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A NOx absorber catalyst comprising a substrate monolith coated with one or more washcoat layers and comprising a first component comprising a nitrogen oxide storage component, at least one precious metal and a dispersed rare earth oxide supported on a refractory support material, and a second compon

A NOx absorber catalyst comprising a substrate monolith coated with one or more washcoat layers and comprising a first component comprising a nitrogen oxide storage component, at least one precious metal and a dispersed rare earth oxide supported on a refractory support material, and a second component comprising a precious metal supported on a bulk reducible oxide that is substantially free of nitrogen oxide storage material, wherein the precious metal present in the second component comprises Pt, Pd or a combination of both Pt and Pd and wherein the bulk reducible oxide is an oxide, a composite oxide or a mixed oxide comprising at least one of manganese, iron, cobalt, copper, tin or cerium.

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1. A NOx absorber catalyst comprising a substrate monolith coated with one or more washcoat layers and comprising a first component comprising a nitrogen oxide storage component, at least one precious metal and a dispersed rare earth oxide supported on a refractory support material, and a second com

1. A NOx absorber catalyst comprising a substrate monolith coated with one or more washcoat layers and comprising a first component comprising a nitrogen oxide storage component, at least one precious metal and a dispersed rare earth oxide supported on a refractory support material, and a second component comprising a precious metal supported on a bulk reducible oxide that is substantially free of nitrogen oxide storage material, wherein the precious metal present in the second component comprises Pt, Pd or a combination of both Pt and Pd and wherein the bulk reducible oxide is an oxide, a composite oxide or a mixed oxide comprising at least one of manganese, iron, cobalt, copper, tin or cerium. 2. A NOx absorber catalyst according to claim 1, wherein the first component and the second component are present in the same washcoat layer. 3. A NOx absorber catalyst according to claim 1, wherein the second component is in a different layer from a layer comprising the first component. 4. A NOx absorber catalyst according to claim 3, wherein the layer comprising the first component comprises a fourth component comprising a precious metal supported on a bulk reducible oxide, wherein the precious metal present in the second component comprises Pt, Pd or a combination of both Pt and Pd. 5. A NOx absorber catalyst according to claim 1, wherein the bulk reducible oxide is doped with 0.5 to 80 wt.-% of at least one oxide of an element selected from the group consisting of zirconium, silicon, scandium, yttrium, lanthanum and the rare earth metals or mixtures thereof, based on the total weight of the storage material. 6. A NOx absorber catalyst according to claim 1, wherein the mixed oxide or composite oxide further comprises zirconium oxide. 7. A NOx absorber catalyst according to claim 1, wherein the refractory support material in the first component is alumina, magnesia, amorphous silica-alumina, titania, zirconia, a molecular sieve or a mixture, composite oxide or mixed oxide of any two or more thereof. 8. A NOx absorber catalyst according to claim 7, wherein the refractory support is a homogeneous magnesium aluminate. 9. A NOx absorber catalyst according to claim 1, wherein the dispersed rare earth oxide in the first component comprises oxides of elements selected from the group consisting of cerium, praseodymium, neodymium, lanthanum, samarium and mixtures thereof. 10. A NOx absorber catalyst according to claim 1, wherein the nitrogen oxide storage component is selected from the group consisting of alkaline earth metals, alkali metals, rare earth metals and combinations of any two or more thereof. 11. A NOx storage catalyst according to claim 10, wherein the alkaline earth metal is one or both of barium and strontium. 12. A NOx absorber catalyst according to claim 1 comprising a plurality of layers, wherein a lower layer comprises the first component and wherein a layer overlying the lower layer comprises a third component comprising rhodium supported on a refractory support material. 13. A NOx absorber catalyst according to claim 12, wherein a layer overlying the lower layer comprises at least one molecular sieve. 14. A NOx absorber catalyst according to claim 13 comprising three layers, wherein a layer comprising the molecular sieve is disposed between a layer comprising the lower layer and a layer comprising the third component. 15. A NOx absorber catalyst according to claim 13 comprising three layers, wherein a layer comprising the molecular sieve overlies a layer comprising the third component. 16. A NOx absorber catalyst according to claim 13, wherein the molecular sieve is a silicoaluminophosphate (SAPO) or an aluminosilicate zeolite. 17. A NOx absorber catalyst according to claim 12, wherein an outer layer comprises the second component. 18. An exhaust system for a lean-burn internal combustion engine comprising a NOx absorber catalyst of claim 1. 19. A method of treating exhaust gas from a lean burn internal combustion engine, which method comprising the steps of contacting lean exhaust gas containing nitric oxide with a NOx absorber catalyst according to claim 1, and intermittently contacting the NOx absorber catalyst with enriched exhaust gas.