An atomic X-ray absorption fine structure study of the influence of hydrogen chemisorption and support on the electronic structure of supported Pt particles

The physical principles of atomic XAFS (AXAFS) are presented along with imp ortant details on how to isolate the AXAFS contribution from the experiment al XAFS data. Intuitive illustrations are given showing how various interac tions of the absorber atom with its neighbours influence the AXAFS contribu tion. Hydrogen chemisorbed on the surface of the supported metal particles is shown to have a strong influence on the amplitude of the Fourier transfo rm AXAFS peak. The effect of the support (with different amounts and types of charge compensating ions (H+, K+), different Si/Al ratio and extra-frame work 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 show n that the essence of the metal-support interaction, as revealed in the AXA FS, is a shift in the ionisation potential of the valence d-orbital electro ns brought about by the polarisation induced primarily by the changing char ge on the support oxygen atoms.