NOx adsorber catalyst

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Lean NOx trap catalyst comprising (i) first layer with one or more platinum group metals, first ceria-containing material, and first inorganic oxide and (ii) second layer with one or more noble metails, second ceria-containing material and second 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 later, preferably less than half by weight. Conversely, the loading of the ceria-containing material may be higher in the first later 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. Mixtures or alloys of Pt and Pd supported on the ceria-containing materials are particularly preferred for both layers. Preferably the ceria-containing materials are particularly preferred for both layers. Preferably the ceria-containing material is bulk ceria in both layers. The inorganic oxide is preferably selected from alumina, ceria or a magnesia-alumina composite oxide, more preferably alumina in the second layer.