JP2700386B2 - Exhaust gas purifying material and exhaust gas purifying method - Google Patents

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 inventors have found that a first catalyst comprising a porous inorganic oxide carrying a specific amount of a silver component and a copper component alone or Using an exhaust gas purifying material formed by separating a second catalyst supporting a copper component and a W-based component and a third catalyst supporting a component such as Pt, hydrocarbons and When an exhaust gas is brought into contact with the above catalyst at a specific temperature after addition of an oxygen-containing organic compound, nitrogen oxides are reduced on the silver catalyst and nitrogen-containing substances such as nitrites and ammonia are produced as by-products. Compounds and aldehydes are generated, and these nitrogen-containing compounds are reduced to nitrogen with a copper-based catalyst, and residual hydrocarbons and carbon monoxide are removed with a platinum-based catalyst. Effective for nitrogen oxides over a wide temperature range It discovered that can be removed, thereby completing the present invention.

That is, the first exhaust gas purifying material of the present invention for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than the theoretical reaction amount of coexisting unburned components is the exhaust gas purifying material. From the inflow side to the outflow side, it has first to third catalysts, and the first catalyst is a porous aluminum.
Na, titania and / or zeolite
Silver and / or a silver compound as an active species in a complex oxide or a mixed oxide thereof, or a mixture thereof 0.2 to 15;
% (In terms of silver element), and the second catalyst contains 0.2 to 30% by weight of copper oxide and / or copper sulfate as an active species on porous γ-alumina and / or titania.
It carries (copper metal basis), the third catalyst A
Lumina, titania, zirconia, silica, zeolite
At least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and Au as an active species in one or more porous inorganic oxides selected from the group consisting of 0.01 to 5;
It is characterized by being supported by weight% (in terms of metal element).

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 a theoretical reaction amount for co-existing unburned components, From the inflow side to the outflow side, the first catalyst has first to third catalysts, and the first catalyst is formed on a porous inorganic oxide by using silver and / or a silver compound as an active species or a mixture thereof in a range of 0.2 to 15; Weight percent (in terms of silver element), and the second catalyst is a porous inorganic oxide in which 0.2 to 30 weight% of copper oxide and / or sulfate as an active species (in terms of copper element) Value) and an oxide or sulfate of at least one element selected from the group consisting of W, V, and Mo, in an amount of 30% by weight or less (in terms of a metal element), and the third catalyst is porous. Pt, Pd, Ru, R as active species on high quality inorganic oxides
It is characterized by carrying at least one element selected from the group consisting of h, Ir and Au in an amount of 0.01 to 5% by weight (in terms of a metal element).

Further, 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 excess of the theoretical reaction amount for coexisting unburned components, comprises: And the exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds are added on the upstream side of the purification material is brought into contact with the purification material at 150 to 600 ° C., whereby the hydrocarbons and / or The nitrogen oxide is removed by a reaction with an oxygen-containing organic compound.

Hereinafter, the present invention will be described in detail. In the first exhaust gas purifying material of the present invention, a first catalyst in which silver and / or a silver compound as active species are supported on a porous inorganic oxide or a mixture thereof is formed on the exhaust gas inflow side. , Pt, Pd, Ru, R which are active species on the porous inorganic oxide on the outflow side
h, forming a third catalyst carrying at least one element selected from the group consisting of Ir and Au, between the first catalyst and the third catalyst, a porous inorganic oxide An exhaust gas purifying material formed by forming a second catalyst carrying an active species copper oxide and / or copper sulfate is installed in an exhaust gas conduit,
A hydrocarbon and / or an oxygen-containing organic compound is added to the exhaust gas on the upstream side from the installation position of the purifying material, and the exhaust gas is brought into contact with the purifying material. Nitrogen oxidation in the exhaust gas using the hydrocarbon and the oxygen-containing organic compound as a reducing agent The substance is reduced and removed.

In the second exhaust gas purifying material of the present invention,
On the exhaust gas inflow side, a first catalyst comprising silver and / or a silver compound, which is an active species, or a mixture thereof is formed on a porous inorganic oxide, and on the outflow side, a porous inorganic oxide is formed. Forming a third catalyst carrying at least one element selected from the group consisting of active species Pt, Pd, Ru, Rh, Ir, and Au, the first catalyst and the third catalyst In between, the porous inorganic oxide carries copper oxide and / or sulfate as an active species and oxide or sulfate of at least one element selected from the group consisting of W, V and Mo. Exhaust gas purifying material forming the second catalyst is installed in an exhaust gas conduit, and hydrocarbons and / or oxygen-containing organic compounds are added to the exhaust gas upstream of the installation position of the purifying material to remove the exhaust gas. Nitric acid in exhaust gas by contacting this purification material with hydrocarbons and oxygen-containing organic compounds as reducing agents Things to the 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 preferable that it is composed of two or more parts such as an intermediate part and an outlet part. Examples of the structure include a honeycomb structure type, a foam type, a three-dimensional network structure type formed of a fibrous refractory, a granular shape, a pellet shape, and 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 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 The first catalyst is formed by supporting silver and / or a silver compound or a mixture thereof on a porous inorganic oxide, and is formed on the inflow side of exhaust gas. Acts on oxide removal. 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 preferably, a silver oxide and / or
Or silver chloride. As the porous inorganic oxide, porous alumina, silica, titania, zirconia, zeolite and composite oxides thereof and the like can be used, preferably γ-alumina, any of or including titania A composite oxide or a mixed oxide thereof is used. Reaction of added hydrocarbons, oxygen-containing organic compounds and / or residual hydrocarbons in exhaust gas with nitrogen oxides in exhaust gas by using γ-alumina, titania or their composite oxides or mixed oxides thereof Occurs efficiently.

The specific surface area of the porous inorganic oxide such as alumina used for the first catalyst is preferably 10 m ² / g or more. If the specific surface area is less than 10 m ² / g, the 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 preferably, the specific surface area of the porous inorganic oxide is 30 m.
² / g or more.

The amount of the silver component supported as an active species on the inorganic oxide such as γ-alumina is determined by the amount of the inorganic oxide 10
0.2 to 15% by weight with respect to 0% by weight (in terms of silver element)
And 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. The preferred loading of the silver component is 0.5 to 12% 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. 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.

It has been observed that a silver component supported on a porous inorganic oxide using an aqueous solution of silver nitrate or the like forms a circular aggregate when fired in an oxidizing atmosphere. In the purification material of the present invention, the average diameter of the silver component aggregate is 10 to 10,000 n
m is preferable. In general, the smaller the diameter of the silver component aggregate, the higher the reaction characteristics, but the average diameter is 10n.
If it is less than m, only the oxidation reaction of the hydrocarbon and / or the oxygen-containing organic compound as the reducing agent proceeds, and the 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 5
000 nm, more preferably 10 to 2000 nm. Here, the average means an arithmetic average.

When the purifying material is in the above-described first preferred embodiment, the thickness of the first catalyst provided on the purifying material substrate generally depends on the thermal expansion characteristics of the substrate material and the catalyst. Often limited by differences. The thickness of the catalyst provided on the purifying material base is preferably 300 μm or less. With such a thickness, it is possible to prevent the purifying material from being damaged by thermal shock or the like during use. A method for forming a catalyst on the surface of the purifying material base is performed by a known washcoat method or the like.

Further, the amount of the first catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / l based on 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 exceeds 300 g / liter, the removal characteristics do not increase so much and the pressure loss increases. More preferably, the first catalyst provided on the surface of the purifying material base is provided with 50 to
200 g / liter.

(2) Second Catalyst The second catalyst comprises a porous inorganic oxide carrying catalytically active species. Examples of the porous inorganic oxide include alumina and its oxides (γ-alumina-titania, γ-alumina-silica, γ-alumina-zirconia, etc.), zirconia, titania and other heat-resistant ceramics having a large surface area. No. Preferably, either alumina or titania, a composite oxide containing them, or a mixed oxide thereof is used. Similar to the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

In the first exhaust gas purifying material of the present invention, copper oxide and / or copper sulfate is used as the active species of the second catalyst. By using the second catalyst, while reducing nitrogen oxides such as nitrogen oxides and nitrites generated by the first catalyst to nitrogen to remove nitrogen oxides ,
Ammonia generated in the first catalyst can be oxidized to nitrogen . Assuming that the porous inorganic oxide is 100% by weight, the supported amount of the copper component is 0.2 to 30% by weight (in terms of a metal element).
And the preferred amount of the carrier is 0.5 to 25% by weight.

In the second exhaust gas purifying material of the present invention, the active species of the second catalyst is at least one selected from the group consisting of oxides and / or sulfates of copper and W, V and Mo. And an oxide or a sulfate of the element (a). W, V, M
Of o, it is preferable to use W and / or V. By using the second catalyst, nitrogen oxides can be reduced by reducing nitrogen oxides and nitrogen-containing compounds generated by the first catalyst, such as nitrite and ammonia, to nitrogen. Assuming that the porous inorganic oxide is 100% by weight, the supported amount of copper oxide and / or copper sulfate is 0.2 to 30% by weight (in terms of a metal element), and the supported amount of W component is 30% by weight. The following are the values (in terms of metal elements). The total loading of the copper component and the W-based component is 0.2 to 60% by weight (in terms of metal element).
(Metal element conversion value). The preferred loading of the copper component is 0.5 to 25% by weight (in terms of a metal element), and the preferred loading of the W-based component is not more than 25% by weight (in terms of a metal element). Is preferably 0.5 to 50% by weight (in terms of a metal element).

For loading the active species on the second catalyst, 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 a carbonate, nitrate, acetate, sulfate or the like of the catalytically active species element. In the case of a copper component, an aqueous solution such as copper sulfate or copper nitrate is used. W,
In the case of V or Mo, a porous inorganic oxide is immersed in an aqueous solution of an ammonium salt, oxalate or the like of each element for use. 50
After drying at ~ 150 ° C, especially at 70 ° C, the temperature is raised stepwise at 100-600 ° 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 the form of the purifying material is the first preferred embodiment described above, the thickness of the second catalyst provided on the purifying material base is preferably 300 μm or less. The amount of the second 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 is:
The ratio is preferably set to 5: 1 to 1: 5. When the ratio is less than 1: 5 (the amount of the first 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 exceeds 5: 1 (most of the first catalyst)
The purification ability of nitrogen oxides at 400 ° C. or lower does not increase. That is, the reaction between the reducing agent and the nitrogen oxide at a relatively low temperature does not sufficiently proceed. More preferably, the weight ratio of the first catalyst to the second catalyst is from 4: 1 to 1: 4.

(3) 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 range. And at the same time, oxidize and remove carbon monoxide and hydrocarbons. As the porous inorganic oxide, it is preferable to use one or more oxides or composite oxides selected from the group consisting of alumina, titania, zirconia, silica, and zeolite. Similar to the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

The active species of the third catalyst include Pt, P
d, Ru, Rh, using at least one element selected from the group consisting of Ir and Au, it is preferable to use at least one of Pt, Pd, Ru, Rh and Au, particularly at least Pt, Pd and Au One is preferred. The total of the active species supported on the inorganic oxide by the third catalyst is based on the above-mentioned porous inorganic oxide.
(100% by weight) is 0.01 to 5% by weight, preferably 0.01 to 4% by weight. Even when the amount of the catalytically active species exceeds 5% by weight of the porous inorganic oxide, the performance of removing nitrogen oxides is not improved.

The active species of the third catalyst may further include at least one selected from the group consisting of rare earth elements such as La and Ce, alkaline earth elements such as Ca and Mg, and alkali metal elements such as Na and K. It is preferable to carry one or more elements in an amount of 10% by weight or less. By supporting a rare earth, alkaline earth, or alkali metal element, the heat resistance of a platinum-based catalyst can be improved.

For loading the active species on the third catalyst, known impregnation methods, precipitation methods and the like can be used. When using the impregnation method, the porous inorganic oxide is immersed in an aqueous solution such as a chloride or hexachlorometallic acid of a catalytically active species element, dried at 70 ° C., and then gradually heated at 100 to 700 ° C. and fired. This is done by: The calcination is performed under a nitrogen stream or a hydrogen-containing or oxygen-containing nitrogen stream. Preferably, the calcination is performed under a nitrogen stream, and then the calcination is performed under a hydrogen-containing nitrogen stream or an oxygen-containing nitrogen stream. Although the Pt-based loading component is shown as a metal element, the loading component exists in a state of a metal and an oxide under a normal use temperature condition of the purification material.

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.

The weight ratio of the first catalyst to the third catalyst is
The ratio is preferably set to 5: 1 to 1: 5. When the ratio is less than 1: 5 (the amount of the first 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 exceeds 5: 1 (most of the first catalyst)
In this case, the purification performance of nitrogen oxides at 400 ° C. or lower does not increase, and the removal rate of carbon monoxide and hydrocarbons decreases. More preferably, the weight ratio of the first catalyst to the third catalyst is from 4: 1 to 1: 4.

If the purifying material having the above-described structure is used, 150
In a wide temperature range of up to 600 ° C., excellent removal of nitrogen oxides can be performed even with exhaust gas containing about 10% of water.

Next, the method of the present invention will be described. First, the exhaust gas conduit so that the first catalyst faces the exhaust gas inlet, the third catalyst faces the exhaust gas outlet, and the second catalyst is located between the first catalyst and the second catalyst. Installed in the middle of

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

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

The amount of the hydrocarbon and / or oxygen-containing organic compound introduced from the outside is determined by the weight ratio (weight of added reducing agent / 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.

In the present invention, the apparent space velocity of the first catalyst and the second catalyst is set to 150,000 / hour or less, and The apparent space velocity is preferably not more than 200,000 / hour.

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

[0045]

The present invention will be described in more detail with reference to the following specific examples. Example 1 11.7 g of commercially available γ-alumina pellets (particle size: 0.5 to 2 mm, specific surface area: 200 m ² / g) (apparent volume: 21.
7 ml) was immersed in a silver nitrate aqueous solution (a solution prepared by dissolving 0.76 g of silver nitrate in 22 ml of water) for 20 minutes, taken out, and dried at 70 ° C. for 2 hours. Then, the temperature is gradually increased to 600 ° C. in the air, and then calcined for 5 hours.
A first catalyst carrying silver was prepared.

Next, 3.1 g (apparent volume: 3.1 ml) of titania pellets (particle size: 0.5 to 2 mm, specific surface area: 50 m ² / g) were immersed in an aqueous copper sulfate solution (copper concentration: 7.7% by weight). And dried in air at 80 ° C, 100 ° C and 120 ° C for 2 hours each. Subsequently, under a nitrogen stream containing 20% of oxygen, 1
The temperature was raised stepwise from 20 ° C. to 500 ° C. and calcined at 500 ° C. for 5 hours to prepare a second catalyst supporting 4.4% by weight of copper sulfate (converted to a copper element) with respect to titania.

Further, the same titania as pellets15.
5 g (apparent volume 15.5 ml) was immersed in a chloroplatinic acid aqueous solution for 20 minutes, and then dried in air at 80 ° C. for 2 hours.
The mixture was calcined in a nitrogen stream at 120 ° C. for 2 hours and 200 to 400 ° C. for 1 hour each. 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 prepare a third catalyst carrying 0.21% by weight (converted to metal element) of Pt with respect to titania.

[0048] The first catalyst 1.
7 g (3.1 ml), 3.4 g (3.1 m) of the second catalyst
l), 3.1 g (3.1 ml) of the third catalyst were combined as a purifying material, and set in a reaction tube. Next, a gas (nitrogen monoxide, oxygen, ethanol, carbon dioxide, nitrogen and moisture) having a composition shown in Table 1 was flowed at a flow rate of 2 liters per minute (standard state) (first, second and third flows). The apparent space velocity of the catalyst is about 40,000 h ^-1 ), and the temperature of the exhaust gas in the reaction tube is 3
Ethanol and nitrogen oxide were reacted while keeping the temperature in the range of 00 to 600 ° C.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured by a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 3 shows the results.

Table 1 Component concentration Nitric oxide 1000 ppm Oxygen 10% by volume Ethanol 1250 ppm Carbon dioxide 10% by volume Nitrogen Residual water 10% by volume (based on the total volume of the above components)

Example 2 The same first and second catalysts as in Example 1 were used. Then, in the same manner as in Example 1, a third catalyst was prepared in which 0.19% by weight (in terms of a metal element) of Pd was supported on pelletized titania using an aqueous palladium chloride solution (palladium concentration: 0.5% by weight). .

The first catalyst 1.
7 g (3.1 ml), 3.4 g (3.1 m) of the second catalyst
l), 3.1 g (3.1 ml) of the third catalyst were combined as a purifying material, and set in a reaction tube. Evaluation was carried out under the same reaction conditions as in Example 1 (approximate space velocity of the first, second and third catalysts of about 40,000 h ^-1 ) using the gas having the composition shown in Table 1. Table 3 shows the results.

Example 3 2.9 ml of water was added to 2.9 g of ammonium paratungstate parapentahydrate and 1.5 g of oxalic acid, and dissolved by heating on a water bath.
5.5 wt%), pelletized titania (particle size 0.5 to
6.2 g (approximate volume 6.2 ml) of ² mm and a specific surface area of 50 m ² / g were charged and immersed for 20 minutes. Thereafter, the titania was separated from the solution, and the mixture was heated at 80 ° C and 100 ° C in air.
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. A prepared W-based catalyst was prepared. 3.4 g (3.1 ml apparent volume) of this catalyst was added to an aqueous copper sulfate solution (copper concentration: 9.0% by weight).
For 20 minutes, and dried and calcined in the same manner as the second catalyst of Example 1 to obtain an oxide of W against titania.
A second catalyst supporting 4% by weight and 3.7% by weight of copper sulfate (in terms of a metal element) was prepared.

In the order from the exhaust gas inflow side, 1.7 g (3.1 ml) of the first catalyst of Example 1 and 3.7 g of the second catalyst described above were used.
g (3.1 ml) and 3.1 g of the third catalyst of Example 1
(3.1 ml) was combined as a purifying material and set in a reaction tube. Reaction conditions similar to Example 1 (apparent space velocity of the first, second and third catalysts: about 40,000 h ^-1 )
The evaluation was performed using a gas having a composition shown in Table 1. Table 3 shows the results.

Example 4 Using a rhodium chloride aqueous solution (rhodium concentration: 0.5% by weight), 3.1 g of pelletized titania (3.1 ml in apparent volume) was treated with Rh in the same manner as in the third catalyst of Example 1. To 0.
A third catalyst supporting 19% by weight (converted to a metal element) was prepared.

In order from the exhaust gas inflow side, 1.7 g (3.1 ml) of the first catalyst of Example 1, 3.7 g (3.1 ml) of the second catalyst of Example 3, and the third catalyst described above. 3.1g
(3.1 ml) was combined as a purifying material and set in a reaction tube. Reaction conditions similar to Example 1 (apparent space velocity of the first, second and third catalysts: about 40,000 h ^-1 )
The evaluation was performed using a gas having a composition shown in Table 1. Table 3 shows the results.

Example 5 Oxalic acid was added to vanadium pentoxide and dissolved by heating on a water bath, and then cooled and cooled (a vanadium concentration of 7.8).
% By weight), pelletized titania (particle size: 0.5 to 2 m)
m, specific surface area 50 m ² / g) 6.2 g (apparent volume 6.
2 ml) and immersed for 20 minutes. Thereafter, the titania was separated from the solution, and the air was heated at 80 ° C., 100 ° C.,
Dried at 20 ° C. for 2 hours each. Subsequently, the temperature was increased from 120 ° C. to 500 ° C. in 5 hours under a nitrogen gas stream containing 20% oxygen, and calcined at 500 ° C. for 4 hours. A supported V-based catalyst was prepared. 3.3 g of this V-based catalyst (3.
1 ml) to an aqueous solution of copper sulfate (copper concentration 9.0% by weight).
For 2 minutes, and dried and calcined in the same manner as the second catalyst of Example 1 to obtain 3.8% by weight of an oxide of V and 4.0% by weight of copper sulfate (in terms of a metal element) based on titania. A supported second catalyst was prepared.

In the order from the exhaust gas inflow side, 1.7 g (3.1 ml) of the first catalyst of Example 1 and 3.6 g of the second catalyst described above were used.
g (3.1 ml) and 3.1 g of the third catalyst of Example 1
(3.1 ml) was combined as a purifying material and set in a reaction tube. Reaction conditions similar to Example 1 (apparent space velocity of the first, second and third catalysts: about 40,000 h ^-1 )
The evaluation was performed using a gas having a composition shown in Table 1. Table 3 shows the results.

Example 6 3.3 g of the V-based catalyst prepared in Example 5 (apparent volume: 3.
1 ml) in an aqueous solution of copper nitrate (copper concentration 9.5% by weight).
For 2 minutes, and dried and calcined in the same manner as in the second catalyst of Example 1 to obtain 3.8% by weight of oxides of V and 3.8% by weight of copper with respect to titania (in terms of metal element). ) Was prepared.

In the order from the inflow side of the exhaust gas, 1.7 g (3.1 ml) of the first catalyst of Example 1 and 3.4 g of the second catalyst described above were used.
g (3.1 ml) and 3.1 g of the third catalyst of Example 1
(3.1 ml) was combined as a purifying material and set in a reaction tube. Reaction conditions similar to Example 1 (apparent space velocity of the first, second and third catalysts: about 40,000 h ^-1 )
The evaluation was performed using a gas having a composition shown in Table 1. Table 3 shows the results.

Example 7 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 was gradually raised to 600 ° C. in the air, and the mixture was calcined for 5 hours to prepare a first catalyst supporting 3% by weight (in terms of metal element) of silver with respect to alumina. 0.26 g of the first catalyst was used as a commercially available cordierite honeycomb-shaped formed body (diameter 20 mm, length 8.3 mm,
The coating was carried out at 400 cells / inch ² ), dried and baked stepwise to 600 ° C. to prepare a silver-based purifying material (a purifying material coated with a first catalyst).

Next, a powdery zeolite (SiO ₂ : Al ₂ O ₃ molar ratio is 27. Specific surface area: 50 m ² / g) is immersed in an aqueous copper acetate solution (copper concentration: 7.7% by weight).
The zeolite exchanged for copper ions is separated 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 400 ° C.
Then, the temperature was raised stepwise and calcined at 400 ° C. for 5 hours to prepare a second catalyst supporting 5.19% by weight of copper component (converted to copper element) with respect to zeolite. After the second catalyst was slurried, 0.1% was formed on the same honeycomb formed body as the silver-based purifying material.
23 g of the second catalyst was coated, dried and calcined under the same conditions as the silver-based purifying material to prepare a copper-based purifying material (a purifying material coated with the second catalyst).

Further, powdered titania (specific surface area 35 m
² / g) in a chloroplatinic acid aqueous solution for 20 minutes, dried in air at 80 ° C. for 2 hours, and baked in a nitrogen stream at 120 ° C. for 2 hours and stepwise from 200 to 400 ° C. for 1 hour each. . Then, under a nitrogen gas flow containing 4% of hydrogen gas, 50 ° C.
The temperature was raised to 400 ° C. over 5 hours, calcined at 400 ° C. for 4 hours, and further heated to 50 ° C. under a nitrogen stream containing 10% oxygen.
The temperature was raised to 500 ° C. over 5 hours and calcined at 500 ° C. for 5 hours to prepare a third catalyst supporting 0.25% by weight (converted to metal element) of Pt with respect to titania. 0.26 g of the third catalyst was coated on the same honeycomb formed body as the silver-based purifying material. Drying and baking were performed under the same conditions as the silver-based purifying material to prepare a platinum-based purifying material (a purifying material coated with a third catalyst).

A silver-based purifying material, a copper-based purifying material, and a platinum-based purifying material were set in this order from the inflow side to the outflow side of the exhaust gas in the reaction tube. Next, a gas having the composition shown in Table 2 (nitrogen monoxide,
Oxygen, ethanol, sulfur dioxide, nitrogen and water) at a flow rate of 3.48 liters per minute (standard condition) (the apparent space velocity of each purifying material is about 80,000 h ^-1 ). The exhaust gas temperature was kept in the range of 350 to 550 ° C., and ethanol and nitrogen oxide were reacted.

The concentration of nitrogen oxides in the gas after passing through the reaction tube was measured by a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 3 shows the results.

Table 2 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 8 Powdered titania (specific surface area: 35 m ² / g) was immersed in an aqueous solution of copper nitrate (copper concentration: 7.7% by weight), and dried in air.
It dried at each of 2 degreeC, 100 degreeC, and 120 degreeC. continue,
The temperature was increased stepwise from 120 ° C. to 500 ° C. under a nitrogen gas stream containing 20% of oxygen, and calcined at 500 ° C. for 5 hours to carry 4.5% by weight of copper oxide (converted to copper element) with respect to titania. A second catalyst was prepared. After slurrying the second catalyst, a honeycomb formed body similar to the copper-based purifying material of Example 7 was coated with 0.26 g of the second catalyst, dried and calcined to obtain a copper-based purifying material (second Purification material coated with the above catalyst was prepared.

From the inflow side to the outflow side of the exhaust gas in the reaction tube, the silver-based purifying material of Example 7, the copper-based purifying material,
Was set respectively. Next, Example 7
In the same manner as described above, ethanol and nitrogen oxides were reacted using a gas having the composition shown in Table 2 (the apparent space velocity of each purification material was about 80,000 h ^-1 ). 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 3 shows the results.

COMPARATIVE EXAMPLE 1 Using the first catalyst and the second catalyst prepared in Example 1, 1.7 g (3.1 m) of the first catalyst was supplied from the exhaust gas inflow side.
l), 3.1 g (3.1 ml) of the third catalyst were combined in this order to obtain a purifying material, which was set in the reaction tube. Evaluation was carried out under the same reaction conditions as in Example 1 (approximate space velocity of the first, second and third catalysts of about 40,000 h ^-1 ) using the gas having the composition shown in Table 1. Table 3 shows the results.

Table 3 Removal rate of nitrogen oxides (NOx) Removal rate of nitrogen oxides (%) Reaction temperature (° C.) 300 350 400 450 500 Example 1 75.2 92.7 92.5 79.6 64.9 Example 2 79.7 97.1 94.2 80.4 62.5 Execution Example 3 73.4 92.1 95.9 85.6 66.4 Example 4 80.9 96.2 96.1 84.9 66.8 Example 5 74.1 91.7 89.6 77.2 65.3 Example 6 79.8 92.8 89.1 76.5 60.9 Example 7 68.1 80.5 83.7 82.0 78.6 Example 8 48.4 69.8 77.1 80.9 76.8 Comparative Example 1 64.5 79.5 78.7 73.6 59.9

As can be seen from Table 3, in Examples 1 to 8, good removal of nitrogen oxides was observed in a wide exhaust gas temperature range as compared with Comparative Example 1 using only silver and platinum catalysts.

[0072]

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

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location B01J 23/847 B01J 27/053 A 23/85 ZAB 29/068 A 27/053 B01D 53/36 102C 29/068 102H ZAB B01J 23/84 301A (56) References JP-A-6-238166 (JP, A) JP-A-6-221139 (JP, A)

Claims (7)

(57) [Claims] 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 a coexisting end combustion component, wherein the purifying material is disposed from an exhaust gas inflow side to an exhaust side. In order has a first to third catalyst, the first catalyst is porous alumina, titania and
Any of zeolite or a composite oxide containing them or
Silver and / or silver compound as an active species to a mixed oxide thereof, or it carries a mixture thereof 0.2 to 15 wt% (silver metal basis), the second catalyst is a porous γ-
Copper oxide and / or copper sulfate as active species on alumina and / or titania 0.2 to 30% by weight (converted to copper element)
And the third catalyst is alumina, titania
A, zirconia, silica, zeolite
P as an active species in one or more of the porous inorganic oxides
An exhaust gas purifying material characterized by carrying at least one element selected from the group consisting of t, Pd, Ru, Rh, Ir and Au in an amount of 0.01 to 5% by weight (in terms of a metal element). 2. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen larger than a theoretical reaction amount of coexisting unburned components. It has a first to third catalysts in order, and the first catalyst is a porous inorganic oxide, in which silver and / or a silver compound, or a mixture thereof is used as an active species.
15% by weight (in terms of silver element), and the second catalyst contains 0.2 to 30% by weight of copper oxide and / or sulfate as an active species on a porous inorganic oxide (copper element). Conversion value)
And an oxide or sulfate of at least one element selected from the group consisting of W, V, and Mo, in an amount of 30% by weight or less (in terms of a metal element), and the third catalyst is porous. Pt, Pd, Ru, Rh, I as active species in the inorganic oxide
An exhaust gas purifying material characterized by carrying at least one element selected from the group consisting of r and Au in an amount of 0.01 to 5% by weight (in terms of a metal element). 3. The exhaust gas purifying material according to claim 2 , wherein the porous inorganic oxide is one of alumina, titania and zeolite, or a composite oxide containing them, for the first catalyst and the second catalyst. An exhaust gas purifying material, wherein the mixed oxide and the third catalyst are at least one oxide selected from the group consisting of alumina, titania, zirconia, silica, and zeolite. 4. The exhaust gas purifying material according to any one of claims 1 to 3, the first, second, and one or more Serammikusu made or surface of the metal substrate of the third catalyst An exhaust gas purifying material characterized by being coated. 5. The exhaust gas purifying material according to any one of claims 1-3, wherein the first, wherein the second and third one or more of the catalyst is in the form of pellets or granules Exhaust gas purifying material. 6. The exhaust gas purifying material according to any one of claims 1 to 5, wherein the silver compound oxides of silver, silver halide, is at least one selected from the group consisting of silver sulfate and phosphate silver An exhaust gas purifying material characterized by that: 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 for a coexisting end combustion component, 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 a hydrocarbon and / or an oxygen-containing organic compound is added at an upstream side of the purifying material is subjected to the purifying material at 150 to 600 ° C. Exhaust gas purifying method, wherein the nitrogen oxides are removed by contact with a hydrocarbon and / or an oxygen-containing organic compound in the exhaust gas.