JP2001314764A - Catalyst and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst which is obtained by forming an alumina thin film on the surface of a carrier and is excellent in pressure loss, heat resistance, cleaning resistance and regenerating characteristic, and to provide a method for manufacturing the catalyst. SOLUTION: This catalyst is obtained by coating the surface of every particle of the silicon-containing ceramic carrier with the thin film of alumina containing the oxide of a rare earth metal such as ceria and depositing a catalytically active component on the surface of the thin film. This method for manufacturing the catalyst comprises, for example, heating the silicon-containing ceramic carrier at 1,000-1,500 deg.C to form an oxidized film of silicide, immersing the ceramic carrier thus heated in the solution of an aluminum-containing metallic compound, heating/drying the ceramic carrier thus immersed, heating/calcining the ceramic carrier thus dried at a higher temperature than 300 to 500 deg.C to form an amorphous alumina thin film, immersing the ceramic carrier thus heated/calcined in boiled water of 100 deg.C, drying the ceramic carrier thus immersed, regularly calcining the ceramic carrier thus dried at 500-1,200 deg.C and depositing the active component on the alumina thin film on the surface of the carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst and a method for producing the same, and more particularly, to carbon monoxide (CO) and hydrocarbon (H) contained in exhaust gas of a diesel engine.
In addition to efficiently removing C) by oxidation and reducing and removing nitrogen oxides (NOx), we propose a catalyst with low pressure loss, high diesel particulate collection efficiency, and good regeneration rate. .

[0002]

2. Description of the Related Art Conventionally, a catalyst for purifying exhaust gas of an automobile, for example, a catalyst for purifying exhaust gas of a diesel engine.
As the (filter), each cell 101 serving as an exhaust gas passage as shown in FIGS. 1 (a) and 1 (b) is formed into a honeycomb shape with a porous silicon carbide sintered body having excellent heat resistance and thermal conductivity. A honeycomb filter 100 formed and alternately plugged with the cells 101 is used. Then, the honeycomb filter 100 is connected to the exhaust side of the diesel engine, and PM (particulate matter) or H
It is common to use a catalyst of the type that oxidizes and decomposes C and CO.

[0003] As such a catalyst, for example, a filter wall of a heat-resistant carrier formed of a honeycomb shape such as cordierite or the like.
It is well known that a support layer made of γ-alumina is formed on the surface of (cell wall) 102 and a catalytically active component made of a noble metal such as Pt, Pd, Rh or the like is supported on the support layer.

[0004] As a carrier used for such a catalyst, Japanese Patent Application Laid-Open No. 5-68892 discloses a fine powder obtained by adding an inorganic binder to γ-alumina, mixing and pulverizing the slurry into a slurry. There is a honeycomb carrier in which an alumina layer 103 is formed by so-called wash coating in which the wall surface of the honeycomb carrier made of Elite is uniformly sprayed and coated.

[0005]

As shown in FIG. 2 (a), the prior art, that is, the wash-coated alumina layer 103 (wash-coat alumina layer) is used as shown in FIG.
It is formed of a thin film that uniformly covers the wall of 102, and has a pore structure as shown in the partial enlarged view of FIG. 2 (b). The pore size in such a pore structure is mainly 20 to 500 angstroms, and usually shows a specific surface area of 50 to 300 m ² / g. Also, such an alumina layer 103
Since the surface becomes a catalyst supporting layer for dispersing and supporting a catalytically active component such as a noble metal, the specific surface area must be large and a certain thickness (about 50 to 100 μm) is required.

However, the wash-coated alumina layer 103 has a small pore diameter and a low porosity, and has a high resistance at the time of ventilation, so that the pressure loss is remarkably increased as compared with a carrier having no alumina layer. There was a problem.

Further, a wash-coated alumina layer
103 is simply coated evenly on the surface of the carrier, which is the filtration wall 102, and therefore has poor adhesion, and may be peeled off when cleaning ash (ash) that accumulates when purifying exhaust gas. there were. Further, as described above, although the washcoat alumina layer 103 has a pore structure,
The pore size is as small as 20 to 500 angstroms, and when exposed to a high temperature for a long period of time, sintering proceeds, phase transition to the α phase occurs, and the surface area is reduced. Furthermore, since the surface area is small, the distance between the particles of the catalytically active component (noble metal) supported on the alumina layer 103 is reduced. As a result, when sintering proceeds, the specific surface area is further reduced, and the catalytic action is reduced. There has been a problem that this leads to a decrease in the quality.

As is apparent from the above description, one of the important characteristics of the catalyst is to maintain the surface of the active component support layer, particularly the alumina support layer covering the support, in a stable state for a long time. It is. Therefore, an object of the present invention is to improve the structure of an alumina thin film formed on the surface of a carrier, thereby increasing the pore diameter and porosity, reducing pressure loss, and increasing the efficiency of collecting diesel particulates. It is to propose a manufacturing method. Another object of the present invention is to propose a catalyst which is excellent in carrying characteristics (fixing characteristics) of a catalytically active component, and is excellent in heat resistance, regeneration characteristics and washing resistance, and a method for producing the same.

[0009]

As a means for solving the above problems, the present invention basically comprises a silicon-containing ceramic carrier,
In a catalyst having a catalytically active component dispersed and supported on its surface, the silicon-containing ceramic support was coated on its surface with a thin film of alumina containing a rare earth oxide for each particle unit forming the support. It is advantageous to use a catalyst in which the above-mentioned catalytically active component is carried on the uneven surface of the rare earth oxide-containing alumina thin film.

The silicon-containing ceramic carrier is composed of a non-oxide ceramic such as silicon carbide or silicon nitride, or a silicide carrier containing an oxide ceramic such as sialon, mullite or cordierite. Are preferred.

[0011] The silicon-containing ceramic carrier is a porous body, a fiber molded body or a pellet molded body, and is preferably formed of a honeycomb-shaped porous silicon carbide sintered body. Has a SiO ₂ layer and the amount of SiO _{2 in the} carrier is 0.001 to 20 m
It is a preferred embodiment to use what is ass%.

In the present invention, the alumina thin film covering the surface of each particle in the ceramic carrier is ceria (CeO).
₂ ) and a rare earth oxide such as lanthana (La ₂ O ₃ ) is contained on the surface and / or inside thereof. The micro cross-sectional shape is 2-50 nm in diameter, 20-300 nm in length, and total length / diameter. Has a flocked structure in which small fibers having a shape of 5 to 100 are in a forest, has a specific surface area of 50 to 300 m ² / g, and the alumina thin film has an alumina amount of 0.
A preferred embodiment is a ratio of 1 to 15 mass%.

In the present invention, the alumina thin film containing the rare earth oxide covering the carrier is coated on the carrier at a rate of 0.1 to 15 mass% in terms of the amount of alumina, and is contained in the alumina thin film. In a preferred embodiment, the rare earth oxide to be contained has a content of 10 to 80 mass% with respect to the alumina.

Further, in the present invention, it is a preferred embodiment that at least a part of the rare earth oxide forms a composite oxide with zirconium.

In the present invention, the composite oxide of rare earth oxide and zirconium has a particle diameter of 1 to 30 nm.
Is a preferred embodiment.

Next, the catalyst according to the present invention is applied to the surface of each particle constituting the silicon-containing ceramic support as follows.
It can be produced by forming a rare earth oxide-containing alumina thin film through the steps (a) to (e), and then supporting a catalytically active component such as a noble metal on the uneven surface of the rare earth oxide-containing alumina thin film. (a) Solution impregnation step: The above-mentioned carrier is immersed in a solution of a rare earth oxide and a metal compound containing aluminum. (b) Drying step: The carrier is dried by heating. (c) Preliminary firing step: An amorphous alumina thin film containing a rare earth oxide is formed by heating and firing the above carrier at a temperature of 300 to 500 ° C. or higher. (d) Heat treatment step: The carrier is immersed in hot water at 100 ° C and then dried. (e) Main firing step: Main firing at 500 to 1200 ° C.

Further, another method of manufacturing the carrier according to the present invention is to provide a rare earth oxide-containing alumina thin film on the surface of each particle constituting the silicon-containing ceramic carrier through the following steps (a) to (f). It can be manufactured by forming and then carrying a catalytically active component such as a noble metal on the uneven surface of the rare earth oxide-containing alumina thin film. (a) Pretreatment step: 1000 parts of the above silicide ceramic carrier
The film is heated to a temperature in the range of 1 to 1500 ° C. to form a silicide oxide film. (b) Solution impregnation step: The carrier is immersed in a solution of a metal compound containing aluminum and a rare earth oxide. (c) Drying step: The carrier is dried by heating. (d) Pre-firing step: The above-mentioned carrier is heated and fired at a temperature of 300 to 500 ° C. or more to form an amorphous alumina thin film containing a rare earth oxide. (e) Heat treatment step: The above carrier is immersed in hot water at 100 ° C and then dried. (f) Main firing step: Main firing at 500 to 1200 ° C.

In each of the above production methods, the component composition, structure and properties of the silicon-containing ceramic carrier are as follows.
As described above, the rare-earth oxide-containing alumina thin film covering the surface of each ceramic particle is the same as that described above. Further, the rare earth oxide is at least partially or entirely formed as a composite oxide with zirconium, and the particle diameter thereof is 1 to 30 nm. It is.

The above-mentioned catalytically active components include Pt, Rh, Pd,
At least one metal, alloy, or compound thereof selected from Ce, Cu, V, Fe, Tu, and Ag is used.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION A catalyst according to the present invention is a porous silicon-containing ceramic sintered body (hereinafter simply referred to as "porous SiC sintered body") whose carrier is preferably a silicon-containing ceramic, for example, silicon carbide. The filter wall 2 is formed by a predetermined method, but is not limited to this.) An alumina thin film 3 serving as a catalyst-supporting layer is formed on a surface of the filter wall 2, in particular, on each surface of each SiC particle. Individually coated with a thickness, and a catalytically active component such as Pt or Pd is formed on the alumina thin film 3.
(Hereinafter, simply referred to as “active ingredient”).

The silicon-containing ceramic carrier used in the catalyst according to the present invention includes, in addition to silicon carbide powder,
An organic binder, a lubricant, a plasticizer and water are mixed and kneaded with oxide ceramics such as silicon nitride and powder, or ceramic powders belonging to oxides such as sialon, mullite and cordierite. Extrusion molding and then sintering can be used. Thus, a wall flow honeycomb type filter as shown in FIG. 1 is formed. Hereinafter, an example in which a SiC sintered body is used as a silicon-containing ceramic carrier will be described.

The carrier (filter) 1 has a plurality of through holes.
(Cell) is made of a SiC sintered body having a substantially square cross-section and formed regularly along the axial direction. The cells are separated from each other by a filtration wall 2 (hereinafter, also referred to as a “cell wall”), and the opening of each cell is sealed at one end face side by a sealing body 104. The other end face is open, and as a whole, the open section and the sealing section are arranged such that each of the end faces has a checkered pattern. The carrier (filter) 1 made of the SiC sintered body has a large number of cells 10 having a square cross section.
1 is formed. In other words, these filters have a honeycomb structure. The density of the cells 101 is 200 to 350 cells / square inch. That is, of the large number of cells 101, about half of the cells are open at the upstream end face, and the remaining cells are open at the downstream end face,
The thickness of the cell wall 2 separating the cells 101 is set to about 0.4 mm.

As described above, the carrier 1 made of the SiC sintered body
Has a structure partitioned by a porous cell wall 2 as shown in FIG. 3 (a), and the pores of the porous cell wall 2 have an average pore diameter measured by a mercury intrusion method. Preferably, the value is in the range of 5 μm to 15 μm, and the value of the standard deviation in the pore size distribution when the pore size is represented by a common logarithm is 0.20 or less. When the cell wall 2 has such a pore diameter, it is also suitable for collecting fine particulates. That is, by setting the average pore diameter of the cell wall 2 within the above range, it is possible to reliably collect the diesel particulates. On the other hand, if the average value of the pore diameter of the cell wall 2 is less than 5 μm, the pressure loss when the exhaust gas passes through the inner wall becomes extremely large, which may cause the engine to stop. On the other hand, when the average value of the pore diameter exceeds 15 μm, it becomes impossible to efficiently collect fine particulates.

The carrier 1 is manufactured by, for example, adding 70 parts by weight of a silicon carbide powder having an average particle diameter of about 10 μm as a raw material to about 30 parts by weight of a silicon carbide powder having an average particle diameter of about 0.5 μm. Parts, about 6 parts by weight of methylcellulose as a binder with respect to 100 parts by weight of ceramic powder, and about 25 parts by weight of a dispersion medium containing an organic solvent and water with respect to 100 parts by weight of ceramic powder. And Next, after kneading the compounded raw materials, the mixture is extruded and formed into a honeycomb shape, and a part of the cell 101 is sealed in a checkered pattern. Next, after drying and degreasing the molded body, 2200 ° C under an inert atmosphere,
By firing for 4 hours, a desired ceramic carrier is obtained.

The most characteristic structure of the present invention is that the surface of the cell wall 2 substantially constituting the ceramic carrier 1, particularly the surface of each particle constituting the cell wall 2, is formed of a rare earth oxide-containing alumina thin film. It is to cover with. To say this more precisely, the Si that constitutes the cell wall 2
C The surface of each particle is individually coated with a thin film of alumina containing rare earth oxide by various methods for each particle of the sintered body. FIG. 2 (b) shows a prior art in which an alumina layer 103 is uniformly formed on the surface of the cell wall 102 by a wash coat method, while FIGS. 3 (b) and 3 (c) show the prior art. FIG. 3 is an explanatory view of a carrier used in the present invention, wherein each SiC particle 4 constituting a cell wall 2 is formed.
・ A rare earth oxide-containing alumina thin film 3 (hereinafter, referred to as “rare earth oxide-containing alumina thin film”
(Abbreviated simply as “alumina thin film”) are individually coated.

As described above, the carrier film (alumina thin film), which is a characteristic feature of the catalyst according to the present invention, is different from the prior art in that the wall surface of the cell wall 2 which is a filter wall for exhaust gas is simply formed by the alumina layer 103. Is not uniformly coated. For example, if the wall surface is uniformly coated as in the related art, the gap between the particles will be closed and plugged, and the air permeability will be impaired. On the other hand, in the case of the carrier used in the present invention, the surface of each SiC particle 4 constituting the cell wall 2 is individually coated with the alumina thin film 3. Therefore, according to the present invention, the pores are maintained as pores without completely closing the pores of the cell wall 2 itself, that is, the gaps generated between the particles. The pressure loss is significantly smaller in comparison. Moreover,
Excellent heat resistance, and furthermore, since the alumina thin film 3 individually covers each SiC particle itself, for example, the thin film does not peel off from the cell wall during cleaning, and is excellent in cleaning resistance. become. Therefore, the pressure loss characteristics, heat resistance, washing resistance and regeneration characteristics of the alumina thin film as a carrier film used in the catalyst according to the present invention will be described below.

Pressure Loss Characteristics of Alumina Thin Film; In general, the pressure loss characteristics when exhaust gas passes through the cell wall, which is a filtration wall, can be considered as follows. That is, the pressure loss when the diesel exhaust gas passes through the carrier (filter) can be shown in FIG. In this case, each of the resistances ΔP1, ΔP2, and ΔP3 depends on the cell structure of the filter, and is a constant value Δpi independent of the passage of time such as the accumulation of diesel particulates.
= (ΔP1 + ΔP2 + ΔP3), which is referred to as an initial pressure loss. ΔP4 is the resistance when passing through the accumulated diesel particulates, and is 2 to the initial pressure loss.
The value is three times or more.

The surface area of the carrier having a cell structure of 14/200 is 8.931 cm ² / cm ³ , and the density of the carrier is 0.675 g / cm ^3.
m ³ , the cell wall surface area is 0.0013 m ² / g. On the other hand, the pore surface area in the cell wall is 0.12 m ² / g as measured by a mercury porosimeter, and has about 100 times the surface area.
This means that when the same weight of alumina is coated on the cell wall surface to form a thin film, rather than coating the cell wall surface uniformly so as to cover the cell wall surface, each of the particles constituting the cell wall is formed. If the surfaces are individually coated, the thickness of alumina for achieving the same effect can be reduced to 1/100. That is,
When an alumina thin film is uniformly formed under a conventional technique such as a wash coat, the thickness of the alumina layer is 50 μm in order to cover about 3 mass% of alumina required for the activity of the catalyst.
m is required. The pressure loss at this time increases the resistance passing through the alumina layer in addition to the resistance ΔP3 passing through the inside of the cell wall. Further, the aperture becomes smaller and ΔP1 becomes larger. For this reason, the pressure loss becomes significantly larger than that of a filter not coated with alumina, and this tendency becomes more prominent when particulates are deposited on the filter. In this regard, when the surface of each SiC particle constituting the cell wall is coated with alumina as in the carrier used in the present invention, the thickness of the alumina coating layer of about 3 mass% required for activating the catalyst is required. Is at most 0.5 μ
m. The increase in pressure loss at this time is caused by the resistance ΔP
3 is slightly increased, but other pressure losses are substantially negligible, and the pressure loss characteristics are dramatically improved as compared with the conventional washcoat alumina layer.

Heat resistance of this alumina thin film: Generally, alumina has a high specific surface area and is suitable as a catalyst-carrying membrane. In particular, at present, the development of highly heat-resistant catalysts that operate stably at higher temperatures is desired.
Higher heat resistance is also required for alumina-supported films. In this regard, in the present invention, in order to improve the heat resistance of alumina, the shape of each alumina particle is made into a small fiber shape and a rare earth oxide such as ceria is contained. In particular, by adopting the former configuration, it is possible to reduce the number of contacts between each alumina particle, suppress the grain growth by lowering the sintering speed, and thereby increase the specific surface area, and thus improve the heat resistance I do. That is, in the present invention, the alumina thin film covering the surface of each particle of the carrier has a micro-cross-sectional shape in which each alumina particle has a fibril-like or forested flocking structure, and therefore, adjacent alumina fibrils come into contact with each other. Since the number of points is reduced, heat resistance is remarkably improved.

Next, the heat resistance can be improved by adding ceria and the like. The reason for this is that a new compound is formed on the surface of the crystal grains constituting the alumina, thereby inhibiting the growth of the alumina particles.

In the case of the present invention, SiC is supplied at the time of heat treatment from SiC or SiO ₂ existing on the very surface layer of the SiC, and the function of blocking the mass transfer path is also improved, so that the heat resistance is improved. According to a study by the inventors, it has been found that heat treatment is further improved when SiC is intentionally treated at a high temperature to form an oxide film.

Regarding the washing resistance of the alumina thin film; the main component of the particulates deposited on the cell wall surface is carbon, which can be oxidized and removed by a method such as combustion. However, some substances remain as ash after combustion. This is due to the fact that compounds such as Ca, Mg and Zn added to the engine oil to have a role as a neutralizer or lubricant are oxidized or converted to sulfate, Some catalysts, such as CeO ₂ and CuO, mixed for carbon combustion are deposited together with particulates. These ash components accumulate as the vehicle travels for a long time and increase the pressure loss of the filter. Therefore, it is necessary to wash the ash with high-pressure water or the like. At this time, ash can be completely removed by washing at a pressure of 30 kg / cm ² or more.

Regarding this point, in the case of the conventional alumina uniform film formed by wash coating on the cell wall surface, there is a thick coat layer formed by physical adsorption on the entire cell wall surface, and therefore, it is often peeled off during the above-mentioned washing. On the other hand, in the support film (alumina thin film) used in the present invention,
Alumina is thinly and individually coated on the surface of each particle constituting the SiC carrier, and Si is supplied from the SiC constituting the carrier and chemically bonded.
It is in a state of being tightly adhered to each particle. Therefore, the adhesiveness is high, the resistance to washing is high, and the durability as a coating is strong.

Regeneration characteristics of alumina thin film; In the present invention, the above-mentioned alumina thin film contains ceria (Ce
Rare earth oxides such as O ₂ ) and lantana (La ₂ O ₃ )
10～80Mass% approximately with respect ₂ O _3, preferably 20~40mas
These oxides are uniformly dispersed on the surface or inside of the thin film by adding about s%. When ceria or the like is added to the alumina thin film (preferably, it is more preferable to add it together with a catalytically active component such as Pt), the supply of oxygen into the exhaust gas is activated by the oxygen concentration control action of the ceria, and the The efficiency of burning and removing soot (diesel particulate) adhering to the catalyst is improved, and the regeneration rate of the catalyst carrier is significantly improved.

That is, rare earth oxides such as ceria are made of aluminum.
Not only improves the heat resistance of the catalyst, but also
It also plays a role in adjusting the element concentration. In general,
Hydrocarbons and carbon monoxide present by oxidation
O_XIs removed by the reduction reaction, but the exhaust gas composition is
Is constantly fluctuating between rich and lean
Therefore, the working atmosphere on the catalyst surface also fluctuates drastically.
You. By the way, ceria added to the catalyst is Ce³⁺And Ce
⁴⁺Has a relatively small oxidation-reduction potential, the following formula: 2CeO₂ ⇔ Ce₂O₃+ 1 / 2O₂  Proceeds reversibly. In other words, the exhaust gas is rich
Then the above reaction proceeds to the right to supply oxygen to the atmosphere
However, on the contrary, when it comes to the lean area, it proceeds to the left and
Stores excess oxygen. In this way, oxygen in the atmosphere
By adjusting the concentration, the ceria can become
Carbon oxide or NO_XAir-fuel ratio
It acts to widen the width.

FIG. 12 shows ceria (CeO).₂)
Not Al₂O₃Thin film (a) and Al with ceria added
₂O₃The catalyst using the thin film (b) as a supporting film
To explain the mechanism of each oxidation rate
is there. As shown in the figure, CeO₂(A)
Activates oxygen in the exhaust gas,
(Soot) is oxidized. This reaction activates oxygen in the fluid
Inefficient because it must be converted. On the other hand, CeO
₂For the catalyst (b) in which is present, the following reaction: CeO₂ ⇔ CeO_2-x+ X / 2O₂  Supplies oxygen. That is, spitting in the atmosphere
The released oxygen and oxygen in the exhaust gas are converted into catalysts (precious metals)
Reacts with soot (carbon) activated by CO₂
(CeO_2-xIs oxidized to the original CeO₂Return to). Ma
CeO₂Soot is exhaled for direct contact
This soot can be efficiently oxidized even if the amount of oxygen
Because Moreover, CeO in this case₂Is the catalyst (precious
(Oxygen storage function) by supporting
Make it bigger. This is because the catalyst (precious metal)
Activates oxygen, CeO near noble metal₂Active on surface oxygen
Therefore, the OSC increases.

FIGS. 13 and 14 show the effect of adding a rare earth oxide such as ceria to an alumina thin film.
O ₂ / Acicular Al ₂ O ₃ catalyst (Invention Example), Pt / Acicular Al ₂ O _3
3 shows the results of experiments on the regeneration characteristics of (Comparative Example) and Pt / Al ₂ O ₃ (wash coat) catalysts. In this experiment, a diesel particulate filter (DPF, total length = 150 mm) with soot (medium) attached was housed in an electric furnace and heated to 650 ° C, while a diesel engine at 1100 rpm and 3.9 Nm was connected and the exhaust gas was connected. (350 ° C) when the filter temperature (145
(Fig. 13) and regeneration (combustion)
The speed (the ratio of the temperature rise ΔT to the elapsed time Δt, FIG. 14) was examined. As shown in FIG. 13, the conventional example (washcoat alumina) is 50 sec-70 O ₂ becomes the rate-determining
Peak temperature at 0 ° C, and comparative example (no ceria)
However, O ₂ is rate-determining and reaches a peak temperature at 80 sec-800 ° C., but in the present invention example, a high peak temperature is reached at a rapid rate of 45 sec-900 ° C., soot removal efficiency is high, and high regeneration is achieved. It turns out that it shows a rate. This is also evident in the difference in regeneration (combustion) rates in FIG. FIG. 15 compares the regeneration rates themselves, and it is clear that the effect of the present invention example (ceria-containing catalyst) is outstanding.

As the rare earth oxide, it is more preferable to use, for example, a composite oxide of a rare earth element and zirconium in addition to the single oxide (CeO ₂ ) in the above-described example. It is considered that the zirconium oxide contained in the rare earth oxide improves the control characteristic of the oxygen concentration through the suppression of the grain growth of the rare earth oxide.

The rare earth oxide in the form of a composite oxide with zirconium preferably has a particle size of about 1 to 30 nm, more preferably a size of 2 to 20 nm. The reason is that complex oxides having a particle size of less than 1 nm are difficult to produce. On the other hand, when the particle size exceeds 30 nm,
Particles are easy to sinter, the particle surface area is reduced, and the contact area with exhaust gas is reduced,
This is because the problem that the activity is weakened remains. In addition, there is a concern that the pressure loss at the time of passing the exhaust gas becomes large.

FIG. 5 shows the structure of the alumina thin film.
Carrier with SiC particle surface coated with alumina thin film (this invention)
Comparison of electron micrographs (× 10K) and (× 30K) with electron micrographs (× 10K) and (× 30K) of a carrier (prior art) uniformly coated with an alumina film on the cell wall surface However, in the case of the carrier of the present invention, it was clearly seen that needle-like (fibrillar) aluminas stood on the surface of each SiC particle and exhibited a flocking structure as shown in FIG. 3 (c). I can take it.

The structure of the alumina thin film required in the catalyst of the present invention, that is, the crystal structure of the alumina thin film formed by coating the surface of each particle such as SiC is γ-Al ₂ O ₃ , At least one of δ-Al ₂ O ₃ and θ-Al ₂ O ₃ is included, and the diameter of the small fiber protruding alumina constituting the alumina thin film is 2 to 50 nm, and the length is 20 to 50 nm.
It has a shape with a length / diameter ratio of 5 to 50 at 300 nm. And the thickness of the thin film having such a structure is 0.
Below 5 μm, the specific surface area of alumina based on alumina is
It is preferably 50 to 300 m ² / g. The thickness of the alumina thin film referred to here is the average of the distance from the surface of the SiC particles to the furthest part of the alumina in the form of small fibers from the surface of the SiC particles. The diameter of alumina is more preferably 5 to 20 nm, and the ratio of the total length / diameter is more preferably 10 to 30.

The reason for limiting the characteristics of the fibril-projection-alumina thin film as described above is that if the length of the fibril-projection-alumina is less than 20 nm, it becomes difficult to secure a required specific surface area. If it is larger than 300 nm, it becomes structurally brittle. When the diameter is smaller than 2 nm, the diameter becomes equal to or less than the size of the catalyst such as a noble metal, and the layer does not function as a support layer. On the other hand, when the diameter is larger than 50 nm, it becomes difficult to secure a desired specific surface area. Also, regarding the length / diameter ratio,
If the ratio is less than 5, it is difficult to secure a required specific surface area. On the other hand, if the ratio is more than 50, the fibrous projection may be broken due to washing work or the like.

Also, regarding the specific surface area of the alumina thin film,
The reason for limiting as above is 50m ²Smaller than / g
Sintering of alumina with fiber projections proceeds excessively,
Poor durability. On the other hand, the specific surface area is 300m²greater than / g
Means that the fibrous projection alumina becomes too fine.
Tastes, does not function as a so-called carrier layer or is structurally
It becomes brittle. The preferred specific surface area is 50 to 200 m²/
g range.

Next, in the above ceramic carrier, the amount of the alumina thin film serving as the supporting film is determined by the alumina ratio.
0.1-15 mass% is preferred. The reason for this is that if it is less than 0.1 mass%, the effect of improving heat resistance is small, while if it is more than 15 mass%, the pressure loss increases and the filter function decreases. More preferably, it is 1-4 mass%.

Next, in this ceramic carrier, when the carrier is, for example, porous silicon carbide (SiC), the content of silicon is preferably 0.01 to 10 mass%. The reason is that if the silicon content is less than 0.01 mass%,
This is because the supply capacity is insufficient and the effect of improving the heat resistance is small. On the other hand, if the silicon content is more than 10 mass%, the strength of the honeycomb filter decreases. This silicon content is
The same applies to other silicon-containing ceramics.
It is preferably set to 01 to 10 mass%, more preferably 0.1 to 10 mass%.
It is from 0.01 to 5 mass%, more preferably from 0.01 to 2 mass%.

Each of the above-mentioned SiC particles is individually coated with an alumina thin film, and the ceramic carrier has an appearance as if the carrier surface is completely covered with an alumina thin film (supporting film). An active ingredient such as Pt, Rh, Pd, Ce, Cu, V, Fe, Au, Ag, etc. is supported to form a catalyst. Various methods are conceivable for supporting these active components on the alumina-supported membrane, and methods that are advantageously applicable to the present invention include impregnation methods, for example, evaporation to dryness,
Equilibrium adsorption method, incipient wetness method or spray method can be applied. Above all, the incipient wetness method is advantageous. In this method, an aqueous solution containing a predetermined amount of an active ingredient is dripped little by little toward a carrier, and when the surface of the carrier becomes slightly and uniformly wet (incipient), the pores of the carrier of the active ingredient are reduced. In this method, the impregnation is stopped, followed by drying and firing to carry the material. That is, the method is carried out by dropping the active ingredient-containing solution on the surface of the carrier using a burette or a syringe. The loading amount is determined by adjusting the concentration of the solution.

As the noble metal component useful as the catalytically active component, binary or ternary alloys such as Pt / Rh and Pt / Rh / Pd are used. (It is more advantageous to use with rare earth oxides such as ceria and lantana;
(Lead poisoning, phosphorus poisoning, sulfur poisoning) and low thermal degradation, so it has excellent durability.

Next, a method for producing a catalyst carrier according to the present invention will be described. A feature of the method for producing a catalyst according to the present invention is that an alumina thin film containing a rare earth oxide is formed on the uneven surface of the silicon-containing ceramic carrier by a sol-gel method, and in particular, a cell wall formed by immersion in a solution. The surface of each ceramic particle such as SiC to be produced is individually coated with a rare earth oxide-containing alumina thin film, and after calcining, a hydrothermal treatment step is performed to change the micro cross-sectional structure of the alumina thin film to ceria. Is converted to an alumina thin film (supporting film) that has a flocking structure that resembles fibrous alumina fibers that are dispersed.Then, a predetermined amount of active component is adsorbed on the surface of the alumina supporting film and immobilized. (Support). Hereinafter, each step ((1) formation of a carrier, (2) loading of an active ingredient) will be described in detail.

(1) Coating of a silicon-containing ceramic support with an alumina thin film a. Pre-treatment step This step consists of adding Si on the surface of each silicon-containing ceramic particle such as SiC to promote chemical bonding with alumina.
It is a process of oxidizing by heating at 800 to 1600 ° C. for 5 to 100 hours to provide a quantity. Of course, if there is a sufficient oxide film on the surface of the ceramic particles, this step can be omitted. For example, a SiC sintered body originally contains about 0.8 mass% of SiO ₂ . These are present on the surface and grain boundaries of SiC, and it is easily assumed that the Si is supplied. Further, there is also a meaning of increasing SiO ₂ in order to improve heat resistance. In this case, 800 to 1600 ° C. in an oxidizing atmosphere.
For 5 to 100 hours. This is 80
If the temperature is lower than 0 ° C., the oxidation reaction hardly occurs. On the other hand, if the temperature exceeds 1600 ° C., the oxidation reaction proceeds too much, and the strength of the filter is reduced. Recommended conditions are 1000-1500 ° C. for 5-20 hours. Under these conditions, sufficient SiO ₂ can be formed on the surface to supply Si, and the porosity and pore diameter of the filter are hardly changed, so that the pressure loss characteristics are not impaired. Because.

B. Solution impregnation step In this step, a solution of a metal compound containing aluminum and a rare earth element, such as a mixed aqueous solution of aluminum nitrate and cerium nitrate, is applied to the surface of each ceramic particle constituting the cell wall. This is a treatment for coating the rare earth oxide-containing alumina thin film by impregnation by a gel method.

In the above mixed aqueous solution, for the solution of the aluminum-containing compound, the starting metal compound includes a metal inorganic compound and a metal organic compound. Al (NO ₃ ) ₃ , AlCl ₃ , AlOCl, AlPO ₄ , Al
₂ (SO ₄ ) ₃ , Al ₂ O ₃ , Al (OH) ₃ , Al and the like are used. Among them, Al (NO ₃ ) ₃ and AlCl ₃ are particularly preferable because they are easily dissolved in solvents such as alcohol and water and are easy to handle. Examples of metal organic compounds include metal alkoxides,
There are metal acetylacetonate and metal carboxylate. As specific examples, Al (OCH ₃ ) ₃ , Al (OC ₂ H ₃ ) ₃ , Al (i
so-OC ₃ H ₇ ) ₃ and the like.

On the other hand, of the mixed aqueous solution, cerium-containing
For solutions of organic compounds, Ce (NO ₃)₃, CeCl₃, Ce₂
(SO₄)₃, CeO₂, Ce (OH)₃, Ce₂(CO₃)₃Etc. are used
Can be

As a solvent for the mixed solution, at least one of water, alcohol, diol, polyhydric alcohol, ethylene glycol, ethylene oxide, triethanolamine, xylene and the like is mixed in consideration of dissolution of the above metal compound. use. Further, as a catalyst for preparing a solution, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, or hydrofluoric acid may be added. Further, in order to improve the heat resistance of the alumina thin film, in addition to rare earth oxides, Li, K, Ca, Sr, B
Simple substances and compounds of a, La, Pr, Nd, Si, and Zr may be added to the starting materials.

Examples of preferred metal compounds in the present invention
Al (NO₃)₃And Ce (NO ₃)₃To give
Although they can be dissolved in solvents at relatively low temperatures,
The preparation of the liquid is easy. Also, as an example of a preferred solvent
Recommends 1,3 butanediol. The first reason for recommendation
The reason is that the viscosity is appropriate and the gel state is appropriate on the SiC particles.
This is because a gel film having a large thickness can be provided. Second
The reason is that this solvent forms the metal alkoxide in solution.
Metal oxide composed of oxygen, metal and oxygen
Easy to form polymer, ie precursor of metal oxide gel
Because it is.

It is desirable that the amount of Al (NO ₃ ) ₃ is 10 to 50 mass%. If the amount is less than 10 mass%, the amount of alumina having a surface area sufficient to maintain the activity of the catalyst cannot be supported, while if the amount is more than 50 mass%, a large amount of heat is generated at the time of dissolution and gelation is likely to occur. Also, Ce (NO
₃ ) The amount of ₃ is preferably 1 to 30 mass%. The reason is that if it is less than 1 mass%, soot oxidation cannot be promoted, and if it is more than 30 mass%, grain growth of CeO ₂ occurs after firing. On the other hand, the mixing ratio of Al (NO ₃ ) ₃ and Ce (NO ₃ ) ₃ is preferably 10: 2. The reason is Al
This is because by making (NO ₃ ) ₃ rich, the degree of dispersion of CeO ₂ particles after firing can be improved.

The temperature for preparing the impregnating solution of the metal compound is preferably 50 to 130 ° C. If the temperature is lower than 50 ° C., the solubility of the solute is low. On the other hand, if the temperature is higher than 130 ° C., the reaction proceeds rapidly and gelation occurs, so that it cannot be used as a coating solution. The stirring time is desirably 1 to 9 hours.
The reason for this is that the viscosity of the solution is stable within the above range.

The above cerium-containing metal compound (Al (NO ₃ )
₃ and Ce (NO ₃ ) ₃ ), in addition to the examples described above, in order to generate a composite oxide or solid solution with zirconium, as a zirconium source, for example, ZrO (NO ₃ ) ₂ or ZrO
With _2, they were mixed solution dissolved in water or ethylene glycol is impregnated into the mixed solution, dried and fired, it is preferable to obtain the composite oxide.

It is important in the present invention that the solution of the metal compound prepared as described above is spread and penetrates into all pores which are gaps between the ceramic particles in the cell wall. . For this purpose, for example, a method in which a catalyst carrier (filter) is placed in a container and the metal compound solution is filled and degassed, or a method in which the solution is poured from one of the filters and degassed from the other, may be employed. preferable. In this case, as a device for degassing, a vacuum pump or the like may be used in addition to the aspirator. With such a device, air in the pores in the cell wall can be evacuated,
As a result, the solution of the metal compound can be spread evenly on the surface of each ceramic particle.

C. Drying Step This step is a treatment for evaporating and removing volatile components such as NO ₂ , gelling the solution and fixing it on the surface of the ceramic particles, and simultaneously removing the excess solution.
Heat to a degree. When the heating temperature is lower than 120 ° C., the volatile components are difficult to evaporate, while when the heating temperature is higher than 170 ° C., the gelled film thickness becomes non-uniform.

D. Preliminary firing step This step removes residual components and removes amorphous
This is a preliminary firing process to form a mina thin film.
It is desirable to heat to a temperature of 500 ° C. Temporary firing temperature
Below 300 ° C, it is difficult to remove residual organic matter, while 500
Al higher than ℃ ₂O₃Crystallizes for subsequent hydrothermal treatment
The formation of small fibrous projections of boehmite
It is.

E. Hot Water Treatment Step In this step, a treatment of immersing the calcined catalyst carrier in hot water is performed to form the structure of the alumina thin film specific to the present invention described above. Immediately after such hydrothermal treatment, the particles on the surface of the amorphous alumina thin film are peptized and released into the solution in a sol state, and the boehmite particles generated by hydration become small fibrous projections. Condensing,
Create a stable state against peptization. That is, by this hot water treatment, the rare earth oxide-containing alumina individually adhered to the surface of each ceramic particle becomes small fibers (needle-like particles), stands, and exhibits a so-called flocked structure, resulting in a rough surface.
Therefore, a thin film having a high specific surface area is formed. In general, sintering of alumina proceeds mainly by surface diffusion, and the specific surface area rapidly decreases when phase transition to α-alumina occurs. But,
Since the silica is incorporated in the alumina particles, it is considered that the silica fills the pore sites of the alumina during the heat treatment process or moves to the surface of the acicular particles to suppress surface diffusion and sintering between the particles. Therefore, in the early stage of sintering of the carrier, the viscous flow mechanism by sintering from the contact point between the acicular particles is dominant, but in the latter stage, the silica blocks the mass transfer path between the acicular particles, so that α -It is considered that the transition to alumina is inhibited, and a high specific surface area is maintained without further sintering.

The temperature of the hot water treatment is desirably 50 to 100 ° C. If the temperature is lower than 50 ° C., the hydration of the amorphous alumina thin film does not proceed, and the small fiber projection-like boehmite is not formed. On the other hand, when the temperature is higher than 100 ° C., water evaporates, and it is difficult to maintain the process for a long time. The processing time is preferably one hour or more. If the time is shorter than 1 hour, the hydration of the amorphous alumina becomes insufficient.

D. Main firing step In this step, a treatment is performed to convert the boehmite generated by hydration into membrane water to form alumina crystals. The preferable temperature of the main firing is 500 to 1000 ° C., and the treatment is performed for 5 to 20 hours.
If this temperature is lower than 500 ° C., crystallization does not proceed, while if it is higher than 1000 ° C., sintering proceeds too much,
This is because the surface area tends to decrease.

(2) Loading of active ingredient a. Solution adjusting step The surface of the SiC ceramic carrier (filter) is coated with a rare earth oxide-containing alumina thin film (supporting film) having a flocking structure as shown in FIG. 3 (c). It carries an active ingredient such as Pt. In this case, the loading amount of the active ingredient is determined by dropping and impregnating an aqueous solution containing Pt or the like by an amount equal to the water absorption of the carrier so that the surface slightly wets. For example, the water absorption of the SiC ceramic carrier is defined as the measured value of the water absorption of the dried carrier being 22.46 mass%, the mass of the carrier being 110 g, and the volume being
If it has 0.163 l, this carrier will absorb 24.7 g / l of water. Here, as a starting material of Pt, for example, a dinitrodiammine platinum nitrate solution ([Pt (NH ₃ ) ₂ (NO ₂ )
₂ ] HNO ₃ , Pt concentration 4.53 mass%) is used. In order to support a predetermined amount of 1.7 g / l of Pt, 1.7 (g / l)
^{* Since} 0.163 (l) = 0.272 g of Pt only needs to be supported, dinitrodiammine platinum nitric acid solution (Pt concentration 4.5
3%). That is, the weight ratio of dinitrodiammine platinum nitrate solution (Pt concentration 4.53 mass%) / distilled water X
(%) Is X = 0.272 (g of Pt) /24.7 (g of water) /4.53
(Pt concentration mass%) is calculated as 24.8 mass%.

B. Liquid impregnation step A predetermined amount of the aqueous solution of dinitrodiammineplatinic nitric acid adjusted as described above is dropped on both end surfaces of the carrier at regular intervals using a pipette. For example, 40 to 80 drops are dropped at regular intervals on one side, and Pt is uniformly dispersed and fixed on the surface of the alumina supporting film covering the SiC carrier.

C. Drying and baking process After the aqueous solution has been dropped, the carrier is dried at 110 ° C. for about 2 hours to remove water, then transferred to a desiccator, left for 1 hour, and deposited on an electronic balance. Is measured. Next, sintering is performed in an N ₂ atmosphere at about 500 ° C. for about one hour to metallize Pt.

The catalyst according to the present invention is used as a filter for purifying exhaust gas. One of the uses is as an example of a transparent honeycomb carrier, an oxidation catalyst for a gasoline engine, a three-way catalyst, and an oxidation catalyst for a diesel engine. Another application is a diesel particulate filter in which honeycombs are alternately plugged in a checkered pattern. This diesel particulate filter (hereinafter, referred to as
The abbreviated "DPF") is itself a particulate (suspended particulate matter: PM) filter wall (cell wall 102)
Although it has only the function of trapping in the exhaust gas, it is possible to oxidize hydrocarbons and carbon monoxide in the exhaust gas by supporting the catalytically active component on the exhaust gas. Further, NO _x which can reduce NO _x even in an oxidizing atmosphere such as diesel exhaust gas
NO if a selective reduction catalyst component or a storage catalyst component is supported
Reduction of _x is also possible. Note that the PM trapped in the DPF causes an increase in the pressure loss of the DPF together with the accumulation, and therefore it is usually necessary to remove and regenerate the PM by a combustion treatment or the like. The temperature at which the combustion of soot (carbon), the main component of PM contained in ordinary diesel exhaust gas, starts is about 550-630 ° C. In this regard, the catalytically active component is D
When supported on PF, the soot combustion reaction path changes,
The energy barrier can be lowered, and the combustion temperature can be greatly reduced to 300 to 400 ° C, and the energy required for regeneration can be reduced. A DPF system can be constructed.

As described above, it can be said that the catalyst according to the present invention is preferably applied particularly to a diesel exhaust gas treatment system, but the following functions can be expected. A. Function as an oxidation catalyst for diesel exhaust gas Exhaust gas purification function: THC, CO oxidation Function that does not hinder engine operation: Pressure loss Function as a diesel particulate filter with catalyst Exhaust gas purifying function: soot combustion temperature, THC,
CO oxidation Function that does not hinder engine operation: Pressure loss

[0069]

EXAMPLE 1 This example was performed to confirm the operation and effect of a ceria-containing alumina thin film formed on a carrier surface. The purification test was performed by attaching the catalyst carrier (Examples 1-1 and 1-2 of the present invention and Comparative Example 1) manufactured under the conditions shown in Table 1 to a particulate filter (DFP) in an exhaust gas purification device for a diesel vehicle. went. Through this test, pressure loss characteristics, heat resistance, and cleaning resistance of the filter were investigated. The results of the investigation are shown in the same table and in FIGS. 6, 7 and 8.

[0070]

[Table 1]

A. As shown in FIG. 6, before the particulate matter (suspended particulate matter: PM) is accumulated, Example 1-1 of the present invention shows almost the same pressure loss characteristics as when there is no alumina thin film. It was found that, even after the accumulation, the pressure loss when flowing the same gas was remarkably small as compared with Comparative Example 1. b. Further, as shown in FIG. 7, when compared with Comparative Example 1, Examples 1-1 and 1-2 of the present invention showed a small decrease in the alumina specific surface area when heat-treated at the same temperature, and were excellent in heat resistance. I knew it was there. c. Further, as shown in Table 1, it was found that Examples 1-1 and 1-2 of the present invention were significantly superior to Comparative Example 1 in terms of cleaning resistance. d. FIG. 15 shows the regeneration rate (the amount of C removed from the regeneration filter / the amount of C adhering to the filter before regeneration). In the case of the alumina thin film containing ceria, 45% was obtained. In the case of the washcoat alumina uniform film, only 20% of the carbon was removed.

Embodiment 2 This embodiment relates to a diesel particulate filter.
FIG. 3 shows the results of tests on various characteristics when platinum (Pt) was loaded on a ceramic carrier as an active ingredient on (DPF). Table 2 shows the implementation conditions and characteristics.
Shown in The results are also shown in FIGS. 8, 9, and 10. In this example, the carrier had an alumina supporting film (8 g / l) on the particle surface of the carrier, the reference example had no supporting film on the carrier surface, and the comparative example had wash coat alumina on the carrier surface. A uniform film was formed.

[0073]

[Table 2]

Pressure loss characteristics: As shown in FIG. 8, when comparing the embodiment, the reference example, and the comparative example, the embodiment conforming to the present invention has almost the same pressure loss as that of the reference example having no supporting membrane. The characteristics are shown, and a remarkable effect is recognized as compared with the comparative example.

Heat resistance: As shown in FIGS. 9A and 9B,
When the transition of the specific surface area of the alumina thin film when heated to 1200 ° C. and the transition of the equilibrium temperature when heated to 900 ° C. are compared between the example and the comparative example, the effect of the example conforming to the present invention is remarkable. It can be seen that it is.

Soot combustion characteristics: The ability of the catalyst to burn soot was evaluated by an equilibrium temperature test method. This test method is as follows. That is, a diesel engine is installed in the test device, and a catalyst (DP
F) is inserted and installed, and operation is started in this state. Then, soot is collected in the DPF with the operation time, so that the pressure loss increases. In this case, if the exhaust temperature is increased by some method, at a certain temperature, a point (equilibrium temperature) where the soot deposition rate and the soot oxidation reaction rate equilibrate appears, and the pressure at this time (equilibrium pressure) )
Can be measured. The lower the equilibrium temperature and equilibrium pressure, the better the catalyst. In this test, as a method of increasing the exhaust gas temperature, an electric heater was inserted between the diesel engine and the DPF. This method has the advantage that the composition of the diesel exhaust gas does not change during the test, and the equilibrium temperature and the equilibrium pressure can be accurately obtained because the engine speed and the load can be kept constant. The test conditions were as follows: Diesel engine displacement: 273 cc, rotation speed: 1250 RPM, load: 3 Nm, steady operation, and the filter deposited was □ 34 × 150 mmL and 0.16 liter.

FIG. 10 shows the results of the above test. FIG.
Among them, an example of a carrier not supporting a catalyst was used as a reference example. As can be seen from the figure, the filter temperature rises as the exhaust gas temperature rises, but an equilibrium point is seen at about 500 ° C.
Comparing the example and the comparative example which conforms to the present invention, the equilibrium temperature was slightly superior at 400 ° C. and 410 ° C. respectively, but the equilibrium pressure at that time was improved by nearly 20% to 11 KPa and 9.2 KPa. are doing. Further, after performing aging in an oxidizing atmosphere at 850 ° C. for 20 hours, a similar test was carried out. In the present invention, the equilibrium temperature and pressure hardly deteriorated. It deteriorated to the same state as when it was not carried.

THC, CO purification rate; This property is a general method for evaluating an oxidation catalyst. So-called T
It is an investigation of the relationship between the purification temperature of HC (total hydrocarbons) to CO ₂ and water and the temperature of purification of CO to CO ₂ .
It can be said that this characteristic is a catalyst system in which the conversion is higher than the low temperature. The measurement was carried out by using an engine and a filter, measuring the amounts of THC and CO before and after the filter with an exhaust gas analyzer, and measuring the purification rate with respect to the temperature. As shown in FIG. 11, the embodiment of the present invention has a CO or THC purification temperature of about
30 ° C lower, showing excellent performance. This is because in the embodiment of the present invention, the catalyst is uniformly dispersed in the particles in the wall,
The time to pass through the wall is clearly longer than the time to pass through the washcoat, and the active point of Pt has CO,
It is considered that the chance of THC adsorption has increased.

Regeneration rate; DPF filters soot in exhaust gas. Therefore, soot is deposited in the DPF. The act of removing the deposited soot is called regeneration. Therefore,
The ratio of the regenerated soot weight to the deposited soot weight is expressed as a percentage and is defined as the regeneration rate.

[0080]

As described above, according to the present invention,
The collection efficiency of diesel particulates is high, and on the other hand, pressure loss is small and heat resistance is excellent.
It is possible to provide an exhaust gas purifying catalyst having excellent washing resistance and regeneration characteristics, and to establish an advantageous production technique thereof.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a typical catalyst carrier.

FIG. 2 is a conceptual diagram of a conventional washcoat alumina layer.

FIG. 3 is a conceptual diagram of an alumina thin film of the present invention.

FIG. 4 is an explanatory diagram of pressure loss characteristics.

FIG. 5 is an electron micrograph showing a particle structure of a catalyst carrier.

FIG. 6 is a comparative explanatory diagram of pressure loss characteristics in Example 1.

FIG. 7 is a comparative explanatory view of heat resistance in Example 1.

FIG. 8 is a comparative explanatory diagram of pressure loss characteristics in Example 2.

FIG. 9 is a comparative explanatory view of the heat resistance of the alumina thin film and the catalyst in Example 2.

FIG. 10 is a comparative explanatory diagram of soot combustion characteristics in Example 2.

FIG. 11 is a comparative explanatory diagram of the THC and CO purification characteristics in Example 2.

FIG. 12 is a schematic diagram illustrating a mechanism of improving the oxidation rate by adding CeO ₂ .

FIG. 13 is a comparison graph of soot oxidation characteristics affecting regeneration characteristics of a DPF.

FIG. 14 is a comparison graph of a regeneration (combustion) speed that affects the regeneration characteristics of the DPF.

FIG. 15 is a comparison graph of a DPF regeneration rate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Catalyst support 2 Cell wall 3 Alumina thin film 4 SiC particle 101 Cell 102 Cell wall 103 Alumina layer

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F01N 3/10 F01N 3/28 301P 3/28 301 B01D 53/36 104A 104B (72) Inventor Noriyuki Taoka Ibi-gun, Gifu 1-1, Ibikawa-cho Kitakata IBIDEN Co., Ltd. (72) Inventor Noriyoshi Tsunoda 2-1 Kitayama-cho, Toyohashi-shi, Aichi Prefecture Higashiura 4-302 Takashi Residence 4-302 (72) Inventor Akira Hasegawa Oochi, Hachinohe-shi, Aomori Prefecture Uenodaira 16-1 Uenodaira dormitory No.404 F-term (reference) 3G090 AA02 3G091 GB06W GB10X GB17X 4D048 AA06 AA13 AA18 AB01 AB02 AB05 BA03X BA03Y BA06X BA06Y BA08X BA08Y BA10X BA10Y BA18Y BA19X BA41X BA41ABAABAA04 A04 BA02A01 BA02A BA02B BA05A BA05B BA13A BA13B BB06A BB06B BB11A BB15A BC38A BD04A BD05A BD05B CA03 CA07 CA08 CA09 CA18 EA03X EA08 EB01 EB18X EB18Y EC02X EC03X EC03Y FB16 FB23 FB30

Claims (14)

[Claims] 1. A catalyst comprising a silicon-containing ceramic carrier having a catalytically active component dispersedly supported on the surface thereof, the ceramic carrier comprising an alumina containing a rare earth oxide for each particle unit forming the carrier. A catalyst characterized in that the catalyst active component is supported on uneven surfaces of the rare earth oxide-containing alumina thin film. 2. A porous material or a fiber, wherein the silicon-containing ceramic carrier contains a non-oxide ceramic such as silicon carbide or silicon nitride, or an oxide ceramic such as sialon, mullite or cordierite. 2. The catalyst according to claim 1, wherein the catalyst is constituted by one of a molded body and a pellet molded body. Wherein said silicon-containing ceramic carrier, characterized in that the support on the surface of each particle build form a has a SiO ₂ layer, and the SiO ₂ amount occupying the carrier is 0.001 ~20mass% The catalyst according to claim 1 or 2, wherein 4. The rare earth oxide-containing alumina thin film covering the surface of each particle in the silicon-containing ceramic carrier has a micro cross-sectional shape having a diameter of 2 to 50 nm, a length of 20 to 300 nm, and a ratio of the total length / diameter. Has an irregular surface consisting of a flocking structure in which fibrils having a shape of 5 to 100 are established, and the specific surface area of the surface is 50 to 300 m ² / g.
4. The catalyst according to any one of the above items 3. 5. The alumina thin film containing the rare-earth oxide covering the carrier, wherein the alumina thin film is converted to an amount of alumina with respect to the carrier by 0.1%.
It is coated at a rate of 1 to 15 mass%, and the amount of the rare earth oxide contained in the alumina thin film is 10 to the alumina.
The content is from 1 to 80 mass%.
5. The catalyst according to any one of the above items 4. 6. The catalyst according to claim 1, wherein at least a part of the rare earth oxide forms a composite oxide with zirconium. . 7. The catalyst according to claim 6, wherein the composite oxide of the rare earth oxide and zirconium has a particle size of 1 to 30 nm. 8. The following steps (a) to (e): (a) a solution impregnating step: a step of impregnating the carrier with a metal compound containing aluminum and a rare earth oxide on the surface of each particle constituting the silicon-containing ceramic carrier. Dipping in a solution, (b) drying step: heating and drying the carrier, (c) pre-baking step: heating and baking the carrier at a temperature of 300 to 500 ° C. or more to form an amorphous alumina thin film, (d) Heat treatment step: The carrier is immersed in hot water at 100 ° C and then dried. (e) Main firing step: Main firing at 500 to 1200 ° C., forming a rare earth oxide-containing alumina thin film through the step, and then dispersing and supporting a catalytically active component on the uneven surface of the rare earth oxide-containing alumina thin film. A method for producing a catalyst, comprising: 9. The following steps (a) to (f): (a) pretreatment step: applying the silicon-containing ceramic carrier to the surface of each particle constituting the silicon-containing ceramic carrier.
(B) solution impregnation step: immersing the carrier in a solution of a metal compound containing aluminum and a rare earth oxide, (c) Drying step: heating and drying the carrier; (d) calcination step: heating and sintering the carrier to a temperature of at least 300 to 500 ° C. to form an amorphous alumina thin film. (E) heat treatment step: Dipping in hot water at 100 ° C. followed by drying. (F) Main firing step: firing at 500 to 1200 ° C., forming a rare earth oxide-containing alumina thin film through the step, and then containing the rare earth oxide A method for producing a catalyst, comprising dispersing and supporting a catalytically active component on an uneven surface of an alumina thin film. 10. The silicon-containing ceramic carrier includes a non-oxide ceramic such as silicon carbide and silicon nitride;
10. The manufacturing method according to claim 8, wherein the manufacturing method comprises a porous body, a fiber molded body, or a pellet molded body containing an oxide ceramic such as sialon, mullite, and cordierite. Method. 11. The silicon-containing ceramic carrier has a SiO ₂ layer on the surface of each particle forming the carrier, and the amount of SiO _{2 in the} carrier is 0.001 to 20 mass%. The method according to any one of claims 8 to 10. 12. The rare earth oxide-containing alumina thin film covering the carrier is converted to an amount of alumina with respect to the carrier.
It is coated at a rate of 0.1 to 15 mass%, and the amount of rare earth oxide contained in the alumina thin film is
9. A content of 10 to 80 mass%.
12. The production method according to any one of items 11 to 11. 13. The rare earth oxide according to claim 8, wherein at least a part of the rare earth oxide forms a complex oxide with zirconium.
The production method according to the paragraph. 14. The production method according to claim 13, wherein the composite oxide of the rare earth oxide and zirconium has a particle size of 1 to 30 nm.