JPH10165816A - Cleaning agent consisting of silver catalyst and silver, iron and copper catalyst for exhaust gas and cleaning method of exhaust gas using ethanol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove nitrogen oxide from a combustion exhaust gas containing a larger amt. of oxygen than the stoichiometric amt. by depositing a specified amt. of one or more kinds selected from silver and silver compds. on a porous inorg. oxide to prepare first and second catalysts and depositing each specified amt. of iron oxides and copper oxides on the second catalyst. SOLUTION: The first catalyst is prepared by depositing one or more kinds selected from silver and silver compds. on a porous inorg. oxide. the amt, of the silver component deposited is 0.2 to 15wt.% (calculated as silver element) to 100wt.% porous inorg. oxide. The second catalyst is prepared by depositing one ore more kinds selected from silver and silver compds. by 0.2 to 15wt.% (calculated as silver element) and iron oxides and copper oxides by each 0.1 to 30wt.% (calculated as each metal element) on 100wt.% porous inorg oxide. The first and second catalysts are disposed in a conduit for exhaust gas in such a manner that the first catalyst is arranged in the entrance side of the cleaning material for the exhaust gas where the gas flows and that the second catalyst is disposed on the exit side of the flow.

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 simply referred to as ethanol). 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 called NOx) such as nitric oxide and nitrogen dioxide together with excess oxygen. Here, nitrogen oxides (NOx) refer to nitric oxide and / or nitrogen dioxide, and “containing excess oxygen”
This 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.

[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.

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, a catalyst for catalytic reduction of nitrogen oxides by a hydrocarbon comprising a metal oxide such as titania or 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.

On the other hand, there has been proposed 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 (Japanese Patent Application Laid-Open No. H8-10574). 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. It is an object of the present invention 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 with respect to water and a method using the same.

[0010]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has found that an exhaust gas to which ethanol is added in an amount corresponding to the amount of nitrogen oxides contained in the exhaust gas is (1)
A catalyst in which a specific amount of silver and / or a silver compound is supported on a porous inorganic oxide; and (2) a specific amount of a silver component, an iron oxide, and a copper oxide on the porous inorganic oxide. By contacting the exhaust gas purifying material consisting of the supported catalyst with a specific temperature at a specific temperature, nitrogen oxides can be effectively removed, and the added ethanol is not released unreacted or incompletely reacted. Discovered and completed the present invention.

That is, the 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. 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 selected from the group consisting of silver and silver compounds in 100% by weight of a porous inorganic oxide. 0.2 to 15
% (In terms of silver element), and the second catalyst is (a) 0.1 to 30% based on 100% by weight of the porous inorganic oxide.
At least one selected from the group consisting of silver and silver compounds in terms of weight% (in terms of metal element), (b) 0.1-30% by weight (in terms of metal element) of iron oxide, and (c) 0 0.1 to 30% by weight (in terms of metal element) of copper oxide.

Further, the exhaust gas purifying method of the present invention is a method 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 is installed in the middle of an exhaust gas conduit, and ethanol not more than 5 times the weight of nitrogen oxides in the exhaust gas is added to the upstream side of the purifying material, and the exhaust gas is cooled at 150 to 650 ° C. The method is characterized in that the nitrogen oxides are removed by contacting with a purifying material, thereby reacting the nitrogen oxides with the ethanol.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. [1] Exhaust gas purifying material The 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 comprising (a) one or more members selected from the group consisting of silver and silver compounds, (b) an iron oxide, and (c) a copper oxide. The exhaust gas purifying material of the present invention has a first catalyst on the exhaust gas inflow side and a second catalyst on the outflow side.

(1) First Catalyst The first catalyst supports at least one member selected from the group consisting of porous inorganic oxide silver and silver compounds, and acts on nitrogen oxide removal in a wide temperature range. .

As the porous inorganic oxide, alumina alone or a composite or mixed oxide of any of titania, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and zeolite with alumina 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 exceeds 15% by weight, oxidation of the reducing agent 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 The second catalyst is a porous inorganic oxide comprising (a) one or more members selected from the group consisting of silver and silver compounds, (b) an iron oxide, and (c) ) Copper oxide.

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 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 0.1 to 30% by weight (in terms of silver element) based on 100% by weight of the porous inorganic oxide. If the amount is less than 0.1% by weight, the removal rate of nitrogen oxides decreases. If the silver component is carried in an amount exceeding 30% by weight, the reducing agent itself is likely to be oxidized, and the nitrogen oxide removal rate is rather lowered. The preferable loading amount of the silver component is 0.5 to 20% 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.

The amount of iron oxide supported is 10
As 0% by weight, 0.1 to 30% by weight (in terms of metal element). When the content is less than 0.1% by weight, the effect of supporting the iron oxide is not remarkable, and even when the amount of the iron oxide exceeds 30% by weight, the performance of removing nitrogen oxide is not improved. I can't see it. The preferred upper limit of the amount of iron oxide supported is 20% by weight.

The amount of copper oxide supported is 10
As 0% by weight, 0.1 to 30% by weight (in terms of metal element). If the amount is less than 0.1% by weight, the effect of supporting the copper oxide will not be remarkable, and even if the amount of the copper oxide exceeds 30% by weight, the nitrogen oxide removal performance will not improve. I can't see it. The preferred upper limit of the amount of copper oxide carried is 20% by weight.

As a method of supporting a silver component, an iron oxide, and a copper oxide on an inorganic oxide such as γ-alumina, a known immersion method, a 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 then dried at about 70 ° C.
It is preferable to raise the temperature stepwise at ~ 600 ° C and bake.
An aqueous metal salt solution or alcohol solution is reacted with ammonium halide by a precipitation method to precipitate as a halide on the porous inorganic oxide. This is 50-150 ° C,
In particular, it is preferable that after drying at about 70 ° C., the temperature is increased stepwise at 100 to 600 ° C. and firing is performed. Firing is performed in an oxygen atmosphere,
It is preferable to carry out the reaction under a nitrogen atmosphere or a hydrogen gas flow. 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.

By using the second catalyst, an organic oxide such as acetaldehyde or 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) 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 Purifying Material for Exhaust Gas A first preferable 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 used in combination. Examples of the ceramic material forming the base of the purifying material include heat-resistant ceramics having a large surface area such as alumina, zirconia, and titania-zirconia. When high heat resistance is required, it is preferable to use cordierite, mullite, alumina and a composite thereof. In addition, a known metal material can be used for the base of the exhaust gas purifying material.

The shape and size of the substrate of the exhaust gas purifying material
Various changes can be made according to the purpose. 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.

[0029] 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.

When the form of the purifying material is the first preferred embodiment described above, 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, the amount of the catalyst is 300 g
When the pressure exceeds 1 / liter, the removal characteristics do not increase so much 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.

According to the following method using the purifying material having the above-described 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.

Ethanol is externally introduced into the exhaust gas as a reducing agent. The position where the reducing agent is introduced is upstream of the position where the purifying material is installed.

[0035] The amount of ethanol added to the exhaust gas is not more than 5 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 that the lower limit of the addition amount be 0.1 times.

[0036] In the present invention, in order to advance the reduction removal of nitrogen oxides with ethanol efficiently, 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 purification material installation site is set to 150 to 6
Keep at 50 ° C. 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 650 ° C., ethanol is burned, and the reduction and removal characteristics of nitrogen oxides are greatly reduced.

[0037]

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, a commercially available powdery γ-alumina (specific surface area: 200 m ² /
g) was loaded with 10% by weight of silver, 10% by weight of iron, and 5% by weight of copper (each converted to an element) to prepare a second catalyst. After slurrying 0.26 g of the second catalyst, it was coated on a honeycomb formed body (diameter 20 mm, length 8.3 mm, 200 cells / inch ² ) in the same manner as the silver-based purifying material, and dried to 600 ° C. By firing stepwise, a silver, iron and copper based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst) was prepared.

A silver-based purifying material is provided on the exhaust gas inflow side in the reaction tube,
Silver, iron, and copper-based purifying materials were set on the outflow side. Next, Table 1
Gas (nitrogen monoxide, oxygen, ethanol, sulfur dioxide, nitrogen and water) at a flow rate of 4.35 liters per minute (standard condition) (at this time, the space velocity of the silver-based purifying material is 50,000). an h ^-1, silver, iron, space velocity of the copper-based purification material is 100,000 h ^-1.), the exhaust gas temperature in the reaction tube maintained at a range of 350 to 600 ° C., the reaction of ethanol and nitrogen oxides I let it.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured by a chemiluminescent nitrogen oxide analyzer, and the removal rate of nitrogen oxides was determined. 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, 4% by weight of a 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, a commercially available powdered silica-alumina (silica content 3% by weight, specific surface area 350 m ² /
g) was loaded with 5% by weight of silver, 15% by weight of iron, and 4% by weight of copper (each converted in terms of element) to prepare a second catalyst.
After slurrying 0.26 g of the second catalyst, a honeycomb-shaped formed body (diameter 20 mm, length 8.
3 mm, 200 cells / inch ² ) and after drying 6
It was fired stepwise to 00 ° C. to prepare a silver-, iron-, and copper-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst).

The silver-based purifying material was set on the inflow side of the exhaust gas in the reaction tube, and the silver, iron and copper-based purifying materials were 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 was 4.35 liters per minute (standard state), the space velocity of the silver-based purifying material was 50,000 h- ¹ , and the silver, iron, and copper-based materials were used). The space velocity of the purifying material was 100,000 h ^-1 ), the temperature of the exhaust gas in the reaction tube was kept in the range of 350 to 600 ° C., and 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 oxides and the concentration of acetaldehyde in the gas after passing through the reaction tube were measured, and the removal rate of nitrogen oxides was determined. Table 2 shows the results.

Table 2 Removal rate of nitrogen oxides (%) and concentration of acetaldehyde (ppm) (1) Removal rate of nitrogen oxides (%) Exhaust gas temperature Example 1 Example 2 Comparative example 1 350 ° C. 32 31 30 400 ° C. 57 56 45 450 ° C. 88 86 74 500 ° C. 86 85 72 550 ° C. 77 75 70 600 ° C. 60 59 60 (2) Acetaldehyde concentration (ppm) exhaust gas temperature Example 1 Example 2 Comparative example 1 350 ° C. 350 310 1600 400 ° C. 43 45 234 450 ° C 00 16 500 ° C 0 0 0 550 ° C 0 0 0 0 0 600 ° C 0 0 0

As can be seen from the above, in Examples 1 and 2, 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 produced in the low exhaust gas temperature range was low. . on the other hand,
In Comparative Example 1 having no silver, iron, or copper-based catalyst (second catalyst) and only a silver-based catalyst, the removal rate of nitrogen oxides decreased over the entire exhaust gas temperature range, and a large amount of acetaldehyde was removed in a low exhaust gas temperature range. Generation was seen.

[0050]

As described above in detail, according to the purifying material and the method of the present invention, nitrogen oxides in exhaust gas containing excess oxygen can be efficiently removed, and the amount of added reducing agent can be reduced. Generation of complete reactants 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.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI B01D 53/36 102H

Claims (6)

[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 at least one member selected from the group consisting of silver and a silver compound in an amount of 0.2 to 15% by weight (in terms of silver element), and the second catalyst comprises 100% by weight of a porous inorganic oxide.
(A) at least one member selected from the group consisting of silver and silver compounds in an amount of 0.1 to 30% by weight (in terms of a metal element);
1 to 30% by weight (in terms of metal element) of iron oxide;
(c) An exhaust gas purifying material which carries 0.1 to 30% by weight (in terms of metal element) of copper oxide. 2. 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 purification material. 3. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxides of the first catalyst and the second catalyst are each composed of alumina alone, titania, silica, zirconia, zinc oxide, An exhaust gas purifying material, which is a composite or mixed oxide of any one of tin oxide, magnesium oxide and zeolite with alumina. 4. 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. 5. 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. 6. 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 for coexisting unburned components.
The exhaust gas purifying material according to any one of Items 1 to 5, wherein the exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and an amount of ethanol equal to or less than 5 times the weight of nitrogen oxides in the exhaust gas is provided on the upstream side of the purifying material. Adding the exhaust gas to the purification material at 150 to 650 ° C., thereby reacting the nitrogen oxide with the ethanol to remove the nitrogen oxide.