JPH08164327A - Waste gas purifying material and waste gas purifying method - Google Patents

Abstract

PURPOSE: To effectively remove NOx from the waste gas contg. NOx and excess oxygen by reduction by using a waste gas purifying material having specified first, second and third catalysts from the waste gas inlet side to the outlet side. CONSTITUTION: The first catalyst is obtained by depositing 0.2-1.2wt.% silver component (expressed in terms of silver element) on a porous inorg. oxide as an active species. The second catalyst is formed by depositing 0.5-15wt.% siver component (expressed in terms of silver element), which is a higher deposition rate than the first catalyst, on a porous inorg. oxide as an active species. The third catalyst is obtained by depositing 0.2-10wt.% oxide or sulfate of at least one kind of element among W, V, Mo, Mn, Nb and Ta (expressed in terms of metallic element) and 0.01-5wt.% at least one kind among Pt, Pd, Ru, Rh, Ir and Au (expressed in terms of metallic element) on a porous inorg. oxide as an active species. The first, second and third catalysts are arranged in this order from the waste gas inlet side of the purifying material to the outlet side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying material capable of effectively reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and excess oxygen, and a purification method using the same.

[0002]

2. Description of the Related Art Excessive combustion exhaust gas discharged from internal combustion engines such as automobile engines, combustion equipment installed in factories, household fan heaters, and the like is excessive. It contains nitrogen oxides such as nitric oxide and nitrogen dioxide together with oxygen. Here, "containing excess oxygen" means that the exhaust gas contains more oxygen than the theoretical amount of oxygen necessary to burn unburned components such as carbon monoxide, hydrogen, and hydrocarbons. I do. In the following, nitrogen oxide refers to nitric oxide and / or nitrogen dioxide.

[0003] This nitrogen oxide is one of the causes of acid rain and is a major environmental problem. Therefore, various methods for removing nitrogen oxides in exhaust gas discharged from various combustion equipments are being studied.

[0004] As a method for removing nitrogen oxides from a combustion exhaust gas containing excess oxygen, a selective catalytic reduction method using ammonia is used particularly for a large-scale fixed combustion device (a large-scale combustor in a factory or the like). Has been put to practical use.

However, in this method, ammonia used as a reducing agent for nitrogen oxides is expensive, and ammonia is toxic. Therefore, the nitrogen oxides in the exhaust gas must be removed so that unreacted ammonia is not discharged. There are problems that the amount of injected ammonia must be controlled while measuring the concentration, and that the apparatus generally becomes large.

As another method, there is a non-selective catalytic reduction method in which a nitrogen oxide is reduced by using a gas such as hydrogen, carbon monoxide, or a hydrocarbon as a reducing agent. In order to reduce and remove nitrogen oxides, it is necessary to add a reducing agent in an amount equal to or more than a theoretical reaction amount with oxygen in exhaust gas, and there is a disadvantage that a large amount of the reducing agent is consumed. For this reason, the non-selective catalytic reduction method is practically effective only for exhaust gas having a low residual oxygen concentration burned near the stoichiometric air-fuel ratio, and is not practical because of poor versatility.

In view of the above, a method has been proposed for removing nitrogen oxides by using a zeolite or a catalyst supporting a transition metal on the zeolite and adding a reducing agent having a theoretical reaction amount or less with oxygen in the exhaust gas (for example, Japanese Patent Application Laid-Open Publication No. H11-163873). No.63-100919, 63-28372
No. 7, JP-A No. 1-130735).

However, in these methods, effective removal of nitrogen oxides can be obtained only in a narrow temperature range, and in an exhaust gas containing water, the removal rate of nitrogen oxides is significantly reduced. In other words, it contains about 10% water,
It is difficult to effectively remove nitrogen oxides from exhaust gas from a vehicle or the like whose temperature changes greatly depending on operating conditions.

Accordingly, it is an object of the present invention to provide a method for producing nitrogen oxides, carbon monoxide, hydrogen, hydrocarbons and the like, such as combustion exhaust gas from a fixed combustion device and a gasoline engine, a diesel engine or the like, which burns under oxygen excess conditions. From combustion exhaust gas containing more than the theoretical reaction amount for unburned components,
An object of the present invention is to provide an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently reducing and removing nitrogen oxides.

[0010]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has found that an organic compound such as ethanol is converted to oxygen and nitrogen on a catalyst comprising a porous inorganic oxide carrying a silver component. It has been found that it reacts with exhaust gas containing oxides to reduce nitrogen oxides to nitrogen gas and to generate nitrogen-containing compounds such as nitrites and ammonia and aldehydes as by-products. A second silver-based catalyst capable of effectively removing nitrogen oxides using the generated aldehyde is further provided to oxidize soluble organic components (hereinafter abbreviated as SOF) in carbon monoxide, hydrocarbons and diesel exhaust gas. Using an exhaust gas purifying material formed by combining a catalyst carrying a W-based component and a platinum-based component to be removed, any one of hydrocarbons and oxygen-containing organic compounds having 2 or more carbon atoms in the exhaust gas or It has been discovered that nitrogen oxides can be effectively removed in a wide temperature range by adding a fuel containing the gas and bringing the exhaust gas into contact with the above-mentioned purifying material at a specific temperature and space velocity, and completed the present invention. .

That is, the exhaust gas purifying material of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than the theoretical reaction amount of coexisting unburned components is a porous inorganic oxide. A first catalyst supporting 0.2 to 12% by weight (in terms of silver element) of silver and / or a silver compound or a mixture thereof as an active species, and silver and silver as active species on a porous inorganic oxide; And / or a silver compound or a mixture thereof, in which 0.5 to 15% by weight (in terms of silver element) and a second catalyst supporting an amount larger than the active species loading of the first catalyst, Oxide or sulfate of at least one element selected from the group consisting of W, V, Mo, Mn, Nb, and Ta as active species in the inorganic oxide of
0% by weight (in terms of a metal element) and at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au.
A first catalyst, the second catalyst, and the second catalyst in order from the exhaust gas inflow side to the outflow side of the purification material. It has three catalysts.

Further, the exhaust gas purifying method of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in excess of the theoretical reaction amount for coexisting unburned components uses the above exhaust gas purifying material. The exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and the exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds are added upstream of the purifying material is
The nitrogen oxides are removed by contacting the purifying material at 50 to 600 ° C. and reacting with the hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas.

Hereinafter, the present invention will be described in detail. The exhaust gas purifying material of the present invention comprises a porous inorganic oxide containing silver and / or a silver compound as an active species, or a mixture thereof in an amount of 0.2 to 12 as an active species.
A first catalyst supporting the weight% (in terms of silver element);
Silver and / or a silver compound or a mixture thereof as active species is added to the porous inorganic oxide in an amount of 0.5 to 15% by weight (in terms of silver element) and more than the active catalyst loading of the first catalyst. An oxide or a sulfate of at least one element selected from the group consisting of W, V, Mo, Mn, Nb, and Ta as active species in a porous inorganic oxide and a second catalyst to be supported. 2 to 10% by weight (converted to metal element), Pt, Pd, R
at least one selected from the group consisting of u, Rh, Ir, and Au
A third catalyst supporting 0.01 to 5% by weight (in terms of metal element) of a seed element. The first catalyst, the second catalyst, in order from the exhaust gas inflow side to the outflow side of the purification material,
An exhaust gas purifying material having the third catalyst was installed in an exhaust gas conduit, and either a hydrocarbon or an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing the same was added upstream from the installation position of the purifying material. The exhaust gas is brought into contact with the purifying material to reduce and remove nitrogen oxides in the exhaust gas.

A first preferred embodiment of the exhaust gas purifying material of the present invention is a purifying material obtained by coating a purifying material base with a catalyst comprising a powdery porous inorganic oxide carrying catalytically active species. Examples of the ceramic material forming the substrate of the purifying material include porous materials such as γ-alumina and its oxides (γ-alumina-titania, γ-alumina-silica, γ-alumina-zirconia, etc.), zirconia, titania-zirconia, and the like. A heat-resistant material having a large surface area can be used. When high heat resistance is required, it is preferable to use cordierite, mullite, alumina and a composite thereof. In addition, a known metal material can be used for the base of the exhaust gas purifying material.

The shape and size of the substrate of the exhaust gas purifying material
Various changes can be made according to the purpose. Practically, at the entrance,
It is preferred that it comprises two or more parts, such as an intermediate part and an outlet part. In addition, as its structure, honeycomb structure type,
Foam type, three-dimensional network structure type made of fibrous refractory,
Alternatively, granules, pellets and the like can be mentioned.

A second preferred embodiment of the exhaust gas purifying material of the present invention is a catalyst comprising a porous inorganic oxide in the form of a pellet or a granular powder carrying a catalytically active species, or a powder comprising a catalytically active species, respectively. It is a purifying material obtained by molding a porous inorganic oxide into pellets or granules into a casing having a desired shape.

The following catalyst is formed on the purifying material of the present invention. (1) First catalyst and second catalyst The first catalyst and the second catalyst are formed by supporting silver and / or a silver compound or a mixture thereof on a porous inorganic oxide, and on the inflow side of the exhaust gas. And acts to remove nitrogen oxides in a wide temperature range. The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate, silver phosphate, and the like, and is preferably one or more of silver oxide, silver chloride, and silver sulfate, More preferred are silver oxide and / or silver chloride. As the porous inorganic oxide, it is preferable to use either alumina or titania or a composite or mixed oxide containing them. When a composite or mixed oxide of alumina is used, the content of alumina is preferably set to 50% by weight or more. alumina,
By using titania or a composite or mixed oxide thereof, a reaction between added hydrocarbons, oxygen-containing organic compounds and / or residual hydrocarbons in exhaust gas and nitrogen oxides in exhaust gas occurs efficiently.

The specific surface area of the porous inorganic oxide such as alumina used for the first catalyst and the second catalyst is 10 m ² / g.
It is preferable that this is the case. If the specific surface area is less than 10 m ² / g, the contact area between the exhaust gas and the inorganic oxide (and the silver component carried thereon) becomes small, and good nitrogen oxides cannot be removed. More preferred specific surface area of the porous inorganic oxide is 30 m ² / g or more.

In the first catalyst, the amount of the silver component supported as an active species on the above-mentioned inorganic oxide such as γ-alumina is 0.2 to 12% by weight (100% by weight of the inorganic oxide). (Element conversion value). If the amount is less than 0.2% by weight, the removal rate of nitrogen oxides decreases. If the silver component is carried in an amount exceeding 12% by weight, the combustion of the hydrocarbon and / or the oxygen-containing organic compound itself tends to occur, and the nitrogen oxide removal rate is rather lowered. A preferable silver component loading is 0.5 to 1
0% by weight.

In the second catalyst, the amount of the silver component supported as an active species on the inorganic oxide such as γ-alumina is 0.5 to 15% by weight (100% by weight of the inorganic oxide). (In terms of element) and more than the loading rate of the active species of the first catalyst. That is, the content of the silver component with respect to the porous inorganic oxide in the second catalyst is always higher than that in the first catalyst. If it is less than 0.5% by weight or less than the active catalyst loading of the first catalyst, the removal of nitrogen oxides using the aldehyde generated by the first catalyst is not performed. In addition, when a silver component in an amount exceeding 15% by weight is supported, combustion of hydrocarbons and / or oxygen-containing organic compounds themselves tends to occur,
The nitrogen oxide removal rate is rather reduced. The loading amount of the silver component in the preferred second catalyst is 1 to 12% by weight.

As a method for supporting silver on an inorganic oxide such as alumina, a known impregnation method, precipitation method, or the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, chloride, sulfate, carbonate, or the like, or an aqueous ammonia solution. Alternatively, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, dried, and then immersed again in an aqueous solution of ammonium chloride or ammonium sulfate. In the precipitation method, silver nitrate is reacted with ammonium halide to precipitate silver halide on the porous inorganic oxide. This is 50
After drying at about 150 ° C, especially about 70 ° C, 100 to 600
It is preferred to raise the temperature stepwise at a temperature of ° C. and to perform firing. Firing
It is preferable to carry out in air, under a flow of nitrogen containing oxygen or under a flow of hydrogen gas. When the treatment is performed under a hydrogen gas stream, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last.

It has been observed that a silver component supported on a porous inorganic oxide using an aqueous solution of silver nitrate or the like forms a circular aggregate when fired in an oxidizing atmosphere. In the purification material of the present invention, the average diameter of the silver component aggregate is 10 to 10,000 n
m is preferable. In general, the smaller the diameter of the silver component aggregate, the higher the reaction characteristics, but the average diameter is 10n.
If it is less than m, only the oxidation reaction of the hydrocarbon and / or the oxygen-containing organic compound as the reducing agent proceeds, and the nitrogen oxide removal rate decreases. On the other hand, when the average diameter exceeds 10,000 nm, the reaction characteristics of the silver component are reduced, and the nitrogen oxide removal rate is reduced. The average diameter of the preferred silver component aggregate is 10 to 5
000 nm, more preferably 10 to 2000 nm. Here, the average means an arithmetic average.

When the purifying material is in the above-described first preferred embodiment, the thicknesses of the first catalyst and the second catalyst provided on the purifying material base are generally the same as those of the base material and the catalyst. Are often limited due to differences in thermal expansion characteristics. The thickness of the catalyst provided on the purifying material base is preferably 300 μm or less. With such a thickness, it is possible to prevent the purifying material from being damaged by thermal shock or the like during use. A method for forming a catalyst on the surface of the purifying material base is performed by a known washcoat method or the like.

The amount of the first catalyst and the amount of the second catalyst provided on the surface of the purifying material base are 20 to
Preferably it is 300 g / l. The amount of catalyst is 2
If it is less than 0 g / liter, good NOx removal cannot be performed.
On the other hand, when the amount of the catalyst exceeds 300 g / liter, the removal characteristics do not increase so much and the pressure loss increases. More preferably, the first catalyst and the second catalyst provided on the surface of the purifying material base are each 50 to 200 g / liter of the purifying material base.

(2) Third Catalyst The third catalyst comprises a porous inorganic oxide carrying catalytically active species and is formed on the exhaust gas outflow side, and acts to remove nitrogen oxides in a low temperature region. And at the same time, oxidize and remove carbon monoxide and hydrocarbons. As the porous inorganic oxide, it is preferable to use one or more oxides selected from the group consisting of alumina, titania, zirconia, silica, and zeolite, or a composite or mixed oxide thereof. Like the first catalyst, the specific surface area of the porous inorganic oxide is 10 m
It is preferably at least ² / g.

The active species of the third catalyst are W,
Oxides or sulfates of at least one element selected from the group consisting of V, Mo, Mn, Nb, Ta, and Pt, Pd, R
at least one selected from the group consisting of u, Rh, Ir, and Au
Seed elements are used. W, V, Mo, Mn, Nb, Ta
Of these, it is preferable to use W and / or V, and Pt, P
Among d, Ru, Rh and Au, it is particularly preferable to use at least one of Pt, Pd and Au. 10 porous inorganic oxides
Assuming 0% by weight, the supported amount of the W-based component is 0.2 to 10% by weight (converted to metal element), and the supported amount of the platinum-based component is 0.01 to 5% by weight (converted to metal element). . The preferred amount of the W-based component is 0.2 to 9% by weight (in terms of a metal element), and the preferred amount of the platinum-based component is 0.01 to 9% by weight.
4% by weight (in terms of metal element). By using the third catalyst, harmful substances such as carbon monoxide, hydrocarbons, and SOF can be oxidized and removed. Moreover, oxidation of sulfur dioxide can be suppressed even in the treatment of exhaust gas containing sulfur dioxide.

For supporting the active species on the third catalyst, a known impregnation method, precipitation method, or the like can be used. When the impregnation method is used, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, nitrate, acetate, sulfate, chloride, hexachlorometal acid, or the like of a catalytically active species element. W, V, Mo, Mn, Nb,
In the case of Ta, a porous inorganic oxide is immersed in an aqueous solution of an ammonium salt, oxalate or the like of each element for use. 50-1
After drying at 50 ° C., particularly 70 ° C., the temperature is raised stepwise at 100 to 600 ° C. and firing is performed. This calcination is performed in air under a nitrogen stream containing oxygen. It is also an effective method to use metatitanic acid (hydrous titanium oxide) as a starting material instead of titania and to carry V, W, and Mo. When zeolite is used as the inorganic oxide, it is preferable to support the zeolite by an impregnation method or a known ion exchange method.

When the form of the purifying material is the above-described first preferred embodiment, the thickness of the third catalyst provided on the purifying material base is preferably 300 μm or less. The amount of the third catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter based on the purifying material base.

The weight ratio of the first catalyst to the second catalyst (the ratio of the total weight of the porous inorganic oxide and the catalytically active species) is 1:
It is preferably 10 to 20: 1. When the ratio is less than 1:10 (the amount of the first catalyst is small), 150 to 600 ° C.
Over a wide temperature range, the purification rate of nitrogen oxides decreases overall. On the other hand, when the ratio exceeds 20: 1 and the amount of the second catalyst is small, the oxidation characteristics of carbon monoxide and SOF deteriorate. More preferred weight ratio of the first catalyst to the second catalyst is 1: 5 to 10:
It is one.

The ratio of the total weight of the first catalyst and the second catalyst to the weight of the third catalyst (ratio of the total weight of the porous inorganic oxide and the catalytically active species) is 10: 1 to 1: It is preferably set to 5. When the ratio is less than 1: 5 (the amount of the first catalyst and the amount of the second catalyst are small), the purification rate of nitrogen oxides is generally reduced in a wide temperature range of 150 to 600 ° C. On the other hand, when the ratio exceeds 10: 1 and the amount of the third catalyst is small, nitrite and ammonia formed on the first catalyst are not effectively used for reducing nitrogen oxides. More preferably, the weight ratio of the total weight of the first catalyst and the second catalyst to the weight of the third catalyst is 5: 1.
１ ： 1: 4.

If the purifying material having the above configuration is used, 150
In a wide temperature range of up to 600 ° C., good removal of nitrogen oxides can be performed even with an exhaust gas containing about 10% of moisture and sulfur oxides.

Next, the method of the present invention will be described. First, a first catalyst, a second catalyst, and a third catalyst are installed in the exhaust gas conduit in order from the exhaust gas inflow side to the outflow side of the purifying material.

The exhaust gas contains ethylene, propylene and the like to some extent as residual hydrocarbons. However, since the amount is generally not enough to reduce NOx in the exhaust gas, hydrocarbons and / or oxygen-containing organic substances are supplied from the outside. A compound, preferably an oxygen-containing organic compound or a reducing agent obtained by mixing the compound with a hydrocarbon fuel is introduced into the exhaust gas. The introduction position of the reducing agent
It is upstream from the position where the purifying material is installed.

As the hydrocarbons introduced from the outside, gaseous or liquid alkanes, alkenes and / or alkynes can be used under standard conditions. In particular, in the case of an alkane or alkene, it preferably has 2 or more carbon atoms. Specific examples of hydrocarbons that are liquid in the standard state include gas oil, cetane,
Examples include hydrocarbons such as heptane, kerosene, gasoline and the like.
Among them, hydrocarbons having a boiling point of 50 to 350 ° C are particularly preferable. As the oxygen-containing organic compound introduced from the outside, alcohols such as ethanol and isopropyl alcohol having 2 or more carbon atoms, or a fuel containing them can be used.

The amount of the hydrocarbon and / or oxygen-containing organic compound introduced from the outside is determined by the weight ratio (weight of the reducing agent to be added / weight).
(Weight of nitrogen oxides in the exhaust gas) is preferably 0.1 to 5. If the weight ratio is less than 0.1, the removal rate of nitrogen oxides does not increase. On the other hand, if it exceeds 5, fuel efficiency will be degraded.

When a fuel containing a hydrocarbon or an oxygen-containing organic compound is added, it is preferable to use gasoline, light oil, kerosene, or the like as the fuel. In this case, the amount of the reducing agent is set such that the weight ratio (the weight of the reducing agent to be added / the weight of the nitrogen oxide in the exhaust gas) is 0.1 to 5 in the same manner as described above.

In the present invention, the space velocity of each of the first catalyst and the second catalyst is 150,000 h ^-1 or less in order to efficiently promote the reduction and removal of nitrogen oxides by an oxygen-containing organic compound, a hydrocarbon or the like. , Preferably 100,000 h ^-1 or less. The space velocity of the first catalyst and the second catalyst is 150,0
If it exceeds 00 h ⁻¹ , the reduction reaction of nitrogen oxides does not sufficiently occur, and the nitrogen oxide removal rate decreases. The space velocity of the third catalyst 200,000 ^-1 or less, preferably 150,000H ^-1 or less.

In the present invention, the temperature of the exhaust gas at the purification material installation site where the hydrocarbon and / or the oxygen-containing organic compound reacts with the nitrogen oxide is set to 150 to 600 ° C.
To keep. If the temperature of the exhaust gas is lower than 150 ° C., the reaction between the reducing agent and the nitrogen oxide does not proceed, and it is not possible to remove the nitrogen oxide satisfactorily. On the other hand, if the temperature exceeds 600 ° C., the combustion of the hydrocarbon and / or the oxygen-containing organic compound itself starts, and the reduction and removal of nitrogen oxides cannot be performed. The preferred exhaust gas temperature is from 200 to 550C, more preferably from 300 to 500C.

[0039]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A commercially available γ-alumina powder (specific surface area: 200 m ² / g) was immersed in an aqueous silver nitrate solution, taken out, and dried at 70 ° C. for 2 hours. Then, the temperature is raised stepwise to 600 ° C. in the air, and calcined for 5 hours.
A first catalyst supporting silver by weight (in terms of a metal element) was prepared. 0.26 g of the first catalyst was charged with a commercially available cordierite honeycomb formed body (diameter 20 mm, length 8.3 m).
m, 400 cells / inch ² ) and after drying 600
The mixture was baked stepwise to ℃ to prepare a silver-based purifying material (a purifying material coated with a first catalyst).

In the same manner as in the above-mentioned silver-based catalyst, a second catalyst in which 5.0% by weight (in terms of metal element) of silver was supported on powdered alumina was prepared, and the same honeycomb-shaped formed body as described above was obtained. 0.26 g of the second catalyst was coated, and a second silver-based purifying material (a purifying material coated with the second catalyst) was prepared in the same manner.

Next, powdered titania (specific surface area 50 m ²⁾
/ G) in a chloroplatinic acid aqueous solution for 20 minutes, dried in air at 80 ° C. for 2 hours, and dried at 120 ° C. in a nitrogen stream at 120 ° C.
The firing was carried out step by step from 200 to 400 ° C. for 1 hour each. Then, under a nitrogen gas flow containing 4% of hydrogen gas, 50 ° C.
The temperature was raised to 400 ° C. over 5 hours, calcined at 400 ° C. for 4 hours, and further heated to 50 ° C. under a nitrogen stream containing 10% oxygen.
The temperature was raised to 500 ° C. over 5 hours, and calcined at 500 ° C. for 5 hours to carry 1% by weight (converted to metal element) of Pt on titania. After adding water to ammonium tungstate parapentapentahydrate and oxalic acid and dissolving by heating on a water bath, the powdered titania was added to a cooled aqueous solution (tungsten concentration: 15.5% by weight), Soak for minutes. Thereafter, the titania was separated from the solution and, in air,
It dried at 0 degreeC, 100 degreeC, and 120 degreeC for 2 hours each. Subsequently, under a nitrogen stream containing 20% of oxygen, the temperature is raised from 120 ° C to 500 ° C.
To 5 ° C. in 5 hours, and calcined at 500 ° C. for 4 hours to support 3% by weight (converted to metal element) of W oxide with respect to titania. ) Was prepared. After slurrying 0.26 g of the third catalyst, it was coated on the same honeycomb formed body as the above-mentioned silver-based purifying material, and dried and fired under the same conditions as the silver-based purifying material to obtain a W, Pt-based purifying material ( A purification material coated with a third catalyst) was prepared.

A silver-based purifying material, a second silver-based purifying material, and a W and Pt-based purifying material were sequentially set from the inflow side to the outflow side of the exhaust gas in the reaction tube. Next, a gas (nitrogen monoxide, oxygen, ethanol, sulfur dioxide, nitrogen and moisture) having a composition shown in Table 1 was flowed at a flow rate of 3.48 liters per minute (standard state) (apparent space velocity of each purification material). Are about 80,000 h ^-1
), The temperature of the exhaust gas in the reaction tube was kept in the range of 350 to 550 ° C, and ethanol and nitrogen oxide were reacted.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured by a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 2 shows the results.

Table 1 Component concentration Nitric oxide 800 ppm Oxygen 10% by volume Ethanol 1560 ppm Sulfur dioxide 30 ppm Nitrogen Residual water 10% by volume (based on the total volume of the above components)

Example 2 As in Example 1, 3.1% by weight (in terms of metal element) of commercially available silica-alumina powder (silica content: 5% by weight, specific surface area: 350 m ² / g) using an aqueous silver nitrate solution. The first catalyst was prepared by carrying silver of value (1). First catalyst 0.2
6 g of a commercially available cordierite honeycomb-shaped molded product (diameter: 20 mm, length: 8.3 mm, 400 cells / inch ² )
And dried and fired stepwise to 600 ° C. to prepare a silver-based purifying material (a purifying material coated with a first catalyst).

In the same manner as the above-mentioned silver-based catalyst, a second catalyst in which 5% by weight (in terms of a metal element) of silver was supported on powdery silica / alumina was prepared, and the same honeycomb-shaped formed body as above was prepared. 0.26 g of the second catalyst was coated, and a second silver-based purifying material (a purifying material coated with the second catalyst) was prepared in the same manner.

In order from the inflow side to the outflow side of the exhaust gas in the reaction tube, a silver-based purifying material, a second silver-based purifying material, W, Pt of Example 1
System purifying material was set. The same reaction conditions as in Example 1 (the apparent space velocity of each purification material was about 80,000 h ^-1
The evaluation was performed using a gas having the composition shown in Table 1. Table 2 shows the results.

Example 3 Using an aqueous chloroplatinic acid solution, 1.0% by weight of platinum was supported on the same titania as in the third catalyst of Example 1. Oxalic acid was added to vanadium pentoxide, heated and dissolved in a water bath, and then cooled and cooled (a vanadium concentration of 7.8% by weight).
This powdery titania was put into the container and immersed for 20 minutes.
Thereafter, the titania was separated from the solution and in air,
It dried at each of 2 degreeC, 100 degreeC, and 120 degreeC. continue,
The temperature was increased from 120 ° C. to 500 ° C. in 5 hours under a nitrogen gas stream containing 20% oxygen, and calcined at 500 ° C. for 4 hours. ) Supported to prepare a V, Pt-based catalyst (third catalyst). After slurrying 0.26 g of the third catalyst, it was coated on the formed honeycomb body in the same manner as in Example 1, dried and fired to obtain a V, Pt-based purification material (a purification material coated with the third catalyst). ) Was prepared.

The silver-based purifying material of Example 1, the second silver-based purifying material of Example 1, and the V and Pt-based purifying materials were set in this order from the inflow side to the outflow side of the exhaust gas in the reaction tube. Evaluation was performed using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity of each purification material was about 80,000 h ^-1 ). Table 2 shows the results.

Comparative Example 1 The same honeycomb formed body was coated with 0.52 g of the first catalyst prepared in Example 1, dried and fired to prepare a silver-based purifying material. Set the silver purifying material in the exhaust gas conduit,
The same reaction conditions as in Example 1 (apparent space velocity was about 80,
000 h ⁻¹ ), and evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Table 2 Removal rate of nitrogen oxide (NOx) Removal rate of nitrogen oxide (%) Reaction temperature (° C.) 350 400 450 500 550 Example 1 53.6 79.5 94.7 95.0 88.6 Example 2 48.7 78.8 90.1 92.9 85.8 Example 3 58.1 82.5 93.4 94.8 87.2 Comparative Example 1 24.5 46.8 68.7 82.6 78.5

As can be seen from Table 2, in Examples 1 to 3, good removal of nitrogen oxides was observed in a wide exhaust gas temperature range as compared with Comparative Example 1 using only a silver catalyst. It was also confirmed that carbon monoxide, residual hydrocarbons, and SOF were effectively oxidized and removed.

[0053]

As described above in detail, the use of the exhaust gas purifying material of the present invention makes it possible to efficiently remove nitrogen oxides in exhaust gas containing excess oxygen in a wide temperature range. INDUSTRIAL APPLICABILITY The exhaust gas purifying material and the purification method of the present invention can be widely used for purifying exhaust gas of various types of combustors, automobiles and the like.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B01D 53/36 102 A 102 B 104 A

Claims (6)

[Claims] 1. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in excess of the theoretical reaction amount of coexisting unburned components, wherein the porous inorganic oxides are used as active species. 0.2 to 12% by weight of silver and / or a silver compound or a mixture thereof (in terms of silver element)
And a silver and / or silver compound as an active species in a porous inorganic oxide, or a mixture thereof in an amount of 0.5 to 15% by weight (in terms of silver element) and the first catalyst. A second catalyst supporting a larger amount of the active species than the active species of the catalyst; and W, V, M as active species on the porous inorganic oxide.
O, Mn, Nb, Ta oxide or sulfate of at least one element selected from the group consisting of Ta 0.2 to 10% by weight
(Metal element conversion value) and at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au 0.01 to 5
% Of the catalyst (in terms of a metal element), the first catalyst, the second catalyst, and the third catalyst in order from the exhaust gas inflow side to the outflow side of the purifying material. An exhaust gas purifying material comprising: 2. The exhaust gas purifying material according to claim 1, wherein at least one of the first, second and third catalysts is coated on the surface of a ceramic or metal substrate. An exhaust gas purifying material characterized by that: 3. The exhaust gas purifying material according to claim 1, wherein at least one of the first, second and third catalysts is in the form of pellets or granules. 4. The exhaust gas purifying material according to claim 1, wherein the silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate, and silver phosphate. An exhaust gas purifying material characterized by that: 5. The exhaust gas purifying material according to claim 1, wherein said porous inorganic oxide is alumina or titania in the first and second catalysts, or a composite or mixed material containing them. Oxides, alumina for the third catalyst,
An exhaust gas purifying material comprising at least one oxide selected from the group consisting of titania, zirconia, silica, and zeolite. 6. An exhaust gas purifying material according to claim 1, wherein nitrogen oxide is reduced from a combustion exhaust gas containing nitrogen oxide and oxygen in an amount larger than a theoretical reaction amount for a coexisting unburned component. In the exhaust gas purifying method for removing, the exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and the exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds are added on the upstream side of the purifying material is subjected to the purifying material at 150 to 600 ° C. Exhaust gas purifying method, wherein the nitrogen oxides are removed by contact with a hydrocarbon and / or an oxygen-containing organic compound in the exhaust gas.