NOx storage materials and traps resistant to thermal aging

1. A nitrogen oxide storage catalyst comprising: a coating on a substrate, the coating comprising a nitrogen oxide storage material comprising as-prepared, spray dried and calcined alkaline earth carbonate/ceria composite particles having a BET surface area between 40-60 m 2 /g, the ceria prior to aging having a crystallite size of between about 10 and 20 nm and the alkaline earth carbonate prior to aging having a crystallite size of between about 20-40 nm.

2. The nitrogen oxide storage catalyst of claim 1 , wherein the alkaline earth carbonate comprises BaCO 3 and the coating further comprises at least one member of platinum group metals selected from the group consisting of platinum, palladium, rhodium, iridium and mixtures thereof supported on refractory oxide particles.

3. The nitrogen oxide storage catalyst of claim 2 , wherein the refractory oxide particles comprise aluminum oxide mixed with one or more of zirconia and lanthana, and wherein the aluminum oxide particles have a surface area of 150-250 m 2 /g.

4. The nitrogen oxide storage catalyst of claim 3 , wherein the refractory oxide particles comprise alumina particles and the BaCO 3 is fixed to the ceria particles such that the BaCO 3 does not migrate to the aluminum oxide particles.

5. The nitrogen oxide storage catalyst of claim 4 , wherein the BaCO 3 is fixed within the pores of the ceria particles.

6. The nitrogen oxide storage catalyst of claim 5 , wherein the aluminum oxide particles have an average pore volume of about 0.3 to about 0.8 ml/g.

7. The nitrogen oxide storage catalyst of claim 6 , wherein the pores in the aluminum oxide particles have an average pore diameter of between about 3 nm and about 20 nm.

8. The nitrogen oxide storage catalyst of claim 2 , wherein the nitrogen oxide storage material comprises spray dried and calcined material calcined between 550 and 750° C.

9. A catalytic trap disposed in an exhaust passage of an internal combustion engine which operates periodically between lean and stoichiometric or rich conditions, for abatement of NO x in an exhaust gas stream which is generated by the engine, comprising a catalytic trap material including a catalytic component comprising the nitrogen oxide storage catalyst of claim 1 .

10. The catalytic trap of claim 9 , wherein the alkaline earth carbonate comprises BaCO 3 and the coating further comprises at least one member of platinum group metals selected from the group consisting of platinum, palladium, rhodium, iridium and mixtures thereof supported on refractory oxide particles.

11. The catalytic trap of claim 9 , wherein the refractory oxide particles comprise aluminum oxide mixed with one or more of zirconia and lanthana, and wherein the aluminum oxide particles have a surface area of 150-250 m 2 /g.

12. The catalytic trap of claim 11 , wherein the BaCO 3 is fixed to the ceria particles such that the BaCO 3 does not migrate to the aluminum oxide particles.

13. The nitrogen oxide storage catalyst of claim 11 , wherein the BaCO 3 is fixed within the pores of the ceria particles.

14. The catalytic trap of claim 13 , wherein the aluminum oxide particales have an average pore volume of about 0.3 to about 0.8 ml/g.

15. The catalytic trap of claim 14 , wherein the pores in the the aluminum oxide particales have an average pore diameter of between about 3 nm and about 20 nm.