Method for cleaning exhaust gas from an internal combustion engine

An exhaust gas cleaning method for an internal combustion engine, comprising:

• placing an exhaust gas cleaning catalyst in an exhaust gas flow path of the internal combustion engine, said catalyst capturing NOx when the air-fuel ratio of exhaust gas is higher than theoretical air-fuel ratio, and removing said captured NOx by reduction when the air-fuel ratio of exhaust gas is less than or equal to theoretical air-fuel ratio;
• and
• causing an exhaust gas having an air-fuel ratio higher than the theoretical air-fuel ratio and an exhaust gas having an air-fuel ratio less than or equal to the theoretical air-fuel ratio alternately to contact said catalyst, thereby removing nitrogen oxides in exhaust gas;
• wherein;
• said catalyst contains;
• at least one alkaline or alkaline earth metal selected from a first group consisting of Na, Mg, K, Li, Cs, Sr and Ca, on the surface of a porous carrier;
• at least one element selected from a second group consisting of Pd, Ir and Ru;
• and
• at least one element selected from a third group consisting of Ti, Si and Zr;
• ratios of components relative to 100 parts by weight of said porous carrier are 5 to 30 parts by weight for alkaline metal or alkaline earth metal in total, 8 to 35 parts by weight for Ti, 3 to 25 parts by weight for Si, 3 to 25 parts by weight for Zr, 0.05 to 0.5 parts by weight for Rh, 1.5 to 5 parts by weight for Pt, and 0.25 to 3 parts by weight for Pd, Ir and Ru in total;
• said catalyst has a CO desorption capacity that reaches a maximum level at a temperature within the range from 200 to 220° C. when a heating test is performed exclusively on said catalyst by heating it at the rate of 5 to 10° C./min. in a He gas flow after said catalyst is saturated with CO by adsorption at 100° C.;
• said catalyst comprises a composite oxide formed between said at least one element selected from said first group and said at least one element selected from said third group.

An exhaust gas cleaning method for an internal combustion engine, comprising:

• placing an exhaust gas cleaning catalyst in an exhaust gas flow path of the internal combustion engine, said catalyst capturing NOx when the air-fuel ratio of exhaust gas is higher than theoretical air-fuel ratio, and removing said captured NOx by reduction when the air-fuel ratio of exhaust gas is less than or equal to theoretical air-fuel ratio;
• and
• causing an exhaust gas having an air-fuel ratio higher than the theoretical air-fuel ratio and an exhaust gas having an air-fuel ratio less than or equal to the theoretical air-fuel ratio alternately to contact said catalyst, thereby removing nitrogen oxides in exhaust gas;
• wherein;
• said catalyst contains;
• at least one alkaline or alkaline earth metal selected from a first group consisting of Na, Mg, K, Li, Cs, Sr and Ca, on the surface of a porous carrier;
• a CO adsorbent compound comprising at least one element selected from a second group consisting of Pd, Ir and Ru;
• and
• at least one element selected from a third group consisting of Ti, Si and Zr;
• ratios of components relative to 100 parts by weight of said porous carrier are 5 to 30 parts by weight for alkaline metal or alkaline earth metal in total, 8 to 35 parts by weight for Ti, 3 to 25 parts by weight for Si, 3 to 25 parts by weight for Zr, 0.05 to 0.5 parts by weight for Rh, 1.5 to 5 parts by weight for Pt, and 0.25 to 3 parts by weight for Pd, Ir and Ru in total;
• said catalyst has a CO desorption capacity that reaches a maximum level at a temperature within the range from 200 to 220° C. when a heating test is performed exclusively on said catalyst by heating it at the rate of 5 to 10° C./min. in a He gas flow after said catalyst is saturated with CO by adsorption at 100° C.;
• and
• said catalyst comprises a composite oxide formed between said at least one element selected from said first group and said at least one element selected from said third group.

A method for cleaning an exhaust gas emitted from an internal combustion engine, wherein:

• exhaust gas having an air-fuel ratio higher than a theoretical air-fuel ratio and exhaust gas having an air-fuel ratio less than or equal to the theoretical air-fuel ratio are alternately made to contact a catalyst to clean the exhaust gas discharged from the internal combustion engine thereby removing nitrogen oxides in exhaust gas;
• said catalyst contains;
• at least one element selected from a first group consisting of alkaline and alkaline earth metals;
• Rh and Pt;
• at least one element selected from a second group consisting of Ti, Si and Zr;
• and
• a CO adsorbent component where the absolute value of CO adsorbent enthalpy on the metal single crystal surface is 142 KJ/mol or more, said CO adsorbent component comprising at least one element selected from the group consisting of Pd, Ir, and Ru;
• said catalyst has a CO desorption capacity that reaches a maximum level at a temperature within the range from 200 to 220° C. when a heating test is performed exclusively on said catalyst by heating at the rate of 5 to 10° C./min. in a He gas flow after said catalyst is saturated with CO by adsorption at 100° C.;
• and
• said catalyst comprises a composite oxide formed between said at least one element selected from said first group and said at least one element selected from said second group.

A method for cleaning an exhaust gas emitted from an internal combustion engine, wherein:

• exhaust gas having an air-fuel ratio higher than a theoretical air-fuel ratio and exhaust gas having an air-fuel ratio less than or equal to the theoretical air-fuel ratio are alternately made to contact a catalyst to clean the exhaust gas discharged from the internal combustion engine thereby removing nitrogen oxides in exhaust gas;
• said catalyst contains;
• at least one element selected from a first group consisting of alkaline and alkaline earth metals;
• Rh and Pt;
• at least one element selected from a second group consisting of Ti, Zr;
• and
• a CO adsorbent component where the absolute value of CO adsorbent enthalpy on the metal single crystal surface is 142 KJ/mol or more, said CO adsorbent component comprising at least one element selected from the group consisting of Pd, Ir, and Ru;
• said catalyst has a CO desorption capacity that reaches a maximum level at a temperature within the range from 200 to 220° C. when a heating test is performed exclusively on said catalyst by heating at the rate of 5 to 10° C./min. in a He gas flow after said catalyst is saturated with CO by adsorption at 100° C.;
• said catalyst comprises a composite oxide formed between said at least one element selected from said first group and said at least one element selected from said second group;
• and
• said composite oxide is formed by heat treatment of said catalyst.