METHOD FOR IMPROVING THE COATING OF A HONEYCOMB BODY WITH A CATALYTICALLY ACTIVE COATING

Description

[0001] Method for improving the coating of a honeycomb body with a catalytically active coating Technical area

[0002] The invention relates to a method for producing a device for the aftertreatment of exhaust gases and for coating a honeycomb body provided in the device with a catalytically active surface coating, wherein the honeycomb body is formed from a plurality of metallic, at least partially structured foils which are stacked on top of one another and wound up so that the honeycomb body forms a plurality of flow channels through which flow can occur along a main flow direction, wherein the honeycomb body is accommodated in an inner casing and is permanently connected to the latter, wherein the inner casing is arranged in an outer casing serving as a housing and is permanently connected to the latter. State of the art

[0003] Honeycomb bodies for catalysts for exhaust aftertreatment of internal combustion engines have a plurality of flow channels through which flow can occur along a main flow direction. Honeycomb bodies, in particular metal honeycomb bodies, are formed by a plurality of smooth and / or at least partially structured metal foils that are stacked on top of one another and wound to form the final honeycomb body. The matrix formed from the metal foils is inserted into a housing and permanently bonded to it for stabilization and to protect against mechanical interference.

[0004] In the simplest case, the housing is formed by a tube designed to accommodate the matrix. Another function of the housing is to ensure air flow through the honeycomb body and, in particular, to prevent exhaust gas from flowing past the honeycomb body.

[0005] The matrix must be permanently mounted in the housing, while at the same time the housing should be as lightweight and thin-walled as possible. Some catalyst designs feature an inner shell that directly accommodates the matrix. The inner shell is then supported by suitable supports relative to the housing or outer shell.

[0006] US 2017 / 369123 A1 discloses a catalyst for treating exhaust gases from a motorcycle engine. The catalyst comprises a housing with an upstream end and a downstream end. The housing body extends between the upstream end and the downstream end. A catalyst shell is disposed within the housing body such that a cavity is formed between the catalyst shell and the housing body. A catalyst is disposed within the catalyst shell. An insulator is disposed in the cavity between the housing body and the catalyst shell.

[0007] US 2019 / 112960 A1 discloses a catalyst device comprising a catalyst carrier, a tubular portion accommodating the catalyst carrier, a support mat supporting the catalyst carrier, an insulator provided over the outer peripheral surface of the tubular portion, and a heat insulating member disposed between the insulator and the tubular portion. The region of the outer peripheral surface of the tubular portion between the upstream end and the downstream end in the exhaust gas flow direction is divided into two subregions arranged in the direction of the axis of the tubular portion.

[0008] WO 2015 / 013545 A1 discloses a process for forming coated substrates for use in catalysts and detergent compositions. Furthermore, the document discloses a process suitable for producing the coated substrates and the coated substrates formed thereby, which in some cases utilize iron-exchanged zeolite particles, offering improved performance such as lower exhaust temperatures and lower pollutant levels in exhaust gases. The catalytic material is produced by a plasma-assisted process, which exhibits a lower tendency for the support material to migrate at high temperatures and is thus less susceptible to catalyst aging after prolonged use. Furthermore, catalysts comprising the coated substrates are disclosed, which exhibit advantageous properties compared to catalysts deposited on substrates using solution chemistry.

[0009] US 2020 / 171529 A1 discloses an apparatus and method for coating substrates with washcoats. In particular, it concerns the coating of substrates used for exhaust gas purification.

[0010] A particular disadvantage of the prior art devices is that air gaps can develop between the individual elements of a catalyst, for example, between the inner and outer shells. These gaps can become clogged when the matrix is ​​coated with a catalytically active material, the so-called washcoat. Mechanical vibrations and thermal influences during operation can cause the material trapped in the air gaps to become dislodged, which can lead to damage and / or catalytic deactivation of downstream exhaust gas aftertreatment components.

[0011] Another disadvantage is that the washcoat applied in a gap does not participate in the catalytic reaction in the honeycomb body, thus serving no function. The actual amount of washcoat required to coat the honeycomb body is therefore actually lower. This unnecessary additional consumption is particularly disadvantageous when the washcoat contains precious metals, which are expensive. Description of the invention, task, solution, advantages

[0012] Therefore, it is the object of the present invention to provide a method which makes it possible to coat the honeycomb body in a housing as accurately as possible with the minimum necessary amount of washcoat and in particular to avoid the introduction of washcoat into areas which do not participate in the catalytic reaction.

[0013] The problem with regard to the method is solved by a method having the features of claim 1.

[0014] One embodiment of the invention relates to a method for producing a device for the aftertreatment of exhaust gases and for coating a honeycomb body provided in the device with a catalytically active surface coating, wherein the honeycomb body is formed from a plurality of metallic, at least partially structured foils that are stacked on top of one another and wound up so that the honeycomb body forms a plurality of flow channels through which flow can take place along a main flow direction, wherein the honeycomb body is accommodated in an inner shell and is permanently connected to it, wherein the inner shell is arranged in an outer shell serving as a housing and is permanently connected to it, wherein before introducing the catalytically active coating into the flow channels formed by the honeycomb body, an air gap or air gaps that have formed between the outer shell and the inner shell,be filled with a filler.,

[0015] A basic method for manufacturing a device with a honeycomb body in an inner shell, which is permanently housed in an outer shell, is known from the prior art. The matrix is ​​created by stacking metal foils, which are at least partially structured, and then winding the resulting layer stack around one or more mandrels. The matrix of the honeycomb body is connected to the inner shell, for example, by means of a soldering process, after the matrix has been inserted into the inner shell.

[0016] The inner shell is preferably very thin and essentially serves to stabilize the matrix so that it does not roll up or fan out.

[0017] The honeycomb body is then inserted into a housing formed by an outer shell, which serves as a seal against the environment, and is permanently bonded to it, for example, by soldering. The outer shell is significantly thicker than the inner shell and serves to guide the exhaust gas flow, mechanically protect the honeycomb body, and connect it to other exhaust aftertreatment components.

[0018] Gaps can form, particularly between the inner and outer casings, due to tolerances or simply due to the geometry of the individual components. This typically results in a gap that runs completely around the circumference between the inner and outer casings. The air gap usually extends axially only along a section where the inner and outer casings meet. This air gap forms a cavity that is accessible from the volume enclosed in the outer casing, the exhaust gas flow path.

[0019] To coat the matrix, a coating material is pressed or sucked through the flow channels of the matrix, for example by overpressure or under pressure. This coats the surface of the flow channels and creates a catalytically active surface on which the chemical reaction with the exhaust gas takes place. By introducing the coating material, it can happen that structures outside the matrix are also exposed to the coating material; in particular, the coating material can penetrate into the formed air gap and remain there. On the one hand, this significantly increases the amount of coating material remaining in the device and, on the other hand, the coating material can detach from the air gap during operation, whereby it is carried along in the exhaust gas flow and possibly damages downstream components for exhaust gas aftertreatment.In particular, so-called poisoning can occur when catalytically active material comes into contact with different catalytically active material on other honeycomb structures. This can then lead to a chemical reaction that completely or at least partially destroys a downstream catalyst. Therefore, it is imperative to prevent catalytically active coating material from accumulating in areas not intended for coating.

[0020] To prevent the coating material from penetrating the air gap, it is filled with a filler before the coating material is applied. This filler can be injected into the gap using an injection needle, for example.

[0021] The filler solidifies in the air gap so much that it is not displaced by the introduction of the coating agent and does not run out of the air gap on its own or is sucked out of it.

[0022] The filler can preferably be introduced into the air gap through an opening outside the outer jacket. Alternatively, it can be introduced directly into the air gap from the open cross-section of the outer jacket.

[0023] It is particularly advantageous if the filler is a gel-like organic mass. A gel-like organic mass is advantageous to ensure that the entire air gap can be filled quickly and easily by injecting the filler directly into the air gap. The filler preferably has material properties that allow it to be injected into the air gap. Furthermore, the filler is designed in such a way that it achieves sufficient strength within the air gap so that it cannot be easily sucked or squeezed out of the air gap.

[0024] It is also advantageous if the filler is introduced into the gap before the device undergoes further heat treatment, such as drying or calcining. This is advantageous because drying or calcining significantly increases the temperature of the device, and the filler preferably has limited thermal stability, so that beyond a certain temperature exposure it is no longer stable or dissolves completely.

[0025] A preferred embodiment is characterized in that the filler is removed from the air gap after the catalytically active coating has been applied. This is advantageous for removing the filler before commissioning the device. Otherwise, the filler could detach from the air gap during operation under the mechanical stresses and thermal interactions. This could block flow channels or cause damage to components in the exhaust system.

[0026] It is also preferable if the filler is removed from the air gap through a thermal process. This is advantageous because the honeycomb body, or the entire device, regularly undergoes several process steps in which it is exposed to significantly elevated temperatures. This ensures, without requiring an additional process step, that the filler is heated above a critical temperature, thereby dissolving it.

[0027] Furthermore, it is advantageous if the air gap is filled in such a way that the opening cross-section facing the insertion point through which the catalytically active coating is applied is closed by the filler. This is particularly important to ensure that no coating material can become trapped in the air gap. This is ensured by closing the opening cross-section.

[0028] In a preferred embodiment, the filler can be designed in such a way that it expands after introduction and, if necessary, a portion of the introduced filler swells out of the air gap to ensure that no coating material can get into the air gap.

[0029] Advantageous further developments of the present invention are described in the subclaims and in the following description of the figures. Short description of the drawings

[0030] The invention is explained in detail below using an exemplary embodiment with reference to the drawing. The drawing shows: Fig. 1 a sectional view through a honeycomb body which is accommodated in an outer shell, wherein the air gap formed between the inner shell of the honeycomb body and the outer shell is filled with a filler. Preferred embodiment of the invention

[0031] The Figure 1 shows a sectional view of a device for exhaust gas aftertreatment. A honeycomb body 1, formed from a metallic matrix, is arranged centrally. The honeycomb body 1 is housed in an inner casing 2, which fixes the matrix, protects it from fanning out and rolling up, and simultaneously protects the matrix from mechanical influences. Honeycomb bodies of this design are known in many different forms in the prior art.

[0032] In the illustration of the Figure 1 A heating disc 3 is arranged in front of the honeycomb body 1 and is connected to the honeycomb body 1 via support pins 4. The heating disc 3 is connected to a voltage source via the electrical feedthrough 5 shown and can thus be energized, thereby achieving heating.

[0033] The honeycomb body 1 with its inner shell 2 is inserted into an outer shell 6 and permanently connected to it, for example, by soldering. An air gap 7 is formed between the outer shell 6 and the inner shell 2. This can be deliberately created due to the component geometry or can also be formed due to tolerances between the components. Air gaps are also conceivable between all components of the device.

[0034] The air gap 7 is in the embodiment of the Figure 1 filled with a filler 8 so that nothing can penetrate into the air gap 7, particularly from the side facing the heating disc 3.

[0035] The washcoat, with which the matrix of the honeycomb body 1 is coated, is pressed into the honeycomb body using positive pressure and / or drawn through it using negative pressure, for example. The honeycomb body 1 can also be rinsed with the washcoat. With all of these methods, it is very likely that washcoat would penetrate the air gap 7 if it is not sealed.

[0036] The filler can be introduced into the air gap 7 in a targeted manner, for example by means of an injection needle, in order to fill it and in particular to fill the open cross-section.

[0037] The embodiment of the Figure 1 In particular, it is not restrictive and serves to clarify the inventive concept.

Claims

1. Method for producing a device for the aftertreatment of exhaust gases and for coating a honeycomb body (1), provided in the device, with a catalytically active surface coating, wherein the honeycomb body (1) is formed from a multiplicity of metallic, at least partially structured foils which are stacked one on top of another and wound so that the honeycomb body forms a multiplicity of flow channels through which fluid can flow along a main flow direction, wherein the honeycomb body is received in an inner casing (2) and is durably connected thereto, wherein the inner casing (2) is arranged in an outer casing (6) serving as a housing and is durably connected thereto, characterized in that, before the introduction of the catalytically active coating into the flow channels formed by the honeycomb body (1), an air gap (7) or air gaps, which have been formed between the outer casing (6) and the inner casing (2), are filled by a filler (8).

2. Method according to Claim 1, characterized in that the filler (8) is a gel-like organic composition.

3. Method according to either of the preceding claims, characterized in that the filler (8) is introduced into the air gaps (7) before the device is subjected to a further heat treatment, for example drying or calcining.

4. Method according to one of the preceding claims, characterized in that the filler (8) is removed from the air gap (7) after the introduction of the catalytically active coating.

5. Method according to one of the preceding claims, characterized in that the filler (8) is removed from the air gap (7) by a thermal process.

6. Method according to one of the preceding claims, characterized in that the filling of the air gap (7) is carried out in such a way that the opening cross section facing toward the introduction site through which the catalytically active coating is introduced is sealed by the filler (8).