Chemical state and reactivity of supported palladium I. Characterization by XPS and uv-visible spectroscopy

The chemical state and environment of palladium supported on silica, titania, and alumina have been studied by uv-visible and X-ray photoelectron spectroscopy. This investigation has concerned the interaction between the supports and the precursor solution, and the nature of the surface complexes produced upon impregnation and drying, in relation to the state of the active phase after reducing pretreatments. Evidence is given that, even when the exchange ability of the support is negligible, a chemical interaction occurs during impregnation and drying, and the nature of the species involved (PdCl4post2−, aquocomplexes) depends on the nature of the support. The XPS data obtained on reduced samples show the presence of surface complexes involving a part of the Pd atoms and containing chlorine. The influence of various preparation factors on the photoelectron spectra is also discussed.