JPH0957064A - Waste gas purifying material and waste gas purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a waste gas purifying material capable of efficiently reducing and removing NOx by using the mixture of a catalyst prepared by depositing silver or silver compd. on a porous inorg. oxide and a catalyst prepared by depositing copper, iron or cobalt on a porous inorg. oxide as an active species and specifying the composition ratio of the respective catalytic components. SOLUTION: This waste gas purifying material is used for reducing and removing NOx from a waste gas contg. NOx and the oxygen more than the stoichiometry of the reaction to the coexistent unburned components. The material is formed by mixing a first catalyst prepared by depositing 0.2-15wt.% (expressed in terms of silver element) >=1 kind of element or compd. selected from the group consisting of silver and silver compd. on a porous inorg. oxide and a second catalyst prepared by depositing 0.1-15wt.% (expressed in terms of metallic element) >=2 kinds of element or compd. selected from the group consisting of copper, iron and cobalt as an active species on a porous inorg. oxide. Consequently, the NOx in the waste gas contg. excess oxygen are efficiently removed in a wide temp. range.

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). Further, 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 Application Laid-Open No. HEI 4-4-260). 354536).

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 exhaust gas purifying material comprising a mixture of a silver-based catalyst and copper, nickel, and cobalt catalysts is used to form carbonized exhaust gas. It has been discovered that nitrogen oxides can be effectively removed over a wide temperature range by adding either hydrogen or an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing them, and bringing the exhaust gas into contact with the above-mentioned purifying material. Thus, the present invention has been completed.

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 It is characterized by being mixed with a second catalyst supporting 0.1 to 15% by weight of a compound (in terms of a metal element).

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 in an amount larger than the theoretical reaction amount for coexisting unburned components,
A first catalyst in which a porous inorganic oxide carries 0.2 to 15% by weight (in terms of silver element) of one or more elements and / or compounds selected from the group consisting of silver and silver compounds; 0.1 to 15% by weight (in terms of metal element) of copper and 4% by weight or less of at least one element selected from the group consisting of alkali metal elements and rare earth elements on a low-quality inorganic oxide. It is characterized by being mixed with a second 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 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 50 ° C. with a hydrocarbon and / or an oxygen-containing organic compound 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. Mixing a first catalyst and a second catalyst comprising a porous inorganic oxide carrying two or more elements and / or compounds selected from the group consisting of copper, iron and cobalt as active species Become.

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.

In the first exhaust gas purifying material, the first catalyst and the second catalyst are mixed and used. By this mixing, a synergistic effect between the first catalyst and the second catalyst is obtained, and particularly high removal of nitrogen-containing compounds is obtained even in a low temperature range. The weight ratio of the first catalyst to the second catalyst (the ratio of the total weight of the porous inorganic oxide and the catalytically active species) is preferably 1:10 to 20: 1. More preferably, the weight ratio of the first catalyst to the second catalyst is 1: 5 to 10: 1. The mixing of the first catalyst and the second catalyst can be performed by a known method.

[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. Mixed with a porous inorganic oxide and a second catalyst comprising at least one element selected from the group consisting of an alkali metal element and a rare earth element mixed with a porous inorganic oxide. Do it.

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 porous inorganic oxide carrying copper and at least one element selected from the group consisting of alkali metal elements and rare earth elements. . 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 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),
The preferred loading is 0.5 to 12% by weight (in terms of 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.

In the second exhaust gas purifying material, the first catalyst and the second catalyst are mixed and used. By this mixing, a synergistic effect between the first catalyst and the second catalyst is obtained, and particularly high removal of nitrogen-containing compounds is obtained even in a low temperature range. The weight ratio of the first catalyst to the second catalyst (the ratio of the total weight of the porous inorganic oxide and the catalytically active species) is preferably 1:10 to 20: 1. More preferably, the weight ratio of the first catalyst to the second catalyst is 1: 5 to 10: 1. The mixing of the first catalyst and the second catalyst can be performed by a known method.

[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 mixed 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 are as follows:
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 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, 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.

In the case where 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 due to 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 650 ° C., particularly in a low temperature range, 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] Method for Purifying Exhaust Gas First, the above-mentioned exhaust gas purifying material is placed in the middle of an exhaust gas conduit.

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

As the hydrocarbon introduced from the outside, gaseous or liquid alkanes, alkenes and / or alkynes can be used under standard conditions. In particular, alkanes preferably have 2 or more carbon atoms. Specific examples of the hydrocarbon in a liquid state in a standard state include hydrocarbons such as light oil, cetane, heptane, kerosene, and gasoline. Among them, boiling point 5
Hydrocarbons at 0-350 ° C are particularly preferred. As the oxygen-containing organic compound introduced from the outside, alcohols such as ethanol and isopropyl alcohol having 2 or more carbon atoms, or a fuel containing them can be used.

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

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

In the present invention, the space velocity is 500,000 h ^-1 or less, preferably 300,0 h or less, in order to efficiently promote the reduction and removal of nitrogen oxides by oxygen-containing organic compounds and hydrocarbons.
00h ^-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 650 ° 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 650 ° C., combustion of the hydrocarbon and / or the oxygen-containing organic compound itself starts, and reduction and removal of nitrogen oxides cannot be performed. The preferred exhaust gas temperature is from 200 to 600 ° C, more preferably from 350 to 550 ° C.

[0047]

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.

Using an aqueous solution of copper nitrate and an aqueous solution of ferric nitrate, 10% by weight of powdery γ-alumina (average particle size: 0.05 mm, specific surface area: 200 m ² / g) (metal element) (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 mixing 0.40 g of the first catalyst and 0.12 g of the second catalyst to form a slurry, a commercially available cordierite honeycomb-shaped formed body (diameter: 20 mm, length: 1)
6.6 mm, 400 cells / inch ² ), dried in air at 80 ° C. for 3 hours, gradually heated to 100 ° C. to 600 ° C., and calcined at 600 ° C. for 3 hours to obtain an exhaust gas purifying material. Was prepared.

The exhaust gas purifying material was set in the reaction tube. Next, gases having the composition shown in Table 1 (nitrogen monoxide, oxygen,
Ethanol, sulfur dioxide, nitrogen and water) at 3.4
At a flow rate of 8 liters (standard state) (the apparent space velocity of the purifying material is about 40,000 h ^-1 ), the temperature of the exhaust gas in the reaction tube is kept in the range of 350 to 550 ° C, and ethanol and nitrogen oxides are discharged. Was 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 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 water 10% by volume (to 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 added with 4% by weight (in terms of silver element) using an aqueous silver nitrate solution. ) Was carried and calcined in the same manner as in Example 1 to prepare a silver-based catalyst (first catalyst).

Using an aqueous solution of copper nitrate and an aqueous solution of cobalt nitrate, 10% by weight (in terms of a 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 the silver catalyst. ) And 2% by weight (in terms of metal element) of cobalt oxide were supported to prepare a copper / cobalt-based catalyst (second catalyst).

After mixing 0.40 g of the first catalyst and 0.12 g of the second catalyst to form a slurry, a honeycomb formed body (diameter 20 mm, length 16.6 m) was prepared in the same manner as in Example 1.
m, 400 cells / inch ² ) and after drying 600
The mixture was fired stepwise to ℃ to prepare an exhaust gas purifying material.

The exhaust gas purifying material was set in a reaction tube. 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 purification material was about 40,000 h ^-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, powdered silica / alumina (silica content 5% by weight, specific surface area 350 m ² / g, average particle size) in the same manner as in Example 1 0.05 mm) 10 g of 8.0 wt% copper, 0.1 g.
A copper-based catalyst (second catalyst) was prepared by supporting 4% by weight of lanthanum and 0.4% by weight of cesium (each converted to a metal element).

0.40 g of the first catalyst of Example 2 and 0.
After mixing with 12 g of the second catalyst to form a slurry, a honeycomb formed body (diameter 20 m) was formed in the same manner as in Example 1.
m, length 16.6 mm, 400 cells / inch ² ), dried and fired stepwise to 600 ° C to prepare an exhaust gas purifying material.

The exhaust gas purifying material was set in a reaction tube. 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 purification material was about 40,000 h ^-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 37.3 68.6 83.4 84.6 76.8 Example 2 38.6 64.3 89.7 88.5 76.3 Example 3 37.2 54.8 79.3 82.2 64.3 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 in which a silver-based catalyst and a copper-based catalyst were used in combination were used in a wide exhaust gas temperature range. Good removal was observed.

[0063]

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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B01J 23/75 B01J 23/74 301A 311A

Claims (7)

[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 characterized by being mixed with a second catalyst which supports １５15% 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 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 conversion value), a first catalyst supporting a porous inorganic oxide, copper in an amount of 0.1 to 15% by weight (a metal element conversion value), and a group consisting of an alkali metal element and a rare earth element. An exhaust gas purifying material characterized by being mixed with a second catalyst supporting at least one selected element of 4% by weight or less. 3. The exhaust gas purifying material according to claim 1, wherein the silver, copper, iron, and cobalt compounds are at least one selected from the group consisting of oxides, halides, sulfates, and phosphates. An exhaust gas purifying material characterized by the following. 4. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is alumina alone in the first catalyst, or is titania, silica, zirconia, zinc oxide, or tin oxide. 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. 5. The exhaust gas purifying material according to claim 1, wherein a mixed catalyst of the first catalyst and the second catalyst is coated on a surface of a ceramic or metal substrate. An exhaust gas purifying material characterized by the following. 6. The exhaust gas purifying material according to claim 1, wherein the mixed catalyst of the first catalyst and the second catalyst 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. 7. A method for reducing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than a theoretical reaction amount of unexisting unburned components using the exhaust gas purifying material according to claim 1. In the exhaust gas purifying method for removing, the exhaust gas purifying material is provided 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 650 ° 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.