DE10305387A1 - Process for coating components with aluminum oxide comprises feeding a component into a coating arrangement containing a water-containing bath, adding alkali and/or alkaline earth hydroxide, removing the component, and drying - Google Patents

Abstract

Process for coating components with aluminum oxide comprises feeding a component partially into a coating arrangement containing a water-containing bath, adding alkali and/or alkaline earth hydroxide to the bath, removing the component from the bath, and drying. The bath contains metallic aluminum and/or aluminum-containing alloys. An independent claim is also included for a coated component produced by the above process.

Description

The present invention relates to a process for coating components for catalysts with aluminum oxides.

Find catalysts in particular in the context of automotive exhaust gas catalysts Use. For after Internal combustion engines operating on the gasoline engine principle Three-way catalysts have been working very well for years to disposal. In contrast, in diesel engines, series-ready catalysts / soot filters Although developed and also partially in use, however, show these compared to the three-way catalytic converters known from gasoline engines but disadvantages. The present invention finds use especially in the field of diesel engines, but also other internal combustion engines and can about it can also be transferred to adjacent technical areas.

Within the European Union plans are underway, from 2005 limit values for nitrogen oxide as well as the soot emissions for diesel engine operated To tighten motor vehicles. However, due to structural changes Diesel engines only one of the two aforementioned pollutant emissions can be reduced, with the other pollutant component then simultaneously an increased Emission. Therefore can probably the limit values planned by the European Union can only be complied with if the exhaust gas is aftertreated Diesel engines done.

So-called "soot filters" are mainly used to reduce soot emissions. These are then spatially separated in the exhaust duct of a motor vehicle together with corresponding catalysts. For example, disclosed EP 0 835 684 A2 a process for the treatment of exhaust gases from light trucks and passenger cars, the exhaust gas being conducted here over two catalysts connected in series. The first catalyst oxidizes the nitrogen monoxide contained in the exhaust gas to nitrogen dioxide, with the second catalyst / soot filter then ensuring that the soot particles deposited on it are oxidized to carbon dioxide (CO ₂ ) by the nitrogen dioxide formed previously, whereas the nitrogen dioxide to nitrogen monoxide ( NO) and optionally also to nitrogen (N ₂ ) is reduced.

Instead of a second catalyst can also be a pure soot filter be provided as disclosed in WO 99/09307. In which Part of the cleaned exhaust gas is disclosed there via a cooler passed and then mixed with the intake air of the diesel engine.

The exhaust gas from diesel engines includes in addition to aforementioned nitrogen oxides and soot emissions still carbon monoxide, unburned hydrocarbons as well as sulfur oxides and others volatile organic Components (VOC = Volatile Organic Compounds). The latter divorce settle on the carbon nuclei contained in the exhaust gas and form soot particles, on which sulfates can also be absorbed.

A major problem with soot separation in the catalyst is that the flow resistance of the catalyst / soot filter increases with increasing soot loading. The filters must therefore be regenerated again by burning the soot, for example by providing additional heating elements in the catalyst / soot filter. Alternatively, fuel additives can also be provided for the regeneration of the particle filter, or additives can be added directly to the catalytic converter / soot filter in the exhaust system. In the case of thermal combustion of the soot particles, very high temperatures well above 600 ° C. are necessary, which can be reduced by providing catalysts in the filter. In order to achieve complete removal of the soot particles from the catalyst / soot filter, according to the disclosure the EP 0 835 684 A2 there is a sufficient amount of nitrogen dioxide. This is opposed by the fact that modern diesel engines mostly have exhaust gas recirculation (so-called "EGR system") in order to reduce nitrogen oxide emissions. Therefore, it is necessary to maximize the amount of nitrogen dioxide in the exhaust gas in view of the combustion of the soot particles.

Object of the present invention is now a process for coating components for catalysts, to disposal to provide, through which a solid and durable coating with a large surface disposal is provided.

• – in einem ersten Schritt mindestens ein Bauteil zumindest teilweise in eine ein Wasser enthaltendes Bad umfassende Beschichtungsvorrichtung, gegebenenfalls auch mehrmals, eingeführt wird, wobei das Bad metallisches Aluminium und/oder Al-haltige Legierungen aufweist, oder aber metallisches Aluminium und/oder Al-haltige Legierungen nach Einführung des Bauteils in die Beschichtungsvorrichtung in das Bad eingegeben wird;
• – in einem zweiten Schritt ein Alkali- und/oder Erdalkalihydroxid dem Bad zugegeben wird;
• – in einem dritten Schritt nach einer Einwirkzeit das Bauteil dem Bad entnommen, und
• – in einem vierten Schritt das Bauteil getrocknet wird.

This object is achieved according to the invention by a method for coating components for catalysts with aluminum oxides, wherein

• - In a first step, at least one component is at least partially introduced into a coating device comprising a water-containing bath, possibly also several times, the bath comprising metallic aluminum and / or aluminum-containing alloys, or metallic aluminum and / or aluminum-containing alloys Alloys are introduced into the bath after the component has been introduced into the coating device;
• - In a second step, an alkali and / or alkaline earth hydroxide is added to the bath;
• - In a third step, after a contact time, the component is removed from the bath, and
• - The component is dried in a fourth step.

As alloys containing Al are among to name others from Al with Cu, Ni, Co and / or Ag. In particular can several alloys containing Al can also be provided.

Components within the meaning of the invention include carrier bodies, molded parts, filter elements, metal films, mesh and knitted fabrics (nonwovens) or similar understood, which can be provided with a carrier coating, in particular to increase catalytic activity. The components can be of metallic origin, but they can also be made from ceramic materials and, in particular, can also be sintered. In particular, the component to be coated can be produced from materials from a group comprising papers, textiles, polymer membranes, metals, plastics, fiber materials (here in particular nonwovens, felts, knitted fabrics and / or knitted fabrics), ceramic materials and / or combinations thereof. The components to be coated are further preferably produced from metals and / or ceramic materials in powder and / or fiber form.

As are metallic materials not only materials made of pure metals, but also materials made of metal alloys and / or material mixtures made of different metals and metal alloys for the Component to be coated can be used. In particular, this includes steels, preferably Chrome-nickel steels, Bronzes, nickel-based alloys, Hastalloy, Inconel or the like, whereby the material mixtures can contain high-melting components such as for example platinum. The molded body to be coated can also be made from fibers, with preference being given to those based on ferrous materials (e.g. according to the German Material standards 1.4404, 1.4767 or 1.4841) and / or alloys the base iron-chromium-aluminum or nickel-aluminum.

The components can be whole or in part be coated. There is also a screen printing process possible, partial areas of the component are covered by means of masks and subsequently the coating is done. Possible soot filter elements are, for example the wall flow filters known from the prior art, which with a porous honeycomb body mutually closed flow channels exist. This honeycomb body is in a casing pipe or converter in the exhaust line of a motor vehicle arranged.

In particular, the filters in and DE 197 04 147 A1 disclosed arrangements. Catalyst / soot filter arrangements are particularly preferred which, on the one hand, comprise a carrier body, for example a metal foil with or without embossing to achieve flow guidelines, and with a filter body, in particular a wire mesh or knitted fabric or a nonwoven fabric, in particular a sintered one. Such catalyst / soot filter arrangements are arranged in a casing pipe in the exhaust duct of a motor vehicle. In the case of such a catalyst / soot filter arrangement, on the one hand only the filter element or the support body, or in particular the inside of the casing tube, can also be partially coated, but both the support body and the filter element and optionally the inside of the casing tube can also be at least partially coated his.

The method according to the invention can thus be used find on the one hand in the coating of catalyst / soot filters Arrangements as disclosed in WO 99/09307, on the other hand in particular also when coating spatial not separate catalyst / soot filter arrangements, which the big one Have the advantage that this be arranged in a space-saving manner in the exhaust line of a motor vehicle can. You can which are coated with the method according to the invention Components for Catalyst / soot filter arrangements as well as the initial equipment as well for the retrofit be provided.

The catalyst / soot filter assemblies can thereby in the direction of the particle and exhaust gas flow flowing through them a gradient not only in the cell density of the carrier body or the porosity of the filter element, but also in the strength of Coating. So can provided catalysts tailored to the respective vehicle type become. these can for example, in the form of known disk catalysts.

After the drying in the fourth step, which also includes calcination, the coating obtained by the process according to the invention has a specific surface area of at least 5 m ² / g, preferably more than 10 m ² / g, more preferably more than 50 m ² / g, and consists of aluminum oxide. It is activated aluminum oxide, which has the different crystal structures of the transition series of the crystallographic phases of the aluminum oxide. These arise depending on the temperature used for drying, with χ-, η -, γ-, κ-, - and δ- and θ-Al ₂ O ₃ to be mentioned in detail. In the fourth step, drying is particularly preferably carried out in at least two partial steps, in a first partial step at room temperature in air, and in a second partial step at a temperature of at least 400 ° C., preferably at least 550 ° C., more preferably at least 700 ° C. is dried. A temperature range from approximately 450 ° C. to approximately 550 ° C. is preferred. Drying at elevated temperatures in the second sub-step is preferably carried out with the exclusion of oxygen, for example in a nitrogen-hydrogen atmosphere (mixed gas atmosphere) or under pure nitrogen or hydrogen. At temperatures above 400 ° C, a coating is obtained on the at least partially coated components, which adheres very firmly to the component and shows no signs of aging, even after running times corresponding to 50,000 kilometers of road. This is a significant advantage over the dispersion coating used known from the prior art Layering process in which an aqueous dispersion of, for example, γ-Al ₂ O ₃ is placed, in which the components to be coated are immersed and then dried and calcined. With these methods, however, a so-called "washcoat" remains, in particular when coating fiber components between the fibers, as a result of which the flow resistance is increased.

The reason for the extremely high liability the coating according to the inventive method on components and their extremely large specific surface area as also activating effect on those stored or to be stored in it Catalyst components / compounds are likely to have an in situ coating using in particular presented metallic Aluminum. The metallic aluminum used, however the Al-containing alloys can be in the form of wires, chips, powders etc. used become. However, the use of aluminum chips, which are particularly preferred in particular by scraping metallic aluminum blocks using conventional ones Tools emerge.

A possibly still necessary higher Adhesion of the coating on the component is thereby according to the invention accomplished that before the introduction of the component in the coating device, in particular in the Bath the same, the component is pre-oxidized, for example by it is heated to temperatures of up to 950 ° C. This will create a Oxide layer on the surface of the component, insofar as it is a metallic component, whereby the surface roughness of the same elevated.

To ensure high uniformity the coating according to the inventive method To achieve, it is further advantageous that after adding the alkali and / or Alkaline earth metal hydroxide in the second step, the solution contained in the bath is stirred. in principle is advantageous if the component in the solution in the bath for at least 4 hours, preferably 8 hours, more preferably more than 16 hours, lingers in it before it is removed from the bathroom. As an alkali and / or alkaline earth metal hydroxides are preferably sodium hydroxide and / or Potassium hydroxide used. Their concentration moves, related to the entire solution in the bathroom, in a range of about 0.5 mol / l to about 10 mol / l, preferably about 1 mol / l to about 5 mol / l, depending on the type of desired Coating. The concentration of the added is preferably Hydroxides in a range from about 0.8 mol / l to 2 mol / l.

In a further advantageous embodiment of the inventive method before the fourth step of the same, the now coated is first Component washed, if necessary several times. The washing can in this case in particular with distilled water to the extent that a pH of the collected washing water of ≤ 8, preferably ≤ 7.5, measured becomes. By washing the freshly coated component immediately after removing it from the bathroom, it will ultimately be after the one that has been taken Drying including the calcination a well-adhering coating with great active specific surface area.

The solution contained in the bath contains during the coating method according to the invention in addition to water and possibly other additives as solvents, an alkali and / or alkaline earth hydroxide, metallic aluminum and from the reaction between the aluminum and the alkali and / or alkaline earth hydroxide aluminum hydroxide in its different states, especially in the crystallized and amorphous state. Farther can be the solution but also contain catalyst components or compounds which as a reduction or Oxidation catalysts the implementation of the exhaust gas of an internal combustion engine contained gaseous Affect components positively. This process is called "doping" below. In particular is a doping with platinum group precious metals, in particular Platinum, beneficial. Because this causes the oxidation of nitrogen monoxide Nitrogen dioxide accelerates, which is then used for the oxidation the soot particle to disposal stands. If a catalyst / soot filter arrangement is therefore provided, which is made up of a carrier body with a filter element, especially spiral wrapped, and is at least the filter element and optionally also the carrier body according to the inventive method coated and the coating doped with platinum, so immediately at the point of origin of the nitrogen dioxide, this immediately with the in the soot filter, that is, the soot particles contained and collected in the filter element, react so that a almost complete The same burns.

Other particularly advantageous catalyst components or compounds are those that determine the ignition temperature of the soot particles reduce and thus the soot burn-off promote. Here are, for example, vanadium-containing compounds such as Silver, lithium, sodium, potassium and cervanadate, vandadium pentoxide and / or called potassium or silver perrhenate. But also those Degradation of reactions that catalyze sulfur dioxide ultimately sulfur trioxide is formed, such as titanium dioxide and silicon dioxide or their particular organometallic predecessor forms can be found in the solution in the bathroom according to the present Procedure.

Furthermore, it is also possible to provide the component with one of the aforementioned catalyst components before or after preoxidation thereof, for example by means of the known dispersion coating method, even before the component is introduced into the coating device. Be However, it is particularly advantageous if, after calcining the possibly doped coating, the same is still provided with catalytically active substances. This can be done by impregnation or by means of a sol / gel process, in particular for the provision of sols containing Ti or for the formation of zeolites. For this purpose, the coated component can be immersed in solutions, especially aqueous ones, which contain the corresponding catalytic components and then removed from the bath, blown out and then dried and optionally calcined. This impregnation can take place in addition to a doping, but also without a previous doping.

The present invention relates to furthermore a coated component, produced according to the method according to the invention, as well as a catalyst, soot filter and / or a soot filter / catalyst arrangement with at least one partially according to the inventive method coated component. Other applications of the coated Components can be found, for example, in microreactors.

The invention is based on the following embodiment explained in more detail:

Example:

On the one hand, a carrier body with flow guidelines (company Emitec Gesellschaft für Emissionstechnologie mbH, Lohmar, Germany) of the type "PM Kat", usually used for catalysts, with a flat dimension of 100 × 150 mm and a cell density of 200 cpsi (cells per square inch) from the iron-based material according to the German material standard 1.4767, and on the other hand a metal knitted fabric made of the same material with a flat dimension of 100 × 150 mm and a surface (GSA, geometrically determined) of about 10 m ² / m ² coated. Carrier bodies with cell densities of 900 cpsi and larger can be coated using the method according to the invention.

Both the carrier body and the metal knitted fabric, which can serve as filter and / or catalyst elements before introducing the coating device to temperatures greater than 900 ° C for Formation of wiskers ("surface oxides") heated.

Then they were placed in the coating device introduced and introduced into the bath, which distilled 10 1 several times Contained water. You can the components to be coated (metal carrier and filter element) a grate in the bathroom. Then 1 kg of aluminum chips Made of pure metallic aluminum with a length in a range of approximately 50 μm to 1,000 μm and one average thickness, measured over the whole length, added to the bath in a range of approximately 5 to 100 μm. Then was about 1.5 kg of sodium hydroxide were added to the bath. This reacts with the submitted aluminum and forms aluminum hydroxide. simultaneously hydrogen is formed, which ensures an even distribution of aluminum hydroxide in the bathroom. In addition, if necessary touched become.

In order to achieve a higher coating, after a dwell time of 24 hours again the same amounts on aluminum chips and sodium hydroxide added to the bath. After another wait, which can also be up to 24 hours, they are now coated components removed from the bath and with pure water washed, which is why the wash water was almost neutral. Then were the coated components first at room temperature (i.e. at a temperature in a range of 18 to 25 ° C) air-dried, then in an oven first for several hours at 120 ° C (in a range of 100 ° C up to 180 ° C) and then in a convection oven several hours at 550 ° C and more calcined. The second drying step in an oven at temperatures in a range of 80 to 180 ° C, preferred 100 ° C to 150 ° C, are carried out. The calcination in a convection oven was carried out at temperatures of up to 800 ° C.

The coated components obtained in this way had a large specific surface area of more than 50 m ² / g, which also has a very activating effect on catalyst components, in particular platinum. At the same time, the coating applied in this way adheres extremely firmly to the carrier body or metal knitted fabric.

In addition, the coating by doping and / or impregnation, in particular with cerium, Cerium copper and / or titanium salt solutions or platinum and / or rhodium solutions to acquire catalytic skills be provided. Acetates may also be mentioned in particular as salts. The catalytically active components are in an amount of more than 3% by weight, preferably more than 8% by weight, more preferably more than 15% by weight, based in each case on the total amount of the coating, in this added.

By means of the coating method according to the invention can ultimately, in particular, auto-catalytic converters for diesel engines Manufactured both in the original equipment and in the retrofit be what problem-free application in particular to achieve of limit values greater than the norm Find EURO 2, especially EURO 4 and 5.

Claims (12)

Process for coating components for catalysts with aluminum oxides, wherein - in a first step, at least one component at least partially into a water-containing one Coating device comprising the bath is introduced, the bath having metallic aluminum and / or Al-containing alloys or metallic aluminum and / or Al-containing alloys being introduced into the bath after the component has been introduced into the coating device; - In a second step, an alkali and / or alkaline earth hydroxide is added to the bath; - in a third step after a contact time the component is removed from the bath and - in a fourth step the component is dried. Method according to claim 1, characterized in that between the second and third step, the solution contained in the bath is stirred. Procedure according to a of the preceding claims, characterized in that in fourth step drying in a first sub-step at room temperature in the air and in a second step at temperatures of at least 400 ° C. Procedure according to a of the preceding claims, characterized in that the Concentration of the aqueous hydroxide forming in the bath in one area from 0.5 mol / l to 10 mol / l becomes. Procedure according to a of the preceding claims, characterized in that before the fourth step the component is washed. Procedure according to a of the preceding claims, characterized in that before the first step, the component is pre-oxidized by heating. Procedure according to a of the preceding claims, characterized in that the solution contains catalytically active substances in the bathroom. Procedure according to a of the preceding claims, characterized in that after the drying of the component with catalytically active substances is provided. Coated component, manufactured according to a of claims 1 to 8. Catalyst with at least one partially according to one of claims 1 to 8 coated component. soot filter with at least one partially according to one of claims 1 to 8 coated component. Rußfilter- / catalyst assembly with at least one partially according to one of claims 1 to 8 coated component.