Probing of Pd4+ Species in a PdOx-CeO2 System by X-Ray Photoelectron Spectroscopy

The oxidized palladium nanoparticles comprising Pd4+ species were prepared by radio frequency (RF) discharge in an O-2 atmosphere and analyzed with X-ray photoelectron spectroscopy. PdOx particles were deposited on CeO2 or the reference support (Ta2O5) with variation of the RF sputtering time. Regardless of the used support, small PdOx 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 PdOx/CeO2 system was stable during heating in ultra-high vacuum conditions up to 250 degrees 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.

Automated summary

The study prepared oxidized palladium nanoparticles containing Pd4+ species through RF discharge in an O2 atmosphere, showing that Pd4+ species on CeO2 support exhibited a high reaction probability for oxidation processes at low temperatures.