JP3093647B2 - Nitrogen oxide decomposition equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide decomposer for decomposing nitrogen oxides (hereinafter, sometimes abbreviated as NOx) harmful to the human body.

[0002]

2. Description of the Related Art Conventionally, this type of nitrogen oxide decomposing apparatus has generally been disclosed in Japanese Patent Application Laid-Open No. 50-32092. As shown in FIG. 8, an anode 2 and a cathode 3 made of platinum (hereinafter abbreviated as Pt) are provided on the surface of a solid electrolyte 1 having high oxygen ion mobility, as shown in FIG.
The solid electrolyte 1 is fixed inside the chamber 4, a DC power supply is connected between the anode 2 and the cathode 3,
It is configured such that a gas containing Ox is introduced into the vicinity of the cathode 3 in the chamber 4.

[0003] The NOx introduced into the chamber 4 is adsorbed on the surface of the cathode 3, the NOx is dissociated into nitrogen atoms and oxygen atoms, and a voltage is applied between the electrodes 2 and 3 by a DC power supply to thereby dissociate the nitrogen. Atoms are released from the surface of the cathode 3 as nitrogen gas (N ₂ ), and dissociated oxygen atoms are moved as oxygen ions in the solid electrolyte 1 to the anode 2 side,
The oxygen gas (O ₂ ) is released from the surface of the anode 2.

According to this apparatus, if the atmosphere does not contain a large amount of oxygen gas, the operating temperature is 500 to 950 ° C.
NOx with an inlet concentration of 1 to 5000 ppm
It is said that 0% or more can be decomposed.

[0005] The present inventors have disclosed in Japanese Patent Application No. 7-197623.
In the Japanese Patent Application, a nitrogen oxide decomposing apparatus in which a cathode is composed of a composite oxide containing an alkaline earth metal and a noble metal (Au, Ag, Pt, Pd) is proposed.

According to this apparatus, even if a large amount of oxygen gas is contained in the atmosphere, the composite oxide containing the alkaline earth metal selectively adsorbs a small amount of NOx. % To operating temperature of 300 to 600
At 0 ° C., 20 to 80% of NOx having an inlet concentration of 1 to 5000 ppm can be decomposed.

[0007]

However, in the conventional nitrogen oxide decomposing apparatus, the above-mentioned Japanese Patent Application Laid-Open No. 50-32092 is disclosed.
In the case of the device disclosed in Japanese Patent Application Laid-Open No. H07-260, since the cathode 3 is made of Pt, if a large amount of oxygen gas is contained in the atmosphere, this oxygen gas becomes nitric oxide (hereinafter referred to as NO) of NOx.
However, there is a problem that NO can hardly be decomposed.

In the case of Japanese Patent Application No. 7-197623, the cathode of the composite oxide containing an alkaline earth metal and a noble metal (Au, Ag, Pt, Pt) are used.
d), if the atmosphere contains a large amount of carbon dioxide (CO ₂ ), this carbon dioxide (CO ₂ )
Since Ox is preferentially adsorbed on the cathode surface over Nitric Oxide (NO), there is a problem that NO can hardly be decomposed.

According to the present invention, there is provided a nitrogen oxide capable of efficiently decomposing nitrogen oxide in an introduced gas even when a large amount of oxygen gas or carbon dioxide gas is contained in the atmosphere. It is an object to provide a disassembly device.

[0010]

In order to achieve the above object, the present invention provides an electrolyte having high oxygen ion mobility, an anode and a cathode provided on the surface of the electrolyte, and applying a voltage between the anode and the cathode. A nitrogen oxide decomposer having a direct current power supply, wherein an oxidizing means for oxidizing nitrogen monoxide to nitrogen dioxide and an oxygen supply means for supplying oxygen into the chamber are provided.

According to the present invention, nitric oxide (NO), which is hardly adsorbed on the cathode surface, is oxidized by the oxidizing means and is changed to nitrogen dioxide (NO ₂ ) which is easily adsorbed on the cathode surface. Even if oxygen gas or carbon dioxide gas is contained, NOx in the introduced gas is adsorbed on the cathode surface,
It is decomposed into nitrogen gas and oxygen gas.

[0012]

[0013]

[0014]

[0015]

[0016]

Further, according to the present invention, the oxygen supply means for supplying oxygen into the chamber is provided, and the oxygen concentration in the chamber is increased, so that the oxidation means can promote the oxidation of NO.

In the above invention, the oxygen supply means includes a second electrolyte having high oxygen ion mobility, a second anode and a second cathode provided on the surface of the second electrolyte, and a second anode and a second cathode provided between the second anode and the second cathode. And a second DC power supply for applying a voltage to the second cathode to move oxygen in the outside air as oxygen ions on the second cathode in the second electrolyte,
This is advantageous because it can be supplied into the chamber as oxygen molecules on the second anode.

In the present invention, the cathode is made of a composite oxide containing at least one kind of alkaline earth metal (eg, Ba, Ca, Sr) and a noble metal (eg, Au, Ag, Pt,
It is preferable to include Pd) because the composite oxide containing an alkaline earth metal has excellent NOx adsorption characteristics in an atmosphere having a high oxygen concentration.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a first embodiment of the present invention comprises a solid electrolyte 1 having a flat plate shape and an anode 2 provided on one surface and a cathode 6 provided on the other surface.
, A catalyst 11 containing them, and an external DC power supply 5 for applying a voltage between the anode 2 and the cathode 6.

The solid electrolyte 1 is made of 8 mol% yttria-stabilized zirconia (8Y ₂ O ₃ .92ZrO ₂ ),
The size is 25mm x 12.5mm x 0.5mm,
Ultrasonic cleaning with acetone was performed before electrode formation. Anode 2
A Pt paste is used for forming the Pt paste, and a Pt paste is used for forming the Cathode 6. Yttrium barium copper oxide (Y
Ba ₂ Cu ₃ O _7-d (hereinafter abbreviated as YBCO)).
Screen printing on one side and the other side of
Drying was performed for 15 minutes at 820 ° C. for 10 minutes in the air in an electric furnace. The anode 2 and the cathode 6 have a size of 23 mm × 10.5 mm and a thickness of 15 μm and 30 μm, respectively.
μm.

The catalyst 7 as oxidizing means has a particle size of about 1 μm.
The porous Pt powder formed into a pellet by a tableting machine was placed in the vicinity of the cathode 6.

According to the present embodiment, when a large amount of a mixed gas of oxygen gas, carbon dioxide gas and a small amount of NOx is introduced, NO in the introduced gas is oxidized by the catalyst 7 to N
Changes in O _2. NO ₂ originally contained in the NO ₂ and introduced in the gas adsorbed on the YBCO surface of the cathode 6, dissociate into nitrogen and oxygen atoms. When a voltage is applied between the anode 2 and the cathode 6 by the DC power supply 5, nitrogen atoms adsorbed on the YBCO surface are released from the cathode 6 side as nitrogen gas, and oxygen atoms adsorbed on the YBCO surface are discharged. It travels in the solid electrolyte 1 as oxygen ions and is released as oxygen gas on the anode 2.
Therefore, NOx can be efficiently decomposed even in an atmosphere containing a large amount of oxygen gas or carbon dioxide gas.

In the present embodiment, the shape of the solid electrolyte 1 is not limited to the above, but a flat electrolyte is preferable because an electrode can be easily formed on the surface thereof, but it may be tubular. Providing the anode 2 and the cathode 6 on one surface of the surface of the solid electrolyte 1 has the advantage of facilitating the formation of the electrodes. However, the provision of the anodes 2 and the cathodes 6 on the front and back surfaces is preferable because a large electrode area can be secured. Further, the material of the solid electrolyte 1 may be zirconia, ceria, or the like.

YBCO is preferable because it has a high ability to adsorb a small amount of NOx in an atmosphere having a high oxygen concentration at a temperature of 300 to 500 ° C. The amount of YBCO added to the Pt paste is 20 to 30 watts based on the NOx adsorption characteristics and conductivity.
t% is preferred. Instead of YBCO, gadolinium barium copper oxide (GdBa ₂ Cu ₃ O _7-d ) or yttrium strontium copper (YSr ₂ Cu) having the property of selectively adsorbing NOx in an atmosphere having a high oxygen concentration
The same effect can be obtained with a composite oxide containing another alkaline earth metal such as ₃ O _7-d ) or barium platinum oxide (BaPtO _x ).

In the second embodiment of the present invention, as shown in FIG. 2, instead of the catalyst of the first embodiment, a ceramic body 8 supporting a catalyst is used as an oxidizing means.
Are laminated on the cathode 6.

The ceramic body 8 has a size of 26 mm × 1
3mm × 2mm dry ceramic nonwoven fabric impregnated with chloroplatinic acid diluted with pure water _{(H 2 PtCl 5 · 6H 2} O) of, after drying at 100 ° C., is obtained by calcining 600 ° C. × 10 minutes in the atmosphere . The amount of Pt after firing was as small as 60 mg. The ceramic body 8 was laminated on the cathode 6 and fixed to a solid electrolyte with an inorganic adhesive.

The apparatus obtained in this way is equipped with a 200p
pmNOx, a mixed gas of 10% oxygen gas and 0.5% carbon dioxide gas was introduced at a flow rate of 200 cc / min, the temperature of the apparatus was maintained at 450 ° C., a voltage was applied between the anode 2 and the cathode 6, and NOx on the outlet side was applied. The concentration was measured with a chemiluminescent NOx meter. FIG. 3 shows the change in the NOx concentration on the outlet side due to the applied current between the anode 2 and the cathode 6. As shown in FIG. 3, when the ceramic body 8 was present, at a current of 10 mA, 35 ppm corresponding to about 20% of the total NOx was decomposed. When the gas composition on the outlet side was measured by gas chromatography, a stoichiometric N ₂ gas corresponding to the above-mentioned decomposed NOx amount was detected. On the other hand, when there is no ceramic body 8, it is understood that NOx is hardly decomposed.

According to this embodiment, since the oxidizing means can be laminated on the cathode 6, the same effects as those of the first embodiment can be obtained, and the apparatus can be downsized. Further, since a small amount of catalyst can be distributed in a desired size and shape, NO can be efficiently oxidized to NO ₂ .

In the present embodiment, the substrate of the ceramic body 8 may be a porous ceramic plate, but the above-mentioned ceramic nonwoven fabric is preferable because it is light in weight and can secure a large specific surface area.

In the third embodiment of the present invention, as shown in FIG. 4, a thick film catalyst 9 is used as an oxidizing means, and the thick film catalyst 9 is formed on the cathode 6.

The thick film catalyst 9 is composed of the solid electrolyte 1 and the anode 2
After printing and firing the cathode 6 and the same, the same Pt paste used for printing the anode 2 was printed thickly on the cathode 6, dried, and fired at 600 ° C. for 10 minutes in the atmosphere to form.

According to this embodiment, since the oxidizing means can be formed on the cathode 6, the same effects as those of the first embodiment can be obtained, and the apparatus can be downsized. Further, it is preferable because no means for supporting the thick film catalyst 9 is required in addition to the cathode 6, and the structure is simple.

In this embodiment, the same effect can be obtained by forming the thick film catalyst 9 on the solid electrolyte 1 together with the anode 2 and the cathode 6 and firing them at the same time.
Further, the paste for forming the thick film catalyst 9 may be a paste of another noble metal or a perovskite-type composite oxide serving as an oxidation catalyst.

In the fourth embodiment of the present invention, as shown in FIG. 5, a powder catalyst 10 is used as an oxidizing means, and the powder catalyst 10 is filled in a chamber 11.

The powder catalyst 10 is a well-mixed Pt powder having a particle size of about 1 μm and quartz sand.
After installing the solid electrolyte 1 in which electrodes are formed and wired,
Filled.

According to the present embodiment, the catalyst is supplied to the chamber 11.
NO can be more efficiently oxidized to NO ₂ because it can be uniformly distributed in the inside. In addition, since the manufacturing method is simple such that the powder catalyst 10 is filled in the chamber 11, the manufacturing is easy.

In the fifth embodiment of the present invention, as shown in FIG. 6, a discharge device 12 for generating a discharge in a chamber 13 is provided as oxidizing means.

The discharge device 12 includes a pair of electrodes 14 and 15 opposed to each other in a chamber 13.
And an AC power supply 16 connected to the power supply 15.

According to the present embodiment, since oxygen gas in the atmosphere becomes radicals by discharge, NO can be more reliably oxidized to NO ₂ .

In the sixth embodiment of the present invention, as shown in FIG. 7, an oxygen supply device 17 for supplying oxygen from the outside air into the chamber 18 is added to the configuration of the first embodiment (FIG. 1). Things.

The oxygen supply device 17 is provided on a part of the outer wall of the chamber 18 and has the second anode 20 on its inner surface.
A second electrolyte 19 having high oxygen ion mobility having a second cathode 21 formed on the outer surface;
DC power supply 2 for applying a voltage between the second DC power supply 2 and the second cathode 21
And 2.

According to the present embodiment, by applying a DC voltage between the second anode 20 and the second cathode 21,
Since oxygen in the outside air can be moved as oxygen ions on the second cathode 21 through the second electrolyte 19 and supplied to the chamber 18 as oxygen molecules on the second anode 20, the oxidation of NO by the oxidizing means 7 can be performed. Can be promoted.

[0045]

According to the present invention, nitric oxide (NO), which is hardly adsorbed on the cathode surface, is oxidized by the oxidizing means and changed to nitrogen dioxide (NO ₂ ) which is easily adsorbed on the cathode surface. Even if a large amount of oxygen gas or carbon dioxide gas is contained, NOx in the introduced gas is adsorbed on the cathode surface,
It is decomposed into nitrogen gas and oxygen gas.

According to the present invention, since the oxygen supply means for supplying oxygen is provided in the chamber, the oxygen concentration in the chamber is increased, so that the oxidation of NO by the oxidizing means can be promoted.

In the present invention, the cathode is made of a composite oxide containing at least one kind of alkaline earth metal (eg, Ba, Ca, Sr) and a noble metal (eg, Au, Ag, Pt,
(Pd, Ir, Rh) is preferable because a composite oxide containing an alkaline earth metal has excellent NOx adsorption characteristics in an atmosphere having a high oxygen concentration.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a second embodiment of the present invention.

FIG. 3 shows an outlet NOx according to a second embodiment of the present invention.
FIG. 4 is a diagram showing the dependence of concentration on applied current.

FIG. 4 is a schematic sectional view showing a third embodiment of the present invention.

FIG. 5 is a schematic sectional view showing a fourth embodiment of the present invention.

FIG. 6 is a schematic sectional view showing a fifth embodiment of the present invention.

FIG. 7 is a schematic sectional view showing a sixth embodiment of the present invention.

FIG. 8 is a schematic sectional view showing a conventional example.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte 2 Anode 5 DC power supply 6 Cathode 7 Catalyst 8 Ceramic body 9 Thick film catalyst 10 Powder catalyst 11, 13, 18 Chamber 12 Discharge device 17 Oxygen supply means 19 Second electrolyte 20 Second cathode 21 Second anode 22 Second DC power supply

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B01D 53/94 (72) Inventor Akio Fukuda 1006 Ojidoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Yellow Kenzo Chichi 1006 Kazuma Kadoma, Kazuma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-61-78421 (JP, A) JP-A-58-183947 (JP, A) JP-A-8-24579 (JP, A) JP-A-5-15737 (JP, A) JP-A-7-185261 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/32 B01D 53 / 56 B01D 53/74

Claims (3)

(57) [Claims] 1. A nitrogen oxide decomposition apparatus comprising: an electrolyte having high oxygen ion mobility; an anode and a cathode provided on the surface of the electrolyte; and a DC power supply for applying a voltage between the anode and the cathode. An oxidizing means for oxidizing nitrogen to nitrogen dioxide and supplying oxygen to the chamber.
An apparatus for decomposing nitrogen oxides, comprising an oxygen supply means for supplying oxygen . 2. The oxygen supply means has high oxygen ion mobility.
And a second electrolyte provided on the surface of the second electrolyte.
An anode and a second cathode, and the second anode and the second
A second DC power supply for applying a voltage between the cathodes;
Motomeko 1 nitrogen oxide decomposing apparatus according. 3. The cathode comprises at least one alkali.
2. A composite oxide containing an earth metal and a noble metal.
Or the nitrogen oxide decomposer according to 2 .