JP2010240568A - Gas decomposition composite and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas decomposition composite that is small sized and has high decomposition efficiency and low pressure drop loss, and whose durability over shock or vibration is high, and a method for manufacturing the same. <P>SOLUTION: The gas decomposition composite 10 includes a porous metal 1 that composes the base body of the gas composition composite and a reaction section 20 in which a plurality of granules are connected, which are positioned on a surface of the porous metal, the reaction section 20 contains materials composing cathode, electrolyte, and anode for electrochemical reaction, and the porous metal is composed of three-dimensional mesh-like metallic body having air holes that continue isotropically. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gas decomposition composite and a method for producing the same, and more specifically to a gas decomposition composite that can efficiently decompose gas and has high durability, and a method for producing the same.

As for automobiles, automobiles equipped with diesel engines tend to increase. However, it is necessary to satisfy the waste gas regulations, and various catalytic devices for reducing exhaust gas from diesel engines have been developed. Among these catalytic devices, the urea selective reduction system is recommended as a device that efficiently reduces and purifies NOx into nitrogen and water in a temperature range where the engine speed is low (Non-patent Document 1). These exhaust gas purification devices are attached to the exhaust path of an automobile engine and purify the exhaust gas. For this purpose, the temperature of the exhaust passage and the NOx concentration are measured to control the injection amount of urea into the exhaust passage. For example, a device has been proposed in which a NOx sensor is provided at the subsequent stage of urea injection, and NO and NO ₂ are separately determined stoichiometrically to control the optimum urea injection amount (Patent Document 1). In addition, an oxidation catalyst and a urea selective reduction device are arranged in the exhaust path in the exhaust path, and NOx decomposition is performed using two NOx sensors arranged before and after the oxidation catalyst in the front stage of the urea selective reduction device. There is also a proposal of a method (patent document 2).
Further, there has been proposed a method for electrochemically decomposing NOx by mixing and dispersing a NOx reduction catalyst, a hydrocarbon oxidation catalyst, and an ion conductive solid electrolyte on the surface of a metal honeycomb. (Patent Document 3). In the present invention, a honeycomb structure obtained by superimposing corrugated stainless steel and a stainless steel plate is cited as a metal honeycomb (Patent Document 4).
In addition, regarding ammonia detoxification, there has been a proposal for an exhaust gas treatment of a semiconductor manufacturing apparatus using a hydrogen-oxygen fuel cell type decomposition method in order to obtain an inexpensive running cost without input of energy or chemicals. (Patent Document 5).

JP 2004-1000069 A Japanese Patent Laid-Open No. 2007-100508 JP 2001-070755 A Japanese Patent Laid-Open No. 05-301048 JP 2003-45472 A

Hirata, K., et al., “Urea Selective Reduction System for Large Car Diesel”, Automotive Technology, Vol.60, No.9, 2006, pp28-33

Regarding the urea selective reduction device that decomposes NOx, a urea selective reduction device that is large for an automobile is arranged in the exhaust system, resulting in an increase in weight. For automobiles, as a matter of course, it is strongly required to be small and light.
In addition, the method in which the NOx reduction catalyst or the like is dispersedly arranged on the surface of the metal honeycomb has the advantage that the metal honeycomb is thin and the pressure loss is reduced to some extent, but the density of the electrochemical reaction site is not so improved, and the pressure is reduced. Loss reduction is not sufficient. That is, it is insufficient in terms of promoting both miniaturization and decomposition efficiency.
As for ammonia, the exhaust gas treatment using the hydrogen-oxygen fuel cell type decomposition method can decompose harmful components while reducing maintenance costs. However, it is insufficient in that it can be efficiently decomposed to an extremely low concentration of, for example, 10 ppm or less.
In addition to the above problems, vibrations and shocks are frequently received. Therefore, in the case of a device with a complicated mechanism or a device including a fragile part such as a solid electrolyte ceramic sheet, a considerable shock countermeasure is required for the support mechanism. . In general applications as well as automobiles, durability against impacts cannot be neglected, but it is particularly important in automobiles.
The above problem can be summarized as follows.
1. 1. Achieving both miniaturization and high abatement efficiency and low pressure loss High durability against shock and vibration And 2. Is not limited to ammonia and NOx, but the same can be said for the decomposition of VOC (Volatile Organic Compounds) such as methane and ethane, which are malodorous gas components.

  An object of the present invention is to provide a gas decomposition composite having a small size, high decomposition efficiency, low pressure loss, and high durability against shock and vibration, and a method for manufacturing the same.

  The gas decomposition composite of the present invention decomposes a gas component by an electrochemical reaction. The gas decomposition composite includes a porous metal that forms a base of the gas decomposition composite, and a reaction portion that is located on the surface of the porous metal and is connected to a plurality of powder particles. Therefore, the porous metal is made of a three-dimensional network metal body having pores that are isotropically continuous, including materials constituting the cathode, the electrolyte, and the anode.

According to said structure, a reaction part can be provided in the surface of a solid network metal body with a high density. In addition, since the solid network metal body turbulently flows the gas containing the gas component, the contact with the reaction part can be brought into an advantageous form for promoting the reaction. For this reason, it is possible to realize a small and high decomposition efficiency. Further, since the solid network metal having pores that are isotropically continuous is used as the base, the ventilation is good and it is easy to suppress the pressure loss. In addition, since a plurality of granular reaction parts are fixed to an infinite number of three-dimensional network metal bodies and there are no fragile parts, they have high durability against impacts and vibrations. Furthermore, the above-described electrochemical reaction does not require voltage application because the material constituting the reaction part is selected so that the electrochemical reaction proceeds in a natural direction without applying voltage from the outside.
Here, the powder is a powder having a diameter in the range of about 1 nm to 10 μm. The form in which the small powder is bonded to the large powder, that is, the form in which the large powder carries the small powder may be employed.

  All the three-dimensional net-like metal bodies can be formed by a plating method. Thereby, since the ratio of the pores can be increased and the three-dimensional network-like metal-plated portion can be reduced, a range having a high porosity can be selected and widely taken. As a result, it becomes easy to reduce pressure loss. It should be noted that the determination of whether or not all of the three-dimensional network metal bodies are formed by the plating method is based on observation of the cross-sectional structure using an optical microscope, composition analysis of trace components using various solid spectroscopy, etc. Can carry out. In particular, it is very easy to distinguish between the fact that it does not depend on powder sintering that causes plastic flow due to machining, and that it does not depend on casting in which a temperature gradient is unavoidable.

A structure in which a solid network metal body is formed of a plating skeleton part and a plating surface layer part located in contact with the skeleton part, and the reaction part is located on the plating skeleton part using the plating surface layer part as a connection layer Can be taken. This makes it possible to efficiently form a reaction portion in which powder particles are connected to the plating skeleton using a composite plating method or a dispersion plating method. In particular, since the plating skeleton is formed by plating, the production efficiency can be dramatically improved by arranging a dispersion plating process that forms the plating surface layer portion in succession to the final plating step of the plating skeleton. Can do.
The distinction between the plating skeleton part and the plating surface layer part is due to the presence of powder particles and other component composition even if the metal plating is mainly composed of the same Ni or the like. It can be reliably performed by solid spectroscopy.
Note that the plating skeleton part may be simply referred to as a skeleton part or a skeleton body.

  The reaction part can be made into the structure connected to the solid network metal body by baking. According to this, a solid electrolyte and metal particles are applied to a paste in which an organic solvent or the like in which a resin is dissolved is applied, or immersed in the paste and then baked, so that the solid electrolyte and metal particles are arranged on a solid network metal body. be able to. The organic solvent in which the resin is dissolved evaporates by firing. For this reason, a gas decomposition composite can be manufactured easily.

  The porosity of the solid network metal body or the plating skeleton can be 0.6 or more and 0.98 or less. Thereby, it is possible to obtain a gas decomposition composite having a small size and high reaction efficiency while reducing pressure loss.

  By plating a three-dimensional network metal body or plating skeleton on the resin formed through a foaming process that forms countless bubbles in the resin and a continuous opening process that opens the bubbles by making the bubbles continuous. It can be formed. Thereby, a three-dimensional network metal body or a plating skeleton can be easily and efficiently obtained using a resin such as urethane or melamine.

When urethane is used for the resin in the production of a solid network metal body, when the pore diameter of the solid network metal body or the plating skeleton is x (mm) and the specific surface area is y (m ² / m ³ ) , 400 ≦ (x−0.3) y. As a result, the pressure loss can be reduced and the density of the reaction part can be increased. The high-density arrangement of the reaction parts can achieve high decomposition efficiency while reducing the size.

  All of the three-dimensional network metal body can be formed by metal plating containing Ni as a main component, and the three-dimensional network metal body can also serve as a cathode electrode for electrochemical reaction. Thus, depending on the gas component to be decomposed, the solid network metal body itself has a catalytic action for promoting decomposition. For this reason, the electron conduction path | route in an electrochemical reaction can serve as a cathode electrode. Further, using Ni, which is a metal that is easy to plate and is relatively stable (difficult to rust) in the atmosphere, a solid network metal body can be obtained inexpensively and efficiently.

  The reaction part may include solid electrolyte ceramic powder and at least one metal powder. Thereby, a high-density reaction part can be easily provided on the substrate surface.

  The method for producing a gas decomposition composite of the present invention produces a gas decomposition composite for decomposing a gas component by an electrochemical reaction. In this manufacturing method, a solid network metal skeleton having isotropic continuous pores is prepared, and a solid electrolyte powder and one or more metal powders for an electrochemical reaction are prepared. A step of preparing a metal plating solution for plating on the skeleton body, mixing the solid electrolyte powder and one or more kinds of metal powders with the metal plating solution, and stirring the mixture; Immersing the skeleton in a metal plating solution, and forming a plating layer comprising the metal of the metal plating solution, solid electrolyte powder, and one or more metal powders on the skeleton. It is characterized by.

  Accordingly, the high-density reaction part can be arranged on the solid network metal body relatively easily by the dispersion plating method. In particular, it is possible to dramatically improve the production efficiency by disposing a dispersion plating process for forming a plating layer continuously in the final plating step of the skeleton body. Here, the plating layer is the above-described plating surface layer portion, and the skeleton body is the plating skeleton portion.

  In the step of preparing the solid electrolyte powder and one or more kinds of metal powders, the one or more kinds of metal powders can be supported on the solid electrolyte by firing. Thereby, the connection between the solid electrolyte powder and the metal powder or the catalyst constituting each electrode can be reliably obtained at the stage before the dispersion plating treatment. As a result, the reaction part that functions reliably can be arranged on the substrate with high density.

  Another method for producing a gas decomposition composite of the present invention produces a gas decomposition composite for decomposing a gas component by an electrochemical reaction. This production method produces a solid network metal body having isotropic continuous pores, a solid electrolyte powder, and one or more metal powders for an electrochemical reaction. Preparing a coating solution by mixing a solid electrolyte powder and one or more metal powders with the coating solvent, stirring the coating solution, and preparing a coating solution; It is characterized by comprising a step of applying or impregnating a solid network metal body and then firing.

  According to the above method, a paste can be produced by dispersing solid electrolyte and metal particles in an organic solvent in which a resin is dissolved. By applying this paste to a solid network metal body, or by immersing the metal body in the paste and then firing, a reaction part formed of solid electrolyte powder and metal powder can be easily formed on the solid network metal body. Can be formed. The organic solvent in which the resin is dissolved evaporates by firing. For this reason, a gas decomposition composite can be manufactured easily.

  According to the gas decomposition composite of the present invention and the method for producing the same, it is small, has high decomposition efficiency and low pressure loss, and has high durability against impact and vibration.

The gas decomposition composite_body | complex in Embodiment 1 of this invention is shown, (a) is the whole external appearance shape, (b) is a figure which shows a solid network metal body and an infinite number of reaction parts. It is a figure which shows typically the electrochemical reaction in the reaction part of FIG.1 (b). The surface of a solid network metal body is shown, (a) is a SEM image, and (b) is a schematic diagram of (a). It is an enlarged view of the A part in FIG. 3, (a) is a SEM image about a precipitation part, (b) is a schematic diagram of (a). It is a figure which shows the result of having conducted a composition analysis by ESCA about the white particle | grains scattered in FIG. It is a figure which shows the result of having performed the composition analysis by ESCA about parts other than the white grain scattered in FIG. 3 is a flowchart of a method for manufacturing the gas decomposition composite according to Embodiment 1. It is a flowchart of the manufacturing method of a metal-plating frame | skeleton part or a solid network metal body. It is a figure which shows the relationship between the hole diameter and specific surface area of the solid network metal body or frame | skeleton part which were manufactured with the manufacturing method of FIG. It is a figure which shows the gas decomposition composite_body | complex of Embodiment 2 of this invention. 6 is a diagram schematically showing a reaction part of a gas decomposition composite according to Embodiment 2. FIG. 5 is a flowchart of a method for manufacturing a gas decomposition composite according to Embodiment 2.

(Embodiment 1)
FIG. 1 is a diagram showing a gas decomposition complex 10 according to Embodiment 1 of the present invention. As shown in FIG. 1A, the gas decomposition composite 10 has a sheet-like appearance as a whole, but the material forming the sheet is the solid network metal body 1. In this three-dimensional network metal body 1, all metal parts are formed by metal plating. Any metal plating may be used, but Ni plating mainly composed of Ni is particularly preferably used. The reason will be explained later. In FIG. 1 (a), the portion that emphasizes the appearance of a sheet and the portion that emphasizes the solid network metal body 1 are shown separately, but in reality, the gas decomposition composite 10 is all Needless to say, it is formed of a finer three-dimensional network metal body 1.
As shown in FIG. 1B, innumerable reaction parts 20 are provided in a granular form on the surface of the solid network metal body 1 (1a). One of the features of the solid network metal body 1 formed by plating is that the ratio of pores 1s that are voids of the solid network metal body is high. Although the manufacturing method will be described in detail later, the average size and porosity of the pores 1s can be easily controlled and changed in a large range region. For this reason, both the gas containing the gas component to be decomposed and the gas that forms a pair with the gas component in the electrochemical reaction are both (1) reduced in pressure loss and (2) both gases are solid network metal. A turbulent flow is generated in the body 1 (1a), and a contact form preferable for the reaction with the reaction unit 20 can be realized. In the case of a reaction section located on a plane, the gas flowing along the plane generates a laminar flow in the reaction section, and the reaction does not proceed easily due to the surface layer flow that stagnates over the reaction section. In this embodiment, in order to increase the efficiency of the electrochemical reaction, a solid network metal body that disturbs the laminar flow and promotes the turbulent flow in which the gas in the surface layer is continuously separated and replaced is used. The gas flowing in the solid network metal body 1 (1a) naturally becomes turbulent and the reaction occurs actively.

  In terms of low pressure loss, the above-described three-dimensional network metal body 1 does not allow other follow-up. For example, in FIG. 2, the NOx before the electrochemical reaction and the counterpart gas and the gas after the reaction flow in substantially the same direction. For this reason, it is hard to occur that the gas before reaction and the gas after reaction interfere with a velocity component in the reverse direction. On the other hand, in a reaction part fixed on a flat plate that is somewhat wide, when gas is blown onto the reaction part, the gas after reaction (and unreacted gas) rebounds with a velocity component in the direction opposite to the original direction. This results in interference and increases pressure loss. In the three-dimensional network metal body 1 in the present embodiment, although it has resistance to generate turbulent flow, the degree to which the gas has a velocity component in the reverse direction is very low. As shown in FIG. The latter gas flows in almost the same direction.

  When the reaction part 20 is formed on the surface of the solid network metal body 1 by the dispersion plating method, the plating layer 1a is formed together with the reaction part 20 on the surface of the skeleton part formed by plating. For this reason, the solid network metal body 1 is formed by the skeleton and the plating surface layer 1a. Moreover, when the reaction part 20 is arrange | positioned by paste baking containing the metal powder etc. which are demonstrated in Embodiment 2, the frame | skeleton part becomes the solid network metal body 1 as it is. Regardless of which method is used to provide the reaction unit 20, the symbol of the solid network metal body 1 is used. When it is set as the solid network metal body 1 (1a), it has shown that the reaction part 20 was provided in the solid network metal body 1 by the dispersion plating method, and the plating layer 1a was incidentally formed.

FIG. 2 is a diagram schematically showing an electrochemical reaction in the reaction unit 20. In the present embodiment, the gas component to be decomposed and the counterpart gas that forms a pair with the gas component in the electrochemical reaction are introduced together into the solid network metal body 1. In FIG. 2, the gas component to be decomposed is NOx, and the counterpart gas is CH ₄ , H ₂ , CO, or the like. The cathode 21 also serves as the solid network metal body 1 (1a) containing Ni as a main component. That is, no powder to be the cathode is provided in particular (it goes without saying), and the portion of the solid network metal 1 (1a) acts as the cathode 21. The solid electrolyte powder 22 is ion permeable but not conductive. Moreover, the silver particle 23 plays the role of an anode.
In order to distinguish and emphasize the side of the cathode 21 that is the oxygen ion generation part and the side of the anode silver particle 23 that is the electron generation part in the central and left reaction parts 20 in FIG. The distribution of silver particles supported on (scandium stabilized zirconia) 22 is unevenly distributed on one side (electron generation side and oxygen ion receiving side). However, in reality, it is uniformly distributed on the surface of SSZ22, and exchange of electrons and exchange of oxygen ions are performed in a small local portion where silver particles of SSZ22 are located.

In the electrochemical reaction in FIG. 2, since the potential of the cathode 21 is higher than the potential of the anode 23 by a predetermined value or more, the electrons are attracted to the cathode through the three-dimensional network metal body 1 (1a) and proceed automatically. The cathode 21, the solid electrolyte 22, and the anode 23 are in contact with each other. A cathode reaction of 2NO + 4e ⁻¹ → N ₂ + 2O ²⁻ or 2NO ₂ + 8e ⁻¹ → N ₂ + 4O ²⁻ occurs at the interface between the cathode 21 and the solid electrolyte 22. When the counterpart gas is CH ₄ , a reaction of CH ₄ + 4O ²⁻ → 2H ₂ O + CO ₂ + 8e ⁻¹ occurs at the anode. Oxygen ions pass through the solid electrolyte 22 from the cathode to the anode. The counterpart gas of NOx is not limited to CH _4, and may be CO or H ₂ . The reduction potentials of NO and NO ₂ are approximately 1.5V and 1.4V, respectively, using a metal mainly composed of Ni as a catalyst. Further, in the silver particles of the anode 23, the oxidation potentials of CO ₂ / C, H ⁺ / H ₂ , and CO ₂ / CO are approximately 0.2 V, 0 V, and −0.1 V, respectively. For this reason, the potential of the portion of the cathode 21 where NOx reacts is considerably higher than the potential of the portion of the anode 23 where the counterpart gas is oxidized. For this reason, the decomposition reaction of NOx naturally progresses not only when the counterpart gas is CH ₄ but also when the counterpart gas is H ₂ or CO.

Further, when ammonia is used as a gas component to be decomposed and the other gas is used as oxygen or air, the following electrochemical reaction is performed although not shown. The ammonia decomposition electrochemical reaction also proceeds spontaneously without applying a driving force (voltage) from the outside because the cathode potential is higher than the anode potential by a predetermined value or more. Ions passing through the solid electrolyte 22 are oxygen ions.
(Cathode reaction): O ₂ + 2e ⁻¹ → O ²⁻
(Anode reaction): 2NH ₃ + 3O ^{2 −} → N ₂ + 3H ₂ O + 6e ⁻¹
In the combination of the gas component (NOx, ammonia) to be decomposed and the other gas, oxygen ions move from the cathode 21 to the anode 23 as the electrons move. Depending on the combination of gases, proton H ⁺ instead of oxygen ions moves through the solid electrolyte 22. In addition, there is a combination in which phosphate ions move.

  In order to make the electrochemical reaction proceed efficiently, it is preferable to heat the reaction section 20 to a high temperature. At high temperatures, the time for ions to pass through the solid electrolyte 22 can be shortened, and the reactions at the anode 23 / solid electrolyte 22 and cathode 21 / solid electrolyte 22 interfaces can be promoted. In the case of NOx decomposition reaction, it is preferable to heat to 250 ° C to 650 ° C. In the case of ammonia decomposition, it is preferable to heat to 700 ° C to 950 ° C. In an actual gas decomposition apparatus, the entire gas decomposition composite 10 is heated by a heater or the like. When mounted on an automobile, such as NOx decomposition, heat generated by an internal combustion engine or the like is preferably used by assisting or using the main body.

FIG. 3 is a diagram showing the surface of a three-dimensional network metal body. (A) shows a SEM (Scanning Electron Microscopy) image, and (b) is a schematic diagram of (a). Countless fine granular parts are attached to the surface of the solid network metal body 1 (1a). This granular part is the reaction part 20. It can be seen that the diameter or width of the mesh thread (skeleton) of the three-dimensional network metal body 1 is about 300 μm.
FIG. 4 is an enlarged view of a portion A in FIG. (A) is a SEM image about a precipitation part, (b) is a schematic diagram of (a). The gray, relatively large mass is the SSZ of the solid electrolyte 22. White particles are scattered on the gray lump, and the white particles scattered are the anodes 23 of silver particles. The cathode 21 is shared by Ni of the solid network metal body 1. 4A and 4B, the SSZ of the solid electrolyte 22 is about 0.2 μm to 1 μm across, and the silver particles that share the anode 23 are about 0.005 μm to 0.05 μm across. The silver particles 23 are first supported on the SSZ 22, and then the SSZ 22 supporting the silver particles 23 appears to be subjected to a dispersion plating process on the three-dimensional network metal body 1. Although the manufacturing method will be described later, in fact, SSZ22 supporting silver particles 23 is dispersed in a Ni plating solution, and Ni plating is performed on the three-dimensional network skeleton using the Ni plating solution, thereby forming reaction part 20 as a metal. 1 is fixed on the surface.

  FIG. 5 shows the results of a composition analysis performed on scattered white particles by ESCA (Electron Spectroscopy for Chemical Analysis). A large peak of characteristic X-rays in the vicinity of 3 nm derived from silver (Ag) is recognized together with zirconium (Zr) which is the composition of the base SSZ and nickel (Ni) of the plating base. On the other hand, FIG. 6 shows the ESCA analysis results of places (gray portions) other than the scattered white grains. In FIG. 6, there is no strong peak in the vicinity of 3 nm derived from Ag, and a peak derived from Zr and a peak derived from Ni appear strongly.

FIG. 7 is a diagram showing a method for manufacturing the gas decomposition composite 10 of the present embodiment. First, a solid network metal body (skeleton part) is prepared. A method for manufacturing the skeleton part of the three-dimensional network metal will be described shortly. In addition, a commercially available product may be purchased as the three-dimensional network metal body. For example, Celmet (registered trademark) manufactured by Sumitomo Electric Industries, Ltd. can be used. The pore diameter and the porosity or specific surface area are classified, and can be purchased by specifying the classification number. Usually, it is marketed in the form of a sheet having a predetermined thickness.
In order to obtain a good surface state for plating on the skeleton of the three-dimensional network metal body, (1) cathodic electrolytic degreasing is performed, and (2) acid activity is performed. Cathodic electrolytic degreasing treatment is performed using an alkaline degreasing agent (for example, A-screen A220) under the conditions of a current density of 5 A / dm2, a temperature of 50 ° C., a degreasing time of 30 seconds, and a stirrer stirring speed of 300 rpm. The acid activity is carried out by keeping a solution having a concentration of activator Kokeisan RP of 180 g / L at 55 ° C. and immersing the skeleton of the solid network metal body after the cathodic electrolysis degreasing.
In parallel with the surface treatment of the skeleton, a solid electrolyte powder carrying a metal powder is formed. In the present embodiment, silver particles are used as the metal powder, and SSZ (scandium stabilized zirconia) is used as the solid electrolyte powder. In order to form SSZ carrying silver particles, a silver aqueous solution is prepared, and SSZ powder is prepared in this silver aqueous solution. For example, 2 cc of an aqueous silver solution and 0.4 g of SSZ powder are preferably prepared. SSZ powder carrying silver particles can be obtained by removing moisture by performing heat treatment at 200 ° C. for 1 hour on a hot plate. In addition to the above SSZ, solid electrolytes include YSZ (yttrium stabilized zirconia), SDC (samarium stabilized ceria), LSGM (lanthanum strontium gallium manganite (lanthanum gallate)), GDC (gadria stabilized ceria), CsH. ₂ PO ₄ or the like can be used.
Thereafter, the silver particle-supported SSZ powder is preferably mixed with a cationic surfactant (for example, an aqueous solution of a conditioner 231 and stirred for 5 minutes. Next, an aqueous solution of a cationic surfactant containing the silver particle-supported SSZ powder in a Ni plating solution. The Ni plating solution consists of 300 g / L of sulfuric acid, 45 g / L of nickel chloride, 45 g / L of boric acid, UPS (3-[(amino-iminomethyl) -thio] -1-propanesulfone). Acid) 1 cc / L is prepared, and the proportion of the cationic surfactant aqueous solution is preferably about 20 cc with respect to the Ni plating solution 480 cc. A Ni plating solution containing is simply referred to as a Ni plating solution.
In FIG. 7, the surface-treated skeleton is immersed in the above-described Ni plating solution to perform dispersion (composite) Ni plating. The conditions are a current density of 5 A / dm2, a plating time of 5 minutes, a plating bath temperature of 50 ° C., and a stirrer stirring speed of 300 rpm. Thereby, the solid network metal body 1 having the Ni plating layer 1a on the surface layer of the skeleton is formed. Thereafter, a gas decomposition composite is produced by performing a drying process at 50 ° C. for 30 minutes. As shown in FIGS. 3 and 4, SSZ powder 22 carrying silver particles 23 is fixed to the surface of the solid network metal body 1. The reaction part 20 is formed using the silver particles 23 as an anode, Ni of the solid network metal body 1 as a cathode, and SSZ22 as a solid electrolyte.

Next, an example of a method for producing a three-dimensional network metal body or a skeleton portion thereof (hereinafter simply referred to as a skeleton portion unless otherwise specified) formed by metal plating will be described. FIG. 8 is a diagram illustrating an example of a method for manufacturing a skeleton part. In FIG. 8, first, a foamed resin is prepared by foaming a resin such as urethane. Subsequently, the pore continuation process which continues the foamed pore is performed. The pore continuation process mainly includes a film removal process. The thin film formed on the pores is continuously pored by removing the membrane by pressure treatment such as explosion treatment or chemical treatment. Thereafter, a conductive carbon film is attached to the pore inner walls, or a conductive thin film is formed by electroless plating or the like. Next, a metal plating layer is formed on the conductive carbon film or the conductive thin film by electroplating. This metal plating layer becomes a skeleton part of the solid network metal body. Metal plating uses a plating solution containing nickel ions to form a Ni plating layer. Ni has a relatively high resistance to high-temperature oxidation and can easily form a plating layer. Next, the resin is dissipated by heat treatment, leaving only the metal plating layer, to form a solid network Ni body or Ni skeleton, or Ni plating porous body.
When the solid network Ni body or Ni skeleton is exposed to a stronger oxidizing atmosphere or used at a higher temperature, the Ni skeleton is alloyed to further improve the oxidation resistance. Apply. This alloying treatment is performed by introducing Cr, Al, and other metals from the outside into the surface layer. Usually, alloying is stopped only on the surface layer to form a plated porous body with an alloyed surface layer.
Although not shown in FIG. 8, nickel ions and other metal ions can be dissolved in the plating solution to make the plated body a nickel alloy. As such, a nickel alloy skeleton may be formed by directly forming an alloy plating layer.

The alloying of the Ni skeleton is performed by adding Al or Cr. Al addition is performed by aluminizing. In aluminizing, the Ni skeleton is embedded in a steel case together with a preparation composed of Fe—Al alloy powder and NH ₄ Cl powder. Next, the case is sealed, and the sealed case is charged into a furnace and heated to 900 ° C. to 1050 ° C. Thereby, an Al diffusion / permeation layer can be obtained, and high-temperature oxidation resistance, wear resistance, and the like can be improved. Cr addition is performed by chromizing. In chromizing, the Ni skeleton is embedded in a case together with a preparation composed of Cr powder, Al ₂ O ₃ powder and NH ₄ Cl powder. A Cr diffusion / permeation layer can be obtained by heating to 900 ° C. to 1100 ° C. in a furnace while passing H ₂ gas or Ar gas through the case. This Cr diffusion layer can also improve the high temperature oxidation resistance. Although only the powder method has been described for both aluminizing and chromizing, Al or Cr can be diffused and permeated using any existing method such as a gas method or a molten salt method.

FIG. 9 shows the relationship between the specific surface area (y: m ² / m ³ ) and the pore diameter (x: mm) of the Ni skeleton or solid network Ni body produced by the method shown in FIG. The small black circles in FIG. 9 are actually measured values. It can manufacture by said method over hole diameter 0.05mm-3.2mm. When the urethane is used, the actual measurement value has a large specific surface area at the same pore diameter as compared to the hyperbola of (x−0.3) y = 400 or 600. Here, the minimum limit value (asymptotic line) of 0.3 mm of the hyperboloid hole diameter is obtained when urethane is used. If the value of (x−0.3) y is large, it will come into contact with both gases introduced into the gas decomposition complex 10, making the gas turbulent and the reaction unit 20 will always come into contact with new gas and react. Creates the effect of reducing pressure loss while maintaining the functions that can be performed. For this reason, it is preferable to satisfy 400 ≦ (x−0.3) y. More preferably, 600 ≦ (x−0.3) y. If the pore diameter is made too large, there is a risk that the component gas to be decomposed may pass through, so the upper limit is about 3000, more preferably about 2000.
When melamine is used instead of urethane, the minimum limit value of the pore diameter is 0.05 mm. For skeletal parts manufactured using melamine, the expression of the product of pore diameter and specific surface area is not shown, but if the porosity falls within the range of 0.6 to 0.98, the metal manufactured using melamine Porous materials are also within the scope of the present invention.
In the case of a metal powder sintered body, the hole diameter is in the range of 0.05 mm to 0.3 mm, more preferably in the range of 0.10 to 0.2 mm. Further, the specific surface area is in a considerably smaller range than the relationship (x−0.3) y = 400 shown in FIG. 9 manufactured using a urethane porous resin mold. The porosity is also affected by the shape of the skeleton, but generally the higher the porosity, the greater the specific surface area. Therefore, the Ni skeleton produced by the method shown in FIG. 8 can reduce the pressure loss as compared with the metal powder sintered body while obtaining the same conductivity and the same turbulent flow generation action.

(Embodiment 2)
FIG. 10 is a diagram showing the gas decomposition complex 10 according to Embodiment 2 of the present invention. This gas decomposition composite 10 has a cylindrical appearance, that is, a tubular shape, but is made of the same solid network metal body 1 as that of the first embodiment. In FIG. 10, a portion that emphasizes the appearance of a tubular shape and a portion that emphasizes the three-dimensional net-like metal body 1 are shown separately. It is the same as the case of Embodiment 1 that it is formed with a fine three-dimensional network metal body 1. As in FIG. 1B of Embodiment 1, the innumerable reaction parts 20 are fixed to the surface of the solid network metal body 1 or the solid network Ni body 1.
In the present embodiment, since the plating method is not used to fix the reaction part 20, the solid reticulated Ni body does not change before and after the reaction part 20 is fixed, and the plating layer 1a is not formed on the surface. Moreover, the kind of powder material which comprises the reaction part 20 is also a little different. The kind of the powder material constituting the reaction part 20 can be produced by the dispersion plating method of the first embodiment, regardless of the production method. However, the electrochemical reaction of the gas component to be decomposed is the same as that shown in FIG.

FIG. 11 is a diagram schematically showing the reaction section 20 of the gas decomposition complex 10 of the present embodiment. As in FIG. 2 of the first embodiment, the gas component to be decomposed is NOx, and the counterpart gas is CH ₄ , H ₂ , CO, or the like. The cathode 21 is a Ni grain chain 21 having an oxide layer 21b formed by oxidizing the surface layer of the Ni grain chain 21a. It can be considered that the solid reticulated Ni body formed by Ni plating is also included in the cathode 21. The anode 23 is formed of barium carbonate 23b and silver particles 23a. Silver particles 23a may be supported on barium carbonate 23b. The solid electrolyte powder 22 is YSZ, but may be SSZ, SDC, LSCM, GDC, or the like.
The difference with the reaction part of Embodiment 1 exists in the following point.
(1) The Ni particle chain 21 formed of the oxide layer 21b and the Ni particle chain 21a is used for the cathode 21. Although the Ni particle chain 21a alone functions as a catalyst for the NOx decomposition reaction, the Ni oxide layer 21b has a strong catalytic action and greatly promotes the cathode reaction for NOx decomposition.
Furthermore, since the Ni particle chain 21a has high electron conductivity, the electron conduction becomes a bottleneck, and in the case where the entire electrochemical reaction is delayed, the accelerating effect is exhibited remarkably.
The method for producing the Ni grain chain with oxide layer will be described later.
(2) The anode 23 includes not only silver particles but also barium carbonate. Barium carbonate, particularly barium, has the ability to adsorb NOx, and can release NOx to the cathode 21 located in the vicinity, thereby contributing to the promotion of the NOx decomposition reaction. In FIG. 11, the anode 23 and the cathode 21 are drawn with a large gap, but in reality, the cathode 21 and the anode 23 are often located very close to each other and contribute to the promotion of NOx decomposition by barium carbonate. Is obtained.
Further, when ammonia is used as a gas component to be decomposed and the other gas is oxygen or air, ammonia decomposition is possible as in the first embodiment, although not shown.

FIG. 12 is a flowchart for explaining a method for producing a gas decomposition composite according to the present embodiment. First, a solid network metal body or a solid network Ni body is prepared. Usually, since the three-dimensional network Ni body 1 is marketed as a sheet having a predetermined thickness, it is formed into a tube shape. In the forming process, the end portion is provisionally welded in a dot shape along the pipe or the like. Depending on the mechanical strength and application of spot welding, spot welding alone may be used. If spot welding alone is not possible, the cylindrical body is formed by seam welding the end portion by electron beam welding, laser beam welding, TIG welding, or the like.
In parallel with this, the powder of each material which comprises the reaction part 20 is prepared. One or more types of metal powders M1 to Mk and one or more types of solid electrolyte powders S1 to Sl are prepared. In the present embodiment, Ni powder, barium carbonate powder, and silver (Ag) powder are prepared as metal powder. The average diameter of the Ag powder is preferably 10 nm to 100 nm. The Ni powder preferably has a diameter of less than 100 nm. This is because Ni powder is aggregated to form Ni grain chains during the paste firing step, and Ni grain chains are used. In order to promote the electrochemical reaction, the Ni grain chain is preferably oxidized to have a Ni grain chain with an oxide layer.
SSZ, YSZ, SDC, LSGM, GDC, etc. can be used for the solid electrolyte powder. One or more types can be selected from YSZ, GDC, SDC, LSGM, and the like. Since these solid electrolytes are ceramics, they should be ground with a mortar. The average diameter of the solid electrolyte powder is preferably about 0.5 μm to 50 μm.
The compounding ratio of the surface-oxidized Ni particle chain 21 and SSZ22 is in the range of 0.1 to 10 in terms of molar ratio.
The organic solvent is composed of a resin and a solvent. In order to easily enter the solid network metal body 1, the organic solvent preferably has a viscosity in the range of 10 to 100 Pa · S. Moreover, what dissipates easily by heating at about 400 ° C. is preferable. For this purpose, for example, solute ethyl cellulose (EC vehicle manufactured by Nisshin Kasei Co., Ltd.) may be used. The mixing ratio is preferably a weight ratio of metal powder: solid electrolyte powder: organic solvent = 20: 20: 60. By stirring and mixing the above mixture, a paste in which the metal powder and the solid electrolyte powder are uniformly dispersed can be obtained.
Next, the paste is impregnated into the above-described three-dimensional reticulated Ni body. Next, after performing preliminary baking at 400 ° C. for 2 hours and then performing main baking at 1100 ° C. for 2 hours, the reaction unit 20 can be fixed to the surface of the solid network Ni body. One set of impregnation and firing may be repeated, and several sets of impregnation and firing may be repeated. In firing a tube-like object, one end of the tube is fixed to the rotation drive unit with a common shaft center, and while rotating, while being partially fired along the longitudinal direction of the tube by a mobile heating furnace or a reflective heater The whole may be fired by moving the mobile heating furnace. Alternatively, the entire tube may be stored in a large heating furnace and heated in a batch manner to be fired. The temperature change of heating and cooling during firing is preferably about 5 ° C./min.
During the paste baking, the Ni particles are aggregated and oxidized to form the Ni particle chain 21 with the oxide layer. When the aggregation of Ni grains does not proceed, the grains become single grains, but the Ni grains with single oxide layer (single grains) can still maintain the above-mentioned action, although the effect of electron conductivity is reduced. For this reason, it may be a single Ni grain or a Ni grain (single grain) with an oxide layer.
The Ni powder is mixed to form a paste, and instead of forming a Ni particle chain with an oxide layer when firing the paste, a Ni particle chain with an oxide layer or Ni particles separately prepared from the beginning A chain may be mixed in the paste. By preparing separately, the Ni grain chain can be reliably included in the paste. At the time of paste firing, the Ni grain chain with oxide layer maintains the form as it is, and the Ni grain chain has an oxide layer formed on the surface layer.

Next, the Ni grain chain with an oxide layer and the Ni grain chain when separately prepared will be described. The Ni grain chain 21 may contain Ni as a main component and a little iron (Fe). More preferably, Ti contains a trace amount of about 2 to 10000 ppm. As described above, it has a catalytic action for promoting the decomposition of Ni itself, NOx, ammonia and the like. Further, the catalytic action can be further enhanced by containing a small amount of Fe or Ti. Furthermore, the nickel oxide formed by oxidizing this Ni can further enhance the effect of promoting the simple metal.
In the anode reaction, free electrons e ⁻ are generated and supplied to the cathode 21. If the electron e ⁻ is supplied to the cathode 21 and does not participate in the cathode reaction, the entire electrochemical reaction is hindered. The Ni grain chain 21 is elongated in the shape of a string, and the content 21a covered with the oxide layer 21b is a good conductor metal (Ni). The electrons e ⁻ flow smoothly in the longitudinal direction of the string-like Ni particle chain 21a. For this reason, the electrons e ⁻ move smoothly in the cathode, and the movement of the electrons does not become a bottleneck of the electrochemical reaction.

A method for manufacturing the Ni grain chain 21 when prepared separately will be described. The Ni grain chain 21 is preferably manufactured by a reduction precipitation method. The reduction precipitation method of the Ni grain chain 21 is described in detail in Japanese Patent Application Laid-Open No. 2004-332047. The reduction precipitation method introduced here is a method using trivalent titanium (Ti) ions as a reducing agent, and the precipitated metal particles (Ni particles and the like) contain a small amount of Ti. For this reason, it can identify with what was manufactured by the reduction | restoration precipitation method by trivalent titanium ion by quantitatively analyzing Ti content. By changing the metal ions present together with the trivalent titanium ions, desired metal grains can be obtained. In the case of Ni, Ni ions are allowed to coexist. When a small amount of Fe ions is added, a Ni grain chain containing a small amount of Fe is formed.
In order to form a chain, the metal must be a ferromagnetic metal and have a predetermined size or more. Since both Ni and Fe are ferromagnetic metals, a metal particle chain can be easily formed. The size requirement is that the ferromagnetic metal forms a magnetic domain and bonds with each other by magnetic force, and in the combined state, the metal is deposited → the growth of the metal layer occurs, and the entire metal body is integrated. ,is necessary. Even after metal grains of a predetermined size or more are bonded by magnetic force, metal deposition continues, for example, the neck at the boundary of the bonded metal grains grows thicker together with other portions of the metal grains. The average diameter D of the Ni particle chain 21 forming the cathode 21 is preferably in the range of 5 nm to 500 nm. The average length L is preferably in the range of 0.5 μm or more and 1000 μm or less. The ratio between the average length L and the average diameter D is preferably 3 or more. However, it may have dimensions outside these ranges.

The surface oxidation treatment of the Ni grain chain is preferably performed by three types: (i) heat treatment oxidation by a vapor phase method, (ii) electrolytic oxidation, and (iii) chemical oxidation. (Ii) and (iii) are used when a Ni grain chain with an oxide layer is formed before mixing with the paste. (I) is preferably processed in the atmosphere at 500 to 700 ° C. for 1 to 30 minutes, but the surface oxidation layer 21b is used as the oxide layer formed during baking of the paste without performing surface oxidation treatment in particular. You can also.
In (ii), surface oxidation is performed by applying a potential to about 3 V with reference to a standard hydrogen electrode and performing anodization. However, the oxide film thickness can be controlled by the amount of electricity according to the surface area. However, when the area is increased, it is difficult to uniformly form an oxide film. In (iii), the surface is oxidized by being immersed in a solution in which an oxidizing agent such as nitric acid is dissolved for about 1 to 5 minutes. Although the oxide film thickness can be controlled by time, temperature, and type of oxidizer, cleaning of chemicals is troublesome. Either method is suitable, but (i) or (iii) is preferred.

  In the product of the gas decomposition composite 10, the desirable thickness of the oxidized layer of the Ni particle chain is 1 nm to 100 nm, more preferably 10 nm to 50 nm. However, it may be outside this range. If the oxide layer is too thin, the catalytic function will be insufficient. In addition, even a slight reducing atmosphere may cause metallization. On the other hand, if the oxide layer is too thick, the catalytic property is sufficiently maintained, but on the other hand, the electron conductivity at the interface is impaired and the power generation performance is lowered.

  The gas decomposition composite 10 in the present embodiment can be used in the same manner as the gas decomposition composite in the first embodiment, and can obtain the same effects. Furthermore, taking advantage of being a cylindrical body, for example, a gas component to be decomposed can be flowed on the inner surface side of the tube, and a gas for an electrochemical reaction can be flowed on the outer side of the tube. However, since the tube is formed of a three-dimensional net-like metal body, both are mixed as it advances along the tube. Even when mixing is performed, the gas that has passed through the tube inner surface side and the gas that has passed through the tube outer surface side can be distinguished formally at the outlet of the tube. Thus, knowing the gas composition and the like on both sides at the tube outlet may be beneficial for subsequent processing.

(Other embodiments)
1. In the embodiment, it has been mainly explained that NOx and ammonia are decomposed, but it is not necessary to limit to them. As long as the electrochemical reaction proceeds spontaneously in combination with the other party gas, acetaldehyde or the like can be targeted for decomposition. Further, there may be a plurality of gas components to be decomposed.
Accordingly, ions that move through the solid electrolyte are not limited to oxygen ions, and may be anything such as protons and phosphate ions.
2. Examples of the electrode (anode, cathode) and catalyst materials include nickel (Ni), Ni grain chain with an oxide layer, silver particles, and barium carbonate (BaCO ₃ ), but are not limited thereto. . Platinum, palladium, or the like may be used.
3. As the manufacturing method, the dispersion plating method or the composite plating method and the paste baking method are exemplified, but the manufacturing method is not limited to this, and the manufacturing method may be performed using a vapor phase method.
4). Although the heating apparatus is not shown in the figure, heating is very useful for efficiently operating the gas decomposition composite of the present invention. Not only an electric heater but also exhaust heat of an internal combustion engine of an automobile can be effectively utilized.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the present invention, a gas decomposition composite having a small size, high decomposition efficiency and low pressure loss, and high durability against impact and vibration can be obtained without using a large-scale apparatus. It is unrivaled in that it can perform a highly efficient decomposition reaction with a particularly low pressure loss. In addition, there are a wide variety of manufacturing methods, and an appropriate method can be adopted in consideration of economy and required performance.

DESCRIPTION OF SYMBOLS 1 Three-dimensional network-like metal body, 1a Surface plating layer, 1s porosity, 10 Gas decomposition composite, 20 Reaction part, 21 Cathode, 21a Ni particle chain, 21b Oxidation layer, 22 Solid electrolyte, 23 Anode or silver particle, 23a Silver Particles, 23b Barium carbonate.

Claims (12)

A gas decomposition composite for decomposing a gas component by an electrochemical reaction,
A porous metal forming a base of the gas decomposition composite;
A reaction part located on the surface of the porous metal and connected with a plurality of grains,
The reaction part includes materials constituting a cathode, an electrolyte, and an anode for the electrochemical reaction,
The gas decomposition composite according to claim 1, wherein the porous metal comprises a solid network metal body having isotropic continuous pores.   The gas decomposition composite according to claim 1, wherein all of the three-dimensional network metal bodies are formed by a plating method.   The three-dimensional network metal body is formed of a plating skeleton part and a plating surface layer part located in contact with the skeleton part, and the reaction part is located on the plating skeleton part using the plating surface layer part as a connection layer. The gas decomposition composite according to claim 1, wherein the gas decomposition composite is provided.   The gas decomposition composite according to any one of claims 1 to 3, wherein the reaction part is connected to the solid network metal body by firing.   The gas decomposition composite according to any one of claims 1 to 4, wherein a porosity of the three-dimensional network metal body or the plating skeleton is 0.6 or more and 0.98 or less.   The three-dimensional net-like metal body or the plating skeleton plating is applied to the resin formed through a foaming process for forming countless bubbles in the resin and a continuous opening process for opening the bubbles by making the bubbles continuous. The gas decomposition composite according to any one of claims 1 to 5, wherein the gas decomposition composite is formed. In the case where urethane is used as the resin, when the pore diameter of the solid network metal body or the plating skeleton is x (mm) and the specific surface area is y (m ² / m ³ ), 400 ≦ (x− The gas decomposition composite according to claim 6, wherein 0.3) y is satisfied.   All of the said three-dimensional network metal body is formed by the metal plating which has Ni as a main component, The said three-dimensional network metal body serves as the cathode electrode of the said electrochemical reaction, It is characterized by the above-mentioned. The gas decomposition composite body of any one of these.   The gas decomposition composite according to any one of claims 1 to 8, wherein the reaction part contains ceramic powder of solid electrolyte and at least one kind of metal powder. A method for producing a gas decomposition composite for decomposing a gas component by an electrochemical reaction,
Preparing a three-dimensional network metal skeleton having isotropic continuous pores;
Preparing a solid electrolyte powder and one or more metal powders for the electrochemical reaction;
Preparing a metal plating solution for plating the skeleton body, mixing the solid electrolyte powder and one or more metal powders in the metal plating solution, and stirring;
The skeleton body is immersed in the mixed and agitated metal plating solution, and a plating layer comprising the metal of the metal plating solution, the solid electrolyte powder, and one or more kinds of metal powders is used. And a step of forming the gas decomposition composite.   The step of preparing the solid electrolyte powder and one or more kinds of metal powders, wherein the one or more kinds of metal powders are supported on the solid electrolyte by firing. The manufacturing method of the gas decomposition composite_body | complex described. A method for producing a gas decomposition composite for decomposing a gas component by an electrochemical reaction,
Preparing a three-dimensional network metal body having isotropic continuous pores;
Producing a solid electrolyte powder and one or more metal powders for the electrochemical reaction;
Preparing a coating solution, mixing the solid electrolyte powder and one or more metal powders with the coating solvent and stirring to produce a coating solution;
A method for producing a gas-decomposing composite, comprising: applying or impregnating the coating solution onto the solid network metal body, and then baking.

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