JP2013081883A - Exhaust gas purifying catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst in which the early activation of the catalyst is achieved, and that can exert an excellent exhaust gas purification performance.SOLUTION: The exhaust gas purifying catalyst includes: a support provided with a gas passage; a catalyst layer formed at the gas passage side of the support and including a catalyst containing a catalyst component; and an underlayer formed between the support and the catalyst layer and including a base material. Either one of or both of the inside of a surface side of the support and the inside of the underlayer have an insulation zone including an air gap. The underlayer has an open pore at the gas passage side, and the air gap of the insulation part of the inside of the underlayer is formed by the underlayer and the catalyst disposed so that at least a portion of the open pore may remain. The support has an open pore at the gas passage side, the air gap in the insulation part of the inside of the surface side of the support is formed by the support and the base material disposed so that at least a portion of the open pore may remain.

Description

  The present invention relates to an exhaust gas purification catalyst. More specifically, the present invention relates to an exhaust gas purification catalyst that can realize early activation of the catalyst and exhibit excellent exhaust gas purification performance.

  Conventionally, a ceramic catalyst body with low pressure loss and high purification performance, in which pressure loss is suppressed and catalyst performance is improved, has been proposed. This ceramic catalyst body is an exhaust gas purification ceramic catalyst body in which a main catalyst component and a promoter component are supported on a ceramic carrier capable of directly supporting a catalyst component on the surface of a base ceramic (see Patent Document 1). .

Patent No. 4079717

  However, in the ceramic catalyst body described in the above-mentioned Patent Document 1, in the study by the present inventors, there are very many portions where the catalyst component is in direct contact with the ceramic carrier, so that early activation of the catalyst is inhibited. There was a problem that an excellent exhaust gas purification performance was not obtained.

  The present invention has been made in view of such problems of the prior art. An object of the present invention is to provide an exhaust gas purification catalyst that realizes early activation of the catalyst and can exhibit excellent exhaust gas purification performance.

The inventors of the present invention have made extensive studies in order to achieve the above object.
As a result, the apparatus includes a support having a gas flow path, a catalyst layer formed on the gas flow path side of the support, and an underlayer formed between the support and the catalyst layer, and the surface side of the support It has been found that the above object can be achieved by having a heat insulating part including a void in at least one of the inside and the inside of the base layer, and the present invention has been completed.

That is, the exhaust gas purification catalyst of the present invention includes a carrier having a gas flow path, a catalyst layer containing a catalyst containing a catalyst component formed on the gas flow path side of the carrier, and a gap between the carrier and the catalyst layer. And a base layer including a base material formed on the substrate.
In the exhaust gas purifying catalyst of the present invention, a heat insulating portion including a void is provided in one or both of the inside of the surface of the carrier and the inside of the base layer.

According to the present invention, a substrate provided with a gas channel, a catalyst layer containing a catalyst containing a catalyst component, formed on the gas channel side of the carrier, and a substrate formed between the carrier and the catalyst layer And having a heat insulating portion including a void in at least one of the inside of the surface of the carrier and the inside of the underlayer.
Therefore, it is possible to provide an exhaust gas purification catalyst that realizes early activation of the catalyst and can exhibit excellent exhaust gas purification performance.

1 is a perspective view showing an outline of an exhaust gas purification catalyst according to an embodiment of the present invention. It is typical sectional drawing along the II-II line of the exhaust gas purification catalyst shown in FIG. FIG. 3 is a schematic enlarged cross-sectional view surrounded by line III of the exhaust gas purification catalyst shown in FIG. 2. It is sectional drawing which shows typically the structure of the exhaust gas purification catalyst which concerns on 1st Embodiment. It is sectional drawing which shows typically the structure of the exhaust gas purification catalyst which concerns on 2nd Embodiment. It is sectional drawing which shows typically the structure of the exhaust gas purification catalyst which concerns on the conventional form. It is a graph which shows the relationship between the catalyst inlet gas temperature and NOx conversion rate in each example. It is a scanning electron micrograph (magnification: 200 times) (a) and a scanning electron micrograph (magnification: 2000 times) (b) of the cross section of the exhaust gas purifying catalyst of Example 1. It is a scanning electron micrograph (magnification: 200 times) (a) and a scanning electron micrograph (magnification: 2000 times) (b) of the cross section of the exhaust gas purification catalyst of Comparative Example 1.

  Hereinafter, an exhaust gas purification catalyst according to an embodiment of the present invention will be described in detail with reference to the drawings. In addition, the dimension ratio of drawing quoted by the following embodiment is exaggerated on account of description, and may differ from an actual ratio.

  FIG. 1 is a perspective view schematically showing an exhaust gas purification catalyst according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view taken along the line II-II of the exhaust gas purification catalyst shown in FIG. FIG. 3 is a schematic enlarged cross-sectional view of the exhaust gas purification catalyst shown in FIG.

  As shown in FIG. 1 and FIG. 2, in the exhaust gas purification catalyst 1 of the present embodiment, a carrier 2 having a honeycomb structure includes a gas flow path 2a along the gas flow direction. In addition, the arrow X in FIG. 1 shows a gas flow direction.

  As shown in FIG. 3, the exhaust gas purification catalyst 1 of the present embodiment includes a catalyst layer 6 formed between the carrier 2 and the catalyst layer 6 formed on the gas flow path 2 a side of the carrier 2 having a honeycomb structure. The underlayer 4 is formed.

  In addition, although mentioned later in detail, the exhaust gas purification catalyst of this embodiment has a heat insulation part including the space | gap which is not illustrated in either one or both inside the surface side of a support | carrier, and a base layer inside. The catalyst layer contains a catalyst containing a catalyst component (not shown). Further, the underlayer includes a base material (not shown).

  In the present invention, “inside of the carrier on the surface side” means, for example, when the thickness of the carrier (cell wall) sandwiched between the gas channels is 1, the depth from the surface side facing the gas channel. The range up to 1/4.

  By adopting such a configuration, it is possible to suppress (delay) the heat generated by the catalytic reaction in the catalyst component from spreading to the entire support (delay), and further promote early activation of the catalyst component. It becomes an exhaust gas purification catalyst that can exhibit the exhaust gas purification performance.

  Further, in the exhaust gas purifying catalyst of the present embodiment, for example, the underlayer has open pores on the gas flow path side, and the space in the heat insulating portion inside the underlayer has at least a part of the underlayer and the open pores. It is preferably formed with the catalyst arranged so as to remain.

  By adopting such a configuration, it is not essential to use other materials when forming a heat insulating part that suppresses (delays) the heat generated by the catalytic reaction of the catalyst component from spreading to the entire support. It becomes. Therefore, early activation of the catalyst component can be more reliably promoted, and an exhaust gas purification catalyst that can exhibit excellent exhaust gas purification performance is obtained.

  Further, in the exhaust gas purifying catalyst of the present embodiment, for example, the carrier has open pores on the gas flow path side, and the space in the heat insulating portion inside the surface of the carrier has at least a part of the carrier and the open pores. It is preferable to form with the base material arrange | positioned so that it may remain.

  Even with such a configuration, it is not essential to use other materials when forming a heat insulating portion that suppresses (delays) the heat generated by the catalytic reaction of the catalyst component from spreading to the entire support. It will be a thing. Therefore, early activation of the catalyst component can be more reliably promoted, and an exhaust gas purification catalyst that can exhibit excellent exhaust gas purification performance is obtained.

In the exhaust gas purifying catalyst of the present embodiment, for example, the relationship between the thermal conductivity of the underlayer and the thermal conductivity of the constituent components of the carrier preferably satisfies the relationship of the following formula (1). It is more preferable that the thermal conductivity of is smaller than the thermal conductivity of the constituent components of the carrier.
λ _PC ≦ λ _CC (1)
(In formula (1), λ _PC represents the thermal conductivity of the underlayer, and λ _CC represents the thermal conductivity of the constituent components of the carrier.)

By adopting such a configuration, it is possible to more reliably suppress (delay) the heat generated by the catalytic reaction at the catalyst component from being diffused to the entire support. And it becomes possible to accelerate | stimulate early activation of a catalyst component more reliably, and it becomes an exhaust gas purification catalyst which can exhibit the outstanding exhaust gas purification performance.
In addition, as a method for realizing such a configuration, for example, a material having a lower thermal conductivity than the constituent component of the carrier is applied as a constituent material of the underlayer, or a preparation is performed so as to increase the porosity. It is done.

  Furthermore, in the exhaust gas purifying catalyst of the present embodiment, for example, the gap in the heat insulating portion inside the surface side of the carrier is formed by the carrier and the base material arranged so that almost all of the open pores remain. preferable.

  Even with such a configuration, it is possible to more reliably suppress (delay) the heat generated by the catalytic reaction at the catalyst component from being diffused to the entire support. And it becomes possible to accelerate | stimulate early activation of a catalyst component more reliably, and it becomes an exhaust gas purification catalyst which can exhibit the more excellent exhaust gas purification performance.

  Each of the above configurations will be described in more detail.

[Carrier]
As the carrier 2, for example, if it is an exhaust gas purification catalyst for automobiles, a honeycomb-shaped one as shown in FIG. 1 is preferably used, but is not limited thereto. That is, as long as it can form a gas flow path, it is also possible to use a material that is appropriately molded (aggregated) using shapes such as pellets, powders, foams, fibers, and hollow fibers. . In addition, although the gas flow path shape in the cross section of the support | carrier shape | molded by the honeycomb shape shown in FIG. 1 is a square, this invention is not limited to this. For example, a conventionally known shape such as a triangle or a hexagon can be applied to the gas flow path shape in the cross section of the carrier in the exhaust gas purification catalyst.

  In addition, as a carrier, for example, a carrier containing cordierite as a main component is suitably used for an exhaust gas purification catalyst for automobiles or the like that requires high heat resistance, but is not limited thereto. That is, a carrier using a ceramic material such as alumina, spinel, mullite, aluminum titanate, zirconium phosphate, silicon carbide, zeolite, perovskite, or silica alumina can be used.

  Further, as the carrier, for example, a carrier having a large number of open pores on its surface can be used. Specifically, the open pores are composed of at least one of a defect (oxygen defect or lattice defect) in the ceramic crystal lattice, a fine crack on the ceramic surface, and a defect of the elements constituting the ceramic, and a combination of plural types. It can also be formed. The open pores formed on the surface of the cordierite are not particularly limited with respect to the diameter and width, but (1) ensure the strength of the carrier, and (2) ensure the formation of a heat insulating portion. Is preferably as small as possible with a diameter or width of the open pores of 4 μm or less. Preferably, it is 0.1 nm to 100 μm. Further, the depth of the open pores is not particularly limited, but from the same viewpoint as described above, the depth of the open pores is preferably 0.05 nm or more. Preferably, it is 0.05 nm-4 micrometers.

Of the open pores formed on the surface of the ceramic carrier, the crystal lattice defects include oxygen defects and lattice defects (metal vacancies and lattice strain). The oxygen defect is a defect caused by a lack of oxygen for constituting the crystal lattice. A lattice defect is a lattice defect caused by taking in more oxygen than necessary to constitute a ceramic crystal lattice, and is formed by crystal lattice distortion or metal vacancies.
When the carrier having these open pores is applied, the possibility that the catalyst is directly supported on the carrier is increased, but this can be avoided by adopting a configuration described later in detail. Moreover, there exists an advantage that a heat insulation site | part can be formed in the surface side inside of a support | carrier by setting it as the structure mentioned later.
In the present invention, a carrier having no open pores can also be used.

  The carrier having open pores can be formed, for example, by the method described below.

  In order to form oxygen defects in the crystal lattice, in the step of forming, degreasing, and firing a cordierite raw material containing a silicon (Si) source, an aluminum (Al) source, and a magnesium (Mg) source, (1) The firing atmosphere is a reduced pressure or reducing atmosphere, (2) by using a compound that does not contain oxygen in at least a part of the raw material, by firing in a low oxygen concentration atmosphere, the oxygen in the firing atmosphere or starting material is insufficient, (3) A method of substituting at least one kind of constituent elements of the ceramic other than oxygen with an element having a lower valence than the element can be employed. In the case of cordierite, the constituent elements have positive charges such as Si (4+), Al (3+), and Mg (2+). Therefore, when these elements are replaced with an element having a small valence, the valence with the substituted element And the positive charge corresponding to the substitution amount is insufficient, and the electric neutrality as a crystal lattice is maintained, so that O (2-) having a negative charge is released, and an oxygen defect is formed.

  In addition, lattice defects can be formed by (4) substituting a part of ceramic constituent elements other than oxygen with an element having a higher valence than the element. When at least part of the constituent elements of cordierite, silicon (Si), aluminum (Al), and magnesium (Mg), is replaced with an element having a higher valence than that element, the difference in valence with the replaced element The positive charge corresponding to the substitution amount becomes excessive, and a necessary amount of O (2-) having a negative charge is taken in to maintain the electrical neutrality as the crystal lattice. The incorporated oxygen becomes an obstacle, and the cordierite crystal lattice cannot be arranged in an orderly manner, and lattice strain is formed. The firing atmosphere in this case is an air atmosphere so that oxygen is sufficiently supplied. Moreover, in order to maintain electrical neutrality, a part of silicon (Si), aluminum (Al), and magnesium (Mg) is discharged, and vacancies are formed. In addition, since it is thought that the magnitude | size of these defects is several angstroms or less, it cannot measure as a specific surface area with the normal measuring method of a specific surface area like the BET method using a nitrogen molecule.

[Underlayer]
As the underlayer 4, for example, if it is an automobile exhaust gas purification catalyst, a substrate formed by applying a base material so that the catalyst layer can be easily formed on the surface of the carrier as shown in FIG. 1 is preferably used. However, it is not limited to this.

  Examples of the base material included in the underlayer include a high specific surface area group of ceramics such as alumina, silica, zirconia, silica alumina, zirconia alumina, titania alumina, zirconia titania alumina, magnesia alumina, silicon carbide, zeolite, and perovskite. Material can be applied.

  Furthermore, as a base layer, the base material which has many open pores on the surface can be used, for example. Specifically, the open pores are composed of at least one of a defect (oxygen defect or lattice defect) in the ceramic crystal lattice, a fine crack on the ceramic surface, and a defect of the elements constituting the ceramic, and a combination of plural types. It can also be formed. The diameter and width of the open pores formed on the surface of the alumina are not particularly limited, but from the viewpoint of reliably forming the heat insulating portion, the diameter or width of the open pores is 100 nm or less and is as small as possible. Is preferred. Preferably, it is 0.1-100 nm. Further, the depth of the open pores is not particularly limited, but from the same viewpoint as described above, the depth of the open pores is preferably 0.05 nm or more. Preferably, it is 0.05 to 100 nm.

Among the open pores formed on the surface of the ceramic substrate, crystal lattice defects include oxygen defects and lattice defects (metal vacancies and lattice strain). The oxygen defect is a defect caused by a lack of oxygen for constituting the crystal lattice. A lattice defect is a lattice defect caused by taking in more oxygen than necessary to constitute a ceramic crystal lattice, and is formed by crystal lattice distortion or metal vacancies.
When the base material having these open pores is applied, the possibility that the catalyst component is directly supported on the carrier is increased. However, this can be avoided by adopting the configuration described later in detail. Moreover, there exists an advantage that a heat insulation site | part can be formed inside a base layer by setting it as the structure mentioned later.
In the present invention, a substrate having no open pores can also be used.

[Catalyst layer]
The catalyst layer 6 is not particularly limited as long as it contains a catalyst containing a catalyst component. That is, examples of the catalyst include those containing a catalyst component and a high specific surface area base material supporting the catalyst component.
Further, in the present invention, the “catalyst including a catalyst component” should be interpreted to include particles composed of only the catalyst component.
Furthermore, examples of the catalyst component include a main catalyst component and a promoter component.

For example, platinum (Pt), rhodium (Rh), palladium (Pd) and the like are preferably used as the catalyst noble metal as the main catalyst component, and at least one of them can be used as necessary. Moreover, when using a promoter component further, the required amount of a promoter component can be decreased compared with the past. For example, the amount of the promoter component on the outer surface of the support can be reduced.
As the promoter component, various components can be used depending on the purpose. For example, in a NOx adsorption purification catalyst for automobiles, a NOx adsorption component that adsorbs and desorbs NO in accordance with changes in ambient oxygen concentration and temperature is preferably used. Specific examples of the NOx adsorption component having such an action include alkaline earth metal elements such as magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and alkali metals such as sodium (Na). An element etc. can be mentioned. In addition, for example, in an automobile three-way catalyst, an oxygen storage capacity component that absorbs and releases oxygen in accordance with fluctuations in ambient oxygen concentration is preferably used. Specific examples of the oxygen storage capacity component having such an action include oxides of rare earth elements such as cerium (Ce), yttrium (Y), praseodymium (Pr), lanthanum (La), neodymium (Nd), and the like. Examples thereof include oxides (solid solutions) according to any combination.
Needless to say, a metal element other than the noble metal can be used as the main catalyst component.

The open pores of the carrier are formed after the binder component or pore former is burned or the components contained in the raw material are dissolved during firing. Further, the open pores of the base material are also caused by the manufacturing process and generation conditions.
Therefore, by making the average particle diameter of such a catalyst or substrate larger than the pore diameter of the open pores of the substrate or carrier, the catalyst and the carrier can be configured not to come into direct contact. It is possible to more reliably suppress (delay) the heat generated by the catalytic reaction from spreading to the entire support. And it becomes possible to accelerate | stimulate early activation of a catalyst component more reliably, and it becomes an exhaust gas purification catalyst which can exhibit the more excellent exhaust gas purification performance.

(First embodiment)
FIG. 4 is an enlarged cross-sectional view schematically showing the structure of the exhaust gas purification catalyst according to the first embodiment of the present invention. In addition, the arrow X in FIG. 4 shows a gas flow direction. Further, the carrier in FIG. 4 shows a half of the thickness of the carrier (cell wall) sandwiched between the gas flow paths, and the inside of the surface side of the carrier is from the surface side facing the gas flow path. This is a range up to 1/2 the depth.

As shown in FIG. 4, the exhaust gas purification catalyst 1 of the present embodiment includes a catalyst layer 6 including a carrier 2 and a catalyst 6 a formed on the gas flow path side of the carrier 2 and containing a catalyst component (not shown). And a base layer 4 including a base material 4 a formed between the carrier 2 and the catalyst layer 6.
Then, in this embodiment, it has both the inner surface side internal and the underlayer of the support 2, a gap _(v 2, _{v 4)} insulation portion _(I 2, _{I 4),} including a.

Moreover, in this embodiment, as shown in FIG. 4, the base material 4 a constituting the base layer 4 is used that has open pores, and the void v ₄ of the heat insulating portion I ₄ inside the base layer _4. Is formed of the base material 4a constituting the base layer 4 and the catalyst 6 arranged so that at least a part of the open pores remains.
Examples of the catalyst capable of forming such a structure include, for example, the catalyst component itself having a particle diameter larger than the pore diameter of the open pores of the underlayer or the substrate, or the pore diameter of open pores of the underlayer or the substrate. The thing which carry | supported the catalyst component on the high specific surface area base material which made the particle size coarser can be mentioned.

Furthermore, in this embodiment, as shown in FIG. 4, a carrier 2 having open pores on the gas flow path side is used, and the gap v ₂ of the heat insulating part I ₂ inside the surface side of the carrier ₂ is It is formed by the carrier 2 and the base material 4a arranged so that almost all of the open pores remain.
Examples of the substrate that can form such a structure include a substrate whose aspect ratio is adjusted so as not to enter the open pores of the carrier.
Specifically, it is a base material having a plate-like shape, a scale-like shape, or the like, and the length (size) of the short side is larger than the maximum pore diameter of the open pores.

  By adopting such a configuration, it is possible to more reliably suppress (delay) the heat generated by the catalytic reaction at the catalyst component from being diffused to the entire support. And it becomes possible to accelerate | stimulate early activation of a catalyst component more reliably, and it becomes an exhaust gas purification catalyst which can exhibit the more excellent exhaust gas purification performance.

(Second Embodiment)
FIG. 5 is an enlarged cross-sectional view schematically showing the structure of the exhaust gas purifying catalyst according to the second embodiment of the present invention. In addition, about the thing equivalent to what was demonstrated in the said embodiment, the code | symbol same as them is attached | subjected and description is abbreviate | omitted.

As shown in FIG. 5, the exhaust gas purifying catalyst 1 of the present embodiment is different in that a coarse material capable of closing the open pores of the carrier 2 is applied as the base material 4 a constituting the foundation layer 4. have. In other words, there is a difference that the gap v ₂ of the heat insulating portion I ₂ inside the surface side of the carrier 2 is formed by the carrier 2 and the base material 4a arranged so that a part of the open pores remains. Yes.

  Even with such a configuration, it is possible to more reliably suppress (delay) the heat generated by the catalytic reaction at the catalyst component from being diffused to the entire support. And it becomes possible to accelerate | stimulate early activation of a catalyst component more reliably, and it becomes an exhaust gas purification catalyst which can exhibit the outstanding exhaust gas purification performance.

(Conventional form)
FIG. 6 is a cross-sectional view schematically showing a configuration of an exhaust gas purification catalyst according to a conventional form. In addition, about the thing equivalent to what was demonstrated in the said embodiment, the code | symbol same as them is attached | subjected and description is abbreviate | omitted.

As shown in FIG. 6, the exhaust gas purifying catalyst 1 of the conventional form does not have a base layer, and further has no significant heat insulating part including a void inside the surface side of the carrier 2. It is what has.
With such a configuration, the heat generated by the catalytic reaction at the catalyst component is thermally diffused throughout the carrier, making it difficult to achieve early activation of the catalyst component.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

Example 1
First, a carrier was prepared. As the cordierite raw material, talc, kaolin, alumina, and aluminum hydroxide are used, and 5% of the Si source is replaced with W, and 5% of the Si source is replaced with Co. It was prepared as follows. Next, appropriate amounts of a binder, a lubricant, a humectant, and moisture were added to the raw material and kneaded to form a honeycomb shape having a cell wall of 100 μm, a cell density of 400 cpsi (number of cells per square inch), and a diameter of 50 mm. Thereafter, the obtained honeycomb formed body was fired at 1260 ° C. in an air atmosphere to obtain a ceramic carrier made of a cordierite honeycomb structure having open pores having a pore diameter of 4 μm on the gas flow path side.

Next, an underlayer having a lower thermal conductivity than cordierite was formed on the ceramic support. As the substrate, plate-like alumina powder having a specific surface area of 200 m ² / g and a short side of 5 μm was used. An appropriate amount of a binder and moisture were added to this powder and mixed to prepare an underlayer slurry. Next, an underlayer slurry was applied to the carrier, excess slurry was removed, dried, and fired at 600 ° C. in an air atmosphere to form an underlayer.

  Next, a catalyst layer was formed on the ceramic carrier on which the base layer was formed. Platinum-supported alumina (average particle size: 3 μm) was used as a catalyst. An appropriate amount of a binder and moisture were added to the catalyst and mixed to prepare a catalyst layer (middle layer) slurry. Next, a catalyst layer (intermediate layer) slurry was applied to the support, and after removing excess slurry, the slurry was dried and baked at 600 ° C. in an air atmosphere to form a catalyst layer (intermediate layer). Furthermore, platinum / rhodium supported alumina (average particle size: 2 μm) was used as a catalyst. An appropriate amount of binder and moisture were added to the catalyst and mixed to prepare a catalyst layer (surface layer) slurry. Next, a catalyst layer (surface layer) slurry is applied to the carrier, and after removing excess slurry, the slurry is dried and fired at 600 ° C. in an air atmosphere to form a catalyst layer (surface layer), as shown in FIG. The exhaust gas purification catalyst of this example was obtained.

(Example 2)
First, a carrier was prepared. As the cordierite raw material, talc, kaolin, alumina, and aluminum hydroxide are used, and 5% of the Si source is replaced with W, and 5% of the Si source is replaced with Co. It was prepared as follows. Next, appropriate amounts of a binder, a lubricant, a humectant, and moisture were added to the raw material and kneaded to form a honeycomb shape having a cell wall of 100 μm, a cell density of 400 cpsi (number of cells per square inch), and a diameter of 50 mm. Thereafter, the obtained honeycomb formed body was fired at 1260 ° C. in an air atmosphere to obtain a ceramic carrier made of a cordierite honeycomb structure having open pores having a pore diameter of 4 μm on the gas flow path side.

Next, an underlayer having a lower thermal conductivity than cordierite was formed on the ceramic support. As the substrate, granular alumina powder having a specific surface area of 200 m ² / g and an average particle diameter of 3 μm was used. An appropriate amount of activated carbon (average particle diameter: 2 μm), a binder, and moisture as a pore former were added to this powder and mixed to prepare an underlayer slurry. Next, an underlayer slurry was applied to the carrier, excess slurry was removed, dried, and fired at 600 ° C. in an air atmosphere to form an underlayer.
In addition, the pore diameter of the open pores of the underlayer of this example was 2 μm.

  Next, a catalyst layer was formed on the ceramic carrier on which the base layer was formed. Platinum-supported alumina (average particle size: 3 μm) was used as a catalyst. An appropriate amount of a binder and moisture were added to the catalyst and mixed to prepare a catalyst layer (middle layer) slurry. Next, a catalyst layer (intermediate layer) slurry was applied to the support, and after removing excess slurry, the slurry was dried and baked at 600 ° C. in an air atmosphere to form a catalyst layer (intermediate layer). Furthermore, platinum / rhodium supported alumina (average particle size: 3 μm) was used as a catalyst. An appropriate amount of binder and moisture were added to the catalyst and mixed to prepare a catalyst layer (surface layer) slurry. Next, a catalyst layer (surface layer) slurry is applied to the carrier, and after removing excess slurry, the slurry is dried and baked at 600 ° C. in an air atmosphere to form a catalyst layer (surface layer), as shown in FIG. The exhaust gas purification catalyst of this example was obtained.

(Example 3)
First, a carrier was prepared. As the cordierite raw material, talc, kaolin, alumina, and aluminum hydroxide are used, and 5% of the Si source is replaced with W, and 5% of the Si source is replaced with Co. It was prepared as follows. Next, appropriate amounts of a binder, a lubricant, a humectant, and moisture were added to the raw material and kneaded to form a honeycomb shape having a cell wall of 100 μm, a cell density of 400 cpsi (number of cells per square inch), and a diameter of 50 mm. Thereafter, the obtained honeycomb formed body was fired at 1260 ° C. in an air atmosphere to obtain a ceramic carrier made of a cordierite honeycomb structure.

Next, an underlayer having a lower thermal conductivity than cordierite was formed on the ceramic support. As the substrate, granular alumina powder having a specific surface area of 200 m ² / g and an average particle diameter of 5 μm was used. An appropriate amount of a binder and moisture were added to this powder and mixed to prepare an underlayer slurry. Next, an underlayer slurry was applied to the carrier, excess slurry was removed, dried, and fired at 600 ° C. in an air atmosphere to form an underlayer.
In addition, the pore diameter of the open pores of the underlayer of this example was 2 μm.

  Next, a catalyst layer was formed on the ceramic carrier on which the base layer was formed. Platinum-supported alumina (average particle size: 3 μm) was used as a catalyst. An appropriate amount of a binder and moisture were added to the catalyst and mixed to prepare a catalyst layer (middle layer) slurry. Next, a catalyst layer (intermediate layer) slurry was applied to the support, and after removing excess slurry, the slurry was dried and baked at 600 ° C. in an air atmosphere to form a catalyst layer (intermediate layer). Furthermore, platinum / rhodium supported alumina (average particle size: 3 μm) was used as a catalyst. An appropriate amount of binder and moisture were added to the catalyst and mixed to prepare a catalyst layer (surface layer) slurry. Next, the catalyst layer (surface layer) slurry is applied to the carrier, and after removing the excess slurry, it is dried and baked at 600 ° C. in an air atmosphere to form a catalyst layer (surface layer). A catalyst was obtained.

(Comparative Example 1)
A catalyst layer was formed on the ceramic support obtained in Example 1. Platinum and rhodium were used as catalysts. Specifically, it is immersed in an ethanol solution of chloroplatinic acid so as to have the same concentration as in the above examples, and after removing the excess solution, it is dried and baked at 600 ° C. in the atmospheric air to be metallized, After immersing in an ethanol solution of chloroplatinic acid and rhodium chloride and removing the excess solution, it was dried and baked at 600 ° C. in an air atmosphere to be metallized. As shown in FIG. An exhaust gas purification catalyst was obtained.

[Performance evaluation]
With respect to the exhaust gas purifying catalyst of each of the above examples, the NOx conversion rate at each catalyst inlet gas temperature was measured under the following conditions. Of the obtained results, the results of Example 1 and Comparative Example 1 are shown in FIG. Moreover, the scanning electron micrograph (magnification: 200 times) (a) and the scanning electron micrograph (magnification: 2000 times) (b) of the cross section of the exhaust gas purification catalyst of Example 1 and Comparative Example 1 are shown in FIGS. 9 shows.

(Evaluation conditions)
・ Catalyst capacity: 150 g / L
・ Flow rate: GHSV = 70000 hr ⁻¹
Catalyst temperature: 300-450 ° C
-Gas composition: Gasoline exhaust gas composition (= exhaust gas composition during stoichiometric air-fuel ratio combustion)

As shown in FIG. 7, Example 1 belonging to the scope of the present invention has a void (air reservoir) functioning as a heat insulating portion inside the surface of the base layer and the carrier, and therefore, it comprises a large air reservoir especially on the surface side inside the carrier. Since it has a heat insulation part, it turns out that early activation is accelerated | stimulated compared with the comparative example 1 outside this invention which does not have a heat insulation part.
This is also clear from the observation results of the scanning electron micrographs of FIGS.
It is also considered that the thermal conductivity of the underlayer is made smaller than the thermal conductivity of the constituent components of the carrier (the same applies to Example 2 and Example 3).
In addition, although not shown in figure, Example 2 and Example 3 understood that early activation was promoted clearly rather than Comparative Example 1 although early activation was harder to promote than Example 1. This is because Example 2 has voids (air pockets) functioning as heat insulation sites inside the surface of the base layer and the carrier, while Example 3 has voids (air pools) functioning as heat insulation sites on the surface of the carrier. This is probably because it is not inside the side.

  As mentioned above, although this invention was demonstrated with some embodiment and an Example, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.

  For example, the configuration described in each embodiment and each example described above is not limited to each embodiment, for example, to change the details of the voids, the open pores and the base material constituting the void, The configuration of each embodiment may be a combination other than the above-described embodiments.

1 exhaust gas purifying catalyst 2 carrier 2a gas channel 4 underlying layer 4a substrate 6 catalyst layer 6a catalyst I _{2, I 4} adiabatic portion V _{2, V 4} gap

Claims (5)

A carrier comprising a gas flow path;
A catalyst layer containing a catalyst containing a catalyst component, formed on the gas flow path side of the carrier;
A base layer including a base material formed between the carrier and the catalyst layer;
An exhaust gas purifying catalyst comprising a heat insulating portion including a void in at least one of the inside of the surface of the carrier and the inside of the underlayer. The base layer has open pores on the gas flow path side,
2. The exhaust gas purification catalyst according to claim 1, wherein the space in the heat insulating portion inside the base layer is formed by the base layer and a catalyst arranged so that at least a part of the open pores remains. . The carrier has open pores on the gas flow path side,
The space in the heat insulating portion inside the surface of the carrier is formed by the carrier and a base material arranged so that at least a part of the open pores remains. Exhaust gas purification catalyst. The relationship between the thermal conductivity of the underlayer and the thermal conductivity of the constituent components of the carrier satisfies the relationship of the following formula (1), according to any one of claims 1 to 3. Exhaust gas purification catalyst.
λ _PC ≦ λ _CC (1)
(In formula (1), λ _PC represents the thermal conductivity of the underlayer, and λ _CC represents the thermal conductivity of the constituent components of the carrier.)   5. The gap according to claim 3 or 4, wherein a gap in a heat insulating portion inside the surface side of the carrier is formed by the carrier and a base material arranged so that almost all of the open pores remain. Exhaust gas purification catalyst.

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