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Abstract:
XPS binding energies have been obtained for the components of zeolites in a wide range of Si/Al ratios and
framework structures (from A to ZSM-5 zeolites) in the Na and H forms. For several of these zeolites,
Auger parameters have been measured for the framework elements and the cation (Na). The XPS binding
energies follow trends reported earlier in the literature, while the Auger parameters reveal that (with an exception
in the case of Al) these trends have to be ascribed to initial-state effects. A possible influence of the Madelung
potential on the XPS binding energy has been investigated by lattice-energy calculations using energy-minimized
zeolite models. These model calculations show that among the initial-state effects, the influence of the
Madelung potential prevails over that of the electron-density variations at the emitting atoms. In addition,
the influence of covalent bonding between framework and cation on the XPS binding energies (e.g., in H
zeolites) has been found to arise from changes in the Madelung potentials, which are modified due to the
reduced charge on the atoms engaged in the covalent bond.
