JPH0857264A - Exhaust gas purifying material and method therefor - Google Patents

Abstract

PURPOSE: To efficiently remove NOx , CO and HC from exhaust gas by constituting an exhaust gas purifying material from a first catalyst obtained by supporting a silver component on porous inorg. oxide, a second catalyst obtained by supporting oxide of W or the like on porous inorg. oxide and a third catalyst obtained. by supporting platinum or the like on porous inorg. oxide and arranging the first catalyst on an exhaust gas inflow side while arranging the second and third catalysts on an exhaust gas outflow side. 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. The first catalyst is arranged on an exhaust gas inflow side and the mixed catalyst of the second and third catalysts is arranged on an exhaust gas outflow side. Porous inorg. oxide is alumina composite oxide in the first catalyst and titania composite oxide in the second catalyst.

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.

Therefore, the present inventors have provided a silver-based catalyst on the exhaust gas inflow side and a W, V platinum-based catalyst on the outflow side, and can effectively remove nitrogen oxides even in an exhaust gas containing 10% moisture. At the same time, a purifying material capable of removing carbon monoxide and hydrocarbons was previously proposed (Japanese Patent Application No. 6-85770). However, it has been found that in the exhaust gas in which the sulfur oxide is present, the silver component tends to be sindered, the surface area of the catalytically active species is reduced, and the nitrogen oxide removal rate is reduced.

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 gasoline engines, diesel engines, and the like, which burn in a fixed combustion apparatus and 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.

[0009]

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. A catalyst containing a W-based component and a catalyst containing a platinum-based component are mixed, and an exhaust gas purifying material formed by combining the silver-based catalyst and the mixed catalyst is used. Adding any one or more of oxygen-containing organic compounds or a fuel containing them;
By contacting the exhaust gas with the above-mentioned purifying material at a specific temperature and space velocity, it has been discovered that even in an exhaust gas containing sulfur oxides, nitrogen oxides can be effectively removed in a wide temperature range, and the present invention completed.

That is, the exhaust gas purifying material of the present invention comprises a porous inorganic oxide containing 0.2 to 15% by weight of the inorganic oxide.
A first catalyst supporting silver and / or a silver compound thereof (in terms of silver element) or a mixture thereof, and 0.5 to 30% by weight of the inorganic oxide (metal A second catalyst supporting an oxide of at least one element selected from the group consisting of W, V, and Mo
The porous inorganic oxide carries at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and Au in an amount of 5% by weight or less (in terms of a metal element) of the inorganic oxide. Exhaust gas purification comprising a third catalyst comprising: a first catalyst on an exhaust gas inflow side; and a mixed catalyst comprising a mixture of the second catalyst and the third catalyst on an exhaust gas outflow side. In the material, the porous inorganic oxide is an alumina composite oxide containing 50% by weight or less of at least one oxide selected from the group consisting of silica, titania, and zirconia in addition to alumina in the first catalyst, The second catalyst is titania alone, or a titania composite oxide containing at least one oxide selected from the group consisting of alumina, zirconia, and silica, and the third catalyst is alumina, titania, zirconia, or silica. Is at least one oxide of selected from the group consisting, thus characterized in that it can remove nitrogen oxides in an exhaust gas sulfur oxides are present.

[0011] Further, while reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides, oxygen in excess of the theoretical reaction amount for co-existing unburned components, and sulfur oxides,
The exhaust gas purifying method of the present invention for oxidizing and removing residual and unreacted carbon monoxide and hydrocarbons is also provided, wherein the exhaust gas purifying material is provided in the middle of the exhaust gas conduit, and the exhaust gas purifying material is provided in the middle of the exhaust gas conduit, Hydrocarbons and / or upstream of the purification material
Alternatively, an exhaust gas to which an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing the same is added is brought into contact with the purifying material at 150 to 600 ° C, and the nitrogen oxide is thereby reacted with the oxygen-containing organic compound in the exhaust gas. It is characterized in that, in addition to removing substances, residual and unreacted carbon monoxide and hydrocarbons are also 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 exhaust gas purifying material of the present invention, 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. I do. 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 and the mixed catalyst of the second catalyst and the third catalyst may be coated on different positions of the same substrate, or may be used in combination after being coated on different substrates.

A second preferred embodiment of the exhaust gas purifying material of the present invention is a catalyst in which a catalytically active species is supported on a pellet, granular or powdery porous inorganic oxide, or a catalyst in which a catalytically active species is supported, respectively. It is a purifying material obtained by molding a powdered porous inorganic oxide into pellets or granules and filling the casing with 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, an alumina composite oxide composed of alumina and at least one oxide selected from the group consisting of porous silica, titania and zirconia, and the like can be used. However, a composite oxide composed of alumina and silica is preferably 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, an alumina oxide mixed with an inorganic oxide sol such as a silica sol, or a composite 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 above-mentioned 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 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 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 a difference in thermal expansion characteristics between the base material and the 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.

Further, 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 is formed by supporting a porous inorganic oxide with 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. . 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 purifying material base is made of a porous inorganic oxide such as titania, a predetermined amount of a W, V and / or Mo oxide can be carried on the porous inorganic oxide and used as the purifying material. 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 is a porous inorganic oxide which has 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 heat-resistant ceramics having a large surface area, such as a porous and large surface area, such as at least one oxide selected from the group consisting of alumina, titania, zirconia, silica, and zeolite. 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 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 equal to 20 parts of the purifying material base.
It is preferably from 300 to 300 g / liter.

The weight ratio of the second catalyst to the third catalyst (ratio of the total weight of the porous inorganic oxide and the catalytically active species) is 2:
The ratio is preferably set to 1 to 100: 1. 100: 1 ratio
(The amount of the third catalyst is small), it is 150-600 ° C.
Over a wide temperature range, the purification rate of nitrogen oxides decreases overall. On the other hand, if the ratio is less than 2: 1 and the amount of the second catalyst is small,
The removal rate of hydrocarbons and carbon monoxide decreases. More preferably, the weight ratio of the second catalyst to the third catalyst is 5: 1 to 80: 1.
It is.

In the present invention, the weight ratio of the first catalyst to the mixed catalyst (the ratio of the total weight of the porous inorganic oxide to the catalytically active species) is preferably from 10: 1 to 1: 5. preferable.
When the ratio is less than 1: 5 (the amount of the first catalyst is small), 1
In a wide temperature range of 50 to 600 ° C., the purification rate of nitrogen oxides is reduced as a whole. On the other hand, when the ratio exceeds 10: 1 and the amount of the mixed catalyst is small, the ammonia formed on the first catalyst does not react and is discharged as it is, and the removal rate of carbon monoxide and hydrocarbon is reduced. 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-described structure is used, 150
Good removal of nitrogen oxides can be performed in a wide temperature range of up to 600 ° C.

Next, the method of the present invention will be described. First, the exhaust gas purifying material is installed in the exhaust gas conduit so that the first catalyst faces the exhaust gas inlet and the catalyst obtained by mixing the second catalyst and the third catalyst is at the exhaust gas outlet. .

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 carbon atoms having a carbon number of 2 are not provided. 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 hydrocarbon 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 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 of the catalyst obtained by mixing the second catalyst and the third catalyst is 150,000 h ^-1 or less, preferably 100,000 h ^-1 or less. If the space velocity of the mixed catalyst exceeds 150,000 h ^-1 , the oxidizing and removing properties of hydrocarbons, carbon monoxide, etc., deteriorate.

In the present invention, the temperature of the exhaust gas is maintained at 150 to 600 ° C. at the site where the purifying material is installed, which is the 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.

[0044]

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. (Specific surface area 50 m ² / g) 10 g was charged and immersed for 30 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 raised from 120 ° C. to 500 ° C. over 5 hours under a nitrogen stream containing 20% oxygen,
Baking at 0 ° C. for 4 hours, 9 wt% of W with respect to titania
(Converted to metal element) W-based purifying material (second catalyst)
Was prepared.

Further, powdery γ-alumina (specific surface area 2
0.2% by weight (converted to metal element) of platinum with respect to γ-alumina is supported on an aqueous solution of chloroplatinic acid at 60 m ² / g), dried, and calcined to 700 ° C. A third catalyst) was prepared.

The weight ratio of the second catalyst to the third catalyst is 40:
1 and slurried, and then 1.5
The mixture was molded into a pellet having a length of 2 to 3 mm and a mixed catalyst was prepared.

About 3.6 g of a silver catalyst and about 3.6 g of a mixed catalyst were set in the reaction tube on the inflow side of the exhaust gas and on the outflow side of the exhaust gas, respectively. 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. After flowing for 100 hours (the space velocity of the silver-based catalyst is about 30,000 h ^-1 and the space velocity of the mixed catalyst is about 30,000 h ^-1 ), the exhaust gas temperature in the reaction tube is set to 300.
The temperature was changed from 50 ° C. to 600 ° C. every 50 ° C., and ethanol and nitrogen oxide were reacted at each temperature.

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
Approximately 1.0 g (dry weight) of a catalyst in which silver chloride was supported at 4% by weight (in terms of silver element) by a precipitation method using an aqueous silver nitrate solution and ammonium chloride in 50 m ² / g), and a commercially available cordierite honeycomb shape was prepared. Molded body (diameter 30 mm, length about 12.
5 mm, 400 cells / inch ² ) and after drying 6
By baking stepwise to 00 ° C., a silver-based purifying material (a purifying material coated with a first catalyst) was prepared.

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
Dipped for 0 minutes, dried and fired under the same conditions as in Example 1, and
A system catalyst was prepared. The content of V ₂ O ₅ relative to titania was 5% by weight (in terms of metal element).

Then, powdered silica (specific surface area: 360 m
² / g) was loaded with 0.2% by weight of Pt using a chloroplatinic acid solution, dried and calcined to prepare a platinum catalyst.

A V-based catalyst and a platinum catalyst were mixed at a weight ratio of 20: 1 to form a slurry, and 1.0 g (dry weight) of the catalyst mixed with a similar honeycomb-shaped formed body (12.5 mm in length) was mixed. ) Coating, drying and firing were performed to prepare a purification material supporting the mixed catalyst.

A silver-based purifying material was set on the exhaust gas inflow side and a mixed purifying material was set on the exhaust gas outflow side in the reaction tube, and evaluated in the same manner as in Example 1 using gas having the composition shown in Table 1 (space of the silver-based purifying material). Speed about 30,000 h ^-1 , space velocity of mixed purification material about 3
000h- 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.
A supported catalyst was prepared (in terms of metal element). The W and V-based catalysts and the platinum catalyst of Example 2 were mixed at a weight ratio of 10: 1 to form a slurry, which was mixed with the same honeycomb-shaped formed body (12.5 mm in length) as in Example 2. 1.0 catalyst
g (dry weight), dried under the same conditions as in Example 2, and calcined to prepare a purification material supporting the mixed catalyst.

The silver-based purifying material of Example 2 was provided on the exhaust gas inflow side,
The mixed purifying material was set in the reaction tube on the outflow side of the exhaust gas, and evaluated with the gas having the composition shown in Table 1 under the same conditions as in Example 2 (the space velocity of the silver-based purifying material was about 30,000 h ^-1 , the mixed purifying material was used). The space velocity of the material is about 30,000 h ^-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 75 76 70 3145 HC 55 57 53 25 30 350 NOx 79 83 78 42 65 65 CO 81 84 78 52 52 61 HC 60 62 58 27 38 400 400 NOx 90 95 9552 86 84 82 58 65 HC 72 73 75 34 34 450 450 NOx 94 98 97 60 84 CO 90 96 92 68 75 HC 75 78 80 58 61 500 NOx 76 73 75 50 75 CO 100 100 100 76 82 50 96 96 98 98 98 NOx 50 48 52 38 7 CO 100 100 100 82 92 HC 100 100 100 71 82 600 NOx 40 38 40 26 38 CO 100 100 100 88 96 HC 100 100 100 78 84

As shown in Table 2, Examples 1 to 3 show more effective removal of nitrogen oxides over a wider temperature range than Comparative Examples 1 and 2, and a higher nitrogen oxide removal rate even at a low temperature range. It was observed.

[0062]

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.

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Claims (7)

[Claims] 1. A first material comprising a porous inorganic oxide carrying 0.2 to 15% by weight (in terms of silver element) of silver and / or a silver compound, or a mixture thereof, of the inorganic oxide. A catalyst, and a porous inorganic oxide containing 0.5 to 3 of the inorganic oxide.
A second catalyst supporting 0% by weight (in terms of a metal element) of an oxide of at least one element selected from the group consisting of W, V, and Mo; Pt, Pd, Ru, R in 5% by weight or less (metal element conversion value) of the product
h, Ir and a third catalyst carrying at least one element selected from the group consisting of Au, the first catalyst being provided on the exhaust gas inflow side, and the third catalyst being provided on the exhaust gas outflow side. In an exhaust gas purifying material having a mixed catalyst obtained by mixing a second catalyst and the third catalyst, the porous inorganic oxide includes:
The first catalyst is an alumina composite oxide containing 50% by weight or less of at least one oxide selected from the group consisting of silica, titania and zirconia in addition to alumina.
The second catalyst is titania alone, or a titania composite oxide containing at least one oxide selected from the group consisting of alumina, zirconia, and silica, and the third catalyst is a group consisting of alumina, titania, zirconia, and silica. An exhaust gas purifying material, which is at least one oxide selected from the group consisting of at least one oxide, and is capable of removing nitrogen oxides even in an exhaust gas containing sulfur oxides. 2. The exhaust gas purifying material according to claim 1, wherein the weight ratio of the second catalyst to the third catalyst is 2: 1 to 1
An exhaust gas purifying material having a ratio of 00: 1. 3. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide of the first catalyst is an alumina composite oxide composed of alumina 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 oxide 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 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. A method for reducing and removing nitrogen oxides from a flue gas containing nitrogen oxides, oxygen in excess of a theoretical reaction amount for coexisting unburned components, and sulfur oxides, and for removing residual and unreacted carbon monoxide. And an exhaust gas purifying method for oxidizing and removing hydrocarbons, wherein the exhaust gas purifying material according to any one of claims 1 to 6 is installed in the middle of an exhaust gas conduit, and carbonized upstream of the purifying material. Hydrogen and / or
Alternatively, an exhaust gas to which an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing the same is added is brought into contact with the purifying material at 150 to 600 ° C, and the nitrogen oxide is thereby reacted with the oxygen-containing organic compound in the exhaust gas. A method for purifying exhaust gas, comprising removing matter and oxidizing and removing residual and unreacted carbon monoxide and hydrocarbons.