Proton solid-state nuclear magnetic resonance studies of zeolite catalysts

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1992

OSTI ID:5503292

White, J L

The goal of the research presented was to develop and demonstrate variable-temperature [sup 1]H magic-angle spinning (MAS) nuclear magnetic resonance (NMR) methods for the study of zeolites, both in the absence and presence of catalytically important adsorbates. This approach allowed simultaneous spectroscopic observation of both the catalyst and adsorbates. Reliable sample preparation techniques were developed which allowed routine characterization by NMR methods over a wide temperature range while preserving sample integrity. Other developments associated with this project including high-temperature NMR investigations of cracking chemistry, methods for sensitivity enhancement, and variable-temperature [sup 1]H combined rotation and multiple-pulse NMR spectroscopy are described. The structure and dynamics of hydrogen-bonded adsorption complexes between various adsorbates and the Bronsted acid site in zeolite H-ZSM5 were determined using variable-temperature [sup 1]H MAS NMR. The chemical shift of the Bronsted acid site was found to be extremely sensitive to the amount and type of molecule adsorbed. NMR experiments previously developed revealed a specific hydrogen-bonding interaction between the adsorbate and the strong acid site only. Quantitative treatment of the observed changes in the Bronsted chemical shift upon introduction of adsorbates resulted in the determination of equilibrium constants for the formation of the complex as well as hydrogen-bond distances. The spectroscopic properties of H-ZSM5 were characterized in detail using one- and two-dimensional MAS [sup 1]H NMR methods. These experiments revealed thermally-activated chemical exchange occurs between Bronsted acid protons and weakly acidic protons of the zeolite. Upon adsorption of ammonia, proton chemical exchange between all three types of protons was observed. These experiments revealed proton NMR spectroscopy may be used to monitor diffusion in zeolites on a macroscopic and microscopic level.

• Research Organization: Texas A and M Univ., College Station, TX (United States)
• OSTI ID: 5503292
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
664000 -- Atomic & Molecular Physics-- (1992-)
665100* -- Nuclear Techniques in Condensed Matter Physics -- (1992-)
74 ATOMIC AND MOLECULAR PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ADSORPTION
BROENSTED ACIDS
CATALYSIS
CATALYSTS
CHEMICAL REACTIONS
CHEMICAL SHIFT
CONTROL
CRACKING
DECOMPOSITION
FEASIBILITY STUDIES
HETEROGENEOUS CATALYSIS
HYDROCARBONS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOMERIZATION
MAGNETIC RESONANCE
MATERIALS
MINERALS
NUCLEAR MAGNETIC RESONANCE
ORGANIC COMPOUNDS
PHYSICS
PYROLYSIS
RESONANCE
SAMPLE PREPARATION
SENSITIVITY
SILICATE MINERALS
SOLID STATE PHYSICS
SORPTION
TEMPERATURE CONTROL
THERMOCHEMICAL PROCESSES
ZEOLITES