Applications of multinuclear magnetic resonance to the characterisation of zeolites

Abstract

The following research is primarily concerned with the characterisation of the novel, unidimensional, zeolite theta-1 by solid-state multinuclear magnetic resonance spectroscopy. Some study has also been made of the zeolites ZSM-5 and NaY. The high-silica form of as-synthesised theta-1 is studied by high-resolution (^13)C and (^29)Si MASNMR. The (^13)C spectra are interpreted as showing the presence of both neutral and protonated diethylamine template molecules. These observations are discussed in terms of the possible presence of acid sites and their spatial distribution. The (^29)Si NMR results are consistent with the template molecules occupying the 10-T channels only. The (^29)Si spin-lattice relaxation mechanism is investigated under a variety of conditions. Changes in the (^29)Si NMR spectra on calcinations indicate the possibility of a minor framework rearrangement.Theta-1 synthesised using a diethanolamine template is also investigated. The template distribution is examined, and evidence for structural modification by the presence of the template is presented. The nature of the non-framework aluminium species produced on hydrothermal dealumination and the broad linewidths observed for such species in (^27) A1 NMR are also investigated. The signal response to the application of a single pulse of finite duration to a system of I=(^3)/2 nuclei is used to illustrate the differences between selective and non-selective excitation of the central transition, and the requirements for quantitivity. A series of model compounds is investigated by quadrupole nutation NMR, and more complex zeolite systems containing quadrupolar nuclei are investigated by a variety of techniques.