Accession Number : ADA321984

Title :   A NEXAFS Study on the Coordination Geometry of Aluminum in Minerals and Y Zeolite. Comparison of Experiment and Theory.

Descriptive Note : Technical rept.,

Corporate Author : GEORGE WASHINGTON UNIV WASHINGTON DC DEPT OF CHEMISTRY

Personal Author(s) : Van Bokhoven, J. A. ; Sambe, H. ; Koningsberger, D. C. ; Ramaker, D. E.

PDF Url : ADA321984

Report Date : JAN 1997

Pagination or Media Count : 9

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.

Descriptors :   *ALUMINUM, *GEOMETRY, *X RAY ABSORPTION ANALYSIS, *MINERALS, *MOLECULAR ORBITALS, SCATTERING, NUCLEAR MAGNETIC RESONANCE, COMPUTATIONS, COMPARISON, ATOMS, CLUSTERING, PLANAR STRUCTURES, ION EXCHANGE, ATOMIC STRUCTURE.

Subject Categories : Inorganic Chemistry
      Physical Chemistry
      Atomic and Molecular Physics and Spectroscopy

Distribution Statement : APPROVED FOR PUBLIC RELEASE