JP2971274B2 - Nitrogen oxide removal catalyst and nitrogen oxide removal method using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst for removing nitrogen oxides and a method for removing nitrogen oxides using the same. More specifically, a catalyst for removing nitrogen oxides from exhaust gas discharged from an internal combustion engine such as an automobile engine, for example, a gasoline engine, a diesel engine, a boiler industrial plant, etc., and a nitrogen oxide removal method using the same It is about.

[0002]

2. Description of the Related Art In recent years, internal combustion engines such as automobiles, boilers,
Nitrogen oxides in exhaust gas discharged from an industrial plant harmful components (hereinafter sometimes referred to NO _x as a generic term of the nitrogen oxides) is included and is responsible for air pollution. Therefore, removal of the NO _x in the flue gas has been studied from various quarters. Conventionally, for example, in the case of automobile exhaust gas, the exhaust gas is treated using a three-way catalyst, and the hydrocarbon (H
C) and carbon monoxide (CO) at the same time a method of removing NO _x are used. This method is performed under the condition that air is introduced so that the fuel completely burns (the ratio of air to fuel is referred to as “A / F”). However, when the A / F is increased (hereinafter referred to as “oxidizing atmosphere state”), oxygen is present in excess of the amount of oxygen necessary to completely burn unburned components such as hydrocarbons and carbon monoxide in the exhaust gas. By doing
It is difficult to reduce and remove NO _x by a conventional three-way catalyst in such an oxidizing atmosphere state.

In a diesel engine boiler among internal combustion engines, a method using a reducing agent such as ammonia, hydrogen or carbon monoxide is generally used to remove nitrogen oxides. However, this method has a problem that a special device is required for collecting and treating the unreacted reducing agent.

Recently, as a method for removing NO _x, a method using a NO _x decomposition catalyst comprising a crystalline aluminosilicate containing copper ions has been proposed (see Japanese Patent Application Laid-Open No. Sho 60-1).
No. 25250, U.S. Pat. No. 4,297,328) This merely indicates that nitric oxide (NO) can be decomposed into nitrogen (N ₂ ) and oxygen (O ₂ ). It is difficult to effectively remove nitrogen oxides under actual exhaust gas conditions.

Further, in JP-A-63-100919, reaction when treating an exhaust gas by using a copper-containing catalyst and NO _x and hydrocarbon is accelerated preferentially in an oxidizing atmosphere in the presence of a hydrocarbon , NO _x can be efficiently removed. The hydrocarbons used in this method may be hydrocarbons contained in the exhaust gas or hydrocarbons added as necessary from the outside, and as a specific embodiment, the exhaust gas is first contacted with a copper-containing catalyst. There is also disclosed a method of removing NO _x and then contacting it with an oxidation catalyst to remove hydrocarbons, carbon monoxide and the like.
This method has a high temperature at which nitrogen oxides can be removed, and has little effect at low temperatures.

Furthermore since the catalyst is exposed to high-temperature exhaust gas poor in heat resistance NO _x decomposition performance is lowered, the catalyst is arranged in parallel as a countermeasure, when the exhaust gas becomes high temperature, an oxidation catalyst or A method of bypassing to a three-way catalyst side is disclosed (Japanese Patent Laid-Open No. 1-171625).

[0007] Thus, the NO _x in the exhaust gas was efficiently decomposed and removed, yet the nitrogen oxide decomposing catalyst having excellent high-temperature resistant is has not yet been developed.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide NO _x
And to provide a nitrogen oxide removing catalyst having excellent high-temperature heat resistance.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and have found that at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earths, iridium and fire resistance. The present inventors have found a catalyst for removing nitrogen oxides in which a catalytically active substance comprising an inorganic oxide powder is coated on an integral structure, and have completed the present invention. The nitrogen oxide removing catalyst and the nitrogen oxide
Nitrogen oxides in the method for removing oxides include nitrous oxide.
Not included.

More specifically, a catalytically active substance containing at least one metal selected from the group consisting of tantalum, niobium, yttrium, and rare earth elements, iridium, and a refractory inorganic oxide is coated on an integral structure. A method for removing nitrogen oxides, comprising passing an exhaust gas in an oxidizing atmosphere in the presence of a hydrocarbon through a catalyst. As the iridium source, a water-soluble salt such as iridium chloride and trichlorohexammineiridium is preferably used. The content of iridium is preferably 1 to 10% by weight based on the refractory inorganic oxide. When less than 1 wt% is for NO _x removal efficiency is lowered, 1
Even if it is carried in excess of 0% by weight, the activity corresponding to the carried amount cannot be obtained. Further, it is preferable that iridium is supported on the refractory inorganic oxide.

As a method for supporting iridium on the refractory inorganic oxide, a usual supporting method is used. For example, (1) a method of impregnating an aqueous solution of iridium salt with a refractory inorganic oxide, drying and burning, and (2) adding a refractory inorganic oxide to an aqueous solution of iridium salt, mixing and reducing hydrazine and the like. And carrying out reduction carrying with an agent.

As a starting source of at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earth elements, salts soluble in organic solvents such as chlorides, nitrates and sulfates and water-soluble salts can be used. .

Rare earth elements include lanthanum, cerium, praseodymium, neodymium, samarium, terbium,
Other rare earth elements and mixed rare earth elements thereof can be used.

The content of at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earth elements is preferably 0.1 to 10% by weight based on the refractory inorganic oxide. When the amount is less than 0.1% by weight, the NO _x removal efficiency decreases after the heat resistance test, and when the amount exceeds 10% by weight, the NO _x removal efficiency decreases after the heat resistance test. .

The loading ratio of iridium to at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earth is preferably from 1: 5 to 20: 1.
In the ratio of 20: 1, when the loading of iridium decreases, the initial activity decreases, and in the ratio of 1: 5, when the loading of iridium increases, the NO _x removal efficiency after the heat test decreases. Is what you do.

The refractory inorganic oxide may be any one as long as it is generally used as a catalyst carrier. For example, α-alumina or activated alumina such as γ, δ, η, θ, titania, zirconia, or a mixture thereof Complex oxides, for example, alumina-titania, alumina-zirconia, titania-zirconia and the like can be used,
Activated alumina is preferred.

These refractory inorganic oxides are BET
Preferably, it is a refractory inorganic oxide having a surface area of 50 to 200 m ² / g.

[0018] Normally, indicating specific embodiments of the catalyst using the present invention, a carrier is said to three-dimensional structures, for example, a honeycomb monolith carrier, foamed carrier, there is Koruketo shaped carrier and the like, the material is made of ceramic, Metals are preferred.

The catalyst composition is wet-ground with a ball mill or the like,
There is a method in which a three-dimensional structure is immersed in a slurry and coated to form a catalyst.

Hereinafter, a method for preparing the catalyst will be described.

[0021]

(2) When an integral structure or an inert inorganic carrier (hereinafter, referred to as “integral structure”) is used,
(A) A method in which the catalyst composition is collectively put into a ball mill or the like, wet-pulverized to form an aqueous slurry, an integrated structure or the like is immersed, dried and burned, and (b) a refractory inorganic oxide is subjected to a ball mill or the like. It is wet-pulverized to form an aqueous slurry, and the integrated structure or the like is immersed, dried and burned. Next, the integrated structure coated with the refractory inorganic oxide is immersed in an iridium-containing aqueous solution, dried and calcined, and further, at least one selected from the group consisting of tantalum, niobium, yttrium, and a rare earth element (hereinafter, referred to as a rare earth element) A method of immersing the integrated structure in a solution of a metal salt of “tantalum or the like”), drying and burning,
(C) Iridium is supported on the refractory inorganic oxide in advance to obtain an iridium-supported refractory inorganic oxide, which is then converted into an aqueous slurry by a ball mill or the like, and the integrated structure is immersed in the slurry, dried and calcined. A method of obtaining an integrated structure coated with iridium-supported refractory inorganic oxide, then immersing in a solution of a metal salt such as tantalum, drying and burning,
(D) A solution of a metal salt of tantalum is impregnated with a refractory inorganic oxide, ignited, and the resulting powder is wet-pulverized with a ball mill or the like to obtain an aqueous slurry. A method of drying, burning, and obtaining an integrated structure coated with a supported refractory inorganic oxide such as tantalum, then immersing in an iridium-containing aqueous solution, drying, and burning. (E) There is a method in which iridium and tantalum are preliminarily supported on a refractory inorganic oxide, then wet-pulverized with a ball mill or the like to form an aqueous slurry, and the integrated structure is immersed in the slurry, dried and calcined. , (2) (a) (b) (c) (d) (e) are preferred.

When the integral structure is coated with the catalyst component, the coating amount of the catalyst component is preferably 50 to 300 g per liter of the integral structure. When the amount is less than 50 g, the catalyst activity is reduced, and the amount is less than 300 g.
When the ratio exceeds the above, the activity corresponding to the amount of the carrier cannot be obtained.

The amount of hydrocarbons present in the exhaust gas is 500
When the hydrocarbons do not have these concentrations in the exhaust gas, the addition of the hydrocarbons by a cylinder, the partial addition of the fuel, and the conversion of the fuel by a catalyst or the like are appropriately performed. By adding and introducing a hydrocarbon such as the obtained hydrocarbon, the amount of the hydrocarbon can be compensated to be removed by decomposition.

[0025]

According to the present catalyst, high-temperature heat resistance is improved by supporting at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earth elements on iridium and the refractory inorganic oxide. even when exposed to high temperature exhaust gas in which NO _x decomposition activity is maintained.

[0026]

The present invention will now be described more specifically with reference to examples.

(Example 1) BET surface area 100 m ² / g
An aqueous iridium chloride solution containing 5 g of iridium was added to 100 g of activated alumina having the above, mixed, dried at 120 ° C. for 2 hours, and calcined at 500 ° C. for 2 hours. An isopropyl alcohol solution containing 9.9 g of tantalum chloride [TaCl ₅ ] is added to the obtained powder, mixed, dried and then dried.
The mixture was calcined at 0 ° C. for 2 hours. This powder was wet-pulverized with a ball mill to obtain an aqueous slurry, and a commercially available cordierite-type honeycomb carrier (manufactured by Nippon Insulator, having a cross section of 400 gas per square inch and a diameter of 33 m)
mφ, length 76 mmL, volume 65 ml)
Excess slurry was blown off with compressed air. Then, drying was performed at 120 ° C. for 2 hours to obtain a completed catalyst (A). This catalyst supported 5% by weight of iridium and 5% by weight of tantalum based on activated alumina.

(Example 2) A complete catalyst (B) was obtained in the same manner as in Example 1, except that 2.0 g of tantalum chloride was used instead of the isopropyl alcohol solution containing 9.9 g of tantalum chloride. Was. This catalyst supported 5% by weight of iridium and 1% by weight of tantalum based on activated alumina.

Example 3 Example 1 was the same as Example 1 except that an aqueous solution of iridium chloride containing 1 g of iridium and 39.6 g of tantalum chloride were used instead of the aqueous solution of iridium chloride containing 5 g of iridium and 9.9 g of tantalum chloride. In the same manner, a completed catalyst (C) was obtained.

This catalyst had 1% by weight of iridium and 20% by weight of tantalum supported on activated alumina.

Example 4 Example 1 was repeated, except that an isopropyl alcohol solution containing 14.5 g of niobium chloride [NbCl ₅ ] was used instead of the isopropyl alcohol solution containing 9.9 of tantalum chloride. Then, a completed catalyst (D) was obtained. This catalyst supported 5% by weight of iridium and 5% by weight of niobium based on activated alumina.

Example 5 In Example 1, yttrium nitrate [Y (NO ₃ ) ₃ .6H ₂ O] was used instead of the isopropyl alcohol solution containing 9.9 g of tantalum chloride.
A completed catalyst (E) was obtained in the same manner as in Example 1 except that an aqueous solution containing 5 g was used. This catalyst supported 5% by weight of iridium and 5% by weight of yttrium based on activated alumina.

Example 6 In Example 1, 15.6 g of lanthanum nitrate [La (NO ₃ ) ₃ .6H ₂ O] was used instead of the isopropyl alcohol solution containing 9.9 g of tantalum chloride.
In the same manner as in Example 1 except for using an aqueous solution containing, a completed catalyst (F) was obtained. Was supported on activated alumina by 5% by weight of iridium and 5% by weight of lanthanum.

(Example 7) Instead of the isopropyl alcohol solution containing 9.9 g of tantalum chloride in Example 1, 15.5 g of cerium nitrate [Ce (NO ₃ ) ₃ .6H ₂ O] was used.
In the same manner as in Example 1 except for using an aqueous solution containing, a completed catalyst (G) was obtained. This catalyst supported 5% by weight of iridium and 5% by weight of cerium based on activated alumina.

Comparative Example 1 An aqueous iridium chloride solution containing 5 g of iridium was added to 100 g of the activated alumina used in Example 1, mixed, dried at 120 ° C. for 2 hours, and then dried at 500 ° C.
For 2 hours. This powder was wet-pulverized with a ball mill to obtain an aqueous slurry. Hereinafter, the same procedure as in Example 1 was performed to obtain a completed catalyst (I).

This catalyst had 5% by weight of iridium supported on activated alumina.

(Comparative Example 2) A method for preparing ZSM-5 type zeolite is described in the literature (Rapid Crystallizer).
ion Method, Proceedings 8t
h International Congress
on Catalysis, Berlin, 1984.
Vol. 3, P569). The obtained zeolite was confirmed to be a ZSM-5 type zeolite by X-ray diffraction. This ZSM-5 type zeolite 10
After adding 400 g of pure water to 0 g and stirring at 98 ° C. for 2 hours, a 0.2 mol / L aqueous solution of a copper ammine complex was slowly added dropwise at 80 ° C. The dropped zeolite was filtered, sufficiently washed, and then dried at 120 ° C. for 24 hours. The obtained powder was wet-pulverized by a ball mill to obtain an aqueous slurry. Hereinafter, it carried out similarly to Example 1 and obtained the completed catalyst (II). In this catalyst, 5.6% by weight of copper was supported on the ZSM-5 type zeolite.

Example 8 Catalysts (A) to (G), (I) and (II) prepared in Examples 1 to 7 and Comparative Examples 1 and 2
Were subjected to the following initial performance test and time-dependent performance test.

[Reaction gas composition] Nitric oxide (NO) 75
0 ppm, propylene (C ₃ H ₆ ) 1000 ppm (converted to methane), carbon monoxide (CO) 0.2% by volume, oxygen 2.
0 volume%, water vapor 10 volume%, carbon dioxide 13.5 volume%, the remaining nitrogen.

[Initial performance] diameter 34.5 mmφ, length 3
After filling a catalyst into a 00 mm stainless steel reaction tube, a reaction gas having the above composition was introduced at a space velocity of 20,000 hr- ¹ . The catalyst performance was evaluated by measuring the NO _x cleaning rate at a catalyst bed inlet temperature of 300 ° C. Table 1 shows the results.

[Aging Performance Test] Each catalyst was filled in a multi-converter, and the exhaust gas from the cruising of a commercially available gasoline electronically controlled engine was mixed with air to fill the packed catalyst bed, and the air-fuel ratio (A / F) was 20/1. After the preparation, the space velocity (SV) is 160,000 hr- ¹ and the catalyst bed temperature is 700 ° C.
For 20 hours. Thereafter, the initial performance test was performed in the same manner as above, and the NO _x purification rate was measured to evaluate the catalyst performance. Table 1 shows the results.

[0042]

[Table 1]

Example 9 The initial performance and the aging performance of each catalyst were evaluated in the same manner as in Example 8, except that the oxygen concentration in the reaction gas was changed from 2.0% by volume to 10% by volume. did. Table 2 shows the results.

[0044]

[Table 2]

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-154603 (JP, A) JP-A-6-154604 (JP, A) JP-B 62-41066 (JP, B2) (58) Field (Int.Cl. ⁶ , DB name) B01J 21/00-38/74 B01D 53/86-53/94

Claims (6)

(57) [Claims] 1. An integral structure coated with a catalytically active substance comprising at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earth elements, iridium, and a refractory inorganic oxide powder. Oxygen atmosphere
For removal of nitrogen oxides (excluding nitrous oxide) in the dry state . 2. The catalyst for removing nitrogen oxides (excluding nitrous oxide) according to claim 1, wherein the refractory inorganic oxide is activated alumina. 3. The amount of at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earths is 0.1 to 10% by weight based on the refractory inorganic oxide.
The amount of iridium is 1 to 10% by weight based on the refractory inorganic oxide, and the loading ratio of the metal and iridium is 1: 5 to 20: 1. Catalyst for removing nitrogen oxides (excluding nitrous oxide) . 4. An integral structure coated with a catalytically active substance comprising at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earth elements, iridium, and a refractory inorganic oxide powder. A method for removing nitrogen oxides (excluding nitrous oxide), comprising passing an exhaust gas in an oxidizing atmosphere in the presence of a hydrocarbon through a catalyst. 5. The method for removing nitrogen oxides (excluding nitrous oxide) according to claim 4, wherein the refractory inorganic oxide is activated alumina. 6. The amount of at least one metal selected from the group consisting of tantalum, niobium, yttrium and rare earth elements is 0.1 to 10% by weight based on the refractory inorganic oxide, and the amount of iridium is There is a 1 to 10% by weight with respect to the refractory inorganic oxide, and loading ratio of the metal to iridium is 1: 5 to 20: 1 is claimed in claim 4 or nitrogen oxide according to 5 (nitrite Excluding nitric oxide) removal method.