KR20030079443A - Nano tertiary ferrite catalyst for co2 decomposition and method for preparing the same - Google Patents

Abstract

PURPOSE: A nano tertiary ferrite catalyst having high carbon dioxide decomposition efficiency and a method for preparing the same are provided. CONSTITUTION: The nano tertiary ferrite catalyst is characterized in that it is represented as the following Formula: NixZn1-xFe2O4-δ, where x is 0.1 to 0.9, and δ is the extent of oxygen deficiency, wherein the nano ternary ferrite catalyst for decomposition of carbon dioxide is formed by adding 0.5 to 2.5 wt.% of Pt or Pd to nano ternary ferrite. The method of preparing the nano ternary ferrite catalyst for decomposition of carbon dioxide comprises the processes of manufacturing nano ternary ferrite powder of NixZn1-xFe2O4 (x=0.1 to 0.9) by hydrothermal synthesis or coprecipitation method using x mol (x=0.1 to 0.9) of Ni salt,(1-x) mol of Zn salt and 2 mol of Fe salt as starting raw materials; reducing the manufactured nano ternary ferrite powder at a hydrogen atmosphere; and manufacturing nano ternary ferrite catalyst by adding 0.5 to 2.5 wt.% of Pt or Pd to the reduced nano ternary ferrite powder by charge titration method.

Description

Nano tertiary ferrite catalyst for CO2 decomposition and method for preparing the same}

The present invention relates to a ternary ferrite catalyst for decomposing carbon dioxide, and more particularly, to a ternary ferrite catalyst in a nano-sized ultrafine powder state having high carbon dioxide decomposition efficiency and a method of manufacturing the same.

As global warming and abnormal weather due to the accumulation of CO ₂ gas in the atmosphere have emerged as a serious international environmental problem, developed countries have already made considerable efforts and investments in developing related technologies in various directions to reduce air pollution emissions. In particular, as one of the methods for reducing CO ₂ gas emission in exhaust gas, efforts have been made to develop a CO ₂ gas cracker using catalytic materials.

By the study on the catalytic material capable of decomposing the CO ₂ gas, to metals such as Fe, Ni, Ba, Ca, Sr, Al, Cu, Mg was found to possess the ability to decompose the CO ₂ gas In particular, the development of a CO ₂ gas cracker using the above metals as a catalyst has been made. However, when metals such as Fe, Ni, Ba, Ca, Sr, Al, Cu, and Mg are used as catalyst materials, most of them have a high reaction temperature and a low CO ₂ decomposition rate of 20% or less. For example, when a clean surface of Fe metal is exposed to a CO ₂ atmosphere, a H ₂ gas and Bosch reaction occurs at 527 to 627 ° C., at which time the CO ₂ decomposition rate is only very low 10 to 20%.

Ferrite is one of the materials that has recently attracted much attention as a catalyst material for improving the problems of the catalyst made of the above metal. The ferrite is synthesized by the ultra-fine powders of nano-size, if possess a crystal structure of oxygen deficient states, sikimyeo decomposition of CO ₂ gas to the C and the O ₂ gas, and the CO ₂ at a low temperature when there is H ₂ in CH ₄ Has the ability to convert Became known this fact has been research and development to develop a system in which the ferrite powder can reduce the CO ₂ pollution gas emissions using a catalytic material is actively pursued around some developed countries, as the material for the CO ₂ gas exploded far The ferrites researched and developed include binary ferrites such as NiFe ₂ O ₄ , CoFe ₂ O ₄ , and ZnFe ₂ O ₄ .

However, ternary ferrites having superior CO ₂ decomposition characteristics than binary ferrites have not been specifically studied and published.

An object of the present invention is to develop a material having excellent CO ₂ decomposition function by synthesizing a new ternary ferrite ultrafine powder improved CO ₂ decomposition function than the existing binary ferrite.

Another object of the present invention is to provide a ternary ferrite catalyst material having improved CO ₂ decomposition by further solid solution of a noble metal on the ternary ferrite surface.

Still another object of the present invention is to provide a method for preparing the three-way ferrite catalyst.

1 is a diagram showing an x-ray diffraction pattern of ferrite powder, Ni _0.5 Zn _0.5 Fe ₂ O ₄ , synthesized by hydrothermal synthesis and coprecipitation;

Figure 2 is a TEM photograph of Ni _x Zn _1-x Fe ₂ O ₄ , ferrite powder, (a) is a photograph of the ferrite powder prepared by the coprecipitation method, (b) is a photograph of the ferrite powder prepared by the hydrothermal synthesis method It is a photograph,

3 is a TEM photograph of Ni _x Zn _1-x Fe ₂ O ₄ ferrite added with Pt and Pd,

4 is a schematic diagram of a CO ₂ decomposition reaction cell using a ternary ferrite ultrafine powder as a catalyst,

5 is a graph showing the effect of reduction time on the CO ₂ decomposition rate of Ni _0.5 Zn _0.5 Fe ₂ O _4-δ ferrite,

FIG. 6 is a graph showing the CO ₂ decomposition rate of Ni _x Zn _1-x Fe ₂ O _4-δ ferrite synthesized by hydrothermal synthesis, measured in an open system, wherein the gas injected into the reactor was 10% CO ₂ -90% N ₂ mixed gas, 0% CO ₂ is a state in which the injected CO ₂ gas is completely decomposed, 10% CO ₂ is a state that almost no decomposition occurs,

7 is a graph showing the CO ₂ decomposition rate of Ni _x Zn _1-x Fe ₂ O _4-δ ferrite synthesized by coprecipitation method, measured in an open system,

8 is a graph showing the change of CO ₂ partial pressure of Ni _x Zn _1-x Fe ₂ O _4-δ ferrite synthesized by hydrothermal synthesis, measured in a closed system,

9 is a graph showing the CO ₂ partial pressure change of Ni _x Zn _1-x Fe ₂ O _4-δ ferrite synthesized by coprecipitation method, measured in a closed system,

FIG. 10 is a graph showing the CO ₂ partial pressure change of Pt, Pd-added Ni _x Zn _1-x Fe ₂ O _4-δ ferrite synthesized by hydrothermal synthesis, measured in a closed system, and (a) is Ni _0.5 Zn. _0.5 Fe ₂ O _4-δ , (b) is Pt-Ni _0.5 Zn _0.5 Fe ₂ O _4-δ , (c) is the case of Pd-Ni _0.5 Zn _0.5 Fe ₂ O _4-δ ,

FIG. 11 is a graph showing the change of CO ₂ partial pressure of Pt-, Pd-added Ni _x Zn _1-x Fe ₂ O _4-δ ferrite synthesized by coprecipitation method measured in a closed system, (a) is Ni _0.5 Zn _0.5 Fe ₂ O _4-δ , (b) shows the case of Pt-Ni _0.5 Zn _0.5 Fe ₂ O _4-δ , (c) Pd-Ni _0.5 Zn _0.5 Fe ₂ O _4-δ .

The ultrafine ternary ultrafine ferrite catalyst of the present invention is represented by the formula Ni _x Zn _1-x Fe ₂ O ₄ (x = 0.1 to 0.9), which is a conventional binary ferrite (NiFe ₂ O ₄ , CoFe ₂ O ₄ , Etc.) shows a better CO ₂ decomposition rate.

By designing and manufacturing a reaction cell capable of decomposing CO ₂ gas using ternary ferrite ultrafine powder having excellent CO ₂ decomposition characteristics, and installing it in facilities and equipment that emit CO ₂ gas, Significantly reduces CO ₂ emissions, a major component of, can be used to efficiently reduce air pollution.

The ternary ferrite ultrafine catalyst material of the present invention synthesizes nano-sized ultrafine powders by wet synthesis method such as hydrothermal synthesis method and coprecipitation method using starting materials of Ni salt, Zn salt and Fe salt. The synthesized ultrafine powder is prepared again by hydrogen reduction to ferrite in an oxygen deficient state, thereby greatly improving the CO ₂ decomposition rate. Ni salts, Zn salts and Fe salts used as starting materials in the present invention in particular Ni (NO ₃ ) ₂ · 6H ₂ O, Zn (NO ₃ ) ₂ · 6H ₂ O, Fe (NO ₃ ) ₃ · 9H ₂ Nitrate type such as O, and sulfate type such as NiSO ₄ · 6H ₂ O, ZnSO ₄ · 7H ₂ O, FeSO ₄ · 7H ₂ O are preferable. Hydrothermal synthesis and coprecipitation itself, which are applied in the production of the ternary ferrite ultrafine catalyst material of the present invention, are well known methods known in the art, and in the present invention, these known methods can be applied as they are.

In addition, in the present invention, by adding a trace amount of precious metals such as Pt or Pd to the surface of the ultrafine ternary ferrite catalyst material prepared as described above by a charge titration method, the CO ₂ decomposition rate of the ternary ferrite ultrafine catalyst material is further increased. Can be improved. The charge titration method applied at this time can use a well-known method.

The preparation of the ultrafine ternary ferrite catalyst material of the present invention (hereinafter also referred to as "ternary ferrite ultrafine powder") will be described in detail.

(1) Synthesis of Ternary Ferrite Ultrafine Powder

The CO ₂ decomposition efficiency of ferrites varies greatly depending on the manufacturing method and various process conditions. In the present invention, in order to improve the CO ₂ decomposition rate, ternary ferrite is synthesized in the form of ultra fine powder of several tens of nm or less using hydrothermal synthesis and coprecipitation.

As starting materials, Ni _x Zn _1-x Fe ₂ O ₄ (x = 0.1 to 0.9) is prepared by hydrothermal synthesis or coprecipitation using Ni salt, Zn salt, and Fe salt.

Examples of the preparation of ferrite powder by hydrothermal synthesis include distilled water with x mol of Ni (NO ₃ ) ₂ · 6H ₂ O, (1-x) mol of Zn (NO ₃ ) ₂ · 6H ₂ O, 2 mol Fe (NO ₃ ) ₃ .9H ₂ O was mixed in an appropriate molar ratio to suit the composition range of x = 0.1 to 0.9 to prepare an aqueous solution, followed by stirring with NaOH aqueous solution to an appropriate pH ( For example, the pH is adjusted to 8.0 to 10.0), and the hydrothermal reaction is performed in a stainless steel autoclave reactor at 140 to 200 ° C. for 1 to 2 hours. At this time, the mixed solution is continuously stirred. The mixed solution subjected to hydrothermal reaction was centrifuged at a high speed of 10,000 to 20,000 rpm to separate the precipitate, and the separated precipitate was washed with distilled water and ethanol and finally dried in a vacuum dryer for 20 to 24 hours.

For example, the production of ferrite powder by coprecipitation method, the aqueous solution of the same composition as the hydrothermal synthesis method is maintained at 40 to 80 ℃ and adjusted to an appropriate pH (for example, pH 8 to 10) while adding an aqueous NaOH solution. The mixed solution was placed in an Erlenmeyer flask and subjected to coprecipitation for several ten minutes in an atmosphere of several tens C and N ₂ , followed by centrifugation, washing, and drying in the same manner as in hydrothermal synthesis.

The powder thus obtained was heat-treated at 200 to 300 ° C. for several hours in an N ₂ atmosphere to remove H ₂ O or OH groups remaining therein, and each Ni _x Zn _1-x Fe ₂ O ₄ (x = 0.1 to 0.9) powder.

Specific conditions such as temperature, reaction time and the like in performing the above hydrothermal synthesis method and coprecipitation method can be appropriately selected and applied by those skilled in the art.

(2) Preparation of Ferrite Powder Added Pt and Pd

Ternary Ferrite CO₂In order to improve the decomposition effect, Ni prepared by the hydrothermal synthesis method or coprecipitation method as described above_xZn_1-xFe₂O₄(x = 0.1-0.9) Pt and Pd0.5-2.5 weight% are added to a powder by a charge titration method. The charge titration method applied at this time is known.

If the added amount of Pt or Pd is less than 0.5% by weight, the effect of the addition is insufficient. If it exceeds 2.5% by weight, it may be added in a large cluster state or unevenly added, and Pt and Pd may be Since these are very expensive precious metals, the addition of a large amount is not preferable because of their deterioration in economic efficiency.

For example, in the preparation of Pt and Pd-added ferrite powders, 0.1 mol or less of PtCl ₄ and PdCl ₂ aqueous solutions were prepared, respectively, and then maintained at 40 to 80 ° C. to protect the ferrite powder from damage at low pH. Adjust the solution to the appropriate pH (e.g. pH 4-5) while adding the solution, and add to each solution an appropriate amount (15-20 ml of PtCl ₄ or PdCl ₂ solution + 5-7 g of ferrite powder) Raw ferrite ultrafine powder is added and titrated to increase the pH while adding NaOH little by little. The solution was filtered and dried in a vacuum dryer for about one day to prepare a ternary ferrite ultrafine powder containing 0.5 to 2.5 wt% of Pt or Pd, respectively.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The following examples are merely illustrative of the present invention and the present invention is not limited to these examples.

Example 1

In this embodiment, a ternary ferrite ultrafine powder was prepared by hydrothermal synthesis.

150 mol of distilled water, x mol (x = 0.3, 0.5, 0.7) of Ni (NO ₃ ) ₂ · 6H ₂ O, (1-x) mol of Zn (NO ₃ ) ₂ · 6H ₂ O, 2 mol of Fe ( NO ₃ ) ₃ · 9H ₂ O was mixed to prepare an aqueous solution, and the mixture was titrated with pH 3 while stirring using an aqueous 3 M NaOH solution, and placed in a stainless steel autoclave reactor at 170 ° C. ( 7.5 MPa) was subjected to hydrothermal reaction for 5 hours. At this time, the mixed solution was continuously stirred. The mixed solution subjected to hydrothermal reaction was centrifuged at 10000 rpm to separate the precipitates, and the separated precipitates were washed with distilled water and ethanol and finally dried in a vacuum dryer at 60 ° C. for 24 hours.

The powder thus obtained was heat-treated for 1 hour at 300 ° C. and N ₂ atmosphere in order to remove H ₂ O or OH groups remaining therein, and thus Ni _x Zn _1-x Fe ₂ O ₄ (x = 0.3, 0.5, 0.7) to obtain a powder.

Example 2

In this embodiment, the ternary ferrite ultrafine powder was prepared by the coprecipitation method.

150 ml of distilled water, x mol (x = 0.3, 0.5, 0.7) of Ni (NO ₃ ) ₂ · 6H ₂ O, (1-x) mol of Zn (NO ₃ ) ₂ · 6H ₂ O, 2 mol of Fe ( NO ₃ ) _3. 9H ₂ O was mixed to prepare an aqueous solution, and the aqueous solution was maintained at 60 ° C. and titrated until the pH was 9 while adding an aqueous NaOH solution. The mixed solution was placed in an Erlenmeyer flask and subjected to coprecipitation for about 1 hour at 60 ° C. and N ₂ atmosphere, and the precipitate was separated by centrifugation at 10000 rpm. The separated precipitate was separated from distilled water and ethanol. After washing with, finally dried for 24 hours in a vacuum dryer at 60 ℃.

The powder thus obtained was heat-treated for 1 hour at 300 ° C. and N ₂ atmosphere in order to remove H ₂ O or OH groups remaining therein, and thus Ni _x Zn _1-x Fe ₂ O ₄ (x = 0.3, 0.5, 0.7) to obtain a powder.

Analysis of Ternary Ferrite Ultrafine Powder

Powders obtained by the hydrothermal synthesis and coprecipitation method obtained in Examples 1 and 2 were analyzed by composition by energy dispersive spectroscopy (EDS), and X-ray diffractometer (XRD) The crystal structure and particle size were analyzed using a transmission electron microscope (TEM), and the BET (Brunauer, Emmett and Teller) specific surface area analysis was performed. The analysis results are shown in Table 1 below, and the results in Table 1 are obtained by averaging five analysis results.

Sample Chemical composition BET specific surface area (m ² / g) Particle size (nm) Way x * Example 1 (hydrothermal synthesis method) 0.3 (Ni ²⁺ _0.31 Zn ²⁺ _0.75 ) Fe ³⁺ _1.91 O ₄ 121.8 5-9 0.5 (Ni ²⁺ _0.47 Zn ²⁺ _0.51 ) Fe ³⁺ _2.00 O ₄ 113.2 6-9 0.7 (Ni ²⁺ _0.66 Zn ²⁺ _0.32 ) Fe ³⁺ _2.02 O ₄ 127.5 6 to 8 Example 2 (Coprecipitation Method) 0.3 (Ni ²⁺ _0.29 Zn ²⁺ _0.74 ) Fe ³⁺ _1.91 O ₄ 79.1 9-10 0.5 (Ni ²⁺ _0.51 Zn ²⁺ _0.51 ) Fe ³⁺ _2.00 O ₄ 77.6 8 to 10 0.7 (Ni ²⁺ _0.72 Zn ²⁺ _0.32 ) Fe ³⁺ _1.95 O ₄ 89.5 9 to 11

* x is the mole fraction of Ni (NO ₃ ) ₂ .6H ₂ O before the reaction.

As shown in Table 1, the composition ratio of the ferrite powder obtained after the reaction was found to have almost the same composition as the initial mole number mixed before the reaction as an EDS analysis result.

Meanwhile, XRD results of Ni _x Zn _1-x Fe ₂ O ₄ [x = 0.5] prepared in Examples 1 and ₂ are the same as in FIG. 1. As can be seen from the XRD results, it was confirmed that the crystal structures of the two ferrites had a typical spinel structure, and no peak of the second phase such as α-Fe ₂ O ₃ was observed.

FIG. 2 is a photograph of ferrite powders synthesized by the hydrothermal synthesis method and the coprecipitation method in Examples 1 and 2 using TEM. As can be seen from the photograph, it was observed that the ferrite particles synthesized by the hydrothermal synthesis method of Example 1 were well dispersed and formed very fine and uniform spherical particles of 10 nm or less. In contrast, ferrite synthesized by the coprecipitation method of Example 2 was able to obtain very small particles having an average particle size of 12 nm or less, although the particles were aggregated and the shape of the particles was not uniform.

Example 3

In this embodiment, to improve the CO ₂ decomposition effect of the ferrite powder, Pt and Pd were added to the ferrite powders prepared in Examples 1 and 2 by charge titration.

Each of 2.94 × 10 ⁻² mol of PtCl ₄ and 15 ml of PdCl ₂ was prepared, and titrated until the pH reached 4.5 with addition of 0.1 mol NaOH maintained at 65 ° C. 5 g of Ni _0.5 Zn _0.5 Fe ₂ O ₄ powder prepared by the hydrothermal synthesis method and the coprecipitation method in 1 and Example 2 were added thereto, and the mixture was titrated to pH 10 while adding 0.1 mol of NaOH at 65 ° C. little by little. The solution was filtered and dried in a vacuum dryer at 65 ° C. for 24 hours to prepare ferrites containing about 1 wt% of Pt and Pd, respectively.

Analysis of Ternary Ferrite Ultrafine Powder Added with Pt and Pd

The ternary ferrite powder added with Pt and Pd prepared in Example 3 was analyzed in the same manner as that for the ferrite powders of Examples 1 and 2. The lattice constant was obtained by extrapolation of the (cos ² θ / sinθ + cos ² θ / θ) value and the linear Nelson-Riley function expressed as a function of the lattice constant using a diffraction pattern obtained by XRD analysis. The results are shown in Table 2 below. The results of chemical composition ratios in Table 2 are the average values obtained by averaging five analysis results.

Sample (method) Precious metals Chemical composition BET specific surface area (cm ² / g) Lattice constant (nm) Example 1 (hydrothermal synthesis method) None Ni ²⁺ _0.47 Zn ²⁺ _0.51 Fe ³⁺ _2.00 O ₄ 113.2 0.8400 Pt Ni ²⁺ _0.47 Zn ²⁺ _0.48 Fe ³⁺ _2.04 O ₄ 111.9 0.8396 Pd Ni ²⁺ _0.47 Zn ²⁺ _0.49 Fe ³⁺ _2.03 O ₄ 110.1 0.8399 Example 2 (Coprecipitation Method) None Ni ²⁺ _0.51 Zn ²⁺ _0.51 Fe ³⁺ _1.94 O ₄ 77.6 0.8403 Pt Ni ²⁺ _0.49 Zn ²⁺ _0.53 Fe ³⁺ _1.98 O ₄ 81.9 0.8400 Pd Ni ²⁺ _0.49 Zn ²⁺ _0.52 Fe ³⁺ _1.99 O ₄ 79.4 0.8400

As shown in Table 2, from the EDS analysis result, the composition ratio of the ferrite powder obtained after the Pt and Pd addition reaction was found to have almost the same composition as the initial composition (Ni _0.5 Zn _0.5 Fe ₂ O ₄ ) mixed before the reaction, The amount of Pt and Pd added was found to be a very small amount of about 1 to 1.5% by weight.

FIG. 3 is a shape of a powder observed by TEM after adding Pd to Ni _0.5 Zn _0.5 Fe ₂ O ₄ powders synthesized by coprecipitation and hydrothermal synthesis in Examples 1 and 2, respectively. It is close to a sphere and is very small, about 10 nm in diameter. In addition, the powders synthesized by coprecipitation have agglomerated forms, whereas the powders synthesized by hydrothermal synthesis have spherical shapes dispersed from each other.

CO of ternary ferrite ultrafine powder ₂ Degradation Characteristic Evaluation

The CO ₂ decomposition rate of the ternary ferrite ultrafine powders prepared in Examples 1 and 2 was tested in two types of reactors, an open system and a closed system, respectively.

4 shows a schematic view of a CO ₂ decomposition reaction cell designed according to the present invention.

Prior to measuring the CO ₂ decomposition rate, the ferrite powder was reduced in a hydrogen atmosphere in order to obtain ferrite in an oxygen deficient state, and an appropriate reduction time having the highest oxygen deficiency was determined. Thus, when the injecting is CO ₂ gas in the reduced oxygen deficient ferrite to make an oxygen-deficient state by reduction treatment to the mechanism of oxygen CO ₂ is combined with the oxygen vacancy in the spinel crystal lattice, and the carbon is left on the surface of the ferrite This is because the CO ₂ decomposition is performed, so that the ferrite must be ferrite in an oxygen depletion state in order to be able to decompose the CO ₂ gas.

FIG. 5 is a Ni _0.5 Zn _0.5 Fe ₂ O ₄ ferrite powder prepared by the coprecipitation method in Example 2 was put into a reactor at 300 ° C. [FIG. 4], and 99.99% purity H ₂ gas was supplied at a flow rate of 10 ml / min. After reducing for 1 to 4 hours, the graph shows the time when the amount of CO ₂ flowing out through the outlet of the reactor is 5% when CO ₂ gas is flowed at a flow rate of 10 ml / min. to be. The ferrite reduced for 3 hours lasted the longest time to decompose CO _2. This is because the reduction of ferrite, that is, oxygen deficiency (δ), increases with the reduction time, and the number of anion oxygen vacancies increases in the crystal. The same can be said. However, after 3 hours, the CO ₂ decomposition rate of the ferrite decreased, which may be due to the decomposition of the single phase spinel to produce a second phase such as α-Fe ₂ O ₃ . Therefore, on the basis of this result, the experiment was conducted in two ways, the open system and the closed system, with the hydrogen reduction time fixed at 3 hours.

[Experiment in open system]

The experiment in the open system was carried out as follows. 1 g of ferrite powder prepared by the hydrothermal synthesis method in Example 1 was placed in a Pyrex glass tube in an open system reactor, and both sides of the sample were packed with glass fiber. First, the temperature of the reactor was maintained at 300 ° C., and then reduced to 3 hours while flowing H ₂ gas at a flow rate of 10 ml / min. And, at the same temperature for 10% CO ₂ - send flow at a rate of 90% N ₂ mixed gas 60 ml / min of the, according to the composition of the gas discharged from the outlet at the time thermal conductivity detector: with (TCD thermal conductivity detector) It was measured by gas chromatography (shimadzu model GC-8A). The result of measuring the amount of CO ₂ in the gas discharged to the reactor outlet as a function of the reaction time is shown in FIG. 6.

As can be seen in FIG. 6, the ternary oxygen-deficient ferrite [x = 0.3, 0.5, 0.7] completely decomposed CO ₂ into C and O ₂ for about 7 minutes, after which the CO ₂ decomposition rate gradually decreased to about 10 After minutes, the ferrite's ability to decompose completely lost. This will not, after the oxygen vacancy produced by the hydrogen reduction completely filled by reaction with CO ₂ in oxygen it is no longer proceeds the decomposition of the CO _2. However, binary ferrite [x = 1.0] shows a slow decrease after about 5 minutes of CO ₂ decomposition.

7 is a result obtained by experimenting the ferrite powder 1 g prepared by the coprecipitation method in Example 2 under the same conditions. In this case, ternary ferrite (Ni _x Zn _1-x Fe ₂ O _4-δ ) of _x≥0.5 completely decomposed CO ₂ into C and O ₂ for about 5 minutes, after which the rate of CO ₂ decomposition gradually increased. After about 10 minutes of reduction, the degradation ability of ferrite was lost completely. In addition, when comparing the CO ₂ resolution of ferrite according to the composition ratio of Ni and Zn, when the Zn content is large (Ni _0.3 Zn _0.7 Fe ₂ O ₄ ), the retention time of CO ₂ was longest, and in the other two cases I got almost the same result. In addition, as in the ferrite powder prepared by the hydrothermal synthesis method, the ternary ferrites [x = 0.3, 0.5, 0.7] were maintained for a longer time to continuously decompose CO ₂ than the binary Ni ferrites [x = 1.0]. It has been shown that ternary ferrite has better CO ₂ decomposition capacity. In addition, comparing the CO ₂ decomposition efficiency according to the synthesis method was able to obtain a better result than the ferrite prepared by the hydrothermal synthesis method by the coprecipitation method.

[Experiment in Closed System]

In the second method, experiments in a closed system were carried out as follows. 3 g of ferrite powder was charged to a closed system reactor [FIG. 4], and oxygen-deficient ferrite was prepared in the same manner under the same reducing conditions as the open system, and then the inside of the reactor was kept in a vacuum state using a vacuum pump. 20 ml of CO ₂ was injected into a vacuum reactor at 300 ° C., and CO ₂ decomposition efficiency was measured using a pressure change in the reactor generated by CO ₂ decomposition by a ferrite material.

8 is a result of measuring the degree of CO ₂ decomposition of the ferrite prepared by the hydrothermal synthesis method in Example 1 using a closed system reactor in a vacuum state (PCO ₂ = 0) to about 70 mmHg reactor initial pressure. The zero point on the vertical axis represents a vacuum value and the horizontal axis represents the time elapsed after injecting CO ₂ . In the early stage of the reaction, decomposition occurs rapidly, so that the partial pressure of CO _{2 in the} reactor decreases rapidly and becomes constant over time. As shown in FIG. 8, ferrite having a large amount of Ni could not be decomposed after 5 minutes, and when Ni composition is 0.5 or less, relatively good CO ₂ decomposition efficiency can be obtained. These results are consistent with those obtained in open systems.

Figure 9 shows the CO ₂ partial pressure change with time when using the ferrite prepared by the coprecipitation method in Example 2. It can be seen that the reaction occurs at an early stage as in the ferrite prepared by hydrothermal synthesis, and the change in the partial pressure of CO ₂ was larger when the composition of Ni was 0.5 or less. However, the ferrite prepared by the coprecipitation method showed a smaller overall CO ₂ partial pressure change than the ferrite prepared by the hydrothermal synthesis method. This shows that ferrites prepared by hydrothermal synthesis can achieve better CO ₂ decomposition efficiency, as shown in open systems. As a result, the powder synthesized by hydrothermal synthesis with small particle size and large specific surface area continued CO ₂ decomposition for a longer time.

CO of ternary ferrite ultrafine powder with Pt and Pd added ₂ Degradation Characteristic Evaluation

The ferrite powder (Example 3) in which Pt and Pd were added in a small amount to Ni _0.5 Zn _0.5 Fe ₂ O _4-δ powder synthesized by the hydrothermal synthesis method in Example 1 was placed in a closed system reactor and the same method as described above at 300 ° C. CO ₂ partial pressure change over time was measured. The results are shown in FIG. As can be seen in Figure 10, the ternary ferrite ((b) and (c)) with the addition of Pt or Pd has a CO ₂ partial pressure over time compared to the ternary ferrite (a) without the addition of Pt or Pd Much decreased and decomposition occurred for a long time. This indicates that the CO ₂ decomposition mechanism of the ferrite is an oxidation / reduction reaction, and Pt or Pd, which is a noble metal, can improve the oxidation / reduction reaction. In other words, the separation adsorption of H ₂ to 2H _ads in the reduction reaction occurs on the surface of the Pd and Pt metals, and the adsorbed H _ads can move very easily to the ferrite phase, and react quickly with oxygen of the ferrite to form H ₂ O. do. On the other hand, it can be seen that the ferrite (c) added with Pd has a larger change in the partial pressure of CO ₂ over time than the ferrite (b) added with Pt. In other words, the CO ₂ decomposition efficiency varies depending on the kind of the noble metal added to the ternary ferrite of the same composition. In this experiment, the ferrite added with Pd was excellent.

FIG. 11 is a graph obtained through a catalytic reaction in a closed system using a powder obtained by adding Pt and Pd to a Ni _0.5 Zn _0.5 Fe ₂ O _4-δ powder prepared by coprecipitation. CO ₂ decomposition efficiency could be improved by adding two noble metals such as ferrite prepared by hydrothermal synthesis, and it was confirmed that the catalytic effect by Pd addition was better.

As described above, ultrafine ternary ferrite (Ni _x Zn _1-x Fe ₂ O ₄ ) having CO ₂ decomposition characteristics was synthesized by wet synthesis methods such as hydrothermal synthesis and coprecipitation, and the following conclusions were obtained.

(1) The CO ₂ decomposition time of Ni _x Zn _1-x Fe ₂ O _4-δ synthesized by hydrothermal synthesis and coprecipitation through reduction reaction for 3 hours in hydrogen atmosphere at 300 ° C was maintained for about 10 minutes. CO ₂ decomposition rate was higher than that of binary ferrite and NiFe ₂ O ₄ . Also, the ternary ferrite synthesized by hydrothermal synthesis method was more effective in CO ₂ decomposition than the ferrite prepared by coprecipitation method.

(2) After titration of the PtCl ₄ and PdCl ₃ solutions, a small amount (a few percent by weight) of precious metals Pt and Pd could be added by mixing with Ni _x Zn _1-x Fe ₂ O _4-δ ferrite. Pt and Pd The CO ₂ decomposition efficiency of the added Ni _x Zn _1-x Fe ₂ O _4-δ was better than the same ferrite without addition.

In conclusion, the ternary ferrite ultrafine catalyst material obtained through the present invention has excellent CO ₂ decomposition rate than the existing catalysts, so that CO ₂ gas is emitted in various thermal power plants, steel mills, cement plants, and district heating. It is expected that it can be usefully used as a catalyst material for CO ₂ decomposition systems that can reduce CO ₂ gas emitted from cogeneration plants.

Claims (7)

An ultrafine ternary ferrite catalyst for decomposing carbon dioxide, represented by the formula Ni _x Zn _1-x Fe ₂ O _4-δ [x = 0.1 to 0.9, where δ is an oxygen deficiency degree]. An ultrafine ternary ferrite catalyst for decomposing carbon dioxide, wherein 0.5 to 2.5% by weight of Pt or Pd is added to the ultrafine ternary ferrite of claim 1. Ni _x Zn _1-x Fe ₂ O ₄ [x by hydrothermal synthesis using x mol (x = 0.1 to 0.9) Ni salt, (1-x) mol Zn salt, and 2 mol Fe salt as starting materials [x 0.1 to 0.9], wherein the ultrafine ternary ferrite catalyst for decomposing carbon dioxide according to claim 1, wherein the ultrafine ternary ferrite powder is reduced in a hydrogen atmosphere. Ni _x Zn _1-x Fe ₂ O ₄ [x _by coprecipitation using Ni mol of x mol (x = 0.1 to 0.9), Zn salt of (1-x) mol, and 2 mol of Fe salt as starting materials. 0.1 to 0.9], wherein the ultrafine ternary ferrite catalyst for decomposing carbon dioxide according to claim 1, wherein the ultrafine ternary ferrite powder is reduced in a hydrogen atmosphere. Ni _x Zn _1-x Fe ₂ O by hydrothermal synthesis or coprecipitation using Ni mol of x mol (x = 0.1 to 0.9), Zn salt of (1-x) mol, and 2 mol of Fe salt as starting materials. ₄ [x = 0.1 to 0.9] ternary ferrite ultrafine powder is prepared, reduced in a hydrogen atmosphere, and then prepared by adding 0.5 to 2.5% by weight of Pt or Pd by a charge titration method. Method for producing ultrafine ternary ferrite catalyst for carbon dioxide decomposition. The Ni salt of claim 3, wherein the Ni salt is Ni (NO ₃ ) ₂ .6H ₂ O, the Zn salt is Zn (NO ₃ ) ₂ .6H ₂ O, and the Fe salt is Fe (NO ₃ ). ₃ · 9H ₂ O, characterized in that the method. The method according to any one of claims 3 to 5, wherein the Ni salt is NiSO ₄ .6H ₂ O, the Zn salt is ZnSO ₄ .7H ₂ O, and the Fe salt is FeSO ₄ .7H ₂ O.