Synthesis and characterization of Ln-ZSM-5/MCM-41 (Ln = La, Ce) by using kaolin as raw material

Lanthanide ion-containing (Ln = La3+, Ce3+) micro/mesoporous composite molecular sieves Ln-ZSM-5/MCM-41 were prepared under hydrothermal condition using kaolin as silica and alumina sources. X-ray diffraction patterns and nitrogen adsorption data confirmed the presence of mesoporous MCM-41 and microporous ZSM-5 in the composite. High resolution transmission electron microscope and scanning electron microscope studies revealed that the micro- and mesoporosity of the composite were different from that of the mechanical mixture of ZSM-5 and MCM-41. The overall local environment of lanthanide ion in the composite molecular sieves was investigated by Fourier-transform infrared and ultraviolet–visible spectroscopy. The lanthanide ions were tetrahedrally or distorted tetrahedrally coordinated by oxygen ions. Pyridine-infrared spectroscopy was used to detect the acidic sites of the samples. A large amount of Brønsted and Lewis acidic sites were measured, and the amount of Brønsted acidic sites was increased significantly by La3+ or Ce3+ incorporation. Thus, the inexpensive kaolin can be used as alumina and silica source for ordered micro/mesoporous composite molecular sieves. The catalytic activity of the samples was tested by the esterification of acetic acid with n-butyl alcohol and showed high conversion.