WO2019065741A1 - Particulate filter - Google Patents

Abstract

The purpose of the present invention is to provide a particulate filter with which it is possible to enhance the PM combustion speed and still prevent thermal runaway. Proposed is a particulate filter provided with a filter substrate having a configuration in which gas inflow cells in which the upstream side with respect to the flow of exhaust gas is open and the downstream side is sealed, and gas outflow cells in which the upstream side with respect to the flow of exhaust gas is sealed and the downstream side is open, are provided adjacent to each other with a partition wall interposed therebetween, wherein: a silver catalyst layer containing silver and palladium at a ratio of 21:1 to 98:1 by mass is formed in a region, on the surface of the partition wall within the gas inflow cells, that extends from the opening part of the gas inflow cells toward the sealed-part side by a length corresponding to 75-95% of the total longitudinal length of the gas inflow cells; and no catalyst layer is formed in the region on the sealed-part side of the silver catalyst layer.

Description

Particulate filter

The present invention is directed to a catalyst-processed particulate filter (also referred to as a CSF (Catalyzed Soot Filter) that can be used to purify exhaust gas emitted from an internal combustion engine, particularly an internal combustion engine such as a diesel engine or a gasoline engine). Referred to).

Exhaust gases emitted from internal combustion engines such as diesel engines and gasoline engines include sulfates based on sulfur in fuel, tar-like particulate matter (also referred to as "PM") derived from incomplete combustion, nitrogen Oxide (NOx) etc. are included.

BACKGROUND ART As an apparatus for removing PM contained in exhaust gas of an internal combustion engine, an exhaust gas purification apparatus is known which collects PM with a particulate filter and burns and removes the collected PM at appropriate timing.
In such particulate filters, a porous filter base having a honeycomb structure usually forms a framework, and when exhaust gas flows inside the partition of the base, PM is collected on the surface of the partition It is supposed to

By the way, in this type of particulate filter, one using silver as a catalytically active component instead of expensive platinum (platinum) has recently been proposed.

For example, in Patent Document 1 (WO2014 / 002772), a gas inflow cell having an opening on the upstream side where the exhaust gas flows and a closed cell on the downstream side, and an upstream side in which the exhaust gas flows is closed, and the downstream side is a gas outflow A diesel particulate filter comprising a filter substrate having a structure in which a cell and a cell are provided adjacent to each other via a partition wall, wherein a silver alloy containing silver and palladium is used as a catalytically active component on the partition surface of the gas inflow cell. There is disclosed a diesel particulate filter having a configuration formed by forming a silver catalyst layer contained therein.

Patent Document 2 (WO2014 / 189115) discloses a gas outflow cell which is open at the upstream side where the exhaust gas flows, the gas inflow cell whose downstream side is sealed, and the upstream side where the exhaust gas flows, and whose downstream side is open. And a diesel particulate filter provided with a filter base having a configuration provided adjacent to each other through a partition, containing an alloy containing silver and palladium supported on an inorganic porous body, and A diesel comprising an inorganic porous layer having a surface asperity portion having a thickness of 50% or more of the thickness of the inorganic porous layer formed on part or all of the partition wall surface of the gas inflow cell Particulate filters are disclosed.

WO 2014/002772 Publication WO 2014/189115 Publication

As disclosed in Patent Documents 1 and 2, when a catalyst layer containing a catalytically active component containing silver and palladium is formed on the partition wall surface of the gas inflow cell, a noble metal such as Pt is used as the catalytically active component. It has been confirmed that the PM burning rate can be increased compared to the case.

However, if the present inventors form the catalyst layer as described above by significantly increasing the ratio of silver in the catalytically active component containing silver and palladium to further enhance the PM burning rate, thermal runaway is likely to occur. I found that.
Thermal runaway means that during CSF regeneration, that is, during PM combustion, under operating conditions such as low idle, the flow rate of exhaust gas flowing into CSF decreases sharply, and the amount of heat removed from CSF is increased. Since the amount of deposited PM burns at once, the temperature in the CSF becomes high, exceeding the allowable heat resistance limit, and the CSF is broken.

Therefore, the present invention is intended to provide a new particulate filter that can increase the PM burning rate and still suppress the occurrence of thermal runaway.

The present invention relates to a gas inflow cell having an upstream side open in the flow direction of exhaust gas and a closed downstream side in the flow direction of exhaust gas, and a gas outflow cell formed by closing the upstream side and opening the downstream side And a particulate filter comprising a filter substrate provided adjacent to each other via a partition wall,
In the area of the partition wall in the gas inflow cell, in the area from the opening of the gas inflow cell to the blockade side by 75 to 95% of the entire length in the longitudinal direction of the gas inflow cell, We propose a particulate filter in which a silver catalyst layer containing palladium in a ratio of 21: 1 to 98: 1 is formed, and no catalyst layer is formed in the area on the side of the block part.

In the case of using a catalyst containing silver and palladium as described above, which has a high PM burning rate, the inventor of the present invention is likely to excessively increase the temperature of CSF when operating conditions such as low idle during CSF regeneration are reached. We studied the cause, that is, the cause of thermal runaway. As a result, when a catalyst with a high PM burning rate is used, PM combustion heat is accumulated in the block part side in the gas inflow cell, and the accumulated heat quantity is rapidly more than the heat quantity carried away from CSF by the exhaust gas. It was found that the cause is that the temperature on the side of the sealed part of CSF rapidly rises and quickly exceeds the allowable temperature limit.
And as a result of researching also about a raise of PM burning rate, it turned out that PM burning speed rises, so that a catalyst bed is provided from an opening of each gas inflow cell to a blockade side. In addition, PM deposited on the side closer to the sealing portion than the length of 75% to 95% of the entire length in the longitudinal direction of the gas inflow cell is self-ignited because the temperature of the sealing portion side of the gas inflow cell becomes high due to PM combustion heat accumulation Ease of combustion, and it is also understood that the increase in PM burning rate reaches equilibrium even when the catalyst layer is provided on the block side of 75% to 95% of the entire longitudinal length of the gas inflow cell The

Therefore, as the present invention proposes, a silver catalyst layer is formed using a catalytically active component containing silver and palladium in a mass ratio of 21: 1 to 98: 1, while the opening of the gas inflow cell is A silver catalyst layer is formed only on the partition wall surface of the region extending to the sealing portion side by a length of 75 to 95% of the entire length in the longitudinal direction of the gas inflow cell, and no catalyst layer is formed on the partition wall surface on the sealing portion side. The PM burning rate can be increased, and the occurrence of thermal runaway can be suppressed.

It is the perspective view which showed an example of CSF of this invention typically. FIG. 7 is a partially enlarged cross-sectional view schematically showing an example of the CSF of the present invention as well. It is the partial expanded sectional view which showed an example of the silver catalyst layer typically. FIG. 1 is a cross-sectional view schematically showing an example of an exhaust gas purification apparatus using the CSF of the present invention. It is the figure which showed conditions, such as an engine speed, at the time of the DTI test performed by the Example. It is the figure which showed the measurement part of the temperature of CSF at the time of the DTI test similarly conducted in the Example.

Next, a particulate filter (referred to as “the present CSF”) 1 subjected to catalyst processing as one example of a mode for carrying out the present invention will be described.

<This CSF>
The present CSF 1 is a particulate filter having a structure in which a silver catalyst layer 5 containing a catalytically active component containing silver and palladium is formed on the surface of the partition 2 a on the side where the exhaust gas flows in the filter substrate 2. It is.

In the present CSF 1, the exhaust gas can flow through the inside of the partition 2a of the filter substrate 1, and when the exhaust gas flows through the inside of the partition 2a, PM in the gas can be collected on the surface of the partition 2a. The collected PM can be effectively burned by the combustion catalytic action of the catalytically active component in the silver catalyst layer 5.

(Base material)
As shown in FIGS. 1 and 2, the filter base material 2 forming the framework of the present CSF has a honeycomb structure, and has a plurality of cells 3 communicated in the flow direction of the exhaust gas. Separated, the ends of adjacent cells are alternately sealed. That is, the gas inflow cell 3A which opens the upstream side in the flow direction of the exhaust gas and communicates with the flow direction (this communication direction is also referred to as "longitudinal direction") and the downstream side in the flow direction of the exhaust gas is closed The upstream side is closed, and the gas outflow cell 3B communicating with the flow direction, ie, the longitudinal direction and opening the downstream side is disposed adjacent to each other through the partition wall 2a. There is.

The material of the filter substrate 2 may be a porous material made of a ceramic material, a metal material or the like.
The material of the ceramic base material is a refractory ceramic material such as silicon carbide (SiC), cordierite, cordierite-alpha alumina, silicon nitride, zircon mullite, spodumene, alumina-silica magnesia, zirconium silicate, sillimanite, silica Examples include magnesium acid, zircon, petalite, alpha alumina, and aluminosilicates.
Examples of the material of the metal base include refractory metals such as stainless alloys, Fe-Cr-Al alloys, mullite, alumina, aluminum titanate (AT) and the like.
Among these, silicon carbide (SiC) and aluminum titanate (AT) are particularly preferable from the viewpoint of high heat capacity.

The formation density of the cells 3 is not particularly limited, and it is preferable that, for example, 10 to 100 cells are formed per 1 cm ^{2 of the} cross section of the base material.
The thickness of the partition wall 2a is not particularly limited, and is preferably in the range of, for example, 10 μm to 300 μm.

(Silver catalyst layer)
In the present CSF, as shown in FIG. 2, in each of the gas inflow cells 3A of the filter base material 2, the partition wall surface in the area for a predetermined distance from the opening of each gas inflow cell 3A The silver catalyst layer 5 is formed on the partition wall surface on the side facing the inflow cell 3A, and the closed side, that is, the closed side of the region for a predetermined distance from the opening of each gas inflow cell 3A toward the closed side In other words, it is preferable not to form a catalyst layer on the partition wall surface closer to the sealing portion than the silver catalyst layer 5.

The silver catalyst layer 5 extends from the opening of each gas inflow cell 3A to the blockage side by a length of 75 to 95% of the total length in the longitudinal direction of the gas inflow cell 3A among the partition wall surfaces in the gas inflow cell 3A. It is preferable to form in the area.
In each gas inflow cell 3A, the PM burning rate increases as the position where the silver catalyst layer is formed is closer to the blocker side. On the other hand, when the silver catalyst layer is formed on the sealing portion side further than the position of 75% of the entire length in the longitudinal direction of the gas inflow cell 3A from the opening to the sealing portion side, It has been found that as the amount of heat stored increases, the increase in PM burning rate reaches equilibrium, ie does not increase.
Therefore, from the viewpoint of suppressing the amount of heat accumulated and suppressing the occurrence of thermal runaway while increasing the PM burning rate, the silver catalyst layer 5 is provided in each of the gas inflow cells 3A from the opening thereof. It is preferable to form on the partition wall surface in the region leading to the sealed portion side by a length of 75% to 95%, particularly 80% to 95%, and particularly 85% to 95% of the total length in the longitudinal direction.
The total length in the longitudinal direction of the gas inflow cell 3A refers to the distance from the end face (opening) on the opening side of the gas inflow cell 3A to the end face (bottom face) on the closing side. It can be calculated by subtracting the thickness value of the sealed portion of the gas inflow cell 3A from the value of the total length in the longitudinal direction.

The silver catalyst layer 5 does not completely cover the partition wall surface of the gas inflow cell 3A in any region in order not to inhibit the flow of exhaust gas, but the through holes reaching the partition wall surface, ie, the partition wall surface In plan view, it is preferable to provide holes at which the partition wall surface can be seen at an appropriate density so that the average coverage (%) of the silver catalyst layer 5 is less than 100%.
Under the present circumstances, "average coverage (%) of the silver catalyst layer 5" means the ratio (%) that the silver catalyst layer 5 exists per unit area of the partition surface, when the partition surface is viewed in plan. , It can measure by the method shown in the Example.

The through holes may be formed, for example, by including an organic substance in the silver catalyst layer-forming composition, applying the silver catalyst layer-forming composition to a base material, and firing it to eliminate the organic substance. It can also be formed by the gaps between the particles when silver and palladium are supported on the particles of the inorganic porous body, as described later. It can also be formed by other means.

With regard to the average coverage (%) of the silver catalyst layer 5, the denser the silver catalyst layer 5, the higher the PM burning rate, and in particular, the amount of heat stored on the block side of the gas inflow cell. Therefore, the average coverage (%) of the silver catalyst layer 5 is not made uniform, but the average coverage of the silver catalyst layer on the opening side region A in the region where the silver catalyst layer is formed in the gas inflow cell %) Is preferably larger than the average coverage (%) of the silver catalyst layer in the block part side region B.
In the opening side area A, in the area where the silver catalyst layer 5 is formed in the inner peripheral wall of the gas inflow cell 3A, 20 from the opening side end of the silver catalyst layer 5 to the entire length in the longitudinal direction of the gas inflow cell. It refers to the area that reaches the blockade side by the length of%. In addition, in the sealed part side area B, in the area where the silver catalyst layer 5 is formed in the gas inflow cell, the length from the end of the sealed part of the silver catalyst layer 5 to 20% of the entire length in the longitudinal direction of the gas inflow cell It refers to the area leading to the opening side.

From this point of view, in the gas inflow cell, the value of the average coverage (%) of the silver catalyst layer in the opening side region A from the value of the average coverage (%) of the silver catalyst layer The value subtracted is preferably 25% to 65%, more preferably 30% or more or 60% or less, more preferably 35% or more or 55% or less, and still more preferably 40% or more.

In the silver catalyst layer 5, the average coverage (%) of the silver catalyst layer 5 gradually decreases from the opening side end toward the blockage side in the region where the silver catalyst layer 5 is formed in the gas inflow cell. It may be formed as follows. By forming the silver catalyst layer 5 in this manner, it is possible to suppress an increase in the amount of heat accumulated particularly at the end portion side of the sealed portion of the gas inflow cell.

The average coverage of the silver catalyst layer in the opening-side region A is preferably 65% to 95% from the viewpoint of suppressing the amount of heat accumulated and preventing thermal runaway while increasing the PM burning rate. % Or more, preferably 75% or more.

The average coverage of the silver catalyst layer in the block part side region B is preferably 10% to 90% from the viewpoint of suppressing the amount of heat accumulated to prevent thermal runaway while increasing the PM burning rate. % Or more, or 80% or less, preferably 25% or more or 65% or less, more preferably 50% or less.

As described above, in order to adjust the average coverage of the silver catalyst layer 5 in the gas inflow cell, for example, as shown in FIG. 3, through holes reaching the partition wall surface are provided at appropriate locations in plan view of the silver catalyst layer 5. At the same time, the thickness of the catalyst layer 5 is reduced, and the thickness of the silver catalyst layer 5 is reduced by causing the portion where the silver catalyst layer 5 does not exist in plan view in the end portion of the closed portion. Average coverage can be adjusted as described above. However, it is not limited to this method.

Silver in the silver catalyst layer 5 is preferably contained in an amount of 1 g / L or more based on the volume of the base material, and more preferably 1.5 g / L or more or 10 g / L or less, and more preferably 2.0 g / L or more It is more preferable to

The mass ratio of silver to palladium in the catalytic active component containing silver and palladium is preferably 21: 1 to 98: 1.
By containing silver at a mass ratio of 21 times or more with respect to palladium, the catalytic activity effect of silver can be enhanced to further enhance the PM burning rate. On the other hand, by containing silver at a ratio of 98 times or less by mass ratio to palladium, it is possible to reduce the PM combustion rate and to suppress the heat amount generated by the PM combustion.
From this point of view, the mass ratio of silver to palladium is preferably 21: 1 to 98: 1, more preferably 22: 1 or more or 85: 1, and still more preferably 22: 1 or more or 65: 1. .
When the PM burning rate is further increased by increasing the amount of silver to 21: 1 or more in the mass ratio of silver to palladium, the possibility of thermal runaway increases, so the effects of the present invention can be enjoyed. .

The catalytically active component may contain an element other than silver and palladium, as long as the effects of silver and palladium are not impaired. For example, at least one element selected from the group consisting of Pt, Nb, La, Fe, Y, Pr, Ba, Ca, Mg, Sn and Sr, or an oxide thereof may be contained. At this time, from the viewpoint of not preventing the effects of silver and palladium, the content thereof is preferably 1 to 35% by mass.

Moreover, in the silver catalyst layer 5, silver and palladium contained in the catalytically active component may be present separately without being alloyed, or may be present in a partially alloyed state, and they are fully alloyed. It may exist in the state. From the viewpoint of increasing the PM burning rate, silver and palladium contained in the catalytically active component are preferably present in a fully alloyed state.

In the silver catalyst layer 5, the catalytically active component containing silver and palladium is preferably present in a state supported by the inorganic porous material.

Here, as the inorganic porous body, for example, an oxide of one kind of metal selected from the group consisting of silicon, aluminum, titanium, manganese, cerium and zirconium, a complex oxide of two or more kinds of metals, or Mention may be made of porous bodies consisting of a mixture. More specifically, for example, alumina, silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia, alumina-ceria, yttrium manganate compound (YMnO ₃ , YMn ₂ O ₅ ) and lanthanum manganate compound can be mentioned _{(LaMnO 3, LaMn 2 O 5} ) consists of a compound selected from the porous body.

Among them, it is more preferable that the porous body is an oxide of one metal selected from the group consisting of aluminum, cerium and zirconium, a composite oxide of two or more metals, or a mixture thereof.
Among them, the inorganic porous material containing cerium oxide is more preferable, and the inorganic porous material made of cerium-zirconium composite oxide in which the amount of cerium oxide is 5 to 50% by mass is particularly preferable. If the amount of cerium oxide is 50% by mass or less, the specific surface area of the support does not decrease even at high temperature, for example, when heated to a temperature of 700 ° C. or more, and the catalyst is thermally deteriorated. Because it can prevent that.
Further, the inorganic porous body may contain at least one element selected from the group consisting of Nb, Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn and Sr.

The silver catalyst layer 5 may contain other components such as a binder component and a stabilizer component.
Examples of the binder component include at least one binder component selected from the group consisting of SiO ₂ , TiO ₂ , ZrO ₂ and Al ₂ O ₃ .
As a stabilizer, an alkaline earth metal and an alkali metal can be mentioned, for example. Among them, one or more of metals selected from the group consisting of magnesium, barium, thorium, calcium, potassium, sodium, cesium and strontium can be selected.

It is preferable that the thickness of the silver catalyst layer 5 becomes thinner from the opening side toward the closing side in the longitudinal direction of the gas inflow cell 3A.

The average thickness of the silver catalyst layer 5, that is, the average thickness of a plurality of portions in the longitudinal direction of the gas inflow cell 3A and a plurality of portions in the circumferential direction is preferably 0.5 μm to 30 μm.
If the average thickness of the silver catalyst layer 5 is 30 μm or less, the size of the support particles (particles obtained by supporting the catalytically active component on the particles of the inorganic porous material) is not too large, so It is possible not only to secure the contact opportunity of silver and PM to maintain the catalyst performance, but also to adjust the average coverage of the silver catalyst layer 5 as described above. On the other hand, if it is 0.5 μm or more, heat resistance can be maintained.
From this point of view, the average thickness of the silver catalyst layer is preferably 0.5 μm to 30 μm, more preferably 2 μm or more and 25 μm or less, and still more preferably 5 μm or more and 20 μm or less.
In addition, in order to reduce the thickness of the silver catalyst layer 5, it is possible to reduce the particle size of the supported particles instead of simply reducing the coating amount, and to maintain the silver content with respect to the substrate volume. It is preferable to thin the catalyst layer. However, it does not limit to this.

(Precious metal catalyst layer)
In the present CSF, a noble metal catalyst layer containing at least one kind of noble metal selected from the group consisting of Pt, Pd and Rh and / or an oxide of the noble metal is laminated on part or all of the surface of the partition wall of the gas outflow cell 3B. You may do it.
However, the noble metal catalyst layer is preferably provided as necessary, and is not necessarily provided.
From the viewpoint of suppressing an excessive rise in the temperature of CSF when operating conditions such as low idle (low idle) decrease sharply during CSF regeneration, that is, during PM combustion, It is preferable not to provide an oxidation catalyst layer such as a noble metal catalyst layer.

When the noble metal catalyst layer is provided, the noble metal catalyst layer may be provided so as to be embedded from the surface of the partition wall of the gas outflow cell 3B toward the inside, or a part of the noble metal catalyst layer is formed of the gas outflow cell 3B. It may be provided on the surface of the partition wall so as to be partially embedded.
By providing a noble metal catalyst layer on part or all of the partition walls of the gas outflow cell 3B, CO, HC, etc. which are unburned fuel added to raise the exhaust gas temperature can be efficiently obtained by this noble metal catalyst layer. In some cases, it can be oxidized.

As the noble metal in the noble metal catalyst layer, Rh, Pt, Pd, Ir or Au noble metal having higher electronegativity than silver (Ag) is preferably used alone or in combination. In particular, Rh, Pt and Pd are preferable, and it is preferable to use these alone or in combination.

The noble metal in the noble metal catalyst layer is preferably contained in an amount of 0.01 g to 10 g, more preferably 0.1 g or more or 5 g or less, per liter of the volume of the porous substrate. When the catalyst contains a noble metal in such an amount, the exhaust gas can be efficiently purified.

In the noble metal catalyst layer, the noble metal is preferably present in a state of being supported by the inorganic porous body.

Here, as the inorganic porous material, for example, an inorganic porous material selected from the group consisting of silica, alumina and a titania compound, or a porous material comprising an OSC material such as a cerium compound, a zirconium compound, ceria-zirconia composite oxide, etc. The body can be mentioned.
More specifically, there can be mentioned, for example, a porous body comprising a compound selected from alumina, silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia and alumina-ceria.
Among them, an inorganic porous body made of a cerium-zirconium composite oxide in which the amount of cerium oxide is 5 to 50% by mass is particularly preferable. When the amount of cerium oxide exceeds 50% by mass, heating to a temperature of, for example, 700 ° C. or higher at a high temperature tends to reduce the specific surface area of the support and eventually cause the thermal degradation of the catalyst.
Further, the inorganic porous body may contain at least one element selected from the group consisting of Nb, Nd, La, Fe, Y, Pr, Ba, Ca, Mg, Sn and Sr.

The noble metal catalyst layer may contain other components such as a binder component and a stabilizer component.
Examples of the binder component include at least one binder component selected from the group consisting of SiO ₂ , TiO ₂ , ZrO ₂ and Al ₂ O ₃ .
As a stabilizer, an alkaline earth metal and an alkali metal can be mentioned, for example. Among them, one or more of metals selected from the group consisting of magnesium, barium, thorium, calcium and strontium can be selected.

The thickness of the noble metal catalyst layer is preferably 10 μm to 100 μm. When the thickness of the precious metal catalyst layer is too large, the contact efficiency between the catalytically active component in the precious metal catalyst layer and the exhaust gas is reduced, and the decomposition efficiency is lowered. If it is too thin, the heat resistance will be reduced. From this viewpoint, the thickness of the noble metal catalyst layer is more preferably 10 μm or more or 70 μm or less, and still more preferably 20 μm or more or 50 μm or less.

<Manufacturing method>
Next, an example of a method of producing the CSF will be described.

The silver catalyst layer 5 is prepared by adding an organic pore-forming material of a predetermined size together with an inorganic porous powder such as silica or alumina to a silver-palladium solution formed by mixing an aqueous solution of silver nitrate and an aqueous solution of palladium nitrate. And may be applied to a predetermined area of the surface of the partition wall of the gas inflow cell 3A. At this time, the thickness of the entire coating layer (the layer that becomes the silver catalyst layer 5 after firing) is reduced, and the thickness of the coating layer is reduced from the opening side of the gas inflow cell 3A toward the sealing portion. It is preferable to make it thinner than the size of the organic pore-forming material at the end portion on the side of the sealing portion.

In addition, adjustment of the length and thickness of an application layer can be performed by adjusting the viscosity of a slurry. The lower the viscosity of the slurry, the longer and thinner the coating. Adjustment of the viscosity of the slurry can be performed by increasing or decreasing the solid content of the slurry, or adding a thickener. Moreover, in order to reduce the thickness of the coating layer from the inlet side to the outlet side of the gas inflow cell, it may be possible to adjust the viscosity of the slurry in some cases. It can also be performed by forming it separately. At that time, for example, the viscosity and the application amount of the slurry applied in the second time can be different from the viscosity and the application amount of the slurry applied in the first time.

In addition, the filter base material is prepared before the sealing portion of the gas inflow cell is formed, the slurry is injected from the inlet side of the gas inflow cell, and suction is applied from the outlet side to form the coating layer, and then the sealing portion is provided. In this case, the length and thickness of the coating layer can also be adjusted by adjusting the suction force of the slurry. The stronger the suction of the slurry, the longer and thinner the coating. In order to reduce the thickness of the coating layer from the inlet side to the outlet side of the gas inflow cell, for example, it can be performed by gradually increasing the suction force when suctioning the slurry.

After the application as described above, the silver catalyst layer 5 may be formed by drying and firing, for example, at 400 to 700 ° C. in an oxidizing atmosphere such as air or oxygen-enriched air. However, it is not limited to such a method.

The organic pore forming material may be of any nature as long as it scatters and disappears by firing, and carbon, a polymer compound such as a foamed resin, and an organic substance such as starch can be mentioned. However, it is not limited to these.

In addition, regarding formation of the silver catalyst layer 5, it is preferable to keep a slurry from penetrating as much as possible in a base material (inside a partition). When the silver in the slurry penetrates into the base material (within the partition walls) and reacts with, for example, SiC or the like, the silver is deactivated. However, since the base material (partition wall) is porous, permeation of the slurry into the base material is unavoidable.

<This exhaust gas purification device>
Next, an exhaust gas purification device (referred to as “the present exhaust gas purification device”) using the above-described present CSF will be described.

For example, as shown in FIG. 4, the present exhaust gas purification apparatus needs the above CSF1 to be disposed in the gas flow passage 10 through which the exhaust gas discharged from the internal combustion engine flows, and is required on the upstream side of the CSF1. In accordance with the above, it is preferable to arrange the catalyst structure 11 provided with the oxidation catalyst, and further to arrange the fuel injection means 12 on the upstream side thereof.

At this time, the CSF 1 and the catalyst structure 11 may be disposed in the same casing, or the CSF 1 and the catalyst structure 11 may be disposed in different casings, respectively.

(Catalyst structure)
The catalyst structure 11 can be formed, for example, using a porous ceramic base or a metal base.
The porous ceramic substrate can be made of, for example, cordierite, silicon carbide, silicon nitride or the like.

As this base material, it has a form in which a large number of through holes (cells) are formed in the longitudinal direction, and those in which each through hole is partitioned by a partition can be preferably used.

The oxidation catalyst preferably contains at least one noble metal selected from the group consisting of Rh, Pt, Pd, Ir and Au, and / or an oxide of the noble metal. Among them, at least one noble metal selected from the group consisting of Rh, Pt and Pd is preferable, and these can be used alone or in combination.

The oxidation catalyst preferably contains a noble metal as described above in an amount of 0.1 to 10 g, preferably 1 to 5 g, per liter of the volume of the porous substrate. When the catalyst contains a noble metal in such an amount, the fuel injected from the fuel injection means 12 can be oxidized and burned efficiently.

The noble metal contained in the oxidation catalyst is preferably present in a state supported by the inorganic porous material.
Here, as the inorganic porous material, for example, an inorganic porous material selected from the group consisting of silica, alumina and a titania compound, or a porous material comprising an OSC material such as a cerium compound, a zirconium compound, ceria-zirconia composite oxide, etc. The body can be mentioned.

The oxidation catalyst can further contain alumina or alumina composite oxide whose heat resistance is enhanced.

(Fuel injection means)
When PM in exhaust gas is collected and accumulated in the CSF, the pressure loss of the CSF increases and the engine output decreases, so it is necessary to burn the PM deposited in the CSF to regenerate the CSF. .
The catalytically active component contained in the silver catalyst layer of the present CSF does not work effectively at a low temperature of 500 ° C. or less. In normal operation, the temperature of the exhaust gas from the internal combustion engine passing through the present CSF is about 200 to 350 ° C., and at this temperature, PM can not be burned by the catalytically active component.
Therefore, by injecting fuel from the fuel injection means 12 at appropriate timing and burning the fuel by the catalyst structure 11, the catalytically active component effectively acts to burn PM at 550 ° C. or higher, preferably The temperature of the exhaust gas is raised to 600 to 650 ° C., and the PM deposited on this CSF is burned by the catalytic action of silver and palladium.

Examples of the fuel injection means 12 include means for directly spraying the fuel used in the internal combustion engine.

Further, the exhaust gas purification apparatus may further be provided with a NOx reduction catalyst (not shown). By arranging the NOx reduction catalyst, most of the NOx can be processed and exhausted as N ₂ .
As the NOx reduction catalyst used here, a commonly used urea SCR catalyst or NOx storage reduction catalyst can be used.

<Explanation of the phrase>
In the present specification, when expressing as “X to Y” (where X and Y are arbitrary numbers), “preferably more than X” or “preferably Y” with the meaning of “X or more and Y or less” unless otherwise stated. Also includes the meaning of "smaller".
Also, when expressed as “X or more” (X is an arbitrary number) or “Y or less” (Y is an arbitrary number), “greater than X is preferable” or “preferably less than Y” It also includes the intention.

Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples.

Example 1
To 2000 g of pure water, 300 g of CeO ₂ particle powder, an aqueous solution of silver nitrate and an aqueous solution of palladium nitrate were added to impregnate CeO ₂ particles with an aqueous solution of silver nitrate and an aqueous solution of palladium nitrate, and evaporated to dryness at 150 ° C. The resultant was calcined at 600 ° C. for 3 hours in an air atmosphere to obtain an AgPd-containing particulate combustion catalyst powder in which at least a part of Ag and Pd is alloyed. At this time, the mass ratio of Ag to Pd in the catalyst powder was 35: 1.

To 800 g of pure water, 180 g of AgPd-containing particulate combustion powder, 90 g of an organic pore former and 20 g of binder (aluminum oxide) were added and mixed, and wet-pulverized by a ball mill to obtain an AgPd slurry. In this case, the ball mill in this case uses an alumina ball mill (size: 20 nm) as media (ballstone), sets the number ratio of the ball mill to the amount of slurry to 30%, and performs grinding at a rotation speed of 40 rpm for 6 hours. The

A 143.8 mm diameter, 127.0 mm long SiC filter substrate (300 cells / square inch, wall thickness 12 mils) alternately sealed only at the inlet side of the filter substrate (the side to which the exhaust gas flows) A density of 760.8 g / L) was prepared. That is, although the prepared filter substrate is sealed on the inlet side of the filter substrate on the inlet side of the gas outflow cell, the filter substrate on the outlet side (the side where the exhaust gas flows out) The outlet end of the gas inlet cell is not sealed.

The AgPd slurry was injected into the gas inflow cell from the inlet side and sucked from the outlet side of the filter substrate. At this time, the viscosity of the slurry is appropriately adjusted, and the thickness of the coated layer of AgPd slurry is reduced from the inlet side to the outlet side of the gas inflow cell, and the entire length of the gas inflow cell in the longitudinal direction An applied layer of AgPd slurry was provided by 80%. Then, after drying at 70 ° C. for 3 hours, it was fired at 500 ° C. for 1 hour in the air. Then, the sealing part was formed so that the thickness of the sealing part might be 7 mm. Specifically, after filling the plugging slurry into the end on the outlet side of the gas inflow cell, it was dried by a hot air drier, and the end on the outlet side of the gas inflow cell was sealed to form a sealing portion. As a result, a CSF formed by forming a silver catalyst layer containing a catalytically active component containing Ag and Pd on the entire surface of the partition wall from the inlet side of the gas inflow cell to a position of 80% in the length direction was obtained. At this time, the average thickness of the silver catalyst layer was 15 μm.

(Example 2)
In Example 1, CSF was obtained in the same manner as in Example 1 except that the range in which the coating layer of AgPd slurry was provided was changed from 80% to 85% of the total length in the longitudinal direction of the gas inflow cell from the end on the inlet side. At this time, the average thickness of the silver catalyst layer was 13 μm.

(Example 3)
In Example 1, CSF was obtained in the same manner as in Example 1 except that the range in which the coating layer of AgPd slurry was provided was changed from 80% to 91% of the total length in the longitudinal direction of the gas inflow cell from the end on the inlet side. At this time, the average thickness of the silver catalyst layer was 11 μm.

(Example 4)
In Example 1, CSF was obtained in the same manner as in Example 1 except that the range in which the coating layer of AgPd slurry was provided was changed from 80% to 95% of the total length in the longitudinal direction of the gas inflow cell from the end on the inlet side. At this time, the average thickness of the silver catalyst layer was 10 μm.

(Example 5)
A CSF was obtained in the same manner as in Example 2 except that the filter base made of AT (aluminum titanate) was changed to a filter base made of AT (aluminum titanate) in Example 2. At this time, the average thickness of the silver catalyst layer was 15 μm.

(Example 6)
A CSF was obtained in the same manner as in Example 2 except that the following AgPd-containing particulate combustion catalyst powder was used in place of the AgPd-containing particulate combustion catalyst powder in Example 2. At this time, the average thickness of the silver catalyst layer was 40 μm.

AgPd-containing particulate combustion catalyst powder
To 2000 g of pure water, 300 g of Al ₂ O ₃ particle powder, an aqueous solution of silver nitrate and an aqueous solution of palladium nitrate were added to impregnate Al ₂ O ₃ particles with an aqueous solution of silver nitrate and an aqueous solution of palladium nitrate, and evaporated to dryness at 150 ° C. The resultant was calcined at 600 ° C. for 3 hours in an air atmosphere to obtain an AgPd-containing particulate combustion catalyst powder. At this time, the mass ratio of Ag to Pd in the catalyst powder was 35: 1.

(Example 7)
In Example 2, instead of the AgPd-containing particulate combustion catalyst powder in which the mass ratio of Ag to Pd is 35: 1, the AgPd-containing particulate combustion catalyst powder in which the mass ratio of Ag to Pd is 25: 1 is used. CSF was obtained in the same manner as Example 2 except for the above. At this time, the average thickness of the silver catalyst layer was 13 μm.

(Example 8)
In Example 2, instead of the AgPd-containing particulate combustion catalyst powder having a mass ratio of Ag to Pd of 35: 1, the AgPd-containing particulate combustion catalyst powder having a mass ratio of Ag to Pd of 50: 1 was used. CSF was obtained in the same manner as Example 2 except for the above. At this time, the average thickness of the silver catalyst layer was 13 μm.

(Comparative example 1)
In Example 1, CSF was prepared in the same manner as in Example 1, except that the platinum-containing catalyst layer was formed instead of the silver catalyst layer using the following Pt-containing particulate combustion catalyst powder instead of the AgPd-containing particulate combustion catalyst powder. Obtained. At this time, the average thickness of the platinum-containing catalyst layer was 35 μm.

~ Pt-containing particulate combustion catalyst powder ~
To 2000 g of pure water, 300 g of Al ₂ O ₃ particle powder and an aqueous dinitrodiamine platinum solution were added to impregnate the Al ₂ O ₃ particles with the aqueous dinitrodiamine platinum aqueous solution and evaporated to dryness at 150 ° C. The resultant was calcined at 600 ° C. for 3 hours in an air atmosphere to obtain a platinum-containing particulate combustion catalyst powder.

(Comparative example 2)
In Example 1, CSF was obtained in the same manner as in Example 1 except that the range in which the coating layer of AgPd slurry was provided was changed from 80% to 50% of the total length in the longitudinal direction of the gas inflow cell from the end on the inlet side. At this time, the average thickness of the silver catalyst layer was 24 μm.

(Comparative example 3)
In Example 1, CSF was obtained in the same manner as in Example 1 except that the range in which the coating layer of AgPd slurry was provided was changed from 80% to 70% of the total length in the longitudinal direction of the gas inflow cell from the end on the inlet side. At this time, the average thickness of the silver catalyst layer was 17 μm.

(Comparative example 4)
In Example 1, CSF was obtained in the same manner as in Example 1 except that the range in which the coating layer of AgPd slurry was provided was changed from 80% to 100% of the total length in the longitudinal direction of the gas inflow cell from the end on the inlet side. At this time, the average thickness of the silver catalyst layer was 10 μm.

(Comparative example 5)
A CSF was obtained in the same manner as in Example 2 except that the following AgPd-containing particulate combustion catalyst powder was used in place of the AgPd-containing particulate combustion catalyst powder in Example 2. At this time, the average thickness of the silver catalyst layer was 45 μm.

AgPd-containing particulate combustion catalyst powder
To 2000 g of pure water, 300 g of Al ₂ O ₃ particle powder, an aqueous solution of silver nitrate and an aqueous solution of palladium nitrate were added to impregnate Al ₂ O ₃ particles with an aqueous solution of silver nitrate and an aqueous solution of palladium nitrate, and evaporated to dryness at 150 ° C. The resultant was calcined at 600 ° C. for 3 hours in an air atmosphere to obtain an AgPd-containing particulate combustion catalyst powder. At this time, the mass ratio of Ag to Pd in the catalyst powder was 4: 1.

<Average coverage of silver catalyst layer>
The average coverage of the silver catalyst layer of CSF obtained in Examples and Comparative Examples was measured as follows. In addition, regarding the comparative example 1, the average coverage was similarly measured by making a platinum containing catalyst layer into object instead of the said silver catalyst layer.
CSF was cut in half along the longitudinal direction. The silver catalyst layer provided in the gas inflow cell is divided into an opening side area A, a sealing part side area B, and other areas, and then each is divided by a microscope (VHX-5000 manufactured by Keyence Corporation) at a magnification of 300 times. I photographed the area. The image taken with the image processing software attached to the microscope, according to the brightness (brightness, color) of the object, the silver catalyst layer and the filter substrate (including the voids present in the substrate) Binarized. Binarization was performed under the following conditions in the automatic area measurement mode of the image processing software.

“Extraction mode”: brightness “measurement area”: standard “extraction area”: bright area (in this embodiment, the silver catalyst layer is brighter than the filter substrate)
"Fill in hole": OFF
"Small particle removal function": OFF
“Threshold”: In each Example and Comparative Example, a sample in which the area of the silver catalyst layer and the area of the filter substrate are known in advance is prepared, and binarization is performed to obtain a sample of each Example and Comparative Example. The threshold was determined. The threshold value of each example and comparative example was "-20".

From the binarized image, the coverage (%) of the silver catalyst layer in each region was calculated by the following equation. The coverage of each region was similarly calculated for the other four gas inflow cells. The average value of the five calculated coverage values was taken as the average coverage (%) of each area.
(Formula) Cover ratio (%) = area occupied by silver catalyst layer / area of entire image The average cover ratio (%) of each obtained region is shown in Table 1 below.

In order to obtain the average coverage of the silver catalyst layer, the opening side end and the closing side end of the silver catalyst layer, and the opening side area A and the closing side area B were determined as follows.
First, CSF was cut in half along the longitudinal direction. The gas inflow cell was divided into 100 regions uniformly from the opening side end to the closing side end along the longitudinal direction. The coverage (%) of the silver catalyst layer was determined as described above for the obtained 100 regions.
Next, among the boundaries between the region where the coverage (%) of the silver catalyst layer is 10% or more and the region where the coverage is less than 10%, the opening side is closed with the opening side end of the silver catalyst layer and the boundary The part side was an end of the silver catalyst layer on the side of the sealing part. In other words, the portion where the coverage of the silver catalyst layer was 10% or more was defined as the region where the silver catalyst layer was formed. In the examples and comparative examples, the opening side end of the silver catalyst layer is the same as the opening side end of the gas inflow cell.
The “opening side region A” is 20% of the entire length in the longitudinal direction of the gas inflow cell from the opening side end of the silver catalyst layer in the region where the silver catalyst layer is formed in the inner peripheral wall of the gas inflow cell. The "sealing portion side region B" is the entire length in the longitudinal direction of the gas inflow cell from the sealing portion side end portion of the silver catalyst layer in the region where the silver catalyst layer is formed. The area extending to the opening side by a length of 20% of the above is defined as the area other than the area between the “opening side area A” and the “closing side area B”.

<PM burning rate>
The PM burning rate of CSF obtained in Examples and Comparative Examples was measured as follows.
The CSF obtained in Examples and Comparative Examples was subjected to durability treatment at 700 ° C. for 10 hours in an electric furnace. The CSF after durability treatment was placed in the DPF test system (DPG manufactured by Cambustion). 8 g / L of PM was collected by the CSF placed. PM was burned by flowing a gas having a gas temperature of 600 ° C. and an oxygen concentration of 5.5 vol% in the vicinity of the CSF inlet into the CSF for 10 minutes. The mass change amount of CSF before and after PM combustion was measured, and the PM combustion rate (g / min) was calculated from this value.

The obtained PM burning rate (g / min) and the evaluation results thereof are shown in Table 1 below. The evaluation criteria in Table 1 are as follows.
= Evaluation criteria =
○ (good): PM burning rate is 1.4 g / min or more × (poor): PM burning rate is less than 1.4 g / min

<Maximum temperature during DTI (Drop To Idle) test>
The maximum temperature at the DTI test of CSF obtained in Examples and Comparative Examples was measured as follows.
The CSF obtained in Examples and Comparative Examples was subjected to durability treatment at 700 ° C. for 10 hours in an electric furnace. After DOC (Diesel Oxidation Catalyst) was placed in the exhaust pipe of the engine bench, CSF after durability treatment was placed downstream of the DOC (Diesel Oxidation Catalyst). The engine used a 2.0 L common rail turbo engine. Next, 10 g / L of PM was allowed to be collected by CSF placed. Next, the temperature in the vicinity of the CSF inlet was raised to 600 ° C., and when PM combustion started, the engine speed was reduced to the idling state. The conditions such as the number of revolutions of the engine are shown in FIG. 5, and the measurement site of the CSF temperature is shown in FIG.
The timing for dropping the engine speed to the idling state was optimized for each sample to be measured so that the maximum temperature of CSF to be measured becomes the highest.

The maximum temperatures (° C.) during the obtained DTI test and the evaluation results thereof are shown in Table 1 below. The evaluation criteria in Table 1 are as follows.
= Evaluation criteria =
((Very good): 1000 ° C. or less ○ (good): 1000 ° C. or more and 1050 ° C. or less × (poor): 1050 ° C. or more

<Discussion>
According to the above examples and the test results that the inventor has conducted, according to the catalyst active component containing silver and palladium in a weight ratio of 21: 1 to 98: 1, a silver catalyst layer is formed while A silver catalyst layer is formed only on the partition wall surface in a region extending from the opening of the cell to 75 to 95% of the entire length in the longitudinal direction of the gas inflow cell, and the partition wall surface on the block side It has been found that by not forming a catalyst layer, it is possible to increase the PM burning rate, yet to prevent the thermal runaway of CSF.

Furthermore, the average coverage (%) of the silver catalyst layer is formed so as to decrease from the opening side end toward the closing side, and in this case, the average coverage (%) of the opening side region A It is found that the temperature rise on the side of the sealing portion can be further suppressed by making the average coverage (%) of the silver catalyst layer of the sealing portion side region B smaller, and thermal runaway can be prevented more reliably. The

Claims (5)

A gas inflow cell which is open at the upstream side in the flow direction of exhaust gas and closed at the downstream side in the flow direction of exhaust gas, and a gas outflow cell formed by closing the upstream side and opening the downstream side A particulate filter provided with an adjacent filter base via
In the area of the partition wall in the gas inflow cell, in the area from the opening of the gas inflow cell to the blockade side by 75 to 95% of the entire length in the longitudinal direction of the gas inflow cell, A particulate filter in which a silver catalyst layer containing palladium in a ratio of 21: 1 to 98: 1 is formed, and a catalyst layer is not formed in a region on the closed side thereof. In the area where the silver catalyst layer is formed in the gas inflow cell, the opening side area extending from the opening side end of the silver catalyst layer by 20% of the entire length of the gas inflow cell in the longitudinal direction The average coverage (%) of the silver catalyst layer of A is from the end of the sealed side of the silver catalyst layer to 20% of the length in the longitudinal direction of the gas inflow cell in the closed side B The particulate filter according to claim 1, which is larger than the average coverage (%) of the silver catalyst layer. The particulate filter according to claim 2, wherein the average coverage (%) of the silver catalyst layer on the opening side region A is 65 to 95%. A value obtained by subtracting the value of the average coverage (%) of the sealed part side region B from the value of the average coverage (%) of the silver catalyst layer of the opening side region A is 25 to 65%. Or the particulate filter according to 3. The particulate filter according to any one of claims 1 to 4, wherein the catalytically active component is contained in the silver catalyst layer in a state of being supported by the inorganic porous material.

Images