JPH07265701A - Exhaust gas purifying material and method - Google Patents

Abstract

PURPOSE:To achieve the removal of nitrogen oxide and the oxidative removal of residual and unreacted carbon monoxide and hydrocarbon by combining a catalyst wherein silver and W or V components are supported on porous inorg. oxide with a catalyst wherein a platinum component is supported on porous inorg. oxide. CONSTITUTION:An exhaust gas purifying material removes nitrogen oxide from combustion exhaust gas containing nitrogen oxide and oxygen whose amt. is larger than the theoretical reaction amt. to a coexisting unburnt component and also oxidizes residual and unreacted carbon monoxide and hydrocarbon to remove them. In this case, the exhaust gas purifying material is constituted of two kinds of catalysts, that is, a first catalyst wherein 0.2-15wt.% of silver and/or a silver compd. or a mixture of them and 10wt.% or less of oxide of at least one element selected from the group consisting of W, V and the others are supported on porous inorg. oxide and a second catalyst wherein 5wt.% or less of at least one element selected from the group consisting of Pt, Pd and the others is supported on porous inorg. oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification material for effectively 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 amounts of combustion exhaust gas emitted from internal combustion engines such as automobile engines, combustion equipment installed in factories, household fan heaters, etc. Nitrogen oxides such as nitric oxide and nitrogen dioxide are contained together with oxygen. Here, "containing excess oxygen" means containing more oxygen than the theoretical oxygen amount necessary to burn unburned components such as carbon monoxide, hydrogen, and hydrocarbons contained in the exhaust gas. To do. Moreover, the nitrogen oxide in the following refers to nitric oxide and / or nitrogen dioxide.

This nitrogen oxide is considered to be one of the causes of acid rain and is a serious environmental problem. Therefore, various methods for removing nitrogen oxides in exhaust gas discharged from various combustion devices have been studied.

As a method for removing nitrogen oxides from combustion exhaust gas containing excess oxygen, a selective catalytic reduction method using ammonia is used, particularly for large-scale fixed combustion devices (large combustors such as factories). It 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, so that unreacted ammonia is discharged so that nitrogen oxides in exhaust gas are not discharged. There are problems that the amount of ammonia injection must be controlled while measuring the concentration and that the apparatus is generally large.

[0006] As another method, there is a non-selective catalytic reduction method for reducing nitrogen oxides by using a gas such as hydrogen, carbon monoxide or hydrocarbon as a reducing agent, but this method is effective. In order to reduce and remove nitrogen oxides, it is necessary to add a reducing agent in an amount equal to or larger than a theoretical reaction amount with oxygen in exhaust gas, and there is a drawback that a large amount of reducing agent is consumed. Therefore, the non-selective catalytic reduction method is practically effective only for the exhaust gas having a low residual oxygen concentration that is burned in the vicinity of the theoretical air-fuel ratio, and is not versatile and impractical.

Therefore, there has been proposed a method for removing nitrogen oxides by adding a reducing agent in an amount equal to or less than a theoretical reaction amount with oxygen in exhaust gas by using zeolite or a catalyst supporting a transition metal thereon (for example, a special method). Kaisho 63-100919, 63-28372
No. 7, JP-A-1-130735, and the 59th Annual Meeting of the Chemical Society of Japan
(1990) 2A526, 60th Autumn Meeting (1990) 3L420, 3L422
, 3L423, "Catalyst" vol.33 No.2, page 59, 1991 etc.).

However, it has been found that these methods have a narrow temperature range for removing nitrogen oxides and that the exhaust gas containing water has a significantly low nitrogen oxide removal rate. Therefore, the present inventors have a silver-based catalyst on the exhaust gas inflow side and a platinum-based catalyst on the outflow side, and can effectively remove nitrogen oxides even with exhaust gas containing 10% water, We have previously proposed a purification material that can also remove hydrocarbons (Japanese Patent Application No. 4-328895). However, the removal rate of nitrogen oxides, etc. in the low exhaust gas temperature region is not yet sufficient.

Therefore, an object of the present invention is to remove nitrogen oxides, carbon monoxide, hydrogen, hydrocarbons, etc., such as combustion exhaust gas from a fixed combustion device and a gasoline engine, a diesel engine, etc. that burn under an excess oxygen condition. From the combustion exhaust gas that contains more than the theoretical reaction amount of oxygen for unburned components,
An exhaust gas purifying material and an exhaust gas purifying method capable of efficiently removing nitrogen oxides and also oxidizing and removing residual and unreacted carbon monoxide and hydrocarbons.

[0010]

As a result of earnest research in view of the above problems, the present inventor has found that a porous inorganic oxide carries a catalyst composed of a silver component, W and V based components, and a platinum based component. Using an exhaust gas purification material formed by combining with a catalyst formed by adding a hydrocarbon and an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing them to the exhaust gas at a specific temperature and space velocity. The present invention has been completed by discovering that if the exhaust gas is brought into contact with the above-mentioned purification material, the nitrogen oxides can be effectively removed even in the exhaust gas containing 10% of water in a low temperature range.

That is, the nitrogen oxides are removed from the combustion exhaust gas containing the nitrogen oxides and oxygen in a larger amount than the theoretical reaction amount for the coexisting unburned components, and the residual and unreacted carbon monoxide and hydrocarbons are also removed by oxidation. The exhaust gas purifying material of the present invention comprises (1) porous inorganic oxide (a) silver and / or
Or a silver compound, or a mixture thereof 0.2 to 15% by weight
First, which comprises (a silver element conversion value) and (b) 10% by weight or less (a metal element conversion value) of an oxide of at least one element selected from the group consisting of W, V, Mn and Mo. (C) Pt, Pd, Ru, R in the catalyst of (2) porous inorganic oxide
It is characterized by comprising a second catalyst carrying 5% by weight or less (at a metal element conversion value) of at least one element selected from the group consisting of h, Ir and Au.

Further, nitrogen oxides are removed from the combustion exhaust gas containing nitrogen oxides and oxygen in a larger amount than the theoretical reaction amount for coexisting unburned components, and residual and unreacted carbon monoxide and hydrocarbons are also removed by oxidation. In the exhaust gas purifying method of the present invention, the exhaust gas purifying material is installed in the middle of the exhaust gas conduit, the exhaust gas purifying material is installed in the middle of the exhaust gas conduit, and the hydrocarbon and the carbon number of 2 or more are provided on the upstream side of the purification material. Exhaust gas added with any one or more of oxygen-containing organic compounds or a fuel containing them is brought into contact with the purification material at 150 to 650 ° C. to remove the nitrogen oxides.

The present invention will be described in detail below. [1] Purifying material In the present invention, (1) the porous inorganic oxide includes (a) silver and / or
Or a silver compound, or a mixture thereof 0.2 to 15% by weight
First, which comprises (a silver element conversion value) and (b) 10% by weight or less (a metal element conversion value) of an oxide of at least one element selected from the group consisting of W, V, Mn and Mo. (C) Pt, Pd, Ru, R in the catalyst of (2) porous inorganic oxide
An exhaust gas purifying material comprising a second catalyst supporting 5% by weight or less of at least one element selected from the group consisting of h, Ir and Au (metal element conversion value) is installed in the exhaust gas conduit, Hydrocarbons and carbon number 2 upstream from the installation position of the purification material
Exhaust gas to which any one or more of the above oxygen-containing organic compounds or fuel containing them is added is brought into contact with this purification material to reduce and remove nitrogen oxides in the exhaust gas. In the present invention, the first catalyst and the second catalyst are used in combination,
It is preferable to arrange the first catalyst on the exhaust gas inflow side and the second catalyst on the outflow side. By arranging in this way, nitrogen oxides can be effectively reduced and removed in a wide exhaust gas temperature range.

In the present invention, the weight ratio of the first catalyst and the second catalyst (the ratio of the total weight of the porous inorganic oxide and the catalytically active species) is 10: 1 to 1: 5. Is preferred. The ratio is less than 1: 5 (less first catalyst)
Then, in a wide temperature range of 150 to 650 ° C., the purification rate of nitrogen oxides is lowered overall. On the other hand, when the ratio exceeds 10: 1 and the amount of the second catalyst is small, the oxidation and removal characteristics of CO and hydrocarbons formed on the first catalyst and the residue at low temperatures deteriorate. More preferable weight ratio of the first catalyst to the second catalyst is 9: 1.
~ 1: 4.

In a first preferred form of the exhaust gas purifying material of the present invention, the purifying material substrate is coated with the first and second catalysts, each of which is a powdery porous inorganic oxide carrying a catalytically active species. Or a powdery porous inorganic oxide coated on a purifying material base, and then carrying a catalytically active species. As the ceramic material forming the substrate of the purification material, γ-alumina and its oxides (γ-alumina-titania, γ-alumina-silica, γ-alumina-zirconia, etc.), zirconia, titania-zirconia, etc. are porous. A heat-resistant material having a large surface area can be used.
When high heat resistance is required, cordierite, mullite, alumina and their composites are preferably used. Also, a known metal material can be used for the substrate of the exhaust gas purifying material.

The shape and size of the substrate of the exhaust gas purifying material are
Various changes can be made according to the purpose. Also, the base body is the inlet portion,
It is also possible to use two or more parts such as an outlet part in combination. Examples of the structure of the substrate include a honeycomb structure type, a foam type, a three-dimensional network structure type made of fibrous refractory, a granular form, a pellet form and the like. The first catalyst and the second catalyst may be coated on different positions of the same substrate, or may be coated on different substrates and then used in combination.

A second preferred form of the exhaust gas purifying material of the present invention is to fill a casing having a desired shape with a catalyst having a catalytic active species supported on a porous inorganic oxide in the form of pellets, granules or powder. It is a purifying material.

[2] First Catalyst The first catalyst comprises a porous inorganic oxide (a) silver and / or a silver compound, or a mixture thereof, and (b) W, V, Mn and Mo. It carries an oxide of at least one element selected from the group.

(1) Porous Inorganic Oxide As the porous inorganic oxide, porous alumina, silica, titania, zirconia and their composite oxides can be used, but γ-is preferable. Alumina or an alumina-based composite oxide is used. By using γ-alumina or an alumina-based composite oxide, the reaction between the added hydrocarbon, the oxygen-containing organic compound or the fuel containing them and the nitrogen oxide in the exhaust gas occurs efficiently.

The specific surface area of the porous inorganic oxide is 10 m ²
/ G or more is preferable. Specific surface area of 10 m ² / g
If it is less than the above range, the contact area between the exhaust gas and the inorganic oxide (and the silver component carried on the exhaust gas) becomes small, and the nitrogen oxide cannot be removed well. The specific surface area of the porous inorganic oxide is
It is preferably 30 m ² / g or more.

(2) Silver and / or silver compound or mixture thereof The silver compound is at least one selected from the group consisting of silver oxide, silver halide, silver sulfate and silver phosphate, and preferably silver. Oxide, silver chloride, and silver sulfate, and more preferably silver oxide and / or silver chloride. The silver component supported on the porous inorganic oxide is in the form of fine particles, and preferably has an average particle size of 10 to 10,000 nm. Generally, the smaller the average particle size of the silver component particles is, the better the reaction characteristics are. However, if the average particle size is less than 10 nm, the oxidation reaction of the reducing agent hydrocarbon or the oxygen-containing organic compound proceeds too much. The removal rate is low. On the other hand, when the average particle diameter of the silver component particles exceeds 10,000 nm, the reaction characteristics of the silver component deteriorate and the nitrogen oxide removal rate decreases.
The average particle diameter of the silver component particles is preferably 20 to 2000 nm. Here, the average particle diameter is obtained by the arithmetic mean of the diameters of the particles. The silver component supported on the porous inorganic oxide is in a state of either metal or oxide in the temperature range of exhaust gas.

The amount of the silver component (a) supported as an active species on the above-mentioned inorganic oxide such as γ-alumina varies slightly depending on the type of organic compound and fuel added to the exhaust gas, the contact time with the exhaust gas, etc. However, it is 0.2 to 15% by weight (in terms of silver element) with respect to 100% by weight of the inorganic oxide. If it is less than 0.2% by weight, the removal rate of nitrogen oxides is lowered. On the other hand, when silver is supported in an amount of more than 15% by weight, the hydrocarbon and / or the oxygen-containing organic compound itself is easily burned, and the nitrogen oxide removal rate is rather lowered. The amount of the silver component supported is preferably 0.5 to 12% by weight.

(2) W, V, Mo and Mn Components Among W, V, Mo and Mn, it is preferable to use W and / or V. W-based oxide supported on inorganic oxide (b)
Is 10% by weight or less (metal element conversion value), preferably 0.01 to 8% by weight (metal element conversion value) based on the above-mentioned porous inorganic oxide (100% by weight). The amount of W-based oxide supported is 1 with respect to the inorganic oxide.
Even if it exceeds 0% by weight, the effect remains unchanged. By using the W-based oxide, the conversion rate of NO _X to N ₂ is increased.

(4) Method of supporting catalytically active species Silver, W, V, Mo and M are added to an inorganic oxide such as γ-alumina.
As a method for supporting the n component, a known impregnation method, precipitation method, or the like can be used. At that time, when the impregnation method is used, silver is an aqueous solution of nitrates, chlorides, sulfates, carbonates or the like or an ammoniacal aqueous solution, W and V components are ammonium salts,
An aqueous solution such as oxalate is used. As a precipitation method, silver can be precipitated and supported as silver halide on an inorganic oxide carrier by the reaction of silver nitrate and ammonium ammonium. 50 to 15 by immersing the porous inorganic oxide in the mixed solution of the above-mentioned aqueous solutions or in each of the aqueous solutions in order.
After drying at 0 ° C., particularly about 70 ° C., it is preferable to raise the temperature step by step at 100 to 600 ° C. and to bake. The firing is preferably performed in an oxygen atmosphere, a nitrogen atmosphere or a hydrogen gas flow. When it is carried out under a nitrogen atmosphere or under a flow of hydrogen gas, it is preferable to finally carry out an oxidation treatment at 300 to 650 ° C.

In the first preferred embodiment of the purification material, the thickness of the first catalyst provided on the purification material substrate is generally limited due to the difference in thermal expansion characteristics between the substrate material and this catalyst. In many cases. The thickness of the catalyst provided on the purifying material substrate is preferably 300 μm or less. With such a thickness, it is possible to prevent the purification material from being damaged by thermal shock during use. The method of forming the catalyst on the surface of the purification material substrate is performed by a known wash coating method, powder method, or the like.

The amount of the first 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 catalyst is less than 20 g / liter, good NOx cannot be removed. On the other hand, the amount of catalyst is 300
If it exceeds g / liter, the removal property does not improve so much,
Pressure loss increases. More preferably, the first catalyst provided on the surface of the purification material substrate is 50 to 250 of the purification material substrate.
g / liter.

[3] Second Catalyst The second catalyst is at least selected from the group consisting of (c) Pt, Pd, Ru, Rh, Ir and Au which are catalytically active species in the porous inorganic oxide. It carries one kind of metal element.

(1) Porous Inorganic Oxide Examples of the porous inorganic oxide include heat-resistant ceramics having a large surface area such as titania, alumina, zirconia and silica, or composite oxides thereof. To be Preferably, titania or a composite oxide containing titania is used.

(2) Pt, Pd, Ru, Rh, Ir and Au components Of Pt, Pd, Ru, Rh, Ir and Au, Pt, Pd, Ru, Rh and
It is preferable to use at least one of Au, especially Pt and Pd.
At least one of Au and Au is preferable. Pt, Pd, Ru, Rh,
The loading of at least one of Ir and Au is 10 for the inorganic oxide.
As 0% by weight, 5% by weight or less (elemental conversion value).
If the supported amount exceeds 5% by weight of the inorganic oxide, the removal effect by the silver component is greatly reduced. The lower limit of the supported amount is preferably 0.01% by weight. A more preferable loading amount is 0.01 to 4% by weight. Further, a known oxidation catalyst, an alkaline earth metal element, a rare earth element, or the like can be added to improve the durability of the platinum component.

(3) Supporting method for catalytically active species As a method for supporting at least one of Pt, Pd, Ru, Rh, Ir and Au in the second catalyst, known impregnation method, precipitation method, powder method and the like can be used. Can be used. At that time, the porous inorganic oxide is immersed in a mixed aqueous solution of ammonium salt, oxalate, sulfate, carbonate, nitrate or hydrochloride of each element, or
Porous inorganic oxides are sequentially dipped in the respective elemental compound aqueous solutions and dried at 50 to 150 ° C., particularly 70 ° C., and then 1
It is performed by gradually raising the temperature at 00 to 600 ° C. and firing. This firing is performed in air, under an oxygen atmosphere, under a nitrogen atmosphere, or under a hydrogen gas flow, but when firing under a nitrogen atmosphere or a hydrogen gas flow, the final temperature is 300 to 650 ° C.
It is effective to carry out oxidation treatment at.

In the first preferred embodiment of the purification material, the thickness of the second catalyst provided on the purification material substrate is 300 μm.
It is preferably m or less. Further, the amount of the second catalyst provided on the surface of the purification material substrate is 20 to 300 g / of the purification material substrate.
It is preferably liter.

If the purifying material having the above structure is used,
In a wide temperature range of up to 650 ° C., good nitrogen oxides can be removed even with exhaust gas containing about 10% of water.

[4] Exhaust Gas Purification Method Next, the method of the present invention will be described. First, an exhaust gas purification material having a first catalyst and a second catalyst is installed in the middle of an exhaust gas conduit. Preferably, the first catalyst faces the exhaust gas inlet and the second catalyst faces the exhaust gas outlet.

Although the exhaust gas contains ethylene, propylene and the like as residual hydrocarbons to some extent, it is generally not sufficient to reduce NOx in the exhaust gas, so hydrocarbons and carbon atoms of 2 or more are externally supplied. A reducing agent composed of any of the oxygen-containing organic compounds or a mixed fuel containing them is introduced into the exhaust gas. The introduction position of the reducing agent is upstream of the position where the purification material is installed.

As the hydrocarbon introduced from the outside, gaseous or liquid alkane, alkene and / or alkyne in a standard state can be used. As a gaseous hydrocarbon in a standard state, an alkane alkene having 2 or more carbon atoms,
Alternatively, alkyne is preferred. As the liquid hydrocarbon in the standard state, specifically, heptane, cetane, kerosene, light oil,
Hydrocarbons such as gasoline and heavy oil are mentioned. Among them, hydrocarbons having a boiling point of 50 to 350 ° C. are particularly preferable.

As the oxygen-containing organic compound introduced from the outside, alcohols having 2 or more carbon atoms such as ethanol and isopropyl alcohol, or fuel containing them can be used. The amount of the reducing agent introduced from the outside is the weight ratio (weight of the reducing agent to be added / nitrogen oxide (N
The weight of O) is preferably 0.1 to 5. If this weight ratio is less than 0.1, the nitrogen oxide removal rate does not increase. On the other hand, if the weight ratio exceeds 5,
It leads to deterioration of fuel efficiency.

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

In the present invention, the total apparent space velocity of the purifying material is set to 500,000 h ^-1 or less in order to efficiently proceed the reduction and removal of nitrogen oxides by the oxygen-containing organic compound, hydrocarbons and the like. When the space velocity exceeds 500,000 h ^-1 , the reduction reaction of nitrogen oxides does not sufficiently occur and the removal rate of nitrogen oxides decreases. The preferable space velocity is 300,000 h ^-1 or less.

Further, in the present invention, the temperature of the exhaust gas at the purification material installation site, which is the site where the hydrocarbon and / or the oxygen-containing organic compound reacts with the nitrogen oxide, is 150 to 650 ° C.
Keep on. If the temperature of the exhaust gas is less than 150 ° C., the reaction between the reducing agent and the nitrogen oxide does not proceed, and the nitrogen oxide cannot be removed satisfactorily. On the other hand, if the temperature is higher than 650 ° C., combustion of hydrocarbons and / or oxygen-containing organic compounds themselves takes precedence, and the reduction removal rate of nitrogen oxides decreases. A preferable exhaust gas temperature is 250 to 600 ° C.

[0040]

The present invention will be described in more detail by the following specific examples. Example 1 Commercially available pelletized γ-alumina (diameter 1.5 mm, length about 2
Silver (4% by weight (elemental conversion value)) was supported on 10 g of ˜3 mm and specific surface area of 260 m ² / g) by using an aqueous solution of silver nitrate, dried and calcined stepwise in air to 600 ° C.
0.06% by weight of molybdenum of alumina (elemental conversion value) was obtained by using an aqueous solution prepared by further heating and dissolving a mixture of ammonium molybdate, oxalic acid and water in this alumina.
It was supported, dried and baked under the same conditions as above to prepare a silver-based catalyst (first catalyst).

Then, 2 g of the same pellet γ-alumina was mixed with 0.2 g of γ-alumina by using an aqueous solution of chloroplatinic acid.
After loading by weight, in air, 80 ℃, 100 ℃, 12
It was dried at 0 ° C. for 2 hours each. Then, under a nitrogen stream containing 20% oxygen, the temperature was raised from 120 ° C. to 500 ° C. over 5 hours and calcined at 500 ° C. for 4 hours to prepare a platinum-based catalyst (second catalyst).

About 3 g of silver-based catalyst and about 0.6 g of platinum-based catalyst
The purifying material consisting of was set in the reaction tube so that the silver catalyst was located on the inflow side of the exhaust gas and the platinum catalyst was located on the outflow side. Next, a gas (nitric oxide, carbon dioxide, oxygen, ethanol, nitrogen, and water) having the composition shown in Table 1 was flowed at a flow rate of 4.4 liters per minute (standard state) (total apparent space velocity of about 30). 1,000 h ⁻¹ ), the exhaust gas temperature in the reaction tube was changed from 250 ° C. to 550 ° C. at every 50 ° C., and ethanol and nitrogen oxide were reacted at each temperature.

Table 1 Component Concentration Nitric oxide 800 ppm (dry basis) Carbon dioxide 10% by volume (dry basis) Oxygen 10% by volume (dry basis) Ethanol 3 times the weight of nitric oxide (dry basis) Nitrogen balance moisture 10 Volume% (relative to the total volume of the above ingredients)

Nitrogen oxide (NO +) of the gas after passing through the reaction tube
The concentration of NO ₂ ) was measured by a chemiluminescence type nitrogen oxide analyzer, and the removal rate of nitrogen oxides [(initial concentration of nitric oxide-concentration of nitrogen oxides after passage) / initial amount of nitric oxide] Density × 100%] was determined. The results are shown in Table 2.

Example 2 In the same manner as in Example 1, 4% by weight of silver was supported on powdery γ-alumina (specific surface area: 200 m ² / g) using an aqueous solution of silver nitrate, and molybdenum was added using an aqueous solution of ammonium molybdate. 0.06% by weight of alumina (element conversion value)
About 1.0 g of the supported catalyst was put into a commercially available cordierite honeycomb-shaped compact (diameter 30 mm, length about 10 mm, 400
Cell / inch ² ) was coated, dried and then calcined stepwise to 600 ° C. to prepare a silver-based purification material (purification material coated with the first catalyst).

Next, 0.2% by weight of platinum (based on γ-alumina) was loaded on the same γ-alumina powder using an aqueous solution of chloroplatinic acid, and then slurried to form a honeycomb similar to the above silver-based catalyst. 0.25 g (dry basis) of the slurry was coated on the green compact (diameter: 30 mm, length: about 2.5 mm), dried and calcined under the same conditions as the platinum catalyst of Example 1, and the platinum-based purification material (first A purification material coated with the second catalyst was prepared.

On the inflow side of the exhaust gas in the reaction tube, a silver-based purifying material,
Platinum-based purification materials were set on the outflow side, and the gases having the compositions shown in Table 1 were evaluated in the same manner as in Example 1 (total apparent space velocity of about 30,000 h ⁻¹ ). The experimental results are shown in Table 2.

Comparative Example 1 In the same manner as in Example 1, only 3.6 g of a catalyst supporting 4% by weight of silver (converted to silver element) was set in the reaction tube, and the gas having the composition shown in Table 1 was added at 4 minutes per minute. At a flow rate of 4 liters (standard state) (total apparent space velocity of about 30,000
h ⁻¹ ), the exhaust gas temperature in the reaction tube was kept in the range of 250 ° C. to 550 ° C., and ethanol was reacted with nitrogen oxides.
The experimental results are also shown in Table 2.

Table 2 Nitrogen Oxide (NOx) Removal Rate Reaction Temperature Nitrogen Oxide Removal Rate (%) (° C.) Example 1 Example 2 Comparative Example 1 250 80.0 88.0 30.0 300 89. 8 92.5 50.2 350 80.2 90.0 65.8 400 65.0 76.0 75.1 450 48.0 53.5 70.5 500 40.3 43.4 60.1 550 38. 4 43.0 50.4

As can be seen from the above, as compared with Comparative Example 1 using only the silver catalyst, Examples 1 and 2 showed good removal of nitrogen oxides in a wide exhaust gas temperature range, particularly in a low exhaust gas temperature range. .

Example 3 Using the purification material of Example 1, simulated gas (nitric oxide, carbon monoxide, oxygen, propylene, nitrogen and water) shown in Table 3 in which propylene was added to the composition corresponding to the exhaust gas was supplied every minute. Flowing at a flow rate of 4.4 liters (standard state) (total apparent space velocity is 30,000 h ⁻¹ ) and changing the exhaust gas temperature in the reaction tube from 300 ° C. to 600 ° C. at every 50 ° C., respectively. The propylene and nitrogen oxide were reacted at the temperature of.

Table 3 Component Concentrations Nitric oxide 800 ppm (dry basis) Carbon monoxide 100 ppm (dry basis) Oxygen 10% by volume (dry basis) Propylene 1714 ppm (dry basis, 3 times the weight of nitric oxide) Nitrogen Remaining water content 10% by volume (based on the total volume of the above components)

Nitrogen oxides (NO +) of the gas after passing through the reaction tube
The concentration of NO ₂ ) was measured by a chemiluminescence type nitrogen oxide analyzer to determine the nitrogen oxide removal rate. Further, the concentrations of carbon monoxide and hydrocarbon were measured by a CO meter and an HC meter, respectively, and the removal rates of carbon monoxide and hydrocarbon were obtained. The results are shown in Table 4.

Example 4 Using the purifying material of Example 2, a simulated gas (nitric oxide, carbon monoxide, oxygen, propylene, nitrogen and water) shown in Table 3 in which propylene was added to the composition corresponding to the exhaust gas was supplied every minute. Flowing at a flow rate of 4.4 liters (standard state) (total apparent space velocity is 30,000 h ⁻¹ ) and evaluated under the same conditions as in Example 3. The experimental results are also shown in Table 4.

Comparative Example 2 In the same manner as in Example 1, only 3.6 g of a silver-based catalyst carrying 4% by weight of silver (converted to silver element) was set in the reaction tube, and the gas having the composition shown in Table 3 was used for each. Min 4.4 liters (standard condition)
At a flow rate of (total apparent space velocity of about 30,000
h ^-1 ) and the same conditions as in Example 3 were evaluated. The experimental results are also shown in Table 4.

Table 4 Nitrogen oxide (NOx), carbon monoxide (CO) and hydrocarbon (HC) removal rates Reaction temperature Removal components Removal rate (%) (° C) Example 3 Example 4 Comparative Example 2 300 NOx 0 5 0 CO 90.5 90.8 40 HC 66 66 66 30 350 NOx 10 15 0 CO 95.7 95.5 60 HC 71 76 35 400 NOx 30 35 20 CO 100 100 100 70 HC 96 95 40 40 450 NOx 65 70 60 CO 100 100 70 HC 98 98 65 65 500 NOx 55 60 55 CO 100 100 80 HC 100 100 100 550 NOx 35 35 25 CO 100 100 100 90 HC 100 100 85 600 NOx 20 25 10 CO 100 100 98 98 HC 100 100

As can be seen from the above, in Examples 3 and 4, good removal of nitrogen oxides and hydrocarbons was observed in a wide exhaust gas temperature range. The carbon monoxide removal rate is excellent at 90% or more. On the other hand, in Comparative Example 2 using only the silver catalyst, the temperature range of nitrogen oxide removal was narrow and the removal rate of carbon monoxide and hydrocarbons was low.

Example 5 Commercially available pelletized γ-alumina (diameter 1.5 mm, length about 2)
~ 3 mm, specific surface area 260 m ² / g) 10 g was immersed in an aqueous solution of silver nitrate, and then an aqueous solution of ammonium chloride was added,
Silver nitrate on γ-alumina was precipitated as silver chloride to obtain alumina pellets carrying 4% by weight (elemental conversion value) of silver in the form of silver chloride. Then, the alumina pellets were dried and then fired stepwise in air to 600 ° C. An aqueous solution prepared by heating and dissolving a mixture of ammonium tungstate, oxalic acid, and water on this alumina was used to carry 6 wt% of alumina (metal element conversion value) of tungsten oxide, and the tungsten oxide was dried under the same conditions as above. Calcination was performed to prepare a silver chloride catalyst (first catalyst).

Next, 2 g of the same pellet γ-alumina was mixed with 0.2 g of γ-alumina by using an aqueous solution of chloroplatinic acid.
After loading by weight, in air, 80 ℃, 100 ℃, 12
It was dried at 0 ° C. for 2 hours each. Then, under a nitrogen stream containing 20% oxygen, the temperature was raised from 120 ° C. to 500 ° C. over 5 hours and calcined at 500 ° C. for 4 hours to prepare a platinum-based catalyst (second catalyst).

About 3 g of silver chloride-based catalyst and about 0.
A purification material consisting of 6 g was set in the reaction tube so that the silver chloride catalyst was located on the inflow side of the exhaust gas and the platinum catalyst was located on the outflow side. Next, a gas (nitric oxide, carbon dioxide, oxygen, ethanol, nitrogen, and water) having the composition shown in Table 1 was flowed at a flow rate of 4.4 liters per minute (standard state) (total apparent space velocity of about 30). 000h ^-1 ), the temperature of the exhaust gas in the reaction tube from 250 ° C to 550 ° C at 50 ° C
Each time, ethanol was reacted with nitrogen oxide at each temperature.

Nitrogen oxides (NO +) of the gas after passing through the reaction tube
The concentration of NO ₂ ) was measured by a chemiluminescence type nitrogen oxide analyzer, and the removal rate of nitrogen oxides [(initial concentration of nitric oxide-concentration of nitrogen oxides after passage) / initial amount of nitric oxide] Density × 100%] was determined. The results are shown in Table 5.

Example 6 In the same manner as in Example 5, 4% by weight of silver chloride was supported on powdery γ-alumina (specific surface area 200 m ² / g) and tungsten oxide was added at 6% by weight of alumina (metal). About 1.0 g of the supported catalyst was added to a commercially available cordierite honeycomb-shaped compact (diameter 30 mm, length about 10 mm, 4
00 cells / inch ² ) and dried and then fired stepwise to 600 ° C. to prepare a silver chloride purification material (purification material coated with the first catalyst).

Next, 0.2% by weight (on the basis of γ-alumina) of platinum was supported on the same γ-alumina powder using an aqueous solution of chloroplatinic acid, and then slurried to obtain the same silver chloride catalyst as above. Honeycomb shaped body (diameter 30 mm, length about 2.5 mm
) To 0.25 g (dry basis) of the slurry,
Platinum-based purification material (purification material coated with the second catalyst) was prepared by performing drying and firing under the same conditions as in the platinum-based catalyst of Example 5.

A silver chloride purification material was set on the inflow side of the exhaust gas and a platinum purification material was set on the outflow side of the reaction tube, and the gas having the composition shown in Table 1 was evaluated in the same manner as in Example 5 (total apparent space). Speed about 30,000 h ^-1 ). The experimental results are shown in Table 5.

Comparative Example 3 In the same manner as in Example 5, only 3.6 g of a catalyst supporting 4% by weight of silver chloride (converted to silver element) was set in the reaction tube,
A gas having the composition shown in Table 1 was flowed at a flow rate of 4.4 liters per minute (standard state) (total apparent space velocity of about 3,0
00h ^-1 ), the exhaust gas temperature in the reaction tube is set to 250 ° C to 550
The temperature was kept in the range of ° C, and ethanol was reacted with nitrogen oxide. The experimental results are also shown in Table 5.

Table 5 Nitrogen Oxide (NOx) Removal Rate Reaction Temperature Nitrogen Oxide Removal Rate (%) (° C.) Example 5 Example 6 Comparative Example 3 250 78.2 86.5 28.3 300 86. 5 92.0 48.2 350 83.0 90.2 63.2 400 67.3 78.2 76.5 450 52.3 58.6 72.2 500 44.8 46.2 62.2 550 42. 2 45.6 52.3

As can be seen from the above, as compared with Comparative Example 3 using only the silver catalyst, Examples 5 and 6 showed good removal of nitrogen oxides in a wide exhaust gas temperature range, particularly in a low exhaust gas temperature range. .

[0068]

As described above in detail, by using the exhaust gas purifying material of the present invention, nitrogen oxides in exhaust gas containing excess oxygen can be efficiently removed in a wide temperature range. INDUSTRIAL APPLICABILITY The exhaust gas purifying material and the purifying method of the present invention can be widely used for purifying exhaust gas of various combustors, automobiles and the like.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/652 27/132 ZAB A F01N 3/08 ZAB B 3/28 301 G B01J 23/64 103 A

Claims (7)

[Claims] 1. Nitrogen oxides are removed from a combustion exhaust gas containing nitrogen oxides and oxygen in a larger amount than the theoretical reaction amount for coexisting unburned components, and residual and unreacted carbon monoxide and hydrocarbons are also removed by oxidation. In the exhaust gas purification material, (1) 0.2 to 15% by weight (silver element conversion value) of (a) silver and / or a silver compound or a mixture thereof in a porous inorganic oxide, and (b) W, A first catalyst carrying 10% by weight or less of an oxide of at least one element selected from the group consisting of V, Mn and Mo (metal element conversion value);
(2) A porous inorganic oxide carrying (c) at least one element selected from the group consisting of Pt, Pd, Ru, Rh, Ir and Au in an amount of 5% by weight or less (metal element conversion value). An exhaust gas purification material comprising a second catalyst. 2. 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 purification material. 3. The exhaust gas purifying material according to claim 1 or 2, wherein the purifying material has the first catalyst on an exhaust gas inflow side and the second catalyst on an exhaust gas outflow side. Exhaust gas purification material. 4. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxide is alumina or an alumina-based composite oxide in the first catalyst, and titania in the second catalyst. An exhaust gas purification material comprising alumina, zirconia, silica and a composite oxide thereof. 5. The exhaust gas purifying material according to claim 1, wherein the purifying material is obtained by coating the surface of a ceramic or metal base with the first and second catalysts. Characteristic exhaust gas purification material. 6. The exhaust gas purifying material according to claim 1, wherein the porous inorganic oxides of the first and second catalysts are in the form of pellets or granules, respectively. Purifying material. 7. Nitrogen oxides are removed from a combustion exhaust gas containing nitrogen oxides and oxygen in a larger amount than the theoretical reaction amount for coexisting unburned components, and residual and unreacted carbon monoxide and hydrocarbons are also removed by oxidation. In the exhaust gas purification method, the exhaust gas purification material according to any one of claims 1 to 6 is used, the exhaust gas purification material is installed in the middle of an exhaust gas conduit, and hydrocarbons and carbon atoms of 2 or more are provided upstream of the purification material. 9. An exhaust gas purification method, characterized in that the exhaust gas to which any one or more of the oxygen-containing organic compounds or the fuel containing them is added is brought into contact with the purification material at 150 to 650 ° C. to remove the nitrogen oxides.