WO2019182240A1 - Method for recovering surface oxide of catalyst - Google Patents

Abstract

The present invention relates to an electrochemical cell used when carbon dioxide is decomposed and reduced to a useful conversion product, and to a catalyst to be used in an electrode for a negative electrode within the cell. According to the present invention, a method for recovering a catalyst can be provided, the method comprising the steps of: preparing a metal oxide catalyst having a reduced surface; and applying a voltage greater than or equal to the copper oxidation potential to the reduced metal oxide catalyst by applying a predetermined charge amount or more to reoxidize the metal oxide catalyst. Thus, it is possible to reuse the metal oxide catalyst without additional materials and/or equipment.

Description

How to recover the surface oxides of the catalyst

The present invention relates, in particular, to a method for recovering the surface oxides of copper oxide catalysts used in the electrodes for cathodes in electrochemical cells used when decomposing carbon dioxide to reduce them to useful conversions.

As the industry develops, energy use is greatly increased, and accordingly, the use of hydrocarbons including fossil fuels is also rapidly increasing. All hydrocarbons are basically in a certain proportion of carbon and hydrogen, which inevitably generates carbon dioxide when they are burned.

Carbon dioxide is known to be a major cause of global warming. Accordingly, the reduction of carbon dioxide has emerged as a very important issue worldwide.

On the other hand, there are many industrial plants, chemical plants, steel mills, and cement plants, which emit a lot of carbon dioxide.

The application of energy to carbon dioxide has recently received a lot of attention as a method of removing carbon dioxide generated by the conversion technology that converts it into useful resources such as carbon compounds and oxygen. Pressure conversion at high temperatures or the use of catalysts include such conversion techniques.

Among the conversion techniques, the method of using a catalyst has many advantages that the apparatus and the method itself are very simple, can use electricity produced from renewable energy as it is, and is very easy to scale up to a commercial scale. In addition, the method using the catalyst has the advantage that it can selectively produce a variety of carbon compounds.

On the other hand, in order for the method using the catalyst to be put into practical use, C2 or more useful hydrocarbons such as ethylene, ethanol, propanol and butanol having excellent practicality must be stably and continuously produced.

Recently, Cu-based catalysts have been reported to have an effect on the generation of C2 or more hydrocarbons have attracted attention.

Among them, the pure Cu catalyst has a stable phase of Cu (111), and the Cu catalyst generates more C1 (carbon monovalent hydrocarbon) than C2 + (carbon bivalent hydrocarbon) among the products produced by the reduction of carbon dioxide. It is known.

Meanwhile, in the case of the Cu ₂ O catalyst, the C2 + production rate is higher than the C1 production rate. However, the reduction reaction proceeds in accordance with Cu ₂ O in the catalyst from the monovalent Cu + 1 ions are to occur the reduction of the Cu atom thereby C2 + generation rate of carbon dioxide, there is a problem that continues to decrease.

End in order to maintain the hydrocarbon formation efficiency than C2 of the Cu ₂ O catalyst high and a method which can develop or restore the reduced Cu ₂ O catalyst has excellent durability that can suppress the reduction of the Cu ₂ O Catalyst Catalyst seek Should be.

Accordingly, the present invention seeks to invent a method of stably reoxidizing a Cu ₂ O catalyst in order to decompose carbon dioxide so as to stably and continuously produce hydrocarbons of C 2 or more.

In a catalyst for a cathode in which a reduction reaction of an electrochemical cell used for the decomposition of carbon dioxide occurs, the present invention has a selectivity to react only with carbon dioxide while at the same time stably and continuously providing useful by-products such as C2 or more hydrocarbons. It is an object to provide a method for recovering the surface oxides of a Cu ₂ O catalyst in order to be able to produce them.

In addition, through the development of a method for more quickly removing the hydrocarbons present on the surface of the Cu ₂ O catalyst, the present invention is another object to provide a method for reducing the process time for restoring the surface oxide of the Cu ₂ O catalyst. .

According to one embodiment of the present invention, there is provided a method of recovering a surface oxide of a Cu ₂ O catalyst, comprising: preparing a metal oxide catalyst having a reduced surface; A method for recovering a catalyst comprising a; reoxidizing by applying a voltage above a copper oxidation potential to the reduced metal oxide catalyst by a predetermined charge amount or more.

Preferably the metal oxide catalyst is a copper oxide (Cu _x O); may be provided with a catalyst recovery method.

Preferably, the metal component of the metal oxide catalyst is Ta, Os, Nb, Mo, Ir, Ag, V, Ru, Mn, Rh, Pd, Ni, Co, Fe, Cr, Hf, Ti, Y, Zr, Sc One or two or more of these metals or alloys thereof may be provided.

Preferably, the voltage in the reoxidation step is +0.8 to 1.5V; may be provided a catalyst recovery method characterized in that.

Preferably the amount of charge in the reoxidation step is 1 C / ㎠ or more; may be provided a method for recovering the catalyst characterized in that.

By providing a way to more quickly remove the carbide hydroxide present in the Cu ₂ O catalyst surface according to another embodiment of the present invention it can more reduce the process time for restoring the surface oxide of the Cu ₂ O catalyst, the re-oxidation step before In addition to the step of removing the hydrocarbon from the catalyst surface; there may be provided a method for recovering the catalyst further comprising.

At this time, the step of removing the hydrocarbon is applying a pulse of a current value of 5 to 10 times the normal reduction current at a voltage above the oxygen reduction reaction (ORR) potential; recovery of the catalyst, characterized in that A method may be provided.

Preferably the reoxidation step is initiated when the measured hydrocarbon fraction value is less than or equal to a set threshold value. A catalyst recovery method may be provided.

Preferably, the reoxidation step may be started when the current or power value measured in the electrochemical cell in which the catalyst is used is lower than a set threshold.

According to the recovery method of the metal oxide catalyst of the present invention, the metal oxide catalyst, which is a catalyst for a negative electrode decomposing carbon dioxide, can be recovered repeatedly, reproducibly and very effectively.

This allows the metal oxide catalyst to be reused as is without additional materials and / or equipment.

In addition, the recovery method of the metal oxide catalyst of the present invention can shorten the recovery time of the metal oxide catalyst.

In this way, the recovery method of the metal oxide catalyst of the present invention can increase the total uptime of the electrochemical cell by increasing the uptime for the carbon dioxide decomposition and reducing the downtime for the catalyst reoxidation in the electrochemical cell for the reduction decomposition reaction of carbon dioxide. Can be.

1 is a schematic diagram of a typical electrochemical cell for decomposing and reducing carbon dioxide.

FIG. 2 illustrates the ratio of hydrocarbons generated when carbon dioxide is decomposed on a surface of a copper oxide catalyst composed of a Cu catalyst and a Cu ion having an oxidation number of +1.

Figure 3 shows the crystal structure of the negative electrode measured by XRD before and after the carbon dioxide reduction reaction in the experimental example using Cu ₂ O as the negative electrode catalyst in the electrochemical cell for carbon dioxide decomposition.

4 is a Pourbaix diagram (potential-pH diagram) of Cu ₂ O.

FIG. 5 shows the ratio of ethylene (C ₂ H ₄ ) in hydrocarbons produced when carbon dioxide is reduced using a catalyst composed of Cu _x O and a catalyst composed of pure Cu, each of which is oxidized to the surface of pure Cu.

Figure 6 shows a three-electrode (anode electrode / reduction electrode / reference electrode) system used for the performance evaluation of the catalyst in the present invention.

Figure 7 shows the results of the analysis of the microstructure and surface components before and after the carbon dioxide reduction reaction in a catalyst consisting of copper oxide (Cu _x O).

Figure 8 shows the results of the analysis of the microstructure and surface components before and after the carbon dioxide reduction reaction in a catalyst consisting of pure copper (Cu).

9 and 10 show that the catalyst composed of copper oxide (Cu _x O) undergoes a carbon dioxide reduction reaction for at least 100 minutes, and the conversion rate from carbon dioxide to C 2 or more hydrocarbon is deteriorated, and then the oxidation potential is applied to the catalyst again. It is the electron microscope photograph which observed the surface of the catalyst with the electron microscope.

11 shows a schematic of a two electrode carbon dioxide reactor for performance evaluation of a copper oxide (Cu _x O) catalyst.

FIG. 12 shows the actual shape of a two-electrode carbon dioxide reactor for performance evaluation of a copper oxide (Cu _x O) catalyst.

FIG. 13 illustrates a Faradaic efficiency of ethylene (C ₂ H ₄ ) generated by applying a copper oxide (Cu _x O) catalyst to a cathode of a two-electrode reactor and reducing and decomposing carbon dioxide.

Hereinafter, a catalyst and a method of preparing the same according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, only this embodiment to make the disclosure of the present invention complete and to those skilled in the art to fully understand the scope of the invention It is provided to inform you.

In order to clearly describe the present invention, parts irrelevant to the description are omitted, and like reference numerals designate like elements throughout the specification. In addition, some embodiments of the invention will be described in detail with reference to exemplary drawings. In adding reference numerals to components of each drawing, the same components may have the same reference numerals as much as possible even though they are shown in different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description may be omitted.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) can be used. These terms are only to distinguish the components from other components, and the terms are not limited in nature, order, order or number of the components. If a component is described as being "connected", "coupled" or "connected" to another component, that component may be directly connected to or connected to that other component, but between components It is to be understood that the elements may be "interposed" or each component may be "connected", "coupled" or "connected" through other components.

In addition, in the implementation of the present invention may be described by subdividing the components for convenience of description, these components may be implemented in one device or module, or one component is a plurality of devices or modules It can also be implemented separately.

1 is a schematic diagram of a typical electrochemical cell for decomposing and reducing carbon dioxide.

As shown in FIG. 1, the electrochemical cell includes a cathode in which an oxidation reaction in which oxygen is generated and a cathode in which reduction of carbon dioxide occurs, a compartment for accommodating an electrolyte containing the anode and the cathode, and between the cathode and the anode And a membrane that selectively passes only the desired components on the electrolyte.

Although not shown in FIG. 1, the cell includes an energy supply source for supplying energy from the outside to drive the cell. In addition, an extractor for extracting the by-product generated from the reduction of the carbon dioxide is further included. In addition, an electrolyte supply device may be added as necessary.

Apart from this, if the by-product resulting from the reduction of carbon dioxide requires another additional reaction, a secondary reactor for the reaction may optionally be included.

When carbon dioxide is decomposed and reduced in a cell as shown in FIG. 1, it is known that various by-products (or conversion products or products) are produced depending on the type of catalyst in which a reduction reaction occurs.

For example, when Ag or Sb is used as a catalyst, carbon dioxide is reduced and carbon monoxide is produced through the following reaction formula (1) in the catalyst. On the other hand, when Cu ₂ O is used as a catalyst, it is known that carbon dioxide is decomposed through the following reaction formulas (2) to (5) to generate resources such as methane, ethane, and ethylene.

_{^{CO 2 + 2H + + 2e -}} → CO + H 2 O -0.51 V (1)

_{^{CO 2 + 8H + + 8e -}} → CH 4 + 2H 2 O -0.24 V (2)

_{^{2CO 2 + 12H + + 12e -}} → C 2 H 4 + 4H 2 -0.33 V (3)

_{^{2CO 2 + 12H + + 12e -}} → C 2 H 5 OH + 3H 2 O -0.32 V (4)

_{^{3CO 2 + 18H + + 18e -}} → C 3 H 7 OH + 5H 2 O -0.31 V (V vs.NHE) (5)

On the other hand, in the oxidation electrode, water is oxidized through the following equation (6) and oxygen, hydrogen ions, and electrons are generated.

_{n / 2 H 2 O → nH} + + n / 4O 2 + ne - (6)

Therefore, when Cu ₂ O is used as a catalyst, not only various kinds of hydrocarbons can be produced, but also there are advantages that C2 or more useful hydrocarbons such as ethylene, ethanol, propanol and butanol can be produced. For this reason, Cu ₂ O has recently attracted much attention as a carbon dioxide catalyst.

FIG. 2 illustrates the ratio of hydrocarbons generated when carbon dioxide is decomposed on a surface of a copper oxide catalyst composed of a Cu catalyst and a Cu ion having an oxidation number of +1.

As shown in FIG. 2, when Cu in a metal state is used as a catalyst, CH ₄ and C ₂ H ₄ are generated on the surface of the Cu catalyst by reduction of carbon dioxide. At this time, the formation rate of each of CH ₄ and C ₂ H ₄ is similar, but it can be seen that CH ₄ occupies more fraction than C ₂ H ₄ .

In contrast, if Cu having an oxidation number of +1 is used as the catalyst, the reduction of carbon dioxide at the surface of the +1 Cu catalyst produces mainly CH ₄ and C ₂ H ₄ . However, C ₂ H ₄ in the resulting hydrocarbon is the ratio of CH ₄ can be seen to occupy a greater fraction of up to 15 or more times that of the C ₂ H ₄ CH _4. Accordingly, it can be seen that Cu having an oxidation number of +1 has a very advantageous effect on the generation of C2 or more hydrocarbons as a catalyst of an electrochemical cell for reducing carbon dioxide.

On the other hand, the reason for the difference in the hydrocarbons produced according to the type of catalyst is that if the catalyst of the cathode in which the reduction reaction of carbon dioxide occurs is Cu whose oxidation number is +1, the bonding strength between carbon dioxide and C1 hydrocarbon increases and as a result, the bond between C1-C1 It is presumed that this is because the reaction is encouraged to produce more useful hydrocarbon compounds of C2 or more.

Therefore, when Cu ₂ O is used as a catalyst for carbon dioxide reduction, carbon dioxide is initially converted at the surface of the catalyst to produce C2 or more useful hydrocarbon compounds.

However, as the reduction reaction of carbon dioxide proceeds, the Cu ₂ O catalyst is reduced to Cu of the metal by the reduction reaction at the negative electrode. Reduction of the Cu ₂ O catalyst into Cu causes most of the hydrocarbons produced in the catalyst to be converted to C 1 hydrocarbons.

Figure 3 shows the crystal structure of the negative electrode measured by XRD before and after the carbon dioxide reduction reaction in the experimental example using Cu ₂ O as the negative electrode catalyst in the electrochemical cell for carbon dioxide decomposition.

As shown in FIG. 3, the cathode before the reduction reaction may be present in the Cu ₂ O state over the entire thickness regardless of the thickness.

On the other hand, the cathodes measured by XRD after the reduction reaction were all present as Cu regardless of the thickness. The XRD measurement result means that only the reduction of the reactant carbon dioxide should occur at the cathode in the electrochemical cell, but the reduction of the catalyst itself is also very active.

The reduction of the catalyst in the electrochemical cell for carbon dioxide decomposition is due to the electrochemical properties of the material itself of the Cu ₂ O catalyst.

4 is a Pourbaix diagram (potential-pH diagram) of Cu ₂ O. The Pourbaix diagram shows the relationship between the pH and the potential at which a metal or metal ion is stably present in an aqueous solution under atmospheric pressure (meaning 1 atm). In other words, the Pourbaix diagram shows the region of the metal or metal ion or metal compound in a stable state at pH and standard hydrogen potential conditions.

As predicted from the standard reduction potential values of Fig. 4 and the above formulas (2) to (5), copper is a Cu atom itself in the range of -0.33 to -0.24 V, which are potential values at which hydrocarbons are generated by reduction of carbon dioxide. It can be seen that the presence is a thermodynamically stable state.

In other words, even if copper is present in the Cu (ion) state with +1 or +2 valence oxidation before or during the carbon dioxide reduction reaction, or as Cu ₂ O or CuO, the copper is external or Under the condition that a potential of 0 V or less is applied by the electrochemical reaction, it means that it is present as a Cu atom by a reduction reaction from Cu oxide to Cu.

Eventually, the XRD measurement results of FIG. 3 experimentally showing that the cathodes were all reduced to Cu in Cu ₂ O after the carbon dioxide reduction reaction was in good agreement with the results predicted by FIGS. 4 and (2) to (5).

Therefore, to be returned to in order to increase the durability of the Cu ₂ O catalyst is Cu ₂ O in the oxidation catalyst maintained at +1 Ga Cu state or of the reduced Cu + 1 is again the status Cu or Cu ₂ O.

The first and easiest way to think of this is to continuously and stably supply oxygen to the reduced Cu atom inside or outside the converted metal to convert the Cu metal atoms back to Cu having +1 valence.

However, the continuous supply of oxygen from inside or outside to the cathodic catalyst or electrochemical cell increases the cost of the device, increases the volume of the system, and requires additional materials and equipment.

Accordingly, the present invention has been accomplished by regenerating the catalyst itself for the cathode of an electrochemical cell, which does not involve device cost or volume increase and further requires no additional materials and equipment.

More specifically, the present invention can continuously maintain the conversion efficiency of carbon dioxide to C2 or more hydrocarbons by regenerating an oxide on the surface of the Cu ₂ O catalyst used as a catalyst for a cathode while using the apparatus of a conventional electrochemical cell as it is. Method was developed.

FIG. 5 shows the ratio of ethylene (C ₂ H ₄ ) in hydrocarbons produced when carbon dioxide is reduced using a catalyst composed of Cu _x O and a catalyst composed of pure Cu, each of which is oxidized to the surface of pure Cu.

The results of FIG. 5 were measured through the three electrode (oxidation electrode / reduction electrode / reference electrode) system shown in FIG. 6.

The three-electrode system of an embodiment of the present invention includes a gas sealed quartz reactor and a reference electrode, a working electrode and a counter electrode located on top of the reactor as shown in FIG. Cu _x O or pure Cu which oxidized the surface of pure Cu was used as a reduction electrode, and Pt and Ag / AgCl were used as an oxidation electrode and a reference electrode, respectively. As an electrolyte, 0.1 M KHCO ₃ was used at pH 6.8, and a reaction gas generated by applying a charge amount of 4 to 10 coulombs (C) at -1.9 V (vs. Ag / AgCl) was collected. The collected reaction gases were analyzed using gas chromatography (GC).

Catalysts made of copper oxide (Cu _x O) were determined to have higher ethylene (C ₂ H ₄ ) production efficiency over the entire reaction time than catalysts made of pure copper (Cu) (FIG. 5). And the result of FIG. 5 is in good agreement with the result of FIG. 2. On the other hand, as the reaction time of the carbon dioxide reduction reaction proceeds, it can be seen that the ethylene (C ₂ H ₄ ) production efficiency is reduced not only in the catalyst made of dms copper oxide (Cu _x O) but also in the catalyst made of pure copper (Cu).

7 and 8 show the results of analysis of the microstructure and surface components before and after the carbon dioxide reduction reaction in the catalyst consisting of copper oxide (Cu _x O) and the catalyst consisting of pure copper (Cu), respectively.

As shown in the microstructure and component analysis of FIG. 8, the catalyst composed of copper oxide (Cu _x O) includes several micrometer-sized oxides on the surface at a rate of several tens at.% Before the carbon dioxide reduction reaction. On the other hand, after 150 minutes of carbon dioxide reduction, the photomicrograph shows that the fraction of oxides decreased on the surface of the catalyst, and furthermore, the proportion of oxygen on the surface of the catalyst decreased by several at.%. have.

The surface tissue photographs and the results of the component analysis in FIG. 8 are in good agreement with the results in previous FIGS. 2 to 4. The catalyst consisting of copper oxide (Cu _x O) used in the carbon dioxide reduction reaction includes a high portion of copper oxide (Cu _x O) on the surface of the catalyst at the beginning of the reduction reaction. On the other hand, as the reduction reaction proceeds, the fraction of copper oxide and oxygen on the surface of the catalyst decreases.

The change in the catalyst surface made of copper oxide (Cu _x O) causes a change in the microstructure and components on the catalyst surface as the reduction reaction proceeds, and as a result, as shown in FIG. Degradation of the conversion rate occurs.

Meanwhile, the surface of the catalyst made of pure copper (Cu) and having a {100} preferred orientation on the surface, as shown in FIG. 7, contained no oxide prior to the carbon dioxide reduction reaction, and oxygen was found on the surface of the catalyst even in the component analysis results. Hardly observed. On the other hand, the catalyst after 150 minutes of carbon dioxide reduction reaction was observed that the surface does not contain particles that can be identified as an oxide or the like, as shown in the microscopic image, but the oxygen is present at the catalyst surface by a few at.%. The analysis result confirmed.

This change in microstructure and components in the catalyst made of pure copper (Cu) (FIG. 7) results in a change in the conversion ratio of carbon dioxide to hydrocarbon in FIG. 5. Specifically, catalysts made of pure copper (Cu) undergo some degree of conversion to C2 or more hydrocarbons due to {100} preferred orientation at the surface early in the carbon dioxide reduction reaction. However, as the reduction reaction proceeds, some oxidation occurs on the surface of the copper catalyst and the oxidation screens out the {100} preferred orientation effect on the surface of the catalyst. As a result, even after the reduction reaction to some extent even in the catalyst made of pure copper (Cu), it is determined that the degradation of the conversion ratio to C2 or more hydrocarbons.

Accordingly, a method of restoring a degraded catalyst surface after a carbon dioxide reduction decomposition reaction has been developed in the present invention.

9 and 10 show that the catalyst composed of copper oxide (Cu _x O) undergoes a carbon dioxide reduction reaction for at least 100 minutes, and the conversion rate from carbon dioxide to C 2 or more hydrocarbon is deteriorated, and then the oxidation potential is applied to the catalyst again. It is the electron microscope photograph which observed the surface of the catalyst with the electron microscope.

The catalyst made of copper oxide (Cu _x O) in FIGS. 9 and 10 is applied with + 1.5V from the outside (based on the standard hydrogen electrode, and all potential values are based on the standard hydrogen electrode). It is a reoxidized catalyst.

More specifically, copper (Cu) is a thermodynamically more stable state of copper oxide (CuO) than pure copper (Cu) at a voltage condition of + 0.52V or more. If a voltage of more than + 0.52V is applied to the copper from the outside, pure copper is oxidized from the surface, and the proportion of oxygen on the surface increases with voltage application.

First, when the oxidation potential of +1.5 V is applied to the catalyst made of copper oxide (Cu _x O) for 3 minutes, as shown in the left photograph of FIGS. 9 and 10, first, the reoxidation of copper causes partial surface area of the catalyst. In the region where the oxygen content was 13.92 at.% (Hereinafter referred to as%) was observed (FIG. 9). Also copper oxides having a component of Cu _x O _y of about 100 nm size were present in the region where copper reoxidation occurred (FIG. 10). These observations of FIGS. 9 and 10 indicate that oxidation has already begun or is progressing on the surface of the catalyst even if the copper oxide catalyst is reoxidized for a short time of 3 minutes.

When the reoxidation time increased to 12 minutes again for the catalyst consisting of copper oxide (Cu _x O), the reoxidation of copper occurred in a wider area of the catalyst surface as shown in the middle photo of FIGS. 9 and 10. As the reoxidation time increased from 3 minutes to 12 minutes, the oxygen content at the surface where the reoxidation of the catalyst took place was determined to be higher (17.18%) (Fig. 9) of the copper oxides having components of Cu _x O _y . It can be seen that the size also grew to about 500 nm (Fig. 10).

When the reoxidation time increased to 63 minutes for the catalyst consisting of copper oxide (Cu _x O), reoxidation of copper occurred in most areas of the catalyst surface, as shown in the photo on the right of FIGS. 9 and 10. If re-oxidation time is 63 minutes, and the average content of oxygen takes place at the surface of the catalyst reoxidation is the size of the copper oxide having the composition of were measured to be significantly increased to over 50% (Figure 9) Cu _x O _y, too 1㎛ It can be seen that the further growth (Fig. 10).

The process conditions of the method of restoring the surface oxidation degree by applying an oxidation potential externally to the catalyst made of copper oxide (Cu _x O) through the electrochemical experiment with the microstructure observation results of FIGS. 9 and 10 are as follows. Can be established.

First, the copper oxide potential applied from the outside is preferably +0.8 to 1.5V based on the standard hydrogen potential.

If the externally applied oxidation potential is +0.52 V or more, reoxidation of copper is thermodynamically possible at the catalyst surface made of copper oxide (Cu _x O). However, in order to overcome the activation energy for the copper oxidation reaction, additional electrochemical energy must be supplied in addition to + 0.52V. At this time, if the oxidation potential is less than + 0.8V, the time for reoxidation on the surface of the copper oxide (Cu _x O) catalyst becomes too long. If the reoxidation time at the catalyst surface is longer than the operating time of the electrochemical cell for carbon dioxide reduction, the long reoxidation time is undesirable since it does not meet the object of the invention of carbon dioxide decomposition.

On the other hand, the oxidation potential for reoxidation is preferably less than 1.5V. If the externally applied oxidation potential is higher than 1.5V, a peroxidation phenomenon occurs in which oxidation occurs not only on the surface of the catalyst but also on the inside thereof, causing a problem of deteriorating the life of the catalyst. Furthermore, an excessively high oxidation potential is not preferable because it is higher than the oxygen reduction reaction (ORR) potential, and as a result, oxygen may be generated to cause energy loss.

On the other hand, the amount of charge required for reoxidation of the copper oxide (Cu _x O) catalyst is preferably 1 C / cm 2 or more.

Electrochemical reactions, including carbon dioxide reduction reactions, are typically surface reactions that occur on the surface of a catalyst (or an electrode comprising a catalyst). Therefore, the surface properties of the catalyst affect the electrochemical reaction, and the internal or bulk properties of the catalyst have little effect on the surface properties. It is known that the surface range from which the surface properties in the catalyst can be determined is typically up to several micrometers deep at the surface. Therefore, in the present invention, the amount of charge required for reoxidation of the copper oxide catalyst is calculated to be approximately 1 C / cm 2.

If the amount of charge used for reoxidation of the copper oxide catalyst is less than 1 C / cm 2, there is a problem in that reoxidation of the catalyst surface does not occur sufficiently, and thus, recovery of the catalyst does not occur completely.

On the other hand, the upper limit of the amount of charge used for reoxidation of the copper oxide catalyst is not particularly limited. However, if the amount of charge is too large, energy consumption is increased, reoxidation occurs to the inside of the catalyst, and the reoxidation time is too long. Problems may occur in which the efficiency of the electrochemical cell for decomposition is lowered.

Meanwhile, according to another embodiment of the present invention, in order to shorten the time required for reoxidation of the copper oxide (Cu _x O) catalyst, a process of removing hydrocarbon adsorbed on the surface of the catalyst immediately before the oxidation potential may be added. .

More specifically, the surface of the copper oxide (Cu _x O) catalyst is a hydrocarbon produced through the carbon dioxide reduction reaction. The hydrocarbons are physically or chemically adsorbed by the reaction with the catalyst on the surface of the catalyst. Therefore, if the adsorbed hydrocarbons are present on the surface of the catalyst, the surface reoxidation reaction of the catalyst is delayed due to the hydrocarbon adsorbed on the surface of the catalyst, thereby requiring the surface reoxidation of the copper oxide (Cu _x O) catalyst. The time taken will increase.

Therefore, according to another embodiment of the present invention, in order to shake off the hydrocarbon adsorbed on the catalyst surface, a pulse having an oxygen reduction reaction (ORR) potential or more and a current value of 5-10 times or more of the normal reduction current is applied. Hydrocarbons adsorbed on the surface of the catalyst through the pulse driving may be physically separated from the surface of the catalyst by the generated oxygen bubbles. As a result, the time required for reoxidation of the catalyst can be shortened.

Meanwhile, the frequency for reoxidation of the copper oxide (Cu _x O) catalyst in the embodiment of the present invention can be determined in various ways.

The reoxidation cycle may be determined to chemically measure the hydrocarbon fraction of C2 or higher among the hydrocarbons produced first and to reoxidize the catalyst when the measured hydrocarbon fraction of C2 or higher is below the threshold.

The method has the advantage of being able to determine the reoxidation time of the copper oxide (Cu _x O) catalyst most accurately, while the disadvantage is that in-situ is difficult.

On the other hand, if the electrochemical cell for carbon dioxide reduction decomposition is set and the characteristics of the cell are determined by the hydrocarbon fraction, the reoxidation time of the catalyst can be stably set and operated.

Contrary to the hydrocarbon measurement method described above, the timing of reoxidation of the catalyst may be determined by measuring the total power of the carbon dioxide electrochemical cell.

The method has the disadvantage that it cannot accurately determine the reoxidation time of the copper oxide (Cu _x O) catalyst, but has the advantage that in-situ is possible.

If the component analysis of the hydrocarbons produced together with the total power of the electrochemical cell is mutually calibrated, the reoxidation time of the copper oxide (Cu _x O) catalyst is determined in-situ by electrical measurement methods. It becomes possible.

The regeneration method of the catalyst for carbon dioxide reduction of the present invention is applicable to other types of metal oxide catalysts in addition to copper (Cu). Furthermore, the catalyst regeneration method of the present invention is applicable to a metal oxide catalyst in the form of an alloy containing copper (Cu) and other kinds of metals.

The catalyst regeneration method of the present invention is a non-limiting example, Ta, Os, Nb, Mo, Ir, Ag, V, Ru, Mn, Rh, Pd, Ni, Co, Fe, Cr, Hf, Ti, Y, Zr, Application is also possible for catalysts comprising one or more metals of the Scs or alloys thereof.

<Example>

11 and 12 are two electrodes used to evaluate the performance of a copper oxide (Cu _x O) catalyst reoxidized for 63 minutes by an externally applied oxidation potential of 1.5V, as shown previously in FIGS. 9 and 10 of the present invention. A schematic and actual shape of a carbon dioxide reactor is shown.

A two-electrode reactor capable of injecting carbon dioxide in the gas phase and evaluating the performance of the system is located in the middle of the membrane in which H ⁺ or OH ^- ions are transferred to the catalyst by direct or indirect contact with the electrolyte, as shown in FIG. And a catalyst layer (reduction electrode or membrane electrode assembly, MEA) supported on a support such as carbon, and a gas diffusion electrode for introducing gases involved in the reaction into the catalyst and discharging the formed hydrocarbon.

FIG. 12 shows the actual shape of the two-electrode reactor of FIG. 11.

FIG. 13 illustrates a Faradaic efficiency of ethylene (C ₂ H ₄ ) generated by applying a copper oxide (CuxO) catalyst to a cathode of the two-electrode reactor and reducing and decomposing carbon dioxide.

In the Faraday efficiency (Faradaic efficiency) in Figure 13 the component analysis of the C ₂ H ₄ gas using gas chromatography and Faraday efficiency was calculated by the following equation.

Faradaic Efficiency = {(number of generated C ₂ H ₄ moles XC ₂ H ₄ number of electrons needed to produce X Faraday constant) / (total charge applied to the reducing electrode)} X 100%

In the case of reductive decomposition of carbon dioxide using an initial copper oxide (Cu _x O) catalyst, the maximum Faraday efficiency of C ₂ H ₄ gas was measured at about 20%. As the reduction reaction of carbon dioxide proceeds, the efficiency of the C ₂ H ₄ gas decreases as the reaction time elapses. It can be seen that after about 100 minutes of reaction time, the efficiency of the C ₂ H ₄ gas converges to near zero.

When the efficiency of the C ₂ H ₄ gas converges to almost zero, the copper oxide (Cu _x O) catalyst undergoes reduction at the surface, as is the surface microstructure on the right side in FIG. _x O) The content of oxygen in the catalyst is estimated to be greatly reduced.

In an embodiment of the present invention, the surface of the copper oxide catalyst was reoxidized and recovered by applying an oxidation potential of + 1.5V to the surface for about 60 minutes to the reduced copper oxide (Cu _x O) catalyst.

As shown in FIG. 13, when a reduction potential of −1.1 V is again applied to the recovered copper oxide catalyst of the embodiment of the present invention to reduce carbon dioxide, the maximum value of the C ₂ H ₄ gas efficiency of the recovered copper oxide catalyst and The minimum value was found to be maintained at about the same level as the C ₂ H ₄ gas efficiency of the original copper oxide catalyst.

In addition, the total decomposition time required for reduction decomposition of carbon dioxide in the initial copper oxide catalyst was determined to be about the same as the total decomposition time in the recovered copper oxide catalyst according to the embodiment of the present invention.

Furthermore, even if the surface of the recovered copper oxide catalyst is reduced again, if the oxide is re-recovered by applying an external + 1.5V oxidation potential to the reduced catalyst for about 60 minutes, the recovered copper oxide catalyst is also the first copper oxide. It was measured to have substantially the same efficiency characteristics of the C ₂ H ₄ gas as the catalyst or recovered copper oxide catalyst.

The result of the embodiment of the present invention of FIG. 13 can be said to prove that the reoxidation method of the copper oxide catalyst developed in the present invention is a method of recovering the copper oxide catalyst repeatedly, reproducibly and very effectively.

As described above, the present invention has been described with reference to the drawings, but the present invention is not limited to the embodiments and drawings disclosed herein, and various modifications may be made by those skilled in the art within the scope of the technical idea of the present invention. It is obvious that modifications can be made. In addition, even if the above described embodiments of the present invention while not explicitly described and described the operation and effect according to the configuration of the present invention, it is obvious that the effect predictable by the configuration is also to be recognized.

Claims (9)

1. Preparing a metal oxide catalyst having a reduced surface;

   Reoxidizing by applying a voltage higher than a copper oxidation potential to the reduced metal oxide catalyst by a predetermined charge amount or more;

   Recovery method of the catalyst comprising a.
2. The method of claim 1,

   The metal oxide catalyst is copper oxide (Cu _x O);

   Recovery method of the catalyst, characterized in that.
3. The method of claim 1,

   The metal component of the metal oxide catalyst is one of Ta, Os, Nb, Mo, Ir, Ag, V, Ru, Mn, Rh, Pd, Ni, Co, Fe, Cr, Hf, Ti, Y, Zr, Sc Or one or more of two or more metals or alloys thereof;

   Recovery method of the catalyst, characterized in that.
4. The method of claim 1,

   The voltage in the reoxidation step is +0.8 to 1.5V;

   Recovery method of the catalyst, characterized in that.
5. The method of claim 1,

   The charge amount in the reoxidation step is 1 C / cm 2 or more;

   Recovery method of the catalyst, characterized in that.
6. The method of claim 1,

   Further removing the hydrocarbon from the catalyst surface prior to the reoxidation step;

   Recovery method of the catalyst further comprising.
7. The method of claim 6,

   The removing of the hydrocarbon may include applying a pulse having a current value of 5 to 10 times or more the normal reduction current at a voltage above an oxygen reduction reaction potential;

   Recovery method of the catalyst, characterized in that.
8. The method of claim 1,

   The reoxidation step begins when the measured hydrocarbon fraction value is below a set threshold;

   Recovery method of the catalyst, characterized in that.
9. The method of claim 1,

   The reoxidation step begins when the current or power value measured in the electrochemical cell in which the catalyst is used is below a set threshold;

   Recovery method of the catalyst, characterized in that.

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