Catalyst for purifying exhaust gas and exhaust gas purifying method

• US 6,461,579 B1
• Filed: 07/21/2000
• Issued: 10/08/2002
• Est. Priority Date: 12/08/1997
• Status: Expired due to Fees

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Ikeda, Yasuo, Hachisuka, Ichiro
• Primary Examiner(s): Silverman, Stanley S.
• Assistant Examiner(s): Vanoy, Timothy C.
• Application Number:
  US09/555,384
• Time in Patent Office: 809 Days
• Field of Search: 502/302, 502/303, 502/325, 502/328, 502/339, 423/213.2, 423/213.5, 423/239.1, 423/245.3, 423/247
• US Class Current: 423/213.5
• CPC Class Codes: B01D 53/8628 Processes characterised by a specific catalyst
• CPC Class Codes: B01D 53/945 characterised by a specific catalyst
• CPC Class Codes: B01J 23/002 Mixed oxides other than spinels, e.g. perovskite
• CPC Class Codes: B01J 23/464 Rhodium
• 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 2523/00 Constitutive chemical elements of heterogeneous catalysts
• CPC Class Codes: B01J 2523/11 Lithium
• CPC Class Codes: B01J 2523/13 Potassium
• CPC Class Codes: B01J 2523/23 Calcium
• CPC Class Codes: B01J 2523/25 Barium
• CPC Class Codes: B01J 2523/31 Aluminium
• CPC Class Codes: B01J 2523/3706 Lanthanum
• CPC Class Codes: B01J 2523/47 Titanium
• CPC Class Codes: B01J 2523/48 Zirconium
• CPC Class Codes: B01J 2523/822 Rhodium
• CPC Class Codes: B01J 2523/828 Platinum
• CPC Class Codes: B01J 35/19 Catalysts containing parts with different compositions
• CPC Class Codes: B01J 35/40 characterised by dimensions, e.g. grain size in a colloidal state B01J35/23; crystallite size B01J35/77
• CPC Class Codes: B01J 37/0248 Coatings comprising impregnated particles
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies

Abstract

A catalyst for purifying exhaust of an internal combustion engine is prepared by mixing first powders in which at least Pt is loaded on a first support and second powders in which at least Rh is loaded on a second support and loading NO_x occluding material, for example an alkaline-earth metal, alkali metal or rare-earth metal, at least on the first support. In such catalyst, the second support is made of a stabilized zirconia stabilized by alkaline-earth metal or rare-earth element. The second support, having been become alkaline by the alkaline-earth metal or the rare-earth element, is excellent in absorbing performance of the steam (H₂O), so that the steam reforming reaction by Rh advances sufficiently. Therefore, the created hydrogen greatly contributes to the reduction of NO_x and to the sulfur poisoning prevention of the NO_x occluding material. Also, the oxidizing ability of Pt is maintained high, Rh sufficiently exhibits the steam reforming reaction activity and the sulfur poisoning of NO_x occluding material is restrained. An exhaust gas from an internal combustion engine is combusted where mixed gas of rich atmosphere containing excessive fuel is supplied to mixed gas of lean atmosphere containing excessive oxygen like a pulse. The exhaust gas is then introduced to the catalyst wherein the exhaust gas is purified.

Claims

1. A catalyst for purifying exhaust gas comprising a mixture of first powders comprising platinum (Pt) loaded on a first support made of porous particles, and second powders comprising rhodium (Rh) loaded on a second support, wherein NO_x occluding material is loaded at least on the first support, and the second support is made of zirconia containing an alkaline-earth metal, wherein the alkaline-earth metal is present in an amount not more than 11.35 mole %.

2. A catalyst for purifying exhaust gas according to claim 1, wherein the alkaline-earth metal is selected from the group consisting of barium and calcium.

3. An exhaust gas purifying method for purifying exhaust gas discharged from an internal combustion engine in which fuel is combusted in condition where mixed gas of rich atmosphere containing excessive fuel is supplied to mixed gas of lean atmosphere containing excessive oxygen like a pulse, by contacting the exhaust gas with a catalyst for purifying exhaust gas comprising a mixture of first powders comprising platinum (Pt) loaded on a first support made of porous particles, and second powders comprising rhodium (Rh) loaded on a second support, wherein NO_x occluding material is loaded at least on the first support, and the second support is made of zirconia containing an alkaline-earth metal, wherein the alkaline-earth metal is present in an amount not more than 11.35 mole %.

4. An exhaust gas purifying method according to claim 3, wherein the alkaline-earth metal is selected from the group consisting of barium and calcium.

5. A catalyst for purifying exhaust gas comprising a mixture of first powders comprising platinum (Pt) loaded on a first support made of porous particles, and second powders comprising rhodium (Rh) loaded on a second support, wherein NO_x occluding material is loaded at least on the first support, and the second support is made of zirconia containing a rare-earth metal, wherein the rare-earth metal is present in an amount not more than 11.0 mole %.

6. A catalyst for purifying exhaust gas according to claim 5, wherein the rare-earth element is lanthanum.

7. An exhaust gas purifying method for purifying exhaust gas discharged from an internal combustion engine in which fuel is combusted in condition where mixed gas of rich atmosphere containing excessive fuel is supplied to mixed gas of lean atmosphere containing excessive oxygen like a pulse, by contacting the exhaust gas with a catalyst for purifying exhaust gas comprising a mixture of first powders comprising platinum (Pt) loaded on a first support made of porous particles, and second powders comprising rhodium (Rh) loaded on a second support, wherein NO_x occluding material is loaded at least on the first support, and the second support is made of zirconia containing a rare-earth element, wherein the rare-earth metal is present in an amount not more than 11.0 mole %.

8. An exhaust gas purifying method according to claim 7, wherein