JP5746986B2 - Manufacturing method of exhaust gas purification filter - Google Patents

Description

The present invention includes a honeycomb base body, a method of manufacturing the exhaust gas purifying filter and a carbon-based material combustion catalyst supported on the honeycomb substrate.

  2. Description of the Related Art There is known an exhaust gas purification filter that collects particulates (hereinafter, appropriately referred to as PM) in exhaust gas discharged from an internal combustion engine such as a diesel engine and purifies the exhaust gas. As such an exhaust gas purification filter, for example, a honeycomb body base material carrying a carbon-based material combustion catalyst for promoting PM combustion is used. The honeycomb base material has porous partition walls arranged in a lattice pattern and a plurality of cells formed in the axial direction surrounded by the partition walls, and among these cells, exhaust gas flows. The one in which the end on the downstream side of the inflow cell and the end on the upstream side of the exhaust cell for discharging the exhaust gas are closed by a plug portion is used. For example, Patent Document 1 discloses a honeycomb base material containing silicon carbide as a main component and further containing a sintering aid.

  In the exhaust gas purification filter having the above configuration, the exhaust gas flows into the inflow cell, passes through the porous partition wall, and is then discharged from the exhaust cell. At this time, the exhaust gas is purified by trapping PM in the exhaust gas in the partition wall having a large number of pores. Further, the PM collected by the partition walls is burned and removed at a predetermined timing. At this time, as described above, the carbon-based material combustion catalyst that promotes the combustion of PM is supported on the partition walls, whereby the PM trapped in the partition walls by the catalytic reaction can be efficiently burned and removed.

The exhaust gas purification filter is produced, for example, as follows.
First, a carbon-based material combustion catalyst is dispersed in a liquid such as water to prepare a catalyst slurry. Then, the honeycomb base material is immersed in the catalyst slurry. Thereby, the catalyst slurry can be impregnated into the porous partition walls of the honeycomb body base material. Next, the honeycomb base material impregnated with the catalyst slurry is dried and heated. Thereby, the said carbonaceous material combustion catalyst is carry | supported by the said honeycomb body base material, and the said exhaust gas purification filter can be obtained.

International Publication WO2006 / 035645 Pamphlet

In the exhaust gas purification filter, exhaust gas containing PM is introduced from the inflow cell side and passes through the porous partition wall, so that most of PM is collected on the inflow cell side of the partition wall. Moreover, high temperature exhaust gas is also introduced from the inflow cell side during the combustion of the PM collected in the partition wall. Therefore, PM combustion proceeds more actively on the inflow cell side than on the discharge cell side.
However, in the conventional exhaust gas purification filter, the carbon-based material combustion catalyst is supported uniformly over the entire partition wall of the honeycomb body base material. Therefore, the amount of catalyst may be insufficient on the inflow cell side of the partition where a large amount of carbon-based material combustion catalyst is required, and an excessive amount of carbon-based material combustion catalyst is required on the discharge cell side of the partition. Was carried. Therefore, in the conventional exhaust gas purification filter, the total supported amount of the carbon-based material combustion catalyst cannot be fully utilized for the PM combustion performance. Therefore, development of an exhaust gas purification filter that can perform PM combustion more efficiently has been demanded.

The present invention was made in view of such background, it is intended to provide a method of manufacturing an exhaust gas purifying filter that can efficiently burn and remove the particulates trapped in the partition wall.

The reference invention includes a columnar honeycomb body substrate having porous partition walls arranged in a lattice shape and a plurality of cells extending in the axial direction surrounded by the partition walls, and at least the partition walls of the honeycomb body substrate. In an exhaust gas purification filter having a supported carbon-based material combustion catalyst,
Among the plurality of cells in the honeycomb body base material, the downstream end portion of the inflow cell into which the exhaust gas flows and the upstream end portion of the exhaust cell from which the exhaust gas is discharged are blocked by the plug portion,
The total weight of the carbon-based material combustion catalyst supported on the honeycomb body base material on the wall surface of the partition wall facing the inflow cell and in the region from the wall surface facing the inflow cell to half the wall thickness. The exhaust gas purifying filter is characterized in that 80% or more of is supported .

One embodiment of the present invention is a columnar honeycomb body substrate having porous partition walls arranged in a lattice shape and a plurality of cells extending in the axial direction surrounded by the partition walls, and at least the honeycomb body base material In the method of manufacturing an exhaust gas purification filter having a carbon-based material combustion catalyst supported on the partition wall,
Of the plurality of cells in the honeycomb body base material, the honeycomb body base in which an end on the downstream side of an inflow cell into which exhaust gas flows and an end on the upstream side of an exhaust cell from which exhaust gas is discharged are closed by a plug portion Preparing a material, immersing the honeycomb body substrate in a liquid not containing the carbon-based material combustion catalyst, and impregnating the liquid into the pores of the partition wall;
A step of immersing the honeycomb body base material after the liquid impregnation step in a catalyst slurry containing the carbon-based material combustion catalyst, and attaching the catalyst slurry to at least the partition walls of the honeycomb body base material; and
The surface of the partition wall facing the inflow cell and the wall surface of the partition wall facing the inflow cell by blowing gas to the upstream end surface of the inflow cell and performing suction from the downstream end surface of the discharge cell The pores of the partition walls are impregnated with the catalyst slurry in a region from the wall thickness to half the wall thickness, and the partition walls in the region from the wall surface of the partition wall facing the discharge cell to a depth of half the wall thickness. A catalyst impregnation step of at least partially removing the liquid present in the pores and the catalyst slurry adhering to the partition wall facing the discharge cell;
And a heating step of heating the honeycomb body base material after the catalyst impregnation step and supporting the carbon-based material combustion catalyst on the partition walls of the honeycomb body base material. There is .

  In the exhaust gas purification filter, the carbon-based material combustion catalyst is not uniformly supported over the entire partition wall, but more carbon-based material combustion catalyst is unevenly supported on the inflow cell side in the partition wall. Yes. That is, as described above, the carbon-based material combustion catalyst carried on the honeycomb body base material on the wall surface facing the inflow cell and in the region from the wall surface facing the inflow cell to half the depth of the wall thickness. 80% or more of the total weight is supported. Therefore, PM can be sufficiently removed by combustion on the inflow cell side where PM is easily deposited and PM combustion occurs more actively. On the other hand, the amount of the carbon-based material combustion catalyst supported can be reduced on the exhaust cell side having little influence on PM combustion. Therefore, in the exhaust gas purification filter, PM can be efficiently removed by combustion without increasing the total amount of catalyst supported.

In the method for manufacturing the exhaust gas purification filter, the liquid impregnation step, the catalyst slurry immersion step, the catalyst impregnation step, and the heating step are performed.
In the liquid impregnation step, the honeycomb body base material is immersed in a liquid not containing the carbon-based material combustion catalyst. Thereby, the liquid is impregnated into the pores of the partition walls of the honeycomb body base material.
Next, in the catalyst slurry immersion step, the honeycomb body base material is immersed in a catalyst slurry containing the carbon-based material combustion catalyst. Thereby, the catalyst slurry can be adhered to at least the surface of the partition wall of the honeycomb body base material. In the honeycomb body base material after the liquid impregnation step is performed, the liquid is present in the pores on the discharge cell side in the partition walls, and the pores are blocked. Therefore, when the catalyst slurry immersion step is performed after the liquid impregnation step, the catalyst slurry is prevented from entering the pores of the partition walls, and as described above, most of the catalyst slurry adheres to the surfaces of the partition walls. To do.

Next, in the catalyst impregnation step, gas is blown to the upstream end face of the inflow cell, and suction is performed from the downstream end face of the discharge cell. As a result, the pores of the partition walls are impregnated with the catalyst slurry in the region from the surface of the partition wall facing the inflow cell and the wall surface of the partition wall facing the inflow cell to half the wall thickness. The liquid present in the pores of the partition wall in the region from the wall surface of the partition wall facing the discharge cell to half the wall thickness and the catalyst slurry adhering to the partition wall facing the discharge cell. Remove at least partially.
Next, in the heating step, the honeycomb substrate is heated. Thereby, the carbon-based material combustion catalyst in the catalyst slurry impregnated in the partition walls of the honeycomb body base material can be supported on the partition walls. In the catalyst impregnation step, the catalyst slurry is impregnated so as to be biased toward the inflow cell side of the partition wall. Therefore, after the heating step, the carbon-based material combustion catalyst can be biased to the inflow cell side of the partition wall.
The exhaust gas purification filter obtained by the production method can efficiently remove the carbon-based material combustion catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing the appearance of an exhaust gas purification filter in Example 1. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing an axial sectional structure of an exhaust gas purification filter in Example 1. Explanatory drawing which shows the expanded cross section of the partition of the exhaust gas purification filter in Example 1. FIG. FIG. 3 is an explanatory diagram showing an axial cross-sectional structure of a honeycomb body base material in Example 1. FIG. 3 is an explanatory view showing a state in which a honeycomb body base material is immersed in a liquid in Example 1. FIG. 3 is an explanatory view showing an enlarged cross section of a partition wall of a honeycomb body base material impregnated with a liquid in Example 1; FIG. 3 is an explanatory view showing a state in which a honeycomb body base material is immersed in a catalyst slurry in Example 1. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the expanded cross section of the partition of the honeycomb body base material which made the catalyst slurry adhere to the surface of the partition in Example 1. FIG. FIG. 3 is an explanatory view showing an enlarged cross section of a partition wall of a honeycomb body base material after a catalyst impregnation step in Example 1; Explanatory drawing which shows a mode that a some honeycomb body base material is joined in a side surface. FIG. 3 is an explanatory view showing the appearance of a joining type exhaust gas purification filter in which a carbon-based material combustion catalyst is supported on a joining type honeycomb base material in which a plurality of honeycomb body base materials are joined on the side surfaces.

Next, a preferred embodiment of the present invention will be described.
The exhaust gas purification filter includes the honeycomb body base material and the carbon-based material combustion catalyst. The honeycomb base material can have an outer shape such as a columnar shape or a prism shape.
The exhaust gas purification filter can also be used as it is for exhaust gas purification, but can be used as a joining type in which a plurality of honeycomb base materials each carrying a carbon-based material combustion catalyst supported on partition walls are joined to each other.

In the exhaust gas purification filter, on the wall surface of the partition wall facing the inflow cell and in a region from the wall surface facing the inflow cell to a half depth of the wall thickness (hereinafter referred to as “inflow cell side region” as appropriate). 80% or more of the total weight of the carbon-based material combustion catalyst supported on the honeycomb body base material is supported.
If the amount of the carbon-based material combustion catalyst supported on the inflow cell side region of the partition wall is less than 80% of the total weight of the carbon-based material combustion catalyst supported on the honeycomb body, the amount of the carbon-based material combustion catalyst is not sufficient for PM combustion. The amount of catalyst that does not contribute increases, and there is a risk that PM cannot be burned efficiently for the amount of catalyst supported.

The ratio of the amount (weight) of the catalyst supported on the inflow cell side region to the total weight of the catalyst supported on the honeycomb body can be examined as follows.
That is, the wall surface is elementally mapped using an electron beam microanalyzer (EPMA, Electron Probe Micro Analyzer). Then, the ratio of the characteristic X-ray intensity in the inflow cell side region to the total intensity of characteristic X-rays obtained from the elements constituting the catalyst is examined.

The honeycomb body substrate can be made of, for example, α-alumina, cordierite, SiC, aluminum titanate, or the like.
Preferably, at least the partition walls of the honeycomb body base material are mainly composed of α-alumina, and the carbon material combustion catalyst includes an alkali metal element source and / or a mixture of an alkaline earth metal element source and zeolite, or sodalite. An alkali catalyst obtained by firing at a temperature of 600 ° C. or higher is preferred .
In this case, the carbon material combustion catalyst composed of the alkali catalyst exhibits excellent combustion promoting characteristics with respect to PM, and the carbon-based material combustion catalyst serves as a material for the partition walls (α alumina) of the honeycomb body base material. And reaction at high temperatures can be prevented. For this reason, it is possible to suppress the activity of the carbon-based material combustion catalyst from being lowered and to stably purify the exhaust gas. Further, the carbon-based material combustion catalyst composed of the alkali catalyst is difficult to elute the alkali even in the presence of moisture, and the catalytic activity is difficult to decrease.
In the exhaust gas purification filter, it is preferable that no precious metal is supported on the honeycomb body base material except for inevitable impurities.

In the honeycomb base material, it is preferable that not only the partition walls but also the whole honeycomb base material has α-alumina as a main component.
When producing the above honeycomb body base material mainly composed of α-alumina, inevitable impurities are mixed in the α-alumina itself used, or additives such as alkaline earth metal oxides are added as described later. Or can be added. In this case, it is preferable that 99.0 wt% or more of the partition walls of the honeycomb base material or the entire honeycomb base material is made of α-alumina. More preferably, 99.6 wt% or more, further preferably 99.7 wt% or more, and even more preferably 99.8 wt% or more is made of α-alumina.

The partition preferably contains 0.03 to 0.4 parts by mass of an alkaline earth metal oxide with respect to 100 parts by mass of α-alumina.
In this case, the strength of the honeycomb body base material can be improved. When the content of the alkaline earth metal oxide is too small, there is a possibility that the effect of improving the strength by the addition cannot be sufficiently obtained. Therefore, the content of the alkaline earth metal oxide is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, as described above. On the other hand, when the content of the alkaline earth metal oxide is too large, the strength of the honeycomb body base material may be lowered. Accordingly, the content of the alkaline earth metal oxide is preferably 0.4 parts by mass or less, more preferably 0.3 parts by mass or less, and still more preferably 0.2 parts by mass or less, as described above.

As the alkaline earth metal oxide, one kind or two or more kinds can be used.
Preferably, the alkaline earth metal is at least Mg and / or Ca. In this case, the above-mentioned strength improvement effect by containing the alkaline earth metal oxide can be more remarkably obtained.

Next, the honeycomb body base material is porous, and preferably has a porosity of 40 to 70%, an average pore diameter of 10 to 20 μm, and an A-axis strength of 2 MPa or more .
When the porosity is less than 40% or when the average pore diameter is less than 10 μm, the pressure loss of the honeycomb base material may increase. On the other hand, when the porosity exceeds 70%, it may be difficult to ensure sufficient strength of the honeycomb base material. Further, when the average pore diameter exceeds 20 μm, PM tends to slip through the honeycomb body base material, and it may be difficult to sufficiently collect PM. The porosity of the honeycomb base material is more preferably 50 to 60%, and the average pore diameter is more preferably 12 to 18 μm.
Further, when the A-axis strength is less than 2 MPa, the honeycomb body base material may be easily damaged during canning of the exhaust gas purification filter into the DPF converter, that is, when the exhaust gas purification filter is housed in the case. . In addition, thermal shock cracking is likely to occur. More preferably, the A-axis strength is 4 MPa or more.

The porosity and average pore diameter of the honeycomb base material can be measured with a mercury porosimeter based on the principle of mercury porosimetry. The average pore diameter is the pore diameter at an integrated value of 50% in the pore distribution determined with a mercury porosimeter.
Further, the A-axis strength of the honeycomb body base material indicates the compressive strength defined in JASO standard M505-87, which is an automobile standard issued by the Japan Automobile Technical Association. This is the breaking strength when a compressive load is applied in the direction of flow of the honeycomb body base material, that is, in the direction perpendicular to the cross section.

The above honeycomb body base material containing α-alumina as a main component can be manufactured by performing the following mixing step, forming step, and firing step.
In the mixing step, coarse particles, fine particles, α-alumina precursor particles, an organic binder, and water are mixed to prepare a clay made of a raw material mixture.

  The coarse particles are particles made of α-alumina and having a median diameter of 20 to 60 μm. When the median diameter of the coarse particles is less than 20 μm or exceeds 60 μm, the average pore diameter of the honeycomb body substrate becomes too small, and the pressure loss of the honeycomb body substrate may increase. The median diameter of the coarse particles is preferably 25 to 55 μm, more preferably 30 to 50 μm.

The fine particles are particles made of α-alumina and having a median diameter of 2 μm or less. When the median diameter of the fine particles exceeds 2 μm, the sintering of α-alumina in the firing step described later becomes insufficient, and the strength of the honeycomb body substrate may be insufficient. The median diameter of the fine particles is preferably 1 μm or less, and more preferably 0.5 μm or less. From the viewpoint of increasing raw material costs, the median diameter of the fine particles is preferably 0.05 μm or more.
The median diameter means a particle diameter at an integrated value of 50% in a particle size distribution obtained by a laser diffraction / scattering method.

The α-alumina precursor particles are made of a substance that generates α-alumina after firing. Specifically, for example, aluminum hydroxide, γ alumina, θ alumina, aluminum chloride, aluminum hydride, and the like can be used. One or more of these substances can be used. Preferably, the α-alumina precursor particles are made of aluminum hydroxide.
Further, as the α-alumina precursor particles, for example, those having a median diameter of 1 to 10 μm can be used.

In the mixing step, it is preferable to mix 5 to 30 parts by mass of the fine particles and 0.5 to 15 parts by mass of the α-alumina precursor particles with respect to 100 parts by mass of the coarse particles.
When the fine particles are less than 5 parts by mass or when the α-alumina precursor particles are less than 0.5 parts by mass, the sintering of α-alumina in the firing step described below becomes insufficient, increasing the porosity. There is a possibility that the strength of the manufactured honeycomb body base material becomes insufficient. On the other hand, when the fine particles exceed 30 parts by mass, the average pore diameter of the honeycomb base material becomes too small, and the pressure loss of the honeycomb base material may increase. When the α-alumina precursor particles exceed 15 parts by mass, the average pore diameter of the honeycomb base material becomes too small, and the pressure loss of the honeycomb base material may increase. More preferably, the addition amount of the fine particles with respect to 100 parts by mass of the coarse particles is 8 to 20 parts by mass, and the addition amount of the α-alumina precursor particles is 1 to 10 parts by mass.

  In the mixing step, the coarse particles, the fine particles, and the α-alumina precursor are mixed in a dispersion medium such as water to prepare a clay made of a clay-like raw material mixture. In the molding process described later, in order to facilitate molding into a desired shape, the organic binder can be mixed with the raw material mixture and adjusted to a desired viscosity.

In the mixing step, an alkaline earth metal is further added to the raw material mixture, and the amount of the alkaline earth metal added is a total of 100 masses of the coarse particles, the fine particles, and the α-alumina precursor particles. It is preferable that it is 0.03-0.4 mass part with the oxide conversion amount of an alkaline-earth metal with respect to a part.
In this case, the alkaline earth metal serves as a sintering aid, and the strength of the honeycomb body substrate obtained after the firing step described later can be improved. If the amount of the alkaline earth metal added is too small or too large, the effect of improving the strength may not be sufficiently obtained. The addition amount of the alkaline earth metal is more preferably 0.1 parts by mass or more and 0.3 parts by mass or less. More preferably, it is 0.2 parts by mass or less. The alkaline earth metal added in the mixing step is contained in the fired honeycomb substrate as an alkaline earth metal oxide.

As the alkaline earth metal added to the raw material mixture, one or more selected from alkaline earth metals can be used. Preferably, the alkaline earth metal is at least Mg and / or Ca.
In this case, the effect of improving the strength of the above-described honeycomb body base material by containing the alkaline earth metal oxide can be more remarkably obtained.

The alkaline earth metal added in the mixing step can be added to the raw material mixture as an oxide of an alkaline earth metal, a compound other than an oxide, or a salt.
Preferably, in the mixing step, an alkaline earth metal salt is preferably added as the alkaline earth metal.
In this case, the alkaline earth metal can be uniformly dispersed in the clay. Therefore, firing of the formed body can be uniformly progressed in the firing step described later, and variation in strength of the honeycomb body base material obtained after the firing step can be reduced. Therefore, the strength of the entire honeycomb body base material can be improved. As the alkaline earth metal salt, nitrate, acetate or the like is preferably used.
The alkaline earth metal salt can be added to the raw material mixture as an aqueous solution. In this case, the dispersibility of the alkaline earth metal in the clay can be further improved.

  In the forming step, the clay is formed into the shape of the honeycomb base material to obtain a honeycomb formed body. At this time, it is formed into a honeycomb shape having partition walls arranged in a lattice shape and a plurality of cells surrounded by the partition walls and extending in the axial direction.

In the firing step, the honeycomb formed body is fired.
In the firing step, firing is preferably performed at a firing maximum temperature of 1200 to 2000 ° C.
When the maximum firing temperature is less than 1200 ° C., the sintering of α-alumina does not proceed sufficiently, and it may be difficult to ensure sufficient strength of the honeycomb body base material. On the other hand, when it exceeds 2000 ° C., α-alumina is softened or melted, and it may be difficult to ensure the desired average pore diameter and porosity of the honeycomb body base material.

In the firing step, the oxygen concentration of the atmospheric gas is preferably adjusted to 5% by volume or less at a temperature lower than 1200 ° C. at the time of temperature rise.
When the oxygen concentration at a temperature lower than 1200 ° C. exceeds 5% by volume, the coarse particles, the fine particles, and the α alumina precursor particles are added at a temperature lower than 1200 ° C. at which α alumina starts sintering. There is a risk that the organic binder to be held will burn. Therefore, it may be difficult to hold the structure of the honeycomb formed body after firing.

  Moreover, in the case of closing the end portion on the downstream side of the inflow cell into which the exhaust gas flows and the end portion on the upstream side of the exhaust cell from which the exhaust gas is discharged, of the plurality of cells of the honeycomb body base material, For example, the plug portion can be formed after the firing step. The plug portion can be formed of, for example, a silica-alumina composite material. Moreover, a plug part can also be formed with respect to the said honeycomb molded body before performing the said baking process.

The honeycomb substrate can have a substantially cylindrical outer shape.
In the forming step, a honeycomb formed body having the same shape as the substantially columnar final product is formed, and the honeycomb formed body is fired in the firing step, whereby a honeycomb body base material of the final product can be obtained. On the other hand, in the forming step, a rectangular column-shaped honeycomb formed body is formed, fired, a plurality of rectangular columnar honeycomb body base materials are produced, these are joined, and the outer shape is polished to join a substantially cylindrical joining die. It can also be a honeycomb body substrate.

Next, a method for manufacturing the exhaust gas purification filter having the honeycomb body base material and a carbon-based material combustion catalyst supported on the partition walls of the honeycomb body base material will be described.
In the manufacturing method of the exhaust gas purification filter, a liquid impregnation step, a catalyst slurry immersion step, a catalyst impregnation step, and a heating step are performed.
In the liquid impregnation step, the honeycomb body base material is immersed in a liquid not containing the carbon-based material combustion catalyst. Thereby, the liquid is impregnated into the pores of the partition walls of the honeycomb body base material. As the liquid, for example, water can be used.

In the catalyst slurry immersion step, the honeycomb base material after the liquid impregnation step is immersed in a catalyst slurry containing the carbon-based material combustion catalyst.
In the honeycomb body base material after the liquid impregnation step is performed, the liquid is present in the pores of the partition walls to block the pores. Therefore, when the catalyst slurry immersion step is performed, the catalyst slurry is prevented from entering the pores of the partition walls, and the catalyst slurry can be adhered to at least the surfaces of the partition walls.
The catalyst slurry can be prepared by dispersing the carbon-based material combustion catalyst in a liquid such as water. In addition to the carbon-based material combustion catalyst, an inorganic binder such as alumina sol and a dispersing material can be added to the catalyst slurry.

In the catalyst impregnation step, gas is blown onto the upstream end face of the inflow cell and suction is performed from the downstream end face of the discharge cell. Thus, the catalyst slurry is impregnated in the pores of the partition wall in the region from the surface of the partition wall facing the inflow cell and the wall surface of the partition wall facing the inflow cell to a depth half the wall thickness. On the other hand, a region having a depth of more than half the wall thickness from the wall surface of the partition wall facing the inflow cell, in other words, a region from the wall surface of the partition wall facing the discharge cell to a depth of half the wall thickness (hereinafter referred to as the wall thickness). The liquid present in the pores of the partition walls and the catalyst slurry adhering to the partition walls are removed at least partially in the “discharge cell side region” as appropriate.
In the catalyst impregnation step, as the gas, an inert gas such as air or nitrogen gas at room temperature can be used.

In the catalyst impregnation step, the gas flow velocity (wind velocity) at the suction end surface is preferably 5 to 80 m / s .
When the flow rate is less than 5 m / s, there is a possibility that the residual amount of the liquid becomes too large not only on the inflow cell side but also on the discharge cell side. As a result, it may be difficult to carry a sufficient amount of the carbon-based material combustion catalyst biased toward the inflow cell. In addition, it may be difficult to support a sufficient amount of the carbon-based material combustion catalyst over the entire partition wall. On the other hand, when the flow velocity exceeds 80 m / s, the catalyst slurry may be almost removed not only on the discharge cell side but also on the inflow cell side. As a result, it may be difficult to carry a sufficient amount of the carbon-based material combustion catalyst biased toward the inflow cell.

Next, in the heating step, the carbon-based material combustion catalyst is supported on the partition walls of the honeycomb body substrate by heating the honeycomb body substrate after the catalyst impregnation step.
Heating can be performed at a temperature of 300 to 800 ° C., for example.
Moreover, the drying process which dries the said honeycomb body base material can be performed between the said catalyst impregnation process and the said heating process.

Example 1
Next, an embodiment of the exhaust gas purification filter will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the exhaust gas purification filter 1 of this example is a columnar honeycomb body having partition walls 21 arranged in a square lattice shape and a plurality of cells 22 surrounded by the partition walls 21 and extending in the axial direction. The substrate 2 and a carbon-based material combustion catalyst supported on at least the partition walls 21 of the honeycomb body substrate 2 are included. In FIG.1 and FIG.2, description of a carbonaceous material combustion catalyst is abbreviate | omitted.

  The honeycomb base material 2 contains α-alumina as a main component. Out of the plurality of cells 22 in the honeycomb substrate 2, the downstream end 24 of the inflow cell 221 into which the exhaust gas flows and the upstream end 23 of the exhaust cell 222 from which the exhaust gas is discharged are blocked by the plug 25. Has been. The plug portion 25 alternately closes the openings of the adjacent cells 22 on both end faces 23 and 24 of the honeycomb body base material 2 and is arranged in a so-called checkered pattern. The upstream end 23 of the inflow cell 221 and the downstream end 24 of the discharge cell 222 are open, and an opening 26 is formed.

As shown in FIGS. 2 and 3, the partition wall 21 is porous, and has a ceramic region 211 made of α-alumina and pores 212. A carbon-based material combustion catalyst 3 is supported on the wall surface 213 of the partition wall 21 and in the pores 212. In the exhaust gas purification filter 1 of this example, the honeycomb body is formed on the wall surface 213 of the partition wall 21 facing the inflow cell 221 and in the region from the wall surface 213 facing the inflow cell 221 to the depth a / 2 that is half the wall thickness a. 80% or more of the total weight of the carbon-based material combustion catalyst 3 supported on the substrate 2 is supported.
The carbon material combustion catalyst 3 is an alkali catalyst formed by firing a mixture of sodalite and an alkali metal element source (potassium carbonate).

In producing the exhaust gas purification filter of this example, first, a honeycomb body substrate was produced as follows.
Specifically, first, 100 parts by mass of coarse particles having a median diameter of 45 μm made of α-alumina, 10 parts by mass of fine particles having a median diameter of 0.2 μm and a maximum particle size of 0.5 μm made of α-alumina, and aluminum hydroxide Then, 5.5 parts by mass of precursor particles having a median diameter of 5 μm were dry-mixed. Subsequently, water, an organic binder, and a moisturizing material were added to the raw material mixture, and an aqueous magnesium nitrate solution was further added and mixed to make the raw material mixture into a clay state to obtain a clay (mixing step). In this example, the clay was prepared by setting the addition amount of the magnesium nitrate aqueous solution to 1500 ppm in terms of magnesium oxide with respect to the total amount of coarse particles, fine particles, and precursor particles.

  Next, by extruding and cutting the kneaded material, the cylindrical outer peripheral wall, the porous partition walls arranged in the form of a quadrangular lattice in the outer peripheral wall, and the axial direction surrounded by the partition walls extend in the axial direction. A honeycomb formed body having a honeycomb structure having a plurality of cells was obtained (forming step). In this example, a cylindrical honeycomb formed body having a diameter of 30 mm and a length of L50 mm was produced.

  Next, the honeycomb formed body was fired at a maximum temperature of 1650 ° C. in an electric furnace. Specifically, first, nitrogen was circulated to adjust the inside of the electric furnace to an atmosphere having an oxygen concentration of 0.5% by volume, and in this atmosphere, the honeycomb formed body was heated at a heating rate of 50 ° C./hour, and the temperature was 1200. When the temperature reached 0 ° C., the nitrogen circulation into the electric furnace was stopped. Next, while increasing the oxygen concentration in the electric furnace by introducing the atmosphere into the electric furnace, the honeycomb formed body was heated at a temperature rising rate of 50 ° C./hour and held for 10 hours when the temperature reached 1650 ° C. ( Firing step). In this way, a honeycomb body substrate 2 was obtained (see FIGS. 1 and 2).

Next, the average pore diameter and the porosity of the honeycomb body substrate 2 obtained as described above were measured.
For the measurement of average pore diameter and porosity, Autopore IV9500 manufactured by Shimadzu Corporation was adopted as a mercury porosimeter based on the principle of mercury intrusion. In the measurement, the contact angle at the time of press-fitting mercury into the pores of the honeycomb body substrate can be set to 140 °, the surface tension can be set to 480 dynes / cm, and the pressure can be set to 0.0045 to 420 MPa. Also, the measurement step (μm) is set to 200, 150, 70, 40, 20, 10, 5.0, 2.0, 1.0, 0.5, 0.1, 0.05, 0.03 can do. In addition, this measurement step is a pore diameter.
In this way, the pore diameter and the volume distribution are obtained for the honeycomb body substrate. The average pore diameter is the pore diameter at an integrated value of 50% in the pore distribution determined with a mercury porosimeter.
The porosity can be calculated based on the formula of total pore volume / (total pore volume + 1 / 3.98) × 100, assuming that the true specific gravity of α-alumina is 3.98.
The average pore diameter of the honeycomb substrate of this example was 14.5 μm, and the porosity was 54%.

Further, the A-axis strength of the honeycomb body base material was measured.
Specifically, first, a cylindrical measurement sample having a diameter of 15 mm × length L15 mm was cut out from each sample. And the compressive strength (A-axis strength) prescribed | regulated to JASO specification M505-87 which is an automobile specification issued by the Japan Society for Automotive Engineers was measured using an autograph. As a result, the A-axis strength of the honeycomb body base material of this example was 18.5 MPa.

Next, water, an organic binder, and a humectant were added to the alumina material and mixed to prepare a clay-like plug portion forming material. Then, one of the openings on both end faces of each cell of the honeycomb base material was closed with the plug portion forming material, and the cell openings were alternately closed on one end face of the honeycomb base material. Next, using an electric furnace, the honeycomb body base material was heated to a maximum temperature of 1600 ° C. at a rate of temperature increase of 200 ° C./hour in an air atmosphere, and heat treatment was performed by heating at this maximum temperature for 3 hours.
Thus, as shown in FIG. 4, among the plurality of cells 22, the end 24 on the downstream side of the inflow cell 221 into which the exhaust gas flows and the end 25 on the upstream side of the exhaust cell 222 from which the exhaust gas is discharged are plugged. A honeycomb body substrate 2 closed by the portion 25 was obtained.

Next, a carbon-based material combustion catalyst supported on the honeycomb body base material 2 was produced as follows.
Specifically, first, the sodalite _{(3 (Na 2 O · Al} 2 O 3 · 2SiO 2) · 2NaOH) 100 parts by weight of potassium carbonate 10 parts by mass was poured into water, and mixed in water. Next, the mixed liquid was heated at a temperature of 150 ° C. to evaporate water, thereby obtaining a solid content (a mixture of sodalite and potassium carbonate). Next, this solid content was baked at a temperature of 850 ° C. Specifically, the solid content was heated at a rate of temperature increase of 50 ° C./hour, and when the temperature reached 850 ° C. (calcination temperature), the solid content was held for 10 hours to perform firing. Next, the fired product was pulverized to a median diameter of 2 μm or less and a maximum particle diameter of 20 μm or less to obtain a powdery carbon-based material combustion catalyst.

Next, the carbon-based material combustion catalyst was supported on the honeycomb base material as follows.
Specifically, first, as shown in FIG. 5, the honeycomb body base material 2 was immersed in the liquid 4 (liquid impregnation step). As the liquid 4, water was used. As a result, as shown in FIG. 6, the porous partition walls 21 of the honeycomb body base material were impregnated with the liquid 4. The liquid 4 is impregnated throughout the partition wall 21.

Next, a catalyst slurry 5 was prepared by adding a carbon material combustion catalyst (alkali catalyst), an inorganic binder, and a dispersing agent to water and stirring the mixture (see FIG. 7). Next, as shown in FIG. 7, the honeycomb substrate 2 after the liquid impregnation step was immersed in the catalyst slurry 5 (catalyst slurry immersion step).
As a result, as shown in FIG. 8, the catalyst slurry 5 was adhered on the wall surface 213 of the partition wall 21 facing the inflow cell and on the wall surface 214 of the partition wall 21 facing the discharge cell. The liquid 4 already exists in the pores 212 of the partition wall 21, and the intrusion of the catalyst slurry 5 is suppressed.

  Next, as shown in FIG. 4, air 10 is blown from the end face 23 on the upstream side of the inflow cell 221 to the honeycomb body base 2, and the air 10 is sucked from the end face 24 on the downstream side of the discharge cell 222 of the honeycomb body 2. (Catalyst impregnation step). In this example, the catalyst impregnation step was performed at a wind speed of 40 m / s on the end surface 24 on the suction side. As a result, as shown in FIG. 9, a region (inflow cell side) from the wall surface 213 of the partition wall 21 facing the inflow cell and the wall surface 213 of the partition wall 21 facing the inflow cell to the depth 2 / a of half the wall thickness a. In the region), the catalyst slurry 5 was impregnated in the pores 212 of the partition walls 21. On the other hand, in the region from the wall surface 214 of the partition wall 21 facing the discharge cell 222 to the depth 2 / a that is half the wall thickness (discharge cell side region), the liquid 4 existing in the pores 212 of the partition wall 21. And the catalyst slurry 5 adhering to the wall surface 214 was almost removed. Thereby, an empty space where no liquid exists is present in the pores 212 in the discharge cell side region of the partition wall 21.

  Next, using a hot air generator, hot air at a temperature of 200 ° C. was sent to the honeycomb body substrate to completely remove residual moisture in the honeycomb body substrate (drying step). Next, in the electric furnace, the honeycomb body substrate was heated to a maximum temperature of 650 ° C. at a temperature increase rate of 200 ° C./hour in an air atmosphere, and heat treatment was performed to heat the honeycomb body substrate at this maximum temperature for 3 hours ( Heating step).

  Thus, an exhaust gas purification filter in which a carbon-based material combustion catalyst was supported on a honeycomb body substrate made of α-alumina was obtained. In this example, the loading amount of the carbon-based material combustion catalyst is 40 g per 1 L of the exhaust gas purification filter. In the exhaust gas purification filter of the present example, the ratio of the amount of carbon-based material combustion catalyst supported on the inflow cell side region to the total amount of carbon-based material combustion catalyst supported on the honeycomb body base material is set to the above-described method. Was found to be 88%.

Next, the effect of the exhaust gas purification filter of this example will be described.
In the exhaust gas purification filter 1 of this example, the carbon-based material combustion catalyst is not uniformly supported over the entire partition wall, but more carbon is added to the inflow cell 221 side in the partition wall 21 as shown in FIGS. The system material combustion catalyst 3 is biased. That is, the total weight of the carbon-based material combustion catalyst 3 supported on the honeycomb body base material 2 on the wall surface 213 facing the inflow cell 221 and in the region from the wall surface 213 to the depth 2 / a which is half the wall thickness. 80% or more is supported. Therefore, PM can be easily removed and burned and removed sufficiently on the inflow cell 221 side where PM combustion occurs more actively. On the other hand, the amount of the carbon-based material combustion catalyst 3 supported can be reduced on the exhaust cell 222 side that has little influence on the combustion of PM. Therefore, in the exhaust gas purification filter 1, PM can be efficiently removed by combustion without increasing the total supported amount of the catalyst 3.

  Further, the partition walls 21 of the honeycomb body base material 2 are mainly composed of α-alumina, and the carbon material combustion catalyst 3 is a mixture of an alkali metal element source and / or an alkaline earth metal element source and zeolite, or sodalite at a temperature of 600. It is an alkali catalyst obtained by firing at a temperature of 0 ° C. or higher. Therefore, the carbon material combustion catalyst 3 made of an alkali catalyst exhibits excellent combustion promotion characteristics with respect to PM, and the carbon-based material combustion catalyst 3 reacts with the material (α alumina) of the partition wall 21 of the honeycomb body base material 2 at a high temperature. Can be prevented. For this reason, it is possible to suppress the activity of the carbon-based material combustion catalyst 3 from being lowered and to purify the exhaust gas stably. Further, the carbon-based material combustion catalyst 3 made of an alkali catalyst is difficult to elute the alkali even in the presence of moisture, and the catalytic activity is difficult to decrease.

  The partition wall 21 contains 0.03 to 0.4 parts by mass of an alkaline earth metal oxide with respect to 100 parts by mass of α-alumina. Therefore, the honeycomb body substrate 2 can exhibit excellent strength.

In the method of manufacturing the exhaust gas purification filter 1 of this example, the liquid impregnation step, the catalyst slurry immersion step, the catalyst impregnation step, and the heating step are performed.
In the liquid impregnation step, the honeycomb substrate 2 is immersed in the liquid 4 that does not contain the carbon-based material combustion catalyst (see FIG. 5). Thereby, the liquid 4 can be impregnated in the pores 212 of the partition walls 21 of the honeycomb body base material 2 (see FIG. 6).

  Next, in the catalyst slurry immersion step, the honeycomb body base material 2 is immersed in the catalyst slurry 5 containing the carbon-based material combustion catalyst (see FIG. 7). Thereby, as shown in FIG. 8, the catalyst slurry 5 can be adhered onto at least the wall surfaces 213 and 214 of the honeycomb body base material 2. In the honeycomb body base material 2 after the liquid impregnation step, the liquid 4 exists in the pores 212 in the partition walls 21 and closes the pores 212 (see FIG. 6). Therefore, when the catalyst slurry immersion step is performed, the catalyst slurry 5 is prevented from entering the pores 212 of the partition wall 21, and the catalyst slurry 5 can be attached to the wall surfaces 213 and 214 as described above (see FIG. 8).

In the catalyst impregnation step, the gas 10 is blown onto the upstream end face 23 of the inflow cell 221 and suction is performed from the downstream end face 24 of the discharge cell 222 (see FIG. 4). As a result, the catalyst slurry 5 enters the pores 212 of the partition wall 21 on the wall surface 213 of the partition wall 21 facing the inflow cell 221 and in the region from the wall surface 213 facing the inflow cell 221 to the depth a / 2 that is half the wall thickness. Is impregnated (see FIG. 9). On the other hand, in the region from the wall surface 214 of the partition wall 21 facing the discharge cell 222 to the depth a / 2 that is half the wall thickness, the liquid 4 existing in the pores 212 of the partition wall 21 and the wall surface 214 were adhered. Most of the catalyst slurry is removed (see FIG. 9).
In this example, the catalyst impregnation step is performed by setting the gas flow velocity (wind velocity) on the suction side end face to 5 to 80 m / s. Therefore, it is easy to selectively remove the liquid 4 and the catalyst slurry 5 present in the partition wall 21 in the discharge cell side region while impregnating the partition wall 21 with the catalyst slurry 5 in the inflow cell side region (FIG. 8 and FIG. 8). (See FIG. 9).

In the heating process, the honeycomb body substrate 2 is heated. As a result, the carbon-based material combustion catalyst 3 in the catalyst slurry 5 impregnated in the partition walls 21 of the honeycomb body base material 2 can be supported on the partition walls 21 (see FIGS. 2, 3, and 9).
In the catalyst slurry immersion step, the catalyst slurry 5 is impregnated so as to be biased toward the inflow cell side of the partition wall 21 (see FIG. 9), so that the carbon-based material combustion catalyst 3 is placed in the partition wall 21 after the heating step. It can be biased to the inflow cell side (see FIG. 3).

  Thus, according to this example, it is possible to provide the exhaust gas purification filter 1 that can efficiently burn and remove the particulates collected in the partition wall 21.

(Example 2)
This example is a bonded exhaust gas purification comprising a bonded honeycomb substrate formed by bonding a plurality of honeycomb bonded substrates on the side surfaces, and a carbon-based material combustion catalyst supported on the partition walls of the honeycomb substrate. It is an example of a filter.
As shown in FIG. 11, the exhaust gas purification filter 7 of this example includes a plurality of porous partition walls 61 arranged in a lattice shape and a plurality of cells 62 surrounded by these partition walls 61 and extending in the axial direction. It has a joining type honeycomb body base material 6 in which the honeycomb body base material 60 is joined on the side surface, and a carbon-based material combustion catalyst (not shown) supported on the partition walls 61 of the honeycomb body base material 6.

Each honeycomb body base 60 constituting the bonded type honeycomb body base 6 is mainly composed of α-alumina as in the first embodiment, and the downstream end of the inflow cell into which the exhaust gas flows and the exhaust that discharges the exhaust gas. The end portion on the upstream side of the cell is closed by a plug portion 65. The honeycomb body substrate 60 has the same configuration as the honeycomb body substrate of the first embodiment.
In addition, the carbon-based material combustion catalyst is supported on the partition wall 61 of each honeycomb body base material 60 in a manner biased toward the inflow cell as in the first embodiment.

  In producing the joining type exhaust gas purification filter of this example, first, a plurality of honeycomb body base materials are prepared. Specifically, as shown in FIG. 10, a prismatic honeycomb body base having porous partition walls 61 arranged in a lattice shape and a plurality of cells 62 surrounded by these partition walls 61 and extending in the axial direction. A plurality of materials 60 were prepared. As in the first embodiment, the honeycomb body base material 60 is formed by closing the end portion on the downstream side of the inflow cell into which the exhaust gas flows and the end portion on the upstream side of the exhaust cell from which the exhaust gas is discharged with the plug portion 65. Is used. The honeycomb body substrate 60 can be manufactured in the same manner as in Example 1 except that the overall shape is changed to a prismatic shape.

Next, in the same manner as in Example 1, each honeycomb body base material 60 was supported with a carbon-based material combustion catalyst.
Next, as shown in FIG. 10, the honeycomb body base materials 6 carrying the carbon-based material combustion catalyst were joined to each other at the side surfaces 66 to obtain a joined type honeycomb body base material. Then, as shown in FIG. 11, the outer periphery of the joining type honeycomb body base material 6 was processed into a cylindrical shape by cutting or the like, and the joining type exhaust gas purification filter 7 was obtained. In FIG. 11, for the convenience of drawing, the cells, partition walls, plug portions, etc. of each honeycomb body substrate 60 except for a part of the honeycomb body base 60 constituting the bonded type honeycomb body substrate. The configuration is omitted.

The joining type exhaust gas purification filter 7 manufactured in this example has the same configuration as that of Example 1 except that a joining type honeycomb body base material is used. The effect can be shown.
In this example, the carbon-based material combustion catalyst is supported on each honeycomb body base material 60 and then joined as described above to produce the joining type exhaust gas purification filter 7. It is also possible to produce the exhaust gas purification filter 7 by supporting the carbon-based material combustion catalyst after the material 60 is joined in advance and the joined-type honeycomb body base material 6 is produced.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification filter 2 Honeycomb body base material 21 Partition wall 212 Fine pore 213 Wall surface (inflow cell side)
214 Wall surface (discharge cell side)
22 cells 221 inflow cells 222 discharge cells 3 carbon material combustion catalyst

Claims (4)

Columnar honeycomb base body having a plurality of cells (22 and 62) which is surrounded by rating child shape disposed porous partition walls (21, 61) and the partition wall (21, 61) extending in the axial direction (2, 6, 60) and an exhaust gas purification filter (1) having a carbon-based material combustion catalyst (3) supported on at least the partition walls (21, 61) of the honeycomb substrate (2, 6, 60). 7) In the manufacturing method of
Out of the plurality of cells (22, 62) in the honeycomb body substrate (2, 6, 60), the downstream end (24) of the inflow cell (221) into which the exhaust gas flows and the exhaust cell for discharging the exhaust gas The above honeycomb body base material (2, 6, 60) in which the end (23) on the upstream side of (222) is blocked by the plug sections (25, 65) is prepared, and the honeycomb body base material (2, 6) is prepared. 60) is immersed in the liquid (4) not containing the carbon-based material combustion catalyst (3), and the liquid (4) is impregnated into the pores (212) of the partition walls (21, 61). A liquid impregnation step;
The honeycomb substrate (2, 6, 60) after the liquid impregnation step is immersed in a catalyst slurry (5) containing the carbon-based material combustion catalyst (3), and the catalyst slurry (5) is immersed in the honeycomb. A catalyst slurry immersion step for adhering to at least the partition walls of the body substrate (2, 6, 60);
The gas (10) is blown onto the upstream end surface (23) of the inflow cell (221), and suction is performed from the downstream end surface (24) of the discharge cell (222), whereby the inflow cell (221). The partition walls (21, 61) and the partition walls (21, 61) in the region from the wall surface (213) facing the inflow cell (221) to the half depth of the wall thickness. 61) The catalyst slurry (5) is impregnated into the pores (212) of the wall 61) and the wall thickness (214) of the partition wall (21, 61) facing the discharge cell (222) is half the wall thickness. In the area up to this point, the liquid (4) present in the pores (212) of the partition walls (21, 61) and the catalyst slurry adhering to the partition walls facing the discharge cell are at least partially removed. And the impregnation step,
The honeycomb body substrate (2, 6, 60) after the catalyst impregnation step is heated, and the carbon-based material combustion catalyst (3) is converted into the partition walls (21, 21) of the honeycomb body substrate (2, 6, 60). 61) A method for producing an exhaust gas purification filter (1, 7), comprising a heating step carried on 61). 2. The manufacturing method according to claim 1 , wherein at least the partition walls (21, 61) of the honeycomb substrate (2, 6, 60) are mainly composed of α-alumina, and the carbon material combustion catalyst (3) is an alkali A method for producing an exhaust gas purification filter (1, 7), wherein a mixture of a metal element source and / or an alkaline earth metal element source and zeolite, or sodalite is fired at a temperature of 600 ° C or higher. 3. The manufacturing method according to claim 1, wherein the honeycomb base material ( 2 , 6, 60) has a porosity of 40 to 70%, an average pore diameter of 10 to 20 μm, and an A-axis strength of 2 MPa or more. A method for producing an exhaust gas purification filter (1, 7), wherein In the manufacturing method as described in any one of Claims 1-3, in the said catalyst impregnation process, the flow rate of the gas (10) in the said end surface (24) of a suction side shall be 5-80 m / s. A method for producing an exhaust gas purification filter (1, 7).

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