JP2649217B2 - Exhaust gas purifying material and exhaust gas purifying method - Google Patents

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 catalyst comprising a copper-based or copper-based component capable of reducing these nitrogen-containing compounds to nitrogen and a catalyst comprising a platinum-based component are mixed, and formed by combining a silver-based catalyst and the above mixed catalyst. Using a waste gas purifying material to be used, add one of hydrocarbons and oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing them into the flue gas, and contact the flue gas with the purifying material at a specific temperature and space velocity. By doing so, they discovered that nitrogen oxides could be effectively removed in a wide temperature range, and completed the present invention.

That is, the first exhaust gas purifying material of the present invention comprises a porous inorganic oxide containing 0.2 to 15% by weight (in terms of silver element) of silver and / or a silver compound or a mixture thereof as active species. A first catalyst supported on the porous inorganic oxide, copper oxide and / or sulfate as an active species of 0.2 to 0.2 to
A second catalyst supporting 30% by weight (in terms of a copper element) and Pt, Pd, Ru, and R as active species on a porous inorganic oxide;
a third catalyst supporting at least one element selected from the group consisting of h, Ir, and Au in an amount of 0.01 to 5% by weight (in terms of a metal element), wherein the first catalyst is an exhaust gas. A mixed catalyst formed by mixing the second catalyst and the third catalyst facing the inflow side faces the exhaust gas outflow side.

Further, the second exhaust gas purifying material of the present invention comprises a porous inorganic oxide containing silver and / or a silver compound as an active species;
Alternatively, a first catalyst supporting 0.2 to 15% by weight (in terms of silver element) of a mixture thereof, and a porous inorganic oxide containing copper oxide and / or sulfate 0.2% as an active species. ~ 3
0% by weight (converted to a copper element) and 30% by weight or less (converted to a metal element) of an oxide or sulfate of at least one element selected from the group consisting of W, V, and Mo. Pt, P as active species on the second catalyst and the porous inorganic oxide
d, a third catalyst supporting at least one element selected from the group consisting of Ru, Rh, Ir and Au in an amount of 0.01 to 5% by weight (in terms of a metal element); Wherein the mixed catalyst formed by mixing the second catalyst and the third catalyst faces the exhaust gas outflow side.

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, comprises: And the exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds are added on the upstream side of the purification material is brought into contact with the purification material at 150 to 600 ° C., whereby the hydrocarbons and / or The nitrogen oxide is removed by a reaction with an oxygen-containing organic compound.

Hereinafter, the present invention will be described in detail. In the first exhaust gas purifying material of the present invention, silver and / or a silver compound or a mixture thereof is used as an active species in a porous inorganic oxide.
A first catalyst supporting 2 to 15% by weight (in terms of silver element), and a porous inorganic oxide containing copper oxide and / or sulfate as an active species 0.2 to 30% by weight (copper Element conversion value)
And at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and Au as active species in the porous inorganic oxide, 0.01 to 5% by weight. % (In terms of metal element), an exhaust gas purifying material comprising a third catalyst is installed in an exhaust gas conduit, and a hydrocarbon and an oxygen-containing organic compound having 2 or more carbon atoms are located upstream of the purifying material installation position. An exhaust gas to which any of the compounds or a fuel containing the compound is added is brought into contact with the purifying material to reduce and remove nitrogen oxides in the exhaust gas. The exhaust gas purifying material is disposed such that the first catalyst faces the exhaust gas inflow side and the mixed catalyst obtained by mixing the second catalyst and the third catalyst faces the exhaust gas outflow side.
With this arrangement, nitrogen oxides can be effectively reduced and removed in a wide exhaust gas temperature range.

In the second exhaust gas purifying material of the present invention, 0.2 to 15% by weight of silver and / or a silver compound as an active species or a mixture thereof (in terms of silver element) is added to the porous inorganic oxide.
, A copper oxide and / or a sulfate as an active species in a porous inorganic oxide in an amount of 0.2 to 30% by weight (in terms of a copper element), W, V, and Mo. Oxide or sulfate of at least one element selected from the group consisting of
Weight% or less (in terms of a metal element) and a porous inorganic oxide containing Pt, Pd, and R as active species on a porous inorganic oxide.
at least one selected from the group consisting of u, Rh, Ir, and Au
An exhaust gas purifying material comprising a third catalyst carrying 0.01 to 5% by weight (converted to a metal element) of a seed element is installed in an exhaust gas conduit, and a hydrocarbon is provided upstream of the installation position of the purifying material. And an exhaust gas to which any one of oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing the same is added is brought into contact with the purification material to reduce and remove nitrogen oxides in the exhaust gas. Like the first exhaust gas purifying material, the second exhaust gas purifying material is such that the first catalyst faces the exhaust gas inflow side and the mixed catalyst obtained by mixing the second catalyst and the third catalyst flows out of the exhaust gas purifying material. Place it so that it faces the side.

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 are as follows:
Various changes can be made according to the purpose. Practically, it is preferable to have two parts such as an inlet part and an outlet part. Examples of the structure include a honeycomb structure type, a foam type, a three-dimensional network structure type formed of a fibrous refractory, a granular shape, a pellet shape, and the like.

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 The first catalyst is formed by supporting silver and / or a silver compound or a mixture thereof on a porous inorganic oxide, and is formed on the inflow side of exhaust gas. Acts on oxide removal. 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 preferably, a silver oxide and / or
Or silver chloride. As the porous inorganic oxide, porous alumina, silica, titania, zirconia, zeolite and composite oxides thereof and the like can be used, preferably γ-alumina, any of or including titania A composite oxide is used. By using γ-alumina, titania or a composite oxide thereof, the reaction between the added hydrocarbons, oxygen-containing organic compounds and / or residual hydrocarbons in the exhaust gas and nitrogen oxides in the exhaust gas occurs efficiently.

The specific surface area of the porous inorganic oxide such as alumina used for the first catalyst is preferably 10 m ² / g or more. 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 preferably, the specific surface area of the porous inorganic oxide is 30 m.
² / g or more.

The amount of the silver component supported as an active species on the inorganic oxide such as γ-alumina is determined by the amount of the inorganic oxide 10
0.2 to 15% by weight with respect to 0% by weight (in terms of silver element)
And 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 15% 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. The preferred loading of the silver component is 0.5 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 thickness of the first catalyst provided on the purifying material substrate generally depends on the thermal expansion characteristics of the substrate material and the catalyst. Often limited by differences. 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 provided on the surface of the purifying material base is preferably 20 to 300 g / liter of the purifying material base. If the amount of the catalyst is less than 20 g / liter, good NOx removal cannot be performed. On the other hand, when the amount of the catalyst is 300
When the amount exceeds g / liter, the removal characteristics do not increase so much.
Pressure loss increases. More preferably, the first catalyst provided on the surface of the purifying material base is 50 to 200
g / liter.

(2) Second Catalyst The second catalyst comprises a porous inorganic oxide carrying catalytically active species. As the porous inorganic oxide, it is preferable to use any of alumina, titania and zeolite, a composite oxide containing them, or a mixed oxide thereof. As in the first catalyst, the specific surface area of the porous inorganic oxide is 10
It is preferably at least m ² / g.

In the first exhaust gas purifying material of the present invention, copper oxide and / or sulfate is used as the active species of the second catalyst. By using the second catalyst, nitrogen oxides can be reduced by reducing nitrogen oxides and nitrogen-containing compounds generated by the first catalyst, such as nitrite and ammonia, to nitrogen. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the copper component is 0.2 to 30% by weight (in terms of a metal element), and the preferable supported amount is 0.5 to 25% by weight.
(Metal element conversion value).

In the second exhaust gas purifying material of the present invention, the active species of the second catalyst is at least one selected from the group consisting of oxides and / or sulfates of copper and W, V and Mo. And an oxide or a sulfate of the element (a). W, V, M
Of o, it is preferable to use W and / or V. By using the second catalyst, nitrogen oxides can be reduced by reducing nitrogen oxides and nitrogen-containing compounds generated by the first catalyst, such as nitrite and ammonia, to nitrogen. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the copper oxide or copper sulfate is 0.2 to 30% by weight (in terms of a metal element), and the supported amount of the W-based component is 30% by weight or less ( Metal element). The total amount of the copper component and the W-based component is 0.2 to 60% by weight (converted to metal element) (converted to metal element). The preferred loading of the copper component is 0.5 to
It is 25% by weight (in terms of metal element), the preferred amount of the W-based component is 25% by weight or less (in terms of metal element), and the preferred total amount of the copper component and the W-based component is 0.5.
To 50% by weight (in terms of metal element).

For loading the active species on the second catalyst, 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 a carbonate, nitrate, acetate, sulfate or the like of the catalytically active species element. In the case of a copper component, an aqueous solution such as copper sulfate or copper nitrate is used. W,
In the case of V or Mo, a porous inorganic oxide is immersed in an aqueous solution of an ammonium salt, oxalate or the like of each element for use. 50
After drying at ~ 150 ° C, especially at 70 ° C, the temperature is raised stepwise at 100-600 ° 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 the form of the purifying material is the first preferred embodiment described above, the thickness of the second catalyst provided on the purifying material base is preferably 300 μm or less. The amount of the second catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter of the purifying material base.

(3) 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 or composite oxides selected from the group consisting of alumina, titania, zirconia, silica, and zeolite. Similar to the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

The active species of the above third catalyst include Pt, P
d, Ru, Rh, using at least one element selected from the group consisting of Ir and Au, it is preferable to use at least one of Pt, Pd, Ru, Rh and Au, particularly at least Pt, Pd and Au One is preferred. The total of the active species supported on the inorganic oxide by the third catalyst is based on the above-mentioned porous inorganic oxide.
(100% by weight) is 0.01 to 5% by weight, preferably 0.01 to 4% by weight. Even when the amount of the catalytically active species exceeds 5% by weight of the porous inorganic oxide, the performance of removing nitrogen oxides is not improved.

The active species of the third catalyst may further include at least one selected from the group consisting of rare earth elements such as La and Ce, alkaline earth elements such as Ca and Mg, and alkali metal elements such as Na and K. It is preferable to carry one or more elements in an amount of 10% by weight or less. By supporting a rare earth, alkaline earth, or alkali metal element, the heat resistance of a platinum-based catalyst can be improved.

For loading the active species on the third catalyst, 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 such as a chloride or hexachlorometallic acid of a catalytically active species element, dried at 70 ° C., and then gradually heated at 100 to 700 ° C. and fired. This is done by: The calcination is performed under a nitrogen stream or a hydrogen-containing or oxygen-containing nitrogen stream. Preferably, the calcination is performed under a nitrogen stream, and then the calcination is performed under a hydrogen-containing nitrogen stream or an oxygen-containing nitrogen stream. Although the Pt-based loading component is shown as a metal element, the loading component exists in a state of a metal and an oxide under a normal use temperature condition of the purification material.

When the form of the purifying material is the first preferred embodiment described above, 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.

In the present invention, the second catalyst and the third catalyst are mixed and used. By this mixing, the reducing action of the second catalyst and the oxidizing action of the third catalyst can proceed simultaneously without affecting each other. In the case where the purifying material is the first preferred embodiment, the thickness of the mixed catalyst of the second catalyst and the third catalyst provided on the purifying material base is preferably 300 μm or less. Further, the amount of the mixed catalyst of the second catalyst and the third catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter with respect to the purifying material base.

The weight ratio of the second catalyst to the third catalyst (the ratio of the total weight of the porous inorganic oxide to the catalytically active species) is 10
The ratio is preferably set to 0: 1 to 100: 50. If the amount of the third catalyst is less than 1 part by weight based on 100 parts by weight of the second catalyst, the removal rate of hydrocarbons and carbon monoxide decreases. On the other hand, 50 parts by weight of the third catalyst were added to 100 parts by weight of the second catalyst.
If the amount is more than 100 parts by weight, the purification rate of nitrogen oxides is lowered as a whole in a wide temperature range of 150 to 600 ° C. More preferably, the weight ratio of the second catalyst to the third catalyst is 100: 1 to 10
0:30.

In the present invention, the weight ratio of the first catalyst to the mixed catalyst of the second catalyst and the third catalyst (the ratio of the total weight of the porous inorganic oxide to the catalytically active species) is: 10: 1 to 1
The ratio is preferably set to 1: 5. When the ratio is less than 1: 5 (the amount of the first catalyst is small), the purification rate of nitrogen oxides is reduced overall 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 mixed catalyst is small, the nitrogen-containing compounds such as nitrites and ammonia formed on the first catalyst do not react and are discharged as they are, or they are discharged as they are, carbon monoxide, hydrocarbons or the like. Removal rate decreases. More preferably, the weight ratio of the first catalyst to the mixed catalyst is 5: 1 to 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, an exhaust gas purifying material is installed in the exhaust gas conduit so that the first catalyst faces the exhaust gas inlet and the mixed catalyst obtained by mixing the second catalyst and the third catalyst is at the exhaust gas outlet. I do.

The exhaust gas contains ethylene, propylene and the like to some extent as residual hydrocarbons. However, the amount is generally not sufficient to reduce NOx in the exhaust gas. 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 hydrocarbon 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 the first catalyst (silver-based catalyst) is 150,000 h ^-1 in order to efficiently promote the reduction and removal of nitrogen oxides by an oxygen-containing organic compound, hydrocarbon or ammonia. Or less, preferably 100,000h ^-1
The following is assumed. When the space velocity of the first catalyst exceeds 150,000 h ^-1 , the reduction reaction of nitrogen oxides does not sufficiently occur, and the nitrogen oxide removal rate decreases. The space velocity in the catalyst obtained by mixing a second catalyst and 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, which is the 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.

[0047]

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).

Next, powdery titania (specific surface area: 50 m ² / g) is immersed in an aqueous solution of copper sulfate (copper concentration: 7.7% by weight), and in air at 80 ° C., 100 ° C. and 120 ° C. for 2 hours each. Dried. Subsequently, under a nitrogen stream containing 20% of oxygen, 12
The temperature was increased stepwise from 0 ° C. to 500 ° C. and calcined at 500 ° C. for 5 hours to prepare a second catalyst supporting 4.4% by weight of copper sulfate (converted to copper element) with respect to titania.

Further, the same titania was immersed in an aqueous solution of chloroplatinic acid for 20 minutes, dried in air at 80 ° C. for 2 hours, and dried at 120 ° C. for 2 hours in a nitrogen stream at 200 to 400 ° C.
Each step was baked for 1 hour. And 4% hydrogen gas
The temperature was raised from 50 ° C. to 400 ° C. over 5 hours under a nitrogen stream containing, and calcined at 400 ° C. for 4 hours.
% In a nitrogen stream containing 5% over a period of 5 hours from 50 ° C. to 500 ° C., and calcined at 500 ° C. for 5 hours.
Was prepared at a concentration of 0.21% by weight (in terms of a metal element).

The weight ratio of the second catalyst to the third catalyst is 40:
After mixing the second catalyst and the third catalyst so as to obtain a slurry and forming a slurry, 0.26 g of the mixed catalyst was coated on a honeycomb formed body similar to the silver-based purifying material. Drying and baking were performed under the same conditions as those for the silver-based purifying material to prepare copper and platinum-based purifying materials (purifying materials coated with the second and third catalysts).

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

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured with 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 Water was added to ammonium paratungstate parapentahydrate and oxalic acid, dissolved by heating on a water bath, and then added to a cooled aqueous solution (tungsten concentration: 15.5% by weight) to obtain a powdery titania. (Specific surface area: 50 m ² / g) and immersed for 20 minutes. Thereafter, the titania was separated from the solution, and dried in air at 80 ° C, 100 ° C, and 120 ° C for 2 hours each.
Subsequently, the temperature is changed from 120 ° C. to 5 ° C under a nitrogen stream containing 20% of oxygen.
The temperature was raised to 00 ° C. in 5 hours and calcined at 500 ° C. for 4 hours to prepare a W-based catalyst supporting 7.4% by weight (in terms of metal element) of an oxide of W with respect to titania. This catalyst was immersed in an aqueous solution of copper sulfate (copper concentration: 9.0% by weight) for 20 minutes, and dried and calcined in the same manner as the second catalyst of Example 1 to obtain an oxide of W with respect to titania of 7.4. A second catalyst was prepared, which supported 3.7% by weight of copper sulfate and 3.7% by weight (in terms of metal element).

The above-mentioned second catalyst and the third catalyst prepared in Example 1 were mixed at a weight ratio of 40: 1 to form a slurry. .26 g of the mixed catalyst was coated, dried and calcined,
Copper, W, and platinum-based purifying materials (purifying materials coated with second and third catalysts) were prepared.

The silver-based purifying material of Example 1 was set on the inflow side of the exhaust gas in the reaction tube, and the copper, W, and platinum-based purifying materials were set on the outflow side. The same reaction conditions as in Example 1 (the apparent space velocities of the silver-based purifying material and the copper, W, and platinum-based purifying materials were about 8
(At 0000 h ⁻¹ )), and the evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 3 Oxalic acid was added to vanadium pentoxide, and dissolved by heating on a water bath, and then cooled and cooled (a vanadium concentration of 7.8).
% By weight), powdered titania (specific surface area: 50 m ² / g)
, And immersed for 20 minutes. Thereafter, the titania was separated from the solution, and dried in air at 80 ° C, 100 ° C, and 120 ° C for 2 hours each. Subsequently, the temperature was increased from 120 ° C. to 500 ° C. in 5 hours under a nitrogen stream containing 20% of oxygen, and 50 ° C.
By calcining at 0 ° C. for 4 hours, a V-based catalyst carrying 3.8% by weight (converted to metal element) of V oxide with respect to titania was prepared. 3.3 g of this V-based catalyst (3.1 m in apparent volume)
l) was immersed in an aqueous solution of copper sulfate (copper concentration: 9.0% by weight) for 20 minutes and dried and calcined in the same manner as the second catalyst of Example 1 to obtain an oxide of V against titania of 3.8. A second catalyst was prepared, which supported 4.0% by weight of copper sulfate and 4.0% by weight of copper sulfate (in terms of metal element).

The second catalyst and the third catalyst prepared in Example 1 were mixed at a weight ratio of 20: 1 to form a slurry. .26 g of the mixed catalyst was coated, dried and calcined,
Copper, V, and platinum-based purifying materials (purifying materials coated with second and third catalysts) were prepared.

The silver-based purifying material of Example 1 was set on the inflow side of the exhaust gas in the reaction tube, and the copper, V, and platinum-based purifying materials were set on the outflow side. The same reaction conditions as in Example 1 (the apparent space velocities of the silver-based purifying material and the copper, V, and platinum-based purifying materials were about 8
(At 0000 h ⁻¹ )), and the evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 4 3.3 g of V-based catalyst prepared in Example 3 (apparent volume: 3.
1 ml) in an aqueous solution of copper nitrate (copper concentration 9.5% by weight).
For 2 minutes, and dried and calcined in the same manner as in the second catalyst of Example 1 to obtain 3.8% by weight of an oxide of V and 4.5% by weight of an oxide of copper with respect to titania (in terms of a metal element). ) Was prepared.

The second catalyst and the third catalyst prepared in Example 1 were mixed at a weight ratio of 20: 1 to form a slurry. .26 g of the mixed catalyst was coated, dried and calcined,
Copper, V, and platinum-based purifying materials (purifying materials coated with second and third catalysts) were prepared.

The silver-based purifying material of Example 1 was set on the inflow side of the exhaust gas in the reaction tube, and the copper, V, and platinum-based purifying materials were set on the outflow side. The same reaction conditions as in Example 1 (the apparent space velocities of the silver-based purifying material and the copper, V, and platinum-based purifying materials were about 8
(At 0000 h ⁻¹ )), and the evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 5 Powdered titania was immersed in an aqueous solution of copper nitrate (copper concentration: 9.5% by weight) for 20 minutes in the same manner as in Example 1, and dried in the same manner as in the second catalyst of Example 1. It was calcined to prepare a second catalyst which supported 4.5% by weight (in terms of a metal element) of a copper oxide with respect to titania.

The second catalyst and the third catalyst prepared in Example 1 were mixed at a weight ratio of 20: 1 to form a slurry. .26 g of the mixed catalyst was coated, dried and calcined,
Copper and platinum-based purifying materials (purifying materials coated with second and third catalysts) were prepared.

The silver purifying material of Example 1 was set on the inflow side of the exhaust gas in the reaction tube, and the copper and platinum purifying materials were set on the outflow side. The same reaction conditions as in Example 1 (the apparent space velocities of the silver-based purifying material, the copper-based purifying material and the platinum-based purifying material were about 80,000, respectively)
h- ¹ ), the evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Comparative Example 1 A honeycomb molded body was coated with the silver-based purifying material prepared in Example 1 on the inflow side of the exhaust gas and 0.26 g of the third catalyst prepared in Example 1 in the same manner as in Example 1. A platinum purifying material was set on each of the exhaust gas outflow sides. Evaluation was carried out under the same reaction conditions as in Example 1 (the apparent space velocities of the silver-based purifying material and the platinum-based purifying material were respectively about 80,000 h ^-1 ) and the gases having the compositions shown in Table 1. Table 2 shows the results.

Table 2 Removal rate of nitrogen oxides (NOx) Removal rate of nitrogen oxides (%) Reaction temperature (° C.) 300 350 400 450 500 Example 1 65.2 78.5 82.7 82.5 76.6 Example 2 63.4 75.8 82.1 85.9 78.8 Execution Example 3 64.1 74.5 81.7 89.6 77.2 Example 4 69.8 78.7 82.8 89.1 76.6 Example 5 45.4 64.5 75.4 78.3 74.3 Comparative Example 1 20.5 32.5 38.7 42.6 40.5

As can be seen from Table 2, in Examples 1 to 5, good removal of nitrogen oxides was observed in a wide exhaust gas temperature range as compared with Comparative Example 1 using only silver and platinum catalysts.

[0069]

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 Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location B01J 27/053 B01J 27/08 A 27/08 27/18 A 27/18 29/072 A 29 / 072 29/076 A 29/076 B01D 53/36 102H 104A ZAB (72) Acquisition of Inventor Naoko 4-1-1, Suehiro, Kumagaya-shi, Saitama Pref. RIKEN Kumagaya Plant (72) Inventor Kiyohide Yoshida Kumagaya, Saitama 4-14-1, Suehiro, Ichino Examiner, Naoto Noda, Rikken Kumagaya Works Co., Ltd. (56) References JP-A-6-327942 (JP, A) JP-A-6-319997 (JP, A) JP-A-6-319 238166 (JP, A)

Claims (8)

(57) [Claims] 1. A first catalyst comprising a porous inorganic oxide carrying silver and / or a silver compound or a mixture thereof as an active species in an amount of 0.2 to 15% by weight (in terms of silver element), A second catalyst comprising a porous inorganic oxide supporting copper oxide and / or sulfate as an active species in an amount of 0.2 to 30% by weight (in terms of a copper element); As active species
Exhaust gas purification comprising a third catalyst carrying at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au in an amount of 0.01 to 5% by weight (in terms of a metal element). The exhaust gas purifying material, wherein the first catalyst faces the exhaust gas inflow side, and the mixed catalyst obtained by mixing the second catalyst and the third catalyst faces the exhaust gas outflow side. . 2. A first catalyst comprising a porous inorganic oxide carrying as active species silver and / or a silver compound or a mixture thereof in an amount of 0.2 to 15% by weight (in terms of silver element), 0.2-30% by weight of copper oxide and / or sulfate as active species in the porous inorganic oxide (in terms of copper element);
30% by weight or less of oxide or sulfate of at least one element selected from the group consisting of V and Mo (converted value of metal element)
And at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au as active species on the porous inorganic oxide. In an exhaust gas purifying material comprising a third catalyst supporting the catalyst by weight (in terms of a metal element), the first catalyst faces the exhaust gas inflow side, and the second catalyst and the third catalyst An exhaust gas purifying material, characterized in that a mixed catalyst obtained by mixing the components faces the exhaust gas outflow side. 3. The exhaust gas purifying material according to claim 1, wherein the weight ratio of the second catalyst to the third catalyst is 10%.
An exhaust gas purifying material having a ratio of 0: 1 to 100: 50. 4. The exhaust gas purifying material according to claim 1, wherein at least one of the first, second, and third catalysts is on a surface of a ceramic or metal substrate. An exhaust gas purifying material characterized by being coated. 5. 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. Exhaust gas purifying material. 6. 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: 7. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is selected from the group consisting of alumina and titania or a composite oxide containing them in the first catalyst. In the catalyst of alumina, titania and zeolite, or a composite oxide containing them or a mixed oxide thereof, and in the third catalyst alumina, titania,
An exhaust gas purifying material comprising at least one oxide selected from the group consisting of zirconia, silica, and zeolite. 8. The method for reducing nitrogen oxides from a combustion exhaust gas containing the nitrogen oxides and oxygen in an amount larger than the theoretical reaction amount for the co-existing unburned components, using the exhaust gas purifying material according to any one of claims 1 to 7. 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 a hydrocarbon and / or an oxygen-containing organic compound is added at an 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.