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 10(3)-10(4) L O-18-enriched SO2 exposure at 130 K (or room temperature) on vacuum-annealed powders, thermal desorption of (SOO)-O-16-O-18 and (SO2)-O-18 with a small amount of (SO2)-O-16 gases was observed in the temperature ranges 140-250 and 350-700 K. Above room temperature, the O-18 concentration of desorbed SO2 decreased to about 60% of that of exposed gases, indicating that oxygen isotope exchange takes place between (SO2)-O-18 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. (C) 1997 Elsevier Science B.V.