Exhaust gas purifying catalyst and method for purifying exhaust gas

1. An exhaust gas purifying catalyst system comprising:

a first catalyst component containing a refractory inorganic oxide carrying a platinum family metal, a nitrogen oxide adsorbent, and a hydrocarbon adsorbent; and

a second catalyst component for the purification of nitrogen oxide;

wherein said first catalyst component is disposed at a high concentration on the upstream side and said second catalyst component is disposed at a high concentration on the downstream side relative to the flow direction of the exhaust gas.

2. A catalyst system according to claim 1 , wherein said first catalyst component said nitrogen oxide adsorbent includes nickel or hydrated iron oxide, said hydrocarbon adsorbent includes zeolite, and said platinum family metal is at least one member selected from the group consisting of platinum, palladium, rhodium and mixtures thereof.

3. A catalyst system according to claim 2 , wherein said zeolite is at least one member selected from the group consisting of Pentasil zeolite, Y zeolite, mordenite, ferrierite and mixtures thereof.

4. A catalyst system according to claim 3 , wherein said zeolite is at least one member selected from the group consisting of Pentasil zeolite, Y zeolite and a mixture thereof.

5. A catalyst system according to claim 1 , wherein said refractory inorganic oxide is at least one member selected from the group consisting of alumina, silica, silica-alumina, zirconia, titania, zeolite and mixtures thereof.

6. A catalyst system according to claim 5 , wherein said refractory inorganic oxide is at least one member selected from the group consisting of alumina, silica, silica-alumina and mixtures thereof.

7. A catalyst system according to claim 1 , wherein said platinum family metal is at least one member selected from the group consisting of platinum, palladium and a mixture thereof.

8. A catalyst system according to claim 1 , wherein an amount of said platinum family metal comprises from 0.001 to 1 g, as reduced to metal, per liter of the catalyst.

9. A catalyst system according to claim 8 , wherein the amount of said platinum family metal comprises from 0.01 to 0.5 g, as reduced to metal, per liter of the catalyst.

10. A catalyst system according to claim 1 , wherein an amount of the refractory inorganic oxide comprises from 2 to 50 g per 1 g of the platinum family metal.

11. A catalyst system according to claim 10 , wherein the amount of the refractory inorganic oxide comprises from 5 to 20 g per 1 g of the platinum family metal.

12. A catalyst system according to claim 1 , wherein an amount of said nitrogen oxide adsorbent comprises from 10 to 100 g, as reduced to oxide, per liter of the catalyst.

13. A catalyst system according to claim 1 , wherein an amount of said hydrocarbon adsorbent comprises from 10 to 100 g per liter of the catalyst.

14. A catalyst system according to claim 1 , wherein an amount of the second catalyst component comprises from 10 to 300 g per liter ofthe catalyst.

15. A catalyst system according to claim 14 , wherein the amount of the second catalyst component comprises from 50 to 150 g per liter of the catalyst.

16. A catalyst system according to claim 1 , wherein said catalyst is a set of at least two pieces and said first catalyst component is disposed on the upstream side and said second catalyst component on the downstream side respectively relative to the flow direction of the exhaust gas.

17. A catalyst system according to claim 1 , wherein the second catalyst component contains a porous inorganic oxide carrying a Pt material.

18. A catalyst system according to claim 17 , wherein the porous inorganic oxide is a zeolite.