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Solid State NMR Techniques Study the Structural Characteristics of As-Synthesized ITQ-33

Zhang, Zhanpei, Guo, Youmin, Liu, Xiaolong
The Journal of Physical Chemistry C 2017 v.121 no.21 pp. 11568-11575
aluminum, anions, cations, chemical bonding, crystals, magnetism, moieties, nuclear magnetic resonance spectroscopy, silicon, stable isotopes, zeolites
Multinuclear solid state NMR techniques have been applied to study the structural characteristics of extra-large-pore zeolite ITQ-33. Through analysis of 2D ²⁹Si{¹⁹F} HETCOR NMR spectra, the configurations of Ge-D4R units in ITQ-33 can be confirmed to have the most separation between Si and Ge atoms. Because F anions are not in the center of D4R units for shorter Ge–F bond lengths and Ge-D4R units with Ge–F bonds in the crystals are related by mirror symmetries, ²⁹Si NMR signals of D4R units are magnetically inequivalent, therefore two ²⁹Si peaks are observed in ¹⁹F–²⁹Si CP/MAS and ¹⁹F–²⁹Si HETCOR spectra. The formation of specific D4R configurations proves that Ge atoms and F– anions play important structural directing roles in the formation process of zeolite ITQ-33. ²⁷Al 5QMAS experimental results confirm that a major amount of Al atoms is incorporated into the 3-ring in the framework. 1D ¹³C–²⁷Al S-RESPDOR experimental results show that Al atoms in the framework are spatially close to the methyl groups of HM²⁺ cations in the 18-ring channels. Therefore, it can be suggested that the delicate electrostatic balances between the negative charge centers such as F– anions in Ge-D4R units and Al atoms in 3-ring in the zeolite framework and the HM²⁺ cations orient the formation of ultralarge pores (18R) in zeolite ITQ-33. Our observations could be helpful in the design and synthesis of new extra-large-pore zeolites.