JP2892259B2 - Ceramic honeycomb catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a peripheral wall, also called an outer wall, and a partition arranged inside the peripheral wall, and a plurality of cell-shaped through-holes having a polygonal cross section are arranged adjacent to each other across the partition in the flow direction. A ceramic honeycomb structure as a catalyst carrier,
The present invention relates to a ceramic honeycomb catalyst comprising a catalyst component supported on the honeycomb structure.

[0002]

2. Description of the Related Art Ceramic honeycomb catalysts having the above-described structure are widely used, for example, as catalysts in exhaust gas purification systems for automobiles. BACKGROUND ART A ceramic honeycomb structure as a catalyst carrier has a low pressure loss when passing exhaust gas due to a high aperture ratio, and has been widely used as a material exhibiting excellent exhaust gas purification performance. The ceramic honeycomb structure conventionally used in practice has a partition wall thickness of 0.170 mm and a cell density of 1 cm.
It is said that 60 pieces per ² .

[0003] In recent years, regulations on exhaust gas related to environmental problems have been tightened. For example, hydrocarbons (H2) in LA-4 mode, one of the exhaust gas evaluation test modes in the United States, have been
(Also referred to as C) With the demand for the reduction of the total amount of emissions, ceramic honeycomb structures are expected to achieve more excellent exhaust gas purification performance than ever before. Especially when the engine has just been started, so-called cold start, the catalyst has not been activated enough because the catalyst is not so warm.
The purification efficiency is significantly reduced. For this reason, the early activation of the catalyst at the time of a cold start is regarded as the most important issue for meeting the exhaust gas regulations. From this viewpoint, in general terms, the partition walls in the ceramic honeycomb structure are formed thinner, the aperture ratio is further increased, the pressure loss is reduced, the structure weight is reduced, the heat capacity of the catalyst is reduced, and 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, ceramic honeycomb structures with thin partition walls require careful handling because it is difficult to achieve a predetermined minimum guaranteed value for isostatic fracture strength, which is one index of strength as a structure, During the mounting operation that is held in the catalytic converter casing and prevents the honeycomb structure from moving due to vibration or the like in actual use, that is, so-called “canning”, the catalyst carrier may be damaged. Mainly, canning is held on the outer peripheral surface of the honeycomb structure, but a holding method in the flow direction or a combination holding method in the outer surface and the flow direction may be adopted. The above minimum guaranteed value is generally 5 kgf / cm ² or more in isostatic breaking strength, preferably
It is said that 10 kgf / cm ² or more is required. Conventionally, thinning of the partition walls in the ceramic honeycomb structure and realization of a sufficient isostatic breaking strength were generally recognized as mutually contradictory problems,
Heretofore, a ceramic honeycomb structure having a partition wall thickness of less than 0.170 mm that can be practically used has not been obtained.

[0004]

DISCLOSURE OF THE INVENTION Accordingly, an object of the present invention is to provide a ceramic honeycomb structure having a thin partition wall despite having a sufficient isostatic breaking strength, based on a novel idea capable of solving the above-mentioned problems at once. An object of the present invention is to propose a ceramic honeycomb catalyst having a small heat capacity and provided 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 an unprecedented thin partition wall thickness and a suitable opening ratio, and 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 satisfies the aperture ratio of the honeycomb structure, the wall thickness of the peripheral wall is at least 0.1 mm, and 50 k
A-axis compression 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 the heat capacity of the catalyst is 450 kJ / K or less, preferably 410 kJ / K or less per 1 m ^{3 of} catalyst capacity.

Another basic feature of the ceramic honeycomb catalyst according to the present invention is that a ceramic honeycomb structure as a catalyst carrier has an unprecedented thin partition wall thickness and a suitable opening ratio, and the following formula: 0.050 ≦ t ≦ 0.150 k × {1 − (− 0.58 × t + 0.98)} ≦ G ≦ k × 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 × (1 − Material porosity), the wall thickness of the peripheral wall is at least 0.1 mm, and 50 k
A-axis compression 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 the heat capacity of the catalyst is 450 kJ / K or less, preferably 410 kJ / K or less per 1 m ^{3 of} catalyst capacity.

[0007] Here, the A-axis compressive strength refers to JASO standard M505, which is an automotive standard issued by the Society of Automotive Engineers of Japan.
-87 refers to the compressive strength, which is the breaking strength when a compressive load is applied in the flow direction of the honeycomb structure, that is, in the direction perpendicular to the cross section. The B-axis compressive strength is a fracture strength when a compressive load is applied in a direction parallel to the transverse section of the honeycomb structure and perpendicular to the partition walls, and is also specified in the JASO standard. It is. Further, the isostatic strength is isostatic, that is, the compressive rupture strength when an isotropic hydrostatic load is applied to the honeycomb structure, and is indicated by the pressure value at the time of rupture. JASO
It is specified in the standard. Since the A-axis compressive strength applies a compressive load in the direction of the flow path, the A-axis compressive strength is not significantly affected by defects in the honeycomb structure such as the degree of deformation of the partition walls and has a strong correlation with the material strength. In contrast, the B-axis compressive strength also depends on the material strength, but is strongly affected by defects in the honeycomb structure such as the degree of partition wall deformation. In this respect, the isostatic strength is the same. Therefore, both the isostatic strength and the B-axis compressive strength are indicators of the strength characteristics of the structure. However, since the B-axis compressive strength is measured without the peripheral wall, 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 the outer peripheral surface bears the load during canning. When the peripheral wall breaks, the inner peripheral partition walls also receive an abnormal load and start a chain-like failure, 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 the different load conditions and the resulting stress distribution. The higher the B-axis compressive strength, the higher the isostatic strength. Tend to be. As described above, the A-axis compression strength and the B-axis compression strength are basic indices of the strength characteristics of the honeycomb structure. The A-axis compression strength mainly indicates the degree of influence of the material strength, and the B-axis compression strength is the honeycomb. It shows the degree of influence of the structure. The isostatic strength indicating practical strength characteristics as a structural body appears as a result of the influence of the material and the honeycomb structure, and the peripheral wall structure typified by the peripheral wall thickness entangled with each other. In addition,
The thickness of the peripheral wall is preferably 0.15 mm or more from the viewpoint of formability.

According to the present invention, a partition wall of a ceramic honeycomb structure as a catalyst carrier in a ceramic honeycomb catalyst is formed as a thin wall as compared with a conventionally known one, thereby increasing an aperture ratio and reducing a pressure loss. ,
This reduces the heat capacity of the honeycomb structure as a catalyst carrier and, consequently, the heat capacity of the catalyst. It goes without saying that the smaller the heat capacity of the catalyst, the faster the catalyst temperature rises at the time of cold start, and the earlier the catalyst starts to be activated, so that the exhaust gas purification performance is improved. further,
The present invention satisfies the above-mentioned certain conditions between the wall thickness of the partition walls and the opening ratio and / or bulk density of the honeycomb structure, and thus practically satisfies the fact that the partition walls are thin walls. It is intended to realize the required compressive strength characteristics.

In the ceramic honeycomb catalyst of the present invention having the above-mentioned basic characteristics, the upper limit of the wall thickness t of the partition wall in the honeycomb structure as a catalyst carrier is set to 0.150 mm, preferably 0.124 mm, and the lower limit of the opening ratio OFA. A configuration where 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 compressive strength characteristics that are practically satisfactory,
Particularly excellent exhaust gas purification performance is realized. In addition, the opening ratio of the honeycomb structure is set to 0.70 or more at the lower limit or the bulk density G of the honeycomb structure is set to k at the upper limit.
When it is not more than × 0.30, it is 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, for example, when a ceramic honeycomb catalyst is used as a catalyst in an exhaust gas purification system for an automobile, it also contributes to a reduction in the weight of an automobile body, thereby improving fuel efficiency. The effect can be expected.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail hereinafter with reference to the drawings.

FIG. 1 shows a ceramic honeycomb structure 10 according to one embodiment of the present invention. Honeycomb structure
Numeral 10 includes a peripheral wall 11 and a partition wall 12 disposed inside the peripheral wall 11, and a cell 13 having a polygonal cross section, for example, a triangular, square or hexagonal cross section, is provided between the partition walls 12 as a flow path. The external shape of the honeycomb structure 10 is not only a cross-sectional shape (round shape) in a cross section perpendicular to the flow path direction shown in FIG. 1 but also an oval shape having an oval or elliptical shape or other irregular cross-sectional shapes. Are also in practical use. In addition, the external shape of the honeycomb structure 10 is not limited to the shape in which the flow direction axis is straight, and the shape in which the flow direction 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 includes cordierite, mullite, alumina, silicon carbide,
It is an integrally extruded product made of silicon nitride or zirconia, and is substantially an integrally extruded product of cordierite, which is a material having low thermal expansion and a low Young's modulus mainly from a spalling resistance property, and has a rectangular cross-section through-hole. What you have is the mainstream. When the honeycomb structure 10 according to the present invention is used as a catalyst carrier, for example, after coating a substrate such as γ-alumina on the surface of the partition wall 12 with at least 100 g / l with respect to the catalyst capacity, Pt, Rh , Pd and at least 2 g / l of a catalyst active component based on at least the catalyst capacity. In this case, the heat capacity of the ceramic honeycomb catalyst obtained by coating the honeycomb structure 10 with the base material and the catalytically active component as described above is 450 kJ / K or less per 1 m ^{3 of} catalyst capacity, preferably 410 kJ / K.
J / K or less.

In the present invention, the A-axis compression strength of the ceramic honeycomb structure 10 is 50 kgf / cm ² or more, and the B-axis compression strength is 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 set to at least 0.
1 mm, wall thickness t of partition 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 satisfy the following formula: 0.65 ≦ OFA ≦ −0.58 × t + 0.98 k × {1 − (− 0.58 × t + 0.98)} ≦ G ≦ k × 0.35 . Here, k is the true specific gravity of the material × (1
-Material porosity). Needless to say, the opening ratio OFA and the bulk density G of the honeycomb structure 10 are complementary when the true specific gravity and the porosity of the material are known and one of them is defined. Relationship. The relationship between the wall thickness t, the aperture ratio OFA and the bulk density G according to the present invention is as shown in FIGS. 3 and 4, respectively, and the area satisfying the above conditions is the shaded area in FIGS. The upper limit (−0.58 × t + 0.98) of the aperture ratio OFA in the above equation is obtained by changing the wall thickness t of the honeycomb structure and changing the relationship between the aperture ratio and the local deformation of the peripheral wall, as shown in FIG. Is an approximation formula based on the result of investigating and determining the pass or fail based on the degree of deformation. That is, the honeycomb structure is transported to the next step while holding the outer peripheral surface of the peripheral wall against the pedestal immediately after the extrusion molding as shown in FIG. 6A. In this transport, as shown schematically in FIG. Local deformation of the peripheral wall may occur. When the peripheral wall is locally deformed in this way, a partial contact of the honeycomb structure occurs at the time of canning, or a partition wall near the deformed peripheral wall follows and deforms, resulting in a decrease in isostatic strength and a honeycomb. The risk of damage to the structure increases. Therefore, the pass / fail is determined by paying attention to 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 constituting 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 spacing in the honeycomb structure,
As shown in FIG. It is clear from FIG. 7 that the partition spacing increases sharply at a certain aperture ratio for any partition thickness. Further studies on the relationship between this aperture ratio and the partition wall thickness revealed that the aperture ratio OFA was -0.
When it exceeds 58 × 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 follows the peripheral wall. It has been confirmed that the deformation may cause a decrease in isostatic strength in some cases. If the partition wall and the peripheral wall are not deformed and have an ideally accurate shape, the compressive stress field predominantly acts on the honeycomb structure due to the isostatic load, but the deformation does not occur. If it occurs, a tensile stress may be generated at that location. In this case, the isostatic strength is governed by the tensile stress, and therefore, a sharp decrease in strength is caused.

The excellent functional characteristics of the ceramic honeycomb catalyst according to the present invention having the ceramic honeycomb structure 10 satisfying the above 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 pressure loss characteristics in a 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 in the measuring unit 23, and the blower 21 pumps air through the rectifying unit 22 to form a honeycomb structure. The pressure difference is measured by a manometer 25 while passing through the body 24 and the pressure difference before and after the honeycomb structure 24. Using this measuring device 20, the pressure loss characteristics of a group of ceramic honeycomb structures having a fixed size (cross-sectional area and volume) and a different aperture ratio were measured while changing the air flow rate. The measurement results are as shown in FIG. It is clear from FIG. 9 that the pressure loss increases as the aperture ratio decreases. FIG. 10 shows a change in pressure loss due to 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 at an opening ratio of 70% or less, particularly at 65% or less. From this result, the lower limit of the aperture ratio is 65
% (= 0.65), preferably 70% (= 0.70).

Next, the effect of the ceramic honeycomb structure 10 on the engine output characteristics in the ceramic honeycomb catalyst according to the present invention will be described in relation to the aperture ratio. FIG. 11 shows a test device 30 for a honeycomb structure using an actual engine. The test device 30 is a six-cylinder 30
An exhaust manifold 32 having a length of 50 cm is connected to a 00 cc gasoline engine 31, a converter 33 including a honeycomb structure to be measured is disposed immediately below the exhaust manifold 32, and a 1700 cc capacity underfloor converter 34 and a muffler are provided downstream thereof. The dynamometer 36 is connected to the output shaft of the engine 31 while connecting the 35. The maximum output of the engine 31 per group of converters equipped with a catalyst carrier consisting of a ceramic honeycomb structure having a fixed size (capacity of 1700 cc) and a different opening ratio as the converter 33 immediately below the manifold using the test apparatus 30 is shown. The engine output at the time was measured by a dynamometer 36. The measurement results are as shown in FIG. From FIG. 12, it is recognized that the tendency of the engine output to decrease becomes remarkable at an opening ratio of 70% or less, particularly at 65% or less.

Next, the exhaust gas purifying performance when the automotive exhaust gas purifying system is equipped with the ceramic honeycomb catalyst according to the present invention will be described. In general, exhaust gas measurement of an actual vehicle is performed in a driving state with a vehicle speed pattern defined in a predetermined driving 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 diagram showing a vehicle speed pattern in the initial 505 seconds in the LA-4 mode. 6
Equipped with a ceramic catalyst carrier with a fixed size (capacity: 1200 cc) and cell density (60 cells / cm ² ) with only a constant wall thickness, as a converter directly below the exhaust manifold in a test vehicle equipped with a 2500 cc cylinder gasoline engine With respect to the group of converters, the cumulative amount of hydrocarbon (HC) emission in the initial 505 seconds in the LA-4 mode was measured. The measurement results are as shown in FIG.
From FIG. 14, it is recognized that the thinner the partition walls, the lower the hydrocarbon emission amount. FIG. 15 shows the amount of hydrocarbon emissions during the initial 505 seconds in the LA-4 mode for the above-described converter group to be measured. From FIG. 15, it is also recognized that the thinner the partition wall, the smaller the amount of hydrocarbon emission, and the decreasing tendency becomes remarkable when the wall thickness is 0.124 mm or less. Furthermore, when the relationship between the amount of hydrocarbon emissions and the heat capacity of the catalyst was investigated, as shown in Fig. 16, the smaller the heat capacity, the lower the amount of hydrocarbon emissions.
/ m ³ K or less, preferably 410 kJ / m ³ K or less. Further, the catalyst heat capacity and each emission component (NOx, CO, HC) up to the second peak of Bag A
When checking the relationship between the purification efficiency of, as shown in FIG. 17, improves as the purification efficiency is also small heat capacity for either emission component, the improvement trend heat capacity 450 kJ / m ³ K below, suitably Was found to be significant below 410 kJ / m ³ K.

The purification performance of an automotive exhaust gas purification system at the time of cold start depends on the superiority of the temperature rise characteristics of the catalyst carrier itself, and the smaller the bulk density of the catalyst carrier, that is, the smaller the heat capacity of the catalyst, the better the purification performance. . Therefore, as a converter immediately below the exhaust manifold in a test vehicle equipped with a 6-cylinder 2500cc gasoline engine, the size (capacity 1200cc) and cell density (60
/ cm ² ) For a plurality of converters equipped with ceramic catalyst carriers having different wall thicknesses of the partition walls, the temperature change of the catalyst carriers in the initial 505 seconds in the LA-4 mode was measured from the exhaust gas inlet side in the center of the carrier. It was measured at a position of 15 mm. The measurement results are as shown in FIG. From FIG. 18, it is recognized that the thinner the partition walls, and thus the lower the bulk density, the better the temperature-raising characteristics of the carrier. From FIG. 18, it is also recognized that the metal honeycomb catalyst has a lower rate of temperature rise than the ceramic honeycomb catalyst. This is considered to be due to the fact that the metal has a higher thermal conductivity than the ceramic and, as a result, the amount of heat radiation during the temperature raising process is larger than that of the ceramic.

Further, a converter equipped with a ceramic honeycomb catalyst carrier and a converter equipped with a metal honeycomb catalyst carrier as converters immediately below the exhaust manifold in a test vehicle equipped with a 6-cylinder 2500 cc gasoline engine are LA-4 mode. Early 505 in
The emission (NOx, CO, HC) emission per second was measured. The measurement results are as shown in the bar graph of FIG. From these measurement results, the superiority of the ceramic honeycomb catalyst carrier in the exhaust gas purification performance over the metal honeycomb catalyst carrier is apparent.

As described above, the ceramic honeycomb structure as a catalyst carrier in the ceramic honeycomb catalyst according to the present invention has an A-axis compression strength of 50 kgf / cm ² or more and a B-axis compression strength of 5 kgf / cm ² or more. is there. The inventors have conducted intensive studies and experiments with the aim of improving the compressive strength characteristics of the ceramic honeycomb structure, and found that deformation and loss of the partition walls at the manufacturing stage of the honeycomb structure led to a decrease in the compressive strength, and excellent. In order to realize the compressive strength characteristics, it has been found that it is particularly important to quantitatively maintain the degree of deformation and the degree of loss of the partition walls within predetermined ranges.

First, bending as one mode of deformation of the partition wall
The deformation will be described. Such bending deformation, for example,
Occurs inside the ramic honeycomb structure
Are likely to occur on the partition wall near the joint with the peripheral wall,
When the cam structure is observed from the flow channel direction,
Can be recognized. In this case, as shown in FIG.
In addition, a gap for forming an arbitrary through-hole in the honeycomb structure
A wall (referred to as a “unit partition”), for example, curved in an arc shape
Connect the centers of the circles inscribed on both sides of the partition wall
Is defined as the center line of the partition, and any two
Straight line distance L between points_AAnd the center line length L between the two points_BWith
The length ratio, that is, the length ratio L illustrated in FIG. 21A, for example._B
/ L_AFocusing on, the degree of bending deformation is quantified. length
Ratio L_B/ L_AThe two points on the center line for calculating the length ratio L_B
/ L_AIs to be maximized. Shape of bending deformation of partition wall
The state is a curved arc outside the entire length, FIG. 21B and
As shown in FIG. 21C, the fold line or partially curved
There is also In the present invention, the length ratio L_B/ L_AHani
1 or more for almost all partition walls in cam structure 1.10
And the length ratio L_B/ L_AExceeds 1.10
The total number of bulkheads that is 1.15 or less is 1% or less of the total number of bulkheads
It is assumed that. FIG. 22 shows the change of the partition in one carrier.
Shape quantity, that is, length ratio L_B/ L_AMaximum value and isoster
It is a graph which shows the relationship with tick intensity. Isoster
Become a break point before performing a tick destruction test
Length ratio L_B/ L
_AWas measured. After that, the isostatic breakdown test
And the length ratio L of the partition wall at the breaking point_B/ L_AAnd iso
The relationship with the static strength was investigated by changing the wall thickness of the bulkhead.
Was. Here, Hani 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. Upper song in Fig. 22
Lines show data for thicker bulkheads and lower
Curves show data for thin wall partitions, respectively.
You. From this survey, the length ratio L_B/ L_AIs less than 1.10
And isostatic strength tend to increase sharply
It has been found. Figure 23 shows an arbitrary crossing of one honeycomb
The rate of occurrence of partition walls with bending deformation in the plane,
Length ratio L_B/ L_AOf the partition wall
It is a graph which shows typically whether it exists. Length ratio L_B/
L_AHoneycomb structure with only 1.10 or less partition walls
If present, length ratio L_B/ L_AWith a barrier 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 to the total number of bulkheads (%)
It is a graph which shows the relationship with so static strength. Fig. 24
The upper curves in are data for thick wall partitions
The lower curve shows the data for a thin wall partition.
Are shown respectively. From this graph, the quantity ratio
 The isostatic strength sharply increases below 1.0%
It is recognized that there is a tendency to increase. The reason is as follows
It is as follows. In other words, the existence of the partition walls that
When the presence ratio increases, the deformed partition wall as shown in FIG. 25A
When comrades are crowded, in other words, two or more deformed bulkheads
Continuity increases stochastically;
It is possible that wills are next to each other. This deformed barrier
The case where the wall is dense and the partition wall which is deformed as shown in FIG. 25B
Stations at that location when scattered at a certain distance
Comparing the partial structural strengths,
However, it is clear that the cells are easily crushed and the structural strength is reduced.
It is easy. And Hani where the deformed partition is dense
Perform isostatic fracture test on cam structure
Since such a low-strength part becomes a breaking point,
The isostatic strength also decreases. The quantity ratio is 1.0
%, The density of the partition walls that caused bending deformation stochastically
Parts are more likely to be present, reducing the isostatic strength
You. Conversely, if the quantity ratio is 1.0% or less,
It is difficult to have densely packed bulkheads that have stochastically deformed.
And deformed partition walls are scattered, and the structural strength is high even when viewed locally.
It improves the isostatic strength
is there.

Next, a crushing deformation as another mode of the deformation of the partition wall will be described. This crushing deformation is different from the bending deformation of the partition walls described above, and occurs as a change in the intersection angle of the adjacent partition walls. In other words, for example, in the case of a square cell, the crushing deformation occurs as a rhombus in the cell shape. In this case, as shown in FIG. 26, for an arbitrary cell in the honeycomb structure, the center of the largest inscribed circle inscribed in at least three corners within the intersection on both sides of each unit partition wall constituting the cell is defined as the lattice of the cell. As points, deformation is quantified by focusing on the length ratio Lmax / Lmin between the maximum length Lmax and the minimum length Lmin in each diagonal line connecting the opposing grid points. In the present invention, this length ratio is set to 1 or more and 1.73 or less in the case of the square cell shown in FIG.
In the case of the hexagonal cell shown in (1), it should be 1.15 or more and 1.93 or less.
FIGS. 28 and 29 are graphs showing the relationship between the diagonal length ratio Lmax / Lmin and the isostatic strength in the rectangular cell and the hexagonal cell when the wall thickness of the partition wall is changed, respectively. The upper curves in FIGS. 28 and 29 show data for a partition with a thick wall, and the lower curves show data for a partition with a thin wall. From these graphs, it is recognized that the isostatic strength tends to sharply increase 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.

Also, unlike the above-described bending deformation and crushing deformation of the partition wall, the isostatic strength of the honeycomb structure is reduced even when a gap is generated in an arbitrary cross section due to the lack of the partition wall in the flow direction. FIG. 30A and FIG.
30B shows the shape of the defect observed in the flow channel direction. The loss of the partition wall may occur at an arbitrary position between the lattice points or at the lattice points.
Count. In the present invention, the total number of partitions having voids in an arbitrary cross-section due to the lack of partitions in the flow channel direction is preferably 1.0% of the total number of partitions in the honeycomb structure.
The following is assumed. In addition, the total number of the partition walls having voids in an arbitrary cross section due to the lack of the partition walls in the flow path direction in the entire peripheral region containing 20 cells inside from the outermost periphery, preferably the total number of partition walls in the honeycomb structure. 0.5% or less. FIG. 31 and FIG. 32 are graphs each showing the relationship between the total number of partitions having a defect and the isostatic strength when the partition wall thickness is changed. The upper curves in FIGS. 31 and 32 show data for a partition with a thick wall, and the lower curves show data for a partition with a thin wall. FIG.
From this, it is recognized that the isostatic strength tends to sharply increase when the ratio of the total number of partition walls having a defect to the total number of partition walls in the honeycomb structure is 1.0% or less. Further, when examining the relationship with the location of occurrence of the partition wall defect, from FIG. 32, the total number of partition walls having a defect in the flow channel direction in the entire circumferential area including 20 cells inside from the outermost periphery is the same in the honeycomb structure. It can be seen that the isostatic strength tends to increase sharply when the proportion of the total number of partitions is 0.5% or less.

The data of the isostatic strength shown in the above description is based on a honeycomb structure having a quadrangular cell shape and a round outer shape. Similar results are obtained for a honeycomb structure having triangular and hexagonal cell shapes. Are obtained, and a similar result is obtained for a honeycomb structure having an oval outer shape.

[0024]

As is clear from the above, 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 as compared with the conventionally known ones. By configuring, the pressure loss is reduced by increasing the aperture ratio, and when the honeycomb structure is used as a catalyst carrier, the heat capacity of the carrier is reduced. On the other hand, the wall thickness of the partition and the opening of the honeycomb structure are reduced. By satisfying the above-mentioned certain conditions between the ratio and the bulk density, in particular, by maintaining the degree of deformation / defect that can occur in the partition walls in the manufacturing stage of the honeycomb structure quantitatively within a predetermined range. Although the partition walls are thin, it is possible to realize practically satisfactory compressive strength characteristics.

[Brief description of the drawings]

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

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

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

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

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

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

FIG. 7 is a graph showing a relationship between an aperture ratio and a partition interval in a ceramic honeycomb structure.

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

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

FIG. 10 is a graph showing a change in pressure loss accompanying a change in aperture ratio when the air flow rate is kept constant, measured using the measuring device of FIG. 8;

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

FIG. 12 is a graph showing engine output characteristics measured using the measurement device of FIG. 11;

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

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

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

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

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

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

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

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

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

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

FIG. 23 is a graph schematically showing a generation ratio of a partition wall in which deformation occurs in an arbitrary cross section of one honeycomb.

[Figure 24] length ratio L _B / L _A is greater than 1.10, and, 1.15
It is a graph which shows the relationship between the number ratio (%) of the total number of the following partitions to the total number of partitions and the isostatic strength.

FIGS. 25A and 25B are explanatory diagrams showing the form of existence of a partition wall which has been bent and deformed.

FIG. 26 is an explanatory diagram of a deformation amount accompanying a crush deformation of a partition wall in a honeycomb structure having square cells.

FIGS. 27A and 27B are explanatory views showing a state before and after crushing deformation of a partition wall in a honeycomb structure having hexagonal cells. FIGS.

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 view showing a state where a partition wall is missing in a honeycomb structure having square cells.

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

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-207845 (JP, A) JP 4-70053 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01J 35/04 B01D 53/86

Claims (13)

(57) [Claims] 1. A ceramic honeycomb structure as a catalyst carrier having a peripheral wall and a partition wall disposed inside thereof, a cell having a polygonal cross section as a flow path between the partition walls, and a ceramic honeycomb structure supported by the honeycomb structure. A honeycomb structure comprising the following catalyst components, 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 Satisfies the opening ratio of the body, the wall thickness of the surrounding wall is at least 0.1 mm,
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.
A ceramic honeycomb catalyst characterized by being 450 kJ / K or less per m ³ . 2. The upper limit of the wall thickness of the partition walls in the honeycomb structure is 0.124 mm, the lower limit of the aperture ratio is 0.70, and the upper limit of the heat capacity of the catalyst is 410 kJ / K per 1 m ^{3 of the} catalyst capacity. The ceramic honeycomb catalyst according to claim 1, wherein: 3. A ceramic honeycomb structure as a catalyst carrier having a peripheral wall and a partition wall disposed inside thereof, a cell having a polygonal cross section as a flow path between the partition walls, and a ceramic honeycomb structure supported by the honeycomb structure. Wherein the honeycomb structure has the following formula: 0.050 ≦ t ≦ 0.150 k × {1 − (− 0.58 × t + 0.98)} ≦ G ≦ k × 0.35 where t is G is the bulk density of the honeycomb structure, k is the true specific gravity of the material × (1−porosity of the material), and the wall thickness of the 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.
A ceramic honeycomb catalyst characterized by being 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 upper 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} catalyst capacity.
The ceramic honeycomb catalyst according to claim 3, wherein the temperature is equal to or lower than K. 5. A center line between any two points on the center line, wherein a line connecting the centers of circles inscribed on both surfaces of an arbitrary unit partition wall in the cross section of the honeycomb structure is defined as a center line of the partition wall. 4. The ceramic honeycomb catalyst according to claim 1, wherein 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 line between any two points on the center line, wherein a line connecting the centers of circles inscribed on both surfaces of an arbitrary unit partition in the transverse section of the honeycomb structure is defined as a center line of the partition. The total number of partitions having a line length and a length ratio of a straight line distance between the two points exceeding 1.10 and not more than 1.15 is 1% or less of the total number of partitions. 4. The ceramic honeycomb catalyst according to 3. 7. In any cell of the honeycomb structure, when the center of the largest inscribed circle inscribed in at least three corners within the intersection on both sides of each unit partition wall constituting the cell is set as a lattice point of the cell. In each diagonal line connecting the opposing grid points, the length ratio between the maximum length and 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.
The ceramic honeycomb catalyst according to claim 1, wherein the ceramic honeycomb catalyst has a ratio of 15 to 1.93. 8. The total number of partitions having voids in an arbitrary cross section due to the lack of partitions in the flow direction of the honeycomb structure is 1% of the total number of partitions in the cross section of the honeycomb structure.
The ceramic honeycomb catalyst according to claim 1 or 3, wherein: 9. The honeycomb structure according to claim 1, further comprising:
Within the entire peripheral area in which the cells are contained, the total number of partition walls having voids in an arbitrary cross section due to the lack of the partition walls in the flow path direction is 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, characterized in that: 10. The ceramic honeycomb catalyst according to claim 1, wherein the honeycomb structure is formed by integral extrusion. 11. The ceramic honeycomb catalyst according to claim 1, 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 rectangular cross section and is made of cordierite, and the catalyst is provided in an exhaust gas purification system for automobiles. The ceramic honeycomb catalyst according to the above. 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. .