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

Author:
Zhang, Zhanpei, Guo, Youmin, Liu, Xiaolong
Source:
The Journal of Physical Chemistry C 2017 v.121 no.21 pp. 11568-11575
ISSN:
1932-7455
Subject:
aluminum, anions, cations, chemical bonding, crystals, magnetism, moieties, nuclear magnetic resonance spectroscopy, silicon, stable isotopes, zeolites
Abstract:
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.
Agid:
5695122