KR20180057276A - Catalyst for reduction of carbon dioxide and process of preparing the same - Google Patents

Abstract

The present invention relates to a catalyst for the reduction of carbon dioxide and a method of preparing the same, and more specifically, to a catalyst for carbon dioxide reduction which is prepared by forming gold nanoparticles by liquid sputtering in a polyethylene glycol solvent, and a method for preparing the same. The gold nanoparticles (PEG-Au/C) synthesized according to the present invention can show carbon dioxide reduction efficiency twice as good as that of commercially available Au/C.

Description

TECHNICAL FIELD The present invention relates to a catalyst for reducing carbon dioxide and a method for preparing the same,

TECHNICAL FIELD The present invention relates to a catalyst for carbon dioxide reduction and a production method thereof, and more specifically, to a catalyst for carbon dioxide reduction produced by forming gold nanoparticles in a polyethylene glycol solvent by liquid sputtering, and a method for producing the same.

Catalysts for reducing carbon dioxide, for example, metal particles such as gold, silver and copper, are known to have good activity at a constant size (15 nm or less). In addition, the carbon dioxide reduction catalyst is required to have low activity for the side reaction other than the carbon dioxide reduction reaction, especially for the hydrogen production reaction through the proton reduction in the case of the reaction in the aqueous solution.

Usually, many catalysts, including carbon dioxide reduction catalysts, are produced and used in the form of nanoparticles carried on carbon or the like to have a large specific surface area and high weight-wise activity. In order to chemically synthesize a catalyst satisfying the above-mentioned requirements, various surfactants and the like are used as an additive during catalyst synthesis. The purpose of the addition of the additives is to synthesize uniform and small-sized nanoparticles. There are various methods for forming uniform and small nanoparticles, but it is still difficult to form small and uniform nanoparticles by a simple method.

When the carbon dioxide reduction reaction is carried out on an aqueous solution, the efficiency of the carbon dioxide reduction reaction deteriorates as the reactant concentration limitation due to the low solubility (33 mM) of carbon dioxide in the aqueous solution and the proton reduction reaction as the competitive reaction occur on the same catalyst surface to be. In order to solve such problems and to carry out an efficient carbon dioxide reduction reaction, it is important to increase the concentration of carbon dioxide transferred to the surface of the catalyst and to form nanoparticles having small and large surface area which lowers the proton reduction reactivity. .

United States Patent Application Publication No. 2008/0274344 Japanese Patent Application Laid-Open No. 2009-259417 Korean Patent Application Publication No. 10-2015-0059692

The present invention is to overcome the limitations of the prior art and provide a catalyst preparation method which is excellent in activity and selectivity for the carbon dioxide reduction reaction and can also improve the catalyst stability.

In one aspect of the present invention, there is provided a method for producing a metal nanoparticle, comprising: (A) obtaining a first dispersion in which metal nanoparticles are dispersed by performing sputtering using a metal target on a dispersion medium, (B) dispersing the support in the first dispersion, And (C) subjecting the second dispersion to heat treatment. The present invention also relates to a method for producing a catalyst for carbon dioxide reduction.

The gold nanoparticles (PEG-Au / C) synthesized according to the present invention can exhibit a carbon dioxide reduction efficiency twice as good as that of commercially available Au / C.

1 is a schematic view showing the difference between a liquid sputtering method and an existing chemical synthesis method.
FIG. 2 shows a photomicrograph, a particle size distribution, and an X-ray diffraction pattern and a thermogravimetric analysis of gold nanoparticles (PEG-Au / C) prepared using polyethylene glycol as a solvent. (a) SEM micrograph and particle size distribution of PEG-Au / C prepared by liquid sputtering, (b) Scanning electron micrograph and particle size distribution of the synthesized particles after heat treatment of Example 2, c) X-ray diffraction chart of PEG-Au / C particles before and after the heat treatment of Example 2, and (d) PEG-Au / C.
3. PEG-Au / C (red), commercially available Pt / C (black), PEG-Au / C (pink) after heat treatment of Example 2, and PEG added by liquid sputtering method in aqueous solution (B) Linear current-voltage measurement data (a) measured using Au / C (gray) and carbon monoxide generation efficiency graph calculated by detecting carbon monoxide generated at this time. Electrochemical reduction current measurements were performed using Ag / AgCl as a reference electrode in an aqueous solution saturated with carbon dioxide. The formation of carbon monoxide was measured by gas chromatography.
4. Results of the chronoamperometry measurements of the stability of carbon dioxide reduction using PEG-Au / C prepared by liquid sputtering. (a pink solid line and a blue solid line) measured before the heat treatment (pink solid line and red dotted line) of Example 2 of PEG-Au / C and after the heat treatment (light blue solid line and blue dotted line) of Example 2, Carbon monoxide production current (red dotted line and blue dotted line) reflecting production efficiency. (b) Time-of-day current method to investigate the effect of heat treatment of PEG-Au / C on carbon monoxide generation current of Example 2; PEG-Au / C (red) and PEG-Au / C (blue) after heat treatment of Example 2. (c)

Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.

In one aspect of the present invention, there is provided a method for producing a metal nanoparticle, comprising: (A) obtaining a first dispersion in which metal nanoparticles are dispersed by performing sputtering using a metal target on a dispersion medium, (B) dispersing the support in the first dispersion, And (C) subjecting the second dispersion to heat treatment. The present invention also relates to a method for producing a catalyst for carbon dioxide reduction.

1 is a conceptual diagram showing the difference between the conventional liquid sputtering method and the conventional chemical synthesis using the high frequency sputtering described in the above embodiment. For general chemical synthesis, a metal precursor, a catalyst support, a surfactant, and a reducing agent are added to a solvent at a constant concentration, and the temperature of the reaction solution is adjusted to initiate a reduction reaction. After initiating the reduction reaction, the metal nanoparticles synthesized on the support are collected after filtering and washing. At this time, the solution remaining after synthesis still contains an unreacted precursor and a surfactant, which makes it difficult to recycle and the synthesis process is complicated.

On the other hand, the synthesis using a liquid sputter simply places the metal target on the solvent as described in the above technical examples and directly injects the metal material into the solvent containing the catalyst support by sputtering. The catalyst particles produced at this time can be recovered through a filtering process and used as a catalyst such as carbon dioxide reduction. The remaining solution after the catalyst synthesis can be reused because there is no chemical substance such as a metal precursor or a surfactant.

In one embodiment, the metal is selected from gold, silver, copper and alloys of two or more of these metals. It is also important that the first dispersion contains no support. In the case of metals not listed above such as platinum, a catalyst is obtained even if sputtering is performed on the dispersion containing the support. In the case of the metal used in the present invention, if the support is not dispersed after sputtering, It was confirmed that it was practically impossible to obtain the catalyst.

In another embodiment, the dispersion medium is selected from polyethylene glycol, polyethyleneimine, tetraethylenepentamine and mixtures of two or more thereof.

In a preferred embodiment, the dispersion medium is polyethylene glycol.

In a more preferred embodiment, the dispersion medium is a polyethylene glycol having a weight average molecular weight of 500 to 1,000. When the dispersion medium is polyethylene glycol and the weight average molecular weight is in the above range, the catalyst prepared by using such a polyethylene glycol as a dispersion medium or solvent has a low activity against a competitive proton reduction reaction and has a low activity against a desired carbon dioxide reduction reaction Activity was found to be high.

In another embodiment, the support is carbon particles

In yet another embodiment, the dispersion of step (B) is performed by ultrasonic treatment.

In another embodiment, the heat treatment comprises: (C1) first heat treating the second dispersion in an air atmosphere at 130 to 200 ° C for 1 to 5 hours, (C2) heat treating the first heat- Followed by a secondary heat treatment for 1 to 5 hours in a reducing atmosphere at 200 캜. If the heat treatment is not carried out in the above two steps or if the temperature range and the time range of each heat treatment are out of range, the content of the dispersion medium bound to the catalyst is changed, which is undesirable.

In another embodiment, the reducing atmosphere is a mixed gas of hydrogen and argon.

Hereinafter, the present invention will be described in more detail with reference to Examples and the like, but the scope and content of the present invention can not be construed to be limited or limited by the following Examples. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the present invention as set forth in the following claims. It is natural that it belongs to the claims.

In addition, the experimental results presented below only show representative experimental results of the embodiments and the comparative examples, and the respective effects of various embodiments of the present invention which are not explicitly described below will be specifically described in the corresponding part.

Example

Example 1

For the synthesis of metal nanoparticles using liquid sputtering, the base pressure of a radio-frequency sputter reactor and the working pressure under argon gas were maintained at ¹ × 10 ^-5 Torr and 1 × 10 ^-2 Torr, respectively. For gold nanoparticle synthesis, a gold target (99.95%) was placed at a distance of 20 cm from the liquid surface. At this time, 20 mL of polyethylene glycol (PEG, weight average molecular weight: 600) was used as the liquid. To form metal nanoparticles, the power of the high-frequency sputter was raised to 300 W and sputtered in solution for one hour.

After the sputtering process, 20 mg of carbon particles to be used as a support of the nanoparticles were dispersed on the liquid in which the gold nanoparticles were dispersed. At this time, by ultrasonication of the solution in which the metal catalyst nanoparticles and the carbon support are dispersed, the metal nanoparticles are prevented from aggregating due to the interaction between the metal nanoparticles, and the metal nanoparticles are adsorbed on the carbon support.

Carbon-supported metal nanoparticles dispersed in PEG were filtered out, washed with ethanol and dried at 75 ° C for 5 hours. Thereafter, the carbon-supported metal nanoparticles were subjected to a heat treatment at 160 ° C. for 2 hours in an air atmosphere, followed by a reduction heat treatment at 160 ° C. for 2 hours in a mixed gas atmosphere of 5% hydrogen and 95% argon. Thereafter, the metal nanoparticles were washed for 3 hours in 1 molar sulfuric acid and 1 molar nitric acid mixed solution to remove the remaining impurities.

Comparative Example 1

For metal nanoparticle synthesis using liquid sputtering, the base pressure of a radio-frequency sputter reactor and the working pressure under argon gas were maintained at ¹ × 10 ^-5 Torr and 1 × 10 ^-2 Torr, respectively. For gold nanoparticle synthesis, a gold target (99.95%) was placed at a distance of 20 cm from the liquid surface. At this time, 20 mL of polyethylene glycol (PEG, weight average molecular weight: 600) was used as the liquid.

First, a method of previously dispersing a substance to be used as a support of metal nano-particles on a solution and forming metal particles on a support was used. 20 mg of the carbon support was dispersed in the PEG solution, and the supported metal nanoparticles were sputtered for one hour by raising the power of the high frequency sputtering to 300 W.

As a result, it was confirmed that the gold particles were aggregated to a size of several tens of nanometers due to the interaction between the gold particles before being formed on the carbon support member, and were not effectively supported on the carbon support because the gold particles were formed without being subjected to the ultrasonic treatment in the sputtering process.

Example 2

The catalyst prepared in Example 1 was heat-treated for 1 hour in an air atmosphere at 400 ° C to control the amount of the polymer (PEG) present on the surface of gold nanoparticles.

Test Example 1: Carbon Dioxide Reduction Through Gold Nanoparticles Synthesized by Liquid Sputtering

As shown in FIG. 2, the size of the PEG-Au / C particles synthesized by liquid sputtering was found to be about 11 nm, which is the size of the gold nanoparticles (about 15 nm or less) known to be required for a good carbon dioxide reduction reaction. .

In the case of the catalyst of Example 2 which was heat-treated at 400 ° C, the gold nanoparticle size of PEG-Au / C was increased to about 14 nm.

As a result of X-ray diffraction analysis of the crystal structure of PEG-Au / C with respect to the catalysts of Examples 1 and 2, it was found that the crystal structure of gold nanoparticles did not change depending on the presence or absence of PEG coating or heat treatment Respectively.

Through the thermogravimetric analysis, it was confirmed that the PEG was oxidized by heat treatment at 400 ° C. and the PEG coating on the surface was partially removed (see FIG. 2).

The evaluation results of the catalytic activity for the electrochemical reduction reaction of PEG-Au / C are shown in FIG. At this time, regardless of the heat treatment in Example 2, PEG-Au / C exhibited excellent total reduction and CO ₂ reduction activity as compared with the commercial gold catalyst. The electrochemical carbon dioxide reduction reaction in the aqueous solution competes with the reduction reaction (hydrogen generation reaction) of the protons present in the aqueous solution. In the case of PEG-Au / C, the total current density including the proton reduction reaction and the carbon dioxide reduction reaction Showed higher activity than commercial Au / C catalysts. For example, PEG-Au / C and commercial Au / C showed a total reduction current of about 7 mA cm ^-2 and 4 mA cm ^-2 at -1.4 V vs. Ag / AgCl reference electrode, respectively, The PEG-Au / C catalyst showed about 70% higher reduction current than commercial Au / C catalyst.

At this time, the total reduction current value does not increase even when PEG is added to commercially available Au / C to observe the PEG effect in the reduction reaction. In the case of PEG-Au / C, it was confirmed that even when heat treatment was performed at 400 ° C to remove a certain amount of PEG on the surface, the change in the reduction current value was not large (FIG.

When the product (carbon monoxide) of the reduction reaction was confirmed by gas chromatography, PEG-Au / C was superior to commercially available Au / C in view of the carbon dioxide reduction activity using PEG-Au / C and commercial Au / (FIG. 3B). For example, PEG-Au / C exhibits more than twice the CO2 reduction efficiency (Faraday Efficiency, 100% vs. 45%) than commercial Au / C at -1.2 V vs. Ag / AgCl reference electrode (Fig. 3B).

When PEG was added to commercial Pt / C through post-treatment, the carbon dioxide reduction efficiency increased from 45% to 67%. Also, it was observed that when the PEG-Au / C prepared by the liquid sputtering method was heat-treated in Example 2 to remove a certain amount of PEG, the carbon dioxide efficiency of PEG-Au / C was reduced from 100% to 75% 3b). The PEG-Au / C catalyst prepared through liquid sputtering showed excellent carbon dioxide reducing activity through the above experiment and its activity shows correlation with PEG used as a solvent in the liquid sputtering process.

The reduction activity of PEG-Au / C catalyst over time was measured by time-domain current method to show the stability of catalytic activity synthesized by liquid sputtering. As a result, about 20% reduction activity was observed after 10 hours , Which corresponds to about 2% deactivation per hour (Figure 4a, pink solid line). At this time, the catalyst having slightly removed PEG through the heat treatment in Example 2 showed a similar decrease in activity (FIG. 4A, solid blue line).

The carbon dioxide reduction efficiency in the total reduction current was measured by gas chromatography. As a result, the carbon dioxide reduction efficiency of the PEG-Au / C without heat treatment in Example 2 was half as low as 100% for 10 hours ), The carbon dioxide reduction efficiency of the heat-treated PEG-Au / C of Example 2 decreased to 80% after 10 hours from the initial 100%. Through this, it can be seen that PEG coated on the surface affects the reduction efficiency of carbon dioxide.

Through the above experiments, PEG-Au / C produced by liquid sputter shows higher total reduction activity and carbon dioxide reduction activity than commercial Au / C, and the stability of carbon dioxide reduction reaction is also superior to commercial Au / C Respectively.

Claims (9)

(A) obtaining a first dispersion in which metal nanoparticles are dispersed by performing sputtering using a metal target on a dispersion medium,
(B) dispersing the support in the first dispersion to obtain a second dispersion,
(C) heat-treating the second dispersion. The method according to claim 1, wherein the metal is selected from gold, silver, copper, and alloys of two or more thereof,
Wherein the first dispersion contains no support. ≪ RTI ID = 0.0 > 11. < / RTI > 3. The method of claim 2, wherein the dispersion medium is selected from the group consisting of polyethylene glycol, polyethyleneimine, tetraethylenepentamine, and mixtures of two or more thereof. 4. The method of claim 3, wherein the dispersion medium is polyethylene glycol. 5. The method for producing a catalyst for reducing carbon dioxide according to claim 4, wherein the dispersion medium is polyethylene glycol having a weight average molecular weight of 500 to 1,000. 6. The method of claim 5, wherein the support is carbon particles. The method of claim 6, wherein the dispersion of step (B) is performed by ultrasonic treatment. The method of claim 7, wherein the heat treatment comprises: (C1) first heat treating the second dispersion in an air atmosphere at 130 to 200 ° C for 1 to 5 hours, (C2) Lt; RTI ID = 0.0 > 1 C < / RTI > for 1 to 5 hours. The method for producing a carbon dioxide catalyst according to claim 8, wherein the reducing atmosphere is a mixed gas of hydrogen and argon.

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