JP3300062B2 - Method for producing metal-containing silicate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a metal-containing silicate applied to a catalyst.

[0002]

2. Description of the Related Art As a catalyst for purifying exhaust gas of an engine,
Oxidation of CO (carbon monoxide) and HC (hydrocarbon) and N
Three-way catalysts that simultaneously reduce Ox (nitrogen oxide) are known. As a three-way catalyst, a catalyst in which Pt (platinum), Pd (palladium), and Rh (rhodium) are supported on γ-alumina is known, and the air-fuel ratio (A /
When F) is around 14.7, which is the stoichiometric air-fuel ratio, high purification efficiency is obtained.

[0003] Among the exhaust gases of the above engines, NOx
Due to the great potential for adverse effects on human bodies and ecosystems, their release into the atmosphere must be minimized. There are several methods for preventing the emission, but in the case of a mobile engine, it is practical to purify the exhaust gas with a catalyst installed in the engine exhaust system.

On the other hand, in the field of automobiles, lean burn engines, so-called lean burn engines, have been put to practical use in order to comply with fuel regulations for engines. But,
In the case of the lean burn engine, since the exhaust gas is in an oxygen-rich atmosphere due to a high air-fuel ratio, CO and HC can be oxidized and purified by the above three-way catalyst, but NOx Reduction purification cannot be performed.

[0005] Therefore, even in an atmosphere in which the exhaust gas has a high oxygen concentration, NOx can be directly or directly reduced by a reducing agent (for example, C
As a catalyst that can be catalytically decomposed into N ₂ and O ₂ by the presence of O, HC, etc., a catalyst made of zeolite carrying a transition metal by, for example, ion exchange is considered to be promising.

[0006] The active species supporting base material for supporting noble metals, such as Cu in transition metals, as an active species, contains not only zeolite but also other metals instead of or in addition to aluminum in zeolite in such a catalyst. It is also possible to use a metal-containing silicate as a supporting base material.

[0007] Most of the metal-containing silicates applied to the exhaust gas purifying catalyst are synthetic products, and the synthesizing method is described in, for example, Japanese Patent Application Laid-Open No. Sho 64-15142. It is synthesized using, as a precursor, a gel having a silica source such as glass and a required metal salt as essential components. That is, the gel as the precursor is charged into a container and charged in an autoclave, and becomes a crystalline metal-containing silicate having fine pores by a hydrothermal reaction.

[0008]

DISCLOSURE OF THE INVENTION The present inventor has sought to obtain a metal-containing silicate having an aptitude such that excellent NOx purification characteristics can be exhibited by supporting a metal active species. We worked diligently on the manufacturing method. As a result, it is needless to say that the above-mentioned metal-containing silicate is characterized by a catalyst structure after the active species is supported by a unique structure based on the crystal structure and the contained metal species, but the metal-containing silicate having the same structure is used. Even when the same metal is supported on the silicate by the same process as the active species to form the catalyst, there is a remarkable difference in the performance of the finally obtained catalyst, especially the performance of the catalyst after heating. We noticed that there is a problem that
Then, various experiments were conducted on the step of obtaining the metal-containing silicate by the hydrothermal synthesis method, and depending on the form of the gel as the precursor to be subjected to the hydrothermal synthesis, the difference in the behavior of crystallization at the stage of the progress of the synthesis was different. Found that it is happening.

That is, the gel charged in the autoclave vessel in which the hydrothermal synthesis is carried out contains a large amount of air (O ₂ ) by vigorous stirring under the atmosphere received during the gel synthesis, and is dispersed and held in the gel. I have. Therefore, the effect received from the atmosphere in which the hydrothermal reaction takes place at the stage of crystallization of the gel differs depending on the amount of air entrained and retained in the gel. Then, it was found that the difference in suitability of the metal-containing silicate caused by this difference affects the performance of the final catalyst as described above.

[0010] In view of the above, the present invention provides a catalyst which is capable of stably obtaining excellent catalytic performance when the catalyst is constituted by carrying an active species and even after the catalyst is heated. It is another object of the present invention to obtain a metal-containing silicate as an active species supporting base material.

[0011]

Means for Solving the Problems and Action Thereof The present inventor has proposed a catalyst having excellent exhaust gas purification characteristics by carrying active species when the air entrained in the gel is removed as much as possible. It has been confirmed that a metal-containing silicate having the suitability to be able to be constituted can be obtained, and the present invention has been completed.

[0012] Therefore, in order to achieve the above object, a solution taken by the first aspect of the present invention is directed to a method for producing a crystalline metal-containing silicate. The method includes a step of obtaining a hydrated gel, a step of degassing the hydrated gel, and a step of crystallizing the dehydrated gel by a hydrothermal reaction.

[0013] The invention of claim 2 is to determine the degree of degassing of the gel so that a metal-containing silicate having better suitability as an active species-supporting matrix can be obtained. In the constitution of claim 1, the dehydration step of the hydrated gel is such that the hydrated gel has a degree of vacuum of 200 to
This is a configuration performed by maintaining an atmosphere of 10 mmHg.

According to the first and second aspects of the present invention, when the gel as the precursor of the metal-containing silicate is degassed in the above range, the metal-containing silicate having the required suitability can be obtained as follows. It is thought to be based on such an effect.

That is, the gel body is obtained by mixing a plurality of gel-forming composition liquids and performing a gelling reaction with vigorous stirring. Since this gelling reaction is performed in the air for the benefit of the above stirring and the like, it is inevitable that a large amount of air (O ₂ ) is entrained in the gel and is dispersed and held. Therefore, even if an attempt is made to replace the atmosphere in the autoclave with nitrogen in the hydrothermal synthesis for crystallizing the gel, a large amount of O ₂ is held in the gel and complete O ₂ -N ₂ substitution cannot be performed. The nitrogen substitution is meaningless.

Such a large amount of residual O ₂ in the gel is a factor that hinders crystal growth when the gel is crystallized to become a metal-containing silicate. In other words, in addition to leading to each silicon in gel fraction and aluminum content and the required O ₂ react to form a crystal structure of the metal-containing silicate (zeolite), O ₂ is proper that a large amount embracing gel It behaves like O ₂ exceeding the amount of oxygen and producing SiO ₂ , Al ₂ O _3, etc. which do not contribute to the crystal structure. As a result, in the metal-containing silicate obtained by hydrothermal synthesis, the growth of homogeneous crystals having a proper arrangement is inhibited, and the suitability when applied to a catalyst is reduced.

However, according to the first and second aspects of the present invention, the gel as a precursor of the metal-containing silicate is degassed and subjected to hydrothermal synthesis. Be eliminated. Therefore, when the crystal growth of the metal-containing silicate proceeds ideally, and when the catalyst is formed, particularly, even after the catalyst is heated, the characteristic that the excellent NOx purification characteristics are exhibited is improved by the hydrothermal reaction. It is applied to the metal-containing silicate obtained by the above.

In the method for producing a metal-containing silicate according to the present invention, the degree of deaeration of the gel is, for example, 500 mm.
If the degree of degassing is low enough to be performed in an atmosphere of about Hg, after forming the catalyst by supporting the active species, particularly, it is possible to remove NOx effectively after heating the catalyst. Are not synthesized. In addition, when the gel is degassed in an atmosphere of, for example, 5 mmHg, water in the gel evaporates remarkably, and bumping easily occurs, so that a stable degassing state of the gel cannot be obtained.

Therefore, the gel was degassed at a vacuum of 300
In the range of 10 to 10 mmHg, preferably in a vacuum of 200 to 10
It is desirable to carry out in an atmosphere in the range of mmHg.

[0020]

Embodiments of the present invention will be described below.

-Synthesis of precursor gel of metal-containing silicate- First liquid and second liquid as each mixed component as shown in Table 1.
A liquid and a third liquid were prepared. In Table 1, TP
AB is an abbreviation for tetra-N-propylene ammonium bromide, and the TPAB serves as a template for hydrothermal synthesis of metal-containing silicate.

[0022]

[Table 1]

The mixing amount (g) of the metal salt of the first liquid indicated by Note 1 in Table 1 and the mixing amount (g) of the water glass of the second liquid indicated by Note 2 are each adjusted to an appropriate amount. By selection, the first to third liquids are hydrated and synthesized into a gel, which is further crystallization by a hydrothermal reaction as described in detail below. The ratio of each oxide of Si and other contained metal species can be determined.

The mixing amount (g) of the TPAB of the second liquid shown in Note 3 is the amount of the hydrated gel when the hydrated gel is crystallized into a metal-containing silicate by the following hydrothermal synthesis.
5, which can be determined in relation to a crystal structure such as a mordenite type.

First, the first liquid and the second liquid were dropped into the third liquid over about 6 minutes while cooling the third liquid with ice and stirring vigorously. At this time, the pH of the solution being mixed is 9-11.
NaOH aqueous solution or sulfuric acid aqueous solution was appropriately added so as to be able to be maintained at a pH of 0.1 to 1 μm. After the first and second liquids were added dropwise to the third liquid, stirring was continued for about 2 minutes to obtain a hydrated gel as a precursor of the metal-containing silicate.

As far as the composition of the above hydrated gel is concerned,
It is almost the same as the composition of the gel used in the conventional production method.

In the synthesis of this hydrated gel, if aluminum sulfate is used as the metal salt in the first liquid, zeolite Z
This is the starting composition for synthesizing SM-5. By using metal sulfate other than aluminum alone or aluminum sulfate and other metal sulfate as the metal salt,
Pentasil-type metal-containing silicates can also be synthesized. Other metal species include B, Ga, Mn, Fe, N
Base metals such as i, Co, V, W, Sn, Pb, Zn, and P
Noble metals such as t, Pd, Rh, and Ir can be used. Further, the ratio of silica to metal oxide (Caban ratio in the case of zeolite) can be freely set between 15 and 2,000 depending on the amount of these contained metal species. In particular, the metal-containing silicate set so that the SiO ₂ / metal oxide ratio is 15 to ₂₀₀ can be used for NOx after supporting the active species.
The purification characteristics are improved.

In this example, TPAB was used as a template. However, by using a composition other than TPAB, the obtained metal-containing silicate can have various crystal structures.

-Degassing of Gel-The gel obtained by the above synthesis was transferred to a pressure-resistant container, and the gel in the pressure-resistant container was degassed by suction with a vacuum pump.

At this time, when the degree of deaeration is low (the pressure in the pressure vessel is high) as described above, the intended effect of deaeration cannot be obtained, and the degree of deaeration is too high (in the pressure vessel). When the pressure is too low), the evaporation of the water in the gel becomes remarkable, and in any case, it is not preferable. Therefore, it is efficient that the deaeration at this stage is performed within a vacuum range of 200 to 10 mmHg.

Therefore, the deaeration in this embodiment was performed at a degree of vacuum in which the inside of the pressure vessel was maintained at an atmosphere of 20 mmHg, and degassing was performed at this degree of vacuum for one hour. This deaeration time is 30
The range from minutes to about 2 hours was appropriate. If the degree of deaeration was high (if the pressure in the pressure vessel was low), the deaeration time could be shortened accordingly.

During degassing, the gel is appropriately stirred so as not to be bumped, and the temperature of the gel is lowered with a decrease in the pressure in the pressure vessel. The container was kept warm.

In this embodiment, the gel was deaerated by transferring the gel to a pressure-resistant container for deaeration after the synthesis of the gel. However, as a modification of the embodiment, the gel charged in the container loaded in the autoclave was used. Alternatively, a means for performing a deaeration operation may be used. In any case, the degassing of the gel may be performed before the hydrothermal synthesis.

-Hydrothermal synthesis- The degassed gel is charged in an appropriate amount in a container capable of being loaded in an autoclave, loaded in the autoclave, and water is poured between the outer wall surface of the container and the inner wall surface of the autoclave, The autoclave was sealed in a state where the gel body could be stirred by a stirring device attached to the autoclave.

Next, the atmosphere in the autoclave was replaced with nitrogen, so that the partial pressure of nitrogen became 3 kgf / cm ² . The autoclave was heated while stirring the gel, and the internal temperature was raised to 160 ° C. in 160 minutes, and then to 200 ° C. in 800 minutes to perform hydrothermal synthesis.

After cooling to room temperature, the crystal product was taken out and washed with pure water. After washing, drying and firing at 600 ° C. for 3 hours, a metal-containing silicate (zeolite) according to the method of the present invention was produced.

-Evaluation of properties of metal-containing silicate- Evaluation of presence or absence of degassing The metal-containing silicate produced as described above
0 g was weighed, and 69 g of copper acetate and 3 liters of water were added thereto, followed by stirring at 8 ° C. for 8 hours at 50 ° C. to exchange Cu ions. After cooling to room temperature, filtration and washing were performed to prepare a Cu ion exchanged zeolite catalyst having an ion exchange rate of about 100%. This catalyst is referred to as an example catalyst.

The ion-exchange species are Co, Co,
It goes without saying that Ni, Pt, Pd, Rh, Ir and the like can be appropriately supported as catalytically active species.

On the other hand, a gel having the same composition as the above-mentioned precursor gel is converted into zeolite obtained by hydrothermal synthesis according to a conventional method (without degassing the gel and using the same amount as in the above example). The catalyst was prepared by performing Cu ion exchange by the same means as in the preparation of the catalyst of the above example. This catalyst is referred to as a conventional catalyst.

The catalyst of the above example and the catalyst of the prior art were replaced with O ₂ :
10%, H ₂ O: 10%, He: 60 in the remaining atmosphere
Each was heated at 0 ° C. × 8 hours. The NOx purification characteristics of the example catalyst after heating and the conventional example catalyst were evaluated by a model gas evaluation device, and the results are shown in FIG. The composition of the model gas was NOx: 2000 ppm,
CO: 0.18%, HC: 6000 ppm C, CO ₂ :
8.4%, O ₂ : 8.0%, N ₂ : balance, S
V was set to 90000h ^-1 .

According to the results shown in FIG. 1, when the metal-containing silicate produced by the method of the present invention is formed into a catalyst by carrying an active species, it exhibits excellent NOx even after heating. It is clear that the resulting catalyst has purification properties.

Evaluation by Degree of Deaeration Next, the gel was degassed so as to have various deaeration degrees as shown in Table 2, and the gel was subjected to hydrothermal synthesis.

[0043]

[Table 2]

That is, each metal-containing silicate obtained by performing hydrothermal synthesis on a gel degassed to have a degassing degree as shown in Table 2 carries active species (Cu ion exchange). At the very least, a NOx purification catalyst is constituted, and further heated (for example, O ₂ : 10%, H ₂
O: 10%, He: 600 ° C. × 8 hours in the remaining atmosphere)
did. Thereafter, a model gas of SV = 90000h ^-1 (for example, NOx: 2000 ppm, CO: 0.18
%, HC: 6000 ppm C, CO ₂ : 8.4%,
O ₂ : 8.0%, N ₂ : balance of composition)
x The purification rate was evaluated. The evaluation results were as shown in Table 2 above.

From the results of this evaluation, the metal-containing silicate obtained by degassing the gel as a precursor of the metal-containing silicate at a certain degree of vacuum and subjecting the gel to hydrothermal synthesis has the active species supported thereon. As a result, when the catalyst is constituted, it has been confirmed that the catalyst has an appropriate property of exhibiting excellent NOx purification characteristics in a relatively low temperature range.

Evaluation based on length of degassing time The suitability of the metal-containing silicate obtained by subjecting the degassed gel to hydrothermal synthesis to be applied to the catalyst is the same as the degree of vacuum when degassing the gel. Then, it was evaluated how it was affected by the length of the degassing time.

That is, the atmosphere for degassing the gel was set to a vacuum degree of 2.
The degassing time under this degree of vacuum was maintained at 0 mmHg as shown in Table 3, and each metal-containing silicate was hydrothermally synthesized using each gel degassed under these conditions.

Each metal-containing silicate was formed in each catalyst in the same manner as in the case of the evaluation based on the degree of degassing, and the NOx purification characteristics of each catalyst were measured. Table 3 shows the measurement results.

[0049]

[Table 3]

When the relationship between the NOx purification characteristics and the deaeration time is evaluated based on the results shown in Table 3, the longer the deaeration time, the better the low-temperature activity, but there is a tendency that the activity is saturated at a certain level. Therefore, from the viewpoint of working efficiency, it is determined that it is advantageous to set the gel degassing time in the range of 30 minutes to 2 hours.

[0051]

As described above, according to the method for producing a metal-containing silicate according to the first aspect of the present invention, the gel as the precursor of the metal-containing silicate is mixed with the air mixed into the gel by stirring during the synthesis. Is degassed before being subjected to hydrothermal synthesis, so that the crystal growth in the hydrothermal synthesis is not hindered by air (O ₂ ), and crystal growth is ideally performed. A metal-containing silicate having good suitability as an active species-supporting base material can be obtained.

According to the second aspect of the present invention, the degassing of the gel is performed in an atmosphere having a degree of vacuum of 200 to 10 mmHg, so that the gel is used as a catalyst in a metal-containing silicate obtained by hydrothermal synthesis. Good suitability is ensured.

[Brief description of the drawings]

FIG. 1 is a graph showing the NOx purification characteristics of a catalyst in an example according to the present invention.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Makoto Kyogoku 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (56) References JP-A-3-37111 (JP, A) JP-A-1 -172206 (JP, A) JP-A-64-5905 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 39/00-39/54 B01J 29/00 B01D 53/86 , 53/94 B01J 20/00 JICST file (JOIS) WPI / L (QUESTEL)

Claims (2)

(57) [Claims] 1. A process for producing a crystalline metal-containing silicate, comprising the steps of: mixing and stirring the raw materials of the metal-containing silicate to obtain a hydrated gel; degassing the hydrated gel; Crystallizing the air-hydrated hydrated gel by a hydrothermal reaction. 2. The method for producing a metal-containing silicate according to claim 1, wherein the dehydration step of the hydrated gel is performed by maintaining the hydrated gel in an atmosphere having a degree of vacuum of 200 to 10 mmHg.