| 摘要 |
The invention discloses an exhaust gas purification catalyst apparatus which is capable of efficiently removing, foralongperiodoftime, hydrocarbons, carbonmonoxide, nitrogen oxides, and particulate components such as soot contained in exhaust gas from a lean burn engine. It is provided an exhaust gas purification apparatus arranged with an oxidation catalyst (DOC) comprising a noble metal component for oxidizing nitrogen oxides (NO) in an exhaust gas discharged from a diesel engine, a reducing agent spraying means for supplying the reducing agent selected from a urea component or an ammonia component, and a selective reduction catalyst (SCR) not comprising a noble metal for removing by reduction nitrogen oxides (NO x ) by contacting with the reducing agent, in this order from the upstream side of an exhaust gas passage, characterized in that activity of the selective reduction catalyst (SCR) is maintained by setting that the noble metal component of the oxidation catalyst (DOC) comprises platinum and palladium, and ratio of platinum particles existing alone is 20% or less, or average particle diameter of the noble metal is 4 nm or larger, and by suppressing volatilization of platinum from the oxidation catalyst (DOC), even when catalyst bed temperature increases up to 900°C. |
