Extremely High Field NMR Techniques and Instrumentation for the Study of Catalysts and Materials.

Abstract

The main goal of the research presented in this dissertation is to develop and apply solid-state nuclear magnetic resonance (NMR) techniques to study catalytic materials. Several solid state NMR techniques were developed and have been applied to a series of catalyst systems. The construction and operation of several NMR spectrometers, and the design of NMR probes are discussed. The most novel is a broadband pulsed NMR spectrometer with digital phase shifting and a 0 to 18 Tesla magnet. The development and construction of a field-swept NMR spectrometer is described in detail. This instrument provides a means of acquiring high-quality solid state NMR spectra with very large spectral widths. The instrument provides satisfactory quantification ability. Operation at 4.2 K largely suppresses ion or water motion in samples. The instrument has been used to obtain $\sp{23}$Na and $\sp{27}$Al NMR spectra for several zeolites. The results of these applications demonstrate that this instrument performs well on very broad lines. Some previously "invisible" nonframework $\sp{27}$Al resonances with very large quadrupole coupling constants, on the order of 10 MHz, have been found in hydrothermally-treated hydrogen faujasite zeolites. This research will open a new area of NMR not only in the study of zeolites, but also in the entire field of material science. A research plan is proposed to determine, for the first time, the sign of deuterium quadrupole coupling constants in metal hydride complexes. The correlation between the molecular structure and the sign of the quadrupole coupling constant is also discussed. The modification and operation of an 18 Tesla superconducting magnet with a $\rm \sp3He$-$\sp4$He dilution refrigerator from Oxford Instrument, which can provide extreme experimental conditions for the sign determination, is described in detail. Solid-state deuterium NMR spectroscopy has been applied to extract geometric and electric structural information pertaining to the adsorbed $\rm \sp2H\sb2$ on supported metals. Several possible metal hydride sites are proposed. The application of solid state deuterium NMR spectroscopy to obtain the activation energy for methyl group rotation on the supported metal surfaces is discussed. The instrumentation design for this research is also reported.