JPH09267029A - Exhaust gas purifying material and method for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove nitrogen oxide in exhaust gas containing excess oxygen over a wide temp. region by separately depositing a silver component and a platinum based component on the carrier and then mixing it as a purifying agent for exhaust gas. SOLUTION: As a first catalyst, 0.2-15wt.% (expressed in terms of metallic element) of more than one kind element and/or compd. selected from silver and a silver compd. are deposited on a porous org. oxide such as alumina alone and almina composite material. Further, 0.001-0.5wt.% (expressed in terms of metallic element) Pt and 0.001-0.05wt.% (expressed in terms of metallic element) Rh are deposited on the porous org. oxide such as alumina alone and alumina composite material as the second catalyst. The purifying agent for the exhaust gas is made by sparately depositing the silver component and the platinum based component on the carriers then mixing it like this. The oxygen of more than theoretical reaction amount per nitrogen oxide and an unburned component is incorporated in the purifying agent, and the nitrogen oxide is efficiently reduced and removed from a combustion exhaust gas containing water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Excessive combustion exhaust gas emitted from internal combustion engines such as automobile engines, combustion equipment installed in factories, household fan heaters, and the like is excessive. It contains nitrogen oxides such as nitric oxide and nitrogen dioxide together with oxygen. Here, "containing excess oxygen" means that the exhaust gas contains more oxygen than the theoretical amount of oxygen necessary to burn unburned components such as carbon monoxide, hydrogen, and hydrocarbons. I do. In the following, nitrogen oxide refers to nitric oxide and / or nitrogen dioxide.

[0003] This nitrogen oxide is one of the causes of acid rain and is a major environmental problem. Therefore, various methods for removing nitrogen oxides in exhaust gas discharged from various combustion equipments are being studied.

[0004] As a method for removing nitrogen oxides from a combustion exhaust gas containing excess oxygen, a selective catalytic reduction method using ammonia is used particularly for a large-scale fixed combustion device (a large-scale combustor in a factory or the like). Has been put to practical use.

However, in this method, ammonia used as a reducing agent for nitrogen oxides is expensive, and ammonia is toxic. Therefore, the nitrogen oxides in the exhaust gas must be removed so that unreacted ammonia is not discharged. There are problems that the amount of injected ammonia must be controlled while measuring the concentration, and that the apparatus generally becomes large.

As another method, there is a non-selective catalytic reduction method in which a nitrogen oxide is reduced by using a gas such as hydrogen, carbon monoxide, or a hydrocarbon as a reducing agent. In order to reduce and remove nitrogen oxides, it is necessary to add a reducing agent in an amount equal to or more than a theoretical reaction amount with oxygen in exhaust gas, and there is a disadvantage that a large amount of the reducing agent is consumed. For this reason, the non-selective catalytic reduction method is practically effective only for exhaust gas having a low residual oxygen concentration burned near the stoichiometric air-fuel ratio, and is not practical because of poor versatility.

Therefore, a catalyst for catalytic reduction of nitrogen oxides by a hydrocarbon comprising a metal oxide such as titania or alumina, a rare earth oxide and at least one of Ru, Rh, Pd, silver and Pt has been proposed ( JP-A-4-27431). However, according to the experimental results of the present inventors, this catalyst has a low nitrogen oxide removal rate at a high space velocity, and particularly in a region where the exhaust gas temperature is low, the nitrogen oxide removal is low.
Further, in an exhaust gas containing water, the removal rate of nitrogen oxides is significantly 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. An object of the present invention is to provide an exhaust gas purifying material and an exhaust gas purifying method which can efficiently reduce and remove nitrogen oxides from a combustion exhaust gas containing oxygen at a theoretical reaction amount or more with respect to an unburned portion and containing water.

[0009]

Means for Solving the Problems In view of the above problems, as a result of intensive studies, the present inventor has found that by separately supporting a silver component and a platinum-based component on a carrier and then mixing the components, the catalyst components interfere with each other. Completed the present invention by discovering that oxidation and reduction reactions can be promoted without using Pt and Rh among the platinum components at the same time can effectively remove nitrogen oxides over a wide temperature range. did.

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 for coexisting unburned components is a porous inorganic material. One or more elements and / or compounds selected from the group consisting of silver and silver compounds in the oxide;
A first catalyst supporting 2 to 15% by weight (in terms of a metal element) and a porous inorganic oxide having Pt of 0.001 to 0.
5% by weight (in terms of metal element) and Rh 0.001 to 0.
It is characterized in that it is mixed with a second catalyst that carries 0.05% by weight (in terms of a 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 the theoretical reaction amount of coexisting unburned components is a porous inorganic material. One or more elements and / or compounds selected from the group consisting of silver and silver compounds in the oxide;
15% by weight (converted to a metal element), a first catalyst, and 0.001 to 0.5% by weight of Pt in a porous inorganic oxide (converted to a metal element); 05
% By weight (in terms of a metal element) and a second catalyst supporting 2% by weight or less of at least one element selected from the group consisting of rare earth elements.

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 uses the above exhaust gas purifying material. The exhaust gas purifying material was installed in the middle of an exhaust gas conduit, and at least one selected from the group consisting of gaseous hydrocarbons, kerosene, light oil, and liquid hydrocarbons including gasoline was added upstream of the purifying material. Contacting the exhaust gas with the purifying material at 300 to 550 ° C;
Thus, the nitrogen oxides are removed by a reaction with hydrocarbons in the exhaust gas.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. [1] Exhaust gas purifying material The exhaust gas purifying material of the present invention comprises a mixed catalyst obtained by mixing a first catalyst and a second catalyst described later.

In the present invention, the above-mentioned purifying material is installed in an exhaust gas conduit, and the exhaust gas to which hydrocarbons are added at the upstream side of the installation position of the purifying material is brought into contact with the purifying material to reduce nitrogen oxides in the exhaust gas. Remove.

A first preferred embodiment of the exhaust gas purifying material of the present invention is a purifying material obtained by coating the mixed catalyst on a purifying material base. Examples of the ceramic material forming the base of the purifying material include heat-resistant ceramics having a large surface area such as alumina, zirconia, and titania-zirconia. 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. Also, as its structure,
Examples include a honeycomb structure type, a foam type, a three-dimensional network structure type made of a fibrous refractory, a granular form, a pellet form, and the like. An exhaust gas purifying material can be manufactured by coating the above-mentioned substrate with the mixed catalyst using a wash coat method, a sol-gel method, a powder method or the like, and then sintering.

In a second preferred embodiment of the exhaust gas purifying material of the present invention, the mixed catalyst is formed into a honeycomb structure, a foam, a plate, a pellet, or a granule, and then sintered to obtain a casing having a desired shape. Purifying material filled in

The following catalyst is formed on the purification material of the present invention. (1) First catalyst The first catalyst comprises a porous inorganic oxide carrying one or more elements and / or compounds selected from the group consisting of silver and silver compounds, and performs nitrogen oxidation in a wide temperature range. Acts on object removal. As the porous inorganic oxide, alumina alone, or titania, silica, zirconia, zinc oxide, tin oxide,
A composite or mixed oxide of either magnesium oxide or zeolite and alumina can be used. When an alumina-containing composite or mixed oxide is used, the alumina content is preferably 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 tin oxide referred to in the present invention includes tin oxide in various oxidation states, such as stannous oxide and stannic oxide.

The particle size of the porous inorganic oxide such as alumina used for the first catalyst is preferably 0.1 mm or less.
When the particle size exceeds 0.1 mm, the contact area between the catalyst and the exhaust gas is reduced, and the effect of the catalytically active species cannot be sufficiently exhibited.
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 dispersion of the silver component is reduced, and good removal of nitrogen oxides cannot be performed. More preferred specific surface area of the porous inorganic oxide is 30 m ² / g or more.

The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate, silver phosphate and the like, and preferably at least one of silver oxide, silver chloride and silver sulfate. And more preferably silver oxide and / or silver chloride. The supported amount of the silver component is 0.2 to 15% by weight (in terms of silver element) based on 100% by weight of the porous inorganic oxide. If the amount is less than 0.2% by weight, the removal rate of nitrogen oxides decreases. When the silver component is carried in an amount exceeding 15% by weight, hydrocarbons are easily generated, and the nitrogen oxide removal rate is rather lowered. The preferred amount of the silver component is 0.1.
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. To prepare silver halide by the precipitation method, silver nitrate and ammonium halide are reacted to precipitate silver halide on the porous inorganic oxide. After drying at 50 to 150 ° C., particularly at about 70 ° C., it is preferable to raise the temperature stepwise at 100 to 600 ° C. for firing. The calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream of hydrogen gas. When the treatment is performed under a hydrogen gas stream, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last. In carrying silver on alumina, an alumina-based mixed or composite oxide, it is effective to use alumina hydrate such as boehmite as a starting material.

(2) Second Catalyst In the first purifying material of the present invention, the second catalyst comprises a porous inorganic oxide carrying Pt and Rh as catalytically active species. In the second purification material of the present invention, the second catalyst supports Pt, Rh, and at least one element selected from the group consisting of rare earth elements as catalytically active species on the porous inorganic oxide. It becomes. As the porous inorganic oxide, alumina,
One or more composite or mixed oxides selected from the group consisting of titania, zeolite, silica, zirconia, zinc oxide, tin oxide, and magnesium oxide are used.
Similar to the first catalyst, the specific surface area of the porous inorganic oxide is preferably 10 m ² / g or more.

With the porous inorganic oxide as 100% by weight,
The supported amount of the Pt component is 0.001 to 0.5% by weight (in terms of the metal element), and the supported amount of the Rh component is 0.001 to 0.5% by weight.
It is 0.05% by weight (value in terms of metal element). The preferred loading of the Pt component is 0.01 to 0.4% by weight (in terms of metal element), and the preferred loading of the Rh component is 0.005%.
0.04% by weight (in terms of metal element).

In the first exhaust gas purifying material of the present invention, the durability of the purifying material is improved by supporting the rare earth element on the second catalyst. As the rare earth element, lanthanum, cerium, and neodymium are preferably used, but misch metal, which is a mixture of rare earth elements, can also be used. It is preferable that the supporting amount of the rare earth element be 2% by weight or less (converted value of the rare earth element) with the porous inorganic oxide being 100% by weight. If the amount of the supported rare earth element exceeds 2% by weight, the removal rate of nitrogen oxides decreases. The preferable loading amount of the rare earth element is 0.1 to 1.5% by weight.

The total amount of active species carried in the second catalyst is 0.05 to 2.5% by weight, preferably 0.1 to 2.5% by weight (100% by weight) based on the above-mentioned porous inorganic oxide.
2.0% by weight. If the amount of the catalytically active species is less than 0.05% by weight with respect to the inorganic oxide, the effect of supporting the catalyst is not remarkable, and the NOx reduction characteristics deteriorate. On the other hand, 2.5
When the amount of the catalyst carried is more than the weight%, only the oxidizing combustion of the hydrocarbon proceeds, and the characteristic of reducing nitrogen oxides is reduced.

The active species can be supported by a known impregnation method, precipitation method,
An ion exchange method or the like can be used. First, it is carried out by supporting a catalytically active species, drying at 50 to 150 ° C., particularly 70 ° C., and then gradually increasing the temperature at 100 to 600 ° C. and calcining. The calcination is preferably performed in air, under a stream of nitrogen containing oxygen or under a stream of hydrogen gas. When the treatment is performed under a hydrogen gas stream, it is preferable to perform the oxidation treatment at 300 to 650 ° C. at last. 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. When zeolite is used as the inorganic oxide, it is effective to carry the zeolite by an impregnation method or a known ion exchange method. On the second catalyst thus prepared, each of the catalytically active species exists in the form of an element or any one or more of oxides, halides and sulfates thereof.

In the present invention, a mixed catalyst obtained by mixing the first catalyst and the second catalyst is used. The weight ratio of the first catalyst to the second catalyst (the ratio of the total weight of the porous inorganic oxide and the catalytically active species) is preferably 1: 1 to 200: 1. A more preferred weight ratio of the first catalyst to the second catalyst is 5: 1 to 1
150: 1.

In the case where the form of the purifying material is the first preferred embodiment described above, the thickness of the mixed catalyst provided on the purifying material base is generally determined by the difference in thermal expansion characteristics between the base material and this catalyst. Often restricted. 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. The method of forming the mixed catalyst on the surface of the purification material base is performed by a known wash coat method or the like.

The amount of the mixed catalyst provided on the surface of the purifying material base is preferably 20 to 300 g / liter of the purifying material base. If the amount of the catalyst is less than 20 g / liter, good NOx removal cannot be performed. On the other hand, when the amount of the catalyst is 300
When the amount exceeds g / liter, the removal characteristics do not increase so much.
Pressure loss increases. More preferably, the mixed catalyst provided on the surface of the purification material substrate is 50 to 200 g of the purification material substrate.
/ Liter.

If the purifying material having the above configuration is used, 300
In a wide temperature range of up to 550 ° C., good removal of nitrogen oxides can be performed even with exhaust gas containing about 10% of water.

[2] Exhaust gas purification method Next, the method of the present invention will be described. First, an exhaust gas purifying material comprising a mixed catalyst of the first catalyst and the second catalyst is provided in the middle of an exhaust gas conduit.

The exhaust gas contains ethylene, propylene, etc. to some extent as residual hydrocarbons. However, since the amount is generally not enough to reduce NOx in the exhaust gas, the exhaust gas contains hydrocarbons as a reducing agent from the outside. To be introduced. 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,
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.

The amount of hydrocarbons introduced from the outside is preferably such that the weight ratio (weight of reducing agent to be added / weight of nitrogen oxides in exhaust gas) is 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 mixed catalyst of the first catalyst and the second catalyst is 200,000 h ^-1 or less in order to efficiently promote the reduction and removal of nitrogen oxides by hydrocarbons.
Preferably it is 150,000 h ^-1 or less.

Further, in the present invention, the temperature of the exhaust gas is maintained at 300 to 550 ° C. at the purification material installation site where hydrocarbons and nitrogen oxides react. Exhaust gas temperature is 30
When the temperature is lower than 0 ° C., the reaction between the reducing agent and the nitrogen oxide does not proceed, and good removal of the nitrogen oxide cannot be performed. On the other hand, if the temperature exceeds 550 ° C., the combustion of the hydrocarbon itself starts, and the reduction and removal of nitrogen oxides cannot be performed. The preferred exhaust gas temperature is 300 to 500 ° C, more preferably 3 to 500 ° C.
50-500 ° C.

[0037]

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) using an aqueous solution of silver nitrate was 3.0% by weight (in terms of a metal element).
After drying, the mixture was dried and calcined in air stepwise to 600 ° C. to prepare a first catalyst.

Using the same γ-alumina powder and an aqueous solution of chloroplatinic acid and an aqueous solution of rhodium chloride, 0.1% by weight (converted to metal element) of Pt and 0.01% by weight (converted to Rh element).
After drying, the mixture was dried and calcined in air stepwise to 600 ° C. to prepare a second catalyst.

The first catalyst and the second catalyst are mixed at a weight ratio of 10: 1, and a binder (alumina sol binder)
Was added, kneaded, dried, and fired stepwise in the air to 600 ° C., pulverized, and formed into pellets having an average particle size of 3 mm to prepare an exhaust gas purifying material.

1.5 g of the above exhaust gas purifying material was set in a reaction tube, and a gas (nitrogen monoxide, oxygen, propylene, nitrogen and water) having a composition shown in Table 1 was flowed at a rate of 1.8 liters per minute (standard state). (The contact time of the purification material is 0.05g
· Sec / ml, apparent space velocity is about 30,00
0h ^-1 . ), The temperature of the exhaust gas in the reaction tube is 300 to 5
Keeping in the range of 00 ° C., propylene 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 3 shows the results.

Table 1 Ingredient concentration Nitric oxide 800 ppm Oxygen 10% by volume Propylene 1714 ppm (3 times the mass of nitrogen oxide) Nitrogen Residual moisture 10% by volume (based on the total volume of the above components)

Example 2 In the same manner as in Example 1, powdery γ was prepared using an aqueous silver nitrate solution.
4% by weight (in terms of metal element) of silver was supported on alumina / silica (silica content: 5% by weight, specific surface area: 350 m ² / g), and calcined in the same manner as in Example 1 to obtain a first catalyst Was prepared.

Next, in the same manner, 0.1 g of powdery γ-alumina was added.
1 wt% (converted to metal element) Pt and 0.01 wt%
Rh (metal equivalent) and 1% by weight (element equivalent) of Ce using an aqueous cerium nitrate solution, and calcined in the same manner as in Example 1 to obtain a second catalyst. Produced.

The first catalyst and the second catalyst are mixed at a weight ratio of 50: 1, and a binder (alumina sol binder)
Was added, kneaded, dried, and fired stepwise in the air to 600 ° C., pulverized, and formed into pellets having an average particle size of 3 mm to prepare an exhaust gas purifying material.

1.5 g of the above exhaust gas purifying material was set in the reaction tube. The same reaction conditions as in Example 1 (flow rate 1.8 l / min, apparent space velocity of the purification material was about 30,000 h)
^-1 ) was evaluated using a gas having the composition shown in Table 1. Table 3 shows the results.

Example 3 In the same manner as in Example 1, a powdery γ-alumina (specific surface area: 200
m ² / g), 3% by weight (in terms of metal element) of silver chloride was carried thereon, and calcined in the same manner as in Example 1 to produce a first catalyst.

Next, in the same manner, 0.1 g of powdery γ-alumina was added.
1 wt% (converted to metal element) Pt and 0.01 wt%
Rh (metal equivalent) and 1% by weight (element equivalent) La using an aqueous lanthanum nitrate solution, and calcined in the same manner as in Example 1 to obtain a second catalyst. Produced.

The first catalyst and the second catalyst were mixed at a weight ratio of 50: 1. After slurrying 1 g of the mixed catalyst, a commercially available cordierite honeycomb-shaped formed body (30 m in diameter)
m, length 12.6 mm, 400 cells / inch ² ), dried and fired stepwise to 600 ° C to prepare an exhaust gas purifying material (a purifying material coated with a mixed catalyst).

An exhaust gas purifying material was set in the reaction tube. Reaction conditions similar to Example 1 (flow rate 4.4 liter / min, apparent space velocity of purifying material is about 30,000 h ^-1 )
The evaluation was performed using a gas having a composition shown in Table 1. Table 3 shows the results.

Example 4 In the same manner as in Example 1, powdery γ was prepared using an aqueous solution of silver nitrate.
-Alumina / silica (silica content: 5% by weight, specific surface area: 350 m ² / g) loaded with 5% by weight (in terms of metal element) of silver and calcined in the same manner as in Example 1 to obtain a first catalyst Was prepared.

Next, in the same manner, 0.1 g of powdery γ-alumina was added.
A second catalyst was prepared by carrying 05% by weight (converted to metal element) of Pt and 0.01% by weight (converted to metal element) of Rh and calcining the same as in Example 1.

The first catalyst and the second catalyst were mixed at a weight ratio of 100: 1. After slurrying 1 g of the mixed catalyst,
A commercially available cordierite honeycomb-shaped molded product (30 m in diameter)
m, length 12.6 mm, 400 cells / inch ² ), dried and fired stepwise to 600 ° C to prepare an exhaust gas purifying material (a purifying material coated with a mixed catalyst).

The exhaust gas purifying material was set in the reaction tube, and under the same reaction conditions as in Example 3 (flow rate 4.4 liter / min, apparent space velocity of the purifying material was about 30,000 h ^-1 ),
Evaluation was performed using a gas having a composition shown in Table 2. Table 3 shows the results.

Table 2 Component concentration Nitric oxide 800 ppm Oxygen 10% by volume Light oil 3 times the mass of nitrogen oxides Nitrogen Residual water 10% by volume (based on the total volume of the above components)

Example 5 In the same manner as in Example 1, 3% by weight (in terms of metal element) of silver was supported on powdered stannic oxide (specific surface area: 71 m ² / g) using an aqueous silver nitrate solution. By calcination in the same manner as in Example 1, a first catalyst was prepared.

The first catalyst and the second catalyst of Example 3 were mixed at a weight ratio of 50: 1. After slurrying 1 g of the mixed catalyst, it was coated on a commercially available cordierite honeycomb-shaped formed body (diameter 30 mm, length 12.6 mm, 400 cells / inch ² ), dried and calcined stepwise to 600 ° C. A purifying material (a purifying material coated with a mixed catalyst) was prepared.

An exhaust gas purifying material was set in the reaction tube. Reaction conditions similar to Example 1 (flow rate 4.4 liter / min, apparent space velocity of purifying material is about 30,000 h ^-1 )
The evaluation was performed using a gas having a composition shown in Table 1. Table 3 shows the results.

[0059] and calcined to 600 ° C. After the binder (alumina sol binder) were added to and mixed with the first catalyst of Comparative Example 1 Example 1 to prepare a silver-based catalyst. This silver-based catalyst was formed into pellets having an average particle size of 3 mm to prepare a silver-based exhaust gas purifying material.

1.5 g of a silver-based exhaust gas purifying material was set in an exhaust gas conduit, and under the same reaction conditions as in Example 1 (apparent space velocity was about 30,000 h ^-1 ), a gas having a composition shown in Table 1 was used. The evaluation was performed using. Table 3 shows the results.

Comparative Example 2 1.5 g of the first catalyst of Example 1 was used in the same manner as in Example 3.
A commercially available cordierite honeycomb-shaped molded product (30 m in diameter)
m, length 12.6 mm, 400 cells / inch ² ), dried and fired stepwise to 600 ° C to prepare an exhaust gas purifying material (a purifying material coated with a mixed catalyst). The purifying material was set in an exhaust gas conduit, and evaluated under the same reaction conditions as in Example 4 (apparent space velocity was about 30,000 h ^-1 ) using a gas having a composition shown in Table 2. Table 3 shows the results
Shown in

Table 3 Exhaust gas temperature (° C.) Example No. 300 350 400 450 500 Example 1 10 36 65 70 50 Example 2 8 34 55 80 75 Example 3 8 35 58 83 72 Example 4 7 30 52 78 68 Example 5 10 38 60 80 68 Comparative Example 1 2 10 40 88 80 Comparative Example 2 17 45 70 54

As can be seen from Table 3, the first catalyst and the second catalyst according to the present invention were mixed with each other in comparison with Comparative Examples 1 and 2 using only the silver catalyst as the first catalyst. In Examples 1 to 5 used, excellent removal of nitrogen oxides was observed in a wide exhaust gas temperature range, particularly in a low temperature range.

[0064]

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 removing nitrogen oxides from exhaust gas of various combustors, automobiles and the like.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location B01J 23/60 B01J 29/068 A23 / 62 B01D 53/36 ZAB 29/068 102A 102B B01J 23 / 56 301A

Claims (7)

[Claims] 1. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than a theoretical reaction amount for coexisting unburned components, wherein silver and silver are used as porous inorganic oxides. 0.2 to 15% by weight of one or more elements selected from the group consisting of compounds and / or compounds
(A metal element equivalent), a first catalyst supporting the porous inorganic oxide, 0.001 to 0.5% by weight of Pt (metal element equivalent), and 0.001 to 0.05% by weight of Rh. An exhaust gas purifying material characterized by being mixed with a second catalyst (metal element conversion value). 2. An exhaust gas purifying material for reducing and removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in an amount larger than a theoretical reaction amount for coexisting unburned components, wherein silver and silver are used as porous inorganic oxides. 0.2 to 15% by weight of one or more elements selected from the group consisting of compounds and / or compounds
(A metal element equivalent), a first catalyst supporting the porous inorganic oxide, 0.001 to 0.5% by weight of Pt (metal element equivalent), and 0.001 to 0.05% by weight of Rh. An exhaust gas purifying material comprising a mixture of (a metal element conversion value) and a second catalyst supporting at least one element selected from the group consisting of rare earth elements at 2% by weight or less. . 3. 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. Exhaust gas purifying material. 4. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide of the first catalyst is alumina alone or titania, silica, zirconia, zinc oxide, tin oxide, Magnesium oxide, a composite or mixed oxide of either zeolite and alumina,
The exhaust gas purifying material, wherein the porous inorganic oxide of the second catalyst is at least one selected from the group consisting of alumina, titania, silica, zirconia, zinc oxide, tin oxide, magnesium oxide, and zeolite. . 5. The exhaust gas purifying material according to claim 1, wherein a mixed catalyst obtained by mixing the first catalyst and the second catalyst is coated on a surface of a ceramic or metal substrate. An exhaust gas purifying material characterized by being made. 6. The exhaust gas purifying material according to claim 1, wherein the mixed catalyst obtained by mixing the first catalyst and the second catalyst has a honeycomb shape, a foam shape, a plate shape, and a pellet shape. An exhaust gas purifying material, which is formed into any one of granular and granular forms. 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 method for purifying exhaust gas to be removed, the exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and is selected from the group consisting of gaseous hydrocarbons, kerosene, light oil, and liquid hydrocarbons including gasoline on the upstream side of the purifying material. An exhaust gas purifying method, comprising contacting an exhaust gas containing at least one of the above-mentioned ones with the purifying material at 300 to 550 ° C., thereby removing the nitrogen oxides by reacting with hydrocarbons in the exhaust gas.