System for exhaust gas purification and method for exhaust gas purification using said system

• US 5,884,473 A
• Filed: 06/19/1996
• Issued: 03/23/1999
• Est. Priority Date: 06/23/1995
• Status: Expired due to Fees

• Current Assignee: NGK Insulators Limited
• Original Assignee: NGK Insulators Limited
• Inventors: Noda, Naomi, Takahashi, Akira, Shibagaki, Yukinari, Mizuno, Hiroshige
• Primary Examiner(s): Wolfe, Willis R.
• Application Number:
  US08/668,208
• Time in Patent Office: 1,007 Days
• Field of Search: 60/274, 60/297, 60/299, 60/301, 60/311, 422/170, 422/171, 422/177, 422/178, 422/180, 423/212, 423/213.2, 423/213.5, 423/213.7, 423/403, 502/325, 502/326, 502/334
• US Class Current: 60/274
• CPC Class Codes: B01D 53/945 characterised by a specific catalyst
• CPC Class Codes: B01D 53/9481 Catalyst preceded by an adsorption device without catalytic function for temporary storage of contaminants, e.g. during cold start
• 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: F01N 2240/18 an adsorber or absorber
• CPC Class Codes: F01N 2570/12 Hydrocarbons
• CPC Class Codes: F01N 3/0835 Hydrocarbons
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

A system for exhaust gas purification disposed in the exhaust pipe of an internal combustion engine, includes followings (i) a catalyst giving an excellent light-off performance at low temperatures, including a carrier and a catalyst layer supported thereon, the catalyst layer including a precious metal and a substance having an electron donatability and/or a nitrogen dioxide absorbability and releasability, and (ii) an adsorbent comprising a carrier and an adsorbent layer having a hydrocarbon adsorbability, supported on the carrier. This system for exhaust gas purification can effectively purify the harmful substances contained in the exhaust gases discharged from internal combustion engines of automobiles, etc., particularly the hydrocarbons discharged in a large amount from a gasoline engine during cold start.

Claims

1. A system for exhaust gas purification disposed in an exhaust pipe of an internal combustion engine, comprising:

a catalyst composition giving an excellent light-off performance at low temperatures, which comprises a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, and

optionally an adsorbent having hydrocarbon adsorbability.

2. A system for exhaust gas purification according to claim 1, wherein the combustible components contained in an exhaust gas to be purified are reacted with nitrogen dioxide in the presence of said catalyst composition giving an excellent light-off performance at low temperatures, at a temperature lower than the light-off temperature of the oxidation reaction between said combustible components and oxygen;

thereby, part of the exhaust gas is purified;

the heat generated by the above reaction increases the temperatures of said catalyst composition and its surroundings;

thereby, the hydrocarbons, nitrogen oxides and carbon monoxide contained in the exhaust gas are purified.

3. A system for exhaust gas purification according to claim 1, wherein the substance having an electron donatability, present in said catalyst composition giving an excellent light-off performance at low temperatures supplies electrons to the precious metal also present in said catalyst composition;

whereby, the adsorbability of the precious metal for at least one of hydrocarbons and carbon monoxide contained in an exhaust gas to be purified is reduced and said at least one of the hydrocarbons and carbon monoxide is reacted with oxygen at a temperature lower than the light-off temperature of a three-way catalyst not containing any substance having an electron donatability;

whereby, part of the exhaust gas is purified;

the heat generated by the above reaction increases the temperatures of said catalyst composition and its surroundings; and

whereby, the hydrocarbons, nitrogen oxides and carbon monoxide contained in the exhaust gas are purified.

4. A system for exhaust gas purification according to claim 1, wherein the precious metal is at least one of Pt, Pd and Rh.

5. A system for exhaust gas purification according to claim 1, wherein the precious metal is at least one of Pt and Pd.

6. A system for exhaust gas purification according to claim 1, wherein said adsorbent is disposed upstream of said catalyst composition in the flow path of exhaust gas.

7. A system for exhaust gas purification according to claim 1, wherein said adsorbent and said catalyst composition are disposed at nearly same positions in the flow path of exhaust gas with no distance being taken between them.

8. A system for exhaust gas purification according to claim 1, wherein another catalyst for exhaust gas purification is disposed downstream of said adsorbent and said catalyst composition in the flow path of exhaust gas.

9. A system for exhaust gas purification according to claim 1, wherein another catalyst for exhaust gas purification is disposed upstream of said adsorbent and said catalyst composition in the flow path of exhaust gas.

10. A system for exhaust gas purification according to claim 1, wherein said adsorbent contains a catalyst component.

11. A system for exhaust gas purification according to claim 10, wherein the adsorbent containing a catalyst component contains a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability.

12. A system for exhaust gas purification according to claim 10, wherein the adsorbent containing a catalyst component contains a rare earth element oxide.

13. A system for exhaust gas purification according to claim 1, wherein said adsorbent comprises zeolite.

14. A system for exhaust gas purification according to claim 13, wherein the zeolite has a SiO₂ /Al₂ O₃ molar ratio of 40 or more.

15. A system for exhaust gas purification according to claim 13, wherein the zeolite comprises at least one precious metal selected from the group consisting of Pt, Pd and Rh.

16. A system for exhaust gas purification according to claim 13, wherein the zeolite comprises at least one of the ions of group IB elements (Cu, Ag and Au) of the periodic table.

17. A system for exhaust gas purification according to claim 1, wherein the substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability is at least one element selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements, transition metals and actinide elements;

an oxide thereof;

or a compound oxide containing at least one of said elements.

18. A system for exhaust gas purification according to claim 17, wherein the at least one element is selected from the group consisting of Li, Cs, Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, La, Ce, Pr, Nd, Th and U.

19. A system for exhaust gas purification according to claim 17, wherein the at least one element is selected from the group consisting of Cs, Mg, Sr, Ba, Y, Zr, Hf, La, Ce and Th.

20. A system according to claim 17, wherein said at least one element is a member selected from the group consisting of Mg, Ba, Zr, La and Cs.

21. A system according to claim 17, wherein said compound oxide containing at least one of said elements is YBa₂ Cu₃ O₇.

81. A method for exhaust gas purification using the system for exhaust gas purification according to claim 1, 22 or 53, comprising at least one of adding an oxidizing gas to an exhaust gas to be purified and controlling the amounts of air and fuel fed into the engine so that the oxygen amount in the exhaust gas is increased, for a certain length of time during engine cold start.

22. A system for exhaust gas purification disposed in an exhaust pipe of an internal combustion engine, comprising:

a catalyst giving an excellent light-off performance at low temperatures, comprising a carrier and a catalyst layer supported thereon, the catalyst layer comprising a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, and

optionally an adsorbent comprising a carrier and an adsorbent layer having a hydrocarbon adsorbability, supported on the carrier.

23. A system for exhaust gas purification according to claim 22, wherein the combustible components contained in an exhaust gas to be purified are reacted with nitrogen dioxide in the presence of said catalyst giving an excellent light-off performance at low temperatures, at a temperature lower than the light-off temperature of the oxidation reaction between said combustible components and oxygen;

whereby, part of the exhaust gas is purified;

the heat generated by the above reaction increases the temperatures of said catalyst and its surroundings; and

the hydrocarbons, nitrogen oxides and carbon monoxide contained in the exhaust gas are purified.

24. A system for exhaust gas purification according to claim 22, wherein the substance having an electron donatability, present in said catalyst giving an excellent light-off performance at low temperatures supplies electrons to the precious metal also present in said catalyst;

whereby, the adsorbability of the precious metal for at least one of the hydrocarbons and carbon monoxide contained in an exhaust gas to be purified is reduced and said at least one of the hydrocarbons and carbon monoxide is reacted with oxygen at a temperature lower than the light-off temperature of a three-way catalyst not containing any substance having an electron donatability;

whereby, part of the exhaust gas is purified;

the heat generated by the above reaction increases the temperatures of said catalyst and its surroundings; and

the hydrocarbons, nitrogen oxides and carbon monoxide contained in the exhaust gas are purified.

25. A system for exhaust gas purification according to claim 22, wherein the catalyst layer of said catalyst comprises a layer containing a precious metal and a layer containing a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, with the individual layers being supported on one same carrier in a pile-up state.

26. A system for exhaust gas purification according to claim 22, wherein the precious metal and the substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability are present in a mixed state in the catalyst layer of the catalyst.

27. A system for exhaust gas purification according to claim 22, wherein the precious metal is at least one of Pt, Pd and Rh.

28. A system for exhaust gas purification according to claim 22, wherein the precious metal is at least one of Pt and Pd.

29. A system for exhaust gas purification according to claim 22, wherein said adsorbent is disposed upstream of said catalyst in the flow path of exhaust gas.

30. A system for exhaust gas purification according to claim 22, wherein said adsorbent and said catalyst are formed in one monolithic carrier and the adsorbent is disposed at the upstream side of the carrier and the catalyst is disposed at the downstream side of the carrier in the flow path of exhaust gas.

31. A system for exhaust gas purification according to claim 22, wherein another catalyst for exhaust gas purification is disposed downstream of said adsorbent and said catalyst in the flow path of exhaust gas.

32. A system for exhaust gas purification according to claim 22, wherein another catalyst for exhaust gas purification is disposed upstream of said adsorbent and said catalyst in the flow path of exhaust gas.

33. A system for exhaust gas purification according to claim 22, wherein the substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability is at least one element selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements, transition metals and actinide elements;

an oxide thereof;

or a compound oxide containing at least one of said elements.

34. A system for exhaust gas purification according to claim 33, wherein the at least one element is selected from the group consisting of Li, Cs, Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, La, Ce, Pr, Nd, Th and U.

35. A system for exhaust gas purification according to claim 33, wherein the at least one element is selected from the group consisting of Cs, Mg, Sr, Ba, Y, Zr, Hf, La, Ce and Th.

36. A system for exhaust gas purification according to claim 22, wherein the adsorbent layer of said adsorbent comprises a catalyst component.

37. A system for exhaust gas purification according to claim 36, wherein the adsorbent layer containing a catalyst component contains a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability.

38. A system for exhaust gas purification according to claim 36, wherein the adsorbent layer containing a catalyst component comprises a rare earth element oxide.

39. A system for exhaust gas purification according to claim 22, wherein a layer containing a catalyst component is formed on the surface of the adsorbent layer of said adsorbent or between the adsorbent layer and the carrier.

40. A system for exhaust gas purification according to claim 39, wherein the layer containing a catalyst component contains a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability.

41. A system for exhaust gas purification according to claim 39, wherein the layer containing a catalyst component comprises a rare earth element oxide.

42. A system for exhaust gas purification according to claim 22, wherein the adsorbent layer of said adsorbent comprises zeolite.

43. A system for exhaust gas purification according to claim 42, wherein the zeolite has a SiO₂ /Al₂ O₃ molar ratio of 40 or more.

44. A system for exhaust gas purification according to claim 42, wherein the zeolite contains at least one precious metal selected from the group consisting of Pt, Pd and Rh.

45. A system for exhaust gas purification according to claim 42, wherein the zeolite contains at least one of the ions of group IB elements (Cu, Ag and Au) of the periodic table.

46. A system for exhaust gas purification according to claim 22, wherein the carrier of said catalyst giving an excellent light-off performance at low temperatures is a monolithic carrier.

47. A system for exhaust gas purification according to claim 46, wherein the catalyst layer of said catalyst comprises a layer containing a precious metal and a layer containing a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, with the individual layers being supported on different monolithic carriers.

48. A system for exhaust gas purification according to claim 46, wherein the catalyst layer of said catalyst comprises a layer containing a precious metal and a layer containing a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, with the individual layers being supported on one same monolithic carrier apart in the flow direction of exhaust gas.

49. A system for exhaust gas purification according to claim 46, wherein the precious metal is supported in an amount of 10-700 g/ft³.

50. A system for exhaust gas purification according to claim 22, wherein the carrier of said adsorbent is a monolithic carrier.

51. A system for exhaust gas purification according to claim 50, wherein a blowing-through portion is formed in the monolithic carrier so as to allow the blowing of exhaust gas through the portion.

52. A system for exhaust gas purification according to claim 51, wherein the blowing-through portion is formed parallel to the passages of the monolithic carrier.

53. A system for exhaust gas purification disposed in an exhaust pipe of an internal combustion engine, comprising:

a catalyst giving an excellent light-off performance at low temperatures, comprising a carrier and a catalyst layer supported thereon, the catalyst layer comprising a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, and

optionally an adsorbent-catalyst comprising a monolithic carrier, an adsorbent layer having a hydrocarbon adsorbability and a catalyst layer having at least one of a three-way catalytic activity and an oxidizing ability, the adsorbent layer and the catalyst layer being separately supported on the monolithic carrier in at least part of the cross sections of the adsorbent-catalyst perpendicular to the flow direction of exhaust gas.

54. A system for exhaust gas purification according to claim 53, wherein the combustible components contained in an exhaust gas to be purified are reacted with nitrogen dioxide in the presence of said catalyst giving an excellent light-off performance at low temperatures, at a temperature lower than the light-off temperature of the oxidation reaction between said combustible components and oxygen;

whereby, part of the exhaust gas is purified;

the heat generated by the above reaction increases the temperatures of said catalyst and its surroundings; and

the hydrocarbons, nitrogen oxides and carbon monoxide contained in the exhaust gas are purified.

55. A system for exhaust gas purification according to claim 53, wherein the substance having an electron donatability, present in said catalyst giving an excellent light-off performance at low temperatures supplies electrons to the precious metal also present in said catalyst;

whereby, the adsorbability of the precious metal for at least one of the hydrocarbons and carbon monoxide is reacted with oxygen at a temperature lower than the light-off temperature of a three-way catalyst not containing any substance having an electron donatability;

whereby, part of the exhaust gas is purified;

the heat generated by the above reaction increases the temperatures of said catalyst and its surroundings; and

the hydrocarbons, nitrogen oxides and carbon monoxide contained in the exhaust gas are purified.

56. A system for exhaust gas purification according to claim 53, wherein the catalyst layer of said catalyst comprises a layer containing a precious metal and a layer containing a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, with the individual layers being supported on one same carrier in a pile-up state.

57. A system for exhaust gas purification according to claim 53, wherein the precious metal and the substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability are present in a mixed state in the catalyst layer of the catalyst.

58. A system for exhaust gas purification according to claim 53, wherein the precious metal is at least one of Pt, Pd and Rh.

59. A system for exhaust gas purification according to claims 53, wherein the precious metal is at least one of Pt and Pd.

60. A system for exhaust gas purification according to claim 53, wherein the adsorbent layer of said adsorbent-catalyst comprises zeolite.

61. A system for exhaust gas purification according to claim 60, wherein the zeolite has a SiO₂ /Al₂ O₃ molar ratio of 40 or more.

62. A system for exhaust gas purification according to claim 60, wherein the zeolite contains at least one precious metal selected from the group consisting of Pt, Pd and Rh.

63. A system for exhaust gas purification according to claim 60, wherein the zeolite contains at least one of the ions of group IB elements (Cu, Ag and Au) of the periodic table.

64. A system for exhaust gas purification according to claim 53, wherein said adsorbent-catalyst is disposed upstream of said catalyst in the flow path of exhaust gas.

65. A system for exhaust gas purification according to claim 53, wherein said adsorbent-catalyst and said catalyst are formed in one monolithic carrier and the adsorbent-catalyst is disposed at the upstream side of the carrier and the catalyst is disposed at the downstream side of the carrier in the flow path of exhaust gas.

66. A system for exhaust gas purification according to claim 53, wherein another catalyst for exhaust gas purification is disposed downstream of said adsorbent-catalyst and said catalyst in the flow path of exhaust gas.

67. A system for exhaust gas purification according to claim 53, wherein another catalyst for exhaust gas purification is disposed upstream of said adsorbent-catalyst and said catalyst in the flow path of exhaust gas.

68. A system for exhaust gas purification according to claim 53, wherein the substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability is at least one element selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements, transition metals and actinide elements;

an oxide thereof;

or a compound oxide containing at least one element mentioned above.

69. A system for exhaust gas purification according to claim 68, wherein the at least one element is selected from the group consisting of Li, Cs, Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, La, Ce, Pr, Nd, Th and U.

70. A system for exhaust gas purification according to claim 68, wherein the at least one element is selected from the group consisting of Cs, Mg, Sr, Ba, Y, Zr, Hf, La, Ce and Th.

71. A system for exhaust gas purification according to claim 53, wherein the adsorbent layer of said adsorbent-catalyst comprises a catalyst component.

72. A system for exhaust gas purification according to claim 71, wherein the adsorbent layer containing a catalyst component comprises a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability.

73. A system for exhaust gas purification according to claim 71, wherein the adsorbent layer containing a catalyst component contains a rare earth element oxide.

74. A system for exhaust gas purification according to claim 53, wherein a layer containing a catalyst component is formed on at least one of the surface of the adsorbent layer of said adsorbent-catalyst and between the adsorbent layer and the carrier.

75. A system for exhaust gas purification according to claim 74, wherein the layer containing a catalyst component contains a precious metal and a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability.

76. A system for exhaust gas purification according to claim 74, wherein the layer containing a catalyst component comprises a rare earth element oxide.

77. A system for exhaust gas purification according to claim 53, wherein the carrier of said catalyst giving an excellent light-off performance at low temperatures is a monolithic carrier.

78. A system for exhaust gas purification according to claim 77, wherein the catalyst layer of said catalyst comprises a layer containing a precious metal and a layer containing a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, with the individual layers being supported on different monolithic carriers.

79. A system for exhaust gas purification according to claim 77, wherein the catalyst layer of said catalyst comprises a layer containing a precious metal and a layer containing a substance having at least one of an electron donatability and a nitrogen dioxide absorbability and releasability, with the individual layers being supported on one same monolithic carrier apart in the flow direction of exhaust gas.

80. A system for exhaust gas purification according to claim 77, wherein the precious metal is supported in an amount of 10-700 g/ft³.