Mesoporous carbon supported heteroatom doped metal catalyst and preparation method thereof

Abstract

The present application relates to a kind of mesoporous carbon supported heteroatom doped metal catalyst and its preparation method.The preparation method described in the present application.The present application provides a kind of ligand-induced crystallization-mesoporous confined pyrolysis strategy preparation mesoporous carbon supported heteroatom doped metal catalyst, this method includes the metal precursor is formed MOF or metal organic salt by ligand-induced crystallization in the mesoporous of carbon carrier, and two processes of mesoporous confined pyrolysis.The method provided in the present application solves the problems of yield, mass transfer and stability of traditional heteroatom doped carbon supported metal catalyst.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a mesoporous carbon supported heteroatom doped metal catalyst and a preparation method thereof. BACKGROUND

[0002] The information disclosed in the background of the present application is only intended to increase the understanding of the overall background of the present application and should not necessarily be regarded as acknowledging or implying in any form that this information constitutes prior art known to those skilled in the art.

[0003] Fuel cell technology is an important technology for efficient conversion of hydrogen energy. Currently, the main catalysts for the cathode and anode of fuel cells are Pt / C catalysts, and the high price of platinum limits the development and popularization of hydrogen energy technology. Recently, heteroatom doped metal catalysts have shown catalytic effects comparable to commercial Pt / C. ZIF-67 direct pyrolysis obtained N-doped Co metal particles, which have higher initial activity than Pt / C in cathode oxygen reduction reaction; HKUST pyrolysis at a certain temperature can obtain Ni / NiO metal particles, which show high anode hydrogen oxidation activity and CO poisoning resistance; by post-loading method, Pt metal particles are coupled with base metal nitrogen-doped carbon supports derived from ZIF pyrolysis, which realizes higher PEM fuel cell activity than commercial Pt / C with low Pt dosage. Although MOF (metal organic framework) derived heteroatom doped metal catalysts have good prospects, there are still some technical problems in industrial application. For example: 1) the production process of MOF consumes a large amount of solvent and it is difficult to remove excess ligand anions, the yield is low, and batch production is problematic; 2) the carbon supported heteroatom metal catalyst derived from MOF often inherits the micropore and micron size of the MOF, which is not conducive to mass transfer during the reaction; 3) metal particles are prone to agglomeration and growth during the reaction, and the heteroatom is prone to protonation in acidic electrolyte, which is difficult to work for a long time under high current density. SUMMARY

[0004] In order to solve the problems of yield, mass transfer and stability of traditional heteroatom doped carbon supported metal catalysts mentioned above, the present application provides a ligand induced crystallization-mesoporous confined pyrolysis strategy for preparing mesoporous carbon supported heteroatom doped metal catalysts, which includes two processes of ligand induced crystallization of metal precursors in the mesopores of carbon supports to form MOF or metal organic salt, and mesoporous confined pyrolysis. This method realizes the confined growth of MOF or metal organic salt in the mesopores, and reduces the problem of large amount of solvent used in the synthesis of MOF. After pyrolysis, the pre-grown MOF or metal organic salt in the mesopores will be converted in situ into a heteroatom doped metal catalyst, and the confinement effect of the mesopores further enhances the stability of the catalyst.

[0005] To achieve the above object, the present application provides the following technical solutions.

[0006] In a first aspect of the present application, a preparation method of a mesoporous carbon loaded heteroatom doped metal catalyst is provided, which comprises: preparing a mesoporous carbon loaded metal precursor, ligand induced crystallization and pyrolysis, and specifically comprises the following steps:

[0007] (1) Dissolve or disperse the metal precursor in an aqueous phase or an organic phase, add mesoporous carbon or mesoporous carbon precursor polymer, filter or rotary evaporate to remove the solvent, and reduce under a protective atmosphere to obtain a mesoporous carbon loaded metal precursor;

[0008] (2) Place the mesoporous carbon loaded metal precursor obtained in (1) and the ligand in the same container, according to different metal precursors, which can be dispersed together in a liquid phase or placed in a sealed container, heat to make the ligand react with the metal precursor, then collect the reacted powder by filtration, and further place it in a sealed glass bottle for heating to enhance the cleanliness;

[0009] (3) Pyrolyze the carbon carrier encapsulating the MOF or metal organic salt obtained in (2) at 400-1200℃ for 1-6 hours under a protective atmosphere, and cool to obtain the mesoporous carbon loaded heteroatom doped metal catalyst.

[0010] Further, the metal precursor is selected from one or more of chloroplatinic acid, platinum tetrachloride, potassium hexachloroplatinate, platinum acetylacetone, cobalt nitrate, potassium cobalt cyanide, potassium nickel cyanide, nickel nitrate, cobalt chloride, nickel chloride, cobalt sulfate, nickel sulfate, potassium ferricyanide, ferrous sulfate, zinc nitrate, zinc chloride, molybdic acid, ammonium molybdate, phosphomolybdic acid, tungsten chloride, and ruthenium chloride.

[0011] Further, the mesoporous carbon is a carbon carrier with a pore size of 2-50 nm. Preferably, it is selected from one or more of spherical mesoporous carbon, ordered mesoporous carbon, commercial CMK-3, commercial CMK-5, and commercial CMK-8.

[0012] Further, the mesoporous carbon precursor polymer is prepared by the following method: 28-31 g of 2,4-dihydroxybenzoic acid, 32-37 g of pluronic P123, 8-10 g of urotropine, and 5-8 g of ethylenediamine are dissolved in 800 mL of water, mixed uniformly, then loaded into a polytetrafluoroethylene reaction kettle, heated at 120-140℃ for 2-6 hours, cooled to room temperature after the reaction is completed, and then washed and dried.

[0013] Further, the mass ratio of the metal precursor to the mesoporous carbon is between 1:20 and 2:5, and the mass ratio of the metal precursor to the mesoporous carbon polymer is between 1:10 and 1:1.

[0014] Further, the ligand is selected from one or more of imidazole, dimethylimidazole, dicyandiamide, monocyandiamide, melamine, urea, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, tannic acid, phytic acid, 2,2-bipyridine, thiophene, benzothiophene, 2,2'-bithiophene, sodium dodecylsulfonate, disodium 1,2-ethanedisulfonate, 1,3,5-benzenetricarboxylic acid.

[0015] Further, the mass ratio of the ligand to the mesoporous carbon loaded metal precursor is 0.1:1-10:1.

[0016] Further, the protective atmosphere is selected from one of nitrogen, argon, hydrogen-argon mixed gas.

[0017] In a second aspect of the present application, a mesoporous carbon loaded heteroatom doped metal catalyst prepared by the above preparation method is provided.

[0018] Further, the metal element is selected from one or more of Pt, Co, Fe, Ni, Zn, Mo, W, Ru, preferably one or more of Pt, Co, Ni, and the content thereof accounts for 1-40 wt% of the total amount of the catalyst; the heteroatom is selected from one or more of N, C, O, P, S, preferably one or more of N, C, P, and the content thereof accounts for 0.5%-15% of the total amount of the catalyst.

[0019] The present application has the following beneficial effects: the present application realizes the confined growth of MOF or metal organic salt in mesopores, and reduces the problem of large amount of solvent used in the synthesis of MOF; the MOF or metal organic salt pre-grown in the mesopores is converted in situ into a heteroatom doped metal catalyst after pyrolysis, and the confinement effect of the mesopores further enhances the stability of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0020] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application. The present application should not be limited by the accompanying drawings.

[0021] Figure 1 is the crystallization induced growth MOF process of Example 3.

[0022] Figure 2 is the CoNC electrochemical application.

[0023] Figure 3 is the CoNC electron microscope photo. DETAILED DESCRIPTION

[0024] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0025] Example 1

[0026] Preparation of spherical mesoporous carbon precursor polymer: 30.8 g 2,4-dihydroxybenzoic acid, 35 g pluronic P123, 9.08 g urotropine, 6 g ethylenediamine were dissolved in 800 mL water, after mixing evenly, loaded into a 1 L polytetrafluoroethylene reaction kettle, heated at 130 °C for 4 hours. After the reaction was completed and cooled to room temperature, washed and dried to obtain the spherical mesoporous carbon polymer precursor.

[0027] Example 2

[0028] Preparation of spherical mesoporous carbon loaded Co3O4 precursor: 13.45 g of cobalt nitrate hexahydrate was dissolved in 960 mL of water, after complete dissolution, 240 mL of concentrated ammonia was added. Then 55 g of the polymer of Example 1 was added thereto, mixed evenly, heated at 50 °C for 6 h, and the polymer was filtered and dried. The dried polymer was pyrolyzed at 500 °C under H2 / Ar protective gas for 2 h, and finally spherical mesoporous carbon encapsulated Co3O4 was obtained.

[0029] Example 3

[0030] Preparation of ZIF-67 pre-encapsulated in spherical mesoporous: 3 g of mesoporous carbon loaded Co3O4 prepared in Example 2 was laid flat at the bottom of a 500 mL conical flask by induced crystallization, then 3 g of dimethylimidazole was added, vacuumed by vacuum pump to maintain a vacuum degree of 100 mbar, then sealed with a plug, and then heated at 155 °C for 6 h. Then the powder was placed in a sealed glass bottle and heated at 200 °C for 24 h. After cooling, ZIF-67 pre-encapsulated in spherical mesoporous was obtained (conversion process is shown in Figure 1 ).

[0031] Example 4

[0032] Preparation of spherical mesoporous carbon loaded N-doped Co particles: the ZIF-67 pre-encapsulated in spherical mesoporous of Example 3 was pyrolyzed under Ar / H2 gas, and the reduction temperature was 500 °C~800 °C (as shown in Figure 3 ). The catalyst has excellent oxygen reduction activity, and can be assembled into a zinc-air battery for long-term operation (as shown in Figure 2 ).

[0033] Example 5

[0034] Preparation of mesoporous carbon supported P-doped Co particles: 0.5 g of the encapsulated spherical mesoporous ZIF-67 of Example 3 was dispersed into 500 mL of ethanol solution, after being uniformly dispersed, 1.25 mL of phytic acid was added, after stirring at room temperature for 1 h, then by centrifugation, washing, drying, mesoporous carbon supported phosphorus coordinated MOF precursor was obtained. Finally, the sample was pyrolyzed at 500°C under Ar for 3 h to obtain mesoporous carbon supported P-doped Co particles.

[0035] Example 6

[0036] Preparation of mesoporous carbon supported O-passivated Ni particles: 1 g of commercial CMK-3 and 1 g of Ni(NO3)2 6H2O were added to 100 mL of ethanol and ultrasonically dispersed for 30 minutes, then the solution was heated to 60°C to evaporate the solvent, and then the powder was reduced at 200°C under Ar / H2 gas. After cooling to room temperature, the sample was placed in a polytetrafluoroethylene reaction kettle, 80 mL of DMF and 1 g of trimesic acid were added, and heated at 155°C for 12 h. After cooling, the sample was centrifuged, washed and dried. Finally, the sample was pyrolyzed at 500°C under Ar for 3 h to obtain mesoporous carbon supported surface-passivated Ni particles.

[0037] Example 7

[0038] Preparation of mesoporous carbon supported S-doped Ni / Fe particles: 1 g of commercial CMK-5 and 0.5 g of Fe(NO3)2 6H2O were added to 100 mL of ethanol and ultrasonically dispersed for 30 minutes, then the solution was heated to 60°C to evaporate the solvent, and then the powder was placed in a tube furnace, 1 g of imidazole was placed at the front end, and heated at 350°C for 12 h under Ar. After cooling, the powder was placed in a round-bottom flask, 100 mL of water and 0.8 g of 1,2-ethanedithioic acid di sodium were added, and heated at 60°C for 12 h under reflux, after cooling, centrifugation, washing and drying, the powder was pyrolyzed at 700°C under Ar for 3 h to obtain mesoporous carbon supported S-doped Ni / Fe particles.

[0039] Example 8

[0040] Preparation of ordered mesoporous carbon supported N-doped PtCo alloy particles: 6 g 3-aminophenol, 4 g urotropine, 4 g pluronic F127 were dissolved in 800 mL water, heated at 130 °C in a polytetrafluoroethylene reactor for 12 h, and dried after cooling to obtain a polymer. 2 g of the polymer was dispersed in 100 mL of 1 mol / L HCl solution, and 0.256 g of potassium ferricyanide and 0.213 g of potassium chloroplatinate were added to the solution. The solution was stirred at room temperature for 8 h, and the polymer was collected by filtration. The polymer was pyrolyzed under Ar / H2 gas at a reduction temperature of 500 °C to obtain ordered mesoporous carbon supported PtCo clusters. 0.3 g of ordered mesoporous carbon supported PtCo clusters was weighed and placed at the bottom of a 50 mL conical flask, and then 0.1 g of dimethylimidazole was added. The conical flask was sealed with a stopper and vacuumed to maintain a vacuum degree of 100 mbar using a vacuum pump, and then heated at 155 °C for 6 h. The powder was then placed in a sealed glass bottle and heated at 200 °C for 24 h. Then pyrolysis was carried out under Ar gas at 700 °C to obtain ordered mesoporous carbon supported N-doped PtCo alloy.

[0041] The preferred embodiments of the present application have been described above with the specific embodiments. It is not intended that the application be limited to the above embodiments but rather that it is intended to cover modifications and variations of the embodiments which would be apparent to those skilled in the art. It is intended to cover all modifications and variations of this application which come within the scope of the appended claims and their equivalents.

Claims

1. A method for preparing a mesoporous carbon-supported heteroatom-doped metal catalyst, characterized in that, The preparation method includes: preparing a mesoporous carbon-supported metal precursor, ligand-induced crystallization, and pyrolysis, specifically including the following steps: (1) Dissolve or disperse the metal precursor in an aqueous or organic phase, add mesoporous carbon or mesoporous carbon precursor polymer, remove the solvent by filtration or rotary evaporation, and reduce under a protective atmosphere to obtain a mesoporous carbon-supported metal precursor. (2) The mesoporous carbon-supported metal precursor and ligand obtained in (1) are placed in the same container. Depending on the different metal precursors, they are dispersed together in the liquid phase, or placed in a closed container and heated to react the ligands with the metal precursors. The powder after the reaction is collected by filtration and then placed in a closed glass bottle for heating to enhance the cleanliness. (3) The mesoporous carbon encapsulated with MOF or organometallic salt obtained in (2) is pyrolyzed at 400~1200℃ for 1~6 hours in a protective atmosphere and cooled to obtain the heteroatom-doped metal catalyst supported on the mesoporous carbon. The metal precursor is selected from one or more of the following: chloroplatinic acid, platinum tetrachloride, potassium hexachloroplatinate, platinum acetylacetonate, cobalt nitrate, potassium cobalt cyanide, potassium nickel cyanide, nickel nitrate, cobalt chloride, nickel chloride, cobalt sulfate, nickel sulfate, potassium ferrocyanide, ferrous sulfate, zinc nitrate, zinc chloride, molybdic acid, ammonium molybdate, phosphomolybdic acid, tungsten chloride, and ruthenium chloride. The mesoporous carbon precursor polymer was prepared by the following method: 28-31g of 2,4-dihydroxybenzoic acid, 32-37g of pluronic P123, 8-10g of hexamethylenetetramine, and 5-8g of ethylenediamine were dissolved in 800 mL of water, mixed evenly, and then placed in a polytetrafluoroethylene reactor. The mixture was heated at 120-140℃ for 2-6 hours. After the reaction was completed, the mixture was cooled to room temperature and then washed and dried.

2. The preparation method according to claim 1, characterized in that, The mesoporous carbon is a carbon support with a pore size of 2~50 nm.

3. The preparation method according to claim 1, characterized in that, The mesoporous carbon is selected from one or more of commercial CMK-3, commercial CMK-5, and commercial CMK-8.

4. The preparation method according to claim 1, characterized in that, The mass ratio of metal precursor to mesoporous carbon is between 1:20 and 2:5, and the mass ratio of metal precursor to mesoporous carbon precursor polymer is between 1:10 and 1:

1.

5. The preparation method according to claim 1, characterized in that, The ligand is selected from one or more of the following: imidazole, dimethylimidazolium, dicyandiamide, cyanamide, melamine, urea, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, tannic acid, phytic acid, 2,2-bipyridine, thiophene, benzothiophene, 2,2'-bisthiophene, sodium dodecyl sulfonate, disodium 1,2-ethanedisulfonate, and 1,3,5-benzenetricarboxylic acid.

6. The preparation method according to claim 1, characterized in that, The mass ratio of ligand to mesoporous carbon-supported metal precursor is 0.1:1 to 10:

1.

7. The preparation method according to claim 1, characterized in that, In step (1) or (3), the protective atmosphere is selected from nitrogen, argon, or a mixture of hydrogen and argon.

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