JPH05138045A - Production of catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To enhance the NOx purifying capacity of a catalyst for purifying exhaust gas by enhancing the support amount of the metallic active sead on a porous material. CONSTITUTION:A catalyst agent wherein a metallic active seed is supported on a porous material and an acidic binder are slurried so that a slurry is made basic. For example, by adding aqueous ammonia to the slurry, the slurry is made basic. By gelling the slurry under heating, the visicosity of the slurry is adjusted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to NOx in exhaust gas.
The present invention relates to a method for producing an exhaust gas purifying catalyst for purifying (nitrogen oxide).

[0002]

2. Description of the Related Art In recent years, lean burn engines with low fuel consumption have been under development. This lean burn engine is used in an engine combustion chamber in an oxygen excess atmosphere (lean).
It's being driven in. At that time, in the exhaust gas discharged from the engine, NOx is harmful to the human body and the environment. Therefore, it is necessary to purify this NOx to prevent its release into the atmosphere.

In purifying NOx, in the case of a mobile engine mounted on an automobile or the like, a catalyst is installed in an exhaust passage of exhaust gas extending from the engine, and this catalyst is used to
It is practical to purify Ox.

Conventionally, a three-way catalyst is well known as a catalyst for purifying NOx. However, the above three-way catalyst is
NOx could not be purified from the exhaust gas of the lean burn engine.

Therefore, as an exhaust gas purifying catalyst capable of coping with a lean burn engine and effectively purifying NOx, a copper ion-exchanged zeolite catalyst in which copper is ion-exchanged and supported on zeolite, and a metal active species-supported γ- Alumina catalysts have been developed. These exhaust gas purifying catalysts have a large amount of metal active species that accelerates the NOx reduction reaction supported on a porous material.
A high NOx purification rate exceeding 0% could be obtained.

[0006]

In the conventional exhaust gas purifying catalyst described above, a metal active species is supported on a porous material such as zeolite or γ-alumina to form a catalyst agent, and the catalyst agent is used as an acidic binder. It is manufactured by coating it on a carrier in a slurry state with
There is a problem that the slurry becomes acidic due to the acidic binder, the metal active species on the porous material are eluted, the amount of the metal active species supported decreases, and the NOx purification performance deteriorates.

Further, in manufacturing the above-mentioned conventional exhaust gas purifying catalyst, when supporting the metal active species on the porous material, the porous material is agitated with a solution of the metal active species. Since the air present in the pores of the porous material inhibits the solution of the metal active species from penetrating into the pores, there is also a problem that the amount of the metal active species supported decreases and the NOx purification performance deteriorates. ..

The present invention has been made in view of the above points, and an object of the present invention is to improve the amount of metal active species supported on a porous material and to exhibit high NOx purification performance. An object of the present invention is to provide a method for producing a gas purification catalyst.

[0009]

In order to achieve the above object, the invention according to claim 1 forms a slurry by slurrying a catalyst agent comprising a porous material carrying metal active species with an acidic binder. Then, in the method for producing an exhaust gas purifying catalyst in which the carrier is coated with this slurry,
The slurry is adjusted to be basic before coating on a carrier.

According to a second aspect of the present invention, in the above-mentioned first aspect of the invention, the basicity of the slurry is adjusted by adding aqueous ammonia.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the hydrated alumina is used as the acidic binder, and the slurry is heated to gel the hydrated alumina. Is to be adjusted.

[0012]

With the above construction, in the invention according to claim 1,
By adjusting the basicity of the slurry, it is possible to prevent acidification of the slurry by the acidic binder, so that elution of metal active species from the porous material is prevented, and the amount of metal active species supported on the exhaust gas purification catalyst is reduced. Will increase.

According to the second aspect of the invention, since ammonia is volatile, Na, which is a metal component, does not remain on the exhaust gas purifying catalyst after the slurry is coated on the carrier. It is possible to prevent a decrease in activity due to the presence.

According to the third aspect of the invention, the viscosity of the slurry is lowered by becoming basic, but the viscosity is retained by the hydrated alumina that is gelled by heating, so that the slurry is easily supported on the carrier. It

[0015]

EXAMPLE A first example of the present invention will be described below.

In producing the exhaust gas purifying catalyst,
First, with respect to a porous material such as γ-alumina or a crystalline metal-containing silicate having micropores, Cu, Mn,
A catalytic agent is formed by supporting an active metal species such as Co or Ni. Next, the catalyst agent is mixed with water and 1 of an acidic binder.
Slurry is formed with the seeded hydrated alumina to form a slurry. At this time, the pH of the slurry is adjusted so that the slurry becomes basic before adding hydrated alumina.
This slurry is coated on a honeycomb carrier made of cordierite or the like.

The metal-containing silicate as the above-mentioned porous material is preferably a zeolite such as ZSM-5, mordenite, but other than this, other alumina silicates and Si
A silicate such as -Tb-O, Si-Mn-O, Si-Nd-O may be used.

Although hydrated alumina is desirable as the acidic binder, other acidic binders such as silica sol may be used.

The method of adjusting the basicity of the slurry is carried out, for example, by adding aqueous ammonia to the slurry. The viscosity of the slurry is lowered by becoming basic, but as a countermeasure against this, the slurry is heated so that the hydrated alumina in the slurry is gelated. When the ammonia water is added, the temperature of the heated slurry is preferably about 50 ° C. or lower in order to suppress the evaporation of ammonia and keep the basicity.

The method for preparing the slurry in a basic manner is, in addition to the addition of ammonia water, an alkali consisting of an organic base compound or a solution of these in a water-soluble solvent such as acetone or alcohol (triethylamine, trimethylamine, etc.). An aqueous solution may be added, or these organic base compounds may be gasified and blown into the slurry. However, as the alkali component used, N
Those that are difficult to decompose by heat such as aOH and KOH, and NaC
A substance such as O ₃ or the like in which a metal content remains even if decomposed by heat is not so preferable.

The pH of the slurry is preferably a value of 8 or more, but may be a basic value of 8 or less.

Next, the operation of this embodiment will be described.
By adjusting the slurry to be basic, it is possible to prevent acidification of the slurry by the acidic binder, so that the elution of metal active species from the catalyst agent is prevented and the amount of metal active species supported on the exhaust gas purification catalyst is reduced. To increase. As a result, the NOx purification performance of the exhaust gas purification catalyst can be improved.

Further, since ammonia used for adjusting the pH of the slurry is volatile, Na, which is a metal component, does not remain on the exhaust gas purifying catalyst after the slurry is coated on the carrier, so that other than the active species. It is possible to prevent a decrease in activity due to the presence of the metal.

Further, the viscosity of the slurry is lowered by becoming basic, but the viscosity of the slurry is maintained by gelling the hydrated alumina in the heated slurry, so that the slurry is easily supported on the carrier. become able to.

Specific examples of the first embodiment will be listed below together with comparative examples, and the operation thereof will be further described.

Comparative Examples 1 to 16 ZSM-5, which is a kind of zeolite, was used as a porous material to prepare a catalyst agent carrying copper by ion exchange.
To 5 g of this catalyst agent and 15 ml of water, 10 wt%, 20 wt% and 3 wt% of hydrated alumina were used as acidic binders, respectively.
0 wt% was added to form three slurries. Also, as a slurry for blank test without adding acidic binder,
A slurry was formed with only 5 g of the above catalyst and 15 ml of water.
Further, the above four kinds of slurries were prepared under various conditions. This preparation was performed when the temperature was kept at room temperature and the stirring time was changed to 30 minutes, 1 hour, and 2 hours, and when the temperature was kept at 50 ° C. and stirring was performed for 2 hours.

Specific Examples 1 to 12 ZSM-5, which is a kind of zeolite, was used as a porous material to prepare a catalyst agent carrying ion-exchanged copper.
To 5 g of this catalyst and 15 ml of water, 1 ml of 28% ammonia water was added, and 10 wt%, 20 wt% and 30 wt% of hydrated alumina were added as an acidic binder to form three kinds of slurries. Further, the above three kinds of slurries were prepared under various conditions. This preparation was performed when the temperature was kept at room temperature and the stirring time was changed to 30 minutes, 1 hour, and 2 hours. Instead of directly adding 1 ml of the ammonia water to the slurry, ammonia gas may be blown into the slurry for 5 minutes.

Comparative Examples 1 to 16 and Concrete Examples 1 to 12
When the ion exchange rate was measured for the catalyst agent after preparation of each slurry, the results shown in Table 1 were obtained. That is, as compared with the blank test of Comparative Examples 13 to 16, the ion exchange rate of the catalyst agent was significantly decreased in Comparative Examples 1 to 12 when hydrated alumina was added. However, the catalyst agents of specific examples 1 to 12 are
Oxidation of the slurry was prevented, and an ion exchange rate similar to that in the blank test could be obtained. It was also found that the ion exchange rate was hardly affected by the amount of hydrated alumina, the stirring time and the temperature of the slurry. The ion exchange rate is calculated from the amount of copper ions bound to the alumina based on the amount of alumina in the zeolite,
The calculation was performed by excluding the aluminum content in the hydrated alumina.

FIG. 1 shows a case where a slurry was formed by using 10 wt% of hydrated alumina (corresponding to Comparative Examples 1 to 4) and a case where ammonia water was further added to form a slurry (Specific Examples 1 to 4). Corresponding to b), the relationship between the temperature and viscosity of the slurry is shown. As can be seen from FIG. 1, when the catalysts were prepared by supporting the slurries of Comparative Examples 1 to 12 and Concrete Examples 1 to 12 on a honeycomb carrier, Comparative Examples 1 to 12 could be easily supported. , Specific Example 1
Regarding Nos. 12 to 12, the viscosity of the slurry was insufficient, and it was difficult to load the slurry on the honeycomb carrier. Therefore, specific examples 1 to
When the slurry of No. 12 was heated to 40 to 50 ° C., the viscosity of the slurry increased and it became possible to carry it. The slurries of Examples 1 to 12 did not increase in viscosity at 40 ° C. or lower, and at 50 ° C. or higher, ammonia was remarkably evaporated and it became difficult to maintain basicity.

Next, Comparative Examples 1 to 12 and Concrete Example 1
NOx for each catalyst loaded with ~ 12 slurries
The purification performance was tested. The test results are shown in Table 1 as the NOx purification rate at the highest active point. The slurry was supported on each catalyst so that the amount of the catalyst agent was the same. Also, the composition of the reaction gas for the test is NOx 20
00ppm, HC 6000ppm, C, O ₂ 8%, CO
Was 0.18%, CO ₂ was 8.4%, and the reaction gas was flowed at a space velocity SV = 25000 h ⁻¹ . As a result, compared with the catalysts of Comparative Examples 1-12, NO of the catalysts of Specific Examples 1-12
x Purification rate has improved significantly.

[0031]

[Table 1]

Comparative Examples 17 to 32 γ-alumina having a high specific surface area was used as the porous material,
This was impregnated with copper to prepare a copper-supported catalyst agent. Three kinds of slurries were formed in the same manner as in Comparative Examples 1 to 12 with respect to 10 g of this catalyst agent and 25 ml of water. As a slurry for blank test, 10 g of the above catalyst agent and 25 ml of water were used.
A slurry was formed by itself. Further, the above four kinds of slurries were prepared under the same conditions as in Comparative Examples 1 to 16.

Specific Examples 13 to 24 γ-alumina having a high specific surface area was used as the porous material,
This was impregnated with copper to prepare a copper-supported catalyst agent. Three kinds of slurries were formed in the same manner as in Examples 1 to 12 with respect to 10 g of this catalyst agent and 25 ml of water. Further, the above three kinds of slurries were prepared under the same conditions as in Comparative Examples 1 to 12.

Comparative Examples 17 to 32 and Concrete Examples 13 to
When the copper supporting rate was measured for each of the 24 catalyst agents after slurry preparation, the results shown in Table 2 were obtained. That is, as compared with the blank test of Comparative Examples 29 to 32, the loading rate of the catalyst agent was significantly reduced in Comparative Examples 17 to 28 when hydrated alumina was added. However, the catalyst agents of specific examples 13 to 24 are
Oxidation of the slurry was prevented, and it was possible to obtain a loading rate similar to that in the blank test. It was also found that the loading rate of the metal active species such as copper was hardly affected by the amount of hydrated alumina, the stirring time and the temperature of the slurry. In addition,
This loading rate was the weight% of copper in the catalyst agent, and was calculated by excluding the aluminum content in the hydrated alumina.

FIG. 2 shows a case where a slurry was formed by using 10 wt% of hydrated alumina (corresponding to Comparative Examples 17 to 20).
And the case where ammonia water is further added to form a slurry (corresponding to specific examples 13 to 16) d, the relationship between the temperature and the viscosity of the slurry is shown. As can be seen from FIG. 2, when the respective catalysts of Comparative Examples 17 to 28 and Concrete Examples 13 to 24 were carried on a honeycomb carrier to make a catalyst, Comparative Examples 17 to 28 could be easily carried. In Examples 13 to 24, the viscosity of the slurry was insufficient, and it was difficult to load the slurry on the honeycomb carrier. Then, when the slurries of specific examples 13 to 24 were heated to 40 to 50 ° C., the viscosity of the slurries increased and it became possible to carry them. In addition, the slurries of Specific Examples 13 to 24 are 40
If the temperature is lower than 0 ° C, the viscosity does not increase, and if the temperature is higher than 50 ° C, the evaporation of ammonia becomes remarkable and it becomes difficult to maintain the basicity.

Next, the NOx purification performances of the catalysts carrying the slurries of Comparative Examples 17 to 28 and Concrete Examples 13 to 24 were tested in the same manner as in Concrete Examples 1 to 12. The results are shown in Table 2 as the NOx purification rate at the highest active point. As shown in Table 2, Comparative Examples 17-28
The NOx purification rates of the catalysts of Concrete Examples 13 to 24 were significantly improved as compared with the catalyst of Example 1.

[0037]

[Table 2]

The second embodiment of the present invention will be described below.

In producing the exhaust gas purifying catalyst,
First, a solution containing at least one metal active species of Cu, Mn, Co, Ni and the like is added to a porous material such as a metal-containing silicate or γ-alumina, and the mixture is stirred to give the metal activity. The seed is supported on the porous material to form a catalytic agent. When the solution of the metal active species and the porous material are stirred, the porous material is degassed. After that, a slurry is formed in the same manner as in the first embodiment, the slurry is prepared, and then the honeycomb carrier is coated.

Next, the operation of this embodiment will be described. In supporting the metal active species on the porous material, by stirring the metal active species solution and the porous material while degassing the porous material, Since the air that has impeded the permeation of the metal active species solution in the pores of the porous material is removed, the metal active species solution permeates into the pores, and the amount of metal active species supported increases. As a result, N of the exhaust gas purification catalyst
Ox purification performance can be improved. Further, since the porous material is pulverized by degassing the porous material, the honeycomb carrier can be easily coated.

Further, as in the first embodiment, by adjusting the slurry to be basic, the elution of metal active species from the catalyst agent is prevented, and the amount of metal active species supported on the exhaust gas purification catalyst is increased. Of the exhaust gas purification catalyst N
Ox purification performance can be improved.

Furthermore, by using ammonia for adjusting the pH of the slurry, since Na, which is a metal component, does not remain on the exhaust gas purifying catalyst, it is possible to prevent a decrease in activity due to the presence of metals other than active species. ..

Moreover, although the viscosity of the slurry is lowered by becoming basic, the hydrated alumina in the heated slurry gels and the viscosity of the slurry is maintained, so that the slurry can be easily supported on the carrier. Like

Specific examples of the second embodiment will be listed below together with comparative examples, and the operation thereof will be further described.

Comparative Examples 33 to 36 Metal active species solutions consisting of Cu, Co, Mn, and Ni acetate solutions were prepared, and the above metal active species solutions were used as stirrers and as specific porous materials as porous materials. A zeolite (ZSM-5) having a ratio was placed in a container under normal pressure, the temperature of the metal active species solution was adjusted to 40 to 90 ° C., and ion exchange was performed for 4 to 48 hours while stirring with a stirrer. Then, the zeolite was taken out, filtered, washed, and dried to obtain a catalyst agent.

Specific Examples 25 to 28 Similar to Comparative Examples 33 to 36, metal active species solutions, stir bars, and zeolites were prepared, and these were placed in a container capable of holding a reduced pressure state, for example, an eggplant type flask. While degassing the inside of this container with a vacuum pump, it was stirred with a stirrer. At the time of this degassing, the pressure inside the container should be 20 mmHg or less,
The temperature of the metal active species solution was maintained at 20 ° C. and degassing was performed for 8 hours or more. During degassing, the metal active species solution was constantly stirred in order to prevent bumping of the metal active species solution. Then, the pressure in the container was returned to normal pressure, and the same operation as in Comparative Examples 33 to 36 was performed to obtain a catalyst agent.

Comparative Examples 33 to 36 and Concrete Examples 25 to
When the ion exchange rate of the metal active species was measured for each of the 28 catalyst agents, the results shown in Table 3 were obtained. As a result, the ion exchange rates of the catalyst agents of Concrete Examples 25 to 28 were significantly improved as compared with the catalyst agents of Comparative Examples 33 to 36.

Further, for each of the catalyst agents of Comparative Examples 33 to 36 and Concrete Examples 25 to 28, NO with respect to exhaust gas was obtained.
x Purification performance tested. The test results are shown in Table 3 as the NOx purification rate at the highest active point. The composition of the reaction gas for the test is NOx 2000ppm, HC
6000 ppm-C, O ₂ 8%, CO 0.18%,
CO ₂ was adjusted to 8.4% and N _{2 was} balanced, and the reaction gas was allowed to flow at a space velocity SV = 25000 h ⁻¹ . As a result, the NOx purification rates of the catalyst agents of Concrete Examples 25 to 28 were significantly improved as compared with the catalyst agents of Comparative Examples 33 to 36.

[0049]

[Table 3]

Comparative Examples 37 to 40 First, preparation was performed to obtain γ-alumina as a porous material. That is, 1 g of a mixed solution of 120 g of aluminum isopropoxide and 108 g of hexylene glycol was added.
The temperature was kept at 20 ° C., and the mixture was stirred for 4 hours using a rotary evaporator. Then, the mixed solution was heated to 85 ° C. and water was added to gel the mixture, and the gel was allowed to stand at 80 ° C. for 16 hours for aging. After this aging, a γ-alumina precursor was obtained by drying under reduced pressure using a rotary evaporator. This γ-alumina precursor was heat-treated at 600 ° C. for 3 hours to obtain γ-alumina as a porous material. Next, Cu, Co, Mn,
Prepare a metal active species solution consisting of Ni acetate solutions,
Each of the metal active species solutions, together with a stir bar and the γ-alumina, was placed in a container under normal pressure, the temperature of the metal active species solution was adjusted to 40 to 90 ° C., and the mixture was stirred with a stirrer for 4 to 48 hours. The γ-alumina was impregnated with the activated species solution. Then, γ-alumina was taken out, filtered, washed, and then dried to obtain a catalyst agent.

Specific Examples 29 to 32 Similar to Comparative Examples 37 to 40, a metal active species solution, a stirrer, and γ-alumina were prepared, and a container capable of holding these under reduced pressure, for example, an eggplant type flask. Then, the inside of this container was stirred with a stirrer while being deaerated with a vacuum pump. During this degassing, the atmospheric pressure in the container was kept at 20 mmHg or less, and the temperature of the metal active species solution was kept at 20 ° C.
Deaerated for more than an hour. During degassing, the metal active species solution was constantly stirred in order to prevent bumping of the metal active species solution. Then, the pressure in the container was returned to normal pressure, and the same operation as in Comparative Examples 37 to 40 was performed to obtain a catalyst agent.

Comparative Examples 37 to 40 and Concrete Examples 29 to
When the ion exchange rate of the metal active species was measured for each of the 32 catalyst agents, the results shown in Table 4 were obtained. As a result, each of the catalyst agents of Concrete Examples 29 to 32 had a significantly improved ion exchange rate as compared with each of the catalyst agents of Comparative Examples 37 to 40.

Further, for each of the catalyst agents of Comparative Examples 37 to 40 and Concrete Examples 29 to 32, the above Comparative Examples 33 to 36 were used.
Similarly, the NOx purification performance was tested. The test results are shown in Table 4 as the NOx purification rate at the highest active point. As a result, as compared with the catalyst agents of Comparative Examples 37 to 40,
The NOx purification rates of the catalyst agents of Concrete Examples 29 to 32 were significantly improved.

[0054]

[Table 4]

[0055]

As described above, according to the method for producing an exhaust gas purifying catalyst of claim 1, the basicity of the slurry prevents the elution of active metal species from the catalyst agent. Since the amount of metal active species carried on the exhaust gas purification catalyst increases, the NOx purification performance of the exhaust gas purification catalyst can be improved.

Further, according to the method for producing an exhaust gas purifying catalyst of claim 2, since the ammonia used for adjusting the pH of the slurry is volatile, Na which is a metal component on the exhaust gas purifying catalyst is used. Does not remain, and a decrease in activity due to the presence of metals other than active species can be prevented.

Further, according to the method for producing an exhaust gas purifying catalyst of claim 2, since the hydrated alumina in the heated slurry gels to maintain the viscosity of the slurry, the slurry can be used as a carrier. It can be easily supported.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the temperature and viscosity of slurry when zeolite is used as a catalyst agent in the method for producing an exhaust gas purifying catalyst of the present invention.

FIG. 2 is a graph showing a relationship between temperature and viscosity of a slurry when γ-alumina is used as a catalyst agent.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location B01J 29/36 A 6750-4G

Claims (3)

[Claims] 1. A method for producing an exhaust gas purifying catalyst, comprising: forming a slurry by slurrying a catalyst agent, which comprises a porous material supporting a metal active species, with an acidic binder, and coating the slurry on a carrier. A method for producing an exhaust gas purifying catalyst, characterized in that the slurry is adjusted to be basic before being coated on a carrier. 2. In adjusting the slurry to be basic,
The method for producing an exhaust gas purifying catalyst according to claim 1, which is carried out by adding aqueous ammonia. 3. The acidic binder is hydrated alumina, and the viscosity of the slurry is adjusted by heating the slurry to gel the hydrated alumina.
A method for producing the exhaust gas purifying catalyst described above.