JPH11267501A - Carrier for exhaust gas cleaning catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier which can repress a solid phase reaction between rhodium (RH) and a composite oxide carrier. SOLUTION: A first solid solution 2 where the solution amount of zirconia into ceria is at a molar fraction satisfying 0<Zr/(Ce+Zr)<0.7 and at least one of a second solid solution 3 where the solution amount of zirconia into ceria is at a molar fraction satisfying 0.7<=Zr/(Ce+Zr) and undissolved zirconia coexist, and at least one of the second solid solution 3 and the undissolved zirconia are contained by 30 mol.% or higher base on the total molar quantity of the ceria and the zirconia. The Rh 5 supported on at least one of the second solid solution 3 and the zirconia is prevented from being dissolved into alumina or the like, and from interacting with the ceria-zirconia solid solution. This can prevent a deactivation caused by an endurance test.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for an exhaust gas purifying catalyst used for purifying exhaust gas discharged from an internal combustion engine such as an automobile engine. The support of the present invention is particularly effective when supporting rhodium (Rh) as a catalytic noble metal.

[0002]

As a conventional than the automobile exhaust gas purifying catalyst, a three-way catalyst for purifying performing the reduction of the oxidized and NO _x CO and HC in the exhaust gas simultaneously is used. As such a three-way catalyst, for example, a carrier layer made of γ-Al ₂ O ₃ is formed on a heat-resistant honeycomb substrate made of cordierite or the like, and platinum (Pt), rhodium (Rh), or the like is formed on the carrier layer. What carried the catalyst noble metal is widely known.

[0003] By the way, the condition of the carrier for exhaust gas purifying catalyst is that the specific surface area is large and the heat resistance is high.
Generally, alumina, silica, zirconia, titania and the like are often used. In addition, the use of ceria having oxygen storage ability is also used to mitigate fluctuations in the atmosphere of exhaust gas. Furthermore, it is known that the durability of ceria's oxygen storage ability can be improved by using ceria as a composite oxide with zirconia.

However, in a conventional catalyst for purifying exhaust gas, 8
When exposed to a high temperature such as exceeding 00 ° C., the specific surface area of the support decreases, sintering of the catalyst noble metal occurs, and the oxygen storage capacity of ceria also decreases. there were. Therefore, JP-A-4-
Japanese Patent No. 4043 discloses an exhaust gas purifying catalyst in which a catalytic noble metal is supported on a composite oxide carrier composed of a composite oxide of alumina, ceria, and zirconia. A catalyst in which an arbitrary catalyst noble metal is supported on such a composite oxide carrier has high purification performance even after firing at 850 ° C. at a high temperature. It is stated that the decrease is suppressed.

[0005]

However, with a catalyst in which Rh is supported as a catalytic noble metal on a composite oxide carrier composed of a composite oxide of alumina, ceria and zirconia, a decrease in the oxygen storage capacity of ceria after a durability test is suppressed. Although,
It became clear that the purification activity by Rh decreased. This is considered to be because Rh causes a solid-phase reaction with the composite oxide carrier in a high-temperature oxidizing atmosphere.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a carrier capable of suppressing a solid phase reaction between Rh and a composite oxide carrier when Rh is carried.

[0007]

Means for Solving the Problems The feature of the carrier for exhaust gas purifying catalyst of the present invention which solves the above-mentioned problem is that the carrier containing at least a complex oxide composed of ceria and zirconia has a zirconia solid solution amount in ceria of a mole fraction. 0 <Zr /
A solid solution of ceria and zirconia (Ce + Zr) <0.7 (first solid solution), and a solid solution of ceria and zirconia in which the amount of zirconia solid solution in ceria is 0.7 ≦ Zr / (Ce + Zr) ( At least one of the second solid solution) and the undissolved zirconia coexists, and at least one of the second solid solution and the undissolved zirconia accounts for at least 30 mol% of the total molar amount of ceria and zirconia in the carrier containing the composite oxide. Is to be included.

[0008] The characteristic feature of the carrier for exhaust gas purifying catalyst according to the second aspect is that the carrier for an exhaust gas purifying catalyst according to the first aspect comprises a solution containing at least cerium ions and zirconium ions and further containing a surfactant. It has been produced by firing the coprecipitated precipitate.
Further, the characteristic of the exhaust gas purifying catalyst carrier according to claim 3 is that in the exhaust gas purifying catalyst carrier according to claim 2,
The surfactant is to be a cationic surfactant.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a conventional catalyst in which Rh is supported on a composite oxide carrier comprising at least ceria and zirconia, the following may be considered as causes of deactivation of Rh in a high-temperature oxidizing atmosphere. (1) Rh reacts with alumina or the like in a solid phase. (2) An interaction between Rh and the ceria-zirconia solid solution occurs, and Rh forms a complex oxide or the like and is deactivated.

Therefore, in the carrier of the present invention, the zirconia solid solution amount in ceria is 0 <Zr / (Ce + Zr) <0.7, and the zirconia solid solution amount in ceria is a mole fraction. At least one of the second solid solution and undissolved zirconia satisfying a ratio of 0.7 ≦ Zr / (Ce + Zr) coexists. Since Rh is supported on the entire carrier, it is supported not only on the first solid solution but also on the second solid solution or undissolved zirconia.

Here, it is clear that Rh supported on the second solid solution having a large amount of zirconia solid solution or undissolved zirconia is prevented from dissolving in alumina, which is another component of the carrier. Was. In addition, since the second solid solution or undissolved zirconia has a high zirconia composition ratio with respect to other components, Rh supported on the zirconia has a reduced interaction with ceria, thereby forming a composite oxide composed of ceria and zirconia. It is considered that the solid phase reaction with Rh is suppressed.
Therefore, the catalyst in which Rh is supported on the support of the present invention shows high purification activity even after the durability test, and a decrease in the activity is suppressed as compared with the conventional catalyst.

In order for the above effects to be exhibited, at least one of the second solid solution having a high zirconia solid solution amount and the undissolved zirconia is at least 30 mol% of the total molar amount of ceria and zirconia contained in the carrier. In order not to deactivate the effect, the content is desirably 85 mol% or less, more desirably 70 mol% or less. In order for the effect to be more remarkably exhibited, the total molar amount of ceria and zirconia contained in the carrier is preferably at least 25 mol% based on the total molar amount of all components of the carrier. In order not to deactivate, the content is desirably 80 mol% or less.

The particle size of at least one of the second solid solution and the undissolved zirconia is not particularly limited. For example, ceria-zirconia solid solution powder and zirconia powder may be mixed, or fine zirconia particles may be precipitated on the surface of ceria-zirconia solid solution particles. The zirconia solid solution amount in ceria is 0 <Zr / (Ce + Zr) <0.7
In the first solid solution, it is more preferable that the zirconia solid solution amount in ceria be 0.1 ≦ Zr / (Ce + Zr) in molar fraction. When the molar fraction Zr / (Ce + Zr) is less than 0.1, the thermal stability decreases. When the molar fraction Zr / (Ce + Zr) exceeds 0.7, the oxygen storage capacity decreases, so that Zr / (Ce + Zr) <0.7. A more desirable range is Zr / (Ce + Zr) ≦ 0.4.

In at least one of the second solid solution having a large zirconia solid solution amount and the undissolved zirconia, the zirconia solid solution amount in ceria is 0.7 ≦ Zr / (Ce + Zr) in mole fraction.
However, undissolved zirconia which does not form a solid solution with ceria may be used. When Zr / (Ce + Zr) <0.7,
The effect of suppressing the interaction between Rh and ceria decreases. In the carrier for an exhaust gas purifying catalyst of the present invention, if the first solid solution and at least one of the second solid solution and the undissolved zirconia coexist in the above range, components other than the composite oxide composed of ceria and zirconia are particularly There is no limitation, and alumina, silica, silica-alumina, titania, barium oxide, lantana, neodia, and the like can further coexist. The amount is not particularly limited.

By the way, when a carrier comprising alumina, ceria and zirconia is produced by a coprecipitation method, a surfactant is added to the carrier so that a sufficient amount of the first solid solution and a sufficient amount of catalyst to improve the catalytic activity can be obtained. It became clear that it can coexist with the second solid solution. Although the reason for this is not clear, micelles composed of aluminum ions, zirconium ions and cerium ions were formed, thereby having a composition ratio of cerium and zirconium of the present invention, and allowing the first solid solution and the second solid solution to coexist. It is presumed that a solid solution is formed.

Examples of the surfactant include anionic surfactants such as alkyl benzene sulfonic acid, alpha olefin sulfonic acid and alkyl sulfate, and non-ionic surfactants such as polyoxyalkylene glycol, polyoxyethylene alkylamine and polyoxyethylene alkyl ether. Any of an ionic surfactant and a cationic surfactant such as a polyethylene polyamine fatty acid amide salt and an amine acetate-oleate salt can be used, but it is particularly preferable to use a cationic surfactant. It is also desirable to select one that can be easily decomposed and removed by firing.

The addition amount of the surfactant can provide a certain effect if it is added as little as possible, but is preferably in the range of about 2 to 30% by weight based on the final product obtained from the mixed solution. If the amount is less than this, the second solid solution or undissolved zirconia is difficult to generate, and if it is more than this, the effect is saturated and the number of steps for removing the surfactant increases. The carrier of the present invention can be used as a three-way catalyst or an oxidation catalyst by supporting a catalytic noble metal such as Pt, Rh, or Pd by a conventional method. Further, it is possible to further be conjugated to a carrier or supporting an alkali metal or alkaline earth metal, is used as a NO _x storage-and-reduction type catalysts. In particular, by supporting Rh as a catalytic noble metal, the solid phase reaction between Rh and the carrier is suppressed, so that even when used at a high temperature, deactivation of Rh can be prevented and the durability is excellent.

[0018]

The present invention will be specifically described below with reference to examples and comparative examples. First, the following solutions were prepared. <Solution A> aluminum nitrate _{(Al (NO 3) 3 ·} 9H 2 O) 147.
1 g (0.392 mol) was dissolved in 500 cm ³ of pure water. <Solution B> 18.1 g of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O)
(0.042 mol) was dissolved in 200 cm ³ of pure water. <Solution C> oxy nitrate _{(ZrO (NO 3) 2 ·} 2H 2 O)
Was dissolved in 250 cm ³ of pure water. <Solution D> 2.2 g (0.008m) of barium nitrate (Ba (NO ₃ ) ₂ )
ol) was dissolved in 50 cm ³ of pure water. <Solution E> 28% ammonia water 101.1 cm ³ (1.661 m
ol) and 0.7 g of ammonium carbonate ((NH ₄ ) ₂ CO ₃ ) (0.
01 mol) was dissolved in 400 cm ³ of pure water.

(Example 1) Solution A, solution B, solution C and solution D were placed in a beaker, and a surfactant comprising amine acetate and oleate ("Armak T-50")
Lion Corporation). The amount of surfactant added
The amount is 10% by weight of the final product. After stirring for 1 hour, the solution E was added to obtain a gel-like white suspension.
Stirred for minutes.

This was filtered to separate a white precipitate by filtration.
At 650 ° C for 3 hours after drying at 300 ° C for 4 hours.
After calcination for an hour, a target carrier powder was obtained. The composition ratio of this support is Al ₂ O ₃ / CeO ₂ / ZrO ₂ / BaO in a molar ratio of 1 / 0.21 / 0.21 / 0.0
4 Using this carrier powder, a pellet catalyst was prepared by supporting platinum (Pt) and rhodium (Rh) as follows.

First, a predetermined amount of carrier powder is impregnated with a predetermined amount of an aqueous solution of dinitrodiamineplatinum (Pt (NO ₂ ) ₂ (NH ₃ ) ₂ ) at a predetermined concentration, and calcined at 300 ° C. for 1 hour in the atmosphere. Pt was loaded. Next, the obtained Pt-supported carrier was impregnated with a predetermined amount of a rhodium chloride (RhCl ₃ ) aqueous solution of a predetermined concentration, and dried at 120 ° C. for 12 hours to support Rh. Table 1 shows the amount of noble metal supported on the catalyst and the structure of the carrier.

After green compacting the obtained catalyst powder, 0.5 to 1
It was pulverized into pellets of mm to obtain a new pellet catalyst. (Example 2) Solution A, solution B and solution C were placed in a beaker, and a surfactant composed of amine acetate and oleate ("Armac T-50" manufactured by Lion Corporation) was further added. The amount of surfactant added is such that it amounts to 10% by weight of the final product. After stirring for 1 hour, a solution E excluding ammonium carbonate was added to obtain a gel-like white suspension.
Stirred for 20 minutes.

This was filtered to separate a white precipitate by filtration.
At 650 ° C for 3 hours after drying at 300 ° C for 4 hours.
After calcination for an hour, the target carrier was obtained. The composition ratio of this carrier is
Al_TwoO _Three/ CeO_Two/ ZrO_TwoThe molar ratio is 1 / 0.21 / 0.21. This
Pt and Rh were loaded using the same carrier as in Example 1.
A pellet catalyst was prepared.

(Example 3) Solution A, solution B, solution C and solution D were placed in a beaker, and a surfactant comprising amine acetate and oleate ("Armac T-50")
Lion Corporation). The amount of surfactant added
The amount is 10% by weight of the final product. After stirring for 1 hour, the solution E was added to obtain a gel-like white suspension.
Stirred for minutes.

This was filtered to separate a white precipitate by filtration.
, And calcined at 300 ° C for 4 hours, and then calcined at 650 ° C for 3 hours to prepare a composite oxide carrier. This is the same as the carrier of Example 1. This composite oxide carrier 120
g of zirconyl oxynitrate (ZrO (NO
₃ ) An aqueous solution in which 40.1 g (0.15 mol) of ₂ · 2H ₂ O was dissolved was added and stirred for 1 hour. A 1.2-fold equivalent aqueous ammonia solution was added thereto to precipitate a zirconium hydroxide on the composite oxide support.

The obtained yellowish white precipitate was dried at 110 ° C. for 12 hours or more, calcined at 300 ° C. for 4 hours, and calcined at 650 ° C. for 3 hours to prepare a target carrier. The composition ratio of this carrier is Al ₂ O ₃ /
The molar ratio of CeO ₂ / ZrO ₂ / BaO is 1 / 0.21 / 0.43 / 0.04.
Using this carrier, Pt and Rh were carried in the same manner as in Example 1 to prepare a pellet catalyst.

(Example 4) Solution A, solution B, solution C and solution D were placed in a beaker, and a surfactant comprising amine acetate and oleate ("Armac T-50")
Lion Corporation). The amount of surfactant added
The amount is 10% by weight of the final product. After stirring for 1 hour, the solution E was added to obtain a gel-like white suspension.
Stirred for minutes.

This was filtered to separate a white precipitate by filtration.
, And calcined at 300 ° C for 4 hours, and then calcined at 650 ° C for 3 hours to prepare a composite oxide carrier. 120 g of this composite oxide carrier was dispersed in pure water, and an aqueous solution in which 66.8 g (0.25 mol) of zirconyl oxynitrate (ZrO (NO ₃ ) ₂ .2H ₂ O) was added, followed by stirring for 1 hour. A 1.2-fold equivalent aqueous ammonia solution was added thereto to precipitate a zirconium hydroxide on the composite oxide support.

The obtained yellow-white precipitate was dried at 110 ° C. for 12 hours or more, calcined at 300 ° C. for 4 hours, and calcined at 650 ° C. for 3 hours to prepare a target carrier. The composition ratio of this carrier is Al ₂ O ₃ /
The molar ratio of CeO ₂ / ZrO ₂ / BaO is 1 / 0.21 / 0.57 / 0.04.
Using this carrier, Pt and Rh were carried in the same manner as in Example 1 to prepare a pellet catalyst.

Example 5 First, the following solution was prepared. <Solution 1> 18.1 g of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O)
(0.042 mol) was dissolved in 200 cm ³ of pure water. <Solution 2> oxy nitrate _{(ZrO (NO 3) 2 ·} 2H 2 O)
Was dissolved in 250 cm ³ of pure water. <Solution 3> 15.3 cm ^{3 of} 28% aqueous ammonia (0.252 m
ol) was dissolved in 200 cm ³ of pure water. <Solution 4> oxy nitrate _{(ZrO (NO 3) 2 ·} 2H 2 O)
Was dissolved in 250 cm ³ of pure water.

Using the solutions 1 to 3, a gel-like white suspension was prepared by a coprecipitation method, and further stirred for 20 minutes. This was filtered, dried at 110 ° C. for 12 hours or more, calcined at 300 ° C. for 4 hours, and calcined at 650 ° C. for 3 hours to obtain a ceria-zirconia solid solution. 73.8 g of this ceria-zirconia solid solution was added to γ
-120 g of Al ₂ O ₃ powder was mixed with a wet ball mill,
Dry at 12 ° C. for 12 hours. 120 g of this mixed powder was dispersed in pure water, solution 4 was added, and the mixture was stirred for 1 hour. A 1.2-fold equivalent aqueous ammonia solution was added thereto to precipitate a zirconium hydroxide on the powder. 110 ° C.
For 12 hours, calcined at 300 ° C. for 4 hours, and then calcined at 650 ° C. for 3 hours to obtain a target carrier. The composition ratio of this carrier is 1 / 0.21 / 0.57 in a molar ratio of Al ₂ O ₃ / CeO ₂ / ZrO ₂ .

Using this carrier, Pt was prepared in the same manner as in Example 1.
And Rh were supported to prepare a pellet catalyst. (Comparative Example 1) Solution A, solution B, solution C and
Add solution D, stir for 1 hour, add solution E and add gel white
A color suspension was obtained and stirred for another 20 minutes. So far, the world
The same as Example 1 except that no surfactant was used.
The resulting white suspension is allowed to settle and the supernatant is removed.
After drying at 110 ° C for 12 hours or more, calcining at 300 ° C for 4 hours
Thereafter, the support was calcined at 650 ° C. for 3 hours to obtain a carrier. Composition of this carrier
The ratio is Al_TwoO_Three/ CeO_Two/ ZrO _TwoIn a molar ratio of / BaO, 1 / 0.21 / 0.21 /
0.04.

Using this carrier, Pt was prepared in the same manner as in Example 1.
And Rh were supported to prepare a pellet catalyst. Comparative Example 2 120 g of γ-Al ₂ O ₃ powder and 74 g of ceria-zirconia solid solution powder were mixed to obtain a carrier of Comparative Example 2.
The composition of the ceria-zirconia solid solution powder is Ce / (Ce + Zr) =
0.5. The composition ratio of this carrier is Al ₂ O ₃ / CeO ₂ / ZrO
_At a molar ratio of ₂ , it is 1 / 0.21 / 0.21.

Using this carrier, Pt was prepared in the same manner as in Example 1.
And Rh were supported to prepare a pellet catalyst. Comparative Example 3 First, the following solution was prepared. <Solution 1> aluminum nitrate _{(Al (NO 3) 3 ·} 9H 2 O) 147.
1 g (0.392 mol) was dissolved in 500 cm ³ of pure water. 3.6g of <Solution 2> cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O)
(0.008 mol) was dissolved in 200 cm ³ of pure water. <Solution 3> oxy nitrate _{(ZrO (NO 3) 2 ·} 2H 2 O)
Was dissolved in 250 cm ³ of pure water. <Solution 4> 2.2 g of barium nitrate (Ba (NO ₃ ) ₂ ) (0.008 m
ol) was dissolved in 50 cm ³ of pure water. <Solution 5> 98.5 cm ³ of ammonia water with a concentration of 28% (1.620 m
ol) and 0.7 g of ammonium carbonate ((NH ₄ ) ₂ CO ₃ )
0.01 mol) was dissolved in 400 cm ³ of pure water.

Solutions 1 to 4 were placed in a beaker, and a surfactant consisting of an amine acetate and an oleate ("Armac T-50" manufactured by Lion Corporation) was further added. The amount of surfactant added is such that it amounts to 10% by weight of the final product.
After stirring for 1 hour, solution 5 was added to obtain a gel-like white suspension, and the mixture was further stirred for 20 minutes. This is filtered and at 110 ° C
After drying for 12 hours or more, it was calcined at 300 ° C for 4 hours and calcined at 650 ° C for 3 hours to obtain a carrier containing a ceria-zirconia solid solution. The composition ratio of this carrier is 1 / 0.04 / 0.38 / 0.04 as a molar ratio of Al ₂ O ₃ / CeO ₂ / ZrO ₂ / BaO.

Using this carrier, Pt was prepared in the same manner as in Example 1.
And Rh were supported to prepare a pellet catalyst. Comparative Example 4 First, the following solution was prepared. <Solution 1> aluminum nitrate _{(Al (NO 3) 3 ·} 9H 2 O) 14
7.1 g (0.392 mol) was dissolved in 500 cm ³ of pure water. <Solution 2> 9.0 g of cerium nitrate _{(Ce (NO 3) 3 ·} 6H 2 O)
(0.021 mol) was dissolved in 200 cm ³ of pure water. <Solution 3> oxy nitrate _{(ZrO (NO 3) 2 ·} 2H 2 O)
Was dissolved in 250 cm ³ of pure water. <Solution 4> 2.2 g of barium nitrate (Ba (NO ₃ ) ₂ ) (0.008 m
ol) was dissolved in 50 cm ³ of pure water. <Solution 5> 99.6 cm ³ of ammonia water with a concentration of 28% (1.638 m
ol) and 0.7 g of ammonium carbonate ((NH ₄ ) ₂ CO ₃ )
0.01 mol) was dissolved in 400 cm ³ of pure water.

Solutions 1 to 4 were placed in a beaker, and a surfactant comprising an amine acetate and an oleate ("Armac T-50" manufactured by Lion Corporation) was further added. The amount of surfactant added is such that it amounts to 10% by weight of the final product.
After stirring for 1 hour, solution 5 was added to obtain a gel-like white suspension, and the mixture was further stirred for 20 minutes. This is filtered and at 110 ° C
After drying for 12 hours or more, it was calcined at 300 ° C for 4 hours and calcined at 650 ° C for 3 hours to obtain a carrier containing a ceria-zirconia solid solution. The composition ratio of this carrier is 1 / 0.11 / 0.32 / 0.04 as a molar ratio of Al ₂ O ₃ / CeO ₂ / ZrO ₂ / BaO.

Using this carrier, Pt was prepared in the same manner as in Example 1.
And Rh were supported to prepare a pellet catalyst. Table 1 summarizes the amount of the noble metal carried and the structure of the carriers of the catalysts of the examples and comparative examples. (Analysis) With respect to the carriers of Example 1 and Comparative Examples 1 and 2, durability tests were respectively performed using the model gases shown in Table 2 under the conditions described later. An X-ray diffraction analysis was performed on each of the carriers after the durability test, and the results are shown in FIGS.

1 and 2, the carrier of Comparative Example 2 shows a sharp bilaterally symmetrical peak of the ceria-zirconia solid solution, and the peak position is in the middle between the peak position of ceria alone and the peak position of zirconia alone. It is shown that the zirconia solid solution amount is Zr / (Ce + Zr) = 0.5 in molar fraction. However, it is considered that at least two types of ceria-zirconia solid solutions exist in the carrier of Example 1. The strongest peak indicating the ceria-zirconia solid solution has a diffraction angle located at a lower angle side than that of the carrier of Comparative Example 2, and has a broad peak at a high angle side where tailing is observed. Therefore, in the carrier of Example 1,
It is believed that there are at least two ceria-zirconia solid solutions having different composition ratios.

In the carrier of Example 1, the zirconia solid solution amount of the ceria-zirconia solid solution showing a clear strongest peak was calculated to be Zr / (Ce + Zr) = about 0.21 in molar fraction, which is referred to in the present application. Refers to the first solid solution. Furthermore, from the peak area ratio, the amount of zirconia solid solution in ceria
The amount of the second solid solution in which 0.7 ≦ Zr / (Ce + Zr) is calculated to be about 34 mol% in the total solid solution. In addition, the second solid solution in which the zirconia solid solution amount in ceria is 0.7 ≦ Zr / (Ce + Zr) in a molar fraction is not observed as a clear peak in the X-ray diffraction, so that the second solid solution becomes fine particles of less than 5 nm. It is thought that there is.

On the other hand, in the carrier of Comparative Example 1, the position of the strongest peak was slightly shifted to the peak position side (low angle side) of ceria alone as compared with the carrier of Comparative Example 2, and the zirconia solid solution calculated from this was a mole fraction. The ratio is Zr / (Ce + Zr) = about 0.42, which indicates the first solid solution referred to in the present application. In the carrier of Comparative Example 1, the presence of a ceria-zirconia solid solution having a small but different composition ratio was observed. From the peak area ratio, the amount of zirconia solid solution in ceria was 0.7 ≦ Zr / (Ce + Z
The amount of the second solid solution, which is r), is calculated to be about 25 mol%, which is outside the scope of the present invention.

In the same manner as described above, the amounts of zirconia dissolved in the first solid solution calculated from the X-ray diffraction chart and the total moles of ceria and zirconia contained in the carriers were determined for each of the carriers of the examples and comparative examples. Table 3 shows the molar ratio of the second solid solution or undissolved zirconia in which 0.7 ≦ Zr / (Ce + Zr).

[0043]

[Table 1] (Test / Evaluation) For each new catalyst obtained,
A durability test was performed in which the sample was exposed to a model gas at 1000 ° C. for 5 hours. As model gas, model gas 1 shown in Table 2 and
Oxygen gas was added to this model gas 1 to make it a 5% oxygen-excess atmosphere, and model gas 2 was allowed to flow in a cycle of 10 minutes. The total gas flow was about 1 liter / min.

[0044]

[Table 2] For each of the catalysts after the durability test, the purification rate of NOx, CO, and HC when the temperature was raised from 100 ° C. to 500 ° C. was measured using a fixed bed flow type catalyst evaluation device. The results are shown in Table 3 at 50% purification temperature. Note that the measurement was performed using a stoichiometric model gas under the conditions of a fluctuation width of the air-fuel ratio of 4% and a fluctuation cycle of 2 seconds centering on the stoichiometry.

[0045]

[Table 3] From Table 3, it is clear that the catalysts of the examples show high purification performance even after the durability test, and are superior to the catalysts of Comparative Examples 1 to 4. This is because a zirconia solid solution in ceria has a molar fraction of Zr / (Ce + Zr) <0.7, and a zirconia solid solution in ceria has a molar fraction of 0.7 ≦ Zr / (Ce + Zr ) Is at least one of the second solid solution and undissolved zirconia is apparently an effect due to coexistence,
At this time, the second solid solution and undissolved zirconia are present in an amount of 30 mol% or more of the total molar amount of ceria and zirconia contained in the carrier.

In the carrier of Comparative Example 1, since the surfactant was not used at the time of production, the zirconia solid solution amount of the first solid solution was larger than in Examples 1 and 2, and a sufficient amount of the second solid solution was formed. I haven't. Therefore, although the purification performance is slightly higher than that of the catalyst of Comparative Example 2 having a smaller amount of the second solid solution, the purification performance after the durability test is lower than that of the catalyst of Example. In Comparative Examples 3 and 4, Zr of the first solid solution was used.
Since / (Ce + Zr) is 0.7 or more, the oxygen storage capacity of ceria is insufficient and the purification activity is low.

When the examples are compared with each other, the purification activities of the catalysts of the examples 3 and 4 are further improved as compared with the catalysts of the examples 1 and 2. This indicates that it is more effective to newly add undissolved zirconia later to the second solid solution generated during the preparation of the carrier. In Example 5, since the alumina powder and the ceria-zirconia solid solution were mixed by a wet ball mill, the alumina powder and the ceria-zirconia solid solution were mixed as a solution in the liquid phase and then coprecipitated to obtain the carrier of Examples 1 and 2. In comparison, the dispersibility of alumina and ceria-zirconia solid solution is low. For this reason, the oxygen storage capacity of ceria is slightly reduced, and the purification performance is slightly lowered.

The reason why the first solid solution and the second solid solution and at least one of the undissolved zirconia coexist and exhibit high activity even after the durability test is explained as follows. FIG. 3 shows a schematic cross-sectional view of the catalyst of Example 2. The carrier is composed of γ-alumina 1, a first solid solution 2, and a second solid solution 3, and Pt4 and Rh5 are supported on the carrier.

Here, Rh5 supported on γ-alumina 1
Is dissolved in one phase of γ-alumina during the durability test and its activity is reduced. Further, Rh5 supported on the first solid solution 2 is inhibited from solid solution in γ-alumina 1, but its activity decreases due to interaction with ceria. However, Rh5 supported on the second solid solution 3 having a low composition ratio of ceria with respect to other components.
Means that while the solid solution in the γ-alumina 1 is prevented, the interaction on the second solid solution 3 is smaller than that of the first solid solution 2, the formation of complex oxides and the like is suppressed, and Rh Is maintained.

Therefore, in the catalyst of Example 2, since Rh supported on the second solid solution 3 maintains a high activity,
It shows high purification activity even after the durability test. Example 3
In No. 4, since zirconia in which ceria was not dissolved at all was added later, Rh supported on the undissolved zirconia was used.
Inhibits both solid solution in γ-alumina and interaction with ceria, and shows higher activity.

(Example 6) Al ₂ O ₃ / Ce obtained in Example 4
240 parts by weight of a carrier powder having a molar ratio of O ₂ / ZrO ₂ / BaO of 1 / 0.21 / 0.57 / 0.04, 20.8 parts by weight of aluminum nitrate nonahydrate, 3.6 parts by weight of ghee bemite, and 177 parts by weight of pure water Was mixed and pulverized to prepare a slurry. On the other hand, a step of preparing a cordierite honeycomb base material (1.3 L, 400 cells), dipping in this slurry, pulling it up, blowing off excess slurry, drying at 110 ° C. for 2 hours, and firing at 600 ° C. for 1 hour Is repeated twice to obtain 2 per liter of honeycomb substrate.
30 g of a coat layer was formed. And a predetermined concentration of Pt (NO ₂ ) ₂
A predetermined amount of an aqueous solution of (NH ₃ ) ₂ was impregnated into the coat layer, air-dried at 120 ° C. for 1 hour, and baked at 300 ° C. for 1 hour to carry 1.5 g of Pt per liter of honeycomb substrate. Further, the coat layer was impregnated with a predetermined amount of a rhodium nitrate aqueous solution having a predetermined concentration, and then dried by ventilation at 120 ° C. to carry 0.3 g of Rh per liter of the honeycomb substrate, thereby obtaining a monolith catalyst of Example 6.

(Example 7) The monolith catalyst of Example 6 carrying Pt and Rh was further impregnated with a predetermined amount of an aqueous solution of palladium nitrate having a predetermined concentration into a coat layer, and dried and fired to obtain a honeycomb substrate 1. A monolith catalyst carrying 0.5 g of Pd per liter was prepared. (Example 8) The same procedure as in Example 6 was carried out except that a honeycomb substrate having the same coating layer as in Example 6 was used, and an aqueous solution of palladium nitrate and an aqueous solution of rhodium nitrate were used. A monolith catalyst supporting 1.5 g of Pd and 0.3 g of Rh was prepared.

(Comparative Example 5) 120 parts by weight of the γ-Al ₂ O ₃ powder used in Comparative Example 2, 74 parts by weight of ceria-zirconia solid solution powder, 20.8 parts by weight of aluminum nitrate nonahydrate, and 3.6 parts by weight of ghee bemite And 177 parts by weight of pure water were mixed and pulverized to prepare a slurry, and a coat layer of 190 g per liter of the honeycomb substrate was formed in the same manner as in Example 6. Then, Pt and Rh were supported in the same manner as in Example 6, and a monolith catalyst of Comparative Example 5 was prepared.

(Test / Evaluation) The four types of monolith catalysts of Examples 6 to 8 and Comparative Example 5 were each installed immediately below the engine having a displacement of 2000 cc, and the gas inlet temperature was 850 ° C. (catalyst bed temperature 9
(50 ° C) for 100 hours. Catalysts after the durability test was arranged in an engine bench equipped with a 2000cc engine, respectively, were measured NO _x, 50% purification temperature of CO and HC, respectively. The maximum HC purification rate at 400 ° C was also measured.
Table 4 shows the results.

[0055]

[Table 4] From Table 4, it can be seen that the monolith catalysts of the examples are superior in purification performance after the durability test as compared with Comparative Example 5, and the carrier of the present invention has excellent durability even when used as a full-size monolith catalyst, and has a high performance. It is clear that it shows activity.

[0056]

According to the carrier for an exhaust gas purifying catalyst of the present invention, the solid solution of Rh in alumina or the like is suppressed, and the interaction between Rh and ceria is reduced. Therefore, according to the exhaust gas purifying catalyst supporting Rh on the carrier of the present invention, since the solid phase reaction between Rh and the composite oxide carrier is suppressed, the catalyst exhibits high purification activity even after a durability test and has excellent durability. .

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction chart of the carriers of Example 1, Comparative Examples 1 and 2.

FIG. 2 is an explanatory diagram showing a method of calculating a zirconia solid solution amount in a ceria-zirconia solid solution from an X-ray diffraction chart.

FIG. 3 is a schematic cross-sectional view of a catalyst manufactured using the carrier of Example 2 of the present invention.

[Explanation of symbols]

1: γ-alumina 2: first solid solution
3: Second solid solution 4: Pt 5: Rh

Claims (3)

[Claims] 1. A carrier containing a composite oxide comprising at least ceria and zirconia, wherein the solid solution amount of zirconia in ceria is 0 <Zr / (Ce + Z
r) A solid solution of ceria and zirconia (<0.7), and the amount of zirconia solid solution in ceria is 0.7 ≦ Zr / (Ce
+ Zr) is a solid solution of ceria and zirconia (second solid solution)
And at least one of undissolved zirconia coexists, and at least one of the second solid solution and the undissolved zirconia is at least 30 mol% of the total molar amount of ceria and zirconia in the carrier containing the composite oxide. A carrier for an exhaust gas purifying catalyst, wherein the carrier is contained. 2. The exhaust gas purification according to claim 1, characterized in that it is produced by calcining a precipitate containing at least cerium ions and zirconium ions and coprecipitated from a solution containing a surfactant. Catalyst carrier. 3. The carrier for an exhaust gas purifying catalyst according to claim 2, wherein the surfactant is a cationic surfactant.