CN114643061A

CN114643061A - Reduction method of catalyst for preparing carbon nano tube

Info

Publication number: CN114643061A
Application number: CN202210265347.3A
Authority: CN
Inventors: 沈宇栋; 漆祯祯
Original assignee: Wuxi Dongheng New Energy Technology Co Ltd
Current assignee: Wuxi Dongheng New Energy Technology Co Ltd
Priority date: 2022-03-17
Filing date: 2022-03-17
Publication date: 2022-06-21
Anticipated expiration: 2042-03-17
Also published as: CN114643061B

Abstract

The invention relates to a reduction method of a catalyst for preparing a carbon nano tube, belonging to the technical field of catalysts and comprising the following steps: dissolving magnesium nitrate, aluminum nitrate nonahydrate, ferric nitrate, cobalt nitrate hexahydrate, ammonium molybdate, citric acid, EDTA and ammonia water in water, fully reacting, and cooling to room temperature after the reaction is finished to obtain a mixed solution; putting the mixed solution into a muffle furnace for carbonization at a constant temperature of 500 ℃; controlling the temperature of the muffle furnace to be 450 ℃ and continuing roasting for 240min, and then naturally cooling to room temperature; sieving and crushing the obtained solid product by using a 80-mesh screen to obtain solid powder; uniformly spreading a certain mass of solid powder in a quartz boat, and then placing the quartz boat in a tube furnace; introducing 1000sccm inert gas, and simultaneously heating to 300 ℃; after the temperature reaches 300 ℃, controlling the flow of the inert gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 20sccm hydrogen, and heating to 700 ℃ at a speed of 10 ℃/min; and after the reaction is finished, naturally cooling under the protection of argon, and taking out a product after cooling to obtain the catalyst for preparing the carbon nano tube.

Description

Reduction method of catalyst for preparing carbon nano tube

Technical Field

The invention relates to a reduction method of a catalyst for preparing a carbon nano tube, belonging to the technical field of catalysts.

Background

In recent years, carbon nanotubes have been widely used as an excellent conductive agent in the lithium battery industry of new energy automobiles. And the use of a catalyst is indispensable in the preparation of carbon nanotubes. According to statistics, more than 90% of industrial processes use catalysts, such as chemical industry, petrochemical industry, biochemical industry, environmental protection and the like. The catalyst has various types, and a good catalyst can greatly improve the product quality, the operation cost and the like of enterprises, so that the catalyst plays an extremely important role in the modern chemical industry.

At present, the methods for preparing carbon nanotubes mainly include arc discharge methods, laser evaporation methods and chemical vapor deposition methods. The method for preparing the carbon nano tube by arc discharge or laser evaporation requires higher reaction temperature and high process requirement; the chemical vapor deposition method has the advantages of lower working temperature, simpler process and equipment, lower cost and high growth controllability of the carbon tube, and meets the industrial requirement on the production of carbon tube materials, and the key point of adopting the chemical vapor deposition method to prepare the synthetic carbon nanotube is the selection and preparation of the catalyst. In the process of synthesizing the carbon nano tube, the components, the appearance and the physical and chemical properties of the catalyst can influence the structure and the properties of the finally obtained carbon nano tube to different degrees, and the catalytic activity of the catalyst used for synthesizing the carbon nano tube directly determines the initial purity of the carbon nano tube and directly influences the quality and the production cost of the carbon nano tube.

The reduction method for preparing the carbon nanotube catalyst known at present generally uses hydrogen, and the principle is that the metal oxide in the calcined catalyst is reduced into active metal by utilizing the strong reducibility of the hydrogen, but the transition metal element is easy to sinter and agglomerate by using the hydrogen reduction, so that the activity of the catalyst is reduced, the yield is reduced, and the pipe diameter consistency of the produced carbon nanotube is also poor. Therefore, it is desirable to provide a method for reducing the transient reduction of the catalyst, so as to reduce the sintering agglomeration of the catalyst and improve the activity of the catalyst.

Disclosure of Invention

[ problem ] to

In the prior art, hydrogen is used for reduction, and the phenomenon of sintering and agglomeration of transition metal elements is easy to occur, so that the activity of the catalyst is reduced, the yield is reduced, and the consistency of the pipe diameter of the produced carbon nano tube is also poor. Therefore, it is desirable to provide a method for reducing the transient reduction of the catalyst, so as to reduce the sintering agglomeration of the catalyst and improve the activity of the catalyst.

[ solution ]

The invention utilizes the method of combining the weak reduction effect of carbon monoxide and the reducibility of hydrogen, combines the TPR curve of the catalyst, finds out the better reduction activation condition of the catalyst, and obtains after a plurality of experiments that when the content ratio of carbon monoxide to hydrogen is 25: the catalyst activity is strongest at 1.

A first object of the present invention is to provide a method for reducing a catalyst for preparing carbon nanotubes, comprising the steps of:

(1) dissolving magnesium nitrate, aluminum nitrate nonahydrate, ferric nitrate, cobalt nitrate hexahydrate, ammonium molybdate, citric acid, EDTA and ammonia water in water under the heating condition, fully reacting, and cooling to room temperature after the reaction is finished to obtain a mixed solution;

(2) transferring the mixed solution obtained in the step (1) into a crucible, and carbonizing at a constant temperature of 500 ℃ in a muffle furnace until the crucible is free of liquid; controlling the temperature of the muffle furnace to be 450 ℃ and continuing roasting for 240min, and then naturally cooling to room temperature; sieving and crushing the obtained solid product by using a 80-mesh screen to obtain solid powder;

(3) uniformly paving a certain amount of the solid powder obtained in the step (2) in a quartz boat, and then placing the quartz boat in a tube furnace;

s1, introducing 1000sccm inert gas into the tube furnace, and simultaneously heating to 300 ℃;

s2, after the temperature reaches 300 ℃, controlling the flow of the inert gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 20sccm hydrogen, and heating to 700 ℃ at a speed of 10 ℃/min;

and S3, after the reaction is finished, naturally cooling under the protection of argon, and taking out a product after cooling to obtain the catalyst for preparing the carbon nano tube.

As an embodiment of the present invention, the step (1) is specifically: 102.6g of magnesium nitrate, 30g of aluminum nitrate nonahydrate, 8.9g of ferric nitrate, 5.2g of cobalt nitrate hexahydrate, 0.71g of ammonium molybdate, 100g of citric acid, 20.9g of EDTA and 123g of ammonia water are dissolved in 585g of water under the water bath heating condition at the temperature of 92 ℃ for full reaction, and after the reaction is finished, the solution is cooled to room temperature to obtain a mixed solution.

The second purpose of the invention is to provide the catalyst for preparing the carbon nano tube prepared by the method.

The third purpose of the present invention is to provide the application of the catalyst for preparing carbon nanotubes in the preparation of carbon nanotubes.

A fourth object of the present invention is to provide a method for preparing a carbon nanotube, comprising the steps of:

s01, introducing 1000sccm inert gas into the tube furnace, and simultaneously heating to 300 ℃;

s02, after the temperature reaches 300 ℃, controlling the flow of the inert gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 20sccm hydrogen, and heating to 700 ℃ at a speed of 10 ℃/min;

s03, stopping introducing the carbon monoxide and the hydrogen when the temperature reaches 700 ℃, controlling the flow of the argon gas to be 500sccm, introducing 300sccm ethylene, and keeping the constant temperature of 700 ℃ for reacting for 90 min;

and S04, after the reaction is finished, naturally cooling under the protection of argon, and taking out the product after cooling to obtain the carbon nano tube.

The fourth object of the present invention is to provide a carbon nanotube obtained by the above method.

A fifth object of the present invention is to provide the use of the aforementioned carbon nanotubes as a conductive agent.

Has the advantages that:

1. conventional reduction methods for preparing a catalyst for carbon nanotubes use a single gas of hydrogen or carbon monoxide as a reducing agent. The transition metal elements are easy to be excessively reduced, sintered and agglomerated, and the activity of the catalyst is influenced. The method of the invention adopts the combination of the strong reducing agent and the weak reducing agent to reduce the phenomena of excessive reduction, sintering and agglomeration of transition metal elements, when the content ratio of carbon monoxide to hydrogen is 25: the catalyst activity is strongest at 1.

2. The invention uses nitrogen or argon as protective gas in the whole process, avoids the reaction phenomenon caused by the interaction of carbon monoxide and hydrogen, simultaneously blocks the entry of air or other impurities, and ensures the safe and reliable performance of the experiment.

3. The invention adopts a temperature programming reduction method, has strong controllability in the whole process, has clear reaction in each stage, and ensures that each gas can be introduced in the first time.

4. The catalyst prepared by the method has high activity, can produce the carbon nano tube with high yield, and simultaneously, the consistency of the tube diameter of the carbon nano tube is better improved.

5. The catalyst produced by the invention has high uniformity and is beneficial to the balanced growth of the carbon nano tube.

6. The invention produces less harmful substances and has simple tail gas treatment.

Drawings

FIG. 1 is a scanning electron micrograph of the catalyst prepared in example 1 after the co-reduction of carbon monoxide and hydrogen in step 6: FIG. 1(a) is a scanning electron micrograph of a monolithic catalyst at 50 μm scale of example 1; FIG. 1(b) is a scanning electron micrograph of a plurality of catalysts of example 1 taken at different angles of 50 μm.

FIG. 2 is a scanning electron micrograph of the catalyst prepared in comparative example 1 according to the present invention after reduction with hydrogen gas in step 6.

FIG. 3 is a scanning electron micrograph of a catalyst of comparative example 2 of the present invention after reduction of carbon monoxide in step 6.

Fig. 4 is a carbon nanotube produced by the catalyst prepared in example 1.

FIG. 5 shows carbon nanotubes produced by the catalyst prepared in example 2-1.

FIG. 6 is a carbon nanotube produced by the catalyst prepared in example 2-3.

Detailed Description

The method for reducing the catalyst of the present invention will be specifically described below with reference to specific examples.

The main medicament is as follows: magnesium nitrate, aluminum nitrate nonahydrate, ferric nitrate, cobalt nitrate hexahydrate, ammonium heptamolybdate, citric acid, EDTA, ammonia water (reagent grade) and pure water.

Main experimental apparatus and equipment: beaker, graduated cylinder, glass rod, medicine spoon, precision electronic scale, water bath, stirrer, muffle furnace, quartz boat, tube furnace, and flowmeter.

Example 1

1. 102.6g of magnesium nitrate, 30g of aluminum nitrate nonahydrate, 8.9g of ferric nitrate, 5.2g of cobalt nitrate hexahydrate, 585g of pure water, 0.71g of ammonium heptamolybdate, 100g of citric acid, 20.9g of EDTA and 123g of ammonia water (reagent grade) were weighed.

2. Placing the weighed medicaments in a 1000mL beaker, heating in a water bath at 92 ℃, stirring at the rotation speed of 400rpm for 2 hours to fully dissolve and react each medicament, and then taking out the beaker and cooling at normal temperature for 1 hour.

3. And (3) after the muffle furnace is kept at the constant temperature of 500 ℃, transferring the solution into a crucible and putting the crucible into the muffle furnace at the temperature of 500 ℃ for carbonization, controlling the temperature of the muffle furnace to be 450 ℃ for roasting for 240min after the carbonization is finished when no liquid exists in the crucible, closing the muffle furnace, naturally cooling, and sieving and crushing the obtained solid product by using a 80-mesh screen to obtain solid powder, namely the catalyst.

4. 500mg of the solid powder is weighed and evenly spread in a quartz boat, and then the quartz boat is placed in a tube furnace with the diameter of 80 mm.

5. Introducing 1000sccm argon into the tube furnace, and heating to 300 ℃ at a speed of 10 ℃/min;

6. after the temperature reaches 300 ℃, controlling the flow rate of argon gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 20sccm hydrogen (see table 1), and continuously heating to 700 ℃ at a speed of 10 ℃/min;

7. after the temperature reaches 700 ℃, stopping introducing the reducing gas (carbon monoxide and hydrogen), controlling the flow of the argon gas to be 500sccm, simultaneously introducing 300sccm ethylene, and keeping the constant temperature of 700 ℃ for 90min for reaction.

8. And after the reaction is finished, naturally cooling under the protection of argon, and taking out a product after cooling to obtain the carbon nano tube.

The micron-sized scanning electron microscope image of the catalyst prepared in example 1 and reduced in step 6 is shown in fig. 1. As can be seen from fig. 1(a), under the micron-sized scanning electron microscope image, the catalyst is in a layered distribution, and each sheet-shaped catalyst has many small pores, which increases the specific surface area of the catalyst, enables more active metals to be attached to the surface, and enhances the activity of the catalyst. As can be seen from fig. 1(b), this layered morphology of the catalyst is universal, uniform, i.e. all the catalyst is in a sheet-like structure, rather than in a single sheet or two.

Fig. 4 is a carbon nanotube produced by the catalyst prepared in example 1. As can be seen from fig. 4, the tube diameters of the carbon nanotubes have high uniformity.

Comparative example 1 conventional hydrogen alone as a reducing gas

Referring to example 1, the only difference is that in comparative example 1, the carbon monoxide feed was omitted in step 6, while the optimum hydrogen flow rate was selected according to the catalyst performance. The flow rates of argon, carbon monoxide and hydrogen were adjusted in step 6 as shown in table 1, and the other steps and parameters were kept the same as those in example 1. Specifically, the method comprises the following steps:

6. after the temperature reaches 300 ℃, controlling the flow rate of argon gas to be 500sccm, simultaneously controlling the flow rate of 200sccm hydrogen (see table 1), and continuously heating to 700 ℃ at the speed of 10 ℃/min;

7. and stopping introducing the reducing gas (hydrogen) when the temperature reaches 700 ℃, controlling the flow of the argon gas to be 500sccm, introducing 300sccm ethylene at the same time, and keeping the constant temperature of 700 ℃ for reacting for 90 min.

FIG. 2 is an electron micrograph of the catalyst of comparative example 1 according to the present invention after hydrogen reduction of step 6. As can be seen from FIG. 2, the catalyst particles prepared in comparative example 1 have different sizes and are not uniformly distributed, and a large agglomeration phenomenon occurs in some places.

Comparative example 2 carbon monoxide alone as reducing gas

Referring to example 1, the only difference is that the introduction of hydrogen was omitted in step 6 of comparative example 2, while the optimum carbon monoxide flow rate was selected according to the catalyst performance. The flow rates of argon, carbon monoxide and hydrogen were adjusted in step 6 as shown in table 1, and the other steps and parameters were kept the same as those in example 1.

6. after the temperature reaches 300 ℃, controlling the flow rate of argon gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide (see table 1), and continuously heating to 700 ℃ at 10 ℃/min;

7. and stopping introducing the reducing gas (carbon monoxide) when the temperature reaches 700 ℃, controlling the flow of the argon gas to be 500sccm, introducing 300sccm ethylene at the same time, and keeping the constant temperature of 700 ℃ for reacting for 90 min.

FIG. 3 is a scanning electron micrograph of a catalyst of comparative example 2 of the present invention after reduction of carbon monoxide in step 6. As can be seen from fig. 3, the catalyst prepared in comparative example 2 was irregular in bulk and varied in size, and produced carbon tubes in a lower yield when carbon nanotubes were prepared, and also had a higher specific resistance than example 1 (see table 2).

Example 2

Referring to example 1, except that the flow rates of argon, carbon monoxide and hydrogen were adjusted in step 6 in examples 2-1, 2-2 and 2-3 as shown in table 1, the other steps and parameters were the same as those in example 1.

TABLE 1

	Argon gas/sccm	Carbon monoxide/sccm	Hydrogen/sccm
				Example 1	500	500	20
Comparative example 1	500	0	200
				Comparative example 2	500	500	0
Example 2-1	500	500	10
				Examples 2 to 2	500	500	40
Examples 2 to 3	500	500	60

Example 2-1

Referring to example 1, the only difference is that the hydrogen flow rate is reduced in step 6 of example 2-1, specifically:

3. And (3) after the muffle furnace is kept at the constant temperature of 500 ℃, transferring the solution into a crucible, putting the crucible into the muffle furnace at the temperature of 500 ℃ for carbonization, controlling the temperature of the muffle furnace to be 450 ℃ for roasting for 240min when the carbonization is finished when no liquid exists in the crucible, closing the muffle furnace, naturally cooling, sieving and crushing the obtained solid product by using a 80-mesh sieve to obtain solid powder, namely the catalyst.

6. after the temperature reaches 300 ℃, controlling the flow rate of argon gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 10sccm hydrogen (see table 1), and continuously heating to 700 ℃ at a speed of 10 ℃/min;

FIG. 5 shows that the carbon nanotubes produced by the catalyst prepared in example 2-1 were able to grow in an aligned manner, but they were entangled with each other, and the yield and resistivity of the carbon nanotubes were not as good as those of example 1, as compared to those of the carbon nanotubes produced in example 1 (see Table 2).

Examples 2 to 2

Referring to example 1, the only difference is that the hydrogen flow rate was changed in step 6 of example 2-1, specifically:

1. 102.6g of magnesium nitrate, 30g of aluminum nitrate nonahydrate, 8.9g of ferric nitrate, 5.2g of cobalt nitrate hexahydrate, 585g of pure water, 0.71g of ammonium heptamolybdate, 100g of citric acid, 20.9g of EDTA and 123g of ammonia water (reagent grade) are weighed.

6. after the temperature reaches 300 ℃, controlling the flow rate of argon gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 40sccm hydrogen (see table 1), and continuously heating to 700 ℃ at a speed of 10 ℃/min;

7. and stopping introducing the reducing gases (carbon monoxide and hydrogen) when the temperature reaches 700 ℃, controlling the flow of the argon gas to be 500sccm, introducing 300sccm ethylene at the same time, and keeping the constant temperature of 700 ℃ for reacting for 90 min.

FIG. 6 is a carbon nanotube produced by the catalyst prepared in examples 2-3. As can be seen from the graph, when the hydrogen content was further increased, the produced carbon nanotubes were varied in thickness, entangled with each other inside, and the yield and resistivity were not as good as those of example 1 (see Table 2).

Examples 2 to 3

6. after the temperature reaches 300 ℃, controlling the flow rate of argon gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 60sccm hydrogen (see table 1), and continuously heating to 700 ℃ at 10 ℃/min;

Example 3

Referring to example 1, the only difference is that the temperature rise rate is changed in step 6, specifically:

6. after the temperature reaches 300 ℃, controlling the flow rate of argon gas to be 500sccm, simultaneously introducing 500sccm carbon monoxide and 20sccm hydrogen (see table 1), and continuously heating to 700 ℃ at a speed of 20 ℃/min;

The results of the performance tests of the examples and comparative examples are shown in table 2.

The test method of the micro-morphology comprises the following steps: carrying out Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) tests on the carbon nano tube;

the method for testing the apparent density of the catalyst comprises the following steps: the catalyst was allowed to fall naturally, and the mass of the catalyst was divided by the volume of the catalyst after the natural fall (which could not be tapped).

The method for testing the yield of the carbon tube comprises the following steps: the mass of the carbon nanotubes actually obtained was divided by the mass of the catalyst used.

The carbon tube resistivity test method comprises the following steps: and pressing the carbon nano tube into a sheet, and then testing the sheet by using a four-probe tester to obtain the carbon nano tube.

The method for testing the loose density of the carbon tube comprises the following steps: the carbon nanotubes are naturally dropped, and the bulk density is obtained by dividing the mass of the carbon nanotubes by the volume of the carbon nanotubes (which cannot be compacted) after the natural dropping.

TABLE 2

Referring to example 1, example 3 changed the temperature increase rate in the reduction stage from 10 ℃/min to 20 ℃/min, and the yield of carbon nanotubes was significantly reduced.

The loose packed density of the catalyst in the prior art is 0.15g/ml, the yield of the prepared carbon nano tube is 16 times, the resistivity is 60 omega.m, and the loose packed density of the carbon tube is 0.012 g/ml. The invention adopts CO and H₂By optimizing the flow ratio of the reducing gas, the temperature programmed parameters of catalyst reduction and the like, the combined reduction method ensures that the catalyst is more uniformly distributed, the layered structure is more obvious, and the apparent density of the catalyst is higher (0.20 g/ml); the yield of the prepared carbon nano tube is higher (25 times), the resistivity is lower (45 omega. m), the loose packing density of the carbon nano tube is higher (0.020g/ml), and the method is more beneficial to practical production.

Claims

1. A reduction method of a catalyst for preparing carbon nanotubes, comprising the steps of:

s1, introducing 1000sccm inert gas into the tubular furnace, and simultaneously heating to 300 ℃;

2. The method according to claim 1, wherein step (1) is specifically: 102.6g of magnesium nitrate, 30g of aluminum nitrate nonahydrate, 8.9g of ferric nitrate, 5.2g of cobalt nitrate hexahydrate, 0.71g of ammonium molybdate, 100g of citric acid, 20.9g of EDTA and 123g of ammonia water are dissolved in 585g of water under the water bath heating condition at the temperature of 92 ℃ for full reaction, and after the reaction is finished, the solution is cooled to room temperature to obtain a mixed solution.

3. The catalyst for the preparation of carbon nanotubes prepared according to the method of claim 1 or 2.

4. Use of the catalyst for the preparation of carbon nanotubes of claim 3 for the preparation of carbon nanotubes.

5. A method for preparing carbon nanotubes, comprising the steps of:

s01, introducing 1000sccm inert gas into the tubular furnace, and simultaneously heating to 300 ℃;

6. The carbon nanotubes prepared according to the method of claim 5.

7. Use of the carbon nanotubes of claim 6 as a conductive agent.