The Study And Synthesis Of MCM-22 And Fe Substituted MCM-22

Because of the special characters, comprising two kinds of different and non-intersecting pore systems, MCM-22 zeolite shows distinctive acidic performance and catalytic reactivity to some chemical reactions. It has been expected a promising application in chemical industry. In this dissertation, the influences of crystallizing temperature and crystallizing time on the crystallization procedure of MCM-22 have been studied deliberately under condition of rotating synthesis and using Hexamethyleneimine (HMI) as Structure Directing Agent (SDA). It has been made known that a relative low crystallizing temperature and long crystallizing time are favorable conditions for synthesizing pure MCM-22 crystal with high crystallinity. On the contrary, the phase of ZSM-35 zeolite can be formed, even as pure crystal and with high crystallinity, under high crystallizing temperature or prolonged reacting time in such a synthesis system. Also, the pure phase of ZSM-5 or that of Mordenite zeolites can be yielded selectively by controlling appropriate reaction temperature and crystallizing time. More successfully, some kinds of co-crystalline zeolites, such as the co-crystalline zeolites of MCM-22 and ZSM-35, that of ZSM-5 and ZSM-35, and that of Mordenite and ZSM-35, can be produced quantificationally by selecting the synthesis conditions. By analyzing crystallization procedure and structural characters of the co-crystalline zeolites, it can be thought that the reason why the crystal transformations happen between above zeolites during the crystallization procedure is that the stability changing of the channel systems propel the occurrence of crystal transforming with little resistance because of the same 5-ring sub-units they all have. Furthermore, it is impossible to stabilize the existence of MCM-22 by adding crystal seeds of MCM-22.On the base of the above knowledge of synthesizing MCM-22, The Fe substituted MCM-22 is given an intensive investigation. [Fe-Al]-MCM-22 can be successfully synthesized by using silica sol as silica source, of which the longer crystallizing time is needed and the crystallinity drops with the increasing of Fe2O3 content. In comparison with silica sol, the crystallizing process is similar to synthesize [Fe-Al]-MCM-22 with lower content of Fe2O3 when using sodium silicate as silica source. However, high crystallinity of [Fe-Al]-MCM-22 zeolite can be gotten in shorter crystallizing time, and pure phase of Fe-MCM-22 can also be obtained by using this kind of silica source. The Fe atoms locating in the framework of [Fe-Al]-MCM-22 results in the increment of c parameter of unit cells and the unitvolume of samples. The c parameter of unit cells and the unit volume of samples become larger for [Fe-Al]-MCM-22 zeolite with higher Fe2O3 content than lower Fe2O3 content and much more than Al-MCM-22 without Fe2O3. The vibration frequency of [Fe-Al]-MCM-22 in IR band also gives evidence of Fe-O-Si linking mode in the framework, since the asymmetry vibrating frequency of it shifts to lower number than that of the Al-MCM-22. Compared with Fe2O3/MCM-22, [Fe-Al]-MCM-22 has higher temperature reduction peaks in H2-TPR experiment. This indicates that [Fe-Al]-MCM-22 has framework Fe3+, which is difficult to be reduced because of stabilizing effect of the framework situation. That only little change of the signal at g=4.45 of ESR, resulted from the Fe3+ locating in the framework of zeolite, has been observed after the high temperature calcinations of [Fe-Al]-MCM-22 zeolite shows the very stable framework Fe3+ in [Fe-Al]-MCM-22 zeolite.