combining different experimental techniques [infrared spectroscopy (IR) of adsorbed probe molecules, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and solid-state magic-angle spinning nuclear magnetic resonance (SS MAS NMR)]. 27 Al SS MAS NMR showed that the synthesis method allowed us to introduce for the first time Al ions in a magadiite framework in tetrahedral positions. Variable-temperature XRD analysis showed that the introduction of Al in tetrahedral position does not affect the thermal stability of the silica layers. The presence of Al ions led to a modification of the surface acidity of magadiite. Indeed, Fourier transform infrared (FTIR) measurements of CO adsorbed at 100 K indicated the presence of Brønsted acidity similar to that found in highly acidic zeolites. The amount of acid sites is progressively increased by introducing increasing amounts of Al in the framework. Moreover, different families of Brønsted acid sites with different acid strengths are present at higher Al content, thus revealing the possibility to tune the surface acidity of these materials.