JP2002119857A - CATALYST FOR PURIFYING NOx AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for purifying NOx which is capable of high efficiently purifying with a smaller quantity of a catalytic active metal. SOLUTION: The catalyst for purifying NOx is formed by carrying plural pieces of fine metallic particles having catalytic activity directly on the surface of an electrical conductive material to be in contact with each other to electrically connect the particles to each other, and performs the reduction reaction of NOx in the electrical conductive metallic particles and the oxidation reaction of a reducing agent electrochemically by moving ions via the electrical conductive material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the internal combustion engines used in automobiles and small power generator, heater such as a fan heater and stoves, incinerators etc. for purifying NO _x from the exhaust gas discharged from the it relates _the NO _x purification catalyst for combustion exhaust gases.

[0002]

_The NO _x purification BACKGROUND OF THE INVENTION exhaust gas used in an internal combustion engine, such as a conventional automobile, as typified by the use of three-way catalysts, NOx such as NO and NO ₂ in the exhaust gas A method has been put into practical use in which a reaction for reducing substances to nitrogen and a reaction for oxidizing reducing substances such as hydrocarbons (hereinafter abbreviated as HC) and CO in exhaust gas are performed on the same catalyst, thereby purifying with high efficiency. ing.

[0005] For example, FIG. 5 shows the document “New Catalyst Chemistry (Second Edition)” (published by Sankyo Publishing Co., Ltd., 1997).
The weight ratio of air to fuel (air-fuel ratio) and NO _x for the three-way catalyst for gasoline engines described on pages 1 to 133,
The relationship with the conversion (purification) rates of HC and CO is shown. If the air-fuel ratio is around 14.7, the conversion of all three components is 8
Since it is 0% or more, the combustion state of the engine is controlled so as to always maintain this air-fuel ratio. At this time, NO _x with a reducing agent in the exhaust gas supplied to the three-way catalyst becomes chemically substantially equal amounts. In addition, as described in the literature, the three-way catalyst has been used a high noble metal catalytic activity, among them NO _x high reducing ability Rh and HC and CO with high oxidation ability Pt, composed of Pd Pt-Pd-Rh-based catalysts are widely used.

FIG. 6 is a diagram schematically showing the function of a conventional three-way catalyst. Reference numeral 6 denotes fine metal particles having catalytic activity (noble metal fine particles), and reference numeral 7 denotes a substrate supporting the metal particles. Alumina having a large surface area is used for this substrate from the viewpoints of increasing the amount of metal carried and heat resistance. In FIG. 6, NO _x and a reducing agent (HC or CO) dissociated and adsorbed on the same metal surface cause an oxidation-reduction reaction, and N ₂ ,
Converted to CO ₂ and H ₂ O.

[0005]

As described above, conventional three-way catalysts having a structure in which noble metal fine particles are supported on a substrate having high heat resistance and a large surface area, such as alumina, are widely used. By the way, since noble metals have a limited amount of resources and are expensive, it is required to reduce the amount used.
As a measure therefor, a method of increasing the reaction efficiency by increasing the surface area per weight of the noble metal by increasing the surface area per weight of the noble metal and increasing the number of reaction sites on the surface of the noble metal has been used in order to increase the use efficiency of the noble metal. However, depending on the kind of the noble metal, even if the particle diameter is reduced, the catalyst may be heated at the time of purifying the exhaust gas, so that the particle diameter may grow. As a result, the surface area of the noble metal is reduced, so that the catalytic reaction is less likely to occur, and the reaction efficiency is reduced. Therefore, there is a problem that the durability is low.

As a countermeasure against the above-mentioned problems, it is most effective to increase the amount of catalyst particles to be added. However, since the main material used for the catalyst particles is a noble metal, the amount of addition should be reduced in view of the amount of resources and the price. There was a problem that it was difficult to increase.

Accordingly, an object of the present invention is to provide a catalyst for purifying exhaust gas with high efficiency with a smaller amount of catalytically active metal.

[0008]

Means for Solving the Problems A first catalyst of the present invention comprises:
A plurality of fine metal particles having catalytic activity are directly contacted and supported on the surface of the electrically conductive material and electrically connected between the particles, and ions or ions and electrons move through the electrically conductive material. it allows an oxidation reaction of the reducing reaction with a reducing agent of the NO _x about _the NO _x purification catalyst, wherein electrochemically be carried out in the fine metal particles.

The second catalyst of the present invention is the first catalyst, wherein the electric conductivity is obtained from at least one kind of ionic conductive substance and at least one kind of electron conductive substance. conductive material relates _the NO _x purification catalyst consisting disposed so as to electrically short-circuit between the fine metal particles.

A third catalyst of the present invention, in the first or second catalyst, osmium fine metal particles, iridium, platinum, palladium, rhodium, NO _x purifying catalyst comprising at least one element selected from ruthenium About.

[0011] A fourth catalyst of the present invention, in the first, second or third catalyst, a catalyst for _the NO _x purification of electrically conductive material has a hydrogen ion conductivity.

[0012] A fifth catalyst of the present invention, in the first, second or third catalyst, a catalyst for _the NO _x purification of electrically conductive material has oxygen ion conductivity.

A sixth catalyst according to the present invention is the fourth or fifth catalyst, wherein the electrically conductive substance is a composite oxide.
_{xRelated to} purification catalyst.

The seventh catalyst of the present invention relates to the first catalyst, wherein the electrically conductive substance has both ionic and electronic conductivity.

The eighth catalyst of the present invention, in the seventh catalyst, an electrically conductive material is the chemical formula _{Ce 0. 8 A 0.2 O 1.9 (} A represents Yb, Y, Gd, Sm, and Nd or La) It relates _the NO _x purification catalyst is a composite oxide represented.

The manufacturing method of the first of the NO _x purifying catalyst of the present invention, first, second, third, fourth, fifth, sixth, seventh or _the NO _x purification catalyst according to an eighth catalyst The method according to the above, wherein a plurality of water-soluble precursor compounds containing the constituent elements in the electrically conductive substance are uniformly mixed, and then calcined at 800 ° C. or lower to obtain the electrically conductive substance. the method of manufacturing of the NO _x purifying catalyst.

The manufacturing method of the second of the NO _x purifying catalyst of the present invention, first, second, third, fourth, fifth, sixth, seventh or _the NO _x purification catalyst according to an eighth catalyst In the manufacturing method, the electrically conductive material is immersed in an aqueous solution containing a metal compound, and the surface of the electrically conductive material is coated with an aqueous solution containing the metal compound, and then baked to form fine metal particles on the surface of the electrically conductive material. NO _x characterized by being carried
The present invention relates to a method for producing a purification catalyst.

A catalyst system for electrochemically performing an oxidation reaction and a reduction reaction using a plurality of fine metal particles having catalytic activity has been filed by the present applicant and disclosed in Japanese Patent Application Laid-Open No. Hei 10-270055. Have been. Also,
A method of increasing the durability of a fuel cell against carbon monoxide poisoning by using the “electrochemical catalyst” is disclosed in Japanese Patent Application Laid-Open No. Hei 10-270056 by the present applicant. In the present invention, it is applied to _the NO _x purification catalyst using this "electrochemical catalyst" in the combustion exhaust gas applications, newly developed as a catalyst to replace the mostly conventional three-way catalyst.

[0019]

FIG. 1 is a schematic diagram showing the structure of a first NO _x purification catalyst. In FIG. 1, 1 and 2 are fine metal particles having catalytic activity, and 3 is an electrically conductive substance. The arrows in the electrically conductive substance 3 indicate the directions of the flow of ions and electrons when oxygen ions and electrons are used as charge carriers, and the arrows in the electron conductive impurities 4 indicate the directions of flow of the electrons. . FIG. 2 shows the second N
It is a schematic diagram showing the structure of O _x purification catalyst. In FIG. 2, 1 and 2 are fine metal particles having catalytic activity, 4 is an ion conductive material, and 5 is an electron conductive material arranged to electrically short the fine metal particles. The arrow in the ion conductive material 4 indicates the direction of ion flow when oxygen ions are used as charge carriers, and indicates the direction of the electron conductive material 5.
The arrow in the middle indicates the direction in which electrons flow.

NO _x contained in the exhaust gas and HC and CO contained as the reducing agent are adsorbed on the surface of the fine metal particles 1 or 2. At this time, if NO _x and the reducing agent are adsorbed on the same metal particle surface, an oxidation-reduction reaction occurs on the single metal particle as in the conventional three-way catalyst, and H ₂ O and C ₂
Decomposed into O ₂ and N ₂ . However, in the present invention, NO
_{Even when x} and the reducing agent are adsorbed on the surfaces of different fine metal particles, electrochemical oxidation-reduction occurs because the metal particles are electrically connected by an electrically conductive substance or an ion conductive substance and an electron conductive substance. A reaction occurs. That is, NO _x adsorbed on the fine metal particles A is decomposed into N ₂ and oxygen ions, and the oxygen ions pass through the electrically conductive material or the ion conductive material and move to another fine metal particle B. On the surface of the fine metal particles B, oxygen ions oxidize HC adsorbed on the particle surface, and generate CO ₂ and H ₂ O. The surplus electrons generated at that time pass through the electrically conductive material 3 or the electron conductive material 5, move to the fine metal particles A, and are used to generate oxygen ions on the particles. In the first catalyst, the surplus electrons do not necessarily have to move through the electrically conductive substance 3, but may move through electron conductive impurities present on the catalyst surface.

As described above, in the present invention, in addition to the oxidation-reduction reaction of NO _x and a reducing agent on the same fine metal particles,
For the reduction reaction and oxidation reaction of HC of the NO _x it is possible to cause the surface of the different fine metal particles, necessary and NO _x and HC as in the conventional three-way catalyst is contacted on the same fine metal particles Absent. That is, since the purification reaction only needs to contact NO _x and HC in any one of the fine metal particles on the surface is to proceed, causing the redox reaction NO _x and the reducing agent is in contact with the fine metal particle surface The probability increases. As a result, the same effect as in the case of expanding the surface area of the fine metal particles, can be obtained in quantity metallic particles having less catalytic activity, NO _x purification efficiency is improved than before.

Further, as described above, the probability that NO _x comes into contact with the catalyst surface to be reduced increases, so that NO _x
And the oxidation-reduction reaction rate between HC and HC are also improved. As a result, it becomes possible to purify NO _x even when large quantities flowing exhaust gas.

FIG. 3 is a potential diagram showing an electrochemical elementary reaction of a substance involved in the NO _x purification catalyst of the present invention in which fine metal particles are directly supported on the surface of an electrically conductive material. Note that the potential in FIG. 3 is represented by a value based on the reversible hydrogen potential. As described in the literature “Electrochemical Handbook”, the reduction potentials of NO and NO ₂ are represented by the formulas (1) and (2), respectively, and the oxidation potentials of carbon, H ₂ and carbon monoxide are represented by the formulas Expressions (3), (4) and (5) are used. Note that HC is a general term for various hydrocarbons such as methane and propane, but it is already known that HC is almost equivalent to the potential of carbon.

Formula (1) NO + 4H ⁺ + 4e ⁻ → N ₂ + 2H ₂ O E = 1.495V Formula (2) NO ₂ + 8H ⁺ + 8e ⁻ → N ₂ + 4H ₂ O E = 1.363V Formula (3) C + 2H _{20 ^{→ CO 2 + 4H + + 4e}} - E = 0.207V formula ^{_{(4) H 2 → 2H +}} + 2e - E = 0.000V formula _{(5) CO + H 2 0} → CO 2 + 2H + + 2e - E = -0.103V

Formulas (1) to (5) describe the electrochemical element reaction and its potential when hydrogen ions are interposed. However, even when oxygen ions are interposed, the products and potentials are basically the same. Will be the same.

Equations (1) and (2) are derived from NO _x to N ₂
, And equations (3), (4) and (5) are oxidation reactions of the reducing agent. When the reduction reaction and the oxidation reaction are compared, the potential difference exceeds 1 V or more, and an electromotive force is generated between them. This electromotive force becomes a driving force for moving ions and electrons. In the present invention, therefore, only needs to contact NO _x and HC on the fine metal particle surface, occurs redox reaction by electrochemical reactions, NO _x purification progresses.

As the electron conductive substance in the second catalyst, any substance having a low electronic resistance can be used. Specifically, a material having free electrons such as a metal material such as gold, silver, copper, iron, and nickel, or La _1-x Sr _x Mn
A composite oxide having an electron vacancy inside the structure, such as O ₃ (0.05 <x <0.3), can be used. Exhaust gas contains unsaturated hydrocarbons and trace amounts of metals, which have electronic conductivity.Use these substances, which are adsorbed to short-circuit between fine metal particles, as electron conductive substances. It is also possible.

The average particle diameter of the fine metal particles is 1 to 100 n.
m, preferably 1 to 50 nm. If the average particle size is less than 1 nm, it tends not to be supported as particles, and if it exceeds 100 nm, the surface area with respect to the weight of the metal becomes small, and the activity of the catalyst tends to decrease.

The fine metal particles having catalytic activity include:
Those that dissociate and adsorb NO _x are preferably used. Specifically, in the third catalyst of the present invention, osmium (Os), iridium (Ir),
Ruthenium (Ru), platinum (Pt), rhodium (R
h), palladium (Pd), and mixtures or alloys thereof are used.

The first of the present invention 4, in the fifth catalyst, the electrically conductive material, using an oxygen ion conductive material or a proton conductive material, an electrochemical redox reaction of NO _x with a reducing agent Is induced. Further, in the sixth catalyst, a composite oxide is used as the electrically conductive substance. As a result, the material stability at high temperatures is increased, and it is possible to withstand the rapid temperature rise of the catalyst that occurs during high-speed operation, thereby increasing the durability of the catalyst.

Specifically, for example, a perovskite oxide represented by the following formula (I), a composite oxide represented by the following formula (II) and the like can be used.

Formula (I): La _{1- x} Sr _x Ga _{1- y} Mg _y O ₃
(X is a numerical value from 0.05 to 0.3, y is 0.1 to 0.
Numerical values up to 3. ) Formula _{(II): Ce 1- x A} x O y (x is number between 0.5 to 0.1, y is a number between from 1.75 to 2, A is Yb, Y,
Gd, Sm, Nd or La. Of these, cerium (C
e) and samarium (Sm) are oxides having high oxygen ion conductivity at about 400 ° C.
It also has some degree of electron conductivity and is the most desirable material.

The substance represented by the formula (II) is H ₂ O
Coexists to form a hydrogen ion conductive material.

In the seventh catalyst, the electrically conductive substance has both ionic and electronic conductivity. This eliminates the need to introduce an electron conductive material, and enables a reduction in material processes and simplification of a manufacturing process. As such an electrically conductive substance, for example, in the eighth catalyst, Ce _0.8 A _0.2 O _1.9 (A is Yb,
Y, Gd, Sm, Nd or La. ) Is used.

The crystal grain size in the particles of the electrically conductive substance is preferably 5 to 100 nm. 5 grain size
If it is less than nm, the area of the crystal grain boundaries contained in the particles becomes large, so that the electrical conductivity tends to be greatly reduced.
If it exceeds 00 nm, the surface area of the particles becomes small, so that the amount of supported metal tends to decrease.

In the first method for producing a NO _x purifying catalyst of the present invention, the electric conductive substance is obtained by mixing a plurality of aqueous solution precursors containing the constituent elements of the electric conductive substance and then calcining the mixture. .

The sintering temperature of the electrically conductive material is set at X
In the crystal structure evaluation by line diffraction, it is sufficient that the temperature is higher than a predetermined firing temperature at which a diffraction peak of the composite oxide crystal is obtained. However, if the temperature is too high, the crystal grain size increases and the surface area decreases. That is, the temperature may be 500 ° C. or higher,
It is desirable to fire at 1000 ° C. or lower.

The sintering time of the electrically conductive material is 0.5 to 20.
Preferably, it is time. If the firing time is less than 0.5 hour, the desired electrical conductivity tends not to be obtained,
When the time exceeds 0 hours, the crystal grain size tends to exceed 100 nm.

Second NO of the present invention_xManufacturing method of purification catalyst
In the law, NO_xThe purification catalyst uses an electrically conductive substance.
Immersed in an aqueous solution of a metal compound,
After coating with a compound,
Can be. By this method, on the surface of the electrically conductive material,
It is possible to carry finer fine metal particles, and NO
_xConversion can be improved.

It is preferable that the firing temperature of the electrically conductive material carrying fine metal particles is 250 to 700 ° C. and the firing time is 0.5 to 6 hours. If the sintering temperature is less than 250 ° C. or the sintering time is less than 0.5 hours, the binder material is not sintered, and the catalyst tends to be brittle and easily peeled off. If the time is exceeded, the catalyst tends to deteriorate.

[0041]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Lanthanum nitrate hydrate, strontium nitrate hydrate, gallium nitrate hydrate, and magnesium nitrate were mixed in a metal component molar ratio of 8: 2: 8: 2 and uniformly dissolved in water. Was. The solution was dropped and mixed with an aqueous oxalic acid solution to precipitate a precursor. Thereafter, the powder was filtered under reduced pressure, washed with distilled water and dried, and calcined at 800 ° C. for 10 hours and then pulverized to obtain a lanthanum strontium gallium magnesium composite oxide having a perovskite structure (La).
_0.8 Sr _0.2 Ga _0.8 Mg _0.2 O ₃ ) was obtained.

This lanthanum strontium gallium magnesium composite oxide was dispersed in water, and a predetermined amount of an aqueous solution in which dinitroammineplatinic nitric acid was dissolved was added and sufficiently stirred. Ammonia water was added until the pH of the dispersion solution reached 8, and then filtration was performed.
Perform a baking treatment at 0 ° C. for 3 hours and at 250 ° C. for 3 hours,
A lanthanum strontium gallium magnesium composite oxide carrying platinum was obtained.

Example 2 An aqueous solution in which a powder obtained by mixing lanthanum nitrate hydrate, strontium nitrate hydrate and manganese nitrate hydrate at a metal component molar ratio of 9: 1: 10 was dissolved was dropped into an oxalic acid aqueous solution. As a result, a precursor was precipitated to prepare a suspension. After adding the platinum-supported lanthanum strontium gallium magnesium composite oxide prepared in Example 1 to this suspension and sufficiently stirring, the pressure was reduced. Thereafter, the powder washed and dried with distilled water was baked at 700 ° C. for 10 hours, and then pulverized to obtain a lanthanum strontium manganese composite oxide La _0.9 Sr _0.1 MnO ₃ which is electron-conductive. A strontium gallium magnesium composite oxide was obtained.

Example 3 Cerium nitrate hydrate and samarium nitrate hydrate were mixed at a metal component molar ratio of 8: 2 and uniformly dissolved in water. The solution was dropped and mixed with an aqueous oxalic acid solution to precipitate a precursor. Thereafter, the powder was filtered under reduced pressure, washed with distilled water, and dried. The powder was calcined at 800 ° C. for 10 hours and then pulverized to obtain a cerium-samarium composite oxide (Ce _0.8 Sm _0.2
O _1.9 ) was obtained.

This cerium-samarium composite oxide was dispersed in water, and a predetermined amount of an aqueous solution in which dinitroammineplatinic nitric acid was dissolved was added and sufficiently stirred. P of this dispersion solution
After adding ammonia water until H becomes 8, filtration is performed, and the separated solid is subjected to a calcination treatment at 120 ° C. for 3 hours and at 250 ° C. for 3 hours to obtain a cerium-samarium composite oxide carrying platinum. Was.

Example 4 Barium oxalate hydrate, cerium nitrate hydrate and yttrium nitrate were mixed at a metal component molar ratio of 10: 8: 2 and uniformly dissolved in water. The solution was dropped and mixed with an aqueous oxalic acid solution to precipitate a precursor. After that, filtration under reduced pressure was performed, and the powder washed and dried with distilled water was treated with 800
Baked at 10 ° C. for 10 hours, and then pulverized to obtain a barium-cerium-yttrium composite oxide (BaC
was obtained _{e 0.8 Y 0 .2 O 3- α} ).

The barium-cerium-yttrium composite oxide was dispersed in water, and a predetermined amount of an aqueous solution in which dinitroammineplatinic nitric acid was dissolved was added and sufficiently stirred. After adding ammonia water until the pH of the dispersion solution becomes 8, filtration was performed, and the separated solid was separated at 120 ° C. for 3 hours.
A firing treatment was performed at 250 ° C. for 3 hours to obtain a barium-cerium-yttrium composite oxide carrying platinum.

Examples 5 to 9 In the same manner as in Example 3, instead of samarium nitrate hydrate, ytterbium nitrate hydrate, yttrium nitrate hydrate, gadolinium nitrate hydrate, neodymium nitrate hydrate, respectively using lanthanum nitrate hydrate, cerium, ytterbium complex oxide _{(Ce 0.8 Yb 0.2 O 1.9)} , cerium yttrium composite oxide _{(Ce 0.8 Y 0. 2 O 1.9} ),
Cerium gadolinium composite oxide (Ce _0.8 Gd _0.2 O
_1.9 ), cerium-neodymium composite oxide (Ce _0.8 Nd)
_0.2 O _1.9 ), cerium-lanthanum composite oxide (Ce _0.8 L
a _0.2 O _1.9 ).

Each of these cerium-containing composite oxides was dispersed in water, and a predetermined amount of an aqueous solution in which dinitroammineplatinic nitric acid was dissolved was added and sufficiently stirred. After adding ammonia water until the pH of the dispersion solution becomes 8, filtration was performed, and the separated solid was separated at 120 ° C. for 3 hours.
A calcination treatment was performed at 250 ° C. for 3 hours to obtain a cerium-containing composite oxide carrying platinum.

Examples 10 to 18 The composite oxides obtained in Examples 1 to 9 were used in Examples 1 to 9
In the same manner as in 1, a dinitroamminepalladium nitrate was used instead of dinitroammineplatinum nitrate to obtain an ion-conductive substance carrying fine palladium particles.

Examples 19 to 27 Using the composite oxides obtained in Examples 1 to 9, Examples 1 to 9
In the same manner as described above, rhodium nitrate was used instead of dinitroammineplatinum nitrate to obtain an ion-conductive substance carrying rhodium fine particles.

Examples 28 to 36 The composite oxides obtained in Examples 1 to 9 were used in Examples 1 to 9
Osmium nitrate was used in place of dinitroammineplatinum nitrate to obtain an ion-conductive substance carrying osmium fine particles in the same manner as described above.

Examples 37 to 45 The composite oxides obtained in Examples 1 to 9 were used in Examples 1 to 9
In the same manner as described above, iridium nitrate was used in place of dinitroammineplatinum nitrate to obtain an ion-conductive substance carrying iridium fine particles.

Examples 46 to 54 Using the composite oxides obtained in Examples 1 to 9, Examples 1 to 9
In the same manner as in Example 1, ruthenium nitrate was used instead of dinitroammineplatinum nitrate to obtain an ion-conductive substance carrying ruthenium fine particles.

Examples 55 to 63 The composite oxides obtained in Examples 1 to 9 were used in Examples 1 to 9
In the same manner as described above, instead of dinitroammineplatinum nitrate, using a mixture of dinitroammineplatinum nitrate and rhodium nitrate at a molar ratio of 1: 1 to form an ionic conductive material carrying platinum and ruthenium fine particles. Obtained.

A slurry was prepared by mixing 9 parts by weight of the ion-conductive substance powder carrying the fine metal particles obtained in Examples 1 to 63 and 1 part by weight of a silica binder powder and dispersing them in water. This slurry is applied inside a 400 cell / inch, 6 mil honeycomb (material: cordierite), and then fired at 500 ° C. for 2 hours in the air to support a fine metal particle-carrying ionic conductive material. I got The amount of the metal particle component carried in the honeycomb is 0.1 to 1.5.
g / L.

Comparative Example 1 γ-crystalline alumina was dispersed in water, and a predetermined amount of an aqueous solution obtained by mixing and dissolving dinitroammineplatinic nitric acid, dinitroamminepalladium nitric acid, and rhodium nitrate at a molar ratio of 5: 5: 1 was added. Stir well. The pH of this dispersion solution is 8
After the addition of aqueous ammonia, filtration was performed, and the separated solid was calcined at 120 ° C. for 3 hours and at 250 ° C. for 3 hours to obtain a γ-alumina powder supporting a noble metal. 9 parts by weight of this platinum-supported alumina powder and 1 part by weight of a silica binder powder were mixed and dispersed in water to prepare a slurry. This slurry was applied inside a 400 cell / inch, 6 mil honeycomb (material: cordierite), and then fired at 500 ° C. for 2 hours in the air.
A honeycomb supporting the noble metal-supported γ-alumina was obtained. The amount of the metal particle component carried in the honeycomb was 2.0 g / L.

(Evaluation 1) In the honeycomb supporting the powder obtained in Examples 1 to 63 and the honeycomb obtained in Comparative Example 1,
The evaluation of the NO _x conversion was carried out by passing a simulation gas of exhaust gas at an air-fuel ratio of 14.7 (stoichiometric combustion state).

FIG. 4 shows the temperature dependence of the NO _x conversion of these honeycombs. A, B, C, D, E, respectively, showing the NO _x conversion temperature dependence of Examples 1 to 3 and Comparative Example 1. As a result, the catalyst obtained by the present invention has a low temperature (especially 300 ° C.) despite the fact that only platinum is supported, as compared with the platinum / palladium / rhodium supported alumina catalyst which is the basic structure of the conventional three-way catalyst.
℃ or below) is high. From the above, a catalyst obtained by the present invention, it is clear that excellent _the NO _x purification performance.

(Evaluation 2) In the honeycomb supporting the powders obtained in Examples 1 to 63 and the honeycomb obtained in Comparative Example 1,
Through the simulation gas of the exhaust gas in the stoichiometric combustion state, the NO _x purification rate in each example at the exhaust gas temperatures of 250 ° C. and 300 ° C. was evaluated. The results are summarized in Tables 1 to 8.

[0062]

[Table 1]

[0063]

[Table 2]

[0064]

[Table 3]

[0065]

[Table 4]

[0066]

[Table 5]

[0067]

[Table 6]

[0068]

[Table 7]

[0069]

[Table 8]

As described above, the catalyst obtained according to the present invention is:
It is apparent that the catalyst has superior performance as compared with a conventional three-way catalyst (a precious metal supported on an alumina substrate).

[0071]

According to the first catalyst of the present invention, a plurality of fine metal particles having catalytic activity are directly supported on the surface of an electrically conductive material to electrically connect the particles, and it's the electrochemically to perform an oxidation reaction of the reducing reaction with a reducing agent of the NO _x in the fine metal particles by ion or ions and electrons move through the sexual material, and NO _x in different fine metal particles since the reducing agent it is possible to cause a redox reaction even if the adsorption, it is possible to further enhance the _the NO _x purification efficiency.

According to the second catalyst of the present invention, the purification catalyst of the first catalyst has at least one electric conductivity.
Obtained from a kind of ion conductive material and at least one kind of electron conductive material, wherein the ion conductive material and the electron conductive material are arranged so as to electrically short between the fine metal particles, Since the electronic resistance between the metal particles is reduced, the efficiency of the electrochemical redox reaction is improved. As a result, it is possible to further enhance the _the NO _x purification efficiency.

According to the third catalyst of the present invention, the first or the first catalyst
In the second catalyst, fine metal particles contain osmium,
Rhidium, platinum, palladium, rhodium, ruthenium
NO at least one of these elements_x
And the reducing agents HC and CO dissociate and adsorb,
The redox reaction is more likely to occur. As a result, NO _x
Purification efficiency can be further increased.

According to the fourth catalyst of the present invention, the first to third catalysts
In the above catalyst, when the electrically conductive substance has hydrogen ion conductivity, an electrochemical oxidation-reduction reaction between NO _x and the reducing agent is induced. As a result, it is possible to further enhance the _the NO _x purification efficiency.

According to the fifth catalyst of the present invention, the first to third catalysts
In the above catalyst, when the electrically conductive substance has oxygen ion conductivity, an electrochemical oxidation-reduction reaction between NO _x and the reducing agent is induced. As a result, it is possible to further enhance the _the NO _x purification efficiency.

According to the sixth catalyst of the present invention, in the fourth or fifth catalyst, since the electrically conductive substance is a composite oxide, material stability at a high temperature is improved. As a result, it is possible to withstand the rapid temperature rise of the catalyst during high-speed operation, and the durability of the catalyst is increased.

According to the seventh catalyst of the present invention, in the first or third to sixth catalysts, since the electrically conductive substance has both ionic and electronic conductivity, an electron conductive substance is introduced. It becomes unnecessary to do it. As a result, the number of types of materials is reduced, so that material costs can be reduced and the manufacturing process can be simplified.

According to the eighth catalyst of the present invention, in the seventh catalyst, the electrically conductive substance has a chemical formula Ce _0.8 A _0.2 O _1.9
Since the composite oxide is represented by (A = Yb, Y, Gd, Sm, Nd, La), a material that is stable even at a high temperature is used. As a result, it is not necessary to introduce an electron conductive material, thereby reducing the material cost and simplifying the manufacturing process, and at the same time, being able to withstand the rapid temperature rise of the catalyst that occurs during high-speed operation, etc. Increases the durability.

According to the first method for producing a NO _x purifying catalyst of the present invention, a method for producing an electrically conductive substance in the first to eighth catalysts comprises a method for producing a plurality of aqueous solutions containing constituent elements of the electrically conductive substance. By baking at 800 ° C. or lower after mixing the conductive precursor, an electrically conductive material having high electric conductivity and a large surface area can be obtained. As a result, it is possible to carry more fine metal particles on the surface of the electrically conductive substance, and as a result, it is possible to obtain a catalyst having a high reaction efficiency with a smaller amount of the electrically conductive substance.

According to the second method for producing a NO _x purification catalyst of the present invention, in the first to eighth catalyst production methods, the electric conductive substance is immersed in an aqueous solution of a metal compound, and the surface of the electric conductive substance is Is coated with a metal compound, followed by baking, whereby metal particles having fine catalytic activity can be carried on the surface of the electrically conductive substance. as a result,
It is possible to obtain a larger surface area with a smaller amount of metal, the catalytic activity per amount of metal is improved, and also possible to improve the NO _x reaction efficiency.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a NO _x purification catalyst in a first catalyst of the present invention.

FIG. 2 is a conceptual diagram showing a NO _x purification catalyst in a second catalyst of the present invention.

FIG. 3 is a potential diagram relating to a NO _x purification redox electrochemical reaction occurring on a plurality of fine metal particles in the present invention.

FIG. 4 is an example of temperature dependence of NO _x purification efficiency of a honeycomb supporting a catalyst powder according to the present invention.

FIG. 5 is a diagram showing the relationship between the weight ratio of air and fuel (air-fuel ratio) and the conversion (purification) rates of NO _x , HC, and CO for a conventional three-way catalyst for gasoline engines.

FIG. 6 is an explanatory view showing the operation of a conventional exhaust gas NO _x purification catalyst.

[Explanation of symbols]

1 Fine metal particles A, 2 Fine metal particles B, 3 Electrically conductive material, 4 Ion conductive material, 5 Electron conductive material.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/10 B01D 53/36 102B 3/28 301 B01J 23/56 301A 23/64 104A (72) Inventor Tetsuya Honda 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Hidenori Koseki 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Wachi Satoshi 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation (72) Inventor Hideaki Katashiba 2-3-2 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 3G091 AB04 BA14 CA16 CA18 GB05W GB06W GB07W GB10X 4D048 AA06 AB01 AB02 BA01X BA02X BA15X BA17X BA18X BA18Y BA19X BA19Y BA30X BA30Y BA31X BA31Y BA32X BA32Y BA33X BA33Y BA42X BA42Y EA10 4G069 AA03 AA08 AA14 BB06A BB06B BC10B BC12B BC13B BC17B BC38A BC40A BC40B BC41A BC42A BC42B BC43A BC43B BC70A BC70B BC71A BC71B BC72A BC72B BC73A BC73B BC74CABC13CA03 BC75BCA7

Claims (10)

[Claims] 1. A plurality of fine metal particles having catalytic activity are directly supported on the surface of an electrically conductive material and electrically connected between the particles, and ions or ions are formed via the electrically conductive material. by electrons move, NO _x purifying catalyst, characterized by performing the oxidation reaction of the reducing reaction with a reducing agent of the NO _x in the fine metal particles electrochemically. 2. The method according to claim 1, wherein the at least one ion conductive material and the at least one electron conductive material are electrically conductive. becomes disposed so as to short-circuit according to claim 1 NO _x purifying catalyst according. 3. The N according to claim 1, wherein the fine metal particles comprise at least one element of osmium, iridium, platinum, palladium, rhodium and ruthenium.
_Ox purification catalyst. 4. The method of claim 1, 2 or 3 NO _x purifying catalyst according electrically conductive material has a hydrogen ion conductivity. 5. The NO _x purification catalyst according to claim 1, wherein the electrically conductive substance has oxygen ion conductivity. 6. The method of claim 4 or 5 NO _x purifying catalyst according electrically conductive material is a composite oxide. 7. The N according to claim 1, wherein the electrically conductive substance has both ionic and electronic conductivity.
_Ox purification catalyst. 8. An electroconductive substance having a chemical formula of Ce _0.8 A _0.2 O
The NO according to claim 7, wherein the NO is a complex oxide represented by _1.9 (A represents Yb, Y, Gd, Sm, Nd or La).
_x Purification catalyst. 9. The method for producing a NO _x purification catalyst according to claim 1, 2, 3, 4, 5, 6, 7, or 8, wherein a plurality of water-soluble precursors containing a constituent element of an electrically conductive substance are provided. After mixing body, the manufacturing method of the NO _x purifying catalyst, characterized in that to obtain an electrically conductive material by baking. 10. A method according to claim 7 or 8 NO _x purifying catalyst according to immersing the electrically conductive material in an aqueous solution the metal compound, the electrical conductivity A method for producing a NO _x purification catalyst, comprising coating a surface of a conductive substance with a metal compound and then baking the fine particles to support the surface of the electrically conductive substance.