Porous ceramic structure and catalyst structure

Abstract

To provide a technique to improve performance of a porous ceramic structure.SOLUTION: A porous ceramics structure comprises, as a principal component, a proton-conductive composite oxide and having multiple pores, the structure containing no binder, with a specific surface area exceeding 25 m2 / g and a compressive strength exceeding 30 N / mm2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to porous ceramic structures. [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-conductive solid oxide that functions as a catalyst support. Patent Document 2 discloses an α-alumina porous support used as a catalyst support for producing ethylene oxide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-042673 [Patent Document 2] Japanese Patent Application Publication No. 11-043380 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 does not mention the pore size distribution or specific surface area of the catalyst support, and the specific surface area of the alumina porous support described in Patent Document 2 is not sufficient, so a technology for improving the performance of the catalyst support is desired. This problem is not limited to catalyst compositions, but is a problem common to various porous ceramic structures 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 embodiment of the present disclosure, there is provided a porous ceramic structure having a plurality of pores and containing a composite oxide having proton conductivity as a main component. The porous ceramic structure does not contain a binder and has a specific surface area of 25 m 2 / g and a compressive strength of 30N / mm 2 Greater than.

[0006] According to this type of porous ceramic structure, since it does not contain a binder, changes in the specific surface area and pore diameter can be suppressed even if the porous ceramic structure is heated during use, etc. Furthermore, since it does not contain a binder, the pores are not blocked by the binder, and a decrease in the specific surface area can be suppressed. Furthermore, although it does not contain a binder, sufficient strength is ensured, so cracking of the porous ceramic structure can be suppressed. Furthermore, since it does not contain a binder, the specific surface area is sufficiently large and a sufficient reaction field can be ensured, so the performance of the porous ceramic structure can be improved. When the binder is detected with any detector, if it is below the detection limit (e.g., 10 ppm), it is said to be "binder-free."

[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.

[0008] (2) In the porous ceramic structure of the above embodiment, the pores may have a diameter of more than 2 nm and a porosity of 38% or more, which can increase the probability that the porous ceramic structure has interconnected pores.

[0009] (3) In the porous ceramic structure of the above embodiment, the composite oxide may contain at least one of cerium (Ce) and zirconium (Zr). In this way, the porous ceramic structure 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.

[0010] (4) In the porous ceramic structure of the above embodiment, the composite oxide may be ceria (CeO2) doped with a rare earth element, which generates oxygen vacancies in the composite oxide, thereby increasing the proton conductivity and accelerating the reaction involving the transfer of protons.

[0011] (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 catalyst 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 volume of the reaction for producing hydrogen by a hydrogenation reaction or a dehydrogenation reaction of carbon dioxide.

[0012] (6) The catalyst structure of the above form may be a catalyst structure for a methanation reaction. By using this catalyst structure, the methanation reaction can be promoted.

[0013] The present disclosure can be realized in various forms other than those described above, such as a method for manufacturing porous ceramics, 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]

[0014] [Figure 1] 1 is an explanatory diagram showing a schematic configuration of a porous ceramic structure according to a first embodiment. [Figure 2] 1A to 1C are process diagrams showing an example of a method for manufacturing a porous ceramic structure. [Figure 3] FIG. 10 is a diagram showing the pore size distribution of sample S1. [Figure 4] FIG. 10 is a diagram showing the evaluation results of sample S1. [Figure 5] FIG. 1 is a graph showing the dependence of compressive strength on firing temperature. [Figure 6] FIG. 10 is a diagram showing evaluation results of samples. [Figure 7] FIG. 1 is a diagram showing the correlation between specific surface area and compressive strength. [Figure 8] FIG. 1 is a diagram showing the correlation between porosity and compressive strength. [Figure 9] FIG. 1 shows XRD patterns of samples S1 and S4. [Figure 10] FIG. 1 is a graph showing the behavior of specific surface area, porosity, and compressive strength relative to firing temperature. [Figure 11] FIG. 1 is a diagram showing the calculation results of the crystallite size of each sample. [Figure 12] FIG. 4 is an explanatory diagram conceptually showing the configuration of a catalyst structure of a second embodiment. [Figure 13] FIG. 1 is an explanatory diagram illustrating a configuration of an evaluation device. [Figure 14] FIG. 1 is a graph showing the carbon dioxide conversion rate of each sample. [Figure 15] FIG. 1 shows the maximum carbon dioxide conversion rate for each sample. [Figure 16] FIG. 1 shows the methane and carbon monoxide yields for each sample. [Figure 17] FIG. 1 shows the maximum carbon dioxide conversion rate, maximum methane yield, and maximum carbon monoxide yield for each sample. DETAILED DESCRIPTION OF THE INVENTION

[0015] First Embodiment A. Composition of porous ceramic structure: 1 is an explanatory diagram conceptually illustrating the configuration of a porous ceramic structure 100 according to an embodiment of the present disclosure. The porous ceramic structure 100 of this embodiment is mainly composed of a composite oxide having proton conductivity, and has a plurality of pores 20. The porous ceramic structure 100 may further contain, for example, unavoidable trace components derived from the raw material powder.

[0016] As shown in Fig. 1, the porous ceramic structure 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 structure 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 structure may be a cylinder, polygonal pillar, sphere, pellet, honeycomb, or the like.

[0017] As shown in an enlarged view in Fig. 1, the porous ceramic structure 100 has a ceramic portion 10 and a plurality of pores 20. The plurality of pores 20 communicate with each other to form a plurality of communicating pore portions 22. As shown in Fig. 1, a gas supplied to the porous ceramic structure 100 flows through the communicating pore portions 22. In other embodiments, other fluids such as liquids may be supplied.

[0018] The ceramic portion 10 can be formed of 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, examples of the metal oxide contained in the composite oxide that constitutes the main component of the ceramic portion 10 include fluorite-structure 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 structure 100 of this embodiment is subjected to an electric field, as described below. When the porous ceramic structure 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.

[0019] 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).

[0020] The porous ceramic structure 100 does not contain a binder. When the binder is detected by any detector and the binder content is below the detection limit (e.g., 10 ppm), it is said to be "binder-free." For example, if a carbon-sulfur analysis (CS analysis) is performed and the results of quantitative analysis of carbon and sulfur are below the detection limit, it can be said to be binder-free. Since the porous ceramic structure 100 does not contain a binder, changes in the specific surface area and pore diameter can be suppressed even when the porous ceramic structure 100 is heated during use, such as in a catalyst metal loading process. Furthermore, since the porous ceramic structure 100 does not contain a binder, the pores 20 are not blocked by the binder, and a decrease in the specific surface area can be suppressed.

[0021] The specific surface area of the porous ceramic structure 100 is 25 m 2 / g. In this way, the reaction field can be enlarged. The larger the specific surface area, the larger the reaction field, so it is preferable. 2 / g or less, it is preferable because a moderate strength can be obtained. The compressive strength of the porous ceramic structure 100 is 30 N / mm 2 Because the compressive strength is large, cracking of the porous ceramic structure 100 can be suppressed. The larger the compressive strength, the more preferable it is. 2 The following is preferable because it allows the specific surface area to be appropriately increased. Although the porous ceramic structure 100 does not contain a binder, it can ensure sufficient strength, and therefore cracking of the porous ceramic structure 100 can be suppressed. Furthermore, since the porous ceramic structure 100 does not contain a binder, has a sufficiently large specific surface area, and can ensure a sufficient reaction field, it can improve performance.

[0022] In the porous ceramic structure 100, the diameter of the pores 20 and the porosity are not particularly limited, but it is preferable that the diameter of the pores 20 is greater than 2 nm and the porosity is 38% or more. This can improve the probability of forming communicating pore portions 22 in which a plurality of pores 20 are connected to each other. It is preferable that the diameter of the pores 20 is 300 nm or less and the porosity is 60% or less. Here, the diameter of the pores 20 is the peak pore diameter in a pore size distribution in which the horizontal axis represents pore diameter and the vertical axis represents Log differential pore volume.

[0023] B. Method for manufacturing porous ceramic structures: FIG. 2 is a process diagram showing an example of a method for manufacturing a porous ceramic structure. In step P102, raw material powder constituting the ceramic portion 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.

[0024] In step P104, the raw material powder is pulverized using a planetary ball mill at a predetermined rotation speed for a predetermined time. This step pulverizes the raw material powder finely and mixes it with a solvent to produce a slurry. In this step, the specific surface area can be increased by pulverizing the raw material powder, and the firing temperature can be lowered.

[0025] 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.

[0026] In step P108, the powdered porous ceramic obtained in step P106 is mixed with a binder, a solvent, and a pore-forming material (organic beads) for adjusting the porosity, 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.

[0027] 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, a honeycomb shape, etc. It can also be molded into a pellet shape.

[0028] In step P111, a CIP (Cold Isostatic Pressing) machine is used to apply isotropic pressure to the green compact formed in step P110. For example, pressure of about 147 MPa can be applied.

[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, 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 (e.g., 400°C to 600°C) at which necking does not progress significantly and the shape can be maintained. If the firing temperature is too high, grain growth progresses, the particles become connected to each other, and the specific surface area decreases. On the other hand, if the firing temperature is too low, the connection between the particles becomes poor and the material becomes more susceptible to fracture. In step 114, by performing heat treatment at a temperature at which necking does not progress significantly and the shape can be maintained, the specific surface area and strength can be optimized. Methods for measuring the degree of necking include observing the cross-sectional structure of the porous ceramic sintered body using an SEM and measuring the specific surface area to check whether the value has decreased. [Example]

[0031] Several samples of porous ceramic structures with multiple pores were prepared and their porosity, specific surface area, pore size distribution, and compressive strength were investigated. All of the samples had the same composition of the main composite oxide, but were fired at different temperatures. The main composite oxide was GDC (Gd 0.2 Ce 0.8 O 1.9 ) Each sample was produced by the production method shown in FIG. 2. Steps P102 to P112 were common to all samples, and only the firing temperature in step 114 was different.

[0032] [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.

[0033] [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.

[0034] [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.

[0035] [Measurement of pore size distribution] The pore size distribution was measured by gas adsorption using a rectangular columnar sample of the size shown in Figure 4.

[0036] [Compression strength measurement] A cylindrical sample with a diameter of 2.8 mm and a height of 4.0 mm was prepared, and the compressive strength was measured by applying a compressive force perpendicular to the bottom (flat surface) using an autograph (AGS-X: Shimadzu Corporation) at a speed of 0.5 mm / min.

[0037] Figure 3 shows the pore size distribution of sample S1, and Figure 4 shows the evaluation results of sample S1. Figure 4 shows an SEM image of the fracture surface of sample S1, as well as the total porosity (%), specific surface area, and appearance. The sintering temperature for sample S1 was 600°C. Prismatic and cylindrical samples were prepared as shown.

[0038] Sample S1 was produced by the production method shown in Figure 2, and does not contain any binder components because the binder components were volatilized in step P112. In Figure 3, the horizontal axis represents pore diameter, the vertical axis represents Log differential pore volume, and the vertical axis represents cumulative pore volume, plotted as squares and circles, respectively. The pore diameter at the peak of the Log differential pore volume is approximately 6 nm. As shown in Figure 4, sample S1 has a total porosity of 38% (average of five samples) and a specific surface area of 47.3 (m 2 / g).

[0039] FIG. 5 is a diagram showing the dependency of compressive strength on firing temperature. In FIG. 5, measured values are plotted with black circles, and average values are plotted with white circles. FIG. 6 is a table showing the evaluation results of the samples shown in FIG. 5. Of the samples shown in FIG. 6, FIG. 5 shows samples H-1 to H-24. As shown in FIG. 5, the higher the firing temperature, the higher the compressive strength. As the firing temperature increases, grain growth progresses and particles become connected, thereby improving strength.

[0040] Fig. 7 is a diagram showing the correlation between specific surface area and compressive strength. In Fig. 7, measured values are plotted with white circles, and average values are plotted with black circles. Fig. 7 also shows samples H-1 to H-24 from the samples shown in Fig. 6. Sample S1 shown in Figs. 3 and 4 corresponds to the measured value shown surrounded by the dashed line in Fig. 7. As shown in Fig. 7, the larger the specific surface area, the smaller the compressive strength. As mentioned above, when grain growth progresses and particles become connected, the compressive strength increases, but when the particles become connected, the specific surface area decreases. Considering the use of a porous ceramic structure as a catalyst support, gas adsorbent, filter, etc., a compressive strength of 30 N / mm 2 As shown in Figure 7, when the specific surface area is 25m, the occurrence of cracks and fractures can be suppressed. 2 / g and a compressive strength of 30N / mm 2 Larger porous ceramic structures could be fabricated.

[0041] Fig. 8 is a diagram showing the correlation between porosity and compressive strength. Fig. 8 also shows samples H-1 to H-24 among the samples shown in Fig. 6. As shown in the diagram, samples with a porosity of 38% or more and a compressive strength of 30 N / mm 2 Larger porous ceramic structures were identified.

[0042] FIG. 9 shows the XRD patterns obtained by powdering samples S1 and S4 and performing powder X-ray diffraction. 0.8 Gd 0.2 O 1.9 ) peak positions are also shown. As shown in Figure 9, in samples S1 and S4, the GDC (Ce 0.8 Gd 0.2 O 1.9 ) crystal layer could be confirmed.

[0043] FIG. 10 is a diagram showing the behavior of specific surface area, porosity, and compressive strength with respect to firing temperature. In FIG. 10, the specific surface area is plotted as a circle, and the compressive strength is plotted as a diamond. The firing temperatures for samples S1 to S4 were 400°C to 600°C. All of samples S1 to S4 had a specific surface area of 25 m 2 / g and a compressive strength of 30N / mm 2 The porosity was greater than 38%, which means that a high surface area and adequate strength were achieved.

[0044] FIG. 11 shows the results of calculating the crystallite size of each sample. FIG. 11 shows the results of calculating the crystallite size from the XRD results for the above-mentioned samples S1 to S4. In FIG. 11, the horizontal axis represents the crystallite radius and the vertical axis represents the specific surface area, with the theoretical values shown by the dashed lines. As shown in the figure, the values for each sample are approximately consistent with the theoretical values. The theoretical values were calculated using the following formula: S(m 2 / g)=3 / (ρ×r) Here, S(m 2 / g): Specific surface area, ρ(g / cm 3 ): density, r (μm): radius.

[0045] Second Embodiment Fig. 12 is an explanatory diagram conceptually showing the configuration of a catalyst structure 200 of the second embodiment. The catalyst structure 200 of the second embodiment includes a porous ceramic structure 100 as a catalyst support, and a catalyst 110 supported on the porous ceramic structure 100. Although not shown in Fig. 12, the porous ceramic structure 100 has a plurality of pores 20 as shown in Fig. 1.

[0046] The catalyst 110 is not particularly limited and may be appropriately selected from catalytic metals and oxide catalysts depending on the reaction to be carried out using the catalyst structure 200. 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 manganese (Mn), cobalt (Co), nickel (Ni), iron (Fe), copper (Cu), or zinc (Zn). The method for supporting the catalytic metal on the porous ceramic structure 100 is not particularly limited, and various known methods may be used, such as an impregnation method in which the porous ceramic structure 100 is impregnated with a solution containing the catalytic metal and then fired, a coprecipitation method, or an ion exchange method.

[0047] When an oxide catalyst is used as the catalyst, various metal oxide catalysts or composite oxide catalysts such as perovskite-type oxide catalysts can be used. There are no particular limitations on the method for supporting the oxide catalyst on the porous ceramic structure 100, 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.

[0048] Furthermore, since the composite oxide constituting the porous ceramic structure 100 of this embodiment has proton conductivity, catalytic activity can be enhanced by using the porous ceramic structure 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 a hydrogenation reaction of carbon dioxide (a reduction reaction of carbon dioxide) and a reaction that produces hydrogen by a dehydrogenation reaction.

[0049] 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 structure 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.

[0050] CO2+ 6H + + 6e - → CH3OH + H2O … (1) CO2+ 8H + + 8e - → CH4 + 2H2O … (2) CO2+ 2H + + 2e - → HCOOH … (3) CO2+ 2H + + 2e - → CO + HO … (4)

[0051] 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.

[0052] 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)

[0053] The above-described catalytic metals can be activated by applying an electric field. Therefore, when using the catalyst structure 200 including the porous ceramic structure 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 structure 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 makes it possible, for example, to proceed with the reaction involving the exchange of protons described above 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.

[0054] As described above, the catalyst structure 200 of this embodiment uses the porous ceramic structure 100 as a catalyst support, thereby improving handleability compared to powder or granular catalyst supports. Furthermore, as described above, metal electrodes can be provided on both ends of the catalyst structure 200 to form an electric field application catalyst. As described above, since the porous ceramic structure 100 does not contain a binder, changes in the specific surface area and pore size can be suppressed even when the porous ceramic structure 100 is heated during use, such as during a catalyst metal loading process. Furthermore, although the porous ceramic structure 100 does not contain a binder, sufficient strength can be ensured, thereby suppressing cracking of the catalyst structure 200. Furthermore, since the porous ceramic structure 100 does not contain a binder, the specific surface area is sufficiently large and a sufficient reaction field can be secured, thereby improving the catalytic performance of the catalyst structure 200. [Example]

[0055] Several samples of the catalyst structure were prepared, and an electric field was applied to the samples to cause the methanation reaction shown in formula (2) above between carbon dioxide and hydrogen, and the carbon dioxide conversion rate, methane yield, and carbon monoxide yield were investigated. In other words, the several samples are catalysts for methanation reactions. The several samples differ in the composition of the oxide that is the main component of the porous ceramic structure. The specifications of the samples will be described later. The porous ceramic structure of each sample was prepared by the manufacturing method shown in Figure 2.

[0056] Each sample has a porous ceramic structure supporting 0.4 wt% of nickel (Ni) as a catalytic metal. Sample 1 is a comparative catalyst structure, and the oxide that is the main component of the porous ceramic is a single oxide, ceria (CeO2). Samples 2 to 4 are examples of the catalyst structure 200 of the second embodiment, and the oxide that is the main component of the porous ceramic structure 100 is a composite oxide, GDC (Gadolinia-Doped Ceria / Gadolinium-Doped Ceria: gadolinium solid-doped ceria). The doping amount of gadolinium (Gd) as a doping element is 10 mol% for Sample 2, 20 mol% for Sample 3, and 30 mol% for Sample 4. In this example, a commercially available GDC is used as the raw material powder, but Gd may be doped into CeO2 in step P102 shown in FIG. 2 so that the doping amount of Gd is as described above.

[0057] The doping amount (mol%) was determined using XRF (X-ray fluorescence analysis). Each sample was crushed in a mortar, and the powder was quantitatively analyzed, and the output results were converted to mol%. The doping amount was determined after confirming in advance by XRD (X-ray diffraction) that the doping source had formed a solid solution.

[0058] The amount of supported nickel was determined by ICP-AES analysis (inductively coupled plasma atomic emission spectroscopy). The amount of supported nickel (wt%) is the amount of nickel (wt) relative to the total amount (wt) of the catalyst structure 200.

[0059] Fig. 13 is an explanatory diagram showing the configuration of an evaluation apparatus 1000. Fig. 13 illustrates a state in which samples of catalyst structure 200 are placed. As illustrated, each sample has electrodes 250 on both ends. The evaluation apparatus 1000 includes a power source 290 for applying an electric field to the catalyst structure 200, a reaction vessel 300 that houses the catalyst structure 200 therein and has a space for causing a catalytic reaction to proceed, a furnace 400 that houses the reaction vessel therein, a raw material gas supply unit 500 that supplies a mixed gas of carbon dioxide and hydrogen as a raw material gas into the reaction vessel 300, and an analyzer 600 that analyzes the mixed gas containing the product gas generated by the catalytic reaction.

[0060] The reaction vessel 300 is a hollow tube, and has lids 310 at both ends to seal the internal space. The furnace 400 is configured to be able to control the internal temperature, and the power supply 290 is configured to be able to control the current applied to the catalyst structure 200. The analysis device 600 is configured to be able to analyze the composition of the mixed gas discharged from the reaction vessel 300. In this example, a gas chromatograph was used as the analysis device 600.

[0061] The evaluation conditions are as follows: ·Furnace temperature: 250℃ (when no electric field is applied) Furnace pressure: 1 atmosphere Raw material gas flow rate: 50sccm Raw material gas composition: hydrogen (H2) / carbon dioxide (CO2) = 4 Space velocity (SV) of gas in the reactor: 3000 h -1 Current settings: 0, 0.1, 0.5, 1, 2, 3, 4, 5, 10, 15, 20mA (11 conditions)

[0062] After each sample is placed in the evaluation device 1000, a reduction process is performed using a reducing gas instead of the raw material gas. In the reduction process, nickel oxide (NiO) is reduced with hydrogen without applying an electric field to form nickel (Ni). The reduction process conditions are as follows: ·Furnace temperature: 350℃ Furnace pressure: 1 atmosphere Reducing gas flow rate: 60sccm Reducing gas composition: Hydrogen (H2) / Argon (Ar) = 1 / 2 Processing time: 30 minutes

[0063] Figure 14 shows the carbon dioxide conversion rate of each sample. Figure 14(A) is a graph with the horizontal axis representing the applied current (mA) and the vertical axis representing the carbon dioxide conversion rate (%), while Figure 14(B) is a graph with the horizontal axis representing the applied power (W) and the vertical axis representing the carbon dioxide conversion rate (%). Here, the carbon dioxide conversion rate is the proportion of carbon dioxide consumed by the reaction out of the amount of carbon dioxide supplied to the reaction vessel 300.

[0064] Fig. 15 is a diagram showing the maximum carbon dioxide conversion rate of each sample. Fig. 15 shows the maximum carbon dioxide conversion rate (%) when the catalytic reaction is caused by changing the current applied to each sample as shown in Fig. 14, the set current at which the carbon dioxide conversion rate is maximized, the result of calculating the input power from the response voltage, and the actual measured value of the temperature inside the reaction vessel 300. As mentioned above, the target reaction in this example is a methanation reaction, which is an exothermic reaction (ΔH 298 =-165 kJ / mol), the temperature inside the reaction vessel 300 is higher than the set temperature of the furnace 400, 250°C.

[0065] The main component oxide of the porous ceramic structure of Sample 1 is ceria (CeO2), and the doping amount of the doping element is 0 mol%. The main component oxide of the porous ceramic structures 100 of Samples 2 to 4 is GDC, and the doping amounts of the doping element Gd are 10 mol%, 20 mol%, and 30 mol%, respectively.

[0066] 14, the carbon dioxide conversion rate could be improved in all samples by applying an electric field. Furthermore, Samples 2 to 4, in which the oxide of the main component of the porous ceramic structure 100 was a composite oxide doped with a doping element, were able to improve the maximum carbon dioxide conversion rate compared to Comparative Example Sample 1, in which the oxide of the main component was a single oxide, at all doping amounts of 10 mol%, 20 mol%, and 30 mol%.

[0067] From the results shown in Figures 14 and 15, it was confirmed that when the main component of the porous ceramic structure 100 is a composite oxide doped with a doping element, the maximum carbon dioxide conversion rate can be improved compared to when the main component is an oxide not doped with a doping element. Carbon dioxide hydrogenation is a reaction involving the exchange of protons, and proton conductivity is exhibited by the generation of oxygen vacancies in the crystal. It is believed that Samples 2 to 4 were able to improve the maximum carbon dioxide conversion rate compared to Sample 1 because the doping with the doping element increased the number of oxygen vacancies, improving proton conductivity.

[0068] 15, Sample 1 has the smallest maximum carbon dioxide conversion rate despite having the largest input power among Samples 1 to 4. That is, Sample 1 has poorer power efficiency than Samples 2 to 4. This result also suggests that it is preferable to make the porous ceramic structure 100 from a composite oxide doped with a doping element.

[0069] Furthermore, since an improvement in carbon monoxide yield was confirmed for all doping amounts of the doping element ranging from 10 mol% to 30 mol%, it can be said that a doping amount of 10 mol% or more is preferable. Note that doping increases oxygen vacancies, which may improve proton conductivity and allow CO2 adsorption into the oxygen vacancies, so it can be said that even a doping amount of 5 mol% is effective. In other words, a doping amount of 5 mol% or more is preferable.

[0070] 15, among Samples 1 to 4, Sample 4 has the highest maximum carbon dioxide conversion rate and the lowest input power, and therefore has the best power efficiency. Therefore, the most preferable doping amount of the doping element is 30 mol %.

[0071] FIG. 16 shows the methane and carbon monoxide yields for each sample. FIG. 16(A) is a graph with the horizontal axis representing the applied current (mA) and the vertical axis representing the methane yield (%), while FIG. 16(B) is a graph with the horizontal axis representing the applied current (mA) and the vertical axis representing the carbon monoxide yield (%). Here, the yield of each gas is the amount of each gas relative to the amount of mixed gas discharged from the reaction vessel 300. Carbon monoxide is produced by a reaction called the "reverse shift reaction," which is the first step in the stepwise methanation reaction. The reverse shift reaction is the reaction shown in formula (4) above.

[0072] FIG. 17 is a diagram showing the maximum carbon dioxide conversion rate, maximum methane yield, and maximum carbon monoxide yield for each sample.

[0073] As shown in FIG. 16, the application of an electric field improved the methane yield and carbon monoxide yield in all samples. For Samples 2 to 4, the methane yield decreased while the carbon monoxide yield increased when the applied current was 10 mA or higher. For Samples 2 to 4, the selectivity of the reverse shift reaction in the reaction between carbon dioxide and hydrogen increased when the applied current was 10 mA or higher. For Sample 1, both the methane yield and the carbon monoxide yield improved as the applied current increased up to 20 mA. Thus, when the main component of the porous ceramic structure 100 is a composite oxide doped with a doping element, the target reaction can be selectively promoted by changing the applied current.

[0074] 17, Sample 4 achieved the best results in terms of maximum carbon dioxide conversion rate, maximum methane yield, and maximum carbon monoxide yield among Samples 1 to 4. This result also indicates that the most preferable doping amount of the doping element is 30 mol%.

[0075] In Samples 1 to 4, a ceria-based oxide is used as the oxide of the main component of the porous ceramic structure 100, but the same effect can be obtained by using a proton-conductive oxide other than a ceria-based oxide as the main component oxide. In addition, the proton conductivity allows the application of an electric field, which can promote the methanation reaction at low temperatures.

[0076] Although gadolinium is used as the doping element in Samples 1 to 4, the methane and carbon monoxide yields can be similarly improved by using at least one of other rare earth elements and alkaline earth metal elements as the doping element. Proton conductivity is exhibited by the generation of oxygen vacancies in the crystal. For example, since cerium is a +4 element, substituting it with a +3 rare earth element or a +2 alkaline earth metal element generates oxygen vacancies, thereby increasing proton conductivity. As a result, the methanation reaction and the reverse shift reaction can be promoted.

[0077] 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.

[0078] The present disclosure can also be realized in the following forms. [Application example 1] A porous ceramic structure having a plurality of pores and containing a proton-conducting composite oxide as a main component, Does not contain binder Specific surface area is 25m 2 / g or more, and Compression strength is 30N / mm 2 characterized in that it is greater than Porous ceramic structures. [Application example 2] The porous ceramic structure according to Application Example 1, The diameter of the pores is greater than 2 nm, and The porosity is 38% or more. Porous ceramic structures. [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 structure according to any one of Application Examples 1 to 3, The composite oxide is characterized in that ceria (CeO2) is doped with a rare earth element. Porous ceramic structures. [Application example 5] A catalyst structure comprising: A porous ceramic structure according to any one of Application Examples 1 to 3, a catalyst supported on the porous ceramic structure, which promotes 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] The catalyst structure according to Application Example 5, A catalyst structure for a methanation reaction, Catalyst structure. [Explanation of symbols]

[0079] 10...Ceramics section 20...pore 22...Communication hole 100...Porous ceramic structure 110...Catalyst 200...Catalyst structure 250...electrode 290…Power supply 300...Reaction vessel 310…Lid part 400...Furnace 500: Raw material gas supply unit 600…Analyzer 1000...Evaluation device

Claims

1. A porous ceramic structure having a plurality of pores and containing a proton-conducting composite oxide as a main component, Does not contain binder Specific surface area is 25m 2 / g or more, and Compression strength is 30N / mm 2 characterized in that it is greater than Porous ceramic structures.

2. The porous ceramic structure according to claim 1, The diameter of the pores is greater than 2 nm; and The porosity is 38% or more. Porous ceramic structures.

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

4. The porous ceramic structure according to claim 3, The composite oxide is ceria (CeO 2 ) is doped with a rare earth element, Porous ceramic structures.

5. A catalyst structure comprising: The porous ceramic structure according to any one of claims 1 to 4, a catalyst supported on the porous ceramic structure, which promotes a reaction of producing hydrogen by a hydrogenation reaction or a dehydrogenation reaction of carbon dioxide; characterized in that it comprises Catalyst structure.

6. 6. The catalyst structure of claim 5, A catalyst structure for a methanation reaction, Catalyst structure.

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