DE102011100017A1 - Process for the preparation of zoned catalysts - Google Patents

Abstract

A method for producing a catalyst is provided, comprising a) providing a shaped catalyst body which contains a plurality of flow channels, each of which has an inlet opening and an outlet opening; and b) stepwise impregnation of the flow channels with a solution of a compound of a catalytically active component. Furthermore, a catalyst and a use of the catalyst are specified.

Description

The present invention relates to a process for producing a catalyst, a catalyst and a use of the catalyst.

The prior art describes honeycomb bodies and their use as catalyst supports which consist of ceramic, for example cordierite, or metal, for example a FeCr alloy. Such catalyst supports are also referred to herein as shaped catalyst bodies. Ceramic honeycomb bodies are extruded from a ceramic mass, wherein the extrusion can be carried out so that preferably straight-line axially extending channels. Metallic honeycombs are typically made by winding metal foils, winding a corrugated and a smooth film together. Again, straight axial channels can arise.

In known processes, an Al ₂ O _3- coated, for example, honeycomb-shaped, catalyst support is immersed in a noble metal-containing aqueous solution and maintained until the noble metal is completely adsorbed to produce catalysts. The immersion and the total adsorption can lead to a substantially homogeneous impregnation of the catalyst support. As in Structured Catalysts and Reactors; Second edition; Page 761; 2006; Taylor and Francis Group however, it may be difficult to achieve a homogeneous distribution of noble metal upon adsorption impregnation.

Furthermore, suspensions are used for the production of noble metal-coated honeycomb catalysts in which a noble metal is present bound and in which the honeycomb catalyst support is immersed. This results in large losses of catalytically active material, eg. As a noble metal, and the desired loadings, in particular loads with flowing gradients are technically difficult to implement, as in Structured Catalysts and Reactors; Second edition; Page 764; 2006; Taylor and Francis Group is set forth.

The invention is therefore based on the object to provide a comparison with the prior art improved process for the preparation of a catalyst and an improved catalyst.

This object is achieved by a method for producing a catalyst, comprising a) providing a shaped catalyst body which contains a plurality of flow channels, each having an inlet opening and an outlet opening; and b) stepwise impregnating the flow channels with a solution of a compound of a catalytically active component.

The invention further relates to a catalyst obtainable or obtained by the above process.

There is further provided a catalyst comprising a shaped catalyst body containing a plurality of flow channels each having an inlet opening and an outlet opening, the respective flow channels having a flow-directional concentration gradient of a catalytically active component.

In addition, the invention provides the use of a catalyst, available or obtained by the above method, for exhaust gas purification.

By the method, a concentration gradient of the catalytically active component is generated in the catalyst along the flow channels. For example, a higher noble metal content can be adjusted on the gas entrance side of the catalyst compared to the gas exit side of the catalyst. It can thereby be achieved that the reaction in the catalyst proceeds rapidly even at lower temperatures. Due to the heat of reaction, which results from the high concentration of the catalytically active component at the gas inlet side, the reaction is accelerated in the back of the honeycomb. Furthermore, in the region of the catalyst which follows in the flow direction to the gas inlet side, the amount of catalytically active component can be reduced with good performance of the catalyst. As a result, catalytically active material is saved, which leads to noticeable cost savings, especially for noble metals as a catalytically active component. This is particularly desirable in the manufacture of catalysts for the automotive market.

According to embodiments, the method also allows the production of so-called zoned catalysts, that is catalysts with zones of different content of catalytically active component. For example, such a zoned catalyst is a cylindrical honeycomb catalyst with parallel to the Cylinder axis extending flow channels and a parallel to the cylinder axis concentration gradient of catalytically active component.

Other features and advantages will become apparent from the following description of embodiments, the figures, the examples and the subclaims.

All non-mutually exclusive features of embodiments described herein may be combined. Elements of one embodiment may be used in the other embodiments without further mention. Like elements of the embodiments are given the same reference numerals in the following description. Embodiments of the invention will now be described in more detail by the following examples with reference to figures, without wishing to restrict thereby. Show it:

1 schematically an embodiment of the method for producing a catalyst;

2 schematically another embodiment of the method for producing a catalyst;

3 a representation of a catalyst generated in an example;

4 a representation of a catalyst generated in an example;

5 a representation of a catalyst generated in an example; and

6 a diagram of the loading of zoned catalyst honeycombs produced in the examples.

The term zoned catalysts used here stands for catalysts which have zones of different concentrations of catalytically active component. In the following description of embodiments, the terms shaped catalyst bodies and shaped bodies are used synonymously and can also be called carriers or catalyst carriers. Farmer is the term concentration gradient here also called concentration gradient or gradient, wherein the concentration gradient and gradient may include a graded or flowing change in concentration. Flowing change or fluid transition in embodiments means a gradually decreasing or increasing concentration. In addition, embodiments of the invention are described below with reference to a cylindrical honeycomb shaped catalyst body and platinum as a catalytically active component, without limiting the invention thereto.

In embodiments, the shaped catalyst body may have a cylindrical shape. Furthermore, the shaped catalyst body can have flow channels which are longitudinally oriented and / or extend parallel to the cylinder axis of the shaped body. The shaped catalyst body may also have two end surfaces, wherein the inlet openings of the flow channels are present in the one end face and the outlet openings of the flow channels in the other end face are present. The flow channels may have a round or a polygonal cross-section. For example, the shaped catalyst body may be a honeycomb body, e.g. B. with hexagonal cross-section of the flow channels.

In embodiments, the catalytically active component may contain one or more noble metals, e.g. B. selected from platinum, palladium, gold, silver, ruthenium, rhodium, cobalt, nickel, vanadium, copper, iron, tungsten, and manganese.

A solution of a strongly chemisorbing compound, for example a platinum-containing aqueous solution, can be used as the solution of a compound of a catalytically active component. For example, platinum-sulfite-acid or platinum-nitrate, which are very strong chemisorbing platinum compounds, can be used as the compound and can be applied to catalyst honeycombs by adsorption or total adsorption, among others. In other embodiments, a solution of a low or zero chemisorbent compound of a catalytically active component can be used, e.g. As a solution of a little or no chemisorbierenden platinum compound.

The invention can be applied to all chemisorbing systems. For example, the material of the carrier or a coating on the carrier, for. As a monolith, be selected from Al ₂ O ₃ , TiO ₂ , ZrO ₂ , SiO ₂ , and / or a CeZrW mixed oxide. Platinum sulfite acid chemisorbs extremely strongly on an Al ₂ O ₃ layer or on a layer containing silicon or zirconium. Containing Al ₂ O ₃ Layers chemisorbed platinum nitrate less strongly than platinum sulfite acid. Platinum tetraamine hydroxide hardly chemisorbed on Al ₂ O ₃ containing layers. There are a variety of chemisorbierenden systems conceivable, for. For example, all common materials for the surface of a catalyst support, such as oxide layers with a large surface, combined with all metal compounds used for the catalysis, which undergo chemisorption with the material of the surface.

The impregnation can be carried out stepwise starting from the inlet openings of the flow channels and / or in zones. In examples, the impregnation can be carried out stepwise starting from the inlet openings of the flow channels to their outlet openings. In embodiments, sequential impregnation may produce successive zones of the respective flow channels.

The lengths of the zones are arbitrarily adjustable and can be varied with the rate of pumping in the solution of the compound of the catalytically active component, the time or holding time between several successive steps of impregnation, the levels after the introduction of the solution and the strength of the chemisorption. Thus, any zone length, zones of equal and / or different lengths, any number of zones, or a gradient with graded or flowing transitions between zones may be generated.

Furthermore, by the stepwise impregnation of successive zones, for. B. at least two successive zones, the respective flow channels are successively cumulatively impregnated. For example, n consecutive zones of the catalyst may be generated and / or the impregnation of the nth (n.) Zone may include impregnation of the 1st (1st) to the nth (n-1) zone. In embodiments, n may be selected from 2 to 100, e.g. B. 2 to 30 or 2 to 20 or 2 to 10, such as. B. 2, 3, 4, 5, 6.

By means of the method according to embodiments, a flow gradient of the catalytically active component along the flow channels can be generated. For example, a sloping and / or stepped flow gradient is generated. The concentration gradient can run from the respective inlet opening to the respective outlet opening of the flow channels. In embodiments of the method in which successive zones of the respective flow channels arise, the zones may form a stepped concentration gradient.

In embodiments of the method, the stepwise impregnation is performed by incrementally introducing or pumping the solution into the flow channels. The introduction can also be carried out by dipping the catalyst shaped body into the solution or filling it with the solution. Ie. when introducing the solution, the flow channels and / or the entire molded body can be wetted by the solution. The introduction or pumping can be done starting from the inlet openings of the flow channels. In examples, the solution is introduced from the inlet openings to the outlet openings of the flow channels. Furthermore, during impregnation, the shaped catalyst body may be substantially horizontal or substantially vertical, i. H. substantially perpendicular or substantially parallel to the vertical, also called perpendiculars, are aligned. This is especially done with moldings having parallel channels, the channels being substantially horizontal or vertical, i.e. H. be aligned substantially perpendicular or parallel to the vertical.

The compound of the catalytically active component may in embodiments be a chemisorbing compound or precursor compound of the catalytically active component. As mentioned above, the compound is, for example, platinum sulfite acid or platinum nitrate. Other examples are platinum ethanolamine, platinum tetraamine hydroxide, or all other metal salts or soluble compounds of e.g. As platinum, palladium, gold, silver, ruthenium, rhodium, cobalt, nickel, vanadium, copper, iron, tungsten, and manganese or a mixture of all the compounds mentioned.

In the method according to embodiments, between two or more successive steps of impregnation, the solution is held in the filled zones for a period of time. In this case, it is possible to set an identical or a different time duration between a plurality of successive steps of impregnation. Depending on the adsorption or chemisorption strength of the solution and / or the set time duration, a concentration gradient of the catalytically active component extending in the flow direction can be generated along the flow channels.

For example, the catalyst molding is not dipped but a chemisorbing platinum compound in solution is gradually pumped through the catalyst molding. This embodiment is schematically illustrated in FIG 1 shown, with the individual steps are shown from left to right. First, a storage vessel 10 with a pump (not shown), e.g. B. a piston pump, and a stamp 20 provided. in the upper region of the storage vessel 10 becomes a solution 12 the chemisorbing platinum compound introduced with the stamp 20 the pump from the storage vessel 10 can be pressed. The storage vessel 10 is with a cylindrical container 30 , which is aligned substantially parallel to the vertical, via a conduit 32 connected. In the cylindrical container 30 becomes a cylindrical shaped catalyst body 40 introduced with parallel to the cylinder axis of the shaped body flow channels such that the flow channels parallel to the axis of the cylindrical container 30 run. The flow channels of the catalyst molding 40 are further arranged so that their inlet openings in the direction of the storage vessel 10 , ie at the inlet opening of the cylindrical container 30 are arranged. The outlet openings of the flow channels are arranged opposite to the inlet openings of the flow channels.

In the next step of in 1 As shown, a first zone of the flow channels, and thus the catalyst, is generated by pumping the solution of platinum compound to a desired upper zone boundary of the first zone. In the subsequent step, the solution of platinum compound is further into the cylindrical container 30 pumped, up to the upper zone boundary of a desired second zone. In the following step of the method of the present embodiment, the solution of the platinum compound becomes further into the cylindrical container 30 pumped to the upper zone boundary of a desired third zone. Finally, the solution of the platinum compound becomes even further into the cylindrical container 30 pumped in, so that in the 1 represented upper end of the shaped catalyst body is also penetrated by the solution and a fourth zone of the molding is produced.

How out 1 As can be seen, in the present embodiment, therefore, the desired zones are produced by pumping the solution of the platinum compound gradually from the inlet openings to the outlet openings of the flow channels, whereby the successive zones produced therewith are successively cumulatively impregnated. The latter causes the formed first zone of the shaped catalyst body, ie the zone leading to the inlet opening of the cylindrical container 30 is aligned in each pumping step of the process is penetrated by the solution of the platinum compound. In the present embodiment, a total of four zones of the catalyst are produced. This happens cumulatively, so that the impregnation of the second zone also includes impregnation of the first zone. Impregnating the third zone involves impregnating the first and second zones. And impregnating the fourth zone involves impregnating the first to third zones as well.

In the embodiment of the method, which in 1 is shown, the solution of the platinum compound is pumped stepwise through the substantially vertically provided catalyst molding. In order to allow the adsorption of the noble metal, a certain time is waited between the individual pumping steps. This waiting time, also called hold time, can be adjusted depending on the adsorption strength of the platinum compound and on the desired gradient. By adsorbing the platinum compound in the first step of the process, the concentration of platinum compound in the solution decreases. If the solution is pumped further, less platinum compound is thus absorbed in the next zone and a gradient forms over the entire catalyst shaped body along the flow channels in the flow direction.

In this way, in the catalyst prepared by the method of in 1 is produced embodiment shown, four successive zones generated, which have a decreasing platinum concentration from the gas inlet side of the catalyst to the gas outlet side of the catalyst. Each zone of the catalyst molding thus has a different platinum concentration from the other zones.

In embodiments of the process, a solution of a platinum compound that is chemisorbing is pumped through the catalyst body in a stepwise fashion. This creates a gradient caused by adsorption or total adsorption. The longer the waiting time between the individual pumping steps, the more pronounced the adsorption and the stronger the gradient of the platinum compound. The platinum gradient can also be influenced by the pumped volume of the platinum compound solution.

The process of the present embodiment is suitable for impregnating a shaped catalyst body with a chemisorbing compound or precursor compound of the catalytically active component, e.g. Platinum sulfite acid or platinum nitrate, but is not limited thereto.

According to embodiments, the impregnated shaped catalyst body may be calcined. This can be done under inert gas, for. As inert gas or argon, and / or at a temperature of at least 750 ° C happen. Before calcining, the excess solution may be drained from the impregnated shaped catalyst body and / or the impregnated shaped catalyst body may be dried.

In a further embodiment of the method, the stepwise impregnation is carried out by repeatedly introducing or pumping the solution into the flow channels up to different fill levels. The fill levels can correspond to zone boundaries of the successive zones. Furthermore, different concentrations of the solution can be selected for different fill levels.

The concentration of the catalytically active compound or precursor compound in the solution may be between 0 to 100% by weight, for example more than 0% by weight to 100% by weight, preferably 1% by weight to 99% by weight. %, more preferably 5 wt% to 95 wt% or 10 wt% to 90 wt%, e.g. B. 10 wt .-% to 50 or 40 wt .-%. It corresponds to 100 wt .-% of a 100% saturation of the salt or soluble metallic compound of the catalytically active compound in solution.

In embodiments, the compound of the catalytically active component may be a substantially non-weakly or only slightly chemisorbent compound or precursor compound of the catalytically active component. For example, the compound may be selected from platinum sulfite acid, platinum nitrate, platinum ethanolamine, platinum tetraamine hydroxide, or any other metal salts or soluble metal compounds of e.g. As platinum, palladium, gold, silver, ruthenium, rhodium, cobalt, nickel, vanadium, copper, iron, tungsten, and manganese or a mixture of all the compounds mentioned.

In some embodiments, depending on the concentration of the solution and the amount of compound received by the catalyst body, a downstream concentration gradient of the catalytically active component along the flow channels may be generated.

2 schematically shows steps of the method of another embodiment. It is only the container for each step 30 shown, with the individual steps in 2 be shown from left to right. First, the shaped catalyst body 40 in the container 30 provided substantially parallel to the vertical. In the process steps is in the container 30 by means of a pump (not shown) from bottom to top a solution 13 pumped at different concentrations of the catalytically active compound. In the process of 2 the pumping is carried out such that first the first zone of the catalyst with the solution 13 wets a certain concentration. In the next step then becomes the second zone of the catalyst with the solution 13 a wetted compared to the previous step lower concentration. In this case, no catalytically active component or its compound are adsorbed more in the first zone, since it is the compound used is not or only slightly chemisorbierende compound of the catalytically active component. The second zone of the catalyst is then generated by adding the solution 13 the catalytically active compound is pumped to a level corresponding to the upper limit of the second zone. In a further step of the process, the solution is up to a filling level which corresponds to the upper limit of the third zone of the catalyst 13 introduced with a lower concentration of catalytically active component than in the previous step. Subsequently, the upper end of the shaped catalyst body with the solution 13 the catalytically active component or its compound, wherein the solution 13 in this step, the lowest concentration of all previously used solutions 13 the catalytically active component has.

For example, in the process described in U.S. Pat 2 is placed, to be coated carrier honeycomb for a catalyst in a closed container, wherein the flow channels are aligned perpendicular to the ground. Then, in a desired amount, concentration and speed, a metal salt solution is added from below. This creates a gradient that increases from top to bottom.

In embodiments, the first to fourth zones are generated one after the other from the first zone to the fourth zone. However, in a modification of embodiments, the steps may also be performed in a different order and / or with different concentrator variations.

The amount of catalytically active component applied may, in the case of a compound of the catalytically active component which is not or only slightly chemisorbing, be substantially dependent on the concentration of the solution and on the amount absorbed in the molding.

In embodiments described herein, the more the chemisorption of the catalytically active component on the adsorbate material, i. H. the carrier, the more crucial is the duration of wetting. Thus, in a wetting, is continuously impregnated in steps, z. B. pumped from bottom to top, the lowest or first wetted zone have the highest loading of catalytically active component.

According to a further embodiment, the flow channels of the catalyst molding can be unilaterally, z. B. up to one-third of their height, be impregnated with metal solution. Thereafter, the flow channels can be impregnated with the same impregnation procedure from the opposite side. This results in two oppositely directed gradients of the metal concentration with the highest loadings at the inlet and outlet openings. In the middle of the flow channels here is the lowest concentration of active components.

In the process of the present embodiment, in some steps, the solution is pumped to fill levels smaller than the overall length of the catalyst body. As a result, doping with the catalytically active component or impregnation with its compound is produced only in the wetted flow channels. The amount of catalytically active component applied depends on the concentration of the solution and on the amount adsorbed on the shaped catalyst body. This results in fewer losses of catalytically active component and the desired gradient of catalytically active component is procedurally easy to implement.

The method according to the present embodiment is particularly suitable for, but not limited to, a substantially non or only weakly chemisorbing compound or precursor compound of the catalytically active component.

Subsequent to the method of the embodiment, which in 2 is shown, a calcination can be carried out, which is as described above.

The method may further comprise, according to embodiments, at least one of the steps of: draining the excess solution from the flow channels; Drying the impregnated catalyst-farm body; Calcining the impregnated shaped catalyst body; Calcination of the impregnated shaped catalyst body under inert gas or argon; Calcining the impregnated catalyst article at at least 750 ° C; Transferring the catalytically active component to the oxidation state 0; and converting the catalytically active component to the oxidation state 0 by hydrogen. The derivation can z. B. by blowing out with compressed air or another gas or by pumping out.

In the method of embodiments, the catalytically active component may be a noble metal. In this case, the catalytically active component may be selected from z. Platinum, palladium, gold, silver, ruthenium, rhodium, cobalt, nickel, vanadium, copper, iron, tungsten and manganese, or a combination thereof.

In embodiments, the shaped catalyst body may consist of a carrier material. Alternatively, the shaped catalyst body can have a carrier material, which is applied as a layer, for example, on the shaped body or in its flow channels. In this case, an open-pore carrier material can be used. For example, the carrier material may be an inorganic carrier material. In embodiments, the support material may be selected from titanium oxide, γ-alumina, θ-alumina, Δ-alumina, ceria, silica, zinc oxide, magnesia, alumina-silica, silicon carbide, magnesium silicate, zirconia and a mixture of two or more of the foregoing materials.

As explained above, the shaped catalyst body may be a carrier with parallel flow channels, for example a honeycomb body. Particularly preferred is a cordierite honeycomb or a metal honeycomb. Cordierite can z. With the structural formula (M) ₂ (Al ₂ Si) [Al ₂ Si ₄ O ₁₈ ], M = Mg or Fe.

The invention further relates to a catalyst obtainable or obtained by the method according to embodiments. The catalyst thus produced has a plurality of flow channels, each having an inlet opening and an outlet opening, wherein the respective flow channels have a flow-directional concentration gradient of a catalytically active component. Of the Catalyst thus contains a gradient of the concentration of the catalytically active component running along or parallel to the flow channels. This gradient can also be graded in zones. For example, the concentration decreases from the inlet openings to the outlet openings of the flow channels of the catalyst molding. That is, for example, a catalyst used in internal combustion engines has a higher content of catalytically active component on the gas entry side, e.g. As a precious metal, has as on the gas outlet side. As a result, the catalyzed reaction proceeds rapidly at temperatures which are lower than the temperatures which are carried out with a catalyst which has no gradient of the catalytically active component along the flow channels. In addition, due to the heat of reaction formed in the first zone of the catalyst, the reaction in the subsequent zones of the catalyst is accelerated. Thus, the amount of catalytically active component that must be used to produce the catalyst, be lower than in a catalyst having no gradient of the catalytically active component, because in the remote from the gas inlet side zones of the flow channels less catalytically active component is needed ,

In the catalyst according to embodiments, the concentration gradient of the catalytically active component can form successive zones of the respective flow channels. The concentration gradient may include a gradient sloping and / or stepped in the flow direction. The concentration gradient can also extend from the respective inlet opening to the respective outlet opening of the flow channels.

The catalyst according to embodiments may also be used for exhaust gas purification, for example in internal combustion engines, for stationary and mobile exhaust gas purification, for the operation of fuel cells, for shift reactions and / or for reforming. The catalyst may thus be used in or in connection with fuel cell applications, such as shift reactions, such as the water gas shift reaction, or reforming, such as steam reforming.

Examples

In the following examples, shaped catalyst bodies with four zones each are produced, wherein the shaped catalyst bodies are honeycomb-shaped and are referred to below as honeycombs. For the production of Examples 1 to 3, Al ₂ O ₃ coated cordierite honeycombs were impregnated with platinum sulfite acid (PSA). The Al ₂ O ₃ loading of the honeycombs was 50 g / l. The volume of honeycomb to be coated was 38.0 ml. Further, the honeycomb had a diameter of 2.54 cm (1 inch), a length of 7.5557 cm (2.955 inches) and 400 flow channels per 6.4516 cm ² (400 cells per square inch). The final platinum concentration on the honeycomb should be 1 g of platinum per liter of honeycomb volume. For the impregnation, an aqueous solution of platinum was prepared from PSA, the platinum concentration of which corresponds to the amount to be applied to the respective honeycomb. To prepare the platinum solution, 0.36 g of PSA solution (10.510% by weight of platinum) was made up to 50 ml with distilled water.

The coated honeycombs were calcined at 550 ° C for 3 hours in each example.

The platinum content of the zones of the honeycombs was determined as a function of the platinum concentration of the PSA solution as follows: The calcined honeycombs were sawed in each case corresponding to the 4 zones with a band saw and the respective honeycomb piece was analyzed by chemical digestion and ICP. The analyzes were carried out with an ICP of the company: Spectro; Model: Modula performed. The samples were digested "dokimastisch". The chemicals used were: copper flux, nitric acid 69% p. A. hydrochloric acid 37% p. A. Pt standard solution β = 1000 mg / l, scandium standard solution β = 1000 mg / l. Composition of the flux: 420 g of Cu ₂ O, 800 g of Na ₂ CO ₃ , 360 g of Na ₂ B ₄ O ₇ , 140 g of sand, 240 g of tartar. 25 g of flux were presented in a teaspoon crucible. Subsequently, 2 g of sample were weighed. In addition, a heaped spoonful of potassium hydrogenateate was added. The sample, the potassium hydrogenate and the flux were well homogenized with a spoon. The crucibles were placed in the high temperature oven. The furnace program was started with the generator parameters: Plasma power: 1400 W, pumping speed: 30 rpm, cooling gas: 14.00 l / min, auxiliary gas: 1.40 l / min, atomizing gas: 0.85 l / min. After the crucibles were cooled to room temperature, they were hammered with a hammer and the copper regulus was knocked out. The Regulus was placed in a 250 ml beaker and redistilled with about 5 ml. H ₂ O, 20 ml of hydrochloric acid, 15 ml of nitric acid and a stirred fish. With heating and stirring, the copper regulus was completely dissolved. The solution was transferred to a 250 ml volumetric flask containing 0.250 ml of standard scandium solution. Subsequently, the solution was tempered, filled and shaken. The measurements were carried out in ICP at the following wavelengths: 214.423 nm corrected with Sc 361, 384 nm; 299.777 nm corrected with Sc 256.023 nm; 177.708 nm; 306.471 nm; 191.170 nm corrected with Sc 256.023 nm; and 304.264 nm corrected with 256.023 nm Sc.

For calibration, a Pt standard was prepared beforehand as explained above, without sample being added. After the copper regulus dissolved and the solution was transferred to a 250 ml volumetric flask in which 0.250 ml Sc standard had been placed, the Pt standard solution was added and measured.

example 1

In Example 1, in a first honeycomb (honeycomb 1) of the above-mentioned honeycomb volume of 38.0 ml, the PSA solution was pumped up to a quarter of the honeycomb height from below, with the honeycomb arranged vertically as in 1 shown. Subsequently, the PSA solution was held in the honeycomb for 15 seconds. The PSA solution was then pumped to half the height of the honeycomb and also held for 15 seconds. Subsequently, up to three quarters of the honeycomb height was pumped and the PSA solution was held in the honeycomb for 15 seconds. Finally, the PSA solution was pumped up to the honeycomb level and held again for 15 seconds in the honeycomb. Thereafter, the PSA solution was pumped out of the honeycomb body.

3 shows the produced honeycomb 1 of Example 1, which was provided by the stepwise pumping of the PSA solution and the holding time of 15 seconds with four zones (zones 1 to 4). Platinum content of the zones [g / l] Platinum content of the zones [%] Zone 1 1,753 0,125 Zone 2 1,024 0.073 Zone 3 0.814 0.058 Zone 4 0.631 0,045 Average load 1.06 0.301

3 shows the honeycomb 1 produced in Example 1, at the edge of flow channels are opened. You can see from the discoloration of in 3 shown opened flow channels that the zone 1 is darker than the other zones and thus the platinum loading in zone 1 is higher than in the other zones and zoned graduated to zone 4 decreases.

Example 2

In this example, Example 1 was repeated with a second honeycomb (honeycomb 2), with the hold time being 30 seconds after each pumping step. Table 2 shows the platinum loadings of each zone. Platinum content of the zones [g / l] Platinum content of the zones [%] Zone 1 1,899 0.184 Zone 2 1,115 0.108 Zone 3 0.764 0.074 Zone 4 0.444 0.043 Average load 1.06 0.409

4 shows the honeycomb 2 obtained in Example 2, at the edge of flow channels are open. Here, too, it can be seen from the discoloration of the zones that, starting from zone 1 to zone 4, the platinum content decreases in a stepped manner.

Example 3

In Example 3, Example 1 was repeated except that after each pumping step the PSA solution in the honeycomb (honeycomb 3) was held for 60 seconds. Table 3 shows the obtained platinum loading of the honeycomb. Platinum content of the zones [g / l] Platinum content of the zones [%] Zone 1 2,009 0.217 Zone 2 1,250 0.135 Zone 3 0.648 0.07 Zone 4 0.315 0.034 Average load 1.06 0.456

5 shows the honeycomb 3 produced in Example 3, at the edge of flow channels are opened. Overall, the honeycomb 3 has a darker discoloration in the flow channels than the honeycomb 1 and 2, where also a brightening of the discoloration of zone 1 to zone 4 is observed, which illustrates a decreasing platinum content from zone 1 to zone 4.

6 FIG. 4 illustrates a comparison of the zoned honeycombs 1 to 3 obtained in Examples 1 to 3 with respect to the platinum loading per zone. It is 6 It can be seen that in each example the platinum loading decreases from zone 1 to zone 4. In addition, it can be seen that a higher platinum concentration of the PSA solution, as in Example 3 (honeycomb 3), leads to a higher uptake of platinum into the honeycomb walls and thereby to a higher platinum loading in zones 1 and 2.

The honeycombs of Examples 1 to 3 were each coated with 1 g of platinum per liter of honeycomb volume. Since the honeycomb volume was 0.038 l each, an absolute amount of platinum of 0.038 g was applied to the honeycombs. For a uniform, d. H. homogeneous coating of the shaped catalyst body without concentration gradient, each zone would have absorbed a lot of platinum of 1 g / l. By contrast, the invention makes it possible to impregnate each zone of the honeycomb with an arbitrary amount of platinum, depending on the retention time of the platinum solution. This applies to any number of zones.

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited non-patent literature

• Structured Catalysts and Reactors; Second edition; Page 761; 2006; Taylor and Francis Group [0003]
• Structured Catalysts and Reactors; Second edition; Page 764; 2006; Taylor and Francis Group [0004]

Claims (19)

Process for the preparation of a catalyst comprising a) providing a shaped catalyst body ( 40 ) containing a plurality of flow channels each having an inlet opening and an outlet opening; and b) stepwise impregnating the flow channels with a solution ( 12 ; 13 ) a compound of a catalytically active component. Method according to claim 1, wherein the impregnation is carried out stepwise starting from the inlet openings of the flow channels and / or in zones; and or wherein successive zones of the respective flow channels are produced by the stepwise impregnation; and or wherein sequentially impregnating successive zones of the respective flow channels are successively cumulatively impregnated. Method according to claim 1 or 2, wherein a downstream concentration gradient of the catalytically active component is created along the flow channels; and or wherein a downstream sloping and / or stepped concentration gradient is generated; and or wherein the concentration gradient extends from the respective inlet opening to the respective outlet opening of the flow channels. Process according to any one of the preceding claims, wherein the stepwise impregnation is carried out by incrementally introducing or pumping the solution ( 12 ) is performed in the flow channels. Method according to one of the preceding claims, wherein the compound is a chemisorbing compound or precursor compound of the catalytically active component; and or wherein the compound is platinum sulfite acid or platinum nitrate. A method according to any one of the preceding claims, wherein between two or more successive impregnation steps, the solution is held in the filled zones for a period of time Method according to claim 6, wherein an equal or a different period of time is set between several successive steps of impregnation; and or wherein, depending on the adsorption or chemisorption strength of the solution and the set period of time, a flow gradient of the catalytically active component is generated along the flow channels. Method according to one of the preceding claims, wherein the stepwise impregnation by repeated introduction or pumping of the solution ( 13 ) is performed in the flow channels to different levels. Method according to claim 8, wherein the fill levels correspond to zone boundaries of the successive zones and / or different concentrations of the solution are selected for different fill levels. Method according to claim 8 or 9, wherein the compound is a substantially non or weakly chemisorbent compound or precursor compound of the catalytically active component; and or wherein the compound is selected from salts or compounds of platinum, palladium, gold, silver, ruthenium, rhodium, cobalt, nickel, vanadium, copper, iron, tungsten, manganese or a combination thereof. Method according to one of claims 8 to 10, wherein depending on the concentration of the solution and the amount absorbed by the catalyst body of the compound, a flow-directional concentration gradient of the catalytically active component along the flow channels is generated. The method of any one of the preceding claims, further comprising at least one of: deriving the excess solution from the flow channels; Drying the impregnated catalyst shaped body; Calcining the impregnated shaped catalyst body; Calcination of the impregnated shaped catalyst body under inert gas or argon; Calcining the impregnated catalyst article at at least 750 ° C; Transferring the catalytically active component to the oxidation state 0; and converting the catalytically active component to the oxidation state 0 by hydrogen. A method according to any one of the preceding claims, wherein the catalytically active component is a noble metal; and / or wherein the catalytically active component is selected from platinum, palladium, gold, silver, ruthenium, rhodium, cobalt, nickel, vanadium, copper, iron, tungsten, manganese or a combination thereof. Method according to one of the preceding claims, wherein the catalyst shaped body and / or the flow channels comprise a carrier material or are coated with a carrier material, wherein the carrier material is open-pore; and or wherein the carrier material is an inorganic carrier material; and or wherein the support material is selected from titanium oxide, γ-alumina, θ-alumina, Δ-alumina, ceria, silica, zinc oxide, magnesia, alumina-silica, silicon carbide, magnesium silicate, zirconia, and a mixture of two or more of the foregoing materials. A method according to any one of the preceding claims, wherein the shaped catalyst body is at least one element selected from a parallel flow channel carrier, a honeycomb body, a cordierite honeycomb and a metal honeycomb. Catalyst obtainable or obtained by a process according to any one of the preceding claims. A catalyst, in particular according to claim 16, comprising a catalyst-shaped body containing a plurality of flow channels, each having an inlet opening and an outlet opening; wherein the respective flow channels have a flow-directional concentration gradient of a catalytically active component. Catalyst according to claim 16 or 17, wherein the concentration gradient of the catalytically active component forms successive zones of the respective flow channels; and or wherein the concentration gradient comprises a decreasing in the flow direction and / or stepped concentration gradient; and or wherein the concentration gradient extends from the respective inlet opening to the respective outlet opening of the flow channels. Use of a catalyst according to one of claims 16 to 18 for exhaust gas purification, for stationary and / or mobile exhaust gas purification, for the operation of fuel cells, for shift reactions and / or for reforming.

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