Reforming catalyst

Abstract

Provided is a catalyst that is used while having an electric field applied thereto, and that is capable of causing a catalytic reaction at a lower reaction temperature compared to conventional products. This catalyst is used while having an electric field applied thereto, and comprises: a porous honeycomb substrate; and a catalyst layer that covers the surface of the honeycomb substrate. A high-resistance layer having an electrical resistivity higher than that of the catalyst layer is provided between the honeycomb substrate and the catalyst layer.

Description

reforming catalyst

[0001] The present disclosure relates to reforming catalysts, and in particular to electric field reforming catalysts.

[0002] In recent years, electrocatalysis, which is used by applying an electric field, has become known (see, for example, Patent Document 1). Electrocatalysis, which is used by applying electrical energy, can induce catalytic reactions at lower temperatures than conventional catalysts, and has therefore attracted attention as a new type of catalyst.

[0003] The electric field catalyst disclosed in Patent Document 1 is a catalyst that has a catalyst layer formed on a honeycomb-structured support made of an insulating material, and that promotes a reaction by bringing electrodes into contact with the support and / or the catalyst layer and applying an electric field. The catalyst layer is formed by sintering catalyst particles that have a catalyst metal supported on carrier particles made of mixed ionic and electronic conductive ceramic, and the inter-catalyst resistivity at 450°C measured between the electrodes is 50 Ω·m or more and 270 Ω·m or less.

[0004] JP 2017-87088 A

[0005] In catalytic steam reforming and the like, if the catalytic reaction could be caused to occur at a lower temperature, there is an advantage in that the heat resistance temperature required for the reactor can be set lower. In Patent Document 1, the lower limit of the reaction temperature for steam reforming using an electric field catalyst is set at 450°C, and there is a demand for an electric field catalyst that can cause the catalytic reaction to occur at an even lower temperature (for example, 300°C).

[0006] One object of an embodiment of the present invention is to provide a catalyst that is used by applying an electric field and that can cause a catalytic reaction at a lower reaction temperature than conventional catalysts.

[0007] A first aspect of the present invention is a catalyst that is used by applying an electric field, and includes a porous honeycomb substrate and a catalyst layer covering the surface of the honeycomb substrate, and a high-resistivity layer having a higher electrical resistivity than the catalyst layer is provided between the honeycomb substrate and the catalyst layer.

[0008] A second aspect of the present invention is the catalyst according to the first aspect, wherein the electrical resistivity of the high-resistance layer is at least twice as high as the electrical resistivity of the catalyst layer.

[0009] A third aspect of the present invention is the catalyst according to the first or second aspect, wherein the honeycomb substrate has porous holes on the surface thereof, and at least a portion of the holes is filled with the high-resistance layer.

[0010] A fourth aspect of the present invention is the catalyst according to any one of the first to third aspects, wherein the catalyst layer is made of an electric field catalyst material containing Ru, Ba, Zr, Y, and O, and the high-resistance layer is made of an insulating material containing Ba, Zr, Y, and O.

[0011] The catalyst according to the embodiment of the present invention can cause a catalytic reaction at a lower reaction temperature than conventional catalysts by applying an electric field to the catalyst.

[0012] Fig. 1 is a schematic cross-sectional view illustrating a catalyst according to an embodiment of the present invention. Fig. 2 is a partially enlarged cross-sectional view of region A in Fig. 1. Fig. 3 is a partially enlarged cross-sectional view of region B in Fig. 2. Fig. 4 is a partially enlarged cross-sectional view illustrating a catalyst according to a first modified example. Fig. 5 is a partially enlarged cross-sectional view illustrating a catalyst according to a second modified example. Fig. 6 is a schematic view showing an example of a reaction apparatus used in a gas reforming method using a catalyst.

[0013] A particular challenge with electric field catalysts is how to utilize the applied electrical energy to activate the catalytic reaction. To solve this problem, Patent Document 1 proposes controlling the inter-catalyst resistivity at 450°C to between 50 Ω·m and 270 Ω·m. "450°C" is considered to be the lower limit of the reaction temperature for the steam reforming reaction, and Patent Document 1 also assumes that the catalytic reaction occurs at 450°C or higher. Furthermore, a reaction temperature of 450°C is a temperature at which the catalytic reaction proceeds to some extent even when the power applied to the electric field catalyst is 0 W (i.e., when no electric field is applied).

[0014] The present inventors have conducted extensive research to obtain an electric field catalyst that can realize a steam reforming reaction or the like even at lower reaction temperatures, particularly at reaction temperatures (e.g., 300°C) so low that the catalytic reaction does not proceed when an applied power of 0 W is applied. As a result, they discovered that by providing a high-resistance layer with higher electrical resistance than the catalyst layer between the substrate and the catalyst layer, the catalytic reaction can be achieved even at low reaction temperatures, which led to the completion of the present invention.

[0015] The catalyst according to the embodiment will be described in detail below.

[0016] (Catalyst 100) FIG. 1 is a schematic cross-sectional view of a catalyst 100 according to an embodiment of the present invention. FIG. 2 is a partially enlarged cross-sectional view of region A in FIG. 1 . FIG. 3 is a partially enlarged cross-sectional view of region B in FIG. 2 . The catalyst 100 is a so-called electric field catalyst that is used by applying an electric field. The catalyst 100 includes a porous honeycomb substrate 110 and a catalyst layer 130 covering a surface 110s of the honeycomb substrate 110. The honeycomb substrate 110 shown in FIG. 1 has a cylindrical outer shape and includes a large number of cells 150 (gas passages through which the gas to be treated passes). The cells 150 extend in the axial direction of the cylindrical shape (perpendicular to the plane of FIG. 1 ). The honeycomb substrate 110 shown in FIG. 1 is a type having cells 150 with rectangular cross sections. Honeycomb substrates with cells having hexagonal or circular cross sections are also known. Adjacent cells 150 are separated from each other by partition walls 160.

[0017] In this specification, the "surface 110s of the honeycomb substrate 110" refers to the inner surface of the cell 150 of the honeycomb substrate 110, that is, the surface of the partition wall 160. The gas to be treated passing through the cell 150 comes into contact with the surface 110s of the honeycomb substrate 110. Therefore, by forming the catalyst layer 130 so as to cover the surface 110s, the gas to be treated comes into contact with the catalyst layer 130, thereby accelerating gas treatment.

[0018] The catalyst 100 according to the embodiment has a high resistance layer 120 provided between a honeycomb substrate 110 and a catalyst layer 130. The high resistance layer 120 has a higher electrical resistivity than the catalyst layer 130.

[0019] By providing the high resistance layer 120 between the honeycomb substrate 110 and the catalyst layer 130, it is possible to concentrate current in the catalyst layer 130 when an electric field is applied to the catalyst 100. In other words, because electrical energy is concentrated in the catalyst layer 130, the electrical energy is efficiently used for the catalytic reaction that occurs in the catalyst layer 130. As a result, it is possible to cause a catalytic reaction even at a low reaction temperature where a catalytic reaction would not occur in the past.

[0020] Because the catalyst layer 130 and the high-resistance layer 120 are thinly formed on the surface 110s of the honeycomb substrate 110, it may be difficult to directly measure their electrical resistivities. In such cases, the actual catalyst 100 is analyzed to examine the component composition and structure (particularly porosity) of each of the catalyst layer 130 and the high-resistance layer 120, and samples having similar component composition and structure are prepared. The electrical resistivity of the samples is then measured, thereby making it possible to estimate the electrical resistivity of each of the catalyst layer 130 and the high-resistance layer 120.

[0021] The electrical resistivity of the high-resistance layer 120 is preferably at least twice as high as that of the catalyst layer 130. In other words, it is preferable that (electrical resistivity of the high-resistance layer 120) / (electrical resistivity of the catalyst layer 130) is 2.0 or higher. This is expected to result in a more pronounced effect of concentrating current flow in the catalyst layer 130. (electrical resistivity of the high-resistance layer 120) / (electrical resistivity of the catalyst layer 130) is more preferably 3.0 or higher, even more preferably 10.0 or higher, and particularly preferably 50.0 or higher.

[0022] As shown in FIG. 3 , the surface 110s of the honeycomb substrate 110 may have holes 110a (open pores) resulting from the porous structure. It is preferable that at least a portion of these holes 110a be filled with the high-resistivity layer 120. In this specification, the phrase "at least a portion of the holes 110a" can have two meanings. The first meaning is that a plurality of holes 110a are present, and some of the holes 110a are filled with the high-resistivity layer 120, while others are not. The second meaning is that, for each of the plurality of holes, a portion of the pore volume of the hole is filled with the high-resistivity layer 120 (see, for example, FIG. 5 ). The second meaning will be described in detail below with reference to FIGS. 3 to 5 .

[0023] In the example of the catalyst 100 shown in Fig. 3, the high-resistance layer 120 fills all of the holes 110a and also covers the entire surface 110s of the honeycomb substrate 110. Fig. 4 shows a first modified example of the catalyst 101, in which the high-resistance layer 120 fills all of the holes 110a and the surface of the high-resistance layer 120 is approximately flush with the surface 110s of the honeycomb substrate 110. In the first modified example, the surface 110s of the honeycomb substrate 110 is not covered with the high-resistance layer 120.

[0024] 5 shows a second modified example of the catalyst 102, in which the high-resistance layer 120 fills only a portion of the internal cavity of each hole 110a. As a result, the surface of the high-resistance layer 120 does not reach the surface 110s of the honeycomb substrate 110, and even after the high-resistance layer 120 is formed, recesses remain on the surface 110s of the honeycomb substrate 110 due to the unfilled holes 110a (although these recesses are shallower than before the high-resistance layer 120 was formed). These recesses are filled with a portion 130a of the catalyst layer 130 that is formed later.

[0025] By at least partially filling the holes 110a opened on the surface 110s of the honeycomb substrate 110 with the high-resistance layer 120, the volume of the "portion 130a of the catalyst layer 130" that enters the holes 110a can be reduced compared to when the high-resistance layer 120 is not provided. This is expected to have the following effects.

[0026] Because the gas to be treated passing through the cell 150 has difficulty reaching the portion 130a of the catalyst layer 130 present in the hole 110a, the portion 130a of the catalyst layer 130 hardly contributes to the catalytic reaction. However, when an electric field is applied to the catalyst, a current also flows through the portion 130a of the catalyst layer 130 present in the hole 110a. In other words, because a current flows through the region of the catalyst layer 130 that does not contribute to the catalytic reaction, the amount of current that contributes to the catalytic reaction is reduced. By filling at least a portion of the hole 110a with the high-resistance layer 120, the amount of catalyst layer 130 that enters the hole 110a is reduced, thereby reducing the amount of current that does not contribute to the catalytic reaction (i.e., increasing the amount of current that contributes to the catalytic reaction), and thus promoting the catalytic reaction.

[0027] Furthermore, since the amount of catalyst layer 130 that enters into the holes 110a can be reduced, it is expected that the amount of catalyst material used when forming the catalyst layer 130 can be reduced.

[0028] These effects are enhanced as the proportion of the volume of the hole 110a filled with the high-resistance layer 120 increases. Therefore, it is particularly preferable that the entire hole 110a is filled with the high-resistance layer 120 (FIGS. 3 and 4). This not only achieves the above-mentioned effects, but also makes it possible to make the thickness 130t (see FIG. 3) of the catalyst layer 130 more uniform throughout the catalyst layer 130, which is expected to further reduce current bias and promote the catalytic reaction more efficiently.

[0029] Even if a portion of the hole 110a is not filled with the high-resistance layer 120, as long as the catalyst layer 130 cannot penetrate further inward than the surface 110s of the honeycomb substrate 110, the same effect as when the hole 110a is completely filled with the high-resistance layer 120 can be obtained. For example, even if a cavity that could not be filled with the high-resistance layer 120 remains inside the hole 110a, if the opening 110b of the hole 110a is completely blocked by the high-resistance layer 120, the catalyst layer 130 cannot penetrate into the remaining cavity, and the same effect as when the hole 110a is completely filled can be expected.

[0030] In the catalysts 101 and 102 shown in FIGS. 4 and 5 , the surface 110 s of the honeycomb substrate 110 is exposed from the high-resistivity layer 120. In this case, the surface 110 s of the honeycomb substrate 110 comes into contact with the catalyst layer 130. Depending on the combination of the material constituting the honeycomb substrate 110 and the catalyst material constituting the catalyst layer 130, a chemical reaction may occur between the honeycomb substrate 110 and the catalyst layer 130, which may adversely affect the catalytic reaction. Therefore, as in the catalyst 100 shown in FIG. 3 , it is particularly preferable to cover the entire surface 110 s of the honeycomb substrate 110 with the high-resistivity layer 120 to avoid contact between the surface 110 s of the honeycomb substrate 110 and the catalyst layer 130.

[0031] Although the above description has been given of the holes 110a (open pores) that open to the surface 110s of the honeycomb substrate 110, the porous honeycomb substrate 110 also has voids 110c (closed pores) that do not open to the surface 110s inside the partition walls 160. Such voids 110c may or may not be filled with the high-resistance layer 120.

[0032] The thickness 120t of the high-resistance layer 120 is not particularly limited, but is, for example, 0 μm to 70 μm, preferably 5 μm to 70 μm, and more preferably 10 μm to 40 μm. Note that the thickness 120t of the high-resistance layer 120 is measured from the surface 110s of the honeycomb substrate 110. Therefore, when the high-resistance layer 120 fills only a portion of the hole 110a as shown in Fig. 5, the thickness of the high-resistance layer 120 may be 0 μm even though the high-resistance layer 120 is present between the honeycomb substrate 110 (more specifically, the inner surface of the hole 110a of the honeycomb substrate 110) and the catalyst layer 130.

[0033] The thickness 130t of the catalyst layer 130 is preferably 5 μm to 80 μm, more preferably 10 μm to 50 μm, and particularly preferably 20 μm to 40 μm.

[0034] Increasing the thickness of the high-resistance layer 120 and the catalyst layer 130 increases the amount of material used and the risk of clogging the cells 150 of the honeycomb substrate 110 during coating. For example, for a 3 mil / 750 cpsi honeycomb substrate 110, the total thickness of the high-resistance layer 120 and the catalyst layer 130 is preferably 80 μm or less.

[0035] The thickness 120t of the high-resistance layer 120 and the thickness 130t of the catalyst layer 130 are measured by SEM observation (1000x or 2000x magnification) of the cross section of the sample. The honeycomb substrate 110 is cut at a cross section (the cross section shown in Figures 1 and 2) perpendicular to the extension direction of the cells 150 (the flow direction of the gas to be treated). At the cross section, the thickness 130t of the catalyst layer 130 and the thickness 120t of the high-resistance layer 120 are measured in the direction perpendicular to the side of the cell 150 (the X-X direction in Figure 2) at approximately the center of one side 150L of the cell 150. Three cross sections are created, and thickness measurements are performed on three randomly selected sides of each cross section. The cross sections are formed at positions excluding 1 / 10 of the total length of the honeycomb substrate 110 (the dimension of the honeycomb substrate 110 in the extension direction of the cells 150) from both ends. When three sides are randomly selected, they are selected from sides located within a range of 1 / 10 of the circumference.

[0036] The catalyst layer 130 may be formed from an electric field catalyst material containing Ru, Ba, Zr, Y, and O, and the high resistance layer 120 may be formed from an insulating material containing Ba, Zr, Y, and O. Specifically, the electric field catalyst material constituting the catalyst layer 130 may be an oxide of Ba, Zr, and Y (chemical formula: Ba(Zr,Y)O ３ The catalyst layer 130 is preferably made of a material containing Cr as a main component and Ru as an active metal. By controlling the amount of Ru added, the conductivity (electrical resistivity) of the catalyst layer 130 can be controlled.

[0037] The preferred contents of each element (Y, Ru) are preferably as follows, assuming that the Ba content is 1.0 mole: Y: 0 to 0.03 moles Ru: 0.04 to 0.20 moles. When Y is within the above range, a catalytic material with high electric field activity can be obtained. When Ru is within the above range, the electrical resistivity of the catalytic layer 130 can be sufficiently reduced and a catalytic material with high electric field activity can be obtained. Note that adding Ru beyond the upper limit of Ru does not adversely affect the catalytic action, but adding Ru in excess of 0.20 moles saturates the electrocatalytic activity and simply increases costs, so the preferred upper limit is 0.20 moles.

[0038] More preferred contents of Y and Ru are as follows, when the content of Ba is 1.0 mole: Y: 0 to 0.02 moles; and Ru: 0.04 to 0.12 moles.

[0039] The insulating material constituting the high resistance layer 120 is an oxide of Ba, Zr and Y (chemical formula: Ba(Zr,Y)O ３ The high resistance layer 120 does not contain Ru, which is an element that provides conductivity, and is therefore insulating.

[0040] Since the main components of the catalyst layer 130 and the high resistance layer 120 are the same, chemical reactions are unlikely to occur between the catalyst layer 130 and the high resistance layer 120, and deterioration of the catalytic reaction of the catalyst layer 130 due to chemical reactions can be suppressed.

[0041] In addition to the above, the catalyst material constituting the catalyst layer 130 may be YSZ containing Ni, BaZrO containing Ni, or the like. ３ CeO supporting at least one of Pd, Pt, Rh, and Ru ２ The insulating material constituting the high resistance layer 120 is not particularly limited as long as it has a higher electrical resistivity than the catalyst layer 130. ２ O ３ It is also possible to use general ceramics such as those mentioned above. It is also desirable to select a material that has low reactivity with both the material (usually an insulating material) that constitutes the honeycomb substrate 110 and the catalyst material that constitutes the catalyst layer 130, and that has a thermal expansion coefficient close to both materials.

[0042] The porous honeycomb substrate 110 is usually made of an insulating material, which prevents current from flowing through the honeycomb substrate 110 when an electric field is applied to the electrocatalyst, and allows the current to be concentrated in the catalyst layer 130. An example of a material suitable for the honeycomb substrate 110 is cordierite.

[0043] (Method for manufacturing catalyst 100) The method for manufacturing the catalyst 100 includes, in this order: 1) a step of preparing a honeycomb substrate 110; 2) a step of forming a high-resistance layer 120; and 3) a step of forming a catalyst layer 130. Generally known methods can be applied to the manufacturing of the catalyst 100. A representative method for manufacturing the catalyst 100 will be described below.

[0044] Step 1) Step of preparing honeycomb substrate 110 The honeycomb substrate 110 is obtained by extruding ceramics having an appropriate resistivity (e.g., cordierite, alumina, stabilized zirconia, etc.), drying, and firing the extrusion. In the case of cordierite, commercially available honeycomb substrates can also be used.

[0045] Step 2) Step of forming the high resistance layer 120 The high resistance layer 120 can be formed from, for example, an insulating material. There is no limitation on the synthesis method of the insulating material, and synthesis methods used in the synthesis of ceramic materials, such as the solid phase method and coprecipitation method, can be applied. Here, the solid phase method will be explained. ３ , and ZrO ２ The mixture is then dried in an oven at a temperature of 100-150°C, and then fired in air at 900-1300°C for 1-6 hours to obtain an insulating material.

[0046] The obtained insulating material is mixed with water as a solvent and, optionally, a pore-forming agent (carbon, resin, etc.) in a ball mill for two hours to prepare a coating slurry. The pore-forming agent controls the porosity and pore size of the high-resistance layer 120, thereby reducing stress caused by the difference in thermal expansion coefficient between the high-resistance layer 120 and the honeycomb substrate 110.

[0047] A predetermined amount of slurry for the high resistance layer 120 is applied (wash coated) to the entire surface of the honeycomb substrate 110 and dried to form the high resistance layer 120 (containing a pore-forming agent).

[0048] Step 3) A step of forming the catalyst layer 130. ２ , and RuO ２ The mixture is then dried in an oven at a temperature of 100-150°C, and then calcined in air at 900-1200°C for 1-6 hours to obtain a catalyst material.

[0049] The resulting catalyst material is mixed with water as a solvent and, optionally, a pore-forming agent (carbon, resin, etc.) in a ball mill for two hours to prepare a coating slurry. The pore-forming agent controls the porosity and pore size of the catalyst layer 130, reducing stress caused by differences in thermal expansion coefficients between the catalyst layer 130 and the honeycomb substrate 110. It is also possible to form a supply path for the gas to be treated into the catalyst layer 130.

[0050] A predetermined amount of slurry for the catalyst layer 130 is applied (washcoated) to the entire surface of the honeycomb substrate 110 on which the high-resistance layer 120 has been formed, and then dried to form the catalyst layer 130 (containing a pore-forming agent). The resulting mixture is then fired at 500 to 900°C for 1 to 6 hours. The optionally added pore-forming agent is burned away by combustion, thermal decomposition, or the like during firing. In this manner, the catalyst 100 according to the embodiment can be formed.

[0051] The manufacturing method described here is merely an example, and it goes without saying that a person skilled in the art can manufacture the catalyst 100 according to the embodiment by a different method in consideration of known techniques.

[0052] (Gas reforming apparatus using catalyst 100) Fig. 6 is a schematic diagram showing an example of a reaction apparatus 10 used in a gas reforming method using the catalyst 100 according to the embodiment. As the reaction apparatus 10, for example, an atmospheric pressure fixed-bed flow reactor equipped with a pair of electrodes 13, 14 can be used. The catalyst 100 is placed inside a reaction vessel 12 of the atmospheric pressure fixed-bed flow reactor (reaction apparatus) 10, and both ends of the catalyst 100 are directly contacted with the pair of electrodes 13, 14, respectively. When reforming gas, a voltage is applied between the pair of electrodes 13, 14 to apply an electric field to the catalyst 100.

[0053] During gas reforming, the electric field catalyst is heated to a reaction temperature of 200°C to 400°C (473K to 673K) and an electric field is applied. The gas to be reformed (e.g., hydrocarbon) is brought into contact with the electric field catalyst in this state, causing the gas to react (be reformed).

[0054] The essence of the present invention is not limited to the examples described herein, but lies in the ability to provide a more efficient catalyst even if the optimum conditions vary depending on the substrate and catalyst material used.

[0055] The honeycomb substrate 110 used was a commercially available cylindrical honeycomb substrate made of cordierite (φ30 mm×30 mmt, cell count: 750 cpsi) (manufactured by NGK Insulators, Honeyceram, 3 mil / 750 cpsi).

[0056] The high resistance layer 120 is made of BaCO 3 with the ratio of each element shown in Table 2. ３ , ZrO ２ and Y ２ O ３ The raw materials were weighed, and then balls and water were added and wet mixed to obtain a mixture. Since Sample No. 13 does not contain Ba, the raw materials were weighed so that the molar ratios of each element other than Ba ​​were as shown in Table 2. The obtained mixture was dried in an oven at a temperature of 120°C, and then fired in air at 1100°C for 1 hour to obtain an insulating material.

[0057] The obtained insulating material was mixed with water as a solvent and a pore-forming agent in a ball mill for 2 hours to prepare a coating slurry. The pore-forming agent used was an acrylic resin with an average particle size of 1.8 μm (MX-180TA manufactured by Soken Chemical & Engineering Co., Ltd.). The amount of pore-forming agent added was the amount shown in Table 2, expressed as a ratio when the total solid content in the slurry was 100% by mass. The slurry for the high-resistance layer 120 was applied (wash-coated) to the entire surface of the honeycomb substrate 110 in the amount shown in Table 2 and dried to form the high-resistance layer 120 (including the pore-forming agent).

[0058] The catalyst layer 130 is made of BaCO 3 with the ratio of each element shown in Table 1. ３ , ZrO ２ , Y ２ O ３ and RuO ２ The mixture was then dried in an oven at 120°C and calcined in air at 1100°C for 1 hour to obtain a catalyst material.

[0059] The resulting catalyst material was mixed with water as a solvent and a pore-forming agent in a ball mill for two hours to prepare a coating slurry. The pore-forming agent used was an acrylic resin with an average particle size of 0.8 μm (MX-80H3wT, manufactured by Soken Chemical & Engineering Co., Ltd.). The amount of pore-forming agent added was the amount shown in Table 1, expressed as a ratio when the total solids content in the slurry was 100% by mass. The entire surface of the honeycomb substrate 110 on which the high-resistance layer 120 was formed was washed with the slurry for the catalyst layer 130 in the amount shown in Table 1 and dried to form the catalyst layer 130 (including the pore-forming agent). The sample was then fired at 800°C for three hours. The pore-forming agent was burned off during firing due to combustion, thermal decomposition, etc. In this manner, a catalyst sample for measurement was prepared.

[0060] In the comparative sample 14, the application of the slurry for the high resistance layer 120 was omitted, and the catalyst layer 130 was formed directly on the surface of the honeycomb substrate 110.

[0061] The thickness 130t of the catalyst layer 130 and the thickness 120t of the high-resistance layer 120 were measured by SEM observation (1000x or 2000x magnification) of the cross section of the sample. The honeycomb substrate 110 was cut at a cross section (the cross section shown in Figures 1 and 2) perpendicular to the extension direction of the cells 150 (the flow direction of the gas to be treated). In the cross section, the thickness 130t of the catalyst layer 130 and the thickness 120t of the high-resistance layer 120 were measured at approximately the center of one side 150L of the cell 150 in the direction perpendicular to the one side of the cell 150 (the X-X direction in Figure 2). The thickness measurements were performed automatically using image processing software.

[0062] Three cross sections were created, and on each cross section, the thickness 130t of the catalyst layer 130 and the thickness 120t of the high resistance layer 120 were measured on three randomly selected sides.The arithmetic mean values ​​of the measurement results at a total of nine points were taken to determine the thickness 130t of the catalyst layer 130 and the thickness 120 of the high resistance layer 120 of that sample.

[0063] <Activity Evaluation> An electric field activity evaluation was carried out on the obtained sample. The activity evaluation was carried out for the steam reforming reaction. A honeycomb catalyst was set in a quartz reaction tube of a fixed-bed catalytic reaction device, and SUS electrodes (positive and negative electrodes) were brought into contact with the upper and lower ends of the honeycomb. The electric furnace temperature was set to 300°C, and a reaction gas was introduced. An electric field was applied using a DC power supply, and an electric field steam reforming reaction was evaluated. The detailed reaction conditions were as follows: Reaction gas: CH ４ :1200cc / min, N ２ Steam: 2400 cc / min. Space velocity (SV): about 10,000 / hr. S / C (steam / carbon ratio): 2.0. Electric furnace temperature: 300°C. The methane conversion rate without application of an electric field was 0%.

[0064] <Resistivity Evaluation> In the present invention, the resistance value of each layer is an important design value. The resistivity (ρ) was evaluated using the following method, and its relationship with catalytic activity was analyzed. The ceramics and pore-forming agent used in the catalyst layer 130 and the high-resistance layer 120 were prepared in the mixing ratios shown in Tables 1 and 2, and after adding a solvent and a binder, the mixture was kneaded and press-molded. The molded product was fired at the same temperature as the honeycomb firing to obtain a sample for resistance measurement.

[0065] The sample size was 4 mm x 3 mm x 30 mm, and measurements were made using the four-terminal method. Resistivity is expressed by the following formula, which is a value normalized from thickness, width, and length, and takes into account the influence of the material, pores, and the contact state between materials. ρ = R x A / T Where, ρ: resistivity (Ωcm), R: resistance (Ω), A: sample cross-sectional area (cm ２ ) T: sample length (cm).

[0066] Table 3 shows the measurement results when an electric field was applied with an input power of 100 W.

[0067] Samples 1 to 13 are examples, and a high-resistance layer 120 was provided between the honeycomb substrate 110 and the catalyst layer 130. The high-resistance layer 120 allowed current to concentrate on the catalyst layer 130, improving the methane conversion rate (the methane conversion rate was more than twice as high as in the comparative example described below). Depending on the amount of coating used when forming the high-resistance layer 120, the form of the high-resistance layer 120 was one of those shown in Figures 3 to 5.

[0068] On the other hand, Sample 14 (Comparative Example) did not have a high-resistance layer 120. Therefore, in Sample 14, the holes 110a opening in the surface 110s of the honeycomb substrate 110 were filled with a portion of the catalyst layer 130. The portion 130a of the catalyst layer 130 present in the hole 110a does not come into contact with the gas to be treated passing through the cell 150, and therefore current flows through the portion 130a of the catalyst layer 130 even though it hardly contributes to the catalytic reaction. As a result, the amount of current flowing through the portion of the catalyst layer 130 that contributes to the catalytic reaction (mainly the upper portion of the catalyst layer 130 adjacent to the cell 150) is thought to have decreased, resulting in a lower methane conversion rate.

[0069] Samples 1 to 13, which are examples, will now be examined in more detail.

[0070] In Sample 1, a catalyst layer 130 having a thickness 130t of 10 μm was provided using a catalyst material containing 0.04 Ru (molar ratio). The high-resistance layer 120 had a thickness 120t of 10 μm. Because the amount of Ru in the catalyst layer was relatively small and the catalyst layer was relatively thin, the electrical resistance of the catalyst as a whole was relatively high, and the methane conversion rate was lower than in the examples.

[0071] Sample 2 was the same as Sample 1, except that the thickness 130t of the catalyst layer 130 was 20 μm. Because the catalyst layer was thicker than in Sample 1, the electrical resistance of the entire catalyst was lower, allowing more current to flow, and as a result, the methane conversion rate was improved.

[0072] In Samples 3 to 5, the Ru content (molar ratio) in the catalyst material was varied to 0.08, 0.10, and 0.12, and a catalyst layer 130 with a thickness 130t of 10 μm was provided. The thickness 120t of the high-resistivity layer 120 was 10 μm. As the Ru content increased, the resistivity of the catalyst layer decreased, and the electrical resistance of the entire catalyst also decreased. However, with regard to methane conversion, Samples 3 and 4, which had low Ru contents, exhibited higher methane conversion rates than Sample 5, which had a high Ru content. This is because the increased Ru content reduced the degree of dispersion of Ru, and the Ru and BaZrYO, which are thought to be the reaction field for the electrocatalytic reaction, became more dispersed. ３ This is thought to be due to the decrease in the interface.

[0073] Samples 6 to 9 were prepared using a catalyst material containing 0.08 Ru (molar ratio) and had catalyst layers 130 with thicknesses 130t ranging from 5 to 30 μm. The high-resistance layer 120 had a thickness 120t of 10 μm. Sample 6, in which the catalyst layer 130 had a thickness 130t of 5 μm, had a slightly higher overall electrical resistance, resulting in a slightly lower methane conversion rate. Sample 8, in which the catalyst layer 130 had a thickness 130t of 20 μm, and Sample 9, in which the catalyst layer 130 had a thickness 130t of 30 μm, had lower overall catalyst electrical resistance, but lower methane conversion rates than Sample 6. This is thought to be because the thickness of the catalyst layer 130 prevented the lower portion of the catalyst layer (the portion of the catalyst layer 130's thickness 130t facing the honeycomb substrate 110) from fully contributing to the catalytic reaction.

[0074] Sample 7, in which the thickness 130t of the catalytic layer 130 was 15 μm, had a higher electrical resistance of the entire catalyst than samples 8 and 9, but the methane conversion rate was improved. Sample 3, in which the Ru content (molar ratio) was 0.08 (the thickness 130t of the catalytic layer 130 was 10 μm), also had a higher methane conversion rate than samples 8 and 9. These results show that when the Ru content (molar ratio) is 0.08, the most efficient methane conversion is achieved when the thickness 130t of the catalytic layer 130 is 10 to 15 μm.

[0075] For samples 10 to 12, the Ru content (molar ratio) in the catalyst layer was fixed at 0.08, the thickness 130t of the catalyst layer 130 was fixed at 10 μm, and the thickness 120t of the high-resistance layer 120 was varied in the range of 0 to 40 μm. In sample 10, the high-resistance layer 120 was formed with a coating amount of 40 g / L, but only partially filled the holes (more precisely, only partially filled the spaces inside the holes) that opened on the surface of the honeycomb substrate 110 ( FIG. 5 ). Therefore, the "thickness 120t of the high-resistance layer 120" measured from the surface 110s of the honeycomb substrate 110 was 0 μm.

[0076] In Sample 10, some of the holes 110a on the surface 110s of the honeycomb substrate 110 were not filled with the high-resistivity material, leaving recesses on the surface 110s of the honeycomb substrate 110 (Figure 5). As a result, a portion 130a of the catalyst layer 130 entered the recesses. The current flowing through the portion 130a of the catalyst layer 130 did not contribute to the catalytic reaction, which is thought to have slightly reduced the methane conversion rate. Furthermore, because most of the surface 110s of the honeycomb substrate 110 was exposed from the high-resistivity layer, the surface 110s of the honeycomb substrate 110 and the catalyst layer 130 were in contact. At the contact surface, slight interdiffusion of elements was observed, which is presumed to be due to a chemical reaction between the material constituting the honeycomb substrate 110 and the catalyst material constituting the catalyst layer 130. This chemical reaction is also thought to be one of the causes of the reduced methane conversion rate.

[0077] In Samples 11 and 12, the surface 110s of the honeycomb substrate 110 and the holes 110a in the catalyst layer 130 were completely filled with the high-resistance layer, and the entire surface of the honeycomb substrate was also covered with the high-resistance layer. As a result, the methane conversion rate was significantly improved.

[0078] Sample 13 was the same as Sample 3, except that the composition of the high-resistance layer 120 was changed to a composition that did not contain Ba. Compared to Sample 3, Sample 13 was able to achieve a similar level of methane conversion rate.

[0079] When the electrical resistivity of the high-resistance layer 120 was at least twice as high as that of the catalyst layer 130, the electrocatalytic reaction was efficiently induced (Samples 1 and 2). It is more preferable that the electrical resistivity of the high-resistance layer 120 be at least one order of magnitude higher than that of the catalyst layer 130 (Samples 3 to 13).

[0080]

[0081]

[0082]

[0083] The catalyst according to the present disclosure is expected to enable catalytic reactions at low temperatures by being applied to steam reforming, tri-reforming, dry reforming, methanation treatment, reverse water gas shift (RWGS) reaction, oxidative coupling of methane (OCM) reaction, ammonia synthesis, dehydrogenation reaction from methylcyclohexane (MCH), three-way catalytic reaction for waste methane treatment, and the like.

[0084] This application claims priority based on Japanese Patent Application No. 2023-047176, filed on March 23, 2023, the entire contents of which are incorporated herein by reference.

[0085] 100, 101, 102 Catalyst 110 Honeycomb substrate 110a Hole 110s Surface of honeycomb substrate 120 High resistance layer 130 Catalyst layer 150 Cell 160 Partition wall

Claims

1. A catalyst used by applying an electric field, The honeycomb substrate includes a porous honeycomb substrate and a catalyst layer covering the surface of the honeycomb substrate. a high-resistivity layer having a higher electrical resistivity than the catalytic layer is provided between the honeycomb substrate and the catalytic layer; A catalyst, wherein the electrical resistivity of the high resistance layer is at least twice as high as the electrical resistivity of the catalyst layer.

2. A catalyst used by applying an electric field, comprising: The honeycomb substrate includes a porous honeycomb substrate and a catalyst layer covering the surface of the honeycomb substrate. a high-resistivity layer having a higher electrical resistivity than the catalytic layer is provided between the honeycomb substrate and the catalytic layer; the catalyst layer is made of an electric field catalyst material containing Ru, Ba, Zr, Y, and O; The high resistance layer is made of an insulating material containing Ba, Zr, Y, and O.

3. The honeycomb substrate has porous holes on the surface thereof, The catalyst according to claim 1 or 2, wherein at least a portion of the holes is filled with the high resistance layer.