Porous ceramic, catalyst structure, and method for producing porous ceramic

Abstract

To provide a technique to make pores inside a porous ceramic available for use.SOLUTION: A porous ceramic comprising, as a principal component, a proton-conductive composite oxide and having multiple pores, the ceramic having two peaks in the differential pore volume distribution of the pore size distribution.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to porous ceramics. [Background technology]

[0002] Porous supports have been known as supports for supporting catalysts. For example, Patent Document 1 discloses a granular catalyst composition obtained by crushing pellets having a plurality of pores, as a catalyst composition having a proton-conducting solid oxide that functions as a catalyst support. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-042673 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned Patent Document 1, fluids such as gases and liquids cannot flow through the pores inside the porous support, and there is a risk that the pores inside the porous support cannot be fully utilized. This problem is not limited to catalyst compositions, but is a common problem in various products that utilize the pores of porous ceramics, such as gas adsorbents and filters. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms. (1) According to one aspect of the present disclosure, there is provided a porous ceramic material containing a proton-conducting composite oxide as a main component and having a plurality of pores, the porous ceramic material having two peaks in the differential pore volume distribution of the pore size distribution.

[0006] This type of porous ceramic has two peaks in the differential pore volume distribution of the pore size distribution, allowing it to achieve the benefits of both small and large pores. Because the porous ceramic has large pores, the resistance to fluid flow through the pores inside the porous ceramic is reduced compared to porous ceramics with only small pores, allowing the pores inside the porous ceramic to be fully utilized. Furthermore, compared to porous ceramics with only large pores, the specific surface area can be increased, thereby increasing the area available for reaction. Here, "small pores" and "large pores" are classified based on the relative pore sizes of the two peaks in the pore size distribution.

[0007] Since porous ceramics of this type have proton conductivity, their catalytic activity can be enhanced by using them as a support for a catalyst that promotes reactions 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), the reaction of producing hydrogen by dehydrogenation, and the ammonia synthesis reaction. (2) In the porous ceramic of the above embodiment, the difference in pore diameter between the two peaks in the pore diameter distribution may be 10 times or more. This allows the porous ceramic to have relatively large pores while maintaining its structure, thereby further reducing pressure loss and improving the flow of fluid within the pores. (3) In the porous ceramic of the above embodiment, the composite oxide may contain at least one of cerium (Ce) and zirconium (Zr). In this case, the porous ceramic can be used as an electric field application catalyst support. When the porous ceramic is used as an electric field application catalyst support, applying an electric field to the catalyst support can lower the temperature of the catalytic reaction. (4) The porous ceramics of the above form may be a sintered body molded into a predetermined shape, which can improve the handling properties compared to powder or granular porous ceramics. (5) According to another aspect of the present disclosure, there is provided a catalyst structure. The catalyst structure includes the porous ceramic of the above aspect and a catalytic metal supported on the porous ceramic to promote a reaction for producing hydrogen by a hydrogenation reaction or a dehydrogenation reaction of carbon dioxide. The catalyst structure of this aspect can increase the reaction yield of the reaction for producing hydrogen by a hydrogenation reaction or a dehydrogenation reaction of carbon dioxide.

[0008] (6) According to yet another aspect of the present disclosure, there is provided a method for producing the porous ceramics described in (4) above, which comprises uniaxially pressing a plurality of granular materials of the composite oxide filled in a mold to form a molded body, and then firing the molded body without applying pressure to the molded body by cold isostatic pressing to obtain the porous ceramics.

[0009] This method for producing porous ceramics does not require cold isostatic pressing, leaving large pores, and as a result, a porous ceramic sintered body can be obtained that has two peaks in the differential pore volume distribution of the pore size distribution.

[0010] The present disclosure can be realized in various forms other than those described above, such as a method for manufacturing a catalyst structure, a method for hydrogenating carbon dioxide, a method for producing hydrogen by a dehydrogenation reaction, a method for manufacturing ammonia, etc. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is an explanatory diagram conceptually showing a schematic configuration of a porous ceramic according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing the pore size distribution of porous ceramics. [Figure 3] FIG. 2 is an explanatory diagram showing a schematic configuration of a porous ceramic of a comparative example. [Figure 4] 1 is a process diagram showing an example of a method for producing porous ceramics. FIG. [Figure 5] FIG. 1 is a process diagram showing a manufacturing method for samples 1 and 3. [Figure 6] FIG. 10 is a diagram showing evaluation results. [Figure 7] FIG. 1 is a diagram showing the pore size distributions of Samples 1 and 2. [Figure 8] FIG. 1 shows the pore size distributions of Samples 3 and 4. [Figure 9] FIG. 10 is a diagram showing the compressive strength of each sample. [Figure 10] FIG. 1 shows XRD patterns of Samples 1 to 4. [Figure 11] FIG. 4 is an explanatory diagram conceptually showing a schematic configuration of a catalyst structure according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment A. Composition of porous ceramics: 1 is an explanatory diagram conceptually illustrating a schematic configuration of a porous ceramic 100 according to an embodiment of the present disclosure. The porous ceramic 100 of this embodiment is primarily composed of a proton-conductive composite oxide and has a plurality of pores. The porous ceramic 100 may further contain, for example, unavoidable trace components derived from the raw material powder.

[0013] As shown in FIG. 1 , the porous ceramic 100 of this embodiment is a sintered body molded into a prism shape with a rectangular bottom. This allows for improved handling compared to powdered or granular porous ceramics. Furthermore, for example, when the porous ceramic 100 of this embodiment is used as a catalyst support, metal electrodes can be provided on both ends to form an electric field application catalyst. In other embodiments, the shape of the porous ceramic may be cylindrical, polygonal, spherical, powdered, granular, pelleted, honeycomb, or the like. Furthermore, the porous ceramic does not have to be a sintered body. In other words, the porous ceramic does not have to be fired.

[0014] As shown enlarged in FIG. 1, the porous ceramic 100 has a ceramic portion 10, a plurality of first pores 20, and a plurality of second pores 30. The second pores 30 have a larger pore diameter than the first pores 20. The first pores 20 communicate with each other to form a plurality of first communicating pores 22, and the second pores 30 communicate with each other to form a plurality of second communicating pores 32. As will be described in detail later, the porous ceramic 100 has two peaks in the differential pore volume distribution of the pore size distribution. In other words, the porous ceramic 100 has bimodal pores.

[0015] The ceramic portion 10 can be formed from any ceramic having proton conductivity. Proton conduction in the ceramic portion 10 may occur either inside the ceramic portion 10 or on its surface. Examples of the composite oxide that constitutes the main component of the ceramic portion 10 include composite oxides containing alumina (Al2O3), silica (SiO2), and titania (TiO2). Furthermore, metal oxides contained in the composite oxide that constitutes the main component of the ceramic portion 10 can be fluorite-structured metal oxides, specifically, CeO2-based oxides containing cerium and ZrO2-based oxides containing zirconium. Among these, cerium oxide (CeO2) is preferred. These metal oxides are suitable for use when the porous ceramic 100 of this embodiment is used with an applied electric field, as described below. When the porous ceramic 100 is used as an electric field-applied catalyst support, applying an electric field to the catalyst support can lower the temperature of the catalytic reaction.

[0016] The metal oxide contained in the ceramic portion 10 may be a metal oxide other than those mentioned above. For example, a metal oxide having a perovskite structure exhibiting proton conductivity (e.g., BaCeO3-based oxide), a metal oxide having a fergusonite structure or a scheelite structure exhibiting proton conductivity (e.g., LaNbO4-based oxide), a metal oxide having a pyrochlore structure exhibiting proton conductivity (e.g., La2Zr2O7-based oxide), a metal oxide having a mayenite structure exhibiting proton conductivity (e.g., Ce 12 Al 14 O 33 Examples of usable materials include metal oxides with a Brownmillerite structure that exhibit proton conductivity (e.g., Ba2In2O5-based oxides), metal oxides based on a fluorite structure that exhibit proton conductivity (e.g., La6WO6-based oxides), phosphate compounds that exhibit proton conductivity (e.g., LaPO4-based, SnP2O7-based, and CsH2PO4-based), and sulfate compounds that exhibit proton conductivity (e.g., CsHSO4-based).

[0017] FIG. 2 is a diagram showing the pore size distribution of the porous ceramic 100. In FIG. 2, the horizontal axis represents the pore size, the vertical axis represents the differential pore volume, and the vertical axis represents the cumulative pore volume, as shown by a solid line and a dashed line, respectively. The pore size distribution shown in FIG. 2 was measured by mercury intrusion porosimetry. As shown in the figure, the porous ceramic 100 has two peaks in the differential pore volume distribution.

[0018] The pore diameters of the two peaks in the pore diameter distribution are not particularly limited, but the difference between the pore diameters of the two peaks is preferably 10 to 500 times. This allows the porous ceramic 100 to have relatively large pores while maintaining its structure, thereby further reducing pressure loss and improving the flow of fluid within the pores. When the peak with the smaller pore diameter is designated the first peak and the peak with the larger pore diameter is designated the second peak, the difference between the pore diameters of the two peaks is expressed as (pore diameter of the second peak / pore diameter of the first peak) times.

[0019] In the example shown in Figure 2, the pore diameter of the first peak is approximately 0.005 µm, and the pore diameter of the second peak is approximately 0.7 µm. The difference between the pore diameter of the first peak and the pore diameter of the second peak is 140 times, which is more than 10 times. The pore diameter of the first pore 20 shown in Figure 1 is approximately 0.005 µm, and the pore diameter of the second pore 30 is approximately 0.7 µm.

[0020] FIG. 3 is an explanatory diagram showing a schematic configuration of a porous ceramic 100P of a comparative example. FIG. 3(A) shows the pore size distribution, and FIG. 3(B) conceptually shows the configuration of the porous ceramic 100P. As shown in FIG. 3, the porous ceramic 100P of the comparative example has one peak in the differential pore volume distribution of the pore size distribution, and the pore size of the peak is approximately the same as the pore size of the first peak in this embodiment. That is, the porous ceramic 100P of the comparative example has a plurality of first pores 20 and a plurality of first communicating pore portions 22, but does not have second pores 30.

[0021] According to the porous ceramic 100 of this embodiment, the differential pore volume distribution of the pore size distribution has two peaks, and therefore it is possible to obtain the advantages of both small pores and large pores. As shown in Fig. 1, in the porous ceramic 100 of this embodiment, a fluid flows through the first communicating pores 22 and the second communicating pores 32. As shown in Fig. 3, in the porous ceramic 100P of the comparative example, a fluid flows through the first communicating pores 22.

[0022] The porous ceramic 100 of this embodiment has second pores 30 with a relatively large pore diameter, and therefore, compared to a porous ceramic 100P having only first pores 20, the resistance to fluid flow through the pores inside the porous ceramic 100 is smaller, allowing the pores inside the porous ceramic 100 to be fully utilized. Furthermore, compared to porous ceramics having only large pores, the specific surface area can be increased, and therefore the area available for reaction can be increased.

[0023] For example, when the porous ceramic 100 of this embodiment is used as a catalyst support, the relatively large second pores 30 allow the metal precursor of the catalytic metal to penetrate deep into the catalyst support, improving the metal loading rate. Furthermore, the porous ceramic 100 has the second pores 30, allowing the reactive gas to reach the interior and increasing the reaction area. Furthermore, the porous ceramic 100 has the second pores 30, improving gas flow and improving pressure loss compared to the comparative porous ceramic 100P. Meanwhile, the porous ceramic 100 has the relatively small first pores 20, resulting in a large specific surface area and highly dispersed catalytic metal loading. Even when the porous ceramic 100 is used as something other than a catalyst support, such as a gas adsorbent, the porous ceramic 100 has the second pores 30, allowing the adsorbed gas to reach the interior, and the first pores 20 increase the specific surface area, improving gas adsorption efficiency.

[0024] B. Manufacturing method of porous ceramics: FIG. 4 is a process diagram showing an example of a method for manufacturing porous ceramics. In step P102, raw material powder constituting the ceramic part 10 is mixed with a solvent. For example, GDC (Gd X Ce 1-X Oγ), strontium zirconate (SrZrO3), etc. can be used. Ethanol, for example, can be used as the solvent. GDC (Gd X Ce 1-X Oγ), for example, (Gd 0.2 Ce 0.8 O 1.9 ) can be used.

[0025] In step P104, the raw material powder is pulverized using a planetary ball mill at a predetermined rotation speed for a predetermined time, whereby the raw material powder is finely pulverized and mixed with a solvent to produce a slurry.

[0026] In step P106, the slurry obtained in step P104 is transferred to a bowl and dried in a water bath at 80°C to thoroughly volatilize the ethanol and turn it into a powder. Through steps P102 to P106, a powder (granular) porous ceramic is produced.

[0027] In step P108, the powdered porous ceramic obtained in step P106 is mixed with a binder and a solvent, and the mixture is mixed in a mortar until the solvent is completely evaporated, producing granular (particulate) porous ceramic. For example, Cerna SE604 (Chukyo Yushi Co., Ltd.) can be used as the binder, and ethanol can be used as the solvent.

[0028] In step P110, a predetermined mold is used and the mixture is pressed in a uniaxial press to obtain a green compact. Depending on the shape of the pressing mold used in step P110, the final porous ceramic can be formed into a desired shape. For example, it can be molded into a rectangular column (Figure 1), a cylindrical shape, etc. It can also be molded into a pellet shape.

[0029] In step P112, the binder component in the powder compact is volatilized by heating. The heating temperature may be any temperature at which the binder component in the powder compact is volatilized, and the powder compact is heated to, for example, 200° C. to 350° C. (in the air).

[0030] In step P114, the molded body obtained in step P112 is fired to obtain a porous ceramic sintered body. In step P114, firing is performed at a temperature (for example, 400°C to 600°C) at which necking does not progress significantly and at which the shape can be maintained.

[0031] According to this manufacturing method, after forming the green compact in a uniaxial press in step P110, cold isostatic pressing (CIP) is not performed to increase the percentage of pores formed between the granular porous ceramic particles that remain uncrushed. The green compact formed in step P110 has relatively small pores in the granular porous ceramic particles and relatively large pores formed between the granular porous ceramic particles. Furthermore, since the sintering step (step P114) is performed at a temperature that does not significantly promote necking, the porous ceramic sintered body produced by this manufacturing method has two peaks in the differential pore volume distribution of the pore size distribution. That is, the porous ceramic produced by this manufacturing method has a plurality of first pores 20 and a plurality of second pores 30, as shown in FIG. 1 .

[0032] To produce powder or granular porous ceramics having two peaks in the differential pore volume distribution of the pore size distribution, a pore-forming material powder is mixed in at step P108. The material of the pore-forming material powder can be removed in a subsequent step by a method appropriate for the pore-forming material powder, and can be selected arbitrarily. For example, a resin powder such as acrylic fine particles (e.g., BMSA-18GN, manufactured by Sekisui Plastics Co., Ltd.) can be used. The same steps are then followed up to the debinding step at step P112, and the resulting debound material is crushed and sized by sieving, to obtain powder or granules having two peaks in the differential pore volume distribution of the pore size distribution. [Example]

[0033] Porous ceramic samples 1 to 4 with multiple pores were fabricated and their porosity, specific surface area, pore size distribution, and compressive strength were investigated. Samples 1 to 4 all have the same composition of the main composite oxide, but differ in their manufacturing methods and conditions. The main composite oxide is strontium zirconate (SrZrO3).

[0034] FIG. 5 is a process diagram showing the manufacturing method of Samples 1 and 3. In FIG. 5, the same steps as in FIG. 4 are assigned the same step numbers. The manufacturing method shown in FIG. 5 includes a CIP step (step P111) between steps P110 and P112 in the manufacturing method shown in FIG. 4. In step P111, a CIP machine is used to apply an isotropic pressure of 147 MPa to the green compact molded in step P110. In step P112, the green compact after step P111 is debound.

[0035] Samples 2 and 4 were manufactured by the manufacturing method shown in Fig. 4. The firing conditions in step P114 were 650°C for 12 hours for Samples 1 and 2, and 1150°C for 12 hours for Samples 3 and 4.

[0036] [SEM image of fracture surface] The rectangular columnar sample was broken, and the fracture surface was observed using a scanning electron microscope (SEM) to take a secondary electron image. The incident voltage was 5 kV.

[0037] [Porosity measurement] The porosity was measured by the Archimedes method, and the total porosity, which is the sum of the ratio of the open pore volume and the ratio of the closed pore volume, was measured.

[0038] [Measurement of specific surface area] The specific surface area was evaluated using the BET method, and the BET specific surface area is the surface area per unit weight (m 2 / g) and surface area per unit volume (m 2 / cm 3 ) is written as follows.

[0039] [Measurement of pore size distribution] The pore size distribution was measured by mercury intrusion porosimetry using a rectangular columnar sample of the size shown in FIG.

[0040] [Compression strength measurement] For each sample to be measured, a cylindrical sample of the size shown in Figure 6 was prepared, and the compressive strength was measured by applying a compressive force perpendicular to the bottom surface (flat surface) using an autograph.

[0041] Fig. 6 shows the evaluation results. Fig. 6 shows the SEM image of the fracture surface of each sample, the total porosity (%), the specific surface area, and the appearance. Fig. 7 shows the pore size distribution of Samples 1 and 2, and Fig. 8 shows the pore size distribution of Samples 3 and 4. For each of Samples 1 to 4, rectangular and cylindrical samples were prepared as shown in the figures.

[0042] As shown in Figures 7 and 8, Samples 2 and 4 have two peaks in the differential pore volume distribution of the pore size distribution, while Samples 1 and 3 have one peak. As mentioned above, Samples 1 and 2 were fired under the same conditions, and Samples 3 and 4 were fired under the same conditions. Therefore, a comparison was made between Samples 1 and 2 and Samples 3 and 4. Sample 2 had an increased total porosity and specific surface area compared to Sample 1. Furthermore, Sample 4 had an increased total porosity and specific surface area compared to Sample 3. These results suggest that porous ceramics can be manufactured without CIP, resulting in porous ceramics with two peaks in the differential pore volume distribution of the pore size distribution. Furthermore, it was confirmed that the total porosity and specific surface area can be increased by not performing CIP compared to when CIP is performed.

[0043] FIG. 9 shows the compressive strength of each sample. The upper part of FIG. 9 shows a graph, and the lower part shows the respective values. For comparison, FIG. 9 also shows the compressive strength of a pressed body. The pressed body had the same composition as Samples 1 to 4 and was produced by carrying out steps P102 to P112 of the production method shown in FIG. 4. FIG. 9 plots the results of measuring the compressive strength of a plurality of sintered bodies produced for each of Samples 1 to 4.

[0044] As shown in Figure 9, Samples 1 to 4 had higher compressive strength than the pressed bodies, confirming that firing increased the strength of the compacts. Sample 2 had lower compressive strength than Sample 1, and Sample 4 had lower compressive strength than Sample 3, but higher compressive strength than the pressed bodies. For example, when each sample was used as a catalyst support, it could be said that sufficient strength could be achieved. Samples 2 and 4 had higher total porosity and larger specific surface area than Samples 1 and 3, respectively, and it could be said that porous ceramics with sufficient strength were achieved.

[0045] Figure 10 shows the XRD patterns obtained by powdering Samples 1 to 4 and performing powder X-ray diffraction. In Figure 10, the sample number is written next to each XRD pattern. Figure 10 also shows the peak positions of the raw metal oxides strontium zirconate (SrZrO3), zirconium oxide (ZrO2), and strontium carbonate (SrCO3). As shown in Figure 10, a crystalline layer of strontium zirconate (SrZrO3) was confirmed in all of Samples 1 to 4.

[0046] Second Embodiment Fig. 11 is an explanatory diagram conceptually showing a schematic configuration of a catalyst structure 200 of the second embodiment. The catalyst structure 200 of the second embodiment includes a porous ceramic 100 as a catalyst support and a catalyst metal 110 supported on the porous ceramic 100. Although not shown in Fig. 11, the porous ceramic 100 has a plurality of first pores 20 and a plurality of second pores 30 as shown in Fig. 1.

[0047] The catalyst metal 110 is not particularly limited and may be appropriately selected depending on the reaction to be carried out using the catalyst structure 200. The catalyst 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 manganese (Mn), cobalt (Co), nickel (Ni), iron (Fe), copper (Cu), or zinc (Zn).

[0048] The method for supporting the catalytic metal 110 on the porous ceramic 100 is not particularly limited, and various known methods for supporting a catalytic metal on a support can be used. For example, an impregnation method can be used, i.e., a method in which the porous ceramic 100 is immersed in a solution containing a catalytic metal salt, followed by calcination and reduction treatment to disperse and support the catalytic metal 110 on the porous ceramic 100. In this case, if the porous ceramic 100 is immersed in the solution containing the catalytic metal salt under negative pressure conditions, the solution can easily penetrate into the pores (first pores 20 and second pores 30) formed in the porous ceramic 100, making it easier to support the catalytic metal 110 on the surfaces of the pores formed inside the porous ceramic 100. In addition to the impregnation method described above, various methods for supporting a catalytic metal on a support can be used to support the catalytic metal 110 on the porous ceramic 100, such as arc discharge, sputtering, ion plating, vacuum deposition, and plating.

[0049] Furthermore, since the composite oxide constituting the porous ceramic 100 of this embodiment has proton conductivity, catalytic activity can be enhanced by using the porous ceramic 100 as a support 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) and a reaction that produces hydrogen through a dehydrogenation 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 (1), a reaction that produces methane from carbon dioxide shown in the following formula (2), and a reaction that produces formic acid from carbon dioxide shown in the following formula (3). Another example of a carbon dioxide hydrogenation reaction is a reaction that produces carbon monoxide from carbon dioxide. This reaction is shown in the following formula (4). When the composite oxide included in the porous ceramic 100 of this embodiment is an oxide of an alkaline earth metal or an oxide of an alkali metal, the composite oxide has a relatively high basicity and a tendency to easily adsorb carbon dioxide, which is desirable because it facilitates increasing the activity of the above-mentioned reaction in which carbon dioxide is a reactant.

[0051] CO2+ 6H + + 6e - → CH3OH + H2O … (1) CO2+ 8H + + 8e - → CH4 + 2H2O … (2) CO2+ 2H + + 2e - → HCOOH … (3) CO2+ 2H + + 2e - → CO + HO … (4)

[0052] Examples of reactions that produce hydrogen through dehydrogenation reactions include the dehydrogenation of hydrocarbons and alcohols. Specifically, reactions that produce hydrogen from hydrocarbons and alcohols through steam reforming or partial oxidation reactions are examples of such reactions. Below, as examples of such reactions, the general formula for the steam reforming reaction of hydrocarbons is shown in equation (5). The general formula for the partial oxidation reaction of hydrocarbons is shown in equation (6), 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 (7). Examples of reactions that produce hydrogen from alcohol include the steam reforming reaction of methanol shown in equation (8), the steam reforming reaction of ethanol shown in equation (9), and the partial oxidation reaction of methanol shown in equation (10). All of these reactions involve the exchange of protons.

[0053] C n H m + 2nH2O → (m / 2+2n)H2+ nCO2… (5) C n H m + (n / 2)O2→ nCO + (m / 2)H2… (6) CO + H2O → CO2+H2… (7) CH3OH + H2O → CO2+ 3H2… (8) C2H5OH + 3H2O → 2CO2+ 6H2… (9) CH3OH + 1 / 2O2→ CO2+ 2H2… (10)

[0054] The above-described catalytic metals can be activated by applying an electric field. Therefore, when using the catalyst structure 200 including the porous ceramic 100, for example, a pair of electrodes can be brought into contact with the catalyst layer formed on the catalyst structure 200, 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. In particular, since the composite oxide included in the porous ceramic 100 of this embodiment has proton conductivity, the application of an electric field can significantly increase proton conduction, for example, on the surface of the composite oxide, thereby enhancing the catalytic activity. This allows, for example, the above-described reaction involving the exchange of protons to proceed under relatively mild conditions (relatively low temperature conditions or relatively low pressure conditions). However, the catalyst structure 200 may also be used without applying an electric field.

[0055] As described above, the catalyst structure 200 of this embodiment uses the porous ceramic 100 having bimodal pores as a catalyst support, thereby achieving both the advantages of small pores and large pores. In manufacturing the catalyst structure 200, when a catalytic metal is supported on the porous ceramic 100, the porous ceramic 100 has large pores, allowing the metal precursor to penetrate deep into the porous ceramic 100, thereby improving the catalytic metal support rate. Furthermore, the porous ceramic 100 has small pores, resulting in a large specific surface area, allowing the catalytic metal to be supported in a highly dispersed manner. For example, when the catalytic metal is nickel (Ni), the metal precursor is a solution of nickel nitrate dissolved in pure water or an organic solvent.

[0056] When the catalyst structure 200 is used as a catalyst, the large pores allow the reaction gas to reach the interior, and the entire catalyst structure 200, including the interior thereof, can serve as a reaction field. Furthermore, the large pores allow the reaction gas to flow well, reducing pressure loss compared to a case where only small pores are present. As a result, for example, the power of a pump for sending the reaction gas to the catalyst structure 200 can be reduced, improving energy efficiency.

[0057] 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.

[0058] The present disclosure can also be realized in the following forms. [Application example 1] A porous ceramic material containing a proton-conductive composite oxide as a main component and having a plurality of pores, It is characterized by having two peaks in the differential pore volume distribution of the pore size distribution. Porous ceramics. [Application example 2] The porous ceramic according to Application Example 1, The difference in pore diameters between the two peaks in the pore diameter distribution is 10 times or more. Porous ceramics. [Application example 3] The porous ceramic according to Application Example 1 or 2, The composite oxide contains at least one of cerium (Ce) and zirconium (Zr). Porous ceramics. [Application example 4] The porous ceramic according to any one of Application Examples 1 to 3, A sintered body molded into a predetermined shape. Porous ceramics. [Application example 5] A catalyst structure comprising: The porous ceramic according to any one of Application Examples 1 to 4, a catalytic metal supported on the porous ceramic and accelerating a reaction of producing hydrogen by a hydrogenation reaction or a dehydrogenation reaction of carbon dioxide; characterized in that it comprises Catalyst structure. [Application Example 6] A method for producing the porous ceramic according to any one of Application Examples 1 to 5, A plurality of the composite oxide granules filled in a mold are uniaxially pressed to form a compact, and then The porous ceramic is obtained by firing the molded body without applying pressure to the molded body by cold isostatic pressing. A method for producing porous ceramics. [Explanation of symbols]

[0059] 10...Ceramics section 20...First pore 22...First communication hole 30...Second pore 32…Second communication hole 100, 100P...Porous ceramics 110...catalytic metal 200...Catalyst structure

Claims

1. A porous ceramic material containing a proton-conductive composite oxide as a main component and having a plurality of pores, It is characterized by having two peaks in the differential pore volume distribution of the pore size distribution. Porous ceramics.

2. The porous ceramic according to claim 1, The difference in pore diameters between the two peaks in the pore diameter distribution is 10 times or more. Porous ceramics.

3. The porous ceramic according to claim 1, The composite oxide contains at least one of cerium (Ce) and zirconium (Zr). Porous ceramics.

4. The porous ceramic according to any one of claims 1 to 3, A sintered body molded into a predetermined shape. Porous ceramics.

5. A catalyst structure comprising: The porous ceramic according to claim 4; a catalytic metal supported on the porous ceramic to promote a reaction of producing hydrogen by a hydrogenation reaction or a dehydrogenation reaction of carbon dioxide; characterized in that it comprises Catalyst structure.

6. The method for producing the porous ceramic according to claim 4, A plurality of the composite oxide granules filled in a mold are uniaxially pressed to form a compact, and then The porous ceramic is obtained by firing the molded body without applying pressure to the molded body by cold isostatic pressing. A method for producing porous ceramics.

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