JPH07313885A - Nitrogen oxides removing catalyst and method - Google Patents

Abstract

PURPOSE:To effectively remove nitrogen oxides from a combustion exhaust gas contg. excess oxygen by adding a reducing agent to the combustion exhaust gas and bringing the resulting exhaust gas into contact with a catalyst consisting of a specific first catalyst and a specific second catalyst. CONSTITUTION:This catalyst consists of the first catalyst obtained by depositing 0.2 to 15wt.% (expressed in terms of metal element) of metal selected among Al, Sn and In or oxide thereof on a porous inorganic oxide, and the second catalyst obtained by depositing 0.2 to 50wt.% (in the same terms as above) of any one of oxide, sulfate and oxysulfate of metal element selected among W, V, Mn, Mo, Nb, Ta, Fe and Cu and 0.05 to 5wt.% (in the same terms as above) of metal element selected among Pt, Pd, Ru, Rh, Ir and Au on a porous inorganic oxide. The combustion exhaust gas to which a reducing agent is added is brought into contact with the catalyst at 150 to 600 deg.C.

Description

Detailed Description of the Invention

[0001]

The present invention effectively removes nitrogen oxides from flue gas containing nitrogen oxides and excess oxygen, and also oxidizes compounds such as residual and unreacted carbon monoxide and hydrocarbons. It relates to catalysts and methods that can be removed.

[0002]

2. Description of the Related Art Excessive amounts of combustion exhaust gas discharged from internal combustion engines such as automobile engines, combustion equipment installed in factories, household fan heaters, etc. Nitrogen oxides (generally called NOx) such as nitric oxide and nitrogen dioxide are contained together with oxygen. Here, the nitrogen oxides generally refer to nitric oxide and / or nitrogen dioxide, and the phrase "containing excess oxygen" means carbon monoxide, hydrogen,
It is meant to contain more oxygen than the theoretical amount of oxygen required to burn unburned components such as hydrocarbons.

Such nitrogen oxides are considered to be one of the causes of acid rain and have become 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 the above method, ammonia used as a reducing agent for nitrogen oxides is expensive, and the amount of injected ammonia is measured while measuring the nitrogen oxide concentration in the exhaust gas so that unreacted ammonia is not discharged. Must be controlled, and the size of the device must be 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 59th Annual Meeting of the Chemical Society of Japan
(1990) 2A526, 60th Autumn Meeting (1990) 3L420, 3L42
2, 3L423, etc.).

However, although these methods can remove nitrogen oxides with high efficiency from a simulated exhaust gas containing no water, the actual exhaust gas contains about 10% of water, so It was found that the oxide removal rate was significantly reduced. Also, with these methods,
There is also the disadvantage that the optimum temperature for the reduction reaction of nitrogen oxides is relatively high at around 400-600 ° C.

A method in which methanol is added to exhaust gas and the exhaust gas containing methanol is brought into contact with alumina at about 300 ° C. to reduce nitrogen oxides (“Catalyst” vol.33, No. 33).
(Page 2, 59, 1991) is also proposed, but this method is not practical because it has a low nitrogen oxide reducing property.

Therefore, an object of the present invention is to provide unburned components such as nitrogen oxides, carbon monoxide, and hydrocarbons, such as combustion exhaust gas from a fixed combustion device and a gasoline engine, a diesel engine, etc. that burn under excess oxygen conditions. A catalyst and a catalyst capable of efficiently removing nitrogen oxides from a combustion exhaust gas containing more than the theoretical reaction amount of oxygen with respect to, and also oxidizing and removing compounds such as residual and unreacted carbon monoxide and hydrocarbons It is to provide a removal method.

[0011]

As a result of intensive studies in view of the above problems, the present inventors have found that the amount of residual hydrocarbons or hydrocarbons or oxygen-containing organic compounds added in an amount commensurate with the amount of nitrogen oxides contained in the exhaust gas. Nitrogen oxide in which exhaust gas containing a compound is combined with a catalyst in which a porous inorganic oxide supports Al, Sn, and In and a catalyst in which a porous inorganic oxide supports V-based elements and platinum-based elements It was discovered that contact with a removal catalyst at a predetermined temperature can effectively remove nitrogen oxides and also remove residual and unreacted compounds such as carbon monoxide and hydrocarbons by oxidation. Completed the invention.

That is, 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 compounds such as carbon monoxide and hydrocarbons are removed. The catalyst of the present invention which also oxidizes and removes (1) porous inorganic oxide (a) A
a first catalyst supporting 0.2 to 15% by weight (elemental conversion value) of at least one metal and / or oxide selected from the group consisting of l, Sn and In; The inorganic oxide (b) contains at least one of oxides, sulfates and oxysulfates of at least one element selected from the group consisting of W, V, Mn, Mo, Nb, Ta, Fe and Cu. 2 to 50% by weight (metal element conversion value), and (c) Pt of 0.05 to 5% by weight (element conversion value) of the inorganic oxide,
It is characterized by comprising a second catalyst supported with at least one element selected from the group consisting of Pd, Ru, Rh, Ir and Au.

In addition, 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 compounds such as carbon monoxide and hydrocarbons are removed. In the method of the present invention for oxidizing and removing also the above-mentioned nitrogen oxide removing catalyst, the nitrogen oxide removing catalyst is installed in the middle of an exhaust gas conduit, and hydrocarbon and / or carbon number is 2 or more on the upstream side of the catalyst. The nitrogen oxides are removed by bringing the exhaust gas added with the oxygen-containing organic compound or the fuel containing the same into contact with the catalyst at 150 to 600 ° C.

The present invention will be described in detail below. [1] Nitrogen Oxide Removal Catalyst In the present invention, (1) porous inorganic oxide (a) Al, S
a first catalyst supporting 0.2 to 15% by weight (element conversion value) of at least one metal and / or oxide selected from the group consisting of n and In; and (2) porous inorganic As the oxide, (b) an oxide of at least one element selected from the group consisting of W, V, Mn, Mo, Nb, Ta, Fe, and Cu, a sulfate, and an oxysulfate are used. 2 to 50% by weight (metal element conversion value) and (c) 0.05 to 5% by weight (element conversion value) Pt of the inorganic oxide,
A nitrogen oxide removal catalyst consisting of at least one element selected from the group consisting of Pd, Ru, Rh, Ir and Au and a second catalyst supported thereon is installed in the exhaust gas conduit to remove nitrogen oxides. Exhaust gas added with a hydrocarbon and / or an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing the same is brought into contact with the catalyst on the upstream side of the catalyst installation position to remove nitrogen oxides in the exhaust gas. In the present invention, the first catalyst and the second catalyst are used in combination, but it is preferable to dispose 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. Nitrogen-containing compounds such as ammonia and hydrogen cyanide are produced in the first catalyst and are used to further reduce the nitrogen oxides on the second catalyst.

The first preferred form of the nitrogen oxide removing catalyst of the present invention is that the catalyst 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 catalyst substrate and then carrying a catalytically active species. As the ceramic material forming the base of the catalyst, γ-alumina and its composite oxide (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 nitrogen oxide removal catalyst.

The shape and size of the substrate of the nitrogen oxide removing catalyst can be variously changed according to the purpose. Further, the substrate may be used in combination of two or more parts such as an inlet part and an outlet part. 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 form of the nitrogen oxide removal catalyst of the present invention is a pellet-like, granular-like or powder-like porous inorganic oxide carrying a catalytically active species, or a porous body carrying a catalytically active species. It is a catalyst obtained by filling a casing having a desired shape with a catalyst obtained by molding an inorganic oxide into pellets, granules or powder.

(1) First Catalyst The first catalyst comprises (a) at least one metal and / or oxide selected from the group consisting of Al, Sn, and In supported on a porous inorganic oxide. Use what is done. As the porous inorganic oxide, it is possible to use porous alumina, silica, titania, zirconia and their composite oxides, preferably γ-alumina alone, or a group consisting of silica, titania and zirconia. An alumina-based composite oxide containing at least one selected from the above 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. When the content of alumina is less than 50% by weight, the initial removal property of the catalyst is 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.

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.

In the present invention, a catalyst in which Al, Sn, and In are supported on the above-mentioned inorganic oxide such as γ-alumina and alumina-based composite oxide is used, and the total supported amount thereof is the weight of the inorganic oxide. 0.2 to 15% by weight (elemental conversion value) is preferable. When the supported amount is less than the lower limit value of the above range, the effect of removing nitrogen oxides is not significant, and even if the amount exceeds the upper limit value, the removal rate of nitrogen oxides is not improved, and
The upper limit is 15% by weight. A more preferable loading amount is 0.5 to 10% by weight based on the weight of the inorganic oxide.

The metal and / or oxide of Al, Sn, and In is supported on the inorganic oxide by using the above-mentioned porous inorganic oxide in an aqueous solution of hydrochloride, nitrate or the like or an organic solvent solution such as ethanol. Dip and dry at 70 ° C and 200 ° C,
It can be carried out by immersing in ammonia water and gradually heating at 70 to 600 ° C. and firing. Note that Al, Sn, and In are considered to exist in the form of oxides in the catalyst obtained by firing.

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

The amount of the first catalyst provided on the surface of the substrate is preferably 20 to 300 g / liter of the substrate. If the amount of catalyst is less than 20 g / liter, good NOx cannot be removed. On the other hand, when the amount of the catalyst exceeds 300 g / liter, the removal characteristics do not improve so much and the pressure loss increases. More preferably, the first catalyst provided on the surface of the substrate is 50 to 250 g / liter of the substrate.

(2) Second catalyst The second catalyst is (b) W, V, Mn, Mo, Nb, Ta, Fe and Cu which are catalytically active species in the porous inorganic oxide.
At least one element oxide, sulfate and oxysulfate selected from the group consisting of, and
(C) It carries at least one metal element selected from the group consisting of Pt, 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, Ta, Fe and Cu, W, V, Mo and / or Mn are preferably used, and Mo, W and / or V are more preferably used. The amount of the W-based element (c) supported on the inorganic oxide by the second catalyst is based on the above-mentioned porous inorganic oxide (10
0% by weight) is 0.2 to 50% by weight (metal element conversion value), preferably 0.5 to 8% by weight, and more preferably 0.5 to 5% by weight (metal element conversion value). The effect does not change even when the amount of the W-based element carried exceeds 50% by weight with respect to the inorganic oxide. By using a W-based element or the like, it becomes possible to remove nitrogen oxides using a nitrogen-containing compound such as ammonia or hydrogen cyanide as a reducing agent. Also,
In the present invention, any catalyst that accelerates the reduction reaction of nitrogen oxides by a nitrogen-containing compound such as ammonia can be used without being limited to W-based elements and the like.

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 preferable is 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. 5% by weight of inorganic oxide
If it exceeds, 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,
Known impregnation method, precipitation method, sol-gel method, powder method and 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,
100-600 after drying at 50-150 ° C, especially 70 ° C
It is carried out by gradually raising the temperature at ℃ and firing.
This firing is carried out in air, under an oxygen atmosphere, under a nitrogen atmosphere, or under a flow of hydrogen gas. When firing under a nitrogen atmosphere or under a flow of hydrogen gas, it is effective to finally carry out an oxidation treatment at 300 to 650 ° C. .

In the first preferred embodiment of the above catalyst, the thickness of the second catalyst provided on the catalyst substrate is 300 μm.
The following is recommended. Further, the amount of the second catalyst provided on the surface of the catalyst substrate is preferably 20 to 300 g / liter of the catalyst substrate.

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 20: 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 20: 1 and the amount of the second catalyst is small, the nitrogen-containing compounds such as ammonia and hydrogen cyanide formed on the first catalyst do not react,
As it is discharged as it is, the concentration of nitrogen-containing compounds in the discharged gas increases. More preferable weight ratio of the first catalyst and the second catalyst is 1
It is 5: 1 to 1: 1.

[2] Method for removing nitrogen oxide First, a nitrogen oxide catalyst having a first catalyst and a second catalyst is installed in the middle of an exhaust gas pipe. Preferably, the first catalyst is arranged on the exhaust gas inlet side and the second catalyst is arranged on the exhaust gas outlet side.

The exhaust gas contains ethylene, propylene and the like as residual hydrocarbons to some extent, but when the amount is not sufficient to reduce the nitrogen oxides in the exhaust gas, hydrocarbons and / or carbon are externally supplied. A reducing agent composed of several oxygen-containing organic compounds or a mixed fuel containing them is introduced into the exhaust gas. The reducing agent is added to the exhaust gas on the upstream side of the site where the catalyst 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. Specific examples of the liquid hydrocarbon in the standard state include hydrocarbons such as heptane, cetane, kerosene, light oil, gasoline and heavy oil. 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 depends on the weight ratio (weight of the reducing agent added / nitrogen oxide (NO
It is preferable that the weight) calculated as 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 in exhaust gas) is 0.1 to 5 similarly to the above.

In the present invention, the overall apparent space velocity of the catalyst is 50 in order to efficiently proceed the reduction and removal of nitrogen oxides by oxygen-containing organic compounds, hydrocarbons or ammonia.
It shall be less than 0,000 h ^-1 . 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, the space velocity in the first catalyst is 150,0
It is set to 00h ^-1 or less, preferably 100,000h ^-1 or less. When the space velocity of the first catalyst exceeds 150,000 h ^-1 , the reduction reaction of nitrogen oxides does not sufficiently occur and the removal rate of nitrogen oxides decreases. The space velocity in the second catalyst is 200,0.
It is set to 00h ^-1 or less, preferably 150,000h ^-1 or less. When the space velocity of the second catalyst exceeds 200,000 h ^-1 , the oxidative removal characteristics of hydrocarbons, carbon monoxide, etc. deteriorate.

Further, in the present invention, the temperature of the exhaust gas at the catalyst installation site where the reaction between the reducing agent and the nitrogen oxide occurs is maintained at 150 to 600 ° C. If the temperature of the exhaust gas is less than 150 ° C., the reaction characteristics between the reducing agent and the nitrogen oxides deteriorate, and the nitrogen oxides cannot be removed well. On the other hand, 6
When the temperature exceeds 00 ° C, the added reducing agent itself starts to burn, and the nitrogen oxides cannot be reduced and removed efficiently by adding these substances. The exhaust gas temperature is preferably 20
The temperature is 0 to 550 ° C.

[0037]

The present invention will be described in more detail by the following specific examples. Example 1 10 g of commercially available pelletized γ-alumina (diameter: 1.5 m
m, length about 2 to 3 mm, specific surface area 260 m ² / g) is immersed in an aqueous solution of indium nitrate, dried at 70 ° C., and then in air 100 ° C., 125 ° C., 150 ° C., 200 ° C., 300
2 hours each at ℃, 400 ℃ and 500 ℃, 5 at 600 ℃
It was calcined for a period of time to prepare an indium catalyst (first catalyst) supporting 3.2% by weight of indium (metal element conversion value) with respect to γ-alumina.

Next, 2 g of the same γ-alumina pellet was loaded with 1% by weight of platinum (elemental conversion value) using an aqueous solution of chloroplatinic acid, and then ammonium vanadate and oxalic acid were added to water, and the mixture was placed on a water bath. It is put into an aqueous solution which is dissolved by heating and allowed to cool, immersed for 30 minutes, and 5% by weight of vanadium is supported on alumina pellets (metal element conversion value), dried and fired in the same manner as above, and then at 80 ° C and 100 ° C. , 120
Each was dried at 2 ° C for 2 hours, and then heated from 120 ° C to 500 ° C over 5 hours in a nitrogen stream containing 20% oxygen to prepare a Pt, V catalyst (second catalyst).

First catalyst (indium catalyst) about 13.5
g and the second catalyst (Pt, V catalyst) of about 1.2 g were set in the reaction tube so that the indium catalyst was located on the inflow side of the exhaust gas and the Pt, V catalyst was on the outflow side. Next, a gas having the composition shown in Table 1 (nitrogen monoxide, carbon monoxide, oxygen, ethanol, nitrogen, and water) was flowed at a flow rate of 4.4 liters per minute (standard state) (the appearance of the first catalyst). the space velocity of about 8,000h ^-1, apparent space velocity of the second catalyst is about 100,000h ^-1.), 550 ℃ the exhaust gas temperature in the reaction tube from 0.99 ° C.
Up to 50 ° C., and ethanol and nitrogen oxide were reacted at each temperature.

Table 1 Component Concentrations Nitric oxide 500 ppm (dry basis) Oxygen 10% by volume (dry basis) Carbon monoxide 100 ppm (dry basis) Ethanol 500 ppm (dry basis) Nitrogen Residual water 10% by volume (of the above ingredients) (For total volume)

The concentration of nitrogen oxides (total amount of nitric oxide and nitrogen dioxide) in the gas after passing through the reaction tube was measured by a chemiluminescence type nitrogen oxide analyzer to determine the removal rate of nitrogen oxides. The results are shown in Table 2.

Example 2 Using the same catalyst as in Example 1, except that among the components shown in Table 1, propylene (500 ppm) was used instead of ethanol, a nitrogen oxide removal experiment was conducted in the same manner as in Example 1. . Further, the concentrations of carbon monoxide and hydrocarbon (propylene) were measured with a CO meter and an HC meter, respectively, and the removal rates of carbon monoxide and hydrocarbon were obtained. The experimental results are shown in Table 2.

Example 3 In the same manner as in Example 1, 10 g of γ-alumina was immersed in an ethanol solution of stannous chloride, dried at 70 ° C., and then treated in air at 200 ° C. for 2 hours each. Then, it is impregnated with aqueous ammonia solution at room temperature, dried again, and finally at 600 ° C.
It was calcined for a period of time to prepare a tin catalyst (first catalyst) supporting 2% by weight of tin (metal element conversion value) on γ-alumina.

A catalyst comprising about 13.5 g of the first catalyst (tin catalyst) and about 1.2 g of the same second catalyst (Pt, V catalyst) as in Example 1 was used. It was set in the reaction tube so that the Pt and V catalysts were located on the outflow side. Next, a nitrogen oxide removal experiment was conducted under the same conditions as in Example 1 using the mixed gas having the composition shown in Table 1. The experimental results are shown in Table 2.

Example 4 Indium nitrate was used on powdery γ-alumina (specific surface area 200 m ² / g) in the same manner as in Example 1 to support indium in an amount of 2.6% by weight (metal element conversion value). About 3.3 g of the catalyst was added to a commercially available cordierite honeycomb formed body (diameter 30 mm, length about 37.5 mm, 400 cells /
An indium catalyst (first catalyst) was prepared by coating the coating film on an inch ² ), drying it, and then calcining it stepwise to 600 ° C.

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. Honeycomb shaped body similar to the above indium catalyst (diameter 30 mm, length about 4.2 m
m) was coated with 0.4 g (dry basis) of the slurry.
Drying and firing were performed under the same conditions as in Example 1 to prepare a platinum / tungsten catalyst (second catalyst).

An indium catalyst was set on the inflow side of the exhaust gas in the reaction tube, and a Pt and W catalyst were set on the outflow side, and the gas having the composition shown in Table 1 was evaluated in the same manner as in Example 1 (the apparent space velocity of the indium catalyst was About 10,000 h ^-1 , Pt,
The apparent space velocity of the W catalyst is about 90,000 h ^-1 . ). The experimental results are shown in Table 2.

Example 5 An indium catalyst was prepared in the same manner as in Example 4.
In the same manner as in Example 4, 1% by weight of platinum, 1% by weight of tungsten and 2% of vanadium were added to the powdered titania.
After supporting the weight% (each metal element conversion value), the honeycomb formed body was coated to prepare a Pt, W, V catalyst (second catalyst).

An indium catalyst was set on the inflow side of the exhaust gas in the reaction tube, and a Pt, W, and V catalyst was set on the outflow side, and the same composition as that used in Example 2 was used for evaluation in the same manner as in Example 2 ( Apparent space velocity of indium catalyst is about 10,
000h ^-1 , apparent space velocity of Pt, W, V catalyst is about 9
It is 10,000 h ^-1 . ). The experimental results are shown in Table 2.

Comparative Example 1 Using only the indium catalyst used in Example 1 and using the gas having the composition shown in Table 1, under the same conditions as in Example 1 (apparent space velocity is 8,000 h ⁻¹ ). A nitrogen oxide removal experiment was conducted. The results are shown in Table 2.

Comparative Example 2 Example 2 was carried out using only the indium catalyst used in Example 1.
A nitrogen oxide removal experiment was conducted using the gas having the same composition as used in Example 2 under the same conditions as in Example 2 (the apparent space velocity was 8,000 h ⁻¹ ). The results are shown in Table 2.

Table 2 Nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbon (HC) removal rates Reaction temperature Removal rates (NOx, CO, HC) (%) (° C) Removal components Example 1 Implementation Example 2 Example 3 Example 4 150 NOx − − 15.7 − CO − − − − HC − − − − 200 NOx − − 50.3 − CO − − − − HC − − − − 250 NOx 28.5 − 64.3 32.2 CO − − − − HC − − − − 300 NOx 67.6 23.2 72.6 69.7 CO − 100 − − HC − 88 − − 350 NOx 52.4 48.8 5250 .5 CO-100-HC-100-400 NOx 42.1 83.8 35.5 41.5 CO-100-HC-100--450 NOx 30.1 70.2 32.1 25.6 C - 100 - - HC - 100 - - 500 NOx - 45.5 30.3 - CO - 100 - - HC - 100 - - 550 NOx - 20.4 25.5 - CO - 100 - - HC -100- (Note)-: Not measured

Table 2 (continued) Removal rate of nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) Reaction temperature Removal rate (NOx, CO, HC) (%) (° C) Removal component implementation Example 5 Comparative Example 1 Comparative Example 2 250 NOx-14.2-CO --- HC --- 300 NOx 20.1 55 25.5 CO 91.5-43 HC 75.4-35.4 350 NOx 32. 2 50.2 43.3 CO 100-62 HC 82.2-35.7 400 NOx 58.4 40.6 70.3 CO 100-74.3 HC 100-43.5 450 NOx 60.4-61. 6 CO 100-75.5 HC 100-65.2 500 NOx 40.1-38.7 CO 100-83 HC 100-72.2 550 NOx 20.4-18.9 CO 100 94.5 HC 100-88.5 (Note)-: Not measured

As can be seen from Table 2, when Example 1 and Comparative Example 1 both using ethanol as the reducing agent, or Example 2 and Comparative Example 2 both using propylene as the reducing agent are compared, both are Examples. The nitrogen oxide removal rate was higher. Further, the removal rates of carbon monoxide and hydrocarbons were higher in Examples 2 and 5 than in Comparative Example 2.

[0055]

As described in detail above, according to the catalyst and method of the present invention, nitrogen oxides in exhaust gas containing excess oxygen can be efficiently removed. Further, with the catalyst and method of the present invention, nitrogen oxides can be efficiently removed even when the exhaust gas contains about 10% of water. Furthermore, compounds such as carbon monoxide and hydrocarbons can be removed efficiently.

INDUSTRIAL APPLICABILITY The catalyst and method for removing nitrogen oxides of the present invention can be widely used for removing nitrogen oxides contained in exhaust gas from various combustors and automobiles.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 23/08 ZAB A 23/14 ZAB A 23/84 ZAB 23/847 23/85 ZAB A B01D 53 / 36 104 A B01J 23/84 301 A (72) Inventor Mika Saito 4-14-1, Suehiro, Kumagaya, Saitama Prefecture Riken Kumagaya Works (72) Inventor Kiyohide Yoshida 4-Suehiro, Kumagaya, Saitama 14th No. 1 Stock Company Riken Kumagaya Works

Claims (6)

[Claims] 1. A compound such as residual and unreacted carbon monoxide and hydrocarbons, as well as removing nitrogen oxides from a flue gas containing nitrogen oxides and oxygen in excess of the stoichiometric amount for coexisting unburned components. It is also a catalyst for oxidizing and removing (1) porous inorganic oxide (a) Al, Sn and In
A first catalyst supporting 0.2 to 15% by weight (elemental conversion value) of at least one metal and / or oxide selected from the group consisting of (2) porous inorganic oxide ( b)
0.2 to 50 of any one or more of oxides, sulfates and oxysulfates of at least one element selected from the group consisting of W, V, Mn, Mo, Nb, Ta, Fe and Cu.
Wt% (metal element conversion value) and (c) 0.05 to 5 weight% (element conversion value) of Pt, Pd, Ru, Rh of the inorganic oxide,
A nitrogen oxide removing catalyst, comprising a second catalyst supported with at least one element selected from the group consisting of Ir and Au. 2. The nitrogen oxide removal catalyst according to claim 1, wherein the catalyst has the first catalyst on the exhaust gas inflow side and the second catalyst on the exhaust gas outflow side. Nitrogen oxide removal catalyst. 3. The nitrogen oxide removal catalyst according to claim 1, wherein the porous inorganic oxide is at least alumina selected from the group consisting of alumina, silica, titania and zirconia in the first catalyst. Alumina-based composite oxide containing one kind, with the second catalyst titania, alumina,
A nitrogen oxide removing catalyst, which is one of zirconia and silica or a composite oxide thereof. 4. The nitrogen oxide removing catalyst according to claim 1, wherein the catalyst is formed by coating the surface of a ceramic or metal substrate with the first and second catalysts. A nitrogen oxide removal catalyst characterized by: 5. The nitrogen oxide removing catalyst according to claim 1, wherein the porous inorganic oxides of the first and second catalysts are in the form of pellets or granules, respectively. Nitrogen oxide removing catalyst. 6. A compound such as residual and unreacted carbon monoxide and hydrocarbons, as well as removing nitrogen oxides from a combustion exhaust gas containing nitrogen oxides and oxygen in a larger amount than the theoretical reaction amount for coexisting unburned components. In the method for oxidizing and removing also, the nitrogen oxide removal catalyst according to any one of claims 1 to 5 is used, the nitrogen oxide removal catalyst is installed in the middle of an exhaust gas conduit, and hydrocarbons and And / or nitrogen oxides characterized by removing the nitrogen oxides by contacting an exhaust gas to which an oxygen-containing organic compound having 2 or more carbon atoms or a fuel containing the same is added to the catalyst at 150 to 600 ° C. Removal method.