Pt-Pd diesel oxidation catalyst with CO/HC light-off and HC storage function

1. A diesel oxidation catalyst for abatement of exhaust gas emissions from a diesel engine containing hydrocarbons and carbon monoxide comprising:

(a) a carrier substrate;

(b) a bottom washcoat layer coated on said carrier substrate comprising a high-surface area support material and a precious metal catalyst containing platinum (Pt) and palladium (Pd) in a Pt:Pd weight ratio, wherein said support is a substantially silica-free high-surface area support material, and wherein said bottom washcoat layer does not contain a hydrocarbon storage component;

(c) a top washcoat layer coated over said bottom washcoat layer comprising a high-surface area support material, one or more hydrocarbon storage components, and a precious metal catalyst containing platinum (Pt) and palladium (Pd) in a Pt:Pd weight ratio; and

(d) wherein said Pt:Pd weight ratio in said top washcoat layer is from about 2:1 to up to about 4:1 and is greater than said Pt:Pd weight ratio of said bottom washcoat layer, and wherein the oxidation catalyst oxidizes the carbon monoxide and hydrocarbons to carbon dioxide and water.

2. The diesel oxidation catalyst of claim 1 , wherein said Pt:Pd ratio of said bottom washcoat layer is from less than about 2:1 to about 1:2.

3. The diesel oxidation catalyst of claim 1 , wherein said Pt:Pd ratio of said bottom washcoat layer is 7:5 and said Pt:Pd ratio of said top washcoat layer is 3:1.

4. The diesel oxidation catalyst of claim 1 , wherein said bottom washcoat and/or top washcoat layer further comprises zirconium oxide.

5. The diesel oxidation catalyst of claim 1 , wherein said bottom washcoat layer further comprises lanthanum oxide.

6. The diesel oxidation catalyst of claim 1 , wherein said support material of said bottom washcoat layer is selected from the group consisting of alumina, zirconia, titania and mixtures thereof.

7. The diesel oxidation catalyst of claim 1 , wherein said support material of said top washcoat layer is selected from the group consisting of silica, alumina, zirconia, titania and mixtures thereof.

8. The diesel oxidation catalyst of claim 1 , wherein said hydrocarbon storage component is a zeolite and said zeolite is selected from the group consisting of faujasite, chabazite, clinoptilolite, mordenite, silicalite, zeolite X, zeolite Y, ultrastable zeolite Y, ZSM zeolite, offretite, and beta zeolite.

9. A diesel oxidation catalyst for abatement of exhaust gas emissions from a diesel containing hydrocarbons and carbon monoxide engine comprising:

(a) a carrier substrate;

(b) an upstream washcoat layer coated over an upstream portion of said carrier substrate comprising a high-surface area support material, one or hydrocarbon storage components, and a precious metal catalyst containing platinum (Pt) and palladium (Pd) in a Pt:Pd weight ratio;

(c) a downstream washcoat layer zone coated over a downstream portion of said carrier substrate comprising a high-surface area support material and a precious metal catalyst containing a platinum (Pt) and palladium (Pd) in a Pt:Pd weight ratio, wherein said support is a substantially silica-free high-surface area support material, and wherein said downstream washcoat layer does not contain a hydrocarbon storage component; and

(d) wherein said Pt:Pd weight ratio in said upstream washcoat layer is from about 2:1 to up to about 4:1 and is greater than said Pt:Pd weight ratio of said downstream washcoat layer, and wherein the oxidation catalyst oxidizes the carbon monoxide and hydrocarbons to carbon dioxide and water.

10. The diesel oxidation catalyst of claim 9 , wherein said Pt:Pd ratio of said downstream washcoat layer is from less than about 2:1 to about 1:2.

11. The diesel oxidation catalyst of claim 9 , wherein said Pt:Pd ratio of said upstream washcoat layer is 3:1 and said Pt:Pd ratio of said downstream washcoat layer is 7:5.

12. The diesel oxidation catalyst of claim 9 , wherein said hydrocarbon storage component is a zeolite and said zeolite is selected from the group consisting of faujasite, chabazite, clinoptilolite, mordenite, silicalite, zeolite X, zeolite Y, ultrastable zeolite Y, ZSM zeolite, offretite, and beta zeolite.

13. The diesel oxidation catalyst of claim 9 , wherein said substrate has an upstream edge and a downstream edge and said upstream washcoat layer is zone coated over a length from about 5% to about 70% of said substrate from said upstream edge.

14. The diesel oxidation catalyst of claim 12 , wherein said downstream washcoat layer is zone coated over a length from about 95% to about 30% of said substrate from said downstream edge.

15. A method for treating a diesel exhaust gas stream, the method comprising the steps of:

(a) providing a diesel oxidation catalyst comprising;

(i) a carrier substrate having an upstream edge and a downstream edge;

(ii) a bottom washcoat layer coated on said carrier substrate comprising a high-surface area support material and a precious metal catalyst containing platinum (Pt) and palladium (Pd) in a Pt:Pd weight ratio, wherein said support is a substantially silica-free high-surface area support material, and wherein said bottom washcoat layer does not contain a hydrocarbon storage component;

(iii) a top washcoat layer coated over said bottom washcoat layer comprising a high-surface area support material, one or hydrocarbon storage components, and a precious metal catalyst containing platinum (Pt) and palladium (Pd) in a Pt:Pd weight ratio;

and (iv) wherein said Pt:Pd weight ratio in said top washcoat layer is from about 2:1 to up to about 4:1 and is greater than said Pt:Pd weight ratio of said bottom washcoat layer; and

(b) contacting said diesel exhaust gas stream with said diesel oxidation catalyst from said upstream edge to said downstream edge for the treatment of exhaust gas emissions so that the oxidation catalyst oxidizes hydrocarbons and carbon monoxide in the exhaust gas to carbon dioxide water.

16. The method of claim 15 , wherein said Pt:Pd ratio of said bottom washcoat layer is 7:5 and said Pt:Pd ratio of said top washcoat layer is 3:1.

17. The method of claim 15 , wherein said diesel exhaust gas stream subsequent to contacting said diesel oxidation catalyst is directed to a catalyzed soot filter (CSF) located downstream of said diesel oxidation catalyst.

18. The method of claim 17 , wherein diesel exhaust gas stream subsequent to contacting said catalyzed soot filter (CSF) is directed to a selective catalytic reduction (SCR) component located downstream of said catalyzed soot filter (CSF).