CN111495380B

CN111495380B - Preparation method of carbon nanotube catalyst and carbon nanotube

Info

Publication number: CN111495380B
Application number: CN201910099975.7A
Authority: CN
Inventors: 谢宝东; 朱玉莲; 徐壮; 张美杰; 郑涛; 毛鸥
Original assignee: Jiangsu Cnano Technology Ltd
Current assignee: Jiangsu Cnano Technology Ltd
Priority date: 2019-01-31
Filing date: 2019-01-31
Publication date: 2023-07-07
Anticipated expiration: 2039-01-31
Also published as: CN111495380A

Abstract

The invention discloses a preparation method of a carbon nano tube catalyst, which comprises the following technical steps ofThe key point is to configure a material containing Mg ²⁺ 、Al ³⁺ 、Co ²⁺ And the mixed solution of the catalyst auxiliary agent containing metal ions is added with the weak base solution and calcined at high temperature to prepare the catalyst with the spinel structure, so that the yield of the carbon nano tube can be improved, and the prepared carbon nano tube has small tube diameter distribution, large specific surface area and good electric conductivity.

Description

Preparation method of carbon nanotube catalyst and carbon nanotube

Technical Field

The present invention relates to the field of carbon nanotube preparation technology, and in particular, to a method for preparing a carbon nanotube catalyst and a carbon nanotube prepared by using the catalyst.

Background

The carbon nano tube is of a one-dimensional tubular structure, has extremely high length-diameter ratio and excellent conductivity, can be added into an electrode material of a lithium ion battery to effectively form a conductive network, improves the conductivity of the electrode, ensures that the lithium ion battery has excellent performance, is particularly characterized by large battery capacity and long cycle life, and is suitable for high-end digital batteries and new energy automobile batteries.

At present, the industrialized method for preparing the carbon nano tube is mainly a CVD method, and a lot of work is done on catalysts used by the CVD method. The metals which play a catalytic role in the preparation of the carbon nano tube are generally iron, cobalt and nickel; the carrier is alumina, magnesia, etc.; the auxiliary agent is molybdenum, lanthanum, tungsten and other metals. However, the catalyst structure obtained by different preparation processes is quite different from the catalytic performance.

Patent CN 1718278 provides a catalyst for carbon nanotube growth and a preparation method thereof. The catalyst consists of a metal oxide and spinel composite oxide; the preparation sequence is that firstly, mixed alkali liquor prepared by sodium hydroxide and inorganic sodium salt is used for precipitating metal ions, so as to prepare a catalyst precursor with a hydrotalcite structure, and then the catalyst is obtained by calcining. The concentration of metal ions in the precipitation process is 0.4-1.2M, the diameter of the carbon nanotube grown by the catalyst is 20-40nm, the number of layers is more than 18, the conductivity is poor, and the yield is not more than 300%.

The patent CN107252682 provides a preparation method of a carbon nanotube catalyst, which specifically comprises preparing a mixture with a precipitant or a complexing agent or a dispersing agent, spray-drying, and calcining to obtain the carbon nanotube catalyst. However, the direct spray drying is unavoidable to leave impurity elements in the catalyst without the processes of filtration, washing, etc. Such as chloride ions or nitrate ions in the catalyst salts, sodium ions in the precipitants, etc., tend to deactivate the catalyst. And the catalyst metal in the catalyst prepared by the method exists in the form of oxide.

Patent JP2016140781 also provides a catalyst for the preparation of multi-walled tubes and a method of preparation. The catalyst is composed of cobalt or iron and at least four elements of nickel, magnesium, aluminum and molybdenum. Adding the salt containing the catalyst into water, adding the organic acid, mixing, drying and calcining. However, it is mentioned in the patent that the calcination temperature of this method cannot exceed 650 degrees, otherwise the catalyst is susceptible to sintering deactivation. This necessarily results in inefficiency of the catalyst because the growth temperature of the carbon nanotubes is typically in the range of 670-1200 degrees.

Disclosure of Invention

Aiming at the defects existing in the prior art, the invention aims to provide a preparation method of a carbon nano tube catalyst, which has the advantages of high activity and high yield of carbon nano tubes.

The prepared carbon nano tube has the characteristics of small tube diameter distribution, large specific surface area and good conductivity.

The technical aim of the invention is realized by the following technical scheme:

a method for preparing a carbon nanotube catalyst, comprising the steps of:

a: preparing a salt solution: the configuration contains Mg ²⁺ 、Al ³⁺ 、Co ²⁺ And a mixed solution of catalyst auxiliary agent containing metal ions, wherein the mol ratio of Mg to Co to Al to metal ions in the catalyst auxiliary agent is = (1-3) 1 (1-1.5): (0.02-0.6), and the total molar concentration of metal ions in the salt solution is 1.0-3.0mol/L.

B: preparing a weak base solution: preparing weak base solution with weak base salt and total cation molar concentration of 0.05-0.3mol/L.

C: heating up the salt solution, keeping the temperature of the salt solution at 40-100 ℃, slowly dripping the weak base solution into the salt solution, controlling the dripping time to be 2-10 h, preserving the heat for 2-24h, filtering, washing, drying, and calcining at 700-900 ℃ to obtain the catalyst;

the steps a and B are not limited in sequence, i.e., the steps a and B may be configured separately or simultaneously.

The invention reduces the reaction speed by adding weak base, and ensures that the catalyst with spinel structure can be obtained under the condition of low-temperature calcination.

Wherein the catalyst auxiliary agent is a compound containing at least one of Mo, Y and Mn and capable of ionizing out metal ions.

Wherein the catalyst auxiliary agent is at least one of yttrium nitrate hexahydrate, ammonium molybdate and manganese nitrate.

Wherein the weak alkali salt is a buffer solution prepared from carbonate and bicarbonate.

Wherein the weak alkali salt is at least one of ammonium carbonate, ammonium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate; and the total molar concentration of cations in the weak base solution is 0.5-1.5 mol/L.

Wherein at least one of urea and hexamethylenetetramine is added as a precipitant to the salt solution in the step A, wherein the molar ratio of the total mole number of urea or hexamethylenetetramine or urea and hexamethylenetetramine to the catalyst metal ions is (2-4): 1.

The uniform decomposition of urea and hexamethylenetetramine in the solution is used for providing hydroxyl, or buffer solution prepared by carbonate and bicarbonate is used for reducing the reaction speed of the catalyst, so that the spinel structure catalyst with larger crystal form can be obtained under the condition of low-temperature calcination.

Wherein, after adding the precipitant, heating the salt solution, keeping the temperature of the salt solution at 80-100 ℃, and preserving the temperature for 6 hours.

Wherein, in the step A, mg ²⁺ 、Al ³⁺ 、Co ²⁺ Is a nitrate compound.

Wherein the temperature in the step C is increased to the calcining temperature at a speed of 10-15 ℃/min, and then the temperature is kept for 0.8-1.2h.

In the step C, the alkaline solution is dripped until the pH value of the solution system is 9-9.5, and the process can be stopped.

The catalyst is prepared by preparing a multi-element metal hydrotalcite precursor containing an active component and calcining. The catalyst has a multi-component composite structure comprising a metal oxide and a spinel structure. Specifically brucite, cobalt oxide, molybdenum oxide and/or yttrium oxide and/or manganese oxide, magnesium aluminate and cobalt aluminate. The yield of the carbon nano tube grown by the catalyst reaches 1200-4000%, the diameter of the carbon nano tube is distributed at 3-14nm, and the specific surface area of the carbon nano tube is 270-450m ² /g, and has excellent electrical conductivity.

The catalyst comprises CoO and Co ₂ O ₃ 、Co ₃ O ₄ CoAl ₂ O ₄ Four forms exist, the carrier of which comprises brucite and magnesium aluminate. The carrier element aluminum is present as spinel structure in the catalyst. Wherein Mo has three existing forms, moO and MoO ₂ And MoO ₃ . Y is present in the form of Y ₂ O ₃ . Mn exists in the form of MnO and MnO ₂ 。

The carbon nano tube is prepared by the catalyst preparation method.

The specific method comprises the steps of placing a catalyst in a fluidized bed, introducing nitrogen, keeping the temperature of a furnace at 670-850 ℃, and then introducing one or more of ethylene, propylene, propane, butane, methane, ethanol, propanol, isopropanol and methanol, wherein the flow rate of the nitrogen is as follows: propylene flow rate= (0.8-1.2): (0.8-1.2), reacting for 30min, and collecting carbon nanotubes at room temperature; wherein the specific surface area of the prepared carbon nano tube ranges from 270 m to 450m ² And/g, wherein the pipe diameter is distributed at 2-14nm.

Preferably, the catalyst is placed in a quartz blind furnace fluidized bed with the diameter of 60mm,introducing nitrogen at a flow rate of 1000ml/min; the furnace is heated to 700 ℃ at the speed of 10 ℃/min, then ethylene is introduced, the flow rate is 1000ml/min, and after 30min of reaction, the carbon nano tube can be collected at room temperature; wherein the specific surface area of the prepared carbon nano tube ranges from 270 m to 450m ² And/g, wherein the pipe diameter is distributed at 2-14nm. In summary, compared with the prior art, the invention has the following beneficial effects: the catalyst containing the auxiliary agent prepared by adopting the weak base precipitation method or the weak base uniform precipitation method and the weak base precipitation method has high activity, the yield can reach 1200-5000%, the pipe diameter of the carbon nano-tube is distributed between 2nm and 14nm, and the specific surface area of the carbon nano-tube reaches 270-450m ² And/g, has excellent electrical conductivity.

Drawings

FIG. 1 is an XRD pattern of a catalyst of the invention;

FIG. 2 is a graph showing the pipe diameter distribution of 100 carbon nanotubes prepared using the catalyst prepared in example 1;

FIG. 3 is a graph showing the distribution of the tube walls of 100 carbon nanotubes prepared using the catalyst prepared in example 1;

FIG. 4 is a graph showing the pipe diameter distribution of 100 carbon nanotubes prepared using the catalyst prepared in example 3;

FIG. 5 is a graph showing the wall profile of 100 carbon nanotubes prepared using the catalyst prepared in example 3.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

Example 1

Step A: preparing a salt solution: 9.60 g of cobalt nitrate hexahydrate, 25.38 g of magnesium nitrate hexahydrate, 24.76 g of aluminum nitrate nonahydrate and 1.26 g of yttrium nitrate hexahydrate were weighed and added to 400 g of pure water, wherein the metal ion concentration was 0.5mol/L, and the molar ratio of metal elements was Mg: co: al: Y=3:1:2:0.1.

And (B) step (B): 20.73 g of potassium carbonate and 42 g of sodium bicarbonate were weighed out and dissolved in 600 g of water to prepare a weak base solution.

Step C: slowly dripping the weak base solution into the salt solution at the temperature of 100 ℃ for 10 hours, keeping the final pH value at 9.5, continuously preserving the heat for 10 hours at 95 ℃, and then filtering and washing until the pH value of the washing liquor is less than 8, thus preparing the catalyst precursor. Drying the prepared catalyst precursor at 200 ℃, then placing the dried catalyst precursor in a high-temperature furnace, rising to 900 ℃ at the speed of 15 ℃/min, and preserving heat for 1 hour to obtain the catalyst, wherein the catalyst has a spinel structure, as shown in figure 1.

Example 2

Step A: preparing a salt solution: 9.60 g of cobalt nitrate hexahydrate, 21.15 g of magnesium nitrate hexahydrate, 18.56 g of aluminum nitrate nonahydrate and 0.30 g of ammonium molybdate were weighed and added to 600 g of pure water, wherein the metal ion concentration was 0.33mol/L, and the molar ratio of metal elements was Mg: co: al: mo=2.5:1:1.5:0.05.

And (B) step (B): 70.12 g of potassium bicarbonate and 18.02 g of potassium carbonate were weighed and dissolved in 400 g of water to prepare a weak base solution.

Step C: slowly dripping the weak base solution into the salt solution at 65 ℃ for 10 hours, keeping the final pH value at 9.5, continuously preserving the temperature at 65 ℃ for 10 hours, and then filtering and washing until the pH value of the washing liquid is less than 8, thus preparing the catalyst precursor. And (3) drying the prepared catalyst precursor at 200 ℃, then placing the dried catalyst precursor in a high-temperature furnace, rising to 700 ℃ at a speed of 15 ℃/min, and preserving heat for 1 hour to obtain the catalyst.

Example 3

Step A: preparing a salt solution: 9.60 g of cobalt nitrate hexahydrate, 16.92 g of magnesium nitrate hexahydrate, 12.37 g of aluminum nitrate nonahydrate and 0.117 g of ammonium molybdate, 0.63 g of yttrium nitrate hexahydrate are weighed and added into 150 g of pure water, wherein the metal ion concentration is 0.90 mol/L, and the molar ratio of metal elements is Mg, co, al and Mo: y=2:1:1:0.02:0.05.

And (B) step (B): 7.81 g of ammonium bicarbonate and 8.93 g of ammonium carbonate were weighed and dissolved in 400 g of water to prepare a weak base solution.

Step C: slowly dripping the weak base solution into the salt solution at 60 ℃ for 10 hours, keeping the final pH value at 9.0, continuously preserving the temperature at 60 ℃ for 3 hours, and then filtering and washing until the pH value of the washing liquid is less than 8, thus preparing the catalyst precursor. And (3) drying the prepared catalyst precursor at 200 ℃, then placing the dried catalyst precursor in a high-temperature furnace, rising to 750 ℃ at a speed of 15 ℃/min, and preserving heat for 1 hour to obtain the catalyst.

Example 4

Step A: preparing a salt solution: 9.60 g of cobalt nitrate hexahydrate, 16.92 g of magnesium nitrate hexahydrate, 18.56 g of aluminum nitrate nonahydrate and 0.24 g of yttrium nitrate were weighed and added to 1200 g of pure water, wherein the metal ion concentration was 0.13mol/L, and the molar ratio of metal elements was Mg: co: al: Y=2:1:1.5:0.04.

And (B) step (B): 11.66 g of sodium carbonate and 37.04 g of potassium bicarbonate were weighed out and dissolved in 400 g of water to prepare a weak base solution.

Step C: slowly dripping the weak base solution into the salt solution at 70 ℃ for 5 hours, keeping the final pH value at 9.2, continuously preserving the temperature at 70 ℃ for 10 hours, and then filtering and washing until the pH value of the washing liquid is less than 8, thus preparing the catalyst precursor. And (3) drying the prepared catalyst precursor at 200 ℃, then placing the dried catalyst precursor in a high-temperature furnace, rising to 800 ℃ at a speed of 15 ℃/min, and preserving heat for 1 hour to obtain the catalyst.

Example 5

Step A: preparing a salt solution: 9.60 g of cobalt nitrate hexahydrate, 13.54 g of magnesium nitrate hexahydrate, 17.33 g of aluminum nitrate nonahydrate, 0.24 g of yttrium nitrate and 0.117 g of ammonium molybdate were weighed out and added to 1300 g of pure water, wherein the metal ion concentration was 0.1mol/L, and the molar ratio of metal elements Mg to Co to Al to Mo=1.6 to 1 to 1.4 to 0.04 to 0.02.

And (B) step (B): 40.90 g of potassium bicarbonate and 8.68 g of sodium carbonate were weighed and dissolved in 400 g of water to prepare a weak base solution.

Step C: slowly dripping the weak base solution into the salt solution at 85 ℃ for 6 hours, keeping the final pH value at 9.5, continuously preserving the heat for 10 hours at 85 ℃, and then filtering and washing until the pH value of the washing liquid is less than 8, thus preparing the catalyst precursor. And (3) drying the prepared catalyst precursor at 200 ℃, then placing the dried catalyst precursor in a high-temperature furnace, rising to 720 ℃ at a speed of 15 ℃/min, and preserving heat for 1 hour to obtain the catalyst.

Example 6

Step A: preparing a salt solution: 9.60 g of cobalt nitrate hexahydrate, 16.92 g of magnesium nitrate hexahydrate, 12.37 g of aluminum nitrate nonahydrate and 0.59 g of manganese nitrate were weighed and added to 550 g of pure water, wherein the metal ion concentration was 0.25 mol/L, and the molar ratio of metal elements was Mg: co: al: mn=2:1:1: 0.1. 4.52 g of urea and 11.07 g of hexamethylenetetramine are weighed into the previously prepared solution and heated to 85 ℃ and kept for 5 hours.

And (B) step (B): 5.18 g of sodium carbonate and 16.46 g of potassium hydrogencarbonate were weighed out and dissolved in 200 g of water to prepare a weak base solution.

Step C: and D, dropwise adding the weak base solution into the solution in the step A for 5 hours, keeping the final pH value at 9.0, keeping the temperature at 85 ℃ for 3 hours, and performing suction filtration and washing until the pH value of the washing liquor is less than 8, thereby preparing the catalyst precursor. And (3) drying the prepared catalyst precursor at 200 ℃, then placing the dried catalyst precursor in a high-temperature furnace, rising to 900 ℃ at a speed of 15 ℃/min, and preserving heat for 6 hours to obtain the catalyst.

Example 7

Step A: preparing a salt solution: 9.60 g of cobalt nitrate hexahydrate, 16.92 g of magnesium nitrate hexahydrate, 12.37 g of aluminum nitrate nonahydrate and 0.59 g of manganese nitrate were weighed and added to 550 g of pure water, wherein the metal ion concentration was 0.25 mol/L, and the molar ratio of metal elements was Mg: co: al: mn=2:1:1: 0.1. 4.52 g of urea and 11.07 g of hexamethylenetetramine are weighed and dissolved in the solution prepared before, heated to 85 ℃ and kept for 5 hours.

And (B) step (B): 12.44 g of sodium carbonate was weighed and dissolved in 200 g of water to prepare an alkali solution.

Step C: and D, dropwise adding the alkali solution into the solution in the step A for 5 hours, keeping the final pH value at 9.0, keeping the temperature at 85 ℃ for 3 hours, and performing suction filtration and washing until the pH value of the washing liquor is less than 8, thereby preparing the catalyst precursor. And (3) placing the prepared catalyst precursor in a high-temperature furnace, rising to 900 ℃ at a speed of 15 ℃/min, and preserving heat for 6 hours to obtain the catalyst.

Comparative example 1:

the catalyst was prepared according to the catalyst preparation method provided in CN 107252682. 9.60 g of cobalt nitrate hexahydrate, 16.92 g of magnesium nitrate hexahydrate, 12.37 g of aluminum nitrate nonahydrate, 0.117 g of ammonium molybdate were weighed and added to 600 g of pure water, wherein the metal ion concentration was 0.22mol/L, and the molar ratio of metal elements was Mg: co: mo=2:1:1: 0.02. 80.30 g potassium bicarbonate was weighed and dissolved in 400 g water to prepare an alkali solution.

Slowly dripping the alkaline solution into the salt solution at 60 ℃ for 10 hours, wherein the final pH value is 9.0, and then directly spray-drying to obtain the catalyst precursor.

The catalyst precursor prepared above was placed in a high temperature furnace, and heated to 750℃at a rate of 15℃per minute, and further heat-preserved for 1 hour to obtain comparative catalyst 1.

Comparative example 2:

9.60 g of cobalt nitrate hexahydrate, 21.15 g of magnesium nitrate hexahydrate, 18.56 g of aluminum nitrate nonahydrate and 0.30 g of ammonium molybdate were weighed and added to 600 g of pure water, wherein the metal ion concentration was 0.33mol/L, and the molar ratio of metal elements was Mg: co: al: mo=2.5:1:1.5:0.05. 13 g of sodium hydroxide was weighed and dissolved in 400 g of water to prepare an alkali solution.

Slowly dripping the alkaline solution into the salt solution at 65 ℃ for 10 hours, keeping the final pH value at 9.5, continuously preserving the temperature at 65 ℃ for 10 hours, and then filtering and washing until the pH value of the washing liquid is less than 8.

The catalyst precursor prepared above was placed in a high temperature furnace, and heated to 700 c at a rate of 15 c/min, and further heat-preserved for 1 hour to obtain comparative catalyst 2.

Catalyst preparation of carbon nanotubes

Taking 1.5 g of each of the catalysts prepared in examples 1, 2, 3, 4, 5, 6 and 7 and comparative examples 1 and 2, putting the catalysts into a quartz blind tube furnace fluidized bed with the diameter of 60mm, and introducing nitrogen at the flow rate of 1000ml/min; the furnace is heated to 700 ℃ at a speed of 10 ℃/min, ethylene is introduced, the flow rate is 1000ml/min, the growth of the carbon nano tube is carried out, and the room temperature is reached after the reaction is carried out for 30 min.

And collecting the product, weighing, and testing the pipe diameter and the pipe wall layer number of the carbon nano-tube. And each carbon nanotube is prepared into carbon nanotube slurry, 98.5% of NCM+0.4% of CNT+0.1% of dispersant+1% of PVDF, and the slurry solid content is 74%, and the slurry is used for the NCM 523 slurry mixing, coating (PET film) and the volume resistivity after the coating is tested. TEM analysis is carried out on the prepared carbon nanotubes, and Gatan Digital Micrograph software is used for testing the tube diameter and the tube wall thickness of 100 carbon nanotubes, wherein the tube diameter refers to the outer diameter of the carbon nanotubes. The data obtained are shown in Table one below.

From table one, it can be seen that according to the catalyst preparation method provided in chinese patent No. CN107252682, comparative example 1 was prepared with a lower yield, a thicker tube diameter and poor conductivity.

The carbon nanotubes prepared in the same manner as the catalysts prepared in example 1 and example 3 according to the present invention are shown in FIGS. 2 to 5.

The productivity of the catalyst prepared according to the preparation method of the example of chinese patent No. CN 1718278 is not more than 300%, whereas the productivity of the catalyst prepared in the example of japanese patent No. JP2016140781 is similar to the present invention but the reaction time is as long as 4-8 hours, whereas the reaction time of the catalyst of the present invention is only 0.5 hours.

The foregoing is merely exemplary embodiments of the present invention and is not intended to limit the scope of the invention, which is defined by the appended claims.

Claims

1. A preparation method of a carbon nano tube catalyst is characterized in that: the method comprises the following steps:

a: preparing a salt solution: the configuration contains Mg ²⁺ 、Al ³⁺ 、Co ²⁺ And a mixed solution of catalyst auxiliary agent containing metal ions, wherein the mol ratio of Mg to Co to Al to metal ions in the catalyst auxiliary agent is = (1-3) 1 (1-1.5): (0.02-0.6), and the total molar concentration of metal ions in the salt solution is 1.0-3.0mol/L;

adding precipitants urea and hexamethylenetetramine into the salt solution prepared in the step A, wherein the molar ratio of the total mole number of urea and hexamethylenetetramine to the mole number of catalyst metal ions is (2-4): 1;

b: preparing a weak base solution: preparing weak base solution with weak base salt and total cation molar concentration of 0.05-0.3mol/L, wherein the weak base solution is buffer solution prepared from carbonate and bicarbonate;

c: heating the salt solution after adding the precipitant: maintaining the temperature of the salt solution after adding the precipitant at 40-100 ℃, slowly dripping the weak base solution into the salt solution after adding the precipitant until the pH value of the solution system is 9-9.5, stopping dripping, controlling the dripping time to be within 2-10 h, preserving the heat for 2-24h, filtering, washing, drying, and calcining at 700-900 ℃ to obtain the catalyst;

the step A and the step B do not limit the sequence.

2. The method for preparing a carbon nanotube catalyst according to claim 1, wherein: the catalyst auxiliary agent is a compound containing at least one of Mo, Y and Mn and capable of ionizing out metal ions.

3. The method for preparing a carbon nanotube catalyst according to claim 1, wherein: the catalyst auxiliary agent is at least one of yttrium nitrate hexahydrate, ammonium molybdate and manganese nitrate.

4. The method for preparing a carbon nanotube catalyst according to claim 1, wherein: the weak alkali salt is at least one of ammonium carbonate, ammonium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate, and the total molar concentration of cations in the weak alkali solution is 0.5-1.5 mol/L.

5. The method for preparing a carbon nanotube catalyst according to claim 1, wherein: after adding the precipitant, heating the salt solution, maintaining the temperature of the salt solution at 80-100 ℃, and preserving the temperature for 6 hours.

6. The method for preparing a carbon nanotube catalyst according to claim 1, wherein: mg in the step A ² ⁺ 、Al ³⁺ 、Co ²⁺ Is a nitrate compound.

7. The method for preparing a carbon nanotube catalyst according to claim 1, wherein: the temperature in the step C is increased to the calcining temperature at the speed of 10-15 ℃/min, and then the temperature is kept for 0.8-1.2h.