The oxidized palladium nanoparticles comprising Pd⁴⁺ species were prepared by radio frequency (RF) discharge in an O₂ atmosphere and analyzed with X-ray photoelectron spectroscopy. PdO_x particles were deposited on CeO₂ or the reference support (Ta₂O₅) with variation of the RF sputtering time. Regardless of the used support, small PdO_x particles (d < 1 nm) contained only Pd²⁺ species, while an increase of the particle size led to the appearance of the additional oxidized Pd state—Pd⁴⁺. The stabilization of Pd⁴⁺ on the surface of defect PdO particles was proposed. The Pd⁴⁺ species in the PdO_x/CeO₂ system was stable during heating in ultra-high vacuum conditions up to 250 °C. Pd⁴⁺ species demonstrated a high reaction probability toward CO oxidation at room temperature. However, a transition from the relatively inert support (Ta₂O₅) to the reducible oxide (CeO₂) did not lead to a significant improvement of the Pd⁴⁺ reaction probability. Pd⁴⁺ species could not be recovered by the exposure of the reduced systems to molecular oxygen at room temperature. The obtained results bring new insights into consideration of Pd⁴⁺ species as active sites for oxidation processes at low temperatures.

中文翻译：

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通过 X 射线光电子能谱探测 PdOx-CeO2 系统中的 Pd4+ 物种

在O ₂气氛中通过射频(RF)放电制备包含Pd ⁴⁺物质的氧化钯纳米颗粒并用X射线光电子能谱分析。随着RF溅射时间的变化，PdO _x颗粒沉积在CeO ₂或参考载体(Ta ₂ O ₅ )上。无论使用何种载体，小的 PdO _x颗粒（d < 1 nm）仅包含 Pd ²⁺物质，而颗粒尺寸的增加导致额外氧化的 Pd 状态——Pd ^{4+ 的出现}。Pd ⁴⁺的稳定性提出了在缺陷 PdO 颗粒的表面上。PdO _x /CeO ₂系统中的 Pd ⁴⁺物质在超高真空条件下加热至 250 °C 时是稳定的。Pd ⁴⁺物种在室温下表现出对 CO 氧化的高反应概率。然而，从相对惰性的载体 (Ta ₂ O ₅ ) 到可还原氧化物 (CeO ₂ ) 的转变并未导致 Pd ⁴⁺反应概率的显着提高。Pd ⁴⁺物质不能通过在室温下将还原的系统暴露于分子氧而回收。获得的结果为考虑 Pd 带来了新的见解⁴⁺种作为低温氧化过程的活性位点。