Electron paramagnetic resonance studies have been carried out on Pd/Y,O, and Pd/La,03 systems with low Pd loading. The samples were prepared by coprecipitation and by decomposition of amorphous citrate precursors. Oxidation of yttria-containing samples at 870 K leads to the formation of Pd3+, which converts into Pd' on evacuation at 870 K, both species being stabilized in the bulk. Mild reduction of doped yttria and lanthana in hydrogen gives another type of Pd+ ions localized within the surface and subsurface layers. Formation of 0; radical anions coordinated with Y3+ or La3+ cations occurs readily at 77 K upon oxygen admission. The decay and formation of adsorbed radical anions is sensitive to the electron-donating properties of the sample (i.e. the surface concentration of Pd+).
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