United States Patent No. US 626 B2 Tang et Date Patent: Apr.pdfstore.patentorder.com/pdf/us/626/us9017626.pdf · 2015. 4. 29. · FOREIGN PATENT DOCUMENTS GB g6gg46 5/1961 GB 2493449

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&12~ United States PatentTang et al.

(10) Patent No. : US 9,017,626 B2(45) Date of Patent: Apr. 28, 2015

(54) SELECTIVE CATALYTIC REDUCTIONCATALYST SYSTEM

(71) Applicant: BASE Corporation, Florham Park, NJ(US)

(72) Inventors: Weiyong Tang, East Brunswick, NJ(US); Jaya L. Mohanan, Edison, NJ(US)

(73) Assignee: BASE Corporation, Florham Park, NJ(US)

(56)

502/527. 12, 527.13; 423/213. 2, 239.1,423/239. 2; 60/274, 299, 301

See application file for complete search history.

References Cited

U.S. PATENT DOCUMENTS

3,030,181 A 4/1962 Milton et al.4,268,488 A 5/1981 Ginger

(Continued)

FOREIGN PATENT DOCUMENTS

(65) Prior Publication Data

US 2014/0301923 Al Oct. 9, 2014

Related U.S.Application Data

(60) Provisional application No. 61/781, 760, filed on Mar.14, 2013.

(51) Int. Cl.B01D 53/94F01N 3/10

(2006.01)(2006.01)

(Continued)

(52) U.S. Cl.CPC ........... B01D 53/9431 (2013.01);B01J21/063

(2013.01);B01J23/22 (2013.01);B01J23/30(2013.01);B01D 53/9404 (2013.01);B01J29/061 (2013.01);B01J29/072 (2013.01);

(Continued)

(58) Field of ClassiTication SearchUSPC ............. 502/60, 64, 300, 325, 304, 340, 353,

( * ) Notice: Subject to any disclaimer, the term of thispatent is extended or adjusted under 35U.S.C. 154(b) by 0 days.

(21) Appl. No. : 14/20S, S17

(22) Filed: Mar. 13, 2014

DEEP

102007003155 Al1876331

7/20088/2009

(Continued)

OTHER PUBLICATIONS

Primary Examiner Timothy Vanoy

(74) Attorney, Agent, or Firm Melanic Brown

(57) ABSTRACT

Described are SCR catalyst systems comprising a first SCRcatalyst composition and a second SCR catalyst compositionarranged in the system, the first SCR catalyst compositionpromoting higher N2 formation and lower N20 formationthan the second SCR catalyst composition, and the secondSCR catalyst composition having a different compositionthan the first SCR catalyst composition, the second SCRcatalyst composition promoting lower N2 formation andhigher N20 formation than the first SCR catalyst composi-tion. The SCR catalyst systems are useful in methods andsystems to catalyze the reduction of nitrogen oxides in thepresence of a reductant.

20 Claims, 11 Drawing Sheets

Krocher, Oliver et al. , Combination of V&04/WOs-TIOz, Fe-ZSMS,and Cu-ZSMS Catalysts for the Selective Catalytic Reduction ofNitric Oxide with Ammonia, Ind. Eng. Chem. Res. vol, 47 2008,8588-8593.

(Continued)

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US 9,017,626 B2Page 2

(51) Int. CI.FOJN 3/24 (2006.01)801J21/06 (2006.01)801J23/22 (2006.01)801J23/30 (2006.01)801J23/00 (2006.01)801J23/745 (2006.01)801J29/06 (2006.01)801J29/072 (2006.01)801J29/70 (2006.01)801J29/76 (2006.01)FOJN 3/20 (2006.01)

(52) U.S. CI.CPC ............ 801J29/7015 (2013.01);801J29/763

(2013.01);80JD 2255/9022 (2013.01);80JD2255/9032 (2013.01);FOJN3/J0 (2013.01);

FOJN3/2066 (2013.01);FOJN2510/'0682(2013.01);FOJN 2510/0684 (2013.01);FOJN2570/I 8 (2013.01);801D 53/9418 (2013.01);80JD 2255/2047 (2013.01);80JD 2255/2065

(2013.01);80JD 2255/20707 (2013.01);80JD2255/207/5 (2013.01);80JD 2255/20723

(2013.01);80JD 2255/20738 (2013.01);80JD2255/2076/ (2013.01);80JD 2255/20776

(2013.01);80JD 2255/2092 (2013.01);80JD2255/40 (2013.01);80JD 2255/50 (2013.01);

80JD 2255/9/ I (2013.01); Y/OS 502/527/2(2013.01); YIOS 502/527I3 (2013.01)

(56) References Cited

U.S. PATENT DOCUMENTS

4,440, 871 A4,544, 53g A4,735,927 A4,79g, g13 A4,952,545 A5,409,6gl A5,516,497 A5,833,932 A6, 125,629 A6, 162,415 A7,264,789 Bl7,462,340 B2 *7,601,622 B27,951,742 B2 *g,741,240 B2 *

200g/0241034 Al *2009/0196812 Al2009/0285737 Al2010/016662g Al2013/0121902 Al

4/198410/19854/19ggI/1989g/19904/19955/1996

11/199g10/200012/20009/2007

12/200 g

10/20095/20116/2014

10/200 gg/2009

11/20097/20105/2013

Lok et al.ZonesGerdes et al.Kato et al.Imanari et al.Kato et al.Speronello et al.SchmelzPatchettLiu et al.Verduijn et al.Schwefer et al. . .... ... .. 423/239. 1

KimChen et al. .. ... .... ... ... ... ... . 502/64Hihara et al. .. .... ... ... .. 423/213. 2Schwefer et al. . .... ... .. 423/239. 2Bull et al.Bull et al.Soeger et al.Adelmann et al.

FOREIGN PATENT DOCUMENTS

GB g6gg46 5/1961GB 2493449 A 2/2013WO WO 2011/131324 * 10/2011

OTHER PUBLICATIONS... BOIJ 29/72

English Language Abst, of DE 102007003155 Jul. 24, 200g.International Search Report Jul. 7, 2014.

~ cited by examiner

U.S. Patent Apr. 28, 2015 Sheet 1 of 11 US 9,017,626 B2




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US 9,017,626 B21

SELECTIVE CATALYTIC REDUCTIONCATALYST SYSTEM

CROSS-REFERENCE TO RELATEDAPPLICATIONS

This application claims the benefit of priority under 35U.S.C. )119(e) to U.S. Provisional Patent Application No.61/781,760, filed on Mar. 14, 2013, which is hereby incorpo-rated by reference in its entirety.

TECHNICAL FIELD

The present invention pertains to the field of selective cata-lytic reduction catalysts. More particularly, embodiments ofthe invention relate to selective catalytic reduction catalystsystems comprising a first SCR catalyst composition and asecond SCR catalyst composition, a lean burn engine exhaustsystem, and methods of using these catalyst systems in avariety of processes such as abating pollutants in exhaustgases.

BACKGROUND

Operation of lean burn engines, e.g. diesel engines and leanburn gasoline engines, provide the user with excellent fueleconomy and have very low emissions of gas phase hydro-carbons and carbon monoxide due to their operation at highair/fuel ratios under fuel lean conditions. Diesel engines, inparticular, also offer significant advantages over gasolineengines in terms of their durability and their ability to gener-ate high torque at low speed.

From the standpoint of emissions, however, diesel enginespresent problems more severe than their spark-ignition coun-terparts. Emission problems relating to particulate matter

(PM), nitrogen oxides (NO ), unburned hydrocarbons (HC)and carbon monoxide (CO). NO is a term used to describevarious chemical species of nitrogen oxides, including nitro-

gen monoxide (NO) and nitrogen dioxide (NO2), among oth-ers. NO is ofconcern because it is believed to under a processknown as photo-chemical smog formation, through a series ofreactions in the presence of sunlight and hydrocarbons, andNO is a significant contributor to acid rain. NO2, on the otherhand, has a high potential as an oxidant and is a strong lungirritant. Particulates (PM) are also connected with respiratoryproblems. As engine operation modifications are made toreduce particulates and unburned hydrocarbons on dieselengines, the NO and NO2 emissions tend to increase.

Effective abatement of NO from lean burn engines is dif-ficult to achieve because high NO conversion rates typicallyrequire reductant-rich conditions. Conversion of the NOcomponent of exhaust streams to innocuous components gen-erally requires specialized NO abatement strategies foroperation under fuel lean conditions

Selective catalytic reduction (SCR), using ammonia orammonia precursor as reducing agent is believed to be themost viable technique for the removal ofnitrogen oxides fromthe exhaust of diesel vehicles. In typical exhaust, the nitrogenoxides are mainly composed of NO (&90%), so the SCRcatalyst favors the conversion of NO and NH3 into nitrogenand water. Two major challenges in developing catalysts forthe automotive application of the ammonia SCR process areto provide a wide operating window for SCR activity, includ-ing low temperatures of from 200' C. and higher andimprovement of the catalyst's hydrothermal stability for tem-peratures above 500' C. As used herein hydrothermal stabil-ity refers to retention of a material's capability to catalyze the

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SCR of NO, with a preference for the retention to be at least85% of the material's NO conversion ability prior to hydro-thermal aging.

Metal-promoted zeolite catalysts including, among others,iron-promoted and copper-promoted zeolite catalysts, where,for instance, the metal is introduced via ion-exchange, for theselective catalytic reduction of nitrogen oxides with ammoniaare known. Iron-promoted zeolite beta has been an effectivecatalyst for the selective reduction of nitrogen oxides withammonia. Unfortunately, it has been found that under harshhydrothermal conditions, such as reduction of NO from gasexhaust at temperatures exceeding 500' C., the activity ofmany metal-promoted zeolites, such as Cu and Fe versions ofZSM-5 and Beta, begins to decline. This decline in activity isbelieved to be due to destabilization of the zeolite such as bydealumination and consequent loss ofmetal-containing cata-lytic sites within the zeolite.

To maintain the overall activity of NO reduction,increased levels of the washcoat loading of the iron-promotedzeolite catalyst must be provided. As the levels of the zeolitecatalyst are increased to provide adequate NO removal, thereis an obvious reduction in the cost efficiency of the process forNO removal as the costs of the catalyst rise.

In some SCR systems, particularly heavy duty diesel(HDD), controlling secondary pollutant N20 emitted fromthe SCR system has become more important. Additionally,certain existing catalysts, such as copper promoted zeolites(e.g Cu-SSZ-13), tend to produce unacceptably high N20emissions. Because N20 is a greenhouse gas and emissionsregulations are becoming increasingly stringent, there is aneed for systems that reduce the amount ofN20 emitted fromSCR systems.

SUMMARY

One aspect of the invention pertains to a selective catalyticreduction (SCR) catalyst system. In a first embodiment, thesystem comprises a first SCR catalyst composition and asecond SCR catalyst composition arranged in the system, thefirst SCR catalyst composition promoting higher N2 forma-tion and lower N20 formation than the second SCR catalystcomposition, and the second SCR catalyst composition hav-

ing a different composition than the first SCR catalyst com-position, the second SCR catalyst composition promotinglower N2 formation and higher N20 formation than the firstSCR catalyst composition.

In a second embodiment, the first SCR catalyst composi-tion is modified so that the first SCR catalyst composition andthe second SCR catalyst composition are disposed on a com-mon substrate.

In a third embodiment, the SCR catalyst system the first orsecond embodiments is modified so that the first SCR catalystcomposition is located upstream of the second SCR catalystcomposition.

In a fourth embodiment, the SCR catalyst system of thefirst through third embodiments is modified so that the firstSCR catalyst composition and the second SCR catalyst com-position are disposed on different substrates.

In a fifth embodiment, the system of the first through fourthembodiments is modified so that first SCR catalyst composi-tion is located upstream of the second SCR catalyst compo-sition.

In a sixth embodiment, the first or second embodiments aremodified wherein the first SCR catalyst composition and thesecond SCR catalyst composition are in a layered relation-ship, with the first SCR catalyst composition layered on top ofthe second SCR catalyst composition.

US 9,017,626 B2

In seventh embodiment, any of the first through sixthembodiments, the SCR catalyst system ofclaim the first SCRcatalyst composition comprises a mixed oxide.

In an eighth embodiment, seventh embodiment can bemodified so that the mixed oxide is selected from Fe/titania,Fe/alumina, Mg/titania, Cu/titania, Ce/Zr, vanadia/titania,

and mixtures thereof.In a ninth embodiment, the eighth embodiment is modified

so that the mixed oxide comprises vanadia/titania.In a tenth embodiment, the ninth embodiment is modified

so that the vanadia/titania is stabilized with tungsten.In an eleventh embodiment, any of the first through tenth

embodiments can be modified wherein the second SCR cata-lyst comprises a metal-exchanged 8-ring small pore molecu-lar sieve.

In a twelfth embodiment, the eleventh embodiment can bemodified wherein the molecular sieve has a structure typeselected from the group consisting ofAEI, AFT, AFX, CHA,EAB, ERI, KFI, LEV, SAS, SAT, DDR, and SAV.

In a thirteenth embodiment, the twelfth embodiment ismodified wherein the molecular sieve is an aluminosilicatezeolite and has the CHA structure type.

In a fourteenth embodiment, the thirteenth embodiment ismodified wherein the zeolite is selected from SSZ-13 andSSZ-62.

In a fifteenth embodiment, any of the eleventh throughfourteenth embodiments can be modified wherein the metal isselected from the group consisting of Cu, Fe, Co, Ce and Ni.

In a sixteenth embodiment, the fifteenth embodiment ismodified, wherein the metal is selected from Cu.

In a seventeenth embodiment, the sixteenth embodiment ismodified, wherein the zeolite is exchanged with Cu in therange of 2% to 8% by weight.

An eighteenth embodiment pertains to a selective catalyticreduction (SCR) catalyst system comprising a first SCR cata-

lyst composition comprising vanadia/titania disposed on asubstrate and a second SCR catalyst composition comprisinga metal-exchanged 8-ring small pore molecular sieve dis-

posed on a substrate.In a nineteenth embodiment, the eighteenth embodiment is

modified, wherein molecular sieve has a structure typeselected from the group consisting ofAEI, AFT, AFX, CHA,EAB, ERI, KFI, LEV, SAS, SAT, DDR, and SAV.

In a twentieth embodiment, the nineteenth embodiment ismodified, wherein the molecular sieve is an aluminosilicatezeolite and has the CHA structure type.

In a twenty-first embodiment, the twentieth embodiment ismodified, wherein the zeolite is selected from SSZ-13 andSSZ-62.

In a twenty-second embodiment, the eighteenth throughtwenty-first embodiments are modified, wherein the metal isselected from the group consisting of Cu, Fe, Co, Ce and Ni.

In a twenty-third embodiment, the twenty-second embodi-ment are modified, wherein the metal is selected from Cu.

In a twenty-fourth embodiment the eighteenth throughtwenty-third embodiments are modified, wherein the zeoliteis exchanged with Cu in the range of 2% to 8% by weight.

In a twenty-fifth embodiment, the eighteenth throughtwenty-fourth embodiments are modified wherein the vana-

dia/titania is stabilized with tungsten.In a twenty-sixth embodiment, the eighteenth through

twenty-fifth embodiments are modified, wherein the firstSCR catalyst composition and second SCR catalyst compo-sition are disposed on a common substrate.

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In a twenty-seventh embodiment, the eighteenth throughtwenty-sixth embodiments are modified, wherein the firstSCR catalyst composition is located upstream of the secondSCR catalyst composition.

In a twenty-eighth embodiment, the eighteenth throughtwenty-seventh embodiments are modified, wherein vanadia/titania promotes higher N~ formation and lower N20 forma-tion than the metal-exchanged 8-ring small pore molecularsieve, and wherein the metal-exchanged 8-ring small poremolecular sieve promotes lower N~ formation and higherN~O formation than the vanadia/titania.

In a twenty-ninth embodiment, the eighteenth throughtwenty-fifth embodiments are modified, where the first SCRcatalyst composition and second SCR catalyst compositionare disposed on separate substrates.

In a thirtieth embodiment, the twenty ninth embodiment ismodified, wherein the first SCR catalyst composition islocated upstream of the second SCR catalyst composition.

In a thirty-first embodiment, the twenty-sixth embodimentis modified wherein the first SCR catalyst composition andthe second SCR catalyst composition are in a layered rela-tionship, with the first SCR catalyst composition is layered ontop of the second SCR catalyst composition.

In a thirty-second embodiment, the thirty-first embodimentis modified, wherein molecular sieve has a structure typeselected from the group consisting ofAEI, AFT, AFX, CHA,EAB, ERI, KFI, LEV, SAS, SAT, DDR, and SAV.

In a thirty-third embodiment, the thirty-second embodi-ment is modified, wherein the molecular sieve is an alumino-silicate zeolite and has the CHA structure type.

In a thirty-fourth embodiment, the thirty-third embodimentis modified, wherein the zeolite is selected from SSZ-13 andSSZ-62.

In a thirty-fifth embodiment, the thirty-first through thirty-fourth embodiments are modified, wherein the metal isselected from the group consisting of Cu, Fe, Co, Ce, and Ni.

In a thirty sixth embodiment, the thirty fifth embodiment ismodified, wherein the metal is selected from Cu.

In a thirty seventh embodiment, the thirty-third embodi-ment is modified, wherein the zeolite is exchanged with Cu.

In a thirty-eighth embodiment, the thirty-first throughthirty-seventh embodiments are modified, wherein the vana-dia/titania is stabilized with tungsten.

Another aspect of the invention pertains to a lean burnengine exhaust as treatment system. In a thirty-ninth embodi-ment, a lean burn engine exhaust gas treatment system com-prises the catalyst system of any of the first through thirty-seventh embodiments, a lean burn engine, and an exhaust gasconduit in fluid communication with the lean burn engine,wherein the catalyst system is downstream of the engine.

In a fortieth embodiment, the thirty-ninth embodiment ismodified, wherein the engine is a heavy duty diesel engine.

Another aspect of the invention pertains to a method ofremoving nitrogen oxides from exhaust gas of a lean burnengine. In a forty-first embodiment, a method of removingnitrogen oxides from exhaust gas from a lean burn engine, themethod comprising contacting an exhaust gas stream with aselective catalytic reduction (SCR) catalyst system includinga first SCR catalyst composition comprising vanadia/titaniadisposed on a substrate and a second SCR catalyst composi-tion comprising a metal-exchanged 8-ring small poremolecular sieve disposed on a substrate.

In a forty-second embodiment, the forty-first embodimentis modified, wherein the exhaust gas comprises NO .

In a forty-third embodiment, the forty-first and forty-sec-ond embodiments are modified, wherein the lean burn engineis a heavy duty diesel engine.

US 9,017,626 B2

In a forty-fourth embodiment, a lean burn engine exhaustgas treatment system comprises the catalyst system of thenineteenth embodiment, a lean burn engine, and an exhaustgas conduit in fluid communication with the lean burn engine,wherein the catalyst system is downstream of the engine.

In a forty-fifth embodiment, the forty-fourth embodimentis modified, wherein the engine is a heavy duty diesel engine.

A forty-sixth embodiment pertains to a method of remov-ing nitrogen oxides from exhaust gas from a lean burn engine,the method comprising contacting the exhaust gas with selec-tive catalytic reduction (SCR) catalyst system including a firstSCR catalyst composition and a second SCR catalyst com-position arranged in the system, the first SCR catalyst com-position promoting higher N~ formation and lower N~O for-mation than the second catalyst composition, and the secondcatalyst composition having a different composition than thefirst SCR catalyst composition, the second catalyst composi-tion promoting lower N~ formation and higher N~O formationthan the first SCR catalyst composition.

In a forty-seventh embodiment, the first through thirtyseventh embodiments are modified, wherein the second cata-lyst composition has a higher NH3 storage capacity that thefirst catalyst composition.

In a forty-eighth embodiment, a selective catalytic reduc-tion (SCR) catalyst hybrid system for removing NOx fromengine exhaust, the system comprises a first SCR catalystcomposition and a second SCR catalyst compositionarranged in the system, the first SCR catalyst compositionhaving a faster DeNOx response time when exposed toammonia than the second catalyst composition and the sec-ond SCR catalyst composition has a higher steady stateDeNOx performance than the first catalyst composition andthe first SCR catalyst composition provides a target DeNOxpercentage at a lower ammonia storage level than the secondSCR catalyst composition to provide the same DeNOx per-centage, and wherein the system provides higher DeNOxsteady state performance than the first catalyst composition.

In a forty-ninth embodiment, the forty-eighth embodimentis modified, wherein under acceleration conditions in whichsudden increases of exhaust temperature are produced,ammonia desorbed from the hybrid system due to the tem-perature increase is less than ammonia desorbed from a sys-tem having only the second catalyst composition.

In a fiftieth embodiment, the forty-eight or forty-ninthembodiments are modified, wherein the first catalyst compo-sition comprises vanadia/titania stabilized with tungsten.

In a fifty-first embodiment, the fiftieth embodiment ismodified, wherein the second catalyst composition comprisesa metal-exchanged 8-ring small pore molecular sieve.

In a fifty-second embodiment, the fifty-first embodiment ismodified, wherein the molecular sieve has a structure typeselected from the group consisting ofAEI, AFT, AFX, CHA,EAB, ERI, KFI, LEV, SAS, SAT, DDR, and SAV.

In a fifty-third embodiment, the fifty-second embodimentis modified, wherein the molecular sieve is an aluminosilicatezeolite and has the CHA structure type.

In a fifty-fourth embodiment, the forty-eighth throughfifty-third embodiments are modified, wherein the zeolite isselected from SSZ-13 and SSZ-62 and the metal comprisesCU.

In a fifty fifth embodiment, the system of the first throughthirty-eighth embodiments are modified wherein the firstSCR catalyst composition promotes higher N~ formation andlower N~O formation than the second SCR catalyst compo-sition, and the second SCR catalyst composition promoteslower N~ formation and higher N~O formation for a tempera-ture range of 200' C. to 600' C.

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In a fifty-sixth embodiment, the forty-eighth through fi fty-fourth embodiments are modified, wherein the first SCR cata-lyst composition has a faster DeNOx response time when

exposed to ammonia than the second catalyst compositionand the second SCR catalyst composition has a higher steadystate DeNOx performance than the first catalyst compositionand the first SCR catalyst composition provides a targetDeNOx percentage at a lower ammonia storage level than thesecond SCR catalyst composition to provide the sameDeNOx percentage, and wherein the system provides higherDeNOx steady state performance than the first catalyst com-position formation for a temperature range of200' C. to 600'C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a partial cross-sectional view of a SCR cata-lyst system according to one or more embodiments;



FIG. 4 is a graph comparing N~O emissions for a SCRcatalyst system according to one or more embodiments and acomparative system;

FIG. 5 is a graph comparing N~O emissions for a SCRcatalyst system according to one or more embodiments and acomparative system;

FIG. 6 is a graph comparing N~O emissions for a SCRcatalyst system according to one or more embodiments and acomparative system, both systems with an upstream dieseloxidation catalyst;

FIG. 7 is a graph comparing N~O emissions for a SCRcatalyst system according to one or more embodiments and acomparative system, both systems with an upstream dieseloxidation catalyst.

FIG. S is a graph comparing NO conversions for a SCRcatalyst system according to one or more embodiments and acomparative system, both systems with an upstream dieseloxidation catalyst;

FIG. 9 is a graph comparing NO conversions after sulfa-tion for a SCR catalyst system according to one or moreembodiments and a comparative system, both systems withan upstream diesel oxidation catalyst;

FIG. 10 is a graph generated by a computer model asdescribed in Example 6, showing an Analysis of ResponseCurves-DeNO vs. Time at 225' C. and 10%NO~; and

FIG. 11 is a graph generated by a computer model asdescribed in Example 6, showing an Analysis of ResponseCurves-DeNO vs. Total Absorbed NH3 at 225' C. and 10%NO~.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of theinvention, it is to be understood that the invention is notlimited to the details ofconstruction or process steps set forthin the following description. The invention is capable ofotherembodiments and of being practiced or being carried out invarious ways.

Governmental regulations require the use ofNO reductiontechnologies for light and heavy-duty lean burn enginevehicles. Selective catalytic reduction (SCR) of NO usingurea is an effective and dominant emission control technol-

ogy for NO control. To meet future governmental regula-tions, an SCR catalyst system that has improved performancecompared to the current Cu-SSZ-13 based systems. Embodi-

US 9,017,626 B2

ments of the invention pertain to an SCR catalyst systemhaving lower N~O emissions and also NO conversion eflI-ciency improvement at low NH3 storage levels than singleSCR catalysts and other dual SCR catalyst systems. Withoutintending to be bound by theory, it is thought that the dynamicresponse of the SCR catalyst system according to one or moreembodiments is provided by improved NH3 storage capacity.The features of the invention described herein should beprovided over the entire SCR temperature range of interest,namely 200' C. to 600' C.According to one or more embodi-ments, the first and second SCR catalyst compositionsexclude platinum group metals such as Pt, Pd and Rh.

Embodiments of the invention are directed to SCR catalystsystems, methods for their preparation, exhaust gas purifica-tion systems, and methods of abating nitrogen oxides fromexhaust gases using such SCR catalyst systems.

Embodiments are directed to the use of SCR catalyst sys-tems providing improved NO performance for lean burnengines. While the SCR catalyst systems can be used in anylean burn engine, in specific embodiments, the catalyst sys-tems are to be used in heavy duty diesel applications. Heavyduty diesel applications include diesel engine poweredvehicles having a gross vehicle weight rating (GVWR) ofabove 8,500 lbs federally and above 14,000 lbs in California(model year 1995 and later). The SCR catalyst systemsaccording to embodiments may have use in other engines aswell, including, but not limited to, nonroad diesel engines,locomotives, marine engines, and stationary diesel engines.The invention may have applicability to other lean burnengines types as well such as light duty diesel, compressednatural gas and lean burn gasoline direct injected engines.

With respect to the terms used in this disclosure, the fol-lowing definitions are provided.

As used herein, the term "catalyst" or "catalyst composi-tion" refers to a material that promotes a reaction. As usedherein, the phrase "catalyst system" refers to a combination oftwo or more catalysts, for example a combination of a firstSCR catalyst and a second SCR catalyst. The catalyst systemmay be in the form of a washcoat in which the two SCRcatalysts are mixed together.

As used herein, the terms "upstream" and "downstream"refer to relative directions according to the flow of an engineexhaust gas stream from an engine towards a tailpipe, with theengine in an upstream location and the tailpipe and any pol-lution abatement articles such as filters and catalysts beingdownstream from the engine.

As used herein, the term "stream" broadly refers to anycombination of flowing gas that may contain solid or liquidparticulate matter. The term "gaseous stream" or "exhaust gasstream" means a stream of gaseous constituents, such as theexhaust of a lean burn engine, which may contain entrainednon-gaseous components such as liquid droplets, solid par-ticulates, and the like. The exhaust gas stream of a lean burnengine typically further comprises combustion products,products of incomplete combustion, oxides ofnitrogen, com-bustible and/or carbonaceous particulate matter (soot), andun-reacted oxygen and nitrogen.

As used herein, the term "substrate" refers to the mono-lithic material onto which the catalyst composition is placed,typically in the form of a washcoat containing a plurality ofparticles containing a catalytic composition thereon. A wash-coat is formed by preparing a slurry containing a specifiedsolids content (e.g. , 30-90%by weight) ofparticles in a liquidvehicle, which is then coated onto a substrate and dried toprovide a washcoat layer.

As used herein, the term "washcoat" has its usual meaningin the art of a thin, adherent coating of a catalytic or other

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material applied to a substrate material, such as a honeycomb-type carrier member, which is sufficiently porous to permitthe passage of the gas stream being treated.

"Catalytic article" refers to an element that is used to pro-mote a desired reaction. For example, a catalytic article maycomprise a washcoat containing catalytic compositions on asubstrate.

In one or more embodiments, the substrate is a ceramic ormetal having a honeycomb structure. Any suitable substratemay be employed, such as a monolithic substrate of the typehaving fine, parallel gas flow passages extending therethrough from an inlet or an outlet face of the substrate suchthat passages are open to fluid flow there through. The pas-sages, which are essentially straight paths from their fluidinlet to their fluid outlet, are defined by walls on which thecatalytic material is coated as a washcoat so that the gasesflowing through the passages contact the catalytic material.The flow passages of the monolithic substrate are thin-walledchannels, which can be of any suitable cross-sectional shapeand size such as trapezoidal, rectangular, square, sinusoidal,hexagonal, oval, circular, etc. Such structures may containfrom about 60 to about 900 or more gas inlet openings (ke.cells) per square inch of cross section.

The ceramic substrate may be made of any suitable refrac-tory material, e.g. cordierite, cordierlte-u-alumina, siliconnitride, zircon mullite, spodumene, alumina-silica-magnesia,zircon silicate, sillimanite, a magnesium silicate, zircon, pet-alite, u-alumina, an aluminosilicate and the like.

The substrates useful for the catalyst compositions ofembodiments of the present invention may also be metallic innature and be composed of one or more metals or metalalloys. The metallic substrates may be employed in variousshapes such as pellets, corrugated sheet or monolithic form.Specific examples of metallic substrates include the heat-resistant, base-metal alloys, especially those in which iron isa substantial or major component. Such alloys may containone or more of nickel, chromium, and aluminum, and the totalof these metals may advantageously comprise at least about15 wt. % of the alloy, for instance, about 10 to 25 wt. %chromium, about I to 8 wt. % of aluminum, and about 0 to 20wt. % of nickel.

According to a first aspect of the invention, a selectivecatalytic reduction (SCR) catalyst system comprises a firstSCR catalyst composition and a second SCR catalyst com-position arranged in the system. In one or more embodiments,the second SCR catalyst composition has a different compo-sition than first SCR catalyst composition. The first SCRcatalyst composition promotes higher N~ formation andlower N~O formation than the second SCR catalyst compo-sition, while the second catalyst composition promotes lower

N~ formation and higher N~O formation than the first SCRcatalyst composition. To reduce NH3 emissions, in one ormore embodiments, the first SCR catalyst should have a lowerNH3 adsorption capacity/desorption temperature than thesecond SCR catalyst composition.

In one or more embodiments, the first SCR catalyst com-position and the second SCR catalyst composition are on thesame or a common substrate. In other embodiments, the firstSCR catalyst composition and second SCR catalyst compo-sition are on separate substrates.

In one embodiment, the first SCR catalyst and the secondSCR catalyst are arranged in a laterally zoned configuration,with the first catalyst upstream from the second catalyst. Theupstream and downstream catalysts can be arranged on thesame substrate or on different substrates separated from eachother. In another specific embodiment, the first SCR catalystand the second SCR catalyst are in a layered arrangement

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with the second SCR catalyst being disposed on a substrateand the first SCR catalyst in a layer overlying the second SCRcatalyst. Each of these embodiments will be described inmore detail below.

In specific embodiments, each of the first SCR catalystcomposition and second SCR catalyst composition is used asa molded catalyst, still more specifically as a molded catalystwherein the SCR catalyst composition is deposited on a suit-able refractory substrate, still more specifically on a "honey-comb" substrate, for the selective reduction of nitrogenoxides NO, i.e. for selective catalytic reduction of nitrogenoxides. According to embodiments of the invention, the SCRcatalyst composition can be in the form of self-supportingcatalyst particles or as a honeycomb monolith formed of theSCR catalyst composition.

According to one or more embodiments, the first SCRcatalyst composition comprises a mixed oxide. As usedherein, the term "mixed oxide" refers to an oxide that containscations of more than one chemical element or cations of asingle element in several states of oxidation. In one or moreembodiments, the mixed oxide is selected from Fe/titania(e.g. FeTi03), Fe/alumina (e.g. FeA1~03), Mg/titania (e.g.MgTi03), Mg/alumina (e.g. MgA1~03), Mn/alumina, Mn/ti-

tania (e.g. MnOJTIO~) (e.g. MnOJA1~03), Cu/titania (e.g.Cu Ti03), Ce/Zr (e.g. CeZrO~), Ti/Zr (e.g. TIZrO~), vanadia/titania (e.g. V~05/TIO~), and mixtures thereof. In specificembodiments, the mixed oxide comprises vanadia/titania.The vanadia/titania oxide can be activated or stabilized withtungsten (e.g. WO3) to provide V~05/TIO~/WO3.

According to one or more embodiments, a first SCR cata-lyst composition comprising vanadia/titania generates sig-nificantly less N, O than zeolite SCR catalysts, especiallyunder rich NO~ conditions. In one or more embodiments, thefirst SCR catalyst composition comprises titania on to whichvanadia has been dispersed. The vanadia can be dispersed atconcentrations ranging from I to 10wt%, including I, 2, 3, 4,5, 6, 7, 8, 9, 10 wt %. In specific embodiments the vanadia isactivated or stabilized by tungsten (WO3). The tungsten canbe dispersed at concentrations ranging from 0.5 to 10 wt %,including I, 2, 3, 3. 4, 5, 6, 7, 8, 9, and 10, wt %. Allpercentages are on an oxide basis.

According to one or more embodiments, the second SCRcatalyst comprises a metal-exchanged molecular sieve. Themetal is selected from Cu, Fe, Co, Ni, Ce and Pt. In specificembodiments, the metal is Cu.

As used herein, the term "molecular sieves" refers to mate-rials based on an extensive three-dimensional network ofoxygen ions containing generally tetrahedral type sites andhaving a pore distribution. Molecular sieves such as zeoliteshave been used extensively to catalyze a number of chemicalreactions in refinery and petrochemical reactions, and cataly-sis, adsorption, separation, and chromatography. Forexample, with respect to zeolites, both synthetic and naturalzeolites and their use in promoting certain reactions, includ-ing conversion of methanol to olefins (MTO reactions) andthe selective catalytic reduction (SCR) of nitrogen oxideswith a reductant such as ammonia, urea or a hydrocarbon inthe presence ofoxygen, are well known in the art. Zeolites arecrystalline materials having rather uniform pore sizes which,depending upon the type ofzeolite and the type and amount ofcations included in the zeolite lattice, range from about 3 to 10Angstroms in diameter.

Catalyst compositions employed in the SCR process ide-ally should be able to retain good catalytic activity over thewide range of temperature conditions of use, for example,200' C. to 600' C. or higher, under hydrothermal conditions.Hydrothermal conditions are often encountered in practice,

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such as during the regeneration ofa soot filter, a component ofthe exhaust gas treatment system used for the removal ofparticles.

According to specific embodiments, the molecular sievesof the second SCR catalyst composition have 8-ring poreopenings and double-six ring secondary building units, forexample, those having the following structure types: AEI,AFT, AFX, CHA, EAB, ERI, KFI, LEV, SAS, SAT, DDR, andSAV. According to one or more embodiments, it will beappreciated that by defining the molecular sieves by theirstructure type, it is intended to include the structure type andany and all isotypic framework materials such as SAPO,AIPO and MeAPO materials having the same structure type.

Zeolites having 8-ring pore openings and double-six ringsecondary building units, particularly those having cage-likestructures have recently found interest in use as SCR cata-lysts. A specific type of zeolite having these properties ischabazite (CHA), which is a small pore zeolite with 8 mem-ber-ring pore openings (having a pore size in at least onedimension of less than 43 Angstroms, e.g. about 3.8 Ang-stroms) accessible through its 3-dimensional porosity. A cagelike structure results from the connection of double six-ringbuilding units by 4 rings.

Metal-promoted, particularly copper-promoted alumino-silicate zeolites having the CHA structure type (e.g. , SSZ-13and SSZ-62) and a silica to alumina molar ratio greater than I,particularly those having a silica to alumina ratio greater thanor equal to 5, 10, or 15 and less than about 1000, 500, 250, 100and 50 have recently solicited a high degree of interest ascatalysts for the SCR of oxides of nitrogen in lean burningengines using nitrogenous reductants. This is because of thewide temperature window coupled with the excellent hydro-thermal durability of these materials, as described in U.S.Pat.No. 7,601,662. Prior to the discovery of metal promotedzeolites described in U.S. Pat. No. 7,601,662, while the lit-erature had indicated that a large number of metal-promotedzeolites had been proposed in the patent and scientific litera-ture for use as SCR catalysts, each of the proposed materialssuffered from one or both of the following defects: (I) poorconversion of oxides of nitrogen at low temperatures, forexample 350' C. and lower; and (2) poor hydrothermal sta-bility marked by a significant decline in catalytic activity inthe conversion ofoxides ofnitrogen by SCR. Thus, the inven-

tion described in U.S. Pat. No. 7,601,662 addressed a com-pelling, unsolved need to provide a material that would pro-vide conversion ofoxides of nitrogen at low temperatures andretention of SCR catalytic activity after hydrothermal aging attemperatures in excess of 650' C.

Zeolitic chabazite include a naturally occurring tectosili-cate mineral of a zeolite group with approximate formula:(Ca,Na~, K~,Mg)AI~Si40». 06H~O (e.g. , hydrated calciumaluminum silicate). Three synthetic forms of zeolitic chaba-zite are described in "Zeolite Molecular Sieves, "by D. W.Breck, published in 1973 by John Wiley & Sons, which ishereby incorporated by reference. The three synthetic formsreported by Breck are Zeolite K-G, described in J. Chem.Soc., p. 2822 (1956), Barrer et al; Zeolite D, described inBritish Patent No. 868,846 (1961);and Zeolite R, describedin U.S.Pat. No. 3,030,181,which are hereby incorporated byreference. Synthesis of another synthetic form of zeoliticchabazite, SSZ-13, is described in U.S. Pat. No. 4,544, 538,which is hereby incorporated by reference. Synthesis of asynthetic form of a molecular sieve having the chabazitecrystal structure, silicoaluminophosphate 34 (SAPO-34), isdescribed in U.S. Pat. No. 4,440,871 and No. 7,264,789,which are hereby incorporated by reference. A method ofmaking yet another synthetic molecular sieve having chaba-

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zite structure, SAPO-44, is described in U.S. Pat. No. 6, 162,415, which is hereby incorporated by reference.

In more specific embodiments, reference to an aluminosili-cate zeolite structure type limits the material to molecularsieves that do not include phosphorus or other metals substi-tuted in the framework. Of course, aluminosilicate zeolitesmay be subsequently ion-exchanged with one or more pro-moter metals such as iron, copper, cobalt, nickel, cerium orplatinum group metals. However, to be clear, as used herein,"aluminosilicate zeolite" excludes aluminophosphate mate-rials such as SAPO, AIPO, and MeAPO materials, and thebroader term "zeolite" is intended to include alumino silicatesand aluminophosphates. In one or more embodiments, themolecular sieve can include all aluminosilicate, borosilicate,gallosilicate, MeAPSO, and MeAPO compositions. Theseinclude, but are not limited to SSZ-13, SSZ-62, natural cha-bazite, zeolite K-G, Linde D, Linde R, LZ-218, LZ-235.LZ-236, ZK-14, SAPO-34, SAPO-44, SAPO-47, ZYT-6,CUSAPO-34, CUSAPO-44, and CUSAPO-47.

In one or more embodiments, the molecular sieve of thesecond SCR catalyst composition has a structure typeselected from the group consisting ofAEI, AFT, AFX, CHA,EAB, ERI, KFI, LEV, SAS, SAT, DDR, and SAV. In a specificembodiment, the molecular sieve is an alumino silicate zeoliteand has the CHA structure type, for example SSZ-13 orSSZ-62. In another specific embodiment, the molecular sieveis an aluminosilicate zeolite and has the AEI structure type,for example SSZ-39.

In specific embodiments, the 8-ring small pore molecularsieve promoted with copper has a mole ratio of silica toalumina greater than about 15, even more specifically greaterthan about 20. In specific embodiments, the 8-ring small poremolecular sieve promoted with copper has a mole ratio ofsilica to alumina in the range from about 20 to about 256,more specifically in the range from about 25 to about 40.

In specific embodiments, the atomic ratio of copper toaluminum exceeds about 0.25. In more specific embodi-ments, the ratio of copper to aluminum is from about 0.25 toabout I, even more specifically from about 0.25 to about 0.5.In even more specific embodiments, the ratio of copper toaluminum is from about 03 to about 0.4.

In general, the SCR catalyst system according to one ormore embodiments should exhibit both good low temperatureNO conversion activity (NO conversion &50% at 200' C.)and good high temperature NO conversion activity (NOconversion &70% at 450' C.). The NO activity is measuredunder steady state conditions at maximum NH3-slip condi-tions in a gas mixture of500 ppm NO, 500 ppm NH3, 10%O~,5% H~O, balance N~ at a volume-based space velocity of80,000 h '.

According to one or more embodiments, to reduce NH3emissions, the first SCR catalyst composition should have alower NH3 adsorption/desorption temperature than the sec-ond SCR catalyst composition.

According to one or more embodiments, the second SCRcatalyst composition comprises a metal-exchanged 8-ringsmall pore molecular sieve. In other words, the second SCRcatalyst composition is an 8-ring small pore molecular sievethat is promoted with a metal. In one or more embodiments,the metal can be selected from the group consisting ofCu, Fe,Co, Ce, and Ni. In a specific embodiment, the metal isselected from Cu.Wt % of Promoter Metal:

The promoter metal (e.g. Cu) content of the metal-ex-changed 8-ring small pore molecular sieve, calculated as themetal oxide, in specific embodiments is at least about 2 wt. -

%, even more specifically at least about 2.5 wt. -% and in even

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more specific embodiments at least about 3 wt. -%, reportedon a volatile-free basis. In even more specific embodiments,the metal (e g. Cu) content ofthe metal-exchange 8-ring small

pore molecular sieve, calculated as the metal oxide, is in therange ofup to about 8 wt. -%, based on the total weight of thecalcined molecular sieve reported on a volatile free basis.Therefore, in specific embodiments, ranges of the 8-ringsmall pore molecular sieve promoted with a metal selectedfrom Cu, Fe, Co, Ce, and Ni, calculated as the metal oxide, arefrom about 2 to about 8 wt. -%, more specifically from about2 to about 5 wt. -%, and even more specifically from about 2.5to about 3.5 wt. -%, in each case reported on an oxide basis.

In one or more embodiments, the first SCR catalyst and thesecond SCR catalyst are arranged in a laterally zoned con-figuration, with the first catalyst upstream from the secondcatalyst. As used herein, the term "laterally zoned" refers tothe location of the two SCR catalysts relative to one another.Lateral means side-by-side such that the first SCR catalystcomposition and the second SCR catalyst composition arelocated one beside the other with the first SCR catalyst com-position upstream of the second SCR catalyst composition.According to one or more embodiments, the laterally zonedfirst and second SCR catalysts can be arranged on the same ora common substrate or on different substrates separated fromeach other.

According to one or more embodiments, the vanadia/tita-nia and the metal-exchanged 8-ring small pore molecularsieve are disposed on a common or the same substrate. Inother embodiments, the vanadia/titania and the metal-ex-changed 8-ring small pore molecular sieve are disposed onseparate substrates. Whether on the same substrate or ondifferent substrates, according to one or more embodiments,the vanadia/titania is located upstream of the metal-ex-changed 8-ring small pore molecular sieve.

In one or more embodiments, the vandia/titania promoteshigher N~ formation and lower N~O formation than the metal-exchanged 8-ring small pore molecular sieve, and the metal-exchanged 8-ring small pore molecular sieve promotes lower

N~ formation and higher N~O formation than the vanadia/titania.

Compositions used commercially, especially in mobileapplications, comprise TIO~ on to which WO3 and V~05 havebeen dispersed at concentrations ranging from 5 to 20 wt. %and 0.5 to 6 wt. %, respectively. These catalysts may containother inorganic materials such as SIO~ and ZrO~ acting asbinders and promoters.

Referring to FIG. 1, an exemplary embodiment of a later-

ally spaced system is shown. The SCR catalyst system 10 isshown in a laterally zoned arrangement where the first SCRcatalyst composition 1S is located upstream of the secondSCR catalyst composition 20 on a common substrate 12.Thesubstrate 12 has an inlet end 22 and an outlet end 24 definingan axial length L. In one or more embodiments, the substrate12 generally comprises a plurality of channels 14 of a hon-eycomb substrate, of which only one channel is shown incross-section for clarity. The first SCR catalyst composition1S extends from the inlet end 22 of the substrate 12 throughless than the entire axial length L of the substrate 12. The

length of the first SCR catalyst composition 1S is denoted asfirst zone 1Sa in FIG. 1.The first SCR catalyst composition 1Scan, in specific embodiments comprise vanadia/titania. Thesecond SCR catalyst composition 20 can, in specific embodi-ments, comprise a metal-exchanged 8-ring small poremolecular sieve. The second SCR catalyst composition 20extends from the outlet end 24 of the substrate 12 through lessthan the entire axial length L ofthe substrate 12.The length ofthe second catalyst composition is denoted as the second zone

13US 9,017,626 B2

1420b in FIG. 1.The SCR catalyst system 10 is effective for theselective catalytic reduction of NO .

It will be appreciated that length of the first zone and thesecond zone can be varied. In one or more embodiments, thefirst zone and second zone can be equal in length. In otherembodiments, the first zone can be 20%, 25%, 35% or 40%,60%, 65%, 75% or 80% of the length L of the substrate, withthe second zone respectively covering the remainder of thelength L of the substrate.

Referring to FIG. 2, another embodiment of a laterallyzoned SCR catalyst system 110 is shown. The SCR catalystsystem 110shown is a laterally zoned arrangement where thefirst SCR catalyst composition 118 is located upstream of thesecond SCR catalyst composition 120 on separate substrates112 and 113.The first SCR catalyst composition 118 is dis-

posed on a substrate 112, and the second SCR catalyst com-position is disposed on a separate substrate 113. The sub-

strates 112and 113can be comprised of the same material ora different material. The substrate 112 has an inlet end 122aand an outlet end 124a defining an axial length Ll. Thesubstrate 113 has an inlet end 122b and an outlet end 124bdefining an axial length L2. In one or more embodiments, thesubstrates 112 and 113 generally comprise a plurality ofchannels 114 of a honeycomb substrate, of which only onechannel is shown in cross-section for clarity. The first SCRcatalyst composition 118 extends from the inlet end 122a ofthe substrate 112 through the entire axial length Ll of thesubstrate 112 to the outlet end 124a. The length of the firstSCR catalyst composition 118is denoted as first zone 11Sa inFIG. 2. The first SCR catalyst composition 118 can, in spe-cific embodiments, comprise vanadia/titania. The secondSCR catalyst composition 120 can, in specific embodiments,comprise a metal-exchanged 8-ring small pore molecularsieve. The second SCR catalyst composition 120 extendsfrom the outlet end 124b of the substrate 113 through theentire axial length L2 of the substrate 113 to the inlet end122b. The second catalyst composition 120 defines a secondzone 120a. The SCR catalyst system 110 is effective for theselective catalytic reduction of NO . The length of the zones11Saand 120a can be varied as described with respect to FIG.1.

One or more embodiments of the present invention aredirected to a selective catalytic reduction (SCR) catalyst sys-tem comprising a first SCR catalyst composition comprisingvanadia/titania disposed on a substrate and a second SCRcatalyst composition comprising a metal-exchanged 8-ringsmall pore molecular sieve disposed on a substrate, whereinthe first SCR catalyst composition and the second SCR cata-lyst composition are in a layered arrangement or relationship.In one or more embodiments, the first SCR catalyst compo-sition is layered on top of the second SCR catalyst composi-tion.

According to one or more embodiments, the second SCRcatalyst composition is washcoated onto a substrate, and thenthe first SCR catalyst composition is washcoated in a layeroverlying the second SCR catalyst composition. In one ormore embodiments, the layering is designed to optimize thefirst catalyst composition/second catalyst composition drygain for a desirable balance between the benefits of acting asa protective shield and the potential drawbacks of diffusionbarrier increase. Under low temperatures for extended opera-tions, sulfur is a major concern for Cu-CHA catalysts. Incomparison, vanadia/titania (V~05/TIO~) SCR catalysts areknown for having superior sulfur tolerance.

The first and second SCR catalyst compositions caninclude the compositions as described above.

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Referring to FIG. 3, an exemplary embodiment ofa layeredSCR catalyst system 210 is shown. The SCR catalyst systemcan be in a layered arrangement where the first SCR catalystcomposition 218 is layered on top of the second SCR catalystcomposition 220 on a common substrate 212. The substrate212 has an inlet end 222 and an outlet end 224 defining an

axial length L3. In one or more embodiments, the substrate212 generally comprises a plurality of channels 214 of ahoneycomb substrate, ofwhich only one channel is shown incross-section for clarity. The first SCR catalyst composition218 extends from the inlet end 222 of the substrate 212through the entire axial length L3 of the substrate 212 to theoutlet end 224. The length of the first SCR catalyst composi-tion 218 is denoted as 21Sa in FIG. 3. The first SCR catalystcomposition 218 can, in specific embodiments, comprisevanadia/titania. The second SCR catalyst composition 220can, in specific embodiments, comprise a metal-exchanged8-ring small pore molecular sieve. The second SCR catalystcomposition 220 extends from the outlet end 224 of the sub-

strate 212 through the entire axial length L3 of the substrate212 to the outlet end 224. The SCR catalyst system 210 iseffective for the selective catalytic reduction of NO .

It will be appreciated that the thickness of the layer 218 canbe relatively thin compared to the thickness of the layer 220.The thickness of layer 218 can be sufficiently thick to form aprotective overcoat on layer 220 to protect the catalyst com-position of layer 220 from sulfation. In one embodiment, thethickness of the first catalyst composition layer 218 is 5-10%ofthe overall thickness ofthe composite layer 218 and 220. Inother embodiments, the thickness of the first catalyst compo-sition layer is 20-30% of the overall thickness of the compos-ite layer 218 and 220. In some embodiments, the thickness ofthe first catalyst composition layer is 30-40% of the overallthickness of the composite layer 218 and 220.Exhaust Gas Treatment System:

In one aspect of the invention, exhaust gas treatment sys-tem comprises a lean burn engine, and exhaust gas conduit influid communication with the lean burn engine, and a selec-tive catalytic reduction catalyst system including a first SCRcatalyst composition and a second SCR catalyst compositionarranged in the system according to one or more embodi-ments. In specific embodiments, the lean burn engine is aheavy duty diesel engine.

In one or more embodiments, the exhaust gas treatmentsystem includes an exhaust gas stream containing a reductantsuch as ammonia, urea and/or hydrocarbon, and in specificembodiments, ammonia and/or urea. In specific embodi-ments, the exhaust gas treatment system further comprises asecond exhaust gas treatment component, for example, a sootfilter or a diesel oxidation catalyst.

The soot filter, catalyzed or non-catalyzed, may beupstream or downstream of the SCR catalyst system accord-ing to one or more embodiment. The diesel oxidation catalystin specific embodiments is located upstream of the SCR cata-lyst system according to one or more embodiments. In spe-cific embodiments, the diesel oxidation catalyst and the cata-lyzed soot filter are upstream from the SCR catalyst system.

In specific embodiments, the exhaust is conveyed from thelean burn engine to a position downstream in the exhaustsystem, and, in more specific embodiments, containing NO,where a reductant is added and the exhaust stream with theadded reductant is conveyed to the SCR catalyst systemaccording to one or more embodiments.

In specific embodiments, the soot filter comprises a wall-flow filter substrate, where the channels are alternatelyblocked, allowing a gaseous stream entering the channels

15US 9,017,626 B2

16from one direction (inlet direction), to flow through the chan-nel walls and exit from the channels from the other direction(outlet direction).

An ammonia oxidation catalyst may be provided down-

stream of the SCR catalyst system to remove any slippedammonia from the system. In specific embodiments, theAMOX catalyst may comprise a platinum group metal suchas platinum, palladium, rhodium or combinations thereof. Inmore specific embodiment, the AMOX catalyst can include awashcoat containing SCR catalyst system including a firstSCR catalyst composition disposed on a substrate and a sec-ond SCR catalyst composition disposed on a substrate.

AMOX and/or SCR catalyst composition can be coated onthe flow through or wall-flow filter. Ifa wall flow substrate isutilized, the resulting system will be able to remove particu-late matter along with gaseous pollutants. The wall-flow filtersubstrate can be made from materials commonly known in theart, such as cordierite, aluminum titanate or silicon carbide. Itwill be understood that the loading of the catalytic composi-tion on a wall flow substrate will depend on substrate prop-erties such as porosity and wall thickness, and typically willbe lower than loading on a flow through substrate.SCR Activity:

The invention is now described with reference to the fol-lowing examples. Before describing several exemplaryembodiments of the invention, it is to be understood that theinvention is not limited to the details of construction or pro-cess steps set forth in the following description. The inventionis capable of other embodiments and of being practiced orbeing carried out in various ways.

EXAMPLES

Example I

Preparation of Catalyst Materials

Vanadia- Titania CatalystA standard vanadia/titania/tungsten (V~05 (2.5'zo)/WO3

(10'zo)/TIO~) catalyst was prepared and a slurry was made atabout 30-40'zo solids by milling to provide a washcoat slurry.

Cu-ZeoliteA CuCHA (SSZ-13)powder catalyst was prepared by mix-

ing 100g ofNa-form CHA, having a silica/alumina mole ratioof 30, with 400 mL of a copper (II) acetate solution of about1.0 M. The pH was adjusted to about 3.5 with nitric acid. Anion-exchange reaction between the Na-form CHA and thecopper ions was carried out by agitating the slurry at about80' C. for about I hour. The resulting mixture was thenfiltered to provide a filter cake, and the filter cake was washedwith deionized water in three portions until the filtrate wasclear and colorless, and the washed sample was dried.

The obtained CuCHA catalyst comprised CuO at a range ofabout 2.5 to 3.5'zo by weight, as determined by ICP analysis.A CuCHA slurry was prepared to 40'zo target solids. Theslurry was milled and a binder of zirconium acetate in diluteacetic acid (containing 30'zo ZrO~) was added into the slurrywith agitation.

Example 2

Catalyst System Laterally Zoned

The slurries described above were separately coated onto12oDx6oL cellular ceramic substrate having a cell density of400 cpsi (cells per square inch) and a wall thickness of 4 mil.The coated substrates were dried at 110' C. for 3 hours and

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calcined at about 400' C. for I hour. The coating process wasrepeated once to obtain a target washcoat loading of in therange of 3 g/in on the vanadia-titania coated core, and 2.1

g/in on the CuCHA coated core. The samples were aged for200 hours at 550' C. on a heavy duty diesel engine test cell.

Comparative Example 3

Catalyst System Laterally Zoned

Example 2 was repeated except both substrates werecoated with CuCHA at the same loading.

Example 4

Engine Testing of Laterally Zoned Systems

The catalyst systems in Example 3 and 4 were tested out ona 9 L heavy duty engine together with a motoring electricdynamometer. The test bench is capable of running bothsteady-state and transient test cycles. In the current work,both a Heavy duty transient test cycle (HDTP) and a non-roadtransient test cycle (NRTC) were run. Catalysts samples werefull size 12o diameters parts (400/4), which were 200 h-550'C. engine aged prior to evaluations. To demonstrate theadvantage of the lateral zoned system of a 12ox6o V-SCRbrick upstream of a 12ox6o Cu-CHA brick, a referencesequential 12ox6o Cu+12ox6o Cu SCR system was alsoevaluated. In such a comparative study, only the first SCRcatalyst brick were switched between V-SCR and Cu-SCR,other systems such as the second SCR brick, urea injectionsystem, sample probing locations were kept the same.

During evaluation tests, two MKS FTIR samplers werepositioned at SCR upstream and downstream, respectively,for gaseous emissions measurements, including, but not lim-ited to, NO, NO2, and N20 etc. Exhaust sampling lines wereheated at constant 190' C.All evaluation tests in this Examplewere run with ULSD (ultra low sulfur diesel) fuel wheresulfur concentration is less than 15 ppm (wt 'zo).

In one configuration, a diesel oxidation catalyst and cata-lyzed soot filter were placed upstream of the SCR catalystsystem to simulate a heavy duty engine transient cycle. Inanother configuration, the SCR catalyst system was testedwithout upstream catalysts or filters.

FIG. 4 shows the results from the HDTP cycle and FIG. 5shows the results from the NRTC cycle. Both tests showed thesignificant reduction in N~O emission for the samples inwhich the vanadia-titania catalyst was placed upstream of theCu-zeolite sample.

The tests were repeated with an upstream diesel oxidationcatalyst and catalyzed soot filter. FIG. 6 shows the results forthe HDTP cycle, and FIG. 7 shows the results for the NRTC.Again, the system with the vanadia-titania catalyst upstreamof the Cu Zeolite system showed much lower N~O emissions.

Example 5

Preparation of Layered Catalyst System

Washcoats from Example I were utilized and coated ontoa single substrate in a layered configuration as described withrespect to FIG. 3. The layering was varied as follows for thefollowing samples.Comparative Sample 5A CuCHA Single Coat 2.1 g/inComparative Sample 5B Bottom Coat CuCHA 2.1 g/in; TopCoat 0.2 g/in Titania

17US 9,017,626 B2

18Sample 5C CuCHA Bottom Coat~uCHA 2.1 g/in; TopCoat 0.1 g/in Vanadia TitaniaSample 5D CuCHA Bottom Coat 2.1 g/in; Top Coat 0.2 g/in

Vanadia TitaniaSample 5E CuCHA Bottom Coat 2.1 g/in; Top Coat 0.5 g/inVanadia- TitaniaSample 5F CuCHA Bottom Coat 2.1 g/in3; Top Coat I g/inVanadia Titania

Example 6

Testing of Layered System

Nitrogen oxides selective catalytic reduction (SCR) efft-ciency and selectivity of a fresh catalyst core was measured

by adding a feed gas mixture of 500 ppm of NO, 500 ppm ofNH3, 10% O~, 5% H~O, balanced with N~ to a steady statereactor containing a I "Dx3"L catalyst core. The reaction wascarried at a space velocity of 80,000 hr ' across a 150' C. to460' C. temperature range.

The samples were aged in the presence of 10%H~O at 550'C. for 4 hours, followed by measurement of the nitrogenoxides SCR efficiency and selectivity by the same process asoutlined above for the SCR evaluation on a fresh catalyst core.

Nitrogen oxides selective catalytic reduction (SCR) efft-ciency and selectivity of a fresh catalyst core was measured

by adding a feed gas mixture of 500 ppm of NO, 500 ppm ofNH3, 10% O~, 5% H~O, balanced with N~ to a steady statereactor containing a I "Dx3"L catalyst core. The reaction wascarried at a space velocity of 80,000 hr ' across a 150' C. to460' C. temperature range.

Samples prepared as above were tested for SCR perfor-mance. In addition, all of the samples except for 5F wereexposed to sulfur (sulfation) at 300' C. at 20 ppm SO~ and 5%H~O and 10% O~ in a feed gas upstream of a DOC core withthe SCR catalysts downstream for 6 hours.

FIG. S shows the NO conversion versus temperature forsamples 5A-F before sulfation and FIG. 9 shows NOx con-version versus temperature after sulfation. The fresh conver-sions were comparable for all samples, except for sample 5F.For the sulfated sample, FIG. 9 shows that sample 5E hadsignificantly better NO conversion.

Example 9

Dynamic Response Modeling

FIGS. 10 and 11 illustrate the improvements in dynamicresponse behavior of a system according to one or moreembodiments. FIGS. 10 and 11were prepared using a com-puter model. Lab reactor and engine lab DeNO performancemeasurements to describe the performance of the individualcomponents within the system are the input for the computermodel used. The example in FIG. 10 shows the DeNO per-formance as a function of time obtained with fresh systemswithout ammonia stored prior to the start of the simulation/urea dosing. A Cu-SSZ13 system and a Vanadia based SCRsystem are compared with the Vanadia/Cu-SSZ-13 hybridsystem. The Vanadia based SCR catalyst was placed in frontof the Cu-SSZ13 catalyst with a 50/50 size ratio within themodeled hybrid system. Low temperature operation at 225'C. exhaust temperature and 50000 I/h space velocity at 500ppm NO inlet concentration at an NO~/NO ratio of 10%wasused for the comparison. These SCR inlet conditions can beseen as being typical for systems operated in engine applica-tions with a low precious metal loading on an oxidationsystem in front of the SCR or in SCR only systems. The NSR

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was chosen at 1.1 in order to reach relatively fast the maxi-mum DeNO performance of the systems studied. Althoughthe Cu-SSZ13 system reaches higher DeNO performancesafter 700 sec. of dosing, the DeNO response behavior afterstart of dosing at 0 sec. has a different ranking. The responseof the Vanadia based SCR system is faster relative to theDeNO increase after start of dosing compared with the Cu-SSZ13 system (e.g. up to 350 sec.).The hybrid system Vana-dia-based SCR in combination with the Cu-SSZ13 has theadvantage of being close to the dynamic response behavior ofthe Vanadia-based SCR and additionally delivering highersteady state DeNO performances as indicated in FIG. 10after, for example, 1000 sec.

FIG. 11was generated by re-plotting FIG. 10 by using thetotal adsorbed NH3 on the catalysts in grams as the x-axisresults. The practical advantage of the hybrid system can beseen when comparing the necessary ammonia stored on thecatalysts to reach e.g. 70% DeNO . The Cu-SSZ13 systemneeds approximately 4.5 g NH3, while the Vanadia-basedsystem would need approximately 2.5 g, and the proposedhybrid system approximately 3 g ammonia stored. The hybridsystem therefore would deliver DeNO performance fasterand at lower NH3 storage levels compared with the Cu-SSZ13SCR system. Furthermore the hybrid system would deliverhigher DeNO steady state performance compared with theVanadia based SCR system. The higher DeNO performancereached at lower NH3 storage levels has a further advantagewhen the engine accelerates with sudden increases in exhausttemperature. In this case, the amount of ammonia desorbedfrom the catalysts due to the temperature increase is less forthe hybrid system compared with the Cu-SSZ13 system andtherefore would result into lower NH, slip values behind theSCR portion of the aftertreatment system. Even when usingan ammonia oxidation catalyst is used to control the NH3 slipcoming from the SCR, very high ammonia peaks from accel-eration events are often issues for the ammonia oxidationcatalyst due to the typical volumes installed in combinationwith the ammonia light-off characteristics.

Reference throughout this specification to "one embodi-ment, ""certain embodiments, ""one or more embodiments"or "an embodiment" means that a particular feature, structure,material, or characteristic described in connection with theembodiment is included in at least one embodiment of theinvention. Thus, the appearances of the phrases such as "inone or more embodiments, " "in certain embodiments, " "inone embodiment" or "in an embodiment" in various placesthroughout this specification are not necessarily referring tothe same embodiment of the invention. Furthermore, the par-ticular features, structures, materials, or characteristics maybe combined in any suitable manner in one or more embodi-ments.

Although the invention herein has been described withreference to particular embodiments, it is to be understoodthat these embodiments are merely illustrative of the prin-ciples and applications of the present invention. It will beapparent to those skilled in the art that various modificationsand variations can be made to the method and apparatus ofthepresent invention without departing from the spirit and scopeof the invention. Thus, it is intended that the present inventioninclude modifications and variations that are within the scopeof the appended claims and their equivalents.

What is claimed is:1. A selective catalytic reduction (SCR) catalyst system

comprising a first SCR catalyst composition and a secondSCR catalyst composition arranged in the system, the firstSCR catalyst composition promoting higher N~ formationand lower N~O formation than the second SCR catalyst com-

19US 9,017,626 B2

20position, and the second SCR catalyst composition having adifferent composition than the first SCR catalyst composi-tion, the second SCR catalyst composition promoting lower

N~ formation and higher N~O formation than the first SCRcatalyst composition, wherein the first SCR catalyst compo-sition and the second SCR catalyst composition are in alayered relationship, with the first SCR catalyst compositionlayered on top of the second SCR catalyst composition.

2. The SCR catalyst system of claim 1, wherein the firstSCR catalyst composition comprises a mixed oxide.

3. The SCR catalyst system of claim 2, wherein the mixedoxide is selected from Fe/titania, Fe/alumina, Mg/titania,Cu/titania, Ce/Zr, vanadia/titania, and mixtures thereof.

4. The SCR catalyst system of claim 3, wherein the mixedoxide comprises vanadia/titania.

5. The SCR catalyst system of claim 4, wherein the vana-dia/titania is stabilized with tungsten.

6. The SCR catalyst system ofclaim 2, wherein the secondSCR catalyst comprises a metal-exchanged 8-ring small poremolecular sieve.

7. The SCR catalyst system of claim 6, wherein themolecular sieve has a structure type selected from the groupconsisting of AEI, AFT, AFX, CHA, EAB, ERI, KFI, LEV,SAS, SAT, DDR, and SAV.

S. The SCR catalyst system of claim 7, wherein themolecular sieve is an alumino silicate zeolite and has the CHAstructure type.

9. The catalyst of claim S, wherein the zeolite is selectedfrom SSZ-13 and SSZ-62.

10. The catalyst system of claim 6, wherein the metal isselected from the group consisting of Cu, Fe, Co, Ce and Ni.

11.The catalyst system of claim 10, wherein the metal isselected from Cu.

12. The catalyst system of claim S, wherein the zeolite isexchanged with Cu in the range of 2% to 8% by weight.

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13.A selective catalytic reduction (SCR) catalyst systemcomprising a first SCR catalyst composition comprisingvanadia/titania disposed on a substrate and a second SCRcatalyst composition comprising a metal-exchanged 8-ringsmall pore molecular sieve disposed on a substrate, whereinthe first SCR catalyst composition and the second SCR cata-lyst composition are in a layered relationship, with the firstSCR catalyst composition layered on top of the second SCRcatalyst composition.

14. The catalyst system of claim 13, wherein the secondcatalyst composition comprises Cu and an aluminosilicatezeolite having the CHA structure type.

15.The catalyst system of claim 14, wherein the zeolite isselected from SSZ-13 and SSZ-62.

16. The catalyst system of claim 13, wherein vanadia/titania promotes higher N~ formation and lower N~O forma-tion than the metal-exchanged 8-ring small pore molecularsieve, and wherein the metal-exchanged 8-ring small poremolecular sieve promotes lower N~ formation and higherN~O formation than the vanadia/titania, and the metal-ex-changed 8-ring small pore molecular sieve has a higherammonia storage capacity than the vanadia/titania.

17.A lean burn engine exhaust gas treatment system com-prising the catalyst system ofclaim 1, a lean burn engine, andan exhaust gas conduit in fluid communication with the leanburn engine, wherein the catalyst system is downstream oftheengine.

1S.The system of claim 17, wherein the engine is a heavyduty diesel engine.

19.A method of removing nitrogen oxides from exhaustgas from a lean burn engine, the method comprising contact-ing an exhaust gas stream the catalyst system of claim 1.

20. The method of claim 19, wherein the lean burn engineis a heavy duty diesel engine.

Documents

United States Patent No. US 626 B2 Tang et Date Patent: Apr.pdfstore.patentorder.com/pdf/us/626/us9017626.pdf · 2015. 4. 29. · FOREIGN PATENT DOCUMENTS GB g6gg46 5/1961 GB 2493449