Synthesis and characterization of thermally stable MCM-41/γ-Al2O3 composite materials

A thermally stable MCM-41/γ-Al2O3 composite (“Composite 2”) was obtained by in situ synthesis using boehmite, a hydrated γ-Al2O3, and compared to a MCM-41/γ-Al2O3 composite (“Composite 1”) made using pure γ-Al2O3. The two composites were studied by means of X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), laser particle size analyzer, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDS), and nitrogen adsorption isotherm measurements. The results showed that with boehmite as the initial material, the thermal stability of the MCM-41 in Composite 2 was greatly improved and thus its specific surface area and pore volume were significantly increased. It was also found that in the two composites MCM-41 grew in two different mechanisms: in Composite 1 MCM-41 grew on the outer surface of γ-Al2O3 or occurred as non-in situ crystallization product, whereas in Composite 2 MCM-41 overgrew only on the internal surface of boehmite grains.