JPH04367724A - Catalyst and method for removing nitrogen oxide - Google Patents

Abstract

PURPOSE:To remove nitrogen oxide in the exhaust gas discharged from an internal combustion engine such as a car engine, for example, a gasoline engine or a diesel engine, a boiler or an industrial plant. CONSTITUTION:A catalyst for removing nitrogen oxide is obtained by immersing a monolithic structure composed of refractory inorg. oxide having platinum supported thereon in an aqueous solution of at least one kind of a compound selected from nitrate, carbonate and hydroxide of sodium and/or potassium and subsequently drying and calcining the impregnated structure. Exhaust gas in an oxidizing atmosphere state is passed through the catalyst composed of the monolithic structure of catalytically active components containing sodium and/or potassium, platinum and refractory inorg. oxide to remove nitrogen oxide.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a method for removing nitrogen oxides, and more particularly, the present invention relates to a method for removing nitrogen oxides from exhaust gases emitted from internal combustion engines such as automobile engines, such as gasoline engines, diesel engines, boilers, industrial plants, etc. The present invention relates to a method for removing nitrogen oxides.

0002

[Prior Art] In recent years, exhaust gas emitted from internal combustion engines such as automobiles, boilers, and industrial plants contains harmful components such as nitrogen oxides (hereinafter sometimes referred to as NOx), which cause air pollution and It causes acid rain, etc. For this reason. This NOx removal has been studied from various perspectives.

Conventionally, a three-way catalyst has been used to remove nitrogen oxides from automobile exhaust gas.
NOx is also removed along with carbon monoxide (CO). This method introduces a sufficient amount of air to completely burn the fuel. However, since this method decomposes NOx in a reducing atmosphere, the A/F
When the is lean (A/F; air/fuel has a large amount of air), it is suitable for purifying HC and CO in exhaust gas, but it is suitable for purifying NOx due to excess oxygen. ,
It cannot reduce and remove NOx.

[0004] Furthermore, among internal combustion engines, in the case of diesel engines, boilers, etc., methods are used to remove NOx using reducing agents such as ammonia, hydrogen, or carbon monoxide. There is a problem in that special equipment is required to recover and process the reducing agent.

Furthermore, to exemplify general literature, as a method for reducing nitrogen oxides with hydrocarbons, a method using a catalyst in which platinum and barium are supported on activated alumina (Japanese Unexamined Patent Publication No. 55-67334); A method using a catalyst in which rhodium and tungsten and sodium and/or potassium chlorides are supported on alumina (Japanese Patent Publication No. 58
No. 45288) has been disclosed, but none of these methods is sufficient to remove nitrogen oxides when there is a large excess of oxygen in the exhaust gas.

[0006] Furthermore, a method for removing nitrogen oxides by reacting NOx with hydrocarbons using a copper-containing catalyst in an oxidizing atmosphere and in the presence of hydrocarbons (Japanese Patent Laid-Open No. 63-10091
No. 9) has been disclosed, but this method requires a high temperature at which nitrogen oxides can be removed and cannot effectively remove nitrogen oxides at low temperatures.

[0007]

[Problems to be Solved by the Invention] Therefore, it is desired to develop a method that can efficiently remove nitrogen oxides from low to high temperatures in an oxidizing atmosphere.

[0008]

[Means for Solving the Problems] As a result of intensive research, the present inventors discovered the following catalyst and method as a method for solving the above problems and completed the invention.

(1) The first aspect of the present invention is to coat an integral structure with a refractory inorganic oxide supporting platinum, and then cover the integral structure with sodium and/or potassium nitrates and carbonates. or hydroxides, the catalyst is immersed in at least one kind of aqueous solution selected from the group consisting of hydroxides, dried, and calcined.

As sources of sodium and/or potassium, mention may be made of nitrates, carbonates or hydroxides. Salts or compounds other than these do not provide the desired activity.

[0011] The content of sodium and/or potassium is preferably 1% to 20% by weight based on the refractory inorganic oxide in terms of each metal element. More preferably 5% by weight or more
It is 10% by weight. If it is less than 1% by weight, the NOx removal efficiency will decrease in a high temperature range, and if it exceeds 20% by weight, the NOx purification efficiency will decrease in each temperature range.

[0012] The refractory inorganic oxide may be any of those commonly used as catalyst carriers, such as α alumina or activated alumina such as γ, δ, η, θ, titania, or zirconia. Alternatively, composite oxides thereof such as alumina titania, alumina zirconia, titania zirconia, etc. can be used,
Activated alumina is preferred.

[0013] These refractory inorganic oxides also have BET
Preferably, it is a refractory inorganic oxide having a surface area of 50 to 200 m2/g.

As the platinum source, water-soluble salts such as chloroplatinic acid, dinitrodiamine platinum, potassium platinate, or sodium platinate are preferably used. The amount of platinum supported is preferably 0.5% to 10% by weight, more preferably 2% to 10% by weight, based on the refractory inorganic oxide.
It is 5% by weight. When the amount is less than 1% by weight, the NOx removal efficiency decreases in each temperature range, and even if it is supported in excess of 10% by weight, the activity commensurate with the amount of support cannot be obtained. Further, platinum is preferably supported on a refractory inorganic oxide.

[0015] The monolithic structure includes those commonly used as carriers for catalysts, such as inorganic oxide honeycomb monoliths such as cordierite, metal honeycomb monoliths, corrugates, plug honeycombs, pellets, etc.
Preferably it is a honeycomb monolith.

The method for preparing the catalyst according to the present invention is as follows: (1) A refractory inorganic substance is made into a slurry, an integral structure is immersed in the slurry, excess slurry is removed, and the integral structure is dried and calcined. The structure is immersed in a platinum-containing aqueous solution, the excess liquid is removed, and then dried and fired.Then, this integrated structure is immersed in a specified sodium aqueous solution, the excess liquid is removed, and the finished catalyst is dried and fired. I got it. (2) Platinum is supported on a refractory inorganic oxide using a conventional method, this is made into a slurry, the integral structure is immersed, the excess slurry is removed, and the integral structure is dried and fired. The catalyst was immersed in an aqueous sodium solution, the excess liquid was removed, and the catalyst was dried and calcined to obtain a finished catalyst. (3) A refractory inorganic substance is made into a slurry, the integral structure is immersed in it, the excess slurry is removed, the integral structure is dried and fired, and then the integral structure is immersed in a mixed aqueous solution containing platinum and a specified amount of sodium. After removing the slurry, it was dried and calcined to obtain a finished catalyst. Among this preparation procedure, drying is preferably performed at 80°C to 150°C for 30 minutes to 3 hours, and baking is preferably performed at 300°C to 600°C for 1 hour to 5 hours. Moreover, among these preparation methods, the preparation method (2) is preferable.

(2) A catalyst formed by covering exhaust gas in an oxidizing atmosphere in the presence of hydrocarbons with a catalytically active component containing sodium and/or potassium, platinum, and a refractory inorganic oxide on an integral structure. This is a method for removing nitrogen oxides, characterized by passing the nitrogen oxides through the nitrogen oxides.

The hydrocarbons may be saturated or unsaturated chain, cyclic or aromatic hydrocarbons, but unsaturated chain hydrocarbons are preferred, such as ethylene, propylene, butene, etc. can be given.

It is preferable that the content of hydrocarbons (in terms of methane) and nitrogen oxides in the exhaust gas is in a molar ratio of 0.5 to 0.02. If it exceeds 0.5, hydrocarbons react preferentially and it becomes difficult to react with NOx, which reduces the NOx removal efficiency, and if it exceeds 0.02, the hydrocarbon concentration decreases. Even if the temperature is increased beyond this level, it is difficult to see a commensurate NO removal effect.

[0020]Although hydrocarbons are normally contained in exhaust gas, for example, diesel engine exhaust gas has a low hydrocarbon content and may not be within the above range of hydrocarbon to nitrogen oxide content ratio. In such a case, in order to sufficiently remove nitrogen oxides, it is necessary to newly add hydrocarbons to the catalyst from the exhaust gas inlet side to make up for the deficiency.

(Examples) The present invention will be explained in detail with reference to Examples below, but the invention is not limited thereto unless it goes against the spirit of the invention.

(Example 1) BET surface area 100m/g2
An aqueous solution of dinitrodiamine platinum containing 5 g of platinum was added to 100 g of activated alumina having 5 g of platinum, mixed, dried at 120° C. for 2 hours, and calcined at 500° C. for 2 hours. The obtained powder was wet-pulverized using a ball mill to obtain an aqueous slurry, and a commercially available cordierite honeycomb carrier (manufactured by Nippon Insulators) with a cross section of 400 gas flow cells per square inch was added to the slurry. After immersing a slurry (diameter: 33 mmφ, length: 76 m, volume: 65 ml), excess slurry was blown off with compressed air. Next, it was dried at 120°C for 2 hours and fired at 500°C for 2 hours to obtain a honeycomb carrier coated with platinum-supported alumina powder.

Further, the obtained honeycomb carrier was immersed in a 4.3 mol/l (liter) aqueous sodium nitrate solution, and then the excess solution was blown off with compressed air.
It was dried at 20°C for 2 hours and calcined at 500°C to obtain a finished catalyst (A). This catalyst supported 5% by weight of platinum and 10% by weight of sodium based on activated alumina.

(Example 2) In Example 1, instead of 4.3 mol/l of sodium nitrate aqueous solution, 2.1 mol/l of sodium nitrate aqueous solution was used.
A completed catalyst (B) was obtained in the same manner as in Example 1, except that 1 of the sodium nitrate aqueous solution was used. This catalyst supported 5% by weight of platinum and 5% by weight of sodium based on activated alumina.

(Example 3) In Example 2, 5 g of platinum
platinum 1 instead of the dinitrodiamine platinum aqueous solution containing
A finished catalyst (C) was obtained in the same manner as in Example 2, except that an aqueous solution of dinitrodiamine platinum containing g was used. This catalyst supported 1% by weight of platinum and 5% by weight of sodium based on activated alumina.

(Example 4) In Example 1, the 4.3 mol/l sodium nitrate aqueous solution was replaced with 2.5 mol/l.
A completed catalyst (D) was obtained in the same manner as in Example 1, except for using the potassium carbonate aqueous solution. This catalyst supported 5% by weight of platinum and 10% by weight of potassium based on activated alumina.

(Example 5) In Example 1, the 4.3 mol/l sodium nitrate aqueous solution was replaced with 4.3 mol/l.
A finished catalyst (E) was obtained in the same manner as in Example 1, except for using an aqueous sodium carbonate solution. This catalyst supported 5% by weight of platinum and 10% by weight of sodium based on activated alumina.

(Example 6) In Example 1, the 4.3 mol/l sodium nitrate aqueous solution was replaced with 4.3 mol/l.
A completed catalyst (F) was obtained in the same manner as in Example 1, except for using an aqueous sodium hydroxide solution. This catalyst supported 5% by weight of platinum and 10% by weight of sodium based on activated alumina.

(Comparative Example 1) In Example 1, 4.3 mol/l of sodium nitrate aqueous solution was used instead of 4.3 mol/l of sodium nitrate aqueous solution.
A finished catalyst (G) was obtained in the same manner as in Example 1, except for using the aqueous sodium chloride solution. This catalyst supported 5% by weight of platinum and 10% by weight of sodium based on activated alumina.

(Comparative Example 2) A dinitrodiamine platinum aqueous solution containing 5 g of platinum and an aqueous solution containing 36.9 g of sodium nitrate were added to and mixed with 100 g of activated alumina used in Example 1, and then dried at 120° C. for 2 hours and heated to 500° C. It was baked at ℃ for 2 hours. The obtained powder was wet-milled using a ball mill to obtain an aqueous slurry. A honeycomb carrier similar to that used in Example 1 was immersed in this slurry, and then excess slurry was blown off with compressed air. Then 120℃
The finished catalyst (H
) was obtained. This catalyst supported 5% by weight of platinum and 10% by weight of sodium based on activated alumina.

(Comparative Example 3) An aqueous solution of dinitrodiamine platinum containing 5 g of platinum was added to the activated alumina used in Example 1 and mixed, dried at 120°C for 2 hours, and heated to 500°C.
Baked for 2 hours. Sodium nitrate 36.9
After adding and mixing an aqueous solution containing g, the mixture was dried at 120°C for 2 hours and fired at 500°C for 2 hours. The obtained powder was wet-pulverized in a ball mill to obtain an aqueous slurry. A honeycomb carrier similar to that used in Example 1 was immersed in this slurry, and the excess slurry was blown off with compressed air. Next, it was dried at 120°C for 2 hours and calcined at 500°C for 2 hours to obtain a completed catalyst (I). This catalyst has
Platinum is 5% by weight and sodium is 1% by weight based on activated alumina.
It was supported at 0% by weight.

(Comparative Example 4) After adding and mixing an aqueous solution containing 36.9 g of sodium nitrate to the activated alumina used in Example 1, drying at 120°C for 2 hours, and drying at 500°C for 2 hours.
Baked for an hour. After adding and mixing an aqueous solution of dinitrodiamine platinum containing 5 g of platinum to this powder, the mixture was dried at 120°C for 2 hours and calcined at 500°C for 2 hours. This powder was wet-pulverized in a ball mill to obtain an aqueous slurry. A honeycomb carrier similar to that used in Example 1 was immersed in this slurry, and the excess slurry was blown off with compressed air. Next, it was dried at 120°C for 2 hours and calcined at 500°C for 2 hours to obtain a finished catalyst (J). This catalyst contains 5% by weight platinum and 10% by weight sodium based on activated alumina.
It was being carried.

(Comparative Example 5) The method for preparing ZSM-5 type zeolite is described in the literature (Rapidonal Crystal
lingMethod,Proceeding
8th International Congr.
Ess on Catalysis, Berlin
, Berlin, 1984, Vol. 3, P. 569). The obtained zeolite was confirmed to be ZSM-5 type zeolite by X-ray diffraction.

[0034] 400 g of pure water was added to 100 g of ZSM-5 type zeolite obtained by the above procedure, stirred at 98°C for 2 hours, and 0.2 mol/l copper ammine Sakuta medical solution was slowly added dropwise at 80°C. . 12 at 80 degrees even after dripping
The mixture was heated and stirred for hours to perform ion exchange. Furthermore, the ion-exchanged zeolite was filtered and thoroughly washed until nitrate ions were no longer detected. This ion-exchanged zeolite was dried at 120°C for 24 hours. The obtained powder was wet-pulverized in a ball mill to obtain an aqueous slurry, into which a cordierite honeycomb carrier similar to that used in Example 1 was immersed, and the excess slurry was blown off with compressed air. .

[0035] Next, it was dried at 120°C for 2 hours, and
The finished catalyst (K) was obtained by calcination at ℃. This catalyst has
The copper loading rate is 5.8 for ZSM-5 type zeolite.
% by weight.

(Example 7) Examples 1-6 and Comparative Examples 1-
A catalytic activity test was conducted on the catalysts (A) to (K) prepared in 5 under the following conditions. Diameter 34.5mm
A stainless steel reaction tube with a diameter of 300 mm in length was filled with a catalyst, and the reaction gases were NO 750 ppm, propylene 1000 ppm (methane equivalent), and CO 0.2% by volume.
, using a gas in which water vapor is 10% by volume, carbon dioxide 13.5% by volume, and the remainder is nitrogen, and the SV is 20000/H.
It was introduced under the conditions of r. Catalyst inlet temperature is 200℃~40℃
The catalyst was evaluated in the range of 0°C, and the results are shown in Table 1.

[0037] In addition, oxygen of the reaction gas in the above catalyst evaluation 2.
Change 0 volume% to 10 volume% and evaluate the catalyst in the same way,
The raw results are shown in Table 2.

(Example 8) In Example 7, except that the catalyst for evaluation was changed to the catalyst (A) obtained in Example 1, and the concentration of propylene and the concentration of NO were changed to each concentration shown in Table 3. The catalyst was evaluated in the same manner as in Example 7, and the raw results are shown in Table 3.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

Claims (5)

[Claims] Claim 1: A monolithic structure is coated with a refractory inorganic oxide carrying platinum, and then the monolithic structure is coated with a refractory inorganic oxide supporting platinum.
or a catalyst for removing nitrogen oxides, which is obtained by immersing the catalyst in at least one aqueous solution selected from the group consisting of potassium nitrates, carbonates, and hydroxides, drying, and calcining the catalyst. 2. The catalyst according to claim 1, wherein the refractory inorganic oxide is activated alumina. [Claim 3] Exhaust gas in an oxidizing atmosphere is processed in the presence of hydrocarbons into a catalyst comprising a monolithic structure coated with a catalytic active component containing sodium and/or potassium, platinum, and a refractory inorganic oxide. A method for removing nitrogen oxides, characterized by passing through the nitrogen oxides. 4. The method according to claim 3, wherein the molar ratio of hydrocarbons (in terms of methane) to nitrogen oxides in the exhaust gas is 0.5 to 0.02. 5. The catalyst comprises a monolithic structure coated with a platinum-supported refractory inorganic oxide, and then the monolithic structure is formed from a group consisting of sodium and/or potassium nitrates, carbonates, and hydroxides. 4. The method according to claim 3, which is obtained by immersing in at least one selected aqueous solution, drying, and baking.