JPH08168650A - Material and method for purifying exhaust gas - Google Patents

Abstract

PURPOSE: To provide an exhaust gas purifying material which can efficiently reduce and remove nitrogen oxide from combustion exhaust gas containing oxygen in the quantities equal to or larger than theoretical reaction amount with respect to unburned components such as nitrogen oxide, carbon monoxide, hydrogen, hydrocarbon. CONSTITUTION: A first catalyt prepared by supporting 0.2-15wt.% (reduced value of silver element) of silver and/or silver compounds or a mixture thereof, as active species, on porous inorganic oxides and a second catalyst prepared by supporting 0.5-30wt.% (reduced value of silver element) of one kind or more of elements and/or compounds selected from the group consisting of copper and copper compounds, as active species, on porous inorganic oxides are mixed together to provide an exhaust gas purifying material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying material capable of effectively reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and excess oxygen, and a purification method using the same.

[0002]

2. Description of the Related Art Excessive combustion exhaust gas emitted from internal combustion engines such as automobile engines, combustion equipment installed in factories, household fan heaters, and the like is excessive. It contains nitrogen oxides such as nitric oxide and nitrogen dioxide together with oxygen. Here, "containing excess oxygen" means that the exhaust gas contains more oxygen than the theoretical amount of oxygen necessary to burn unburned components such as carbon monoxide, hydrogen, and hydrocarbons. I do. In the following, nitrogen oxide refers to nitric oxide and / or nitrogen dioxide.

[0003] This nitrogen oxide is one of the causes of acid rain and is a major environmental problem. Therefore, various methods for removing nitrogen oxides in exhaust gas discharged from various combustion equipments are being studied.

[0004] As a method for removing nitrogen oxides from a combustion exhaust gas containing excess oxygen, a selective catalytic reduction method using ammonia is used particularly for a large-scale fixed combustion device (a large-scale combustor in a factory or the like). Has been put to practical use.

However, in this method, ammonia used as a reducing agent for nitrogen oxides is expensive, and ammonia is toxic. Therefore, the nitrogen oxides in the exhaust gas must be removed so that unreacted ammonia is not discharged. There are problems that the amount of injected ammonia must be controlled while measuring the concentration, and that the apparatus generally becomes large.

As another method, there is a non-selective catalytic reduction method in which a nitrogen oxide is reduced by using a gas such as hydrogen, carbon monoxide, or a hydrocarbon as a reducing agent. In order to reduce and remove nitrogen oxides, it is necessary to add a reducing agent in an amount equal to or more than a theoretical reaction amount with oxygen in exhaust gas, and there is a disadvantage that a large amount of the reducing agent is consumed. For this reason, the non-selective catalytic reduction method is practically effective only for exhaust gas having a low residual oxygen concentration burned near the stoichiometric air-fuel ratio, and is not practical because of poor versatility.

In view of the above, a method has been proposed for removing nitrogen oxides by using a zeolite or a catalyst supporting a transition metal on the zeolite and adding a reducing agent having a theoretical reaction amount or less with oxygen in the exhaust gas (for example, Japanese Patent Application Laid-Open Publication No. H11-163873). No.63-100919, 63-28372
No. 7, JP-A No. 1-130735).

However, in these methods, effective removal of nitrogen oxides can be obtained only in a narrow temperature range, and in an exhaust gas containing water, the removal rate of nitrogen oxides is significantly reduced. In other words, it contains about 10% water,
It is difficult to effectively remove nitrogen oxides from exhaust gas from a vehicle or the like whose temperature changes greatly depending on operating conditions.

Accordingly, it is an object of the present invention to provide a method for producing nitrogen oxides, carbon monoxide, hydrogen, hydrocarbons and the like, such as combustion exhaust gas from a fixed combustion device and a gasoline engine, a diesel engine or the like, which burns under oxygen excess conditions. From combustion exhaust gas containing more than the theoretical reaction amount for unburned components,
An object of the present invention is to provide an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently reducing and removing nitrogen oxides.

[0010]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has found that an organic compound such as ethanol is converted to oxygen and nitrogen on a catalyst comprising a porous inorganic oxide carrying a silver component. Reacts with exhaust gas containing oxides to reduce nitrogen oxides to nitrogen gas in exhaust gas containing oxygen, moisture, sulfur dioxide, etc., and to generate nitrogen-containing compounds such as nitrites and ammonia and aldehydes as by-products I found that. Using an exhaust gas purifying material formed by mixing a copper-based catalyst and a silver-based catalyst that can effectively remove nitrogen oxides under exhaust gas conditions containing nitrogen-containing compounds and aldehydes such as generated nitrites and ammonia, If hydrocarbons and oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing them are added to the exhaust gas, and the exhaust gas is brought into contact with the above-mentioned purifying material at a specific temperature and space velocity, a wide temperature range is obtained. The present inventors have found that nitrogen oxides can be effectively removed, and have completed the present invention.

That is, the first exhaust gas purifying material of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen that is larger than the theoretical reaction amount of coexisting unburned components is a porous inorganic material. Silver and / or
Or 0.2 to 15% by weight of a silver compound or a mixture thereof
(A silver element-converted value), and one or more elements and / or compounds selected from the group consisting of copper and copper compounds as active species on a porous inorganic oxide.
It is characterized by being mixed with a second catalyst carrying 30% by weight (in terms of copper element).

A second exhaust gas purifying material of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than the theoretical reaction amount for coexisting unburned components is a porous inorganic material. A first catalyst in which silver and / or a silver compound or a mixture thereof is supported on the oxide as an active species in an amount of 0.2 to 15% by weight (in terms of silver element); One or more elements and / or compounds 0.5 to 30 selected from the group consisting of copper and copper compounds
Wt.% (In terms of copper element) and 5% by weight or less (in terms of metal element) of at least one element selected from the group consisting of an alkali metal element and a rare earth element and / or a metal oxide. It is characterized by being mixed with two catalysts.

Further, the third exhaust gas purifying material of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than the theoretical reaction amount of coexisting unburned components is a porous inorganic material. 0.2 to 15% by weight of silver and / or silver compound or a mixture thereof as an active species in the oxide
(A silver element-converted value), and one or more elements and / or compounds selected from the group consisting of copper and copper compounds as active species on a porous inorganic oxide.
30% by weight (in terms of copper element), W, V, Mo, Mn,
Characterized in that it is mixed with a second catalyst carrying 30% by weight or less (in terms of metal element) of an oxide or sulfate of at least one element selected from the group consisting of Nb and Ta. I do.

The exhaust gas purifying method of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than the theoretical reaction amount of coexisting unburned components uses the above exhaust gas purifying material, An exhaust gas purifying material is installed in the middle of the exhaust gas conduit, and hydrocarbons and / or
Alternatively, the exhaust gas to which the oxygen-containing organic compound is added is
The method is characterized in that the nitrogen oxides are removed by contacting the purification material at 00 ° C. and reacting with hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas.

Hereinafter, the present invention will be described in detail. The first exhaust gas purifying material of the present invention comprises a first catalyst in which silver and / or a silver compound or a mixture thereof is supported as an active species on a porous inorganic oxide; It is obtained by mixing with a second catalyst carrying at least one selected from the group consisting of copper and a copper compound as an active species.

The second exhaust gas purifying material of the present invention comprises a first catalyst comprising a porous inorganic oxide carrying silver and / or a silver compound or a mixture thereof as an active species, and a porous inorganic oxide. One or more elements and / or compounds selected from the group consisting of copper and copper compounds as active species in the oxide, and one or more elements and / or metal oxides selected from the group consisting of alkali metal elements and rare earth elements And a second catalyst carrying the above.

The third exhaust gas purifying material of the present invention comprises a first catalyst comprising a porous inorganic oxide carrying silver and / or a silver compound or a mixture thereof as active species, and a porous inorganic oxide. One or more elements and / or compounds selected from the group consisting of copper and copper compounds as active species in the oxide;
A mixture is prepared by mixing an oxide or a sulfate of at least one element selected from the group consisting of V, Mo, Mn, Nb, and Ta with a second catalyst.

[0018] In a preferred embodiment of the present invention, the first to the above
The third exhaust gas purifying material further comprises Pt, Pd, Ru, R
at least one selected from the group consisting of h, Ir and Au
It is preferred to have a third catalyst carrying the seed element. A mixed catalyst comprising the first catalyst and the second catalyst is disposed on the exhaust gas inflow side of the purifying material, and the third catalyst is disposed on the outflow side.

In another preferred embodiment of the present invention, the first to third exhaust gas purifying materials further include W, V, Mo,
Oxides or sulfates of at least one element selected from the group consisting of Mn, Nb, Ta, and Pt, Pd, Ru, R
at least one selected from the group consisting of h, Ir and Au
It is preferable to have a third catalyst that carries the seed element. A mixed catalyst comprising the first catalyst and the second catalyst is disposed on the exhaust gas inflow side of the purifying material, and the third catalyst is disposed on the outflow side.

In the present invention, the above-mentioned purifying material is installed in an exhaust gas conduit, and either hydrocarbon or an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing the same is added upstream of the purifying material installation position. The exhaust gas is brought into contact with the purifying material to reduce and remove nitrogen oxides in the exhaust gas.

A first preferred embodiment of the exhaust gas purifying material of the present invention is a purifying material obtained by coating a purifying material substrate with a catalyst comprising a porous inorganic oxide in the form of powder and carrying a catalytically active species. Examples of the ceramic material forming the base of the purifying material include porous materials such as γ-alumina and its oxides (γ-alumina-titania, γ-alumina-silica, γ-alumina-zirconia, etc.), zirconia, titania-zirconia, etc. A heat-resistant material having a large surface area can be used. When high heat resistance is required, it is preferable to use cordierite, mullite, alumina and a composite thereof. In addition, a known metal material can be used for the base of the exhaust gas purifying material.

The shape and size of the substrate of the exhaust gas purifying material
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.

A second preferred form of the exhaust gas purifying material of the present invention is a catalyst comprising a porous inorganic oxide in the form of a pellet or a granular powder carrying a catalytically active species, or a powder comprising a catalytically active species, respectively. It is a purifying material obtained by molding a porous inorganic oxide into pellets or granules into a casing having a desired shape.

The following catalyst is formed on the purifying material of the present invention. (1) First catalyst The first catalyst is formed by supporting silver and / or a silver compound or a mixture thereof on a porous inorganic oxide, and is formed on the inflow side of exhaust gas. Acts on oxide removal. The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate, silver phosphate, and the like, and is preferably one or more of silver oxide, silver chloride, and silver sulfate, More preferred are silver oxide and / or silver chloride. As the porous inorganic oxide, any one of alumina, titania, and zeolite or a composite or mixed oxide containing them can be used, but it is preferable to use alumina or a composite or mixed oxide of alumina. When a composite or mixed oxide of alumina is used, the content of alumina is preferably set to 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 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 preferable specific surface area of the porous inorganic oxide is 30 m ² /
g or more.

In the first catalyst, the amount of the silver component supported as an active species on the inorganic oxide such as γ-alumina is 0.2 to 15% by weight (100% by weight of the inorganic oxide). (Element conversion value). If the amount is less than 0.2% by weight, the removal rate of nitrogen oxides decreases. If the silver component is carried in an amount exceeding 15% by weight, the combustion of the hydrocarbon and / or the oxygen-containing organic compound itself tends to occur, and the nitrogen oxide removal rate is rather lowered. A preferable silver component loading is 0.5 to 1
2% by weight.

As a method for supporting silver on an inorganic oxide such as alumina, a known impregnation method, precipitation method, or the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, chloride, sulfate, carbonate, or the like, or an aqueous ammonia solution. Alternatively, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, dried, and then immersed again in an aqueous solution of ammonium chloride or ammonium sulfate. In the precipitation method, silver nitrate is reacted with ammonium halide to precipitate silver halide on the porous inorganic oxide. This is 50
After drying at about 150 ° C, especially about 70 ° C, 100 to 600
It is preferred to raise the temperature stepwise at a temperature of ° C. and to perform firing. Firing
It is preferable to carry out in air, under a flow of nitrogen containing oxygen or under a flow of hydrogen gas. When the treatment is performed under a hydrogen gas stream, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last.

When the silver component carried on the porous inorganic oxide using an aqueous solution of silver nitrate or the like is fired in an oxidizing atmosphere, the silver component forms a well-wetted, approximately circular aggregate with the inorganic oxide. It has been observed that In the purification material of the present invention,
The average diameter of the silver component aggregate is preferably set to 10 to 10000 nm. In general, the smaller the diameter of the silver component aggregate, the higher the reaction characteristics. However, if the average diameter is less than 10 nm, only the oxidation reaction of hydrocarbon and / or oxygen-containing organic compound as a reducing agent proceeds, Nitrogen oxide removal rate decreases. On the other hand, when the average diameter exceeds 10,000 nm, the reaction characteristics of the silver component are reduced, and the nitrogen oxide removal rate is reduced. The average diameter of a preferable silver component aggregate is 10 to 5000.
nm, more preferably 10 to 2000 nm. Here, the average means an arithmetic average.

When the form of the purifying material is the above-described first preferred embodiment, the thickness of the first catalyst provided on the purifying material base is generally the thickness of the base material and the thermal expansion characteristic of the catalyst. Often limited by differences. The thickness of the catalyst provided on the purifying material base is preferably 300 μm or less. With such a thickness, it is possible to prevent the purifying material from being damaged by thermal shock or the like during use. A method for forming a catalyst on the surface of the purifying material base is performed by a known wash coat 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 30
If it exceeds 0 g / liter, the removal characteristics do not increase so much and the pressure loss increases. More preferably, the first catalyst provided on the surface of the purifying material base is 50 to 2
00 g / liter.

(2) Second Catalyst The second catalyst comprises a porous inorganic oxide carrying catalytically active species. As the porous inorganic oxide, any one of alumina, titania, zeolite, silica, zirconia and the like, or a composite or mixed oxide containing them is used. Like the first catalyst, the specific surface area of the porous inorganic oxide is 10 m ² /
g or more.

In the first exhaust gas purifying material of the present invention, one or more elements and / or compounds selected from the group consisting of copper and copper compounds are used as the active species of the second catalyst. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the copper component is 0.5 to 30% by weight (value in terms of a metal element), and the preferable supported amount is 0.5 to 25% by weight (in terms of a metal element). It is.

In the second exhaust gas purifying material of the present invention, as the active species of the second catalyst, one or more elements and / or compounds selected from the group consisting of copper and a copper compound, and an alkali metal element A material supporting at least one element selected from the group consisting of rare earth elements and / or a metal oxide is used. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the copper component is 0.5 to 30% by weight (in terms of a metal element), and the supported amount of the alkali metal element and / or the rare earth element component is 5% by weight or less. (Metal element conversion value). The preferred loading of the copper component is 0.5 to 25% by weight (converted to metal element), and the preferred loading of the alkali metal element and / or rare earth element is 4% by weight or less (converted to metal element).
It is.

In the third exhaust gas purifying material of the present invention, as the active species of the second catalyst, at least one element and / or compound selected from the group consisting of copper and a copper compound;
An oxide or a sulfate of at least one element selected from the group consisting of V, Mo, Mn, Nb, and Ta is used.
Of W, V, Mo, Mn, Nb and Ta, it is preferable to use W and / or V. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the copper component is 0.5 to 30% by weight (in terms of a metal element), and the supported amount of the W component is 30% by weight.
The following are the values (in terms of metal elements). The preferred loading amount of the copper component is 0.5 to 25% by weight (in terms of a metal element),
The preferable loading amount of the system component is 25% by weight or less (in terms of a metal element).

For supporting the active species on the second catalyst, a known impregnation method, precipitation method, or the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, nitrate, acetate, sulfate or the like of the catalytically active species element. In the case of a copper component, an aqueous solution of copper acetate, copper sulfate, copper nitrate or the like is used.
In the case of W, V, Mo, Mn, Nb, and Ta, a porous inorganic oxide is used by immersing it in an aqueous solution of an ammonium salt, oxalate, or the like of each element. After drying at 50 to 150 ° C., particularly 70 ° C., the temperature is raised stepwise at 100 to 600 ° C. and firing is performed. This calcination is performed in air under a nitrogen stream containing oxygen. Also, metatitanic acid (hydrous titanium oxide) is used as a starting material instead of titania, and V, W, M
Carrying o is also an effective method. When zeolite is used as the inorganic oxide, it is effective to carry the zeolite by an impregnation method or a known ion exchange method.

When the form of the purifying material is the above-described first preferred embodiment, the thickness of the second catalyst provided on the purifying material base is preferably 300 μm or less. The amount of the second catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter of the purifying material base.

The first catalyst and the second catalyst are used as a mixture. The mixing can be performed, for example, by stirring the powders of both catalysts together. Further, when coating a molded article, the mixed catalyst can be used as a slurry.

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:
It is preferably 10 to 10: 1. When the ratio is less than 1:10 (the amount of the first catalyst is small), 150 to 600 ° C.
Over a wide temperature range, the purification rate of nitrogen oxides decreases overall. On the other hand, when the ratio exceeds 10: 1 and the amount of the second catalyst is small, nitrogen-containing compounds such as nitrites and ammonia cannot be effectively reduced to nitrogen, or the aldehyde formed on the first catalyst cannot be reduced to nitrogen. Not used effectively for oxide reduction. A more preferred weight ratio of the first catalyst to the second catalyst is 1:
5 to 10: 1.

(3) Third Catalyst The third catalyst comprises a porous inorganic oxide carrying catalytically active species and is formed on the exhaust gas outflow side, and acts to remove nitrogen oxides in a low temperature region. And at the same time, oxidize and remove carbon monoxide and hydrocarbons. As the porous inorganic oxide, it is preferable to use one or more oxides selected from the group consisting of alumina, titania, zirconia, silica, and zeolite, or a composite or mixed oxide thereof. Like the first catalyst, the specific surface area of the porous inorganic oxide is 10 m
It is preferably at least ² / g.

In a preferred embodiment of the present invention, the active species of the third catalyst is Pt, Pd, Ru, Rh, Ir and A
At least one element selected from the group consisting of u is used. Of Pt, Pd, Ru, Rh and Au, particularly P
It is preferable to use at least one of t, Pd and Au. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the platinum-based component is 0.01 to 5% by weight (in terms of a metal element). The preferable loading amount of the platinum component is 0.01 to 4% by weight (in terms of metal element). By using the third catalyst, harmful substances such as carbon monoxide, hydrocarbons, and SOF can be oxidized and removed.

In another preferred embodiment of the present invention, the active species of the third catalyst is W, V, Mo, Mn, Nb,
An oxide or a sulfate of at least one element selected from the group consisting of Ta and at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and Au are used. Of W, V, Mo, Mn, Nb, and Ta, W and / or V are preferably used, and Pt, Pd, Ru,
Among Rh and Au, it is particularly preferable to use at least one of Pt, Pd and Au. 1 porous inorganic oxide
Assuming that the weight is 00% by weight, the supported amount of the W-based component is 0.2 to 10% by weight (in terms of metal element), and the supported amount of the platinum-based component is 0.01 to 5% by weight (in terms of metal element). . The preferred amount of the W-based component is 0.2 to 9% by weight (in terms of a metal element), and the preferred amount of the platinum-based component is 0.01 to 9% by weight.
4% by weight (in terms of metal element). By using this third catalyst, harmful substances such as carbon monoxide, hydrocarbons, and SOF can be oxidized and removed, and the oxidation of sulfur dioxide can be suppressed by exhaust gas containing sulfur dioxide.

For loading the active species on the third catalyst, a known impregnation method, precipitation method or the like can be used. When the impregnation method is used, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, nitrate, acetate, sulfate, chloride, hexachlorometal acid, or dinitrodiamine metal compound of a catalytically active species element. In the case of W, V, Mo, Mn, Nb, and Ta, a porous inorganic oxide is used by immersing it in an aqueous solution of an ammonium salt, oxalate, or the like of each element. After drying at 50 to 150 ° C., particularly 70 ° C., the temperature is raised stepwise at 100 to 600 ° C. and firing is performed. This calcination is performed in air under a nitrogen stream containing oxygen. In addition, instead of titania, metatitanic acid (hydrous titanium oxide) is used as a starting material, and V,
Carrying W and Mo is also an effective method. When zeolite is used as the inorganic oxide, it is preferable to support the zeolite by an impregnation method or a known ion exchange method.

When the form of the purifying material is the first preferred embodiment described above, the thickness of the third catalyst provided on the purifying material base is preferably 300 μm or less. The amount of the third catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter based on the purifying material base.

The ratio of the weight of the mixed catalyst of the first catalyst and the second catalyst to the weight of the third catalyst (the ratio of the total weight of the porous inorganic oxide and the catalytically active species) is 1: 5. It is preferably set to 20: 1. When the ratio is less than 1: 5 (the amount of the mixed catalyst is small), the purification rate of nitrogen oxides generally decreases over a wide temperature range of 150 to 600 ° C. On the other hand, the ratio is 20: 1
If the third catalyst is less than the above, the oxidation characteristics of hydrocarbons, carbon monoxide, and SOF deteriorate. More preferably, the ratio of the weight of the mixed catalyst to the weight of the third catalyst is 1: 4 to 10: 1.
It is.

If the purifying material having the above-described structure is used, 150
In a wide temperature range of up to 600 ° C., good removal of nitrogen oxides can be performed even with an exhaust gas containing about 10% of moisture and sulfur oxides.

Next, the method of the present invention will be described. First, the exhaust gas purifying material is installed in the middle of the exhaust gas conduit.
When the third catalyst is used, a mixed catalyst of the first catalyst and the second catalyst is provided on the exhaust gas inflow side of the purifying material, and the third catalyst is provided in the exhaust gas conduit on the outflow side.

Although the exhaust gas contains ethylene, propylene and the like to some extent as residual hydrocarbons, the amount is generally not sufficient to reduce NOx in the exhaust gas. A compound, preferably an oxygen-containing organic compound or a reducing agent obtained by mixing the compound with a hydrocarbon fuel is introduced into the exhaust gas. The introduction position of the reducing agent
It is upstream from the position where the purifying material is installed.

As the hydrocarbon introduced from the outside, gaseous or liquid alkanes, alkenes and / or alkynes can be used under standard conditions. In particular, in the case of an alkane or alkene, it preferably has 2 or more carbon atoms. Specific examples of hydrocarbons that are liquid in the standard state include gas oil, cetane,
Examples include hydrocarbons such as heptane, kerosene, gasoline and the like.
Among them, hydrocarbons having a boiling point of 50 to 350 ° C are particularly preferable. As the oxygen-containing organic compound introduced from the outside, alcohols such as ethanol and isopropyl alcohol having 2 or more carbon atoms, or a fuel containing them can be used.

The amount of the hydrocarbon and / or oxygen-containing organic compound introduced from the outside is determined by the weight ratio (weight of the reducing agent to be added / weight).
(Weight of nitrogen oxides in the exhaust gas) is preferably 0.1 to 5. If the weight ratio is less than 0.1, the removal rate of nitrogen oxides does not increase. On the other hand, if it exceeds 5, fuel efficiency will be degraded.

When a fuel containing a hydrocarbon or an oxygen-containing organic compound is added, it is preferable to use gasoline, light oil, kerosene or the like as the fuel. In this case, the amount of the reducing agent is set such that the weight ratio (the weight of the reducing agent to be added / the weight of the nitrogen oxide in the exhaust gas) is 0.1 to 5 in the same manner as described above.

In the present invention, the space velocity of the mixed catalyst of the first catalyst and the second catalyst is 150,000 in order to efficiently promote the reduction and removal of nitrogen oxides by oxygen-containing organic compounds, hydrocarbons and the like. h ^-1 or less, preferably 100,000
h ^-1 or less. The space velocity of the third catalyst is 200,000h ^-1
Or less, preferably 150,000 h ^-1 or less.

Further, in the present invention, the temperature of the exhaust gas at the purification material installation site where the hydrocarbon and / or the oxygen-containing organic compound reacts with the nitrogen oxide is set to 150 to 600 ° C.
To keep. If the temperature of the exhaust gas is lower than 150 ° C., the reaction between the reducing agent and the nitrogen oxide does not proceed, and it is not possible to remove the nitrogen oxide satisfactorily. On the other hand, if the temperature exceeds 600 ° C., the combustion of the hydrocarbon and / or the oxygen-containing organic compound itself starts, and the reduction and removal of nitrogen oxides cannot be performed. The preferred exhaust gas temperature is from 200 to 550 ° C, more preferably from 300 to 550 ° C.

[0053]

The present invention will be described in more detail with reference to the following specific examples. Example 1 Commercially available silica-alumina powder (silica content 5% by weight,
The specific surface area (350 m ² / g) was immersed in an aqueous silver nitrate solution, taken out, and dried at 70 ° C. for 2 hours. Then, the temperature is gradually raised to 600 ° C. in the air, and then calcined for 5 hours to prepare a first catalyst carrying 3.1% by weight (in terms of metal element) of silver with respect to silica / alumina. did.

Powdered titania (specific surface area 35 m ² / g)
Immersed in an aqueous solution of copper sulfate for 20 minutes,
It dried at 100 degreeC and 120 degreeC for 2 hours each. Subsequently, the temperature is increased stepwise from 120 ° C. to 500 ° C. under a nitrogen stream containing 20% of oxygen, and calcined at 500 ° C. for 5 hours. 4.4% by weight of copper sulfate (converted to metal element) with respect to titania. Supported, and a copper-based catalyst (second catalyst) was prepared. After mixing 0.35 g of the first catalyst and 0.12 g of the second catalyst to form a slurry, a commercially available cordierite honeycomb formed body (diameter 2)
0 mm, length 13.2 mm, 400 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver- and copper-based exhaust gas purifying material.

The above purifying material was set in the reaction tube. 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 3.48 liters per minute (standard state) (the apparent space velocity was about 50, 000 h ^-1 ), and the temperature of the exhaust gas in the reaction tube is 3
Ethanol and nitrogen oxide were reacted while keeping the temperature in the range of 00 to 600 ° C.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured with a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 2 shows the results.

Table 1 Component concentration Nitric oxide 800 ppm Oxygen 10% by volume Ethanol 1560 ppm Sulfur dioxide 30 ppm Nitrogen Residual water 10% by volume (based on the total volume of the above components)

Example 2 A commercially available γ was prepared in the same manner as in Example 1 using an aqueous silver nitrate solution.
- to prepare a first catalyst to silver carrying alumina powder (specific surface area 200 meters ² / g) to 3.0 wt% (in terms of metal element value).

Next, a powdery zeolite (SiO ₂ / Al
The molar ratio of ₂ O ₃ is 27. ) Is impregnated with an aqueous solution of copper acetate to obtain a zeolite in which copper ions have been exchanged. Then, the zeolite is separated from the solution, and in air at 80 ° C, 100 ° C,
After drying at 120 ° C. for 2 hours, the temperature was increased stepwise from 120 ° C. to 400 ° C. under a nitrogen stream containing 20% of oxygen, and 5.19% by weight of copper (equivalent to a metal element) was supported on the zeolite. , A copper-based catalyst (second catalyst) was prepared. 0.35g
The first catalyst and 0.12 g of the second catalyst were mixed to form a slurry, and then coated on a commercially available cordierite honeycomb formed body (diameter 20 mm, length 13.2 mm, 400 cells / inch ² ). After drying, the mixture was baked stepwise to 600 ° C. to prepare a silver- and copper-based exhaust gas purifying material.

The above purifying material was set in a reaction tube. The same reaction conditions as in Example 1 (apparent space velocity was about 50,000
0 h ^-1 ), and was evaluated using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 3 In the same manner as in Example 2, an aqueous silver nitrate solution was used to prepare a commercially available powdery alumina powder (specific surface area: 200 m ² / g).
A first catalyst was prepared by supporting silver by weight (in terms of a metal element) by weight.

Powdered alumina (specific surface area: 200 m ² /
g) in copper nitrate, lanthanum nitrate, cesium nitrate aqueous solution
Immersed for 0 minutes and dried and calcined in the same manner as the second catalyst of Example 1, 10.0% by weight of copper based on alumina,
A copper-based catalyst (second catalyst) was prepared by carrying 0.4% by weight of lanthanum and 0.4% by weight of cesium (in terms of a metal element). After mixing and slurrying 0.35 g of the first catalyst and 0.12 g of the second catalyst, a commercially available cordierite honeycomb-shaped formed body (diameter 20 mm, length 13.2 mm,
400 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver and copper based exhaust gas purifying material.

The purifying material was set in the reaction tube. The same reaction conditions as in Example 1 (apparent space velocity was about 50,000
0 h ^-1 ), and was evaluated using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 4 Oxalic acid was added to vanadium pentoxide and dissolved by heating on a water bath, and then powdered titania (specific surface area: 35 m ² / g) was put into a cooled aqueous solution and immersed for 20 minutes. . Then, the titania was separated from the solution, and in air at 80 ° C.
It dried at 100 degreeC and 120 degreeC for 2 hours each. Subsequently, the temperature was increased from 120 ° C. to 500 ° C. in 5 hours under a nitrogen stream containing 20% oxygen over 5 hours, and calcined at 500 ° C. for 4 hours. A supported V-based catalyst was prepared. The V-based catalyst was immersed in an aqueous solution of copper sulfate for 20 minutes, dried and calcined in the same manner as in the second catalyst of Example 1, and 4.8% by weight of V oxide with respect to titania, and copper sulfate 4. 5% by weight (metal element conversion value)
, A copper-based, V-based catalyst (second catalyst) was prepared.
After 0.35 g of the first catalyst of Example 3 and 0.12 g of the second catalyst were mixed and slurried, a commercially available cordierite honeycomb-shaped formed body (diameter: 20 mm, length: 1)
3.2 mm, 400 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver- and copper-based exhaust gas purifying material.

The above purifying material was set in the reaction tube. The same reaction conditions as in Example 1 (apparent space velocity was about 50,000
0 h ^-1 ), and was evaluated using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 5 A powdery titania (specific surface area: 35 m ² / g) was immersed in a chloroplatinic acid aqueous solution for 20 minutes, dried in air at 80 ° C. for 2 hours, and dried at 120 ° C. for 2 hours in a nitrogen stream. 200-40
It was fired stepwise for 1 hour to 0 ° C. Then, the temperature was raised from 50 ° C. to 400 ° C. over 5 hours under a nitrogen stream containing 4% of hydrogen gas, and calcined at 400 ° C. for 4 hours. And then calcined at 500 ° C. for 5 hours to carry 1% by weight (converted to metal element) of Pt on titania to prepare a Pt-based catalyst (third catalyst). After slurrying 0.26 g of the third catalyst, a honeycomb formed body (diameter 20 mm, length 6.6 mm, 4 mm) similar to the silver- and copper-based purifying material of Example 1 was obtained.
00 cells / inch ² ), dried and fired under the same conditions to prepare a Pt-based purifying material (a purifying material coated with a third catalyst).

The silver and copper-based purifying material of Example 1 were set on the inflow side of the exhaust gas in the reaction tube, and the Pt-based purifying material was set on the outflow side. The same reaction conditions as in Example 1 (silver, copper-based purifying material, Pt
The apparent space velocity of the system purifying material is about 50,000,
It is 100,000h- ¹ . ) Was evaluated using a gas having the composition shown in Table 1. Table 2 shows the results.

Example 6 Powdery titania (specific surface area: 35 m ² / g) was immersed in a chloroplatinic acid aqueous solution for 20 minutes, dried in air at 80 ° C. for 2 hours, and dried at 120 ° C. for 2 hours in a nitrogen stream. 200-40
It was fired stepwise for 1 hour to 0 ° C. Then, the temperature was raised from 50 ° C. to 400 ° C. over 5 hours under a nitrogen stream containing 4% of hydrogen gas, and calcined at 400 ° C. for 4 hours. Until 5 hours, and calcined at 500 ° C. for 5 hours to carry 1% by weight (in terms of metal element) of Pt on titania. next,
In the same manner as in Example 4, 3.3% by weight (in terms of metal element) of an oxide of V was supported on the titania, and V and Pt were loaded.
A system catalyst (third catalyst) was prepared. After slurrying 0.26 g of the third catalyst, a honeycomb formed body (diameter 20 mm, length 6.6 m) similar to the silver- and copper-based purifying material of Example 1 was obtained.
m, 400 cells / inch ² ), and dried and fired under the same conditions to prepare a V, Pt-based purifying material (a purifying material coated with a third catalyst).

The silver and copper-based purifying material of Example 1 were set on the inflow side of the exhaust gas in the reaction tube, and the V and Pt-based purifying materials were set on the outflow side. The same reaction conditions as in Example 1 (the apparent space velocities of the silver, copper-based purifying material, and Pt-based purifying material were about 50, respectively)
000, 100,000 h ^-1 . ) Was evaluated using a gas having the composition shown in Table 1. Table 2 shows the results.

COMPARATIVE EXAMPLE 1 0.52 g of the first catalyst prepared in Example 2 was mixed with the same honeycomb formed body (diameter 20 mm, length 13.2 mm, 400
Cells / inch ² ), and dried and fired to prepare a silver-based purifying material. The silver-based purifying material was set in an exhaust gas conduit, and evaluated under the same reaction conditions as in Example 1 (the apparent space velocity was about 50,000 h ^-1 ) using a gas having a composition shown in Table 1. . Table 2 shows the results.

Table 2 Removal rate of nitrogen oxides (NOx) Removal rate of nitrogen oxides (%) Reaction temperature (° C.) 300 350 400 450 500 550 600 Example 1 34.8 53.2 68.1 64.5 60.4 55.3 54.3 Example 2 35.4 56.7 70.3 64.7 59.4 53.7 50.6 Example 3 35.6 54.7 68.5 64.7 60.4 56.8 54.3 Example 4 30.4 52.2 63.6 60.3 58.4 50.5 49.5 Example 5 27.7 47.8 59.7 54.0 50.4 47.8 46.7 Example 6 28.2 48.6 60.6 54.6 50.3 46.8 45.8 Comparative example 1 6.5 15.6 33.6 38.9 43.3 45.7 43.7

As can be seen from Table 2, in Examples 1 to 6, good removal of nitrogen oxides was observed in a wide exhaust gas temperature range as compared with Comparative Example 1 using only a silver catalyst.

[0073]

As described above in detail, the use of the exhaust gas purifying material of the present invention makes it possible to efficiently remove nitrogen oxides in exhaust gas containing excess oxygen in a wide temperature range. INDUSTRIAL APPLICABILITY The exhaust gas purifying material and the purification method of the present invention can be widely used for purifying exhaust gas of various types of combustors, automobiles and the like.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location B01J 23/50 A 23/78 A 27/055 A 29/072 A 29/076 A B01D 53/36 102 B 102 H

Claims (10)

[Claims] 1. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in excess of the theoretical reaction amount of coexisting unburned components, wherein the porous inorganic oxides are used as active species. 0.2 to 15% by weight of silver and / or a silver compound or a mixture thereof (in terms of silver element)
And one or more elements and / or compounds selected from the group consisting of copper and copper compounds as active species in a porous inorganic oxide on a porous inorganic oxide (copper element). An exhaust gas purifying material characterized by being mixed with a second catalyst carrying (converted value). 2. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than a theoretical reaction amount of coexisting unburned components, wherein the porous inorganic oxides are used as active species. 0.2 to 15% by weight of silver and / or a silver compound or a mixture thereof (in terms of silver element)
And one or more elements and / or compounds selected from the group consisting of copper and copper compounds as active species in a porous inorganic oxide on a porous inorganic oxide (copper element). Conversion value) and at least one element and / or metal oxide 5 selected from the group consisting of alkali metal elements and rare earth elements
An exhaust gas purifying material, which is obtained by mixing a second catalyst supporting at most 10% by weight (converted to a metal element). 3. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than a theoretical reaction amount of coexisting unburned components, wherein the porous inorganic oxides are used as active species. 0.2 to 15% by weight of silver and / or a silver compound or a mixture thereof (in terms of silver element)
And one or more elements and / or compounds selected from the group consisting of copper and copper compounds as active species in a porous inorganic oxide on a porous inorganic oxide (copper element). (Converted value) and an oxide or sulfate of at least one element selected from the group consisting of W, V, Mo, Mn, Nb, and Ta at 30% by weight or less (converted value of metal element). An exhaust gas purifying material characterized by being mixed with a second catalyst. 4. The exhaust gas purifying material according to claim 1, wherein said exhaust gas purifying material further comprises Pt, P
a third catalyst supporting at least one element selected from the group consisting of d, Ru, Rh, Ir, and Au (in terms of a metal element) in an amount of 0.01 to 5% by weight; An exhaust gas purifying material comprising: a mixed catalyst comprising the first catalyst and the second catalyst on an exhaust gas inflow side; and the third catalyst on an outflow side. 5. The exhaust gas purifying material according to claim 1, wherein the exhaust gas purifying material further comprises W, V, and M.
O, Mn, Nb, Ta oxide or sulfate of at least one element selected from the group consisting of Ta 0.2 to 10% by weight
(Converted to metal element), Pt, Pd, Ru, Rh, Ir
And a third catalyst carrying at least one element selected from the group consisting of Au and 0.01 to 5% by weight (in terms of a metal element) in the exhaust gas inflow side of the purification material. An exhaust gas purifying material comprising: a mixed catalyst comprising one catalyst and the second catalyst; and the third catalyst on an outflow side. 6. The exhaust gas purifying material according to claim 1, wherein the silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate and silver phosphate. The exhaust gas purifying material, wherein the copper compound is at least one selected from the group consisting of copper oxides, halides, and sulfates. 7. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is alumina, titania, zeolite, or a composite or mixed oxide containing them in the first catalyst. Product, the second catalyst is alumina, titania, zeolite, silica, a composite or mixed oxide containing any of them or zirconia, and the third catalyst is alumina, titania, zirconia, silica, any of zeolite or contains them An exhaust gas purifying material characterized by being a composite or mixed oxide. 8. The exhaust gas purifying material according to claim 1, wherein at least one of the first, second, and third catalysts is coated on a surface of a ceramic or metal substrate. An exhaust gas purifying material characterized in that it has been manufactured. 9. The exhaust gas purifying material according to claim 1, wherein at least one of the first, second and third catalysts is in the form of pellets or granules. Exhaust gas purifying material. 10. A method for reducing nitrogen oxides from a combustion exhaust gas containing the nitrogen oxides and oxygen that is larger than the theoretical reaction amount of unexisting unburned components using the exhaust gas purifying material according to claim 1. Description: In the exhaust gas purifying method for removing, the exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and the exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds are added on the upstream side of the purifying material is subjected to the purifying material at 150 to 600 ° C. Exhaust gas purifying method, wherein the nitrogen oxides are removed by contact with a hydrocarbon and / or an oxygen-containing organic compound in the exhaust gas.