Influence of Ti substitution on the 29Si NMR spectra of silicalite.: A computational study
Influence of Ti substitution on the 29Si NMR spectra of silicalite.: A computational study
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DOI：
10.1524/zpch.1999.209.part_1.021
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发表时间：
1999-01-01
影响因子：
2.5
通讯作者：
Sauer, J
中科院分区：
文献类型：
--
作者：
Ricchiardi, G;Sauer, J
采用从头算与分子力学相结合的方法研究了沸石分子筛骨架中Ti取代Si对Si-29核磁共振化学位移的影响。取代导致相邻Si核的29Si核磁共振信号向较低场的位移仅为1 ppm，而化学位移对平均T-O-T角的依赖保持不变。通过晶格的结构扭曲和Si-O-Ti桥的水解，发现框架Ti位的水化作用强烈地影响了Si-29核磁共振化学位移。氢键和Ti的存在对Q(3)的化学位移的影响也可以忽略不计。Ti47-49核磁共振屏蔽常数强烈依赖于Ti周围的局部结构，并且在水合作用下显示高达150 ppm的变化。
The effect of the substitution of Si by Ti in the framework of the zeolite silicalite on the Si-29 NMR chemical shift is studied with a combined ab initio/molecular mechanics method. Substitution causes a shift of the 29Si NMR signal of neighbouring Si nuclei of only similar to 1 ppm to lower fields, while the dependence of the chemical shift on the average T-O-T angle remains unaltered. Hydration of the framework Ti site is found to strongly influence the Si-29 NMR chemical shift via structural distortions of the lattice and by hydrolysis of Si-O-Ti bridges. The effect of hydrogen bonds and of the presence of Ti on the chemical shift of Q(3) species is also found to be negligible. Ti47-49 NMR Shielding constants strongly depend on the local structure around Ti and show variations of up to 150 ppm upon hydration.