JPH08309190A - Combustion gas purifying material and purification of combustion gas - Google Patents

Abstract

PURPOSE: To efficiently reduce and remove nitrogen oxide from a combustion gas containing water and oxygen in amount exceeding the theoretical reaction quantity to react with unburned portion of carbon monoxide, hydrogen, etc., by specifying the compositions and contents of components of respective catalysts installed respectively in a waste gas flowing-in side and a flowing-out side of a waste gas purifying material. CONSTITUTION: A first catalyst consists of a porous inorganic oxide and 0.2-15wt.% of at least one element and/or compound selected from silver and silver compounds and 0.01-10wt.% (based on conversion to metal elements, hereafter as same) of at least one element selected from W, V, Mo, Mn, Nb, and Ta deposited on the inorganic oxide. Further, a second catalyst consists of a porous inorganic oxide and 0.5-30wt.% of at least one element and/or compound as an active species selected from copper, nickel, and silver and not more than 30wt.% of a compound of at least one element selected from W, V, Mo, Mn, Nb, and Ta deposited on the inorganic oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying material 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 carrying a transition metal on the zeolite and adding a reducing agent having a theoretical reaction amount or less with oxygen in exhaust gas (for example, Japanese Patent Application Laid-Open No. H11-157572). Kaisho 63-100919, 63-283727
No., Japanese Patent Application Laid-Open No. 1-130735). In addition, a method has been proposed in which a catalyst in which an alkaline earth metal and / or silver is supported on a carrier such as γ-alumina is used to decompose nitrogen oxides in exhaust gas while supplying a hydrocarbon gas (Japanese Patent Laid-Open No. Hei 4 (1990) -104). 35453
No. 6).

However, according to these methods, effective removal of nitrogen oxides can be obtained only in a narrow temperature range, and in the case of exhaust gas from a vehicle or the like which contains water and whose exhaust gas temperature greatly changes depending on operating conditions, The nitrogen oxide removal rate is significantly reduced.

Accordingly, it is an object of the present invention to provide a method for producing nitrogen oxides, carbon monoxide, hydrogen, hydrocarbons, and the like, such as combustion exhaust gas from 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 an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently reducing and removing nitrogen oxides from a combustion exhaust gas containing oxygen and water in an amount not less than a theoretical reaction amount with respect to an unburned component.

[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 on a catalyst comprising a porous inorganic oxide carrying a silver component and a W-based component. Reacts with exhaust gas containing oxygen and nitrogen oxides, reduces nitrogen oxides to nitrogen gas even in exhaust gas containing water, sulfur dioxide, etc., and nitrogen-containing compounds and aldehydes such as nitrites and ammonia as by-products. Was generated. Silver, nitrite produced by a W-based catalyst, one or more of copper, nickel, silver capable of effectively removing nitrogen compounds under exhaust gas conditions including nitrogen-containing compounds such as ammonia and aldehydes, and W-based components Using an exhaust gas purifying material obtained by combining the catalyst carrying the above with the silver-based catalyst, adding a hydrocarbon and any one of oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing them to the exhaust gas, It has been discovered that if exhaust gas is brought into contact with the above-mentioned purifying material at a temperature and a space velocity, nitrogen oxides can be effectively removed in a wide temperature range, and further, a platinum-based or platinum-based or W-based catalyst is provided at the rear of the purifying material. By arranging, it is possible to remove residual carbon monoxide, hydrocarbons and SOF (soluble organic components) in the exhaust gas. Particularly, by using platinum and a W-based catalyst, the exhaust gas containing sulfur dioxide can be removed. Stomach,
The inventors have found that the oxidation of sulfur dioxide can be suppressed, and 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 in an amount larger than the theoretical reaction amount for coexisting unburned components is a first catalyst and a first catalyst. A second catalyst, wherein the first catalyst comprises a porous inorganic oxide and one or more elements and / or compounds selected from the group consisting of silver and silver compounds.
~ 15 wt% (converted to silver element), W, V, Mo, M
a compound of at least one element selected from the group consisting of n, Nb, and Ta; and 0.01 to 10% by weight (in terms of a metal element) of the second catalyst. One or more elements and / or compounds selected from the group consisting of copper, nickel and silver as active species
% By weight (converted to metal element), W, V, Mo, Mn, N
b, a compound of one or more elements selected from the group consisting of Ta and 30% by weight or less (in terms of a metal element), and the first catalyst is discharged to the exhaust gas inflow side of the exhaust gas purifying material. Characterized in that it has the second catalyst on its side.

[0012] The 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 larger than the theoretical reaction amount of coexisting unburned components is a first catalyst, a second catalyst. And a third catalyst, wherein the first catalyst comprises a porous inorganic oxide and one or more elements and / or compounds selected from the group consisting of silver and silver compounds.
2 to 15% by weight (in terms of silver element), W, V, Mo, M
a compound of at least one element selected from the group consisting of n, Nb, and Ta; and 0.01 to 10% by weight (in terms of a metal element) of the second catalyst. One or more elements and / or compounds selected from the group consisting of copper, nickel and silver as active species
% By weight (converted to metal element), W, V, Mo, Mn, N
b, a compound of one or more elements selected from the group consisting of Ta and not more than 30% by weight (in terms of a metal element), and the third catalyst comprises Pt, Pd,
It carries at least one element selected from the group consisting of Ru, Rh, Ir, and Au in an amount of 0.01 to 5% by weight (in terms of a metal element), from the exhaust gas inflow side to the outflow side of the exhaust gas purifying material. It is characterized by having the first catalyst, the second catalyst and the third catalyst in order.

[0013] 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 for coexisting unburned components is a first catalyst, a second catalyst, And a third catalyst, wherein the first catalyst comprises a porous inorganic oxide and one or more elements and / or compounds selected from the group consisting of silver and silver compounds.
2 to 15% by weight (in terms of silver element), W, V, Mo, M
a compound of at least one element selected from the group consisting of n, Nb, and Ta; and 0.01 to 10% by weight (in terms of a metal element) of the second catalyst. One or more elements and / or compounds selected from the group consisting of copper, nickel and silver as active species
% By weight (converted to metal element), W, V, Mo, Mn, N
b, and a compound of 30% by weight or less (in terms of a metal element) of one or more elements selected from the group consisting of Ta, and the third catalyst comprises W, V, 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 at least one element selected from the group consisting of Au and 0.01 to 5% by weight (in terms of metal element), and the first exhaust gas purifying material in order from the exhaust gas inflow side to the exhaust side. , The second catalyst and the third catalyst.

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 and a second catalyst. It has the first catalyst on the exhaust gas inflow side and the second catalyst on the outflow side. The second and third exhaust gas purifying materials of the present invention comprise a first catalyst, a second catalyst and a third catalyst,
The exhaust gas purifying material includes the first catalyst, the second catalyst, and the third catalyst in order from the exhaust gas inflow side to 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 base with a catalyst comprising a powdery porous inorganic oxide carrying catalytically active species. As the ceramic material forming the base of the purifying material, cordierite, mullite, alumina and a composite thereof are preferably used. 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. The catalyst may be coated on the substrate using a wash coat method, a powder method, or the like, or a wash coat method, a sol
After coating the porous inorganic oxide using a gel method or the like, the catalytically active species can be supported using a known impregnation method, an ion exchange method, or 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 pellets, granules, powders, honeycombs or plates carrying a catalytically active species, or a catalyst. It is a purifying material obtained by molding a powdery porous inorganic oxide carrying each active species into pellets or granules and filling the resultant 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 composed of a porous inorganic oxide and one or more elements and / or compounds selected from the group consisting of silver and a silver compound, and W, V, Mo, Mn, Nb, and Ta. And a compound of at least one element selected from the group consisting of: formed on the inflow side of the exhaust gas and acts to remove nitrogen oxides in a wide temperature range. As a porous inorganic oxide,
Alumina alone or a composite or mixed oxide of any of titania, silica, zirconia, and zeolite with alumina can be used. 50% by weight alumina content
It is preferable to make the above. 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 dispersion of the silver component is reduced, and good removal of nitrogen oxides cannot be performed.
More preferable 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, 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 loading amount of the silver component is 0.5 to 12% by weight.
It is.

The compounds of W, V, Mo, Mn, Nb and Ta are at least one selected from the group consisting of oxides, halides and sulfates, and preferred compounds are oxides and / or sulfates. Assuming that the porous inorganic oxide is 100% by weight, the loading amount of the W-based component is 0.01 to 10% by weight.
(Metal element conversion value), and preferably 0.05 to 8% by weight (metal element conversion value).

As a method of supporting silver on an inorganic oxide such as alumina, a known impregnation method, precipitation method, or the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of 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. 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. This is 50 ~ 15
After drying at 0 ° C., especially 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 performing under a hydrogen gas stream, 30
The oxidation treatment is preferably performed at 0 to 650 ° C.

When the purifying material is in the above-described first preferred embodiment, the thickness of the first catalyst provided on the purifying material substrate generally depends on the thermal expansion characteristics of the substrate material and 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 is composed of a porous inorganic oxide and one or more elements and / or compounds selected from the group consisting of copper, nickel and silver as catalytically active species, and W, V , Mo, Mn, Nb,
And a compound of one or more elements selected from the group consisting of Ta. 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.
As zeolite, ferrierite, mortenite, Z
Various zeolites such as SM-5 can be used.
Similar to the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

Preferred combinations of copper, nickel and silver include copper alone or a combination of copper with nickel and / or silver. The nickel compound is at least one selected from the group consisting of oxides, halides, sulfates, and the like of nickel. The same silver compound as the above-mentioned first catalyst can be used. The copper compound is at least one selected from the group consisting of copper oxides, halides, sulfates and the like. 10 porous inorganic oxides
Assuming 0% by weight, the total carrying amount of copper, nickel and silver is 0.1%.
It is 5 to 30% by weight (converted to metal element), and the preferred total loading is 0.5 to 25% by weight (converted to metal element).

When the nickel component and the silver component are used at the same time, the weight ratio between the nickel element and the silver element is 1: 5 to 5: 1.
Similarly, the weight ratio between the nickel element and the copper element is 1: 5.
５5: 1, and the weight ratio of silver element to copper element is 1: 5
The ratio is preferably 5: 1.

The compounds of W, V, Mo, Mn, Nb and Ta are at least one selected from the group consisting of oxides, halides and sulfates, and preferred compounds are oxides and / or sulfates. Assuming that the porous inorganic oxide is 100% by weight, the loading amount of the W-based component is 30% by weight or less (in terms of a metal element), preferably 0.05 to 20% by weight.
(Metal element conversion value).

The active species can be supported by a known impregnation method, precipitation method,
An ion exchange method or the like can be used. First, a W-based component is supported, dried at 50 to 150 ° C., particularly 70 ° C., and then dried.
After the temperature is increased stepwise at 0 to 600 ° C. and calcined, copper, nickel and silver components are supported, and further 50 to 150 ° C., particularly 7
After drying at 0 ° 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. 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 copper, nickel and silver components, 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. 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 effective to carry the zeolite by an impregnation method or a known ion exchange method. The loading of the silver catalyst can be carried out in the same manner as in the first catalyst.
On the second catalyst thus prepared, silver, nickel,
Copper is present in the form of one or more of silver, nickel, copper or oxides, halides, and sulfates thereof, respectively.

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

In the case where the form of the purifying material is the above-described first preferred form, 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 based on the purifying material base.

(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 the second exhaust gas purifying material of the present invention, at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au is used as the active species of the third catalyst. Among Pt, Pd, Ru, Rh and Au, it is particularly preferable to use at least one of Pt, Pd and Au. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the platinum component is 0.01 to 5% by weight (in terms of a metal element).
It is. The preferable loading amount of the platinum component is 0.01 to 4% by weight (in terms of metal element).

In the third exhaust gas purifying material of the present invention, the active species of the third catalyst is W, V, Mo, Mn, Nb, Ta.
Oxides or sulfates of at least one element selected from the group consisting of: Pt, Pd, Ru, Rh, Ir, and Au
And at least one element selected from the group consisting of Of W, V, Mo, Mn, Nb and Ta, W and / or
Or V is preferably used, and Pt, Pd, Ru, Rh
And Au, it is particularly preferable to use at least one of Pt, Pd and Au. 100 porous inorganic oxides
In terms of% by weight, the loading amount of the W component is 0.2 to 10% by weight.
(In terms of metal element), and the supported amount of the platinum-based component is 0.1.
It is from 0.01 to 5% by weight (in terms of metal element). The preferable loading amount of the W-based component is 0.2 to 9% by weight (in terms of metal element).
The preferred amount of the platinum-based component is 0.01 to 4% by weight (in terms of a metal element).

By using a Pt-based or Pt / W-based catalyst, residual carbon monoxide, hydrocarbons, SOF and the like in exhaust gas can be effectively oxidized and removed. In particular, when a Pt or W-based catalyst is used, even in an exhaust gas containing sulfur dioxide, the oxidation of sulfur dioxide is suppressed, and residual carbon monoxide, hydrocarbons,
SOF and the like can be effectively oxidized and removed.

For supporting 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.

Ratio of the weight of the first catalyst to the weight of the third catalyst (ratio of the total weight of the porous inorganic oxide and the catalytically active species)
Is preferably 1: 2 to 20: 1. The ratio is 1:
When it is less than 2 (the amount of the first catalyst is small), the purification rate of nitrogen oxides decreases. On the other hand, when the ratio exceeds 20: 1 and the amount of the third catalyst is small, the oxidation characteristics of hydrocarbons, carbon monoxide, and SOF deteriorate. A more preferred ratio of the weight of the first catalyst to the weight of the third catalyst is from 1: 1 to 15: 1.

When the form of the purifying material is the above-described first preferred embodiment, 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.

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

Next, the method of the present invention will be described. First, in the first purifying material of the present invention, the exhaust gas purifying material is placed in the exhaust gas conduit such that the first catalyst is on the exhaust gas inflow side and the second catalyst is on the exhaust gas outflow side. In the second and third purifying materials of the present invention, the exhaust gas purifying material is placed in the middle of the exhaust gas conduit so as to become the first catalyst, the second catalyst, and the third catalyst in order from the exhaust gas inflow side to the exhaust gas outflow side. Install.

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 hydrocarbons 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.

[0047] In the present invention, oxygen-containing organic compound, the reduction and removal of nitrogen oxides in order to efficiently proceed by hydrocarbons and the like, the space velocity of the first catalyst 150,000H ^-1 or less, preferably 100,000 h ^{- 1} or less. The space velocity of the second catalyst is 150,000 h ^-1 or less, preferably 100,000 h ^-1 or less. The space velocity of the third catalyst 200,000 ^-1 or less, preferably 150,000H ^-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 250 to 550 ° C.

[0049]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A commercially available silica-alumina powder (silica content: 5% by weight, specific surface area: 350 m ² / g) was added to a solution in which ammonium tungstate was added to water, and oxalic acid was added to dissolve the solution. The silica / alumina powder was separated from the solution, heated to 600 ° C. in air in a stepwise manner, and calcined to prepare a catalyst carrying 3% by weight (converted to metal element) of tungsten. The catalyst was loaded with 3.1% by weight of silver (in terms of a metal element) using an aqueous silver nitrate solution. After drying, the catalyst was baked in air in a stepwise manner to 600 ° C. to form a first tungsten / silver loaded silver. A catalyst was prepared. 0.26g
After the first catalyst of the above was slurried, a commercially available cordierite honeycomb-shaped formed body (diameter 20 mm, length 8.3 m)
m, 400 cells / inch ² ) and after drying 600
The mixture was baked stepwise to ℃ to prepare a W, silver-based exhaust gas purifying material (a purifying material coated with a first catalyst).

5 wt% of tungsten oxide is added to powdery silica / alumina in the same manner as in the above-mentioned method of loading silver on a silver catalyst.
(Supported metal element) After loading, using an aqueous solution of copper nitrate, 4.4% by weight of copper oxide (calculated as a metal element) was added to powdered silica / alumina in the same manner as in the case of supporting W and silver of a silver-based catalyst. ) To prepare a second catalyst. After slurrying 0.26 g of the second catalyst, the honeycomb-shaped formed body (diameter 20 mm, length 8.3 mm,
00 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a copper-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst).

A W- and silver-based purifying material was set on the inflow side of the exhaust gas in the reaction tube, and a copper-based purifying material was set on the outflow side. Next, a gas (nitrogen monoxide, oxygen, ethanol, nitrogen and water) 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 of each purification material was about 80,
000 h ^-1 ), and the temperature of the exhaust gas in the reaction tube is from 250 to
Ethanol and nitrogen oxide were reacted at a temperature of 550 ° 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 Nitrogen Residual water 10% by volume (based on the total volume of the above components)

Example 2 In the same manner as in Example 1, commercially available powdered alumina (specific surface area: 20%) was prepared using an aqueous solution of ammonium molybdate and silver nitrate.
0 m ² / g), 3.0% by weight (converted to metal element) of silver and 1% by weight (converted to metal element) of molybdenum are supported, dried, and fired stepwise in air to 600 ° C. Mo, a silver-based catalyst (first catalyst) was prepared. 0.26 g of the first catalyst was used in the same manner as in Example 1 to obtain a commercially available cordierite honeycomb-shaped molded product (diameter 20 mm, length 8.3 mm, 40
0 cells / inch ² ) to prepare a Mo, silver-based exhaust gas purifying material (a purifying material coated with a first catalyst).

In the same manner as in Example 1, 3.3% by weight of a vanadium oxide (in terms of a metal element) was loaded on a commercially available alumina powder (specific surface area: 200 m ² / g) using ammonium vanadate, and then nitric acid was added. Using an aqueous copper solution, 7% by weight of copper (in terms of a metal element) was supported in the same manner as in Example 1 to prepare a second catalyst. After slurrying 0.26 g of the second catalyst, a honeycomb formed body (diameter 20 mm, length 8.3 mm, 400 cells / inch) was prepared in the same manner as in Example 1.
² ) Coated, dried and baked to 600 ° C step by step,
A copper-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst) was prepared.

Mo and silver-based purifying materials were set on the inflow side of the exhaust gas in the reaction tube, and copper-based purifying materials were set on the outflow side. Evaluation was performed using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity of each purification material was about 80,000 h ^-1 ). Table 2 shows the results.

Example 3 In the same manner as in Example 1, commercially available alumina powder (specific surface area 2
After carrying 1.2% by weight (in terms of metal element) of an oxide of vanadium using ammonium vanadate on a surface area of 100 m ² / g), 3.0% by weight (in terms of metal element) of silver was used using an aqueous silver nitrate solution. After drying, 6
It was calcined to 00 ° C. to prepare a vanadium-silver catalyst (first catalyst). 0.26 g of the first catalyst was used in the same manner as in Example 1 to obtain a commercially available cordierite honeycomb formed body (20 mm in diameter, 8.3 mm in length, 400 cells / inch).
² ) to prepare a vanadium / silver exhaust gas purifying material (a purifying material coated with the first catalyst).

After 4% by weight (in terms of a metal element) of tungsten sulfate was supported on powdered titania (specific surface area: 35 m ² / g) using an aqueous solution of tungsten sulfate, it was immersed in an aqueous solution of silver sulfate and copper sulfate for 20 minutes. 0.5% by weight copper sulphate,
A second catalyst was prepared by supporting 2.5% by weight of silver sulfate (each converted to a metal element). After slurrying 0.26 g of the second catalyst, it was coated on a honeycomb formed body (20 mm in diameter, 8.3 mm in length, 400 cells / inch ² ) in the same manner as in Example 1, and dried to 600 ° C. Then, a copper- and silver-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst) was prepared.

Vanadium, on the inflow side of the exhaust gas in the reaction tube,
A silver-based purifying material and copper and silver-based purifying materials were set on the outflow side. Evaluation was performed using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity of each purification material was about 80,000 h ^-1 ). Table 2 shows the results.

Example 4 In the same manner as in Example 1, 4% by weight of a tungsten oxide was supported on powdered alumina, and then 4.4% by weight of copper and 7% by weight of copper oxide and nickel nitrate were used. A second catalyst was prepared by supporting nickel (each metal element converted value). After slurrying 0.26 g of the second catalyst, it was coated on a honeycomb-shaped formed body (diameter 20 mm, length 8.3 mm, 400 cells / inch ² ) in the same manner as in Example 1, dried, and stepwise cooled to 600 ° C. To prepare a copper- and nickel-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst).

Powdered titania (specific surface area 35 m ² / g)
Is immersed in chloroplatinic acid aqueous solution for 20 minutes,
Dried at 0 ° C. for 2 hours, under a nitrogen stream at 120 ° C. for 2 hours,
It was baked stepwise for 1 hour from 200 to 400 ° C. Then, under a nitrogen stream containing 4% of hydrogen gas, at 50 ° C. to 400 ° C.
And then calcined at 400 ° C. for 4 hours, and further heated to 50 ° C. to 500 ° C. under a nitrogen stream containing 10% oxygen.
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). 0.18g
After the third catalyst was made into a slurry, a honeycomb formed body (diameter 20 mm, length 6.6 mm, 400
Cells / inch < ² >), dried and baked stepwise to 600 [deg.] C. to prepare a Pt-based exhaust gas purifying material (an exhaust gas purifying material coated with a third catalyst).

The W, silver-based purifying material, copper, nickel-based purifying material and Pt-based purifying material of Example 1 were set in this order from the inflow side to the outflow side of the exhaust gas in the reaction tube. The same reaction conditions as in Example 1 (the apparent space velocities of W, silver-based purifying material, copper, and nickel-based purifying material were respectively about 80,000 h ^-1 and
The apparent space velocity of the system purifying material was about 100,000 h ^-1 ), and the evaluation was performed using a gas having a composition shown in Table 1.
Table 2 shows the results.

Example 5 In the same manner as in Example 1, Pt was loaded on powdered titania using an aqueous chloroplatinic acid solution in an amount of 1.0% by weight (in terms of a metal element), and then ammonium vanadate was used. 3.3% by weight (converted to metal element) of V oxide on powdered titania supporting Pt in the same manner as in the first catalyst, to prepare a V, Pt-based catalyst (third catalyst) did. 0.
After slurrying 18 g of the third catalyst, a honeycomb formed body (diameter 20 mm, length 6.6 mm,
400 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a V, Pt-based exhaust gas purifying material (an exhaust gas purifying material coated with a third catalyst).

The Mo, silver-based purifying material of Example 2, the copper-based purifying material of Example 2, and the V and Pt-based purifying materials were set in order from the inflow side to the outflow side of the exhaust gas in the reaction tube. Evaluation was carried out under the same reaction conditions as in Example 1 (V, the apparent space velocity of the Pt-based purifying material was about 100,000 h ^-1 ) using gases having the compositions shown in Table 1. Table 2 shows the results.

Comparative Example 1 A commercially available alumina powder (specific surface area: 200 m ² / g) was loaded with 3.0% by weight (in terms of a metal element) of silver using an aqueous silver nitrate solution, dried, and stepwise in air. By baking to 600 ° C., a silver-based catalyst (first catalyst) was prepared. 0.54 g of the first catalyst was used in the same manner as in Example 1 to obtain a commercially available cordierite honeycomb-shaped formed body (diameter: 20 mm, length: 16.6 m)
m, 400 cells / inch ² ) to prepare a silver-based exhaust gas purifying material (a purifying material coated with a first catalyst).

The silver-based purifying material was set on the inflow side of the exhaust gas in the reaction tube, and the Pt-based purifying material of Example 4 was set on the outflow side. Evaluation was performed using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity of the silver-based purifying material was about 50,000 h ^-1 ). Table 2 shows the results.

Table 2 Removal rate of nitrogen oxides (NOx) Removal rate of nitrogen oxides (%) Reaction temperature (° C.) 250 300 350 400 450 500 550 Example 1 70.5 85.6 80.4 76.5 69.6 52.0 34.3 Example 2 75.6 92.7 82.5 74.0 70.2 40.3 35.3 Example 3 74.4 89.2 79.6 73.0 68.6 56.2 42.5 Example 4 75.7 89.8 79.2 75.0 68.5 45.8 38.7 Example 5 78.2 89.6 79.5 70.2 62.3 50.2 40.3 Comparative Example 1 25.6 56.5 60.6 58.6 55.9 43.3 35.7

As can be seen from Table 2, in Examples 1 to 5 using the purifying material of the present invention, compared with Comparative Example 1 using the purifying material comprising a silver-based or Pt-based catalyst, a wide exhaust gas temperature range, particularly Good removal of nitrogen oxides was observed in the lower temperature range.

[0069]

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.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B01J 23/64 ZAB B01J 23/85 ZABA 23/648 B01D 53/36 ZAB 23/68 ZAB 102B 23 / 85 ZAB 102C 102H B01J 23/64 102A

Claims (8)

[Claims] 1. 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 exhaust gas purifying material comprises a first catalyst and A second catalyst, wherein the first catalyst comprises a porous inorganic oxide and one or more elements and / or compounds 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) ), W, V, M
o, Mn, Nb, and Ta, and carries 0.01 to 10% by weight (in terms of a metal element) of a compound of one or more elements selected from the group consisting of One or more elements and / or compounds selected from the group consisting of copper, nickel and silver as active species in the oxide;
% By weight (converted to metal element), W, V, Mo, Mn, N
b, a compound of one or more elements selected from the group consisting of Ta and 30% by weight or less (in terms of a metal element), and the first catalyst is discharged to the exhaust gas inflow side of the exhaust gas purifying material. An exhaust gas purifying material comprising the second catalyst on a side thereof. 2. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than a theoretical reaction amount of coexisting unburned components, wherein the exhaust gas purifying material is a first catalyst, The first catalyst comprises a second catalyst and a third catalyst, and the first catalyst comprises a porous inorganic oxide and one or more elements selected from the group consisting of silver and a silver compound and / or
Or 0.2 to 15% by weight of a compound (in terms of silver element);
0.01 to 10% by weight of a compound of at least one element selected from the group consisting of W, V, Mo, Mn, Nb and Ta
(In terms of a metal element), and the second catalyst contains at least one element and / or compound selected from the group consisting of copper, nickel and silver as active species on a porous inorganic oxide. 5 to 30% by weight (converted to metal element), W, V,
A compound of at least 30% by weight (in terms of a metal element) of a compound of one or more elements selected from the group consisting of Mo, Mn, Nb, and Ta, and the third catalyst contains Pt on a porous inorganic oxide. , Pd, Ru, Rh, Ir and Au carrying at least one element selected from the group consisting of 0.01 to 5% by weight (in terms of a metal element), from the exhaust gas inflow side of the exhaust gas purifying material. An exhaust gas purifying material comprising: the first catalyst, the second catalyst, and the third catalyst in order to an outflow side. 3. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than a theoretical reaction amount of coexisting unburned components, wherein the exhaust gas purifying material is a first catalyst, The first catalyst comprises a second catalyst and a third catalyst, and the first catalyst comprises a porous inorganic oxide and one or more elements selected from the group consisting of silver and a silver compound and / or
Or 0.2 to 15% by weight of a compound (in terms of silver element);
0.01 to 10% by weight of a compound of at least one element selected from the group consisting of W, V, Mo, Mn, Nb and Ta
(In terms of a metal element), and the second catalyst contains at least one element and / or compound selected from the group consisting of copper, nickel and silver as active species on a porous inorganic oxide. 5 to 30% by weight (converted to metal element), W, V,
A compound of one or more elements selected from the group consisting of Mo, Mn, Nb, and Ta, in an amount of 30% by weight or less (in terms of a metal element), and the third catalyst contains W on a porous inorganic oxide. , An oxide or a sulfate of at least one element selected from the group consisting of V, Mo, Mn, Nb, and Ta.
0% by weight (in terms of metal element), Pt, Pd, Ru, R
at least one selected from the group consisting of h, Ir and Au
0.01% to 5% by weight (in terms of metal element) of the seed element, and the first catalyst, the second catalyst and the second catalyst in order from the exhaust gas inflow side to the outflow side of the exhaust gas purifying material. An exhaust gas purifying material comprising three catalysts. 4. The exhaust gas purifying material according to claim 1, wherein said W, V, Mo, Mn, Nb, Ta.
Is at least one member selected from the group consisting of oxides, halides and sulfates, and the silver compound is at least one member selected from the group consisting of silver oxides, silver halides, silver sulfate and silver phosphate. Wherein the nickel compound is nickel oxide and / or nickel sulfate;
The exhaust gas purifying material, wherein the copper compound is a copper oxide and / or a copper sulfate. 5. The exhaust gas purifying material according to any one of claims 1 to 4, wherein the porous inorganic oxide comprises alumina alone in the first catalyst, or alumina and any one of titania, silica, zirconia, and zeolite. Composite or mixed oxide, alumina or titania, zeolite, silica, zirconia or a composite or mixed oxide containing any of them for the second catalyst, and alumina, titania, zirconia, silica, zeolite for the third catalyst An exhaust gas purifying material characterized by comprising or a composite or mixed oxide containing them. 6. 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. 7. 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 a pellet, a granule, a honeycomb, or a plate. An exhaust gas purifying material characterized by the following. 8. The method for reducing nitrogen oxides from a combustion exhaust gas containing the nitrogen oxides and oxygen in an amount larger than the theoretical reaction amount for the co-existing unburned components, using the exhaust gas purifying material according to any one of claims 1 to 7. 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 a hydrocarbon and / or an oxygen-containing organic compound is added at an 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.