Patent ID: 6883305

Claim:
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 in an amount of from 0.25 to 3 grams per 100 grams of a carrier for said catalyst; 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.