Catalyst-carrying honeycomb structure and method for manufacturing the same

Abstract

To provide a catalyst-carrying honeycomb structure capable of improving the conversion rate of ammonia while improving the lifespan of a catalyst.SOLUTION: A catalyst-carrying honeycomb structure 1 comprises: a ceramic honeycomb structure 2; a catalyst layer 3 that is formed in a flow path 2a of the honeycomb structure 2 and decomposes ammonia; and electrodes 4a, 4b that are formed on side surfaces of the honeycomb structure 2. The honeycomb structure 2 is energized.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a honeycomb structure supporting a catalyst for decomposing ammonia and a method for manufacturing the same. [Background technology]

[0002] In light of the recent global warming, efforts toward a hydrogen society that focuses on using hydrogen as a combustion source are gaining momentum. Ammonia is attracting attention for producing hydrogen. This is because ammonia is composed of hydrogen and nitrogen atoms, and does not produce CO2 during the ammonia decomposition reaction. In addition, this method does not require hydrogen stations to supply hydrogen or hydrogen pressure vessels filled with hydrogen. For this reason, technology that decomposes ammonia to produce hydrogen and oxygen is beginning to be used in automobile fuel cells and industrial furnaces.

[0003] Patent Document 1 discloses an invention in which a catalyst for decomposing ammonia is supported on a metal honeycomb structure, and ammonia is passed through a flow path in the honeycomb structure to decompose the ammonia and generate hydrogen and oxygen. The decomposition reaction of ammonia is an endothermic reaction. In order to supply the heat required for the decomposition of ammonia, the invention described in Patent Document 1 brings a heater into contact with the upstream side of the honeycomb structure, and supplies heat to the honeycomb structure by the heater. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-195642 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the invention described in Patent Document 1, the metal honeycomb structure supporting the catalyst is heated by contacting it with a heater, which means that the temperature distribution in the honeycomb structure cannot be made uniform, and there is a problem in that it is not possible to improve both the ammonia conversion rate and the catalyst life.

[0006] To explain this, in the decomposition reaction of ammonia, increasing the reaction temperature can improve the conversion rate of ammonia. On the other hand, increasing the reaction temperature causes the catalyst fine particles to grow, shortening the catalyst's lifespan. In the invention described in Patent Document 1, when trying to improve the conversion rate of ammonia, the lifespan of the high-temperature part of the catalyst is shortened, and when trying to extend the catalyst's lifespan, the conversion rate of ammonia in the low-temperature part of the catalyst is reduced.

[0007] The present invention has been made in consideration of the above problems, and aims to provide a catalyst-supported honeycomb structure and a manufacturing method thereof that can achieve both improved ammonia conversion rate and improved catalyst life. [Means for solving the problem]

[0008] In order to solve the above problems, one aspect of the present invention is a catalyst-supported honeycomb structure comprising a ceramic honeycomb structure, a catalyst layer formed in a flow path of the honeycomb structure for decomposing ammonia, and an electrode formed on a side surface of the honeycomb structure, and passing electricity through the honeycomb structure.

[0009] Another aspect of the present invention is a method for manufacturing a catalyst-loaded honeycomb structure, comprising the steps of: sintering a honeycomb formed body containing silicon carbide powder, silicon nitride powder, and carbon to produce a honeycomb structure; forming electrodes on side surfaces of the honeycomb structure; and forming a catalyst layer for decomposing ammonia in a flow path of the honeycomb structure, and passing electricity through the honeycomb structure. Effect of the Invention

[0010] According to the present invention, since the honeycomb structure can be uniformly heated, it is possible to improve both the ammonia conversion rate and the catalyst life. [Brief description of the drawings]

[0011] [Figure 1] 1 is an external perspective view of a catalyst-supporting honeycomb structure according to an embodiment of the present invention; [Diagram 2] FIG. 2 is an external perspective view of a honeycomb structure. [Diagram 3] 2A to 2C are schematic diagrams of a honeycomb formed body containing silicon carbide powder, silicon nitride powder, and carbon before and after sintering. [Figure 4] FIG. 2 is a perspective view of a catalyst-supporting honeycomb structure elongated in the gas flow direction. [Diagram 5] FIG. 2 is a perspective view of a catalyst-supporting honeycomb structure elongated in a direction perpendicular to the gas flow. [Figure 6] FIG. 2 is a front view of a honeycomb structure produced in an example. [Figure 7] FIG. 7(a) is a graph showing temperature changes T1, T2, and T3 when a current of 5 A is applied to the honeycomb structure, and FIG. 7(b) shows a thermograph of the honeycomb structure when T2=165°C. [Figure 8] FIG. 8(a) is a graph showing temperature changes T1, T2, and T3 when a current of 10 A is applied to the honeycomb structure, and FIG. 8(b) shows a thermograph of the honeycomb structure when T2=300°C. [Figure 9] FIG. 9(a) is a graph showing temperature changes T1, T2, and T3 when a current of 20 A is applied to the honeycomb structure, and FIG. 9(b) shows a thermograph of the honeycomb structure when T2=400°C. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, a catalyst-supported honeycomb structure and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. However, the catalyst-supported honeycomb structure and the manufacturing method thereof according to the present invention can be embodied in various forms and are not limited to the embodiments described in this specification. This embodiment is provided with the intention of enabling those skilled in the art to fully understand the invention by fully disclosing the specification. (Catalyst-supported honeycomb structure)

[0013] Fig. 1 is an external perspective view of a catalyst-supported honeycomb structure according to one embodiment of the present invention. The catalyst-supported honeycomb structure 1 of this embodiment includes a ceramic honeycomb structure 2, a catalyst layer 3 formed in a flow path 2a of the honeycomb structure 2, and a pair of electrodes 4a, 4b formed on the side surface of the honeycomb structure 2. The catalyst-supported honeycomb structure 1 is accommodated in a reaction vessel (not shown) that includes a gas inlet and a gas outlet. The shape of the catalyst-supported honeycomb structure 1, the number of flow paths 2a, and the like are not limited, and may be cylindrical (see Fig. 4), oval, rectangular, or the like (see Fig. 1).

[0014] When ammonia is supplied to the gas inlet of the reaction vessel, the ammonia flows through the flow passage 2a of the honeycomb structure 2. When the ammonia flows through the flow passage 2a, the catalyst layer 3 decomposes the ammonia according to reaction formula 1 to generate hydrogen and nitrogen. The generated hydrogen and nitrogen are discharged from the gas outlet of the reaction vessel. (Formula 1) 2NH3→N2+3H2

[0015] Formula 1 is an endothermic reaction. In order to reduce the amount of heat absorbed, ammonia and air may be supplied to the gas inlet of the reaction vessel and the ammonia and air may be allowed to flow through the flow passage 2a of the honeycomb structure 2. When ammonia and air are allowed to flow through the flow passage 2a, heat is generated by the catalytic reaction between ammonia and oxygen as shown in formula 2. This heat can reduce the amount of heat absorbed. (Formula 2) NH3+3 / 4O2→1 / 2N2+3 / 2H2O (Honeycomb structure)

[0016] As shown in Fig. 2, the honeycomb structure 2 has a plurality of cells 2a that form flow paths 2a through which ammonia flows, extending from an end face on the inlet side to an end face on the outlet side, porous partition walls 2b that partition and define the plurality of cells 2a, and an outer peripheral wall 2c located on the outermost periphery. The shape of the honeycomb structure 2, the number of cells 2a, the thickness of the partition walls 2b, etc. are not limited and are appropriately designed as necessary. For example, the shape of the honeycomb structure 2 may be an elongated cylinder.

[0017] The honeycomb structure 2 is made of ceramics. The honeycomb structure 2 is conductive. The honeycomb structure 2 contains silicon carbide as a main component and nitrogen as an impurity. "Containing silicon carbide as a main component" means that the honeycomb structure 2 contains silicon carbide in an amount of 90 mass % or more of the entire honeycomb structure.

[0018] The honeycomb structure 2 is produced by sintering a honeycomb molded body containing silicon carbide powder, silicon nitride powder, and carbon. The silicon carbide powder is used as aggregate for the honeycomb structure 2. The silicon nitride powder and carbon are used as binders for binding the silicon carbide powder.

[0019] 3(a) shows a schematic diagram of the particles of the honeycomb molded body before sintering. Reference numeral 5 denotes silicon carbide powder, reference numeral 6 denotes silicon nitride powder, and reference numeral 7 denotes carbon. When the honeycomb molded body is sintered, silicon nitride and carbon react to synthesize silicon carbide, as shown in the following formula 3. (Formula 3) Si3N4+3C → 3SiC+2N2

[0020] As shown in Fig. 3(b), the synthesized silicon carbide 8 binds the silicon carbide powder 5 used as aggregate. The reaction temperature of formula 3 is lower than the softening point of silicon carbide particles. By using silicon nitride powder 6 and carbon 7 as binders for binding the silicon carbide powder 5, grain growth of the silicon carbide powder 5 can be suppressed, and a fine and uniform pore size distribution of the honeycomb structure 2 can be achieved.

[0021] The honeycomb structure 2 contains nitrogen derived from silicon nitride powder as an impurity. Nitrogen functions as a dopant that contributes to electrical conduction, making the honeycomb structure 2 conductive. When electricity is applied to the honeycomb structure 2, the honeycomb structure 2 generates heat. Since the honeycomb structure 2 has a fine and uniform pore size distribution, the honeycomb structure 2 is heated uniformly.

[0022] An example of a method for producing the honeycomb structure 2 will be described below. First, a molding raw material is produced by adding water, a binder, etc. to silicon carbide powder, silicon nitride powder, and carbon. The average particle size of the silicon carbide powder is 1 to 50 μm. The content of the silicon carbide powder relative to the silicon carbide powder, silicon nitride powder, and carbon is 20 to 70 mass %. The carbon is graphite, carbon black, etc. The molar ratio of silicon constituting the silicon nitride to the carbon is in the range of 1.0 to 2.0.

[0023] The binder is methyl cellulose or the like. The binder content is 2 to 15 parts by mass when the total mass of the silicon carbide powder, silicon nitride powder, and carbon is 100 parts by mass. The water content is 20 to 30 parts by mass when the total mass of the silicon carbide powder, silicon nitride powder, and carbon is 100 parts by mass. In addition to the above raw materials, a surfactant such as ethylene glycol, dextrin, fatty acid soap, or polyalcohol may be added.

[0024] Next, the obtained forming raw materials are mixed to prepare a clay, and the clay is extruded to prepare a honeycomb formed body. After drying the honeycomb formed body, the honeycomb formed body is sintered at a temperature of, for example, 1800°C to 2300°C in a nitrogen-free non-oxidizing atmosphere such as a vacuum or an inert gas, to prepare a honeycomb structure 2.

[0025] The honeycomb structure 2 may contain a silicon-silicon carbide composite material as a main component. The silicon-silicon carbide composite material contains silicon carbide particles as aggregates and metallic silicon as a binder for binding the silicon carbide particles. (electrode)

[0026] 1, a pair of electrodes 4a, 4b are formed on the side surfaces of the honeycomb structure 2. The electrodes 4a, 4b are strip-shaped and extend in the same direction as the cells 2a of the honeycomb structure 2. The electrodes 4a, 4b are disposed to face each other with the center of the honeycomb structure 2 in between.

[0027] The electrodes 4a, 4b are made of a material having electrical conductivity. The material of the electrodes 4a, 4b is a metal, a conductive ceramic, a composite material combining a metal and an oxide ceramic, etc. The metal is silver, copper, iron, aluminum, tungsten, alloy steel, etc. The conductive ceramic is silicon carbide, chromium silicide, boron carbide, chromium boride, tantalum silicide, etc. The oxide ceramic is glass, cordierite, mullite, etc.

[0028] An intermediate layer (not shown) having a lower thermal expansion coefficient than the electrodes 4a, 4b may be provided on the honeycomb structure 2 side of the electrodes 4a, 4b. The electrodes 4a, 4b have a higher thermal expansion coefficient than the honeycomb structure 2. By providing the intermediate layer, the difference in thermal expansion coefficient between the electrodes 4a, 4b and the honeycomb structure 2 can be reduced. The intermediate layer is made of a metal, an oxide ceramic, or the like, like the electrodes 4a, 4b.

[0029] The intermediate layer and the electrodes 4a, 4b are formed, for example, as follows: Metal powder and glass powder are mixed to prepare ceramic raw material. A binder, a surfactant, and water are added to the ceramic raw material to prepare a paste for the intermediate layer. The paste for the intermediate layer is applied onto the honeycomb structure 2 and dried to form a coating. The honeycomb structure 2 with the coating formed thereon is sintered to form the intermediate layer.

[0030] The electrodes 4a, 4b formed on the intermediate layer are also formed in the same manner. That is, metal powder and glass powder are mixed to prepare ceramic raw material. A binder, a surfactant, and water are added to the ceramic raw material to prepare a paste for the electrodes. The paste for the electrodes is applied onto the intermediate layer of the honeycomb structure 2 and dried to form a coating film. The honeycomb structure 2 on which the coating film is formed is sintered to form the electrodes 4a, 4b. Here, the honeycomb molded body and the intermediate layer may be sintered simultaneously, or the honeycomb molded body, the intermediate layer, and the electrodes 4a, 4b may be sintered simultaneously.

[0031] The intermediate layer and the electrodes 4a, 4b may be formed by spraying a spray material onto the honeycomb structure 2. In this case, the spray material preferably contains tungsten carbide as a main component and nickel. The nickel content of the spray material is preferably 3 to 40 mass %, and the tungsten carbide content of the spray material is preferably 60 to 90 mass %. (catalyst layer)

[0032] As shown in Fig. 1, a catalyst layer 3 is formed in a cell 2a of a honeycomb structure 2. The catalytic active species used in the catalyst layer 3 is not particularly limited as long as it decomposes ammonia into hydrogen. At least one element selected from the group consisting of Groups 6, 7, 8, 9, 10, and 11 is selected as the catalytic active species. The catalytic metal is, for example, ruthenium, rhodium, palladium, platinum, etc.

[0033] The catalytically active species can be used by being supported on a catalyst carrier made of an oxide containing at least one element selected from the group consisting of Al, Si, Ti, Zr, Group 1, Group 2, and Group 3. The oxide may be a composite oxide containing two or more oxides. The oxide may also be a zeolite. Supporting the catalytically active species on a catalyst carrier made of such an oxide contributes to improving the dispersibility of the catalytically active species and improving the mechanical strength of the catalyst.

[0034] A conventional method can be used for forming the catalyst layer 3. For example, a method of wet-pulverizing catalytically active species to produce a slurry and coating the honeycomb structure 2 with the slurry, a method of wet-pulverizing a powder in which catalytically active species are supported on a catalyst carrier made of an oxide to produce a slurry and coating the honeycomb structure 2 with the slurry, a method of wet-pulverizing a catalyst carrier made of an oxide to produce a slurry, coating the honeycomb structure 2 with the slurry, thereafter wet-pulverizing catalytically active species to produce a slurry, and further coating the honeycomb structure 2 with the slurry, and the like can be used. (Support for longer lengths)

[0035] When the catalyst-supported honeycomb structure 1 is elongated in the gas flow direction, a plurality of catalyst-supported honeycomb structures 1-1, 1-2, and 1-3 are arranged in the gas flow direction, and insulating layers 9 are provided between the catalyst-supported honeycomb structures 1-1, 1-2, and 1-3, as shown in Fig. 4. Electrodes 4a and 4b are provided on the catalyst-supported honeycomb structures 1-1, 1-2, and 1-3 so that they can be individually energized. Electric wires 16a and 16b are connected to the electrodes 4a and 4b to supply power.

[0036] When the catalyst-supported honeycomb structure 1 is elongated in the radial direction (perpendicular to the gas flow), as shown in FIG. 5, a plurality of catalyst-supported honeycomb structures 1-4, 1-5, and 1-6 are arranged in the direction perpendicular to the gas flow, and an insulating layer 9 is provided between the catalyst-supported honeycomb structures 1-4, 1-5, and 1-6. Electrodes 4a and 4b are provided in each of the catalyst-supported honeycomb structures 1-4, 1-5, and 1-6 so that electricity can be applied individually. Electric wires 16a and 16b for supplying electricity are connected to the electrodes 4a and 4b. Note that a plurality of catalyst-supported honeycomb structures may be arranged in the direction perpendicular to the gas flow, and a plurality of catalyst-supported honeycomb structures may be arranged in the gas flow direction.

[0037] The type and amount of catalyst of the catalyst-supported honeycomb structures 1-1, 1-2, and 1-3 shown in FIG. 4 may be the same or at least one may be different. Similarly, the type and amount of catalyst of the catalyst-supported honeycomb structures 1-4, 1-5, and 1-6 shown in FIG. 5 may be the same or at least one may be different. When at least one of the type and amount of catalyst is different, the heating temperature (amount of heat) may be changed according to the type and amount of catalyst. For example, a catalyst capable of oxidizing and decomposing ammonia may be used for the upstream catalyst-supported honeycomb structure 1-1 in FIG. 4, a catalyst capable of decomposing ammonia may be used for the downstream catalyst-supported honeycomb structures 1-2 and 1-3, and the heating temperature of the downstream catalyst-supported honeycomb structures 1-2 and 1-3 may be higher than the heating temperature of the upstream catalyst-supported honeycomb structure 1-1.

[0038] The insulating layer 9 is a plate-shaped insulator such as silica or alumina, or an air layer (gap) provided between the catalyst-supporting honeycomb structures 1-1, 1-2, and 1-3. When a plate-shaped insulator is used, the multiple honeycomb molded bodies and the plate-shaped insulator are degreased and fired to be integrated, and electrodes 4a and 4b are formed on each honeycomb structure 2. (effect) The effects of the catalyst supporting honeycomb structure 1 of this embodiment will be described below.

[0039] According to the catalyst-supporting honeycomb structure 1 of the present embodiment, the honeycomb structure 2 can be uniformly heated, so that it is possible to improve both the ammonia conversion rate and the catalyst life.

[0040] Since the honeycomb structure 2 is mainly composed of silicon carbide and contains nitrogen, the honeycomb structure 2 can be heated more uniformly.

[0041] Since a plurality of catalyst-supported honeycomb structures 1-1, 1-2, and 1-3 are arranged in the gas flow direction and an insulating layer 9 is provided between the catalyst-supported honeycomb structures 1-1, 1-2, and 1-3, the plurality of catalyst-supported honeycomb structures 1-1, 1-2, and 1-3 elongated in the gas flow direction can be uniformly heated. Similarly, a plurality of catalyst-supported honeycomb structures 1-4, 1-5, and 1-6 are arranged in a direction perpendicular to the gas flow and an insulating layer 9 is provided between the catalyst-supported honeycomb structures 1-4, 1-5, and 1-6, the plurality of catalyst-supported honeycomb structures 1-4, 1-5, and 1-6 elongated in the direction perpendicular to the gas flow can be uniformly heated. In addition, electricity can be applied separately to each of the plurality of catalyst-supported honeycomb structures 1-1, 1-2, and 1-3 or 1-4, 1-5, and 1-6. (Example)

[0042] A honeycomb structure 2 shown in FIG. 6 was produced. A molding raw material was produced by adding water, a binder, etc. to silicon carbide powder, silicon nitride powder, and carbon. The average particle size of the silicon carbide powder was 10 μm. The content of the silicon carbide powder relative to the silicon carbide powder, silicon nitride powder, and carbon was 50 mass %. Carbon black was used as the carbon. The molar ratio of silicon constituting the silicon nitride relative to the carbon was 1.5.

[0043] The binder used was methyl cellulose. The binder content was 10 parts by mass when the total mass of the silicon carbide powder, silicon nitride powder, and carbon was 100 parts by mass. The water content was 25 parts by mass when the total mass of the silicon carbide powder, silicon nitride powder, and carbon was 100 parts by mass.

[0044] The obtained forming raw materials were mixed to prepare a clay, which was then extruded to prepare a honeycomb formed body. After drying the honeycomb formed body, the honeycomb formed body was sintered at a temperature of 2100°C in a nitrogen-free non-oxidizing atmosphere to prepare a honeycomb structure 2.

[0045] The size of the honeycomb structure 2 was 50 mm square x 50 mm long, the structure of the cells 2a was 50 cpsi / 25 mil, and the resistance of the honeycomb structure 2 was 0.5 Ωcm. The resistance was measured by a four-terminal method in accordance with JIS R 1650-2:2002. In addition, the nitrogen concentration of the honeycomb structure 2 was measured in accordance with JIS R 1616:2007, and the presence of nitrogen was confirmed.

[0046] Carbon felts 11a, 11b were sandwiched between the honeycomb structure 2 and the electrodes 4a, 4b, and the electrodes 4a, 4b were pressed from above and below. Constant currents of 5 A, 10 A, and 20 A were supplied to the honeycomb structure 2, and temperatures T1, T2, and T3 at the bottom, middle, and top of the honeycomb structure 2 were measured.

[0047] As shown in Fig. 7(a), when a current of 5 A was supplied to the honeycomb structure 2, the temperatures T1, T2, and T3 increased with time, but the temperatures T1, T2, and T3 were approximately the same value. Moreover, as shown in the thermograph at T2 = 165 °C in Fig. 7(b), the entire honeycomb structure 2 was heated uniformly.

[0048] 8(a) and (b), when a current of 10 A was applied to the honeycomb structure 2, the results were approximately the same as when a current of 5 A was applied to the honeycomb structure 2. Note that FIG. 8(b) shows a thermograph at T2=300° C.

[0049] As shown in Fig. 9(a), when a constant current of 20A was applied to the honeycomb structure 2, the contact resistance of the electrodes 4a, 4b, the carbon felts 11a, 11b, and the honeycomb structure 2 had a large effect, causing slight variations in temperatures T1, T2, and T3. However, even in this case, as shown in the thermograph at T2 = 400°C in Fig. 9(b), the entire honeycomb structure 2 could be heated almost uniformly. Since uniform heating is possible, the ammonia conversion rate can be improved when a catalyst is supported. [Explanation of symbols]

[0050] 1...Catalyst-supporting honeycomb structure 2…Honeycomb structure 3...Catalyst layer 4a,4b…electrode 9…Insulating layer

Claims

1. A ceramic honeycomb structure, A catalyst layer formed in a flow path of the honeycomb structure and configured to decompose ammonia; an electrode formed on a side surface of the honeycomb structure, A catalyst-supporting honeycomb structure for passing electricity through the honeycomb structure.

2. 2. The catalyst-supporting honeycomb structure according to claim 1, wherein the honeycomb structure is mainly composed of silicon carbide and contains nitrogen.

3. 3. The catalyst-supporting honeycomb structure according to claim 1, wherein a plurality of the catalyst-supporting honeycomb structures are arranged in the gas flow direction and / or in a direction perpendicular to the gas flow, and an insulating layer is provided between the catalyst-supporting honeycomb structures.

4. A step of sintering a honeycomb formed body containing silicon carbide powder, silicon nitride powder, and carbon to produce a honeycomb structure; forming an electrode on a side surface of the honeycomb structure; forming a catalyst layer for decomposing ammonia in the flow passage of the honeycomb structure, A method for manufacturing a catalyst-supporting honeycomb structure, comprising: passing electricity through the honeycomb structure.

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