JPH0985053A - Exhaust gas purifying material and exhaust gas purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove nitrogen oxide from combustion exhaust gas by specifying the support amts of catalyst components in a first catalyst wherein an element and/or a compd. selected from silver and a silver compd. are supported on porous inorg. oxide and a second catalyst wherein titanium oxide is supported on porous inorg. oxide. SOLUTION: This exhaust gas purifying material reduces and removes nitrogen oxide from combustion exhaust gas containing nitrogen oxide and oxygen larger then stoichiometic reaction quantity to a coexisting non-combustion component and consists of a first catalyst formed by supporting 0.2-15wt.% (in terms of a silver element) of an element and/or a compd. selected from silver and a silver compd. on porous inorg. oxide and a second catalyst formed by supporting 0.1-50wt.% (in terms of TiO2 ) of titanium oxide on porous inorg. oxide. If this exhaust gas purifying material is used, nitrogen oxide can be well removed even from exhaust gas containing about 10% of sulfur oxide or moisture within a wide temp. range of 150-650 deg.C.

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 exhaust gas containing sulfur oxides and moisture, the removal rate of nitrogen oxides is significantly reduced. I do.

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 research, the present inventor has found that an exhaust gas purifying material composed of a silver-based catalyst and a titanium oxide catalyst is used, and that hydrocarbons and carbon atoms of 2 in the exhaust gas are used. If any 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, the residual oxygenated organic compounds and intermediate products such as aldehydes generated from the silver catalyst and titanium are added. The inventors have found that nitrogen oxides can be effectively removed over a wide temperature range by the action of an oxide catalyst, and have completed the present invention.

That is, the first exhaust gas purifying material of the present invention reduces and removes nitrogen oxides from combustion exhaust gas containing nitrogen oxides and oxygen which is larger than the theoretical reaction amount of coexisting unburned components. Catalyst comprising at least one element selected from the group consisting of silver and a silver compound and / or 0.2 to 15% by weight (in terms of silver element) of a porous inorganic oxide; And a second catalyst comprising 0.1 to 50% by weight (calculated as TiO ₂ ) of titanium oxide on a high quality inorganic oxide.

A second exhaust gas purifying material of the present invention is a 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. One or more elements and / or compounds selected from the group consisting of silver and silver compounds in the inorganic oxide;
~ 15 wt% (converted to silver element), copper, iron, cobalt,
At least one element selected from the group consisting of nickel and / or
Alternatively, a first catalyst supporting 2% by weight or less of a compound (in terms of a metal element) and 0.1-50% by weight (in terms of TiO ₂ ) of a titanium oxide supported on a porous inorganic oxide. And a second catalyst.

The exhaust gas purifying method of the present invention is a method for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than a theoretical reaction amount of coexisting unburned components. Used, 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,
The method is characterized in that the nitrogen oxide is removed by contacting the purification material at 150 to 650 ° C. with a hydrocarbon and / or an oxygen-containing organic compound in the exhaust gas.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION 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 is obtained by supporting a porous inorganic oxide with 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 carrying a titanium oxide, the first catalyst on the exhaust gas inflow side of the exhaust gas purifying material, and the second catalyst on the outflow side. Having the second catalyst.

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 is formed by supporting one or more elements and / or compounds selected from the group consisting of silver and silver compounds on a porous inorganic oxide, and is formed on the exhaust gas inflow side. And acts on nitrogen oxide removal in a wide temperature range. As the porous inorganic oxide, alumina alone, or a composite or mixed oxide of alumina and any one or more of titania, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and zeolite may be used. it can. When a composite or mixed oxide of alumina is used, the content of alumina should be 50
It is preferable that the content be not less than weight%. 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 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.

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 preferably at least one of silver oxide, silver chloride and silver sulfate. And more preferably silver oxide and / or silver chloride.

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. When carrying silver chloride, the porous inorganic oxide is immersed in an aqueous silver nitrate solution, 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. This is 50 ~ 15
After drying at 0 ° C., especially about 70 ° C., it is preferable to raise the temperature stepwise at 100 to 600 ° C. for firing. The calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream of hydrogen gas. When performing under a hydrogen gas stream, 30
The oxidation treatment is preferably performed at 0 to 650 ° C. 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 comprises a porous inorganic oxide carrying an oxide of titanium. As the porous inorganic oxide, at least one selected from the group consisting of alumina, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and zeolite can be used. Like the first catalyst, the specific surface area of the porous inorganic oxide such as alumina is 10 m ² /
g or more.

The titanium oxide is not particularly limited. For example, titania includes anatase type and rutile type. The specific surface area of the titanium oxide is preferably 10 m ² / g or more. By using the second catalyst supporting the titanium oxide, the reduction characteristics of the nitrogen oxide can be improved, and the decomposition products of the silver-based catalyst can be oxidized and removed.

The amount of titanium oxide supported as an active species on the above-mentioned inorganic oxide such as alumina is 100
0.1 to 50% by weight relative to% by weight (TiO ₂ equivalent)
And If the amount is less than 0.1% by weight, the removal rate of nitrogen oxides decreases. If the amount exceeds 50% by weight, combustion of the hydrocarbon and / or the oxygen-containing organic compound itself tends to occur, and the nitrogen oxide removal rate is rather lowered. The preferable loading amount of titanium oxide is 0.5 to 30% by weight.

The titanium oxide is supported on an inorganic oxide such as alumina by mixing a titanium compound solution, slurry or the like with the inorganic oxide, followed by drying and firing. A solution of a titanium compound, as an example of a slurry, a solution in which a titanium alkoxide such as titanium isopropoxide or titanium tetraisopropoxide is dissolved in an alcohol such as ethanol or isopropanol, an aqueous solution of titanium chloride, or ion-exchanged water in a titania sol. In addition, a homogenized slurry and the like can be mentioned. Like the first catalyst, after drying at 50 to 150 ° C., particularly about 70 ° C., 1
It is preferable to raise the temperature in a stepwise manner at 00 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.

The ratio of the weight of the first catalyst to the weight of the second catalyst (both the total weight of the porous inorganic oxide and the catalytically active species) is preferably 1:10 to 20: 1. If the weight ratio is out of this range, the nitrogen oxide removal performance is reduced. 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 comprises a porous inorganic oxide and one or more elements and / or compounds selected from the group consisting of silver and silver compounds. A first catalyst supporting one or more elements and / or compounds selected from the group consisting of copper, iron, cobalt, and nickel, and a titanium oxide supported on a porous inorganic oxide. A first catalyst on the exhaust gas inflow side of the exhaust gas purifying material and the second catalyst on an outflow side of the exhaust gas purifying material.

The purifying material is installed in an exhaust gas conduit, and an exhaust gas containing a hydrocarbon and / 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 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 The first catalyst is a porous inorganic oxide composed of one or more elements and / or compounds selected from the group consisting of silver and silver compounds, and a group consisting of copper, iron, cobalt, and nickel. Carrying one or more elements and / or compounds selected from
It is formed on the exhaust gas inflow side and acts to remove nitrogen oxides in a wide temperature range. As the porous inorganic oxide, alumina alone, or a composite or mixed oxide of alumina and any one or more of titania, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and zeolite may be used. it can. When a composite or mixed oxide of alumina is used, the content of alumina is preferably 20% 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.

As with the first exhaust gas purifying material, the specific surface area of the porous inorganic oxide such as alumina used for the first catalyst is 1%.
It is preferably at least 0 m ² / g, more preferably at least 30 m ² / g.

The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate and silver phosphate, and preferably at least one of silver oxide, silver chloride and silver sulfate. And more preferably silver oxide and / or silver chloride.

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.

The copper, iron, cobalt and nickel compounds are each at least one selected from the group consisting of oxides, halides, sulfates and phosphates. Assuming that the porous inorganic oxide is 100% by weight, the total supported amount of copper, iron, cobalt, and nickel is 2% by weight or less (in terms of metal element), and the preferable total supported amount is 1.5% by weight or less (metal element (Converted value).

As a method of supporting silver, copper, iron, cobalt, and nickel 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, copper, iron, cobalt, nickel nitrate, chloride, sulfate, carbonate, or the like, or an ammoniacal aqueous solution. When carrying silver chloride, the porous inorganic oxide is immersed in an aqueous silver nitrate solution, 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 this at 50 to 150 ° C, especially about 70 ° C,
It is preferable that the temperature is raised stepwise at 00 ° C. and firing is performed. 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. 6
Compounds may be oxidatively decomposed by firing at up to 50 ° C., but when these compounds are used as starting materials, the removal rate of nitrogen oxides is improved.

(2) Second catalyst As the second catalyst, the second catalyst of the first exhaust gas purifying material described in the above section [1] and (2) can be used.

In the second exhaust gas purifying material, the weight ratio of the first catalyst to the second catalyst is preferably set to 1:10 to 20: 1. 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 each of the above catalysts 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 purification material obtained by forming a catalyst in which a catalytically active species is supported on a powdery porous inorganic oxide 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 650 ° C., good removal of nitrogen oxides can be performed even with exhaust gas containing sulfur oxides and 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, it is generally not an amount sufficient to reduce nitrogen oxides in the exhaust gas. An oxygen organic 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 position where the reducing agent is introduced is upstream of 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 having 2 or more carbon atoms, such as ethanol and isopropyl alcohol, aldehydes which are components of thermal decomposition products of alcohols, and fuels 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 150,000H ^-1 or less, preferably 100,000 h ^{- 1} or less. The space velocity of the second catalyst is 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 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.

[0050]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A commercially available γ-alumina powder (specific surface area: 200 m ² / g) was supported with 4% by weight (in terms of silver element) of silver using an aqueous silver nitrate solution to prepare a silver-based catalyst (first catalyst). . 0.52
g of the first catalyst was slurried, and then a commercially available cordierite honeycomb-shaped formed body (diameter: 20 mm, length: 16.6)
mm, 200 cell / inch ²⁾ to the Court, in the air, 8
After drying at 0 ° C. for 3 hours, the temperature was raised stepwise from 100 ° C. to 600 ° C. and calcined to prepare a silver-based exhaust gas purifying material (a purifying material coated with a first catalyst).

Commercially available γ-alumina powder (specific surface area 200
m ² / g), and the mixture was slurried. Titanium oxide sol was added, followed by stirring for 12 hours. Then, drying was performed at 70 ° C., and the temperature was raised to 600 ° C. in a stepwise manner, followed by firing to prepare a titania-based catalyst (second catalyst) in which 1% by weight (calculated as TiO ₂ ) of titanium oxide was supported on alumina. After slurrying 0.26 g of the second catalyst, it was coated on a cordierite honeycomb molded body (diameter 20 mm, length 8.3 mm, 200 cells / inch ² ) similar to the silver-based exhaust gas purifying material, and air After drying at 80 ° C for 3 hours,
The temperature was raised stepwise from 00 ° C. to 600 ° C. and calcined to prepare a titania 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.
A titania purifying material was 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 4.35 liters per minute (standard state) (silver-based purification material and titania purification). The apparent space velocity of the material is about 50,000 h ^-1 , 10
0,000h ^-1), the exhaust gas temperature in the reaction tube 35
Ethanol and nitrogen oxide were reacted while keeping the temperature in the range of 0 to 600 ° C.

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

Table 1 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, 4% by weight of a commercially available γ-alumina powder (specific surface area: 200 m ² / g) was added using an aqueous silver nitrate solution.
(Silver element converted value) silver, and then 0.1 wt% (metal element converted value) copper using an aqueous solution of copper nitrate,
After baking in the same manner as in Example 1 to prepare a silver-copper-based catalyst (first catalyst), 0.52 g of the first catalyst was slurried, and a commercially available cordierite honeycomb-shaped formed body (diameter: 20 mm, length 16.6 mm, 200 cells / inch ² ) and baked as in Example 1,
Silver and copper based exhaust gas purifying materials (purifying materials coated with the first catalyst) were prepared.

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

Example 3 Using a silver nitrate aqueous solution and an ammonium chloride aqueous solution, 4.0% by weight of powdery silica-alumina (silica content 5% by weight, specific surface area 350 m ² / g) was prepared in the same manner as in Example 1. Silver chloride (silver element equivalent value), followed by an additional 0.01% by weight of iron using an aqueous ferric nitrate solution,
By calcining under the same conditions as the first catalyst of Example 1, a silver-iron-based catalyst (first catalyst) was prepared. After slurrying 0.52 g of the first catalyst, a honeycomb formed body (diameter 20 mm, length 16.6 mm, 200 cells /
Inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver-iron-based exhaust gas purifying material (an exhaust gas purifying material coated with a first catalyst).

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

Comparative Example 1 The silver-based exhaust gas purifying material of Example 1 was set in an exhaust gas conduit, and the same reaction conditions as in Example 1 (apparent space velocity was about 5
(At 0000 h ⁻¹ )), and the evaluation was performed 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.) 350 400 450 500 550 600 Example 1 48 70 85 85 80 62 Example 2 50 73 87 88 81 60 Example 3 52 78 88 90 80 58 Comparative Example 1 30 45 74 72 70 60

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 titanium oxide catalyst over a wide exhaust gas temperature Good removal of oxides was observed.

[0062]

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.

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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
(Silver element equivalent) and a porous inorganic oxide containing 0.1 to 50% by weight of titanium oxide (T
an exhaust gas purifying material comprising: a second catalyst supporting iO ₂ conversion value). 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
(In terms of silver element) and one or more elements and / or compounds 2 selected from the group consisting of copper, iron, cobalt and nickel
Weight% or less (in terms of metal element) and a porous inorganic oxide containing titanium oxide 0.1 to 0.1%.
An exhaust gas purifying material comprising a second catalyst supporting 50% by weight (in terms of TiO ₂ ). 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 the silver, copper, iron, cobalt, and nickel compounds are each selected from the group consisting of oxides, halides, sulfates, and phosphates. An exhaust gas purifying material characterized by being at least one selected from. 5. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide of the first catalyst is alumina alone, or titania, silica, zirconia, zinc oxide, tin oxide. , Magnesium oxide, a composite or mixed oxide of any one or more of zeolite and alumina, the porous inorganic oxide of the second catalyst is alumina, silica, zirconia, zinc oxide, tin oxide, magnesium An exhaust gas purifying material characterized by being at least one member selected from the group consisting of oxides and zeolites. 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 formed into a pellet, a granule, a honeycomb, a foam, or a plate. An exhaust gas purifying material characterized in that: 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 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.