JP3363160B2 - Nitrogen oxide removal catalyst - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing nitrogen oxides, and more particularly to nitrogen oxides in exhaust gas discharged from internal combustion engines such as automobiles such as gasoline engines, diesel engines, boilers and industrial plants. The present invention relates to a method for efficiently removing the.

[0002]

2. Description of the Related Art In recent years, exhaust gas emitted from internal combustion engines such as automobiles, boilers, and industrial plants contains harmful components of nitrogen oxides (hereinafter sometimes referred to as NOx), which may cause air pollution. Has become. Therefore, removal of NOx in the exhaust gas has been studied from various viewpoints.

Conventionally, for example, in the case of exhaust gas of automobiles, a method of treating exhaust gas by using a three-way catalyst to remove NOx together with hydrocarbon (HC) and carbon monoxide (CO) has been used. This method is carried out under the condition that the air is introduced in an amount sufficient to completely burn the fuel. However, when the ratio of air to fuel (air-fuel ratio = air / fuel) becomes large, excess oxygen is present in excess of the amount required to completely burn unburned components such as hydrocarbons and carbon monoxide in exhaust gas. In such an oxidizing atmosphere, NOx cannot be reduced and removed by the three-way catalyst.

Further, in the case of a diesel engine or a boiler among the internal combustion engines, a method of removing NOx using a reducing agent of ammonia, hydrogen or carbon monoxide is used. However, this method has a problem that a special device is required for collecting and treating unreacted reducing agent.

Recently, as a method for removing NOx, a method using a NOx decomposition catalyst composed of a crystalline aluminosilicate containing copper ions has been proposed (Japanese Patent Laid-Open No. 60-125).
250, U.S. Pat. No. 4,297,328). However, this publication simply mentions nitric oxide (NO).
Is only shown to be decomposable into nitrogen (N ₂ ) and oxygen (O ₂ ), its effectiveness under actual exhaust gas conditions and that unsaturated hydrocarbons are effective in decomposing NOx. Is not listed.

Further, in Japanese Patent Laid-Open No. 63-100919, when exhaust gas is treated with a copper-containing catalyst in the presence of hydrocarbons in an oxidizing atmosphere, the reaction between NOx and hydrocarbons is preferentially promoted. It is described that NOx can be efficiently removed. The hydrocarbons used in this method are:
It may be a hydrocarbon contained in the exhaust gas or a hydrocarbon added from the outside as needed.
Further, as a specific embodiment thereof, a method is also disclosed in which exhaust gas is first contacted with a copper-containing catalyst to remove NOx and then with an oxidation catalyst to remove hydrocarbons, carbon monoxide and the like.

However, in Japanese Patent Laid-Open No. 1-171625, the catalyst is inferior in heat resistance and NOx decomposition performance is deteriorated when exposed to high temperature exhaust gas. Therefore, as a countermeasure against this, the catalysts are arranged in parallel. The method of bypassing the oxidation catalyst or the three-way catalyst when the exhaust gas becomes hot is described.

As described above, the present situation is that a catalyst for decomposing NOx in exhaust gas with high efficiency and high temperature heat resistance has not been developed yet.

[0009]

The object of the present invention is NO.
It is an object of the present invention to provide a catalyst for removing nitrogen oxides, which has excellent x-decomposing performance, excellent high-temperature heat resistance, and can decompose and remove NOx efficiently even under a high space velocity (SV).

[0010]

Means for Solving the Problems As a result of intensive research to solve the above problems, the present inventors have found that activated alumina supporting tungsten and copper, H-type ferrierite,
Based on this finding, it was found that the above object can be achieved by supporting a catalyst component composed of at least one zeolite selected from H-type mordenite and H-type ZSM-5 on a honeycomb-shaped carrier having an integral structure. The invention was completed. That is, the present invention relates to (A) activated alumina supporting tungsten and copper and (B)
H-type ferrierite, H-type mordenite and H-type ZS
The average particle size in the slurry of the catalyst component containing at least one zeolite selected from the group consisting of M-5
Relates to a catalyst for removing nitrogen oxides, which is carried on a honeycomb-shaped carrier having an integral structure as a slurry having a particle size of 0.1 to 5 μm . Hereinafter, the present invention will be described in detail.

The component (A) of the present invention comprises tungsten and copper supported on activated alumina. In this component (A), particularly, the loading ratios of tungsten and copper are 0.2 to 20% by weight (preferably 0.5 to 4% by weight) and 1 to 20% by weight (preferably, to active alumina), respectively. 2 to 10% by weight, and the weight ratio of copper to tungsten (copper / tungsten) is 1/1 to 1
When it is in the range of 0/1 (preferably 2/1 to 8/1), the catalytic activity, that is, the NOx decomposition performance is excellent, and the high temperature heat resistance is improved. It is considered that this is because the addition of tungsten to copper suppresses the sintering of copper and improves the high temperature heat resistance.

If the loading ratio of tungsten and copper is less than the above range, the catalytic activity is lowered, and even if the loading ratio is increased, the catalytic activity cannot be improved to a corresponding extent. Further, when the weight ratio of copper to tungsten is less than 1/1 or exceeds 10/1, improvement in high temperature heat resistance cannot be observed.

In the component (A), nickel is added to the activated alumina in an amount of 0.2 to 1 in addition to tungsten and copper.
When loaded at a rate of 0% by weight, high temperature heat resistance is further improved.

Component (A) can be prepared by any method, but is usually obtained by dissolving or dispersing a tungsten source such as tungsten oxide and a copper source such as an inorganic or organic salt of copper in an aqueous medium. It is preferable that the mixed aqueous solution is mixed with activated alumina, dried at a temperature of about 80 to 150 ° C, and then calcined at a temperature of about 300 to 600 ° C.

The activated alumina has a specific surface area of 50 m.
It is preferably ² / g or more, and particularly preferably 80 m2 / g or more.

The component (B) of the present invention is at least one zeolite selected from H-type ferrierite, H-type mordenite and H-type ZSM-5. This component (B)
By combining and using the above component (A), NOx can be efficiently decomposed and removed even under a high space velocity. This uses NOx in the exhaust gas by utilizing hydrocarbons in the exhaust gas or hydrocarbons introduced separately into the exhaust gas.
It is considered that the zeolite of the component (B) functions as a hydrocarbon adsorbent when decomposing the, and adsorbs as much hydrocarbon as possible on the catalyst surface.

As the above zeolite, one having a silicon / aluminum (atomic ratio) of 8/1 or more is particularly preferably used. The H-type zeolite is usually Na-type or K-type zeolite in which Na or K is replaced with H (proton).

The mixing ratio of component (A) and component (B) (component (A) / component (B) weight ratio) is usually 0.25 / 1.
˜2 / 1, particularly preferably 0.5 / 1 to 1.5 / 1. If this mixing ratio exceeds 2/1, the component (B)
The NOx decomposing ability is lowered because the proportion of the zeolite of No. 2 is reduced and the amount of adsorbed hydrocarbons is reduced, but the mixing ratio is 0.
Even if a large amount of the component (B) zeolite is used so as to be smaller than 25/1, the NOx resolution is not improved correspondingly.

The catalyst of the present invention is prepared by coating and supporting a catalyst component containing the above component (A) and component (B) on a honeycomb-shaped carrier having an integral structure. The method for coating and supporting the catalyst component is not particularly limited, but in the present invention, the component (A) and the component (B) are wet pulverized to form a slurry, which is impregnated into a honeycomb-shaped carrier to obtain an excess amount. A method of removing the slurry by a means such as blowing compressed air and then drying is preferably used.

The average particle size of the slurry in the above method is preferably in the range of 0.1 to 5 μm, and particularly 0.5.
It is preferably in the range of ˜2 μm. If the average particle size exceeds 5 μm, the NOx decomposing ability of the obtained catalyst is lowered, but this is because the distance between the hydrocarbon adsorbed by the component (B) and the NOx adsorbed by the component (A) becomes large, It is considered that the reaction between the hydrocarbon and NOx is less likely to occur. On the other hand, even if the average particle size is smaller than 0.1 μm, the NOx resolution corresponding to that is not improved.
It is considered that this is because the distance between the adsorbed hydrocarbon and NOx is already sufficient for the reaction.

Examples of the honeycomb-shaped carrier having an integral structure used in the present invention include a monolith honeycomb carrier, a metal honeycomb carrier, and a plug honeycomb carrier. In the present invention, the amount of the catalyst component loaded on the honeycomb-shaped carrier having an integrated structure is preferably 50 to 200 g per 1 liter of the volume of the honeycomb-shaped carrier. By contacting the exhaust gas with the catalyst for removing nitrogen oxides of the present invention, the nitrogen oxides in the exhaust gas can be efficiently decomposed and removed. This can be carried out using an ordinary fixed bed type, moving bed type, fluidized bed type reactor or the like.

When the exhaust gas has a low hydrocarbon content like a diesel engine exhaust gas, the hydrocarbon may be appropriately added and introduced. Further, when the exhaust gas is decomposed in an oxidizing atmosphere, air may be introduced to adjust the air-fuel ratio to an appropriate range.

[0023]

[Effect] The catalyst for removing nitrogen oxides of the present invention is (1) NO
Excellent in decomposition performance of x, (2) excellent heat resistance at high temperature, (3) NOx efficiently even under high space velocity
Has an advantage that it can be decomposed and removed.

Therefore, by using the catalyst for removing nitrogen oxides of the present invention, exhaust gas in a wide temperature range from high temperature exhaust gas to low temperature exhaust gas is treated, and NOx in the exhaust gas is removed stably and efficiently for a long period of time. It becomes possible.

[0025]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Example 1 As a honeycomb carrier having an integral structure, the cross section has a diameter of 33 m having about 400 gas flow cells per square inch.
m, length 76 mm, volume 65 mL (L = liter) columnar cordierite honeycomb carrier (Nippon Insulators Co., Ltd.)
Manufactured) was used.

2.6 g of tungsten oxide sol (tungsten oxide content, 50% by weight) and copper nitrate [Cu (N
_{O 3) 2 · 3H 2 O} ] were mixed with activated alumina 50g with a mixed aqueous solution and a specific surface area of 100 m @ 2 / g containing 19.4 g, after drying for 2 hours at 120 ° C., calcined in air for two hours at 500 ° C. Then, tungsten-copper-activated alumina powder was obtained.

Separately, aluminum sulfate [Al ₂ (SO ₄ )
₃・ 16H ₂ O] 24.3 g and sodium silicate (SiO
2 content, 58.5% by weight) 307 g and using "Rap
idCrystalization Metho
d ", Proceedings 8th Interna
regional Congestion on Cataly
sis, Berlin, 1984, Vol. 3, p56
According to the method described in No. 9, Na-type ZSM-5 (Si / Al
Atomic ratio, 80/1) zeolite was prepared. It was confirmed by X-ray diffraction that the obtained zeolite was Na-type ZSM-5. Next, this Na-type ZSM-5 powder was put into a 1 mol aqueous ammonium nitrate solution, stirred at 80 ° C. for 3 hours, washed with water at room temperature, and subsequently at 120 ° C. for 24 hours.
After drying for 3 hours, calcination in air at 550 ° C for 3 hours
A type ZSM-5 powder was obtained.

50 g of the above tungsten-copper-activated alumina powder and 50 g of H-type ZSM-5 powder were wet-stirred with a ball mill to prepare an aqueous slurry having an average particle size of 1 μm. The honeycomb-shaped carrier was immersed in this aqueous slurry, taken out, and then blown with excess slurry and compressed air in the cells to remove clogging of all cells. Then,
It was dried at 20 ° C. for 2 hours to obtain a finished catalyst (A).

The loading rate of tungsten and copper in this catalyst (A) was 2 with respect to that of activated alumina.
% And 8% by weight, activated alumina and H-type ZS
The mixing ratio of M-5 (activated alumina / H-type ZSM-5 weight ratio) was 1/1.

Example 2 A completed catalyst (B) was obtained in the same manner as in Example 1 except that the time for wet pulverization was adjusted to prepare an aqueous slurry having an average particle size of 4 μm.

The loading ratio of tungsten and copper in this catalyst (B) was 2 with respect to that of activated alumina.
% And 8% by weight, activated alumina and H-type ZS
The mixing ratio with M-5 (weight ratio of activated alumina / H type ZSM-5) was 1/1.

Example 3 Example 1 was repeated except that the time for wet pulverization was adjusted to prepare an aqueous slurry having an average particle size of 0.3 μm.
The same operation as above was performed to obtain a finished catalyst (C).

The loading ratio of tungsten and copper in this catalyst (C) was 2 with respect to that of activated alumina.
% And 8% by weight, activated alumina and H-type ZS
The mixing ratio with M-5 (weight ratio of activated alumina / H type ZSM-5) was 1/1.

Example 4 In Example 1, H-type ferrierite (Si / Al atomic ratio, 16/1) was used instead of 50 g of H-type ZSM-5 powder.
The same operation as in Example 1 was carried out except that 50 g was used to obtain a finished catalyst (D).

The loading rates of tungsten and copper in this catalyst (D) were as follows for activated alumina.
They were 2% by weight and 8% by weight, and the mixing ratio of activated alumina and H-type ferrierite (activated alumina / ferrierite weight ratio) was 1/1.

Example 5 In Example 1, H-type mordenite (Si / Al atomic ratio, 20/1) 5 was used instead of 50 g of H-type ZSM-5 powder.
The same operation as in Example 1 was carried out except that 0 g was used to obtain a finished catalyst (E).

The loading ratio of tungsten and copper in this catalyst (E) was 2 with respect to activated alumina.
% By weight and 8% by weight, and the mixing ratio of activated alumina and H-type mordenite (weight ratio of activated alumina / H-type mordenite) was 1/1.

Example 6 In Example 1, the amount of tungsten-copper-activated alumina powder used was changed from 50 g to 20 g, and H type ZSM-5 was used.
The same operation as in Example 1 was carried out except that the amount of the powder used was changed from 50 g to 80 g to obtain a finished catalyst (F). The loading ratio of tungsten and copper in this catalyst (F) is
2% by weight and 8% by weight, respectively, with respect to activated alumina, and the mixing ratio of activated alumina and H-type ZSM-5 (activated alumina / H-type mordenite weight ratio) was 0.2.
It was 5/1.

Example 7 In Example 1, the amount of the tungsten-copper-activated alumina powder used was changed from 50 g to 65 g, and H type ZSM-5 was used.
The same operation as in Example 1 was carried out except that the amount of the powder used was changed from 50 g to 35 g to obtain a finished catalyst (G).

The loading ratio of tungsten and copper in this catalyst (G) was 2 with respect to activated alumina, respectively.
% And 8% by weight, activated alumina and H-type ZS
The mixing ratio with M-5 (activated alumina / H-type ZSM-5 weight ratio) was 1.9 / 1.

Example 8 In Example 1, the amount of tungsten oxide sol used was changed from 2.6 g to 1.3 g, and the amount of copper nitrate used was changed to 19.
The same operation as in Example 1 was carried out except that the amount was changed from 4 g to 2.4 g to obtain a finished catalyst (H).

The loading ratio of tungsten and copper in this catalyst (H) was 1 for activated alumina, respectively.
% And 1% by weight, activated alumina and H-type ZS
The mixing ratio with M-5 (weight ratio of activated alumina / H type ZSM-5) was 1/1.

Example 9 In Example 1, the amount of copper nitrate used was changed from 19.4 g to 4
The same operation as in Example 1 was carried out except that the amount was changed to 8.4 g to obtain a finished catalyst (I).

The loading ratio of tungsten and copper in this catalyst (I) was 2 with respect to that of activated alumina.
% By weight and 20% by weight, activated alumina and H type Z
Mixing ratio with SM-5 (activated alumina / H type ZSM-5
The weight ratio) was 1/1. Example 10 In Example 1, 2.6 g of tungsten oxide sol, 19.4 g of copper nitrate and nickel nitrate [Ni (NO3) 2.6H2O were used instead of the aqueous solution containing 2.6 g of tungsten oxide sol and 19.4 g of copper nitrate. ] The same operation as in Example 1 was carried out except that an aqueous solution containing 5.0 g was used to obtain a finished catalyst (J).

In this catalyst (J), tungsten,
The loading rates of copper and nickel are as follows:
2% by weight, 8% by weight and 2% by weight, respectively,
The mixing ratio of activated alumina and H-type ZSM-5 (weight ratio of activated alumina / H-type ZSM-5) was 1/1.

Comparative Example 1 400 g of pure water was added to 100 g of the same H-type ZSM-5 powder used in Example 1, and the mixture was stirred at 98 ° C. for 2 hours and then 80
A 0.2 mol / L copper ammine complex aqueous solution was slowly added dropwise at 0 ° C. After completion of dropping, the mixture was heated and stirred at 80 ° C. for 12 hours to perform ion exchange. The ion-exchanged zeolite was filtered and thoroughly washed with water. The ion-exchanged zeolite was dried at 120 ° C. for 24 hours. The same operation as in Example 1 was carried out except that the powder thus obtained was used to obtain a finished catalyst (K).

The loading rate of copper in this catalyst (K) is
It was 5.8 wt% with respect to H type ZSM-5.

Comparative Example 2 Aqueous solution containing 19.4 g of copper nitrate and 100 g of activated alumina.
Were mixed, dried at 120 ° C. for 2 hours, and then calcined at 500 ° C. for 2 hours to obtain a copper-activated alumina powder. A completed catalyst (L) was obtained by performing the same operation as in Example 1 except that the powder thus obtained was used.

The loading rate of copper in this catalyst (L) is
It was 4% by weight based on the activated alumina.

Comparative Example 3 An aqueous solution containing 19.4 g of copper nitrate and 50 g of activated alumina were mixed, dried at 120 ° C. for 2 hours and then at 500 ° C. for 2 hours.
It was calcined for a time to obtain a copper-activated alumina powder. 50 g of this copper-activated alumina powder and the same H-type Z as used in Example 1
50g of SM-5 powder was wet-milled to have an average particle size of 1 μm.
An aqueous slurry of was prepared. Thereafter, the same operation as in Example 1 was performed to obtain a completed catalyst (M).

The loading rate of copper in this catalyst (M) is
It is 8% by weight with respect to the activated alumina, and the mixing ratio of activated alumina and H type ZSM-5 (activated alumina / H type ZSM-5
The SM-5 weight ratio) was 1/1.

Comparative Example 1 Average particle size in Example 1 was adjusted by adjusting the wet grinding time.
Example 1 except that an aqueous slurry having a diameter of 9 μm was prepared.
The same operation was performed to obtain a finished catalyst (N).

In the catalyst (N), tungsten and
The loading ratios of copper and copper are respectively
2% and 8% by weight, activated alumina and H type Z
Mixing ratio with SM-5 (activated alumina / H type ZSM-5
The weight ratio) was 1/1. Reference Example 1 The catalysts (A) to ( N ) prepared in Examples 1 to 10 and Comparative Examples 1 to 3 were subjected to the following initial performance test and aging performance test.

[Initial performance test] A 300 mL stainless steel reaction tube was filled with a catalyst, and then a reaction gas having the following composition was introduced under the condition of a space velocity of 20000 hr- ¹ . The catalyst performance was evaluated by measuring the NOx purification rate at the catalyst layer inlet temperature of 400 ° C. (initial performance). The results are shown in Table 1.

Reaction gas composition Nitric oxide (NO) 750 ppm, propylene (C
₃ H ₆ ) 1000 ppm (methane conversion), carbon monoxide (C
O) 0.2 volume%, oxygen 2.0 volume%, water 10 volume%,
Carbon dioxide 13.5% by volume, residual nitrogen [Performance test over time] Each catalyst was filled in a multi-converter, and the exhaust gas of a commercially available gasoline electronic control engine during cruising was mixed with air in this packed catalyst bed to obtain an air-fuel ratio. After adjusting (A / F) to 20/1, the space velocity (S.
V. ) The mixture was passed under conditions of 160,000 Hr -1 and catalyst bed temperature of 700 ° C for 20 hours. Then, the same operation as in the initial performance test was performed to measure the NOx purification rate to evaluate the catalyst performance (time-dependent performance). The results are shown in Table 1.

The NOx purification rate was determined by the following equation by measuring nitric oxide (NO) (ppm) in the exhaust gas at the catalyst layer outlet.

NOx purification rate (%) = (750−NO concentration of outlet exhaust gas) / 750 (× 100)

[0059]

[Table 1]

Reference Example 2 The same operation as in Test Example 1 was carried out except that the oxygen concentration in the reaction gas was changed from 2.0% by volume to 10% by volume, and the initial performance and aging performance of each catalyst were evaluated. The results are shown in Table 2.

[0061]

[Table 2]

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomohisa Ohata 1 992, Nishikioki, Kamahama-ku, Aboshi-ku, Himeji-shi, Hyogo Nihon Shokubai Co., Ltd. Catalysis Research Institute (58) Fields investigated (Int.Cl. ⁷ , DB name) B01J 21 / 00-38/74 B01D 53 / 86,53 / 94

Claims (4)

(57) [Claims] 1. An active alumina loaded with (A) tungsten and copper and (B) at least one zeolite selected from the group consisting of H-type ferrierite, H-type mordenite and H-type ZSM-5. The catalyst component is added so that the average particle size in the slurry is in the range of 0.1 to 5 μm.
A catalyst for removing nitrogen oxides, which is obtained by coating and supporting as a slurry on a honeycomb-shaped carrier having an integral structure. 2. The loadings of tungsten and copper are 0.2 to 20% by weight and 1 to 20% by weight, respectively, based on activated alumina, and the weight ratio of copper to tungsten (copper / tungsten) is 1 /. The catalyst for removing nitrogen oxides according to claim 1, which is 1 to 10/1. Wherein the weight ratio of component component to (B) (A) (( A) / (B)) is a nitrogen oxide removal according to claim 1 or 2 is 0.25 / 1-2 / 1 Catalyst. 4. Nickel is added to activated alumina in an amount of 0.2 to 0.2.
The support according to any one of claims 1 to 3, which is supported at a ratio of 10% by weight.
The catalyst for removing nitrogen oxides according to any one of the above.