JPH07232036A - Material and method for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To provide a material for purifying exhaust gas which can remove nitrogen oxides efficiently by reduction from combustion exhaust containing nitrogen oxides and oxygen not less than theoretical amount of the reaction with unburnt components such as nitrogen oxides and carbon monoxide and also can remove carbon monoxide and hydrocarbons by oxidation. CONSTITUTION:An exhaust gas purifying material is used which is composed of the first catalyst comprising a porous inorganic oxide carrier loaded with silver or silver oxide and the second catalyst comprising a porous inorganic oxide carrier loaded with at least one kind of oxide of an element selected from the group consisting of (a) W, V, Mn, Mo, Nb, and Ta and at least one kind of element selected from the group consisting of (b) Pt, Pd, Ru, Rh, and Au. Hydrocarbons and/or organic compounds containing oxygen are added externally into the exhaust gas as a reductant to remove nitrogen oxides by reduction.

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. under high space velocity 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-mentioned problems, the present inventors have found that an organic compound such as ethanol is added on a catalyst prepared by supporting a silver component on a porous inorganic oxide.
It was found that it reacts with an exhaust gas containing oxygen and nitrogen oxides to reduce the nitrogen oxides to nitrogen gas, and also produces ammonia as a by-product. With the above silver-based catalyst,
W that can reduce nitrogen oxides using ammonia as a reducing agent,
An exhaust gas purifying material formed by combining a V-based catalyst and a platinum-based catalyst is used, and a hydrocarbon and an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing them is added to the exhaust gas at a specific temperature. Further, it was discovered that nitrogen oxides can be effectively removed in a wide temperature range even in an exhaust gas containing 10% of water by contacting the exhaust gas with the above-mentioned purification material at a space velocity, and the present invention has been completed. .

That is, the nitrogen oxides are reduced and removed from the combustion exhaust gas containing the nitrogen oxides and oxygen in a larger amount than the theoretical reaction amount with respect to the coexisting unburned components, and residual and unreacted carbon monoxide and hydrocarbons are also oxidized. The exhaust gas purifying material of the present invention to be removed is a first catalyst comprising a porous inorganic oxide carrying 0.2 to 15% by weight (elemental conversion value) of silver or silver oxide of the inorganic oxide. A porous inorganic oxide (a) containing at least one element selected from the group consisting of W, V, Mn, Mo, Nb and Ta in an amount of 10% by weight or less (metal element conversion value) of the inorganic oxide. Oxide, and (b) 5 wt% or less (elemental conversion value) of Pt, Pd of the inorganic oxide,
At least 1 selected from the group consisting of Ru, Rh, Ir and Au
It is characterized by comprising a second catalyst carrying a seed element.

Further, the nitrogen oxides are reduced and 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 oxidized. In the exhaust gas purification method of the present invention for removing, the exhaust gas purification material is installed in the middle of an exhaust gas conduit, and hydrocarbon and / or an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing the same is provided upstream of the purification material. The exhaust gas added with is brought into contact with the purification material at 150 to 650 ° C., and thereby the nitrogen oxides are removed by the reaction with the oxygen-containing organic compound in the exhaust gas.

The present invention will be described in detail below. In the present invention, the porous inorganic oxide has 0.2 to 1 of the inorganic oxide.
5% by weight (elemental conversion value) of a first catalyst supporting silver or silver oxide, and porous inorganic oxide (a) 10% by weight or less of the inorganic oxide (metal element conversion value) W, V,
An oxide of at least one element selected from the group consisting of Mn, Mo, Nb and Ta, and (b) 5 wt% or less (elemental conversion value) of Pt, Pd, Ru, Rh and Ir of the inorganic oxide. as well as
An exhaust gas purification material comprising a second catalyst carrying at least one element selected from the group consisting of Au is installed in the exhaust gas conduit, and hydrocarbons and carbon are provided upstream of the installation position of the purification material. Exhaust gas to which any one of several oxygen-containing organic compounds or a fuel containing it 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 a first preferred form of the exhaust gas purifying material of the present invention, the purifying material base 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 composite 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 is
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.

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

The following two catalysts are formed on the purification material of the present invention. (1) First catalyst The first catalyst comprises silver or silver oxide supported on a porous inorganic oxide. As the porous inorganic oxide, porous alumina, silica, titania, zirconia and their complex oxides can be used, but preferably γ-
Alumina alone or an alumina-based composite oxide containing at least one selected from the group consisting of silica, titania and zirconia is used. When the alumina-based composite oxide is used as the porous inorganic oxide, the content of alumina is preferably 50% by weight or more. If the content of alumina is less than 50% by weight, the initial removal characteristics of the purification material will be significantly deteriorated. By using γ-alumina or an alumina-based composite oxide, the reaction between the added oxygen-containing organic compound or the fuel containing the same and the nitrogen oxide in the exhaust gas occurs efficiently. Especially by using an alumina-based composite oxide,
Even in the presence of SO ₂ gas, the durability and heat resistance of the purification material are improved, and the oxidation of SO ₂ can be suppressed.

The specific surface area of the porous inorganic oxide such as alumina used in the first catalyst is preferably 10 m ² / g or more. When the specific surface area is less than 10 m ² / g, the contact area between the exhaust gas and the inorganic oxide (and the silver component supported on it) becomes small, and the nitrogen oxide cannot be removed well.
More preferable specific surface area of the porous inorganic oxide is 30 m ² /
g or more.

The amount of the silver component supported as an active species on the above-mentioned inorganic oxide such as γ-alumina varies somewhat depending on the type of oxygen-containing organic compound and fuel added to the exhaust gas, the contact time with the exhaust gas, and the like. Is 0.2 to 15% by weight (silver element conversion value) 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, if silver is loaded in an amount of more than 15% by weight, the oxygen-containing organic compound itself is easily burned, and the nitrogen oxide removal rate is rather lowered. The preferred amount of silver component supported is 0.
It is 5 to 12% by weight.

As a method for supporting silver on an inorganic oxide such as γ-alumina, known impregnation methods, precipitation methods and the like can be used. At that time, it is preferable to immerse the porous inorganic oxide in an aqueous solution of a nitrate or the like, dry it at 50 to 150 ° C., particularly about 70 ° C., and then gradually raise the temperature at 100 to 600 ° C. 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 coat method, powder method or the like.

Further, the amount of the first catalyst provided on the surface of the purification material substrate is preferably 20 to 300 g / liter of the purification material substrate. 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.

(2) Second catalyst The second catalyst is at least one selected from the group consisting of (a) W, V, Mn, Mo, Nb and Ta which are catalytically active species in the porous inorganic oxide. Elemental oxides of (b) Pt,
It carries at least one metal element selected from the group consisting of Pd, Ru, Rh, Ir and Au. Examples of the porous inorganic oxides include porous and large surface area heat-resistant ceramics such as titania, alumina, zirconia and silica, or composite oxides thereof. Preferably, titania or a composite oxide containing titania is used.

Of W, V, Mo, Mn, Nb and Ta, W, V, Mo and / or Mn are preferably used, and W and / or V are more preferably used. The amount of the W-based oxide supported on the inorganic oxide by the second catalyst is 10 based on the above-mentioned porous inorganic oxide (100% by weight).
Weight% or less (metal element conversion value), preferably 0.0
1 to 10% by weight, more preferably 0.2 to 8% by weight, and further preferably 0.5 to 5% by weight (metal element conversion value). The amount of the W-based oxide carried on the inorganic oxide is
Even if it exceeds 10% by weight, the effect remains unchanged. By using a W-based oxide, it becomes possible to remove nitrogen oxides using ammonia as a reducing agent. Further, in the present invention, if a catalyst that promotes the reduction reaction of nitrogen oxides with ammonia,
It is possible to use not only W-based oxides.

Of Pt, Pd, Ru, Rh, Ir and Au,
It is preferable to use at least one of Pt, Pd, Ru, Rh, and Au, and particularly preferably at least one of Pt, Pd, and Au. The supported amount of at least one of Pt, Pd, Ru, Rh, Ir and Au is 5% by weight or less (elemental conversion value) with 100% by weight of the inorganic oxide. 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 0.1 to 4% by weight.

The W-based oxide and Pt, Pd, and
As a method of supporting one or more of Ru, Rh, Ir and Au,
A known impregnation method, precipitation method, sol-gel method or the like can be used. At that time, the porous inorganic oxide is immersed in a mixed aqueous solution of ammonium salts, oxalates, sulfates, carbonates, nitrates or hydrochlorides of the respective elements, or the porous inorganic oxide is added to the aqueous solution of each element compound. Dip in order, 50 ~
After drying at 150 ℃, especially 70 ℃, 100-600 ℃
It is carried out by gradually heating and firing at. This firing is performed in air, under an oxygen atmosphere, under a nitrogen atmosphere, or under a flow of hydrogen gas, but when firing under a nitrogen atmosphere or under a flow of hydrogen gas, it is effective to finally perform an oxidation treatment at 300 to 650 ° C. .

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. Further, when the purifying material substrate is made of a porous inorganic oxide such as titania, a predetermined amount of W and / or V oxide can be supported on them to be used as a purifying agent. In addition, a porous inorganic oxide such as titania carrying a predetermined amount of W and / or V oxide may be molded into a molded body such as a honeycomb and used.

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: 2. Is preferred. The ratio is less than 1: 2 (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 ammonia produced on the first catalyst does not react and is discharged as it is, and the ammonia concentration in the discharged gas increases. A more preferable weight ratio of the first catalyst to the second catalyst is 9: 1 to 1: 4.

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. Also, ammonia reacts with nitrogen dioxide more preferentially, thus reducing the proportion of harmful nitrogen dioxide in the nitrogen oxides.

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 / or carbon atoms of 2 are externally added. The oxygen-containing organic compound or a reducing agent composed of 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. The gaseous hydrocarbon in the standard state is preferably an alkane, alkene or alkyne having 2 or more carbon atoms. 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 preferably such that the weight ratio (weight of reducing agent added / weight of nitrogen oxide in exhaust gas) is 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 (NO) in exhaust gas) is 0.1 to 5 as in the above.

In the present invention, the overall apparent space velocity of the purifying material is 5 in order to efficiently proceed the reduction and removal of nitrogen oxides by the oxygen-containing organic compound, hydrocarbon or ammonia.
It shall be 00,000h ^-1 or less. 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. Preferred space velocity is 450,000
h ^-1 or less, more preferably space velocity and 300,000H ^-1 or less. Among them, a space velocity in the first catalyst (silver-based catalyst) is 200,000 ^-1 or less, preferably 150,000H ^-1 or less. When the space velocity of the first catalyst exceeds 200,000 h ^-1 , the reduction reaction of nitrogen oxides does not sufficiently occur, and the removal rate of nitrogen oxides decreases. The space velocity of the second catalyst (platinum, V-based catalyst) is 250,000 h ^-1 or less, preferably 200,000 h ^-1 or less. The space velocity of the second catalyst is 2
If it exceeds 50,000 h ^-1 , the oxidation-removing properties of hydrocarbons, carbon monoxide, etc. will deteriorate. When SO ₂ is present in the exhaust gas, the space velocity in the second catalyst (platinum, V-based catalyst) is 10,000 to 250,000 h ⁻¹ . When the space velocity of the second catalyst is less than 10,000 h ^-1 , SO ₂ is easily oxidized, which is not preferable.

Further, in the present invention, the temperature of the exhaust gas at the site where the purifying material is installed, which is the site where the oxygen-containing organic compound reacts with the nitrogen oxide, is maintained at 150 to 650 ° C. 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 exceeds 650 ° C., combustion of the oxygen-containing organic compound itself has priority, and the reduction removal rate of nitrogen oxides decreases. A preferable exhaust gas temperature is 250 to 600 ° C.

[0037]

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
˜3 mm, specific surface area 260 m ² / g) 10 g, silver 4% by weight of γ-alumina (elemental conversion value) was carried by using an aqueous solution of silver nitrate, dried and then calcined stepwise to 600 ° C. in air to obtain silver. A system catalyst (first catalyst) was prepared.

Next, 2 g of similar pelletized γ-alumina
Platinum was added to γ-alumina by using an aqueous solution of chloroplatinic acid.
After supporting 2% by weight, 1.8 g of ammonium tungstate parapentahydrate and 1.0 g of oxalic acid were added with 6.2 ml of water, and the mixture was heated in a water bath and added to the dissolved aqueous solution.
Soaked for a minute. Then, the alumina pellets were separated from the solution and dried in air at 80 ° C., 100 ° C. and 120 ° C. for 2 hours each. Then, under a nitrogen stream containing 20% oxygen, 1
Temperature rise from 20 ℃ to 500 ℃ in 5 hours, 500 ℃
And was burned for 4 hours to prepare a W-based catalyst (second catalyst) supporting 1% by weight of tungsten on the alumina pellets (metal element conversion value).

About 3 g of silver-based catalyst and about 0.
The purification material consisting of 6g, the silver catalyst on the inflow side of the exhaust gas,
The Pt and W catalysts were set in the reaction tube so that they were 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 300 ° C to 550 ° C
Each time, ethanol was reacted with nitrogen oxide at each temperature.

Table 1 Component Concentration Nitric oxide 1000 ppm (dry basis) Carbon dioxide 10% by volume (dry basis) Oxygen 10% by volume (dry basis) Ethanol 1250 ppm (dry basis) Nitrogen Residual water 10% by volume (of the above ingredients) (For total volume)

After passing through the reaction tube, the nitrogen oxides (NO +
The concentration of NO ₂ ) was measured by a chemiluminescence type nitrogen oxide analyzer to determine the nitrogen oxide removal rate. The results are shown in Table 2.

Example 2 In the same manner as in Example 1, about 4% by weight of silver (based on γ-alumina) was used as a catalyst to support powdery γ-alumina (specific surface area 200 m ² / g) using an aqueous silver nitrate solution. 1.0 g
Commercially available cordierite honeycomb shaped body (diameter 30 mm,
A length of about 10 mm, 400 cells / 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 ammonium vanadate and oxalic acid were added to 30 ml of water, It was heated and dissolved in a water bath, and then poured into an aqueous solution which was allowed to cool and immersed for 30 minutes to form a slurry. Honeycomb shaped body similar to the above silver catalyst (diameter 30m
m, length about 2.5 mm) was coated with 0.25 g (dry basis) of the slurry. The content of vanadium with respect to the alumina powder was 1% by weight (metal element conversion value). Example 1
The tungsten-Pt / alumina catalyst of No. 2 was dried and calcined under the same conditions to prepare a Pt, V-based purification material (purification material coated with the second catalyst).

On the inflow side of the exhaust gas in the reaction tube, a silver-based purification material,
Pt and V-based purifying 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 Only 3.6 g of the silver-based catalyst prepared by the same method as in Example 1 was set in the reaction tube, and the gas having the composition shown in Table 1 was added per minute.
Flowing at a flow rate of 4 liters (standard state) (total apparent space velocity of about 30,000 h ⁻¹ ), keeping the exhaust gas temperature in the reaction tube in the range of 300 to 550 ° C. to react ethanol and nitrogen oxides. . The experimental results are also shown in Table 2.

Table 2 Removal rate of nitrogen oxides (NOx) Reaction temperature Removal rate of nitrogen oxides (%) (° C.) Example 1 Example 2 Comparative example 1 300 60.8 68.5 50.2 350 75. 2 80.7 65.8 400 85.7 90.0 75.1 450 80.0 90.5 70.5 500 65.3 70.4 60.1 550 60.4 64.0 50.4

As can be seen from the above, in Examples 1 and 2, good removal of nitrogen oxides was observed in a wide exhaust gas temperature range. On the other hand, in Comparative Example 1 using only the silver catalyst, the nitrogen oxide removal rate was lower than in Examples 1 and 2.

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 exhaust gas equivalent composition was prepared 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 mass 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 purification 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 exhaust gas equivalent composition 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 Only 3.6 g of a silver-based catalyst prepared in the same manner as in Example 1 was set in a reaction tube, and a gas having the composition shown in Table 3 was supplied at a rate of 4.
It was flowed at a flow rate of 4 liters (standard state) (total apparent space velocity of about 30,000 h ⁻¹ ) and evaluated under the same conditions as in Example 3. 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 5 10 0 CO 90.5 90.8 40 HC 66 66 66 30 350 NOx 20 25 0 CO 95.7 95.5 60 HC 71 76 35 400 NOx 45 50 20 CO 100 100 70 70 HC 96 95 40 40 450 NOx 65 70 60 CO 100 100 70 HC 98 98 65 65 500 NOx 60 65 55 CO 100 100 80 80 HC 100 100 70 550 NOx 35 50 25 CO 100 100 90 90 HC 100 100 85 600 NOx 20 25 10 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 To 10 g of commercially available powdery silica-alumina (SiO ₂ content 5% by weight, specific surface area 350 m ² / g), an aqueous silver nitrate solution was used to add silver to 4% by weight of silica-alumina (elemental conversion value). ), Dried and calcined stepwise in air to 600 ° C., and pelletized into pellets having a diameter of 1.5 mm and a length of 2 to 3 mm to prepare a silver-based catalyst (first catalyst).

Next, pelletized titania (diameter 1.5 m
m, length 2 to 3 mm, specific surface area 35 m ² / g) 2 g of chloroplatinic acid aqueous solution and 1% by weight of platinum (elemental conversion value)
After supporting it, ammonium vanadate and oxalic acid were added to water, and the mixture was heated and dissolved in a water bath, poured into an aqueous solution that had been allowed to cool, and immersed for 30 minutes. Vanadium was added to the titania pellets in an amount of 3 wt% (metal element conversion). Value) supported, dried and baked in the same manner as above, dried at 80 ° C., 100 ° C. and 120 ° C. for 2 hours each, and then in a nitrogen stream containing 20% oxygen for 5 hours from 120 ° C. to 500 ° C. To raise
A Pt, V-based purification material (second catalyst) was prepared.

A purifying agent comprising about 3.6 g of the first catalyst (silver-based catalyst) and about 1.2 g of the second catalyst (Pt, V-based catalyst) was used. Pt on the side,
It was set in the reaction tube so that the V-based catalysts were located respectively. Next, a gas having the composition shown in Table 5 (nitrogen monoxide, carbon monoxide, oxygen, ethanol, propylene, sulfur dioxide, nitrogen, and water) was flowed at a flow rate of 4.4 liters per minute (standard state) (first). The apparent space velocity of one catalyst is about 30,000.
0h ^-1 , the apparent space velocity of the second catalyst is about 100,000
It is 0h- ¹ . ), The exhaust gas temperature in the reaction tube was changed from 250 ° C. to 600 ° C. at every 50 ° C., and ethanol and nitrogen oxide were reacted at each temperature.

Table 5 Component Concentration Nitric oxide 800 ppm (dry basis) Oxygen 10% by volume (dry basis) Carbon monoxide 100 ppm (dry basis) Ethanol 3 times the mass of nitric oxide (dry basis) Propylene 100 ppm ( Dry basis) Sulfur dioxide 80 ppm (dry basis) Nitrogen Residual water 10% by volume (based on total volume of the above ingredients)

After passing through the reaction tube, nitrogen oxide (NO +
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, sulfur dioxide and hydrocarbon (propylene) were measured with a CO meter, SOx meter and HC meter, respectively, and the carbon monoxide and hydrocarbon removal rates and the sulfur dioxide oxidation rate were determined. However, the removal rates of carbon monoxide and hydrocarbons were obtained under the condition that ethanol was not added. The results are shown in Table 6.

Example 6 In the same manner as in Example 5, a catalyst in which 4% by weight of silver was supported on powdered silica-alumina using an aqueous silver nitrate solution was used.
0 g of commercially available cordierite honeycomb shaped body (diameter 30 mm, length about 12.5 mm, 400 cells / inch)
² ) coated, dried and then fired stepwise to 600 ° C,
A silver-based purification material (purification material coated with the first catalyst) was prepared.

Next, titania powder (specific surface area 50 m ² /
An aqueous solution prepared by supporting 1% by weight of platinum (based on titania) with an aqueous solution of chloroplatinic acid (g) and then adding ammonium tungstate parapentahydrate and oxalic acid and heating them in a water bath to dissolve them. 3 minutes by weight of tungsten with respect to titania (metal element conversion value)
Supported and made into a slurry. 0.4 g (dry basis) of the slurry was coated on the same honeycomb-shaped molded body (diameter 30 mm, length about 4.2 mm) as the above silver-based purification material. Drying and firing were performed under the same conditions as in Example 5 to prepare a Pt, W-based purification material (purification material coated with the second catalyst).

On the inflow side of the exhaust gas in the reaction tube, a silver-based purifying material,
Pt and W-based purification materials were set on the outflow side, and the gases having the compositions shown in Table 5 were evaluated in the same manner as in Example 5 (the apparent space velocity of the silver-based purification material was about 30,000 h ⁻¹ , Pt, W). The apparent space velocity of the system purification material is about 90,000 h ^-1 .) The experimental results are shown in Table 6.

Example 7 A silver-based purification material was prepared in the same manner as in Example 6. In the same manner, 1% by weight of platinum was added to the powdered titania,
After supporting 2% by weight of tungsten and 3% by weight of vanadium (each converted to a metal element), the honeycomb-shaped molded body was coated to prepare a platinum-based purification material.

On the inflow side of the exhaust gas in the reaction tube, a silver-based purification material,
Pt, W, and V-based purification materials were set on the outflow side, and the gases having the compositions shown in Table 5 were evaluated in the same manner as in Example 5 (the apparent space velocity of the silver-based purification material was about 30,000 h ^-1 , Pt. ,
The apparent space velocity of W and V purification materials is about 90,000 h ^-1
Is. ). The experimental results are shown in Table 6.

Comparative Example 3 Only 3.6 g of a silver-based catalyst prepared by the same method as in Example 5 was set in the reaction tube, and the gas having the composition shown in Table 5 was supplied at a rate of 4.
It was flowed at a flow rate of 4 liters (standard state) (total apparent space velocity of about 30,000 h ⁻¹ ) and evaluated under the same conditions as in Example 5. The experimental results are also shown in Table 6.

Table 6 Nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbon (HC) removal rate and sulfur dioxide (SO ₂ ) oxidation rate Reaction temperature Removal components Removal rate (NOx, CO, HC) And oxidation rate (SO ₂ ) (%) (° C.) Example 5 Example 6 Example 7 Comparative Example 3 250 NOx 18 15 20 12 CO 80 75 75 70 15 HC 50 45 50 50 SO ₂ − − − − 300 NOx 50 48 55 30 CO 90 89 88 88 40 HC 65 65 65 68 32 SO ₂ − − − − 350 NOx 70 65 72 72 50 CO 95 95 95 95 60 HC 70 70 70 70 32 SO ₂ − − − − 400 NOx 85 88 82 82 60 CO 100 100 100 100 70 HC 95 95 95 94 40 SO ₂ 5 55-450 NOx 78 80 74 70 CO 100 100 100 100 70 HC 98 98 96 96 65 SO ₂ 7 7 7 7-500 NOx 70.5 74 72 60.2 CO 100 100 100 100 80 HC 100 100 100 100 70 SO ₂ 12 12 12 12-550 NOx 50.5 55 52.1 52 CO 100 100 100 100 90 HC 100 100 100 100 85 SO ₂ 15 15 15 15-600 NOx 10 20 15 15 20 CO 100 100 100 100 98 HC 100 100 100 100 90 SO ₂ 20 20 20 20-

As shown in Table 6, in comparison with Comparative Example 3, Examples 5 to 7 show effective removal of nitrogen oxides in a wide temperature range, and high removal of carbon monoxide and hydrocarbons even in a low temperature region. was gotten. Furthermore, the oxidation characteristics of sulfur dioxide were low by using the alumina composite oxide as the porous inorganic oxide.

[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.

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Claims (6)

[Claims] 1. Nitrogen oxides are reduced and 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 oxidized. In the exhaust gas purifying material to be removed, the porous inorganic oxide has a content of 0.2 to
15% by weight (elemental conversion value) of a first catalyst supporting silver or silver oxide, and porous inorganic oxide (a) 10% by weight or less of the inorganic oxide (metal element conversion value) W of
An oxide of at least one element selected from the group consisting of V, Mn, Mo, Nb and Ta, and (b) 5 wt% or less (elemental conversion value) of Pt, Pd, Ru and Rh of the inorganic oxide. , Ir
And a second catalyst carrying at least one element selected from the group consisting of Au and Au. 2. The exhaust gas purifying material according to claim 1, wherein the purifying material has the first catalyst on an exhaust gas inflow side and the second catalyst on an exhaust gas outflow side. Purifying material. 3. The exhaust gas purifying material according to claim 1 or 2, wherein the porous inorganic oxide in the first catalyst is alumina alone or at least one selected from the group consisting of silica, titania and zirconia. An exhaust gas purification material comprising an alumina-based composite oxide containing titania, alumina, zirconia, silica and a composite oxide thereof as the second catalyst. 4. 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. 5. 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. 6. Nitrogen oxides are reduced and 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 oxidized. In an exhaust gas purification method for removing, the exhaust gas purification material according to any one of claims 1 to 5 is used, the exhaust gas purification material is installed in the middle of an exhaust gas conduit, and hydrocarbons and / or carbon are provided upstream of the purification material. Number 2
Exhaust gas added with the oxygen-containing organic compound or the fuel containing the oxygen-containing organic compound is brought into contact with the purification material at 150 to 650 ° C., thereby removing the nitrogen oxides by reaction with the oxygen-containing organic compound in the exhaust gas. At the same time, residual and unreacted carbon monoxide and hydrocarbons are also removed by oxidation, and an exhaust gas purification method.