(19) United States
`(12) Patent Application Publication (10) Pub. N0.2 US 2002/0044897 A1
`(43) Pub. Date:
`Apr. 18, 2002
`Kakwani et al.
`
`US 20020044897A1
`
`(54) EXHAUST SYSTEM FOR ENHANCED
`REDUCTION OF NITROGEN OXIDES AND
`PARTICULATES FROM DIESEL ENGINES
`
`Related US. Application Data
`
`(63) Non-provisional of provisional application No.
`60/225,478, ?led on Aug. 15, 2000.
`
`(76) Inventors: Ramesh M. Kakwani, Whitehouse
`Station, NJ (US); Kenneth C. Voss,
`Somerville, NJ (US); Joseph A.
`Patchett, Basking Ridge, NJ (US);
`Karl R. Grimston, Upper Strensharn
`(GB)
`Correspondence Address:
`Stephen I. Miller
`ENGELHARD CORPORATION
`101 Wood Avenue
`P.O. Box 770
`Iselin, NJ 08830-0770 (US)
`
`(21) Appl. No.:
`
`09/816,912
`
`(22) Filed:
`
`Mar. 23, 2001
`
`Publication Classi?cation
`
`(51) Int. c1.7 ........................ .. B01D 53/56; B01D 50/00;
`B01D 53/34
`(52) US. Cl. ................. .. 422/172; 423/2132; 423/239.1;
`423/213.5; 422/169; 422/168
`
`(57)
`
`ABSTRACT
`
`Adiesel engine aftertreatrnent exhaust system uses catalyzed
`soot ?lters for particulate matter reduction and urea SCR
`catalysts for NOX reduction on diesel engines in a combined
`system to loWer particulate matter and NOX at the same
`time. With this integral emission control system, diesel
`engines are able to meet ultra low emission standards.
`
`1
`
`JM 1032
`Johnson Matthey v BASF
`IPR2015-01266
`
`

`

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`Patent Application Publication Apr. 18, 2002 Sheet 7 0f 15
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`Patent Application Publication Apr. 18, 2002 Sheet 8 0f 15
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`Patent Application Publication Apr. 18, 2002 Sheet 9 0f 15
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`US 2002/0044897 A1
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`Patent Application Publication Apr. 18, 2002 Sheet 10 0f 15
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`Patent Application Publication Apr. 18, 2002 Sheet 11 0f 15
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`Patent Application Publication Apr. 18, 2002 Sheet 12 0f 15
`
`US 2002/0044897 A1
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`Patent Application Publication Apr. 18, 2002 Sheet 13 0f 15
`
`US 2002/0044897 A1
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`

`

`Patent Application Publication Apr. 18, 2002 Sheet 14 0f 15
`
`US 2002/0044897 A1
`
`15
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`

`Patent Application Publication Apr. 18, 2002 Sheet 15 0f 15
`
`US 2002/0044897 A1
`
`T>16
`
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`
`16
`
`

`

`US 2002/0044897 A1
`
`Apr. 18, 2002
`
`EXHAUST SYSTEM FOR ENHANCED
`REDUCTION OF NITROGEN OXIDES AND
`PARTICULATES FROM DIESEL ENGINES
`
`CROSS REFERENCE TO PATENT
`APPLICATION UNDER 35 USC §119
`
`[0001] This application claims the bene?t of US. Provi
`sional Application No. 60/225,478, ?led Aug. 15, 2000,
`entitled “EXHAUST SYSTEM FOR ENHANCED
`REDUCTION OF NITROGEN OXIDES AND PARTICU
`LATES FROM DIESEL ENGINES”.
`
`BACKGROUND
`[0002] A) Field of Invention
`[0003] This invention relates generally to a diesel exhaust
`aftertreatment system and more particularly to a diesel
`exhaust treatment system that simultaneously provides for a
`high level reduction of nitrogen oxides (NOx) and particu
`late emissions under lean engine operating conditions.
`[0004] B) Incorporation by Reference
`[0005] The folloWing United States patents are incorpo
`rated by reference herein and made a part hereof. Speci?
`cally, the compositions of the catalysts disclosed in the
`patents beloW and hoW the compositions are made and/or
`applied to the disclosed ?lter or SCR catalysts are incorpo
`rated herein so that such material need not be repeated or
`explained again in detail in the Detailed Description of this
`invention.
`
`[0006] US. Pat. No. 4,833,113 to Imanari et al.,
`issued May 23, 1989, entitled “Denitration Catalyst
`for Reducing Nitrogen Oxides in Exhaust Gas”;
`
`[0007] US. Pat. No. 4,961,917 to Byrne, issued Oct.
`9, 1990, entitled “Method for Reduction of Nitrogen
`Oxides With Ammonia Using Promoted Zeolite
`Catalysts”;
`
`[0008] US. Pat. No. 5,100,632 to Dettling et al.,
`issued Mar. 31, 1992, entitled “CatalyZed Diesel
`Exhaust Particulate Filter”; and,
`
`[0009] US. Pat. No. 5,804,155 to Farrauto et al.,
`issued Sep. 8, 1998, entitled “Basic Zeolites as
`Hydrocarbon Traps for Diesel Oxidation Catalysts”.
`
`[0010] While the catalysts disclosed in the patents incor
`porated by reference herein may be used in the present
`invention, they do not, per se, or, in and of themselves, form
`the present invention.
`[0011] C) Prior Art
`[0012] Compression ignition diesel engines have great
`utility and advantage as vehicle poWer plants because of
`their inherent high thermal efficiency (i.e. good fuel
`economy) and high torque at loW speed. Diesel engines run
`at a high A/F (air to fuel) ratio under very fuel lean
`conditions. Because of this they have very loW emissions of
`gas phase hydrocarbons and carbon monoxide. HoWever,
`diesel exhaust is characteriZed by relatively high emissions
`of nitrogen oxides (NOx) and particulates. The particulate
`emissions, Which are measured as condensed material at 52
`EC, are multi phase being comprised of solid (insoluble)
`carbon soot particles, liquid hydrocarbons in the form of
`
`lube oil and unburned fuel, the so called soluble organic
`fraction (SOF), and the so called “sulfate” in the form of
`SO3+H2O=H2SO4.
`[0013] Both NOx and particulates have been difficult
`diesel exhaust components to convert and future emissions
`standards have been recently adopted in the US and Europe
`for both heavy duty and light duty diesel poWered vehicle
`Which are expected to require reduction of both of these
`emissions by at least 50% and quite likely by 70-90%.
`[0014] One commercial aftertreatment technology Which
`has proven very successful for reduction of NOx under lean
`exhaust conditions for stationary sources is Selective Cata
`lytic Reduction (SCR). In this process NOx is reduced to N2
`With NH3 over a catalyst (e.g. Zeolite, V/T i). This technology
`is capable of NOx reduction in excess of 90% and thus it is
`one of the best candidates for meeting the aggressive NOx
`reduction goals. SCR is currently under development for
`mobile source, vehicle applications using urea (e.g. aqueous
`solution) as the source of NH3. SCR is very efficient for NOx
`reduction as long as the exhaust temperature is Within the
`active temperature range of the catalyst (e.g. >300 EC).
`Unfortunately diesel exhaust temperatures are many times
`considerably loWer than that required for good catalyst
`ef?ciency (i.e., beloW “light-off”). This is especially true for
`light duty (LD) diesel applications such as diesel autos
`Which operate at light load for the most part, resulting in
`very loW exhaust temperatures (150-250 EC). Even diesel
`trucks operate under conditions Which result in exhaust
`temperatures beloW the optimum temperatures for SCR
`catalysts. Unfortunately, one of the best, most stable, SCR
`catalysts, Which is of the Zeolite type (eg The assignee,
`Engelhard Corporation’s ZNX catalyst, a Fe-Beta Zeolite),
`also has the highest optimum operating temperature. As a
`result its effectiveness is greatly diminished at diesel exhaust
`temperatures of interest.
`[0015] One key aftertreatment technology under develop
`ment for very high level particulate reduction is the diesel
`particulate ?lter. There are many knoWn ?lter structures that
`can be used to remove particulates from diesel exhaust,
`including honeycomb Wall-?oW ?lters, Wound or packed
`?ber ?lters, open-cell foams, sintered metal ?lters, etc.
`HoWever, ceramic Wall-?oW ?lters have received the most
`attention. These ?lters are capable of removing over 90% of
`the particulate material from diesel exhaust and thus can
`meet this emissions reduction goal. The ?lter is a physical
`structure for removing particles from exhaust and the accu
`mulating particles Will increase the back pressure from the
`?lter on the engine. Thus the accumulating particles (soot+
`hydrocarbons) have to be continuously or periodically
`burned out of the ?lter to maintain an acceptable backpres
`sure level. Unfortunately, the carbon soot particles require
`temperatures in excess of 500-550 EC to be combusted
`under oxygen rich (lean) exhaust conditions. This is higher
`than typical diesel exhaust temperatures. A means must be
`provided to loWer the soot burning temperature in order to
`provide for “passive” regeneration of the ?lter. One good
`Way to accomplish this is to provide a suitably formulated
`catalyst Which is applied to the ?lter The presence of the
`catalyst has been found to provide soot combustion and
`thereby regeneration of the ?lter at temperatures accessible
`Within the diesel engine’s exhaust under realistic duty
`cycles. In this Way a CatalyZed Soot Filter (CSF) or Cata
`lyZed Diesel Particulate Filter (CDPF) can be an effective
`
`17
`
`

`

`US 2002/0044897 A1
`
`Apr. 18, 2002
`
`Way to provide for >90% particulate reduction along With
`passive burn-out of the accumulating soot and thereby ?lter
`regeneration.
`[0016] In stationary applications, a number of arrange
`ments routinely use ?lters upstream of an SCR catalyst With
`an ammonia reductant injected betWeen ?lter and SCR
`catalyst. Several arrangements are disclosed in Nitrogen
`Oxides Control Technology Fact Book, 1992, Noyes Data
`Corporation, pages 84-105. HoWever, all the temperatures
`for SCR are high and the ?lters, discussed generally, are of
`the dust particulate type such as electrostatic precipitators.
`
`[0017] Hug Engineering AG has developed a gas puri?
`cation stationary system described in SAE paper 930363,
`“Of-Highway Exhaust Gas After-Treatment Combining
`Urea-SCR, Oxidation Catalysis and Traps”. In this system,
`NH3 is injected upstream of catalyst beds containing an SCR
`folloWed by an oxidation catalyst. In a later Hug brochure
`(1996) a soot ?lter bed (optional) is provided in a casing
`adjacent to and upstream of a SCR reactor adjacent to and
`upstream of an oxidation catalyst and the urea injected into
`the Waste gases passing through, in sequence, the ?lter, SCR
`and oxidation catalyst. The soot ?lter is described as a
`?brous bundle Which ?lters ?ne soot particles from the
`exhaust stream that have a carcinogenic effect. The Hug
`system disclosed has been applied to a ferry and other large
`diesel engine applications operating for the most part at
`steady speeds and higher temperatures than the vehicular
`applications of the present invention. A Hug brochure for
`stationary gas puri?cation systems describes Hug’s “Staru”
`system in Which the soot ?lter is split from the SCR and
`oxidation catalysts With NH3 injected therebetWeen. The
`soot ?lter described as ?brous to continue the function of
`trapping ?ne soot particles but is catalytically coated to
`regenerate or burn off the soot at 450 EC. In general, the Hug
`systems have shoWn the ability to reduce NOx exhaust
`emissions from large diesel engines operating generally
`steady state at higher temperatures than light duty diesel
`engines by injecting NH3 upstream of SCR-oxidation cata
`lysts and using a doWnstream ?brous, regeneration ?lter to
`trap ?ne soot particles.
`
`[0018] The patent literature discloses US. Pat. No. 5,746,
`989 to Murachi et al. issued May 5, 1998 and PCT appli
`cation PCT/GB99/03281 (published Apr. 20, 2000 as WO
`00/21647) Which use NOx absorbers that are periodically
`regenerated. DoWnstream of the NOx absorber is an oxida
`tion catalyst and betWeen absorber and oxidation catalyst is
`a particulate ?lter. In the ’989 patent, the absorber is
`regenerated by varying the A/F ratio and in the PCT appli
`cation, NOx reactant is injected upstream of the absorber.
`
`[0019] US. Pat. No. 4,912,776 to Alcorn issued Mar. 27,
`1990 discloses an oxidation catalyst, an SCR catalyst doWn
`stream and adjacent to the oxidation catalyst, and a reductant
`source introduced to the exhaust betWeen the oxidation
`catalyst and the SCR catalyst. Consistent With at least one of
`the theories of the present invention, the Alcorn concept is
`believed to produce improved NOx reduction. Avariation of
`Alcorn is disclosed in PCT application NO. PCT/GB99/
`00292 (published Aug. 12, 1999 as WO 99/39809)in Which
`upstream of Alcorn’s oxidation catalyst is placed a particu
`late ?lter and the source of reductant is positioned doWn
`stream of the SCR catalyst and upstream of the particulate
`?lter. The particulate ?lter is disclosed as a Wall-?oW ?lter
`
`effective to cause “combustion” at relatively loW tempera
`tures in the presence of NO2 Which is not believed especially
`bene?cial in the arrangement disclosed in the PCT applica
`tion. US. Pat. No. 4,902,487 to Cooper et al. issued Feb. 20,
`1990 should also be noted for its disclosure of a particulate
`?lter upstream of a platinum based catalyst Which arrange
`ment is said to generate NO2 from the exhaust gas.
`
`SUMMARY OF THE INVENTION
`[0020] Accordingly, it is one of the major undertakings of
`this invention to provide an aftertreatment system con?g
`ured With a CatalyZed Soot Filter (Pt/ZrO2—CeO2) up
`stream of a Zeolite (e.g. ZNX) SCR Catalyst to produce
`substantially better NOx conversion performance than the
`Zeolite SCR Catalyst alone, especially for higher NSR
`(normaliZed stoichiometric ratio) levels of reductant and at
`loWer exhaust temperatures.
`[0021] Particularly, the CSF and ZNX con?guration
`makes the SCR more viable for LD diesel (lean burn)
`applications Where duty cycles are characteriZed by loW
`exhaust temperatures. The CSF and ZNX SCR con?guration
`also exhibits better utiliZation of the NH3 (preferred embodi
`ment) reductant derived from injected urea solution than the
`ZNX SCR catalyst alone con?guration and exhibits Zero or
`very loW NH3 slip under all conditions. The CSF and ZNX
`SCR catalyst con?guration is a viable aftertreatment system
`for simultaneous high level (eg >80%) reduction of both
`TPM and NOx for diesel engines.
`
`[0022] One aspect of this invention is to combine particu
`late ?ltration With SCR to achieve the required high levels
`(>90%) of NOx and particulate removal from diesel exhaust
`simultaneously and thereby meet the objectives and over
`come the emissions related problems. Speci?cally, the con
`?guration of the invention combines a catalyZed soot ?lter in
`the exhaust up-stream of the SCR catalyst. Although any
`type of CSF can be used for this invention, the preferred type
`is one having a relatively high platinum (Pt) loading. This
`gives good soot burning (i.e., ?lter regeneration) character
`istics along With other unanticipated advantages (see syn
`ergy, beloW). Although either V/T i of Zeolite SCR catalysts
`can be used, a Zeolite catalyst such as ZNX is preferred
`because of its excellent hydrothermal stability.
`[0023] An important factor of this invention is the discov
`ery that there is an important synergy betWeen the CSF and
`the SCR catalyst in that the presence of the CSF up-stream
`of the SCR catalyst signi?cantly enhanced the NOx reduc
`tion performance of the SCR catalyst. In this con?guration
`the ZNX SCR catalyst exhibited higher NOx conversion
`than the SCR catalyst alone at all temperatures, plus it
`extended the effective NOx conversion range of the ZNX
`SCR catalyst doWn to temperatures at least as loW as 200 EC
`Which is Well beloW the effective temperature range of the
`ZNX catalyst alone.
`
`[0024] It is thus an object of the invention to provide a
`system for improved conversion of NOx emissions from a
`diesel engine, or in another sense, for improved NOx
`emission conversion for any type of internal combustion
`engine of a lean burn type Which produces relatively high
`NOx emissions.
`
`[0025] It is another object of the invention to provide an
`improved exhaust treatment system Which removes particu
`lates and reduces NOx from diesel engine exhaust gases.
`
`18
`
`

`

`US 2002/0044897 A1
`
`Apr. 18, 2002
`
`[0026] Yet another object of the invention is to provide an
`improved exhaust treatment system for diesel engines Which
`extends the loWer temperature range at Which an SCR
`catalyst used in the system is effective to reduce NOx
`emissions.
`
`[0027] Still another speci?c object of the invention is to
`provide an improved exhaust treatment system for diesel
`engines Which has an ability to better utiliZe an external
`reductant or reducing agent in the reduction of NOx mini
`miZing the tendency of the system to produce reductant slip.
`
`[0028] Still another object of the invention is to provide a
`simple tWo part (?lter & SCR) emission system sufficient to
`oxidiZe CO and HC, reduce the particulate emissions and
`reduce NOx emissions to N2. That is an oxidation catalyst
`(doWnstream of the SCR catalyst) is strictly speaking, not
`necessary to meet emission regulations. An oxidation cata
`lyst may, hoWever, be provided to insure against ammonia
`slip Which is potentially possible under transient emission
`conditions. Such oxidation catalyst, if used, Would be of
`smaller capacity than those conventionally used to oxidiZe
`ammonia slip occurring in conventional ammonia reductant
`systems.
`[0029] These and other objects, features and advantages of
`the invention Will become apparent to those skilled in the art
`upon reading and understanding the Detailed Description of
`the Invention set forth beloW taken in conjunction With the
`draWings described beloW.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0030] The invention may take form in certain parts and in
`an arrangement of certain parts taken together and in con
`junction With the attached draWings Which form a part
`hereof and Wherein:
`
`[0031] FIG. 1 is a schematic arrangement depicting a 7.2
`liter Heavy Duty 300 HP diesel engine exhaust system and
`particularly an engine bench set-up for testing the catalyZed
`soot ?lter and urea SCR catalyst of the present invention;
`
`[0032] FIG. 2 is a plot of graphs of engine test results
`comparing NOx conversion performance of an exhaust
`system using an SCR catalyst alone and an exhaust system
`using CSF and SCR catalysts as a function of NSR at 470
`EC inlet temperature for the engine of FIG. 1 operated under
`100% load at 1,800 rpm producing engine out NOx of 780
`ppm at space velocity of 51.33 k hr-1;
`
`[0033] FIG. 3 is a plot of graphs of engine test results
`comparing maximum NH3 break through for an exhaust
`system having CSF and SCR catalysts and an exhaust
`system having only an SCR catalyst as a function of NSR
`under the same engine conditions set forth for FIG. 2;
`
`[0034] FIG. 4 is a plot of graphs similar to FIG. 2
`shoWing engine test results comparing NOx conversion
`performance of exhaust systems having only an SCR cata
`lyst and CSF and SCR catalysts as function of NSR at 345
`EC SCR inlet temperature for the engine of FIG. 1 operated
`under 60% load at 1,800 rpm producing engine out NOx of
`400 ppm at space velocity of 46.94 k hr.—1;
`
`[0035] FIG. 5 is a plot of graphs shoWing engine test
`results comparing average and maximum NH3 break
`through for an exhaust system having the SCR catalyst alone
`
`and an exhaust system having the CSF and SCR catalysts as
`a function of NSR at conditions speci?ed in FIG. 4;
`
`[0036] FIG. 6 is a plot of graphs similar to FIGS. 2 and
`4 shoWing NOx conversion performance of an exhaust
`system having only an SCR catalyst and an exhaust system
`having the CSF and SCR catalysts as a function of NSR at
`200 EC SCR inlet temperature for the engine of FIG. 1
`operated under 14% load at 1,800 ppm producing engine out
`NOx of 200 ppm at space velocity of 28.33 k hr.—1;
`
`[0037] FIG. 7 is a plot of graphs similar to that shoWn in
`FIGS. 3 and 5 of maximum NH3 breath through for an
`exhaust system having the CSF and SCR catalysts and the
`SCR catalyst alone as a function of NSR at engine condi
`tions speci?ed in FIG. 6;
`[0038] FIG. 8 is a plot of graphs of test results for exhaust
`systems con?gured With the CSF and SCR catalysts shoWing
`NOx conversion as function of NSR (normaliZed stoichio
`metric ratio) at different exhaust temperatures produced by
`the engine of FIG. 1 operated at 2200 rpm under different
`loads;
`[0039] FIG. 9 is a plot of graphs of engine test results
`comparing NOx conversion performance of emission sys
`tem using the CSF and SCR catalysts and an emission
`system using an SCR catalyst alone as a function of inlet
`temperature for a high range of NSR values (0.61 to 0.78);
`
`[0040] FIG. 10 is a plot of curves of ESC (13 mode OICA
`cycle) test results (NOx and NSR) for an emission system
`using an SCR catalyst only scaled to the normal 300 HP
`engine rating;
`[0041] FIG. 11 is a plot of curves similar to FIG. 10 and
`for the ESC test but using an emission system having a CSF
`and SCR catalyst con?guration scaled to the normal 300 HP
`engine rating;
`[0042] FIG. 12 is a plot of curves similar to FIG. 10 and
`for the ESC test for an emission system using only an SCR
`catalyst scaled to a normal 180 HP engine rating;
`
`[0043] FIG. 13 is a plot of curves similar to FIG. 10 and
`for the ESC test for an emission system using a CSF and
`SCR catalyst con?guration scaled to a normal 180 HP
`engine rating;
`[0044] FIG. 14A is a schematic depiction of the preferred
`embodiment of the present invention;
`
`[0045] FIGS. 14B and 14C are schematic depictions of
`possible alternative con?gurations of the system of the
`present invention; and,
`[0046] FIGS. 15 and 16 are schematic end vieW and
`section vieWs, respectively, of a catalyZed Wall ?oW ?lter
`used in the invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`[0047] Referring noW to the draWings Where the shoWings
`are for the purpose of illustrating a preferred embodiment of
`the invention only and not for the purpose of limiting same,
`there is shoWn in FIG. 1 a bench test unit 10 Which does not
`represent the commercial embodiment of the invention in its
`preferred embodiment. (The preferred embodiment is sche
`matically illustrated in FIG. 14A.) The test unit 10 is shoWn
`
`19
`
`

`

`US 2002/0044897 A1
`
`Apr. 18, 2002
`
`in FIG. 1 because the unanticipated synergy betWeen an
`up-stream CSF 12 and an SCR catalyst 14 Was discovered
`via engine tests in an engine-dynamometer test cell depicted
`schematically in FIG. 1.
`
`[0048] The engine 15 Was a Model Year 1998 Caterpillar
`3126 (7.2 liter) Direct Injected, Turbo-Charged/Intercooled
`engine rated at 300 HP @ 2200 RPM. For the purposes of
`the tests the engine Was calibrated to produce 4 g/bhp-hr
`NOx emissions over the US. Heavy Duty Transient Test
`Cycle.
`
`[0049] For the tests the fuel Was an ultra-loW sulfur (ULS)
`diesel fuel provided by Phillips Petroleum. This fuel had a
`nominal sulfur content of 3 ppm.
`
`[0050] The soot ?lter substrate used for the tests Was an
`EX-80 cordierite Wall-?oW ?lter purchased from Corning
`Inc. The substrate Was 10.5“ in diameter and 12.0“ long. This
`?lter had a total volume of 17.03 liters (1039 m3) or 2.4
`times the sWept displacement of the engine. It had a hon
`eycomb cell spacing of 100 cpsi With a 17 mil Wall thick
`ness. The soot ?lter catalyst used for the tests Was the
`assignee, Engelhard Corporation’s, ?lter catalyst designated
`MEX 003. This catalyst is comprised of 250 g/ft3 ZrO2
`applied to the soot ?lter substrate by solution impregnation
`as Zirconium acetate solution and then dried, plus 500 g/ft3
`CeO2 applied next by solution impregnation as cerium (III)
`nitrate/citric acid solution (Ce:citrate mole ratio=1:1) and
`then dried and calcined at 450 EC, plus 75 g/ft3 platinum
`applied by solution impregnation as amine-solubiliZed Pt(II)
`hydroxide (i.e. Pt “A” Salt) Which Was then dried and
`calcined at 450 EC. This comprised the catalyZed soot ?lter
`in the preferred embodiment or CSF 12.
`
`[0051] SCR catalysts 14A, 14B used for the tests Were the
`assignee’s, (Engelhard Corporation), ZNX catalyst. TWo
`SCR units 14A, 14B arranged in a “Y” split are shoWn
`because FIG. 1 is a bench unit capable of testing different
`catalysts so that a reference catalyst performance can be
`compared to a modi?ed catalyst. With respect to the subject
`invention, both SCR catalysts 14A, 14B are identical. The
`SCR catalysts 14A, 14B, each Were comprised of ca. (cal
`culated) 2 g/in3 Iron-exchanged Beta Zeolite together With 4
`Wt % ZrO2 binder. This catalyst Was coated onto ?oW-thru
`monolith substrates Which Were 10.5 “ in diameter and 6.0“
`long With a cell spacing of 300 cpsi. Each substrate had a
`volume of 8.51 liters (520 m3) for a total catalyst volume of
`17.02 liters or 1040 m3.
`
`[0052] As can be seen from FIG. 1, the exhaust from
`engine 15 containing particulates and NOx is conveyed to an
`inlet 16 of CSF 12. On passing through CSF 12 the particu
`lates including soot and SOF (soluble organic fractions) are
`largely removed (>90%). In addition gas phase HC’s and
`carbon monoxide are removed from the exhaust by the
`catalyst on the soot ?lter. The resultant cleaned exhaust
`contains primarily NOx as the main regulated emission.
`
`[0053] DoWn-stream of the CSF a solution of urea in Water
`is injected into the exhaust, in this case via an air assisted
`noZZle designated generally by reference numeral 18. The
`concentration of urea in the solution Was 32.5 Wt % and it
`Was delivered to the injection noZZle via a pump. The
`injection rate of urea solution Was regulated via the pump
`rate so that the ratio of urea injected to NOx in the exhaust
`could be controlled and knoWn. As is Well knoWn, the urea
`
`(H4N2CO) molecule can be decomposed by hydrolysis in
`the exhaust to give ammonia (NH3)Wh1Ch1S the active NOx
`reductant. Each urea molecule yields tWo molecules of NH3.
`Because of this 2:1 yield and for the purposes of describing
`the testing and results the urea-to-NOx ratio Will be referred
`to as the NormaliZed Stoichiometric Ratio (NSR). This
`simply means that for an NSR of 1 the NH3:NOx molar ratio
`in the exhaust is 1:1. A 1:1 molar ratio of NH3 to NOx is the
`theoretical ratio to achieve 100% NOx conversion to N2.
`
`[0054] The exhaust stream containing the injected urea
`and/or ammonia products at the desired NSR Was next
`conveyed to the ZNX SCR catalysts 14A, 14B. As noted
`above, for the tests, the exhaust How Was split using a
`Y-connector 19 and conveyed to tWo ZNX catalysts or
`bricks 14A, 14B Which are mounted in parallel as shoWn.
`This arrangement gave a total volume of SCR catalyst 14 of
`17.03 liters or 2.4 times the sWept displacement of the
`engine. DoWn-stream of the ZNX SCR catalysts 14A, 14B
`the exhaust streams Were brought back together via a
`Y-connector 20 and the exhaust gas, noW cleaned of both
`particulates and NOx Was conveyed out of the test cell.
`
`[0055] Sampling points for exhaust analysis are shoWn in
`FIG. 1 by lines designated by reference numerals 22A, 22B,
`22C and 22D. The normal exhaust emission bench Was used
`for analyZing NOx, HC’s and CO. The NOx Was determined
`by the chemiluminescence technique. In addition, Fourier
`Transform Infrared Spectroscopy (FTIR) Was used to ana
`lyZe for nitrogen-species at the sampling points. The FTIR
`alloWed for accurate determination of NO, N02, N20 and
`NH3 in the exhaust. Exhaust temperatures Were also mea
`sured via thermocouples at sampling points 22A, 22B, 22C
`and 22D.
`
`[0056] Control tests Were run for comparison With the
`ZNX SCR catalysts 14A, 14B alone. In this case, CSF 12
`Was removed from the exhaust system and replaced by a
`straight pipe (not shoWn). Avalve (not shoWn) doWn-stream
`of the SCR catalysts Was used to provide the same back
`pressure on the engine as When the CSF Was present in order
`to maintain the same engine-out NOx levels. The valve
`provides an adjustable back pressure for the step load tests
`discussed beloW.
`
`[0057] Steady state tests Were run at 1800 RPM on the
`engine. Engine load Was varied to achieve different exhaust
`temperatures. The steady state test conditions and corre
`spondence to draWings to be subsequently discussed are
`summariZed beloW in Table 1:
`
`TABLE 1
`
`Steady State Speed of 1800 rpm
`
`SCR Cat Inlet
`T
`
`SCR Cat
`Exhaust
`GHSV
`FloW
`(SCFM) (1000 Hr-1)
`
`200EC
`345EC
`468EC
`
`285
`471
`515
`
`28.3
`46.9
`51.3
`
`Load
`
`14%
`60%
`100%
`
`NOx
`(ppm)
`
`214
`420
`770
`
`FIGS.
`
`6, 7
`4, 5
`2 3
`
`a
`
`[0058] At each of these steady state conditions urea solu
`tion Was injected into the exhaust at different rates to vary
`the NSR level. Emissions Were measured for each NSR level
`and the NOx conversion and NH3 slip (break through)
`
`20
`
`

`

`US 2002/0044897 A1
`
`Apr. 1 8, 2002
`
`determined. This was done for the CSF and ZNX SCR
`catalyst configuration and the ZNX SCR Catalyst alone
`configuration. The results are discussed below. The results
`based on the FTIR measurements are shown, but these were
`in good agreement with the chemiluminescence results.
`
`[0059] FIG. 2 shows the NOX conversion levels as a
`function of NSR for the CSF and ZNX SCR configuration
`indicated by the trace passing through circles designated by
`reference numeral 30 and for the ZNX SCR catalyst con-
`figuration alone indicated by the trace passing through
`diamonds designated by reference numeral 31 at the 100%
`load/468 EC SCR inlet condition. As can be seen there
`appears to be a slight advantage for the CSF and ZNX
`catalysts configuration, but
`the NOX conversion perfor-
`mance of both systems is very similar. The NOx conversion
`levels are essentially at or slightly above theoretical for the
`calculated NSR level thus showing very high level utiliza-
`tion of the urea reductant and thereby very high NOX
`conversion. Note from Table 1 that the exhaust inlet tem-
`
`perature of 468 EC is well within the ZNX SCR catalyst
`temperature window for optimum catalyst activity. The
`addition of CSF catalyst 12 does not materially change the
`N02 conversion efficiency which would be expected. That
`is, one would expect the SCR catalyst to perform within its
`operating temperature window and improved results by
`addition of an upstream catalyst should not occur.
`
`[0060] FIG. 3 shows the maximum NH3 break through
`levels as a function of NSR for the same runs at 100%
`load/468 EC SCR inlet condition. As can be seen NH3 break
`through for the ZNX SCR catalyst alone configuration is
`very low to at least an NSR level of ca. 0.7. However, at an
`NSR of ca. 0.96 the ZNX alone configuration indicated by
`the trace passing through diamonds designated by reference
`numeral 34 exhibits a maximum NH3 break through of
`nearly 40 ppm. The goal should be to keep NH3 slip at all
`times below ca 20 ppm and preferably below 10 ppm. The
`CSF and ZNX configuration, on t