Exhaust treatment system and catalyst system

1. A method of using a catalyst system comprising:

passing an exhaust stream over a catalyst system comprising

a gold catalyst having a gold particle size less than or equal to 10 nm supported on a first support which is a metal oxide; and

a hydrocarbon oxidation catalyst comprising a hydrocarbon adsorbing material, and an oxidation catalyst being platinum or palladium supported on a second support comprising an inorganic oxide,

wherein the first and second supports are separate and the gold catalyst and the hydrocarbon oxidation catalyst are in a physical mixture;

and oxidizing at least a portion of CO present in the exhaust stream.

2. The method of claim 1 , wherein greater than or equal to 50% CO in the exhaust stream is converted to CO 2 at a space velocity less than or equal to 250,000 hr −1 at a temperature less than or equal to about 100° C.

3. A method of treating one or more exhaust streams comprising carbon monoxide, one or more hydrocarbons, and one or more nitrogen oxides, comprising:

passing the one or more exhaust streams over a combination of catalytic components comprising

a gold catalyst having a gold particle size less than or equal to 10 nm supported on a first support which is a metal oxide; and

a hydrocarbon oxidation catalyst comprising a hydrocarbon adsorbing material, and an oxidation catalyst being platinum or palladium supported on a second support comprising an inorganic oxide,

wherein the first and second supports are separate and the gold catalyst and the hydrocarbon oxidation catalyst are in a physical mixture;

and oxidizing at least a portion of the carbon monoxide in the one or more exhaust streams.

4. The method of claim 3 , wherein greater than or equal to 50% CO in the exhaust stream is converted to CO 2 at a space velocity less than or equal to 250,000 hr −1 at a temperature less than or equal to about 100° C.

5. A method of protecting a gold catalyst, having a gold particle size less than or equal to 10 nm which is supported on a first support which is a metal oxide, from deactivation by a hydrocarbon in an exhaust gas which comprises

adsorbing and oxidizing the hydrocarbon in the exhaust gas with a hydrocarbon oxidation catalyst comprising a hydrocarbon adsorbing material, and an oxidation catalyst being platinum or palladium which is supported on a second support comprising an inorganic oxide,

wherein the first and second supports are separate and the gold catalyst and the hydrocarbon oxidation catalyst are in a physical mixture.

6. The method of claim 5 , wherein the temperature of the exhaust gas is equal to or greater than about 125° C.

7. The method of claim 5 , wherein the temperature of the exhaust gas ranges from about 25° C. to about 300° C.

8. The method of claim 1 , wherein the second support comprises an alumina selected from the group consisting of the gamma alumina, delta alumina, and theta alumina.

9. The method of claim 1 , wherein a ratio of a gold catalyst volume to a hydrocarbon oxidation catalyst volume is greater than or equal to about 1:12.5.

10. The method of claim 3 , wherein the second support comprises an alumina selected from the group consisting of the gamma alumina, delta alumina, and theta alumina.

11. The method of claim 3 , wherein a ratio of a gold catalyst volume to a hydrocarbon oxidation catalyst volume is greater than or equal to about 1:12.5.

12. The method of claim 5 , wherein the second support comprises an alumina selected from the group consisting of the gamma alumina, delta alumina, and theta alumina.

13. The method claim 5 , wherein a ratio of a gold catalyst volume to a hydrocarbon oxidation catalyst volume is greater than or equal to about 1:12.5.

14. The method of claim 1 , wherein the hydrocarbon adsorbing material is a zeolite selected from the group consisting of beta zeolite, ultra-stable Y zeolite and UTD-1 zeolite.

15. The method of claim 3 , wherein the hydrocarbon adsorbing material is a zeolite selected from the group consisting of beta zeolite, ultra-stable Y zeolite and UTD-1 zeolite.

16. The method of claim 5 , wherein the hydrocarbon adsorbing material is a zeolite selected from the group consisting of beta zeolite, ultra-stable Y zeolite and UTD-1 zeolite.