Engine exhaust catalysts containing palladium-gold
An emission control catalyst that exhibits improved CO and HC reduction performance includes a supported platinum-based catalyst, and a supported palladium-gold catalyst. The two catalysts are coated onto different layers, zones, or monoliths of the substrate for the emission control catalyst such that the platinum-based catalyst encounters the exhaust stream before the palladium-gold catalyst. Zeolite may be added to the emission control catalyst as a hydrocarbon absorbing component to boost the oxidation activity of the palladium-gold catalyst.
1. An emission control catalyst for treating an engine exhaust comprising a first catalytically active zone and a second catalytically active zone, wherein the first catalytically active zone is positioned to encounter the engine exhaust before the second catalytically active zone, and wherein the first catalytically active zone includes a first supported catalyst comprising platinum-containing metal particles supported on an oxide carrier and the second catalytically active zone includes a second supported catalyst consisting essentially of palladium-gold metal particles supported on an oxide carrier, wherein the second supported catalyst has palladium to gold weight ratio range of about 0.5:1 to about 1:0.5.
2. The emission control catalyst according to claim 1 , further comprising a substrate having a honeycomb structure with gas flow channels, wherein the first supported catalyst and the second supported catalyst are coated on the walls of the gas flow channels.
3. The emission control catalyst according to claim 2 , wherein multiple layers are coated on the walls of the gas flow channels, and a bottom layer that is directly above the walls of the gas flow channels includes the second supported catalyst and a top layer that is positioned to be in direct contact with the engine exhaust includes the first supported catalyst.
4. The emission control catalyst according to claim 3 , wherein the first supported catalyst comprises platinum-palladium metal particles.
5. The emission control catalyst according to claim 3 , wherein the top layer further includes zeolite.
6. The emission control catalyst according to claim 3 , wherein the multiple layers further include a middle layer between the bottom layer and the top layer.
7. The emission control catalyst according to claim 6 , wherein the middle layer comprises zeolite.
8. The emission control catalyst according to claim 1 , further comprising a substrate having an upstream zone and a downstream zone, the upstream zone being positioned to encounter the engine exhaust before the downstream zone, wherein the first supported catalyst is coated on the upstream zone of the substrate and the second supported catalyst is coated on the downstream zone of the substrate.
9. The emission control catalyst according to claim 1 , further comprising an upstream monolith and a downstream monolith, the upstream monolith being positioned to encounter the engine exhaust before the downstream monolith, wherein the first supported catalyst is coated on the upstream monolith and the second supported catalyst is coated on the downstream monolith.
10. An emission control catalyst for treating an engine exhaust comprising a substrate having a first washcoat metal particles comprising platinum and a second washcoat containing metal particles consisting essentially of palladium and gold in close contact, wherein the first washcoat is positioned to encounter the engine exhaust prior to the second washcoat, wherein the second supported catalyst has a palladium to gold weight ratio range of about 0.5:1 to about 1:0.5.
11. The emission control catalyst according to claim 10 , wherein the first washcoat further includes zeolite.
12. The emission control catalyst according to claim 10 , further comprising a third washcoat containing zeolite.
13. The emission control catalyst according to claim 10 , wherein the substrate has a honeycomb structure with gas flow channels and multiple layers of washcoats are coated on the walls of the gas flow channels, and wherein a bottom layer that is directly in contact with the walls of the gas flow channels includes the second washcoat and a top layer that is positioned to be in direct contact with the engine exhaust includes the first washcoat.
14. The emission control catalyst according to claim 13 , wherein the multiple layers include a middle layer between the bottom layer and the top layer, and the middle layer includes a third washcoat containing zeolite.
15. The emission control catalyst according to claim 10 , wherein the substrate has an upstream zone and a downstream zone, the upstream zone being positioned to encounter the engine exhaust before the downstream zone, and wherein the first washcoat is coated on the upstream zone of the substrate and the second washcoat is coated on the downstream zone of the substrate.
16. The emission control catalyst according to claim 10 , wherein the substrate has an upstream monolith and a downstream monolith, and wherein the first washcoat is coated on the upstream monolith of the substrate and the second washcoat is coated on the downstream monolith of the substrate.
17. An emission control catalyst comprising a first catalyst comprising platinum-containing metal particles, a second catalyst comprising palladium-gold containing metal particles other than platinum-palladium-gold metal particles, and physically separate zones for each of the first catalyst and the second catalyst, wherein the second supported catalyst has a palladium to gold weight ratio range of about 0.5:1 to about 1:0.5.
18. The emission control catalyst according to claim 17 , further comprising a buffer zone between the physically separate zones for the first catalyst and the second catalyst.
19. The emission control catalyst according to claim 17 , wherein the first catalyst comprises a platinum-palladium catalyst having a Pt:Pd weight ratio of 2:1 to 4:1.
20. The emission control catalyst according to claim 19 , further comprising a zeolite mixture having beta zeolite and ZSM-5 zeolite having a weight ratio of about 1:1.