Preparation and Characterization of MMM Zeolite
WANG Dianzhong *, SHU Xingtian, HE Mingyuan(Research Institute of Petroleum Processing, SINOPEC, Beijing 100083, China)
Zeolites have been used extensively in catalysis owing to their microporous structure and proper acidity. But one of the reason that zeolites have not yet been applied widely in industrial heterogeneous catalysis is that diffusion limitations often influence the reaction rate. It is possible to overcome this difficulty by using a zeolite that has microporous and mesoporous sturcture (MMM zeolite). MMM zeolite could be obtained by treating ZSM-5 with alkali solution. In this paper, MMM zeolite was prepared, and its physicochemical property was characterized by XRD, XRF, XPS, SEM and N_2 adsorption techniques. The results showed that alkali-treatment can change the morphological structure of the zeolite, and influence its chemical composition, structure, n(Al)/ n(Si) and pore volume, and the effectiveness was connected with the concentration of alkali solution. The partial silicon can be removed selectively through treating ZSM-5 zeolite by alkali solution, hence, the n(Al)/ n(Si) increases. The process of desilicification began from surface to inner for crystal particle of zeolite. When the alkalinity increased, part of the microporous structure would be destroyed, and mesopore as well as extra framework aluminum formed. The process of desilicification from ZSM-5 includes three steps: (1) removal of the amorphous silicon presented in the zeolite crystal; (2) removal of the framework silicon on the outer surface of zeolite particles; (3) removal of the inner silicon of the zeolite particles.