JPH08215569A - Exhaust gas purification catalyst and exhaust gas purification device equipped with exhaust gas purification catalyst - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a three-way catalyst that can achieve a high purification rate by suppressing fluctuations in the oxygen storage capacity of cerium, and an exhaust gas purification device equipped with this three-way catalyst. [Structure / Function] The catalyst supporting layer of the three-way catalyst has a cerium-zirconium composite oxide prepared from a metal alkoxide. As a result, the Ce-Zr composite oxide maintains a higher oxygen storage capacity than before from the beginning of use to the endurance at high temperature. Also, cerium oxide is 700 ° C in advance.
The heat treatment has been completed. As a result, there is little change in the oxygen storage capacity of the cerium oxide, and the oxygen storage capacity is properly maintained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst and an exhaust gas purifying apparatus equipped with the exhaust gas purifying catalyst.

[0002]

2. Description of the Related Art Conventionally, there is known an exhaust gas purification device provided with an exhaust gas purification catalyst and an air-fuel ratio control device which are provided in an exhaust system of an internal combustion engine. The exhaust gas purifying catalyst (three-way catalyst) is, for example, a carrier base material made of heat-resistant ceramics such as cordierite, a catalyst supporting layer made of activated alumina or the like formed on the carrier base material, and the catalyst supporting layer. And a catalytic metal such as Pt supported on the substrate. This three-way catalyst purifies hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) in the exhaust gas of an internal combustion engine,
Cerium (Ce) oxide is added as a main component to the catalyst supporting layer. This cerium oxide has an oxygen storage capacity of storing oxygen in an oxidizing atmosphere and releasing oxygen in a reducing atmosphere according to the following formula. For example,
Japanese Patent Publication No. 58-20307 discloses a technique using cerium.

[0003]

Embedded image

Further, it is said that a three-way catalyst containing a catalytic metal and a cerium oxide, when used at a high temperature of 800 ° C. or higher, tends to have a reduced oxygen storage capacity due to crystal growth of the cerium oxide. There is. Therefore, in order to suppress the crystal growth of cerium oxide and maintain a high oxygen storage capacity, means for adding zirconium (Zr) oxide in addition to cerium oxide has also been developed (JP-A-63-1).
16741, JP-A-3-131343).
For example, in Japanese Patent Laid-Open No. 63-116741, at least a part of a cerium oxide and a zirconium oxide is a composite oxide or a solid solution (cerium-zirconium composite oxide (Ce-Zr composite oxide)).

On the other hand, in the air-fuel ratio control device, Japanese Patent Laid-Open No. 61-
As described in Japanese Patent No. 237858, an upstream oxygen sensor is provided on the upstream side of the three-way catalyst, and a downstream oxygen sensor is provided on the downstream side of the three-way catalyst. These upstream oxygen sensor and downstream oxygen sensor are connected via a control circuit. Is connected to the air-fuel ratio adjusting means. The upstream oxygen sensor detects a rich or lean air-fuel ratio (A / F) on the upstream side of the three-way catalyst, and outputs its output signal to the control circuit. Further, the downstream oxygen sensor detects the oxygen concentration of the exhaust gas after purification on the downstream side of the three-way catalyst and outputs its output signal to the control circuit. Therefore, the air-fuel ratio adjusting means adjusts the air-fuel ratio of the internal combustion engine to near the stoichiometric air-fuel ratio (stoichiometric) according to the output of the upstream oxygen sensor, and changes the characteristics of the upstream oxygen sensor according to the output of the downstream oxygen sensor ( A rich shift or a lean shift is detected, and the upstream oxygen sensor is corrected for deterioration.

Thus, in the exhaust gas purifying device to which the air-fuel ratio control device is connected, the three-way catalyst effectively operates under the precise A / F control.

[0007]

However, it has been clarified that the conventional three-way catalyst and the exhaust gas purification apparatus equipped with this three-way catalyst are still unsatisfactory in terms of purification rate. That is, in the above-mentioned conventional three-way catalyst, the oxygen storage capacity of the cerium oxide after the endurance is significantly reduced. Even when the cerium oxide is the above-mentioned conventional Ce-Zr composite oxide, since this Ce-Zr composite oxide is prepared from nitrate and is only partially compounded or solid-soluted, oxygen storage after endurance Noh is greatly reduced. In other words, in the conventional three-way catalyst, although the high oxygen storage capacity of cerium oxide can provide a high purification rate of HC, CO, and NO _{x in} the exhaust gas of the internal combustion engine in the early stage of use, the vehicle has tens of thousands of times. After traveling for, for example, km, the oxygen storage capacity of cerium oxide decreases, and the purification rate also becomes low. This is because the cerium oxide crystals are enlarged and the surface area is reduced after the durability test at high temperature.

Further, in the exhaust gas purifying apparatus equipped with such a three-way catalyst, the oxygen storage capacity of the cerium oxide in the three-way catalyst is high during the initial period of use, and it is thermally unstable. Since the oxygen storage capacity is low and it is thermally stabilized, deterioration correction of the upstream oxygen sensor is performed according to the oxygen storage capacity after stabilization. For this reason, in the initial stage of use, for example, when the upstream oxygen sensor has a rich displacement, the cerium oxide continues to release oxygen for a long time, and the downstream oxygen sensor cannot detect the oxygen concentration of the exhaust gas itself. That is, in this exhaust gas purifying apparatus, the detection of richness and leanness of the downstream oxygen sensor is delayed during the initial period of use, which delays the deterioration correction of the upstream oxygen sensor.

For this reason, the conventional three-way catalyst and the exhaust gas purification apparatus equipped with this three-way catalyst are still unsatisfactory in terms of purification rate. An object of the present invention is to provide a three-way catalyst that can achieve a high purification rate by suppressing fluctuations in the oxygen storage capacity of cerium, and an exhaust gas purification device equipped with this three-way catalyst.

[0010]

[Means for Solving the Problems]

(1) The exhaust gas purifying catalyst according to claim 1 is provided in an exhaust system of an internal combustion engine, and is supported on a carrier base material, a catalyst carrying layer formed on the carrier base material, and the catalyst carrying layer. In an exhaust gas purifying catalyst including a catalytic metal, the catalyst supporting layer has a cerium-zirconium composite oxide prepared from a metal alkoxide.

(2) An exhaust gas purifying apparatus having an exhaust gas purifying catalyst according to claim 2 is provided with an exhaust gas purifying catalyst and an air-fuel ratio control device which are provided in an exhaust system of an internal combustion engine. The apparatus controls an upstream oxygen sensor provided upstream of the exhaust gas purification catalyst, a downstream oxygen sensor provided downstream of the exhaust gas purification catalyst, the upstream oxygen sensor and the downstream oxygen sensor. A circuit connected via a circuit that adjusts the air-fuel ratio of the internal combustion engine to near the stoichiometric air-fuel ratio in accordance with the output of the upstream oxygen sensor and corrects the deterioration of the upstream oxygen sensor in accordance with the output of the downstream oxygen sensor. Fuel ratio adjusting means,
In the exhaust gas purifying apparatus including the exhaust gas purifying catalyst, the exhaust gas purifying catalyst has a cerium-zirconium composite oxide prepared from a metal alkoxide.

In the first and second aspects, the metal alkoxide may be any of methoxide, ethoxide, butoxide, etc., but those having high solubility in alcohol as a solvent are preferable. In addition, an acetyl acetate salt may be used instead of the metal alkoxide. Any alcohol can be used as the solvent. Further, the exhaust gas purifying catalyst according to claim 1 or 2 (three-way catalyst)
It is preferable that at least one of neodymium (Nd) oxide and praseodymium (Pr) oxide is added to or complexed with or solid-soluted in addition to the cerium-zirconium complex oxide (Ce-Zr complex oxide). Such a three-way catalyst can maintain a higher oxygen storage capacity. In this case, neodymium oxide or the like can also be prepared from the metal alkoxide.

(3) An exhaust gas purifying apparatus having an exhaust gas purifying catalyst according to claim 3 is provided with an exhaust gas purifying catalyst and an air-fuel ratio control device provided in an exhaust system of an internal combustion engine. The apparatus controls an upstream oxygen sensor provided upstream of the exhaust gas purification catalyst, a downstream oxygen sensor provided downstream of the exhaust gas purification catalyst, the upstream oxygen sensor and the downstream oxygen sensor. A circuit connected via a circuit that adjusts the air-fuel ratio of the internal combustion engine to near the stoichiometric air-fuel ratio in accordance with the output of the upstream oxygen sensor and corrects the deterioration of the upstream oxygen sensor in accordance with the output of the downstream oxygen sensor. Fuel ratio adjusting means,
In the exhaust gas purifying device including the exhaust gas purifying catalyst, the exhaust gas purifying catalyst is characterized in that the exhaust gas purifying catalyst contains cerium oxide that has been heat-treated at 700 ° C. or higher in advance.

In the third aspect, the lower limit of the temperature of the heat treatment is set to 700 ° C. The reason is that if the temperature is less than 700 ° C., the effect of suppressing the oxygen storage capacity at the initial stage of use due to the crystal growth of cerium oxide is small. This is because the heat treatment requires a long time. On the other hand, the upper limit of the heat treatment temperature is preferably 900 ° C. This is because if the temperature exceeds 900 ° C., the crystal growth of cerium oxide is remarkable and the oxygen storage capacity during use as well as during the initial use is suppressed.

The heat-treated cerium oxide preferably has a primary particle size of 100 Å or less and a BET specific surface area of 30 m ² / g or more. If the primary particle size exceeds 100Å and the BET specific surface area is less than 30 m ² / g, the crystal growth of cerium oxide will be remarkable, and not only the initial use, but also the oxygen storage capacity during use will be suppressed. Is.

The exhaust gas purifying catalyst (three-way catalyst) according to the third aspect of the exhaust gas purifying apparatus can be manufactured by the following method. That is, (a) First, cerium oxide powder is prepared. The cerium oxide powder is preliminarily heat-treated to be thermally stabilized. This cerium oxide powder is made into a coating slurry together with alumina powder and the like, and a catalyst supporting layer is formed on the carrier substrate by this slurry. Then, a catalyst metal such as Pt is supported on this catalyst supporting layer.

(B) First, cerium oxide powder is prepared. The cerium oxide powder is preliminarily heat-treated to be thermally stabilized. A catalyst metal such as Pt is added to this cerium oxide powder. The cerium oxide powder carrying the catalytic metal is mixed with alumina powder or the like to prepare a coating slurry, and the slurry forms a catalyst supporting layer on the carrier substrate.

In the production method (a) or (b), it is preferable to employ a cerium oxide powder prepared from a metal alkoxide, as in the first and second aspects. Moreover, it is preferable to manufacture a three-way catalyst by the manufacturing method of (b). This is because when the catalyst metal is added to the powder of cerium oxide and the catalyst-supporting layer is supported as in the production method of (b), the cerium oxide and the catalyst metal are produced more than in the production method of (a). Are close to each other, the interaction between the cerium oxide and the catalyst metal is enhanced, and a high oxygen storage capacity can be obtained after stabilization.

Further, in the three-way catalyst according to the third aspect, as in the first and second aspects, in addition to the cerium oxide, at least one of zirconium oxide, neodymium oxide and praseodymium oxide is added, compounded or solidified. It is preferably solubilized. In this case, the cerium oxide or the like can be prepared from the metal alkoxide as in the first and second aspects.

[0020]

[Action]

(1) In the three-way catalyst of claim 1, the Ce-Zr composite oxide contained in the catalyst supporting layer is prepared from a metal alkoxide. The Ce-Zr composite oxide thus prepared from the solution by the sol-gel method is more preferable than the Ce-Zr composite oxide prepared from the conventional nitrate and only partially compounded or solid-soluted. And are uniformly mixed at the atomic or molecular level to form a small primary particle size, and each particle is almost entirely a complex oxide or solid solution. Then, this Ce-Zr composite oxide will be contained in the three-way catalyst with a uniform and small particle size by optimally performing the firing. Therefore, this Ce-Zr composite oxide maintains a higher oxygen storage capacity than before from the initial stage of use until after endurance at high temperature.

(2) In the exhaust gas purifying device according to claim 2,
Ce-Zr three-way catalyst prepared from metal alkoxide
It has a complex oxide. The Ce—Zr composite oxide prepared from the solution in this way maintains a higher oxygen storage capacity than before from the initial stage of use to the endurance at high temperature, as in the first aspect. (3) In the exhaust gas purifying apparatus according to claim 3, since the three-way catalyst has the cerium oxide that has been heat-treated in advance, the cerium oxide is crystal-grown to some extent. For this reason,
Even in the initial stage of use, the oxygen storage capacity of cerium oxide is thermally stabilized. That is, the characteristic change of the oxygen storage capacity is small, and the oxygen storage capacity is appropriately maintained. For this reason, in this exhaust gas purifying apparatus, the upstream oxygen sensor is quickly corrected for deterioration without the detection of richness and leanness of the downstream oxygen sensor being delayed during the initial period of use.

[0022]

EXAMPLES The inventions described in each claim will be described below by tests 1 and 2. {Test 1} In Test 1, Examples 1 and 2 embodying Claims 1 and 2 will be described together with Comparative Examples 1 and 2. (Example 1) "Preparation of Ce-Zr composite oxide" First, cerium ethoxide _{(Ce (OC 2 H 5)} 2) and cerium alkoxide alcohol solution dissolving 0.25 mol / l in ethyl alcohol, zirconium ethoxy De (Zr (OC
₂ H ₅ ) ₂ ) in ethyl alcohol 0.55 mol / l
A dissolved zirconium alkoxide alcohol solution is prepared.

Then, the cerium alkoxide alcohol solution and the zirconium alkoxide alcohol solution are mixed to form a uniform solution. This solution is stirred and mixed for 2 hours or more while being kept at 80 ° C. Then, pure water diluted with ethyl alcohol is slowly added to the solution to cause hydrolysis. The amount of water used for hydrolysis was 1/2 of the alkoxide ligand in the solution. The obtained solution was filtered under reduced pressure to separate the solvent and the solute and obtain a precursor powder.

Next, the obtained precursor powder is fired at 600 ° C. for 5 hours. Thus, the Ce-Zr composite oxide (Ce
/ Zr ratio = 5) is obtained. However, the Ce / Zr ratio is 0.1 to
It can be any value between 10. The above compositions are added, stirred and mixed to obtain a coating slurry.

[Catalyst Support Layer Formation] Pure water is dipped in a cordierite honeycomb carrier substrate (1.7 liters), drawn out, and then excess water is blown off to be dipped in the above slurry. This is taken out, excess slurry is blown off, and dried at a temperature of 250 ° C. for 20 minutes. This is baked at 500 ° C. for 1 hour. Thus, the catalyst supporting layer is formed on the carrier substrate. The catalyst supporting layer was 120 g per liter of the carrier substrate.

"Support of catalyst metal" A carrier substrate having a catalyst support layer formed thereon is impregnated with a dinitrodiammine platinum solution and a rhodium nitrate solution, pulled up, and then dried at 250 ° C., whereby Pt is 2.0 g / l. And Rh is 0.2g / l
And carry. Thus, the three-way catalyst of Example 1 is obtained. (Example 2) "Preparation of Ce-Zr-Nd-Pr composite oxide" First, 0.29 mol / l of the same kind of cerium alkoxide alcohol solution and 0.33 mol / l of zirconium alkoxide alcohol solution, and neodymium ethoxy. (Nd (OC ₂ H ₅ ) ₂ ) in ethyl alcohol.
Neodymium alkoxide alcohol solution dissolved in 03 mol / l and prasedium ethoxide (Pr (OC ₂
A praseodymium alkoxide alcohol solution prepared by dissolving H ₅ ) ₂ ) in ethyl alcohol at 0.33 mol / l is prepared.

Then, the cerium alkoxide alcohol solution, the zirconium alkoxide alcohol solution, the neodymium alkoxide alcohol solution, and the praseodymium alkoxide alcohol solution are mixed to form a uniform solution. Using this solution, as in Example 1, C
An e-Zr-Nd-Pr composite oxide is obtained. However, Ce /
As for the Zr / Nd / Pr ratio, Ce is 1 and Zr = 0.1.
~ 10.0, Nd = 0.01 to 10.0, Pr = 0.0
It can take any value between 1 and 10.0.

"Preparation of Coating Slurry" Instead of the Ce-Zr composite oxide of Example 1, Ce-Zr-N was used.
A slurry for coating is prepared in the same manner as in Example 1 except that the d-Pr composite oxide is used. Then, in the same manner as in Example 1, "formation of catalyst support layer" and "support of catalyst metal" are performed to obtain the three-way catalyst of Example 2. (Comparative Example 1) The above compositions are added, stirred and mixed to obtain a coating slurry.

Then, in the same manner as in Example 1, "formation of the catalyst supporting layer" is performed. "Support of Ce-Zr complex oxide" Cerium nitrate (Ce
(NO ₃ ) ₃ ) and zirconium oxynitrate (ZrO
A mixed aqueous solution in which (NO ₃ ) ₃ ) and is dissolved is prepared. The carrier substrate on which the catalyst supporting layer has been formed as described above is immersed in this mixed aqueous solution for 1 minute, and is withdrawn, and then excess water is blown off. This is dried at 250 ° C. for 20 minutes and then baked in air at 500 ° C. for 1 hour. As a result, the supported amount per 1 l of the catalyst is Ce / Zr ratio = 0.25 / 0.05mo
1 of Ce-Zr composite oxide (Ce / Zr ratio = 5) is supported.

"Support of catalytic metal" As in Example 1, Ce was used.
-Pt and Rh on the catalyst supporting layer supporting the -Zr composite oxide
And carry. Thus, the three-way catalyst of Comparative Example 1 is obtained. (Comparative Example 2) "Preparation of Ce-Zr composite oxide" commercially available CeO ₂ powder (average particle diameter; 20 [mu] m or less, BET specific surface area; 50 m ²
/ G or more) is prepared, and this CeO ₂ powder is immersed in an aqueous zirconium oxynitrate solution. After pulling this out, 2
Dry at 50 ° C for 20 minutes and in air at 500 ° C for 1 min.
Bake for hours. Thereby, the Ce-Zr composite oxide (C
e / Zr ratio = 5) is obtained.

[0031] The above compositions are added, stirred and mixed to obtain a coating slurry.

Then, in the same manner as in Example 1, "forming the catalyst supporting layer" and "supporting the catalytic metal" are carried out to obtain the three-way catalyst of Comparative Example 2. (Evaluation 1) An engine (displacement amount; each three-way catalyst of Examples 1 and 2 and Comparative Examples 1 and 2) to which an air-fuel ratio control device was connected
It is installed in the exhaust system of 2l). Then, with respect to each exhaust gas purifying apparatus, performance evaluation by engine exhaust gas was performed.

The performance evaluation items are as follows. 50% purification temperature (° C) ... A / F = 14.6 (stoichi)
The exhaust gas temperature was raised from the low temperature side, and the temperature at which the purification rate reached 50% was measured. 400 ° C purification rate (%) ... A / F = 14.6 (stoichi)
Set the exhaust gas temperature of 400 ℃, HC, CO and N
The purification rate of O _x was determined.

Ce particle size (Å) ... XRD of cerium oxide
The particle size was calculated from the peak. Emission (g / mile) ... Durability is gas temperature 8
At 00 ° C., amplitude was applied in a constant cycle centered on A / F = 14.5 (stoichiometric) for 100 hours. The activity after this endurance was evaluated. The results are shown in Tables 1 and 2.

[0035]

[Table 1]

[0036]

[Table 2]

From Tables 1 and 2, the exhaust gas purifying apparatuses having the three-way catalysts of Examples 1 and 2 are more durable than the exhaust gas purifying apparatuses having the three-way catalysts of Comparative Examples 1 and 2. HC, C
It can be seen that the activities of O and NO _x are improved. This is a Ce-Zr composite oxide and Ce-Zr-Nd-Pr.
This is because the composite oxide is prepared from the metal alkoxide, and thus the particle size is maintained finer than that of the Ce-Zr composite oxides of Comparative Examples 1 and 2.

Therefore, the exhaust gas purifying apparatuses of Examples 1 and 2 were made of Ce-Zr composite oxide and Ce-Zr-Nd-.
From the initial use of Pr compound oxides to the endurance at high temperatures,
It can be seen that it has a higher oxygen storage capacity than before and can exhibit a high purification rate. In particular, it can be seen that the exhaust gas purifying apparatus of Example 2 has improved activity of HC, CO, and NO _x after endurance as compared with the exhaust gas purifying apparatuses of Example 1 and Comparative Examples 1 and 2. This is Ce-Zr-Nd-Pr
This is because the composite oxide maintains a higher oxygen storage capacity than the Ce-Zr composite oxide.

Therefore, it is understood that the exhaust gas purifying apparatus of the second embodiment can exhibit a higher purification rate due to the higher oxygen storage capacity. {Test 2} In Test 2, Example 3 in which Claim 2 is embodied
6 will be described together with Comparative Examples 3 and 4. (Example 3) "Preparation and heat treatment of activated alumina powder containing cerium oxide" Activated alumina powder (BET specific surface area; 200 m ²
/ G) in a mixed aqueous solution of cerium nitrate and zirconium oxynitrate. After this, it is dried and calcined in air at 800 ° C. for 5 hours. Thus, it is thermally stabilized with 25% by weight of cerium oxide and 3.5% by weight.
To obtain activated alumina powder containing zirconium oxide. The primary particle size of the Ce-Zr composite oxide was 80Å.

[0040] The above compositions are added, stirred and mixed to obtain a coating slurry.

[Catalyst Support Layer Formation] Pure water is dipped in a cordierite honeycomb carrier substrate (1.7 l) to draw it out, and then excess water is blown off to be dipped in the above slurry. This is taken out, excess slurry is blown off, and dried at a temperature of 250 ° C. for 20 minutes. This is baked at 500 ° C. for 1 hour. Thus, the catalyst supporting layer is formed on the carrier substrate. The catalyst supporting layer was 120 g per liter of the carrier substrate.

"Supporting of catalyst metal" The carrier substrate on which the catalyst supporting layer is formed is impregnated with a dinitrodiammine platinum solution and a rhodium nitrate solution, pulled up, and then dried at 250 ° C to obtain Pt of 1.0 g / l. And Rh is 0.2g / l
And carry. Thus, the three-way catalyst of Example 3 is obtained. (Example 4) "Preparation and heat treatment of the cerium oxide" commercially available CeO ₂ powder (average particle diameter; 20 [mu] m or less, BET specific surface area; 50 m
² / g or more) is prepared, and this CeO ₂ powder is impregnated with an aqueous zirconium oxynitrate solution. After pulling this out,
Dry and bake in air at 800 ° C. for 5 hours. Thus, 15% by weight of zirconium oxide is dissolved in CeO ₂ to obtain a thermally stabilized Ce-Zr composite oxide. The primary particle size of Ce-Zr composite oxide is 100Å, BE
The T specific surface area was 30 m ² / g.

[0043] The above compositions are added, stirred and mixed to obtain a coating slurry.

Then, in the same manner as in Example 3, "formation of catalyst supporting layer" and "support of catalytic metal" are carried out to obtain the three-way catalyst of Example 4. "Preparation of cerium oxide, the heat treatment and the addition of the catalyst metal" (Example 5) Similarly to Example 4, a zirconium oxide CeO ₂ is 15 wt% solid solution, Ce-Zr composite was thermally stabilized Obtain the oxide.

Next, the Ce-Zr composite oxide is dipped in a dinitrodiammine platinum solution, extracted, and dried. Thus, 2 wt% Pt was added to the Ce-Zr composite oxide.
Is added. "Preparation of coating slurry" Ce-Z of Example 4
A slurry for coating is prepared in the same manner as in Example 4 except that Ce-Zr composite oxide containing Pt is used instead of the r composite oxide.

[Preparation of three-way catalyst] Then, as in Example 3, "formation of catalyst supporting layer" is carried out. The carrier base material on which the catalyst supporting layer is formed is impregnated with a rhodium nitrate solution, pulled up, and then dried at 250 ° C. Thus, Pt is 1.0 g /
1 and Rh of 0.2 g / l. Thus, the three-way catalyst of Example 5 is obtained. Example 6 Commercially available CeO ₂ powder (average particle size: 20 μm)
Below, BET specific surface area; 50 m ² / g or more) is prepared,
An aqueous solution of zirconium oxynitrate, an aqueous solution of praseodymium nitrate and an aqueous solution of neodymium nitrate are respectively impregnated, dried, and then baked in air at 800 ° C. for 5 hours.

Thus, the Ce-Zr composite oxidation of Example 4 was performed.
50% by weight of CeO instead of ₂And 40% by weight
ZrO₂And 5 wt% NdO₂And 5% by weight of PrO
₂A composite oxide containing and is used. Other conditions are as in Example 4.
Similarly, the three-way catalyst of Example 6 is obtained. Ce-Zr-N
The primary particle size of d-Pr composite oxide is 80Å, BET ratio surface
Product is 50m²/ G. (Comparative Example 3) "Preparation of activated alumina powder containing cerium oxide" activity
Alumina powder (BET specific surface area; 200 m²/ G)
In a mixed aqueous solution of cerium acid and zirconium oxynitrate
Impregnate. After this it is dried and dried in air at 50
Bake at 0 ° C. for 5 hours. In this way, it stabilizes thermally
25 wt% cerium oxide, 3.5 wt% without
% Activated zirconium oxide to obtain activated alumina powder
It The primary particle size of Ce-Zr composite oxide is 30Å
Was.

Then, in the same manner as in Example 3, "preparation of slurry for coating", "formation of catalyst supporting layer" and "support of catalytic metal" are carried out to obtain the three-way catalyst of Comparative Example 3. Comparative Example 4 “Preparation of Cerium Oxide” Commercially available CeO ₂ powder (average particle size: 20 μm or less, BET specific surface area: 50 m ² / g or more) was prepared, and this CeO ₂ powder was impregnated in an aqueous zirconium oxynitrate solution. To do. After pulling this out, dry it,
Bake for 5 hours at 500 ° C. in air. Thus
15% by weight of zirconium oxide is dissolved in CeO ₂ powder to obtain a Ce-Zr composite oxide that is not thermally stabilized. The primary particle size of Ce-Zr composite oxide is 80Å, B
The ET specific surface area was 100 m ² / g.

Then, in the same manner as in Example 4, "preparation of coating slurry", "formation of catalyst supporting layer" and "support of catalytic metal" are carried out to obtain the three-way catalyst of Comparative Example 4. (Evaluation 2) An engine (displacement amount; each of the three-way catalysts of Examples 3 to 6 and Comparative Examples 3 and 4 to which an air-fuel ratio control device is connected)
It is provided in the 2l) exhaust system. Then, with respect to each exhaust gas purifying apparatus, performance evaluation by engine exhaust gas was performed. The performance evaluation is that the exhaust temperature is 800 ° C. and A / F = 14.
Amplitude was applied at a fixed period centered on 5 (Stoichi) 10
This is a 0-hour durability test. Then, the oxygen storage capacity and purification rate of each three-way catalyst before and after the durability test were evaluated on the engine bench.

The performance evaluation items are as follows. Oxygen storage capacity… Set exhaust gas temperature to 400 ℃,
A / F is changed between 14.0 (rich) and 15.0 (lean) at 0.1 Hz, the oxygen concentration at the outlet side of each three-way catalyst at that time is detected, and measured by the theoretical air-fuel ratio holding time. did. Purification rate ... Measured with A / F set to 14.6 (stoichiometric) and exhaust gas temperature set to 400 ° C.

The results are shown in Table 3.

[0052]

[Table 3]

Next, each three-way catalyst was attached to the exhaust system of the engine (displacement: 2 liters) vehicle, and the emission in the LA # 4 mode was measured. Two oxygen sensors are installed on the exhaust system on the upstream side of the three-way catalyst and immediately after the downstream side of the three-way catalyst.
Is controlled. The results are shown in Table 4.

[0054]

[Table 4]

From Tables 3 and 4, in the exhaust gas purifying apparatuses equipped with the three-way catalysts of Examples 3 to 6, the cerium oxide of the three-way catalyst was stabilized in advance by heat treatment.
It can be seen that the change in the oxygen storage capacity before and after the endurance is smaller than that of the exhaust gas purifying device equipped with the three-way catalyst. Therefore, it is understood that the exhaust gas purifying devices of Examples 3 to 6 can suppress the deterioration of NO _x emission particularly in the initial stage of use.

Therefore, in the exhaust gas purifying apparatuses of Examples 3 to 6, since the characteristic change of the oxygen storage capacity of the cerium oxide in the three-way catalyst is small and the oxygen storage capacity is properly maintained, the oxygen storage capacity during the initial period of use is reduced. However, it turns out that a high purification rate can be exhibited. Further, in the exhaust gas purification devices of Examples 3 to 6, compared with the exhaust gas purification devices of Comparative Examples 3 and 4, the crystal growth of the catalyst metal accompanying the crystal growth of cerium oxide was suppressed, and the performance after durability was improved. You can see that

Particularly, in the exhaust gas purifying apparatus of the fifth embodiment,
Since Pt was added to the cerium oxide, Example 4
It can be seen that the cerium oxide and Pt interaction are enhanced and the performance is improved, as compared with the exhaust gas purifying device.
Further, in the exhaust gas purifying apparatus of the sixth embodiment, zirconium oxide, neodymium oxide and praseodymium oxide are added to the cerium oxide to improve the heat resistance of the cerium oxide. Compared to purification equipment,
It can be seen that the performance improvement after endurance is great.

[0058]

As described above in detail, since the inventions described in each claim employ the configurations described in each claim, a high purification rate can be exhibited. That is, in the three-way catalyst of claim 1, Ce-
Since the Zr composite oxide maintains a higher oxygen storage capacity than before, a high purification rate can be exhibited.

According to the exhaust gas purifying apparatus of claim 2,
Since the Ce-Zr composite oxide maintains a higher oxygen storage capacity than before from the initial use to the endurance at high temperature,
A high purification rate can be exhibited. Further, claim 3
In the exhaust gas purification device of No. 3, since the characteristic change of the oxygen storage capacity of the cerium oxide in the three-way catalyst is small and the oxygen storage capacity is properly maintained, it is possible to exhibit a high purification rate even during the initial period of use. .

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01J 23/56 ZAB

Claims (3)

[Claims] 1. Exhaust gas purification provided in an exhaust system of an internal combustion engine, comprising a carrier substrate, a catalyst supporting layer formed on the carrier substrate, and a catalyst metal supported on the catalyst supporting layer. A catalyst for exhaust gas purification, wherein the catalyst-supporting layer has a cerium-zirconium composite oxide prepared from a metal alkoxide. 2. An exhaust gas purification catalyst and an air-fuel ratio control device, which are provided in an exhaust system of an internal combustion engine, wherein the air-fuel ratio control device is an upstream oxygen sensor provided upstream of the exhaust gas purification catalyst. A downstream oxygen sensor provided on the downstream side of the exhaust gas purifying catalyst, the upstream oxygen sensor and the downstream oxygen sensor via a control circuit, and the internal combustion engine according to the output of the upstream oxygen sensor. And an exhaust gas purifying device including an exhaust gas purifying catalyst, which adjusts the air-fuel ratio of the exhaust gas to near the theoretical air-fuel ratio and corrects the deterioration of the upstream oxygen sensor according to the output of the downstream oxygen sensor. In the exhaust gas purifying apparatus, the exhaust gas purifying catalyst comprises a cerium-zirconium composite oxide prepared from a metal alkoxide. 3. An upstream oxygen sensor provided in an exhaust system of an internal combustion engine, comprising an exhaust gas purification catalyst and an air-fuel ratio control device, wherein the air-fuel ratio control device is provided upstream of the exhaust gas purification catalyst. A downstream oxygen sensor provided on the downstream side of the exhaust gas purifying catalyst, the upstream oxygen sensor and the downstream oxygen sensor via a control circuit, and the internal combustion engine according to the output of the upstream oxygen sensor. And an exhaust gas purifying device including an exhaust gas purifying catalyst, which adjusts the air-fuel ratio of the exhaust gas to near the theoretical air-fuel ratio and corrects the deterioration of the upstream oxygen sensor according to the output of the downstream oxygen sensor. In the exhaust gas purifying apparatus, the exhaust gas purifying catalyst comprises cerium oxide that has been heat-treated at 700 ° C. or higher in advance.