An XPS Study of the Interaction of a Palladium Foil with NO2

The interaction of a palladium foil with nitrogen dioxide in a temperature range of 30–450°C at three NO 2 pressures of 10 –6 , 10 –5 , and 10 –4 mbar was studied by X-ray photoelectron spectroscopy (XPS). In all cases, a three-dimensional oxide film was formed on the surface of palladium metal starting with a temperature of 150°C. Based on the measurements of the Pd 3 d 5/2 , Pd 3 p 3/2 , and O 1 s binding energies and the [Pd] : [O] atomic ratio, it was found that the film consisted of the palladium oxide PdO. The oxide film thickness d was estimated based on the weakening of the Pd 3 d line of metallic palladium. As the interaction temperature was increased, d initially increased to reach a maximum of ~3.5–5 nm; thereafter, it began to decrease due to the decomposition of PdO to a metallic state.