A NOx reduction system using highly active double-layered NOx trap catalysts with various regeneration properties

A double-layered catalyst, which is composed of top-layered and bottom-layered catalyst components, i.e., some materials as a catalyst promoter and NOx trap catalyst components, respectively, has been examined at 300 to 550°C in rich/lean operations in the presence of 50ppm of SOx to know NOx reduction performance and SOx tolerance. Some top-layered catalysts have given high durability to the NOx reduction system. The durability depended on the material for the promoter and the NOx trap catalyst component and reaction temperature. Some combinations showed high tolerance at 300°C. However, in a long term the combinations deteriorated. At 550°C, all combinations deteriorated in a short term. Nevertheless, a combination could be regenerated partially at 400°C and perfectly at 500°C in reducing conditions.