Interaction of SO2 and CO with the Ti2O3(101-bar2) surface.

Abstract

The interaction of sulfur dioxide with the nearly perfect (101\ifmmode\bar\else\textasciimacron\fi{}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}$${\mathrm{O}}_{3}$ surface. Dissociative adsorption of ${\mathrm{SO}}_{2}$ continues for exposures up to at least ${10}^{4}$ L (1 L${=10}^{\mathrm{\ensuremath{-}}6}$Torr sec). The reaction is accompanied by large scale surface disorder and by an increase in the work function of 1.32 eV. In contrast, CO adsorbs molecularly for exposures \ensuremath{\ge}${10}^{5}$ L, with an extramolecular relaxation-polarization shift of 3.0 eV. For CO exposures \ensuremath{\le}${10}^{4}$ L, the chemisorption mechanism is tentatively identified as dissociative adsorption at defect sites. Inclusive of this study, the interaction of four oxygen-containing molecules (${\mathrm{SO}}_{2}$, CO, ${\mathrm{H}}_{2}$O, and ${\mathrm{O}}_{2}$) with ${\mathrm{Ti}}_{2}$${\mathrm{O}}_{3}$(101\ifmmode\bar\else\textasciimacron\fi{}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}$.