PROCESS FOR PRODUCING A NOBLE METAL-MODIFIED GRAPHITIZED CARBON MATERIAL AND SUPPORTED CATALYST

Abstract

The present invention relates to a process for producing a noble metal-modified, graphitized carbon material, comprising providing a graphitized carbon material, wherein the graphitized carbon material has a degree of graphitization of at least 10%, impregnating the graphitized carbon material with a composition and thermal treatment of the impregnated, graphitized carbon material. The composition comprises an organic solvent and at least one organic noble metal complex dissolved in the organic solvent. The invention further relates to a supported catalyst produced by this process and to an electrochemical cell containing this supported catalyst.

Claims

1. A process for producing a noble metal-modified, graphitized carbon material, comprising the following process steps: (a) providing a graphitized carbon material, wherein the graphitized carbon material has a degree of graphitization of at least 10%, (b) impregnating the graphitized carbon material with a composition, wherein the composition comprises (i) an organic solvent and (ii) at least one organic noble metal complex dissolved in the organic solvent, (c) thermal treatment of the impregnated, graphitized carbon material.

2. The process according to claim 1, wherein the noble metal is at least one metal of the platinum metal group.

3. The process according to claim 1, wherein the composition is a non-colloidal solution.

4. The process according to claim 1, wherein the composition comprises from 30 to 90 wt % organic solvent.

5. The process according to claim 1, wherein the composition comprises 10 to 70 wt % of the at least one organic noble metal complex.

6. The process according to claim 1, wherein the at least one organic noble metal complex is a noble metal complex having a diolefin ligand L and C6-C18 monocarboxylate ligands.

7. The process according to claim 1, wherein the at least one organic noble metal complex is a noble metal complex selected from the group consisting of noble metal complexes of the type [LPt[O(CO)R1]X].sub.n, [LPd[O(CO)R1]X].sub.n, [LRh[O(CO)R1]].sub.m, and [LIr[O(CO)R1]].sub.m, wherein X is selected from bromide, chloride, iodide, and O(CO)R2, wherein O(CO)R1 and O(CO)R2 denote identical or different non-aromatic C6-C18 monocarboxylic acid residues, and wherein n is an integer ? 1, and m is an integer ? 2.

8. The process according to claim 6, wherein the diolefin ligand L is selected from the group consisting of COD (1,5-cyclooctadiene), NBD (norbornadiene), COT (cyclooctatetraene), and 1,5-hexadiene.

9. The process according to claim 1, wherein the composition comprises 2.5 to 25 wt % noble metal, relative to the total weight of the composition.

10. The process according to claim 1, wherein the support material is present in an amount of 1 to 70 wt % during the impregnation step.

11. The process according to claim 1, wherein the support material and the noble metal derived from the at least one organic noble metal complex are present in a weight ratio of at least 1:1.

12. The process according to claim 1, wherein the thermal treatment of the impregnated, graphitized carbon material results in decomposition of the at least one organic noble metal complex.

13. A noble metal-modified, graphitized carbon material obtainable by means of the process according to claim 1.

14. The noble metal-modified, graphitized carbon material according to claim 13, containing the noble metal in an amount of 5 to 70 wt %.

15. An electrochemical cell, containing a noble metal-modified, graphitized carbon material according to claim 13.

Description

[0186] The invention is explained in more detail with reference to the following examples.

Example 1 (Modification of a Carbon with Platinum According to the Invention)

[0187] A solution of 65 mmol of (COD) PtCl.sub.2 was stirred in 100 mL of dichloromethane, and a solution of 260 mmol of sodium-2-neodecanoate was added to 500 ml of water. The two-phase mixture was emulsified at 20? C. for 24 h by vigorous stirring. The dichloromethane phase turned yellow. The dichloromethane phase was separated, and the solvent was distilled off. The viscous yellow residue was taken up in 150 mL of petroleum spirit (40-60), and the solution was dried with magnesium sulfate and filtered. The petroleum spirit was then completely distilled off. A viscous yellow residue of (COD) Pt[O(CO)(CH.sub.2).sub.5C(CH.sub.3).sub.3].sub.2 remained.

[0188] 10 g of the yellow residue was dissolved in 20 g of a solvent mixture (50 wt % ethanol, 50 wt % propylene glycol monopropyl ether).

[0189] 10 g of carbon (Heraeus Porocarb?; BET: 68 m.sup.2/g; degree of graphitization: 73%) was mixed with 100 mL of the solution containing 10 wt % platinum and vigorously stirred and homogenized for 30 min. The homogeneous mixture was treated at 250? C. in the first batch of a distillation apparatus under reduced pressure (0.1 mbar) over a period of 60 minutes. The solvent and the decomposition products were collected in the first batch and discarded. The product was cooled in the absence of oxygen and under an N.sub.2 atmosphere.

[0190] The proportion by weight of the platinum particles was 40%, relative to the total weight of carbon and metal. The particle size distribution of the platinum particles was determined by means of small-angle X-ray scattering. The average particle diameter was determined to be 1.6 nm, with the most common particle diameter being 1.8 nm. TEM images were taken of the platinum-modified carbon at various magnifications. FIG. 1 illustrates a very homogeneous distribution with a high degree of dispersion of the metallic platinum particles. FIG. 2 shows a representation of an image at a high magnification, which demonstrates the narrow size distribution of the platinum particles, which can also be deduced from the data of the particle size determination.

Comparative Example 1 (Modification of a Carbon with Platinum)

[0191] The carbon from Example 1 was slurried with 100 ml of water, placed in a jacketed reactor, and filled to 2 L with water. The suspension was heated to 70? C. while stirring. After a holding time of 1 h, 30 g of a nitric acid Pt nitrate solution (10 wt % Pt) was added and then held for 1 h with constant mixing and temperature. Subsequently, the pH was adjusted to 1.5 by adding Na.sub.2CO.sub.3. Formic acid was then added in stoichiometric excess. After stirring at 70? C. for 8 h, the solid was filtered off from the aqueous medium, washed with water, and dried at 110? C. under a nitrogen atmosphere.

[0192] The proportion by weight of the platinum particles was 30%, relative to the total weight of carbon and metal. The representative TEM image in FIG. 3 shows a lower homogeneity of the metal particle distribution and a higher degree of clustering compared to the modified carbon according to the invention.

Example 2 (Modification of a Carbon with Palladium According to the Invention)

[0193] A solution of 35 mmol of (COD)PdCl.sub.2 was stirred in 200 mL of dichloromethane, and a solution of 140 mmol of sodium-2-ethyl hexanoate was added to 150 ml of water. The two-phase mixture was emulsified at 20? C. for 24 h by vigorous stirring. The dichloromethane phase turned yellow. The dichloromethane phase was separated, and the solvent was distilled off. The viscous yellow residue was taken up in petroleum spirit (40-60), and the solution was dried with magnesium sulfate and filtered. The petroleum spirit was then completely distilled off. A viscous yellow residue of (COD)Pd[O(CO)CH(C.sub.2H.sub.5)C.sub.4H.sub.9].sub.2 remained.

[0194] 5 g of the yellow residue was dissolved in 5.6 g of a solvent mixture (50 wt % ethanol, 50 wt % propylene glycol monopropyl ether).

[0195] 10 g of carbon was added to 100 mL of the 10 wt % palladium. The rest of the preparation was the same as described in Example 1.