DE102019100097A1 - Process for the production of catalytically active wall flow filters - Google Patents

Abstract

Particle filters are commonly used to filter exhaust gases from a combustion process. New filter substrates and their specific use in exhaust gas aftertreatment are also specified.

Description

The present invention is directed to a method of making particle filters. Particulate filters are commonly used to filter exhaust gases from a combustion process. New filter substrates and their specific use in exhaust gas aftertreatment are also specified.

The exhaust gas from, for example, 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 mainly consist of soot residues and possibly adhering organic agglomerates. These are referred to as primary emissions. CO, HC and particles are products of the incomplete combustion of the fuel in the combustion chamber of the engine. Nitrogen oxides are generated in the cylinder from nitrogen and oxygen in the intake air when the combustion temperatures locally exceed 1400 ° C. Sulfur oxides result from the combustion of organic sulfur compounds, which are always contained in small amounts in non-synthetic fuels. A large number of catalytic exhaust gas purification technologies have been developed to remove these emissions, which are harmful to the environment and health, from motor vehicles, the basic principle of which is usually based on the fact that the exhaust gas to be cleaned is passed over a catalytic converter which consists of a flow or wall flow honeycomb body (wall flow filter) and a catalytically active coating applied thereon and / or therein. The catalyst promotes the chemical reaction of various exhaust gas components with the formation of harmless products such as carbon dioxide and water.

Particles can be removed from the exhaust gas very effectively using particle filters. Wall-flow filters made from ceramic materials have proven particularly useful. These have two end faces and are made up of a large number of parallel channels of a certain length, which are formed by porous walls and extend from one end face to the other. The channels are mutually sealed at one of the two ends of the filter so that first channels are formed which are open on the first side of the filter and closed on the second side of the filter, and second channels which are on the first side of the filter closed and open on the second side of the filter. The exhaust gas flowing into the first channels, for example, can only leave the filter again via the second channels, and for this purpose has to flow through the porous walls between the first and second channels. When the exhaust gas passes through the wall, the particles are retained.

Wall flow filters can be catalytically active. The catalytic activity is achieved by coating the filter with catalytically active material. Contacting the catalytically active materials with the wall flow filter is referred to in the trade as "coating". This term generally means the application of catalytically active materials and / or storage components to a largely inert support body / substrate. The coating takes on the actual catalytic function and often contains storage materials and / or catalytically active metals, which are usually deposited in a highly dispersed form on temperature-stable, high-surface metal compounds, in particular oxides. The coating is usually carried out by applying an aqueous suspension of the storage materials and catalytically active components - also called washcoat - to or in the wall of the wall flow filter. After the suspension has been applied, the carrier is generally dried and optionally calcined at elevated temperature. The coating can consist of one layer or be composed of several layers, which are applied one above the other (multilayer) and / or offset to one another (as zones) on a corresponding filter. The catalytically active material can be applied to the porous walls between the channels (so-called effort coating). However, this can lead to an unacceptable increase in the back pressure of the filter. Against this background, for example, JPH01-151706 and WO2005016497A1 propose to coat a wall flow filter with a catalyst in such a way that the latter penetrates the porous walls (so-called in-wall coating).

So-called three-way catalytic converters are used to reduce emissions in stoichiometric combustion engines. Three-way catalysts (TWCs) are well known to those skilled in the art and have been required by law since the 1980s. The actual catalyst mass here mostly consists of a high-surface area metal compound, in particular oxidic support material, on which the catalytically active components are deposited in the finest distribution. The noble metals of the platinum group, platinum, palladium and / or rhodium are particularly suitable as catalytically active components for the purification of stoichiometrically composed exhaust gases. Suitable carrier materials are, for example, aluminum oxide, silicon dioxide, titanium oxide, zirconium oxide, cerium oxide and their mixed oxides and zeolites. So-called active aluminum oxides with a specific surface area (BET surface area measured according to DIN 66132 - latest version on the filing date) of more than 10 m ² / g are preferably used. To improve the dynamic conversion, three-way catalysts also contain oxygen-storing components. These include cerium / zirconium mixed oxides, which may contain lanthanum oxide, praseodymium oxide and / or yttrium oxide. Zoned and multilayer systems with three-way activity are now also known ( US8557204 ; US8394348 ). If such a three-way catalytic converter is located on or in a particle filter, one speaks of a cGPF (catalyzed gasoline particle filter; e.g. EP2650042B1 ).

The particle filter has in common that it has to be regenerated at certain time intervals. This means that the accumulated soot particles have to be burned off in order to keep the exhaust gas back pressure in an acceptable range. Exhaust gas temperatures of approx. 600 ° C are required for filter regeneration and initiation of soot combustion. Very high temperatures can occur during the burn-up, which can be> 800 ° C.

Furthermore, as already reported above, care must be taken to ensure that wall flow filters coated with catalytically active material have the most neutral possible influence on the exhaust gas back pressure, since increased exhaust gas back pressure has a negative effect on fuel consumption and thus on CO2 emissions. Techniques have been described in the prior art on how the exhaust gas back pressure of catalytically coated wall flow filters can be reduced.

The targeted loading of a porous filter with a coating suspension is carried out in the EP2727640A1 described. The pores on the inflow side of the filter have particles in the interior which completely fill the pores at least across their cross-section, essentially transversely to the direction of flow, and due to this porous filling, the pore volume of the filled pores is 50 to 90% based on the pore volume of unfilled pores. The pore volume of the filled pores on the upstream side of the filter is less than the pore volume of the filled pores in the flow direction further away from the upstream side of the filter and the pore volume of the filled pores in the flow direction increases the further away the pores are from the upstream side of the filter .

The EP1716903B1 proposes a method for coating filter bodies, in which the filter, after coating, is freed from too much coating dispersion by repeatedly applying pressure pulses to one end of the filter body in such a way that excess coating suspension is forced out of the filter body until it reaches its optimum Coating weight has reached. The goal seems to be to reduce the exhaust gas back pressure of the filter. This is obviously an in-wall coating.

The US20040254071A1 describes a method for coating a wall flow filter. Here, a coating suspension is introduced into a wall flow filter and an excess is removed. Zoned coatings can thus be obtained in or on wall flow filter channels. It is not explicitly stated from which side the coating takes place. The aim here is to obtain a specific coating geometry through the solids content of the coating suspension. The coating concentration is usually increased on the side through which the coating is introduced into the wall flow filter.

The WO2006042699A1 is also directed to a method for coating wall flow filters, among other things. Here, a support body is contacted with a suspension after vertical alignment from below. Excess suspension is then removed from the support body. For the purpose of weight loyalty, additional coating suspension can be applied to the support body from above via a spray nozzle.

There have been several attempts to control the permeability of a wall flow filter along its longitudinal axis. This is usually attempted by using a variable coating thickness ( EP1554473A1 , US7981370BB , US8591820BB ). However, there is still a need for wall-flow filter substrates which, in the triangle of requirements of catalytic effectiveness, filtration efficiency and exhaust gas back pressure, are able to deliver optimum performance, particularly in the area of stoichiometric combustion gasoline engines.

The object of the present invention is to specify a production process for catalytically coated, ceramic wall-flow filter substrates, which in particular makes it possible to generate wall-flow filter substrates which are improved compared to the prior art. The wall flow filters produced in this way should be superior to the substrates produced according to the prior art, in particular with regard to the requirement of the lowest possible exhaust gas back pressure with sufficient catalytic activity and filtration efficiency. It was also an object of the present invention to specify filter substrates produced by the above process and their use in exhaust gas aftertreatment.

These and other tasks that result from the state of the art in an obvious manner are solved by a method with the features of the claims 1. The dependent claims dependent on these claims are directed to preferred embodiments of the method according to the invention. Claims 8-12 are directed to the wall flow filters themselves and their use.

1. i) man in den vertikal arretierten Wandflussfilter durch die untere Stirnfläche eine Suspension aufweisend ein katalytisch aktives Material für weniger als 100% der Länge L des Wandflussfilters hineindrückt dergestalt, dass die festen Bestandteile der Suspension zu weniger als 20 Gew.-% bezogen auf die Menge an festen Bestandteilen in die Wand eindringen können,
2. ii) man überschüssige Suspension über die untere Stirnfläche des Wandflussfilters entfernt und
3. iii) man den Wandflussfilter im Schritt ii) oder ggf. in einem folgenden Schritt durch Anlegen einer Druckerhöhung an der oberen Stirnfläche und/oder Druckerniedrigung an der unteren Stirnfläche des Wandflussfilters in Form mindestens eines Druckimpulses behandelt, und dabei in Abhängigkeit der Fließgrenze (γ) und den von den Poren des Filters abhängigen Kapillarkräften (4 σ cos Θ) mindestens einen der Druckimpulse so dimensioniert, dass die Druckerhöhung an der oberen Stirnfläche und/oder Druckerniedrigung an der unteren Stirnfläche des Wandflussfilters mindestens folgendem Wert entspricht: $$\Delta p\left(stat\right)=\left(4\sigma \text{ cos }\theta \right)/d+\Upsilon ,$$
   
   gelangt man äußerst überraschend, dafür aber nicht minder vorteilhaft zur Lösung der gestellten Aufgabe. Durch intensive Untersuchung hat es sich herausgestellt, dass der über die Wand eines Filters strömende Volumenstrom des Abgases maßgeblich durch große Poren bewerkstelligt wird. Legt man an Poren eine Druckdifferenz an, dann strömt das Gas laminar durch die Poren. Der Volumenstrom ist dann proportional zu d⁴. D.h., durch einen 4 x größeren Porendurchmesser [d] strömt das 256-fache an Gas. Sofern man diese Poren durch mindestens einen relativ kurzen Druckimpuls von auf der Wand sitzendem katalytisch aktiven Material befreit, kann hier der Volumenstrom ohne wesentlich höheren Abgasgegendruck durch die Wand des keramischen Filters hindurchströmen. Auf den kleineren Poren, welche den Großteil der Gesamtporosität des Filtermaterials ausmachen, kann das katalytisch aktive Material weiterhin vorhanden sein, ohne damit das durchfließende Abgas über die Maßen zu behindern. Die so hergestellten Substrate zeigen in Kombination mit anderen katalytisch aktiven Beschichtungszonen eine ausreichende katalytische Aktivität bei gegenüber den katalytisch aktiven Filtern des Standes der Technik vermindertem Abgasgegendruck.

The fact that in a process for the production of catalytically coated ceramic wall flow filters with optimized exhaust gas back pressure for the treatment of exhaust gases from a combustion process, the wall flow filter having a first end face, a second end face and a length L and a porosity of at least 50% to a maximum of 80% (DIN 66133 - latest version on the filing date) and an average pore diameter of 5 - 50 µm (DIN 66134 - latest version on the filing date), such that:

1. i) one presses a suspension comprising a catalytically active material for less than 100% of the length L of the wall flow filter into the vertically locked wall flow filter through the lower end face in such a way that the solid components of the suspension are less than 20% by weight based on the amount can penetrate the wall with solid components,
2. ii) excess suspension is removed via the lower end face of the wall flow filter and
3. iii) the wall flow filter is treated in step ii) or, if appropriate, in a subsequent step by applying a pressure increase on the upper end face and / or a pressure decrease on the lower end face of the wall flow filter in the form of at least one pressure pulse, and in this case as a function of the flow limit (γ) and the capillary forces (4 σ cos Θ), which are dependent on the pores of the filter, dimension at least one of the pressure pulses such that the pressure increase on the upper end face and / or pressure decrease on the lower end face of the wall-flow filter corresponds at least to the following value: $$\Delta p\left(stat\right)=\left(\mathrm{4th}\sigma \text{cos}\theta \right)/d+\Upsilon ,$$
   
   one arrives extremely surprisingly, but no less advantageous for solving the task. An intensive investigation has shown that the volume flow of the exhaust gas flowing over the wall of a filter is largely caused by large pores. If a pressure difference is applied to pores, the gas flows laminarly through the pores. The volume flow is then proportional to d ⁴ . Ie, through a 4 x larger pore diameter [d], 256 times the gas flows. If these pores are freed of catalytically active material sitting on the wall by at least a relatively short pressure pulse, the volume flow can flow through the wall of the ceramic filter without a significantly higher exhaust gas back pressure. The catalytically active material can still be present on the smaller pores, which make up the majority of the total porosity of the filter material, without excessively impeding the exhaust gas flowing through. The substrates produced in this way, in combination with other catalytically active coating zones, have sufficient catalytic activity with reduced exhaust gas back pressure compared to the catalytically active filters of the prior art.

$$\Delta p\left(stat\right)=\Delta p\left(K\right)+\gamma$$

$$\Delta p\left(stat\right)=\left(4\sigma \text{ cos }\theta \right)/d+\gamma$$

• Δp (K) : nötige Druckdifferenz zum Öffnen der Kapillare mit dem Durchmesser d
• d : Durchmesser der Kapillare (Poren)
• σ : Oberflächenspannung
• Θ : Kontaktwinkel
• γ : Fließgrenze

To empty the pores, the static forces such as the capillary forces in the pores [Δp (K)] (https://de.wikipedia.org/w/index.php?title=Kapillarit%C3%A4t&oldid=183101365) and the yield point [γ] of the suspension can be overcome. The above formula describes the minimum pressure difference in order to open the corresponding pores and to remove particles from the filter cake. $$\Delta p\left(K\right)=\rho GH=\left(\mathrm{4th}\sigma \text{cos}\theta \right)/d$$

$$\Delta p\left(stat\right)=\Delta p\left(K\right)+\gamma$$

$$\Delta p\left(stat\right)=\left(\mathrm{4th}\sigma \text{cos}\theta \right)/d+\gamma$$

• Δp (K): pressure difference required to open the capillary with the diameter d
• d: diameter of the capillary (pores)
• σ: surface tension
• Θ: contact angle
• γ: yield point

According to DIN EN ISO 3219-1 (latest version on the filing date) the yield point is determined. It is defined as the smallest shear stress γ above which a sample behaves like a liquid and can flow. Below the yield point, it behaves more like a solid. Suspensions are advantageously used which, as a filter cake, that is to say as a coating applied to the wall of the wall flow filter, have a flow limit which is so great that the pores opened by the pressure pulse are not closed again by a flowing suspension. Due to the increase in the concentration of the coating suspension caused by the water absorption of the porous filter from, for example, approx. 35% to greater than 45%, the yield point increases significantly ( Chateau et al., J. Rheol. 52, 489-506 (2008) ). The yield point for suspensions with correspondingly high solids concentrations after coating in the filter cake is advantageously between 1 Pa and 300 Pa, preferably between 5 and 200 Pa and very preferably between 10 and 100 Pa. The yield point of suspensions is usually determined using a plate-cone or plate-plate rheometer (for example the HAAKE RheoStress 600). The density of the suspensions used can preferably be between 1050 kg / m ³ to 1700kg / m ³ , more preferably between 1100kg / m ³ and 1600kg / m ³ and particularly preferably between 1100kg / m ³ and 1550kg / m ³ . The value of the surface tension and the contact angle for water can be approximately assumed for the surface tension of the ceramic suspensions. The surface tension value is 72.75 mN / m at 20 ° C and the contact angle is around 20 °. If you insert this amount into the equation, the minimum required pressure pulse for emptying pores with a pore diameter of, for example, 10 µm at 280 mbar plus the value of the yield point [γ] from 3 to 10 mbar at 283-290 mbar is calculated. If you want to open the pores> 30µm, the minimum pressure pulse drops to approx. 100mbar at the same yield point. These pressure pulse indications mean that the wall flow filter is treated with a corresponding negative pressure.

As a rule, the pressure pulse Δp described above will not be increased over a certain intensity. The value is preferably at most 1.5 times, preferably 1.2 times, most preferably 1.1 times the pressure Δp (stat) specified by the formula.

The pressure pulse described under iii) according to the invention is therefore in particular a measure which is sufficient to largely free the larger channels or pores (e.g. ≥d50 of the pore diameter) through the wall from the catalytically active material applied via these pores. As a rule, only the large, continuous pores or channels that reach through the wall are "blown free" or "sucked free" as already described above. However, the catalytically active substance remains predominantly on the smaller pores of the filter walls. To further discriminate between large and smaller pores, it may be beneficial for the pressure pulse to develop fully in a relatively short period of time. The maximum pressure difference should be reached within ≤ 0.5 s, more preferably ≤ 0.2 s and very preferably ≤ 0.1 s. The total duration of the pressure pulse should also not exceed a value of 2 s, preferably 1 s and particularly preferably 0.5 s.

Likewise, the pressure pulse should not exceed 350 mbar, more preferably 370 mbar and very preferably 400 mbar, since otherwise too much oxide mass will be removed. By blowing / sucking especially the large pores, an optimal balance between exhaust gas back pressure, filtration efficiency and catalytic activity of this coating zone is achieved.

In the present case, a so-called expense coating is generated. This means that as much of the catalytic coating as possible should be deposited on the wall and not in the pores of the wall. Accordingly, it is preferred if the solid constituents of the suspension can penetrate the wall of the filter to less than 15% by weight, more preferably less than 10% by weight, based on the amount of solid constituents. To determine the proportion of the washcoat in the wall of the wall flow filter and the proportion of the washcoat on the wall of the wall flow filter, scanning electron microscope images are evaluated with the aid of a statistical grayscale evaluation. Free pores / air appear black in a catalytically coated filter, while the heaviest elements appear white. By a specialist Known suitable choice of measurement settings, the difference between active material and filter substrate can be evaluated in this way due to the separation of the gray levels.

Expensive coatings are preferably achieved in that the catalytically active material contains high-surface metal compounds, in particular oxides, whose average particle diameter (DIN 66160 - latest version on the filing date) prefers d50 to the Q3 distribution in relation to the average pore diameter of the filter d50 to the Q3 distribution > 1: 6 and <1: 1 and particularly preferably at> 1: 3 and <1: 2 (https://de.wikipedia.org/wiki/Partikelgr%C3%B6%C3%9Fen Distribution). An upper limit is generally the value which the person skilled in the art can judge to be sensible in the case of appropriate cost coatings. The correct choice of the average particle size can control how much of the catalytically active materials should be positioned in the wall or on the wall of the wall flow filter. The smaller the particle radii of the advantageously high-temperature stable metal oxide components, the more of these components can be positioned in the small pores of the wall. The ratio of preferably oxidic components present on the wall to the wall naturally also has a significant influence on the exhaust gas back pressure of the filter substrate produced in this way.

It has proven to be advantageous if a pressure-free holding time is built in before the application of the pressure pulse. During the holding time, the porous matrix of the filter wall can continue to absorb liquid and more liquid can penetrate into the neighboring cell, so that when the pressure is reversed, more liquid flows back and particles can come out of the filter cake ( 8th ). The holding time can be adapted to the requirements of the wall flow filter. If more backflowing liquid is desired when the pressure is reversed, the holding time is increased accordingly. The holding time is preferably between 0s and 10s, more preferably between 0s and 5s and particularly preferably between 0 and 2s.

In a first step in the method according to the invention, a suspension which has catalytically active materials is introduced into the filter via the lower end face of the wall-flow filter. The pressure difference used for filling is preferably between 0.05 bar and 4 bar, more preferably between 0.1 and 3 bar and particularly preferably between 0.5 and 2.5 bar. This pressure difference is preferably selected as a function of the viscosity of the suspension and the cell dimensions of the wall flow filter such that the filling speed in the cells is between 10 mm / s up to 250 mm / s, preferably between 20 mm / s and 200 mm / s and entirely is preferably between 30 mm / s and 180 mm / s. By filling the channels of the wall flow filter with the suspension, an expense coating is created according to the invention that is less than the maximum length of the wall flow filter. In this case one speaks of a zone. The zone length can be> 15%, more preferably 20% - 85%, very preferably 25% - 75% and extremely preferably 30% - 70% of the length L of the wall flow filter. In other aspects of the invention, this coating can also reach only at least 1.25 cm from the lower end face.

In an advantageous embodiment of the present invention, the catalytic coating of the wall flow filter produced in this way has a positive gradient for the amount of catalytically active material in the coating direction. This means that there are fewer catalytically active materials in the vicinity of the lower end face after step iii) than viewed further in the middle of the wall flow filter in the longitudinal direction ( 3rd ). The expense zone created according to the invention has an amount of material, measured in material / unit length, which, after the plugs have been removed, is 20% to 70% less than in a subsequent area over a range of 15 to 40 mm from the coating inlet end. The amount of active components in the coating direction over the length of 80 mm of the substrate has a positive concentration gradient in the range from 20% to 100%, more preferably 25% to 90%. The concentration gradient due to the different amount and distribution of the catalytically active materials can be determined, for example, gravimetrically, by evaluating X-ray absorption data (XRF measurement) or by measuring the BET surface area of certain filter sections along the longitudinal axis of the filter.

The coating method according to the invention can advantageously be carried out several times in succession with the same or different catalytically active materials. It is important here that a corresponding pressure pulse according to the invention is set in between while still moist, which ensures that the large pores are blocked as little as possible by the coating components of the catalytically active material. It should be mentioned that the coating can be carried out with the same or different catalytically active materials, with and without intermediate drying. For example, a first catalytically active material can be specifically introduced into the pores of the wall of the filter substrate and a second catalytically active material can be applied to the wall of the filter substrate in a subsequent coating in accordance with steps i) - iii).

However, it is also advantageous according to the invention if steps i) - iii) are carried out and then carried out again from the other side after turning the wall flow filter. Architectures can thus be achieved as in 3rd shown as an example. The layers ( 10a ) can overlap in the longitudinal direction of the wall flow filter, then preferably for more than 5%, more preferably up to 20% and very preferably for 7% - 15% of the length L of the wall flow filter. Here, too, the coating can be carried out using the same or different catalytically active materials or amounts, with or without intermediate drying.

In a further preferred embodiment of the present invention, a method is carried out as previously described. Without rotating the wall flow filter in its orientation, a certain amount of a suspension comprising a catalytically active material (identical or different from the first) is additionally applied to the upper end face during or afterwards - with or without intermediate drying, and this is applied by applying a pressure increase to the front face introduced the upper end face and / or pressure reduction on the lower end face of the wall flow filter in the vertically locked wall flow filter, so that this coating extends to less than 100% of the length of the wall flow filter. The length of this zone coating in the channels adjacent to the first coating can be determined by a person skilled in the art. It is at least 20% and at most 95% of the length L of the wall flow filter, preferably 40% to 85%, particularly preferably 50% to 70%. A possible embodiment is in 4th pictured. Here, too, the layers (400 or 500) can overlap in the longitudinal direction of the wall flow filter.

However, the zones formed by the two coatings do not have to overlap. A range of max. 50%, preferably max. 33% and very preferably max. 25% of the length L of the wall flow filter - if desired - remain free. The filtration efficiency of the free area can then be specifically adjusted to the requirements of the wall-flow filter after drying by means of a subsequent powder coating. The powder coating to increase the filtration efficiency is known to the person skilled in the filter technology under the term precoat ( US4010013 ).

However, the last washcoat coating preferably overlaps with the coating according to steps i) -iii) to at least 5%, more preferably up to 20% and very preferably for 7% -15% of the length L of the wall-flow filter.

In an extremely preferred form according to the present invention, the process steps i) - iii) according to the invention are combined with the process step just mentioned in such a way that the introduction of the suspension from the upper end face and the treatment of the coating according to steps i) - iii) with the at least one pressure pulse happens at the same time. In this case, by means of the at least one pressure pulse used to treat the coating supplied from below, the suspension applied to the upper end face of the wall flow filter is simultaneously sucked or pressed into the wall flow filter. One proceeds step by step so that first the suspension is inserted into the wall flow filter from below, then the suspension is applied to the upper face and then both suspensions are treated with the at least one pressure pulse. This leads to a particularly preferred method, since two identical or different coatings in the same or different amounts from different ends of the wall-flow filter can be introduced into the same in a few work steps. As a result, filter architectures of the 4th be preserved. As already mentioned, the suspensions applied from below or from above can be very general or different. If different coating suspensions are used, it is optionally possible to apply the top coating applied as an overhead coating ( 4th ) or as an in-wall coating ( 5 ) to dimension. If an expense coating is targeted from above, reference is made to what has been said above regarding expense coatings with regard to the configuration of this suspension.

The zone on the wall created with steps i) to iii) can additionally be combined with a zone in the porous wall which was also created by the sequence of steps i) to iii) after the substrate was rotated through 180 ° ( 5 ). The order of the zone application is arbitrary.

For an in-wall coating, the particle diameter d99 of the Q3 distribution in the suspension in relation to the average pore diameter of the pores in the filter walls (d50 of the Q3 distribution) should be preferably <0.6: 1, more preferably <0.5: 1 and particularly preferably <0.4: 1. It is thus possible to get a large proportion of the suspension of> 80%, more preferably> 90% and very preferably> 95% and more into the pores of the wall of a wall flow filter. It can then be used to manufacture wall-flow filters, for example in 5 are shown. The two zones ( 10a , 10b ) do not have to overlap. A range of max. 20%, preferably max. 10% and very preferably max. 5% of the length L of the Wall flow filters - if desired - remain free. This last coating preferably overlaps with the coating according to steps i) -iii) but at least 5%, more preferably up to 20% and very preferably for 7% -15% of the length L of the wall flow filter.

The zone on the wall applied from above, with a comparable loading, a comparable zone length and a comparable particle size distribution in the coating, has a significantly lower permeability overall than the zone on the wall, which over the lower end face with pressure pulse according to steps i) - iii) has been introduced, see also Table 2. When two zones overlap, particularly high loads can occur in the area of the overlap, since the zones are then on both sides of the porous wall or in the wall and on the wall. If additional filtration efficiency is required, it can be created with a powder coating (see above) in the area of high permeability. This is especially true if the zones do not overlap. Powder coatings for increasing filtration efficiency have long been state of the art in filters for air pollution control (The Effects of Newly Formulated Filter Aids Material Loading on Pressure Drop and Particle Penetration, S. Hajar, M. Rashid, A. Nurnadia, MR Ammar, International Conference on Mechanics, Materials and Structural Engineering (ICMMSE 2016)).

An application zone applied over the upper end face, however, has a gradient with respect to the coating concentration along the longitudinal axis of the filter that remains the same within the scope of the error accuracy or, if so, then falls slightly in the coating direction ( 4th ). This expense zone therefore has a permeability in the coating direction that remains constant within the scope of the error accuracy or, if so, increases slightly. The wall-flow filter produced as indicated above can be dried between the processes for applying the catalytically active coatings, but it does not have to - as already indicated. As a rule, calcination does not follow in the usual way until the application of the final coating has been completed.

The present invention also relates to a catalytically coated ceramic wall-flow filter produced according to the invention for the treatment of exhaust gases from a combustion process. In a particularly preferred embodiment, the catalytic coating of the wall flow filter produced according to steps i) - iii) has a positive gradient of the coating concentration (g / l) in the coating direction (see above). This preferably results in a negative gradient (decrease) with regard to the permeability in the coating direction.

Further advantageous embodiments for the method just described also apply to the wall flow filter specified here, provided that they have an influence on the spatial-physical design of the filter.

A very preferred wall flow filter - as described - has a catalytically active coating in the channels from both sides, of which at least one coating represents a porous expenditure coating (e.g. 4th / 5). In this form, the filter has no preferred direction. However, it is preferably installed in the exhaust system of a vehicle with a stoichiometrically operated internal combustion engine in such a way that the cost coating of steps i) - iii) according to the invention is located in the outlet duct, as seen in the flow direction ( 1 ).

1. a) Permeabilität im Bereich der Beschichtung ausgehend von der ersten Stirnfläche im Rahmen der Fehlergenauigkeit gleichbleibend oder in Beschichtungsrichtung fallend;
2. b) Permeabilität im Überschneidungsbereich der Beschichtungen gleich oder geringer als im Bereich unter a);
3. c) Permeabilität im Bereich der restlichen Beschichtung kontinuierlich steigend. Ganz besonders vorteilhaft ist, wenn es sich bei beiden Beschichtungen um Aufwandbeschichtungen handelt und die Permeabilität an der zweiten Stirnfläche, der Stirnfläche des Abgasaustritts, die höchste Permeabilität des Filters aufweist.

Special wall flow filters can be produced by the method according to the invention. These have a unique permeability distribution in the direction of the longitudinal axis of the wall flow filter, which is due to the manufacturing process but is very advantageous. If the combination of an application of a suspension with catalytically active materials via the lower end face of the wall flow filter according to the invention is coupled with the coating over the upper end face according to the invention, a wall flow filter which is particularly advantageous for use in the exhaust gas system of a stoichiometrically burning automobile engine is produced. The cost coating from above is particularly preferably in the inlet channel (E) of the exhaust gas flow, while the cost coating from below is in the outlet channel (A) of the exhaust gas flow ( 1 ). In such a case, there is a wall flow filter in which the permeability curve along the longitudinal axis of the wall flow filter from the first end face of the exhaust gas inlet to the second end face (outlet of the exhaust gas) behaves as follows:

1. a) permeability in the area of the coating proceeding from the first end face within the scope of the error accuracy or falling in the coating direction;
2. b) permeability in the overlap area of the coatings is equal to or less than in the area under a);
3. c) Permeability continuously increasing in the area of the remaining coating. It is very particularly advantageous if both coatings are complex coatings and the permeability on the second end face, the end face of the exhaust gas outlet, has the highest permeability of the filter.

The mutatis mutandis preferred embodiments for the method therefore also apply to the filter itself and its use.

The present invention also relates to the use of the wall flow filter according to the invention in a process for the oxidation of hydrocarbons and / or carbon monoxide and / or in a process for nitrogen oxide reduction. This method is preferably the one that takes place in a three-way catalytic converter in the stoichiometric exhaust gas. It is preferred if, in addition to this wall flow filter, there is also a three-way catalytic converter on the downstream side or placed on the upstream side in the exhaust system. Possibly. there are also 2 separate three-way catalysts, particularly preferably one on the upstream side and one on the downstream side of the wall-flow filter according to the invention in the exhaust system. The wall flow filter is very particularly preferably used as a cGPF with a three-way function.

Wall-flow filters with a catalytic activity, which remove nitrogen oxides and hydrocarbons and carbon monoxide (HC, CO and NOx) in the stoichiometric exhaust gas (λ = 1 conditions), are mostly referred to as catalytically activated gasoline particle filters (cGPF). They can also convert the oxides of nitrogen under rich exhaust gas conditions and CO and HC under lean conditions. The coatings considered here mostly contain platinum group metals, such as Pt, Pd and Rh, as catalytically active components, with Pd and Rh being particularly preferred. The catalytically active metals are often highly dispersed on high-surface oxides of aluminum, cerium, zirconium and titanium or mixtures or mixed oxides thereof, which by further transition elements such. B. lanthanum, yttrium, praseodymium, etc. can be stabilized. Such three-way catalysts also contain oxygen storage materials (e.g. Ce / Zr mixed oxides; see below). A suitable three-way catalytic coating is, for example, in EP1181970B1 , EP1541220B1 , WO2008113445A1 , WO2008000449A2 to which reference is hereby made with regard to the use of catalytically active powders (see also introduction).

The requirements for petrol particulate filters (cGPF) differ significantly from the requirements for diesel particulate filters (cDPF). Diesel engines without DPF can have up to ten times higher particle emissions, based on the particle mass, than petrol engines without GPF ( Maricq et al., SAE 1999-01-01530 ). In addition, there are significantly fewer primary particles in the gasoline engine and the secondary particles (agglomerates) are significantly smaller than in the diesel engine. Emissions from gasoline engines are in the range of particle sizes smaller than 200 nm ( Hall et al., SAE 1999-01-3530 ) up to 400 nm (Mathis et al., Atmospheric Environment 38 4347) with the maximum in the range of around 60 nm to 80 nm. Due to their low particle relaxation time, small particles follow the streamlines almost without inertia. This even, convection-driven movement is overlaid with a random "trembling movement". Therefore, the filtration of the nanoparticles in GPF has to be done mainly via diffusion separation. For particles smaller than 300 nm, the separation by diffusion (Brownian molecular motion) and electrostatic forces becomes increasingly important with decreasing size (Hinds, W .: Aerosol technology: Properties and behavior and measurement of airborne particles. Wiley, 2nd edition 1999). For this reason, special optimization with regard to filtration efficiency with low exhaust back pressure is particularly important, especially with a cGPF.

Different catalytic functions can also be combined with each other. The three-way catalysts just mentioned can be equipped with a nitrogen oxide storage functionality in the powder (TWNSC). As stated at the outset, these catalysts consist of materials which give the catalyst the function of a three-way catalytic converter under stoichiometric exhaust gas conditions and which have a function for storing nitrogen oxides under lean exhaust gas conditions. These stored nitrogen oxides are regenerated during short, rich operating phases in order to restore their storage capacity. A corresponding TWNSC is preferably produced by combining materials which are used for the construction of a three-way catalytic converter and a nitrogen oxide storage catalytic converter. A particularly preferred embodiment for such a catalyst is described, for example, in US Pat WO2010097146A1 or WO2015143191A1 described. An air / fuel mixture which corresponds to a λ of 0.8 to 1 is preferably maintained during the regeneration. This value is particularly preferably between 0.85 and 0.99, very particularly preferably between 0.95 and 0.99.

All ceramic materials customary in the prior art can be used as wall flow monoliths or wall flow filters. Porous wall flow filter substrates made of cordierite, silicon carbide or aluminum titanate are preferably used. These wall-flow filter substrates have inflow and outflow channels, the outflow-side ends of the inflow channels and the upstream-side ends of the outflow channels being sealed off from one another with 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 requires an excellent particle filter effect. The filters can be symmetrical or asymmetrical. This means that the inflow channels are either the same size as the outflow channels or the inflow channels are enlarged compared to the outflow channels, that is to say they have a larger so-called “open frontal area” (OFA) compared to the outflow channels. Due to the porosity, pore / radius distribution and thickness of the wall, the filtration property can be designed for particles. The open porosity of the uncoated wall flow filters is usually more than 50% to a maximum of 80%, generally from 50% to 75%, especially from 50% to 70% [measured according to DIN 66133 - latest version on the filing date]. The average pore diameter (average pore diameter; d50) of the uncoated filter is at least 5 µm, e.g. B. from 7 microns to 35 microns, preferably more than 10 microns, particularly more preferably from 10 microns to 25 microns or very preferably from 15 microns to 20 microns [measured according to DIN 66134 - latest version on the filing date]. The finished filters with an average pore diameter (d50) of generally 10 μm to 20 μm and a porosity of 50% to 65% are particularly preferred.

The wall-flow filter considered here has its significant character due to the way it is coated, i.e. the application with one or more catalytically active materials. The starting point is a special coating applied to the filter, which is made porous by the application of a pressure pulse and therefore has a desired high permeability. This coating can be combined with a coating in the adjacent ducts as an in-wall or an outlay. As a result, the wall flow filter thus produced has a special permeability profile along its longitudinal axis. This has surprising advantages over "normal" coated wall flow filters. In particular, with such configurations according to the invention, optimized particle filters can be produced, which can be tailored precisely to the respective application or the particular exhaust gas problem. Against the background of the known prior art, this was not to be expected.

Figure list

• 1 shows an example of the effect of different combinations of the different coating architectures using samples 1 (top) - 4 (bottom). With regard to their effect in the exhaust gas flow. The combination of two coatings with a high permeability has the lowest pressure loss, but is otherwise weaker than the other samples according to the invention in terms of filtration efficiency, light-off temperature and OSC (oxygen storage). The combination of two coatings with low permeability shows very good values in terms of light-off temperature, OSC and filtration efficiency, but does result in an enormous increase in pressure. The best combination of all features (pressure loss, filtration efficiency, light-off temperature and OSC) is shown by the combination of a coating with low permeability in the input cell (inlet side of the filter in the exhaust gas; E) with a porous coating according to the invention with a high permeability in the output cell (Outlet side of the filter in the exhaust gas; A). The optimal setting of the two zone lengths depends on the requirements of the respective motor. You can set the quality criteria of the coated filter over the zone length like with a slider.
• The 2nd describes the process step of filling the filter with a suspension (washcoat) from below. The coating suspension is used in excess and is more in quantity than is required in the finished filter. The filter has cells in parallel 10th going through a wall 100 are separated. The wall has a high open porosity. The cells are alternately with stoppers 160 locked. The cells that are open at the top can have different dimensions than the cells that are open at the bottom. The suspension 140 moves by applying a pressure difference between the top face 20 and the lower face 30th into the open cells below 10th . Due to the pressure difference and the capillary forces, more or less liquid of the suspension penetrates 130 possibly with a small proportion of particles through the open porous walls 100 and gathers in the neighboring cell 40 on. If the particle sizes are selected accordingly, the particles in the suspension are deposited on the cell wall surface. A filter cake forms 50 that helps with further filtration. The level or the amount of liquid 150 in the cell 40 that is open at the top depends on the parameters of the suspension 140 , the filter cake 50 and porous ceramics 100 from. The last two form the flow resistance for the liquid passing through.
• 3rd schematically shows the product with two expense zones ( 10a ), which result from the coating method according to the invention with steps i) - iii) over the respective lower end face of the filter.
• The 4th schematically shows the product with two application zones, which result from the combination of the coating processes over the lower end face according to steps i) - iii) and over the upper end face of the filter. On the porous basic matrix of the filter 100 with the stopper 160 there is a porous coating 400 , also called filter cake, with a high permeability, produced by the coating from below, and a low porous coating 500 with a low permeability, produced by the coating from above. The exhaust gas 600 overflows the coating 500 and flows through the porous matrix of the filter 100 and the open porous coating 400 . The layer 400 is also overflowed after the flow.
• 5 relates to the combination of an expense coating produced according to the invention ( 10a ) and an additional in-wall coating ( 10b ) coming from the other side. The preferred embodiment is shown with an overlap.
• 6 The figures show four exemplary embodiments of patterns 1 to pattern 4
• 7 shows the coating concentration along the longitudinal direction of two wall flow filters produced according to the invention (patterns 1 and 3) and a wall flow filter not according to the invention (pattern 4). All three variants have the same total coating quantity for loading. The five panes per variant were shown (standardized) relative to the loading of the first pane on the left. The distribution of the washcoat load over the length of the filter measured by determining the BET surface area is shown by way of example for different combinations of coatings for two zones on the wall.
• 8a shows the filtration process in detail when filling the cells of the vertically locked wall flow filter through the lower end face with a suspension (step i.). The suspension 140 moves through the application of a pressure difference between the two faces of the filter into the cell, the air or more generally the gas 110 escapes through the porous wall into the neighboring cell and is discharged upwards. The particles 120 are on the porous surface of the filter 100 separated and form a filter cake 50 , which supports further filtration. The liquid 130 flows with at most a small proportion of particles through the porous wall and collects in the neighboring cell ( 150 ). It is a surface filtration with the formation of a filter cake.
• 8b shows the local detachment of the particle layer when the pressure pulse according to the invention is applied. This method is known to the person skilled in the art when used for water filters and exhaust air filters. The filters and the process run under the name backwash filter ( EP154726A2 , EP656223A1 ). The suspension 140 , 8a , is removed from the cell by reversing the pressure difference compared to coating. Air or gas flows ( 200 ) and the liquid 150 as a current 210 from the neighboring cell ( 150 ) from the previous coating step against the contact surface of the filter layer 50 through the porous wall 100 . From the filter layer 50 become particles 70 detached. Detachment occurs when the resistance of the particles caused by the liquid or gas flow or the force resulting from the pressure difference exceeds the adhesive force of the layer. This makes the layer more porous. The particles 70 be together with the liquid 210 and the gas 200 carried down ( 170 ).
• 9 shows the permeability distribution of two effort zones produced according to the invention.

Examples:

The exemplary experiments for the production of filters with application zones were carried out with the following starting materials.

Filter substrates: cordierite, 4.66 "x 4.66" x 6.00 ", 300/8, average pore diameter d50 = 17.5µm

Precious metal loading: 36 g / ft ³ (Pt = 0 / Pd = 30 / Rh = 6)

Washcoat load: 100 g / L

Specification for the particle size distribution (particle diameter) of the application coatings: d50 = 4.2 - 5.0 µm, d90 = 9.0 - 18 µm

• Da der für die Musterherstellung verwendete Filter ein Volumen von 1,68 Liter hat, beträgt die Washcoatbeladung 168 g. Wird nur eine Zone von 80% der Länge aufgebracht, so enthält die Zone für diese Vergleiche die 168 g. Werden zwei Zonen mit 60 % der Länge L des Filters aufgebracht, so enthält jede Zone 50 % der Oxide und somit 84 g Oxid. Würde eine Zone mit 80 % der Substratlänge mit einer Zone mit 40 % der Substratlänge kombiniert, so hätte die 80 % lange Zone in diesem Vergleich 2/3 der Oxidmenge (= 112 g) und die 40 % lange Zone 1/3 der Oxidmenge (= 56 g).

Distribution of the washcoat coating in the wall flow filter:

• Since the filter used for the sample production has a volume of 1.68 liters, the washcoat load is 168 g. If only a zone of 80% of the length is applied, the zone contains the 168 g for these comparisons. If two zones with 60% of the length L of the filter are applied, each zone contains 50% of the oxides and thus 84 g of oxide. If a zone with 80% of the substrate length were combined with a zone with 40% of the substrate length, the 80% long zone in this comparison would have 2/3 of the oxide amount (= 112 g) and the 40% long zone 1/3 of the oxide amount ( = 56 g).

Experimental part for the production of the zoned effort samples 1-4:

General:

Alumina stabilized with lanthanum oxide was suspended in water together with a first oxygen storage component, which comprised 40 wt. Both oxygen storage components were used in equal parts. A palladium nitrate solution and a rhodium nitrate solution were then added to the suspension thus obtained with constant stirring. The resulting coating suspension (washcoat) was used directly to coat a commercially available wall-flow filter substrate.

In the following, the processes for producing products are described, each of which has two application zones, which have been coated from different end faces of the filter and each extend over approximately 60% of the length of the filter. The loading of the finished catalysts consists of 100 g / L ceramic oxides and 36 g / cft (= 1.27 g / L) precious metal (ratio of palladium to rhodium 5: 1), which with a filter volume of 1.6761 L means a total oxide loading of 167.6 g / filter and a total amount of precious metal of 2.13 g / filter. The ratio of ceramic oxides to precious metals is the same in the washcoat of both zones and is constant across the entire filter. The total amount of oxide and noble metal is divided equally between the two zones during the coating, whereby ideally an oxide amount of 83.55 g and a noble metal amount of 1.07 g are applied in each zone coating step.

Pattern 1

Both washcoat zones a) and b) of sample 1 ( 6a) were produced using the same coating method, the excess ceramic suspension being first brought into the filter by applying a pressure difference (pressure from below). The excess of oxides is then removed by reversing the pressure difference, ie by re-applying a pressure difference (suction from below) which is opposite to the first.

First, zone a) is coated from below from front face A. For this purpose, the suspension has a solids content of around 33% and is pressed into the substrate until 60% of the substrate length is filled with washcoat from bottom to top. The excess washcoat is then removed from the filter with a short suction pulse opposite to the coating direction (approx. 330 mbar negative pressure, 1.5 sec.). After drying and calcining, the filter is coated from the front side B from below to produce zone b). The coating is carried out analogously to the coating of zone a), only the coating parameters differ slightly (solids concentration around 35%, suction pulse vacuum around 210 mbar, suction pulse duration around 0.5 sec., Rise in suction pulse within 0.2 seconds to that Maximum). The filter is then dried and calcined.

Pattern 2 and Pattern 3

Pattern 2 ( 6b) and pattern 3 ( 6c ) were produced according to a procedure, the coating of zone a) and zone b) each having a different coating process.

First, zone a) is coated from below from front face A. For this purpose, the suspension has a solids content of around 34% and is pressed into the substrate until 60% of the substrate length is filled with washcoat from bottom to top. The excess washcoat is then removed from the filter with a short suction pulse (around 330 mbar negative pressure, 1.5 sec. Suction pulse duration, increase in the suction pulse within 0.2 sec to the maximum). After drying and calcining, the filter is coated from the front side B from above to produce zone b). For this purpose, a measured amount of washcoat (solids content approx. 44%) is added to face B from above and there is a short suction pulse (250 mbar Vacuum, 3 sec.) To distribute the washcoat in the filter. The filter is then dried and calcined.

Pattern 4

Both washcoat zones a) and b) of pattern 4 ( 6d ) were produced using the same coating method, the ceramic suspension being applied to the wall-flow filter from above and brought into the filter by applying a pressure difference (suction from below) (not according to the invention).

First, zone a) is coated from above from front face A. For this purpose, the suspension has a solids content of around 43-45% and is added in a measured amount from the top to face A. A pressure difference in the form of a short suction pulse (250 mbar vacuum, 1 sec.) Is applied to distribute the washcoat in the filter. After drying and calcining, the filter is coated from the front side B from above to produce zone b). The coating parameters for this are analogous to those for coating zone a). The filter is then dried and calcined.

Characterization:

The effectiveness of a catalytically active filter is determined by the interaction of the functional variables catalytic performance, filtration efficiency and exhaust gas back pressure (backpressure), which essentially result from the distribution of the catalytic material and the permeability of the washcoat layers. The distribution and quantity of the catalytically active material in the flow direction of the filter is determined by measuring the BET surface area (DIN 66132 - latest version on the filing date), and the permeability by measuring the back pressure on filter samples of samples 1 to 4.

• Die Proben für die Analysen in Hinblick auf die Bestimmung der Gradienten (Bestimmung der Verteilung des katalytischen Materials in axialer Längsrichtung) wurden nach dem Beschichten und Kalzinieren folgendermaßen hergestellt:
  • • Abschneiden der Filterstopfen auf beiden Seiten (Filter um 2x 10mm gekürzt)
  • • Aufteilen des Restes in Längsrichtung auf 5 gleichlange Teile (Filterscheiben)
  • • Zur Bestimmung des BET-Gradienten wurden die 5 Scheiben gemahlen und analysiert.

Analysis of the gradient of the washcoat distribution (oxide distribution) and the permeability:

• The samples for the analyzes with a view to determining the gradients (determining the distribution of the catalytic material in the axial longitudinal direction) were produced as follows after coating and calcining:
  • • Cut off the filter plug on both sides (filter shortened by 2x 10mm)
  • • Divide the rest in the longitudinal direction into 5 parts of the same length (filter discs)
  • • The 5 slices were ground and analyzed to determine the BET gradient.

For the permeability measurement, a block with 10mmx10mmx20mm (width x depth x height) was sawn out of each disc in the middle. Every second channel was mutually blocked, so that a small mini filter was created. For this mini filter, the pressure loss is measured at an air flow of 6 l / min. In a first approximation, the pressure loss is set to be proportional to the permeability.

7 shows an example of the differences in washcoat loading (gradients in the disks) between the five filter sections with respect to the BET surface area, which can be seen when using the different processes a) coating with washcoat excess and changing direction of the pressure difference and b) coating without and only with a slight washcoat excess without changing pressure difference for the combination of the expense zones. The suspensions used had identical particle size distributions and identical Pd to oxide ratios. Due to the different processes, the suspensions had different viscosities and different solids concentrations. The gradient was always standardized with the value of the disc on the left.

All 3rd Variants (Pattern 1, Pattern 2/3, Pattern 4) have the same amount of washcoat as a load. The 5 Slices per variant were shown on the left side relative to the loading of the first slice (standardized). So the left pane is always 100%.

Coating by the process according to the invention (coating with excess washcoat and changing direction of the pressure difference according to process steps i) to iii)) results in an increasing gradient in the coating direction, while coating without a change in pressure difference results in a uniform distribution of the catalytic material without a gradient. The effect of the coating process on the permeability is in 9 shown as an example for pattern 2.

9 shows the course of the permeability as an example for the combination of two application zones, whereby the zone on the left was generated with a washcoat excess and a change in the pressure difference during the coating according to process steps i) to iii), while the right zone without a washcoat excess and without a change in the pressure difference was generated. Both zones contain the same amount of oxides and both cover 60% of the length of the filter.

To determine the permeability, the plugs of the filter were first removed. The rest was divided into 5 equally long discs with a length of approx. 26mm. Small blocks with a base area of 10mm x 10mm and a height of 26mm were made from the panes. The channels were provided with plugs so that 5 small filter bodies were created. A pressure difference volume flow curve was now determined for the small filters and the permeability was calculated using the Darcy equation. The left zone was used to standardize the permeability of the five small filters.

The first pane of the zone, hereinafter referred to as area A, which was produced with a washcoat excess and a change in the pressure difference during the coating, has a 4 to 20 times higher permeability in the first 15 to 50 mm than the zone in the has the following mm. The length L was measured from the end face after removal of the stopper, which had the first contact with the washcoat when coated with excess washcoat and a change in the pressure difference. The zone that was created without excess washcoat and without reversing the pressure difference during coating has a permeability with the same grain size distribution of the oxides in the washcoat, the same amount of oxide in the zone, which corresponds to only 5% to 25% of the permeability of area A. The same applies to the area of the zone which was generated with a washcoat excess and a reversal of the pressure difference during the coating, which is further away from the end face than area A.

Tab. 1 shows the distribution of the oxides and the resulting permeability in a zone that was generated from below according to process steps i) to iii) (the length measurement starts behind the stopper). The range 0-26 mm was used for standardization to 100% Tab. 1 0mm-26mm 26mm-52mm Oxide loading 100% 132% permeability 100% 12%

In comparison, Tab. 2 shows the different permeabilities of the coatings from above (without excess and without pressure reversal) and below (the length measurement starts behind the stopper). The area 0-26mm of the coating from below was used for standardization to 100% Tab. 2 Permeability in the first 26 mm after the stopper Coating from below 100% Coating from above 16%

• Nachdem in den vorangegangenen Ausführungen die Muster 1 bis 4 hinsichtlich der Verteilung des katalytischen Materials und der Permeabilität charakterisiert wurden, werden nachfolgend die katalytische Wirksamkeit, die Filtrationseffizienz und der Abgasgegendruck der vier unterschiedlichen Muster bestimmt.

Catalytic characterization of the products:

• After the samples 1 to 4 were characterized in the preceding explanations with regard to the distribution of the catalytic material and the permeability, the catalytic effectiveness, the filtration efficiency and the exhaust gas back pressure of the four different samples are subsequently determined.

The particle filters samples 1 to 4 were subjected to an engine test bench aging. This consists of a fuel cut-off switch with 950 ° C exhaust gas temperature in front of the catalyst inlet (maximum bed temperature 1030 ° C). The aging time was 19 hours (see Motortechnische Zeitschrift, 1994, 55, 214-218).

The catalytically active particle filters were then tested in an aged state on an engine test bench in the so-called "light-off test" and in the "OSC test". With the light-off test, that will be Starting behavior with stoichiometric exhaust gas composition with constant mean air ratio λ determined (λ = 0.999 with ± 3.4% amplitude).

Table 3 below contains the temperatures T70 of samples 1 to 4, at which 70% of the components considered are converted in each case. Tab. 3 # T70 HC stoch T70 CO stoch T70 NOx stoch 1 403 431 431 2nd 401 424 429 3rd 396 413 417 4th 392 406 409

The particle filter pattern 2 shows a slight improvement in the light-off behavior compared to pattern 1 in the aged state. The particle filters patterns 3 and 4 show a clear improvement in the light-off behavior compared to pattern 1 in the aged state.

To calculate the oxygen storage capacity of the particle filter in mg / L, the particle filter was placed between two lambda probes and the time offset of the two sensor signals during a jump test (OSC test) with lambda jumps of Ä = 0.96 - 1.04 was measured (car exhaust gas catalysts, basic - manufacturing - Development - Recycling - Ecology, Christian Hagelüken, 2nd edition, 2005, p. 62). Table 4 shows the results of the OSC tests for samples 1 to 4. Tab. 4 # OSC [mg / L] 1 159 2nd 166 3rd 199 4th 196

Samples 3 and 4 show a significantly increased oxygen storage capacity after aging compared to sample 1.

The particle filters samples 1 to 4 were compared on a cold blow test bench with regard to the exhaust gas back pressure.

The following Table 5 contains pressure loss data which were determined at an air temperature of 21 ° C and a volume flow of 300 m ³ / h. Tab. 5 # bp @ 300 m3 / h bp @ 300 m3 / h (relative to # 1) 1 28.8 mbar - 2nd 43.2 mbar + 50% 3rd 40.5 mbar + 41% 4th 64.9 mbar + 125%

The combination of two layers, each of which was produced by a coating process according to steps i) - iii) (sample 1), has the lowest pressure loss. The combination of two layers, each of which was produced using a coating process excluding steps i) - iii) (sample 4), has an enormous increase in pressure compared to sample 1. The two patterns in which the Differentiating coating processes for zone a) and zone b) have an acceptable increase in pressure loss with respect to sample 1, but have a significantly lower pressure loss compared to sample 4.

The particle filters described were examined on the engine test bench in the real exhaust gas of an engine operated with an average stoichiometric air / fuel mixture with regard to the fresh filtration efficiency. A globally standardized test procedure for determining exhaust emissions, WLTP (Worldwide harmonized Light vehicles Test Procedure), was used. The driving cycle used was WLTC Class 3. The particulate filter was installed 30 cm after a conventional three-way catalytic converter, which was the same for all measured particulate filters. In order to be able to detect the particle emissions during the test, a particle counter was installed in front of the three-way catalytic converter and after the particle filter. Table 6 shows the results of the filtration efficiency measurement. Tab. 6 # FE [%] 1 77 2nd 86 3rd 82 4th 91

The lowest filtration efficiency is shown in sample 1, in which both zones were produced using the same coating method in accordance with steps i) - iii). On the other hand, sample 4, in which both zones were also produced by the same coating method, but different from sample 1, with the exclusion of steps i) - iii), has the highest filtration efficiency. The two samples 2 and 3, in which the coating processes for zone a) and zone b) differ, have a lower filtration efficiency than sample 4, but they result in a significant increase in filtration efficiency compared to sample 1.

The 1 shows an example of a summary of the effect of different combinations of different overhead washcoat layers with regard to the effect in the exhaust gas flow The combination of two layers with a high permeability, each of which was produced using a coating method according to the invention in accordance with process steps i) to iii) by applying a pressure difference and then reversing the pressure difference (sample 1), has the lowest pressure loss, but is otherwise less efficient in terms of filtration, the light-off temperature and the OSC weaker than the other samples 2 to 4. The combination of two layers with low permeability, each of which was produced by applying a pressure difference according to the invention (sample 4), shows very well values with regard to light -Off temperature, OSC and filtration efficiency, but results in an enormous increase in pressure. The best combination of all features (pressure loss, filtration efficiency, light-off temperature and OSC) surprisingly shows the combination of a layer in the input cell (upstream side of the filter in the exhaust gas) with low permeability, which was produced according to the invention by applying a pressure difference with a layer in the output cell (outflow side of the filter in the exhaust gas) with a high permeability, which was produced via a coating process according to the invention with process steps i) to iii). The optimal setting of the two zone lengths depends on the requirements of the respective motor. You can set the quality criteria of the coated filter over the zone length like with a slider.

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

• WO 2005016497 A1 [0004]
• US 8557204 [0005]
• US 8394348 [0005]
• EP 2650042 B1 [0005]
• EP 2727640 A1 [0008]
• EP 1716903 B1 [0009]
• US 20040254071 A1 [0010]
• WO 2006042699 A1 [0011]
• EP 1554473 A1 [0012]
• US 7981370 B [0012]
• US 8591820 B [0012]
• US 4010013 [0029]
• EP 1181970 B1 [0042]
• EP 1541220 B1 [0042]
• WO 2008113445 A1 [0042]
• WO 2008000449 A2 [0042]
• WO 2010097146 A1 [0044]
• WO 2015143191 A1 [0044]
• EP 154726 A2 [0046]
• EP 656223 A1 [0046]

Non-patent literature cited

• DIN EN ISO 3219-1 [0017]
• Chateau et al., J. Rheol. 52, 489-506 (2008) [0017]
• Maricq et al., SAE 1999-01-01530 [0043]
• Hall et al., SAE 1999-01-3530 [0043]

Claims (12)

Process for the production of catalytically coated ceramic wall flow filters with optimized exhaust back pressure for the treatment of exhaust gases from a combustion process, the wall flow filter having a first end face, a second end face and a length L and a porosity of at least 50% to a maximum of 80% and an average pore diameter of 5 - Has 50 microns, and wherein: i) in the vertically locked wall flow filter through the lower end face a suspension having a catalytically active material for less than 100% of the length of the wall flow filter is pressed in such a way that the solid components of the suspension to less than 20 wt .-% based on the amount of solid constituents can penetrate into the wall, ii) excess suspension is removed via the lower end face of the wall flow filter and iii) the wall flow filter is applied in step ii) or in a subsequent step by applying a pressure increase the upper face and / or he pressure reduction on the lower end face of the wall flow filter is treated in the form of at least one pressure pulse, characterized in that, depending on the flow limit and the capillary forces dependent on the pores of the filter, at least one of the pressure pulses is dimensioned such that the pressure increase on the upper end face and / or Pressure reduction on the lower end face of the wall flow filter corresponds at least to the following value: $$\Delta p\left(stat\right)=\left(\mathrm{4th}\sigma \text{cos}\theta \right)/d+\gamma .$$

Procedure according to Claim 1 , characterized in that the material contains high-surface metal compounds, the d50 value of the Q3 distribution of the mean particle diameter in relation to the mean pore diameter d50 of the Q3 distribution is> 1: 6 and <1: 1 Procedure according to Claim 1 and / or 2, characterized in that one maintains an unpressurized hold time between steps i) and ii) of up to 10 s. Procedure according to one of the Claims 1 - 3rd , characterized in that the catalytic coating of the wall flow filter has a positive gradient for the amount of catalytically active material in the coating direction. Procedure according to one of the Claims 1 - 3rd , characterized in that steps i) - iii) are then carried out from the other side using the same or different catalytically active material or different amounts. Method according to one of the preceding Claims 1 - 4th , characterized in that additionally a certain amount of a suspension comprising a catalytically active material is applied to the upper end face and this is introduced into the vertically locked wall flow filter by applying a pressure increase on the upper end face and / or a pressure decrease on the lower end face of the wall flow filter that this coating extends to less than 100% of the length of the wall flow filter and with the coating according to steps i) - iii) des Claim 1 overlaps to at least 5% of the length of the wall flow filter. Procedure according to Claim 6 , characterized in that the introduction of the suspension from the upper end face and the treatment of the coating according to steps ii) - iii) after Claim 1 happens with the at least one pressure pulse at the same time. Catalytically coated ceramic wall flow filter for the treatment of exhaust gases from a combustion process manufactured according to one of the preceding claims. Wall flow filter with at least one zone behind Claim 8 , characterized in that the catalytic coating of the zone according to steps i) - iii) of Claim 1 has a positive quantity gradient in the coating direction in the wall flow filter. Wall flow filter manufactured according to Claim 6 and / or 7, characterized in that the permeability curve along the longitudinal axis of the wall flow filter from the first end face to the second end face behaves as follows: a) Permeability in the area of the coating starting from the first end face remains constant within the scope of the error accuracy or falls in the coating direction ; b) permeability in the overlap area of the coatings is lower than in the area under a); c) Permeability continuously increasing in the area of the remaining coating. Wall flow filter manufactured according to Claim 10 , characterized in that the permeability at the lower end face is above the highest permeability of the area under a). Use the wall flow filter according to one of the Claims 8 - 11 in a process for the oxidation of hydrocarbons and / or carbon monoxide and / or in a process for nitrogen oxide reduction.

Images