Carbon dioxide reduction catalyst, methanol production apparatus, carbon monoxide and formic acid production apparatus, carbon dioxide treatment apparatus, and carbon dioxide reduction method

Abstract

To provide a carbon dioxide reduction catalyst capable of efficiently reducing carbon dioxide.SOLUTION: A carbon dioxide reduction catalyst reduces carbon dioxide. A metal made of a transition metal or a typical metal is supported on a hydrido-containing oxide represented by a general formula (1). The metal is at least one of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, In, Sn, and Au. [Chemical formula 1] BaTiO3-xHx ---(1) [x in the general formula (1) meets 0<x<0.8.]SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to a carbon dioxide reduction catalyst, a methanol production apparatus, a carbon monoxide and formic acid production apparatus, a carbon dioxide treatment apparatus, and a carbon dioxide reduction method.

Background Art

[0002] Conventionally, hydride-containing oxides in which a part of oxide ions O 2- of titanium-containing oxides are substituted with hydride ions (hydrogenide ions) H - have been proposed (see, for example, Patent Document 1). Since this hydride-containing oxide has both hydride ion conductivity and electron conductivity, various studies have been made on its use in various electrochemical devices and the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in recent years, in order to reduce the adverse effects on the global environment, regulations on exhaust emissions from internal combustion engines, boilers, etc. have been further advanced. Therefore, the development of a catalyst capable of reducing carbon dioxide contained in these exhaust gases is required, and the use of a hydride-containing oxide having the above-described hydride ion conductivity and electron conductivity is expected for such a catalyst.

[0005]

Means for Solving the Problems

[0006] (1) The present invention provides a carbon dioxide reduction catalyst for reducing carbon dioxide, in which a metal composed of a transition metal or a typical metal is supported on a hydride-containing oxide represented by the following general formula (1), and the metal is 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.]

[0007] (2) In the carbon dioxide reduction catalyst of (1), the metal may be Co.

[0008] (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% by mass.

[0009] (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% by mass.

[0010] (5) In the carbon dioxide reduction catalyst according to any one of (1) to (4), x in the general formula (1) may satisfy 0.3 ≤ x ≤ 0.6.

[0011] (6) In the carbon dioxide reduction catalyst according to any one of (1) to (4), x in the general formula (1) may satisfy 0.5 ≤ x ≤ 0.6.

[0012] (7) The present invention also provides a methanol production device including an electrode that reduces carbon dioxide dissolved in an aqueous solution to produce methanol, and the electrode has a carbon dioxide reduction catalyst according to any one of (1) to (6).

[0013] (8) The present invention also provides a carbon monoxide and formic acid production apparatus including an electrode for reducing carbon dioxide dissolved in an aqueous solution to produce carbon monoxide and formic acid, wherein the electrode has any one of the carbon dioxide reduction catalysts of (1) to (6).

[0014] (9) The present invention also provides a carbon dioxide treatment apparatus for reducing and treating carbon dioxide contained in exhaust gas, which has any one of the carbon dioxide reduction catalysts of (1) to (6).

[0015] (10) The present invention also provides a carbon dioxide reduction method for electrochemically reducing carbon dioxide on any one of the carbon dioxide reduction catalysts of (1) to (6).

Advantages of the Invention

[0016] According to the present invention, a carbon dioxide reduction catalyst capable of efficiently reducing carbon dioxide can be provided.

Brief Description of the Drawings

[0017]

Figure 1

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Figure 13

Mode for Carrying Out the Invention

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0019] [Carbon Dioxide Reduction Catalyst] The carbon dioxide reduction catalyst according to one embodiment of the present invention (hereinafter, also simply referred to as a catalyst) is a carbon dioxide reduction catalyst capable of efficiently reducing carbon dioxide. Specifically, the carbon dioxide reduction catalyst according to the present embodiment is obtained by supporting a metal composed of a transition metal or a typical metal on a hydride-containing oxide represented by the following general formula (1).

[0020] [Chemical Formula 1] BaTiO 3-x H x ···(1) [In the general formula (1), x satisfies 0 < x < 0.8.]

[0021] As represented by the general formula (1), the carrier used in this embodiment is a hydride-containing oxide in which a part of the oxide ions O in barium titanate BaTiO3 (hereinafter also referred to as BTO), which is a titanium-containing oxide 2- is replaced by hydride ions H - and consists of a hydride-containing oxide (hereinafter also referred to as BTOH). Here, the hydride-containing oxide is a hydrogen oxyhydride in which oxide ions O 2- and hydride ions H - coexist. Usually, since the compatibility between oxide ions O 2- and hydride ions H - is not good, it is difficult to encapsulate an amount of hydride ions H - exceeding the level of the oxygen defect amount in the titanium-containing oxide. In contrast, the carrier composed 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, so that the hydride ions H - can stably exist by binding to Ba.

[0022] Also, in the carrier composed of the hydride-containing oxide according to this embodiment, a part of the oxide ions O 2- is replaced by hydride ions H - , resulting in an imbalance in charge, and Ti 4+ is reduced to a lower oxidation number. Therefore, it is considered that while electrical neutrality is maintained, the catalytic activity is enhanced by the change in the electronic state on the carrier surface, enabling high-selectivity and high-speed reduction of carbon dioxide. Therefore, according to the carbon dioxide reduction catalyst according to this embodiment, carbon dioxide can be efficiently reduced.

[0023] In the above general formula (1), x is preferably 0.3 ≦ x ≦ 0.6. When the concentration of hydride ions H - is low, the hydride ions H - diffuse by being exchanged with oxide ions O 2- . On the contrary, when the concentration of hydride ions H - is sufficiently high, the hydride ions H - ​- and only anion (negative ion) defects result in a diffusion path for hydride ion H - and because the mass and charge of the migration medium are small, hydride ion H - is likely to diffuse, resulting in enhanced catalytic activity, and it is considered that carbon dioxide can be reduced highly selectively and at 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.

[0024] As the supported metal supported on the carrier, a metal composed of a transition metal or a typical metal, specifically, at least one of Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, In, Sn, and Au can be mentioned. Among these supported metals, Fe, Co, Ni, Cu, and Zn are preferably supported.

[0025] Among these supported metals, Co is preferably used. By supporting Co on the carrier composed of the hydride-containing oxide represented by the general formula (1), carbon dioxide can be more reliably and efficiently reduced. Further, by using Co as the supported metal, as described later, carbon dioxide can be reduced by 6 electrons, and methanol can be efficiently produced.

[0026] As the supported amount of the above-mentioned supported metal, it is preferably 0.1 to 50% by mass based on the entire carbon dioxide reduction catalyst. Thereby, carbon dioxide can be more reliably and efficiently reduced. Further, if the supported amount of the metal is too large, as described later, electrons flow excessively and the 2-electron reduction of carbon dioxide is completed, and only carbon monoxide and formic acid can be produced. However, when the supported amount of the metal is within the range of 0.1 to 50% by mass, electrons flow moderately and carbon dioxide can be reduced by 6 electrons, and methanol can be efficiently produced. A more preferable supported amount is 5 to 10% by mass.

[0027] Next, the multi-electron reduction reaction of carbon dioxide by the carbon dioxide reduction catalyst according to the present embodiment will be described. First, as the multi-electron reduction reaction of carbon dioxide, the two-electron reduction represented by the following reaction formulas (2) and (3), the four-electron reduction represented by the following reaction formula (4), the six-electron reduction represented by the following reaction formula (5), and the eight-electron reduction represented by the following reaction formula (6) are known.

[0028] [Chemical formula 2] CO2 + 2H + + 2e - → HCOOH ···(2) CO2 + 2H + + 2e - → CO + H2O ···(3) CO2 + 4H + + 4e - → HCHO + H2O ···(4) CO2 + 6H + + 6e - → CH3OH + H2O ···(5) CO2 + 8H + + 8e - → CH4 + 2H2O ···(6)

[0029] Here, in the conventional carbon dioxide reduction catalyst, it was only possible to proceed up to the two-electron reduction in which CO or formic acid is generated. However, in the carbon dioxide reduction catalyst according to the present embodiment, the multi-electron reduction reaction system of carbon dioxide in cooperation with hydrogen ions as described above can proceed up to six-electron reduction by causing hydrogen ions to cooperate with carbon dioxide without adding hydrogen. This is considered to be because, in the carbon dioxide reduction catalyst according to the present embodiment, by using a hydride-containing oxide, electrons can be accumulated and transferred to carbon dioxide, and hydrogen generation caused by proton reduction can be suppressed. Therefore, according to the carbon dioxide reduction catalyst according to the present embodiment, carbon dioxide can be six-electron reduced to highly selectively produce methanol without adding hydrogen.

[0030] Note that the electrode coated with the carbon dioxide reduction catalyst according to the present embodiment can be manufactured by going through a carrier synthesis step, a step of supporting a metal on the carrier, and a step of coating the catalyst on the electrode substrate. Details will be described in the examples in the latter part.

[0031] [Methanol production device] The methanol production device according to this embodiment is a device that reduces carbon dioxide dissolved in an aqueous solution to produce methanol, and includes an electrode having the above-described carbon dioxide reduction catalyst. According to the methanol production device according to this embodiment, carbon dioxide dissolved in the aqueous solution can be efficiently reduced to produce methanol.

[0032] [Carbon monoxide and formic acid production device] The carbon monoxide and formic acid production device according to this embodiment is a device that reduces carbon dioxide dissolved in an aqueous solution to produce carbon monoxide and formic acid, and includes an electrode having the above-described carbon dioxide reduction catalyst. According to the carbon monoxide and formic acid production device according to this embodiment, carbon dioxide dissolved in the aqueous solution can be efficiently reduced to produce carbon monoxide and formic acid.

[0033] [Formaldehyde production device] The formaldehyde production device according to this embodiment is a device that reduces carbon dioxide dissolved in an aqueous solution to produce formaldehyde, and includes an electrode having the above-described carbon dioxide reduction catalyst. According to the formaldehyde production device according to this embodiment, carbon dioxide dissolved in the aqueous solution can be efficiently reduced to produce formaldehyde.

[0034] [Methane production device] The methane production device according to this embodiment is a device that reduces carbon dioxide dissolved in an aqueous solution to produce methane, and includes an electrode having the above-described carbon dioxide reduction catalyst. According to the methane production device according to this embodiment, carbon dioxide dissolved in the aqueous solution can be efficiently reduced to produce methane.

[0035] [Carbon dioxide treatment device] The carbon dioxide treatment apparatus according to this embodiment is a carbon dioxide treatment apparatus that reduces and treats carbon dioxide contained in exhaust gas, and includes an electrode having the above-described carbon dioxide reduction catalyst. According to the carbon dioxide treatment apparatus according to this embodiment, carbon dioxide contained in exhaust gas can be efficiently reduced and treated. For example, it can treat carbon dioxide in exhaust gas after combustion of an internal combustion engine, a boiler, etc.

[0036] The carbon dioxide reduction method according to this embodiment is a method of electrochemically reducing carbon dioxide on the above-described carbon dioxide reduction catalyst. According to the carbon dioxide reduction method according to this embodiment, carbon dioxide can be efficiently reduced and treated.

[0037] The present invention is not limited to the above embodiment, and modifications and improvements within the scope that can achieve the object of the present invention are included in the present invention.

Example

[0038] Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[0039] [Example 1: 10 mass% Co / BaTiO 2.5 H 0.5 As Example 1, a 10 mass% Co / BaTiO 2.5 H 0.5 catalyst in which 10 mass% of Co is supported on hydrogenated oxide BTOH (BaTiO 2.7 H 0.3 ) was applied to an electrode substrate to produce an electrode. Specifically, through the synthesis process of hydrogenated oxide BTOH (BaTiO 2.5 H 0.5 ) as a carrier, the process of supporting a metal on the carrier, and the process of applying the catalyst to the electrode substrate, a 10 mass% Co / BaTiO 2.5 H 0.5 electrode was produced. The details of each process are as follows.

[0040] (Synthesis process of carrier) First, as a carrier composed of a hydride-containing oxide, hydrogenated oxide BTOH (BaTiO​2.5 H 0.5 ) was synthesized. 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 under a nitrogen atmosphere and ground for 30 minutes, and then formed into tablets (for 3 pellets) with a press machine.

[0041] Next, the tablets obtained as described above were placed in a glass tube, then vacuum-sealed and heated and reacted at a temperature of 833 K for 7 days. After the reaction was completed, the obtained crude product was placed in a 300 ml beaker, 200 ml of MeOH and about 0.1 M of NH4Cl were added, and the mixture was stirred for 5 hours. After stirring, it was suction-filtered and dried to obtain hydrogenated barium titanate BTOH (BaTiO 2.5 H 0.5 ) as the product.

[0042] (Step of loading metal onto the carrier) Next, a metal was loaded onto hydrogenated barium titanate BTOH (BaTiO 2.5 H 0.5 ). Specifically, 50 mg of a precursor of the supported metal Co (the supported metal content per catalyst corresponds to 10% by mass) and hydrogenated barium titanate 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. Then, after dispersing for 5 minutes with ultrasonic waves, it was heated and dried in a hot water bath while stirring. After drying, product A was obtained.

[0043] Next, the obtained product A was placed in a ceramic boat, which was put into a tubular furnace and subjected to a hydrogen reduction treatment. The hydrogen reduction treatment was carried out at a temperature of 473 K at which thermal damage to BTOH was not caused with a hydrogen gas flow rate of 20 ml / min for 1 hour. Thereby, 10% by mass Co / BaTiO 2.5 H 0.5 catalyst with 10% by mass of Co supported on hydrogenated barium titanate BTOH (BaTiO 2.5 H 0.5 ) was obtained.

[0044] (Step of coating the catalyst on the electrode substrate) Next, a catalyst was applied to carbon paper as the electrode substrate. Specifically, in a sample tube, 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 catalyst obtained as described above were placed, and then stirred by ultrasonic waves. After stirring, the suspension was dropped onto carbon paper heated to 393 K. 2.5 H 0.5 After that, the suspension was dropped onto carbon paper heated to 393 K.

[0045] Next, an ITO film was placed on the carbon paper onto which the suspension had been dropped as described above, heated to 423 K, and pressed at 4 MPa for 5 minutes. Then, a conducting wire was fixed with In, and the portion other than the catalyst surface was insulated, and then dried at a temperature of 343 K for 12 hours. Thus, an electrode in which the 10 mass% Co / BaTiO 2.5 H 0.5 catalyst of Example 1 was applied to carbon paper was obtained. The obtained electrode was used as the working electrode of the electrochemical measurement device 1 described later.

[0046] [Example 2: 10 mass% Fe / BaTiO 2.5 H 0.5 As Example 2, an electrode in which a 10 mass% Fe / BaTiO 2.5 H 0.5 catalyst in which 10 mass% of Fe was supported on hydrogenated BTOH (BaTiO 2.5 H 0.5 was applied to the electrode substrate was produced. Specifically, it was produced by the same operation as in Example 1 except that the type of the supported metal was changed from Co to Fe.

[0047] [Example 3: 10 mass% Ni / BaTiO 2.5 H 0.5 As Example 3, a 10 mass% Ni / BaTiO 2.5 H 0.5 catalyst in which 10 mass% of Ni was supported on hydrogenated BTOH (BaTiO 2.5 H 0.5 ​​An electrode was fabricated by applying a catalyst to an electrode substrate. Specifically, it was fabricated by the same procedure as in Example 1, except that the type of supported metal was changed from Co to Ni.

[0048] [Example 4: 10 mass% Cu / BaTiO 2.5 H 0.5 As Example 4, a 10 mass% Cu / BaTiO 2.5 H 0.5 catalyst in which 10 mass% of Cu was supported on hydrogenated BTOH (BaTiO 2.5 H 0.5 ) was used to fabricate an electrode by applying it to an electrode substrate. Specifically, it was fabricated by the same procedure as in Example 1, except that the type of supported metal was changed from Co to Cu.

[0049] [Example 5: 5 mass% Co / BaTiO 2.7 H 0.3 As Example 5, a 5 mass% Co / BaTiO 2.7 H 0.3 catalyst in which 5 mass% of Co was supported on hydrogenated BTOH (BaTiO 2.7 H 0.3 ) was used to fabricate an electrode by applying it to an electrode substrate. Specifically, it was fabricated by the same procedure as in Example 1, except that hydrogenated BTOH was changed from BaTiO 2.5 H 0.5 to BaTiO 2.7 H 0.3 and the supported amount of Co was changed from 10 mass% to 5 mass%.

[0050] [Example 6: 10 mass% Co / BaTiO 2.7 H 0.3 As Example 6, a 10 mass% Co / BaTiO 2.7 H 0.3 catalyst in which 10 mass% of Co was supported on hydrogenated BTOH (BaTiO 2.7 H 0.3 ) was used to fabricate an electrode by applying it to an electrode substrate. Specifically, hydrogenated BTOH was changed from BaTiO 2.5 H 0.5 to BaTiO​​​2.7 H 0.3 It was prepared by the same operation as in Example 1 except that it was changed to H.

[0051] [Comparative Example 1: BaTiO 2.7 H 0.3 As Comparative Example 1, an electrode was prepared by applying an oxyhydroxide BTOH (BaTiO 2.7 H 0.3 ) without supporting a metal on the electrode substrate. Specifically, BaTiO 2.5 H 0.5 was changed to BaTiO 2.7 H 0.3 , and the synthesized oxyhydroxide BTOH (BaTiO 2.7 H 0.3 ) was directly used in the coating step on the electrode substrate without going through the step of supporting the metal on the carrier. It was prepared by the same operation as in Example 1.

[0052] [Comparative Example 2: 10 mass% Co / BTO] As Comparative Example 2, an electrode was prepared by applying a 10 mass% Co / BTO catalyst in which 10 mass% of Co was supported on a carrier made of barium titanate BTO to the electrode substrate. Specifically, it was prepared by the same operation as in Example 1 except that BTO was directly used as the carrier instead of oxyhydroxide BTOH without going through the synthesis step of the carrier.

[0053] [Comparative Example 3: Co] As Comparative Example 3, an electrode was prepared by directly applying metallic Co to the electrode substrate. Specifically, it was prepared by the same operation as in Example 1 except that Co was used instead of the 10 mass% Co / BaTiO 2.5 H 0.5 catalyst in the coating step of the catalyst on the electrode substrate without going through the synthesis step of the carrier or the step of supporting the metal on the carrier.

[0054] [Comparative Example 4: Electrode substrate only] As Comparative Example 4, an electrode composed only of the carbon paper of the electrode substrate was prepared.

[0055] ​ [Comparative Example 5: BaTiO 2.5 H 0.5 As Comparative Example 5, an electrode was prepared by applying hydrogenated oxide BTOH (BaTiO 2.5 H 0.5 ) without supporting a metal on the electrode substrate. Specifically, it was prepared by the same operation as in Example 1 except that the synthesized hydrogenated oxide BTOH (BaTiO 2.5 H 0.5 ) was directly subjected to the coating process on the electrode substrate without going through the process of supporting the metal on the carrier.

[0056] [SEM, EDS Measurement] Among the electrodes of each Example and Comparative Example obtained as described above, as a representative example, for the 10 mass% Co / BaTiO 2.5 H 0.5 electrode of Example 1, SEM (scanning electron microscope) observation and EDS (energy dispersive X-ray elemental analysis) measurement were carried out under the following conditions.

[0057] (SEM, EDS Measurement Conditions) Measuring device: Scanning electron microscope "JSM-IT100LA" manufactured by JEOL Ltd. Observation conditions: Acceleration voltage 15.0 kV, magnification 40 - 300 times 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)

[0058] Figure 1 is a diagram showing the SEM image of the 10 mass% Co / BaTiO 2.5 H 0.5 electrode of Example 1. More specifically, Figure 1 is an SEM image when the electrode surface of Example 1 was magnified and observed at 300 times. As shown in Figure 1, it was confirmed that deposits considered to be catalysts were attached to the carbon fibers in the carbon paper.

[0059] Figure 2 is the 10 mass% Co / BaTiO 2.5 H 0.5 ​This is a diagram showing the EDS measurement results of the electrode. More specifically, Fig. 2 shows the enlarged SEM image of the region surrounded by the two-dot chain line in Fig. 1 and the elemental distribution diagrams of C, Co, Ti, Ba, and O. In each elemental distribution diagram, the whiter the part, the higher the concentration of each element. As shown in Fig. 2, it was confirmed that the elemental distributions of C, Co, Ti, Ba, and O corresponded to the distribution of carbon fibers, and it was confirmed that the catalyst of Example 1 was coated on the carbon paper.

[0060] [Electrochemical Measurement] 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 redox characteristics of carbon dioxide from a current-potential curve (cyclic voltammogram, hereinafter referred to as a CV curve) obtained by arranging an electrode in a stationary solvent in which carbon dioxide is dissolved and measuring the current flowing when the potential is repeatedly swept at a constant sweep rate to increase and decrease the potential. In addition, the electrochemical measurement apparatus 1 is an apparatus capable of measuring the production concentration of a product by the electrolysis current generated at that time by the potentiostatic electrolysis method in which carbon dioxide dissolved in a solvent is electrochemically oxidized and reduced on an electrode maintained at a constant potential.

[0061] As shown in Fig. 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, bubble introduction valves 22, 32, and a GC introduction valve 41.

[0062] In this example, the electrochemical measurement was 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 for 5 cycles, sweep rate 100 mV / S Potentiostatic electrolysis: -1.8 V × 10 hours Solvent in Chamber 10: containing 0.1 M tetraethylammonium tetrafluoroborate (Et4NBF4), acetonitrile (MeCN):H20 = 99:1 (v:v) Amount of solvent: 15 ml on the counter electrode side and 17 ml on the working electrode side Working electrode 11: An electrode in which the catalysts of each example and comparative example are coated on carbon paper Counter electrode 12: Pt electrode Reference electrode 13: Ag / AgNO3 electrode Proton permeable membrane 15: Nafion (registered trademark) membrane

[0063] Also, in this example, the electrochemical measurement was carried out according to the following procedure. First, for both the chamber 10 on the working electrode 11 side and the chamber 10 on the counter electrode 12 side, the gas supply valves 21 and 31 were opened to supply Ar gas through the gas supply paths 17a and 17b, and purging with Ar gas was carried out for 15 minutes. Then, CV measurement was carried out under the above-mentioned CV conditions.

[0064] Next, the gas in the chamber was introduced into the GC (gas chromatograph) by opening the GC introduction valve 41, and a leak check was carried out. After the leak check was completed, for both the chamber 10 on the working electrode 11 side and the chamber 10 on the counter electrode 12 side, the gas supply valves 21 and 31 were opened to supply carbon dioxide gas through the gas supply paths 17a and 17b, and bubbling with carbon dioxide gas was carried out for 15 minutes to dissolve carbon dioxide gas in the solvent. Then, CV measurement was carried out under the above-mentioned CV conditions.

[0065] Next, the gas in the chamber was introduced into the GC (gas chromatograph) by opening the GC introduction valve 41, and a leak check was carried out. After the leak check was completed, the potentiostat 14 was controlled to carry out the reduction of carbon dioxide for 10 hours under the above-mentioned constant potential electrolysis conditions.

[0066] For each electrode of Examples 1 to 4, the results of CV measurement are shown in FIGS. 4 to 7. Specifically, FIG. 4 shows 10 mass% Co / BaTiO of Example 1 2.5 H 0.5It is a diagram showing the CV curve of the electrode. Fig. 5 shows the 10 mass% Fe / BaTiO of Example 2 2.5 H 0.5 It is a diagram showing the CV curve of the electrode. Fig. 6 shows the 10 mass% Ni / BaTiO of Example 3 2.5 H 0.5 It is a diagram showing the CV curve of the electrode. Fig. 7 shows the 10 mass% Cu / BaTiO of Example 4 2.5 H 0.5 It is a diagram showing the CV curve of the electrode. In these Figs. 4 to 7, the horizontal axis represents the applied potential (potential with respect to the reference electrode), and the vertical axis represents the current.

[0067] In Figs. 4 to 7, the solid line indicates the CV curve after purging with Ar gas, and the dashed line indicates the CV curve after dissolving carbon dioxide gas in the solvent, respectively. As shown in Figs. 4 to 7, when the potential is swept at a constant sweep rate to increase or decrease the potential, it can be seen that reduction waves and oxidation waves occur. Specifically, it can be seen that a reduction wave occurs when the potential is swept in the negative direction, and an oxidation wave occurs when the battery is swept in the positive direction.

[0068] Here, in each of Figs. 4 to 7, when comparing the CV curve after purging with Ar gas and the CV curve after dissolving carbon dioxide gas in the solvent, if the current difference between the two is large at -2.0 V, which is the sweep start / end potential, it means that a large reduction current of carbon dioxide flows, and it can be said that it is promising as an 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 values between the case of Ar gas and the case of carbon dioxide gas.

[0069] Next, for the electrodes of Examples 1 to 6 and Comparative Examples 1 to 5, the production amounts and Faraday efficiencies of each product (MeOH, H2, CO, HCOOH) when constant potential electrolysis was carried out under the above conditions were as shown in Table 1.

[0070]

Table 1

[0071] Fig. 8 shows Example 5 (5 mass% Co / BaTiO2.7 H 0.3 ) Example 6 (10% by mass Co / BaTiO 2.7 H 0.3 ) Comparative Example 1 (BaTiO 2.7 H 0.3 ) The figure shows the amounts of each product (MeOH, H2, CO, HCOOH) produced when potentiostatic electrolysis was carried out under the above conditions for the electrodes of Comparative Example 2 (10% by mass Co / BTO) and Comparative Example 3 (Co). Further, Fig. 9 is a diagram showing the Faraday efficiency of each product when potentiostatic electrolysis was carried out for the electrodes of Example 5, 6 and Comparative Examples 1 to 3. In Figs. 8 and 9, the thick black line is the error bar (the same applies to Figs. 10 and 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 the six-electron reduction of carbon dioxide. From this result, it was confirmed that according to this example, reduction with more electrons than the usual six-electron reduction is possible.

[0072] Also, by comparing the results of Example 5 (5% by mass Co / BaTiO 2.7 H 0.3 ) and Example 6 (10% by mass Co / BaTiO 2.7 H 0.3 ) shown in Fig. 8, it was found that when the loading amount of Co with respect to the hydrogenated oxide BTOH (BaTiO 2.7 H 0.3 ) increased from 5% by mass to 10% by mass, the production amount of methanol increased by 20%. From this result, it was confirmed that by increasing the loading amount of the metal, the number of flowing electrons also increases, so that the production rate of methanol by the six-electron reduction of carbon dioxide increases. However, as shown in Fig. 9, in terms of the Faraday efficiency of methanol production, when the loading amount of Co increased from 5% by mass to 10% by mass, the ratio of electrons flowing excessively and proceeding to six-electron reduction decreased, and it was also confirmed that the methanol production efficiency decreased.

[0073] Next, Fig. 10 shows Example 1 (10% by mass Co / BaTiO 2.5 H 0.5 ) Example 6 (10% by mass Co / BaTiO2.7 H 0.3 ) and FIG. 10 is a diagram showing the amounts of each product (MeOH, H2, CO, HCOOH) produced when potentiostatic electrolysis was performed on the electrodes of Comparative Example 2 (10% by mass Co / BTO). Further, FIG. 11 is a diagram showing the Faraday efficiency of each product when potentiostatic electrolysis was performed on the electrodes of Example 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, also from this result, it was confirmed that according to the present example, carbon dioxide can be highly selectively reduced by 6 electrons.

[0074] Also, by comparing the results of Example 1 (10% by mass Co / BaTiO 2.5 H 0.5 ) and Example 6 (10% by mass Co / BaTiO 2.7 H 0.3 ) shown in FIG. 10, it was found that the methanol production amount increases as the hydride content in BTOH increases. Also from the results of Example 1 and Example 6 shown in FIG. 11, it was found that the Faraday efficiency of methanol production improves as the hydride content in BTOH increases. Therefore, it was confirmed that by increasing the hydride content in BTOH, hydrogen production is suppressed and the methanol selectivity increases. In FIG. 11, the Faraday efficiency of Example 1 exceeds 100%, but this is considered to be due to hydrogen generated by the stoichiometric reaction of hydride in BTOH and water in the solvent.

[0075] Next, FIG. 12 shows Example 1 (10% by mass Co / BaTiO 2.5 H 0.5 ), Example 2 (10% by mass Fe / BaTiO 2.5 H 0.5 ), Example 3 (10% by mass Ni / BaTiO 2.5 H 0.5 ), Example 4 (10% by mass Cu / BaTiO 2.5 H 0.5 ), Comparative Example 4 (electrode substrate only), and Comparative Example 5 (BaTiO 2.5 H 0.5This is a diagram showing the production amounts of each product (MeOH, H2, CO, HCOOH) when potentiostatic electrolysis is performed on the electrode of ( ). Further, FIG. 13 is a diagram showing the Faraday efficiency of each product when potentiostatic electrolysis is performed on the electrodes of Examples 1 to 4 and Comparative Examples 4 and 5. As shown in FIG. 12, as the supported metal becomes Fe, Co, Ni, Cu, which are metals with a large number of electrons, the number of electrons flowing increases, so it was found that the production of formic acid and hydrogen increases. Also, as shown in FIG. 13, it was found that the Faraday efficiency of methanol production and the Faraday efficiency of formic acid are higher in Examples 1 to 4 than in Comparative Examples 4 and 5, and it was confirmed that carbon dioxide can be efficiently reduced. In FIG. 13, there are some where the Faraday efficiency exceeds 100%, which is considered to be due to hydrogen generated by the stoichiometric reaction of hydride in BTOH and water in the solvent.

Explanation of symbols

[0076] 1 Electrochemical measurement device 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

1. A carbon dioxide reduction catalyst for reducing carbon dioxide, wherein a metal composed of a transition metal is supported on a hydride-containing oxide represented by the following general formula (1), and the metal is at least one of Fe, Co, Ni, and Cu. The carbon dioxide reduction catalyst. [Chemical formula 1] BaTiO ３－ｘ H ｘ ・・・(1) [In the general formula (1), x satisfies 0 < x < 0.8.]

2. The carbon dioxide reduction catalyst according to claim 1, wherein the metal is Co.

3. 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% by mass.

4. The carbon dioxide reduction catalyst according to claim 1 or 2, wherein the content of the metal in the carbon dioxide reduction catalyst is 5 to 10% by mass.

5. 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.

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.

7. A methanol production apparatus comprising an electrode for reducing carbon dioxide dissolved in an aqueous solution to produce methanol, wherein the electrode has the carbon dioxide reduction catalyst according to any one of claims 1 to 6. The methanol production apparatus.

8. A carbon monoxide and formic acid production apparatus comprising an electrode for reducing carbon dioxide dissolved in an aqueous solution to produce carbon monoxide and formic acid, wherein the electrode has the carbon dioxide reduction catalyst according to any one of claims 1 to 6. The carbon monoxide and formic acid production apparatus.

9. A carbon dioxide treatment apparatus for reducing and treating carbon dioxide contained in exhaust gas, which has the carbon dioxide reduction catalyst according to any one of claims 1 to 6. The carbon dioxide treatment apparatus.

10. A carbon dioxide reduction method for electrochemically reducing carbon dioxide on the carbon dioxide reduction catalyst according to any one of claims 1 to 6.

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