铁离子在ZSM-5分子筛中存在位置的理论研究

Predicting locations of non-framework Fe cations in zeolite ZSM-5

对磷铁改性的ZSM-5分子筛粉末进行X射线扫描,获得了较高分辨率的衍射数据,并由X射线荧光分析数据得到分子筛的化学组成。采用分子模拟软件中的建模及结构优化工具,构建了硅铝比为23.77的ZSM-5分子筛的三维空间构型,用分子力学方法计算二价铁离子在分子筛孔道中的位置并用Rietveld精修的方法验证铁离子在ZSM-5分子筛孔道中的位置。结果表明,金属改性的ZSM-5分子筛中二价铁离子主要存在于十元环S形孔道和直孔道交叉处,少量存在于直孔道中。计算了Fe^(2+)离子在孔道内的配位间距,对改性的ZSM-5分子筛进行了结构参数分析,最终确定了两种Fe^(2+)在孔道内的确切坐标分数。

In the catalytic pyrolysis process （CPP） , modified ZSM-5 zeolite is the main active component of cracking catalyst for mass production of light olefins. The loading, position, Occupation and coordination of Fe2＋ on ZSM-5 zeolite directly affect not only the acid amount （density of acid centers）, acidic intensity and the ratio of BrOnsted acid to Lewis acid, but also the catalytic activity of the CPP catalyst In an effort to understand the position of Fe2＋ in ZSM-5 zeolite, the modified zeolite was characterized by XRD. Three-dimensional spatial configuration of the sample with Si-A1 ratio 23.77 was built with the modeling and structure-optimization tools of the molecular simulation software. The position of the ferrous irons in the zeolite pore was calculated by molecular mechanic methods and refined by Rietveld method. Simulation results indicated that most of the ferrous irons existed in the intersections of 10-membered ring S-shaped channel and straight channel, and some of them can also be found in the straight channel of the zeolite.