JPH0857263A - Exhaust gas purifying material and method therefor - Google Patents

Abstract

PURPOSE: To efficiently remove nitrogen oxide in exhaust gas containing excessive oxygen within a wide temp. range by using an exhaust gas purifying material obtained by supporting a catalyst composed of silver or a silver compd., a catalyst composed of oxide of W or the like and a catalyst composed of Pt or the like on porous inorg. oxide. CONSTITUTION: This exhaust gas purifying material is composed of a first catalyst obtained by supporting 0.2-15wt.% (in terms of silver element) of silver and/or a silver compd. or a mixture of them on porous inorg. oxide, a second catalyst obtained by supporting 0.5-30wt.% (in terms of a metal element) of oxide of at least one element selected from a group consisting of W, V and Mo on porous inorg. oxide and a third catalyst obtained by supporting 5wt.% or less (in terms of a metal element) of at least one element selected from a group consisting of Pt, Pd, Ru, Rh, Ir and Au on porous inorg. oxide.

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 for effectively removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides, excess oxygen, and sulfur oxides, 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 and the 59th Annual Meeting of the Chemical Society of Japan
(1990) 2A526, `` Catalyst '' vol.33 No.2, p.59, 199
1 year).

However, it has been found that in these methods, the temperature range for removing nitrogen oxides is narrow, and in the case of exhaust gas containing water, the removal rate of nitrogen oxides is significantly reduced. Therefore, the present inventors have provided a silver-based catalyst on the inflow side of the exhaust gas and a platinum-based catalyst on the outflow side. A purifying material that can also remove hydrocarbons has been previously proposed (JP-A-6-142523). However, it has been found that in the exhaust gas containing sulfur oxides, the scintillation of the catalyst component easily occurs, the surface area of the catalytically active species decreases, and the nitrogen oxide removal rate decreases.

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. Exhaust gas that can efficiently remove nitrogen oxides from combustion exhaust gas containing oxygen and sulfur oxides in excess of the theoretical reaction amount with respect to unburned components, and can also oxidize and remove residual and unreacted carbon monoxide and hydrocarbons An object of the present invention is to provide a purification material and an exhaust gas purification method.

[0010]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has found that a catalyst comprising a silver component supported on an alumina composite inorganic oxide containing a specific amount of an inorganic oxide such as silica. It has been found that an organic compound such as ethanol reacts with an exhaust gas containing oxygen and nitrogen oxides to reduce nitrogen oxides to nitrogen gas and to produce ammonia as a by-product. Using an exhaust gas purifying material formed by combining the above silver-based catalyst, a catalyst carrying a W-based component capable of reducing nitrogen oxides with ammonia as a reducing agent, and a catalyst carrying a platinum-based component, If any of the hydrocarbons and oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing them is added, and the exhaust gas is brought into contact with the purifying material at a specific temperature and space velocity, sulfur oxides are contained. The present inventors have found that nitrogen oxides can be effectively removed from exhaust gas in a wide temperature range, and have completed the present invention.

That is, while reducing and removing nitrogen oxides from a flue gas containing nitrogen oxides and oxygen in excess of the theoretical reaction amount for coexisting unburned components, residual and unreacted carbon monoxide and hydrocarbons are also oxidized. The exhaust gas purifying material of the present invention to be removed has a porous inorganic oxide carrying 0.2 to 15% by weight (in terms of silver element) of silver and / or a silver compound of the inorganic oxide or a mixture thereof. The first catalyst, the porous inorganic oxide to the inorganic oxide 0.5 ~
A second catalyst supporting 30% by weight (in terms of metal element) of an oxide of at least one element selected from the group consisting of W, V, and Mo; Of Pt, Pd, Ru,
And a third catalyst supporting at least one element selected from the group consisting of Rh, Ir and Au.

In addition, nitrogen oxides are reduced and removed from a combustion exhaust gas containing nitrogen oxides and oxygen in excess of the theoretical reaction amount for coexisting unburned components, and residual and unreacted carbon monoxide and hydrocarbons are also oxidized. In the exhaust gas purifying method of the present invention, the exhaust gas purifying material is provided in the middle of an exhaust gas conduit, the exhaust gas purifying material is provided in the middle of the exhaust gas conduit, and the hydrocarbon and / or carbon number is upstream of the purifying material. 2
The oxygen-containing organic compound or the exhaust gas to which the fuel containing it is added is brought into contact with the purifying material at 150 to 600 ° C., thereby removing the nitrogen oxides by the reaction with the oxygen-containing organic compound in the exhaust gas. In addition, residual and unreacted carbon monoxide and hydrocarbons are oxidized and removed.

Hereinafter, the present invention will be described in detail. In the present invention, the porous inorganic oxide may contain the inorganic oxide in an amount of 0.2 to 1%.
5% by weight (in terms of silver element) of a first catalyst supporting silver and / or a silver compound or a mixture thereof, and 0.5 to 30% by weight of the inorganic oxide on a porous inorganic oxide %
A second catalyst supporting an oxide of at least one element selected from the group consisting of W, V, and Mo (in terms of metal elements); Pt, Pd, Ru, Rh, Ir and
An exhaust gas purifying material comprising a third catalyst carrying at least one element selected from the group consisting of Au is installed in an exhaust gas conduit, and hydrocarbons and carbon are located upstream of the purifying material installation position. Exhaust gas to which any one of several or more oxygen-containing organic compounds or a fuel containing the same is added is brought into contact with the purifying material to reduce and remove nitrogen oxides in the exhaust gas. In the present invention, the first catalyst, the second catalyst, and the third catalyst are used in combination, but the first catalyst, the second catalyst, and the third catalyst are arranged in order from the exhaust gas inflow side to the outflow side. Is preferred.
With this arrangement, nitrogen oxides can be effectively reduced and removed in a wide exhaust gas temperature range.

In a first preferred embodiment of the exhaust gas purifying material of the present invention, first, second and third catalysts each comprising a powdery porous inorganic oxide carrying a catalytically active species are provided on a purifying material substrate. A purifying material formed by coating a purifying material substrate with a coated purifying material or a powdery porous inorganic oxide and then carrying a catalytically active species. As a ceramic material forming the base of the purifying material, γ-alumina and its composite oxide (γ
-Alumina-titania, γ-alumina-silica, γ-alumina-zirconia, etc.), zirconia, titania-zirconia, and other heat-resistant porous materials having a large surface area. When high heat resistance is required, it is preferable to use cordierite, mullite, alumina, a composite thereof, and the like. 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. In addition, the base body is the entrance part,
Two or more parts such as an outlet part can be used in combination. Examples of the structure of the substrate 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. The first catalyst, the second catalyst, and the third catalyst may be coated on different positions on the same substrate, or may be coated on different substrates and used in combination.

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 pellets, granules or powder carrying a catalytically active species, or a powder comprising a catalytically active species. 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 three catalysts are formed in 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 exhaust gas inflow side. The silver compound is at least one selected from the group consisting of oxides of silver, silver chloride, silver sulfate, silver phosphate, and the like, preferably silver oxides, silver chloride or silver sulfate,
More preferably, silver oxide or silver chloride is used.

As the porous inorganic oxide, alumina alone, or an alumina composite oxide comprising alumina and at least one oxide selected from the group consisting of porous silica, titania and zirconia, and the like are used. Preferably, a composite oxide composed of alumina and silica is used. By using an alumina composite oxide, particularly an alumina-silica composite oxide, even in a high exhaust gas temperature such as 700 ° C. in the presence of a sulfur oxide, a reduction in the surface area of the purifying material and the sintering of the catalytically active species hardly occur. As a result, the heat resistance and durability of the purification material are improved.

The alumina composite oxide is a commercially available product such as an alumina-silica composite oxide, a composite obtained by mixing alumina with an inorganic oxide sol such as a silica sol, or prepared by a sol-gel method. Use something. The content of components other than alumina in the alumina composite oxide is 50% by weight or less, and preferably 0.1 to 40% by weight.
It is. When the content of components other than alumina is less than 0.1% by weight, the removal rate of nitrogen oxides is reduced when the reaction is carried out for a long time in the presence of sulfur oxides. The nitrogen oxide removal rate in the range is reduced.

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 varies somewhat depending on the type of the organic compound and the fuel added to the exhaust gas, the contact time with the exhaust gas, and the like. The content is 0.2 to 15% by weight (in terms of silver element) based on 100% by weight of the inorganic oxide.
If the amount is less than 0.2% by weight, the removal rate of nitrogen oxides decreases.
In addition, when the silver content exceeds 15% by weight, the oxygen-containing organic compound itself tends to burn, and the nitrogen oxide removal rate is rather lowered. The preferred amount of the silver component is 0.5 to
It is 12% by weight.

The silver component carried on the porous inorganic oxide is granular, but in the purifying material of the present invention, the silver component particles have an average diameter of 10 to 1000 nm. In general,
The smaller the particle diameter of the silver component, the higher the reaction characteristics. However, if the average particle diameter is less than 10 nm, only the oxidation reaction of the hydrocarbon and / or the oxygen-containing organic compound as the reducing agent proceeds to remove nitrogen oxides. The rate drops. On the other hand, when the average particle size is 1000
If it exceeds nm, the reaction characteristics of the silver component are reduced, and the nitrogen oxide removal rate is reduced. Preferred average particle size is 10 to 500
nm, more preferably 10 to 200 nm. In addition,
The average here means an arithmetic average.

As a method of 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 a nitrate such as silver nitrate, chloride, sulfate, carbonate or the like. In the precipitation method, silver nitrate and ammonium halide are reacted to precipitate silver halide on a porous inorganic oxide. After drying at 50 to 150 ° C., particularly at about 70 ° C., it is preferable to raise the temperature stepwise at 100 to 600 ° C. for firing. The firing is preferably performed in an oxygen atmosphere, a nitrogen atmosphere, or a hydrogen gas flow. In the case of performing in a nitrogen atmosphere or a flow of hydrogen gas, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last.

In the first preferred embodiment of the purifying material, the thickness of the first catalyst provided on the purifying material base is generally limited by the difference in thermal expansion characteristics between the base material and this catalyst. Often. 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 wash coat method, a powder 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 250
g / liter.

(2) Second Catalyst The second catalyst comprises a porous inorganic oxide carrying an oxide of at least one element selected from the group consisting of W, V, and Mo, which are catalytically active species. Become. Examples of the porous inorganic oxide include titania alone or a titania composite inorganic oxide containing another porous inorganic oxide. Preferably, titania alone or a titania composite oxide containing one or more oxides selected from the group consisting of alumina, silica, and zirconia is used. When using a titania composite oxide, the content of components other than titania is set to 50% by weight or less, preferably 0.1 to 40% by weight.

It is preferable to use W and / or V among W, V and Mo. The amount of the W-based oxide supported on the inorganic oxide by the second catalyst is 0.5 to 30% by weight (in terms of a metal element) based on the above-mentioned porous inorganic oxide (100% by weight), Preferably, it is 1 to 20% by weight (value in terms of metal element). Even if the amount of the W-based oxide exceeds 30% by weight based on the weight of the inorganic oxide, the effect is not changed. By using a W-based oxide, it is possible to remove nitrogen oxides using ammonia as a reducing agent. In the present invention, any catalyst that promotes the reduction reaction of nitrogen oxides by ammonia can be used without being limited to W-based oxides.

As a method for supporting the W-based oxide in the second catalyst, known impregnation methods, precipitation methods, sol-gel methods,
A powder method or the like can be used. At that time, the porous inorganic oxide is immersed in an aqueous solution of an ammonium salt, an oxalate or the like of each element, dried at 50 to 150 ° C., particularly 70 ° C., and then dried.
It is carried out by raising the temperature stepwise at 0 to 600 ° C. and firing. This firing is performed in air, under an oxygen atmosphere, under a nitrogen atmosphere, or under a hydrogen gas flow. When firing is performed under a nitrogen atmosphere or a hydrogen gas flow, it is effective to perform an oxidation treatment at 300 to 650 ° C. at last. .

In the first preferred embodiment of the purifying material, the thickness of the second catalyst provided on the purifying material base is 300 μm.
m or less. The amount of the second catalyst provided on the surface of the purifying material base is 20 to 300 g / p of the purifying material base.
It is preferably liter. When the purifying material base is made of a porous inorganic oxide such as titania, a predetermined amount of an oxide of W, V and / or Mo can be carried thereon and used as a purifying agent. In addition, a porous inorganic oxide such as titania carrying a predetermined amount of an oxide of W, V and / or Mo can be used after being formed into a formed body such as a honeycomb.

(3) Third catalyst The third catalyst comprises a porous inorganic oxide and a catalytically active species of P
It carries at least one metal element selected from the group consisting of t, Pd, Ru, Rh, Ir and Au. Examples of the porous inorganic oxide include a heat-resistant ceramic having a large surface area, such as at least one oxide selected from the group consisting of alumina, titania, zirconia, and silica. Preferably, γ-alumina is used.

Of Pt, Pd, Ru, Rh, Ir and Au, Pt, P
It is preferable to use at least one of d, Ru, Rh and Au, and particularly preferable to use at least one of Pt, Pd and Au. P
The loading amount of at least one of t, Pd, Ru, Rh, Ir, and Au is set to 5% by weight or less (in terms of a metal element) based on 100% by weight of the inorganic oxide. If the supported amount exceeds 5% by weight of the inorganic oxide, the removal effect of the silver component is greatly reduced. In addition, it is preferable to set the lower limit of the supported amount to 0.01% by weight. A more preferred loading is from 0.01 to 4% by weight.

It is preferable that at least one element selected from the group consisting of an alkali metal element, an alkaline earth metal element and a rare earth element is supported by 10% by weight or less as an active species of the third catalyst. By supporting these elements, the heat resistance of the platinum-based catalyst can be improved.

As a method for supporting one or more of Pt, Pd, Ru, Rh, Ir and Au in the third catalyst, a known impregnation method, precipitation method and the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, chloride, nitrate, acetate, hydroxide, or the like of a catalytically active species element,
After drying at 70 ° C., the temperature is raised stepwise at 100 to 700 ° C. and firing is performed.

In the first preferred embodiment of the purifying material, the thickness of the third catalyst provided on the purifying material base is 300 μm.
m or less. Further, the amount of the third catalyst provided on the surface of the purification material base is 20 to 300 g / p of the purification material base.
It is preferably liter.

In the present invention, the weight ratio of the first catalyst to the second catalyst (the ratio of the total weight of the porous inorganic oxide to the catalytically active species) is from 10: 1 to 1: 5. Is preferred. The ratio is less than 1: 5 (less first catalyst)
As a result, the purification rate of nitrogen oxides as a whole decreases over a wide temperature range of 150 to 600 ° C. On the other hand, when the ratio exceeds 10: 1 and the amount of the second catalyst is small, the oxidative removal rates of residual carbon monoxide, hydrocarbons, and ammonia decrease. A more preferred weight ratio of the first catalyst to the second catalyst is 5: 1 to 1: 4.

On the other hand, the weight ratio of the first catalyst to the third catalyst (ratio of the total weight of the porous inorganic oxide and the catalytically active species)
Is preferably 20: 1 to 1: 5. The ratio is 1:
If it is less than 5 (the amount of the first catalyst is small), 150 to 60
In a wide temperature range of 0 ° C., the purification rate of nitrogen oxides is reduced overall. On the other hand, if the ratio exceeds 20: 1 and the amount of the third catalyst is small, the removal rate of hydrocarbons and carbon monoxide decreases. More preferably, the weight ratio of the first catalyst to the third catalyst is 15: 1.
１1: 1.

If the purifying material having the above-described structure is used, 150
In a wide temperature range of up to 600 ° C., good removal of nitrogen oxides can be performed even with exhaust gas containing sulfur oxides.

Next, the method of the present invention will be described. First, an exhaust gas purifying material having a first catalyst, a second catalyst, and a third catalyst is provided in the middle of an exhaust gas conduit. Preferably, the first catalyst faces the exhaust gas inlet, the third catalyst faces the exhaust gas outlet, and the second catalyst is located between the first catalyst and the third catalyst.

Although the exhaust gas contains ethylene, propylene and the like to some extent as residual hydrocarbons, it is generally not enough to reduce NOx in the exhaust gas. The above oxygen-containing organic compound or a reducing agent comprising a mixed fuel containing them is introduced into exhaust gas. The position where the reducing agent is introduced is upstream of 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. As the gaseous hydrocarbon in the standard state, an alkane, alkene or alkyne having 2 or more carbon atoms is preferable. Specific examples of the hydrocarbon in a liquid state in a standard state include hydrocarbons such as heptane, cetane, kerosene, light oil, gasoline, and heavy oil. 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 having 2 or more carbon atoms, such as ethanol and isopropyl alcohol, or fuels containing them can be used. The amount of the reducing agent introduced from the outside is determined by the weight ratio (weight of the reducing agent to be added / nitrogen oxide (N
O) is preferably from 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 the weight ratio exceeds 5,
This leads to poor fuel economy.

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 reduce and remove nitrogen oxides with 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 of the second catalyst (W-based catalyst) is 200,000 h ^-1 or less, preferably 150,0 h
00h ^-1 or less. Space velocity of the second catalyst is 200,000h
^If it exceeds ^-1 , the oxidizing and removing properties of hydrocarbons, carbon monoxide, etc., deteriorate. The space velocity in the third catalyst (platinum catalyst) is 200,000 ^-1 or less, preferably 150,000H ^-1 or less. When the space velocity of the third catalyst exceeds 200,000 h ^-1 , the oxidizing and removing properties of hydrocarbons, carbon monoxide and the like deteriorate.

Further, in the present invention, the temperature of the exhaust gas is maintained at 150 to 600 ° C. at the purification material installation site where the oxygen-containing organic compound reacts with the nitrogen oxide. 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, when the temperature exceeds 600 ° C., the combustion of the oxygen-containing organic compound itself takes precedence, and the reduction and removal rate of nitrogen oxides decreases. The preferred exhaust gas temperature is between 250 and 600C.

[0045]

The present invention will be described in more detail with reference to the following specific examples. Example 1 To 10 g of a commercially available powdered silica-alumina composite oxide (silica content: 5% by weight, specific surface area: 350 m ² / g), 4% by weight based on silica-alumina using an aqueous silver nitrate solution
After carrying silver (in terms of silver element), drying, and calcination in air in a stepwise manner to 600 ° C., this is formed into pellets having a diameter of 1.5 mm and a length of 2 to 3 mm, and a silver catalyst ( First catalyst) was prepared.

Next, water (6.2 ml) was added to 1.8 g of ammonium tungstate parapentapentahydrate and 1.0 g of oxalic acid, and dissolved by heating on a water bath, and then titania (particles) was added to the cooled aqueous solution. Diameter 0.5-2.0mm, specific surface area 35m
² / g) 10 g was added and immersed for 30 minutes. afterwards,
Separate the titania particles from the solution and in air at 80 ° C, 1
It dried at 00 degreeC and 120 degreeC for 2 hours each. Then, oxygen 2
A temperature of 120 ° C. to 500 ° C. in 5 hours under a nitrogen gas stream containing 0%, and calcined at 500 ° C. for 4 hours to carry 9% by weight of W to titania (converted to metal element). A purifying material (second catalyst) was prepared.

Further, pelletized γ-alumina (diameter: 1.5 mm, length: about 2 to 3 mm, specific surface area: 260 m ² /
g) using an aqueous chloroplatinic acid solution, carrying 0.2% by weight (in terms of metal element) of platinum with respect to γ-alumina, drying and calcining to 700 ° C. to form a platinum-based catalyst (third catalyst). catalyst)
Was prepared.

In order from the inflow side to the outflow side of the exhaust gas, about 3.6 g of a silver-based catalyst, about 3.6 g of a W-based catalyst, and about 1.
2 g was set in the reaction tube. Next, simulated exhaust gas (nitrogen monoxide, carbon monoxide, oxygen, ethanol, propylene, sulfur dioxide, nitrogen, and water) having the composition shown in Table 1 was flowed at a flow rate of 4.4 liters per minute (standard state) at 450 ° C. , 10
After flowing for 0 hours (space velocity of the silver-based catalyst is about 30,000 h
^-1 , the space velocity of the W-based catalyst is about 30,000 h ^-1 , the space velocity of the platinum-based catalyst is about 90,000 h ^-1 ), and the exhaust gas temperature in the reaction tube is changed from 300 ° C. to 600 ° C. every 50 ° C. At each temperature, ethanol and nitrogen oxide were reacted.

Table 1 Component concentrations Nitric oxide 800 ppm (dry basis) Carbon monoxide 100 ppm (dry basis) Oxygen 10% by volume (dry basis) Ethanol 1250 ppm (dry basis) (3 times the weight of nitric oxide) Propylene 100 ppm (dry basis) Sulfur dioxide 80 ppm (dry basis) Nitrogen Residual moisture 10% by volume (based on the total volume of the above components)

The nitrogen oxides (NO +
The concentration of NO ₂ ) was measured with a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. The concentrations of carbon monoxide and hydrocarbons were measured with a CO meter and a HC meter, respectively.
The removal rates of carbon monoxide and hydrocarbons were determined under the condition that ethanol was not added to the exhaust gas. Table 2 shows the results.

Example 2 The same powdery silica-alumina as in Example 1 (specific surface area: 3
About 1.0 g of a catalyst in which 4 wt% of silver chloride (in terms of silver element) was supported by a precipitation method using an aqueous solution of silver nitrate and ammonium chloride in 50 m ² / g), and a commercially available cordierite honeycomb molded body (diameter: 30mm, length about 12.5mm, 40
0 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver-based purifying material (a purifying material coated with a first catalyst).

Next, 20 g of V ₂ O ₅ was suspended in 30 ml of water, and the mixture was stirred on a water bath at about 90 ° C. for 1 hour.
After allowing to cool, water was added to make up to 80 ml. This aqueous solution
After sampling 2.8 ml of water and adding 2.8 ml of water to make 6.8 ml, 10 g of powdered titania (specific surface area: 50 m ² / g) was added, and
It was immersed for 0 minutes to form a slurry. 1.0 g (dry base) of a slurry was coated on a honeycomb-shaped formed body similar to the silver-based purifying material. The content of V ₂ O ₅ relative to titania was 5% by weight (in terms of metal element). WO of Example 1
₃ / Dried and calcined under the same conditions as for the titania catalyst.
A system purification material (a purification material coated with a second catalyst) was prepared.

Further, powdery γ-alumina (specific surface area 20
0 m ² / g), 0.2% by weight of Pt was supported using a chloroplatinic acid solution, and then slurried. A similar honeycomb-shaped formed body (4.2 mm in length) was coated with 0.4 g (dry weight). ,
After drying, it was fired to 700 ° C. to prepare a platinum-based purifying material (a purifying material coated with a third catalyst).

A silver-based purifying material, a V-based purifying material, and a platinum-based purifying material were set in a reaction tube in order from the inflow side to the outflow side of the exhaust gas, and evaluated in the same manner as in Example 1 using gases having the compositions shown in Table 1. (The space velocity of the silver-based purifying material is about 30,000 h ^-1 , the space velocity of the V-based purifying material is about 30,000 h ^-1 , and the space velocity of the platinum-based purifying material is about 90,000 h ^-1 ). Table 2 shows the experimental results.

Example 3 In the same manner as in Example 2, powdered titania (specific surface area: 50 m ² /
g) containing 4% by weight and 2% by weight of oxides of W and V, respectively.
(Value in terms of metal element) 1.0 g (dry base) of the supported catalyst was made into a slurry. This slurry was coated on a honeycomb formed body (diameter 30 mm, length 12.5 mm, 400 cells / square inch) similar to that in Example 2. Drying and firing were performed under the same conditions as in Example 2 to prepare W and V-based purifying materials.

The silver-based purifying material of Example 2, the W and V-based purifying materials and the platinum-based purifying material of Example 2 were set in the reaction tube in order from the inflow side to the outflow side of the exhaust gas. was evaluated under the same conditions as in example 2 with the gas (space velocity of about 30,000 h ^-1 of silver-based purification material, W, space velocity of about 30,000 h ^-1 of the V-based purification material, spatial platinum-based purification material Speed is about 9
000h- ¹ ). Table 2 shows the experimental results.

Comparative Example 1 A commercially available pelletized γ-alumina (1.5 mm in diameter, about 2-3 mm in length, specific surface area of 260) was prepared in the same manner as in Example 1.
m ² / g) to support 4% by weight of silver to prepare a silver-based purifying material. 3.6 g of a silver-based purifying material was set in a reaction tube, and evaluated using a gas having a composition shown in Table 1 under the same conditions as in Example 1 (space velocity: about 30,000 h ^-1 ). Table 2 shows the experimental results.

Comparative Example 2 7.2 g of a silver-based purifying material prepared in the same manner as in Comparative Example 1
The sample was set in a reaction tube, and evaluated using the gas having the composition shown in Table 1 under the same conditions as in Example 1 (space velocity: about 15,000 h ^-1 ). Table 2 shows the experimental results.

Table 2 Removal rates of nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) Reaction temperature Removal components Removal rate (%) (° C.) Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 300 NOx 70 72 68 26 50 CO 82 84 80 3 145 HC 61 63 60 25 30 350 NOx 79 83 78 78 42 65 CO 86 88 82 52 61 HC 65 67 63 27 38 38 400 NOx 90 95 9552 91 95 93 58 65 HC 78 80 82 34 34 450 450 NOx 94 98 97 60 84 CO 98 100 98 68 75 HC 82 84 85 85 58 61 500 NOx 76 73 75 50 75 75 CO 100 100 100 76 82 50 96 96 98 98 98 NOx 50 48 52 38 47 CO 100 100 100 82 82 HC 100 100 100 71 71 82 600 NOx 40 38 40 26 38 CO 100 100 100 100 88 96 HC 100 100 100 78 84

As shown in Table 2, as compared with Comparative Examples 1 and 2, Examples 1 to 3 show more effective removal of nitrogen oxides over a wide temperature range, and have higher carbon monoxide and hydrocarbons even in a low temperature range. Was obtained. Further, by using the silica / alumina composite oxide as the porous inorganic oxide of the first catalyst, the reduction in the removal rate by sulfur dioxide was small.

[0061]

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 indication B01J 23/28 ZAB A 23/30 ZAB A 23/42 ZAB A 23/44 ZAB A 23/46 ZAB A 301 A 311 A 23/50 ZAB A 23/52 ZAB A 27/10 ZAB A B01D 53/36 104 A

Claims (8)

[Claims] 1. A method for reducing and removing nitrogen oxides from a flue gas containing nitrogen oxides and oxygen in excess of a theoretical reaction amount for coexisting unburned components, and also oxidizing residual and unreacted carbon monoxide and hydrocarbons. In the exhaust gas purifying material to be removed, the porous inorganic oxide is added to the inorganic oxide in an amount of 0.2 to 0.2%.
15% by weight (in terms of silver element) of silver and / or a silver compound,
Or a first catalyst carrying a mixture thereof, and 0.5 to 30% by weight of the inorganic oxide in the porous inorganic oxide.
A second catalyst supporting an oxide of at least one element selected from the group consisting of W, V, and Mo (in terms of metal elements); Pt, Pd, Ru, Rh, Ir and
An exhaust gas purifying material comprising: a third catalyst supporting at least one element selected from the group consisting of Au. 2. The exhaust gas purifying material according to claim 1, wherein the purifying material includes the first catalyst, the second catalyst, and the third catalyst in order from an exhaust gas inflow side to an outflow side. Exhaust gas purifying material. 3. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is at least one selected from the group consisting of alumina alone or silica, titania and zirconia in the first catalyst. 50% by weight of oxide
The following contains alumina composite oxide, the second catalyst is titania alone, or alumina, zirconia, a titania composite oxide containing at least one oxide selected from the group consisting of silica, the third catalyst is alumina An exhaust gas purifying material, which is at least one oxide selected from the group consisting of, titania, zirconia, and silica. 4. The exhaust gas purifying material according to claim 1, wherein the purifying material is formed by coating the first, second, and third catalysts on the surface of a ceramic or metal substrate. An exhaust gas purifying material comprising: 5. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxides of the first, second and third catalysts are each 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 an oxide of silver, silver chloride,
An exhaust gas purifying material, which is at least one selected from the group consisting of silver sulfate and silver phosphate. 7. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide of the first catalyst is an alumina composite oxide comprising alumina and silica. Purifying material. 8. A method for reducing and removing nitrogen oxides from a flue gas containing nitrogen oxides and oxygen in excess of a theoretical reaction amount for coexisting unburned components, and also oxidizing residual and unreacted carbon monoxide and hydrocarbons. In the exhaust gas purifying method for removing, using the exhaust gas purifying material according to any one of claims 1 to 7, the exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and hydrocarbons and / or carbon are disposed upstream of the purifying material. Number 2
The oxygen-containing organic compound or the exhaust gas to which the fuel containing it is added is brought into contact with the purifying material at 150 to 600 ° C., thereby removing the nitrogen oxides by the reaction with the oxygen-containing organic compound in the exhaust gas. A method for purifying exhaust gas, comprising oxidizing and removing residual and unreacted carbon monoxide and hydrocarbons.