Porous support, catalyst member, and method for producing porous support

Abstract

To secure a specific surface area of a porous support that bears a catalyst and to achieve high dispersion of the catalyst carried on the support.SOLUTION: A porous support comprises a first metal oxide as a main component, wherein, in an SEM image of a cross section of the porous support, 60% or more of the particles of the first metal oxide have a packing density of 0.9 or less, and the porous support has a specific surface area exceeding 5 m2 / g.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] The present disclosure relates to a porous support, a catalyst body, and a method for manufacturing the porous support. [Background technology]

[0002] Conventionally, catalysts having a catalyst supported on a carrier have been known as catalyst bodies having a catalyst for promoting various reactions. For example, Patent Document 1 discloses a catalyst composition having a catalyst for promoting hydrocarbon decomposition reactions on a carrier composed of a proton-conductive solid oxide. Specifically, Patent Document 1 describes a configuration in which a proton-conductive solid oxide, graphite for forming a plurality of pores, and Fe2O3 (iron (III) oxide) as a catalyst are mixed, compressed into pellets, calcined, and the calcined pellets are crushed and sieved to obtain a catalyst composition supported on Fe2O3.

[0003] Patent Document 2 also discloses a method for producing an alumina porous carrier to be used as a catalyst carrier. This describes a method for producing an alumina porous carrier by adding walnut grains as a pore-forming agent together with a forming aid and a binder to an alumina raw material such as alumina powder, kneading the mixture, forming the mixture, and firing it. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-42673 [Patent Document 2] Japanese Patent Application Publication No. 11-43380 Summary of the Invention [Problem to be solved by the invention]

[0005] In a catalyst body in which a catalyst is supported on a support, it is known that increasing the specific surface area of ​​the support and improving the dispersion state of the catalyst supported on the support are useful in improving catalytic activity. For example, as disclosed in Patent Documents 1 and 2, when a pore-forming material is used to form pores (air pores), the pore-forming material disappears during the calcination process, resulting in a porous support with pores (air pores). However, the more the calcination process progresses, the lower the specific surface area of ​​the support generally becomes. Techniques for ensuring the specific surface area of ​​the support and for highly dispersing the catalyst supported on the support have not been sufficiently studied, and further improvements are desired. [Means for solving the problem]

[0006] The present disclosure can be realized in the following forms. [1] According to one aspect of the present disclosure, there is provided a porous support comprising a first metal oxide as a main component, wherein, in an SEM image of a cross section of the porous support, 60% or more of particles of the first metal oxide have a density of 0.9 or less, and the specific surface area of ​​the porous support is 5 m 2 / g or more. According to this type of porous carrier, the specific surface area of ​​the porous carrier is 5m 2 / g, the catalyst can be supported in a more highly dispersed state when supported on the porous support, thereby enhancing catalytic activity. Furthermore, by ensuring that the proportion of first metal oxide particles having a density of 0.9 or less is 60% or more in an SEM image of the cross section of the porous support, it becomes easier to ensure a larger specific surface area for the first metal oxide particles constituting the porous support. Furthermore, when a catalyst is supported on a porous support, sintering of the catalyst can be suppressed, thereby maintaining a highly dispersed state of the catalyst supported on the porous support. Therefore, it becomes possible to ensure both a high specific surface area of ​​the porous support and high dispersibility of the catalyst when supported on the porous support at a higher level. [2] In the porous support of the above embodiment, the porous support may comprise, under a specific reducing atmosphere, the first metal oxide and a second metal oxide different from the first metal oxide, wherein the first metal oxide is a metal oxide that is not reduced when present alone under the specific reducing atmosphere, and the second metal oxide is a metal oxide that is reduced when present alone under the specific reducing atmosphere. This configuration comprises, under the specific reducing atmosphere, the first metal oxide as a main component that is not reduced when present alone under the specific reducing atmosphere, and the second metal oxide that is reduced when present alone under the specific reducing atmosphere. In such a porous support, the second metal oxide is not exposed to the specific reducing atmosphere even under the specific reducing atmosphere, i.e., is covered by the first metal oxide, thereby improving the strength of the porous support without reducing the specific surface area of ​​the porous support. Furthermore, by subjecting the porous support to a treatment including a reduction treatment under the specific reducing atmosphere, a porous support can be obtained in which the metal contained in the second metal oxide or the second metal oxide is not present on the surface. Therefore, the presence of the second metal oxide on the surface can prevent the surface properties of the porous support from being impaired due to the porous support being made up of the first metal oxide. [3] In the porous support of the above embodiment, the total porosity may be 50% or more and 75% or less. This configuration makes it easier to ensure the specific surface area of ​​the porous support, allowing more catalyst to be supported on the pore surfaces inside the porous support. Therefore, when the porous support is used as a catalyst support, the reaction site promoted by the catalyst can be increased, thereby enhancing catalytic activity. Furthermore, pressure loss can be reduced when a gas containing a reactant is passed through the porous support. [4] In the porous support of the above embodiment, the first metal oxide may be a proton-conducting material. With this configuration, when a catalyst that promotes a reaction involving the transfer of protons is supported on the porous support to produce a catalyst body, catalytic activity can be enhanced. [5] In the porous support of the above embodiment, the first metal oxide may contain at least one of cerium (Ce) and zirconium (Zr). This configuration makes it easy to make the first metal oxide a proton-conducting material. [6] In the porous support of the above embodiment, the second metal oxide may contain a transition metal. In this configuration, the porous support can be easily produced by using, as the second metal oxide, a metal oxide that is easily reduced and the metal obtained by reduction is easily dissolved by acid. [7] In the porous support of the above embodiment, the transition element may include at least one of nickel (Ni) and copper (Cu). In this configuration, the porous support can be easily produced by using, as the second metal oxide, a metal oxide that is easily reduced and the metal obtained by reduction is easily dissolved by acid. [8] In the porous support of the above embodiment, the first metal oxide may contain cerium (Ce), and the second metal oxide may contain nickel (Ni). This configuration ensures the proton conductivity of the first metal oxide, enhances the reducibility of the second metal oxide, and makes it easy to ensure that the metal obtained by reducing the second metal oxide is easily dissolved in acid. [9] According to another aspect of the present disclosure, there is provided a catalyst body, comprising the porous support according to any one of [1] to [8] and a carbon dioxide reduction catalyst disposed on the surface of the porous support. This form of catalyst body can ensure a high specific surface area in the porous support and high dispersibility of the catalyst supported on the porous support, thereby improving the performance of the catalyst body, which has the activity of promoting the carbon dioxide reduction reaction.

[10] According to yet another aspect of the present disclosure, there is provided a catalyst body, comprising the porous support according to any one of [1] to [8], and a catalyst disposed on the surface of the porous support and activatable by application of an electric field. According to this form of catalyst, in a catalyst body in which a high specific surface area of ​​the porous support and high dispersibility of the catalyst supported on the porous support are ensured, catalytic activity can be increased by applying an electric field to the catalyst, making it possible to proceed with the reaction under milder conditions (relatively low temperature conditions or relatively low pressure conditions).

[11] According to yet another aspect of the present disclosure, there is provided a method for producing a porous support, the method comprising: preparing a first metal oxide as a main component that has been pulverized in advance; and a second metal oxide different from the first metal oxide; mixing and molding the prepared first and second metal oxides to produce a molded body; calcining the molded body; reducing the fired molded body in a specific reducing atmosphere in which the first metal oxide present alone is not reduced and the second metal oxide present alone is reduced; and acid-treating the reduced molded body under conditions in which a metal element constituting the second metal oxide is eluted in a metallic state; and producing a porous support having a specific surface area of ​​5 m or less, in which, in an SEM image of a cross section of the porous support, 60% or more of the particles of the first metal oxide have a density of 0.9 or less and the specific surface area of ​​the porous support is 5 m or less. 2 / g or more of porous carrier is obtained. According to this embodiment of the method for producing a porous support, the first metal oxide that has been crushed in advance is calcined in a state where the second metal oxide is mixed therein, and then the second metal oxide is removed by reduction treatment and acid treatment. As a result, in an SEM image of the cross section of the porous support, the proportion of particles of the first metal oxide having a density of 0.9 or less is 60% or more, and the specific surface area of ​​the porous support is 5 m 2 / g, a porous support having a specific surface area exceeding 1 / 2000 of that of the catalyst can be obtained. Therefore, a high specific surface area can be ensured in the porous support, and when a catalyst is supported on such a porous support, high dispersibility of the catalyst can be achieved. The present disclosure can be realized in various forms other than those described above, for example, a method for manufacturing a catalyst body, a method for improving the strength of catalytic activity in a catalyst body, a method for hydrogenating carbon dioxide, a method for producing hydrogen by a dehydrogenation reaction, etc. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a flowchart showing a method for manufacturing a porous carrier. [Figure 2] FIG. 2 is an explanatory diagram showing the process of manufacturing a porous carrier. [Figure 3] FIG. 2 is an explanatory diagram conceptually showing the relationship between the particle density of a porous support and firing conditions. [Figure 4] FIG. 2 is an explanatory diagram conceptually showing the relationship between the particle density of a porous support and firing conditions. [Figure 5] FIG. 1 is an explanatory diagram showing a simplified Ellingham diagram. [Figure 6] 10A to 10C are explanatory diagrams showing examples of the state of an image in each process in a series of image processes. [Figure 7] FIG. 1 is an explanatory diagram showing an SEM image of a cross section of a sample. [Figure 8] FIG. 1 is an explanatory diagram showing an SEM image of a cross section of a sample. [Figure 9] FIG. 10 is an explanatory diagram showing how particle contour information is extracted from an SEM image. [Figure 10] FIG. 10 is an explanatory diagram showing how particle contour information is extracted from an SEM image. [Figure 11] FIG. 10 is an explanatory diagram showing the frequency and cumulative percentage for each density section. [Figure 12] FIG. 10 is an explanatory diagram showing the distribution of the number of particles belonging to each density range. [Figure 13] FIG. 2 is an explanatory diagram showing the results of measuring the specific surface area and total porosity of each sample. [Figure 14] FIG. 2 is an explanatory diagram showing the methane yield calculated by performing an activity evaluation test on the catalyst body. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. Porous Carrier Composition: The porous support 10 of this embodiment is a ceramic porous body containing a first metal oxide as a main component, and is formed as an aggregate of first metal oxide particles. When the density of the first metal oxide particles in such a porous support 10 is examined in a scanning electron microscope (SEM) image of a cross section of the porous support 10, the proportion of particles having a density of 0.9 or less is 60% or more, more preferably 63% or more, and even more preferably 66% or more. Here, the density of the first metal oxide particles is the value obtained by dividing the area of ​​the first metal oxide particles in the SEM image of the cross section of the porous support 10 by the convex hull area of ​​the first metal oxide particles, and is expressed by the following formula: The convex hull area refers to the area of ​​the convex hull obtained by creating the outline of each first metal oxide particle through image analysis of the SEM image of the cross section of the porous support 10.

[0009] Density = (area of ​​first metal oxide particles) / (area of ​​convex hull of first metal oxide particles)

[0010] The density is a value greater than 0 and equal to or less than 1, and the closer the density value is to 1, the more rounded and spherical the shape of the first metal oxide particles can be evaluated.The smaller the density value is, the more recessed the shape of the first metal oxide particles can be evaluated to be, and the more angular the shape.

[0011] Generally, when ceramic porous bodies are produced by molding ceramic particles and then firing them, necking occurs during the firing process, causing the ceramic particles to become rounded and their density to increase, resulting in a higher proportion of ceramic particles with a density of 0.9 or higher. Therefore, when examining the density of first metal oxide particles in an SEM image of a cross section of a porous support, a ratio of 60% or more of particles with a density of 0.9 or lower indicates a higher proportion of angular ceramic particles compared to typical ceramic porous bodies obtained by firing a molded ceramic particle body. In this embodiment, the porous support 10 is produced by mixing a powder of a second metal oxide, which is reduced under a specific reducing atmosphere in which the first metal oxide is not reduced, with the raw material powder as a pore-forming agent, and using the powder as a pore-forming agent. The method for producing the porous support 10 will be described in detail later.

[0012] As described above, the relatively high proportion of particles having a density of 0.9 or less, i.e., the relatively high proportion of angular particles, enables the catalyst to be supported in a more highly dispersed state when a catalyst body is formed using the porous support 10 of this embodiment as a catalyst support, thereby improving catalytic activity. The reason why the dispersion state of the catalyst supported on the porous support 10 of this embodiment can be improved is thought to be, first, because the relatively angular shape of the first metal oxide particles increases the specific surface area of ​​the first metal oxide particles compared to when the first metal oxide particles are relatively rounded. Second, because the relatively angular shape of the first metal oxide particles reduces catalyst sintering during the heat treatment included in the process of supporting the catalyst on the porous support compared to when the first metal oxide particles are relatively rounded. Catalyst sintering refers to the phenomenon in which catalyst particles aggregate under high temperature conditions, etc. In the case of a metal catalyst, the metal particles grow and their surface area decreases. For example, when comparing metal oxide particles of the same particle size carrying the same amount of catalyst, particles with relatively angular and complex shapes have a larger surface area than more rounded particles, which is thought to increase the distance between catalyst particles on the support and suppress aggregation of the catalyst particles.

[0013] In addition to the above-mentioned characteristics related to density, the porous carrier 10 of this embodiment further has a specific surface area of ​​5 m 2 / g, and the specific surface area is 6m 2 / g or more is more preferable, and 8m 2 / g or more is even more preferable. By ensuring a large specific surface area of ​​the porous support 10, when the porous support 10 of this embodiment is used as a catalyst support, the catalyst can be highly dispersed into finer particles. As a result, a wider reaction area for the catalytic reaction can be secured, thereby enhancing catalytic activity. The specific surface area of ​​the porous support 10 can be adjusted by the shape of the ceramic particles constituting the porous support 10, the particle size of the ceramic particles (first metal oxide particles and second metal oxide particles described below) used during production, the density of the porous support 10, which is determined by the degree of sintering, etc. Specifically, for example, by previously pulverizing at least one of the first metal oxide particles and the second metal oxide particles described below used as raw material powder during production of the porous support 10 to fine particles, the above-mentioned characteristics related to the specific surface area can be easily satisfied. There is no particular upper limit to the specific surface area of ​​the porous support 10, as long as it is within a range that ensures sufficient strength of the porous support 10. The specific surface area of ​​the porous carrier 10 is, for example, 15 m 2 / g or less.

[0014] Furthermore, the porous carrier 10 of this embodiment preferably has a total porosity of 50% or more, more preferably 60% or more, and even more preferably 70% or more. This makes it easier to ensure the specific surface area of ​​the porous carrier 10. By ensuring a large total porosity as described above, it becomes possible to support more catalyst on the inner pore surfaces of the porous carrier 10, increasing the number of reaction sites promoted by the catalyst and improving catalytic activity. Furthermore, it is possible to reduce pressure loss when a gas containing reactants is passed through the porous carrier 10. The total porosity of the porous carrier 10 is not particularly limited as long as the strength of the porous carrier 10 can be ensured, but it is preferably, for example, 75% or less. The total porosity of the porous support 10 can be adjusted, for example, by the mixing ratio and particle size of the second metal oxide particles described below that are mixed as a pore-forming material into a raw material powder containing particles of the first metal oxide during the production of the porous support 10, the particle size of the first metal oxide particles contained in the raw material powder, and the firing temperature and firing time during the production of the porous support 10.

[0015] The first metal oxide constituting the porous support of this embodiment is not particularly limited, and may be any metal oxide capable of forming a porous body by granulating, shaping, and calcining the first metal oxide powder as a raw material. The first metal oxide may be appropriately selected depending on the intended use of the porous support 10. For example, if an ion-conductive material is used as the first metal oxide, when a catalyst that promotes a reaction involving the transfer of ions is supported on the porous support 10 to prepare a catalyst body, the efficiency of supplying ions required for the reaction to the catalyst and the efficiency of transferring ions generated by the reaction from the catalyst are improved, thereby increasing the amount of reaction involving the transfer of ions and enhancing catalytic activity. Specifically, for example, if a proton-conductive material is used as the first metal oxide, when a catalyst that promotes a reaction involving the transfer of protons is supported on the porous support 10 to prepare a catalyst body, the catalytic activity can be enhanced. Furthermore, the first metal oxide may have electronic conductivity in addition to or instead of proton conductivity. In this case, when the reaction promoted by the catalyst supported on the porous carrier 10 involves the transfer of electrons, the catalytic activity can be increased.

[0016] When a proton-conducting material (proton-conducting ceramic) is used as the first metal oxide, proton conduction in the proton-conducting ceramic may occur either inside the proton-conducting ceramic or on its surface. The proton-conducting ceramic, which is the first metal oxide, preferably contains at least one of cerium (Ce) and zirconium (Zr). Fluorite-structure metal oxides, specifically, CeO2-based composite oxides, which are oxides containing cerium, and ZrO2-based composite oxides, which are oxides containing zirconium, are preferably used. TiO2-based composite oxides, which are oxides containing titanium, can also be used. Among these, oxides containing cerium (Ce) are preferred. These metal oxides are also suitable for use when a catalyst body including the porous support 10 is used, for example, under the application of an electric field.

[0017] As the proton-conducting ceramic, which is the first metal oxide, metal oxides other than those mentioned above may be used. For example, metal oxides having a perovskite structure exhibiting proton conductivity (e.g., BaCeO3-based oxides), metal oxides having a fergusonite structure or a scheelite structure exhibiting proton conductivity (e.g., LaNbO4-based oxides), metal oxides having a pyrochlore structure exhibiting proton conductivity (e.g., La2Zr2O7-based oxides), metal oxides having a mayenite structure exhibiting proton conductivity (e.g., Ce 12 Al 14 O 33 Metal oxides having a Brownmillerite structure that exhibit proton conductivity (e.g., Ba2In2O5-based oxides), and metal oxides having a fluorite structure that exhibit proton conductivity (e.g., La6WO6-based oxides) can be used.

[0018] In addition to the first metal oxide, the porous support 10 may further comprise a second metal oxide different from the first metal oxide. The second metal oxide is a metal oxide that is reduced in a specific reducing atmosphere in which the first metal oxide is not reduced. That is, the first metal oxide is a metal oxide that is not reduced when present alone in the specific reducing atmosphere, and the second metal oxide is a metal oxide that is reduced when present alone in the specific reducing atmosphere. The "specific reducing atmosphere" refers to an atmosphere set in the manufacturing process of the porous support 10 to reduce only the second metal oxide by treating a sintered body in which the first metal oxide and the second metal oxide are mixed. The specific reducing atmosphere will be described in detail later.

[0019] In this embodiment, when producing the porous support 10, a powder of a second metal oxide is mixed with a raw material powder as a pore-forming material together with a powder of a first metal oxide, and after firing a compact of the raw material powder, the fired body is made porous by performing a reduction treatment and an acid treatment to remove the second metal oxide from the fired body. At this time, there may be second metal oxide particles that are not reduced by the reduction treatment, and in this case, the second metal oxide particles will remain in the porous support 10. The second metal oxide will be described below.

[0020] The second metal oxide is an oxide of a metal that is more easily reduced than the metal that constitutes the first metal oxide. As described above, the second metal oxide alone is reduced under a specific reducing atmosphere in which the first metal oxide alone is not reduced. The second metal oxide is required to be able to create a specific reducing atmosphere in combination with the first metal oxide. Furthermore, the second metal oxide is required to be reduced under a specific reducing atmosphere, and the metal obtained by the reduction of the second metal oxide can be eluted by acid treatment. The second metal oxide preferably contains a transition metal because it is easily reduced and the metal obtained by the reduction is easily dissolved by acid. Specifically, the second metal oxide can be at least one of manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). From the above viewpoint, it is particularly desirable for the second metal oxide to contain at least one of nickel (Ni) and copper (Cu).

[0021] The presence of the first metal oxide and the second metal oxide in the porous carrier 10 can be confirmed by micro-X-ray diffraction. When performing analysis by micro-X-ray diffraction, a cross section of the porous carrier 10 can be polished by CP (cross-section polisher) processing using an ion milling method prior to the micro-X-ray diffraction. In this embodiment, the first metal oxide being the "main component" means that the content of the first metal oxide in the porous carrier 10 is 99 mol% or more. In the porous carrier 10 of this embodiment, the content of the second metal oxide may be less than 1 mol%. The content ratios of the first metal oxide and the second metal oxide 22 can be calculated by calculating and comparing the sum of the peak heights for each metal oxide in the XRD patterns obtained by micro-X-ray diffraction.

[0022] B. Method for producing porous carrier: FIG. 1 is a flowchart showing an example of a method for producing a porous carrier 10. FIG. 2 is an explanatory diagram showing the steps of producing the porous carrier 10. When producing the porous carrier 10, at least one of the first metal oxide 21 and the second metal oxide 22 is first pulverized into fine particles (step T100, FIG. 2(A)). The pulverization performed in step T100 is a process for easily adjusting the specific surface area of ​​the finally obtained porous carrier 10 to the desired numerical range described above. It is desirable to pulverize at least the first metal oxide 21, and more desirable to pulverize both the first metal oxide 21 and the second metal oxide 22. The pulverization process in step T100 is preferably performed using, for example, a planetary ball mill or a bead mill. If the first metal oxide and the second metal oxide are available with sufficiently small particle sizes, the pulverization process in step T100 can be omitted. However, if general commercially available first metal oxides and second metal oxides are used, it is desirable to perform the pulverization process.

[0023] After the pulverization treatment in step T100, the particle sizes of the first metal oxide 21 and the second metal oxide 22 become so small that it may be difficult to confirm the pulverized state using general particle size distribution measurement or the like. In such cases, the pulverized state of the first metal oxide 21 and the second metal oxide 22 after the treatment in step T100 can be confirmed, for example, by the crystallite size calculated using the Scherrer equation based on the analysis results of powder X-ray diffraction intensity measurement. Here, crystallite refers to a single crystal that constitutes the polycrystalline metal oxide particle. The Scherrer equation is expressed by the following formula (I):

[0024] D=Kλ / Bcosθ … (I) (where D is the crystallite size (nm), K is the Scherrer constant, λ is the wavelength of the X-ray (nm), B is the broadening of the diffraction line width (rad), and θ is the Bragg angle (rad).)

[0025] As the particle sizes of first metal oxide 21 and second metal oxide 22 decrease through the pulverization treatment in step T100, the particle sizes of the metal oxides become infinitesimally close to the crystallite sizes, and the individual single crystals constituting the metal oxide particles also become smaller. This is inferred from the fact that an investigation into the relationship between the specific surface area and crystallite sizes of metal oxides shows a similar trend to the relationship between the specific surface area and particle size of metal oxides (data not shown). The crystallite size of first metal oxide 21 after pulverization determined as described above can be, for example, 100 to 250 (Å), and the crystallite size of second metal oxide 22 after pulverization can be, for example, 90 to 170 (Å).

[0026] The pulverized first metal oxide 21 and second metal oxide 22 are then mixed and molded to produce a compact 12. Specifically, a solvent 23 is added to a powder of the first metal oxide 21 and a powder of the second metal oxide 22 in a predetermined ratio to form a slurry 11 (step T110, FIG. 2(B)). The mixing ratio of the first metal oxide 21 to the second metal oxide 22 may be set according to the total porosity of the desired porous support 10, and the total porosity can be increased by increasing the mixing ratio of the second metal oxide 22. The mixing ratio of the first metal oxide 21 to the total metal oxides used can be, for example, 40 to 70% by volume, and the mixing ratio of the second metal oxide 22 to the total metal oxides used can be 30 to 60% by volume. A dispersant (e.g., IONET S-20 manufactured by Sanyo Chemical Industries, Ltd.) may be further added to the slurry 11.

[0027] Thereafter, a green compact 12 is produced (step T120). Here, prior to compaction, the solvent 23 may be removed from the slurry 11 (FIG. 2(C)). The solvent may be removed, for example, by granulating the slurry 11 using a spray-drying method or by volatilizing the solvent 23 by heating. A binder 24 for compaction may be further applied to the mixed powder obtained by removing the solvent 23 (FIG. 2(D)). The green compact 12 may be produced by, for example, press molding such as uniaxial pressing or CIP molding, or both (FIG. 2(E)). Note that the binder 24 may be mixed after the solvent is removed from the slurry 11 as described above, or may be mixed simultaneously with the operation of mixing the first metal oxide 21 and the second metal oxide 22 to form a slurry in step T100. The binder 24 may be selected appropriately depending on the solvent used and the molding method of the porous carrier 10, and when press molding is performed using ethanol as the solvent, for example, Cerna SE604 manufactured by Chukyo Yushi Co., Ltd. can be used as the binder.

[0028] After producing the compact 12 in step T120, the resulting compact 12 is fired (step T130). Prior to firing, degreasing may be performed to remove the binder. Degreasing may be performed by heating in an air atmosphere at 200 to 500°C for about four hours. However, degreasing is not essential and may be omitted, for example, if only a small amount of binder is used. The firing conditions may be set depending on the types of first and second metal oxides used so that the first metal oxide is sufficiently sintered. For example, firing may be performed by heating in an air atmosphere at 800 to 1200°C for about four to six hours. This densifies the first metal oxide 21, resulting in a sintered compact 14 composed of a mixture of the first metal oxide 21 and the second metal oxide 22 (FIG. 2(F)). When the sintered body 14 is produced using a second metal oxide together with a first metal oxide as in this embodiment, the second metal oxide may function as a sintering aid, for example, when a metal oxide having a lower melting point than the first metal oxide is used as the second metal oxide. By using the second metal oxide as a sintering aid in this way, it is believed that the first metal oxide can be more sufficiently sintered and densified even under milder firing conditions (e.g., lower firing temperature) than when the first metal oxide is fired without adding the second metal oxide.

[0029] The sintered compact (sintered compact 14) is then subjected to a reduction treatment (step T140). This reduction treatment is performed under the specific reducing atmosphere described above, i.e., an atmosphere in which the first metal oxide 21 is not reduced when present alone, but the second metal oxide 22 is reduced when present alone. The specific reducing atmosphere is set as a combination of temperature and oxygen partial pressure depending on the combination of the first metal oxide 21 and the second metal oxide 22, as described below. Specifically, for example, an atmosphere containing hydrogen and water vapor may be set at a temperature in the range of 300 to 700°C for approximately 6 hours, so that the oxygen partial pressure is appropriate to satisfy the above conditions depending on the combination of the first metal oxide 21 and the second metal oxide 22. By performing this reduction treatment, the second metal oxide 22 that is exposed to the specific reducing atmosphere is reduced to metal 25, while the second metal oxide 22 that is not exposed to the specific reducing atmosphere remains in the form of metal oxide (FIG. 2(G)).

[0030] After the sintered body 14 is reduced in step T140, it is further subjected to an acid treatment (step T150) to complete the porous support 10 (FIG. 2(H)). The acid treatment may be performed under conditions that allow the metal 25 produced by the reduction of the second metal oxide 22 in step T140 to be eluted. The acid treatment can be performed by immersing the reduced body in an acid solution such as hydrochloric acid, sulfuric acid, or hydrofluoric acid. Stirring the acid solution with a stirrer using a stirrer bar enables the entire sintered body 14 to be treated more uniformly. The acid treatment elutes the metal 25, forming pores 26 in the areas where the metal 25 was previously present. This increases the porosity of the sintered body 14, resulting in the porous support 10. The second metal oxide 22, which remains in the form of a metal oxide without being exposed to a specific reducing atmosphere during the reduction treatment in step T140, remains as the second metal oxide 22 even after the acid treatment in step T150.

[0031] In step T130, the compact 12 is densified as it is fired. However, even after firing, fine voids remain between the particles of the first metal oxide 21 and the second metal oxide 22 within the compact 12. In the reduction treatment in step T140, the second metal oxide 22 present within the compact 12 is exposed to a specific reducing atmosphere through these fine voids and reduced to metal 25. As a result of firing, some of the second metal oxide 22 may assume a multilayer structure, a so-called "core-shell" state, in which the entire surface is covered by the first metal oxide 21. Because the second metal oxide 22 constituting this core-shell is not exposed to a reducing atmosphere in step T140 due to its entire surface being covered by the first metal oxide 21, it remains as a metal oxide even after the reduction treatment. Therefore, it remains as second metal oxide 22 without elution during the subsequent acid treatment in step T150.

[0032] The amount of second metal oxide 22 remaining on the porous support 10 can be adjusted, for example, by the density of the sintered body 14 formed in step T130. When the compact 12 is fired in step T120, necking, in which particles of the first metal oxide 21 bond together, progresses to a certain degree, resulting in densification, forming a core-shell structure in which the second metal oxide 22 is covered with the first metal oxide 21. The density of the sintered body 14 can be adjusted, for example, by the firing temperature and firing time. The degree of sintering increases with increasing firing temperature and lengthening firing time. Therefore, as described above, by appropriately adjusting the firing conditions within a temperature range of, for example, 800 to 1200°C, the core-shell structure can be formed in part of the second metal oxide 22. The amount of second metal oxide 22 remaining on the porous support 10 can also be adjusted by the mixing ratio of the second metal oxide 22 to the first metal oxide 21 in step T100.

[0033] Since pores 26 are formed by exposing the second metal oxide 22 to a reducing atmosphere in step T140 and then performing the acid treatment in step T150, it is desirable to suppress the formation of the core-shell structure from the viewpoint of ensuring a large porosity and specific surface area in the porous support 10. However, the formation of the core-shell structure leaves the second metal oxide 22 in the porous support 10, which can improve the strength of the porous support 10. The amount of second metal oxide 22 remaining in the porous support 10 can be adjusted appropriately so that the porous support 10 exhibits the desired performance in terms of porosity and strength.

[0034] Furthermore, when the second metal oxide 22 is left in the porous support 10 as described above, it is desirable to use a metal oxide having a smaller specific gravity than the first metal oxide 21 as the second metal oxide 22. This allows the entire porous support 10 to be made lighter. For example, when the first metal oxide 21 contains cerium (Ce) and the second metal oxide 22 contains nickel (Ni), the specific gravity of gadolinium-doped ceria (GDC) is 7.22 g / cm. 3 The specific gravity of NiO is about 6.67 g / cm 3 However, it is also possible that the second metal oxide 22 does not remain in the porous carrier 10.

[0035] In the above description, the porous carrier 10 having the pores 26 formed therein is produced by removing the second metal oxide 22 through reduction treatment and acid treatment, but the porosity of the porous carrier 10 may be adjusted by further adding a pore-forming material different from the second metal oxide 22 to the slurry formed in step T100. As the pore-forming material, for example, a resin powder such as acrylic fine particles can be used.

[0036] 3 and 4 are explanatory diagrams conceptually illustrating the relationship between the density of particles constituting a porous carrier and firing conditions. Fig. 3 is an explanatory diagram illustrating a case in which a porous sintered body 114 is obtained by controlling the firing conditions (firing temperature and firing time) without using a pore-forming material when firing a compact of ceramic particles 121. Fig. 4 is an explanatory diagram illustrating a case in which a porous carrier 10 is obtained by firing a compact in which a first metal oxide 21 and a second metal oxide 22 are mixed using a second metal oxide 22 as a pore-forming material, as in this embodiment, and then removing the second metal oxide 22 by the reduction treatment and acid treatment described above.

[0037] 3, when a porous sintered body 114 is obtained by suppressing the firing conditions, the firing conditions are set so that sufficient pores 26 are formed between the ceramic particles 121, so that although the ceramic particles 121 bond together by necking, the progress of grain growth of the ceramic particles 121 is relatively suppressed. As a result, the shape of each ceramic particle 121 becomes nearly spherical, and the proportion of ceramic particles 121 with a density of 0.9 or less is suppressed.

[0038] In contrast, as shown in FIG. 4 , when the second metal oxide 22 is used as a pore-forming material, the second metal oxide 22 forms pores 26. Therefore, by adjusting the amount of the second metal oxide 22 mixed to achieve the desired porosity and setting the firing conditions to sufficiently advance sintering, it is possible to achieve both high porosity and strength in the porous support 10. That is, because the pores 26 in the porous support 10 are formed by the second metal oxide 22, which is subsequently removed, there is no need to leave gaps between the particles of the first metal oxide 21 to form the pores 26 in the firing step. Therefore, the compact 12 can be sufficiently sintered, thereby increasing the strength of the final porous support 10. By sufficiently advancing sintering accompanied by grain growth as described above, the formation of gaps between the particles of the first metal oxide 21 and the particles of the second metal oxide 22 is suppressed in the sintered body 14 obtained by firing in step T130, and these particles are in close proximity to each other. As sintering progresses in this way, the particles come into close proximity to each other, and the shape of each particle, which was spaced apart or joined only at necked portions and was nearly spherical in the early stages of sintering, becomes more angular. As a result, the proportion of particles having a density of 0.9 or less among the particles of the first metal oxide that make up the porous support 10 increases. As described above, by using the second metal oxide 22, which is a pore-forming material that does not disappear during sintering and can be removed after sintering, and by performing sintering sufficiently, it is possible to achieve "60% or more of the particles of the first metal oxide having a density of 0.9 or less" and "the specific surface area of ​​the porous support 10 is 5m or less." 2 / g.

[0039] Note that when using only resin beads or the like as the pore-forming material, which disappear during sintering, the pore-forming material is lost during firing, and the firing conditions are set so that pores remain after the pore-forming material is lost. Therefore, as in the case of Figure 3, the grain growth of the ceramic particles 121 is suppressed, and the proportion of ceramic particles 121 with a density of 0.9 or less is reduced. Furthermore, when obtaining a porous sintered body 114 through the firing conditions as shown in Figure 3, or when producing a porous carrier using a pore-forming material such as resin beads, the firing conditions must be set to suppress grain growth so that sufficient pores remain after firing, making it difficult to produce a porous body with sufficient strength and a total porosity of 50% or more.

[0040] C. Specific reducing atmospheres: As described above, a "specific reducing atmosphere" that satisfies the condition that the first metal oxide 21 is not reduced when present alone and the second metal oxide 22 is reduced when present alone is set as a temperature and oxygen partial pressure condition depending on the combination of the first metal oxide 21 and the second metal oxide 22. The "specific reducing atmosphere" that satisfies the above condition can be set, for example, using an Ellingham diagram. The Ellingham diagram is a well-known diagram that shows the ease with which a substance is oxidized, and plots the temperature dependence of the Gibbs energy change (ΔG) of various reaction formulas, with the standard reaction Gibbs energy on the vertical axis and the temperature on the horizontal axis.

[0041] FIG. 5 is a graph constituting an Ellingham diagram, and is an explanatory diagram showing a simplified version of a graph related to the explanation of the oxidation-reduction of the first metal oxide 21 and the second metal oxide 22. In FIG. 5, gadolinium-doped ceria (GDC) is used as the first metal oxide 21. x Ce 1-x O δ , where δ is a value determined to satisfy the condition of electrical neutrality), and assuming that copper oxide (CuO) is used as second metal oxide 22, graphs relating to the oxidation reactions of copper, cerium, and gadolinium are shown. The oxidation reaction of copper is shown below as formula (1), the oxidation reaction of cerium as formula (2), and the oxidation reaction of gadolinium as formula (3).

[0042] 4Cu+O2= 2Cu2O … (1) Ce + O2 = CeO2… (2) 4 / 3Gd+O2= 2 / 3Gd2O3… (3)

[0043] As can be seen from Figure 5, when the temperature is 400°C, the oxygen partial pressure when the oxidation reaction of copper (Cu) shown in equation (1) reaches equilibrium is 10 -18 Therefore, if the temperature is 400°C, the oxygen partial pressure is 10 -18 When the oxygen partial pressure is lower than 10 atm, the reduction reaction of copper (Cu) proceeds. -18 At higher than 10 atm, the oxidation reaction of copper (Cu) proceeds. Similarly, the oxidation reaction of cerium (Ce) shown in equation (2) reaches equilibrium when the oxygen partial pressure is 10 -73 Therefore, if the temperature is 400°C, the oxygen partial pressure is 10 -73 When the oxygen partial pressure is lower than 10 atm, the reduction reaction of cerium (Ce) proceeds. -73 At temperatures higher than 10 ...

[0044] From the above, if the temperature is 400°C, the oxygen partial pressure is 10 -18 At temperatures above 10 atm, the reactions that produce copper oxide (Cu2O), cerium oxide (CeO2), and gadolinium oxide (Gd2O3) occur. -18 10 lower than ATM -73 At temperatures above 10 atm, the reactions that produce copper (Cu), cerium oxide (CeO2), and gadolinium oxide (Gd2O3) occur. -73 At temperatures below 1000 K, the reactions that produce copper (Cu) and cerium (Ce) occur. At the same time, the reactions that produce gadolinium occur depending on the oxygen partial pressure, producing either gadolinium (Gd) or gadolinium oxide (Gd2O3).

[0045] Therefore, under the condition of a temperature of 400°C, the first metal oxide (CeO2) when present alone is not reduced, and the second metal oxide (Cu2O) when present alone is reduced. -18 10 lower than ATM -73 The oxygen partial pressure can be set in a range higher than 10 ...

[0046] D. Catalyst body with porous support: A catalyst body can be formed by disposing a catalyst on the surface of the porous carrier 10 of this embodiment. As described above, the porous carrier 10 used as a catalyst carrier can be formed into a molded body in various shapes, such as a powder, pellet, or honeycomb shape. There are no particular restrictions on the catalyst to be disposed on the surface of the porous carrier 10, and it may be appropriately selected from catalytic metals and oxide catalysts depending on the type of reaction to be promoted using the catalyst body.

[0047] When a catalytic metal is used as the catalyst, the catalytic metal may be, for example, a noble metal such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), or osmium (Os), or may be a base metal such as cobalt (Co), nickel (Ni), iron (Fe), or copper (Cu). There are no particular limitations on the method for supporting the catalytic metal on the porous support 10, and various known methods can be used, such as an impregnation method in which the porous support 10 is impregnated with a solution containing the catalytic metal and then calcined, a coprecipitation method, or an ion exchange method.

[0048] Furthermore, when an oxide catalyst is used as the catalyst, various metal oxide catalysts and composite oxide catalysts such as perovskite-type oxide catalysts can be used as the oxide catalyst. There are no particular limitations on the method for supporting the oxide catalyst on the porous support 10, and various known methods can be used. For example, when a composite oxide catalyst is used as the oxide catalyst, methods such as a solid-phase reaction method, a coprecipitation method, a Pechini method, a citrate complex method, and a sol-gel method can be used.

[0049] Furthermore, when the porous carrier 10 of this embodiment has proton conductivity, the catalytic activity can be enhanced by using the porous carrier 10 as a carrier for a catalyst that promotes a reaction involving the exchange of protons. Examples of reactions involving the exchange of protons include the hydrogenation reaction of carbon dioxide (reduction reaction of carbon dioxide), a reaction that produces hydrogen by a dehydrogenation reaction, and an ammonia synthesis reaction.

[0050] Examples of carbon dioxide hydrogenation reactions include reactions that produce organic substances such as hydrocarbons and alcohols from carbon dioxide. Examples of such reactions include a reaction that produces methanol from carbon dioxide shown in the following formula (4), a reaction that produces methane from carbon dioxide shown in the following formula (5), and a reaction that produces formic acid from carbon dioxide shown in the following formula (6). Another example of a carbon dioxide hydrogenation reaction is a reaction that produces carbon monoxide from carbon dioxide. Such a reaction is shown in the following formula (7).

[0051] CO2+ 6H + + 6e - → CH3OH + H2O … (4) CO2+ 8H + + 8e - → CH4 + 2H2O … (5) CO2+ 2H + + 2e - → HCOOH … (6) CO2+ 2H + + 2e - → CO + HO … (7)

[0052] Examples of reactions that produce hydrogen through dehydrogenation reactions include the dehydrogenation of hydrocarbons and alcohols. Specifically, examples include reactions that produce hydrogen from hydrocarbons and alcohols through steam reforming or partial oxidation. Below, as examples of such reactions, the general formula for the steam reforming reaction of hydrocarbons is shown in Equation (8). The general formula for the partial oxidation reaction of hydrocarbons is shown in Equation (9), and the shift reaction that produces carbon dioxide and hydrogen from the carbon monoxide and steam produced in the partial oxidation reaction is shown in Equation (10). Examples of reactions that produce hydrogen from alcohol include the steam reforming reaction of methanol shown in Equation (11), the steam reforming reaction of ethanol shown in Equation (12), and the partial oxidation reaction of methanol shown in Equation (13). All of these reactions involve the transfer of protons and electrons.

[0053] C n H m + 2nH2O → (m / 2+2n)H2+ nCO2… (8) C n H m + (n / 2)O2→ nCO + (m / 2)H2… (9) CO + H2O → CO2+H2… (10) CH3OH + H2O → CO2+ 3H2… (11) C2H5OH + 3H2O → 2CO2+ 6H2… (12) CH3OH + 1 / 2O2→ CO2+ 2H2… (13)

[0054] The ammonia synthesis reaction is shown in the following formula (14): This reaction also involves the exchange of protons and electrons.

[0055] 3H2 + N2 → 2NH3… (14)

[0056] There are no particular limitations on the catalyst that promotes the reaction involving the transfer of protons as described above. For example, manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn) can be used as base metal catalysts that have catalytic activity to promote the reduction reaction of carbon dioxide.

[0057] The above-mentioned catalytic metals can be activated by applying an electric field. Therefore, when using a catalyst body including the porous support 10, for example, a pair of electrodes can be brought into contact with the catalyst layer formed on the catalyst body, and an electric field can be applied to the catalyst layer. As a result, the catalytic activity can be improved by the applied electric energy. This makes it possible to proceed with, for example, the above-mentioned reaction involving the exchange of protons under relatively mild conditions (relatively low temperature conditions or relatively low pressure conditions). When using the catalyst body with an electric field applied to it, CeO2-based oxides, which are oxides containing cerium, or ZrO2-based oxides, which are oxides containing zirconium, can be suitably used as the first metal oxide included in the porous support 10. However, the catalyst body may also be used without applying an electric field.

[0058] According to the porous carrier 10 of the present embodiment configured as described above, in an SEM image of a cross section of the porous carrier 10, the ratio of particles having a density of 0.9 or less among particles of the first metal oxide, which is the main component, is 60% or more, and the specific surface area of ​​the porous carrier 10 is 5 m 2 / g. As described above, by ensuring a large specific surface area of ​​the porous support, the catalyst can be supported in a more highly dispersed state when supported on the porous support, thereby improving catalytic activity. Furthermore, the fact that the density of the first metal oxide particles satisfies the above condition indicates that the shape of the first metal oxide particles is relatively angular. Therefore, compared to when the particles are spherical, the specific surface area of ​​the first metal oxide particles is larger, making it easier to increase the specific surface area of ​​the porous support. Furthermore, the relatively angular shape of the first metal oxide particles can suppress sintering of the catalyst during the heating process when supporting the catalyst on the porous support, thereby further improving catalytic activity. Furthermore, the relatively angular shape of the first metal oxide particles can suppress sintering of the catalyst that occurs with use, even when a catalyst body in which the catalyst is supported on a porous support is used under relatively high temperature conditions. Therefore, deterioration of the catalyst body can be suppressed.

[0059] In particular, the porous support 10 of this embodiment is made using a pore-forming material that does not disappear during firing, like the second metal oxide particles, but is removed in a process after firing. The use of such a pore-forming material makes it easy to ensure the specific surface area of ​​the porous support, and because the pore-forming material does not disappear during firing, it is possible to ensure a large specific surface area of ​​the porous support while sintering sufficiently. By allowing firing to proceed sufficiently in this manner while the second metal oxide particles are mixed in, the first metal oxide particles in the porous support can be shaped to satisfy the above-mentioned density value.

[0060] E. Other Embodiments In the above-described embodiment, the porous support 10 is composed of the first metal oxide 21 and the second metal oxide 22. However, the porous support 10 may further contain other components. For example, to enhance the function of the catalyst body in which a catalyst is supported on the porous support 10, the porous support 10 may further contain one or more types of third metal oxides different from the first metal oxide 21 and the second metal oxide 22. For example, when a proton-conductive metal oxide is used as the first metal oxide 21, further including an electron-conductive third metal oxide can further enhance the performance of the catalyst body when a catalyst that promotes a reaction involving the exchange of protons and electrons is supported to form the catalyst body. In this case, the third metal oxide may be a metal oxide that is not reduced when present alone in the specific reducing atmosphere described above. [Example]

[0061] <Preparation of porous carrier> [Samples S1-S5] As the first metal oxide, gadolinium-doped ceria (GDC20, manufactured by Shin-Etsu Chemical Co., Ltd., with a BET specific surface area of ​​13.4 m 2 / g, particle size D50 is 0.56 μm), and nickel oxide (nickel oxide Green, manufactured by Seido Chemical Industry Co., Ltd., BET specific surface area is 3.4 m) was used as the second metal oxide. 2 / g, particle size D50 of 0.8 μm) was used to prepare samples S1 to S5 as the porous carrier 10 according to the method shown in Fig. 1. In other words, samples S1 to S5 were prepared by repeatedly preparing porous carriers 10 of the same composition using the same method.

[0062] When preparing the porous carriers 10 of samples S1 to S5, in step T100, the first metal oxide and the second metal oxide were each pulverized using ethanol as a solvent in a planetary ball mill. Then, in step T110, the pulverized first metal oxide and the second metal oxide were mixed to prepare a slurry. Specifically, ethanol was used as the solvent, and IONET S-20 (manufactured by Sanyo Chemical Industries, Ltd.) as a dispersant and 3 mm diameter zirconia balls were added. The slurry was prepared by mixing for 15 hours at 110 rpm in a ball mill. The volume ratio of gadolinium-doped ceria (GDC) to nickel oxide (NiO) was 60:40. The amount of dispersant added was 1.12 wt % of the total powder amount used to prepare the slurry. Ethanol was added in an amount of 77 wt % of the total powder amount used to prepare the slurry.

[0063] The slurry obtained in step T110 was then dried to obtain a powder. A PVB binder (Cerna SE604 manufactured by Chukyo Yushi Co., Ltd.) was then added, and the mixture was molded into a rectangular column shape using a uniaxial press. A pressure of 147 MPa was then applied using CIP molding to produce a green compact 12 (step T120). The green compact 12 was then fired at 1040°C for 4 hours in an air atmosphere to obtain a sintered compact 14 (step T130). The resulting sintered compact 14 was then subjected to a reduction treatment in a H2 / N2 atmosphere at 600°C for 5 hours (step T140). The reduction treatment conditions correspond to the "specific reducing atmosphere" set by the method based on the Ellingham diagram described with reference to FIG. 5. That is, the reduction treatment atmosphere was controlled so that, at a temperature of 600°C, the first metal oxide (GDC) was not reduced when present alone, but the second metal oxide (NiO) was reduced when present alone. Thereafter, the reduced compact was placed in 200 mL of a 6 mol / L hydrochloric acid solution and subjected to acid treatment at room temperature for 72 hours (step T150), thereby obtaining samples S1 to S5 as the porous carrier 10.

[0064] [Sample S6] Samples S1 to S5 were prepared in the same manner as samples S1 to S5, except that the step of pulverizing the first metal oxide and the second metal oxide in step T100 was not carried out.

[0065] [Samples S7 and S8] The ceramic particles constituting the porous support were gadolinium-doped ceria (GDC20, manufactured by Shin-Etsu Chemical Co., Ltd., with a BET specific surface area of ​​13.4 m). 2 Porous supports of the same composition were repeatedly prepared using a powder of gadolinium-doped ceria (a sintered body containing 10 ...

[0066] [Sample S9] It was prepared in the same manner as samples S7 and S8, except that strontium zirconate (SrZrO3) was used as the ceramic particles constituting the porous carrier, and the firing conditions for sintering the compact were set to 1050°C for 10 hours.

[0067] [Sample S10] Cerium oxide (CeO2) was used as the ceramic particles that make up the porous carrier, acrylic resin beads (BMSA-18GN (particle size 0.8 μm) manufactured by Sekisui Chemical Co., Ltd.) were added as a pore-forming material when preparing the slurry, and the firing conditions were 1500°C for 4 hours. Except for this, samples S7 and S8 were prepared in the same manner. Here, cerium oxide and acrylic resin beads were mixed so that the added ratio of the acrylic resin beads was 21.3 volume %.

[0068] <Preparation of catalyst body> Samples S1, S6, and S7 were used as the porous supports prepared as described above to support catalysts and produce catalyst bodies. Each sample used as a support weighed approximately 1.4 to 1.5 g and had a rectangular columnar shape measuring 35 mm x 5 mm x 2 mm. The supported catalyst metal was nickel (Ni), and nickel nitrate (Ni(NO3)2) was used as the raw material for supporting the catalyst. Specifically, a nickel nitrate solution was dissolved in pure water, and the nickel nitrate solution was dropped onto each sample by the incipient wetness method to support the catalyst metal to a catalyst loading of 0.1 wt%. The samples were then dried at 100°C for 24 hours and baked at 5550°C for 2 hours to obtain catalyst bodies for each sample.

[0069] <Measurement of specific surface area> The specific surface area of ​​each porous carrier was measured by the BET method. The specific surface area is the surface area relative to the weight (m 2 / g).

[0070] <Measurement of total porosity> The porosity of each porous carrier was measured by Archimedes' method. The total porosity, which is the sum of the ratio of open pore volume and the ratio of closed pore volume, was measured.

[0071] <Image processing method> To measure the density of the ceramic particles that make up the porous carrier, image processing was performed on SEM images of the cross section of each sample. The sample cross section to be measured was a fracture surface, and each sample was broken at a specified location and the fracture surface was observed. Here, using the image analysis software ImageJ, an SEM image (grayscale image: 8-bit monochrome image) obtained by observing an area with a field of view of 6.0 μm x 4.5 μm at a resolution equivalent to 0.013 μm per pixel was used as the input image, and the following processing was performed.

[0072] 6 is an explanatory diagram showing an example of the state of an image in each process in a series of image processes. Each image in FIG. 6 shows the state after the following processes. Process 1: The vertical and horizontal sizes of the input image were expanded by four times using the bilinear method (Image (A)). Processing 2: The image after "Processing 1" was blurred (smoothed) three times using a 3x4 kernel filter (Image (B)). Processing 3: The image after "Processing 2" was subjected to contrast enhancement processing using histogram normalization (Image (C)). Process 4: The image after "Process 3" was subjected to edge detection processing using a Sobel filter (square root of the sum of squares in the x and y directions) (Image (D)). Process 5: The image after “Process 4” was binarized using a discriminative binarization method (Image (E)). Process 6: After "Process 5", the image was subjected to close processing (expansion processing → contraction processing) to remove single points (Image (F)). Process 7: The image after "Process 6" was thinned by dilation processing (Image (G)). Process 8: For the image after "Process 7", connected particles were automatically separated and separated using watershed processing (Image (H)). Process 9: The contour information of each separated area was extracted from the image after "Process 8" (Image (I)). Process 10: Based on the contour information extracted in “Process 9”, the density was calculated using the following equation (15).

[0073] Density = (area inside the contour) / (area of ​​the convex hull) … (15)

[0074] <Catalyst activity evaluation test> The catalytic performance of each catalyst was evaluated by using the catalyst to carry out the methanation reaction represented by the following formula (16), i.e., the reaction of producing methane from carbon dioxide represented by the above-mentioned formula (5).

[0075] CO2+ 4H2→ CH4+ 2H2O … (16)

[0076] The catalytic performance of each catalyst was evaluated using a fixed-bed flow reactor. Each catalyst was placed in a quartz tube packed with quartz wool. In the catalysts prepared using the method described above, the catalyst metal baked onto the support was in the oxide state. Therefore, prior to the methane production reaction, a reduction treatment was performed in the fixed-bed flow reactor to reduce the nickel oxide to nickel. The reduction treatment was performed under the following conditions: furnace temperature: 350°C, furnace pressure: 1 atm, hydrogen (H2) flow rate: 20 sccm, argon (Ar) flow rate: 40 sccm, and treatment time: 30 min. The methane production reaction was then carried out at furnace temperatures of 250°C, 300°C, and 350°C, respectively, under the following conditions: furnace pressure: 1 atm, hydrogen (H2) flow rate: 40 sccm, and carbon dioxide (CO2) flow rate: 10 sccm. Under each temperature condition, gas was collected in a 1 mL sample tube 10 minutes after the start of the methanation reaction, and the concentrations of carbon dioxide (CO2), hydrogen (H2), methane (CH4), and carbon monoxide (CO) contained in the gas after the reaction were measured using a gas chromatograph "GC-4000 Plus" (manufactured by GL Sciences Inc.). The methane yield [%] was calculated from the measured concentration values.

[0077] <Evaluation results> 7 and 8 are explanatory diagrams showing SEM images of the cross sections of each sample. FIG. 7 shows samples S1 to S6, and FIG. 8 shows samples S7 to S10. FIG. 9 and FIG. 10 are explanatory diagrams showing the results of extracting particle contour information from the SEM images using process 9 of the image processing method described above. FIG. 9 shows samples S1 to S6, and FIG. 10 shows samples S7 to S10. All of the images shown in FIGS. 7 to 10 were captured at the same magnification, but scale bars are added to the image of sample S1 in FIG. 7 and the image of sample S7 in FIG. 8.

[0078] FIG. 11 is an explanatory diagram showing the results of measuring the density of each of the first metal oxide particles contained in the images of samples S1 to S10 shown in FIGS. 9 and 10, dividing the density values ​​into intervals in increments of 0.05, tallying the number of particles (frequency) contained in each interval, and plotting the cumulative percentage of particles belonging to each interval. In FIG. 11, intervals where the density is greater than 0.85 and less than or equal to 0.90 are indicated by hatching. As shown in FIG. 11, samples S1 to S6, which were prepared using the first metal oxide (GDC) and the second metal oxide (nickel oxide) as a pore-forming agent, had a density of 0.9 or less of 60% or more, while samples S7 to S10, which were prepared without using the second metal oxide, had a density of 0.9 or less of less than 60%.

[0079] Figure 12 is an explanatory diagram showing the distribution of the number of particles belonging to each of the above-mentioned density ranges for sample S1, an example of a porous support prepared using a first metal oxide and a second metal oxide, and sample S7, an example of a porous support prepared without using the second metal oxide. Figure 12 is a normalized histogram, with the horizontal axis representing the density range and the vertical axis representing the proportion of particles in the image for each sample, assuming the total number of particles in the image is 1. As shown in Figure 12, for sample S1, the peak where the proportion of particles belonging to a range is high is located in a range with a lower density value, confirming that the proportion of particles with a lower density value is higher overall.

[0080] FIG. 13 is an explanatory diagram showing the results of measuring the specific surface area and total porosity for each of samples S1 to S10. Here, for the specific surface area of ​​each of samples S1, S2, S3 to S5, and S7 and S8, a representative value measured for one of the samples is shown. Furthermore, the total porosity was measured for all samples, but for samples S1 to S5 and S7 and S8, which are groups produced with the same composition and the same manufacturing method, the average value of the measured values ​​for each sample within the group is shown. Furthermore, FIG. 13 also shows the "proportion of particles with a compactness of 0.9 or less," but here, it shows the value rounded to one decimal place from the value shown in FIG. 11.

[0081] 14 is an explanatory diagram showing the results of calculating the methane yield by carrying out an activity evaluation test on the catalyst bodies including Sample S1, Sample S6, and Sample S7. As shown in FIG. 13, Sample S1 has the following characteristics: "(i) in an SEM image of the cross section of the porous support, the proportion of particles of the first metal oxide having a density of 0.9 or less is 60% or more" and "(ii) the specific surface area of ​​the porous support is 5m 2 / g or more. Sample S6 is a sample that satisfies the above requirement (i) but not requirement (ii). Sample S7 is a sample that does not satisfy both requirements (i) and (ii). As shown in Figure 14, the catalyst body including sample S1 that satisfies the above requirements (i) and (ii) exhibits the highest catalytic activity, and it was confirmed that it exhibits high catalytic activity even in a relatively low temperature range, such as 250°C to 300°C. In this way, it was confirmed that a porous support that satisfies the above requirements (i) and (ii) functions as an excellent catalyst support that achieves higher catalytic activity.

[0082] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0083] The present disclosure can also be realized in the following forms. [Application example 1] A porous carrier, The first metal oxide is the main component. In an SEM image of a cross section of the porous support, the proportion of particles having a density of 0.9 or less among particles of the first metal oxide is 60% or more; The specific surface area of ​​the porous carrier is 5 m 2 / g Porous carrier. [Application example 2] The porous carrier according to Application Example 1, the porous support comprises, under a specific reducing atmosphere, the first metal oxide and a second metal oxide different from the first metal oxide; The first metal oxide is a metal oxide that is not reduced when it exists alone in the specific reducing atmosphere, and the second metal oxide is a metal oxide that is reduced when it exists alone in the specific reducing atmosphere. Porous carrier. [Application example 3] The porous carrier according to Application Example 1 or 2, The total porosity is between 50% and 75%. Porous carrier. [Application example 4] A porous carrier according to any one of Application Examples 1 to 3, The first metal oxide is a proton-conducting material. Porous carrier. [Application example 5] The porous carrier according to Application Example 4, The first metal oxide contains at least one of cerium (Ce) and zirconium (Zr). Porous carrier. [Application Example 6] The porous carrier according to Application Example 2, The second metal oxide contains a transition metal. Porous carrier. [Application Example 7] The porous carrier according to Application Example 6, The transition element includes at least one of nickel (Ni) and copper (Cu). Porous carrier. [Application Example 8] The porous carrier according to Application Example 2, the first metal oxide includes cerium (Ce); The second metal oxide contains nickel (Ni). Porous carrier. [Application Example 9] A porous carrier according to any one of Application Examples 1 to 8, a carbon dioxide reduction catalyst disposed on the surface of the porous support; A catalyst body comprising: [Application Example 10] A porous carrier according to any one of Application Examples 1 to 8, a catalyst disposed on the surface of the porous support and capable of being activated by application of an electric field; A catalyst body comprising: [Application Example 11] A method for producing a porous carrier, comprising: A first metal oxide as a main component that has been crushed in advance and a second metal oxide different from the first metal oxide are prepared; preparing a compact by mixing the first metal oxide and the second metal oxide and molding the mixture; sintering the compact; the fired compact is subjected to a reduction treatment under a specific reducing atmosphere in which the first metal oxide present alone is not reduced and the second metal oxide present alone is reduced; the reduced compact is subjected to an acid treatment under conditions in which the metal element constituting the second metal oxide is eluted in a metallic state; In the porous carrier, in an SEM image of a cross section of the porous carrier, the ratio of particles having a density of 0.9 or less among particles of the first metal oxide is 60% or more, and the specific surface area of ​​the porous carrier is 5 m 2 / g or more of porous carrier Method for producing a porous carrier. [Explanation of symbols]

[0084] 10...Porous carrier 11...Slurry 12...Molded body 14,114...Sintered body 21...First metal oxide 22...Second metal oxide 23...Solvent 24...Binder 25...metal 26... Stoma 121...ceramic particles

Claims

1. A porous carrier, The first metal oxide is a main component. In an SEM image of a cross section of the porous support, the proportion of particles having a density of 0.9 or less among particles of the first metal oxide is 60% or more; The specific surface area of ​​the porous carrier is 5 m ２ / g Porous carrier.

2. The porous carrier according to claim 1, the porous support comprises, under a specific reducing atmosphere, the first metal oxide and a second metal oxide different from the first metal oxide; The first metal oxide is a metal oxide that is not reduced when it exists alone in the specific reducing atmosphere, and the second metal oxide is a metal oxide that is reduced when it exists alone in the specific reducing atmosphere. Porous carrier.

3. The porous carrier according to claim 1, The total porosity is 50% or more and 75% or less. Porous carrier.

4. The porous carrier according to claim 1, The first metal oxide is a proton-conducting material. Porous carrier.

5. The porous carrier according to claim 4, The first metal oxide contains at least one of cerium (Ce) and zirconium (Zr). Porous carrier.

6. The porous carrier according to claim 2, The second metal oxide contains a transition metal. Porous carrier.

7. The porous carrier according to claim 6, The transition element includes at least one of nickel (Ni) and copper (Cu). Porous carrier.

8. The porous carrier according to claim 2, the first metal oxide comprises cerium (Ce); The second metal oxide contains nickel (Ni). Porous carrier.

9. A porous carrier according to any one of claims 1 to 8; a carbon dioxide reduction catalyst disposed on the surface of the porous support; A catalyst body comprising:

10. A porous carrier according to any one of claims 1 to 8; a catalyst disposed on the surface of the porous support and capable of being activated by application of an electric field; A catalyst body comprising:

11. A method for producing a porous carrier, comprising: A first metal oxide as a main component that has been crushed in advance and a second metal oxide different from the first metal oxide are prepared; preparing a compact by mixing and molding the first metal oxide and the second metal oxide; sintering the compact; the fired compact is subjected to a reduction treatment under a specific reducing atmosphere in which the first metal oxide present alone is not reduced and the second metal oxide present alone is reduced; the reduced compact is subjected to an acid treatment under conditions in which the metal element constituting the second metal oxide is eluted in a metallic state; In the porous carrier, in an SEM image of a cross section of the porous carrier, the ratio of particles having a density of 0.9 or less among particles of the first metal oxide is 60% or more, and the specific surface area of ​​the porous carrier is 5 m ２ / g or more of a porous carrier is obtained. Method for producing a porous carrier.

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