WO2001044114A1

WO2001044114A1 - Synthesis of transition-metal aluminates with high specific surfaces by crystallisation from alumosilicates containing transition metals

Info

Publication number: WO2001044114A1
Application number: PCT/EP2000/010704
Authority: WO
Inventors: Wolfgang Schmidt; Claudia Weidenthaler
Original assignee: Studiengesellschaft Kohle Mbh
Priority date: 1999-12-17
Filing date: 2000-10-31
Publication date: 2001-06-21
Also published as: DE19960867A1

Abstract

The invention relates to a method for producing transition-metal aluminates with high specific surfaces, which crystallise from alumosilicates containing transition metals. According to said method, alumosilicates containing transition metals are heated to temperatures of between 500 and 1500 °C and after being cooled, are subjected to alkaline or acidic leaching. Transition-metal aluminates are thus obtained with specific surfaces greater than 50 m2/g. If certain elements, for example cobalt or nickel are used as the transition metal, materials are obtained with specific surfaces greater than 140 m2/g.

Description

Synthesis of transition metal aluminates with high specific surface areas by crystallization from transition metal-containing ones

Alumosiiicaten

The present invention relates to a process for the production of transition metal aluminates with high specific surfaces, which crystallize from transition metal-containing aluminosilicates by heat treatment.

In many applications of transition metal aluminates, such as in heterogeneous catalysis, high specific surface areas of the materials are desired, which are then used as catalysts or as catalyst supports. Due to their thermal resistance, transition metal aluminates are used, among other things, in reactions which take place at temperatures which are so high that other catalysts can no longer be used, e.g. in the total oxidation of methane or hydrogen [G. Busca et al., Catal. Today 33 (1997) 239-249]. In order to achieve conversion even at lower temperatures in spite of the moderate catalytic activity of the transition metal aluminates, the catalytically active surface must be correspondingly large.

Transition metal aluminates are typically produced by mixing and then annealing the respective oxides. The materials that are obtained usually have low specific surface areas of 1-5 m ² / g [MA Valenzuela et al., Appl. Catal. A: General 148 (1997) 315-324; C. Otero Arean et al., Mater. Lett. 39 (1999) 22-27; Insley, R. et al., US 3995184 (1976); K. Shioya et al., US 4469721 (1984)]. Products with higher specific surfaces can be obtained by co-precipitation of the corresponding hydroxides from corresponding salt solutions and subsequent annealing [MA Valenzuela et al., Appl. Catal. A: General t48 (1997) 315-324; G. Busca et al., Chem. Mater. 4 (1992) 595-605; R. Roesky et al., Appl. Catal. A: General 176 (1999) 213-220; JM Lee et al. US 4446201 (1984)]. The transition metal aluminates produced in this way have specific surfaces of up to approximately 100 m ² / g. Even higher specific surfaces of 100-250 m ² / g can be achieved if the precursor phases, which are subsequently annealed, are produced by sol-gel processes, usually using alkoxides or other organic metal compounds [MA Valenzuela et al., Appl , Catal. A: General 148 (1997) 315-324; C. Otero Arean et al., Mater. Lett. 39 (1999) 22-27; G. Busca et al., Catal. Today 33 (1997) 239-249; E. Escalona Platero et al., Res. Chem. Intermed. 25 No 2 (1999) 187-194]. The size of the specific surfaces is determined by the respective particle size, whereby smaller particles, based on the weight of the sample, result in larger surfaces.

In the case of materials which are produced by co-precipitation, aluminum oxide (also amorphous aluminum oxide) often occurs in the form of secondary phases, which can account for a not inconsiderable proportion of the measured specific surface, as a result of which higher surfaces of the transition metal aluminates are simulated than actually exist. Aluminum oxides cannot be easily removed by dissolution like silicates. Some of them are also catalytically active, which can lead to undesirable reactions when using the aluminum oxide-containing materials as catalysts or as catalyst supports. The highest specific surfaces to date can be achieved by producing the transition metal aluminate precursor phases using sol-gel methods. The advantage of the high specific surface areas has to be bought through the use of alkoxides or other organic metal compounds. Some of these are expensive and, due to their organic content, place higher demands on occupational safety (tempering up to 1000 ° C!) Than inorganic materials. It is therefore desirable to develop an inexpensive process with which it is possible to reproducibly obtain transition metal aluminates without high alumina contents with high surfaces from purely inorganic materials, in which the use of organic metal compounds can be dispensed with.

The process according to the invention solves this problem: by heating transition metal-containing aluminosilicates such as zeolites, which are used here as novel precursors for transition metal aluminates, to temperatures in the range of 500-1500 ° C., transition metal aluminates crystallize in a solid matrix. The mostly amorphous matrix essentially represents a solid solution of the transition metal cations in an alumosilicatic material with a high dispersion of the elements at the atomic level. The homogeneous element distribution is already specified in the transition metal-containing aluminosilicates, which can be obtained, for example, by ion exchange or by impregnation , The aluminosilicates can contain elements from groups 3-12 of the periodic table, wherein divalent and trivalent elements such as Cr, Mn, Fe, Co, Ni, Cu or Zn can be introduced into the aluminosilicates particularly easily by ion exchange.

The transition metal-aluminate particles created by the temperature treatment of the transition metal-containing aluminum silicates have sizes in the nanometer range. In order to obtain the small transition metal-aluminate particles with the correspondingly high surfaces in free form, the silicate matrix must be removed by dissolving, for example in alkali metal solution or hydrofluoric acid solution. This step is necessary to make the surface of the transition metal aluminates accessible. Any impurities still present, such as hydroxides, can be easily removed by washing with an alkaline and / or acidic and / or neutral solution. Materials in which the transition metal aluminates are embedded in the matrix only have a specific surface area of 1-5 m ² / g, whereas the transition metal aluminates freed from the matrix have specific surfaces of at least 50 m ² / g. Depending on the transition metals used, such as in the case of cobalt or nickel aluminates, materials with specific surfaces of over 140 m ² / g can be obtained. Some of the materials (e.g. ZnAl2θ4, C0AI2O4, NiAl2θ4) crystallize in the spinel structure, but other types of structure can also arise (e.g. FeAlOa). The sizes of the specific surfaces and the resulting particle diameters agree well with the particle sizes determined by transmission electron microscopy and X-ray analysis (reflection widths).

There is therefore a process available which, on the one hand, starting from inexpensive starting materials, can be used to obtain transition metal aluminates without undesirable secondary phases such as aluminum oxide with high specific surfaces, but on the other hand it is possible to dispense with organic lead phases.

example 1

Production of CoAI ₂ 0 from Co ²⁺ Exchanged Zeolite A In 5 g, Na-containing zeolite A (Si / Al = 1, 0), Na ^{+ was} mixed with Co by repeated ion exchange in 200 ml of 0.1 m Co ²⁺ solution ²⁺ exchanged. The exchanged zeolite was dried at 90 ° C. and then heated to 850 ° C. After cooling, the sample had a BET surface area of 5 m ² / g_aüf. It was transferred to a sealable vessel with 1N NaOH solution and placed in the solution in an oven heated to 90 ° C. for 12 hours. Leach with 1N NaOH solution was repeated. After the sample had cooled, it was washed with 1N NaOH solution and then with 1N HCl solution. After washing with deionized water, the sample was dried. The resulting material had a BET surface area of 147 m ² / g. The transition metal aluminate obtained (spinel structure, a = 0.8076 nm) was in pure phase.

The X-ray powder diffractogram of a sample prepared as above, measured with Cu radiation and a secondary-side monochromator, showed very broad reflections at the following angular positions:

2 theta relative intensity

19.026 9.1

31, 256 32.1

36.837 100.0

44.942 37.9

55.676 9.5

59.429 33.7

65.406 57.07

Example 2

Production of CoAI ₂ 0 from Co ²⁺ exchanged zeolite X

In 5 g of Na / K-containing zeolite X (Si / Al = 1.0), Na ⁺ or K ^{+ was} exchanged for Co ²⁺ by repeated ion exchange in 200 ml of 0.1 m Co ²⁺ solution. The exchanged zeolite was dried at 90 ° C. and then heated to 850 ° C. After cooling, the sample had a BET surface area of 4 m ² / g. It became a lockable

Transfer the vessel with 1N NaOH solution and place in the solution for 12 hours in an oven heated to 90 ° C. Leaching with 1 n NOH -

Solution was repeated. After the sample had cooled, 1 n

NaOH solution and then washed with 1N HCl solution. To Washing with deionized water, the sample was dried. The resulting material had a BET surface area of 154 m ² / g. The transition metal aluminate obtained (spinel structure, a = 0.8068 nm) was in pure phase.

2 theta relative intensity

19.054 10.6

31, 306 28.0

36.831 100.0

45.001 63.3

55,663 8.3

59,495 31, 1

65.511 86.5

Example 3

Production of CoAI ₂ 0 ₄ from Co ²⁺ Exchanged Zeolite Y In 5 g of Na-containing zeolite Y (Si / Al = 2.2), ion exchange in 200 ml of 0.1 m Co ²⁺ solution Na ⁺ for Co ²⁺ exchanged. The exchanged zeolite was dried at 90 ° C. and then heated to 950 ° C. After cooling, the sample had a BET surface area of 2 m ² / g. It was transferred to a sealable vessel with 1N NaOH solution and placed in the solution in an oven heated to 90 ° C. for 12 hours. The leaching with 1N NaOH solution was repeated. After the sample had cooled, it was washed with 1N NaOH solution and then with 1N HCl solution. After washing with deionized water, the sample was dried. The resulting material had a BET surface area of 76 m ² / g. The Transition metal aluminate obtained (spinel structure, a = 0.8106 nm) was present in pure phase.

2 theta relative intensity

19.745 10.6

31, 183 53.7

36.740 100.0

44.690 22.3

55.501 12.2

59.196 31, 9

65.045 49.4

Example 4

Production of NiAI ₂ 0 from Ni ²⁺ Exchanged Zeolite A In 5 g of Na-containing zeolite A (Si / Al = 1, 0), Na ^{+ was} mixed with Ni ² by repeated ion exchange in 200 ml of 0.1 m Ni ²⁺ solution ⁺ exchanged. The exchanged zeolite was dried at 90 ° C. and then heated to 1100 ° C. After cooling, the sample had a BET surface area of 2 m ² / g. It was transferred to a sealable vessel with 1N NaOH solution and placed in the solution in an oven heated to 90 ° C. for 12 hours. The leaching with 1N NaOH solution was repeated. After the sample had cooled, it was washed with 1N NaOH solution and then with 1N HCl solution. After washing with deionized water, the sample was dried. The resulting material had a BET surface area of 152 m ² / g. The transition metal aluminate obtained (spinel structure, a = 0.8045 nm) was in pure phase. The X-ray powder diffractogram of a sample prepared as above, measured with Cu radiation and a secondary-side monochromator, showed very broad reflections at the following angular positions:

2 theta relative intensity

19.114 6.8

31, 511 10.6

36.950 67.7

45.010 88.8

59.624 15.5

65,573 100.0

Example 5

Preparation of NiAl ₂ 0 getauschtem from Ni ²⁺ zeolite X in 5 g Na / K-containing zeolite X (Si / Al = 1, 0) by repeated ion exchange m in 200 ml Ni ²⁺ 0.1 - Na ⁺ or solution K ⁺ exchanged for Ni ²⁺ . The exchanged zeolite was dried at 90 ° C. and then heated to 1100 ° C. After cooling, the sample had a BET surface area of 2 m ² / g. It was transferred to a sealable vessel with 1N NaOH solution and placed in the solution in an oven heated to 90 ° C. for 12 hours. The leaching with 1N NaOH solution was repeated. After the sample had cooled, it was washed with 1N NaOH solution and then with 1N HCl solution. After washing with deionized water, the sample was dried. The resulting material had a BET surface area of 104 m ² / g. The transition metal aluminate obtained (spinel structure, a = 0.8052 nm) was in pure phase.

The X-ray powder diffractogram of a sample prepared as above, measured with Cu radiation and a secondary-side monochromator, showed very broad reflections at the following angular positions: 2 theta relative intensity

19.114 4.5

31, 390 8.5

36.930 59.2

44.943 74.9

56.055 3.5

59.640 15.9

65.483 100.0

Example 6

Preparation of NiAl ₂ 0 ₄ getauschtem from Ni ²⁺ zeolite Y in 5 g Na-containing zeolite Y (Si / Al = 2.2) was prepared by repeated ion exchange m in 200 ml Ni ²⁺ 0.1 - Na ⁺ solution to Ni ⁺ exchanged. The exchanged zeolite was dried at 90 ° C. and then heated to 1100 ° C. After cooling, the sample had a BET surface area of 2 m ² / g. It was transferred to a sealable vessel with 1N NaOH solution and placed in the solution in an oven heated to 90 ° C. for 12 hours. The leaching with 1N NaOH solution was repeated. After the sample had cooled, it was washed with 1N NaOH solution and then with 1N HCl solution. After washing with deionized water, the sample was dried. The resulting material had a BET surface area of 124 m ² / g. The transition metal aluminate obtained (spinel structure, a = 0.8050 nm) was in pure phase.

19.112 7.5

31, 681 7.4

36,891 51, 6

44.977 100.0

59.782 11.5

65.503 99.1

Example 7

Production of FeAI0 from Fe ²⁺ Exchanged Zeolite Y In 5 g of Na-containing zeolite Y (Si / Al = 2.2), Na ^{+ was} exchanged for Fe ²⁺ by repeated ion exchange in 200 ml of 0.1 m Fe ²⁺ solution , The exchanged zeolite was dried at 90 ° C. and then heated to 1100 ° C. After cooling, the sample had a BET surface area of 3 m ² / g. It was transferred to a sealable vessel with 1N NaOH solution and placed in the solution in an oven heated to 90 ° C. for 12 hours. The leaching with 1N NaOH solution was repeated. After the sample had cooled, it was washed with 1N NaOH solution and then with 1N HCl solution. After washing with deionized water, the sample was dried. The resulting material had a BET surface area of 91 m ² / g. The transition metal aluminate obtained (orthorhombic, a = 0.4943 nm, b = 0.8474 nm, c = 0.9149) was in pure phase.

14.192 19.5

22.903 29.8

28.245 51.4

30.858 56.9

33.628 100.0

35.937 44.3

37.581 59.1

41, 375 61, 7

47.085 45.5

48.056 28.8

49.890 24.6

50.938 28.8

54.410 37.0

62.8532 64.9

65.414 34.9

Example 8

Production of ZnAI ₂ 0 ₄ from Zn ²⁺ Exchanged Zeolite A In 5 g of Na-containing zeolite A (Si / Al = 1, 0), Na ^{+ was} exchanged with Zn by repeated ion exchange in 200 ml of 0.1 m Zn ²⁺ solution ²⁺ exchanged. The exchanged zeolite was dried at 90 ° C. and then heated to 1000 ° C. After cooling, the sample had a BET surface area of 3 m ² / g. It was transferred to a sealable vessel with 1N NaOH solution and placed in the solution in an oven heated to 90 ° C. for 12 hours. The leaching with 1N NaOH solution was repeated. After the sample had cooled, it was washed with 1N NaOH solution and then with 1N HCl solution. After washing with deionized water, the sample was dried. The resulting material had a BET surface area of 76 m ² / g. The transition metal aluminate obtained (spinel structure, a = 0.8092 nm) was in pure phase.

2 theta relative intensity

18.860 0.9

31, 234 66.3

36.802 100.0

44.772 9.1

49.032 4.9

55.591 16.4

59.296 31.5

65,174 37.0

Claims

1. Process for the preparation of transition metal aluminates with elements of groups 3-12 of the periodic table with high specific surfaces, wherein transition metal-containing aluminosilicates are heated to temperatures of 500-1500 ° C., the solid is leached alkaline or acid after cooling, the leached solid is separated from the solution.

2. The method according to claim 1, wherein zeolites are used as Alumosüicate.

3. The method according to claim 1, wherein the transition metal aluminates contain cations of the elements Cr, Mn, Fe, Co, Ni, Cu and Zn.

4. The method according to claims 1-3, wherein the transition metals are introduced by ion exchange in the Alumosüicate.

5. The method of claim 1, wherein the transition metal aluminate particles are present in a solid matrix after the temperature treatment.

6. The method according to claims 1 to 5, wherein the transition metal Aiuminat particles are obtained by dissolving the solid matrix with alkalis or acids.

7. The method of claim 1, wherein the solid is washed alkaline, acidic or neutral after leaching and separating from the solution.

8. The method according to claims 1-7, wherein the transition metal aluminates obtained have specific surfaces of over 50 m ² / g.

9. The method according to claims 2-8, wherein from Ni or Co-containing zeolites after temperature treatment and leaching transition metal aluminates with specific surfaces of over 140 m ² / g are obtained.

10. The method according to claims 2-9, wherein transition metal alloys with a spinel structure are obtained from Ni or Co-containing zeolites after temperature treatment and leaching.