EP3826789A1

EP3826789A1 - Metal foam element containing cobalt and method for producing same

Info

Publication number: EP3826789A1
Application number: EP20775651.1A
Authority: EP
Inventors: René Poss; Meike Roos; Monika BERWEILLER
Original assignee: Evonik Operations GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2019-09-25
Filing date: 2020-09-25
Publication date: 2021-06-02
Also published as: US20220395816A1; KR20220069941A; KR20220068221A; JP2022549861A; WO2021058719A1; JP2022549860A; US20220362757A1; CN114531855A; WO2021058705A1; EP3826788A1; CN114466698A

Abstract

The present invention relates to a method for producing supported catalysts, comprising: providing a metal foam element A, which consists of metallic cobalt, an alloy of nickel and cobalt, or an arrangement of layers of nickel and cobalt lying one over the other; applying an aluminum-containing powder MP to metal foam element A in order to obtain metal foam element AX; thermally treating metal foam element AX to achieve alloy formation between metal foam element A and aluminum-containing powder MP, in order to obtain metal foam element B; oxidatively treating metal foam element B in order to obtain metal foam element C; and applying a catalytically active layer, comprising at least one support oxide and at least one catalytically active component, to at least part of the surface of metal foam element C in order to obtain a supported catalyst. The present invention further relates to the supported catalysts that can be obtained using the method and to the use of said supported catalysts in chemical transformations.

Description

Metal foam bodies containing cobalt and processes for their production

background

The present invention relates to processes for the production of supported catalysts, which comprise the following steps: coating of metal foam bodies made of metallic cobalt, an alloy of nickel and cobalt, or an arrangement of superimposed layers of nickel and cobalt with aluminum, subsequent thermal treatment in order to form an alloy achieve between metal foam and aluminum, subsequent oxidative treatment of the aluminum surface, as well as application of a catalytically active layer, which comprises at least one carrier oxide and at least one catalytically active component. The present invention also relates to the supported catalysts obtainable by the process and their use in chemical transformations.

State of the art

The use of metal foams as support bodies for catalytically active coatings is known from the prior art. The catalytically active coatings on the metallic support bodies are typically composed of a carrier oxide which enlarges the microscopic surface and catalytically active metals which are applied to the carrier oxide (cf. e.g. WO 9511752 A1). The monolithic supported catalysts obtained in this way can be used in a wide variety of applications, but their usability is limited by the extremely poor adhesion of the catalytically active coating, which is mainly composed of oxidic components, to the metallic support body. In the event of mechanical stress and possibly also during operation of the supported catalyst in flow-through reactors, the poor adhesion leads to the detachment of parts of the catalytically active layer with a correspondingly reduced service life of the catalyst and possibly disruptions in plant operation due to detached solid particles.

Alternatively, sol-gel processes are used as catalyst support bodies for coating metal foams. However, these processes require special equipment and the use of expensive reagents, which have a high hazard potential and are difficult to handle.

Another method known from the prior art for the production of metal foam supported catalysts makes use of the fact that relatively stable oxide layers can be produced on metal surfaces by “atomic layer deposition” (ALD). For example, US 20120329889 A1 discloses a method for producing metal foam support catalysts for the Fischer-Tropsch synthesis, in which a thin ALOs film is produced on a metal foam by “atomic layer deposition” (ALD) and then an oxidic coating by dip coating, drying and subsequent calcination is applied. US 20120329889 A1 explicitly points out that a stable coupling between the metal foam surface and the oxidic coating is difficult to achieve (cf. paragraphs [0068] - [0069]), and that this is achieved by applying the oxidic intermediate layer by means of ALD. The method disclosed in US 20120329889 A1, however, is extremely complex in terms of apparatus. With regard to the poor access to stable metal foam supported catalysts, the object of the present invention was to provide a method as simple as possible and suitable for the production of large quantities in order to produce a supported catalyst with a catalytic coating from a catalytically inert metal foam body. The pores provided by the foam base structure should not clog and the catalytic coating should be as easy to apply as possible, but should nevertheless be characterized by very good adhesion to the metal foam body. The processes of the present invention and the products obtained by these processes meet this need.

The present invention

Processes according to the invention for the production of supported catalysts comprise the following steps:

(a) Provision of a metal foam body A, which consists of metallic cobalt, an alloy of nickel and cobalt, or an arrangement of superimposed layers of nickel and cobalt,

(b) applying an aluminum-containing powder MP to metal foam body A, so that metal foam body AX is obtained,

(c) thermal treatment of metal foam body AX in order to achieve alloy formation between metal foam body A and aluminum-containing powder MP, so that metal foam body B is obtained, the highest temperature of the thermal treatment of metal foam body AX being in the range from 680 to 715 ° C, and wherein the total duration of the thermal treatment in the temperature range from 680 to 715 ° C is between 5 and 240 seconds,

(d) oxidative treatment of metal foam body B, so that metal foam body C is obtained,

(e) Applying a catalytically active layer, comprising at least one carrier oxide and at least one catalytically active component, to at least part of the surface of metal foam body C, so that a supported catalyst is obtained.

From the prior art, nickel foam bodies, onto which aluminum is first applied, alloyed and then partially leached again, are known as an alternative to classic Raney-type catalysts (cf., for example, EP 2764916 A1). The foam bodies thus obtained are activated all-metal catalysts of the Raney type, which are typically used in hydrogenation reactions.

Metal foam bodies are also known from the prior art, onto which aluminum is first applied and alloyed and which are then oxidized (cf. Wen-Wen Zeng et al. “Synthesis and compression property of oxidation-resistant Ni-Al foams”, Acta metallurgica Sinica, Volume 30, No. 10, October 1, 2017, pages 965-972). However, in the Wen-Wen Zeng et al. the entire cross-section of the originally present metal foam alloyed with aluminum (see page 972, Conclusion) while in the method of the present invention the alloy formation is limited to the upper layers of the metal foam, so that unalloyed areas remain in central regions of the metal foam.

Experimental results obtained in connection with the present invention show that the choice of temperature conditions for the thermal treatment for alloy formation has a considerable influence on the result. The methods according to the invention make it possible to limit the alloy formation to the upper layers of the metal foam, so that unalloyed areas remain in central regions of the metal foam. The presence of these unalloyed areas affects, among other things, the mechanical stability of the supported catalyst obtained. The BruclW compressive strength decreases significantly with increasing degree of alloying, and complete alloying of the metal foam leads to very brittle supported catalysts which tend to break under mechanical stress. This fact is of considerable practical importance, because continuously operated fixed bed reactors used on an industrial scale can have fixed bed volumes of up to 100 m ³ , so that depending on the bulk density and height of the fixed bed used, several metric tons may weigh on its lower layers. If the supported catalyst used to build up the fixed bed does not have sufficient mechanical stability and resilience to carry these weights for several thousand hours of operation, the support structures may break and the catalytically active areas may break mechanically (catalyst breakage). Broken material can be carried out with the fluid from the reactor into adjacent system parts and / or lead to caking in the fixed bed. In both cases, significant disruptions to the operation of the system are the result.

In connection with the present invention, metal foam body A is understood to mean a foam-shaped metal body. Foam-shaped metal bodies are disclosed, for example, in Ullmann's Encyclopedia of Industrial Chemistry, chapter “Metallic Foams”, published online on July 15, 2012, DOI: 10.1002 / 14356007. c16_c01 pub2. In principle, metal foams with various morphological properties with regard to pore size and shape, layer thickness, surface density, geometric surface, porosity, etc. are suitable. Metal foam A preferably has a density in the range from 400 to 1500 g / m ² , a pore size from 400 to 3000 μm, preferably from 400 to 800 μm and a thickness in the range from 0.5 to 10 mm, preferably from 1.0 to 5.0 mm. The production can take place in a manner known per se. For example, a foam can be made from an organic polymer are first coated with a metal and then the polymer is removed by thermolysis to obtain a metal foam. For coating with at least one first metal or a precursor thereof, the foam composed of the organic polymer can be brought into contact with a solution or suspension which contains the first metal. This can e.g. B. be done by spraying or dipping. Deposition by means of chemical vapor deposition (CVD) is also possible. A polymer foam suitable for producing moldings in the form of a foam preferably has a pore size in the range from 100 to 5000 μm, particularly preferably from 450 to 4000 μm and in particular from 450 to 3000 μm. A suitable polymer foam preferably has a layer thickness of 0.5 to 10 mm, particularly preferably from 1.0 to 5.0 mm. A suitable polymer foam preferably has a density of 300 to 1200 kg / m ³ . The specific surface area is preferably in a range from 100 to 20,000 m ² / m ³ , particularly preferably from 1000 to 6000 m ² / m ³ . The porosity is preferably in a range from 0.50 to 0.95.

The metal foam bodies A used in step (a) of the method according to the invention can have any shape, for example cubic, cuboid, cylindrical, etc. The metal foam bodies can, however, also be shaped, for example, into monoliths.

The application of the aluminum-containing powder MP in step (b) of the process according to the invention can be carried out in a variety of ways, e.g. B. by bringing metal foam body A into contact with a composition of the aluminum-containing powder MP by rolling or dipping, or by applying a composition of the aluminum-containing powder MP by spraying, sprinkling or pouring. For this purpose, the composition of the aluminum-containing powder MP can be present as a suspension or in the form of a powder.

The actual application of the composition of the aluminum-containing powder MP to metal foam body A in step (b) of the method according to the invention is preferably preceded by a prior impregnation of metal foam body A with a binder. The impregnation can take place, for example, by spraying the binder or dipping metal foam body A into the binder, but is not limited to these possibilities. The composition of the metal-containing powder MP can then be applied to the metal foam body A prepared in this way.

Alternatively, the binder and composition of the aluminum-containing powder MP can be applied in one step. For this purpose, the composition of the aluminum-containing powder MP is either suspended in the liquid binder itself before application, or the composition of the aluminum-containing powder MP and the binder are suspended in an auxiliary liquid F.

The binder is a composition that can be completely converted into gaseous products by thermal treatment in the temperature range from 100 to 400 ° C, comprising an organic compound that promotes adhesion of the composition of the aluminum-containing powder MP to the metal foam body. The organic compound is preferably selected from the following group: polyethyleneimine (PEI),

Polyvinylpyrrolidone (PVP), ethylene glycol, mixtures of these compounds. PEI is particularly preferred. The molecular weight of the polyethyleneimine is preferably in a range from 10,000 to 1,300,000 g / mol. The molecular weight of the polyethyleneimine (PEI) is preferably in a range from 700,000 to 800,000 g / mol.

Auxiliary liquid F must be suitable to suspend the composition of the aluminum-containing powder MP and the binder and to be able to be converted completely into gaseous products by thermal treatment in the temperature range from 100 to 400 ° C. Auxiliary liquid F is preferably selected from the following group: water, ethylene glycol, PVP and mixtures of these compounds. If auxiliary liquid is used, the binder is typically suspended in water at a concentration in the range from 1 to 10% by weight, and the composition of the aluminum-containing powder MP is then suspended in this suspension.

The aluminum-containing powder MP used in step (b) of the process according to the invention comprises pulverulent aluminum, but can also contain additives which contribute to increasing the flowability or water resistance. Such additives must be able to be converted completely into gaseous products by thermal treatment in the temperature range from 100 to 400 ° C.

The aluminum-containing powder MP preferably has an aluminum content in the range from 80 to 99.8% by weight. Powders in which the aluminum particles have a particle size of not less than 5 μm and not greater than 200 μm are preferred. Powders in which 95% of the aluminum particles have a particle size of not less than 5 μm and not greater than 75 μm are particularly preferred. It is possible that the aluminum-containing powder MP also contains aluminum components in oxidized form in addition to the aluminum component in elemental form. This oxidized fraction is usually in the form of oxidic compounds such as oxides, hydroxides and / or carbonates. The mass fraction of oxidized aluminum is typically in the range from 0.05 to 10% by weight of the total mass of the aluminum-containing powder MP.

In step (c) of the method according to the invention, a thermal treatment takes place in order to achieve the formation of one or more alloys.

Experimental results obtained in connection with the present invention show that the choice of temperature conditions for the thermal treatment for alloy formation has a considerable influence on the course of alloy formation. The inventive method allow the alloy formation on the upper layers of the To limit metal foam, so that unalloyed areas remain in central regions of the metal foam.

In step (c) of the method according to the invention, metal foam body AX is thermally treated in order to achieve alloy formation between metal foam body A and aluminum-containing powder MP, so that metal foam body B is obtained, the highest temperature of the thermal treatment of metal foam body AX in the range from 680 to 715 ° C., and the total duration of the thermal treatment in the temperature range from 680 to 715 ° C. being between 5 and 240 seconds.

The thermal treatment usually comprises the step-by-step heating of the metal foam body AX and the subsequent cooling to room temperature. The thermal treatment takes place under inert gas or under reductive conditions. Reductive conditions are understood to mean the presence of a gas mixture which contains hydrogen and at least one gas which is inert under the reaction conditions. Suitable is z. B. a gas mixture that contains 50 vol% N2 and 50 vol% H2. The inert gas used is preferably nitrogen. The heating can, for. B. be done in a belt furnace. Suitable heating rates are in the range from 10 to 200 K / min, preferably 20 to 180 K / min. During the thermal treatment, the temperature is typically first increased from room temperature to about 300 to 400 ° C. and at this temperature for a period of about 2 to 30 minutes moisture and organic constituents are removed from the coating. The temperature is then increased to in the range from 680 to 715 ° C. and an alloy is formed between the metal foam body A and the aluminum-containing powder MP. The metal foam body is then quenched by contact with the protective gas environment at a temperature of approx. 200 ° C.

In order to limit the alloying of the metals involved according to the invention to the upper areas of the metal foam and to leave unalloyed areas inside the metal foam, it is necessary that the highest temperature of the thermal treatment of metal foam body AX in step (c) is in the range from 680 to 715 ° C, and that the total duration of the thermal treatment in the temperature range from 680 to 715 ° C is between 5 and 240 seconds. To a certain extent, the duration of the thermal treatment can compensate for the level of the highest treatment temperature and vice versa; However, it is found that the frequency of experiments in which alloying is achieved in the upper area of the metal foam while unalloyed areas remain inside the metal foam, decreases sharply if the temperature interval between 680 and 715 ° C at the maximum temperature of the thermal treatment is left and / or the duration of the thermal treatment in the temperature interval between 680 and 715 ° C is outside the range of 5 to 240 seconds. If the maximum temperature is too high and / or if the metal foam body remains in the region of the maximum temperature for too long, the alloy formation progresses into the deepest layers of the metal foam and no unalloyed areas remain. Too low a maximum temperature and / or too short If the metal foam body remains in the range of the maximum temperature, the alloy formation does not even begin.

The thermal treatment of the metal foam in step (c) of the process according to the invention leads to the formation of aluminum-containing phases. The ratio V of the masses of metal foam body B to metal foam body A, V = m (metal foam body B) / m (metal foam body A), is a measure of how much aluminum was alloyed into the foam in step (c) of the process according to the invention.

In a preferred embodiment, the ratio V of the masses of metal foam body B to metal foam body A, V = m (metal foam body B) / m (metal foam body A) is in the range from 1.1: 1 to 1.5: 1. In a further preferred embodiment, the ratio V of the masses of metal foam body B to metal foam body A, V = m (metal foam body B) / m (metal foam body A) is in the range from 1.2: 1 to 1.4: 1.

In step (d) of the method according to the invention, an oxidative treatment of metal foam body B takes place, so that metal foam body C is obtained.

The aim of the oxidative treatment of metal foam body B in step (d) of the method according to the invention is to provide the aluminum present on the surface of metal foam body B with an external aluminum oxide layer. This goal can be achieved, for example, by exposing the metal foam body B either in a heated state to an oxidative gas atmosphere (e.g. air), or by first forming aluminum hydroxide on the surface of the metal foam body B, e.g. by bringing it into contact with an alkaline solution, and then applying the aluminum hydroxide thermal treatment under oxidizing conditions is converted into aluminum oxide.

In order to expose the metal foam body B in a heated state to an oxidative gas atmosphere, it is sufficient, for example, to heat the metal foam body to a suitable temperature in an oven with the admission of air.

If metal foam body B is heated in the presence of air without prior formation of aluminum hydroxide, the temperature should be selected between 200 ° C and 1200 ° C, or between 200 ° C and 1000 ° C, or between 200 ° C and 750 ° C. According to the invention, the thermal oxidation is preferably carried out over a period of 1 to 60 minutes at a temperature of 200 ° C. to 700 ° C. in air.

If aluminum hydroxide is initially formed on the surface of metal foam body B, e.g. by bringing it into contact with an alkaline solution and only then thermally treated, at least some of the aluminum on the surface is first converted to aluminum hydroxide and then at least some of the aluminum hydroxide formed on the surface is converted to aluminum oxide. The conversion of at least part of the aluminum lying on the surface to aluminum hydroxide is preferably achieved by bringing the metal foam body into contact with an aqueous alkaline solution.

The aqueous alkaline solution particularly preferably contains sodium hydroxide, potassium hydroxide, lithium hydroxide or a combination thereof in a concentration of 0.05 to 30% by weight, preferably 0.5 to 5% by weight, and metal foam body B is with the aqueous alkaline solution over a period of Brought into contact for 5 to 120 minutes, preferably a maximum of 30 minutes and particularly preferably a maximum of 10 minutes. This treatment can take place in a temperature range between 10 ° C and 110 ° C. Treatment at 20 ° C. (room temperature) is preferred.

Subsequently, at least part of the aluminum hydroxide formed on the surface is thermally converted to aluminum oxide in an oxidizing atmosphere. For this purpose, the mixture is heated to a temperature of 20 ° C (room temperature) to 700 ° C over a period of 1 minute to 8 hours with the admission of air. According to the invention, the thermal oxidation is preferably carried out over a period of 1 to 60 minutes at a temperature of 200 ° C. to 700 ° C. in air.

Metal foam body C serves as a support body for a suitable catalyst, which can be specifically selected for the particular reaction that is to be catalyzed.

In step (e) of the method according to the invention, a catalytically active layer, comprising at least one carrier oxide and at least one catalytically active component, is applied to at least part of the surface of metal body C, so that a supported catalyst is obtained.

Metal foam bodies C according to the invention can be equipped particularly well with a catalytically active layer according to the invention, since the aluminum oxide skin produced on the surface of metal foam body C ensures extremely good binding of the carrier oxides and a long durability and service life as well as extremely high mechanical stability, in particular abrasion resistance , causes.

The catalytically active layer, comprising at least one carrier oxide and at least one catalytically active component, can be applied, for example, to metal foam body C by sucking or pumping a coating suspension through the continuous cavities of open-pore metal foam body C. In terms of continuous cavities and high dimensional stability, metal foam body C is similar to the monolithic substrates used in car exhaust catalysis. Also the application of a coating suspension in dipping processes (so-called "dip coating") or in spraying processes (so-called “spray coating”) is possible. Which of the application methods known in principle in the prior art is to be preferred depends on the one hand on the composition and the flow properties of the coating suspension and on the other hand on the actual structure of the metal foam body according to the invention. Dip coating has the highest possible tolerance to varying properties of the coating suspension and is therefore suitable for coating all metal foam bodies according to the invention.

According to the present invention, in step (e), following the bringing into contact with the coating suspension, the coated metal foam body is calcined and the supported catalyst is thus obtained.

According to the invention, the catalytically active layer comprises at least one carrier oxide. For the purposes of the present invention, carrier oxides are inorganic oxides with high specific surface areas, which are typically between 50 and 200 m ² / g. These carrier oxides have several functions in the finished catalyst: On the one hand, they serve to enlarge the macroscopic, ie geometric surface provided by the metal foam bodies according to the invention, which in the context of this invention is referred to as the contact surface of the catalyst with the reaction medium, in the microscopic level. On the other hand, they can interact with the catalytically active species and thus influence the course of the reaction.

For example, the choice of carrier oxide influences the selectivity of complex hydrogenation reactions in which several functional groups of organic substrate molecules can react with hydrogen. Furthermore, they provide the microscopic surface on which the catalytically active components are distributed. They also form a matrix in which further functional components and additives can be distributed, which are used to set special functions of the catalytic converter when it is adapted to a specific application.

Carrier oxides are preferably selected from the group consisting of aluminum oxide, silicon dioxide, titanium oxide and mixtures thereof.

Transition metals or compounds of transition metals are used as catalytically active components of the catalytically active layer, the transition metals preferably being selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, cerium, copper, Silver, gold and mixtures thereof.

As further functional components and additives, the catalytically active layer can contain inorganic oxides, preferably selected from the oxides of the alkaline earth metals, the oxides of the transition metals, the rare earths, the oxides of aluminum and gallium, the oxides of silicon, germanium and tin and / or mixtures thereof.

The catalytically active layers according to the present invention can contain one or more carrier oxides, one or more catalytically active components and, if appropriate, further functional components and additives. In order to apply the catalyst to the metal foam bodies according to the invention, a coating suspension is produced by introducing the constituents into water. The application of the catalytic components to the carrier oxides takes place either by prior impregnation of the carrier oxides with appropriate metal salt solutions (precursor solutions) or by adding precursor solutions directly to the coating suspension and optionally precipitation or chemically induced deposition or decomposition of the precursor compound on the / the already suspended carrier oxide / s. Functional components and additives can also be introduced in this way or added directly as oxidic solids. Alternatively, all of the constituents of the catalyst resulting from soluble precursors can be added by post-impregnation processes after the carrier oxides have been applied to the metal foam bodies according to the invention. The choice of the preparation method is determined by the target composition and the properties of the resulting catalyst to be set.

The catalytically active layer applied to the metal foam bodies in step (e) of the process according to the invention is preferably fixed by calcination in air.

According to the invention, this calcination is carried out over a period of 1 minute to 8 hours at a temperature of 200 ° C. to 800 ° C. in air. According to the invention, the calcination is preferably carried out over a period of 1 to 480 minutes at a temperature of 200 ° C. to 680 ° C. in air. The calcination is particularly preferably carried out over a period of 1 to 480 minutes at a temperature of 300 ° C. to 650 ° C. in air.

According to the invention, the thermal oxidation in step (d) over a period of 1 to 60 minutes at a temperature of 200 ° C. to 680 ° C. in air and the calcination in step (e) over a period of 1 to 480 minutes at a Temperature from 200 ° C to 680 ° C carried out in air.

The process according to the invention for producing supported catalysts is significantly less expensive than existing processes. Furthermore, a metal foam body according to the invention forms a pure aluminum oxide layer on the surface due to its excess of Al, which means a diffusion barrier between the carrier material and the catalytic layer.

Catalytic layers based on the carrier oxide aluminum oxide and the aluminum oxide on the surface of the metal foam body are systems of the same type. The expansion coefficients are therefore similar, spalling under thermal loads is low and the connection resistance due to a calcination process is very good. In addition to the processes according to the invention for preparing supported catalysts, the supported catalysts themselves obtainable by these processes and their use in chemical transformations are also a subject of the present invention.

Supported catalysts according to the invention can, for example, advantageously be used in chemical fixed bed processes.

Example of co-foam

1. Provision of metal foam bodies

Six metal foam bodies (a - f) made of cobalt were provided (manufacturer: AATM, dimensions: 100 mm x 100 mm x 2 mm, weight per unit area: 1000 g / m ² , average pore diameter: 580 μm), which were produced by electrodeposition of cobalt on a polyurethane foam and subsequent thermolysis of the plastic components.

2. Deposition of aluminum

Binder solution was then sprayed onto metal foam bodies a, b, c, d, e, f (polyethyleneimine (2.5% by weight) in water) and then powdered aluminum (manufacturer: AMG, average particle size: <63 μm, with 3% by weight) % Addition of ethylene bis (stearamide)) applied as a dry powder (approx. 400 g / m ² ).

3. Thermal treatment

Then metal foam bodies a, b, c, d, e were subjected to a thermal treatment in an oven under a nitrogen atmosphere. It was initially heated from room temperature to the maximum temperature in about 15 minutes, this was maintained for a defined period of time and then quenched by contacting with a nitrogen atmosphere of 200 ° C.

Maximum temperature for metal foam bodies a, d, e:

700 ° C for 2 minutes

Temperature profile of metal foam body b:

600 ° C for 2 minutes

Temperature profile of metal foam body c:

750 ° C for 2 minutes

4. Determination of alloy size

The extent of the alloy formation in the metal foam bodies was then determined. For this purpose, cross sections of the metal foam bodies were examined under a microscope and a scanning electron microscope. While with the metal foam bodies a, d, e superficial alloy formation has taken place, but unalloyed areas inside the Metal foam have remained, no alloy formation has taken place in metal foam body b, and in metal foam body c the alloy formation has progressed so far that no unalloyed areas remain in the interior of the metal foam.

5. Oxidative treatment

An oxidative treatment of the metal foam bodies a and d was then carried out.

Metal foam body a was exposed to an oxidative gas atmosphere in a heated state. For this purpose, the metal foam body was heated to 700 ° C. in an oven with admission of air.

Metal foam body d was first brought into contact with an alkaline solution (5% by weight aqueous NaOH for 10 min at 20 ° C.). A white precipitate forms on the foam. The precipitate is the conversion of aluminum to aluminum hydroxide. Metal foam body d was then dried in air. The dried metal foam body with the white precipitate is pre-oxidized in a preheated oven at 700 ° C. and normal atmosphere, in which the aluminum hydroxide is converted into aluminum oxide.

The oxidic pretreatment has several functions:

Protection of the carrier material against further oxidation Adhesion promoter between metallic and ceramic system Diffusion barrier of alloy elements on the carrier material into the catalytic ceramic layer

6. Comparative treatment

Metal foam body f, which had previously remained untreated, was provided with an aluminum oxide layer, as described in the prior art (cf. WO95 / 11752A1, Example 3). For this purpose, metal foam bodies f were completely immersed in a saturated sodium aluminate solution for 3 hours, then swiveled in deionized water until the hydrolysis reaction had subsided, and finally heated at 500 ° C. for 3 hours with access to air.

7. Application of the catalytically active layer

A catalytically active layer was then applied to metal foam bodies a, d, e and f by spraying. For this purpose, the metal foam body was moistened with water. A 2.5% polyethyleneimine suspension was then mixed with c-aluminum oxide with a high surface area. The mixture of water / polyethyleneimine and aluminum oxide was sprayed on. The spraying was followed by a drying process at 140 ° C. for 30 minutes in air in a drying oven. For calcination, the sample was baked in an oven at 650 ° C. for 5 hours. The process of coating, drying and calcination was repeated several times until the desired amount of coating was applied. 8. Investigation of the supported catalyst obtained

Finally, the supported catalysts obtained were examined, among other things the resistance of the catalytically active layer on the metal foam bodies to mechanical stress was examined. In many cases, a scratch test can be carried out in order to determine the bonding quality of the oxidic, catalytically active layer to the carrier foam. In the present case, however, this test is not possible due to the irregular structure of the foam. Therefore, to investigate the mechanical stability of the catalytically active layer, a temperature change test was carried out, which provides a measure of the quality of the bond between the oxidic layer and the carrier foam. For this purpose, metal foam bodies a, d, e and f were heated to 500 ° C. and then quenched in cold water. The amount lost, i.e. the mass of the flaked catalytic layer of each sample, was then determined by filtering off, drying and weighing the flaked material.

The result was as follows:

Metal foam body a and d: 3 mg loss, metal foam body f: 10 mg loss, metal foam body e: 50 mg loss

While the catalytically active layer on the metal foam bodies a and d had a high resistance to mechanical stress, the resistance of the catalytically active layer on metal foam bodies f was significantly lower and on metal foam bodies e very low.

Example for NiCo foam

2. Provision of metal foam bodies

Six metal foam bodies (a-f) made of nickel-cobalt were provided (manufacturer: AATM, dimensions: 100 mm x 100 mm x 2 mm, weight per unit area: 1000 g / m ² , average pore diameter: 580 pm), which were electrodeposited of nickel on a polyurethane foam, furthermore cobalt was deposited on nickel and subsequent thermolysis of the plastic components had been produced.

2. Deposition of aluminum

3. Thermal treatment Then metal foam bodies a, b, c, d, e were subjected to a thermal treatment in an oven under a nitrogen atmosphere. It was initially heated from room temperature to the maximum temperature in about 15 minutes, this was maintained for a defined period of time and then quenched by contacting with a nitrogen atmosphere of 200 ° C.

Maximum temperature for metal foam bodies a, d, e:

700 ° C for 2 minutes

Temperature profile of metal foam body b:

600 ° C for 2 minutes

Temperature profile of metal foam body c:

750 ° C for 2 minutes

4. Determination of alloy size

The extent of the alloy formation in the metal foam bodies was then determined. For this purpose, cross sections of the metal foam bodies were examined under a microscope and a scanning electron microscope. While with the metal foam bodies a, d, e superficial alloy formation has taken place, but unalloyed areas have remained inside the metal foam, with metal foam body b no alloy formation has taken place, and with metal foam body c the alloy formation has progressed so far that no unalloyed areas inside the Metal foam are left.

5. Oxidative treatment

An oxidative treatment of the metal foam bodies a and d was then carried out.

The oxidic pretreatment has several functions:

Protection of the carrier material against further oxidation Adhesion promoter between metallic and ceramic system Diffusion barrier of alloy elements on the carrier material into the catalytic ceramic layer 6 Comparative Treatment

7. Application of the catalytically active layer

A catalytically active layer was then applied to metal foam bodies a, d, e and f by spraying. For this purpose, the metal foam body was moistened with water. A 2.5% polyethyleneimine suspension was then mixed with c-aluminum oxide with a high surface area. The mixture of water / polyethyleneimine and aluminum oxide was sprayed on. The spraying was followed by a drying process at 140 ° C. for 30 minutes in air in a drying oven. For calcination, the sample was baked in an oven at 650 ° C. for 5 hours. The process of coating, drying and calcination was repeated several times until the desired amount of coating was applied.

8. Investigation of the supported catalyst obtained

The result was as follows:

Metal foam body a and d: 4 mg loss, metal foam body f: 12 mg loss, metal foam body e: 48 mg loss

While the catalytically active layer on the metal foam bodies a and d had a high resistance to mechanical stress, the resistance was the catalytically active layer on metal foam body f significantly lower and on metal foam body e very low.

Claims

1. A method for producing a supported catalyst comprising the following steps:

2. The method according to claim 1, wherein the oxidative treatment of metal foam body B in step (d) is selected from the following:

Heating of metal foam body B in contact with an oxidative gas atmosphere without prior formation of aluminum hydroxide on the surface of the metal foam body,

Heating metal foam body B in contact with an oxidative gas atmosphere after aluminum hydroxide is previously formed on the surface of the metal foam body.

3. The method according to any one of claims 1 to 2, wherein for the oxidative treatment of metal foam body B in step (d) metal foam body B is heated in contact with an oxidative gas atmosphere without prior formation of aluminum hydroxide on the surface of the metal foam body.

4. The method according to claim 3, wherein the heating in contact with an oxidative

Gas atmosphere is carried out for a period of 1 to 60 minutes at a temperature of 200 ° C to 700 ° C in air.

5. The method according to any one of claims 1 to 2, wherein for the oxidative treatment of metal foam body B in step (d) metal foam body B in contact with an oxidative gas atmosphere is heated after aluminum hydroxide has previously been formed on the surface of the metal foam body.

6. The method according to claim 5, wherein aluminum hydroxide is formed on the surface by bringing the metal foam body into contact with an aqueous alkaline solution.

7. The method according to claim 6, wherein the aqueous alkaline solution contains sodium hydroxide, potassium hydroxide, lithium hydroxide or combinations thereof and the metal foam body is brought into contact with the aqueous alkaline solution over a period of a maximum of 30 minutes.

8. The method according to any one of claims 5 to 7, wherein the heating in contact with an oxidative gas atmosphere, after aluminum hydroxide has previously been formed on the surface of the metal foam body, for a period of 1 to 60 minutes at a temperature of 200 ° C to 700 ° C is run in air.

9. The method according to any one of claims 1 to 8, wherein the carrier oxide of the catalytically active layer applied in step (e) is selected from the group consisting of aluminum oxide, silicon dioxide, titanium oxide and mixtures thereof.

10. The method according to any one of claims 1 to 9, wherein the catalytically active component is a transition metal or the compound of a transition metal, wherein the transition metal is selected from the group consisting of iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium , Platinum, cerium, copper, silver, gold and mixtures thereof.

11. Supported catalyst obtainable by a process according to any one of claims 1 to 10.

12. Use of a supported catalyst according to one of claims 1 to 10 in chemical transformations.