JP2002119860A - Catalyst and method of manufacturing for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the pressure drop of gaseous emission and to improve mechanical strength. SOLUTION: A ceramic carrier 15 containing zirconium phosphate is coated with thin alumina films 3 by each of particle units forming this carrier 15. A catalyst active component is deposited on the rugged surfaces of the thin alumina films 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a catalyst for purifying exhaust gas and a method for producing the same. Specifically, carbon monoxide (CO) contained in diesel engine exhaust gas
Removal of hydrocarbons and hydrocarbons (HC) and reduction and removal of nitrogen oxides (NOx) can be performed efficiently.
The present invention proposes a catalyst having a small pressure loss, a high collection efficiency of diesel particulates and a good regeneration rate, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as an exhaust gas purifying catalyst for automobiles, for example, there is a catalyst for purifying exhaust gas of a diesel engine. Each of the cells 101 serving as an exhaust gas passage as shown in FIGS. 16A and 16B is formed in a honeycomb shape from a porous silicon carbide sintered body having excellent heat resistance and heat conductivity. A catalyst-carrying filter 100 in which cells 101 are alternately sealed is used. Then, this catalyst-carrying filter 100 is connected to the exhaust side of the diesel engine,
Usually, particulates (PM: particulate matter), HC, CO, and the like deposited in the filter are oxidatively decomposed.

As such a catalyst-carrying filter 100, for example, a support layer made of γ-alumina is formed on the surface of a cell wall 102 of a heat-resistant ceramic carrier 105 formed into a honeycomb shape. Pd, Rh
Those carrying a catalytically active component composed of a noble metal such as the above are well known.

[0004] As such a catalyst-carrying filter 100, Japanese Patent Application Laid-Open No. 5-68892 discloses a fine powder obtained by adding an inorganic binder to gamma-alumina, mixing and pulverizing the slurry, and forming the slurry into a honeycomb shape. The catalyst carrier layer 103 is formed by so-called wash coating that uniformly sprays and coats the wall surface of the ceramic carrier 105.

[0005]

The prior art, that is, the wash-coated catalyst coat layer 103 (wash coat alumina layer) is, as shown in FIG.
1 is formed of a thin film that uniformly covers the wall surface of the cell wall 102.
It has a pore structure as shown in the partial enlarged view of FIG. 7 (b). The pore diameter in such a pore structure is 20 to 500.
Mainly Angstrom, usually 50-300m
^It usually shows a specific surface area of ² / g. In addition, such a catalyst coat layer 103 must have a large specific surface area and a certain thickness (about 50 to 100 μm) because a catalyst active component such as a noble metal is dispersed and supported on the surface.

However, the wash-coated catalyst coat layer 103 has a small pore diameter and small porosity.
The resistance when the exhaust gas passes through the catalyst supporting filter 100 is large. For this reason, there is a problem that the pressure loss is significantly increased as compared with the ceramic carrier 105 having no catalyst coat layer. The “pressure loss” refers to a value obtained by subtracting a downstream pressure value from an upstream pressure value of the catalyst-carrying filter 100. Exhaust gas undergoes resistance as it passes through the filter, which is the largest contributor to pressure loss. Therefore, when the pressure loss increases, heat resistance, mechanical strength, and collection efficiency decrease, and the composition becomes chemically unstable.

Further, since the wash-coated catalyst coat layer 103 is simply uniformly coated on the surface of the carrier, which is the cell wall 102, it has poor adhesion and ash deposits when purifying exhaust gas ( (Ash) during cleaning. As described above, although the catalyst coat layer 103 has a pore structure, the pore size is as small as 20 to 500 angstroms, and sintering proceeds when exposed to a high temperature for a long time, and the phase transition to the α phase causes a specific surface area. However, there is also a problem that heat resistance is inferior due to the decrease in heat resistance. Further, since the specific surface area is small, the catalyst coat layer 10
Thus, the distance between the particles of the catalytically active component supported on the catalyst 3 becomes small, and as a result, when sintering proceeds, the specific surface area becomes smaller, resulting in a problem that the catalytic action itself is reduced.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a catalyst having not only a small pressure loss of exhaust gas but also excellent mechanical strength and a method for producing the same. .

[0009]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, there is provided a catalyst comprising a catalytically active component dispersed and supported on the surface of a ceramic support containing a tetravalent metal acidic insoluble salt. The surface of the ceramic carrier is coated with a thin film of alumina containing a rare earth oxide for each particle unit forming the carrier, and the surface of the ceramic carrier is roughened on the uneven surface of the alumina thin film containing a rare earth oxide. The gist is that the catalyst active component is supported.

[0010] According to a second aspect of the present invention, there is provided a catalyst comprising a zirconium compound-containing ceramic carrier having a catalytically active component dispersed and supported on a surface thereof, wherein the ceramic carrier is provided for each particle unit forming the carrier. The gist is that the surface is coated with a thin film of alumina containing a rare earth oxide, and the catalytically active component is supported on the uneven surface of the alumina thin film containing a rare earth oxide.

[0011] According to the third aspect of the present invention, there is provided a catalyst in which a catalytically active component is dispersed and supported on the surface of a tetravalent metal phosphate-containing ceramic carrier. The surface of each particle unit is coated with a thin film of alumina containing a rare earth oxide, and the gist is that the catalytically active component is supported on the uneven surface of the rare earth oxide containing alumina thin film. .

[0012] According to a fourth aspect of the present invention, in the catalyst according to the first aspect, the ceramic support containing an acidic insoluble salt of a tetravalent metal is selected from the group consisting of zirconium phosphate, titanium phosphate, zirconium arsenate and titanium arsenate. Including any,
The gist of the present invention is that it is composed of any of a porous body, a fiber molded body, and a pellet molded body.

According to the fifth aspect of the present invention, the first to fourth aspects are provided.
In the catalyst described in any one of the above, the rare earth oxide-containing alumina thin film covering the surface of each particle in the ceramic support has a micro cross-sectional shape having a diameter of 2 to 50 mm and a length of 2
It has an irregular surface consisting of a flocking structure in which small fibers having a length / diameter ratio of 0 to 300 nm and a length / diameter ratio of 5 to 100 stand, and the specific surface area of the surface is 50 to 300 m ² / g. And

According to the sixth aspect of the present invention, the first to fifth aspects are provided.
In the catalyst according to any one of the above, the alumina thin film containing the rare earth oxide, which covers the ceramic carrier, is 0.1 to 15 mass in terms of an amount of alumina with respect to the carrier.
%, And the amount of the rare earth oxide contained in the alumina thin film is 10 to 80 m with respect to the alumina.
The content should be ass%.

According to the seventh aspect of the present invention, the first to sixth aspects are provided.
In the catalyst according to any one of the above, the gist is that at least a part of the rare earth oxide forms a composite oxide with zirconium.

According to an eighth aspect of the present invention, in the catalyst according to the seventh aspect, the composite oxide of the rare earth oxide and zirconium has a particle diameter of 1 to 30 nm.

According to the ninth aspect of the present invention, a rare earth oxide-containing alumina thin film is formed on the surface of each particle constituting the tetravalent metal acidic insoluble salt-containing ceramic support through the following steps (a) to (e). Then, a catalyst can be produced by carrying 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 ceramic carrier is immersed in a solution of a metal compound containing aluminum and a rare earth oxide. (B) Drying step: heating and drying the ceramic carrier. (C) Preliminary firing step: 300-50 of the ceramic carrier
By heating and firing at a temperature of 0 ° C. or more, an amorphous alumina thin film is formed. (D) Heat treatment step: The ceramic carrier is immersed in hot water at 100 ° C. and then dried. (E) Main firing step: Main firing at 500 to 1200 ° C.

According to the tenth aspect of the present invention, a rare earth oxide-containing alumina thin film is formed on the surface of each particle constituting the tetravalent metal acidic insoluble salt-containing ceramic support through the following steps (a) to (f). Then, a catalyst can be produced by dispersing and supporting a catalytically active component on the uneven surface of the rare earth oxide-containing alumina thin film. (A) Pre-treatment step: the ceramic carrier is heated at 1000 ° C.
Heat to a temperature of ~ 1500C to form an oxide film of silicide. (B) Solution impregnation step: The ceramic support is immersed in a solution of a metal compound containing aluminum and a rare earth oxide. (C) Drying step: heating and drying the ceramic carrier. (D) Pre-baking step: the ceramic carrier is placed in the range of 300 to 50
By heating and firing at a temperature of 0 ° C. or more, an amorphous alumina thin film is formed. (E) Heat treatment step: The ceramic carrier is immersed in hot water at 100 ° C. and then dried. (F) Main firing step: Main firing at 500 to 1200 ° C.

In the invention according to claim 11, in the method for producing a catalyst according to claim 9 or 10, the ceramic support containing a tetravalent metal acid-insoluble salt comprises zirconium phosphate, titanium phosphate, zirconium arsenate and The gist of the present invention is that it is constituted by any of a porous body, a fiber molded body, and a pellet molded body containing titanium arsenate.

According to the twelfth aspect of the present invention, the ninth to nineteenth aspects of the present invention are described below.
In the method for producing a catalyst according to any one of the first to eleventh aspects, the alumina thin film containing the rare earth oxide, which covers the ceramic carrier, is 0.1% in terms of alumina amount with respect to the carrier.
The amount of the rare earth oxide contained in the alumina thin film is in the range of 10 to 80 mass% with respect to the alumina.

According to the thirteenth aspect, in the ninth aspect,
13. The method for producing a catalyst according to any one of the above items 12, wherein at least a part of the rare earth oxide forms a composite oxide with zirconium.

According to the fourteenth aspect, in the thirteenth aspect,
In the method for producing a catalyst described in above, the gist is that the composite oxide of the rare earth oxide and zirconium has a particle size of 1 to 30 nm.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. As shown in FIGS. 1 to 3, the catalyst 10 according to the present embodiment includes a ceramic carrier 15 made of a porous sintered body. The ceramic carrier 15 is made of a ceramic containing a tetravalent metal insoluble salt. In the present embodiment, zirconium phosphate (Zr (H
PO ₄ ) ₂ .nH ₂ O) is used. The cell wall 12 is formed on the ceramic carrier 15. The surface of the zirconium phosphate particles 4 constituting the cell wall 12 is individually coated with a catalyst coat layer 2 with a predetermined thickness.

The catalyst coat layer 2 is obtained by supporting a catalytically active component and a co-catalyst on a support material. In the present embodiment, the support material is alumina (Al ₂ O ₃ )
(Hereinafter, referred to as an alumina thin film) 3. In addition to alumina, zirconia (zirconium dioxide: Z
rO ₂ ), titania (titanium oxide: TiO ₂ ), and silica (silicon oxide: SiO ₂ )
The number may be arbitrarily changed as long as it includes one.

More specifically, one type of oxide is ZrO ₂ , TiO ₂ or SiO ₂ . The two types of oxides include Al ₂ O ₃ / ZrO ₂ and Al ₂ O ₃ / Ti
O ₂ , Al ₂ O ₃ / SiO ₂ , ZrO ₂ / TiO ₂ or ZrO
₂ / SiO ₂ . As the three kinds of oxides, Al ₂ O ₃
/ ZrO ₂ / TiO ₂ , Al ₂ O ₃ / ZrO ₂ / SiO ₂ , A
l ₂ O ₃ / TiO ₂ / SiO ₂ or ZrO ₂ / TiO ₂ / Si
There is O _2. The four types of oxides are Al ₂ O ₃ / ZrO ₂
/ There is a TiO ₂ / SiO _2.

As the ceramic carrier 15 containing a tetravalent metal acidic insoluble salt, for example, titanium phosphate, zirconium arsenate and titanium arsenate can be used in addition to zirconium phosphate. Thus, a wall flow honeycomb type filter as shown in FIGS. 1A, 1B and 2 is formed.

An example in which a zirconium phosphate sintered body is used as the ceramic support 15 containing a tetravalent metal acidic insoluble salt will be described below. The ceramic carrier 15 is made of a zirconium phosphate sintered body having a substantially square cross section in which a plurality of cells 11 as through holes are regularly formed along the axial direction. The cell 11 has a cell wall 1
2, the opening of each cell 11 is sealed on one end face side by a sealing body 14, and the other end face of the corresponding cell 11 is opened, and as a whole, each end face is The opening portion and the sealing portion are arranged so as to have a checkered pattern, respectively. A large number of cells 11 having a rectangular cross section are formed in the ceramic carrier 15. In other words, these ceramic carriers 15 have a honeycomb structure.

The cell 11 has a density of 200 to 35.
0 pieces / square inch. That is, of the large number of cells 11, about half of them are open at the upstream end face, and the remaining ones are open at the downstream end face, and the thickness of the cell wall 12 separating each cell 11 is about 0.4 mm. Is set to

As described above, the ceramic carrier 15 made of zirconium phosphate has a structure partitioned by the porous cell walls 12 as shown in FIG. The average pore diameter measured by the mercury intrusion method is 10 μm to 500 μm.
Within the range. In addition to this range, the ceramic carrier 1
The average pore diameter of No. 5 may be changed to any value within the range of 20 mm to 250 mm.

When the cell wall 12 has such a pore diameter, it is suitable for collecting fine particulates. That is,
By setting the average pore diameter of the cell wall 12 within the above range, diesel particulates can be reliably collected. On the other hand, the average value of the pore diameter of the cell wall 12 is 1
If it is less than 0 μm, as shown in FIG.
The pressure loss when the exhaust gas passes through the engine becomes extremely large, which may cause the engine to stop. On the other hand, when the average value of the pore diameter exceeds 300 μm, it becomes impossible to efficiently collect fine particulates.

The porosity of the porous cell wall 12 in the ceramic carrier 15 is set to 30 to 70%. In addition to this value, the porosity of the ceramic carrier 15 is set to 4
It may be changed to any value within the range of 0 to 60%. FIG.
If the porosity is less than 30% as shown in FIG.
2, the pressure loss when the exhaust gas passes through becomes extremely large, which may cause the engine to stop. On the other hand, when the porosity exceeds 70%, it is not possible to efficiently collect fine particulates. 6 (a),
The data showing the characteristics of the pressure loss in (b) all show the case where the flow rate of the exhaust gas is 10 m / s.

At the same time, when the porosity exceeds 70% as shown in FIG. 6 (c), cracks tend to occur in the ceramic carrier 15 due to a decrease in mechanical strength. That is, the porosity of the ceramic carrier 15 and the mechanical strength are in inverse proportion. Therefore, if the porosity is set to be larger than 70% in order to increase the amount of the catalyst coat layer 2 loaded on the zirconium phosphate particles 4 of the ceramic carrier 15, the honeycomb structure cannot be formed.

As described above, since the average pore diameter of the ceramic carrier 15 is set at 10 to 500 μm and the porosity is set at 30 to 70%, the pressure loss can be reduced and the mechanical strength is improved. be able to. At the same time, the collection efficiency of the particulates contained in the exhaust gas can be increased.

When such a ceramic carrier 15 is produced, for example, 0.1 parts of a zirconium phosphate powder having an average particle diameter of about 10 μm is added as a raw material.
About 30 parts by weight of zirconium phosphate powder having an average particle diameter of about 5 μm, about 6 parts by weight of methylcellulose as a binder with respect to 100 parts by weight of zirconium phosphate powder, and a dispersion medium containing an organic solvent and water in phosphorus A mixture of about 25 parts by weight with respect to 100 parts by weight of zirconium oxide powder is used. Next, after kneading the compounded raw material, the mixture is extruded and formed into a honeycomb shape, and a part of the cell 11 is sealed in a checkered pattern. Next, the formed body is dried and degreased, and then fired in an inert atmosphere to obtain a desired ceramic carrier 15.

The zirconium phosphate used as a raw material has an amorphous property as shown in Table 1 below.
Some have crystallinity. If amorphous zirconium phosphate is used, the specific surface area of zirconium phosphate can be increased. In the present embodiment, α-zirconium phosphate shown in Table 1 is used. In addition to the α-zirconium phosphate, zirconium phosphate having another crystal structure may be used.

[0036]

[Table 1] The most characteristic configuration in the present embodiment is a surface of the cell wall 12 substantially constituting the ceramic carrier 15,
In particular, the purpose is to cover the surface of each zirconium phosphate particle 4 constituting the cell wall 12 with the rare earth oxide-containing alumina thin film 3. More precisely, for each zirconium phosphate particle 4 of the zirconium phosphate sintered body constituting the cell wall 12, the surface of each zirconium phosphate particle 4 is individually subjected to various types. That is, it is covered with the rare earth oxide-containing alumina thin film 3 by the method.

FIG. 17B shows a conventional technique in which the surface of the cell wall 12 is uniformly coated with the catalyst coat layer 2 by a wash coat method.
(A), (b) is explanatory drawing of the ceramic carrier 15 used by this embodiment. On the surface of each zirconium phosphate particle 4 constituting the cell wall 12, a rare earth oxide-containing alumina thin film 3 (hereinafter, this "rare earth oxide-containing alumina thin film 3" is simply abbreviated as "alumina thin film 3") is individually provided. In the state of being coated on the surface.

As described above, the catalytically active component according to the present embodiment has a characteristic configuration (alumina thin film 3).
However, unlike the prior art, the wall surface of the cell wall 12 of the exhaust gas is not simply covered with the catalyst coat layer 2 uniformly. For example, if the cell wall 12 is uniformly coated as in the conventional case, the gap between the zirconium phosphate particles 4 is closed and plugged, thereby impairing air permeability. In contrast, the ceramic carrier 15 used in the present embodiment has a structure in which the surface of each zirconium phosphate particle 4 constituting the cell wall 12 is individually coated with the alumina thin film 3.

Therefore, in the present embodiment, the cell wall 1
The pores 2 are maintained as pores without completely closing pores of the zirconium phosphate particles 4 themselves, that is, gaps formed between the zirconium phosphate particles 4. Is remarkably small. Moreover, since the alumina thin film 3 individually covers each zirconium phosphate particle 4 itself, for example, the thin film does not peel off from the cell wall 12 during cleaning, and thus has excellent heat resistance. It has excellent cleaning properties. Further, the area where the exhaust gas contacts the catalytically active component increases. Therefore, the oxidation of CO and HC in the exhaust gas can be promoted.

The pressure loss characteristics, heat resistance, washing resistance, and regeneration characteristics of the alumina thin film 3 as a support film used for the catalytically active component according to the present embodiment will be described below.

Pressure drop characteristics of the alumina thin film 3;
Generally, the pressure loss characteristics when exhaust gas passes through the cell wall 12 are considered as follows. That is, the pressure loss when the diesel exhaust gas passes through the ceramic carrier 15 can be shown in FIG. In this case, the resistances ΔP1, ΔP2, and ΔP3 each depend on the cell structure of the filter, and are constant values Δpi = (Δ) independent of the passage of time such as the accumulation of diesel particulates.
P1 + ΔP2 + ΔP3), which is referred to as an initial pressure loss.
ΔP4 is the resistance when passing through the accumulated diesel particulates, and is a value that is two to three times or more the initial pressure loss.

The specific surface area of the ceramic carrier 15 having a cell structure of 14/200 is 8.931 cm ² / cm ³ ,
Since the density of the ceramic carrier 15 is 0.675 g / cm ³ , the specific surface area of the cell wall 12 is 0.0013 m ² / g.
Becomes On the other hand, the pore specific surface area in the cell wall 12 is 0.12 m ² / g as measured by a mercury porosimeter,
It has about 50-100 times the surface area. This means that when the alumina thin film 3 having the same weight is formed on the surface of the cell wall 12, each phosphor layer constituting the cell wall 12 is formed rather than simply covering the surface of the cell wall 12 uniformly. When the surfaces of the zirconium oxide particles 4 are individually coated, the thickness of the alumina thin film 3 for obtaining the same effect can be reduced by 1/50 to 1/10.
Can be zero.

That is, when the alumina thin film 3 is uniformly formed under a conventional technique such as a wash coat, the thickness of the alumina thin film 3 is required to cover about 3 mass% of alumina required for the activity of the catalytically active component. Needs to be 50 μm.
The pressure loss at this time is the resistance Δ passing through the cell wall 12.
In addition to P3, the resistance passing through the alumina thin film 3 increases. Further, the aperture becomes smaller and ΔP1 becomes larger. Therefore, the pressure loss is significantly higher than that of a filter not coated with alumina, and the tendency becomes more remarkable when particulates are deposited on the filter.

In this respect, when the surface of the zirconium phosphate particles 4 constituting the cell wall 12 is coated with alumina like the ceramic carrier 15 used in the present embodiment,
In order to make the alumina thin film 3 of about 3 mass% necessary for activating the catalytically active component, its thickness is at most about 0.5 μm. The increase in the pressure loss at this time slightly increases the resistance ΔP3, but the other pressure losses are substantially negligible, and the pressure loss characteristics are lower than those of the alumina layer formed by the conventional wash coat. Improve dramatically.

Heat resistance of the alumina thin film 3; In general, alumina has a high specific surface area and is suitable as a film for supporting a catalytically active component. In particular, at present, there is a demand for the development of a high heat-resistant catalyst 10 that operates stably at higher temperatures.
Accordingly, the alumina thin film 3 is also required to have higher heat resistance.

In this regard, in the present embodiment, in order to improve the heat resistance of alumina, (1) the shape of each alumina particle is made into small fibers, and (2) a rare earth oxide such as ceria (cerium oxide). Was decided to be contained.

In particular, by employing the former configuration (1), the number of contacts between the alumina particles can be reduced.
Grain growth is suppressed by lowering the sintering rate, and the specific surface area can be increased, thereby improving heat resistance.

That is, in the present embodiment, the alumina thin film 3 covering the surface of each zirconium phosphate particle 4 of the ceramic carrier 15 has a flocked structure in which the micro cross-sectional shape of each alumina particle is small fiber or stand. . Therefore, the contact points between adjacent alumina fibrils are reduced, so that the heat resistance is remarkably improved.

Next, regarding (2), 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 particles constituting the alumina thin film 3 to prevent the growth of the alumina particles.

Regarding the washing resistance of the alumina thin film 3: The main component of the particulates deposited on the surface of the cell wall 12 is carbon, which can be oxidized and removed by a method such as combustion. However, some substances remain as ash after combustion. Such a substance contains Ca, added to the engine oil, to have a role as a neutralizing agent or a lubricant.
Some compounds such as Mg and Zn are oxidized or turned into sulfates. In addition, CeO is contained in the fuel in advance.
Some catalyst active components such as 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, cleaning with high-pressure water or the like is necessary. At this time, 30kg / c
Washing with a pressure of at least m ² can completely remove ash.

In this regard, in the case of the conventional alumina thin film formed by wash coating on the surface of the cell wall 12, since there is a thick coat layer by physical adsorption on the entire surface of the cell wall 12, it is often peeled off during the above-mentioned cleaning. . On the other hand, in the support film (alumina thin film 3) used in the present embodiment, alumina is thinly and individually coated on the surface of each zirconium phosphate particle 4 constituting the ceramic carrier 15, and furthermore, it is chemically bonded. Therefore, the zirconium phosphate particles are in a state of being tightly adhered to the individual particles. Therefore, the adhesiveness is high, the resistance to washing is high, and the durability as a coating is strong.

With respect to the reproduction characteristics of the alumina thin film 3, in the present embodiment, the alumina thin film 3 contains a rare earth oxide such as ceria (CeO ₂ ) or lantana (La ₂ O ₃ ) and A1 ₂ O _3. About 10 to 80 mass%, preferably about 20 to 40 mass%, to uniformly disperse these oxides on the surface and inside of the alumina thin film 3.

When ceria or the like is added to the alumina thin film 3 (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 controlled by the oxygen concentration adjusting action of the ceria. When activated, the efficiency of burning and removing soot (diesel particulate) adhering to the filter is improved, and the regeneration rate of the catalyst 10 is significantly improved. Further, the durability of the catalyst 10 can be improved.

That is, rare earth oxides such as ceria not only improve the heat resistance of alumina but also play a role in adjusting the oxygen concentration on the catalyst surface. In general, hydrocarbons and carbon monoxide present in the exhaust gas are removed by an oxidation reaction and NOx is removed by a reduction reaction, but the composition of the exhaust gas fluctuates constantly between a fuel rich region and a lean region. Therefore, the working atmosphere on the catalyst surface also fluctuates drastically. By the way, ceria added to the catalyst has a relatively small oxidation-reduction potential of Ce ³⁺ and Ce ⁴⁺ , and the following formula ₂ CeO ₂
反 応 The reaction of Ce ₂ O ₃ + 1 / 2O ₂ proceeds reversibly. That is, when the exhaust gas enters a rich region, the above-described reaction proceeds to the right to supply oxygen to the atmosphere. Conversely, when the exhaust gas enters a lean region, the reaction proceeds to the left to occlude excess oxygen in the atmosphere. In this way, by adjusting the oxygen concentration in the atmosphere,
The ceria acts to widen the range of the air-fuel ratio at which hydrocarbons, carbon monoxide or NOx can be efficiently removed.

FIG. 12A explains the mechanism of the oxidation rate of the alumina thin film 3 to which ceria (CeO ₂ ) is not added. FIG. 12B, on the other hand, explains the mechanism of the oxidation rate of the alumina thin film 3 when ceria is added. As shown in FIG.
The catalyst free of O ₂ oxidizes soot by activating oxygen in the exhaust gas. This reaction is
It is inefficient because oxygen in the fluid must be activated.

On the other hand, for a catalyst in which CeO ₂ is present, oxygen is supplied by the following reaction: CeO ₂ ⇔CeO _{2 -x} + x / 2O ₂ . That is, the oxygen discharged into the atmosphere and the oxygen in the exhaust gas are activated by the catalytically active component (noble metal) and react with soot (carbon) to become CO ₂ (CeO _{2 -x} is oxidized). Original Ce
Back to O _2). In addition, since CeO ₂ and soot are in direct contact, even if the amount of oxygen exhaled is small, the soot can be oxidized efficiently.

In addition, CeO ₂ in this case increases the OSC (oxygen storage function) by supporting a catalytically active component (noble metal). This is because the catalytically active component activates oxygen in the exhaust gas and also activates oxygen on the surface of CeO ₂ near the noble metal, so that the OSC increases.

FIGS. 13 and 14 show the alumina thin film 3.
Regarding the effect of adding rare earth oxides such as ceria to the inside, a catalyst 10 (embodiment) in which the catalytically active component is Pt, the co-catalyst is CeO ₂ , and the support material is acicular Al ₂ O ₃ , Pt / acicular Al
₃ shows the results of experiments on the regeneration characteristics of ₂ O ₃ (Comparative Example) and Pt / Al ₂ O ₃ (wash coat) catalysts. In this experiment, a soot-attached diesel particulate filter (DPF, total length = 150 mm) was housed in an electric furnace and heated to 650 ° C., while 1100 rpm
m, 3.9 Nm diesel engine, and the transition of the filter temperature (temperature measurement at 145 mm from the inlet) when the exhaust gas (350 ° C.) is introduced into the filter (FIG. 13), and regeneration ( (Combustion) speed (ratio of temperature rise ΔT to elapsed time Δt, FIG. 14).

As shown in FIG. 13, in the conventional example (catalyst coat layer 2 formed by wash coat), O ₂ became the rate-limiting and reached a peak temperature at 50 sec-700 ° C., and the comparative example (ceria (cocatalyst) ) None) Even though O ₂ is rate-limiting and reaches a peak temperature at 80 sec-800 ° C,
In the present embodiment, the peak temperature is reached at a high rate of 45 sec-900 ° C., indicating that the soot oxidation removal efficiency is high and a high regeneration rate is exhibited. This is also evident as the difference in regeneration (combustion) rates in FIG.

FIG. 15 compares the regeneration rates themselves, and it is clear that the effect of this embodiment (ceria-containing catalyst) is outstanding. DPF filters soot in the exhaust gas. Therefore, soot is deposited in the DPF. The act of removing the deposited soot is called regeneration. Thus, the ratio between the regenerated soot weight and the deposited soot weight is expressed as a percentage, and this is defined as the regeneration rate.

The rare earth oxides include, for example, the single oxide (CeO ₂ ) in the above-described example,
It is more preferable to use a composite oxide of a rare earth element and zirconium. 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 diameter of about 1 to 30 nm, more preferably 2 to 20 mm. The reason is that complex oxides having a particle diameter of less than 1 nm are difficult to produce. On the other hand, when the particle diameter is 3
When it exceeds 0 nm, the particles are easily sintered,
This is because the particle surface area is reduced, and the contact area with the exhaust gas is reduced, and the problem that the activity is reduced remains. In addition, there is a concern that the pressure loss at the time of passing the exhaust gas increases.

FIG. 5 shows the structure of the alumina thin film 3.
FIG. 4 is an enlarged view showing a ceramic carrier 15 in which the surface of each zirconium phosphate particle 4 is coated with an alumina thin film 3 and a carrier (prior art) in which the surface of a cell wall 12 is uniformly coated with an alumina film. Needle-like (small fibrous) aluminas stand on the surface of each zirconium phosphate particle 4, and have a flocking structure as shown in FIG. 3 (b). Since the object to be coated with the alumina thin film 3 is the zirconium phosphate particles 4, it is easy to form alumina in a needle shape.

The structure of the alumina thin film 3, that is, the crystal structure of the alumina thin film 3 formed by coating the surface of each zirconium phosphate particle 4 has γ-Al ₂
At least one of O ₃ , δ-Al ₂ O ₃ and θ-Al ₂ O ₃
One is included. The diameter of the small fiber protruding alumina constituting the alumina thin film 3 is 2 to 50 nm, and the length is 2 to 50 nm.
It has a shape with a length / diameter ratio of 5 to 50 at 0 to 300 nm. The thickness of the alumina thin film 3 having such a structure is preferably 0.5 μm or less, and the specific surface area of alumina based on alumina is preferably 50 to 300 m ² / g.

The thickness of the alumina thin film 3 here is the average of the distance from the surface of the zirconium phosphate particles 4 to the farthest part of the small fiber protruding alumina. 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-projecting alumina thin film 3 as described above is that if the length of the fibril-projecting alumina is less than 20 nm, it becomes difficult to secure a required specific surface area. , 300 nm, it is structurally brittle. When the diameter is smaller than 2 nm, the diameter becomes equal to or less than the size of the catalytically active component such as a noble metal, and the catalyst does not function as a catalyst-supporting layer. It is. Also,
When the ratio of the total length / diameter is smaller than 5, it is difficult to secure a required specific surface area. On the other hand, when the ratio is larger than 50, the structure becomes brittle and the fibrous projections may be broken due to washing work or the like. This is because it occurs.

The reason why the specific surface area of the alumina thin film 3 is limited as described above is that if the specific surface area is less than 50 m ² / g, the sintering of alumina having small fiber protrusions proceeds excessively, resulting in poor durability. On the other hand, the specific surface area is 30
If it exceeds 0 m ² / g, it means that the fibril-projecting alumina becomes too fine. It does not function as a so-called catalyst support layer or becomes brittle structurally. The preferred specific surface area is in the range of 50 to ²⁰⁰ m ² / g.

Next, in the ceramic carrier 15 as described above, the amount of the alumina thin film 3 serving as a supporting film is preferably 0.1 to 15 mass% in terms of an alumina ratio. The reason for this is
If the content is less than 0.1 mass%, the effect of improving the heat resistance is small, while if it is more than 15 mass%, the pressure loss increases and the filter function deteriorates. More preferably 1-4 mass
%.

Each surface of the zirconium phosphate particles 4 is individually coated with the alumina thin film 3, and the surface of the ceramic carrier 15 is completely covered with the alumina thin film (supporting film) 3. The above-mentioned ceramic carrier 15 exhibiting an aspect carries a noble metal element as a catalytically active component, and an element selected from the group VIa of the periodic table and the group VIII of the periodic table. Specific examples of this element include platinum (Pt), palladium (Pd),
Rhodium (Rh), nickel (Ni), cobalt (C
o), molybdenum (Mo), tungsten (W), cerium (Ce), copper (Cu), vanadium (V), iron (F
e), gold (Au), silver (Ag) and the like.

Accordingly, the catalytically active components are Pt, Au, Ag, Cu as noble metal elements, Mo and W as elements of group VIa of the periodic table, and F as elements of group VIII of the periodic table.
e, Co, Pd, Rh, Ni, and at least one element or compound selected from V and Ce as elements of the periodic table other than these may be supported on the alumina thin film 3.

For example, a binary alloy or a ternary alloy based on a combination of the above elements is used as the compound. These alloys are more advantageously used with rare earth oxides such as ceria and lantana that act as promoters as described above. Such a catalyst 10 is less susceptible to poisoning (lead poisoning, phosphorus poisoning, sulfur poisoning) and also has a small thermal deterioration, so that it has excellent durability. It should be noted that, other than the alloy based on the combination of the above elements, a compound (oxide, nitride or carbide) based on a combination with another element may be used.

Incidentally, binary alloys include Pt / P
d, Pt / Rh, Pt / Ni, Pt / Co, Pt / M
o, Pt / W, Pt / Ce, Pt / Cu, Pt / V, P
t / Fe, Pt / Au, Pt / Ag, Pd / Rh, Pd
/ Ni, Pd / Co, Pd / Mo, Pd / W, Pd / C
e, Pd / Cu, Pd / V, Pd / Fe, Pd / Au,
Pd / Ag, Rh / Ni, Rh / Co, Rh / Mo, R
h / W, Rh / Ce, Rh / Cu, Rh / V, Rh / F
e, Rh / Au, Rh / Ag, Ni / Co, Ni / M
o, Ni / W, Ni / Ce, Ni / Cu, Ni / V, N
i / Fe, Ni / Au, Ni / Ag, Co / Mo, Co
/ W, Co / Ce, Co / Cu, Co / V, Co / F
e, Co / Au, Co / Ag, Mo / W, Mo / Ce,
Mo / Cu, Mo / V, Mo / Fe, Mo / Au, Mo
/ Ag, W / Ce, W / Cu, W / V, W / Fe, W /
Au, W / Ag, Ce / Cu, Ce / V, Ce / Fe,
Ce / Au, Ce / Ag, Cu / V, Cu / Fe, Cu
/ Au, Cu / Ag, V / Fe, V / Au, V / Ag,
There are Fe / Au, Fe / Ag and Au / Ag.

Further, as a ternary alloy, Pt / Pd /
Rh, Pt / Pd / Ni, Pt / Pd / Co, Pt / P
d / Mo, Pt / Pd / W, Pt / Pd / Ce, Pt /
Pd / Cu, Pt / Pd / V, Pt / Pd / Fe, Pt
/ Pd / Au, Pt / Pd / Ag, Pt / Rh / Ni,
Pt / Rh / Co, Pt / Rh / Mo, Pt / Rh /
W, Pt / Rh / Ce, Pt / Rh / Cu, Pt / Rh
/ V, Pt / Rh / Fe, Pt / Rh / Au, Pt / R
h / Ag, Pt / Ni / Co, Pt / Ni / Mo, Pt
/ Ni / W, Pt / Ni / Ce, Pt / Ni / Cu, P
t / Ni / V, Pt / Ni / Fe, Pt / Ni / Au,
Pt / Ni / Ag, Pt / Co / Mo, Pt / Co /
W, Pt / Co / Ce, Pt / Co / Cu, Pt / Co
/ V, Pt / Co / Fe, Pt / Co / Au, Pt / C
o / Ag, Pt / Mo / W, Pt / Mo / Ce, Pt /
Mo / Cu, Pt / Mo / V, Pt / Mo / Fe, Pt
/ Mo / Au, Pt / Mo / Ag, Pt / W / Ce, P
t / W / Cu, Pt / W / V, Pt / W / Fe, Pt /
W / Au, Pt / W / Ag, Pt / Ce / Cu, Pt /
Ce / V, Pt / Ce / Fe, Pt / Ce / Au, Pt
/ Ce / Ag, Pt / Cu / V, Pt / Cu / Fe, P
t / Cu / Au, Pt / Cu / Ag, Pt / V / Fe,
Pt / V / Au, Pt / V / Ag, Pt / Fe / Au,
There are Pt / Fe / Ag and Pt / Au / Ag.

Various methods are conceivable for supporting these catalytically active components on the alumina thin film 3. Methods that are advantageously applicable to the present embodiment include impregnation methods such as an evaporation to dryness method and an equilibrium adsorption method. The incipient wetness method or the spray method can be applied. Above all, the incipient wetness method is advantageous. According to this method, an aqueous solution containing a predetermined amount of a catalytically active component is dripped little by little toward a ceramic carrier 15, and when the surface of the carrier becomes uniformly and slightly wet (incipient), the catalytically active component is dropped. Is to stop impregnating into the pores of the ceramic carrier 15 and then drying and firing. That is, it is carried out by dropping the solution containing the catalytically active component on the surface of the ceramic carrier 15 using a burette or a syringe. The amount of the catalytically active component carried is determined by adjusting the concentration of the solution.

Next, a method for producing the catalyst 10 will be described. The feature of the method for producing the catalyst 10 according to the present embodiment is as follows.
An object of the present invention is to form an alumina thin film 3 containing a rare earth oxide on the uneven surface of the zirconium phosphate-containing ceramic carrier 15 by a sol-gel method. In particular, zirconium phosphate particles 4 forming cell walls 12 by immersion in a solution
A rare earth oxide-containing alumina thin film 3
Are individually coated. After the calcination, a hydrothermal treatment step is performed to form an alumina thin film (supporting film) exhibiting a flocking structure in which the micro cross-sectional structure of the alumina thin film 3 is made up of small fibers of alumina in which ceria or the like is dispersed. 3) and then immobilize (support) by adsorbing a predetermined amount of catalytically active component on the surface of the alumina thin film 3.
It is in the point to let.

The following steps ((1) ceramic carrier 15)
And (2) loading of a catalytically active component). (1) Coating of alumina thin film 3 on zirconium phosphate-containing ceramic carrier 15 a. Pretreatment Step In this step, a heating and oxidizing treatment is performed on each surface of the zirconium phosphate particles 4 so as to provide an amount of zirconium phosphate necessary to promote chemical bonding with alumina. . b. Solution Impregnation Step In this step, a solution of a metal compound containing aluminum and a rare earth element, for example, a mixed aqueous solution of aluminum nitrate and cerium nitrate is applied to the surface of each zirconium phosphate particle 4 constituting the cell wall 12. A treatment for covering the rare earth oxide-containing alumina thin film 3 is performed by impregnating the alumina thin film 3 using the sol-gel method.

In the mixed aqueous solution, for the solution of the aluminum-containing compound, as the starting metal compound, a metal inorganic compound and a metal organic compound are used. Al (NO ₃ ) ₃ , AlCl ₃ , Al
OCl, AlPO ₄ , Al ₂ (SO ₄ ) ₃ , Al ₂ O ₃ , Al
(OH) ₃ , Al or the like is used. In particular, Al
(NO ₃ ) ₃ and AlCl ₃ are preferable because they are easily dissolved in solvents such as alcohol and water and are easy to handle.

Examples of the metal organic compound include a metal alcohol
Oxide, metal acetylacetonate, metal carboxylate
There is a A specific example is Al (OCH_Three)_Three, Al
(OC _TwoH_Three)_Three, Al (iso-OC_ThreeH₇)_ThreeEtc.

On the other hand, of the mixed aqueous solution, the solution of the cerium-containing compound is Ce (NO ₃ ) ₃ , CeCl 2
₃ , Ce ₂ (SO ₄ ) ₃ , CeO ₂ , Ce (OH) ₃ , Ce ₂
(CO ₃ ) ₃ or the like is used.

As a solvent of the mixed solution, at least one selected from water, alcohol, diol, polyhydric alcohol, ethylene glycol, ethylene oxide, triethanolamine, xylene and the like is mixed and used.

In preparing a solution, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, and hydrofluoric acid may be added as a catalytically active component. Further, in order to improve the heat resistance of the alumina thin film 3, Ce, La, Pr, N
d, Ba, Ca, Li, K, Sr, Si, Zr, at least one element selected from compounds or compounds other than oxides (nitrates, chlorides, sulfates, hydroxides or carbonates)
May be added to the starting material.

In the present embodiment, examples of preferable metal compounds include Al (NO ₃ ) ₃ and Ce (NO ₃ ) _3, which are dissolved in a solvent at a relatively low temperature, and Easy to make. As an example of a preferable solvent, 1,3-butanediol is recommended. The first reason for the recommendation is that the viscosity is appropriate and a gel film having an appropriate thickness can be formed on the zirconium phosphate particles 4 in a gel state. The second reason is that this solvent is
Since metal alkoxide is formed in solution, oxygen, metal,
This is because it is easy to form a metal oxide polymer composed of oxygen bonds, that is, a precursor of a metal oxide gel.

The amount of Al (NO ₃ ) ₃ is 10 to 50
It is desirably mass%. If the amount is less than 10% by mass, the amount of alumina having a surface area enough to maintain the activity of the catalytically active component for a long period of time cannot be carried. .

The amount of Ce (NO ₃ ) ₃ is 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 that by making Al (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. When the temperature is lower than 50 ° C., the solubility of the solute is low. On the other hand, when the temperature is higher than 130 ° C., the reaction proceeds rapidly, leading to gelation, 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 cerium-containing metal compound (Al (N
As for O ₃ ) ₃ and Ce (NO ₃ ) ₃ ), in addition to the examples described above, in order to form a composite oxide or solid solution with zirconium, for example, ZrO (N
O ₃ ) ₂ or ZrO ₂ is used. It is preferable that the composite oxide is obtained by dissolving these in water or ethylene glycol to form a mixed solution, impregnating the mixed solution, and then drying and firing.

What is important in the present embodiment is that the solution of the metal compound prepared as described above spreads over all pores which are gaps between the zirconium phosphate particles 4 in the cell wall 12 and penetrates. It is to make it. For this purpose, for example, a method in which the ceramic carrier 15 is placed in a container and the metal compound solution is filled to deaerate the solution, or a method in which the solution is poured from one of the ceramic carriers 15 and deaerated 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. By using such an apparatus, the air in the pores in the cell wall 12 can be evacuated, and the solution of the metal compound can be evenly spread over the surface of each zirconium phosphate particle 4. c. Drying Step In this step, a volatile component such as NO ₂ is removed by evaporation, and the solution is gelled and fixed on the surface of the zirconium phosphate particles 4, and at the same time, an excess solution is removed.
Heating is performed at about 0 to 170 ° C. × 2 hours. If the heating temperature is lower than 120 ° C., the volatile components are difficult to evaporate, while if the heating temperature is higher than 170 ° C., the gelled film thickness becomes uneven. d. Preliminary firing step In this step, a preliminary firing process is performed to remove the residual components and form the amorphous alumina thin film 3. Specifically, it is desirable to heat to a temperature of 300 to 500C. The temperature of the provisional retardant is difficult to remove the low residual organics than 300 ° C., whereas higher than 500 ° C. is Al ₂ O ₃ crystallizes Subsequent hydrothermal treatment, can not be formed fibrils protruding boehmite Because. e. Hot Water Treatment Step In this step, in order to form the alumina thin film 3 having a structure unique to the above-described embodiment, a treatment of immersing the calcined ceramic carrier 15 in hot water is performed. Immediately after such hydrothermal treatment, the particles on the surface of the amorphous alumina thin film 3 are peptized and released into the solution in a sol state, and the boehmite particles generated by hydration are converted into small fibrous projections. Condensed to 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 zirconium phosphate particle 4 becomes small fibrous (needle-like particles) and stands.
It has a so-called flocking structure and a rough surface. Therefore, the alumina thin film 3 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 ceramic carrier 15, 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. To α
-It is considered that the transfer 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 it is lower than 50 ° C, amorphous alumina thin film 3
This is because hydration does not progress and no small fiber projection-like boehmite is 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. 1 for processing time
Desirably more than hours. If the time is shorter than 1 hour, the hydration of the amorphous alumina becomes insufficient. d. Main firing step In this step, the boehmite produced by the hydration is subjected to a process for forming a film to form alumina crystals. A preferable main firing temperature is 500 to 1000 ° C, and a preferable main firing temperature is 5 to 20. If the temperature is lower than 500 ° C., crystallization does not proceed. On the other hand, if the temperature is higher than 1000 ° C., sintering proceeds too much and the surface area tends to decrease.

(2) Carrying of catalytically active component a. Solution Adjusting Step The surface of the ceramic carrier 15 is coated with a rare earth oxide-containing alumina thin film (supporting film) 3 having a flocking structure as shown in FIG. Is supported. In this case, the supported amount of the catalytically active component is determined such that the aqueous solution containing Pt or the like is dropped and impregnated by the amount of water absorbed by the ceramic carrier 15 so that the surface slightly wets.

For example, the amount of water absorption held by the ceramic carrier 15 means that the measured value of the amount of water absorption of the dried carrier is 22.46.
mass%, the mass of the carrier is 110 g, and the volume is 0.1
If it has a volume of 63 l, this carrier is 24.79 /
Absorb 1 l of water.

Here, as a starting material of Pt, for example,
Dinitrodiammine platinum nitrate solution ([Pt (NH_Three)
_Two(NO_Two)_Two] HNO_Three, Pt concentration 4.53 mass%)
To use. To carry a predetermined amount of 1.7 g / l of Pt
Has a carrier of 1.7 (g / l) ^*0.163 (l) =
It is sufficient to carry 0.272 g of Pt.
Dinitrodiammine platinum nitrate solution (Pt concentration 4.53)
%). That is, dinitrodiammine platinum nitrate solution
Liquid (Pt concentration 4.53 mass%) / weight ratio of distilled water X
(%) Is X = 0.272 (Pt amount g) /24.7 (including
Water amount g) /4.53 (Pt concentration mass%)
4.8 mass%. b. Liquid impregnation process Predetermined amount of dinitrodiammine adjusted as described above
A platinum nitric acid aqueous solution is applied to both end surfaces of the ceramic carrier 15.
Drip with a pipette at regular intervals. For example, 40 to one side
80 drops are dropped at regular intervals to cover the ceramic carrier 15
Pt is uniformly dispersed and fixed on the surface of the alumina thin film 3. c. Drying and Firing Step The ceramic carrier 15 after the dripping of the aqueous solution is
At 2 ° C for about 2 hours to remove moisture
Then, move it into a desiccator and let it stand for 1 hour.
To determine the amount of adhesion. Then N_TwoIn the atmosphere, about
Baking under the condition of about 500 ° C. for 1 hour, and gold of Pt
Attribution.

The catalyst 10 according to the present embodiment is used for an application as an exhaust gas purifying filter. One of the applications is an oxidation catalyst for a gasoline engine, a three-way catalyst and a three-way catalyst as an example of a transparent honeycomb ceramic carrier 15. It is an oxidation catalyst for diesel engines. Another application is a diesel particulate filter in which honeycombs are alternately plugged in a checkered pattern.

The diesel particulate filter (hereinafter simply abbreviated as “DPF”) per se is capable of converting particulates (suspended particulate matter: PM) into the cell wall 1.
Although it has only the function of trapping in 2), by supporting a catalytically active component on it, it is possible to oxidize hydrocarbons and carbon monoxide in exhaust gas.

Further, even in an oxidizing atmosphere such as diesel exhaust gas, NOx can be reduced by carrying a NOx selective reduction catalyst component or an occlusion catalyst component capable of reducing NOx. Note that the particulates collected in the DPF cause an increase in the pressure loss of the DPF together with the accumulation, and therefore it is usually necessary to remove and regenerate the particulate by a combustion treatment or the like. The temperature at which combustion of soot (carbon), which is the main component of particulates contained in ordinary diesel exhaust gas, starts is about 550 to 630 ° C. In this respect, when the catalytically active component is carried on the DPF, the combustion reaction path of the soot changes, and the energy barrier can be reduced. As a result, the combustion temperature can be significantly reduced to 300 to 400 ° C., the energy required for regeneration can be reduced, and a DPF system with high regeneration efficiency can be constructed in combination with the above-mentioned effect of ceria.

As described above, it can be said that the catalyst 10 according to the present embodiment is preferably applied to a diesel exhaust gas treatment system, but the following functions can be expected. A. Function as oxidation catalyst for diesel exhaust gas (1) Exhaust gas purification function: THC (total hydrocarbons), CO
(2) Function that does not hinder engine operation: pressure loss Function as a diesel particulate filter with catalyst (1) Exhaust gas purification function: Soot combustion temperature, THC, C
O oxidation (2) Function that does not hinder engine operation: pressure loss

[0098]

EXAMPLE (Example 1) This example was performed to confirm the operation and effect of the ceria-containing alumina thin film 3 formed on the surface of the ceramic carrier 15. Ceramic carrier 15 manufactured under the conditions shown in Table 2
(Example 1, Comparative Example 1 and Comparative Example 2) were attached to a particulate filter (DPF) in an exhaust gas purification device for a diesel vehicle, and a purification test was performed. 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 are shown in FIGS. 6, 7 and 8.

[0099]

[Table 2] (A) As shown in Table 2, before particulate matter (suspended particulate matter: PM) is accumulated, Example 1 shows almost the same pressure loss characteristics as when there is no alumina thin film 3;
Even after the accumulation, it was found that the pressure loss when the same gas was circulated was remarkably small as compared with Comparative Examples 1 and 2.

(B) As shown in FIG. 7, it can be seen that, in comparison with Comparative Example 1, Example 1 exhibited a smaller decrease in alumina specific surface area when heat-treated at the same temperature, and was excellent in heat resistance. Was.

(C) Further, as shown in Table 2, it was found that the cleaning resistance of Example 1 was remarkably superior to Comparative Examples 1 and 2. (D) FIG. 15 shows the regeneration rate (the amount of C removed from the re-filter / the amount of C attached to the filter before regeneration). In the case of the alumina thin film 3 containing ceria, as much as 45% of the carbon was removed, whereas in the case of the wash coat alumina uniform film, only 20% was removed.

(Example 2) This example shows the results of tests on various characteristics when platinum (Pt) was loaded on a ceramic carrier 15 as a catalytically active component in a diesel particulate filter (DPF). is there. Table 3 shows the implementation conditions and characteristics. The results are shown in FIGS. 8, 9, and 10.

In this embodiment, the ceramic carrier 15
Has an alumina-supported film (8 g / l) 3 on the surface of the zirconium phosphate particles 4. In the reference example, there is no supporting film on the surface of the ceramic carrier 15. In the comparative example, an alumina uniform film was formed on the surface of the ceramic carrier 15 by wash coating.

[0104]

[Table 3] (1) Pressure loss characteristics: As shown in FIG. 8, when comparing the example, the reference example, and the comparative example, the present example shows almost the same pressure loss characteristics as the reference example having no supporting membrane, A remarkable effect is recognized as compared with the comparative example.

(2) Heat resistance: As shown in FIGS. 9 (a) and 9 (b), the change in the specific surface area of the alumina thin film 3 when heated to 1200 ° C. was obtained for the example and the comparative example.
Comparing the transition of the equilibrium temperature when heated to ° C., it can be seen that the effect of this embodiment is remarkable.

(3) Soot Combustion Characteristics: The ability of the catalyst 10 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 apparatus, a catalyst (DPF) 10 is inserted and installed in the exhaust pipe, 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, when the exhaust temperature is increased by any method, a point (equilibrium temperature) where the soot deposition rate and the soot oxidation reaction rate equilibrate at a certain temperature appears, and the pressure (equilibrium pressure) ) Can be measured. It can be said that the lower the equilibrium temperature and equilibrium pressure are, the better the catalyst 10 is.

In this test, as a method for increasing the exhaust gas temperature, a diesel engine and a DPF were used.
An electric heater was inserted between them. in this way,
Since the engine speed and load can be kept constant, 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. The test conditions were as follows: diesel engine displacement 273 cc, rotation speed 12
Steady-state operation was performed at 50 rpm and a load of 3 Nm. The deposited filter was □ 34 × 150 mmL and 0.16 Litt.
er.

FIG. 10 shows the results of the above test. FIG.
Among them, the example of the ceramic carrier 15 not supporting the catalytically active component was used as a reference example. As can be seen from the figure, the filter temperature rises as the exhaust gas temperature rises.
An equilibrium point can be seen at about ° C. Comparing the present example with the comparative example, the equilibrium temperatures were slightly different at 400 ° C. and 410 ° C. respectively, but the equilibrium pressure at that time was 11 k
Pa and 9.2 kPa, which are almost 20% higher.

After aging in an oxidizing atmosphere at 850 ° C. for 20 hours, a similar test was performed. In this example, the equilibrium temperature and pressure hardly deteriorated. In this case, the state deteriorated to the same state as when no catalytically active component was supported. (4) THC, CO purification rate; This property is a general method for evaluating an oxidation catalyst. The relationship between the temperature of so-called THC (total hydrocarbon) purification to CO ₂ and water and the temperature of purification of CO to CO ₂ was investigated. It can be said that this characteristic is a catalyst system in which the conversion is higher than the low temperature. As a measurement method, using an engine and a filter,
The measurement was performed by 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, in this example, the purification temperature of both CO and THC was lowered by about 30 ° C. as compared with the comparative example, showing excellent performance. This is because, in the present embodiment, since the catalytically active component is uniformly dispersed in the zirconium phosphate particles 4 on the cell wall 12, the time when the exhaust gas passes through the cell wall 12 is compared with the time when the exhaust gas passes through the wash coat. Is clearly long, and it is considered that the chance of CO and THC adsorption to the active site of Pt has increased. From another viewpoint, since the catalytically active component is uniformly dispersed in the zirconium phosphate particles 4, the contact area of the exhaust gas with the catalyst coat layer 2 can be increased. Therefore, the oxidation of CO and HC in the exhaust gas can be promoted.

Next, in addition to the technical idea described in the claims, the technical idea grasped by the above-described embodiment will be described below. (1) A catalyst, wherein a catalyst coat layer comprising a catalytically active component, a co-catalyst, and a support material is formed on particles of a ceramic support containing a tetravalent metal acid-insoluble salt.

(2) A catalyst characterized in that a catalyst coat layer comprising a catalytically active component, a co-catalyst and a support material is formed on particles of a zirconium compound-containing ceramic carrier. (3) A catalyst comprising a catalyst coat layer comprising a catalytically active component, a co-catalyst, and a support material formed on particles of a tetravalent metal phosphate-containing ceramic carrier.

(4) Claims 1-8, (1)-
In any one of (3), the catalytically active component includes a noble metal element, an element of Group VIa of the periodic table, and a periodic table VIII.
A catalyst comprising an element selected from the group consisting of elements.

(5) In any one of the above (1) to (4), the co-catalyst is at least one selected from cerium (Ce), lanthanum (La), barium (Ba) and calcium (Ca). A catalyst comprising at least one element or a compound.

(6) The catalyst according to any one of (1) to (5), wherein the support material contains at least one selected from alumina, zirconia, titania and silica.

(7) Claims 1-8, (1)-
(6) The catalyst according to any one of (6), wherein the ceramic carrier has a honeycomb structure having a plurality of through holes defined by cell walls.

(8) Claims 1-8, (1)-
(7) The catalyst according to any one of (7), wherein both ends of the ceramic carrier are alternately plugged in a checkered pattern by a sealing body.

[0118]

As described in detail above, according to the present invention,
The pressure loss of the exhaust gas can be reduced, and the mechanical strength can be improved. Further, the collection efficiency of the particulates contained in the exhaust gas can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a catalyst carrier in one embodiment.

FIG. 2 is an enlarged perspective view showing a part of a catalyst carrier.

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

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

FIG. 5 is an enlarged schematic view showing a zirconium phosphate particle structure of a catalyst carrier.

6A is a graph showing a relationship between a pore diameter and a pressure loss, FIG. 6B is a graph showing a relationship between a porosity and a pressure loss,
(C) is a graph showing the relationship between the porosity and the bending strength of the ceramic carrier.

FIG. 7 is a comparative explanatory diagram 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 diagram 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 DPF.

FIG. 14 is a graph showing a specific softness of a regeneration (combustion) rate affecting the regeneration characteristics of the DPF.

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

FIG. 16 is a schematic diagram of a catalyst carrier in the prior art.

FIG. 17 is a conceptual diagram of a washcoat alumina layer.

[Explanation of symbols]

3 ... alumina thin film, 4 ... zirconium phosphate particles, 10
... catalyst, 15 ... ceramic carrier.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/10 F01N 3/24 E 3/24 3/28 301P 3/28 301 B01D 53/36 104B F-term (reference) 3G090 AA03 BA04 CB11 EA02 3G091 AA02 AA18 AB13 BA00 BA07 BA11 BA14 BA15 BA19 BA38 BA39 CA03 FB10 GA01 GA05 GA06 GA16 GA20 GA24 GB01W GB01X GB04W GB04X GB05W GB06W GB07W GB07X GB10X 4D048 AA06 AABAXA13A18A14A18A14A18A14A18A14A13A18A14A13A18A14A15 BA22Y BA44X BA44Y BB01 BB02 BB04 BB05 BB08 BB17 4G069 AA01 AA03 AA08 AA12 BA01A BA01B BA13A BA13B BB14A BB14B BC27A BC38A BC43B BC50A BC51A BC51B BD07A BD07B CA03 CA03 EA02 EB02 EA02 EB02 EB02 EB02 EB02

Claims (14)

[Claims] 1. A catalyst in which a catalytically active component is dispersed and supported on the surface of a ceramic support containing a tetravalent metal acid-insoluble salt, wherein the surface of the ceramic support is rare earth for each particle unit forming the support. A catalyst coated with a thin film of alumina containing an oxide, wherein the catalytically active component is carried on uneven surfaces of the alumina thin film containing a rare earth oxide. 2. A catalyst comprising a zirconium compound-containing ceramic carrier having a catalytically active component dispersedly supported on the surface thereof, wherein the surface of the ceramic carrier contains a rare earth oxide for each particle unit forming the carrier. A catalyst, characterized in that the catalyst active component is supported on the uneven surface of the rare earth oxide-containing alumina thin film. 3. A catalyst in which a catalytically active component is dispersed and supported on the surface of a phosphate-containing ceramic carrier of a tetravalent metal, wherein the ceramic carrier has a surface for each particle unit forming the carrier. A catalyst coated with a thin film of alumina containing a rare earth oxide, wherein the catalytically active component is carried on the uneven surface of the thin film of alumina containing a rare earth oxide. 4. The porous body, fiber molded body or pellet molded body, wherein the ceramic carrier containing a tetravalent metal acidic insoluble salt contains any one of zirconium phosphate, titanium phosphate, zirconium arsenate and titanium arsenate. The catalyst according to claim 1, wherein the catalyst is constituted by any of the following. 5. The rare earth oxide-containing alumina thin film covering the surface of each particle in the ceramic carrier has a micro cross section having a diameter of 2 to 50 mm and a length of 20 to 300 nm,
Claim ratio of the total length / diameter has an uneven surface made of flocked structure fibrils bristled having the shape of 5-100, the specific surface area of the surface is characterized by a 50 to 300 m ² / g 1 A catalyst according to any one of claims 1 to 4. 6. The alumina thin film containing the rare earth oxide, which covers the ceramic carrier, is coated on the carrier at a ratio of 0.1 to 15 mass% in terms of alumina amount, and is contained in the alumina thin film. The catalyst according to any one of claims 1 to 5, wherein the amount of the rare earth oxide is 10 to 80 mass% based on the alumina. 7. The catalyst according to claim 1, wherein at least a part of the rare earth oxide forms a composite oxide with zirconium. 8. The catalyst according to claim 7, wherein the composite oxide of the rare earth oxide and zirconium has a particle size of 1 to 30 nm. 9. The following steps (a) to (e) are carried out on the surface of each particle constituting the ceramic support containing a tetravalent metal acid-insoluble salt; (a) a solution impregnation step: the ceramic support is made of aluminum and rare earth oxides. (B) drying step: heating and drying the ceramic carrier, and (c) pre-baking step: sintering the ceramic carrier for 30 minutes.
Forming an amorphous alumina thin film by heating and baking at a temperature of 0 to 500 ° C. or more. (D) Heat treatment step: dipping the ceramic support in hot water at 100 ° C., followed by drying; Process: 500-120
A method for producing a catalyst, comprising forming a rare earth oxide-containing alumina thin film through a step of firing at 0 ° C., and then dispersing and supporting a catalytically active component on the uneven surface of the rare earth oxide-containing alumina thin film. . 10. The following steps (a) to (f) on the surface of each particle constituting the ceramic support containing a tetravalent metal acidic insoluble salt;
(B) solution impregnating step: dipping the ceramic carrier in a solution of a metal compound containing aluminum and a rare earth oxide, (c) drying Step: heating and drying the ceramic support; (d) Pre-baking step: forming an amorphous alumina thin film by heating and firing the ceramic support to a temperature of 300 to 500 ° C. or higher; (e) Heat treatment step: the ceramic The carrier is immersed in hot water at 100 ° C. and then dried. (F) Main firing step: 500 to 1
Baking at 200 ° C., forming a rare earth oxide-containing alumina thin film through a process, and then dispersing and supporting a catalytically active component on the uneven surface of the rare earth oxide-containing alumina thin film. Production method. 11. The porous, fiber-formed or pellet-formed body containing the tetravalent metal acid-insoluble salt-containing ceramic carrier containing zirconium phosphate, titanium phosphate, zirconium arsenate and titanium arsenate. The method for producing a catalyst according to claim 9 or 10, wherein: 12. The alumina thin film containing the rare earth oxide, which covers the ceramic carrier, is coated on the carrier at a ratio of 0.1 to 15 mass% in terms of an amount of alumina, and is contained in the alumina thin film. The method for producing a catalyst according to any one of claims 9 to 11, wherein the amount of the rare earth oxide is 10 to 80 mass% with respect to the alumina. 13. The catalyst according to claim 9, wherein at least a part of the rare earth oxide forms a composite oxide with zirconium. Method. 14. The 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.