Enhancement of selectivity for preferential CO oxidation over SO 2-pretreated Ru/Al 2O 3 catalyst by the presence of sulfur compounds

Abstract

The preferential CO oxidation on a monolith Ru/Al 2O 3 catalyst pretreated with SO 2 in the reactant gas was investigated in the presence/absence of 0.21–20 ppm sulfur compounds (SO 2 or H 2S). In the presence of 2.1 ppm sulfur compound, CO was preferentially oxidized over the SO 2-pretreated catalyst at 150 °C. On the other hand, in the absence of sulfur compounds, the H 2 oxidation was promoted. By in situ IR measurements, multicarbonyl species and SO 4 2− species were found on Ru in the presence of SO 2. The presence of multicarbonyl species at a high frequency (2154 cm −1) and that of SO 4 2− species on Ru suggested that Ru was oxidized. Since the rate of CO oxidation was low on oxidized Ru, the selectivity for CO oxidation was low over the SO 2-pretreated catalyst in the absence of sulfur compounds. On the other hand, the increase in the selectivity in the presence of sulfur compounds suggested that weakly adsorbed sulfur compounds suppressed the migration of dissociatively adsorbed H atom on Ru or decreased the H atoms next to adsorbed O atom for the H 2 oxidation.