CN116159566A - Catalyst for preparing single-walled carbon nanotubes and preparation method thereof - Google Patents

Catalyst for preparing single-walled carbon nanotubes and preparation method thereof Download PDF

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CN116159566A
CN116159566A CN202211447165.4A CN202211447165A CN116159566A CN 116159566 A CN116159566 A CN 116159566A CN 202211447165 A CN202211447165 A CN 202211447165A CN 116159566 A CN116159566 A CN 116159566A
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王结祥
马向阳
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Changzhou Guore Material Technology Co ltd
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    • C01B32/158—Carbon nanotubes
    • C01B32/159—Carbon nanotubes single-walled
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Abstract

The catalyst provided by the invention has good stability and small particles, active component particles are not agglomerated under the high temperature condition, the pipe diameter of the prepared single-walled carbon nanotube is uniform, the active components of the catalyst are distributed on the body and the surface of the carrier, and the active components of the catalyst and the carrier have strong interaction, so that the active components are uniformly dispersed and are not easy to agglomerate; the content of the active component in the carrier inner body and surface can be regulated and controlled by a preparation method, and can be regulated according to actual requirements and different specific active components; the carrier area is uniformly dispersed with rare earth oxide elements, the rare earth oxide elements can improve the dispersibility of the surface active component iron-based metal particles, and particularly, the agglomeration and the falling-off of active metals can be effectively prevented under a high-temperature environment.

Description

Catalyst for preparing single-walled carbon nanotubes and preparation method thereof
Technical Field
The invention relates to the technical field of catalysts, in particular to a catalyst for preparing single-walled carbon nanotubes and a preparation method thereof.
Background
Single-walled carbon nanotubes (SWNTs) have a high aspect ratio and are typical one-dimensional tubular nanomaterials, and this particular tubular structure determines that the carbon nanotubes have excellent physical, chemical, electrical and mechanical properties. The existing preparation methods of single-wall carbon nanotubes mainly comprise an electric arc method, a laser ablation method and a chemical vapor deposition method. The arc method is the earliest method applied to SWNTs synthesis, is simple to operate and high in preparation speed, and the preparation method tends to be mature, and has the defects of high arc temperature, difficult reaction control and low yield; the laser ablation method has the advantages of high SWNTs growth speed, high SWNTs preparation quality, few impurities and easy purification, and has the defects of complex instrument and equipment, high price, high laser energy consumption, unsafe and low SWNTs yield. The two methods have higher cost in realizing industrialization, more demanding requirements and poor industrialization prospect. The Chemical Vapor Deposition (CVD) method has simple equipment and process, can realize continuous mass production of high-quality SWNTs, has low cost, and is the most widely studied and commonly applied method in the growth of the SWNTs.
The process of growing SWNTs by the CVD method is carried out under the high-temperature condition and can be mainly summarized into four reaction stages: (1) The carbon source molecules are adsorbed on the catalyst particles and are cracked into carbon atom fragments with high activity under the high-temperature condition and the catalysis of the catalyst; (2) The carbon atoms are dissolved and diffused on the surface or the bulk phase of the catalyst particles; (3) After carbon in the catalyst is saturated, carbon atoms are separated out on the surface of the catalyst particles and are mutually connected to form five-membered rings and six-membered rings, and a carbon cap structure is formed by nucleation; (4) Under the continuous supply of carbon source, the open end of the carbon cap is continuously combined with carbon atoms to prepare the single-walled carbon nanotube.
Therefore, the catalyst adopted in the CVD method is important, and the stability and the dispersibility of active components such as iron, cobalt, nickel and the like are important to maintain, so that the obtained single-wall carbon nano tube can be ensured; the size of the active catalyst particles is maintained, the diameter of the carbon nano tube can be effectively controlled, and the effective length-diameter ratio is obtained. The existing CVD catalyst porous powder carriers are prepared by loading active metals on the surfaces of carriers, and after the active metals react at high temperature, the dispersed active metals are easy to agglomerate, so that the activity is reduced, and the pore sizes of the prepared carbon nanotubes are greatly different.
In order to solve the above problems, the present invention provides a catalyst for preparing single-walled carbon nanotubes, comprising porous silica, nano-iron-based metal and nano-rare earth metal, wherein the nano-iron-based metal is embedded in the body and inner and outer surfaces of the porous silica, and the nano-lanthanoid metal is uniformly dispersed on the outer surface of the porous silica.
Disclosure of Invention
The invention aims to solve the defects in the prior art, and provides a catalyst for preparing single-walled carbon nanotubes and a preparation method thereof, wherein the catalyst provided by the invention has good stability, active components are not agglomerated under the high temperature condition, the diameter of the prepared single-walled carbon nanotubes is uniform, the active components of the catalyst are distributed on the body of a carrier and the inner and outer surfaces of the carrier, and the active components of the catalyst and the carrier have strong interaction, so that the active components are uniformly dispersed and are not easy to agglomerate; the content of the active component on the carrier body and the inner and outer surfaces can be regulated and controlled by a preparation method, and can be regulated according to actual requirements and different specific active components; the rare earth oxide is uniformly dispersed on the carrier area, the rare earth oxide can improve the dispersibility of the surface active iron metal, particularly in a high-temperature environment, the active metal can be effectively prevented from agglomerating and falling off, the rare earth oxide is connected to the surface of the carrier through the silane coupling agent, and the rare earth oxide is uniformly distributed and is not easy to fall off.
The invention provides a catalyst for preparing single-wall carbon nanotubes, which comprises porous silicon oxide, nano iron metal and nano rare earth oxide, wherein the nano iron metal is embedded in the body and the inner and outer surfaces of the porous silicon oxide, and the nano rare earth oxide is uniformly dispersed on the surface of the porous silicon oxide.
In the catalyst, the weight content of porous silicon oxide is 80-95%, the content of nano iron metal is 1-15%, and the content of rare earth oxide is 2-5%. Preferably, the content of the porous silicon oxide is 85-95%, the content of the nano iron-based metal is 1-12%, and the content of the rare earth oxide is 2-4%. Further preferably, the content of porous silica is 85-90%, the content of nano iron-based metal is 6-11%, and the content of rare earth oxide is 2-4%.
Through researches, the nano iron-based metal is uniformly embedded in the porous silica body and the inner and outer surfaces within the content range of the components, the rare earth oxide and the nano iron-based metal can cooperate, the catalyst activity is high, and the obtained single-walled carbon nanotube has uniform tube diameter; the catalyst has good high-temperature stability, and can keep high catalytic activity in high-temperature and long-time catalytic reaction; in particular, the activity is highest in the range of 85-90% of porous silicon oxide, 6-11% of nano iron metal and 2-4% of rare earth oxide, and the high-temperature stability is best.
Furthermore, the content of the nano iron-based metal embedded in the porous silica body and the inner and outer surfaces of the porous silica body can be adjusted by a preparation method, and the content ratio of the nano iron-based metal embedded in the porous silica body to the inner and outer surfaces is preferably 1-10:1, more preferably 2-8:1, still more preferably 2-5:1, and most preferably 3-4:1; it has been found that the stability and activity of the catalyst can be ensured by adjusting the content of the nano iron-based metal in the porous silica support body and the inner and outer surfaces, and it has been further found that when the content ratio of the nano iron-based metal embedded in the porous silica support body is 1-10:1, the catalyst has good activity and good stability, and further preferably 2-5:1, and most preferably 3-4:1, the catalyst has good activity and excellent stability.
Further, the nano-iron-based metal of the present invention is one or more of iron, cobalt and nickel, more preferably two or more of iron, cobalt and nickel, and most preferably iron and nickel or iron and cobalt. Wherein further, the molar ratio of iron to nickel is 2-5:1; the molar ratio of iron to cobalt is 2-4:1, and the research shows that the iron and nickel, iron and cobalt are used as iron series active metals to be doped into the body of porous silicon oxide and embedded into the inner and outer surfaces together, so that the activity and stability of the catalyst can be improved, and the molar ratio of iron to nickel is 2-5:1; better performance is obtained with a molar ratio of iron to cobalt in the range of 2-4:1.
Further, the rare earth oxide of the catalyst is one or more oxides of rare earth elements scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm) and europium (Eu), and preferably, the rare earth oxide is one or more oxides of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr) and neodymium (Nd); preferably, the rare earth metal oxide is specifically one or more of lanthanum oxide, cerium oxide or praseodymium oxide, and most preferably lanthanum oxide and cerium oxide, wherein the molar ratio of lanthanum oxide to cerium oxide is 3-7:1, and most preferably 4:1; it was found that the use of lanthanum oxide and cerium oxide can better improve the activity and stability of the catalyst than one or three rare earth metal elements, and that the best effect can be obtained when the molar ratio of lanthanum oxide to cerium oxide is 4:1.
Further, the porous silica in the catalyst of the present invention is not limited to a specific kind, and the porous silica generally contains micropores, mesopores or macropores, and only needs to have a porous structure.
Further, the catalyst for preparing the single-walled carbon nanotube comprises porous silicon oxide, nano iron metal and nano rare earth oxide, wherein the nano iron metal is embedded in the body and the inner and outer surfaces of the porous silicon oxide, and the nano rare earth oxide is uniformly dispersed on the surface of the porous silicon oxide; the content of porous silicon oxide is 85-90%, the content of nano iron metal is 8-12%, and the content of rare earth oxide is 3-4%; the content ratio of the nano iron-based metal embedded porous silicon oxide body to the inner surface and the outer surface is 3-4:1; the nano iron-based metal is iron and nickel or iron and cobalt; the rare earth metal oxides are specifically lanthanum oxide and cerium oxide.
In another aspect of the present invention, there is provided a method for preparing a catalyst for preparing single-walled carbon nanotubes, the method comprising the steps of:
(1) Dissolving a nonionic surfactant in a mixed solution of deionized water and hydrochloric acid to form a nonionic surfactant solution A;
(2) Dissolving an iron-based metal salt solution in an organic acid solution to form an iron-based metal salt solution B;
(3) Under the condition of stirring, simultaneously dropwise adding an iron-based metal salt solution B and a silicon source into the solution A, then adjusting the pH value of the mixed solution, transferring the mixed solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction for 18-48h at the temperature of 100-150 ℃, cooling, filtering and drying to obtain a porous oxide containing iron-based metal;
(4) Dissolving rare earth metal salt solution in DMF solvent, stirring to dissolve; then adding an organic ligand, uniformly stirring, dropwise adding a proper amount of silane coupling agent, adding the porous oxide containing iron metal obtained in the step (3) into the mixed solution, uniformly stirring, transferring into a high-pressure reaction kettle, maintaining the temperature at 80-120 ℃, respectively cleaning and drying with deionized water and DMF, calcining for 1-5h at 500-600 ℃ in air atmosphere, and introducing hydrogen for reduction for 30-60min to obtain the catalyst.
The nonionic surfactant in the step (1) is any one or more of nonionic surfactants F108 and F127 (polyoxyethylene-polyoxypropylene polymerization), and P123 and P56 (polyoxyethylene ether-polyoxypropylene ether-polyoxyethylene ether triblock polymer).
The organic acid in the step (2) is one or more of acetic acid, citric acid, oxalic acid and malic acid, preferably one or two of citric acid and malic acid. The iron-based metal salt in the step (2) is nitrate, chloride, carbonate, sulfate or acetate of iron, cobalt or nickel; preferably, the catalyst is selected from the group consisting of ferric chloride, cobalt chloride, nickel chloride, cobalt nitrate, nickel nitrate, ferric sulfate, nickel sulfate, and cobalt sulfate.
The silicon source in the step (3) is ethyl orthosilicate; the pH in the step (3) is 3-6, further preferably 4-5, most preferably 4.5; the content of the iron-based metal in the porous silica body and the surface distribution, which is directly affected by the pH in the step (3), was found by the study, and it was found that the iron-based metal was best distributed in the porous silica body and the inner and outer surfaces when the ph=4.5, and a good catalytic activity was obtained.
The rare earth metal salt in the step (4) is one or more of nitrate, chloride or sulfate in rare earth metals scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm) and europium (Eu); further preferred are one or more of chloride and nitrate.
The organic ligand A in the step (4) is one of terephthalic acid, trimesic acid, 2-amino terephthalic acid and 1, 4-phthalic acid; the ratio of the rare earth metal salt to the organic ligand in the amount of the substance in the step (4) is 1:2 to 9, preferably 1:2 to 4.
The Silane coupling agent in the step (4) is Silane-PEG-COOH, and the weight ratio of the Silane coupling agent to the organic ligand is 1:5-15, and more preferably 1:8-12.
In another aspect, the present invention provides a method for preparing single-walled carbon nanotubes, specifically, a catalyst prepared by the above catalyst preparation method or a single-walled carbon nanotube prepared by the above catalyst.
The method for preparing the single-walled carbon nanotube adopts a chemical vapor deposition method, and comprises the following specific preparation methods: bubbling ethanol with 70-120ml/min hydrogen, introducing steam into the reactor, adjusting the temperature of the center of the reactor to 750-950 ℃ and growing for 8-20min; stop bubbling at 100ml/min H 2 And cooling to room temperature under the protection of 300ml/min Ar to obtain the single-walled carbon nanotube.
The single-walled carbon nanotube obtained by the preparation method provided by the invention has uniform tube diameter, the tube diameter is intensively distributed at 1-3nm, the single-walled carbon nanotube prepared by the catalyst provided by the application has high yield, the catalyst has good activity, and the high dispersity and stability can be maintained in a high-temperature environment.
The invention has the following beneficial effects:
the catalyst provided by the invention has a special structure, the iron-based active metal is embedded in the porous silica carrier body and the inner and outer surfaces, the active metal is fixed by the silica, the aggregation of the active metal and the loss of the active metal under the high-temperature reaction condition can be prevented, and the catalytic activity and the high-temperature stability of the catalyst are improved.
According to the invention, a part of active metal component is embedded in the porous silica carrier inner body, a part of active metal component is embedded in the porous silica outer surface, and the catalyst structure is stable; the invention realizes the adjustment of the content of active metal in the porous carrier body and the outer surface by adjusting the pH value of the solution during solvothermal reaction, and the method is the method proposed by the inventor for the first time, and can efficiently adjust the activity of the catalyst.
The rare earth metal oxide is uniformly dispersed on the outer surface of the porous silica carrier of the catalyst, the rare earth metal oxide is fixed on the surface of the porous silica carrier through a silica rare earth metal bond, and the rare earth metal oxide on the outer surface has higher high-temperature catalytic stability and better activity than the common impregnated oxide; and researches show that the type and composition of rare earth metal oxide have important influence on the stability and catalytic activity of the catalyst; the rare earth metal oxide can improve the high temperature stability and activity of the active metal.
The invention adds silane coupling agent into the solution containing porous oxide of iron metal, rare earth metal element and organic ligand, fixes part of rare earth metal oxide on the outer surface of porous silicon oxide carrier through solvothermal reaction, the catalyst obtained by the preparation method has good high temperature stability, rare earth metal oxide can be stabilized on the outer surface of porous silicon oxide carrier, and can not fall off or transfer due to high temperature.
According to the invention, a great amount of researches show that when the iron-based metal only contains iron and cobalt, the iron and the nickel are doped into the body of the porous silicon oxide and embedded into the inner and outer surfaces, the activity and the stability of the catalyst can be improved, and the molar ratio of the iron to the nickel is 2-5:1; better performance is obtained with a molar ratio of iron to cobalt in the range of 2-4:1.
The invention discovers through practical production that the kind and the content of rare earth metal oxide can have important influence on the high-temperature stability and the activity of the catalyst.
The method is characterized in that the method adopts the iron-based metal to be doped into the porous silica carrier for the first time, then the iron-based metal is dried only after solvothermal reaction, the rare earth metal salt, the organic ligand and the silane coupling agent are directly added for solvothermal reaction without calcination, and then the reaction is performed at a high temperature.
Drawings
FIG. 1 is an SEM image of single-walled carbon nanotubes prepared by obtaining a catalyst 1 according to example 1 of the present invention;
FIG. 2 is a TEM image of single-walled carbon nanotubes prepared by the catalyst 1 obtained in example 2 of the present invention;
FIG. 3 is an SEM image of single-walled carbon nanotubes prepared by obtaining catalyst 8 according to example 8 of the present invention;
FIG. 4 is a TEM image of single-walled carbon nanotubes prepared by the catalyst 8 obtained in example 8 of the present invention;
fig. 5 is an SEM image of single-walled carbon nanotubes prepared from the catalyst E2 obtained in comparative example 2.
Detailed Description
The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to fig. 1 to 5 of the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a catalyst for preparing single-wall carbon nanotubes, which comprises porous silicon oxide, nano iron metal and nano rare earth oxide, wherein the nano iron metal is embedded in the body and the inner and outer surfaces of the porous silicon oxide, and the nano rare earth oxide is uniformly dispersed on the surface of the porous silicon oxide.
In the catalyst, the weight content of porous silicon oxide is 80-95%, the content of nano iron metal is 1-15%, and the content of rare earth oxide is 2-5%. Preferably, the content of the porous silicon oxide is 85-95%, the content of the nano iron-based metal is 1-12%, and the content of the rare earth oxide is 2-4%. Further preferably, the content of porous silica is 85-90%, the content of nano iron-based metal is 6-11%, and the content of rare earth oxide is 2-4%.
Further, the content ratio of the nano-iron-based metal embedded porous silica body to the inner and outer surfaces is 1-10:1, preferably 2-8:1, more preferably 2-5:1, and most preferably 3-4:1.
Further, the nano-iron-based metal of the present invention is one or more of iron, cobalt and nickel, more preferably two or more of iron, cobalt and nickel, and most preferably iron and nickel or iron and cobalt. Wherein further, the molar ratio of iron to nickel is 2-5:1; the molar ratio of iron to cobalt is 2-4:1.
Further, the rare earth oxide of the catalyst is one or more oxides of rare earth elements scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm) and europium (Eu), and preferably, the rare earth oxide is one or more oxides of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr) and neodymium (Nd); preferably, the rare earth metal oxide is specifically one or more of lanthanum oxide, cerium oxide or praseodymium oxide, and most preferably lanthanum oxide and cerium oxide, and the molar ratio of lanthanum oxide to cerium oxide is 3-7:1, and most preferably 4:1.
Further, the porous silica in the catalyst of the present invention is not limited to a specific kind, and the porous silica generally contains micropores, mesopores or macropores, and only needs to have a porous structure.
In another aspect of the present invention, there is provided a method for preparing a catalyst for preparing single-walled carbon nanotubes, the method comprising the steps of:
(1) Dissolving a nonionic surfactant in a mixed solution of deionized water and hydrochloric acid to form a nonionic surfactant solution A;
(2) Dissolving an iron-based metal salt solution in an organic acid solution to form an iron-based metal salt solution B;
(3) Under the condition of stirring, simultaneously dropwise adding an iron-based metal salt solution B and a silicon source into the solution A, then adjusting the pH value of the mixed solution, transferring the mixed solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction for 18-48h at the temperature of 100-150 ℃, cooling, filtering and drying to obtain a porous oxide containing iron-based metal;
(4) Dissolving rare earth metal salt solution in DMF solvent, stirring to dissolve; then adding an organic ligand, uniformly stirring, dropwise adding a proper amount of silane coupling agent, adding the porous oxide containing iron metal obtained in the step (3) into the mixed solution, uniformly stirring, transferring into a high-pressure reaction kettle, maintaining the temperature at 80-120 ℃, respectively cleaning and drying with deionized water and DMF, calcining for 1-5h at 500-600 ℃ in air atmosphere, and introducing hydrogen for reduction for 30-60min to obtain the catalyst.
The nonionic surfactant in the step (1) is any one or more of nonionic surfactants F108 and F127 (polyoxyethylene-polyoxypropylene polymerization), and P123 and P56 (polyoxyethylene ether-polyoxypropylene ether-polyoxyethylene ether triblock polymer).
The organic acid in the step (2) is one or more of acetic acid, citric acid, oxalic acid and malic acid, preferably one or two of citric acid and malic acid. The iron-based metal salt in the step (2) is nitrate, chloride, carbonate, sulfate or acetate of iron, cobalt or nickel; preferably, the catalyst is selected from the group consisting of ferric chloride, cobalt chloride, nickel chloride, cobalt nitrate, nickel nitrate, ferric sulfate, nickel sulfate, and cobalt sulfate.
The silicon source in the step (3) is ethyl orthosilicate; the pH in the step (3) is 3-6, further preferably 4-5, most preferably 4.5.
The rare earth metal salt in the step (4) is one or more of nitrate, chloride or sulfate in rare earth metals scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm) and europium (Eu); further preferred are one or more of chloride and nitrate.
The organic ligand A in the step (4) is one of terephthalic acid, trimesic acid, 2-amino terephthalic acid and 1, 4-phthalic acid; the ratio of the rare earth metal salt to the organic ligand in the amount of the substance in the step (4) is 1:2 to 9, preferably 1:2 to 4.
The Silane coupling agent in the step (4) is Silane-PEG-COOH, and the weight ratio of the Silane coupling agent to the organic ligand is 1:5-15, and more preferably 1:8-12.
In another aspect, the present invention provides a method for preparing single-walled carbon nanotubes, specifically, a catalyst prepared by the above catalyst preparation method or a single-walled carbon nanotube prepared by the above catalyst.
The method for preparing the single-walled carbon nanotube adopts a chemical vapor deposition method, and comprises the following specific preparation methods: bubbling ethanol with 70-120ml/min hydrogen, introducing steam into the reactor, adjusting the temperature of the center of the reactor to 750-950 ℃ and growing for 8-20min; stop bubbling at 100ml/min H 2 And cooling to room temperature under the protection of 300ml/min Ar to obtain the single-walled carbon nanotube.
The invention will be further illustrated with reference to specific examples
Example 1
4.0g F127 was dissolved in a mixed solution of 20ml deionized water and 3ml1M hydrochloric acid, and stirred at 45℃for 2 hours to form a nonionic surfactant solution A; weighing ferric nitrate and nickel nitrate with the total mass of 2.0g, wherein the molar ratio of the ferric nitrate to the nickel nitrate is 3:1, adding metal salt into citric acid solution, and stirring for 4 hours to form iron-series metal salt solution B; under the condition of stirring, simultaneously dropwise adding an iron-based metal salt solution B and 12.3g of tetraethoxysilane into the solution A, then adopting ammonia water to adjust the pH=4.5 of the mixed solution, transferring the mixed solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction for 24 hours at 120 ℃, cooling, filtering and drying to obtain a porous oxide containing iron-based metal; according to lanthanum oxide: weighing lanthanum chloride and cerium chloride with the total mass of 0.5g according to a cerium oxide molar ratio of 4:1, preparing into an aqueous solution, dripping the aqueous solution into a DMF solvent, and stirring until the solution is uniform; then adding 1.5g of trimesic acid, uniformly stirring, dropwise adding 0.15g of silane coupling agent, adding a certain amount of porous oxide containing iron metal obtained in the steps into the mixed solution, uniformly stirring, transferring to a high-pressure reaction kettle, maintaining the temperature at 110 ℃, respectively cleaning and drying with deionized water and DMF, calcining for 4 hours at 550 ℃ in air atmosphere, and introducing hydrogen for reduction for 50 minutes to obtain the catalyst 1.
The structure of the catalyst 1 was structurally characterized using a multifunctional high resolution Transmission Electron Microscope (TEM). The samples were pre-treated as follows before testing: taking a small amount of samples, fully dispersing the samples in absolute ethyl alcohol under ultrasonic oscillation, then taking a drop of carbon film deposited on a copper grid support, airing the carbon film, placing the carbon film in an electron microscope for observation, and carrying out observation, wherein the body and the surface of a porous silicon oxide carrier contain nano metal particles, and the size of the metal nano particles is 2nm.
The adsorption and desorption isotherms of the samples were determined using an ASAP2020 surface area nitrogen analyzer under liquid nitrogen conditions. Samples were subjected to vacuum prior to testing. The test results showed that catalyst 1 had a porous structure, and the specific surface area of the catalyst was 752.1m as calculated by the BET model and BJH model 2 /g; the average pore diameter was 5.2nm.
And taking part of samples for composition analysis, wherein the content of silicon oxide, iron, nickel and cerium in the catalyst obtained through analysis is 87.9%, 5.8%, 2.1%, 2.4% and 0.6%.
Measuring and analyzing the content of active metal and the content of bulk active metal in the surface layer of a sample, firstly taking a proper amount of sample, soaking the sample for 0.5h by adopting hydrochloric acid, filtering to obtain filtrate and filter residue powder, and measuring the content of active metal iron and nickel in the filtrate; dissolving filter residues by adopting HF acid, and then measuring the content of active metal iron and nickel in the dissolved solution; because the active metal embedded on the surface of the porous silica carrier can be dissolved in hydrochloric acid solution, the active metal embedded on the body framework is preserved due to the coverage of the silica; then, dissolving silicon oxide by adopting hydrofluoric acid, exposing active metal on the body framework, and reacting with the hydrofluoric acid; the content of the active metal on the surface and in the body of the porous silicon oxide can be effectively measured by the measuring method. The results of the measurement of the active metal content distribution of the catalyst 1 are: the content ratio of the nano iron-based metal embedded porous silicon oxide body to the inner surface and the outer surface is 3.1:1.
Example 2
The procedure was consistent with the experimental procedure and method of example 1 except that the pH of the mixed solution was adjusted to 3 using aqueous ammonia, to obtain catalyst 2, and the same procedure was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Example 3
The procedure was consistent with the experimental procedure and method of example 1 except that the pH of the mixed solution was adjusted to 5.5 using aqueous ammonia, to obtain catalyst 3, and the same procedure was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Example 4
The iron nitrate and nickel nitrate raw materials were changed to cobalt nitrate and nickel nitrate, and the molar ratio of cobalt nitrate and nickel nitrate was 3:1, and the other steps were consistent with the experimental steps and methods of example 1, to obtain catalyst 4, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Example 5
2.0g of iron nitrate and nickel nitrate were changed to iron nitrate of equal mass, and the other steps were consistent with the experimental steps and methods of example 1, to obtain catalyst 5, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Example 6
2.0g of iron nitrate and nickel nitrate were changed to nickel nitrate of equal mass, and the other steps were consistent with the experimental procedure and method of example 1, to obtain catalyst 6, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Example 7
The catalyst 7 was obtained by replacing 2.0g of iron nitrate and nickel nitrate as raw materials with cobalt nitrate of equal mass and the other steps were consistent with the experimental steps and methods of example 1, and characterized by the same method, and the parameters of the obtained catalyst were as shown in table 1 below.
Example 8
The iron nitrate and nickel nitrate raw materials were changed to iron nitrate and cobalt nitrate in a molar ratio of 3:1, and the other steps were consistent with the experimental steps and methods of example 1, to obtain a catalyst 8, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Example 9
According to lanthanum oxide: lanthanum chloride and cerium chloride were weighed in a molar ratio of 3:1 and the total mass of lanthanum chloride and cerium chloride was 0.5g, and the other steps were consistent with the experimental procedure and method of example 1, to obtain catalyst 9, and the same method was used for characterization, and the parameters of the obtained catalyst were as shown in table 1 below.
Example 10
According to lanthanum oxide: lanthanum chloride and cerium chloride were weighed in a molar ratio of 7:1 and the total mass of lanthanum chloride and cerium chloride was 0.5g, and the other steps were consistent with the experimental procedure and method of example 1, to obtain catalyst 10, and the same method was used for characterization, and the parameters of the obtained catalyst were as shown in table 1 below.
Example 11
The lanthanum oxide and cerium oxide were replaced with lanthanum oxide of equal mass, and the other steps were consistent with the experimental procedure and method of example 1, to obtain catalyst 11, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Example 12
Lanthanum oxide and cerium oxide were replaced with equal mass of cerium oxide, lanthanum oxide and neodymium oxide, wherein the equimolar ratios of cerium oxide, lanthanum oxide and neodymium oxide were formulated, and the other steps were consistent with the experimental procedure and method of example 1, resulting in catalyst 12, and characterized by the same method, and the parameters of the resulting catalyst are shown in table 1 below.
Example 13
The rare earth metal salt of example 5 was replaced with lanthanum chloride, and the other steps were consistent with the experimental steps and methods of example 5, to obtain catalyst 13, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Examples 14 to 16
The amount of the organic silicon, the amount of lanthanum chloride and the amount of the rare earth metal salt added in example 13 were adjusted, and the other steps were the same as those of the experimental step and method of example 13, to obtain catalysts 14 to 16, and the same method was used for characterization, and the parameters of the obtained catalysts are shown in table 1 below.
Comparative example 1
The pH in the preparation was adjusted to 1.5, and the other steps were consistent with the experimental procedure and method of example 13, to give comparative catalyst E1, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Comparative example 2
The pH in the preparation was adjusted to 7, and the other steps were consistent with the experimental procedure and method of example 13, to give comparative catalyst E2, and the same method was used for characterization, and the parameters of the obtained catalyst are shown in table 1 below.
Comparative example 3
The addition amount of the organic silicon, the addition amount of lanthanum chloride and the addition amount of the rare earth metal salt in example 13 were adjusted, and other steps were kept in agreement with the experimental steps and methods of example 13, to obtain comparative catalysts E3 to E4, and the same methods were used for characterization, and the parameters of the obtained catalysts are shown in table 1 below.
Table 1 characterization of physical parameters of the catalysts
Figure BDA0003949946510000111
Figure BDA0003949946510000121
Figure BDA0003949946510000131
Application example
Adding the same amount of catalyst into a reactor, introducing mixed gas of nitrogen and hydrogen into the reactor to exhaust air, then bubbling ethanol with 100ml/min hydrogen, introducing steam into the reactor, regulating the central temperature of the reactor to 800 ℃ by a temperature programming mode, and growing for 50min (time)The long time can judge the high temperature stability according to the growth length of the carbon nano tube, and the longer the carbon nano tube is, the better the stability and the better the activity of the catalyst are; stopping bubbling at 100ml/min H 2 And cooling to room temperature under the protection of 300ml/min Ar to obtain the single-walled carbon nanotube.
The morphology of SWNTs samples was observed using SEM (Hitachi, reglus 8100) and TEM (JEOL, JEM-2100F). To count the diameter distribution of SWNTs samples, AFM (Briak, multiMode 8-HR) characterization was performed, the AFM image was smoothed, and the diameter information was obtained by measuring the height difference of SWNTs. The structural feature information of the SWNTs obtained is as follows:
TABLE 2 corresponding carbon nanotube parameters prepared with catalysts
Figure BDA0003949946510000132
Figure BDA0003949946510000141
The data in table 2 shows that the size of the nano-metal particles on the surface of the catalyst affects the diameter of the corresponding carbon nanotubes, wherein the type and amount ratio of the active metal, the type and amount of the rare earth metal, and the amount ratio of the active metal on the porous silica support body and the outer surface are both effective on the length and diameter of the single-walled carbon nanotubes, and the above effects reflect the high-temperature activity and stability of the catalyst. And controlling the average diameter of the active metal nanoparticles to be between 2.0 and 3.0nm can facilitate nucleation and growth of single-walled carbon nanotubes thereon, excessive catalyst surfaces may be prone to carbon coating.
The active iron metal on the surface of the catalyst is semi-embedded or partially embedded on the porous silicon oxide carrier, the active metal and the porous silicon oxide have larger acting force, the active metal can be fixed, the growth mechanism of the carbon nano tube grows according to the bottom growth mode, the longer single-wall carbon nano tube can be obtained in the mode, and the single-wall carbon nano tube with uniform diameter can be obtained.
Fig. 1-2 show SEM images and TEM images of single-walled carbon nanotubes prepared by the catalyst 1 according to the present invention, and it can be seen from the images that the obtained single-walled carbon nanotubes have a relatively uniform diameter, a relatively long length, and a small average diameter.
FIG. 3 is an SEM image and a TEM image of single-walled carbon nanotubes prepared by the catalyst 8 obtained in example 8 of the present invention; it can be seen from the figure that the obtained single-walled carbon nanotubes have relatively uniform diameter, longer length and small average diameter.
FIG. 5 is an SEM image of single-walled carbon nanotubes prepared from the catalyst E2 obtained in comparative example 2; it can be seen from the figure that the obtained single-walled carbon nanotubes are not uniform in diameter size and are relatively large in diameter.
Finally, it should be noted that: the foregoing description is only illustrative of the preferred embodiments of the present invention, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments described, or equivalents may be substituted for elements thereof, and any modifications, equivalents, improvements or changes may be made without departing from the spirit and principles of the present invention.

Claims (12)

1. The catalyst for preparing single-wall carbon nanotube includes porous silica, nanometer iron metal and nanometer RE oxide, and features that the nanometer iron metal is embedded inside the body and the inner and outer surfaces of the porous silica and the nanometer RE oxide is dispersed homogeneously on the outer surface of the porous silica.
2. The catalyst according to claim 1, wherein the porous silica has a weight content of 80-95%, the nano-iron-based metal has a content of 1-15%, and the rare earth oxide has a content of 2-5%; preferably, the content of the porous silicon oxide is 85-95%, the content of the nano iron-based metal is 1-12%, and the content of the rare earth oxide is 2-4%; further preferably, the content of porous silica is 85-90%, the content of nano iron-based metal is 6-11%, and the content of rare earth oxide is 2-4%.
3. The catalyst according to claim 1, wherein the nano-iron-based metal intercalated porous silica body is present in an amount of 1-10:1, preferably 2-8:1, further preferably 2-5:1, most preferably 3-4:1, relative to the inner and outer surfaces.
4. The catalyst according to claim 1, wherein the nano-iron-based metal is one or more of iron, cobalt, and nickel, more preferably two or more of iron, cobalt, and nickel, and most preferably iron and nickel or iron and cobalt; the molar ratio of iron to nickel is 2-5:1; the molar ratio of iron to cobalt is 2-4:1.
5. The catalyst according to any one of claims 1 to 4, wherein the rare earth oxide is one or more oxides of the rare earth elements scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), preferably the rare earth oxide is selected from the oxides of one or more rare earth metals of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd); preferably, the rare earth metal oxide is specifically one or more of lanthanum oxide, cerium oxide or praseodymium oxide, and most preferably lanthanum oxide and cerium oxide, and the molar ratio of lanthanum oxide to cerium oxide is 3-7:1, and most preferably 4:1.
6. A process for preparing the catalyst of any one of claims 1 to 5, comprising the steps of:
(1) Dissolving a nonionic surfactant in a mixed solution of deionized water and hydrochloric acid to form a nonionic surfactant solution A;
(2) Dissolving an iron-based metal salt solution in an organic acid solution to form an iron-based metal salt solution B;
(3) Under the condition of stirring, simultaneously dropwise adding an iron-based metal salt solution B and a silicon source into the solution A, then adjusting the pH value of the mixed solution, transferring the mixed solution into a hydrothermal reaction kettle, carrying out hydrothermal reaction for 18-48h at the temperature of 100-150 ℃,
cooling, filtering and drying to obtain porous oxide containing iron metal;
(4) Dissolving rare earth metal salt solution in DMF solvent, stirring to dissolve; then adding the organic ligand and stirring uniformly,
and (3) dropwise adding a proper amount of silane coupling agent, adding the porous oxide containing the iron-based metal obtained in the step (3) into the mixed solution, uniformly stirring, transferring into a high-pressure reaction kettle, maintaining the temperature at 80-120 ℃, respectively cleaning and drying with deionized water and DMF, calcining for 1-5h at 500-600 ℃ in air atmosphere, and introducing hydrogen for reduction for 30-60min to obtain the catalyst.
7. The preparation method according to claim 6, wherein the nonionic surfactant in the step (1) is any one or more of nonionic surfactants F108, F127 (polyoxyethylene-polyoxypropylene polymerization), P123, P56 (polyoxyethylene-polyoxypropylene-polyoxyethylene-triblock polymer).
8. The method according to claim 6, wherein the organic acid in the step (2) is one or more of acetic acid, citric acid, oxalic acid and malic acid, preferably one or two of citric acid and malic acid; the iron-based metal salt in the step (2) is nitrate, chloride, carbonate, sulfate or acetate of iron, cobalt or nickel; preferably, the catalyst is selected from the group consisting of ferric chloride, cobalt chloride, nickel chloride, cobalt nitrate, nickel nitrate, ferric sulfate, nickel sulfate, and cobalt sulfate.
9. The method according to any one of claims 6 to 8, wherein the silicon source in the step (3) is ethyl orthosilicate; the pH in the step (3) is 3-6, further preferably 4-5, most preferably 4.5.
10. The method according to any one of claims 6 to 9, wherein the rare earth metal salt in the step (4) is one or more of nitrate, chloride or sulfate of rare earth metals scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu); further preferred are one or more of chloride and nitrate;
the organic ligand A in the step (4) is one of terephthalic acid, trimesic acid, 2-amino terephthalic acid and 1, 4-phthalic acid; the ratio of the rare earth metal salt to the organic ligand in the step (4) is 1:2-9, preferably 1:2-4;
the Silane coupling agent in the step (4) is Silane-PEG-COOH, and the weight ratio of the Silane coupling agent to the organic ligand is 1:5-15, and more preferably 1:8-12.
11. A method for producing single-walled carbon nanotubes, characterized in that the single-walled carbon nanotubes are produced using the catalyst produced by the production method of any one of claims 6 to 10 or the catalyst of any one of claims 1 to 5.
12. The method of claim 11, wherein the method for preparing single-walled carbon nanotubes is performed by chemical vapor deposition, and the specific preparation method is as follows: bubbling ethanol with 70-120ml/min hydrogen, introducing steam into the reactor, adjusting the temperature of the center of the reactor to 750-950 ℃ and growing for 8-20min; stopping bubbling at 100ml/min H 2 And cooling to room temperature under the protection of 300ml/min Ar to obtain the single-walled carbon nanotube.
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