M-ZSM-48的晶化和孔道性质研究

STUDIES ON THE CRYSTALLIZATION AND PORE PROPERTIES OF M ZMS 48

采用自生压力的水热合成方法，以ＨＭＤＡ为模板剂，在１６０℃下，合成了４种杂原子ＺＳＭ－４８型分子筛：Ｂ－ＺＳＭ－４８，Ｇｅ－ＺＳＭ－４８，Ｃｒ－ＺＳＭ－４８和Ｖ－ＺＳＭ－４８。实验结果表明，该类分子筛晶化条件变化范围较小，易和ＺＳＭ－５分子筛相伴生。晶化过程中，相对于晶体生长来说，成核是一个慢过程。在最佳合成的条件下，晶化速度的顺序为：Ｂ－ＺＳＭ－４８＞Ｇｅ－ＺＳＭ－４８＞Ｓｉ－ＺＳＭ－４８＞Ｖ－ＺＳＭ－４８＞Ｃｒ－ＺＳＭ－４８。杂原子对硅产生同晶取代并以畸变四面体配位方式占据分子筛骨架位置，使分子筛的孔道及骨架性质发生明显变化。尤其是非Ⅳ价态杂原子Ｂ和Ｃｒ，使分子筛骨架电性改变，从而导致孔道吸附性能、骨架酸性和对模板剂的束缚能力发生显著变化。

Four kinds of heteroatom ZSM 48 type molecular sieves(B ZSM 48, Ge ZSM 48, Cr ZSM 48 and V ZSM 48) were synthesized in hydrothermal system at autogeneous pressure using HMDA as templating agent. It was shown by the results that these zeolites have a small crystallizing field and overgrowth easily with ZSM 5. The nucleation is slow than crystal growth. Under the best synthesis conditions, the order of the crystallizing speeds is as follows: B ZSM 48>Ge ZSM 48>Si ZSM 48>V ZSM 48>Cr ZSM 48. It changes the properties of pores and frameworks that hetro atoms replace Si isomorphously and enter the frameworks of M ZSM 48 at the sites of distorted tetrahedral coordination. Especially, non Ⅳ valence hetro atom B or Cr changes the frameworks change of M ZSM 48, the adsorption ability, the framework acidity and the ability of holding templating agent obviously.