KR100599875B1 - Method of manufacturing carbon nanofibers using mechanochemically activated catalyst - Google Patents

Abstract

The present invention relates to a method for producing a high quality carbon nanofiber having a chemically stable and uniform structure, and specifically, to a transition metal supported catalyst by mechanochemical treatment of a catalyst precursor, which is a hydroxide of a transition metal, and a carrier, which is a hydroxide of a metal. Preparing, reducing the transition metal supported catalyst to hydrogen gas, and supplying a hydrocarbon gas at a temperature of 500 to 900 ° C. to grow carbon nanofibers on the reduced transition metal supported catalyst. Provided is a method for producing carbon nanofibers by chemical vapor deposition.

Description

Method for producing carbon nanofibers by mechanochemical treatment of catalysts {METHOD OF MANUFACTURING CARBON NANOFIBERS USING MECHANOCHEMICALLY ACTIVATED CATALYST}             

1 is a diagram of nickel hydroxide / magnesium hydroxide catalyst powder prepared by mechanical chemical bonding method by mixing nickel hydroxide as a metal catalyst precursor and magnesium hydroxide as a carrier and milling for 0, 60, 120 and 720 minutes, respectively. X-ray diffraction (XDR) graph,

FIG. 2 is a scanning electron microscope (SEM) photograph of the nickel hydroxide / magnesium hydroxide catalyst powder, and FIGS. 2A, 2B, 2C, and 2D show milling times of 0 minutes, 60 minutes, 120 minutes, and 360 minutes, respectively. ego,

FIG. 3 is an SEM image of carbon nanofibers grown by chemical vapor deposition using the nickel hydroxide / magnesium hydroxide catalyst powder. FIGS. 3A, 3B, 3C, and 3D show growth temperatures of carbon nanofibers at 600 ° C. and 700, respectively. In the case of ℃, 800 ℃ and 900 ℃,

FIG. 4 is an SEM image of carbon nanofibers grown by chemical vapor deposition using the nickel hydroxide / magnesium hydroxide catalyst powder, and FIGS. 4A, 4B, 4C, and 4D have milling times of 0 minutes, 60 minutes, and 120 minutes, respectively. And 360 minutes.

The present invention prepares a transition metal supported catalyst by mechanochemical treatment of a metal catalyst precursor having a hydroxyl group and a carrier, and grows carbon nanofibers on the catalyst by chemical vapor deposition to have a chemically stable and uniform structure. The present invention relates to a method for producing carbon nanofibers economically.

      Carbon nanofibers, also called graphite nanofibers or carbon filaments, are mainly manufactured by interacting hydrocarbon gases with high temperature metal particles. Since the 1970s, full-scale research has revealed the shape, microstructure and growth mechanisms of carbon nanofibers, and research on the control of diameter and mass synthesis has continued. The carbon nanofibers produced on the transition metal catalyst particles such as nickel, iron, and cobalt are very fine and have a diameter of about 100 to 200 nm, which is only about one hundredth of that of general carbon fibers having a diameter of about 10 μm. Carbon nanofibers are highly regarded as materials having high applicability in fields such as composite materials and electrode materials because of their excellent electrical conductivity, adsorption and mechanical properties.

Carbon nanofibers are produced by an electric discharge method, a laser sublimation method, a gas phase pyrolysis method and an electrolysis method of hydrocarbons, etc. These methods have low economical efficiency and have a problem of generating a large amount of amorphous carbon agglomerates during the synthesis process.

Recently, as a method for economically mass synthesizing high quality carbon nanofibers, a chemical vapor deposition method for growing carbon nanofibers on a catalyst by pyrolyzing hydrocarbons in the presence of transition metal catalysts such as nickel, cobalt and iron has been used. In the chemical vapor deposition method, a transition metal supported catalyst including various kinds of transition metal precursors and a carrier supporting the same may be used. The stability of carbon nanofibers grown on the catalyst, uniformity of diameter, shape and structure may be used. Varies greatly depending on the type and nature of the catalyst.

In the conventional supported catalyst production, a wet method using an impregnation method or an ion exchange method has been mainly used. However, in the case of preparing a supported catalyst for producing carbon nanofibers by the wet method, it is required to control many variables such as hydrogen ion concentration, amount of catalyst precursor to the carrier, impregnation time, and solvent. In addition, complex steps are required, such as impregnation of the precursor and carrier with a strong stirring action, followed by drying for a considerable time to obtain a powder, heat treatment at high temperature to maintain a stabilized powder.

 Accordingly, the present inventors mechanically pulverize a catalyst precursor and a carrier mixture of a metal material having a hydroxyl group to produce a carbon nanofiber by chemical vapor deposition, thereby generating a mechanochemical effect of inducing a change in crystal structure and a high surface area. By discovering that the transition metal supported catalyst can be prepared in a short time by a simple dry method, and by growing the carbon nanofibers on the transition metal supported catalyst by the thermochemical vapor deposition method, as compared to the instability of the wet method, a high quality carbon The present invention was completed by confirming that nanofibers can be economically produced.

An object of the present invention is to provide a catalytic technique for producing high quality carbon nanofibers economically by a relatively simple operation through a dry method rather than a wet method such as the conventional impregnation method.

According to the object, the present invention comprises the steps of 1) preparing a transition metal supported catalyst by mechanochemical treatment of a mixture of a transition metal hydroxide and a metal carrier; And 2) reducing the transition metal supported catalyst under a hydrogen atmosphere, to provide a method for producing a metal catalyst for producing carbon nanofibers.

The present invention provides a method for producing carbon nanofibers, comprising growing carbon nanofibers by supplying a hydrocarbon gas at a temperature of 500 to 900 ° C. to the metal catalyst prepared as described above.

Hereinafter, the present invention will be described in detail.

The method for producing a metal catalyst of the present invention is characterized by producing a metal catalyst for carbon nanofiber production by mixing a catalyst precursor, which is a transition metal hydroxide, and a metal carrier with a mechanochemical treatment. By the mechanochemical treatment of the mixture of the transition metal hydroxide and the metal carrier as described above, it is possible to prepare a transition metal supported catalyst that not only reduces the particle size but also uniformly mixes and increases the surface activity, preferably, the transition metal By applying the supported catalyst to a known chemical vapor deposition method, it can be used for producing uniform and stable high quality carbon nanofibers.

In step 1) according to the method for preparing a metal catalyst of the present invention, the mechanochemical treatment is performed by mechanically milling a mixture of a transition metal hydroxide and a metal carrier for 15 to 720 minutes at a speed of 600 to 1800 rpm. It may be carried out, and more preferably may be subjected to mechanical grinding for 60 to 180 minutes at a speed of 600 to 1800 rpm. For example, the transition metal hydroxide and the metal carrier are first mixed at a speed of 300 to 600 rpm, filled into a mixer mill, and then at a speed of 600 to 1800 rpm for 15 to 720 minutes, preferably 60 minutes. By milling for from 180 minutes, the mechanochemical treatment may be such that a change in the crystal structure of the catalyst occurs. In the above mechanical grinding process may be performed with a pause of about 1 minute at regular intervals of about 15 minutes. If desired, the mechanochemically treated catalyst may be further dried, for example at about 80 ° C. for about 24 hours, and the drying process may be carried out using a convection oven or the like. As shown in Figures 2a to 2d, as the milling time is increased, the small particles cluster into larger particles and break up into smaller particles again between 60 and 180 minutes and again in bulk form as the milling time is increased. Appear crowded. In addition, according to an embodiment of the present invention, when the milling time is 120 minutes or later, MgO appears, which shows that the mixture is ground and the crystal phase is changed by the high energy milling process. As such, particle size reduction and crystal phase change by mechanochemical treatment show that the transition metal-supported catalyst is not only small and uniform, but also has increased activity, which can be usefully used for producing high quality carbon nanofibers.

In the mechanochemically treated catalyst according to the present invention, the transition metal fine powder of 100 to 200 nm is fixed in a uniform and solid state on the surface of the carrier having a reduced particle size. Therefore, the term "transition metal supported catalyst" in the present invention means that the fine transition metal powder is uniformly and firmly fixed on the surface of the carrier according to the mechanochemical treatment method as described above, and thus can be used for reactions such as growth of carbon nanofibers. It is said that the activity is increased so that the transition metal hydroxide used to prepare the transition metal supported catalyst is abbreviated as "transition metal supported catalyst precursor" or simply "catalyst precursor".

In order to manufacture the catalyst used in chemical vapor deposition in an economically uniform quality, the catalyst can be supported on a carrier having a large surface area. Carbon nanofibers having a uniform shape can be obtained, and the occurrence of other carbon impurities can be suppressed by clustering the metal catalysts during high temperature reaction. In addition, compared to the case of using a single metal catalyst has the advantage that the mass production of carbon nanofibers and the shape control can be performed at the same time.

Nickel hydroxide (Ni (OH) ₂ ), iron hydroxide (Fe (OH) ₂ ), cobalt hydroxide (Co (OH) ₂ ) and mixtures thereof may be used as the transition metal hydroxide used as the catalyst precursor in the present invention. As a carrier supporting the transition metal from these catalyst precursors, various carriers such as oxides or carbonates can be used. In the case of using sulfides including carbonates as carriers, harmful gases may be generated during high temperature evaporation. More preferably, magnesium hydroxide (Mg (OH) ₂ ), aluminum hydroxide (Al (OH) ₃ ) and mixtures thereof are used.

In the above, the mixing ratio of the transition metal hydroxide serving as the catalyst precursor and the metal hydroxide serving as the carrier is in a molar ratio of 1: 0.1 to 1:10, more preferably 1: 1 to 1: 4.

As described above, by the method of the present invention for mechanochemical treatment of the transition metal hydroxide catalyst precursor and the metal carrier, it is possible to obtain the effect of increasing the surface activity through the crystal phase change along with the reduction of the size of the transition metal supported catalyst.

In step 2) of the catalyst preparation method of the present invention, the transition metal supported catalyst produced by the mechanochemical treatment by mixing the transition metal hydroxide and the metal carrier in the step 1) is pretreated by reducing in a hydrogen atmosphere. For example, a fine grain is formed on the surface of the catalyst particles by placing the mechanochemically treated transition metal supported catalyst in a high purity alumina boat in the presence of hydrogen gas and reducing for 20 to 30 minutes using an electric furnace equipped with a quartz tube. Can be formed.

The transition metal supported catalyst prepared according to the method of the present invention may be used for the production of carbon nanofibers by general chemical vapor deposition. Specifically, the transition metal supported catalyst reduced under a hydrogen atmosphere is 500 to 900 ° C., Preferably, carbon nanofibers are grown on the catalyst by supplying a hydrocarbon gas at a temperature of 600 to 800 ° C. At this time, the growth temperature of the carbon nanofibers is very important. If the growth temperature is lower than 500 ° C., the carbon nanofibers are hardly grown. If the growth temperature is higher than 900 ° C., the desorption rate of the hydrocarbon from the catalyst is greater than the diffusion rate. Is formed. As the hydrocarbon gas, acetylene (C ₂ H ₂ ), ethylene (C ₂ H ₄ ), methane (CH ₄ ), propane (C ₃ H ₈ ) and propylene (C ₃ H ₇ ) may be used. The carbon nanofibers grown according to the present invention may further include cooling under an argon atmosphere, for example, may be cooled under an argon atmosphere at a rate of about 4 ° C./min.

Carbon nanofibers grown in accordance with the present invention has a uniform particle size and structurally very stable form of about 100 to 200 nm, it can be usefully used in the field of composites, electrode materials and the like.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited by the embodiment.

Example 1 Preparation of Catalysts by Mechanochemical Treatment of Nickel Hydroxide / Magnesium Hydroxide

Nickel hydroxide and magnesium hydroxide were uniformly mixed at a speed of 600 rpm in a 1: 1 molar ratio of nickel and magnesium, and then charged into a tungsten carbide grinder and a speed of 1800 rpm using a grinding ball of the same material. Milled. The milling time was divided into 15 minutes, 30 minutes, 60 minutes, 120 minutes, 240 minutes, 360 minutes, 720 minutes, respectively, milling was carried out with a 1 minute rest at regular intervals of 15 minutes.

The obtained catalyst powder was analyzed using X-ray diffraction analysis (XRD) and scanning electron microscope (SEM), and XRD results and SEM images are shown in FIGS. 1 and 2, respectively.

The peak change of Ni (OH) ₂ and Mg (OH) ₂ phase was observed from FIG. 1, and MgO peak began to be observed after 120 minutes of milling time.

As the milling time increased, small particles clustered into large particles and when they reached 120 minutes again broken up into smaller particles, after which the particles clustered to take the form of bulk (Figs. 2a, 2b. 2c and 2d).

Example 2 Preparation of Carbon Nanofibers by Thermochemical Vapor Deposition Using Nickel / Magnesium Hydroxide Catalysts

The transition metal-supported catalyst powder of Example 1 obtained by mechanochemical treatment of nickel hydroxide / magnesium hydroxide was placed in a high purity alumina boat and reduced in a hydrogen atmosphere for 20 minutes using an electric furnace equipped with a quartz tube. Subsequently, acetylene gas was supplied to the reduced catalyst powder to grow carbon nanofibers on the catalyst, and then cooled in an argon atmosphere at a rate of 4 ° C./min to obtain carbon nanofibers.

In order to select the optimum carbon nanofiber growth temperature, the carbon nanofibers grown by applying the thermochemical vapor deposition method at 600 ° C, 700 ° C, 800 ° C and 900 ° C, respectively, were obtained, and a scanning electron microscope (SEM) The obtained carbon nanofibers were analyzed (Fig. 3a, 3b, 3c and 3d). 3a, 3b, 3c and 3d are the results of carbon nanofibers growth thermally vapor-deposited at 600 ° C., 700 ° C., 800 ° C. and 900 ° C. on transition metal supported catalysts prepared by milling for 120 minutes, respectively. As a result, when the growth temperature of the carbon nanofibers to 600 ℃ it was shown to induce the most desirable growth of high quality carbon nanofibers.

Meanwhile, carbon nanofibers were grown by thermochemical vapor deposition at 600 ° C. using catalysts prepared at various milling times, and the growth patterns of carbon nanofibers according to the change of milling time are shown in FIG. 4, FIGS. 4A, 4B, and 4C. And 4d are SEM images of carbon nanofibers prepared using a catalyst having milling times of 0 minutes, 60 minutes, 120 minutes, and 360 minutes, respectively. As can be seen from FIG. 4, the catalyst milled for 120 minutes was found to have the best growth characteristics, and the diameter of the carbon nanofibers obtained was uniform as 100 to 200 nm.

As described above, according to the method of the present invention, it is possible to economically produce high-quality carbon nanofibers which are chemically stable and uniform in structure, which can be usefully used in fields such as composite materials and electrode materials by a simple dry method.

Claims (12)

delete delete delete delete delete delete delete delete 1) preparing a transition metal supported catalyst by mechanochemical treatment of a mixture of a transition metal hydroxide and a metal hydroxide carrier; And 2) growing carbon nanofibers on the metal catalyst by supplying a hydrocarbon gas at a temperature of 500 to 900 ° C. to the metal catalyst prepared by the method comprising reducing the transition metal supported catalyst under a hydrogen atmosphere. A method of producing carbon nanofibers, comprising. The method of claim 9, Hydrocarbon gas is selected from acetylene, ethylene, methane, propane and propylene, the carbon nanofiber manufacturing method. The method of claim 9, Method for producing carbon nanofibers, characterized in that the growth temperature of the carbon nanofibers is 600 to 800 ℃. The method of claim 9, After the carbon nanofibers are grown, further comprising the step of cooling under an argon atmosphere, the carbon nanofibers manufacturing method.

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