JP5767980B2 - Method for manufacturing honeycomb body base material - Google Patents

Description

The present invention relates to a method for manufacturing a honeycomb base body used to carry an alkali catalyst containing an alkali metal to purify an exhaust gas.

  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, it has porous partition walls arranged in a lattice shape, and a plurality of cells formed in the axial direction surrounded by the partition walls, of which the exhaust gas is A carbon-based material combustion catalyst that promotes the combustion of PM is supported on a honeycomb body substrate in which the downstream end of the inflowing cell and the upstream end of the exhaust cell that discharges exhaust gas are closed by a plug. There is what I did. As the honeycomb body base material, one made of cordierite, SiC, aluminum titanate or the like is used (see Patent Documents 1 to 3).

  When exhaust gas is purified using the exhaust gas purification filter having the above configuration, exhaust gas flows into the inflow cell, passes through the porous partition wall, and is then discharged from the exhaust cell. At this time, PM in the exhaust gas is collected in the partition wall having a large number of pores, and the exhaust gas is purified. The PM collected by the partition walls is burned and removed at a predetermined timing. At this time, by supporting the catalyst that promotes the combustion of PM on the partition walls, the PM trapped in the partition walls by the catalytic reaction can be efficiently burned and removed.

  By the way, as the carbon-based material combustion catalyst supported on the honeycomb body base material, for example, an alkali catalyst containing an alkali metal is known. Such an alkali catalyst is excellent in combustion promotion characteristics for PM, and is expected as a catalyst replacing an expensive noble metal catalyst.

International Publication WO2006 / 025498 Pamphlet JP 2008-173626 A JP 2008-169104 A

  However, when an alkali catalyst is supported on a honeycomb body made of cordierite, SiC, aluminum titanate, or the like, the honeycomb body base and the alkali catalyst react at a high temperature. As a result, there is a problem that the catalytic activity of the alkali catalyst is reduced.

The present invention was made in view of such background, be supported on an alkali catalyst, it is intended to provide a method of manufacturing a honeycomb base body which can suppress the reduction in catalytic activity.

One aspect of the reference invention is a columnar honeycomb body substrate having porous partition walls arranged in a lattice shape and a plurality of cells surrounded by the partition walls and extending in the axial direction.
The honeycomb body substrate is used by supporting an alkali catalyst containing an alkali metal on the partition wall,
At least the partition walls of the honeycomb body base material are in the honeycomb body base material containing α-alumina as a main component .

One embodiment of the present invention includes a porous partition wall that is used while supporting an alkali catalyst containing an alkali metal, and has a plurality of cells that are surrounded by the partition wall and extend in the axial direction. In the method for manufacturing a columnar honeycomb body substrate,
Coarse particles having a median diameter of 20 to 60 μm made of α-alumina, fine particles having a median diameter of 0.5 μm or less made of α-alumina, α-alumina precursor particles that form α-alumina after firing, an organic binder, water, Mixing step of preparing a clay made of a raw material mixture by mixing
A molding step of forming the clay into the shape of the honeycomb body base material to obtain a honeycomb molded body;
By firing the honeycomb molded body at a maximum firing temperature of 1200 to 2000 ° C., it has a firing step to obtain the honeycomb base body,
In the firing step, the method of manufacturing a honeycomb body base material is characterized in that the oxygen concentration of the atmospheric gas at a temperature lower than 1200 ° C. during temperature rise is adjusted to 0.5 to 5% by volume .

Another aspect of the reference invention is an exhaust gas purification filter in which an alkali catalyst containing an alkali metal is supported on the partition walls of the honeycomb body base material .

  The honeycomb base material is used by supporting an alkali catalyst containing an alkali metal on the partition walls as a combustion catalyst for a carbon-based material (particulate: PM). And as for the said honeycomb body base material, at least the said partition has alpha alumina as a main component. Therefore, in the honeycomb base material, even if the alkali catalyst is supported on the partition walls, the alkali catalyst hardly reacts with the material of the honeycomb base material (α alumina). Therefore, it can suppress that the activity of the said alkali catalyst falls. Therefore, the exhaust gas can be stably purified.

Next, in the manufacturing method, the honeycomb body substrate is manufactured by performing the mixing step, the forming step, and the firing step. And in the said mixing process, while using the particle | grains of the alpha alumina from which the magnitude | size of the median diameter 20-60micrometer which consists of alpha alumina and the fine particle whose median diameter which consists of alpha alumina is 0.5 micrometer or less differs, it calcinates. Α-alumina precursor particles that later produce α-alumina are used. Therefore, it is possible to obtain a honeycomb body substrate having a sufficiently excellent strength even if it is porous.
The honeycomb base material obtained by the manufacturing method is made of α-alumina. For this reason, even when the alkali catalyst is supported on the partition walls of the honeycomb body base material and exposed to a high temperature environment, the alkali catalyst hardly reacts with the material (α alumina) of the honeycomb body base material. Therefore, it is possible to suppress a decrease in the activity of the alkali catalyst, and it is possible to stably purify the exhaust gas.

  Next, in the exhaust gas purification filter, an alkali catalyst containing an alkali metal is supported on the partition walls of the honeycomb body base material containing α-alumina as a main component. Therefore, in the exhaust gas purification filter, it is possible to prevent the activity of the alkali catalyst from being reduced due to the reaction between the alkali catalyst and the material of the honeycomb body base material (α alumina) even in a high temperature environment. it can. Therefore, the exhaust gas purification filter can stably purify the exhaust gas for a long period of time.

Explanatory drawing which shows CB combustion start temperature of each sample (sample X1-sample X7 and sample X0) in the reference example 1. FIG. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing the overall appearance of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory view showing a cross-sectional structure of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the median diameter of coarse particles and the average pore diameter of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the median diameter of coarse particles and the porosity of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the median diameter of coarse particles and the A-axis strength of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the median diameter of fine particles and the average pore diameter of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the median diameter of fine particles and the porosity of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the median diameter of fine particles and the A-axis strength of a honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the blending ratio of fine particles and the average pore diameter of the honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the mixing ratio of fine particles and the porosity of the honeycomb body base material in Example 1 . FIG. 3 is an explanatory diagram showing the relationship between the mixing ratio of fine particles and the A-axis strength of the honeycomb body base material in Example 1 . Explanatory drawing which shows the relationship between the temperature at the time of the heating in the mixed gas atmosphere (oxygen concentration 5 volume%) in Example 1 , and expansion / contraction degree. Explanatory drawing which shows the relationship between the temperature at the time of the heating in an atmospheric gas atmosphere (oxygen concentration about 21 volume%) in Example 1 , and an expansion-contraction degree. Explanatory drawing which shows the whole external appearance of the exhaust gas purification filter in Reference Example 2 . Explanatory drawing which shows the cross-section of the exhaust gas purification filter in Reference Example 2 . Explanatory drawing which shows the relationship between preset maximum temperature and PM combustion speed in the reference example 2. FIG. FIG. 4 is an explanatory diagram showing the relationship between the amount of MgO added to a honeycomb body base material and the A-axis strength of the honeycomb body base material in Example 2 . Explanatory drawing which shows the relationship between forced regeneration temperature (setting maximum temperature) and PM combustion speed in the reference example 3. FIG. Explanatory drawing which shows a mode that a some honeycomb body base material is joined. Explanatory drawing which shows the external appearance of the joining type honeycomb body base material with which the several honeycomb body base material was joined.

Next, a preferred embodiment of the present invention will be described.
The honeycomb body base material has a columnar shape, and has porous partition walls arranged in a lattice shape and a plurality of cells extending in the axial direction surrounded by the partition walls.
In the honeycomb base material, among the plurality of cells, the end on the downstream side of the inflow cell into which the exhaust gas flows and the end on the upstream side of the exhaust cell from which the exhaust gas is discharged can be blocked by the plug portion. The above honeycomb body base material can be used for collecting particulate matter (PM) in exhaust gas discharged from an internal combustion engine such as a diesel engine and purifying the exhaust gas.

The honeycomb base material can have an outer shape such as a columnar shape or a prism shape.
In addition, the honeycomb body base material can be used as it is for purification of exhaust gas, but can be used as a joining type honeycomb body base material.
Specifically, as shown in FIG. 20, a prismatic honeycomb body base having porous partition walls 52 arranged in a lattice shape and a plurality of cells 53 surrounded by these partition walls 52 and extending in the axial direction. A plurality of materials 5 are prepared. Here, as shown in FIG. 20, as the honeycomb body base material 5, 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 are blocked by the plug portion 55. Can be used. Next, as shown in the figure, the honeycomb body base materials 5 are joined to each other at the side surfaces 56. Thereafter, the outer periphery of the joined body of the honeycomb body base material is processed into a cylindrical shape by cutting or the like, and as shown in FIG. 21, a plurality of honeycomb body base materials 5 are joined to each other at the side surfaces. 6 can be obtained. In FIG. 21, for the convenience of drawing, the configuration of the cells, cell walls, plugs, etc. of the honeycomb body base material 5 is omitted except for a part of the honeycomb body base material 5.

At least the partition walls of the honeycomb base material have α-alumina as a main component. In the case where the partition walls are made of, for example, cordierite, SiC, aluminum titanate, etc. other than α-alumina, the partition walls of the honeycomb body base material react with the alkali catalyst supported on the partition walls in a high temperature environment, and the alkali The activity of the catalyst may be reduced. Further, in the honeycomb body base material, it is preferable that not only the partition walls but also the whole honeycomb body base material has α-alumina as a main component.
In addition, inevitable impurities are mixed in the α-alumina itself, or additives such as alkaline earth metal oxides can be added as described later. It is preferable that 99.0 wt% or more of α 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 may be 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 substrate may be easily damaged when the honeycomb body substrate is canned into the DPF converter, that is, when the honeycomb body substrate is housed in the case. There is. 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 exhaust gas purification filter can be constructed by supporting an alkali catalyst on at least the partition walls of the honeycomb body base material.
The alkali catalyst is a catalyst containing an alkali metal. As the alkali catalyst, for example, a catalyst obtained by impregnating the honeycomb body base material with an alkali salt and firing it can be used. 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.

Preferably, the alkali catalyst is obtained by calcining 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 ° C. or higher .
In this case, the above-described effect of suppressing the decrease in the activity of the alkali catalyst can be remarkably exhibited, and the alkali catalyst itself can exhibit excellent water resistance. That is, the alkali catalyst formed by calcining 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 ° C. or more is difficult to elute the alkali even in the presence of moisture. , The catalyst activity is difficult to decrease.

Next, in manufacturing the honeycomb body base material, the mixing step, the forming step, and the firing step are performed.
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, for example, 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 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 were less than 5 parts by mass or when the α-alumina precursor particles were less than 0.5 parts by mass, the α-alumina was not sufficiently sintered in the firing step, and the porosity was increased. There is a possibility that the strength of the honeycomb substrate is 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 step, in order to facilitate molding into a desired shape, the organic binder can be mixed into 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 substrate obtained after the firing step 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 may be 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, the firing of the formed body can be uniformly progressed in the firing step, and the 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 porous partition walls arranged in a lattice pattern and a plurality of cells surrounded by the partition walls and extending in the axial direction. Further, among the cells of the honeycomb formed body, the downstream end portion of the inflow cell into which the exhaust gas flows and the upstream end portion of the discharge cell from which the exhaust gas is discharged can be blocked by the plug portion.

In the firing step, the honeycomb formed body is fired.
In the baking step, it is preferable to perform the baking at a maximum firing 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.

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.

( Reference Example 1)
In this example, α-alumina is an excellent example of the material of the honeycomb base material that supports the alkali catalyst. Specifically, an alkali catalyst and various honeycomb body base materials (α alumina, θ alumina, γ alumina, cordierite, silicon carbide, and aluminum titanate) are mixed, and the catalytic activity of the alkali catalyst is examined.

First, an alkali catalyst was produced as follows.
That is, first, 100 parts by mass of sodalite (3 (Na ₂ O.Al ₂ O ₃ .2SiO ₂ ) .2NaOH) and 10 parts by mass of potassium carbonate were put 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 size of 20 μm or less to obtain a powdery alkali catalyst. This is designated as Sample X1.

  Next, 5 parts by mass of an alkali catalyst (sample X1) and 100 parts by mass of powdered α-alumina having a median diameter of 2 μm and a maximum particle diameter of 10 μm were mixed for a certain time using an agate mortar. The mixture was then heat treated at a temperature of 650 ° C. Specifically, the mixture was heated at a heating rate of 200 ° C./hour, and when the temperature reached 650 ° C. (heat treatment temperature), heat treatment was performed by holding for 3 hours. This is designated as Sample X2.

  Further, 5 parts by mass of an alkali catalyst (sample X1) and 100 parts by mass of powdery θ-alumina having a median diameter of 2 μm and a maximum particle diameter of 10 μm were mixed for a certain time using an agate mortar. The mixture was then heat treated at a temperature of 650 ° C. Specifically, the mixture was heated at a heating rate of 200 ° C./hour, and when the temperature reached 650 ° C. (heat treatment temperature), heat treatment was performed by holding for 3 hours. This is designated as Sample X3.

  Further, 5 parts by mass of an alkali catalyst (sample X1) and 100 parts by mass of powdery γ-alumina having a median diameter of 2 μm and a maximum particle diameter of 10 μm were mixed for a certain time using an agate mortar. The mixture was then heat treated at a temperature of 650 ° C. Specifically, the mixture was heated at a heating rate of 200 ° C./hour, and when the temperature reached 650 ° C. (heat treatment temperature), heat treatment was performed by holding for 3 hours. This is designated as Sample X4.

  Further, 5 parts by mass of an alkali catalyst (sample X1) and 100 parts by mass of powdered cordierite having a median diameter of 2 μm and a maximum particle diameter of 10 μm were mixed for a certain time using an agate mortar. The mixture was then heat treated at a temperature of 650 ° C. Specifically, the mixture was heated at a heating rate of 200 ° C./hour, and when the temperature reached 650 ° C. (heat treatment temperature), heat treatment was performed by holding for 3 hours. This is designated as Sample X5.

  Further, 5 parts by mass of an alkali catalyst (sample X1) and 100 parts by mass of powdered silicon carbide (SiC) having a median diameter of 2 μm and a maximum particle diameter of 10 μm were mixed for a certain time using an agate mortar. The mixture was then heat treated at a temperature of 650 ° C. Specifically, the mixture was heated at a heating rate of 200 ° C./hour, and when the temperature reached 650 ° C. (heat treatment temperature), heat treatment was performed by holding for 3 hours. This is designated as Sample X6.

  Further, 5 parts by mass of an alkali catalyst (sample X1) and 100 parts by mass of powdered aluminum titanate having a median diameter of 2 μm and a maximum particle diameter of 10 μm were mixed for a certain time using an agate mortar. The mixture was then heat treated at a temperature of 650 ° C. Specifically, the mixture was heated at a heating rate of 200 ° C./hour, and when the temperature reached 650 ° C. (heat treatment temperature), heat treatment was performed by holding for 3 hours. This is designated as Sample X7.

  Next, 500 mg of each sample (samples X1 to X7) and 25 mg of carbon black (CB) were accurately weighed with an electronic balance. Using an agate mortar, each sample (mass): CB (mass) = 20: 1 was mixed for a certain period of time to obtain seven types of evaluation samples containing each sample and CB. Further, an evaluation sample (sample X0) consisting only of CB was prepared for comparison without using a catalyst species. Also about the evaluation sample of CB alone, what was mixed for a fixed time using the agate mortar was used similarly to the other samples. That is, as an evaluation sample, CB alone (sample X0), a mixture of samples X1 and CB, a mixture of samples X2 and CB, a mixture of samples X3 and CB, a mixture of samples X4 and CB, and samples X5 and CB 8 types of samples, a mixture of Sample X6 and CB, and a mixture of Sample X7 and CB were prepared.

  Next, using a thermal analysis-differential thermogravimetric (TG-DTA) simultaneous measurement device (TG8120 manufactured by Rigaku Corporation), each evaluation sample 18 mg was heated to a maximum temperature of 750 ° C. at a temperature rising rate of 10 ° C./min, and then CB. The DTA exothermic peak rising temperature (hereinafter defined as “CB combustion start temperature”) was measured. In addition, about the evaluation sample which consists only of CB, CB combustion start temperature was measured using 0.9 mg. The heating was performed while flowing air through the evaluation sample at a flux of 50 mL / min. The measurement result of the CB combustion start temperature when each catalyst type is used is shown in FIG.

As is known from FIG. 1, Sample X1 to Sample X7 containing an alkali catalyst have a lower CB combustion start temperature than CB alone Sample X0, and can burn CB at a low temperature.
In addition, Sample X2 containing α-alumina and an alkali catalyst showed a CB combustion start temperature as low as Sample X1 containing an alkali catalyst alone. This is because α-alumina hardly reacts with the alkali catalyst even in a high-temperature environment, and a decrease in catalytic activity can be suppressed. On the other hand, samples X3 to X7 containing an alkali catalyst and a material other than α-alumina.
The CB combustion start temperature was higher than that of the sample X1 containing an alkali catalyst alone. This is because θ alumina, γ alumina, cordierite, silicon carbide, and aluminum titanate react with the alkali catalyst in a high temperature environment, and the catalytic activity of the alkali catalyst is reduced.

  Thus, according to this example, it can be seen that the use of α-alumina as the material for the honeycomb body base material can suppress a decrease in catalyst activity even in a high temperature environment.

(Example 1 )
In this example, a honeycomb body substrate made of α-alumina is manufactured, and the manufacturing conditions thereof are examined.
The honeycomb body substrate 1 of this example is made of α-alumina, and as shown in FIGS. 2 and 3, porous partition walls 12 arranged in a lattice shape, and a plurality of axial partition walls surrounded by the partition walls 12. Cell 13. In this example, the honeycomb body base material 1 has a cylindrical outer peripheral wall 11 and partition walls 12 arranged in a rectangular lattice shape in the outer peripheral wall 11. A large number of cells 13 partitioned by the partition walls 12 are formed. Each cell 13 is formed so as to extend in the axial direction of the cylindrical honeycomb substrate 1, and is open at both end portions 18 and 19 of the honeycomb substrate 1.

In manufacturing the honeycomb body base material of this example, the mixing step, the forming step, and the firing step are performed as follows.
In the mixing step, coarse particles having a median diameter of 20 to 60 μm made of α-alumina, fine particles having a median diameter of 2 μm or less made of α-alumina, α-alumina precursor particles that form α-alumina after firing, an organic binder, Mix with water to make a clay made of raw material mixture.
In the forming step, the clay is formed into the shape of the honeycomb base material to obtain a honeycomb formed body.
In the firing step, the honeycomb formed body is fired to obtain the honeycomb base material.

In this example, particles having different sizes are employed as coarse particles in the mixing step, and a plurality of honeycomb body base materials are produced and their characteristics are evaluated.
Specifically, first, 100 mass parts of coarse particles having a median diameter of 15 μm made of α-alumina, 10 mass parts of fine particles having a median diameter of 0.2 μm and a maximum particle diameter 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 mixed, thereby making the raw material mixture into a clay and obtaining a clay (mixing step).

  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 1500 ° 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 heating rate of 50 ° C./hour, and held for 10 hours when the temperature reached 1500 ° C. ( Firing step). In this way, a honeycomb body substrate 1 was obtained (see FIGS. 2 and 3). This is designated as sample Y1.

Further, in this example, four types of honeycomb base materials (sample Y2 to sample Y5) were prepared using four types of particles whose median diameter of coarse particles used in the mixing step is different from that of sample Y1.
Specifically, the sample Y2 is a honeycomb body substrate manufactured using coarse particles made of α-alumina and having a median diameter of 30 μm.
Sample Y3 is a honeycomb substrate made of coarse particles having a median diameter of 45 μm made of α-alumina.
Sample Y4 is a honeycomb substrate made of coarse particles made of α-alumina and having a median diameter of 60 μm.
Sample Y5 is a honeycomb substrate made of coarse particles having a median diameter of 85 μm made of α-alumina.
These samples Y2 to Y5 are honeycomb body substrates manufactured in the same manner as the sample Y1 except that the median diameter of the coarse particles was changed.

Furthermore, in this example, a honeycomb substrate (sample Y6) was produced using fine particles and α-alumina precursor particles without using coarse particles as a raw material of α-alumina in the mixing step.
In preparing the sample Y6, first, 100 parts by mass of fine particles having a median diameter of 0.2 μm made of α-alumina and a maximum particle diameter of 0.5 μm, and 5 parts by mass of precursor particles made of aluminum hydroxide having a median diameter of 5 μm. Dry mixed. Subsequently, water, an organic binder, and a moisturizing material were added to the raw material mixture and mixed to make the raw material mixture clay (mixing step). Thereafter, the forming step and the firing step were performed in the same manner as the sample Y1 to obtain a honeycomb body base material (sample Y6).

Next, the average pore diameter and the porosity of each of the honeycomb body substrates of Sample Y1 to Sample Y6 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.

Further, the A-axis strength was measured for each of the honeycomb body base materials of Sample Y1 to Sample Y6.
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.

  FIG. 4 shows the relationship between the median diameter (average particle diameter) of the coarse particles used for the raw material and the average pore diameter of the honeycomb body substrate for each sample Y1 to Y6. In the figure, the horizontal axis represents the median diameter (μm) of the coarse particles, and the vertical axis represents the average pore diameter (μm) of the honeycomb body substrate. FIG. 5 shows the relationship between the median diameter of the coarse particles used as the raw material and the porosity of the honeycomb body base material. In the figure, the horizontal axis represents the median diameter (μm) of the coarse particles, and the vertical axis represents the porosity (%) of the honeycomb body substrate. FIG. 6 shows the relationship between the median diameter of the coarse particles used as the raw material and the A-axis strength of the honeycomb body base material. In the figure, the horizontal axis indicates the median diameter (μm) of the coarse particles, and the vertical axis indicates the A-axis strength (MPa) of the honeycomb body substrate.

As can be seen from FIG. 4, the average pore diameter of the honeycomb body substrate can be adjusted within a range of 10 to 20 μm by using coarse particles having a median diameter of 20 to 60 μm. Therefore, a honeycomb body substrate with low pressure loss and excellent PM collection performance can be obtained.
Further, as can be seen from FIG. 5, it can be seen that the porosity of the honeycomb substrate can be adjusted within a range of 40 to 70% by using coarse particles having a median diameter of 20 to 60 μm. Therefore, a honeycomb body substrate having a low pressure loss and excellent strength can be obtained.
As can be seen from FIG. 6, a honeycomb base material having a high A-axis strength of 2 MPa or more can be obtained by using coarse particles having a median diameter of 20 to 60 μm.
Thus, according to this example, it is understood that coarse particles having a median diameter of 20 to 60 μm are preferably used in the manufacture of the honeycomb body base material.

Next, in this example, as the fine particles in the mixing step, particles having different sizes are adopted to produce a plurality of honeycomb body base materials, and the characteristics thereof are evaluated.
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 3 μm and a maximum particle size of 4 μm made of α-alumina, and a median diameter of 5 μm made of aluminum hydroxide. The precursor particles of 5.5 parts by mass were dry mixed. Subsequently, water, an organic binder, and a moisturizing material were added to the raw material mixture and mixed to make the raw material mixture clay (mixing step). Next, a forming step and a firing step were performed in the same manner as the sample Y1, and a honeycomb body substrate having the same shape as the sample Y1 was obtained. This is designated as Sample Y7.

Further, in this example, four types of honeycomb body base materials (sample Y8 to sample Y11) were manufactured using four types of particles whose median diameter of fine particles used in the mixing step is different from that of the sample Y7.
Specifically, sample Y8 is a honeycomb body substrate manufactured using fine particles made of α-alumina and having a median diameter of 2 μm and a maximum particle diameter of 2.8 μm.
Sample Y9 is a honeycomb body substrate manufactured using fine particles made of α-alumina and having a median diameter of 1 μm and a maximum particle diameter of 1.6 μm.
Sample Y10 is a honeycomb body substrate manufactured using fine particles made of α-alumina and having a median diameter of 0.5 μm and a maximum particle diameter of 0.9 μm.
Sample Y11 is a honeycomb body substrate manufactured using fine particles made of α-alumina and having a median diameter of 0.2 μm and a maximum particle diameter of 0.5 μm.
These samples Y8 to Y11 are honeycomb body substrates manufactured in the same manner as the sample Y7 except that the median diameter of the fine particles was changed.

  Next, the average pore diameter, the porosity, and the A-axis strength of each of the honeycomb body base materials of Sample Y7 to Sample Y11 obtained as described above were measured in the same manner as Samples Y1 to Y6. FIG. 7 shows the relationship between the median diameter of the fine particles used for manufacturing each honeycomb body base material and the average pore diameter of the honeycomb body base material. In the figure, the horizontal axis represents the median diameter (μm) of the fine particles, and the vertical axis represents the average pore diameter (μm) of the honeycomb body substrate. FIG. 8 shows the relationship between the median diameter of the fine particles and the porosity of the honeycomb body base material. In the figure, the horizontal axis represents the median diameter (μm) of the fine particles, and the vertical axis represents the porosity (%) of the honeycomb body substrate. FIG. 9 shows the relationship between the median diameter (particle diameter) of the fine particles and the A-axis strength of the honeycomb body base material. In the figure, the horizontal axis represents the median diameter (μm) of the fine particles, and the vertical axis represents the A-axis strength (MPa) of the honeycomb body substrate.

As is known from FIG. 7, it can be seen that the average pore diameter of the honeycomb body substrate can be adjusted within a range of 10 to 20 μm by using fine particles having a median diameter of 2 μm or less. Therefore, a honeycomb body substrate with low pressure loss and excellent PM collection performance can be obtained.
Further, as can be seen from FIG. 8, it can be seen that the porosity of the honeycomb base material can be adjusted within a range of 40 to 70% by using fine particles having a median diameter of 2 μm or less. Therefore, a honeycomb body substrate having a low pressure loss and excellent strength can be obtained.
Further, as is known from FIG. 9, a honeycomb body substrate having a high A-axis strength of 2 MPa or more can be obtained by using fine particles having a median diameter of 2 μm or less.
As described above, according to this example, it is found that it is preferable to use fine particles having a median diameter of 2 μm or less in manufacturing the honeycomb body base material.

Next, in this example, a plurality of honeycomb body base materials are produced by changing the mixing ratio of the fine particles in the mixing step, and the characteristics are evaluated.
Specifically, first, 100 parts by mass of coarse particles having a median diameter of 45 μm made of α-alumina, 3 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 mixed to make the raw material mixture clay (mixing step). Next, a forming step and a firing step were performed in the same manner as the sample Y1, and a honeycomb body substrate having the same shape as the sample Y1 was obtained. This is designated as Sample Y12.

Further, five kinds of honeycomb base materials (sample Y13 to sample Y17) were produced by changing the blending ratio of fine particles to coarse particles in the mixing step.
Specifically, the sample Y13 is a honeycomb base material manufactured using 5 parts by mass of fine particles with respect to 100 parts by mass of coarse particles in the mixing step.
Sample Y14 is a honeycomb body substrate manufactured using 10 parts by mass of fine particles with respect to 100 parts by mass of coarse particles in the mixing step.
Sample Y15 is a honeycomb body substrate manufactured using 20 parts by mass of fine particles with respect to 100 parts by mass of coarse particles in the mixing step.
Sample Y16 is a honeycomb base material produced by using 30 parts by mass of fine particles with respect to 100 parts by mass of coarse particles in the mixing step.
Sample Y17 is a honeycomb body substrate manufactured using 50 parts by mass of fine particles with respect to 100 parts by mass of coarse particles in the mixing step.
These samples Y13 to Y17 are honeycomb body substrates manufactured in the same manner as the sample Y12 except that the blending ratio of the fine particles was changed.

  Next, the average pore diameter, the porosity, and the A-axis strength of each of the honeycomb body substrates of Sample Y12 to Sample Y17 obtained as described above were measured in the same manner as Samples Y1 to Y6. And the relationship between the mixture ratio of the fine particles with respect to 100 parts by mass of coarse particles in the mixing step and the average pore diameter of the honeycomb body base material is shown in FIG. In the figure, the horizontal axis indicates the blending ratio (parts by mass) of fine particles, and the vertical axis indicates the average pore diameter (μm) of the honeycomb body substrate. Further, FIG. 11 shows the relationship between the blending ratio of fine particles with respect to 100 parts by mass of coarse particles in the mixing step and the porosity of the honeycomb body substrate. In the figure, the horizontal axis indicates the mixing ratio (parts by mass) of fine particles, and the vertical axis indicates the porosity (%) of the honeycomb body substrate. Further, FIG. 12 shows the relationship between the blending ratio of fine particles with respect to 100 parts by mass of coarse particles in the mixing step and the A-axis strength of the honeycomb body substrate. In the figure, the horizontal axis indicates the blending ratio (parts by mass) of fine particles, and the vertical axis indicates the A-axis strength (MPa) of the honeycomb body substrate.

As can be seen from FIG. 10, in the mixing step, the average pore diameter of the honeycomb substrate can be adjusted within a range of 10 to 20 μm by using 5 to 30 parts by mass of fine particles with respect to 100 parts by mass of coarse particles. I understand. Therefore, a honeycomb body substrate with low pressure loss and excellent PM collection performance can be obtained.
Further, as can be seen from FIG. 11, it is understood that the porosity of the honeycomb base material can be adjusted within a range of 40 to 70% by using 5 to 30 parts by mass of fine particles with respect to 100 parts by mass of coarse particles. Therefore, a honeycomb body substrate having a low pressure loss and excellent strength can be obtained.
Further, as is known from FIG. 12, a honeycomb base material having a high A-axis strength of 2 MPa or more can be obtained by using 5 to 30 parts by mass of fine particles with respect to 100 parts by mass of coarse particles.
Thus, according to this example, it can be seen that it is preferable to use 5 to 30 parts by mass of fine particles with respect to 100 parts by mass of coarse particles in the manufacture of the honeycomb body base material.

  Next, in this example, a plurality of honeycomb body base materials are produced by changing the firing conditions in the firing step, and the characteristics are evaluated. In examining the firing conditions, in order to investigate the sintering behavior during firing, the fine particles are used in the mixing step without using coarse particles.

  Specifically, first, 100 parts by mass of fine particles having a median diameter of 0.2 μm made of α-alumina and a maximum particle size of 0.5 μm and 5 parts by mass of precursor particles made of aluminum hydroxide having a median diameter of 5 μm are dry-mixed. did. Subsequently, water, an organic binder, and a moisturizing material were added to and mixed with the raw material mixture, whereby the raw material mixture was made into a clay. Next, a forming process was performed in the same manner as the sample Y1, and a honeycomb formed body (a cylindrical shape with a diameter of 30 mm and a length of L50 mm) having the same shape as the sample Y1 was obtained.

Next, a cylindrical honeycomb molded body having a diameter of 5 mm and a length of L20 mm was cut out from the cylindrical honeycomb molded body, and this was used as a sample for evaluation. Next, using a thermomechanical analysis (TMA) apparatus (TMA-60H manufactured by Shimadzu Corporation), the sample for evaluation of the honeycomb formed body was heated to a maximum temperature of 1400 ° C. at a temperature rising rate of 20 ° C./min. Heating was performed while flowing a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration of 5% by volume) or air (oxygen concentration of about 21% by volume) through the honeycomb molded body sample at a flow rate of 50 mL / min. And the expansion-contraction degree (%) of the sample for evaluation at the time of a heating was measured with the TMA apparatus. The results are shown in FIGS.
FIG. 13 shows the relationship between the temperature and the degree of expansion and contraction during heating in a mixed gas atmosphere of nitrogen and oxygen (oxygen concentration 5% by volume). On the other hand, FIG. 14 shows the relationship between the temperature and the expansion / contraction degree during heating in an atmospheric gas atmosphere (oxygen concentration of about 21% by volume). In both FIG. 13 and FIG. 14, the horizontal axis indicates the temperature during heating (° C.), and the vertical axis indicates the degree of expansion / contraction (%).

  As is known from FIG. 13, the honeycomb formed body is observed to rapidly shrink from a temperature of 1200 ° C. as α alumina is sintered. Therefore, in order to obtain a desired base material strength, it is preferable to perform firing at a maximum firing temperature of 1200 or more. Further, if the firing temperature is higher, α-alumina can be sintered in a shorter time, and thus a honeycomb body substrate having a desired strength can be obtained in a shorter time.

  Further, as is known from FIG. 13, it can be seen that the expansion and contraction behavior can be measured up to a temperature of 1400 ° C. in a firing atmosphere having an oxygen concentration of 5% by volume. That is, in a firing atmosphere having an oxygen concentration of 5% by volume, the honeycomb formed body can maintain its honeycomb structure up to a temperature of at least 1400 ° C. On the other hand, as known from FIG. 14, the honeycomb molded body contracted instantaneously at about 280 ° C. in an air firing atmosphere having an oxygen concentration of about 21%. This indicates that, under firing conditions with a high oxygen concentration, the binder holding the α-alumina particles and the α-alumina precursor particles in the honeycomb molded body burns, and the honeycomb structure of the honeycomb molded body collapses. Therefore, in the firing step, it is preferable to adjust the oxygen concentration of the atmospheric gas at a temperature below 1200 ° C. to 5% by volume or less.

( Reference Example 2 )
This example is an example in which an exhaust gas purification filter in which an alkali catalyst is supported on a honeycomb body substrate made of α-alumina is manufactured and its characteristics are evaluated.
As shown in FIGS. 15 and 16, the exhaust gas purification filter 2 of this example has a honeycomb body base 3 made of α-alumina. The honeycomb base material 3 includes a cylindrical outer peripheral wall 31, porous partition walls 32 arranged in a square lattice pattern in the outer peripheral wall 31, and a large number of cells 33 that are surrounded by the partition walls 32 and extend in the axial direction. And have. Each cell 33 is formed to extend in the axial direction of the cylindrical honeycomb substrate 3.

  In the honeycomb body base material 3, among the plurality of cells 33, the end portion 39 on the downstream side of the inflow cell 331 into which the exhaust gas flows and the end portion 38 on the upstream side of the exhaust cell 332 from which the exhaust gas is discharged are formed by the plug portion 35. It is blocked. The plug portions 35 alternately close the openings of the adjacent cells 33 on both end faces 38 and 39 of the honeycomb body base material, and are arranged in a so-called checkered pattern.

  In the exhaust gas purification filter 2 of this example, an alkali catalyst (not shown) is supported on the partition walls 32 of the honeycomb body base material 3. In this example, the alkali catalyst is obtained by firing a mixture of sodalite and an alkali metal element source (potassium carbonate).

Hereinafter, the manufacturing method of the exhaust gas purification filter of this example will be described.
Specifically, first, a honeycomb base material (see FIGS. 2 and 3) in which both ends of the cell were opened was prepared. As such a honeycomb body base material, the sample Y3 of Example 1 was used.
Next, water, an organic binder, and a humectant were added to and mixed with the silica-alumina composite material to prepare a clay-like plug part forming material. Then, one of the openings on both end faces of each cell of the honeycomb substrate (sample Y3) is closed with the plug forming material, and the cell openings are alternately arranged on one end face of the honeycomb substrate. I closed it. Next, using an 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 by heating at this maximum temperature for 3 hours.
In this way, as shown in FIGS. 15 and 16, among the plurality of cells 33, the downstream end portion 39 of the inflow cell 331 into which the exhaust gas flows and the upstream end portion 38 of the exhaust cell 332 from which the exhaust gas is discharged. And honeycomb body substrate 3 closed by plug portion 35 was obtained.

Next, an alkali catalyst to be supported on the honeycomb body base material was prepared. In this example, the sample X1 of Reference Example 1 was used as the alkali catalyst.
And the catalyst slurry was produced by adding an alkali catalyst (sample X1), an inorganic binder, and a dispersing agent to water, and stirring. Next, the honeycomb body base material in which the plug portions were formed as described above was immersed in this catalyst slurry, and the honeycomb body base material was impregnated with the catalyst slurry.

Next, air was blown to one end face of the honeycomb body base material, and suction was performed from the other end face of the honeycomb body base material, whereby residual moisture was simply removed from the honeycomb body base material. Thereafter, using a hot air generator, hot air having a temperature of 200 ° C. was sent to the honeycomb body substrate to completely remove residual moisture in the honeycomb body substrate. 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.
Thus, an exhaust gas purification filter in which an alkali catalyst was supported on a honeycomb body substrate made of α-alumina was obtained. This is designated as Sample E1. In sample E1, the supported amount of alkali catalyst is 40 g per 1 L of exhaust gas purification filter.

Next, in order to evaluate the heat resistance of the sample E1, using an electric furnace, the sample E1 is heated up to a maximum temperature of 750 ° C. at a temperature rising rate of 200 ° C./hour in an air atmosphere. A heat treatment was performed for 20 hours. Let the sample after this heat processing be the sample E2.
Further, in order to evaluate the heat resistance of the sample E1, the temperature of the sample E1 was raised to a maximum temperature of 800 ° C. at a temperature rising rate of 200 ° C./hour in an air atmosphere using an electric furnace, and 50 ° C. at this temperature of 800 ° C. A heat treatment for holding for a time was performed. Let the sample after this heat processing be the sample E3.

Further, in this example, an exhaust gas purification filter in which an alkali catalyst was supported on a honeycomb body substrate made of cordierite was manufactured as a comparison with the sample E1.
Specifically, first, a cylindrical honeycomb substrate made of cordierite and having a diameter of 30 mm and a length of L50 mm was prepared. The honeycomb body base material is the same as the honeycomb body of the sample E1 except that the material is cordierite instead of α-alumina, and the end face is plugged in a checkered pattern like the sample E1. The part is formed.

Next, an alkali catalyst was supported on a honeycomb body substrate made of cordierite. The loading method was performed in the same manner as the sample E1. In this manner, a comparative exhaust gas purification filter in which an alkali catalyst was supported on a honeycomb body substrate made of cordierite was obtained. This is designated as Sample C1. In sample C1, the amount of alkali catalyst supported is 40 g per 1 L of exhaust gas purification filter, as in sample E1.
Further, in order to evaluate the heat resistance of the sample C1, using an electric furnace, the sample C1 is heated up to a maximum temperature of 750 ° C. at a temperature rising rate of 200 ° C./hour in an air atmosphere. A heat treatment for holding for a time was performed. Let the sample after this heat processing be the sample C2.

Further, as a further comparison with respect to the samples E1 to E3, the sample C1, and the sample C2, a sample for evaluation standard (sample C0) was prepared from an exhaust gas purification filter mounted on an actual vehicle.
Specifically, a sample of a cylindrical exhaust gas purification filter having a diameter of 30 mm and a length of L50 mm was cut out from an exhaust gas purification filter mounted on a diesel vehicle having a travel history of 180,000 km. In this exhaust gas purification filter, a noble metal catalyst is supported on a honeycomb body substrate made of cordierite. The honeycomb base material has a cylindrical outer peripheral wall, porous partition walls arranged in a square lattice pattern in the outer peripheral wall, and a plurality of cells that are surrounded by the partition walls and extend in the axial direction.

  Next, water, an organic binder, and a humectant were added to and mixed with the silica-alumina composite material to prepare a clay-like plug part forming material. Then, the plug portion forming material closes one of the openings on both end surfaces of each cell of the exhaust gas purification filter that has been cut out as described above, and the opening of the cell is formed on one end surface of the exhaust gas purification filter. It was closed alternately. Next, using an 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 by heating at this maximum temperature for 3 hours. In this manner, a plug portion was formed in the same manner as the sample E1. This is designated as an evaluation reference sample C0.

Next, an actual particulate matter (PM) is deposited on each evaluation sample (samples E1 to E3, sample C1, sample C2, and sample C0) using a 2.2 L direct injection common rail diesel engine. It was. The amount of PM deposited was 6.7 g per liter of evaluation sample.
Next, using a model gas evaluation apparatus manufactured by HORIBA, Ltd., each evaluation sample on which PM is deposited is heated to each set maximum temperature (450 ° C., 500 ° C., 550 ° C. or 600 ° C.) to burn the PM. It was. At this time, the PM combustion amount is calculated from the production amounts of carbon monoxide (CO) and carbon dioxide (CO ₂ ) resulting from PM combustion, and the PM combustion rate per 1 L of the evaluation sample and per unit time (min) is obtained. It was.

Specifically, while supplying a mixed gas of oxygen and nitrogen (oxygen concentration: 10% by volume, flow rate: 40 L / min) to each evaluation sample, each evaluation sample is heated to a temperature of 290 ° C. at a heating rate of 50 ° C./min. Heat. When the temperature reaches 290 ° C., it is switched to an oxygen-free atmosphere (100% by volume of nitrogen gas, flow rate 40 / min), and at a temperature rising rate of 50 ° C./min, a temperature that is 75 ° C. lower than the above set maximum temperatures, specifically Is 375 ° C when the preset temperature is 450 ° C, 425 ° C when the preset temperature is 500 ° C, 475 ° C when the preset temperature is 550 ° C, and 525 ° C when the preset temperature is 600 ° C. Heated. When the temperature reaches 75 ° C. lower than the set maximum temperature, the gas is again switched to a mixed gas of oxygen and nitrogen (oxygen concentration: 10 vol%, flow rate: 40 L / min), and each temperature increase rate is 50 ° C./min. It heated to preset maximum temperature (450 degreeC, 500 degreeC, 550 degreeC, or 600 degreeC), and hold | maintained for 20 minutes at each set maximum temperature. At this time, evaluation was made from the amounts of carbon monoxide (CO) and carbon dioxide (CO ₂ ) produced in 16 minutes immediately after switching to the mixed gas of oxygen and nitrogen after reaching a temperature lower than the set maximum temperature by 75 ° C. The PM combustion rate per 1 L of sample and per unit time (min) was determined, and this was taken as the PM combustion rate at each set maximum temperature. The result is shown in FIG. In the figure, the horizontal axis indicates the set maximum temperature (° C.), and the vertical axis indicates the PM combustion rate (g / L / min).

  As is known from FIG. 17, the PM burning rate at a temperature of 600 ° C. is 0.15 g / L / min in the sample C 0, whereas the PM burning is equivalent at a sufficiently low temperature of about 440 ° C. in the sample E 1. The speed has been reached. Further, both the sample E2 and the sample E3 reach a burning rate comparable to the PM burning rate (0.15 g / L / min) of the sample C0 at a temperature of about 480 ° C. and a temperature of 600 ° C. In addition, since the PM combustion rates at the set maximum temperatures of the sample E2 and the sample E3 are substantially the same, the thermal deterioration has converged in these samples, and the alkali catalyst is supported on the honeycomb substrate made of α-alumina. It can be seen that the exhaust gas purification catalyst thus made is less susceptible to heat deterioration.

  On the other hand, the sample C1 reaches a combustion rate equivalent to the PM combustion rate (0.15 g / L / min) of the sample C0 at a temperature of about 475 ° C. at a temperature of 600 ° C. This is inferior to the sample E1. Further, in the sample C2 obtained by heat-treating the sample C1, the heating temperature required to reach a combustion rate equivalent to the PM combustion rate of the sample C0 at a temperature of 600 ° C. increased to about 580 ° C. This indicates that in an exhaust gas purification catalyst in which an alkali catalyst is supported on a honeycomb body substrate made of cordierite, heat deterioration is likely to occur compared to a honeycomb body substrate made of α-alumina.

  As described above, according to the present example, the exhaust gas purification catalyst (sample E1 to sample E3) in which the alkali catalyst is supported on the honeycomb body substrate made of α-alumina has the alkali catalyst applied to the honeycomb body substrate made of cordierite. It can be seen that the catalyst performance is less likely to deteriorate in a high temperature environment as compared with the supported exhaust gas purification catalysts (sample C1 and sample C2).

(Example 2 )
In this example, a honeycomb base material containing α-alumina as a main component and further containing an alkaline earth metal is produced.
In this example, a cylindrical outer peripheral wall, and porous partition walls arranged in a square lattice shape in the outer peripheral wall, as in Example 1 and a plurality of cells extending in an axial direction and is surrounded by the partition wall A honeycomb body substrate having a similar structure is produced.

  In the preparation, first, 100 parts by mass of coarse particles having a median diameter of 45 μm made of α-alumina, 10 parts by weight 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 are used. Then, 5.5 parts by mass of precursor particles having a median diameter of 5 μm were dry-mixed. Next, an organic binder and a moisturizing material were added to the raw material mixture, and a magnesium nitrate aqueous 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 amount of magnesium nitrate aqueous solution added is 0 ppm, 300 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, and 4000 ppm in terms of magnesium oxide with respect to the total amount of coarse particles, fine particles, and precursor particles. Thus, a plurality of clays having different amounts of magnesium nitrate were prepared.

Next, the clay was extruded and formed in the same manner as in the sample Y1 of Example 1 to produce a cylindrical honeycomb formed body having a diameter of 30 mm and a length of L50 mm (forming step).
Next, the honeycomb formed body was fired at a maximum temperature of 1650 ° C. in an electric furnace. Firing was performed in the same manner as the sample Y1 of Example 1 except that the maximum temperature was changed to 1650 ° C. (firing step). In this way, a honeycomb body substrate was obtained. The thus obtained honeycomb body base materials are designated as samples Y18 to Y24.
Samples Y18 to Y24 were prepared in the same manner except that the amount of magnesium nitrate aqueous solution added was 0, 300, 500, 1000, 2000, 3000, and 4000 ppm, respectively, in terms of magnesium oxide. (See Table 1 below).

Moreover, in this example, in the mixing step, a honeycomb body base material was manufactured by adding magnesium oxide particles instead of the magnesium nitrate aqueous solution.
Specifically, first, similarly to the above-described samples Y18 to Y24, coarse particles, fine particles, and precursor particles were mixed to obtain a raw material mixture. Water, an organic binder, and a moisturizing material were added to the raw material mixed powder, and further, magnesium oxide particles were added and mixed to make the raw material mixture into a clay and obtain a clay (mixing step). In this example, the amount of magnesium oxide particles added is 300 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, and 4000 ppm with respect to the total amount of coarse particles, fine particles, and precursor particles. A number of different clays were produced.
Next, in the same manner as the samples Y18 to Y24, a forming step and a firing step were performed to obtain a honeycomb body base material. The honeycomb body base material thus obtained is designated as Samples Y25 to Y30.

  Samples Y25 to Y30 are honeycomb body substrates manufactured in the same manner except that the amount of magnesium oxide added is 300 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, and 4000 ppm, respectively (see Table 1 described later). ).

Next, the compressive strength (A-axis strength) was measured in the same manner as in Example 1 for each of the honeycomb body base materials of Samples Y18 to Y30. In the measurement, 50 measurement samples were prepared for each sample, and the A-axis strength was measured. Table 1 shows the A-axis intensity (average value of 50 measurement samples) of each sample.
FIG. 18 shows the relationship between the amount of MgO added and the A-axis strength for Samples 18 to Y30. In the figure, the horizontal axis indicates the amount of MgO added, and the vertical axis indicates the A-axis strength. In the same figure, those using magnesium nitrate as the magnesium oxide source are represented by circled plots, and those using magnesium oxide are represented by triangular plots. Further, in FIG. 18, the variation in the A-axis intensity in 50 measurement samples is represented by the length of a bar extending vertically from each plot point.

In the honeycomb base material (samples Y19 to Y30) prepared by adding an alkaline earth metal compound such as magnesium nitrate and magnesium oxide into the clay, alkaline earth such as magnesium oxide is added to the fired honeycomb base material. Metal oxides are formed. As is known from Table 1, these honeycomb body base materials (samples Y19 to Y30) have an improved A-axis strength compared to a honeycomb body base material (sample Y18) prepared without adding an alkaline earth metal. It was.
In addition, as known from Table 1, the addition of an alkaline earth metal salt such as magnesium nitrate improves the strength even more than the addition of an alkaline earth metal oxide such as magnesium oxide to the clay. Can be made.

Further, as is known from FIG. 18, the honeycomb body base material (samples Y19 to Y24) manufactured by adding an alkaline earth metal salt was prepared by adding an alkaline earth metal oxide. Compared to (Samples Y25 to Y30), the A-axis strength can be further improved, and variations in strength can be reduced.
In a honeycomb body base material, if there is a portion with low strength partially inside the base material, the low strength portion serves as a fracture base point, so that the strength of the entire honeycomb body base material may be reduced. When alkaline earth metal salt is used as in samples Y19 to Y24, the alkaline earth metal can be uniformly dispersed in the clay. Therefore, firing can be progressed uniformly in the firing step, and the variation in strength of the honeycomb body base material can be reduced as shown in FIG. Therefore, the overall strength of the honeycomb body base material can be improved.

  Thus, according to the present example, in the mixing step, an alkaline earth metal is added to the clay, and the honeycomb body base material containing α-alumina as a main component contains the alkali metal oxide, whereby the honeycomb body The strength of the substrate can be improved. Further, by adopting an alkaline earth metal salt as the alkaline earth metal compound added to the clay, not only can the strength of the honeycomb body substrate be further improved, but also the strength of the honeycomb body substrate. The variation of can be reduced.

( Reference Example 3 )
In this example, an exhaust gas purification filter is prepared in which an alkali catalyst is supported on a honeycomb body base material containing α-alumina as a main component and further containing an alkaline earth metal, and its characteristics are evaluated.
The exhaust gas purification filter of this example has the same configuration as that of Reference Example 2 except that it has a honeycomb body base material containing an alkaline earth metal (see FIGS. 15 and 16).

In producing the exhaust gas purification filter of this example, first, samples Y18 to Y24 of Example 2 were prepared as honeycomb body bases having both ends of the cell opened. Next, in the same manner as in Reference Example 2 , among the plurality of cells of the honeycomb body base material, the end on the downstream side of the inflow cell into which the exhaust gas flows and the end on the upstream side of the exhaust cell from which the exhaust gas is discharged are plugged. Occlusion.
Next, the sample X1 of Reference Example 1 was prepared as an alkali catalyst to be supported on the honeycomb body base material, and this alkaline catalyst was supported on the honeycomb body base material in the same manner as in Reference Example 2 .
In this way, exhaust gas purification filters (samples E4 to E10) in which an alkali catalyst was supported on each honeycomb substrate (samples Y18 to Y24) were obtained.
Samples E4 to E10 are exhaust gas purification filters produced in the same manner except that Samples Y18 to Y24 of Example 2 were used as the honeycomb body base materials, respectively. In Samples E4 to E10, the supported amount of the alkali catalyst is 40 g per 1 L of the exhaust gas purification filter.

Next, actual particulate matter (PM; particulate matter) was deposited on each evaluation sample (samples E4 to E10) using a 2.2 L direct injection common rail diesel engine. The amount of PM deposited was 6.7 g per liter of evaluation sample.
Next, using a model gas evaluation device manufactured by HORIBA, Ltd., each evaluation sample on which PM is deposited is heated to each set maximum temperature (450 ° C, 500 ° C, or 550 ° C) to force PM to burn. Went. At this time, the PM combustion amount is calculated from the production amounts of carbon monoxide (CO) and carbon dioxide (CO ₂ ) resulting from PM combustion, and the PM combustion rate per 1 L of the evaluation sample and per unit time (min) is obtained. It was. Specifically, the measurement was performed in the same manner as in Reference Example 2 . The result is shown in FIG. In the figure, the horizontal axis represents forced regeneration temperature (set maximum temperature) (° C.), and the vertical axis represents PM combustion rate (g / L / min).

As known from FIG. 19, an exhaust gas purification filter (samples E5 to E5) in which an alkali catalyst is supported on a honeycomb body base (samples Y19 to Y24) containing α-alumina as a main component and further containing an alkaline earth metal oxide. E10) is made of α-alumina and has a high PM combustion at a low temperature comparable to that of an exhaust gas purification filter (sample E4) in which an alkali catalyst is supported on a honeycomb base material (sample Y18) that does not contain an alkaline earth metal. Showed speed. Therefore, even if an alkaline earth metal oxide is contained in the honeycomb body base material, the PM combustion performance is not adversely affected. On the other hand, as shown in Example 2 described above, the strength of the honeycomb body base material can be improved.

  As described above, according to the present example, the exhaust gas purification filter in which an alkali catalyst is supported on a honeycomb body base material containing α-alumina as a main component and further containing an alkaline earth metal oxide is a honeycomb made of α-alumina. It can be seen that the PM exhibits excellent purification performance with respect to PM, similarly to the exhaust gas purification filter in which an alkaline catalyst is supported on the body substrate.

1 honeycomb base material 12 partition wall 13 cell

Claims (6)

A columnar honeycomb substrate having an alkali catalyst containing an alkali metal and having porous partition walls arranged in a lattice pattern and a plurality of cells extending in the axial direction surrounded by the partition walls. In the manufacturing method,
Coarse particles having a median diameter of 20 to 60 μm made of α-alumina, fine particles having a median diameter of 0.5 μm or less made of α-alumina, α-alumina precursor particles that form α-alumina after firing, an organic binder, water, Mixing step of preparing a clay made of a raw material mixture by mixing
A molding step of forming the clay into the shape of the honeycomb body base material to obtain a honeycomb molded body;
By firing the honeycomb molded body at a maximum firing temperature of 1200 to 2000 ° C., it has a firing step to obtain the honeycomb base body,
In the firing step, a method for manufacturing a honeycomb body base material, wherein an oxygen concentration of an atmospheric gas at a temperature lower than 1200 ° C. at a temperature rise is adjusted to 0.5 to 5% by volume . 2. The production method according to claim 1 , wherein in the mixing step, 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. A method for manufacturing a honeycomb substrate, comprising mixing parts. The manufacturing method according to claim 1 or 2 , wherein the α-alumina precursor particles are made of aluminum hydroxide. In the production method according to any one of claims 1 to 3, in the mixing step, the raw material mixture further adding an alkaline earth metal, the addition amount of the alkaline earth metal, and the coarse particles A honeycomb body base comprising 0.03 to 0.4 parts by mass in terms of oxide equivalent of alkaline earth metal with respect to a total of 100 parts by mass of the fine particles and the α-alumina precursor particles A method of manufacturing the material. The manufacturing method according to claim 4 , wherein the alkaline earth metal is at least Mg and / or Ca. The method of manufacture according to claim 4 or 5, in the mixing step, as the alkaline earth metals, the manufacturing method of the honeycomb base body, characterized in adding an alkaline earth metal salt.

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