Interaction ofSO2with nearly perfect and defectTiO2(110) surfaces

The interaction of sulfur-containing molecules with titanium oxide surfaces is of significant technological importance since ${\mathrm{TiO}}_2$ is a widely studied catalyst support and sulfur is a notorious catalyst poison. We report here a study of the interaction of sulfur dioxide with both nearly perfect and high-defect-density ${\mathrm{TiO}}_2$(110) surfaces. By use of ultraviolet photoemission spectroscopy, x-ray photoemission spectroscopy, and low-energy electron diffraction, it is shown that ${\mathrm{SO}}_2$ interacts only weakly, if at all, with the nearly perfect ${\mathrm{TiO}}_2$(110) surface, but reacts vigorously with defects on this surface. The ${\mathrm{SO}}_2$ dissociates at defect sites, producing ${\mathrm{TiO}}_2$- and ${\mathrm{TiS}}_2$-like structures at the surface. Although no direct sulfur-oxygen bond exists, the photoemission data indicate a significant indirect interaction. The dissociative reaction continues until all the ion-bombardment-induced ${\mathrm{Ti}}^{3+}$ cations have been removed by reaction with the ${\mathrm{SO}}_2$. The behavior of ${\mathrm{SO}}_2$ on ${\mathrm{TiO}}_2$ is contrasted with that on ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$, the only other single-crystal transition-metal oxide whose interaction with ${\mathrm{SO}}_2$ has been studied in detail.