Study On Microwave-Assisted Synthesis Of MWW-Type Zeolites

MCM-22, having MWW toplogy, has received much research attentions in last two decades. Conventionally, it is prepared using hexamethyleneimine (HMI) as an organic structure directing agent (SDA) by hydrothermal synthesis (HTS) process, which requires several days. Thus, from the viewpoint of minimizing the energy for crystallization, new facile routes which are more efficient than HTS are desirable.The synthesis of porous materials under microwave (MW) irradiation is known to have many advantages such as fast crystallization, increased phase purity and selectivity, narrow particle size distribution. The MW synthesis of microporous materials has been shown to be applicable to several zeolite structures like MFI and MEL, but to the best of our knowledge, it has not yet succeeded in synthesizing MCM-22 so far. In this thesis, the crystallization of MCM-22 zeolite by MW heating has been investigated. The thesis is mainly made up of following four sections:MCM-22 zeolites have been synthesized successfully from hydrogels with microwave (MW) heating method. As-synthesized sample had good quality in phase purity, crystallinity, textual properties and incorporated tetrahedral Al ions as evidence by the characterizations with XRD, ICP, IR, and SEM techniques. The crystallization mechanism was investigated by comparing different heaing methods by means of crystallization curves, SEM and FT-IR techniques.The crystallization parameters such as MW step methods, HMI/Si ratio, reation temperature, Si/Al ratio were investigated closely under MW-assissted heating. The HMI/Si ratio played a paramount role in successful crystallization of MCM-22. Meanwhile, multi-step MW method is the desirable one. Other parameters were almost the same as HTS synthesis method.Besides water, my work tried other additives as another dielectric medium on the crystallization of the materials prepared by MW. Due to the inner-heating mechanism of MW, a small amount of methanol in the intial gel could help to further shorten the reation time.I further successfully synthesized [Al, B]-MCM-22 with variable Si/Al ratio under MW heating, and also carried out an initial study on applying MW heating to the synthesis of other MWW-type metallosilicates such as Ti-MWW and Zr-MWW.