A method for preparing modified carbon nanotube metal catalyst

Abstract

The invention relates to the technical field of carbon nanotube modified catalysts, and in particular to a method for preparing a modified carbon nanotube metal catalyst, which can better load the metal catalyst and improve the catalytic efficiency, comprising the following steps: (1) pretreating the carbon nanotubes by an oxidation method; (2) heating the single-mouth flask in the step (1) in an oil bath for reflux and stirring, and after cooling to room temperature, adjusting the pH to 6-7, and filtering and drying the obtained carbon nanotubes; (3) mixing and grinding nitrogen-containing organic matter with the carbon nanotubes obtained in the step (2), placing the mixture in a porcelain boat, and calcining in a tube furnace to obtain grafted modified carbon nanotubes; and (4) dissolving the metal catalyst in an organic solvent, adding the modified carbon nanotubes prepared in the step (3), heating and reflux at a certain temperature, washing the obtained product with deionized water for 2-3 times, filtering and drying in a vacuum drying oven at 80°C for 12 h, and obtaining the modified carbon nanotube metal catalyst.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nanotube modified catalysts, and in particular to a method for preparing a modified carbon nanotube metal catalyst. Background Art

[0002] With the continuous development of science and technology, metal catalysts have been widely used in chemical synthesis. However, metal catalysts themselves also have many problems: 1. High toxicity, harmful to the environment and human health; 2. Poor stability, easily oxidized or reduced during the reaction, resulting in reduced catalytic activity; 3. Poor selectivity, due to the multiple reaction paths, often leading to many by-products, low selectivity and other problems. In this regard, the study found that the introduction of carriers can enhance the stability of metal catalysts and improve catalytic efficiency and selectivity.

[0003] The carrier can not only improve the dispersibility of metal nanoparticles in the catalyst, but also change the spatial configuration of the metal catalyst through the interaction between the functional groups on the carrier and the metal nanoparticles, thereby improving its catalytic activity and solving the problem of poor selectivity. An ideal carrier usually has some characteristics, including: 1. Suitable pore structure and large specific surface area; 2. Good stability; 3. Excellent conductivity.

[0004] Carbon nanotubes have a unique pore structure and a large relative area, excellent mechanical properties and chemical stability, and good electrical conductivity, so they are considered to be an excellent carrier material. As a carrier of metal catalysts, carbon nanotubes can well disperse the active components of metal catalysts and improve their reaction activity and selectivity. At the same time, since carbon nanotubes have a strong adsorption effect on many reactants, it is conducive to the adsorption-catalysis process. Similarly, carbon nanotubes also have some problems. Since the surface of carbon nanotubes is inert, neither hydrophilic nor lipophilic, it is difficult to dissolve or disperse in various solvents, which greatly limits the application of carbon nanotubes in the field of catalysis. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for preparing a modified carbon nanotube metal catalyst, which can enhance the interaction between carbon nanotubes and metal catalysts. The modified carbon nanotubes can better load the metal catalyst and improve the catalytic efficiency.

[0006] The technical solution is as follows: a method for preparing a modified carbon nanotube metal catalyst, characterized in that it comprises the following steps: (1) Pretreatment of carbon nanotubes by oxidation: The carbon nanotubes to be treated are transferred to a single-necked flask, an oxidant is added, and ultrasonic treatment is performed for a period of time to make the carbon nanotubes evenly dispersed in the solution; (2) The single-necked flask in step (1) is heated to reflux in an oil bath with stirring, and after cooling to room temperature, the pH is adjusted to 6-7, and the obtained carbon nanotubes are filtered and dried; (3) After mixing and grinding the nitrogen-containing organic matter with the carbon nanotubes obtained in step (2), the mixture is placed in a porcelain boat and calcined in a tube furnace to obtain grafted modified carbon nanotubes; (4) dissolving the metal catalyst in an organic solvent, adding the modified carbon nanotubes prepared in step (3), heating and refluxing at a certain temperature, washing the obtained product with deionized water for 2-3 times, filtering and drying in a vacuum drying oven at 80° C. for 12 h, and obtaining a modified carbon nanotube metal catalyst.

[0007] It is further characterized in that in step (1), the oxidant is one or a mixture of concentrated nitric acid, sulfuric acid, potassium permanganate, hydrogen peroxide, potassium dichromate; In step (2), the oil bath temperature is 50-200°C and the oil bath time is 6-24h; In step (2), deionized water or an ammonia solution is used to adjust the pH; In step (3), the nitrogen-containing organic compound is a nitrogen-containing heterocyclic organic compound containing one or more pyrrole rings, naphthyridine rings, pyridine rings, or triazine rings; In step (4), the heating reflux temperature is 100-150° C. and the reflux time is 10-20 h; In step (4), the metal catalyst is an organic metal complex, and the ligand is a nitrogen-containing heterocyclic organic compound containing one or more pyrrole rings, naphthyridine rings, pyridine rings, or triazine rings.

[0008] In step (4), the organic solvent is one of anhydrous pyridine, N,N-dimethylformamide, glacial acetic acid and N-methylpyrrolidone.

[0009] After adopting the present invention, the carbon nanotubes are modified by the grafting method, and more sites for anchoring metal catalysts are created without destroying their original structure. Different types of metal catalysts can be flexibly adapted and have a wider selectivity. While the metal catalysts are evenly distributed on the surface of the carbon nanotubes, the interaction between the metal catalysts and the carbon nanotubes is enhanced, which can not only increase the loading amount of the metal catalyst, but also promote the electron transfer between the two, thereby achieving a better catalytic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a schematic diagram comparing the comparative example with the embodiment. DETAILED DESCRIPTION

[0011] A method for preparing a modified carbon nanotube metal catalyst comprises the following steps: (1) Pre-treating carbon nanotubes by oxidation: transferring the carbon nanotubes to be treated into a single-necked flask, adding an oxidant and ultrasonicating for a period of time to make the carbon nanotubes evenly dispersed in the solution; wherein the oxidant is one or a mixture of concentrated nitric acid, sulfuric acid, potassium permanganate, hydrogen peroxide, and potassium dichromate; (2) The single-necked flask in step (1) is heated to reflux and stirred in an oil bath at a temperature of 50-150° C. for a time of 6-24 h. After cooling to room temperature, the pH is adjusted to 6-7 using deionized water or an ammonia solution, and the obtained carbon nanotubes are filtered and dried; (3) After mixing and grinding the nitrogen-containing organic matter with the carbon nanotubes obtained in step (2), the mixture is placed in a porcelain boat and calcined in a tube furnace to obtain grafted modified carbon nanotubes; wherein the nitrogen-containing organic matter is a nitrogen-containing heterocyclic organic matter containing one or more pyrrole rings, naphthyridine rings, pyridine rings, and triazine rings; (4) Dissolve a certain amount of metal catalyst in an organic solvent, add the modified carbon nanotubes prepared in step (3), and heat under reflux at a certain temperature for 10-20 hours. The obtained product is washed with deionized water 2-3 times, filtered, and dried in a vacuum drying oven at 80°C for 12 hours to obtain a modified carbon nanotube metal catalyst.

[0012] The following are specific examples.

[0013] Embodiment 1: Add 10g of multi-walled carbon nanotubes to a 250 ml round-bottom single-mouth flask, then add 150 ml of concentrated nitric acid and sonicate in an ultrasonicator for 5 min. Connect a condenser to the top of the single-mouth flask, and circulating cooling water flows in the tube. Immerse the bottom of the flask in a 120℃ oil bath, heat to reflux and stir for 10 h. After cooling to room temperature, add a certain amount of deionized water to adjust the pH value to 6~7. Dry the separated carbon nanotubes at 120℃ to obtain carbon nanotube powder. Weigh 1g of 4-amino-2,2,6,2-terpyridine powder and mix and grind it with 8g of carbon nanotube powder for 30min. Put the mixed sample into a porcelain boat and put it into a tube furnace. Calcine it at 320℃ for 2h at a heating rate of 5℃ / min in a hydrogen / nitrogen mixed atmosphere. Weigh 1g of the calcined carbon nanotube mixture and 0.5g of the terpyridine platinum complex into 120ml of N-methylpyrrolidone, and heat and reflux at 100°C for 20h. After the reaction, wash with deionized water three times, filter and dry in a vacuum oven at 80°C for 12h.

[0014] Embodiment 2: Add 15g of multi-walled carbon nanotubes to a 500 ml round-bottom single-mouth flask, then add 200 ml of concentrated sulfuric acid and sonicate in an ultrasonicator for 5 min. Connect a condenser to the top of the single-mouth flask, and circulating cooling water flows in the tube. Immerse the bottom of the flask in a 100℃ oil bath, heat to reflux and stir for 10 h. After cooling to room temperature, add a certain amount of deionized water to adjust the pH value to 6~7. Dry the separated carbon nanotubes at 120℃ to obtain carbon nanotube powder. Weigh 1g of 5-amino-1,10-phenanthroline powder and mix and grind it with 10g of carbon nanotube powder for 30min. Put the mixed sample into a porcelain boat and put it into a tube furnace. Calcine it at 350℃ for 2h at a heating rate of 5℃ / min under a nitrogen atmosphere. Weigh 1g of the calcined carbon nanotube mixture and 0.5g of phenanthroline copper complex into 120ml of glacial acetic acid, and heat and reflux at 150°C for 10h. After the reaction, wash with deionized water three times, filter and dry in a vacuum drying oven at 80°C for 12h.

[0015] Embodiment 3: Add 5g of multi-walled carbon nanotubes to a 250 ml round-bottom single-mouth flask, then add 80 ml of concentrated sulfuric acid and 20 ml of hydrogen peroxide, and sonicate in an ultrasonicator for 5 min. Connect a condenser to the top of the single-mouth flask, and circulating cooling water flows in the tube. Immerse the bottom of the flask in a 50°C oil bath, heat to reflux and stir for 24 h. After cooling to room temperature, add a certain amount of deionized water to adjust the pH value to 6~7. Dry the separated carbon nanotubes at 120°C to obtain carbon nanotube powder. Weigh 1g of 6-phenyl-pyridin-3-ylamine powder and mix and grind it with 10g of carbon nanotube powder for 30min. Put the mixed sample into a porcelain boat and put it into a tube furnace. Calcine at 450°C for 2h at a heating rate of 5°C / min in an argon / hydrogen atmosphere. Weigh 1g of the calcined carbon nanotube mixture and 0.5g of the pyridine cobalt complex into 120ml of anhydrous pyridine, and heat and reflux at 135°C for 12h. After the reaction, wash with deionized water three times, filter and dry in a vacuum drying oven at 80°C for 12h.

[0016] Embodiment 4: Add 12g of multi-walled carbon nanotubes to a 500ml round-bottomed single-mouth flask, then add 50ml of concentrated sulfuric acid and 150ml of concentrated nitric acid, and sonicate in an ultrasonicator for 5 minutes. Connect a condenser to the top of the single-mouth flask, and circulating cooling water flows in the tube. Immerse the bottom of the flask in a 150℃ oil bath, heat to reflux and stir for 6 hours. After cooling to room temperature, add a certain amount of deionized water to adjust the pH value to 6~7. Dry the separated carbon nanotubes at 120℃ to obtain carbon nanotube powder. Weigh 1g of 2,9-diamino-1,10-phenanthroline powder and mix and grind it with 8g of carbon nanotube powder for 30 minutes. Put the mixed sample into a porcelain boat and put it into a tube furnace. Calcine it at 350℃ for 2h at a heating rate of 5℃ / min under an argon atmosphere. Weigh 1g of the calcined carbon nanotube mixture and 0.5g of phenanthroline iron complex into 120ml of N,N-dimethylformamide, and heat and reflux at 120°C for 15h. After the reaction, wash with deionized water three times, filter and dry in a vacuum oven at 80°C for 12h.

[0017] See Figure 1 As shown, the carbon tubes in the comparative example are carbon nanotubes that have not been modified by grafting, and the performance is compared with the carbon tubes in the embodiment of the present invention that are carbon nanotubes that have been modified by grafting.

[0018] The modified carbon nanotube metal catalyst prepared by the present invention has a large specific surface area, many active sites, good stability, and strong electron conduction ability. It can make up for the defects of traditional metal catalysts, enhance the stability of metal catalysts, and improve their selectivity. At the same time, by strengthening the interaction between metal catalysts and carbon nanotubes, it is beneficial to the conduction of electrons in the entire catalytic system, greatly improving the catalytic efficiency and service life of the metal catalyst, which is more advantageous than traditional metal catalysts.

Claims

1. A method for preparing a modified carbon nanotube metal catalyst, characterized in that: It includes the following steps: (1) Pretreatment of carbon nanotubes by oxidation: The carbon nanotubes to be treated are transferred to a single-necked flask, an oxidant is added, and ultrasonic treatment is performed for a period of time to make the carbon nanotubes evenly dispersed in the solution; (2) The single-necked flask in step (1) is heated to reflux in an oil bath with stirring, and after cooling to room temperature, the pH is adjusted to 6-7, and the obtained carbon nanotubes are filtered and dried; (3) After mixing and grinding the nitrogen-containing organic matter with the carbon nanotubes obtained in step (2), the mixture is placed in a porcelain boat and calcined in a tube furnace to obtain grafted modified carbon nanotubes; (4) Dissolving the metal catalyst in an organic solvent, adding the modified carbon nanotubes prepared in step (3), heating and refluxing at a certain temperature, washing the obtained product with deionized water for 2-3 times, filtering and drying in a vacuum drying oven at 80°C for 12 h, and obtaining a modified carbon nanotube metal catalyst.

2. The method for preparing a modified carbon nanotube metal catalyst according to claim 1, characterized in that: In step (1), the oxidant is one or a mixture of concentrated nitric acid, sulfuric acid, potassium permanganate, hydrogen peroxide, and potassium dichromate.

3. The method for preparing a modified carbon nanotube metal catalyst according to claim 1, characterized in that: In step (2), the oil bath temperature is 50-200°C, and the oil bath time is 6-24h.

4. The method for preparing a modified carbon nanotube metal catalyst according to claim 1, characterized in that: In step (2), deionized water or an ammonia solution is used to adjust the pH.

5. The method for preparing a modified carbon nanotube metal catalyst according to claim 1, characterized in that: In step (3), the nitrogen-containing organic compound is a nitrogen-containing heterocyclic organic compound containing one or more pyrrole rings, naphthyridine rings, pyridine rings, or triazine rings.

6. The method for preparing a modified carbon nanotube metal catalyst according to claim 1, characterized in that: In step (4), the heating reflux temperature is 100-150° C. and the reflux time is 10-20 h.

7. The method for preparing a modified carbon nanotube metal catalyst according to claim 1, characterized in that: In step (4), the metal catalyst is an organic metal complex, and the ligand is a nitrogen-containing heterocyclic organic compound containing one or more pyrrole rings, naphthyridine rings, pyridine rings, or triazine rings.

8. The method for preparing a modified carbon nanotube metal catalyst according to claim 1, characterized in that: In step (4), the organic solvent is one of anhydrous pyridine, N,N-dimethylformamide, glacial acetic acid and N-methylpyrrolidone.

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