JP2737189B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalyst for purifying exhaust gas discharged from an internal combustion engine of an automobile, a boiler of a factory, and the like, and a method for producing the catalyst.

[Related Art] In recent years, various methods for purifying harmful components in exhaust gas discharged from internal combustion engines such as industrial plants and automobiles have been studied. Conventionally, there is a method of removing harmful components in exhaust gas by contacting the catalyst with a catalyst. For example, there is an effective method called catalytic reduction method, which uses ammonia, hydrogen,
Alternatively, a reducing agent such as carbon monoxide is required, and a special device for collecting or decomposing the unreacted reducing agent may be required. On the other hand, the catalytic cracking method does not require a special reducing agent and can remove harmful components, particularly nitrogen oxides, in the exhaust gas simply by passing the exhaust gas through the catalyst layer. This is the preferred method. As a catalyst used in this process, there is a crystalline aluminosilicate catalyst having a molar ratio of SiO ₂ / Al ₂ O ₃ containing copper ions of 20 to 100 (JP-A-60-125250).

[Problems to be Solved by the Invention] However, in the catalyst for purifying a crystalline aluminosilicate exhaust gas containing copper ions, there is a problem that the activity is remarkably reduced at a high use temperature. That is, in the case of a crystalline aluminosilicate catalyst containing copper ions, there has been a problem that the crystallinity is significantly reduced by contact with a high-temperature exhaust gas, and as a result, the catalyst activity is significantly reduced.

The present inventors have [Means for Solving the Problems], in order to prevent deterioration of exhaust gas purification activity by contact with the hot exhaust gas of the exhaust gas purifying catalyst is a conventional problem described above, a result of various studies, SiO ₂ / Al ₂ O ₃ molar ratio is
A crystalline aluminosilicate of 20 or more is treated with a water-soluble ammonium salt, and substantially all of the counter ions of Al in the crystalline aluminosilicate are ammonium ions, and thereafter, a pH range of 4 to 12 containing ammonia is used. By carrying out copper ion exchange in a copper salt aqueous solution, a catalyst having high exhaust gas purification activity even after contact with high-temperature exhaust gas has been found, and the present invention has been achieved.

That is, the present invention, Na ₂ O and 0 to 0.2 wt%, copper CuO / Al ₂ O ₃
It contains 0.9 or more in terms of molar ratio, and 0.5 to 1 copper atom.
The exhaust gas purifying catalyst, characterized in that the molar ratio of SiO ₂ / Al ₂ O ₃ containing the above ammonia is a crystalline aluminosilicate of 20 or more, and the molar ratio of SiO ₂ / Al ₂ O ₃ is 20 The present invention relates to a method for producing an exhaust gas purifying catalyst, comprising treating a crystalline aluminosilicate as described above with a water-soluble ammonium salt, and exchanging copper ions in a copper salt aqueous solution containing ammonia in a pH range of 4 to 12.

 Hereinafter, the present invention will be described in detail.

It is essential that the crystalline aluminosilicate used as a substrate of the catalyst in the present invention has a molar ratio of SiO ₂ / Al ₂ O ₃ of 20 or more. When the molar ratio is less than 20, the heat resistance as the object of the present invention is not improved. Further, the molar ratio is preferably 20 or more immediately after the synthesis of the crystalline aluminosilicate,
Further, the manufacturing method is not particularly limited. For example, ZSM-5, mordenite and the like can be used as a base material of the catalyst.

The crystalline aluminosilicate used as a base material of the catalyst in the present invention has almost no activity of purifying exhaust gas.

It is essential that the crystalline aluminosilicate used as the base material of the catalyst in the present invention be treated with a water-soluble ammonium salt. As the water-soluble ammonium salt, an ammonium salt of an organic acid or an inorganic acid, for example, ammonium chloride, ammonium nitrate, ammonium sulfate or ammonia can be used. As a treatment method, a water-soluble ammonium salt is charged into a slurry of a crystalline aluminosilicate. Do or
The crystalline aluminosilicate is introduced into an aqueous solution of a water-soluble ammonium salt, and the solution is heated at room temperature to 80 ° C., preferably at 50 to 70 ° C. for 2 hours.
What is necessary is just to make it contact under stirring for 3 to 3 hours or more.

The concentration of the crystalline aluminosilicate slurry is not particularly limited, but is preferably 10 to 40%. If it is less than 10%, a large volume of solution processing is performed, and the efficiency tends to be deteriorated. If it exceeds 40%, stirring becomes difficult and operability is reduced. The ammonium salt concentration and the ammonium salt aqueous solution concentration in the slurry are preferably 1 mol / L or more. After the treatment, the mixture is separated into solid and liquid, and sufficiently washed with water.

By the above treatment, Na in the crystalline aluminosilicate is changed to Na
It becomes 0.2% by weight or less in terms of ₂ O, and the effect of the present invention can be sufficiently exhibited.

When the cations in the crystalline aluminosilicate are exchanged for copper ions using the production method according to the present invention, it is essential to perform ion exchange using an aqueous solution containing a water-soluble copper salt and ammonia. As the water-soluble copper salt, an organic or inorganic salt, for example, copper sulfate, copper chloride, copper acetate, copper nitrate, etc. can be used. As the ammonia, ammonia water, an aqueous ammonia compound or an aqueous solution in which ammonia gas is dissolved Etc. can be used. It is essential to add ammonia so that the pH in the solution containing the crystalline aluminosilicate is in the range of 4 to 12. If the pH is less than 4,
Since the ion exchange rate is very slow, copper ion exchange does not proceed sufficiently. On the other hand, when the pH exceeds 12, copper as an impurity precipitates, and the exhaust gas purification activity decreases.

The time required for copper ion exchange is about 2 hours or more, and the temperature is preferably room temperature to 50 ° C. If the temperature is too high, the ammonia evaporates and the pH changes.

The concentration of copper ions in the aqueous solution can be arbitrarily set according to the target copper ion exchange rate of the crystalline aluminosilicate. Usually, 0.1 mol / L or more is preferable.

It is essential that the amount of copper contained in the crystalline aluminosilicate by ion exchange be 0.9 or more in terms of CuO expressed as CuO / Al ₂ O ₃ . The reason is that when the copper content is less than 0.9 in CuO / Al ₂ O ₃ , the exhaust gas purification activity is small.

Copper ions are the cations in crystalline aluminosilicates and Cu ions.
⁺ , Cu ²⁺ , [Cu (NH ₃ ) ₄ ] ²⁺ and the like. Some of the cations of the crystalline aluminosilicate are also in NH ₄ ⁺ form.

Further, in the present invention, it is essential to contain 0.5 or more ammonia for 1 copper atom. This is because it is necessary for improving the catalytic activity.

By the above-mentioned preparation method, copper ion exchange rate can be 100% or more as bivalent copper in one ion exchange. After completion of ion exchange, by washing with water and drying, a crystalline aluminosilicate exhaust gas purifying catalyst having high exhaust gas purifying activity even after heat treatment at a high temperature can be obtained.

The catalyst of the present invention can be used after being molded using a binder such as a clay mineral.

Here, NH in the exhaust gas purification catalyst obtained by the present invention
_For the quantitative determination of ₃ , see "Analytical Chemistry Handbook" (Maruzen Co., Ltd.
1971) was determined by the ammonia analysis method and the neutralization titration method. The principle is that crystalline aluminosilicate exhaust gas
OH solution was added and the NH ₃ liberated by distillation, absorbed a certain excess of the standard solution of the acid, excess acid can be determined by back titration with NaOH standard solution.

The reason why the heat resistance of the exhaust gas purifying catalyst using the production method of the present invention is improved is considered to be that almost no Na ion is present in the counter ion of the Al atom in the crystalline aluminosilicate. That is, the atoms constituting the substance are thermally vibrated by the heat energy. This also applies to the atoms that make up a solid. As the temperature rises and the thermal energy increases, the thermal oscillations increase. On the other hand, the cations taken into the crystalline aluminosilicate by ion exchange,
It is only supplemented by the binding force due to electrostatic interaction with Al atoms in the crystal, and easily overcomes the binding force due to the electrostatic interaction due to the increase in thermal vibration due to the increase in thermal energy, It moves freely in the crystal and breaks the bond between Al atom and Si atom. Thus, it is considered that the crystallinity is reduced and the activity is reduced. By treating with a water-soluble ammonium salt, the cations taken into the crystalline aluminosilicate can be made lighter and smaller. It is considered that a catalyst exhibiting high exhaust gas purification activity was obtained even after this.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.
The present invention is not limited to these examples.

Reference Example (Synthesis of Catalyst Substrate) The crystalline aluminosilicate as the substrate of the catalyst used in the present invention was synthesized according to the method described in JP-A-59-54620. It was confirmed by X-ray powder diffraction that the obtained crystalline aluminosilicate was basically the same as the crystalline aluminosilicate disclosed in the publication. The chemical composition of the crystalline aluminosilicate, expressed as a molar ratio of oxides on an anhydrous basis, was:

_{1.08Na 2 O · Al 2 O 3} · 40.3SiO 2 Example 1 (Preparation of the exhaust gas purifying catalyst) The crystalline aluminosilicate obtained in Reference Example was 10 grams collected, Al in the crystalline aluminosilicate 10 for the number of atoms
2mol / L weighed to double the number of ammonium molecules
It was poured into an aqueous ammonium chloride solution and stirred at a liquid temperature of 60 ° C. for 12 hours. After the solid-liquid separation, the mixture was sufficiently washed with water and dried at 100 ° C. for 10 hours. Subsequently, 0.1 mol / l weighed so that the number of copper atoms was equal to the number of Al atoms in the crystalline aluminosilicate.
Pour into aqueous copper acetate solution and stir at room temperature, then immediately
2.5% NH ₃ water was added to adjust the slurry to pH 10.5. Thereafter, the mixture was stirred at room temperature for 12 hours. After the solid-liquid separation, the mixture was sufficiently washed with water and dried at 100 ° C. for 10 hours. Copper ion exchange rate of the exhaust gas purification catalyst determined by chemical analysis, copper content,
Table 1 shows the sodium content. The copper ion exchange rate was determined on the assumption that the copper was exchanged as divalent copper. The ratio of the ammonia in the exhaust gas purification catalyst obtained by the neutralization titration method to the number of copper atoms of 1 is also shown.

Comparative Example 1 (Preparation of Comparative Catalyst 1) 10 g of the crystalline aluminosilicate obtained in Reference Example was collected and weighed so that the number of copper atoms was equal to the number of Al atoms in the crystalline aluminosilicate. The solution was added to the 0.1 mol / l aqueous copper acetate solution, stirred at room temperature, and immediately thereafter, 2.5% aqueous NH ₃ was added to adjust the slurry to pH 10.5. Thereafter, the mixture was stirred at room temperature for 12 hours. After the solid-liquid separation, the mixture was sufficiently washed with water and dried at 100 ° C. for 10 hours. Table 1 shows the copper ion exchange rate, copper content, and sodium content of Comparative Catalyst 1 determined by chemical analysis. The copper ion exchange rate was determined on the assumption that the copper was exchanged as divalent copper. In addition, the value of ammonia in the comparative catalyst determined by the neutralization titration method was determined to be 1
The ratios to are also shown.

Comparative Example 2 (Preparation of Comparative Catalyst 2) 10 g of the crystalline aluminosilicate obtained in Reference Example was sampled and weighed so that the number of copper atoms was equal to the number of Al atoms in the crystalline aluminosilicate. The solution was added to the 0.1 mol / l aqueous copper acetate solution, and stirred at room temperature for 12 hours. After solid-liquid separation, the product was sufficiently washed with water, and this operation was repeated three times, followed by drying at 100 ° C. for 10 hours. Table 1 shows the copper ion exchange rate, copper content, and sodium content of the comparative catalyst determined by chemical analysis. The copper ion exchange rate was determined on the assumption that the copper was exchanged as divalent copper. Ammonia in the comparative catalyst 2 is
Basically it was not included.

Comparative Example 3 (Preparation of Comparative Catalyst 3) 10 g of the crystalline aluminosilicate obtained in Reference Example was collected, and 10 g of the crystalline aluminosilicate was added to the number of Al atoms in the crystalline aluminosilicate.
2mol / L weighed to double the number of ammonium molecules
It was poured into an aqueous ammonium chloride solution and stirred at a liquid temperature of 60 ° C. for 12 hours. After the solid-liquid separation, the mixture was sufficiently washed with water and dried at 100 ° C. for 10 hours. Subsequently, 0.1 mol / l weighed so that the number of copper atoms was equal to the number of Al atoms in the crystalline aluminosilicate.
It was poured into an aqueous solution of copper acetate and stirred at room temperature for 12 hours. After solid-liquid separation, wash thoroughly with water and repeat this operation three times.
Dry at 0 ° C. for 10 hours. Table 1 shows the copper ion exchange rate, copper content, and sodium content of Comparative Catalyst 1 determined by chemical analysis. The copper ion exchange rate was determined on the assumption that the copper was exchanged as divalent copper. Further, the value of ammonia in the comparative catalyst obtained by the neutralization titration method is also shown for the ratio to the number of copper atoms of 1.

Example 2 (Evaluation of heat resistance of exhaust gas purifying catalyst) The exhaust gas purifying catalyst obtained in Example 1 was placed in an electric furnace, heated to 900 ° C. at a rate of 5 ° C./min., And held for 6 hours. did. The power was turned off and the system was left to cool to room temperature. The processing atmosphere was dry air. Heat resistance is powder X
The heat resistance was evaluated from the magnitude of this value, with the ratio of the peak intensity of the same d value as that of the exhaust gas purifying catalyst obtained in Example 1 in the X-ray diffraction pattern obtained by the X-ray diffraction method as crystallinity. Table 2 shows the results.

Comparative Example 4 (Evaluation of heat resistance of Comparative catalyst 1) Comparative catalyst 1 obtained in Comparative example 1 was treated in the same manner as in Example 2, and the heat resistance was the same as that of Comparative catalyst 1 of Comparative example 1. The heat resistance was evaluated from the magnitude of this value, with the strength ratio as the crystallinity. Table 2 shows the results.

Comparative Example 5 (Evaluation of Heat Resistance of Comparative Catalyst 2) Comparative Catalyst 2 obtained in Comparative Example 2 was treated in the same manner as in Example 2, and the heat resistance was the same as that of Comparative Catalyst 2 of Comparative Example 2. The heat resistance was evaluated from the magnitude of this value, with the strength ratio as the crystallinity. Table 2 shows the results.

Comparative Example 6 (Evaluation of Heat Resistance of Comparative Catalyst 3) Comparative Catalyst 3 obtained in Comparative Example 3 was treated in the same manner as in Example 2, and the heat resistance was the same as that of Comparative Catalyst 3 of Comparative Example 3. The heat resistance was evaluated from the magnitude of this value, with the strength ratio as the crystallinity. Table 2 shows the results.

Example 3 (Evaluation of Heat Resistance by Exhaust Gas Purifying Ability 1) 0.65 g of the exhaust gas purifying catalyst prepared in Example 1 was charged into a normal-pressure fixed-bed reaction tube, and the reaction gas having the following composition was passed through (60)
0ml / min.), After pre-treatment at 500 ° C for 0.5 hour,
The temperature was raised to 0 ° C., and the NO purification rate at each temperature was measured (Reaction 1).

Reaction gas composition NO 1000 ppm O ₂ 4% CO 1000 ppm C ₃ H ₆ 500 ppm H ₂ O 4% Subsequently, it was kept at 800 ° C. for 5 hours to perform heat treatment. After cooling, 2
After pretreatment of holding at 00 ° C for 0.5 hour, again at a constant speed of 800 ° C
The NO purification rate was measured at each temperature (reaction 2).

Table 3 shows the evaluation results of the heat resistance based on the change in the NO purification rate in Reaction 1 and Reaction 2 where the harmful component in the reaction gas was NO.
Shown in

 The NO purification rate is represented by the following equation.

NO conversion rate _{(%) = (NO in -NO} out) / NO in × 100 NO in: fixed bed reaction tube inlet NO concentration NO _out: the exhaust gas purification ability of the fixed bed reaction tube outlet NO concentration Comparative Example 7 (Comparative Catalyst 1 Evaluation of heat resistance of Comparative Catalyst 1 obtained in Comparative Example 1 was evaluated by using the same method as in Example 3, and the results are shown in Table 3.

Comparative Example 8 (Evaluation of Heat Resistance Based on Exhaust Gas Purifying Ability of Comparative Catalyst 2) Table 3 shows the results of evaluating the heat resistance of Comparative Catalyst 2 obtained in Comparative Example 2 using the same method as in Example 3.

Comparative Example 9 (Evaluation of Heat Resistance Based on Exhaust Gas Purifying Ability of Comparative Catalyst 3) Table 3 shows the results of evaluating the heat resistance of Comparative Catalyst 3 obtained in Comparative Example 3 using the same method as in Example 3.

Table 3 shows that the crystalline aluminosilicate exhaust gas purifying catalyst using the production method according to the present invention has a lower exhaust gas purifying ability than the comparative catalysts 1, 2 and 3 even when kept at 800 ° C. for 5 hours in the reaction gas. It can be seen that it was suppressed in the high temperature part and the heat resistance was improved.

Example 4 (Evaluation of Heat Resistance 2 by Exhaust Gas Purifying Ability) 0.65 g of the exhaust gas purifying catalyst prepared in Example 1 was filled in a normal-pressure fixed-bed reaction tube, and the reaction gas having the following composition was passed through the reaction tube (60).
0ml / min.), After pre-treatment at 500 ° C for 0.5 hour,
The temperature was raised to 0 ° C., and the NO purification rate at each temperature was measured (Reaction 3).

Reaction gas composition NO 1000 ppm O ₂ 6% CO 1000 ppm C ₃ H ₆ 500 ppm H ₂ O 4% Subsequently, it was kept at 800 ° C. for 5 hours to perform heat treatment. After cooling, 2
After pretreatment of holding at 00 ° C for 0.5 hour, again at a constant speed of 800 ° C
The NO purification rate was measured at each temperature (Reaction 4).

Table 4 shows the results of evaluating the heat resistance by changing the NO purification rate in Reaction 3 and Reaction 4 with NO as the harmful component in the reaction gas.
Shown in

[Effects of the Invention] As described above, according to the present invention, a crystalline aluminosilicate having a molar ratio of SiO ₂ / Al ₂ O ₃ of 20 or more is treated with a water-soluble ammonium salt, and then treated with a pH 4 containing ammonia. by copper ion-exchanged with copper salt aqueous solution in the range 12 to, Na ₂ O
Is 0 to 0.2% by weight, the molar ratio of SiO ₂ / Al ₂ O ₃ containing copper in the CuO / Al ₂ O ₃ molar ratio of 0.9 or more and containing ammonia of 0.5 or more with respect to 1 copper atom is 20. An exhaust gas purifying catalyst comprising the above-mentioned crystalline aluminosilicate can be manufactured, and the catalyst has an effect of maintaining a high exhaust gas purifying activity even after contact with high-temperature exhaust gas.

Claims (2)

(57) [Claims] 1. SiO ₂ / Al containing 0 to 0.2% by weight of Na ₂ O and 0.9 or more of copper in a molar ratio of CuO / Al ₂ O ₃ and containing ammonia of 0.5 or more per 1 copper atom. An exhaust gas purifying catalyst comprising a crystalline aluminosilicate having a molar ratio of ₂ O ₃ of 20 or more. 2. A crystalline aluminosilicate having a molar ratio of SiO ₂ / Al ₂ O ₃ of 20 or more is treated with a water-soluble ammonium salt, and then treated with a copper salt aqueous solution containing ammonia in the pH range of 4 to 12. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the catalyst is subjected to ion exchange.