JP2000024516A - Catalyst for cleaning exhaust gas and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability by supporting most of a metal oxide in pores of a porous support in a catalyst for cleaning exhaust gas in which the metal oxide having an oxygen occlusion/release capacity and a noble metal are supported on the porous support. SOLUTION: In a catalyst for cleaning the exhaust gas of motor cars and others, most of a metal oxide having an oxygen occlusion/release capacity is supported in the pores of a porous support. In this way, a large surface area is kept even after a durability test, and the deterioration of the oxygen occlusion/release capacity is controlled. A silica porous body to be used is at least 1,000 in molar ratio and contains exceeding 0.070 cm3/g total volume of meso-pores 4 mm or below in diameter, and a noble metal and the metal oxide 4 nm or below in particle size having the oxygen storage/release capacity are supported in the meso-pores. Such catalyst for cleaning exhaust gas is produced by a process in which the porous support is impregnated with the sol of a compound containing the metal of the metal oxide or the solution of an alkoxide of the metal and baked.

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 for purifying automobile exhaust gas and the like, and a method for producing the same. The exhaust gas purifying catalyst of the present invention can be used for, for example, hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (N
It is useful as a three-way catalyst for simultaneously redoxing and purifying O _x ).

[0002]

2. Description of the Related Art Conventionally, as a catalyst for purifying exhaust gas of automobiles, CO and CO in exhaust gas at a stoichiometric air-fuel ratio (stoichiometric) have been used.
A three-way catalyst that purifies exhaust gas by simultaneously oxidizing HC and reducing NO _x is used. As such a three-way catalyst, for example, a porous carrier layer made of γ-alumina is formed on a heat-resistant substrate made of cordierite or the like, and platinum (Pt), rhodium (Rh), or the like is formed on the porous carrier layer. Which carry noble metals are widely known.

[0003] On the other hand, cerium oxide (ceria) is known as an oxygen storage and release material because it has an action of storing and releasing oxygen, and is widely used as an auxiliary catalyst of an exhaust gas purifying catalyst for purifying exhaust gas from an internal combustion engine. . For example, a three-way catalyst is used in a state where the air / fuel (A / F) ratio is controlled to approximately the stoichiometric air-fuel ratio, but the air-fuel ratio may deviate from the stoichiometric air-fuel ratio in a transition region. In such a case, if a catalyst containing ceria is used, the air-fuel ratio can be controlled close to the stoichiometric air-fuel ratio by the oxygen storage / release action of ceria, and the width (window) of the air-fuel ratio increases, thereby improving the purification performance. Further, since the oxygen partial pressure is adjusted to be substantially constant, there is also an effect that grain growth of the noble metal as a catalyst component is prevented. Since it is desirable to increase the specific surface area in order to increase the oxygen storage / release capacity, ceria is used in a powder state.

However, since the exhaust gas purifying catalyst is used at a high temperature, it is necessary to exhibit a high purifying activity even after being exposed to a high temperature. So in Celia,
Even when the powder is used so as to have a high specific surface area, it is required that the specific surface area does not decrease much when used at a high temperature, that is, the powder has excellent heat resistance.
Therefore, it has been conventionally proposed to use an oxide of a rare earth element other than zirconia and cerium dissolved in ceria.

For example, JP-A-3-131343, JP-A-4-5
No. 5315 discloses an exhaust gas purifying catalyst in which a composite oxide of ceria and zirconia is formed by utilizing a precipitation reaction from an aqueous solution, and a slurry containing the composite oxide is applied to a monolithic carrier. In this exhaust gas purifying catalyst, since zirconia is dissolved in ceria, a superior oxygen storage / release capacity can be obtained as compared with a case where ceria is used alone or a case where ceria and zirconia are mixed in a powder state. As shown, zirconia has excellent heat resistance due to its stabilizing action.

As a carrier for a three-way catalyst or the like, alumina is generally used, and alumina having a noble metal such as platinum (Pt) supported thereon is widely used. Then, in order to further impart oxygen storage / release capability, for example, JP-A-8-155302 discloses that a noble metal and an average particle size of 5 to 100 nm are used.
An exhaust gas purifying catalyst in which ceria is supported on a porous carrier is disclosed. By carrying ceria in a highly dispersed state as fine particles in this manner, a high oxygen storage / release capability is exhibited due to an increase in surface area. By supporting as a ceria-zirconia composite oxide, increase in surface area at high temperature is suppressed, and durability is improved.

On the other hand, NO purifying by selectively reduce NO _{x
As a} selective reduction type exhaust gas purifying catalyst, a diesel exhaust gas purifying catalyst having a noble metal supported on zeolite is known. Zeolites have many acid sites and are acidic in nature.
It has excellent HC adsorption ability and adsorbs HC in exhaust gas. Therefore, even in the exhaust gas in an oxygen excess atmosphere, the vicinity of the catalyst is HC
The atmosphere becomes stoichiometric to rich, and HC and NO released from zeolite are catalyzed by the supported noble metal.
_{The x} reacts with NO to reduce and purify NO _x .

[0008] Zeolite has a cracking effect, and is composed of mordenite, ZSM-5, ultra-stable Y-type zeolite (US
Zeolites such as -Y) exhibit particularly high cracking effects. Therefore, by using these zeolites as catalyst carriers, SOF (Soluble
Organic Fraction) is cracked into low-molecular-weight HC that is more susceptible to reaction, whereby NO _x can be reduced and purified more efficiently. Zeolite with a small SiO ₂ / Al ₂ O ₃ ratio has many ion exchange sites and exhibits high cracking ability and high HC adsorption ability, so catalysts supporting a noble metal on them have excellent HC purification ability and NO _x purification ability. I have.

Therefore, an exhaust gas purifying catalyst having both zeolite and a metal oxide such as ceria having the ability to occlude and release oxygen has been recalled, and is disclosed in Japanese Patent Application Laid-Open No. Hei 10-128122 (Japanese Patent Application No. Hei 8-128122).
No. 284050) discloses an exhaust gas purifying catalyst comprising a support containing a porous oxide, a zeolite and a metal oxide having an oxygen storage / release capability, and a noble metal supported on the support.

In this catalyst, the metal oxide having the oxygen storage / release capability stores oxygen excessively contained in the exhaust gas at a low temperature range. Then, oxygen is released from the metal oxide when the temperature is raised. Since the released oxygen has high activity, it reacts with the hydrocarbon adsorbed on the zeolite to activate the hydrocarbon. The activated hydrocarbons have high reactivity, is considered to react with NO _x to reduce and purify NO _x even in low temperature range, thereby improving the _the NO _x purification performance in low temperature range.

[0011]

However, in the conventional exhaust gas purifying catalyst described above, when a high-temperature durability test is performed, the oxygen storage / release capability of the metal oxide having the oxygen storage / release capability is gradually reduced, and the purification is accordingly performed. There is a problem that performance is also reduced. In addition, when the metal oxide having the ability to occlude and release oxygen and the noble metal are close to each other, there is also a problem that grain growth easily occurs in the noble metal during the durability test.

[0012] In the case of zeolite having a small SiO ₂ / Al ₂ O ₃ ratio and a large number of ion-exchange sites, a hydrothermal endurance test shows that zeolite is deoxidized.
(Four coordination in the zeolite structure becomes six coordination), so that the acid sites are easily lost and the cracking ability is lowered. Furthermore, in such a catalyst in which a noble metal is ion-exchanged and supported on zeolite, the crystal structure is destroyed due to the removal of Al during the hydrothermal durability test, and the activity of the noble metal is greatly reduced due to grain growth of the noble metal, resulting in low durability. was there.

For example, Japanese Patent Application Laid-Open No. 4-176337 discloses that a noble metal is supported on a high silica zeolite having a Si / Al ratio of 40 to less than 1000 (80 to less than 2000 in terms of SiO ₂ / Al ₂ O ₃ ). An exhaust gas purifying catalyst is disclosed. In zeolite having a large Si / Al ratio, grain growth of a noble metal due to Al removal is suppressed. However, in zeolites having a large Si / Al ratio, it is difficult to sufficiently support a noble metal because of a small number of ion exchange sites. Therefore, there is a problem that the NO _x purification ability is low from the beginning of use. In addition, precious metals are concentrated on a small number of ion exchange sites, making it difficult to carry precious metals in a highly dispersed state.Because noble metals are easy to move on zeolite, grain growth easily occurs after a durability test, resulting in excellent durability. It is hard to say that.

The present invention has been made in view of such circumstances, and an object of the present invention is to suppress a decrease in durability of an exhaust gas purifying catalyst supporting a metal oxide having an oxygen storage / release capability and a noble metal. And

[0015]

According to a first aspect of the present invention, there is provided a catalyst for purifying exhaust gas, which comprises a metal oxide having oxygen storage / release capability and a noble metal supported on a porous carrier. In the catalyst for use, most of the metal oxide is supported in the pores of the porous carrier.

A feature of the exhaust gas purifying catalyst according to the present invention is that, in the exhaust gas purifying catalyst in which a noble metal is supported on a carrier made of porous silica, the silica porous material has a molar ratio (SiO ₂ / Al ₂ O _3). ) Is not less than 1000 and contains mesopores having a diameter of 4 nm or less in a total volume exceeding 0.070 cm ³ / g,
At least in the mesopores, a metal oxide having a noble metal and oxygen storage / release capability and having a particle size of 4 nm or less is supported.

The feature of the production method according to claim 3 that can produce the catalyst for purifying exhaust gas according to claim 1 or 2 is that the porous carrier has a metal oxide having an oxygen storage / release capability and a noble metal. In a method for producing a supported exhaust gas purifying catalyst, a porous carrier is impregnated with a sol of a compound containing a metal constituting a metal oxide or an alkoxide solution of a metal constituting a metal oxide, and then calcined.

The feature of the production method according to claim 4 that can produce the exhaust gas purifying catalyst according to claim 1 or 2 is that the porous carrier has a metal oxide having an oxygen storage / release capability and a noble metal. In a method for producing a supported exhaust gas purifying catalyst, a porous carrier and a metal oxide powder having a particle diameter smaller than the pore diameter of the porous carrier are mixed and then calcined.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst according to the first aspect, most of the metal oxide having the ability to occlude and release oxygen is supported in the pores of the porous carrier. Therefore, since it is difficult for the metal oxide having the oxygen storage / release capability to grow grains larger than the diameter of the supported pores, a high surface area can be maintained even after the durability test, and the decrease in the oxygen storage / release capability is suppressed. It is thought that.

Further, in the conventional exhaust gas purifying catalyst, the noble metal supported on the metal oxide having the oxygen storage / release capability or the noble metal close to the metal oxide having the oxygen storage / release capability is the same as that of the metal oxide. It is considered that the grains grow along with the grain growth. However, in the exhaust gas purifying catalyst of the present invention, since the grain growth of the metal oxide itself is suppressed, the grain growth of the noble metal is also suppressed, thereby improving the durability.

In the production method according to the third aspect, which is most suitable for producing the exhaust gas purifying catalyst, a sol of a compound containing a metal constituting a metal oxide having an oxygen storage / release capability or a metal constituting a metal oxide is provided. Is impregnated in a porous carrier. The colloid particles in the sol as the metal oxide source are very fine particles, and the alkoxide as the metal oxide source is a liquid dissolved in alcohol. Therefore, the metal oxide source easily penetrates into the pores of the porous carrier, and most of the metal oxide having an oxygen storage / release capability generated by firing it is supported in the pores. Thereafter, the noble metal is supported according to a conventional method. Alternatively, a porous carrier that already supports a noble metal may be used.

Further, the exhaust gas purifying catalyst can be produced by the production method according to the fourth aspect. In this production method, a porous carrier and a metal oxide powder having an oxygen storage / release capability are mixed. As the powder of the metal oxide having the ability to store and release oxygen, a powder having a particle diameter smaller than the pore diameter of the porous carrier is used. Therefore, the metal oxide powder easily enters the pores of the porous carrier, and the metal oxide powder is also supported in the pores. Since it is relatively difficult to produce a fine powder of a metal oxide, it is preferable to apply the production method according to the present invention when the pore diameter of the porous carrier is large.

As the porous carrier used in the exhaust gas purifying catalyst and the method for producing the same, at least one selected from alumina, silica, titania, zirconia, silica-alumina, titania-zirconia, zeolite and the like can be used. Alumina is α-alumina, γ
-Alumina or the like can be used. Examples of the metal oxide having the oxygen storage / release capability include rare earth metal oxides such as CeO ₂ and PrO ₄ and transition metal oxides such as NiO ₂ , Fe ₂ O ₃ , CuO and Mn ₂ O ₅ .

This metal oxide having the ability to store and release oxygen
Is 10 to 400 parts by weight for 100 parts by weight of the porous carrier.
It is preferable to carry them together. Has oxygen storage / release capability
If the ratio of metal oxide is less than 10 parts by weight, activation of HC
Becomes difficult and NO in low temperature range _xNo improvement in purification ability
No. Mixing more than 400 parts by weight lowers the catalytic activity
I do.

As the noble metal, at least one of platinum (Pt), palladium (Pd), rhodium (Rh) and iridium (Ir) can be used. The noble metal may be supported on any of a porous carrier and a metal oxide having an oxygen storage / release capability. The amount of the noble metal carried is desirably in the range of 0.01 to 30 g per liter of the catalyst. Can hardly purify NO _x is less than 0.01 g, since activity was more than 30g bearing is saturated, further bearing is only results in an increase in cost.

In the production method according to the third aspect, the sol of the compound containing a metal constituting the metal oxide is a metal oxide by firing such as a sol of the metal oxide itself or a sol of various salts or complex salts. Can be used. Further, the sol or alkoxide solution enters the pores even under atmospheric pressure due to the capillary action, but it may be difficult to enter due to the air present in the pores. Therefore, it is preferable to forcibly enter the pores under reduced pressure or increased pressure. It is also effective to apply vibration with ultrasonic waves or the like. By doing so, most of the metal oxide having the ability to occlude and release oxygen can be supported in the pores.

The order of loading the metal oxide having the oxygen storage / release capability and the noble metal is not particularly limited. Either one may be loaded first, or the two may be loaded simultaneously if devised. And in the exhaust gas purifying catalyst according to claim 2,
The molar ratio (SiO ₂ / Al ₂ O ₃ ) is 1000 or more and the diameter is 4 nm
A porous silica material containing the following mesopores in an amount exceeding 0.070 cm ³ / g is used as a carrier, and a noble metal and cerium oxide having a particle size of 4 nm or less are supported in at least the mesopores of the carrier.

Examples of the porous silica used in the present invention include fluorite group, borosoda group, A-type zeolite group, faujasite group, soda-fluorite group, mordenite group, and kiffite group, and synthetic zeolites whose structure is still unknown. And zeolite or silicalite. And, in the present invention, among the porous silica, SiO ₂ / Al ₂
A carrier having an O ₃ ratio of 1000 or more is used. SiO ₂ / A
If the l ₂ O ₃ ratio is less than 1,000, the pore structure (zeolite structure, etc.) peculiar to the substance is easily destroyed due to the removal of Al during hydrothermal durability, and the number of ion exchange sites increases, so Although the catalyst noble metal is highly dispersed and supported, the activity of the catalyst noble metal deteriorates due to the grain growth of the catalyst noble metal due to the removal of Al, which causes a problem in durability.

Crystals of crystalline silica porous material such as zeolite are usually crystals having a regular shape such as a rectangular parallelepiped or hexagonal column, but rarely have a distorted shape. It is considered that the distorted particles are not single crystals but a state in which a plurality of single crystals are bonded (twin), but the cause of such distorted particles has not been elucidated yet. The distorted particles are not single crystals but a plurality of single crystals bonded to each other, and there are mesopores having a diameter larger than ordinary pores at grain boundaries between the bonded single crystals.

Therefore, in the present invention, a porous silica material containing mesopores having a diameter of 4 nm or less in a total volume exceeding 0.070 cm ³ / g is used as a carrier. Mesopore is 2-5nm
The pores having a diameter smaller than 2 nm are called micropores and are distinguished. Therefore, in the present invention, a silica porous material having 2 to 4 nm mesopores can be used. When the total amount of 2 to 4 nm mesopores in the porous silica is 0.070 cm ³ / g or less in total volume, the amount of metal oxide having an oxygen storage / release capability in the pores decreases, and The durability of the release ability is reduced, and the purification performance after the durability test is also reduced. The pore distribution can be measured using an N ₂ adsorption method or the like.

In the exhaust gas purifying catalyst of the present invention, at least in the mesopores, a noble metal and a metal oxide having a particle diameter of 4 nm or less and capable of occluding and releasing oxygen are supported. Therefore, noble metals and metal oxides are unlikely to come out of the mesopores, and because their movement is regulated, grain growth to a size larger than the diameter of the mesopores is suppressed. It is estimated that the oxide is maintained in a highly dispersed state. Therefore, even after the durability test, high oxygen storage / release capability is maintained, and high purification performance is maintained.

The exhaust gas purifying catalyst according to the second aspect can also be produced by the production method according to the third or fourth aspect. The type and amount of the metal oxide having oxygen storage / release capability that can be used, and the type and amount of the noble metal are the same as those of the catalyst described in claim 1.

[0033]

The present invention will be specifically described below with reference to Test Examples, Examples and Comparative Examples. (Test Example) <HC purification performance> molar ratio _{(SiO 2 / Al 2 O 3} ) 40,200,800,
ZSM-5 powders containing five levels of 1000 and 2000 and four levels of strained particles of 0, 4, 6, and 20% by volume, respectively, were prepared. The amount of the distorted particles is measured by observation with a scanning electron microscope (SEM).

Four types of ZSM-5 sorted by the amount of strained particles
The powder has a pore size of 4 almost independent of the SiO ₂ / Al ₂ O ₃ ratio.
nm or less of mesopores each 0.042cm ³ /g,0.070cm ³ /
g, contains 0.094cm ³ / g and 0.126cm ³ / g, a positive correlation between the amount of mesopores quantity and distorted particles. The amount of the mesopores is measured by N ₂ adsorption method. Each of the ZSM-5 powders is immersed in a predetermined concentration of tetraammine platinum hydroxide aqueous solution, filtered, and dried at 110 ° C for 120 minutes.
Pt was loaded. The loading amount of Pt is 1.6% by weight.

The SiO ₂ / Al ₂ O ₃ ratio is set to 40,200,800,1000 and
ZSM-5 powders containing 5 levels of 2000 and 2 levels of strained particles at 0 and 20% by volume, respectively, were prepared. Then, immersed in an aqueous solution of hexaammine rhodium hydrochloride at a predetermined concentration, and after filtration 1
It was dried at 10 ° C for 120 minutes and calcined at 400 ° C for 2 hours to carry Rh. The loading amount of Rh is 0.83% by weight. Each of the obtained catalyst powders was formed into a pellet having a diameter of 0.5 to 1.4 mm by a conventional method, to obtain a pellet catalyst.

Each of the obtained pellet catalysts was subjected to a durability test of heating at 800 ° C. for 5 hours in a nitrogen gas stream containing 10% by volume of oxygen gas and 10% by volume of steam. After the endurance test, each of the pellet catalysts was placed in a model gas flow passage, and stoichiometric gas shown in Table 1 was flowed at a flow rate of 10 liter / min with respect to 1.4 g of the pellet catalyst, to thereby determine the HC purification rate at each temperature. It was measured. Then, the 50% purification temperature of HC in each pellet catalyst was calculated from the obtained data, and the results are shown in FIG.

[0037]

[Table 1] Table 2 shows a list of catalysts corresponding to the symbols in FIG.

[0038]

[Table 2] Than 1, indicated by the symbol ○ and ◎, 4 nm or less of the amount of mesopores 0.094cm ³ / g and 0.126cm ³ / g, the amount of distorted particles of 6 and 20% by volume of ZSM-5 powder It can be seen that the pellet catalyst used exhibited extremely excellent purification performance when the SiO ₂ / Al ₂ O ₃ ratio was 1000 or more. In addition, the lower limit for the use of those having a mesopore size of 4 nm or less of 0.070 cm ³ / g as indicated by the symbol △ is the lower limit.

(Example 1) Therefore, SiO ₂ / Al ₂ O ₃ was used as a carrier.
Mesopores having a ratio of 1900 and a pore diameter of 4 nm or less are 0.126 cm ³ / g
Using 100 g of the ZSM-5 powder, both Pt and Rh were ion-exchanged in the same manner as in the test examples. The loading amount of Pt is 2 g,
The supported amount of Rh is 0.1 g. Based on the total amount of the Pt-Rh-supported ZSM-5 powder, 150 g of ceria sol (CeO ₂ concentration: 20% by weight) having a colloid particle diameter of 3 nm, that is, 30 g as CeO ₂
The mixture was evaporated to dryness, dried at 120 ° C., and calcined at 500 ° C. for 2 hours to prepare a catalyst powder.

The obtained catalyst powder was made into a paste by a conventional method, and was used as a cordierite honeycomb carrier base material (volume 1.3).
L) to prepare the monolith catalyst of Example 1.
The coating amount is 100 g / L. Then, the obtained monolith catalyst is cut into a size of 30 mm in diameter and 50 mm in length, and N ₂ + O ₂
By measuring the amount of CO ₂ generated in the model gas fluctuated as 2% ← → N ₂ + CO ₁ %, 300 ° C, 400 ° C and 5%
The initial oxygen storage amount at 00 ° C. was measured. Next, a durability test was conducted in which the monolithic catalyst produced in the same manner was placed in the exhaust system of a stoichiometric engine and heated at an inlet gas temperature of 800 ° C. for 50 hours. And about the monolith catalyst after the durability test,
The oxygen storage amount was measured in the same manner as in the initial stage, and the measured oxygen storage amount was used as the oxygen storage amount after durability. Each result is shown in FIG.

(Example 2) 24 g of cerium triethoxide
Was dissolved in 200 g of isopropyl alcohol, and the whole amount of Pt-Rh-supported ZSM-5 powder prepared in the same manner as in Example 1 was added thereto, followed by stirring at 70 ° C. for 5 hours. Next, it was dried at 120 ° C. in vacuum and then calcined at 500 ° C. for 2 hours to prepare a catalyst powder.

Using this catalyst powder, a monolith catalyst was prepared in the same manner as in Example 1, and the oxygen storage amounts at the initial stage and after the endurance were measured in the same manner. The results are shown in FIG. (Comparative Example 1) Pt-Rh supported Z prepared in the same manner as in Example 1
A catalyst powder was prepared in the same manner as in Example 1 except that SM-5 powder was used and 50 g of ceria sol (CeO ₂ concentration: 20% by weight) having a colloid particle diameter of 5 nm was used. Using this catalyst powder, a monolith catalyst was prepared in the same manner as in Example 1, and the oxygen storage amounts at the initial stage and after the durability were measured in the same manner. The results are shown in FIG.

Comparative Example 2 Prepared in the same manner as in Example 1.
The total amount of Pt-Rh-supported ZSM-5 powder and 50 g of ceria powder having an average particle size of 1 μm were mixed to prepare a catalyst powder. Using this catalyst powder, a monolith catalyst was prepared in the same manner as in Example 1, and the oxygen storage amounts at the initial stage and after the durability were measured in the same manner.
The results are shown in FIG.

(Evaluation) Table 3 summarizes the constitution of each of the above-mentioned catalysts.

[0045]

[Table 3] From FIG. 2, it can be seen that the catalysts of the respective examples show a higher oxygen storage amount than the comparative example even after the durability test, and are excellent in durability. From the comparison between Example 1 and Comparative Example 1, the durability was significantly improved by changing the particle size of the ceria sol from 5 nm to 3 nm. Therefore, the particle size of ceria greatly affected the durability. It is clear that In addition, the maximum diameter of the mesopores is 4 nm, and the durability greatly changes around the particle diameter in the vicinity.

[0046]

According to the exhaust gas purifying catalyst of the present invention, the decrease in the oxygen storage / release capability of the metal oxide having the oxygen storage / release capability during the durability test is suppressed.
The durability is improved. Further, according to the method for producing an exhaust gas purifying catalyst of the present invention, the exhaust gas purifying catalyst having the excellent performance described above can be produced reliably, stably and easily.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the SiO ₂ / Al ₂ O ₃ ratio and the HC 50% purification temperature.

FIG. 2 is a graph showing the relationship between measured temperature and oxygen storage amount for catalysts of Examples and Comparative Examples.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01D 53/36 102G 104A F-term (Reference) 4D048 AA06 AA13 AA18 AB01 AB02 BA03X BA03Y BA06X BA06Y BA10X BA11X BA19X BA30X BA33X BA41X BA41Y BB02 BB17 EA04 4G069 AA03 BA01A BA01B BA02A BA02B BA07B BA13B BA21B BA21C BA27C BA37 BC43B BC43C BC69A BC71B BC71C BC75B BC75C BE06C BE44C CA03 CA07 CA08 CA09 EA02Y EA18 EB18E13 EB18 EB18 EB18 EB18

Claims (4)

[Claims] 1. An exhaust gas purifying catalyst comprising a porous carrier carrying a metal oxide having an oxygen storage / release capability and a noble metal, wherein most of the metal oxide is carried in pores of the porous carrier. An exhaust gas purifying catalyst, comprising: 2. In an exhaust gas purifying catalyst in which a noble metal is supported on a support made of porous silica, the porous silica has a molar ratio (SiO ₂ / Al ₂ O ₃ ) of 1000 or more and a diameter of 4 nm.
The following mesopores are contained in an amount having a total volume exceeding 0.070 cm ³ / g, and at least in the mesopores, a metal oxide having an oxygen storage / release ability and a particle size of 4 nm or less is supported. An exhaust gas purifying catalyst, comprising: 3. A method for producing an exhaust gas purifying catalyst in which a metal oxide having an oxygen storage / release capability and a noble metal are supported on a porous carrier, comprising: a sol of a compound containing a metal constituting the metal oxide; A method for producing an exhaust gas purifying catalyst, comprising impregnating a porous carrier with a solution of an alkoxide of a metal constituting an oxide and then calcining the porous carrier. 4. A method for producing an exhaust gas purifying catalyst in which a metal oxide having no oxygen storage / release capability and a noble metal are supported on a porous carrier, wherein the porous carrier and particles smaller than the pore diameter of the porous carrier are provided. A method for producing an exhaust gas purifying catalyst, comprising mixing a metal oxide powder having a diameter and baking the mixture.