Desorption of CO (3.8•10 19 molecules gcat -1 ) shows only a low-intensity peak at higher temperatures with its maximum at 478 °C. Since CO desorption from metallic Ru occurs in the temperature range between 25 °C and 250 °C , this peak also results from the decomposition of adsorbed surface species. For comparison, the TPD spectrum recorded after O150 and subsequent CO/Ar pulse reduction shows a comparable low-intensity peak at high- temperatures, and little intensity at temperatures below 270 °C . Comparable results were also obtained for desorption from a surface pretreated by O150 and H2/CO2 pulsing .