JP6797976B2 - Manufacturing method of exhaust gas purification catalyst - Google Patents

Description

The present invention relates to a method for producing an exhaust gas purification catalyst, and more particularly to a method for producing an exhaust gas purification catalyst emitted from an internal combustion engine such as an automobile.

Exhaust gas emitted from internal combustion engines such as automobiles contains components harmful to the human body, such as carbon monoxide (CO), nitrogen oxides (NO _x ), and hydrocarbons (C _{x Hy} ). These harmful components are purified by the exhaust gas purification catalyst and then released into the atmosphere. As this catalyst, a three-way catalyst in which a noble metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) is supported on a porous carrier is widely used.

More specifically, a catalyst converter coated with the three-way catalyst on a base material having a honeycomb structure formed of ceramics such as cordierite is arranged at a predetermined position on an exhaust passage. The catalytic converter decomposes the harmful components contained in the exhaust gas and detoxifies them into carbon dioxide (CO ₂ ) and nitrogen (N ₂ ).

The ternary catalyst has oxygen storage capacity on the surface of alumina (Al ₂ O ₃ ), which is a carrier, with platinum (Pt), palladium (Pd), or rhodium (Rh), which are noble metals as catalyst materials. Cerium oxide (CeO ₂ : sometimes referred to as "ceria"), a composite oxide of cerium oxide and zirconium oxide (CeO _2- ZrO ₂ ), or a composite oxide of cerium oxide and lanthanum oxide as a co-catalyst material. Those bearing (CeO _2- La ₂ O ₃ ) are used.

By the way, it is known that the exhaust gas of an automobile has a wide temperature of 200 to 1000 ° C. under conditions where the load on the internal combustion engine is different, such as when the automobile is idling or accelerating. Especially in the high temperature range of 1000 ° C. or higher, the specific surface area of the co-catalyst and / or the catalyst is reduced by the syntering of the metal oxide having an oxygen occlusion ability as the co-catalyst and the noble metal as the catalyst, so that the three-way catalyst is used. The catalytic activity of is reduced. For this reason, the development of a technique for maintaining the catalytic activity of the three-way catalyst in a high temperature range is underway.

Further, in recent years, with the spread of hybrid automobiles, there is a demand for a catalyst that exhibits high catalytic activity at a lower temperature by further lowering the temperature of exhaust gas. Against this background, development is underway to maintain the high catalytic activity of the three-way catalyst in the lower temperature range and to suppress the decrease in the catalytic activity of the three-way catalyst in the higher temperature range.

For example, in Patent Document 1, Au and Rh are used as the noble metals of the catalyst, Au is the maximum component of the central portion, and Rh is the maximum component of the outer peripheral portion, and the composite fine particles containing Au and Rh are used to obtain Rh. It is described that the decrease in catalytic activity due to oxidation can be suppressed and the catalytic activity in a low temperature range can be improved.

Further, Patent Document 2 describes that by supporting the noble metal particles covered with an oxide layer on the surface of silicon carbide, the catalytic activity at a low temperature can be improved by the interfacial interaction between the noble metal particles and the oxide layer. Has been done.

Further, in Patent Document 3, in addition to the fine particles of the catalyst and the co-catalyst, cobalt (Co), manganese (Mn), copper (Cu), nickel (Ni), magnesium (Mg), lanthanum (La) and strontium (Sr) are described. It is described that by supporting one or more of these elements and iron (Fe) on a porous carrier, syntaring of a co-catalyst in a high temperature range can be suppressed.

Japanese Unexamined Patent Publication No. 2012-179573 Japanese Unexamined Patent Publication No. 2015-9213 Japanese Unexamined Patent Publication No. 2016-209862

However, the method of Patent Document 1 cannot suppress a decrease in the catalytic activity of the three-way catalyst due to sintering of the noble metal in a high temperature region. Further, in the method of Patent Document 2, since silicon carbide is oxidized at 800 ° C. or higher, it is also impossible to suppress a decrease in the catalytic activity of the three-way catalyst in a high temperature range.

Further, although the method of Patent Document 3 can suppress the sintering of the co-catalyst in the high temperature region, the suppression of the sintering of the noble metal itself constituting the catalyst is not mentioned, and the catalytic activity of the three-way catalyst in the high temperature region is not mentioned. There is room for consideration as to the technology for maintaining the above.

Theoretically, as a method for maintaining the high catalytic activity of the three-way catalyst, it is conceivable to increase the amount of noble metal particles having a predetermined specific surface area used in the catalytic converter. However, precious metals are a rare resource and their prices have risen in recent years, which poses economic restrictions. That is, in reality, it is difficult to manufacture a catalytic converter using an excessive amount of precious metal.

In view of the above problems, the present invention is a method for producing an exhaust gas purification catalyst, which makes it possible to suppress a decrease in catalytic activity of a three-way catalyst in both a high temperature region and a low temperature region without increasing the amount of noble metal supported. The purpose is to provide.

The present invention is a method for producing an exhaust gas purification catalyst.
The exhaust gas purifying catalyst includes a carrier, which is supported on the surface of the carrier, and a cocatalyst body made of a metal oxide having oxygen storage capacity, it is selectively supported on the surface of the co-catalyst, Pt, Pd , Or with noble metal particles consisting of at least one of Rh,
It is characterized by having a step of subjecting a material containing the carrier and / or the raw material of the carrier, the co-catalyst / or the raw material of the co-catalyst, and the raw material of the noble metal particles to a hydrothermal reaction at 100 ° C. or higher. ..

According to the exhaust gas purification catalyst obtained by the above method, the noble metal particles (Z) contained in the exhaust gas purification catalyst are hardly or hardly supported on the carrier (X), and most of them are made of a metal oxide having an oxygen storage capacity. It is "selectively" supported on the surface of the co-catalyst (Y). That is, most of the precious metal particles (Z) included in the exhaust gas purification catalyst according to the present invention have a chemical bond called "anchor effect" acting on the co-catalyst (Y) to act as a co-catalyst. It is firmly supported on the surface of (Y). As a result, the noble metal particles (Z) firmly supported on the surface of the co-catalyst (Y) are maintained in the initial dispersed state, and the sintering of the noble metal particles (Z) is suppressed.

Specifically, it is assumed that 95% by mass or more of the noble metal particles (Z) contained in the exhaust gas purification catalyst are supported on the surface of the co-catalyst (Y). can do.

According to the present invention, it is possible to realize an exhaust gas purification catalyst capable of suppressing a decrease in catalytic activity of a three-way catalyst in a high temperature region and a low temperature region without increasing the amount of noble metal supported.

It is a drawing which shows typically the structure of the exhaust gas purification catalyst of 1st Embodiment of this invention. It is a drawing which shows typically the structure of the conventional exhaust gas purification catalyst. It is a drawing which shows typically the structure of the exhaust gas purification catalyst of the 2nd Embodiment of this invention. It is a STEM image of the exhaust gas purification catalyst of Example 1. It is a STEM image of the exhaust gas purification catalyst of Example 2. It is a STEM image of the exhaust gas purification catalyst of Comparative Example 2. It is an observation image of each element in the STEM-EDX analysis result of the exhaust gas purification catalyst of Example 1. It is an observation image of each element in the STEM-EDX analysis result of the exhaust gas purification catalyst of Comparative Example 2.

<First Embodiment>
The first embodiment of the exhaust gas purification catalyst of the present invention will be described.

[catalyst]
FIG. 1 is a drawing schematically showing the structure of an exhaust gas purification catalyst according to the first embodiment of the present invention. In FIG. 1, the dimensional ratio on the drawing and the actual dimensional ratio do not match. The same applies to the following drawings.

As schematically shown in FIG. 1, the exhaust gas purification catalyst of the present invention (corresponding to "exhaust gas purification catalyst 1" in FIG. 1) is supported on the carrier (X) and the surface of the carrier (X). It is composed of a co-catalyst (Y) and noble metal particles (Z) selectively supported on the surface of the co-catalyst (Y). In FIG. 1, only a part of the co-catalyst (Y) supported on the carrier (X) and the noble metal particles (Z) selectively supported on the co-catalyst (Y) are extracted and shown. Has been done.

(Carrier (X))
The carrier (X) constitutes a base material on which the co-catalyst (Y) is supported, and is provided for the purpose of suppressing a decrease in the specific surface area of the co-catalyst (Y) due to sintering.

Since the support of the co-catalyst (Y) on the carrier (X) is very strong, the co-catalyst (Y) moves on the carrier (X) even in a high temperature region and the co-catalyst (Y) is supported. ) Sintering with each other is unlikely to occur. That is, the support of the co-catalyst (Y) by the carrier (X) maintains the initial dispersed state of the co-catalyst (Y), and as a result, also maintains the initial dispersed state of the noble metal particles (Z).

The exhaust gas purification catalyst preferably has high heat resistance because exhaust gas up to 1000 ° C. may pass through. More specifically, as the constituent material of the carrier (X) included in the exhaust gas purification catalyst of the present invention, Al ₂ O ₃ (alumina), TiO ₂ , ZrO ₂ , or SiO ₂ is preferable, and Al ₂ O ₃ or ZrO ₂ is more preferable, and Al ₂ O ₃ is even more preferable. Furthermore, from the viewpoint of a large amount of co-catalyst body (Y) can be _{supported, Al 2 O γ-Al 2} O 3 is large specific surface area among the _three is more preferable.

The content (Xw) of the carrier (X) in the exhaust gas purification catalyst of the present invention is preferably 60 to 60 from the viewpoint of having both an effect of retaining high catalytic activity in a low temperature range and an effect of suppressing a decrease in catalytic activity in a high temperature range. It is 99% by mass, more preferably 70 to 96% by mass, and even more preferably 77 to 94% by mass.

(Co-catalyst (Y))
As schematically shown in FIG. 1, the co-catalyst (Y) included in the exhaust gas purification catalyst of the present invention is supported on the surface of the carrier (X). The co-catalyst (Y) is a secondary particle formed by aggregating primary particles of a metal oxide having an oxygen occlusion ability. Then, on the surface of the co-catalyst (Y), all or most of the precious metal particles (Z) are Pt-O-Ce, Rh-O-Ce, Pd-O-Ce, etc., which are called "anchor effect". It is firmly supported on the co-catalyst (Y) by the chemical bond of.

The metal oxide used as the material of the co-catalyst (Y) provided in the exhaust gas purification catalyst of the present invention includes CeO ₂ , CeO _2- ZrO ₂ , and CeO _2- La ₂ O ₃ from the viewpoint of heat resistance and oxygen storage capacity. Alternatively, one or more selected from CeO _2- ZrO _2- La ₂ O ₃ is preferable, and one selected from CeO _2- ZrO ₂ , CeO _2- La ₂ O ₃ , and CeO _2- ZrO _2- La ₂ O _3. Alternatively, two or more types are more preferable, and CeO _2- ZrO ₂ or CeO _2- La ₂ O ₃ is even more preferable. That is, in the present specification, the "metal oxide" is a concept including a composite metal oxide.

The content (Yw) of the co-catalyst (Y) in the exhaust gas purification catalyst of the present invention is preferably 1 to 30% by mass from the viewpoint of effectively suppressing the syntering of the precious metal particles (Z) by the anchor effect. Yes, more preferably 4 to 25% by mass, and even more preferably 6 to 20% by mass.

Further, the mass ratio (Xw / Yw) of the content (Xw) of the carrier (X) and the content (Yw) of the co-catalyst (Y) in the exhaust gas purification catalyst of the present invention is high in catalytic activity in the low temperature range. From the viewpoint of having both a retention effect and an effect of suppressing a decrease in catalytic activity in a high temperature range, it is preferably 2 to 99, more preferably 2.8 to 24, and even more preferably 3.8 to 15.7. ..

The particle size of the primary particles of the metal oxide constituting the co-catalyst (Y) is preferably 2 to 20 nm, more preferably 2 to 15 nm, and even more preferably 2 to 12 nm from the viewpoint of having a high oxygen storage capacity. Here, in the present specification, the particle size of particles means a range of particle sizes (length of major axis) of several tens of particles measured by observation with an electron microscope of SEM or TEM.

As shown in FIG. 1, in the exhaust gas purification catalyst of the present invention, a plurality of cocatalysts (Y) are supported on the surface of the carrier (X). The coverage of the carrier (X) by the co-catalyst (Y) is 0.5 to 20 area% from the viewpoint of having both the effect of retaining high catalytic activity in the low temperature range and the effect of suppressing the decrease in catalytic activity in the high temperature range. Preferably, 2 to 17 area% is more preferable, and 3 to 15 area% is particularly preferable. Here, the coverage (% of area) of the carrier (X) by the co-catalyst (Y) is measured when the exhaust gas purification catalyst is observed with an electron microscope of SEM or TEM, and the carrier (X) is observed. [P3 / (P2 + P3)] when the size (number of pixels) of the region is P2 and the size (number of pixels) of the region where the cocatalyst (Y) on the carrier (X) is observed is P3. ] Corresponds to a value of x100.

(Precious metal particles (Z))
As schematically shown in FIG. 1, the noble metal particles (Z) included in the exhaust gas purification catalyst of the present invention are configured to be "selectively" supported on the surface of the co-catalyst (Y). That is, in the exhaust gas purification catalyst of the present invention, all or most of the noble metal particles (Z) are supported on the surface of the cocatalyst (Y), and no or almost are supported on the surface of the carrier (X). .. FIG. 2 schematically shows the exhaust gas purification catalyst 2 according to the prior art, in which the noble metal particles (z) are also supported on the surface of the carrier (X) for comparison.

Of the noble metal particles (Z) contained in the exhaust gas purification catalyst of the present invention, the proportion of the noble metal particles (Z) supported on the surface of the co-catalyst (Y) is preferably 95% by mass or more, preferably 97% by mass. It is more preferably% or more, and even more preferably 98% by mass or more.

The content (Zw) of the noble metal particles (Z) in the exhaust gas purification catalyst of the present invention is preferably 0.01 to 10% by mass, more preferably 0, from the viewpoint of exhibiting high catalytic activity in a wide temperature range. It is .05 to 5% by mass, and even more preferably 0.1 to 3% by mass.

Further, the mass ratio (Yw / Zw) of the content (Yw) of the co-catalyst (Y) and the content (Zw) of the noble metal particles (Z) in the exhaust gas purification catalyst of the present invention is determined by the anchor effect. From the viewpoint of effectively suppressing the catalysting of Z), it is preferably 1 to 3000, more preferably 1 to 500, and further preferably 1 to 200.

The noble metal particles (Z) contained in the exhaust gas purification catalyst of the present invention are selected from at least one of Pt, Pd, and Rh, and the particle size thereof is preferably 0.1 to 5 nm from the viewpoint of obtaining good catalytic activity. , 0.1 to 3 nm is more preferable, and 0.1 to 2 nm is even more preferable.

Further, the coverage of the co-catalyst (Y) by the noble metal particles (Z) in the exhaust gas purification catalyst of the present invention has a viewpoint of having both an effect of retaining high catalytic activity in a low temperature range and an effect of suppressing a decrease in catalytic activity in a high temperature range. Therefore, 10 to 90 area% is preferable, 20 to 90 area% is more preferable, and 30 to 90 area% is even more preferable. Here, the coverage (area%) of the co-catalyst (Y) with the noble metal particles (Z) is the co-catalyst (Y) measured when the exhaust gas purification catalyst is observed with an electron microscope of SEM or TEM. When the size (number of pixels) of the region where is observed is P3 and the size (number of pixels) of the region where the noble metal particles (Z) on the cocatalyst (Y) are observed is P4, [P4 / (P3 + P4)] corresponds to the value of × 100.

All or almost all of the noble metal particles (Z) are selectively supported on the surface of the co-catalyst (Y) made of a metal oxide. That is, all or almost all of the precious metal particles (Z) contained in the exhaust gas purification catalyst of the present invention are firmly supported on the surface of the co-catalyst (Y) by the anchor effect. As a result, even if the exhaust gas purification catalyst is operated in a high temperature region for a long time, these precious metal particles (Z) do not move and sinter, or sintering is extremely unlikely to occur.

On the other hand, for example, the noble metal particles (z) are the co-catalyst (Y) like the exhaust gas purification catalyst according to the prior art (hereinafter, referred to as “exhaust gas purification catalyst 2”) schematically shown in FIG. ), When the exhaust gas purification catalyst 2 is operated on the surface of the carrier (X) for a long time in a high temperature region, it is supported on the surface of the carrier (X). The movement of the noble metal particles (z) occurs, and finally the catalysting of the noble metal particles (z) occurs. That is, when the exhaust gas purification catalyst 2 shown in FIG. 2 is used as an exhaust gas purification catalyst, the catalytic activity tends to decrease due to the decrease in the specific surface area of the noble metal particles (z).

That is, according to the exhaust gas purification catalyst of the present invention shown in FIG. 1, sintering is unlikely to occur when used as an exhaust gas purification catalyst, even though the same amount of co-catalyst (Y) and precious metal particles (Z) as those in the prior art are used. Since the noble metal particles (Z) can maintain a high specific surface area, a decrease in catalytic activity is suppressed.

[Production method]
The exhaust gas purification catalyst of the first embodiment of the present invention can be produced by the following method. The details will be described later with reference to Examples.

The exhaust gas purification catalyst of the present invention is a material containing the raw material of the co-catalyst (Y) and the raw material of the noble metal particles (Z), or the raw material of the co-catalyst (Y) and the noble metal particles (Z). The material containing the above is produced by including a step of subjecting the material to a hydrothermal reaction of 100 ° C. or higher. By utilizing such a hydrothermal reaction (hydrothermal synthesis), the noble metal particles (Z) can be selectively supported on the co-catalyst (Y).

The combination of the co-catalyst (Y), the raw material of the co-catalyst (Y), and the raw material of the noble metal particles (Z) is not particularly limited in subjecting to the hydrothermal reaction at 100 ° C. or higher. Three types of manufacturing methods can be adopted. Regarding the carrier (X), the raw material of the carrier (X) and / or the carrier (X) is used as the raw material of the co-catalyst (Y) and / or the co-catalyst (Y), and the noble metal particles (Z). ), And at the same time, it may be subjected to a hydrothermal reaction.

The first production method is a mixture obtained by mixing the raw material of the co-catalyst (Y), the raw material of the noble metal particles (Z), the raw material of the carrier (X) and / or the carrier (X), and the pH adjuster. Is subjected to a hydrothermal reaction at 100 ° C. or higher to obtain an exhaust gas purification catalyst (I).

The second manufacturing method is
Step (II-1) of obtaining a co-catalyst (Y) by a solid-phase method, a coprecipitation method, a sol-gel method, a melting method, etc.
The cocatalyst (Y) obtained in the step (II-1), the raw material of the noble metal particles (Z), the raw material of the carrier (X) and / or the carrier (X), and the pH adjuster were mixed and obtained. Step of subjecting the mixture to a hydrothermal reaction at 100 ° C. or higher to obtain an exhaust gas purification catalyst (II-2)
Have.

The third manufacturing method is
Step (III-1) of obtaining a co-catalyst (Y) by a solid-phase method, a coprecipitation method, a sol-gel method, a melting method, etc., and
The co-catalyst (Y) obtained in step (III-1), the raw material of the co-catalyst (Y), the raw material of the noble metal particles (Z), the raw material of the carrier (X) and / or the carrier (X), and the pH. Step of mixing the adjusting agent and subjecting the obtained mixture to a hydrothermal reaction at 100 ° C. or higher to obtain an exhaust gas purification catalyst (III-2).
Have.

In the step (II-1) in the second production method or the step (III-1) in the third production method, the mixture containing the raw material of the co-catalyst (Y) and the pH adjuster is 100 ° C. or higher. A method of subjecting to a hydrothermal reaction can be used.

As each raw material to be subjected to the hydrothermal reaction, metal nitrate, sulfate, chloride, organic acid salt, or alkoxide is preferable from the viewpoint of solubility and efficiency of the hydrothermal reaction.

The amount of water used in each slurry for the hydrothermal reaction is 1 mol in total for each metal atom contained in the slurry from the viewpoints of solubility or dispersibility of each raw material, ease of stirring, efficiency of hydrothermal reaction, and the like. 10 to 300 mol is preferable, and 50 to 200 mol is more preferable.

The pH of each slurry when subjected to a hydrothermal reaction is preferably 7 to 14. Therefore, when preparing the slurry, it is preferable to use a pH adjuster as appropriate. Examples of such a pH adjusting material include sodium hydroxide, lithium hydroxide, potassium hydroxide, and aqueous ammonia, and sodium hydroxide or aqueous ammonia is preferable.

When the slurry is subjected to a hydrothermal reaction, it is preferably carried out in a pressure-resistant container. The reaction temperature when subjected to a hydrothermal reaction is 100 ° C. or higher, preferably 100 to 200 ° C., more preferably 100 to 160 ° C. The time for the hydrothermal reaction is preferably 10 minutes to 24 hours, more preferably 30 minutes to 18 hours. The atmosphere of the hydrothermal reaction is preferably air or an inert gas (nitrogen gas or the like).

The obtained hydrothermal reaction product can be isolated by filtering, washing with water, and drying. When washing the hydrothermal reaction product with water, it is preferable to use 5 to 100 parts by mass of water with respect to 1 part by mass of the hydrothermal reaction product. Further, as the drying means, freeze-drying or vacuum drying is used, and freeze-drying is preferable among them.

The obtained hydrothermal reaction product may be calcined, and particularly when the carrier (X) obtained by the hydrothermal reaction is a hydrate such as boehmite, calcining is performed from the viewpoint of removing water of crystallization. Is preferable. The firing temperature is preferably 300 to 1000 ° C, more preferably 400 to 1000 ° C. The firing time is preferably 10 minutes to 10 hours, more preferably 30 minutes to 6 hours. Further, the firing atmosphere is preferably an air atmosphere from the viewpoint of effectively converting the hydrate obtained by the hydrothermal reaction into an oxide.

<Second embodiment>
Regarding the second embodiment of the exhaust gas purification catalyst of the present invention, only the parts different from the first embodiment will be described.

[catalyst]
FIG. 3 is a drawing schematically showing the structure of the exhaust gas purification catalyst according to the second embodiment of the present invention. As schematically shown in FIG. 3, in the present embodiment, the co-catalyst (Y) included in the exhaust gas purification catalyst of the present invention (corresponding to “exhaust gas purification catalyst 1a” in FIG. 3) is a carrier ( It has a hollow nanorod shape supported on the surface of X). The co-catalyst (Y) is a secondary particle formed by aggregating primary particles of a metal oxide having an oxygen occlusion ability into a hollow nanorod shape. Then, in the exhaust gas purification catalyst of the present invention, a plurality of co-catalysts (Y) showing the shape of the hollow nanorods are supported on the surface of the carrier (X). On the surface of the co-catalyst (Y), the precious metal particles (Z) are formed by Pt—O—Ce and Rh—O, which are referred to as “anchor effect”, as in the exhaust gas purification catalyst according to the first embodiment of the present invention. It is firmly supported on the co-catalyst (Y) by a chemical bond such as −Ce or Pd—O—Ce.

It should be noted that the noble metal particles (Z) are hardly or not supported on the surface of the carrier (X) and are selectively supported on the co-catalyst (Y), which is common to the first embodiment.

The length of the co-catalyst (Y) included in the exhaust gas purification catalyst of the second embodiment of the present invention in the lateral direction is preferably 5 to 60 nm, more preferably 5 to 50 nm, from the viewpoint of firmly supporting the carrier (X). It is preferably 5 to 40 nm, even more preferably. The length of the co-catalyst (Y) in the longitudinal direction is preferably 10 to 1000 nm, more preferably 10 to 800 nm, and even more preferably 10 to 600 nm from the viewpoint of reliably forming a hollow shape. That is, the aspect ratio of the co-catalyst (Y) is preferably 2 to 30, more preferably 3 to 25, and even more preferably 4 to 20. The "aspect ratio" referred to here is a value of L1 / L2 when the length in the longitudinal direction of the co-catalyst (Y) showing the nanorod shape is L1 and the length in the lateral direction is L2. Correspond.

Further, the wall thickness of the co-catalyst (Y) having a hollow nanorod shape is preferably 1 to 20 nm, more preferably 1 to 17 nm, from the viewpoint of giving the co-catalyst (Y) high mechanical strength. , 1 to 15 nm is even more preferable. The "thickness" here refers to the thickness between the inner surface (Y2) and the outer surface (Y1) of the co-catalyst (Y) having a hollow nanorod shape.

As schematically shown in FIG. 3, the exhaust gas purification catalyst of the second embodiment of the present invention has a plurality of co-catalysts (Y) exhibiting a unique shape called a hollow nanorod shape on the surface of the carrier (X). It is supported. That is, the noble metal particles (Z) are firmly supported on the surface of the co-catalyst (Y) by the anchor effect, and further, the co-catalyst (Y) has a unique shape of hollow nanorods, which is less likely to cause sintering. As a result, even if the exhaust gas purification catalyst is operated in a high temperature range for a long time, the co-catalyst (Y) is unlikely to be deformed, so that it is difficult for these precious metal particles (Z) to approach each other to a state where sintering occurs. Therefore, sintering is suppressed.

That is, according to the exhaust gas purification catalyst of the second embodiment of the present invention, the effect of suppressing the decrease in catalytic activity is further enhanced as compared with the configuration of the first embodiment. The co-catalyst body (Y) included in the exhaust gas purification catalyst of the second embodiment of the present invention may have at least a hollow nanorod shape.

[Production method]
The exhaust gas purification catalyst of the second embodiment of the present invention includes a step of subjecting the raw material of the co-catalyst (Y) and the material containing the raw material of the noble metal particles (Z) to a hydrothermal reaction at 100 ° C. or higher. Manufactured in. As a result, the primary particles of the metal oxide constituting the co-catalyst (Y) grow in a specific direction, the secondary particles showing the hollow nanorod shape are formed, and the co-catalyst showing the hollow nanorod shape is formed. The noble metal particles (Z) are selectively supported with respect to (Y).

That is, almost all co-catalysts (Y) in the first manufacturing method described above, and some co-catalysts (Y) in the third manufacturing method described above are exhaust gases of the second embodiment. It has a hollow nanorod shape like a purification catalyst.

Further, in the exhaust gas purification catalyst of the second embodiment of the present invention, in the above-mentioned second production method, the material containing the raw material of the co-catalyst (Y) is added to the step (II-1) at 100 ° C. or higher. It can also be obtained when a production method subject to a hydrothermal reaction is adopted. In this production method, almost all co-catalysts (Y) serve as the exhaust gas purification catalyst of the second embodiment.

[Example]
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the contents of each Example and Comparative Example.

[Manufacturing Example 1] (Manufacturing of ceria by hydrothermal method)
0.3 g of NaOH was mixed with 10 g of water to obtain a solution A1. Further, to obtain a solution B1 by mixing _{Ce (NO 3) 3 · 6H} 2 O 0.33g water 30g. Next, the obtained solution B1 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and the solution A1 was added dropwise at 50 mL / min to obtain a slurry C1. The pH of such slurry C1 was 13.5.

The obtained slurry C1 was put into an autoclave, and a hydrothermal reaction at 140 ° C. and 0.4 MPa was carried out for 1 hour. The produced solid content was suction-filtered, and then the obtained solid content was washed with 10 parts by mass of water with respect to 1 part by mass of the solid content. The solid content after washing was freeze-dried at −50 ° C. for 12 hours to obtain ceria (CeO ₂ ) having a hollow nanorod shape.

[Manufacturing Example 2] (Manufacturing of ceria by the coprecipitation method)
Water 250g were mixed _{Ce (NO 3) 3 · 6H} 2 O 2.17g to give a solution A2. Further, 0.42 g of K ₂ CO ₃ was mixed with 100 g of water to obtain a solution B2. Next, 100 g of water was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and the obtained solutions A2 and B2 were added dropwise at 50 mL / min to obtain a slurry C2. The pH of such slurry C2 was 6.0. The slurry C2 was suction filtered, and the obtained solid content was washed with 10 parts by mass of water with respect to 1 part by mass of the solid content. The solid content after washing was dried at 70 ° C. for 2 hours to obtain powder D2. The obtained powder D2 was calcined at 220 ° C. for 2.5 hours in an air atmosphere and then calcined at 600 ° C. for 3 hours to obtain granular ceria (CeO ₂ ) having an average particle size of 20 nm.

[Manufacturing Example 3] (Manufacturing of boehmite by hydrothermal method)
12 g of NaOH was mixed with 30 g of water to obtain solution A3. Further, to obtain a solution B3 was mixed with _{Al 2 (SO 4) 3 ·} 16H 2 O 31.51g of water 50 g. Next, the obtained solution B3 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and the solution A3 was added dropwise at 50 mL / min to obtain a slurry C3. The pH of such slurry C3 was 9.5.

The obtained slurry C3 was put into an autoclave, and a hydrothermal reaction at 140 ° C. and 0.4 MPa was carried out for 1 hour. The produced solid content was suction-filtered, and then the obtained solid content was washed with 10 parts by mass of water with respect to 1 part by mass of the solid content. The solid content after washing was freeze-dried at −50 ° C. for 12 hours to obtain boehmite (AlOOH).

[Example 1] (Co-catalyst (Y): CeO ₂ (hydrothermal method), precious metal particles (Z): Pt + Rh (hydrothermal method), second production method)
In 30 g of water, 0.15 g of ceria (CeO ₂ ) obtained in Production Example 1, 0.65 g of a 1% rhodium chloride aqueous solution, 2.72 g of a 1% hexachloroplatinic acid aqueous solution, and boehmite obtained in Production Example 3 1. 50 g was mixed to obtain slurry A4. The pH of the slurry A4 was 13.0, and it contained 0.03 mol Ce, 0.001 mol Rh and 0.002 mol Pt with respect to 1 mol of Al.

The obtained slurry A4 was put into an autoclave, and a hydrothermal reaction at 140 ° C. and 0.4 MPa was carried out for 1 hour. The produced solid content was suction-filtered, and then the obtained solid content was washed with 10 parts by mass of water with respect to 1 part by mass of the solid content. The washed solid content was freeze-dried at −50 ° C. for 12 hours to obtain a precursor B4 of an exhaust gas purification catalyst.

The obtained exhaust gas purification catalyst precursor B4 was calcined at 500 ° C. for 6 hours in an air atmosphere to obtain an exhaust gas purification catalyst A. The BET specific surface area of the obtained exhaust gas purification catalyst A was 170 m ² / g. Further, the obtained exhaust gas purification catalyst A is a mixed phase (Al: Ce: Rh:) of γ-Al ₂ O ₃ which does not support Rh and Pt and CeO ₂ which has a hollow nanorod shape which supports Rh and Pt. Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

[Example 2] (Co-catalyst (Y): Ce _0.5 Zr _0.5 O ₂ (hydrothermal method), precious metal particles (Z): Pt + Rh (hydrothermal method), first production method)
Example 1, ceria _(CeO 2) 0.15 g obtained in Production Example _{1, Ce (NO 3) 3} · 6H 2 O 0.17g and ZrO (NO ₃₎ to ₂ · _{2H 2} O 0.14g Exhaust gas purification catalyst B was obtained in the same manner as in Example 1 except for the change (pH of slurry A4 was 13.5). The BET specific surface area of the obtained exhaust gas purification catalyst B was 170 m ² / g. Further, the obtained exhaust gas purification catalyst B is composed of γ-Al ₂ O ₃ which does not support Rh and Pt and Ce _0.5 Zr _0.5 O ₂ which has a hollow nanorod shape which supports Rh and Pt. It was a mixed phase (Al: Ce: Zr: Rh: Pt (molar ratio) = 1: 0.015: 0.015: 0.001: 0.002).

[Example 3] (Co-catalyst (Y): CeO ₂ (coprecipitation method), precious metal particles (Z): Pt + Rh (hydrothermal method), second production method)
Examples of Example 1 except that 0.15 g of ceria (CeO ₂ ) obtained in Production Example 1 was changed to 0.15 g of ceria obtained in Production Example 2 (slurry A4 has a pH of 13.0). An exhaust gas purification catalyst C was obtained in the same manner as in 1. The BET specific surface area of the obtained exhaust gas purification catalyst C was 160 m ² / g. Further, the obtained exhaust gas purification catalyst C is a mixed phase (Al: Ce: Rh: Pt) of γ-Al ₂ O ₃ which does not support Rh and Pt and CeO ₂ which has a grain shape supporting Rh and Pt. The molar ratio) = 1: 0.03: 0.001: 0.002).

[Comparative Example 1] (Co-catalyst (Y): CeO ₂ (hydrothermal method), precious metal particles (Z): Pt + Rh (impregnation method))
Water _{30g, Ce (NO 3) 3} · 6H 2 O 0.33g, and then mixing the resulting boehmite (AlOOH) 1.50 g in Preparation Example 3 to obtain a slurry A5. Further, 0.30 g of NaOH was mixed with 10 g of water to obtain a solution B5. Next, the obtained slurry A5 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and the solution B5 was added dropwise at 50 mL / min to obtain a slurry C5. The pH of the slurry C5 was 13.5, and 0.03 mol of Ce was contained with respect to 1 mol of Al.

The obtained slurry C5 was put into an autoclave, and a hydrothermal reaction at 140 ° C. and 0.4 MPa was carried out for 1 hour. Next, the water content of the slurry D5 obtained by the hydrothermal reaction was removed by an evaporator, and then the slurry D5 was fired at 500 ° C. for 3 hours in an air atmosphere to obtain a powder E5.

Slurry F5 was obtained by mixing 1.65 g of the powder E5 obtained in 20 g of water, 0.65 g of the 1% rhodium chloride aqueous solution and 2.72 g of the 1% hexachloroplatinic acid aqueous solution. Next, the obtained slurry F5 was stirred at a stirring speed of 300 rpm for 3 hours while maintaining the temperature at 25 ° C., and water was removed using an evaporator to obtain powder G5.

The obtained powder G5 was calcined at 500 ° C. for 3 hours in an air atmosphere to obtain an exhaust gas purification catalyst D. The BET specific surface area of the obtained exhaust gas purification catalyst D was 165 m ² / g. Further, the obtained exhaust gas purification catalyst D is a mixed phase (Al: Ce: Rh: Pt) of γ-Al ₂ O ₃ supporting Rh and Pt and CeO ₂ having a hollow nanorod shape supporting Rh and Pt. The molar ratio) = 1: 0.03: 0.001: 0.002).

[Comparative Example 2] (Co-catalyst (Y): CeO ₂ (impregnation method), precious metal particles (Z): Pt + Rh (impregnation method))
Water 20g, a mixture of _{Ce (NO 3) 3 · 6H} 2 O 0.33g, and boehmite 1.50g obtained in Production Example 3 to obtain a slurry A6. The slurry A6 contained 0.03 mol of Ce with respect to 1 mol of Al. Next, the obtained slurry A6 was stirred at a stirring speed of 300 rpm for 3 hours while maintaining the temperature at 25 ° C., and water was removed using an evaporator to obtain powder B6.

The obtained powder B6 was calcined at 500 ° C. for 3 hours in an air atmosphere to obtain powder C6. Slurry D6 was obtained by mixing 1.65 g of powder C6 obtained in 20 g of water, 0.65 g of a 1% rhodium chloride aqueous solution and 2.72 g of a 1% hexachloroplatinic acid aqueous solution. Next, the obtained slurry D6 was stirred at a stirring speed of 300 rpm for 3 hours while maintaining the temperature at 25 ° C., and water was removed using an evaporator to obtain powder E6.

The obtained powder E6 was calcined at 500 ° C. for 3 hours in an air atmosphere to obtain an exhaust gas purification catalyst E. The BET specific surface area of the obtained exhaust gas purification catalyst E was 155 m ² / g. Further, the obtained exhaust gas purification catalyst E is a mixed phase of γ-Al ₂ O ₃ carrying Rh and Pt and granular CeO ₂ supporting Rh and Pt (Al: Ce: Rh: Pt (molar ratio) =. It was 1: 0.03: 0.001: 0.002).

<STEM (scanning transmission electron microscope) image>
For the exhaust gas purification catalysts obtained in Examples 1 and 2 and Comparative Example 2, in order to confirm the particle size and particle shape of Pt, Rh and CeO ₂ (Ce _0.5 Zr _0.5 O ₂ ), STEM ( ARM-200F, manufactured by JEOL Ltd.) was observed. STEM photographs are shown in FIGS. 4A-4C.

Furthermore, in order to confirm the element distribution of Al, Ce, Pt, and Rh for the exhaust gas purification catalysts obtained in Example 1 and Comparative Example 2, STEM-EDX analysis ((ARM-200F, manufactured by JEOL Ltd.) + ( JEM-3200FS, manufactured by JEOL Ltd.)). Observation images of each of these elements are shown in FIGS. 5A to 5B.

According to the photographs shown in FIGS. 4A and 4B, in the exhaust gas purification catalysts of Examples 1 and 2, the co-catalyst (Y) grown into a hollow nanorod shape having a large aspect ratio can be confirmed. Further, according to the photograph shown in FIG. 5A, in the exhaust gas purification catalyst of Example 1, precious metal particles (Z) of Pt and Rh are selectively formed on the surface of the co-catalyst (Y) showing the shape of the hollow nanorod. It can be confirmed that it is supported on.

On the other hand, according to the photographs shown in FIGS. 4C and 5B, in Comparative Example 2, the noble metals of Pt and Rh were found not only on the surface of the granular co-catalyst (y) but also on the surface of the carrier (X). It can be confirmed that the particles (Z) are supported.

<Evaluation of catalytic activity>
Using the exhaust gas purifying catalyst obtained in all examples and all of the comparative example, a harmful components CO, to evaluate the degradation activity of the C ₃ H ₆ and NO.

Specifically, each of the obtained exhaust gas purification catalysts was filled in a stainless steel reaction tube, and both sides of the exhaust gas purification catalyst were filled with quartz wool to fix the exhaust gas purification catalyst. A mixed gas (NO 500 ppm, CO 5000 ppm, C ₃ H ₆ 250 ppm, O ₂ 3300 ppm, CO ₂ 6000 ppm, N ₂ balance) simulating automobile exhaust gas is placed in the reaction tube at 400 ml / min (space velocity: 24000 / hour). It was distributed.

Then, the reaction tube was heated in an electric furnace to 100 to 400 ° C., exhaust gas analyzer (Riero Japan Co., Auto5.1) using, _CO, C 3 _{H 6,} and NO conversion rate of 50% The reaction temperature T ₅₀ was evaluated. Further, in the heating temperature of 1000 ° C., after 1 hour and after 48 hours, CO, by measuring the conversion of C 3 _{H 6,} and NO, to evaluate the durability of the exhaust gas purifying catalyst in a high temperature range. The results are shown in Table 1.

From T _{50 in} Table 1, the reaction temperature at which the conversion rates of CO, C ₃ H ₆ and NO of all the examples became 50% was lower than that of each Comparative Example 1 or 2, respectively, and the exhaust gas purification catalyst of the present invention was used. It can be seen that the catalytic activity at low temperature is high.

Furthermore, from the evaluation results of the conversion rate at 1000 ° C. in Table 1, all the examples showed higher values for the conversion rate after 48 hours as compared with Comparative Example 1 or 2, and the exhaust gas purification of the present invention. It can be seen that the catalyst is excellent in the effect of suppressing a decrease in catalytic activity in a high temperature range.

Furthermore, from the evaluation results of the conversion rate at 1000 ° C. in Table 1, all the examples showed higher values for the conversion rate after 48 hours as compared with Comparative Example 1 or 2, and the exhaust gas purification catalyst of the present invention. Is excellent in the effect of suppressing a decrease in catalytic activity in a high temperature range.

The superiority of the above-mentioned catalytic activity in the exhaust gas purification catalyst of the present invention is that the noble metal particles (Z) are selectively supported on the co-catalyst (Y) with no or little support on the carrier (X). The strong anchoring effect on the surface of the cocatalyst (Y) suppresses the progress of sintering of the noble metal particles (Z) and makes it possible to maintain the initial dispersed state, that is, the noble metal particles (Z) are sintered. This is because a large specific surface area can be maintained without a ring.

Further, as in the exhaust gas purification catalyst of the second embodiment of the present invention, the co-catalyst (Y) forms a hollow nanorod, so that the co-catalyst (Y) exhibits a large specific surface area and at a high temperature. This is because the shape in which the sintering of the noble metal particles (Z) is difficult to proceed further enhances the effect of suppressing the sintering of the precious metal particles (Z) and can maintain a large specific surface area.

1, 1a: Exhaust gas purification catalyst (invention)
2: Exhaust gas purification catalyst (conventional technology)
X: Carrier Y: Cocatalyst Z, z: Precious metal particles

Claims (7)

It is a method of manufacturing an exhaust gas purification catalyst.
The exhaust gas purification catalyst includes a carrier, a co-catalyst made of a metal oxide having an oxygen occlusion ability supported on the surface of the carrier, and Pt and Pd selectively supported on the surface of the co-catalyst. , Or with noble metal particles consisting of at least one of Rh,
The step (a) of obtaining the co-catalyst by subjecting the raw material of the co-catalyst to a hydrothermal reaction at 100 ° C. or higher,
Having a step (b) of subjecting a material containing the carrier and / or the raw material of the carrier, the cocatalyst obtained in the step (a), and the raw material of the noble metal particles to a hydrothermal reaction at 100 ° C. or higher. A method for producing an exhaust gas purification catalyst. In the step (b), the co-catalyst obtained in the step (a), the raw material of the noble metal particles, the carrier and / or the raw material of the carrier, and the pH adjuster are mixed to obtain a mixture. The method for producing an exhaust gas purification catalyst according to claim 1, wherein the step is a step of subjecting the mixture to a hydrothermal reaction at 100 ° C. or higher. The step (c) for obtaining the carrier is provided.
The step (b) is obtained by mixing the carrier obtained in the step (c), the cocatalyst obtained in the step (a), the raw material of the noble metal particles, and the pH adjuster. The method for producing an exhaust gas purification catalyst according to claim 2, further comprising a step of subjecting the mixture to a hydrothermal reaction at 100 ° C. or higher. The method for producing an exhaust gas purification catalyst according to any one of claims 1 to 3, further comprising a firing step after the step ( b ). The metal oxide is one or more selected from CeO ₂ , CeO _2- ZrO ₂ , CeO _2- La ₂ O ₃ , or CeO _2- ZrO _2- La ₂ O _3. Item 8. The method for producing an exhaust gas purification catalyst according to any one of Items 1 to 4. The method for producing an exhaust gas purification catalyst according to any one of claims 1 to 5, wherein the noble metal particles have a particle size of 0.1 to 5 nm. The exhaust gas purification catalyst according to any one of claims 1 to 6, wherein the carrier is one kind or two or more kinds selected from Al ₂ O ₃ , TiO ₂ , ZrO ₂ , or SiO _2. Manufacturing method.