Cobalt-containing metal foam element and preparation method thereof

Abstract

The present invention relates to a method for preparing a supported catalyst, comprising: providing a metal foam body A made of metallic cobalt, an alloy of nickel and cobalt, or an arrangement of superimposed layers of nickel and cobalt; applying an aluminum-containing powder MP to the metal foam body A to obtain a metal foam body AX; heat-treating the metal foam body AX to form an alloy between the metal foam body A and the aluminum-containing powder MP, thereby obtaining a metal foam body B; oxidatively treating the metal foam body B to obtain a metal foam body C; and applying a catalytically active layer comprising at least one support oxide and at least one catalytically active component to at least a portion of the surface of the metal foam body C to obtain a supported catalyst. The present invention also relates to a supported catalyst obtainable using this method and to the use of the supported catalyst in chemical conversions.

Description

Technical Field

[0001] The present invention relates to a method for producing a supported catalyst, comprising the steps of coating a metal foam body made of metallic cobalt, an alloy of nickel and cobalt, or an arrangement of superimposed layers of nickel and cobalt with aluminum, followed by a heat treatment to achieve alloy formation between the metal foam and the aluminum, followed by an oxidation treatment of the aluminum surface and application of a catalytically active layer comprising at least one support oxide and at least one catalytically active component. The invention also relates to the supported catalyst obtainable by this method and its use in chemical conversions. Background Art

[0002] The use of metal foams as supports for catalytically active coatings is known in the prior art. Catalytically active coatings on metal supports typically consist of a support oxide that increases the microscopic surface area and a catalytically active metal applied to the support oxide (see, for example, WO 9511752 A1). The monolithic supported catalysts thus obtained can be used in a variety of applications, but their usability is limited by the very poor adhesion of the catalytically active coating, which primarily consists of the oxidizing component, to the metal support. Under mechanical stress, and possibly also during operation of the supported catalyst in a flow-through reactor, poor adhesion can lead to partial detachment of the catalytically active layer, which in turn reduces the service life of the catalyst and can disrupt the operation of the system due to detached solid particles.

[0003] An alternative approach is to use sol-gel methods to coat metal foams as catalyst supports. However, these methods require specialized equipment and use expensive reagents that are potentially hazardous and difficult to handle.

[0004] Another method for preparing metal foam supported catalysts known from the prior art utilizes the ability to produce a relatively stable oxide layer on a metal surface by atomic layer deposition (ALD). For example, US 20120329889 A1 discloses a method for preparing a metal foam supported catalyst for Fischer-Tropsch synthesis, wherein a thin Al2O3 film is prepared by atomic layer deposition (ALD) on a metal foam, followed by applying an oxide coating by dip coating, drying, and then calcining. US 20120329889 A1 explicitly mentions that it is difficult to achieve a stable coupling between the metal foam surface and the oxide coating (see paragraphs

[0068] and

[0069] ), and this is achieved by applying an oxide intermediate layer by ALD. However, the method disclosed in US 20120329889 A1 does require extremely complex equipment.

[0005] Given the difficulties in obtaining stable metal foam-supported catalysts, the object of the present invention is to provide a method that is as simple as possible and suitable for mass production for producing catalytically inert metal foam-supported catalysts having a catalytic coating. In such catalysts, the pores provided by the foam base structure should not clog, and the catalytic coating should be as simple as possible to apply while still being characterized by very good adhesion to the metal foam. The methods of the present invention and the products obtainable by these methods meet this need. Summary of the Invention

[0006] The method for preparing a supported catalyst according to the present invention comprises the following steps:

[0007] (a) providing a metal foam body A made of metallic cobalt, an alloy of nickel and cobalt, or an arrangement of superimposed layers of nickel and cobalt,

[0008] (b) applying an aluminum-containing powder MP to a metal foam body A to obtain a metal foam body AX,

[0009] (c) heat treating the metal foam body AX to achieve alloy formation between the metal foam body A and the aluminum-containing powder MP, thereby obtaining a metal foam body B,

[0010] wherein the maximum temperature during the heat treatment of the metal foam body AX is in the range of 680°C to 715°C,

[0011] and wherein the total duration of the heat treatment in the temperature range of 680° C. to 715° C. is between 5 seconds and 240 seconds,

[0012] (d) oxidizing the metal foam body B to obtain the metal foam body C,

[0013] (e) applying a catalytically active layer comprising at least one support oxide and at least one catalytically active component to at least a portion of the surface of the metal foam body C to obtain a supported catalyst.

[0014] Nickel foams to which aluminum is first applied, alloyed and then partially leached again are alternatives to the classic Raney-type catalysts known in the prior art (see, for example, EP 2764916 A1). The foams thus obtained are activated all-metal catalysts of the Raney type commonly used in hydrogenation reactions.

[0015] Also known from the prior art are metal foams to which aluminum is first applied and alloyed, and then oxidized (see Wen-Wen Zeng et al. "Synthesis and compression properties of oxidation-resistant Ni-Al foams", Acta Metallurgica Sinica, volume 30, No. 10, 1 October 2017, pages 965-972). However, in the method of Wen-Wen Zeng et al., the entire cross-section of the initially present metal foam is alloyed with aluminum (see page 972, conclusion), whereas in the method of the present invention, alloy formation is limited to the upper layer of the metal foam, so that unalloyed areas remain in the central region of the metal foam.

[0016] The experimental results obtained in conjunction with the present invention show that the choice of temperature conditions for the heat treatment of alloy formation has a considerable influence on the results. The method according to the present invention can limit the alloy formation to the upper layer of the metal foam, so that the non-alloyed area remains in the central area of the metal foam. The presence of these unalloyed areas affects in particular the mechanical stability of the supported catalyst obtained. The fracture strength / compressive strength decreases significantly with increasing degree of alloying, and complete alloying of the metal foam leads to a very brittle supported catalyst that tends to break under mechanical stress. This fact is of considerable practical significance, because the continuously operated fixed-bed reactors used on an industrial scale can have a volume of up to 100 m 3 The fixed bed volume means that, depending on the bulk density and height of the fixed bed used, there may be several metric tons of weight pressing on its lower layer. If the supported catalyst used to form the fixed bed does not have sufficient mechanical stability and durability to withstand such a weight over thousands of hours of operation, this will lead to damage to the support structure and therefore mechanical failure (catalyst breakage) of the catalytically active area. The damaged material may be discharged from the reactor together with the fluid into adjacent device components and / or cause the fixed bed to agglomerate. In both cases, all will cause serious interruptions to the operation of the equipment.

[0017] In the context of the present invention, metal foam body A is understood to mean a metal body in foam form. Metal bodies in foam form are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, section "Metallic Foams," published online on July 15, 2012, DOI: 10.1002 / 14356007.c16_c01.pub2. Metal foams with varying morphological properties (pore size and shape, layer thickness, areal density, geometric surface area, porosity, etc.) are generally suitable. Metal foam A preferably has a density of 400 g / m². 2 Up to 1500g / m 2 The foam can be made of an organic polymer and has a density in the range of 100 μm to 5000 μm, a pore size of 400 μm to 3000 μm, preferably 400 μm to 800 μm, and a thickness in the range of 0.5 mm to 10 mm, preferably 1.0 mm to 5.0 mm. It can be produced in a manner known per se. For example, a foam made of an organic polymer can first be coated with a metal and then the polymer is removed by pyrolysis to produce a metal foam. In order to be coated with at least one first metal or a precursor thereof, the foam made of an organic polymer can be contacted with a solution or suspension containing the first metal. This can be done, for example, by spraying or dipping. It can also be deposited by chemical vapor deposition (CVD). Polymer foams suitable for producing molded bodies in the form of foams preferably have a pore size in the range of 100 μm to 5000 μm, more preferably 450 μm to 4000 μm, in particular 450 μm to 3000 μm. Suitable polymer foams preferably have a layer thickness of 0.5 mm to 10 mm, more preferably 1.0 mm to 5.0 mm. Suitable polymer foams preferably have a density of 300 kg / m 3 Up to 1200kg / m 3 The specific surface area is preferably 100m 2 / m 3 Up to 20,000m 2 / m 3 , more preferably 1000m 2 / m 3 Up to 6000m 2 / m 3 The porosity is preferably in the range of 0.50 to 0.95.

[0018] The metal foam body A used in step (a) of the process according to the invention may have any desired shape, for example a cube, a cuboid, a cylinder, etc. The metal foam body may alternatively be formed, for example, as a monolithic block.

[0019] The aluminum-containing powder MP can be applied in step (b) of the method according to the invention in various ways, for example by contacting the metal foam A with the composition containing aluminum powder MP by rolling or dipping, or by spraying, spreading, or pouring the composition containing aluminum powder MP. For this purpose, the composition containing aluminum powder MP can be in the form of a suspension or a powder.

[0020] Before the actual application of the composition containing aluminum powder MP to the metal foam body A in step (b) of the method according to the invention, the metal foam body A is preferably pre-impregnated with a binder. Impregnation can be accomplished, for example, by spraying the binder or immersing the metal foam body A in the binder, but is not limited to these options. The composition containing metal powder MP can then be applied to the metal foam body A thus prepared.

[0021] Alternatively, the binder and the composition containing aluminum powder MP can be applied in one step. To this end, the composition containing aluminum powder MP is suspended in the liquid binder itself before application, or the composition containing aluminum powder MP and the binder are suspended in an auxiliary fluid F.

[0022] The binder is a composition that can be completely converted into a gaseous product by heat treatment at a temperature range of 100°C to 400°C. It contains an organic compound that promotes adhesion of the composition containing aluminum powder MP to the metal foam. The organic compound is preferably selected from the group consisting of polyethyleneimine (PEI), polyvinylpyrrolidone (PVP), ethylene glycol, and mixtures of these compounds. PEI is particularly preferred. The molecular weight of polyethyleneimine is preferably in the range of 10,000 g / mol to 1,300,000 g / mol. The molecular weight of polyethyleneimine (PEI) is preferably in the range of 700,000 g / mol to 800,000 g / mol.

[0023] The auxiliary fluid F must be capable of forming a suspension of the composition containing aluminum powder MP and the binder, and fully converting them into gaseous products upon thermal treatment at a temperature ranging from 100°C to 400°C. Auxiliary fluid F is preferably selected from the group consisting of water, ethylene glycol, PVP, and mixtures of these compounds. When an auxiliary fluid is used, the binder is typically suspended in water at a concentration ranging from 1% to 10% by weight, and the composition containing aluminum powder MP is subsequently suspended in this suspension.

[0024] The aluminum-containing powder MP used in step (b) of the process according to the invention comprises powdered aluminum but may also contain additives which contribute to increased fluidity or water stability. Such additives must be completely converted into gaseous products by heat treatment at a temperature in the range of 100° C. to 400° C.

[0025] The aluminum-containing powder MP preferably has an aluminum content in the range of 80% to 99.8% by weight. Powders in which the aluminum particles have a particle size of no less than 5 μm and no more than 200 μm are preferred. Particularly preferred are powders in which 95% of the aluminum particles have a particle size of no less than 5 μm and no more than 75 μm. The aluminum-containing powder MP may contain an aluminum component in oxidized form in addition to the elemental aluminum component. This oxidized portion is typically in the form of an oxidized compound, such as an oxide, hydroxide, and / or carbonate. The mass proportion of aluminum oxide, based on the total mass of the aluminum-containing powder MP, is typically in the range of 0.05% to 10% by weight.

[0026] In step (c) of the method according to the invention, a heat treatment is performed to achieve the formation of one or more alloys.

[0027] Experimental results obtained in conjunction with the present invention indicate that the choice of temperature conditions for the heat treatment used for alloy formation has a significant impact on the alloy formation process. The method according to the present invention can limit alloy formation to the upper layer of the metal foam, so that the non-alloyed area remains in the central region of the metal foam.

[0028] In step (c) of the method according to the invention, the metal foam body AX is subjected to a heat treatment to achieve alloy formation between the metal foam body A and the aluminum-containing powder MP, thereby obtaining the metal foam body B, the maximum temperature in the heat treatment of the metal foam body AX being in the range of 680° C. to 715° C., and the total duration of the heat treatment in the temperature range of 680° C. to 715° C. being between 5 seconds and 240 seconds.

[0029] Heat treatment typically involves gradual heating of the metal foam body AX and subsequent cooling to room temperature. The heat treatment is carried out under an inert atmosphere or under reducing conditions. Reducing conditions are understood to mean the presence of a gas mixture containing hydrogen and at least one gas that is inert under the reaction conditions. A suitable example is a gas mixture containing 50% by volume N2 and 50% by volume H2. The inert gas used is preferably nitrogen. Heating can be carried out, for example, in a belt furnace. Suitable heating rates range from 10 K / min to 200 K / min, preferably from 20 K / min to 180 K / min. During the heat treatment, the temperature is typically first increased from room temperature to approximately 300°C to 400°C, at which point moisture and organic components are removed from the coating over a period of approximately 2 to 30 minutes. The temperature is then increased to a range of 680°C to 715°C, resulting in alloy formation between the metal foam body A and the aluminum-containing powder MP. The metal foam body is then quenched by contact with an inert gas atmosphere at a temperature of approximately 200°C.

[0030] For the metals according to the present invention, in order to limit alloy formation to the upper region of the metal foam and leave unalloyed regions within the metal foam, it is necessary that the maximum temperature during the heat treatment of the metal foam body AX in step (c) is within the range of 680°C to 715°C, and the total duration of the heat treatment within the temperature range of 680°C to 715°C is between 5 seconds and 240 seconds. The duration of the heat treatment can compensate to some extent for the level of the maximum treatment temperature, and vice versa. However, it has been found that the frequency of experiments in which alloy formation is achieved in the upper region of the metal foam while leaving unalloyed regions within the metal foam decreases significantly when the maximum temperature during the heat treatment is outside the temperature range of 680°C to 715°C and / or the duration of the heat treatment within the temperature range of 680°C to 715°C is outside the temperature range of 5 seconds to 240 seconds. If the maximum temperature is too high and / or the metal foam body remains in the maximum temperature range for too long, this can cause alloy formation to penetrate into the lowest depths of the metal foam, leaving no unalloyed regions. If the maximum temperature is too low and / or the metal foam body does not remain in the maximum temperature range for a sufficiently long time, alloy formation may not even begin.

[0031] The heat treatment of the metal foam in step (c) of the method according to the invention results in the formation of an aluminum-containing phase. The mass ratio V of the metal foam B to the metal foam A, V=m(metal foam B) / m(metal foam A), is a measure of how much aluminum is alloyed into the foam in step (c) of the method according to the invention.

[0032] In a preferred embodiment, the mass ratio of metal foam B to metal foam A, V, V = m (metal foam B) / m (metal foam A), is in the range of 1.1:1 to 1.5:1. In a further preferred embodiment, the mass ratio of metal foam B to metal foam A, V, V = m (metal foam B) / m (metal foam A), is in the range of 1.2:1 to 1.4:1.

[0033] In step (d) of the method according to the invention, an oxidation treatment of the metal foam body B is carried out to obtain the metal foam body C.

[0034] The purpose of the oxidative treatment of the metal foam body B in step (d) of the process according to the invention is to provide an outer aluminum oxide layer on the aluminum present on the surface of the metal foam body B. This purpose can be achieved, for example, by exposing the metal foam body B in a heated state to an oxidizing gas atmosphere (e.g. air), or by initial surface formation of aluminum hydroxide on the metal foam body B (e.g. by contact with an alkaline solution) and then converting the aluminum hydroxide into aluminum oxide by heat treatment under oxidizing conditions.

[0035] In order to expose the metal foam body B in a heated state to an oxidizing gas atmosphere, it is sufficient to heat the metal foam body to a suitable temperature in a furnace through which air is passed, for example.

[0036] If the metal foam body B is heated with air flow without prior formation of aluminum hydroxide, the temperature selected should be between 200° C. and 1200° C., or between 200° C. and 1000° C., or between 200° C. and 750° C. According to the invention, it is preferred that the thermal oxidation be carried out in air at a temperature of 200° C. to 700° C. for a period of 1 minute to 60 minutes.

[0037] If aluminum hydroxide is first formed on the surface of the metal foam body B, for example by contact with an alkaline solution, and then subjected to heat treatment, at least some of the aluminum present on the surface is initially converted to aluminum hydroxide, and at least some of the aluminum hydroxide formed on the surface is subsequently converted to aluminum oxide.

[0038] The conversion of at least part of the surface-present aluminum into aluminum hydroxide is preferably achieved by contacting the metal foam with an alkaline aqueous solution.

[0039] The alkaline aqueous solution particularly preferably contains sodium hydroxide, potassium hydroxide, lithium hydroxide, or a combination thereof at a concentration of 0.05 to 30% by weight, preferably 0.5 to 5% by weight, and the metal foam B is contacted with the alkaline aqueous solution for 5 to 120 minutes, preferably no longer than 30 minutes, and more preferably no longer than 10 minutes. This treatment can be carried out at a temperature between 10°C and 110°C. Treatment at 20°C (room temperature) is preferred.

[0040] Subsequently, at least part of the aluminum hydroxide formed on the surface is thermally converted to aluminum oxide in an oxidizing atmosphere. This is accomplished by heating to a temperature of 20° C. (room temperature) to 700° C. for a period of 1 minute to 8 hours while passing air. According to the invention, thermal oxidation is preferably carried out in air at a temperature of 200° C. to 700° C. for a period of 1 minute to 60 minutes.

[0041] The metal foam C serves as a support for a suitable catalyst, which can be selected specifically for the particular reaction to be catalyzed.

[0042] In step (e) of the process according to the invention, a catalytically active layer comprising at least one support oxide and at least one catalytically active component is applied to at least a portion of the surface of the metal body C to obtain a supported catalyst.

[0043] The metal foam body C according to the invention can be provided particularly easily with the catalytically active layer according to the invention, since the aluminum oxide scale produced on the surface of the metal foam body C ensures very good bonding of the support oxide and provides a long durability and service life as well as very high mechanical stability, in particular wear resistance.

[0044] The catalytically active layer comprising at least one support oxide and at least one catalytically active component can be applied to the metal foam body C, for example, by drawing or pumping a coating suspension through the continuous cavities of the open-pore metal foam body C. This is possible because the metal foam body C resembles monolithic substrates used in automotive exhaust catalysis in terms of its continuous cavities and high dimensional stability. The coating suspension can also be applied by impregnation (referred to as "dip coating") or by spraying (referred to as "spray coating"). Which of the application methods known in principle from the prior art is preferred depends firstly on the composition and flow properties of the coating suspension and secondly on the actual structure of the metal foam body according to the present invention. Dip coating offers the greatest possible tolerance to the varying properties of the coating suspension and is therefore suitable for coating all metal foam bodies according to the present invention.

[0045] According to the invention, after contacting with the coating suspension, the coated metal foam is calcined in step (e) to obtain the supported catalyst.

[0046] The catalytically active layer according to the invention comprises at least one support oxide. For the purposes of the present invention, a support oxide is a 2 / g and 200m 2 / g of high specific surface area inorganic oxides. These support oxides have multiple functions in the finished catalyst: first, they are used to increase the macroscopic surface area (i.e., geometric surface area) provided by the metal foam of the present invention on a microscopic level, which is referred to as the contact area of the catalyst with the reaction medium in the context of the present invention. Secondly, they themselves can interact with the catalytically active species and therefore affect the reaction process. For example, the choice of support oxide affects the selectivity of complex hydrogenation reactions (wherein multiple functional groups of organic substrate molecules can react with hydrogen). In addition, they provide a microscopic surface on which the catalytically active components are dispersed. They also form a matrix in which more functional components and additives can be dispersed, which is used to adjust specific catalyst functions when adjusting the catalyst for a specific application.

[0047] The support oxide is preferably selected from alumina, silica, titania and mixtures thereof.

[0048] Used as catalytically active components of the catalytically active layer are transition metals or transition metal compounds, 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.

[0049] As further functional components and additives, the catalytically active layer may comprise inorganic oxides, preferably selected from oxides of alkaline earth metals, transition metal oxides, rare earth oxides, oxides of aluminum and gallium, oxides of silicon, germanium and tin, and / or mixtures thereof.

[0050] The catalytically active layer according to the invention can comprise one or more support oxides, one or more catalytically active components and optionally further functional components and additives.

[0051] To apply the catalyst to the metallic foam of the present invention, a coating suspension is prepared by introducing the ingredients into water. The catalytic components are applied to the support oxide by pre-impregnation of the support oxide with a solution of an appropriate metal salt (precursor solution) or by adding the precursor solution directly to the coating suspension and optionally precipitating or chemically inducing deposition or decomposition of the precursor compound on the already suspended support oxide. Functional components and additives can also be introduced in this manner or added directly in the form of oxidized solids. Alternatively, all components of the catalyst produced from soluble precursors can be added by a re-impregnation process after application of the support oxide to the metallic foam of the present invention. The choice of preparation method depends on the target composition and the properties desired for the resulting catalyst.

[0052] The fixing of the catalytically active layer applied to the metal foam body in step (e) of the process according to the invention is preferably achieved by calcination in air.

[0053] According to the present invention, the calcination is carried out in air at a temperature of 200° C. to 800° C. for a period of 1 minute to 8 hours. According to the present invention, preferably, the calcination is carried out in air at a temperature of 200° C. to 680° C. for a period of 1 minute to 480 minutes. Particularly preferably, the calcination is carried out in air at a temperature of 300° C. to 650° C. for a period of 1 minute to 480 minutes.

[0054] According to the present invention, it is preferred that the thermal oxidation in step d) is carried out in air at a temperature of 200° C. to 680° C. for a period of 1 minute to 60 minutes, and the calcination in step e) is carried out in air at a temperature of 200° C. to 680° C. for a period of 1 minute to 480 minutes.

[0055] The method for preparing supported catalysts according to the present invention is much more cost-effective than existing methods. In addition, the metal foam of the present invention forms a pure aluminum oxide layer due to the excess Al at its surface, which represents a diffusion barrier between the support material and the catalytic layer.

[0056] The catalytic layer based on aluminum oxide as a support oxide and the aluminum oxide at the surface of the metal foam are of the same type of system. Therefore, the expansion coefficients are similar, flaking under thermal stress is low, and the stability of the compound as a result of the calcination operation is very good.

[0057] In addition to the methods according to the invention for preparing supported catalysts, the present invention also provides the supported catalysts themselves obtainable by these methods, and the use of said catalysts in chemical conversions.

[0058] The supported catalyst according to the invention can be used advantageously, for example, in a chemical fixed-bed process.

[0059] Example of Co foam

[0060] 1. Provide metal foam

[0061] Six metal foam bodies (af) made of cobalt (manufacturer: AATM, size: 100 mm × 100 mm × 2 mm, weight per unit area: 1000 g / m 2 , average pore size 580 μm), which are produced by electrolytic deposition of cobalt on polyurethane foam and subsequent pyrolysis of the plastic component.

[0062] 2. Apply aluminum

[0063] The binder solution (2.5% by weight aqueous polyethyleneimine solution) was then first sprayed onto the metal foams a, b, c, d, e and f, followed by the application of powdered aluminum in dry powder form (approximately 400 g / m 2 ) (Manufacturer: AMG, average particle size: <63 μm, contains 3% by weight of added ethylenebis(stearamide)).

[0064] 3. Heat treatment

[0065] The metal foams a, b, c, d, and e were then heat treated in a furnace under a nitrogen atmosphere. First, the furnace was heated from room temperature to a maximum temperature over a period of about 15 minutes, held for a certain period of time, and then quenched by contact with a nitrogen atmosphere at 200°C.

[0066] Maximum temperature of metal foam a, d, e:

[0067] 700℃ for 2 minutes

[0068] Temperature course of metal foam b:

[0069] 600℃ for 2 minutes

[0070] Temperature course of metal foam c:

[0071] 750℃ for 2 minutes

[0072] 4. Determination of alloying degree

[0073] The extent of alloy formation in the metal foams was then determined. This was accomplished by examining cross-sections of the metal foams under a microscope and a scanning electron microscope. While surface alloy formation occurred in metal foams a, d, and e, unalloyed regions remained within the metal foams. In the case of metal foam b, no alloy formation occurred. In metal foam c, alloy formation was so advanced that no unalloyed regions remained within the metal foams.

[0074] 5. Oxidation treatment

[0075] The metal foams a and d were then subjected to oxidation treatment.

[0076] The metal foam body a is exposed to an oxidizing gas atmosphere in a heated state. This is accomplished by heating the metal foam body to 700°C in a furnace through which air is passed.

[0077] Metal foam d was first contacted with an alkaline solution (5 wt% aqueous NaOH solution at 20°C for 10 minutes). A white precipitate formed on the foam. The precipitate represented the conversion of aluminum to aluminum hydroxide. Metal foam d was then dried in air. The dried metal foam with the white precipitate was pre-oxidized in a preheated furnace at 700°C and standard atmospheric pressure, where the aluminum hydroxide was converted to aluminum oxide.

[0078] Oxidative pretreatment has many functions:

[0079] - Protects the support material from further oxidation

[0080] -Adhesion promoter between metal and ceramic systems

[0081] - a barrier for the diffusion of alloying elements on the support material into the catalytic ceramic layer

[0082] 6. Contrast processing

[0083] As described in the prior art (see WO 95 / 11752 A1, Example 3), a previously untreated metal foam body f was provided with an aluminum oxide layer. This was accomplished by completely immersing the metal foam body f in a saturated sodium aluminate solution for 3 hours, then tilting it back and forth in deionized water until the hydrolysis reaction subsided, and finally heating it at 500° C. for 3 hours while passing air.

[0084] 7. Applying the catalytically active layer

[0085] The catalytically active layer was then applied to the metal foams a, d, e, and f by spraying. This was done by moistening the metal foams with water. A 2.5% polyethyleneimine suspension was then stirred with high-surface-area χ-alumina. The water / polyethyleneimine and alumina mixture was sprayed. After spraying, the samples were dried in air at 140°C in a drying oven for 30 minutes. For calcination, the samples were baked in an oven at 650°C for 5 hours. The coating, drying, and calcination process was repeated multiple times until the desired coating was applied.

[0086] 8. Study on the Supported Catalyst

[0087] Finally, the resulting supported catalysts were investigated, particularly the resistance of the catalytically active layer on the metal foam to mechanical stress. In many cases, a scratch test can be performed to determine the adhesion quality of the oxidative, catalytically active layer to the support foam. However, in the present case, this test was not possible due to the irregular structure of the foam. Therefore, the mechanical stability of the catalytically active layer was investigated using a temperature ramp test, which provides a measure of the adhesion quality of the oxidative layer to the support foam. This was accomplished by heating metal foams a, d, e, and f to 500°C and then quenching them in cold water. The amount lost, i.e., the mass of the catalytic layer removed from each sample, was then determined by filtering, drying, and weighing the exfoliated material.

[0088] This gives the following result:

[0089] Metal foams a and d: 3 mg loss

[0090] Metal foam f: 10mg loss

[0091] Metal foam e: 50mg loss

[0092] While the catalytically active layers on the metal foam bodies a and d have a high resistance to mechanical stress, the resistance of the catalytically active layers on the metal foam body f is significantly lower and is very low on the metal foam body e.

[0093] Examples of NiCo foam

[0094] 2. Provide metal foam

[0095] Six nickel-cobalt metal foam bodies (af) (manufacturer: AATM, size: 100 mm × 100 mm × 2 mm, weight per unit area: 1000 g / m 2 , average pore diameter 580 μm), which are produced by electrolytic deposition of nickel on polyurethane foam, in addition to deposition of cobalt on the nickel, and subsequent pyrolysis of the plastic components.

[0096] 2. Apply aluminum

[0097] The binder solution (2.5% by weight aqueous polyethyleneimine solution) was then first sprayed onto the metal foams a, b, c, d, e and f, followed by the application of powdered aluminum in dry powder form (approximately 400 g / m 2 ) (Manufacturer: AMG, average particle size: <63 μm, contains 3% by weight of added ethylenebis(stearamide)).

[0098] 3. Heat treatment

[0099] The metal foams a, b, c, d, and e were then heat treated in a furnace under a nitrogen atmosphere. First, the furnace was heated from room temperature to a maximum temperature over a period of about 15 minutes, held for a certain period of time, and then quenched by contact with a nitrogen atmosphere at 200°C.

[0100] Maximum temperature of metal foam a, d, e:

[0101] 700℃ for 2 minutes

[0102] Temperature course of metal foam b:

[0103] 600℃ for 2 minutes

[0104] Temperature course of metal foam c:

[0105] 750℃ for 2 minutes

[0106] 4. Determination of alloying degree

[0107] The extent of alloy formation in the metal foams was then determined. This was accomplished by examining cross-sections of the metal foams under a microscope and a scanning electron microscope. While surface alloy formation occurred in metal foams a, d, and e, unalloyed regions remained within the metal foams. In the case of metal foam b, no alloy formation occurred. In metal foam c, alloy formation was so advanced that no unalloyed regions remained within the metal foams.

[0108] 5. Oxidation treatment

[0109] The metal foams a and d were then subjected to oxidation treatment.

[0110] The metal foam body a is exposed to an oxidizing gas atmosphere in a heated state. This is accomplished by heating the metal foam body to 700°C in a furnace through which air is passed.

[0111] Metal foam d was first contacted with an alkaline solution (5 wt% aqueous NaOH solution at 20°C for 10 minutes). A white precipitate formed on the foam. The precipitate represented the conversion of aluminum to aluminum hydroxide. Metal foam d was then dried in air. The dried metal foam with the white precipitate was pre-oxidized in a preheated furnace at 700°C and standard atmospheric pressure, where the aluminum hydroxide was converted to aluminum oxide.

[0112] Oxidative pretreatment has many functions:

[0113] - Protects the support material from further oxidation

[0114] -Adhesion promoter between metal and ceramic systems

[0115] - a barrier for the diffusion of alloying elements on the support material into the catalytic ceramic layer

[0116] 6. Contrast processing

[0117] As described in the prior art (see WO 95 / 11752 A1, Example 3), a previously untreated metal foam body f was provided with an aluminum oxide layer. This was accomplished by completely immersing the metal foam body f in a saturated sodium aluminate solution for 3 hours, then tilting it back and forth in deionized water until the hydrolysis reaction subsided, and finally heating it at 500° C. for 3 hours while passing air.

[0118] 7. Applying the catalytically active layer

[0119] The catalytically active layer was then applied to the metal foams a, d, e, and f by spraying. This was done by moistening the metal foams with water. A 2.5% polyethyleneimine suspension was then stirred with high-surface-area χ-alumina. The water / polyethyleneimine and alumina mixture was sprayed. After spraying, the samples were dried in air at 140°C in a drying oven for 30 minutes. For calcination, the samples were baked in an oven at 650°C for 5 hours. The coating, drying, and calcination process was repeated multiple times until the desired coating was applied.

[0120] 8. Study on the Supported Catalyst

[0121] Finally, the resulting supported catalysts were investigated, particularly the resistance of the catalytically active layer on the metal foam to mechanical stress. In many cases, a scratch test can be performed to determine the adhesion quality of the oxidative, catalytically active layer to the support foam. However, in the present case, this test was not possible due to the irregular structure of the foam. Therefore, the mechanical stability of the catalytically active layer was investigated using a temperature ramp test, which provides a measure of the adhesion quality of the oxidative layer to the support foam. This was accomplished by heating metal foams a, d, e, and f to 500°C and then quenching them in cold water. The amount lost, i.e., the mass of the catalytic layer removed from each sample, was then determined by filtering, drying, and weighing the exfoliated material.

[0122] This gives the following result:

[0123] Metal foams a and d: 4 mg loss

[0124] Metal foam f: 12 mg loss

[0125] Metal foam e: 48 mg loss

[0126] While the catalytically active layers on the metal foam bodies a and d have a high resistance to mechanical stress, the resistance of the catalytically active layers on the metal foam body f is significantly lower and is very low on the metal foam body e.

Claims

1. A method for preparing a supported catalyst, comprising the steps of: (a) providing a metal foam body A made 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 a metal foam body A to obtain a metal foam body AX, (c) heat treating the metal foam body AX to achieve alloy formation between the metal foam body A and the aluminum-containing powder MP, thereby obtaining a metal foam body B, wherein the maximum temperature during the heat treatment of the metal foam body AX is in the range of 680°C to 715°C, and wherein the total duration of the heat treatment in the temperature range of 680° C. to 715° C. is between 5 seconds and 240 seconds, The alloy formation is limited to the upper region of the metal foam and leaves unalloyed regions within the metal foam, (d) oxidizing the metal foam body B to obtain a metal foam body C having an aluminum oxide skin formed on the surface thereof, (e) applying a catalytically active layer comprising at least one support oxide and at least one catalytically active component to at least a portion of the surface of the metal foam body C to obtain a supported catalyst, wherein the support oxide is selected from the group consisting of aluminum oxide, silicon dioxide, titanium oxide and mixtures thereof.

2. The method according to claim 1, wherein the oxidation treatment of the metal foam B in step (d) is selected from: - heating the metal foam body B in contact with an oxidizing gas atmosphere without the prior formation of aluminum hydroxide on the surface of the metal foam body, After aluminum hydroxide is previously formed on the surface of the metal foam body, the metal foam body B is heated in contact with an oxidizing gas atmosphere.

3. The method according to any one of claims 1 and 2, wherein for the oxidation treatment of the metal foam body B in step (d), the metal foam body B is heated in contact with an oxidizing gas atmosphere without pre-forming aluminum hydroxide on the surface of the metal foam body. 4 . The method according to claim 3 , wherein the heating in contact with the oxidizing gas atmosphere is performed in air at a temperature of 200° C. to 700° C. for a period of 1 minute to 60 minutes.

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

6. The method of claim 5, wherein aluminum hydroxide is formed on the surface by contacting the metal foam with an alkaline aqueous solution.

7. The method of claim 6, wherein the alkaline aqueous solution contains sodium hydroxide, potassium hydroxide, lithium hydroxide, or a combination thereof, and the metal foam is contacted with the alkaline aqueous solution for a period of time not exceeding 30 minutes.

8. The method according to claim 5, wherein after aluminum hydroxide is preliminarily formed on the surface of the metal foam body, the heating in contact with the oxidizing gas atmosphere is performed in air at a temperature of 200 to 700°C for a period of 1 to 60 minutes.

9. The method according to claim 1 or 2, wherein the catalytically active component is a transition metal or a transition metal compound, and the transition metal is selected from iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, cerium, copper, silver, gold and mixtures thereof.

10. A supported catalyst obtainable by the process according to any one of claims 1 to 9.

11. Use of the supported catalyst according to claim 10 in chemical conversion.