Catalyst system for the reduction of NOx and NH3 emissions

• US 7,332,135 B2
• Filed: 10/22/2002
• Issued: 02/19/2008
• Est. Priority Date: 10/22/2002
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Cheng, Yisun, Hammerle, Robert Henry, Cavataio, John Vito, Gandhi, Haren S
• Primary Examiner(s): Caldarola; Glenn
• Assistant Examiner(s): DUONG, THANH P
• Application Number:
  US10/065,470
• Publication Number:
  US 20040076565A1
• Time in Patent Office: 1,946 Days
• Field of Search: 422/171, 422/177, 422/180, 602/85, 602/86
• US Class Current: 422/177
• CPC Class Codes: B01D 53/8631 Processes characterised by a specific device
• CPC Class Codes: F01N 13/0097 the purifying devices are arranged in a single housing
• CPC Class Codes: F01N 2240/25 an ammonia generator
• CPC Class Codes: F01N 2510/06 for exhaust purification, e.g. catalytic reaction
• CPC Class Codes: F01N 3/0814 combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/108 Auxiliary reduction catalysts
• CPC Class Codes: Y02C 20/10 of nitrous oxide (N2O)
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

This catalyst system simultaneously removes ammonia and enhances net NOx conversion by placing an NH₃-SCR catalyst formulation downstream of a lean NOx trap. By doing so, the NH₃-SCR catalyst adsorbs the ammonia from the upstream lean NOx trap generated during the rich pulses. The stored ammonia then reacts with the NOx emitted from the upstream lean NOx trap—enhancing the net NOx conversion rate significantly, while depleting the stored ammonia. By combining the lean NOx trap with the NH₃-SCR catalyst, the system allows for the reduction or elimination of NH₃ and NOx slip, reduction in NOx spikes and thus an improved net NOx conversion during lean and rich operation.

Claims

1. An emission control system for controlling NOx and NH₃ emissions from an exhaust stream, the system comprising:

a lean NOx trap in communication with the exhaust stream for reducing NOx emissions, wherein the lean NOx trap is optimized for NH₃ generation by removing oxygen storage capacity of the lean NOx trap; and

a NH₃-SCR catalyst in communication with the exhaust stream for adsorbing NH₃, wherein the NH₃ adsorbed by the NH₃-SCR catalyst reacts with NOx in the exhaust stream to improve the reduction of NOx and NH₃.

2. The emission control system of claim 1, wherein one or more alternating layers of the lean NOx trap and the NH₃-SCR catalyst are provided in a single catalytic converter shell such that a top layer comprising the lean NOx trap positioned over a bottom layer comprising the NH₃-SCR catalyst is repeated one or more times.

3. The emission control system of claim 1, wherein one or more alternating layers of the lean NOx trap and NH₃-SCR catalyst are provided in a single substrate such that a top layer comprising the lean NOx trap positioned over a bottom layer comprising the NH₃-SCR catalyst is repeated one or more times.

4. The emission control system of claim 1, wherein one or more alternating zones of the lean NOx trap and NH₃-SCR catalyst are provided in a single catalytic converter shell such that an upstream zone comprising the lean NOx trap positioned upstream of a downstream zone comprising the NH₃-SCR catalyst is repeated one or more times.

5. The emission control system of claim 4, wherein each alternating zone of the lean NOx trap and alternating zone of the NH₃-SCR catalyst have a 1″

length and 1″

width.

6. The emission control system of claim 4, wherein each alternating zone of the lean NOx trap and alternating zone of the NH₃-SCR catalyst have a ½

″

length and a width of ½

″

.

7. The emission control system of claim 4, wherein each alternating zone of the lean NOx trap and alternating zone of the NH₃-SCR catalyst have a length of ¼

″ and

a width of ¼

″

.

8. The emission control system of claim 1, wherein one or more alternating zones of the lean NOx trap and NH₃-SCR catalyst are provided in a single substrate such that an upstream zone comprising the lean NOx trap positioned upstream of a downstream zone comprising the NH₃-SCR catalyst is repeated one or more times.

9. The emission control system of claim 1, wherein the lean NOx trap generates a sufficient quantity of NH₃ to force the reaction between NOx and NH₃, whereby NH₃ emissions are eliminated and net NOx conversion improved.

10. The emission control system of claim 1, wherein the lean NOx trap is optimized for NH₃ generation by removing oxygen storage capacity of the lean NOx trap.

11. The emission control system of claim 1, wherein the lean NOx trap comprises a precious metal selected from the group consisting of platinum, palladium, rhodium and combinations thereof;

and a NOx storage material selected from the group consisting of alkali metals, alkali earth metals, rare earth metals and combinations thereof.

12. The emission control system of claim 1, wherein the lean NOx trap comprises platinum.

13. The emission control system of claim 1, wherein the lean NOx trap comprises a composite of cerium and zirconium.

14. The emission control system of claim 1, wherein the lean NOx trap comprises one or more materials for NH₃ generating and NOx storage.

15. The emission control system of claim 1, wherein the NH₃-SCR catalyst comprises one or more NH₃ adsorbing materials, wherein the NH₃ adsorbing materials are capable of converting NOx and NH₃ to nitrogen.

16. The emission control system of claim 1, wherein the NH₃-SCR catalyst comprises a base metal and a support selected from the group consisting of alumina, silica titania, zeolite and their combinations.

17. The emission control system of claim 1, wherein the NH₃-SCR catalyst comprises a metal selected from the group consisting of Cu, Fe and Ce and a zeolite.

18. The emission control system of claim 1, wherein the lean NOx trap and the NH₃-SCR catalyst are placed in a single catalytic converter shell.

19. The emission control system of claim 1, wherein the NH₃-SCR catalyst is separate from and downstream from the lean NOx trap.

20. An emission control system for controlling NOx and NH₃ emissions from an exhaust stream produced by the combination of an air/fuel mixture in an internal combustion engine, the system comprising:

a lean NOx trap in communication with the exhaust stream for NOx reduction wherein the lean NOx trap comprises a lean NOx trap formulation which includes one or more NOx storage and wherein the lean NOx trap is optimized for generation by minimizing oxygen storage capacity of the lean NOx trap;

a NH₃-SCR catalyst in communication with the exhaust stream for adsorbing NH₃, wherein the NH₃-SCR catalyst comprises a NH₃-SCR catalyst formulation which includes one or more NH₃ adsorbing materials; and

wherein the lean NOx trap formulation and the NH₃-SCR catalyst formulation are placed on one substrate.

21. The emission control system of claim 20, wherein a layer of the lean NOx trap formulation and a layer of the NH₃-SCR catalyst formulation are placed on the substrate to form a two-layer washcoat.

22. The emission control system of claim 20, wherein the lean NOx trap formulation and the NH₃-SCR catalyst formulation are homogeneously mixed to form a single washcoat layer on the substrate.

23. The emission control system of claim 20, wherein the lean NOx trap formulation and the NH₃-SCR catalyst formulation are heterogeneously mixed to form a single washcoat layer on the substrate.

24. An emission control system for controlling NOx and NH₃ emissions from an exhaust stream produced by the combination of an air/fuel mixture in an internal combustion engine, the system comprising:

a lean NOx trap in communication with the exhaust stream for NOx reduction, to provide a NOx reducing exhaust stream including NOx and NH₃, wherein the lean NOx trap is optimized for NH₃ generation by removing oxygen storage capacity; and

a NH₃-SCR catalyst in communication with the exhaust stream for adsorbing NH₃, wherein the NH₃ adsorbed by the NH₃-SCR catalyst reacts with NOx in the NOx reduced exhaust stream to improve the reduction of NOx and NH₃.

25. The emission control system of claim 24, wherein the lean NOx trap generates a sufficient quantity of NH₃ to force the reaction between NOx and NH₃, whereby NH₃ emissions are eliminated and net NOx conversion improved.

26. The emission control system of claim 24, wherein the lean NOx trap comprises a precious metal selected from the group consisting of platinum, palladium, rhodium and combinations thereof;

and a NOx storage material selected from the group consisting of alkali metals, alkali earth metals, rare earth metals and combinations thereof.

27. The emission control system of claim 24, wherein the lean NOx trap comprises platinum.

28. The emission control system of claim 24, wherein the lean NOx trap comprises a composite of cerium and zirconium.

29. An emission control system for controlling NOx and NH₃ emissions from an exhaust stream produced by the combination of an air/fuel mixture in an internal combustion engine, the system comprising:

a lean NOx trap in communication with the exhaust stream for NOx reduction, to provide a NOx reducing exhaust stream including NOx and NH₃, wherein the lean NOx trap is optimized for NH₃ generation by minimizing oxygen storage capacity; and

a NH₃-SCR catalyst in communication with the exhaust stream for adsorbing NH₃, wherein the NH₃ adsorbed by the NH₃-SCR catalyst reacts with NOx in the NOx reduced exhaust stream to improve the reduction of NOx and NH₃.