JP2002001119A - Method for manufacturing catalyst for purification of exhaust gas and catalyst for purification of exhaust gas manufactured by that method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a catalyst for purification of exhaust gas such that noble metals can be quickly adsorbed and deposited even when a pellet carrier or ceramic-coated honeycomb carrier is used. SOLUTION: In the method for manufacturing a catalyst for purification exhaust gas, one or more kinds of noble metal salts are mixed with water, a mixture solvent of water and organic solvent or a solvent consisting of organic solvent, and a protecting agent, the mixture solution is refluxed to reduce the noble metal salts in the solution to prepare a colloid solution with suspension of noble metal particles, and the colloid solution is adsorbed to a carrier consisting of a porous material. In this method, the colloid solution to be adsorbed contains a quaternary ammonium salt mixed as the protecting agent. The protecting agent is preferably a quaternary ammonium salt having at least one alkyl group having 1 to 4 carbon atoms and a quaternary ammonium salt containing sulfur or chlorine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst used for purifying exhaust gas, and more particularly to a method for producing an exhaust gas purifying catalyst for an automobile and a catalyst obtained by the method.

[0002]

2. Description of the Related Art In recent years, NOx storage reduction type catalysts have been widely used as catalysts for purifying lean burn automobile exhaust gas. This NOx storage reduction type catalyst is coated with noble metal particles having catalytic activity such as platinum and palladium, and carbonates of alkaline earth metals such as barium, and pellets of alumina or zirconia, or honeycomb molded bodies or ceramics. Supported on a carrier such as a metal honeycomb formed of a porous material. In this NOx storage reduction catalyst, the noble metal particles act as a catalyst component for accelerating the decomposition of NOx, while the alkaline earth metal has a role as a NOx storage agent, and it is difficult to decompose NOx. In an oxidizing atmosphere, NOx is stored in the form of nitrate, and when the atmosphere is changed to a reducing atmosphere in which NOx can be easily decomposed, the stored NOx is released so as to be immediately decomposed.

[0003] Such NOx storage catalysts are conventionally manufactured by adsorbing an aqueous solution of a noble metal salt (for example, an aqueous solution of dinitrodiammine nitrate) on a carrier and adsorbing the molecular noble metal in the aqueous solution on the surface of the carrier. For alkaline earth metals such as barium, a carrier is adsorbed with a predetermined concentration of an aqueous solution of acetate or barium carbonate or the like and calcined, and then the noble metal is loaded.

[0004] The conventional NOx storage-reduction type catalyst has a problem in that the catalyst activity and the NOx storage amount decrease due to poor heat resistance and continuous operation. Thermal degradation is one of the factors that cause the catalyst activity and NOx occlusion amount to decrease over time. Precious metals are oxidized by the operation in which the exhaust gas temperature rises, and are easily separated and diffused from the loading position during catalyst production. Noble metal particles are combined with the noble metal particles to cause grain growth, so that the effective surface area is reduced. Such noble metal particle growth is more likely to occur as the size of the noble metal particle is smaller.
It is considered that the catalyst loaded with the molecular noble metal has a small noble metal particle diameter, and thus causes a decrease in catalytic activity.

Therefore, the present inventors have proposed a method of adsorbing a noble metal colloid solution onto a carrier in place of an aqueous solution containing a molecular noble metal in the production process of a NOx storage reduction catalyst. Here, the colloid solution refers to a solution in which fine particles (colloid particles) having a particle diameter of 1 to several tens of nm formed by aggregating a large number of noble metal atoms are dispersed and suspended in a liquid solvent. By using a colloidal solution, it is possible to carry metal particles having a larger particle diameter than in the case of carrying atomic and molecular metals, so that grain growth can be suppressed and the particle diameter is set to an appropriate range. This makes it possible to maintain the catalytic activity. Another advantage of using a colloidal solution is that the use of a colloidal solution in which a plurality of noble metal agglomerated colloidal particles are suspended allows a plurality of noble metals to be easily supported in a complex manner. That is, detachment and diffusion of the noble metal particles can be suppressed by carrying a noble metal having a high affinity for alumina as a carrier, such as rhodium, in combination with platinum.

In the production of a NOx storage-reduction type catalyst using this colloid solution, the present inventors added polyvinylpyrrolidone (hereinafter referred to as PVP) to the colloid solution as a protective agent for noble metal particles. A method for adsorbing carboxylic acid on a carrier has been proposed. This protective agent is a compound that chemically or physically binds and adsorbs to the periphery of colloid particles in a colloid solution, suppresses aggregation of the colloid particles and controls and stabilizes the particle size distribution within an appropriate range. A thing. That is, by adding the protective agent to the colloid solution, the particle size of the colloid particles can be adjusted to an appropriate range (about 1 to 5 nm) for the catalyst, and the colloid particles can be stably adsorbed on the carrier.

However, as a result of the study by the present inventors,
When a catalyst is produced using a PVP mixed colloid solution,
In particular, it has been clarified that the adsorption speed for pellet-shaped carriers and ceramic-coated honeycomb carriers is extremely low. When the rate of adsorption of the colloidal solution to the carrier is low, the productivity of the catalyst is significantly reduced. In addition, when the adsorption speed of the colloid solution is low, a sufficient amount of noble metal cannot be adsorbed on the carrier unless sufficient time is taken. Here, the distribution of noble metal loading affects the activity of the catalyst itself in the case of an automobile exhaust gas catalyst having a high space velocity.

[0008]

SUMMARY OF THE INVENTION The present invention has been made under the above-mentioned background, and a method for producing a catalyst for purifying exhaust gas, comprising adding a protective agent to a noble metal colloid solution and adsorbing the same on a carrier. Accordingly, an object of the present invention is to provide a method for producing an exhaust gas purifying catalyst capable of rapidly adsorbing and supporting a noble metal even when a pellet-shaped carrier or a ceramic carrier coated with a honeycomb carrier is used.

[0009]

Means for Solving the Problems The present inventors have examined the problem of the adsorption rate of a colloid solution using PVP as a protective agent on a carrier, and found that the cause was that the particle size of the noble metal particles including the protective agent was reduced. It was concluded that the point was too large. Then, as a result of diligent research on a method for producing a catalyst using a protective agent that reduces the noble metal particle diameter, the present invention has been reached.

That is, the invention according to claim 1 of the present application comprises mixing one or more kinds of noble metal salts with water or a mixed solvent of water and an organic solvent or an organic solvent with a protective agent,
By refluxing the mixed solution, a noble metal ion in the solution is reduced to produce a colloidal solution in which the noble metal particles are suspended, and the colloidal solution is adsorbed on a porous carrier. This is a method for producing an exhaust gas purifying catalyst that adsorbs a colloid solution mixed with a quaternary ammonium salt as an agent.

Since the quaternary ammonium salt has a significantly smaller molecular weight than PVP, it is considered that the overall particle size when coordinated on the colloid particles in the colloid solution is smaller than that when PVP is added. Can be Therefore, according to the first aspect of the present invention, the colloid solution can be quickly adsorbed to the carrier regardless of the type of the carrier, and the productivity of the catalyst can be improved.

Quaternary ammonium salts, like PVP, have good affinity for noble metal particles and easily coordinate with the surface of noble metal particles in a colloid solution, so that they have a sufficient effect as a protective agent. It is possible to suppress coarsening of the particles and to uniformly disperse the colloid particles. Therefore, when a catalyst is produced from the colloid solution according to claim 1, the activity of the catalyst can be made sufficient.

[0013] The quaternary ammonium salt to be added to the colloid solution is preferably a compound having 1 carbon atom.
It is preferable to add a quaternary ammonium having at least one alkyl group. That is, the protective agent 4
At least one of the substituents of the quaternary ammonium salt is a short-chain alkyl group. This is to make the colloid solution with the protective agent added hydrophilic.
In particular, in the production of automobile exhaust gas catalysts, since it is common to dissolve a water-soluble noble metal compound in water as in the prior art, an organic solvent can be newly used in the present invention. If, for example, its flammability and work environment need to be newly considered, it becomes industrially difficult.

Further, as a quaternary ammonium salt to be added in the present invention, a quaternary ammonium salt containing no sulfur and chlorine is preferable. This is because, when a catalyst is produced using a catalyst colloid solution containing sulfur, the sulfur remains in the catalyst layer on the carrier and becomes a factor of catalyst poisoning. Also, in the case of chlorine, when chlorine remains in the catalyst layer, hydrogen chloride gas is mixed into the catalytic reaction gas due to the chlorine, causing a problem of corrosion in a device on which the catalyst is mounted.

The quaternary ammonium salts satisfying the condition that they do not contain chlorine and sulfur include tetramethylammonium salts and tetraethylammonium salts as quaternary ammonium salts having a short-chain alkyl group containing no chlorine and sulfur. Salts, tetra-n-propylammonium salts, tetraisopropylammonium salts, tetrabutylammonium salts, benzyltrimethylammonium salts are fried.

It is preferable that chlorine and sulfur are not contained in the quaternary ammonium salt as well. Therefore, as the quaternary ammonium salt used in the present invention, sulfates and chlorides whose anion component is a sulfate ion or a chloride ion are not suitable. At least one of oxides, acetates, carbonates, nitrates, and nitrites, which are compound ions, acetate ions, carbonate ions, nitrate ions, and nitrite ions.
Preferably, a seed is added. ,

As described above, the catalyst for purifying exhaust gas, which is the object of the present invention, is generally a catalyst carrying an alkaline earth metal such as barium in order to promote the decomposition of NOx in addition to the noble metal particles. Used. In order to manufacture such an exhaust gas purifying catalyst, a carrier on which barium or the like is supported is usually used prior to supporting the noble metal, and the quaternary ammonium salt of the present invention is used as a protective agent for such a carrier. When adsorbing colloids
As described in claim 6, it is preferable that a chelating agent is added to the colloid solution so that the colloid solution is adsorbed on the carrier.

The reason for this is that as a result of further studies on the present invention by the present inventors, an attempt was made to adsorb the catalyst colloid of the present invention on a carrier on which an alkaline earth metal was previously supported. In this case, it is based on the finding that the adsorption speed of the noble metal particles is lower than that in the case of using a normal carrier (a carrier without supporting an alkaline earth metal). According to the present inventors, such a decrease in the adsorption rate is caused by the fact that the noble metal colloid particles to which the quaternary ammonium salt is coordinated, when an alkaline earth metal (ion) coexists in the colloid, It is considered that the salting out reaction occurs with the metal ions to cause aggregation.

The invention described in claim 6 has been made to solve the salting out of the noble metal colloid particles and the alkaline earth metal ions. According to the invention of claim 6, since the chelating agent captures the alkaline earth metal ion eluted from the carrier, the noble metal particles in the colloid are promptly affected by the alkaline earth metal ion. It adsorbs on the carrier.

The chelating agent herein means a compound having a polydentate ligand which can easily react with an alkaline earth metal ion such as barium to form a chelate compound. As the chelating agent, a compound having two or more carboxyl groups as ligands is preferable as described in claim 7, and particularly, ethylenediamminetetraacetic acid (E) described in claim 8 is preferable.
DTA) is preferred.

The amount of the chelating agent added is as follows:
It depends on the volume of the colloidal solution and the amount of the alkaline earth metal supported on the carrier.
It is preferable to add about 01 to 1.0 wt%. 0.0
This is because the addition of 1 wt% or less has no effect of capturing the eluted barium ions, and the addition of 1.0 wt% or more shows no change in the effect and no change in the adsorption characteristics.

On the other hand, according to the invention of claim 6, although there is no problem in the adsorption speed of the noble metal particles, the alkali earth metal carried on the carrier is still eluted from the carrier. Therefore, it is considered that the effect of the alkaline earth metal when used as a catalyst is reduced by the elution of the alkaline earth metal. Therefore, the present inventors have proposed a method for preventing the elution of alkaline earth metal supported on a carrier while maintaining the adsorption rate of noble metal particles, as in the invention according to claim 9, wherein the colloidal solution is further added to the colloidal solution. An alkaline earth metal salt was added to adsorb the colloid solution to the carrier.

The ninth aspect of the present invention is based on the consideration that the alkaline earth metal on the carrier is eluted in balance with the alkaline earth metal (ion) in the colloid solution. According to the method of claim 9, the alkaline earth metal ion concentration in the colloid solution is increased by previously mixing the alkaline earth metal salt in the colloid solution. Elution can be suppressed.

The amount of the alkaline earth metal salt to be added depends on the amount of the alkaline earth metal previously supported on the carrier.
It is preferable to add about 50 to 5000 ppm to the colloid solution. As the alkaline earth metal salt to be added to the colloid solution, for example, it is preferable to add in the form of nitrate.

In the method for producing an exhaust gas purifying catalyst described above, the method for adsorbing the colloid solution on the carrier is not particularly limited. Therefore, it is also possible to spray a colloid solution (in some cases, a colloid solution containing a chelating agent or an alkaline earth metal salt) onto the carrier by spraying. It is preferred that the solution be adsorbed on the carrier. This is because the immersion method allows the colloid solution to easily penetrate the carrier and allows the noble metal particles to be adsorbed without deviation.

The colloid solution used in the present invention is a suspension of platinum, gold, silver, palladium, ruthenium, rhodium, iridium and osmium as noble metal particles. Is prepared by dissolving a salt such as dinitrodiammine nitrate in a solvent.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will be described below.

First Embodiment : 3.12 g of dinitrodiammineplatinum and 0.25 g of rhodium nitrate are dissolved in 2 L of water, 600 mL of tetrahydrofuran and 800 mL of ethanol are added thereto, and 15 wt% of tetramethyl hydroxide as a protective agent is further added. An aqueous ammonium solution (88.36 g) was added, and the mixture was heated under reflux for 10 hours.

After evaporating the solution to dryness, acetone 25
The solution was redissolved in a mixed solvent of 00 mL / 500 mL of water, and the solution was distilled to remove acetone.
% To obtain a tetramethylammonium-platinum / rhodium bimetallic colloid.

Then, 6.00 g of γ-alumina powder was dispersed in 50 mL of water, and 10 g of the above-mentioned platinum / rhodium colloid was added dropwise. The mixture was stirred at room temperature for 30 minutes to adsorb the platinum / rhodium colloid on γ-alumina. Supported.

Thereafter, this was filtered, dried at 110 ° C. for 2 hours, and calcined at 450 ° C. for 2 hours to obtain a platinum / rhodium supported catalyst. The amount of supported platinum per gram of alumina powder of this catalyst was 0.0166 g, and the amount of supported rhodium was 9.6.
6 × 10 ⁻⁴ g.

Comparative Example 1 : 3.12 g of dinitrodiammineplatinum and 0.25 g of rhodium nitrate were dissolved in 2 L of water, 500 mL of ethanol was added thereto, PVP was further added as a protective agent, and the mixture was heated and refluxed for 8 hours. .

This solution was distilled and concentrated until the platinum concentration became 4 wt% to obtain a PVP-protected platinum / rhodium bimetallic colloid.

Then, 6.00 g of γ-alumina powder was dispersed in 50 mL of water, and 2.5 g of the above-mentioned platinum / rhodium colloid was added dropwise.
Rhodium colloid was adsorbed and supported on γ-alumina.

Thereafter, the same operation as in the first embodiment was performed to obtain a platinum / rhodium supported catalyst. The amount of platinum carried per gram of alumina powder of this catalyst was 0.0166 g,
The amount of rhodium supported is 9.66 × 10 ⁻⁴ g.

Comparative Example 2 : 6.00 g of γ-alumina powder was dispersed in 50 mL of water, and an aqueous nitric acid solution (containing platinum: 0.1 g) containing a dinitrodiammine platinum complex was added dropwise thereto. With stirring, dinitrodiammine platinum was adsorbed and supported on γ-alumina.

Then, a supported catalyst was obtained by the same operation as in the first embodiment. The amount of platinum carried per gram of alumina powder of this catalyst was 0.0166 g.

Experimental Example 1 (Heat Resistance Test) : The catalysts produced in the first embodiment and Comparative Examples 1 and 2 were heated in air at 800 ° C. for 5 hours, and the particle size of the noble metal particles on the catalyst was measured. Then, the situation of coarsening of the noble metal particles of each catalyst was examined. In the measurement of the noble metal particle diameter, a diffraction image obtained by XRD (X-ray diffraction) is obtained by the Debye-Scherrer method. Table 1 shows the values of the particle diameters of the noble metal particles of the catalyst measured before and after heating as described above.

[0039]

[Table 1]

According to Table 1, in the catalyst manufactured in the first embodiment, the particle size of the noble metal particles after heating was almost the same as that of the catalyst manufactured from the colloidal solution using PVP as a protective agent in Comparative Example 2. Met. These values are smaller than those of the catalyst produced by absorbing a molecular noble metal salt solution (a dinitrodiammine platinum complex solution) which is presumed to have caused grain growth. Therefore, it was confirmed that the catalyst using the quaternary ammonium salt according to the present invention has the same effect of suppressing the growth of noble metal particles as PVP.

Experimental Example 2 (Study on Catalyst Performance) : The catalyst performance of each catalyst of the first embodiment and Comparative Examples 1 and 2 after the high-temperature durability test was conducted in Experimental Example 1 was examined.
In the experiment, each catalyst was brought into contact with a reaction gas having the following composition to perform gas occlusion until saturation, and the NOx occlusion amount was measured by TG-DTA (thermal mass-differential thermal analysis). Table 2 shows the results.

[0042]

[0043]

[Table 2]

As shown in Table 2, the catalyst of the first embodiment is 800
Even after heating at 10 ° C. for 10 hours, it has activity as a NOx storage catalyst, and its NOx storage amount is 18.6 mg /
This is almost the same as Comparative Example 1 using g and PVP. On the other hand, in Comparative Example 2, the NOx storage amount was 11.3 mg.
/ G, which means that the activity was reduced by heating. This decrease in activity is considered to be caused by the growth of the noble metal particles by heating. From these results, it was confirmed that the colloid solution of the present invention can produce a catalyst without causing grain growth.

Third Embodiment In this embodiment, a catalyst was produced by adsorbing the tetramethylammonium-platinum / rhodium colloid solution used in the first embodiment on a ceramic-coated honeycomb carrier.

The colloid produced in the first embodiment was diluted with water until the platinum concentration became 200 ppm, and 150 mL of the colloid was diluted with an alumina-coated honeycomb carrier (alumina amount: 2.85 g).

Then, the carrier is taken out of the solution, and 11
After drying at 0 ° C. for 2 hours, it was calcined at 450 ° C. for 2 hours to obtain a platinum / rhodium supported catalyst.

Comparative Example 3 Here, the catalyst was produced by adsorbing the PVP-platinum / rhodium colloid solution used in Comparative Example 1 on a ceramic-coated honeycomb carrier as in the third embodiment.

The colloid produced in Comparative Example 1 was diluted with water until the platinum concentration reached 200 ppm, and 150 mL was taken.
A honeycomb carrier coated with alumina (alumina amount: 2.85 g) was immersed in this.

Then, the carrier is taken out of the solution and
After drying at 0 ° C. for 2 hours, it was calcined at 450 ° C. for 2 hours to obtain a platinum / rhodium supported catalyst.

Experimental Example 3 : The third embodiment and comparative example 3
In the production process of the catalyst of No. 1, the adsorption speed of the colloid solution was compared. In the experiment, the solution was sampled at regular intervals while stirring the solution, and the platinum concentration was measured by ICP (inductively coupled plasma emission spectroscopy). For comparison, the adsorption rate of a nitric acid aqueous solution containing a dinitrodiammine platinum complex on a carrier was also measured.

FIG. 1 shows the change in the platinum concentration of each solution when the carrier was immersed. From this figure, it can be seen that the rate of decrease of the platinum concentration when the third embodiment (protective agent: tetramethylammonium hydroxide) is adsorbed (that is, the platinum adsorption rate) is significantly higher than that of Comparative Example 3 (protective agent: PVP). The adsorption was completed in about 4 hours. The adsorption rate was almost the same as that of the dinitrodiammine platinum complex aqueous solution. Therefore, it was confirmed that the colloid solution of the present invention can be sufficiently quickly adsorbed even if the carrier is a ceramic coating layer on a honeycomb.

Fourth Embodiment : In this embodiment, a honeycomb carrier having barium previously supported on a carrier is used, and ethylenediamminetetraacetic acid is added as a chelating agent to a colloidal solution. Produced a catalyst.

To 150 mL of the same colloidal solution (platinum concentration: 200 ppm) as in the third embodiment, 0.5 g (0.33 wt%) of ethylene diamminetetraacetic acid was added as a chelating agent, dissolved, and then dissolved in a honeycomb coated with alumina. A carrier (alumina amount: 2.85 g) was immersed.

After the colloid solution was adsorbed on the carrier, a platinum / rhodium supported catalyst was produced by the same treatment as in the third embodiment.

Experimental Example 4 In this catalyst production process, as in Experimental Example 3, the solution was sampled at regular intervals, the platinum concentration was measured, and the adsorption rate was examined.

FIG. 2 shows the change in the platinum concentration of each solution with the carrier immersed. Also in this experimental example, the adsorption speed of the nitric acid aqueous solution containing the dinitrodiammine platinum complex was measured and compared. From this figure, it can be seen that the carrier preloaded with barium as in the present embodiment also shows that the addition of the chelating agent to the colloid solution allows the noble metal particles to be adsorbed at the same adsorption rate as the nitric acid aqueous solution containing the dinitrodiammine platinum complex. It was confirmed that.

Fifth Embodiment : In this embodiment, the same barium carrier as in the fourth embodiment is used, and a chelating agent and a barium salt are added to a colloid solution, and the catalyst is produced in the same manner as in the fourth embodiment. Was manufactured.

Colloid solution (platinum concentration: 200 ppm)
After adding 0.5 g (0.33 wt%) of ethylenediamminetetraacetic acid as a chelating agent to 150 mL, and further adding barium nitrate as a barium salt, a honeycomb carrier coated with alumina (alumina amount: 2.85 g)
Was immersed. In this case, the colloid solution is 500 p
pm, 1000 ppm, and the amount of barium nitrate added was changed to adjust two types, and the amount of barium eluted for each colloid solution was examined.

After the colloid solution was adsorbed on the carrier, a platinum / rhodium supported catalyst was produced by the same treatment as in the fourth embodiment.

Experimental Example 5 : In this catalyst manufacturing process, the barium concentration in the colloid solution was measured by sampling the solution at regular intervals, and the results shown in FIG. 3 were obtained. FIG.
From this, it can be seen that the barium concentration in the solution is saturated at about 1500 ppm regardless of the added barium concentration. Therefore, when the carrier is immersed in the colloid solution without adding the barium salt, the amount of barium eluted from the carrier is 1500 ppm, whereas by adding the barium salt to the colloid solution, about 10 ppm is obtained at the added amount of 500 ppm.
It is about 500 ppm when the amount is 00 ppm and the amount added is 1000 ppm, and it can be said that the amount of barium eluted from the carrier can be reduced by adding the barium salt to the colloid solution in advance. It was also found that the amount of barium eluted can be reduced as the concentration of the added barium salt increases.

[0062]

As described above, the present invention relates to an exhaust gas purifying catalyst in which a colloid solution containing a protective agent is adsorbed on a carrier, wherein the protective agent is changed from conventional PVP to a quaternary ammonium salt. ADVANTAGE OF THE INVENTION According to this invention, a colloid solution can be made to adsorb | suck a support | carrier more quickly than the colloid solution to which PVP was added, and the productivity of a catalyst can be improved.

When the carrier supports an alkaline earth metal such as barium, a chelating agent is added to the colloid solution in the present invention. Thereby, the colloid solution can be efficiently adsorbed on the carrier without being affected by the alkaline earth metal eluted from the carrier. Further, by further adding an alkaline earth metal salt to the colloid solution, elution of the alkaline earth metal from the carrier can be suppressed, and the NOx storage characteristics of the produced catalyst can be secured.

The catalyst produced according to the present invention has excellent NOx purification characteristics due to the above-mentioned effects, and can suppress the growth of noble metal particles and maintain the catalyst characteristics for a long period of time, as in the case of using PVP. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in the concentration of platinum in a colloid solution during a catalyst production process according to a third embodiment and Comparative Example 3.

FIG. 2 is a diagram showing a change in the concentration of platinum in a colloid solution during a catalyst manufacturing process according to a fourth embodiment.

FIG. 3 is a diagram showing a change in barium concentration in a colloid solution during a catalyst production process according to a fifth embodiment.

Continued on the front page (72) Inventor Masayuki Saito 2-73, Shinmachi, Hiratsuka-shi, Kanagawa Prefecture Inside the Technology Development Center, Tanaka Kikinzoku Kogyo Co., Ltd. F-term (reference) 3G091 AA02 AB06 BA14 BA39 GB03W GB05W GB06W GB07W 4G069 AA03 AA08 BA01B BB05A BB10A BB12A BB16A BC08A BC13A BC32A BC33A BC69A BC70A BC71A BC71B BC72A BC73 BE13BCA13 BC13 BE13BCA13 BC75

Claims (12)

[Claims] 1. A mixture of one or more noble metal salts, water or a mixed solvent of water and an organic solvent or a solvent comprising an organic solvent, and a protective agent. A method for producing a colloidal solution in which noble metal particles are suspended by reducing a noble metal salt, and a method for producing an exhaust gas purifying catalyst comprising adsorbing the colloidal solution on a porous carrier, wherein a quaternary ammonium salt is used as the protective agent A method for producing an exhaust gas purifying catalyst for adsorbing a colloidal solution containing a mixture thereof. 2. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein a quaternary ammonium having at least one alkyl group having 1 to 4 carbon atoms is added as a protective agent. 3. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein a quaternary ammonium salt containing no sulfur and chlorine is added as the quaternary ammonium salt. 4. A quaternary ammonium salt comprising a tetramethylammonium salt, a tetraethylammonium salt, a tetra-n-propylammonium salt, a tetraisopropylammonium salt, a tetrabutylammonium salt, and a benzyltrimethylammonium salt. Item 4. The method for producing an exhaust gas purifying catalyst according to Item 3. 5. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein at least one of a hydroxide, an acetate, a carbonate, a nitrate and a nitrite is added as the quaternary ammonium salt. 6. A collating solution further comprising a chelating agent,
The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the colloid solution is adsorbed on a carrier. 7. The method for producing an exhaust gas purifying catalyst according to claim 6, wherein a compound having two or more carboxyl groups is added as a chelating agent. 8. The method for producing an exhaust gas purifying catalyst according to claim 6, wherein ethylenediamminetetraacetic acid is added as a chelating agent. 9. The method for producing an exhaust gas purifying catalyst according to claim 6, wherein a salt of an alkaline earth metal is further added to the colloid solution, and the colloid solution is adsorbed on a carrier. 10. The method for producing an exhaust gas purifying catalyst according to claim 1, wherein the carrier is immersed in a tank containing the colloid solution, and the colloid solution is adsorbed on the carrier. 11. The method according to claim 1, wherein the noble metal salt is a salt of platinum, gold, silver, palladium, ruthenium, rhodium, iridium, and osmium. 12. An exhaust gas purifying catalyst produced by the method according to any one of claims 1 to 11.