Method of treating diesel exhaust gases

• US 6,813,884 B2
• Filed: 01/29/2002
• Issued: 11/09/2004
• Est. Priority Date: 01/29/2002
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: McCabe, Robert Walter, Carberry, Brendan Patrick, Shigapov, Albert Nazipovich
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, DIEM T
• Application Number:
  US09/683,642
• Publication Number:
  US 20030140620A1
• Time in Patent Office: 1,015 Days
• Field of Search: 602/95, 602/97, 603/11, 423/215.5, 55D/IG.30
• US Class Current: 60/295
• CPC Class Codes: B01D 2251/2062 Ammonia
• CPC Class Codes: B01D 2251/2067 Urea
• CPC Class Codes: B01D 2251/208 Hydrocarbons
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 53/9418 for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2610/08 with prior mixing of the substances with a gas, e.g. air
• CPC Class Codes: F01N 3/0231 using special exhaust apparatus upstream of the filter for producing nitrogen dioxide, e.g. for continuous filter regeneration systems [CRT]
• CPC Class Codes: F01N 3/035 with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/206 Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents F01N3/2066 takes precedence

Abstract

A diesel exhaust treatment system and method of oxidizing NO to NO₂ at low temperatures are provided. The system utilizes a platinum catalyst on a zirconia-stabilized silica support which oxidizes NO in the exhaust gas to NO₂ and uses the NO₂ in an amount sufficient to oxidize particulate trapped on a particulate filter. The catalyst is preferably pre-treated at a temperature of between about 500 to 650° C. in a NO-oxygen-nitrogen mixture to increase conversion at low temperatures. The catalyst preferably includes an additional oxide component selected from the group consisting of TiO₂, P₂O₅, WO₃, B₂O₃, and Al₂O_3. or a heteropolyacid component to further increase activity at low temperatures or to decrease platinum loading at the same level of performance.

Claims

1. A diesel exhaust gas treatment system comprising:

an oxidation catalyst positioned in an exhaust gas passage of a diesel engine for converting at least a portion of NO contained in said exhaust gas to NO₂ at a temperature between about 175°

C. to 250°

C., said oxidation catalyst comprising platinum and a support material comprising zirconia-silica, said support material having strong acid sites; and

a particulate filter for receiving said exhaust gas.

2. The system of claim 1 wherein said oxidation catalyst is positioned between said exhaust passage and said particulate filter.

3. The system of claim 1 wherein said oxidation catalyst is combined with said particulate filter.

4. The system according to claim 1 further including a second catalyst positioned downstream from said particulate filter.

5. The system according to claim 4 wherein said second catalyst comprises a selective reduction catalyst.

6. The system according to claim 1 further including a NOx trap positioned downstream from said oxidation catalyst.

7. The system of claim 1 wherein said oxidation catalyst comprises from about 1 to 5 wt. % platinum on a support containing from about 3 to 20 wt. % zirconia, and the balance silica.

8. The system of claim 1 wherein said support includes one or more oxides selected from the group consisting of TiO₂, P₂O₅, WO₃, B₂O₃, and Al₂O₃.

9. The system of claim 1 wherein said support has been prepared with the addition of a heteropolyacid selected from H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀.

10. The diesel exhaust gas treatment system of claim 1 wherein said zirconia-silica support has been formed by impregnating silica gel with a zirconium citrate ammonium complex, drying said support, and calcinating said support at 800°

C.

11. A method for treating diesel exhaust gases comprising:

positioning an oxidation catalyst in an exhaust gas passage of a diesel engine, said oxidation catalyst comprising platinum and a support material comprising zirconia-stabilized silica, said support material having strong acid sites;

providing a particulate filter downstream of said oxidation catalyst;

exposing said oxidation catalyst to diesel exhaust gas containing NO such that at least a portion of said NO contained in said exhaust gas is converted to NO₂ at a temperature between about 175°

C. to 250°

C.; and

passing said NO₂ through said particulate filter in an amount sufficient to oxidize particulate matter trapped on said filter.

12. The method of claim 11 wherein said oxidation catalyst comprises from about 1 to 5 wt. % platinum on a support containing from about 3 to 20 wt. % zirconia and the balance silica.

13. The method of claim 11 including pretreating said oxidation catalyst in a gas mixture containing NO, O₂ and N₂ prior to positioning said catalyst in said exhaust stream.

14. The method of claim 13 wherein said gas mixture comprises about 500 ppm of NO, about 3% by volume O₂, and the balance N₂.

15. The method of claim 13 wherein said pretreatment is carried out a temperature of between about 500 to 650°

C.

16. The method of claim 11 including adding one or more oxides to said support prior to positioning said oxidation catalyst in said exhaust stream, said one or more oxides being selected from the group consisting of TiO₂, P₂O₅, WO₃, B₂O₃, and Al₂O₃.

17. The method of claim 11 including adding a heteropolyacid selected from H₃PW₁₂O₄₀ and H₄SiW₁₂O₄₀ to said support prior to positioning said oxidation catalyst in said exhaust stream.

18. The method of claim 11 wherein about 60% to about 96% of NO contained in said exhaust gas is converted to NO₂.

19. The method of claim 11 further including providing a second catalyst downstream of said particulate filter and passing said exhaust gas over said second catalyst.

20. The method of claim 19 wherein said second catalyst is a selective reduction catalyst.

21. The method of claim 11 further including a NOx trap positioned downstream of said oxidation catalyst.

22. The method of claim 11 wherein said conversion of NO to NO₂ occurs at a temperature of between about 200 to 250°

C.

23. The method of claim 11 wherein said oxidation of particulate occurs at a temperature less than about 250°

C.

24. A method for treating diesel exhaust gases comprising:

positioning an oxidation catalyst in an exhaust gas passage of a diesel engine, said oxidation catalyst comprising platinum and a support material comprising zirconia-stabilized silica, said support material having strong acid sites;

providing a particulate filter in combination with said oxidation catalyst;

exposing said oxidation catalyst to diesel exhaust gas containing NO such that at least a portion of said NO contained in said exhaust gas is converted to NO₂ at a temperature between about 175°

C. to 250°

C.; and

passing said NO₂ through said particulate filter in an amount sufficient to oxidize particulate matter trapped on said filter.

25. A diesel exhaust gas treatment system comprising:

a particulate filter for receiving diesel exhaust gas from a diesel engine;

an oxidation catalyst for converting at least a portion of NO contained in said diesel exhaust gas to NO₂ at a temperature between about 175°

C. to 250°

C., said oxidation catalyst comprising platinum and a support material comprising zirconia-silica, said support material having strong acid sites;

wherein said oxidation catalyst is impregnated in said particulate filter.

26. A diesel exhaust gas treatment system comprising:

a first oxidation catalyst for converting at least a portion of NO contained in said diesel exhaust gas to NO₂ at a temperature of between about 175°

C. to 250°

C., said oxidation catalyst comprising platinum and a support material comprising zirconia-silica, said support material having strong acid sites; and

a second oxidation catalyst different from said first oxidation catalyst;

wherein said first and second oxidation catalyst are positioned in combination in the exhaust gas passage of a diesel engine.