Nanocrystalline doped cerium oxide as a catalyst for SO₂ reduction by CO

Nanocrystalline processing by inert gas condensation has the inherent advantages of generating: (1) high surface area nanoclusters, (2) non-stoichiometric oxides, and (3) high dispersions of dopants. This approach is exploited in the synthesis of fluorite-structured catalysts for SO₂ reduction by CO. Nanocrystalline CeO_2-x, La-doped CeO_2-x, and Cu-doped CeO_2-x were produced by magnetron sputtering from a pure or mixed metal target, followed by controlled oxidation of the metallic clusters. The as-prepared doped and undoped nanocrystalline CeO_2-x materials were found to be excellent catalysts for complete SO₂ conversion to elemental sulfur. Undoped nanocrystalline CeO_2-x enabled light-off at 460 °C, a temperature approximately 120 °C lower than that over polycrystalline CeO₂, which is a novel effective catalyst itself. The high catalytic activity of the nanocrystals was associated with their high concentration of oxygen vacancies. Excellent poisoning resistance was also exhibited by the nanocrystalline CeO_2-x samples. These materials have stable activity in the presence of excess CO₂.