Oxygen exchange between SO2 adsorbate and TiO2 surfaces

SO2 adsorption on TiO2 (rutile) powders was investigated with temperature-programmed desorption gas analysis and Auger electron spectroscopy under ultra high vacuum condition. After 103–104 L 18O-enriched SO2 exposure at 130 K (or room temperature) on vacuum-annealed powders, thermal desorption of S16O18O and S18O2 with a small amount of S16O2 gases was observed in the temperature ranges 140–250 and 350–700 K. Above room temperature, the 18O concentration of desorbed SO2 decreased to about 60% of that of exposed gases, indicating that oxygen isotope exchange takes place between S18O2 and TiO2 surfaces. A single S Auger peak was observed at about 151 eV after SO2 exposure at room temperature, suggesting the TiS bond formation.