Synthesis of Lanthanum-Doped MCM-48 Molecular Sieves and Its Catalytic Performance for the Oxidation of Styrene

Abstract

Lanthanum-doped MCM-48 molecular sieves with different La contents were synthesized hydrothermally and characterized by X-ray diffraction (XRD), nitrogen sorption, transmission electron microscopy (TEM), UV-visible spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy. The results show that the majority of La cations have been incorporated into the framework of MCM-48 molecular sieves. When the molar ratio of La/Si is >0.039 in the sample, some of lanthanum species exist in the extraframework. Compared with pure silicate MCM-48, lanthanum-doped MCM-48 samples show the medium strong acidity that is due to the incorporation of La in the framework of silica. In the oxidation of styrene with H(2)O(2) as the oxidant over the lanthanum-doped MCM-48 catalysts, benzaldehyde is the main product with a small amount of styrene oxide. The La content in the catalysts, reaction temperature, reaction time, and solvent affect greatly the catalytic oxidation of styrene. The conversion of styrene and the selectivity to styrene oxide increase noticeably when a small amount of NaOH aqueous solution is added into the reaction mixture. Ln-doped MCM-48 catalysts with 14 kinds of rare earth elements were synthesized hydrothermally and evaluated for the oxidation of styrene. The results show that their catalytic performance is tremendously different and depends on the nature of rare earth elements doped in the MCM-48 mesoporous materials.