Effect of samarium on the thermal stability and activity of the [formula omitted] catalyst in the oxidation of CO

Abstract

There have been many reports on catalytic oxidation of carbon monoxide with respect to prevention of air pollution. Various kinds of catalysts are involved such as precious metals, base metal catalysts, and composite base metal catalysts. Some catalysts containing silver such as Mn/Cu/Co/Ag and Mn/Co/Ag composite oxides are also active. However, details of the action of silver or other constituents are not known. The authors clarified that the high activity of manganese-silver composite oxide catalysts was due to the cooperative action of Mn and Ag. When active oxygen on Ag was consumed in the oxidation of CO, lattice oxygen of Mn was immediately transferred to the reduced Ag, thus maintaining the active oxidized state of Ag. The Mn acted as an oxygen reservoir. Therefore, silver in the composite catalysts was protected from deactivation due to metallization and aggregation at temperatures about 400 C at which single component silver oxides readily aggregate to metallic state. Although the manganese-silver composite catalysts have considerable thermal stability as described above, they must endure more severe operating conditions in order to be used as practical combustion catalysts. Previously, the authors found that an addition of small amount of samarium improved the thermal stability and activitymore » of transition metal oxides of the first series in the periodic table. In this work the manganese-silver composite catalyst was treated at high temperatures under a reducing atmosphere, and the effect of samarium on the stability of this catalyst was investigated.« less