EP4034299A1

EP4034299A1 - Metal-foam body and method for the production thereof and the use thereof as a catalyst

Info

Publication number: EP4034299A1
Application number: EP20775332.8A
Authority: EP
Inventors: René Poss; Monika Berweiler; Meike Roos
Original assignee: Evonik Operations GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2019-09-25
Filing date: 2020-09-25
Publication date: 2022-08-03
Also published as: CN114514070B; US20230001388A1; KR20220068220A; US20230338932A2; CN114514070A; JP2022551426A; WO2021058704A1

Abstract

The invention relates to a method for producing a metal-foam body, comprising the steps of (a) providing a metal-foam body A, which consists of nickel, cobalt, copper, or alloys or combinations thereof, (b) applying an aluminium-containing material MP to metal-foam body A so as to obtain metal-foam body AX, (c) thermally treating metal-foam body AX, with the exclusion of oxygen, to achieve the formation of an alloy between the metallic components of metal-foam body A and the aluminium-containing material MP so as to obtain metal-foam body B, wherein the duration of the thermal treatment is chosen in dependence on the temperature of the thermal treatment and the temperature of the thermal treatment is chosen in dependence on the thickness of the metal-foam body AX. The invention also relates to the metal-foam bodies obtainable by the methods according to the invention and to the use thereof as catalysts for chemical transformations.

Description

METAL FOAM BODIES AND METHOD FOR THEIR MANUFACTURING AND THEIR USE AS

CATALYST

BACKGROUND AND PRIOR ART The present invention relates to processes for the production of metal foam bodies, the metal foam bodies themselves which can be produced by these processes, and the use of these metal foam bodies as catalysts for chemical transformations.

So-called Raney metal catalysts or activated porous metal catalysts are highly active, usually powdery catalysts, which have found wide commercial use. The precursor to Raney metal catalysts is usually alloys / intermetallic phases which contain at least one catalytically active metal and at least one alloy component which is soluble (leachable) in alkalis. Typical catalytically active metals are, for example, Ni, Co, Cu, with additions of Fe, Cr, Pt, Ag, Au, Mo and Pd, and typical leachable alloy components are e.g. B. Al, Zn and Si. The manufacture of the

Raney metal from the alloys is usually carried out through an activation process in which the leachable component is removed using concentrated sodium hydroxide solution.

A decisive disadvantage of powdered Raney metal catalysts is the need to separate them from the reaction medium of the catalyzed reaction by expensive sedimentation and / or filtration processes.

Several attempts have therefore already been made to immobilize Raney metal catalysts and to make them available as fixed bed catalysts. For example, EP 2 764 916 describes a process for the production of foam-shaped shaped catalyst bodies which are suitable for hydrogenation, in which: a) a metal foam shaped body is provided which contains at least one first metal selected, for example, from Ni, Fe, Co, Cu, Cr , Pt, Ag, Au and Pd, b) at least one second leachable component or a component which can be converted into a leachable component by alloying, which is selected, for example, from Al, Zn and Si, and c) by applying to the surface of the metal foam molded body Alloying the metal foam molding obtained in step b) forms an alloy at least on part of the surface, and d) subjecting the foamed alloy obtained in step c) to a treatment with an agent capable of leaching out the leachable components of the alloy. From WO 2019057533A1 a similar method for the production of foam-shaped

Known catalyst moldings. There, too, metal powders are applied to monolithic foam-shaped metal bodies and then thermally treated so that alloys are formed in the contact area between the foam-shaped metal body and metal powder. WO2019057533A1 discloses a large number of metals and metal combinations which can be selected for the foamed metal body and the metal powder, as well as general ones Information on the implementation of the thermal treatment for alloy formation as well as some concrete examples for the treatment of aluminum powder on nickel foam.

The present invention relates to processes for the production of metal foam bodies, which comprise the provision of a metal foam body, the subsequent application of aluminum-containing material, and a thermal treatment for the formation of an alloy. The extent of the alloy formation depends on the conditions of the thermal treatment: a long thermal treatment at high temperatures leads, for example, to alloy formation in lower areas of the metal foam, while a shorter thermal treatment at lower temperatures only leads to alloy formation in the upper areas of the metal foam and unalloyed areas remain inside the metal foam. Since the remaining unalloyed areas in the interior of the metal foam has a positive effect on the mechanical stability of the metal foam, there is a need in the prior art for methods which make such metal foams accessible. Temperature control of the thermal treatment according to the invention makes 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 methods according to the invention also take into account the thickness of the treated metal foam bodies.

The present invention

Processes according to the invention for producing metal foam bodies comprise the following steps:

Providing a metal foam body A, which consists of nickel, cobalt, copper, or their alloys or combinations,

Application of an aluminum-containing material MP to metal foam body A, so that metal foam body AX is obtained, thermal treatment of metal foam body AX, in the absence of oxygen, in order to achieve alloy formation between the metallic components of metal foam body A and the aluminum-containing material MP, so that metal foam body B is obtained, where the duration H of the thermal treatment (in minutes), depending on the temperature T of the thermal treatment (in ° C), is selected as follows:

Hmin <H <Hmax, with maximum duration Hmax = d1 + (a1 - d1) / (1 + (T / c1) ^A b1), and minimum duration Hmm = d2 + (a2 - d2) / (1 + (T / c2) ^A b2), where a1 = 366.1; b1 = 129.0; c1 = 650.9; d1 = 8.7; a2 = 33.5; b2 = 235.5; c2 = 665.8; d2 = 1.8; and where the temperature T of the thermal treatment, depending on the thickness D of the metal foam body AX, is selected as follows: for O mm <D <10 mm applies 600 ° C <T <680 ° C, for 10 mm <D <20 mm applies 600 ° C <T <675 ° C, for 20 mm <D <30 mm applies 600 ° C <T <665 ° C for 30 mm <D applies 600 ° C <T <660 ° C.

Experimental results obtained in connection with the present invention show that the choice of 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 chemical and mechanical stability of the metal foam obtained.

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 different morphological properties in terms of pore size and shape, layer thickness, surface density, geometric surface, porosity, etc. are suitable. The metal foam preferably has a bulk density in the range from 100 to 1500 kg / m ³ , more preferably from 200 to 1200 kg / m ³ and most preferably from 300 to 600 kg / m ³ . The mean pore size is preferably from 400 to 3000 μm, more preferably from 400 to 800 μm. Preferred metal foams have a specific BET surface area of 100 to 20,000 m ² / m ³ , more preferably 1,000 to 6,000 m ² / m ³ . The porosity is preferably in a range from 0.50 to 0.95. The bulk density of the metal foam is determined in accordance with ISO 845. The mean pore size is determined by the Visiocell® analytical method from Recticel, which is described in "The Guide 2000 of Technical Foams", Book 4, Part 4, pages 33-41. In particular, the pore size is measured by an optical measurement of the pore diameter by superimposing calibrated rings, printed on transparent paper, on the selected cell. This pore size measurement is carried out for at least 100 different cells in order to obtain an average cell diameter. The BET specific surface area is measured by gas adsorption on a metal foam sample up to a maximum of 2 g in accordance with DIN 9277. The porosity is determined using the following equation:

V _T = volume of the metal foam sample in mm ³ 1/1 / = weight of the metal foam sample in gp = density of the metal in g / cm ³ (e.g. 8.9 g / cm ³ for Ni)

The production can take place in a manner known per se. For example, a foam made of an organic polymer can be coated with two metal components one after the other or at the same time, and the polymer can then be removed by thermolysis, a metal foam being obtained. 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. So z. B. coated a polyurethane foam one after the other with one or two metals and then thermolyzed the polyurethane foam. A polymer foam suitable for producing molded bodies 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 5 to 60 mm, particularly preferably 10 to 30 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, e.g. cubic, cuboid, cylindrical, etc., but also more complex geometries.

The aluminum-containing material MP, which is applied to the metal foam body in step (b), contains metallic Al in an amount of 80 to 100% by weight, preferably from 80 to 99.8% by weight, and especially from 90 to 99.5% by weight , based on the aluminum-containing material MP. High purity Aluminum is highly flammable and should be handled in a protective gas atmosphere. In addition to metallic aluminum (AI), the material can also contain aluminum Al (III). This Al (III) component is typically in the form of oxidic compounds selected from the group of aluminum oxides, hydroxides and / or carbonates. The Al (III) proportion is particularly preferably in the range from 0.05 to <10% by weight, very particularly preferably in the range from 0.1 to 8% by weight, based on the aluminum-containing material MP. In addition to Al and Al (III), the mixture can also contain organic compounds and / or another metal or metal oxide or metal carbonate, the other metals preferably being selected from the group of promoter elements such as Ti, Ta, Zr, V, Cr , Mo, W, Mn, Rh, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Ce and Bi. The organic compounds are preferably selected from the group of hydrocarbons, polymers and resins , Waxes, amines and alcohols.

The aluminum-containing material MP, which is applied to the metal foam body in step (b), is preferably an aluminum-containing powder. In preferred embodiments, the aluminum-containing powder contains 1 to 5% by weight, particularly preferably 2 to 4% by weight and most preferably about 3% by weight of organic compounds, in particular a wax, and 94.5 to 98.8% by weight, particularly preferably 95, 5 to 97.8 wt% and most preferably 96.5 to 96.8 wt% Al. The particles of the aluminum-containing powder preferably have a diameter of not smaller than 5 μm and not larger than 200 μm. Powders in which 95% of the particles have a diameter of 5 to 75 μm are particularly preferred.

The aluminum-containing powder is usually fixed on the surface of the metal foam body with the aid of an organic binder. In one embodiment, the metal foam body is impregnated with the organic binder prior to the actual application of the aluminum-containing powder. The impregnation can take place, for example, by spraying the binding agent, dipping the metal foam body into the binding agent, pumping through or sucking through, but is not limited to these possibilities. The binder is usually used in an amount such that the layer thickness on the metal foam body is 10 to 60 μm, preferably 10 to 30 μm. The aluminum-containing powder can then be applied to the metal foam body prepared in this way.

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

The application of the aluminum-containing powder in step (b) of the method according to the invention can be carried out in a variety of ways, e.g. B. by bringing the metal foam body into contact with the aluminum-containing powder by rolling or dipping, or applying the aluminum-containing powder by spraying, sprinkling or pouring. The aluminum-containing powder can do this present as a pure powder, or it is suspended in the binder and / or an auxiliary liquid. If an auxiliary liquid is used, this is preferably water.

The binder is an organic compound that promotes adhesion of the aluminum-containing powder to the metal body. The binder is preferably selected from polyvinylpyrrolidone (PVP), ethylene glycol, waxes, polyethyleneimine (PEI) and mixtures of these compounds. PVP or PEI are particularly preferred as binders, for example with M = 10,000 to 1,300,000 g / mol, determined by gel permeation chromatography using polystyrene standards. PEI is preferably used as the binder, e.g. with M = 500,000 to 1,000,000 g / mol or M = 600,000 to 900,000 g / mol. Typically, the PEI is used in aqueous solution, preferably in concentrations of 0.5 to 15% by weight, more preferably 1 to 10% by weight or 2 to 5% by weight and most preferably 2 to 3% by weight, based on the weight of PEI and Water. The aluminum-containing powder can be suspended in the binder, optionally dissolved in an auxiliary liquid such as water, for example in the aqueous PEI solution, and the amount of aluminum-containing powder in the suspension is preferably 30 to 70% by weight, particularly preferably 40 to 60% by weight % By weight, most preferably 45 to 55% by weight, based on the total weight of the suspension.

Alternative methods of applying the aluminum-containing material MP in step (b) include, for example, dipping the metal foam body into a molten metal, sputtering or chemical vapor deposition of the aluminum-containing material MP, and depositing the aluminum-containing material MP as metal salts and subsequent reduction to metal. Combinations of all of the application methods mentioned are also possible.

In a preferred embodiment of the present invention, the aluminum-containing material MP is an aluminum-containing powder and an organic binder is applied to metal foam body A together with or before the aluminum-containing powder.

The coated metal foam bodies are soft and can therefore be easily deformed if necessary. For example, the coated metal foam bodies can be embossed on the surface, for example with a wave profile. The embossing can be carried out with a conventional tool, such as a profiled roller, a stamp or another embossing tool. Furthermore, the coated metal foam bodies can be folded or rolled up, if necessary after previous embossing. A modified metal foam body can also be obtained by stacking several metal foam bodies, optionally after previous embossing, wherein the body can consist only of coated metal foam bodies or one uncoated metal foam body is placed between two coated ones. Rolled up, folded or stacked metal foam bodies are also referred to herein as multilayered and can optionally be further deformed by various shaping processes. Due to the deformation,

Reshaping and / or stacking of the coated metal foam bodies can be a Metal foam moldings AX can be produced with a desired geometry, depending on the intended area of application.

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 relatively strict temperature control is necessary in order to limit the alloy formation to the upper regions of the metal foam and to leave unalloyed regions in the interior of the metal foam. In addition, the thickness D of the metal foam body AX must be taken into account when selecting the conditions for the thermal treatment. The thermal treatment of metal foam body AX in step (c) of the process according to the invention must be carried out with the exclusion of oxygen.

The duration H of the thermal treatment (in minutes) is selected as follows depending on the temperature T of the thermal treatment (in ° C):

Hmin <H <Hmax, with maximum duration Hmax = d1 + (a1 - d1) / (1 + (T / c1) ^A b1), and minimum duration H _mi n = d2 + (a2 - d2) / (1 + ( T / c2) ^A b2), where a1 = 366.1 b1 = 129.0 c1 = 650.9 d1 = 8.7; a2 = 33.5; b2 = 235.5; c2 = 665.8; d2 = 1.8; and where the temperature T of the thermal treatment, depending on the thickness D of the metal foam body AX, is selected as follows: for O mm <D <10 mm applies 600 ° C <T <680 ° C, for 10 mm <D <20 mm applies 600 ° C <T <675 ° C, for 20 mm <D <30 mm applies 600 ° C <T <665 ° C for 30 mm <D applies 600 ° C <T <660 ° C. The thickness D of the metal foam body AX is determined as follows:

In the case of metal foam bodies with a simple geometry, e.g. cuboid cutouts made of metal foam mats, D denotes the length of the shortest edge of such cutouts, i.e. in many cases simply the thickness of the metal foam mat. For objects with more complicated geometry, D is determined with a rough estimate, in which, in case of doubt, a value that is too high should be assumed for D rather than too low. The value of D is estimated here as twice the value of the smallest distance to the surface, from the point within the body whose smallest distance to the surface is maximal. In any case, when determining D, the foam pores and their surfaces should be disregarded, i.e. the foam pores should be regarded as filled for this determination. In addition, recesses in the bodies under consideration with a diameter of less than 1 cm should not be viewed as a surface, but rather as filled areas.

The thermal treatment comprises the heating of the metal foam body AX, usually in stages, 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. 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 a maximum of 350 ° C. and kept at this temperature for a period of about 2 to 30 minutes in order to remove moisture and organic constituents from the coating. No alloy formation takes place in this section of the thermal treatment.

The temperature is then increased to the range above 600 ° C., and an alloy is formed between the metallic components of metal foam body A and the aluminum-containing material MP, so that metal foam body B is obtained.

In order to limit the alloy formation to the upper areas of the metal foam and to leave unalloyed areas in the interior of the metal foam, it is necessary to suitably select the duration H of the thermal treatment as a function of the temperature T of the thermal treatment. According to the invention, the duration H of the thermal treatment (in minutes) is selected as a function of the temperature T of the thermal treatment (in ° C) as follows:

Hmin <H <Hmax, with maximum duration Hmax = d1 + (a1 - d1) / (1 + (T / c1) ^A b1), and minimum duration H _mi n = d2 + (a2 - d2) / (1 + ( T / c2) ^A b2), where a1 = 366.1; b1 = 129.0; c1 = 650.9; d1 = 8.7; a2 = 33.5; b2 = 235.5; c2 = 665.8; d2 = 1.8; and where the temperature T of the thermal treatment, depending on the thickness D of the metal foam body AX, is selected as follows: for O mm <D <10 mm applies 600 ° C <T <680 ° C, for 10 mm <D <20 mm applies 600 ° C <T <675 ° C, for 20 mm <D <30 mm applies 600 ° C <T <665 ° C for 30 mm <D applies 600 ° C <T <660 ° C.

After the alloy has been formed, the metal foam body is cooled with the exclusion of oxygen. The cooling can be carried out simply by interrupting the thermal treatment, for example the metal foam body is removed from the heated environment, e.g. the furnace, with the exclusion of oxygen and slowly cooled to ambient temperature. Preferably, however, the shaped catalyst body is brought to a temperature below 200 ° C. as quickly as possible in order to "freeze" the leachable intermetallic phases. This can be done by means of a suitable cooling medium; the cooling is preferably achieved in a cooling zone of the furnace, for example the belt furnace. This can e.g. be surrounded by a cooling water jacket. The preferred cooling rate is 5 to 500 K / min, particularly preferably 20 to 400 K / min and most preferably 30 to 200 K / min.

During the thermal treatment and cooling, the molded body must be kept in an oxygen-free environment. "In the absence of oxygen" or "oxygen-free environment" herein means in an inert gas atmosphere or under a reducing atmosphere. The inert gas used is preferably nitrogen. Mixtures of inert gas with hydrogen, for example N2 / H2, preferably in a volume ratio of 50/50, are suitable as reducing atmospheres. The shaped body is preferably heated and cooled under a stream of nitrogen, typically at a flow rate in the range from 5 to 30 m ³ / h, particularly preferably 10 to 30 m ³ / h.

Too high a temperature T and / or too long a duration H result in the alloy formation proceeding into the deepest layers of the metal foam and none unalloyed areas remain. If the temperature T is too low and / or the duration H is too short, the alloy formation does not start at all.

If time intervals with different temperatures T in the range according to the invention are selected during the alloy formation, an average value weighted according to the duration of these time intervals can be used to determine Hmin and Hmax for the temperature T of the thermal treatment.

If two metallic components are present in metal foam body A, in a preferred embodiment the mass ratio of the two metallic components in metal foam body A is in the range from 1: 1 to 20: 1, particularly preferably in the range from 1: 1 to 10: 1.

In a preferred embodiment, the metal foam body A consists of metallic nickel.

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 1.1: 1 to 1.5: 1, particularly preferably in the range from 1.2: 1 to 1.4: 1.

In a further aspect, the present invention further comprises a method with the following step (d): activating the metal foam body B by treatment with a leaching agent. The treatment of the metal foam body B with a leaching agent serves to at least partially dissolve metal components of the applied composition of the aluminum-containing material MP and alloys between metallic components of metal foam body and the composition of the aluminum-containing material MP and in this way to remove them from the metal foam body. The aluminum content in the metal foam body has an influence on the catalytic performance and service life, in particular on the hydrogenation activity and on the chemical stability in the reaction medium. Typically 30 to 70% by weight, preferably 40 to 60% by weight, of the aluminum, based on the original total weight of aluminum in the metal body, is dissolved out. It is true that the hydrogenation activity of the metal foam body according to the invention is higher, the lower the residual aluminum content. Residual aluminum contents of 2 to 20% by weight, particularly preferably 5 to 15% by weight, very particularly preferably 2 to 17% by weight, and most preferably 3 to 12% by weight, based on the total mass of the metal foam body, are preferably set.

Any agent which selectively dissolves aluminum from the intermetallic phases is suitable as a leaching agent; it can be alkaline or acidic or it can have a complexing effect. Preferably the leaching agent is an aqueous solution of a base such as a hydroxide Alkali hydroxide, particularly preferably NaOH, KOH and / or LiOH or mixtures thereof, very preferably NaOH.

In a preferred embodiment, the treatment of the metal foam body B with a basic solution for a duration in the range from 5 minutes to 8 hours, at a temperature in the range from 20 to 120 ° C, preferably at 60 to 115 ° C, and particularly preferably 80 up to 110 ° C, the basic solution being an aqueous NaOH solution with an NaOH concentration between 2 and 30% by weight. Preferably the leaching time, i.e. the treatment time in step (f) with the leaching agent, such as an aqueous NaOH solution, is 15 to 90 minutes.

The activation in step (d) of the process according to the invention can be carried out, for example, in the sump or trickle mode. After the treatment with the leaching agent, the shaped catalyst body is preferably washed with a washing medium selected from water, Ci-C ₄ alkanols and mixtures thereof. Suitable Ci-C ₄ alkanols are methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol.

With a suitable choice of the metallic components, metal foam bodies that are obtained as a result of the treatment with basic solution can be used as catalysts, as disclosed, for example, in WO2019057533A1.

In some embodiments, the activated metal foam body can be modified in step (e) by post-doping with further metals, these doping elements, also referred to as promoter elements, preferably being selected from the transition metals. For post-doping, the metal foam body is treated with a preferably aqueous solution of the doping element or the doping elements to be applied. The doping solution typically has a pH value> 7 so as not to damage the metal foam body. A chemically reductive component can be added to the solution of the doping element or the doping elements to be applied in order to reductively deposit the dissolved doping element or the dissolved doping elements on the metal foam body. Preferred doping elements for modification are selected from the group consisting of Mo, Pt, Pd, Rh, Ru, Cu and mixtures thereof. Suitable methods for doping are described, for example, in WO 2019/057533 on pages 20 to 25. The metal foam body activated in step (d) and optionally post-doped in step (e) can either be used directly as a catalyst or can be stored. In order to prevent oxidation processes on the surface and a limited catalytic effectiveness, the metal foam body is preferably stored under water after activation.

In a further aspect, the present invention further comprises coated metal foam bodies obtainable by one of the processes according to the invention. Activated and optionally doped metal foam bodies obtainable by one of the processes according to the invention can be used as catalysts for numerous catalyzed chemical reactions of organic compounds in particular, such as hydrogenation, isomerization, hydration, hydrogenolysis, reductive amination, reductive alkylation, dehydrogenation, oxidation, dehydrogenation and rearrangement, preferred for hydrogenation reactions. In principle, the shaped catalyst bodies according to the invention are very suitable for all hydrogenation reactions which are catalyzed with Raney metal catalysts. Preferred uses of the catalytically active metal foam bodies according to the invention are selective hydrogenation processes of carbonyl compounds, olefins, aromatic rings, nitriles and nitro compounds. Specific examples are the hydrogenation of carbonyl groups, the hydrogenation of nitro groups to amines, the hydrogenation of polyols, the hydrogenation of nitriles to amines, e.g. the hydrogenation of fatty nitriles to fatty amines, the dehydrogenation of alcohols, the reductive alkylation, the hydrogenation of olefins to alkanes and the hydrogenation of azides to amines. Use in the hydrogenation of carbonyl compounds is particularly preferred.

In a further aspect, the present invention therefore comprises the use of activated and optionally doped metal foam bodies obtainable by one of the processes according to the invention as catalysts for chemical transformations, preferably for chemical transformations selected from hydrogenation, isomerization, hydration, hydrogenolysis, reductive amination, reductive alkylation, dehydrogenation, Oxidation, dehydration and rearrangement.

Examples

1. Provision of metal foam bodies

Three metal foam mats (a, b, c) made of nickel were provided (manufacturer: AATM, thickness: 1.9 mm, weight per unit area: 1000 g / m ² , average pore diameter: 580 μm).

2. Application of aluminum powder

Then binder solution (polyethyleneimine (2.5% by weight) in water) was first sprayed onto all metal foam mats and then powdered aluminum (manufacturer: Mepura, average particle size: <63 μm, with 3% by weight of ethylene bis (stearamide)) as dry Powder applied (approx. 400 g / m ² ).

After the foam mats had been coated, 6 cuboid foam bodies of different thicknesses (a1, a2, a3, b1, b2, b3) were produced by stacking individual layers with a thickness of 1.9 mm (length and width 25 mm each). In order to increase the number of contact points and the contact area, the foam bodies were then compressed by approx. 30%. Metal foam body a1, a2 and a3: thickness 9 mm (7 layers each 1. 9 mm thick = 13.3 mm thickness; compression to 9 mm) Metal foam body b1, b2 and b3: thickness 12 mm (9 layers each 1. 9 mm thick = 17.1 mm thickness, compression to 12 mm

3. Thermal treatment Then all metal foam bodies were subjected to thermal treatment in an oven under a nitrogen atmosphere. The binder was first removed thermally at 350 ° C for 30 min and then heated to the maximum temperature in 10 min, this was maintained for a defined period (duration of the treatment) and then quenched to below 200 ° C.

4. Determination of alloy size

At the end, the extent of the alloy formation in the metal foam bodies was determined. For this purpose, cross sections of the metal foam bodies were examined under a microscope and a scanning electron microscope.

The result was the following:

While with metal foam bodies a1 and b1 superficial alloy formation has taken place, but unalloyed areas have remained inside the metal foam, with metal foam bodies a2 and b2 no alloy formation has taken place, and with

Metal foam bodies a3 and b3, the alloy formation has progressed so far that no unalloyed areas have remained in the interior of the metal foam.

The following is also known from previous experiments: If the temperature for alloy formation is selected above 680 ° C, for example 700 ° C, the aluminum reacts with the nickel in an uncontrolled manner and the shaped body burns off and only powder residues remain.

This result clearly shows that a deviation from the conditions of the thermal treatment according to the invention leads to the fact that a superficial alloy formation with remaining unalloyed areas inside the metal foam becomes difficult to achieve.

5. Determination of the position of the limit curves for the heating duration On the basis of the above-mentioned results, the position of the limit curves for the heating time, which at a given heating temperature leads to surface alloy formation while remaining unalloyed areas inside the metal foam, was determined using a sigmoid model (heating time = d + (a - d) / (1 + (Heating temperature / c) ^A b)) determined.

The following values were used as limit values for the position of the upper curve (maximum heating duration):

Temp (° C) - duration (min) 680 10 675 12 665 30 660 60

The following values were used as limit values for the position of the lower curve (minimum heating duration):

Temp (° C) - duration (min) 680 2,675 3

665 20 660 30 The following result was obtained for the position of the limit curves (specification of H in minutes and specification of T in ° C): maximum duration Hmax = d1 + (a1 - d1) / (1 + (T / c1) ^A b1), with a1 = 366.1; b1 = 129.0; c1 = 650.9; d1 = 8.7; and minimum duration Hmin = d2 + (a2 - d2) / (1 + (T / c2) ^A b2), with a2 = 33.5; b2 = 235.5; c2 = 665.8; d2 = 1.8. 6. Determination of the interval limits for the temperature of the thermal treatment as a function of the thickness of the treated metal foam bodies

The position of the interval limits for the temperature of the thermal treatment as a function of the thickness of the treated metal foam bodies resulted from the results presented above and other empirical values.

The temperature T of the thermal treatment (in ° C) should be selected as follows, depending on the thickness D of the metal foam body AX (in millimeters): for 0 mm <D <10 mm, 600 ° C <T <680 ° C applies, for 10 mm <D <20 mm applies 600 ° C <T <675 ° C, for 20 mm <D <30 mm applies 600 ° C <T <665 ° C for 30 mm <D applies 600 ° C <T <660 ° C.

Claims

1. A method for producing a metal foam body, comprising the following steps:

(a) Provision of a metal foam body A, which consists of nickel, cobalt, copper, or their alloys or combinations,

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

(c) Thermal treatment of metal foam body AX, with exclusion of oxygen, in order to achieve alloy formation between the metallic components of metal foam body A and the aluminum-containing material MP, so that metal foam body B is obtained, the duration H of the thermal treatment (in minutes) depending on on the temperature T of the thermal treatment (in ° C), is selected as follows:

Hmin <H <Hmax, with maximum duration Hmax = d1 + (a1 - d1) / (1 + (T / c1) ^A b1), and minimum duration H _mi n = d2 + (a2 - d2) / (1 + ( T / c2) ^A b2), where a1 = 366.1 b1 = 129.0 c1 = 650.9 d1 = 8.7; a2 = 33.5; b2 = 235.5; c2 = 665.8; d2 = 1.8; and where the temperature T of the thermal treatment, depending on the thickness D of the metal foam body AX, is selected as follows: for O mm <D <10 mm applies 600 ° C <T <680 ° C, for 10 mm <D <20 mm applies 600 ° C <T <675 ° C, for 20 mm <D <30 mm applies 600 ° C <T <665 ° C for 30 mm <D applies 600 ° C <T <660 ° C.

2. The method according to claim 1, wherein the aluminum-containing material MP is an aluminum-containing powder and an organic binder is applied to metal foam body A together with or before the aluminum-containing powder.

3. The method according to any one of claims 1 to 2, wherein the metal foam body A consists of nickel.

4. The method according to any one of claims 1 to 3, wherein the metal foam body A has a bulk density in the range from 100 to 1500 kg / m ³ , preferably from 200 to 1200 kg / m ³ and particularly preferably from 300 to 600 kg / m ³ .

5. The method according to any one of claims 1 to 4, wherein metal foam body A has a specific BET surface area of 100 to 20,000 m ² / m ³ , preferably 1,000 to 6,000 m ² / m ³ .

6. The method according to any one of claims 1 to 5, wherein metal foam body A has a porosity of 0.50 to 0.95.

7. The method according to any one of claims 1 to 6, wherein the aluminum-containing material MP in step (b) metallic aluminum in an amount of 80 to 100% by weight, preferably from 80 to 99.8% by weight, and particularly preferably from 90 to 99 , 5% by weight, based on the aluminum-containing material MP.

8. The method according to any one of claims 1 to 7, wherein the aluminum-containing material MP is a powder of particles, 95% of which have a diameter in the range from 5 to 75 μm.

9. The method according to any one of claims 1 to 8, further comprising the following step:

(d) Activation of the metal foam body B by treatment with a leaching agent.

10. The method according to claim 9, wherein the treatment of the metal foam body B with leaching agent is carried out for a period in the range of 5 minutes to 8 hours, at a temperature in the range of 20 to 120 ° C, and wherein the leaching agent is an aqueous NaOH solution with a NaOH concentration between 2 and 30% by weight.

11. The method according to any one of claims 9 to 10, further comprising the following step:

(e) Post-doping of the activated metal foam body B with a promoter element, preferably selected from Mo, Pt, Pd, Rh, Ru, Cu and mixtures thereof.

12. Metal foam body obtainable by a method according to any one of claims 1 to 8.

13. Metal foam body obtainable by a method according to any one of claims 9 to 11.

14. Use of a metal foam body according to claim 13 as a catalyst for a chemical transformation.

15. Use according to claim 14, wherein the chemical transformation is selected from hydrogenation, isomerization, hydration, hydrogenolysis, reductive amination, reductive alkylation, dehydrogenation, oxidation, dehydrogenation and rearrangement.