Method of purifying exhaust gas of internal combustion engine and apparatus thereof

• US 6,305,161 B1
• Filed: 12/09/1998
• Issued: 10/23/2001
• Est. Priority Date: 12/09/1997
• Status: Expired due to Term

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Hitachi, Ltd., Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Oono, Hiroshi, Takanohashi, Toshikatsu, Kuroda, Osamu, Iizuka, Hidehiro, Yamashita, Hisao, Kitahara, Yuichi
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): Tran, Binh
• Application Number:
  US09/207,600
• Time in Patent Office: 1,049 Days
• Field of Search: 602/86, 602/74, 602/95, 602/97, 602/99, 603/01, 603/03, 603/02
• US Class Current: 60/301
• CPC Class Codes: B01D 2251/208 Hydrocarbons
• CPC Class Codes: B01D 2255/1021 Platinum
• CPC Class Codes: B01D 2255/1023 Palladium
• CPC Class Codes: B01D 2255/1025 Rhodium
• CPC Class Codes: B01D 2255/2022 Potassium
• CPC Class Codes: B01D 2255/2027 Sodium
• CPC Class Codes: B01D 2255/2045 Calcium
• CPC Class Codes: B01D 2255/2047 Magnesium
• CPC Class Codes: B01D 2255/2063 Lanthanum
• CPC Class Codes: B01D 2255/2065 Cerium
• CPC Class Codes: B01D 2255/20707 Titanium
• 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: B01D 53/9495 Controlling the catalytic process
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• 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: F02D 41/0275 the exhaust gas treating apparatus being a NOx trap or adsorbent

Abstract

A method of and apparatus for purifying an exhaust gas of an internal combustion engine comprising an NO_x purifying catalyst arranged in an exhaust gas passage, wherein the NO_x purifying catalyst is made of a composite material containing at least one kind of element selected from alkaline metals and alkaline earth metals, at least one kind of element selected from rare earth metals, at least one kind of element selected from platinoid metals, and titanium (Ti), the NO_x purifying catalyst adsorbing NO_x in the exhaust gas onto the surface when the exhaust gas is lean, and reducing the adsorbed NO_x to N₂ when the exhaust gas is stoichiometric or rich, and wherein the exhaust gas is purified by adsorbing NO_x in the exhaust gas in the NO_x purifying catalyst when the internal combustion engine is being operated under a lean condition, and by setting, after the adsorption, the exhaust gas to a stochiometric state or a rich state for 0.5 second to 4.5 seconds to reduce the NO_x adsorbed in said NO_x purifying catalyst to N₂ through catalytic reaction with the reducing agent.

Claims

1. A method of purifying an exhaust gas of an internal combustion engine comprising an NO_x purifying catalyst arranged in an exhaust gas passage, wherein

said NO_x purifying catalyst is made of a composition consisting of at least one kind of element selected from the group consisting of rare earth metals, at least one kind of element selected from the group consisting of alkaline metals and alkaline earth metals, at least one kind of element selected from the group consisting of platinoid metals (so-called noble metals), and titanium (Ti), said NO_x purifying catalyst adsorbing NO_x in the exhaust gas onto a surface thereof when the exhaust gas is lean, and reducing the adsorbed NO_x to N₂ when the exhaust gas is not leaner than stoichiometric, and wherein

the exhaust gas is purified by adsorbing NO_x in the exhaust gas onto said NO_x purifying catalyst when the internal combustion engine is being operated under a lean condition, and by setting, after the adsorption, the exhaust gas to an air-fuel ratio state not leaner than stoichiometric for 0.5 second to 4.5 seconds to reduce the NO_x adsorbed on said NO_x purifying catalyst to N₂ through catalytical reaction with a reducing agent.

2. A method of purifying an exhaust gas of an internal combustion engine according to claim 1, wherein said alkaline metal of said NO_x purifying catalyst is potassium (K) and sodium (Na), said alkaline earth metal being magnesium (Mg), calcium (Ca) and strontium (Sr), said rare earth metal being lanthanum (La) and cerium (Ce), said platinoid metal being platinum (Pt), rhodium (Rh) and palladium (Pd).

3. A method of purifying an exhaust gas of an internal combustion engine according to claim 1, wherein said compositition is supported on a heat resistant porous metal oxide.

4. A method of purifying an exhaust gas of an internal combustion engine according to claim 1, wherein in said not leaner than stoichiometric state, a depth of said rich state is between 13.0 to 14.7 by air-to-fuel ratio A/F.

9. A method of purifying an exhaust gas of an internal combustion engine according to claim 1, wherein said engine is a gasoline engine.

5. An apparatus for purifying an exhaust gas of an internal combustion engine comprising an NO_x purifying catalyst arranged in an exhaust gas passage and a control unit, wherein

said NO_x purifying catalyst is made of a composition consisting of at least one kind of element selected from the group consisting of alkaline metals and alkaline earth metals, at least one kind of element selected from the group consisting of rare earth metals, at least one kind of element selected from the group consisting of platinoid metals, and titanium (Ti), said NO_x purifying catalyst adsorbing NO_x in the exhaust gas on the surface when the exhaust gas is lean, and reducing the adsorbed NO_x to N₂ when the exhaust gas is not leaner than stoichiometric, and wherein

said control unit has air-to-fuel ratio control means, said air-to-fuel ratio control means having means for controlling the exhaust gas to a not leaner than stoichiometric state for 0.5 second to 4.5 seconds to purify the exhaust gas by reducing the NO_x adsorbed on said NO_x purifying catalyst to N₂ through catalytic reaction with a reducing agent when the internal combustion engine is being operated under a lean condition.

6. An apparatus for purifying an exhaust gas of an internal combustion engine according to claim 5, wherein said alkaline metal of said NO_x purifying catalyst is potassium (K) and sodium (Na), said alkaline earth metal being magnesium (Mg), calcium (Ca) and strontium (Sr), said rare earth metal being lanthanum (La) and cerium (Ce), said platinoid metal being platinum (Pt), rhodium (Rh) and palladium (Pd).

7. An apparatus for purifying an exhaust gas of an internal combustion engine according to claim 5, wherein said compositition is supported on a heat resistant porous metal oxide.

8. An apparatus for purifying an exhaust gas of an internal combustion engine according to claim 5, wherein in said control of the exhaust gas to a not leaner than stoichiometric state, a depth of said rich state is between 13.0 to 14.7 by air-to-fuel ratio A/F.