JP2014213303A - Exhaust emission control system and exhaust emission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of clarifying exhaust gas containing NOat excellent power efficiency, even not using noble metal as a catalyst.SOLUTION: The exhaust emission control system includes: an exhaust emission control element 10 having an anode electrode 2 as an electrode catalyst containing Cu and CeO, a cathode electrode 3 and an oxygen ion conductive solid electrolyte 1 arranged between the electrodes; an exhaust gas flow passage 4 with the exhaust emission control element arranged inside; electric current supplying means to the anode electrode and the cathode electrode; exhaust gas supply means 5 for supplying the exhaust gas to the exhaust gas flow passage; and clarified gas discharge means 6 for discharging clarified gas B from the exhaust gas flow passage. The exhaust emission control system supplies exhaust gas A of a stoichiometric or rich atmosphere containing the NOto the exhaust gas flow passage while supplying an electric current to the anode electrode and the cathode electrode, and brings the exhaust gas A into contact with the anode electrode thereby reducing NOin the exhaust gas to the N, so that clarified gas containing Nis obtained.

Description

  The present invention relates to an exhaust gas purification system and an exhaust gas purification method.

In recent years, the electrode exerted by applying a voltage to an exhaust gas purification element including a solid electrolyte having oxygen ion conductivity and a pair of catalytic electrodes disposed with the solid electrolyte interposed therebetween. Research has been conducted on a method for electrochemically purifying exhaust gas containing nitrogen oxides (NO _x ) and hydrocarbons (HC) using the catalytic activity of the surface.

  For example, Japanese Patent Laid-Open No. 2006-189023 (Patent Document 1) combines a catalyst carrier made of a solid electrolyte, an exhaust passage side electrode provided on the exhaust passage side of the catalyst carrier, and the exhaust passage side electrode. The exhaust gas is provided with an atmosphere side electrode for generating a potential difference in the catalyst carrier and a control means for controlling a voltage applied to the exhaust path side electrode and the atmosphere side electrode in accordance with the air-fuel ratio of the exhaust gas flowing into the exhaust passage. A gas purification device is described, and a method for purifying exhaust gas by controlling the oxygen concentration in the exhaust gas is described. However, the exhaust gas purification device described in Patent Document 1 has a problem that a large amount of current is required to maintain a sufficient exhaust gas purification performance, resulting in an increase in power consumption. Furthermore, it was necessary to use a noble metal such as platinum as a catalyst.

  Japanese Patent Laid-Open No. 2006-200520 (Patent Document 2) discloses a solid electrolyte that has ionic conductivity and can provide oxygen ions on one side, a first electrode provided on each side of the solid electrolyte, and An exhaust gas purification method using a porous purification structure having a second electrode is described. In Patent Document 2, first, exhaust gas is permeated from the first electrode side (anode side) of the purification structure to the second electrode side (cathode side) to collect unburned particulates on the first electrode side and oxidize. Then, ceria as an oxygen storage material arranged on the second electrode side, platinum as a catalyst, and nitrogen oxides contained in exhaust gas permeated from the first electrode side by an adsorbent can be oxidized and reduced. Have been described. However, in the method described in Patent Document 2, it is necessary to use platinum as a catalyst, and it is difficult to purify a reducing gas such as HC and CO, and a problem that power consumption is large. Had.

In addition, Y. Sakamoto et al., Catalysis Today, 146, 2009, p. In 299-307 (Non-Patent Document 1), a voltage is applied to a conductive chemical catalyst (Me / YSZ / Au (Me = Rh, RhPt, Pt)) having a noble metal electrode on both sides of a YSZ substrate, and the conductive A method is described in which a mixed gas is brought into contact with a chemical chemical catalyst to purify NO, C ₃ H ₆ and O ₂ in the mixed gas. However, even in the conductive chemical catalyst described in Non-Patent Document 1, it was necessary to use a noble metal such as Rh, RhPt, Pt, or Au as an electrode in order to purify the gas component.

N. Kakridis et al., International journal of Hydrogen Energy, 37, 2012, p. 16722-16732 (Non-Patent Document 2) discloses a solid electrolyte battery in which Cu—CeO ₂ is applied to the inner bottom of a YSZ tube to form an anode electrode, and a Pt film is disposed on the outer wall of the YSZ tube as a counter electrode. (SOFC) is described, and a method for modifying CH ₃ COOH in a gas containing CH ₃ COOH and H ₂ O at the anode electrode is described. However, Non-Patent Document 2 relates to a solid electrolyte battery (SOFC), and the document does not describe anything about purifying nitrogen oxides (NO _x ) in exhaust gas.

JP 2006-189023 A JP 2006-200520 A

Y. Sakamoto et al., Catalysis Today, 146, 2009, p. 299-307 N. Kakridis et al., International Journal of Hydrogen Energy, 37, 2012, p. 16722-16732

The present invention has been made in view of the above-described problems of the prior art, and an exhaust gas purification system and an exhaust gas purification system that can purify exhaust gas containing NO _x with excellent power efficiency without using a noble metal as a catalyst. It aims to provide a method.

As a result of intensive studies to achieve the above object, the present inventors have arranged an anode electrode as an electrode catalyst containing Cu and CeO ₂ , a cathode electrode, and the anode electrode and the cathode electrode. By using an exhaust gas purifying element comprising an oxygen ion conductive solid electrolyte, the exhaust gas in a stoichiometric or rich atmosphere containing NO _x is brought into contact with the anode electrode while energizing the anode electrode and the cathode electrode. The present inventors have found that even if the anode electrode is an electrode that does not normally exhibit excellent catalytic activity such as a noble metal, it is possible to reduce NO _x in exhaust gas to N ₂ with sufficiently low power consumption. . Further, the present inventors have found that in such an exhaust gas purification system, reducing gases such as CO and HC in the exhaust gas can be oxidized, and the exhaust gas can be sufficiently purified. The invention has been completed.

That is, the exhaust gas purification system of the present invention is
An exhaust gas purification element comprising: an anode electrode as an electrode catalyst containing Cu and CeO ₂ ; a cathode electrode; and an oxygen ion conductive solid electrolyte disposed between the anode electrode and the cathode electrode;
An exhaust gas flow path in which the exhaust gas purification element is disposed,
Means for energizing the anode electrode and the cathode electrode;
Exhaust gas supply means for supplying exhaust gas to the exhaust gas flow path, and
A purifying gas discharging means for discharging the purifying gas from the exhaust gas flow path;
While energizing the anode electrode and the cathode electrode, the exhaust gas in a stoichiometric or rich atmosphere containing NO _x is supplied to the exhaust gas flow path and brought into contact with the anode electrode, whereby NO _x in the exhaust gas is N _2. To obtain purified gas containing N ₂ by reducing to
It is characterized by.

Moreover, the exhaust gas purification method of the present invention comprises:
Using an anode electrode as an electrode catalyst containing Cu and CeO _2, and a cathode electrode, an exhaust gas purification device and a said anode electrode and an oxygen ion conductive solid electrolyte disposed between the cathode electrode, the anode while supplying current to the electrodes and the cathode electrode, by contacting the exhaust gas of a stoichiometric or rich atmosphere containing NO _x to said anode electrode, containing N ₂ and allowed to reduce NO _x in the exhaust gas to N ₂ purification It is characterized by obtaining gas.

In the exhaust gas purification system and the exhaust gas purification method of the present invention, the mass ratio (Cu: CeO ₂ ) between the Cu content and the CeO ₂ content in the anode electrode is preferably 60:40 to 95: 5. .

The reason why the present invention makes it possible to purify exhaust gas with excellent power efficiency without using a noble metal as a catalyst is not necessarily clear, but the present inventors speculate as follows. That is, in the exhaust gas purifying element according to the present invention, when the anode electrode and the cathode electrode are energized, oxygen ions (O ²⁻ ) pumped from the oxygen ion conductive solid electrolyte on the anode electrode spill over (outflow). ) Depending on conditions, such oxygen ions exist as oxygen ions (O ^δ− ) having low reactivity with the gas phase gas, and affect the catalytic activity of the electrode. by containing Cu and CeO _2, which O ^.delta. is effectively generated at the interface between the interface or Cu-CeO ₂ and vapor gas of CeO ₂ and the gas phase gas and the present inventors speculate . Since such O ^δ− improves the NO _x adsorption selectivity with respect to oxygen (O ₂ ) in the gas phase gas, Cu becomes Cu ⁺ by reaction with NO _x, and reducing gases such as CO and HC. Thus, the reaction cycle in which the Cu ⁺ returns to Cu is not inhibited by O ₂ , and the reduction of NO _x to N ₂ is promoted. Furthermore, since the O ^δ− also improves the oxidation catalytic ability of reducing gases such as CO and HC in Cu, the decomposition and removal performance of NO _x , CO, HC and the like by the exhaust gas purification element is improved. The inventors speculate. Furthermore, since the O ^δ− acts on the anode electrode as an electrode catalyst and is not consumed by the reaction, in the present invention, NO _x , CO, HC and the like are directly purified by an electrolysis reaction. The present inventors infer that the amount of current required for the reaction can be sufficiently reduced as compared with the method, and the power consumption can be reduced.

On the other hand, in the exhaust gas purification apparatus described in Patent Document 1, since the oxygen is moved as a current in order to change the oxygen concentration in the exhaust gas, the present inventors say that the power consumption increases. I guess. Further, in the exhaust gas purification method described in Patent Document 2, although with ceria and adsorbent with the catalyst at the cathode, because the reduction of the NO _x in the catalyst is due to the electrolysis reaction, also the power consumption The present inventors infer that this increases.

According to the present invention, it is possible to provide an exhaust gas purification system and an exhaust gas purification method capable of purifying exhaust gas containing NO _x with excellent power efficiency without using a noble metal as a catalyst.

1 is a schematic longitudinal sectional view showing a preferred embodiment of an electrochemical cell according to an exhaust gas purification system and an exhaust gas purification method of the present invention. It is the side view which looked at the exhaust gas purification element in FIG. 1A from the X direction. It is a mimetic diagram showing a suitable embodiment of an exhaust gas purification system of the present invention. Example 1, NO conversion in Comparative Examples 1 to 5 _is a graph showing C 3 _{H 6} conversion, and current.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and duplicate descriptions are omitted.

The exhaust gas purification system of the present invention is
An exhaust gas purification element comprising: an anode electrode as an electrode catalyst containing Cu and CeO ₂ ; a cathode electrode; and an oxygen ion conductive solid electrolyte disposed between the anode electrode and the cathode electrode;
An exhaust gas flow path in which the exhaust gas purification element is disposed,
Means for energizing the anode electrode and the cathode electrode;
Exhaust gas supply means for supplying exhaust gas to the exhaust gas flow path, and
A purifying gas discharging means for discharging the purifying gas from the exhaust gas flow path;
While energizing the anode electrode and the cathode electrode, the exhaust gas in a stoichiometric or rich atmosphere containing NO _x is supplied to the exhaust gas flow path and brought into contact with the anode electrode, whereby NO _x in the exhaust gas is N _2. To obtain purified gas containing N ₂ by reducing to
It is characterized by.

  FIG. 1A is a schematic longitudinal sectional view showing a preferred embodiment of an electrochemical cell according to the exhaust gas purification system of the present invention, and FIG. 1B is a side view of the exhaust gas purification element 10 in FIG. 1A. The exhaust gas purification element 10 shown in FIGS. 1A to 1B includes an anode electrode 2, a cathode electrode 3, and an oxygen ion conductive solid electrolyte 1 disposed between the anode electrode 2 and the cathode electrode 3.

The solid electrolyte 1 is an oxygen ion conductive solid electrolyte having oxygen ion (oxide ion, O ²⁻ ) conductivity. Such an oxygen ion conductive solid electrolyte is not particularly limited. For example, zirconia [(Y ₂ O ₃ ) _1-x (ZrO ₂ ) _x (x = 0. 57 to 0.99)], in cerium oxide _{[Ce 1-m B m O 2} ( wherein, B denotes at least one member selected from the group consisting of Sm, Gd, Y and Ca .0 <m ≦ 0.4.)], Lanthanum-gallium oxide [La _1-a Sr _a Ga _1-b-c Mg _b A _c O ₃ (wherein A is from the group consisting of Co, Fe, Ni and Cu) At least one selected, a = 0.05-0.3, b = 0-0.29, c = 0.01-0.3, b + c = 0.025-0.3. Examples thereof include oxygen-ion conductive solids described in Kai 2000-96278. Among these, from the viewpoints of stability and oxygen ion conductivity when decomposing high-temperature NO _x discharged from an internal combustion engine such as an automobile, the solid electrolyte 1 is preferably a zirconia-based material, and stable by yttrium oxide. It is more preferable that it is converted zirconia [(Y ₂ O ₃ ) _1-x (ZrO ₂ ) _x (wherein x = 0.57 to 0.99)].

  The shape of the solid electrolyte 1 is not particularly limited, but is preferably a shape having a constant thickness such as a plate shape from the viewpoint that exhaust gas purification can be performed more efficiently. The thickness is preferably 0.02 to 5.0 mm, and more preferably 0.1 to 1.0 mm. If the thickness is less than the lower limit, it tends to be difficult to maintain the mechanical strength of the solid electrolyte 1. On the other hand, if the thickness exceeds the upper limit, the electrical resistance of the solid electrolyte 1 increases, and exhaust gas purification is performed. Power efficiency tends to decrease.

The anode electrode 2 is an electrode containing Cu and CeO ₂ and functions as a catalyst electrode that oxidizes reducing gas in the exhaust gas. Further, since the anode electrode 2 improves the NO _x adsorption selectivity with respect to oxygen (O ₂ ) in the exhaust gas, Cu becomes Cu ⁺ by reaction with NO _x, and the Cu is reduced by reducing gases such as CO and HC. ^The reaction cycle in which ⁺ returns to Cu is not inhibited by O ₂ , and the reduction of NO _x to N ₂ is promoted. In the present invention, by containing CeO ₂ in this way, even if a Cu electrode that does not normally exhibit excellent catalytic activity such as a noble metal is an anode electrode, excellent exhaust gas purification with sufficiently low power consumption Performance is demonstrated. In the anode electrode 2, CeO ₂ may be supported on the electrode surface made of Cu, but O ^δ- is uniformly spilled over to Cu to purify exhaust gas containing NO _x with higher power efficiency. From the viewpoint that it is possible to perform the process, Cu and CeO ₂ are preferably a mixture in which the Cu and CeO ₂ are uniformly dispersed with each other, and are obtained as a uniform body by sputtering or baking of a mixture of Cu and CeO _2. It is more preferable.

The mass ratio (Cu: CeO ₂ ) between the Cu content and the CeO ₂ content in the anode electrode 2 is preferably 60:40 to 95: 5, and 70:30 to 90:10. Is more preferable. When the content of CeO ₂ is less than the lower limit, the spillover of O ^δ- tends to be non-uniform. On the other hand, when the upper limit is exceeded, the electrical resistance increases and the mobility of oxygen ions decreases. O ^δ- spillover tends to be insufficient.

The shape of the anode electrode 2 is not particularly limited, but is preferably a shape that increases the area in contact with the solid electrolyte 1 and the surface area in contact with the exhaust gas from the viewpoint that exhaust gas purification can be performed efficiently. The plate-like solid electrolyte 1 is preferably formed in a film shape on one surface. As a method for forming such an anode electrode 2, a film as an electrode is formed on at least a part (preferably the entire surface) of one surface of the plate-shaped solid electrolyte 1 by sputtering a mixture of Cu and CeO _2. Examples thereof include a method of forming, a method of forming a film as an electrode by mixing Cu and CeO ₂ in a solvent, applying the mixture onto the surface, and baking (for example, a baking temperature of 800 to 1100 ° C.). Moreover, as thickness of the anode electrode 2 at this time, it is preferable that it is 50-5,000 nm, and it is more preferable that it is 100-500 nm. When the thickness is less than the lower limit, the electrical resistance of the anode electrode 2 tends to increase, and it tends to be difficult to apply a voltage uniformly to the solid electrolyte 1. On the other hand, when the thickness exceeds the upper limit, It tends to be difficult to exchange oxygen ions.

Further, the surface area of the anode electrode 2 at this time is appropriately set depending on the capacity, flow rate, composition, system scale, etc. of the exhaust gas to be purified. For example, 1 to 10 ³ cm per liter of the exhaust gas in the exhaust gas passage 4 ² is preferable, and 10 to 10 ² cm ² is more preferable. When the surface area is less than the lower limit, the reaction on the anode electrode 2 tends to be insufficient, and it is difficult to sufficiently purify the supplied exhaust gas. On the other hand, when the upper limit is exceeded, more than necessary. It is necessary to prepare a large system, and power consumption tends to increase.

The cathode electrode 3 is not particularly limited as long as it is an electrode capable of energizing the solid electrolyte 1, but is an electrode having a catalytic action from the viewpoint of further promoting the reduction of NO _x to N ₂ . It is preferable. Examples of such electrodes include electrodes made of metals such as Au, Ag, Cu, Co, Ni, Fe, Mn, and Cr. The metal may be used alone or in an alloy of two or more. In the present invention, as the cathode electrode 3, the electrode surface tends to be an oxide in exhaust gas purification, so that it is difficult to oxidize Au, Ag, Cu, Ni, or the like, or has conductivity even if it becomes an oxide. An electrode made of metal is preferred.

The shape of the cathode electrode 3 is not particularly limited, but is preferably a shape that increases the area in contact with the solid electrolyte 1 from the viewpoint that exhaust gas purification can be carried out efficiently. It is preferable that the solid electrolyte 1 is formed in a film shape on the surface opposite to the anode electrode 2. As a method for forming such a cathode electrode 3, a film as an electrode is formed on at least a part (preferably the entire surface) of the plate-like solid electrolyte 1 opposite to the anode electrode 2 by sputtering the metal. , A method of forming a film as an electrode by adding the metal to a solvent and applying it on the surface and baking (for example, a baking temperature of 800 to 1100 ° C.), and a film made of the metal The method of laminating | stacking films | membranes, such as an electrode, etc. is mentioned. In addition, the thickness of the cathode electrode 3 at this time is preferably 50 to 5,000 nm, and more preferably 100 to 1,000 nm. If the thickness is less than the lower limit, the electrical resistance of the cathode electrode 3 tends to increase, and it tends to be difficult to apply a voltage to the solid electrolyte 1 uniformly. This makes it difficult to supply oxygen, and O ^δ- spillover tends to be insufficient. Further, the surface area of the cathode electrode 3 at this time is not particularly limited, but if the area of the anode electrode and the area of the cathode electrode are greatly different, the spillover of O ^δ− on the anode electrode tends to be insufficient. From this viewpoint, the surface area is preferably the same as that of the anode electrode 2.

  The form of the exhaust gas purification element 10 according to the present invention is not limited to this. For example, the anode electrode 2 and the cathode electrode 3 or the cathode electrode respectively on the inside and outside of the solid electrolyte 1 formed into a tubular shape. 3 and the anode electrode 2 may be arranged, or the anode electrode 2 and the cathode electrode 3 may be arranged on the same plane of the plate-shaped solid electrolyte 1 so as not to contact each other.

  In the exhaust gas purification system of the present invention, as shown in FIGS. 1A to 1B, the exhaust gas purification element 10 is arranged inside the exhaust gas flow path 4 to constitute an electrochemical cell. In the exhaust gas purification system of the present invention, the exhaust gas is purified by bringing the anode electrode 2 and the exhaust gas into contact with each other in a batch type or a continuous type (flow type) in such an electrochemical cell. The shape of the exhaust gas flow path 4 may be a tube with a lid with a bottom or a cylindrical shape depending on the contact method or the like, but from the viewpoint of purifying exhaust gas continuously and more efficiently, A tubular shape is preferred.

The capacity in the exhaust gas flow path 4 is appropriately set according to the capacity, flow rate, composition, system scale, etc. of the exhaust gas to be purified. For example, when exhaust gas is purified in a batch manner, it is more efficient. in terms of being able to purify the exhaust gas, it is preferably 1L less of the surface area 1 cm ² of the anode electrode 2 contained in the exhaust gas passage 4, and more preferably 0.01～0.2L. The material for the exhaust gas flow path 4 is preferably one substantially impermeable to gas, as such a material, when disassembling the hot of the NO _x discharged from the internal combustion engine such as an automobile From the viewpoint of excellent stability, glass such as quartz glass, stainless steel, and alumina are preferable.

The form of the electrochemical cell according to the exhaust gas purification system of the present invention is not limited to this, and a temperature sensor such as a thermocouple, a sensor for detecting a gas such as NO _x , a pressure reducing / pressurizing valve, and the like are further provided. It may be provided, and when purifying the exhaust gas in a batch manner, a fan for circulating the exhaust gas may be further provided. Moreover, as a form of the electrochemical cell according to the exhaust gas purification system of the present invention, a form provided with a plurality of exhaust gas purification elements 10 inside the exhaust gas flow path 4 may be used.

  FIG. 2 shows a preferred embodiment of the exhaust gas purification system of the present invention. As shown in FIGS. 1A, 1B, and 2, in the exhaust gas purification system of the present invention, the exhaust gas is discharged from the internal combustion engine 102 to the electrochemical cell 100 in which the exhaust gas purification element 10 is disposed inside the exhaust gas flow path 4. Exhaust gas is supplied to the exhaust gas passage 4 through the exhaust gas supply passage 5 (exhaust gas supply means) (in the direction of the open arrow A), and is purified by the electrochemical cell 100 to become purified gas, and the purified gas discharge passage 6 (purified gas discharge means) ) Through (open arrow B direction).

  The exhaust gas supply means according to the exhaust gas purification system of the present invention is not particularly limited as long as it can supply exhaust gas discharged from the internal combustion engine 102 or the like to the electrochemical cell 100, but the exhaust gas atmosphere, temperature, flow rate For example, in addition to the internal combustion engine 102 and the exhaust gas supply path 5, a supply exhaust gas control means 101 such as a sensor or a valve for controlling the exhaust gas supplied to the anode electrode 2 is further provided. Is preferred. Such a control method is not particularly limited, and a known method can be used as appropriate. For example, as a method for changing the atmosphere of the exhaust gas to a stoichiometric or rich atmosphere described later, the vicinity of the outlet of the internal combustion engine 102 is used. A sensor is arranged and an internal combustion engine that emits exhaust gas is controlled based on a signal detected by the sensor to switch the air-fuel consumption of the exhaust gas, or a valve or the like is provided upstream of the exhaust gas supply path 5 to provide the composition and flow rate of the exhaust gas. There is a method of adjusting.

  Further, the purification gas discharge means according to the exhaust gas purification system of the present invention is not particularly limited as long as the purification gas can be discharged from the electrochemical cell 100. When the anode electrode 2 and the exhaust gas are continuously brought into contact with each other to purify the exhaust gas by a flow method, the exhaust gas is supplied from the purified gas discharge passage 6 while maintaining the flow velocity when supplied from the exhaust gas supply passage 5. Although it is preferable to discharge continuously as the purified gas, if the flow rate of the gas is controlled according to the degree of purification, or if the exhaust gas is purified in a batch manner, the emission of the purified gas is controlled as necessary. The exhaust gas control means such as a check valve, a sensor, a valve, and a fan may be further provided.

  The exhaust gas supply path 5 and the purified gas discharge path 6 are not particularly limited, but from the viewpoint of excellent stability against high-temperature gas discharged from an internal combustion engine such as an automobile, each is independently, for example, quartz glass or the like. Of these, a glass tube, an alumina tube, and a stainless tube are preferable.

  In a preferred embodiment of the exhaust gas purification system of the present invention, as shown in FIGS. 1A, 1B, and 2, the anode electrode 2 and the cathode electrode 3 are connected to the energizing means 103 through the anode electrode wiring 7 and the cathode electrode wiring 8, respectively. Is done. The energization means 103 energizes between the anode electrode 2 and the cathode electrode 3 through the anode electrode wiring 7 and the cathode electrode wiring 8. Such energization means 103 is not particularly limited, and a known power source can be used as appropriate. Furthermore, the anode electrode wiring 7 and the cathode electrode wiring 8 are not particularly limited, and publicly known wirings can be used as appropriate. Examples thereof include a Pt line, a W line, a Ni line, a Cr line, and an Au line.

  Further, in the exhaust gas purification system of the present invention, as shown in FIG. 2, the supply exhaust gas control means 101 and the energization means 103 are electrically connected to a control unit 104 including a CPU, ROM, RAM, input / output port, storage device and the like. It is preferable that it is connected to. Note that such an electrical connection form is not limited to this, and determination means such as a program previously installed in a computer and control means such as the distribution exhaust gas control means are further connected in series or in parallel. Also good.

  Further, the configuration of the exhaust gas purification system according to the present invention is not limited to this. For example, an open flow channel for circulating the exhaust gas discharged from the internal combustion engine is directly used as the exhaust gas flow channel 4, and the flow is Even if the exhaust gas purification element 10 is arranged in the passage, the exhaust gas passage 4 is a bottomed cylindrical lidded container, and the exhaust gas supply passage 5 and the purified gas discharge passage 6 both penetrate the lid. Even if it is the structure arrange | positioned, it is the structure provided with the electrochemical cell 100 in the inside of the some exhaust gas flow path 4 where the exhaust gas supply path 5 is branched in multiple numbers, and each is arrange | positioned downstream of each exhaust gas supply path 5, respectively. Also good.

In the exhaust gas purification system of the present invention, by supplying the exhaust gas in a stoichiometric or rich atmosphere containing NO _x to the exhaust gas flow path 4 and bringing it into contact with the anode electrode 2 while energizing the anode electrode 2 and the cathode electrode 3, obtaining a purified gas containing _{N 2} by allowed reducing the NO _x in the exhaust gas to _{N 2.}

  The voltage applied to the anode electrode 2 and the cathode electrode 3 is preferably 1 to 3V. If the applied voltage is less than the lower limit, sufficient exhaust gas purification performance tends not to be exhibited. On the other hand, if the applied voltage exceeds the upper limit, the solid electrolyte 1 tends to be destroyed. Further, since the exhaust gas purification system of the present invention is excellent in power efficiency, even if the applied voltage is 2 V or less (more preferably 1 to 1.5 V), the exhaust gas purification system can exhibit sufficient exhaust gas purification performance. is there.

The exhaust gas to be purified by the exhaust gas purification system of the present invention is a stoichiometric or rich atmosphere exhaust gas containing NO _x (nitrogen oxide). Examples of such exhaust gas include a mixed gas discharged from an internal combustion engine such as an automobile. The contained components include NO _x , HC, CO, H ₂ , O ₂ , CO ₂ , H ₂ O. , N _{2 and the} like. As the concentration of NO _x in the exhaust gas of interest to purify the exhaust gas purifying system of the present invention is not particularly limited, it is usually preferable to be 0.01 to 1.0 volume%.

In the present invention, that the exhaust gas is in a stoichiometric or rich atmosphere means that the stoichiometric atmosphere is in a stoichiometric equivalence ratio or a rich atmosphere in which oxygen is insufficient. Such an exhaust gas preferably contains a reducing gas, and the concentration of the reducing gas in the exhaust gas is more preferably 0.1% by volume or more, and preferably 0.1 to 10% by volume. Is more preferable. If the concentration of the reducing gas is less than the lower limit, the reduction reaction of NO _x tends not to proceed. On the other hand, if the concentration exceeds the upper limit, the reducing gas tends to remain in the resulting purified gas. is there. Examples of the reducing gas include hydrogen (H ₂ ), carbon monoxide (CO), and hydrocarbon (HC). One of these may be used alone, or two or more may be used in combination. Also good. By contacting the exhaust gas in such a stoichiometric or rich atmosphere with the anode electrode 2, it becomes possible to purify the exhaust gas containing NO _x with excellent power efficiency. In the present invention, even if carbon monoxide or hydrocarbon is contained as the reducing gas in the exhaust gas, these reducing gases can be oxidized and decomposed and removed at the anode electrode 2.

  In addition, when the exhaust gas to be brought into contact with the anode electrode 2 contains oxygen, the concentration is preferably 5% by volume or less within a range where the exhaust gas is in a stoichiometric or rich atmosphere. If the oxygen concentration exceeds the upper limit, the exhaust gas purification efficiency in the anode electrode 2 tends to decrease and the power consumption tends to increase.

  Furthermore, the temperature of the exhaust gas brought into contact with the anode electrode 2 is preferably a temperature of 200 to 800 ° C, and more preferably a temperature of 300 to 500 ° C. If the temperature of the exhaust gas is less than the lower limit, the exhaust gas purification performance tends to be lowered. On the other hand, the temperature exceeding the upper limit becomes an unrealistic temperature for purification of diesel exhaust gas, for example.

When the anode electrode 2 and the exhaust gas are continuously contacted to purify the exhaust gas by a flow method, the flow rate of the exhaust gas supplied to the exhaust gas passage 4 is appropriately set depending on the area of the anode electrode 2 and the space capacity. However, for example, the flow rate is preferably 2 × 10 ⁵ / hr or less, more preferably 10 ⁵ / hr or less, in the space velocity (SV) of the exhaust gas channel 4 as a whole.

In the exhaust gas purification system of the present invention, the exhaust gas is supplied to the exhaust gas flow path 4 and brought into contact with the anode electrode 2 while energizing the anode electrode 2 and the cathode electrode 3 by the energization means 103 as described above, thereby making the exhaust gas it can be obtained purified gas containing N ₂ and NO _x in and brought reduced to N _2. That is, in the anode electrode 2, reduction of NO _x by a reducing gas (for example, NO + CO → 1 / 2N ₂ + CO ₂ , 18NO + 2C ₃ H ₆ → 9N ₂ + 6CO ₂ + 6H ₂ O, etc.) proceeds and contains N ₂ . The purified gas to be discharged is discharged from the purified gas discharge path 6. Thus, with the exhaust gas purification system of the present invention, NO _x in the exhaust gas is reduced, and a purified gas in which the NO _x concentration and the reducing gas concentration are sufficiently reduced can be obtained.

The exhaust gas purification method of the present invention comprises:
Using an exhaust gas purification element comprising an anode electrode as an electrode catalyst containing Cu and CeO ₂ , a cathode electrode, and an oxygen ion conductive solid electrolyte disposed between the anode electrode and the cathode electrode,
While energizing the anode electrode and the cathode electrode, by the exhaust gas of the stoichiometric or rich atmosphere containing NO _x into contact with the anode electrode, containing N ₂ and allowed to reduce NO _x in the exhaust gas to N ₂ It is characterized by obtaining purified gas.

In such an exhaust gas purification method of the present invention, the exhaust gas purification element includes the exhaust gas purification element 10 described in the exhaust gas purification system of the present invention, and the exhaust gas purification method of the present invention is based on the exhaust gas purification system of the present invention. It can implement suitably. Specifically, according to a preferred embodiment of the exhaust gas purification system of the present invention shown in FIGS. 1A, 1B and 2, the exhaust gas purification element 10 is placed in the exhaust gas flow channel 4 while energizing the anode electrode 2 and the cathode electrode 3. The exhaust gas is supplied into the arranged electrochemical cell 100 by the exhaust gas supply means, and the anode electrode 2 and the exhaust gas are brought into contact with each other in a batch type or a continuous type (flow type), thereby reducing NO _x in the exhaust gas. obtaining the purified gas containing N ₂ by allowed reduced to N _2. The obtained purified gas can be recovered by the purified gas discharge means.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not limited to a following example.

Example 1
<Production of electrochemical cell>
First, the exhaust gas purification element 10 shown in FIGS. 1A to 1B was produced. As the solid electrolyte 1, a zirconia substrate (YSZ substrate, “TZ-8Y” manufactured by Tosoh Corporation, diameter: 15 mm, thickness: 1.0 mm) stabilized with yttrium oxide (8 mol%) was used. Also, sputtering is performed on one surface of the YSZ substrate in an Ar atmosphere containing Cu by volume ratio of Cu and CeO ₂ (Cu: CeO ₂ ) of 85:15 and containing 10% by volume of O _2. As a result, a Cu—CeO ₂ electrode (Cu: CeO ₂ = 85: 15, diameter 15 mm, thickness 400 nm) made of Cu and CeO ₂ was formed and used as the anode electrode 2. As the cathode electrode 3, an Au electrode (diameter: 15 mm, thickness: 400 nm) made of Au formed by sputtering on the surface opposite to the anode electrode 2 of the YSZ substrate was used.

Next, a quartz test tube with an upper and lower lid having an inner diameter of 2.5 cm and a length of 30 cm was used as the exhaust gas flow path 4, and the exhaust gas purification element 10 was fixed therein to produce an electrochemical cell. In addition, the angle of the exhaust gas purification element 10 was adjusted so that the electrode with which the gas supplied from the exhaust gas supply path 5 first contacts was a Cu—CeO ₂ electrode. Next, a stainless steel tube having an inner diameter of 1.0 mm is used as the exhaust gas supply path 5 and the purified gas discharge path 6, and the Cu—CeO ₂ electrode (anode electrode 2) and the Au electrode (cathode electrode 3) have a diameter of 0.2 mm. The wires (the anode electrode wiring 7 and the cathode electrode wiring 8) were respectively connected and connected to a direct current power source (manufactured by Hokuto Denko Corporation, “potentiostat (model number HA-151)”) as the energizing means 103.

<Exhaust gas purification test>
From the exhaust gas supply path 5, a mixed gas composed of NO (0.3% by volume), C ₃ H ₆ (0.1% by volume), O ₂ (0.3% by volume) and He (remaining) is supplied to It was allowed to flow under conditions of 50 cc / min and a temperature of 400 ° C. A voltage of 1 V was applied so that the Cu—CeO ₂ electrode was the anode electrode and the Au electrode was the cathode electrode, and the NO concentration in the gas discharged from the purified gas discharge path 6 was measured using a quadrupole mass spectrometer (Canon Anelva Co., Ltd.). Obtained by measuring the signal intensity of mass number 30 obtained by “M-101QA”), and the NO conversion rate (%) is calculated from the difference between the NO concentration in the mixed gas and the NO concentration in the exhaust gas. Calculated. Further, the C ₃ H ₆ concentration in the gas discharged from the purified gas discharge path 6 is obtained by measuring the signal intensity of the mass number 41 obtained by the quadrupole mass spectrometer, C ₃ H ₆ concentration _C 3 _{H 6} conversion from the difference between the _C 3 _{H 6} concentration in the exhaust gas (%) was calculated. Moreover, while controlling the voltage applied using a potentiostat, current (mA) was measured.

(Comparative Example 1)
In the exhaust gas purification test, an exhaust gas purification test was performed in the same manner as in Example 1 except that no voltage was applied to the electrode, and NO conversion rate (%) and C ₃ H ₆ conversion rate (%) were calculated. (MA) was measured.

(Comparative Example 2)
An electrochemical cell was prepared and an exhaust gas purification test was conducted in the same manner as in Example 1 except that a Cu electrode made of Cu was used as the anode electrode 2 instead of the Cu—CeO ₂ electrode, and NO conversion rate (% ) And C ₃ H ₆ conversion (%) were calculated, and current (mA) was measured. The Cu electrode was produced in the same manner as in Example 1 except that CeO ₂ was not used.

(Comparative Example 3)
An electrochemical cell was produced as in Example 1 except that a Cu—Al ₂ O ₃ electrode made of Cu and Al ₂ O ₃ was used as the anode electrode 2 instead of the Cu—CeO ₂ electrode, and exhaust gas was produced. A purification test was performed, NO conversion rate (%) and C ₃ H ₆ conversion rate (%) were calculated, and current (mA) was measured. The Cu—Al ₂ O ₃ electrode was produced in the same manner as in Example 1 except that Al ₂ O ₃ was used instead of CeO ₂ .

(Comparative Example 4)
An electrochemical cell was prepared and an exhaust gas purification test was performed in the same manner as in Example 1 except that instead of the Cu—CeO ₂ electrode, a Cu—TiO ₂ electrode made of Cu and TiO ₂ was used as the anode electrode 2. The NO conversion rate (%) and the C ₃ H ₆ conversion rate (%) were calculated, and the current (mA) was measured. The Cu—TiO ₂ electrode was produced in the same manner as in Example 1 except that TiO ₂ was used instead of CeO ₂ .

(Comparative Example 5)
In the exhaust gas purification test, an exhaust gas purification test was conducted in the same manner as in Example 1 except that the voltage was applied so that the Cu—CeO ₂ electrode was the cathode electrode and the Au electrode was the anode electrode, and the NO conversion rate (%) and C ₃ H ₆ conversion (%) was calculated, and current (mA) was measured.

A graph showing the NO conversion rate (%), C ₃ H ₆ conversion rate (%) and current (mA) calculated in Example 1 and Comparative Examples 1 to 5 is shown in FIG. As is apparent from the results shown in FIG. 3, in the exhaust gas purification system and the exhaust gas purification method of the present invention, sufficiently high NO conversion is achieved with a small amount of current by applying a voltage using the Cu—CeO ₂ electrode as an anode electrode. It was confirmed that the rate and C ₃ H ₆ conversion were achieved. On the other hand, in the comparative example, although the current amount is almost the same as that of the present invention, it is confirmed that the NO conversion rate and the C ₃ H ₆ conversion rate are both significantly low and the exhaust gas purification performance is inferior. It was.

As described above, according to the present invention, it is possible to provide an exhaust gas purification system and an exhaust gas purification method capable of purifying exhaust gas containing NO _x with excellent power efficiency without using a noble metal as a catalyst. It becomes. Therefore, since the exhaust gas purification system and the exhaust gas purification method of the present invention are excellent in economic efficiency, they are useful as a purification method for diesel exhaust gas and the like.

  DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte, 2 ... Anode electrode, 3 ... Cathode electrode, 4 ... Exhaust gas flow path, 5 ... Exhaust gas supply path, 6 ... Purified gas discharge path, 7 ... Anode electrode wiring, 8 ... Cathode electrode wiring, 10 ... Exhaust gas purification Element: 100 ... electrochemical cell, 101 ... supply exhaust gas control means, 102 ... internal combustion engine, 103 ... energization means, 104 ... control unit.

Claims (4)

An exhaust gas purification element comprising: an anode electrode as an electrode catalyst containing Cu and CeO ₂ ; a cathode electrode; and an oxygen ion conductive solid electrolyte disposed between the anode electrode and the cathode electrode;
An exhaust gas flow path in which the exhaust gas purification element is disposed,
Means for energizing the anode electrode and the cathode electrode;
Exhaust gas supply means for supplying exhaust gas to the exhaust gas flow path, and
A purifying gas discharging means for discharging the purifying gas from the exhaust gas flow path;
While energizing the anode electrode and the cathode electrode, the exhaust gas in a stoichiometric or rich atmosphere containing NO _x is supplied to the exhaust gas flow path and brought into contact with the anode electrode, whereby NO _x in the exhaust gas is N _2. To obtain purified gas containing N ₂ by reducing to
An exhaust gas purification system characterized by _2. The exhaust gas purification system according to claim 1, wherein a mass ratio (Cu: CeO ₂ ) of Cu content to CeO ₂ content in the anode electrode is 60:40 to 95: 5. Using an anode electrode as an electrode catalyst containing Cu and CeO _2, and a cathode electrode, an exhaust gas purification device and a said anode electrode and an oxygen ion conductive solid electrolyte disposed between the cathode electrode, the anode while supplying current to the electrodes and the cathode electrode, by contacting the exhaust gas of a stoichiometric or rich atmosphere containing NO _x to said anode electrode, containing N ₂ and allowed to reduce NO _x in the exhaust gas to N ₂ purification An exhaust gas purification method comprising obtaining gas. The exhaust gas purification method according to claim 3, wherein a mass ratio (Cu: CeO ₂ ) of Cu content to CeO ₂ content in the anode electrode is 60:40 to 95: 5.