JP7340954B2 - Exhaust gas purification device and its manufacturing method - Google Patents

Description

The present invention relates to an exhaust gas purification device and a manufacturing method thereof.

Generally, in an exhaust gas purification device, a catalyst layer is formed on a honeycomb base material made of cordierite or the like. The catalyst layer includes noble metal catalyst particles, carrier particles supporting the noble metal catalyst particles, and promoter particles. It is known to use ceria-zirconia composite oxide having oxygen storage capacity (OSC) as one of the co-catalyst particles.

In recent years, consideration has been given to using ceria-zirconia composite oxide particles as co-catalyst particles not in the catalyst layer but as one of the constituent materials of the honeycomb base material. For example, Patent Document 1 discloses an exhaust gas purification device in which a honeycomb base material contains ceria-zirconia composite oxide particles. This exhaust gas purification device does not have a catalyst layer, and noble metal catalyst particles are directly attached to the honeycomb base material by impregnating the honeycomb base material with a solution containing the noble metal. Since such an exhaust gas purification device does not have a catalyst layer, its heat capacity is small, and the temperature of the honeycomb base material can be easily increased and high warm-up performance can be obtained.

Such a honeycomb base material and an exhaust gas purification device are also disclosed in Patent Documents 2 and 3.

Incidentally, as a coating method for forming a catalyst layer on a honeycomb base material made of general cordierite or the like, methods such as those described in Patent Documents 4 and 5 are known.

Japanese Patent Application Publication No. 2015-85241 Japanese Patent Application Publication No. 2015-77543 JP2016-34781A Japanese Patent Application Publication No. 2008-302304 International Publication No. 2010/114132

An object of the present invention is to provide an exhaust gas purification device that has high exhaust gas purification performance and uses a honeycomb base material containing ceria-zirconia composite oxide particles as one of the constituent materials.

The present inventors have discovered that the above problems can be solved by the present invention having the following aspects.
《Aspect 1》
An exhaust gas purification device comprising a honeycomb base material having a plurality of exhaust gas flow paths separated by a porous wall, and one or more catalytic noble metals supported on the honeycomb base material,
The honeycomb base material includes ceria-zirconia composite oxide particles as one type of constituent material,
the catalytic noble metal is selected from the group consisting of platinum, palladium, and rhodium, and the honeycomb substrate comprises:
The 50% by mass support depth of the noble metal for the specific noble metal that is one of the one or more catalytic noble metals is equal to the distance from the surface of the porous wall to the center of the inside of the porous wall. having a precious metal enriched surface area of less than 50%;
The 50% by mass supported noble metal depth is defined as the depth at which 50% by mass of the specific noble metal is supported, based on the amount of the specific noble metal supported from the surface of the porous wall to the center of the inside of the porous wall. The depth of
Exhaust gas purification equipment.
《Aspect 2》
The exhaust gas purification device according to aspect 1, wherein the specific noble metal is platinum or palladium.
《Aspect 3》
The specific precious metal is platinum or palladium,
the catalytic noble metal includes rhodium;
The exhaust gas purification device according to aspect 2.
《Aspect 4》
The honeycomb base material is composed of an inlet side part that accounts for 60% or less of the total length of the honeycomb base material from the inlet side of the exhaust gas flow path, and the other body part, and the noble metal enriched surface The exhaust gas purification device according to any one of aspects 1 to 3, wherein the exhaust gas purification device is present at least in the main body portion.
《Aspect 5》
The exhaust gas purification device according to aspect 4, wherein the length of the inlet side portion constituting the honeycomb base material is 10% or more of the total length of the honeycomb base material.
《Aspect 6》
The honeycomb base material is composed of an inlet side part that is 30 mm or less from the inlet side of the exhaust gas flow path and the other main body part, and the noble metal enriched surface part is present at least in the main body part. The exhaust gas purification device according to any one of aspects 1 to 5, wherein
《Aspect 7》
The exhaust gas purification device according to aspect 6, wherein the length of the inlet side portion constituting the honeycomb base material is 10 mm or more.
《Aspect 8》
According to any one of aspects 4 to 7, the amount of the specific noble metal supported on the inlet side portion of the honeycomb base material is greater than the amount of the specific noble metal supported on the main body portion. Exhaust gas purification equipment.
《Aspect 9》
Any one of aspects 4 to 8, wherein a 50% by mass support depth of the specific noble metal on the inlet side of the honeycomb base material is greater than a 50% by mass support depth of the specific noble metal in the main body. The exhaust gas purification device according to item 1.
《Aspect 10》
The exhaust gas purification device according to any one of aspects 1 to 9, wherein the honeycomb base material has a porosity of 30 to 70%.
《Aspect 11》
The exhaust gas purification device according to any one of aspects 1 to 10, wherein at least a portion of the exhaust gas flow path does not have a catalyst layer.
《Aspect 12》
A method for manufacturing an exhaust gas purification device, including at least the following (a) to (c):
(a) providing a solution containing one or more catalytic noble metal salts and a thickener from one open side of a honeycomb substrate having a plurality of exhaust gas channels separated by porous walls; wherein the solution has a viscosity of 10 to 400 mPa at a shear rate of 380 s ⁻¹ and the catalytic noble metal is selected from the group consisting of platinum, palladium, and rhodium;
(b) suctioning the provided solution from an opening side of the honeycomb substrate opposite to the side to which the solution was provided and/or an opening side of the honeycomb substrate to which the solution was provided; and (c) drying and/or firing the honeycomb substrate.
《Aspect 13》
The method according to aspect 12, further comprising (d):
(d) After immersing the honeycomb base material in a solution containing the salt of the catalytic noble metal so as to include the inlet side part of the exhaust gas flow path of the honeycomb base material within 30 mm or less of the total length thereof, the honeycomb base material drying and/or calcining, thereby increasing the amount of the catalytic noble metal supported on the inlet side portion than the amount of the catalytic noble metal supported on the main body portion other than the inlet side portion.

FIG. 1(a) is a perspective view schematically showing one embodiment of the exhaust gas purification device of the present invention. FIG. 1(b) is a side sectional view schematically showing one embodiment of the exhaust gas purification device of the present invention. FIG. 2 is an enlarged view schematically showing the porous wall of the honeycomb base material of the exhaust gas purification device of the present invention.

《Exhaust gas purification device》
The exhaust gas purification device of the present invention includes a honeycomb base material having a plurality of exhaust gas flow paths separated by a porous wall, and one or more catalytic noble metals supported on the honeycomb base material.

The catalytic noble metal in the exhaust gas purification device of the present invention may be a platinum group element, specifically, for example, one or more selected from the group consisting of platinum, palladium, and rhodium. The catalytic noble metal in the present invention may be a noble metal containing platinum and/or palladium, may be a noble metal containing platinum or palladium, may be a noble metal containing platinum and/or palladium, and rhodium, particularly platinum. Alternatively, it may be a noble metal containing palladium and rhodium.

The honeycomb base material in the exhaust gas purification device of the present invention is
A porous material containing ceria-zirconia composite oxide particles as one of the constituent materials and having a supporting depth of 50% by mass of a specific noble metal that is one of one or more catalytic noble metals. The noble metal enriched surface area is less than 50% of the distance from the surface of the wall to the center of the interior of the porous wall.

The present inventors were considering supporting noble metal catalyst particles on a honeycomb base material containing ceria-zirconia composite oxide particles as one of the constituent materials, and found that the viscosity of the solution containing the catalyst noble metal salt was adjusted. It was discovered that by coating the honeycomb substrate with catalytic metal particles, the depth from the substrate surface to which these catalytic precious metal particles are supported changes. On the other hand, the present inventors investigated and found that in the method described in Patent Document 1, for example, in the method of supporting palladium on a honeycomb base material by impregnating the honeycomb base material with a solution of palladium salt, the honeycomb base material It was found that palladium was evenly supported even inside the base material.

Therefore, by adjusting the viscosity of a solution containing salts of catalytic precious metals, the present inventors supported a high concentration of catalytic noble metals near the surface of the exhaust gas flow path of the base material. We found that it is possible to improve This is considered to be because the catalytic noble metal is present at a high concentration on the surface of the exhaust gas flow path, which increases the probability of contact between the exhaust gas and the catalytic noble metal.

The present invention is characterized in that the honeycomb substrate has a specific noble metal, which is one of one or more catalytic noble metals, supported at a depth of 50% by mass from the surface of the porous wall to the inside of the porous wall. The requirement is that the noble metal-enriched surface area is less than 50% of the distance to the center of the metal.

In this specification, the "precious metal 50% by mass supported depth" refers to the amount of a specific noble metal supported from the surface of the porous wall to the center of the interior of the porous wall at an arbitrary position. This is the depth at which 50% by mass of the precious metal is supported. As shown in FIG. 2, there is a support depth of 50% by mass of noble metal between the surface of the porous wall and the center of the wall. When the specific noble metal is supported at a completely uniform concentration in the depth direction of the porous wall, the 50 mass% noble metal supported depth is the intermediate position between the surface of the porous wall and the center of the wall. depth. The fact that the 50 mass % noble metal support depth is less than 50% of the distance from the wall surface to the center of the wall (in other words, less than 25% of the wall thickness) means that This means that more specific precious metals are supported.

In the noble metal enriched surface portion, the depth of supporting 50% by mass of the specific noble metal is less than 50%, 46% or less, 40% or less, 35% of the distance from the surface of the porous wall to the center of the interior of the porous wall. % or less, 30% or less, or 25% or less. Expressing these values on the basis of the thickness of the porous wall, the depth at which 50% by mass of the specific precious metal is supported in the noble metal enriched surface area is less than 25% and 23% or less of the thickness of the porous wall. , 20% or less, 17.5% or less, 15% or less, or 12.5% or less. Specifically, in the noble metal enriched surface area, the depth of supporting 50% by mass of the specific noble metal is, on average, within 25 μm, within 22.5 μm, within 20 μm, within 17.5 μm, within 15 μm, and 12.5 μm. or within 10 μm.

In the noble metal enriched surface portion, the depth of supporting 50% by mass of a specific noble metal can be an average value at three or more positions.

The noble metal enriched surface portion may be present throughout the exhaust gas flow path of the honeycomb base material, or may be present in a portion thereof. For example, the precious metal enriched surface portion may extend over 1/10 or more, 1/5 or more, 1/3 or more, 1/2 or more, or 2/3 or more of the total length of the exhaust gas flow path of the honeycomb base material. , 2/3 or less, 1/2 or less, 1/3 or less, 1/5 or less, or 1/10 or less.

If the part of the honeycomb base material up to a predetermined length from the inlet side of the exhaust gas flow path is defined as the inlet side part of the honeycomb base material, and the other part is defined as the main body part of the honeycomb base material, the precious metal enriched surface part is preferably present at least in the main body. The length of the inlet side of the honeycomb base material may be 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, or 60% or more of the total length of the exhaust gas flow path. It may be 60% or less, 50% or less, 40% or less, 30% or less, 20% or less, or 10% or less of the total length of. The length of the inlet side of the honeycomb substrate may be, for example, 10 mm or more, and may be, for example, 30 mm or less. When the total length of the gas flow path is 80 mm, the length of the inlet side of 10 mm corresponds to 12.5% of the total length of the gas flow path.The length of the inlet side of 30 mm corresponds to 37.5% of the total length of the gas flow path. .

The specific noble metal in the noble metal enriched surface portion may be one selected from the group consisting of platinum, palladium, and rhodium, and may be platinum or palladium.

Further, the present inventors have found that the exhaust gas purification device of the present invention becomes more advantageous by supporting a large amount of catalytic noble metal on the exhaust gas inlet side. When a large amount of catalytic noble metal was supported on the exhaust gas inlet side, the warm-up performance of the exhaust gas purification device of the present invention could be greatly improved. This is because while the exhaust gas purification device is in use, the temperature rises from the inlet side, so the presence of a large amount of catalytic precious metals on the inlet side causes the exhaust gas and catalyst to remain at a relatively high temperature even in the early stages of operation. It is thought that it can react with precious metals and purify exhaust gas more effectively.

Therefore, it is preferable that a large amount of the catalytic noble metal is supported on the inlet side of the honeycomb substrate, and the amount of the catalytic noble metal supported on the inlet side is greater than the amount of the catalytic noble metal supported on the main body. A large number is preferable.

For example, the amount of catalytic precious metal supported on the inlet side is 1.1 times or more, 1.3 times or more, 1.5 times or more, 2.0 times the amount of catalytic precious metal supported on the main body. It may be 10 times or more, 3.0 times or more, or 5.0 times or more, or 10 times or less, 5.0 times or less, 3.0 times or less, or 2.0 times or less.

Furthermore, it has been found that it is particularly effective to support the catalytic noble metal at a deeper position on the inlet side of the exhaust gas purification device than in the main body. This is because the exhaust gas flowing through the inlet side of the exhaust gas purification device contains more exhaust gas components that should be purified, whereas the exhaust gas flowing through the main body contains fewer exhaust gas components that should be purified. Therefore, at the inlet side, the catalyst precious metal is supported even inside the porous wall of the honeycomb base material to thoroughly purify the exhaust gas, and the remaining exhaust gas is purified at least on the precious metal enriched surface area in the main body. This is because purifying the precious metal is advantageous from the viewpoint of precious metal distribution.

Therefore, the depth of supporting 50% by mass of precious metal on the inlet side is preferably larger than the depth of supporting 50% by mass of precious metal on the main body. It may be 1.05 times, 1.1 times, 1.2 times, 1.3 times, 1.5 times, or 2.0 times, and not more than 3.0 times, 2. It may be 5 times or less, 2.0 times or less, or 1.5 times or less.

The catalytic precious metal supported at a deeper position than the main body at the inlet side of the exhaust gas purification device may be one selected from the group consisting of platinum, palladium, and rhodium, and may be platinum or palladium. . The catalytic precious metal supported at a deeper position than the main body at the inlet side of the exhaust gas purification device may be of the same kind as the specific precious metal on the precious metal-enriched surface of the base material, or may be of a different kind. You can leave it there.

However, from the viewpoint of thoroughly purifying the exhaust gas by supporting the catalytic noble metal inside the porous wall of the honeycomb base material at the inlet side, and then purifying the remaining exhaust gas at the precious metal enriched surface, it is difficult to purify the exhaust gas. The catalytic noble metal supported deeper than the main body on the inlet side of the device may be of the same type as the specific noble metal on the noble metal enriched surface.

therefore,
The amount of the specific noble metal supported on the inlet side of the honeycomb base material may be greater than the amount of the specific noble metal supported on the main body, and the amount of the specific noble metal supported on the inlet side of the honeycomb base material is The 50% by mass support depth may be greater than the 50% by mass support depth of the noble metal for the specific noble metal of the main body.

FIG. 1(a) is a perspective view schematically showing one embodiment of the exhaust gas purification device of the present invention, and FIG. 1(b) is a side view schematically showing one embodiment of the exhaust gas purification device of the present invention. FIG. The exhaust gas purification device 10 has a honeycomb base material having a plurality of exhaust gas passages 2 separated by a porous wall 1 of the honeycomb base material. For example, 1/4 or less of the total length from the inlet side of the exhaust gas flow path 2 of the honeycomb base material can be used as the inlet side part a of the honeycomb base material, and the other part can be used as the main body part b of the honeycomb base material. , the amount of the catalytic noble metal, such as platinum and/or palladium, in particular platinum or palladium, supported on the inlet side a is greater than the amount of the catalytic noble metal, such as platinum and/or palladium, in particular platinum or palladium, supported on the body part b. It is preferable that the amount is greater than the amount of . An enlarged portion of the broken line circle in FIG. 1(b) is shown in FIG.

<Honeycomb base material>
The honeycomb base material used in the exhaust gas purification device of the present invention contains ceria-zirconia composite oxide particles as one of its constituent materials. That is, the honeycomb base material is different from the currently used honeycomb base material made of cordierite, and is, for example, a honeycomb base material as disclosed in Patent Documents 1 to 3.

For example, the honeycomb base material may contain ceria-zirconia composite oxide particles in an amount of 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, or 70% by mass or more. It may be contained in an amount of 95% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less. For example, the honeycomb base material may contain ceria-zirconia composite oxide particles in an amount of 30% by mass to 95% by mass, or 50% by mass to 90% by mass. Ceria-zirconia composite oxide particles are particles used as an oxygen storage material in the field of exhaust gas purification devices, and may be particles of a solid solution of ceria and zirconia. This solid solution may further contain a rare earth element such as lanthanum (La) or yttrium (Y).

The honeycomb substrate may also contain carrier particles, such as alumina particles, such as those used in the prior art as carriers for noble metal catalyst particles, as well as inorganic binders such as alumina, zirconia, yttria, titania, and silica. May contain. Furthermore, the honeycomb base material may include alumina particles of the θ layer as described in Patent Document 1 and/or tungsten composite oxide particles as described in Patent Document 2.

The honeycomb substrate has a plurality of exhaust gas channels separated by porous walls. The exhaust gas flow path has a plurality of cells arranged in a lattice shape with each flow path lined up linearly and in parallel, and these plurality of cells are open to both the inlet side and the outlet side. A so-called straight flow type honeycomb base material may also be used. In addition, it has a plurality of cells partitioned by porous partition walls, and these cells include an inlet side cell whose inlet side is open and an outlet side sealed, and an outlet side cell which is open and an inlet side sealed. It may be a so-called wall flow type honeycomb base material composed of outlet side cells.

The number of exhaust gas passages is called the cell number and is expressed in the number of exhaust gas passages per square inch. The number of cells of the honeycomb base material is 30 cells/inch ² or more, 50 cells/inch ² or more, 100 cells/inch ² or more, 200 cells/inch ² or more, 300 cells/inch ² or more, 400 cells/inch ² or more, 600 cells/inch ² or more, or 800 cells/inch ² or more, 1200 cells/inch ² or less, 1000 cells/inch ² or less, 800 cells/inch ² or less, 500 cells/inch ² or less, or 300 cells/inch 2 or less Cells/inch may be ² or less. For example, the number of cells of the honeycomb base material may be 100 cells/inch ² or more and 1200 cells/inch ² or less, or 200 cells/inch ² or more and 1000 cells/inch ² or less.

The length of the exhaust gas flow path of the honeycomb base material or the length of the honeycomb base material may be 50 mm or more, 60 mm or more, 80 mm or more, 100 mm or more, 120 mm or more, or 150 mm or more, and 300 mm or less, 250 mm or less, or 200 mm. Below, it may be 150 mm or less, or 120 mm or less. For example, the length of the exhaust gas flow path of the honeycomb base material or the length of the honeycomb base material may be 50 mm or more and 300 mm or less, or 60 mm or more and 200 mm or less.

The cross-sectional area of the honeycomb substrate may be 60 cm ² or more, 80 cm ² or more, 100 cm ² or more, 120 cm ² or more, or 150 cm ^{2 or} more, and 300 cm ² or less, 250 cm ² or less, 200 cm ² or less, 150 cm ^{2 or} less, Or it may be 120 cm ² or less. For example, the cross-sectional area of the honeycomb base material may be 60 cm ² or more and 300 cm ² or less, or 100 cm ² or more and 250 cm ^{2 or} less.

The capacity of the honeycomb base material may be 500 cc or more, 600 cc or more, 800 cc or more, 1000 cc or more, or 1500 cc or more, and may be 3000 cc or less, 2500 cc or less, 2000 cc or less, 1500 cc or less, or 1200 cc or less. For example, the capacity of the honeycomb base material may be 500 cc or more and 3000 cc or less, or 600 cc or more and 1500 cc or less.

The thickness of the porous wall of the honeycomb base material is not particularly limited, but may be 50 μm or more, 70 μm or more, 80 μm or more, 100 μm or more, 120 μm or more, or 150 μm or more, and 300 μm or less, 200 μm or less, 150 μm or less, Alternatively, it may be 120 μm or less. For example, the thickness of the porous wall of the honeycomb base material may be 50 μm or more and 300 μm or less, or 70 μm or more and 150 μm or less.

The porosity of the honeycomb base material is not particularly limited, but may be, for example, 30% or more, 40% or more, 50% or more, or 60% or more, and 80% or less, 70% or less, or 60% or less. It's okay. The porosity can be determined from the ratio of the weight of the porous body to the theoretical solid weight based on the material of the porous body. For example, the porosity of the honeycomb base material may be 30% or more and 70% or less, or 40% or more and 60% or less.

The specific surface area of the honeycomb base material is not particularly limited, but may be, for example, 10 m ² /g or more, 20 m ² /g or more, or 30 m ^{2 /g or more, and 200 m 2 /} g or less, 100 m ² /g or less, Or it may be 50 m ² /g or less. The specific surface area can be determined from the BET flow method using Macsorb™ HM model-1230 (Mountech Co., Ltd.) using a nitrogen adsorption method. For example, the specific surface area of the honeycomb base material may be 10 m ² /g or more and 200 m ² /g or less, or 20 m ² /g or more and 100 m ² /g or less.

<Catalytic precious metal particles>
The catalytic noble metal in the exhaust gas purification device of the present invention may be, for example, one or more selected from the group consisting of platinum, palladium, and rhodium.

The exhaust gas purification device of the present invention may include at least platinum and/or palladium supported on a honeycomb substrate, for example, as catalyst noble metal particles. Platinum and/or palladium is added to the honeycomb base material, based on the capacity of the entire honeycomb base material, at least 0.10 g/L, at least 0.30 g/L, at least 0.50 g/L, at least 0.80 g/L, It may be supported at 1.00 g/L or more, 1.50 g/L or more, 2.00 g/L or more, or 3.00 g/L or more, and 6.00 g/L or less, 4.00 g/L or less, It may be supported at 3.00 g/L or less, 2.00 g/L or less, 1.50 g/L or less, 1.20 g/L or less, or 1.00 g/L or less. For example, platinum and/or palladium is supported in an amount of 0.30 g/L or more and 6.00 g/L or less, or 0.50 g/L or more and 3.00 g/L or less, based on the capacity of the entire honeycomb substrate. Good too.

Platinum and/or palladium is added to the inlet side of the honeycomb base material, based on the capacity of the inlet side, at least 0.80 g/L, at least 1.00 g/L, at least 1.50 g/L, and at 2.00 g/L. L or more, or 3.00 g/L or more may be supported, and 8.00 g/L or less, 6.00 g/L or less, 5.00 g/L or less, 4.00 g/L or less, or 3.00 g /L or less may be supported. For example, platinum and/or palladium is added to the inlet side of the honeycomb base material in a range of 1.00 g/L to 8.00 g/L, or 2.00 g/L to 5.00 g, based on the capacity of the inlet side. /L or less may be supported. Furthermore, platinum and/or palladium is added to the main body of the honeycomb base material, based on the capacity of the main body, at least 0.50 g/L, at least 0.30 g/L, at least 0.50 g/L, and at least 0.80 g/L. L or more, 1.00 g/L or more, 1.50 g/L or more, 2.00 g/L or more, or 3.00 g/L or more may be supported, and 6.00 g/L or less, 4.00 g/L It may be supported in an amount of L or less, 3.00 g/L or less, 2.00 g/L or less, 1.50 g/L or less, 1.20 g/L or less, or 1.00 g/L or less. For example, platinum and/or palladium may be added to the main body of the honeycomb base material from 0.30 g/L to 6.00 g/L, or from 0.50 g/L to 3.00 g/L, based on the capacity of the main body. It may be supported by:

The exhaust gas purification device of the present invention can further include rhodium as the catalytic noble metal particles. Rhodium is supported at 0.10 g/L or more, 0.30 g/L or more, 0.50 g/L or more, 0.80 g/L or more, or 1.00 g/L or more based on the capacity of the entire honeycomb base material. It may be supported at 1.50 g/L or less, 1.20 g/L or less, 1.00 g/L or less, 0.80 g/L or less, or 0.50 g/L or less. For example, rhodium may be supported in an amount of 0.10 g/L or more and 1.50 g/L or less, or 0.30 g/L or more and 1.00 g/L or less, based on the capacity of the entire honeycomb substrate.

<Catalyst layer>
It is preferable that at least a part of the exhaust gas purification device of the present invention does not have a catalyst layer, which is formed on a cordierite honeycomb substrate or the like in the prior art. Therefore, in the exhaust gas purification device of the present invention, a catalyst layer having a composition substantially different from that of the honeycomb base material is not present in at least a portion of the exhaust gas flow path of the honeycomb base material.

《Manufacturing method of exhaust gas purification device》
The method for manufacturing an exhaust gas purification device of the present invention includes providing a solution containing a catalytic precious metal salt and a thickener from one opening side of a honeycomb base material having a plurality of exhaust gas flow paths separated by a porous wall. suctioning the provided solution from the open side of the honeycomb substrate opposite to the side to which the solution was provided and/or pumping the provided solution from the open side of the honeycomb substrate to which the solution was provided; and drying and/or calcining the honeycomb substrate, wherein the solution has a viscosity of 10 to 400 mPa at a shear rate of 380 s ^-1 . The method for manufacturing an exhaust gas purification device of the present invention includes, for example, providing a solution containing a catalytic precious metal salt and a thickener from the inlet side of a honeycomb base material; and supplying the provided solution from the outlet side of the honeycomb base material. It may include suctioning and/or pumping from the inlet side of the honeycomb substrate; and drying and/or calcining the honeycomb substrate.

By adding a thickener to a solution containing a salt of a catalytic noble metal, the viscosity of the solution can be adjusted and the depth of supporting 50% by mass of the noble metal can be reduced, that is, the catalytic noble metal can be concentrated on the surface side of the porous wall. can be made into The viscosity of the solution at a shear rate of 380 s ^-1 was determined using a viscometer TV-33 type viscometer (manufactured by Toki Sangyo Co., Ltd.) at 25°C and the rotation speed was changed from 1 to 100 rpm to 1°34 When measured using a cone-shaped cone of '×R24, it may be 10 mPa or more, 50 mPa or more, or 100 mPa or more, and may be 400 mPa or less, 300 mPa or less, or 200 mPa or less. In addition, the viscosity of the solution at a shear rate of 4 s ^-1 is measured at room temperature using a viscometer TVE-30H (manufactured by Toki Sangyo Co., Ltd.) and is 100 mPa or more, 500 mPa or more, 1000 mPa or more, 3000 mPa or more, or 5000 mPa or more. or more, and may be 30,000 mPa or less, 10,000 mPa or less, 7,000 mPa or less, 5,000 mPa or less, or 3,000 mPa or less.

Among the catalytic noble metals, examples of salts of platinum and/or palladium include strong acid salts of platinum and/or palladium, particularly nitrates or sulfates of platinum and/or palladium. Further, when the solution contains a salt of rhodium, a similar salt can be used. Further, the solution does not need to contain carrier particles of inorganic oxides such as alumina, silica, and ceria-zirconia composite oxides, which have been used as carriers for catalytic noble metals in the prior art.

Examples of thickeners include water-soluble polymers such as hydroxyl ethyl cellulose, carboxymethyl cellulose, methyl cellulose, and polyvinyl alcohol.

For a method of applying a solution containing a catalytic precious metal salt and a thickener to a honeycomb substrate, reference can be made to Patent Document 4.

When drying the honeycomb base material, the drying temperature may be, for example, 50°C or higher, 100°C or higher, 150°C or higher, or 200°C or lower, or 150°C or lower. For example, the drying temperature may be 100°C or more and 200°C or less. The drying time may be 1 hour or more, 2 hours or more, or 5 hours or more, and may be 10 hours or less or 5 hours or less. For example, the drying time may be 1 hour or more and 10 hours or less. Further, when firing the honeycomb base material, the firing temperature may be, for example, 400°C or higher, 500°C or higher, 550°C or higher, or 600°C or higher, or 1000°C or lower, 800°C or lower, or 700°C. It may be the following. For example, the firing temperature may be 400°C or more and 1000°C or less, or 500°C or more and 800°C or less. The firing time may be 30 minutes or more, 1 hour or more, 2 hours or more, or 4 hours or more, and may be 12 hours or less, 10 hours or less, or 8 hours or less. For example, the firing time may be 30 minutes or more and 12 hours or less, or 1 hour or more and 8 hours or less.

The exhaust gas purification device obtained by the method for manufacturing an exhaust gas purification device of the present invention may be the exhaust gas purification device of the present invention described above. Further, for each configuration of the method for manufacturing an exhaust gas purification device of the present invention, each configuration described above regarding the exhaust gas purification device of the present invention can be referred to.

The method for manufacturing an exhaust gas purification device of the present invention includes: immersing a honeycomb base material in a solution containing a salt of a catalytic precious metal so as to include the inlet side portion of the honeycomb base material having a predetermined length from the inlet of the exhaust gas flow path; It may further include removing from the solution and drying and/or firing the honeycomb substrate. In this case, part or all of the inlet side may be immersed in the solution, or even a part of the main body other than the inlet side may be immersed in the solution.

By including this step, more catalytic noble metal can be supported on the inlet side of the honeycomb substrate than on the main body. Furthermore, since the honeycomb base material is immersed in a solution to support the catalytic noble metal, only the depth at which 50% by mass of the noble metal is supported on the inlet side can be increased. As a result, high warm-up performance can be provided to the resulting exhaust gas purification device, and precious metal distribution can be made more efficient. The solution used in this step may be the same as the solution used in the coating described above, but may not contain a thickener.

This step may be performed after the step of drying and/or firing the honeycomb base material, or may be performed before the step of drying and/or firing the honeycomb base material. When this step is performed after the step of drying and/or firing the honeycomb base material, the step of drying and/or firing the honeycomb base material as described above can be performed after this step.

The present invention will be explained in more detail with reference to the following examples, but the present invention is not limited thereto.

《Manufacturing example》
<Example 1>
The base material is a ceria-zirconia composite oxide with a capacity of 860 cc, a base length of 80 mm, a diameter of 117 mm, a cell count of 400 cells/inch ² , a wall thickness of 120 μm, and a ceria equivalent weight of 21% and a zirconia equivalent weight of 25% by weight. A ceria-zirconia-based (CZ-based) monolithic honeycomb base material was used. The cell shape was square. A coating solution was poured onto this honeycomb substrate by the method described in Patent Document 4, and unnecessary solution was blown away using a blower. Here, the coating solution contains palladium nitrate in an amount of 0.12 wt% in terms of palladium (Pd) and rhodium nitrate in an amount of 0.06 wt% in terms of rhodium (Rh), as mass per unit volume of the honeycomb base material in pure water. , and a thickener (hydroxyethylcellulose, Daicel Co., Ltd.), and using a viscometer TV33 type viscometer (manufactured by Toki Sangyo Co., Ltd.), the rotation speed was changed from 1 to 100 rpm at 25°C. The viscosity at a shear rate of 380 s ⁻¹ was 300 mPa, as measured using a conical plate type cone of 1°34'×R24. Thereafter, it was dried for 2 hours in a dryer at 120°C, and then fired for 2 hours in an electric furnace at 500°C. At that time, the amounts of palladium and rhodium supported on the substrate were 0.51 g/L and 0.24 g/L, respectively.

After that, in order to further support 1.1 g of palladium per honeycomb base material at a position up to 20 mm from the inlet side of the exhaust gas flow path of the honeycomb base material, the front side of the honeycomb base material was It was immersed in a palladium nitrate aqueous solution to absorb water and carry it. After that, the honeycomb base material was taken out from the solution, unnecessary solution was blown away using a blower, and then it was dried in a dryer at 120°C for 2 hours, and then fired for 2 hours in an electric furnace at 500°C. Ta. Thereby, the exhaust gas purification device of Example 1 was obtained.

<Example 2>
The same procedure as in Example 1 was carried out, except that 1.1 g/piece of palladium was further supported on the honeycomb substrate at a position up to 32 mm from the inlet side of the exhaust gas flow path. , the exhaust gas purification device of Example 2 was obtained.

<Example 3>
The exhaust gas purification device of Example 3 was obtained in the same manner as Example 1, except that the amount of thickener in the coating solution was increased to have a viscosity of 200 mPa at a shear rate of 380 s ^-1 .

<Comparative example 1>
As the base material, a cordierite-based (Co-based) monolith type honeycomb base material having a capacity of 875 cc, a diameter of 118 mm, 600 cells square, and a wall thickness of 3 mil was used. A lower layer slurry containing palladium nitrate, lanthanum oxide composite alumina, ceria-zirconia composite oxide, barium nitrate, and an alumina sol binder is prepared, and the lower layer slurry is poured into a honeycomb base material by the method described in Patent Document 4, A blower was used to blow away unnecessary slurry. Thereafter, it was dried in a dryer at 120°C for 2 hours, and then fired in an electric furnace at 500°C for 2 hours to form a lower layer on the honeycomb base material. This lower layer contains 0.7 g/L of palladium, 50 g/L of alumina, 50 g/L of ceria-zirconia composite oxide, and 5 g/L of barium sulfate as mass per unit volume of honeycomb base material. Ta.

Next, prepare an upper layer slurry containing rhodium nitrate, lanthanum oxide composite alumina, ceria-zirconia composite oxide, barium nitrate, and an alumina sol binder, and form the upper layer on top of the lower layer in the same manner as when forming the lower layer. Formed. This upper layer had 0.2 g/L of rhodium, 55 g/L of alumina, and 50 g/L of ceria-zirconia composite oxide as mass per unit volume of the honeycomb base material. As a result, an exhaust gas purification device of Comparative Example 1 was obtained.

<Comparative example 2>
Palladium and rhodium were supported on the honeycomb base material containing ceria-zirconia composite oxide as a constituent material used in Example 1 by the method described in Patent Document 1 and in the same weight as used in Example 1. Ta. Specifically, the honeycomb substrate was made to support palladium and rhodium by immersing the substrate in an aqueous solution in which rhodium nitrate and rhodium chloride were dispersed in required amounts and leaving it for a certain period of time.

"Test method"
<Palladium (Pd) 50% support depth>
Of the total amount of palladium existing in the depth direction from the surface of the wall of the base material to the center of the wall, the depth at which 50% by mass of noble metal was supported from the surface where 50% by mass of palladium was present was investigated. For example, in Table 1, in Example 1 with a wall thickness of 120 μm, the support depth of 50% by mass of noble metal is 20 μm, which means that 50% of palladium is supported within 20 μm from the wall surface. This means that the remaining 50% of palladium is supported in a range of more than 20 μm to 60 μm from the surface. Table 1 also shows the depth of supporting 50% by mass of noble metal with respect to the distance from the surface of the porous wall to the center of the porous wall (60 μm), and the depth of supporting 50% by mass of noble metal with respect to the thickness of the porous wall (120 μm). Indicated.

The supporting depth was analyzed by filling the exhaust gas purification catalyst with resin and cutting it, and measuring the porous wall using FE-EPMA (JXA-8530F, JEOL Ltd.). Specifically, by measuring the distribution of palladium with a field magnification of 400 times, a minimum beam diameter, an accelerating voltage of 20 kV, an irradiation current of 100 nA, and a collection time of 50 seconds, the number of pixels was set to 256 x 256. The supporting depth of 50% by mass of noble metal was determined.

<Warm-up characteristics and HC purification rate>
The exhaust gas purification device of each example was installed in the exhaust system of a V-type 8-cylinder engine, and exhaust gas in stoichiometric and lean atmospheres was repeatedly flowed for a certain period of time at a catalyst bed temperature of 950° C. for 50 hours.

After that, the exhaust gas purification devices were reinstalled into the exhaust systems of the in-line four-cylinder engines, and exhaust gas with an air-fuel ratio (A/F) of 14.4 and an exhaust gas mass flow rate Ga = 19 g/s was supplied to remove hydrocarbons (HC). ) The time to reach 50% purification rate (= warm-up characteristics (~500°C)) was evaluated.

In addition, exhaust gas was supplied at an air-fuel ratio (A/F) of 14.2 and an exhaust gas mass flow rate Ga of 24 g/s, and the hydrocarbon (HC) purification rate at a catalyst bed temperature of 500° C. was measured.

"result"
The results are shown in the table below:

1 Porous wall 2 Exhaust gas flow path a Inlet side b Main body 10 Exhaust gas purification device

Claims (13)

An exhaust gas purification device comprising a honeycomb base material having a plurality of exhaust gas flow paths separated by a porous wall, and one or more catalytic noble metals supported on the honeycomb base material,
The honeycomb base material includes ceria-zirconia composite oxide particles as one type of constituent material,
the catalytic noble metal is selected from the group consisting of platinum, palladium, and rhodium, and the honeycomb substrate comprises:
The 50% by mass support depth of the noble metal for the specific noble metal that is one of the one or more catalytic noble metals is equal to the distance from the surface of the porous wall to the center of the inside of the porous wall. having a precious metal enriched surface area of less than 50%;
The 50% by mass supported noble metal depth is defined as the depth at which 50% by mass of the specific noble metal is supported, based on the amount of the specific noble metal supported from the surface of the porous wall to the center of the inside of the porous wall. depth ,
The honeycomb base material is composed of an inlet side part that accounts for 60% or less of the total length of the honeycomb base material from the inlet side of the exhaust gas flow path, and the other body part, and the noble metal enriched surface is present at least in the main body,
A 50% by mass support depth of the specific noble metal on the inlet side of the honeycomb base material is greater than a 50% by mass support depth of the specific noble metal in the main body.
Exhaust gas purification equipment. The exhaust gas purification device according to claim 1, wherein the specific noble metal is platinum or palladium. The specific precious metal is platinum or palladium,
the catalytic noble metal includes rhodium;
The exhaust gas purification device according to claim 2. The exhaust gas purification according to any one of claims 1 to 3, wherein the 50% by mass support depth of the noble metal is 35% or less of the distance from the surface of the porous wall to the center inside the porous wall. Device. The exhaust gas purification device according to any one of claims 1 to 4 , wherein the length of the inlet side portion constituting the honeycomb base material is 10% or more of the total length of the honeycomb base material. The exhaust gas purification device according to any one of claims 1 to 5, wherein the honeycomb base material is composed of an inlet side part that is 30 mm or less from the inlet side of the exhaust gas flow path, and the other main body part. . The exhaust gas purification device according to claim 6, wherein the length of the inlet side portion constituting the honeycomb base material is 10 mm or more. According to any one of claims 1 to 7, the amount of the specific noble metal supported on the inlet side portion of the honeycomb base material is greater than the amount of the specific noble metal supported on the main body portion. exhaust gas purification equipment. The amount of the specific noble metal supported on the inlet side portion of the honeycomb base material is 1.5 times or more and 5.0 times or less the amount of the specific noble metal supported on the main body portion. 8. The exhaust gas purification device according to 8. The exhaust gas purification device according to any one of claims 1 to 9, wherein the honeycomb base material has a porosity of 30 to 70%. The exhaust gas purification device according to any one of claims 1 to 10, wherein at least a portion of the exhaust gas flow path does not have a catalyst layer. The method for manufacturing an exhaust gas purification device according to any one of claims 1 to 11 , comprising at least the following (a) to (c):
(a) providing a solution containing one or more catalytic noble metal salts and a thickener from one open side of a honeycomb substrate having a plurality of exhaust gas channels separated by porous walls; wherein the solution has a viscosity of 10 to 400 mPa at a shear rate of 380 s ⁻¹ and the catalytic noble metal is selected from the group consisting of platinum, palladium, and rhodium;
(b) suctioning the provided solution from an opening side of the honeycomb substrate opposite to the side to which the solution was provided and/or an opening side of the honeycomb substrate to which the solution was provided; and (c) drying and/or firing the honeycomb substrate. The method of claim 12, further comprising (d):
(d) After immersing the honeycomb base material in a solution containing the salt of the catalytic noble metal so as to include the inlet side part of the exhaust gas flow path of the honeycomb base material within 30 mm or less of the total length thereof, the honeycomb base material drying and/or calcining, thereby increasing the amount of the catalytic noble metal supported on the inlet side portion than the amount of the catalytic noble metal supported on the main body portion other than the inlet side portion.

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