JP5359475B2 - NOx decomposition element and power generator - Google Patents

Description

  The present invention relates to a NOx decomposition element and a power generation apparatus for decomposing NOx, and more particularly to measures for improving oxidation resistance.

In recent years, nitrogen oxides in exhaust gas discharged from automobiles, particularly diesel engines, have been subject to regulation from the viewpoint of preventing environmental pollution. Nitrogen oxides include NO, NO _2, N ₂ O, N ₂ O ₃ , N ₂ O ₄ , N ₂ O _5, etc., and these are collectively called NOx. Thus, many proposals have been made regarding a device for decomposing NOx using a catalyst in a purification device for an internal combustion engine of an automobile.
In Non-Patent Document 1, a urea selective reduction system is recommended as one that efficiently reduces and purifies NOx into nitrogen and water in a temperature range where the engine speed is low. 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. Related technologies include the following.
In Patent Document 2, a NOx sensor is provided at the latter stage of urea injection, and NO and NO ₂ are individually calculated in stoichiometry to control the optimum urea injection amount.
In Patent Document 2, an oxidation catalyst and a urea selective reduction device are arranged in the exhaust path in the exhaust path, and two NOx sensors arranged in front of and behind the oxidation catalyst in the front stage of the urea selective reduction device are used for NOx. Disassemble.

On the other hand, as known by summer photochemical smog and the like, not only a diesel engine but also a gaseous environment containing NOx is not preferable for a living organism.
Therefore, Patent Document 3 proposes a photocatalyst in which calcium phosphate is dispersed and arranged in islands on a titanium oxide thin film covering the surface of a porous carrier in order to decompose and remove NOx and the like in the atmosphere.

JP 2004-1000069 A Japanese Patent Laid-Open No. 2007-100508 Japanese Patent Laid-Open No. 2001-232206

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

The urea selective reduction device as described above is a device that arranges a urea selective reduction device that is large for an automobile in an exhaust system, resulting in an increase in weight. In addition, urea replenishment is required. For this reason, in the automobile field, there has been a demand for a NOx decomposing element that does not require replenishment of a reducing agent such as urea and that is easy to maintain and, if possible, maintenance-free. For automobiles, of course, small size and light weight create great value.
In addition, the photocatalyst that removes harmful substances such as NOx in the atmosphere is not limited to automobiles, and there is a tendency that the decomposition rate or decomposition efficiency is insufficient. Airports, railway stations, and other places where people are crowded require rapid decomposition of harmful substances, and photocatalytic decomposition may not be possible.

  An object of the present invention is to provide a low-cost NOx decomposition element that can be miniaturized and has high oxidation resistance.

The NOx decomposition element of the present invention includes a porous cathode into which a gas containing at least NOx is introduced, and a porous anode into which a gas containing hydrogen atoms is introduced. Further, an ionic conductive material having ionic conductivity is interposed between the anode and the cathode. Here, the cathode is composed of nickel (Ni) and / or iron (Fe) as a main component, and includes metal particulates whose outermost layer is oxidized.
Some metal particles include only metal particles, only metal particle chains, and a mixture of both. The metal particle chain refers to a bead-like long and narrow metal body made of metal particles.

With the above configuration, when a gas containing at least NOx is introduced on the cathode side and a gas containing hydrogen atoms is introduced on the anode side, the following effects are obtained.
At the anode, a gas containing hydrogen atoms (for example, H ₂ O ) is decomposed (anode reaction) and electrons are generated. Electrons generated by the anodic reaction are sent from the outside to the cathode. At the cathode, NOx is decomposed and N ₂ is generated by an electrochemical reaction (cathode reaction) between electrons sent from the anode and NOx, and oxygen in NOx is anionized. This anion is sent to the anode through the ion conductive material, and promotes the anode reaction by an electrochemical reaction.
At this time, in the cathode, the oxide film of the metal granular material serves as a catalyst, and the electrochemical reaction between electrons and NOx is promoted. In particular, it is known that when a gas containing NOx having a relatively high temperature (for example, about 250 ° C. to 600 ° C.) is introduced into the cathode, the electrochemical reaction at the anode and the cathode is promoted. Therefore, if the NOx decomposing element is used at a relatively high temperature, a large processing capacity can be secured with a small element. In addition, since it is not necessary to use an expensive noble metal such as platinum ( Pt ), the cost can be reduced.

Here, the surface region of the metal granular body is composed mainly of Ni or Fe, which is a ferromagnetic material. Thereby, in the precipitation process from the solution containing a ferromagnetic metal ion and a reducing ion, the aggregation action of a metal granular material is accelerated | stimulated. In other words, the ratio of the metal granular body becomes a chain that is continuous in the form of a bead or string. As a result, the conductivity of the metal particles is increased, the cathode reaction, which is an electrochemical reaction, is promoted, and the movement of anions to the ionic roadway material is also promoted.
Therefore, it is possible to realize a small-sized NOx decomposition element that is suitable for mounting in an automobile, has a large processing capacity, and is low in cost.

  It is preferable that the surface region of the metal granule is made of a high heat resistant alloy. Since NOx is generally a gas having a very high oxidizing power, a highly oxidizing atmosphere having a strong oxidizing power is generated in the range of 250 ° C. to 600 ° C. Even in such a high oxidation atmosphere, the surface region of the metal granular material is made of a high heat-resistant alloy, thereby exhibiting high oxidation resistance. Therefore, deterioration of the cathode is suppressed, generation of deposits due to oxidation is also suppressed, and as a result, maintenance is almost unnecessary. Therefore, the running cost can be reduced.

  In particular, the surface region of the metal granular body is rich in chromium (Cr) and / or aluminum (Al), so that high oxidation resistance can be exhibited even in a highly oxidizing atmosphere. Examples of the processing for this purpose include chromizing and aluminizing.

  When the thickness of the oxidized outermost layer of the metal granular material is 0.5 to 100 nm, for example, in a highly oxidizing atmosphere at about 250 ° C. to 500 ° C., the oxidation resistance and the electronic conductivity are ensured. can get.

  The cathode is preferably a sintered body containing a metal granular body and an ion conductive ceramic. Accordingly, it is possible to ensure the flowability of NOx at all positions of the cathode and to proceed the reaction between oxygen and anions in NOx while ensuring the catalytic action and the electronic conductivity.

  A current collector of a porous metal body can be disposed on the opposite side of the anode and / or cathode from the ion conductive material. Thereby, the flowability of the gas containing hydrogen atoms can be ensured at the current collector / electrode (anode, cathode) portion. Furthermore, since high electron conductivity can be ensured in the current collector / electrode (anode, cathode) portion, electrons can be exchanged reliably without loss.

  It can be set as the structure which can take out electric power from a cathode and an anode. As a result, ammonia, which is one of the gas containing hydrogen atoms, can be used as fuel, and a fuel cell can be configured by the NOx decomposition element to generate power.

  Said NOx decomposition | disassembly element is mounted in the motor vehicle which has an internal combustion engine, and can make the exhaust heat of the said internal combustion engine the heat source for a heating. This makes it possible to perform NOx decomposition with high energy efficiency.

  According to the NOx decomposition element of the present invention, it is possible to reduce the size and realize a low-cost NOx decomposition element. It is also easy to have a high oxidation resistance function.

It is a block diagram which shows roughly the structure of the NOx decomposition element which concerns on Embodiment 1 of this invention. 2 is a cross-sectional view showing the internal structure of the NOx decomposition element according to Embodiment 1. FIG. It is explanatory drawing of the flow of the molecule | numerator, ion, and an electron in a cathode collector and a cathode. It is explanatory drawing of the flow of the molecule | numerator, ion, and electron in an anode. (A), (b) is a figure which shows the procedure of an aluminizing and a chromizing process by a chemical reaction formula in order. It is a block diagram which shows roughly the structure of the NOx decomposition element which concerns on Embodiment 2 of this invention.

(Embodiment 1)
FIG. 1 is a block diagram schematically showing the configuration of the NOx decomposition element 10 according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing the internal structure of the NOx decomposition element 10 according to the first embodiment.
As shown in FIG. 1, the NOx decomposition element 10 includes an anode 2 and a cathode 3 that face each other with the solid electrolyte 1 interposed therebetween. An anode current collector 8 is disposed outside the anode 2, and a cathode current collector 7 is disposed outside the cathode 3.

上記表１は、水素原子を含むガスが分解素子１０の使用態様を示すものである。

Table 1 above shows the usage of the decomposition element 10 in which the gas containing hydrogen atoms.

  As shown in Table 1, the NOx decomposition element 10 can generate electric power as a fuel cell, or can be operated by supplying power as an electrolysis apparatus. In the first embodiment, as shown in FIG. 1, a case where the NOx decomposition element 10 is used as an electrolysis apparatus will be described. This corresponds to the electrochemical reaction of R2 to R3 in Table 1. In view of the ease of use of the gas introduced into the anode 2, a configuration is generally used in which water, which is a gas containing hydrogen atoms, is introduced into the anode 2, NOx to be decomposed is introduced into the cathode 3, and power is supplied. . Also in this embodiment, a case where water is introduced into the anode 2 and NOx is introduced into the cathode 3, that is, a case where an electrochemical reaction of R3 in Table 1 is performed will be described.

  The anode 2 is a sintered body mainly composed of a metal granular body 21 having a configuration to be described later and an oxygen ion conductive ceramic 22. The metal granular material 21 includes a metal particle and a metal particle chain formed by connecting metals. In the present embodiment, the case where the metal particle 21 is a metal particle chain will be described.

  As the oxygen ion conductive ceramic 22, SSZ (scandium stabilized zirconia), YSZ (yttrium stabilized zirconia), SDC (samarium stabilized ceria), LSGM (lanthanum gallate), GDC (gadria stabilized ceria) and the like are used. be able to.

  The cathode 3 is a porous body having a void 3h, and is a sintered body mainly composed of a metal granular body 31 whose outermost surface is oxidized, an oxygen ion conductive ceramic 32, and preferably silver particles 33. It is. The metal granular body 31 contains nickel (Ni) or iron (Fe) as a main component, and more preferably contains a trace amount of Ti of about 2 to 10000 ppm. At least the surface region of the metal granular body 31 is made into a high heat resistant alloy. Examples of the high heat-resistant alloying treatment include chromizing and aluminizing. The metal granular material 21 includes a metal particle and a metal particle chain formed by connecting metals. In the present embodiment, the case where the metal particle 21 is a metal particle chain will be described.

As the oxygen ion conductive ceramic 32, SSC (samarium strontium cobaltite), LSC (lanthanum strontium cobaltite), LSM (lanthanum strontium manganite), or the like can be used.
As the electrolyte 1, a solid oxide, molten carbonate, phosphoric acid, solid polymer, or the like having oxygen ion conductivity can be used. In particular, a solid oxide is preferable because it can be miniaturized and easily handled. As the solid oxide, SSZ, YSZ, SDC, LSGM, GDC, or the like can be used.

  The cathode current collector 7 and the anode current collector 8 are porous metal bodies having continuous pores, and are composed mainly of nickel (Ni) and / or iron (Fe). Further, at least the surface region of the metal porous body is made into a high heat-resistant alloy. Examples of the high heat-resistant alloying treatment include chromizing and aluminizing.

FIG. 3 is an explanatory diagram of the flow of molecules, ions, and electrons in the cathode current collector 7 and the cathode 3. FIG. 4 is an explanatory diagram of the flow of molecules, ions and electrons in the anode 2. Hereinafter, the operation of the NOx decomposing element 10 of the present embodiment will be described with reference to FIGS. 2, 3 and 4.
In the present embodiment, the gas to be decomposed is NOx, and this NOx supplies oxygen ions. The gas that reacts with oxygen ions at the anode 2 may be ammonia, VOC (such as CH ₄ ), or water vapor. Thereby, NOx decomposition by the electrochemical reaction of numbers R1 to R3 shown in Table 1 is possible. Among these reactions, since water vapor ( H ₂ O ) is easy to handle and economical, it will be described below by limiting it to the electrochemical reaction of R3.
The water vapor passed through the anode current collector 8 diffuses to the anode 2 through the gap of the anode current collector 8. In the anode 2, the following reaction formula (1)
H ₂ O + O ₂ − → O ₂ + H ₂ + 2e ⁻ (1)
The electrochemical reaction (anode reaction) according to the above occurs, and the gas containing hydrogen atoms is decomposed. This reaction occurs at the three-layer interface where the outermost layer (oxide film) of the metal granular body 21, the solid electrolyte 1, and the air layer are in contact. O ₂ + H ₂ which is a fluid after the reaction is released from the anode 2.
The important functions of the metal particles 21 in the anode reaction are a function as a catalyst for an electrochemical reaction and a conductive function for transmitting electrons e ⁻ generated by the electrochemical reaction.

When NOx is passed from the cathode current collector 7 to the cathode 3, oxygen in the NOx introduced into the cathode 3 is represented by the following reaction formula (2)
2NO + 4e ⁻ → N ₂ + 2O ²⁻ (2)
Electrochemical reaction (cathode reaction) according to This reaction occurs at the three-layer interface where the outermost layer (oxide film) of the metal granular body 31, the solid electrolyte 1, and the air layer are in contact. Oxygen ions O ²⁻ produced by the reaction reach the anode 2 from the ceramic 32 in the cathode 3 through the solid electrolyte 1. The oxygen ions O ²⁻ that have reached the anode 2 undergo an anodic reaction shown in the reaction formula (1) with water vapor, and the water vapor is decomposed.
The important functions of the metal particles 31 in the cathode reaction are a function as a catalyst for an electrochemical reaction and a conductive function for passing an electron e ⁻ for the electrochemical reaction.

Further, the electrons e ⁻ generated at the anode 2 flow toward the cathode 3 through an external circuit. The NOx decomposed at the cathode becomes nitrogen gas and is released from the cathode 3 and the cathode current collector 7.
In the above reaction, the electrochemical reaction does not proceed unless the potential of the cathode 3 is higher than that of the anode 2. However, since more electrons are consumed at the cathode 3 than electrons generated at the anode 2, the potential of the anode 2 is higher. Therefore, in order to continue the electrochemical reaction, it is necessary to apply a potential at which the cathode 3 side becomes positive by the power source 9.

In the case of the NOx decomposition element 10, it is preferable to shorten the passage time of oxygen ions in the electrolyte 1 and to secure the electrochemical reaction rate at each electrode. Therefore, in order to promote the entire electrochemical reaction, the heater is heated to, for example, 250 ° C. to 600 ° C. However, the distinction between the low temperature region and the high temperature region, or the strength of the oxidizing power, varies depending on the ratio of NO and NO _{2 in} NOx, the concentration in the atmosphere, and so on, so it is not necessary to separate them so clearly.

-Points on the cathode side configuration-
In the NOx decomposition element, NOx decomposition is performed at 250 ° C. to 600 ° C. in an atmosphere in which NOx having a large oxidizing power flows, that is, a highly oxidizing atmosphere. However, for the metal granular material 31 made of Ni or the like, catalytic action deterioration and conductivity deterioration due to oxidation occur.
Therefore, the metal granular body 31 in the cathode 3 of the present embodiment has high oxidation resistance in addition to the catalytic function and the conductive function. Specifically, at least the surface region of the metal granule 31 is made of a high heat-resistant alloy, and the thickness of the outermost oxide film is suitable for a high oxidation atmosphere in the range of 250 ° C. to 600 ° C., Is the point.
In the present embodiment, the metal particles 31 of the cathode 3 are mainly composed of nickel (Ni) and / or iron (Fe), and at least the surface region is made of a high heat-resistant alloy. The inside of the metal granular body 31 does not need to be made of a high heat resistant alloy. Rather, since the inside of the metal granular body 31 is not made of a high heat-resistant alloy, the electrical resistance value can be lowered and the conductivity can be increased. More preferably, the catalyst function is further enhanced by containing a trace amount of Ti of about 2 to 10000 ppm.
In particular, nickel (Ni) is a very suitable metal for producing a metal porous body having continuous pores because it is easy to produce a plated body and fine particles, and has a certain oxidation resistance performance. Has the advantage of

Examples of the high heat-resistant alloying treatment include chromizing and aluminizing. Thereby, the surface area | region of the metal granular material 31 becomes the enriched layer of Cr and / or Al. Ni and Fe itself have a catalytic action to promote the decomposition of oxygen, but the oxide of the Cr and / or Al-enriched layer formed by chromizing or aluminizing further enhances the promoting action of these metals. Can do.
The thickness of the outermost oxide layer 31b of the metal granular body 31 is in the range of 0.5 to 100 nm. By forming in this thickness range, it is possible to ensure electronic conductivity and high oxidation resistance against a highly oxidizing atmosphere. If the thickness of the oxide layer 31b is less than 0.5 nm, the catalytic effect does not appear, and if it exceeds 100 nm, the electrical resistance value increases and the electron conductivity decreases. That is, when the thickness of the oxide layer 31b is in the range of 0.5 to 100 nm, both the catalytic effect and the electronic conductivity can be achieved.

Moreover, a conductive function can be further improved by making the metal granule 31 into a metal grain chain. The metal particle chain (metal particle 31) is elongated in a string shape, and the content 31a covered with the oxide layer 31b is a good conductor metal (Ni). The electrons e ⁻ flow smoothly through the contents 31 a in the longitudinal direction of the string-like metal particle chain. For this reason, the conductivity of the electron e ^{− to} the cathode 3 can be kept high.

-Anode configuration-
The action of the metal granule 31 mainly composed of Ni in the cathode 3 is the same as that of the metal granule 21 in the anode 2 by replacing the gas from NOx to water vapor.
Therefore, the metal granular material 21 of the anode 2 is also preferably a metal particle chain made of nickel (Ni). Ni may contain a little iron (Fe). More preferably, the catalyst function is further enhanced by containing a trace amount of Ti of about 2 to 10000 ppm.

-Effect of Embodiment 1-
As described above, NOx, which is a gas with high oxidizing power, is introduced into the cathode 3 and the cathode current collector 7. Metals exposed to an atmosphere (high oxidation atmosphere) in which a gas having a high oxidizing power flows at a relatively high temperature of 250 ° C. to 600 ° C. (except for special metals) are oxidized by the gas and cannot be used after a predetermined period of time. become. The form in which the cathode 3 becomes unusable is clogging due to increased oxidation (decreased air permeability, increased pressure loss), reduced current collecting performance, and the like. Note that the cathode current collector 7 also has the same deterioration in air permeability and conductivity due to high-temperature oxidation.
On the other hand, since the reducing gas flows on the anode side such as the anode 2 and the anode current collector 8, the problem of high-temperature oxidation hardly occurs.

Here, in the present embodiment, at least the surface region of the metal granular body 31 is subjected to high heat-resistant alloying treatment such as chromizing and aluminizing. Therefore, even in a highly oxidative atmosphere, high oxidation resistance is exhibited. Therefore, it is possible to suppress the deterioration of the metal portion of the cathode 3 and the deposition of reaction products in a highly oxidizing atmosphere.
Therefore, almost no maintenance is required, and the running cost can be greatly reduced.

Moreover, the anode reaction and cathode reaction proceed at a very high reaction rate due to the configuration of the anode 2 and the cathode 3 described above. For this reason, a gas containing a large amount of NOx can be efficiently decomposed by a small element having a simple structure.
Moreover, since an expensive noble metal such as platinum (Pt) is not used, the initial cost can be reduced.
Furthermore, since power generation is possible as described above, for example, it is not necessary to supply the power of the heater built in the NOx decomposition element 10 of the present embodiment from the outside, or the supply amount from the outside can be reduced. . For this reason, it is excellent in energy efficiency.

Note that the decomposition of the decomposition target gas proceeds only by raising the temperature and bringing the decomposition target gas into contact with the catalyst. It is disclosed in prior literature and is well known as described above.
However, as described above, in the element constituting the NOx decomposition element, oxygen ions are involved in the reaction at high temperature from the cathode 3 through the ion conductive solid electrolyte 1, and as a result, the generated electrons are conducted outside. Thus, the decomposition reaction rate is dramatically improved. One of the major features of the present invention is that it has the function of the cathode 3 and a configuration that provides the function.

表２は、クロム処理による耐食性の向上効果を示すデータである。この試験は、ＳＵＳ３０４（８〜１０％Ｎｉ，１８〜２０％Ｃｒ），ＳＵＳ３１０Ｓ（１９〜２２％Ｎｉ，２４〜２６Ｃｒ），４５Ｃｒ３０Ｎｉ合金の板材について、行なっている。試験温度は８００℃，９００℃で、０．１％ＳＯ _２ ，１５％ＣＯ _２ ，２％Ｏ _２ ，残Ｎ _２ の成分のガスを、１００ｈｒの間流している。
表２に示されるように、クロマイジング処理を施したＳＵＳ等は、無処理材よりも、約５〜２０倍の耐食性，耐腐食量があることがわかる。つまり、カソード３の金属粒状体３１に、高耐熱合金化を行うことにより、高温の酸化雰囲気における耐酸化性が向上することがわかる。８００℃よりも低い温度範囲２５０℃〜６００℃においても、ＮＯｘという酸化力の強いガスが流れる雰囲気は、酸化力の高い高酸化雰囲気である。よって、表２に示す結果は、本実施の形態のＮＯｘ分解素子１０にも当てはまる。

Table 2 is data showing the effect of improving the corrosion resistance by the chromium treatment. This test is conducted on plate materials of SUS304 (8-10% Ni, 18-20% Cr), SUS310S (19-22% Ni, 24-26Cr), 45Cr30Ni alloy. The test temperatures are 800 ° C. and 900 ° C., and gas of components of 0.1% SO ₂ , 15% CO ₂ , 2% O ₂ and remaining N ₂ is allowed to flow for 100 hours.
As shown in Table 2, it can be seen that SUS or the like subjected to chromizing treatment has about 5 to 20 times the corrosion resistance and corrosion resistance than the untreated material. That is, it can be seen that the oxidation resistance in a high-temperature oxidizing atmosphere is improved by forming the metal granular body 31 of the cathode 3 into a high heat-resistant alloy. Even in a temperature range of 250 ° C. to 600 ° C. lower than 800 ° C., an atmosphere in which a gas having a strong oxidizing power called NOx flows is a highly oxidizing atmosphere having a high oxidizing power. Therefore, the results shown in Table 2 also apply to the NOx decomposition element 10 of the present embodiment.

-Manufacturing method of metal granules-
Next, the manufacturing method of the metal granular materials 21 and 31 of said NOx decomposition element 10 is demonstrated.
1. Formation of metal particles The cathode and anode metal particles 21 and 31 are preferably produced by a reduction deposition method. The reduction precipitation method of the metal particulates 21 and 31 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. Further, in order to form a metal particle chain, Ni ions are allowed to coexist in the case of Ni. 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 is preferably a ferromagnetic metal and has 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.
Therefore, the average diameter D of the metal particles contained in the metal particles 21 and 31 of the anode 2 or the cathode 3 is preferably in the range of 5 nm or more and 500 nm or less. The average length L of the metal particle chain 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.

Next, the metal particle chain 31 of the cathode 3 is subjected to a heat-resistant alloying treatment such as aluminizing and chromizing shown in FIGS. 5 (a) and 5 (b). Both aluminizing and chromizing, or other high heat-resistant alloying treatments may be performed.
FIG. 5A shows a specific example of aluminizing. In this way, the non-treated product, ^{F e} - embedded in a steel casing with an Al alloy powder and NH ₄ consisting of Cl powder preparation. Next, the case is sealed, and the sealed case is charged into a furnace and heated to 900 ° C. to 1050 ° C. As a result, an Al diffusion / permeation layer can be obtained, and high-temperature oxidation resistance, wear resistance, and the like can be improved.
FIG. 5B shows a specific example of chromizing. In this method, a Ni-plated porous body (Me) is embedded in a case together with a preparation composed of Cr powder, Al ₂ O ₃ powder and NH ₄ Cl powder. Then, while passing H ₂ gas or Ar gas into the case, and heated at a furnace to 900 ° C. C. to 1100 ° C.. As a result, a Cr diffusion / permeation layer can be obtained, and the high-temperature oxidation resistance can be enhanced.
In FIGS. 5A and 5B, only the powder method is shown for both aluminizing and chromizing, but Al or Cr is diffused by using an existing arbitrary method such as a gas method or a molten salt method. Can penetrate.

The high heat-resistant alloying treatment may be performed after sintering described later. Before the process shown in FIGS. 5A and 5B, sintering described later is performed. Then, the fine powder containing Cr, or the fine powder containing Cr and the fine powder containing Al are rubbed into the porous portion of the sintered body and kept at a high temperature. Alternatively, chromizing and aluminizing are performed by maintaining a high temperature while flowing a gas containing Cr and Al through the sintered body.
Thereby, Cr, Al, etc. are infiltrated into the surface area of the metal granular bodies 31, 21, and chromizing, aluminizing, etc. are performed. Further, in order to reduce the cost, chromium oxide ( CrO ₃ ) can be used instead of Cr. Thereafter, the next surface oxidation treatment is performed.
By this method, it is not necessary to raise the temperature region of the highly heat-resistant alloy to the sintering temperature, so that the catalytic function and the high-temperature oxidation resistance function can be kept high.
Moreover, only the surface area | region of the metal granule 21 and 31 exposed after sintering can be heat-resistant alloy-ized. In other words, when heat-resistant alloying treatment was performed before sintering, it was separated before sintering, but the boundaries of the metal particles or metal particle chain bonded after sintering were also made into a heat-resistant alloy, and the conductive function Gets worse. On the other hand, in this method, the boundary portion remains a metal mainly composed of Ni or Fe, so that the conductive function is maintained high.

2. Sintering The average diameter of the raw material powder of the ceramics 22 or 32 contained in the anode 2 or the cathode 3 is about 0.5 μm to 50 μm. The compounding ratio between the surface-oxidized metal particles 21 and 31 and SSZ22 and LSZ32 is in the range of 0.1 to 10 in terms of mol ratio.
A sintering method is performed by hold | maintaining for 30 minutes-180 minutes, for example in air | atmosphere atmosphere at the temperature of 1000 to 1600 degreeC.
The cathode 3 is composed of a sintered body such as a metal particle chain 31 with an oxide layer, LSM, and Ag particles 33. The average diameter of the Ag particles is preferably 10 nm to 100 nm. The compounding ratio of silver and LSM is preferably about 0.01 to 10.

3. Surface oxidation The metal particles 21 and 31 in the anode 2 and the cathode 3 are subjected to surface oxidation in order to enhance the catalytic action for promoting the electrochemical reaction.
Three types of surface oxidation treatments are suitable: (i) heat treatment oxidation by a vapor phase method, (ii) electrolytic oxidation, and (iii) chemical oxidation. In (i), it is good to process at 500-700 degreeC for 1 to 30 minutes in air | atmosphere. This is the simplest method. 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 more preferred.
A desirable thickness of the oxide layer is 0.5 to 100 nm. However, it may be outside this range. If the oxide film is too thin, the catalyst function will be insufficient. In addition, even a slight reducing atmosphere may cause metallization. Furthermore, since the ions are carried through the oxide film, a certain thickness is required. On the other hand, if the oxide film is too thick, the catalytic property is sufficiently maintained, but on the other hand, the electronic conductivity at the interface is impaired and the power generation performance is lowered. In particular, in a relatively low temperature range of about 250 ° C., sufficient oxidation resistance can be obtained even if it is thin. Therefore, a thin oxide film is sufficient to increase electronic conductivity.
The time of surface oxidation of the chain metal powder may be before the above-mentioned sintered body formation, but is preferably after the sintered body formation.

Next, a manufacturing process of the cathode current collector 7, in particular, a continuous pore porous body (hereinafter referred to as a plated porous body) will be schematically described.
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 treatment includes a method of removing a film by dissolving a thin film remaining in the pores with a chemical solution having urethane solubility, or removing the film by an explosion treatment. However, it is not restricted to these methods. Further, urethane obtained by continuous pore processing with Bridgestone or the like can be obtained, and this method is preferably used. 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 the skeleton of the pore body. For metal plating, a plating solution containing nickel ions is preferably used to form a Ni plating layer. Ni has high-temperature oxidation resistance in the above-mentioned low temperature range, and the formation of a plating layer is easy. Next, the resin is dissipated by heat treatment to leave only the metal plating layer, thereby forming a Ni-plated porous body.
In order to obtain oxidation resistance at higher temperatures, an alloying treatment is applied to the Ni-plated porous body as described above. 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.
Further, 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.

(Embodiment 2)
FIG. 6 is a block diagram schematically showing the configuration of the NOx decomposition element according to Embodiment 2 of the present invention. The reaction in the present embodiment corresponds to the reaction R1 in Table 1, and is also a power generation element (fuel cell). NOx is introduced into the cathode 3 through the cathode current collector 7 as a flow path, and ammonia is introduced into the anode 2. The cathode reaction is the same as in Embodiment 1, but the anode reaction is represented by the following formula (3).
2NH ₃ + 3O ²⁻ → N ₂ + 3H ₂ O + 6e ⁻ (3)
Follow.
In this case, the amount of electrons generated at the anode 2 is larger than the amount of electrons consumed at the cathode 3. Therefore, the potential of the anode current collector 8 naturally becomes higher than the potential of the cathode current collector 7, and power can be extracted. For example, the load 5 in FIG. 6 can be supplied to the heater as a heater (not shown).

As described above, although there is a difference in generation and consumption of electric power from the first embodiment, the configurations of the anode 2 / electrolyte 1 / cathode 3 and current collectors 7 and 8 are the same as those in the first embodiment. It is.
That is, the anode 2 and the cathode 3 are also composed of sintered bodies of the surface-oxidized metal particulates 21 and 31 and the ceramics 22 and 32 as in the first embodiment. As in the first embodiment, at least the surface region of the metal granular body 31 of the cathode 3 is made of a high heat resistant alloy. Therefore, a high oxidation resistance function can be exhibited in a high-temperature oxidizing atmosphere.
As a result, even with the NOx decomposition element 10 of the present embodiment, a large amount of NOx can be quickly processed with a small and simple element, and the initial cost and running cost are low.

  As described in the first embodiment, it is well known to decompose a gas to be decomposed under a catalyst. However, in this embodiment, in order to obtain carbon dioxide as a source of oxygen ions in the electrochemical reaction and participate in the reaction to obtain a practical decomposition rate, it is easy to maintain and manage while heating at 250 ° C to 600 ° C. Can be. Regarding the improvement of the NOx decomposition rate, as in the first embodiment, the oxygen ion generation promotion of the catalyst (silver particles, metal particle chain with oxide layer) at the cathode and the same configuration excluding the silver particles at the anode and By providing the effect, the reaction speed can be greatly improved.

  Next, an example of actual verification using a specimen will be described. The test specimens used are Example A1 of the present invention and Comparative Example B1. All are as shown in Table 3.

The test shows the ability to decompose gas containing 0.1% (1000 ppm) NOx (initially 10% NO, the balance using a gas cylinder balanced with an inert gas such as Ar) at a given temperature. Transition was measured. The results are shown in Table 4. However, the processing capacity under the basic conditions in Table 4 refers to that at the time when 5 hours (5 hours) have elapsed at a temperature of 400 ° C. using the specimen of Example 2. The treatment capacity at this time is a removal efficiency of 90% when a gas containing 1000 ppm of NOx is flowed at 50 mmol / cm ² · min. Table 4 shows that this value is 100, and the treatment capacity of each specimen is relative. Indicated by value.

Table 4 shows the following.
Looking only at Example 1 (test numbers t1 to t3) in which the metal particles of the cathode were composed of Fe20% Ni, as the decomposition temperature increased to 300 ° C, 400 ° C, and 500 ° C, the initial (5h) Although the processing capacity is high, if it is used for a long time (10000 hours (10000 hours)), the processing capacity decreases. This is thought to be due to the deterioration of the surface of the metal particulates.
Examples 1, 3, and 4 (test numbers t2, t5, and t6) in which the metal granular body was made of Ni, the surface layer was enriched with Cr, and the thickness of the oxide layer was changed to 10 nm, 0.5 nm, and 100 nm. ), The thinner the oxide layer, the higher the initial processing capacity (5 h), but when used for a long time (10000 h), the processing capacity tends to decrease. This is presumably because the thinner the oxide layer, the more easily the surface of the metal particulates deteriorates.
Examples 2, 5, 6, 7 in which the thickness of the oxide layer is 10 nm and the decomposition temperature is 400 ° C., and the surface of the metal granular body is Cr-enriched, Ni only, Al-enriched, and CrAl-enriched In comparison, each of the processing capacities of Examples 2, 6, and 7 (test numbers t4, t8, and t9) after lapse of 10,000 hours maintains 50% or more of the basic conditions (when 5 hours have elapsed). In particular, the processing capacity of Example 7 in which the surface layer of the metal granular body was enriched with CrAl maintains 75% of the basic conditions even after 10000 hours. On the other hand, the processing capacity of Example 5 after 10000 h has been reduced to 10% of the basic condition (when 5 h has elapsed). Therefore, high heat resistance is obtained even under high oxidation conditions by alloying the surface layer of the metal granular body with Cr, Al, CrAl or the like. In particular, a remarkable effect can be exhibited by chromizing and aluminizing the surface of the metal granule.
In the case of Example 8 (test number t10) in which the metal granular body was composed of Ni and added with Ag 10% (test number t10), the initial processing capacity (at the time of 5 hours) was high, but after 10,000 hours, the processing capacity was 40 of the basic condition. It has fallen to about%. Therefore, it can be seen that sufficient oxidation resistance is not obtained only by addition of Ag.
In Comparative Examples 1 and 2 (test numbers t13 and t14) in which the metal granular material is made of Ni, the surface layer is not alloyed, and the thickness of the oxide layer is 0.3 nm and 1000 nm, both of them elapse for a long time. Later processing capacity has dropped to 30% to 35% of basic conditions. In particular, it can be seen that when the thickness of the oxide layer is reduced to 0.3 nm, the processing capability is remarkably lowered by such long use at a high temperature. That is, the catalyst function is not sufficiently developed due to the deterioration of the metal particulates. Therefore, the thickness of the oxide layer is preferably 0.5 nm or more.
When Comparative Example 2 in which the thickness of the oxide layer is 1000 nm is compared with Example 3 in which the thickness of the oxide layer is 0.5 nm, Comparative Example 2 has a greater reduction in processing capability. In addition, when such a thick oxide layer is present, the electron conductivity is lowered. Therefore, the thickness of the oxide layer is preferably 100 nm or less.

  The structure of the embodiment of the present invention disclosed above is merely an example, and the scope of the present invention is not limited to the scope of these descriptions. 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.

  The NOx decomposing element of the present invention can be used as a NOx decomposing apparatus for environmental protection or a power generation apparatus.

DESCRIPTION OF SYMBOLS 1 Ion conductive electrolyte 2 Anode 3 Cathode 3h Air gap 5 Load 7 Cathode current collector 7a Skeletal part 7h Air gap 8 Anode current collector 9 Power source 21 Metal granular material 22 Ceramic 31 Metal granular material 32 Ceramic 33 Silver particle

Claims (7)

An element used to decompose NOx,
A porous cathode into which a gas containing at least NOx is introduced;
A porous anode that is paired with the cathode and into which a gas containing hydrogen atoms is introduced;
An ionic conductive material interposed between the anode and the cathode and having ionic conductivity;
The cathode is composed of nickel (Ni) and / or iron (Fe) as a main component, and includes metal particles whose outermost layer is oxidized ,
The NOx decomposition element, wherein the oxidized outermost layer has a thickness of 0.5 to 100 nm . The NOx decomposition element according to claim 1,
A NOx decomposition element in which at least a surface region of the metal particles of the cathode is made of a high heat-resistant alloy and an outermost layer thereof is oxidized. The NOx decomposition element according to claim 2,
The surface region of the metal particulate is a NOx decomposition element enriched with chromium (Cr) and / or aluminum (Al). In the NOx decomposition element according to any one of claims 1 to 3 ,
The cathode is a NOx decomposition element, which is a sintered body of the metal granular body and an ion conductive ceramic. In the NOx decomposition element according to any one of claims 1 to 4 ,
A NOx decomposing element, wherein a current collector of a porous metal body is disposed on the opposite side of the anode and / or cathode to the ion conductive material. In the NOx decomposition element according to any one of claims 1 to 5 ,
A heater for heating the ion conductive material, the anode and the cathode;
A NOx decomposition element in which electric power extracted from the cathode and the anode is supplied to the heater. In the NOx decomposition element according to any one of claims 1 to 6 ,
A NOx decomposition element that is mounted on an automobile having an internal combustion engine and uses the exhaust heat of the internal combustion engine as a heat source for heating.

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