JP2992629B2 - Exhaust gas purification material and exhaust gas purification method using ethanol - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for effectively removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and excess oxygen, and adding ethanol or ethanol to which water is added (hereinafter referred to as ethanol). TECHNICAL FIELD The present invention relates to an exhaust gas purifying material and a purifying method which are not discharged as unreacted or incompletely reacted.

[0002]

2. Description of the Related Art An internal combustion engine such as an automobile engine, a combustion device installed in a factory or the like, a stationary diesel engine for cogeneration,
Various combustion exhaust gases discharged from household fan heaters and the like contain nitrogen oxides (generally referred to as NOx) such as nitric oxide and nitrogen dioxide together with excess oxygen. Here, nitrogen oxides (NOx) are nitrogen monoxide and / or
Or, refers to nitrogen dioxide, "contains excess oxygen" means that the exhaust gas contains more oxygen than the theoretical amount of oxygen required to burn unburned components such as carbon monoxide, hydrogen, and hydrocarbons Means that.

[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 from 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.

[0006] As another method, there is a non-selective catalytic reduction method in which nitrogen oxides are 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 the theoretical reaction amount with oxygen in the 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, a catalyst for catalytic reduction of nitrogen oxides by a hydrocarbon comprising a metal oxide such as titania and alumina, a rare earth oxide and at least one of Ru, Rh, Pd, Ag and Pt has been proposed ( JP-A-4-27431). However, according to the experimental results of the present inventors, this catalyst has a low nitrogen oxide removal rate at a high space velocity, and particularly in a region where the exhaust gas temperature is low, the nitrogen oxide removal is low.

Further, a method of purifying an exhaust gas using hydrogen in an exhaust gas by supporting a noble metal element and molybdenum on a porous carrier has been proposed (JP-A-8-10574). However, in this method, although the nitrogen oxide removal rate is high in a region where the exhaust gas temperature is low, the nitrogen oxide removal ratio is extremely low in a temperature region of 300 ° C. or higher and contains carbon monoxide, unsaturated hydrocarbon, and the like. In the exhaust gas, the removal rate of nitrogen oxides is significantly reduced.

Accordingly, an object of the present invention is to provide an unburned fuel such as nitrogen oxides, carbon monoxide, and hydrocarbons, 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. An object of the present invention is to provide a purifying material capable of efficiently removing nitrogen oxides from a combustion exhaust gas containing oxygen in an amount equal to or more than a theoretical reaction amount, and a method using the same.

[0010]

Means for Solving the Problems In view of the above problems, as a result of diligent research, the present inventor has found that an exhaust gas to which an amount of ethanol corresponding to the amount of nitrogen oxides contained in the exhaust gas has been added is converted into (1) a porous material. A catalyst in which a specific amount of silver and / or a silver compound is supported on an inorganic oxide; and (2) a catalyst in which a specific amount of tin oxide or a tin oxide and a platinum-based element are supported on a porous inorganic oxide. If it is brought into contact with exhaust gas purifying material consisting of
The present inventors have found that nitrogen oxides can be effectively removed, and that added ethanol is not discharged as unreacted or incompletely reacted, and the present invention has been completed.

That is, the first exhaust gas purifying material of the present invention is an exhaust gas purifying material for removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than a theoretical reaction amount for coexisting unburned components. A first catalyst on the exhaust gas inflow side of the exhaust gas purifying material and a second catalyst on the outflow side, wherein the first catalyst is 100% by weight of a porous inorganic oxide;
Supports at least one element and / or compound selected from the group consisting of silver and silver compounds in an amount of 0.2 to 15% by weight (in terms of silver element), and the second catalyst comprises tin oxide. It is characterized by the following.

Further, the second exhaust gas purifying material of the present invention is an exhaust gas purifying material for removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than a theoretical reaction amount for coexisting unburned components. The exhaust gas purifying material has a first catalyst on an exhaust gas inflow side and a second catalyst on an outflow side, and the first catalyst is composed of silver and a silver compound in 100% by weight of a porous inorganic oxide. One or more elements selected from the group and / or
Alternatively, the second catalyst carries 0.2 to 15% by weight (in terms of silver element) of a compound, and the second catalyst comprises (1) 100 to 50% by weight of a porous inorganic oxide and (a) 0.1 to 50% by weight. % (In terms of metal element) of tin oxide and (b) 0.1% by weight or less (in terms of metal element) of at least one selected from the group consisting of Pt, Pd, Ru, Au and Ir (2) Tin oxide 10
0% by weight or less of 0.1% by weight (metal element conversion value) of Pt,
It is characterized by carrying at least one selected from the group consisting of Pd, Ru, Au and Ir.

Further, in the exhaust gas purifying method of the present invention, using the above exhaust gas purifying material, the exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and the amount of nitrogen oxide in the exhaust gas is measured upstream of the purifying material. Add 5 times or less ethanol and add 15
Contacting the exhaust gas with the purifying material at 0 to 650 ° C;
Thus, the nitrogen oxides are reacted with the ethanol to remove the nitrogen oxides.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. [1] Exhaust gas purifying material The first exhaust gas purifying material of the present invention comprises a first catalyst comprising a porous inorganic oxide carrying at least one member selected from the group consisting of silver and a silver compound; And a second catalyst made of a material.

The second exhaust gas purifying material of the present invention comprises a first catalyst comprising a porous inorganic oxide carrying at least one member selected from the group consisting of silver and a silver compound; The product carries (1) tin oxide and at least one selected from the group consisting of Pt, Pd, Ru, Au and Ir, or (2)
The second catalyst comprises at least one metal element selected from the group consisting of Pt, Pd, Ru, Au and Ir supported on tin oxide.

Both the first and second exhaust gas purifying materials of the present invention have a first catalyst on the exhaust gas inflow side and a second catalyst on the outflow side.

(1) First Catalyst The first catalyst comprises a porous inorganic oxide carrying at least one selected from the group consisting of silver and silver compounds, and is used for removing nitrogen oxides in a wide temperature range. Works.

As the porous inorganic oxide, alumina alone or a composite or mixed oxide of alumina with any one of titania, silica, zirconia, zinc oxide, tin oxide, magnesium oxide and zeolite can be used. Preferably, γ-alumina alone or a composite or mixed oxide of γ-alumina and any one of titania, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and zeolite is used. When an alumina-containing composite or mixed oxide is used, the alumina content is preferably 50% by weight or more. The use of alumina or a composite or mixed oxide of alumina improves the heat resistance and durability of the catalyst.

The specific surface area of the porous inorganic oxide is 10 m ^2.
/ G or more. Specific surface area is 10m ² / g
If it is less than 1, the contact area between the exhaust gas and the inorganic oxide becomes small, and good nitrogen oxides cannot be removed. More preferred specific surface area of the porous inorganic oxide is 30 m ² / g or more.

The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate and silver phosphate, and preferably at least one of silver oxide, silver chloride and silver sulfate. And more preferably silver oxide and / or silver chloride. The supported amount of the silver component is 0.2 to 15% by weight (in terms of silver element) based on 100% by weight of the porous inorganic oxide. 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, oxidation of ethanol itself is likely 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. The silver supported on the inorganic oxide is in a metal or oxide state in the temperature range of the exhaust gas, and can be easily converted into each other.

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. To prepare silver halide by the precipitation method, silver nitrate and ammonium halide are reacted to precipitate silver halide on the 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 calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream 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. In carrying silver on alumina, an alumina-based mixed or composite oxide, it is effective to use alumina hydrate such as boehmite as a starting material.

(2) Second catalyst (i) In the first exhaust gas purifying material of the present invention, the second catalyst comprises tin oxide. Tin oxide may be used alone or may be supported on a porous inorganic oxide.

As the porous inorganic oxide, alumina,
One kind of inorganic oxide selected from the group consisting of titania, silica, zirconia, zinc oxide, magnesium oxide and zeolite, or a composite or mixed oxide of two or more kinds can be used. Preferably, it is any one of γ-alumina, titania, zinc oxide and magnesium oxide, or a composite or mixed oxide thereof. Like the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

When supported on a porous inorganic oxide, the supported amount of tin oxide is 100% by weight of the inorganic oxide.
0.1 to 50% by weight (in terms of metal element). 0.1
If the content is less than 50% by weight, the effect of supporting the tin oxide will not be remarkable, and even if the content of the tin oxide exceeds 50% by weight, the performance of removing nitrogen oxides will not be improved. The preferred upper limit of the amount of supported tin oxide is 30% by weight, more preferably 15% by weight.

As a method for supporting tin oxide on an inorganic oxide such as γ-alumina, a known immersion method, precipitation method, or the like can be used. For example, in the impregnation method, after a porous inorganic oxide is immersed and supported in an aqueous solution of tin chloride, it is heated at 70 ° C.
After drying at about the same level, it is preferable to raise the temperature stepwise at 100 to 600 ° C. and bake. The firing is preferably performed in an oxygen atmosphere, a nitrogen atmosphere, or a hydrogen gas flow.

(Ii) In the second exhaust gas purifying material of the present invention,
The second catalyst is (1) tin oxide and P
t, at least one metal element selected from the group consisting of Pd, Ru, Au and Ir, or (2) tin oxide
It supports at least one metal element selected from the group consisting of Pt, Pd, Ru, Au and Ir.

As the porous inorganic oxide, alumina,
One type of inorganic oxide selected from the group consisting of titania, silica, zirconia, zinc oxide, magnesium oxide, and zeolite, or a composite or mixed oxide of two or more types can be used. Preferably, it is any one of γ-alumina, titania, zinc oxide, and magnesium oxide, or a composite or mixed oxide thereof. Like the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

When supported on a porous inorganic oxide, the supported amount of tin oxide is 0.1% based on 100% by weight of the inorganic oxide.
1 to 50% by weight (converted to metal element). If the content is less than 0.1% by weight, the effect of supporting tin oxide is not remarkable, and even if more than 50% by weight of tin oxide is supported,
No improvement in nitrogen oxide removal performance is observed. A preferred upper limit of the amount of supported tin oxide is 15% by weight.

Of Pt, Pd, Ru, Au or Ir, Pt, Pd or
It is preferable to use Ru. In particular, it is more preferable to use Pt or Pd. When supported on a porous inorganic oxide, when the porous inorganic oxide is 100% by weight, and when supported on a tin oxide, the tin oxide is 100% by weight, and Pt, Pd, Ru,
The total carrying amount of Au or Ir is set to 0.1% by weight or less (in terms of a metal element). Even if the supported amount exceeds 0.1% by weight, no improvement in the removal effect is observed. A more preferred loading is 0.0
Between 0.5 and 0.1% by weight.

A method for supporting tin oxide and Pt, Pd, Ru, Au or Ir on an inorganic oxide such as γ-alumina, or a method for supporting Pt, Pd, Ru, Au or Ir on a tin oxide includes: A known immersion method, precipitation method, or the like can be used. For example, in the impregnation method, a porous inorganic oxide is immersed and supported in an aqueous solution of nitrate or hydrochloride, and dried at about 70 ° C.
It is preferable to raise the temperature in a stepwise manner at 0 to 600 ° C. for firing. An aqueous metal salt solution or an ethanol solution is reacted with ammonium halide by a precipitation method to precipitate as a halide on the porous inorganic oxide. This is 50-150
After drying at about 70 ° C., particularly 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.

By using the second catalyst, an organic oxide such as acetaldehyde and a nitrogen-containing intermediate product generated by the first catalyst depending on exhaust gas conditions can act as a reducing agent to remove nitrogen oxides. Therefore, as a result, the generation of oxides such as aldehydes is suppressed, and the performance of removing nitrogen oxides is improved.

(3) The weight ratio of the first catalyst to the second catalyst The weight ratio of the first catalyst to the second catalyst (the ratio of the total weight of the porous inorganic oxide and the catalytically active species) is , 1: 10-20:
It is preferably set to 1. More preferably, the weight ratio of the first catalyst to the second catalyst is 1: 5 to 10: 1.

(4) Form of Exhaust Gas Purifying Material A first preferred embodiment of the purifying material used in the present invention is a purifying material obtained by coating the purifying material substrate with the first catalyst and the second catalyst, respectively. The first catalyst and the second catalyst may be supported on different portions of the same substrate, respectively, or may be supported on different substrates and combined. Alumina, as a ceramic material forming the base of the purifying material,
Heat-resistant porous materials having a large surface area, such as zirconia and titania-zirconia, may be used. When high heat resistance is required, it is preferable to use cordierite, mullite, alumina and a composite thereof. Further, 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. Also, as its structure,
Examples include a honeycomb structure type, a foam type, a three-dimensional network structure type made of a fibrous refractory, a granular form, a pellet form, and the like. An exhaust gas purifying material can be produced by coating the above substrate with a catalyst using a wash coat method, a sol-gel method, a powder method, or the like, and then sintering.

In a second preferred embodiment of the purifying material used in the present invention, the catalyst is a honeycomb structure type, a foam type, a plate type,
It is a purifying material obtained by sintering pellets or granules and then filling a desired shape of the casing.

In the case where the form of the purifying material is the above-described first preferred embodiment, the thickness of each catalyst provided on the purifying material base is generally limited by the difference in thermal expansion characteristics between the base material and the catalyst. Often done. 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. The method of forming each catalyst on the surface of the purifying material base is performed by a known wash coat method or the like.

The amount of each 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 g /
If it exceeds 1 liter, the removal characteristics are not so improved, and the pressure loss increases. More preferably, each catalyst provided on the surface of the purifying material base is 50 to 200 g / liter of the purifying material base.

When removing harmful substances such as hydrocarbons and carbon monoxide other than nitrogen oxides, Pt, Pd, Ru, Au and Ir are further added to the porous inorganic oxide behind the exhaust gas purifying material.
At least one element selected from the group consisting of 0.01
A purifying material comprising a platinum-based oxidation catalyst (third catalyst) supporting 5% by weight (in terms of metal element) can be arranged. When processing exhaust gas from diesel engines,
In order to suppress the oxidation of sulfur dioxide in the exhaust gas, instead of the platinum-based purifying material, W, V, M
O, an oxide of at least one element selected from the group consisting of Mn, Nb and Ta, 0.2 to 10% by weight (in terms of a metal element), and an oxide selected from the group consisting of Pt, Pd, Ru, Au and Ir W, platinum-based catalyst (third catalyst) supporting 0.01 to 5% by weight (converted to a metal element) of at least one element obtained
An exhaust gas purifying material consisting of In addition, the platinum-based component and the W-based component can be supported by a known method.

According to the following method using the purifying material having the above structure, in a wide temperature range of 150 to 650 ° C.
Good removal of nitrogen oxides can be performed.

[2] Exhaust Gas Purification Method Next, the method of the present invention will be described. The exhaust gas purifying material described above is installed in the exhaust gas conduit so as to have the first catalyst on the exhaust gas inflow side and the second catalyst on the outflow side.

The exhaust gas contains ethylene and propylene to some extent as residual hydrocarbons, and these hydrocarbons are used as a reducing agent for removing nitrogen oxides. If the amount of residual hydrocarbons in the exhaust gas is not sufficient to reduce NOx, ethanol is externally introduced into the exhaust gas as a reducing agent. The introduction position of the ethanol is upstream from the position where the purifying material is installed. Ethanol may be one having a high concentration or one to which water has been added.

[0042] The amount of ethanol added to the exhaust gas is not more than five times the weight of the nitrogen oxides in the exhaust gas. If it exceeds 5 times, the additive is often excessive, and unreacted ethanol remains in the exhaust gas, which is not preferable. Preferably, the amount of addition is four times or less the amount of nitrogen oxides. Further, it is preferable to set the lower limit of the addition amount to 0.1 times.

[0043] In the present invention, the reduction removal of nitrogen oxides with ethanol in order to proceed efficiently, the space velocity of the first catalyst 150,000H ^-1 or less, preferably 100,000 h ^-1
The space velocity of the second catalyst is 200,000 h ^-1 or less,
Preferably it is 150,000 h ^-1 or less. In the present invention,
The temperature of the exhaust gas at the purifying material installation site is set to 150 to 650.
Keep at ° C. If the temperature of the exhaust gas is lower than 150 ° C., the reaction between ethanol and nitrogen oxides does not proceed, and good nitrogen oxides cannot be removed. On the other hand, when the temperature exceeds 650 ° C., ethanol is burned, and the reduction and removal characteristics of nitrogen oxides are greatly reduced.

[0044]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A commercially available powdery γ-alumina (specific surface area: 200 m ² / g) was immersed in an aqueous silver nitrate solution, dried at 70 ° C., and dried in air.
The first catalyst (silver-based catalyst) was prepared by firing stepwise to 0 ° C. and supporting 4% by weight of silver (converted to silver element) with respect to γ-alumina. After slurrying 0.52 g of the first catalyst, it was coated on a commercially available cordierite honeycomb-shaped formed body (diameter: 20 mm, length: 16.6 mm, 200 cells / inch ² ), and dried in air at 80 ° C. for 3 hours. After drying for 1 hour
The temperature was raised stepwise from 00 ° C. to 600 ° C. and calcined at 600 ° C. for 3 hours to prepare a silver-based exhaust gas purifying material (a purifying material coated with a first catalyst).

Next, using a tin chloride aqueous solution, tin 2% by weight was added to commercially available powdery γ-alumina (specific surface area: 200 m ² / g).
(Equivalent to tin dioxide) and a second catalyst (tin-based catalyst)
Was prepared. After slurrying 0.26 g of the second catalyst, a honeycomb-shaped formed body (20 m in diameter) was made in the same manner as the silver-based purifying material.
m, length 8.3 mm, 200 cells / inch ² ), dried under the same conditions as above, and baked stepwise to 600 ° C to obtain a tin-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst). ) Was prepared.

A silver-based purifying material on the exhaust gas inflow side in the reaction tube;
A tin-based purifying material was set on the outflow side. Next, a gas (nitrogen monoxide, oxygen, ethanol, sulfur dioxide, nitrogen and moisture) having a composition shown in Table 1 was flowed at a flow rate of 4.35 liters per minute (standard state) (at this time, a silver-based purifying material was used). Has a space velocity of 50,000 h ^-1 and the tin-based purifying material has a space velocity of 100,000.
h ^-1 . ), The temperature of the exhaust gas in the reaction tube is set to 350 to 60
Ethanol and nitrogen oxide were reacted while keeping the temperature at 0 ° C.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured by a chemiluminescent nitrogen oxide analyzer to determine the removal rate of nitrogen oxides, and at the same time, the concentration of acetaldehyde was determined by gas chromatography. did. Table 2 shows the results
Shown in

Table 1 Concentration of components (dry basis) Nitric oxide 800 ppm Oxygen 10% by volume Ethanol 1560 ppm (3 times the mass of nitric oxide) Sulfur dioxide 30 ppm Nitrogen Residual moisture 10% by volume based on the above total volume

Example 2 In the same manner as in Example 1, an aqueous tin chloride solution was added to a commercially available powdery γ
-Add to alumina (specific surface area 200 m ² / g) and stir,
After forming a uniform slurry, an aqueous solution of dinitrodiamineplatinum was added, and the mixture was further stirred for 12 hours. After drying at 70 ° C., it is baked stepwise in the air to 600 ° C., and 1% by weight of tin (in terms of tin dioxide) and 0.01% by weight of platinum (in terms of platinum element) with respect to γ-alumina. Supported to prepare a second catalyst (tin-based catalyst). After slurrying 0.26 g of the second catalyst, a honeycomb formed body (diameter 20 mm, length 8.3 mm, 200 cells / inch) was prepared in the same manner as in Example 1.
² ) Coated, dried and baked to 600 ° C step by step,
A tin-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst) was 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 tin-based purifying material was set on the outflow side. Next, using the gas having the composition shown in Table 1, the same conditions as in Example 1 (the flow rate of 4.35 liters per minute (standard state), the space velocity of the silver-based purifying material was 50,000 h- ¹ , and the tin-based purifying material was used. The space velocity of the material was 100,000 h ^-1 ), and the temperature of the exhaust gas in the reaction tube was kept in the range of 350 to 600 ° C., and ethanol and nitrogen oxides were reacted.

In the same manner as in Example 1, the concentration of nitrogen oxides in the gas after passing through the reaction tube was measured with a chemiluminescent nitrogen oxide analyzer, and the nitrogen oxide removal rate was determined.
The acetaldehyde concentration in the gas was measured. Table 2 shows the results
Shown in

Example 3 In the same manner as in Example 1, 4% by weight of commercially available powdery silica-alumina (silica content: 3% by weight, specific surface area: 350 m ² / g) was prepared using an aqueous solution of silver nitrate and an aqueous solution of ammonium chloride. A first catalyst (silver-based catalyst) was prepared by carrying silver chloride (in terms of silver element value). After slurrying 0.52 g of the first catalyst, a commercially available cordierite honeycomb-shaped formed body (diameter 20 mm, length 16.6 mm, 200 cells /
² ), dried in air at 80 ° C for 3 hours, and then gradually heated to 100 ° C to 600 ° C,
For 3 hours to prepare a silver-based purifying material (a purifying material coated with a first catalyst).

Next, after slurrying 0.26 g of powdered tin chloride (specific surface area: 72 m ² / g), a honeycomb-shaped formed body (diameter: 20 mm, length: 8.3 mm,
200 cells / inch ² ), and after drying, firing stepwise to 600 ° C. to prepare a tin-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst).

A silver-based purifying material is provided on the inflow side of the exhaust gas in the reaction tube.
A tin-based purifying material was set on the outflow side. Next, using the gas having the composition shown in Table 1, the same conditions as in Example 1 (flow rate of 4.3 per minute) were used.
5 liters (standard condition), space velocity of silver-based purification material is 50,0
A 00h ^-1, the space velocity of the tin-based purification material was 100,000 h ^-1. ), The exhaust gas temperature in the reaction tube is set to 350 to 600.
While maintaining the temperature in the range of ° C., ethanol and nitrogen oxide were reacted.

In the same manner as in Example 1, the concentration of nitrogen oxide and the concentration of acetaldehyde in the gas after passing through the reaction tube were measured, and the removal rate of nitrogen oxide was determined. Table 2 shows the results.

Comparative Example 1 The silver-based purifying material of Example 1 was set in a reaction tube. next,
Using the gas having the composition shown in Table 1, the same conditions as in Example 1 (flow rate: 4.35 liters per minute (standard state), space velocity: 50,0
00h ^-1 . ), The temperature of the exhaust gas in the reaction tube is set to 350
Ethanol and nitrogen oxide were reacted while keeping the temperature in the range of -600 ° C.

In the same manner as in Example 1, the concentration of nitrogen oxide and the concentration of acetaldehyde in the gas after passing through the reaction tube were measured, and the removal rate of nitrogen oxide was determined. Table 2 shows the results.

Table 2 Removal rate of nitrogen oxide and concentration of acetaldehyde (1) Removal rate of nitrogen oxide (%) Exhaust gas temperature Example 1 Example 2 Example 3 Comparative Example 1 350 ° C. 35 32 32 30 400 ° C. 55 52 55 45 450 ° C. 85 78 82 74 500 ° C. 88 80 85 72 550 ° C. 76 72 75 70 600 ° C. 62 59 61 60 (2) Acetaldehyde concentration (ppm) exhaust gas temperature Example 1 Example 2 Example 3 Comparative Example 1 350 ° C. 337 100 320 1600 400 ° C. 32 0 35 234 450 ° C. 00 016 500 ° C. 00 000 550 ° C. 0 00 0 600 ° C. 0 0 0 0

As apparent from the above, in Examples 1 to 3, good removal of nitrogen oxides was observed at the exhaust gas temperature of 350 to 600 ° C., and at the same time, the amount of acetaldehyde generated in the low exhaust gas temperature range was low. Was. on the other hand,
In Comparative Example 1 in which there was no tin-based catalyst (second catalyst) and only the silver-based catalyst was used, the nitrogen oxide removal rate was reduced in the entire exhaust gas temperature range, and a large amount of acetaldehyde was generated in a low exhaust gas temperature range. Was.

[0060]

As described in detail above, according to the present invention,
Nitrogen oxides in the exhaust gas containing excess oxygen can be efficiently removed, and generation of incomplete reactants of the added ethanol can be suppressed. INDUSTRIAL APPLICABILITY The exhaust gas purifying material and method of the present invention can be widely used for removing nitrogen oxides contained in exhaust gas from various combustors, automobiles and the like.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI B01D 53/36 102A 102B 102C (56) References JP-A-9-122488 (JP, A) JP-A-8-1882931 (JP, A) JP-A-8-10574 (JP, A) JP-A-7-232036 (JP, A) JP-A-6-315635 (JP, A) JP-A-6-154613 (JP, A) JP-A-4 -27431 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 53/94 B01D 53/86 ZAB B01J 23/14 B01J 23/50 ZAB B01J 23/54

Claims (7)

(57) [Claims] 1. An exhaust gas purifying material for removing nitrogen oxides from a flue gas containing nitrogen oxides and oxygen which is larger than a theoretical reaction amount of coexisting unburned components, wherein a first gas is provided on an exhaust gas inflow side of the exhaust gas purifying material. And a second catalyst on the outflow side, wherein the first catalyst is a porous inorganic oxide 10
0% by weight carries 0.2 to 15% by weight (in terms of silver element) of at least one selected from the group consisting of silver and silver compounds, and the second catalyst comprises tin oxide. Exhaust gas purifying material. 2. An exhaust gas purifying material for removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen that is larger than a theoretical reaction amount of coexisting unburned components, wherein a first exhaust gas is provided on an exhaust gas inflow side of the exhaust gas purifying material. And a second catalyst on the outflow side, wherein the first catalyst is a porous inorganic oxide 10
0% by weight carries at least one member selected from the group consisting of silver and silver compounds in an amount of 0.2 to 15% by weight (in terms of silver element), and the second catalyst comprises (1) a porous inorganic material. Oxide 100
(A) 0.1 to 50% by weight (in terms of metal element) of tin oxide and (b) 0.1% by weight or less (in terms of metal element)
Or at least one metal element selected from the group consisting of Pt, Pd, Ru, Au and Ir, or (2) 0.1% by weight or less per 100% by weight of tin oxide (in terms of metal element) Value)
An exhaust gas purifying material characterized by carrying at least one metal element selected from the group consisting of Pt, Pd, Ru, Au and Ir. 3. The exhaust gas purifying material according to claim 1, wherein said silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate and silver phosphate. Exhaust gas purifying material. 4. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide of the first catalyst is alumina alone or titania, silica, zirconia, zinc oxide, tin oxide, A composite or mixed oxide of any of magnesium oxide and zeolite and alumina, wherein the porous inorganic oxide of the second catalyst is alumina,
An exhaust gas purifying material characterized by being one or more compound or mixed oxides selected from the group consisting of titania, silica, zirconia, zinc oxide, magnesium oxide and zeolite. 5. The exhaust gas purifying material according to claim 1, wherein the exhaust gas purifying material is coated on a surface of a ceramic or metal substrate. 6. The exhaust gas purifying material according to claim 1, wherein the exhaust gas purifying material is formed into any one of a honeycomb type, a foam type, a plate shape, a pellet shape, and a granular shape. Exhaust gas purifying material. 7. An exhaust gas purifying method for removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than a theoretical reaction amount with respect to co-existing unburned components.
7. The exhaust gas purifying material according to any one of items 1 to 6, wherein the exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and the amount of ethanol not more than 5 times the weight of nitrogen oxides in the exhaust gas is provided upstream of the purifying material. And contacting the exhaust gas with the purifying material at 150 to 650 ° C., thereby reacting the nitrogen oxides with the ethanol to remove the nitrogen oxides.