Exhaust gas treatment catalyst
Provided are an exhaust treatment catalyst and an exhaust article containing the catalyst. The catalyst comprises: (a) a carrier; (b) a first layer deposited on the carrier, said first layer comprising substantially only at least one refractive metal oxide; (c) a second layer deposited on the first layer, said second layer comprising substantially only at least one oxygen storage component and at least one binder therefor; and (d) a third layer deposited on the second layer, said third layer comprising at least one layer of one or more platinum group metal components supported on a refractory metal oxide support. Optionally, a fourth layer is deposited on the third layer wherein the fourth layer comprises one or more platinum group metal components supported on a refractory metal oxide support. As a further option, an overcoat layer may be deposited on the third or fourth layer wherein the overcoat layer comprises a catalyst poison sorbent. Also provided are methods for preparing the catalyst and methods for monitoring the exhaust storage capacity of an exhaust article containing the catalyst.
1. An exhaust gas treatment catalyst comprising: (a) a carrier; (b) a first washcoat layer deposited on the carrier, said first washcoat layer comprising substantially only at least one refractory metal oxide; (c) a second washcoat layer deposited on the first washcoat layer, said second washcoat layer comprising substantially only at least one oxygen storage component and at least one binder therefor; and (d) a third washcoat layer deposited on the second washcoat layer, said third washcoat layer comprising at least one layer of one or more platinum group metal components supported on a refractory metal oxide support.
2. The catalyst of claim 1 wherein the third washcoat layer further comprises at least one oxygen storage component and at least one binder therefor.
3. The catalyst of claim 1 further comprising a fourth washcoat layer deposited on the third washcoat layer, said fourth washcoat layer comprising one or more platinum group metal components supported on a refractory metal oxide support.
4. The catalyst of claim 3 wherein the fourth washcoat layer further comprises at least one oxygen storage component and at least one binder therefor.
5. The catalyst of claim 3 wherein the refractory metal oxide employed in the first layer, third layer and the fourth layer is independently selected from the group consisting of alumina; titania; zirconia; mixtures of alumina with one or more of titania, zirconia, and ceria; ceria coated on alumina; and titania coated on alumina.
6. The catalyst of claim 3 further comprising an overcoat layer deposited on the third or the fourth washcoat layer, said overcoat layer comprising at least one catalyst poisons sorbent.
7. The catalyst of claim 6 wherein the carrier comprises a ceramic or metal having a honeycomb cellular structure comprising hexagonal, rectangular or square cells.
8. The catalyst of claim 7 wherein the first, second, third, fourth and overcoat layers have thicknesses at their respective edges and corners of the cells as follows:
Layer
Edge Thickness, μ
Corner Thickness, μ
First
about 3 to about 15
about 30 to about 200
Second
about 5 to about 15
about 30 to about 100
Third
about 5 to about 15
about 30 to about 100
Fourth
about 5 to about 15
about 30 to about 100
Overcoat
about 5 to about 15
about 30 to about 100.
9. An exhaust gas treatment system comprising the catalyst of claim 7 , an upstream EGO or air/fuel ratio sensor, and a downstream EGO sensor.
10. An exhaust gas treatment system comprising the catalyst of claim 3 , an upstream EGO or air/fuel ratio sensor, and a downstream EGO sensor.
11. The catalyst of claim 1 wherein the oxygen storage component is selected from the group consisting of ceria, praseodymia, a ceria-praseodymia composite, a ceria-praseodymia-zirconia composite and a ceria-praseodymia-zirconia-neodymia composite, and the binder comprises zirconia.
12. The catalyst of claim 1 wherein the catalyst comprises at least two catalytic zones.
13. The catalyst of claim 1 , wherein the first layer comprises at least 76 weight % of one refractory metal oxide.
14. The catalyst of claim 13 , wherein the first layer comprises active ingredients in a quantity not exceeding approximately 12 weight %.
15. The catalyst of claim 14 , wherein the first layer comprises stabilizers in a quantity not exceeding approximately 12 weight %.
16. The catalyst of claim 15 , wherein the second layer comprises at least 76 weight % of one refractory metal oxide.
17. The catalyst of claim 16 , wherein the second layer comprises active ingredients in a quantity not exceeding approximately 12 weight %.
18. The catalyst of claim 17 , wherein the second layer comprises stabilizers in a quantity not exceeding approximately 12 weight %.
19. An exhaust gas treatment system comprising the catalyst of claim 1 , an upstream EGO or air/fuel ratio sensor, and a downstream EGO sensor.