XPS Study of Nanostructured Rhodium Oxide Film Comprising Rh⁴⁺ Species

Abstract

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 RhOx 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/RhOx film was observed at 100 °C under treatment with molecular O2. However, Rh4+ species were not recovered under such conditions.