Synthesis and characterization of cerium-modified cubic mesoporous silica

摘要

The cerium-modified cubic mobil composition of matters 48 (MCM-48) molecular sieves were synthesized using cetyltrimethylammonium bromide (CTAB) as templates at low molar ratio of surfactant to inorganic precursor. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results show that the well-ordered cubic mesostructure was obtained when the Ce/Si molar ratio is less than 0.05. With the increase of Ce/Si molar ratio, the increase of unit cell parameters and the change of Fourier transform infrared spectroscopy (FTIR) provide powerful evidences for the incorporation of cerium in the framework of mesoporous molecular sieves. Nitrogen sorption data indicate that the Brunauer-Emmett-Teller (BET) surface area and the average pore diameter of Ce(Ⅲ)-MCM-48 are 1288 m 2·g -1 and 4.2 nm, and those of Ce(Ⅳ)-MCM-48 are 1228 m 2·g -1 and 3.7 nm, respectively. Diffuse reflectance UV-visible (UV-vis) spectroscopy confirms the presence of Ce(Ⅲ) in the octahedral position and Ce(Ⅳ) in the fluorite structure. X-ray photoelectron spectroscopy (XPS) studies further reveal that Ce(Ⅲ) and Ce(Ⅳ) coexist in the framework of mesoporous molecular sieves.