Dual bed catalyst system for NOx reduction in lean-burn engine exhaust
View Patent ↗A method for reducing nitrogen oxides including NO and NO 2 in an exhaust stream also including oxygen, carbon monoxide and hydrocarbons at a temperature above about 150° C. includes oxidizing NO in the exhaust stream to NO 2 , adding diesel fuel hydrocarbons and their oxygenates to the exhaust stream for the reduction of nitrogen oxides, and flowing the exhaust stream through a dual bed catalyst system including a first bed and a second bed, wherein the first bed is a single layer catalyst bed and the second bed is a double layer catalyst bed including a first layer and a second layer to reduce the nitrogen oxides to N 2 .
1. A method for reducing nitrogen oxides including NO and NO 2 in an exhaust stream also comprising oxygen, carbon monoxide and hydrocarbons at a temperature above about 150° C., the method comprising:
oxidizing NO in the exhaust stream to NO 2 ;
adding diesel fuel hydrocarbons and their oxygenates to the exhaust stream for the reduction of nitrogen oxides; and
flowing the exhaust stream through a dual bed catalyst system comprising a front bed and a rear bed to reduce the nitrogen oxides to N 2 , wherein the front bed is a single layer catalyst bed and the rear bed is a double layer catalyst bed comprising a first layer including a first layer catalyst produced from the same materials as the single layer catalyst of the front bed and a second layer including a second layer catalyst, the single layer catalyst continuously forming NH 3 when the exhaust stream reacts with the single layer catalyst and the second layer catalyst of the rear bed reacts with the formed NH 3 to substantially eliminate the formed NH 3 to produce N 2 .
2. The method of claim 1 :
wherein the front bed comprises a single layer catalyst selected from the group consisting of Ag/Al 2 O 3 , Ag/Y, Ag/ZSM5, Ag/Ba/Y, or a combination thereof; and
wherein the rear bed comprises a double layer catalyst wherein the first layer is selected from the group consisting of Ag/Al 2 O 3 , Ag/Y, Ag/ZSM5, Ag/Ba/Y, or a combination thereof and the second layer is selected from the group consisting of Pt/Al 2 O 3 , Pt/Ba/Al 2 O 3 , Cu/ZSM5, CuCo/Y, Pd/Al 2 O 3 , or a combination thereof.
3. The method of claim 1 :
wherein the front bed comprises a single layer catalyst of Ag/Al 2 O 3 ; and
wherein the rear bed comprises a double layer catalyst wherein the first layer is Ag/Al 2 O 3 and the second layer is Pt/Al 2 O 3 .
4. The method of claim 1 , wherein the exhaust stream is a diesel engine exhaust stream.
5. The method of claim 1 , wherein oxidizing NO in the exhaust stream to NO 2 comprises treating the exhaust stream with an oxidation catalyst.
6. The method of claim 1 , further comprising adding an OHC to the exhaust stream as vapor in an air stream.
7. The method of claim 1 , comprising adding an OHC and a hydrocarbon to the exhaust stream, wherein the OHC and hydrocarbon can be added to the exhaust stream separately or as a mixture or combination thereof.
8. The method of claim 7 , wherein the OHC is ethanol, and the hydrocarbon is dodecane.
9. The method of claim 1 , comprising reducing nitrogen oxides including NO and NO 2 in an exhaust stream also comprising oxygen, carbon monoxide and hydrocarbons at a temperature above about 200° C.
10. A NOx reduction catalyst for a hydrocarbon-fueled automotive engine operated at a fuel-lean air-to-fuel ratio, the catalyst comprising a dual bed catalyst system comprising a front bed and a rear bed to reduce the nitrogen oxides to N 2 , wherein the front bed is a single layer catalyst bed and the rear bed is a double layer catalyst bed comprising a first layer including a first layer catalyst produced from the same materials as the single layer catalyst bed and a second layer including a second layer catalyst, the single layer catalyst continuously forming NH 3 when the exhaust stream reacts with the single layer catalyst and the second layer catalyst of the rear bed reacts with the formed NH 3 to substantially eliminate the formed NH 3 to produce N 2 .
11. The catalyst of claim 10 :
wherein the front bed comprises a single layer catalyst selected from the group consisting of Ag/Al 2 O 3 , Ag/Y, Ag/ZSM5, Ag/Ba/Y, or a combination thereof; and
wherein the rear bed comprises a double layer catalyst wherein the first layer is selected from the group consisting of Ag/Al 2 O 3 , Ag/Y, Ag/ZSM5, Ag/Ba/Y, or a combination thereof and the second layer is selected from the group consisting of Pt/Al 2 O 3 , Pt/Ba/Al 2 O 3 , Cu/ZSM5, CuCo/Y, Pd/Al 2 O 3 , or a combination thereof.
12. The catalyst of claim 10 :
wherein the front bed comprises Ag/Al 2 O 3 ; and
wherein the rear bed comprises a double layer catalyst wherein the first layer is Ag/Al 2 O 3 and the second layer is Pt/Al 2 O 3 .
13. A system for reducing nitrogen oxides including NO and NO 2 in an exhaust stream also comprising oxygen, carbon monoxide and hydrocarbons at a temperature above about 150° C., comprising a dual bed catalyst system comprising a front bed and a rear bed to reduce the nitrogen oxides to N 2 , wherein the front bed is a single layer catalyst bed and the rear bed is a double layer catalyst bed comprising a first layer including a first layer catalyst produced from the same materials as the single layer catalyst bed and a second layer including a second layer catalyst, the single layer catalyst continuously forming NH 3 when the exhaust stream reacts with the single layer catalyst and the second layer catalyst of the rear bed reacts with the formed NH 3 to substantially eliminate the formed NH 3 to produce N 2 .
14. The system of claim 13 :
wherein the front bed comprises a single layer catalyst selected from the group consisting of Ag/Al 2 O 3 , Ag/Y, Ag/ZSM5, Ag/Ba/Y, or a combination thereof; and
wherein the rear bed comprises a double layer catalyst wherein the first layer is selected from the group consisting of Ag/Al 2 O 3 , Ag/Y, Ag/ZSM5, Ag/Ba/Y, or a combination thereof and the second layer is selected from the group consisting of Pt/Al 2 O 3 , Pt/Ba/Al 2 O 3 , Cu/ZSM5, CuCo/Y, Pd/Al 2 O 3 , or a combination thereof.
15. The system of claim 13 :
wherein the front bed comprises Ag/Al2O3; and
wherein the rear bed comprises a double layer catalyst wherein the first layer is Ag/Al 2 O 3 and the second layer is Pt/Al 2 O 3 .
16. The system of claim 13 , wherein the exhaust stream is a diesel engine exhaust stream.
17. The system of claim 13 , further comprising an oxidation catalyst for oxidizing NO in the exhaust stream to NO 2 .
18. The system of claim 17 , wherein the oxidation catalyst is selected from the group consisting of Pt, Pd, Rh, or a mixture or combination thereof.
19. The system of claim 13 , further comprising a non-thermal plasma reactor, wherein oxidizing NO in the exhaust stream to NO 2 comprises passing air through the non-thermal plasma reactor to generate ozone-containing air plasma and adding the air plasma to the exhaust stream for oxidation of NO to NO 2 .
20. The system of claim 13 , further comprising a fuel reformer for adding an OHC to the exhaust stream as vapor in an air stream.
21. The system of claim 13 , further comprising a fuel reformer for adding an OHC and a hydrocarbon to the exhaust stream, wherein the OHC and hydrocarbon are added to the exhaust stream separately or as a mixture or combination thereof.
22. The system of claim 21 , wherein the OHC is ethanol, and the hydrocarbon is dodecane.