JPH0739760A - Ceramic honeycomb catalyst - Google Patents

Abstract

(57) [Summary] [Object] To provide a ceramic honeycomb catalyst having a small heat capacity, which comprises a ceramic honeycomb structure having sufficient isostatic fracture strength as a catalyst carrier despite having thin partition walls. [Structure] A ceramic honeycomb structure (10) as a catalyst carrier has a peripheral wall (11) having a wall thickness of at least 0.1 mm, and a partition wall (12) forming a flow path (13) inside the peripheral wall (11). (T) is 0.050 mm or more and 0.150 mm or less, and the aperture ratio OFA is
Alternatively, when the bulk density G is k, where k is the true specific gravity of the material × (1-material porosity), the following equations are respectively satisfied: 0.65 ≦ OFA ≦ −0.58 × t + 0.98 k × {1-(− 0.58 × t + 0.98 )} ≦ G ≦ k × 0.35 is satisfied. The heat capacity of the catalyst with the catalyst components supported on the honeycomb structure (10) is 450 per 1 m ^{3 of} catalyst capacity.
kJ / K or less. The honeycomb structure (10) can have an A-axis compressive strength of 50 kgf / cm ² or more and a B-axis compressive strength of 5 kgf / cm ² or more, even though the heat capacity of the catalyst is low.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention includes a peripheral wall, which is also called an outer wall, and a partition wall disposed inside the peripheral wall, and cell-like through holes having a large number of polygonal cross sections are adjacent to each other with the partition wall separated. A ceramic honeycomb structure as a catalyst carrier,
The present invention relates to a ceramic honeycomb catalyst including a catalyst component supported on the honeycomb structure.

[0002]

BACKGROUND ART A ceramic honeycomb catalyst having the above-described structure is widely used as a catalyst in, for example, an automobile exhaust gas purification system. The ceramic honeycomb structure as a catalyst carrier has been widely spread because it has a low pressure loss when passing exhaust gas due to its high aperture ratio and exhibits excellent exhaust gas purification performance. The ceramic honeycomb structure that has been put into practical use has a partition wall thickness of 0.170 mm and a cell density of 1 cm.
It is said to be 60 pieces per ² .

Recently, exhaust gas regulations have been strengthened due to environmental problems, for example, hydrocarbons (H) in the LA-4 mode, which is one of the exhaust gas evaluation test modes in the United States.
Along with the demand for a reduction in the total amount of exhaust gas, it is expected that the ceramic honeycomb structure will achieve more excellent exhaust gas purification performance than ever. Especially when the engine has just started, so-called cold start, the catalyst has not warmed up so much that it has not been fully activated.
The reduction in purification efficiency is remarkable. Therefore, early activation of the catalyst at cold start is considered to be the most important issue for clearing the exhaust gas regulations. From such a point of view, as a general theory, the partition walls in the ceramic honeycomb structure are formed thinner, the aperture ratio is further increased to reduce the pressure loss and the structure weight is reduced, and the heat capacity of the catalyst is decreased to reduce the catalyst capacity. It has been proposed to increase the heating rate. In this case, since a large geometric surface area can be obtained, miniaturization of the honeycomb structure can be expected. On the other hand, the ceramic honeycomb structure with thin partition walls requires careful handling because it is difficult to achieve the predetermined minimum guaranteed value for the isostatic fracture strength, which is an index of the strength of the structure. There is a possibility that the catalyst carrier may be damaged during the mounting operation, that is, "canning", in which the honeycomb structure is held in the catalytic converter casing so that the honeycomb structure does not move due to vibration or the like in actual use. The mainstream of the canning is held by the outer peripheral surface of the honeycomb structure, but a holding method in the flow channel direction or a combined holding method in the outer peripheral surface and the flow channel direction may be adopted in some cases. The minimum guaranteed value mentioned above is generally 5 kgf / cm ² or more in terms of isostatic fracture strength, and preferably
It is said that 10 kgf / cm ² or more is required. And, conventionally, the thinning of the partition walls in the ceramic honeycomb structure and the realization of sufficient isostatic fracture strength have been generally recognized as mutually conflicting problems,
Conventionally, no ceramic honeycomb structure having a partition wall thickness of less than 0.170 mm that can be put to practical use has been obtained.

[0004]

DISCLOSURE OF THE INVENTION Therefore, the object of the present invention is to provide a ceramic honeycomb structure having thin partition walls despite having a sufficient isostatic fracture strength, based on a novel idea which can solve the above-mentioned problems all at once. The object is to propose a ceramic honeycomb catalyst having a small heat capacity, which is used as a catalyst carrier.

The basic feature of the ceramic honeycomb catalyst according to the present invention is that the ceramic honeycomb structure as a catalyst carrier has a thin partition wall thickness and a suitable aperture ratio which have never been obtained by the following formula: 0.050 ≤ t ≤ 0.150 0.65 ≦ OFA ≦ −0.58 × t + 0.98 where t is the wall thickness of partition wall [mm] OFA satisfies the aperture ratio of the honeycomb structure and the wall thickness of the peripheral wall is at least 0.1 mm, and 50 k
A-axis compressive strength of gf / cm ² or more and 5 kgf / cm ² or more, preferably
It has a B-axis compressive strength of 10 kgf / cm ² or more, and further has a heat capacity of 450 kJ / K or less, preferably 410 kJ / K or less per 1 m ^{3 of} catalyst capacity.

Another basic characteristic of the ceramic honeycomb catalyst according to the present invention is that the ceramic honeycomb structure as a catalyst carrier has a thin partition wall thickness and a suitable opening ratio which have never been obtained by the following formula: 0.050 ≤ t ≤ 0.150 k x {1-(-0.58 x t + 0.98)} ≤ G ≤ k x 0.35 where t is the wall thickness of the partition wall [mm] G is the bulk density of the honeycomb structure k is the true specific gravity of the material x (1 -Material porosity), the wall thickness of the peripheral wall is at least 0.1 mm, and
A-axis compressive strength of gf / cm ² or more and 5 kgf / cm ² or more, preferably
It has a B-axis compressive strength of 10 kgf / cm ² or more, and further has a heat capacity of 450 kJ / K or less, preferably 410 kJ / K or less per 1 m ^{3 of} catalyst capacity.

Here, the A-axis compressive strength means JASO standard M505, which is an automobile standard issued by the Society of Automotive Engineers of Japan.
It refers to the compressive strength specified by -87, and is the breaking strength when a compressive load is applied in the flow channel direction of the honeycomb structure, that is, in the direction perpendicular to the cross section. The B-axis compressive strength is the breaking strength when a compressive load is applied in a direction parallel to the cross section of the honeycomb structure and perpendicular to the partition walls, and is also defined in the JASO standard. Is. Furthermore, the isostatic strength is isostatic to the honeycomb structure, that is, the compressive fracture strength when an isotropic hydrostatic load is applied, and is indicated by the pressure value when fracture occurs, which is also the above. JASO
It is specified in the standard. Since the A-axis compressive strength applies a compressive load in the flow direction, it is not significantly affected by defects in the honeycomb structure such as the degree of deformation of partition walls, and has a strong correlation with the material strength. In contrast to this, although the B-axis compressive strength also depends on the material strength, it is strongly affected by defects in the honeycomb structure such as the degree of partition wall deformation. In this respect, the isostatic strength is also the same. Therefore, both the isostatic strength and the B-axis compressive strength are indicators of the strength characteristics of the structure, but the B-axis compressive strength is measured without the peripheral wall, so the peripheral wall is not measured. Structural effects are excluded. Needless to say, the peripheral wall functions as an outer shell that protects the internal honeycomb structure from external pressure, and its outer peripheral surface bears the load during canning. When the peripheral wall breaks, the partition wall inside the peripheral wall also receives an abnormal load and starts chain-like destruction, so that the peripheral wall plays an important role. There is no clear correlation between the isostatic strength and the B-axis compressive strength due to different load conditions and the generated stress distribution. However, the higher the B-axis compressive strength, the higher the isostatic strength. Tends to become. As described above, the A-axis compressive strength and the B-axis compressive strength are basic indices of the strength characteristics of the honeycomb structure, the A-axis compressive strength mainly indicates the degree of influence of the material strength surface, and the B-axis compressive strength is the honeycomb strength. It shows the degree of influence of the structural aspect. Then, the isostatic strength exhibiting practical strength characteristics as a structure appears as a result of the effects of the material, the honeycomb structure, and the peripheral wall structure represented by the peripheral wall thickness intertwined with each other. In addition,
The peripheral wall thickness is preferably 0.15 mm or more from the viewpoint of formability.

According to the present invention, the partition wall of the ceramic honeycomb structure as the catalyst carrier in the ceramic honeycomb catalyst is formed as a thin wall in comparison with the conventionally known one, so that the aperture ratio is increased and the pressure loss is reduced. ,
It is intended to reduce the heat capacity of the honeycomb structure as the catalyst carrier, and thus the heat capacity of the catalyst. Needless to say, the smaller the heat capacity of the catalyst, the faster the temperature rise of the catalyst at the cold start and the earlier the catalyst starts to be activated, so that the exhaust gas purification performance is improved. further,
INDUSTRIAL APPLICABILITY The present invention satisfies practical requirements by satisfying the above-described certain conditions between the wall thickness of partition walls and the aperture ratio and / or bulk density of the honeycomb structure, so that the partition walls are thin walls but are practically satisfied. It realizes a proper compressive strength characteristic.

In the ceramic honeycomb catalyst of the present invention having the above-mentioned basic characteristics, the upper limit value of the wall thickness t of the partition wall in the honeycomb structure as the catalyst carrier is 0.150 mm, preferably 0.124 mm, and the lower limit of the aperture ratio OFA. A configuration in which the value is 0.65, preferably 0.70, or the upper limit of the bulk density G is k × 0.35, preferably k × 0.30 is advantageous from a practical point of view for the following reasons. That is, when the wall thickness t is 0.124 mm or less, when the honeycomb structure is used as a catalyst carrier, while realizing the compressive strength characteristics that are practically satisfactory,
Particularly excellent exhaust gas purification performance is realized. In addition to this, the aperture ratio of the honeycomb structure is 0.70 or more on the lower limit side, or the bulk density G of the honeycomb structure is k on the upper limit side.
When it is set to 0.30 or less, it becomes possible to realize satisfactory compression strength characteristics while realizing excellent pressure loss characteristics and exhaust gas purification performance. As an additional effect, since the weight of the honeycomb structure is reduced, when using a ceramic honeycomb catalyst as a catalyst in an automobile exhaust gas purification system, for example, it contributes to a reduction in the vehicle body weight of an automobile, which in turn improves fuel efficiency. There are points that can be expected to be effective.

[0010]

The present invention will be described in more detail with reference to the drawings.

FIG. 1 shows a ceramic honeycomb structure 10 according to an embodiment of the present invention. Honeycomb structure
The reference numeral 10 includes a peripheral wall 11 and partition walls 12 arranged inside the peripheral wall 11, and has cells 13 each having a polygonal cross section, for example, a triangular shape, a quadrangular shape, or a hexagonal cross section as a flow path between the partition walls 12. The outer shape of the honeycomb structure 10 is not only the cross-sectional shape in the cross section perpendicular to the flow path direction shown in FIG. 1 which is circular (round shape), but also the oval shape which is oval or elliptical or other irregular cross-sectional shape. The ones are also put to practical use. The outer shape of the honeycomb structure 10 is not limited to one in which the flow axis in the flow path direction is straight, and one in which the flow path direction axis is bent is also known. The honeycomb structure 10 is, for example, for a catalyst carrier in an automobile exhaust gas purification system, and is made of cordierite, mullite, alumina, silicon carbide,
It is an integrally extruded product made of silicon nitride or zirconia, and is essentially an integrally extruded product of cordierite, which is a material with low thermal expansion and low Young's modulus from the viewpoint of spalling resistance, and has a rectangular cross-section through-hole. Those that have are the mainstream. When the honeycomb structure 10 according to the present invention is used for a catalyst carrier, for example, after coating a base material such as γ-alumina on the surface of the partition wall 12 at least 100 g / l or more with respect to the catalyst capacity, Pt, Rh , Pd, a catalytically active component consisting of at least one noble metal is supported in an amount of at least 2 g / l with respect to the catalytic capacity. In this case, the heat capacity of the ceramic honeycomb catalyst obtained by coating the above-mentioned base material and catalytically active component on the honeycomb structure 10 is 450 kJ / K or less, preferably 410 kJ / m ^{3 of} catalyst capacity.
J / K or less.

In the present invention, the ceramic honeycomb structure 10 has an A-axis compressive strength of 50 kgf / cm ² or more and a B-axis compressive strength of 5 kgf / cm ² or more, preferably 10 kgf / cm ² or more. Then, the wall thickness of the peripheral wall 11 of the honeycomb structure 10 is at least 0.
1 mm, the wall thickness t of the partition wall 12 (see FIG. 2) is 0.050 mm or more and 0.15
0 mm or less. In this case, the honeycomb structure 10
The aperture ratio OFA and the bulk density G of each of them satisfy the following expressions: 0.65 ≦ OFA ≦ −0.58 × t + 0.98 k × {1-(− 0.58 × t + 0.98)} ≦ G ≦ k × 0.35 . Where k is the true specific gravity of the material × (1
-Material porosity). Needless to say, the aperture ratio OFA and the bulk density G in the honeycomb structure 10 are complementary when one of them is defined and the other is defined by itself when the true specific gravity and porosity of the material are known. Have a relationship. The relationship between the wall thickness t and the aperture ratio OFA and the bulk density G according to the present invention is as shown in FIGS. 3 and 4, and the region satisfying the above conditions is the hatched region in FIGS. 3 and 4. Note that the upper limit value (−0.58 × t + 0.98) of the aperture ratio OFA in the above formula is, as shown in FIG. 5, the relationship between the aperture ratio and the local deformation of the peripheral wall by changing the wall thickness t in the honeycomb structure. Is an approximate expression based on the result of examining and determining pass / fail based on the degree of deformation. That is, as shown in FIG. 6A, the honeycomb structure is conveyed to the next step immediately after being extruded while holding the outer peripheral surface of the peripheral wall against the pedestal, and during this conveyance, as shown schematically in FIG. 6B. Local deformation of the peripheral wall may occur. When the peripheral wall is locally deformed in this way, uneven contact of the honeycomb structure occurs during canning, or the partition wall near the deformed peripheral wall deforms following the deformation, which leads to a decrease in isostatic strength, and The risk of structural damage increases. Therefore, the pass / fail judgment is made by focusing on the degree of deformation of the peripheral wall in relation to the aperture ratio in the honeycomb structure. As the value of the aperture ratio OFA increases, the cell density decreases, the number of partition walls forming the honeycomb decreases, and the interval (cell pitch) between the partition walls supporting the peripheral wall increases.
The relationship between the aperture ratio and the partition wall interval in the honeycomb structure is
This is as shown in FIG. It is clear from FIG. 7 that the partition wall spacing rapidly increases at a certain aperture ratio regardless of the partition wall thickness. After further studying the relationship between the aperture ratio and the partition wall thickness, the aperture ratio OFA was -0.
When it exceeds 58 x t + 0.98, the peripheral wall supported between the partition walls is easily bent, and as a result, local deformation of the peripheral wall is likely to occur, and the partition wall supporting the peripheral wall also follows the peripheral wall. It was confirmed that the deformation may cause a decrease in isostatic strength. If the partition walls and the peripheral wall are not deformed and have an ideally accurate shape, the compressive stress field predominantly acts on the honeycomb structure by the load of the isostatic load, but the deformation does not occur. If it occurs, tensile stress may be generated at that location. In this case, the isostatic strength is dominated by the tensile stress, which causes a sudden decrease in strength.

The excellent functional properties of the ceramic honeycomb catalyst according to the present invention, which has the ceramic honeycomb structure 10 satisfying the above-mentioned conditions as a catalyst carrier, will be described below based on experimental results.

First, the relationship between the pressure loss characteristic of the ceramic honeycomb structure 10 and the aperture ratio in the ceramic honeycomb catalyst according to the present invention will be described. FIG. 8 shows an apparatus 20 for measuring the pressure loss characteristic of the honeycomb structure. The measuring device 20 includes a blower 21, a rectifying unit 22, and a measuring unit 23, a honeycomb structure 24 as a measurement target is connected to the measuring unit 23, and air is blown by the blower 21 through the rectifying unit 22 to form a honeycomb structure. The pressure difference before and after the honeycomb structure 24 is passed through the body 24, that is, the pressure loss is measured by the manometer 25. Using this measuring device 20, pressure loss characteristics were measured by changing the air flow rate for a group of ceramic honeycomb structures having a constant size (cross-sectional area, capacity) and different only in aperture ratio. The measurement result is as shown in FIG. It is also clear from FIG. 9 that the pressure loss increases as the aperture ratio decreases. Further, FIG. 10 shows a change in pressure loss with a change in aperture ratio when the air flow rate is constant (5 m ³ / min) for the same measurement target group as described above. From FIG. 10, it is recognized that the increasing tendency of the pressure loss becomes remarkable when the aperture ratio is 70% or less, particularly 65% or less. From this result, the lower limit of the aperture ratio is 65
% (= 0.65), preferably 70% (= 0.70).

Next, the influence of the ceramic honeycomb structure 10 in the ceramic honeycomb catalyst according to the present invention on the engine output characteristics will be described in relation to the aperture ratio. FIG. 11 shows a honeycomb structure testing apparatus 30 using an actual engine. This test device 30 has 6 cylinders 30
An exhaust manifold 32 of 50 cm in length is connected to a 00cc gasoline engine 31, a converter 33 including a honeycomb structure to be measured is arranged directly below the exhaust manifold 32, and an underfloor converter 34 with a capacity of 1700cc and a muffler are arranged on the downstream side of the exhaust manifold 32. 35 is connected and the dynamometer 36 is connected to the output shaft of the engine 31. Using the test device 30, as the converter 33 immediately below the manifold, the maximum output of the engine 31 was obtained for a group of converters equipped with a catalyst carrier composed of a ceramic honeycomb structure with a constant size (capacity 1700cc) and different aperture ratios only. The engine output at that time was measured by a dynamometer 36. The measurement result is as shown in FIG. From FIG. 12, it can be seen that the tendency of the engine output to decrease becomes remarkable when the aperture ratio is 70% or less, particularly 65% or less.

Next, the exhaust gas purification performance of the automobile exhaust gas purification system equipped with the ceramic honeycomb catalyst according to the present invention will be described. Generally, exhaust gas measurement of an actual vehicle is performed in an operating state with a vehicle speed pattern defined in a predetermined running test mode. FIG. 13A is a diagram showing a vehicle speed pattern based on the LA-4 mode as a representative example of the vehicle running test mode, and FIG. 13B is a detailed view showing a vehicle speed pattern in the initial 505 seconds in the LA-4 mode. 6
As a converter directly under the exhaust manifold in a test vehicle equipped with a 2500cc cylinder gasoline engine, equipped with a ceramic catalyst carrier that has a constant size (capacity: 1200cc) and cell density (60 cells / cm ² ) and different wall thicknesses of partition walls The accumulated hydrocarbon (HC) emission amount in the initial 505 seconds in the LA-4 mode was measured for each of the converters. The measurement result is as shown in FIG.
From FIG. 14, it is recognized that the thinner the partition wall, the smaller the hydrocarbon emission amount. Further, FIG. 15 shows the hydrocarbon emission amount in the initial 505 seconds in the LA-4 mode for the converter group to be measured described above. From Fig. 15, it is also recognized that the thinner the partition wall, the smaller the hydrocarbon discharge amount, and that the decreasing tendency becomes more remarkable when the wall thickness is 0.124 mm or less. Furthermore, when the relationship between the hydrocarbon discharge amount and the catalyst heat capacity was investigated, as shown in Fig. 16, the smaller the heat capacity, the smaller the hydrocarbon discharge amount, and the decreasing tendency was that the heat capacity was 450 kJ.
It has been found that it becomes remarkable at / m ³ K or less, preferably at 410 kJ / m ³ K or less. Also, the catalyst heat capacity and each emission component (NOx, CO, HC) up to the second peak of Bag A.
As shown in Fig. 17, the smaller the heat capacity of any of the emission components, the higher the purification efficiency, and the improvement tendency is that the heat capacity is 450 kJ / m ³ K or less. Was found to be significant below 410 kJ / m ³ K.

The purification performance of an automobile exhaust gas purification system at cold start depends on the superiority or inferiority of the temperature rising characteristics of the catalyst carrier itself, and the smaller the bulk density of the catalyst carrier and hence the heat capacity of the catalyst, the better the purification performance. . Therefore, as a converter directly under the exhaust manifold in a test vehicle equipped with a 6-cylinder 2500cc gasoline engine, the size (capacity 1200cc) and cell density (60 pieces)
/ cm ² ) is constant and the wall thickness of the partition walls is different, the temperature change of the catalyst carrier in the initial 505 seconds in the LA-4 mode is measured from the exhaust gas inlet side at the center of the carrier. It was measured at a position of 15 mm. The measurement result is as shown in FIG. It can be seen from FIG. 18 that the thinner the partition walls, and thus the smaller the bulk density, the more the temperature rising characteristics of the carrier. It is also recognized from FIG. 18 that the metal honeycomb catalyst has a lower temperature rising rate than the ceramic honeycomb catalyst. It is considered that this is because the metal has a higher thermal conductivity than the ceramic, and as a result, the heat release amount in the temperature rising process is larger than that of the ceramic.

Further, as converters directly below the exhaust manifold in a test vehicle equipped with a 6-cylinder 2500cc gasoline engine, a converter equipped with a ceramic honeycomb catalyst carrier and a converter equipped with a metal honeycomb catalyst carrier were in an LA-4 mode. Early in 505
Emissions (NOx, CO, HC) emissions per second were measured. The measurement results are shown in the bar graph of FIG. From these measurement results, it is clear that the ceramic honeycomb catalyst carrier is superior to the metal honeycomb catalyst carrier in the exhaust gas purification performance.

As described above, the ceramic honeycomb structure as the catalyst carrier in the ceramic honeycomb catalyst according to the present invention has an A-axis compressive strength of 50 kgf / cm ² or more and a B-axis compressive strength of 5 kgf / cm ² or more. is there. The inventors conducted extensive studies and experiments with the aim of improving the compressive strength characteristics of the ceramic honeycomb structure. As a result, if the partition walls are deformed or damaged during the manufacturing process of the honeycomb structure, the compressive strength is lowered, which is excellent. It was found that it is particularly important to quantitatively maintain the deformation degree and the defect degree of the partition wall within a predetermined range in order to realize the compressive strength characteristics.

First, bending as one mode of deformation of the partition wall
The modification will be described. Such bending deformation is, for example,
May occur inside the Lamic honeycomb structure
Easily occur on the partition wall near the joint with the peripheral wall,
When the cam structure is observed from the flow direction,
And can be recognized. In this case, as shown in Figure 20
In addition, a space for forming an arbitrary through hole in the honeycomb structure is formed.
A wall (referred to as a "unit partition") that is curved, for example, in an arc shape.
Connect the centers of circles inscribed on both sides of the bulkhead
Defined as the center line of the partition, and any 2 on the center line
Straight line distance L between points_AAnd the length L of the center line between the two points_BWith
The length ratio, that is, the length ratio L illustrated in FIG. 21A, for example._B
/ L_AQuantify the degree of bending deformation by focusing on. length
Ratio L_B/ L_AThe two points on the center line for calculating_B
/ L_AIs selected to be maximum. Shape of bending deformation of partition wall
21B and
As shown in FIG. 21C, it may be bent or partially curved.
There is also. In the present invention, the length ratio L_B/ L_AHani
1 or more for almost all partitions in the cam structure 1.10
And the length ratio L_B/ L_AExceeds 1.10, or
The total number of partition walls that are 1.15 or less is 1% or less of the total number of partition walls
It is what Figure 22 shows the partition wall changes in one carrier.
Shape amount, ie length ratio L_B/ L_AMaximum and isostere
It is a graph which shows the relationship with tick intensity. Isosta
Prior to conducting a tick rupture test, it becomes the rupture point in advance
The length ratio L for a bulky partition with a large deformation_B/ L
_AWas measured. After that, an isostatic destructive test
Perform, and the partition wall length ratio L at the breaking point_B/ L_AAnd Iso
The relationship with static strength was investigated by changing the wall thickness of the partition wall.
It was Here is the Hani that was used for the isostatic destruction test.
Each cam structure has a round shape with an outer diameter of about 100 mm.
It has a standard size. The upper song in Figure 22
The line shows data for bulky bulkheads, and also for the bottom
The curves show the data for thin walls, respectively.
You From this survey, the length ratio L_B/ L_AIs less than 1.10
And the isostatic strength tends to increase sharply
It has been found. Figure 23. Any cross section of one honeycomb
Proportion of partition walls that have undergone bending deformation in the plane,
Which length ratio L_B/ L_AHow often is the bulkhead
It is a graph which shows whether it exists. Length ratio L_B/
L_AHoneycomb structure with partition walls of 1.10 or less
If there is a length ratio L_B/ L_AHani with a bulkhead of 1.10 or more
It goes without saying that there is also a cam structure. Furthermore, the figure
24 is the length ratio L_B/ L_AExceeds 1.10 and 1.15 or less
Of the total number of bulkheads in the total number of bulkheads (%) and eye
It is a graph which shows the relationship with a static strength. Figure 24
The upper curve in is the data for thick wall bulkheads.
Also, the lower curve shows the data for a thin wall bulkhead.
Are shown respectively. From this graph,
 The isostatic strength increases sharply at 1.0% or less.
It is recognized that there is a tendency to add. The reason is as follows
It is as follows. That is, the presence of the partition wall that has been bent and deformed
When the proportion of the partition increases, the partition wall deformed as shown in FIG. 25A.
In the case where the two are close to each other, in other words, there are two or more deformed partition walls.
The number of cases that continue will increase stochastically.
It is possible that the ambitions are next to each other. The distance thus deformed
When the walls are dense and when they are deformed as shown in Figure 25B
If there are scattered at a distance and the station of that part
Comparing the partial structural strength, the partition walls are denser
However, it is clear that the cells are easily crushed and the structural strength decreases.
It's mild. And the honey that the deformed partition is dense
Perform isostatic destructive testing on cam structures
Then, such a low-strength part becomes the breaking point, so
Isostatic strength also decreases. The quantity ratio is 1.0
If the percentage exceeds%, densely packed partition walls that have undergone stochastic bending deformation
Parts are more likely to exist and the isostatic strength is reduced.
It On the contrary, if the quantity ratio is 1.0% or less,
It is unlikely that there will be dense parts of the partition walls that have undergone stochastic bending deformation.
The deformed partition walls are scattered, and the structural strength is low even when viewed locally.
As the isostatic strength is improved,
is there.

Next, crush deformation as another mode of deformation of the partition wall will be described. Unlike the above-described bending deformation of the partition walls, this crush deformation occurs as a change in the crossing angle of the adjacent partition walls. That is, for example, in the case of a quadrangular cell, the collapse deformation occurs as a rhombus of the cell shape. In this case, as shown in FIG. 26, for any cell in the honeycomb structure, the center of the maximum inscribed circle inscribed in at least three corners within the intersections on both sides of each unit partition wall forming the cell is the lattice of the cell. In the case of points, the deformation is quantified by paying attention to the length ratio Lmax / Lmin between the maximum length Lmax and the minimum length Lmin on each diagonal connecting the opposing grid points. In the present invention, this length ratio is 1 or more and 1.73 or less in the case of the rectangular cell shown in FIG. 27, and FIG. 27A and FIG. 27B.
In the case of the hexagonal cell shown in, it is 1.15 or more and 1.93 or less.
28 and 29 are graphs showing the relationship between the diagonal length ratio Lmax / Lmin and the isostatic strength in a square cell and a hexagonal cell, respectively, when the wall thickness of the partition wall is changed. The upper curve in FIGS. 28 and 29 shows data for a partition wall with a large wall thickness, and the lower curve shows data for a partition wall with a thin wall thickness. From these graphs, it is recognized that when the length ratio Lmax / Lmin is 1.73 or less in the case of a square cell and 1.93 or less in the case of a hexagonal cell, the isostatic strength tends to rapidly increase.

Further, unlike the above-described bending deformation and crushing deformation of the partition walls, the isostatic strength of the honeycomb structure is lowered even when voids are formed in an arbitrary cross section due to the partition wall defects in the flow channel direction. Figure 30A and Figure
30B shows the shape of the defect observed in the flow direction. The defect of the partition wall may occur at any position between the lattice points or at the lattice point. In either case, the number of defects is one.
And count. In the present invention, the total number of partition walls having voids in any cross section due to partition wall loss in the flow channel direction is preferably 1.0% of the total number of partition walls in the honeycomb structure.
Below. Further, the total number of partition walls having voids in any cross section due to the partition wall loss in the flow channel direction within the entire circumferential region including 20 cells from the outermost periphery to the inside is preferably the total number of partition walls in the honeycomb structure. 0.5% or less. FIG. 31 and FIG. 32 are graphs showing the relationship between the total number of defective partition walls and the isostatic strength when the wall thickness of the partition walls is changed. The upper curves in FIGS. 31 and 32 show the data for partition walls with a large wall thickness, and the lower curves show the data for partition walls with a thin wall thickness. Figure 31
From the results, it is confirmed that the isostatic strength tends to rapidly increase when the ratio of the total number of partition walls with defects to the total number of partition walls in the honeycomb structure is 1.0% or less. In addition, considering the relationship with the location where the partition wall defect occurs, from FIG. 32, the total number of partition walls having a defect in the flow channel direction within the entire circumferential area including 20 cells from the outermost periphery to the inside is the honeycomb structure. It is recognized that the isostatic strength tends to increase sharply when the ratio to the total number of partition walls is 0.5% or less.

All the isostatic strength data shown in the above description are based on a honeycomb structure having a quadrangular cell shape and a round outer shape. Similar results are obtained for the honeycomb structures having triangular and hexagonal cell shapes. And a similar result was obtained for a honeycomb structure having an oval outer shape.

[0024]

As is apparent from the above detailed description, according to the present invention, on the other hand, the partition walls in the honeycomb structure as the catalyst carrier in the ceramic honeycomb catalyst are formed as thin walls in comparison with those conventionally known. By configuring, while increasing the aperture ratio and reducing the pressure loss, when the honeycomb structure is used as a catalyst carrier, it lowers the heat capacity of the carrier, and on the other hand, the wall thickness of the partition walls and the opening of the honeycomb structure. By satisfying the above-mentioned certain conditions between the ratio and / or the bulk density, and in particular, by quantitatively maintaining the degree of deformation / deficiency that can occur in the partition walls in the manufacturing stage of the honeycomb structure within a predetermined range, respectively. Even though the partition wall is thin, it is possible to realize the compressive strength characteristics that are practically satisfactory.

[Brief description of drawings]

FIG. 1 is a perspective view showing the overall structure of a ceramic honeycomb catalyst according to an embodiment of the present invention.

FIG. 2 is a schematic view showing channels and partition walls in a catalyst carrier of a ceramic honeycomb catalyst.

FIG. 3 is a graph showing the relationship between the wall thickness and the aperture ratio in the catalyst carrier of the ceramic honeycomb catalyst according to the present invention.

FIG. 4 is a graph showing the relationship between wall thickness and bulk density in the catalyst carrier of the ceramic honeycomb catalyst according to the present invention.

FIG. 5 is a graph showing the relationship between the aperture ratio and the degree of deformation of the peripheral wall.

FIG. 6A is an explanatory view showing a transportation mode of a ceramic honeycomb structure immediately after extrusion molding, and B is an explanatory view showing a local deformation of a peripheral wall during transportation.

FIG. 7 is a graph showing the relationship between the aperture ratio and the partition wall spacing in the ceramic honeycomb structure.

FIG. 8 is a diagram showing an apparatus for measuring pressure loss characteristics of a catalyst carrier of a ceramic honeycomb catalyst.

9 is a graph showing pressure loss characteristics measured using the measuring device of FIG.

10 is a graph showing a change in pressure loss with a change in the opening ratio when the air flow rate is constant, which is measured using the measuring device in FIG.

FIG. 11 is a diagram showing a honeycomb structure testing apparatus using an actual engine.

12 is a graph showing engine output characteristics measured using the measuring device of FIG.

FIG. 13A shows L as a typical example of a vehicle running test mode.
A diagram showing a vehicle speed pattern based on A-4 mode, B is L
It is a detailed view showing a vehicle speed pattern in the initial 505 seconds in A-4 mode.

FIG. 14 is a graph showing cumulative hydrocarbon emissions in the LA-4 mode for the initial 505 seconds.

FIG. 15 is a graph showing the hydrocarbon discharge amount in the initial 505 seconds in the LA-4 mode.

FIG. 16 is a graph showing the relationship between hydrocarbon discharge amount and catalyst heat capacity.

FIG. 17 is a graph showing the relationship between the purification efficiency and the catalyst heat capacity for each emission component.

FIG. 18 is a graph showing the temperature change of the catalyst carrier in the LA-4 mode in the initial 505 seconds.

FIG. 19 is a graph showing the emission amount of emission in the initial 505 seconds in the LA-4 mode.

FIG. 20 is a schematic view showing the definition of the center line of partition walls in the honeycomb structure.

21A, 21B, and 21C are explanatory diagrams of an example of bending deformation of partition walls in the honeycomb structure and an amount of deformation in that case.

FIG. 22 is a graph showing the relationship between the maximum value of the deformation amount of the partition wall (length ratio L _B / L _A ) and the isostatic strength.

[Fig. 23] Fig. 23 is a graph schematically showing the rate of occurrence of deformed partition walls in an arbitrary cross section of one honeycomb.

FIG. 24: Length ratio L _B / L _A exceeds 1.10 and 1.15
7 is a graph showing the relationship between the number ratio (%) of the total number of partition walls to the total number of partition walls and the isostatic strength.

FIG. 25A and FIG. 25B are explanatory views showing the existing form of the partition wall that is bent and deformed.

[Fig. 26] Fig. 26 is an explanatory diagram of the amount of deformation associated with the crushing deformation of partition walls in a honeycomb structure having square cells.

FIG. 27A and FIG. 27B are explanatory diagrams showing a state before crush deformation and a state after crush deformation of partition walls in a honeycomb structure having hexagonal cells.

FIG. 28 is a graph showing the relationship between the diagonal length ratio Lmax / Lmin and the isostatic strength in a rectangular cell when the wall thickness of the partition wall is changed.

FIG. 29 is a graph showing the relationship between the diagonal length ratio Lmax / Lmin and the isostatic strength in a hexagonal cell when the wall thickness of the partition wall is changed.

FIG. 30 is an explanatory diagram showing a defective state of partition walls in a honeycomb structure having square cells.

FIG. 31 is a graph showing the relationship between the total number of defective partition walls and the isostatic strength when the wall thickness of the partition walls is changed.

FIG. 32 is a graph showing the relationship between the total number of partition walls having defects and the isostatic strength when the wall thickness of the partition walls is changed.

[Explanation of symbols]

10 ceramic honeycomb structure, 11 peripheral walls, 12 partition walls,
13 channels

Claims (13)

[Claims] 1. A ceramic honeycomb structure as a catalyst carrier, which comprises a peripheral wall and partition walls arranged inside the partition wall, and has cells having a polygonal cross section as flow channels between the partition walls, and a ceramic honeycomb structure supported on the honeycomb structure. A ceramic honeycomb catalyst including a catalyst component, wherein the honeycomb structure has the following formula: 0.050 ≤ t ≤ 0.150 0.65 ≤ OFA ≤ -0.58 × t + 0.98 where t is the wall thickness of the partition wall [mm] OFA is the honeycomb structure Satisfying the opening ratio of the body, the wall thickness of the peripheral wall is at least 0.1 mm, 50 k
It has an A-axis compressive strength of gf / cm ² or more and a B-axis compressive strength of 5 kgf / cm ² or more, and the heat capacity of the catalyst is 1
Ceramic honeycomb catalyst characterized in that it is 450 kJ / K or less per m ³ . 2. The upper limit of wall thickness of partition walls in the honeycomb structure is 0.124 mm, the lower limit of aperture ratio is 0.70, and the upper limit of heat capacity of the catalyst is 410 kJ / K per 1 m ^{3 of} catalyst capacity. The ceramic honeycomb catalyst according to claim 1, characterized in that 3. A ceramic honeycomb structure as a catalyst carrier, comprising a peripheral wall and partition walls arranged inside the partition wall, and having cells having a polygonal cross section as flow paths between the partition walls, and a ceramic honeycomb structure supported on the honeycomb structure. A ceramic honeycomb catalyst including a catalyst component having a honeycomb structure of the following formula: 0.050 ≤ t ≤ 0.150 k x {1-(-0.58 x t + 0.98)} ≤ G ≤ k x 0.35, where t is Wall thickness of partition wall [mm] G is bulk density of honeycomb structure k is true specific gravity of material x (1-material porosity), wall thickness of peripheral wall is at least 0.1 mm, and 50 k
It has an A-axis compressive strength of gf / cm ² or more and a B-axis compressive strength of 5 kgf / cm ² or more, and the heat capacity of the catalyst is 1
Ceramic honeycomb catalyst characterized in that it is 450 kJ / K or less per m ³ . 4. The upper limit of the wall thickness of the partition walls in the honeycomb structure is 0.124 mm, the lower limit of the bulk density G is k × 0.30, and the upper limit of the heat capacity of the catalyst is 410 kJ / m ^{3 of the} catalyst capacity.
The ceramic honeycomb catalyst according to claim 3, which is K or less. 5. When the line connecting the centers of circles inscribed on both sides of an arbitrary unit partition in the cross section of the honeycomb structure is defined as the center line of the partition, the center between any two points on the center line The ceramic honeycomb catalyst according to claim 1 or 3, characterized in that a length ratio between a line length and a linear distance between the two points is 1 or more and 1.10 or less. 6. A center between any two points on the center line when a line connecting the centers of circles inscribed on both sides of an arbitrary unit partition in the cross section of the honeycomb structure is defined as the center line of the partition. The total number of partition walls whose length ratio between the line length and the straight line distance between the two points exceeds 1.10 and is 1.15 or less is 1% or less of the total number of partition walls, or 1 or 3. The ceramic honeycomb catalyst according to item 3. 7. When the center of the largest inscribed circle inscribed in at least three corners of the intersections on both sides of each unit partition wall forming the cell in any cell of the honeycomb structure is the lattice point of the cell , In each diagonal connecting the opposite grid points, the length ratio of the maximum length to the minimum length is 1 or more and 1.73 or less in the case of a square cell, and 1. in the case of a hexagonal cell.
It is 15 or more and 1.93 or less, The ceramic honeycomb catalyst of Claim 1 or 3 characterized by the above-mentioned. 8. The total number of partition walls in the cross section of the honeycomb structure is 1% of the total number of partition walls having voids in an arbitrary cross section due to the lack of partition walls in the flow direction of the honeycomb structure.
The ceramic honeycomb catalyst according to claim 1 or 3, characterized in that: 9. The honeycomb structure is provided with 20 inside from the outermost periphery.
Within the entire circumferential area containing cells, the total number of partition walls that have voids in any cross section due to the loss of partition walls in the flow direction should be 0.5% or less of the total number of partition walls in the cross section of the honeycomb structure. The ceramic honeycomb catalyst according to claim 1 or 3, which is characterized. 10. The ceramic honeycomb catalyst according to claim 1 or 3, wherein the honeycomb structure is integrally extruded. 11. The ceramic honeycomb catalyst according to claim 1 or 3, which is a catalyst for an exhaust gas purification system of an internal combustion engine. 12. The honeycomb structure according to claim 1, wherein the through hole has a quadrangular cross section and is made of cordierite, and the catalyst is provided in an exhaust gas purifying system for automobiles. The described ceramic honeycomb catalyst. 13. The ceramic honeycomb catalyst according to claim 1, wherein the honeycomb structure is made of at least one selected from the group consisting of mullite, alumina, silicon carbide, silicon nitride and zirconia. .