Al K-Edge Near-Edge X-ray Absorption Fine Structure (NEXAFS) Study on the Coordination Structure of Aluminum in Minerals and Y Zeolites

Abstract

Curved-wave−multiple-scattering cluster calculations with the FEFF6 code were used to interpret experimental AlK-edge near-edge X-ray absorption fine structure (NEXAFS) spectra of various minerals and Y zeolites for energies ∼15 eV above threshold. Octahedral, tetrahedral, and square planar geometries of Al can be easily distinguished from each other utilizing characteristic features in the NEXAFS data. NEXAFS line shapes are used for determining the geometrical conformations of Al atoms in Y zeolites with one or more conformational geometries. In the H−Y zeolite, separate contributions to the NEXAFS from tetrahedrally and octahedrally coordinated Al atoms are identified. The differences in the octahedrally coordinated Al spectra in the H−Y zeolite compared with spectra for standard octahedrally coordinated Al compounds can be attributed to the presence of very small nonregular clusters of octahedrally coordinated Al dispersed over the zeolite. However, the presence of some pentacoordinated Al cannot be excluded.