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 degrees C at three NO2 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 degrees C. Based on the measurements of the Pd 3d(5/2), Pd 3p(3/2), and O 1s 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 3d line of metallic palladium. As the interaction temperature was increased, d initially increased to reach a maximum of similar to 3.5-5 nm; thereafter, it began to decrease due to the decomposition of PdO to a metallic state.