An XPS Study of the Interaction of Rhodium Foil with NO2

Abstract

The interaction of rhodium foil with nitrogen dioxide over a temperature range of 30–450°C at three NO₂ pressures of 10^–6, 10^–5, and 10^–4 mbar was studied using X-ray photoelectron spectroscopy (XPS). At all of the three pressures, a three-dimensional surface oxide film with the Rh₂O₃ stoichiometry was formed on the foil surface starting from a temperature of 150°C. As the interaction temperature was increased at an NO₂ pressure of 10^–6 mbar, the film thickness d initially increased to reach a maximum of ~2.0 nm at 350°C and then decreased due to the decomposition of Rh₂O₃ to the metal. At pressures of 10^–5 and 10^–4 mbar, a monotonic increase in d up to 3.0 or 4.7 nm, respectively, was observed in a temperature range of 150–450°C. In the case of the interaction with the participation of molecular oxygen at a pressure of 10^–4 mbar and temperatures of 30–450°C, the Rh foil surface was not oxidized. The results of the study on the interaction of NO₂ with Rh were compared with the data obtained earlier for Pd and Pt under comparable conditions.