Molecular sieve catalyst compositions, catalyst composites, systems, and methods
Described is a selective catalytic reduction material comprising a spherical particle including an agglomeration of crystals of a molecular sieve. The catalyst is a crystalline material that is effective to catalyze the selective catalytic reduction of nitrogen oxides in the presence of a reductant at temperatures between 200° C. and 600° C. A method for selectively reducing nitrogen oxides and an exhaust gas treatment system are also described.
1. A method for selectively reducing nitrogen oxide (NOx), the method comprising
contacting an exhaust gas stream containing NOx with a selective catalytic reduction material comprising a spherical particle,
wherein the spherical particle has a median particle size of about 0.5 to about 5 microns and comprises an agglomeration of crystals of a molecular sieve,
wherein the spherical particle has a monodispersed snowball structure defined as an arrangement of crystals,
wherein the crystals have approximately the same crystal size, wherein the same crystal size is selected from the range of about 1 to about 250 nm,
wherein the molecular sieve has a structure type selected from the group consisting of AEI, AFT, AFX, CHA, EAB, EMT, ERI, GME, JSR, KFI, LEV, LTL, LTN, MOZ, MSO, MWW, OFF, SAS, SAT, SAV, SBS, SBT, SFW, SSF, SZR, TSC, WEN, and combinations thereof, and
wherein the molecular sieve is promoted with a metal selected from Cu, Fe, Co, Ni, La, Ce, Mn, V, Ag, and combinations thereof.
2. The method of claim 1 , wherein the molecular sieve comprises a d6r unit.
3. The method of claim 2 , wherein the molecular sieve has a structure type selected from AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, and SAV.
4. The method of claim 3 , wherein the molecular sieve has a structure type selected from AEI, CHA, and AFX.
5. The method of claim 4 , wherein the molecular sieve has the CHA structure type.
6. The method of claim 5 , wherein the molecular sieve having the CHA structure type is selected from an aluminosilicate zeolite, a borosilicate, a gallosilicate, a SAPO, an ALPO, a MeAPSO, and a MeAPO.
7. The method of claim 5 , wherein the molecular sieve having the CHA structure type 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.
8. The method of claim 7 , wherein the molecular sieve is selected from SSZ-13 and SSZ-62.
9. The method of claim 5 , wherein the molecular sieve having the CHA structure type has a silica to alumina ratio in the range of 10 to 100.
10. The method of claim 1 , wherein the molecular sieve is promoted with a metal selected from Cu, Fe, and combinations thereof.
11. The method of claim 1 , wherein the selective catalytic reduction material is effective to catalyze the selective catalytic reduction of nitrogen oxides in the presence of a reductant at temperatures between 200° C. and 600° C.
12. The method of claim 1 , wherein the metal is present in an amount in a range of about 0.1 to about 10 wt. % on an oxide basis.
13. The method of claim 1 , wherein the spherical particle has a median particle size in the range of about 1.2 to about 3.5 microns.
14. The method of claim 1 , wherein the crystals have a crystal size in the range of about 100 to about 250 nm.
15. The method of claim 1 , wherein the selective catalytic reduction material is in the form of a washcoat.
16. The method of claim 15 , wherein the washcoat is a layer deposited on a substrate.
17. The method of claim 16 , wherein the substrate comprises a filter.
18. The method of claim 17 , wherein the filter is a wall flow filter.
19. The method of claim 16 , wherein the substrate is a flow through substrate.
20. The method of claim 1 , wherein at least 80% of the spherical particles have a median particle size in the range of 0.5 to 2.5 micron.
21. The method of claim 1 , wherein the molecular sieve comprises a zeolitic framework material of silicon and aluminum atoms, wherein a fraction of the silicon atoms are isomorphously substituted with a tetravalent metal.
22. The method of claim 21 , wherein the tetravalent metal comprises a tetravalent transition metal.
23. The method of claim 22 , wherein the tetravalent transition metal is selected from the group consisting of Ti, Zr, Hf, Ge, and combinations thereof.
24. The method of claim 22 , wherein the tetravalent transition metal comprises Ti.