An Atomic X-ray Absorption Fine Structure Study of the Influence of Hydrogen Chemisorption and Support on the Electronic Structure of Supported Pt Particles

Abstract

The physical principles of atomic XAFS (AXAFS) are presented along with important details on how to isolate the AXAFS contribution from the experimental XAFS data. Intuitive illustrations are given showing how various interactions of the absorber atom with its neighbours influence the AXAFS contribution. Hydrogen chemisorbed on the surface of the supported metal particles is shown to have a strong influence on the amplitude of the Fourier transform AXAFS peak. The effect of the support (with different amounts and types of charge compensating ions (H+, K+), different Si/Al ratio and extra-framework Al) on the experimental AXAFS spectra of Pt dispersed in zeolites (LTL,Y) and on flat supports (Al2O3–SiO2, MgO–Al2O3) are summarised. It is shown that the essence of the metal–support interaction, as revealed in the AXAFS, is a shift in the ionisation potential of the valence d-orbital electrons brought about by the polarisation induced primarily by the changing charge on the support oxygen atoms.