Method for purifying exhaust gas

A method for purifying exhaust gas discharged from an internal combustion engine of a vehicle, using an exhaust gas purifying catalyst comprising a composite oxide represented by the following general formula (1):

• AO.x(B2-yCyO3-α) (1)
• wherein A represents an element selected from monovalent elements, divalent elements and lanthanides;
• B represents a trivalent element;
• and C represents a noble metal;
• x represents an integer of 1;
• y represents an atomic ratio satisfying the following relation:
• 0<y<2;
• and α represents a deficient atomic ratio of oxygen atoms;
• and
• wherein the composite oxide has a spinel type crystal phase, and
• wherein the exhaust gas purifying catalyst removes carbon monoxide (CO) exhaust gas discharged from the internal combustion engine of the vehicle.

A method for producing a catalyst composition comprising a composite oxide represented by the following general formula (1):

• AO.x(B2-yCyO3-α) (1)
• wherein A represents an element selected from monovalent elements, divalent elements and lanthanides;
• B represents a trivalent element;
• and c represents a noble metal;
• x represents an integer of 1;
• y represents an atomic ratio satisfying the following relation:
• 0<y<2;
• and α represents a deficient atomic ratio of oxygen atoms;
• the method comprising:
• a coprecipitation step of coprecipitating a mixture of a salt of A and a salt of B from the elements of the composite oxide AO.x(B2-yCyO3-α),
• a primary baking of primarily baking a coprecipitate after drying at a temperature of 500 to 1000° C., thereby producing a primary composite oxide, and
• a secondary baking step of secondarily baking the primary composite oxide, after adding a salt solution of C thereto and drying, at a temperature of 500 to 1400° C., thereby producing a composite oxide represented by the above general formula (1).