JP2000237602A - Catalyst for cleaning exhaust gas of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning exhaust gas using a hexagonal cell-type monolith support capable of cleaning exhaust gas more excellently than a catalyst using a rectangular cell-type monolith support. SOLUTION: This catalyst is constituted of a monolith support 10 having hexagonal cells 15 in 200 meshes or more and partition walls 11 forming the cells with 25% or higher porosity and a catalyst layer 2 containing catalyst components for exhaust gas cleaning and formed on the surface of the partition walls 11 of the monolith support 10. The thickness of the catalyst layer 2 is 10-70 μm in the thinner parts 21 and the thickness of the thicker parts is not more than 12 times as thick as that of the thinner parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a catalyst for purifying exhaust gas of an internal combustion engine in an automobile or the like.

[0002]

2. Description of the Related Art As a system for purifying exhaust gas discharged from an internal combustion engine such as an automobile engine, a carrier carrying a noble metal such as platinum or rhodium as a catalyst is provided in an exhaust pipe, and HC and CO in the exhaust gas are provided. , NOx, etc.,
Alternatively, there is a catalytic converter system that purifies by an oxidation or reduction reaction.

[0003] This catalytic converter system generally comprises a honeycomb-shaped ceramic carrier having a large number of cells (holes),
A so-called monolithic carrier is used as a base material, and a catalyst layer containing a catalyst component is supported in cells of the monolithic carrier. In a conventional monolithic carrier, a square is generally adopted as the cell shape. For a monolithic carrier having such a square cell (square cell), various techniques for improving the purification efficiency of exhaust gas have been conventionally proposed.

[0004] For example, in the catalyst loading step, a slurry-like aqueous solution containing a catalyst component is generally used, so that it is preferable to improve the water absorption of the partition walls. For this reason, use of a monolith with improved porosity of the partition walls and enhanced water absorption is currently being studied.

[0005] In addition, many studies have been conducted on the thickness of the catalyst layer and the catalytic performance for a long time. For example, Japanese Patent Publication No. 53-149886 proposes that if the average thickness of the catalyst layer is 50 to 300 μm, a long-life low-temperature active catalyst can be obtained. Also, Japanese Patent Application Laid-Open
No. 74453 discloses that a wash coat layer is formed of two layers.
It has been proposed that, when a layer is formed, if the total film thickness is 30 to 70 μm, the early activity and the purification performance at a high SV value (Space Velocity value) are improved.

[0006]

However, the above-mentioned prior arts all involve a case where a catalyst is supported on a monolith having a square cell. On the other hand, various cell shapes other than squares, such as triangles and hexagons, have been proposed. Among them, hexagonal cells (hexagonal cells) are closer to a circular shape than a square shape when viewed from a geometrical surface, so that the catalyst layer can be carried in a more uniform state than a square cell.

For this reason, attention has been paid to the use of a monolith having a hexagonal cell as a purification catalyst in response to recent severe exhaust gas regulations. However, when a monolith having the above hexagonal cells is used as a carrier, no proposal has been made as to how to optimally support the catalyst layer and the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is intended for exhaust gas using a hexagonal-cell monolithic carrier, which can exhibit a better purification performance than when a square-celled monolithic carrier is used. It is intended to provide a purification catalyst.

[0009]

According to the first aspect of the present invention, there is provided a monolithic carrier in which hexagonal cells are provided in a size of 200 mesh or more, and a porosity of partition walls forming the cells is 25% or more;
A catalyst layer is disposed on the surface of the partition wall of the monolithic carrier and contains a catalyst component for purifying exhaust gas. The thickness of the catalyst layer is 10 to 70 μm in a thin portion and a thick portion. Is a purifying catalyst for exhaust gas of an internal combustion engine, having a thickness of 12 times or less of the thin portion.

The most remarkable point in the present invention is that the hexagonal honeycomb monolithic carrier having the specific mesh and porosity is used, and the catalyst layer having the specific thickness is supported on the monolithic carrier. .

As described above, a monolithic carrier having hexagonal cells (hexagonal cells) of 200 mesh or more is used as described above. Here, the mesh represents the number of cells existing per unit area of 1 inch square (1 in ² ). If the hexagonal cell has a mesh size of less than 200 meshes, there is a problem that the purification performance is not improved because the catalyst carrying area is small. Therefore, more preferably, 40
0 mesh or more is good.

In order to increase the mesh of the cell, it is preferable to reduce the thickness of the partition. The thickness of the partition in this case is, for example, 6 mil (about 150 to 1).
70 μm), and further, it can be reduced to a thinner 2 to 4 mil.

In the monolithic carrier, the porosity of the partition walls forming the hexagonal cells is 25% or more. Porosity of 25
%, There is a problem that the water absorption of the partition walls is reduced and the cost of the catalyst supporting step is increased. That is, when a catalyst is supported, it is common practice to apply a slurry containing the catalyst component to the partition walls of the cell and dry the slurry to obtain the catalyst layer. In this case, if the porosity is less than 25%, sufficient water absorption of the partition walls cannot be obtained, the application amount of the slurry per application decreases, and a number of application steps may be required. is there. On the other hand, the upper limit of the porosity is 6 to maintain the strength of the partition walls.
It is preferably set to 0%.

Next, the catalyst layer has a thin portion of 10-7.
It is supported so as to have a thickness in the range of 0 μm. here,
The thin portion of the catalyst layer refers to the thinnest portion, that is, the thickness of the catalyst layer carried on the center of each side of the hexagon cell farthest from the apex of the hexagon.

If the thickness of the thin portion is less than 10 μm, there is a problem that the life of the exhaust gas purifying catalyst is shortened. On the other hand, when the thickness of the thin portion exceeds 70 μm,
There is a problem in that a catalyst component more than necessary is supported, and a space through which the exhaust gas passes is reduced, resulting in a large pressure loss.

Further, the catalyst layer is supported such that its thick portion is 12 times or less the thin portion. here,
The thick portion of the catalyst layer refers to the thickest portion, that is, the thickness of the catalyst layer carried on the hexagonal top of the hexagonal cell. The thickness of the thick portion increases as the thickness of the thin portion increases. On the other hand, the ratio of the thick portion to the thin portion tends to increase as the thickness of the thin portion decreases. When the thickness of the thick portion exceeds 12 times the thickness of the thin portion, there is a problem that it is difficult to maintain the thickness of the thin portion at 10 μm or more.

The catalyst components of the catalyst layer include noble metals such as platinum and rhodium. The catalyst layer can be composed of, for example, a mixture of these catalyst components and alumina powder. In addition, cordierite and other ceramics can be used as the material of the monolithic carrier.

Next, the operation and effect of the present invention will be described.
As described above, the exhaust gas purifying catalyst for an internal combustion engine of the present invention uses a monolithic carrier having hexagonal cells of 200 mesh or more and a porosity of the partition walls of 25% or more. 70 μm, and the thick part is
A catalyst layer having a thickness of twice or less is supported. Therefore, the exhaust gas purifying catalyst of the present invention can improve the purifying performance while reducing the pressure loss as compared with the case where a conventional monolithic carrier of a square cell is used, as will be described in detail in an embodiment described later. Can be improved. Further, the performance of the catalyst after the initial deterioration by starting to use the purification catalyst can be maintained higher than that of the conventional square cell.

Therefore, according to the present invention, it is possible to provide an exhaust gas purification catalyst using a hexagonal cell monolithic carrier, which can exhibit more excellent purification performance than when a square cell monolithic carrier is used.

Next, as in the second aspect of the present invention, the porosity of the partition wall is preferably 30% or more. As a result, the water absorption of the partition walls can be further improved, and the work of supporting the catalyst can be facilitated and the cost can be reduced.

According to a third aspect of the present invention, the thickness of the catalyst layer is such that the thin portion has a thickness of 20 to 50 μm, and
It is preferable that the thickness of the thick part is thicker than the thin part and is not more than six times the thin part. That is, by setting the thin portion of the catalyst layer to 20 to 50 μm, the life of the exhaust gas purifying catalyst can be more reliably maintained and the pressure loss can be suppressed. Further, by making the thickness of the thick portion of the catalyst layer thicker than the thin portion (greater than 1 times the thin portion) and not more than 6 times the thin portion,
Further, it is possible to easily maintain the thickness of the thin portion in the optimum range, and to suppress the excessive thickness of the thick portion.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 An exhaust gas purifying catalyst for an internal combustion engine according to an embodiment of the present invention will be described with reference to FIGS. In this example, as shown in FIG.
As the exhaust gas purifying catalyst 1 used in Example 1, a catalyst having hexagonal cells (samples E1 to E4) and a catalyst having square cells (sample C1) were produced, and their pressure loss characteristics were compared.

First, the exhaust gas purifying catalyst 1 according to the samples E1 to E4 as the product of the present invention is provided with a hexagonal cell 15 of 200 mesh or more as shown in FIGS. The porosity of the partition 11 to be formed is 2
It comprises a monolithic carrier 10 of 5% or more and a catalyst layer 2 disposed on the surface of the partition wall 11 of the monolithic carrier and containing a catalyst component for purifying exhaust gas. As shown in FIG. 2, the thickness A of the thin layer 21 is 10 to 70.
μm, and the thickness B of the thick portion 22 is 12 times or less the thickness A of the thin portion 21. In FIG. 1, the exact hexagonal shape of the cell is not shown for the convenience of drawing.

This will be described more specifically. As shown in FIGS. 1 and 2, the monolith carrier 10 of this example has a thickness of 6 mils.
Partition walls 11 having a thickness of about 150 to 170 μm are provided in a hexagonal lattice, and four hexagonal cells (hexagonal cells) 15 are provided.
It has 00 mesh. The monolith carrier 10 was made of a ceramic containing cordierite as a main component, and the porosity of the partition walls 11 was 35%. The monolith carrier 10 was formed in a columnar shape having an outer diameter of 93 mm and a length of 147 mm.

The loading of the catalyst on the monolith carrier 10 is as follows.
Platinum and rhodium were used as catalyst components, and a slurry was prepared by adding alumina powder and water to this. That is, the catalyst layer 2 was provided on the surface of the partition 11 by applying the slurry to the partition 11 of the monolith carrier 10 and drying the slurry.

In this example, four types of exhaust gas purifying catalysts (samples E1 to E4) were prepared in which the thickness A of the thin portion 21 of the catalyst layer 2 was changed between 26.5 and 67.5 μm. . Specifically, the thickness A of the thin portion 21 of the catalyst layer 2 was 26.5 μm for sample E1, 41.5 μm for sample E2, 57.0 μm for sample E3, and 67.5 μm for sample E4.
The thickness B of the thick portion 22 of the catalyst layer 2 is 12
0 μm, sample E2 is 135 μm, sample E3 is 150 μm
m, the sample E4 was 160 μm, and the thickness A of the thin portion 21 was all
And within 6 times A.

Next, in this example, as shown in FIG. 3, a sample C1 as a purification catalyst for exhaust gas using a monolith carrier 90 having a square cell (square cell) 95 was prepared as a comparative product. . Monolith carrier 9 of sample C1
0 is 6 mil (about 150 to 170) as shown in FIG.
Partitions 91 having a thickness of μm) are provided in a square lattice shape, and square cells 95 have 400 meshes. Also,
This monolithic carrier 90 was made of ceramic containing cordierite as a main component, similarly to the samples E1 to E4, and the porosity of the partition walls 11 was 35%.

Further, the monolithic carrier 90 in sample C1 was used.
Were also the same as those of the monolith carriers 10 of the samples E1 to E4. The sample C1 carries the catalyst using the same slurry as in the case of the samples E1 to E4, and the thickness a of the thin portion 31 is changed.
Catalyst layer 3 having a thickness of 30 μm and a thickness b of the thick portion 32 of 260 μm
Was provided. Others are the same as the samples E1 to E4.

Next, in this example, the pressure loss (pressure loss) of each sample was measured. The pressure loss is 150
It was determined by measuring the difference between the inlet pressure and the outlet pressure of the exhaust gas when passing the exhaust gas at a flow rate of 0 liter / min. FIG. 4 shows the measurement results. In the figure, the horizontal axis represents the thickness of the thin portion of the catalyst layer (sample No.), and the vertical axis represents the pressure loss (kPa).

As can be seen from the figure, in samples E1 to E4 as the products of the present invention, the pressure loss increased as the thickness of the thin portion of the catalyst layer increased, but the pressure loss was larger than that of sample C1 as a comparative product. Was small, indicating a good result. From this, the product of the present invention having a hexagonal cell shape is:
It can be seen that the pressure loss characteristics can be improved as compared with the conventional product having a square cell shape.

Second Embodiment In this embodiment, as shown in FIG. 5, the HC 50% purification time was measured using the samples E1 to E4 and C1 in the first embodiment. The conditions for this measurement are 75
According to the conditions defined in LA # 4 of FTP. And
The time from when the used engine was started until the HC concentration on the outlet side of the catalytic converter became 50% of the inlet side was measured. In addition, this measurement was performed for A when each sample was in a new state, and for B when it was in a deteriorated state equivalent to 80,000 km running. The size of the monolith carrier of each sample was changed to a cylindrical shape having an outer diameter of 93 mm and a length of 37 mm.

FIG. 5 shows the measurement results. In the figure, the horizontal axis indicates the thickness of the thin portion of the catalyst layer (sample No.), and the vertical axis indicates the HC 50% purification time (sec). As can be seen from the figure, in both the new state A and the deteriorated state B, all of the samples E1 to E1 of the present invention were obtained.
E4 has a shorter HC 50% purification time than the comparative sample C1. This shows that the product of the present invention is also advantageous in early performance of purification performance.

Embodiment 3 In this embodiment, as shown in FIG. 6, the bag values (THC values) in the cold mode were measured using the samples E1 to E4 and C1 in Embodiment 1. The conditions for this measurement were also in accordance with the conditions defined in LA # 4 of 75FTP in the United States. That is, it is a cold back value (g / mile) of the LA # 4 mode, and the data is not multiplied by the weighting coefficient. Here, the weighting coefficient has three back values (cold = 0.43 × 3.6 / 7.5, hot 1 = 3.9 /
7.5, Hot 2 = 0.57 x 3.6 / 7.5), but this time I omit multiplying them. In addition,
The size of the monolith carrier of each sample was changed to a cylindrical shape having an outer diameter of 93 mm and a length of 147 mm.

FIG. 6 shows the measurement results. In the figure, the abscissa indicates the thickness of the thin portion of the catalyst layer (sample No.), and the ordinate indicates the THC value (g / mile). As can be seen from the figure,
Samples E1 to E4 of the present invention are all comparative samples C
An excellent THC value almost equal to or higher than 1 was shown.
These measured values of 0.10 or less can be said to be excellent values for the THC value.

As shown in the above embodiments, the product of the present invention having hexagonal cells (samples E1 to E4) is equal to or more in all measured items than the comparative product having square cells (sample C1). Showed excellent performance. For this reason, a monolithic carrier having hexagonal cells of 200 mesh or more (400 cells) is used, and the porosity of the partition walls is 25%.
Above (35%), the thickness of the catalyst layer is 10-7
It can be seen that by setting the thickness to 0 μm and the thickness to 12 times or less the thickness of the thin part, the purification performance superior to that of the conventional square cell is exhibited.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a structure of a catalytic converter according to a first embodiment.

FIG. 2 is an explanatory view showing a state in which a catalyst layer of an exhaust gas purifying catalyst of the present invention is supported in a first embodiment.

FIG. 3 is an explanatory diagram showing a catalyst layer carrying state of a comparative exhaust gas purification catalyst according to the first embodiment.

FIG. 4 is an explanatory diagram showing a relationship between a catalyst layer thin portion thickness and a pressure loss in the first embodiment.

FIG. 5 is a diagram showing a catalyst layer thin portion thickness and HC in Embodiment 2;
Explanatory drawing which shows the relationship with 50% purification time.

FIG. 6 is an explanatory diagram showing a relationship between a catalyst layer thin portion thickness and a THC value in a cold mode in a third embodiment.

[Explanation of symbols]

 1. . . 9. purification catalyst for exhaust gas; . . Monolithic carrier, 11. . . 14. partition walls, . . Cell, 2. . . Catalyst layer,

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Keiji Ito 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Takahiro Kida 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Denso Corporation F term (reference) 4D048 AA06 AA13 BA30X BA30Y BA33X BA33Y BB02 CA01 4G069 AA08 BA01B BC71B BC75B CA03 EA19 EA28 EB12X EB12Y EB15X EB15Y EB16X EB16Y FB23

Claims (3)

[Claims] 1. A hexagonal cell having a mesh size of 200 mesh or more is provided, and a porosity of a partition wall forming the cell is 25.
% Of the monolithic carrier, and a catalyst layer disposed on the surface of the partition wall of the monolithic carrier and containing a catalyst component for purifying exhaust gas.
An exhaust gas purifying catalyst for an internal combustion engine, wherein the thickness of the thin portion is 12 μm or less and the thick portion has a thickness of 12 times or less the thin portion. 2. The exhaust gas purifying catalyst for an internal combustion engine according to claim 1, wherein the porosity of the partition wall is 30% or more. 3. The catalyst layer according to claim 1, wherein the thickness of the thin portion is 20 to 50 μm, and the thickness of the thick portion is thicker than the thin portion. Part 6
An exhaust gas purifying catalyst for an internal combustion engine, wherein the catalyst is not more than twice.