Catalyst for purifying exhaust gas
View Patent ↗PROBLEM The present invention is directed to provide a catalyst for purifying exhaust gas capable of maintaining a superior catalytic performance even when the catalyst is exposed to an exhaust gas at a high temperature of 800° C. or higher. SOLUTION The catalyst for purifying exhaust gas of the present invention comprises a catalytically active component containing a noble metal and a promoter containing an oxygen storage material both being supported on a carrier. The oxygen storage material comprises cerium, zirconium, and iron, and content of iron in the oxygen storage material is 0.01% by mass or more and less than 0.70% by mass (Fe 2 O 3 conversion) relative to the total mass of the oxygen storage material. And the oxygen storage material is (a) a complex oxide or a solid solution of iron and a metal comprising cerium and zirconium; or (b) an iron is supported on a complex oxide or a solid solution of a metal comprising cerium and zirconium.
1. A catalyst for purifying exhaust gas comprising at least two catalyst layers laminated on a carrier, at least one of the catalyst layers having a catalytically active component containing a noble metal and also having a promoter component containing an oxygen storage material, wherein:
the oxygen storage material comprises cerium, zirconium and iron;
the content of iron in the oxygen storage material is 0.01% by mass or more and less than 0.70% by mass (calculated as Fe 2 O 3 ) relative to the total mass of the oxygen storage material; and
the oxygen storage material is
(a) a complex oxide or a solid solution of iron, cerium, and zirconium; or
(b) an iron supported on the surface of a complex oxide or a solid solution of cerium and zirconium; and wherein different noble metals are arranged in different layers of the at least two catalyst layers.
2. The catalyst for purifying exhaust gas according to claim 1 , wherein the oxygen storage material further comprises at least a metal selected from the group consisting of lanthanum, yttrium, neodymium, and praseodymium.
3. The catalyst for purifying exhaust gas according to claim 1 , wherein the noble metal comprises at least a metal selected from the group consisting of platinum, palladium, and rhodium.
4. The catalyst for purifying exhaust gas according to claim 3 , wherein the oxygen storage material exists in a rhodium-containing layer among the catalyst layers.
5. The catalyst for purifying exhaust gas according to claim 1 , wherein the carrier has a 3-dimensional structure.
6. The catalyst for purifying exhaust gas according to claim 2 , wherein the noble metal comprises at least one metal selected from a group consisting of platinum, palladium, and rhodium.
7. The catalyst for purifying exhaust gas according to claim 6 , wherein the oxygen storage material exists in a rhodium-containing layer among the catalyst layers.
8. The catalyst for purifying exhaust gas according to claim 2 , wherein the carrier has a 3-dimensional structure.
9. The catalyst for purifying exhaust gas according to claim 3 , wherein the carrier has a 3-dimensional structure.
10. The catalyst for purifying exhaust gas according to claim 7 , wherein the carrier has a 3-dimensional structure.
11. The catalyst for purifying exhaust gas according to claim 4 , wherein the carrier has a 3-dimensional structure.
12. The catalyst for purifying exhaust gas according to claim 6 , wherein the carrier has a 3-dimensional structure.
13. A method for purifying exhaust gas comprising a step where the catalyst for purifying exhaust gas according to claim 1 is exposed to an exhaust gas discharged from an internal combustion engine.
14. The method for purifying exhaust gas according to claim 13 comprising:
a step where the catalyst for purifying exhaust gas is exposed to an exhaust gas whose temperature is 800° C. or higher and 1000° C. or lower, and an air/fuel ratio is 10 or more; and after that
a step where said catalyst for purifying exhaust gas is exposed to an exhaust gas whose temperature is 0° C. or higher and 800° C. or lower.