Bimetal catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a bimetallic catalyst and a preparation method and application thereof. The preparation method of the bimetallic catalyst provided by the invention comprises the following steps: mixing a metal organic framework material, noble metal salt and a polar solvent, heating to boiling, adding a reducing agent, and reacting to obtain a precursor material; the precursor material is subjected to pyrolysis, and the bimetallic catalyst is obtained. The preparation method provided by the invention can further improve the dispersibility of the active metal on the catalyst, and can significantly reduce the hydrogen evolution overpotential by using the bimetallic synergistic effect of the transition metal and the noble metal. Meanwhile, the bimetallic particles are protected by a carbon skeleton formed by pyrolysis of the metal organic framework material, so that the stability of the bimetallic catalyst can be further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a bimetallic catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] As a clean and efficient secondary energy source, hydrogen energy is a key carrier for achieving the carbon neutrality goal. The current mainstream hydrogen production technologies (such as natural gas reforming and coal gasification) have high carbon emission problems, while the electrocatalytic water splitting hydrogen production technology (especially using renewable energy electricity) can produce "green hydrogen", but its core bottleneck lies in the catalyst cost and performance.

[0003] In the prior art, although the noble metal platinum-based catalyst has high hydrogen evolution reaction (HER) activity, its high cost and scarcity limit its wide application. Non-precious metal catalysts (such as Fe, Ni-based materials) are inexpensive, but their activity and stability are insufficient, and they are prone to corrosion especially in acidic electrolytes.

[0004] Metal-organic framework (MOF) materials have become an ideal choice for catalyst carriers due to their high specific surface area, porous structure, and adjustable chemical properties. However, how to uniformly disperse noble metals in the MOF structure and maintain a high density of active sites after pyrolysis is still a technical difficulty. Most of the prior art directly loads by physical adsorption, which easily leads to agglomeration of metal particles and reduces the catalytic efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a bimetallic catalyst, a preparation method thereof, and an application thereof.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of a bimetallic catalyst, comprising the following steps:

[0008] Mix a metal-organic framework material, a noble metal salt, and a polar solvent, heat to boiling, then add a reducing agent and react to obtain a precursor material; the metal-organic framework material is formed by a transition metal ion and an organic ligand;

[0009] Pyrolyze the precursor material to obtain the bimetallic catalyst.

[0010] Preferably, the transition metal ion includes Fe 3+ , Co 2+ or Ni 2+ ; the organic ligand includes terephthalic acid, trimesic acid, or 2-aminoterephthalic acid.

[0011] Preferably, the particle size of the metal-organic framework material is 70-150 nm.

[0012] Preferably, the noble metal salt includes chloroplatinic acid, ruthenium chloride or chloroiridic acid; the polar solvent includes at least one of ethanol, DMF and water;

[0013] The mass ratio of the metal-organic framework material to the noble metal salt is 30 to 100:1;

[0014] The dosage ratio of the metal-organic framework material to the polar solvent is 80 to 120 mg: 25 to 35 mL.

[0015] Preferably, the heating to boiling is carried out under stirring, and the stirring time after heating to boiling and before adding the reducing agent is 20 to 40 min.

[0016] Preferably, the reducing agent includes ascorbic acid or sodium borohydride;

[0017] The mass ratio of the noble metal salt to the reducing agent is 3:2 to 5;

[0018] The reaction is carried out under stirring, and the stirring time is 20 to 40 min.

[0019] Preferably, the pyrolysis temperature is 500 to 600 °C, the heating rate to the pyrolysis temperature is 5 to 10 °C / min, and the holding time is 20 to 40 min;

[0020] The pyrolysis is carried out under a protective atmosphere.

[0021] The present invention also provides a bimetallic catalyst prepared by the preparation method described in the above technical solution, including a carbon skeleton, transition metal particles and noble metal particles;

[0022] The transition metal particles are embedded inside the carbon skeleton;

[0023] The noble metal particles are loaded on the surface of the carbon skeleton.

[0024] Preferably, the mass percentage content of the transition metal particles on the bimetallic catalyst is 15 to 25%;

[0025] The mass percentage content of the noble metal particles on the bimetallic catalyst is 1 to 5%.

[0026] The present invention also provides the application of the bimetallic catalyst described in the above technical solution in electrolytic water hydrogen production, fuel cell oxygen reduction reaction or CO2 electrochemical reduction.

[0027] The present invention provides a method for preparing a bimetallic catalyst, comprising the following steps: mixing a metal-organic framework material, a noble metal salt, and a polar solvent, heating to boiling, then adding a reducing agent and reacting to obtain a precursor material; the metal-organic framework material is formed by transition metal ions and organic ligands; pyrolyzing the precursor material to obtain the bimetallic catalyst.

[0028] Compared with the prior art, the advantages of the present invention are as follows:

[0029] High activity: By utilizing the bimetallic synergistic effect of transition metals and noble metals, the present invention can significantly reduce the hydrogen evolution overpotential. As can be seen from the tests in the examples, the overpotential of the bimetallic catalyst provided by the present invention is only 18 mV (vs. RHE) at a current density of 10 mA / cm 2 ;

[0030] Low cost: The loading amount of the noble metal in the bimetallic catalyst provided by the present invention is as low as 1-5 wt%, and the cost is reduced by 70% compared with the commercial Pt / C catalyst;

[0031] High stability: By using the carbon framework formed by pyrolyzing the metal-organic framework material to protect the bimetallic particles, the present invention can further improve the stability of the bimetallic catalyst, and the activity decay is <5% after 100 hours of continuous testing. Description of the Drawings

[0032] Figure 1 SEM image of the MIL-101 powder obtained in Example 1;

[0033] Figure 2 SEM image of the Fe / Pt bimetallic catalyst obtained in Example 1;

[0034] Figure 3 LSV curve of the Fe / Pt bimetallic catalyst obtained in Example 1. Detailed Embodiments

[0035] The present invention provides a method for preparing a bimetallic catalyst, comprising the following steps:

[0036] Mixing a metal-organic framework material, a noble metal salt, and a polar solvent, heating to boiling, then adding a reducing agent and reacting to obtain a precursor material; the metal-organic framework material is formed by transition metal ions and organic ligands;

[0037] Pyrolyzing the precursor material to obtain the bimetallic catalyst.

[0038] In the present invention, a metal-organic framework material, a noble metal salt, and a polar solvent are mixed, heated to boiling, then a reducing agent is added and reacted to obtain a precursor material.

[0039] In the present invention, the metal-organic framework material is formed by transition metal ions and organic ligands, and the transition metal ions preferably include Fe 3+ , Co 2+ or Ni 2+ ; the organic ligands preferably include terephthalic acid, trimesic acid or 2-aminoterephthalic acid.

[0040] In the present invention, the preparation method of the metal-organic framework material preferably includes the following steps:

[0041] Mix a transition metal salt, an organic ligand and a solvent, and carry out a hydrothermal reaction to obtain the metal-organic framework material.

[0042] In the present invention, the transition metal salt preferably includes FeCl3, Co(NO3)2 or NiCl2; the organic ligand preferably includes terephthalic acid, trimesic acid or 2-aminoterephthalic acid; the mass ratio of the transition metal salt to the organic ligand is preferably 1-2:1. In the present invention, the solvent preferably includes DMF, ethanol or water; the dosage ratio of the transition metal salt to the solvent is preferably 100-200 mg: 50-60 mL. In the present invention, the mixing is preferably carried out under ultrasonic conditions. In the present invention, the temperature of the hydrothermal reaction is preferably 100-150 °C, specifically 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C; the heat preservation time is preferably 24-48 h, specifically 24 h, 30 h, 36 h, 42 h, 48 h. In the present invention, after the hydrothermal reaction, it preferably further includes post-treating the obtained reaction system, and the post-treatment preferably includes: after cooling the reaction system, successively carrying out ethanol washing and drying; the number of times of ethanol washing is preferably 3 times, the ethanol washing method is preferably centrifugal washing, and the rotation speed of the centrifugal washing is preferably 6000 rpm and the time is preferably 6 min.

[0043] In the present invention, the particle size of the metal-organic framework material is preferably 70-150 nm.

[0044] In the present invention, the noble metal salt preferably includes chloroplatinic acid, ruthenium chloride or chloroiridic acid; the polar solvent preferably includes at least one of ethanol, DMF and water; the mass ratio of the metal-organic framework material to the noble metal salt is preferably 30-100:1; the dosage ratio of the metal-organic framework material to the polar solvent is preferably 80-120 mg: 25-35 mL. In the present invention, the heating to boiling is carried out under stirring conditions, and the stirring time after heating to boiling and before adding the reducing agent is preferably 20-40 min.

[0045] In the present invention, the reducing agent preferably includes ascorbic acid or sodium borohydride; the mass ratio of the noble metal salt to the reducing agent is preferably 3:2 to 5; the reaction is preferably carried out under stirring, and the stirring time is preferably 20 to 40 min. In the present invention, after the reaction, it preferably further includes washing the obtained reaction system with water to remove excess impurities.

[0046] After obtaining the precursor material, the present invention pyrolyzes the precursor material to obtain the bimetallic catalyst.

[0047] In the present invention, the temperature of the pyrolysis is preferably 500 to 600 °C, specifically it can be 500 °C, 520 °C, 540 °C, 550 °C, 580 °C, 600 °C; the heating rate for heating up to the pyrolysis temperature is preferably 5 to 10 °C / min, and the holding time is preferably 20 to 40 min; the pyrolysis is carried out under a protective atmosphere; the protective atmosphere preferably includes nitrogen, argon or helium.

[0048] The present invention also provides a bimetallic catalyst prepared by the preparation method described in the above technical solution, including a carbon skeleton, transition metal particles and noble metal particles; the transition metal particles are embedded inside the carbon skeleton; the noble metal particles are loaded on the surface of the carbon skeleton.

[0049] In the present invention, the transition metal particles preferably include Fe, Co or Ni; the mass percentage content of the transition metal particles on the bimetallic catalyst is preferably 15 to 25%. In the present invention, the particle size of the transition metal particles is preferably 3 to 5 nm. In the present invention, the noble metal particles preferably include Pt, Ru or Ir; the particle size of the noble metal particles is preferably 5 to 20 nm; the mass percentage content of the noble metal particles on the bimetallic catalyst is preferably 1 to 5%.

[0050] In the present invention, the particle size of the bimetallic catalyst is preferably 50 to 60 nm. In the present invention, the specific surface area of the bimetallic catalyst is preferably 800 to 850 m 2 / g, and the pore diameter is preferably 2 to 50 nm.

[0051] The present invention also provides the application of the bimetallic catalyst described in the above technical solution in hydrogen production by electrolysis of water, oxygen reduction reaction of fuel cells or electrochemical reduction of CO2.

[0052] Unless otherwise specified, the materials and equipment used in the present invention are commercially available products in the art.

[0053] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0054] Example 1

[0055] Weigh 155 mg of FeCl3 powder and 109 mg of terephthalic acid powder, dissolve them in 50 mL of N,N-dimethylformamide, and then use ultrasound to mix the solution evenly. Then transfer the solution to a reaction kettle and react at 120 °C for 36 h. After the solution cools, centrifuge and wash it with ethanol three times. The centrifuge spins at 6000 rpm for 6 min to obtain the precipitate. Finally, dry and dehydrate it in an oven to obtain MIL-101 powder.

[0056] Weigh 100 mg of MIL-101 powder and 3 mg of chloroplatinic acid, dissolve them in 30 mL of ethanol solution, mix them evenly, transfer them to a flask, heat them to boiling and stir them in a high-temperature magnetic stirrer. After 30 min, add 2.5 mg of ascorbic acid and continue to stir for 30 min. After the reaction system cools, centrifuge and wash to remove excess impurities. Finally, in a tubular furnace, under a nitrogen atmosphere, heat it to 550 °C at a rate of 8 °C / min, hold for 30 min for pyrolysis, and then naturally cool to obtain the Fe / Pt bimetallic catalyst.

[0057] Among them, the particle size of Fe particles is 3.5 nm, and the loading amount is 20%; the particle size of Pt particles is 10 nm, and the loading amount is 3%; the particle size of the obtained Fe / Pt bimetallic catalyst is 50 nm, the specific surface area is 820 m 2 / g, and the pore size is 3.2 nm.

[0058] Example 2

[0059] Prepare MIL-101 powder in the same way as in Example 1.

[0060] Weigh 120 mg of MIL-101 powder and 4 mg of chloroplatinic acid, dissolve them in 35 mL of ethanol solution, mix them evenly, transfer them to a flask, heat them to boiling and stir them in a high-temperature magnetic stirrer. After 30 min, add 3 mg of ascorbic acid and continue to stir for 30 min. After the reaction system cools, centrifuge and wash to remove excess impurities. Finally, in a tubular furnace, under a nitrogen atmosphere, heat it to 550 °C at a rate of 8 °C / min, hold for 30 min for pyrolysis, and then naturally cool to obtain the Fe / Pt bimetallic catalyst.

[0061] Among them, the particle size of the Fe particles is 4 nm, and the loading amount is 22%; the particle size of the Pt particles is 12 nm, and the loading amount is 4%; the particle size of the obtained Fe / Pt bimetallic catalyst is 51 nm, and the specific surface area is 830 m 2 / g, and the pore diameter is 3.5 nm.

[0062] Example 3

[0063] Weigh 180 mg of Co(NO3)2 powder and 120 mg of terephthalic acid powder, dissolve them in 50 mL of N,N-dimethylformamide, and then use ultrasound to mix the solution evenly. Then transfer the solution to a reaction kettle and react at 120 °C for 36 h. After the solution cools, use ethanol to centrifuge and wash it 3 times. The centrifuge is centrifuged at 6000 rpm for 6 min to obtain the precipitate. Finally, dry and dehydrate it in an oven to obtain Co-MOF powder;

[0064] Weigh 100 mg of Co-MOF powder and 3 mg of chloroplatinic acid, dissolve them in 30 mL of ethanol solution, mix them evenly and transfer them to a flask, heat them to boiling and stir them in a high-temperature magnetic stirrer. After 30 min, add 2.8 mg of ascorbic acid and continue to stir for 30 min; after the reaction system cools, centrifuge and wash to remove excess impurities. Finally, in a tube furnace, heat it to 550 °C at a rate of 8 °C / min under a nitrogen atmosphere, keep it warm for 30 min for pyrolysis, and then naturally cool it to obtain the Co / Pt bimetallic catalyst

[0065] Among them, the particle size of the Co particles is 4 nm, and the loading amount is 22%; the particle size of the Pt particles is 11 nm, and the loading amount is 3.5%; the particle size of the obtained Co / Pt bimetallic catalyst is 52 nm, and the specific surface area is 825 m 2 / g, and the pore diameter is 3 nm.

[0066] Example 4

[0067] Weigh 160 mg of NiCl2 powder and 110 mg of terephthalic acid powder, dissolve them in 50 mL of N,N-dimethylformamide, and then use ultrasound to mix the solution evenly. Then transfer the solution to a reaction kettle and react at 120 °C for 36 h. After the solution cools, use ethanol to centrifuge and wash it 3 times. The centrifuge is centrifuged at 6000 rpm for 6 min to obtain the precipitate. Finally, dry and dehydrate it in an oven to obtain Ni-MOF powder;

[0068] Weigh 100 mg of Ni-MOF powder and 3 mg of chloroplatinic acid, dissolve them in 30 mL of ethanol solution, mix well, transfer to a flask, heat to boiling in a high-temperature magnetic stirrer and stir. After 30 min, add 2.6 mg of ascorbic acid and continue stirring for 30 min. After the reaction system cools, centrifuge and wash to remove excess impurities. Finally, in a tubular furnace, heat to 550 °C at a rate of 8 °C / min under a nitrogen atmosphere, hold for 30 min for pyrolysis, and then cool naturally to obtain the Ni / Pt bimetallic catalyst.

[0069] Among them, the particle size of Ni particles is 4.5 nm, and the loading amount is 23%; the particle size of Pt particles is 13 nm, and the loading amount is 3.8%; the particle size of the obtained Ni / Pt bimetallic catalyst is 58 nm, and the specific surface area is 835 m 2 / g, and the pore size is 3.8 nm.

[0070] Performance test

[0071] Test example 1

[0072] Figure 1 is the SEM image of the MIL-101 powder obtained in Example 1. Figure 2 is the SEM image of the Fe / Pt bimetallic catalyst obtained in Example 1. From Figure 1 and Figure 2 it can be seen that during the pyrolysis process, the structure of the MOF material changes. The unpyrolyzed MOF usually shows a clear geometric shape, with a smooth surface and sharp edges, and the loaded metal is on the surface. After pyrolysis, the structure collapses, the surface becomes rough and porous, the nanoparticles are embedded in the carbon matrix, the MOF is partially decomposed, and part of the crystal structure is retained, and the metal particle size is small.

[0073] Test example 2

[0074] The electrocatalytic hydrogen production performance of the Fe / Pt bimetallic catalyst obtained in Example 1 was tested. The test process was as follows: The prepared Fe / Pt bimetallic catalyst was dispersed in the electrolyte, and linear sweep voltammetry (LSV) test was carried out using a three-electrode system. The scanning range was from -0.2 V to 0.2 V (vs. RHE), and the scanning rate was 5 mV / s. The test was carried out under standard conditions. The electrolyte was 0.5 mol / L H2SO4 solution, the test temperature was 25 °C, and all potentials were corrected for IR drop.

[0075] The obtained LSV curve is as Figure 3 shown. From Figure 3It can be seen that a very low overpotential of 19 mV is achieved in HER, and the activity is better than that of commercial Pt / C (30 mV). This bimetallic MOF catalyst has the potential for high stability through the synergistic effect of bimetals and the confinement protection of the carbon framework. Its performance advantages stem from: the optimization of hydrogen adsorption energy by bimetals; the inhibition of particle agglomeration by the MOF-derived carbon support; and the promotion of charge transfer by the highly conductive carbon matrix.

[0076] Test Example 3

[0077] The stability of the Fe / Pt bimetallic catalyst obtained in Example 1 was tested:

[0078] Test procedure: 100 mg of the Fe / Pt bimetallic catalyst was evenly filled in a reaction tube, and quartz wool was filled at both ends to prevent scattering. Pretreatment: Heat to the reaction temperature in argon and keep it for 2 hours to remove surface adsorbates.

[0079] 1. Continuous reaction test:

[0080] (1) Switch to the reaction gas (CO / O2 volume ratio is 1:2), and adjust the flow rate to the target space velocity (30000 h -1 ).

[0081] (2) Collect the outlet gas data every 1 hour and record the CO conversion rate.

[0082] 2. Data analysis: Plot the conversion rate-time curve. If the activity decay is <5% after 100 hours of continuous testing, it indicates that the catalyst stability meets the standard.

[0083] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, not all embodiments. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a bimetallic catalyst, characterized in that, It includes the following steps: After mixing a metal-organic framework material, a noble metal salt and a polar solvent, heat the mixture to boiling, then add a reducing agent and carry out a reaction to obtain a precursor material; the metal-organic framework material is formed by a transition metal ion and an organic ligand; Pyrolyze the precursor material to obtain the bimetallic catalyst.

2. The preparation method according to claim 1, wherein The transition metal ions include Fe 3+ , Co 2+ or Ni 2 + ; The organic ligands include terephthalic acid, trimellitic acid or 2-aminoterephthalic acid.

3. The preparation method according to claim 1 or 2, characterized in that, The particle size of the metal-organic framework material is 70 - 150 nm.

4. The preparation method according to claim 3, characterized in that, The noble metal salt includes chloroplatinic acid, ruthenium chloride or iridium chlorate; the polar solvent includes at least one of ethanol, DMF and water; The mass ratio of the metal-organic framework material to the noble metal salt is 30 - 100:1; The dosage ratio of the metal-organic framework material to the polar solvent is 80 - 120 mg:25 - 35 mL.

5. The preparation method according to claim 1 or 4, characterized in that, The heating to boiling is carried out under stirring, and the stirring time after heating to boiling and before adding the reducing agent is 20 - 40 min.

6. The preparation method according to claim 5, wherein The reducing agent includes ascorbic acid or sodium borohydride; The mass ratio of the noble metal salt to the reducing agent is 3:2 - 5; The reaction is carried out under stirring, and the stirring time is 20 - 40 min.

7. The preparation method according to claim 1, characterized in that, The temperature of the pyrolysis is 500 - 600 °C, the heating rate to the pyrolysis temperature is 5 - 10 °C / min, and the holding time is 20 - 40 min; The pyrolysis is carried out under a protective atmosphere.

8. The bimetallic catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It includes a carbon skeleton, transition metal particles and noble metal particles; The transition metal particles are embedded inside the carbon skeleton; The noble metal particles are loaded on the surface of the carbon skeleton.

9. The bimetallic catalyst according to claim 8, wherein The mass percentage content of the transition metal particles on the bimetallic catalyst is 15 - 25%; The mass percentage content of the noble metal particles on the bimetallic catalyst is 1 - 5%.

10. Use of the bimetallic catalyst according to claim 8 or 9 in hydrogen production by electrolysis of water, oxygen reduction reaction of fuel cells or electrochemical reduction of CO2.

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