ALUMINUM SITING IN THE ZSM-22 AND THETA-1 ZEOLITES REVISITED: A QM/MM STUDY

作者：Sklenak Stepan^*; Dedecek Jiri; Li Chengbin; Gao Fei; Jansang Bavornpon; Boekfa Bundet; Wichterlova Blanka; Sauer Joachim

来源：Collection of Czechoslovak Chemical Communications, 2008, 73(6-7): 909-920.

DOI：10.1135/cccc20080909

• QM/MM calculations
• Ab initio calculations
• BLYP
• GIAO
• Zeolites
• Al-27 3Q MAS NMR spectroscopy
• ZSM-5 catalyst
• Heterogeneous catalysis

The Al siting in the silicon rich ZSM-22 and Theta-1 zeolites of the TON structure was investigated analyzing already published Al-27 3Q MAS NMR experimental data using QM/MM calculations. The results of our computations show that Al atoms can be located in 6 framework T positions because the two eightfold sites ( T1 and T2) split into four fourfold T sites after an Al/Si substitution. The observed resonance at 55.5 ppm corresponds to the T4 site which is predominantly occupied by Al. This site is not located on the surface of the TON ten-membered ring channel and thus the protonic sites related with the majority of Al atoms in the TON structure exhibit a significantly limited reaction space. The Al-27 NMR signals centered at 57.6 and 58.7 ppm correspond to either the T2 and T3 sites, respectively, or only to T2. The T2 and T3 sites accommodate some 40% and up to 10%, respectively, of Al while the T1 site is unoccupied by Al. Isotropic shifts of 61.1 and 61.6 ppm were calculated for Al atoms located in the T1-1 and T1-2 sites, respectively. The effect of a silanol "nest" as a next-next-nearest neighbor on the Al-27 isotropic chemical shift of Al located in the T4 site is calculated to be less than 1 ppm.

• 出版日期2008