Catalyst for treating exhaust gas
Provided is a method for reducing N 2 O emissions in an exhaust gas comprising contacting an exhaust gas containing NH 3 and an inlet NO concentration with an SCR catalyst composition containing small pore zeolite having an SAR of about 3 to about 15 and having about 1-5 wt. % of an exchanged transition metal.
1. A method for reducing N 2 O emissions in an exhaust gas comprising contacting an exhaust gas containing NH 3 and an inlet NO concentration with an SCR catalyst composition containing small pore zeolite having an SAR of about 3 to about 15 and having about 1 - 5 wt. % of an exchanged transition metal to produce a purified gas containing an outlet NO concentration and an outlet N 2 O concentration,
a. wherein the inlet NO concentration and outlet NO concentration have a relative ratio of > about 4,
b. wherein the inlet NO concentration and outlet N 2 O concentration have a relative ratio of > about 50, and
c. wherein the small pore zeolite has a framework selected from AD, AFT, and AFX.
2. The method of claim 1 , wherein the inlet NO concentration and outlet NO concentration have a relative ratio of > about 5.
3. The method of claim 1 , wherein the inlet NO concentration and outlet NO concentration have a relative ratio of > about 10.
4. The method of claim 1 , wherein the inlet NO concentration and outlet N 2 O concentration have a relative ratio of > about 80.
5. The method of claim 4 , wherein the inlet NO concentration and outlet N 2 O concentration have a relative ratio of > about 100.
6. The method of claim 1 , wherein the transition metal is copper.
7. The method of claim 1 , wherein the small pore zeolite has a SAR of about 5 to about 9.
8. The method of claim 1 , wherein the small pore zeolite has a SAR of about 10 to about 15.
9. The method of claim 1 , wherein the small pore zeolite has a framework selected from AFT and AFX.
10. The method of claim 1 , wherein the small pore zeolite has an AEI framework.
11. The method of claim 1 , wherein the NO and NO 2 are present in a ratio of about 4:1 to about 1:3by volume.
12. The method of claim 1 , wherein the NH 3 is present in exhaust gas entering the SCR catalyst at an NH 3 /NO ratio of about 0.5:1 to about 1:2 and an NH 3 /NO 2 ratio of about 1:1 to about 6:3.
13. A system for treating an exhaust gas comprising, in series and in fluid communication, a diesel oxidation catalyst, a source of nitrogen-based reductant, and an SCR catalyst, wherein the SCR catalyst comprises a small pore zeolite having a framework selected from AEI, AFX and AFT, having an SAR of about 3 to about 15and having about 1 - 5 wt. % of an exchanged transition metal, and wherein the SCR catalyst is coated on a honeycomb wall-flow filter or flow-through monolith or is an extruded honeycomb body.