Method of making ceramic wall flow filter substrate loaded with porous wall coating

Abstract

A method of preparing a ceramic honeycomb wall flow filter substrate loaded with a wall coating, the wall coated filter substrate segments having a pore volume of at least 15.0% having a diameter of 0.05 [mu] m to 0.5 [mu] m, expressed as the percentage mercury pressed-in volume of the segments, analyzed by mercury intrusion method, comprising the steps of: (i) preparing a slurry, the slurry comprises water, a carboxylic acid, inorganic oxide particles, or a mixture of two or more inorganic oxide particles, the inorganic oxide particles having a D (v, 0.9) of from 8 [mu] m to 20 [mu] m; and 10% to 35% by weight, relative to 100% by weight of the inorganic oxide particles, of a particulate insoluble cellulose pore former having a non-uniform morphology and having an equivalent spherical diameter D (v, 0.5) of 0.5 [mu] m to 14 [mu] m and a modal aspect ratio (width / length) of 0.3 to 0.9; (ii) applying the slurry on at least a first channel of the substrate, wherein the substrate has an average pore size (D50) of from 6 [mu] m to 15 [mu] m prior to any application and has a porosity of less than 60% prior to any application; and (iii) drying and calcining the slurry coated substrate, whereby sufficient slurry is coated on the substrate such that the product of step (iii) has a coating loading of 0.07 g / in3 to 0.4 g / in3 (4.3 g / L to 24.4 g / L) relative to the weight of the substrate prior to step (ii), and wherein the average wall coating thickness of the coated substrate is 5 [mu] m to 70 [mu] m.

Description

Technical Field

[0001] The present invention relates to a method for preparing a ceramic honeycomb wall-flow filter substrate carrying a porous wall coating, the ceramic honeycomb wall-flow filter substrate being used for treating exhaust gases from a diesel engine or an internal combustion engine configured to operate on a gaseous fuel containing hydrogen (H2) as a main fuel mass. The present invention also relates to a ceramic honeycomb wall-flow filter substrate carrying a porous wall coating, the ceramic honeycomb wall-flow filter substrate being obtained or obtainable by the method of the present invention; a wall-coated ceramic honeycomb wall-flow filter substrate being used for treating exhaust gases containing particulate matter discharged from an internal combustion engine; and an exhaust system for an internal combustion engine, the exhaust system comprising the ceramic honeycomb wall-flow filter substrate. Background Art

[0002] As emissions regulations continue to tighten worldwide for vehicles, including those equipped with compression-ignition engines in their powertrains, there is a growing need to reduce particulate matter emissions, both in size and quantity, throughout the vehicle's entire operating cycle (i.e., between ignition and shutdown, including immediately after ignition / cold start).

[0003] This can be seen, for example, in the new emissions regulations introduced in Europe. In Europe, from September 1, 2019, all new passenger cars entering the European market for the first time will be tested according to new regulations called "Real Driving Emissions" (RDE) tests. The RDE test is a more realistic road emissions test conducted under real driving conditions, measuring NO x The test was carried out using a portable emission measurement system (PEMS) attached to the car while driving under real conditions on the road.

[0004] Separately, a new laboratory-based test, called the Worldwide Harmonized Light Vehicles Test Procedure (WLTP), was implemented as the European vehicle certification procedure from September 1, 2017, to replace the outgoing New European Driving Cycle (NEDC). The WLTP is a globally harmonized standard developed by the United Nations Economic Commission for Europe (UNECE) for determining pollutant levels, CO2 emissions, and fuel consumption for conventional and hybrid vehicles.

[0005] The third phase of the RDE testing program for Euro 6d-TEMP and Euro 6d vehicles (Regulation (EC) 2017 / 1154) introduced a particle number (PN) measurement protocol and stipulated that a related conformity factor of 1.5 (relative to the WLTP limit, including a 0.5 margin) would apply to new vehicle models (or "type approvals") from September 1, 2017, with a transition period for existing models ending September 1, 2019. Furthermore, Euro 6e (Regulation (EC) 2017 / 1151), which came into effect in September 2023, introduced revisions to the RDE testing procedure, whereby the previously defined "conformity factor" was redefined as a "PEMS error margin," including a reduction in the PN margin to 0.34, equivalent to a reduction in the conformity factor from 1.5 to 1.34.

[0006] Separately, the European Parliament, the European Council, and the European Commission are negotiating the highly anticipated Euro 7 proposal, which would establish new emission standards for all road vehicles sold in the EU, including light-duty vehicles (cars and vans) and heavy-duty vehicles (trucks and buses). The proposal would combine the subsequent provisions of Euro 6 (Regulation (EC) 715 / 2007) and Euro VI (Regulation (EC) 595 / 2009) into a single act, referred to as Euro 7 for both light-duty and heavy-duty vehicle regulations (and discontinue Euro VII for heavy-duty vehicle regulations). According to a press release issued by the European Parliament and the European Council on December 18, 2023, provisional agreement had been reached on the EU7 proposal under consideration by the European Parliament as of the filing date. The proposal includes maintaining the current Euro 6e exhaust gas limit values ​​for cars and vans (light-duty vehicles), but with a limit for solid particulate matter starting at 10 nanometers (PM10) in diameter, rather than the current 23 nanometers under Euro 6. For heavy-duty vehicles, in addition to limiting solid particle emissions starting with PM10, the Euro 7 proposal also includes setting the NOx limit in the World Harmonised Transient Cycle to 200mg / kWh (originally 460mg / kWh); and introducing limits for ammonia and N2O.

[0007] The Euro 7 regulations proposed by the European Commission would come into force on 1 July 2025 for new light-duty vehicles and on 1 July 2027 for new heavy-duty vehicles. The interim agreement reached in the tripartite negotiations between the European Parliament, the European Council and the European Commission amends these dates, reverting to a two-date scheme initially for new vehicle models, subsequently extending to all newly registered vehicles. These dates are expressed as a number of months after the regulations come into force. For light-duty vehicles, the interim agreement currently provides for 30 months for new vehicle models and 42 months for all vehicle models. For heavy-duty vehicles, the interim agreement currently provides for 48 months for new vehicle models and 60 months for all vehicle models.

[0008] As of the date of submission of this application, the adoption of the Euro 7 regulations is still subject to final formal approval and adoption by the European Parliament and the Member States.

[0009] The method that meets the current emission standard and future emission standard of particulate matter generally relates to the use of filter substrate.It is known that the filter substrate comprising a wall carrier coating includes holes partially derived from the combustion of a pore-forming agent.For example, EP 0736503A1 discloses a waste gas purification filter, which is produced in the following manner: a mixture of ceramic powder (for example, zeolite or preferably alumina) and a connected pore-forming material is applied to the surface of a substrate (for example, cordierite or silicon carbide) with multiple holes, then the substrate is fired to sinter the ceramic powder and form a coating, while burning off the connected pore-forming material to form connected holes in the coating. The waste gas purification filter has a coating, which is arranged on the surface of the substrate with multiple holes, and the multiple holes load exhaust gas purification catalyst. The coating has holes that are connected to the connection of the substrate from its surface. Preferably, the coating is not only formed on the surface of the substrate, but also formed on the inner surface of the hole inside the substrate.

[0010] According to claim 5 of EP 0736503A1, the size of the connected porogen is preferably the same as or smaller than the pores of the substrate. It is said that this enables the connected porogen to penetrate smoothly into the pores, thereby forming connected pores in the coating coating the inner surface of the pores. Alternatively, the connected porogen refers to a combustible material having a size that is the same as or greater than the thickness of the coating, which can be a material such as carbon, resin, wax, etc. The shape of the combustible material can be, for example, whisker-like, needle-like (fibrous, etc.), spherical or columnar. However, if the size of the connected porogen is larger than the pore size of the substrate, the connected porogen will not enter the pores, which may cause the ceramic powder in the pores to be blocked and the pressure loss of the filter to be large. The average pore size of the connected pores is preferably 10 μm to 60 μm.

[0011] refer toFigure 1 Example 1 of EP 0736503A1 only contains the disclosure of the average pore size of the substrate. Example 1 discloses a method for producing an exhaust gas purification filter, wherein a cordierite honeycomb (full flow) filter (Φ140 mm×length 130 mm, 150 pores / inch) is used. 2 mesh, with a wall thickness of 0.45 mm) as a substrate. A slurry consisting of 95 wt% of activated alumina (as ceramic powder) and 5 wt% of alumina solution, and dilute nitric acid for adjusting the pH is added to adjust the pH to 1-3. The average particle size of the activated alumina used is 5 μm to 10 μm. To 100 wt% of the above-mentioned ceramic powder, 1.5 wt% of a gas-generating substance (as a connected pore-forming material) and 25 wt% of carbon powder are added, and distilled water is also added to obtain a slurry. The particle size of the carbon powder is 10 μm to 80 μm, which is larger than the thickness of the formed coating (5 μm to 50 μm). The above-mentioned gas-generating substance is a gas encapsulating material prepared by encapsulating butane gas in a thermoplastic resin and then granulating it. The substrate is immersed in the slurry while stirring and then taken out. Thereafter, the excess slurry is removed by blowing, and dried at 120°C for 2 hours, followed by heating at 700°C for 2 hours to sinter the ceramic powder. During heating, the carbon powder is burned off, and the gas-generating substances of the thermoplastic resin are burned off, and the butane gas encapsulated therein escapes from the coating. This results in the formation of interconnected pores that connect from the interior of the coating to the surface.

[0012] In the finished product of Example 1, the interconnected pores are distributed within a pore size range D of 20 to 40 μm, with an average pore size of 30 μm as measured by mercury intrusion porosimetry. The average pore size of substrate 5 is 20 to 40 μm. Based on the weight difference of the honeycomb filter substrate before and after coating, the substrate is coated with a coating having an apparent volume of 40 g / L. The thickness of coating 1 is 5 to 50 μm. Catalysts such as Pt (platinum) and Rh (rhodium) are supported on the alumina.

[0013] Applicant's WO 2015 / 082892 discloses a catalyzed honeycomb wall-flow filter for treating exhaust gas containing particulate matter from an internal combustion engine. The filter comprises a honeycomb substrate having a first end and a second end, and a set of interconnected porous walls defining a set of longitudinally extending first and second channels, wherein the first channels are laterally adjacent to the second channels and have a larger hydraulic diameter than the second channels, wherein the first channels are capped at the first end of the honeycomb substrate, and the second channels are capped at the second end of the honeycomb substrate, wherein the channel wall surfaces of the first channels comprise a wall-type catalytic washcoat. The present disclosure also relates to an exhaust system including the catalyzed filter and a method of manufacturing the catalyzed filter.

[0014] The disclosure explains that the surface porosity of the washcoat can be increased by including voids therein. "Voids" in a washcoat layer refer to the spaces present in a layer defined by a solid washcoat material. The voids can include any vacancies, pores, tunnel states (cylinders, prisms), slits, etc., and can be introduced by including in the washcoat composition used to coat the filter substrate a material that is combustible during the calcination of the coated filter substrate, such as chopped cotton, plastic beads, or a material that produces pores by forming gases upon decomposition or combustion, such as acetic acid, starch, or other organics. The disclosure further explains that where the method of the present invention involves applying the washcoat to a partially blocked honeycomb substrate, solid pore formers (such as polymer beads and chopped cotton) can be filtered out in the filter along the axial length of the wall so that the pore formers are concentrated at one end of the axial washcoat, in which case liquid pore formers such as citric acid are preferred. The average void fraction of the washcoat may be 5% to 80%, and the average diameter of the voids may be 0.2 μm to 500 μm, such as 10 μm to 250 μm.

[0015] An arrangement in which the hydraulic diameter of the channels (or compartments) in the end face on the inlet side of the filter is larger than the hydraulic diameter of the channels (or compartments) in the end face on the outlet side of the filter is referred to as an asymmetric channel design.

[0016] EP 2158956A1 discloses a second honeycomb filter, which is provided with: a partition wall and a surface layer, the partition wall having a porous partition wall base material, the porous partition wall base material dividing and forming a plurality of compartments serving as flow paths for a fluid; the surface layer being provided only on the inflow side of the partition wall base material or on both the inflow side and the outflow side of the partition wall base material, wherein the arrangement is alternately as follows: each predetermined compartment has one end open on one side and the other end blocked on the other end, and each remaining compartment has one end blocked on one end and the other end open on the other side, the surface layer provided on at least the inflow side of the partition wall base material being composed of a catalyst layer, the catalyst The agent layer contains at least one material selected from the group consisting of aluminum oxide, zirconium oxide, titanium dioxide, zeolite and ceria, and satisfies the following conditions (I) to (V): (I) the peak pore diameter of the surface layer is equal to or less than the average pore diameter of the partition wall base material, and the porosity of the surface layer is greater than the porosity of the partition wall base material; (II) the surface layer has a peak pore diameter of 0.3 μm or greater and less than 20 μm and a porosity of 60% or greater and less than 95% (measured by mercury intrusion porosimetry); (III) the thickness L1 of the surface layer is 0.5% or greater and less than 30% of the thickness L2 of the partition wall; (IV) the mass of the surface layer / filtration area is 0.01 mg / cm 2 or greater and less than 6 mg / cm2 (corresponding to 0.06mg / in 2 Up to 38.71 mg / in 2 ); and (V) the partition wall base material has an average pore diameter of 10 μm or greater and less than 60 μm and a porosity of 40% or greater and less than 65%. In the disclosed second honeycomb filter, the surface layer composed of the catalyst layer preferably carries fine particles of one or both of platinum and palladium. The second honeycomb filter may have an asymmetric design, for example, see claim 14.

[0017] EP 2158956A1 also discloses a method for manufacturing a second honeycomb filter, which includes the following steps: pre-manufacturing a honeycomb structure having a porous partition wall base material as a sintered product, the porous partition wall base material separating and forming a plurality of compartments serving as flow paths for a fluid; mixing at least one material selected from the group consisting of alumina, zirconia, titania, zeolite and cerium dioxide, a pore former which can burn and volatilize at a temperature of 800°C or lower, has an average particle diameter of less than 10 μm and a proportion of 20% by mass or higher and less than 90% by mass in the solid content of the material, with water to obtain a slurry; and depositing the slurry only on the inflow side of the formed honeycomb product, or on both the inflow side and the outflow side of the formed honeycomb product, and then drying or drying and sintering, thereby providing a surface layer only on the inflow side of the formed honeycomb product, or on both the inflow side and the outflow side of the formed honeycomb product.

[0018] EP 2158956A1 discloses a single embodiment (Example 44) comprising a catalyst layer carrying a platinum group metal, wherein a mixture of gamma alumina and ceria (CeO2) in an unspecified weight ratio having an average particle diameter of 5 μm is immersed in a platinum (Pt) solution. Resin particles having an average particle diameter of 3 μm are added as a pore former, and acetic acid and water are also added to obtain a slurry. The amount of pore former contained in the slurry is 71% as a proportion of the solid content of the material (mass %). The slurry is applied as a surface layer in the following manner: from a blocked honeycomb structure having an average pore diameter of 25 μm, a diameter of 144 mm (5.7 inches), a length of 152 mm (6.0 inches), and a thickness of 1 cm -2The outflow side of a honeycomb filter having 46.5 cells (300 cells per square inch) and a partition wall thickness of 300 μm (11.8 mils (thousandths of an inch)) was vacuum-suctioned to deposit the slurry on the inflow side of the partition wall base material. Subsequently, after drying the structure, the structure was fired at 600°C for three hours to obtain a honeycomb filter, in which the plugged honeycomb structure was provided with a surface layer consisting of a catalyst layer (average thickness of 30 μm). The amount of oxides (γ-Al2O3 and CeO2) in the surface layer was 0.75 mg / 1 cm 2 The filter area of ​​the partition wall; and the amount of Pt is 2g / kiloliter of the honeycomb structure volume, the applicant calculated that the above values ​​correspond to 0.13g / in -3 (7.9 g / L) washcoat loading; and 0.0567 g / ft -3 The catalyst layer had a peak pore diameter of 3 μm and a porosity of 82%. Applicants should understand that the "ratio (mass %) of the material solid content of the pore former contained in the slurry for the surface layer" in Table 2 means that the 82% porosity in the catalyst layer was achieved by formulating the slurry for the surface layer so that 71% by mass of the material solid content was the pore former.

[0019] EP 1961481A2 discloses a catalytic converter comprising a three-dimensional structure support, an optional Figure 1 A wall-flow filter, wherein the three-dimensional structural carrier has a plurality of compartments separated by porous compartment walls, wherein the pore diameter of the compartment walls is 10 μm to 50 μm, and the porosity of the compartment walls is 40 volume % or higher; and a catalyst coating containing a catalyst component. The catalyst coating is coated on the surface of the compartment walls of the three-dimensional structural carrier. 50% by mass or more of the total loading of the catalyst components on the three-dimensional structural carrier is present in the region from the surface of the compartment walls of the three-dimensional structural carrier to the surface of the catalyst coating, that is, at most 50% by mass of the total loading of the catalyst components on the three-dimensional structural carrier is present in the porous compartment walls. In Example 4 and Example 12, a catalyst having a loading of 50 g / L (equivalent to 0.82 g / in 3 ) is applied to a silicon carbide honeycomb substrate having a diameter of 144 mm, a length of 152 mm, and a cell density of 400 / in 2 (per cm 2 There are 62 cells), the average pore diameter in the cell walls is 10 to 20 μm, and the porosity is 50 to 60% by volume. No details are given about the particle size of the alumina powder, activated carbon or polystyrene beads.

[0020] WO 2008 / 153828A2 discloses a method for preparing a porous inorganic coating on a porous support using certain organic pore formers, and a porous support coated with the porous inorganic coating. Inorganic particle components such as α-alumina and γ-alumina are disclosed. The coating composition may contain 0.1 wt% to 50 wt% of inorganic particles. Although diesel particulate filter products are mentioned as applications of the present disclosure, no details of suitable such filters or their physical parameters are disclosed, nor are examples given. In addition, none of the exemplary inorganic coatings contain platinum group metals. Example 3 describes the use of protein from skim milk with an average particle size of 0.4 μm (as a pore former) to deposit an α-alumina film (a blend of α-alumina particles with an average particle size of 0.8 μm to 1.1 μm and α-alumina particles with an average particle size of 0.3 μm to 0.4 μm).

[0021] EP 2502662A1 discloses a honeycomb filter comprising a honeycomb base material comprising a porous partition wall matrix that separates and forms a plurality of cells, each of which serves as a fluid passage; a blocking portion disposed in the open frontal area of ​​a predetermined cell located on the end surface on the fluid inflow side and in the open frontal area of ​​the remaining cells located on the end surface on the fluid outflow side; and a porous collecting layer disposed on the surface of the partition wall matrix in at least the remaining cells. The collecting layer has a structure in which a plurality of particles are bound or entangled with each other, and the collecting layer comprises a plurality of flat plate-shaped particles having a defined aspect ratio. The plurality of particles are particles having an average major diameter of 0.2 μm or greater and less than 10 μm, an average value of the ratio of the major diameter to the minor diameter (major diameter / minor diameter) of each particle being less than 3, and an average value of the ratio of the major diameter to the thickness (major diameter / thickness) of each particle being 3 or greater.

[0022] Example 14 of EP 2502662A1 is the only example in which the collection layer contains a platinum group metal (platinum alone, 0.5 mass %). In this example, the coating composition used as the coarse material to form the collection layer contains composite plate-like particles obtained by coating alumina particles having an average major diameter of 5 μm, an average major diameter / minor diameter ratio of 2, and an average major diameter / thickness ratio of 20 with a slurry obtained by mixing 60 g of a ceria sol containing 15 mass % CeO2, 20 g of an alumina sol containing 20 mass % Al2O3, and 4 g of an aqueous platinum chloride solution containing 10 mass % Pt. It should be understood that no pore-forming agent is used because, when the slurry is applied to the partition wall matrix, "the plurality of particles are bonded or entangled with each other in a manner that does not excessively align along the surface of the partition wall matrix. Thus, the aforementioned high open area ratio is achieved," thereby suppressing "an increase in the initial pressure loss of the honeycomb filter." That is, the relatively high aspect ratio of the composite plate-like particles is crucial for achieving the desired suppression of the increase in initial pressure loss.

[0023] WO 2017 / 209083A1 discloses an exhaust gas purification filter that claims to suppress the increase in pressure loss associated with the formation of a catalyst layer and at the same time promote the combustion of particulate matter. The exhaust gas purification filter according to the present invention includes a honeycomb base and a catalyst layer disposed on the honeycomb base. The catalyst layer contains a carrier and a metal catalyst. In an electron microscope observation image of a cross section of the catalyst layer, when the area of ​​the catalyst layer is set to 100%, macropores with a circle-equivalent diameter of more than 5 μm account for 45% or more of the area. The embodiments disclose a number of platinum- and palladium-containing catalyst layers, in which a solution of a platinum group metal salt (platinum and palladium) is impregnated into a "needle-shaped Al2O3 powder" having an average fiber diameter of 0.5 μm and an average fiber length of 6 μm or a "needle-shaped TiO2 powder" having an average fiber diameter of 0.2 μm and an average fiber length of 2 μm. However, embodiments of Al2O3 or TiO2 or CeZr granular powders ground by wet milling are also disclosed, each having an average particle size of 2 μm. In the examples, macropores were introduced by pore formers, which were melamine resin beads of various sizes (average particle size of 2 μm, 5 μm and 10 μm), starch or polymethyl methacrylate resin. Citric acid (blowing agent) was used as a comparative "pore-forming agent". After calcination, the catalyst layer had a pore size of 15 g / L (equivalent to 0.246 g / in 3 ) loading. It is also disclosed that Example 19 is a honeycomb substrate coated with a three-way catalyst composition comprising rhodium and a ceria-zirconia composite oxide. Therefore, it should be understood that Examples 1 to 18 relate to products for treating diesel particulate matter.

[0024] However, in Examples 1 to 18, for the silicon carbide honeycomb base used, in addition to the partition wall thickness (12 thousandths of an inch (mil), equivalent to 0.3048 mm) and the cell density (300 cells per square inch, or 46.5 cells / cm 2 ), no specific details are provided. In other words, there is no correlation between the particle size of the catalyst layer, the pore size of the particle layer derived from the pore-forming agent, and the pore size of the honeycomb base.

[0025] EP 3623048A1 discloses an exhaust gas purification catalytic device, which includes a honeycomb base material and an inlet side coating, wherein: the honeycomb base material includes a plurality of compartments separated by porous partition walls, the plurality of compartments including an inlet side compartment and an outlet side compartment, and is configured so that the exhaust gas flowing into the inlet side compartment can pass through the partition wall and be discharged from the outlet side compartment; and the inlet side coating is present on the surface side of the partition wall of the inlet side compartment, for the through-pore diameter distribution of the partition wall of the coated honeycomb base material, the proportion of through-pores of 4μm to 9μm measured by a pore size distribution meter (permporometer) according to the bubble point method is at least 80 volume%; and the peak pore diameter measured using a mercury intrusion meter is at least 3.0μm larger than the peak through-pore diameter measured by a pore size distribution meter according to the bubble point method.

[0026] The exhaust gas purification catalytic device can be prepared using the following method: a slurry coating containing inorganic oxide particles and a pore-forming material is applied to the inlet side compartment of a honeycomb substrate, and the honeycomb substrate after the slurry coating is baked. The pore-forming material can be organic polymer particles having an average particle diameter of 10 nm or more to 500 nm or less (0.01 μm to 0.5 μm), such as (meth) acrylic resin particles, styrene-(meth) acrylic resin particles, polyurethane resin particles, maleic acid resin particles, styrene-maleic acid resin particles, alkyd resin particles, rosin-modified phenolic resin particles, and ketone resin particles. The general description explains that the median particle size of the inorganic oxide particles is, for example, 0.1 μm or greater, 0.3 μm or greater, 0.5 μm or greater, 0.8 μm or greater, or 1.0 μm or greater, and is, for example, 10 μm or less, 5.0 μm or less, 3.0 μm or less, 2.0 μm or less, 1.5 μm or less, or 1.0 μm or less.

[0027] In the examples of EP 3623048 A1, a cylindrical SiC diesel particulate filter substrate having a honeycomb structure with a diameter of 160 mm and a length of 135 mm (i.e., a volume of 2.71 liters), an average pore diameter of 12 μm (nominal value), and a porosity of 42% by volume is coated with a mixture containing 100 g of Pd / Pt-alumina powder (36.9 g / L or 0.604 g / in 3 ), 50 g of a slurry of ceria-zirconia composite oxide powder, which has been ground to obtain a mixture having an average particle diameter of 1 μm, and then styrene-acrylic resin particles having an average particle diameter of 100 nm (0.1 μm) are added in an amount of 30 wt % based on the solid content in the slurry.

[0028] WO 2021 / 126685A1 discloses a catalyst support coating composition comprising a slurry and at least one pore-forming agent, the slurry comprising at least one platinum group metal and / or at least one non-platinum group metal supported on at least one carrier; the at least one pore-forming agent having a particle size of 100 nm to 5.0 μm, wherein the pore-forming agent is selected from carbon nanotubes, carbon nanofibers, activated carbon, resins, cellulose powders and polymer spheres. Also disclosed is a catalyst product for capturing particulate matter with a particle size range of 1.0 nm to 100 μm, the product comprising a catalyst support coating deposited on a substrate and calcined to form pores, wherein 50% to 100% of the pores have a pore size ranging from 100 nm to 5.0 μm. The only example is a catalyst composite / product coated with a support coating comprising both rhodium and an oxygen storage component (CeO2) containing ceria. That is, the product of this embodiment is used as a gasoline soot filter.

[0029] EP 3263214 A1 discloses a method for producing a catalyst for purifying exhaust gas, the method comprising: a step of obtaining a catalyst slurry, which mixes metal oxide particles, a precious metal raw material and a fibrous organic material so that the amount of the fibrous organic material is in the range of 0.5 to 9.0 parts by mass relative to 100 parts by mass of the metal oxide particles, the metal oxide particles having a cumulative 50% diameter value in a volume-based cumulative particle size distribution in the range of 3 μm to 10 μm measured by a laser diffraction method, the fibrous organic material having an average fiber diameter in the range of 1.7 to 8.0 μm and an average aspect ratio in the range of 9 to 40; a step of forming a catalyst slurry layer, which applies the catalyst slurry to the surface of a substrate so that the catalyst coating after calcination has an average thickness in the range of 25 to 160 μm; and a calcination step, which removes at least a portion of the fibrous organic material in the catalyst slurry layer to obtain a catalyst for purifying exhaust gas. According to the present disclosure, the "aspect ratio of the pores" in the resulting catalyst coating can be determined by analyzing three-dimensional information about the pores based on a cross-sectional image of the catalyst coating cross section perpendicular to the exhaust gas flow direction in the substrate obtained by FIB-SEM (focused ion beam-scanning electron microscope).

[0030] EP 3263214A1 explains that if the average aspect ratio is less than 9, the pore connectivity is insufficient, resulting in insufficient gas diffusivity; and if the mixing amount of the fibrous organic material exceeds 9.0 parts by mass per 100 parts by mass of the metal oxide particles, the thickness of the catalyst coating increases, resulting in increased pressure loss and reduced fuel efficiency. Furthermore, in the catalyst final product, the coating amount of the catalyst coating in the catalyst for purifying exhaust gas is preferably in the range of 50 g / L to 300 g / L, equivalent to 0.819 g / in 3 to 4.916g / in 3 . If the coating amount is less than 50 g / L, the catalyst particles cannot obtain sufficient catalytic activity performance, so that the resulting catalytic performance (such as NOx purification performance) is often insufficient. According to an embodiment, NOx purification performance is measured under gasoline exhaust conditions ("test for measuring NOx removal rate"), that is, "an inline 4-cylinder 2.4L engine is used to perform air-fuel ratio feedback control with a target of 14.1 to 15.1, and the NOx removal rate is calculated based on the average amount of NOx emitted when the A / F is switched. Here, the engine operating conditions and the pipeline settings are adjusted so that the amount of air inhaled is 40 (g / second) and the temperature of the gas flowing into the catalyst is 750°C."

[0031] For example, according to WO 2006 / 031600, a wall-flow filter substrate is coated by coating the inlet channel with a catalytic washcoat from one end of the substrate over an axial length less than the entire axial length of the substrate; and coating the outlet channel with a catalytic washcoat from the other end of the substrate over the remainder of the axial length of the substrate, which advantageously reduces backpressure on the filter substrate relative to a filter substrate in which the inlet channel is uniformly coated over the entire axial length of the filter substrate. However, the skilled person will appreciate that any gaps in the coating over the axial length may result in filtration failure because the exhaust gas (as a fluid similar to a water flow) will pass through the wall of the wall-flow filter where the resistance to airflow is minimal. This means that the exhaust gas will preferentially pass through any axial gaps in the coating. Therefore, the actual manufacture of catalytically coated filters typically targets a small overlap of the coatings for the inlet and outlet channels.

[0032] It is well known that the inorganic oxide particle population used in the washcoat of the present invention will inherently have a particle size distribution including D(v,0.5) (also referred to as "D50") and D(v,0.9) (also referred to as "D90"). See, for example, the subheading 3.2.4 "Particle Size Distribution of the Carrier" in "Catalytic Air Pollution Control - Commercial Technology", 3rd edition, Ronald M. Heck et al., John Wiley & Sons, 2009. This particle size distribution can be adjusted to some extent by mechanical milling (e.g., using a ball mill) or by jet milling. See M. et al., Chemical Engineering Journal, 409 (2021) 128057, from which it is also known that the D50 and D90 of an inorganic oxide particle population for a washcoat can be adjusted by combining, for example, two populations having different particle size distributions (see, for example, U.S. Pat. No. 5,496,788, Examples 1 and Figure 2 ). The difference between D(v,0.5) and D(v,0.9) can partially influence the location of the washcoat when applied to a wall-flow filter substrate, such as on or within the wall.

[0033] In the above-mentioned WO 2015 / 082892, the applicant disclosed that the difference in hydraulic diameters of the inlet channel and the outlet face channel in an asymmetric channel design can be used to produce a wall coating on the inlet channel, which has a larger hydraulic diameter than the outlet face channel. However, in an asymmetric design recently disclosed by the filter manufacturer Ibiden in, for example, the Society of Automotive Engineers (SAE) technical paper 2014-01-1512 and EP 2862610A1, by appropriately capping an unblocked substrate comprising channels with relatively larger and smaller hydraulic diameters, the channels extending from the inlet end face and terminating at the outlet end face have larger hydraulic diameters and smaller hydraulic diameters and are arranged in a repeating pattern around a single larger hydraulic diameter channel extending from the outlet end face and terminating at the inlet end face. This design is referred to by Ibiden as a "valued plugging layout" or VPL TM .

[0034] WO 2021 / 126685 discloses a catalyst for capturing particulate matter.

[0035] There is a need in the art to develop a filter device for modern diesel vehicles that meets proposed emission exhaust gas limits (such as EU7, which includes limits on PM10 emissions), which filter device can balance good cold flow back pressure and soot load back pressure characteristics with good filtration efficiency, and can be manufactured in a cost-effective manner with minimal environmental impact. In addition to vehicle diesel internal combustion engines, there is also a need in the art for a filter device for treating particulate matter in the exhaust gas from vehicle internal combustion engines powered by carbon-neutral fuels (such as hydrogen or hydrogen-rich fuel feedstock). The present invention is intended to meet these needs. Summary of the Invention

[0036] According to a first aspect, the present invention provides a method for preparing a ceramic honeycomb wall-flow filter substrate, the ceramic honeycomb wall-flow filter substrate having an axial length L of a coating on a supporting wall, a fragment of the filter substrate coated on the wall having at least 15.0% of a pore volume of 0.05 μm to 0.5 μm in diameter expressed as a percentage of mercury intrusion volume of the fragment as analyzed by mercury intrusion, the wall-flow filter substrate having a first end and a second end, and comprising a plurality of axially extending first and second channels, each of the first and second channels being partially defined by a porous channel wall having an axially extending porous channel wall surface, each first channel sharing a porous channel wall with an adjacent second channel, wherein in a scanning electron microscope image of a cross-section of the coated substrate, each channel has a geometric hollow cross-sectional shape having at least one vertex, the at least one vertex being partially defined by a vertex angle between two channel surface edges, wherein the first channel is terminated at the second end of the substrate, and the second channel is terminated at the first end of the substrate, the method comprising the steps of:

[0037] (i) preparing a slurry comprising water, a carboxylic acid, inorganic oxide particles, or a mixture of two or more inorganic oxide particles, the inorganic oxide particles having a D(v,0.9) of 8 μm to 20 μm as measured by laser diffraction particle size analysis; and 10 wt% to 35 wt% of a particulate insoluble cellulose pore former, relative to 100 wt% of the inorganic oxide particles, the particulate insoluble cellulose pore former having a heterogeneous morphology and an equivalent spherical diameter D(v,0.5) of 0.5 μm to 14 μm as measured by laser diffraction and a modal aspect ratio (width / length) of 0.3 to 0.9 as measured by direct particle measurement using a flow imaging microscope particle shape analyzer;

[0038] (ii) coating the slurry on at least the porous channel walls of a first channel of the substrate, wherein the substrate has an average pore size (D50) of 6 μm to 15 μm before any coating and a porosity of less than 60% before any coating; and

[0039] (iii) drying and calcining the slurry-coated substrate,

[0040] Sufficient slurry is thereby applied to the substrate so that the product of step (iii) has a viscosity of 0.07 g / in based on the weight of the substrate prior to step (ii). 3 to 0.4g / in 3(4.3 g / L to 24.4 g / L) of coating loading, wherein the average wall coating thickness of the product of step (iii) measured at an angle bisecting the top angle on a scanning electron microscope cross-sectional image of the coated substrate is 5 μm to 70 μm. Applicants have found that the addition of an insoluble cellulose pore former in the amounts shown can pre-set the applied washcoat to an on-wall position rather than an intra-wall position. This can be seen, for example, from the analysis shown in Example 9. It should be understood that in the products of the first and fourth aspects of the invention, the term "on-wall" does not exclude the coating from entering or existing in the porous channel walls of the substrate. However, the products of the first and fourth aspects of the invention are defined by the on-wall coating thickness, and the washcoat applied to the substrate in step (ii) of the first aspect of the invention primarily completes the "on-wall" portion.

[0041] The use of natural cellulosic pore formers in the first aspect of the present invention advantageously reduces the environmental impact relative to the use of, for example, thermoplastic resins, plastic beads, etc. in the prior art, as the combustion of plastics carries the risk of releasing dioxins, furans, mercury and polychlorinated biphenyls (BCPs), or the need to scrub such toxins from the effluent generated by prior art manufacturing processes.

[0042] Applicants prefer that the wall flow filter substrate used in step (ii) of the method of the first aspect of the invention is "bare", ie not coated with a further washcoat or impregnated with an aqueous metal salt solution before step (ii) commences.

[0043] The porous channel walls of the second channel may be uncoated or coated with the same or a different slurry composition according to step (i), i.e., in a first aspect, step (ii) may comprise the step of coating the porous channel walls of the second channel of the filter substrate with the slurry according to step (i), wherein the slurry used to coat the second channel has the same or a different composition as the slurry coated on the porous channel walls of the first channel. For the avoidance of doubt, the coating on the channel walls of the second channel, if present, is also the wall coating.

[0044] According to the second aspect, the present invention provides a ceramic honeycomb wall flow filter substrate with a coating on a load wall, which is used to treat exhaust gas containing particulate matter discharged from an internal combustion engine. The ceramic honeycomb wall flow filter substrate can be obtained by the method according to the first aspect of the present invention.

[0045] In a third aspect, the present invention provides a ceramic honeycomb wall flow filter substrate with a coating on a loaded wall, which is used to treat exhaust gas containing particulate matter discharged from an internal combustion engine, and the ceramic honeycomb wall flow filter substrate is obtained by the method according to the first aspect of the present invention.

[0046] A fourth aspect of the present invention provides a wall-coated ceramic honeycomb wall-flow filter substrate, which is used to treat exhaust gas containing particulate matter discharged from an internal combustion engine. The wall-flow filter substrate has a first end and a second end and a length L between the first end and the second end, and includes a group of axially extending first channels and second channels, each of the first channels and the second channel is partially defined by a porous channel wall having an axially extending porous channel wall surface, and each first channel shares a porous channel wall with an adjacent second channel, wherein in a scanning electron microscope image of a cross section of the coated substrate, each channel has a geometric hollow cross-sectional shape, the geometric hollow cross-sectional shape has at least one vertex, and the at least one vertex is partially defined by the vertex angle between two channel surface edges, wherein the first channel is blocked at the second end of the substrate, and the second channel is blocked at the first end of the substrate, wherein at least the channel wall surface load of the first channel is 0.07 g / in relative to the weight of the substrate before coating. 3 to 0.4g / in 3 (4.3 g / L to 24.4 g / L) of a wall-type washcoat comprising inorganic oxide particles or a mixture of two or more inorganic oxide particles, wherein the average wall coating thickness measured at an angle bisecting the vertex angle on a scanning electron microscope cross-sectional image of the coated substrate is 5 μm to 70 μm, wherein a fragment of the wall-coated filter substrate has, as analyzed by mercury intrusion porosimetry, at least 15.0% of the pore volume having a diameter of 0.05 μm to 0.5 μm, expressed as a percentage of the mercury intrusion volume of the fragment, and wherein the wall washcoat coating comprises non-geometrically uniform voids having an equivalent spherical diameter D(v,0.5) of 0.1 μm to 8 μm and a modal aspect ratio (width / length) of 0.3 to 0.9 as determined by focused ion beam-scanning electron microscopy (FIB-SEM).

[0047] In a fifth aspect, the present invention provides an exhaust system for an internal combustion engine, the exhaust system comprising the ceramic honeycomb wall flow filter substrate according to the fourth aspect of the present invention, wherein the first end of the substrate faces upstream.

[0048] According to a sixth aspect, the present invention provides an internal combustion engine comprising the exhaust system according to the fifth aspect.

[0049] In a seventh aspect, the present invention provides a vehicle comprising a diesel engine according to the sixth aspect of the present invention.

[0050] According to a seventh aspect, the present invention provides a vehicle comprising an internal combustion engine configured to run on a mixture of air and fuel, wherein the fuel in the mixture of air and fuel is a gaseous fuel containing hydrogen (H2) as a main fuel mass, the vehicle comprising a gaseous fuel source and an exhaust system according to the sixth aspect of the present invention, the gaseous fuel source containing hydrogen (H2) as a main fuel mass. DETAILED DESCRIPTION

[0051] Method - First Aspect of the Invention

[0052] Although increasing the "fines" of the inorganic oxide particles in the inorganic oxide particle size distribution by grinding (e.g., adjusting the solid content of the carrier coating in the grinding liquid, the grinding time and the grinding speed, etc.) can also improve the carrier coating adhesion, during the development process, the applicant's invention team found that when the components of the inorganic oxide particles or the inorganic oxide particle mixture have a loose bulk density before grinding of 275g / L to 850g / L, preferably 350g / L to 750g / L, the back pressure, filtration efficiency and carrier coating adhesion are generally more reliably met.

[0053] Refractory metal oxides are typically selected from alumina, silica, titania, magnesia, ceria, zirconia, and mixed oxides or composite oxides thereof, such as mixed oxides or composite oxides of two or more thereof. For example, refractory metal oxides may be selected from silica-alumina, titania-alumina, zirconia-alumina, titania-silica, zirconia-silica, ceria-zirconia, zirconia-titania, and alumina-magnesia. During development, the applicant prepared a coated sample in which the inorganic oxide was rare earth element-doped CeO 2 , but back pressure, filtration efficiency, and carrier coating adhesion characteristics were unsatisfactory (see Example 7 below). Another sample comprising the same CeO 2 inorganic oxide mixed with γ alumina also failed to fully improve these characteristics. With further development, the applicant believes that inorganic oxides containing ceria or mixtures comprising the inorganic oxides containing ceria may be determined for use in related aspects of the present invention. However, in view of the results shown in Example 7, applicants prefer to optionally exclude CeO2-containing inorganic oxide particles from the washcoat, either by themselves or in the mixture.

[0054] Preferably, the inorganic oxide of the inorganic oxide particles comprises or consists of alumina, silica, zirconia, or a mixed oxide or composite oxide of any two or more thereof. This includes inorganic oxide particles comprising gamma alumina or alumina doped with one or more of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), and neodymium (Nd), preferably silicon, wherein the total weight percentage of the dopant present in the doped alumina is preferably 1 wt% to 10 wt%. Preferably, the alumina is not alpha alumina.

[0055] The inclusion of a dopant can thermally stabilize the refractory metal oxide or support material. It should be understood that any reference to "doping" in this context refers to a material in which the bulk or host lattice of the refractory metal oxide is substitutionally or interstitially doped with the dopant. In some cases, a small amount of dopant may be present at the surface of the refractory metal oxide. However, the majority of the dopant is typically present in the bulk of the refractory metal oxide. The chemical and / or physical properties of the refractory metal oxide are generally affected by the presence of the dopant.

[0056] As shown in Example 7, gamma-alumina and doped aluminas meeting the pre-grind loose bulk density range of 275 g / L to 850 g / L exhibited acceptable adhesion, while doped aluminas exceeding this pre-grind loose bulk density did not exhibit acceptable adhesion. However, for ZrO2 that did not meet the pre-grind loose bulk density parameter of 275 g / L to 850 g / L, the adhesion of the ZrO2 could be improved to acceptable adhesion limits by combining it with gamma-alumina and doped aluminas. α-alumina, which does not meet the pre-grind loose bulk density requirement of 275 g / L to 850 g / L, is in any case less preferred, such as for catalytic washcoats, due to its low specific surface area, because, for example, non-rhodium platinum group metals can more easily sinter on the lower specific surface area particulate inorganic oxide supports, rendering their activity less durable.

[0057] Although the present invention is applicable to wall-flow filter substrates in which substantially all juxtaposed channels have equal hydraulic diameters, in a preferred embodiment the method according to the first aspect of the invention is applicable to so-called asymmetric wall-flow filter substrates in which the axially extending first channels of the wall-flow filter substrate have a hydraulic diameter that is greater than the second channels.

[0058] In this first preferred embodiment, step (ii) may include the step of coating the porous channel walls of the second channel of the filter substrate with the slurry according to step (i), and the porous channel walls of the first channel are coated to an axial length of 60% to 90% L, preferably 70% to 85% L, and the porous channel walls of the second channel are coated to an axial length of 10% to 40% L, preferably 15% to 35% L, wherein the sum of the axial lengths of the coatings on the walls in the first and second channels is not less than 100%. Preferably, the upper limit of the overlap is 130% L.

[0059] Where the porous channel wall of the second channel is coated with the slurry according to step (i), for the avoidance of doubt, the g / in defined in the first aspect of the invention is 3 The (g / L) coating loading is the total combined coating loading on the porous channel walls of both the first channel and the second channel, i.e. relative to the weight of the substrate before the coating is applied to the first channel or the second channel. The same applies to the definition of the fourth aspect of the invention.

[0060] In a second preferred embodiment, the axially extending first channels of the wall-flow filter substrate are a combination of channels having a larger hydraulic diameter and a smaller hydraulic diameter, and the hydraulic diameter of the second channels is larger than the first channels having the smaller hydraulic diameter. That is, this embodiment involves applying the first aspect of the invention to the Ibiden VPL described above in conjunction with SAE Technical Paper 2014-01-1512 and EP 2862610A1. TM Filter substrate.

[0061] In this second preferred embodiment, step (ii) may include the step of coating the porous channel walls of the second channel of the filter substrate with the slurry according to step (i), and the porous channel walls of the first channel are coated to an axial length of 60% to 80% L, and the porous channel walls of the second channel are coated to an axial length of 60% to 80% L, wherein the sum of the axial lengths of the coatings on the walls in the first and second channels is not less than 120%, preferably not less than 130%. Preferably, the upper limit of the overlap is 160% L.

[0062] The D(v,0.5) of the porogen in step (i) is preferably smaller than the measured coating thickness to avoid adhesion problems and poor filtration efficiency.

[0063] When the coated filter product of the first aspect of the invention is used to treat particulate matter from an internal combustion engine powered by hydrogen fuel (so-called "H2-ICE"), the wall coating may comprise inorganic oxide particles and be free of platinum group metals. However, for diesel applications and optionally H2-ICE applications, the wall coating is preferably a wall catalyst coating and the slurry of step (i) comprises one or more non-rhodium platinum group metal salts having a platinum group metal salt concentration selected such that the product of step (iii) has a PGM content of 0.5 g / ft 3 Up to 10g / ft 3 (0.018g / L to 0.353g / L), preferably 1g / ft 3 Up to 8g / ft 3 (0.035 g / L to 0.283 g / L) total platinum group metal loading. Upon analysis, applicants have determined that the non-rhodium platinum group metals are fixed to the inorganic oxide and have substantially no affinity for the cellulose pore former.

[0064] The non-rhodium platinum group metal may be platinum alone, or a combination of platinum and palladium, and the product of step (iii) may have a weight ratio of platinum to palladium of 1:0>1:1. Where the non-rhodium platinum group metal is a combination of platinum and palladium, the weight ratio of Pt:Pd in ​​the product of step (iii) is from 10:1 to 1:1, preferably from 6:1 to 2:1.

[0065] Reference Example 4, below, demonstrates how D(v,0.9) can advantageously balance filtration efficiency and backpressure, as well as potential adhesion (see Example 5). For at least these reasons, the inorganic oxide particles preferably have a D(v,0.9) of 9 μm to 15 μm, more preferably 10 μm to 14 μm. When combined with the aforementioned D(v,0.9) parameter range, i.e., inorganic oxide particles having a D(v,0.5) of 3.0 μm to 6.0 μm, further improvements in washcoat adhesion can be achieved. Applicants believe that this improvement in washcoat adhesion may be due to an increase in "fines" in the washcoat.

[0066] During the applicant's development work, its inventive team identified two commercially available particulate insoluble cellulose raw materials that were used as pore formers in the slurry of step (i) of the first aspect of the present invention, thereby producing a product that meets the above-mentioned needs in the art. In a first such embodiment, the particulate insoluble cellulose is microcrystalline cellulose having an equivalent spherical diameter D(v,0.5) of 1 μm to 8.0 μm as determined by laser diffraction and having a modal aspect ratio (width / length) of 0.6 to 0.8 as determined by direct particle measurement using a flow imaging microscope particle shape analyzer. The resulting product comprises Figure 4 Features shown, as determined by FIB-SEM.

[0067] In a second embodiment, the particulate insoluble cellulose is a fibrous cellulose having an equivalent spherical diameter D(v,0.5) of 8.5 μm to 13.0 μm as determined by laser diffraction and a modal aspect ratio (width / length) of 0.4 to 0.7 as determined by direct particle measurement using a flow imaging microscope particle shape analyzer. This produces a cellulose having Figure 3 Products with the indicated characteristics, as determined by FIB-SEM.

[0068] Prior art discloses the use of washcoat slurries containing inorganic, ceramic, or metal fibers for coating filter substrates. These fibers not only pose potential health and safety hazards to manufacturing, such as asbestosis, but they can also make coating control during the manufacturing process more difficult, resulting in channel clogging and slurry clumping. The use of the pore-forming agent of the first aspect of the present invention allows for the production of reliable coating compositions, resulting in reproducible and more uniform products.

[0069] The filter substrate used in the first aspect of the present invention is a ceramic filter substrate, such as a silicon carbide or cordierite structure. When the filter substrate is a silicon carbide filter substrate, it is preferred that the filter substrate has a porosity of 38% to 45% before coating. Applicants have found that this allows the resulting product to meet the EU7 emission standard for PM10.

[0070] In mercury intrusion analysis, applicants have determined that a silicon carbide filter substrate having a pre-coating porosity of 38% to 45% can produce a coated product having a porosity percentage of less than 45.0% (see Example 6 below).

[0071] The product of the first aspect of the invention (i.e., the coated silicon carbide filter substrate) has a pre-coating porosity of 38% to 45% and a porosity of at least 0.230 cm as measured by a combination of helium pycnometer and mercury density measurement. 3 / g of total pore volume (see Example 6 below).

[0072] Alternatively, the filter substrate may be a cordierite filter substrate, in which case the filter porosity prior to coating is preferably 46% to 60%, for example in order to meet the EU7 emission standard for PM10.

[0073] In a preferred product of the invention, sufficient slurry is applied to the substrate so that the product of step (iii) has a viscosity of 0.15 g / in -3 Up to 0.3g / in -3Applicants have discovered that selecting this parameter range produces a product with a favorable balance of back pressure, filtration efficiency, catalytic activity, and adhesion.

[0074] The average wall coating thickness is preferably 10 μm to 60 μm to promote filtration efficiency and moderate back pressure.

[0075] The carboxylic acid may be a dicarboxylic acid or a tricarboxylic acid, preferably citric acid or succinic acid. The carboxylic acid may provide a number of benefits, including improved rheological properties of the slurry, reduction of non-rhodium platinum group metal salts to improve dispersion of the nanoparticles, and some micropores generated by the release of gases during drying and calcination. Preferably, the carboxylic acid concentration in step (i) is selected so that the product of step (ii) has a viscosity of 50 g / ft 3 Up to 400g / ft 3 The lower end of this parameter range is preferred for washcoats that do not contain platinum group metals for H2-ICE applications.

[0076] The geometry of the first channel cross section of the filter substrate used in the present invention is square. Filter substrates with triangular cross-sectional channels are known, but according to the applicant's experience, coating of triangular cross-sectional channels may lead to channel clogging.

[0077] The product itself - the fourth aspect of the invention

[0078] In the fourth aspect of the present invention, preferably, the porous channel walls of the second channels of the filter substrate are also coated with a wall-type washcoat having the same or different composition as the washcoat coated on the porous channel walls of the first channels.

[0079] The refractory metal oxide is generally selected from alumina, silica, titania, magnesia, zirconia, and mixed oxides thereof or composite oxides thereof, such as mixed oxides or composite oxides of two or more thereof. For example, the refractory metal oxide can be selected from silica-alumina, titania-alumina, zirconia-alumina, titania-silica, zirconia-silica, zirconia-titania, and alumina-magnesia.

[0080] Preferably, the inorganic oxide of the inorganic oxide particles comprises or consists of alumina, silica, zirconia or a mixed oxide or composite oxide of any two or more thereof, but preferably is not α-alumina, at least for the reasons explained above. Preferably, the inorganic oxide particles comprise gamma alumina or alumina doped with one or more of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), preferably silicon, wherein the total weight percentage of the dopant present in the doped alumina is 1 wt% to 10 wt%.

[0081] The axially extending first channels of the wall flow filter substrate may have a larger hydraulic diameter than the second channels.

[0082] In a first embodiment according to the fourth aspect of the invention, the porous channel wall of the first channel is coated to an axial length of 60% to 90% L, preferably 70% to 85% L, and the porous channel wall of the second channel is coated to an axial length of 10% to 40% L, preferably 15% to 35% L, wherein the sum of the axial lengths of the coatings on the walls in the first and second channels is not less than 100%. Preferably, the upper limit of the overlap is 130% L.

[0083] In a second embodiment of the fourth aspect of the invention, the axially extending first channels of the wall flow filter substrate are a combination of channels having larger and smaller hydraulic diameters, and the second channels have a larger hydraulic diameter than the first channels having the smaller hydraulic diameter.

[0084] Applicants have discovered that when using known techniques (e.g., Applicant's WO 99 / 47260) to coat a valuable plugged layout filter substrate design and targeting a slight axial overlap of the inlet and outlet channel coatings, the difference in hydraulic diameter of the inlet channels results in the catalyst support coating extending to a longer axial length in the inlet channel with the larger hydraulic diameter than in the adjacent inlet channel with the smaller hydraulic diameter. Thus, in this second embodiment, the porous channel walls of the first channel are coated to an axial length of 60% to 80% L, and the porous channel walls of the second channel are coated to an axial length of 60% to 80% L, wherein the sum of the axial lengths of the coatings on the walls in the first and second channels is not less than 120%, preferably not less than 130%. Preferably, the upper limit of the overlap is 160% L.

[0085] In the case of a wall-coated ceramic honeycomb wall-flow filter substrate particularly intended for use in treating exhaust gases from diesel engines but also possibly from H2-ICEs, the wall coating is preferably a wall-coated catalyst coating at 0.5 g / ft 3 Up to 10g / ft 3(0.018g / L to 0.353g / L), preferably 1g / ft 3 Up to 8g / ft 3 (0.035 g / L to 0.283 g / L) of the total platinum group metal loading includes one or more non-rhodium platinum group metals.

[0086] The non-rhodium platinum group metal may be platinum alone, or a combination of platinum and palladium with a weight ratio of platinum to palladium of 1:0>1:1.

[0087] When the catalyst coating on the wall comprises both platinum and palladium, the Pt:Pd weight ratio may be from 10:1 to 1:1, preferably from 6:1 to 2:1.

[0088] Preferably, for at least the reasons explained above, the wall-mounted washcoat does not comprise inorganic fibers, ceramic fibers, or metal fibers.

[0089] In one embodiment, the filter substrate is a silicon carbide filter substrate having a porosity of 38% to 45% prior to coating, and the coated filter substrate has a porosity percentage of less than 45.0% as measured by mercury intrusion porosimetry (see Example 6 below). The coated filter substrate of this embodiment may have a porosity of at least 0.230 cm as measured by a combination of helium pycnometer and mercury density measurement. 3 / g of total pore volume (see also Example 6 below).

[0090] In another embodiment, the filter substrate is a cordierite filter substrate having a porosity of 46% to 60% prior to coating.

[0091] Preferably, the wall-mounted washcoat coating is applied at 0.1 g / in -3 Up to 0.3g / in -3 The coating was performed with a loading of 6.1 g / L to 18.3 g / L.

[0092] Preferably, the average wall coating thickness is from 10 μm to 60 μm.

[0093] Preferably, the geometric shape of the first channel cross section is square.

[0094] Exhaust system - fifth aspect of the invention

[0095] In the exhaust system according to the fifth aspect of the present invention, a flow-through substrate carrying a diesel oxidation catalyst washcoat is preferably provided upstream of a ceramic honeycomb wall-flow filter substrate. The diesel oxidation catalyst oxidizes NO in the exhaust gas to NO2, which is used to burn particulate matter trapped on the downstream filter substrate. Compared to burning in O2, PM is favorably burned in NO2 at a lower exhaust gas temperature (so-called effect).

[0096] Additionally or alternatively, the exhaust system of the fifth aspect of the present invention includes a flow-through substrate loaded with a selective catalytic reduction catalyst or a wall-flow filter substrate loaded with a selective catalytic reduction catalyst, the flow-through substrate or the wall-flow filter substrate being arranged downstream of a ceramic honeycomb wall-flow filter substrate; and a source of nitrogen-containing reducing agent, preferably urea, and an injector for injecting the nitrogen-containing reducing agent into the flowing exhaust gas, the injector being located at a point between the catalytic ceramic honeycomb wall-flow filter substrate and the flow-through substrate or the wall-flow filter substrate loaded with a selective catalytic reduction catalyst.

[0097] definition

[0098] As used herein, the term "mixed oxide" generally refers to a mixture of oxides in a single phase, as generally known in the art. As used herein, the term "complex oxide" generally refers to a composition of oxides having more than one phase, as generally known in the art.

[0099] As used herein, the acronym “PGM” refers to “Platinum Group Metals.” The term “Platinum Group Metals” generally refers to the metals Ru, Rh, Pd, Os, Ir, and Pt of the periodic table, particularly the metals Ru, Rh, Pd, Ir, and Pt.

[0100] In this paper, g ft -3 (grams per cubic foot) or g in -3 Any reference to quantities in units such as (grams per cubic inch) refers to the average weight of the component per volume of the substrate. The volume of a substrate is the total volume of the substrate calculated from its external dimensions and ignoring any channels extending through the substrate, e.g., the volume of a cylindrical substrate with a diameter of 165 mm and a length of 140.5 mm = h × π × radius 2 = 3.0 liters. 1g ft can be used -3 The conversion rate is 0.035g / L. 1g in -3 To a conversion rate of 61.0 g / L.

[0101] As used herein, the expression "consisting essentially of limits the scope of a feature to its novel and essential characteristics in the context of the defined elements, e.g., the specified materials or steps, and any other materials or steps that do not materially affect the basic characteristics of the feature, such as, for example, trace impurities. The expression "consisting essentially of encompasses the expression "consisting of.

[0102] Total pore volume (cm) of the filter substrate segment coated on the wall 3 / g) was determined by helium pycnometer and mercury density determination. Skeletal density (g / cm3 ) (sometimes also called true density, absolute density, or helium density); and mercury densitometry determines the geometric density (g / cm 3 ). In cm 3 The total pore volume in 1 / g is calculated as the inverse of the geometric density minus the inverse of the skeletal density, ie, total pore volume = (1 / geometric density) - (1 / skeletal density).

[0103] The percent porosity of the wall-coated filter substrate segments was also determined by helium pycnometry and mercury densitometry, where percent porosity = (1 - (skeletal density (g / cm 3 ) / geometric density (g / cm 3 ))×100.

[0104] Direct particle measurement using flow imaging microscopy was performed using a Flowcam 8100 (Yokogawa Fluid Imaging Technologies, Inc., see https: / / www.fluidimaging.com / products / flowcam-nano-submicron-particle-imaging) controlled by Visual Spreadsheet 5 software and equipped with a 20X objective, a FOV50 flow cell, a 0.5 mL syringe, and a grayscale camera. The sample was dispersed in deionized water at a concentration of 0.1 wt % and stirred at 400 rpm for 2 h using a stirring plate with a magnetic stir bar. The suspension was then filtered through a 35 μm nylon mesh. Two drops of the sample were diluted in 1 mL of deionized water for analysis. The solution was analyzed at a flow rate of 150 μL / min. Particle detection was performed using a dark pixel threshold of 20 and 4 closed-cell iterations. Data sets were acquired from >10,000 particles. A list of individual particle features was exported to Microsoft Excel spreadsheet software and analyzed.

[0105] If particle size measurements were obtained by laser diffraction particle size analysis, this was accomplished using a Malvern Mastersizer 2000, which is a volume-based technique (i.e., D(v, 0.1), D(v, 0.5), D(v, 0.9), and D(v, 0.98) may also be referred to as DV10, DV50, DV90, and DV98, respectively (or D10, D50, D90, and D98, respectively), and the Mie mathematical theory model was applied to determine the particle size distribution. Diluted washcoat samples were prepared by sonication at 35 watts for 30 seconds in distilled water without surfactant.

[0106] The term "modal," derived from the mean of the "mode," has its conventional meaning in statistics as "the most frequently occurring value in a set of data values." In a graphical representation of the aspect ratios of particles in a population, the "mode" may appear as the highest "peak."

[0107] When dealing with flow in non-circular pipes and channels, hydraulic diameter is a well-known term in the art. Using this term, many problems can be solved using the same calculation methods as for circular pipes. When the cross section is uniform along the length of the pipe or channel, it is defined as D H = 4A / P, where A is the cross-sectional area of ​​flow and P is the wetted perimeter of the cross section. The cross section and wetted perimeter can be measured by simple measurement of the channel at the end face of the exposed coated filter substrate.

[0108] As used herein, the term "insoluble" requires that the pore former does not dissolve in the slurry during the wash-coating process (i.e., in water and under the process conditions). That is, the pore former is insoluble in water during the process and remains insoluble in the presence of additional washcoat components (such as carboxylic acids). This means that the pore former maintains its heterogeneous morphology throughout the process. Preferably, the pore former is completely insoluble in the washcoat at the coating temperature, regardless of how long it remains in the washcoat, and preferably it remains insoluble even at a temperature of 100°C. The insolubility of the component can be assessed by any known technique, such as assessing the dry weight of the component before and after contact with the washcoat to determine that there is no loss of mass. It can also be assessed that the particles have not lost their morphological heterogeneity.

[0109] The term "non-uniform morphology" is used herein to describe individual particles of the pore former and is used in its usual sense in the art, i.e., the shape of the pore former is not a uniform shape (specifically excluding spherical shapes, which are common within this particle size range, nor any other uniform shape, such as square, columnar, etc.). Similarly, the term "non-geometrically uniform" is used to describe the voids formed during the process after the non-uniform morphology of the pore former particles is removed by calcination. These terms are used synonymously, but refer to different parts (pore former or void) to avoid confusion.

[0110] The invention may also be defined according to one or more of the following definitions.

[0111] 1. A method for preparing a ceramic honeycomb wall-flow filter substrate, the ceramic honeycomb wall-flow filter substrate having an axial length L supporting a coating on the wall, wherein a segment of the filter substrate coated on the wall has at least 15.0% of its pore volume, expressed as a percentage of mercury intrusion volume of the segment, having a diameter of 0.05 μm to 0.5 μm, as analyzed by mercury intrusion, the wall-flow filter substrate having a first end and a second end, and comprising a plurality of axially extending first and second channels, each of the first and second channels being partially defined by a porous channel wall having an axially extending porous channel wall surface, each first channel sharing a porous channel wall with an adjacent second channel, wherein in a scanning electron microscope image of a cross-section of the coated substrate, each channel has a geometric hollow cross-sectional shape, the geometric hollow cross-sectional shape having at least one vertex, the at least one vertex being partially defined by a vertex angle between two channel surface edges, wherein the first channel is terminated at the second end of the substrate, and the second channel is terminated at the first end of the substrate, the method comprising the steps of:

[0112] (i) preparing a slurry comprising water, a carboxylic acid, and inorganic oxide particles, or a mixture of two or more inorganic oxide particles, the inorganic oxide particles having a D(v,0.9) of 8 μm to 20 μm as measured by laser diffraction particle size analysis; and

[0113] 10 to 35 weight percent of a particulate insoluble cellulose pore former, relative to 100 weight percent of the inorganic oxide particles, the particulate insoluble cellulose pore former having a heterogeneous morphology and an equivalent spherical diameter D(v,0.5) of 0.5 to 14 μm as determined by laser diffraction and a modal aspect ratio (width / length) of 0.3 to 0.9 as determined by direct particle measurement using a flow imaging microscope particle shape analyzer;

[0114] (ii) coating the slurry on at least the porous channel walls of the first channels of the substrate, wherein the substrate has an average pore size (D50) of 6 μm to 15 μm before any coating and a porosity of less than 60% before any coating;

[0115] as well as

[0116] (iii) drying and calcining the slurry-coated substrate,

[0117] Sufficient slurry is thereby applied to the substrate so that the product of step (iii) has a relative weight of 0.07 g / in 3 to 0.4g / in 3(4.3 g / L to 24.4 g / L) of coating loading, wherein the average wall coating thickness of the product of step (iii) measured at an angle bisecting the apex angle on the scanning electron microscope cross-sectional image of the coated substrate is 5 μm to 70 μm.

[0118] 2. A method according to claim 1, wherein step (ii) includes the step of coating the porous channel walls of the second channel of the filter substrate with the slurry according to step (i), wherein the slurry used to coat the porous channel walls of the second channel has the same or different composition as the slurry coated on the porous channel walls of the first channel.

[0119] 3. The method according to clause 1 or 2, wherein the inorganic oxide particles or components of the mixture of inorganic oxide particles have a loose bulk density before grinding of 275 g / L to 850 g / L.

[0120] 4. The method of clause 3, wherein the inorganic oxide particles or components of the mixture of inorganic oxide particles have a loose bulk density before grinding of 350 g / L to 750 g / L.

[0121] 5. The method according to clause 1, 2, 3 or 4, wherein the inorganic oxide of the inorganic oxide particles comprises alumina, silica, zirconia or a mixed oxide or composite oxide of any two or more thereof.

[0122] 6. A method according to any of the preceding clauses, wherein the inorganic oxide particles comprise gamma alumina or alumina doped with one or more of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd), preferably silicon.

[0123] 7. The method of clause 6, wherein the total weight percentage of dopants present in the doped alumina is from 1 wt% to 10 wt%.

[0124] 8. The method according to any of the preceding clauses, wherein the inorganic oxide particles themselves or the inorganic oxide particles in the mixture are completely free or partially free of CeO2.

[0125] 9. The method of any preceding clause, wherein the axially extending first channels of the wall-flow filter substrate have a larger hydraulic diameter than the second channels.

[0126] 10. A method according to claim 9, wherein step (ii) includes the step of coating the porous channel wall of the second channel of the filter substrate with the slurry according to step (i), and the porous channel wall of the first channel is coated to an axial length of 60% to 90% L, and the porous channel wall of the second channel is coated to an axial length of 10% to 40% L, wherein the sum of the axial lengths of the coating on the walls of the porous channel walls of the first channel and the second channel is not less than 100%.

[0127] 11. The method of clause 10, wherein the porous channel walls of the first channel are coated to 70% to 85% L of the axial length, and the porous channel walls of the second channel are coated to 15% to 35% L of the axial length.

[0128] 12. A method according to any one of clauses 1 to 8, wherein the axially extending first channel of the wall-flow filter substrate is a combination of channels having a larger hydraulic diameter and a smaller hydraulic diameter, and the hydraulic diameter of the second channel is larger than the first channel having the smaller hydraulic diameter.

[0129] 13. A method according to claim 12, wherein step (ii) includes the step of coating the porous channel wall of the second channel of the filter substrate with the slurry according to step (i), and the porous channel wall of the first channel is coated to an axial length of 60% to 80% L, and the porous channel wall of the second channel is coated to an axial length of 60% to 80% L, wherein the sum of the axial lengths of the coating on the walls of the first channel and the second channel is not less than 120%.

[0130] 14. The method according to clause 13, wherein the sum of the axial lengths of the coating on the walls in the first channel and the second channel is not less than 130%.

[0131] 15. The method according to any of the preceding clauses, wherein the D(v,0.5) of the porogen in step (i) is less than the measured coating thickness.

[0132] 16. A method according to any of the preceding clauses, wherein the wall coating is a wall catalyst coating and the slurry of step (i) comprises one or more non-rhodium platinum group metal salts, the concentration of the platinum group metal salt of the one or more non-rhodium platinum group metal salts being selected so that the product of step (iii) has a P / S ratio of 0.5 g / ft 3 Up to 10g / ft 3 (0.018 g / L to 0.353 g / L) of total platinum group metal loading.

[0133] 17. The method of clause 16, wherein the total platinum group metal loading is 1 g / ft 3 Up to 8g / ft 3 (0.035g / L to 0.283g / L).

[0134] 18. A process according to any preceding clause, wherein the non-rhodium platinum group metal is platinum alone, or a combination of platinum and palladium, and the product of step (iii) has a platinum to palladium weight ratio of 1:0 > 1:1.

[0135] 19. The process according to clause 18, wherein the weight ratio of Pt:Pd in ​​the product of step (iii) is from 10:1 to 1:1, preferably from 6:1 to 2:1.

[0136] 20. The method of any preceding clause, wherein the inorganic oxide particles have a D(v, 0.9) of 9 to 15 μm.

[0137] 21. The method of clause 20, wherein the inorganic oxide particles have a D(v,0.5) of 3.0 μm to 6.0 μm.

[0138] 22. A method according to any of the preceding clauses, wherein the particulate insoluble cellulose is microcrystalline cellulose having an equivalent spherical diameter D(v,0.5) of 1 μm to 8.0 μm as determined by laser diffraction and a modal aspect ratio (width / length) of 0.6 to 0.8 as determined by direct particle measurement using a flow imaging microscopy particle shape analyzer.

[0139] 23. A method according to any one of clauses 1 to 21, wherein the particulate insoluble cellulose is a fibrous cellulose having an equivalent spherical diameter D(v,0.5) of 8.5 μm to 13.0 μm as determined by laser diffraction and a modal aspect ratio (width / length) of 0.4 to 0.7 as determined by direct particle measurement using a flow imaging microscope particle shape analyzer.

[0140] 24. The method of any preceding clause, wherein the inorganic oxide particles are not alpha-alumina.

[0141] 25. The method of any preceding clause, wherein the slurry is free of inorganic, ceramic or metal fibers.

[0142] 26. The method of any of the preceding clauses, wherein the filter substrate is a silicon carbide filter substrate having a porosity of 38% to 45% prior to coating.

[0143] 27. The method of clause 26, wherein the coated filter substrate has a porosity percentage of less than 45.0%.

[0144] 28. The method of clause 26 or 27, wherein the coated filter substrate has a density of at least 0.230 cm as measured by a combination of helium pycnometer and mercury density measurement. 3 / g total pore volume.

[0145] 29. The method of any one of clauses 1 to 25, wherein the filter substrate is a cordierite filter substrate having a porosity of 46% to 60% prior to coating.

[0146] 30. A method according to any preceding clause, wherein sufficient slurry is applied to the substrate so that the product of step (iii) has a viscosity of 0.15 g / in -3 Up to 0.3g / in -3 The coating loading ranged from 9.15 g / L to 18.3 g / L.

[0147] 31. The method of clause 30, wherein the average wall coating thickness is from 10 μm to 60 μm.

[0148] 32. The method according to any of the preceding clauses, wherein the carboxylic acid is a dicarboxylic acid or a tricarboxylic acid, preferably citric acid or succinic acid.

[0149] 33. A process according to any of the preceding clauses, wherein the carboxylic acid concentration in step (i) is selected so that the product of step (ii) has a carboxylic acid content of 50 g / ft 3 Up to 400g / ft 3 (1.77 g / L to 14.1 g / L) of carboxylic acid concentration.

[0150] 34. The method according to any of the preceding clauses, wherein the calcination temperature is greater than 400°C ± 20°C.

[0151] 35. The method of any of the preceding clauses, wherein the first channel cross-sectional geometry is square.

[0152] 36. A ceramic honeycomb wall flow filter substrate carrying a wall coating, the ceramic honeycomb wall flow filter substrate being used for treating exhaust gas containing particulate matter discharged from an internal combustion engine, the ceramic honeycomb wall flow filter substrate being obtainable by the method according to any one of the preceding clauses.

[0153] 37. A ceramic honeycomb wall flow filter substrate carrying a wall coating, the ceramic honeycomb wall flow filter substrate being used for treating exhaust gas containing particulate matter discharged from an internal combustion engine, the ceramic honeycomb wall flow filter substrate being obtained by the method according to any one of clauses 1 to 35.

[0154] 38. A wall-coated ceramic honeycomb wall-flow filter substrate for treating exhaust gas containing particulate matter discharged from an internal combustion engine, the wall-flow filter substrate having a first end and a second end and a length L between the first end and the second end, and comprising a plurality of axially extending first and second channels, each of the first and second channels being partially defined by a porous channel wall having an axially extending porous channel wall surface, each first channel sharing a porous channel wall with an adjacent second channel, wherein in a scanning electron microscope image of a cross-section of the coated substrate, each channel has a geometric hollow cross-sectional shape having at least one vertex, the at least one vertex being partially defined by a vertex angle between two channel surface edges, wherein the first channel is capped at the second end of the substrate, and the second channel is capped at the first end of the substrate, wherein at least the channel wall surface loading of the first channel is 0.07 g / in relative to the weight of the substrate before coating. 3 to 0.4g / in 3

[0155] (4.3 g / L to 24.4 g / L) of a wall-type washcoat, the washcoat comprising inorganic oxide particles or a mixture of two or more inorganic oxide particles, wherein the average wall coating thickness measured at an angle bisecting the apex angle on the scanning electron microscopy cross-sectional image of the coated substrate is 5 μm to 70 μm, wherein fragments of the wall-coated filter substrate have, as analyzed by mercury intrusion porosimetry, at least 15.0% of the pore volume, expressed as a percentage of mercury intrusion volume of the fragment, having a diameter of 0.05 μm to 0.5 μm, and wherein the wall washcoat coating comprises non-geometrically uniform voids having a pore volume as determined by focused ion beam-scanning electron microscopy (FIB-

[0156] The equivalent spherical diameter D(v,0.5) ranged from 0.1 μm to 8 μm and the modal aspect ratio (width / length) ranged from 0.3 to 0.9 as determined by SEM.

[0157] 39. A wall-coated ceramic honeycomb wall-flow filter substrate according to clause 38, wherein the porous channel walls of the second channels of the filter substrate are also coated with the wall-type washcoat, and the wall-type washcoat has the same or different composition as the washcoat coated on the porous channel walls of the first channels.

[0158] 40. The wall-coated ceramic honeycomb wall flow filter substrate of clause 38 or 39, wherein the inorganic oxide of the inorganic oxide particles comprises alumina, silica, zirconia, or a mixed oxide or composite oxide of any two or more thereof.

[0159] 41. A wall-coated ceramic honeycomb wall flow filter substrate according to clause 38, 39 or 40, wherein the inorganic oxide particles comprise gamma alumina or are doped with zirconium (Zr), titanium

[0160] Aluminum oxide of one or more of titanium (Ti), silicon (Si), yttrium (Y), lanthanum (La), praseodymium (Pr), samarium (Sm), and neodymium (Nd), preferably silicon.

[0161] 42. The wall-coated ceramic honeycomb wall flow filter substrate according to clause 41, wherein

[0162] The total weight percentage of dopants present in the doped alumina is 1 wt % to 10 wt %.

[0163] 43. A wall-coated ceramic honeycomb wall flow filter substrate according to any one of clauses 38 to 42, wherein the inorganic oxide particles themselves or the inorganic oxide particles in the mixture are completely free or partially free of CeO2.

[0164] 44. A wall-coated ceramic honeycomb wall flow filter substrate according to clause 38, 39, 40, 41 or 42, wherein the axially extending first channels of the wall flow filter substrate have a larger hydraulic diameter than the second channels.

[0165] 45. A wall-coated ceramic honeycomb wall flow filter substrate according to any one of clauses 38 to 44, wherein the porous channel walls of the first channels are coated to 60% to 90%.

[0166] L in the axial direction, and the porous channel wall of the second channel is coated to 10%

[0167] to 40% of the axial length of L, wherein the sum of the axial lengths of the coating on the walls in the first channel and the second channel is not less than 100%.

[0168] 46. ​​The wall-coated ceramic honeycomb wall flow filter substrate according to clause 45, wherein

[0169] The porous channel walls of the first channels are coated to 70% to 85% L of the axial length, and the porous channel walls of the second channels are coated to 15% to 35% L of the axial length.

[0170] 47. A wall-coated ceramic honeycomb wall flow filter substrate according to any one of clauses 38 to 43, wherein the axially extending first channel of the wall flow filter substrate is a combination of channels having a larger hydraulic diameter and a smaller hydraulic diameter, and the hydraulic diameter of the second channel is larger than the first channel having the smaller hydraulic diameter.

[0171] 48. The wall-coated ceramic honeycomb wall flow filter substrate according to clause 47, wherein

[0172] The porous channel walls of the first channel are coated to an axial length of 60% to 80% L, and the porous channel walls of the second channel are coated to an axial length of 60% to 80% L, wherein the sum of the axial lengths of the coating on the walls in the first channel and the second channel is not less than 120%.

[0173] 49. The wall-coated ceramic honeycomb wall flow filter substrate of clause 48, wherein the sum of the axial lengths of the wall coating in the first channel and the second channel is not less than 130%.

[0174] 50. A wall-coated ceramic honeycomb wall-flow filter substrate according to any one of clauses 38 to 49, wherein the wall coating is a wall catalyst coating having a coating density of 0.5 g / ft 3 Up to 10g / ft 3 (0.018 g / L to 0.353 g / L) of the total platinum group metal loading includes one or more non-rhodium platinum group metals.

[0175] 51. The wall-coated ceramic honeycomb wall flow filter substrate of clause 50, wherein the total platinum group metal loading is 1 g / ft 3 Up to 8g / ft 3 (0.035g / L to 0.283g / L).

[0176] 52. A wall-coated ceramic honeycomb wall-flow filter substrate according to any one of clauses 38 to 48, wherein the non-rhodium platinum group metal is platinum alone, or a combination of platinum and palladium in a platinum to palladium weight ratio of 1:0>1:1.

[0177] 53. The wall-coated ceramic honeycomb wall flow filter substrate of clause 52, wherein the Pt:Pd weight ratio is from 10:1 to 1:1, preferably from 6:1 to 2:1.

[0178] 54. A wall-coated ceramic honeycomb wall flow filter substrate according to any one of clauses 38 to 53, wherein the inorganic oxide particles are not alpha-alumina.

[0179] 55. A wall-coated ceramic honeycomb wall-flow filter substrate according to any one of clauses 38 to 54, wherein the wall-type washcoat is free of inorganic fibers, ceramic fibers or metal fibers.

[0180] 56. A wall-coated ceramic honeycomb wall-flow filter substrate according to any one of clauses 38 to 55, wherein the filter substrate is a silicon carbide filter substrate having a porosity of 38% to 45% prior to coating.

[0181] 57. The wall-coated ceramic honeycomb wall flow filter substrate of clause 56, wherein the coated filter substrate has a porosity percentage of less than 45.0%.

[0182] 58. A wall-coated ceramic honeycomb wall flow filter substrate according to clause 56 or 57, wherein the coated filter substrate has a density of at least 0.230 cm as measured by a combination of helium pycnometer determination and mercury density determination. 3 / g total pore volume.

[0183] 59. A wall-coated ceramic honeycomb wall-flow filter substrate according to any one of clauses 38 to 55, wherein the filter substrate is a cordierite filter substrate having a porosity of 46% to 60% prior to coating.

[0184] 60. A wall-coated ceramic honeycomb wall-flow filter substrate according to any one of clauses 38 to 59, wherein the wall-coated washcoat coating is at a concentration of 0.1 g / in -3 Up to 0.3g / in -3 The coating was performed with a loading of 6.1 g / L to 18.3 g / L.

[0185] 61. The wall-coated ceramic honeycomb wall flow filter substrate of Clause 60, wherein the average wall coating thickness is from 10 μm to 60 μm.

[0186] 62. The wall-coated ceramic honeycomb wall flow filter substrate of any one of clauses 38 to 61, wherein the first channel cross-sectional geometry is square.

[0187] 63. An exhaust system for an internal combustion engine, the exhaust system comprising a ceramic honeycomb wall-flow filter substrate according to any one of clauses 38 to 62, wherein the first end of the substrate faces upstream.

[0188] 64. The exhaust system of clause 63, comprising a flow-through substrate carrying a diesel oxidation catalyst washcoat, the flow-through substrate disposed upstream of the ceramic honeycomb wall flow filter substrate.

[0189] 65. An exhaust system according to claim 63 or 64, wherein the exhaust system comprises a flow-through substrate loaded with a selective catalytic reduction catalyst or a wall-flow filter substrate loaded with a selective catalytic reduction catalyst, the flow-through substrate or the wall-flow filter substrate being arranged downstream of the ceramic honeycomb wall-flow filter substrate; and a source of nitrogen-containing reducing agent, preferably urea, and an injector for injecting the nitrogen-containing reducing agent into the flowing exhaust gas, the injector being located at a point between the catalytic ceramic honeycomb wall-flow filter substrate and the flow-through substrate or the wall-flow filter substrate loaded with a selective catalytic reduction catalyst.

[0190] 66. An internal combustion engine comprising an exhaust system according to clause 60, 64 or 65.

[0191] 67. A vehicle comprising a diesel engine according to clause 66.

[0192] 68. A vehicle comprising an internal combustion engine configured to run on a mixture of air and fuel, wherein the fuel of the mixture of air and fuel is a gaseous fuel containing hydrogen (H2) as a main fuel mass, the vehicle comprising a gaseous fuel source and an exhaust system according to clause 63, 64 or 65, the gaseous fuel source containing hydrogen (H2) as a main fuel mass.

[0193] In order that the present invention may be more fully understood, the following embodiments are provided by way of illustration only and in conjunction with the following drawings, in which:

[0194] Figure 1 is a graph showing the relationship between mercury logarithmic differential intrusion and pore diameter for some samples with pore diameters ranging from 0.05 μm to 0.5 μm in Example 6 and Table 13;

[0195] Figure 2is a backscattered electron scanning electron microscopy (BSE-SEM) image of a cross-section of a coated filter substrate showing juxtaposed inlet and outlet channels of an asymmetric filter substrate and indicating the angle bisecting the top angle between two edges of a square cross-section of these channels (representing orthogonally juxtaposed channel wall surfaces) along which the washcoat thickness on the wall in the channel “corner” is measured;

[0196] Figure 3 is an image analysis report of local three-dimensional pores measured in the washcoat thickness of Sample 1 in Table 4 after processing with reference to the following literature: A. Varambhia et al., Johnson Matthey Technol. Rev., 2022, 66, (3), 355-371; and

[0197] Figure 4 is an image analysis report of the localized three-dimensional pores measured in the washcoat thickness of Sample 1 in Table 4.

[0198] Example

[0199] Example 1 - Evaluation of the Effect of Different Particle Sizes of Pore Formers on Filtration and Backpressure

[0200] Three different samples were prepared, each comprising a cylindrical silicon carbide wall-flow filter substrate (165 mm diameter x 140.5 mm long) having an asymmetric channel arrangement (inlet channels having a larger hydraulic diameter and outlet channels having a smaller hydraulic diameter) with 46.5 cells per square centimeter (300 cells per square inch). The uncoated filter had a porosity of 42% and an average pore size of 14 μm.

[0201] The inlet channel with the larger hydraulic diameter in the asymmetric channel arrangement of each bare substrate was coated with a washcoat having an axial length of 80%; and the outlet channel with the smaller hydraulic diameter was coated with the same washcoat as the inlet channel, having an axial length of 20%. The washcoat in each sample contained particulate gamma-alumina, citric acid, platinum nitrate, a pore former, and a rheology modifier to achieve a desired viscosity for coating the substrate according to the method disclosed in WO 99 / 47260, i.e., the method comprising the steps of: (a) positioning a containment device on top of the substrate, (b) metering a predetermined amount of a liquid component into the containment device in the order of (a) first and then (b) or (b) first and then (a), and (c) applying a vacuum to draw the entire amount of the liquid component into at least a portion of the substrate and retaining substantially the entire amount within the substrate without recirculation.

[0202] The proportions of the washcoat components are selected so that the coated substrate contains 0.3 g / in3 (18.3g / L) of gamma alumina, 250g / ft 3 (8.83g / L) of citric acid, 3g / ft 3 (0.11g / L) of Pt, 0.09g / in 3 That is, to achieve a target loading of 0.3 g / in in the calcined final product. 3 (18.3 g / L) of the desired gamma alumina washcoat solids, the applied washcoat contained 30 wt% pore former. All coated parts were statically calcined at 500°C, a process that resulted in combustion and removal of the pore former in the final product. SEM revealed that the catalyst coating on the inlet and outlet channels in the finished product was essentially wall-mounted.

[0203] The porogen in each sample is described in Table 1 below.

[0204] Table 1

[0205] D(v,0.5) / D(v,0.9), as determined by laser diffraction, assuming equivalent spherical diameters.

[0206] Sample Evaluation—Cold Flow Back Pressure

[0207] Cold flow back pressure analysis was performed on the coated and aged filters using a Superflow SF1020 apparatus commercially available at https: / / superflow.com / products / flowbenches / .

[0208] Under the conditions of 20℃±2℃ ambient temperature and 600m 3 The results are listed in Table 2.

[0209] Table 2

[0210] Sample number <![CDATA[600m 3 / hour cold flow back pressure (mBar (Kpa))]]> Sample 1 57.8(5.78) Sample 2 (comparative example) 63.0(6.30) Sample 3 (comparative example) 64.8(6.48)

[0211] Sample Evaluation—Soot Loading Back Pressure

[0212] Soot Loading Back Pressure ("SLBP") testing was performed using the apparatus and method described in EP1850068 and available from Cambridge, UK. Purchased under the trade name "DPG Particulate Filter Testing System" (see https: / / www.cambustion.com / products / engine-exhaust-emissions / dpg-particulate-filter-testing-system), namely:

[0213] (i) An apparatus for generating and collecting particulate matter resulting from the combustion of a liquid carbonaceous fuel, the apparatus comprising: a fuel burner including a nozzle housed in a vessel, the vessel including a gas inlet and a gas outlet, the gas outlet being connected to a conduit for conveying gas from the gas outlet to the atmosphere; means for detecting the rate of gas flowing through the gas inlet, and means for forcing an oxidizing gas from the gas inlet through the vessel, the gas outlet, and the conduit to the atmosphere; a station for collecting particulate matter from the gas flowing through the conduit, and means for controlling the gas flow forcing means in response to the gas flow rate detected at the gas inlet, thereby maintaining the gas flow rate at the gas inlet at a desired rate to provide substoichiometric combustion of the fuel within the vessel, thereby promoting particulate matter formation; and

[0214] (ii) a method for generating and collecting particulate matter resulting from the combustion of a liquid carbonaceous fuel in an oxidizing gas, the method comprising combusting the fuel in a substoichiometric amount of oxidizing gas in a fuel burner, the fuel burner comprising a nozzle housed in a container;

[0215] forcing an oxidizing gas into a gas inlet of the vessel and into the atmosphere through a gas outlet of the vessel and a conduit connected to the gas outlet; collecting particulate matter at a station located within the conduit;

[0216] The oxidizing gas flow rate at the gas inlet is detected and controlled so as to maintain a desired oxidizing gas flow rate at the gas inlet.

[0217] The filter is inserted into the station and is used to collect particulate matter from the gas flowing through the pipeline. The fresh filter is first pre-treated with low sulfur diesel fuel (S content is 10ppm) in a lean burn combustion flow with an air flow rate of 80kg / hour to increase the filter inlet temperature to 650°C, which is usually used to regenerate soot-laden filters on vehicles. The temperature of this pre-treatment step is much higher than the temperature of soot combustion and ensures that the filter under test is clean at the beginning. Pressure sensors set up upstream and downstream of the station are used to monitor the back pressure on the filter. The SLBP test is carried out in the following way: low sulfur diesel fuel (S content is 10ppm) is burned at an air flow rate of 180kg / hour at a filter inlet temperature of 250°C.

[0218] Filtration efficiency testing was also performed on the DPG particle filter test system as described below. Initial testing used a PN counter to detect the second-by-second particle count (PN) upstream of the filter at a constant flow rate. The upstream PN raw data was averaged (mean) over an 11-second detection period to generate an 11-second averaging window that moved second by second, thereby reducing the effect of any variability in PN generation, where time "t" corresponded to the midpoint of the 11-second window. The sample filter was then tested by detecting the filtered PN (also using a PN counter). The instantaneous filtration efficiency at time "t" in the test is given by the following calculation:

[0219] FE t [%]=( [Average upstream PN at time t - downstream PN at time t] / [Average upstream at time t

[0220] PN])×100%

[0221] The results of the sample SLBP and filtration efficiency analysis are shown in Table 3.

[0222] Table 3

[0223]

[0224] As can be seen from the results shown in Tables 2 and 3, when used as pore formers in the coating of the ceramic honeycomb wall-flow filter substrate according to the present invention, cellulose fibers having an equivalent spherical diameter D(v,0.5) of 0.5 μm to 14 μm produce lower cold flow back pressure and soot loading back pressure than cellulose fiber pore formers having a higher D(v,0.5).

[0225] Example 2 - Laboratory and Engine Evaluation of the Effects of Different Particle Sizes of Pore Formers on Filtration and Backpressure

[0226] Six different samples were prepared, each comprising a cylindrical cordierite wall-flow filter substrate (143.8 mm diameter x 152.4 mm length) having an asymmetric channel arrangement of 46.5 cells per square centimeter (300 cells per square inch). The uncoated filter had a porosity of 47% and an average pore size of 12 μm, with an asymmetric channel arrangement of 46.5 cells per square centimeter (300 cells per square inch). The substrate used was different from that used in Example 1.

[0227] Each sample was prepared according to the method of Example 1, except that different particle sizes were used with a loading of 0.09 g / in 3 (5.5 g / L) of different pore formers (0.3 g / in relative to 100 wt% loading 3 (18.3 g / L) γ-alumina (30 wt%).

[0228] The porogen in each sample is described in Table 4 below.

[0229] Table 4

[0230]

[0231] D(v,0.5) / D(v,0.9), as determined by laser diffraction, assuming equivalent spherical diameters.

[0232] Sample Evaluation—Cold Flow Back Pressure

[0233] In the same manner as described in Example 1, the 3 The cold flow back pressure was evaluated at a flow rate of 100 Å / hour and the results are listed in Table 5.

[0234] Table 5

[0235] Sample number <![CDATA[600m 3 / hour cold flow back pressure (mBar (Kpa))]]> Sample 1 49.9(4.99) Sample 4 54.4(5.44) Sample 5 57.0(5.70) Sample 6 48.7(4.87)

[0236] Sample Evaluation—Soot Loading Back Pressure

[0237] Soot loading back pressure testing was performed as described above in Example 1. The results are listed below in Table 6.

[0238] Table 6

[0239]

[0240] Sample Evaluation—Engine Testing

[0241] Three different samples were prepared, each comprising a different cylindrical silicon carbide wall-flow filter substrate (304.8 mm diameter x 228.6 mm long) having an asymmetric channel arrangement of 46.5 cells per square centimeter (300 cells per square inch) (inlet channels having a larger hydraulic diameter and outlet channels having a smaller hydraulic diameter), but coated with the coatings described in Table 7. The uncoated filter had a porosity of 41% and an average pore size of 9 μm. Each sample was prepared according to the method of Example 1.

[0242] Particle number (PN) evaluations were conducted using a 12L bench-top diesel engine running EUVI B7 fuel. The diesel particulate filter (DPF) to be evaluated was installed downstream of the diesel oxidation catalyst using a removable canister, and a PN counter (AVL) was installed downstream of the DPF. Prior to evaluating "real driving emissions" (RDE) according to the test cycle, each DPF was pre-loaded with 4g / L of filter substrate volume of soot. The post-DPF PN10 data was processed using a moving average window analysis method to generate 90th percentile values ​​for PN / kWh. The results are shown in Table 7.

[0243] Table 7

[0244] Sample number Moving average window PN [PN# / kWh] Sample 1 <![CDATA[1.3×10 10 ]]> Sample 4 <![CDATA[5.9×10 9 ]]> Sample 5 <![CDATA[4.7×10 9 ]]>

[0245] Based on the current EU7 proposal, the limit is 9.0×10 11 Within the RDE test cycle, all three samples met the RDE PN# / KWh of 10nm.

[0246] Example 3 - Pore-Former Loading Study

[0247] Six different samples were prepared, each comprising a cylindrical silicon carbide wall-flow filter substrate (143.8 mm diameter x 150.5 mm long) having an asymmetric channel arrangement (inlet channels having a larger hydraulic diameter and outlet channels having a smaller hydraulic diameter) with 46.5 cells per square centimeter (300 cells per square inch). The uncoated filter had a porosity of 42% and an average pore size of 11 μm. The substrate used was different from that used in Example 1 or Example 2.

[0248] The samples were prepared similarly to Example 1, except that the pore former used in all Example 3 samples was Sample 1.1 of Table 1, but the pore former was added to the 30 wt % of Sample 1.1 at varying wt %. The loading of the pore former added to each sample washcoat is listed in Table 8 below. Sample 1.1 was included as a reference sample.

[0249] Table 8

[0250]

[0251] Sample Evaluation—Soot Loading Back Pressure and Filter Efficiency

[0252] Soot loading back pressure testing was performed as described above in Example 1. The results are listed below in Table 9.

[0253] Table 9

[0254]

[0255] The results shown in Table 9 are unexpected. One skilled in the art would expect that increasing the loading of the cellulosic pore former would be associated with lower filtration efficiency, as the introduction of increased pore volume would create more paths for the soot to pass through. However, the results in Table 9 show that the soot loading backpressure is lower and the filtration efficiency is lower, with the filtration efficiency plateauing at about 98% when the pore former addition is above about 15 wt%.

[0256] Reference Example 4 - Effect of Carrier Coating Particle Size Distribution on Backpressure and Filtration

[0257] Six different samples were prepared, each comprising a cylindrical silicon carbide wall-flow filter substrate (143.8 mm diameter x 150.5 mm long) having an asymmetric channel arrangement (inlet channels having a larger hydraulic diameter and outlet channels having a smaller hydraulic diameter) with 46.5 cells per square centimeter (300 cells per square inch). The uncoated filter had a porosity of 42% and an average pore size of 11 μm. The substrate used was different from that used in Example 1 or Example 2.

[0258] Each sample was prepared according to the method of Example 1 using the pore former of Sample 1. The proportions of the washcoat components were selected so that the coated substrate contained 0.4 g / in 3 (24.4 g / L) of gamma alumina with different particle size distributions, 250 g / ft 3 (8.83g / L) of citric acid, 3g / ft 3 (0.11 g / L) with a ratio of 10:1 Pt:Pd, 0.125 g / in 3 That is, to achieve a target loading of 0.4 g / in in the calcined final product. 3 (24.4 g / L) of the desired gamma alumina washcoat solids, the applied washcoat contained 31.25 wt% of the pore former. The difference between each sample was that the D(v, 0.9) of the gamma alumina was 2 μm different from the previous sample in the study, as listed in Table 10 below. The D(v, 0.9) of the gamma alumina was adjusted by ball milling.

[0259] Table 10

[0260] Sample number D(v,0.9) of γ-alumina (μm) Sample 8.1 20 Sample 8.2 18 Sample 8.3 16 Sample 8.4 14 Sample 8.5 12 Sample 8.6 10

[0261] Sample Evaluation—Soot Loading Backpressure and Filter Efficiency

[0262] Soot loading back pressure testing was performed as described above in Example 1. The results are listed in Table 11 below.

[0263] Table 11

[0264]

[0265]

[0266] From the results shown in Table 11, it can be seen that the filtration efficiency increases with the decrease of D(v,0.9) and the increase of back pressure. 3 For practical use of a washcoat containing 24.4 g / L of diesel exhaust particulate matter, the filtration efficiency of the reference embodiment in this example is too low, and the soot loading backpressure is too high. However, in view of the results in this example, and in order to achieve the goal of meeting current and future emission standards with acceptable adhesion of diesel exhaust particulates (see Example 5 below), applicants prefer that the washcoat for the present invention have a D(v,0.9) particle size range of 9 μm to 15 μm, more preferably 10 μm to 14 μm.

[0267] Example 5 - Adhesion Test

[0268] Before conducting the washcoat adhesion test in the laboratory apparatus described below, hold each sample by hand and tap or pat it on a table. If any washcoat falls off the sample, the sample is immediately deemed to have failed the adhesion test and is not tested on the laboratory apparatus. This test is referred to as the "tap test."

[0269] The washcoat adhesion of samples prepared similarly to Example 1 was evaluated by using a nozzle to discharge high-pressure air in a laboratory test apparatus. A jet of air was delivered vertically downward from 0.5 inches (1.3 cm) above the end face of a vertically positioned filter using a high-pressure air flow rate of 425 L / min. The nozzle was robotically controlled and moved laterally across and relative to the end face of the filter in a zigzag pattern at a rate of 6.7 mm / sec, such that the entire end face of the filter was exposed to the high-pressure air treatment.

[0270] The filter samples to be tested were first heated in an oven at 115°C for 30 minutes to stabilize them, and then weighed. The filter samples were then exposed to pressurized air in the following order to test washcoat adhesion: outlet end; inlet end; and finally outlet end. The samples were reweighed before being allowed to thermally stabilize again. The difference in weight (i.e., weight loss) before and after the pressurized air exposure test was calculated as a percentage of the total calcined coating applied to the filter. The results for various samples from the aforementioned examples are listed in Table 12 below.

[0271] Comparative Samples 2 and 3 failed the "tap test," so they were not fully tested for adhesion.

[0272] Table 12

[0273] Sample number Adhesion loss [%] 1 0.4 4 0.5 5 0.3 7.1 0.5 7.4 0.4 7.7 (Not according to the present invention) 9.8 8.3 (Not according to the present invention) 21.7 8.4 (Not according to the present invention) 2.8 8.5 (not according to the present invention) 1.5 8.6 (not according to the present invention) 0.3

[0274] Any adhesion loss (%) above 2.0 was considered “failed.” From the results shown in Table 12, it can be seen that adhesion loss was observed when >35 wt% porogen was used (Sample 7.7).

[0275] Example 6 - Mercury (Hg) Intrusion Porosimetry

[0276] A silicon carbide wall-flow filter with 300 cells per square inch (equivalent to 46.5 cells per square centimeter) was coated with the test formulations of Examples 9.1 to 9.8. Cylindrical cores of approximately 10 mm diameter x 10 mm length were cut from the filter for analysis. The inlet "face" of the coated substrate had an area of ​​0.79 square centimeters, so 0.79 x 46.5 cells per centimeter = approximately 36 channels, given that the blockage at the end face of the wall-flow filter was a "checkerboard" pattern, half of which were "blocked." That is, analysis was performed on at least 18 coated channel cells from the inlet end of the coated filter sample. The complete cross-section of these cores would not fit into a 3 cc (cubic centimeter) penetrometer sample cup, so the analyst used a serrated surgical scalpel, similar to a chisel, to cut the sample into appropriately sized pieces, which were then loaded into the sample cup. The sample pieces retained a recognizable cell channel appearance at their "open" inlet end, and no further damage was observed after analysis. Therefore, the sample as a whole represents the coated portion of a wall-flow filter. [A fragment of the filter substrate excluding the wall coating would not represent a filter and would not exhibit the desired pore volume of 0.05 μm to 0.5 μm. This is because the pores of such substrates are relatively large. Specifically, the average pore size D50 of the substrate is typically 6 to 15 microns.]

[0277] Porosity data was measured by mercury intrusion according to ASTM method D4284-03 using a Micromeritics AutoPore 9600; the test method for determining the pore volume distribution of the catalyst is mercury intrusion. The intrusion curve was measured over a pressure range of 0.5 psia to 60,000 psia (pounds per square inch absolute) (3.45 kPa to 414 MPa), followed by extrusion down to atmospheric pressure. For each data point on both the intrusion and extrusion curves, an equilibrium time of 15 seconds was used, the mercury contact angle was taken to be 130°, and the mercury surface tension was taken to be 485 dynes / cm.

[0278] The samples were dried in an oven at 115°C overnight before analysis. Temperature and pressure effects exhibited during mercury intrusion porosimetry were accounted for by performing a blank correction on an empty penetrometer tube, which was subsequently subtracted from the experimental data. Data generated at up to 60,000 psia (414 MPa) included the pore volume and size distribution of the alumina component of the washcoat. Alumina was not affected by the addition of pore formers. Therefore, the pore size range of interest, in which the pore formers affect the washcoat porosity, was found to be 0.05 μm to 5 μm in diameter, which corresponds to a pressure range of 0.5 psia to 1000 psia (3.45 kPa to 6890 kPa).

[0279] The Micromeritics AutoPore 9600 instrument has both low-pressure and high-pressure circuits. The low-pressure circuit uses compressed air to pressurize the sample to a maximum of 36 psia. The high-pressure circuit uses an oil-filled chamber. The low-pressure circuit is used to analyze pores up to 300 μm, i.e., the 0.5 psia end of the pressure range mentioned in Example 6. Since this pressure is below atmospheric pressure (i.e., 14.7 psia), it should be understood that the 0.5 psia end of this range is performed under vacuum. To analyze the full pressure range of 0.5 psia to 60,000 psia, it will also be appreciated that the sample / penetrometer must be switched from the low-pressure circuit to the high-pressure circuit, as the high-pressure circuit cannot resolve the 300 μm end of the analytical range. To ensure a seamless analysis when switching from the low-pressure circuit to the high-pressure circuit, care is taken to ensure that the pressure transducer values ​​in each circuit remain matched when switching. Once the maximum pressure is reached, the penetrometer is returned to ambient pressure and the sample is removed. Skeletal density was determined by gas pycnometry according to ISO 12154:2014 – Density by volume displacement – ​​from the geometric density derived from mercury intrusion data and the skeletal density measured by helium pycnometry using a Micromeritics AccuPyc II 1340 pycnometer. The pore volume between 0.05 μm and 0.5 μm was calculated as a percentage of the intrusion volume data. Samples were oven-dried at 115°C overnight prior to analysis.

[0280] Six samples were prepared according to the present invention using the methods and materials described in Sample 1 of Example 1. Details of the loading and pore former content are listed in Table 13. The uncoated filter used in each case was a silicon carbide filter with an asymmetric design having a porosity of 41%, an average pore size of 9 μm, 300 cells per square inch, and a wall thickness of 7 thousandths of an inch (mil) (0.1778 mm).

[0281] Table 13

[0282]

[0283] The results are shown in Table 14, including a bare substrate as a reference.

[0284] Table 14

[0285]

[0286] As can be seen from Table 14, at a constant washcoat loading, increasing the amount of pore former increases the total pore volume, the volume of pores from 0.05 μm to 0.5 μm expressed as mercury intrusion volume percent, and the porosity percent. However, if the amount of pore former added is too high, washcoat adhesion may be affected (see the results of Example 5 below). It can also be seen that at a constant amount of pore former added, increasing the washcoat loading increases the total pore volume, the volume of pores from 0.05 μm to 0.5 μm (expressed as mercury intrusion volume percent), and the porosity percent.

[0287] Example 7 - Support Material Screening - Effect of Bulk Density on SLBP, Filtration Efficiency and Adhesion

[0288] Using the cylindrical cordierite wall-flow filter substrate (143.8 mm diameter x 152.4 mm length) used in Example 2, a series of samples as listed in Table 15 were prepared in a manner similar to Example 1. Each filter substrate sample was coated with a washcoat having the formulation and axial length coating described for Sample 1 in Example 1, except that the gamma alumina support material was replaced with an alternative support material as listed in Table 15. Prior to the addition of the pore former, the support materials were each wet-milled to the indicated D50 and D90.

[0289] Table 15

[0290]

[0291] Each sample was evaluated for cold flow back pressure, SLBP, and filtration efficiency by DPG according to the methods described in Example 1; and adhesion testing was performed according to the methods of Example 5. The results are shown in Table 16. It should be noted that Sample 10.1 from Example 7 and Sample 1 from Example 1 were similarly formulated. However, Sample 10.1 was a freshly prepared sample and therefore different from Sample 1. Therefore, some slight variations in the cold flow back pressure reported in Table 2 and the filtration efficiency in Table 3 are expected.

[0292] Based on the data shown in Table 15, applicants note that the D50 and D90 for each of Samples 10.1 to 10.5 are generally similar, so any differences in backpressure, filtration efficiency, and adhesion can be expected to be due to differences in the properties of the raw materials used.

[0293] Table 16

[0294]

[0295] As can be seen from the results shown in Table 16, despite having good low cold flow backpressure and soot loading backpressure, CeO2 support material sample 10.4 had poor filtration efficiency and significant adhesion issues. When observed under a microscope, the surface coating of sample 10.4 was found to be cracked, with the appearance of dry mud blocks or so-called "crazy paving." The cracks may be the cause of the adhesion loss and poor filtration efficiency, and may also explain the low backpressure. Applicants attempted to improve adhesion by combining sample 10.1 with CeO2 in increasing proportions of sample 10.4, but this did not overcome the negative results for sample 10.4 (results not shown).

[0296] While Sample 10.5 exhibited acceptable soot loading back pressure and filtration efficiency compared to Reference Example Sample 10.1, the adhesion loss was unacceptable. However, Applicants discovered that combining a rare earth element-stabilized ZrO2 support material with the gamma alumina support material of Sample 10.1 in ratios of 80:20 and 60:40 (ZrO2:Al2O3) ultimately improved adhesion (for the 60:40 embodiment), meeting the adhesion requirement (0.6% adhesion loss). Furthermore, soot loading back pressure and filtration efficiency were also improved compared to Reference Example Sample 10.1 (results not shown).

[0297] The higher pore volume alumina sample doped with 5 wt% silica (Sample 10.3) also suffered from insufficient adhesion and surprisingly high back pressure.

[0298] Relative to the gamma alumina and alumina samples doped with 5 wt% silica, i.e., Samples 10.1 and 10.2, it is noted that the support materials of Samples 10.3, 10.4, and 10.5, by themselves, i.e., without mixing with gamma alumina, have loose bulk densities before grinding that are less than about 850 g / L and greater than about 275 g / L. Without wishing to be bound by any theory, applicants believe that there exists a range of loose bulk density parameters before grinding that ranges from 275 g / L to 850 g / L, from which refractory metal oxide support materials having acceptable backpressure, filtration efficiency, and adhesion for use in the present invention can be advantageously selected. The results shown in Table 16 and discussed above also indicate that materials having a loose bulk density before grinding that ranges below 275 g / L can be mixed with support materials in the range of 275 g / L to 850 g / L to improve the adhesion characteristics of the former.

[0299] Example 8—FIB-SEM

[0300] The samples according to Table 2, Example 1 and Example 5 were analyzed using a focused ion beam-backscattered electron (BSE) scanning electron microscope (FIB-SEM) using a gallium beam, with an imaging "slice" spacing of 50 nm and as described in A. Varambhia et al., Johnson Matthey Technol. Rev., 2022, 66, (3), 355-371. After applying vacuum, each sample to be analyzed was placed in resin to ensure that all pores in the sample were filled with resin. The results are shown in Table 17 below and Figure 3 and Figure 4 middle.

[0301] Table 17

[0302] Example sample number 3D pore size (μm) 1 0.1-6.4 5 0.1-5.7

[0303] From these data, it can be seen that the combustion of the cellulosic pore former during calcination and the gas generated by the citric acid in the applied washcoat slurry resulted in the pore structure within the washcoat layer. It can also be seen that due to compression within the washcoat slurry system, the pore size is not necessarily proportional to the particle size distribution of the dried pore former. However, from Figure 3 and Figure 4 It can be seen that the pore size generated by the pore former of Sample 1 in Table 4 is larger than the pore size generated by the pore former of Sample 5 in Table 4.

[0304] Example 9 - Washcoat Layer Thickness

[0305] Three 152.4 mm long segment samples of an asymmetric silicon carbide filter were coated with the washcoat described in Example 1, with varying amounts of pore former, along 60% of the segment's axial length from the inlet end and 40% of the segment's axial length from the outlet end. The inlet channels had a larger hydraulic diameter than the outlet channels.

[0306] As is well known, silicon carbide filters are typically manufactured as segments with square cross-sections that are bonded together to form, for example, a cylindrical filter. This is because silicon carbide itself has a relatively high coefficient of thermal expansion (CTE). Therefore, if a segmented arrangement is not used, catastrophic cracks may form within the sealed filter during use due to stresses.

[0307] The amount of porogen used in each sample is listed in Table 18 below. Backscattered electron (BSE)-SEM image of a channel cross section of a coated sample part. 3 (24.4 g / L) (not according to the invention) and 0.2 g / in 3 SEM images were taken of a section sample of a washcoat coated with 12.2 g / L porogen at an axial point 50.8 mm from the inlet, i.e., the axial point of both the channels with smaller hydraulic diameter and the channels with larger hydraulic diameter; and for a section sample loaded with 0.3 g / in 3 The SEM image of the sample containing 18.3 g / L of porogen was taken at a distance of 50.8 mm from the outlet end. The washcoat coating thickness was measured as the angle that bisects the top angle between the two edges of the square cross section of the channel, which represent the orthogonally juxtaposed channel wall surfaces, as shown in FIG. Figure 1 Thickness measurements were taken at five compartments at each location within each part, and at four corners of each compartment / channel.

[0308] Table 18

[0309]

[0310] From the results shown in Table 18, it can be seen that the thickness of the coating increases with increasing amount of pore former added. According to the applicant's WO 2015 / 082892, the coating on the walls of the asymmetric filter substrate with a smaller hydraulic diameter is thicker than that on the channels with a larger hydraulic diameter. However, the thickest washcoat loading (0.4 g / in) corresponding to Examples 8.3 to 8.6 in Reference Example 4 is 3 (24.4 g / L)) typically exhibits either too high a soot loading backpressure or too low a filtration efficiency and / or adhesion issues (see Example 5 above).

[0311] For the avoidance of any doubt, any and all documents cited herein are hereby incorporated by reference into this application in their entirety.

Claims

1. A method for preparing a ceramic honeycomb wall-flow filter substrate, the ceramic honeycomb wall-flow filter substrate having an axial length L supporting a coating on the wall, wherein a segment of the filter substrate coated on the wall has at least 15.0% of its pore volume, expressed as a percentage of mercury intrusion volume of the segment, having a diameter of 0.05 μm to 0.5 μm, as analyzed by mercury intrusion, the wall-flow filter substrate having a first end and a second end, and comprising a plurality of axially extending first and second channels, each of the first and second channels being partially defined by a porous channel wall having an axially extending porous channel wall surface, each first channel sharing a porous channel wall with an adjacent second channel, wherein in a scanning electron microscope image of a cross-section of the coated substrate, each channel has a geometric hollow cross-sectional shape, the geometric hollow cross-sectional shape having at least one vertex, the at least one vertex being partially defined by a vertex angle between two channel surface edges, wherein the first channel is terminated at the second end of the substrate, and the second channel is terminated at the first end of the substrate, the method comprising the steps of: (i) preparing a slurry comprising water, a carboxylic acid, inorganic oxide particles, or a mixture of two or more inorganic oxide particles, the inorganic oxide particles having a D(v,0.9) of 8 μm to 20 μm as measured by laser diffraction particle size analysis; and 10 wt% to 35 wt% of a particulate insoluble cellulose pore former, relative to 100 wt% of the inorganic oxide particles, the particulate insoluble cellulose pore former having a heterogeneous morphology and an equivalent spherical diameter D(v,0.5) of 0.5 μm to 14 μm as measured by laser diffraction and a modal aspect ratio (width / length) of 0.3 to 0.9 as measured by direct particle measurement using a flow imaging microscope particle shape analyzer; (ii) coating the slurry on at least the porous channel walls of the first channels of the substrate, wherein the substrate has an average pore size (D50) of 6 μm to 15 μm before any coating and a porosity of less than 60% before any coating; as well as (iii) drying and calcining the slurry-coated substrate, Sufficient slurry is thereby applied to the substrate so that the product of step (iii) has a relative weight of 0.07 g / in 3 to 0.4g / in 3 (4.3 g / L to 24.4 g / L) of coating loading, wherein the average wall coating thickness of the product of step (iii) measured at an angle bisecting the apex angle on a scanning electron microscope cross-sectional image of the coated substrate is 5 μm to 70 μm.

2. The method according to claim 1, wherein step (ii) comprises the step of coating the porous channel walls of the second channel of the filter substrate with the slurry according to step (i), wherein the slurry used to coat the porous channel walls of the second channel has the same or different composition as the slurry coated on the porous channel walls of the first channel.

3. The method of claim 1 or 2, wherein the inorganic oxide particles or components of the mixture of inorganic oxide particles have a loose bulk density before grinding of 275 g / L to 850 g / L.

4. A method according to any one of the preceding claims, wherein the axially extending first channels of the wall flow filter substrate have a larger hydraulic diameter than the second channels.

5. A method according to claim 1, 2 or 3, wherein the axially extending first channels of the wall-flow filter substrate are a combination of channels having a larger hydraulic diameter and a smaller hydraulic diameter, and the hydraulic diameter of the second channels is larger than the first channels having the smaller hydraulic diameter.

6. A method according to any one of the preceding claims, wherein the wall coating is a wall catalyst coating and the slurry of step (i) comprises one or more non-rhodium platinum group metal salts, the concentration of the platinum group metal salt of the one or more non-rhodium platinum group metal salts being selected so that the product of step (iii) has a Pt content of 0.5 g / ft 3 Up to 10g / ft 3 (0.018 g / L to 0.353 g / L) of total platinum group metal loading.

7. The method according to any one of the preceding claims, wherein the filter substrate is a silicon carbide filter substrate having a porosity of 38% to 45% before coating.

8. The method of claim 7, wherein the coated filter substrate has a porosity percentage of less than 45.0%.

9. The method of claim 7 or 8, wherein the coated filter substrate has a density of at least 0.230 cm as measured by a combination of helium pycnometer and mercury density measurement. 3 / g total pore volume.

10. The method of any one of claims 1 to 6, wherein the filter substrate is a cordierite filter substrate having a porosity of 46% to 60% prior to coating.

11. A wall-coated ceramic honeycomb wall-flow filter substrate for treating exhaust gas containing particulate matter discharged from an internal combustion engine, the wall-flow filter substrate having a first end and a second end and a length L between the first end and the second end, and comprising a plurality of axially extending first and second channels, each of the first and second channels being partially defined by a porous channel wall having an axially extending porous channel wall surface, each first channel sharing a porous channel wall with an adjacent second channel, wherein in a scanning electron microscope image of a cross-section of the coated substrate, each channel has a geometric hollow cross-sectional shape having at least one vertex, the at least one vertex being partially defined by a vertex angle between two channel surface edges, wherein the first channel is capped at the second end of the substrate, and the second channel is capped at the first end of the substrate, wherein at least the channel wall surface loading of the first channel is 0.07 g / in relative to the weight of the substrate before coating. 3 to 0.4g / in 3 (4.3 g / L to 24.4 g / L) of a wall-type washcoat, the washcoat comprising inorganic oxide particles or a mixture of two or more inorganic oxide particles, wherein the average wall coating thickness measured at an angle bisecting the apex angle on the scanning electron microscope cross-sectional image of the coated substrate is 5 μm to 70 μm, wherein fragments of the wall-coated filter substrate have, as analyzed by mercury intrusion porosimetry, at least 15.0% of the pore volume having a diameter of 0.05 μm to 0.5 μm, expressed as a percentage of the mercury intrusion volume of the fragment, and wherein the wall washcoat coating comprises non-geometrically uniform voids having an equivalent spherical diameter D(v,0.5) of 0.1 μm to 8 μm and a modal aspect ratio (width / length) of 0.3 to 0.9 as determined by focused ion beam-scanning electron microscopy (FIB-SEM).

12. A ceramic honeycomb wall flow filter substrate carrying a wall coating, the ceramic honeycomb wall flow filter substrate being used for treating exhaust gas containing particulate matter discharged from an internal combustion engine, the ceramic honeycomb wall flow filter substrate being capable of being obtained by or through the method according to any one of claims 1 to 10.

13. An exhaust system for an internal combustion engine, comprising the ceramic honeycomb wall-flow filter substrate according to claim 11 or claim 12, wherein the first end portion of the substrate faces upstream.

14. An internal combustion engine comprising the exhaust system according to claim 13.

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