| 摘要 |
<p>A catalyst device for clarification of exhaust gas which is disposed in an exhausting route of an internal combustion engine capable of being operated at least at theoretical and lean air-fuel ratios, characterized in that it has a three component catalyst (4) comprising an inner layer (12a) containing primarily rhodium as a noble metal activating in a reduced oxygen content atmosphere and a surface layer (12b) containing primarily platinum or palladium as a noble metal activating in a enhanced oxygen content atmosphere. The catalyst device effectively removes HC due to activation of platinum or palladium in lean operation and, when O2 is temporarily short in the change from lean to stoichiometric air-fuel ratio, removes HC by supplementing O2 through utilizing the function of platinum or palladium to store O2, and as a result prevents the temporary great decrease of its ability to remove HC. Accordingly, the catalyst device secures the satisfactory performance of removing HC even in lean region without the increase of the amount of a noble metal in the three component catalyst.</p> |
