Catalytic partial wall flow filter

Abstract

Catalytic partial wall-flow filters suitable for use in exhaust gas treatment systems, methods of making catalytic partial wall-flow filters, and methods of using catalytic partial wall-flow filters to reconcile engine exhaust gas flow are disclosed. The filter includes a partial wall flow filter substrate having an inlet end, an outlet end, and a plurality of porous walls forming channels from the inlet end to the outlet end, where some of the channels are clogged channels and some are unclogged flow channels. A selective catalytic reduction (SCR) catalyst is coated on the porous walls.

Description

Technical Field

[0001] This invention relates to a wall-flow filter for the catalytic converter section of an exhaust gas treatment system, such as an automotive internal combustion exhaust system. This invention provides an effective method for controlling engine exhaust flow. Background Technology

[0002] In automotive applications, there are concerns about particulate matter (PM) emissions from internal combustion engines such as diesel, gasoline, or hydrogen engines. The main concern is related to potential health effects, particularly those involving extremely small particles in the nanometer range.

[0003] Diesel particulate filters (DPFs) and gasoline particulate filters (GPFs) are manufactured using a variety of materials, including sintered metals, ceramics, or metal fibers. The most common type in actual mass production is the wall-flow type, made of porous ceramic materials, which are manufactured as a monolithic array of numerous small channels extending along the body length. Alternating channels are blocked at one end, thus forcing exhaust gas through the porous ceramic channel walls, which prevent most particles from passing through, allowing only filtered gas to enter the environment. Commercially produced ceramic wall-flow filters include those made of cordierite, various forms of silicon carbide, and aluminum titanate. The actual shape and size of the practical filters used in vehicles, as well as characteristics such as channel wall thickness and porosity, depend on the application of interest. The average pore size in the filter channel walls of ceramic wall-flow filters through which gas passes is typically in the range of 5 μm to 50 μm, and is usually around 20 μm. In stark contrast, most diesel particulate matter from high-speed diesel engines in modern passenger cars is much smaller, ranging from 10 nm to 200 nm in size.

[0004] The most widely used DPF is the wall-flow filter. A typical wall-flow filter comprises a ceramic honeycomb cell with longitudinally spaced, generally parallel pore channels formed by multiple intersecting porous walls. The pore channels are typically plugged with ceramic plug cement to form a checkered pattern of plugging at the end faces of the honeycomb cell. The filter's pore channels typically have some unplugged ends at the inlet end face of the honeycomb cell, referred to herein as "inlet channels." Similarly, the pore channels typically also have plugged remaining ends to form a checkered pattern of plugging at the outlet end face of the honeycomb substrate, some of which are unplugged, referred herein as "outlet channels."

[0005] like Figure 1The conventional porous wall-flow filter 100 shown includes an inlet end 101, an outlet end 102, and a plurality of generally parallel pore channels (inlet pore channel 111 and outlet pore channel 112) separated by porous pore walls 120. The inlet channel includes a blockage 130 at the outlet end 102. The outlet channel includes a blockage at the inlet end 101. The blockage 130 is typically located at the end of the pore channel and typically has a depth of about 5 mm to 20 mm.

[0006] Some particulate matter (PM) may remain within the pore structure of the filter wall, and in some applications this can gradually accumulate until the pores are bridged by a network of PM, which then allows for the easy formation of a particulate cake on the inner wall of the filter channels. The particulate cake is an excellent filter medium, and its presence provides very high filtration efficiency. In some applications, soot is continuously burned on the filter during deposition, which prevents the accumulation of particulate cake on the filter.

[0007] For some filters, such as light-duty diesel particulate filters, it is necessary to periodically remove captured PM from the filter to prevent the buildup of excessive back pressure, which is detrimental to engine performance and can lead to poor fuel economy. Therefore, in diesel applications, the retained PM is removed from the filter by burning it in air during a process in which the amount of available air and excess fuel required to reach the high temperature needed to ignite the retained PM is carefully controlled. At the end of this process, commonly known as regeneration, removing the last remaining particles from the filter can result in a significant decrease in filtration efficiency and a burst of release of many small particles into the environment. Therefore, the filter may have low filtration efficiency during initial use and subsequently after each regeneration event and also during the latter part of each regeneration process.

[0008] Therefore, it is desirable to always improve and / or maintain filtration efficiency, such as during the early lifespan of the filter when it is first used, and / or during and immediately after regeneration, and / or when the filter is loaded with dust.

[0009] Diesel exhaust systems based on "active" regeneration have become industry standards because they are expected to operate at lower exhaust temperatures and ensure proper soot removal under different engine operating cycles through regeneration. On the other hand, "active" regeneration is accompanied by a loss of fuel economy. Furthermore, conventional filters can exhibit relatively high back pressure. Therefore, systems and filters that operate with fewer regeneration events during operation, and filters that exhibit lower back pressure, are desirable. Summary of the Invention

[0010] According to a first aspect, a catalytic partial wall-flow filter for use in an exhaust gas treatment system is provided, the filter comprising:

[0011] a) A partial wall-flow filter substrate having an inlet end, an outlet end, and multiple porous walls forming channels from the inlet end to the outlet end, wherein some channels are blocked channels and some are unblocked flow channels; and

[0012] b) Selective catalytic reduction (SCR) catalyst, which is coated on a porous wall.

[0013] According to a second aspect, a method for manufacturing a catalytic partial wall flow filter is provided, the method comprising:

[0014] (a) A partial wall-flow filter substrate is provided, the partial wall-flow filter substrate having an inlet end, an outlet end, and a plurality of porous walls forming channels from the inlet end to the outlet end, wherein some of the channels are blocked channels and some are unblocked flow channels; and

[0015] (b) Applying an SCR catalyst support coating slurry to a porous wall to form a coated wall-flow filter substrate;

[0016] (c) Calcining the coated wall-flow filter substrate to produce a partially catalytic wall-flow filter.

[0017] According to a third aspect, a waste gas treatment system for treating combustion exhaust gas streams is provided, the system comprising a catalytic wall-flow filter according to the invention, wherein the inlet end is upstream of the outlet end.

[0018] According to the fourth aspect, a method for processing NO is provided. x A method for processing combustion exhaust gas flow, the method comprising passing the exhaust gas flow through a catalytic section wall-flow filter according to the invention, wherein the inlet end is upstream of the outlet end. Attached Figure Description

[0019] The accompanying drawings described below illustrate exemplary embodiments and should not be considered as limiting the scope of the invention. The drawings are not necessarily drawn to scale, and for clarity and brevity, some features and views may be shown to scale or schematically exaggerated.

[0020] Figure 1 A conventional wall-flow filter substrate is shown.

[0021] Figure 2 A first embodiment of a partial wall-flow filter substrate is shown.

[0022] Figure 3 A second embodiment of a partial wall-flow filter substrate is shown.

[0023] Figure 4 A third embodiment of a partial wall-flow filter substrate is shown.

[0024] Figure 6 A fourth embodiment of a partial wall-flow filter substrate is shown.

[0025] Figure 6 A fifth embodiment of a partial wall-flow filter substrate is shown.

[0026] Figure 7 A partial wall-flow filter substrate coated with an SCR catalyst is shown.

[0027] Figure 8 An exemplary construction of an exhaust gas treatment system is shown.

[0028] Figure 9 An exhaust gas treatment system used for performance testing is shown. Detailed Implementation

[0029] The invention will now be described further. In the following paragraphs, different aspects of the invention are defined in more detail. Unless explicitly indicated to the contrary, each aspect so defined may be combined with any other one or more aspects. In particular, any feature indicated as preferred or advantageous may be combined with any other one or more features indicated as preferred or advantageous.

[0030] According to a first aspect, a catalytic partial wall-flow filter for use in an exhaust gas treatment system is provided, the filter comprising:

[0031] a) A partial wall-flow filter substrate having an inlet end, an outlet end, and multiple porous walls forming channels from the inlet end to the outlet end, wherein some channels are blocked channels and some are unblocked flow channels; and

[0032] b) Selective catalytic reduction (SCR) catalyst, which is coated on a porous wall.

[0033] Catalytic partial wall flow filters include a partial wall flow filter substrate (e.g., a monolithic ceramic honeycomb substrate). Suitable materials for the partial wall flow filter substrate include ceramic-like materials such as cordierite, alumina, silicon carbide, silicon nitride, zirconium oxide, mullite, spodumene, alumina-silica-magnesium oxide, or zirconium silicate, or porous refractory metals. Partial wall flow filter substrates can also be formed from ceramic fiber composite materials.

[0034] Partial wall flow filter substrates are known. See, for example, US 20110132194A1. Partial wall flow filter substrates exhibit a combination of blocked channels and unblocked flow channels. In the unblocked flow channels, the flow typically passes directly through the channel, i.e., without passing through the wall. In the blocked channels, some flow passes through the wall. Therefore, "partial" means that only a portion of the flow passes through the wall, while a portion of the flow passes through the filter without flowing through the wall.

[0035] Suitable partial wall flow filter substrates are described in US 20110132194A1, the entire contents of which are incorporated herein by reference. Figure 2 This is a first embodiment of a partial wall-flow filter substrate 200. The partial wall-flow filter 200 includes a plurality of porous walls 220 forming channels 211, 212, 213, and 214, wherein some of the channels are blocked channels, and the remaining channels are unblocked flow channels (213, 214). In this embodiment, the blocked channels (211, 212) include channels that are blocked adjacent to the inlet end 201 of the filter substrate 200 (i.e., at or near the inlet end 201). The other channels 211 are blocked near the outlet end of the filter substrate 200 (i.e., at or near the outlet end 202). Blockages 230 may be provided, for example, at the end faces of some of the channels, while the remaining channels 213, 214 remain open (unblocked). This differs from... Figure 1 The image shows a conventional wall-flow filter where all the pores are end-blocked (at the inlet or outlet end).

[0036] refer to Figure 3 A second embodiment of a partially wall-flow filter substrate 300 is shown and described. In this embodiment, the filter substrate 300 includes a plurality of porous walls 320 to define and form a plurality of channels. The channels include some unblocked channels (unblocked channels 312) and some blocked channels (blocked channels 311). In this embodiment, all blockages 330 are included on the outlet end 302 of the filter 300. In this embodiment, approximately 50% of the channels are blocked, and the remaining channels consist of flow channels.

[0037] refer to Figure 4 A third embodiment of a partially wall-flow filter substrate 400 is shown and described. In this embodiment, the filter substrate 400 includes a plurality of porous walls 420 to define and form a plurality of channels. The channels include some unblocked channels (unblocked channels 415) and some blocked channels (blocked channels 416). In this embodiment, the blockage 430 is entirely included on the inlet end 402 of the filter 400. In this embodiment, approximately 50% of the channels are blocked, and the remaining channels comprise flow channels.

[0038] The channels in a partial wall-flow filter substrate can have different dimensions. For example, the hydraulic diameter of an unblocked flow channel can differ from the hydraulic diameter of a blocked channel. In some embodiments, the hydraulic diameter of the blocked channel is larger than that of the unblocked flow channel. In other embodiments, the hydraulic diameter of the blocked channel is smaller than that of the unblocked flow channel.

[0039] refer to Figure 5 A fourth embodiment of a partially wall-flow filter substrate 500 is shown and described. In this embodiment, the filter substrate 500 includes a plurality of porous walls 520 to define and form a plurality of channels. The channels include some unblocked channels (unblocked channels 512) and some blocked channels (blocked channels 511). All blockages are contained at the inlet end 501 of the filter substrate 500. Approximately 50% of the channels are blocked, and the remaining channels comprise flow channels. In this embodiment, the width of the unblocked flow channels (512) is greater than that of the blocked channels (channels 511).

[0040] refer to Figure 6 A fifth embodiment of a partially wall-flow filter substrate 600 is shown and described. In this embodiment, the filter substrate 600 includes a plurality of porous walls 620 to define and form a plurality of channels. The channels include some unblocked channels (612) and some blocked channels (611). All blockages are present at the outlet end 602 of the filter substrate 600. Approximately 50% of the channels are blocked, and the remaining channels comprise flow channels. In this embodiment, the width of the unblocked flow channels (612) is smaller than that of the blocked channels (611).

[0041] Partial wall flow filter substrates can have a cylindrical shape. The cross-section of the partial wall flow filter substrate can be circular, oval, elliptical, square, or have other desired shapes. The channels of the partial wall flow filter substrate can have a square cross-section or other types of cross-sections, such as triangular, circular, octagonal, rectangular, hexagonal, or combinations thereof.

[0042] Typically, the substrate of a partial wall-flow filter can 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.

[0043] The catalytic wall-flow filter comprises a selective catalytic reduction (SCR) catalyst coated on a porous wall. "SCR catalyst coated on a porous wall" can be "in-wall," "on-wall," or a combination of both. "In-wall" means that the SCR catalyst is primarily present in the pores within the porous wall. For example, in an "in-wall" coating, the amount of SCR catalyst in the pores within the porous wall is greater than 80%, greater than 85%, greater than 90%, or greater than 95% relative to the total amount of SCR catalyst applied to a portion of the wall-flow filter substrate. "On-wall" means that the SCR catalyst, as a catalyst coating, is primarily present on the surface of the porous wall. For example, in an "on-wall" coating, the amount of SCR catalyst on the surface of the porous wall is greater than 80%, greater than 85%, greater than 90%, or greater than 95% relative to the total amount of SCR catalyst applied to a portion of the wall-flow filter substrate. As those skilled in the art will understand, the percentage of coating present "on-wall" can be determined using known techniques such as scanning electron microscopy (SEM) or optical microscopy.

[0044] SCR catalysts can be applied to a partially wall-flow filter substrate in the form of a carrier coating. The techniques used for “in-wall” or “on-wall” application can depend on the viscosity of the applied carrier coating slurry, the application technique (e.g., spraying or impregnation), and the presence of different solvents. Suitable application techniques are known in the art. The viscosity of the carrier coating slurry is affected, for example, by its solids content. It is also affected by the particle size distribution of the carrier coating (a relatively flat distribution will result in finely ground carrier coatings with sharp peaks having different viscosities) and rheology modifiers (such as guar gum and other gums). Suitable coating methods are described in US6,599,570, US8,703,236, US9,138,735, and US20180229228A1.

[0045] SCR catalysts typically comprise oxides of base metals, molecular sieves, metal-exchanged molecular sieves, or mixtures thereof. Base metals 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, zirconium oxide, titanium dioxide, cerium dioxide, and combinations thereof are well known and widely used commercially in mobile applications. Typical compositions are described in US 4,010,238 and US 4,085,193, the entire contents of which are incorporated herein by reference. Commercially used compositions (particularly for mobile applications) include TiO2, WO3, and V2O5 dispersed on TiO2 at concentrations ranging from 5 wt% to 20 wt% and 0.5 wt% to 6 wt%, respectively. These catalysts may contain other inorganic materials, such as SiO2 and ZrO2, used as binders and / or promoters.

[0046] SCR catalysts may contain vanadium and cerium. The molar ratio of cerium to vanadium may be 0.3 to 0.7 or 0.4 to 0.6. The SCR catalyst may contain vanadium at a weight of 2 wt% to 6 wt% or 3 wt% to 5 wt% based on V₂O₅ and cerium at a weight of 1 wt% to 10 wt% or 2 wt% to 5 wt% based on CeO₂. Using cerium and vanadium in such proportions reduces vanadium volatilization without reducing the activity of the SCR catalyst. The reduced volatilization allows for a larger vanadium loading, which is desirable for improving the efficiency of the SCR catalyst. In addition to vanadium and cerium, the SCR catalyst may also contain antimony. Antimony may be present in amounts such that the molar ratio of antimony to vanadium is 0.6 to 0.9 or 0.7 to 0.8. Antimony may be present as Sb₂O₅. For example, the SCR catalyst may contain 2 wt% to 6 wt% V₂O₅, 2 wt% to 6 wt% CeO₂, and 3 wt% to 8 wt% Sb₂O₅ relative to the total weight of the SCR catalyst.

[0047] SCR catalysts can contain molecular sieves or metal-exchanged molecular sieves. As used herein, "molecular sieve" should be understood to mean a metastable material containing micropores of precise and uniform size, which can be used as an adsorbent for gases or liquids. Molecular sieves can be zeolite molecular sieves, non-zeolite molecular sieves, or mixtures thereof.

[0048] Zeolite molecular sieves are microporous aluminosilicates with 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 the CHA, BEA, FAU, LTA, MFI, and MOR types. Non-limiting examples of zeolites with these structures include chabazite, octahedral zeolite, zeolite Y, ultrastable zeolite Y, β-zeolite, mordenite, silica rock, zeolite X, and ZSM-5. Aluminosilicate zeolites can have a silica to alumina molar ratio (SAR, defined as SiO2 / Al2O3) of 5 to 200, 10 to 180, or about 20 to 150.

[0049] As used herein, the term "non-zeolite molecular sieve" refers to a 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-zeolite molecular sieves include silica-aluminophosphates such as SAPO-34, SAPO-37, and SAPO 44. Silica-aluminophosphates may have a framework structure comprising framework elements present in the zeolite, such as BEA, CHA, FAU, LTA, MFI, MOR, and other types described below.

[0050] SCR catalysts may contain microporous, mesoporous, or macroporous molecular sieves or combinations thereof.

[0051] SCR catalysts may comprise small-pore molecular sieves selected from the group consisting of aluminosilicate molecular sieves, metal-substituted aluminosilicate molecular sieves, aluminophosphate (AlPO) molecular sieves, metal-substituted aluminophosphate (MeAlPO) molecular sieves, silica-aluminophosphate (SAPO) molecular sieves, and metal-substituted silica-aluminophosphate (MeAPSO) molecular sieves, as well as mixtures thereof. SCR catalysts may also comprise small-pore molecular sieves selected from the group 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, as well as mixtures thereof and / or commensal framework types. Small-pore molecular sieves can be selected from groups of framework types consisting of AEI, AFX, CHA, DDR, ERI, ITE, KFI, LTA, LEV, and SFW.

[0052] SCR catalysts may comprise mesoporous molecular sieves selected from the group consisting of framework types 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, as well as mixtures and / or commensal organisms thereof. Mesoporous molecular sieves may be selected from the group consisting of framework types of FER, MFI, and STT.

[0053] SCR catalysts may comprise macroporous molecular sieves selected from the group consisting of framework types 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, as well as mixtures and / or commensal organisms thereof. Macroporous molecular sieves may be selected from the group consisting of framework types of BEA, MOR, and OFF.

[0054] Metal-exchange molecular sieves may contain at least one metal from one of groups VB, VIB, VIIB, VIIIB, IB, or IIB of the periodic table, deposited on an external framework site on the outer surface or within the channels, cavities, or cages of the molecular sieve. The metal may be in several forms, including but not limited to zero-valent metal atoms or clusters, isolated cations, mononuclear or polynuclear oxygen-containing cations, or as extended metal oxides. The metal may be iron, copper, or mixtures or combinations thereof.

[0055] The metal-exchangeable molecular sieve may contain group VB, VIB, VIIB, VIIIB, IB or IIB metals in the range of about 0.10% by weight to about 10% by weight, located on the framework sites on the outer surface or in the channels, cavities or cages of the molecular sieve.

[0056] The metal-exchangeable molecular sieve may be a small-pore molecular sieve loaded with copper (Cu) having copper content of 0.1 wt% to 20.0 wt%, 1 wt% to 6 wt%, or 1.8 wt% to 4.2 wt% relative to the total weight of the metal-exchangeable molecular sieve.

[0057] The metal-exchangeable molecular sieve can be a small-pore molecular sieve loaded with iron (Fe) having 0.1 wt% to 20.0 wt%, 1 wt% to 6 wt%, or 1.8 wt% to 4.2 wt% of iron relative to the total weight of the metal-exchangeable molecular sieve.

[0058] SCR catalysts can be coated onto a portion of the wall-flow filter substrate from the inlet end only, from the outlet end only, or from both the inlet and outlet ends.

[0059] In some implementations, the SCR catalyst has a coating length of 100% of the substrate length (L).

[0060] SCR catalysts can have a coating length of 50% to 90%, 55% to 85%, or 60% to 80% of the substrate length (L).

[0061] Figure 7 A catalytic partial wall flow filter 700 is shown, comprising a partial wall flow filter substrate coated with an SCR catalyst. The catalytic partial wall flow filter 700 includes a plurality of porous walls 720 to form a plurality of channels. The channels include some unblocked channels (unblocked channels 712) and some blocked channels (blocked channels 711). In this embodiment, the blockage 730 is entirely contained at the outlet end 702 of the filter 700. In this embodiment, approximately 50% of the channels are blocked, and the remaining channels comprise flow channels. The SCR catalyst 750 is coated from the inlet end of the filter 700.

[0062] SCR catalysts can have a concentration of 0.1 g / inch. 3 With 5g / inch 3 Between, at 0.1 g / inch 3 With 4.5g / inch 3 Between or at 0.5g / inch 3 With 4g / inch 3 The carrier coating load. "Carrier coating load" refers to the weight of the carrier coating (after calcination) per unit volume of the entire catalytic section wall-flow filter. The volume of the entire catalytic section wall-flow filter is calculated based on its cross-sectional area and length; it does not take into account the number of channels per square inch.

[0063] According to a second aspect, a method for manufacturing a catalytic partial wall flow filter is provided, the method comprising:

[0064] a) Provide a partial wall-flow filter substrate having an inlet end, an outlet end, and a plurality of porous walls forming channels from the inlet end to the outlet end, wherein some of the channels are blocked channels and some are unblocked flow channels; and

[0065] (b) Applying an SCR catalyst support coating slurry to a porous wall to form a coated wall-flow filter substrate;

[0066] (c) Calcining the coated wall-flow filter substrate to produce a partially catalytic wall-flow filter.

[0067] SCR catalyst support coating slurries can have viscosities between 5 cPs and 1500 cPs, between 500 cPs and 1200 cPs, or between 700 cPs and 900 cPs. Viscosities can be measured at 20°C using an SC4-27 spindle on a Brookfield RV DVII+Extra Pro viscometer at a spindle speed of 50 rpm.

[0068] SCR catalyst support coating slurry can be applied to the substrate using known methods. There are many suitable methods for applying SCR catalyst support coating slurry to the substrate. For example, coating the substrate with the support coating slurry can be done by vertically immersing the substrate in the slurry to obtain the desired coating length. The substrate can remain in the slurry for a sufficient time to allow the desired amount of slurry to move into the substrate. The substrate is removed from the slurry, and excess slurry is removed from the wall-flow filter substrate first by allowing it to drain from the substrate's channels, then by blowing compressed air onto the slurry on the substrate, and / or by vacuuming.

[0069] Another method for coating a partial wall-flow filter substrate includes the steps of: (a) depositing a predetermined amount of carrier coating slurry into a receiving device at the upper end of the filter substrate using a spray head, wherein the spray head includes a plurality of orifices arranged to distribute the carrier coating slurry onto the upper end face of the filter substrate; and (b) coating the channel at the upper end of the filter substrate with the predetermined amount of carrier coating slurry from the receiving device by aspirating liquid along a channel having an open end at the upper end of the filter substrate by applying a vacuum to the lower end of the filter substrate. See, for example, US20180229228A1.

[0070] The coated substrate is typically dried at about 110°C and calcined at higher temperatures (e.g., 300°C to 500°C).

[0071] According to a third aspect, a waste gas treatment system for treating combustion exhaust gas streams is provided, the system comprising a catalytic wall-flow filter according to the invention, wherein the inlet end is upstream of the outlet end.

[0072] In addition to the catalytic wall-flow filter according to the present invention, the exhaust gas treatment system may also employ other well-known exhaust gas treatment components known to those skilled in the art. For simplicity, abbreviations are used herein. These include diesel oxidation catalyst (DOC), selective catalytic reduction (SCR) catalyst components, ammonia leak catalyst (ASC), selective catalytic reduction filter (SCRF), ammonia leak catalyst filter (ASCF), diesel particulate filter (DPF), and catalytic soot filter (CSF).

[0073] It has recently been observed that injecting nitrogen-containing reducing agents (especially urea / ammonia) into exhaust gas streams can lead to the formation of certain aggregated compounds. The aggregated material then takes the form of additional fine particulate matter that can be released into the atmosphere.

[0074] A discussion of these polymerized particulate matter exhaust gases can be found in SAE 2017-01-0915. It explains that incomplete decomposition of injected urea, depending on the urea metering feeder, decomposition reaction tube (DRT) design, and operating conditions, can lead to the formation of solid urea deposits in diesel aftertreatment systems. These deposits can result in increased engine back pressure and deterioration of NOx treatment performance. Understanding this transformation process is crucial, as the urea deposits can further transform into chemically more stable substances upon exposure to hot exhaust gases. The authors' experimental results indicate that: 1) below the urea melting temperature (130°C), the formed urea deposits are still primarily urea; 2) in the temperature range of 130°C–190°C, urea transforms into a combination of urea, biuret, and cyanuric acid; and 3) above the biuret melting temperature (190°C), cyanuric acid and cyanuric acid amides are formed. At temperatures above 200°C, urea undergoes rapid chemical transformation via urea decomposition, biuret formation, and subsequent biuret decomposition, eventually converting into cyanuric acid within a short period.

[0075] Therefore, the polymerization of urea and ammonia components in hot exhaust gases can lead to the formation of polymeric particulate matter. This particulate matter is typically very fine, but it is precisely this fine material that is now subject to increasingly stringent regulations. Furthermore, because the formation of particulate matter can only occur after the reducing agent has been quantitatively added to the exhaust gas treatment system, it typically forms after any conventional particulate filters in the system (such as DPF or CSF) and in lower temperature environments (i.e., under-chassis configurations), where routine regeneration of such filters would be difficult.

[0076] Although the exact properties of these particles will vary depending on the properties of the nitrogen-containing reducing agent used and the operating conditions, for simplicity, the particles will generally be referred to as "reducing agent-derived particles" below.

[0077] Due to changing exhaust gas flow conditions and depending on NO x The urea demand varies with the flow rate, and the amount of urea solution injected constantly changes. Therefore, the spray droplet size varies within an injection pulse and over time. Thus, optimizing injection conditions by reintroducing an air-assisted system or applying multiple nozzles with optimized spray droplet sizes may be a promising approach.

[0078] The inventors of this invention have now discovered that these problems can be solved by using a catalytic section wall-flow filter according to the invention in the emission system.

[0079] The exhaust gas treatment system has an upstream end for receiving exhaust gases from the engine, and this upstream end typically includes a manifold. The exhaust gas treatment system also has a downstream end for discharging the treated exhaust gases into the atmosphere. Therefore, the components of the exhaust gas treatment system can be ordered according to their position from upstream to downstream, with upstream components contacting the exhaust gases faster than downstream components.

[0080] The exhaust gas treatment system may sequentially include, from upstream to downstream, a first particulate filter, a device for injecting a nitrogen-containing reducing agent, and a selective catalytic reduction (SCR) component, wherein the system further includes a second particulate filter, which is a catalytic partial wall-flow filter according to the invention, arranged downstream of the device for injecting the nitrogen-containing reducing agent. The first particulate filter is located upstream of the other listed components and is designed to remove soot components from the exhaust gas. The first particulate filter itself may be downstream of the other components, and a preferred system includes a diesel oxidation catalyst (DOC) upstream of the first particulate filter, preferably as the first component of the system. The first particulate filter may be a diesel particulate filter (DPF) or a catalytic soot filter (CSF). In use, these components can be regenerated to address soot accumulation. The upstream first particulate filter prevents soot accumulation on the second particulate filter. This is desirable because the large amount of material accumulation in the end components of the system is difficult to handle due to the relatively low temperatures. If the second particulate filter has soot accumulation, the temperature of the second particulate filter needs to be increased, which would be more energy-intensive. In contrast, the accumulation of reductant-derived particles is relatively low, making regeneration infrequent if necessary.

[0081] Figure 8An example of an exhaust gas treatment system is shown, which, from upstream to downstream, sequentially includes an optional DOC, a first particulate filter as a CSF, an injector, a second particulate filter as a catalytic partial wall-flow filter according to the invention, an SCR component including a flow-through substrate and an SCR catalyst, and an optional ASC catalyst (e.g., an ASC catalyst on a flow-through substrate). According to a fourth aspect, a method for treating a combustion exhaust gas stream containing NOx is provided, the method comprising passing the exhaust gas stream through a catalytic partial wall-flow filter according to the invention, wherein the inlet end is upstream of the outlet end.

[0082] Example 1: Filter A

[0083] A carrier coating slurry was prepared by mixing an aqueous dispersion of vanadium oxalate, antimony triacetate, cerium carbonate, high surface area titanium dioxide powder, and colloidal silica. Specifically, the high surface area titanium dioxide powder used was obtained from Tronox. ® The DT-51d uses an aqueous dispersion of colloidal silica derived from Grace's Ludox. ® AS-40. Aqueous carrier coating slurry with a pH of 5-8.

[0084] The asymmetric cylindrical cordierite partial wall flow filter substrate (300 / 12, length = 3.0 inches, diameter = 9.5 inches, porosity = 65%, average pore size = 16.2 μm) comprises 50% channels with a square cross-section of 0.058 inches × 0.058 inches and 50% channels with a square cross-section of 0.044 inches × 0.044 inches. All the larger channels of the filter substrate are blocked at the outlet end. No smaller channels are blocked.

[0085] Using the coating method disclosed in US20180229228A1, the aforementioned carrier coating slurry was applied to the filter substrate from the inlet to approximately 60% of the substrate length. The coated substrate was dried at 110°C for approximately 15 minutes and then calcined at 500°C for approximately 10 minutes. The calcined portion of the filter (filter A) contained 92 g / ft. 3 Vanadium (V), 131 g / ft 3 Antimony (Sb), 87 g / ft 3 Cerium (Ce), and has a concentration of 2.0 g / inch. 3 The load of the carrier coating.

[0086] Example 2: Filter B

[0087] A carrier coating slurry was prepared by mixing an aqueous dispersion of vanadium oxalate, antimony triacetate, cerium carbonate, high surface area titanium dioxide powder, and colloidal silica. Specifically, the high surface area titanium dioxide powder used was obtained from Tronox. ® The DT-51d uses an aqueous dispersion of colloidal silica derived from Grace's Ludox. ® AS-40. Aqueous carrier coating slurry with a pH of 5-8.

[0088] The asymmetric cylindrical cordierite partial wall flow filter substrate (300 / 12, length = 3.0 inches, diameter = 9.5 inches, porosity = 65%, average pore size = 16.2 μm) comprises 50% channels with a square cross-section of 0.058 inches × 0.058 inches and 50% channels with a square cross-section of 0.044 inches × 0.044 inches. All the larger channels of the filter substrate are blocked at the outlet end. No smaller channels are blocked.

[0089] Using the coating method disclosed in US20180229228A1, the aforementioned carrier coating slurry was applied to the filter substrate from the inlet to approximately 80% of the substrate length. The coated substrate was dried at 110°C for approximately 15 minutes and then calcined at 500°C for approximately 10 minutes. The calcined portion of the filter (filter B) contained 125 g / ft. 3 Vanadium (V), 177 g / ft 3 Antimony (Sb), 117 g / ft 3 Cerium (Ce), and has a concentration of 2.7 g / inch. 3 The load of the carrier coating.

[0090] Example 2: Engine Testing

[0091] Assemble fresh filter A and fresh filter B into the container containing... Figure 9 The exhaust gas treatment system shown is for a diesel engine and includes DOC, CSF, a urea injector, a partial filter, a V-based SCR catalyst containing a flow-through substrate, and optional ASC. The engine was operated under steady-state conditions and under the following conditions to test the SCR performance of the catalyst:

[0092] -13-L heavy-duty diesel engine

[0093] -T=450℃, mass flow rate=900kg / h

[0094] - Ammonia to NOx ratio (ANR) = 0.6, 1.1, 1.35

[0095] -Partial filter brick volume = 213 inches 3

[0096] -Airspeed = 210.000 / h

[0097] The pressure drop across the partial filter is shown in Table 1. NOx conversion, N2O selectivity, and filtration efficiency at various ammonia to NOx ratios are shown in Tables 2 through 4. The results indicate that, over a wide ANR range of 0.6–1.35 and under extreme engine operating conditions (T = 450 °C, mass flow rate = 900 kg / h), using a partial SCR filter downstream of the CSF results in a reduction of PN10- to 0.9 × 10⁻⁶. 11 -2.2×10 11 # / kWh. This allows for a considerable margin in PN10 emissions relative to the PN10 limit specified in the latest Euro 7 HDD revision (6.0 × 10 for WHTC / WHSC cycles). 11 # / kWh).

[0098]

[0099]

[0100]

[0101]

Claims

1. A catalytic wall-flow filter for use in an exhaust gas treatment system, the filter comprising: b) A partial wall-flow filter substrate having an inlet end, an outlet end, and a plurality of porous walls forming a channel from the inlet end to the outlet end, wherein some of the channels are blocked channels and some are unblocked flow channels. as well as c) Selective catalytic reduction (SCR) catalyst, wherein the SCR catalyst is coated on the porous wall.

2. The catalytic wall-flow filter according to claim 1, wherein the channel is blocked only near the inlet end.

3. The catalytic wall-flow filter according to claim 2, wherein approximately 50% of the channels are blocked.

4. The catalytic partial wall-flow filter of claim 1, wherein the channel is blocked only near the outlet end.

5. The catalytic wall-flow filter according to claim 4, wherein approximately 50% of the channels are blocked.

6. The catalytic wall-flow filter according to any one of claims 1 to 5, wherein the hydraulic diameter of the blocked channel is larger than the hydraulic diameter of the unblocked flow channel.

7. The catalytic wall-flow filter according to any one of claims 1 to 5, wherein the hydraulic diameter of the blocked channel is smaller than the hydraulic diameter of the unblocked flow channel.

8. The catalytic partial wall-flow filter according to any of the preceding claims, wherein the SCR catalyst comprises vanadium and antimony.

9. The catalytic wall-flow filter according to claim 8, wherein the SCR catalyst has a molar ratio of antimony to vanadium of 0.6 to 0.

9.

10. The catalytic partial wall-flow filter according to claim 9, wherein the SCR catalyst comprises vanadium, antimony, and cerium.

11. The catalytic partial wall-flow filter according to any of the preceding claims, wherein the SCR catalyst has a coating length of 50% to 90% of the substrate length (L).

12. The catalytic partial wall-flow filter according to any of the preceding claims, wherein the SCR catalyst has a coating length of 60% to 80% of the substrate length (L).

13. A method for manufacturing a catalytic partial wall-flow filter according to any one of claims 1 to 12, the method comprising: (a) Providing a partial wall-flow filter substrate having an inlet end, an outlet end, and a plurality of porous walls forming channels from the inlet end to the outlet end, wherein some of the channels are blocked channels and some are unblocked flow channels; (b) Applying an SCR catalyst support coating slurry to the porous walls to form a coated wall-flow filter substrate. (c) Calcination of the obtained coated wall-flow filter substrate to produce a partially catalytic wall-flow filter.

14. An exhaust gas treatment system for treating combustion exhaust gas streams, the system comprising a catalytic wall-flow filter according to any one of claims 1 to 12.

15. A method for treating a combustion exhaust gas stream containing NOx, the method comprising passing the exhaust gas stream through a catalytic partial wall-flow filter according to any one of claims 1 to 12, wherein the inlet end is upstream of the outlet end.

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