JPH0947660A - Material and process for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce and remove nitrogen oxides from a combustion exhaust gas containing excessive oxygen by specifying the carrying amounts of respective metals in a purifier consisting of a first catalyst composed of silver or the like carried on a porous inorganic oxide and a second catalyst composed of copper, iron or the like carried on a porous inorganic oxide. SOLUTION: A first catalyst is formed by carrying silver and/or a silver catalyst (0.2-15wt.%) (value based on silver element) on a porous inorganic oxide such as alumina or silica. A second catalyst is formed by carrying elements of two kinds or more (0.1-15wt.%) (value based on metal element) selected out of copper, iron and cobalt as active seeds on a similar porous inorganic oxide. The first catalyst is brought into contact with the inflow side, while the second catalyst is brought into contact with the outflow side, and nitrogen oxides are efficiently reduced and removed from combustion exhaust gas containing oxygen of theoretical reaction amount or more and also containing sulfur oxides and a water content.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 used an exhaust gas purifying material comprising a silver-based catalyst and copper, nickel, and cobalt catalysts, and contained hydrocarbons and carbon in the exhaust gas. By adding any of the oxygen-containing organic compounds of several or more or a fuel containing them, and contacting the exhaust gas with the above-mentioned purifying material at a specific temperature and space velocity, nitrogen oxides can be effectively reduced in a wide temperature range. They discovered that they 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 porous inorganic oxide. One or more elements and / or compounds 0.2 selected from the group consisting of silver and silver compounds
And at least two elements selected from the group consisting of copper, iron, and cobalt as active species on a porous inorganic oxide and / or And a second catalyst supporting 0.1 to 15% by weight of the compound (in terms of a metal element).

[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 which is larger than the theoretical reaction amount for coexisting unburned components comprises a first catalyst and a second catalyst. Wherein the first catalyst is 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). The second catalyst is selected from the group consisting of (a) a porous inorganic oxide containing 0.1 to 15% by weight of copper (in terms of a metal element) and an alkali metal element and a rare earth element. A catalyst supporting at least one element of 4% by weight or less, and (b) an element and / or compound of iron and / or cobalt on a porous inorganic oxide.
It is characterized by being mixed with a catalyst supporting 15% by weight (in terms of metal element).

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. [1] First exhaust gas purifying material The first exhaust gas purifying material of the present invention comprises a porous inorganic oxide carrying one or more elements and / or compounds selected from the group consisting of silver and silver compounds. A first catalyst, and a second catalyst comprising a porous inorganic oxide supporting two or more elements and / or compounds selected from the group consisting of copper, iron and cobalt as active species, The exhaust gas purifying material has the first catalyst on the exhaust gas inflow side and the second catalyst on the outflow side.

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

The following catalyst is formed on the first exhaust gas purifying material. (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. As the porous inorganic oxide, alumina alone, or titania,
A composite or mixed oxide of alumina and any one or more of silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and zeolite can be used. When a composite or mixed oxide of alumina is used, the content of alumina is preferably set to 50% by weight or more. By using alumina or a composite or mixed oxide of alumina,
The heat resistance and durability of the catalyst are improved.

The specific surface area of the porous inorganic oxide such as alumina used in the first catalyst is preferably at least 10 m ² / g. 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 for supporting silver on an inorganic oxide such as alumina, a known impregnation method, precipitation method, or the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, chloride, sulfate, carbonate, or the like, or an aqueous ammonia solution. Alternatively, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, dried, and then immersed again in an aqueous solution of ammonium chloride or ammonium sulfate. To prepare silver halide by the precipitation method, silver nitrate and ammonium halide are reacted to precipitate silver halide on the porous inorganic oxide. After drying at 50 to 150 ° C., particularly at about 70 ° C., it is preferable to raise the temperature stepwise at 100 to 600 ° C. for firing. The calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream of hydrogen gas. When the treatment is performed under a hydrogen gas stream, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last. Compounds may be oxidatively decomposed by firing up to 650 ° C., but when these compounds are used as starting materials, the removal rate of nitrogen oxides is improved. The reason is still unknown.

(2) Second Catalyst The second catalyst is obtained by supporting two or more elements and / or compounds selected from the group consisting of copper, iron and cobalt as catalytically active species on a porous inorganic oxide. Become. As the porous inorganic oxide, any one of alumina, titania, zeolite, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, 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 copper, iron and cobalt compounds are each at least one selected from the group consisting of oxides, halides, sulfates and phosphates. 1 porous inorganic oxide
The total supported amount of copper, iron and cobalt is 0.1 to 15% by weight (in terms of a metal element), and the preferable total supported amount is 0.5 to 12% by weight (in terms of a metal element).
It is.

When the copper component and the iron component are used simultaneously, the weight ratio between the copper element and the iron element is 1:10 to 10: 1, and similarly, the weight ratio between the copper element and the cobalt element is 1:10 to 1: 1.
0: 1, and the weight ratio between the iron element and the cobalt element is 1: 1.
It is preferably 0 to 10: 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 the impregnation method is used, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, nitrate, acetate, sulfate, halide, phosphate, or the like of a catalytically active species element. After drying at 50-150 ° C, especially 70 ° C,
It is carried out by raising the temperature stepwise at 100 to 600 ° C. and firing. This calcination is performed in air under a nitrogen stream containing oxygen. 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. On the second catalyst thus prepared, copper, nickel and cobalt are each present alone or in the form of their oxides, halides or sulfates.

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.

[2] Second Exhaust Gas Purifying Material The second exhaust gas purifying material of the present invention carries one or more elements and / or compounds selected from the group consisting of silver and silver compounds on a porous inorganic oxide. A first catalyst comprising:
A catalyst in which copper and at least one element selected from the group consisting of an alkali metal element and a rare earth element are supported on a porous inorganic oxide; and (b) iron and / or Or a second catalyst obtained by mixing a catalyst carrying an element and / or compound of cobalt with the first catalyst on the exhaust gas inflow side of the exhaust gas purifying material and the second catalyst on the outflow side of the exhaust gas purifying material. Having a catalyst of

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

The following catalyst is formed on the second exhaust gas purifying material. (1) First catalyst As the first catalyst, the first catalyst described in the above section [1] (1) can be used.

(2) Second Catalyst The second catalyst comprises (a) a porous inorganic oxide supporting copper and at least one element selected from the group consisting of alkali metal elements and rare earth elements. A copper-based catalyst, and (b)
It is obtained by mixing a porous inorganic oxide with an iron and / or cobalt catalyst comprising an iron and / or cobalt element and / or compound. As the porous inorganic oxide, any one of alumina, titania, zeolite, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and the like, or a composite or mixed oxide containing them is used. As zeolite, ferrierite, mortenite, ZSM-
Various zeolites such as 5 can be used. Like the first catalyst, the specific surface area of the porous inorganic oxide is 10 m
It is preferably at least ² / g.

(A) Copper Catalyst The copper compound is at least one selected from the group consisting of oxides, halides, sulfates, phosphates and the like. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of copper is 0.1%.
To 15% by weight (in terms of a metal element), and a preferable loading amount is 0.5 to 12% by weight (in terms of a metal element).

As the alkali metal element, it is particularly preferable to use cesium, sodium and potassium. As the rare earth element, lanthanum, cerium, and neodymium are preferably used, but a misch metal, which is a mixture of rare earth elements, can also be used. 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 4% by weight or less, preferably 0.5% by weight.
To 3% by weight. Further, it is preferable that the carried amount of the alkali metal element is 2% by weight or less, and the carried amount of the rare earth element is 2% by weight or less. If any of the elements exceeds 2% by weight, the removal rate of nitrogen oxides decreases. The preferred amount of the supported alkali metal is 0.1 to 1.5% by weight. Further, the preferable loading amount of the rare earth element is 0.1 to 1.5% by weight.

The total amount of active species carried in the copper-based catalyst is
0.1 to 19% by weight, preferably 0.5 to 15% by weight, based on the above-mentioned porous inorganic oxide (100% by weight). If the amount of the catalytically active species is less than 0.1% by weight with respect to the substrate, the effect of supporting the catalyst is not remarkable, and NOx
The reduction characteristics are reduced. On the other hand, when the catalyst loading exceeds 19% by weight, only the oxidizing combustion of the hydrocarbon proceeds, and the characteristic of reducing nitrogen oxides is reduced.

(B) Iron and / or cobalt catalysts Iron and cobalt compounds are oxides, halides,
It is at least one selected from the group consisting of sulfates and phosphates. Assuming that the porous inorganic oxide is 100% by weight,
The total supported amount of iron and cobalt is 0.1 to 15% by weight (in terms of a metal element), and the preferable total supported amount is 0.5 to 15% by weight.
It is 12% by weight (value in terms of metal element).

The active species can be supported by a known impregnation method, precipitation method,
An ion exchange 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, halide, phosphate, or the like of a catalytically active species element. After drying at 50-150 ° C, especially 70 ° C,
It is carried out by raising the temperature stepwise at 100 to 600 ° C. and firing. This calcination is performed in air under a nitrogen stream containing oxygen. 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. On the second catalyst thus prepared, copper, nickel and cobalt are each present alone or in the form of their oxides, halides or sulfates.

The mixing of (a) a copper-based catalyst and (b) an iron and / or cobalt catalyst can be performed by a known method. The weight ratio of (a) the copper-based catalyst to (b) the iron and / or cobalt catalyst is preferably 1: 5 to 5: 1.

In the second exhaust gas purifying material, 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 1:10 to 20: 1. It is preferred that More preferably, the weight ratio of the first catalyst to the second catalyst is 1: 5 to 10: 1.

[3] Form of Exhaust Gas Purifying Material A first preferred embodiment of the exhaust gas purifying material of the present invention is a purifying material obtained by coating the above-mentioned catalyst on a purifying material base. 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 the porous inorganic oxide is coated on the substrate 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 embodiment 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, foams, honeycombs or plates carrying a catalytically active species. Or a catalyst obtained by molding a catalyst into a honeycomb, foam, plate, pellet, or granule.

When the form of the purifying material is the first preferred embodiment described above, the thickness of the catalyst provided on the purifying material base is generally limited by the difference in thermal expansion characteristics between the base material and the catalyst. In many cases. 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.

The amount of the catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter of the purifying material base. If the amount of the catalyst is less than 20 g / liter, good NOx removal cannot be performed. On the other hand, when the amount of the catalyst is 300 g /
If it exceeds 1 liter, the removal characteristics are not so improved, and the pressure loss increases. More preferably, the amount of the catalyst provided on the surface of the purifying material base is 50 to 200 g / liter of 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 exhaust gas containing about 10% of water.

When removing harmful substances such as hydrocarbons and carbon monoxide in addition to nitrogen oxides, Pt, Pd, Ru, R
at least one selected from the group consisting of h, Ir and Au
A purifying material composed of a platinum-based oxidation catalyst carrying 0.01 to 5% by weight (converted to a metal element) of a seed element can be arranged. When treating the exhaust gas of a diesel engine, in order to suppress the oxidation of sulfur dioxide in the exhaust gas, instead of the platinum-based purifying material, W,
Oxide of at least one element selected from the group consisting of V, Mo, Mn, Nb, Ta, 0.2 to 10% by weight (in terms of metal element), Pt, Pd, Ru, Rh, Ir and A
at least one element selected from the group consisting of
W supporting 1 to 5% by weight (in terms of metal element),
An exhaust gas purifying material composed of a platinum-based catalyst can be used.

[4] Exhaust gas purifying method First, 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.

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

As the hydrocarbon introduced from 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 added /
(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.

[0048] 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 500,000 ^-1 or less, preferably 300,000H ^{- 1} or less. The space velocity of the second catalyst is 500,000 ^-1 or less, preferably 300,000H ^-1 or less.

Further, in the present invention, the temperature of the exhaust gas at the purification material installation site, which is the site where the hydrocarbon and / or the oxygen-containing organic compound reacts with the nitrogen oxide, is set at 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 350 to 550 ° C.

[0050]

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,
Specific surface area 350 m ² / g, average particle size 0.05 mm) 10
4% by weight using silver nitrate and ammonium chloride aqueous solution
After carrying silver chloride (in terms of silver element) and drying at 80 ° C. for 3 hours, the temperature was increased stepwise from 100 ° C. to 600 ° C. in air, and calcined at 600 ° C. for 3 hours to obtain a silver catalyst ( First catalyst) was prepared. After slurrying 0.52 g of the first catalyst, it was coated on a commercially available cordierite honeycomb formed body (diameter: 20 mm, length: 16.6 mm, 400 cells / inch ² ), and dried in air at 80 ° C. for 3 hours. After drying for 1 hour
The temperature was raised stepwise from 00 ° C. to 600 ° C. and calcined at 600 ° C. for 3 hours to prepare a silver-based exhaust gas purifying material (a purifying material coated with a first catalyst).

Using an aqueous solution of copper nitrate and an aqueous solution of ferric nitrate, 10% by weight (metal element) was added to powdery γ-alumina (average particle size: 0.05 mm, specific surface area: 200 m ² / g) in the same manner as for the silver-based catalyst. (Converted value) of copper oxide and 2% by weight (metal element converted value) of iron oxide, to prepare a copper-iron catalyst (second catalyst). After slurrying 0.26 g of the second catalyst, a honeycomb-shaped formed body (diameter 2
0 mm, length 8.3 mm, 400 cells / inch ² ), dried and baked step by step to 600 ° C, copper and iron based exhaust gas purifying material (exhaust gas purifying material coated with second catalyst)
Was prepared.

A silver-based purifying material is provided on the exhaust gas inflow side in the reaction tube.
Copper and iron 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) (silver-based purifying material and copper, The apparent space velocities of iron-based purifying materials are approximately 40,000 h ^-1 , 80,
000 h ^-1 ), and the temperature of the exhaust gas in the reaction tube is 350 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 Concentrations of components (dry basis) Nitric oxide 800 ppm Oxygen 10% by volume Ethanol 1560 ppm (3 times the mass of nitric oxide) Sulfur dioxide 30 ppm Nitrogen Residual moisture 10% by volume (based on the total volume of the above components) for)

Example 2 In the same manner as in Example 1, 10 g of a commercially available γ-alumina powder (specific surface area: 200 m ² / g, average particle size: 0.05 mm) was treated with 4% by weight (in terms of silver element) using an aqueous silver nitrate solution. ) Was carried out and calcined in the same manner as in Example 1 to prepare a silver-based catalyst (first catalyst). Then, 0.52 g of the first catalyst was slurried, and a commercially available cordierite honeycomb was used. A shaped body (diameter 20 mm, length 16.6 mm, 400 cells / inch ² ) was coated and fired in the same manner as in Example 1 to obtain a silver-based exhaust gas purifying material (a purifying material coated with a first catalyst). Was prepared.

Using an aqueous solution of copper nitrate and an aqueous solution of cobalt nitrate, 10% by weight (in terms of metal element) of powdery γ-alumina (average particle size: 0.05 mm, specific surface area: 200 m ² / g) in the same manner as the silver catalyst. Value) and 2% by weight (converted to metal element) of cobalt oxide, to prepare a copper-cobalt-based catalyst (second catalyst). After slurrying 0.26 g of the second catalyst, a honeycomb-shaped formed body (diameter 20 mm, length 8.3 mm, 400 cells / day) was prepared in the same manner as the silver-based purification material.
² ), dried and baked stepwise to 600 ° C. to prepare a copper- and cobalt-based exhaust gas purifying material (an exhaust gas purifying material coated with a second catalyst).

A silver-based purifying material on the exhaust gas inflow side in the reaction tube;
Copper and cobalt-based purifying materials were set on the outflow side. Example 1
(The apparent space velocities of the silver-based purifying material and the copper- and cobalt-based purifying materials are about 40,000 h ^-1 and 8 respectively.)
(At 0000 h ⁻¹ )), and the evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 3 Using an aqueous solution of copper nitrate, an aqueous solution of lanthanum nitrate and an aqueous solution of cesium nitrate, in the same manner as in Example 1, powdered silica-alumina (silica content 5% by weight, specific surface area 350 m ² / g, average particle size) 0.05 mm) 10 g of 8.0 wt% copper, 0.1 g.
A copper-based catalyst was prepared by supporting 4% by weight of lanthanum and 0.4% by weight of cesium (each converted to a metal element).

Next, using an aqueous solution of cobalt nitrate, 10% by weight (in terms of metal element) of cobalt was supported on the same powdery silica-alumina in the same manner as in Example 1 to prepare a cobalt catalyst.

A second catalyst was prepared by mixing 0.2 g of a copper catalyst and 0.06 g of a cobalt catalyst, and this was made into a slurry.
m, length 8.3 mm, 400 cells / inch ² ), dried and baked stepwise to 600 ° C to prepare copper and cobalt-based exhaust gas purifying materials (exhaust gas purifying materials coated with a second catalyst). did.

A silver-based purifying material is provided on the exhaust gas inflow side in the reaction tube,
Copper and cobalt-based purifying materials were set on the outflow side. Example 1
(The apparent space velocities of the silver-based purifying material and the copper and cobalt purifying materials are about 40,000 h ^-1 and about 8 respectively.)
(At 0000 h ⁻¹ )), and the evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Comparative Example 1 In the same manner as in Example 1, powdery γ-
A silver catalyst was prepared by loading 3% by weight (in terms of silver element) of silver on alumina. A honeycomb formed body (diameter 20 mm, length 16.6 mm, 400 cells / inch ² ) was coated with 0.52 g of a silver catalyst, dried and fired to prepare a silver-based purifying material. The silver-based purifying material was set in the exhaust gas conduit, and the same reaction conditions as in Example 1 (apparent space velocity was about 40,00
0 h ^-1 ), and was evaluated using a gas having a composition shown in Table 1. Table 2 shows the results.

Table 2 Removal rate of nitrogen oxides (NOx) Removal rate of nitrogen oxides (%) Reaction temperature (° C.) 350 400 450 500 550 Example 1 34.3 62.6 88.4 90.6 80.8 Example 2 32.6 58.3 86.7 89.5 79.3 Execution Example 3 33.2 48.8 73.3 85.2 67.3 Comparative Example 1 34.8 45.6 60.2 50.5 35.8

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 copper-based catalyst exhibited nitrogen oxides over a wide exhaust gas temperature range. Good removal was observed.

[0065]

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 number Agency reference number FI Technical display location B01J 23/78 B01D 53/36 102H B01J 23/74 301A 311A

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 in an amount larger than a theoretical reaction amount for coexisting unburned components, wherein silver and silver are used as porous inorganic oxides. 0.2 to 15% by weight of one or more elements selected from the group consisting of compounds and / or compounds
(A silver element-converted value), two or more elements and / or compounds 0.1 selected from the group consisting of copper, iron and cobalt as active species on a porous inorganic oxide.
An exhaust gas purifying material, comprising: a second catalyst supporting about 15% by weight (in terms of a metal element). 2. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen 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 is a porous inorganic oxide and contains 0.2 to 15% by weight of one or more elements and / or compounds selected from the group consisting of silver and silver compounds (in terms of silver element). Value)
The second catalyst comprises (a) a porous inorganic oxide containing copper 0.1
(B) a catalyst supporting 4 wt% or less of at least one element selected from the group consisting of an alkali metal element and a rare earth element; An exhaust gas purifying material comprising a mixture of an oxide and a catalyst comprising 0.1 to 15% by weight (in terms of a metal element) of an element and / or compound of iron and / or cobalt. 3. The exhaust gas purifying material according to claim 1, wherein the exhaust gas purifying material has the first catalyst on an exhaust gas inflow side and the second catalyst on an outflow side. Purifying material. 4. The exhaust gas purifying material according to claim 1, wherein said silver, copper, iron and cobalt compounds are each selected from the group consisting of oxides, halides, sulfates and phosphates. An exhaust gas purifying material characterized by at least one type. 5. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is alumina alone or titania, silica, zirconia, zinc oxide, tin oxide in the first catalyst. Product, magnesium oxide, a composite or mixed oxide of any one or more of zeolite and alumina, the second catalyst alumina, titania,
An exhaust gas purifying material characterized by being any one of zeolite, silica, zirconia, zinc oxide, tin oxide, and magnesium oxide 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 and second catalysts is coated on a surface of a ceramic or metal substrate. An exhaust gas purifying material characterized by the following. 7. The exhaust gas purifying material according to claim 1, wherein at least one of the first and second catalysts is in the form of a pellet, a granule, a honeycomb, a foam, or a plate. An exhaust gas purifying material characterized in that it is molded into a material. 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.