The Synthesis and Characteristics of Vanadoaluminosilicate MCM-41 Mesoporous Molecular Sieves

A series of vanadoaluminosilicate MCM-41 mesoporous molecular sieves with various compositions have been hydrothermally synthesized. Hexadecyltrimethylammonium bromide was used as a surfactant in the synthesis. The samples were characterized with nitrogen sorption, X-ray diffraction, differential thermal analysis, thermogravimetric analysis, Fourier transform-Infrared spectroscopy, UV-visible spectroscopy, scanning electron microscopy, transmission electron microscopy, and solid state NMR. The solid products had the MCM-41 structure and contained only atomically dispersed vanadium and aluminum consistent with framework vanadium and aluminum. The samples were hydrophobic and contained large amount of surfactant in the as-synthesized samples. The surfactant could be removed upon calcination at 450°C. N₂ sorption measurements and TEM demonstrate the high mesoporosity of [V, Al]-MCM-41. The incorporation of vanadium and aluminum into MCM-41 decreased the surface area to some extent. The morphologies of all the samples were the agglomerate of plates. ²⁹Si MAS NMR shows that the pore wall is amorphous. ²⁷Al MAS NMR shows that all of aluminum species were tetrahedrally coordinated even after calcination at 550°C.