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Nitrogen oxides (NOx) storage catalysts comprising cobalt and barium with a lean NOx storage ratio of 1.3 or greater. The NOx storage catalysts can be used to reduce NOx emissions from diesel or gas combustion engines by contacting the catalysts with the exhaust gas from the engines. The NOx storage

Nitrogen oxides (NOx) storage catalysts comprising cobalt and barium with a lean NOx storage ratio of 1.3 or greater. The NOx storage catalysts can be used to reduce NOx emissions from diesel or gas combustion engines by contacting the catalysts with the exhaust gas from the engines. The NOx storage catalysts can be one of the active components of a catalytic converter, which is used to treat exhaust gas from such engines.

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We claim: 1. A NOx storage catalyst comprising cobalt and barium, wherein said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater. 2. The NOx storage catalyst as recited in claim 1, wherein said lean NOx storage ratio is 2.0 or greater. 3. The NOx storage catalyst as recited in

We claim: 1. A NOx storage catalyst comprising cobalt and barium, wherein said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater. 2. The NOx storage catalyst as recited in claim 1, wherein said lean NOx storage ratio is 2.0 or greater. 3. The NOx storage catalyst as recited in claim 1 in combination with a reduction catalyst containing rhodium. 4. The NOx storage catalyst as recited in claim 1, further comprising platinum. 5. The NOx storage catalyst as recited in claim 4, wherein said lean NOx storage ratio is 1.7 or greater. 6. The NOx storage catalyst as recited in claim 1, wherein said cobalt is predominantly in the form of Co3O4 and the barium in the form of BaCO3. 7. The NOx storage catalyst as recited in claim 1, wherein: (i) said cobalt is present from 1 weight % to 8 weight %, and (ii) said barium is present from 2 weight % to 20 weight %, wherein said-weight % is determined on a metal basis with respect to the total weight of the catalyst. 8. The NOx storage catalyst as recited in claim 7, further comprising platinum, wherein said platinum is present from 0.03 weight % to 1.0 weight %. 9. The NOx storage catalyst as recited in claim 7, wherein: (a) said cobalt is present from 2 weight % to 6 weight %, and (b) said barium is present from 3 weight % to 12 weight %. 10. The NOx storage catalyst as recited in claim 9, further comprising platinum, wherein said platinum is present from 0.05 weight % to 0.5 weight %. 11. A NOx storage catalyst consisting essentially of cobalt, platinum, and barium, supported on an inorganic oxide, wherein said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater. 12. A NOx storage catalyst consisting essentially of cobalt and barium supported on an inorganic oxide, wherein said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater. 13. The NOx storage catalyst of claim 12, wherein: (a) said cobalt is present from 1 weight % to 8 weight %, and (b) said barium is present from 2 weight % to 20 weight %, wherein said weight % determined on a metal basis with respect to the total weight of the catalyst. 14. The NOx storage catalyst as recited in claim 13, wherein: (a) said cobalt is present from 2 weight % to 6 weight %, and (b) said barium from 3 weight % to 12 weight %. 15. The NOx storage catalyst as recited in claim 14 further comprising platinum, wherein said platinum is present from 0.05 weight % to 0.5 weight %. 16. A method of reducing NOx emissions from a diesel engine or a gas-combustion engine, comprising, contacting: (a) a NOx storage catalyst, comprising cobalt and barium, wherein said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater; with (b) the exhaust gas from said diesel engine or said gas-combustion engine. 17. The method of reducing NOx emissions as recited in claim 16, wherein said NOx storage catalyst further comprises platinum. 18. A method of reducing NOx emissions from a diesel engine or a gas-combustion engine, comprising, contacting: (a) a NOx storage catalyst, consisting essentially of cobalt in the form of Co3O4, barium in the form of BaCO3, and platinum, supported on an inorganic oxide, with (b) the exhaust gas of the lean-burn said diesel engine or said gas-combustion engine, wherein said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater. 19. The method as recited in claim 18, wherein, in said NOx storage catalyst: (i) said cobalt is present from 1 weight % to 8 weight %; (ii) said barium is present from 2 weight % to 20 weight %; and (iii) said platinum is present from 0.03 weight % to 1.0 weight %; wherein said weight % is determined on a metal basis with respect to the total weight of said NOx storage catalyst. 20. A NOx storage catalyst consisting essentially of cobalt, platinum, and barium, supported on an inorganic oxide, wherein: (a) said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater, and (b) said NOx storage catalyst includes the following X-ray diffraction peaks: (i) approximately 36.8 2θ; (ii) approximately 59.9 2θ; and (iii) approximately 46.0 2θ. 21. A catalyst consisting essentially of 1 weight % to 8 weight % cobalt; 2 weight % to 20 weight % barium; and 0.03 weight % to 1.0 weight % platinum, supported on an inorganic oxide, said weight % determined on a metal basis with respect to the total weight of the catalyst, and said catalyst has a lean NOx storage ratio of 1.3 or greater. 22. A catalytic converter for a vehicle comprising said NOx storage catalyst of claim 1. 23. A catalytic converter for a vehicle comprising said NOx storage catalyst of claim 7. 24. A catalytic converter for a vehicle comprising said catalyst of claim 21. 25. A NOx storage catalyst consisting essentially of cobalt and barium supported on an inorganic oxide, wherein (a) said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater, and (b) said NOx storage catalyst includes the following X-ray diffraction peaks: (i) approximately 37.3 2θ; (ii) approximately 46.0 2θ; and (iii) approximately 59.0 2θ. 26. A process for treating the exhaust gas from a diesel engine or gas-combustion engine, comprising contacting said exhaust gas from said diesel engine or said gas-combustion engine with a NOx storage catalyst consisting essentially of cobalt, platinum, and barium, supported on an inorganic oxide, wherein: (a) said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater, and (b) said NOx storage catalyst includes the following X-ray diffraction peaks: (i) approximately 36.8 2θ; (ii) approximately 59.9 2θ; and (iii) approximately 46.0 2θ. 27. A process for treating the exhaust gas from a diesel engine or gas-combustion engine, comprising contacting said exhaust gas from said diesel engine or said gas-combustion engine with a NOx storage catalyst consisting essentially of cobalt and barium supported on an inorganic oxide, wherein (a) said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater, and (b) said NOx storage catalyst includes the following X-ray diffraction peaks: (i) approximately 37.3 2θ; (ii) approximately 46.0 2θ; and (iii) approximately 59.0 2θ. 28. A process for treating the exhaust gas from a diesel engine or gas-combustion engine, comprising contacting said exhaust gas from said diesel engine or said gas-combustion engine with a NOx storage catalyst, wherein: (a) said NOx storage catalyst comprises cobalt and barium; (b) said NOx storage catalyst has a lean NOx storage ratio of 1.3 or greater; (c) said cobalt is present from 1 weight % to 8 weight %; (d) said barium is present from 2 weight % to 20 weight %; and (e) said weight % is determined on a metal basis with respect to the total weight of the catalyst. 29. A process for treating the exhaust gas from a diesel engine or gas-combustion engine, comprising contacting said exhaust gas from said diesel engine or said gas-combustion engine with a NOx storage catalyst, said NOx storage catalyst consisting essentially of 1 weight % to 8 weight % cobalt; 2 weight % to 20 weight % barium; and 0.03 weight % to 1.0 weight % platinum, supported on an inorganic oxide, said weight % determined on a metal basis with respect to the total weight of the catalyst, and said catalyst has a lean NOx storage ratio of 1.3 or greater.