JP2005052750A - Ceramic honeycomb catalyst for exhaust gas cleaning apparatus and exhaust gas cleaning apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a ceramic honeycomb catalyst for an exhaust gas cleaning apparatus for cleaning the exhaust gas from a diesel engine, whose catalyst-deposited amount per the unit volume can be increased and which is made compact and has high cleaning efficiency. <P>SOLUTION: This ceramic honeycomb catalyst is obtained by depositing a catalytic substance on a ceramic honeycomb structure having an outer peripheral wall and many circulation pores divided inside the outer peripheral wall by partitions in the axial direction. The average pore size of the partitions of the ceramic honeycomb structure is made to be ≥15 μm and the porosity is made to be 50-80%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to exhaust gas purification that purifies exhaust gas from an engine using catalytic action.

Demand for diesel engines is increasing mainly in Europe due to its high fuel efficiency. However, since particulate matter (PM) and nitrogen oxides (NO _x ) contained in the exhaust gas of diesel engines have a great influence on human health, this PM and NO _x reduction technology Various studies have been made.

As an exhaust gas purifying device for reducing PM and NO _x in the exhaust gas, for example, the invention described in Patent Document 1 includes an improvement in which combustion exhaust gas containing NO (nitrogen monoxide) and particulate matter is treated. a SCR mechanism that is, the NO oxidation catalyst to efficiently convert at least part NO 2 _(nitrogen dioxide) of NO in _x, and particulate matter trap, a source of reductant fluid, and SCR (Selective Catalytic Reduction) An SCR mechanism is disclosed in which catalysts are combined in this order. Here, SCR refers to selective catalytic reduction, which purifies by passing high-temperature exhaust gas over the catalyst in the presence of a nitrogen-based reducing agent, particularly ammonia or urea, to convert nitrogen oxides to nitrogen. It is a method to do. According to the present invention, the oxidation catalyst disposed upstream of the SCR catalyst and the particulate matter trap are considered to be particularly effective in increasing the conversion rate from NO _x to N ₂ by the SCR mechanism. In the present invention, for example, a platinum catalyst supported on a through-flow honeycomb carrier made of ceramic or metal is particularly suitable as the oxidation catalyst, and the particulate material trap has a wall flow produced from ceramic. A filter is preferred, and a V ₂ O ₅ / WO ₃ / TiO ₂ catalyst supported on a through-flow honeycomb carrier is preferred for the SCR catalyst.

Further, in the invention described in Patent Document 2, as shown in FIG. 3, the exhaust system 27 of the diesel engine according to the present invention is provided with an SCR catalyst 25 for reducing and purifying NO _x in the exhaust passage 27 of the diesel engine. And an oxidation catalyst 23 in order from the upstream side, and a filter 24 that can collect a sulfate component generated by oxidizing sulfur in exhaust gas by the catalytic action of the oxidation catalyst 23 on the upstream side of the SCR catalyst. An exhaust gas purifying device for a diesel engine characterized by being arranged in series is disclosed. A reducing agent supply device 26 is provided in the exhaust passage 27 between the filter 24 and the SCR catalyst 25. According to the configuration of the present invention, the sulfur content contained in the exhaust gas can be collected together with the dust in the exhaust gas, and the downstream SCR catalyst 25 can be prevented from being poisoned by dust such as the sulfur content and PM. so it can be efficiently reduce and purify NO _x, are the pollution can be reduced by the exhaust gas. In the present invention, the oxidation catalyst 23 is, for example, a cordierite monolith support formed by coating an alumina catalyst support layer on a support and a catalyst component such as platinum is supported on the support layer. A cordierite honeycomb filter in which a large number of exhaust passages are formed in parallel with each other, a filter made of a ceramic nonwoven fabric such as alumina, and the like can be used. Further, the SCR catalyst 25 uses Al ₂ O ₃ , TiO _{2 as} a carrier. The catalyst metal is formed of Pt, V ₂ O ₅ , Fe ₂ O ₃ , CuO, Mn ₂ O ₃ , Cr ₂ O ₃ , MoO ₃ or the like as an active substance.

Japanese translation of PCT publication No. 2002-502927 JP 2000-303826 A

  However, in the exhaust gas purification processing technologies described in Patent Documents 1 and 2, the oxidation catalyst, the DPF, and the SCR catalyst are arranged in series in the exhaust gas passage, and each of the devices includes an outer peripheral wall and an outer peripheral wall. Since a honeycomb structure having a large number of flow holes partitioned on the inner side by partition walls in the axial direction is used, there is a problem that the installation space becomes enormous.

In order to reduce the installation space of the exhaust gas purification device, it is necessary to increase the purification efficiency of the SCR catalyst disposed on each device, particularly the exhaust gas outflow side of the purification device, and to reduce the size of the SCR catalyst. In this SCR catalyst, the exhaust gas is purified by utilizing the catalytic reaction between the catalyst material supported on the partition wall surface of the honeycomb structure and the exhaust gas. There was a need to increase the chances of material contact. For this purpose, it is necessary to increase the amount of the catalyst substance supported on the honeycomb structure by increasing the geometric surface area per unit volume of the honeycomb structure. The geometric surface area per unit volume of the honeycomb structure is expressed by the following equation.
Geometric surface area per unit volume: S = 4 × (P−t) / P ² (mm ² / mm ³ )
Here, P is the pitch (mm) of the partition walls, and t is the thickness (mm) of the partition walls.
Therefore, in order to increase the geometric surface area per unit volume of the honeycomb structure, the partition wall thickness is reduced to less than 0.1 mm or the partition wall pitch is decreased to less than 1.0 mm. It was necessary to use a so-called thin wall, high cell density honeycomb structure having a thickness of 0.05 mm and partition wall pitch of 0.85 mm.

However, when a thin wall, high cell density honeycomb structure is used for the SCR catalyst, the opening area in the direction of the honeycomb structure flow hole decreases, and the pressure loss at the honeycomb structure inlet increases. There is a problem of increased loss. Furthermore, in the case of an SCR catalyst carrier for a diesel engine, since it usually has a large-diameter honeycomb structure with an outer diameter of 140 mm or more, the partition walls are easily deformed by the weight of the honeycomb structure itself at the time of molding, and the isostatic strength is reduced. The so-called thin wall, high cell density honeycomb having a partition wall thickness of less than 0.1 mm and a partition wall pitch of less than 1.0 mm, which has been used as a conventional catalyst support for gasoline engines. In the structure, there is a problem that there is a limit to downsizing and high efficiency of the SCR catalyst device. Further, in the prior art, there is no description about the size of the pores present in the porous partition walls of the ceramic honeycomb structure for the SCR catalyst device, and the pore size is particularly considered. It was not a thing.
An object of the present invention is to solve the above problems and to obtain a ceramic honeycomb catalyst used in an exhaust gas purification device, particularly an SCR catalyst device, which has high purification efficiency and can be downsized.

The present inventor has purified efficiency and miniaturization of the exhaust gas purifying apparatus, in particular the purpose of purification efficiency and downsizing of _the NO _x purification device for a ceramic honeycomb catalyst represented by the SCR catalyst, ceramic honeycomb structure is a catalyst carrier In order to increase the amount of catalyst material supported per unit volume without making the body thin wall and high cell density, it is only necessary to focus on the relationship between the porosity of the partition walls of the honeycomb structure and the average pore diameter I found. As a result, it has been found that the purification efficiency and size reduction of the ceramic honeycomb catalyst for an exhaust gas purification device can be achieved, and the present invention has been conceived.

  That is, in the ceramic honeycomb catalyst for an exhaust gas purifying apparatus of the present invention, the catalyst substance is supported on the ceramic honeycomb structure having a plurality of flow holes partitioned by the porous partition walls in the axial direction inside the outer peripheral wall and the outer peripheral wall. The ceramic honeycomb catalyst is characterized in that the average pore diameter of the partition walls of the ceramic honeycomb structure is 15 μm or more, and the porosity of the partition walls is 50% to 80%.

  In the ceramic honeycomb catalyst for an exhaust gas purification apparatus of the present invention, the wall thickness of the partition walls of the ceramic honeycomb structure is preferably 0.1 to 0.35 mm, and the pitch of the partition walls is preferably 1.0 to 2.0 mm. More preferably, the body is made of cordierite ceramics. In the ceramic honeycomb catalyst for an exhaust gas purification apparatus of the present invention, the catalyst material is preferably an SCR catalyst.

  Another aspect of the present invention is an exhaust gas purification device installed in an exhaust passage of a diesel engine, and has an outer peripheral wall and a large number of flow holes partitioned axially by a porous partition wall inside the outer peripheral wall. An exhaust gas comprising a ceramic honeycomb catalyst in which a catalyst substance is supported on a ceramic honeycomb structure in which the average pore diameter of the partition walls is 15 μm or more and the porosity of the partition walls is 50% to 80%. It is a gas purification device.

  The ceramic honeycomb catalyst for exhaust gas purification apparatus of the present invention has an average pore diameter of 15 μm or more of a porous partition wall having a plurality of flow holes axially partitioned by partition walls inside the outer peripheral wall and the outer peripheral wall. Therefore, the amount of the catalyst substance that can be supported per unit volume of the honeycomb structure can be increased. That is, since the porosity of the partition walls is 50 to 80% and the average pore diameter is relatively large, the catalyst is not only in the partition wall surface but also in the pores opened on the partition wall surface. The substance can be supported. Thus, when the exhaust gas passes through the flow hole from the inflow side to the outflow side, the exhaust gas is purified by the catalytic material supported on the partition wall surfaces in the numerous flow holes partitioned in the axial direction by the partition walls. In addition to being performed, the catalytic substance in the pores opened on the partition wall surface also effectively exhibits a catalytic function to purify the exhaust gas. In this way, in addition to the partition wall surface constituting the flow hole, the surface of the pores formed in the partition wall can be used effectively, and the amount of catalyst supported per unit volume can be increased, improving the purification performance. In addition, it is possible to reduce the size of the ceramic honeycomb catalyst for the exhaust gas purification device, and it is possible to reduce the size of the entire exhaust gas purification device.

FIG. 1 shows a perspective view of a ceramic honeycomb catalyst 11 for an exhaust gas purifying apparatus according to the present invention. FIG. 2 is a schematic cross-sectional view of the ceramic honeycomb catalyst 11 of FIG. As shown in FIGS. 1 and 2, the ceramic honeycomb catalyst 11 for an exhaust gas purifying apparatus of the present invention has an outer peripheral wall 11a and a large number of flow holes 11c surrounded by partition walls 11b on the inner peripheral side of the outer peripheral wall 11a. The ceramic honeycomb catalyst as a whole has a substantially cylindrical shape or a substantially elliptical cylindrical shape.
The catalytic reaction with the exhaust gas in the ceramic honeycomb catalyst 11 for the exhaust gas purifying apparatus of the present invention is performed, for example, as follows. In FIG. 2, exhaust gas 27 (represented by a line as the exhaust gas flow in FIG. 2) flows from the flow holes 11 c opened on the inflow side of the ceramic honeycomb catalyst 11, and enters the pore surfaces of the partition walls 11 b. For example, NO _x in the exhaust gas 27a is purified by the supported catalyst material. At the same time, for example, NO _x in the exhaust gas 27b is purified by the catalyst material supported in the pores opened on the partition wall surface.

The reason why the average pore diameter in the partition walls of the ceramic honeycomb structure used in the ceramic honeycomb catalyst for the exhaust gas purifying apparatus of the present invention is 15 μm or more and the porosity of the partition walls is 50% to 80% is as follows.
When the average pore diameter in the partition walls of the honeycomb structure is less than 15 μm and the porosity of the partition walls is less than 50%, the pores opened on the partition surface cannot be used effectively as in the conventional honeycomb structure. This is because the amount of catalyst per unit volume cannot be remarkably increased, and as a result, the reaction between the exhaust gas and the catalyst substance is not promoted. On the other hand, if the porosity exceeds 80%, the strength of the honeycomb structure is lowered, and there is a risk of damage due to mechanical stress or vibration when used as an exhaust gas purification device. The average pore diameter in the partition walls of the exhaust gas purification catalyst carrier is preferably 18 μm or more and 40 μm or less, and the porosity is preferably 60 to 75%. The porosity and average pore diameter are defined as those measured by mercury porosimetry.

  Of the pores contained in the porous partition walls of the ceramic honeycomb structure used in the ceramic honeycomb catalyst for an exhaust gas purification apparatus of the present invention, the total pore volume with a pore diameter of 20 to 40 μm is 25 of the total pore volume. % Or more is preferable. By setting the volume of pores having a pore diameter of 20 to 40 μm to 25% or more of the total pore volume, the amount of catalyst per unit volume can be further increased, and the exhaust gas purification performance can be improved. At the same time, it is possible to relatively reduce the amount of pores of 40 μm or more, and to prevent a decrease in strength.

  The thickness of the partition walls of the honeycomb structure used in the ceramic honeycomb catalyst for an exhaust gas purification apparatus of the present invention is preferably 0.1 to 0.35 mm, and the pitch of the partition walls is preferably 1.0 to 2.0 mm. The reason is as follows. If the partition wall thickness is less than 0.1 mm, the porosity of the partition wall is set in a high range of 50 to 80%, which is not preferable because the strength of the honeycomb structure is lowered. On the other hand, if the partition wall thickness exceeds 0.35 mm, the opening area of the inlet of the through hole of the carrier is reduced, and the ventilation resistance at the inlet end face with respect to the exhaust gas is increased. is there. A more preferable partition wall thickness is 0.2 to 0.35 mm, and a still more preferable partition wall thickness is 0.29 to 0.35 mm. In addition, if the partition wall pitch is less than 1.0 mm, the opening area of the through hole entrance of the honeycomb structure becomes small, and thus the pressure loss at the entrance of the honeycomb structure becomes large. On the other hand, if the pitch of the partition walls exceeds 2.0 mm, the geometric surface area for supporting the catalyst becomes small, and the amount of catalyst supported decreases. A more preferable partition pitch is 1.4 to 1.7 mm.

The exhaust gas purifying device for a ceramic honeycomb catalyst of the present invention, the it is preferred that the catalyst material is a SCR catalyst, in particular, the SCR catalyst exhaust gas regulations in the future of the diesel engine, especially important in reduction of the NO _x This is because it is considered to be added to an exhaust gas purification device that combines a conventional oxidation catalyst and a DPF, so that a reduction in size is particularly required.
The catalyst material supported on the ceramic honeycomb catalyst for an exhaust gas purifying apparatus of the present invention may be any catalyst material that can purify NO _x , but preferably V ₂ O ₅ , TiO ₂ , WO ₃ Fe ₂ O ₃ , CuO, Mn ₂ O ₃ , Cr ₂ O ₃ , MoO _{3 and the} like.

  As the material constituting the partition walls of the honeycomb structure used in the ceramic honeycomb catalyst for the exhaust gas purifying apparatus of the present invention, the present invention is mainly used for purifying the exhaust gas of the engine. It is preferable to use an excellent material, and it is preferable to use a ceramic material whose main crystal is at least one selected from the group consisting of cordierite, alumina, mullite, silicon nitride, silicon carbide, and LAS. Among them, a honeycomb structure having cordierite as a main crystal is most preferable because it is easy to manufacture, inexpensive, excellent in heat resistance and corrosion resistance, and has low thermal expansion.

The exhaust gas purification device of the present invention is an exhaust gas purification device installed in an exhaust passage of a diesel engine, and is porous in the axial direction inside the outer peripheral wall and the outer peripheral wall. Ceramic in which a catalyst material is supported on a ceramic honeycomb structure having a large number of flow holes partitioned by partition walls, an average pore diameter of the partition walls of 15 μm or more, and a porosity of the partition walls of 50% to 80% Since the honeycomb catalyst is provided, the amount of catalyst material supported per unit volume of the ceramic honeycomb structure can be increased, so that the NO _x purification efficiency is improved and, as described above, more than the conventional exhaust gas purification device. The purification efficiency can be improved and the size can be reduced.

As described above, the ceramic honeycomb catalyst of the present invention is a ceramic honeycomb catalyst in which a catalytic substance is supported on a ceramic honeycomb structure having a plurality of flow holes that are partitioned by partition walls in the axial direction inside the outer peripheral wall and the outer peripheral wall. In addition, when the average pore diameter of the partition walls of the ceramic honeycomb structure is 15 μm or more and the porosity is 50% to 80%, the amount of catalyst supported per unit volume can be increased, and the NO _x purification performance is improved. At the same time, the exhaust gas purification device can be miniaturized. Therefore, by using the cordierite ceramic honeycomb catalyst of the present invention as the SCR catalyst, it becomes possible to supply the exhaust gas purification device with a reduced size.

Hereinafter, embodiments of the present invention will be described in detail.
An example of a method for producing a ceramic honeycomb structure having a peripheral wall used in the ceramic honeycomb catalyst of the present invention and a plurality of flow holes axially partitioned by partition walls inside the peripheral wall will be described. First, an organic binder, a forming aid such as a lubricant, and a pore former are added to the ceramic raw material powder, and after mixing, a predetermined amount of water is injected, and mixing and kneading are performed to prepare a clay having plasticity. Thereafter, the kneaded material is extruded using a known honeycomb structure mold, so that the outer wall and the inner wall of the outer wall are surrounded by a partition wall in the axial direction, and the honeycomb having a square-shaped passage hole. A shaped body is obtained. Thereafter, the ceramic honeycomb structure is cut into a predetermined length, dried and fired to obtain a ceramic honeycomb structure having a large number of flow holes partitioned by a partition wall inside the outer peripheral wall and the outer peripheral wall. At this time, a ceramic honeycomb structure having an average pore diameter of 15 μm or more and a porosity of 50 to 80% can be obtained by appropriately adjusting the type and addition amount of the pore former. Specifically, a pore former having an average particle diameter of 15 μm or more and having a uniform particle diameter is selected, and by adding 10 parts by mass or more to 100 parts by mass of the ceramic raw material powder, the average pore diameter is 15 μm. Thus, a ceramic honeycomb structure having a porosity of 50 to 80% can be obtained.

  In addition, after forming or removing the outer peripheral wall of the ceramic molded body or fired body having the honeycomb structure after firing and the peripheral portion thereof, the ceramic aggregate, the inorganic binder, and the organic on the removed outer peripheral surface Applying a coating material consisting of a binder, etc., drying and curing to form an outer peripheral wall, adopting a method to make a ceramic honeycomb structure having a large number of through holes partitioned by partition walls inside the outer peripheral wall and the outer peripheral wall Also good.

For example, a catalyst material such as V ₂ O ₅ , TiO ₂ , WO ₃ , Fe ₂ O ₃ , CuO, Mn ₂ O ₃ , Cr ₂ O ₃ , or MoO _{3 is} added to the obtained honeycomb structure. The ceramic honeycomb catalyst is obtained by supporting the structure in the partition wall surface and the pores opened in the partition wall surface.
Examples of the present invention will be described below, but the present invention is not limited thereto.

Kaolin, talc, silica, aluminum hydroxide, to adjust the powder, such as alumina, in a mass _{ratio, SiO 2: 47~53%, Al} 2 O 3: 32~38%, MgO: 12~16% , and CaO, Molded into cordierite-producing raw material powder containing 2.5% or less of components inevitably mixed such as Na ₂ O, K ₂ O, TiO ₂ , Fe ₂ O ₃ , PbO, P ₂ O ₅ Add methylcellulose and hydroxypropylmethylcellulose as auxiliaries, and various graphite powders and / or resin powders with an average particle size of 10 to 45 μm as pore-forming agents, inject a specified amount of water, and further mix thoroughly, The extrudable clay was adjusted to the structure. At this time, the particle diameter and the addition amount of the pore-forming agent were selected so that various average pore diameters and porosity of the partition walls were obtained. Then, the obtained kneaded material is extruded by passing through an extrusion mold for a honeycomb structure, and the outer peripheral wall and a flow hole having a rectangular cross section surrounded by partition walls on the inner peripheral side of the outer peripheral wall A formed article having a honeycomb structure was obtained. At this time, the dimensions of the mold were selected so that various partition wall thicknesses and partition wall pitches were obtained. Thereafter, drying, cutting, and firing are performed to have dimensions of an outer diameter of 143.8 mm and a length of 152.4 mm, and various partition wall thicknesses, partition wall pitches, partition wall average pore diameters, and partition wall pores shown in Table 1. Test NO. Having a ratio of the pore volume having a pore diameter of 20 to 40 μm to the total pore volume. 1 to 10 cordierite ceramic honeycomb structures were produced. Here, the average pore size, porosity, and pore volume of 20 to 40 μm in the partition walls were measured by mercury porosimetry using an Autopore III9410 manufactured by Micromeritics.

These 10 kinds of test NO. For 1 to 10 ceramic honeycomb structures, the pressure loss before and after the honeycomb structure at an air flow rate of 7.5 Nm ³ / min and the isostatic strength at hydrostatic pressure were measured. What pressure loss was 300mmH ₂ O or less (◎), those were 350mmH ₂ O or less (○), it was evaluated that exceeds the 350mmH ₂ O as (×). In addition, the isostatic strength is 1.5 MPa or more (◎), 1.0 MPa or more and less than 1.5 MPa (◯), and less than 1.0 MPa (×). evaluated. These results are shown in Table 1.

Next, these 10 types of test Nos. 1 to 10 ceramic honeycomb structures, TiO ₂ , WO ₃ , V ₂ O ₅ powder, alumina sol, silica sol, and water added as a binder to form a slurry, supported by wash coating and tested . 1 to 10 ceramic honeycomb catalysts were obtained. To these ceramic honeycomb catalysts, exhaust gas temperature of 300 ° C., exhaust gas containing 400 ppm of NO _x was introduced, and urea (N conversion) equal to the amount of NO _x in the exhaust gas was added. The NO _x amount in the exhaust gas at the structure outlet was compared, and the NO _x purification performance was investigated. What _the NO _x purification rate was 90% or more (◎), what _the NO _x purification rate is less than 70% 90% (○), those _the NO _x purification rate was less than 70% (X) was evaluated. The results are also shown in Table 1.

Table 1 shows the results of comprehensive determination from the evaluation results of the pressure loss, isostatic strength, and NOx purification rate. Of the evaluation results for pressure loss, isostatic strength, and NO _x purification rate, the one with (×) is the overall judgment (×), and the evaluation result is (○) or (◎) A comprehensive judgment (○) was made, and an evaluation result of (◎) was taken as a comprehensive judgment (◎).

  From Table 1, test NO. Of the present invention example in which the average pore diameter and the porosity of the partition walls of the ceramic honeycomb structure are within the scope of the present invention. 1 is a comparative example having the same partition wall thickness and partition wall pitch. It can be seen that the amount of catalyst supported per unit volume is larger than the ceramic honeycomb catalyst of No. 7. Test No. which is an example of the present invention. 2 is a comparative example having the same partition wall thickness and partition wall pitch. It can be seen that the amount of catalyst supported per unit volume is larger than the ceramic honeycomb catalyst of 8. Test NO. Test No. 2 is a comparative example having the same partition wall thickness and partition wall pitch as the ceramic honeycomb catalyst of FIG. In the ceramic honeycomb catalyst of No. 9, the amount of the catalyst supported per unit volume was increased, but since the porosity was outside the range of the present invention, the isostatic strength was evaluated as (x). In addition, the test No. of the present invention example. 5 is a comparative example having the same partition wall thickness and partition wall pitch. It can be seen that for 10 ceramic honeycomb catalysts, the amount of catalyst supported per unit volume is large.

  As described above, the test NO. The ceramic honeycomb catalyst of 1 to 5 has an average pore diameter of 15 μm or more and a porosity of 50 to 80% of the partition walls of the ceramic honeycomb structure, so that not only the partition wall surface but also the pores opened on the partition wall surface Since it is possible to increase the amount of catalyst supported per unit volume by supporting the catalyst, the evaluation of the NOx purification rate is (（) or (○), as well as the pressure loss and isostatic strength. Since the evaluation was (◎) or (○), the overall judgment was either (◎) or (○).

  On the other hand, test NO. Which is a comparative example of the present invention. 6-8 and test NO. In the ceramic honeycomb catalyst No. 10, the porosity of the ceramic honeycomb structure partition walls is less than 60% or the average pore diameter is less than 15 μm, so that the catalyst can be sufficiently supported in the pores opened on the partition wall surfaces. As a result, the amount of catalyst supported per unit volume decreased, so the evaluation of the NOx purification rate was (x), and the overall judgment was (x). In addition, as a comparative example of the present invention, test NO. Since the ceramic honeycomb catalyst of No. 9 has a porosity of the ceramic honeycomb structure partition wall exceeding 80%, the catalyst can be sufficiently loaded into the pores opened on the partition wall surface, but the isostatic strength is judged. (×), and the overall judgment was (×).

That is, the ceramic honeycomb catalyst of the present invention, because it can increase the catalyst loading to demonstrate the performance of the SCR catalyst, it is possible to improve _the NO _x purification efficiency of the SCR device, it is possible to miniaturize I understand that. Furthermore, 0.1～0.35Mm the thickness of the partition wall with respect to the ceramic honeycomb structure, excellent in _the NO _x purification rate pitch of the partition walls by a 1.0 to 2.0 mm, pressure loss performance and It can be seen that a ceramic honeycomb catalyst having excellent mechanical strength characteristics can be supplied.

Test No. 1 of Example 1 3 is manufactured, and then cut so that the total length of the honeycomb structure having an outer diameter of 143.8 mm and a total length of 152.4 mm is shortened to a partition wall thickness of 0.3 mm and a partition wall pitch. Test NO. 1.5 mm, porosity of partition wall 73%, average pore diameter of partition wall 35 μm, outer diameter 143.8 mm, and total length 100 mm. Eleven ceramic honeycomb structures were obtained. On the other hand, test NO. When extruding the ceramic honeycomb structure of No. 10, test NO. Cut to a length longer than 10, the partition wall thickness is 0.3 mm, the partition wall pitch is 1.5 mm, the partition wall porosity is 66%, the partition wall average pore diameter is 13 μm, the outer diameter is 143.8 mm, and the total length is 168 mm. Test NO. 12 ceramic honeycomb structures were obtained. These test NO. For the ceramic honeycomb structures 11 and 12, pressure loss and isostatic strength were measured in the same manner as in Example 1, and TiO ₂ , WO ₃ , V ₂ O ₅ powders were bound with alumina sol, silica sol, and water as binders. Was added in the form of a slurry and washed and supported by a test coat. 11 and 12 ceramic honeycomb catalysts were obtained. Then, for these ceramic honeycomb catalysts, the NOx purification rate was evaluated in the same manner as in Example 1. These results are shown in test NO. It shows in Table 2 with the evaluation result of 10 ceramic honeycomb catalysts.

  Test No. described in Table 2 The 10 to 12 ceramic honeycomb catalysts all have the same partition wall thickness of 0.3 mm, the partition wall pitch of 1.5 mm, and the outer diameter of 143.8 mm, but the total length is different from 100 to 190 mm. Test No. which is an example of the present invention. Eleventh ceramic honeycomb catalyst had a total length of 100 mm, but the total amount of catalyst supported per catalyst was large, so the overall judgment was (◎). On the other hand, test NO. No. 10 ceramic honeycomb catalyst has a test NO. Although the total length was longer than that of the 11 ceramic honeycomb catalyst, the amount of catalyst supported per catalyst was small, so the determination of the NOx purification rate was (x), and the overall determination was (x). Furthermore, test NO. No. 12, ceramic honeycomb catalyst, test NO. Compared to the ceramic honeycomb catalyst of No. 11, the total length is longer and the amount of catalyst supported per catalyst is large, so the overall judgment was (◎). Compared to 11 ceramic honeycomb catalysts. From the above results, it can be seen that the ceramic honeycomb catalyst of the present invention can improve the NOx purification rate and can be reduced in size by reducing the overall length as compared with the comparative example.

1 is a perspective view of a ceramic honeycomb catalyst of the present invention. 1 is a schematic cross-sectional view of a ceramic honeycomb catalyst of the present invention. It is a block diagram of the exhaust system of the diesel engine which shows the exhaust gas purification apparatus using the ceramic honeycomb catalyst of this invention.

Explanation of symbols

11: Ceramic honeycomb catalyst 11a: Outer peripheral wall of ceramic honeycomb catalyst 11b: Partition walls of ceramic honeycomb catalyst 11c, distribution holes of ceramic honeycomb catalyst 12a: Partition wall surface of ceramic honeycomb catalyst 12b: Surface of pores in partition walls of ceramic honeycomb catalyst 21: Engine 22: Exhaust passage 23: Oxidation catalyst 24: DPF
25: SCR catalyst 26: Reductant supply device 27: Exhaust gas 27a: Exhaust gas purified by catalyst material supported on the partition wall surface 27b: Purified by catalyst material supported in pores opened on the partition wall surface Exhaust gas

Claims (5)

A ceramic honeycomb catalyst in which a catalyst substance is supported on a ceramic honeycomb structure having a large number of flow holes partitioned axially by porous partition walls inside the outer peripheral wall and the outer peripheral wall, the partition walls of the ceramic honeycomb structure A ceramic honeycomb catalyst for an exhaust gas purification apparatus, wherein the average pore diameter of the catalyst is 15 μm or more, and the porosity of the partition walls is 50% to 80%. 2. The ceramic honeycomb for an exhaust gas purification apparatus according to claim 1, wherein the ceramic honeycomb structure has a partition wall thickness of 0.1 to 0.35 mm and a partition wall pitch of 1.0 to 2.0 mm. catalyst. 3. The ceramic honeycomb catalyst for an exhaust gas purifying apparatus according to claim 1, wherein the ceramic honeycomb structure is made of cordierite ceramic. The ceramic honeycomb catalyst for an exhaust gas purification device according to any one of claims 1 to 3, wherein the catalyst material is an SCR catalyst. An exhaust gas purifying device installed in an exhaust passage of a diesel engine, having an outer peripheral wall and a plurality of flow holes partitioned by a porous partition wall in an axial direction inside the outer peripheral wall, and an average pore diameter of the partition wall An exhaust gas purification apparatus comprising: a ceramic honeycomb catalyst in which a catalyst material is supported on a ceramic honeycomb structure having a partition wall porosity of 50% to 80%.

Images