| 摘要 |
An emission control system for a lean-burn internal combustion engine comprises (A) a first catalyst system comprising platinum group metal selected from platinum and/or palladium and/or rhodium, which catalyst system has a ratio of % NOx conversion to % hydrocarbon conversion of at least 0.2 as measured at a temperature of 230 DEG C, a space velocity of 25000hr<-1> and a hydrocarbon:NOx input ratio of 3:1 counting the hydrocarbon as equivalent propane, and (B) a second catalyst system, which has, as measured under the same conditions, à % hydrocarbon conversion of greater than 80 % and a % carbon monoxide conversion of greater than 70 %.
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