Engine exhaust catalysts containing zeolite and zeolite mixtures
A multi-layer emission control catalyst exhibits improved CO and HC reduction performance. The bottom layer includes a supported catalyst comprising platinum and palladium particles or palladium and gold particles. The middle layer includes zeolites. The top layer includes a supported catalyst comprising platinum and palladium particles. The use of zeolite mixture in the middle layer further improves CO and HC reduction performance in comparison with using zeolite of a single type. The use of a supported catalyst comprising palladium and gold particles in the bottom layer further improves CO and HC reduction performance in comparison with using a supported catalyst comprising platinum and palladium particles.
1. An emission control catalyst comprising a substrate having first, second, and third washcoat layers coated thereon in a multi-layer configuration, wherein the first and third washcoat layers include supported precious group metal particles and the second washcoat layer is between the first washcoat layer and the third washcoat layer and contains zeolites of at least one type.
2. The emission control catalyst according to claim 1 , wherein the zeolites of at least one type comprises beta zeolite.
3. The emission control catalyst according to claim 1 , wherein the zeolites of at least one type comprises a mixture of beta zeolite and ZSM-5 zeolite.
4. The emission control catalyst according to claim 3 , wherein a weight ratio of the beta zeolite and the ZSM-5 zeolite in the second washcoat layer is approximately 1:1.
5. The emission control catalyst according to claim 1 , wherein the substrate has a honeycomb structure with gas flow channels, and the first, second, and third washcoat layers are coated on the walls of the gas flow channels.
6. The emission control catalyst according to claim 5 , wherein the first washcoat layer is disposed directly on the walls of the gas flow channels and the third washcoat layer is disposed to be in direct contact with exhaust gases flowing through the gas flow channels.
7. The emission control catalyst according to claim 6 , wherein the first washcoat layer comprises supported platinum-palladium metal particles, and the second washcoat layer comprises beta zeolite, and the third washcoat layer comprises supported platinum-palladium metal particles.
8. The emission control catalyst according to claim 6 , wherein the first washcoat layer comprises supported platinum-palladium metal particles, and the second washcoat layer comprises a mixture of beta zeolite and ZSM-5 zeolite, and the third washcoat layer comprises supported platinum-palladium metal particles.
9. The emission control catalyst according to claim 6 , wherein the first washcoat layer comprises supported palladium-gold metal particles, and the second washcoat layer comprises a mixture of beta zeolite and ZSM-5 zeolite, and the third washcoat layer comprises supported platinum-palladium metal particles.
10. The emission control catalyst according to claim 1 , wherein the supported precious group metal particles comprises palladium and gold particles in close contact.
11. An emission control catalyst comprising:
a substrate having first, second, and third washcoat layers coated thereon in a multi-layer configuration,
wherein the first washcoat layer comprises supported platinum-palladium metal particles, and the third washcoat layer comprises supported platinum-palladium metal particles, and
wherein the second washcoat layer is between the first washcoat layer and the third washcoat layer and contains zeolites of at least one type.
12. The emission control catalyst according to claim 11 , wherein the first washcoat layer is disposed on the substrate, the second washcoat layer on the first washcoat layer, and the third washcoat layer on the second washcoat layer.
13. The emission control catalyst according to claim 12 , wherein the zeolites of at least one type comprises beta zeolite.
14. The emission control catalyst according to claim 12 , wherein the zeolites of at least one type comprises a mixture of beta zeolite and ZSM-5 zeolite.
15. An emission control catalyst comprising:
a substrate having first, second, and third washcoat layers coated thereon in a multi-layer configuration,
wherein the first washcoat layer comprises supported palladium-gold metal particles, and the third washcoat layer comprises supported platinum-palladium metal particles, and
wherein the second washcoat layer is between the first washcoat layer and the third washcoat layer and contains zeolites of at least one type.
16. The emission control catalyst according to claim 15 , wherein the first washcoat layer is disposed on the substrate, the second washcoat layer on the first washcoat layer, and the third washcoat layer on the second washcoat layer.
17. The emission control catalyst according to claim 16 , wherein the zeolites of at least one type comprises beta zeolite.
18. The emission control catalyst according to claim 16 , wherein the zeolites of at least one type comprises a mixture of beta zeolite and ZSM-5 zeolite.