KR20180037729A - Catalyst for reducing carbon dioxide and process of preparing the same - Google Patents

Abstract

The present invention relates to a catalyst for reducing carbon dioxide, which is coated with a polyimine-based polymer and to a manufacturing method thereof. In particular, gold nanoparticles synthesized by using PEI having a molecular average molecular weight of 1,000 to 3,000 as a ligand show a higher carbon dioxide reduction current density and reduction efficiency than conventional commercial catalysts.

Description

[0001] The present invention relates to a catalyst for reducing carbon dioxide and a process for preparing the same,

The present invention relates to a catalyst for reducing carbon dioxide and a method for producing the same using a polymer.

In general, it is known that a catalyst for reducing carbon dioxide has a good activity at a certain size (15 nm or less). The carbon dioxide reduction catalyst is required to have low activity in addition to the carbon dioxide reduction reaction (for example, a hydrogen production reaction through proton reduction). The carbon dioxide reduction catalyst is used in a form supported on carbon or the like to have a wide specific surface area. Various surfactants and the like are used as an additive during catalyst synthesis to synthesize a catalyst satisfying the above-mentioned requirements. 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 with the present technology, but there is a problem that formation of very small and uniform nanoparticles is still difficult.

u Chen, Azam Khan, Douglas R. MacFarlane, Jie Zhang, "Polyethylenimine promoted electrocatalytic reduction of CO2 to CO in aqueous medium by graphene-supported amorphous molybdenum sulphide ", Energy Environ. Sci., 9, 216 (2016) 2. Particle Size Effects in the (2): Zhi Cao, Dohyung Kim, Dachao Hong, Yi Yu, Jun Xu, Song Lin, Xiaodong Wen, Eva M. Nichols, Keunhong Jeong, Jeffrey A. Reimer, Peidong Yang, Catalytic Electroreduction of CO2 on Cu Nanoparticles ", J. Am. Chem. Soc. 138, 8120 (2016)

The present invention is to provide a catalyst for carbon dioxide and a manufacturing method which can solve the problems of the above conventional technologies.

In one embodiment of the present invention for solving the above problem, the size and the degree of dispersion of nanoparticles are controlled by using a polyethylenimine (PEI) containing a terminal amino group as a ligand, and the molecular weight of the polymer is controlled to be 3 nm And synthesize gold nanoparticles with high dispersion.

The gold nanoparticles synthesized by using PEI having a molecular weight of 3,000 or less as a ligand show higher carbon dioxide reduction current density and reduction efficiency than conventional commercial catalysts.

FIG. 1 shows (a) transmission electron microscopy and electron scattering images of (a) HADDF-scanning transmission electron microscopy (HADDF-STEM) and energy dispersive spectrometry (EDS) images of gold nanoparticles synthesized using a lymein polymer (Au, N, C) images of the components.
FIG. 2 shows the results of X-ray diffraction analysis of gold nanoparticles synthesized using polyethyleneimine and (b) the measurement results of gold nanoparticles (red) and polyethyleneimine synthesized using polyethyleneimine The result is a gold nanoparticle (black) thermo-mass spectrometry (TGA) analysis.
3 shows the results of analysis of gold nanoparticles synthesized through polyethyleneimine by X-ray photoelectron spectroscopy (XPS). (A) electron binding energy of a gold element, (b) electron binding energy of a nitrogen atom, and (c) Ray absorption analysis (XANES).
4 is an electrochemical analysis result of a carbon dioxide reduction reaction using metal nanoparticles piled up with polyethyleneimine. (A) of gold nanoparticles (red) deposited with a polyethyleneimine having a weight average molecular weight of 2,000, gold nanoparticles (blue) deposited with a polyethyleneimine having a weight average of 75,000, and gold nanoparticles (black) Current value and (b) carbon monoxide reduction current value calculated by gas chromatography analysis.

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

One aspect of the present invention is A catalyst for reducing carbon dioxide comprising (a) a support and (b) nanoparticles supported on the support, wherein the nanoparticles are metal nanoparticles coated with a polyimine-based polymer will be.

According to one embodiment, the polyimine-based polymer is a polyethyleneimine.

According to another embodiment, the polyethyleneimine has a weight average molecular weight of 1,000 to 3,000.

As is well known, carbon dioxide reduction and proton reduction are competitive reactions, so it is very important to inhibit proton reduction and increase the rate of carbon dioxide reduction reaction. In the present invention, it has been confirmed that the selectivity of carbon dioxide reduction remarkably increases when the polyimine-based polymer is polyethyleneimine and the weight average molecular weight thereof is in the range of 1,000 to 3,000. It was confirmed that no remarkable increase in selectivity was observed when the polyimine-based polymer was not polyethyleneimine or the weight-average molecular weight was outside the above range.

According to another embodiment, the loading amount of the metal nanoparticles carried on the support is 10 to 30% by weight based on the weight of the support.

According to another embodiment, the nanoparticles are 2 to 5 nm in diameter.

Another aspect of the present invention relates to (A) a method for producing a catalyst for reduction of carbon dioxide, which comprises a step of reducing a reducing agent into a dispersion of a polyethyleneimine, a nanoparticle precursor, and a support.

According to one embodiment, the dispersion is a mixed dispersion of a first dispersion comprising the polyimine-based polymer and the support and a second dispersion comprising the nanoparticle precursor.

According to another embodiment, the polyimine-based polymer is a polyethyleneimine.

According to another embodiment, the polyethyleneimine has a weight average molecular weight of 1,000 to 3,000.

According to another embodiment, the reducing agent is sodium borohydride, the nanoparticle precursor is chloroauric acid (HAuCl ₄ ), and the dispersion medium of the dispersion, the first dispersion and the second dispersion is ethanol.

According to another embodiment, the mixed dispersion is obtained by introducing the second dispersion into the first dispersion.

It is important that the second dispersion containing the nanoparticle precursor is added to the first dispersion containing the polyimine polymer and the support in order to obtain nanoparticles of uniform size of 2 to 5 nm, It was confirmed that when the mixed dispersion was obtained by adding the second dispersion to the first dispersion, the size of the formed nanoparticles may not be uniform.

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

Experimental method: Fabrication of gold nanoparticle catalyst packed with polyethyleneimine

(HAuCl ₄ O 3 H ₂ O, hydrogen tetrachloroaurate), a nanoparticle support (carbon, Vulcan-XC72), and a metal precursor reducing agent (sodium borohydride sodium borohydride) were added to the ethanol solvent and the nanoparticles were synthesized by reduction of the metal precursor.

Specifically, the polyethylene in ethanol 740 mL imine _{(M w ~ 2,000, M n} ~ 1800, hereinafter 'PEI 2000' that call) into the carbon powder (Vulcan-XC72) 0.15 g is used as a support in 2400 μL with nanoparticles of carbon powder And ultrasonication was performed for 30 minutes so as to be well dispersed. Separately, 75 mg of a metal precursor (HAuCl ₄ ) was added to ethanol separately in 20 mL of ethanol and vortexed mechanically. The carbon powder and the polyethylene imine solution in the ethanol were stirred by ultrasonication, and then 20 mL of the metal precursor ethanol solution was added to the carbon powder solution. The solution was then mechanically further stirred for 2 hours. Thereafter, a sodium borohydride solution dissolved in 20 mL of ethanol was added to an ethanol solution (760 mL) containing a metal precursor, a carbon powder and a polyethyleneimine to initiate the reduction reaction of the metal precursor. The solution was mechanically stirred for about 12 hours to allow the metal nanoparticles to be completely reduced on the carbon powder. After the metal reduction reaction was completed, the synthesized metal nanoparticles were separated through a filter, and the red nanoparticles were sequentially washed with 800 mL of ethanol and 800 mL of water, and vacuum dried to prepare gold nanoparticles (PEI-Au / C) catalyst was recovered.

Except that polyethyleneimine (hereinafter referred to as 'PEI 700', 'PEI 2000', or 'PEI 75000') having a weight average molecular weight of 700, 2000, or 75,000 was used in place of polyethyleneimine having a weight average molecular weight of 2,000 The catalyst was prepared in the same manner as in Example 1.

Experimental Results: Carbon Dioxide Reduction with Gold Nanoparticle Catalyst Accumulated with Polyethyleneimine

1 is a transmission electron microscope (TEM), electron diffraction image and magnified transmission electron micrograph of (a) gold nanoparticles prepared using PEI 2000 according to the synthesis method described above, and (b) HAADF-scanning transmission electron microscope (HAADF-STEM) and energy dispersive spectroscopy (EDS). According to the analysis, the gold nanoparticles synthesized using polyethyleneimine polymer have a size of about 3 nm. According to energy dispersive spectroscopy, gold and nitrogen distributed on carbon were detected at the same site. It was observed that the nitrogen-containing polyethyleneimine existed on the gold particles in a well-coated form.

As a result of the X-ray diffraction analysis of the gold nanoparticles synthesized using PEI 2000, the polyethyleneimine did not significantly affect the crystallinity of the gold nanoparticles (FIG. 2a), and the gold nanoparticles synthesized using polyethyleneimine The particles were analyzed by a heat-mass spectrometer to confirm that the gold nanoparticles were supported on a carbon support at a mass ratio of 20% (FIG. 2b).

The surface of gold nanoparticles synthesized using PEI 2000 was analyzed by X-ray photoelectron spectroscopy (FIGS. 3A and 3B). As can be seen from the results of energy dispersive spectroscopy (EDS) of FIG. 1, The polyethyleneimine appeared to be well coated on the gold surface, and the X-ray absorption analysis (XANES) of FIG. 3 showed that the polyethylene imine coated on the gold surface did not affect the electronic structure of gold.

The carbon dioxide reduction reaction through gold nanoparticles piled up with polyethyleneimine was analyzed using an electrochemical three - electrode system. At this time, silver / silver chloride (Ag / AgCl) was used as a reference electrode to control the potential of gold nanoparticle electrodes piled up with polyethyleneimine. And an electrode made of carbon and platinum was used as a counter electrode of the 3-electrode system to allow current to flow. Gold nanoparticles deposited with polyethyleneimine were immobilized on a carbon disk electrode using a proton conductive polymer (eg, Nafion), and their activity was analyzed. The reduction reaction of carbon dioxide was analyzed in an aqueous solution saturated with carbon dioxide, and the carbon monoxide produced was analyzed by gas chromatography or the like.

FIG. 4 shows the activity of electrochemical carbon dioxide reduction of gold nanoparticles deposited with polyethyleneimine analyzed through the electrochemical three-electrode system described above. The gold nanoparticles coated with PEI 2000 (Fig. 4a, red) were measured for apparent current values including all reduction reactions that may occur in aqueous solution, including carbon dioxide reduction and proton reduction reactions, using gold nanoparticles coated with PEI 75000 (PEI 2000 coated gold nanoparticles are about 50 mA / cm ² , PEI 75000 coated or uncoated gold nanoparticles) increased by about 20% compared to the uncoated gold particles (FIG. 4A, blue) The particle shows a current value at about 40 mA / cm ² , -1.0 V).

In particular, when comparing only the carbon monoxide production current through carbon dioxide reduction, the gold nanoparticles coated with PEI 2000 had a carbon monoxide production current density (FIG. 4b red) at -1.0 V of about 37 mA / cm ² , about two times the carbon monoxide production current density (Fig. 4b blue, about 4 mA / cm ²⁾ or carbon monoxide production current density of the gold nano-particles (Fig. 4b black, and about 20 mA / cm ²⁾ uncoated gold nanoparticles And 9 times higher than the previous year.

FIG. 4 shows that the average molecular weight of the polyethyleneimine coated with and without the polyethyleneimine has a great effect on the carbon dioxide reducing activity through the gold nanoparticles.

Through the above analysis, it was found that (i) synthesis of metal nanoparticles using polyethyleneimine allows the synthesis of metal nanoparticles coated with a small and uniform (3 nm) polyethyleneimine, and (ii) The particles exhibit unexpectedly excellent carbon dioxide reducing activity.

Claims (11)

A catalyst for reducing carbon dioxide comprising (a) a support, and (b) nanoparticles carried on the support,
Wherein the nanoparticles are metal nanoparticles coated with a polyimine-based polymer. The catalyst for reducing carbon dioxide according to claim 1, wherein the polyimine-based polymer is polyethyleneimine. The catalyst for reducing carbon dioxide according to claim 2, wherein the polyethyleneimine has a weight average molecular weight of 1,000 to 3,000. 4. The catalyst for reducing carbon dioxide according to claim 3, wherein the amount of the metal nanoparticles carried on the support is 10 to 30% by weight based on the weight of the support. 5. The catalyst for reducing carbon dioxide according to claim 4, wherein the nanoparticles have a diameter of 2 to 5 nm. (A) introducing a reducing agent into a dispersion of polyethylene imine, a nanoparticle precursor, and a support to perform a reduction reaction. The method of claim 6, wherein the dispersion is a mixed dispersion of a first dispersion containing the polyimine-based polymer and the support, and a second dispersion containing the nanoparticle precursor. The method for producing a catalyst for reduction of carbon dioxide according to claim 7, wherein the polyimine-based polymer is polyethyleneimine. The method of claim 8, wherein the polyethyleneimine has a weight average molecular weight of 1,000 to 3,000. 10. The method of claim 9, wherein the reducing agent is sodium borohydride,
The nanoparticle precursor is chloroauric acid (HAuCl ₄ )
Wherein the dispersion medium of the dispersion, the first dispersion, and the second dispersion is ethanol. The method for producing a catalyst for reducing carbon dioxide according to claim 10, wherein the mixed dispersion is obtained by introducing the second dispersion into the first dispersion.

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