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

Cite this: J. Phys. Chem. C 2021, 125, 38, 20845–20854
Publication Date (Web):September 16, 2021
https://doi.org/10.1021/acs.jpcc.1c04646
Copyright © 2021 American Chemical Society
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Abstract

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. 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 °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.

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.jpcc.1c04646.

  • Structural and textural characteristics of the CeO2 powder; survey spectra for PdOx/CeO2 and PdOx/Ta2O5 systems; HRTEM data for the RF sputtered Pd particles; and curve-fitted Pd3d and Ce3d spectra for the PdOx–CeO2 system, including data collected after thermal and reductive treatments (PDF)

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