| 简介 |
Lean NOx trap catalyst comprising (i) first layer with one or more platinum group metals, first ceria-containing material, and first inorganic oxide, (ii) second layer with one or more noble metals, second ceria-containing material and second inorganic oxide, and (iii) third layer with one or more reducing noble metals and third inorganic oxide, wherein the first ceria-containing material or the first inorganic oxide comprises a rare earth dopant. The dopant is preferably lanthanum or neodymium, more preferably lanthanum. The total loading of platinum group metals in the first layer may be lower than the total loading of noble metals in the second layer, preferably less than half by weight. Conversely, the loading of the ceria-containing material may be higher in the first layer compared to the second layer, preferably more than double. Preferred platinum group metals are palladium, platinum and rhodium, whereas preferred noble metals additionally comprise silver and gold. Mixture or alloys of Pt and Pd supported on the ceria-containing materials are particularly preferred for the first and second layers, of Pt and Rh for the third. Preferably the ceria-containing material is bulk ceria and the inorganic oxides are alumina in the second layer and ceria in the third. |
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