KR20180131145A - Preparing method for ldh-based catalyst, catalyst prepared by the method, preparing method for ldh-based composite materials and composite materials prepared by the method - Google Patents

Abstract

The present invention relates to a method of preparing a dry reforming catalyst having a novel structure for syngas production. In particular, the method comprises: an LDH preparation step of producing a layered double hydroxide (LDH) by using Ni and a divalent cationic metal more difficult to reduce than Ni; and a catalyst preparation step of thermally treating the prepared LDH to cause only Ni, a divalent cation relatively easier to reduce, to be eluted on the surface. The present invention may produce a Ni catalyst having a novel structure by eluting only Ni from the LDH due to difference in reducing power. Also, the catalyst of the present invention has Ni evenly distributed on the surface of the LDH and also firmly bonded to the lattice of the LDH, and therefore, has excellent effects of reducing carbon accumulation and catalyst enlargement when applied to a dry reforming process for syngas production.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for producing a layered double hydroxide-based catalyst, a catalyst thus prepared, a method for producing a metal-eluted layered double hydroxide-based composite material and a composite material produced thereby, PREPARING METHOD FOR LDH-BASED COMPOSITE MATERIALS AND COMPOSITE MATERIALS PREPARED BY THE METHOD}

The present invention relates to a new structure of a catalyst and a method for producing a composite material, and more particularly to a new structure of a layered double hydroxide-based catalyst and a composite material and a method of manufacturing the same.

Currently, methane gas (CH ₄ ) and carbon dioxide (CO ₂ ), which are considered to be major causes of global warming, can be decomposed and decomposed to produce a syngas gas (CO + H ₂ ). Synthetic gas is an important mediator in the synthesis of chemical raw materials such as ammonia, methanol, acetic acid, DME (diethyl ether), synthetic gasoline and diesel, and environmentally clean raw materials. In order to synthesize clean raw materials, various molar ratios of hydrogen and carbon monoxide are required. Specifically, a molar ratio of 2: 1 is required for methanol synthesis, and a molar ratio of 1: 1 is required for synthesizing acetic acid or DME.

There are two main ways to convert methane gas and carbon dioxide to syngas (hydrogen and carbon monoxide): steam reforming of methane (SRM) and dry reforming of methane (DRM) ).

The production of syngas by the wet process is disadvantageous for the recycling of syngas, which has the highest efficiency when the production ratio of hydrogen and carbon monoxide is about 3: 1 at the ratio of 1: 1, and CO _{2, which} is a greenhouse gas, there is a problem. On the other hand, the dry method is very advantageous for the synthesis of syngas because the ratio of hydrogen to carbon monoxide is close to 1: 1, unlike the wet type. It is possible to simultaneously remove the CO ₂ greenhouse gas, which is the main cause of global warming, There is an advantage to be able to do. In addition, the dry process has the advantage of 20% lower syngas production costs than other methods.

On the other hand, the dry method requires a high heat of reaction to increase the reaction efficiency and uses a catalyst to lower the reaction temperature. In the case of Pt, Ru, Rh and Pd which are typical catalyst materials, the activity, selectivity and stability of the catalyst are good as noble metal, but they are too expensive to be used for industrial use.

As a substitute for such a noble metal catalyst, a Ni-based catalyst composition based on Ni, which has been confirmed to have good activity and selectivity, has been developed. Nickel is relatively inexpensive compared to other transition metals and has the advantage of having a relatively high selectivity and conversion to CO ₂ nitration of methane. However, there is a disadvantage in that the catalyst activity is rapidly vanished as the reaction time becomes longer due to the occurrence of carbon deposition (Coke Deposition) on the surface of the Ni catalyst just after the start of the reaction, I have a serious problem that I have to change to.

As a result, studies have been made to use Fe as an effort to develop catalytic materials that do not use noble metals or Ni. However, satisfactory results have not been obtained. Further, although a technique for performing dry reforming using a high temperature flame plasma without using a catalyst has been developed, there is a disadvantage in that equipment manufacturing cost and equipment operation cost are higher than when a catalyst is used.

Korean Patent Publication No. 10-2016-0107539 Korea Patent No. 10-1277123

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a catalyst capable of reducing carbon storage and enlargement by using Ni as a catalyst material, .

According to another aspect of the present invention, there is provided a method for preparing a layered double hydroxide-based catalyst, the method comprising the steps of: preparing a layered double hydroxide (LDH) containing a divalent cationic metal that is relatively less reducible than Ni and Ni; And a catalyst preparation step of dissolving only the Ni, which is a divalent cation that is relatively easily reduced, on the surface by heat-treating the produced layered double hydroxide.

The present invention provides a method for preparing a catalyst having a novel structure in which Ni is uniformly dispersed and strongly bonded to a support by a method of eluting Ni from the support itself, unlike the conventional catalyst production method in which Ni is simply deposited on a support.

Layered double hydroxide (LDH) is a substance capable of artificial synthesis and consists of divalent and trivalent cationic layers and is a cubic ionic saturate substance having a two-dimensional nanostructure in which various anions can be inserted between layers . It is also called a hydrotalcite compound because it has a structure similar to a natural mineral hydrotalcite (Mg ₆ Al ₂ (OH) ₁₆ CO ₃ -4H ₂ O).

The chemical formula of LDH is generally represented by [M ^{2 +} _{1 x} M ^{3 +} _x (OH) ₂ ] ^{x +} [(A ^m- ) _{x / m} -nH ₂ O] ^x- , M ^{2 +} may be composed of metals such as Mg, Zn, Fe, Ni and Cu, and M ^{3+ which} is a trivalent cation may be composed of metals such as Al, Cr and Ca. A ^m- inserted between layers can contain many organic and inorganic anions such as Cl ^- , NO ₃ ^- , SO ₄ ^2-, and so on.

In the process of producing such a layered double hydroxide, the present invention does not use only one metal as a divalent cation but uses a metal that is less likely to be reduced than Ni and Ni to be used together to produce a layered double hydroxide, and a Ni The layered double hydroxides prepared to be solely eluted were heat-treated to prepare dry reforming catalysts in which Ni eluted in the layered double hydroxide material support was dispersed and dispersed in an island shape.

The LHD preparation step can be coprecipitation or hydrothermal synthesis, and it is advantageous in that it can be easily processed by producing the layered double hydroxides supported by the one-pot method.

Mg is a divalent cation metal that is relatively difficult to reduce relative to Ni, and Al is a trivalent cation metal contained in the layered double hydroxide. It is possible to apply Ni as a method for manufacturing Mg-Al LDH.

In order for Ni to be reduced and eluted, it is preferable that the heat treatment in the catalyst production step is performed in an H ₂ gas atmosphere. The gas atmosphere in the heat treatment process is not particularly limited and may be performed in a nitrogen or argon atmosphere. However, when the heat treatment is performed in a hydrogen gas atmosphere, the reduction effect by hydrogen is enhanced and Ni is reduced at a relatively low temperature It is effective.

The heat treatment is preferably performed at a temperature of 200 ° C or higher. The temperature at which Ni is reduced and eluted is affected by various factors such as the gas atmosphere and the production method. However, when heat treatment is performed in an atmosphere in which hydrogen is flowed, elution due to reduction occurs at a temperature lower than 200 캜. The upper limit of the temperature is not specially defined, but when the temperature exceeds 650 ° C, the energy to be supplied is excessively excessive and the efficiency is deteriorated. In the case of hydrothermal synthesis, the crystallinity is better than that of coprecipitated layered hydroxides, which may increase the temperature required for elution.

A catalyst according to another aspect of the present invention is a layered double hydroxide (LDH) -based support prepared by the above-mentioned method and comprising at least two kinds of divalent cation metals; And Ni dispersed on the surface of the support, wherein the Ni is one of at least two divalent cationic metals contained in the layered double hydroxide, and at least two kinds of divalent cations contained in the layered double hydroxide And is formed by being eluted from the surface of the support due to the difference in reducing power between the cationic metals.

The catalyst of the present invention is described in a specific method including a production method, but this is because it is necessary to specify the catalyst by a manufacturing method to clearly specify the structure of the catalyst. Specifically, according to the above-described method for producing a catalyst, the position where Ni is eluted according to the crystal lattice of the layered double hydroxide is determined, and the bonding method and the bonding force between the eluted Ni and the layered double hydroxide, Since it differs from that which adheres to the layered double hydroxide, the composition of the catalyst can be clearly specified if it is specified by the production method.

At this time, in addition to Ni, the divalent cation metal contained in the layered double hydroxide may be Mg, and the trivalent cation metal contained in the layered double hydroxide may be Al.

A method for preparing a layered double hydroxide based composite material according to an aspect of the present invention includes the steps of preparing a layered double hydroxide (LDH) containing divalent cations and trivalent cations, wherein at least a part of the cations of the same ionic group An LDH producing step of producing a layered double hydroxide so as to include at least two kinds of metals having the same structure as the LDH; And a composite material production step of dissolving the metal on the surface by heat treatment of the produced layered double hydroxide to reduce cations, and the eluted metal is a substance which is relatively easily reduced in the cation of the same ionic water do.

At this time, the cation of the same ionic valence containing at least two kinds of metals having different reducing powers may be a divalent cation and / or a trivalent cation.

The method of producing such a composite material is preferably performed in an H ₂ gas atmosphere. When the heat treatment is performed in a hydrogen gas atmosphere, the reduction effect by hydrogen is enhanced and the reduction of the metal is performed at a relatively low temperature.

A composite material according to an aspect of the present invention comprises a base of a layered double hydroxide (LDH) material prepared by the above method and comprising a divalent cation and a trivalent cation; And a metal material dispersed and distributed on the surface of the base, wherein the layered double hydroxide comprises at least two kinds of metals in which at least a part of cations of the same ionic water have a difference in reducing power, Is one of metals containing at least two kinds or more and is formed by being eluted from the surface of the base due to a difference in reducing power.

At this time, the cation of the same ionic valence containing at least two kinds of metals having different reducing powers may be a divalent cation and / or a trivalent cation.

Since the composite material of the present invention is described in a specific method including the production method, as in the case of the catalyst, the composite material of the present invention is specified when the composition of the composite material is clearly specified, .

The present invention constituted as described above has the effect of producing a Ni catalyst of a new structure by eluting only Ni from the layered double hydroxide due to the difference in reducing power.

In addition, since the catalyst of the present invention is not only uniformly dispersed on the surface of the layered double hydroxide but also strongly bonded to the layered double hydroxide lattice, it is possible to prevent carbon accumulation and catalyst overtreatment when applied to a dry reforming process for synthesis gas production There is an excellent effect of reducing the problem caused by the problem.

Further, according to the present invention, it is possible to manufacture and provide a composite material of a novel structure in which metal is eluted and dispersed on the surface of the layered double hydroxide due to the difference in reducing power.

FIG. 1 is a flow chart showing a process of manufacturing a catalyst according to a first embodiment of the present invention.
2 is a schematic diagram showing the crystal structure of the layered double hydroxide produced in this embodiment.
FIG. 3 is a flowchart illustrating a process of manufacturing a catalyst according to a second embodiment of the present invention.
4 is a result of X-ray diffraction analysis of the layered double hydroxide produced by hydrothermal synthesis.
5 is a scanning electron micrograph of a layered double hydroxide prepared by hydrothermal synthesis.
6 is a scanning electron microscope (SEM) image of a catalyst prepared by hydrothermally treating a layered double hydroxide prepared by hydrothermal synthesis with flowing hydrogen.
7 is a graph comparing hydrogen adsorption capacities of the catalyst prepared by the method of this embodiment and the catalyst of the comparative example.
8 is a graph showing the results of performing a methane dry reforming reaction on a catalyst prepared by the method of this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, embodiments of the present invention will be described in detail.

FIG. 1 is a flow chart showing a process of manufacturing a catalyst according to a first embodiment of the present invention.

The first embodiment produces a layered double hydroxide (LDH) by coprecipitation followed by preparation of the catalyst.

First, a solution containing Mg ²⁺ , Al ³⁺ and Ni ²⁺ ion precursors is prepared. NaOH is added to the prepared solution to adjust the pH to 10 or more, followed by vigorous stirring for more than one day. Separate the precipitated powder with a centrifuge and wash. The precipitated powder can be dried in an oven at 60 ° C to obtain a layered double hydroxide.

The above process is a general method of preparing a layered double hydroxide (Mg-Al LDH) containing Mg and Al by a coprecipitation method. In this embodiment, unlike the conventional Mg-Al LDH, Ni precursor is used together to form a divalent cation And is characterized in that a layered double hydroxide containing Mg and Ni at the same time is produced.

The layered double hydroxide thus prepared is heat-treated at a temperature of 600 캜 in an H ₂ gas atmosphere to prepare a catalyst. In the case of performing the heat treatment in the H ₂ gas atmosphere, it was confirmed that the reduction tendency of the metal became strong and elution occurred at a temperature of 200 ° C. or more. However, in order to improve the heat treatment efficiency, the heat treatment was performed at 600 ° C. . Specifically, since Ni is easily reduced compared to Mg on the basis of electron affinity or ionization tendency, Ni is first reduced to a metal state in the heat treatment process and eluted from the surface of the layered double hydroxide. At this time, since the Ni is located at the crystal lattice of the layered double hydroxide, the position where the Ni is eluted is dispersed at a considerable distance from each other (hereinafter referred to as an island-like dispersed form) . Further, even if Ni is released from the crystal lattice of the layered double hydroxide by elution, it maintains a very strong bonding state with the crystal lattice, so that a strong bonding state that is comparable to that of attaching externally supplied Ni to the surface of the layered double hydroxide , Which can be expressed as Ni being located integrally bonded to the layered double hydroxide. The amount of Ni reduction can be controlled according to the content of H ₂ and the heat treatment temperature and time.

In detail, referring to FIG. 2 showing the crystal structure of a layered double hydroxide having Al and a divalent cation simultaneously containing Mg and Ni as trivalent cations produced in this embodiment, a bivalent and trivalent cationic layer Mg _Mx Ni _x Al ₁ -OH), Ni is located in the crystal lattice and the reduced Ni is eluted at the corresponding position, so that the positions where the Ni is eluted are separated from each other.

As described above, the catalyst prepared by the method of the present invention is used as a catalyst for a dry reforming process for producing syngas because the Ni eluted from the surface of the support composed of the layered double hydroxides is uniformly dispersed and uniformly distributed in the island- There is an excellent effect that the problems due to carbon deposition (coke deposition) and catalyst oversizing are reduced.

FIG. 3 is a flowchart illustrating a process of manufacturing a catalyst according to a second embodiment of the present invention.

In the second embodiment, a layered double hydroxide (LDH) is prepared by a hydrothermal synthesis method and then a catalyst is prepared.

First, a solution containing Mg ²⁺ , Al ³⁺ , Ni ²⁺ and Urea is prepared. The prepared solution is put into a hydrothermal synthesizer and reacted at 120 to 200 ° C. for 10 to 48 hours. Separate the precipitated powder with a centrifuge and wash. The layered double hydroxide can be obtained by drying the washed powder in an oven at 60 ° C.

The above process is a general method for producing a layered double hydroxide (Mg-Al LDH) containing Mg and Al by a hydrothermal synthesis method as in the first embodiment. However, in this embodiment, a Ni precursor is used together to form a Mg- The present invention is characterized in that a layered double hydroxide containing Mg and Ni is produced.

Thereafter, the layered double hydroxide is heat-treated in an H ₂ gas atmosphere to produce a catalyst, which is the same as in the first embodiment, and thus a detailed description thereof will be omitted.

FIG. 4 shows the results of X-ray diffraction analysis of the layered double hydroxides prepared by the hydrothermal synthesis method, and FIG. 5 is a scanning electron micrograph of the layered double hydroxides prepared by hydrothermal synthesis.

It can be confirmed that the crystal is a crystalline material in the X-ray diffraction pattern, and it can be confirmed that Ni and Mg are contained together with Al and Al.

In addition, it can be confirmed from the scanning electron microscope photograph that a layered double hydroxide having a thin sheet structure is produced.

6 is a scanning electron microscope (SEM) image of a catalyst prepared by hydrothermally treating a layered double hydroxide prepared by hydrothermal synthesis with flowing hydrogen.

As shown in the figure, a thin sheet structure is maintained even after the heat treatment, but bright colored Ni is eluted and dispersed on the surface. Furthermore, it can be seen that bright colored Nis show an island type dispersion form separated from each other.

Experiments were conducted to confirm the performance of the catalyst prepared by the method of this embodiment.

7 is a graph comparing hydrogen adsorption capacities of the catalyst prepared by the method of this embodiment and the catalyst of the comparative example.

As a comparative example, a catalyst prepared by immersing Mg-Al layered double hydroxide in a Ni precursor solution and simply adsorbing Ni on the surface was used. The solid line is the hydrogen adsorption capacity of the catalyst according to this embodiment, and the dotted line is the hydrogen adsorption capacity of the catalyst according to the comparative example.

As shown in the figure, it can be seen that the hydrogen adsorbing property is shown at high temperature, as compared with the comparative example in which Ni is widely adsorbed on the surface of the layered double hydroxide, which is simply a thin sheet structure. And that Ni is eluted from the lattice positions of the hydroxides so that Ni is dispersed and dispersed from each other.

8 is a graph showing the results of performing a methane dry reforming reaction on a catalyst prepared by the method of this embodiment.

As shown in the figure, it can be seen that the catalytic performance was not deteriorated in the course of performing the dry reforming reaction for 25 hours. This indicates that the catalyst of this embodiment is a catalyst in which the conventional Ni catalyst has carbon accumulation and non- And the activity of the catalyst is remarkably different from that of the disappearance of the catalyst rapidly as the reaction time elapses.

The catalyst preparation method according to the first embodiment and the second embodiment can be manufactured by a method in which a layered double hydroxide is produced by a one pot method and then only Ni is reduced, thus making it easy to manufacture.

Meanwhile, in the above-described embodiment, a method of preparing a catalyst for eluting Ni as a dry reforming catalyst for synthesis gas from a surface of a layered double hydroxide as a support has been described. However, due to the difference in reducing power, the metal is eluted on the surface of the layered double hydroxide Is not only applicable to Ni but also applicable to various divalent cations and trivalent cations which can constitute layered double hydroxides.

Hereinafter, the composite material in which the metal is eluted on the surface of the layered double hydroxide and the method for producing the same will be described.

When a layered double hydroxide containing two or more kinds of divalent cationic metals differing in reducing power is first prepared and then subjected to heat treatment, a divalent cation that is relatively easily reduced is added to the surface of the layered double hydroxide Lt; / RTI > Specifically, when a layered double hydroxide containing both a metal that is relatively easily reduced and a metal that is relatively difficult to reduce based on the electron affinity or the ionization tendency is heat-treated, the metal that can be easily reduced is first reduced and eluted, Only the metal can be eluted.

Likewise, when a layered double hydroxide containing two or more kinds of trivalent cationic metals having different reducing powers is first prepared and then subjected to heat treatment, a relatively reduced trivalent cation may be eluted on the surface of the layered double hydroxide .

The composite material produced by such a method is characterized in that a divalent and / or trivalent metal is eluted and adhered to the surface of the layered double hydroxide, and the eluted metal has a divalent or trivalent cation position in the crystal lattice of the hydroxide among the layers So that it is dispersed in an island shape and has a characteristic of maintaining a very strong bonding state with the crystal lattice.

Such a composite material may be applied as a metal catalyst widely dispersed in a support as a novel composite material having no new structure, or it may be applied as an electrode material of an electric storage medium, and may be applied in a wide variety of fields.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Those skilled in the art will understand. Therefore, the scope of protection of the present invention should be construed not only in the specific embodiments but also in the scope of claims, and all technical ideas within the scope of the same shall be construed as being included in the scope of the present invention.

Claims (16)

A step of preparing an LDH to produce a layered double hydroxide (LDH) simultaneously containing a divalent cationic metal which is relatively difficult to reduce than Ni and Ni; And
And a catalyst preparation step of dissolving only the Ni, which is a divalent cation which is liable to be relatively reduced, on the surface by heat-treating the produced layered double hydroxide, thereby preparing a layered double hydroxide-based catalyst.
The method according to claim 1,
Wherein the LDH preparation step is carried out by coprecipitation or hydrothermal synthesis.
The method according to claim 1,
Wherein the divalent cation metal which is relatively less likely to be reduced than Ni is Mg.
The method according to claim 1,
Wherein the trivalent cation metal contained in the layered double hydroxide is Al.
The method according to claim 1,
Wherein the heat treatment in the catalyst preparation step is performed in an H ₂ gas atmosphere.
The method according to claim 1,
Wherein the heat treatment in the catalyst preparation step is performed in a temperature range of 200 ° C or higher.
A catalyst prepared by the method of claim 1,
A support of a layered double hydroxide (LDH) material comprising at least two or more divalent cationic metals; And
And Ni dispersed and distributed on the surface of the support,
The Ni is one of at least two divalent cationic metals contained in the layered double hydroxide and is eluted from the surface of the support by the difference in reducing power between at least two divalent cationic metals contained in the layered double hydroxide Lt; / RTI > catalyst.
The method of claim 7,
Wherein the divalent cation metal contained in the layered double hydroxide is Mg other than Ni.
The method of claim 7,
Wherein the trivalent cation metal contained in the layered double hydroxide is Al.
The present invention relates to a process for preparing a layered double hydroxide (LDH) comprising a divalent cation and a trivalent cation, wherein at least a part of the cations of the same ionic group include at least two kinds of metals having different reducing powers, step; And
And a composite material production step of dissolving the metal on the surface by heat treatment of the produced layered double hydroxide to reduce cations,
Wherein the eluted metal is a substance that is relatively easily reduced in the cation of the same ionic water.
The method of claim 10,
Wherein the cation of the same ionic valence including at least two kinds of metals having different reducing powers is a divalent cation.
The method of claim 10,
Wherein the cations of the same ionic hydrogens including at least two kinds of metals having different reducing powers are trivalent cations.
The method of claim 10,
Wherein the heat treatment of the composite material manufacturing step is performed in an H ₂ gas atmosphere.
A composite material produced by the method of claim 10,
A base of a layered double hydroxide (LDH) material comprising divalent cations and trivalent cations; And
And a metallic material dispersed and distributed on the surface of the base,
Wherein the layered double hydroxide comprises at least two kinds of metals in which at least a part of cations of the same ionic water have a difference in reducing power,
Wherein the metal material is one of at least two kinds of metals and is formed by elution from the surface of the base due to a difference in reducing power.
15. The method of claim 14,
Wherein the cation of the same ionic valence including at least two kinds of metals having different reducing powers is a divalent cation.
15. The method of claim 14,
Wherein the cations of the same ionic valence containing at least two kinds of metals differing in reducing power are trivalent cations.

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