Ω型分子筛中两种结晶学不等价四面体位上的铝分布

本文用Monte Carlo模拟实现Ω型分子筛中硅铝分布的物理模型,把由此计算获得的{Si_k(nAl)}结构单元相对数量与~(29)Si MAS NMR实验及Klinowski等的统计计算结果相比较,无论是B位{Si_B(nAl)},还是A位{Si_A(nAl)}分布,从总体上全面的逼近NMR实验分析值.对铝浓度不很高时~(29)SiMAS NMR实验分析呈现出的Isi_(?)(2Al)>Isi_(?)(1Al)的令人费解的情况,也得到了初步阐明.这说明,本文提出的T_B位硅有同时桥联两个骨架铝原子的倾向假设是合理和自洽的,也是影响Ω型分子筛中硅、铝分布的一个因素.

Al-DISTRI BUTIONS ON TWO CRYSTALLOGRAPHICALLY NONEQU IVALENT TETRAHEDRAL SITES IN ZEOLITE OMEGA

In the present work,several models of the Si, Al distribution on the framework of Zeolite Omega are studied. The relative populations of {Sik(nAl)}(k = A,B; n = 0-4) building units are calculated in terms of the Monte Carlo simulation for each distribution model. The calculated results are compared with both the experimental analytical data of 29Si MAS NMR and the statistical calculations by Klinowski et al.In model-3 of us, besides the "Loewenstein rule" and a consideration of the tendency of "the next-nearest-neighbor avoidance" among Al atoms, we assumed further that the SiB tends to connect, via oxygen bridges, two Al atoms as its nearest-neighbors. The calculated results of model-3 gained a great deal of improvements namely not only the distribution of {SiB(nAl)},but also the distribution of {SiA(nAl)} closed ovcrally to the experimental data.As the Al concentrations are not very high the experimental data of Si MAS NMR showed that Isia(2Al)> IsiB(lAl) which had been a puzzlement were explained perliminarily.