JP7708702B2 - Carbon dioxide reduction catalyst, methanol production device, carbon monoxide and formic acid production device, carbon dioxide treatment device, and carbon dioxide reduction method - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act Presented in the 129th Catalyst Symposium Proceedings, Lecture Number P100, published on the website on March 10, 2022

The present invention relates to a carbon dioxide reduction catalyst, a methanol production device, a carbon monoxide and formic acid production device, a carbon dioxide treatment device, and a carbon dioxide reduction method.

Hydride-containing oxides in which part of the oxide ions ^O2- of a titanium-containing oxide are replaced with hydride ions ^H- have been proposed (see, for example, Patent Document 1). Since these hydride-containing oxides have both hydride ion conductivity and electronic conductivity, various studies have been conducted on their use in various electrochemical devices and the like.

Patent No. 5872555

In recent years, in order to reduce the adverse effects on the global environment, regulations on exhaust gases emitted from internal combustion engines, boilers, etc. have become increasingly stringent. This has led to a demand for the development of catalysts that can reduce the carbon dioxide contained in these exhaust gases, and it is hoped that hydride-containing oxides that combine hydride ion conductivity and electronic conductivity as described above can be used for such catalysts.

The present invention has been made in view of the above, and aims to provide a carbon dioxide reduction catalyst that can efficiently reduce carbon dioxide.

(1) The present invention provides a carbon dioxide reduction catalyst that reduces carbon dioxide, comprising a hydride-containing oxide represented by the following general formula (1) supported with a metal selected from transition metals and typical metals, the metal being at least one of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, In, Sn, and Au:
[Chemical formula 1]

BaTiO _3-x H _x ...(1)

[In the general formula (1), x satisfies 0<x<0.8.]

(2) In the carbon dioxide reduction catalyst of (1), the metal may be Co.

(3) In the carbon dioxide reduction catalyst of (1) or (2), the content of the metal in the carbon dioxide reduction catalyst may be 0.1 to 50 mass%.

(4) In the carbon dioxide reduction catalyst of (1) or (2), the content of the metal in the carbon dioxide reduction catalyst may be 5 to 10 mass %.

(5) In any of the carbon dioxide reduction catalysts (1) to (4), x in the general formula (1) may satisfy 0.3≦x≦0.6.

(6) In any one of the carbon dioxide reduction catalysts (1) to (4), x in the general formula (1) may satisfy 0.5≦x≦0.6.

(7) The present invention also provides a methanol generation device having an electrode that reduces carbon dioxide dissolved in an aqueous solution to generate methanol, the electrode having a carbon dioxide reduction catalyst according to any one of (1) to (6).

(8) The present invention also provides a carbon monoxide and formic acid generator having an electrode that reduces carbon dioxide dissolved in an aqueous solution to generate carbon monoxide and formic acid, the electrode having a carbon dioxide reduction catalyst according to any one of (1) to (6).

(9) The present invention also provides a carbon dioxide treatment device that reduces and treats carbon dioxide contained in exhaust gas, the carbon dioxide treatment device having any one of the carbon dioxide reduction catalysts (1) to (6).

(10) The present invention also provides a carbon dioxide reduction method, which comprises electrochemically reducing carbon dioxide on a carbon dioxide reduction catalyst according to any one of (1) to (6).

The present invention provides a carbon dioxide reduction catalyst that can efficiently reduce carbon dioxide.

FIG. 2 shows an SEM image of a 10 wt % Co/BaTiO _2.5 H _0.5 electrode of Example 1. FIG. 2 is a diagram showing the results of EDS measurement of a 10 mass % Co/BaTiO _2.5 H _0.5 electrode of Example 1. FIG. 1 is a diagram showing the configuration of an electrochemical measurement apparatus used in the present example. FIG. 2 is a diagram showing a CV curve of a 10 mass % Co/BaTiO _2.5 H _0.5 electrode of Example 1. FIG. 13 is a diagram showing a CV curve of a 10 mass % Fe/BaTiO _2.5 H _0.5 electrode of Example 2. FIG. 13 is a diagram showing a CV curve of a 10 mass % Ni/BaTiO _2.5 H _0.5 electrode of Example 3. FIG. 13 is a diagram showing a CV curve of a 10 mass % Cu/BaTiO _2.5 H _0.5 electrode of Example 4. FIG. 1 is a graph showing the amount of each product produced when constant potential electrolysis was carried out on the electrodes of Examples 5 and 6 and Comparative Examples 1 to 3. FIG. 1 is a diagram showing the Faraday efficiency of each product when constant potential electrolysis is performed on the electrodes of Examples 5 and 6 and Comparative Examples 1 to 3. FIG. 2 is a graph showing the amount of each product produced when constant potential electrolysis was performed on the electrodes of Examples 1 and 5 and Comparative Example 2. FIG. 1 is a diagram showing the Faraday efficiency of each product when constant potential electrolysis was performed on the electrodes of Examples 1 and 5 and Comparative Example 2. FIG. 1 is a graph showing the amount of each product produced when constant potential electrolysis was carried out on the electrodes of Examples 1 to 4 and Comparative Examples 4 and 5. FIG. 1 is a diagram showing the Faraday efficiency of each product when constant potential electrolysis was performed on the electrodes of Examples 1 to 4 and Comparative Examples 4 and 5.

One embodiment of the present invention will be described in detail below with reference to the drawings.

[Carbon dioxide reduction catalyst]
A carbon dioxide reduction catalyst (hereinafter also simply referred to as a catalyst) according to one embodiment of the present invention is a carbon dioxide reduction catalyst that can efficiently reduce carbon dioxide. Specifically, the carbon dioxide reduction catalyst according to this embodiment is formed by supporting a metal consisting of a transition metal or a typical metal on a hydride-containing oxide represented by the following general formula (1).

[Chemical formula 1]

BaTiO _3-x H _x ...(1)

[In the general formula (1), x satisfies 0<x<0.8.]

As represented by the general formula (1), the support used in this embodiment is made of a hydride-containing oxide (hereinafter also referred to as BTOH) in which a part of the oxide ions O ^2- in barium titanate BaTiO ₃ (hereinafter also referred to as BTO), which is a titanium-containing oxide, is replaced with hydride ions H ^- . Here, the hydride-containing oxide is an oxyhydride in which oxide ions O ^2- and hydride ions H ^- coexist in the crystal lattice. Normally, the compatibility between oxide ions O ^2- and hydride ions H ^- is poor, so it is difficult to include hydride ions H ^- in an amount exceeding the level of oxygen vacancies in a titanium-containing oxide. In contrast, the support made of the hydride-containing oxide according to this embodiment contains Ba, which has a particularly low electronegativity among metal elements having a lower electronegativity than hydrogen, and thus the hydride ions H ^- can exist stably by bonding with Ba.

Furthermore, in the support made of the hydride-containing oxide according to this embodiment, a portion of the oxide ions ^O2- are replaced with hydride ions ^H- , causing an imbalance in charge and reducing Ti4 ⁺ to a lower oxidation number. This is thought to maintain electrical neutrality and increase catalytic activity by changing the electronic state of the support surface, enabling carbon dioxide to be reduced highly selectively and at high speed. Therefore, the carbon dioxide reduction catalyst according to this embodiment can efficiently reduce carbon dioxide.

It is preferable that x in the above general formula (1) is 0.3≦x≦0.6. When the concentration of hydride ions H ⁻ in a hydride-containing oxide is low, the hydride ions H ⁻ are exchanged with oxide ions O ²⁻ , causing the hydride ions H ⁻ to diffuse. On the other hand, when the concentration of hydride ions H ⁻ is sufficiently high, a diffusion path for the hydride ions H ⁻ is generated only by the hydride ions H ⁻ and anion (negative ion) defects, and the mass and charge of the transfer medium are small, so that the hydride ions H ⁻ are easily diffused. As a result, the catalytic activity is enhanced, and it is considered that carbon dioxide can be reduced highly selectively and at a high speed. Therefore, by setting x in the general formula (1) within the range of 0.3≦x≦0.6, carbon dioxide can be reduced more efficiently. A more preferable range of x is 0.5≦x≦0.6.

The supported metal to be supported on the carrier is a transition metal or a typical metal, specifically at least one of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, In, Sn, and Au. Among these supported metals, Fe, Co, Ni, Cu, and Zn are preferably supported.

Among these supported metals, Co is preferably used. By supporting Co on a support made of a hydride-containing oxide represented by general formula (1), carbon dioxide can be reduced more reliably and efficiently. In addition, by using Co as the supported metal, carbon dioxide can be reduced by six electrons, as described below, and methanol can be produced efficiently.

The amount of the above-mentioned supported metal is preferably 0.1 to 50 mass% of the entire carbon dioxide reduction catalyst. This allows for more reliable and efficient reduction of carbon dioxide. Furthermore, if the amount of supported metal is too large, as described below, too many electrons flow, resulting in the completion of two-electron reduction of carbon dioxide, and only carbon monoxide and formic acid can be produced. However, by setting the amount of supported metal within the range of 0.1 to 50 mass%, an appropriate amount of electrons flows, allowing six-electron reduction of carbon dioxide, and methanol can be produced efficiently. A more preferable amount is 5 to 10 mass%.

Next, the multi-electron reduction reaction of carbon dioxide by the carbon dioxide reduction catalyst according to this embodiment will be described.
First, known multi-electron reduction reactions of carbon dioxide include the two-electron reduction shown in the following reaction formulas (2) and (3), the four-electron reduction shown in the following reaction formula (4), the six-electron reduction shown in the following reaction formula (5), and the eight-electron reduction shown in the following reaction formula (6).

[Case 2]
CO ₂ +2H ⁺ +2e ^- → HCOOH...(2)
CO ₂ +2H ⁺ +2e ^- → CO+H ₂ O...(3)
CO ₂ +4H ⁺ +4e ^- → HCHO+H ₂ O...(4)
CO ₂ +6H ⁺ +6e ^- → CH ₃ OH + H ₂ O...(5)
CO ₂ +8H ⁺ +8e ^- → CH ₄ +2H ₂ O...(6)

Whereas conventional carbon dioxide reduction catalysts could only proceed up to two-electron reduction, which produces CO or formic acid, the carbon dioxide reduction catalyst according to this embodiment can proceed up to six-electron reduction by cooperating hydrogen ions with carbon dioxide in the multi-electron reduction reaction system of carbon dioxide in concert with hydrogen ions as described above, without adding hydrogen. This is thought to be because the carbon dioxide reduction catalyst according to this embodiment uses a hydride-containing oxide, which allows electrons to be accumulated and transferred to carbon dioxide, thereby suppressing hydrogen production caused by proton reduction. Therefore, the carbon dioxide reduction catalyst according to this embodiment can perform six-electron reduction of carbon dioxide without adding hydrogen, producing methanol with high selectivity.

The electrode coated with the carbon dioxide reduction catalyst according to this embodiment can be manufactured through a process of synthesizing the carrier, a process of supporting the metal on the carrier, and a process of coating the electrode substrate with the catalyst. Details will be explained in the examples below.

[Methanol production device]
The methanol production apparatus according to this embodiment is an apparatus for producing methanol by reducing carbon dioxide dissolved in an aqueous solution, and includes an electrode having the above-mentioned carbon dioxide reduction catalyst. The methanol production apparatus according to this embodiment can efficiently reduce carbon dioxide dissolved in an aqueous solution to produce methanol.

[Carbon monoxide and formic acid generator]
The carbon monoxide and formic acid generator according to this embodiment is a device that reduces carbon dioxide dissolved in an aqueous solution to generate carbon monoxide and formic acid, and includes an electrode having the carbon dioxide reduction catalyst described above. The carbon monoxide and formic acid generator according to this embodiment can efficiently reduce carbon dioxide dissolved in an aqueous solution to generate carbon monoxide and formic acid.

[Formaldehyde generator]
The formaldehyde generator according to the present embodiment is a device that generates formaldehyde by reducing carbon dioxide dissolved in an aqueous solution, and includes an electrode having the above-mentioned carbon dioxide reduction catalyst. According to the formaldehyde generator according to the present embodiment, carbon dioxide dissolved in an aqueous solution can be efficiently reduced to generate formaldehyde.

[Methane generation device]
The methane generation device according to this embodiment is a device that generates methane by reducing carbon dioxide dissolved in an aqueous solution, and includes an electrode having the above-mentioned carbon dioxide reduction catalyst. The methane generation device according to this embodiment can efficiently reduce carbon dioxide dissolved in an aqueous solution to generate methane.

[Carbon dioxide treatment device]
The carbon dioxide treatment device according to this embodiment is a carbon dioxide treatment device that reduces and treats carbon dioxide contained in exhaust gas, and includes an electrode having the above-mentioned carbon dioxide reduction catalyst. The carbon dioxide treatment device according to this embodiment can efficiently reduce and treat carbon dioxide contained in exhaust gas. For example, it is possible to treat carbon dioxide in exhaust gas after combustion from an internal combustion engine, a boiler, etc.

The carbon dioxide reduction method according to this embodiment is a method for electrochemically reducing carbon dioxide on the carbon dioxide reduction catalyst described above. According to the carbon dioxide reduction method according to this embodiment, carbon dioxide can be efficiently reduced and treated.

The present invention is not limited to the above-described embodiment, and any modifications or improvements that can achieve the object of the present invention are included in the present invention.

Next, examples of the present invention will be described, but the present invention is not limited to these examples.

_[ Example 1: 10 mass% Co/ _BaTiO2.5H0.5 ]
As Example 1, an electrode was prepared by applying a 10 mass% Co _{/ BaTiO2.7H0.3} catalyst, in which 10 mass% Co was supported on the oxyhydride BTOH ( _BaTiO2.5H0.5 ), to an electrode substrate. Specifically, a 10 mass% Co/ _BaTiO2.5H0.5 electrode was prepared through a process of synthesizing the oxyhydride BTOH ( _{BaTiO2.5H0.5 )} as a support, a _process of supporting a metal on the support, and a process of applying the catalyst to the electrode _substrate . Details of each process are as follows.

(Support synthesis process)
First, an oxyhydride BTOH ( _BaTiO2.5H0.5 ) was synthesized as a support made of a hydride _- containing oxide. Specifically, 681 mg (8.76 mmol, 3 eq) of barium titanate BTO and 369 mg (2.92 mmol, 1 eq) of _CaH2 were added to a mortar in a nitrogen atmosphere and mixed for 30 minutes, and then molded into tablets (3 pellets) using a press.

The tablets obtained as described above were then placed in a glass tube, vacuum sealed, and reacted by heating for 7 days at a temperature of 833 K. After the reaction was completed, the crude product obtained was placed in a 300 ml beaker, and 200 ml of MeOH and about 0.1 M of NH ₄ Cl were added and stirred for 5 hours. After stirring, the mixture was suction filtered and dried to obtain the acid hydride BTOH (BaTiO _2.5 H _0.5 ) as the product.

(Process for supporting metal on carrier)
Next, the metal was supported on the acid hydride BTOH (BaTiO _2.5 H _0.5 ). Specifically, the precursor of the supported metal Co (the supported metal content per catalyst is equivalent to 10 mass %) and 50 mg of the acid hydride BTOH (BaTiO _2.5 H _0.5 ) obtained as described above were placed in an evaporating dish, and then 2 ml of water was added. After that, the mixture was dispersed by ultrasonic waves for 5 minutes, and then heated in a hot water bath while stirring and dried. After drying, product A was obtained.

Next, the obtained product A was placed in a ceramic boat, which was then put into a tubular furnace to carry out hydrogen reduction treatment. The hydrogen reduction treatment was carried out for 1 hour at a temperature of 473 K, at which BTOH would not be thermally damaged, with a hydrogen gas flow rate of 20 ml/min. As a result, a 10 mass% Co/ _BaTiO2.5H0.5 catalyst was obtained in which 10 mass% Co was supported on the _{oxyhydride BTOH} ( _BaTiO2.5H0.5 ).

(Process for applying catalyst to electrode substrate)
Next, the catalyst was applied to carbon paper as an electrode substrate. Specifically, 0.9 ml of EtOH, 0.1 ml of water, 10 μl of a 5% Nafion (registered trademark) suspension, and 2.5 mg of the 10 mass % Co/BaTiO _2.5 H _0.5 catalyst obtained as described above were placed in a sample tube, and then ultrasonically stirred. After stirring, the suspension was dropped onto carbon paper heated to 393 K.

Next, the ITO film was placed on the carbon paper onto which the suspension was dropped as described above, heated to 423 K, and pressed at 4 MPa for 5 minutes. After that, the conductor was fixed with In, and the surfaces other than the catalyst surface were insulated, and then dried at a temperature of 343 K for 12 hours. As a result, an electrode was obtained in which the 10 mass % Co/BaTiO _2.5 H _0.5 catalyst of Example 1 was applied to the carbon paper. The obtained electrode was used as the working electrode of the electrochemical measurement device 1 described later.

_[ Example 2: 10 mass% Fe/ _BaTiO2.5H0.5 ]
As Example 2, an electrode was prepared by coating an electrode substrate with a 10 mass% Fe/ _BaTiO2.5H0.5 catalyst in which 10 mass% Fe was supported on the oxyhydride BTOH ( _{BaTiO2.5H0.5 ) .} Specifically, the electrode was prepared in the same manner as in Example 1, except that the type of supported metal was changed from Co to Fe.

_[ Example 3: 10 mass% Ni/ _BaTiO2.5H0.5 ]
As Example 3, an electrode was prepared by coating an electrode substrate with a 10 mass% Ni/ _BaTiO2.5H0.5 catalyst in which 10 mass% Ni was supported on the oxyhydride BTOH ( _{BaTiO2.5H0.5 ) .} Specifically, the electrode was prepared in the same manner as in Example 1, except that the type of supported metal was changed from Co to Ni.

_[ Example 4: 10 mass% Cu/ _BaTiO2.5H0.5 ]
As Example 4, an electrode was prepared by coating an electrode substrate with a 10 mass% Cu/ _BaTiO2.5H0.5 catalyst in which 10 mass% Cu was supported on the oxyhydride BTOH ( _{BaTiO2.5H0.5 ) .} Specifically, the electrode was prepared in the same manner as in Example 1, except that the type of supported metal was changed from Co to Cu.

_[ Example 5: 5 mass% Co/ _BaTiO2.7H0.3 ]
In Example 5, an electrode was prepared by coating an electrode substrate with a 5 mass% Co/ _BaTiO2.7H0.3 catalyst, in which 5 mass% Co was supported on the oxyhydride BTOH _{( BaTiO2.7H0.3} ) _. Specifically, the electrode was prepared in the same manner as in Example 1, except that the oxyhydride BTOH ( _{BaTiO2.5H0.5 )} was changed to _BaTiO2.7H0.3 and the _amount of Co supported was changed from 10 mass% to 5 mass%.

_[ Example 6: 10 mass% Co/ _BaTiO2.7H0.3 ]
As Example 6, an electrode was prepared by coating an electrode substrate with a 10 mass% Co/ _BaTiO2.7H0.3 catalyst in which 10 mass _{% Co} was supported on the oxyhydride BTOH ( _BaTiO2.7H0.3 ) _. Specifically, the electrode was prepared in the same manner as in Example 1, except that the oxyhydride BTOH was changed from _BaTiO2.5H0.5 to _{BaTiO2.7H0.3 .}

[Comparative Example 1: BaTiO _2.7 H _0.3 ]
As Comparative Example 1, an electrode was prepared by applying oxyhydride BTOH ( _BaTiO2.7H0.3 ) to an electrode substrate without supporting a metal. Specifically, the oxyhydride BTOH was changed from _{BaTiO2.5H0.5 to BaTiO2.7H0.3} , and the synthesized oxyhydride BTOH _{( BaTiO2.7H0.3} ) was directly subjected to the application process to the electrode substrate without going through the process of supporting a metal _{on a} carrier. The electrode was prepared in the same manner as in Example 1.

[Comparative Example 2: 10% by mass Co/BTO]
As Comparative Example 2, an electrode was prepared by coating an electrode substrate with a 10 mass% Co/BTO catalyst in which 10 mass% Co was supported on a support made of barium titanate (BTO). Specifically, the electrode was prepared in the same manner as in Example 1, except that BTO was used as the support instead of the oxyhydride BTOH without going through the support synthesis process.

[Comparative Example 3: Co]
As Comparative Example 3, an electrode was prepared by directly applying metallic Co to an electrode substrate. Specifically, the electrode was prepared in the same manner as in Example 1, except that Co was used instead of the 10 mass% Co/ _BaTiO2.5H0.5 catalyst in the catalyst application step to the electrode substrate, without going through the support synthesis step or the metal supporting step _on the support.

[Comparative Example 4: Electrode substrate only]
As Comparative Example 4, an electrode composed only of carbon paper as an electrode substrate was prepared.

[Comparative Example 5: BaTiO _2.5 H _0.5 ]
As Comparative Example 5, an electrode was prepared by applying an oxyhydride BTOH ( _BaTiO2.5H0.5 ) to an electrode substrate without supporting a metal. Specifically, the electrode was prepared in the same manner as in Example 1, except that the synthesized _oxyhydride BTOH ( _BaTiO2.5H0.5 ) was directly subjected to a coating process on an electrode substrate without going through a process of supporting a metal _on a carrier.

[SEM, EDS measurements]
Among the electrodes of the respective Examples and Comparative Examples obtained as described above, the 10 mass % Co/BaTiO _2.5 H _0.5 electrode of Example 1 was used as a representative example and was subjected to SEM (scanning electron microscope) observation and EDS (energy dispersive X-ray elemental analysis) measurement under the following conditions.

(SEM, EDS measurement conditions)
Measuring device: Scanning electron microscope "JSM-IT100LA" manufactured by JEOL Ltd.
Observation conditions: Acceleration voltage 15.0 kV, magnification 40-300x EDS conditions: characteristic X-ray wavelengths of each element (C: 44.70 Å, Ti: 27.05 Å, O: 23.62 Å, Co: 15.97 Å, Ba: 2.78 Å)

Fig. 1 is a view showing an SEM image of the 10 mass % Co/ _{BaTiO2.5H0.5 electrode} of Example 1. More specifically, Fig. 1 is an SEM image of the electrode surface of Example 1 observed at 300 times magnification. As shown in Fig. 1, it was confirmed that a deposit thought to be a catalyst was attached to the carbon fibers in the carbon paper.

2 is a diagram showing the EDS measurement results of the 10 mass% Co/BaTiO _2.5 H _0.5 electrode of Example 1. More specifically, FIG. 2 shows an enlarged SEM image of the area surrounded by the two-dot chain line in FIG. 1 and each element distribution map of C, Co, Ti, Ba and O. In each element distribution map, the whiter the area, the higher the concentration of each element. As shown in FIG. 2, it was confirmed that each element distribution of C, Co, Ti, Ba and O corresponds to the distribution of carbon fiber, and it was confirmed that the catalyst of Example 1 was applied to the carbon paper.

[Electrochemical measurements]
Electrochemical measurements were carried out on the electrodes of each of the examples and comparative examples obtained as described above. Here, FIG. 3 is a diagram showing the configuration of the electrochemical measurement apparatus 1 used in this example. The electrochemical measurement apparatus 1 is an apparatus capable of measuring the oxidation-reduction characteristics of carbon dioxide from a current-potential curve (cyclic voltammogram, hereinafter referred to as a CV curve) obtained by placing an electrode in a stationary solvent in which carbon dioxide is dissolved, repeatedly sweeping the potential at a constant sweep rate, and measuring the current flowing when the potential is increased or decreased. In addition, the electrochemical measurement apparatus 1 is an apparatus capable of measuring the concentration of the product produced by the electrolysis current generated during constant potential electrolysis, which electrochemically oxidizes and reduces carbon dioxide dissolved in a solvent on an electrode maintained at a constant potential.

As shown in Figure 3, the CV measurement apparatus 1 includes a chamber 10, a working electrode 11, a counter electrode 12, a reference electrode 13, a potentiostat 14, a proton (H ⁺ ) permeable membrane 15, stirrers 16a, 16b, gas supply paths 17a, 17b, gas supply valves 21, 31, bubbler introduction valves 22, 32, and a GC introduction valve 41.

In this example, the electrochemical measurements were carried out under the following measurement conditions.
(Electrochemical measurement conditions)
Carbon dioxide supply flow rate: 30 ml/min CV: -0.5 V to -2.0 V, 5 cycles, sweep rate 100 mV/S
Constant potential electrolysis: -1.8 V x 10 hours Solvent in chamber 10: containing 0.1 M tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ), acetonitrile (MeCN):H ₂ O=99:1 (v:v)
Solvent volume: 15 ml on the counter electrode side, 17 ml on the working electrode side
Working electrode 11: Electrode in which the catalyst of each Example and Comparative Example was applied to carbon paper Counter electrode 12: Pt electrode Reference electrode 13: Ag/AgNO ₃ electrode Proton permeable membrane 15: Nafion (registered trademark) membrane

In this example, electrochemical measurements were carried out according to the following procedure.
First, Ar gas was supplied to both the chamber 10 on the working electrode 11 side and the chamber 10 on the counter electrode 12 side through the gas supply paths 17a and 17b by opening the gas supply valves 21 and 31, and purging with Ar gas was performed for 15 minutes. Thereafter, CV measurement was performed under the above-mentioned CV conditions.

Then, the gas in the chamber was introduced into the GC (gas chromatograph) by opening the GC introduction valve 41, and a leak check was performed. After the leak check was completed, the gas supply valves 21, 31 were opened to supply carbon dioxide gas to both the chamber 10 on the working electrode 11 side and the chamber 10 on the counter electrode 12 side through the gas supply paths 17a, 17b, and carbon dioxide gas was bubbled for 15 minutes to dissolve the carbon dioxide gas in the solvent. Then, CV measurement was performed under the above-mentioned CV conditions.

Then, the gas in the chamber was introduced into the GC (gas chromatograph) by opening the GC inlet valve 41, and a leak check was performed. After the leak check was completed, the potentiostat 14 was controlled to perform the reduction of carbon dioxide for 10 hours under the constant potential electrolysis conditions described above.

The results of CV measurements of the electrodes of Examples 1 to 4 are shown in Figures 4 to 7. Specifically, Figure 4 shows a CV curve of the 10 mass% Co/BaTiO _2.5 H _0.5 electrode of Example 1, Figure 5 shows a CV curve of the 10 mass% Fe/BaTiO _2.5 H _0.5 electrode of Example 2, Figure 6 shows a CV curve of the 10 mass% Ni/BaTiO _2.5 H _0.5 electrode of Example 3, and Figure 7 shows a CV curve of the 10 mass% Cu/BaTiO _2.5 H _0.5 electrode of Example 4. In Figures 4 to 7, the horizontal axis represents the applied potential (potential relative to the reference electrode), and the vertical axis represents the current.

In Figures 4 to 7, the CV curves after purging with Ar gas are shown by solid lines, and the CV curves after dissolving carbon dioxide gas in the solvent are shown by dashed lines. As shown in Figures 4 to 7, it can be seen that when the potential is increased or decreased by sweeping at a constant sweep rate, a reduction wave and an oxidation wave are generated. Specifically, it can be seen that when the potential is swept in the negative direction, a reduction wave is generated, and when the battery is swept in the positive direction, an oxidation wave is generated.

When comparing the CV curves after purging with Ar gas and after dissolving carbon dioxide gas in the solvent in each of Figures 4 to 7, if the current difference between the two at the sweep start/end potential of -2.0 V is large, this means that a large carbon dioxide reduction current flows, and it can be said to be a promising active metal. Therefore, from the results of these CV measurements, it was confirmed that Co and Cu are more preferable than Fe and Ni, which have no difference in current value between Ar gas and carbon dioxide gas.

Next, for the electrodes of Examples 1 to 6 and Comparative Examples 1 to 5, the amounts of products (MeOH, H ₂ , CO, HCOOH) produced and the Faraday efficiencies when constant potential electrolysis was carried out under the above-mentioned conditions were as shown in Table 1.

FIG. 8 is a diagram showing the amount of each product _{(MeOH, H 2 , CO, HCOOH) produced when constant potential electrolysis was performed under the above-mentioned conditions for the electrodes of Example 5 (5% by mass Co/BaTiO 2.7 H 0.3 ), Example 6 (10% by mass Co/BaTiO 2.7 H 0.3 ) , Comparative} Example 1 (BaTiO _2.7 H 0.3 ), Comparative Example 2 (10% by mass Co/BTO) and Comparative Example 3 (Co). FIG. 9 is a diagram showing the Faraday efficiency of each product when constant potential electrolysis was performed for the electrodes of Examples 5 and 6 and Comparative Examples 1 to 3. In FIG. 8 and FIG. 9, the thick black lines are error bars (similarly in FIG. 10 and FIG. 11 described later). As shown in FIG. 8, it was found that methanol was produced in Examples 5 and 6, and almost no methanol was produced in Comparative Examples 1 to 3. Methanol is produced by six-electron reduction of carbon dioxide, and from these results it was confirmed that this embodiment enables six-electron reduction, which is more electrons than usual.

In addition, by comparing the results of Example 5 (5 mass% Co/BaTiO _2.7 H _0.3 ) and Example 6 (10 mass% Co/BaTiO _2.7 H _0.3 ) shown in FIG. 8, it was found that the amount of methanol produced increased by 20% when the amount of Co supported on the oxyhydride BTOH (BaTiO _2.7 H _0.3 ) increased from 5 mass% to 10 mass%. From this result, it was confirmed that by increasing the amount of metal supported, the number of electrons flowing also increases, and therefore the rate of methanol production by the 6-electron reduction of carbon dioxide increases. However, as shown in FIG. 9, in the Faraday efficiency of methanol production, it was also confirmed that when the amount of Co supported increased from 5 mass% to 10 mass%, the proportion of electrons flowing too much and proceeding to 6-electron reduction decreased, and the methanol production efficiency decreased.

Next, FIG. 10 is a diagram showing the amount of each product (MeOH, H 2 , CO, HCOOH) produced when constant potential electrolysis is performed on the electrodes of Example 1 (10 mass% Co/BaTiO _2.5 H _0.5 ), Example 6 ( ₁₀ mass% Co/BaTiO _2.7 H _0.3 ), and Comparative Example 2 (10 mass% Co/BTO). FIG. 11 is a diagram showing the Faraday efficiency of each product when constant potential electrolysis is performed on the electrodes of Examples 1, 6, and Comparative Example 2. As shown in FIG. 10, it was found that methanol was produced in Examples 1 and 6, and almost no methanol was produced in Comparative Example 2. Therefore, from this result, it was confirmed that carbon dioxide can be highly selectively reduced by six electrons according to this example.

In addition, by comparing the results of Example 1 (10 mass% Co/BaTiO _2.5 H _0.5 ) and Example 6 (10 mass% Co/BaTiO _2.7 H _0.3 ) shown in FIG. 10 , it was found that the amount of methanol produced increases as the hydride content in BTOH increases. The results of Example 1 and Example 6 shown in FIG. 11 also showed that the faradaic efficiency of methanol production improves as the hydride content in BTOH increases. Therefore, it was confirmed that hydrogen production is suppressed and methanol selectivity is increased by increasing the hydride content in BTOH. In addition, the faradaic efficiency of Example 1 in FIG. 11 exceeds 100%, which was thought to be due to hydrogen produced by the stoichiometric reaction of the hydride in BTOH and water in the solvent.

Next, FIG. 12 is a diagram _showing the amount of each product (MeOH, H 2 , CO, _{HCOOH ) produced when constant potential electrolysis is performed on the electrodes of Example 1 (10 mass% Co/BaTiO 2.5 H 0.5 ), Example 2 (10 mass% Fe/BaTiO 2.5 H 0.5 ) , Example 3} (10 mass% Ni/BaTiO _2.5 H _0.5 ), Example 4 (10 mass% Cu/BaTiO _2.5 H 0.5 ), Comparative Example 4 (electrode base material only), and Comparative Example 5 (BaTiO _2.5 H 0.5 ). Also, FIG. 13 is a diagram showing the Faraday efficiency of each product when constant potential electrolysis is performed on the electrodes of Examples 1 to 4 and Comparative Examples 4 and 5. As shown in Fig. 12, it was found that the production of formic acid and hydrogen increases as the supported metal becomes a metal with a larger number of electrons, such as Fe, Co, Ni, and Cu, because the number of electrons flowing increases. Also, as shown in Fig. 13, it was found that the faradaic efficiency of methanol production and the faradaic efficiency of formic acid were higher in Examples 1 to 4 than in Comparative Examples 4 and 5, and it was confirmed that carbon dioxide was efficiently reduced. Note that in Fig. 13, there are some cases where the faradaic efficiency exceeds 100%, which was thought to be due to hydrogen produced by the stoichiometric reaction of hydride in BTOH and water in the solvent.

REFERENCE SIGNS LIST 1 Electrochemical measurement apparatus 10 Chamber 11 Working electrode 12 Counter electrode 13 Reference electrode 14 Potentiostat 15 Proton permeable membrane 16a, 16b Stirrer 17a, 17b Gas supply path 21, 31 Gas supply valve 22, 32 Bubbler introduction valve 41 GC introduction valve

Claims (10)

A carbon dioxide reduction catalyst for reducing carbon dioxide,
A metal selected from transition metals is supported on a hydride-containing oxide represented by the following general formula (1):
A carbon dioxide reduction catalyst, wherein the metal is at least one of Fe , Co, Ni and Cu.
[Chemical formula 1]

BaTiO _3-x H _x ...(1)

[In the general formula (1), x satisfies 0<x<0.8.] The carbon dioxide reduction catalyst according to claim 1, wherein the metal is Co. The carbon dioxide reduction catalyst according to claim 1 or 2, wherein the content of the metal in the carbon dioxide reduction catalyst is 0.1 to 50 mass %. The carbon dioxide reduction catalyst according to claim 1 or 2, wherein the metal content in the carbon dioxide reduction catalyst is 5 to 10 mass %. The carbon dioxide reduction catalyst according to any one of claims 1 to 4, wherein x in the general formula (1) satisfies 0.3≦x≦0.6. The carbon dioxide reduction catalyst according to any one of claims 1 to 4, wherein x in the general formula (1) satisfies 0.5≦x≦0.6. A methanol production device including an electrode for reducing carbon dioxide dissolved in an aqueous solution to produce methanol,
A methanol production apparatus, wherein the electrode comprises the carbon dioxide reduction catalyst according to claim 1 . A carbon monoxide and formic acid generator comprising electrodes for reducing carbon dioxide dissolved in an aqueous solution to generate carbon monoxide and formic acid,
A carbon monoxide and formic acid generating device, wherein the electrode has a carbon dioxide reduction catalyst according to any one of claims 1 to 6. A carbon dioxide treatment device that reduces and treats carbon dioxide contained in exhaust gas,
A carbon dioxide treatment device comprising the carbon dioxide reduction catalyst according to any one of claims 1 to 6. A carbon dioxide reduction method in which carbon dioxide is electrochemically reduced on a carbon dioxide reduction catalyst according to any one of claims 1 to 6.