A NEXAFS Study on the Coordination Geometry of Aluminum in Minerals and Y Zeolite. Comparison of Experiment and Theory.
Abstract
Curved-wave multiple scattering cluster calculations using the FEFF6 code were successfully used to interpret experimental Al K edge NEXAFS spectra of various minerals and Y zeolites. starting about 5 eV above threshold. The Al octahedral, tetrahedral and square planar geometries can be easily distinguished from each other utilizing the NEXAFS data. Semi-empirical molecular orbital calculations were used to interpret the whitelines below 5 eV in the data. A new assignment is given to the NEXAFS peaks found for Al atoms having a distorted octahedral coordination. Use of NEXAFS for determining the geometrical conformations of a Y zeolite involving Al atoms with mixed conformational geometry is emphasized. In H+Y zeolite, separate contributions to the NEXAFS spectra from tetrahedrally and octahedrally coordinated Al atoms are identified. There are also strong indications for the presence of penta-coordinated Al atoms accompanying the non-framework octahedrally coordinated Al atoms in the H+Y zeolite. We have found that detailed interpretations of the NEXAFS data complement the EXAFS and NMR results by providing unique geometrical information on the Al coordination.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1997
- Accession Number
- ADA321984
Entities
People
- D. C. Koningsberger
- David E. Ramaker
- H. Sambe
- J. A. Van Bokhoven
Organizations
- George Washington University