XPS Study of Nanostructured Rhodium Oxide Film Comprising Rh⁴⁺ Species

Studies of highly oxidized rhodium species as potential active sites in catalytic oxidation reactions are of great interest. In this work, we investigated the properties of highly oxidized nanostructured rhodium film prepared by radio frequency discharge in an oxygen atmosphere. The charge states of Rh in RhO_<i>x</i> particles, their thermal stability, and reactivity toward CO were analyzed in comparison with the properties of thermally prepared Rh₂O₃ oxide. The formation of Rh⁴⁺ species in a composition of Rh⁴⁺/Rh³⁺ oxyhydroxide structures was shown to take place in plasma-synthesized films. The highly oxidized rhodium species was stable up to 150 °C and demonstrated reactivity in a CO oxidation reaction at 100 °C. The reoxidation of a partially reduced Rh/RhO_<i>x</i> film was observed at 100 °C under treatment with molecular O₂. However, Rh⁴⁺ species were not recovered under such conditions

Highly Oxidized Gold Nanoparticles: In Situ Synthesis, Electronic Properties, and Reaction Probability Toward CO Oxidation

Highly oxidized gold nanoparticles prepared by RF-discharge under an oxygen atmosphere were studied by X-ray photoelectron spectroscopy and transmission electron microscopy depending on the particle size. A surface-like gold oxide was found in the case of small nanoparticles (1–2 nm) obtained at the first steps of deposition. With an increase of the particle size up to 5 nm, a bulklike gold oxide was formed. The O 1s spectra exhibited an oxygen peak at binding energy <i>E</i>_b = 529.4 eV for the surface-like oxide and <i>E</i>_b = 530.7 eV for the bulklike gold-oxide. The reaction probability of oxidized gold nanoparticles was examined in the reaction of CO oxidation at room temperature. The surface-like gold oxide interacted with CO with a high reaction probability of approximately 0.005, while CO interaction with the bulklike oxide was characterized by an induction period with lower reaction probability (0.001). The mechanisms of the interaction of oxidized gold nanoparticles with CO depending on its size are discussed