Small pore molecular sieve supported copper catalysts durable against lean/rich aging for the reduction of nitrogen oxides
View Patent ↗A method of using a catalyst comprises exposing a catalyst to at least one reactant in a chemical process. The catalyst comprises copper and a small pore molecular sieve having a maximum ring size of eight tetrahedral atoms. The chemical process undergoes at least one period of exposure to a reducing atmosphere. The catalyst has an initial activity and the catalyst has a final activity after the at least one period of exposure to the reducing atmosphere. The final activity is within 30% of the initial activity at a temperature between 200 and 500° C.
1. A method for using a catalyst comprising:
exposing an SCR catalyst comprising copper and a small-pore molecular sieve having eight-member rings or smaller to a reducing atmosphere comprising NH 3 generated over a NO x adsorber catalyst and using the SCR catalyst to store NH 3 during the exposing step,
contacting the SCR catalyst with NO x in a non-reducing atmosphere to effect selective reduction of said NO x by the stored NH 3 .
2. The method according to claim 1 , wherein the small pore molecular sieve is selected from the group consisting of aluminosilicate molecular sieves, metal-substituted aluminosilicate molecular sieves, and aluminophosphate molecular sieves.
3. The method according to claim 1 , wherein the small pore molecular sieves is selected from the group of Framework Type Codes consisting of: ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG and ZON.
4. The method according to claim 1 , wherein the small pore molecular sieves containing a maximum ring size of eight tetrahedral atoms is selected from the group of Framework Type Codes consisting of LEV, ERI and DDR.
5. The method according to claim 1 , wherein the small pore molecular sieve is selected from the group consisting of a LEV Framework Type Code Nu-3, an AEI Framework Type Code SAPO-18, an ERI Framework Type Code ZSM-34, a DDR Framework Type Code sigma-1, and mixtures thereof.
6. The method of claim 1 , wherein said NO x is slipped past said NO x adsorber catalyst.
7. The method of claim 1 further comprising the steps of:
contacting the NO x adsorber catalyst with a lean exhaust gas comprising NO x , and
utilizing the NO x adsorber catalyst to store at least a portion of the NO in said lean exhaust gas.
8. The method of claim 1 wherein said contacting step involves contacting the SCR catalyst with a lean exhaust gas comprising said NO x at a space velocity of 5000 hr −1 to 500,000 hr −1 .
9. A method for treating an exhaust gas comprising:
a. exposing a NO x adsorber catalyst and an SCR catalyst to a lean exhaust gas, wherein said SCR catalyst is disposed downstream of said NO x adsorber catalyst relative to exhaust gas flow and wherein said SCR catalyst comprises copper and a small-pore molecular sieve having eight-member rings or smaller;
b. exposing said NO x adsorber catalyst and said SCR catalyst to a reducing atmosphere; and
c. repeating steps (a) and (b) in a cyclical manner;
wherein said NO x adsorber catalyst stores NO x during step (a) and releases NO x to generate NH 3 during step (b); and said SCR catalyst stores NH 3 generated by said NO x adsorber catalyst during step (b) and uses the stored NH 3 to selectively reduce NO x during step (a).
10. The method of claim 9 , wherein said reducing atmosphere is generated during one or more events selected from regeneration of a soot particulate filter, regeneration of the NO x adsorber catalyst, and NO x adsorber catalyst desulfation.
11. A system for treating exhaust gas comprising a NO x adsorber catalyst disposed upstream of an SCR catalyst, wherein said SCR catalyst comprises copper and a small-pore molecular sieve having eight-member rings or smaller.
12. The system of claim 11 , wherein the small pore molecular sieve is selected from the group consisting of aluminosilicate molecular sieves, metal-substituted aluminosilicate molecular sieves, and aluminophosphate molecular sieves.
13. The system of claim 11 , wherein the small pore molecular sieve containing a maximum ring size of eight tetrahedral atoms is selected from the group of Framework Type Codes consisting of LEV, ERI and DDR.
14. The system of claim 13 , further comprising an ammonia component, wherein said ammonia component is generated by said NO x adsorber catalyst.
15. The system of claim 13 , further comprising an alternating reducing atmosphere and an oxidizing atmosphere, wherein said SCR catalyst is exposed to said alternating atmospheres.
16. The system of claim 15 , wherein said reducing atmosphere is a lean exhaust gas and said oxidizing atmosphere is a rich exhaust gas.
17. The system of claim 11 , wherein the small pore molecular sieve has a silica-to-alumina ratio of about 8 to about 150.
18. The system of claim 11 , wherein said copper is present in said small pore molecular sieve in an amount from 0.5 to 5 weight percent.
19. The system of claim 11 , wherein said NO x adsorber catalyst comprises a precious metal and a basic material selected from the group consisting of an alkali metal, an alkaline earth metal, and a rare earth metal.
20. The system of claim 8 , wherein said NO x adsorber catalyst is loaded on a first substrate and said SCR catalyst is loaded on a second substrate and the first substrate is disposed in front of the second substrate with respect to the normal flow of exhaust gas through the system.