JP3340169B2 - Manufacturing method of exhaust gas purifying 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 producing an exhaust gas purifying catalyst used for removing nitrogen oxides contained in exhaust gas from automobiles, boilers and the like.

[0002]

_2. Description of the Related Art As a method for removing nitrogen oxides contained in exhaust gas, (1) a selective reduction method using ammonia using a V ₂ O ₅ —TiO ₂ catalyst, and (2) a Pt-Rh / Al ₂ O three-way catalyst method for an automobile consisting of _{3, (3) Pt / Al} 2 O 3, Co 3 O 4, YBa 2 Cu 3 O y
A direct decomposition method using a noble metal catalyst or a metal oxide catalyst is known. However, each of these methods has drawbacks and is never satisfactory. That is, the method (1) uses ammonia, so there are problems in terms of cost and equipment, and (2) and (3)
However, there is a problem that the reaction of removing nitrogen oxides hardly proceeds in the presence of oxygen in excess of the stoichiometric amount.

[0003] For this reason, recently, zeolites containing a copper compound exhibiting relatively high activity even in the presence of excess oxygen have been attracting attention. Examples of the method for producing such a copper compound-containing zeolite catalyst include (a) an ion exchange method utilizing the ion exchange capacity of zeolite, (b) impregnating zeolite with an aqueous solution containing a copper salt, adsorbing, and impregnating the zeolite, c) A precipitation method in which a precipitant is added to an aqueous solution containing a copper salt, and the precipitate is supported on zeolite.

[0004]

An exhaust gas purifying catalyst for removing nitrogen oxides contained in exhaust gas must have high activity and high-temperature durability in the coexistence of oxygen and water vapor. Is required. In this regard, the catalyst obtained by the ion exchange method (a) has disadvantages in that the amount of copper element, which is the main active component, is limited to a low amount, and that copper is not stably supported on zeolite. As a result, copper coagulation occurs when exposed to high temperatures, making it difficult to maintain sufficient activity. In particular, when water vapor is present, the activity tends to further decrease. The catalyst obtained by the impregnation method of (b) is
The stability of supporting copper on zeolite is even lower than that of the ion exchange method, and the dispersibility of copper as an active ingredient is low. Therefore, the catalyst activity and heat resistance are lower than those of the catalyst produced by the ion exchange method. In the deposition method (c), the amount of supported copper is not limited,
Further, there is an advantage that the composite oxide is stably supported on the zeolite. However, the deposition method has limitations in the uniformity and dispersibility of the loaded state of the composite oxide, and further improvement in activity and high-temperature durability cannot be expected.

Accordingly, an object of the present invention is to provide a highly active carrier component which can be supported on a carrier with higher stability, dispersibility, and uniformity than conventional deposition methods, thereby achieving high oxygen and water vapor. An object of the present invention is to provide a production method capable of obtaining an exhaust gas purifying catalyst having high activity for removing nitrogen oxides and having excellent durability at high temperatures even in the coexistence of nitrogen.

[0006]

According to the present invention, in order to solve the above-mentioned problems, the molar ratio of SiO ₂ / Al ₂ O ₃ is 20.
A catalyst for purifying exhaust gas, comprising a zeolite carrier of ~ 200 and a composite oxide of copper and silicon supported on the carrier, wherein the zeolite carrier is added to a solution containing a copper compound and a silicon alkoxide. Adding water in the presence to form a sol, then gelling the sol on the carrier to obtain a gel containing the zeolite carrier, and then calcining the gel. There is provided a method of making a catalyst for use. Hereinafter, the method for producing the exhaust gas purifying catalyst of the present invention will be described in detail.

Active Component The catalyst produced by the production method of the present invention contains a composite oxide of copper and silicon. The catalyst preferably contains 1.0 to 15% by weight, more preferably 2 to 10% by weight, of copper based on the entire catalyst. If the content of copper is too small, the catalytic activity tends to decrease, and if it is too large, the nitrogen oxide removing activity and durability at high temperatures tend to decrease.

The catalyst preferably contains silicon in an amount of 1.0 to 15% by weight, more preferably 2 to 10% by weight, in terms of metal silicon, based on the entire catalyst. If the content of silicon is too small, it is difficult to stably support the composite oxide composed of copper and silicon on the zeolite carrier with a high degree of dispersion, so that it is difficult to obtain sufficient high-temperature durability. On the other hand, if the silicon content is too large, the catalytic activity tends to be significantly reduced.

The composite oxide of copper and silicon in the catalyst is preferably in the range of 2 to 30% by weight, more preferably 4 to 20% by weight, as the total amount of copper and silicon, based on the whole catalyst. The weight ratio of Cu / Si in the composite oxide is expressed in terms of metal.
It is preferably from 0.1 to 5, more preferably from 0.2 to 3.

Carrier In the production method of the present invention, SiO ₂ / Al ₂ O ₃
Zeolites having a molar ratio of 20 to 200, preferably 30 to 80, are used. If the SiO ₂ / Al ₂ O ₃ molar ratio is less than 20, it is difficult to obtain sufficient activity and sufficient high-temperature durability, and SiO ₂ / Al ₂ O ₃
If the molar ratio exceeds 200, the catalytic activity decreases. Any zeolite can be used as long as the above conditions are satisfied. For example, synthesized according to U.S. Patent No. 3702886
ZSM-5, ZSM-1 synthesized according to U.S. Pat.
1, mordenite (trade name: TSZ-640NAA, manufactured by Tosoh Corporation), ferrierite (trade name: TSZ-720KOA, manufactured by Tosoh Corporation) and Y-type zeolite (trade name: TSZ-360HUA, manufactured by Tosoh Corporation) And preferably a ZSM-5 type zeolite.

Formation of Sol In the production method of the present invention, first, water is added to a solution containing a copper compound and a silicon alkoxide in the presence of the zeolite carrier. In this step, the silicon alkoxide and the copper compound undergo hydrolysis, and a sol composed of the composite hydrate containing the zeolite carrier dispersed therein is generated.

The copper compound used in this step includes
As long as it is soluble in the below-mentioned organic solvent used, it can be used without any particular limitation, and examples thereof include copper chloride, copper nitrate, copper sulfate and copper acetate, and preferably copper chloride and copper nitrate. Examples of the silicon alkoxide include silicon tetramethoxide, silicon tetraethoxide, silicon tetrabutoxide, silicon tetraisopropoxide and the like. Preferably, they are silicon tetraethoxide and silicon tetraisopropoxide.

As the organic solvent of the solution containing the copper compound and the silicon alkoxide, alcohols are preferable, and examples thereof include ethanol, hexylene glycol, butanediol, triethanolamine, ethylene glycol and pentanediol. Among them, ethylene glycol and pentanediol are preferred. The solution containing the copper compound and the silicon alkoxide is preferably 0.5 to 2 times the weight of the zeolite carrier, more preferably 0.8 to 2 times.
1.5 times the weight. Preparation of the catalyst becomes difficult if the solution is too small or too large. The concentration of the copper compound in the solution is 5
-30% by weight, more preferably 8-20% by weight. The concentration of silicon alkoxide in the solution is 10
It is preferably from 50 to 50% by weight, more preferably from 15 to 40% by weight.

The method of adding water to the solution containing the copper compound and the silicon alkoxide in the presence of the zeolite carrier is not particularly limited. For example, a method in which an alcohol solution of a copper compound and a silicon alkoxide are mixed with a zeolite carrier, and then water is added to the mixed solution.
At this time, if necessary, the silicon alkoxide may be dissolved in a suitable solvent (usually, the alcohols exemplified above are preferable). Alternatively, the carrier zeolite may be added and dispersed in an alcohol solution of a copper compound, and then silicon alkoxide may be added as it is or as a solution, and then water may be added. Various other variations are possible, and the embodiment is not limited at all.

The solution containing the copper compound and the silicon alkoxide is preferably heated in an inert gas atmosphere such as anhydrous nitrogen in order to obtain a uniform mixed solution. The heating temperature may be about 40 to 90 ° C., and may be about 1 to 3 hours. Without heating, a uniform composite oxide may not be obtained even by hydrolysis. In addition, if the atmosphere at the time of the heat treatment is not anhydrous, the silicon alkoxide is hydrolyzed at the stage of this treatment. Furthermore, the presence of oxygen in the atmosphere can cause an explosion.

Gelation of sol Next, the obtained sol containing the zeolite carrier in a dispersed state is gelled. This gelling usually requires only continuous stirring of the sol. Depending on the conditions, the formation and gelation of the sol occur rapidly and continuously, and it may be difficult to clearly distinguish the two steps.

[0017] By firing the firing thus obtained gel catalyst to obtain the objective. The sintering temperature may be usually from 400 to 600 ° C. Usually, it is preferable to perform calcination after drying the gel. Drying may be performed, for example, by heating at about 70 to 150 ° C.
Thus, the shape of the catalyst obtained by the production method of the present invention,
The form is not particularly limited, and can be used in various shapes and forms. A preferred example is a form in which a binder such as silica or alumina is used to coat a suitable refractory substrate, for example, a monolith substrate made of cordierite or stainless steel.

The exhaust gas purifying catalyst obtained by the production method of the present invention is highly active in removing nitrogen oxides and has excellent high-temperature durability even in the presence of oxygen and water vapor. Is effective in removing nitrogen oxides contained in exhaust gas in which oxygen and water vapor coexist.

[0019]

【Example】

(Preparation of catalyst) Example 1 50 g of zeolite (ZSM-5) having a molar ratio of SiO ₂ / Al ₂ O ₃ of about 50 was dispersed in a solution prepared by dissolving 6.2 g of copper (II) chloride dihydrate in 50 g of ethylene glycol. And heated to 80 ° C. in N ₂ . 16.7 g of silicon tetraethoxide was added dropwise to this solution, and the mixture was heated at 80 ° C. for 2 hours. Then, 14.4 g of distilled water, 10 times the mol of silicon tetraethoxide, was added dropwise and heated at 80 ° C. for 2 hours to obtain a product. Was. After cooling, the product obtained is dried in a vacuum oven at 120
Dry at 24 ° C. for 24 hours. After pulverizing the obtained product, it was calcined in an electric furnace at 540 ° C. for 4 hours to obtain a desired catalyst A-1. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

Example 2 Example 2 was repeated except that 50 g of zeolite (ZSM-5) having a molar ratio of about 40 was used instead of zeolite (ZSM-5) having a molar ratio of SiO ₂ / Al ₂ O ₃ of about 50. In the same manner as in 1, the desired catalyst A-2 was obtained. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

Example 3 Example ₂ was repeated except that 50 g of zeolite (ZSM-5) having a molar ratio of about 80 was used instead of zeolite (ZSM-5) having a molar ratio of SiO ₂ / Al ₂ O ₃ of about 50. In the same manner as in 1, the desired catalyst A-3 was obtained. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

Example 4 The procedure of Example 1 was repeated except that a solution containing 4.4 g of copper (II) nitrate trihydrate, 40 g of hexylene glycol and 33.4 g of silicon tetrabutoxide was used as a solution for dispersing the zeolite. Thus, the desired catalyst A-4 was obtained. The supported components of the obtained catalyst were Cu2.2% by weight and Si9.2% by weight.

Example 5 Example 1 was repeated except that a solution containing 13.1 g of copper (II) nitrate trihydrate, 80 g of butanediol and 16.7 g of silicon tetraisopropoxide was used as a solution for dispersing the zeolite. Similarly, the desired catalyst A-5 was obtained. The supported components of the obtained catalyst were Cu 6.9% by weight and Si 4.6% by weight.

Example 6 Example 1 was repeated except that a solution containing 6.2 g of copper (II) chloride, 50.0 g of triethanolamine and 16.7 g of silicon tetraethoxide was used as a solution for dispersing the zeolite. In the same manner as described above, the desired catalyst A-6 was obtained. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

Comparative Example 1 50 g of ZSM-5 type zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of about 50
Is dispersed in 2 L of an aqueous solution containing 20 g of copper acetate (I) monohydrate, stirred at 50 ° C for 5 hours, ion-exchanged with copper, filtered, washed, and dried in a dryer at 120 ° C for 24 hours. Dried. The obtained product was pulverized and then calcined in an electric furnace at 540 ° C. for 4 hours to obtain a desired catalyst B-1. The supported component of the obtained catalyst is
Cu was 3.5% by weight.

Comparative Example 2 50 g of ZSM-5 type zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of about 50
Was dispersed in 2 L of an aqueous solution containing 8.7 g of copper (II) nitrate trihydrate, and while stirring, an aqueous solution containing 2.5% by weight of ammonia was added dropwise little by little, and the pH was adjusted to 7, followed by filtration and washing. And dried in a dryer at 120 ° C. for 24 hours. After pulverizing the obtained product, it was calcined in an electric furnace at 540 ° C. for 4 hours to obtain a desired catalyst B-2. The supported component of the obtained catalyst was 4.6% by weight of Cu.

Comparative Example 3 The same as Comparative Example 2 except that an aqueous solution containing 8.7 g of copper (II) nitrate and 24.0 g of colloidal silica (SiO ₂ 20%) was used as an aqueous solution for dispersing the zeolite. Thus, the desired catalyst B-3 was obtained. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

Comparative Example 4 50 g of ZSM-5 type zeolite having a SiO ₂ / Al ₂ O ₃ molar ratio of about 50
8.7 g of copper (II) nitrate trihydrate and colloidal silica (SiO ₂ 20
%) Was dispersed in 2 L of an aqueous solution containing 24.0 g, and evaporated to dryness with stirring, followed by drying in a drier at 120 ° C. for 24 hours. After pulverizing the obtained product, it was calcined in an electric furnace at 540 ° C. for 4 hours to obtain a desired catalyst B-4. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

Comparative Example 5 The procedure of Example 1 was repeated except that 50 g of a zeolite (ZSM-5) having a molar ratio of about 15 was used instead of zeolite (ZSM-5) having a molar ratio of about 50 SiO ₂ / Al ₂ O _3. In the same manner as in 1, the desired catalyst B-5 was obtained. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

Comparative Example 6 The procedure of Example 1 was repeated except that 50 g of zeolite (ZSM-5) having a molar ratio of about 500 was used instead of zeolite (ZSM-5) having a molar ratio of about 50 SiO ₂ / Al ₂ O _3. In the same manner as in 1, the desired catalyst B-6 was obtained. The supported components of the obtained catalyst were 4.6% by weight of Cu and 4.6% by weight of Si.

(Evaluation of catalyst) Catalysts A-1 to 6 and catalysts B-1 to 6 obtained in Examples 1 to 6 and Comparative Examples 1 to 6 above.
Was wet-ground with a ball mill together with a mixed solution of colloidal silica and distilled water to obtain a slurry. A commercially available cordierite-based 400-mesh honeycomb carrier (1 inch in diameter, 1.5 inch in length) is immersed in the slurry, taken out, and then the excess slurry is removed with an air knife so that the catalyst amount becomes 100 g / liter. It was adjusted. Next, after drying and firing, a honeycomb supported catalyst was obtained.

(A) Evaluation of Catalytic Activity The honeycomb-supported catalyst was evaluated for nitrogen oxide removal performance in a test gas having the following composition under the following evaluation test conditions. That is, the catalytic activity was evaluated by measuring the conversion of nitrogen oxides to N ₂ .

(1) Gas composition NO 1,200 (ppm) O ₂ 3.2 (%) CO 3,000 (ppm) C ₃ H ₆ 1,600 (ppm) H ₂ 1,000 (ppm) CO ₂ 10.0 (%) H ₂ O 10.0 (% ) N ₂ balance (2) Space velocity SV 100,000 (hr ^-1 ) (3) Reaction temperature 400 ℃ and 500
° C

(B) Evaluation of high-temperature durability After the honeycomb-supported catalyst was subjected to aging treatment at 700 ° C. for 5 hours in air containing 10% steam, the catalytic activity was measured in the same manner as above. Table 1 shows the results.

[0035]

[Table 1]

As is clear from Table 1, the catalyst produced by the production method of the present invention has a higher nitrogen oxide content than the catalyst produced by the conventional production method in which copper or the like is supported on zeolite by ion exchange, impregnation or deposition. It can be seen that the removal performance and the durability at high temperatures are excellent. In addition, zeolite carrier Si
If the O ₂ / Al ₂ O ₃ molar ratio is not in the range of 20 to 200, neither the nitrogen oxide removal performance nor the high-temperature durability is sufficient.

[0037]

As described above, according to the production method of the present invention, the composite oxide of copper and silicon has higher stability,
Since the catalyst is supported in a highly dispersed state and more uniformly, a catalyst having higher activity for removing nitrogen oxides than conventional catalysts for purifying exhaust gas and having excellent durability at high temperatures can be produced. In addition, a catalyst exhibiting such an excellent effect even in the coexistence of oxygen and steam can be obtained.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 21/00-37/36 B01D 53/86

Claims (1)

(57) [Claims] 1. A method for producing an exhaust gas purifying catalyst comprising a zeolite carrier having a SiO ₂ / Al ₂ O ₃ molar ratio of 20 to 200 and a composite oxide of copper and silicon supported on the carrier. Then, water is added to the solution containing the copper compound and the silicon alkoxide in the presence of the zeolite carrier to form a sol, and then the sol on the carrier is gelled to obtain a gel containing the zeolite carrier. Next, a method for producing the exhaust gas purifying catalyst, comprising a step of firing the gel.