US009032709B2
`
`(12) United States Patent
`Patchett et al.
`
`(10) Patent No.:
`
`(45) Date of Patent:
`
`US 9,032,709 B2
`May 19, 2015
`
`(54) METHOD OF FORMINGA CATALYZED
`SELECTIVE CATALYTIC REDUCTION
`FILTER
`
`(75)
`
`Inventors: Joseph Allan Patchett, Basking Ridge,
`NJ (US); Joseph Charles Dettling,
`Howell, NJ (US); Elizabeth Alina
`Przybylski, Edison, NJ (US)
`
`(73) Assignee: BASF Corporation, Florham Park, NJ
`(US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. l54(b) by 462 days.
`
`(21) Appl.No.: 11/676,798
`
`(22)
`
`Filed:
`
`Feb. 20, 2007
`
`(65)
`
`Prior Publication Data
`
`US 2007/0137184 A1
`
`Jun. 21, 2007
`
`Related U.S. Application Data
`
`2255/20738 (2013.01), BOID 2255/2076]
`(2013.01), BOID 2255/502 (2013.01),
`
`(Continued)
`(58) Field of Classification Search
`USPC .......... .. 60/274, 286, 297, 301, 303, 311, 295
`Sec application filc for complete search history.
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,220,633 A
`4,309,386 A
`
`9/1980 Pirsh
`1/1982 Pirsh
`
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`DE
`DE
`
`01323607
`102004040548
`
`12/2004
`2/2006
`
`(Continued)
`OTHER PUBLICATIONS
`
`Durilla, et 211., “Composite SCR Catalysts for NOx Reduction”, Ann.
`Meeting ofthe Industrial Gas Cleaning Inst., (Mar. 1990).
`(Continued)
`
`(62) Division of application No. 10/634,659, filed on Aug.
`5, 2003, now Pat. No. 7,229,597.
`
`Primary Examiner — Thomas Denion
`Assistant Examiner — Diem Tran
`
`(51)
`
`Int. Cl.
`F01N 3/00
`F01N3/10
`
`(2006.01)
`(2006.01)
`(Continued)
`
`(52) U.S. Cl.
`CPC ....... .. F01N3/2892 (2013.01); Y]0T29/49345
`(2015.01); B01D 5/0054 (2013.01); B01D
`5/009 (2013.01); B01D 19/0005 (2013.01);
`B01D 19/0036 (2013.01); B01D 53/9418
`(2013.01); B01D 53/945 (2013.01); BOID
`53/9477 (2013.01); BOID 2251/2062 (2013.01);
`BOID 2251/2067 (2013.01); BOID 2255/102
`(2013.01);B01D 2255/20715 (2013.01);B01D
`
`(74) Attorney, Agent, or Firm — Melanie L. Brown
`
`ABSTRACT
`(57)
`Provided is an emission treatment system and method for
`simultaneously remediating the nitrogen oxides (NOx), par-
`ticulate matter, and gaseous hydrocarbons present in diesel
`engine exhaust streams. The emission treatment system has
`an oxidation catalyst upstream of a soot filter coated with a
`material effective in the Selective Catalytic Reduction (SCR)
`of NOx by a reductant, e.g., ammonia. Also provided is a
`method for disposing an SCR catalyst composition on a wall
`flow monolith that provides adequate catalyst loading, but
`does not result in unsuitable back pressures in the exhaust.
`
`24 Claims, 7 Drawing Sheets
`
`
`
` ENGINE
`
`Oxidation
`
`JM 1001
`
`1
`
`JM 1001
`
`

`
`US 9,032,709 B2
`Page 2
`
`(51)
`
`Int. Cl.
`F01N3/02
`F01N 3/28
`BOID 5/00
`BOID 19/00
`
`(2006.01)
`(2006.01)
`(2006.01)
`(2006.01)
`<2oo6~o1>
`(200501)
`(2006.01)
`(2005.01)
`(200001)
`(201001)
`
`B01129/76
`B01137/02
`F01N3/023
`F0101 3/20
`F011V 13/00
`(52) U.S. Cl.
`CPC . B01D2255/9155 (2013.01); BOID 2255/9202
`(2013~01)9B01D 2255/9205 (2013~01)3 3011)
`2258/012(2013.01);B01129/7615(2013.01);
`B01137/0246 (201301), F01N3/0231
`(2013.01);F01N3/106(2013.01);F01N
`3/2066 (2013.01);F01N2370/04 (2013.01);
`F011‘/2510/063 (2013~01);F01N2610/02
`(2013.01);F01N2610/08(2013.01); YIOS
`.
`.
`55/30 (2013.01); 1710555/10(2013.01); Y02T
`10/22 (2013.01), Y02TIO/24 (2013.01), F01N
`13/009 (2014.06),B01J29/76 (2013.01), F01N
`3/10 (2013.01); F01N3/2828 (2013.01); FOIN
`2330/06 (2013.01); FOIN 2330/30 (2013.01)
`
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`* cited by examiner
`
`3
`
`

`
`U.S. Patent
`
`May 19, 2015
`
`Sheet 1 of7
`
`US 9,032,709 B2
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`U.S. Patent
`
`May 19, 2015
`
`Sheet 2 of 7
`
`US 9,032,709 B2
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`
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`U.S. Patent
`
`May 19, 2015
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`Sheet 3 of 7
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`May 19, 2015
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`U.S. Patent
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`U.S. Patent
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`May 19,2015
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`

`
`US 9,032,709 B2
`
`1
`METHOD OF FORMING A CATALYZED
`SELECTIVE CATALYTIC REDUCTION
`FILTER
`
`This application is a divisional application of U.S. appli-
`cation Ser. No. 10/634,659, filedAug. 5, 2003, the content of
`which is hereby incorporated in its entirety by reference
`thereto.
`
`The present invention relates to an emission treatment sys-
`tem having an oxidation catalyst upstream of a soot filter
`coated with a material effective in the Selective Catalytic
`Reduction (SCR) of NOx by a reductant, e.g., ammonia. In
`one embodiment, the system provides an effective method of
`simultaneously remediating the nitrogen oxides (NOx), par-
`ticulate matter, and gaseous hydrocarbons present in diesel
`engine exhaust streams.
`Diesel engine exhaust is a heterogeneous mixture which
`contains not only gaseous emissions such as carbon monox-
`ide (“CO”), unburned hydrocarbons (“HC”) and nitrogen
`oxides (“NOX”), but also condensed phase materials (liquids
`and solids) which constitute the so-called particulates or par-
`ticulate matter. Often, catalyst compositions and substrates
`on which the compositions are disposed are provided in diesel
`engine exhaust systems to convert certain or all of these
`exhaust components to innocuous components. For example,
`diesel exhaust systems can contain one or more of a diesel
`oxidation catalyst, a soot filter and a catalyst for the reduction
`of NOx.
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`Oxidation catalysts that contain platinum group metals,
`base metals and combinations thereof are known to facilitate
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`the treatment of diesel engine exhaust by promoting the con-
`version of both HC and CO gaseous pollutants and some
`proportion of the particulate matter through oxidation of
`these pollutants to carbon dioxide and water. Such catalysts
`have generally been contained in units called diesel oxidation
`catalysts (DOC’s), which are placed in the exhaust of diesel
`engines to treat the exhaust before it vents to the atmosphere.
`In addition to the conversions of gaseous HC, CO and par-
`ticulate matter, oxidation catalysts that contain platinum
`group metals (which are typically dispersed on a refractory
`oxide support) also promote the oxidation of nitric oxide
`(NO) to N02.
`The total particulate matter emissions of diesel exhaust are
`comprised of three main components. One component is the
`solid, dry, solid carbonaceous fraction or soot fraction. This
`dry carbonaceous matter contributes to the visible soot emis-
`sions commonly associated with diesel exhaust. A second
`component of the particulate matter is the soluble organic
`fraction (“SOF”). The soluble organic fraction is sometimes
`referred to as the volatile organic fraction (“VOF”), which
`terminology will be used herein. The VOF can exist in diesel
`exhaust either as a vapor or as an aerosol (fine droplets of
`liquid condensate) depending on the temperature ofthe diesel
`exhaust. It is generally present as condensed liquids at the
`standard particulate collection temperature of 52° C.
`in
`diluted exhaust, as prescribed by a standard measurement
`test, such as the U.S. Heavy Duty Transient Federal Test
`Procedure. These liquids arise from two sources: (1) lubricat-
`ing oil swept from the cylinder walls of the engine each time
`the pistons go up and down; and (2) unburned or partially
`bun1ed diesel fuel.
`
`The third component of the particulate matter is the so-
`called sulfate fraction. The sulfate fraction is formed from
`
`small quantities of sulfur components present in the diesel
`fuel. Small proportions of S03 are formed during combustion
`ofthe diesel, which in turn combines rapidly with water in the
`exhaust to form sulfuric acid. The sulfuric acid collects as a
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`condensed phase with the particulates as an aerosol, or is
`adsorbed onto the other particulate components, and thereby
`adds to the mass of TPM.
`
`One key aftertreatment technology in use for high particu-
`late matter reduction is the diesel particulate filter. There are
`many known filter structures that are effective in removing
`particulate matter from diesel exhaust, such as honeycomb
`wall flow filters, wound or packed fiber filters, open cell
`foams, sintered metal filters, etc. However, ceramic wall flow
`filters, described below, receive the most attention. These
`filters are capable of removing over 90% of the particulate
`material from diesel exhaust. The filter is a physical structure
`for removing particles from exhaust, and the accumulating
`particles will increase the back pressure from the filter on the
`engine. Thus the accumulating particles have to be continu-
`ously or periodically burned out of the filter to maintain an
`acceptable back pressure. Unfortunately, the carbon soot par-
`ticles require temperatures in excess of 500° C. to burn under
`oxygen rich (lean) exhaust conditions. This temperature is
`higher than what is typically present in diesel exhaust.
`Provisions are generally introduced to lower the soot bum-
`ing temperature in order to provide for passive regeneration of
`the filter. The presence of a catalyst promotes soot combus-
`tion, thereby regenerating the filters at temperatures acces-
`sible within the diesel engine’s exhaust under realistic duty
`cycles. In this way a catalyzed soot filter (CSF) or catalyzed
`diesel particulate filter (CDPF) is effective in providing for
`>80% particulate matter reduction along with passive burning
`of the accumulating soot, and thereby promoting filter regen-
`eration.
`
`Future emissions standards adopted throughout the world
`will also address NOx reductions from diesel exhaust. A
`
`proven NOx abatement technology applied to stationary
`sources with lean exhaust conditions is Selective Catalytic
`Reduction (SCR). In this process, NOx is reduced with
`ammonia (NH3) to nitrogen (N2) over a catalyst typically
`composed of base metals. The technology is capable of NOx
`reduction greater than 90%, and thus it represents one of the
`best approaches for achieving aggressive NOx reduction
`goals. SCR is under development for mobile applications,
`with urea (typically present in an aqueous solution) as the
`source of ammonia. SCR provides efiicient conversions of
`NOx as long as the exhaust temperature is within the active
`temperature range of the catalyst.
`While separate substrates each containing catalysts to
`address discrete components of the exhaust can be provided
`in an exhaust system, use of fewer substrates is desirable to
`reduce the overall size of the system, to ease the assembly of
`the system, and to reduce the overall cost of the system. One
`approach to achieve this goal is to coat the soot filter with a
`catalyst composition effective for the conversion of NOx to
`innocuous components. With this approach, the catalyzed
`soot filter assumes two catalyst functions: removal of the
`particulate component of the exhaust stream and conversion
`of the NOx component of the exhaust stream to N2.
`Coated soot filters that can achieve NOx reduction goals
`require a sufficient loading of SCR catalyst composition on
`the soot filter. The gradual loss ofthe catalytic effectiveness of
`the compositions that occurs over time through exposure to
`certain deleterious components of the exhaust stream aug-
`ments the need for higher catalyst loadings of the SCR cata-
`lyst composition. However, preparation of coated soot filters
`with higher catalyst loadings can lead to unacceptably high
`back pressure within the exhaust system. Coating techniques
`that allow higher catalyst loadings on the wall flow filter, yet
`still allow the filter to maintain flow characteristics that
`
`achieve acceptable back pressures are therefore desirable.
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`US 9,032,709 B2
`
`3
`An additional aspect for consideration in coating the wall
`flow filter is the selection of the appropriate SCR catalyst
`composition. First, the catalyst composition must be durable
`so that it maintains its SCR catalytic activity even after pro-
`longed exposure to higher temperatures that are characteristic
`of filter regeneration. For example, combustion of the soot
`fraction of the particulate matter often leads to temperatures
`above 700° C. Such temperatures re11der many commonly
`used SCR catalyst compositions such as mixed oxides of
`vanadium and titanium less catalytically effective. Second,
`the SCR catalyst compositions preferably have a wide enough
`operating temperature range so that they can accommodate
`the variable temperature ranges over which the vehicle oper-
`ates. Temperatures below 300° C. are typically encountered,
`for example, at conditions of low load, or at startup. The SCR
`catalyst compositions are preferably capable ofcatalyzing the
`reduction of the NOx component of the exhaust to achieve
`NOx reduction goals, even at lower exhaust temperatures.
`The prior art contains descriptions of the use of SCR cata-
`lyst compositions, soot filters and combinations thereof for
`the abatement ofboth the NOx and particulate components of
`diesel exhaust. These references are described below.
`Japanese Kokai 3- 1 30522, for example, discloses the treat-
`ment of diesel exhaust gases characterized by use of an
`ammonia injector and porous ceramic filter having a de11itra-
`tion catalyst within the pores. The filter is installed in the
`wake of the diesel engine exhaust. The ceramic porous filter
`comprises an up stream fine pore path layer, and a downstream
`side course ceramic particle layer on which the denitration
`catalyst was supported. The fine layer can support a platinum
`or palladium or other hydrocarbon combustion catalyst. The
`diesel exhaust gas containing unburned carbon flows through
`the porous ceramic filter and the carbon particles are filtered
`onto the surface. The gas containing nitric oxides and the
`ammonia passes through the denitration catalyst containing
`side of the filter and the nitric oxides are reduced to nitrogen
`and water. The oxidation catalyst on the upstream side causes
`the particulate component to burn off catalytically.
`U.S. Pat. No. 4,912,776 discloses an oxidation catalyst, an
`SCR catalyst downstream and adjacent to the SCR catalyst,
`and a reductant source introduced to the exhaust stream
`
`between the oxidation catalyst and the SCR catalyst. Provid-
`ing a higher feed containing a high proportion of N02 to NO
`to the SCR reactor is said to allow the use of lower tempera-
`tures and higher space velocities than is possible with a feed
`of NO.
`WC) 99/39809 discloses a system for treating combustion
`exhaust gas containing NOx and particulates that has an oxi-
`dation catalyst effective to convert at least a portion ofthe NO
`in the NOx to N02, a particulate trap, a source of reductant
`fluid and an SCR catalyst. The particulate trap is downstream
`of the oxidation catalyst; the reductant fluid source is down-
`stream of the particulate trap; and the SCR catalyst is down-
`stream of the reductant fluid source. Reductant fluids dis-
`closed include ammonia, urea, ammonium carbarnate and
`hydrocarbons (e.g., diesel fuel).
`A catalytic wall flow filter for an exhaust system of a
`combustion engine is described in W0 01/ 12320. The wall
`flow filter has charmels that are in honeycomb arrangement,
`where some of the charmels are blocked at the upstream end
`and some of the channels that are unblocked at the upstream
`end are blocked at the downstream end. An oxidation catalyst
`is disposed on a gas impermeable zone at an upstream end of
`channels that are blocked at the downstream end. The filter
`
`has a gas permeable filter zone that is downstream of the
`oxidation catalyst that is for trapping soot. The oxidation
`catalyst is described to be capable (when in an exhaust sys-
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`tem) of generating N02 from NO to combust the trapped soot
`continuously at temperatures below 400° C. The oxidation
`catalyst preferably includes a platinum group metal. Exhaust
`streams containing NO are initially passed over the oxidation
`catalyst to convert NO to N02 prior to filtering to remove soot.
`The exhaust gas then containing N02 is used to combust the
`soot trapped on the filter.
`In some embodiments of the wall flow filter described in
`W0 01/ 12320 the downstream channels of the soot filter
`
`contain a catalyst for a NOx absorber and an SCR catalyst
`downstream of the NOx absorber. The SCR catalyst can be a
`copper-based material, platinum, a mixed oxide of vanadium
`and titania or a zeolite, or mixtures of two or more thereof
`
`SUMMARY OF THE INVENTION
`
`In one aspect, the invention relates to an emission treatment
`system for treatment of an exhaust stream that contains NOx
`and particulate matter. The emission treatment system
`includes an oxidation catalyst, an injector that periodically
`meters ammonia or an ammonia precursor into the exhaust
`stream; and a wall flow monolith. The injector is in fluid
`communication with the oxidation catalyst, and is positioned
`downstream ofthe oxidation catalyst. The wall flow monolith
`contains an SCR catalyst composition, is in fluid communi-
`cation with the injector, and is positioned downstream of the
`injector.
`The wall flow monolith has a plurality of longitudinally
`extending passages formed by longitudinally extending walls
`bounding and defining said passages. The passages include
`inlet passages that have an open inlet end and a closed outlet
`end, and outlet passages that have a closed inlet end and an
`open outlet end. The wall flow monolith contains an SCR
`catalyst composition that permeates the walls at a concentra-
`tion of at least 1.3 g/in3 (and preferably from 1.6 to 2.4 g/in3).
`The wall flow monolith has a wall porosity of at least 50%
`with an average pore size of at least 5 microns. Preferably, the
`SCR catalyst composition permeates the walls of the wall
`flow monolith so that the walls have a wall porosity offrom 50
`to 75% with an average pore size of from 5 to 30 microns.
`In a preferred embodiment of the emission treatment sys-
`tem, the SCR catalyst composition contains a zeolite and base
`metal component selected from one or more of a copper and
`iron component. Preferably, the base metal component is a
`copper component. Preferred zeolites of the SCR catalyst
`composition have a silica to alumina ratio ofat least about 10.
`For instance, a beta zeolite can be used in the SCR catalyst
`composition.
`Among other things, the oxidation catalyst ofthe system is
`useful for combusting substantial portions of the particulate
`matter, and in particular, the VOF, entrained in the exhaust. In
`addition, a substantial portion of the NO in the NOx compo-
`nent is oxidized to N02 over the oxidation catalyst. In pre-
`ferred embodiments, the oxidation catalyst is disposed on a
`honeycomb flow through monolith substrate or an open cell
`foam substrate. Preferably, the oxidation catalyst includes a
`platinum group metal component, and in particular, a plati-
`num component. In some embodiments, the oxidation cata-
`lyst can also contain a zeolite component.
`In another preferred embodiment ofthe emission treatment
`system, the system also has a diesel engine which is located
`upstream of, and in fluid communication with the oxidation
`catalyst.
`Another aspect of the invention relates to a method for
`treating emissions produced in an exhaust stream that con-
`tains NOx and particulate matter. The method includes:
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`US 9,032,709 B2
`
`5
`(a) passing the exhaust stream through an oxidation cata-
`lyst wherein a substantial portion ofNO is oxidized to NO2 to
`provide an NO2-enriched exhaust stream;
`(b) metering at periodic intervals, ammonia or an ammonia
`precursor into the NO2-enriched exhaust stream; and,
`(c) subsequently passing the exhaust stream through a wall
`flow monolith wherein particulate matter is filtered and a
`substantial portion of NOx is reduced to N2.
`Here again, the wall flow monolith has a plurality of lon-
`gitudinally extending passages formed by longitudinally
`extending walls bounding and defining said passages. The
`passages include inlet passages that have an open inlet end
`and a closed outlet end, and outlet passages that have a closed
`inlet end and an open outlet end. The wall flow monolith
`contains an SCR catalyst composition that permeates the
`walls at a concentration of at least 1.3 g/in3 (and preferably
`from 1.6 to 2.4 g/in3). The wall flow monolith has a wall
`porosity of at least 50% with an average pore size of at least
`5 microns. Preferably, the SCR catalyst composition perme-
`ates the walls of the wall flow monolith so that the walls have
`
`a wall porosity of from 50 to 75% with an average pore size of
`from 5 to 30 microns.
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`In another aspect, the invention relates to a method for
`disposing an SCR catalyst composition on a wall flow mono-
`lith. The method includes:
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`(a) immersing the wall flow monolith in an aqueous slurry
`comprising the SCR catalyst composition from a first direc-
`tion to deposit the SCR catalyst composition on the inlet
`passages;
`(b) removing excess slurry from the inlet passages by forc-
`ing a compressed gas stream through the outlet passages and
`applying a vacuum to the inlet passages;
`(c) immersing the wall flow monolith in the aqueous slurry
`from a second direction, opposite the first direction, to deposit
`the SCR catalyst composition on the outlet passages;
`(d) removing excess slurry from the outlet passages by
`forcing a compressed gas stream through the inlet passages
`and applying a vacuum to the outlet passages; and
`(e) drying and calcining the coated wall flow monolith.
`The wall flow monolith used in the method preferably has
`a porosity of at least 50% (e.g., from 50 to 75%) having a
`mean pore size of at least 5 microns (e.g., from 5 to 30
`microns).
`Preferably, the SCR catalyst composition permeates the
`walls at a concentration of at least 1.3 g/in3 (and preferably
`from 1.6 to 2.4 g/in3).
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. 1A and 1B are schematic depictions oftwo embodi-
`ments of the emission treatment system of the invention.
`FIG. 2 shows a perspective view of a wall flow filter sub-
`strate.
`
`FIG. 3 shows a cutaway view of a section of a wall flow
`filter substrate.
`FIG. 4 shows an embodiment of the emission treatment
`
`system of the invention that includes a urea reservoir and
`injector.
`FIG. 5 shows the pressure drop as a function of the air flow
`for several coated wall flow filter substrates and an uncoated
`wall flow filter substrate.
`
`FIG. 6 is a plot of the DT