Improved catalytic wall flow filter

Abstract

A catalytic wall flow monolith filter for an emission treatment system is disclosed. The filter includes a porous wall, a first face and a second face defining a longitudinal direction therebetween, and a first plurality of channels and a second plurality of channels extending in the longitudinal direction. The first plurality of channels provide a first plurality of inner surfaces and are open at the first face and closed at the second face; and the second plurality of channels provide a second plurality of inner surfaces and are open at the second face and closed at the first face. The filter includes a first selective catalytic reduction (SCR) catalyst coated on the first plurality of interior surfaces of the porous wall to form a first selective catalytic reduction (SCR) catalyst porous layer, a second SCR catalyst within the porous wall, and a third SCR catalyst coated on the second plurality of interior surfaces of the porous wall to form a third SCR catalyst porous layer.

Description

Technical Field

[0001] The present invention relates to a catalyzed wall flow monolith filter suitable for use in an emission treatment system such as an automotive internal combustion exhaust system. The present invention provides an effective method for conditioning an engine exhaust stream. Background Art

[0002] There are issues regarding the emission of particulate matter (PM), commonly referred to as soot, from internal combustion engines, especially diesel and gasoline engines in automotive applications. The main issues are associated with potential health effects, particularly with very small particles with sizes in the nanometer range.

[0003] Diesel particulate filters (DPF) and gasoline particulate filters (GPF) have been manufactured using a variety of materials (including sintered metals, ceramics or metal fibers, etc.), of which the most common type in actual large-scale production is a wall-flow type made of a porous ceramic material, which is manufactured in the form of a monolithic array of many small channels extending along the length of the body. The alternating channels are blocked at one end, so the exhaust is forced to pass through the porous ceramic channel wall, which prevents most of the particles from passing through, so only the filtered gas enters the environment. Ceramic wall-flow filters in commercial production include those made of cordierite, various forms of silicon carbide and aluminum titanate. The actual shape and size of the practical filter on the vehicle and characteristics such as the thickness of the channel wall and its porosity depend on the application of interest. The average size of the pores in the filter channel wall of the ceramic wall-flow filter through which the gas passes is typically in the range of 5μm to 50μm and is typically about 20μm. In stark contrast, most diesel particulate matter from modern passenger car high-speed diesel engines is much smaller in size, for example 10 nm to 200 nm.

[0004] Some PM may remain within the pore structure in the filter wall, and this can gradually accumulate in some applications until the pores are bridged by a network of PM, and this PM network then enables easy formation of a particle cake on the inner walls of the filter channels. The particle cake is an excellent filter medium, and its presence provides very high filtration efficiency. In some applications, the soot is continuously burned on the filter as it is deposited, which prevents the particle cake from accumulating on the filter.

[0005] For some filters, such as light-duty diesel particulate filters, it is necessary to periodically remove trapped PM from the filter to prevent the buildup of excessive back pressure, which is detrimental to engine performance and can result in poor fuel economy. Therefore, in diesel applications, retained PM is removed from the filter by burning it in the air in a process during which the amount of available air and the amount of excess fuel used to reach the high temperatures required to ignite the retained PM are very carefully controlled. Towards the end of this process, which is generally referred to as regeneration, the removal of the last remaining particles in the filter can result in a significant reduction in filtration efficiency and the release of a burst of many small particles into the environment. As a result, the filter may have low filtration efficiency when first used and subsequently after each regeneration event and also during the latter part of each regeneration process.

[0006] Therefore, it is desirable to improve and / or maintain filtration efficiency at all times, such as during the early life of a filter when it is first used, and / or during and immediately after regeneration, and / or when the filter is loaded with soot. Summary of the invention

[0007] According to a first aspect, there is provided a catalyzed wall flow monolith filter for an emission treatment system, the catalyzed wall flow monolith filter comprising a porous wall and having a first face and a second face defining a longitudinal direction therebetween and a first plurality of channels and a second plurality of channels extending in the longitudinal direction,

[0008] wherein the first plurality of channels provide a first plurality of interior surfaces and are open at a first face and closed at a second face, and wherein the second plurality of channels provide a second plurality of interior surfaces and are open at the second face and closed at the first face;

[0009] wherein the monolith filter comprises a first selective catalytic reduction (SCR) catalyst coated on a first plurality of inner surfaces of the porous wall to form a first SCR catalyst porous layer;

[0010] wherein the monolithic filter comprises a second SCR catalyst within the porous walls;

[0011] wherein the monolith filter comprises a third SCR catalyst coated on a second plurality of inner surfaces of the porous walls to form a third SCR catalyst porous layer;

[0012] wherein the first SCR catalyst porous layer is coated from the first side;

[0013] wherein the second SCR catalyst is applied from the second side; and

[0014] The third SCR catalyst porous layer is coated from the second side.

[0015] According to a second aspect, there is provided a method for manufacturing a catalyzed wall flow monolith filter, the method comprising:

[0016] (a) providing a wall-flow monolith substrate comprising a porous wall and having a first end face and a second end face defining a longitudinal direction therebetween and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels are open at the first end face and closed at the second end face, and wherein the second plurality of channels are open at the second end face and closed at the first end face;

[0017] (b) applying a first SCR catalyst washcoat slurry on a first plurality of interior surfaces of the porous walls;

[0018] (c) applying a second SCR catalyst washcoat slurry on a second plurality of inner surfaces of the porous walls such that the second SCR catalyst washcoat slurry penetrates into the porous walls;

[0019] (d) applying a third SCR catalyst washcoat slurry onto a second plurality of interior surfaces of the porous walls;

[0020] (e) calcining the coated wall flow monolith substrate obtained from steps (b), (c) and (d) to produce a catalyzed wall flow monolith filter.

[0021] According to a third aspect, an emission treatment system for treating a combustion exhaust gas flow is provided, the system comprising a catalyzed wall flow monolith filter as described in the present disclosure, wherein the first end face is upstream of the second end face.

[0022] According to a fourth aspect, a method for treating a combustion exhaust stream containing NOx is provided, the method comprising passing the exhaust stream through a catalyzed wall flow monolith filter as described in the present disclosure, wherein the first end face is upstream of the second end face. DETAILED DESCRIPTION

[0023] The present invention will now be further described. In the following paragraphs, different aspects of the present invention are defined in more detail. Unless there is a clear indication to the contrary, each aspect so defined can be combined with any other one or more aspects. In particular, any feature indicated as being preferred or advantageous can be combined with any other one or more features indicated as being preferred or advantageous.

[0024] According to a first aspect, there is provided a catalyzed wall flow monolith filter for an emission treatment system, the catalyzed wall flow monolith filter comprising a porous wall and having a first face and a second face defining a longitudinal direction therebetween and a first plurality of channels and a second plurality of channels extending in the longitudinal direction,

[0025] wherein the first plurality of channels provide a first plurality of interior surfaces and are open at a first face and closed at a second face, and wherein the second plurality of channels provide a second plurality of interior surfaces and are open at the second face and closed at the first face;

[0026] wherein the monolith filter comprises a first SCR catalyst coated on a first plurality of inner surfaces of the porous walls to form a first SCR catalyst porous layer;

[0027] wherein the monolithic filter comprises a second SCR catalyst within the porous walls;

[0028] wherein the monolith filter comprises a third SCR catalyst coated on a second plurality of inner surfaces of the porous walls to form a third SCR catalyst porous layer;

[0029] wherein the first SCR catalyst porous layer is coated from the first side;

[0030] wherein the second SCR catalyst is applied from the second side; and

[0031] The third SCR catalyst porous layer is coated from the second side.

[0032] A catalytic wall-flow monolithic filter comprises a porous wall and has a first face and a second face defining a longitudinal direction therebetween and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels provide a first plurality of inner surfaces and are open at the first face and closed at the second face, and wherein the second plurality of channels provide a second plurality of inner surfaces and are open at the second face and closed at the first face. The channels are preferably parallel to each other to provide a constant wall thickness between the channels. Thus, a gas entering one of the plurality of channels cannot leave the monolithic filter without diffusing through the channel wall into the other plurality of channels. The channels are closed by introducing a sealant material into the open end of the channel. Preferably, the number of channels in the first plurality of channels is equal to the number of channels in the second plurality of channels, and each plurality of channels is uniformly distributed throughout the monolith.

[0033] Catalytic wall-flow monolithic filters are typically prepared by coating a catalytic material onto a wall-flow monolithic substrate. Suitable materials for the wall-flow monolithic substrate include ceramic-like materials such as cordierite, alumina, silicon carbide, silicon nitride, zirconium oxide, mullite, spodumene, alumina-silica magnesia or zirconium silicate or porous refractory metals. The wall-flow monolithic substrate may also be formed of a ceramic fiber composite. Preferred wall-flow substrates are formed of cordierite and silicon carbide. Such materials are capable of withstanding the environments encountered when processing exhaust gas flows (particularly high temperatures) and can be made sufficiently porous. Such materials and their use in making porous monolithic substrates are well known in the art.

[0034] Typically, the wall flow monolith substrate may have a porosity of 40% to 75%. Suitable techniques for determining porosity are known in the art and include mercury intrusion porosimetry and X-ray tomography.

[0035] The first SCR catalyst, the second SCR catalyst and / or the third SCR catalyst ("SCR catalyst") may each comprise an oxide of a base metal, a molecular sieve, a metal-exchanged molecular sieve, or a mixture thereof. The base metal may be selected from the group consisting of cerium (Ce), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), vanadium (V), and mixtures thereof. SCR catalysts consisting of vanadium supported on refractory metal oxides such as alumina, silica, zirconia, titania, cerium dioxide, and combinations thereof are well known and widely used commercially for mobile applications. Typical compositions are described in U.S. Patent Nos. 4,010,238 and 4,085,193, the entire contents of which are incorporated herein by reference. Commercially used compositions (particularly for mobile applications) include TiO 2 , WO 3 and V 2 O 5 The TiO 2 These catalysts may contain other inorganic materials such as SiO as binders and promoters. 2 and ZrO 2 .

[0036] The SCR catalyst may comprise a molecular sieve or a metal-exchanged molecular sieve. As used herein, "molecular sieve" is understood to mean a metastable material containing micropores of precise and uniform size, which can be used as an adsorbent for gas or liquid. Molecules small enough to pass through the pores are adsorbed, while larger molecules are not adsorbed. The molecular sieve may be a zeolitic molecular sieve, a non-zeolitic molecular sieve, or a mixture thereof.

[0037] Zeolite molecular sieves are microporous aluminosilicates having any of the framework structures listed in the Zeolite Structure Database published by the International Zeolite Association (IZA). Framework structures include, but are not limited to, those of CHA, BEA, FAU, LTA, MFI, and MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, zeolite Y, ultrastable zeolite Y, beta zeolite, mordenite, silicalite, zeolite X, and ZSM-5. Aluminosilicate zeolites may have a silica-alumina molar ratio (SAR, defined as SiO 2 / Al 2 O 3 ), with a usable range of approximately 10 to 200.

[0038] As used herein, the term "non-zeolitic molecular sieve" refers to a corner-sharing tetrahedral framework in which at least a portion of the tetrahedral sites are occupied by elements other than silicon or aluminum. Specific non-limiting examples of non-zeolitic molecular sieves include silicoaluminophosphates, such as SAPO-34, SAPO-37, and SAPO 44. Silicoaluminophosphates may have a framework structure comprising framework elements present in zeolites, such as BEA, CHA, FAU, LTA, MFI, MOR, and other types described below.

[0039] The SCR catalyst may comprise small, medium or large pore molecular sieves or a combination thereof.

[0040] The SCR catalyst may include a small pore molecular sieve selected from the group consisting of aluminosilicate molecular sieves, metal-substituted aluminosilicate molecular sieves, aluminophosphate (AlPO) molecular sieves, metal-substituted aluminophosphate (MeAlPO) molecular sieves, silicon-aluminophosphate (SAPO) molecular sieves, and metal-substituted silicon-aluminophosphate (MeAPSO) molecular sieves, and mixtures thereof. The SCR catalyst may include a small pore molecular sieve selected from the group consisting of a framework type of ACO, AEI, AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI, EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, LTA, MER, MON, NSI, OWE, PAU, PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG, and ZON, and mixtures thereof and / or inter-organisms. Preferably, the small pore molecular screen is a group of framework types consisting of AEI, AFX, CHA, DDR, ERI, ITE, KFI, LTA, LEV and SFW.

[0041] The SCR catalyst may comprise a mesoporous molecular sieve selected from the group of framework types consisting of AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, -SVR, SZR, TER, TON, TUN, UOS, VSV, WEI and WEN and mixtures and / or interbionts thereof. Preferably, the mesoporous molecular sieve is selected from the group of framework types consisting of FER, MFI and STT.

[0042] The SCR catalyst may comprise a macroporous molecular sieve selected from the group of framework types consisting of AFI, AFR, AFS, AFY, ASV, ATO, ATS, BEA, BEC, BOG, BPH, BSV, CAN, CON, CZP, DFO, EMT, EON, EZT, FAU, GME, GON, IFR, ISV, ITG, IWR, IWS, IWV, IWW, JSR, LTF, LTL, MAZ, MEI, MOR, MOZ, MSE, MTW, NPO, OFF, OKO, OSI, RON, RWY, SAF, SAO, SBE, SBS, SBT, SEW, SFE, SFO, SFS, SFV, SOF, SOS, STO, SSF, SSY, USI, UWY and VET and mixtures and / or inter-organisms thereof. Preferably, the macroporous molecular sieve is selected from the group of framework types consisting of BEA, MOR and OFF.

[0043] The metal exchanged molecular sieve may have at least one metal from one of the VB, VIB, VIIB, VIIIB, IB or IIB groups of the periodic table, deposited on an external framework site on the external surface or in a channel, cavity or cage of the molecular sieve. The metal may be in one of several forms, including but not limited to zero-valent metal atoms or clusters, isolated cations, mononuclear or polynuclear oxygen-containing cations, or as an extended metal oxide. Preferably, these metals may be iron, copper, and mixtures or combinations thereof.

[0044] The metal exchanged molecular sieve may contain in the range of about 0.10 wt % to about 10 wt % of a Group VB, VIB, VIIB, VIIIB, IB or IIB metal located at an exoframework site on the external surface or within channels, cavities or cages of the molecular sieve.

[0045] The metal exchanged molecular sieve can be a small pore molecular sieve loaded with copper (Cu), which has copper accounting for about 0.1 wt % to about 20.0 wt % of the total weight of the metal exchanged molecular sieve. Preferably, copper is present in an amount of about 1 wt % to about 6 wt % of the total weight of the catalyst, more preferably about 1.8 wt % to about 4.2 wt % of the total weight of the metal exchanged molecular sieve.

[0046] The metal exchanged molecular sieve can be a small pore molecular sieve loaded with iron (Fe), which has an iron content of about 0.1 wt % to about 20.0 wt % of the total weight of the metal exchanged molecular sieve. Preferably, the iron is present in an amount of about 1 wt % to about 6 wt %, more preferably about 1.8 wt % to about 4.2 wt % of the total weight of the metal exchanged molecular sieve.

[0047] In order to provide the catalytic wall-flow monolithic filter of the present invention, the SCR catalyst is usually applied to the porous substrate in the form of a carrier coating. The application can be characterized as "in-wall" application or "on-wall" application. "In-wall" means that the SCR catalyst is present in the pores within the porous material. "On-wall" means that the SCR catalyst is present on the wall of the channel as a catalyst coating. As understood by those skilled in the art, the percentage of the coating present "on the wall" can be determined by techniques in the art such as scanning electron microscopy (SEM) or optical microscopy.

[0048] The technique for "in-wall" or "on-wall" application may depend on the viscosity of the material being applied, the application technique (e.g., spraying or dipping), and the presence of different solvents. Suitable application techniques are known in the art. The viscosity of the carrier coating is affected, for example, by its solids content. It is also affected by the carrier coating particle size distribution (a relatively flat distribution will cause a finely ground carrier coating with a sharp peak in the particle size distribution to have a different viscosity) and rheology modifiers (such as guar gum and other gums). Suitable coating methods are described in U.S. Patent Nos. 6,599,570, 8,703,236, and 9,138,735, which are incorporated herein by reference.

[0049] The monolith filter comprises a first SCR catalyst coated on a first plurality of inner surfaces of the porous walls to form a first SCR catalyst porous layer, wherein the first SCR catalyst is coated from a first face. The first SCR catalyst porous layer covers the inner surfaces of the porous walls ("on-wall" coating).

[0050] The first SCR catalyst porous layer may generally have an average pore size in the range of 0.1 μm to 10 μm, preferably 0.2 μm to 8 μm, more preferably 0.5 μm to 7 μm, 0.75 μm to 6 μm, 0.8 μm to 5 μm, 1 μm to 4 μm, 1.2 μm to 3 μm, 1.5 μm to 2 μm, even more preferably 1.6 μm to 1.8 μm.

[0051] The average pore size of the first SCR catalyst porous layer may be measured by techniques in the art, such as by mercury intrusion porosimetry (MIP) on a Micromeritics Autopore instrument.

[0052] The first SCR catalyst porous layer may have a coating length of 60% to 95% of the total length (L) of the monolith filter from the first face, preferably 80% to 90% of L.

[0053] The first SCR catalyst may have a catalyst content of 0.1 g / in 3 With 5g / in 3 Between, preferably 0.1g / in 3 With 4.5g / in 3Between, more preferably 0.5g / in 3 With 4g / in 3 The washcoat loading is between .

[0054] The monolith filter comprises a second SCR catalyst within the porous wall ("in-wall" coating), wherein the second SCR catalyst is applied from the second side.

[0055] The second SCR catalyst may have a coating length of 60% to 95% of the total length L of the monolith filter starting from the second face, preferably 80% to 90% of L .

[0056] The second SCR catalyst may have a 0.1 g / in 3 With 5g / in 3 Between, preferably 0.1g / in 3 With 4.5g / in 3 Between, more preferably 0.5g / in 3 With 4g / in 3 The washcoat loading is between .

[0057] The monolith filter comprises a third SCR catalyst coated on a second plurality of inner surfaces of the porous wall to form a third SCR catalyst porous layer, wherein the third SCR catalyst is coated from the second face. The third SCR catalyst porous layer covers the inner surfaces of the porous wall ("on-wall" coating).

[0058] The third SCR catalyst porous layer may generally have an average pore size in the range of 0.1 to 10 μm, preferably 0.2 to 8 μm, more preferably 0.5 to 7 μm, 0.75 to 6 μm, 0.8 to 5 μm, 1 to 4 μm, 1.2 to 3 μm, 1.5 to 2 μm, even more preferably 1.6 to 1.8 μm.

[0059] The third SCR catalyst may have a coating length of 5% to 40% of the total length (L) of the monolith filter from the second face, preferably 5% to 30% of L.

[0060] The third SCR catalyst may have 0.05 g / in 3 With 3g / in 3 Between, preferably 0.1g / in 3 With 2.5g / in 3 Between, more preferably 0.2g / in 3 With 2.0g / in 3 The washcoat loading is between .

[0061] According to a second aspect, there is provided a method for manufacturing a catalyzed wall flow monolith filter, the method comprising:

[0062] (a) providing a wall-flow monolith substrate comprising a porous wall and having a first end face and a second end face defining a longitudinal direction therebetween and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels are open at the first end face and closed at the second end face, and wherein the second plurality of channels are open at the second end face and closed at the first end face;

[0063] (b) applying a first SCR catalyst washcoat slurry on a first plurality of interior surfaces of the porous walls;

[0064] (c) applying a second SCR catalyst washcoat slurry on a second plurality of inner surfaces of the porous walls such that the second SCR catalyst washcoat slurry penetrates into the porous walls;

[0065] (d) applying a third SCR catalyst washcoat slurry onto a second plurality of interior surfaces of the porous walls;

[0066] (e) calcining the coated wall flow monolith substrate obtained from steps (b), (c) and (d) to produce a catalyzed wall flow monolith filter.

[0067] The first SCR catalyst carrier coating slurry preferably comprises a molecular sieve or a metal-exchanged molecular sieve as described in the present disclosure, a binder, a pore former, and a solvent (e.g., water). Examples of suitable binders are alumina binders such as boehmite, alpha alumina, beta alumina, and gamma alumina. Examples of pore formers include cellulose pore formers, polyethylene, starch, graphite, polypropylene, polyaramide, polytetrafluoroethylene, polystyrene, cellulose fibers, and polymethacryloyl methacrylates, such as Arbocel, Vivapur, Mipelon PM-200, Propyltex, Orgasol, and Remyrise.

[0068] The molecular sieve and the pore former present in the first SCR catalyst washcoat slurry may have a weight ratio between 10:1 and 1:3, preferably between 8:1 and 1:2.

[0069] The molecular sieve and the binder present in the first SCR catalyst washcoat slurry may have a weight ratio between 20:1 and 1:1, preferably 12:1 to 3:1, more preferably 10:1 to 5:1.

[0070] The first SCR catalyst washcoat slurry may have a viscosity between 5 cPs and 1500 cPs, preferably between 500 cPs and 1200 cPs, more preferably between 700 cPs and 900 cPs.

[0071] Viscosity can be measured at 20°C on a Brookfield RV DVII+ Extra Pro viscometer using a SC4-27 spindle at a spindle speed of 50 rpm.

[0072] The second SCR catalyst washcoat slurry preferably comprises a binder, a solvent (eg, water), and a molecular sieve as described in the present disclosure.Examples of suitable binders are alumina binders such as boehmite, alpha alumina, beta alumina, and gamma alumina.

[0073] The molecular sieve and the binder present in the second SCR catalyst washcoat slurry may have a weight ratio between 20:1 and 1:1, preferably 12:1 to 3:1, more preferably about 9:1.

[0074] The second SCR catalyst washcoat slurry may have a viscosity between 5 cPs and 100 cPs, preferably between 5 cPs and 30 cPs, more preferably between 5 cPs and 15 cPs.

[0075] The third SCR catalyst carrier coating slurry preferably comprises a binder, a pore former, a solvent (e.g., water) and a molecular sieve as described in the present disclosure. Examples of suitable binders are alumina binders such as boehmite, alpha alumina, beta alumina, and gamma alumina. Examples of pore formers include cellulose pore formers, polyethylene, starch, graphite, polypropylene, polyaramid, polytetrafluoroethylene, polystyrene, cellulose fibers, and polymethacryloyl methacrylates, such as Arbocel, Vivapur, Mipelon PM-200, Propyltex, Orgasol, and Remyrise.

[0076] The molecular sieve and the pore former present in the third SCR catalyst washcoat slurry may have a weight ratio between 10:1 and 1:3, preferably between 8:1 and 1:2.

[0077] The molecular sieve and the binder present in the third SCR catalyst washcoat slurry may have a weight ratio between 20:1 and 1:1, preferably 12:1 to 3:1, more preferably 10:1 to 5:1.

[0078] The third SCR catalyst washcoat slurry may have a viscosity between 5 cPs and 1500 cPs, preferably between 500 cPs and 1200 cPs, more preferably between 700 cPs and 900 cPs.

[0079] In a preferred method for making a catalyzed wall flow monolith filter, the third SCR catalyst washcoat slurry is the same as the first SCR catalyst washcoat slurry.

[0080] The first SCR catalyst carrier coating slurry, the second SCR catalyst carrier coating slurry and the third SCR catalyst carrier coating slurry can be applied to the substrate by known methods. There are many suitable ways to apply the SCR catalyst carrier coating slurry to the substrate. For example, coating the substrate with the carrier coating slurry can be carried out by vertically immersing the substrate in the slurry to obtain the required coating length. The substrate can stay in the slurry for a long enough time to allow the required amount of slurry to move into the substrate. Remove the substrate from the slurry, and remove excess slurry from the wall-flow substrate, first discharge it from the channel of the substrate, then blow on the slurry on the substrate with compressed air (against the slurry penetration direction), and then evacuate from the slurry penetration direction.

[0081] Another method of coating a filter substrate comprises the following steps: (a) depositing a predetermined amount of liquid into a receiving device at an upper end of the filter substrate using a shower head, wherein the shower head comprises a plurality of holes arranged to distribute the liquid onto the upper end surface of the filter substrate; and (b) coating the channel having an open end at the upper end of the filter substrate with the predetermined amount of liquid from the receiving device by applying a vacuum to the lower end of the filter substrate to draw the liquid along the channel having an open end at the upper end of the filter substrate. See, for example, EP3122458B1.

[0082] The coated substrate is typically dried at about 100°C and calcined at a higher temperature (eg, 300°C to 450°C).

[0083] According to a third aspect, there is provided an emission treatment system for treating a combustion exhaust gas flow, the system comprising a catalyzed wall flow monolith filter according to the present invention, wherein the first end face is upstream of the second end face.

[0084] According to a fourth aspect, there is provided a method for treating a combustion exhaust gas stream containing NOx, the method comprising passing the exhaust gas stream through a catalyzed wall flow monolith filter according to the invention, wherein the first end face is upstream of the second end face.

[0085] Comparative Example 1

[0086] A washcoat slurry A was prepared containing a Cu-exchanged molecular sieve (CHA, SAR=18.5, Cu loading=3.3 wt%, D90(v)=4.0 μm) and a stabilized gamma alumina (d90(v)≤7 μm) suspended in water at a weight ratio of 9:1. The washcoat slurry had a D90(v) of 4 to 6 μm. Prior to the addition of the gamma alumina, tetraethylammonium hydroxide (TEAH, the amount of TEAH being 4 wt% of the zeolite) was added to the slurry.

[0087] A washcoat slurry B was prepared containing 0.4 wt% Natrasol (cellulose thickener), Cu exchanged zeolite (CHA, SAR = 18.5, Cu loading = 3.3 wt%, D90 (v) = 4.0 μm), Arbocel UFC100 (cellulose supplied by JRS) and boehmite (D90 (v) ≤ 1 μm) suspended in water in a weight ratio of 9:5:1 (zeolite: arbocel: boehmite). The washcoat had a D90 (v) of 20 μm.

[0088] Washcoat slurries A and B were applied to a filter substrate (SC18 supplied by NGK, porosity = 63%, average pore size = 20 μm, 300 cpsi and 12 mil wall thickness) using the method disclosed in EP3122458.

[0089] Washcoat slurry A was applied to the filter substrate from the outlet face to coat about 80% to 85% of the substrate length with a calcined loading of 1.5 g / in 3 Washcoat slurry B was applied to the filter substrate from the inlet face to coat about 80% to 85% of the substrate length with a calcined loading of 0.6 g / in 3 .

[0090] The coated filter substrate (with two doses of coating) was dried at about 100° C. and calcined at 450° C. The resulting catalytic filter contained a first SCR catalyst porous layer (“on-wall” coating) and a second SCR catalyst (“in-wall” coating).

[0091] Example 2

[0092] Washcoat Slurry B was then applied from the outlet face to the coated filter substrate obtained from Comparative Example 1 to coat approximately 20% of the substrate length with a calcined loading of 0.05 g / in 3 .

[0093] The coated filter substrate (with three doses of coating) was dried at about 100° C. and calcined at 450° C. The resulting catalytic filter contained a first SCR catalyst porous layer (“on the wall” coating), a second SCR catalyst (“in the wall” coating), and a third SCR catalyst porous layer (“on the wall” coating).

[0094] Comparative Example 3

[0095] Washcoat slurry C was prepared containing Cu exchanged zeolite (AEI, SAR=20, Cu loading=3.75 wt%, D90(v)=4.0 μm) and stabilized gamma alumina (D90(v)≤μm) suspended in water at a ratio of 9:1. Hypermer was added at 5 wt% and 1 wt% relative to the zeolite, respectively, before adding alumina. TM KD6 (a high molecular weight nonionic dispersant available from Croda) and tetraethylammonium hydroxide (TEAH). The washcoat had a D90(v) of 4 to 6 μm.

[0096] A washcoat slurry D was prepared containing 0.4 wt% Natrasol (cellulose thickener), Cu exchanged zeolite (CHA, SAR=20, Cu loading=3.75 wt%, D90(v)=4.0 μm), Arbocel UFC100 (cellulose supplied by JRS) and boehmite (D90(v)≤1 μm) suspended in water in a ratio of 9:5:1 (zeolite:arbocel:boehmite). The washcoat had a D90(v) of 20 μm.

[0097] Washcoat slurries C and D were applied to a filter substrate (SC18 supplied by NGK, porosity = 63%, average pore size = 20 μm, 300 cpsi and 12 mil wall thickness) using the method disclosed in EP3122458.

[0098] Washcoat slurry C was applied to the filter substrate from the outlet face to coat about 80% to 85% of the substrate length with a calcined loading of 1.3 g / in 3 Washcoat slurry D was applied to the filter substrate from the inlet face to coat about 80% to 85% of the substrate length with a calcined loading of 0.55 g / in 3 .

[0099] The coated filter substrate was dried at about 100° C. and calcined at 450° C. The catalytic filter thus produced comprised a first SCR catalyst porous layer (“on-wall” coating) and a second SCR catalyst (“in-wall” coating).

[0100] Example 4

[0101] Washcoat slurry D was then applied from the outlet face to the coated filter substrate obtained from Comparative Example 3 to coat approximately 20% of the substrate length with a calcined loading of 0.05 g / in 3 .

[0102] The coated filter substrate (with three doses of coating) was dried at about 100° C. and calcined at 450° C. The catalytic filter thus produced contained a first SCR catalyst porous layer (“on the wall” coating), a second SCR catalyst (“in the wall” coating) and a third SCR catalyst porous layer (“on the wall” coating).

[0103] Filtration Efficiency Testing of Coated Filter Substrates from Comparative Example 1 and Example 2

[0104] The filtration efficiency of the coated filter substrate from the above-described embodiments was tested under various conditions. The first condition was an oven clean plus a cold start WLTC test (high quality), the second condition was a hot start WLTC test (high quality), and the third condition was a cold start WLTC (regeneration) test (low quality). WLTC is the World Light Duty Test Cycle, and the regeneration condition is an increase in temperature to break down the soot cake. It is measured using SPCS and is expressed in particles per kilometer. The test results are shown in Tables 1 and 2. Tables 1 and 2 show that the addition of a third porous coating on the outlet channel significantly improves the filtration efficiency of the coated filter.

[0105] Table 1

[0106]

[0107] Table 2

[0108]

Claims

1. A catalyzed wall flow monolith filter for an emission treatment system, the monolith filter comprising a porous wall and having a first face and a second face defining a longitudinal direction therebetween and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels provide a first plurality of interior surfaces and are open at the first face and closed at the second face, and wherein the second plurality of channels provide a second plurality of interior surfaces and are open at the second face and closed at the first face; wherein the monolith comprises a first selective catalytic reduction (SCR) catalyst coated on the first plurality of inner surfaces of the porous wall to form a first SCR catalyst porous layer; wherein the monolith comprises a second SCR catalyst within the porous walls; wherein the monolith comprises a third SCR catalyst, the third SCR catalyst being coated on the second plurality of inner surfaces of the porous walls to form a third SCR catalyst porous layer; wherein the first SCR catalyst is applied from the first side; wherein the second SCR catalyst is applied from the second side; and The third SCR catalyst is coated from the second side. 2 . The catalyzed wall-flow monolith filter according to claim 1 , wherein the first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst each comprise an oxide of a base metal, a molecular sieve, a metal-exchanged molecular sieve, or a mixture thereof. 3 . The catalyzed wall flow monolith filter of claim 1 , wherein the first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst each comprises a molecular sieve or a metal-exchanged molecular sieve.

4. The catalyzed wall-flow monolith filter according to claim 1, wherein the first SCR catalyst, the second SCR catalyst and / or the third SCR catalyst each comprises a small pore molecular sieve selected from the group consisting of aluminosilicate molecular sieves, metal-substituted aluminosilicate molecular sieves, aluminophosphate (AlPO) molecular sieves, metal-substituted aluminophosphate (MeAlPO) molecular sieves, silicon-aluminophosphate (SAPO) molecular sieves and metal-substituted silicon-aluminophosphate (MeAPSO) molecular sieves and mixtures thereof.

5. The catalyzed wall-flow monolith filter of claim 1 , wherein the first SCR catalyst, the second SCR catalyst and / or the third SCR catalyst each comprises a mesoporous molecular sieve selected from the group of framework types consisting of AEL, AFO, AHT, BOF, BOZ, CGF, CGS, CHI, DAC, EUO, FER, HEU, IMF, ITH, ITR, JRY, JSR, JST, LAU, LOV, MEL, MFI, MFS, MRE, MTT, MVY, MWW, NAB, NAT, NES, OBW, PAR, PCR, PON, PUN, RRO, RSN, SFF, SFG, STF, STI, STT, STW, -SVR, SZR, TER, TON, TUN, UOS, VSV, WEI and WEN, and mixtures and / or interbionts thereof.

6. The catalyzed wall-flow monolith filter of claim 1 , wherein the first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst each comprises a metal-exchanged molecular sieve having at least one metal from one of Groups VB, VIB, VIIB, VIIIB, IB, or IIB of the Periodic Table of the Elements deposited onto an exoframework site on an exterior surface or within a channel, cavity, or cage of the molecular sieve.

7. The catalyzed wall flow monolith filter of claim 6, wherein the metal is selected from the group consisting of iron, copper, and mixtures thereof. 8 . The catalyzed wall flow monolith filter of claim 1 , wherein the first SCR catalyst porous layer has a coating length of 60% to 95% of a total length (L) of the monolith filter.

9. The catalyzed wall-flow monolith filter according to claim 1, wherein the first SCR catalyst has a catalyst content of 0.5 g / in 3 With 4g / in 3 The washcoat loading is between . 10 . The catalyzed wall flow monolith filter of claim 1 , wherein the second SCR catalyst has a coating length of 60% to 95% of a total length L of the monolith filter.

11. The catalyzed wall-flow monolith filter according to claim 1, wherein the second SCR catalyst has a catalyst content of 0.5 g / in 3 With 4g / in 3 The washcoat loading is between . 12 . The catalyzed wall flow monolith filter of claim 1 , wherein the third SCR catalyst has a coating length of 5% to 30% of a total length L of the monolith filter.

13. The catalyzed wall-flow monolith filter according to claim 1, wherein the third SCR catalyst has a catalyst content of 0.2 g / in 3 With 2.0g / in 3 The carrier coating loading is between .

14. A method for producing a catalytic wall flow monolith filter according to any one of claims 1 to 25, said method include: (a) providing a wall-flow monolith substrate comprising a porous wall and having a first end face and a second end face defining a longitudinal direction therebetween and a first plurality of channels and a second plurality of channels extending in the longitudinal direction, wherein the first plurality of channels are open at the first end face and closed at the second end face, and wherein the second plurality of channels are open at the second end face and closed at the first end face; (b) applying a first SCR catalyst washcoat slurry on the first plurality of interior surfaces of the porous walls; (c) applying a second SCR catalyst washcoat slurry on the second plurality of inner surfaces of the porous walls such that the second SCR catalyst washcoat slurry penetrates into the porous walls; (d) applying a third SCR catalyst washcoat slurry on the second plurality of interior surfaces of the porous walls; (e) calcining the coated wall flow monolith substrate obtained from steps (b), (c) and (d) to produce the catalytic wall flow monolith filter.

15. The method of claim 14, wherein step (d) is performed before step (b).

16. An emissions treatment system for treating a combustion exhaust stream, the system comprising the catalyzed wall flow monolith filter according to any one of claims 1 to 13.

17. A method for treating a combustion exhaust stream containing NOx, the method comprising passing the exhaust stream through a catalyzed wall flow monolith filter according to any one of claims 1 to 13, wherein the first end face is upstream of the second end face.

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