DE102018220551A1 - Partial flow filter for treating an exhaust gas flow - Google Patents

Abstract

The invention relates to a partial flow filter (26) for treating an exhaust gas flow (21) of an internal combustion engine (20) with a honeycomb structure (42) from a number of essentially parallel to each other closed or open flow channels (38, 40), which are gas permeable Filter walls (30) are limited. The partial flow filter (26) has a coating (34) on an end face (16) facing the exhaust gas flow (21) which contains a catalytically active material (36) which has an oxidizing effect on hydrocarbons, soot and SOF at low exhaust gas temperatures. The invention also relates to a method for producing the partial flow filter (26) and to its use within an exhaust tract of an internal combustion engine (20).

Description

Technical field

The invention relates to a partial flow filter for treating an exhaust gas flow of an internal combustion engine. Furthermore, the invention relates to a method for producing a partial flow filter and to the use of the partial flow filter in the exhaust tract of an internal combustion engine.

State of the art

• Erzeugen eines Abgases mittels einer Verbrennungskraftmaschine, welches zwischen 2 g NO_x/kWh und 12 g NO_x/kWh aufweist; ferner Leiten des Abgases aus der Verbrennungskraftmaschine zu einem Abgasnachbehandlungssystem. Dieses umfasst einen Partikelfilter mit katalytischer Oxidationsfunktion und mindestens einer Mischkammer. Es erfolgt ein katalytisches Oxidieren von Schadstoffen und ein Abscheiden von Partikeln aus dem Abgas mittels des Partikelfilters mit katalytischer Oxidationsfunktion, wobei ein erstes behandeltes Abgas entsteht. Daran schließt sich ein Vermischen des ersten behandelten Abgases mit einem Betriebs-/Hilfsstoff, insbesondere einem Reduktionsmittel, wie beispielsweise einer Harnstoff-Wasser-Lösung, in der mindestens eine Mischkammer zu einem Abgas-/Reduktionsmittel-Gemisch, an.

EP 3 068 989 B1 discloses an exhaust gas aftertreatment system for cleaning the exhaust gas of an internal combustion engine, wherein a particle filter, a device with a catalytic oxidation function and at least one mixing chamber are combined to form a structural unit. The particle filter, the device with a catalytic oxidation function or a particle filter with a catalytic oxidation function and the at least one mixing chamber can be detachably combined with one another to form a structural unit. The structural unit is either arranged in a cylindrical container or forms one. Out EP 3 068 989 B1 there is also a process for purifying exhaust gas with the following process steps:

• Generating an exhaust gas by means of an internal combustion engine, which has between 2 g NO _x / kWh and 12 g NO _x / kWh; further routing the exhaust gas from the internal combustion engine to an exhaust gas aftertreatment system. This comprises a particle filter with a catalytic oxidation function and at least one mixing chamber. There is a catalytic oxidation of pollutants and a separation of particles from the exhaust gas by means of the particle filter with a catalytic oxidation function, a first treated exhaust gas being produced. This is followed by mixing the first treated exhaust gas with an operating agent / auxiliary, in particular a reducing agent, such as a urea-water solution, in the at least one mixing chamber to form an exhaust gas / reducing agent mixture.

WO 2009/024815 discloses an exhaust gas aftertreatment system, which comprises a particle filter with a catalytic oxidation function, and a mixing chamber, both of which are combined to form a structural unit.

US 2011/219745 also discloses an exhaust gas aftertreatment system with an oxidation catalyst, a particle filter and a mixing chamber, which are also combined to form a structural unit.

DE 10 2015 226 039 A1 relates to a particle filter for an exhaust gas aftertreatment system, which has a plurality of flow channels with porous channel walls through which an exhaust gas flow of the internal combustion engine can be passed, at least some flow channels being closed on one side and at least some of the flow channels being open on both sides. The person skilled in the art sometimes refers to such particle filters as partial flow filters.

In contrast to a full flow filter, a partial flow filter has a number of open flow channels that significantly impairs its filtration efficiency.

Partial flow filters for treating the exhaust gas of an internal combustion engine are also called “open particle filters” (abbreviated “OPF”). Such partial flow filters are regularly constructed as honeycomb bodies with cells extending parallel to one another. The cell walls that border the individual cells are gas-permeable. As a rule, the honeycomb bodies are made from porous ceramic, sintered metals or the like. Some of the cells are closed on one end face and another part of the cells is open on both sides.

The closure of flow channels of a partial flow filter which are closed on one side can be arranged at the front in the flow direction or also at the outlet-side end of the honeycomb body.

The partial flow filters are introduced into the exhaust gas flow in such a way that the exhaust gas flows through the individual flow channels. Partial flow filters are used in applications that do not require a closed particle filter, for example in the event that the raw engine emissions almost reach the limit values already required and for this reason a particle filter is not necessary. In addition, partial flow filters are also used in applications when there is no need for active particle filter regeneration or when the absence of particle filter regeneration must be ruled out for safety reasons. Partial flow filters of this type can be used individually or in a cascade design. Such cascades serve to increase the overall filtration efficiency of the exhaust gas aftertreatment system.

Like full-flow filters, such partial-flow filters tend to clog in the area of their front end face due to the deposition of solid (soot, sulfur, ammonium nitrate) and high-boiling, liquid exhaust gas components (long-chain hydrocarbons and their derivatives), especially in applications with a high concentration of Long-chain, sometimes solid hydrocarbons (solid organic fraction, SOF) in the exhaust gas stream - especially when these applications are operated for a long time at low exhaust gas temperatures.

Presentation of the invention

According to the invention, a partial flow filter for treating an exhaust gas flow in the internal combustion engine is proposed, with a honeycomb structure consisting of a number of flow channels which extend essentially parallel to one another and which are formed by closed or open channels and are delimited by gas-permeable filter walls. The partial flow filter has at least one coating on an end face facing the exhaust gas flow, which contains a catalytically active material which has an oxidizing effect on volatile and high-boiling, long-chain hydrocarbons and soot at low exhaust gas temperatures.

The honeycomb structure has a round, oval, or tri-oval cross section. However, special shapes with a rectangular cross-section are possible.

Ceramic materials, in particular cordierite, mullite, aluminum tinanate, silicon dioxide, silicon carbide and mixtures thereof, serve as the ceramic material for building up the honeycomb structure.

The flow channels extending parallel to one another have a predominantly rectangular cross section, in particular predominantly a square cross section. Hexagonal cross sections of the flow channels are possible.

The cell density is more than 15 flow channels per cm ² end face, for example 20 to 160 channels per cm ² , preferably 25 to 140 channels per cm ² , in a special case preferably 28 to 100 channels per cm ² (in Anglo-Saxon dimensions this corresponds to approximately 180 to 650 cpsi, ie cells per in ² ).

The proportion of closed flow channels is more than 5 percent per end face. Filters with a small proportion of closed flow channels are characterized by a comparatively low exhaust gas back pressure. In order to achieve a high filtration efficiency, filters are particularly preferred in which the total proportion of cells closed on at least one end face is 20 to 80 percent. The end faces can have different numbers, areas and patterns of closed flow channels. In this case, when considering exhaust gas back pressure and filtration efficiency, preference is given to filters which have a share of 30 to 70 percent of flow channels open on both sides, for example about 50 percent.

The flow channels sometimes have the same diameter. However, filters are preferred in which a portion of the flow channels has a larger diameter than the other channels. This proportion is preferably about one third to two thirds. If the proportion of the larger channels in a particularly preferred variant is about half of all flow channels, then the larger channels are advantageously no more than twice the wall thickness larger than the other channels. Filters with more than two different diameters of the flow channels are also possible.

The wall thickness within the honeycomb structure is greater than 0.06 mm, in particular 0.08 to 0.38 mm, preferably 0.10 to 0.32 mm (in Anglo-Saxon dimensions this corresponds to approximately 4 to 13 mils, i.e. milli-inches).

Advantageously, the coating of the end face proposed according to the invention, which has a high loading of catalytically active materials at the inlet of the partial flow filter, can locally, namely on the end face, catalytically oxidize exhaust gas components adhering to the end face of short-chain volatile and in particular high-boiling, long-chain hydrocarbons , and soot is already achieved at comparatively low exhaust gas temperatures below the boiling point of long-chain hydrocarbons, which have a boiling point of approximately 174 ° C (such as decane) to approximately 343 ° C (such as eicosan).

Following the solution proposed according to the invention, the partial flow filter for treating an exhaust gas flow is such that the coating is limited to the dimensions of the end face of the partial flow filter.

The coating advantageously has a depth of penetration into the space formed by closed and open flow channels which is <25 mm, in particular <10 mm, preferably 1 to 5 mm or less and in particular ≤ 0.1 mm.

Following the solution proposed according to the invention, the coating on the end face of the partial flow filter comprises substances selected from the following group, namely precious metals and their oxides, as well as other transition metals and their oxides, for example silicon, titanium, aluminum, iron, copper, Vadium, hafnium, tungsten, zirconium, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium and other lanthanides, in particular their oxides, and an admixture of at least traces of actinides, in particular their oxides. Mixed oxides are advantageous educated. Some of these substances belong to the group of so-called rare earths. Careful use of these resources is correspondingly important.

The partial flow filter proposed according to the invention for treating an exhaust gas flow comprises a coating which contains the substances in higher concentrations, as a rule more than 0.03 g per liter, based on the coated space. In the catalytically oxidizing effect, a loading of the coated space of more than 30 g / liter is particularly advantageous.

In a further development of the partial flow filter proposed according to the invention, the catalytically active coating comprises, for example, noble metals and their oxides in a concentration of more than 0.03 g / liter, in particular> 0.3 g / liter, preferably> 3 g / liter of the coated space.

In a further form of the solution proposed according to the invention, the coating on the end face of the partial flow filter is designed such that non-noble transition metal oxides in a concentration> 0.6 g / liter, preferably> 6 g / liter and in particular> 60 g / liter per coated Has space. The maximum loading of the coated space is limited by the maximum permissible exhaust gas back pressure for the application of the internal combustion engine. Coating the room with more than 300 g transition metal oxides / liter usually requires multi-stage coating processes.

The partial flow filter proposed according to the invention for treating an exhaust gas flow can be designed such that the coating contains more than one catalytically active component.

The partial flow filter proposed according to the invention for treating an exhaust gas flow can contain, in addition to the catalytically active coating on the end face, further catalytically active components in the interior of the filter.

In continuation of the idea proposed according to the invention, the partial flow filter for treating an exhaust gas flow in the space formed by the closed or open channels is provided with a further catalytically active coating for the oxidation of hydrocarbons CO and NO, comprising the chemical element platinum in a concentration of more than 0.03 g / liter, in particular> 0.3 g / liter and depending on the requirements of the internal combustion engine sometimes> 3 g / liter, based on the coated space. This further coating can be applied together with other coatings to the space to be coated, or in a multi-stage coating process. The latter has the advantage that the coatings do not necessarily cover the same room. This can offer advantages in terms of catalytic effectiveness, filtration efficiency and exhaust gas back pressure.

The porosity of the partial flow filter coated according to the invention, of the filters delimiting the flow channels in the interior of the honeycomb structure, is more than 40%, preferably more than 45%, in particular between 48% and 70%. The average pore diameter of the porous wall is 10 μm to 30 μm, in particular more than 12 μm, preferably more than 15 μm and particularly preferably between 16 μm to 25 μm, for example 17 μm to 21 μm, measured using the methods of mercury porosimetry on at least one representative sample bodies, preferably averaged from the measurements on at least two representative sample bodies from the vicinity of both end faces of the filter.

A dimensionless parameter “P” is proposed, suitable for describing particularly advantageous filters according to the invention with regard to the consideration of thermomechanical stability, filtration efficiency and exhaust gas back pressure. The parameter "P" is obtained by multiplying the cell density (flow channels per cm ² ) by the square of the wall thickness (cm), whereby one wall per flow channel is taken into account divided by the porosity of the filter walls delimiting the flow channels inside the honeycomb structure.

For the filters proposed according to the invention, this dimensionless parameter is not less than P = 0.2 and not more than P = 2. Filters according to the invention which have a value of this dimensionless parameter between 0.3 to 1.1 are preferred, and filters are particularly preferred with a dimensionless parameter value of P = 0.35 to 0.95.

1. a) Die Wabenstruktur wird mit der Stirnfläche in eine Lösung katalytisch aktives Material enthaltend eingebracht, und/oder
2. b) die Wabenstruktur wird mit ihrer Stirnfläche in eine Suspension eingetaucht, die neben katalytisch aktivem Material Katalysatorträgermaterialen oder Mischungen und/oder deren Mischoxide enthält, wobei deren durchschnittliche Partikelgröße in der Regel einige Dutzend Nanometer bis zu etwa 30 µm beträgt,
3. c) Trocknung der Beschichtung, aufgebracht gemäß der Verfahrensschritte a) oder b), und
4. d) Kalzinieren der gemäß Verfahrensschritt c) getrockneten Beschichtung.

The invention also relates to a method for applying a coating with at least the following method steps:

1. a) The end face of the honeycomb structure is introduced into a solution containing catalytically active material, and / or
2. b) the end face of the honeycomb structure is immersed in a suspension which, in addition to catalytically active material, contains catalyst support materials or mixtures and / or their mixed oxides, the average particle size generally being a few dozen nanometers up to approximately 30 μm,
3. c) drying the coating, applied according to process steps a) or b), and
4. d) calcining the coating dried according to process step c).

If the exhaust gas of the internal combustion engine does not require any further treatment, the partial flow filter proposed according to the invention can be operated without interacting with other catalysts.

However, the use of a partial flow filter proposed according to the invention relates in particular, for example, also to an exhaust tract of an internal combustion engine with one or more further catalytic converters upstream of the partial flow filter. These are in particular one or more oxidation catalysts and / or nitrogen oxide-storing catalysts, for example diesel oxidation catalysts (DOC), NOx storage catalysts (NSC), or three-way catalysts ( three way catalysts, TWC).

The use of a partial flow filter proposed according to the invention also relates the idea further, for example, to an exhaust gas aftertreatment system of an internal combustion engine comprising at least one catalytic converter for selective catalytic reduction (SCR).

The use of a partial flow filter proposed according to the invention in the flow direction of the exhaust gas arranged in front of a full flow filter which, in contrast to a partial flow filter, does not have a number of open flow channels which significantly impairs its degree of filtration, enables lower particle loadings of the full flow filter and facilitates its cleaning or extends its cleaning, or change interval.

The method for operating an exhaust gas aftertreatment system using the partial flow filter proposed according to the invention provides for temperature control of the exhaust gas flow. The determination, calculation and / or control of the exhaust gas temperature before, after and / or in the partial flow filter is advantageous in those applications of the partial flow filter in which the soot separated in the partial flow filter is continuously exposed to oxygen and all or at least in other areas of the possible operating states of the internal combustion engine / or nitrogen dioxide is oxidized.

Controlling the exhaust gas temperature before, after and / or in the partial flow filter is particularly advantageous, however, especially in those applications in which the amount of soot separated in the partial flow filter is cyclical, according to calculated, and / or according to specified time intervals by raising the exhaust gas temperature and the resulting acceleration of the reaction with oxygen and / or nitrogen dioxide is reduced.

Advantages of the invention

The solution proposed according to the invention largely avoids clogging of the end face of a partial flow filter, in particular at low exhaust gas temperatures. This is achieved by coating the end face of the partial flow filter according to the invention with a high load of catalytically active materials on the end face on the flow inlet side, which catalytically oxidizes exhaust gas components such as hydrocarbons and soot adhering to the end face even at comparatively low exhaust gas temperatures, which on the one hand makes the effectiveness of the Partial flow filter increased and on the other hand significantly extended its life. By reducing or avoiding deposits on the end face, the exhaust gas counterpressure is reduced and the internal combustion engine can thus operate more economically. This reduces their fuel consumption and emissions and CO ₂ , often also nitrogen oxide emissions, since the machine can be operated at lower temperatures.

In other areas of application, turbulent flows of the exhaust gas flow are also formed on the end face of the partial flow filter. This increases the effectiveness of the catalytically active material applied there according to the invention compared to material conventionally applied inside a filter, since due to the turbulence the transport of the pollutants from the main phase of the gas flow to the surface of the catalytically active centers is less hampered by counteracting wall surface effects than it is in The inside of a partial flow filter is the case where there are significantly less turbulent flows.

Compared to coating the inside of the entire partial flow filter or parts thereof with the high concentrations of materials having catalytic properties, considerable resources, for example of precious metals, can be saved. For a coating of an end face of a partial flow filter with a diameter of 143 mm (approx. 5.66 ") and a length of 254 mm (approx. 10") and a production-related penetration depth of the coating of approx. 2.54 mm (approx. 1 "), corresponding to a coated face volume of 0.041 liters, with a concentration of 0.6 g platinum per liter and / or 7 g cerium mixed oxides per liter, less than 0.025 g platinum and / or less than 0.3 g cerium-containing mixed oxides are used. If, on the other hand, such a total amount of the catalytically active substances is applied in a conventional manner over the entire partial flow filter, then under the same operating conditions, in particular at the same low outside temperatures, significantly lower conversions of adhering / blocking exhaust gas components are achieved on the end face, since the end face, equal to the total volume of the partial flow filter of 4.1 liters, then only a concentration of 0.006 g of platinum per liter and / or 0.07 g of cerium-containing mixed oxides per liter.

As a result of the solution proposed according to the invention, the coating is applied at the point at which it enables the highest turnover rates, so that the use of rare and / or valuable resources at less turnover-relevant points within the partial flow filter can be dispensed with, or at least significantly reduced, accordingly these resources can be saved.

Another advantage of the solution proposed according to the invention is that heating measures for keeping free or burning free, ie the non-catalytic burning of soot particles on the end face of the partial flow filter, can be significantly reduced or ideally completely avoided. This means that additional fuels, CO ₂ emissions and maintenance work can be saved.

Furthermore, the solution proposed according to the invention completely eliminates flange connections on the housing of the partial flow filter for cleaning the end face in favorable applications. In other cases, the effort for sealing such flanges is reduced due to the less frequent maintenance work.

Due to the lower loading of the end face of the partial flow filter with exhaust gas constituents adhering there, for example hydrocarbons and soot, the partial flow filter generates a significantly lower exhaust gas back pressure, which in turn saves fuel and CO ₂ emissions when operating the internal combustion engine.

Another advantage is that the solution proposed according to the invention, i. a coating of the end face of the partial flow filter, on a coating of the filter interior can often be completely avoided, in particular coatings with a high load of the catalytically active components are omitted, or require lower loads. Eliminating or at least reducing such coatings leads to a significant reduction in the exhaust gas back pressure, since such coating materials settle on the pore wall and / or in the pore structure of the filter. A coating on the end face of the filter largely avoids these disadvantages, or they occur in a very limited space. By coating the end face without forming a greater penetration depth, the pore structure, in particular in the area of the filter walls, is significantly less impaired.

Another advantage of the partial flow filter according to the invention compared to filters conventionally coated over their total volume is to be known in the fact that, in exhaust gas systems with filter cascades, generally only the partial flow filter in front in the flow direction of the exhaust gas requires a coating according to the invention, thus saving resources, for example precious metals and rare earths can be.

The partial flow filter according to the invention is also advantageous with respect to its filtration efficiency and the exhaust gas back pressure compared to other partial flow filters if they are loaded with a comparable amount of particles. On the one hand because an amount adhering to the end face of the coating according to the invention is oxidized and consequently consequently no filter pores suitable for filtration can clog the filter wall and therefore cannot cause any back pressure.

On the other hand, since a higher cell density can already be selected in the design of the partial flow filter according to the invention due to its lower tendency to clog on the end face. Filters with a higher density of parallel flow channels already have a comparable filtration efficiency with a comparable exhaust gas back pressure - or vice versa - with a low wall thickness and / or higher porosity of the filter walls and / or filter length and / or number of filters in a cascade. Accordingly, with the partial flow filter according to the invention, fuel can be saved in order to achieve a desired filtration efficiency and the CO ₂ emissions of the internal combustion engine can be reduced.

Since, as described above, when designing the partial flow filter according to the invention, a smaller flow cross section of the channels can be selected than with other partial flow filters, the aforementioned advantage of improved filtration efficiency can be further increased if flow channels open on the inlet or on both sides have a smaller cross section than on the inlet side closed channels. On the other hand, when designing the filter, the highest possible storage volume for the particles to be separated from the exhaust gas flow and, at the same time, the filtration efficiency unchanged over a long period of time should be achieved it is advantageous if the flow channels open on the inlet side have a larger cross section than the flow channels closed on the inlet side.

Figure list

The invention is described in more detail below with reference to the drawing.

• 1.1 und 1.2 Stirnflächen von Teilstromfiltern nach deren Betrieb,
• 2 beispielhafte Komponenten eines Abgasstrangs einer Verbrennungskraftmaschine,
• 3 eine schematische Darstellung einer ersten Ausführungsvariante des erfindungsgemäßen Teilstromfilters,
• 4 die schematische Darstellung einer weiteren Ausführungsvariante des erfindungsgemäß vorgeschlagenen Teilstromfilters und
• 5a, 5b und 5c asymmetrische Zellstrukturen mit unterschiedlich großen Strömungsquerschnitten.

It shows:

• 1 .1 and 1.2 end faces of partial flow filters after their operation,
• 2nd exemplary components of an exhaust line of an internal combustion engine,
• 3rd 2 shows a schematic representation of a first embodiment variant of the partial flow filter according to the invention,
• 4th the schematic representation of a further embodiment of the partial flow filter proposed according to the invention and
• 5a , 5b and 5c asymmetrical cell structures with flow cross sections of different sizes.

Variants

The 1 .1 and 1.2 show particle filters 10th whose essentially circular filter surfaces 12 after their operation with a particle load 14 , for example of soot particles, are provided. One in 1 .1 less pronounced and in 1 .2 more pronounced particle loading 14 on an end face 16 of the particle filter 10th , affects the effectiveness of such a particle filter 10th and on the other hand increases the gas back pressure in the exhaust tract of an internal combustion engine.

2nd shows in a schematic manner components of an exhaust tract of an internal combustion engine.

In an internal combustion engine 20th Exhaust gas generated is shown in 2nd a first catalyst 22 forwarded. An exhaust gas flow 21st flows in the direction of flow 24th a partial flow filter 26 to. The partial flow filter 26 comprises a share of open and closed on one or both sides channels, which from the exhaust gas flow 21st be flowed through.

From the partial flow filter 26 according to 2nd in the direction of flow 24th escaping exhaust gas, ie that in the partial flow filter 26 treated exhaust gas flow 21st , flows downstream of the partial flow filter 26 arranged further catalyst 28 or another filter arranged there 28 to. In the latter case, the partial flow filter forms 26 with the additional partial or full flow filter 28 consequently a filter cascade.

3rd shows schematically a first embodiment of the partial flow filter proposed according to the invention 26 .

How out 3rd emerges, comprises a honeycomb structure 42 of the partial flow filter 26 a number of essentially parallel flow channels, either channels closed on one side 38 or channels open on both sides 40 .

From the representation according to 3rd shows that the flow direction 24th flowing exhaust gas flow 21st on the face 16 on the input side into the honeycomb structure 42 flows in. At this area of the face 16 is a coating 34 made of catalytically active material 36 upset. The catalytic active material can be substances 37 for the catalytic oxidation of long-chain hydrocarbons and optional substances 39 for the oxidation of CO and NO. After entering the honeycomb body 42 it comes in open channels 40 it to a flow distribution 48 ; the partial exhaust gas flow 23 flows through the gas-permeable filter walls 30th due to the pressure difference between the channels caused by the flowing exhaust gas 40 and 38 . Filter wall 30th can optionally contain additional catalytic material 31 include.

4th shows a further embodiment of the partial flow filter proposed according to the invention.

4th can be seen that the end face 16 of the partial flow filter 26 to the front face 16 delimiting filter walls with the coating 34 made of catalytically active material 36 , including fabrics 37 for the catalytic oxidation of long-chain hydrocarbons and optional substances 39 for the oxidation of CO and NO. With the catalytically active material 36 it is for example gold, platinum, palladium, rhodium, ruthenium, iridium, their mixtures and / or their oxides / mixed oxides, and also other transition metals, for example silicon, titanium, aluminum, iron, copper, vadium, hafnium, scandium, yttrium , Tungsten, zirconium, lanthanum, cerium, praseodymium, neodymium and other lanthanoids and actinoids, in particular their oxides, and their mixed oxides.

How 4th the coating also extends 34 on the filter walls 30th in the area of the face 16 of the partial flow filter 26 in a depth of penetration 44 . The depth of penetration 44 is preferably <10 mm, preferably <5 mm, for example approximately 1 mm.

If the partial flow filter 26 parallel channels closed on one side, compare position 46 in 4th includes that in a ceramic honeycomb structure 42 run - and this in the direction of flow 24th of the exhaust gas flow 21st are arranged on the input side - it is advantageous if the coating 34 does not penetrate deeper into the partial flow filter than the plug 32 are long. The stopper length is a few millimeters, advantageously less than 12 mm, generally between 0.5 and 7 mm, particularly advantageously 1 to 5 mm.

In principle, penetration depths lower than 1 mm are technically possible; so the coating can 34 for example, have very small penetration depths, for example between 5 μm and 0.9 mm.

In extreme cases, the coating thickness can also be a few nanometers, for example if a solution containing a predominantly noble metal has been applied to the end face. Because of a lack of catalytic activity and because of a lack of thermomechanical stability, such thin layers and the associated extremely low concentrations of catalytically active material are due to the depth of penetration 44 Defined coated partial volumes are not preferred since they tend to sinter and the agglomerates formed are less catalytically active.

The catalytically active material 36 which is in the coating 34 is contained, according to the invention in high concentrations on the depth of penetration 44 Defined coated partial volume applied, for example more than 0.1 g of precious metals per liter, in particular> 0.3 g / liter, preferably> 3 g / liter on the coated space.

Concerning catalytically active base transition metal oxides, concentrations of 6 g / liter, preferably> 60 g / liter g / in ^{3 are} applied. It is also possible to use more than one or two catalytically active transition metal oxides together, or at different points on the end face of the filter, or there in different layers.

From the representation according to 4th shows that the unilaterally closed channels 46 within the honeycomb structure 42 on an exit-side end face of the honeycomb body 42 through the plugs 32 are closed.

The honeycomb structure 42 of the partial flow filter 26 For example, a ceramic material is usually pressed as a strand through a mouthpiece - so-called extrusion - and then partially closed, or it is formed from a porous metallic material, for example a sintered metal.

A penetration depth preferably corresponds 44 the coating 34 into the filter walls 30th a length of plugs 32 , Or less.

The coating proposed according to the invention 34 that on an entry-side end face of the honeycomb structure 42 is provided, for example, by immersing the corresponding end face 16 the honeycomb structure 42 in a solution of chemical precursors of the catalytically active material 36 take place, or by immersing the end face of the honeycomb body 42 in a suspension, the catalytically active material 36 , or their chemical precursors. The suspension can be in addition to the catalytically active materials 36 also catalyst support materials such as Al ₂ O ₃ , ie containing aluminum silicates, or their precursors. Solution or suspension can also contain inorganic binders, for example acetic acid clay, transition metal hydroxides, or zirconium acetate. Mixtures of solutions and suspensions are possible. Applying the coating 34 immersion closes the drying of the coating 34 at. It is used to remove excess liquids and to pre-fix the coating on the honeycomb structure. At the drying step of the coating 34 on the face 16 the honeycomb structure is followed by a thermal calcination step at higher temperatures. The calcination, a kiln process, serves to remove organic components from the coating, precursors of the catalytically active materials and binders in the catalytically active materials 36 and to transfer the binders as well as these and any catalyst support materials to the honeycomb structure 42 to fix. The calcination can optionally at least partially be done by the hot exhaust gas flow 21st the internal combustion engine 20th respectively.

The one proposed according to the invention on its entry-side end face 16 or on its outlet end face with a coating 34 made of catalytically active material 36 provided partial flow filter 26 , reduces the risk of clogging and consequently expands the area of application, for example with a higher concentration of hydrocarbons, SOF and soot, and is more suitable, for example, for operation at low exhaust gas temperatures and for operation of the partial flow filter 26 with a lower NO ₂ content in the exhaust gas flow 21st . The partial flow filter proposed according to the invention 26 can be used in combination with other catalysts 22 respectively. 28 be used. For example, an oxidation catalytic converter is connected upstream, and there are also combinations of the partial flow filter proposed according to the invention 26 in combination with NSC, SCR and TWC catalysts possible, as well as in the flow direction of the exhaust gas flow 21st subsequent full flow filter, for example a full flow Particulate filter for cleaning diesel or petrol engine exhaust gases.

The 5a , 5b and 5c show asymmetrical filter structures with flow cross sections of different sizes.

In the 5a , 5b , 5c the given pattern of closed channels on an end face of a filter are shown by way of example. According to 5a are on the face 10th in a pattern with gaps 66 predominantly closed channels with a smaller cross-section, compare position 62 .

5b it can be seen that in each case a channel closed on the end face 62 with a smaller cross section and one on a side wall 64 adjacent closed channel 72 with a large cross section are arranged in an alternating pattern. In the variant according to 5b are open channels with a large cross-section with position 70 designated.

5c it can be seen that within a regular pattern on the face 16 the channels with a smaller cross-section open and the channels 72 are closed with a large cross section.

The invention is not restricted to the exemplary embodiments described here and the aspects emphasized therein. Rather, a large number of modifications are possible within the scope specified by the claims, which lie within the framework of professional action.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included 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.

Patent literature cited

• EP 3068989 B1 [0002]
• WO 2009/024815 [0003]
• US 2011219745 [0004]
• DE 102015226039 A1 [0005]

Claims (11)

Partial flow filter (26) for treating an exhaust gas flow (21) of an internal combustion engine (20) with a honeycomb structure (42) from a number of closed or open flow channels (38, 40), which are delimited by gas-permeable filter walls (30), characterized in that the partial flow filter (26) has at least one coating (34) on an end face (16) facing the exhaust gas flow (21), which has a catalytically active material (36) which has an oxidizing effect on hydrocarbons, SOF and soot at low exhaust gas temperatures. Partial flow filter (26) for treating an exhaust gas flow (21) according to Claim 1 , characterized in that the coating (34) is limited to the end face (16). Partial flow filter (26) for treating an exhaust gas flow (21) according to Claim 1 , characterized in that the coating (34) has a penetration depth (44) into the flow channels formed by the closed or open channels (38, 40) that is <10 mm, preferably <5 mm and particularly preferably <0.1 to 3 mm is. Partial flow filter (26) for treating an exhaust gas flow (21) according to Claim 1 , characterized in that the coating (34) contains substances selected from the following group: precious metals such as gold, platinum, palladium, rhodium, ruthenium, iridium, their mixtures and / or their oxides / mixed oxides, and other transition metals, for example silicon, Titanium, aluminum, iron, copper, vadium, hafnium, scandium, yttrium, tungsten, zircon, lanthanum, cerium, praseodymium, neodymium and other lanthanoids and actinoids, especially their oxides, and their mixed oxides. Partial flow filter (26) for treating an exhaust gas flow (21) according to Claim 4 , characterized in that the coating (34) contains the substance (s) in higher concentrations, characterized in that the coating (34) noble metals or their oxides in a concentration of 0.1 g noble metals per liter of coated filter volume in the area of the penetration depth ( 44), in particular> 0.3 g / liter, preferably> 3 g / liter. Partial flow filter (26) for treating an exhaust gas flow (21) according to Claim 4 , characterized in that the coating (34) contains catalytically active base metal transition oxides in a concentration> 0.6 g / liter of coated filter volume in the area of the penetration depth (44), in particular> 6 g / liter, preferably> 60 g / liter. Partial flow filter (26) for treating an exhaust gas flow (21) according to Claim 5 , characterized in that the coating (34) contains more than one catalytically active transition metal or transition metal oxide. Partial flow filter (26) for treating an exhaust gas flow (21) according to Claim 1 , characterized in that a further platinum-containing coating for the oxidation of CO and NO is arranged in the closed or open channels (38, 40). Method for applying a coating (34) according to one of the Claims 1 to 8th with the following method steps: a) the honeycomb structure (42) is immersed with the end face (16) in a solution and / or suspension containing catalytically active material (36) or its precursors, c) drying the coating (34), applied in accordance with Process steps a) and c) calcining the coating (34) dried according to process step b). Method for using one or more particle filters using at least one partial flow filter (26) according to one of the Claims 1 to 9 in the exhaust tract of an internal combustion engine (20) with an oxidation catalytic converter and / or nitrogen oxide storage catalytic converter or three-way catalytic converter connected upstream of the partial flow filter (26). Process for purifying a gas according to Claim 10 using at least one partial flow filter (26) according to one of the Claims 1 to 9 in the exhaust tract of an internal combustion engine (20) in combination with an SCR catalytic converter.

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