JPH08276131A - Exhaust gas cleaning material and exhaust gas cleaning - Google Patents

Abstract

PURPOSE: To make it possible to effectively reduce and remove nitrogen oxide from a combustion exhaust gas containing nitrogen oxide and excess oxygen by specifying the carried amount of catalyst, in a catalyst consisting of a catalyst carrying silver and a silver compound, a catalyst carrying silver, copper and nickel as active species, and a catalyst carrying Pt and Pd, on a porous inorganic oxide. CONSTITUTION: This exhaust gas cleaning material consists of three catalysts; a first catalyst which carries 0.2 to 15wt.% (silver element conversion value) of porous inorganic element and/or compound; a second catalyst which carries 1 to 30wt.% (metal element conversion value) of two or more different kinds of element and/or compound selected from the group consisting of silver, copper and nickel as active species on a porous inorganic oxide; and a third catalyst which carries 0.01 to 5wt.% (metal element conversion value) of one kind of element selected from the group consisting of Pt, Pd, Ru, Ir and Au on a porous inorganic oxide. The first catalyst is provided on the exhaust gas inflow side of the exhaust gas cleaning medium, and a mixed catalyst of the second and the third catalyst is provided on the outflow side.

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, in these methods, effective removal of nitrogen oxides can be obtained only in a narrow temperature range, and in an exhaust gas containing sulfur oxides and moisture, the removal rate of nitrogen oxides is remarkable. descend.

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. By providing an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently reducing and removing nitrogen oxides from combustion exhaust gas containing oxygen in excess of the theoretical reaction amount with respect to unburned components and containing sulfur oxides and moisture. is there.

[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, reducing nitrogen oxides to nitrogen gas even in exhaust gas containing water, sulfur dioxide, etc., as well as producing nitrogen-containing compounds and aldehydes such as nitrites and ammonia as by-products. I found that. Nitrite produced by a silver-based catalyst,
A mixed catalyst obtained by mixing a platinum-based catalyst with a catalyst carrying two or more of silver, copper, and nickel, which can effectively remove nitrogen compounds under exhaust gas conditions containing nitrogen-containing compounds such as ammonia and aldehydes Using an exhaust gas purifying material obtained by combining the above with the above-mentioned silver-based catalyst.
If any one of the above oxygenated organic compounds or a fuel containing them is added and the exhaust gas is brought into contact with the above-mentioned purifying material at a specific temperature and space velocity, nitrogen oxides can be effectively removed in a wide temperature range. At the same time, they discovered that carbon monoxide, hydrocarbons and SOF (soluble organic components) in exhaust gas could be removed, 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 of coexisting unburned components is a first catalyst, A second catalyst and a third catalyst, wherein the first catalyst is a porous inorganic oxide containing at least one element and / or compound selected from the group consisting of silver and silver compounds in an amount of 0.2 to 15% by weight; (In terms of silver element), and the second catalyst is a porous inorganic oxide, in which two or more elements selected from the group consisting of silver, copper, and nickel as active species and / or compounds 1 to 30% by weight (in terms of a metal element), and the third catalyst comprises a porous inorganic oxide and at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au. 0.01-5% by weight
(Equivalent to a metal element), and the exhaust gas purifying material has the first catalyst on the exhaust gas inflow side and the mixed catalyst of the second catalyst and the third catalyst on the outflow side. Features.

[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), and the second catalyst contains silver as an active species on a porous inorganic oxide.
Copper and nickel carry two or more kinds of elements and / or compounds selected from the group consisting of nickel and 1 to 30% by weight (in terms of metal element), and the third catalyst contains W,
An oxide or a sulfate of at least one element selected from the group consisting of V, Mo, Mn, Nb, and Ta in an amount of 0.2 to 10% by weight (in terms of a metal element), Pt, Pd, Ru, Rh,
At least one element selected from the group consisting of Ir and Au, which carries 0.01 to 5% by weight (in terms of a metal element), and the first catalyst is provided on the exhaust gas inflow side of the exhaust gas purifying material. And a mixed catalyst of the second catalyst and the third catalyst on the outlet side.

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 in an amount 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, a second catalyst, and a third catalyst, and the first catalyst is selected from the group consisting of silver and a silver compound in a porous inorganic oxide. One or more elements and / or compounds are supported, and the second catalyst is a porous inorganic oxide, in which two or more elements and / or compounds selected from the group consisting of silver, copper, and nickel are used as active species. And the third catalyst supports at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au on a porous inorganic oxide, and purifies the exhaust gas. The first catalyst is provided on the exhaust gas inflow side of the material, and the mixed catalyst of the second catalyst and the third catalyst is provided on the outflow side.

The second exhaust gas purifying material of the present invention comprises a first catalyst, a second catalyst and a third catalyst, wherein the first catalyst comprises a porous inorganic oxide and silver and a silver compound. One or more elements and / or compounds selected from the group consisting of two or more elements selected from the group consisting of silver, copper and nickel as active species on the porous inorganic oxide; And / or a compound supported thereon, and the third catalyst comprises W, V, Mo, Mn, Nb, T
a, an oxide or a sulfate of at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and A
and at least one element selected from the group consisting of u, the first catalyst is provided on an exhaust gas inflow side of the exhaust gas purifying material, and the second catalyst and the third catalyst are provided on an outflow side thereof. And a mixed catalyst.

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 comprises a porous inorganic oxide carrying one or more elements and / or compounds selected from the group consisting of silver and silver compounds, and is formed on the inflow side of exhaust gas. Acts on nitrogen oxide removal in a wide temperature range. 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. Either alumina or titania or a composite or mixed oxide containing them can be used as the porous inorganic oxide, but it is preferable to use alumina or a composite or mixed oxide of alumina. Examples of the porous inorganic oxide that is complexed or mixed with alumina and titania include silica and titania. 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 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.

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 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. After drying at 50 to 150 ° C., particularly at about 70 ° C., it is preferable to raise the temperature stepwise at 100 to 600 ° C. for firing. The calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream of hydrogen gas. When the treatment is performed under a hydrogen gas stream, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last.

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 comprises a porous inorganic oxide supporting nickel as a catalytically active species and two or more elements and / or compounds selected from the group consisting of silver and copper. It becomes. 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. Various zeolites such as ferrierite, mortenite, and ZSM-5 can be used as the zeolite. Similar to the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

The nickel compound is at least one selected from the group consisting of nickel oxides, halides, sulfates and the like. 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. Assuming that the porous inorganic oxide is 100% by weight,
The total supported amount of silver, copper, and nickel is 1 to 30% by weight (converted to metal element), and the preferable total supported amount is 1 to 25% by weight (converted to metal element).

As the second catalyst, at least one element and / or oxide selected from the group consisting of an alkali metal element and a rare earth element can be used as a catalytically active species. By using an alkali metal element and / or a rare earth element as the catalytically active species, the durability of the catalyst is improved, and the characteristics of removing nitrogen oxides by residual hydrocarbons are improved. Assuming that the porous inorganic oxide is 100% by weight, the total carrying amount of the alkali metal element and the rare earth element is preferably 5% by weight or less (in terms of metal element), and preferably 4% by weight or less (in terms of metal element). Particularly preferred.

Further, W, V, Mo, M are added to the second catalyst.
An oxide or sulfate of at least one element selected from the group consisting of n, Nb, and Ta can be used as the catalytically active species. By using a W-based compound as a catalytically active species, the removal characteristics of nitrogen oxides by ammonia generated by a silver-based catalyst are improved. 100% by weight of porous inorganic oxide
The total supported amount of the W-based compound is preferably 30% by weight or less (value in terms of metal element), and particularly preferably 15% by weight or less (value in terms of metal element).

When the nickel component and the silver component are used simultaneously, the weight ratio of the nickel element to 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 active species can be supported by a known impregnation method, precipitation method,
An ion exchange 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 or nickel 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. 50-150 ° C, especially 70 ° C
After the drying, the temperature is raised stepwise at 100 to 600 ° C., followed by firing. 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 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.
The catalyst can be mixed in the second catalyst by a known method such as a dry method or a wet method. On the second catalyst thus prepared, silver, nickel, and copper are present in the form 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.

(3) Third Catalyst The third catalyst is formed by supporting catalytically active species on a porous inorganic oxide and formed on the exhaust gas outflow side, and acts to remove nitrogen oxides in a low temperature range. 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 first 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 second 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 catalyst or a 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.

In the exhaust gas purifying material of the present invention, the second catalyst and the third catalyst are mixed and used. The ratio of the weight of 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 preferably 1: 1 to 200: 1. If the ratio is less than 1: 1 (the amount of the second catalyst is small), the nitrogen oxide purification rate decreases. On the other hand, if the ratio exceeds 200: 1 and the third catalyst is low, hydrocarbons,
The oxidation characteristics of carbon monoxide and SOF decrease. More preferably, the ratio of the weight of the second catalyst to the weight of the third catalyst is 1: 1.
１００100: 1.

When the form of the purifying material is the above-described first preferred embodiment, the thickness of the mixed catalyst of the second catalyst and the third catalyst provided on the purifying material base should be 300 μm or less. Good. The amount of the mixed 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., 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 placed on the exhaust gas inflow side by the first catalyst,
The mixed catalyst of the second catalyst and the third catalyst is installed in the exhaust gas conduit so as to be on the exhaust gas outflow side.

Although the exhaust gas contains ethylene, propylene and the like to some extent as residual hydrocarbons, it is generally not enough 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 of the reducing agent).
(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.

[0046] 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. Space velocity of the mixed catalyst of the second catalyst and 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 300 to 550 ° C.

[0048]

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,
^2. Using an aqueous silver nitrate solution to a specific surface area of 350 m ² / g).
1% by weight (in terms of metal element) of silver was supported, dried, and calcined in air stepwise to 600 ° C. to prepare a first catalyst. After slurrying 0.26 g of the first catalyst,
A commercially available cordierite honeycomb-shaped molded product (20 m in diameter)
m, length 8.3 mm, 400 cells / inch ² ), dried, and fired stepwise to 600 ° C. to prepare a silver-based exhaust gas purifying material (a purifying material coated with a first catalyst).

Using an aqueous solution of nickel nitrate and an aqueous solution of copper nitrate, powdery γ-alumina (specific surface area: 200 m ² / g) was mixed with 4% by weight (converted to metal element value) of nickel oxide in the same manner as the silver-based catalyst. A second catalyst was prepared by supporting 10% by weight (in terms of metal element) of copper oxide.

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).

The second catalyst (0.26 g) and 0.00
After mixing with 65 g (1/40 of the weight of the second catalyst) of the third catalyst and making it into a slurry, a honeycomb-shaped formed body (diameter 20 mm, length 8.3 mm, 400 cells) was prepared in the same manner as the silver-based purifying material. / Inch ² ), dried and baked stepwise to 600 ° C to prepare a nickel, copper, Pt-based exhaust gas purifying material (an exhaust gas purifying material coated with a mixed catalyst).

A silver-based purifying material is provided on the exhaust gas inflow side in the reaction tube.
Nickel, copper, and Pt-based purifying materials were set on the outflow side. Next, a gas (nitrogen monoxide, oxygen, ethanol, sulfur dioxide, nitrogen and moisture) having a composition shown in Table 1 was flowed at a flow rate of 3.48 liters per minute (standard state) (apparent space velocity of each purification material). Were about 80,000 h ^-1 ), and the temperature of the exhaust gas in the reaction tube was kept in the range of 300 to 600 ° C., and ethanol and nitrogen oxide were reacted.

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 powdery zeolite (SiO ₂ / Al ₂ O ₃ molar ratio = 27; specific surface area 230 m ² / g) was added in the same manner as in Example 1 by using an aqueous solution of silver acetate and an aqueous solution of copper acetate. 0.0% by weight (converted to metal element) of silver and 4.1% by weight (converted to metal element)
And a second catalyst was prepared.

In the same manner as in Example 1, Pt was loaded on powdered titania using a chloroplatinic acid aqueous solution in an amount of 1.0% by weight (in terms of a metal element), and then vanadium pentoxide was added to oxalic acid, and the mixture was placed on a water bath. After heating and dissolving, powdered titania supporting Pt was put into the cooled aqueous solution, and immersed for 20 minutes. Thereafter, the titania was separated from the solution, and dried in air at 80 ° C, 100 ° C, and 120 ° C for 2 hours each.
Subsequently, under a nitrogen stream containing 20% of oxygen, 120 ° C. to 50 ° C.
The temperature was raised to 0 ° C. in 5 hours, and calcined at 500 ° C. for 4 hours to support 3.3% by weight (converted to metal element) of V oxide with respect to titania. Was prepared.

The second catalyst (0.26 g) and 0.00
After mixing with 65 g (1/40 of the weight of the second catalyst) of the third catalyst and making it into a slurry, a honeycomb-shaped formed body (diameter 20 mm, length 8.3 mm, 400 cells /
Inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver, copper, Pt, V-based exhaust gas purifying material (an exhaust gas purifying material coated with a mixed catalyst).

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

Example 3 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. It was calcined to 600 ° C. to prepare a first catalyst. 0.26 g of the first catalyst was coated on a commercially available cordierite honeycomb formed body (diameter 20 mm, length 8.3 mm, 400 cells / inch ² ) in the same manner as in Example 1, and a silver-based exhaust gas purifying material was used. (Purification material coated with the first catalyst) was prepared.

Using a silver nitrate aqueous solution and a nickel nitrate aqueous solution, powdered silica-alumina (silica content 5% by weight, specific surface area 350 m ² / g) was prepared in the same manner as in Example 1.
A second catalyst was prepared by carrying 0% by weight (converted to metal element) of silver and 10% by weight (converted to metal element) of nickel oxide.

The second catalyst (0.26 g) and 0.00
After mixing with 65 g (1/40 of the weight of the second catalyst) of the third catalyst of Example 1 to form a slurry, a honeycomb-shaped formed body (diameter 20 mm, length 8.3 mm) was obtained in the same manner as in Example 1. ,
400 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver, nickel and Pt-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst).

A silver-based purifying material is provided on the exhaust gas inflow side in the reaction tube,
Silver, nickel, and Pt-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.

COMPARATIVE EXAMPLE 1 0.52 g of the first catalyst prepared in Example 3 was mixed with the same honeycomb formed body (diameter 20 mm, length 16.6 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 using the gas having the composition shown in Table 1 under the same reaction conditions as in Example 1 (the apparent space velocity was about 40,000 h ^-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 37.8 57.2 73.1 63.0 55.4 51.3 42.3 Example 2 45.4 62.7 77.3 74.7 62.4 56.7 51.6 Example 3 39.6 56.7 72.5 66.7 60.4 55.8 53.3 Comparative Example 1 7.5 20.6 30.6 35.9 42.3 40.7 34.7

As can be seen from Table 2, as compared with Comparative Example 1 using only a silver catalyst, Examples 1 to 3 using a combination of a silver-based catalyst and a mixed catalyst had a wide range of exhaust gas temperature in the range of exhaust gas temperature. Good removal was seen.

[0066]

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 Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B01J 23/72 B01D 53/36 102A 23/755 102B 102H B01J 23/74 321A

Claims (9)

[Claims] 1. 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
Alternatively, the second catalyst is a porous inorganic oxide which carries 0.2 to 15% by weight (in terms of silver element) of a compound, and the second catalyst is selected from the group consisting of silver, copper and nickel as active species on a porous inorganic oxide. The above-mentioned element and / or compound carries 1 to 30% by weight (in terms of metal element), and the third catalyst is a group consisting of Pt, Pd, Ru, Rh, Ir and Au on a porous inorganic oxide. At least one element selected from the group consisting of 0.01 to 5% by weight (in terms of a metal element), wherein the first catalyst is provided on an exhaust gas inflow side of the exhaust gas purifying material and the second catalyst is provided on an outflow side thereof. An exhaust gas purifying material, comprising a mixed catalyst of the catalyst described above and the third catalyst. 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
Alternatively, the second catalyst is a porous inorganic oxide which carries 0.2 to 15% by weight (in terms of silver element) of a compound, and the second catalyst is selected from the group consisting of silver, copper and nickel as active species on a porous inorganic oxide. 1 to 30% by weight (in terms of metal element) of the above element and / or compound, and the third catalyst is a group consisting of W, V, Mo, Mn, Nb, and Ta on a porous inorganic oxide. Oxides or sulfates of at least one element selected from the group consisting of 0.2 to 10% by weight (in terms of metal elements) and Pt, P
and at least one element selected from the group consisting of d, Ru, Rh, Ir, and Au (0.01 to 5% by weight (in terms of a metal element)). An exhaust gas purifying material comprising the first catalyst and a mixed catalyst of the second catalyst and the third catalyst on an outflow side. 3. The exhaust gas purifying material according to claim 1, wherein the second catalyst is 5% by weight of a porous inorganic oxide and one or more elements selected from the group consisting of an alkali metal element and a rare earth element. An exhaust gas purifying material characterized by carrying the following (element conversion value). 4. The exhaust gas purifying material according to claim 1, wherein the second catalyst is selected from the group consisting of a porous inorganic oxide and W, V, Mo, Mn, Nb, Ta. Oxide or sulfate of at least one element
An exhaust gas purifying material, wherein the exhaust gas purifying material carries not more than% by weight (in terms of a metal element). 5. 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 nickel compound is nickel oxide and / or nickel sulfate, and the copper compound is copper oxide and / or copper sulfate. 6. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is alumina, titania, or a composite or mixed oxide containing them in the first catalyst. The second catalyst is alumina, titania, zeolite, silica, a composite or mixed oxide containing any of them or zirconia, the third catalyst is alumina, titania, zirconia, silica, a composite containing any of them or zeolite or An exhaust gas purifying material characterized by being a mixed oxide. 7. 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. 8. 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. 9. An exhaust gas purifying material according to claim 1, wherein nitrogen oxide is reduced from a combustion exhaust gas containing nitrogen oxide and oxygen in an amount larger than a theoretical reaction amount for a coexisting unburned component. 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.