Multi-stage catalyst systems and uses thereof
View Patent ↗Catalyst systems and methods provide benefits in reducing the content of nitrogen oxides in a gaseous stream containing nitric oxide (NO), hydrocarbons, carbon monoxide (CO), and oxygen (O 2 ). The catalyst system comprises an oxidation catalyst comprising a first metal supported on a first inorganic oxide for catalyzing the oxidation of NO to nitrogen dioxide (NO 2 ), and a reduction catalyst comprising a second metal supported on a second inorganic oxide for catalyzing the reduction of NO 2 to nitrogen (N 2 ).
1. A catalyst system for reducing the content of nitrogen oxides in a gaseous stream containing nitric oxide (NO) hydrocarbons, carbon monoxide (CO), and oxygen (O 2 ) comprising:
an oxidation catalyst comprising a first metal supported on a first inorganic oxide for catalyzing the oxidation of NO to nitrogen dioxide (NO 2 ); and
a reduction catalyst comprising a second metal supported on a second inorganic oxide for catalyzing the reduction of NO 2 to nitrogen (N 2 ), wherein the second inorganic oxide comprises sulfated zirconia or tungstated zirconia.
2. A catalyst system according to claim 1 wherein the first metal comprises cobalt, silver, or combinations thereof, and the second metal comprises palladium.
3. A catalyst system according to claim 1 wherein the first inorganic oxide and the second organic oxide comprise titania, zirconia, alumina, or combinations thereof.
4. A catalyst system according to claim 1 wherein the oxidation catalyst and Reduction catalyst are disposed on a catalyst bed.
5. A catalyst system according to claim 4 wherein the catalyst bed defines a mixed bed, a monolith bed structure having oxidation and reduction catalysts embedded therein, or a bed comprising alternating layers or sections of oxidation and reduction catalysts.
6. A catalyst system according to claim 1 wherein the oxidation catalyst comprises from about 1 to about 10% by weight of cobalt.
7. A catalyst system according to claim 1 wherein the catalyst system is operable to oxidize the CO in the gaseous stream to carbon dioxide (CO 2 ) in the presence of the oxidation catalyst.
8. A catalyst system according to claim 1 wherein the catalyst system is operable to oxidize the hydrocarbons in the gaseous stream in the presence of the oxidation catalyst.
9. A lean exhaust pollutant removal system comprising:
a catalyst system according to claim 1 ; and
an exhaust outlet configured to deliver the gaseous stream to the catalyst system.
10. A catalyst system for reducing the content of nitrogen oxides in a gaseous stream containing nitric oxide (NO), hydrocarbons, carbon monoxide (CO), and oxygen comprising:
an oxidation catalyst comprising cobalt on a zirconia support for catalyzing the oxidation of nitric oxide (NO) to nitrogen dioxide (NO 2 ); and
a reduction catalyst comprising palladium on a sulfated zirconia support for catalyzing the reduction of NO 2 to nitrogen (N 2 ).
11. A method of reducing the level of pollutants in a gaseous stream comprising:
providing a catalyst system comprising an oxidation catalyst and a reduction catalyst comprising an inorganic oxide support, wherein the inorganic oxide support comprises sulfated zirconia or tungstated zirconia;
feeding a gaseous stream comprising nitric oxide (NO), hydrocarbons, carbon monoxide (CO), and oxygen (O 2 ) to the catalyst system;
oxidizing the NO to nitrogen dioxide (NO 2 ) in the presence of the oxidation catalyst; and
reducing the NO 2 to nitrogen (N 2 ) by reacting with hydrocarbons in the presence of the reduction catalyst to form a treated gaseous stream.
12. A method according to claim 11 further comprising oxidizing the CO to carbon dioxide (CO 2 ) in the presence of the oxidation catalyst.
13. A method according to claim 11 wherein the hydrocarbons comprise methane, ethane, propane, and combinations thereof.
14. A method according to claim 11 further comprising oxidizing at least a portion of the hydrocarbons, the unoxidized hydrocarbons being utilized in the reduction of NO 2 to N 2 .
15. A method according to claim 11 wherein the oxidation occurs at a temperature of about 200 to about 500° C.
16. A method according to claim 11 further comprising,
exposing the treated gaseous stream to an additional oxidation catalyst; and
oxidizing hydrocarbons not reacted in the oxidation or reduction reactions.
17. A method according to claim 11 wherein from about 50% to about 90% of the NO is oxidized to NO 2 .
18. A method according to claim 11 wherein from about 50% to about 80% of the NO 2 is reduced to N 2 .
19. A method according to claim 11 wherein the gaseous stream comprises about 2 to about 15% O 2 .