METAL-FOAM BODY AND METHOD FOR THE PRODUCTION THEREOF AND THE USE THEREOF AS A CATALYST

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 aluminum-containing material MP to metal-foam body A so as to obtain metal-foam body AX, (c) thermally treating of 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 aluminum-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.

Claims

1. A process for producing a metal foam body, comprising the following steps: (a) providing a metal foam body A made of nickel, cobalt, copper or alloys or combinations thereof, (b) applying an aluminum-containing material MP to metal foam bodies A so as to obtain metal foam bodies AX, (c) treating metal foam bodies AX thermally, 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 as to obtain metal foam body B, wherein the duration H of the thermal treatment (in minutes), depending on the temperature T of the thermal treatment (in ° C.), is chosen as follows: Hmin<H<Hmax, with maximum duration H.sub.max=d1+(a1−d1)/(1+(T/c1){circumflex over ( )}b1), and minimum duration H.sub.min=d2+(a2−d2)/(1+(T/c2){circumflex over ( )}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 wherein the temperature T of the thermal treatment, depending on the thickness D of the metal foam body AX, is chosen 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., when 30 mm <D, 600° C. <T≤660° C.

2. The process as claimed in 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 process as claimed in either of claims 1 and 2, wherein metal foam body A consists of nickel.

4. The process as claimed in any of claims 1 to 3, wherein metal foam body A has an apparent density in the range from 100 to 1500 kg/m.sup.3, preferably from 200 to 1200 kg/m.sup.3 and more preferably from 300 to 600 kg/m.sup.3.

5. The process as claimed in any of claims 1 to 4, wherein metal foam body A has a specific BET surface area of 100 to 20 000 m.sup.2/m.sup.3, preferably of 1000 to 6000 m.sup.2/m.sup.3

6. The process as claimed in any of claims 1 to 5, wherein metal foam body A has a porosity of 0.50 to 0.95.

7. The process as claimed in any of claims 1 to 6, wherein the aluminum-containing material MP in step (b) contains metallic aluminum in an amount of 80% to 100% by weight, preferably of 80% to 99.8% by weight and more preferably of 90% to 99.5% by weight, based on the aluminum-containing material MP.

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

9. The process as claimed in any of claims 1 to 8, further comprising the following step: (d) activating the metal foam body B by treatment with a leaching agent.

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

11. The process as claimed in any of claims 9 to 10, further comprising the following step: (e) post-doping the activated metal foam body B with a promoter element, preferably selected from Mo, Pt, Pd, Rh, Ru, Cu and mixtures thereof.

12. A metal foam body obtainable by a process as claimed in any of claims 1 to 8.

13. A metal foam body obtainable by a process as claimed in any of claims 9 to 11.

14. The use of a metal foam body as claimed in claim 13 as catalyst for a chemical transformation.

15. The use as claimed in claim 14, wherein the chemical transformation is selected from hydrogenation, isomerization, hydration, hydrogenolysis, reductive amination, reductive alkylation, dehydrogenation, oxidation, dehydration and rearrangement.

Description

EXAMPLES

[0098] 1. Providing of Metal Foam Bodies

[0099] Three metal foam mats (a, b, c) made of nickel were provided (manufacturer: AATM, thickness: 1.9 mm, basis weight: 1000 g/m.sup.2, average pore diameter: 580 μm).

[0100] 2. Applying of Aluminum Powder

[0101] Subsequently, binder solution (polyethyleneimine (2.5% by weight) in water) was first sprayed onto all metal foam mats, followed by application of pulverulent aluminum (manufacturer: Mepura, average particle size: <63 μm, containing 3% by weight of added ethylenebis(stearamide)) in the form of a dry powder (about 400 g/m2).

[0102] After the foam mats have been coated, 6 cuboidal foam bodies of different thickness (al, a2, a3, b1, b2, b3) were produced by stacking individual layers of thickness 1.9 mm (length and width each 25 mm) one on top of another. In order to increase the number of contact points and the contact area, the foam bodies were then compressed by about 30%.

[0103] Metal foam bodies al, a2 and a3: thickness 9 mm (7 layers each of thickness 1.9 mm =thickness 13.3 mm; compression to 9 mm) Metal foam bodies b1, b2 and b3: thickness 12 mm (9 layers each of thickness 1.9 mm =thickness 17.1 mm; compression to 12 mm) 3. Thermal Treatment

[0104] Thereafter, all metal foam bodies were subjected to a thermal treatment under nitrogen atmosphere in a furnace. This involves first removing the binder thermally at 350° C. for 30 min and then heating up to the maximum temperature within 10 min; this was maintained for a defined period of time (duration of treatment), followed by quenching to below 200° C.

TABLE-US-00001 Treatment Duration of Metal foam body temperature (° C.) treatment (min) a1 (thickness: 679 3 a2 (thickness: 660 15 9 mm a3 (thickness: 679 15 9 mm b1 (thickness: 674 9 12 mm b2 (thickness: 660 15 12 mm b3 (thickness: 679 9 12 mm

[0105] 4. Determination of Extent of Alloying

[0106] At the end, the extent of alloy formation in the metal foam bodies was determined. This was done by examining cross sections of the metal foam bodies under a microscope and scanning electron microscope.

[0107] This gave the following result:

[0108] While superficial alloy formation had taken place in metal foam bodies a1 and b1, but unalloyed regions remained within the metal foam, no alloy formation took place in the case of metal foam bodies a2 and b2, and alloy formation in metal foam bodies a3 and b3 is so far advanced that no unalloyed regions remained within the metal foam.

[0109] Among the findings from prior experiments, moreover, is that: If the temperature for alloy formation is chosen above 680° C., for example 700° C., the aluminum reacts with the nickel in an uncontrolled manner and the shaped body burns off, leaving just powder residues.

[0110] This result clearly shows that departure from the thermal treatment conditions according to the invention has the effect that superficial alloy formation leaving unalloyed regions within the metal foam is difficult to achieve.

[0111] 5. Determination of the Position of the Limiting Curves of the Heating Time

[0112] On the basis of the abovementioned results, the position of the limiting curves for the heating time that, for a given heating temperature, leads to superficial alloy formation leaving unalloyed regions within the metal foam was ascertained by a sigmoidal model (heating time=d+(a−d)/(1+(heating temperature / c){circumflex over ( )}b)).

[0113] The limiting values used for the position of the upper curve (maximum heating time) were the following values:

TABLE-US-00002 Temp (° C.) .fwdarw. Duration (min) 680 .fwdarw. 10 675 .fwdarw. 12 665 .fwdarw. 30 660 .fwdarw. 60

[0114] The limiting values used for the position of the lower curve (minimum heating time) were the following values:

TABLE-US-00003 Temp (° C.) .fwdarw. Duration (min) 680 .fwdarw. 2 675 .fwdarw. 3 665 .fwdarw. 20 660 .fwdarw. 30

[0115] The following result was found for the position of the limiting curves (reporting of H in minutes and reporting of T in ° C.):

[0116] maximum duration H.sub.max=d1+(a1−d1)/(1+(T/c1){circumflex over ( )}b1), with

[0117] a1=366.1;

[0118] b1=129.0;

[0119] c1=650.9;

[0120] d1=8.7;

[0121] and minimum duration H.sub.min=d2+(a2−d2)/(1+(T/c2){circumflex over ( )}b2), with

[0122] a2=33.5;

[0123] b2=235.5;

[0124] c2=665.8;

[0125] d2=1.8.

[0126] 6. Determination of the Interval Limits for the Temperature of the Thermal Treatment Depending on the Thickness of the Metal Foam Bodies Treated

[0127] The position of the interval limits for the temperature of the thermal treatment depending on the thickness of the metal foam bodies treated was found from the results presented above and further experience values.

[0128] The temperature T for the thermal treatment (in ° C.), depending on the thickness D of the metal foam body AX (in millimeters), should be selected as follows:

[0129] 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.