Improved Catalytic Wall-Flow Filter

Abstract

A catalytic wall-flow monolith filter for use in an exhaust gas treatment system is disclosed. The filter includes a porous wall, first and second surfaces defining a longitudinal direction therebetween, and first and second pluralities of channels extending longitudinally. The first pluralities of channels provide a first pluralities of inner surfaces, open at the first surface and closed at the second surface, and the second pluralities of channels provide a second pluralities of inner surfaces, open at the second surface and closed at the first surface. The filter includes a first selective catalytic reduction (SCR) catalyst coated on the first pluralities of inner surfaces of the porous wall to form a first SCR catalyst porous layer, a second SCR catalyst within the porous wall, and a third SCR catalyst coated on the second pluralities of inner surfaces of the porous wall to form a third SCR catalyst porous layer.

Description

[Technical Field]

[0001] The present invention relates to a catalytic wall-flow monolith filter suitable for use in exhaust treatment systems, such as automotive internal combustion engine exhaust systems. The present invention provides an effective method for improving engine exhaust streams. [Background technology]

[0002] There are concerns regarding emissions of particulate matter (PM), commonly referred to as soot, from internal combustion engines, particularly diesel and gasoline engines for automotive applications. The main concerns relate to potential health effects, specifically those related to very small particles with sizes in the nanometer range.

[0003] Diesel particulate filters (DPFs) and gasoline particulate filters (GPFs) have been manufactured using a variety of materials, including sintered metal, ceramic, or metal fiber. However, the most common type in practical mass production is the wall-flow variety, made from porous ceramic material fabricated in the form of a monolithic array of many small channels extending along the length of the body. The alternating channels are plugged at one end, forcing exhaust gases through the porous ceramic channel walls, which prevent the majority of particulates from passing through, allowing only filtered gases to enter the environment. Commercially produced ceramic wall-flow filters include those made from cordierite, various forms of silicon carbide, and aluminum titanate. The actual shape and dimensions of practical filters on vehicles, as well as characteristics such as the thickness and porosity of the channel walls, depend on the application involved. The average size of the pores in the filter channel walls through which gases pass is typically in the range of 5 to 50 μm, usually around 20 μm. In sharp contrast, most diesel particulate matter from modern passenger car high speed diesel engines is much smaller in size, for example, 10-200 nm.

[0004] Some PM may be retained within the pore structure within the filter wall, which in some applications may gradually build up until the pores are bridged by a network of PM, which then readily forms a cake of particulates on the inner walls of the filter channels. The particulate cake is an excellent filter medium, and its presence results in very high filtration efficiency. In some applications, soot is continuously burned on the filter as it is deposited, which prevents the particulate cake from building up on the filter.

[0005] Some filters, such as light-duty diesel particulate filters, require periodic removal of trapped PM from the filter to prevent excessive backpressure buildup, which can be detrimental to engine performance and reduce fuel economy. In diesel applications, retained PM is removed from the filter by burning it in air during a process during which the amount of available air and the amount of excess fuel used to achieve the high temperatures necessary to ignite the retained PM are very carefully controlled. Toward the end of this process, typically called regeneration, removal of the last remaining particulates in the filter can significantly reduce filtration efficiency and lead to the burst release of many small particles into the environment. Thus, filters may have low filtration efficiency when they are first used, after each subsequent regeneration event, and during the latter part of each regeneration process.

[0006] It is therefore desirable to constantly improve and / or maintain filtration efficiency, for example during the initial life of the filter when first used, and / or during and immediately after regeneration, and / or when soot accumulates on the filter. Summary of the Invention

[0007] According to a first aspect, there is provided a catalytic wall-flow monolith filter for use in an emission treatment system, the catalytic wall-flow monolith filter having a porous wall, first and second faces defining a longitudinal direction therebetween, and first and second pluralities of longitudinally extending channels; a first plurality of channels providing a first plurality of inner surfaces, open at the first face and closed at the second face; a second plurality of channels providing a second plurality of inner surfaces, open at the second face and closed at the first face; the monolith filter comprising 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; the monolith filter includes a second SCR catalyst within the porous wall; the monolith filter comprising a third SCR catalyst coated on a second plurality of inner surfaces of the porous wall to form a third SCR catalyst porous layer; a first SCR catalyst porous layer coated from a first surface; a second SCR catalyst is coated on the second surface; A catalytic wall-flow monolith filter is provided having a third SCR catalytic porous layer coated on the second side.

[0008] According to a second aspect, there is provided a method for manufacturing a catalytic wall-flow monolith filter, the method comprising: (a) providing a wall-flow monolith substrate including a porous wall having first and second faces defining a longitudinal direction therebetween and first and second pluralities of channels extending longitudinally therethrough, wherein the first pluralities of channels are open at a first end face and closed at a second end face, and the second pluralities of channels are open at the second end face and closed at the first end face; (b) applying a first SCR catalyst washcoat slurry onto a first plurality of interior surfaces of the porous wall; (c) applying a second SCR catalyst washcoat slurry onto a second plurality of inner surfaces of the porous walls such that the second SCR catalyst washcoat slurry penetrates the porous walls; (d) applying a third SCR catalyst washcoat slurry onto the second plurality of interior surfaces of the porous walls; (e) calcining the coated wall-flow monolith substrate resulting from steps (b), (c), and (d) to produce a catalytic wall-flow monolith filter.

[0009] According to a third aspect, there is provided an emission treatment system for treating a flow of combustion exhaust gas, the system comprising a catalytic wall-flow monolith filter as described herein, wherein a first end face is upstream of a second end face.

[0010] According to a fourth aspect, there is provided a method for treating a flow of combustion exhaust gas containing NOx, the method comprising passing the exhaust stream through a catalytic wall-flow monolith filter described herein, wherein a first end face is upstream of a second end face. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will now be further described. In the following sections, different aspects of the invention are defined in more detail. Each aspect so defined can be combined with any other aspect or aspects, unless otherwise clearly indicated to be contradictory. In particular, any feature indicated as being preferred or advantageous can be combined with any other feature or features indicated as being preferred or advantageous.

[0012] According to a first aspect, there is provided a catalytic wall-flow monolith filter for use in an emission treatment system, the catalytic wall-flow monolith filter having a porous wall, first and second faces defining a longitudinal direction therebetween, and first and second pluralities of longitudinally extending channels; a first plurality of channels providing a first plurality of inner surfaces, open at the first face and closed at the second face; a second plurality of channels providing a second plurality of inner surfaces, open at the second face and closed at the first face; the monolith filter comprising a first SCR catalyst coated on a first plurality of inner surfaces of the porous wall to form a first SCR catalyst porous layer; the monolith filter includes a second SCR catalyst within the porous wall; the monolith filter comprising a third SCR catalyst coated on a second plurality of inner surfaces of the porous wall to form a third SCR catalyst porous layer; a first SCR catalyst porous layer coated from a first surface; a second SCR catalyst is coated on the second surface; A catalytic wall-flow monolith filter is provided having a third SCR catalytic porous layer coated on the second side.

[0013] The catalytic wall-flow monolith filter has a porous wall, a first face and a second face defining a longitudinal direction therebetween, and a first and a second plurality of channels extending longitudinally, the first plurality of channels providing a first plurality of inner surfaces, open at the first face and closed at the second face, and the second plurality of channels providing a second plurality of inner surfaces, open at the second face and closed at the first face. The channels are preferably parallel to each other to provide a consistent wall thickness between the channels. As a result, gas entering one of the channels cannot exit the monolith filter without diffusing through the channel wall to the other channels. The channels are closed by the introduction of a sealant material into the open ends of the channels. Preferably, the number of channels in the first plurality is equal to the number of channels in the second plurality, and each plurality is uniformly distributed throughout the monolith.

[0014] Catalytic wall-flow monolith filters are generally prepared by coating a catalytic material onto a wall-flow monolith substrate. Suitable materials for the wall-flow monolith substrate include ceramic-like materials such as cordierite, alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica magnesia, or zirconium silicate, or porous refractory metals. Wall-flow monolith substrates can also be formed from ceramic fiber composites. Preferred wall-flow substrates are formed from cordierite and silicon carbide. Such materials can withstand the high temperatures encountered in the environment, particularly when treating exhaust streams, and can be made sufficiently porous. Such materials and their use in the manufacture of porous monolith substrates are well known in the art.

[0015] Generally, wall-flow monolith substrates may have a porosity of 40-75%. Suitable techniques for determining porosity are known in the art and include mercury porosimetry and x-ray tomography.

[0016] The first SCR catalyst, second SCR catalyst, and / or third SCR catalyst ("SCR catalyst") may each comprise a base metal oxide, 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 comprised of vanadium supported on refractory metal oxides such as alumina, silica, zirconia, titania, ceria, and combinations thereof are well known and widely used commercially in vehicle applications. Exemplary compositions are described in U.S. Pat. Nos. 4,010,238 and 4,085,193, the entire contents of which are incorporated herein by reference. In particular, compositions used commercially in vehicle applications include TiO2 upon which WO3 and V2O5 are dispersed at concentrations ranging from 5 to 20% by weight and 0.5 to 6% by weight, respectively. These catalysts may also contain other inorganic materials such as SiO2 and ZrO2, which act as binders and promoters.

[0017] The SCR catalyst can include a molecular sieve or a metal-exchanged molecular sieve. As used herein, "molecular sieve" is understood to mean a metastable material containing small pores of precise and uniform size that can be used as an adsorbent for gases or liquids. Molecules small enough to pass through the pores are adsorbed, while larger molecules are not. The molecular sieve can be a zeolitic molecular sieve, a non-zeolitic molecular sieve, or a mixture thereof.

[0018] Zeolite molecular sieves are microporous aluminosilicates having any one of the framework structures listed in the database of zeolite structures published by the International Zeolite Association (IZA). Framework structures include, but are not limited to, CHA, BEA, FAU, LTA, MFI, and MOR types. Non-limiting examples of zeolites having these structures include chabazite, faujasite, Y-type zeolite, ultrastable Y-type zeolite, beta-type zeolite, mordenite, silicalite, X-type zeolite, and ZSM-5. Aluminosilicate zeolites can have a silica to alumina molar ratio (SAR, defined as SiO2 / Al2O3) of at least about 5, preferably at least about 20, with a useful range of about 10-200.

[0019] 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 framework structures containing framework elements found in zeolites such as BEA, CHA, FAU, LTA, MFI, MOR, and other types described below.

[0020] The SCR catalyst may comprise small pore, medium pore, or large pore molecular sieves, or a combination thereof.

[0021] The SCR catalyst may comprise 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, silico-aluminophosphate (SAPO) molecular sieves, and metal-substituted silico-aluminophosphate (MeAPSO) molecular sieves, and mixtures thereof. The SCR catalyst may comprise a small pore molecular sieve selected from the group of framework types consisting 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 and / or intergrowths thereof. Preferably, the small pore molecular sieve is selected from the group of framework types consisting of AEI, AFX, CHA, DDR, ERI, ITE, KFI, LTA, LEV, and SFW.

[0022] The SCR catalyst may comprise a medium pore 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 intergrowths thereof. Preferably, the medium pore molecular sieve is selected from the group of framework types consisting of FER, MFI, and STT.

[0023] The SCR catalyst may comprise a large pore molecular sieve selected from the group of skeletal 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 intergrowths thereof. Preferably, the large pore molecular sieve is selected from the group of framework types consisting of BEA, MOR and OFF.

[0024] The metal-exchanged molecular sieve can have at least one metal from one of Groups VB, VIB, VIIB, VIIIB, IB, or IIB of the periodic table deposited on extraframework sites on the exterior surface or within the channels, cavities, or cages of the molecular sieve. The metal can be in one of several forms, including, but not limited to, zerovalent metal atoms or clusters, isolated cations, mononuclear or polynuclear oxycations, or extended metal oxides. Preferably, the metal can be iron, copper, and mixtures or combinations thereof.

[0025] The metal-exchanged molecular sieve may contain in the range of about 0.10 wt. % to about 10 wt. % of a Group VB, Group VIB, Group VIIB, Group VIIIB, Group IB, or Group IIB metal located on extraframework sites on the outer surface or within the channels, cavities, or cages of the molecular sieve.

[0026] The metal-exchanged molecular sieve can be a copper (Cu)-loaded small pore molecular sieve having about 0.1 to about 20.0 wt% copper based on the total weight of the metal-exchanged molecular sieve. Preferably, the copper is present in an amount of about 1 wt% to about 6 wt% based on the total weight of the catalyst, more preferably about 1.8 wt% to about 4.2 wt% based on the total weight of the metal-exchanged molecular sieve.

[0027] The metal-exchanged molecular sieve can be an iron (Fe)-loaded small pore molecular sieve having about 0.1 to about 20.0 wt% iron based on the total weight of the metal-exchanged molecular sieve. Preferably, the iron is present in an amount of about 1 to about 6 wt%, more preferably about 1.8 to about 4.2 wt%, based on the total weight of the metal-exchanged molecular sieve.

[0028] To provide the catalytic wall-flow monolith filter of the present invention, the SCR catalyst is typically applied to a porous substrate in the form of a washcoat. The application can be characterized as an "in-wall" application or an "on-wall" application. "In-wall" means that the SCR catalyst is present within the pores within the porous material. "On-wall" means that the SCR catalyst is present as a catalytic coating on the walls of the channels. As will be appreciated by those skilled in the art, the percentage of the coating that is present "on-wall" can be determined by techniques in the art, such as scanning electron microscopy (SEM) or optical microscopy.

[0029] Techniques for "in-wall" or "on-wall" application can depend on the viscosity of the material being applied, the application technique (e.g., spraying or dipping), and the presence of different solvents. Such application techniques are known in the art. The viscosity of a washcoat is affected, for example, by its solids content. It is also affected by the washcoat's particle size distribution (a relatively flat distribution will give a different viscosity to a finely ground washcoat with a sharp peak in its particle size distribution), and rheology modifiers such as guar gum and other gums. Suitable coating methods are described in U.S. Pat. Nos. 6,599,570, 8,703,236, and 9,138,735, which are incorporated herein by reference.

[0030] The monolith filter includes a first SCR catalyst coated on a first plurality of inner surfaces of the porous wall to form a first SCR catalyst porous layer, the first SCR catalyst being coated from a first side. The first SCR catalyst porous layer covers the inner surfaces of the porous wall ("on-wall" coating).

[0031] 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, and even more preferably 1.6 μm to 1.8 μm.

[0032] The average pore size of the first SCR catalyst porous layer can be measured by techniques in the art, for example, by Hg intrusion porosimetry (MIP) on a Micromeritics Autopore instrument.

[0033] The first SCR catalyst porous layer may have a coating length of 60 to 95%, preferably 80 to 90% L of the total length (L) of the monolith filter from the first surface.

[0034] The first SCR catalyst is 0.1 g / in 3 ~5g / in 3 , preferably 0.1 g / in 3 ~4.5g / in 3 , more preferably 0.5 g / in 3 ~4g / in 3 The washcoat loading may be

[0035] The monolith filter includes a second SCR catalyst within the porous wall (an "in-wall" coating), the second SCR catalyst being coated from a second side.

[0036] The second SCR catalyst may have a coating length of 60 to 95%, preferably 80 to 90%L of the total length L of the monolith filter from the second surface.

[0037] The second SCR catalyst is 0.1 g / in 3 ~5g / in 3 , preferably 0.1 g / in 3 ~4.5g / in 3 , more preferably 0.5 g / in 3 ~4g / in 3 The washcoat loading may be

[0038] The monolith filter includes a third SCR catalyst coated on a second plurality of inner surfaces of the porous wall to form a third SCR catalyst porous layer, the third SCR catalyst being coated from the second side. The third SCR catalyst porous layer covers the inner surfaces of the porous wall ("on-wall" coating).

[0039] The third 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, and even more preferably 1.6 μm to 1.8 μm.

[0040] The third SCR catalyst may have a coating length of 5 to 40%, preferably 5 to 30% L of the total length (L) of the monolith filter from the second surface.

[0041] The third SCR catalyst is 0.05 g / in 3 ~3g / in 3 , preferably 0.1 g / in 3 ~2.5g / in 3 , more preferably 0.2 g / in 3 ~2.0g / in 3 The washcoat loading may be

[0042] According to a second aspect, there is provided a method for manufacturing a catalytic wall-flow monolith filter, the method comprising: (a) providing a wall-flow monolith substrate including a porous wall having first and second faces defining a longitudinal direction therebetween and first and second pluralities of channels extending longitudinally therethrough, wherein the first pluralities of channels are open at a first end face and closed at a second end face, and the second pluralities of channels are open at the second end face and closed at the first end face; (b) applying a first SCR catalyst washcoat slurry onto a first plurality of interior surfaces of the porous wall; (c) applying a second SCR catalyst washcoat slurry onto a second plurality of inner surfaces of the porous walls such that the second SCR catalyst washcoat slurry penetrates the porous walls; (d) applying a third SCR catalyst washcoat slurry onto the second plurality of interior surfaces of the porous walls; (e) calcining the coated wall-flow monolith substrate resulting from steps (b), (c), and (d) to produce a catalytic wall-flow monolith filter.

[0043] The first SCR catalyst washcoat slurry preferably contains a molecular sieve or metal-exchanged molecular sieve described herein, a binder, a pore former, and a solvent (e.g., water). Examples of suitable binders include 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 polymethacrylates such as Arbocel, Vivapur, Mipelon PM-200, Propyltex, Orgasol, and Remyrise.

[0044] The molecular sieve and pore former present in the first SCR catalyst washcoat slurry may have a weight ratio of 10:1 to 1:3, preferably 8:1 to 1:2.

[0045] The molecular sieve and binder present in the first SCR catalyst washcoat slurry may have a weight ratio of 20:1 to 1:1, preferably 12:1 to 3:1, and more preferably 10:1 to 5:1.

[0046] The first SCR catalyst washcoat slurry may have a viscosity of 5 to 1500 cPs, preferably 500 to 1200 cPs, and more preferably 700 to 900 cPs.

[0047] Viscosity may be measured at 20° C. on a Brookfield RV DVII+Extra Pro viscometer using an SC4-27 spindle at a spindle speed of 50 rpm.

[0048] The second SCR catalyst washcoat slurry preferably comprises the molecular sieve described herein, a binder, and a solvent (e.g., water). Examples of suitable binders include alumina binders such as boehmite, alpha-alumina, beta-alumina, and gamma-alumina.

[0049] The molecular sieve and binder present in the second SCR catalyst washcoat slurry may have a weight ratio of from 20:1 to 1:1, preferably from 12:1 to 3:1, and more preferably about 9:1.

[0050] The second SCR catalyst washcoat slurry may have a viscosity of 5 to 100 cPs, preferably 5 to 30 cPs, and more preferably 5 to 15 cPs.

[0051] The third SCR catalyst washcoat slurry preferably contains the molecular sieve described herein, a binder, a pore former, and a solvent (e.g., water). Examples of suitable binders include 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 polymethacrylates, such as Arbocel, Vivapur, Mipelon PM-200, Propyltex, Orgasol, and Remyrise.

[0052] The molecular sieve and pore former present in the third SCR catalyst washcoat slurry may have a weight ratio of 10:1 to 1:3, preferably 8:1 to 1:2.

[0053] The molecular sieve and binder present in the third SCR catalyst washcoat slurry may have a weight ratio of 20:1 to 1:1, preferably 12:1 to 3:1, and more preferably 10:1 to 5:1.

[0054] The third SCR catalyst washcoat slurry may have a viscosity between 5 and 1500 cPs, preferably between 500 and 1200 cPs, and more preferably between 700 and 900 cPs.

[0055] In a preferred method of manufacturing a catalytic wall-flow monolith filter, the third SCR catalyst washcoat slurry is the same as the first SCR catalyst washcoat slurry.

[0056] The first SCR catalyst washcoat slurry, the second SCR catalyst washcoat slurry, and the third SCR catalyst washcoat slurry can be applied to the substrate by known methods. There are many suitable methods for applying the SCR catalyst washcoat slurry to the substrate. For example, coating the substrate with the washcoat slurry can be performed by vertically dipping the substrate into the slurry to achieve the desired coating length. The substrate can be left in the slurry for a sufficient time to allow the desired amount of slurry to migrate into the substrate. The substrate is removed from the slurry, and excess slurry is removed from the wall-flow substrate by first draining it from the channels of the substrate, then blowing compressed air onto the slurry on the substrate (opposite the direction of slurry penetration), and then applying a vacuum from the direction of slurry penetration.

[0057] Another method for coating a filter substrate includes (a) depositing a predetermined amount of liquid onto a containment means at an upper end of the filter substrate using a showerhead, the showerhead including a plurality of openings arranged to distribute the liquid onto the upper surface of the filter substrate, and (b) applying a vacuum to the lower end of the filter substrate to draw liquid along the open-ended channels at the upper end of the filter substrate, thereby coating the open-ended channels at the upper end of the filter substrate with the predetermined amount of liquid from the containment means. See, e.g., European Patent No. 3122458(B1).

[0058] The coated substrate is typically dried at about 100°C and calcined at a higher temperature (e.g., 300-450°C).

[0059] According to a third aspect, there is provided an emission treatment system for treating a flow of combustion exhaust gas, the system comprising a catalytic wall-flow monolith filter according to the present invention, the first end face being upstream of the second end face.

[0060] According to a fourth aspect, there is provided a method for treating a flow of combustion exhaust gas containing NOx, the method comprising passing the exhaust stream through a catalytic wall-flow monolith filter according to the present invention, wherein a first end face is upstream of a second end face.

[0061] Comparative Example 1 Washcoat Slurry A was prepared containing Cu-exchanged zeolite (CHA, SAR = 18.5, Cu loading = 3.3 wt%, D90(v) = 4.0 μm) and stabilized gamma-alumina (d90(v) ≤ 7 μm) suspended in water in a 9:1 weight ratio. The washcoat slurry had a D90(v) of 4-6 μm. Tetraethylammonium hydroxide (TEAH, the amount of TEAH was 4 wt% of the zeolite) was added to the slurry prior to the addition of the gamma-alumina.

[0062] 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.

[0063] 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 EP 3122458.

[0064] Wash coat slurry A was applied to the filter substrate from the outlet side at a rate of 1.5 g / in. for approximately 80-85% of the substrate length. 3 Washcoat Slurry B was applied to the filter substrate from the inlet face, covering approximately 80-85% of the substrate length at a calcined loading of 0.6 g / in. 3 The coating was carried out at a calcined loading of 1000 ppm.

[0065] The coated filter substrate (with two coating applications) was dried at about 100° C. and calcined at 450° C. The resulting catalytic filter contained a first SCR catalyst porous layer (the "on-wall" coating) and a second SCR catalyst (the "in-wall" coating).

[0066] Example 2 Washcoat Slurry B was then applied to the coated filter substrate from Comparative Example 1 starting from the outlet face to cover approximately 20% of the substrate length at a rate of 0.05 g / in 3 The coating was carried out at a calcined loading of 1000 ppm.

[0067] The coated filter substrate (having three coating applications) 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), a second SCR catalyst ("in-wall" coating), and a third SCR catalyst porous layer ("on-wall" coating).

[0068] Comparative Example 3 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) in a 9:1 ratio suspended in water. Prior to the addition of the alumina, Hypermer™ KD6 (a high molecular weight nonionic dispersant available from Croda) and tetraethyl ammonium hydroxide (TEAH) were added at 5 wt% and 1 wt%, respectively, relative to the zeolite. The washcoat had a D90(v) of 4-6 μm.

[0069] 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.

[0070] 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 EP 3122458.

[0071] Wash coat slurry C was applied to the filter substrate from the outlet side at a rate of 1.3 g / in. 3 Washcoat Slurry D was applied to the filter substrate from the inlet face, covering approximately 80-85% of the substrate length at a calcined loading of 0.55 g / in. 3 The coating was carried out at a calcined loading of 1000 ppm.

[0072] The coated filter substrate was dried at about 100° C. and calcined at 450° C. The catalytic filter thus produced contains a first SCR catalyst porous layer (the "on-wall" coating) and a second SCR catalyst (the "in-wall" coating).

[0073] Example 4 Washcoat Slurry D was then applied to the coated filter substrate from Comparative Example 3 starting from the outlet face to cover approximately 20% of the substrate length at a rate of 0.05 g / in 3 The coating was carried out at a calcined loading of 1000 ppm.

[0074] The coated filter substrate (having three coating applications) was dried at about 100° C. and calcined at 450° C. The catalytic filter thus produced contains a first SCR catalyst porous layer ("on-wall" coating), a second SCR catalyst ("in-wall" coating), and a third SCR catalyst porous layer ("on-wall" coating).

[0075] Filtration Efficiency Testing of Coated Filter Substrates from Comparative Example 1 and Example 2 The filtration efficiency of the coated filter substrates from the above examples was tested under various conditions. The first condition was oven-cleaned in a cold start WLTC test (high mass), the second condition was a hot start WLTC test (high mass), and the third condition was a cold start WLTC (regeneration) test (low mass). WLTC is a worldwide passenger car test cycle, and the regeneration condition is a high temperature to break down the soot cake. Measurements were made using SPCS and reported as particulates per kilometer. The 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 improved the filtration efficiency of the coated filter.

[0076] [Table 1]

[0077]

Table 2

Claims

1. 1. A catalytic wall-flow monolith filter for use in an emission treatment system, the monolith filter having first and second faces with porous walls defining a longitudinal direction therebetween, and first and second pluralities of channels extending in the longitudinal direction; the first plurality of channels provide a first plurality of inner surfaces, open at the first surface and closed at the second surface; the second plurality of channels provide a second plurality of inner surfaces, open at the second surface and closed at the first surface; the monolith includes 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; the monolith containing a second SCR catalyst within the porous wall; the monolith includes a third SCR catalyst coated on the second plurality of inner surfaces of the porous wall to form a third SCR catalyst porous layer; the first SCR catalyst is coated from the first surface; the second SCR catalyst is coated from the second surface; A catalytic wall-flow monolith filter, wherein the third SCR catalyst is coated from the second surface.

2. 10. The catalytic wall-flow monolith filter of claim 1, wherein the first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst each comprise a base metal oxide, a molecular sieve, a metal-exchanged molecular sieve, or a mixture thereof.

3. 10. The catalytic wall-flow monolith filter of claim 1, wherein the first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst each comprise a molecular sieve or a metal-exchanged molecular sieve.

4. 2. The catalytic wall-flow monolith filter of claim 1, wherein the first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst each comprise 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, silico-aluminophosphate (SAPO) molecular sieves, and metal-substituted silico-aluminophosphate (MeAPSO) molecular sieves, and mixtures thereof.

5. The first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst are each selected from the group 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, and OB.

10. The catalytic wall-flow monolith filter of claim 1 comprising a medium pore molecular sieve selected from the group of skeletal types consisting of W, -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 intergrowths thereof.

6. 2. The catalytic wall-flow monolith filter of claim 1, wherein the first SCR catalyst, the second SCR catalyst, and / or the third SCR catalyst each comprise 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 deposited on extra-framework sites on an outer surface or within channels, cavities, or cages of the molecular sieve.

7. 7. The catalytic wall-flow monolith filter of claim 6, wherein the metal is selected from the group consisting of iron, copper, and mixtures thereof.

8. 10. The catalytic wall-flow monolith filter of claim 1, wherein the first SCR catalyst porous layer has a coating length of 60 to 95% of the total length (L) of the monolith filter.

9. The first SCR catalyst is 0.5 g / in ３ ~4g / in ３ 10. The catalytic wall-flow monolith filter of claim 1 having a washcoat loading of

10. 10. The catalytic wall-flow monolith filter of claim 1, wherein the second SCR catalyst has a coating length of 60 to 95% of the overall length L of the monolith filter.

11. The second SCR catalyst is 0.5 g / in ３ ~4g / in ３ 10. The catalytic wall-flow monolith filter of claim 1 having a washcoat loading of

12. 2. The catalytic wall-flow monolith filter of claim 1, wherein the third SCR catalyst has a coating length of 5 to 30% of the overall length L of the monolith filter.

13. The third SCR catalyst is 0.2 g / in ３ ~2.0 g / in ３ 10. The catalytic wall-flow monolith filter of claim 1 having a washcoat loading of

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

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

16. An emission treatment system for treating a flow of combustion exhaust gas, said system comprising a catalytic wall-flow monolith filter according to any one of claims 1 to 13.

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

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