Deka Ramesh Ch, Nasluzov Vladimir A, Ivanova Shor Elena A, Shor Alexei M, Vayssilov Georgi N, Rösch Notker
Department Chemie, Technische Universität München, 85747 Garching, Germany.
J Phys Chem B. 2005 Dec 29;109(51):24304-10. doi: 10.1021/jp050056l.
We studied the preferential location of Ti centers in the framework of the Ti-containing MFI zeolite TS-1 using a hybrid DFT/MM embedding method developed recently. This "covalent elastic polarizable environment" (covEPE) cluster embedding allows a complete and self-consistent treatment of solid covalent systems such as zeolites. For the present study, we used a gradient-corrected density functional approach. The resulting structural features of both Si- and Ti-substituted forms of the zeolite framework fit well with available experimental information. The calculated substitution energy of Ti at the 12 crystallographically different tetrahedral sites of the MFI structure vary within 19 kJ/mol with T12 and T2 as most and least preferred sites, respectively. On the basis of these computational results and the preferential sites for Ti substitution reported from different experimental investigations, we concluded that the Ti distribution in the TS-1 framework is not governed by the thermodynamic stability of the pure material.
我们使用最近开发的混合密度泛函理论/分子力学（DFT/MM）嵌入方法，研究了含钛MFI沸石TS-1骨架中钛中心的优先位置。这种“共价弹性可极化环境”（covEPE）簇嵌入方法能够对沸石等固体共价体系进行完整且自洽的处理。在本研究中，我们采用了梯度校正密度泛函方法。所得的沸石骨架硅取代和钛取代形式的结构特征与现有实验信息吻合良好。计算得出，在MFI结构的12个晶体学不同四面体位置上钛的取代能在19 kJ/mol范围内变化，其中T12和T2分别是最优先和最不优先的位置。基于这些计算结果以及不同实验研究报道的钛取代优先位置，我们得出结论：TS-1骨架中的钛分布不受纯材料热力学稳定性的控制。
