Method for producing carbon monoxide and hydrogen

Abstract

Provided is a method for producing carbon monoxide and hydrogen by applying a voltage to a catalyst to react carbon dioxide and methane in a gas phase, said method having an improved STY of carbon monoxide and hydrogen, which is the objective. A method for producing carbon monoxide and hydrogen in which carbon dioxide and methane are reacted in a gas phase in the presence of a catalyst, in which ruthenium (Ru) is supported on a composite metal oxide carrier configured from cerium (Ce) and Ln (Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids), at a reaction temperature of 80-400°C while a current is passed through the catalyst.

Description

Carbon monoxide and hydrogen production methods

[0001] The presently disclosed subject matter relates to a method for producing synthesis gas comprising carbon monoxide gas and hydrogen gas.

[0002] Efforts to capture and utilize carbon dioxide, a greenhouse gas, have been attracting attention. There is also a need to develop effective ways to utilize methane, another greenhouse gas known as carbon dioxide, instead of using it as fuel. One such effective utilization method is conversion into useful chemicals. However, because both carbon dioxide and methane are typical inert molecules, conversion using conventional catalytic technology is not easy. In recent years, electrocatalytic technology has been developed as a method for converting inert molecules, in which inert molecules are reacted using a catalyst with an applied voltage.

[0003] Patent Document 1 describes an electric field-applied catalytic reaction device that reacts a raw material gas consisting of methane contained in coke oven gas and carbon dioxide contained in steel mill by-product gas to produce carbon monoxide and hydrogen gas.

[0004] In Non-Patent Document 1, La ２ O ３ system and ZrO ２ It is described that carbon monoxide, hydrogen, ethane, and ethylene can be produced from carbon dioxide and methane by applying a voltage to the catalyst. ２ It is disclosed that carbon monoxide and hydrogen can be produced from carbon dioxide and methane by applying a voltage to a catalyst in which Pt is supported on a carrier.

[0005] Japanese Patent Application Laid-Open No. 2019-206453

[0006] Kazumasa Oshima et al., “Oxidative coupling of methane using carbon dioxide in an electric field over La-ZrO2 catalyst at low external temperature”, Fuel, 2013, vol. 107, pp. 879-881 Naoya Nakano et al., “Elucidation of the reaction mechanism on dry reforming of methane in an electric field by in in situ DRIFTs”, RSC Advances, 2022, vol. 12, pp. 9036-9043

[0007] The present disclosure relates to a method for producing carbon monoxide (CO) and hydrogen (H) by reacting carbon dioxide and methane in the gas phase by applying a voltage to a catalyst. ２ The present invention provides a method for producing carbon monoxide and hydrogen from ethanol, which has an improved STY for the target products, carbon monoxide and hydrogen, and a catalyst for use in the method.

[0008] As a result of extensive research, the present inventors have discovered that in the reaction of carbon dioxide and methane, the production of carbon monoxide and hydrogen is promoted by applying a voltage under heated conditions to a catalyst carrying ruthenium (Ru) on a composite metal oxide support composed of cerium (Ce) and Ln (Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids), and have completed the present invention.

[0009] That is, the present disclosure relates to the following [1] to [9]. [1] A method for producing carbon monoxide and hydrogen using carbon dioxide and methane as raw materials, comprising: passing an electric current through a catalyst comprising ruthenium (Ru) supported on a composite metal oxide support composed of cerium (Ce) and Ln (Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids); reacting carbon dioxide and methane in the gas phase in the presence of the catalyst at a reaction temperature of 80 to 400°C. [2] The method according to [1], wherein the catalyst has a Ce / Ln molar ratio of 1 / 100 to 100 / 1. [3] The method according to [1] or [2], wherein the catalyst has Ln representing at least one element selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), and ytterbium (Yb). [4] The manufacturing method according to any one of [1] to [3], wherein the amount of Ru supported on the catalyst is 0.05 to 10 parts by mass relative to 100 parts by mass of the composite metal oxide support. [5] The manufacturing method according to any one of [1] to [4], wherein the reaction is carried out by applying a voltage to the catalyst so that the reaction temperature is 0.02 to 250 W / gRu+composite metal oxide support. [6] The manufacturing method according to any one of [1] to [5], wherein the reaction temperature is 100 to 300°C. [7] The manufacturing method according to any one of [1] to [6], wherein the space velocity of the reaction is 1000 to 50000 / h. [8] The manufacturing method according to any one of [1] to [6], wherein the molar ratio of carbon dioxide to methane (CO ２ / CH ４ [9] An electrocatalyst used for producing carbon monoxide and hydrogen using carbon dioxide and methane as raw materials, the electrocatalyst comprising Ru supported on a composite metal oxide support comprising cerium (Ce) and Ln (Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids), with a Ce / Ln molar ratio in the range of 1 / 100 to 100 / 1.

[0010] According to the present disclosure, it is possible to provide a method for producing carbon monoxide and hydrogen by reacting carbon dioxide and methane in the gas phase by applying a voltage to a catalyst, in which the STY of the target carbon monoxide and hydrogen is improved, and a catalyst used in the method.

[0011] FIG. 1 is a schematic diagram of an apparatus used for the reaction of carbon dioxide and methane in Examples 1 to 8 and Comparative Examples 1 and 2.

[0012] Hereinafter, embodiments of the present invention will be described, but it should be understood that the present invention is not limited to these embodiments and that various applications are possible within the spirit and scope of the present invention. In this disclosure, when "to" is used to describe a numerical range, the numerical values ​​at both ends are the upper and lower limits, respectively, and are included in the numerical range. When multiple upper or lower limits are listed, numerical ranges can be created using all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining the upper and lower limits from those numerical ranges.

[0013] (Catalyst for use in the reaction of carbon dioxide and methane and its manufacturing method) For the reaction of carbon dioxide and methane, an electric field catalyst is used in which ruthenium (Ru) is supported on a composite metal oxide support composed of cerium (Ce) and Ln (Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids).

[0014] In the present disclosure, a composite metal oxide support composed of cerium (Ce) and Ln is a composite metal oxide support in which the metal elements constituting the support are cerium (Ce) and the element Ln.

[0015] A catalyst in which Ru is supported on a composite metal oxide support composed of cerium (Ce) and Ln can be made to function as a catalyst for synthesizing carbon monoxide and hydrogen because the band gap, the electron density of the supported Ru, and the acidity or basicity of the catalyst surface can be arbitrarily changed by changing the type of Ln and the composition ratio of Ce to Ln.

[0016] In the present disclosure, Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids. Lanthanoids are elements ranging from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71. Ln is preferably at least one element selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), and ytterbium (Yb), and more preferably at least one element selected from the group consisting of yttrium (Y), lanthanum (La), and ytterbium (Yb). Without being bound by any theory, the use of these metals generates oxygen vacancy sites in the composite metal oxide, making the electronic state of the supported Ru suitable for functioning as a catalyst for synthesizing carbon monoxide and hydrogen.

[0017] The molar ratio of Ce / Ln is preferably in the range of 1 / 100 to 100 / 1, more preferably in the range of 1 / 10 to 10 / 1, and even more preferably in the range of 1 / 5 to 5 / 1. When the molar ratio of Ce / Ln is in the range of 1 / 100 to 100 / 1, the influence of discharge and the like is small, voltage application is easy, and handling is excellent. When the molar ratio of Ce / Ln is in the range of 1 / 100 to 100 / 1, the STY of carbon monoxide and hydrogen can be increased.

[0018] The composition ratio of Ce and Ln is determined by elemental analysis such as fluorescent X-ray, ICP, SEM-EDX, or the like.

[0019] The formation of a composite metal oxide composed of Ce and Ln can be determined from the X-ray diffraction pattern. A composite metal oxide composed of Ce and Ln has the same defective fluorite structure as cerium oxide. Therefore, if a peak shift to the low-angle or high-angle side in the diffraction pattern according to the difference in the ionic radii of Ce and Ln is observed compared to the X-ray diffraction pattern of cerium oxide, it can be seen that a composite metal oxide composed of Ce and Ln has been formed.

[0020] The method for producing a composite metal oxide support composed of Ce and Ln is not particularly limited. Examples of methods for producing a composite metal oxide support include a solid-phase method, a mechano-ironing method, a coprecipitation method, a sol-gel method, a homogeneous precipitation method, a hydrothermal synthesis method, a complex polymerization method, and a citric acid complex method. Among these, it is preferable to use any of the solid-phase method, the coprecipitation method, the sol-gel method, and the hydrothermal synthesis method, which are easily applicable industrially.

[0021] The amount of Ru (metallic ruthenium) supported is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of the composite metal oxide support. Any combination of these lower and upper limits may be used. For example, the amount of Ru supported is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 7 parts by mass, and even more preferably 0.5 to 3.0 parts by mass, per 100 parts by mass of the composite metal oxide support. When the amount of Ru supported is 0.05 parts by mass or more, the activity per unit catalyst mass or volume can be increased. When the amount of Ru supported is 10 parts by mass or less, the decrease in catalytic activity due to Ru aggregation can be suppressed. The amount of Ru supported is determined by elemental analysis such as ICP or X-ray fluorescence.

[0022] In one embodiment, the method for supporting Ru on a composite metal oxide support includes, in this order, an impregnation step in which the composite metal oxide support is absorbed or impregnated with a Ru salt solution (hereinafter referred to as "impregnation solution"), a drying step, a calcination step, and a reduction step. Other steps may be included between each step. Examples of such other steps include an air-drying step and a transfer step from an impregnation apparatus to a drying apparatus.

[0023] The Ru salt used in the impregnation step is not particularly limited, and examples thereof include ruthenium chloride, ruthenium acetate, tris(acetylacetonato)ruthenium(III), and combinations thereof. Commercially available Ru salts can also be used. The concentration of the Ru salt in the impregnation solution can be determined from the volume of the impregnation solution and the amount of Ru to be supported on the composite metal oxide support.

[0024] The solvent used in the impregnation step is not particularly limited as long as it can dissolve the Ru salt, and examples of such solvents include water, ethanol, and acetone.

[0025] The conditions for the drying step are not particularly limited, but generally the material can be dried in air for 1 to 24 hours at 100 to 200° C. A commercially available dryer can be used for the drying process.

[0026] The conditions for the calcination step are not particularly limited, but calcination can generally be carried out at 400 to 600°C for 0.5 to 12 hours under air flow. A commercially available calcination device such as a muffle furnace can be used for the calcination treatment. In the calcination step, the Ru salt is converted into ruthenium oxide (RuO ２ ) is converted into

[0027] In the reduction step, for example, hydrogen gas or a mixture of hydrogen gas and an inert gas such as nitrogen gas or helium is applied to a catalyst precursor in which ruthenium oxide is supported on a carrier at a space velocity (SV Ｈ２ The reduction step can be carried out by heating at 300 to 600°C for 1 to 5 hours while passing the gas at a flow rate of 4,000 to 16,000 / h. The reduction step is preferably carried out immediately before the reaction of carbon dioxide with methane in the reaction vessel. The oxidation state of the catalyst element after the reduction step with hydrogen gas is determined by the standard oxidation-reduction potential of the oxide / metal. That is, when the standard oxidation-reduction potential is H ＋ / H ２ Compared to 0 V, if the voltage is positive, the metal is easily reduced to the metal, but if the voltage is negative, the metal is not easily reduced to the metal. For example, Ru ３＋ Since the standard oxidation-reduction potential of Ce / Ru is 0.249 V, it is easily reduced to the metal, but since the standard oxidation-reduction potential of Ce, La, Y, and Yb becomes negative from a low oxidation state, they are not reduced to the metal and remain in the oxide state. (Ce ３＋ / Ce: -2.483V, La ３＋ / La: -2.522V, Y ３＋ / Y: -2.372V, Yb ３＋ / Yb: -2.22 V, Source: HANDBOOK of CHEMISTRY and PHYSICS (1st Student Edition)

[0028] (Method for Producing Carbon Monoxide and Hydrogen) Carbon monoxide and hydrogen are produced by reacting carbon dioxide and methane in the gas phase under heated conditions in the presence of a catalyst through which a voltage is applied and a current flows.

[0029] In this reaction system, the dry reforming reaction of carbon dioxide and methane (Equation (1)) and the reverse water gas shift reaction of carbon dioxide and hydrogen (Equation (2)) proceed simultaneously. Therefore, in order to improve the STY of carbon monoxide and hydrogen, it is necessary to set reaction conditions that allow the reaction of Equation (1) to proceed while suppressing the reaction of Equation (2).

[0030] CH ４ +CO ２ → 2CO + 2H ２ (1) CO ２ +H ２ → CO + H ２ O (2)

[0031] Since a portion of the produced hydrogen is consumed by the reaction of formula (2), the proportion of carbon monoxide discharged from the reactor is greater than the proportion of hydrogen gas.

[0032] The reaction temperature is 80 to 400°C. In the present disclosure, the reaction temperature means the temperature downstream of the catalyst layer, near the center of the cross section of the flow path, during the reaction. The reaction temperature is preferably 100°C or higher, more preferably 150°C or higher, preferably 300°C or lower, and more preferably 270°C or lower. Any combination of these lower and upper limits may be used. For example, the reaction temperature is preferably 100 to 300°C, more preferably 150 to 270°C. If the reaction temperature is 80°C or higher, a sufficient current can be passed through the catalyst. If the reaction temperature is 400°C or lower, coke deposition or aggregation of Ru species, which can cause catalyst deterioration, is suppressed. Without being bound by any theory, it is believed that placing the electric field catalyst in a high-temperature environment allows protons (H ＋ ) is generated, and the generated protons are thought to form the conductive paths necessary for catalyst activation.

[0033] The reaction pressure is preferably 0 to 5 MPaG (gauge pressure), more preferably 0 to 3 MPaG (gauge pressure), and even more preferably 0 to 1.5 MPaG (gauge pressure). If the reaction pressure is 0 to 5 MPaG (gauge pressure), side reactions are less likely to proceed and the catalyst is highly stable, allowing the reaction of carbon dioxide and methane to proceed efficiently.

[0034] The space velocity (gas flow rate (mL / h) / catalyst volume (mL) = 1 / h) of the gas containing the reactant gas supplied to the reactor is preferably 1000 / h or more, more preferably 1500 / h or more, even more preferably 2000 / h or more, preferably 50,000 / h or less, more preferably 30,000 / h or less, and even more preferably 15,000 / h or less. Any combination of these lower and upper limits may be used. For example, the space velocity of the gas containing the reactant gas is preferably 1000 to 50,000 / h, more preferably 1500 to 30,000 / h, and even more preferably 2000 to 15,000 / h. A space velocity of 1000 to 50,000 / h ensures sufficient time for the reactant gas to contact the catalyst, allowing the reaction between carbon dioxide and methane to proceed efficiently. The reaction between carbon dioxide and methane can proceed without problems even when an inert gas such as nitrogen or helium is simultaneously passed through.

[0035] (Reaction Raw Material Gas) The form of the reaction raw material gases carbon dioxide and methane is not particularly limited, and commercially available gases can be used. A mixed gas of the reaction raw material gas and an inert gas such as nitrogen gas or argon can also be used for the reaction. In this case, from the viewpoint of efficient reaction progress, it is preferable that the ratio of the volume of the inert gas to the total volume of carbon dioxide and methane (volume of inert gas / volume of (carbon dioxide + methane)) is 0.9 or less.

[0036] The molar ratio of raw materials in the above reaction, i.e., the molar ratio of carbon dioxide to methane (CO ２ / CH ４The molar ratio of the raw materials is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.5 or more, and preferably 20 or less, more preferably 8 or less, and even more preferably 4 or less. Any combination of these lower limit and upper limit values ​​may be used. For example, the raw material molar ratio is preferably 0.05 to 20, more preferably 0.1 to 8, and even more preferably 0.5 to 4. When the raw material molar ratio is 0.05 to 20, the reaction of carbon dioxide and methane can be efficiently promoted, and the reaction of carbon dioxide or methane alone can be suppressed.

[0037] (Reactor) A carbon dioxide and methane reaction apparatus includes a reactor vessel for containing a catalyst and for bringing the catalyst into contact with carbon dioxide and methane, and a means for generating an electric field in the catalyst layer. A schematic diagram of a reactor used for the reaction of carbon dioxide and methane is shown in Figure 1. Figure 1 shows an example of a carbon dioxide and methane reaction apparatus, and usable reactors are not limited to this structure. In Figure 1, the carbon dioxide and methane reaction apparatus 1 includes two spaced electrodes 4 and 5 inside a reaction tube 3, with a catalyst filled between the electrodes to form a catalyst layer 2. The two electrodes 4 and 5 consist of a high-voltage electrode 4 to which a voltage is applied from a power source 6 and a grounded electrode 5. The electrodes 4 and 5 are made of a metal mesh, such as stainless steel, to hold the catalyst and allow the flow of the reactant gas. The reaction tube 3 is made of a non-conductive material to prevent electrical conduction between the electrodes. The reaction apparatus 1 also includes a heating means, such as a heater 7, for heating the catalyst layer 2 and maintaining a predetermined reaction temperature.

[0038] The reaction tube 3 is generally made of a material that is non-conductive and does not affect the reaction between carbon dioxide and methane. A preferred material for the reaction tube 3 is, for example, quartz. The shape of the reaction tube 3 may be a shape other than the cylindrical shape shown in FIG. 1 . The size of the reaction tube 3 may be appropriately set depending on the required processing amount, etc., and is not particularly limited. Various conditions such as the sizes of the high-voltage side electrode 4 and the ground side electrode 5, and the amount of the catalyst layer 2 in the reaction tube 3 may be appropriately set depending on the size of the reaction tube 3, etc., and are not particularly limited.

[0039] In the carbon dioxide and methane reactor 1, carbon dioxide and methane are supplied downward from the top of the reaction tube 3. At this time, a voltage is applied from a power source 6 between a high-voltage electrode 4 and a ground electrode 5, which are spaced apart, to generate an electric field, and a current is passed through the electrode, thereby bringing the reactant gas into contact with the catalyst layer 2 in the electric field. The applied voltage is preferably adjusted so that the power (W) applied to the catalyst layer 2 is 0.02 to 250 W per gram of the total mass of the supported Ru and the composite metal oxide support. That is, the voltage is applied preferably at a level of 0.02 W / g Ru + composite metal oxide support or more, more preferably 1.0 W / g Ru + composite metal oxide support or more, even more preferably 5.0 W / g Ru + composite metal oxide support or more, particularly preferably 10 W / g Ru + composite metal oxide support or more, and preferably 250 W / g Ru + composite metal oxide support or less, more preferably 100 W / g Ru + composite metal oxide support or less, and even more preferably 50 W / g Ru + composite metal oxide support or less. For example, the voltage is preferably applied so as to be 0.02 to 250 W / g Ru + composite metal oxide support, more preferably 1.0 to 100 W / g Ru + composite metal oxide support, and even more preferably 5.0 to 50 W / g Ru + composite metal oxide support. When the voltage is 0.02 to 250 W / g Ru + composite metal oxide support, a voltage can be applied to the catalyst with an appropriate power, and the reaction between carbon dioxide and methane can be effectively promoted.

[0040] The present invention will be further described with reference to the following examples and comparative examples, but the present invention is not limited to these examples.

[0041] (Preparation of Catalyst Precursor A) 100 g of an aqueous solution containing 3.908 g of cerium (III) nitrate hexahydrate, 3.897 g of lanthanum (III) nitrate hexahydrate, and 3.804 g of citric acid was prepared so that the Ce / La molar ratio was 1 / 1. The water was removed using an evaporator, and the mixture was dried in air at 200 ° C. for 5 hours using a muffle furnace and then calcined at 850 ° C. for 3 hours to obtain a Ce—La—O composite metal oxide support. Then, 100 g of an ethanol solution containing 0.0910 g of tris(acetylacetonato)ruthenium (III) was mixed with 2.3 g of the Ce—La—O composite metal oxide support so that the amount of Ru supported was 1 part by mass per 100 parts by mass of the support. After distilling off the ethanol using an evaporator, the mixture was dried at 120 ° C. for 5 hours using a dryer. The resulting Ru salt-supported carrier was then pulverized in an agate mortar for 5 minutes and calcined in air at 450°C for 2 hours using a muffle furnace. The resulting powder was sized to a mesh size of 300 to 500 µm to obtain catalyst precursor A.

[0042] (Preparation of Catalyst Precursor B) Catalyst precursor B was prepared in the same manner as catalyst precursor A, except that the amount of tris(acetylacetonato)ruthenium(III) was changed to 0.0455 g so that the amount of Ru supported was 0.5 parts by mass per 100 parts by mass of the support.

[0043] (Preparation of Catalyst Precursor C) Catalyst precursor C was prepared in the same manner as catalyst precursor A, except that the amount of tris(acetylacetonato)ruthenium(III) was changed to 0.2730 g so that the amount of Ru supported was 3 parts by mass per 100 parts by mass of the support.

[0044] (Preparation of Catalyst Precursor D) Catalyst precursor D was prepared in the same manner as catalyst precursor A, except that the amount of cerium (III) nitrate hexahydrate was changed to 5.862 g and the amount of lanthanum nitrate hexahydrate was changed to 1.949 g so that the Ce / La molar ratio was 3 / 1.

[0045] (Preparation of Catalyst Precursor E) Catalyst precursor E was prepared in the same manner as catalyst precursor A, except that the amount of cerium (III) nitrate hexahydrate was changed to 1.954 g and the amount of lanthanum nitrate hexahydrate was changed to 5.846 g so that the Ce / La molar ratio was 1 / 3.

[0046] (Preparation of Catalyst Precursor F) Catalyst precursor F was prepared in the same manner as catalyst precursor A, except that 3.447 g of yttrium (III) nitrate hexahydrate was used instead of lanthanum (III) nitrate hexahydrate.

[0047] (Preparation of Catalyst Precursor G) Catalyst precursor G was prepared in the same manner as catalyst precursor A, except that 4.042 g of ytterbium (III) nitrate pentahydrate was used instead of lanthanum (III) nitrate hexahydrate.

[0048] (Preparation of Comparative Catalyst Precursor H) Comparative catalyst precursor H was prepared in the same manner as catalyst precursor A, except that 100 g of an aqueous solution containing only 7.816 g of cerium (III) nitrate hexahydrate and 3.804 g of citric acid was used.

[0049] (Preparation of Comparative Catalyst Precursor I) Comparative catalyst precursor I was prepared in the same manner as catalyst precursor A, except that 100 g of an aqueous solution containing only 7.794 g of lanthanum (III) nitrate hexahydrate and 3.804 g of citric acid was used.

[0050] (Reaction of Carbon Dioxide and Methane) The reaction of carbon dioxide and methane was carried out using the reactor 1 shown in FIG. 1 . A cylindrical quartz reactor having an outer diameter of 20 mm, an inner diameter of 9 mm, and a length of 260 mm was used as the reaction tube 3. 0.18 mL of a granulated catalyst precursor (or comparative catalyst precursor; the same applies hereinafter) was packed on a stainless steel mesh ground electrode 5 provided in the reaction tube 3, and a stainless steel mesh high-voltage electrode 4 was brought into contact with the top of the catalyst precursor to form a catalyst layer 2. The thickness of the catalyst layer 2 was 3 mm. The conductive wire connecting the high-voltage electrode 4 to the power source 6 and the conductive wire connecting the ground electrode 5 to earth were both stainless steel rods with a diameter of 3.2 mm. The high-voltage electrode 4 was electrically connected to the power source 6 (DC high-voltage power supply: HAR-10N30, Matsusada Precision Co., Ltd.).

[0051] In the reactor 1, hydrogen gas was supplied from the top of the reaction tube 3 at a rate of 0.9 NL / h, and the heater temperature was adjusted so that the temperature of the catalyst layer 2 would be 400°C. The hydrogen gas was allowed to flow for 1 hour, thereby carrying out a reduction step in which the catalyst precursor was reduced with the hydrogen gas and ruthenium oxide was converted into metallic ruthenium. The space velocity of the hydrogen gas was 5000 / h. The temperature of the catalyst layer 2 was measured by a thermocouple placed below the catalyst layer 2.

[0052] In the reactor 1, carbon dioxide gas and methane gas were supplied as reaction feed gases from the top of the reaction tube 3. The temperature of the catalyst layer 2 was then raised to 180°C using the heater 7. Then, a current was applied from the power supply 6 between the high-voltage electrode 4 and the ground electrode 5 to generate an electric field within the catalyst layer 2, thereby carrying out a reaction between carbon dioxide and methane under atmospheric pressure. The carbon dioxide gas supply rate was 0.92 NL / h, and the methane gas supply rate was also 0.92 NL / h (raw material molar ratio: 1.0), and the space velocity of the reaction feed gas was 10,000 / h. During the reaction, a constant current was applied at the value determined for each example and comparative example listed in Table 1, and the temperature of the heater 7 was adjusted so that the temperature of the catalyst layer 2 was the temperature listed in Table 1. The corresponding voltage was measured using the power supply 6.

[0053] The reaction product gas discharged from the bottom of the reaction tube 3 was analyzed by gas chromatography.

[0054] (Method of Analyzing Gas Products) 1. Hydrogen (H ２) Using the absolute calibration curve method, 40 mL of gas components were collected and the entire amount was passed through a 1 mL gas sampler attached to a gas chromatography analyzer, and analysis was performed under the following conditions. Gas chromatography analyzer: 7890A (Agilent Technology Co., Ltd.) Column: 8 Ft Molecular Sieve 5A 60 / 80 mesh (Agilent Technology Co., Ltd., length 2.4 m, inner diameter 2 mm) Carrier gas: nitrogen gas (split ratio: 80, column flow rate 2 mL / min) Temperature conditions: The temperature of the detector and vaporizer was set to 250°C, and the column temperature was maintained at 50°C for 7 minutes from the start of analysis, and then the temperature was increased to 75°C at a rate of 10°C / min and maintained at 75°C for 1 minute. Thereafter, the temperature was increased to 145°C at a rate of 20°C / min and maintained at 145°C for 3 minutes. Detector: TCD

[0055] 2. Carbon monoxide (CO) The gas sample was introduced into the gas chromatography apparatus in the same manner as in the hydrogen analysis described above. The gas chromatography analysis was carried out under the following conditions. Gas chromatography analyzer: 7890A (Agilent Technology Co., Ltd.) Column: 6 ft HayeSep Q 80 / 100 mesh in Nickel (Agilent Technology Co., Ltd., length 1.8 m, inner diameter 2 mm) and 8 ft Molecular Sieve 5A 60 / 80 mesh (Agilent Technology Co., Ltd., length 2.4 m, inner diameter 2 mm) Carrier gas: Helium (split ratio: 80, column flow rate 2 mL / min) Temperature conditions: The same as in the hydrogen analysis described above. Detector: TCD

[0056] From the above analytical results, the space-time yield (STY) of each product was calculated as follows: Product STY (g / L h) = Amount of product produced (g) / [Volume of catalyst (Ru + support) (L) × Reaction time (h)]

[0057] Example 1 0.18 mL of catalyst precursor A was packed into the reaction tube 3, and after carrying out the reduction step, carbon dioxide and methane were reacted. After carrying out the reaction for 1 hour, the gas product was analyzed and the space-time yields of carbon monoxide and hydrogen were calculated. The reaction conditions and results are shown in Table 1. Note that a volume change occurs when ruthenium oxide is reduced to metallic ruthenium. However, since the mass of metallic ruthenium is about 1 part by mass per 100 parts by mass of the support, which does not change in volume during the reduction step, the volume change was ignored when calculating the STY.

[0058] Example 2 A reaction between carbon dioxide and methane was carried out in the same manner as in Example 1, except that the applied current was set to 10 mA, and analysis was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0059] Examples 3 to 8 Carbon dioxide and methane were reacted and analyzed in the same manner as in Example 1, except that catalyst precursors B to G were packed instead of catalyst precursor A. The results are shown in Table 1.

[0060] Comparative Example 1 A reaction between carbon dioxide and methane was carried out in the same manner as in Example 1, except that comparative catalyst precursor H was packed instead of catalyst precursor A, and analysis was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0061] Comparative Example 2 A reaction between carbon dioxide and methane was carried out in the same manner as in Example 1, except that comparative catalyst precursor I was packed instead of catalyst precursor A and the voltage was set to 2.0 kV, and analysis was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0062] As shown in Table 1, Example 1 shows that the target products, carbon monoxide and hydrogen, were produced by carrying out a reaction while passing an electric current through a catalyst in which Ru was supported on a composite metal oxide support composed of cerium (Ce) and lanthanum (La).

[0063] From Example 2, it can be seen that carbon monoxide and hydrogen were produced even under conditions of different current values.

[0064] From Examples 3 and 4, it can be seen that carbon monoxide and hydrogen were produced even under conditions where the amount of supported metal was different.

[0065] From Examples 5 and 6, it can be seen that carbon monoxide and hydrogen were produced even under conditions where the ratio of cerium (Ce) to lanthanum (La) in the composite metal oxide support was different.

[0066] From Examples 7 and 8, it can be seen that the target products, carbon monoxide and hydrogen, were produced even when a composite metal oxide support composed of cerium (Ce) and Y (yttrium) or Yb (ytterbium) was used.

[0067] Comparing Example 1 with Comparative Examples 1 and 2, in the catalyst in which Ru is supported on a composite metal oxide support composed of cerium (Ce) and lanthanum (La), CeO, which is not a composite metal oxide, ２ Carrier or La ２ O ３ It can be seen that the STY of carbon monoxide and hydrogen is higher than that of the catalyst in which Ru is supported on the carrier. ２ O ３ is an insulator, no current flows through the catalyst even when a voltage of 2.0 kV is applied, and it is therefore not possible to supply the power required to generate carbon monoxide and hydrogen.

[0068]

[0069] 1: Carbon dioxide and methane reactor 2: Catalyst layer 3: Reaction tube 4: High-voltage electrode 5: Ground electrode 6: Power supply 7: Heater

Claims

1. A method for producing carbon monoxide and hydrogen using carbon dioxide and methane as raw materials, which comprises passing an electric current through a catalyst comprising ruthenium (Ru) supported on a composite metal oxide support composed of cerium (Ce) and Ln (Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids), and reacting carbon dioxide and methane in the gas phase in the presence of the catalyst at a reaction temperature of 80 to 400°C.

2. The method according to claim 1, wherein the molar ratio of Ce / Ln in the catalyst is 1 / 100 to 100 / 1.

3. The method according to claim 1 or 2, wherein in the catalyst, Ln is at least one element selected from the group consisting of yttrium (Y), lanthanum (La), neodymium (Nd), samarium (Sm), and ytterbium (Yb).

4. The method according to claim 1 or 2, wherein the amount of Ru supported in the catalyst is 0.05 to 10 parts by mass per 100 parts by mass of the composite metal oxide support.

5. The method according to claim 1 or 2, wherein the reaction is carried out by applying a voltage to the catalyst so that the voltage is 0.02 to 250 W / g Ru+composite metal oxide support.

6. The method according to claim 1 or 2, wherein the reaction temperature is 100 to 300°C.

7. The production method according to claim 1 or 2, wherein the space velocity of the reaction is 1,000 to 50,000 / h.

8. The molar ratio of carbon dioxide to methane in the reaction (CO ２ / CH ４ The method according to claim 1 or 2, wherein the ratio is 0.05 to 20.

9. An electric field catalyst used to produce carbon monoxide and hydrogen using carbon dioxide and methane as raw materials, the electric field catalyst comprising Ru supported on a composite metal oxide carrier composed of cerium (Ce) and Ln (Ln represents at least one element selected from the group consisting of yttrium (Y) and lanthanoids) with a Ce / Ln molar ratio in the range of 1 / 100 to 100 / 1.

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