Ammonia decomposition apparatus and method for manufacturing the same

Abstract

The present invention provides an ammonia decomposition apparatus that can reduce the temperature difference between the upstream ammonia decomposition catalyst-supported honeycomb structure and the downstream ammonia decomposition catalyst-supported honeycomb structure, even as the endothermic reaction that decomposes ammonia proceeds. [Solution] An upstream honeycomb structure 4b supporting ammonia decomposition catalyst and a downstream honeycomb structure 4c supporting ammonia decomposition catalyst are arranged in series with an insulating layer in between inside the case, such that the gas passes through the cells of the upstream honeycomb structure 4b before passing through the cells of the downstream honeycomb structure 4c supporting ammonia decomposition catalyst. The upstream honeycomb structure 4b supporting ammonia decomposition catalyst, which has NTC characteristics where resistance decreases as temperature rises, and the downstream honeycomb structure 4c supporting ammonia decomposition catalyst, which also has NTC characteristics where resistance decreases as temperature rises, are electrically connected in series and heated by applying an electric current.

Description

Technical Field

[0001] The present invention relates to an ammonia decomposition apparatus that decomposes ammonia to generate hydrogen and a method for manufacturing the same.

Background Art

[0002] In recent years, technologies that utilize hydrogen as an energy source have attracted attention due to global warming and fluctuations in the energy supply-demand structure. For example, the development of fuel cell vehicles that use hydrogen as fuel has been underway. However, since hydrogen is a flammable gas, there are problems in its storage, transportation, and supply. In order to solve this problem, attempts have been made to store, transport, and supply ammonia and decompose ammonia to generate hydrogen at hydrogen-consuming locations such as fuel cell vehicles.

[0003] For example, Patent Document 1 discloses an ammonia decomposition method in which an ammonia decomposition apparatus including a honeycomb structure body carrying a catalyst for decomposing ammonia is arranged at a hydrogen-consuming location, ammonia gas is passed through the cells of the honeycomb structure body, and the ammonia gas is decomposed into hydrogen and nitrogen by the catalyst.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, ammonia decomposition is an endothermic reaction. In conventional ammonia decomposition devices, as the endothermic reaction to decompose ammonia proceeds, the temperature of the honeycomb structure supporting the ammonia decomposition catalyst on the upstream side, where the ammonia concentration is high and the ammonia decomposition reaction proceeds easily, drops lower than that of the honeycomb structure supporting the ammonia decomposition catalyst on the downstream side. When the temperature drops, the catalytic activity decreases and the ammonia conversion rate decreases, and there is also a concern that cracks may occur in the honeycomb structure supporting the ammonia decomposition catalyst due to the temperature difference between the upstream and downstream sides.

[0006] The present invention has been made in view of the above problems, and aims to provide an ammonia decomposition apparatus and a method for manufacturing the same that can reduce the temperature difference between the upstream ammonia decomposition catalyst-supported honeycomb structure and the downstream ammonia decomposition catalyst-supported honeycomb structure, even when the endothermic reaction for ammonia decomposition is progressing. [Means for solving the problem]

[0007] To solve the above problems, one aspect of the present invention provides an ammonia decomposition apparatus comprising a case and at least two ammonia decomposition catalyst-supported honeycomb structures having partitions on which ammonia decomposition catalysts are supported to partition a number of cells, wherein an upstream ammonia decomposition catalyst-supported honeycomb structure and a downstream ammonia decomposition catalyst-supported honeycomb structure are arranged in series with an insulating layer in the case such that the gas passes through the cells of the upstream ammonia decomposition catalyst-supported honeycomb structure and then through the cells of the downstream ammonia decomposition catalyst-supported honeycomb structure, and the upstream ammonia decomposition catalyst-supported honeycomb structure having NTC characteristics in which resistance decreases as temperature rises and the downstream ammonia decomposition catalyst-supported honeycomb structure having NTC characteristics in which resistance decreases as temperature rises are electrically connected in series and heated by energization.

[0008] Another aspect of the present invention relates to a method for manufacturing an ammonia decomposition apparatus comprising a case and at least two ammonia decomposition catalyst-supported honeycomb structures having partitions on which ammonia decomposition catalysts are supported to partition a number of cells, the method comprising: arranging an upstream ammonia decomposition catalyst-supported honeycomb structure and a downstream ammonia decomposition catalyst-supported honeycomb structure in series within the case with an insulating layer in between such that the gas passes through the cells of the upstream ammonia decomposition catalyst-supported honeycomb structure and then through the cells of the downstream ammonia decomposition catalyst-supported honeycomb structure; and electrically connecting the upstream ammonia decomposition catalyst-supported honeycomb structure having NTC characteristics in which resistance decreases as temperature rises and the downstream ammonia decomposition catalyst-supported honeycomb structure having NTC characteristics in which resistance decreases as temperature rises in series. [Effects of the Invention]

[0009] According to the present invention, as the endothermic reaction that decomposes ammonia proceeds, the temperature of the upstream ammonia decomposition catalyst-supported honeycomb structure decreases compared to the downstream ammonia decomposition catalyst-supported honeycomb structure, and due to the NTC characteristics, the resistance of the upstream ammonia decomposition catalyst-supported honeycomb structure increases compared to the downstream ammonia decomposition catalyst-supported honeycomb structure. Since the upstream and downstream ammonia decomposition catalyst-supported honeycomb structures are electrically connected in series and the same magnitude of current flows through them, the amount of heat generated by the upstream ammonia decomposition catalyst-supported honeycomb structure becomes greater than that of the downstream ammonia decomposition catalyst-supported honeycomb structure. Therefore, the temperature difference between the upstream and downstream ammonia decomposition catalyst-supported honeycomb structures can be reduced, and the conversion rate of ammonia can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic perspective view showing an example of an ammonia decomposition apparatus according to the first embodiment of the present invention. [Figure 2]This is a schematic perspective view showing an example of the electrical connections in a honeycomb structure supporting an ammonia decomposition catalyst. [Figure 3] This is a schematic perspective view showing an example of the configuration of a honeycomb structure supporting an ammonia decomposition catalyst. [Figure 4] This is a schematic perspective view showing an example of an ammonia decomposition apparatus according to a second embodiment of the present invention. [Modes for carrying out the invention]

[0011] Hereinafter, an ammonia decomposition apparatus and a method for manufacturing the same, according to embodiments of the present invention, will be described in detail based on the attached drawings. However, the ammonia decomposition apparatus and a method for manufacturing the same of the present invention can be embodied in various forms and are not limited to the embodiments described herein. These embodiments are provided with the intention that those skilled in the art will be able to fully understand the invention by making full disclosures in the specification. (First Embodiment)

[0012] Figure 1 is a schematic perspective view showing an example of an ammonia decomposition apparatus 1 according to the first embodiment of the present invention. The ammonia decomposition apparatus 1 of this embodiment comprises a case 2 and at least two (e.g., three) ammonia decomposition catalyst-supported honeycomb structures 4a, 4b, 4c (hereinafter simply referred to as catalyst-supported honeycomb structures 4a, 4b, 4c) arranged in series in the gas flow path within the case 2.

[0013] Case 2 comprises a gas inlet 2a formed in a tapered shape with an increasing inner diameter downstream, a housing section 2b for housing catalyst-supported honeycomb structures 4a, 4b, and 4c, and a gas outlet 2c formed in a tapered shape with a decreasing inner diameter downstream. Ammonia gas or ammonia gas and air are supplied to the gas inlet 2a. By supplying ammonia gas and air, the exothermic reaction between ammonia and oxygen can reduce the amount of heat absorbed in the endothermic reaction when ammonia is decomposed.

[0014] In Case 2, the upstream catalyst-supported honeycomb structure 4a, the upstream catalyst-supported honeycomb structure 4b, and the downstream catalyst-supported honeycomb structure 4c are arranged in series from the upstream side of the gas flow path. The gas passes through the cells of the upstream catalyst-supported honeycomb structure 4a, then through the cells of the upstream catalyst-supported honeycomb structure 4b, and then through the cells of the downstream catalyst-supported honeycomb structure 4c. Insulating layers 5a and 5b are interposed between the catalyst-supported honeycomb structures 4a, 4b, and 4c. The insulating layers 5a and 5b are plate-shaped insulators such as silica or alumina, or air layers.

[0015] The number of catalyst-supported honeycomb structures 4a, 4b, and 4c is not particularly limited as long as it is two or more. By integrating the catalyst-supported honeycomb structures 4a, 4b, and 4c into a long structure, the surface area for the catalytic reaction can be increased, and the amount of hydrogen produced can be increased. However, if the catalyst-supported honeycomb structures 4a, 4b, and 4c are integrated into a long structure, there is a risk that the integrated catalyst-supported honeycomb structures 4a, 4b, and 4c may crack due to the temperature difference between the upstream and downstream sides. To prevent cracking, multiple catalyst-supported honeycomb structures 4a, 4b, and 4c, separated from each other, are arranged in series within the case 2. The catalyst-supported honeycomb structures 4a, 4b, and 4c are fixed to the inner surface of the case 2, for example, by a ceramic fiber mat material wrapped around their outer circumference.

[0016] Upstream of the catalyst-supported honeycomb structures 4a, 4b, and 4c, a honeycomb structure 6 that does not support the ammonia decomposition catalyst is positioned. This honeycomb structure 6 is used to heat the gas and is conductive so that it can be heated by electricity.

[0017] FIG. 2 is a perspective view schematically showing an example of the electrical connection of the catalyst-supporting honeycomb structures 4a, 4b, and 4c. The catalyst-supporting honeycomb structures 4a, 4b, and 4c have NTC (negative temperature coefficient) characteristics in which the resistance decreases as the temperature rises. The catalyst-supporting honeycomb structures 4a, 4b, and 4c are made of, for example, a ceramic mainly composed of silicon carbide and have conductivity so as to be capable of being heated by energization. A pair of electrodes 7 and 8 are provided on the side surfaces of each of the catalyst-supporting honeycomb structures 4a, 4b, and 4c.

[0018] The upstream catalyst-supporting honeycomb structure 4b and the downstream catalyst-supporting honeycomb structure 4c are electrically connected in series. The electrode 7 on the side surface of the catalyst-supporting honeycomb structure 4b is connected to a power supply circuit (not shown) via a cable 11. The electrode 8 on the side surface of the catalyst-supporting honeycomb structure 4b is connected to the electrode 8 on the side surface of the catalyst-supporting honeycomb structure 4c via a cable 12. The electrode 7 on the side surface of the catalyst-supporting honeycomb structure 4c is connected to a power supply circuit (not shown) via a cable 13.

[0019] The same magnitude of current flows through the upstream catalyst-supporting honeycomb structure 4b and the downstream catalyst-supporting honeycomb structure 4c. The current supplied from the power supply circuit to the upstream catalyst-supporting honeycomb structure 4b via the cable 11 passes through the inside of the catalyst-supporting honeycomb structure 4b, passes through the inside of the downstream catalyst-supporting honeycomb structure 4c via the cable 12, and returns to the power supply circuit or flows to the ground via the cable 13.<000-088>

[0020] The upstream catalyst-supporting honeycomb structure 4a, that is, the front-stage catalyst-supporting honeycomb structure 4a, is disposed in front of the catalyst-supporting honeycomb structure 4b. The catalyst-supporting honeycomb structure 4a is heated by energization separately from the catalyst-supporting honeycomb structures 4b and 4c. Cables 14 and 15 different from the cables 11, 12, and 13 are connected to the electrodes 7 and 8 of the front-stage catalyst-supporting honeycomb structure 4a. The current supplied from a power supply circuit (not shown) to the front-stage catalyst-supporting honeycomb structure 4a via the cable 14 passes through the inside of the front-stage catalyst-supporting honeycomb structure 4a and returns to the power supply circuit via the cable 15.

[0021] An explanation will be given for a mechanism that reduces the temperature difference between the upstream catalyst - supported honeycomb structure 4b and the downstream catalyst - supported honeycomb structure 4c. The gas supplied from the gas inlet 2a passes through the cells of the catalyst - supported honeycomb structures 4a, 4b, and 4c, and is decomposed into hydrogen and nitrogen as shown in Equation 1 by an ammonia - decomposition catalyst supported on the partition walls that form the cells. (Equation 1) 2NH3→N2 + 3H2…Endothermic reaction

[0022] As the endothermic reaction of Equation 1 for decomposing ammonia proceeds, the temperature of the upstream catalyst - supported honeycomb structure 4b decreases more than that of the downstream catalyst - supported honeycomb structure 4c, and due to the NTC characteristics, the resistance of the catalyst - supported honeycomb structure 4b increases more than that of the catalyst - supported honeycomb structure 4c. The catalyst - supported honeycomb structure 4b and the catalyst - supported honeycomb structure 4c are electrically connected in series, and since the same magnitude of current flows, the heat - generation amount of the catalyst - supported honeycomb structure 4b becomes larger than that of the catalyst - supported honeycomb structure 4c. Therefore, the temperature difference between the catalyst - supported honeycomb structure 4b and the catalyst - supported honeycomb structure 4c can be reduced, and the conversion rate of ammonia can be improved.

[0023] The electrical resistivity of the catalyst - supported honeycomb structure 4b may be the same as that of the catalyst - supported honeycomb structure 4c, or may be larger than that of the catalyst - supported honeycomb structure 4c. If the electrical resistivity of the catalyst - supported honeycomb structure 4b is larger than that of the catalyst - supported honeycomb structure 4c, the temperature difference between the two can be reduced more.

[0024] The electrode 8 provided on the side surface of the catalyst - supported honeycomb structure 4b and the electrode 8 provided on the side surface of the catalyst - supported honeycomb structure 4c are connected via a cable 12. For this reason, the electrodes 8, 8 and the cable 12 can be connected outside the gas flow path, preventing these connection parts from being corroded by the gas and preventing them from cracking due to heat shock. Also, by connecting the catalyst - supported honeycomb structure 4b and the catalyst - supported honeycomb structure 4c via the cable 12, it becomes easier to install the catalyst - supported honeycomb structures 4b, 4c in the case 2, and it also becomes easier to replace the catalyst - supported honeycomb structures 4b, 4c.

[0025] A catalyst-supported honeycomb structure 4a is placed in front of the catalyst-supported honeycomb structure 4b, and the catalyst-supported honeycomb structure 4a in the front is electrically heated separately from the catalyst-supported honeycomb structure 4b and the catalyst-supported honeycomb structure 4c. This allows for a larger amount of heat to be released from the catalyst-supported honeycomb structure 4a in the front, which has a large heat absorption capacity.

[0026] The electrical resistivity of the catalyst-supported honeycomb structure 4a may be the same as that of the catalyst-supported honeycomb structures 4b and 4c, or it may be greater than that of the catalyst-supported honeycomb structures 4b and 4c. If the electrical resistivity of the catalyst-supported honeycomb structure 4a is greater than that of the catalyst-supported honeycomb structures 4b and 4c, the amount of heat generated by the catalyst-supported honeycomb structure 4a can be increased.

[0027] In the above embodiment, two catalyst-supported honeycomb structures 4b and 4c are electrically connected in series, but three or more catalyst-supported honeycomb structures may be electrically connected in series. Furthermore, in the above embodiment, one catalyst-supported honeycomb structure 4a is placed in front of the catalyst-supported honeycomb structure 4b, but two or more catalyst-supported honeycomb structures may be placed. When two or more catalyst-supported honeycomb structures are placed, they may be electrically connected in series. Furthermore, the catalyst-supported honeycomb structures 4a, 4b, and 4c may be energized individually, and when the gas temperature rises, the two downstream catalyst-supported honeycomb structures 4b and 4c may be electrically connected in series, and when the gas temperature rises further, the three catalyst-supported honeycomb structures 4a, 4b, and 4c may be electrically connected in series. (Configuration of catalyst-supported honeycomb structure)

[0028] The structure of the catalyst-supported honeycomb structure 4b is described below. Note that the structures of the catalyst-supported honeycomb structures 4a and 4c are substantially the same as those of the catalyst-supported honeycomb structure 4b, so they are denoted by the same reference numerals and their descriptions are omitted. The structure of the honeycomb structure 6 shown in Figure 1 is substantially the same as that of the catalyst-supported honeycomb structure 4b, except that it does not support an ammonia decomposition catalyst.

[0029] Figure 3 is a schematic perspective view showing an example of a catalyst-supported honeycomb structure 4b. The catalyst-supported honeycomb structure 4b has a flow path through which gas passes, and comprises a plurality of cells 21 extending from the inlet end face 23 to the outlet end face 24, partition walls 22 that divide the plurality of cells 21, and an outer peripheral wall 25 located on the outermost periphery. An ammonia decomposition catalyst is supported on the inner surfaces of the partition walls 22 and the outer peripheral wall 25. The catalyst-supported honeycomb structure 4b is cylindrical, and its cross-section is circular, but its cross-section may be oval, or a polygonal shape such as a square.

[0030] The catalytically active species used in an ammonia decomposition catalyst is not particularly limited as long as it decomposes ammonia into hydrogen, but at least one element selected from the group consisting of Groups 6, 7, 8, 9, 10, and 11 can be used as the catalytically active species, such as ruthenium, rhodium, palladium, platinum, etc.

[0031] The catalytically active species can be used by supporting them on a catalyst support 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 also be a composite oxide containing two or more oxides. Alternatively, the oxide may be a zeolite. By supporting the catalytically active species on such an oxide catalyst support, it is possible to improve the dispersibility of the catalytically active species and the mechanical strength of the catalyst.

[0032] When the gas introduced into the gas inlet 2a reaches the catalyst-supported honeycomb structure 4b, the gas flows into a cell 21 opening at the inlet end face 22 of the catalyst-supported honeycomb structure 4b, and passes through the cell 21 while in contact with the ammonia decomposition catalyst supported on the partition wall 22. At this time, the ammonia gas is decomposed into hydrogen and oxygen by the ammonia decomposition catalyst. The hydrogen and oxygen flow out from a cell 21 opening at the outlet end face 24 of the catalyst-supported honeycomb structure 4b.

[0033] A pair of electrodes 7 and 8 are provided on the side surface of the catalyst-supported honeycomb structure 4b. The electrodes 7 and 8 are positioned opposite each other, with the center of the catalyst-supported honeycomb structure 4b in between. The electrodes 7 and 8 are strip-shaped and extend in the axial direction of the catalyst-supported honeycomb structure 4b, and are in contact with the entire length of the side surface of the catalyst-supported honeycomb structure 4b. The material of the electrodes 7 and 8 is a conductive material, such as a metal, conductive ceramic, or a composite material combining a metal and an oxide ceramic. Examples of metals include silver, copper, iron, aluminum, tungsten, or alloy steel. Examples of conductive ceramics include silicon carbide, chromium silide, boron carbide, chromium boride, or tantalum silide. Examples of oxide ceramics include glass, cordierite, and mullite.

[0034] An intermediate layer (not shown) with a lower coefficient of thermal expansion than electrodes 7 and 8 may be provided between electrodes 7 and 8 and the catalyst-supported honeycomb structure 4b. The intermediate layer may be made of a metal, oxide ceramic, or the same material as electrodes 7 and 8. Electrodes 7 and 8 have a higher coefficient of thermal expansion than the catalyst-supported honeycomb structure 4b. By providing an intermediate layer, the difference in coefficients of thermal expansion between electrodes 7 and 8 and the catalyst-supported honeycomb structure 4b can be reduced. (Method for manufacturing a catalyst-supported honeycomb structure)

[0035] The honeycomb structure is manufactured by firing a honeycomb molded body containing silicon carbide powder, silicon nitride powder, and carbon. The silicon carbide powder is used as aggregate in the honeycomb structure. The silicon nitride powder and carbon are used as binders to hold the silicon carbide powder together.

[0036] First, a molding raw material is prepared by adding water, a binder, etc., to silicon carbide powder, silicon nitride powder, carbon. The average particle size of the silicon carbide powder is, for example, 1 to 50 μm. The content of silicon carbide powder relative to the silicon carbide powder, silicon nitride powder, and carbon is, for example, 20 to 70% by mass. The carbon is graphite, carbon black, etc. The molar ratio of silicon constituting silicon nitride to carbon is, for example, in the range of 1.0 to 2.0. The binder is methylcellulose, etc. The content of the binder is, for example, 2 to 15 parts by mass when the total mass of silicon carbide powder, silicon nitride powder, and carbon is 100 parts by mass. The content of water is, for example, 20 to 30 parts by mass when the total mass of silicon carbide powder, silicon nitride powder, and carbon is 100 parts by mass. In addition to the above raw materials, surfactants such as ethylene glycol, dextrin, fatty acid soap, and polyalcohol may be added.

[0037] Next, the obtained molding raw materials are kneaded to produce clay, and then the clay is extruded to produce a honeycomb molded body. After drying the honeycomb molded body, it is fired at a temperature of, for example, 1800°C to 2300°C in a vacuum or a nitrogen-free, non-oxidizing atmosphere such as an inert gas, to produce a honeycomb structure. When a honeycomb molded body is fired, silicon nitride and carbon react to synthesize silicon carbide. The synthesized silicon carbide then binds to the silicon carbide powder used as aggregate.

[0038] The honeycomb structure contains nitrogen derived from silicon nitride powder as an impurity. Since nitrogen functions as a dopant that contributes to electrical conductivity, the honeycomb structure is conductive. When electricity is passed through the honeycomb structure, it generates heat. Because the honeycomb structure has a fine and uniform pore size distribution, it heats up uniformly.

[0039] Electrodes 7 and 8 and the intermediate layer are manufactured, for example, as follows: A ceramic raw material is prepared by mixing metal powder and glass powder. A binder, 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 to the honeycomb structure and dried to form a coating film. The honeycomb structure with the coating film is fired to produce the intermediate layer.

[0040] Electrodes 7 and 8 on the intermediate layer are manufactured in the same way as the intermediate layer. Specifically, metal powder and glass powder are mixed to create a ceramic raw material. A binder, surfactant, and water are added to the ceramic raw material to create a paste for the electrodes. The electrode paste is applied to the intermediate layer and dried to form a coating. The honeycomb structure with the coating is fired to form electrodes 7 and 8. Alternatively, the intermediate layer and electrodes 7 and 8 may be manufactured by thermal spraying the thermal spray material onto the honeycomb structure.

[0041] Conventional methods can be used to support the ammonia decomposition catalyst on the honeycomb structure. For example, a method can be used in which the honeycomb structure is immersed in a solution of catalytically active species and then calcined; a method can be used in which a powder on which catalytically active species is supported on a catalyst support made of oxide is wet-milled to produce a slurry, which is then applied to the honeycomb structure and calcined; a method can be used in which a slurry is produced by wet-milling a catalyst support made of oxide, which is then applied to the honeycomb structure and calcined, and then the honeycomb structure is immersed in a solution of catalytically active species and calcined. (Method of manufacturing an ammonia decomposition device)

[0042] Insulating layers 5a and 5b are interposed between catalyst-supported honeycomb structures 4a, 4b, and 4c arranged in series, and a mat material made of ceramic fibers is wrapped around the outer circumference of the catalyst-supported honeycomb structures 4a, 4b, and 4c. Then, the catalyst-supported honeycomb structures 4a, 4b, and 4c with the wrapped mat material are pressed into case 2. Alternatively, the catalyst-supported honeycomb structures 4a, 4b, and 4c with the wrapped mat material are sandwiched between two semi-cylindrical halves of a case. After that, cables 11 to 15 are connected to the terminals of electrodes 7 and 8 of the catalyst-supported honeycomb structures 4a, 4b, and 4c, which protrude from the outside of case 2, on the outside of case 2. (Second Embodiment)

[0043] Figure 4 is a schematic perspective view showing an example of the electrical connections of the catalyst-supported honeycomb structures 4a, 4b, and 4c in the ammonia decomposition apparatus of the second embodiment of the present invention. The catalyst-supported honeycomb structures 4a, 4b, and 4c of the second embodiment have an NTC (negative temperature coefficient) characteristic in which resistance decreases as the temperature rises, similar to the catalyst-supported honeycomb structures 4a, 4b, and 4c of the first embodiment. The configuration of the catalyst-supported honeycomb structures 4a, 4b, and 4c of the second embodiment is the same as that of the catalyst-supported honeycomb structures 4a, 4b, and 4c of the first embodiment, so the same reference numerals are used and their descriptions are omitted.

[0044] In the ammonia decomposition apparatus of the second embodiment, three catalyst-supported honeycomb structures 4a, 4b, and 4c are electrically connected in series. The electrode 7 on the side of the upstream catalyst-supported honeycomb structure 4a is connected to the power supply circuit via cable 31. The electrode 8 on the side of the upstream catalyst-supported honeycomb structure 4a is connected to the electrode 8 on the side of the upstream catalyst-supported honeycomb structure 4b via cable 32. The electrode 7 on the side of the upstream catalyst-supported honeycomb structure 4b is connected to the electrode 7 on the side of the downstream catalyst-supported honeycomb structure 4c via cable 33. The electrode 8 on the side of the downstream catalyst-supported honeycomb structure 4c is connected to the power supply circuit via cable 34.

[0045] The same magnitude of current flows through the catalyst-supported honeycomb structures 4a, 4b, and 4c. The current supplied from the power supply circuit to the upstream catalyst-supported honeycomb structure 4a via cable 31 passes through the inside of catalyst-supported honeycomb structure 4a, through cable 32 to the inside of the upstream catalyst-supported honeycomb structure 4b, through cable 33 to the inside of the downstream catalyst-supported honeycomb structure 4c, and then returns to the power supply circuit or flows to ground via cable 34.

[0046] As in the ammonia decomposition apparatus of the second embodiment, three catalyst-supported honeycomb structures 4a, 4b, and 4c may be electrically connected in series, or four or more catalyst-supported honeycomb structures may be electrically connected in series. [Explanation of Symbols]

[0047] 1…Ammonia decomposition device 2…case 4a, 4b, 4c... Honeycomb structure supporting ammonia decomposition catalyst 5a, 5b... Insulating layer 7,8...electrode 12,33… Cable 21...Cell 22…Bulkhead

Claims

1. The device comprises a case and at least two honeycomb structures supporting ammonia decomposition catalysts, each having a partition wall on which an ammonia decomposition catalyst is supported, forming a series of cells. Within the aforementioned case, an upstream ammonia decomposition catalyst-supported honeycomb structure and a downstream ammonia decomposition catalyst-supported honeycomb structure are arranged in series with an insulating layer in between, such that the gas passes through the cells of the upstream ammonia decomposition catalyst-supported honeycomb structure first, and then through the cells of the downstream ammonia decomposition catalyst-supported honeycomb structure. An ammonia decomposition apparatus that electrically connects an upstream honeycomb structure supporting an ammonia decomposition catalyst, which has NTC characteristics that decrease in resistance as the temperature rises, and a downstream honeycomb structure supporting an ammonia decomposition catalyst, which also has NTC characteristics that decrease in resistance as the temperature rises, in series and heats them by applying an electric current.

2. An ammonia decomposition catalyst-supported honeycomb structure is placed upstream of the aforementioned upstream ammonia decomposition catalyst-supported honeycomb structure. The ammonia decomposition apparatus according to claim 1, characterized in that the preceding ammonia decomposition catalyst-supported honeycomb structure is electrically heated separately from the upstream ammonia decomposition catalyst-supported honeycomb structure and the downstream ammonia decomposition catalyst-supported honeycomb structure.

3. An ammonia decomposition catalyst-supported honeycomb structure is placed upstream of the aforementioned upstream ammonia decomposition catalyst-supported honeycomb structure. The ammonia decomposition apparatus according to claim 1, characterized in that the preceding ammonia decomposition catalyst-supported honeycomb structure, the upstream ammonia decomposition catalyst-supported honeycomb structure, and the downstream ammonia decomposition catalyst-supported honeycomb structure are electrically connected in series and heated by energization.

4. The ammonia decomposition apparatus according to claim 1, characterized in that the catalyst for decomposing ammonia is a catalyst on which at least one element selected from the group consisting of Group 6, Group 7, Group 8, Group 9, Group 10, and Group 11 is supported as a catalytically active species on a catalyst support made of an oxide.

5. The ammonia decomposition apparatus according to claim 4, characterized in that the oxide contains at least one element selected from the group consisting of Al, Si, Ti, Zr, Group 1, Group 2, and Group 3.

6. The ammonia decomposition apparatus according to claim 4 or 5, characterized in that the oxide is a composite oxide containing two or more oxides.

7. The ammonia decomposition apparatus according to claim 4 or 5, characterized in that the oxide is a zeolite.

8. The ammonia decomposition apparatus according to any one of claims 1 to 3, characterized in that the electrical resistivity of the upstream ammonia decomposition catalyst-supported honeycomb structure is greater than that of the downstream ammonia decomposition catalyst-supported honeycomb structure.

9. The ammonia decomposition apparatus according to claim 2 or 3, characterized in that the electrical resistivity of the preceding ammonia decomposition catalyst-supported honeycomb structure is greater than that of the downstream ammonia decomposition catalyst-supported honeycomb structure.

10. The ammonia decomposition apparatus according to any one of claims 1 to 3, characterized in that an electrode provided on the side surface of the upstream ammonia decomposition catalyst-supported honeycomb structure and an electrode provided on the side surface of the downstream ammonia decomposition catalyst-supported honeycomb structure are connected via a cable.

11. A method for manufacturing an ammonia decomposition apparatus comprising a case and at least two honeycomb structures supporting ammonia decomposition catalysts, each having a partition wall on which an ammonia decomposition catalyst is supported to partition a large number of cells, The process involves arranging an upstream ammonia decomposition catalyst-supported honeycomb structure and a downstream ammonia decomposition catalyst-supported honeycomb structure in series within the case, with an insulating layer in between, such that the gas passes through the cells of the upstream ammonia decomposition catalyst-supported honeycomb structure first, and then through the cells of the downstream ammonia decomposition catalyst-supported honeycomb structure. A method for manufacturing an ammonia decomposition apparatus, comprising the step of electrically connecting in series an upstream honeycomb structure supporting an ammonia decomposition catalyst which has an NTC characteristic in which its resistance decreases as the temperature rises, and a downstream honeycomb structure supporting an ammonia decomposition catalyst which has an NTC characteristic in which its resistance decreases as the temperature rises.

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