| 摘要 |
PURPOSE:To obtain a catalyst for purifying NOx having high activity and excellent durability for an exhaust gas from a lean-burn engine in which an excess amt. of oxygen than the stoichiometric amt. exists, by constituting the catalyst of crystalline silicate having a specified Si/Ir atomic ratio and a Si/Al atomic ratio. CONSTITUTION:This catalyst consists of crystalline iridium silicate having 50<Si/Ir<800 (atomic ratio) and 15<Si/Al (atomic ratio). This crystalline irridium silicate has a compsn. expressed by xM2O.yAl2O3.-IrO2.zSiO2.wH2O (wherein M is an alkali metal, w-z are numbers satisfying 0<x/y<=5.0, 0<y<=10, 50<=z<=800, z/y>=30, and 0.01<=w/z<=0.5). This catalyst exhibito excellent activity and selectivity for purification of such an exhaust gas, especially for NOx, which contains a reductive component including hydrocarbons nitrogen oxides, and an excess amts. of oxygen greater than the stoichiometric amt. required to completely oxidize all of the reductive component. |
