Isomorphously substituted catalyst
Described is a selective catalytic reduction catalyst comprising a zeolitic framework material of silicon and aluminum atoms, wherein a fraction of the silicon atoms are isomorphously substituted with a tetravalent metal. The catalyst can include a promoter metal such that the catalyst effectively promotes the reaction of ammonia with nitrogen oxides to form nitrogen and H 2 O selectively over a temperature range of 150 to 650° C. A method for selectively reducing nitrogen oxides and an exhaust gas treatment system are also described.
1. An SCR catalyst comprising a zeolite with a framework material of silicon and aluminum atoms, wherein a fraction of the silicon atoms are isomorphously substituted with Ti; wherein the zeolitic framework material has a zeolitic frame worlds selected from CHA, AFX, and AEI; and wherein the catalyst zeolite is promoted with Cu, Fe, or a combination thereof by ion-exchange into the zeolite.
2. The catalyst of claim 1 , having a silica to alumina ratio in the range of 1 to 300.
3. The catalyst of claim 2 , wherein the silica to alumina ratio is in the range of 1 to 50.
4. The catalyst of claim 1 , having a Ti to alumina ratio in the range of 0.0001 to 1000.
5. The catalyst of claim 4 , wherein the Ti to alumina ratio is in the range of 0.01 to 10.
6. The catalyst of claim 5 , wherein the Ti to alumina ratio is in the range of 0.01 to 2.
7. The catalyst of claim 1 , having a silica to Ti ratio in the range of 1 to 100.
8. The catalyst of claim 7 , wherein the silica to Ti ratio is in the range of 5 to 20.
9. The catalyst of claim 1 , wherein the framework is CHA.
10. The catalyst of claim 1 , wherein the zeolite is promoted with Cu.
11. The catalyst of claim 1 , wherein the catalyst is effective to promote the formation of NO + .
12. The catalyst of claim 1 , wherein the framework is AFX.
13. The catalyst of claim 1 , wherein the framework is AEI.
14. A method for selectively reducing nitrogen oxides (NOx), the method comprising contacting an exhaust gas stream containing NOx with a catalyst in accordance with claim 1 .
15. An exhaust gas treatment system comprising an exhaust gas stream containing ammonia and a catalyst in accordance with claim 1 effective for destroying at least a portion of the ammonia in the exhaust gas stream.
16. A catalyst article comprising a substrate having a catalytic coating disposed thereon, wherein the catalytic coating comprises a catalyst in accordance with claim 1 .
17. The catalyst article of claim 16 , wherein the substrate is ceramic or metal having a honeycomb structure.