JPH0852326A - Exhaust gas purifying material and method - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen oxide in exhause gas containing excessive oxygen and sulfur oxide within a wide temp. range by combining a first catalyst obtained by supporting a silver component on alumina composite inorg. oxide containing a specific amt. of inorg. oxide with a second catalyst obtained by supporting a component such as Pt or the like on porous inorg. oxide. CONSTITUTION:A first catalyst obtained by supporting 0.2-15wt.% of silver and/or a silver compd. or a mixture of them on alumina composite oxide containing 50wt.% or less of oxide such as silica or titania other than alumina is combined with a second catalyst obtained by supporting 0.1-5wt.% of an element such as Pt or Pd being an active seed on porous inorg. oxide to obtain an exhaust gas purifying material. When this exhaust gas purifying material is brought into contact with exhaust gas to which hydrocarbon and/or an oxygen-containing org. compd. is added at specific temp., nitrogen oxide is effectively removed within a wide temp. range even with respect to exhaust gas containing sulfur oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to effectively remove nitrogen oxides from combustion exhaust gas containing nitrogen oxides, excess oxygen and sulfur oxides, and also remove carbon monoxide and hydrocarbons. 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.

The present inventors have developed a purification material comprising a first catalyst in which a silver component is supported on a porous inorganic oxide such as alumina, and a second catalyst in which a platinum component is supported on a porous inorganic oxide. A method of effectively removing not only nitrogen oxides, but also carbon monoxide and residual hydrocarbons by using the method (JP-A-6-142523) has been proposed.

However, it has been found that in an exhaust gas containing a sulfur oxide, silver component tends to be sindered, the surface area of catalytically active species is reduced, and the removal rate of nitrogen oxides and the like is reduced.

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. To provide an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently removing nitrogen oxides, carbon monoxide and hydrocarbons from a combustion exhaust gas containing oxygen and sulfur oxides in an amount not less than a theoretical reaction amount with respect to unburned components. It is.

[0010]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has found that a specific amount of a silver component is supported on an alumina composite inorganic oxide containing a specific amount of an inorganic oxide such as silica. A first catalyst and a second catalyst in which a component such as Pt is supported on a porous inorganic oxide are prepared, and an exhaust gas purifying material formed in combination is used, and hydrocarbon and / or It has been discovered that even if the exhaust gas is brought into contact with the above catalyst at a specific temperature after adding an oxygen-containing organic compound, nitrogen oxides and the like can be effectively removed over a wide temperature range even in an exhaust gas containing sulfur oxides. Thus, the present invention has been completed.

That is, the exhaust gas purifying material of the present invention comprises a porous inorganic oxide carrying silver and / or a silver compound or a mixture thereof at 0.2 to 15% by weight (in terms of silver element). Active species on one catalyst and porous inorganic oxide
A second catalyst comprising at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir, and Au in an amount of 0.1 to 5% by weight (element conversion value); The porous inorganic oxide of one catalyst is silica, titania,
An alumina composite oxide containing 50% by weight or less of one or more oxides selected from the group consisting of zirconia, and the porous inorganic oxide of the second catalyst is any one of alumina, titania, and zirconia or a mixture thereof. The composite oxide is characterized by being able to remove nitrogen oxides, carbon monoxide and hydrocarbons even in an exhaust gas containing sulfur oxides.

[0012] Further, the exhaust gas purifying method for removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in excess of the theoretical reaction amount of coexisting unburned components, comprises installing the exhaust gas purifying material in the middle of an exhaust gas conduit. Then, an exhaust gas to which hydrocarbons and / or an oxygen-containing organic compound having 2 or more carbon atoms has been 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 Alternatively, the nitrogen oxides, carbon monoxide, and hydrocarbons are removed by a reaction with an oxygen-containing organic compound.

Hereinafter, the present invention will be described in detail. In the present invention, on the exhaust gas inflow side, silver and / or a silver compound, which is an active species in a porous inorganic oxide, or a mixture thereof is 0.2 to 0.2%.
15% by weight (in terms of silver element) of the first catalyst is formed, and the porous inorganic oxide is an active species at the outlet side.
Exhaust gas formed by forming a second catalyst supporting at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au in an amount of 0.1 to 5% by weight (in terms of element). A purifying material is installed in the exhaust gas conduit, and hydrocarbons and / or oxygen-containing organic compounds having 2 or more carbon atoms are added to the exhaust gas upstream of the purifying material installation position, and the exhaust gas is brought into contact with the purifying material. Nitrogen oxides in exhaust gas are reduced and removed using hydrogen and / or an oxygen-containing organic compound as a reducing agent.

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
Various changes can be made according to the purpose. Practically, it is preferable to have two or more than two parts consisting of an inlet part and an outlet part. Examples of the structure include a honeycomb structure type, a foam type, a plate shape, a three-dimensional network structure type such as a fibrous refractory, a granular shape, a pellet shape, and the like.

A second preferred embodiment is a catalyst in which pellets, granules, or powdery porous inorganic oxides carry a catalytically active species described below, or a powdery porous inorganic oxide carrying a catalytically active species. It is a purifying material filled with a product formed into a pellet or granule.

The following two catalysts are 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 exhaust gas inflow side. The silver compound is at least one selected from the group consisting of oxides of silver, silver chloride, silver sulfate, silver phosphate, and the like, preferably silver oxides, silver chloride or silver sulfate,
More preferably, silver oxide or silver chloride is used.

As the porous inorganic oxide, an alumina composite oxide comprising alumina and at least one oxide selected from the group consisting of porous silica, titania and zirconia, and the like can be used. However, a composite oxide composed of alumina and silica is preferably used. By using an alumina composite oxide, particularly an alumina-silica composite oxide, even in a high exhaust gas temperature such as 700 ° C. in the presence of a sulfur oxide, a reduction in the surface area of the purifying material and the sintering of the catalytically active species hardly occur. As a result, the heat resistance and durability of the purification material are improved.

The alumina composite oxide is a commercially available product such as an alumina-silica composite oxide, a composite obtained by mixing alumina with an inorganic oxide sol such as a silica sol, or prepared by a sol-gel method. Use something. The content of components other than alumina in the alumina composite oxide is 50% by weight or less, and preferably 0.1 to 40% by weight.
It is. When the content of components other than alumina is less than 0.1% by weight, the removal rate of nitrogen oxides is reduced when the reaction is carried out for a long time in the presence of sulfur oxides. The nitrogen oxide removal rate in the range is reduced.

The specific surface area of the porous inorganic oxide is 10 m ^2.
/ G or more. Specific surface area is 10m ² / g
If it is less than 3, the contact area between the exhaust gas and the inorganic oxide (and the silver component carried on the exhaust gas) becomes small, and good removal of nitrogen oxides cannot be performed.

The amount of the silver component supported as an active species on the alumina composite inorganic oxide is set to 0.2 to 15% by weight (in terms of element) with respect to 100% by weight of the inorganic oxide. If the amount is less than 0.2% by weight, the removal rate of nitrogen oxides decreases. In addition, when silver in an amount exceeding 15% by weight is supported, combustion of the hydrocarbon and / or the oxygen-containing organic compound itself tends to occur, and the nitrogen oxide removal rate is rather lowered. The preferable loading amount of the silver component is 0.5 to 10% by weight.

The silver component carried on the porous inorganic oxide is granular, but in the purifying material of the present invention, the silver component particles have an average diameter of 10 to 1000 nm. In general,
The smaller the particle diameter of the silver component, the higher the reaction characteristics. However, if the average particle diameter is less than 10 nm, only the oxidation reaction of the hydrocarbon and / or the oxygen-containing organic compound as the reducing agent proceeds to remove nitrogen oxides. The rate drops. On the other hand, when the average particle size is 1000
If it exceeds nm, the reaction characteristics of the silver component are reduced, and the nitrogen oxide removal rate is reduced. Preferred average particle size is 10 to 500
nm, more preferably 10 to 200 nm. In addition,
The average here means an arithmetic average.

As a method for supporting the silver component on the alumina composite oxide, a known impregnation method, a kneading method, or the like can be used. The adjustment of the purification material after the support is preferably performed by drying at about 50 to 150 ° C., and then gradually increasing the temperature at 100 to 600 ° C. and firing. The calcination is preferably performed in the air or under a flow of nitrogen, under a flow of hydrogen gas, or while evacuating. By baking at 600 ° C. for one hour or more in an oxidizing atmosphere, the particle size of the supported silver component can be adjusted to a desired size. When the firing temperature is set to 600 ° C. or higher, it is preferable to shorten the firing time. For example, when firing at 700 ° C., the firing time is set within 3 hours. At this time, if nitrogen oxides are present, firing can be performed more effectively. It is preferable that the purifying material fired under the flow of nitrogen gas or hydrogen gas is finally subjected to an oxidation treatment at 700 ° C. or lower.

In the first preferred embodiment of the purifying material, the thickness of the first catalyst provided on the purifying material base is generally limited by the difference in thermal expansion characteristics between the base material and this catalyst. Often. 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 purification material substrate is performed by a known washcoat method, a sol-gel method, a powder 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 of the purifying material base. If the amount of the catalyst is less than 20 g / l, good NOx removal cannot be performed. On the other hand, when the amount of the catalyst exceeds 3000 g / l, 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 50 to 250 g / l of the purifying material base.

(2) Second Catalyst The second catalyst comprises a porous inorganic oxide carrying a catalytically active species and is formed on the exhaust gas outflow side. As the porous inorganic oxide, γ-alumina and its oxides (γ-alumina-titania, γ-alumina-silica, γ-alumina-
And heat-resistant ceramics having a large surface area, such as zirconia), zirconia, and titania-zirconia. Preferably, γ-alumina, titania, zirconia and a composite oxide containing them, particularly preferably, titania or alumina-titania composite oxide are used. As in the first catalyst, the specific surface area of the porous inorganic oxide is 10
It is preferably at least m ² / g.

The active species of the second catalyst include Pt, P
At least one element selected from the group consisting of d, Ru, Rh, Ir and Au is used. In particular, Pt and Rh; Pd and R
h; the combination of Pt, Pd and Rh is effective. The total of active species supported on the inorganic oxide by the second catalyst was 0.1% based on the above-mentioned porous inorganic oxide (100% by weight).
To 5% by weight. When the amount of the catalytically active species is more than 5% by weight based on the substrate, only the oxidative combustion of the hydrocarbon and / or the oxygen-containing organic compound proceeds, and the nitrogen oxide reduction characteristic is reduced. Become. If the amount is less than 0.1% by weight, the effect is not sufficiently exhibited.

Further, as the active species of the second catalyst, it is preferable that at least one element selected from the group consisting of rare earth elements such as La and Ce is supported in an amount of 10% by weight or less.
By supporting the rare earth element, the heat resistance of the platinum-based catalyst can be improved.

For supporting the active species on the second catalyst, a known impregnation method, precipitation method, sol-gel 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, chloride, nitrate, acetate, hydroxide, or the like of a catalytically active species element, dried at 70 ° C, and then heated to 100 to 700 ° C.
This is carried out by raising the temperature stepwise and firing. Although the supported components are shown as metal elements, the supported components exist in the form of metal and oxide under the usual operating temperature conditions of the purifying material.

In the first preferred embodiment of the purifying material, the thickness of the second catalyst provided on the purifying material base is 300 μm.
m or less. The amount of the second catalyst provided on the surface of the purifying material base is 20 to 300 g / p of the purifying material base.
It is preferably 1. The method of coating the purification material substrate with the second catalyst is the same as the method of the first catalyst described above.

In the present invention, the weight ratio of the first catalyst to the second catalyst is preferably from 10: 1 to 1: 5. The ratio is less than 1: 5 (less first catalyst)
As a result, the overall nitrogen oxide purification rate is reduced in a wide temperature range of 250 to 600 ° C. On the other hand, if the ratio exceeds 10: 1 (the amount of the first catalyst is large), the ability to purify hydrocarbons and carbon monoxide does not increase. That is, the reaction between the reducing agent and the nitrogen oxide at a relatively low temperature does not sufficiently proceed. A more preferred weight ratio of the first catalyst to the second catalyst is 5: 1 to 1: 4.

If the purifying material having the above structure is used, 150
In a wide temperature range of up to 600 ° C., good removal of nitrogen oxides can be performed even with exhaust gas containing sulfur oxides. Further, acetaldehyde, hydrocarbons, carbon monoxide, and the like generated by the reaction between the added reducing agent and the purifying material can be effectively oxidized and removed.

Next, the method of the present invention will be described. First, an exhaust gas purifying material is installed in the middle of an exhaust gas conduit. Preferably, the first catalyst is arranged to face the exhaust gas inlet and the second catalyst is arranged to face the exhaust gas outlet.

The exhaust gas contains ethylene, propylene, etc. to a certain extent as residual hydrocarbons. However, since the amount is generally not sufficient to reduce NOx in the exhaust gas, hydrocarbons and / or oxygen-containing organic substances are supplied from outside. A reducing agent comprising a compound is introduced into the exhaust gas. The position where the reducing agent is introduced is upstream of the position where the purifying material is installed.

As the 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,
And hydrocarbons such as heptane and kerosene.

When the exhaust gas is a combustion exhaust gas from an engine using a mixed hydrocarbon of any of liquefied petroleum gas, city gas and liquefied natural gas as a fuel, a mixed hydrocarbon or a hydrocarbon compound is added. As hydrocarbon compounds,
Alkanes, alkenes, alkynes and the like are used. Preferably, methane, ethane, propane, butane and the like are used. As the mixed hydrocarbon, any one of liquefied petroleum gas, city gas, and liquefied natural gas is used. Further, other mixed hydrocarbons may be used. By using these mixed hydrocarbons, the performance of removing nitrogen oxides in a high-temperature region is improved. In the case of using a mixed hydrocarbon, when a saturated hydrocarbon having a small number of carbon atoms is the main component, the nitrogen oxide removal characteristics at a low temperature is reduced. Therefore, it is preferable to add a hydrocarbon having a large number of carbon atoms and use it. .

Examples of the oxygen-containing organic compound introduced from the outside include alcohols. Particularly, alcohols having 2 or more carbon atoms are preferable. Specific examples include oxygen-containing organic compounds such as ethanol and butanol.

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.

In the present invention, the space velocity of the first catalyst is 150,000 h ^-1 or less, and the space velocity of the second catalyst is less than 150,000 h ^-1 in order to efficiently reduce and remove nitrogen oxides by an oxygen-containing organic compound. Is 200,000h ^-1 or less. When the space velocity exceeds the above range, the reduction reaction of nitrogen oxides does not sufficiently occur, and the nitrogen oxide removal rate decreases. The preferred space velocity of the first catalyst is 100,000 h ^-1 or less, and the preferred space velocity of the second catalyst is 150,000 h ^-1 or less.

Further, in the present invention, the temperature of the exhaust gas at the purification material installation site where the hydrocarbon and / or the oxygen-containing organic compound reacts with the nitrogen oxide is set to 150 to 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 200 to 550 ° C, more preferably 300 to 550 ° C.

[0041]

The present invention will be described in more detail with reference to the following specific examples. Example 1 10 g of a commercially available powdered silica-alumina composite oxide (silica content: 5% by weight, specific surface area: 350 m ² / g) was mixed with silica-alumina in an amount of 4% by weight using an aqueous silver nitrate solution.
After carrying silver (in terms of silver element value) and drying, it is baked in air in a stepwise manner to 600 ° C. and formed into pellets having a diameter of 1.5 mm and a length of 2 to 3 mm. Prepared. Next, an aqueous solution of chloroplatinic acid was added to 2 g of the mixed oxide of alumina and titania (titania content: 75% by weight) to obtain Pt.
0.5% by weight, dried, and fired to 700 ° C.
A platinum-based catalyst was prepared.

A purifying material is provided on the inflow side of the exhaust gas by a silver-based catalyst.
It was set in the reaction tube so that 6 g of the Pt-based catalyst was 1.8 g on the outlet side. Next, a gas (nitrogen monoxide, carbon monoxide, oxygen, ethanol, hydrocarbon (propylene), sulfur dioxide, nitrogen and moisture) having a composition shown in Table 1 was flowed at a flow rate of 4.4 liters per minute (standard state). After flowing at 450 ° C. for 100 hours (space velocity of the silver-based catalyst is about 30,000 h ⁻¹ and space velocity of the platinum-based catalyst is about 100,000 h ⁻¹ ), the temperature of the exhaust gas in the reaction tube is in the range of 150 to 650 ° C. , And the removal characteristics of the exhaust gas purifying material were measured.

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. The concentrations of carbon monoxide and hydrocarbons were measured by a CO meter and a HC meter, respectively, and the removal rates of carbon monoxide and hydrocarbons were determined under the condition that ethanol was not added to the exhaust gas. Table 2 shows the results.

Table 1 Component concentration Nitric oxide 800 ppm Carbon monoxide 100 ppm Oxygen 10% by volume Ethanol 3 times the weight of nitric oxide Propylene 100 ppm Sulfur dioxide 80 ppm Nitrogen Residual water 10% by volume (based on the total volume of the above components) for)

Example 2 The same powdery silica-alumina as in Example 1 (specific surface area 2
00m ² / g) with an aqueous solution of ammonium chloride and an aqueous silver nitrate solution prepared catalyst silver chloride is supported 4 wt% (silver metal basis) in the catalyst of about 1.0g of commercially available cordierite honeycomb molded Body (diameter 30mm, length 12.
5 mm, 400 cells / square inch), and after drying,
It was fired stepwise to 600 ° C. to prepare a silver-based purifying material.
The average diameter of the silver compound particles was 50 nm. Also,
In the same manner as in Example 1, 0.5% by weight of Pt was supported on a powdery alumina-titania mixed oxide using a chloroplatinic acid solution, and then a slurry was formed.
2 mm), coat 0.4 g (dry weight), and after drying, 70 g
By baking to 0 ° C., a platinum-based purifying material was prepared.

The exhaust gas was set in a reaction tube such that a silver-based purifying material was provided on the inflow side and a platinum-based purifying material was provided on the outflow side. Evaluation was performed under the same conditions as in Example 1 (the space velocities of the silver-based purifying material and the platinum-based purifying material were 30,000 and 90,000 h, respectively).
It is ^-1 . ). Table 2 shows the experimental results.

Example 3 In the same manner as in Example 2, powdered titania (specific surface area 50 m
² / g) was slurried with a catalyst carrying 0.5% by weight of platinum and coated on the same honeycomb as in Example 2 to prepare a platinum-based purifying material.

The silver-based purifying material prepared in Example 2 on the inflow side of the exhaust gas and the platinum-based purifying material prepared on the outlet side of the exhaust gas were used.
It was set in the reaction tube. Gases having the composition shown in Table 1 (nitrogen monoxide, carbon monoxide, oxygen, moisture, ethanol, and nitrogen) are flowed at a flow rate of 4.4 liters per minute (standard state) (silver-based purification material and platinum-based purification). The space velocity of the material is 3
000 and 90,000 h ^-1 . ), And evaluated under the same conditions as in Example 2. Table 2 shows the results.

Comparative Example 1 In the same manner as in Example 1, a silica / alumina composite oxide (silica content: 80% by weight, specific surface area: 490 m ² / g)
10 g of silver was supported at 4% by weight (in terms of silver element) and formed into pellets to prepare a purifying material. This purifying material 3.6 was set in a reaction tube, and evaluated under the same conditions as in Example 1 using a gas having a composition shown in Table 1 (space velocity is 30,000 h ^-1 ). Table 2 shows the experimental results.

Comparative Example 2 In the same manner as in Example 1, γ-alumina (specific surface area 26
10 g of 0 m ² / g) was loaded with 4% by weight of silver (converted to the value of silver element), and formed into pellets to prepare a purifying material. This purifying material 3.6 was set in a reaction tube, and a gas having a composition shown in Table 1 was used under the same conditions as in Example 1 (the space velocity was 30,000).
h ^-1 . )evaluated. Table 2 shows the experimental results.

Table 2 Removal rate of nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC) Reaction temperature Removal component Removal rate (%) (° C.) Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 250 NOx 15 12 12 10 6 CO 75 70 68 14 12 HC 50 45 45 10 10 300 NOx 45 42 42 26 26 20 CO 87 82 83 40 35 HC 63 62 62 30 30 350 NOx 62 58 5742 92 90 90 60 56 HC 65 61 60 30 28 400 NOx 83 75 73 52 44 CO 98 93 91 65 60 HC 89 82 81 40 38 450 NOx 78 74 74 60 57 57 CO 100 100 100 70 70 65 HC 93 91 91 91 NOx 65 68 68 504 CO 100 100 100 78 75 HC 100 100 100 70 70 550 NOx 35 39 39 36 36 CO 100 100 100 89 88 HC 100 100 100 83 81 600 NOx 27 33 33 20 20 CO 100 100 100 98 98 HC 100 100 100 90 90

As can be seen from the above, in Examples 1 to 3, good removal of nitrogen oxides was observed over a wide exhaust gas temperature range, and high removal of carbon monoxide and hydrocarbons was observed even at low temperatures. On the other hand, in Comparative Examples 1 and 2, the temperature range for removing nitrogen oxides was narrow, and the removal rates of carbon monoxide and hydrocarbons were low.

[0053]

As described in detail above, the use of the exhaust gas purifying material of the present invention efficiently removes nitrogen oxides in exhaust gas containing excess oxygen and sulfur oxides over a wide temperature range, Carbon and hydrocarbons can also be removed. 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 number Agency reference number FI Technical indication location B01J 23/46 301 A 311 A 23/50 ZAB A 23/52 ZAB A 27/053 ZAB A 27 / 10 ZAB A 27/18 ZAB A

Claims (7)

[Claims] 1. A first catalyst comprising a porous inorganic oxide carrying silver and / or a silver compound or a mixture thereof in an amount of 0.2 to 15% by weight (in terms of an elemental silver); 0.1 to 5% by weight of at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au which are active species in the inorganic oxide
In the exhaust gas purifying material comprising the second catalyst carrying (element conversion value), the porous inorganic oxide of the first catalyst is selected from the group consisting of silica, titania, and zirconia in addition to alumina. An alumina composite oxide containing 50% by weight or less of one or more oxides, wherein the porous inorganic oxide of the second catalyst is alumina, titania, zirconia, or a composite oxide of two or more thereof. An exhaust gas purifying material characterized in that nitrogen oxides, carbon monoxide and hydrocarbons can be removed even from exhaust gas containing sulfur oxides. 2. The exhaust gas purifying material according to claim 1, wherein the purifying material has the first catalyst on an exhaust gas inflow side and the second catalyst on an exhaust gas outflow side. Purifying material. 3. The exhaust gas purifying material according to claim 1, wherein the purifying material is formed by coating the first and second catalysts on a surface of a ceramic or metal three-dimensional structure. Exhaust gas purifying material. 4. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxides of the first and second catalysts are each in the form of pellets or granules. 5. The exhaust gas purifying material according to claim 1, wherein the silver compound is silver oxide, silver chloride,
An exhaust gas purifying material, which is at least one selected from the group consisting of silver sulfate and silver phosphate. 6. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide of the first catalyst is an alumina composite oxide comprising alumina and silica. Purifying material. 7. An exhaust gas purifying method for removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides, oxygen in excess of a theoretical reaction amount for coexisting unburned components, and sulfur oxides, according to claim 1, wherein Using the exhaust gas purifying material according to any of the above, the exhaust gas purifying material is installed in the middle of the exhaust gas conduit,
Exhaust gas to which hydrocarbons and / or oxygen-containing organic compounds having 2 or more carbon atoms are added on the upstream side of the purifying material,
An exhaust gas purification method comprising: contacting the purification material at 0 ° C. to remove the nitrogen oxides, carbon monoxide and hydrocarbons by reacting with the hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas. .