111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20050031514Al
`
`(19) United States
`(12) Patent Application Publication
`Patchett et al.
`
`(10) Pub. No.: US 2005/0031514 A1
`Feb.
`2005
`(43) Pub. Date:
`
`(54) CATALYZED SCR FILTER AND EMISSION
`TREATMENT SYSTEM
`
`(75)
`
`Inventors: Joseph Allan Patchett, Basking Ridge,
`NJ (US); Joseph Charles Dettling,
`Howell, NJ (US); Elizabeth Alina
`Przybylski, Edison, NJ (US)
`
`Correspondence Address:
`Chief Patent Counsel
`Engelhard Corporation
`101 Wood Avenue
`P.O. Box 770
`Iselin, NJ 08830-0770 (US)
`
`(73) Assignee: Engelhard Corporation, Iselin, NJ
`
`(21) Appl. No.:
`
`10/634,659
`
`(22) Filed:
`
`Aug. 5, 2003
`
`Publication Classification
`
`Int. Cl.7
`..................................................... BOlD 53/94
`(51)
`(52) U.S. CI. ...................... 423/239.2; 422/180; 422/177;
`422/172; 422/171
`
`(57)
`
`ABSTRACT
`
`Provided is an emission treatment system and method for
`simultaneously remediating the nitrogen oxides (NOx), par(cid:173)
`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.
`
`ENGINE
`
`1
`
`Oxidation
`Catalyst
`
`11
`
`1~
`
`,7
`
`SCR
`CSF
`
`12
`
`14
`
`16
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 1 of 18
`
`

`

`0 -........
`
`16
`
`14
`
`13
`
`Ox. Cat.
`
`Slip
`
`12
`
`CSF
`SCR
`
`11
`
`Catalyst
`
`1------1 Oxidation 1---------i
`
`Figure 1 B
`
`16
`
`14
`
`12
`
`CSF
`SCR
`
`1~
`
`,7
`
`11
`
`Catalyst
`Oxidation
`
`Figure 1A
`
`1
`
`ENGINE
`
`1
`
`ENGINE
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 2 of 18
`
`

`

`Patent Application Publication Feb. 10,2005 Sheet 2 0f 7
`
`US 2005/0031514 A1
`
`Figure2
`
`30 \
`
`Figure 2
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 3 of 18
`
`

`

`~~~~~-z==~/
`
`,3"“\““‘=Eg Figure3
`
`Figure 3
`
`II___
`
`:8
`
`Patent Application Publication Feb. 10, 2005 Sheet 3 0f 7
`
`US 2005/0031514 A1
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 4 of 18
`
`

`

`~ ..... o· =
`'0" --· n
`~ ..... -· 0 = a:
`a -· n
`
`€ '
`
`Patent Application Publication Feb. 10, 2005 Sheet 4 0f 7
`
`US 2005/0031514 A1
`
`16
`
`
`
`Figure 4
`
`18
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 5 of 18
`
`

`

`BJO
`
`700
`
`T en1>eratt.-e, C
`
`5[1]
`
`400
`
`200
`
`100
`
`D
`
`I
`I
`
`" t
`
`J
`I
`
`I
`I
`
`~ ..... o· =
`'0" --· n
`~ ..... -· 0 = a:
`a -· n
`
`€ '
`
`,..,.
`725C
`
`t' ,
`
`,
`
`I
`
`1335C
`
`-_<). -Ti02 -10~·'0 W03 -2~~ V205
`--Cu-beta zeolite
`
`Figure 5
`
`350
`
`.... Q
`< 150
`c
`~ ·:-
`0 ' ~I) (f
`=-e '25 (I
`
`2(11)
`
`40(1
`
`450
`
`5(1 (I
`
`-...
`
`3[]1 c
`
`285C
`
`--------
`
`~0
`
`(l
`
`50
`
`1(0)
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 6 of 18
`
`

`

`~ ..... o· =
`'0" --· n
`~ ..... -· 0 = a:
`a -· n
`
`€ '
`
`'
`I
`
`----,-----------------------------------------------------------------------------
`
`::~_-___ -___ -___ -___ -___ -_------_-_-____ -___ -___ -___ -_-__ -__ ~ ___ -___ -___ -_-__ -___ -___ -___ -___ -___ ----------~_-___ -___ -___ -_------_~ __ -___ -___ -__ -__ -___ -___ -___ -___ -__ ~1
`
`Figure 6
`
`0 e a.. 10
`"'0 e ~ 15
`2 20
`a:
`a..
`ns 25
`
`~
`
`0
`
`600
`
`500
`
`400
`
`300
`
`200
`
`100
`
`0
`
`Flow, CFM
`
`-----------., ------------------------------.. ---------------------------i
`
`---
`
`5
`
`~Example 81
`---er-Example A2
`~ExampleA1
`
`---$-Uncoated filters
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 7 of 18
`
`

`

`~ ..... o· =
`'0" --· n
`~ ..... -· 0 = a:
`a -· n
`
`€ '
`
`SCR
`
`DOC
`
`--·-···
`
`'--·-···-·-scR
`
`Urea Injection
`
`DOC
`
`V6
`
`4 Liter
`
`I FTIR Sample Point
`
`Figure 7
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 8 of 18
`
`

`

`US 2005/0031514 A1
`
`Feb. 10,2005
`
`1
`
`CATALYZED SCR FILTER AND EMISSION
`TREATMENT SYSTEM
`[0001] The present invention relates to an emission treat(cid:173)
`ment system having an oxidation catalyst upstream of a soot
`filter coated with a material effective in the Selective Cata(cid:173)
`lytic Reduction (SCR) of NOx by a reductant, e.g., ammo(cid:173)
`nia. In one embodiment, the system provides an effective
`method of simultaneously remediating the nitrogen oxides
`(NOx), particulate matter, and gaseous hydrocarbons present
`in diesel engine exhaust streams.
`[0002] Diesel engine exhaust is a heterogeneous mixture
`which contains not only gaseous emissions such as carbon
`monoxide ("CO"), unburned hydrocarbons ("HC") and
`nitrogen oxides (""NOx"), but also condensed phase materi(cid:173)
`als (liquids and solids) which constitute the so-called par(cid:173)
`ticulates or particulate 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 compo(cid:173)
`nents. 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.
`[0003] Oxidation catalysts that contain platinum group
`metals, base metals and combinations thereof are known to
`facilitate the treatment of diesel engine exhaust by promot(cid:173)
`ing the conversion of both HC and CO gaseous pollutants
`and some proportion of the particulate matter through oxi(cid:173)
`dation 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 particulate matter, oxidation catalysts that contain
`platinum group metals (which are typically dispersed on a
`refractory oxide support) promote the oxidation of nitric
`oxide (NO) to N02 .
`[0004] 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 contribuites to
`the visible soot emissions commonly associated with diesel
`exhaust. A second component of the particulate matter is the
`soluble organic fraction ("SOF"). The soluble organic frac(cid:173)
`tion 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 tem(cid:173)
`perature of the 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) lubricating oil swept from the cylinder
`walls of the engine each time the pistons go up and clown;
`and (2) unburned or partially burned diesel fuel.
`[0005] 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 of the diesel, which in turn combines rapidly
`with water in the exhaust to form sulfuric acid. The sulfuric
`acid collects as a condensed phase with the particulates as an
`
`aerosol, or is adsorbed onto the other particulate compo(cid:173)
`nents, and thereby adds to the mass of TPM.
`[0006] One key aftertreatment technology in use for high
`particulate 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 continuously or periodically burned out of the
`filter to maintain an acceptable back pressure. Unfortunately,
`the carbon soot particles 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.
`[0007] Provisions are generally introduced to lower the
`soot burning temperature in order to provide for passive
`regeneration of the filter. The presence of a catalyst pro(cid:173)
`motes soot combustion, thereby regenerating the filters at
`temperatures accessible 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 effec(cid:173)
`tive in providing for >80% particulate matter reduction
`along with passive burning of the accumulating soot, and
`thereby promoting filter regeneration.
`[0008] 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 ofNOx
`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 efficient conversions of
`NOx as long as the exhaust temperature is within the active
`temperature range of the catalyst.
`[0009] While separate substrates each containing catalysts
`to address discrete components of the exhaust can be pro(cid:173)
`vided 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
`Nz.
`[0010] Coated soot filters that can achieve NOx reduction
`goals require a sufficient loading of SCR catalyst composi(cid:173)
`tion on the soot filter. The gradual loss of the catalytic
`effectiveness of the compositions that occurs over time
`through exposure to certain deleterious components of the
`exhaust stream augments the need for higher catalyst load-
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 9 of 18
`
`

`

`US 2005/0031514 A1
`
`Feb. 10,2005
`
`2
`
`ings of the SCR catalyst 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 load(cid:173)
`ings on the wall flow filter, yet still allow the filter to
`maintain flow characteristics that achieve acceptable back
`pressures are therefore desirable.
`[0011] 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 prolonged exposure to higher temperatures that are
`characteristic of filter regeneration. For example, combus(cid:173)
`tion of the soot fraction of the particulate matter often leads
`to temperatures above 700° C. Such temperatures render
`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 operates. Temperatures below 300° C. are
`typically encountered, for example, at conditions of low
`load, or at startup. The SCR catalyst compositions are
`preferably capable of catalyzing the reduction of the NOx
`component of the exhaust to achieve NOx reduction goals,
`even at lower exhaust temperatures.
`[0012] The prior art contains descriptions of the use of
`SCR catalyst compositions, soot filters and combinations
`thereof for the abatement of both the NOx and particulate
`components of diesel exhaust. These references are
`described below.
`[0013] Japanese Kokai 3-130522, for example, discloses
`the treatment of diesel exhaust gases characterized by use of
`an ammonia injector and porous ceramic filter having a
`denitration catalyst within the pores. The filter is installed in
`the wake of the diesel engine exhaust. The ceramic porous
`filter comprises an upstream fine pore path layer, and a
`downstream side course ceramic particle layer on which the
`denitration catalyst was supported. The fine layer can sup(cid:173)
`port a platinum or palladium or other hydrocarbon combus(cid:173)
`tion 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 con(cid:173)
`taining 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 compo(cid:173)
`nent to bum off catalytically.
`
`[0014] 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. Providing a higher feed containing a high propor(cid:173)
`tion of N02 to NO to the SCR reactor is said to allow the use
`of lower temperatures and higher space velocities than is
`possible with a feed of NO.
`
`[0015] WO 99/39809 discloses a system for treating com(cid:173)
`bustion exhaust gas containing NOx and particulates that has
`an oxidation catalyst effective to convert at least a portion of
`the 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 downstream of the particulate trap; and the SCR
`catalyst is downstream of the reductant fluid source. Reduc(cid:173)
`tant fluids disclosed include ammonia, urea, ammonium
`carbamate and hydrocarbons (e.g., diesel fuel).
`[0016] A catalytic wall flow filter for an exhaust system of
`a combustion engine is described in WO 01/12320. The wall
`flow filter has channels that are in honeycomb arrangement,
`where some of the channels are blocked at the upstream end
`and some of the channels that are unblocked at the upstream
`end are blocked at the downstream encl. 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 system) of generating N0 2 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.
`[0017]
`In some embodiments of the wall flow filter
`described in WO 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
`
`[0018]
`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 peri(cid:173)
`oclically 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 of the oxidation catalyst. The wall
`flow monolith contains an SCR catalyst composition, is in
`fluid communication with the injector, and is positioned
`downstream of the injector.
`[0019] The wall flow monolith has a plurality of longitu(cid:173)
`dinally extending passages formed by longitudinally extend(cid:173)
`ing 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 permeates 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.
`[0020]
`In a preferred embodiment of the emission treat(cid:173)
`ment system, 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
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 10 of 18
`
`

`

`US 2005/0031514 A1
`
`Feb. 10,2005
`
`3
`
`SCR catalyst composition have a silica to alumina ratio of at
`least about 10. For instance, a beta zeolite can be used in the
`SCR catalyst composition.
`
`(d) removing excess slurry from the outlet passages
`[0032]
`by forcing a compressed gas stream through the inlet pas(cid:173)
`sages and applying a vacuum to the outlet passages; and
`
`[0021] Among other things, the oxidation catalyst of the
`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 component is oxidized to N02 over the oxidation
`catalyst. In preferred embodiments, the oxidation catalyst is
`disposed on a honeycomb flow through monolith substrate
`or an open cell foam substrate. Preferably, the oxidation
`catalystinciudes a platinum group metal component, and in
`particular, a platinum component. In some embodiments, the
`oxidation catalyst can also contain a zeolite component.
`
`In another preferred embodiment of the emission
`[0022]
`treatment system, the system also has a diesel engine which
`is located upstream of, and in fluid communication with the
`oxidation catalyst.
`
`[0023] Another aspect of the invention relates to a method
`for treating emissions produced in an exhaust stream that
`contains NOx and particulate matter. The method includes:
`
`(a) passing the exhaust stream through an oxidation
`[0024]
`catalyst wherein a substantial portion of NO is oxidized to
`N02 to provide an N02-enriched exhaust stream;
`[0025]
`(b) metering at periodic intervals, ammonia or an
`ammonia precursor into the N02-enriched exhaust stream;
`and,
`
`the exhaust stream
`(c) subsequently passing
`[0026]
`through a wall flow monolith wherein particulate matter is
`filtered and a substantial portion of NOx is reduced to N2 .
`[0027] Here again, the wall flow monolith has a plurality
`of longitudinally extending passages formed by longitudi(cid:173)
`nally 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 perme(cid:173)
`ates 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
`permeates 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.
`
`In another aspect, the invention relates to a method
`[0028]
`for disposing an SCR catalyst composition on a wall flow
`monolith. The method includes:
`
`(a) immersing the wall flow monolith in an aqueous
`[0029]
`slurry comprising the SCR catalyst composition from a first
`direction to deposit the SCR catalyst composition on the
`inlet passages;
`
`(b) removing excess slurry from the inlet passages
`[0030]
`by forcing a compressed gas stream through the outlet
`passages and applying a vacuum to the inlet passages;
`
`(c) immersing the wall flow monolith in the aque(cid:173)
`[0031]
`ous slurry from a second direction, opposite the first direc(cid:173)
`tion, to deposit the SCR catalyst composition on the outlet
`passages;
`
`(e) drying and calcining the coated wall flow
`[0033]
`monolith.
`[0034] The wall flow monolith used in the method pref(cid:173)
`erably 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).
`[0035] Preferably, the SCR catalyst composition perme(cid:173)
`ates 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
`
`[0036] FIGS. 1A and 1B are schematic depictions of two
`embodiments of the emission treatment system of the inven(cid:173)
`tion.
`
`[0037] FIG. 2 shows a perspective view of a wall flow
`filter substrate.
`
`[0038] FIG. 3 shows a cutaway view of a section of a wall
`flow filter substrate.
`
`[0039] FIG. 4 shows an embodiment of the emission
`treatment system of the invention that includes a urea
`reservoir and injector.
`
`[0040] 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.
`
`[0041] FIG. 6 is a plot of the DTA signal in microvolts as
`a function of temperature for two SCR catalyst compositions
`mixed with a model particulate mass (carbon black and lube
`oil).
`
`[0042] FIG. 7 is a schematic depiction of a laboratory
`bench system used to evaluate NOx and particulate reduc(cid:173)
`tion for an exemplary emission treatment system of the
`invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`[0043] The invention relates to an em1sswn treatment
`system that effectively provides simultaneous treatment of
`the particulate, matter, the NOx and other gaseous compo(cid:173)
`nents of diesel engine exhaust. The emission treatment
`system uses an integrated soot filter and SCR catalyst to
`significantly minimize the weight and volume required for
`the emissions system. Moreover, due to the choice of
`catalytic compositions implemented in the system, effective
`pollutant abatement is provided for exhaust streams of
`varying temperatures. This feature is advantageous for oper(cid:173)
`ating diesel vehicles under varying loads and vehicle speeds
`which significantly impact exhaust temperatures emitted
`from the engines of such vehicles.
`[0044]
`Integration of NOx reduction and particulate
`removal functions into a single catalyst article is accom(cid:173)
`plished using a wall flow substrate coated with an SCR
`catalyst composition. Applicants have found a method for
`applying an SCR catalyst composition to a wall flow sub(cid:173)
`strate to form a substrate that can be used in an application
`where high filtration efficiency is required. For instance, a
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 11 of 18
`
`

`

`US 2005/0031514 A1
`
`Feb. 10,2005
`
`4
`
`substrate formed with this method is suitable for effectively
`removing particulate matter (e.g., greater than 80%) in the
`emission treatment system of the invention. The coating
`method disclosed herein allows wall flow substrates to be
`loaded with practical levels of SCR catalyst without causing
`excessive back pressure across the coated article when
`implemented in emission treatment systems.
`
`[0045] Achieving practical levels of SCR catalyst compo(cid:173)
`sition on the wall flow substrate is important for providing
`sufficient catalytic activity to achieve mandated NOx reduc(cid:173)
`tion levels, and for lowering the combustion temperature of
`the soot fraction trapped on the filter. Achieving adequate
`levels of SCR washcoat compositions on the soot filter is
`also important to secure adequate durability for the catalyst.
`Over extended use of the emission treatment system, cata(cid:173)
`lysts are invariably exposed to various levels of catalyst
`poisons that may be derived through break down of lubri(cid:173)
`cating oils, or may arise from impurities in the diesel fuel.
`Examples of such catalyst poisons include phosphorus, zinc,
`alkali and alkaline earth elements. Higher levels of catalyst
`compositions are therefore typically deposited on catalyst
`substrates to overcome the inevitable loss of catalytic activ(cid:173)
`ity.
`
`[0046] One embodiment of the inventive emission treat(cid:173)
`ment system is schematically depicted in FIG. 1A. As can
`be seen in FIG. 1A, the exhaust containing gaseous pollut(cid:173)
`ants (including unburned hydrocarbons, carbon monoxide
`and NOx) and particulate matter is conveyed from the
`engine 15 to an oxidation catalyst 11. In the oxidation
`catalyst 11, unburned gaseous and non-volatile hydrocar(cid:173)
`bons (i.e., the VOF) and carbon monoxide are largely
`combusted to form carbon dioxide and water. Removal of
`substantial proportions of the VOF using the oxidation
`catalyst, in particular, helps prevent too great a deposition of
`particulate matter on the soot filter 12 (i.e., clogging), which
`is positioned downstream in the system. In addition, a
`substantial proportion of the NO of the NOx component is
`oxidized to N02 in the oxidation catalyst.
`[0047] Downstream of the oxidation catalyst a reductant,
`in this case ammonia, is injected as a spray via a nozzle (not
`shown) into the exhaust stream. Aqueous urea shown on one
`line 18 can serve as the ammonia precursor which can be
`mixed with air on another line 19 in a mixing station 16.
`Valve 14 can be used to meter precise amounts of aqueous
`urea which are converted in the exhaust stream to ammonia.
`The exhaust stream with the added ammonia is conveyed to
`the soot filter 12 which is coated with an SCR catalyst
`composition. On passing through the soot filter, the NOx
`component is converted through the selective catalytic
`reduction of NOx with ammonia to nitrogen. The increased
`proportion of N02 in the NOx due to the catalytic action of
`the upstream oxidation catalyst facilitates the reduction of
`the NOx as compared to exhaust streams containing smaller
`proportions of N02 in the NOx component.
`[0048] Depending on the desired level of NOx removal,
`additional SCR catalyst can be disposed downstream of the
`soot filter. For example, the additional SCR catalyst may be
`disposed on a monolithic, honeycomb flow through sub(cid:173)
`strate or ceramic foam substrate downstream of the soot
`filter. Even in these embodiments, the use of the coated SCR
`soot filter still achieves a reduction in the total volume of
`catalyst required to meet NOx reduction goals.
`
`[0049] The particulate matter including the soot fraction
`and the VOF are also largely removed (greater than 80%) by
`the soot filter. The particulate matter deposited on the soot
`filter is combusted through the regeneration of the filter,
`which process is also aided by the presence of the SCR
`catalyst composition. The temperature at which the soot
`fraction of the particulate matter combusts is lowered by the
`presence of the catalyst composition disposed on the soot
`filter.
`[0050] An optional configuration is shown in FIG. 1B
`where the emission treatment system is provided with a slip
`oxidation catalyst 13 downstream of the coated soot filter 12.
`The slip oxidation catalyst can be coated, for example, with
`a composition containing base metals and less than 0.5 wt%
`of platinum. This provision can be used to oxidize any
`excess NH3 before it is vented to the atmosphere.
`[0051] Suitable SCR catalyst compositions for use in the
`system are able to effectively catalyze the reduction of the
`NOx component at temperatures below 600 C., so that
`adequate NOx levels can be treated even under conditions of
`low load which typically are associated with lower exhaust
`temperatures. Preferably, the catalyst article is capable of
`converting at least 50% of the NOx component to N2 ,
`depending on the amount of reductant added to the system.
`In addition, SCR catalyst compositions for use in the system
`are also ideally able to aid in the regeneration of the filter by
`lowering the temperature at which the soot fraction of the
`particulate matter is combusted. Another desirable attribute
`for the composition is that it possess the ability to catalyze
`the reaction of 0 2 with any excess NH3 to N2 and H20, so
`that NH3 is not emitted to the atmosphere.
`[0052] Useful SCR catalyst compositions used in the
`inventive system also have thermal resistance to tempera(cid:173)
`tures greater than 650° C. Such high temperatures are often
`encountered during the regeneration of soot filters. Addi(cid:173)
`tionally, SCR catalyst compositions should resist degrada(cid:173)
`tion upon exposure to sulfur components, which are often
`present in diesel exhaust gas compositions.
`[0053] Suitable SCR catalyst compositions are described,
`for instance, in U.S. Pat. Nos. 4,961,917 (the '917 patent)
`and 5,516,497, which are both hereby incorporated by
`reference in their entirety. Compositions disclosed in the
`'917 patent include one or both of an iron and a copper
`promoter present in a zeolite in an amount of from about 0.1
`to 30 percent by weight, preferably from about 1 to 5 percent
`by weight, of the total weight of promoter plus zeolite. In
`addition to their ability to catalyze the reduction of NOx
`with NH3 to N2 , the disclosed compositions can also pro(cid:173)
`mote the oxidation of excess NH3 with 0 2, especially for
`those compositions having higher promoter concentrations.
`[0054] Zeolites used in such compositions are resistant to
`sulfur poisoning, sustain a high level of activity for the SCR
`process, and are capable of oxidation of excess ammonia
`with oxygen. These zeoliteshave pore size large enough to
`permit adequate movement of the reactant molecules NO
`and NH3 in to, and the product molecules N2 and H20 out
`of, the pore system in the presence of sulfur oxide molecules
`resulting from short term sulfur poisoning, and/or sulfate
`deposits resulting from long term sulfur poisoning. The pore
`system of suitable size is interconnected in all three crys(cid:173)
`tallographic dimensions. As is well known to the those
`skilled in the zeolite art, the crystalline structure of zeolites
`
`Umicore AG & Co. KG
`Exhibit 1106
`Page 12 of 18
`
`

`

`US 2005/0031514 A1
`
`Feb. 10,2005
`
`5
`
`exhibits a complex pore structure having more or less
`regularly recurring connections, intersections and the like.
`Pores having a particular characteristic, such as a given
`dimension diameter or cross-sectional configuration, are
`said to be one dimensional if those pores do not intersect
`with other like pores. If the pores intersect only within a
`given plane with other like pores, the pores of that charac(cid:173)
`teristic are said to be interconnected in two ( crystallo(cid:173)
`graphic) dimensions. If the pores intersect with other like
`pores lying both in the same plane and in other planes, such
`like pores are said to be interconnected in three dimensions,
`i.e., to be "three dimensional".lt has been found that zeolites
`which are highly resistant to sulfate poisoning and provide
`good activity for both the SCR process and t