Honeycomb structure, catalyst, and catalytic reactor

Abstract

This ensures sufficient surface area for catalyst support on the catalyst support, while also achieving higher catalyst reactivity. [Solution] In a honeycomb structure having partition walls that divide a plurality of cells extending in the axial direction, the partition walls are composed of Ce 1-x R1 x O 2-σ It is composed of a porous ceramic body whose main component is a composite oxide represented by (wherein R1 is a rare earth element other than cerium (Ce), x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen deficiency required to obtain electrical neutrality).

Description

[Technical Field]

[0001] This disclosure relates to a honeycomb structure, a catalyst, and a catalytic reactor. [Background technology]

[0002] Conventionally, catalysts that promote various reactions are known in which the catalyst is supported on a carrier. In such catalyst carriers, it is desirable to ensure high gas flowability in order to improve the efficiency of processing the reactant gas. One way to ensure high gas flowability in a catalyst is to use a honeycomb structure as the catalyst carrier. As a honeycomb structure used to process the reactant gas, for example, a honeycomb structure mainly composed of cordierite is known (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-197192 [Overview of the project] [Problems that the invention aims to solve]

[0004] In such catalysts, there is a desire to further improve the efficiency of processing the reactant gas. Regarding the support, there has been a need for a technology that can increase the specific surface area for catalyst support and achieve higher reactivity when used to support various catalysts. [Means for solving the problem]

[0005] This disclosure can be implemented in the following forms: [1] According to one embodiment of the present disclosure, a honeycomb structure is provided which comprises partitions that divide a plurality of cells extending in the axial direction. In this honeycomb structure, the partitions are composed of a material with the composition formula Ce 1-x R1x O 2-σ It is composed of a porous ceramic body whose main component is a composite oxide represented by (where R1 is a rare earth element other than cerium (Ce), x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen vacancy required to obtain electrical neutrality). This form of honeycomb structure material ensures high gas flowability by forming a honeycomb shape, and increases the specific surface area of ​​the honeycomb structure by constructing the partitions of the honeycomb structure with porous ceramic material. Furthermore, by having the porous ceramic material constituting the partitions of the honeycomb structure mainly composed of the composite oxide represented by the above composition formula, proton conductivity and electrical conductivity in the porous ceramic material can be ensured. In addition, oxygen vacancies occur in the ceria-based oxide represented by the above composition formula that constitutes the porous ceramic material, making it easier for oxygen atoms to adsorb onto this ceria-based oxide. As a result, oxygen-containing molecules such as carbon dioxide containing oxygen atoms are more easily adsorbed onto the honeycomb structure, thereby increasing the reactivity of reactions involving oxygen-containing molecules on the honeycomb structure. [2] In the honeycomb structure of the above form, the porosity of the ceramic porous material may be 5% or more and 45% or less. With such a configuration, the specific surface area of ​​the honeycomb structure and the gas flowability on the honeycomb structure can be increased, and the strength of the honeycomb structure can be ensured, making it easier to maintain the structure. [3] In the honeycomb structure of the above form, the average pore diameter of the pores in the porous ceramic material may be 1 μm or less. With such a configuration, it is easy to increase the specific surface area of ​​the honeycomb structure. [4] In the honeycomb structure of the above form, the specific surface area of ​​the porous ceramic body is 5 m². 2 The concentration may be set to be 1 / g or higher. With such a configuration, when using a honeycomb structure as a catalyst support, it becomes possible to support the catalyst in a more dispersed state within the pores of the porous ceramic material, thereby improving catalytic performance. [5] In the honeycomb structure of the above form, the rare earth element may be at least one element selected from the group consisting of gadolinium (Gd), lanthanum (La), and yttrium (Y). With such a configuration, the fabrication of cerium oxide doped with rare earth elements becomes easier, and the ionic conductivity of the ceramic porous material can be improved. [6] In the honeycomb structure of the above form, the opening ratio may be 25% or more and 70% or less. With such a configuration, the gas flowability when gas is flowed in the axial direction of the honeycomb structure can be improved, and the strength of the honeycomb structure can be ensured, making it easier to maintain the structure. [7] In the honeycomb structure of the above form, the cross-sectional shape of the plurality of cells may include one selected from triangle, square, hexagon, octagon, and circle. Such a configuration can improve gas flow when gas is flowed in the axial direction of the honeycomb structure. [8] In the honeycomb structure of the above form, the axial compressive strength may be 5 MPa or more. Such a configuration can increase the durability of the honeycomb structure. [9] In the honeycomb structure of the above embodiment, the ceramic porous body may further contain, in addition to the composite oxide, at least one of aluminum oxide (Al2O3) and silicon oxide (SiO2) as a minor component. With such a configuration, the strength of the honeycomb structure can be increased.

[10] In the honeycomb structure of the above embodiment, the ceramic porous body may further include a fibrous material having an aspect ratio of 3 or more, in addition to the composite oxide. With such a configuration, the strength of the honeycomb structure can be increased.

[11] In the honeycomb structure of the above form, the content of the fibrous material in the porous ceramic body may be 5% by volume or more and 30% by volume or less. With such a configuration, the strength of the honeycomb structure can be increased, and the effects of constructing the porous ceramic body with the composite oxide represented by the composition formula described above as the main component can be ensured.

[12] In the honeycomb structure of the above form, the composition formula Ce 1-x R2 x O 2-σ The composite oxide represented by (wherein R2 is a rare earth element other than cerium (Ce) that is the same type as or different from R1, x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen deficiency required to obtain electrical neutrality) may be the main component, and ceramic particles with a particle size smaller than the average pore diameter of the ceramic porous material may be supported on the surface of the ceramic porous material. With such a configuration, the specific surface area of ​​the honeycomb structure can be further increased, and when the honeycomb structure is used as a catalyst support, the catalyst to be supported can be further dispersed. In addition, the ceramic particles can also have proton conductivity and electrical conductivity, and oxygen-containing molecules can be easily adsorbed, so the reactivity of reactions involving oxygen-containing molecules as reactants can be further increased.

[13] According to another embodiment of the present disclosure, a catalyst is provided, comprising a honeycomb structure as described in any one of [1] to

[12] , and a catalyst supported on the ceramic porous material constituting the honeycomb structure. This form of catalyst enhances gas flowability and specific surface area in the honeycomb structure, while also ensuring proton conductivity and electrical conductivity in the porous ceramic material. Furthermore, the occurrence of oxygen vacancies in the ceria oxide constituting the porous ceramic material facilitates the adsorption of oxygen atoms onto the ceria oxide. This enhances the catalytic activity of the catalyst, and in particular, improves the reactivity of reactions involving oxygen-containing molecules.

[14] In the catalyst of the above form, the catalyst may be a metal catalyst composed of at least one metal selected from the group consisting of nickel (Ni), platinum (Pt), palladium (Pd), and ruthenium (Ru). With such a configuration, the methanation reaction that produces methane from carbon dioxide can be effectively promoted in particular.

[15] In the catalyst carrier of the above form, the catalyst may be an electric field catalyst whose catalytic activity is enhanced by the application of an electric field. With such a configuration, the catalytic activity in the catalyst carrier can be improved, and when a reaction involving proton transfer proceeds, the reaction can proceed under relatively mild conditions (relatively low-temperature conditions or relatively low-pressure conditions).

[16] In the catalyst carrier of the above form, the catalyst may be a methanation reaction catalyst. With such a configuration, the activity of the methanation reaction proceeding in the catalyst carrier can be enhanced.

[17] According to still another form of the present disclosure, a catalytic reaction apparatus is provided. This catalytic reaction apparatus includes the catalyst carrier described in

[13] and an electric field application unit that applies an electric field to the catalyst. According to the catalytic reaction apparatus of this form, the catalytic activity in the catalyst carrier can be improved, and when a reaction involving proton transfer proceeds, the reaction can proceed under relatively mild conditions (relatively low-temperature conditions or relatively low-pressure conditions). The present disclosure can be realized in various forms other than the above. For example, it can be realized in forms such as a method for manufacturing a catalyst carrier, a catalyst carrier, a method for manufacturing a catalyst carrier, a method for hydrogenating carbon dioxide, a method for generating hydrogen by a dehydrogenation reaction, and the like.

Brief Description of the Drawings

[0006] [Figure 1] An explanatory diagram showing the appearance of a honeycomb structure. [Figure 2] An explanatory diagram showing an enlarged cross-section of a ceramic porous body. [Figure 3] An explanatory diagram schematically representing the cross-section of a honeycomb structure. [Figure 4] A flowchart representing a method for manufacturing a honeycomb structure. [Figure 5] An explanatory diagram schematically representing an enlarged state of the honeycomb structure of the second embodiment.

Embodiments for Carrying Out the Invention

[0007] A. First Embodiment: (A-1) Structure of the honeycomb structure FIG. 1 is an explanatory view showing the appearance of a honeycomb structure 10 as a first embodiment of the present disclosure. FIG. 2 is an explanatory view showing an enlarged cross-section of a ceramic porous body 20 constituting the honeycomb structure 10. Specifically, it shows an image (an image enlarged 20,000 times) observed using a scanning electron microscope (SEM).

[0008] The honeycomb structure 10 of the present embodiment is a honeycomb structure including partition walls that define a plurality of cells extending in the axial direction. The partition walls of the honeycomb structure 10 are constituted by a ceramic porous body 20 mainly composed of a composite oxide represented by the following compositional formula (1). However, in the compositional formula (1), R1 is a rare earth element other than cerium (Ce), x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen deficiency for obtaining electrical neutrality.

[0009] Ce 1-x R1 x O 2-σ … (1)

[0010] In the present specification, that a specific component is the "main component" means that the content of the specific component is 50% by mass or more. The honeycomb structure 10 of the present embodiment may further contain other materials in addition to the ceramic. In the ceramic porous body 20 constituting the honeycomb structure 10, the content of the composite oxide represented by the above compositional formula is preferably 90% by mass or more, more preferably 99% by mass or more, and still more preferably 100% by mass from the viewpoint of ensuring the ionic conductivity in the ceramic porous body 20 and enhancing the reactivity when the honeycomb structure 10 is used as a catalyst carrier. Note that the content of the composite oxide represented by the above compositional formula being 100% by mass allows for the presence of inevitable trace components derived from the ceramic raw material. The composition of the honeycomb structure 10 and the content of the above composite oxide in the honeycomb structure 10 can be measured, for example, by inductively coupled plasma mass spectrometry (ICP-MS).

[0011] The composite oxide constituting the honeycomb structure 10 of this embodiment is a ceria-based oxide, as shown in the composition formula (1) described above, which is cerium oxide (CeO2) doped with rare earth elements other than cerium. By doping cerium oxide with rare earth elements, oxygen vacancies are created in this ceria-based oxide, which makes it easier for oxygen atoms to adsorb onto the ceria-based oxide. As a result, oxygen-containing molecules such as carbon dioxide, which contain oxygen atoms, are more easily adsorbed onto the honeycomb structure 10, and the reactivity of reactions involving oxygen-containing molecules on the honeycomb structure 10 is improved.

[0012] In the composite oxide constituting the honeycomb structure 10, by setting the value of x in composition formula (1) to 0.05 or higher, the effect of doping cerium oxide with rare earth elements and creating oxygen vacancies in the ceria-based oxide can be obtained as described above. Furthermore, by setting the value of x in composition formula (1) to 0.3 or lower, it becomes possible to sufficiently solid dissolve the rare earth elements in the crystal lattice of cerium oxide, thereby suppressing the formation of a subphase composed of components different from the composite oxide shown in composition formula (1) in the ceramic constituting the honeycomb structure 10.

[0013] The porosity of the ceramic porous material 20 constituting the partitions of the honeycomb structure 10 in this embodiment is preferably 5% or more, from the viewpoint of increasing the specific surface area of ​​the honeycomb structure 10 and improving gas flow on the honeycomb structure 10. Furthermore, the porosity of the ceramic porous material 20 constituting the partitions of the honeycomb structure 10 is preferably 45% or less, from the viewpoint of ensuring the strength of the honeycomb structure 10 and facilitating structural maintenance. The porosity of the ceramic porous material 20 described above represents the total porosity, which is the sum of the ratio of open pore volume and the ratio of closed pore volume. The porosity of the ceramic porous material 20 can be measured by the Archimedes method.

[0014] In this embodiment, the average pore diameter of the ceramic porous material 20 constituting the partition walls of the honeycomb structure 10 is preferably 1 μm or less, from the viewpoint of increasing the specific surface area of ​​the honeycomb structure 10. Alternatively, the average pore diameter of the ceramic porous material 20 can be, for example, 5 nm or more. The average pore diameter of the ceramic porous material 20 can be measured by methods such as mercury intrusion or gas adsorption, depending on the size of the pores in the ceramic porous material 20 being measured.

[0015] The specific surface area of ​​the ceramic porous body 20 that constitutes the partition wall of the honeycomb structure 10 in this embodiment is 5 m². 2 It is desirable that the specific surface area is 1 / g or more. The specific surface area of ​​the porous ceramic body 20 can be evaluated using the BET method, and the BET specific surface area is the surface area per unit weight (m²). 2 The values ​​are expressed in units of g. Such a specific surface area in the ceramic porous material 20 that constitutes the partitions of the honeycomb structure 10 can be easily achieved by adopting the numerical ranges described above as the porosity and average pore diameter of the ceramic porous material 20. When the honeycomb structure 10 is used as a catalyst support, achieving the above-mentioned specific surface area makes it possible to support the catalyst in a more dispersed state within the pores of the ceramic porous material 20, thereby improving the catalytic performance.

[0016] In the composite oxide of compositional formula (1) provided by the honeycomb structure 10 of this embodiment, it is desirable that the rare earth element R1 is at least one element selected from the group consisting of gadolinium (Gd), lanthanum (La), and yttrium (Y). Among the rare earth elements, these three elements have ionic radii that are closer to those of cerium. Therefore, rare earth elements are more easily doped into cerium oxide, and ceria-based oxides with oxygen deficiencies can be more easily produced. As a result, it becomes easier to increase the ionic conductivity of the ceramic porous body 20, specifically, for example, the proton conductivity. When such a honeycomb structure 10 is used as a catalyst support, the increased ionic conductivity in the catalyst support enhances its ability to promote the progress of reactions involving the transfer of ions.

[0017] In this embodiment, the opening ratio of the honeycomb structure 10 is preferably 25% or more from the viewpoint of ensuring gas flow in the honeycomb structure 10. By ensuring a large opening ratio of the honeycomb structure 10, gas flow when gas is flowed in the axial direction of the honeycomb structure can be improved. Furthermore, the opening ratio of the honeycomb structure 10 is preferably 70% or less from the viewpoint of ensuring the strength of the honeycomb structure 10 and facilitating structural maintenance.

[0018] Figure 3 is a schematic diagram illustrating a cross-section of the honeycomb structure 10 perpendicular to the axial direction. As shown in Figure 3, the honeycomb structure 10 is equipped with partition walls 14 made of a ceramic porous material 20, and within the honeycomb structure 10, the partition walls 14 divide and form a plurality of cells 12 that extend in the axial direction. In Figure 3, as an example, the shape of the opening of the cell 12 in the above cross-section is shown to be rectangular.

[0019] The aperture ratio of the honeycomb structure 10 can be determined as follows. First, the openings of each cell 12 are filled with resin on a plane perpendicular to the axial direction of the honeycomb structure 10. Then, the resin-filled surface is polished to make the surface flat, and the polished surface is imaged using an SEM (scanning electron microscope). The obtained image is binarized using image analysis software, and the aperture ratio is determined by calculating the area ratio of the cell 12 openings to the cross-section of the honeycomb structure 10. At this time, by using general-purpose software such as ImageJ as the image analysis software, edge detection in the image, area quantification, and area ratio calculation can be easily performed. The aperture ratio of the honeycomb structure 10 can be expressed by the following equation (2).

[0020] Opening ratio (%) = [(Cross-sectional area of ​​honeycomb structure - Area occupied by partitions within the cross-sectional area of ​​honeycomb structure) / Cross-sectional area of ​​honeycomb structure] × 100 … (2)

[0021] Here, if the size of the opening of a cell 12 in the cross-section of the honeycomb structure 10 is expressed by the average value of the diameters of circles with the same area as the opening of the cell (hereinafter also referred to as "cell diameter"), the cell diameter can be, for example, 0.5 mm or more from the viewpoint of ensuring gas flowability. Also, from the viewpoint of ensuring the specific surface area of ​​the honeycomb structure 10, the cell diameter can be, for example, 2.0 mm or less, and preferably 1.0 mm or less. Furthermore, the width of the partition wall 14 that divides the cell 12 in the cross-section of the honeycomb structure 10 (hereinafter also referred to as "partition wall thickness t") can be, for example, 0.1 mm or more from the viewpoint of ensuring the strength of the honeycomb structure 10. Also, from the viewpoint of ensuring the specific surface area of ​​the honeycomb structure 10, the partition wall thickness t can be, for example, 1.0 mm or less, and preferably 0.4 mm or less.

[0022] The cross-sectional shapes of the multiple cells 12 that open in the cross-section of the honeycomb structure 10 in this embodiment can include, for example, any one selected from triangles, squares, hexagons, octagons, and circles. Figure 3 shows an example where the cross-sectional shape of the cells 12 is square in areas other than the outer periphery where the shape is restricted by the outer periphery of the partition wall 14. As described above, various shapes can be adopted for the cross-sectional shape of the cells 12, but as shown in Figure 3, a shape in which the cross-sectional shapes of the cells 12 are uniform overall and arranged at regular intervals is desirable from the viewpoint of increasing the specific surface area of ​​the honeycomb structure 10.

[0023] Regarding the honeycomb structure 10, for example, in order to fix the honeycomb structure 10 to a reactor for supplying gas to the honeycomb structure 10 and allowing the reaction to proceed, a configuration can be considered in which the honeycomb structure 10 is axially penetrated by a connecting rod attached to the reactor. In such a case, cells with a different shape from the gas-flowing cells 12 may be further provided in the honeycomb structure 10 as holes through which the connecting rod penetrates.

[0024] In this embodiment, the axial compressive strength of the honeycomb structure 10 is preferably 5 MPa or higher. This increases the durability of the honeycomb structure 10. However, the axial compressive strength of the honeycomb structure 10 in this embodiment can usually be, for example, 75 MPa or less. The compressive strength of the honeycomb structure 10 can be measured by applying a compressive force perpendicular to the bottom surface (flat surface) of the ceramic porous body 20 constituting the honeycomb structure 10 using an autograph (e.g., AGS-X: Shimadzu Corporation) at an operating speed of 0.5 mm / min.

[0025] The ceramic porous body 20 constituting the honeycomb structure 10 of this embodiment may further contain at least one of aluminum oxide (Al2O3) and silicon oxide (SiO2) as a minor component, in addition to the composite oxide represented by composition formula (1). By adopting such a configuration, the strength of the honeycomb structure 10 can be increased.

[0026] The ceramic porous body 20 constituting the honeycomb structure 10 of this embodiment may further include a fibrous material having an aspect ratio of 3 or more, in addition to the composite oxide represented by composition formula (1). This configuration can increase the strength of the honeycomb structure 10. One of the factors that reduces the strength of the honeycomb structure 10 is the occurrence and propagation of cracks at grain boundaries within the ceramic porous body 20. By including a fibrous material in the ceramic porous body 20, the propagation of cracks within the ceramic porous body 20 is suppressed by the fibrous material, and as a result, the strength of the honeycomb structure 10 can be increased. Here, "aspect ratio" means the value obtained by dividing the length of the major axis (major axis L) of the fibrous material by the length of the minor axis (minor axis W) (L / W). The fiber diameter of the fibrous material used can be, for example, 1 to 10 μm, and preferably 3 to 5 μm.

[0027] The fibrous material contained in the porous ceramic body 20 may be made of materials that do not disappear during the firing process when manufacturing the honeycomb structure 10, such as ceramic materials, carbon materials, metal materials, or combinations thereof. The ceramic material constituting the fibrous material can be, for example, at least one of aluminum oxide (Al2O3) and silicon oxide (SiO2). When the fibrous material is made of a mixture of aluminum oxide and silicon oxide, the mixing ratio of aluminum oxide to silicon oxide (Al2O3 / SiO2) can be, for example, 80 / 20 to 97 / 3.

[0028] The fibrous material content in the porous ceramic body 20 is preferably 5% by volume or more, from the viewpoint of ensuring the effect of increasing the strength of the honeycomb structure 10. Furthermore, the fibrous material content in the porous ceramic body 20 can be 30% by volume or less, from the viewpoint of ensuring the effect of constructing the porous ceramic body 20 with the composite oxide represented by the aforementioned compositional formula as the main component. The above-mentioned volume ratio in the porous ceramic body 20 can be determined by measuring the area ratio of the fibrous material in the cross-section of the porous ceramic body 20. Specifically, for example, after embedding the porous ceramic body 20 in resin, a polished cross-section of the porous ceramic body 20 is obtained using a cross-section polisher (registered trademark), and the above-mentioned volume ratio can be determined by performing electron microscope observation and EPMA (electron probe microanalyzer) analysis to determine the area ratio of each part. If the porous ceramic body 20 has randomly arranged fibrous material, for example, five random images of the cross-section of the porous ceramic body 20 can be taken, and the area ratio of the fibrous material can be determined as described above, and the average value can be calculated, which can then be considered as the volume ratio of the fibrous material.

[0029] (A-2) Method for manufacturing a honeycomb structure: Figure 4 is a flowchart showing the manufacturing method of the honeycomb structure 10. To manufacture the honeycomb structure 10, first, a raw material powder containing a composite oxide represented by composition formula (1) is prepared (step T100). For example, when producing a honeycomb structure 10 containing the aforementioned auxiliary components and fibrous materials, a raw material powder containing the auxiliary components and fibrous materials, in addition to the composite oxide represented by composition formula (1), should be prepared. Then, a binder is added to the raw material powder prepared in step T100 to produce a slurry (step T110). The binder used can be any binder that can be removed in a later step by decomposition, etc. For example, an organic binder such as an acrylic binder or a polyethylene oxide binder can be used. After that, the slurry is molded to produce a honeycomb-shaped molded body (step T120). In step T120, the molding method is not particularly limited as long as it is possible to mold it into a honeycomb shape. For example, extrusion molding can be suitably employed. After step T120, the resulting honeycomb-shaped molded body is fired to complete the honeycomb structure 10 (step T130). During firing, the binder contained in the molded body disappears, and after firing, a porous fired honeycomb structure 10 is obtained.

[0030] To achieve the desired porosity and average pore size in the honeycomb structure 10, for example, the particle size of the raw material powder prepared in process T100 and the firing conditions in process T130 can be appropriately adjusted. In the composite oxide represented by compositional formula (1), the sinterability of the composite oxide changes depending on the type of rare earth element doped into the cerium oxide. Therefore, the particle size of the raw material powder and the firing conditions can be appropriately set according to the rare earth element to be doped.

[0031] The smaller the particle size of the raw material powder, the easier it is to reduce the porosity and average pore diameter of the ceramic porous body 20. The particle size of the raw material powder can be, for example, 20 nm or larger. Alternatively, the particle size of the raw material powder can be, for example, 5 μm or less, and preferably 300 nm or less.

[0032] Furthermore, during firing, necking occurs between the powder particles constituting the raw material powder, and the gaps between the powder particles gradually become smaller. Therefore, by adjusting the firing conditions, especially the firing temperature, the size of the gaps between the powder particles can be controlled to achieve the desired porosity and average pore diameter. The firing temperature can be, for example, 300°C or higher, and preferably 400°C or higher. Alternatively, the firing temperature can be, for example, 1600°C or lower, and preferably 1000°C or lower. As a result, as shown in Figure 2, a ceramic porous body 20 is produced that is formed from fine particles and has a structure containing many pores.

[0033] (A-3) Catalysts with a honeycomb structure: A catalyst can be constructed by placing a catalyst on the surface of the ceramic porous body 20 that constitutes the honeycomb structure 10 of this embodiment. There are no particular restrictions on the catalyst placed on the surface of the ceramic porous body 20; a catalyst metal or oxide catalyst can be appropriately selected depending on the type of reaction to be promoted using the catalyst.

[0034] When a catalytic metal is used as a catalyst, the catalytic metal may be a noble metal such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), or osmium (Os), or a base metal such as cobalt (Co), nickel (Ni), iron (Fe), or copper (Cu). There are no particular restrictions on the method of supporting the catalytic metal on the honeycomb structure 10, and various known methods can be used, such as an impregnation method in which the honeycomb structure 10 is impregnated with a solution containing the catalytic metal and then calcined, or a coprecipitation method or an ion exchange method.

[0035] Furthermore, 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 restrictions on the method of supporting the oxide catalyst on the honeycomb structure 10, and various known methods can be used. For example, when a composite oxide catalyst is used as the oxide catalyst, methods such as the solid-phase reaction method, coprecipitation method, Pechini method, citrate complex method, and sol-gel method can be used.

[0036] For example, when using a catalyst to promote the methanation reaction described later, it is desirable to use a metal catalyst composed of at least one metal selected from the group consisting of nickel (Ni), platinum (Pt), palladium (Pd), and ruthenium (Ru).

[0037] Furthermore, the composite oxide represented by compositional formula (1) that constitutes the honeycomb structure 10 of this embodiment has both electrical conductivity and proton conductivity. Therefore, by using the honeycomb structure 10 as a support for a catalyst that promotes reactions involving the transfer of protons, catalytic activity can be enhanced. Examples of reactions involving the transfer of protons include the hydrogenation reaction (reduction reaction) of carbon dioxide, or the reaction that produces hydrogen through dehydrogenation. In particular, the composite oxide represented by compositional formula (1) that constitutes the honeycomb structure 10 of this embodiment is a ceria-based oxide, which is cerium oxide (CeO2) doped with a rare earth element. By doping cerium oxide with a rare earth element, oxygen vacancies are created in this ceria-based oxide, which makes it easier for oxygen atoms to adsorb onto the ceria-based oxide. As a result, carbon dioxide containing oxygen atoms is more easily adsorbed onto the honeycomb structure 10, and the effect of improving the reactivity of the hydrogenation reaction of carbon dioxide is enhanced. Furthermore, in reactions that generate hydrogen through dehydrogenation, oxygen-containing molecules such as water and oxygen are involved in the reaction. Therefore, by using the honeycomb structure 10 of this embodiment as a catalyst support, a similar effect of improving reactivity can be obtained.

[0038] Examples of hydrogenation reactions of carbon dioxide include, for example, the reaction that produces organic substances such as hydrocarbons and alcohols from carbon dioxide. Examples of such reactions include the reaction that produces methanol from carbon dioxide, shown in equation (1) below, the reaction that produces methane from carbon dioxide (methanization reaction), shown in equation (2) below, and the reaction that produces formic acid from carbon dioxide, shown in equation (3) below. Another example of a hydrogenation reaction of carbon dioxide is the reaction that produces carbon monoxide from carbon dioxide. Such a reaction is shown in equation (4) below.

[0039] CO2+ 6H + + 6e - → CH3OH + H2O … (1) CO2+ 8H + + 8e - → CH4 + 2H2O … (2) CO2 + 2H + + 2e - → HCOOH … (3) CO2 + 2H + + 2e - → CO + H2O … (4)

[0040] Examples of reactions that produce hydrogen through dehydrogenation include the dehydrogenation of hydrocarbons and alcohols. Specifically, examples include reactions that produce hydrogen from hydrocarbons and alcohols through steam reforming and partial oxidation reactions. Below, as an example of such a reaction, 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 carbon monoxide and water vapor produced in the partial oxidation reaction is shown in equation (7). Furthermore, as examples of reactions that produce hydrogen from alcohols, the steam reforming reaction of methanol is shown in equation (8), the steam reforming reaction of ethanol is shown in equation (9), and the partial oxidation reaction of methanol is shown in equation (10). All of these reactions involve the transfer of protons.

[0041] 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)

[0042] The catalyst metal described above can be activated by applying an electric field. Therefore, the effect of activating the catalytic reaction can be further enhanced by using a catalytic reaction apparatus that includes the catalyst of this embodiment described above and an electric field application unit for applying an electric field to the catalyst of the catalyst. In a catalytic reaction apparatus using a catalyst comprising a honeycomb structure 10, for example, an electric field application unit can be provided that applies an electric field to the catalyst layer by providing a pair of electrodes that come into contact with the catalyst layer formed on the catalyst. This makes it possible to improve catalytic activity by utilizing the applied electrical energy. In particular, since the composite oxide represented by composition formula (1) of the honeycomb structure 10 of this embodiment has proton conductivity, applying an electric field makes, for example, proton conduction on the surface of the composite oxide more pronounced, making it possible to enhance catalytic activity. Furthermore, in the catalyst of this embodiment, since a single structure, the honeycomb structure 10, is used as the catalyst support, the stability of the current can be improved when applying an electric field to the catalyst layer. This makes it possible to carry out reactions involving the transfer of protons, as described above, under relatively mild conditions (relatively low temperature or relatively low pressure). However, the catalyst may be used without applying an electric field.

[0043] As described above, the honeycomb structure 10 of this embodiment ensures high gas flowability by adopting a honeycomb shape, and the specific surface area of ​​the honeycomb structure 10 can be increased by constructing the partitions of the honeycomb structure 10 with ceramic porous material 20. Here, the ceramic porous material 20 constituting the partitions of the honeycomb structure 10 is mainly composed of a composite oxide represented by composition formula (1), thereby ensuring proton conductivity and electrical conductivity in the ceramic porous material 20. Furthermore, oxygen vacancies occur in the ceria-based oxide constituting the ceramic porous material 20, making it easier for oxygen atoms to adsorb onto the ceria-based oxide. This makes it easier for oxygen-containing molecules such as carbon dioxide containing oxygen atoms to adsorb onto the honeycomb structure 10, improving the reactivity of reactions involving oxygen-containing molecules on the honeycomb structure 10.

[0044] B. Second Embodiment: In addition to the ceramic porous body 20 that constitutes the honeycomb structure 10 of the first embodiment, ceramic particles may be further supported on the surface of the ceramic porous body to form a honeycomb structure. Such a honeycomb structure 110 will be described below as a second embodiment.

[0045] Figure 5 is a schematic diagram illustrating a magnified view of a portion of the surface of the honeycomb structure 110 of the second embodiment. The honeycomb structure 110 supports ceramic particles 130 with a particle size smaller than the average pore diameter of the pores of the ceramic porous body 120, on the surface of a ceramic porous body 120 similar to the ceramic porous body 20 of the first embodiment. The ceramic particles 130 mainly consist of a composite oxide represented by the composition formula (3) shown below. However, in composition formula (3), R2 is a rare earth element other than cerium (Ce) that is the same type as R1 in composition formula (1) or a different type, x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen deficiency required to obtain electrical neutrality. It is desirable that R2 is the same type of rare earth element as R1.

[0046] Ce 1-x R2 x O2-σ … (3)

[0047] The particle size of the ceramic particles 130 is not particularly limited as long as it is smaller than the average pore diameter of the pores in the porous ceramic body 120, but it is desirable to have a particle size of 10 nm or larger, for example. Furthermore, it is desirable for the particle size of the ceramic particles 130 to be 500 nm or less, and more preferably 100 nm or less.

[0048] Such a honeycomb structure 110 can be fabricated by first creating a porous ceramic body 120 in the same manner as in Figure 4, and then supporting ceramic particles 130 on the porous ceramic body 120. Specifically, a slurry is prepared by mixing the ceramic particles 130 with any solvent such as ethanol, and the prepared slurry is used to coat the porous ceramic body 120 by a dip method or the like. At this time, the thickness of the coating layer containing the ceramic particles 130 can be adjusted by the number of coatings. After that, the solvent is removed by a drying process, and the honeycomb structure 110 is completed by firing at a lower temperature than the firing temperature used to fabricate the porous ceramic body 120 in step T130. By firing at the low temperature described above, necking can be formed between the ceramic particles 130.

[0049] This configuration allows for an even higher specific surface area in the honeycomb structure 110, and when the honeycomb structure 110 is used as a catalyst support, the supported catalyst can be even more dispersed. As a result, the reactivity of the catalyst can be enhanced. In this case, since the ceramic particles 130 are mainly composed of a composite oxide represented by composition formula (2), proton conductivity and electrical conductivity can be ensured in the ceramic particles 130 as well, thereby enhancing the adsorption of oxygen-containing molecules.

[0050] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-mentioned problems, or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

[0051] This disclosure can also be implemented in the following forms: [Application Example 1] A honeycomb structure comprising partition walls that divide a plurality of cells extending in the axial direction, The aforementioned partition wall is composed of Ce 1-x R1 x O 2-σ It is characterized by being composed of a porous ceramic body whose main component is a composite oxide represented by (wherein R1 is a rare earth element other than cerium (Ce), x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen deficiency required to obtain electrical neutrality). Honeycomb structure. [Application Example 2] The honeycomb structure described in Application Example 1, The ceramic porous material is characterized in that its porosity is 5% or more and 45% or less. Honeycomb structure. [Application Example 3] A honeycomb structure as described in Application Example 1 or 2, The ceramic porous material is characterized in that the average pore diameter is 1 μm or less. Honeycomb structure. [Application Example 4] A honeycomb structure as described in any one of the application examples 1 to 3, The specific surface area of ​​the aforementioned porous ceramic material is 5 m². 2 Characterized by being 1 / g or more Honeycomb structure. [Application Example 5] A honeycomb structure as described in any one of the application examples 1 to 4, The aforementioned rare earth element is characterized by being at least one element selected from the group consisting of gadolinium (Gd), lanthanum (La), and yttrium (Y). Honeycomb structure. [Application Example 6] A honeycomb structure as described in any one of the application examples 1 to 5, It is characterized by having an aperture ratio of 25% or more and 70% or less. Honeycomb structure. [Application Example 7] A honeycomb structure as described in any one of the application examples 1 to 6, The cross-sectional shape of the plurality of cells is characterized by including one selected from a triangle, a square, a hexagon, an octagon, and a circle. Honeycomb structure. [Application Example 8] A honeycomb structure according to any one of the application examples 1 to 7, The axial compressive strength is 5 MPa or more. Honeycomb structure. [Application Example 9] A honeycomb structure according to any one of the application examples 1 to 8, The porous ceramic material is characterized in that, in addition to the composite oxide, it further contains at least one of aluminum oxide (Al2O3) and silicon oxide (SiO2) as a minor component. Honeycomb structure. [Application Example 10] A honeycomb structure according to any one of the application examples 1 to 9, The porous ceramic material is characterized by further containing, in addition to the composite oxide, a fibrous material having an aspect ratio of 3 or more. Honeycomb structure. [Application Example 11] The honeycomb structure described in Application Example 10, The ceramic porous body is characterized in that the content of the fibrous material is 5% by volume or more and 30% by volume or less. Honeycomb structure. [Application Example 12] A honeycomb structure according to any one of the application examples 1 to 11, Composition formula Ce 1-x R2 x O 2-σ The ceramic porous material is characterized in that it is mainly composed of a composite oxide represented by (wherein R2 is a rare earth element other than cerium (Ce) that is the same or different from R1, x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen deficiency required to obtain electrical neutrality), and ceramic particles with a particle size smaller than the average pore diameter of the pores of the ceramic porous material are supported on the surface of the ceramic porous material. Honeycomb structure. [Application Example 13] A catalyst, A honeycomb structure described in any one of the application examples 1 to 12, A catalyst supported on the porous ceramic material constituting the honeycomb structure, Features that Catalyst body. [Application Example 14] The catalyst described in Application Example 13, The catalyst is characterized by being a metal catalyst composed of at least one metal selected from the group consisting of nickel (Ni), platinum (Pt), palladium (Pd), and ruthenium (Ru). Catalyst body. [Application Example 15] A catalyst as described in Application Example 13 or 14, The catalyst is characterized in that it is an electric field catalyst whose catalytic activity is enhanced by the application of an electric field. Catalyst body. [Application Example 16] A catalyst according to any one of the application examples 13 to 15, The catalyst is characterized by being a methanation reaction catalyst. Catalyst body. [Application Example 17] A catalytic reactor, A catalyst described in any one of the application examples 13 to 16, An electric field application unit for applying an electric field to the catalyst, Features that Catalytic reactor. [Explanation of symbols]

[0052] 10,110…Honeycomb structure 12...Cell 14...Bulkhead 20,120…Ceramic porous material 130…Ceramic particles

Claims

1. A honeycomb structure having partition walls that divide a plurality of cells extending in the axial direction, The aforementioned partition wall has the composition formula Ce １－ｘ R1 ｘ O ２－σ It is characterized by being composed of a porous ceramic body whose main component is a composite oxide represented by (wherein R1 is a rare earth element other than cerium (Ce), x satisfies 0.05 ≤ x ≤ 0.30, and σ represents the amount of oxygen deficiency required to obtain electrical neutrality). Honeycomb structure.

2. A honeycomb structure according to claim 1, The ceramic porous material is characterized in that its porosity is 5% or more and 45% or less. Honeycomb structure.

3. A honeycomb structure according to claim 1, The ceramic porous material is characterized in that the average pore diameter is 1 μm or less. Honeycomb structure.

4. A honeycomb structure according to claim 1, The specific surface area of ​​the aforementioned porous ceramic material is 5 m². ２ Characterized by being 1 / g or more Honeycomb structure.

5. A honeycomb structure according to claim 1, The rare earth element is characterized by being at least one element selected from the group consisting of gadolinium (Gd), lanthanum (La), and yttrium (Y). Honeycomb structure.

6. A honeycomb structure according to claim 1, It is characterized by having an opening ratio of 25% or more and 70% or less. Honeycomb structure.

7. A honeycomb structure according to claim 1, The cross-sectional shape of the plurality of cells is characterized by including one selected from a triangle, a square, a hexagon, an octagon, and a circle. Honeycomb structure.

8. A honeycomb structure according to claim 1, The axial compressive strength is 5 MPa or more. Honeycomb structure.

9. A honeycomb structure according to claim 1, The aforementioned porous ceramic material further contains, in addition to the composite oxide, aluminum oxide (Al ２ O ３ ) and silicon dioxide (SiO ２ ) is characterized by containing at least one of the following as a minor component. Honeycomb structure.

10. A honeycomb structure according to claim 1, The porous ceramic material is characterized in that, in addition to the composite oxide, it further contains a fibrous material having an aspect ratio of 3 or more. Honeycomb structure.

11. A honeycomb structure according to claim 10, The ceramic porous body is characterized in that the content of the fibrous material is 5% by volume or more and 30% by volume or less. Honeycomb structure.

12. A honeycomb structure according to claim 1, Composition formula Ce １－ｘ R2 ｘ O ２－σ (However, R2 is a rare earth element other than cerium (Ce) that is the same or different from the aforementioned R1, x satisfies 0.05 ≦ x ≦ 0.30, and σ represents the amount of oxygen deficiency for obtaining electrical neutrality), and ceramic particles having a particle size smaller than the average pore diameter of the pores of the ceramic porous body are supported on the surface of the ceramic porous body Honeycomb structure.

13. A catalyst, A honeycomb structure according to any one of claims 1 to 12, A catalyst supported on the porous ceramic material constituting the honeycomb structure, Features that Catalyst body.

14. The catalyst according to claim 13, The catalyst is characterized by being a metal catalyst composed of at least one metal selected from the group consisting of nickel (Ni), platinum (Pt), palladium (Pd), and ruthenium (Ru). Catalyst body.

15. The catalyst according to claim 13, The catalyst is characterized by being an electric field catalyst, in which catalytic activity is enhanced by the application of an electric field. Catalyst body.

16. The catalyst according to claim 13, The catalyst is characterized by being a methanation reaction catalyst. Catalyst body.

17. A catalytic reactor, The catalyst according to claim 13, An electric field application unit for applying an electric field to the catalyst, Features that Catalytic reactor.

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