Catalyst for purifying exhaust gases

• US 20020081255A1
• Filed: 10/25/2001
• Published: 06/27/2002
• Est. Priority Date: 11/06/2000
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Cutler, Willard A., Ogunwumi, Steven B., Lakhwani, Shahid G., Day, J. Paul
• Granted Patent: US 6,897,182 B2
• Time in Patent Office: Days
• US Class Current: 423/213.5
• CPC Class Codes: B01D 2255/102 Platinum group metals
• CPC Class Codes: B01D 2255/2022 Potassium
• CPC Class Codes: B01D 2255/2042 Barium
• CPC Class Codes: B01D 2255/2045 Calcium
• CPC Class Codes: B01D 2255/2047 Magnesium
• CPC Class Codes: B01D 2255/206 Rare earth metals
• CPC Class Codes: B01D 2255/91 NOx-storage component incorporated in the catalyst
• CPC Class Codes: B01D 53/865 characterised by a specific catalyst
• CPC Class Codes: B01D 53/9422 for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
• CPC Class Codes: B01J 23/58 with alkali- or alkaline earth metals
• CPC Class Codes: B01J 23/63 with rare earths or actinides
• CPC Class Codes: B01J 37/0215 Coating
• CPC Class Codes: C04B 2111/00793 as filters or diaphragms
• CPC Class Codes: C04B 2111/0081 as catalysts or catalyst carriers
• CPC Class Codes: C04B 2235/3206 Magnesium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3208 Calcium oxide or oxide-forming salts thereof, e.g. lime
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/3222 Aluminates other than alumino-silicates, e.g. spinel (MgAl2O4)
• CPC Class Codes: C04B 2235/3234 Titanates, not containing zirconia
• CPC Class Codes: C04B 2235/3236 Alkaline earth titanates
• CPC Class Codes: C04B 2235/3244 : Zirconium oxides, zirconates, hafnium oxides, hafnates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3272 : Iron oxides or oxide forming salts thereof, e.g. hematite, magnetite
• CPC Class Codes: C04B 2235/80 : Phases present in the sintered or melt-cast ceramic products other than the main phase
• CPC Class Codes: C04B 35/117 : Composites
• CPC Class Codes: C04B 35/44 : based on aluminates
• CPC Class Codes: C04B 35/462 : based on titanates
• CPC Class Codes: C04B 35/465 : based on alkaline earth metal titanates
• CPC Class Codes: C04B 38/0006 : Honeycomb structures from one or more corrugated sheets by winding or stacking C04B38/0083
• 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

Abstract

A catalyst for purification of exhaust gases including (1) a catalysis-promoting coating comprising a noble metal catalyst and a NOx storage component loaded onto a carrier material, wherein the NOx storage component comprises an alkali metal and, (2) a ceramic substrate for supporting the catalysis-promoting coating, wherein the ceramic substrate exhibits resistance to alkali metal migration below 1000° C. and a coefficient of thermal expansion of less than about 25×10⁻⁷/° C. (25-800° C.). A second aspect of, the invention is a process for purifying an exhaust gas from a lean burn engine involving simultaneously removing carbon monoxide, hydrocarbons and nitrogen oxides by bringing the exhaust gas from a lean burn engine into contact with the exhaust gas purifying catalyst of the present invention disclosed above. In this process a majority of the nitrogen oxides in the exhaust gas are adsorbed to the NOx storage component on the porous support under a lean burn atmosphere in which oxidizing concentrations are above a stoichiometric point that is required for oxidizing components to be oxidized in the exhaust gas. Furthermore, when the exhaust gas is temporarily change from lean burn to fuel-rich, the adsorbed nitrogen oxides are released and chemically reduced by a reaction with the hydrocarbons and carbon monoxide in the exhaust gas under a stoichiometric atmosphere or a fuel-rich atmosphere in which oxygen concentrations are below stoichiometric point.

Claims

1. A catalyst for purification of exhaust gases in oxygen-rich atmospheres in which oxygen concentrations of the exhaust gases are at the stoichiometric point or more required for oxidizing components to oxidized therein, consisting essentially of:

(1) a catalysis-promoting coating comprising a noble metal catalyst and a NOx storage component loaded onto a carrier material, wherein the NOx storage component comprises an alkali metal and,

(2) a ceramic substrate for supporting the catalysis-promoting coating, wherein the ceramic substrate exhibits resistance to alkali metal migration below 1000°

C., and a coefficient of thermal expansion of less than about 25×

10<sup>−

7</sup>/°

C. (25-800°

C.).

2. The catalyst according to claim 1 wherein the substrate comprises a silicate and phosphate free material.

3. The catalyst according to claim 2 wherein the material selected from the group consisting of calcium aluminate, magnesium dititanate, iron titanate zirconium titanate, and mixtures and solid solutions thereof.

4. The catalyst according to claim 2 wherein the substrate comprises a material selected from the group consisting of 1:

1 CaO;

Al₂O₃, 1;

2 CaO;

Al₂O₃, and combinations thereof.

5. The catalyst according to claim 3 wherein the material further includes a second phase formed with constituents selected from the group consisting of K₂Al₂O₄, Li₂Al₂O₄, MgAl₂O₄, ZnO, SrO and Y₂O₃.

6. The catalyst according to claim 2 wherein the substrate comprises a mixture of 50% Fe₂TiO₅ and 50% ZrTiO₄.

7. The catalyst according to claim 2 wherein the substrate comprises a mixture of 50% MgTi₂O₅ and 50% ZrTiO₄.

8. The catalyst according to claim 1 wherein the substrate exhibits a coefficient of thermal expansion of less than about 15×

10<sup>−

7</sup>/°

C. (25-800°

C.).

9. The catalyst according to claim 2 wherein the carrier material is comprised of a material selected from the group consisting of alumina, zeolite, zirconia, or combinations thereof.

10. The catalyst according to claim 1 wherein the alkali metal of the NO_x storage component is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and francium (Fr).

11. The catalyst according to claim 8 wherein the alkali metal of the NO_x storage component is potassium (K).

12. The catalyst according to claim 10 wherein the NOx storage component further includes a component selected from the group consisting of an alkali-earth metal, a rare earth metal, and combinations thereof.

13. The catalyst according to claim 12 wherein the alkaline-earth metal is selected from the group consisting of barium (Ba), beryllium (Be), magnesium (Mg), calcium (Ca) and strontium (Sr).

14. The catalyst according to claim 13 wherein the NO_x storage component is barium (Ba), magnesium (Mg), or calcium (Ca).

15. The catalyst according to claim 12 wherein rare-earth metal is selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), and neodymium (Nd).

16. The catalyst according to claim 1 wherein the NO_x storage component is loaded in an amount which is effective to store NO_x, in exhaust gases whose oxygen are at stoichiometric point or more than required for oxidizing carbon monoxide (CO) and hydrocarbons (HC).

17. The catalyst according to claim 1 wherein the NO_x storage component is loaded in an amount ranging from 0.025 to 0.5 moles with respect to 1 liter of the porous support.

18. The catalyst according to claim 1 wherein the noble metal catalyst is at least one element selected from the group consisting of platinum (Pt), rhodium (Rh) and palladium (Pa).

19. The catalyst according to claim 1 wherein the noble metal catalyst is loaded in an amount which is effective to purify NOx, CO and HC in exhaust gases whose oxygen are at stoichiometric point or more than required for oxidizing carbon monoxide (CO) and hydrocarbons (HC).

20. The catalyst according to claim 1 wherein the noble metal catalyst is loaded in an amount ranging from 0.1 to 20 grams with respect to 1 liter of the porous support.

21. The catalyst according to claim 1 comprised of a support substrate of calcium aluminate, a carrier material of gamma alumina, a NOx storage component of potassium (K) and a noble metal catalyst of platinum (Pt).

22. A process for purifying an exhaust gas from a lean burn engine, the process comprising:

(a) simultaneously removing carbon monoxide, hydrocarbons and nitrogen oxides by bringing the exhaust gas from a lean burn engine into contact with an exhaust gas purifying catalyst consisting essentially of;

(1) a catalysis-promoting coating comprising a noble metal catalyst and a NOx storage component loaded onto a carrier material, wherein the NOx storage component comprises an alkali metal and,

(2) a ceramic substrate for supporting the catalysis-promoting coating, wherein the ceramic substrate exhibits resistance to alkali metal migration below 1000°

C. and a coefficient of thermal expansion of less than about 25×

10<sup>−

7</sup>/°

C. (25-800°

C.),

wherein a majority of the nitrogen oxides in the exhaust gas are adsorbed to the NO_x storage component on the porous support under a lean burn atmosphere in which oxidizing concentrations are above a stoichiometric point that is required for oxidizing components to be oxidized in the exhaust gas, the exhaust gas is temporarily change from lean burn to fuel-rich, and the adsorbed nitrogen oxides are released and chemically reduced by a reaction with the hydrocarbons and carbon monoxide in the exhaust gas under a stoichiometric atmosphere or a fuel-rich atmosphere in which oxygen concentrations are below stoichiometric point.

23. The method according to claim 22 wherein the catalyst is comprised of a support substrate of calcium aluminate, a carrier material of gamma alumina, a NOx storage component of potassium (K) and a noble metal catalyst of platinum (Pt).