JPH10323541A - Purifying material of exhaust gas for lean burn apparatus and method for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a purifying material of exhaust gas with which oxidation of a reducing agent can be suppressed to the min. and nitrogen oxides can be effectively removed in a wide temp. range by forming a catalyst layer having a specified proportion of silver to cover a noble metal catalyst such as platinum. SOLUTION: The purifying material of exhaust gas is used to reduce and remove nitrogen oxides included in exhaust gas. The purifying material is produced by using a first catalyst and a second catalyst in such a manner that the first catalyst layer covers the upper face of the second catalyst. The first catalyst is prepared by depositing one or more kinds of elements and/or compds. of silver and silver compds. by 0.2 to 15 wt.% on a porous inorg. oxide. The second catalyst is prepared by depositing one noble metal element such as Pt and Pd by 0.001 to 5 wt.% on a porous inorg. oxide. In the purifying process of exhaust gas, the purifying material of exhaust gas is disposed in the conduit of the exhaust gas so as to bring the exhaust gas into contact with the purifying material at 300 to 600 deg.C. Thus, nitrogen oxides are removed by the reaction with residual hydrocarbons and/or oxygen-contg. org. compds. in the exhaust gas.

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 Various combustion exhaust gases discharged from gas engines, gas turbines and the like for cogeneration systems contain nitrogen oxides such as nitric oxide and nitrogen dioxide together with excess oxygen. (Commonly referred to as NOx). 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.

As a method for removing nitrogen oxides from a combustion exhaust gas containing excess oxygen, a non-selective catalytic reduction method for reducing nitrogen oxides using a gas such as hydrogen, carbon monoxide, or a hydrocarbon as a reducing agent is known. However, in this method, in order to effectively 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,
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 addition, effective nitrogen oxide removal can be obtained only in a narrow temperature range.

Therefore, a method of removing nitrogen oxides by using an exhaust gas purifying material in which silver is supported on an inorganic oxide such as alumina and adding alcohol as a reducing agent to the exhaust gas has been proposed (Japanese Patent Application Laid-Open No. Hei 6 (1994)). -327974). Also disclosed is an exhaust gas purifying material having a silver catalyst layer on the exhaust gas inflow side and a copper catalyst layer on the outflow side (JP-A-6-190280).
It shows high nitrogen oxide removal performance at around ° C.
However, the nitrogen oxide removal rate in a wide exhaust gas temperature range, particularly in a low temperature range, is not yet sufficient. It is not practical to add a reducing agent from the outside.

Recently, after providing a platinum-based catalyst layer on a carrier,
A purification catalyst for exhaust gas having a two-layer structure in which a silver-based catalyst layer is further provided on the upper surface (JP-A-6-262075), or an exhaust gas purification catalyst composed of a platinum layer, a Ce layer, a Rh layer, and a silver layer A catalyst (JP-A-9-925) has been proposed. By using these layered catalysts, a high nitrogen oxide removal performance is exhibited at around 400 ° C. in exhaust gas. However, there is a problem that the removal performance of the exhaust gas having a nitrogen oxide concentration of 500 ppm or less is significantly reduced. Further, the performance of removing nitrogen oxides in a low temperature region is not sufficient.

Further, as a problem peculiar to the lean burn gas engine, since the temperature of the exhaust gas is low, mainly around 400 ° C., and the nitrogen oxide concentration is low, the removal rate of the conventional catalyst is not sufficient.

[0008] Accordingly, an object of the present invention is to provide a combustion exhaust gas from a gas-fueled combustion apparatus, which is a combustion exhaust gas containing unreacted nitrogen oxides, carbon monoxide, hydrocarbons, etc., and oxygen in excess of a stoichiometric amount with respect to a partial combustion component. An object of the present invention is to provide an exhaust gas purifying material and an exhaust gas purifying method capable of efficiently removing nitrogen oxides from exhaust gas by using residual hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas as a reducing agent.

[0009]

Means for Solving the Problems In view of the above problems, as a result of intensive research, the present inventors have found that when exhaust gas comes into contact with a platinum catalyst prior to a silver catalyst, a reducing agent such as residual hydrocarbons in the exhaust gas is oxidized. By providing a specific ratio of silver catalyst layer on a precious metal catalyst such as platinum, the oxidation of the reducing agent is minimized and nitrogen oxidation in a wide temperature range, especially in a low temperature range below 400 ° C. The inventors have found that objects can be effectively removed, and completed the present invention.

That is, the exhaust gas purifying material of the present invention for reducing and removing nitrogen oxides contained in an oxygen-excess exhaust gas discharged from a lean burn device using a gas fuel comprises: (a) a porous inorganic oxide containing silver And at least one element and / or compound selected from the group consisting of:
(B) a first catalyst supporting (a metal element conversion value);
At least one noble metal element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au in the porous inorganic oxide 0.00
A second catalyst supporting 1 to 5% by weight (in terms of a metal element), wherein the first catalyst layer is formed so as to cover an upper surface of the second catalyst. And

Further, in the exhaust gas purifying method of the present invention for reducing and removing nitrogen oxides contained in exhaust gas discharged from a lean burn device using a gas fuel, the exhaust gas purifying material is provided in the middle of an exhaust gas conduit. At 300 to 600 ° C. to remove the nitrogen oxides by reacting the nitrogen oxides with residual hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, exhaust gas from a combustion device using any of liquefied petroleum gas, city gas and liquefied natural gas as fuel is brought into contact with an exhaust gas purifying material, and residual hydrocarbons and / or The nitrogen-oxide is removed by reacting the oxygen-containing organic compound with the nitrogen oxide in the exhaust gas. The combustion device is either a lean-burn gas engine or a gas turbine. Hereinafter, the present invention will be described in detail.

[1] Exhaust gas purifying material (1) Structure of exhaust gas purifying material The exhaust gas purifying material of the present invention comprises a first catalyst and a second catalyst described later. A silver-based catalyst as a first catalyst is formed in a layer so as to cover an upper surface of a noble metal-based catalyst as a second catalyst. By covering the noble metal-based catalyst with the silver catalyst, the reducing agent such as residual hydrocarbons in the exhaust gas first contacts the silver catalyst and acts as a reducing agent. It can be carried out.

(A) In a first preferred embodiment of the exhaust gas purifying material of the present invention, a silver catalyst as a first catalyst is formed so as to cover a noble metal catalyst as a second catalyst, and And a purification material obtained by coating a purification material substrate with a second catalyst. Specifically, first, the second catalyst is coated on the substrate of the purifying material by a known method, and then the first catalyst is coated by a known method so as to cover the second catalyst.

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 substrate in the order of the second catalyst and the first catalyst using a wash coat method, a sol-gel method, a powder method or the like, and sintering.

(B) In a second preferred embodiment of the exhaust gas purifying material of the present invention, the second catalyst is formed into a honeycomb structure, a foam, a plate, a pellet, or a granule, and then the first catalyst is formed. On the upper surface of the second catalyst.

The above-mentioned purifying material is placed in an exhaust gas conduit, and the exhaust gas is brought into contact with the purifying material to reduce and remove nitrogen oxides in the exhaust gas.

(2) 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 has a wide temperature range. Acts on the removal of nitrogen oxides. 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 carbonate, silver phosphate, and the like, and is preferably any one of silver oxide, silver chloride and silver sulfate. Or more, 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. If the silver component is carried in an amount exceeding 15% by weight, the oxidation of the reducing agent is likely 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. At this time, an aqueous solution of a silver compound such as silver nitrate is used to carry silver and silver oxide. In the precipitation method, silver halide can be prepared by reacting silver nitrate with ammonium halide, and precipitating silver halide as a silver halide on a porous inorganic oxide. This is 5
After drying at 0 to 150 ° C, especially at about 70 ° C, 100 to 60 ° C
It is preferable that the temperature is raised stepwise at 0 ° 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.

(3) Second catalyst The second catalyst is formed by adding P as a catalytically active species to the porous inorganic oxide.
It carries at least one noble metal element selected from the group consisting of t, Pd, Ru, Rh, Ir and Au. At a low exhaust gas temperature, the presence of the noble metal element-based catalyst converts nitrogen oxides in the exhaust gas into nitrogen dioxide, which can be reduced to nitrogen gas by the silver-based catalyst, thereby improving the nitrogen oxide removal rate in a low temperature region. 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 noble metal component such as platinum is 0.001 to 5% by weight (in terms of a metal element), and the preferable supported amount is 0.0%.
The amount is 1 to 4% by weight (converted to metal element), and the more preferable loading is 0.1 to 3% by weight (converted to metal element).
If the amount of the catalytically active species is less than 0.001% by weight with respect to the inorganic oxide, the effect of supporting the catalyst is not remarkable, and NOx
The reduction characteristics are reduced. On the other hand, if the catalyst loading exceeds 5% by weight, only the oxidizing combustion of the reducing agent such as the residual hydrocarbon proceeds, and the characteristic of reducing nitrogen oxides deteriorates.

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.

(4) Method for Producing Exhaust Gas Purifying Material When the purifying material is in the above-described first preferred embodiment, first, a second catalyst is applied to a substrate by a known method such as a wash coat method, a sol-gel method, or a powder method. And coat 5
After drying at 0-150 ° C, especially 70 ° C, 100-600 ° C
Then, the temperature is increased stepwise and firing is performed. Next, the first catalyst is coated on the substrate coated with the second catalyst by a known method,
After drying at 50-150 ° C, especially 70 ° C, 100-600
The temperature is raised stepwise at ℃ and baked to obtain an exhaust gas purifying material.

When the form of the purifying material is the second preferred form described above, the second catalyst is formed into a honeycomb structure, a foam, a plate, a pellet, or a granule by a known method. After drying at 150 ° C, especially 70 ° C, 100 ~
The temperature is raised stepwise at 600 ° C. and firing is performed. Next, the first catalyst is coated by a known method so as to enclose the second catalyst, and
After drying at 0-150 ° C, especially 70 ° C, 100-600 ° C
The temperature is increased step by step and firing is performed to obtain an exhaust gas purifying material.

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 2:
The ratio is preferably set to 1 to 500: 1. A more preferred weight ratio of the first catalyst to the second catalyst is 10: 1 to 300: 1, and a particularly preferred weight ratio is 50: 1 to 200: 1. If the weight ratio of the first catalyst to the second catalyst is less than 2: 1, the amount of the first catalyst layer is not sufficient, so that the reducing agent may directly contact the second catalyst layer. And leads to a decrease in the removal rate of nitrogen oxides. On the other hand, if the weight ratio of the first catalyst to the second catalyst exceeds 500: 1, the exhaust gas becomes difficult to reach the second catalyst, and the effect of the second catalyst cannot be obtained.

The weight ratio of the catalytically active species of the first catalyst and the second catalyst (the ratio of the total weight of the catalytically active species) is 20: 1.
To 1500: 1, more preferably 1: 1.
00: 1 to 1200: 1, particularly preferably 200: 1 to
1100: 1. If the weight ratio of the catalytically active species of the first catalyst and the second catalyst is less than 20: 1, the noble metal element becomes excessive and the reducing agent such as residual hydrocarbons in the exhaust gas is easily oxidized. On the other hand, when the weight ratio of the catalytically active species is 150
When the ratio exceeds 0: 1, the noble metal element becomes insufficient, and the catalytic effect of the noble metal element cannot be obtained.

In general, the thickness of the catalyst provided on the purifying material substrate is often limited due to the difference in thermal expansion characteristics between the substrate material and the catalyst. It is preferable that the thickness of each of the first catalyst and the second catalyst provided on the purifying material base is 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 total amount of the first catalyst and the second catalyst provided on the surface of the purifying material base is 20 to 3 of the purifying material base.
It is preferably 00 g / liter. The amount of catalyst is 20
If the amount is less than 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 total weight of the catalyst provided on the surface of the purification material base is 50 to 250 g / liter of the purification material base.

When the purifying material having the above-described structure is used, 300
In a wide temperature range of up to 600 ° 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, the exhaust gas purifying material is installed in the middle of the exhaust gas conduit. The exhaust gas of the gas-fuel-lean combustion equipment contains hydrocarbons such as saturated hydrocarbons containing methane as a main component and oxygen-containing organic compounds, and serves as a reducing agent for removing nitrogen oxides. Here, the oxygen-containing organic compound means a mixture of oxygen-containing organic compounds generated by partially burning gaseous fuel in a combustion device.

In the present invention, the space velocity between the exhaust gas and the catalyst is 150,000 h in order to efficiently promote the reduction and removal of nitrogen oxides by residual hydrocarbons and / or oxygen-containing organic compounds.
^-1 or less, preferably 100,000 h ^-1 or less. When the space velocity exceeds 150,000 h ^-1 , the reduction reaction of nitrogen oxides does not sufficiently occur, and the nitrogen oxide removal rate decreases.

Further, in the present invention, the temperature of the exhaust gas is maintained at 300 to 600 ° C. at the purifying material installation site where the reducing agent reacts with the nitrogen oxide. Exhaust gas temperature is 300
If 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 600 ° C., combustion of the reducing agent itself starts, and reduction and removal of nitrogen oxides cannot be performed. The preferred exhaust gas temperature is 350-550 ° C, more preferably 35-550 ° C.
0-500 ° C.

[0036]

The present invention will be described in more detail with reference to the following specific examples. Example 1 A commercially available γ-alumina powder (specific surface area: 200 m ² / g) was 2.0% by weight (in terms of metal element) using an aqueous solution of silver nitrate.
Was dried at 80 ° C. for 3 hours, and then calcined in air stepwise to 600 ° C. to prepare a first catalyst.

A similar γ-alumina powder was loaded with 0.3% by weight (in terms of Rh element) of an aqueous rhodium nitrate solution, dried, and fired stepwise in air to 600 ° C.
A second catalyst was prepared.

After slurrying 2.0 g of the second catalyst,
A commercially available cordierite honeycomb-shaped molded product (having a diameter of 150
mm, length 100 mm, 200 cells / inch ² ), dried and calcined stepwise to 600 ° C., coated with 230 g of a first catalyst slurried, and dried to 600
After calcination stepwise to ° C, an exhaust gas purifying material (a purifying material coated with two layers of a first catalyst layer and a second catalyst layer) was prepared. The weight ratio of the first catalyst to the second catalyst is 1
15: 1.

Nitrogen oxides in the exhaust gas from the gas engine were removed using a nitrogen oxide removing device filled with 16 of the above exhaust gas purifying materials. The gas engine is a lean-burn gas engine of 300 kW, and the space velocity of exhaust gas with respect to all the purification materials is 50,000 h ^-1 . The nitrogen oxide concentration at the inlet of the purifying material was 190 ppm (converted to an oxygen concentration of 0%). The operation of the engine was performed under a 100% load (the oxygen concentration at this time was 11%), and the exhaust gas temperature at the inlet of the purifying material was 378 ° C. The nitrogen oxide concentration was calculated by the following equation: Nitrogen oxide equivalent concentration = Cs × (21−On) / (21−)
Os) where Cs is the concentration of nitrogen oxides in the exhaust gas.
n is the reduced oxygen concentration (here, 0%), and Os is the oxygen concentration in the exhaust gas.

The concentration of nitrogen oxides in the gas after passing through the remover was measured by a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 1 shows the results.

Example 2 In the same manner as in Example 1, 0.3% by weight of Pd was added to γ-alumina powder using an aqueous solution of palladium nitrate and rhodium nitrate.
(Pd element conversion value) and 0.01% by weight of Rh (Rh element conversion value).
And a second catalyst was prepared.

After slurrying 1.5 g of the second catalyst,
A commercially available cordierite honeycomb-shaped molded product (having a diameter of 150
mm, length 100 mm, 200 cells / inch ² ), dried and fired stepwise to 600 ° C., coated with 225 g of the first catalyst slurried in Example 1, dried, and stepped to 600 ° C. After that, an exhaust gas purifying material (a purifying material coated with two layers of a first catalyst layer and a second catalyst layer) was prepared. The weight ratio of the first catalyst to the second catalyst is 150: 1.

Using a nitrogen oxide removing apparatus packed with 16 of the above exhaust gas purifying materials, nitrogen oxides in the exhaust gas from the gas engine were removed under the same conditions as in Example 1. The gas engine is a lean-burn gas engine of 300 kW, and the space velocity of exhaust gas with respect to all the purification materials is 50,000 h ^-1 . The nitrogen oxide concentration at the inlet of the purifying material was 190 ppm (converted to an oxygen concentration of 0%). The operation of the engine is 10
The test was performed at 0% load, and the exhaust gas temperature at the inlet of the purification material was 376 ° C
Met. In the same manner as in Example 1, the concentration of nitrogen oxides in the gas after passing through the remover was measured by a chemiluminescent nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Table 1 shows the results
Shown in

Example 3 3.0 wt% (in terms of metal element) of a commercially available γ-alumina powder (specific surface area: 200 m ² / g) using an aqueous solution of silver nitrate
Was dried at 80 ° C. for 3 hours, and then calcined in air stepwise to 600 ° C. to prepare a first catalyst.

A similar γ-alumina powder was loaded with 0.3% by weight (converted to a Pd element) using an aqueous solution of palladium nitrate, dried, and baked in air stepwise to 600 ° C.
A second catalyst was prepared.

After slurrying 18 mg of the second catalyst,
A commercially available cordierite honeycomb-shaped molded product (30 m in diameter)
m, 16 mm long, 200 cells / inch ² ), dried and fired stepwise to 600 ° C., coated with 1.8 g of the first slurried catalyst, and dried to 600 ° C.
After calcination stepwise, an exhaust gas purifying material (a purifying material coated with two layers of a first catalyst layer and a second catalyst layer) was prepared. The weight ratio of the first catalyst to the second catalyst is 10
0: 1.

The above exhaust gas purifying material is set in a reaction tube,
The nitrogen oxides were removed under the following conditions. The gas engine is a lean-burn gas engine of 300 kW, and the space velocity of exhaust gas with respect to all the purification materials is 50,000 h ^-1 . The nitrogen oxide concentration at the inlet of the purifying material was 190 ppm (converted to an oxygen concentration of 0%). The operation of the engine is 100
% Load, and the exhaust gas temperature at the inlet of the purifying material was 378 ° C. In the same manner as in Example 1, the concentration of nitrogen oxides in the gas after passing through the removing device was measured with a chemiluminescent nitrogen oxide analyzer to determine the concentration of nitrogen oxides. Table 1 shows the results.

Example 4 1% by weight of γ-alumina powder using platinum nitrate aqueous solution
(Pt element conversion value) was carried, and after drying, it was calcined in air stepwise to 600 ° C. to prepare a second catalyst.

After slurrying 18 mg of the second catalyst,
A commercially available cordierite honeycomb-shaped molded product (30 m in diameter)
m, length 16 mm, 200 cells / inch ² ), dried and baked stepwise to 600 ° C., coated with 1.8 g of the first catalyst of Example 3 which was slurried, dried and then dried at 600 ° C. After calcination stepwise, an exhaust gas purifying material (a purifying material coated with two layers of a first catalyst layer and a second catalyst layer) was prepared. In addition, the weight ratio of the first catalyst to the second catalyst is 100: 1.

The above exhaust gas purifying material was set in a reaction tube,
The removal of nitrogen oxides was performed under the same conditions as in Example 3. In the same manner as in Example 1, the concentration of nitrogen oxides in the gas after passing through the removing device was measured with a chemiluminescent nitrogen oxide analyzer to determine the concentration of nitrogen oxides. Table 1 shows the results.

COMPARATIVE EXAMPLE 1 230 g of the first catalyst (silver-based catalyst) of Example 1 was slurried, coated on a cordierite honeycomb-like formed body similar to that of Example 1, and dried stepwise to 600 ° C. After firing, an exhaust gas purifying material was prepared.

As in the first embodiment, the exhaust gas purifying material 1
The evaluation was performed under the same conditions as in Example 1 (the apparent space velocity was about 50,000 h ⁻¹ ), using a nitrogen oxide removing apparatus filled with six pieces. Table 1 shows the results.

Comparative Example 2 After slurrying 120 g of the second catalyst of Example 3, a commercially available honeycomb formed body made of cordierite (having a diameter of 150 m) was prepared.
m, length 100 mm, 200 cells / inch ² ), dried and fired stepwise to 600 ° C., then coated with 120 g of the first catalyst of Example 3, which was slurried, and dried to 600 ° C. After calcination, an exhaust gas purifying material (a purifying material coated with two layers of a first catalyst layer and a second catalyst layer) was prepared. The weight ratio of the first catalyst to the second catalyst is 1: 1.

As in the first embodiment, the exhaust gas purifying material 1
The evaluation was performed under the same conditions as in Example 2 (the apparent space velocity was about 50,000 h ⁻¹ ), using a nitrogen oxide removing apparatus filled with six pieces. Table 1 shows the results.

Comparative Example 3 After 120 g of the second catalyst of Example 1 was slurried, a commercially available cordierite honeycomb-shaped molded product (150 m in diameter) was prepared.
m, length 100 mm, 200 cells / inch ² ), dried and fired stepwise to 600 ° C., then coated with 120 g of the first catalyst of Example 3, which was slurried, and dried to 600 ° C. After calcination, an exhaust gas purifying material (a purifying material coated with two layers of a first catalyst layer and a second catalyst layer) was prepared. The weight ratio of the first catalyst to the second catalyst is 1: 1.

As in the first embodiment, the exhaust gas purifying material 1
The evaluation was performed under the same conditions as in Example 2 (the apparent space velocity was about 50,000 h ⁻¹ ), using a nitrogen oxide removing apparatus filled with six pieces. Table 1 shows the results.

Table 1 Example No. Example 1 47 Example 2 60 Example 3 57 Example 4 39 Comparative example 1 30 Comparative example 2 8 Comparative example 3 5

As can be seen from Table 1, the two-layer exhaust gas purifying material comprising the first catalyst and the second catalyst according to the present invention is different from Comparative Example 1 using only the silver catalyst as the first catalyst. In Examples 1 to 4 used, high nitrogen oxide removal performance was observed. On the other hand, Comparative Example 2 using the same amount of noble metal catalyst as silver catalyst
In Nos. 3 and 3, conversely, the nitrogen oxide removal rate was reduced. This is because the presence of a large amount of the noble metal catalyst (second catalyst) oxidized the reducing agent such as residual hydrocarbons.

[0059]

As described in detail above, 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. INDUSTRIAL APPLICABILITY The exhaust gas purifying material and the purifying method of the present invention can be widely used for removing nitrogen oxides from exhaust gas of various combustion devices, automobiles and the like.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B01J 27/18 B01J 27/232 A 27/232 B01D 53/36 ZAB 102A (72) Inventor Masataka Koyama 4-chome Suehiro, Kumagaya-shi, Saitama No. 14-1 Rikken Kumagaya Office (72) Inventor Ken Nishiya 4-1-1 Suehiro Kumagaya City, Saitama Prefecture Rikan Kumagaya Office (72) Inventor Shigeo Satokawa 2-Togoshiya, Ota-ku, Tokyo 17-10-103 (72) Inventor Kenichi Yamaseki 1-48-63-1303 Higashiikebukuro, Toshima-ku, Tokyo (72) Inventor Fumiyuki Hoshi 2-10-1 Masuodai, Kashiwa-shi, Chiba (72) Inventor Uchida (3) Inventor Masahiro Yahagi 1-28-306 Nishisugamo, Toshima-ku, Tokyo (72) Inventor Hideyasu Yokota 4- Kaminagaya, Konan-ku, Yokohama, Kanagawa 7 7

Claims (7)

[Claims] An exhaust gas purifying material for reducing and removing nitrogen oxides contained in an oxygen-excess exhaust gas discharged from a lean burn device using a gas fuel, comprising: (a) silver and a silver compound as porous inorganic oxides; A first catalyst supporting 0.2 to 15% by weight (in terms of metal element) of one or more elements and / or compounds selected from the group consisting of: (b) Pt on a porous inorganic oxide; 0.001 to 5% by weight of at least one noble metal element selected from the group consisting of Pd, Ru, Rh, Ir and Au
(A metal element conversion value), wherein the first catalyst layer is formed so as to cover an upper surface of the second catalyst. . 2. The exhaust gas purifying material according to claim 1, wherein the weight ratio of the first catalyst to the second catalyst is 2:
An exhaust gas purifying material having a ratio of 1 to 500: 1. 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, silver carbonate and silver phosphate. An exhaust gas purifying material characterized by that: 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 any one of claims 1 to 4, wherein the second catalyst is made of a ceramic having a honeycomb shape, a foam shape, a plate shape, a pellet shape, a granular shape, or An exhaust gas purifying material coated on the surface of a metal substrate. 6. The exhaust gas purifying material according to claim 1, wherein the second catalyst is formed into any one of a honeycomb type, a foam type, a plate shape, a pellet shape, and a granular shape. Exhaust gas purifying material. 7. An exhaust gas purifying method using the exhaust gas purifying material according to any one of claims 1 to 6 to reduce and remove nitrogen oxides contained in exhaust gas discharged from lean burn equipment using gas fuel. The exhaust gas purifying material is installed in the middle of an exhaust gas conduit, and the exhaust gas is brought into contact with the purifying material at 300 to 600 ° C., thereby causing the nitrogen oxides to react with residual hydrocarbons and / or oxygen-containing organic compounds in the exhaust gas. Exhaust gas purifying method, wherein the nitrogen oxides are removed by a method.