JP6625150B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Description

  The present invention relates to a catalyst for purifying exhaust gas, particularly to a catalyst for purifying exhaust gas discharged from an internal combustion engine such as an automobile. The present invention also relates to a method for producing such an exhaust gas purifying catalyst.

The exhaust gas discharged from an internal combustion engine such as an automobile, carbon monoxide (CO), nitrogen oxides (NO _x), such as a hydrocarbon (C _x H _y), which contain harmful ingredients to the human body. These harmful components are released into the atmosphere after being purified by the exhaust gas purifying catalyst. 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.

As the three-way catalyst, platinum (Pt), palladium (Pd), or rhodium (Rh), which is a noble metal as a catalyst material, and an auxiliary material having oxygen storage ability are formed on the surface of alumina (Al ₂ O ₃ ) as a carrier. 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 catalyst material (CeO ₂ -La ₂ O ₃ ) is used.

  Incidentally, the temperature of the exhaust gas discharged from the internal combustion engine has a wide temperature range of 200 ° C. to 1200 ° C. depending on the load conditions of the internal combustion engine and the like. In particular, in a high temperature range of 1000 ° C. or higher, the specific surface area of the noble metal as a catalyst is reduced by sintering, and the catalytic activity of the three-way catalyst is reduced. As a countermeasure, an exhaust gas purifying catalyst containing a large amount of precious metals is conceivable, but it is not practical in terms of cost, and an exhaust gas purifying catalyst that maintains high catalytic activity in a high temperature environment without using a large amount of noble metals is required. Have been.

  For example, in Patent Document 1, in addition to fine particles of a catalyst and a promoter, cobalt (Co), manganese (Mn), copper (Cu), nickel (Ni), magnesium (Mg), lanthanum (La), and strontium ( A technique has been disclosed in which one or more elements of Sr) and iron (Fe) are supported on a porous carrier, thereby suppressing sintering of a promoter in a high-temperature region.

  Further, for example, as in the case of a hybrid vehicle having an internal combustion engine and an electric motor (motor) as power sources, the temperature of exhaust gas discharged from the internal combustion engine expands to a lower temperature range due to the progress of hybrid power sources and the like. It is considered that the exhaust gas purifying catalyst is required to have high catalytic activity even in a low temperature range.

  For example, Patent Document 2 discloses that a composite fine particle containing Au and Rh in which Au and Rh are used as the noble metals of the catalyst, Au is the maximum component in the central portion, and Rh is the maximum component in the outer peripheral portion is used. It is described that a 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 3 describes that by supporting noble metal particles covered with an oxide layer on the surface of silicon carbide, catalytic activity at a low temperature can be improved by interfacial interaction between the noble metal particles and the oxide layer. Have been.

JP-A-2006-209962 JP 2012-179573 A JP-A-2013-9213

  However, although the sintering of the co-catalyst in the high-temperature range can be suppressed in the method of Patent Document 1, there is no mention of the suppression of the sintering of the noble metal itself constituting the catalyst, and a technique for maintaining the catalyst activity in the high-temperature range. There is room for consideration.

  Further, the method disclosed in Patent Document 2 cannot suppress a decrease in catalytic activity of the three-way catalyst due to sintering of a noble metal in a high temperature range. Furthermore, in the method of Patent Document 3, since the silicon carbide is oxidized at 800 ° C. or higher, it is impossible to suppress a decrease in the catalytic activity of the three-way catalyst in a high temperature range.

  The present invention has been made in view of the above problems, and provides an exhaust gas purifying catalyst comprising a three-way catalyst exhibiting good catalytic activity in both a high temperature region and a low temperature region without increasing the amount of noble metal carried, and a method for producing the same. The purpose is to do.

  Thus, the present inventors have conducted various studies, and found that a metal oxide or a metal composite oxide having an oxygen storage ability with specific noble metal fine particles supported on the surface is supported on a specific carrier, so that the temperature increases from a low temperature range to a high temperature range. It has been found that an exhaust gas purifying catalyst capable of maintaining high catalytic activity over a range can be obtained.

  That is, the present invention provides a carrier (X) composed of an oxide (M1) having excellent heat resistance, and a promoter (Y) composed of a metal oxide (M2) having an oxygen storage capacity supported thereon. An object of the present invention is to provide an exhaust gas purifying catalyst comprising a noble metal (M3) particle (Z) (M3 represents at least one of Pt, Pd and Rh) supported on a surface of a catalyst body (Y). is there.

  Further, the present invention provides an exhaust gas purifying catalyst in which at least one of the carrier (X) and the promoter (Y) has a hollow nanorod shape. More specifically, the carrier (X) has a hollow nanorod shape formed by assembling primary particles of the oxide (M1), or the promoter (Y) has primary particles of the metal oxide (M2). It may have a hollow nanorod shape formed as a whole, or both.

The oxide (M1) constituting the carrier (X) is preferably one or more selected from the group consisting of Al ₂ O ₃ , TiO ₂ , ZrO ₂ , and SiO ₂ . The metal oxide (M2) constituting the promoter (Y) is preferably composed of CeO ₂ , CeO ₂ -ZrO ₂ , CeO ₂ -La ₂ O ₃ , and CeO ₂ -ZrO ₂ -La ₂ O _3. One or more selected from the group.

Also, the present invention
A step of subjecting the raw material of the support (X) or the support (X) and the raw material of the co-catalyst (Y), or the support (X) and the co-catalyst (Y) to a hydrothermal reaction at 100 ° C. or higher. It is intended to provide a method for producing the exhaust gas purifying catalyst.

  According to the present invention, it is possible to effectively suppress sintering of a noble metal in a high temperature region and effectively suppress a decrease in the catalyst activity without increasing the amount of the noble metal carried, while maintaining a high catalytic activity in a low temperature region. Thus, it is possible to realize an exhaust gas purifying catalyst that exhibits high catalytic activity in a wide temperature range.

1 is a drawing schematically showing an example of the structure of an exhaust gas purifying catalyst of the present invention. It is a drawing schematically showing the structure of a conventional exhaust gas purifying catalyst. 5 is a STEM image of an exhaust gas purifying catalyst of Example 2. 9 is a STEM image of an exhaust gas purifying catalyst of Example 3. 14 is a STEM image of an exhaust gas purifying catalyst of Example 14. 5 is an STEM image of an exhaust gas purifying catalyst of Comparative Example 1. 9 is a STEM image of an exhaust gas purifying catalyst of Comparative Example 2. 6 is an observation image of each element in an STEM-EDX analysis result of the exhaust gas-purifying catalyst of Example 2. 14 is an observation image of each element in a STEM-EDX analysis result of the exhaust gas-purifying catalyst of Example 14. 5 is an observation image of each element in an STEM-EDX analysis result of the exhaust gas-purifying catalyst of Comparative Example 1.

  Hereinafter, the present invention will be described in detail.

[Configuration of exhaust gas purification catalyst]
FIG. 1 is a drawing schematically showing an example of the structure of the exhaust gas purifying catalyst of the present invention. In FIG. 1, the dimensional ratio on the drawing does not match the actual dimensional ratio.

  The exhaust gas purifying catalyst (denoted by reference numeral 1) of the present invention, as schematically shown in FIG. 1, has an oxygen storage capacity on a carrier (X) made of an oxide (M1) having excellent heat resistance. And a noble metal (M3) particle (Z) supported on the surface of the co-catalyst (Y). In the following, description will be made assuming that the metal oxide (M2) is a cerium (Ce) -containing oxide.

  That is, in the exhaust gas purifying catalyst of the present invention, the promoter (Y) composed of the cerium-containing oxide (M2) having the surface loaded with the noble metal (M3) particles (Z) is composed of the metal oxide (M1). It has a unique shape supported on the surface of the carrier (X). By exhibiting this unique shape, the oxide (M2) firmly supported on the surface of the metal oxide (M1) having excellent heat resistance effectively sinters the oxides (M2) at high temperatures. Be suppressed.

  Further, by configuring the co-catalyst (Y) with the cerium-containing oxide (M2), the noble metal (M3) particles (Z) can form the co-catalyst (Y) by an anchor effect with the cerium-containing oxide (M2). ) Is firmly supported on the surface, so that sintering of the noble metal (M3) in a high-temperature region can be effectively suppressed. The “anchor effect” refers to Pt—O—Ce, Rh—O—Ce, Pd—O—Ce generated between Ce in the cerium-containing oxide (M2) and the noble metal (M3) particles (Z). Etc. refers to a strong chemical bond.

  Hereinafter, each of the carrier (X), the promoter (Y), and the noble metal particles (Z) will be described in detail.

<Carrier (X)>
As described above, the carrier (X) constituting the exhaust gas purifying catalyst of the present invention constitutes a base material on which the promoter (Y) is supported, and has a specific surface area of the promoter (Y) by sintering. It is provided for the purpose of suppressing the decrease.

The exhaust gas purifying catalyst preferably has high heat resistance because high-temperature exhaust gas as high as 1000 ° C. may pass therethrough. More specifically, the oxide (M1) used for the carrier (X) included in the exhaust gas purifying catalyst of the present invention includes a group consisting of Al ₂ O ₃ (alumina), TiO ₂ , ZrO ₂ , and SiO _2. One or more selected from the above. Among them, from the viewpoint of heat resistance, Al ₂ O ₃ and ZrO ₂ are preferable, and Al ₂ O ₃ is 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 average particle diameter (D _x ) of the primary particles of the oxide (M1) constituting the carrier (X) of the exhaust gas purifying catalyst of the present invention is 5 nm from the viewpoint of effectively supporting the promoter (Y). To 5 μm, preferably 5 nm to 3 μm, more preferably 5 nm to 1 μm.

  In the present specification, the average particle diameter of particles means an average value of measured values of particle diameters (lengths of major axes) of several tens of particles observed by an electron microscope of SEM or TEM.

  The shape of the support (X) is not particularly limited, but is preferably a hollow nanorod shape (hereinafter, also referred to as a “hollow fiber shape”) from the viewpoint of supporting a larger amount of the promoter (Y). . With a unique shape having a hollow nanorod called a hollow nanorod, which has a rod-shaped outer shape elongated in the long axis direction, and both side surfaces having a short axis are open holes and having a hollow structure continuous in the long axis direction It has a large surface consisting of the outer surface and the hollow surface, and all of the co-catalysts (Y) carried on those surfaces can be brought into sufficient contact with the atmosphere (exhaust gas). Hereinafter, the carrier (X) exhibiting such a hollow nanorod shape (hollow fiber shape) may be referred to as “hollow carrier (X)”.

The average secondary particle diameter (D _x ) of the support (X) is not particularly limited, but from the viewpoint of firmly supporting the co-catalyst (Y) described later, the major axis of the co-catalyst (Y) is The length is preferably larger than the length in the direction, preferably 100 nm to 1000 μm, more preferably 500 nm to 800 μm, and still more preferably 1 μm to 500 μm.

When the carrier (X) is the hollow carrier (X), the average secondary particle diameter (D _X ) of the carrier (X) indicates the average length in the major axis direction of the hollow carrier (X).

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

<Co-catalyst (Y)>
The promoter (Y) provided in the exhaust gas purifying catalyst of the present invention is supported on the surface of a carrier (X) as schematically shown in FIG.

  The shape of the promoter (Y) is not particularly limited, but from the viewpoint of supporting more noble metal particles (Z), a hollow nanorod (hollow fiber) is preferable as in the case of the carrier (X). FIG. 1 shows a case where the promoter (Y) has a hollow nanorod shape.

  When the promoter (Y) is a hollow nanorod, it has a large surface, and all of the noble metal particles (Z) supported on the surface can be sufficiently brought into contact with the atmosphere (exhaust gas). Hereinafter, the co-catalyst (Y) exhibiting such a hollow nanorod shape (hollow fiber shape) may be referred to as a “hollow co-catalyst (Y)”.

The promoter (Y) included in the exhaust gas purifying catalyst of the present invention is made of a metal oxide (M2) having an oxygen storage ability. As the metal oxide (M2), an oxide containing cerium is preferably selected. Specifically, one or more members selected from the group consisting of CeO ₂ , CeO ₂ -ZrO ₂ , CeO ₂ -La ₂ O ₃ , and CeO ₂ -ZrO ₂ -La ₂ O ₃ are preferable, and CeO ₂ -ZrO ₂ , CeO ₂ -La ₂ O ₃ , and one or more selected from the group consisting of CeO ₂ -ZrO ₂ -La ₂ O ₃ are more preferable, and CeO ₂ -ZrO ₂ , CeO ₂ -La ₂ O ₃ is more preferred. That is, in the present specification, “metal oxide” is a concept including a composite metal oxide.

The average particle diameter (D _Y ) of the metal oxide (M2) nanoparticles constituting the co-catalyst (Y) is determined from the viewpoint of securing a good oxygen storage capacity and the sintering of the noble metal (M3) described later by the anchor effect. From the viewpoint of supporting a sufficient amount of the noble metal (M3) while effectively suppressing the ring, the thickness is preferably 1 nm to 20 nm, more preferably 2 nm to 15 nm, and still more preferably 2 nm to 12 nm.

  When the co-catalyst (Y) is a hollow co-catalyst, the length of the hollow co-catalyst (Y) in the major axis direction is preferably from 10 nm to 1000 nm from the viewpoint of reliably forming the hollow shape. 800 nm is more preferable, and 10 nm to 600 nm is still more preferable. In addition, the length of the hollow promoter body (Y) in the minor axis direction is preferably from 5 nm to 60 nm, more preferably from 5 nm to 50 nm, and still more preferably from 5 nm to 40 nm.

  That is, the aspect ratio of the hollow promoter body (Y) is preferably 2 to 30, more preferably 3 to 25, and still more preferably 4 to 20. Here, the “aspect ratio” is defined as L1 / L2 when the length in the major axis direction of the hollow promoter body (Y) having a nanorod shape is L1 and the length in the minor axis direction is L2. Corresponds to the value.

  In addition, the thickness of the hollow cocatalyst (Y) is preferably 1 nm to 20 nm, more preferably 1 nm to 17 nm, and more preferably 1 nm to 15 nm from the viewpoint of imparting high mechanical strength to the hollow cocatalyst (Y). Is more preferred. Here, the "wall thickness" refers to the thickness between the inner surface (Y2) and the outer surface (Y1) of the hollow promoter (Y) (see FIG. 1).

The ratio of the average particle diameter of the carrier (X) and (D _X) and the average particle size of the co-catalyst _{(Y) (D Y) (} D X / D Y) is a high catalytic activity in the low temperature range It is preferably 1 to 50, more preferably 1.5 to 35, and still more preferably 2 to 25, from the viewpoint of having both the holding effect and the effect of suppressing the decrease in the catalytic activity in a high temperature range. When the promoter (Y) is a hollow promoter, the average particle diameter (D _Y ) is determined based on the length L1 of the hollow promoter (Y) in the major axis direction and is determined by an electron microscope or SEM. It means the average value of several tens of hollow cocatalysts (Y) measured by observation with a microscope.

The content (W _Y ) of the co-catalyst (Y) is preferably 0.1% in the exhaust gas purifying catalyst of the present invention from the viewpoint of effectively suppressing the sintering of the noble metal (M3) described below by the anchor effect. It is from 99% by mass to 30% by mass, more preferably from 3.95% by mass to 25% by mass, still more preferably from 5.9% by mass to 20% by mass.

The content of the content of the carrier _(X) (W X) with a cocatalyst body _(Y) (W Y) and the mass ratio of (W _X / W _Y) is held in a high catalytic activity in the low-temperature region From the viewpoint of having both the effect and the effect of suppressing the decrease in the catalytic activity in a high temperature range, it is preferably 2 to 100, more preferably 2.8 to 24.3, and still more preferably 3.85 to 15.9. .

Further, the coverage of the carrier (X) with the co-catalyst (Y) is preferably 0.5 area from the viewpoint of having both the effect of maintaining high catalytic activity in a low temperature region and the effect of suppressing the decrease in catalytic activity in a high temperature region. % To 20 area%, more preferably 2 to 17 area%, and still more preferably 3 to 15 area%. Here, the coverage (area%) of the carrier (X) with the co-catalyst (Y) refers to the observation of the carrier (X), which is measured when the exhaust gas purifying catalyst is observed with an SEM or TEM electron microscope. When the size (number of pixels) of the region to be treated is P _x 1 and the size (number of pixels) of the region where the promoter (Y) on the carrier (X) is observed is P _x 2, _{P x 2 / (P x 1} + P x 2)] is the value of × 100.

<Noble metal particles (Z)>
The noble metal particles (Z) included in the exhaust gas purifying catalyst of the present invention are particles having at least a part supported on the surface of the promoter (Y) and acting as a catalyst. The noble metal particles (Z) are made of the noble metal (M3). The noble metal (M3) is one or more selected from the group consisting of Pt, Pd, and Rh.

The average particle diameter (D _z ) of the noble metal (M3) particles (Z) is preferably from 0.1 nm to 5 nm, more preferably from 0.1 nm to 3 nm, from the viewpoint of exhibiting good catalytic activity. Preferably it is 0.1 nm to 2 nm.

The ratio of the average particle diameter of the average particle diameter (D _Y) between the noble metal of the co-catalyst (Y) (M3) particles _{(Z) (D Z) (} D Y / D Z) is a noble metal by the anchor effect ( From the viewpoint of effectively suppressing the sintering of M3), the number is preferably 1 to 200, more preferably 1 to 150, and still more preferably 1 to 120.

The content (W _Z ) of the noble metal (M3) particles (Z) is preferably 0.01% by mass to 10% by mass in the exhaust gas purifying catalyst of the present invention from the viewpoint of exhibiting high catalytic activity in a wide temperature range. %, More preferably 0.05% by mass to 5% by mass, still more preferably 0.1% by mass to 3% by mass.

The content of the co-catalyst _(Y) (W Y) and the content of the noble metal particles _(Z) (W Z) and the mass ratio of (W _Y / W _Z), the sintering of precious metal (M3) by the anchor effect From the viewpoint of effectively suppressing the ring, the number is preferably 1 to 3000, more preferably 1 to 500, and still more preferably 1 to 200.

Further, the coverage of the promoter (Y) with the noble metal particles (Z) in the exhaust gas purifying catalyst of the present invention has both an effect of retaining high catalytic activity in a low temperature region and an effect of suppressing a decrease in catalytic activity in a high temperature region. From the viewpoint, it is preferably 10 to 90 area%, more preferably 20 to 90 area%, and still more preferably 30 to 90 area%. Here, the coverage (area%) of the promoter (Y) with the noble metal particles (Z) refers to the promoter (Y) measured when the exhaust gas-purifying catalyst is observed with an SEM or TEM electron microscope. ) the size of the area to be observed (the number of pixels) and P _x 2, the size of the area where the noble metal particles on the promoter element (Y) (Z) is observed (number of pixels) was P _x 3 It corresponds to the value of [P _x 3 / (P _x 2 + P _x 3)] × 100 at this time.

  Preferably, all or almost all of the noble metal particles (Z) are supported on the surface of the cerium oxide (M2) constituting the promoter (Y). In this case, all or almost all of the noble metal particles (Z) included in the exhaust gas purifying catalyst of the present invention are firmly supported on the surface of the promoter (Y) by an anchor effect. As a result, even if the exhaust gas purifying catalyst is operated for a long time in a high temperature range, these noble metal particles (Z) do not move or sinter, or sintering hardly occurs.

  On the other hand, when the cocatalyst (y) is granular, for example, as in a conventional exhaust gas purifying catalyst (hereinafter referred to as “exhaust gas purifying catalyst 2”) schematically shown in FIG. The unevenness of the particle surface disappears by the sintering, and the specific surface area of the promoter (y) is easily reduced. As a result, even if the noble metal particles (Z) are firmly supported on the promoter (y) by the anchor effect, the noble metal particles (Z) are transformed by the deformation of the promoter (y) by sintering. (Z) approach each other to a state where sintering occurs, and eventually, the diameter of the noble metal particles (Z) increases due to the sintering. As described above, in the exhaust gas purifying catalyst 2 shown in FIG. 2, the diameter of the noble metal particles (Z) increases, that is, the specific surface area decreases in a high temperature range, and the catalytic activity decreases.

[Action]
That is, according to the exhaust gas purifying catalyst of the present invention, sintering in a high temperature range is unlikely to occur, and both the cocatalyst (Y) and the noble metal particles (Z) can maintain a high specific surface area. Is suppressed. Further, by making at least one of the carrier (X) and the promoter (Y) into a hollow nanorod shape, the surface on which the promoter (Y) and the noble metal particles (Z) can be supported is increased, and Since a large amount of noble metal particles (Z) can be supported while effectively ensuring the space between the media (Y) or the noble metal particles (Z), more excellent catalytic performance can be obtained. Further, by forming both the carrier (X) and the promoter (Y) in the form of hollow nanorods, the effect can be further enhanced.

[Production method]
Next, a method for producing the exhaust gas purifying catalyst of the present invention will be described. The details will be described later in the section of Examples.

  In the method for producing an exhaust gas purifying catalyst of the present invention, the carrier (X) or the raw material of the carrier (X) and the raw material of the promoter (Y), or the carrier (X) and the promoter (Y) are mixed with 100 A step of subjecting the reaction to a hydrothermal reaction at a temperature of not less than ° C. That is, three types of manufacturing methods can be adopted according to the combination of the raw materials. The manufacturing method will be described below for each combination of raw materials.

  In the above-mentioned hydrothermal reaction at 100 ° C. or higher, all the raw materials may be subjected to one hydrothermal reaction at a time, and the production of one or more carriers (X) and cocatalysts (Y) may be carried out. A plurality of hydrothermal reactions to be performed may be combined, and further, a hydrothermal reaction for selectively supporting the noble metal particles (Z) on the promoter (Y) may be combined. The production methods exemplified below are all production methods using a single hydrothermal reaction.

(First manufacturing method)
In the first production method, an aqueous solution A obtained by mixing water and a pH adjuster with a raw material of the carrier (X), a raw material of the co-catalyst (Y), and a raw material of the noble metal particles (Z) is used. This is a production method in which an exhaust gas purifying catalyst is obtained by subjecting it to a hydrothermal reaction at a temperature of 100 ° C. or higher.

  Each raw material subjected to the hydrothermal reaction is preferably a metal nitrate, a sulfate, a chloride, an organic acid salt, and an alkoxide from the viewpoint of solubility, efficiency of the hydrothermal reaction, and the like.

  From the viewpoints of solubility or dispersibility of each raw material, ease of stirring, efficiency of hydrothermal reaction, etc., the amount of the water used in the aqueous solution A is based on 1 mol of each metal atom contained in the aqueous solution A in total. From 10 mol to 300 mol, and more preferably from 50 mol to 200 mol.

  The pH of the aqueous solution A when subjected to the hydrothermal reaction is preferably 7-14. Therefore, when preparing the aqueous solution A, it is preferable to appropriately use a pH adjuster. Examples of such a pH adjuster include sodium hydroxide, lithium hydroxide, potassium hydroxide, and aqueous ammonia, and sodium hydroxide or aqueous ammonia is preferable.

  When the aqueous solution A is subjected to the hydrothermal reaction, it is preferably performed in a pressure vessel. The reaction temperature for the hydrothermal reaction is 100 ° C. or higher, preferably 100 ° C. to 200 ° C., and more preferably 100 ° C. to 160 ° C. The pressure at this time is preferably 0.2 MPa to 1.4 MPa when performing the reaction at 100 ° C. to 200 ° C., and the pressure when performing the reaction at 100 ° C. to 160 ° C. is 0.2 MPa to 0.8 MPa. It is preferred that Further, the time for the hydrothermal reaction is preferably from 10 minutes to 24 hours, more preferably from 30 minutes to 18 hours. The atmosphere of the hydrothermal reaction is preferably air or an inert gas (such as nitrogen gas).

  The hydrothermal reaction product obtained by subjecting the aqueous solution A to the hydrothermal reaction has a noble metal particle (Z) on the surface of the carrier (X) or a precursor of the carrier (X) (for example, AlOOH (boehmite)). The composite B has the supported promoter (Y) supported thereon. The promoter (Y) is preferably a hollow promoter (Y).

  When the composite B is provided with the carrier (X), the above-mentioned hydrothermal reaction product (composite B) is, after filtration, 5 parts by mass to 100 parts by mass of water per 1 part by mass of the hydrothermal reaction product. It can be isolated by washing with parts by mass and drying. The product obtained by such isolation corresponds to the exhaust gas purifying catalyst of the present invention. In addition, freeze drying or vacuum drying is used as the drying means, and freeze drying is preferable.

  On the other hand, when the composite B includes a hydrate of the oxide (M1) constituting the carrier (X), the obtained hydrothermal reaction product is further subjected to a calcination reaction. Thereby, the hydrate (precursor) of the carrier (X) can be changed to the carrier (X) (oxide). Here, from the viewpoint of making the obtained carrier (X) dense, the firing temperature is preferably from 300 ° C to 1000 ° C, more preferably from 400 ° C to 1000 ° C, in an atmosphere containing oxygen. . The firing time is preferably from 10 minutes to 10 hours, and more preferably from 30 minutes to 6 hours. What was obtained through this calcination reaction corresponds to the exhaust gas purifying catalyst of the present invention.

(Second manufacturing method)
In the second production method, water and a pH adjuster are mixed with the carrier (X), the raw material of the promoter (Y), and the raw material of the noble metal particles (Z), and the obtained slurry C is heated to 100 ° C. or higher. To obtain a catalyst for purifying exhaust gas by subjecting it to a hydrothermal reaction.

The support (X) used when forming the slurry C is one or more oxides (M1) selected from the group consisting of Al ₂ O ₃ , TiO ₂ , ZrO ₂ , and SiO _2. . As the oxide (M1), a commercial product in the form of particles and a pulverized product thereof can be used, but a separately manufactured hollow nanorod-shaped oxide (M1), that is, a hollow carrier (X) can also be used. Hereinafter, a method for producing a hollow carrier (X) of Al ₂ O ₃ will be described as an example.

The method for producing the hollow carrier (X) of Al ₂ O ₃ includes the following steps (I) to (III):
(I) a step of preparing a slurry D containing a ceramic raw material compound containing Al as a main component, organic fibers, and an alkaline solution;
(II) a step of subjecting the obtained slurry D to a hydrothermal reaction to obtain a composite comprising the organic fibers and boehmite covering the organic fibers; and (III) subjecting the obtained composite to a firing reaction. To obtain a hollow carrier (X) of Al ₂ O ₃ .

  Although the metal element contained in the ceramic raw material compound used in the step (I) is mainly composed of Al, even if the metal element other than Al contains 30 mol% or less in 100 mol% of all metal elements including Al. Good. Specific examples of such ceramic raw material compounds include sulfates, nitrates, carbonates, acetates, oxalates, oxides, hydroxides, and halogens of Al or a metal compound composed of Al and an element other than Al. Compounds, organic acid salts, alkoxides and the like can be suitably used. Examples of the element other than Al include metal elements such as Fe, Co, Ni, Cu, Zn, Ga, Tb, Si, Ge, Sn, Ti, Zr, Mn, Eu, Y, Nb, Ce, and Ba. Can be

The hollow support (X) is the resulting Al ₂ O _3, since the organic fibers as a template, depending on the length and inner diameter of the hollow support of Al ₂ O ₃ required (X), organic with appropriate size Fiber is selected. The outer diameter (thickness) of the hollow carrier (X) of Al ₂ O ₃ can be controlled in a hydrothermal reaction in step (II) described later.

  The organic fiber is not particularly limited as long as boehmite is generated on the surface in a hydrothermal reaction in step (II) described below and burned off in a firing reaction in step (III) described later. Cellulose, cellulose nanofiber, wool, cotton, hemp, silk and the like can be used, and synthetic fiber can be aramid, polyamide, polyester, polyethylene, acrylic, rayon and the like. In the preparation of the slurry D, from the viewpoint of having good dispersibility in water, it is preferable to use cellulose nanofiber (CNF) as the organic fiber.

  CNF is a skeletal component that accounts for about 50% of all plant cell walls, and is a lightweight and high-strength fiber that can be obtained by defibrating plant fibers constituting such cell walls to nano-size, etc. Also has good dispersibility. The average fiber diameter of CNF is 10 nm to 30 μm, and the average length is 100 nm to 100 μm.

When preparing the slurry D by mixing the ceramic raw material compound and the organic fiber, water can be used as a dispersion medium. Then, the pH of the slurry D is adjusted to 9 by appropriately using a pH adjuster such as sodium hydroxide, lithium hydroxide, or ammonia so that the metal component dissolved or dispersed in the slurry D becomes a metal hydroxide. 0.5 to 14. When the pH of the slurry D is less than 9.5, NaAl ₃ (SO ₄ ) ₂ (OH) ₆ tends to be produced as a by-product, and the efficiency of producing the Al ₂ O ₃ precursor by the hydrothermal reaction becomes poor. There is.

  When preparing the slurry D, the amount of water used is 50 parts by mass with respect to 100 parts by mass of the ceramic raw material compound in view of the solubility or dispersibility of each raw material, the ease of stirring, and the efficiency of the hydrothermal reaction. Parts to 100,000 parts by mass, more preferably 50 to 80,000 parts by mass. Further, the content of the organic fibers in the slurry D is preferably 5 parts by mass to 2,000 parts by mass, more preferably 5 parts by mass to 1,000 parts by mass, based on 100 parts by mass of the ceramic raw material compound.

In the step (II), the slurry D is subjected to a hydrothermal reaction to form a composite (hereinafter, sometimes referred to as a “boehmite-coated composite”) in which the organic fibers are coated with boehmite (AlOOH). obtain. The temperature of such a hydrothermal reaction is preferably 100 ° C. or higher, more preferably 100 ° C. to 200 ° C. The hydrothermal reaction is preferably performed in a pressure-resistant vessel. When the reaction is performed at 100 ° C. or more, the pressure at this time is preferably 0.3 MPa or more. When the reaction is performed at 100 ° C. to 200 ° C., The pressure is preferably from 0.3 MPa to 1.4 MPa. The hydrothermal reaction time is preferably from 0.1 hours to 12 hours, more preferably from 0.2 hours to 6 hours. When the temperature of the hydrothermal reaction is less than 100 ° C. and the time of the hydrothermal reaction is less than 0.1 hour, crystal growth of the Al ₂ O ₃ precursor does not sufficiently occur, and the Al ₂ O ₃ hollow carrier (X) May have poor mechanical strength. If the temperature of the hydrothermal reaction exceeds 200 ° C. and the time of the hydrothermal reaction exceeds 12 hours, the organic fibers may be dissolved, and a boehmite-coated composite may not be obtained.

When the thickness of the boehmite coating the organic fibers is increased, that is, when the thick hollow Al ₂ O ₃ carrier (X) is obtained, the mass ratio of the ceramic raw material compound / organic fibers in the slurry D is used. Set large. Specifically, the mass ratio of the ceramic raw material compound / organic fiber is set to be larger than 0.5. In the hydrothermal reaction, the lower temperature / pressure environment is continued for a long time so that the crystal growth of individual crystals of boehmite is promoted. Specifically, for example, a hydrothermal reaction may be performed at 130 ° C. and 0.3 MPa for 12 hours.

  After the hydrothermal reaction, the surface of the organic fiber is covered with boehmite, and after separating it from the dispersion medium by filtration or the like, preferably washing with water or the like, drying, and the like, a step described below. The boehmite-coated composite to be subjected to the firing reaction of (III) can be isolated. When washing the boehmite-coated composite with water, it is preferable to use 5 parts by mass to 50 parts by mass of water with respect to 1 part by mass of the boehmite-coated composite from the viewpoint of removing by-products. As the drying means, freeze drying, vacuum drying, hot air drying and the like are used, and freeze drying or hot air drying is preferable.

In step (III), the boehmite-coated composite obtained as described above is further subjected to a firing reaction. As a result, the organic fibers contained in the boehmite-coated composite obtained in the above step (II) are burned off, and at the same time, the cylindrical boehmite is subjected to a calcination reaction to form the Al ₂ O ₃ hollow carrier (X). Obtainable. Here, from the viewpoint of making the obtained Al ₂ O ₃ dense, the firing temperature is preferably from 600 ° C. to 1200 ° C. in an oxygen atmosphere, more preferably from 700 ° C. to 1200 ° C. The firing time is preferably from 10 minutes to 10 hours, and more preferably from 30 minutes to 5 hours. When the firing temperature is 600 ° C. or less than the firing time is less than 10 minutes, Al ₂ O ₃ generation and crystal growth of Al ₂ O ₃ of Al ₂ O ₃ with dehydration of precursor is insufficient, Al ₂ O ₃ Mechanical strength of the hollow carrier (X) may be inferior. If the firing temperature exceeds 1200 ° C. and the firing time exceeds 10 hours, sintering of Al ₂ O ₃ significantly occurs, and a hollow form may not be obtained. Note that the atmospheric oxygen concentration for the firing reaction is not special, and ordinary air may be used.

As described above, the length of the Al ₂ O ₃ hollow carrier (X) and the thickness of the inner space can be arbitrarily controlled by the organic fiber used, so that the Al ₂ O ₃ hollow carrier (X) having a uniform size is used. Or an aggregate of Al ₂ O ₃ hollow carriers (X) having different sizes, or two or more Al ₂ O ₃ hollow carriers (X) having different chemical compositions. May be an aggregate.

  In the second production method, the raw materials of the cocatalyst (Y) and the raw materials of the noble metal particles (Z) to be subjected to the hydrothermal reaction have the same solubility and hydrothermal reaction efficiency as in the first production method. From the viewpoint, metal nitrates, sulfates, chlorides, organic acid salts, and alkoxides are preferred.

  The amount of the water used in the slurry C, the pH of the slurry C when subjected to the hydrothermal reaction, and the hydrothermal reaction conditions are the same as those of the aqueous solution A in the first production method.

  In the hydrothermal reaction product obtained by subjecting the slurry C to the hydrothermal reaction, the hollow co-catalyst (Y) having the noble metal particles (Z) supported on the surface was supported on the surface of the hollow carrier (X). Composite E. The composite E is washed with water in the same manner as the composite B, and then dried to obtain the exhaust gas purifying catalyst of the present invention.

In the second production method, when the oxide (M1) constituting the carrier (X) is other than Al ₂ O ₃ , the main component of the ceramic raw material compound used in the step (I) is oxidized. What is necessary is just to change according to the material of the thing (M1).

  In the second production method, the slurry C containing the hollow carrier (X) produced through the steps (I) to (III) is described as being subjected to a hydrothermal reaction. It is also possible to use a carrier exhibiting a non-hollow shape, and it is also possible to use a carrier (X) partially exhibiting a hollow shape. For example, a carrier (X) obtained by a solid phase method or a sol-gel method can be used.

(Third manufacturing method)
In the third production method, water and a pH adjuster are mixed with the raw materials of the carrier (X), the promoter (Y), and the noble metal particles (Z), and the obtained slurry F is mixed with water at 100 ° C. or higher. This is a method for producing an exhaust gas purifying catalyst by subjecting it to a thermal reaction.

  The method for preparing the slurry F, the hydrothermal reaction conditions, and the method for treating the hydrothermal reaction product are the same as those for the aqueous solution A in the first production method and the slurry C in the second production method.

  After subjecting the slurry F to the hydrothermal reaction, the hydrothermal reaction product was washed with water and dried to obtain an exhaust gas purifying catalyst in which noble metal particles (Z) were supported on the surface of the carrier (X). The promoter (Y) is supported. In addition, when the hollow carrier (X) produced through the steps (I) to (III) described above in the second production method is used as the carrier (X), the exhaust gas purifying catalyst is a hollow carrier. The co-catalyst (Y) in which the noble metal particles (Z) are supported on the surface of (X) is supported.

(Summary)
Regardless of which of the first to third production methods is adopted, the carrier (X) comprising the oxide (M1) having excellent heat resistance according to the present invention is prepared by converting the metal oxide (M2) having an oxygen storage ability into the carrier (X). Thus, an exhaust gas purifying catalyst can be obtained in which the promoter (Y) is supported and the noble metal particles (Z) are supported on the surface of the promoter (Y).

  Among these production methods, the second production method is particularly preferable because an exhaust gas purifying catalyst including the hollow carrier (X), the hollow promoter (Y), and the noble metal particles (Z) can be obtained.

  By using a hydrothermal reaction as a method for supporting the noble metal particles (Z), the noble metal particles (Z) can be selectively supported on the surface of the promoter (Y). However, other methods, such as an impregnation method, may be used. For example, in the first and second production methods, after supporting the promoter (Y) on the surface of the carrier (X) using a hydrothermal reaction, the noble metal particles (Z) are supported using an impregnation method. (Modification) However, when a method other than the hydrothermal reaction is employed, a part of the noble metal particles (Z) is also supported on the carrier (X).

  Further, after supporting the co-catalyst (Y) by the impregnation method on the hollow carrier (X) produced by the above-described method, the precious metal particles (Z) are further supported on the co-catalyst (Y) by the impregnation method. You may let it. In this case, a particulate co-catalyst (Y) is supported on a support (X) having a hollow nanorod shape, and a noble metal is formed on the surface of the co-catalyst (Y) and a part of the surface of the hollow support (X). Particles (Z) are supported.

  Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples.

[Production Example 1] <Production of carrier (X) of Al ₂ O ₃ hollow nanorods shape: hydrothermal method>
0.79 g of Al ₂ (SO ₄ ) ₃ .16H ₂ O, 2.31 g of cellulose nanofiber (PC110T, manufactured by Daicel FineChem, water content 65% by mass), and 72.3 mL of water are mixed for 60 minutes to prepare a slurry A1. did. To the obtained slurry A1, 3.0 mL of a 10 mass% NaOH aqueous solution was added and mixed for 5 minutes to prepare a slurry A2 having a pH of 10.

The slurry A2 was charged into an autoclave, and a hydrothermal reaction was performed at 140 ° C. and 0.3 MPa for 1 hour. After allowing the obtained hydrothermal reaction product to cool, it is filtered, washed with water, and dried with hot air at 80 ° C. for 4 hours to obtain a composite A3 comprising an Al ₂ O ₃ precursor and cellulose nanofibers. Got. The obtained composite A3 was placed in an electric furnace, heated in an air atmosphere to 700 ° C. at a rate of 10 ° C./min, and calcined at 700 ° C. for 1 hour to form a hollow nanorod-shaped γ-Al ₂ O ₃ (primary particle diameter: 10 nm, fiber length: 300 μm, BET specific surface area: 220 m ² / g) was obtained.

[Production Example 2] <Preparation of precursor (boehmite (AlOOH)) of carrier (X): hydrothermal method>
An aqueous solution B1 was obtained by mixing 12 g of NaOH with 30 mL of water. Further, 31.51 g of Al ₂ (SO ₄ ) ₃ .16H ₂ O was mixed with 50 mL of water to obtain an aqueous solution B2. Next, the obtained aqueous solution B2 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and the aqueous solution B1 was dropped at 50 mL / min to obtain a slurry B3. The pH of the slurry B3 was 9.5, and contained 3 mol of Na with respect to 1 mol of Al.

  The obtained slurry B3 was put into an autoclave, and a hydrothermal reaction was performed at 140 ° C. and 0.4 MPa for 1 hour. The generated solid was filtered by suction, and the obtained solid was washed with 10 parts by mass of water with respect to 1 part by mass of the solid. The solid content after washing was freeze-dried at -50 ° C for 12 hours to obtain boehmite (average particle size: 10 nm).

[Production Example 3] <Production of carrier (X) composed of aggregate of Al ₂ O ₃ : sol-gel method>
12 g of aluminum isopropoxide was mixed with 300 mL of ethanol to obtain a solution C1. Next, the obtained solution C1 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and 28% aqueous ammonia was dropped at 50 mL / min to obtain a gel C2. After the gel C2 was cured at 90 ° C. for 10 hours, it was fired at 700 ° C. for 2 hours in an air atmosphere to obtain γ-Al ₂ O ₃ (average particle size: 10 nm, BET specific surface area: 190 m ² / g).

Example 1 <Carrier (X): Al ₂ O _{3 in} hollow nanorod shape, cocatalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, second production method (twice) Hydrothermal reaction>
_{Ce (NO 3) 3 · 6H} 2 O 1.11g, Al 2 O 3 1.28g of hollow nanorods profile obtained in Production Example 1, and water 55mL were mixed for 60 minutes to prepare a slurry D1. To the obtained slurry D1, 9 mL of a 10% by mass aqueous NaOH solution was added and mixed for 5 minutes to prepare a slurry D2.

The slurry D2 was put into an autoclave, and a hydrothermal reaction was performed at 140 ° C. for 3 hours (first hydrothermal reaction). To a slurry of the obtained hollow nanorod-shaped CeO ₂ / hollow nanorod-shaped Al ₂ O ₃ composite, 2.19 g of a 1% RhCl ₃ aqueous solution and 9.14 g of a 1% aqueous hexachlorideplatinic acid (H ₂ PtCl ₆ ) solution were added. After mixing, slurry D3 was obtained.

The obtained slurry D3 was put into an autoclave, and a hydrothermal reaction was performed at 140 ° C. for 1 hour (second hydrothermal reaction). After allowing the hydrothermal reaction product to cool, it is filtered, washed with water, mixed with 50 mL of water and repulped to obtain Pt-Rh / CeO _{2 in the} form of hollow nanorods / Al ₂ O _{3 in the} form of hollow nanorods. A composite slurry D4 was obtained.

The obtained slurry D4 was freeze-dried at −50 ° C. for 12 hours, and the obtained solid content was calcined at 500 ° C. for 3 hours in an air atmosphere to obtain an exhaust gas purifying catalyst P1. The BET specific surface area of the obtained exhaust gas-purifying catalyst P1 was 230 m ² / g. Further, the obtained exhaust gas purifying catalyst P1 has a mixed phase (Al: Ce) of hollow nanorod-shaped γ-Al ₂ O ₃ not supporting Rh and Pt and hollow nanorod-shaped CeO ₂ supporting Rh and Pt. : Rh: Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

[Example 2] <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, second production method (twice water Thermal reaction)>
1.5 g of the boehmite obtained in Production Example 2 and 0.33 g of Ce (NO ₃ ) ₃ .6H ₂ O were mixed with 30 mL of water to obtain a slurry E1. In addition, 0.3 g of NaOH was mixed with 10 mL of water to obtain an aqueous solution E2. Next, the obtained slurry E1 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and an aqueous solution E2 was dropped at 50 mL / min to obtain a slurry E3. The pH of the slurry E3 was 13.5, and contained 0.03 mol of Ce with respect to 1 mol of Al.

The obtained slurry E3 was charged into an autoclave, and a hydrothermal reaction was performed at 140 ° C. and 0.4 MPa for 1 hour (first hydrothermal reaction). 0.65 g of a 1% RhCl ₃ aqueous solution and 2.72 g of a 1% H ₂ PtCl ₆ aqueous solution were mixed with the generated slurry E4 to obtain a slurry E5. The pH of the slurry E5 was 13.0, and contained 0.001 mol of Rh and 0.002 mol of Pt per 1 mol of Al.

  The obtained slurry E5 was put into an autoclave, and a hydrothermal reaction at 140 ° C. and 0.4 MPa was performed for 1 hour (second hydrothermal reaction). The generated solid was collected by suction filtration, and the obtained solid was washed with 10 parts by mass of water with respect to 1 part by mass of the solid. The solid content after the washing was freeze-dried at -50 ° C for 12 hours to obtain an exhaust gas purifying catalyst precursor E6.

The obtained exhaust gas purifying catalyst precursor E6 was calcined at 500 ° C. for 6 hours in an air atmosphere to obtain an exhaust gas purifying catalyst P2. The BET specific surface area of the obtained exhaust gas-purifying catalyst P2 was 170 m ² / g. In addition, the obtained exhaust gas purifying catalyst P2 has a mixed phase (Al: Ce: Rh) of an aggregate of γ-Al ₂ O ₃ that does not support Rh and Pt and a nanorod-shaped CeO ₂ that supports Rh and Pt. : Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

Example 3 <Carrier (X): Al ₂ O ₃ aggregate, cocatalyst (Y): hollow nanorod-shaped Ce _0.5 Zr _0.5 O ₂ , noble metal particles (Z): Pt + Rh, second production method ( Two hydrothermal reactions)>
In Example 2, the _{Ce (NO 3) 3 · 6H} 2 O 0.33g, was changed to _{Ce (NO 3) 3 · 6H} 2 O 0.17g and _{ZrO (NO 3) 2 · 2H} 2 O 0.14g Except for this, the pH of the slurry E3 obtained in Example 3 was 13.5, and an exhaust gas purifying catalyst P3 was obtained in the same manner as in Example 2. The BET specific surface area of the obtained exhaust gas-purifying catalyst P3 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P3 has a mixed phase of an aggregate of γ-Al ₂ O ₃ that does not support Rh and Pt and a hollow nanorod-shaped Ce _0.5 Zr _0.5 O ₂ that supports Rh and Pt ( Al: Ce: Zr: Rh: Pt (molar ratio) = 1: 0.015: 0.015: 0.001: 0.002).

Example 4 <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): hollow nanorod-shaped Ce _0.9 La _0.13 O ₂ , noble metal particles (Z): Pt + Rh, second production method ( Two hydrothermal reactions)>
In Example 2, the _{Ce (NO 3) 3 · 6H} 2 O 0.33g, was changed to _{Ce (NO 3) 3 · 6H} 2 O 0.3g and _{La (NO 3) 3 · 6H} 2 O 0.02g Except that (the pH of the slurry E3 obtained in Example 4 was 13.5), an exhaust gas purifying catalyst P4 was obtained in the same manner as in Example 2. The BET specific surface area of the obtained exhaust gas-purifying catalyst P4 was 170 m ² / g.

In addition, the obtained exhaust gas purifying catalyst P4 has a mixed phase of an agglomerate of γ-Al ₂ O ₃ that does not support Rh and Pt and a hollow nanorod-shaped Ce _0.9 La _0.13 O ₂ that supports Rh and Pt ( Al: Ce: La: Rh: Pt (molar ratio) = 1: 0.027: 0.003: 0.001: 0.002).

[Example 5] <Carrier (X): Al ₂ O ₃ aggregate, promoter (Y): hollow nanorod-shaped Ce _0.5 Zr _0.4 La _0.13 O ₂ , noble metal particles (Z): Pt + Rh, second production Method (two hydrothermal reactions)>
In Example 2, Ce a _{(NO 3) 3 · 6H 2} O 0.33g, Ce (NO 3) 3 · 6H 2 O 0.17g, ZrO (NO 3) 2 · 2H 2 O 0.11g, and La (NO ₃₎ was changed to ₃ · 6H ₂ O 0.02g (pH of the slurry E3 obtained in example 5 is 13.5), in the same manner as in example 2 to obtain the exhaust gas purifying catalyst P5 . The BET specific surface area of the obtained exhaust gas-purifying catalyst P5 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P5 was composed of an aggregate of γ-Al ₂ O ₃ not supporting Rh and Pt and a hollow nanorod-shaped Ce _0.5 Zr _0.4 La _0.13 O ₂ supporting Rh and Pt. It was a mixed phase (Al: Ce: Zr: La: Rh: Pt (molar ratio) = 1: 0.015: 0.012: 0.003: 0.001: 0.002).

[Example 6] <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh + Pd, second production method (two times of water Thermal reaction)>
In Example 2, a 1% RhCl ₃ solution 2.72 g, 1% RhCl ₃ was changed to an aqueous solution 1.36g and 1% PdCl ₃ aqueous solution 0.85 g (pH of the slurry E3 obtained in the sixth embodiment 13.0), and an exhaust gas purifying catalyst P6 was obtained in the same manner as in Example 2. The BET specific surface area of the obtained exhaust gas-purifying catalyst P6 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P6 has a mixed phase of an aggregate of γ-Al ₂ O ₃ that does not support Rh, Pt, and Pd and a hollow nanorod-shaped CeO ₂ that supports Rh, Pt, and Pd ( Al: Ce: Rh: Pt: Pd (molar ratio) = 1: 0.03: 0.001: 0.001: 0.001).

[Example 7] <Carrier (X): Al ₂ O ₃ aggregate, cocatalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Rh, second production method (twice water Thermal reaction)>
In Example 2, 1% RhCl ₃ solution 0.65g and 1% H ₂ PtCl ₆ aqueous solution 2.72 g, 1% RhCl ₃ was changed to an aqueous solution 3.25 g (slurry E3 obtained in this Example 7 The pH was 13.0), and an exhaust gas purifying catalyst P7 was obtained in the same manner as in Example 2. The BET specific surface area of the obtained exhaust gas-purifying catalyst G was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P7 has a mixed phase (Al: Ce: Rh (molar ratio)) of an aggregate of γ-Al ₂ O ₃ not supporting Rh and CeO ₂ in a hollow nanorod shape supporting Rh. ) = 1: 0.03: 0.005).

Example 8 <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, first production method (one time of water Thermal reaction)>
Water _{50mL Al 2 (SO 4) 3} · 16H 2 O 7.88g, Ce (NO 3) 3 · 6H 2 O 0.33g, 1% RhCl 3 solution 0.65g and 1% H ₂ PtCl ₆ aqueous solution 2. The aqueous solution F1 was obtained by mixing 72 g. In addition, 3.30 g of NaOH was mixed with 40 mL of water to obtain an aqueous solution F2. Next, the obtained aqueous solution F1 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and the aqueous solution F2 was dropped at 50 mL / min to obtain a slurry F3. The pH of the slurry F3 was 13.0, and contained 0.03 mol of Ce, 0.001 mol of Rh, and 0.002 mol of Pt per 1 mol of Al.

The obtained slurry F3 was charged into an autoclave, and a hydrothermal reaction was performed at 140 ° C. and 0.4 MPa for 1 hour. The generated solid was filtered by suction, and the obtained solid was washed with 10 parts by mass of water with respect to 1 part by mass of the solid. The solid content after the washing was freeze-dried at -50 ° C for 12 hours to obtain a precursor F4 of an exhaust gas purifying catalyst. The obtained precursor F4 was calcined at 500 ° C. for 6 hours in an air atmosphere to obtain an exhaust gas purifying catalyst P8. The BET specific surface area of the obtained exhaust gas-purifying catalyst P8 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P8 has a mixed phase (Al: Ce :) of an aggregate of γ-Al ₂ O ₃ that does not support Rh and Pt and a hollow nanorod-shaped CeO ₂ that supports Rh and Pt. Rh: Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

Example 9 <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, first production method (twice water Thermal reaction)>
Water _{50mL Al 2 (SO 4) 3} · 16H 2 O 7.88g, and Ce (NO ₃₎ a mixture of ₃ · 6H ₂ O 0.33g, to obtain an aqueous solution G1. Further, 3.3 g of NaOH was mixed with 20 mL of water to obtain an aqueous solution G2. Next, the obtained aqueous solution G1 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and the aqueous solution G2 was dropped at 50 mL / min to obtain a slurry G3. The pH of the slurry G3 was 13.5, and contained 0.03 mol of Ce with respect to 1 mol of Al.

The obtained slurry G3 was charged into an autoclave, and a hydrothermal reaction was performed at 140 ° C. and 0.4 MPa for 1 hour (first hydrothermal reaction). 0.65 g of a 1% RhCl ₃ aqueous solution and 2.72 g of a 1% H ₂ PtCl ₆ aqueous solution were mixed with the slurry G4 obtained by the hydrothermal reaction to obtain a slurry G5. The pH of the slurry G5 was 13.0, and contained 0.001 mol of Rh and 0.002 mol of Pt per 1 mol of Al.

The obtained slurry G5 was put into an autoclave, and a hydrothermal reaction was performed at 140 ° C. and 0.4 MPa for 1 hour (second hydrothermal reaction). The generated solid was filtered by suction, and the obtained solid was washed with 10 parts by mass of water with respect to 1 part by mass of the solid. The solid content after washing was freeze-dried at −50 ° C. for 12 hours to obtain a precursor G6 of an exhaust gas purifying catalyst. The obtained precursor G6 was calcined at 500 ° C. for 6 hours in an air atmosphere to obtain an exhaust gas purifying catalyst P9. The BET specific surface area of the obtained exhaust gas-purifying catalyst P9 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P9 has a mixed phase (Al: Ce :) of an aggregate of γ-Al ₂ O ₃ that does not support Rh and Pt and a hollow nanorod-shaped CeO ₂ that supports Rh and Pt. Rh: Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

[Example 10] <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, second production method (one time of water Thermal reaction)>
To 30 mL of water, 1.50 g of the boehmite obtained in Production Example 2, 0.33 g of Ce (NO ₃ ) ₃ .6H ₂ O, 0.65 g of a 1% RhCl ₃ aqueous solution, and 2.72 g of a 1% H ₂ PtCl ₆ aqueous solution were added. By mixing, a slurry H1 was obtained. Further, 0.3 g of NaOH was mixed with 10 mL of water to obtain an aqueous solution H2. Next, the obtained slurry H1 was stirred at a stirring speed of 300 rpm while maintaining the temperature at 25 ° C., and an aqueous solution H2 was dropped at 50 mL / min to obtain a slurry H3. The pH of the slurry H3 was 13.0, and contained 0.03 mol of Ce, 0.001 mol of Rh, and 0.002 mol of Pt per 1 mol of Al.

The obtained slurry H3 was put into an autoclave, and a hydrothermal reaction was performed at 140 ° C. and 0.4 MPa for 1 hour. The generated solid was filtered by suction, and the obtained solid was washed with 10 parts by mass of water with respect to 1 part by mass of the solid. The solid content after washing was freeze-dried at -50 ° C for 12 hours to obtain a precursor H4 of an exhaust gas purifying catalyst. The obtained precursor H4 was calcined at 500 ° C. for 6 hours in an air atmosphere to obtain an exhaust gas purifying catalyst P10. The BET specific surface area of the obtained exhaust gas-purifying catalyst P10 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P10 is a mixed phase (Al: Ce :) of an aggregate of γ-Al ₂ O ₃ not supporting Rh and Pt and a hollow nanorod-shaped CeO ₂ supporting Rh and Pt. Rh: Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

Example 11 <Carrier (X): Al ₂ O ₃ aggregate, promoter (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, second production method (one time of water Thermal reaction)>
Exhaust gas purification was performed in the same manner as in Example 10, except that 1.27 g of γ-Al ₂ O ₃ obtained in Production Example 3 (sol-gel method) was used instead of 1.50 g of boehmite obtained in Production Example 2. Catalyst P11 was obtained. The BET specific surface area of the obtained exhaust gas-purifying catalyst P11 was 165 m ² / g.

Further, the obtained exhaust gas purifying catalyst P11 has a mixed phase (Al: Ce :) of an aggregate of γ-Al ₂ O ₃ not supporting Rh and Pt, and a hollow nanorod-shaped CeO ₂ supporting Rh and Pt. Rh: Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

[Example 12] <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, second production method (twice water Thermal reaction)>
Exhaust gas purification catalyst P12 was obtained in the same manner as in Example 2, except that 0.30 g of NaOH was changed to 0.15 g in Example 2. In Example 12, the pH of the slurry E3 was 11.5, and the pH of the slurry E5 was 10.5. The BET specific surface area of the obtained exhaust gas-purifying catalyst P12 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst P12 has a mixed phase (Al: Ce :) of an aggregate of γ-Al ₂ O ₃ that does not support Rh and Pt and a hollow nanorod-shaped CeO ₂ that supports Rh and Pt. Rh: Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

[Example 13] <Carrier (X): Al ₂ O ₃ aggregate, co-catalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, second production method (twice water) Thermal reaction)>
In Example 2, an exhaust gas purifying catalyst P13 was obtained in the same manner as in Example 2, except that 0.30 g of NaOH was changed to 0.94 g of 28% ammonia water. In Example 13, the pH of the slurry E3 was 13.5, and the pH of the slurry E5 was 13.0. The BET specific surface area of the obtained exhaust gas-purifying catalyst P13 was 170 m ² / g.

Further, the obtained exhaust gas purifying catalyst 13 has a mixed phase (Al: Ce :) of an aggregate of γ-Al ₂ O ₃ that does not support Rh and Pt and a hollow nanorod-shaped CeO ₂ that supports Rh and Pt. Rh: Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

Example 14 <Carrier (X): Al ₂ O ₃ aggregate, cocatalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh, second production method (two times of water Thermal reaction, modified example)>
The slurry E4 obtained in Example 2 was subjected to suction filtration, and the obtained solid was washed with 10 parts by mass of water with respect to 1 part by mass of the solid. The solid content after the washing was freeze-dried at −50 ° C. for 12 hours, and calcined at 500 ° C. for 6 hours in an air atmosphere to obtain Powder I1. A slurry I2 was obtained by mixing 1.65 g of the obtained powder I1 in 20 mL of water, 0.65 g of an aqueous 1% RhCl ₃ solution, and 2.72 g of an aqueous 1% H ₂ PtCl ₆ solution.

Next, the obtained slurry I2 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 a powder I3. The obtained powder I3 was calcined at 500 ° C. for 3 hours in an air atmosphere to obtain an exhaust gas purifying catalyst P14. The BET specific surface area of the obtained exhaust gas-purifying catalyst P14 was 165 m ² / g.

Further, the obtained exhaust gas purifying catalyst P14 is a mixed phase (Al: Ce: Rh :) of an aggregate of γ-Al ₂ O ₃ supporting Rh and Pt, and a hollow nanorod-shaped CeO ₂ supporting Rh and Pt. Pt (molar ratio) = 1: 0.03: 0.001: 0.002).

[Example 15] <Carrier (X): Al ₂ O ₃ aggregate, promoter (Y): hollow nanorod-shaped Ce _0.5 Zr _0.5 O ₂ , noble metal particle (Z): Pt + Rh, second production method ( Two hydrothermal reactions, modified examples)>
Except that the _{Ce (NO 3) 3 · 6H} 2 O 0.33g of Example 14, was changed to _{Ce (NO 3) 3 · 6H} 2 O 0.17g and _{ZrO (NO 3) 2 · 2H} 2 O 0.14g In the same manner as in Example 14, an exhaust gas purifying catalyst P15 was obtained. The BET specific surface area of the obtained exhaust gas-purifying catalyst P15 was 165 m ² / g.

Further, the obtained exhaust gas purifying catalyst P15 has a mixed phase (Al: Ce _0.5 Zr _0.5 O ₂ ) of agglomerates of γ-Al ₂ O ₃ carrying Rh and Pt and hollow nanorods carrying Rh and Pt. Ce: Zr: Rh: Pt (molar ratio) = 1: 0.015: 0.015: 0.001: 0.002).

[Example 16] <Carrier (X): Al ₂ O ₃ aggregate, cocatalyst (Y): CeO _{2 in} hollow nanorod shape, noble metal particle (Z): Pt + Rh + Pd, second production method (two times of water Thermal reaction, modified example)>
The 1% H ₂ PtCl ₆ aqueous solution 2.72g of Example 14, except that the 1% H ₂ PtCl ₆ solution 1.36g and 1% PdCl ₃ aqueous solution 0.85 g, for exhaust gas purification in the same manner as in Example 14 Catalyst P16 was obtained. The BET specific surface area of the obtained exhaust gas-purifying catalyst P16 was 165 m ² / g.

Further, the obtained exhaust gas purifying catalyst P16 is composed of a mixed phase (Al: CeO _{2 in} the form of hollow nanorods supporting Rh, Pt and Pd and an aggregate of γ-Al ₂ O ₃ supporting Rh, Pt and Pd). Ce: Rh: Pt: Pd (molar ratio) = 1: 0.03: 0.001: 0.001: 0.001).

[Comparative Example 1] <Carrier (X): Al ₂ O ₃ aggregate, cocatalyst (Y ′): CeO ₂ particles, noble metal particles (Z): Pt + Rh>
0.33 g of Ce (NO ₃ ) ₃ .6H ₂ O and 1.5 g of boehmite obtained in Production Example 2 were mixed with 20 mL of water to obtain a slurry J1. The slurry J1 contained 0.03 mol of Ce with respect to 1 mol of Al. Next, the obtained slurry J1 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 a powder J2. The obtained powder J2 was calcined at 500 ° C. for 3 hours in an air atmosphere to obtain powder J3.

A slurry J4 was obtained by mixing 1.65 g of the obtained powder J3 in 20 mL of water, 0.65 g of a 1% aqueous solution of RhCl ₃ and 2.72 g of a 1% aqueous solution of H ₂ PtCl ₆ . Next, the obtained slurry J4 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 a powder J5. The obtained powder J5 was calcined at 500 ° C. for 3 hours in an air atmosphere to obtain an exhaust gas purifying catalyst Q1. The BET specific surface area of the obtained exhaust gas-purifying catalyst Q1 was 155 m ² / g.

Further, the obtained exhaust gas purifying catalyst Q1 has a mixed phase (Al: Ce: Rh: Pt: Pd) of an aggregate of γ-Al ₂ O ₃ carrying Rh and Pt and CeO ₂ particles carrying Rh and Pt. (Molar ratio) = 1: 0.03: 0.001: 0.001: 0.001).

[Comparative Example 2] <Carrier (X): Al ₂ O ₃ aggregate, cocatalyst (Y ′): Ce _0.5 Zr _0.5 O ₂ particles, noble metal particles (Z): Pt + Rh>
Except that the _{Ce (NO 3) 3 · 6H} 2 O 0.33g Comparative Example 1, was changed to _{Ce (NO 3) 3 · 6H} 2 O 0.17g and _{ZrO (NO 3) 2 · 2H} 2 O 0.14g An exhaust gas purifying catalyst Q2 was obtained in the same manner as in Comparative Example 1. The BET specific surface area of the obtained exhaust gas-purifying catalyst Q2 was 155 m ² / g.

Further, the obtained exhaust gas purifying catalyst Q2 has a mixed phase (Al: Ce: Zr) of an aggregate of γ-Al ₂ O ₃ supporting Rh and Pt and Ce _0.5 Zr _0.5 O ₂ particles supporting Rh and Pt. : Rh: Pt (molar ratio) = 1: 0.015: 0.015: 0.001: 0.002).

<STEM (scanning transmission electron microscope) image>
For the exhaust gas purifying catalysts obtained in Examples 2, 3, and 14, and Comparative Examples 1 and 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. 3A to 3E show STEM photographs.

  Further, the exhaust gas purifying catalysts obtained in Examples 2 and 14 and Comparative Example 1 were subjected to STEM-EDX analysis ((ARM-200F, JEOL Ltd.) in order to confirm the element distribution of Al, Ce, Pt, and Rh. Manufactured) + (JEM-3200FS, manufactured by JEOL Ltd.)). Observed images of these elements are shown in FIGS. 4A to 4C.

  According to the photographs shown in FIGS. 3A to 3C, in the exhaust gas purifying catalysts of Examples 2, 3, and 14, a promoter body (Y) that has grown into a hollow nanorod shape having a large aspect ratio can be confirmed. . Further, according to the photographs shown in FIGS. 4A and 4B, in the exhaust gas purifying catalysts of Examples 2 and 14, Pt and Rh were added to the surface of the hollow nanorod-shaped promoter (Y). It can be confirmed that the noble metal particles (Z) are supported.

  In contrast, according to the photographs shown in FIGS. 3D, 3E, and 4C, in the exhaust gas purifying catalysts of Comparative Examples 1 and 2, the promoter (Y ′) does not have a hollow nanorod shape. You can see that. According to the photograph shown in FIG. 3C, it can be confirmed that a large amount of the noble metal particles (Z) of Pt and Rh are supported on the surface of the promoter (Y ′) of Comparative Example 1.

<Evaluation of catalytic activity>
Using the exhaust gas purifying catalysts obtained in all Examples and all Comparative Examples, the decomposition activity of harmful components CO, C ₃ H ₆ and NO was evaluated.

Specifically, a stainless steel reaction tube is filled with each of the exhaust gas purifying catalysts (P1 to P16, Q1 to Q2) obtained in Examples 1 to 16 and Comparative Examples 1 and 2, and the exhaust gas purifying catalyst is filled. The exhaust gas purifying catalysts (P1 to P16, Q1 to Q2) were fixed to the reaction tubes by filling both sides of the catalysts (P1 to P16, Q1 to Q2) with quartz wool. A mixed gas (500 ppm of NO, 5000 ppm of CO, 250 ppm of C ₃ H _6, 250 ppm of O _2, 3300 ppm of O _2, 6000 ppm of CO ₂ , N ₂ balance) simulating the exhaust gas of an automobile is 400 mL / min (space velocity: 24 L / hour) in the reaction tube. It was distributed.

Next, the reaction tube was heated to 100 ° C. to 400 ° C. in an electric furnace, and the conversion of CO, C ₃ H ₆ , and NO was 50% using an exhaust gas analyzer (Auto5.1, manufactured by Riero Japan). _Was evaluated. Further, the durability of the exhaust gas purifying catalyst in a high temperature range was evaluated by measuring the conversion rates of CO, C ₃ H ₆ , and NO after 1 hour and 48 hours at a heating temperature of 1000 ° C.

  Table 1 shows the results.

From T ₅₀ in Table 1, all of Examples 1 to 16 CO, reaction temperature conversion of C ₃ H _6, NO is 50% lower than the respective Comparative Examples 1 or 2, exhaust gas purification of the present invention It can be seen that the catalyst for use has high catalytic activity at low temperatures.

  Furthermore, from the evaluation results of the conversion at 1000 ° C. in Table 1, all Examples 1 to 16 show higher values of the conversion after 48 hours as compared with Comparative Example 1 or 2, indicating that the present invention It can be seen that the exhaust gas purifying catalyst has an excellent effect of suppressing a decrease in catalytic activity in a high temperature range.

  The advantage of the above-mentioned catalytic activity in the exhaust gas purifying catalyst of the present invention is that the carrier (X) and / or the co-catalyst (Y) of the present invention form hollow nanorods and have a large specific surface area and a high temperature. Due to the shape in which sintering does not easily proceed, the noble metal particles (Z) firmly supported on the surface of the promoter body (Y) maintain the initial dispersion state and the noble metal particles (Z) do not sinter. Because a large specific surface area can be maintained.

  In the exhaust gas purifying catalyst of the present invention, at least some of the noble metal particles (Z) may be supported on the surface of the promoter (Y), and some of the noble metal particles (Z) may be supported on the carrier (X). This does not exclude the configuration supported on the surface of ()).

1: Exhaust gas purification catalyst (the present invention)
2: Exhaust gas purification catalyst (prior art)
X: carrier Y, y: promoter Z: noble metal particles

Claims (9)

A support comprising an oxide (M1);
A co-catalyst comprising a metal oxide (M2) having an oxygen storage ability supported on the surface of the carrier;
And noble metal particles of one or more selected from the group consisting of Pt, Pd, and Rh supported on the surface of the promoter.
The co-catalyst has a hollow nanorod shape formed by aggregating primary particles of the metal oxide (M2),
The exhaust gas purifying catalyst, wherein the carrier has a hollow nanorod shape formed by aggregating primary particles of the oxide (M1). The metal oxide (M2) is at least one member selected from the group consisting of CeO ₂ , CeO ₂ -ZrO ₂ , CeO ₂ -La ₂ O ₃ , and CeO ₂ -ZrO ₂ -La ₂ O _3. The exhaust gas purifying catalyst according to claim 1, wherein:   The cocatalyst is a hollow nanorod having an aspect ratio of 2 to 30, and a wall thickness of 1 to 20 nm, formed by aggregating primary particles of the metal oxide (M2) having a particle size of 1 to 20 nm. The exhaust gas purifying catalyst according to claim 1, wherein the catalyst has a shape. The oxide (M1) is characterized by Al ₂ O _3, TiO _2, ZrO _2, and is one or more selected from the group consisting of SiO _2, any of Claim 1 to 3 2. The exhaust gas purifying catalyst according to claim 1.   The carrier is a hollow nanorod having a major axis length of 100 nm to 1000 μm, formed by aggregating primary particles of the oxide (M1) having a particle size of 5 nm to 5 μm. The exhaust gas purifying catalyst according to any one of claims 1 to 4.   The exhaust gas purifying catalyst according to claim 5, wherein the noble metal particles have a particle size of 0.1 nm to 5 nm. A method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 6,
Subjecting the slurry containing the raw material of the oxide (M1) constituting the carrier , organic fibers, and a pH adjuster to a hydrothermal reaction at 100 ° C. or higher to obtain the carrier having a hollow nanorod shape;
Subjecting the carrier, the raw material of the metal oxide (M2) constituting the cocatalyst, the raw material of the noble metal particles, and a slurry containing a pH adjuster to a hydrothermal reaction at 100 ° C. or higher. A method for producing a catalyst for purifying exhaust gas. A method for producing an exhaust gas purifying catalyst according to any one of claims 1 to 6,
Subjecting the slurry containing the raw material of the oxide (M1) constituting the carrier , organic fibers, and a pH adjuster to a hydrothermal reaction at 100 ° C. or higher to obtain the carrier having a hollow nanorod shape;
A step of subjecting the carrier, the raw material of the metal oxide (M2) constituting the cocatalyst, and a slurry containing a pH adjuster to a hydrothermal reaction at 100 ° C. or higher to obtain a mixture;
Supporting the noble metal particles on the mixture. A method for producing an exhaust gas purifying catalyst, comprising:   The method for producing an exhaust gas purifying catalyst according to claim 7, further comprising a firing step after the step of subjecting the slurry containing the raw materials of the noble metal particles to a hydrothermal reaction.