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One- and two-dimensional high-resolution solid-state NMR investigation of zeolite structures

University of British Columbia

The work reported in this thesis describes for the first time the application of two-dimensional ²⁹Si high-resolution solid state NMR experiments to the investigation of the three-dimensional Si-O-Si bonding connectivities in zeolites. 2D COSY type, INADEQUATE type and spin-diffusion experiments are discussed and evaluated, the INADEQUATE experiments being particularly successful in this work. By preparing highly crystalline, highly siliceous samples of zeolites and careful optimization of all experimental parameters, it is possible to directly observe ²⁹Si-O-²⁹Si J couplings in these experiments. The three-dimensional lattice connectivities obtained from this work for ²⁹Si enriched zeolite ZSM-39 and natural abundance ZSM-12 and ZSM-22 are in excellent agreement with the lattice structures determined by XRD techniques. In the case of a ²⁹Si enriched sample of zeolite DD3R, the ²⁹Si 2D NMR results indicate that the structure is of lower symmetry than has been postulated from diffraction studies. Zeolite ZSM-5, which has the most complex three-dimensional framework of all the known zeolites, was extensively studied in its room temperature phase by 2D NMR spectroscopy. In addition, the effects of temperature and the presence of sorbed p-xylene and p-dichlorobenzene on the phase behavior of ZSM-5 were also investigated. The ²⁹Si 2D NMR data on ZSM-11 at high temperature are in good agreement with the known structure, I4m2. Low temperature 2D experiments on ZSM-11 gave the assignment of space group symmetry 14 to the structure which was previous unknown. Finally, ²⁹Si 2D NMR results on ZSM-23 reveal that there are 12 independent T-sites in the structure which is not consistent with the space groups proposed in the literature which have 7 crystallographically inequivalent T-sites.

Text

2011-01-24

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http://hdl.handle.net/2429/30806

Chemistry

University of British Columbia

Graduate