JP4853816B2 - Exhaust gas purification filter and manufacturing method thereof - Google Patents

Description

  The present invention relates to an exhaust gas purifying filter having a metal oxide nanoporous coating composed of two or more kinds of metal oxides and useful as a diesel particulate filter (DPF) and the like, and a method for producing the same.

  Conventionally, various catalysts have been developed as exhaust gas purification filters for purifying harmful components discharged from internal combustion engines such as diesel automobiles, and as such exhaust gas purification filters, various kinds of filters made of silicon carbide or metal have been developed. In general, a substrate in which a metal oxide such as alumina, zirconia, and ceria and a noble metal such as platinum, rhodium, and palladium are supported is used.

  Conventionally, a powder obtained by a wet pulverization method as such a metal oxide is generally used. For example, Japanese Patent Application Laid-Open No. 10-182155 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2002-79097. (Patent Document 2) discloses a method of obtaining a composite metal oxide powder by preparing an oxide precursor from a salt solution of aluminum, cerium and zirconium by a coprecipitation method and firing the precursor in the air. ing. JP-A-7-300315 (Patent Document 3) discloses a composite metal oxide by adding boehmite alumina powder to a mixed solution obtained by mixing an aqueous cerium salt solution and an aqueous zirconium salt solution, followed by drying and firing. A method for obtaining a powder is disclosed.

  Furthermore, JP 2002-11870 A (Patent Document 4) includes a catalyst coating layer containing at least one selected from alumina, zirconia, titania and silica by a sol-gel method on a ceramic support such as silicon carbide. An exhaust gas purifying catalyst that is formed is disclosed.

However, in the case of using the conventional metal oxide powders as described in Patent Documents 1 to 4, adhesion and heat resistance to the base material (particularly silicon carbide base material) are not always sufficient. There was also a limit to the thinning of the coating formed on the substrate. Therefore, a metal oxide having a thin, uniform and high adhesion property using such a conventional metal oxide powder with respect to a silicon carbide substrate having a narrow tubular passage such as a silicon carbide substrate for DPF. There was a problem that it was difficult to form a coating. Furthermore, in the conventional method, a metal oxide thin film is formed on the pore inner wall surface while ensuring a gas flow path for a porous silicon carbide substrate used for a so-called wall-through type filter or the like. I couldn't.
Japanese Patent Laid-Open No. 10-182155 JP 2002-79097 A JP-A-7-300315 Japanese Patent Laid-Open No. 2002-111988

  The present invention has been made in view of the above-described problems of the prior art, and has high adhesion and excellent heat resistance to a silicon carbide substrate such as a silicon carbide substrate for DPF. And a filter for exhaust gas purification having a metal oxide nanoporous material capable of forming a thin film not only on the surface of the silicon carbide base material but also on the inner wall surface of the pores, since the film can be further thinned, and It aims at providing the manufacturing method.

  As a result of intensive studies to achieve the above object, the present inventors have found that the metal oxide obtained by using a colloidal solution of metal oxide or a solution of metal salt as it is is non-uniform and is incompatible with a silicon carbide substrate. Adhesion and heat resistance are not sufficient, but metal oxide colloidal solution and metal salt solution are mixed under high shear rate and heat treated without substantial coprecipitation. Surprisingly, the obtained metal oxide has a nanopore having a diameter of 10 nm or less, and the metal oxide is uniformly dispersed in the wall constituting the nanopore. It has been found that adhesion to a silicon carbide substrate and heat resistance are improved, and further thinning is possible, and the present invention has been completed.

That is, the exhaust gas purifying filter of the present invention includes a silicon carbide base material, alumina, zirconia, titania, iron oxide, ceria, lantana, neodia, yttria, barium oxide, lithium oxide supported on the silicon carbide base material, and A metal oxide nanoporous body composed of a composite metal oxide comprising at least one selected from the group consisting of potassium oxide and containing at least one selected from the group consisting of alumina, zirconia, ceria and titania ; The nanoporous body has nanopores having a diameter of 10 nm or less, and the metal oxide is uniformly dispersed in the wall constituting the nanopore. and,
With respect to all metal oxide metal elements contained in the nanoporous material at 10 at% or more, the thickness of the test sample can be regarded as substantially constant using a transmission electron microscope having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. The average of the relative intensity ratio X obtained by obtaining a spectrum by energy dispersive X-ray spectroscopy at a measurement point in the region and converting the integrated intensity of the fluorescent X-ray peak of each metal element in the obtained spectrum into a relative ratio. The value X _m and the second moment ν ₂ around the average value X _m are given by the following formula (1) for all the metal elements:
ν ₂ / X _m ² ≦ 0.02 (1)
Wherein (1), _{X m} is _{X m = (ΣX) / N} (N is the number of measurement points) the average value of the relative intensity ratio X represented by, [nu ₂ is _{ν 2 = {Σ (X-} X _m ) ² } / N, a second-order moment around the average value X _m represented by ν ₂ / X _m ² represents a second-order moment normalized by the square of the average value X _m . ]
It is characterized by satisfying the condition represented by

  In the exhaust gas purifying filter of the present invention, when the silicon carbide substrate is porous, a thin film made of the metal oxide nanoporous material is formed on the pore inner wall surface of the silicon carbide substrate. Preferably it is.

  In the exhaust gas purifying filter of the present invention, a coating made of the metal oxide nanoporous material may be formed on the surface of the silicon carbide substrate.

  In the exhaust gas purifying filter of the present invention, it is preferable that the following condition (I) is satisfied.

(I) With respect to all the metal oxide metal elements contained in the nanoporous material at 10 at% or more, the thickness of the test sample is approximately equal using a transmission electron microscope having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. Relative intensity ratio obtained by obtaining a spectrum by energy dispersive X-ray spectroscopy at a measurement point in a region that can be regarded as constant, and converting the integrated intensity of the fluorescent X-ray peak of each metal element in the obtained spectrum into a relative ratio The average value X _m of X and the second moment ν ₂ around the average value X _m are expressed by the following formula (1) for all the metal elements:
ν ₂ / X _m ² ≦ 0.02 (1)
Wherein (1), _{X m} is _{X m = (ΣX) / N} (N is the number of measurement points) the average value of the relative intensity ratio X represented by, [nu ₂ is _{ν 2 = {Σ (X-} X _m ) ² } / N, a second-order moment around the average value X _m represented by ν ₂ / X _m ² represents a second-order moment normalized by the square of the average value X _m . ]
The condition represented by is satisfied.

  Furthermore, in the exhaust gas purifying filter of the present invention, it is more preferable that the following condition (II) is satisfied.

(II) With respect to all metal oxide metal elements contained in the nanoporous material in an amount of 10 at% or more, arbitrarily at 10 or more measurement points using a transmission electron microscope having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. A spectrum is obtained by energy dispersive X-ray spectroscopy, and an average value _Xm and an average value of the relative intensity ratio X obtained by converting the integrated intensity of the fluorescent X-ray peak of each metal element in the obtained spectrum into a relative ratio. The second moment ν ₂ around X _m is given by the following formula (2) for all the metal elements:
ν ₂ / X _m ² ≦ 0.1 (2)
Wherein (2), _{X m} is _{X m = (ΣX) / N} (N is the number of measurement points) the average value of the relative intensity ratio X represented by, [nu ₂ is _{ν 2 = {Σ (X-} X _m ) ² } / N, a second-order moment around the average value X _m represented by ν ₂ / X _m ² represents a second-order moment normalized by the square of the average value X _m . ]
The condition represented by is satisfied.

  The metal oxide nanoporous material according to the present invention preferably has nanopores having a diameter of 5 nm or less, and more preferably 2 nm or less.

  The exhaust gas purifying filter of the present invention preferably further comprises a noble metal supported on the surface of the metal oxide nanoporous material coating and / or on the inner wall surface of the pore.

The method for producing an exhaust gas purifying filter of the present invention includes a silicon carbide base material, and alumina, zirconia, titania, iron oxide, ceria, lantana, neodia, yttria, barium oxide, lithium oxide supported on the silicon carbide base material. And at least one selected from the group consisting of alumina, zirconia, ceria and titania, and a metal oxide nanoporous material comprising a composite metal oxide containing at least one selected from the group consisting of alumina, zirconia, ceria and titania A method for producing the exhaust gas purifying filter of the present invention comprising :
Preparing a raw material fluid composition containing the composite metal oxide raw material;
The raw material fluid composition is mixed under a shear rate of 10,000 sec ⁻¹ or more, applied to the surface of the silicon carbide substrate, and then heat-treated without substantial coprecipitation, so that the diameter is 10 nm or less. The metal oxide is uniformly dispersed in the wall body having nanopores and constituting the nanopores ,
With respect to all metal oxide metal elements contained in the nanoporous material at 10 at% or more, the thickness of the test sample can be regarded as substantially constant using a transmission electron microscope having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. The average of the relative intensity ratio X obtained by obtaining a spectrum by energy dispersive X-ray spectroscopy at a measurement point in the region and converting the integrated intensity of the fluorescent X-ray peak of each metal element in the obtained spectrum into a relative ratio. The value X _m and the second moment ν ₂ around the average value X _m are given by the following formula (1) for all the metal elements:
ν ₂ / X _m ² ≦ 0.02 (1)
Wherein (1), _{X m} is _{X m = (ΣX) / N} (N is the number of measurement points) the average value of the relative intensity ratio X represented by, [nu ₂ is _{ν 2 = {Σ (X-} X _m ) ² } / N, a second-order moment around the average value X _m represented by ν ₂ / X _m ² represents a second-order moment normalized by the square of the average value X _m . ]
A step of obtaining a metal oxide nanoporous material that satisfies the conditions represented by :
It is the method characterized by including.

  In the method for producing an exhaust gas purifying filter of the present invention, when the silicon carbide substrate is porous, a thin film made of the metal oxide nanoporous material is formed on the pore inner wall surface of the silicon carbide substrate. Preferably it is formed.

  In the method for producing an exhaust gas purifying filter of the present invention, a coating made of the metal oxide nanoporous material may be formed on the surface of the silicon carbide substrate.

In the method for producing an exhaust gas purifying filter of the present invention, the metal oxide raw material is colloidal particles of alumina, zirconia, titania, iron oxide, ceria, lantana, neodia, yttria, barium oxide, lithium oxide and potassium oxide. And at least two selected from the group consisting of aluminum, zirconium, titanium, iron, cerium, lanthanum, neodymium, yttrium, barium, lithium and potassium .

  According to the present invention, the silicon carbide substrate has high adhesion to a silicon carbide substrate such as a silicon carbide substrate for DPF, has excellent heat resistance, and can be made thinner. It is possible to provide an exhaust gas purifying filter having a metal oxide nanoporous material capable of forming a thin film not only on the surface but also on the inner wall surface of a pore, and a method for producing the same.

  Hereinafter, the present invention will be described in detail with reference to preferred embodiments thereof.

  First, the exhaust gas purifying filter of the present invention will be described. The metal oxide used in the present invention is two or more metal oxides selected from the group consisting of alumina, zirconia, titania, iron oxide, rare earth element oxide, alkali metal oxide, and alkaline earth metal oxide. is there. Examples of rare earth element oxides include oxides such as cerium, lanthanum, neodymium, yttrium, and praseodymium. Examples of alkali metal oxides include oxides such as lithium, sodium, potassium, and cesium, and alkaline earth metals. Examples of the oxide include oxides such as barium, strontium, calcium, and magnesium.

  As such a metal oxide used in the present invention, alumina, zirconia, titania, iron oxide, from the viewpoint that the obtained metal oxide nanoporous material becomes more useful as a filter material for exhaust gas purification, Two or more composite metal oxides selected from the group consisting of ceria, lantana, neodia, yttria, barium oxide, lithium oxide and potassium oxide are preferred, and among these, selected from the group consisting of alumina, zirconia, ceria and titania. A composite metal oxide containing at least one kind is particularly preferable.

  Further, the combination of two or more kinds of metal oxides used in the present invention is not particularly limited, but from the viewpoint that the obtained metal oxide nanoporous material becomes more useful as a filter material for exhaust gas purification. , Alumina / Ceria / Zirconia, Alumina / Zirconia / Titania, Alumina / Zirconia / Lantana, Zirconia / Lantana, Zirconia / Neodia, Zirconia / Yttria, Zirconia / Titania, Ceria / Zirconia, Alumina / Zirconia / Yttria, Ceria / Zirconia / Yttria Alumina / Ceria, Alumina / Zirconia, Alumina / Titania, Alumina / Lantana, Alumina / Ceria / Zirconia / Yttria, Alumina / Ceria / Zirconia / Neodia, Alumina / Ceria / Zirconia / Lantana, A Mina / Ceria / Zirconia / Lantana / Praseodymium, Alumina / Ceria / Zirconia / Lantana / Neodia, Alumina / Ceria / Zirconia / Lantana / Neodia / Yttria, Alumina / Iron Oxide, Ceria / Iron Oxide, Alumina / Ceria / Iron Oxide, Zirconia / iron oxide, alumina / zirconia / iron oxide and the like are preferable, and among them, alumina / ceria / zirconia, alumina / zirconia / titania, alumina / zirconia / lanthana, zirconia / lanthana, zirconia / neodia, zirconia / yttria, zirconia / titania Ceria / zirconia, alumina / zirconia / yttria, ceria / zirconia / yttria, alumina / ceria, alumina / zirconia, and alumina / iron oxide are particularly preferred.

  Further, as a combination of two or more metal oxides according to the present invention, the obtained metal oxide nanoporous material is suitable as a filter material for purifying exhaust gas, particularly as a filter material used under excess oxygen. From these viewpoints, alumina / potassium oxide, alumina / barium oxide, barium oxide / potassium oxide, barium oxide / sodium oxide, barium oxide / lithium oxide, barium oxide / potassium oxide / lithium oxide, titania / barium oxide, titania / oxidation Barium / potassium oxide, titania / barium oxide / sodium oxide, titania / barium oxide / lithium oxide, titania / barium oxide / potassium oxide / sodium oxide, titania / barium oxide / potassium oxide / lithium oxide, titania / barium oxide / potassium oxide / Oxidized Lichi Sodium / sodium oxide, titania / barium oxide / potassium oxide / strontium oxide, etc., among which alumina / potassium oxide, alumina / barium oxide, barium oxide / potassium oxide, barium oxide / lithium oxide, barium oxide / potassium oxide / oxidation Particularly preferred are lithium, titania / barium oxide, titania / barium oxide / potassium oxide, and titania / barium oxide / lithium oxide.

  In addition, the composition ratio of the metal oxide in such various composite metal oxides is not particularly limited, and is appropriately adjusted according to the use and the like.

  The metal oxide nanoporous material according to the present invention is a porous material composed of the above-described metal oxide, has nanopores having a diameter of 10 nm or less, and constitutes the nanopores. The metal oxide is homogeneously dispersed in the wall body.

  As described above, the metal oxide nanoporous material according to the present invention has very fine pores having a diameter of 10 nm or less, preferably 5 nm or less, more preferably 2 nm or less. It is possible to improve adhesion and heat resistance to a silicon carbide substrate, which will be described later, compared to a metal oxide porous body having no pores, and further, as a filter by improving specific surface area and stability of supporting noble metals, etc. An improvement in performance is achieved.

  Further, in the metal oxide nanoporous material according to the present invention, the metal oxide is uniformly dispersed in the wall constituting the nanopore. That is, in the metal oxide nanoporous material according to the present invention, it is considered that two or more kinds of metal oxides constituting the nanoporous material are substantially uniformly dispersed (highly dispersed) at the atomic level. A state in which primary particles of about 100 nm made of each metal oxide are mixed like a conventional metal oxide porous body obtained by a precipitation method or the surface of the primary particles made of one metal oxide is oxidized with the other metal oxide. This is clearly different from the state in which the object is covered. Such a very high level of component uniformity is never obtained with a metal oxide obtained by using a metal oxide colloidal solution or a metal salt solution as it is, and contains two or more metal oxides. This is achieved for the first time by the production method of the present invention described later in which a colloidal solution or a solution containing two or more metal salts is mixed at a high shear rate and heat-treated without substantial coprecipitation. And, in the metal oxide nanoporous material according to the present invention having such extremely high level of component uniformity, surprisingly, compared to the conventional metal oxide porous material obtained by coprecipitation method or the like. Adhesion and heat resistance to the silicon carbide substrate have been dramatically improved.

  In the exhaust gas purifying filter of the present invention, the metal oxide nanoporous material is supported on a silicon carbide substrate, which will be described later, and preferably the metal oxide nanoporous material is a thin film on the surface of the silicon carbide substrate. It is formed as a coating. The thickness of the coating in that case is not particularly limited, and is appropriately adjusted according to the application, etc., but the metal oxide nanoporous material according to the present invention is even thinner than the silicon carbide substrate. Since it is possible to form a uniform coating excellent in adhesion, the thickness of the coating is preferably about 1 to 300 μm, and more preferably about 1 to 50 μm. Further, according to the present invention, since the coating made of a metal oxide can be thinned, a high level of adhesion can be achieved even for a high-density honeycomb that has conventionally been difficult to form a sufficient coating. From this point of view, it is particularly preferable that the thickness of the thin film is about 1 to 30 μm.

  Furthermore, in the exhaust gas purifying filter of the present invention, when the silicon carbide substrate is porous, a thin film made of the metal oxide nanoporous material is formed on the inner wall surface of the pores of the silicon carbide substrate. It is preferable. The thickness of the coating in that case is not particularly limited, but from the viewpoint of forming a thin film while securing a gas flow path for a porous silicon carbide substrate used for a wall-through type exhaust gas purification filter or the like, The thickness of the thin film is preferably about 1 to 5 μm.

  And it is preferable that the metal oxide nanoporous body concerning this invention satisfy | fills the conditions (I) demonstrated below.

That is, the first condition (I) that is preferably satisfied by the metal oxide nanoporous material according to the present invention is that an acceleration voltage of 200 kV is applied to all metal elements of the metal oxide contained in the nanoporous material at 10 at% or more. Using a transmission electron microscope having an electron beam diameter of 1.0 nm, a spectrum is obtained by energy dispersive X-ray spectroscopy at a measurement point in a region where the thickness of the test sample can be regarded as substantially constant. secondary and moments [nu ₂ about the mean value X _m and the average value X _m of the fluorescent X-ray peak of the integrated intensity of the relative relative intensity ratio is determined by converting the ratio X of the respective metal elements, the metal elements The following formula (1) for all:
ν ₂ / X _m ² ≦ 0.02 (1)
The condition represented by is satisfied. In the above formula (1), _Xm represents the following formula:
X _m = (ΣX) / N
(N in the formula indicates the number of measurement points.)
Is the average value of the relative intensity ratio X represented by Also, ν ₂ is the following formula:
ν ₂ = {Σ (X−X _m ) ² } / N
In a second moment around the mean value X _m represented. Furthermore, ν ₂ / X _m ² is a second moment normalized by the square of the average value X _m .

  In addition, although the specific method of such a measurement is not specifically limited, For example, it is preferable to implement according to the measuring method shown below.

<Preparation of sample>
A small amount of the metal oxide nanoporous material is collected and mixed with about 5 to 10 ml of a dispersion medium (for example, ethanol) stored in a container. The obtained mixture is put in a water tank of an ultrasonic cleaning machine, stirred for several minutes with ultrasonic waves, and immediately the container is taken out of the ultrasonic cleaning machine, and the dispersion of the test sample is about 3 mmφ called “microgrid”. One or two drops are dropped on a sample stage dedicated to a transmission electron microscope in which a porous organic film is pasted on a copper foil mesh. Then, after the dispersion medium is completely evaporated, observation with a transmission electron microscope is performed.

<Transmission electron microscope observation>
For observation, a transmission electron microscope (TEM) having an accelerating voltage of 200 kV having a field emission electron gun (FEG) is used. The TEM is equipped with a scanning transmission electron microscope (STEM) observation mode and an energy dispersive X-ray spectroscopy (EDX) detector. Insert the microgrid onto which the above test sample is dropped into the TEM sample chamber, and observe and analyze the sample protruding from the hole of the organic film of the microgrid (that is, the part where the sample does not overlap the organic film) The target of. At that time, a comparatively thin portion of the sample to be tested is selected, and the portion is irradiated with an electron beam focused to 1 nmφ in the STEM observation mode for 30 seconds, and the fluorescent X-ray emitted from the sample is used with an EDX detector. To detect. Then, with respect to the thickness of the sample, based on the total count number of all X-rays obtained by the EDX detector, a portion that is between 10,000 counts and 60,000 counts is suitable for measurement, that is, the thickness of the test sample. It is defined as an area where the length can be regarded as substantially constant.

<Determining the quality of the measurement site>
There is a place where the measurement site is close to the copper foil supporting the organic film of the microgrid, and a part of the fluorescent X-rays emitted from the sample hits the copper foil and good elemental analysis cannot be performed. The characteristics of the EDX detection result obtained from such a place are as follows: (1) The overall count number is low, (2) The count number is low particularly in low energy regions such as fluorescent X-rays of oxygen, (3) Compared to this, the copper count is high. Measurement results obtained from a measurement place where such good elemental analysis cannot be performed are excluded from all points of consideration, and measurement is continued using a test sample in another organic film hole as a new measurement target. For example, in the examples described later, the measurement results obtained from the locations where the ratio of (total oxygen count) / (total Cu count) in the obtained EDX spectrum is less than 2 at all measurement points are calculated. The calculation described later is performed based on the measurement result obtained from the location where the ratio of (total oxygen count) / (total Cu count) in the EDX spectrum is 2 or more.

<Calculation based on measurement results>
In the present invention, when the condition is determined, EDX spectrum data is used without processing. That is, the calculation is based on the fluorescent X-ray count itself, not the numerical value converted into the element weight ratio or the like using any conversion formula. First, from the fluorescent X-ray peaks of, for example, Al, Zr, and Ce, which are main metal elements constituting the sample (metal elements of all metal oxides contained in the sample by 10 at% or more) from the EDX spectrum, (1 One peak is selected for each metal element based on two points: as many counts as possible (2) as few as possible so that the overlap with other peaks is negligible. Then, a necessary and sufficient energy width (about 0.2 to 0.3 keV) that covers all the selected peaks is determined, and all counts of fluorescent X-rays in the range are added, and this is calculated as the integral intensity of the fluorescent X-ray peak of the metal element, so that on the basis of the aforementioned relative intensity ratio X, its mean value X _m, average second moment [nu ₂ around X _m, the average value X _m Secondary moments ν ₂ / X _m ² normalized by the square are sequentially calculated, and it is determined whether or not the condition expressed by the above formula (1) is satisfied.

  The fact that the metal oxide nanoporous material according to the present invention satisfies the condition represented by the formula (1) means that the main metal oxide constituting the nanoporous material is in the wall constituting the nanopore. It shows very even dispersion. Such a very high level of component uniformity is never obtained with a metal oxide obtained by using a metal oxide colloidal solution or a metal salt solution as it is, and is achieved only by the production method of the present invention described later. It has been done. And surprisingly, in the metal oxide nanoporous material that satisfies the condition represented by the formula (1), the adhesion to the silicon carbide substrate is surprising compared to the conventional metal oxide porous material that does not satisfy the condition. In addition, the heat resistance is dramatically improved.

  In addition, the metal oxide nanoporous material according to the present invention, particularly the metal oxide nanoporous material obtained by using a metal salt solution as a raw material fluid composition described later, satisfies the condition (II) described below. It is preferable.

That is, the second condition (II) that is preferably satisfied by the metal oxide nanoporous material according to the present invention is that an acceleration voltage of 200 kV is applied to all metal elements of the metal oxide contained in the nanoporous material by 10 at% or more. Using a transmission electron microscope having an electron beam diameter of 1.0 nm, a spectrum is arbitrarily obtained by energy dispersive X-ray spectroscopy at 10 or more measurement points, and the fluorescence X-ray peak of each metal element in the obtained spectrum is obtained. The average value X _m of the relative intensity ratio X obtained by converting the integrated intensity into the relative ratio and the secondary moment ν ₂ around the average value X _m are expressed by the following formula (2):
ν ₂ / X _m ² ≦ 0.1 (2)
The condition represented by is satisfied. In the above formula (2), _Xm represents the following formula:
X _m = (ΣX) / N
(N in the formula indicates the number of measurement points.)
Is the average value of the relative intensity ratio X represented by Also, ν ₂ is the following formula:
ν ₂ = {Σ (X−X _m ) ² } / N
In a second moment around the mean value X _m represented. Furthermore, ν ₂ / X _m ² is a second moment normalized by the square of the average value X _m .

  The details of the determination method for condition (II) (sample preparation, observation with a transmission electron microscope, determination of the quality of the measurement site, calculation based on the measurement result) are almost the same as the determination method for condition (I). However, it is not necessary to use only the measurement values for the measurement points in the region in which the thickness of the test sample can be regarded as being substantially constant as in the determination method of the condition (I), and any arbitrary measurement point is 10 or more. Good. Therefore, when observing with a transmission electron microscope, the thickness of the test sample is measured with respect to the total count number of all X-rays obtained by the EDX detector as a reference between 10,000 counts and 150,000 counts. It can be adopted as an appropriate area.

  The fact that the metal oxide nanoporous material according to the present invention satisfies the above condition (II) means that the main metal oxides constituting the nanoporous material are very uniformly dispersed in the nanoporous material. Show. Such a very high level of component uniformity is never obtained with a metal oxide obtained by using a metal oxide colloidal solution or a metal salt solution as it is, and is achieved only by the production method of the present invention described later. It has been done. And surprisingly, in the metal oxide nanoporous material satisfying the condition (II), the adhesion and heat resistance to the silicon carbide base material are higher than those of the conventional metal oxide porous material not satisfying the condition. It has improved.

  The metal oxide nanoporous material according to the present invention preferably satisfies one of the above conditions (I) to (II), and satisfies both of the conditions (I) and (II). More preferably. By satisfying a plurality of conditions, the main metal oxide constituting the nanoporous body is dispersed extremely uniformly in the nanoporous body (in the wall constituting the nanopore). Thereby, the adhesion and heat resistance of the metal oxide nanoporous material to the silicon carbide substrate can be synergistically improved.

  The metal oxide nanoporous material according to the present invention has been described above. In such a metal oxide nanoporous material, a second metal oxide powder having an average particle size of 0.01 to 50 μm is mixed. It may be. Examples of the second metal oxide include alumina, zirconia, ceria, titania, silica, lantana, yttria, and the like, and those having an average particle size of less than 0.01 μm are produced by pulverizing the metal oxide. On the other hand, when the thickness exceeds 50 μm, the thickness of the resulting coating tends to be very thick and the adhesion tends to decrease. The amount of the second metal oxide powder added is not particularly limited, but an amount of about 30 to 70% by mass in the obtained metal oxide nanoporous material is preferable.

  Further, the coating or thin film comprising the metal oxide nanoporous material according to the present invention may comprise a single layer, but comprises a plurality of layers comprising the same or different metal oxide nanoporous materials. May be. Thus, if it is a coating or thin film consisting of a plurality of layers made of different metal oxide nanoporous materials, multistage control for the catalytic reaction becomes possible, and the surface side layer and the surface side layer can be controlled by controlling the pore distribution of the surface side layer. It is also possible to control the degree of contribution with the base material side layer.

  The exhaust gas purifying filter of the present invention comprises a silicon carbide substrate and the metal oxide nanoporous material carried thereon. The base material used here is a base material made of silicon carbide (SiC), and the shape thereof is not particularly limited and is appropriately selected according to the use of the obtained exhaust gas purification filter, etc., but the diesel particulate filter Examples thereof include silicon carbide filter base materials (monolith carrier base materials such as honeycomb filter base materials and high-density honeycomb filter base materials), pellet-shaped filter base materials, and plate-shaped filter base materials.

  In recent years, porous silicon carbide substrates have been used for so-called wall-through type exhaust gas purifying filters, and such porous silicon carbide substrates are also useful as substrates according to the present invention. The wall-through type filter generally has a monolithic structure, and the inlets and outlets of the holes are alternately plugged, and the gas flows through the pores in the silicon carbide base material to enter the inlet side. It is led from the hole to the hole on the outlet side. The number of cells per square inch in such a wall-through type filter is generally 50 to 600 (the diameter of the main channel is about 1 to 3.6 mm), the average diameter of the pores is 5 to 100 μm, and A porous silicon carbide substrate having a porosity of about 30 to 80% is generally preferably employed.

  According to the present invention, it is possible to form a very thin thin film not only on the surface of such various silicon carbide substrates but also on the inner wall surface of the pores. Even when the metal oxide nanoporous thin film is formed on the inner wall surfaces of the pores, a gas flow path is secured, and it is possible to sufficiently prevent an increase in pressure loss when the gas flows. Furthermore, if a noble metal is supported on such a metal oxide nanoporous thin film and catalyzed, the contact frequency between the catalyst and the gas can be increased, and the purification performance of harmful components contained in the passing gas can be improved. Further increase is possible. In addition, if a metal oxide nanoporous thin film having a catalytic function is formed in the flow path capable of collecting particulate matter, it is possible to achieve both the collection and purification of particulate matter, and the inner wall surface of the pores. Since the inner diameter of the communication hole can be controlled by controlling the thickness of the thin film formed thereon, it is particularly effective for a diesel particulate filter (DPF) or the like that requires control of particle collection ability.

  The exhaust gas purifying filter of the present invention preferably includes a noble metal supported on the surface of the metal oxide nanoporous material coating and / or on the inner wall surface of the pore. Examples of such noble metals include platinum, rhodium, palladium, osmium, iridium, gold, and the like, but platinum, rhodium, and palladium are preferable from the viewpoint of being more useful as a filter for exhaust gas purification. Further, the amount of such noble metal supported is not particularly limited, and is appropriately adjusted according to the use of the obtained exhaust gas purification filter, but is 0.1 to 10 parts by mass with respect to 100 parts by mass of the metal oxide. The amount to the extent is common.

Next, the manufacturing method of the filter for exhaust gas purification of this invention is demonstrated. That is, a method for producing an exhaust gas purification filter comprising the silicon carbide substrate and the metal oxide nanoporous material supported on the substrate,
Preparing a raw material fluid composition containing raw materials of the two or more metal oxides;
The raw material fluid composition is mixed under a shear rate of 1000 sec ⁻¹ or more, applied to the surface of the silicon carbide substrate, and then heat-treated without substantially co-precipitation, so that the nanometer has a diameter of 10 nm or less. Obtaining a metal oxide nanoporous body having pores and in which the metal oxide is uniformly dispersed in a wall constituting the nanopore;
It is the method characterized by including.

  As the raw material of the metal oxide used in the present invention, alumina, zirconia, titania, iron oxide, rare earth element oxide, alkali metal oxide and alkaline earth metal oxide colloidal particles, aluminum, zirconium, titanium, Suitable examples include at least one selected from the group consisting of iron, rare earth elements, alkali metals, and alkaline earth metal salts.

Moreover, as the raw material fluid composition according to the present invention,
(i) a colloid solution containing at least one selected from the group consisting of colloidal particles of alumina, zirconia, titania, iron oxide, rare earth element oxide, alkali metal oxide and alkaline earth metal oxide, or
(ii) a metal salt solution containing at least one selected from the group consisting of aluminum, zirconium, titanium, iron, rare earth elements, alkali metal and alkaline earth metal salts,
Is preferred.

  First, the colloidal solution according to the present invention will be described. The metal oxide colloidal particles used in the present invention are colloidal particles having an average particle diameter of 5 to 200 nm, preferably 5 to 100 nm. For colloidal particles having an average particle size of less than 5 nm, it is theoretically difficult to produce particles smaller than the size of the metal oxide alone. On the other hand, when the particle size exceeds 200 nm, mixing / dispersibility is reduced and adhesion is poor. Various problems such as a decrease in reactivity and a decrease in reactivity occur.

  The shape of such colloidal particles is not particularly limited, and examples thereof include needle-shaped particles, rod-shaped particles, feather-shaped particles, spherical particles, and irregularly shaped particles. Also, the solvent for adjusting the concentration of the colloidal solution is not particularly limited, and examples thereof include water, alcohol, etc., but are determined in consideration of the amount of metal oxide supported per one time.

  Moreover, when obtaining the nanoporous body which consists of 2 or more types of metal oxides in this invention, about the one part metal oxide, you may further contain in the said colloid solution as a solution of the structural element. As such a solution, a solution in which a metal salt (nitrate, acetate, chloride, sulfate, sulfite, inorganic complex salt, etc.) as a constituent element is dissolved in a solvent such as water or alcohol is preferably used.

  Next, the metal salt solution according to the present invention will be described. The metal salt used as a raw material in the present invention is composed of components that are oxidized by the heat treatment described later to become the above-mentioned metal oxides, that is, aluminum, zirconium, titanium, iron, rare earth elements, alkali metals, and alkaline earth metals. It is a salt of two or more metals selected from the group, and suitable conditions for the two or more metals and combinations thereof are in accordance with the preferred conditions for the metal oxides and combinations thereof.

  In addition, as the two or more kinds of metal salts according to the present invention, the above-mentioned metal nitrates, acetates, chlorides, sulfates, sulfites, inorganic complex salts (for example, aluminum nitrate, zirconium oxynitrate, cerium nitrate) Water-soluble salts such as zirconium acetate, zirconium oxysulfate, titanium tetrachloride, titanyl ammonium oxalate, titanyl sulfate, yttrium nitrate) are preferably used.

  Furthermore, the solvent for preparing the metal salt solution containing two or more metal salts according to the present invention is not particularly limited, and water, alcohol (for example, methanol, ethanol, ethylene glycol, etc., alone or in a mixed system) Various solvents such as (solvent) can be mentioned, and a mixed solvent of water and alcohol is preferable from the viewpoint of improving adhesion to a metal substrate, and the alcohol content is 40 to 100% by mass (particularly preferably 55 to 80% by mass). A mixed solvent of water and alcohol, which is) is particularly preferred.

  Further, the pH of the metal salt solution according to the present invention is not particularly limited, but the pH of the metal salt solution is 3.0 to 6.0 from the viewpoint that metal ions are more stably present in the solution. It is preferable that

  In the present invention, the raw material fluid composition further contains the second metal oxide powder having an average particle size of 0.01 to 50 μm (preferably 0.01 to 10 μm). Also good. In addition, as such a 2nd metal oxide, the thing similar to the above-mentioned 1st metal oxide is used suitably. As the second metal oxide powder, a powder obtained by pulverizing after drying a solution containing a metal salt that becomes a second metal oxide by oxidation is preferably used. Furthermore, the average particle size is desirably equal to or less than the thickness of the coating to be obtained.

  Further, when such a second metal oxide powder is used, the above-mentioned noble metal can be supported on the surface in advance. A specific method for supporting such a noble metal is not particularly limited. For example, the above-described method may be used in a solution in which a salt of a noble metal (nitrate, chloride, acetate, etc.) or a noble metal complex is dissolved in a solvent such as water or alcohol. A method of immersing the powder, removing the solvent, and firing and pulverizing is preferably used.

In the production method of the exhaust gas purifying filter of the present invention, the fluid raw material composition according to the present invention described above of 1,000 sec ^-1 or more, more preferably 10000 sec ^-1 or more, particularly preferably 20000Sec ^-1 or more, under a shear rate of To obtain a coating composition. When the shear rate is less than 1000 sec ⁻¹ , the obtained metal oxide nanoporous material does not satisfy the above-described component uniformity, and sufficient adhesion and heat resistance cannot be obtained. The upper limit of the shear rate is not particularly limited, but is preferably 200,000 sec ⁻¹ or less.

  The apparatus used here is not particularly limited as long as it can be mixed at such a high shear rate, but a homogenizer is preferably used. Further, the mixing time under such a high shear rate is not particularly limited, but is generally about 1 to 20 minutes (preferably 1 to 5 minutes).

  The concentration (solid content concentration) of the raw material fluid composition mixed under such a high shear rate is adjusted to the shape (thickness, etc.) of the target metal oxide nanoporous material, the viscosity suitable for the coating method, etc. The solid content is generally adjusted to about 5 to 50% by mass, and preferably about 10 to 15% by mass.

  Further, in the present invention, in order to sufficiently remove bubbles mixed in the obtained coating composition, the obtained coating composition is gently stirred for about 1 to 2 minutes (for example, 20 to 100 rpm). An air treatment may be further performed.

  In the coating composition obtained by the method described above, the components in the raw material fluid composition are extremely uniformly dispersed, and heat treatment is performed without substantially coprecipitation of the raw material fluid composition. By this, it becomes possible to form the metal oxide nanoporous material according to the present invention having high adhesion to the silicon carbide substrate and having excellent heat resistance, and further obtained metal oxide nanoporous material It is also possible to reduce the film thickness. Therefore, according to the present invention, a metal oxide nanoporous material having a high level of adhesion and excellent heat resistance can be uniformly formed even on a silicon carbide substrate such as a DPF honeycomb filter. Is possible. Further, according to the present invention, the thin film made of the metal oxide nanoporous material can be formed on the pore inner wall surface of a porous silicon carbide base material used for a so-called wall-through type exhaust gas purification filter or the like. It becomes possible.

  Thus, in this invention, it is necessary to heat-process, without substantially coprecipitating a raw material fluid composition. Here, “without substantially coprecipitation” means that the metal element in the raw material fluid composition is solidified by heat treatment without substantially passing through a hydroxide, and becomes a metal oxide. Specifically, it refers to the case where the ratio of hydroxide in the metal component in the raw material fluid composition before the heat treatment is 50 at% or less (more preferably 30 at% or less).

  In the method for producing an exhaust gas purifying filter of the present invention, the raw material fluid composition is mixed under the above-mentioned high shear rate and applied onto the surface of the silicon carbide substrate and / or the inner wall surface of the pores. After that, the exhaust gas purifying filter having the target metal oxide nanoporous material is obtained by heat treatment without substantially coprecipitation. Further, when a metal salt solution is used as the raw material fluid composition, the exhaust gas purifying filter of the present invention is obtained by oxidizing the metal component in the raw material fluid composition by such heat treatment to form a metal oxide. Can do.

  In the present invention, the raw material fluid composition is preferably heat-treated at a high speed after the aforementioned mixing. Although the specific method of such heat treatment is not particularly limited, a method in which the raw material fluid composition is dried at a high speed after the above-mentioned mixing, and further fired as necessary is suitably employed.

  In the present invention, it is desirable that the time until the heat treatment after mixing the raw material fluid composition under the above-mentioned high shear rate is shorter, preferably within 60 minutes, preferably within 30 minutes. It is more preferable. When this time exceeds the above upper limit, the effect of high shear stirring is reduced, the metal oxide aggregates before heat treatment or in the heat treatment step, and a metal oxide nanoporous material with sufficiently improved adhesion and heat resistance is obtained. It becomes difficult.

  Moreover, although the baking process mentioned later may serve as a drying process, it is preferable to remove a solvent and to dry at high speed before baking the said raw material fluid composition, As drying conditions in that case, 60- The condition of drying at a temperature of 180 ° C. (particularly preferably 100 to 150 ° C.) within 10 minutes (particularly preferably within 5 minutes) is more preferable. If the drying temperature is less than the above lower limit, high-speed drying tends to be difficult to achieve sufficiently. Since it is too much, it causes cracks, cracks and the like, and as a result, the adhesion tends to be greatly reduced. In addition, if the drying time exceeds the above upper limit, the effect of high shear stirring is reduced, the metal oxide aggregates in the drying step, and it is difficult to obtain a metal oxide nanoporous material with sufficiently improved adhesion and heat resistance. Tend to be. In this high-speed drying step, it is preferable to dry the raw material fluid composition until the water content becomes 200% by mass or less (particularly preferably 100% by mass or less).

  Furthermore, as firing conditions, the firing is performed at a temperature of 250 to 600 ° C. (particularly preferably 350 to 500 ° C.) for 20 to 70 minutes (particularly preferably 30 to 60 minutes) in an oxidizing atmosphere (for example, air). Conditions are more preferred. When the firing temperature is less than the above lower limit, firing is not sufficiently achieved, and it tends to be difficult to obtain a metal oxide nanoporous material with sufficiently improved adhesion and heat resistance. -The oxidizing atmosphere tends to be accompanied by performance degradation such as sintering. Also, if the firing time is less than the above lower limit, firing is not sufficiently achieved, and it tends to be difficult to obtain a metal oxide nanoporous body with sufficiently improved adhesion and heat resistance, and on the other hand, when the upper limit is exceeded. The effect of high shear stirring is reduced, the metal oxide aggregates in the firing step, and it tends to be difficult to obtain a metal oxide nanoporous material having sufficiently improved adhesion and heat resistance.

  In the method for producing an exhaust gas purification filter of the present invention, the amount of the raw material fluid composition applied to the base material is not particularly limited, and is appropriately adjusted according to the use of the obtained exhaust gas purification filter. The amount that the amount of the metal oxide constituting the thin film is about 10 to 300 g per 1 liter of volume is preferable.

  In addition, a specific method for applying the raw material fluid composition to the base material is not particularly limited. For example, a method of immersing the base material in the raw material fluid composition, a base material by spraying the raw material fluid composition, or the like. A method of coating the surface is preferably used.

  In addition, when using a porous silicon carbide base material used for a so-called wall-through type exhaust gas purification filter or the like, after applying the raw material fluid composition to the base material, a suction operation is performed as necessary to make it excessive. It is preferable to remove the raw material fluid composition. By doing so, it is more reliably prevented that the inlet and outlet of the pores are blocked by the metal oxide nanoporous material, and the metal oxide nanoporous thin film formed on the inner wall surface of the pore is more It tends to be thinner.

  Further, the step of applying the raw material fluid composition to the base material may be repeated until a desired loading amount is obtained. In that case, the raw material fluid composition is applied to the base material and dried, followed by temporary baking. It is preferable. As pre-baking conditions in that case, the conditions of pre-baking for 30 to 60 minutes at a temperature of 250 to 300 ° C. in an oxidizing atmosphere (for example, air) are particularly preferable.

  Furthermore, when obtaining the exhaust gas purifying filter of the present invention, the aforementioned noble metal may be supported on the surface of the filter having the metal oxide nanoporous material obtained above and / or on the inner wall surface of the pore. . A specific method for supporting such a noble metal is not particularly limited. For example, the above-described method may be used in a solution in which a salt of a noble metal (nitrate, chloride, acetate, etc.) or a noble metal complex is dissolved in a solvent such as water or alcohol. A method of immersing the filter, removing the solvent, and firing and pulverizing is preferably used. The drying condition for removing the solvent in the step of supporting the noble metal is preferably within 30 minutes at 30 to 150 ° C. The firing condition is 250 to 300 in an oxidizing atmosphere (for example, air). About 30 to 60 minutes are preferable at ° C. Moreover, you may repeat such a noble metal carrying | support process until it becomes a desired carrying amount.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

  As a homogenizer, T.M. manufactured by Tokushu Kika Kogyo Co., Ltd. was used. K. ROBOMIX (stirring part: TK homomixer MARK II 2.5 type) was used.

Further, alumina _(Al 2 _{O 3)} colloid, Al solution, Zr solution, the Ce solution, the following were used, respectively.
Al ₂ O ₃ colloid: average particle diameter: 5 to 20 nm, acicular particles, nitric acid aqueous solution (solid content concentration: 25% by mass),
Al solution: aluminum nitrate aqueous solution (solid content concentration: 5.44% by mass),
Zr solution: zirconium oxynitrate aqueous solution (solid content concentration: 18% by mass),
Ce solution: cerium nitrate aqueous solution (solid content concentration: 28% by mass).

  In addition, solid content concentration here is the mass ratio (%) with respect to each solution amount of the amount of the metal oxide produced | generated when the solvent of each solution is evaporated, dried and baked to make a metal oxide. It is expressed as

Furthermore, a silicon carbide plate (50 mm × 50 mm × 1.0 mm, porosity 42%, average pore diameter 9 μm) was used as a substrate for evaluating component uniformity, heat resistance, and first adhesion. . Moreover, as a base material for evaluating the cross-sectional properties and the second adhesion, a honeycomb filter made of silicon carbide for DPF of 200 cell / inch ² (30 mmφ, 50 mmL, average pore diameter: 11 μm, porosity: 42%) Was used.

Example 1
Al ₂ O ₃ colloid and Zr solution so that the mass ratio of Al ₂ O ₃ , ZrO ₂ and CeO ₂ in the obtained metal oxide thin film is Al ₂ O ₃ : ZrO ₂ : CeO ₂ = 35: 30: 35. And Ce solution were mixed and diluted with methanol to prepare a colloidal solution having a solid concentration of 12% by mass. The resulting colloidal solution was mixed for 2 minutes with a homogenizer under a shear rate of 20000 sec ⁻¹ , and then mixed bubbles were removed at a gentle stirring speed (20 rpm) for about 1 minute to obtain a coating composition.

  Next, the silicon carbide substrate was immediately immersed in the coating composition obtained above for 1 to 10 seconds, taken out, and then the excess coating composition on the surface was removed by gravity and shaking. And after placing the base material horizontally, 5-10 minutes of gentle drying at normal temperature, 5-10 minutes of drying with warm air (60-100 ° C.) at a wind speed of 2-5 m / s, 250 in an air atmosphere. Pre-baking at a temperature of about 30 minutes was performed, followed by cooling for 5 to 10 minutes with room temperature air at a wind speed of 2 to 5 m / s. Such a treatment was repeated twice, followed by firing at 500 ° C. for about 60 minutes in an air atmosphere to obtain an exhaust gas purifying filter in which a metal oxide thin film was supported on the surface of a silicon carbide substrate.

  When the coating of the metal oxide in the obtained exhaust gas purification filter was observed with a transmission electron microscope (TEM), the thickness of the coating was about 4 μm, and a thin film made of a very uniform metal oxide was formed. It was confirmed that

(Example 2)
Exhaust gas purification filter in which a metal oxide thin film was supported on the surface of a silicon carbide substrate was obtained in the same manner as in Example 1 except that an Al solution was used instead of the Al ₂ O ₃ colloid.

(Comparative Example 1)
Exhaust gas in which a metal oxide thin film is supported on the surface of a silicon carbide base material in the same manner as in Example 1 except that instead of the mixing by the homogenizer, the mixture is gently stirred by a propeller (shear rate of 10 sec ⁻¹ or less). A purification filter was obtained.

(Comparative Example 2)
Using conventional alumina / ceria / zirconia composite oxide powder obtained by the coprecipitation method described in Example 1 of JP-A-10-182155 (Patent Document 1), Al ₂ O in the obtained metal oxide thin film _The conventional alumina / ceria / zirconia composite oxide powder and boehmite (Al ₂ O ₃₎ so that the mass ratio of ₃ to ZrO ₂ and CeO ₂ is Al ₂ O ₃ : ZrO ₂ : CeO ₂ = 35: 30: 35. Colloid) and an aqueous solution of aluminum nitrate are mixed and pulverized by an attritor (wet pulverization), and a slurry having a solid content concentration of 70% by mass is used instead of the colloidal solution, and gently mixed by a propeller instead of the homogenizer. stirring as (shear rate 10 sec ^-1 or less), except that further the sintering temperature and 700 ° C. in the same manner as in example 1 coal Metal oxide thin film to obtain a filter for exhaust gas purification supported on the surface of the silicon substrate.

<Evaluation of component uniformity: Condition (I)>
First, component uniformity was evaluated for the metal oxide thin films obtained by the methods described in Example 1 and Comparative Example 1 as follows. That is, according to the measurement method of the above-mentioned condition (I), these metal oxide thin films are energy dispersive using a transmission electron microscope (JEM2010FEF, manufactured by JEOL Ltd.) having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. The spectrum was determined by X-ray spectroscopy, and the integrated intensity of the fluorescent X-ray peak for Al, Zr and Ce contained in the thin film was determined.

  When observing with a transmission electron microscope, with regard to the thickness of the sample, using the total count of all X-rays obtained with the EDX detector as a reference, the portion between 10,000 count and 60,000 count is appropriate for measurement. This area was adopted as an area where the thickness of the test sample can be regarded as substantially constant.

Then, the relative intensity ratio X mentioned above based on the measurement result, the average value X _m, average second moment [nu ₂ around X _m, second moment normalized by the square of the mean value X _m [nu ₂ / X _m ² was sequentially calculated, and it was determined whether or not the condition represented by the formula (1) was satisfied.

The secondary moments ν ₂ / X _m ² normalized by the square of the average value X _m thus obtained are shown in Table 1, respectively.

  As is clear from the results shown in Table 1, in the metal oxide thin film obtained in Example 1 obtained by the method of the present invention, all the metal elements contained in the metal oxide are represented by the above formula (1). It was confirmed that the metal oxide was dispersed extremely uniformly. On the other hand, in the metal oxide thin film obtained in Comparative Example 1 that was not mixed under a high shear rate, it was confirmed that the condition represented by the above formula (1) was not satisfied.

<Heat resistance test>
The heat resistance of the metal oxide thin film formed on the silicon carbide plate by the method described in Example 1, Comparative Example 1 and Comparative Example 2 was evaluated as follows. That is, the specific surface area (BET specific surface area) after each metal oxide thin film was heated to 500 ° C., 900 ° C., and 1000 ° C. in an oxidizing atmosphere (in the air) and maintained for 5 hours was measured.

  The obtained results are shown in FIG. In FIG. 1, the specific surface area of the metal oxide thin film obtained in Comparative Example 2 is relatively shown as 1.

  As is clear from the results shown in FIG. 1, the metal oxide thin film according to the present invention obtained by mixing the colloidal solution at a high shear rate, applying the colloidal solution to the substrate, drying and firing at high speed, It was confirmed that the performance was greatly improved.

<Adhesion test 1>
The adhesion properties of the metal oxide thin films formed on the silicon carbide plate by the methods described in Example 1, Example 2, and Comparative Example 2 were evaluated as follows. That is, each substrate having a metal oxide thin film formed on the surface was subjected to ultrasonic vibration for 30 minutes × 4 times by applying an ultrasonic cleaner, and the remaining ratio of the thin film (adhesion rate (%), weight basis) was measured. . The obtained results are shown in FIG.

  As is clear from the results shown in FIG. 2, in the metal oxide thin film according to the present invention obtained by mixing the raw material fluid composition at a high shear rate, applying it to the substrate, drying and firing at high speed, It was confirmed that the adhesion to the substrate was greatly improved.

<Adhesion test 2>
The adhesion properties of the metal oxide thin films formed on the DPF silicon carbide honeycomb filter by the method described in Example 1 and Comparative Example 2 were evaluated as follows. That is, each filter having a metal oxide thin film formed on the surface was subjected to ultrasonic vibration for 30 minutes × 4 times through an ultrasonic cleaner, and the remaining ratio of the thin film (adhesion rate (%), weight basis) was measured. The obtained results are shown in FIG.

  As is clear from the results shown in FIG. 3, in the metal oxide thin film according to the present invention obtained by mixing the raw fluid composition at a high shear rate, applying it to the substrate, drying and firing at high speed, It was confirmed that the adhesion to the substrate was greatly improved.

<Evaluation of nanopore>
The metal oxide thin film obtained by the method described in Example 1 was confirmed to have nanopores by the nitrogen adsorption method and the X-ray small angle scattering method as follows.

That is, the nitrogen adsorption method is a method of measuring the amount of gas adsorbed on the solid surface at a certain equilibrium vapor pressure or the amount of gas desorbed from the solid surface by the static volume method. Isotherm data can be obtained by introducing a known amount of adsorbed gas into a sample cell containing a solid sample held at a constant temperature at the adsorbate's critical temperature, or by removing a known amount of adsorbed gas from the sample cell. . The amount of gas adsorbed or desorbed at the equilibrium pressure corresponds to the difference between the amount of gas introduced or removed and the amount of gas necessary to fill the void around the sample. In this measurement, a fully automatic gas adsorption amount measuring device (autosorb 1MP / LP) manufactured by QUANTACHROME was used. Then, using a sample of 0.05 to 0.15 g, the nitrogen adsorption measurement is continued in the range where the measurement temperature is −196 ° C. and the relative pressure P / P ₀ to the atmospheric pressure is 0.00001 to 1, and then P / Nitrogen desorption measurement was performed in the range of P ₀ from 0.01 to 1. An adsorption isotherm can be obtained by plotting the adsorption amount of nitrogen gas, and the pore size distribution was obtained by an analysis method called a BJH method. The BJH method is the most effective model for calculating the mesopore distribution, and is a model assuming that all the holes are cylindrical. The measurement result of the metal oxide porous body obtained by the method described in Example 1 is shown in FIG.

  In addition, the X-ray small angle scattering method used X-rays of an undulator beam line in a synchrotron radiation facility excellent in parallelism and energy density. The X-ray energy is set to 10 keV (wavelength 0.124 nm), and the X-ray beam is first narrowed down to about 0.04 mm □ using a four-quadrant slit to be the starting point of the small-angle scattering method beam. A pinhole having a diameter of 0.5 mm was placed about 65 cm downstream from the starting point to block excess scattered light, and the sample was placed in close contact with the pinhole. The amount of absorption was calculated so that the intensity of the X-ray after passing through the sample was 1 / e (e is the base of the natural logarithm), the appropriate thickness of the sample was calculated, and the green compact of the sample was prepared accordingly. An X-ray was recorded by setting an imaging plate on the exact 50 cm downstream side (115 cm downstream from the starting point) from the sample. An attenuator overlaid with a cover glass was installed at the position of the transmitted X-ray to prevent the imaging plate from being damaged, and the position of the transmitted X-ray was recorded on the imaging plate with an appropriate intensity. In the analysis, an average value of X-ray intensities recorded on a concentric circle centered on a transmission X-ray position on the imaging plate was obtained, and a graph of scattering angle versus intensity was drawn by converting the radius of the concentric circle into an angle. Assuming a spherical scatterer in the sample, the distribution of the scatterer radius was appropriately changed, and an appropriate distribution capable of explaining the graph of the scattering angle versus the intensity was obtained. The measurement result of the metal oxide porous body obtained by the method described in Example 1 is shown in FIG. For comparison, the measurement results for the bulk copper foil (thickness 6 μm) and the aluminum foil (thickness 100 μm) are also shown in FIG. 5.

  As is apparent from the results shown in these drawings, particularly in FIG. 5, the metal oxide porous material obtained by the method of the present invention has very fine nanopores having a diameter of 2 nm or less. Was confirmed.

<Evaluation of sectional properties>
First, the cross-sectional properties of the metal oxide thin film formed at the center and the end of the exhaust gas purifying filter obtained by the method described in Example 1 using the silicon carbide honeycomb filter for DPF were scanned using an electron microscope. And an X-ray microanalyzer (manufactured by JEOL Ltd., JXA-8200). As a result, the metal oxide nanoporous material obtained in Example 1 obtained by mixing the colloidal solution at a high shear rate, applying the colloidal solution to the substrate, drying and firing at high speed, It was confirmed that a very thin film was formed not only on the surface but also on the inner wall surface of the pore.

  Next, the cross-sectional properties of the metal oxide thin film formed at the center and the end of the exhaust gas purifying filter obtained by the method described in Comparative Example 2 using the DPF silicon carbide honeycomb filter are shown in FIG. It observed using the microscope and the X-ray microanalyzer (the JEOL company make, JXA-8200). As a result, the metal oxide obtained in Comparative Example 2 using the slurry containing the conventional alumina / ceria / zirconia composite oxide powder obtained by the coprecipitation method as it was was thick on the surface of the silicon carbide substrate. It was confirmed that a film was formed and was hardly supported in the pores of the silicon carbide substrate.

  As described above, according to the present invention, the raw material fluid composition containing the metal oxide raw material is mixed at a high shear rate, and is substantially co-precipitated after being applied to the surface of the silicon carbide substrate. The metal oxide has a nanopore having a diameter of 10 nm or less, and the metal oxide is uniformly dispersed in the wall constituting the nanopore by performing the heat treatment without any heat treatment. An exhaust gas purifying filter having a nanoporous material can be obtained.

  According to the exhaust gas purifying filter of the present invention, the adhesion and heat resistance to a silicon carbide substrate such as a DPF silicon carbide substrate are improved, and the coating can be made thinner. A thin film can be formed not only on the surface of the substrate but also on the inner wall surface of the pores. Therefore, the present invention is a technique useful for obtaining various exhaust gas purification filters using a silicon carbide substrate, and particularly a porous silicon carbide substrate used for a wall-through type exhaust gas purification filter or the like. On the other hand, it is very useful as a technique for forming a metal oxide thin film on the inner wall surface of a pore while ensuring a gas flow path.

It is a graph which shows the result of a heat resistance test. It is a graph which shows the result of the adhesion test 1. It is a graph which shows the result of the adhesion test 2. FIG. It is a graph which shows the pore diameter distribution of the metal oxide porous body calculated | required by the nitrogen adsorption method. It is a graph which shows the pore diameter distribution of the metal oxide porous body calculated | required by the X-ray small angle scattering method.

Claims (10)

Two types selected from the group consisting of a silicon carbide substrate and alumina, zirconia, titania, iron oxide, ceria, lantana, neodia, yttria, barium oxide, lithium oxide and potassium oxide supported on the silicon carbide substrate. An exhaust gas purifying filter comprising a metal oxide nanoporous body composed of a composite metal oxide comprising at least one selected from the group consisting of alumina, zirconia, ceria and titania ,
The nanoporous body has nanopores having a diameter of 10 nm or less, and the metal oxide is uniformly dispersed in the wall constituting the nanopores ,
With respect to all metal oxide metal elements contained in the nanoporous material at 10 at% or more, the thickness of the test sample can be regarded as substantially constant using a transmission electron microscope having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. The average of the relative intensity ratio X obtained by obtaining a spectrum by energy dispersive X-ray spectroscopy at a measurement point in the region and converting the integrated intensity of the fluorescent X-ray peak of each metal element in the obtained spectrum into a relative ratio. The value X _m and the second moment ν ₂ around the average value X _m are given by the following formula (1) for all the metal elements:
ν ₂ / X _m ² ≦ 0.02 (1)
Wherein (1), _{X m} is _{X m = (ΣX) / N} (N is the number of measurement points) the average value of the relative intensity ratio X represented by, [nu ₂ is _{ν 2 = {Σ (X-} X _m ) ² } / N, a second-order moment around the average value X _m represented by ν ₂ / X _m ² represents a second-order moment normalized by the square of the average value X _m . ]
An exhaust gas purifying filter characterized by satisfying the condition expressed by:   The said silicon carbide base material is a porous thing, The thin film which consists of the said metal oxide nanoporous body is formed on the pore inner wall face of the said silicon carbide base material, The said 1st aspect is characterized by the above-mentioned. Exhaust gas purification filter.   The exhaust gas purifying filter according to claim 1 or 2, wherein a coating made of the metal oxide nanoporous material is formed on a surface of the silicon carbide substrate. The exhaust gas purifying filter according to any one of claims 1 to 3 , wherein the nanoporous body has nanopores having a diameter of 5 nm or less. With respect to all metal oxide metal elements contained in the nanoporous material in an amount of 10 at% or more, an energy dispersion type is arbitrarily used at 10 or more measurement points using a transmission electron microscope having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. A spectrum is obtained by X-ray spectroscopy, and an average value X _m and an average value X _m of the relative intensity ratio X obtained by converting the integrated intensity of the fluorescent X-ray peak of each metal element in the obtained spectrum into a relative ratio. The secondary moment ν ₂ around is the following formula (2) for all the metal elements:
ν ₂ / X _m ² ≦ 0.1 (2)
Wherein (2), _{X m} is _{X m = (ΣX) / N} (N is the number of measurement points) the average value of the relative intensity ratio X represented by, [nu ₂ is _{ν 2 = {Σ (X-} X _m ) ² } / N, a second-order moment around the average value X _m represented by ν ₂ / X _m ² represents a second-order moment normalized by the square of the average value X _m . ]
The exhaust gas purifying filter according to any one of claims 1 to 4 , wherein a condition represented by: The exhaust gas purification according to any one of claims 1 to 5 , further comprising a noble metal supported on the surface of the metal oxide nanoporous material coating and / or on the inner wall surface of the pores. Filter. Two types selected from the group consisting of a silicon carbide substrate and alumina, zirconia, titania, iron oxide, ceria, lantana, neodia, yttria, barium oxide, lithium oxide and potassium oxide supported on the silicon carbide substrate. any of the claims 1 to 6 and a composed nanoporous metal oxide material with at least one complex metal oxide containing a selected from the group consisting of and alumina, zirconia, ceria and titania consists more A method for producing an exhaust gas purifying filter according to claim 1,
Preparing a raw material fluid composition containing the composite metal oxide raw material;
The raw material fluid composition is mixed under a shear rate of 10,000 sec ⁻¹ or more, applied to the surface of the silicon carbide substrate, and then heat-treated without substantial coprecipitation, so that the diameter is 10 nm or less. The metal oxide is uniformly dispersed in the wall body having nanopores and constituting the nanopores ,
With respect to all metal oxide metal elements contained in the nanoporous material at 10 at% or more, the thickness of the test sample can be regarded as substantially constant using a transmission electron microscope having an acceleration voltage of 200 kV and an electron beam diameter of 1.0 nm. The average of the relative intensity ratio X obtained by obtaining a spectrum by energy dispersive X-ray spectroscopy at a measurement point in the region and converting the integrated intensity of the fluorescent X-ray peak of each metal element in the obtained spectrum into a relative ratio. The value X _m and the second moment ν ₂ around the average value X _m are given by the following formula (1) for all the metal elements:
ν ₂ / X _m ² ≦ 0.02 (1)
Wherein (1), _{X m} is _{X m = (ΣX) / N} (N is the number of measurement points) the average value of the relative intensity ratio X represented by, [nu ₂ is _{ν 2 = {Σ (X-} X _m ) ² } / N, a second-order moment around the average value X _m represented by ν ₂ / X _m ² represents a second-order moment normalized by the square of the average value X _m . ]
A step of obtaining a metal oxide nanoporous material that satisfies the conditions represented by :
The manufacturing method of the filter for exhaust gas purification characterized by including. The said silicon carbide base material is a porous thing, The thin film which consists of the said metal oxide nanoporous body is formed on the pore inner wall face of the said silicon carbide base material, The Claim 7 characterized by the above-mentioned. Manufacturing method of exhaust gas purifying filter. The method for producing an exhaust gas purifying filter according to claim 7 or 8 , wherein a coating made of the metal oxide nanoporous material is formed on a surface of the silicon carbide substrate. The metal oxide raw material is alumina, zirconia, titania, iron oxide, ceria, lantana, neodia, yttria, barium oxide, lithium oxide and potassium oxide colloidal particles, aluminum, zirconium, titanium, iron, cerium, lanthanum, The exhaust gas purifying filter according to any one of claims 7 to 9 , wherein the filter is at least two selected from the group consisting of neodymium, yttrium, barium, lithium and potassium salts. Method.

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