8-ring small pore molecular sieve as high temperature SCR catalyst
Described is a selective catalytic reduction catalyst comprising an iron-promoted 8-ring small pore molecular sieve. Systems and methods for using these iron-promoted 8-ring small molecular sieves as catalysts in a variety of processes such as abating pollutants in exhaust gases and conversion processes are also described.
1. A selective catalytic reduction catalyst comprising an 8-ring small pore molecular sieve promoted with greater than 5 wt. % iron so that the catalyst is effective to catalyze the selective catalytic reduction of nitrogen oxides in the presence of a reductant at temperatures between 200° and 600° C.
2. The catalyst of claim 1 , wherein the iron-promoted 8-ring small pore molecular sieve is selected from the group consisting of iron-promoted zeolite having a structure type selected from AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV.
3. The catalyst of claim 2 , wherein the iron-promoted 8-ring small pore molecular sieve has the CHA crystal structure.
4. The catalyst of claim 3 , wherein the iron-promoted 8-ring small pore molecular sieve having the CHA crystal structure is selected from an aluminosilicate zeolite, a borosilicate, a gallosilicate, a SAPO, an ALPO, a MeAPSO, and a MeAPO.
5. The catalyst of claim 4 , wherein the iron-promoted 8-ring small pore molecular sieve is selected from the group consisting of SSZ-13, SSZ-62, natural chabazite, zeolite K-G, Linde D, Linde R, LZ-218, LZ-235, LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, and ZYT-6.
6. The catalyst of claim 3 , wherein the 8-ring small pore molecular sieve having the CHA structure is an aluminosilicate zeolite having the CHA crystal structure.
7. The catalyst of claim 6 , wherein the aluminosilicate zeolite having the CHA crystal structure is selected from iron-promoted SSZ-13 and iron-promoted SSZ-62.
8. The catalyst of claim 7 , wherein the zeolite has a silica to alumina ratio in the range of 5 and 100.
9. The catalyst of claim 8 , wherein the zeolite has a silica to alumina ratio in the range of 10 and 50.
10. The catalyst of claim 1 , comprising iron in the range of 5.1 wt. % to 10 wt. %, calculated as Fe 2 O 3 .
11. The catalyst of claim 7 , comprising iron in the range of t 5.1 wt. % to 10 wt. %, calculated as Fe 2 O 3 .
12. The catalyst of claim 8 , comprising iron in the range of 5.1 wt. % to 10 wt. %, calculated as Fe 2 O 3 .
13. A catalytic article comprising the catalyst of claim 1 in a washcoat deposited on a honeycomb substrate.
14. The catalytic article of claim 13 , wherein the honeycomb substrate comprises a wall flow filter substrate.
15. The catalytic article of claim 13 , wherein the honeycomb substrate comprises a flow through substrate.
16. An exhaust gas treatment system comprising the catalytic article of claim 13 disposed downstream from a diesel engine and an injector that adds a reductant to an exhaust gas stream from the engine.
17. A method for selectively reducing nitrogen oxides, the method comprising contacting a gaseous stream containing nitrogen oxides with a selective catalytic reduction catalyst comprising an 8-ring small pore molecular sieve promoted with greater than 5 wt. % iron to catalyze the selective catalytic reduction of the nitrogen oxides in the presence of a reductant at temperatures between 200° and 600° C.
18. The method of claim 17 , wherein the 8-ring small pore molecular sieve promoted with iron is selected from the group consisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV.
19. The method of claim 18 , wherein the 8-ring small pore molecular sieve promoted with iron has the CHA crystal structure.
20. The method of claim 19 , wherein the 8-ring small pore molecular sieve promoted with iron and having the CHA crystal structure is selected from the group consisting of aluminosilicate zeolite, SAPO, ALPO and MeAPO.