Catalytic particulate filter

Abstract

The present invention relates to a particulate filter, an exhaust gas system comprising same and the use of both to reduce noxious components in the exhaust gas of internal combustion engines. The particulate filter in the form of a wall flow filter unit has a specific permeability distribution of the filter walls along its axial direction.

Description

[0001] Catalytic particulate filter

[0002] Description

[0003] The present invention is directed to a particulate filter, an exhaust system comprising the same, and the use of both for reducing harmful components in the exhaust gases of internal combustion engines. The particulate filter, in the form of a wall-flow filter unit, has a specific permeability distribution of the filter walls along its axial orientation.

[0004] The exhaust gases from combustion engines in motor vehicles typically contain the harmful gases carbon monoxide (CO) and hydrocarbons (HC), nitrogen oxides (NO X ) and possibly sulfur oxides (SO X), as well as particulates, which consist largely of solid carbon-containing particles and possibly adhering organic agglomerates. These are referred to as primary emissions. CO, HC and particulates are products of the incomplete combustion of the fuel in the engine's combustion chamber. Nitrogen oxides are formed in the cylinder from nitrogen and oxygen in the intake air when combustion temperatures exceed 1200°C. Sulfur oxides result from the combustion of organic sulfur compounds, which are always present in small quantities in non-synthetic fuels. Compliance with the legal emission limits for motor vehicles that will apply in future in Europe, China, North America and India requires the extensive removal of these pollutants from the exhaust gas.To remove these environmentally and health-damaging emissions from motor vehicle exhaust gases, a variety of catalytic exhaust gas purification technologies have been developed. Their basic principle is typically based on passing the exhaust gas to be purified through a flow-through or wall-flow honeycomb structure coated with a catalytically active coating. The catalyst promotes the chemical reaction of various exhaust gas components, forming harmless products such as carbon dioxide, water, and nitrogen. Diesel particulate filters (DPF) or gasoline particulate filters (GPF) / gasoline particulate filters (OPF), with or without an additional catalytically active coating, are suitable units for removing particulate emissions.

[0005] The flow-through or wall-flow honeycomb bodies described above are also referred to as catalyst supports, carriers, substrates, monoliths, or substrate monoliths, as they carry the catalytically active coating on their surface or in the walls forming this surface. The catalytically active coating is often applied to the catalyst support in the form of a suspension in a so-called coating process. Many such processes have been published in the past by automotive exhaust catalyst manufacturers (EP1064094B1, EP2521618B1, WG10015573A2, EP1136462B1, US6478874B1, US4609563A, WO9947260A1, JP5378659B2, EP2415522A1, JP2014205108A2).

[0006] Exhaust gases from internal combustion engines that predominantly (>50% of operating time) operate with a stoichiometric air / fuel mixture, such as gasoline or natural gas-powered engines, are conventionally purified using three-way catalysts (TWO). These catalysts are capable of simultaneously converting the engine's three main gaseous pollutants, namely hydrocarbons, carbon monoxide, and nitrogen oxides, into harmless components. Stoichiometric means that, on average, exactly as much air is available for the combustion of the fuel present in the cylinder as is required for complete combustion. The combustion air / fuel ratio A (A / F ratio; air / fuel ratio) relates the air mass mi_,tats actually available for combustion to the stoichiometric air mass mi_,st:

[0007] If A < 1 (e.g., 0.9), this means a "lack of air," and the exhaust mixture is said to be rich. A > 1 (e.g., 1.1) means "excess air," and the exhaust mixture is referred to as lean. A = 1.1 means that 10% more air is present than required for stoichiometric reaction. The same applies to the exhaust gas from combustion engines.

[0008] The catalytically active materials used in known three-way catalysts are typically platinum group metals, particularly platinum, palladium, and rhodium, supported, for example, on y-aluminum oxide. Three-way catalysts also contain oxygen storage materials, such as cerium / zirconium mixed oxides. In the latter case, cerium oxide, a rare earth metal oxide, is the fundamental component for oxygen storage. In addition to zirconium oxide and cerium oxide, these materials can contain additional components such as other rare earth metal oxides or alkaline earth metal oxides. Oxygen storage materials are activated by applying catalytically active materials such as platinum group metals and thus also serve as support materials for the platinum group metals.

[0009] In order to comply with legal standards, it may be desirable for current and future applications for exhaust gas aftertreatment of internal combustion engines to combine particulate filters with catalytically active functionalities for cost reasons and also for installation space constraints. The use of a particulate filter – whether catalytically coated or not – leads to a noticeable increase in exhaust backpressure compared to a flow-through carrier of the same dimensions, and thus to a reduction in engine torque or possibly increased fuel consumption. To prevent an even further increase in exhaust backpressure, the quantities of oxide support materials for the catalytically active elements of the catalyst or oxide catalyst materials are generally applied in smaller quantities in a filter than in a flow-through carrier.There have already been some efforts to provide particulate filters that have good catalytic activity through an active coating and yet exhibit the lowest possible exhaust backpressure. With regard to low exhaust backpressure, it has proven advantageous if the catalytically active coating is not located as a layer on the channel walls of a porous wall-flow filter, but rather the channel walls of the filter are interspersed with the catalytically active material, see for example W02005016497A1, JPH01-151706 and EP1789190B1. For this purpose, the particle size of the catalytic coating is selected so that the particles penetrate the pores of the wall-flow filter and can be fixed there by calcination. The disadvantage of catalytically active filters with an in-wall coating is that the amount of catalytically active substance is limited by the absorption capacity of the porous wall.Further documents describing filter substrates provided with catalytically active coatings are EP3205388A1 , EP3207977A1 ​​, EP3207978A1 , EP3207987A1 , EP3207989A1 , EP3207990A1 and EP3162428A1.

[0010] It has been shown that applying catalytically active substances to the surface of the channel walls of a wall-flow honeycomb body can significantly increase the conversion of pollutants in the exhaust gas. Combinations of surface and in-wall coating with catalytically active material are also possible, which can further enhance catalytic performance without disproportionately increasing the back pressure (EP3501648A1). Combinations of pure in-wall coatings have also been described for wall-flow filters in the patent literature (EP3207989A1). EP2641651A1 attempts to ensure uniform permeability in the axial direction across the filter wall of the wall-flow filter. Uniform permeability is also sought in JP2016148285A2.

[0011] As just mentioned, in addition to catalytic activity, exhaust backpressure also plays a crucial role in the selection of a suitable filter for a car exhaust system. Further improvements are being sought in this area to meet this goal under current and future emissions legislation.

[0012] These and other tasks for the person skilled in the art are solved by a catalytically active particulate filter having the characterizing features of the present claim 1. Claims 2-9, which refer back to claim 1, focus on preferred embodiments of the particulate filter according to the invention. Claims 10 and 11 are directed to an exhaust system comprising the particulate filter according to the invention, and claims 12 and 13 are directed to corresponding uses.

[0013] By specifying a catalytically active particulate filter for purifying the exhaust gas of an internal combustion engine, comprising a wall-flow filter with a length L (total length) and the channels E and A, wherein the channels extend parallel between a first and a second end of the wall-flow filter, are separated by porous walls forming surfaces OE and OA, respectively, and wherein the channels E are closed at the second end and the channels A at the first end, wherein said filter has 3 or 5 zones along the axial length L such that i. in the case of 3 zones, a first zone at the first end of the wall-flow filter has a permeability P1, a second zone has a catalytically active component and has a permeability P2 adjacent to the first zone, and a third zone has a permeability P3 adjacent to the second zone at the second end of the wall-flow filter, wherein the following applies to the permeabilities:

[0014] P1, P3 > P2; or ii. in the case of 5 zones, the wall-flow filter comprises zones arranged in series with the permeabilities P1 to P5, wherein the second and fourth zones have a catalytically active component, and wherein the first zone is located at the first end of the wall-flow filter and the fifth zone is located at the second end of the wall-flow filter, and wherein the following applies:

[0015] By combining P1, P3, P5 > P2, P4, one surprisingly achieves a particulate filter that is superior to comparable filters of the prior art in terms of the interplay of exhaust backpressure and catalytic activity. This was by no means to be expected given the current state of the art.

[0016] In the present case, a wall-flow filter is claimed which has 3 or 5 definable zones along its axial direction. The first zone begins at the first end of the filter and extends a certain proportion of the total length L into the filter. This is followed by a second zone, which is different from the first zone and also runs a proportion of the length L in the axial direction within the filter. In a filter with 3 zones, there is a third, final zone which extends from the end of the second zone to the second end of the filter. At least the second zone has catalytic activity. If, on the other hand, the filter has 5 zones, the result is a corresponding picture for the filter as just sketched. Here, at least zones 2 and 4 each have catalytic activity. Reference is made in this regard to Figures 1, 2 and 3, which schematically show corresponding filters.

[0017] All conventional ceramic materials can be used as wall-flow filters. Porous wall-flow filter substrates made of cordierite, silicon carbide, or aluminum titanate are preferred. These wall-flow filter substrates have inflow and outflow channels, with the downstream ends of the inflow channels and the upstream ends of the outflow channels offset from each other and sealed with gas-tight "plugs." This forces the exhaust gas to be cleaned, which flows through the filter substrate, to pass through the porous wall between the inflow and outflow channels, resulting in an excellent particle filtration effect. The filtration properties for particles can be designed through the porosity, pore / radius distribution, and wall thickness. The porosity of wall-flow filters is typically more than 40%, generally from 40% to 75%, particularly from 45% to 70% [measured according to DIN 66133 - latest version on the date of application].The average pore size (diameter) is at least 3 pm, e.g., from 3 pm to 34 pm, preferably more than 5 pm, in particular from 5 pm to 28 pm or from 7 pm to 22 pm [measured according to DIN 66134, latest version on the filing date]. Permeability is the property of the flow-through area, which describes the backpressure when flowing through the wall as a function of the flow velocity according to Darcy's law (https: / / de. Wikipedia.orq / w / index.php?title=Darcy-Ge- setz&oldid=231809653). Permeabilities can be measured using methods familiar to the person skilled in the art. For example, the filter can be divided into 3 or 5 parts depending on the existing zones, and each zone can be examined for permeability. For this purpose, wall flow filters are manufactured from the 3 or 5 individual parts by means of appropriate channel closure and measured according to 1804022:2018 (latest version on the date of registration).

[0018] Simulations show that a distribution of the permeabilities along the filter axis according to the invention leads to a better utilization of the catalytic properties of the filter and, moreover, results in a more optimal design of the exhaust back pressure (Figs. 4 and 5).

[0019] The permeabilities for the individual zones are usually between T10' 17 m 2 - 1 '10' 10 m 2 , preferably 1 '10' 16 m 2 - 5 10' 11 m 2 In a preferred embodiment, the permeabilities are as follows:

[0020] P1 > P3 or P1, P3 > P2, P5, respectively, for a filter with 3 or 5 zones. This allows the mass flow distribution of the exhaust gas in the inlet and outlet channels to be adjusted so that the distribution of the total exhaust gas mass flow between the inlet and outlet channels ideally corresponds to 50% in the inlet channel and 50% in the outlet channel. The proportions of the mass flows in the inlet and outlet channels depend on the size of the exhaust gas mass flow, the temperature, and the permeabilities or the ratio of the permeabilities in the individual zones.

[0021] Preferred permeability ratios can be found in the following Table 1: Table 1

[0022] *: the commas here represent a logical “or”

[0023] In the filters according to the invention, the zones with the permeabilities P1, P3, P5 preferably have values ​​between T10' 15 m 2 - T10' 1 ° m 2, more preferably T10' 14 m 2 - 1 -10” 11 m 2 . The zones with permeability P2, P4 have preferred values ​​of T10' 17 m 2 - 10- 12 m 2 , more preferably between T10' 16 m 2 - 10' 13 m 2 Both the permeability ratio and the absolute value of the permeabilities determine the back pressure and the mass flow distribution of the exhaust gas in the filter. The absolute value of the permeabilities primarily influences the back pressure, while the permeability ratio primarily influences the mass flow distribution in the inlet and outlet channels.

[0024] The filter according to the invention has zones equipped with catalytic activity. These are zones 2 and possibly 4 (if there are 5 zones in the filter). The catalytic activity can be freely selected by the person skilled in the art, as it is a physical phenomenon and not a chemical one. Due to the higher permeability of the first and last zones in the filter, the exhaust gas, as mentioned above, flows preferentially through these areas and along the catalytically active zones. This results in a longer residence time of the gas in the filter and thus in the catalytically active areas. This achieves better utilization of the catalytically active mass, as the probability of collision of the gas molecules with the catalytically active mass is increased.

[0025] Figure 4 shows, by way of example, the mass flow in the inlet channel as a function of the filter length for a coated filter described in the prior art (solid line) and a coated filter with the design claimed here (dashed line) according to Figure 2. In the presence of a zone of reduced permeability on the inlet and outlet sides, the exhaust gas mass flow in the inlet channel is reduced to a value of approximately 60% in the first third of the filter, with 40% flowing through the porous wall into the outlet channel. In comparison, the solid line shows that almost the entire mass flow in the first third of the filter flows through the porous wall into the outlet channel. The greater the proportion of the exhaust gas mass flow in the inlet or outlet channel, the shorter the residence time of the exhaust gas in the filter.A maximum residence time in the filter would be achieved if 50% of the exhaust gas mass flow would flow through the filter in both the inlet and outlet channels.

[0026] The catalytically active mass (washcoat) can be applied to the filter using methods familiar to those skilled in the art. The washcoat can be located on the wall, in and on the wall, or only on the wall of the channels of the wall-flow filter. On the wall means that >80%, more preferably >90% of the mass of the washcoat is present above the wall of the wall-flow filter channel. In the wall means that >80%, more preferably >90% of the washcoat is present within the wall. It is particularly preferred that the catalytically active component is located in the porous wall of the wall-flow filter. Alternatively, it is particularly preferred that the catalytically active component is located on the porous channel wall of the wall-flow filter. An applied coating is particularly preferred in this context.

[0027] The proportion of the catalytically active component in or on the wall can be evaluated using computer-assisted image analysis based on SEM images of microsections of the coated walls (DE102018111246A1). Corresponding microsections of an inlet and outlet channel were created. In this type of analysis, the average color of the wall surface of the channel without a coating is determined as a reference. This reference is subtracted from the corresponding image of the coated areas. The color difference was determined according to CIE76 of the International Commission on Illumination with a smallest distinguishable color difference of 2.33 (https: / / en.wikipedia.org / wiki / Color difference#CIE76). This makes it possible to determine how much of the washcoat is in or on the wall of the wall-flow filter.

[0028] The catalytic activity of the catalytically active zones is not important for the effect described here. All catalytic activities used by the person skilled in the art in the automotive exhaust gas sector can be used. These are, in particular, those selected from the group consisting of three-way activity, SCR activity, NOx storage catalyst, HC trap, ammonia barrier catalyst. Literature describing the catalytic activities mentioned here is known to the person skilled in the art (EP4079399A1, EP4204143A1, EP4072708A1, EP3794221A1, EP3826754A1, EP4126348A1 and the literature cited therein). If the wall-flow filter according to the invention has five zones, it can be provided that the second and fourth zones of the wall-flow filter exhibit different catalytic activities. In this way, suitable different activities can be combined in one filter unit, e.g.a three-way activity and an SCR activity or an ammonia-blocking catalyst activity. Alternatively, combinations of SCR activity and ammonia-blocking catalyst activity can be created. Different catalytic activities can also be found in the inlet and outlet channels of the wall-flow filter (see Fig. 3).

[0029] A wide variety of catalyst materials are known from the prior art, for example, zeolites with Cu, Fe, V, W, Ce, Sb, Nb, Zr, Mo, Al, Pd can be used for SCR catalysts, as for example from the publications WO 2008 / 132452 A2, WO 2019 / 096785 A1 , WO 2019 / 096786 A1 , WO 2022 / 058404 A1 , WO 2020 / 043662 A1 , WO 2015 / 075083 A1 , WO 2019 / 072527 A1 , WO 2019 / 072527 A1 , WO 2019 / 219629 A1 , WO 2020 / 039074 A1 , WO 2018 / 189177 A1 , WO 2017 / 134001 A1 , WO 2017 / 134005 A1 , WO 2017 / 134006 A1 , WO 2017 / 134007 A1 , WO 2013 / 159825 A1 , WO 2017 / 178576 A1 , WO 2018 / 054928 A1 , WO 2018 / 029330 A1 and WO 2022 / 128523 A1.

[0030] Catalyst materials used for TWC catalysts are known, for example, from WO2022223688A1, WO2021151876A1, WO2021140326A1, W02008000449A2, WO2008113445A1 and W02008113457A1. The person skilled in the art knows which one he would use for the present purpose (see, for example, also WO2019121994A1, WO2019121995A1, WO9535152A1, W02008000449A2, EP0885650A2,

[0031] EP1046423A2, EP1726359A1 , EP1541220A1 , EP1900416B1 , EP3045226A1 , W02009012348A1 and EP1974809B1).

[0032] It should be noted that it is within the scope of the invention for the first or last, or any third, zone with increased permeability to also provide catalytic activity as mentioned above. However, the permeability of these zones must meet the criteria mentioned above. In particular, the permeability of the first, third, and fifth zones is higher than that of the second and fourth zones. The described preferred embodiments also apply here accordingly.

[0033] In general, the person skilled in the art can determine the length of the respective zones. However, it is advantageous if the individual zones with increased permeability of the wall-flow filter are no longer than 50% of the length L. It is particularly advantageous if the length of the first zone is 5%-40%, more preferably 10%-20% of the length L. Likewise, the length of the last zone can preferably be 5%-40%, more preferably 5%-15% of the length L. In a wall-flow filter according to the invention, it is particularly preferred if the first and last zones are smaller relative to the other zone(s) in order to accommodate sufficient catalytic activity on the filter. The length of the catalytically active zone(s) should preferably be 60%-95%, more preferably 60%-80% of the length L. A filter with the following zone profiles is very particularly preferred (Table 2):

[0034] Table 2:

[0035] The ratios of the zone lengths should be designed such that the ratio of the lengths of zones 1, 3 and 5 to the lengths of zones 2 and 4 is between 0.05 - 0.5, more preferably 0.1 - 0.4 and most preferably 0.15 - 0.3.

[0036] As already indicated above, the present invention relates to a wall-flow filter with 3 or 5 zones. There is a first zone and a last zone along the longitudinal axis of the wall-flow filter. In a preferred embodiment, the amount of exhaust gas flowing through the porous wall of the first zone is equal to the amount of exhaust gas flowing through the porous wall of the last zone. With 5 zones, more exhaust gas flows through the middle zone than through the second and fourth zones, which carry catalytic activity here. Such a configuration of the zones is particularly useful when exhaust gas backpressure is a problem. By adding an additional middle zone (in this case the third zone), the exhaust gas backpressure can be further reduced due to the resulting increased permeability. This ensures better adaptation to the desired results with regard to the catalytic conversion or the backpressure to be set.

[0037] In a further aspect, the present invention relates to an exhaust system comprising a particulate filter according to the invention and at least one additional automotive exhaust catalyst connected to the filter upstream and / or downstream. The preferred and alternative embodiments of the wall-flow filter according to the invention also apply here mutatis mutandis.

[0038] The additional automotive exhaust catalyst can be selected by a person skilled in the art. It will be based on the catalytic activities mentioned above. The additional automotive exhaust catalyst is preferably accommodated on a flow-through substrate. Flow-through substrates are catalyst elements commonly used in the art and can consist of metal or glass fiber reinforced paper (corrugated carrier, e.g. WO17153239A1, WO16057285A1, WO15121910A1 and literature cited therein) or ceramic materials. Refractory ceramics such as cordierite, silicon carbide or aluminum titanate, etc., are preferably used. The number of channels per area is characterized by the cell density, which is usually between 300 and 900 cells per square inch (cpsi). The wall thickness of the channel walls for ceramics is between 0.5 and 0.05 mm.

[0039] In a preferred embodiment, the exhaust system has an additional automotive exhaust catalyst, which is a three-way catalyst. Three-way catalysts essentially consist of the components precious metal, a high-surface-area carrier oxide, and an oxygen storage material. The catalytically active components are usually platinum group metals, such as Pt, Pd, and Rh, with Pd and Rh being particularly preferred. The catalytically active metals are often deposited in highly dispersed form on the high-surface-area oxides and the oxygen storage materials. It is particularly preferred if the precious metals are pre-fixed to the oxygen storage material before it is mixed with the other components in the coating mixture. Zoned or layered designs are now the norm for TWCs.In a preferred embodiment, at least one TWC in the exhaust system comprising the catalyst element modified according to the invention has a 2-layer structure with two different three-way coatings, preferably as described in EP3247493A1.

[0040] The oxygen storage materials are particularly those containing cerium / zirconium / rare earth metal mixed oxides. Examples of rare earth metal oxides that come into consideration are lanthanum oxide, yttrium oxide, praseodymium oxide, neodymium oxide, samarium oxide, and mixtures of one or more of these metal oxides. Lanthanum oxide, yttrium oxide, neodymium oxide, and mixtures of one or more of these metal oxides are preferred. Lanthanum oxide, yttrium oxide, and a mixture of lanthanum oxide and yttrium oxide are particularly preferred in this context.

[0041] As support oxides for catalytically active metals, those skilled in the art prefer high-surface-area, temperature-stable oxides. These are generally aluminum oxides, silicon oxides, zirconium oxides, or titanium oxides, or mixtures thereof. Active aluminum oxide, in particular, is known to those skilled in the art in this context. It refers in particular to γ-aluminum oxide with a surface area of ​​100 to 200 m². 2 / g. Active alumina is widely described in the literature and is commercially available. It typically contains silicon oxide or lanthanum oxide as a stabilizer in an amount of up to 10 wt.% based on the alumina.

[0042] The three-way catalytic converter is preferably located upstream of the particulate filter in a position close to the engine. "Close to the engine," as used herein, refers to an area in the exhaust system that is close to the engine, i.e., approximately 10-80 cm, preferably 20-60 cm, from the engine outlet.

[0043] In a further aspect, the present invention relates to the use of a particulate filter according to the invention in a method for treating exhaust gases from an internal combustion engine. The preferred and alternative embodiments of the wall-flow filter according to the invention and the system also apply here mutatis mutandis. All engines known to those skilled in the art are suitable as internal combustion engines. In particular, these are diesel or gasoline engines. Diesel engines are operated with a predominantly lean fuel mixture, while gasoline engines are operated with a predominantly stoichiometric fuel mixture. Exhaust gases from internal combustion engines operated with a predominantly (>50% of operating time) stoichiometric air / fuel mixture, for example, gasoline or natural gas-powered gasoline engines, are purified in conventional methods using three-way catalysts (TWC).These are capable of simultaneously converting the engine's three main gaseous pollutants—hydrocarbons, carbon monoxide, and nitrogen oxides—into harmless components. Stoichiometric means that, on average, exactly as much air is available to combust the fuel present in the cylinder as is required for complete combustion. The combustion air / fuel ratio (A / F ratio) relates the air mass mi_,tats actually available for combustion to the stoichiometric air mass mi_,st:.

[0044] If A < 1 (e.g. 0.9) this means "lack of air" and the exhaust gas mixture is rich, A > 1 (e.g. 1.1) means "excess air" and the exhaust gas mixture is referred to as lean. The statement A = 1.1 means that 10% more air is present than would be necessary for a stoichiometric reaction. The same applies to the exhaust gas from internal combustion engines. Diesel engines, on the other hand, are operated with a predominantly (> 50% of the operating time) lean exhaust gas. In a preferred embodiment, however, the internal combustion engine in question is one that is operated predominantly with a stoichiometric fuel mixture.

[0045] The production of the wall-flow filters according to the invention with 3 zones can comprise the following production steps: i) contacting both ends of the wall-flow filter with a hydrophobizing agent to form a hydrophobized first and third zone; ii) optionally drying the wall-flow filter; iii) coating the wall-flow filter with an aqueous coating suspension (washcoat) comprising a catalytically active component to form the second zone from both sides (in the case of surface coatings) or only from one side (in the case of in-wall coatings); iv) optionally drying and calcining the coated wall-flow filter. v) optionally after a first calcination, coating with an aqueous coating suspension or a powder to adjust the permeability P1 or P3.

[0046] In a first step, the wall-flow filter is contacted with a liquid hydrophobic agent at one end. The other end of the wall-flow filter can then be treated accordingly (optional).

[0047] The hydrophobic masking zone can be applied in a variety of ways. One approach involves using a wax or a viscous oil (e.g., a fatty acid) with a melting point just above room temperature, which has a lower viscosity upon melting. This allows the molten wax to be introduced into the wall-flow filter using, for example, a piston coater (e.g., WÖ2011098450A1) to create channels with a residual layer of wax or viscous oil on the channel surface. The zone length can be precisely controlled by the length of the piston stroke. Various types of wax can be used, such as paraffin wax, which can be obtained from petroleum, coal, or oil shale. Other types of waxes or viscous oils can be synthesized by ethylene polymerization or propylene polymerization.Waxes or viscous oils typically consist of a range of hydrocarbons with a carbon number of 20 to 70 carbon atoms, with alkane components predominating. However, they can also contain a variety of functional groups such as fatty acids, primary and secondary long-chain alcohols, unsaturated bonds, aromatics, amides, ketones, and fatty acid esters. The melting temperature of waxes can be controlled by the carbon number in the chains or by controlling branching, as well as by the presence of the aforementioned functional groups.

[0048] Typically, a wax that melts just above room temperature is required, preferably in the range of 30-80°C, such as paraffin wax, which melts at about 37°C (99°F) and preferably has a boiling / decomposition point between 300°C and 400°C. Paraffin wax, for example, decomposes / boils at 370°C. Other waxes or oils include naturally derived products such as coconut oil, cocoa butter, or others with the appropriate viscosity and melting temperature.

[0049] An alternative approach is to use a high-solids wax emulsion. This approach eliminates the need to heat the wax or oil to achieve the correct viscosity and flowability. After applying the emulsion, the part can be briefly heated to melt the wax and distribute it over the channel surface, thus forming a continuous hydrophobic layer over the support substrate. Waxes and wax emulsions that can be used in the process of the invention are known to those skilled in the art and are commercially available.

[0050] Next, an optional drying step can be performed. This is necessary in cases where the hydrophobizing agent is dissolved in a solution, e.g., in a low-boiling organic solvent or in water. To remove the solvent and allow the hydrophobizing agent to act in the hydrophobized zone, the required temperature should be set. The temperature is usually in the range of 30–150°C, but preferably 40–130°C. However, a solvent may not be required for all hydrophobizing agents. Some solidify at room temperature and liquefy slightly above room temperature. These hydrophobizing agents are particularly preferred. The above-mentioned temperature range of 30–80°C is also an advantageous range in this regard.

[0051] The particulate filter according to the invention can then be coated using methods known to those skilled in the art to form a coating on the area that is not hydrophobicized, e.g., by applying a coating suspension, commonly referred to as a washcoat or slurry, using one of the conventional dip-coating or pump and suction coating processes. The term "coating" refers to the application of catalytically active materials to a wall-flow filter substrate. Many such processes have been published in the past by automotive exhaust catalyst manufacturers (EP1064094B1, EP2521618B1, WO10015573A2, EP1136462B1, US6478874B1, US4609563A, WO9947260A1, JP5378659B2, EP2415522A1, JP2014205108A2). The coating takes over the actual catalytic function.In this case, the coating is carried out by applying a preferably aqueous suspension of the catalytically active components in and / or onto the wall of the wall-flow filter substrate, for example, according to EP1789190B1 or US11161098BB. The most suitable loading amount of a wall-coated filter depends on its cell density, wall thickness, and porosity.

[0052] This generates a second zone, which then contains catalytically active material. In a preferred process, step iii) requires positioning the wall-flow filter vertically and applying the coating suspension to the filter via the hydrophobic zone. In a highly preferred embodiment, a coating is produced in the second zone of the filter according to the invention using a process as described in DE202022000455U1.

[0053] In a further step (iv), the masking zone must be removed again. This can be achieved by thermal post-treatment and / or calcination. This converts the washcoat in the second zone into the catalytically active form and fixes it on the filter. Simultaneously, the hydrophobic components burn out, leaving the filter in this zone uncoated. The temperatures used are typically between 400°C and 600°C. These are the calcination temperatures normally used to calcine a washcoat after coating. Those skilled in the art will know which temperatures to use. Alternatively, the hydrophobizing agent can be removed, for example, by dissolution, e.g., when fatty acids are used as the hydrophobizing agent. These can be dissolved in water in an alkaline medium.

[0054] Optionally, in a further step (v), the coating-free area can then be coated with another coating suspension, different from that in step iii), to adjust the desired permeability if necessary. Alternatively, the permeability can also be adjusted by powder coating, for example, according to the process described in DE102018108346A. The properties of the powder and the powder loading determine the permeability in the corresponding zone.

[0055] The production of a wall-flow filter according to the invention with 5 zones is carried out by performing the above-mentioned steps with corresponding zone length coating twice in succession for each side of the filter. Step (v), however, is preferably carried out only from one end. It should be noted that for 3-zone filters or for purely in-wall coatings, it may be sufficient to hydrophobize and coat only one side. For a 5-zone filter, however, hydrophobization must be carried out twice. A hydrophobic zone must be applied to both ends. The following variations are possible:

[0056] Hydrophobization of the first zone of the filter followed by a suspension coating, followed by drying and calcination; then hydrophobization of the second zone on the other side of the filter followed by another suspension coating on the second side of the filter, followed by drying and calcination. A zone in the center of the filter remains uncoated.

[0057] • Hydrophobicization of the first zone followed by hydrophobicization of the second zone at the other end of the filter, followed by a first suspension coating, followed by a second suspension coating, followed by drying and calcination. A zone in the center of the filter remains uncoated.

[0058] • Hydrophobization of the first zone followed by hydrophobization of the second zone at the other end of the filter, followed by a first suspension coating, followed by drying and calcining the first suspension coating, followed by a second suspension coating, followed by drying and calcining. A zone in the center of the filter remains uncoated.

[0059] In the above description, hydrophobization means the application of the hydrophobizing agent and, if necessary, a drying step for the hydrophobizing agent.

[0060] The present coating design according to the invention enables better utilization of the catalytically active substances on the wall-flow filter while simultaneously optimizing exhaust backpressure. The invention consists, in particular, in designing a filter with two or three zones of lower flow resistance and one or two central zones of higher flow resistance (Figures 1-3). This design allows the exhaust gas flow through the filter to be influenced such that a certain portion of the exhaust gas flows into the outlet channel at the filter inlet. Advantageously, a filter with three zones divides the exhaust gas mass flow into 50% in the inlet and 50% in the outlet channel.

[0061] A particularly advantageous design has the longest possible coated zone in the middle for catalytic performance. The first zone has a lower flow resistance per area than the last zone. This can be achieved by making the area and thus the zone length larger at the inlet than at the outlet and / or by making the flow resistance lower at the inlet than at the outlet, e.g., by applying an additional coating. Another possible design has a further gap in the area of ​​the catalytically active zone. This then enables an optimized design with, if necessary, two different washcoat compositions in zones 2 and 4, both as an overlay and / or in-wall coating (Fig. 3). Such designs were not previously suggested by the known state of the art.

[0062] Figures:

[0063] Figure 1 and Figure 2 show a particle filter according to the invention, each with 3 zones, which comprises a wall-flow filter of length L (1) with channels E (2) and channels A (3) which extend parallel between a first end (4) and a second end (5) of the wall-flow filter and which are separated by porous walls (6) which form surfaces OE (7) and OA (8), respectively, and in which the channels E (2) are closed at the second end (5) and the channels A (3) are closed at the first end (4). Coating (9) is located in the channels (2) on or in the surfaces OE (7) and coating (10) is located in the channels (3) on or in the surfaces OA (8). Figure 1 shows an applied coating. Figure 2 shows an in-wall coating.

[0064] Figure 3 shows a particulate filter according to the invention with 5 zones with in-wall coatings, which comprises a wall-flow filter of length L (1) with channels E (2) and channels A (3) which extend parallel between a first end (4) and a second end (5) of the wall-flow filter and which are separated by porous walls (6) which form surfaces OE (7) and OA (8), respectively, and in which the channels E (2) are closed at the second end (5) and the channels A (3) are closed at the first end (4). Coating (9) is located in 2 zones in the channels (2) in the surfaces OE (7) and coating (10) is located in 2 zones in the channels (3) in the surfaces OA (8). The main flow of the exhaust gas through the wall-flow filter is shown in each case. The coatings on the inlet side and outlet side can be different or the same. At the same time, the front coating can be different from the back coating, so that up to 4 different coatings can be placed on the filter.

[0065] Figure 4 shows the relative exhaust gas mass flow in the filter's inlet channel obtained from numerical calculations (normalized to 100% at the inlet). The solid line correlates to a known coating design in which 80% of the channel length from the outlet side is coated, resulting in a lower wall permeability. Due to the reduced permeability in the rear 80% of the channel, the exhaust gas mainly passes through the wall from the inlet to the outlet channel in the first 20%. The dashed line shows the relative exhaust gas mass flow of a filter according to the invention in which the first and last 10% have no coating. Within the first 10% of the channel length, approximately 40% of the exhaust gas mass flow flows through the wall into the outlet channel. The new design (dash-dotted line) leads to a 30% reduction in back pressure and a 10% increase in the filter residence time.The residence time used is the smaller of the two residence times in the inlet or outlet channel.

[0066] Figure 5 shows the relative exhaust flow rates of different filter designs. The solid line again corresponds to a state-of-the-art design, in which the first 20% of the filter length has no coating and the remainder is coated.

[0067] Figure 6 shows the back pressures and residence times of various filter designs. The filter designs correspond to the mass flow distributions in Figure 5, which were obtained from numerical simulations. All values ​​are normalized to 100% of a design described in the state of the art. A filter with a coating in the outlet channel and a coating length of 80%, as seen from the outlet side of the filter, was chosen as the state-of-the-art comparison design (Figure 7).

[0068] For filters that have a zone of lower permeability (coating-free zone) at both the filter inlet and outlet, the back pressure is significantly reduced. The mass flow distributions in the filter inlet and outlet channels, adjusted by the selected permeabilities, lead to a change in the residence time. The residence time is defined as the minimum residence time in the inlet or outlet channel based on the prevailing mass flow distributions. The designs described here lead to an increase in residence time compared to the filter designs described in the prior art.

[0069] Figure 7 shows a prior art two-zone particulate filter comprising a wall-flow filter of length L (1) with channels E (2) and channels A (3) extending parallel between a first end (4) and a second end (5) of the wall-flow filter and separated by porous walls (6) forming surfaces OE (7) and OA (8), respectively. Channels E (2) are closed at the second end (5) and channels A (3) are closed at the first end (4). Coating (9) is located in channels (3) on surfaces OA (8). Figure 7 shows a coating applied to the wall-flow filter. Experimental section:

[0070] The mass flow distributions of various filter designs (see Fig. 1, Fig. 2, Fig. 3) were investigated using computational fluid dynamics (CFD) simulations. For this purpose, a model of the computational domain was first created. A symmetrical section of the filter was chosen as the computational domain in order to represent the inlet and outlet channels of a filter as well as the porous wall and any catalytically active layer located on it. In the computational domain, different flow properties (permeabilities) were specified for the different regions (filter wall or catalytically coated filter wall). Furthermore, the length and position of the catalytically coated region were varied. The simulations were carried out with Ansys Fluent® (https: / / www.ansys.com / de-de / products / fluids / ansys-fluent).

[0071] Numerically, the Navier-Stokes equation was solved using the finite volume method. The gas density was calculated using the ideal gas law, and the viscosity was used as a function of temperature. The exhaust gas mass flow and temperature were specified as boundary conditions. The following temperatures and mass flows were investigated.

[0072] Table 1 :

[0073] Permeabilities were measured in the range of 0 m 2 up to 3.6-10' 12 m 2 used.

[0074] Figures 4 and 5 show the relative exhaust gas mass flow rates in the inlet channel of a filter as a function of the axial filter length for different designs and different conditions. The value 0 is the inlet side of the filter, and the outlet side of the filter is located at the value 0.153. In Figure 4, the solid horizontal line corresponds to a known coating design in which no catalytic coating is present on the first 20% of the porous wall. The catalytic coating begins after 20% of the axial length and is continuous until the end of the filter on the outlet side. The simulations show that 90% of the exhaust gas mass flow flows through the filter wall into the outlet channel, where no catalytic coating is present. In contrast, the distribution of the exhaust gas mass flow is shown for a design in which both the first 10% and last 10% of the porous wall have no catalytic coating (dash-dotted line).Here it is clearly visible that in the first 10% of the filter approximately 40% of the exhaust gas mass flow flows into the outlet channel and in the last 10% 60% of the exhaust gas mass flow flows into the outlet channel. This has the effect that the calculated back pressure (BP) is 29% lower than with a state-of-the-art design. Secondly, the more even distribution of the exhaust gas mass flow in the inlet and outlet channels increases the effective residence time. The residence time in the filter depends on the effective flow velocity in the channels. This is directly proportional to the mass flow in the respective channels (inlet or outlet channel). The higher the mass flow, the shorter the residence time. An optimal residence time in the filter is achieved when 50% of the exhaust gas mass flow in the inlet and outlet channels flows in the area of ​​the catalytic coating.

[0075] Figure 5 shows the exhaust gas mass flow distributions for additional coating designs corresponding to Figures 1, 2, and 3. The flow resistances of the porous wall are selected so that approximately 50% of the exhaust gas mass flow is located in the inlet and outlet channels. For comparison, Figure 5 also shows a prior art design (Figure 7) (solid line).

[0076] The mass flow distribution in the individual filter channels depends on the flow resistance in the individual zones. This is determined by the length and permeability of the zone. In the examples shown, the permeabilities for a 3-zone filter are:

[0077] • P1=P3 > P2

[0078] And for a 5 zone filter:

[0079] P1=P3=P5>P2,P5

[0080] The results are summarized in Figure 6.

Claims

AMENDED CLAIMS received by the International Bureau on 03 March 2025 (03.03.2025) 1. A catalytically active particulate filter for purifying the exhaust gas of an internal combustion engine, comprising a wall-flow filter with a length L and channels E and A, wherein the channels extend parallel between a first and a second end of the wall-flow filter, are separated by porous walls forming surfaces OE and OA, respectively, and wherein the channels E are closed at the second end and the channels A are closed at the first end, wherein the filter has 3 or 5 zones along the axial length L such that i. in the case of 3 zones, a first zone at the first end of the wall-flow filter has a permeability P1, a second zone has a catalytically active component and has a permeability P2 adjacent to the first zone, and a third zone has a permeability P3 adjacent to the second zone at the second end of the wall-flow filter, wherein the following applies to the permeabilities: P1, P3 > P2; or ii. in the case of 5 zones, the wall-flow filter comprises zones arranged in series with the permeabilities P1 to P5, wherein the second and fourth zones have a catalytically active component, and wherein the first zone is located at the first end of the wall-flow filter and the fifth zone is located at the second end of the wall-flow filter, and wherein the following applies: P1, P3, P5 > P2, P4 characterized in that the length of the catalytically active zone(s) is 60% - 90% of the length L.

2. Particle filter according to claim 1, characterized in that the following applies to the permeabilities: P1 > P3 or P1 , P3 > P5.

3. Particle filter according to claim 1 or 2, characterized in that the catalytically active component is located in the porous wall of the wall-flow filter. AMENDED SHEET (ARTICLE 19) 4. Particle filter according to claim 1 or 2, characterized in that the catalytically active component is located on the porous wall of the wall-flow filter.

5. Particle filter according to claims 1 - 4, characterized in that the wall flow filter has 5 zones and the second and fourth zones exhibit different catalytic activities.

6. Particle filter according to claims 1 - 5, characterized in that the length of the first zone is 5% - 40% of the length L.

7. Particle filter according to claims 1 - 6, characterized in that the length of the last zone is 5% - 40% of the length L.

8. Particle filter according to claims 1 - 7, characterized in that the amount of exhaust gas flowing through the porous wall of the first zone corresponds to the amount of exhaust gas flowing through the porous wall of the last zone.

9. Exhaust system comprising a particulate filter according to claims 1-8 and at least one further car exhaust catalyst connected thereto upstream and / or downstream.

10. Exhaust system according to claim 9, characterized in that the car exhaust catalyst is a three-way catalyst.

11. Use of a particulate filter of claims 1-8 or an exhaust system of claims 9 or 10 in a method for treating exhaust gases of an internal combustion engine.

12. Use according to claim 11, characterized in that AMENDED SHEET (ARTICLE 19) the internal combustion engine is an engine that predominantly runs on a stoichiometric fuel mixture. AMENDED SHEET (ARTICLE 19)

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