MMM分子筛的制备与表征

 以碱溶液处理ZSM－5分子筛，得到了含微孔及介孔的MFI结构分子筛（简称MMM），并采用XRD，XRF，SEM，XPS和低温氮吸附等技术对分子筛进行了表征．结果表明，通过改变处理碱的浓度可以得到具有不同物化性能的MMM分子筛，其化学组成、介孔及微孔的大小和多少，及分子筛晶体上n（Al）／n（Si）均随碱浓度的变化而变化，随着碱浓度的增加，分子筛部分微孔结构遭到破坏，介孔的数量增加，孔径增大，n（Al）／n（Si）增大．碱处理脱硅的过程包括脱除晶粒间的无定形物质，脱除分子筛表面的硅及脱除分子筛体相硅等步骤，硅脱除以后形成了介孔．

Preparation and Characterization of MMM Zeolite

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.