JP2022189523A - NOx PURIFICATION DEVICE AND NOx PURIFICATION METHOD WITH USE THEREOF - Google Patents

Abstract

To provide a NOx purification device which can decompose and remove NOx to N2 with high purification rate even at low temperatures near room temperature.SOLUTION: A NOx purification device comprises: an electrochemical cell 4 having a solid electrolyte 1, an anode electrode film 2 located on face of the solid electrolyte 1, and a cathode electrode film 3 located on the other face of the solid electrolyte 1; an electrification device 5 which is electrically connected to the anode electrode film 2 and the cathode electrode film 3; and a N2O decomposition catalyst located on a downstream side of the electrochemical cell 4. The N2O decomposition catalyst contains a metal oxide carrier, and at least one kind of noble metal which is carried on the metal oxide carrier and is selected from a group comprising Pd and Rh. An anode side incoming gas passage 7a for supplying first incoming gas to the anode electrode film 2, and a cathode side incoming gas passage 8a for supplying second incoming gas to the cathode electrode film 3 are independently provided, and only a cathode side outgoing gas passage 8b is connected to the N2O decomposition catalyst.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a NOx purification device and a NOx purification method using the same, and more particularly to a NOx purification device and NOx purification method using electrolysis of water.

In recent years, research has been conducted on a method of purifying NOx by applying a voltage to an electrochemical element. Further, devices with various configurations have been disclosed as NOx purifiers used in such a method.

For example, Japanese Patent Application Laid-Open No. 2020-110761 (Patent Document 1) discloses a solid electrolyte, an anode electrode film disposed on one side of the solid electrolyte, and the solid electrolyte so as to face the anode electrode film. a cathode electrode film disposed on the other surface of the NOx purification device, and an energization device electrically connected to the anode electrode film and the cathode electrode film; and the anode electrode film and the Exhaust gas containing NOx and water is introduced into the NOx purifier while a voltage is applied between the cathode electrode film and the water in the exhaust gas is electrolyzed on the anode electrode film to generate hydrogen ions. and reacting the hydrogen ions with the NOx in the exhaust gas on the cathode electrode film to remove the NOx. In this method, as described in Patent Document 1, NOx reacts with hydrogen ions (H ⁺ ) on the cathode electrode film and is reduced to nitrogen molecules (N ₂ ) and water molecules (H ₂ O). decomposed. This reductive decomposition reaction proceeds by reacting nitrogen atoms (N) generated by the dissociation of NOx. ), the nitrogen atoms (N) generated by the dissociation of NOx are likely to react with NOx, and dinitrogen monoxide (N ₂ O) is likely to be generated. This dinitrogen monoxide (N ₂ O) reacts with hydrogen ions (H ⁺ ) and is reductively decomposed into nitrogen molecules (N ₂ ) and water molecules (H ₂ O). Since it is difficult to progress at high temperatures (reaction rate is slow), the method described in Patent Document 1 achieves a high NOx purification rate, but has the problem that dinitrogen monoxide (N ₂ O) tends to remain. .

Further, Japanese Patent Application Laid-Open No. 2014-237117 (Patent Document 2) discloses a NOx adsorbent capable of adsorbing NOx, a NOx reduction catalyst arranged downstream of the NOx adsorbent, and a NOx reduction catalyst arranged downstream of the NOx reduction catalyst. an N ₂ O decomposition catalyst, the N ₂ O decomposition catalyst containing at least one active metal selected from the group consisting of Rh, Pt, Cu, Co, Ni, Fe, Au and Ag and Ce. An exhaust gas purification system is disclosed that includes a carrier. In this exhaust gas purification system, NOx is purified by bringing exhaust gas containing nitrogen oxides into contact with the NOx adsorbent and the NOx reduction catalyst, and N ₂ O is generated depending on the conditions (especially in a reducing atmosphere). When the generated N ₂ O is brought into contact with the N ₂ O decomposition catalyst, the active metal such as Rh, which is the N ₂ O decomposition site of the N ₂ O decomposition catalyst, and the fast oxygen adsorption/desorption site on Ce of the support in the vicinity thereof. As a result, the oxygen species generated by the dissociation of N ₂ O are efficiently adsorbed onto the Ce carrier and desorbed by the regeneration function of H ₂ . However, in the exhaust gas purification system described in Patent Document 2, although a high NOx purification rate is achieved, the decomposition efficiency of dinitrogen monoxide (N ₂ O) is not always sufficient.

Japanese Patent Application Laid-Open No. 2020-110761 JP 2014-237117 A

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and provides a NOx purifying device and a NOx purifying method capable of decomposing and removing NOx to _N2 at a high purification rate even at a low temperature near room temperature. for the purpose.

The present inventors have made intensive studies to achieve the above object, and found that when NOx is purified using an electrochemical cell having a solid electrolyte, an anode electrode film, and a cathode electrode film, By supplying only the outgas to the N ₂ O decomposition catalyst, NOx can be decomposed and removed to N ₂ at a high purification rate even at a low temperature around room temperature, and the present invention has been completed.

That is, the NOx purifier of the present invention comprises a solid electrolyte, an anode electrode film arranged on one surface of the solid electrolyte, and an anode electrode film arranged on the other surface of the solid electrolyte so as to face the anode electrode film. an electrochemical cell having a cathode electrode film connected thereto; an energization device electrically connected to the anode electrode film and the cathode electrode film; and an N ₂ O decomposition catalyst disposed downstream of the electrochemical cell. wherein the N ₂ O decomposition catalyst contains a metal oxide support and at least one noble metal selected from the group consisting of Pd and Rh supported on the metal oxide support. and an anode-side incoming gas flow path for supplying a first incoming gas to the anode electrode film and a cathode-side incoming gas flow path for supplying a second incoming gas to the cathode electrode film are provided independently of each other. an anode-side outlet gas flow path for discharging a first output gas from the anode electrode film and a cathode-side output gas flow path for discharging a second output gas from the cathode electrode film; are provided independently of each other, and only the cathode-side exit gas flow path is connected to the N ₂ O decomposition catalyst.

In the NOx purification device of the present invention, the anode electrode film and the cathode electrode film preferably contain a noble metal, and the cathode electrode film is preferably a Pd electrode film or a Pt electrode film. , the solid electrolyte is preferably a proton-conducting polymer solid electrolyte.

Further, in the NOx purification method of the present invention, while applying a voltage between the anode electrode film and the cathode electrode film of the NOx purification device of the present invention, the first incoming gas containing moisture is passed through the anode electrode film. Then, by independently supplying a second input gas containing NOx to the cathode electrode film, the moisture is electrolyzed on the anode electrode film to generate hydrogen ions, and on the cathode electrode film a step of reacting the hydrogen ions with the NOx to decompose the NOx into N ₂ and N ₂ O, and supplying only a second output gas from the cathode electrode film to the N ₂ O decomposition catalyst to and reductively decomposing N ₂ O contained in the second outgas into N ₂ .

The reason why the present invention can decompose and remove NOx to _N2 with a high purification rate even at a low temperature around room temperature is not necessarily clear, but the present inventors speculate as follows. That is, while applying a voltage between the anode electrode film 2 and the cathode electrode film 3 of the electrochemical cell (having the solid electrolyte 1, the anode electrode film 2, and the cathode electrode film 3) shown in FIG. When a gas containing moisture (water vapor, H ₂ O) is brought into contact with the membrane 2, the moisture (water vapor, H ₂ O) is electrolyzed on the anode electrode membrane 2 to produce hydrogen ions (protons, H ⁺ ) and electrons ( e ⁻ ) is generated. Hydrogen ions (H ⁺ ) move through the solid electrolyte 1 , and electrons (e ⁻ ) move through the current-carrying circuit to the cathode electrode film 3 . The hydrogen ions (H ⁺ ) and electrons (e ⁻ ) that have moved to the cathode electrode film 3 react with NOx on the cathode electrode film 3, and NOx is electrochemically converted into nitrogen molecules (N ₂ ) and water molecules (H ₂ O). is reductively decomposed. This reductive decomposition reaction proceeds by reacting nitrogen atoms (N) generated by the dissociation of NOx. ), the nitrogen atoms (N) generated by the dissociation of NOx are likely to react with NOx, and dinitrogen monoxide (N ₂ O) is likely to be generated. This dinitrogen monoxide (N ₂ O) reacts with hydrogen ions (H ⁺ ) and is reductively decomposed into nitrogen molecules (N ₂ ) and water molecules (H ₂ O). Dinitrogen monoxide (N ₂ O) tends to remain because it is difficult to progress at high temperatures (reaction rate is slow). _In the present invention ^, hydrogen ( ^H ₂ ) to the N ₂ O decomposition catalyst reactor 9, the reaction between dinitrogen monoxide (N ₂ O) and hydrogen (H ₂ ) is caused by the N ₂ O decomposition catalyst. Dinitrogen monoxide ( _{N 2} O) is reductively decomposed into nitrogen molecules (N ₂ ) and water molecules (H ₂ O). presumed to be removable.

According to the present invention, it is possible to decompose and remove NOx to _N2 at a high purification rate even at low temperatures near room temperature.

FIG. 2 is a schematic diagram showing the mechanism of NOx decomposition reaction in the present invention. 1 is a longitudinal sectional view schematically showing a preferred embodiment of the NOx purifier of the present invention; FIG. 1 is a longitudinal sectional view schematically showing a NOx purifying device produced in an example; FIG. 4 is a graph showing the N ₂ production rate and the N ₂ O residual rate of the NOx purifiers produced in Examples 1-5 and Comparative Examples 1-4.

Preferred embodiments of the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to the drawings. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description may be omitted.

[NOx purification device]
First, the NOx purification device of the present invention will be explained. FIG. 2 is a longitudinal sectional view schematically showing a preferred embodiment of the NOx purifier of the present invention. The NOx purification device shown in FIG. an electrochemical cell 4 having a cathode electrode film 3 disposed on a surface; an energization device 5 electrically connected to the anode electrode film 2 and the cathode electrode film 3; and an N ₂ O decomposition catalytic reactor 9 disposed therein.

The solid electrolyte used in the present invention is not particularly limited as long as it is a solid electrolyte used in a NOx purifier using an electrochemical reductive decomposition reaction. Polymer solid electrolyte membranes are more preferred. Examples of such a proton-conducting polymer solid electrolyte membrane include conventionally known proton-conducting polymer solid electrolyte membranes such as perfluorosulfonic acid-based polymers known under the trade name of "Nafion (registered trademark)." mentioned. The thickness of such a proton conductive polymer solid electrolyte membrane is not particularly limited, but is preferably 0.01 to 0.5 mm, more preferably 0.05 to 0.2 mm.

An anode electrode film 2 is arranged on one surface of the solid electrolyte 1 used in the present invention, and a cathode electrode film 3 is arranged on the other surface so as to face the anode electrode film 2. . _The anode electrode film and cathode electrode film are not particularly limited as long as they are conductive metal films. From the viewpoint of promoting the reductive decomposition of the electrode film, an electrode film containing noble metals (Pt, Rh, Pd, Ag, Ir, Ru, etc.), Cu, Ti, Sn, etc. is preferable, and a Pd electrode film, a Pt electrode film, IrOx An electrode film is more preferable, and a Pd electrode film and a Pt electrode film are particularly preferable as the cathode electrode film. Such an electrode film may be a porous carbon film supporting the noble metal or the like, carbon paper supporting the noble metal or the like, a porous film made of the noble metal or the like, or a mesh of the noble metal or the like. good too.

The thickness of the anode electrode film and cathode electrode film is not particularly limited, but is preferably 0.1 to 100 μm, more preferably 1 to 50 μm. When the thicknesses of the anode electrode film and the cathode electrode film are less than the lower limit, the catalyst tends to become inactive due to lack of active sites and the resistance of the electrode film increases. , the protons (H ⁺ ) generated at the interface between the electrode film and the solid electrolyte tend not to sufficiently react with NOx, and the contact with moisture, NOx and the like tends to decrease.

The method of forming the anode electrode film and the cathode electrode film is not particularly limited, but for example, a method of thermocompression bonding an electrode material onto the surface of the solid electrolyte (or solid electrolyte precursor), a method of coating, and a method of vapor deposition. mentioned. Electrode materials include metal-supported carbon powder, metal targets (for example, Pt targets), organic metals, and the like.

In the NOx purifier of the present invention, the anode electrode film 2 and the cathode electrode film 3 are electrically connected to the energization device 5 by the electric wiring 6 . Such an energizing device is not particularly limited as long as it can apply a DC voltage, and a known energizing device (DC power supply) can be appropriately employed. The electrical wiring is not particularly limited, and examples thereof include Au wire, Pt wire, Ni wire, Cu wire, and Ag wire. The electric wiring 6 may be directly bonded to the anode electrode film 2 and the cathode electrode film 3, or a metal mesh (Au mesh, Pt mesh, Ni mesh, Ag mesh, etc.) to which the electric wiring 6 is bonded may be used. You may contact the anode electrode film 2 and the cathode electrode film 3 through. Furthermore, the current collector plate to which the electric wiring 6 is joined may be brought into contact with the anode electrode film 2 and the cathode electrode film 3 via the current collector and metal thin plate fins. Examples of the current collecting plate and the current collecting material include a stainless steel plate, a stainless steel plate coated with a precious metal, and a metal mesh such as gold. etc.

Further, in the NOx purifier of the present invention, the first incoming gas is supplied to the anode electrode film 2 of the electrochemical cell 4 having such a solid electrolyte 1, the anode electrode film 2 and the cathode electrode film 3. The anode-side incoming gas channel 7a for supplying the second incoming gas to the cathode electrode film 3 and the cathode-side incoming gas channel 8a for supplying the second incoming gas to the cathode electrode film 3 are connected independently. This makes it possible to independently supply a gas containing moisture (water vapor, H ₂ O) to the anode electrode film 2 and a gas containing NOx to the cathode electrode film 3 .

Further, in the NOx purifying apparatus of the present invention, the anode side outlet gas passage 7b for discharging the first outlet gas from the anode electrode film 2 and the second outlet gas flow path 7b for discharging the second outlet gas from the cathode electrode film 3 are provided. are independently connected to the cathode-side gas passage 8b, and only the cathode-side gas passage 8b is connected to the N ₂ O decomposition catalyst (N ₂ O decomposition catalyst) disposed downstream of the electrochemical cell 4. It is connected to the catalytic reactor 9). As a result, only the second output gas containing dinitrogen monoxide (N ₂ O) and hydrogen (H ₂ ) by-produced on the cathode electrode film 3 is removed by the N ₂ O decomposition catalyst (N ₂ O decomposition catalyst reaction It can be supplied to the device 9), and the action of the N ₂ O decomposition catalyst makes it possible to efficiently reductively decompose N ₂ O to N ₂ .

The N ₂ O decomposition catalyst used in the present invention contains a metal oxide support and at least one noble metal selected from the group consisting of Pd and Rh supported on the metal oxide support. The metal oxide support is not particularly limited, and can be any metal oxide support used for conventionally known N ₂ O decomposition catalysts. Examples thereof include ceria, alumina, zirconia, titania, spinel oxide, and the like. .

The amount of the noble metal to be supported is not particularly limited, but is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, relative to 100 parts by mass of the metal oxide support. If the supported amount of the noble metal is less than the lower limit, the number of active sites present in the N ₂ O decomposition catalyst tends to decrease, resulting in a decrease in catalytic activity.

[NOx purification method]
Next, the NOx purification method of the present invention will be described using the NOx purification device shown in FIG. 2 as an example. The NOx purification method of removing NOx using the NOx purification device shown in FIG. 2 is a preferred embodiment of the NOx purification method of the present invention. Contents overlapping with the contents described in the preferred embodiment of the NOx purifier of the present invention will be omitted.

In the NOx purifying method of the present invention, while applying a voltage between the anode electrode film 2 and the cathode electrode film 3 of the NOx purifying device, the first incoming gas containing moisture is introduced from the anode side incoming gas passage 7a. A second incoming gas containing NOx is supplied to the anode electrode film 2 from the cathode-side incoming gas passage 8a to the cathode electrode film 3 independently, and moisture is supplied to the anode electrode film 2 and NOx is supplied to the cathode electrode film 3. come into contact with As a result, as shown in FIG. 1, water (water vapor, _H.sub.2O ) is electrolyzed on the anode electrode film 2 to generate hydrogen ions (H.sup ^.+ ) and electrons ( ^e.sup.- ). ⁺ ) moves through the solid electrolyte 1 to the surface of the cathode electrode film 3 . Also, the electrons (e ⁻ ) move to the cathode electrode film 3 through the conducting circuit.

On the other hand, on the cathode electrode film 3, NOx is dissociated into nitrogen atoms (N) and oxygen atoms (O), and the oxygen atoms (O) react with the hydrogen ions (H ⁺ ) and electrons (e ⁻ ) to produce moisture. (H ₂ O) is produced. Further, the dissociated nitrogen atoms (N) react with each other to form nitrogen molecules (N ₂ ), and the dissociated nitrogen atoms (N) react with the remaining NO to form dinitrogen monoxide (N ₂ O). is generated. Further, the hydrogen ions (H ⁺ ) react with each other to produce hydrogen molecules (H ₂ ). Therefore, the second output gas from the cathode electrode film 3 is a gas containing nitrogen molecules (N ₂ ), dinitrogen monoxide (N ₂ O) and hydrogen molecules (H ₂ ).

The voltage applied between the anode electrode film 2 and the cathode electrode film 3 is preferably 1-20V, more preferably 1.2-8V. When the applied voltage is less than the lower limit, the ^electrolysis of water required for the reaction tends not to proceed. Also, the solid electrolyte and the electrode film tend to deteriorate.

Also, the current value between the anode electrode film 2 and the cathode electrode film 3 is preferably 0.1 to 500 mA/cm ² , more preferably 1 to 400 mA/cm ² . If the current value between the electrode films is less than the lower limit, the electrolysis of water required for the reaction tends not to proceed, while if it exceeds the upper limit, the solid electrolyte and the electrode films tend to deteriorate.

The first input gas supplied to the anode electrode film ₂ is not particularly limited as long as it contains moisture (water vapor, H ₂ O). is preferable, and a gas containing H ₂ O at a relative humidity of 40% or more is more preferable. By using such a relative humidity gas as the first input gas, the generation of hydrogen ions (H ⁺ ) on the anode electrode film 2 is promoted.

The second input gas supplied to the cathode electrode film 3 is not particularly limited as long as it contains NOx. Exhaust gas from an internal combustion engine is exemplified as such a gas containing NOx.

Next, in the NOx purification method of the present invention, only the second exit gas from the cathode electrode film 3 is passed through the N ₂ O decomposition catalyst (N ₂ O decomposition catalyst reactor 9) arranged downstream of the electrochemical cell. to react dinitrogen monoxide (N ₂ O) and hydrogen molecules (H ₂ ) in the presence of an N ₂ O decomposition catalyst to reductively decompose N ₂ O into nitrogen molecules (N ₂ ) . Since the action of the N ₂ O decomposition catalyst promotes the reaction between N ₂ O and H ₂ , it becomes possible to decompose and remove NOx to N ₂ at a high purification rate even at a low temperature around room temperature.

Although the preferred embodiments of the NOx purification device and NOx purification method of the present invention have been described above with reference to FIGS. 1 and 2, the NOx purification device and NOx purification method of the present invention are limited to the above embodiments. is not.

EXAMPLES The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

(Production example 1)
First, 2.54 g of 1.97% by mass tetraamminepalladium hydroxide water was weighed into a vial (capacity: 30 ml), 8 ml of ion-exchanged water, 5 ml of ethanol and 2 ml of acetic acid were added, and then conductive carbon black was added as a carrier. ("VULCAN XC-72" manufactured by Cabot) was added and mixed. The resulting mixture was heated at 140° C. for 1.5 hours using a microwave synthesizer (“Monowave 450” manufactured by Anton Paar Japan Co., Ltd.) to support palladium (Pd) on the conductive carbon black. After the obtained powder was washed with ion-exchanged water, it was recovered by suction filtration to obtain Pd-supported porous carbon (amount of Pd supported: 33 parts by mass with respect to 100 parts by mass of carbon). This Pd-supporting porous carbon was added to a perfluorosulfonic acid resin solution (“Nafion (registered trademark)” manufactured by DuPont, concentration: 20% by mass) and mixed, and the obtained solution was used to form a Pd-supporting porous carbon. A carbon (Pd/C) electrode film was produced.

In addition, iridium oxide (IrOx) (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., specific surface area: 5 m ² /g) is added to a perfluorosulfonic acid resin solution (manufactured by DuPont “Nafion (registered trademark)”, concentration: 20% by mass). An iridium oxide (IrOx) electrode film was produced using the solution obtained by adding and mixing.

Next, on one surface of a perfluorosulfonic acid-based resin membrane (“Nafion (registered trademark) N115” manufactured by DuPont), which is a proton-conducting polymer solid electrolyte membrane, the Pd-supporting porous carbon (Pd/C) was deposited. An electrode film (area: 12.96 cm ² ) was thermocompression bonded to the other surface of the iridium oxide (IrOx) electrode film (area: 12.96 cm ² ) to form a cathode electrode on the proton conductive polymer solid electrolyte membrane. An electrode/electrolyte membrane assembly (Pd/C-IrOx-MEA) was prepared by joining the Pd/C electrode film as a film and the IrOx electrode film as an anode electrode film.

(Production example 2)
First, platinum (Pt)-supported porous carbon, which is an electrode catalyst for polymer electrolyte fuel cells (platinum catalyst "TEC10V30E" manufactured by Tanaka Kikinzoku Co., Ltd., carbon support: conductive carbon black (manufactured by Cabot Corporation "VULCAN XC-72 ”), Pt supported amount: 30% by mass) was added to a perfluorosulfonic acid-based resin solution (manufactured by DuPont “Nafion (registered trademark)”, concentration: 20% by mass) and mixed, and the resulting solution was used. A Pt-supporting porous carbon (Pt/C) electrode film was produced by the method. Next, a proton conductive polymer solid electrolyte membrane ⁽ perfluoro An electrode/electrolyte membrane assembly (Pt/C-IrOx-MEA) was prepared by bonding the Pt/C electrode film as a cathode electrode film and the IrOx electrode film as an anode electrode film to a sulfonic acid resin film).

(Preparation Example 1)
Add 2.24 g of an aqueous palladium nitrate solution (Pd concentration: 4.5% by mass) to 250 ml of ion-exchanged water and stir, then add 10 g of γ-Al ₂ O ₃ (“MI307” manufactured by Rhodia) and stir. and the resulting mixture was evaporated to dryness. The resulting dried product was calcined in air at 300° C. for 3 hours to obtain Pd-supported γ-Al ₂ O ₃ (Pd supported amount: 1 part by mass per 100 parts by mass of γ-Al ₂ O ₃ ). .

(Preparation Example 2)
0.272 g of rhodium acetate (Rh content: 36.6% by mass) and _0.2196 g of ferric ammonium citrate (Fe content: 16% by mass) were added to 100 ml of ion-exchanged water and stirred. 10 g of "cerium oxide" manufactured by Kigenso Kagaku Kogyo Co., Ltd.) was added and stirred, and the resulting mixture was evaporated to dryness. The obtained dried product was calcined in the atmosphere at 300° C. for 3 hours to obtain RhFe-supported CeO ₂ (amount of Rh supported: 1 part by weight per 100 parts by weight of CeO ₂ , amount of Fe supported: per 100 parts by weight of CeO ₂ 0.35 parts by mass) was obtained.

(Preparation Example 3)
Add 3.67 g of an aqueous rhodium nitrate solution (Rh concentration: 2.75% by mass) to 100 ml of ion-exchanged water and stir, then add 10 g of CeO ₂ ("Cerium oxide" manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.). was stirred and the resulting mixture was evaporated to dryness. The obtained dried product was calcined in air at 300° C. for 3 hours to obtain Rh-supported CeO ₂ (amount of Rh supported: 1 part by weight per 100 parts by weight of CeO ₂ ).

(Comparative Preparation Example 1)
Pt-supported γ-Al ₂ O ₃ (Pt supported amount: 1 part by mass per 100 parts by mass of γ-Al ₂ O ₃ ) was obtained.

(Example 1)
A NOx purifier shown in FIG. 3 was produced. That is, first, the electrode/electrolyte membrane assembly (Pd/C-IrOx-MEA) produced in Production Example 1 was wrapped with two sheets of carbon paper ("TGP-H-060" manufactured by Toray Industries, Inc., thickness: 0.005 mm). 19 mm, electrical resistance: (thickness direction) 80 mΩ・cm, (surface direction) 5.8 mΩ・cm, gas permeability: 1900 ml・mm/(cm ²・hr・mmAq), porosity: 78%, bulk density Solid electrolyte 1 (perfluorosulfonic acid resin film), anode electrode film 2 (IrOx electrode film), anode side carbon paper 2a, cathode electrode film ³ (Pd/C electrode membrane), and an electrochemical cell 4 comprising a carbon paper 3a on the cathode side.

Next, the electrochemical cell 4 is composed of two current collectors 11a (Au-sputtered SUS316 stainless steel mesh, thickness: 0.1 mm), two metal thin plate fins 12 (SUS304 stainless steel corrugated fin, thickness : 0.8 mm), and two current collectors 11b (Au-sputtered SUS316 stainless steel mesh, thickness: 0.1 mm) sandwiched in order, and two current collector plates 13 having openings for gas flow paths. The collector plate 13 was sandwiched between (Pt-sputtered SUS316 stainless steel plates), and the current collector plate 13 was connected by an electrical wiring 6 to an electrification device 5 (direct current power source “2400-C general-purpose source meter” manufactured by Keithley Instruments). Furthermore, using a sealing material (silicone gasket) 14, the anode side gas flow path 7 including the inlet gas flow path 7a and the out gas flow path 7b and the cathode side gas flow including the inflow gas flow path 8a and the out gas flow path 8b are formed. Each channel 8 was formed independently.

Next, 0.8 g of the Pd-supported γ-Al ₂ O ₃ prepared in Preparation Example 1 was filled in the reaction tube as the N ₂ O decomposition catalyst to prepare the N ₂ O decomposition catalyst reactor 9. Only the gas flow path 8b was connected, and the purified gas discharge flow path 10 was connected to the N ₂ O decomposition catalytic reaction device 9 to fabricate the NOx purifier shown in FIG.

(Example 2)
_{NOx purification} shown in _FIG . A device was fabricated.

(Example 3)
_{NOx purification} shown in _FIG . A device was fabricated.

(Example 4)
Except that the electrode/electrolyte membrane assembly (Pt/C-IrOx-MEA) produced in Production Example 2 was used instead of the electrode/electrolyte membrane assembly (Pd/C-IrOx-MEA) produced in Production Example 1. In the same manner as in Example 1, the NOx purifier shown in FIG. 3 was produced.

(Example 5)
_{NOx purification} shown in _FIG . A device was fabricated.

(Comparative example 1)
A NOx purification device was produced in the same manner as in Example 1, except that the N ₂ O decomposition catalytic reaction device 9 was not connected.

(Comparative example 2)
NOx purification was carried out in the same manner as in Example 1 except that 0.8 g of Pt-supported γ-Al ₂ O ₃ prepared in Comparative Preparation Example 1 was used instead of Pd-supported γ-Al ₂ O ₃ prepared in Preparation Example 1. A device was fabricated.

(Comparative Example 3)
A NOx purification device was produced in the same manner as in Example 4, except that the N ₂ O decomposition catalytic reaction device 9 was not connected.

(Comparative Example 4)
A NOx purifier was fabricated in the same manner as in Example 1, except that both the anode-side exit gas flow path 7b and the cathode-side exit gas flow path 8b were connected to the N ₂ O decomposition catalytic reactor 9 .

Table 1 summarizes the configurations of the NOx purifiers produced in Examples and Comparative Examples.

<Performance evaluation test>
First, helium gas was passed through the N ₂ O decomposition catalytic reactor 9 of each of the NOx purifiers fabricated in Examples and Comparative Examples at a flow rate of 100 ml/min and a temperature of 300° C. for 30 minutes for pretreatment.

Next, helium gas to which water was added by a bubbler was applied to the anode electrode film 2 of the electrochemical cell 4 of each NOx purification device, and a mixed gas containing nitrogen monoxide and moisture (NO (1000 ppm) + H ₂ O (5%) + He (balance)) at a flow rate of 120 ml/min, and a voltage of 1.5 V is applied between the anode electrode film and the cathode electrode film for 15 minutes at room temperature (19 to 26°C). applied.

The NO concentration, N ₂ concentration and N ₂ O concentration in the purified gas discharged from the N ₂ O decomposition catalytic reactor 9 (cathode-side gas for Comparative Examples 1 and 3) were measured using a mass spectrometer (Canon ANELVA Co., Ltd.). It was measured at m/z = 28 and 44 using a quadrupole mass spectrometer "M-101QA-TDF" manufactured by the company. The relationship between gas concentration and mass spectrometry peak intensity was calibrated in advance using gases of known concentrations. Based on the results obtained, the ratio of the amount of N ₂ produced to the amount of NO converted (N ₂ production rate) and the ratio of the amount of residual N ₂ O (remaining N ₂ O rate). The results are shown in FIG.

As shown in FIG. 4, when only the cathode side exit gas of the electrochemical cell (NOx decomposition device) was supplied to the N ₂ O decomposition catalyst containing Pd or Rh (Examples 1 to 5), the purified gas No N ₂ O remained inside, and the N ₂ production rate increased. That is, it was found that NOx can be decomposed and removed to _N2 at a high purification rate by using the NOx purification device of the present invention.

On the other hand, when the N ₂ O decomposition catalyst was not arranged downstream of the electrochemical cell (NOx decomposition device) (Comparative Examples 1 and 3), the N ₂ production rate was very low (15% or less), and the N ₂ O residual rate became very high (50% or less). That is, it was found that when a NOx decomposition device not equipped with an N ₂ O decomposition catalyst is used, although the NOx purification rate is high, N ₂ is not sufficiently decomposed, and a large amount of N ₂ O remains in the purified gas. .

In addition, when a catalyst containing Pt was used as the N ₂ O decomposition catalyst (Comparative Example 2), compared to the case of using a NOx decomposition device not equipped with an N ₂ O decomposition catalyst (Comparative Examples 1 and 3), As a result, the N ₂ production rate increased (approximately 25%), but the N ₂ O residual rate was still high (approximately 45%). That is, it was found that catalysts containing Pt are unsuitable as N ₂ O decomposition catalysts.

Furthermore, when both the anode side gas and the cathode side gas of the electrochemical cell (NOx decomposition device) were supplied to the N ₂ O decomposition catalyst containing Pd or Rh (Comparative Example 4), the N ₂ production rate was Very low (approximately 15%) and very high residual N ₂ O (approximately 65%). That is, if all the output gas from the electrochemical cell (NOx decomposition device) is supplied to the N ₂ O decomposition catalyst containing Pd or Rh, the NOx purification rate will be high, but N ₂ will not be sufficiently decomposed into purified gas. It was found that a large amount of N ₂ O remained.

As described above, according to the present invention, it is possible to decompose and remove NOx to _N2 at a high purification rate even at a low temperature around room temperature. Therefore, the NOx purification device and the NOx purification method using the same of the present invention can be used for automobile exhaust gas treatment, low-temperature exhaust gas treatment, distributed cogeneration system, NOx purification in closed spaces such as long-distance tunnels and factories, etc. , NOx purifier for purifying nitrogen oxides (NOx) contained in exhaust gas from internal combustion engines such as diesel engines and lean fuel engines with low fuel consumption rate, and NOx purifying method using the same is particularly useful as

1: Solid electrolyte 2: Anode electrode film 2a: Anode side carbon paper 3: Cathode electrode film 3a: Cathode side carbon paper 4: Electrochemical cell 5: Conductor 6: Electric wiring 7: Anode side gas channel 7a: Anode side Incoming gas passage 7b: Anode side outgoing gas passage 8: Cathode side gas passage 8a: Cathode side incoming gas passage 8b: Cathode side outgoing gas passage 9: N ₂ O decomposition catalytic reactor 10: Purified gas discharge stream Paths 11a, 11b: Current collector 12: Metal thin plate fin 13: Current collector 14: Sealing material

Claims (5)

Electrochemistry comprising a solid electrolyte, an anode electrode film arranged on one surface of the solid electrolyte, and a cathode electrode film arranged on the other surface of the solid electrolyte so as to face the anode electrode film a cell;
an energization device electrically connected to the anode electrode film and the cathode electrode film;
an N ₂ O decomposition catalyst located downstream of the electrochemical cell;
The N ₂ O decomposition catalyst contains a metal oxide support and at least one noble metal selected from the group consisting of Pd and Rh supported on the metal oxide support,
An anode-side incoming gas channel for supplying a first incoming gas to the anode electrode film and a cathode-side incoming gas channel for supplying a second incoming gas to the cathode electrode film are provided independently of each other. and
An anode-side outlet gas flow path for discharging the first output gas from the anode electrode film and a cathode-side output gas flow path for discharging the second output gas from the cathode electrode film are independently provided. is provided,
The NOx purifier, wherein only the cathode-side exit gas flow path is connected to the N ₂ O decomposition catalyst. 2. A NOx purifier according to claim 1, wherein said anode electrode film and said cathode electrode film contain a noble metal. 3. A NOx purifier according to claim 2, wherein said cathode electrode film is a Pd electrode film or a Pt electrode film. The NOx purifier according to any one of claims 1 to 3, wherein the solid electrolyte is a proton-conducting polymer solid electrolyte. While applying a voltage between the anode electrode film and the cathode electrode film of the NOx purifier according to any one of claims 1 to 4, the first incoming gas containing moisture is supplied to the anode electrode. By independently supplying a second input gas containing NOx to the cathode electrode film, the water is electrolyzed on the anode electrode film to generate hydrogen ions, and reacting the hydrogen ions with the NOx to decompose the NOx into _N2 and _N2O ;
a step of supplying only the second output gas from the cathode electrode film to the N ₂ O decomposition catalyst to reduce and decompose N ₂ O contained in the second output gas into N ₂ ;
A NOx purification method comprising:

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