Structure

Abstract

To provide a structure in which a methanation reaction proceeds at a low temperature.SOLUTION: The catalyst has a honeycomb substrate and a catalyst layer provided on the honeycomb substrate, and the catalyst layer contains nickel and a platinum group metal.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a structure. [Background technology]

[0002] Carbon dioxide, a greenhouse gas, is known to be increasing in concentration in the atmosphere due to the recent increase in industrial activity. Therefore, in order to prevent the concentration of carbon dioxide in the atmosphere from increasing, efforts called carbon neutrality, which aims to balance the amount of carbon dioxide emitted and absorbed, are being actively carried out.

[0003] As part of efforts toward carbon neutrality, a reaction known as methanation, in which carbon dioxide reacts with hydrogen to synthesize methane, the main component of natural gas, is attracting attention. The optimum reaction temperature for the methanation reaction is known to be approximately 300°C to 500°C, and a large amount of energy is required to initiate and progress the reaction. Therefore, catalysts that can lower the temperature of the methanation reaction have been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-155227 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with previous catalysts, the methanation reaction started at a temperature of 200°C or higher, and it was still necessary to supply heat from an external source to carry out the methanation reaction. For this reason, there has been a demand for a material that can promote the methanation reaction at even lower temperatures, eliminating the need for external heat supply.

[0006] An object of the present invention is to provide a structure in which a methanation reaction proceeds at low temperatures. [Means for solving the problem]

[0007] The present inventors have investigated factors that promote the methanation reaction and factors that provide heat to the methanation reaction system. As a result, they have found that the methanation reaction can be promoted at low temperatures by combining a platinum group metal, which generates a large amount of heat when hydrogen is burned, with nickel (Ni), which promotes the methanation reaction, and by using a structure that allows carbon dioxide and hydrogen to pass through, thereby completing the present invention.

[0008] That is, the structure of the present invention is The honeycomb substrate and the catalyst layer provided on the honeycomb substrate are included. The catalyst layer is characterized by containing nickel and a platinum group metal.

[0009] The catalyst layer of the structure of the present invention preferably has an upper layer and a lower layer.

[0010] The catalyst layer of the structure of the present invention preferably contains a platinum group metal in the upper layer and nickel in the lower layer.

[0011] In the structure of the present invention, the platinum group metal is preferably at least one selected from platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), and rhodium (Rh).

[0012] Another embodiment of the present invention is a method for producing methane, comprising the steps of: A method for producing methane by supplying a gas containing carbon dioxide, hydrogen, and oxygen to a structure, comprising: The structure has a honeycomb substrate and a catalyst layer provided on the honeycomb substrate, The catalyst layer is characterized by containing nickel and a platinum group metal. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a structure in which a methanation reaction proceeds at low temperatures. [Brief explanation of the drawings]

[0014] [Figure 1A] FIG. 1A is a schematic cross-sectional view of a structure according to an embodiment. [Figure 1B] FIG. 1B is another schematic cross-sectional view of the structure according to the embodiment. [Figure 2] FIG. 2 is a schematic diagram of a method for producing methane according to an embodiment. [Figure 3] FIG. 3 shows the results of measuring the methane concentration in Example 1 and Comparative Examples 1 and 2. [Figure 4] FIG. 4 shows the results of methane concentration measurements in Examples 2 and 3. [Figure 5] FIG. 5 shows the results of measuring the methane concentration in Examples 4 to 9. DETAILED DESCRIPTION OF THE INVENTION

[0015] (structure) The structure according to the embodiment includes a honeycomb substrate and a catalyst layer, and further includes other members as required.

[0016] <Honeycomb substrate> The honeycomb substrate is a member onto which a catalyst layer (described later) is applied. The honeycomb substrate has multiple gas flow paths separated by porous walls called pores. The gas flow paths have multiple cells arranged in a lattice pattern, with each flow path aligned linearly and parallel to one another. The cross section of each flow channel cut perpendicularly to the flow channel may have any shape as long as it is a regular polygon, and is generally a regular rectangle. These multiple cells may be a so-called straight-flow type honeycomb substrate, which is open on both the inlet side and the outlet side, or a so-called wall-flow type honeycomb substrate, which is composed of inlet-side cells that are open on the inlet side and sealed on the outlet side, and outlet-side cells that are open on the outlet side and sealed on the inlet side.

[0017] Conventional methanation reactions have often been carried out in reactors packed with granular catalysts. In such reactors, carbon dioxide and hydrogen gases remain in the gaps between the granular catalysts during the methanation reaction, forming hot spots that become hot due to the heat of reaction, causing catalyst degradation. The use of a honeycomb substrate allows gases such as carbon dioxide, hydrogen, and methane to flow continuously from one end of the substrate to the other, eliminating stagnation of these gases, suppressing the formation of hot spots, and reducing catalyst degradation.

[0018] The material of the honeycomb substrate is not particularly limited and can be appropriately selected depending on the purpose. Examples include cordierite, silicon carbide, aluminotitanate, SUS (stainless steel), and aluminum.

[0019] The shape of the honeycomb substrate is not particularly limited and can be appropriately selected depending on the purpose. Examples include a honeycomb type and a wall-flow type.

[0020] The size of the honeycomb substrate is not particularly limited and can be appropriately selected depending on the purpose.

[0021] <Catalyst layer> The catalyst layer contains nickel and a platinum group metal, and may further contain other components as required.

[0022] The catalyst layer is provided on a honeycomb substrate, where "on the honeycomb substrate" refers to the surface within each pore of the honeycomb substrate, i.e., the surface of each flow path. The catalyst layer may be a single layer or a multi-layer structure of two or more layers, but is preferably a two-layer structure. In the case of a two-layer structure, the side in contact with the honeycomb substrate is referred to as the lower layer, and the side provided on the lower layer is referred to as the upper layer.

[0023] The thickness of the catalyst layer is not particularly limited and can be appropriately selected depending on the purpose.

[0024] When the catalyst layer is a multi-layered layer, the thickness of each layer may be the same or different. The thickness of the catalyst layer can be changed by changing the amount of catalyst applied or by adding an additive.

[0025] When the catalyst layer has two layers, it is preferable that the lower layer contains nickel and the upper layer contains a platinum group metal. By containing nickel in the lower layer and a platinum group metal in the upper layer, heat is generated by the combustion reaction of hydrogen by the platinum group metal in the upper layer, and this heat can be used as a driving force to proceed with the methanation reaction by nickel in the lower layer, allowing the carbon dioxide reaction to proceed efficiently.

[0026] Here, the honeycomb substrate and the catalyst layer will be described with reference to the drawings. 1A is a schematic cross-sectional view of a structure according to an embodiment. The structure 1 has a catalyst layer 12 provided on a honeycomb substrate 11. The catalyst layer 12 contains nickel and a platinum group metal. 1B is another schematic cross-sectional view of a structure according to an embodiment. The structure 1 has a catalyst layer 12 provided on a honeycomb substrate 11. The catalyst layer 12 has a lower layer 21 on the honeycomb substrate side and an upper layer 22 provided on the lower layer 21.

[0027] <<Platinum group metals>> Platinum group metals (PGM) are included to provide heat to the reaction system. Platinum group metals have the property of generating heat when they catalyze the combustion reaction of hydrogen. The heat generated by these platinum group metals promotes the reaction between carbon dioxide and hydrogen.

[0028] Specifically, the platinum group metals are platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), and osmium (Os). These may be used alone or in combination of two or more. Among these, platinum, palladium, ruthenium, iridium, and rhodium are preferred because of their good reactivity.

[0029] The platinum group metal may be a simple substance or a compound. Examples of the compound include oxides, hydroxides, chlorides, etc. These may be used alone or in combination of two or more.

[0030] <<Nickel>> Nickel is included as a catalyst for the reaction of carbon dioxide with hydrogen. Nickel may be a simple substance or a compound. Examples of the compound include oxides, hydroxides, chlorides, etc. These may be used alone or in combination of two or more.

[0031] The mass ratio of platinum group metal to nickel (platinum group / nickel) in the catalyst layer is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 0.025 to 0.500.

[0032] <<Other ingredients>> The other components are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a carrier. Examples of the carrier include ceria (CeO), zirconia (ZrO), a ceria-zirconia solid solution, alumina (AlO), silica (SiO), and zeolite. These may be used alone or in combination of two or more. Among these, a ceria-zirconia solid solution is preferred from the viewpoint of the reaction between platinum group metals and nickel.

[0033] <Other materials> The other members are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a protective layer for the catalyst layer.

[0034] <Method of manufacturing the structure> The method for producing the structure is not particularly limited and can be appropriately selected depending on the purpose. For example, the method may include a metal-supported powder production step, a slurry preparation step, a catalyst layer formation step, etc., and may further include other steps as necessary.

[0035] <<Metal-loaded powder manufacturing process>> The manufacturing process of metal-supported powder involves supporting a metal such as a platinum group metal or nickel on a support. Specifically, the powder is obtained by applying a solution containing metal ions to a support and then calcining the support.

[0036] The solution containing metal ions is a platinum group metal ion solution or a nickel ion solution, for example, platinum nitrate, nickel nitrate, etc. The solvent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include water, ethanol, etc. The concentration of the solution containing metal ions is not particularly limited and can be appropriately selected depending on the purpose.

[0037] Examples of methods for attaching the solution containing metal ions to the support include a method of spraying the solution containing metal ions onto the support, and a method of kneading the solution containing metal ions with the support.

[0038] The firing temperature in the manufacturing process of the metal-supported powder is not particularly limited and can be appropriately selected depending on the purpose. For example, the firing temperature can be 350°C to 600°C. The firing time in the manufacturing process of the metal-supported powder is not particularly limited and can be appropriately selected depending on the purpose, and can be carried out for 30 minutes to 2 hours. The firing in the manufacturing process of the metal-supported powder can be carried out in an air atmosphere.

[0039] <<Slurry preparation process>> The slurry preparation step is a step of preparing a slurry of the metal-supported powder, specifically, a step of mixing the obtained metal-supported powder, water, and, if necessary, a binder. The binder may be, for example, boehmite. The viscosity of the slurry is not particularly limited and can be appropriately selected depending on the purpose.

[0040] <<Catalyst layer formation process>> The catalyst layer forming step is a step of applying a slurry to a honeycomb substrate, specifically by pulverizing the slurry, applying the pulverized slurry, and drying it. The slurry can be pulverized using a ball mill or the like. The particle size of the slurry after pulverization is preferably 0.1 μm to 50 μm.

[0041] The method of applying the slurry to the honeycomb substrate can be carried out by sucking the slurry with a vacuum pump. The drying temperature after coating the slurry is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, 100°C to 200°C.

[0042] <<Other processes>> The other steps are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a calcination step after forming the catalyst layer. The calcination temperature in the calcination step after the formation of the catalyst layer is not particularly limited and can be appropriately selected depending on the purpose. For example, the calcination temperature can be 350°C to 600°C. The calcination time in the calcination step after the formation of the catalyst layer is not particularly limited and can be appropriately selected depending on the purpose, and can be performed for 30 minutes to 2 hours. The calcination in the calcination step after the formation of the catalyst layer can be carried out in an air atmosphere.

[0043] (Method for producing methane) The method for producing methane according to the embodiment is carried out by supplying a gas to a structure. Here, a specific example of a method for producing methane will be described with reference to Fig. 2. The method for producing methane is carried out by a methane production apparatus 100. The methane production apparatus 100 has a gas supply device 110, a reaction device 111, a separation device 112, and a recovery device 113. The gas supply device 110 is a device that supplies gas for the methanation reaction. The gas for the methanation reaction contains carbon dioxide, hydrogen, and oxygen, and may further contain other gases such as nitrogen as necessary. The reactor 111 is a device having a structure. The structure may be any of the structures described above. The separator 112 separates methane produced by the methanation reaction from other gases. The recovery unit 113 is a unit that recovers the produced methane.

[0044] Gas for the methanation reaction is supplied from a gas supply device 110 to a reactor 111 through a gas supply line 211. The gas supply device 110 may supply a single gas or a pre-mixed gas. The gas supplied to the reactor 111 becomes a reactant for the methanation reaction through a structure. The reactor 111 is heated as needed. The gas produced in the reactor 111 and unreacted gas are supplied to a separator 112 through a product gas supply device 212. The separator 112 separates methane from other gases. The methane is sent to a recovery device 113 via a methane supply line 213. A cooling device may be provided in the methane supply line 213 as needed. [Example]

[0045] Next, the present invention will be described with reference to examples, but the scope of the present invention is not limited to these examples.

[0046] Example 1 An aqueous solution of platinum nitrate (Pt(NO3)4) was prepared as the Pt source. A ceria-zirconia solid solution (CeO2: 75% by mass, ZrO2: 25% by mass, Solvay Specialchem ​​Japan Co., Ltd.) was suspended in the Pt source solution and stirred at room temperature for 2 hours, then evaporated to dryness at 80°C. The solution was then calcined at 500°C in air for 1 hour to produce Pt-supported powder (Pt concentration: 2 wt%). An aqueous solution of nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O, manufactured by Kanto Chemical Co., Inc.) was prepared as the Ni source. A ceria-zirconia solid solution (CeO2: 75% by mass, ZrO2: 25% by mass, manufactured by Solvay SpecialChem Japan Co., Ltd.) was suspended in the Ni source solution and stirred at room temperature for 2 hours, then evaporated to dryness at 80°C. The mixture was then calcined at 500°C in air for 1 hour to produce Ni-loaded powder (Ni concentration: 10 wt%). 90 g of the obtained Pt-supported powder, 10 g of boehmite, and 200 g of water were mixed, and the resulting slurry was pulverized in a ball mill. The viscosity was adjusted to facilitate processing in the subsequent steps, thereby preparing a Pt slurry. Next, 90 g of the obtained Ni-supported powder, 10 g of boehmite, and 200 g of water were mixed, and the resulting slurry was pulverized in a ball mill. The viscosity was adjusted to facilitate processing in the subsequent steps, thereby preparing a Ni slurry. 100 g of the obtained Pt slurry and 200 g of Ni slurry were mixed to prepare a Pt / Ni mixed slurry. Next, the obtained Pt, Ni mixed slurry and the honeycomb substrate were placed in a container large enough to hold a honeycomb substrate (product name: Honeyceram, manufactured by NGK Insulators, Ltd.), and the honeycomb substrate was immersed in the Pt, Ni mixed slurry. After that, the excess Pt, Ni mixed slurry was sucked out using negative pressure from a vacuum pump. By sucking out the slurry, the Pt, Ni mixed slurry was applied to the honeycomb substrate. The honeycomb substrate coated with the slurry was dried at 130°C for 10 minutes and then fired at 500°C for 1 hour in an air atmosphere to obtain a structure. The amounts of Pt and Ni in the structure were adjusted to 1 g / L and 10 g / L (Pt / Ni = 0.100).

[0047] (Comparative Examples 1 and 2) The Pt slurry or Ni slurry obtained in Example 1 was applied to a honeycomb substrate, dried, and fired in the same manner as in Example 1. The amount of Pt in the structure of Comparative Example 1 was adjusted to 1 g / L, and the amount of Ni in the structure of Comparative Example 2 was adjusted to 15 g / L.

[0048] The compositions of the structures of Example 1 and Comparative Examples 1 and 2 are shown in Table 1.

[0049] [Table 1]

[0050] The obtained structure was subjected to a methanation reaction, and the amount of methane produced (ppm) was measured under the following test conditions. Evaluation device: BEL CAT II (Microtrack, manufactured by BEL Corporation) Analytical equipment: FAST-1370 (manufactured by Iwata Electric Industry Co., Ltd.) Pretreatment: Hydrogen at 100 mL / min for 60 minutes Pretreatment temperature: 500℃ Measurement gas: 10% carbon dioxide, 15% oxygen, 70% hydrogen, and 5% nitrogen Flow rate during measurement: 80 mL / min ·Measurement temperature: 50℃, 100℃, 150℃, 200℃, 250℃, 350℃, 500℃ The measurement results are shown in Figure 3.

[0051] As shown in FIG. 3, methane was detected from 50°C in the structure of Example 1, demonstrating that the methanation reaction began to proceed from 50°C. In contrast, methane was not detected in the structure of Comparative Example 1 even when the temperature was raised to 350°C, but was detectable when the temperature was raised to 500°C. Furthermore, methane was detected from 150°C in the structure of Comparative Example 2, demonstrating that the methanation reaction began to proceed from 150°C. These results demonstrate that the use of a structure containing nickel and a platinum group metal in the catalyst layer allows the methanation reaction to proceed at low temperatures.

[0052] Example 2 Using the same process as in Example 1, a Pt slurry was prepared using Pt powder prepared so as to have a Pt content of 0.5 wt %. A Ni slurry was prepared by the same process as in Example 1. The Ni slurry and honeycomb substrate were placed in a container large enough to hold a honeycomb substrate (product name: Honeyceram, manufactured by NGK Insulators, Ltd.). The honeycomb substrate was immersed in the Ni slurry, and then the excess Ni slurry was sucked out using negative pressure from a vacuum pump. The Ni slurry was applied to the honeycomb substrate by suctioning the slurry. The honeycomb substrate to which the slurry had been applied was dried at 130°C for 10 minutes and then fired in the air at 500°C for 30 minutes. Next, the honeycomb substrate coated with the Pt slurry and the Ni slurry was placed in the container, and the Pt slurry was applied to the honeycomb substrate coated with the Ni slurry in the same manner as for the Ni slurry. Through these operations, a catalyst layer was formed with a structure containing Ni in the lower layer and Pt, a platinum group metal, in the upper layer. The honeycomb substrate coated with the slurry was dried at 130°C for 10 minutes and then fired in an air atmosphere at 500°C for 30 minutes to obtain a structure. The amounts of Pt and Ni in the structure were adjusted to 0.25g / L and 10g / L, respectively, and the mass ratio of Pt to Ni (Pt / Ni) was adjusted to 0.025. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0053] Example 3 A structure of Example 3 was obtained in the same manner as in Example 2, except that the mass ratio of Pt to Ni (Pt / Ni) in the structure was adjusted to 0.500. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0054] The compositions of the structures of Examples 2 and 3 are shown in Table 2.

[0055] [Table 2]

[0056] As shown in Figure 4, methane was detected from 50°C in the structures of Examples 2 and 3, demonstrating that the methanation reaction began to proceed from 50°C. These results demonstrate that the methanation reaction can be promoted at low temperatures by using a structure containing a platinum group metal in the upper layer of the catalyst layer and nickel in the lower layer.

[0057] Example 4 A structure of Example 4 was obtained in the same manner as in Example 2, except that the mass ratio of Pt to Ni (Pt / Ni) in the structure was adjusted to 0.100. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0058] Example 5 An aqueous solution of nickel (II) nitrate hexahydrate (Ni(NO3)2·6H2O, manufactured by Kanto Chemical Co., Ltd.) was prepared as the Ni source. CeO2 (manufactured by Nikki Co., Ltd.) was suspended in the Ni source solution, stirred at room temperature for 2 hours, and evaporated to dryness at 80°C. The solution was then calcined at 500°C in air for 1 hour to produce Ni-loaded powder (Ni concentration: 10 wt%). 90 g of the obtained Ni-supported powder, 10 g of boehmite, and 200 g of water were mixed together to prepare a Ni slurry. A structure was fabricated in the same manner as in Example 4, except that the lower layer of the structure was changed to the Ni slurry described above. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0059] Example 6 Iridium acetate (Ir(CH3COO)) as an Ir source nA ceria-zirconia solid solution (CeO2: 75% by mass, ZrO2: 25% by mass, Solvay Specialchem ​​Japan Co., Ltd.) was suspended in the Ir source solution as a support, stirred at room temperature for 2 hours, and evaporated to dryness at 80°C. The solution was then calcined at 500°C in air for 1 hour to produce Ir-supported powder (Ir concentration: 2 wt%). 90 g of the obtained Ir-supported powder, 10 g of boehmite, and 200 g of water were mixed to prepare an Ir slurry. A structure was fabricated in the same manner as in Example 4, except that the upper layer of the structure was changed to the above Ir slurry. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0060] Example 7 An aqueous solution of palladium nitrate (Pd(NO3)2) was prepared as the Pd source. A ceria-zirconia solid solution (CeO2: 75% by mass, ZrO2: 25% by mass, Solvay SpecialChem Japan Co., Ltd.) was suspended in the Pd source solution and stirred at room temperature for 2 hours, then evaporated to dryness at 80°C. The solution was then calcined at 500°C in air for 1 hour to produce Pd-supported powder (Pd concentration: 2 wt%). A structure was fabricated in the same manner as in Example 4, except that the upper layer of the structure was changed to the Pd slurry described above. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0061] Example 8 An aqueous solution of ruthenium nitrate (Ru(NO3)3, HNO3) was prepared as the Ru source. A ceria-zirconia solid solution (CeO2: 75% by mass, ZrO2: 25% by mass, Solvay Specialchem ​​Japan Co., Ltd.) was suspended as the support in the Ru source solution, stirred at room temperature for 2 hours, and evaporated to dryness at 80°C. It was then calcined at 500°C in air for 1 hour to produce Ru-supported powder (Ru concentration: 2 wt%). A structure was fabricated in the same manner as in Example 4, except that the upper layer of the structure was changed to the Ru slurry described above. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0062] Example 9 An aqueous solution of rhodium nitrate (Rh(NO3)3) was prepared as the Rh source. A ceria-zirconia solid solution (CeO2: 75% by mass, ZrO2: 25% by mass, Solvay Specialchem ​​Japan Co., Ltd.) was suspended in the Rh source solution as the support, stirred at room temperature for 2 hours, and evaporated to dryness at 80°C. It was then calcined at 500°C in air for 1 hour to produce Rh-supported powder (Rh concentration: 2 wt%). A structure was fabricated in the same manner as in Example 4, except that the upper layer of the structure was changed to the Rh slurry described above. The obtained structure was subjected to a methanation reaction and the amount of methane produced (ppm) was measured in the same manner as in Example 1. The measurement results are shown in FIG.

[0063] The compositions of the structures of Examples 4 to 9 are shown in Table 3.

[0064] [Table 3]

[0065] As shown in Figure 5, methane was detected from 50°C in the structures of Examples 4 to 9, demonstrating that the methanation reaction began to proceed from 50°C. These results demonstrate that the methanation reaction can proceed at low temperatures by using a structure containing a platinum group metal in the upper layer of the catalyst layer and nickel in the lower layer. It was also revealed that this property does not change even when the support is changed.

Claims

1. A structure having a honeycomb substrate and a catalyst layer provided on the honeycomb substrate, The structure, wherein the catalyst layer contains nickel and a platinum group metal.

2. 2. The structure according to claim 1, wherein the catalyst layer has an upper layer and a lower layer.

3. 3. The structure according to claim 1, wherein the upper layer contains a platinum group metal and the lower layer contains nickel.

4. 3. The structure according to claim 1, wherein the platinum group metal is at least one selected from the group consisting of platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), and rhodium (Rh).

5. A method for producing methane by supplying a gas containing carbon dioxide, hydrogen, and oxygen to a structure, comprising: The structure has a honeycomb substrate and a catalyst layer provided on the honeycomb substrate, A method for producing methane, wherein the catalyst layer contains nickel and a platinum group metal.

Images