Bromine Adsorption on Supported Palladium Ultrafine Particles Studied by Br K-Edge EXAFS Spectroscopy

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Abstract
Temperature-dependent Br K-edge EXAFS and XANES spectra of Br-adsorbed Pd ultrafine particles supported on SiO2 were measured and analyzed in order to characterize the surface chemical bondings between adsorbate Br and substrate Pd. It has been revealed that Br2 is not simply adsorbed on the surface but is dissociatively embedded into the Pd particles (embedded phase), resulting in the formation of PdBr2. On the other hand, BBr3 is dissociatively chemisorbed on the surface of the particles (chemisorbed phase). The Br-Pd interatomic distance in the chemisorbed phase is noticeably longer than that in the embedded one, and the Einstein frequency in the former is slightly smaller, indicating the softening of chemical bondings at the surface. XANES spectra have provided supplementary information on the difference between their electronic structures.