X-Ray photoelectron spectroscopic studies of ruthenium-oxygen surfaces

The technique of X-ray photoelectron spectroscopy (XPS) has been used to study the complex surface chemistry of the ruthenium-oxygen system as a function of temperature and under the influence of Ar+ and O2+ ion-bombardment. Interaction of molecular oxygen and O2+ ions with metallic ruthenium produced two forms of oxygen which are not attributable to RuO2, RuO3 and RuO4. A variety of species has been identified on RuO2. On anhydrous RuO2 we found a surface layer of RuO3 present as a gross defect structure of RuO2. On commercially available hydrated samples, both the XPS signal for the oxide and for the water could be observed. In addition, a carbon contamination indicated from a mass spectral analysis and microanalysis was characterized as RuOCO3. In general the XPS approach was found to be valuable in monitoring the surface concentrations of these species and thus in characterizing the chemical composition of this catalyst surface.