Emissions Treatment System with Ammonia-Generating and SCR Catalysts

• US 20140047819A1
• Filed: 10/04/2013
• Published: 02/20/2014
• Est. Priority Date: 04/03/2009
• Status: Active Grant

• Current Assignee: BASF Corporation (BASF SE)
• Original Assignee: BASF SE
• Inventors: Wan, Chung-Zong, Zheng, Xiaolai, Stiebels, Susanne, Wendt, Claudia, Neubauer, Torsten, Boorse, R. Samuel
• Granted Patent: US 9,321,009 B2
• Time in Patent Office: Days
• US Class Current: 60/274
• CPC Class Codes: B01D 2251/2062 Ammonia
• CPC Class Codes: B01D 2255/102 Platinum group metals
• CPC Class Codes: B01D 2255/2042 Barium
• CPC Class Codes: B01D 2255/2045 Calcium
• CPC Class Codes: B01D 2255/206 Rare earth metals
• CPC Class Codes: B01D 2255/2063 Lanthanum
• CPC Class Codes: B01D 2255/2066 Praseodymium
• CPC Class Codes: B01D 2255/2068 Neodymium
• CPC Class Codes: B01D 2255/20753 Nickel
• CPC Class Codes: B01D 2255/20761 Copper
• CPC Class Codes: B01D 2255/2092 Aluminium
• CPC Class Codes: B01D 2255/50 Zeolites
• CPC Class Codes: B01D 2255/9022 Two layers
• CPC Class Codes: B01D 2255/91 NOx-storage component incorporated in the catalyst
• CPC Class Codes: B01D 2255/9155 Wall flow filters
• CPC Class Codes: B01D 2255/9205 Porosity
• CPC Class Codes: B01D 2258/012 Diesel engines and lean burn gasoline engines
• CPC Class Codes: B01D 53/58 Ammonia
• CPC Class Codes: B01D 53/92 of engine exhaust gases exhaust or silencing apparatus for internal combustion engines, machines or engines in general, having means for purifying, rendering innocuous or otherwise treating exhaust gases F01N3/00
• CPC Class Codes: B01D 53/9418 for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• CPC Class Codes: B01D 53/9422 : for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
• CPC Class Codes: B01D 53/9431 : Processes characterised by a specific device
• CPC Class Codes: B01D 53/9472 : in different zones
• CPC Class Codes: B01D 53/9477 : with catalysts positioned on separate bricks, e.g. exhaust systems
• CPC Class Codes: F01N 13/02 : having two or more separate silencers in series
• CPC Class Codes: F01N 2510/063 : zeolites
• CPC Class Codes: F01N 2510/0682 : having a discontinuous, uneven or partially overlapping coating of catalytic material, e.g. higher amount of material upstream than downstream or vice versa
• CPC Class Codes: F01N 3/02 : for cooling, or for removing solid constituents of, exhaust by means of electric or electrostatic separators F01N3/01 ; mixing air with exhaust in tailpipes F01N13/082, F01N13/20
• CPC Class Codes: F01N 3/021 : by means of filters
• CPC Class Codes: F01N 3/035 : with catalytic reactors , e.g. catalysed diesel particulate filters
• CPC Class Codes: F01N 3/0807 : by using absorbents or adsorbents
• CPC Class Codes: F01N 3/0814 : combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
• CPC Class Codes: F01N 3/0821 : combined with particulate filters catalysed diesel particulate filters F01N3/035
• CPC Class Codes: F01N 3/0842 : Nitrogen oxides
• CPC Class Codes: F01N 3/10 : by thermal or catalytic conversion of noxious components of exhaust by using other chemical processes, chemical aspects of catalytic conversion, e.g. using specified catalysts, B01D53/34
• CPC Class Codes: F01N 3/103 : Oxidation catalysts for HC and CO only
• CPC Class Codes: F01N 3/206 : Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents F01N3/2066 takes precedence
• CPC Class Codes: F01N 3/2066 : Selective catalytic reduction [SCR]
• CPC Class Codes: F01N 3/2073 : with means for generating a reducing substance from the exhaust gases
• CPC Class Codes: Y02T 10/12 : Improving ICE efficiencies

Abstract

Provided are emissions treatment systems for an exhaust stream having an ammonia-generating component, such as a NOx storage reduction (NSR) catalyst or a lean NOx trap (LNT) catalyst, and an SCR catalyst disposed downstream of the ammonia-generating catalyst. The SCR catalyst can be a molecular sieve having the CHA crystal structure, for example SSZ-13 or SAPO-34, which can be ion-exchanged with copper. The LNT can be layered, having an undercoat washcoat layer comprising a support material, at least one precious metal, and at least one NOx sorbent selected from the group consisting of alkaline earth elements, rare earth elements, and combinations thereof and a top washcoat layer comprising a support material, at least one precious metal, and ceria in particulate form, the top washcoat layer being substantially free of alkaline earth components. The emissions treatment system is advantageously used for the treatment of exhaust streams from diesel engines and lean burn gasoline engines.

Claims

1. An emissions treatment system for an exhaust stream of a diesel engine or a lean burn gasoline engine comprising:

an in-situ ammonia-generating component; and

an SCR catalyst disposed downstream of the ammonia-generating component, wherein the SCR catalyst comprises a molecular sieve having the CHA crystal structure, wherein the SCR catalyst is effective to reduce a spike in ammonia during cyclic operation of the engine between lean and rich operation.

2. The emissions treatment system of claim 1, wherein the SCR catalyst is present in an amount in the range of 0.5 to 2.5 g/in³.

3. The emissions treatment system of claim 1, wherein the molecular sieve comprises a copper chabazite (CuCHA), and the CuCHA is disposed on a downstream carrier.

4. The emissions treatment system of claim 3, wherein the molecular sieve is a copper chabazite SSZ-13.

5. The emissions treatment system of claim 1, wherein the molecular sieve comprises a copper SAPO (CuSAPO), and the CuSAPO is disposed on a downstream carrier.

6. The emissions treatment system of claim 5, wherein the molecular sieve is copper SAPO-34.

7. The emissions treatment system of claim 1, wherein the downstream carrier comprises a wall flow filter having a plurality of longitudinally extending passages formed by longitudinally extending walls bounding and defining said passages, wherein the passages comprise inlet passages having an open inlet end and a closed outlet end, and outlet passages having a closed inlet end and an open outlet end.

8. The emissions treatment system of claim 7, wherein the filter is coated by the SCR catalyst in the range of about 10% to 100% of the axial length.

9. The emissions treatment system of claim 7, wherein the filter is coated with the SCR catalyst along the axial length in the range of 60 to 40% from an upstream end and with an oxidation catalyst along the axial length in the range of 40 to 60% from a downstream end.

10. The emissions treatment system of claim 1, wherein the ammonia-generating component comprises a lean NOx trap (LNT) catalytic material disposed on an upstream carrier that is a flow through monolith.

11. The emissions treatment system of claim 10, wherein the lean NOx trap (LNT) catalytic material comprises a single washcoat layer having a uniform composition.

12. The emissions treatment system of claim 10, wherein the lean NOx trap (LNT) catalytic material comprises an undercoat washcoat layer and a top washcoat layer, the top washcoat layer exhibiting better low temperature NOx abatement performance than the undercoat washcoat layer.

13. The emissions treatment system of claim 12, wherein the undercoat washcoat layer comprises a support material, at least one precious metal, and at least one NOx sorbent selected from the group consisting of oxides of magnesium, calcium, strontium, barium, lanthanum, cerium, praseodymium, neodymium, and combinations thereof wherein the undercoat washcoat layer is on the carrier;

and

the top washcoat layer comprises a support material, at least one precious metal, and ceria in particulate form, the top washcoat layer being substantially free of alkaline earth components.

14. A method of converting NOx in an exhaust gas stream from a diesel engine or lean burn gasoline engine to N₂ comprising:

routing the exhaust gas stream through the emissions treatment system of claim 1.

15. The method of claim 14, comprising:

(a) contacting the exhaust gas stream comprising NOx in a lean period with the ammonia-generating component that is an LNT to sorb NOx from the exhaust gas stream;

(b) periodically altering the air/fuel ratio of the exhaust stream to provide a rich gaseous stream during a rich period;

(c) contacting the rich gaseous stream with the LNT to reduce a portion of the sorbed NOx to ammonia and sorbing ammonia on the SCR catalyst;

(d) subsequently reacting ammonia sorbed on the SCR catalyst with NOx in the exhaust gas with the SCR catalyst; and

(e) wherein the SCR catalyst is effective to reduce a spike in ammonia.

16. The method of claim 15, wherein step (d) occurs during a lean period of operation.

17. The emissions treatment system of claim 1, wherein the SCR catalyst is effective to reduce a spike in ammonia by at least about 50% or greater.

18. The emissions treatment system of claim 14, wherein the SCR catalyst is effective to reduce a spike in ammonia by at least about 50% or greater.

19. The method of claim 16, wherein the SCR catalyst is effective to reduce a spike in ammonia by at least about 50% or greater.