DE102022002854A1 - Catalytically active particle filter with high filtration efficiency and oxidation function - Google Patents

Abstract

The present invention is directed to a wall flow filter and a corresponding system which has the wall flow filter according to the invention. A method for reducing exhaust gases is also the subject of this invention.

Description

The present invention is directed to a wall flow filter and a corresponding system which has the wall flow filter according to the invention. A method for reducing exhaust gases is also the subject of this invention.

The exhaust gas from internal combustion engines in motor vehicles typically contains the harmful gases carbon monoxide (CO) and hydrocarbons (HC), nitrogen oxides (NO _x ) and possibly sulfur oxides (SO _x ), as well as particles which largely consist of solid carbon-containing particles and possibly adhering organic agglomerates. These are called primary emissions. CO, HC and particulate matter are products of incomplete combustion of 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 contained in small quantities in non-synthetic fuels. Compliance with future legal exhaust emission limits for motor vehicles in Europe, China, North America and India will require the extensive removal of the pollutants mentioned from the exhaust gas. In order to remove these emissions that are harmful to the environment and health from the exhaust gases of motor vehicles, a large number of catalytic exhaust gas purification technologies have been developed, the basic principle of which is usually based on the fact that the exhaust gas to be cleaned is passed through a flow-through or a wall-flow ) honeycomb body with a catalytically active coating applied to it. The catalyst promotes the chemical reaction of various exhaust gas components to form harmless products such as carbon dioxide, water and nitrogen. Diesel particulate filters (DPF) or gasoline particulate filters (GPF)/gasoline particulate filters (OPF) with and without an additional catalytically active coating are suitable units for removing particulate emissions.

The flow-through or wall-flow honeycomb bodies just described are also referred to as catalyst supports, carriers, substrates 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 by car exhaust catalyst manufacturers in the past ( EP1064094B1 , EP2521618B1 , WO10015573A2 , EP1136462B1 , US6478874B1 , US4609563A , WO9947260A1 , JP5378659B2 , EP2415522A1 , JP2014205108A2 ).

Ist λ < 1 (z. B. 0,9) bedeutet dies „Luftmangel“, man spricht von einem fetten Abgasgemisch, λ > 1 (z. B. 1,1) bedeutet „Luftüberschuss“ und das Abgasgemisch wird als mager bezeichnet. Die Aussage λ = 1,1 bedeutet, dass 10% mehr Luft vorhanden ist, als zur stöchiometrischen Reaktion notwendig wäre. Gleiches gilt für das Abgas von Verbrennungsmotoren.Exhaust gases from internal combustion engines operated predominantly (>50% of the operating time) with a stoichiometric air/fuel mixture, i.e. e.g. B. gasoline engines powered by gasoline or natural gas are cleaned in conventional processes using three-way catalysts (TWC). These are able to simultaneously convert the engine's three main gaseous pollutants, namely hydrocarbons, carbon monoxide and nitrogen oxides, into harmless components. Stoichiometric means that on average there is as much air available to burn the fuel in the cylinder as is needed for complete combustion. The combustion air ratio λ (A/F ratio; air/fuel ratio) relates the air mass m _L,tats actually available for combustion to the stoichiometric air mass m _L,st : $$\mathrm{\lambda }=\frac{{\text{m}}_{\text{L}\text{,actually}}}{{\text{m}}_{\text{L}\text{,st}}}$$

If λ < 1 (e.g. 0.9) this means "lack of air", one speaks of a rich exhaust gas mixture, λ > 1 (e.g. 1.1) means "excess air" and the exhaust gas mixture is referred to as lean. The statement λ = 1.1 means that 10% more air is present than would be necessary for the stoichiometric reaction. The same applies to the exhaust gases from internal combustion engines.

The catalytically active materials used in the known three-way catalysts are generally platinum group metals, in particular platinum, palladium and rhodium, which are present, for example, on γ-aluminum oxide as a support material. In addition, three-way catalysts contain oxygen storage materials, for example cerium/zirconium mixed oxides. In the latter, 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 a carrier material for the platinum group metals.

In order to meet legal standards, it may be desirable to combine particle filters with catalytically active functionalities for current and future applications for exhaust aftertreatment of internal combustion engines for reasons of cost but also for reasons of installation space. The use of a particulate filter - whether catalytically coated or not - leads to a noticeable increase in exhaust backpressure compared to a flow carrier of the same dimensions and thus to a reduction in engine torque or possibly increased fuel consumption. In order not to further increase the exhaust gas back pressure, the amounts of oxidic support materials for the catalytically active elements of the catalyst or oxidic catalyst materials are generally applied in smaller quantities to a filter than to a flow support. There have already been some efforts to provide particulate filters that have good catalytic activity through an active coating and yet show the lowest possible exhaust gas back pressure. With regard to low exhaust gas back pressure, it has proven to be 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 WO2005016497A1 , JPH01-151706 and EP1789190B1 . For this purpose, the particle size of the catalytic coating is selected so that the particles penetrate into the pores of the wall flow filters 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.

It has been shown that by applying the catalytically active substances to the surfaces of the channel walls of a wall flow honeycomb body, an increase in the conversion of pollutants in the exhaust gas can be achieved. Combinations of surface and in-wall coating with catalytically active material are also possible, which can further increase the catalytic performance without significantly increasing the dynamic pressure EP3501648 A1

In addition to the catalytic effectiveness, another functionality of the filter that can be improved by a coating is its filtration efficiency, i.e. the filter effect itself WO2011151711A1 describes a method with which a non-coated or catalytically coated filter that carries the catalytic active material in the channel walls (in-wall coating with washcoat) is exposed to a dry aerosol. The aerosol is provided by the distribution of a powdery mineral material and is passed over the inlet side of a wall flow filter by means of a gas stream. Here, the individual particles with a particle size of 0.2 µm to 5 µm agglomerate to form a bridged network of particles and are deposited as a layer on the surface of the individual inlet channels running through the wall flow filter. The typical loading of a filter with the powder is between 5 g and 50 g per liter of filter volume. It is expressly pointed out that it is not desirable to use the metal oxide to achieve a coating in the pores of the wall flow filter.

Another method for increasing the filtration efficiency of catalytically inactive filters is presented in the WO2012030534A1 described. Here, a filtration layer (“discriminating layer”) is created on the walls of the flow channels on the inlet side by depositing ceramic particles via a particle aerosol. The layers consist of oxides of zirconium, aluminum or silicon, preferably in fiber form with a length of 1 nm to 5 µm and have a layer thickness of more than 10 µm, usually 25 µm to 75 µm. After the coating process, the applied powder particles are calcined in a heat process.

Another method in which a membrane (“trapping layer”) is created on the surfaces of the inlet channels of filters to increase the filtration efficiency of catalytically inactive wall flow filters is in the patent US8277880B2 described. The filtration membrane on the surfaces of the inlet channels is created by sucking through a gas stream loaded with ceramic particles (e.g. silicon carbide or cordierite). After the filter layer has been applied, the honeycomb body is fired at temperatures above 1000°C in order to increase the adhesion of the powder layer to the channel walls. In EP2502661A2 and EP2502662B1 Further coatings using powder application are mentioned.

A coating within the pores of a wall flow filter substrate by atomizing dry particles is created in the US8388721 B2 described. Here, however, the powder should penetrate deep into the pores. 20% to 60% of the surface of the wall should be accessible to soot particles and therefore remain open. Depending on the flow rate of the powder-gas mixture, a more or less strong powder gradient can be set between the inlet and outlet sides. The pores of the canal walls of the after US8388721B2 Filters coated with powder in the pores can subsequently be coated with a catalytically active filter Component to be coated. Here too, the catalytically active material is located in the channel walls of the filter.

The powder is also introduced into the pores, e.g. B. using an aerosol generator, in which EP2727640A1 described. Here a non-catalytically coated wall flow filter is used with a z. B. gas stream containing aluminum oxide particles is coated in such a way that the complete particles, which have a particle size of 0.1 μm to 5 μm, are deposited as a porous filling in the pores of the wall flow filter. The particles themselves can realize a further functionality of the filter in addition to the filter effect. For example, these particles are deposited in the pores of the filter in an amount of more than 80 g/l based on the filter volume. They fill 10% to 50% of the volume of the filled pores in the channel walls. Both with soot and without soot, this filter has improved filtration efficiency compared to the untreated filter with a lower exhaust gas back pressure of the soot-laden filter.

In the WO2018115900A1 Wall flow filters are coated with a possibly dry synthetic ash in such a way that a continuous membrane layer is created on the walls of the possibly catalytically coated wall flow filter.

WO 2020/047708 and WO 2020/047503 also describe wall flow filters, in which inorganic secondary particles consisting of aluminum oxide and a silicon-containing binder are deposited on the filter using a gas stream, which results in increased durability of the filtration layer.

All of the prior art patents listed above aim to increase the filtration efficiency of a filter by covering the filter with a powder or a membrane. In this way, wall flow filters can be manufactured that are able to almost completely filter the incoming soot particles. Separation rates and filtration efficiencies of greater than 99% can be achieved in common test cycles. The catalytic coating of these filters with a common washcoat consisting of oxide particles and precious metal components, on the other hand, leads to a decrease in the original filtration efficiency of the initial filter, since the introduction of the coating influences the gas flow through the filter and the pore structure of the filter. It is usually not important whether the catalytic coating is in the pores of the porous filter wall or on the channel surfaces of the outlet channels.

As a result of the particle number measurement range being expanded to 10 nm in EU7 legislation, instead of the previous 23 nm, high filtration efficiency will be essential in the future (PN10 measurement). In addition, the new particle number measurement method means that even very small particles consisting of volatile organic components can be recorded, which in turn is reflected in a higher measured particle number at the end of the exhaust system. In connection with a further legal reduction in the particle number limit for internal combustion engines, this means that wall flow filters with a very high filtration efficiency will be required in the future, which at the same time are able to oxidize volatile organic particles to CO ₂ , so that these will no longer be possible in the future required PN10 measurement can be detected as particles.

The object of the present invention is therefore to provide an appropriately coated particle filter in which, on the one hand, the excellent filtration efficiency of the wall flow filter, which is already provided with a layer that increases filtration efficiency, is maintained and not reduced, and on the other hand, a noble metal component is applied which prevents the oxidation of catalyzed by volatile organic particles. Preferably, neither the filtration performance nor the back pressure of the filter changes as a result of the application of the precious metal component.

These and other tasks arising from the prior art are solved by a particle filter according to claims 1 to 14. Claims 15 and 16 are directed to an exhaust system. Claims 17 and 18 are aimed at a method for exhaust gas purification using the particle filter according to the invention for exhaust gas aftertreatment of internal combustion engines, in particular predominantly stoichiometrically operated internal combustion engines.

The present invention relates to a wall flow filter for removing particles from the exhaust gas of internal combustion engines, in particular predominantly stoichiometrically operated internal combustion engines, which comprises a wall flow filter substrate of length L and different coatings Z and F, the wall flow filter substrate having channels E and A which are parallel between a first and a second end of the wall flow filter substrate, which are separated by porous walls and form surfaces O _E and O _A , respectively, and wherein the channels E at the second end and the channels A at the first end are closed and wherein the coating F in the porous walls and/or or on the surfaces O _E and/or on the surfaces O _A and comprises a filtration-increasing layer and the coating Z is in the porous walls and/or on the surfaces O _E and/or O _A and and/or on the end faces of the Channels E and/or A and/or are located on the components of the coating F, and contain platinum and/or palladium, and is characterized in that the coating Z extends over at least a portion of 3 mm to 100% of the length L of the filter extends.

When the wall flow filter according to the invention is used as intended for cleaning exhaust gas from internal combustion engines, the exhaust gas flows into the filter at one end and leaves it again at the other end after passing through the porous walls. For example, if the exhaust gas enters the filter at the first end, the channels E designate the input channels or upstream channels. After passing through the porous walls, it then exits the filter at the second end, so that the channels A denote the output channels or downstream channels. L represents the average coatable length of the filter. Due to the plugs at the channel ends, the entire length of the filter cannot be coated. L represents the sum of the lengths in the coated channels actually available for coating, averaged over the number of coated channels.

All ceramic wall flow filter substrates known from the prior art and common in the field of automobile exhaust gas catalysis can be used as the wall flow substrate. Porous wall flow filter substrates made of cordierite, silicon carbide or aluminum titanate are preferably used. These wall flow filter substrates have channels E and channels A, which, as described above, function as input channels, which can also be called inflow channels, and as output channels, which can also be called outflow channels. The downstream ends of the inflow channels and the upstream ends of the outflow channels are offset from one another and closed with generally gas-tight “plugs”. Here, the exhaust gas to be cleaned, which flows through the filter substrate, is forced to pass through the porous wall between the inflow and outflow channels, which causes a particle filter effect. The filtration properties for particles can be designed through the porosity, pore/radius distribution and thickness of the wall. According to the invention, the porosity of the uncoated wall flow filter substrates is generally more than 40%, for example from 40% to 75%, especially from 50% to 70% [measured according to DIN 66133 - latest version on the filing date].

The average pore size d ₅₀ of the uncoated wall flow filter substrates is at least 4 µm, for example from 4 µm to 34 µm, preferably more than 6 µm, particularly more preferably from 6 µm to 25 µm or most preferably from 7 µm to 17 µm [measured according to DIN 66134 latest version on the filing date], whereby the d ₅₀ value of the pore size distribution of the wall flow filter substrate is to be understood as meaning that 50% of the total pore volume that can be determined by mercury porosimetry is formed by pores whose diameter is smaller than or equal to the value specified as d ₅₀ . In the case of the wall flow filters according to the invention, the wall flow filter substrates provided with coating Z preferably have no change in the pore size distribution compared to that of the original filter, which is only provided with coating F.

The coating F:

According to the invention, the term “filtration-increasing” means that the wall flow filter acquires the suitability through the coating F to be able to retain particles from the exhaust gas stream better than the original filter, without the exhaust gas back pressure increasing exorbitantly compared to the starting substrate. This preferably means that the filtration efficiency of the filter increases by more than 2 percentage points, more preferably by more than 5 percentage points and very particularly preferably by more than 10 percentage points compared to the starting substrate, without the exhaust gas back pressure increasing by more than 60%, preferably less than 50 % and most preferably less than 40% compared to the starting substrate increases.

The increase in filtration efficiency of the filter with coating F compared to the raw filter is calculated using the following formula: $$\text{FE Rec}\ddot{\text{O}}\text{hung by coating F}>/=\left(100\text{\%}-{\text{FE}}_{\text{before F}}\right)\times \text{increase factor}$$

The increase factor in the case according to the invention is in the range of 0.2 - 0.99, preferably in the range of 0.35 - 0.95 and particularly preferably in the range of 0.5 - 0.85. This is particularly advantageous for filter substrates that already have a high filtration performance in the starting substrate.

The increase in exhaust back pressure can be calculated using the following formula: $$\begin{array}{l}\text{Counter pressure increase through coating F}=((\text{Back pressure with F}/\text{Back pressure without}\\ \text{F})-1)\times 100\end{array}$$

Coating F advantageously does not contain any noble metal. It is therefore preferably not catalytically active in the sense of the present invention. In particular, it is essentially unable to oxidize carbon-containing particles such as soot or volatile hydrocarbon particles or to oxidize the exhaust gas components CO and HC or to reduce NO _x . The coating F therefore preferably consists of ceramic or oxidic components and does not contain any other catalytic components.

Particularly suitable components of the coating F include aluminum oxide, zirconium dioxide, cerium oxide, yttrium oxide, mullite, tin oxide, silicon nitride, zeolite, titanium dioxide, silicon dioxide, aluminum titanate, silicon carbide, cordierites, island silicates, layered silicates, technical silicates, chain silicates, group silicates or mixtures thereof.

F Effort:

The membrane layer preferably has a coherent structure on the surface of the wall of the filter. As such, it preferably rests on the filter wall O _E. It can happen that the components of the membrane layer also penetrate to a small extent into the pores of the filter. In a further preferred embodiment, however, the filtration-increasing coating F is located essentially on the surfaces O _E. This means that the components of the coating F are present in the pores of the wall of the filter to less than 20% of the total mass of the coating, preferably less than 10% and most preferably less than 5%. The amount of coating components in the wall can be as in WO2019197177A1 described.

The coating F preferably forms a coherent membrane layer on the surfaces O _E. The membrane layer is defined in particular as a coherent, porous layer with a porosity in the range of 30-90%, preferably 40-80% (measured according to DIN 66133 - latest version on the filing date). The average pore size d ₅₀ of the membrane layer F is at least 50 nm, for example 50 nm to 5 μm, preferably more than 100 nm to 4 μm, particularly more preferably 200 nm to 2.5 μm, where below the d ₅₀ value Pore size distribution means that 50% of the total pore volume that can be determined by mercury porosimetry is formed by pores whose diameter is smaller than or equal to the value given as d ₅₀ .

Accordingly, coating F preferably has a certain thickness over the wall surface, preferably O _E . The coating F preferably has a layer thickness of 1 to 150 μm, preferably 2 to 50 μm. The wall flow filter is characterized in that the ratio of the wall thickness of the wall flow filter substrate to the thickness of the membrane layer of the coating F is preferably 0.8 to 400, preferably 1 to 300 and particularly preferably 1.25 to 250. In addition, it can happen that the coating F accumulates in the axial direction on the plug area at the end of the channel during coating. In a preferred embodiment, the thickness of the coating F here is preferably 0.1 to 10 mm, in particular 0.25 to 5 mm.

In the embodiment discussed here, the coating F is therefore preferably located on the porous walls of the wall flow filter substrate. The particle size of the ceramic membrane is adapted to the pore size of the wall flow filter substrate. The particles of the coating F thus in particular have a defined particle size distribution. The coating F preferably has a monomodal, or a multimodal or broad q3 particle size distribution. To define the particle size or grain size distribution of the coating F, depending on the method used to determine the amount of particles, a distinction is made between, among other things, number-related (q0) and volume-related (q3) grain size distributions (M. Stieß, Mechanical Process Engineering - Particle Technology 1, Springer, 3rd edition 2009, page 29).

If coating F is located on the porous walls of the wall-flow filter substrate, the d ₅₀ value of the particle size distribution of the membrane particles (q3; DIN 66143 - latest version on the filing date) is advantageously greater than or equal to the d ₅₀ value of the pore size distribution of the wall-flow filter substrate (measured according to DIN 66133 - latest version on the filing date). Furthermore, the d90 value of the particle size distribution of the coating F is preferably greater than or equal to the d95 value of the pore size distribution of the wall flow substrate. Alternatively, the d90 value of the particle size distribution of the coating F is preferably smaller than the d95 value of the pore size distribution of the wall flow substrate.

If the coating F penetrates the porous filter wall, the penetration depth is limited. In particular, the penetration depth of the membrane coating F into the filter wall is a maximum of 50% of the wall thickness, preferably a maximum of 40% and very particularly preferably a maximum of 25%. If the coating F is partially located in the porous walls of the wall flow filter substrate, then preferably between 1 to 50% of the total mass of the coating F is located in the porous walls of the wall flow filter substrate, preferably 1.5 to 40% and very particularly preferably 2 to 25% . This evaluation is carried out analogously WO2019197177A1 . For example, the coating F is a ceramic membrane, preferably a silicon carbide membrane.

F interior:

In an alternative embodiment, the coating F preferably does not form a coherent coating on the surfaces of the filter, preferably the surface O _E (no membrane). In this case, the filtration-enhancing coating is defined in particular as a non-coherent layer that is specifically formed via the pores of the wall flow substrate. Within these ranges, coating F has a porosity in the range of 30-90%, preferably 40-80%, determined analogously WO2019197177A1 ). The average pore size d ₅₀ of the coating F is at least 50 nm, for example 50 nm to 5 μm, preferably more than 100 nm to 4 μm, particularly more preferably 200 nm to 2.5 μm, being below the dso value of the pore size distribution It should be understood that 50% of the total pore volume that can be determined by mercury porosimetry is formed by pores whose diameter is smaller or equal to the value given as d ₅₀ . The values are determined as stated above.

In the embodiment discussed here, the coating F is located entirely or partially in the porous walls of the wall-flow filter substrate. The coating F is preferably present in a proportion of 50 - 100% of the total mass of the coating F in the porous walls of the wall flow filter substrate, preferably 60 - 90% and very particularly preferably 70 - 80%. The evaluation is carried out analogously WO2019197177A1 .

The particle size of the coating F is adapted to the pore size of the wall flow filter substrate. The particles of the coating F thus in particular have a defined particle size distribution. The coating F preferably has a monomodal, or a multimodal or broad q3 particle size distribution. If the coating F is located entirely or partially in the porous walls of the wall-flow filter substrate, the d ₅₀ value of the particle size distribution of the oxides of the membrane particles (q3; DIN 66143 - latest version on the filing date) is preferably smaller than the d ₅₀ value of the pore size distribution of the wall-flow filter substrate (measured according to DIN 66133 - latest version on the filing date). Furthermore, it is preferred that the d90 value of the particle size distribution of the oxides is in particular smaller than the d95 value of the pore size distribution of the wall flow substrate. In this case, the filtration-increasing coating F is preferably made up predominantly of aluminum oxide.

The coating F - whether continuous or not - can be produced according to the instructions of the person skilled in the art. The production of the coating F is carried out, for example, in EP2776144A1 , WO2020/047506A1 , WO2020/047708A1 described in detail. Alternatively, the coating F can also be applied to the surfaces O _E by a wet chemical coating step. For example, the membrane coating F is first coated on the surfaces O _E and then, after calcination, the coating Z is applied ( EP1789190B1 or US11161098 BB).

In a further embodiment, the wall flow filter is characterized in that coating F has an increasing concentration gradient (1st derivative of the concentration curve) in the longitudinal direction of the filter from its first to the second end. According to the invention, “increasing gradients” is understood to mean the fact that the gradient of the powder concentration in the filter increases in the axial direction - from the inlet side to the outlet side - possibly from negative values to more positive values. In In a preferred embodiment, there is more powder near the outlet plugs of the inlet channel and significantly less powder at the inlet of the filter. To describe the gradient, the filter can be divided into three consecutive areas of equal length along its longitudinal axis. In a preferred form, the filter is covered with powder in an area near the inlet side and in an area in the middle of the filter to less than 40% of the wall surface of the inlet channel, while in an area near the outlet side more than 40% of the wall surface of the Input channel are covered with powder, in a particularly preferred form in an area near the inlet side between 5% and 35%, in an area in the middle of the filter between 8% and 38% and in an area near the outlet side between 40% and 60% of the wall surface of the inlet channel is covered with powder and in a particularly preferred form in an area near the inlet side between 5% and 25%, in an area in the middle of the filter between 8% and 30% and in an area near the The outlet side is covered with powder between 45% and 60% of the wall surface of the inlet channel. The degree of coverage of the wall surface was determined using image analysis from light microscopy images. Corresponding photographs of the inlet and outlet channels were taken. In this type of analysis, the average color of the wall surface of the non-powdered outlet channel is determined as a reference. This reference is subtracted from the corresponding image of the powder-covered areas in the inlet channel, whereby the color difference was set according to CIE76 of the International Commission on Illumination with a lowest still distinguishable color difference of 2.33 (https://en.wikipedia.org/wiki /Color_difference#CIE76).

The gradient created during powder coating is advantageous for further increased filtration efficiency. In one embodiment, the concentration gradient, e.g. B. by varying the dusting speed, be designed so that more powder is deposited on the inlet side of the filter than in the middle of the filter and on the outlet side. In a more preferred embodiment, the concentration gradient can be designed such that more powder is deposited on the inlet side of the filter than in the middle of the filter and more powder is deposited on the outlet side (at the other end of the filter) than on the inlet side. Simulation results have shown the following picture in this regard (Table 1). Table 1 - Powder distribution over the filter at different space velocities of the gas: Mass flow Channel length 10m/s 20m/s 40m/s 1/3 26% 18% 11% 2/3 16% 12% 9% 3/3 58% 69% 80%

Simulations of the gas flow in a wall flow filter have shown that the last third of the substrate is mainly responsible for the filtration properties of the overall filter (more than 50%). By increasing the application of coating F in the last third of the filter, the dynamic pressure there is increased, which is due to the lower permeability, and the flow shifts more into the first two thirds of the filter. Therefore, the filter should have a more increasing gradient of coating F from the first to the second end to increase its filtration effectiveness. This applies mutatis mutandis to setting an advantageous exhaust gas backpressure. Accordingly, a less strongly increasing gradient of the concentration of coating F should be selected here.

The wall flow filter preferably has a coating F which has a mass of 1 to 50 g/l, based on the volume of the wall flow filter substrate. More preferably, the mass of the coating F is 5 to 40 g/l, and most preferably 10 to 30 g/l, based on the volume of the wall flow filter substrate.

The components of coating F are preferably fixed on the ceramic wall flow substrate. This can preferably be achieved by using a suitable binder. Such binders are well known to those skilled in the art and, for example, in WO2020047506A1 disclosed. Thermal fixation of the coating F is also preferred. Known methods in this regard are also known to those skilled in the art, for example WO2012030533A1 and EP21164198.0 known.

As an alternative to the powder process just envisaged, the coating F can also be applied using wet technology, like a normal washcoat. It can extend over the entire length L of the wall flow fil tersubstrates or only extend over part of it. For example, coating F extends over 0 to 100%, 25% to 80% or 40% to 60% of the length L of the filter substrate. An extension of over 80% - 100% of the length L is preferred, in particular over 90% - 100%. In one embodiment of the wall flow filter according to the invention, the coating F extends over the entire length L of the channels E and abuts the plugs at the channel end.

Coating Z:

The coating Z is an oxidation-catalytic coating. This coating is intended to oxidize HC and CO as well as soot particles and volatile hydrocarbon particles in the exhaust tract. The person skilled in the art is familiar with what such coatings look like (e.g US11161098 BB). In the present case, the coating Z is characterized in that it has few to no ceramic or oxidic components. The coating therefore preferably has a mass of precious metals in the coating Z of 0.1 - 20 grams per liter of filter volume. 1 - 15 g/L filter volume is preferred, particularly preferably 2 - 10 g/L filter volume in this context. If the coating Z only extends over a partial area of the filter of length L, higher masses of 5 - 30 g/L, preferably 5 - 25 g/L, can occur in this area.

In order to achieve better dispersion and better distribution, coating Z can additionally contain a small amount of oxidic carrier materials. Advantageously, 5 - 40 grams per liter of filter substrate volume of ceramic or oxide carrier materials can be present in coating Z, preferably between 7 - 25 g/L and particularly preferably between 10 - 15 g/L. Common carrier materials here are aluminum oxide, boehmite, aluminum sol, or others known to those skilled in the art and already in use EP3505246A1 disclosed materials. If present, the ceramic or oxide components are preferably selected from the group consisting of aluminum oxide or boehmite. The coating Z preferably contains no zeolite and no molecular sieve. If the coating Z only extends over a partial area of the filter of length L, higher masses of 10 - 85 g/L, preferably 20 - 60 g/L, can occur in this area.

In a preferred embodiment, coating Z extends at least over an axial portion of the length L of the filter. In a preferred embodiment, the minimum length of the coating Z is at least 3 mm, preferably at least 5 mm and most preferably at least 10 mm from the end of the filter. In a further preferred embodiment, the maximum length of the coating Z is 5-100%, preferably 10-100% and very preferably 20-100% based on the length L of the filter. In a further preferred embodiment, coating Z extends over the entire length L of the filter.

Preferred noble metals in the coating Z are platinum and/or palladium. The mass ratio of platinum to palladium is preferably 0.05 - 20, more preferably 0.1 - 10 and very preferably 1.5 - 5. The noble metals in the coating Z are also preferably platinum and / or rhodium. The mass ratio of platinum to rhodium is preferably 0.05 - 20, more preferably 0.1 - 10 and very preferably 1.5 - 5. The noble metals in the coating Z are also preferably platinum and / or rhodium and / or palladium. The mass ratio of platinum to palladium to rhodium is preferably 1 - 10: 1 - 10: 1 -2, more preferably 1 - 10: 1 - 7: 1 -1.5. Coating Z particularly preferably contains the noble metals platinum and/or palladium, with rhodium advantageously only being present as a further noble metal in exceptional cases. Coating Z particularly preferably contains platinum and palladium and no rhodium. In a further embodiment, coating Z contains the precious metals platinum and/or rhodium, with palladium preferably also being present as a further noble metal only in exceptional cases. Coating Z particularly preferably contains palladium and rhodium and no platinum. In a further embodiment, coating Z contains the noble metals platinum, palladium and/or rhodium. In this embodiment too, it is particularly advantageous if the mass ratio of platinum to palladium is 0.05 - 20, preferably 0.07 - 15. The precious metals of the coating Z are preferably not fixed to carrier materials (ceramic or oxidic parts of the coating Z). However, they can deposit on the oxides and components of coating F during coating.

The production of the coating medium for coating Z is known to those skilled in the art (e.g US11161098 BB). The coating Z can be applied to the wall flow filter using methods familiar to those skilled in the art (e.g US11161098 BB). In the simplest case, the precious metal or metals are dissolved in water and applied to the wall flow filter. Due to the few to no oxide or ceramic components in the coating Z, it has a very low viscosity. The viscosity of the coating The medium is preferably less than 0.1 Pas*s, more preferably less than 0.05 Pas*s and very preferably less than 30 Pas*s, each measured at a shear rate of 100 1/s (revolutions per second) (measured analogously WO2020109778A1 ). The viscosity can be adjusted with common thickeners such as methyl cellulose.

In an embodiment according to the invention, coating Z is located in the porous walls and/or on the surfaces O _E and/or O _A and/or on the end faces of the channels E and/or A and/or on the components of the coating F. Preferably the end faces of the channels O _E and/or O _A are also provided with the coating Z. In this embodiment, the plugs of the ends E and/or A of the filter are coated with the coating Z at the respective ends on the outside of the filter. A coating with Z into the pores of the porous filter wall is also particularly preferred. In a further advantageous embodiment, the coating Z is located exclusively in the pores of the filter substrate. The coating Z can also deposit on the particles of coating F. Furthermore, coating Z can also be located on the surfaces O _A.

The coating Z is a catalytically active coating, in particular due to the components platinum and/or palladium and/or rhodium. In the context of the present invention, “catalytically active” is understood to mean the ability to oxidize carbon-containing particles such as soot or volatile hydrocarbon particles or to oxidize the exhaust gas components CO and HC or to reduce NO _x . The coating Z is particularly catalytically active at operating temperatures of 200 to 1100 °C. In particular, the term “catalytically active” means that a filter that has the coatings F and Z is 10% at an exhaust gas temperature of 500 ° C, a lambda value of 1.05 and an exhaust gas mass flow of 70 kg / h in the same time unit. can oxidize more soot and/or hydrocarbons than a filter that only contains coating F, preferably 15% more and very particularly preferably 20% more.

Coating Z preferably has no significant layer thickness and does not rise above the surfaces O _A and/or O _E. The layer thickness of coating Z is preferably less than 5 μm, particularly preferably less than 3 μm and most preferably less than 1 μm.

The wall flow filter according to the invention can be produced by applying the coatings Z and F to a wall flow filter substrate. In a preferred embodiment of the wall flow filter according to the invention, coating F is first applied and then coating Z is applied to the filter substrate. This has the advantage that coating Z is not only deposited on the surface O _E , O _A and in the porous filter wall, but can also be deposited on the particles of the coating F.

In the case according to the invention, the application of the coating Z is associated with only a very small increase in the exhaust gas back pressure. Compared to the filter, which only has the coating F, the back pressure increases by only 15% by applying the coating Z, preferably only by 10% and particularly preferably only by 5%, whereby the increase in the exhaust gas back pressure can be calculated using the following formula : $$\begin{array}{l}\text{Counter pressure increase by Z}=((\text{Back pressure with F and Z}/\text{Counter pressure with F without Z})\\ -1)\times 100\end{array}$$

In the case according to the invention, the application of the coating Z is accompanied by only a very small change in the filtration efficiency of the filter. Compared to the filter that only has the coating F, the filtration efficiency changes by applying the coating Z by only 3 percentage points, preferably only by 2 percentage points and particularly preferably only by 1 percentage point. In the sense of the invention, the term change can be understood to mean both an increase and a decrease by the specified range.

The calculation of the increase in filtration efficiency is calculated using the following formula. $$\begin{array}{l}\text{Filtration self-efficiency increase due to Z}=((\text{Filtration}\text{efficiency}\text{nz with F and Z}/\text{filtration efficiency}\\ \text{enz with F without Z})-1)\times 100\end{array}$$

If the filtration efficiency decreases slightly due to the introduction of Z, the decrease is calculated using the following formula. $$\begin{array}{l}\text{Filtration efficiency decrease due to Z}=(1-(\text{Filtration efficiency}\text{nz with F and Z}/\text{filtration efficiency}\\ \text{ficency with F without Z}))\times 100\end{array}$$

The present invention also relates to a system for cleaning exhaust gases from internal combustion engines, in particular from predominantly stoichiometrically operated internal combustion engines, which has a wall flow filter according to the invention. Further preferred is a system for cleaning exhaust gases, which is characterized in that the wall flow filter according to the invention is arranged in the exhaust system following the exhaust gas as a separate unit after a three-way catalytic converter close to the engine. In particular, it is advantageous if a three-way catalytic converter is located in a position close to the engine, directly upstream of the wall flow filter according to the invention. It is also advantageous if a three-way catalytic converter is located downstream of the wall flow filter according to the invention. It is also advantageous if there is a three-way catalytic converter on the upstream and downstream sides of the wall flow filter according to the invention. Further preferred is, in particular, a system for cleaning exhaust gases, which is characterized in that following the exhaust gas after the wall flow filter according to the invention there is at least one further catalyst, selected from the group of three-way catalyst, oxidation catalyst, NO _x storage catalyst, hydrocarbon trap, SCR catalyst , ammonia slip catalyst is located. The preferred embodiments described for the wall flow filter according to the invention also apply, mutatis mutandis, to the system mentioned here.

Alternatively, the present invention further relates to an exhaust gas purification system which comprises a filter according to the invention and at least one further catalyst. In one embodiment of this system, at least one further catalyst is arranged upstream of the filter according to the invention. This is preferably a three-way catalyst or an oxidation catalyst or an NO _x storage catalyst. In a further embodiment of this system, at least one further catalyst is arranged downstream of the filter according to the invention. This is preferably a three-way catalyst or an SCR catalyst or an NO _x storage catalyst or an ammonia slip catalyst. In a further embodiment of this system, at least one further catalyst is arranged upstream of the filter according to the invention and at least one further catalyst is arranged downstream of the filter according to the invention. Preferably, the upstream catalyst is a three-way catalyst or an oxidation catalyst or an NO _x storage catalyst and the downstream catalyst is a three-way catalyst or an SCR catalyst or an NO _x storage catalyst or an ammonia slip catalyst. The preferred embodiments described for the wall flow filter according to the invention also apply, mutatis mutandis, to the exhaust gas purification system mentioned here.

The present invention also relates to a method for exhaust gas purification of an internal combustion engine, wherein the exhaust gases from the engine are passed through a wall flow filter according to the invention or a system having this. The internal combustion engine is preferably one that is operated predominantly stoichiometrically. The preferred and alternative embodiments of the wall flow filter according to the invention and the system also apply here mutatis mutandis.

Close to the engine in the sense of the invention refers to an area in the exhaust system that is in a position close to the engine, i.e. approx. 10 - 80 cm, preferably 20 - 60 cm away from the engine outlet.

The term coating is therefore understood to mean the application of catalytically active materials to a wall flow filter substrate. The coating Z takes over the actual catalytic function. In the present case, the coating is carried out by applying a correspondingly preferably aqueous suspension of the catalytically active components in or onto the wall of the wall-flow filter substrate, for example according to EP1789190B1 or US1 1 161098 B.B. After the suspension has been applied, the wall flow filter substrate is dried and, if necessary, calcined at an elevated temperature. The most appropriate loading amount of a wall-coated filter depends on its cell density, wall thickness and porosity.

The catalytically coated wall flow filters according to the invention differ from those that arise in the exhaust system of a vehicle due to ash deposition during operation. According to the invention, the catalytically active wall flow filter substrates are specifically provided with an optional membrane coating F. This means that the balance between filtration efficiency and exhaust gas back pressure can be set specifically from the start. Wall flow filters are therefore not included in the present invention ter in which undefined ash deposits have occurred from the combustion of fuel, for example in the cylinder during driving or by means of a burner.

The wall flow filter according to the invention shows excellent filtration efficiency with no or only a very small increase in the exhaust gas back pressure compared to a wall flow filter which only contains coating F but not coating Z. The wall flow filter according to the invention preferably shows an unchanged soot particle separation (filter effect) compared to the initial filter, which only comprises the coating F. The low overall back pressure is probably due to the fact that the presence of coating F does not greatly reduce the cross section of the channels on the input side. It is assumed that coating F forms a porous structure, which has a positive effect on the dynamic pressure. Due to the coating F, a filter according to the invention also has a lower dynamic pressure after loading with soot than an analogous filter without coating F, since this largely prevents the soot from penetrating into the porous filter wall. Coating Z gives the wall flow filter according to the invention an excellent catalytic ability to oxidize soot or hydrocarbon particles by being able to reduce their ignition temperature and thus facilitate their oxidation.

The filter according to the invention is usually used primarily in internal combustion engines, in particular in internal combustion engines with direct injection or intake manifold injection. These are preferably predominantly stoichiometrically operated gasoline or natural gas engines. These are preferably engines with turbocharging. The requirements for gasoline particulate filters (GPF) differ significantly from the requirements for diesel particulate filters (DPF). Diesel engines without DPF can have up to ten times higher particle emissions, based on particle mass, than gasoline engines without GPF (Maricq et al., SAE 1999-01-01530). In addition, the gasoline engine produces significantly fewer primary particles and the secondary particles (agglomerates) are significantly smaller than the diesel engine. The emissions from gasoline engines range from particle sizes smaller than 200 nm (Hall et al., SAE 1999-01-3530) to 400 nm (Mathis et al., Atmospheric Environment 38, 4347) with the maximum in the range from around 60 nm to 80 nm. Therefore, the filtration of the nanoparticles in GPF must take place primarily via diffusion separation. For particles smaller than 300 nm, deposition by diffusion (Brownian molecular motion) and electrostatic forces becomes increasingly important as the size decreases (Hinds, W.: Aerosol technology: Properties and behavior and measurement of airborne particles. Wiley, 2nd edition 1999). Nevertheless, the wall flow filter according to the invention can also be used in the diesel sector.

• 1 betrifft einen Wandflussfiltersubstrat mit den Oberflächen O_E und O_A
• 2 betrifft einen Wandflussfilter der eine Beschichtung F auf den Oberflächen O_E aufweist
• 3 betrifft einen erfindungsgemäßen Wandflussfilter der eine Beschichtung F auf den Oberflächen O_E und eine kurze Zone von Beschichtung Z im Eingangsbereich des Filters aufweist
• 4 betrifft einen erfindungsgemäßen Wandflussfilter der eine Beschichtung F auf den Oberflächen O_E und eine kurze Zone von Beschichtung Z im Eingangsbereich des Filters aufweist, wobei sich Beschichtung F auch auf den Stirnflächen der Stopfen befindet
• 5 betrifft einen erfindungsgemäßen Wandflussfilter der eine Beschichtung F auf den Oberflächen O_E und eine längere Zone von Beschichtung Z im Eingangsbereich des Filters aufweist.
• 6 betrifft einen erfindungsgemäßen Wandflussfilter der eine Beschichtung F auf den Oberflächen O_E und eine kurze Zone von Beschichtung Z im Auslassbereich des Filters aufweist
• 7 betrifft einen erfindungsgemäßen Wandflussfilter der eine Beschichtung F auf den Oberflächen O_E und eine längere Zone von Beschichtung Z im Auslassbereich des Filters aufweist
• 8 betrifft einen erfindungsgemäßen Wandflussfilter der eine Beschichtung F auf den Oberflächen O_E und eine Beschichtung Z aufweist, wobei sich Beschichtung Z über den ganzen Filter erstreckt.
• 9 betrifft einen erfindungsgemäßen Wandflussfilter und zeigt schematisch, dass sich Beschichtung Z auf den Oberflächen O_A und/oder in den Poren des Filtersubstrats und/oder auf den Partikeln der Beschichtung F befinden kann.
• 10 betrifft einen erfindungsgemäßen Wandflussfilter und zeigt schematisch ein Bild auf dem zu erkennen ist, dass sich die Beschichtung Z über ca. 50% der Filterlänge erstreckt.
• 11 zeigt einen Vergleich zwischen einem Filter ohne Beschichtung Z (schwarz) und einem erfindungsgemäßen Filter mit Beschichtung Z (grau) im Partikeloxidationstest.

The coatings Z, F can be arranged on the wall flow filter substrate in various ways. The 1 to 10 explain this as an example, whereby the 2 to 10 Wall flow filters according to the invention relate only to the coatings Z and F.

• 1 relates to a wall flow filter substrate with surfaces O _E and O _A
• 2 relates to a wall flow filter which has a coating F on the surfaces O _E
• 3 relates to a wall flow filter according to the invention which has a coating F on the surfaces O _E and a short zone of coating Z in the entrance area of the filter
• 4 relates to a wall flow filter according to the invention which has a coating F on the surfaces O _E and a short zone of coating Z in the entrance area of the filter, with coating F also being located on the end faces of the plugs
• 5 relates to a wall flow filter according to the invention which has a coating F on the surfaces O _E and a longer zone of coating Z in the entrance area of the filter.
• 6 relates to a wall flow filter according to the invention which has a coating F on the surfaces O _E and a short zone of coating Z in the outlet area of the filter
• 7 relates to a wall flow filter according to the invention which has a coating F on the surfaces O _E and a longer zone of coating Z in the outlet area of the filter
• 8th relates to a wall flow filter according to the invention which has a coating F on the surfaces O _E and a coating Z, with coating Z extending over the entire filter.
• 9 relates to a wall flow filter according to the invention and shows schematically that coating Z can be located on the surfaces O _A and/or in the pores of the filter substrate and/or on the particles of the coating F.
• 10 relates to a wall flow filter according to the invention and shows schematically an image in which it can be seen that the coating Z extends over approximately 50% of the filter length.
• 11 shows a comparison between a filter without coating Z (black) and a filter according to the invention with coating Z (gray) in the particle oxidation test.

(E)

den Eingangskanal/ Anströmkanal des Wandflussfilters

(A)

den Ausgangskanal/ Abströmkanal des Wandflussfilters

(OE)

die von den Eingangskanälen (E) gebildeten Oberflächen

(OA)

die von den Ausgangskanälen (A) gebildeten Oberflächen

(L)

die Länge der Filterwand

(Z)

die Beschichtung Z

(F)

die Beschichtung F

The 2 to 10 show the different coating arrangements of wall flow filters according to the invention, which have already been described in more detail above. Inscribed therein:

(E)

the inlet channel/inflow channel of the wall flow filter

(A)

the outlet channel/outflow channel of the wall flow filter

(OE)

the surfaces formed by the input channels (E).

(OA)

the surfaces formed by the output channels (A).

(L)

the length of the filter wall

(Z)

the coating Z

(F)

the coating F

The invention is explained below using examples.

Example 1 according to the invention:

A ceramic filter substrate was created using an aerosol process ( EP3774036A1 ) with approx. 14 g/L of a filtration coating F, consisting of a mineral layered silicate, and the coating F is then thermally fixed at 900 ° C. The filter was then coated with a precious metal solution over a length of 50% of the entire filter length and then dried and calcined. The precious metal concentration, calculated on the entire filter volume, was 3.355 g/L. The precious metal concentration in the zone of coating Z was accordingly 6.708g/L.

The filter obtained in this way was then examined against a comparison filter that does not contain any coating Z with regard to the back pressure and the oxidation ability of particles on the engine test bench.

First, the pressure loss of the filter before and after coating Z was measured on a cold gas test stand with an air flow of 600 m ³ /h. Before coating Z, the filter had a back pressure of 68.5 mbar, while the back pressure after coating with Z was 68.6 mbar.

Both filters were then loaded with 7 grams of soot on a gasoline engine with direct injection and then weighed. The filters were then reinstalled in the exhaust system of the engine and heated to a temperature of 500°C with rich exhaust gas in the absence of oxygen. The exhaust gas composition was then changed from rich to lean exhaust gas (lambda 1.1) and the decrease in back pressure was then recorded as a function of time. As in 11 As can be seen, the back pressure of the soot-laden filter according to the invention (gray color / Example 1) decreases significantly faster than the back pressure of the comparison filter, which has no coating Z. This is particularly surprising since, contrary to current specialist literature, no support materials with high specific surface areas such as aluminum oxide, cerium oxide, cerium zirconium mixed oxide or other oxides known to those skilled in the art are necessary to catalyze the oxidation of the particles. As in 11 can also be seen in the area of the first 500 seconds of the test, the filter according to the invention including coating Z has the identical back pressure as the equivalent filter without coating F. The filtration efficiency of the filter according to the invention in the WLTP cycle is also 84.7% compared to that of the reference filter unchanged.

The combination of coating F and coating Z therefore offers an elegant way to catalyze the oxidation of soot particles, especially in the range of 10-23 nm, without impairing the original physical properties of the filter, such as the pressure loss.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

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• EP 3774036 A1 [0069]

Claims (18)

Wall flow filter for removing particles from the exhaust gas of, in particular predominantly stoichiometrically operated, internal combustion engines, which comprises a wall flow filter substrate of length L and coatings Z and F that are different from each other, the wall flow filter substrate having channels E and A which are parallel between a first and a second end of the wall flow filter substrate, which are separated by porous walls and form surfaces O _E and O _A , respectively, and wherein the channels E at the second end and the channels A at the first end are closed and wherein the coating F in the porous walls and / or on the Surfaces O _E and / or on the surfaces O _A and comprises a filtration-increasing layer and the coating Z is in the porous walls and / or on the surfaces O _E and / or O _A and / or on the end faces of the channels E and / or A and/or on the components of the coating F, and contains platinum and/or palladium, characterized in that coating Z extends over at least a portion of 3 mm to 100% of the length L of the filter. Wall flow filter according to Claim 1 , characterized in that the coating F is selected from the group consisting of aluminum oxide, zirconium dioxide, cerium oxide, yttrium oxide, mullite, tin oxide, silicon nitride, zeolite, titanium dioxide, silicon dioxide, aluminum titanate, silicon carbide, cordierites, island silicates, layered silicates, technical silicates, chain silicates, Group silicates or mixtures thereof. Wall flow filter according to Claim 1 and/or 2, characterized in that the filtration-increasing coating F is located essentially on the surfaces O _E. Wall flow filter according to Claim 3 , characterized in that the coating F has a layer thickness of 1 to 150 µm. Wall flow filter according to one of the Claims 3 or 4 , characterized in that the ratio of the wall thickness of the wall flow filter substrate to the thickness of the coating F is 0.8 to 400. Wall flow filter according to Claim 3 , 4 or 5 , characterized in that 1 to 50% of the total mass of the coating F is located in the porous walls of the wall flow filter substrate. Wall flow filter according to one of the Claims 1 or 2 , characterized in that the filtration-increasing coating F does not form a coherent coating on the surfaces O _E. Wall flow filter according to one of the preceding claims, characterized in that coating F has an increasing concentration gradient in the longitudinal direction of the filter from its first to the second end. Wall flow filter according to one of the preceding claims, characterized in that coating F advantageously has a mass of 1 to 50 g/l, based on the volume of the wall flow filter substrate. Wall flow filter according to one of the preceding claims, characterized in that the mass of the precious metal of the coating Z is 0.1 - 20 grams per liter of filter volume. Wall flow filter according to one of the preceding claims, characterized in that coating Z additionally contains a small amount of ceramic or oxidic components in the range of 5 - 40 grams per liter of filter substrate volume. Wall flow filter according to one of the preceding claims, characterized in that the ceramic or oxide components of the coating Z are aluminum oxide or boehmite. Wall flow filter according to one of the preceding claims, characterized in that the mass ratio of platinum to palladium is 0.05 - 20. Wall flow filter according to one of the preceding claims, characterized in that first coating F and then coating Z are applied to the filter substrate. System for cleaning exhaust gases from, in particular predominantly stoichiometrically operated, internal combustion engines, which has a wall flow filter analogous to Claims 1 - 14 contains, which is arranged after a three-way catalytic converter close to the engine. System for cleaning exhaust gases in accordance with Claim 15 , characterized in that after the wall flow filter there is at least one further catalyst, selected from the group of three-way catalyst, oxidation catalyst, NO _x storage catalyst, hydrocarbon trap, SCR catalyst, ammonia slip catalyst. Method for reducing exhaust gases from an internal combustion engine, in particular a predominantly stoichiometrically operated internal combustion engine, in which the exhaust gases from the engine pass through a wall flow filter according to one of Claims 1 - 14 be directed. Method for reducing exhaust gases from a predominantly stoichiometrically operated internal combustion engine, in which the exhaust gases from the engine are controlled via a system Claims 15 or 16 be directed.

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