晶化时间及硅源对SAPO-5分子筛的结构及模板剂状态的影响

通过改变硅源和晶化时间的方法,采用水热法合成了系列SAPO-5分子筛材料,用X光衍射(XRD)和²⁷Al MAS NMR对产物的晶相结构进行表征,用¹³C CP MAS NMR研究了不同阶段的产物中模板剂的存在状态。结果可见:以SiO₂凝胶为硅源时;薄水铝石反应物有较高的活性,在48h的晶化时间内,延长晶化时间有助于SAPO-5分子筛的完整结晶,当晶化时间超过48h时,其中已形成的SAPO-5的结构部分被破坏,并转化为SAPO-34.且SAPO-34的量随晶化时间的延长而增多。当以Si(OEt)₄为硅源时,铝反应物的反应活性较低,在72h的晶化时间范围内,延长晶化时间有助于SAPO-5产物的形成,使其结构愈加完整,在SAPO-5分子筛的形成过程中,模板剂的状态随分子筛结构的变化而变化,由于三乙胺(Et₃N)模板剂中的甲基和亚甲基所处位置不同,其弛豫时间受分子筛结构的影响较大,可用其中甲基的¹³C MAS NMR诺线的强度及化学位移来表示分子筛结构的完整性。

EFFECT OF AGING TIME AND SILICON SOURCE ON THE STRUCTURE AND TEMPLATE STATES OF SAPO-5 MOLECULAR SIEVES

A series of SAPO-5 molecular sieves have been synthesized by varying the aging time and silicon source, their structures have been characterlzed by XRD and ²⁷Al MAS NMR spectra. The state of the template in molecular sieves were studied by ¹³C CP MAS NMR. The results reveal that when using silicon gel as silicon source, prolonging aging time can improve the structure of SMO-5 within a linlit of 48 h, when beyond this limit,the produced SAPO-5 is gradually decomposed and some of them is changed into SAPO-34 with a chabazite structure. However, when using Si(OEt)₄ as silicon source, prolonging aging time can improve the structure of SAPO-5 and make Si occupy the framework in the crystallization time of 0 to 72 h. These differences may result from that SiO₂ gel has a higher activity than Si(OEt)₄.The results of ¹³C MAS NMR of the tcmplate in SAPO-5 show that SAPO-5 has some influence on the state of the template. Probably for the methyl group in Et₃N existing at the gate of the pore,the framework can exert some effect on it,so its delay time is different from that of the methylene group connected with nitrogen. Its NMR line intensity decreases with the crystallinity of SAPO-5 and can be used as a pro be to study the crystallinity of SAPO-5.