Interaction of ${\mathrm{SO}}_2$ and CO with the ${\mathrm{Ti}}_2$${\mathrm{O}}_3$(101¯2) surface

The interaction of sulfur dioxide with the nearly perfect (101¯2) surface of the corundum transition-metal oxide ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ has been studied using ultraviolet and x-ray photoemission spectroscopies and low-energy electron diffraction. The reaction of ${\mathrm{SO}}_2$ with ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ is found to be extremely vigorous, with ${\mathrm{SO}}_2$ adsorbing dissociatively and catalyzing the complete oxidation of the surface to ${\mathrm{TiO}}_2$ and ${\mathrm{TiS}}_2$. This result is significant since exposure to large amounts of ${\mathrm{O}}_2$ does not result in the production of large amounts of ${\mathrm{TiO}}_2$ at the ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$ surface. Dissociative adsorption of ${\mathrm{SO}}_2$ continues for exposures up to at least ${10}^4$ L (1 L${=10\mathrm{}}^{\mathrm{-}6}$Torr sec). The reaction is accompanied by large scale surface disorder and by an increase in the work function of 1.32 eV. In contrast, CO adsorbs molecularly for exposures ≥${10}^5$ L, with an extramolecular relaxation-polarization shift of 3.0 eV. For CO exposures ≤${10}^4$ L, the chemisorption mechanism is tentatively identified as dissociative adsorption at defect sites. Inclusive of this study, the interaction of four oxygen-containing molecules (${\mathrm{SO}}_2$, CO, ${\mathrm{H}}_2$O, and ${\mathrm{O}}_2$) with ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$(101¯2) surfaces has been studied, and their behavior is compared and trends isolated with a view to understanding the oxidation of ${\mathrm{Ti}}_2$ ${\mathrm{O}}_3$.