Metal foam and method for producing same and use thereof as catalyst

Abstract

The present invention relates to a method for producing a metal foam, comprising the steps of: (a) providing a metal foam A made from nickel, cobalt, copper, or an alloy or combination thereof; (b) applying an aluminum-containing material MP to the metal foam A to obtain a metal foam AX; and (c) heat-treating the metal foam AX under the exclusion of oxygen to form an alloy between the metal portion of the metal foam A and the aluminum-containing material MP to obtain a metal foam B, wherein the duration of the heat treatment is selected depending on the temperature of the heat treatment, and the temperature of the heat treatment is selected depending on the thickness of the metal foam AX. The present invention further relates to a metal foam obtained by the method according to the invention and to its use as a catalyst for chemical conversions.

Description

[Technical Field]

[0001] Background and Prior Art The present invention relates to a method for producing metal foams, metal foams that can be produced by the method, and the use of the metal foams as catalysts for chemical conversions.

[0002] So-called Raney metal catalysts, or activated porous metal catalysts, are highly active, usually powder-like catalysts that are widely used commercially. Raney metal catalyst precursors are generally alloys / intermetallic phases containing at least one catalytically active metal and at least one alkali-soluble (leachable) alloying component. Typical catalytically active metals include Ni, Co, and Cu with Fe, Cr, Pt, Ag, Au, Mo, and Pd added, while typical leachable alloying components include Al, Zn, and Si. Raney metal production from alloys is typically accomplished by an activation process using concentrated caustic soda to remove the leachable components.

[0003] The main drawback of powdered Raney metal catalysts is that they must be separated from the reaction medium of the catalytic reaction by costly settling and / or filtration processes.

[0004] Therefore, some attempts have been made to immobilize Raney metal catalysts so that they can be used as fixed-bed catalysts.For example, EP2764916A1 describes a method for producing a foam-shaped catalyst body suitable for hydrogenation, which includes:a) providing a metal foam molded body containing at least one first metal selected from, for example, Ni, Fe, Co, Cu, Cr, Pt, Ag, Au, and Pd;b) applying at least one second leachable component selected from, for example, Al, Zn, and Si, or a component that can be converted to a leachable component by alloying, to the surface of the metal foam molded body;c) alloying the metal foam molded body obtained in step b) to form an alloy on at least a part of the surface;d) treating the foam-shaped alloy obtained in step c) with an agent that can leach the leachable components of the alloy.

[0005] A similar method for producing a foam-shaped catalyst body is known from WO2019057533. Here, too, a metal powder is applied to a monolithic foam-shaped metal body, followed by a heat treatment to form an alloy in the contact area between the foam-shaped metal body and the metal powder. WO2019057533 discloses various metals and metal combinations that can be selected for the foam-shaped metal body and the metal powder, as well as a general description of the heat treatment process for forming the alloy, and several specific examples for the treatment of aluminum powder on nickel foam.

[0006] The present invention relates to a method for producing a metal foam, the method comprising the steps of providing a metal foam, then applying an aluminum-containing material, and performing a heat treatment to form an alloy. The degree of alloy formation varies depending on the heat treatment conditions. For example, a long heat treatment at a high temperature results in the formation of an alloy in a deep region of the metal foam, whereas a short heat treatment at a low temperature results in the formation of an alloy only in an upper region of the metal foam, leaving an unalloyed region within the metal foam. The presence of an unalloyed region within the metal foam has a positive effect on the mechanical stability of the metal foam, and therefore, a method for obtaining such a metal foam is needed in the prior art. By controlling the temperature of the heat treatment according to the present invention, the alloy formation can be limited to the upper layer of the metal foam, leaving an unalloyed region in the central region of the metal foam. The method according to the present invention also takes into account the thickness of the metal foam being treated.

[0007] The present invention The method for producing a metal foam according to the present invention comprises: Providing a metal foam A made from nickel, cobalt, copper, or an alloy or combination thereof; applying an aluminum-containing material MP to the metal foam A to obtain a metal foam AX; heat-treating the metal foam AX under oxygen exclusion to form an alloy between the metal portion of the metal foam A and the aluminum-containing material MP to obtain a metal foam B; Here, the duration H (unit: minute) of the heat treatment is selected as follows according to the temperature T (unit: °C) of the heat treatment: H <H < H max where, the maximum duration H max = d1 + (a1 - d1) / (1 + (T / c1)^b1), and the minimum duration H min = d2 + (a2 - d2) / (1 + (T / c2)^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 and the temperature T of the heat treatment is selected as follows according to the thickness D of the metal foam AX: When 0 mm < D ≤ 10 mm, 600 °C < T ≤ 680 °C, When 10 mm < D ≤ 20 mm, 600 °C < T ≤ 675 °C, When 20 mm < D ≤ 30 mm, 600 °C < T ≤ 665 °C, When D > 30 mm, 600 °C < T ≤ 660 °C, and including steps

[0008] From the experimental results obtained in relation to the present invention, it was found that the selection of the heat treatment conditions for alloy formation has a considerable influence on the results. In the method according to the present invention, alloy formation can be limited to the upper layer of the metal foam, so that an unalloyed region remains in the central region of the metal foam. The presence of this unalloyed region affects the properties such as the chemical and mechanical stability of the obtained metal foam.

[0009] In the context of the present invention, metal foam A is understood to mean a foamed metal body. Foamed 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 in terms of pore size and pore shape, layer thickness, areal density, geometric surface, porosity, etc. are suitable. Preferably, the metal foam has a melting point of 100 to 1500 kg / m. 3 , more preferably 200 to 1200 kg / m 3 , most preferably 300 to 600 kg / m 3 The average pore size is preferably 400 to 3,000 μm, more preferably 400 to 800 μm. The preferred metal foam has a bulk density of 100 to 20,000 μm. 2 / m 3 , more preferably 1,000 to 6,000 m 2 / m 3 The porosity is preferably in the range of 0.50 to 0.95.

[0010] The bulk density of metal foams is determined in accordance with ISO 845. The average pore size is determined by the Visiocell® analytical method from Recticel, as described in "The Guide 2000 of Technical Foams," Vol. 4, Part 4, pp. 33-41. In particular, the pore size is measured by optically measuring the pore diameter using a calibrated ring printed on transparent paper, which is superimposed on the selected cell. This pore size measurement is performed on at least 100 different cells, resulting in the average cell size. The BET specific surface area is measured by gas adsorption on a metal foam sample up to 2 g in accordance with DIN 9277. The porosity is calculated using the following formula:

number

[0011] The production can be carried out by known methods. For example, an organic polymer foam can be coated with two metal components, either sequentially or simultaneously, followed by removal of the polymer by pyrolysis, resulting in a metal foam. To coat at least one first metal or its precursor, the organic polymer foam can be brought into contact with a solution or suspension containing the first metal. This can be done, for example, by spraying or immersion. Deposition by chemical vapor deposition (CVD) is also possible. For example, polyurethane foam can be coated sequentially with one or two metals, followed by pyrolysis. Polymer foams suitable for producing molded bodies in the form of foams preferably have pore sizes in the range of 100 to 5000 μm, particularly preferably 450 to 4000 μm, and in particular 450 to 3000 μm. Suitable polymer foams preferably have a layer thickness of 5 to 60 mm, particularly preferably 10 to 30 mm. Suitable polymer foams have a load capacity of preferably 300 to 1200 kg / m. 3 The specific surface area is preferably 100 to 20,000 m 2 / m 3 , particularly preferably 1000 to 6000 m 2 / m 3 The porosity is preferably in the range of 0.50 to 0.95.

[0012] The metal foam A used in step (a) of the method according to the invention can have any desired shape, for example cubic, rectangular, cylindrical, etc., or a more complex geometric shape.

[0013] The aluminum-containing material MP applied to the metal foam in step (b) contains metallic Al in an amount of 80-100% by weight, preferably 80-99.8% by weight, and in particular 90-99.5% by weight, based on the aluminum-containing material MP. High-purity aluminum is highly flammable and must be handled under a protective gas atmosphere. In addition to metallic aluminum (Al), this material can also contain aluminum Al(III). This Al(III) is typically in the form of an oxidizing compound selected from the group consisting of aluminum oxide, aluminum hydroxide, and / or aluminum carbonate. Particularly preferably, the proportion of Al(III) is in the range of 0.05 to <10% by weight, and very particularly preferably in the range of 0.1 to 8% by weight, based on the aluminum-containing material MP. In addition to Al and Al(III), the mixture may further comprise an organic compound and / or a further metal or metal oxide or metal carbonate, the further metal being preferably 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, and the organic compound being preferably selected from the group of hydrocarbons, polymers, resins, waxes, amines and alcohols.

[0014] The aluminum-containing material MP applied to the metal foam in step (b) is preferably an aluminum-containing powder. In a preferred embodiment, the aluminum-containing powder comprises 1-5 wt. %, particularly preferably 2-4 wt. %, and most preferably about 3 wt. % of an organic compound, in particular a wax, and 94.5-98.8 wt. %, particularly preferably 95.5-97.8 wt. %, and most preferably 96.5-96.8 wt. % of Al. Preferably, the particles of the aluminum-containing powder have a diameter of 5 μm to 200 μm. Particularly preferred is a powder in which 95% of the particles have a diameter of 5-75 μm.

[0015] The aluminum-containing powder is typically immobilized on the surface of the metal foam using an organic binder. In one embodiment, the metal foam is impregnated with the organic binder prior to the actual application of the aluminum-containing powder. Impregnation can be achieved, for example, by spraying the binder, immersing the metal foam in the binder, or pumping or sucking the binder through the foam, but is not limited to these methods. Typically, the binder is used in an amount such that the metal foam has a layer thickness of 10 to 60 μm, preferably 10 to 30 μm. The aluminum-containing powder can then be applied to the metal foam thus prepared.

[0016] Alternatively, the organic binder and the aluminum-containing powder can be applied in one step, for which the aluminum-containing powder is suspended in the liquid binder itself before application, or the aluminum-containing powder and binder are suspended or dissolved in an auxiliary liquid.

[0017] The application of the aluminum-containing powder in step (b) of the method according to the invention can be carried out in various ways, for example by bringing the metal foam into contact with the aluminum-containing powder by rolling or immersion, or by applying the aluminum-containing powder by spraying, sprinkling or casting. For this purpose, the aluminum-containing powder can be present as a pure powder or suspended in a binder and / or auxiliary liquid. If an auxiliary liquid is used, this is preferably water.

[0018] The binder is an organic compound that promotes adhesion of the aluminum-containing powder to the metal object. Preferably, the binder is selected from polyvinylpyrrolidone (PVP), ethylene glycol, wax, polyethyleneimine (PEI), and mixtures of these compounds. The M measured by gel permeation chromatography using polystyrene standards. w PVP or PEI having a molecular weight of, for example, 10,000 to 1,300,000 g / mol is particularly preferred as the binder. w= 500,000 to 1,000,000 g / mol or M w PEI with a .DELTA. of 600,000 to 900,000 g / mol is used as the binder. Typically, PEI is used as an aqueous solution, preferably at a concentration of 0.5 to 15 wt. %, more preferably 1 to 10 wt. %, or 2 to 5 wt. %, and most preferably 2 to 3 wt. % based on the weight of PEI and water. The aluminum-containing powder can be optionally dissolved in an auxiliary liquid, such as water, and suspended in, for example, an aqueous PEI solution. The amount of aluminum-containing powder in the suspension is preferably 30 to 70 wt. %, particularly preferably 40 to 60 wt. %, and most preferably 45 to 55 wt. % based on the total weight of the suspension.

[0019] Alternative methods for applying the aluminum-containing material MP in step (b) include, for example, immersion of the metal foam in molten metal, sputtering or chemical vapor deposition of the aluminum-containing material MP, and deposition of the aluminum-containing material MP as a metal salt followed by reduction to the metal. It is also possible to combine all of the above application methods.

[0020] In a preferred embodiment of the present invention, the aluminium-containing material MP is an aluminium-containing powder and the organic binder is applied to the metal foam A together with or before the aluminium-containing powder.

[0021] Because coated metal foams are flexible, they can be easily shaped as needed. For example, the surface of the coated metal foam can be embossed, e.g., corrugated. Embossing can be performed with conventional tools, such as profile rollers, punches, or embossing tools. Furthermore, coated metal foams can be folded or rolled, optionally after embossing. Deformed metal foams can also be obtained by stacking multiple metal foams, optionally after embossing, where the foam can consist solely of coated metal foams or may include uncoated metal foams positioned between two coated metal foams. Rolled, folded, or laminated metal foams, also referred to herein as multilayers, can be further shaped by various forming processes, as appropriate. Shaping, deforming, and / or stacking coated metal foams can produce metal foam AX with desired geometric shapes depending on the application.

[0022] In step (c) of the method of the present invention, one or more alloys are formed by heat treatment. Experimental results obtained in connection with the present invention have shown that relatively strict temperature control is required to limit alloy formation to the upper region of the metal foam, leaving unalloyed regions in the interior of the metal foam. In addition, the thickness D of the metal foam AX must be taken into consideration when selecting the conditions for the heat treatment. The heat treatment of the metal foam AX in step (c) of the method of the present invention must be carried out under oxygen exclusion.

[0023] The duration H of the heat treatment (in minutes) is selected depending on the temperature T of the heat treatment (in °C) as follows: H min <H<H max where: Maximum duration H max =d1+(a1-d1) / (1+(T / c1)^b1), and Minimum duration H min= d2 + (a2 - d2) / (1 + (T / c2)^b2), where here 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 the heat treatment temperature T is selected as follows according to the thickness D of the metal foam AX: When 0 mm < D ≤ 10 mm, 600 °C < T ≤ 680 °C, When 10 mm < D ≤ 20 mm, 600 °C < T ≤ 675 °C, When 20 mm < D ≤ 30 mm, 600 °C < T ≤ 665 °C, When D > 30 mm, 600 °C < T ≤ 660 °C.

[0024] Here, the thickness D of the metal foam AX is determined as follows: When the geometric shape of the metal foam is simple, for example, when cutting out a mat of the metal foam in the shape of a rectangular parallelepiped, D represents the length of the shortest side of the cut-out part, that is, in most cases, the thickness of the mat of the metal foam. For an object with a more complex geometric shape, D is determined approximately, and when in doubt, it is assumed that D is larger than a value that is too small. Here, the value of D is estimated as twice the minimum distance from the point where the minimum distance to the surface among the points inside the foam is the largest to the surface. In any case, when determining D, the pores and their surfaces of the foam should be ignored, that is, in this determination, the pores of the foam should be regarded as filled. Furthermore, the recesses of the foam with a diameter less than 1 cm should also be regarded as filled areas rather than surfaces.

[0025] The heat treatment typically involves stepwise heating of the metal foam AX followed by cooling to room temperature. The heat treatment is carried out under inert or reducing conditions. By reducing conditions, we mean the presence of a gas mixture containing hydrogen and at least one gas that is inert under the reaction conditions, such as a gas mixture containing 50% by volume of N2 and 50% by volume of H2. Nitrogen is preferably used as the inert gas. Heating can be carried out, for example, in a belt furnace. Suitable heating rates are in the range of 10-200 K / min, preferably 20-180 K / min. During the heat treatment, the temperature is typically first increased from room temperature to approximately 300°C up to 350°C, and then maintained at this temperature for approximately 2-30 minutes to remove moisture and organic components from the coating. No alloy formation occurs during this phase of the heat treatment.

[0026] Thereafter, when the temperature is increased to a range above 600° C., an alloy is formed between the metal portion of the metal foam A and the aluminum-containing material MP, resulting in a metal foam B.

[0027] In order to limit the alloy formation to the upper region of the metal foam and leave a non-alloyed region inside the metal foam, it is necessary to appropriately select the duration H of the heat treatment depending on the heat treatment temperature T. According to the present invention, the duration H of the heat treatment (unit: min) is selected depending on the heat treatment temperature T (unit: °C) as follows: H min <H<H max where: Maximum duration H max =d1+(a1-d1) / (1+(T / c1)^b1), and Minimum duration H min =d2+(a2-d2) / (1+(T / c2)^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 and the heat treatment temperature T is selected as follows according to the thickness D of the metal foam AX: When 0 mm < D ≤ 10 mm, 600 °C < T ≤ 680 °C, When 10 mm < D ≤ 20 mm, 600 °C < T ≤ 675 °C, When 20 mm < D ≤ 30 mm, 600 °C < T ≤ 665 °C, When 30 mm < D, 600 °C < T ≤ 660 °C.

[0028] After alloy formation, the metal foam is cooled under oxygen exclusion. This cooling can be performed simply by stopping the heat treatment, for example, by removing the metal foam from the heating environment, such as a furnace, under oxygen exclusion and slowly cooling it to the ambient temperature. However, in order to "freeze" the leachable intermetallic phases, it is preferable to bring the catalyst compact to a temperature below 200 °C as quickly as possible. This can be done with a suitable cooling medium, preferably in the cooling zone of a furnace such as a belt furnace. This may be surrounded, for example, by a jacket of cooling water. The preferred cooling rate is 5 - 500 K / min, particularly preferably 20 - 400 K / min, and most preferably 30 - 200 K / min. Between the heat treatment and the cooling, the compact must be held in an oxygen-free environment. "Under oxygen exclusion" or "oxygen-free environment" means, in this specification, an inert gas atmosphere or a reducing atmosphere. Here, nitrogen is preferably used as the inert gas. As the reducing atmosphere, for example, a mixture of an inert gas and hydrogen such as N2 / H2 with a volume ratio of preferably 50 / 50 is suitable. Preferably, the compact is heated and cooled under a nitrogen flow, typically in the range of 5 - 30 m 3 / h, particularly preferably in the range of 10 - 30 m 3 / h of nitrogen flow rate.

[0029] If the temperature T is too high and / or the duration H is too long, alloy formation proceeds to the deepest layer of the metal foam and no non-alloyed region remains. If the temperature T is too low and / or the duration H is too short, alloy formation does not start at all.

[0030] If the time intervals between different temperatures T are selected within the range according to the invention during alloy formation, the H value for the temperature T of the heat treatment is calculated using an average value weighted according to the duration of the time interval. min and H max can be determined.

[0031] When two metal components are present in the metal foam A, in a preferred embodiment, the weight ratio of the two metal components in the metal foam A is in the range of 1:1 to 20:1, particularly preferably in the range of 1:1 to 10:1.

[0032] In a preferred embodiment, the metal foam A is made of metallic nickel.

[0033] In a further preferred embodiment, the weight ratio V of metal foam B to metal foam A = m(metal foam B) / m(metal foam A) is in the range of 1.1:1 to 1.5:1, particularly preferably in the range of 1.2:1 to 1.4:1.

[0034] In a further aspect, the present invention further includes a method comprising the following step (d): activating the metal foam B by treating it with a leaching agent. Treatment of the metal foam B with the leaching agent serves to at least partially dissolve and thus remove from the metal foam metal components of the applied aluminum-containing material MP and / or alloys between the metal parts of the metal foam and the aluminum-containing material MP. The aluminum content in the metal foam influences the catalyst performance and lifespan, particularly its hydrogenation activity and chemical stability in the reaction medium. Typically, 30 to 70 wt. % of the aluminum is removed, preferably 40 to 60 wt. % of the aluminum is removed, based on the total original weight of aluminum in the metal foam. The lower the residual aluminum content, the higher the hydrogenation activity of the metal foam according to the present invention. Preferably, the residual aluminum content is set to 2 to 20 wt. %, particularly preferably 5 to 15 wt. %, very particularly preferably 2 to 17 wt. %, and most preferably 3 to 12 wt. % of the total weight of the metal foam.

[0035] As leaching agent, any agent which selectively dissolves aluminum from the intermetallic phase is suitable, and may be alkaline or acidic, or may have a complexing action. Preferably, the leaching agent is an aqueous solution of a base, such as an aqueous solution of a hydroxide, preferably an alkali metal hydroxide, particularly preferably NaOH, KOH and / or LiOH or mixtures thereof, very preferably NaOH.

[0036] In a preferred embodiment, the treatment of the metal foam B with the basic solution is carried out at a temperature in the range of 20 to 120°C, preferably 60 to 115°C, particularly preferably 80 to 110°C, for a duration in the range of 5 minutes to 8 hours, wherein the basic solution is an aqueous NaOH solution with an NaOH concentration of 2 to 30% by weight. Preferably, the leaching time, i.e. the treatment time with a leaching agent, e.g., aqueous NaOH solution, in step (d) is 15 to 90 minutes.

[0037] The activation in step (d) of the process according to the invention can be carried out, for example, in the liquid phase or in the trickle mode. After treatment with the leaching agent, the shaped catalyst bodies are preferably washed with a washing medium selected from water, C1-C4 alkanols, and mixtures thereof. Suitable C1-C4 alkanols are methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol.

[0038] When the metal component is appropriately selected, the resulting metal foam after treatment with a basic solution can be used as a catalyst, as disclosed in WO2019057533.

[0039] In some embodiments, the activated metal foam may be modified by post-doping with additional metals in step (e). These doping elements, also referred to as promoter elements, are preferably selected from transition metals. For post-doping, the metal foam is preferably treated with an aqueous solution of the doping element to be applied. To avoid damaging the metal foam, the doping solution typically has a pH of 7 or higher. A chemical reducing component may be added to the solution of the doping element to reductively deposit the dissolved doping element on the metal foam. Preferred doping elements for modification are selected from the group consisting of Mo, Pt, Pd, Rh, Ru, Cu, and mixtures thereof. Suitable doping methods are described, for example, on pages 20-25 of WO 2019 / 057533. The metal foam activated in step (d) and optionally post-doped in step (e) can be used as a catalyst or stored. To prevent oxidation processes on the surface and the associated loss of catalytic activity, the activated metal foam is preferably stored in water.

[0040] In a further aspect, the present invention further comprises a coated metal foam obtainable by the method according to the present invention.

[0041] The activated, optionally doped metal foam obtained by one of the methods according to the present invention can be used as a catalyst for numerous catalytic chemical reactions, especially of organic compounds, such as hydrogenation, isomerization, hydration, hydrogenolysis, reductive amination, reductive alkylation, dehydrogenation, oxidation, dehydration, and rearrangement, preferably as a catalyst for hydrogenation reactions. In principle, the catalyst shaped body according to the present invention is suitable for all hydrogenation reactions catalyzed by Raney metal catalysts. Preferred applications of the catalytically active metal foam according to the present invention are selective hydrogenation processes for carbonyl compounds, olefins, aromatic rings, nitriles, and nitro compounds. Specific examples include the hydrogenation of carbonyl groups, the hydrogenation of nitro groups to form amines, the hydrogenation of polyols, the hydrogenation of nitriles to form amines, e.g., the hydrogenation of fatty nitriles to form fatty amines, the dehydrogenation of alcohols, reductive alkylation, the hydrogenation of olefins to form alkanes, and the hydrogenation of azides to form amines. Particularly preferred is its use in the hydrogenation of carbonyl compounds.

[0042] Thus, in a further aspect, the present invention comprises the use of an activated, optionally doped metal foam obtainable by one of the methods according to the invention as a catalyst for a chemical transformation, preferably selected from hydrogenation, isomerization, hydration, hydrogenolysis, reductive amination, reductive alkylation, dehydrogenation, oxidation, dehydration, and rearrangement.

[0043] Example 1.Providing metal foam Three metallic foam mats (a, b, c) made of nickel were prepared (manufacturer: AATM, thickness: 1.9 mm, weight per unit area: 1000 g / m). 2 , average pore size: 580 μm).

[0044] 2. Application of aluminum powder All metal foam mats were then first sprayed with a binder solution (aqueous solution of polyethyleneimine (2.5 wt%)), and then powdered aluminum (manufacturer: Mepura, average particle size: <63 μm, ethylenebis(stearamide) 3 wt%) was applied as a dry powder (approximately 400 g / m 2 ).

[0045] After coating the foam mat, individual layers of 1.9 mm thickness (25 mm length and width) were stacked to produce six rectangular foam blocks of different thicknesses (a1, a2, a3, b1, b2, b3). The foam was then compressed by approximately 30% to increase the number and area of contact.

[0046] Metal foam a1, a2, and a3: 9mm thick (1.9mm thick x 7 layers = 13.3mm thick, compressed to 9mm) Metal foams b1, b2, and b3: 12 mm thick (1.9 mm thick x 9 layers = 17.1 mm thick, compressed to 12 mm)

[0047] 3.Heat treatment All metal foams were then subjected to a heat treatment in a furnace under nitrogen atmosphere, where the binder was first removed by heating at 350°C for 30 minutes, then heated to the maximum temperature within 10 minutes, held for a specified time (treatment duration), and then rapidly cooled to below 200°C.

[0048] [Table 1]

[0049] 4. Determination of the degree of alloying Finally, the degree of alloy formation in the metal foam was measured. To this end, cross sections of the metal foam were examined under a microscope and a scanning electron microscope. The following results were obtained: In metal foams a1 and b1, alloy formation occurs on the surface but unalloyed regions remain inside the metal foam, whereas in metal foams a2 and b2, no alloy formation occurs, and in metal foams a3 and b3, alloy formation has progressed to the extent that no unalloyed regions remain inside the metal foam.

[0050] Experiments to date have shown, inter alia, that if the alloy formation temperature is chosen to be above 680°C, e.g. 700°C, the aluminum will react uncontrollably with the nickel, causing the compact to burn and leaving only a powder residue.

[0051] This result clearly shows that deviation from the heat treatment conditions according to the present invention makes it difficult to form a superficial alloy, leaving unalloyed regions inside the metal foam.

[0052] 5. Determining the position of the limit curve for heating duration Based on the above results, the position of the limit curve for the heating duration at which superficial alloy formation occurs while leaving unalloyed regions inside the metal foam at a given heating temperature was determined using a sigmoid model (heating duration = d + (ad) / (1 + (heating temperature / c)^b)).

[0053] The following values were used as limits for the position of the upper curve (maximum heating duration): Temperature (℃) → Duration (min) 680→10 675→12 665→30 660→60

[0054] The following values were used as limits for the position of the lower curve (minimum heating duration): Temperature (℃) → Duration (min) 680→2 675→3 665→20 660→30

[0055] Here, the following results were obtained for the position of the limit curve (H data in minutes, T data in °C): Maximum duration H max =d1+(a1-d1) / (1+(T / c1)^b1), where: a1=366.1; b1=129.0; c1=650.9; d1=8.7; and Minimum duration H min =d2+(a2-d2) / (1+(T / c2)^b2), where: a2=33.5; b2=235.5; c2=665.8; d2=1.8;

[0056] 6. Determination of the range limits of heat treatment temperatures depending on the thickness of the treated metal foam From the above results and further experience, the location of the heat treatment temperature range limits was obtained depending on the thickness of the treated metal foam.

[0057] The heat treatment temperature T (unit: °C) is preferably selected according to the thickness D (unit: mm) of the metal foam AX as follows: 0mm <d≦10mmの場合、600℃<t≦680℃であり、10mm <d≦20mmの場合、600℃<t≦675℃であり、20mm <d≦30mmの場合、600℃<t≦665℃であり、30mm< / d≦30mmの場合、600℃<t≦665℃であり、

Claims

1. A method for producing a metal foam, comprising: (a) providing a metal foam A made from nickel, cobalt, copper, or an alloy or combination thereof; (b) applying an aluminum-containing material MP to the metal foam A to obtain a metal foam AX; (c) heat-treating the metal foam AX under oxygen exclusion to form an alloy between the metal portion of the metal foam A and the aluminum-containing material MP to obtain a metal foam B, Here, the duration H (unit: min) of the heat treatment is selected according to the temperature T (unit: ° C.) of the heat treatment as follows: H ｍｉｎ <H<H ｍａｘ where: Maximum duration H ｍａｘ = d1 + (a1 - d1) / (1 + (T / c1)^b1), and Minimum duration H ｍｉｎ = d2 + (a2 - d2) / (1 + (T / c2)^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; The temperature T of the heat treatment is selected according to the thickness D of the metal foam body AX as follows: When 0 mm<D≦10 mm, 600 ° C.<T≦680 ° C., When 10 mm<D≦20 mm, 600 ° C.<T≦675 ° C. When 20 mm<D≦30 mm, 600 ° C.<T≦665 ° C. If 30 mm<D, then 600°C<T≦660°C. and the aluminium-containing material MP is an aluminium-containing powder, and an organic binder is applied to the metal foam A together with or before the aluminium-containing powder.

2. The method of claim 1 , wherein metal foam A comprises nickel.

3. Metal foam A has a strength of 100 to 1500 kg / m ３ 3. The method of claim 1 or 2, wherein the bulk density is in the range of

4. Metal foam A is 100 to 20,000 m ２ / m ３ 4. The method according to claim 1, wherein the sintered body has a BET specific surface area of 0.05 to 0.

15.

5. 5. The method according to claim 1, wherein the metal foam A has a porosity of 0.50 to 0.

95.

6. The method according to any one of claims 1 to 5, wherein the aluminium-containing material MP in step (b) comprises metallic aluminium in an amount of 80 to 100% by weight relative to the aluminium-containing material MP.

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

8. (d) activating the metal foam B by treating it with a leaching agent; 8. The method of claim 1, further comprising:

9. 9. The method of claim 8, wherein the treatment of the metal foam B with the leaching agent is carried out at a temperature ranging from 20 to 120°C for a duration ranging from 5 minutes to 8 hours, and the leaching agent is an aqueous NaOH solution having an NaOH concentration of 2 to 30 wt%.

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

10. The method of claim 8 or 9, further comprising:

11. A metal foam obtainable by the method according to any one of claims 1 to 7.

12. A metal foam obtainable by the method according to any one of claims 8 to 10.

13. 13. Use of the metal foam of claim 12 as a catalyst for chemical conversions.

14. 14. The use according to claim 13, wherein the chemical transformation of the catalyst for chemical transformation is selected from hydrogenation, isomerization, hydration, hydrogenolysis, reductive amination, reductive alkylation, dehydrogenation, oxidation, dehydration, and rearrangement.

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