JPH08168674A - Material and process for purifying exhaust gas - Google Patents

Abstract

PURPOSE: To effectively reduce and remove a nitrogen oxide from combustion exhaust gas containing nitrogen oxide and excessive oxygen by providing a first catalyst, a second catalyst carrying the amount of more carrying rate of active species of the first catalyst and a third catalyst having different active species in order successively starting from the inflow side to the outflow side of a purifying material. CONSTITUTION: An exhaust gas purifying material contains a first catalyst carrying silver and/or a silver compound or a mixture of them of 0.1-12wt.% (silver element conversion value) as active species on a porous inorganic oxygen. It also cantinas a second catalyst carrying silver and/or a silver compound or a mixture of them of 1-15wt.% (silver element conversion value) as active species and also carrying active species of the amount more than the carrying rate of the active species of the first catalyst. It also contains a third catalyst as active species carrying at least an oxide of one kind of element selected out of a group composed of W, V, Mo, Mn, Nb and Ta as active species of 0.5-30wt.% (metal element conversion value).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying material capable of effectively reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and excess oxygen, and a purification method using the same.

[0002]

2. Description of the Related Art Excessive combustion exhaust gas discharged 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 supporting a transition metal on the zeolite and adding a reducing agent having a theoretical reaction amount or less with oxygen in the exhaust gas (for example, Japanese Patent Application Laid-Open Publication No. H11-163873). No.63-100919, 63-28372
No. 7, JP-A No. 1-130735).

However, in these methods, effective removal of nitrogen oxides can be obtained only in a narrow temperature range, and in an exhaust gas containing water, the removal rate of nitrogen oxides is significantly reduced. In other words, it contains about 10% water,
It is difficult to effectively remove nitrogen oxides from exhaust gas from a vehicle or the like whose temperature changes greatly depending on operating conditions.

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. From combustion exhaust gas containing more than the theoretical reaction amount for unburned components,
An object of the present invention is to provide an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently reducing and removing nitrogen oxides.

[0010]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has found that an organic compound such as ethanol is converted to oxygen and nitrogen on a catalyst comprising a porous inorganic oxide carrying a silver component. It has been found that it reacts with exhaust gas containing oxides to reduce nitrogen oxides to nitrogen gas and to generate nitrogen-containing compounds such as ammonia and aldehydes as by-products. A second silver-based catalyst capable of effectively removing nitrogen oxides by utilizing the generated aldehyde, a W-based catalyst capable of effectively removing nitrogen oxides by utilizing the produced ammonia, and Using an exhaust gas purifying material formed by combining a platinum-based catalyst that oxidizes and removes carbon, hydrocarbons, etc., adding either hydrocarbons or oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing them to the exhaust gas And
The present inventors have found that if exhaust gas is brought into contact with the above-mentioned purifying material at a specific temperature and space velocity, nitrogen oxides can be effectively removed in a wide temperature range, and the present invention has been completed.

That is, the 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 of coexisting unburned components is a porous inorganic oxide. A first catalyst supporting 0.2 to 12% by weight (in terms of silver element) of silver and / or a silver compound or a mixture thereof as an active species, and silver and silver as active species on a porous inorganic oxide; And / or a silver compound or a mixture thereof, 1 to 15% by weight (in terms of silver element) and a second catalyst supporting the first catalyst in an amount larger than the active catalyst loading rate, and a porous inorganic material. W as an active species in the oxide,
V, Mo, Mn, Nb, and a third catalyst supporting 0.5 to 30% by weight (in terms of metal element) of an oxide or sulfate of at least one element selected from the group consisting of Ta. The first catalyst, the second catalyst, and the third catalyst are provided in this order from the exhaust gas inflow side to the outflow side of the purification material.

A 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 is a porous inorganic material. A first catalyst in which silver and / or a silver compound or a mixture thereof is supported as an active species on an oxide at 0.2 to 12% by weight (in terms of silver element); A second catalyst comprising silver and / or a silver compound, or a mixture thereof in an amount of 1 to 15% by weight (in terms of silver element) and an amount greater than the active species loading of the first catalyst; W as an active species on a high quality inorganic oxide,
A third catalyst supporting 0.5 to 30% by weight (in terms of a metal element) of an oxide or sulfate of at least one element selected from the group consisting of V, Mo, Mn, Nb, and Ta;
A fourth catalyst comprising at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and Au in an amount of 0.01 to 5% by weight (in terms of a metal element); The third catalyst and the fourth catalyst are mixed, and include the first catalyst, the second catalyst, and the mixed catalyst in order from the exhaust gas inflow side to the outflow side of the purification material. .

Further, an 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 excess of the theoretical reaction amount for coexisting unburned components uses the above exhaust gas purifying material. 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 upstream of the purifying material is
The nitrogen oxides are removed by contacting the purifying material at 50 to 600 ° C. and reacting with the hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas.

Hereinafter, the present invention will be described in detail. The first exhaust gas purifying material of the present invention comprises a first catalyst in which silver and / or a silver compound or a mixture thereof is supported as an active species on a porous inorganic oxide; A second catalyst comprising silver and / or a silver compound or a mixture thereof as an active species and an amount larger than the active species loading rate of the first catalyst; and a porous inorganic oxide as an active species. A third catalyst supporting an oxide or sulfate of at least one element selected from the group consisting of W, V, Mo, Mn, Nb, and Ta. An exhaust gas purifying material having the first catalyst, the second catalyst, and the third catalyst is installed in an exhaust gas conduit in order from an exhaust gas inflow side to an outflow side of the purifying material, and the exhaust gas purifying material is located upstream of the purifying material installation position. Hydrocarbon and carbon number 2
Exhaust gas to which any of the above oxygenated organic compounds or a fuel containing the same is added is brought into contact with this purifying material to reduce and remove nitrogen oxides in the exhaust gas.

The second exhaust gas purifying material of the present invention comprises a first catalyst comprising a porous inorganic oxide carrying silver and / or a silver compound or a mixture thereof as an active species, and a porous inorganic oxide. A second catalyst in which silver and / or a silver compound or a mixture thereof as an active species is supported on the oxide in an amount larger than a loading rate of the active species of the first catalyst; A third catalyst supporting an oxide or sulfate of at least one element selected from the group consisting of W, V, Mo, Mn, Nb, and Ta as active species; and Pt, Pd, Ru, and R
and a fourth catalyst supporting at least one element selected from the group consisting of h, Ir and Au. The third catalyst and the fourth catalyst are mixed, and the first catalyst, the second catalyst, and the exhaust gas purifying material having the mixed catalyst are sequentially exhausted from the exhaust gas inflow side to the outflow side of the purifying material. It is installed in a conduit, and an exhaust gas added with a hydrocarbon and any one of oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing the same is brought into contact with the purification material on the upstream side from the installation position of the purification material. Is reduced and removed.

A first preferred embodiment of the exhaust gas purifying material of the present invention is a purifying material obtained by coating a purifying material base with a catalyst comprising a powdery porous inorganic oxide carrying catalytically active species. Examples of the ceramic material forming the substrate of the purifying material include porous materials such as γ-alumina and its oxides (γ-alumina-titania, γ-alumina-silica, γ-alumina-zirconia, etc.), zirconia, titania-zirconia, and the like. A heat-resistant material having a large surface area can be used. When high heat resistance is required, it is preferable to use cordierite, mullite, alumina and a composite thereof. 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. Practically, at the entrance,
It is preferred that it comprises two or more parts, such as an intermediate part and an outlet part. In addition, as its structure, honeycomb structure type,
Foam type, three-dimensional network structure type made of fibrous refractory,
Alternatively, granules, pellets and the like can be mentioned.

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 a pellet or a granular powder carrying a catalytically active species, or a powder comprising a catalytically active species, respectively. It is a purifying material obtained by molding a porous inorganic oxide into pellets or granules into a casing having a desired shape.

The following catalyst is formed on the purifying material of the present invention. (1) First catalyst and second catalyst The first catalyst and the second catalyst are formed by supporting silver and / or a silver compound or a mixture thereof on a porous inorganic oxide, and on the inflow side of the exhaust gas. And acts to remove nitrogen oxides in a wide temperature range. The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate, silver phosphate, and the like, and is preferably one or more of silver oxide, silver chloride, and silver sulfate, More preferred are silver oxide and / or silver chloride. Either alumina or titania or a composite or mixed oxide containing them can be used as the porous inorganic oxide, but it is preferable to use alumina or a composite or mixed oxide of alumina. When a composite or mixed oxide of alumina is used, the content of alumina is preferably set to 50% by weight or more. The use of alumina or a composite or mixed oxide of alumina improves the heat resistance and durability of the catalyst.

The specific surface area of the porous inorganic oxide such as alumina used for the first catalyst and the second catalyst is 10 m ² / g.
It is preferable that this is the case. If the specific surface area is less than 10 m ² / g, the contact area between the exhaust gas and the inorganic oxide (and the silver component carried thereon) becomes small, and good nitrogen oxides cannot be removed. More preferred 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 12% 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 12% 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
0% by weight.

In the second catalyst, the amount of the silver component supported as an active species on the inorganic oxide such as γ-alumina is 1 to 15% by weight based on 100% by weight of the inorganic oxide.
(In terms of silver element) and an amount larger than the loading ratio of the active species of the first catalyst. That is, the content of the silver component with respect to the porous inorganic oxide in the second catalyst is always higher than that in the first catalyst. If the content is less than 1% by weight or less than the active catalyst loading of the first catalyst, the removal of nitrogen oxides using the aldehyde generated by the first catalyst is not performed. Also, 15
When the silver component is supported in an amount exceeding the 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 loading amount of the silver component in the preferred second catalyst is 1 to 12% by weight.

As a method of supporting silver on an inorganic oxide such as alumina, a known impregnation method, precipitation method, or the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, chloride, sulfate, carbonate, or the like, or an aqueous ammonia solution. Alternatively, the porous inorganic oxide is immersed in an aqueous solution of silver nitrate, dried, and then immersed again in an aqueous solution of ammonium chloride or ammonium sulfate. In the precipitation method, silver nitrate is reacted with ammonium halide to precipitate silver halide on the porous inorganic oxide. This is 50
After drying at about 150 ° C, especially about 70 ° C, 100 to 600
It is preferred to raise the temperature stepwise at a temperature of ° C. and to perform firing. Firing
It is preferable to carry out in air, under a flow of nitrogen containing oxygen or under a flow of hydrogen gas. When the treatment is performed under a hydrogen gas stream, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last.

When the silver component carried on the porous inorganic oxide using an aqueous solution of silver nitrate or the like is fired in an oxidizing atmosphere, the silver component can be well wetted by the inorganic oxide, forming an approximately circular aggregate. Has been observed. In the purification material of the present invention, the average diameter of the silver component aggregate is preferably set to 10 to 10000 nm. In general, the smaller the diameter of the silver component aggregate, the higher the reaction characteristics. However, if the average diameter is less than 10 nm, only the oxidation reaction of hydrocarbon and / or oxygen-containing organic compound as a reducing agent proceeds, Nitrogen oxide removal rate decreases. On the other hand, when the average diameter exceeds 10,000 nm, the reaction characteristics of the silver component are reduced, and the nitrogen oxide removal rate is reduced.
The average diameter of the preferred silver component aggregate is 10 to 5000 n.
m, more preferably 10 to 2000 nm. In addition,
The average here means an arithmetic average.

When the purifying material is in the above-described first preferred embodiment, the thicknesses of the first catalyst and the second catalyst provided on the purifying material substrate are generally the same as the thickness of the base material and the catalyst. Are often limited due to differences in thermal expansion characteristics. 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 first catalyst and the amount of the second catalyst provided on the surface of the purifying material base are 20 to
Preferably it is 300 g / l. The amount of catalyst is 2
If it is less than 0 g / liter, good nitrogen oxides cannot be removed. On the other hand, when the amount of the catalyst exceeds 300 g / liter, the removal characteristics do not increase so much and the pressure loss increases.
More preferably, the first catalyst and the second catalyst provided on the surface of the purifying material base are respectively 50 to 200
g / liter.

(2) Third catalyst The third catalyst comprises a porous inorganic oxide carrying catalytically active species and is formed on the exhaust gas outflow side, and acts to remove nitrogen oxides in a low temperature region. And at the same time, oxidize and remove carbon monoxide and hydrocarbons. As the porous inorganic oxide, it is preferable to use at least one oxide selected from the group consisting of alumina, titania and zeolite, or a composite or mixed oxide thereof. Similar to the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

As the active species of the third catalyst, W,
An oxide or sulfate of at least one element selected from the group consisting of V and Mo is used. W out of W, V and Mo
And / or V is preferably used. Assuming that the porous inorganic oxide is 100% by weight, the loading amount of the W component is 0.5 to 3%.
The amount is 0% by weight (in terms of metal element), and the preferred amount is 1 to 25% by weight (in terms of metal element). By using the third catalyst, nitrogen oxides can be removed using ammonia generated by the first catalyst and the second catalyst.

For loading the active species on the third catalyst, a known impregnation method, precipitation method, or the like can be used. When the impregnation method is used, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, nitrate, acetate, sulfate, chloride, hexachlorometal acid, or the like of a catalytically active species element. W, V, Mo, Mn, Nb,
In the case of Ta, a porous inorganic oxide is immersed in an aqueous solution of an ammonium salt, oxalate or the like of each element for use. 50-1
After drying at 50 ° C., particularly 70 ° C., the temperature is raised stepwise at 100 to 600 ° C. and firing is performed. This calcination is performed in air under a nitrogen stream containing oxygen. It is also an effective method to use metatitanic acid (hydrous titanium oxide) as a starting material instead of titania and to carry V, W, and Mo. When zeolite is used as the inorganic oxide, it is preferable to support the zeolite by an impregnation method or a known ion exchange method.

In the case where the purifying material is in the above-described first preferred embodiment, the thickness of the third catalyst provided on the purifying material base is preferably 300 μm or less. The amount of the third catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter based on the purifying material base.

(3) Fourth catalyst The fourth catalyst is formed by supporting catalytically active species on a porous inorganic oxide, and is formed on the exhaust gas outflow side, and acts to remove nitrogen oxides in a low temperature region. And at the same time, oxidize and remove carbon monoxide and hydrocarbons. As the porous inorganic oxide, it is preferable to use one or more oxides selected from the group consisting of alumina, titania, zirconia, silica, and zeolite, or a composite or mixed oxide thereof. Like the first catalyst, the specific surface area of the porous inorganic oxide is 10 m
It is preferably at least ² / g.

As the active species of the fourth catalyst, Pt, P
At least one element selected from the group consisting of d, Ru, Rh, Ir, and Au is used. Among Pt, Pd, Ru, Rh and Au, it is particularly preferable to use at least one of Pt, Pd and Au. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the platinum-based component is 0.01 to 5% by weight (in terms of a metal element), and the preferable supported amount is 0.01 to 4% by weight (in terms of a metal element). ). By using the fourth catalyst, harmful substances such as carbon monoxide and hydrocarbons can be oxidized and removed.

For supporting the active species on the fourth catalyst, a known impregnation method, precipitation method or the like can be used. When the impregnation method is used, the porous inorganic oxide is immersed in an aqueous solution of a carbonate, nitrate, acetate, sulfate, chloride, hexachlorometal acid, or the like of a catalytically active species element. 50-150 ° C, especially 70 ° C
After the drying, the temperature is raised stepwise at 100 to 600 ° C., followed by firing. This calcination is performed in air under a nitrogen stream containing oxygen.

When the form of the purifying material is the above-described first preferred embodiment, the thickness of the fourth catalyst provided on the purifying material base is preferably 300 μm or less. The amount of the fourth catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter based on the purifying material base.

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 1:
It is preferably 10 to 20: 1. When the ratio is less than 1:10 (the amount of the first catalyst is small), 150 to 600 ° C.
Over a wide temperature range, the purification rate of nitrogen oxides decreases overall. On the other hand, when the ratio exceeds 20: 1 and the amount of the second catalyst is small, the removal characteristics of nitrogen oxides by the aldehyde deteriorate. A more preferred weight ratio of the first catalyst to the second catalyst is 1:
5 to 10: 1.

In the first exhaust gas purifying material of the present invention, the ratio of the total weight of the first catalyst and the second catalyst to the weight of the third catalyst (the total weight of the porous inorganic oxide and the catalytically active species) Ratio)
Is preferably 10: 1 to 1: 5. The ratio is 1:
Less than 5 (first and second catalysts are low)
As a result, the purification rate of nitrogen oxides as a whole decreases over a wide temperature range of 150 to 600 ° C. On the other hand, if the ratio exceeds 10: 1 and the amount of the third catalyst is small, ammonia formed on the first catalyst is not effectively used for reduction of nitrogen oxides. More preferably, the weight ratio of the total weight of the first catalyst and the second catalyst to the weight of the third catalyst is 5: 1 to 1: 4.

In the second exhaust gas purifying material of the present invention, a third catalyst and a fourth catalyst are mixed and used. The weight ratio of the third catalyst to the fourth catalyst (ratio of the total weight of the porous inorganic oxide and the catalytically active species) is preferably from 2: 1 to 100: 1. When the ratio is less than 2: 1 (the amount of the third catalyst is small), the purification rate of nitrogen oxides is reduced overall in a wide temperature range of 150 to 600 ° C. On the other hand, the ratio is 100: 1
When the amount of the fourth catalyst is less than the above, the oxidation characteristics of hydrocarbons and carbon monoxide deteriorate. A more preferred weight ratio of the third catalyst to the fourth catalyst is 5: 1 to 90: 1.

In the second exhaust gas purifying material of the present invention, the ratio of the total weight of the first catalyst and the second catalyst to the total weight of the third catalyst and the fourth catalyst (porous inorganic oxide and catalyst) (The ratio of the total weight to the active species) is preferably 10: 1 to 1: 5. When the ratio is less than 1: 5 (the amount of the first catalyst and the amount of the second catalyst are small), the purification rate of nitrogen oxides is generally reduced in a wide temperature range of 150 to 600 ° C. On the other hand, if the ratio exceeds 10: 1 and the amount of the third catalyst + the fourth catalyst is small, the ammonia formed on the first catalyst is not effectively used for reducing nitrogen oxides, Oxidation characteristics such as carbon oxide are reduced. More preferably, the ratio of the total weight of the first catalyst and the second catalyst to the total weight of the third catalyst and the fourth catalyst is 10: 1 to 1: 2.

If the purifying material having the above configuration is used, 150
In a wide temperature range of up to 600 ° C., good removal of nitrogen oxides can be performed even with an exhaust gas containing about 10% of moisture and sulfur oxides.

Next, the method of the present invention will be described. First, in the first exhaust gas purifying material, the first catalyst, the second catalyst, and the third catalyst are installed in the exhaust gas conduit in order from the exhaust gas inflow side to the outflow side of the purifying material. In the second exhaust gas purifying material, the first catalyst, the second catalyst, and the third catalyst are arranged in the exhaust gas conduit in order from the exhaust gas inflow side to the outflow side of the purifying material.

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, in the case of an alkane or alkene, it preferably has 2 or more carbon atoms. Specific examples of hydrocarbons that are liquid in the standard state include gas oil, cetane,
Examples include hydrocarbons such as heptane, kerosene, gasoline and the like.
Among them, hydrocarbons having a boiling point of 50 to 350 ° C are particularly preferable. As the oxygen-containing organic compound introduced from the outside, alcohols such as ethanol and isopropyl alcohol having 2 or more carbon atoms, or a fuel containing them can be used.

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

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

In the present invention, the space velocities of the first catalyst and the second catalyst are each 150,000 h ^-1 or less so that the reduction and removal of nitrogen oxides by an oxygen-containing organic compound, hydrocarbon and the like can efficiently proceed. , Preferably 100,000 h ^-1 or less. The space velocity of the first catalyst and the second catalyst is 150,0
If it exceeds 00 h ⁻¹ , the reduction reaction of nitrogen oxides does not sufficiently occur, and the nitrogen oxide removal rate decreases. In the first exhaust gas purifying material, the space velocity of the third catalyst is 200,000h ^-1 or less,
Preferably it is 150,000 h ^-1 or less. In the second exhaust gas purification material, the space velocity of the mixed catalyst of the third catalyst and a fourth catalyst 200,000 ^-1 or less, preferably 150,000H ^-1 or less.

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 to 150 to 600 ° C.
To keep. If the temperature of the exhaust gas is lower than 150 ° C., the reaction between the reducing agent and the nitrogen oxide does not proceed, and it is not possible to remove the nitrogen oxide satisfactorily. On the other hand, if the temperature exceeds 600 ° C., the combustion of the hydrocarbon and / or the oxygen-containing organic compound itself starts, and the reduction and removal of nitrogen oxides cannot be performed. The preferred exhaust gas temperature is from 200 to 550C, more preferably from 300 to 500C.

[0047]

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 immersed in an aqueous silver nitrate solution, taken out, and dried at 70 ° C. for 2 hours. Then, the temperature is raised stepwise to 600 ° C. in the air, and calcined for 5 hours.
A first catalyst supporting silver by weight (in terms of a metal element) was prepared. 0.26 g of the first catalyst was charged with a commercially available cordierite honeycomb formed body (diameter 20 mm, length 8.3 m).
m, 400 cells / inch ² ) and after drying 600
The mixture was baked stepwise to ℃ to prepare a silver-based purifying material (a purifying material coated with a first catalyst).

In the same manner as the above-mentioned silver-based catalyst, a second catalyst in which 5.0% by weight (in terms of a metal element) of silver was supported on powdered alumina was prepared, and a second honeycomb-shaped body similar to the above was prepared. 0.26 g of the second catalyst was coated, and a second silver-based purifying material (a purifying material coated with the second catalyst) was prepared in the same manner.

Next, water was added to ammonium tungstate parapentapentahydrate and oxalic acid, and dissolved by heating on a water bath, and then powdered titania (specific surface area 35 m ² / g) was added to the cooled aqueous solution. It was charged and immersed for 20 minutes. afterwards,
Separate the titania from the solution and in air at 80 ° C, 100
The resultant was dried at 120 ° C. for 2 hours. Then, 20% oxygen
The temperature was raised from 120 ° C. to 500 ° C. in 5 hours under a nitrogen gas flow containing, and calcined at 500 ° C. for 4 hours to carry 7.4 wt% (converted to metal element) of W oxide with respect to titania. Then, a W-based catalyst (third catalyst) was prepared. After slurrying 0.26 g of the third catalyst, it was coated on the same honeycomb formed body as the above-mentioned silver-based purifying material, and dried and fired under the same conditions as the silver-based purifying material to obtain a W-based purifying material (third material). Purification material coated with the above catalyst was prepared.

A silver-based purifying material, a second silver-based purifying material, and a W-based purifying material were set in order from the inflow side to the outflow side of the exhaust gas in the reaction tube. Next, a gas (nitrogen monoxide, oxygen, ethanol, sulfur dioxide, nitrogen and moisture) having a composition shown in Table 1 was flowed at a flow rate of 3.48 liters per minute (standard state) (apparent space velocity of each purification material). Were about 80,000 h ^-1 ), and the temperature of the exhaust gas in the reaction tube was kept in the range of 350 to 550 ° C., and ethanol and nitrogen oxides were reacted.

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

Table 1 Component concentration Nitric oxide 800 ppm Oxygen 10% by volume Ethanol 1560 ppm Sulfur dioxide 30 ppm Nitrogen Residual water 10% by volume (based on the total volume of the above components)

Example 2 As in Example 1, 3.1% by weight (in terms of metal element) of commercially available silica-alumina powder (silica content: 5% by weight, specific surface area: 350 m ² / g) using an aqueous silver nitrate solution. The first catalyst was prepared by carrying silver of value (1). First catalyst 0.2
6 g of a commercially available cordierite honeycomb-shaped molded product (diameter: 20 mm, length: 8.3 mm, 400 cells / inch ² )
And dried and fired stepwise to 600 ° C. to prepare a silver-based purifying material (a purifying material coated with a first catalyst).

In the same manner as in the above-mentioned silver-based catalyst, a second catalyst in which 5% by weight (in terms of a metal element) of silver was supported on powdery silica / alumina was prepared. 0.26 g of the second catalyst was coated, and a second silver-based purifying material (a purifying material coated with the second catalyst) was prepared in the same manner.

A silver-based purifying material, a second silver-based purifying material, and a W-based purifying material of Example 1 were set in order from the inflow side to the outflow side of the exhaust gas in the 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 each purification material was about 80,000 h ^-1 ).
Table 2 shows the results.

Example 3 Oxalic acid was added to vanadium pentoxide and dissolved by heating on a water bath. Then, the same powdery titania as the third catalyst of Example 1 was added to the cooled aqueous solution, and Soak for minutes. Thereafter, the titania was separated from the solution and, in air,
It dried at 0 degreeC, 100 degreeC, and 120 degreeC for 2 hours each. Subsequently, under a nitrogen stream containing 20% of oxygen, 120 ° C. to 500 ° C.
Up to 5 hours, bake at 500 ° C for 4 hours,
A V-based catalyst (third catalyst) was prepared by supporting 4.8% by weight (in terms of metal element) of V oxide with respect to titania.
After slurrying 0.26 g of the third catalyst, Example 1 was used.
The honeycomb formed body was coated in the same manner as described above, dried and fired to prepare a V-based purifying material (a purifying material coated with a third catalyst).

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

Example 4 In the same manner as in the third catalyst of Example 1, 4.5 wt% (converted to metal element) of W oxide was supported on the same powdery titania as in Example 1 to obtain W A system catalyst was prepared. Using this V-based catalyst, in the same manner as in Example 3, V-oxide was further supported on titania by 2.2% by weight (in terms of a metal element), and a W, V-based catalyst (third catalyst) was used. Was prepared. 0.26
g of the third catalyst was slurried, coated on a honeycomb formed body in the same manner as in Example 1, dried and fired,
W and V-based purifying materials (purifying materials coated with a third catalyst) were prepared.

The silver-based purifying material of Example 1, the second silver-based purifying material of Example 1, and the W and V-based purifying materials were set in this order from the inflow side to the outflow side of the exhaust gas in the reaction tube. The same reaction conditions as in Example 1 (the apparent space velocities of the respective purifying materials were about 8
(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 5 Powdered titania (specific surface area: 35 m ² / g) was immersed in an aqueous chloroplatinic acid solution for 20 minutes, dried in air at 80 ° C. for 2 hours, and dried at 120 ° C. for 2 hours in a nitrogen stream. 200-40
It was fired stepwise for 1 hour to 0 ° C. Then, the temperature was raised from 50 ° C. to 400 ° C. over 5 hours under a nitrogen gas stream containing 4% of hydrogen gas, calcined at 400 ° C. for 4 hours, and further heated to 50 ° C. to 500 ° C. under a nitrogen gas stream containing 10% oxygen. And then calcined at 500 ° C. for 5 hours to carry 0.21% by weight (converted to metal element) of Pt with respect to titania.
A t-based catalyst (fourth catalyst) was prepared. The weight ratio of the W-based catalyst of Example 1 to the Pt catalyst was 40: 1,
After mixing both catalysts and further forming a slurry, the slurry was coated on a honeycomb formed body of 0.26 g (dry base) in the same manner as in Example 1, dried and fired, and W, Pt
A system purifying material (a purifying material coated with a mixed catalyst) was prepared.

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

Example 6 Example 2 in order from the inflow side of the exhaust gas in the reaction tube to the outflow side.
Silver-based purifying material, second silver-based purifying material of Example 2, Example 5
Was set. The same reaction conditions as in Example 1 (the apparent space velocities of the respective purifying materials were about 80, respectively)
000 h ⁻¹ ), and evaluation was performed using a gas having a composition shown in Table 1. Table 2 shows the results.

Example 7 The same catalyst as in Example 1 was prepared by mixing and further slurrying the V-based catalyst of Example 3 and the Pt catalyst of Example 5 so that the weight ratio thereof was 20: 1. The slurry is then treated with 0.
26 g (dry base) of a honeycomb formed body was coated, dried and fired to prepare a V, Pt-based purifying material (a purifying material coated with a mixed catalyst).

The silver-based purifying material of Example 1, the second silver-based purifying material of Example 1, and the V and Pt-based purifying materials were set in this order from the inflow side to the outflow side of the exhaust gas in the 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 each purification material was about 80,000 h ^-1 ). Table 2 shows the results.

Example 8 After mixing the W and V catalysts of Example 4 and the Pt catalyst of Example 5 so that the weight ratio of the two catalysts was 10: 1 and further forming a slurry, Example 1 was used. 0.26 g (dry base) of the formed honeycomb article was coated with the slurry in the same manner as in
After drying and firing, W, V, and Pt-based purifying materials (purifying materials coated with a mixed catalyst) were prepared.

The silver-based purifying material of Example 1, the second silver-based purifying material of Example 1, and the W, V, and Pt-based purifying materials were set in this order from the inflow side to the outflow side of the exhaust gas in the reaction tube. Example 1
Evaluation was carried out under the same reaction conditions as described above (the apparent space velocity of each purifying material was about 80,000 h ^-1 ) using a gas having a composition shown in Table 1. Table 2 shows the results.

COMPARATIVE EXAMPLE 1 0.52 g of the first catalyst prepared in Example 1 was mixed with the same honeycomb formed body (diameter 20 mm, length 16.6 mm, 400
Cells / inch ² ), and dried and fired to prepare a silver-based purifying material. A silver-based purifying material was set in an exhaust gas conduit, and evaluated under the same reaction conditions as in Example 1 (the apparent space velocity was about 80,000 h ^-1 ) using a gas having a composition shown in Table 1. . Table 2 shows the results.

Table 2 Removal rate of nitrogen oxide (NOx) Removal rate of nitrogen oxide (%) Reaction temperature (° C.) 350 400 450 500 550 Example 1 57.6 78.5 94.7 95.0 90.6 Example 2 54.4 77.8 91.1 93.9 89.8 Execution Example 3 60.1 80.5 94.4 94.8 87.2 Example 4 60.8 78.7 93.8 94.1 89.6 Example 5 58.6 79.5 91.7 93.0 88.6 Example 6 56.4 78.8 88.1 92.9 85.8 Example 7 62.1 82.5 92.4 93.8 84.2 Example 8 64.8 79.7 91.8 93.1 85.6 Comparative Example 1 20.5 30.5 35.7 42.6 40.5

As can be seen from Table 2, in Examples 1 to 8, better removal of nitrogen oxides was observed in a wider exhaust gas temperature range than in Comparative Example 1 using only a silver catalyst. In Examples 5 to 8 using a platinum-based catalyst, it was confirmed that carbon monoxide and residual hydrocarbons were effectively oxidized and removed.

[0070]

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 number Agency reference number FI Technical display location B01J 23/16 A 23/22 A 23/30 A 23/48 A 23/64 A 23/648 23 / 652 27/053 A 27/055 A 32/00 35/02 P B01D 53/36 102 B 102 C 102 H B01J 23/64 102 A 103 A (72) Inventor Kiyohide Yoshida Suehiro 4-chome, Kumagaya City, Saitama Prefecture No. 14-1 Rikken Kumagaya Office

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 excess of the theoretical reaction amount of coexisting unburned components, wherein the porous inorganic oxides are used as active species. 0.2 to 12% by weight of silver and / or a silver compound or a mixture thereof (in terms of silver element)
And a silver and / or silver compound as an active species in a porous inorganic oxide or a mixture thereof in an amount of 1 to 15% by weight (in terms of silver element) and the first catalyst A second catalyst supporting an amount greater than the active species loading rate, and W, V, Mo,
A purifying material comprising a third catalyst carrying 0.5 to 30% by weight (in terms of a metal element) of an oxide or sulfate of at least one element selected from the group consisting of Mn, Nb, and Ta; The first catalyst in order from the exhaust gas inflow side to the outflow side,
An exhaust gas purifying material comprising the second catalyst and the third catalyst. 2. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen which is larger than a theoretical reaction amount of coexisting unburned components, wherein the porous inorganic oxides are used as active species. 0.2 to 12% by weight of silver and / or a silver compound or a mixture thereof (in terms of silver element)
And a silver and / or silver compound as an active species in a porous inorganic oxide or a mixture thereof in an amount of 1 to 15% by weight (in terms of silver element) and the first catalyst A second catalyst supporting an amount greater than the active species loading rate, and W, V, Mo,
A third catalyst supporting 0.5 to 30% by weight (in terms of metal element) of an oxide or sulfate of at least one element selected from the group consisting of Mn, Nb, and Ta; R
at least one selected from the group consisting of u, Rh, Ir, and Au
A fourth catalyst carrying 0.01 to 5% by weight of a seed element (in terms of a metal element), wherein the third catalyst and the fourth catalyst are mixed, and An exhaust gas purifying material comprising: the first catalyst, the second catalyst, and the mixed catalyst in order from an exhaust gas inflow side to an outflow side. 3. The exhaust gas purifying material according to claim 1, wherein at least one of the first, second, third, and fourth catalysts is coated on a surface of a ceramic or metal substrate. An exhaust gas purifying material characterized in that it has been manufactured. 4. The exhaust gas purifying material according to claim 1, wherein at least one of the first, second, third and fourth catalysts is in the form of pellets or granules. Exhaust gas purifying material. 5. The exhaust gas purifying material according to claim 1, wherein the silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate, and silver phosphate. An exhaust gas purifying material characterized by that: 6. The exhaust gas purifying material according to claim 1, wherein said porous inorganic oxide is alumina or titania in the first and second catalysts, or a composite or mixed material containing them. Oxides, alumina for the third catalyst,
An exhaust gas characterized by being one or more oxides selected from the group consisting of titania and zeolite, and the fourth catalyst being one or more oxides selected from the group consisting of alumina, titania, zirconia, silica, and zeolite. Purifying 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 installed in the middle of an exhaust gas conduit, and the exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds are added on the upstream side of the purifying material is subjected to the purifying material at 150 to 600 ° C. Exhaust gas purifying method, wherein the nitrogen oxides are removed by contact with a hydrocarbon and / or an oxygen-containing organic compound in the exhaust gas.