KR102162974B1 - Method for synthesizing metal ion-doped ceria using solvothermal synthesis - Google Patents

Abstract

The present invention comprises the steps of: (a) adjusting the pH by adding a basic substance to the cerium acetate solution; (b) adjusting the pH by adding a basic substance to the metal ion precursor solution; And (c) dispersing the solution obtained in each of the steps (a) and (b) in a solvent, followed by a solvent heat reaction at a temperature of 90 to 160° C. to form a metal ion-doped ceria. As for a method for producing a metal ion-doped ceria using a solvent heat synthesis method comprising, according to the present invention, conventional hydrothermal synthesis of a metal ion doped ceria having a high specific surface area and crystallinity through a solvent heat synthesis method without a surfactant or additional heat treatment It can be economically synthesized at a temperature lower than the temperature (90 to 160°C), and in particular, by using cerium acetate as a cerium precursor, the specific surface area of the metal ion-doped ceria can be dramatically improved.

Description

Manufacturing method of metal ion-doped ceria using solvent heat synthesis method {METHOD FOR SYNTHESIZING METAL ION-DOPED CERIA USING SOLVOTHERMAL SYNTHESIS}

The present invention relates to a method of preparing ceria doped with metal ions, and more particularly, to a method of preparing ceria doped with metal ions using a solvent heat synthesis method.

Cerium oxide, that is, ceria, is applied and used in a very wide range of fields such as solid oxide fuel cells (SOFC), oxygen gas sensors, UV absorbents, abrasives, etc. due to its unique physical and chemical properties. . Ceria acts as an oxidation/reduction function depending on the surrounding oxygen concentration and has excellent oxygen storage capacity. In particular, ceria is widely applied as a catalyst that decomposes the exhaust gas of automobiles and converts them into non-toxic gases. At this time, the activity of the catalyst depends on the surface area, so obtaining a high specific surface area is the key. Nano-sized ceria has a better oxidation/reduction function and oxygen storage capacity (OSC) performance than that of a bulk powder, so it has been studied with constant interest.

On the other hand, as a method for synthesizing ceria nanoparticles, a precipitation method and a sol-gel method are typically known, but the precipitation method and the sol-gel method require an additional high-temperature reaction process to produce a powder having high crystallinity. In this process, the particles aggregate to lower the surface energy and form an irregular shape. To control this, a surfactant is added, and a process for removing the surfactant is required.

Korean Patent Publication No. 10-2010-0108957 (Publication date: 2010.10.08.) Korean Patent Publication No. 10-2016-0121229 (Publication date: 2016.10.19.) Japanese Unexamined Patent Publication 2004-43226 (Publication date: 2004.02.12.)

The technical problem to be solved by the present invention is that metal ion-doped ceria, which is doped with metal ions, has excellent thermal stability at high temperatures, and has a large specific surface area, high purity, and crystallinity, without the need for a surfactant or additional heat treatment. It is to provide a method of manufacturing at a low temperature.

In order to achieve the above technical problem, the present invention includes the steps of: (a) adjusting the pH by adding a basic substance to a cerium acetate solution; (b) adjusting the pH by adding a basic substance to the metal ion precursor solution; And (c) dispersing the solution obtained in each of the steps (a) and (b) in a solvent, and then reacting with a solvent heat at a temperature of 90 to 160° C. to form metal ion-doped ceria; A method for producing metal ion-doped ceria using a synthetic method is proposed.

In addition, the metal ion precursor in the step (b) is an acetate-based precursor, an alkoxide-based precursor, a halide-based precursor, an oxyhalide-based precursor, or a nitrate-based precursor. (Nitrate based) We propose a method for producing metal ion-doped ceria using a solvent heat synthesis method characterized by being a precursor.

In addition, it is proposed a method for producing a metal ion-doped ceria using a solvent heat synthesis method, characterized in that the solvent is water or a mixed solvent of water and alcohol.

In addition, the mixed solvent proposes a method for producing a metal ion-doped ceria using a solvent heat synthesis method, characterized in that it contains not more than 75% by volume of ethanol (EtOH).

In addition, the basic material is ammonium hydroxide (NH ₄ OH), sodium hydroxide (NaOH), or potassium hydroxide (KOH) proposes a method for producing a metal ion-doped ceria using a solvent heat synthesis method.

In addition, it is proposed a method for producing a metal ion-doped ceria using a solvothermal synthesis method characterized in that the solvate reaction is carried out for 2 to 10 hours.

Further, the present invention proposes a metal ion-doped ceria prepared by the above manufacturing method in another aspect of the present invention.

Furthermore. In another aspect of the present invention, the present invention proposes a catalyst for purifying exhaust gas comprising the metal ion-doped ceria as an oxygen storage capacity (OSC) material.

According to the present invention, metal ion-doped ceria having a high specific surface area and crystallinity can be economically synthesized at a temperature lower than the conventional hydrothermal synthesis temperature (90 to 160°C) through a solvent heat synthesis method without a surfactant or additional heat treatment. , By using cerium acetate as a cerium precursor, the specific surface area of the metal ion-doped ceria can be dramatically improved.

In addition, according to the present invention, it has various particle sizes and specific surface areas through control of process variables such as the type of metal ions to be doped, the mixing ratio between solvents of the mixed solvent, pH, and reaction time, and exhibits higher OSC catalyst characteristics than pure ceria. Metal ion-doped ceria can be synthesized.

1 is a flowchart of a method of manufacturing a metal ion-doped ceria using a solvent heat synthesis method according to the present invention.
Figure 2 is a process flow diagram showing each detailed process of the metal ion-doped ceria synthesis using a solvent heat synthesis method in the present embodiment.
3 is an X-ray diffraction analysis (XRD) result of the synthesized ruthenium-doped ceria (Ru-doped CeO ₂ ) nanopowder synthesized in the present example.
4 is an FE-TEM photograph showing a change in the microstructure according to the amount of Ru doping of the ruthenium-doped ceria (Ru-doped CeO ₂ ) nanopowder synthesized in the present example.

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted.

Since the embodiments according to the concept of the present invention can apply various changes and have various forms, specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiments according to the concept of the present invention to a specific form of disclosure, and it should be understood that all changes, equivalents, and substitutes included in the spirit and scope of the present invention are included.

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise" or "have" are intended to designate the presence of a set feature, number, step, action, component, part, or combination thereof, but one or more other features or numbers It is to be understood that the possibility of addition or presence of, steps, actions, components, parts, or combinations thereof is not preliminarily excluded.

Hereinafter, the present invention will be described in detail.

The present invention relates to a novel method capable of producing a metal ion-doped ceria having a high specific surface area through a more economical and simple process compared to the conventional synthesis method.

Specifically, as shown in FIG. 1, a method for preparing a metal ion-doped ceria using a solvent heat synthesis method according to the present invention includes the steps of: (a) adjusting a pH by adding a basic substance to a cerium acetate solution; (b) adjusting the pH by adding a basic substance to the metal ion precursor solution; And (c) dispersing the solution obtained in each of the steps (a) and (b) in a solvent, followed by a solvent heat reaction at a temperature of 90 to 160° C. to form metal ion-doped ceria.

In the step (a), after preparing a cerium acetate solution as a cerium precursor, a basic substance is added to the solution to adjust the pH to 7 to 11.

In the present invention, by using cerium acetate as the cerium precursor as described above, it is possible to prepare a metal ion-doped ceria having a significantly increased specific surface area compared to the case of using other precursors such as cerium nitrate.

In particular, when water is used as a dispersion medium in step (c) to be described later, the effect of increasing the specific surface area of metal ion-doped ceria by using cerium acetate as a cerium precursor is maximized, which is an organic polymer with a long unit of cerium acetate. This is because dispersion occurs largely by the dielectric constant and chains are intercepted between cerium hydroxide, so that particle growth and agglomeration of the powder are effectively suppressed by a steric effect, thereby reducing the overall particle size.

Next, in step (b), a precursor solution of a metal ion doped to ceria is prepared, and then a basic substance is added to the solution to adjust the pH to 7 to 11.

The type of metal ion precursor can be appropriately selected according to the type of metal to be doped into ceria, for example, an acetate based precursor containing a metal ion to be doped, an alkoxide based precursor, and halogenation. It may be a water-based precursor, an oxyhalide-based precursor, or a nitrate-based precursor.

The metal ion precursor may be an acetate-based precursor, an alkoxide-based precursor, a halide-based precursor, or an oxyhalide-based precursor containing the metal ion depending on the type of metal ion to be doped on ceria ( It can be selected from oxyhalide based) precursors or nitrate based precursors.

However, when doping metal ions (Ru, Zn, Cu, Ag, Ba, Sr, Sn, etc.) with an oxidation number of +2, it is possible to synthesize metal ion-doped ceria that is superior to catalytic properties than pure ceria. As the ionic radius of the doped metal ions is smaller than the ionic radius, the degree of reduction of the lattice increases, reducing the particle size and increasing the specific surface area, thereby increasing the catalytic reactivity. It is more preferable to use a precursor.

On the other hand, the type of basic substance added to adjust the pH of each solution in steps (a) and (b) is not particularly limited, and examples include ammonium hydroxide (NH ₄ OH), potassium hydroxide (KOH), and hydroxide. Sodium (NaOH) or the like can be used.

Next, in step (c), both the pH-adjusted cerium acetate solution obtained in step (a) and the pH-adjusted metal ion precursor solution in step (b) are mixed and dispersed in a solvent, and then 90 to 160 Ceria doped with metal ions is synthesized by performing a solvent heat reaction at a temperature of °C.

In this step (c), the solvent for dispersing the cerium acetate solution and the metal ion precursor solution prior to the solvent heating process may be water or a mixed solvent of water and alcohol, and the alcohol may be methanol, ethanol, or propanol. , Butanol, or a mixture of two or more of known alcohols such as ethylene glycol may be used.

In addition, the content ratio of the cerium acetate solution and the metal ion precursor solution dispersed in the solvent in step (c) may be appropriately adjusted according to the desired metal ion doping amount.

In addition, when the reaction temperature of the solvate reaction performed in this step (c) is less than 90 ℃, there is a problem that the solvate reaction is difficult to occur. If the reaction temperature exceeds 160 ℃, the reaction rate of the solvent heat rapidly increases due to excessive heat There is a problem of deteriorating the stability of.

In addition, when the reaction time of the solvate reaction is less than 2 hours, there is a problem that sufficient reaction does not occur, and thus particle formation is difficult, and when it exceeds 10 hours, the size of the particles becomes excessively large and the stability of the particles is also reduced. Can occur.

According to the method for producing a metal ion-doped ceria using the solvent heat synthesis method according to the present invention described above, a metal ion doped ceria having a high specific surface area and crystallinity through a solvent heat synthesis method without a surfactant or additional heat treatment is lower than the conventional hydrothermal synthesis temperature. It can be economically synthesized at a temperature (90~160℃), and in particular, by using cerium acetate as a cerium precursor, the specific surface area of the metal ion-doped ceria can be dramatically improved, and the doped metal ion Metal ion-doped ceria having various particle sizes and specific surface areas and exhibiting higher OSC catalytic properties than pure ceria can be synthesized by controlling process variables such as the type of, the mixing ratio between solvents of the mixed solvent, pH, and reaction time.

Hereinafter, the present invention will be described in more detail with reference to examples.

The embodiments according to the present specification may be modified in various forms, and the scope of the present specification is not construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely describe the present specification to those of ordinary skill in the art.

<Example>

In this example, a ceria nanopowder doped with ruthenium (Ru) ions was synthesized according to the process flow diagram shown in FIG. 2.

Cerium(III) acetate hy-drate [Ce(CH ₃ CO ₂ ) ₃ ·xH ₂ O] as a cerium precursor, and Ruthenium(III) chloride [RuCl ₃ ·nH ₂ O] as a ruthenium ion precursor. Was used, and secondary distilled water was used as water.

First, after preparing an aqueous solution of a cerium precursor and an aqueous ruthenium ion precursor, the pH of each solution was adjusted to 11 using NH ₄ OH. Subsequently, the cerium precursor aqueous solution and the ruthenium ion precursor aqueous solution were redispersed in a solvent (water) so that the molar ratio of Ce and Ru was 95:5, 90:10, 85:15, 80:20, or 75:25, and stirred, and then Teflon Put into a container and subjected to a solvent heat reaction at 120 ℃ for 2 hours. Thereafter, washed 5 times with water and ethanol and dried for 24 hours in a dryer to recover the ceria nanopowder doped with ruthenium ions.

Ceria doped with Zn, Cu, or Ag is a metal ion precursor, respectively Zinc nitrate hexahydrate [Zn(NO ₃ ) ₂ ·6H ₂ O], Copper nitrate [Cu(NO ₃ ) ₂ ] or Silver nitrate hexahydrate [Ag(NO ₃₎ ) ₂ · 6H ₂ O] was prepared according to the same synthesis method as above.

3 is a synthesized ruthenium-doped ceria (Ru-doped CeO ₂ ) synthesized under the conditions of 95:5, 90:10, 85:15, 80:20, and 75:25 of the molar ratio of Ru to Ce as described above. This is the result of X-ray diffraction analysis (XRD) for the nano powder. When the observed XRD phase was compared with ICSD 98-005-3995, the same peak appeared at all positions, so it was confirmed that ceria having a fluorite structure without a secondary phase was synthesized.

Table 1 below (specific surface area and catalyst characterization results of Ru-doped CeO ₂ nanopowder) shows the particle size, specific surface area, and H ₂ -TPR catalyst characterization results calculated using the Scherrer formula. It was confirmed that the average particle size of the prepared ruthenium-doped ceria (Ru-doped CeO ₂ ) was less than 9 nm, which was smaller than that of pure ceria. The ionic radii of Ce ⁴⁺ and Ce ³⁺ are 111 and 128.3Å in 8 coordination, respectively, and Ru ⁴⁺ and Ru ³⁺ appear as 76Å and 82Å in 6 coordination. Considering the ionic radius, it appears that the particle size decreases as the amount of Ru doping increases due to lattice shrinkage due to the substitution of relatively small Ru ions in the ceria lattice.

As the amount of Ru doping in ceria increased to 20 mol%, the specific surface area increased from 135.56 m ² /g to 209.73 m ² /g, but at 25 mol% of Ru doping, the particle size increased to 8.76 nm when compared to 20 mol%. The specific surface area was reduced to 157.72m ² /g. Nevertheless, it was found to have a much higher specific surface area than that of the existing pure ceria (90-100m ² /g).

In addition, it was confirmed that the catalytic properties of ruthenium-doped ceria (Ru-doped CeO ₂ ) having a Ru doping amount of 15 mol% or less are 2 to 3 times better than that of conventional pure ceria (H ₂ consumption: 243.27 umol/g).

4 is a result of FE-TEM measurement of ruthenium-doped ceria (Ru-doped CeO ₂ ), and it was confirmed that the occurrence of a rod phase increased as the Ru content increased. As a result of EDS measurement, the rod phase was observed as a pure ceria phase.

Table 2 (specific surface area and catalytic properties analysis results of metal (Ru, Zn, Cu or Ag) ion doped ceria nanopowder and pure ceria nanopowder) contains 15 mol% of metal (Ru, Zn, Cu or Ag) ions. The particle size, specific surface area, and H ₂ -TPR catalyst characterization results calculated for the ceria nano powder and pure ceria nano powder are shown. According to this, although the difference in specific surface area and catalytic properties between metal ion-doped cerias is large depending on the type of doped metal ions, it was confirmed that all metal ion-doped cerias have higher specific surface area and catalytic properties than pure cerias.

Claims (8)

(a) adjusting the pH by adding a basic substance to the cerium acetate solution;
(b) adjusting the pH by adding a basic substance to the metal ion precursor solution; And
(c) dispersing the solution obtained in each of the steps (a) and (b) in a solvent, and then performing a solvent heat reaction at a temperature of 90 to 160° C. to form metal ion-doped ceria; including,
The metal ion precursor is a ruthenium ion precursor,
In the step (c), the cerium acetate aqueous solution and the ruthenium ion precursor aqueous solution are dispersed in water so that the molar ratio of cerium and ruthenium is 95: 5 to 85: 15. Way. The method of claim 1,
In the step (b), the metal ion precursor,
Solvent heat synthesis method characterized in that it is an acetate-based precursor, an alkoxide-based precursor, a halide-based precursor, an oxyhalide-based precursor, or a nitrate-based precursor. Method for producing metal ion-doped ceria using. delete delete The method of claim 1,
The basic material is ammonium hydroxide (NH ₄ OH), sodium hydroxide (NaOH), or potassium hydroxide (KOH). Method for producing a metal ion-doped ceria using a solvent heat synthesis method. The method of claim 1,
The method for producing a metal ion-doped ceria using a solvothermal synthesis method, characterized in that the solvate reaction is carried out for 2 to 10 hours. A metal ion-doped ceria produced by the method according to any one of claims 1, 2, 5, and 6. A catalyst for purifying exhaust gas comprising the metal ion-doped ceria of claim 7 as an oxygen storage capacity (OSC) material.

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