JP2010156206A - Exhaust gas purifying filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying filter providing high collecting efficiency of particulate matter and having a low pressure loss, even if the deposition amount of particulate matter in exhaust gas is small. <P>SOLUTION: This exhaust gas purifying filter includes a filter base body 11. In the filter base body, an inflow cell 12A with an inflow-side end opened is formed in the inflow side of exhaust gas containing particulate matter of a porous body, an outflow cell 12B with an outflow-side end opened is formed in the exhaust gas outflow side of the porous body, and a partition plate 14 is provided for purifying exhaust gas through the inflow cell 12A and outflow cell 12B. The average pore diameter of the partition plate 14 is set to 5 μm to 50 μm. A porous film 13 having an average pore diameter of 0.05 μm to 5 μm and containing oxides containing cerium is provided on the inner wall surface of the inflow cell 12A. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification filter suitable for use in removing particulate matter from exhaust gas discharged from automobile diesel engines and the like, and more specifically, a porous support made of ceramics constituting the exhaust gas purification filter. The present invention relates to an exhaust gas purification filter having a porous film containing an oxide having oxidation catalyst characteristics on the surface.

Various substances contained in exhaust gas discharged from automobile diesel engines cause air pollution and have caused various environmental problems so far. In particular, particulate matter (PM) contained in exhaust gas is also said to cause allergic diseases such as asthma and hay fever.
In general, in a diesel engine for automobiles, a DPF (Diesel Particulate Filter) having a ceramic-made plug-type honeycomb structure is used as an exhaust gas purification filter for collecting particulate matter (for example, Patent Document 1). 2).
This plug-type honeycomb structure is a ceramic honeycomb structure in which both ends of a cell (gas flow path) are plugged in a checkered pattern, and is taken into the cell from one end face of the honeycomb structure. When the exhaust gas containing particulate matter passes through the pores in the partition walls between the cells, the particulate matter is collected and becomes purified gas, and this purified gas is discharged from the other end face of the honeycomb structure.

  In this DPF, it is particularly required to improve the collection characteristics of particulate matter having a submicron diameter. However, in the conventional DPF, since the average pore diameter of the partition wall is about 5 to 50 μm, the particles in the partition wall The collection efficiency (weight basis of particulate matter) in the DPF in the state where particulate matter is not deposited does not reach 90%, and as particulate matter accumulates on the exhaust gas inflow surface of the partition wall, the exhaust gas of this partition wall The particulate matter layer is formed on the inflow surface, and the new particulate matter is collected in the particulate matter layer, thereby improving the collection efficiency in the DPF and approaching 100%. As described above, in the conventional DPF, although the collection efficiency after the formation of the particulate matter layer is high, the collection efficiency in a state where the amount of the particulate matter accumulation is small is not necessarily satisfactory. It is known (Non-Patent Document 1).

Here, it is known that it is effective to reduce the pore diameter of the partition walls in the DPF in order to increase the collection efficiency in a state where the amount of particulate matter deposited is small. However, if the pore diameter is reduced, the gas permeability in the DPF is lowered and the pressure loss is increased, so that a sufficient exhaust gas flow rate cannot be obtained.
As described above, in the conventional technology, it is impossible to achieve both high collection efficiency and low pressure loss in a state where the amount of particulate matter deposited is small, and a material that satisfies both of these performances is required.

Further, since particulate matter is always discharged from the engine when the automobile is running, the particulate matter is gradually accumulated in the cells of the DPF honeycomb structure. If this accumulation progresses and the amount of accumulated particulate matter becomes excessive, a so-called “clogging” state occurs and pressure loss in the DPF increases, so this particulate matter is periodically removed by some method. Therefore, it is necessary to reduce the pressure loss of the DPF.
Therefore, conventionally, when a predetermined amount of particulate matter has accumulated, an operation called regeneration is performed to raise the exhaust gas temperature and burn the particulate matter, thereby reducing the pressure loss of the DPF.

  However, in this regeneration method, it is necessary to inject fuel into the exhaust gas upstream of the DPF in order to raise the temperature of the exhaust gas, but the fuel used for regeneration does not contribute to the running of the automobile at all. Therefore, in order to effectively use the energy of the fuel and improve the fuel consumption rate, a so-called exhaust gas purification filter having a high regeneration efficiency, in which the time required for the regeneration is short and the fuel used during the regeneration is small, has been demanded. .

As a method for improving the regeneration efficiency in the DPF, a method for promoting oxidation of particulate matter by supporting an oxide catalyst such as platinum or silver noble metal fine particles or oxide fine particles such as cerium oxide on the partition walls of the DPF. Has been proposed (for example, Patent Documents 3 and 4). In this method, by supporting the oxidation catalyst, the temperature required for the DPF regeneration can be lowered, or the high temperature holding time for the regeneration can be shortened, so that the thermal deterioration of the DPF itself can also be reduced.
As a method of supporting these oxidation catalysts on the partition walls of the DPF, a method of impregnating the honeycomb structure itself of the DPF in a slurry containing the oxidation catalyst particles and attaching the oxidation catalyst particles to the partition walls of the DPF (for example, Patent Document 3). 4) After impregnating the DPF honeycomb structure in the solution containing the oxidation catalyst metal compound, the components attached to the partition walls of the DPF are reduced to form metal particles, and the oxidation catalyst particles are attached to the partition walls of the DPF. A method (for example, Patent Document 4) is proposed.

Next, as a filter having a low pressure loss during use and a high particulate collection efficiency, the pore diameter is smaller than the pore diameter of the porous support on the surface of the porous support having a large pore diameter. A filter provided with a thin porous membrane is known.
As such a filter, a ceramic filter in which a porous film is formed on the surface of a support made of porous ceramics is known.
In this ceramic filter, the porous membrane is formed by forming a laminated body made of ceramic particles having a small particle diameter on the surface of a support made of porous ceramics and heat-treating the laminated body. As a method for controlling the pore size of the porous film according to the size of the particles to be collected, a method of adjusting the particle size of the ceramic particles constituting the laminate is used.

By the way, when a porous film having a pore size smaller and thinner than that of the porous ceramic is formed on the surface of the support made of the porous ceramic, the particle diameter of the ceramic particles constituting the porous film is made porous. It was necessary to make it smaller than the pore diameter of the ceramic. For this reason, when forming a porous film, there existed a possibility that the ceramic particle which comprises this porous film might penetrate | invade in the pore of porous ceramics.
Therefore, various methods for solving such problems have been proposed.

For example, there is a method for hydrophobizing a porous support made of ceramics and using an aqueous slurry containing ceramic particles having a small particle diameter so that the aqueous slurry does not enter the pores of the porous support. It has been proposed (for example, Patent Document 5). In this method, in order to adhere the aqueous slurry to the surface of the porous support, a substance that removes the hydrophobic treatment agent or reduces its function is added to the aqueous slurry.
In addition, there is a method in which ceramic particles having a small particle size are made secondary particles having a size equal to or larger than the pore size of the porous support in advance, and a porous film is formed using a slurry containing the secondary particles. As a method for producing secondary particles, a method of pre-calcining ceramic particles (for example, Patent Document 6) or a method of adding a flocculant to a slurry to aggregate ceramic particles (for example, Patent Document 7) has been proposed. Has been proposed.

Furthermore, a method has been proposed in which the pores of the porous support are filled with a removable substance, the pores are closed, and then a slurry containing ceramic particles having a small particle diameter is applied to the surface of the porous support. As a method for closing the pores, a flammable substance is used as a removable substance, and the flammable substance is burned and removed in a subsequent firing step (for example, Patent Document 8). Water or alcohol is used as the removable substance. A method of removing these water and alcohol by drying after application (for example, Patent Documents 9 and 10) has been proposed.
Japanese Patent Laid-Open No. 5-23512 JP-A-9-77573 JP 2005-7259 A JP 2001-73748 A JP 2000-218114 A JP-A-11-33322 JP-A-11-188217 JP-A-1-274815 Japanese Patent Publication No. 63-66566 JP 2000-288324 A SAE Technical Paper 980545 American Society of Automotive Engineers Published in 1998 (SAE Technical Paper 980545, Society of Automotive Engineers (1998))

As described above, in the conventional DPF, since the average pore diameter of the partition wall is on the order of 5 to 50 μm and a micron diameter, the particulate matter having a sub-micron diameter smaller than the average pore diameter is collected. There was a problem that was not easy.
In order to improve the collection characteristics of particulate matter having a submicron diameter, it is one method to reduce the average pore diameter of the partition walls in the DPF. However, if the average pore diameter of the partition walls is reduced, the submicron diameter Although the trapping property of the particulate matter is improved, the air permeability as the DPF is reduced and the pressure loss is increased, so that there is a problem that a sufficient exhaust gas flow rate cannot be obtained. That is, the conventional DPF does not achieve both high collection efficiency and low pressure loss (sufficient exhaust gas flow rate) particularly in a state where the amount of particulate matter deposited is small, and a material that satisfies both of these performances is required. It was.
Therefore, it is considered that the average pore diameter of the partition walls in the DPF remains 5 to 50 μm, and a porous film having an average pore diameter of several tens nm to 5 μm is formed on the surface of the partition walls. When forming this porous film, it is conceivable to apply the above-described conventional technique.

However, the DPF having such a porous membrane also has the following problems.
For example, in order to form a porous film having an average pore diameter of 100 nm, the primary particle diameter of the particles constituting the porous film needs to be about 40 to 60 nm. This particle diameter is the average pore diameter of the DPF. The size is about a few hundredths. As described above, the primary particle diameter of the particles constituting the porous film is very small compared to the particle diameter of the porous film in the above-described prior art on the order of submicron to micron.
Therefore, even when the conventional technique is applied as it is when forming the porous film on the partition walls of the DPF, it is difficult to avoid a part of the particles constituting the porous film from flowing into the pores of the partition walls.

Further, in the honeycomb structure which is the main part of the DPF, each cell has, for example, an elongated cylindrical shape with a cross section of 1 mm square and a length of 150 mm sealed at one end, and these cells are adjacent to each other. Whereas the sealing end portions are alternately provided so that the positions of the sealing end portions of the cells are opposite to each other, they are stacked in a special shape of a honeycomb shape, whereas the partition walls in the above-described prior art are A plate shape or a cylindrical shape with a diameter of the order of centimeters. Therefore, when forming the porous film on the partition walls of the honeycomb structure, which is the main part of the DPF, even if the above prior art is applied, the application is difficult because the shape is significantly different. Moreover, even if the conventional technique is applicable, the process becomes complicated, and it is necessary to devise materials to be used, which may increase the manufacturing cost.
As described above, the technology for forming a porous film on the surface of the partition walls of the honeycomb structure, which is the main part of the DPF, has not yet been established.

In addition, when the oxidation catalyst particles are supported on the partition walls of the DPF, the oxidation catalyst particles enter not only the surface of the partition walls but also the pores of the partition walls in the conventional method, so that the oxidation catalyst particles exist throughout the partition walls. It will be. On the other hand, when the particulate matter in the exhaust gas is collected using this DPF, the particulate matter is layered on the surface of the partition wall of the DPF, and does not penetrate so much into the pores. In particular, this tendency becomes stronger after particulate matter is deposited to some extent (see Non-Patent Document 1).
Thus, since the particulate matter is localized on the surface of the DPF partition wall on the exhaust gas inflow side, the oxidation catalyst particles present in the pores do not come into contact with the particulate matter. It will contribute little and will be useless. Therefore, if the oxidation catalyst particles can be selectively supported on the surface of the partition wall, the catalytic effect of the supported oxidation catalyst particles can be effectively utilized, but such a method has not yet been proposed. .

The present invention has been made to solve the above-described problem, and even when the amount of particulate matter accumulated in the exhaust gas is small, high collection efficiency of particulate matter can be obtained, and pressure loss can be achieved. An object of the present invention is to provide an exhaust gas purification filter having a low level.
Furthermore, by improving the method for supporting the oxidation catalyst in the partition walls, the combustion time of the particulate matter that accumulates on the surface of the partition walls during the regeneration process is shortened, and the use of fuel necessary for raising the exhaust gas temperature during the regeneration process is reduced. Then, it aims at providing the exhaust gas purification filter which can aim at the fall prevention of deterioration of a fuel consumption rate, a filter function, and an oxidation catalyst.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention include an oxide containing cerium in the partition walls of the honeycomb structure constituting the exhaust gas purification filter and have a predetermined average pore diameter. By providing a porous membrane, high trapping efficiency can be obtained even when the amount of particulate matter deposited is small, and at the same time, an increase in pressure loss can be suppressed. As a result, it was found that the combustion time of the particulate matter deposited on the partition walls can be shortened, and the present invention has been completed.

  That is, the exhaust gas purification filter of the present invention includes a filter base made of a porous body, an inflow side gas flow path provided on the inflow side of the exhaust gas containing particulate matter of the filter base and having an inflow side end opened. An exhaust gas passage provided on the exhaust gas outlet side of the filter base, the outlet end of which is opened, and the exhaust gas provided between the inlet gas channel and the outlet gas channel. An exhaust gas purifying filter including a partition wall to be purified by passing, wherein the partition wall has an average pore diameter of 5 μm or more and 50 μm or less, and an average pore diameter of at least 0 on the inner wall surface of the inflow side gas flow path. 0.05 μm or more and 5 μm or less, and a porous film containing an oxide containing cerium is provided.

The oxide containing cerium is cerium oxide alone, or a complex oxide of cerium with one or more elements selected from the group of zirconium, yttrium, and rare earth elements, or zirconium, yttrium, and rare earth elements. It is preferably a mixture of a complex oxide of cerium with one or more elements selected from the group of elements and cerium oxide alone.
The average porosity of the porous membrane is preferably 35% or more and 90% or less.

The average film thickness of the porous film is preferably 40 μm or less.
The porous film is preferably formed by applying a solution containing oxide fine particles to the filter substrate to form a coating film, and then heat-treating the coating film.

  According to the exhaust gas purification filter of the present invention, the average pore diameter of the partition wall between the inflow side gas flow path and the outflow side gas flow path is 5 μm or more and 50 μm or less, and at least on the inner wall surface of the inflow side gas flow path, The average pore size is 0.05 μm or more and 5 μm or less, and a porous film containing an oxide containing cerium is provided, so that the trapping ability of particulate matter can be improved and the pressure loss is reduced. Can do.

  Further, at least the porous film provided on the inner wall surface of the inflow side gas flow path contains an oxide containing cerium as an oxidation catalyst, so that the combustion of particulate matter deposited on the partition wall during the regeneration treatment of the exhaust gas purification filter By shortening the time and reducing the use of fuel necessary for the exhaust gas temperature rise in the regeneration process, it is possible to reduce the fuel consumption rate, and further suppress the deterioration of the exhaust gas purification filter itself and the oxidation catalyst. it can.

  In addition, by providing a porous film containing an oxide containing cerium as an oxidation catalyst, the method for supporting the oxide containing cerium can be improved, and the catalytic effect of the supported oxidation catalyst can be effectively utilized. it can. Therefore, the combustion time of the particulate matter during the regeneration process of the exhaust gas purification filter can be further shortened, the amount of fuel used for raising the exhaust gas temperature for the regeneration process can be further reduced, and the exhaust gas purification filter itself It is possible to further suppress deterioration and deterioration of the oxidation catalyst.

  The best mode for carrying out the exhaust gas purification filter of the present invention will be described. This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

FIG. 1 is a partially broken perspective view showing an exhaust gas purification filter according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a partition wall structure of the exhaust gas purification filter. FIG.
Here, a DPF that is an exhaust gas purification filter used in an automobile diesel engine will be described as an example of the exhaust gas purification filter.

  The DPF 10 includes a filter base 11 made of a cylindrical porous ceramic having a large number of pores (pores), a gas flow path 12 formed in the filter base 11, and an inflow of exhaust gas in the gas flow path 12. And a porous membrane 13 provided on the inner wall surface 12a of the inflow cell (inflow side gas flow path) 12A whose side end is opened.

The filter base 11 is a honeycomb structure made of heat-resistant porous ceramics such as silicon carbide, cordierite, aluminum titanate, and silicon nitride, and made of porous ceramics along the axial direction that is the flow direction of the exhaust gas G. A honeycomb structure is formed by the partition walls 14, and a hollow area in the axial direction surrounded by the partition walls 14 forms a large number of cellular gas flow paths 12.
One end surface α of both end surfaces in the axial direction of the filter base 11 is an inflow surface into which the exhaust gas G containing particulate matter flows, and the other end surface γ has removed the particulate matter from the exhaust gas G. The discharge surface is for discharging the purified gas C.

The average pore diameter of the partition wall 14 is preferably 5 μm or more and 50 μm or less.
If the average pore diameter is less than 5 μm, pressure loss due to the partition wall 14 itself is increased, which is not preferable. On the other hand, if the average pore diameter exceeds 50 μm, the partition wall 14 has insufficient strength or is porous on the partition wall 14. It is not preferable because it is difficult to form the film 13.

  The gas flow path 12 has a structure in which the inflow side end and the outflow side end are alternately closed when viewed from the flow direction (longitudinal direction) of the exhaust gas G, that is, the inflow side that is the inflow side of the exhaust gas G. An inflow cell (inflow side gas flow path) 12A having an open end and an outflow cell (outflow side gas flow path) 12B in which an outflow side end, which is a side for discharging the purified gas C, is opened. Yes.

The porous film 13 does not substantially enter the pores of the porous ceramics constituting the partition wall 14 of the filter base 11, and is formed on the inner wall surface (surface of the partition wall 14 on the inflow cell 12 </ b> A side) 12 a of the inflow cell 12 </ b> A. It is an independent film. That is, the oxide fine particles forming the porous film 13 are formed on the inner wall surface 12a of the inflow cell 12A in a state in which intrusion into the partition wall 14 is suppressed, and the pores formed in the partition wall 14 are blocked. Absent.
Since the porous membrane 13 has a large number of pores, the pores communicate with each other. As a result, the porous membrane 13 has a filter-like porous shape having through holes.

  The porous film 13 may be provided not only on the inner wall surface of the inflow cell 12A, but also on the inner wall surface of the outflow cell 12B (surface on the outflow cell 12B side of the partition wall 14). However, in the following description, it demonstrates as what was provided in the inner wall face of 12 A of inflow cells.

Here, the flow of the exhaust gas in the DPF 10 is shown in FIG.
The exhaust gas G containing particulate matter (PM) 30 flowing in from the inlet side, that is, the end surface α side, passes through the partition wall 14 of the filter base 11 in the process of flowing through the inflow cell 12A from the end surface α side to the end surface γ side. To do. At this time, the particulate matter 30 contained in the exhaust gas G is collected and removed by the porous film 13 formed on the partition wall 14, particularly the inner wall surface 12 a on the inlet cell 12 A side of the partition wall 14. The removed purified gas C flows from the end surface α side to the end surface γ side through the outflow cell 12B, and is finally discharged from the discharge port side, that is, the end surface γ side.

Next, the porous membrane 13 will be described in detail.
This porous film 13 is a film containing an oxide containing cerium as a component, and its average pore diameter is preferably 0.05 μm or more and 5 μm or less, more preferably 0.05 μm or more and 3 μm or less, More preferably, it is 0.1 μm or more and 2 μm or less. This average pore diameter is smaller than the pore diameter of the partition wall 14, that is, about 5 to 50 μm, which is the average pore diameter of the conventional DPF. Thereby, the particulate matter 30 hardly collects into the partition wall 14 and is collected by the porous film 13 from the stage where the amount of deposition is small, and high collection efficiency can be obtained.

  Here, the reason why the average pore diameter of the porous membrane 13 is set to 0.05 μm or more and 5 μm or less is that the average pore diameter is less than 0.05 μm because the pressure loss generated by the porous membrane 13 is not preferable. On the other hand, when the average pore diameter exceeds 5 μm, there is no substantial difference between the pore diameters of the porous membrane 13 and the partition wall 14, and the trapping rate of the particulate matter 30 is reduced. When the amount of accumulated particulate matter is small, it is difficult to obtain high collection efficiency, and it is not preferable because the combustion efficiency of particulate matter is not improved when the DPF 10 is regenerated.

The average porosity of the porous membrane 13 is preferably 35% or more and 90% or less, more preferably 50% or more and 90% or less, and further preferably 60% or more and 90% or less.
Here, the reason why the average porosity is in the range of 35% or more and 90% or less is that when the average porosity is less than 35%, the pressure loss generated by the porous membrane 13 becomes large, while the average porosity is This is because if the rate exceeds 90%, the strength of the porous film 13 may be reduced.

The average film thickness of the porous film 13 is preferably 40 μm or less.
This is because if the average film thickness of the porous film 13 exceeds 40 μm, the pressure loss generated by the porous film 13 increases. The porous film 13 can collect the particulate matter 30 and substantially does not enter the partition wall 14 as long as this condition is satisfied. There is no particular limitation.

The cerium-containing oxide constituting the porous film 13 is preferably fine particles having an average primary particle diameter of 5 nm or more and 300 nm or less.
The pore size of the porous membrane 13 can be controlled by the primary or secondary particle size of the particles forming the porous membrane, but if the average primary particle size of the fine particles is less than 5 nm, the average pore size of the porous membrane is reduced. The pore size becomes too small, and it is difficult to keep the average pore size at 0.05 μm or more, which is not preferable. Further, the production of fine particles having an average primary particle diameter of less than 5 nm is expensive and is not preferable from the viewpoint of productivity.
On the other hand, when the average primary particle diameter exceeds 300 nm, the stability of the coating solution used for obtaining the porous film 13 is lowered, and therefore it is difficult to obtain a coating solution with good stability. Absent.

  Examples of the oxide containing cerium include cerium oxide alone, zirconium, yttrium, rare earth elements (La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. ) Or a composite oxide of cerium with one or more elements selected from the group of), or a composite of cerium with one or more elements selected from the group of zirconium, yttrium and rare earth elements A mixture of an oxide and a simple substance of cerium oxide is preferably used.

  According to the exhaust gas purification filter of the present embodiment, the porous film 13 is provided on the inner wall surface 12a of the inflow cell 12A formed in the filter base 11, and the average pore diameter of the porous film 13 is 0.05 μm or more and 5 μm or less. Therefore, since the average pore diameter of the porous film 13 is smaller than the average pore diameter of the partition wall 14, the particulate matter 30 is trapped on the surface of the porous film 13 from the stage where the amount of deposition is small. Therefore, high collection efficiency can be obtained from the stage where the amount of particulate matter 30 deposited is small.

  Moreover, the average film thickness of this porous film 13 is 40 micrometers or less, and is thinner than 200-400 micrometers which is the general thickness of a filter base | substrate. Moreover, since the average porosity of the porous film 13 is 35% or more and 90% or less, it has many pores.

Accordingly, even if the porous film 13 having an average pore diameter smaller than the average pore diameter of the partition wall 14 of the filter base 11 is formed on the partition wall 14, an increase in pressure loss can be suppressed.
Moreover, since the average pore diameter of the partition walls is 5 μm or more and 50 μm or less, the pressure loss is low, and a sufficient exhaust gas flow rate can be obtained.

As described above, when the exhaust gas purification filter of the present embodiment is used, it is possible to achieve both high collection efficiency and low pressure loss from a state where the amount of particulate matter deposited is small.
Further, since the porous film 13 is provided on the partition wall 14, the particulate material 30 is difficult to enter into the pores of the partition wall 14 when the particulate material 30 is deposited. Compared to the case where the particulate material 30 is not provided, the particulate matter 30 is less likely to block the pores of the partition wall 14, and an increase in pressure loss after the particulate matter 40 is deposited can be suppressed.

  Further, due to the presence of the porous membrane 13, oxygen for burning the particulate matter 30 flows almost evenly through the particulate matter 30 when the exhaust gas purification filter is regenerated. Thereby, the particulate matter 30 to which oxygen is difficult to be supplied decreases, and the oxidation of the particulate matter 30 proceeds evenly. As a result, the combustion time of the particulate matter 30 can be shortened.

Next, the effect of the porous film 13 containing an oxide containing cerium as a component will be described.
As already described in the “Background Art” section, in the conventional exhaust gas purification filter, a certain effect is obtained by supporting cerium oxide on the filter base.

  Since the cerium-containing oxide of the present embodiment contains cerium oxide as a component, it similarly has oxidation catalyst characteristics, that is, combustion catalytic action of the particulate matter 30. Therefore, the porous membrane 13 contains an oxide containing cerium as a component, thereby shortening the combustion time of the particulate matter deposited on the partition wall 14 during the regeneration process of the exhaust gas purification filter and increasing the exhaust gas temperature during the regeneration process. It is possible to reduce the fuel consumption rate and reduce the fuel consumption rate. Furthermore, since the time required for the regeneration process is shortened and the temperature rise during the regeneration process is suppressed, deterioration of the exhaust gas purification filter itself and oxides containing cerium as an oxidation catalyst can be suppressed.

  Here, with respect to the combustion catalytic action of the particulate matter 30 by cerium oxide, it is conventionally assumed that active oxygen is released from cerium oxide, and this active oxygen contributes to the combustion of the particulate matter 30. This active oxygen is known to have a short lifetime.

The oxide containing cerium of the present embodiment takes the form of the porous film 13 and exists on the surface of the partition wall 14. Since the porous membrane 13 has an average pore diameter of 0.05 μm or more and 5 μm or less, the particulate matter 30 is mainly collected by the porous membrane 13. Therefore, at the stage where the particulate matter 30 is collected, the oxide containing cerium and the collected particulate matter 30 are in close proximity.
For this reason, in the structure of the porous film 13 of the present embodiment, the active oxygen generated from the oxide containing cerium is likely to react with the particulate matter 30 before being deactivated, and the oxidation containing cerium is performed. The catalytic activity of the product can be extracted more effectively.

  Further, since the porous film 13 does not substantially enter the pores of the porous ceramics constituting the partition wall 14 of the filter base 11, almost all of it can contribute to the oxidation removal of the particulate matter 30. . Therefore, unlike the conventional exhaust gas purification filter, cerium oxide does not enter the pores of the filter and hardly contribute to the oxidation removal of the particulate matter 30 (is wasted). It is possible to obtain a sufficient oxidation catalyst effect by effectively utilizing without waste.

  Thus, the porous membrane 13 of this embodiment is obtained from the structure of the porous membrane 13 by using an oxide containing cerium as a component and setting the average pore diameter to 0.05 μm or more and 5 μm or less. It is possible to improve the trapping effect of the particulate matter 30, which are advantages, reduce the pressure loss, and shorten the combustion time during regeneration of the exhaust gas purification filter.

  Moreover, the combustion catalytic action of the particulate matter 30 by the oxide containing cerium can provide an effect that the combustion of the particulate matter 30 during regeneration can be promoted. Furthermore, by improving the method for supporting the oxide containing cerium, the catalytic effect of the oxide containing cerium, which is the supported oxidation catalyst, can be made to act effectively. By improving the effect, the combustion time during the regeneration process can be further shortened and the combustion temperature can be lowered.

  As described above, according to the exhaust gas purification filter of the present embodiment, in addition to being excellent in the collection characteristics of the particulate matter 30, the amount of fuel necessary for the regeneration process is further reduced by further shortening the regeneration process time. And the deterioration of the exhaust gas purification filter itself and the oxidation catalyst can be further suppressed.

Next, the manufacturing method of the exhaust gas purification filter of this embodiment will be described.
This exhaust gas purification filter includes fine particles containing a cerium-containing oxide as a component on the surface of a partition constituting a gas flow path of the filter, that is, a porous support having pores having an average pore diameter of 5 to 50 μm. After the coating material for forming a porous film is applied, heat treatment is performed to form a porous film on the surface of the porous support.
According to this method, for example, an exhaust gas purification filter can be manufactured with high productivity as compared with a method of forming a porous film by flowing a gas in which fine particles are dispersed into a filter substrate.

This coating material for forming a porous film contains at least fine particles composed of an oxide containing cerium and a dispersion medium. The fine particles have an average primary particle size of 5 nm to 300 nm and a tap bulk density. 0.5 g / cm ³ or more and 2.0 g / cm ³ or less, the average secondary particle diameter in the paint is 0.1 μm or more and 10 μm or less, and the viscosity of the paint is 2 mPa · s or more and 1000 mPa · s or less. It is.

If the average primary particle diameter, tap bulk density, and average secondary particle diameter in the paint of the fine particles containing an oxide containing cerium as a component are limited to the above ranges, the average pore diameter targeted by the present invention is 0.00. A porous film having a thickness of 05 μm or more and 5 μm or less and an average porosity of 35% or more and 90% or less can be formed.
In addition, the pore diameter of the porous film can be controlled to a desired value by mixing and using a plurality of types of fine particles having different average primary particle diameters and tap bulk densities within the above range.

The “tap bulk density” is “tap bulk density” defined in Japanese Industrial Standard JIS R 1628-1997 “Bulk Density Measurement Method of Fine Ceramics Powder”. A method for measuring tap bulk density is also specified.
The reason why the tap bulk density of the fine particles is smaller than the true density (true specific gravity) is that voids are formed between the fine particles. That is, the ratio (ρt / ρr) between the tap bulk density (ρt) and the true density (ρr) indicates the porosity, that is, the porosity.

As the fine particles containing the cerium-containing oxide as a component, any of the following (a) to (c) is preferable.
(A) cerium oxide alone (b) selected from the group of zirconium, yttrium, and rare earth elements (La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) Complex oxide of one or more elements and cerium (c) Complex oxide of one or more elements selected from the group consisting of zirconium, yttrium and rare earth elements and cerium, and cerium oxide alone Among these materials, a material that can provide desired heat resistance, particulate catalyst combustion catalyst performance, and the like can be appropriately selected.

Such fine oxide particles containing cerium are dispersed in a dispersion medium to obtain a coating material for forming a porous film.
This dispersing step is preferably performed by a wet method. Moreover, as a disperser used in this wet method, any of an open type and a closed type can be used. For example, a ball mill, a stirring mill, a jet mill, a vibration mill, an attritor, a high speed mill, a hammer mill, etc. are suitable. Used for.
Examples of the ball mill include a rolling mill, a vibration mill, and a planetary mill. Examples of the stirring mill include a tower mill, a stirring tank mill, a flow pipe mill, and a tubular mill.

As the dispersion medium, water or an organic solvent is preferably used. In addition, a single polymer monomer or oligomer or a mixture thereof may be used as necessary.
Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, diacetone alcohol, furfuryl alcohol, ethylene glycol and hexylene glycol, and esters such as methyl acetate and ethyl acetate. , Diethyl ether, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), ethylene glycol monobutyl ether (butyl cellosolve), ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dioxane, tetrahydrofuran, acetone , Ketones such as methyl ethyl ketone, acetylacetone, acetoacetate, N, N-dimethylform Acid amides such as amide, toluene, aromatic hydrocarbons such as xylene are preferably used, it is possible to use a mixture of one only or two or more of these solvents.

  As the polymer monomer, acrylic or methacrylic monomers such as methyl acrylate and methyl methacrylate, epoxy monomers, and the like are preferably used. Moreover, as said oligomer, a urethane acrylate oligomer, an epoxy acrylate oligomer, an acrylate oligomer etc. are used suitably.

  Among these dispersion media, water, alcohols, and ketones are preferable for coating materials, and among these, water and alcohols are more preferable, and water is most preferable.

In this coating material, in order to increase the affinity between the oxide fine particles containing cerium and the dispersion medium, the surface modification of the oxide fine particles containing cerium may be performed.
Since these fine particles contain an oxide as a component, examples of the surface modifier include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, cysteamine, tetramethylammonium hydroxide, and aminoethanediol. However, the present invention is not limited to these, and any surface modifier may be used as long as it has a functional group that is adsorbed on the surface of the oxide fine particles and has an end group having an affinity for the dispersion medium.

  In order to provide a binder function between the oxide fine particles containing cerium and a porous support such as the partition wall 14 of the DPF 10, this coating material is appropriately provided with a hydrophilic or hydrophobic polymer. You may contain. The polymer or the like can be appropriately selected within the range in which the average secondary particle diameter of the fine particles in the coating material and the viscosity of the coating material are desired values, as well as being dissolved in the above-described dispersion medium.

Here, when water is used as a dispersion medium, examples of hydrophilic polymers include synthetic alcohols such as polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, polyacrylamide, polystyrene sulfonic acid, polyvinyl pyrrolidone polyacrylate, and polyallylamine. Molecules: natural polymers such as polysaccharides and polysaccharide-derived substances such as cellulose, dextrin, dextran, starch, chitosan, pectin, agarose, carrageenan, chitin, mannan, etc .; gelatin, casein, collagen, laminin, fibronectin, elastin, etc. Proteins and protein-derived substances can be used.
Further, substances such as gels and sols derived from these synthetic polymers, polysaccharides, proteins and the like can also be used.

The ratio of the mass of the polymer to the mass of the fine particles in this paint (the mass of the polymer / the mass of the fine particles) is such that the average secondary particle diameter of the fine particles in the paint and the viscosity of the paint are as desired. The range can be appropriately selected, but a range of 0 or more and 1 or less is preferable.
The above polymer is a component that is eventually burned out by heat treatment and does not remain in the porous membrane. Therefore, if the ratio exceeds 1, the polymer content is too high, resulting in an increase in cost. It is not preferable because it will invite.

In order to ensure the dispersion stability of the paint or to improve the coating property, a surfactant, preservative, stabilizer, antifoaming agent, leveling agent and the like may be appropriately added. These can be appropriately selected so that the average secondary particle diameter of the fine particles in the coating material and the viscosity of the coating material are in a desired range.
There are no particular restrictions on the amount of these surfactants, preservatives, stabilizers, antifoaming agents, leveling agents and the like, and the viscosity of the paint and the average secondary particle size of the fine particles in the paint are within the scope of the present invention. Thus, what is necessary is just to add according to the objective to add.

  In this way, fine particles containing an oxide containing cerium as a component are dispersed in a dispersion medium, and hydrophilic or hydrophobic polymers, surfactants, preservatives, stabilizers, antifoaming agents are used as necessary. Then, a leveling agent or the like is added and mixed to obtain a porous film-forming coating material.

Next, by applying the above-mentioned porous film-forming paint to the surface of the porous support of the exhaust gas purification filter to form a coating film, by heat-treating the obtained coating film to form a porous film, An exhaust gas purification filter can be manufactured.
For example, in the DPF 10, on the surface of the inner wall surface (surface on the inflow cell 12A side of the partition wall 14) 12a of the gas flow path 12 where the exhaust gas inflow side end is opened, the above-described porous film forming coating material is formed. The DPF 10 can be manufactured by forming a porous film 13 by heat-treating the obtained coating film to form a coating film.

  The coating method may be appropriately selected according to the shape and material of the porous support, and is not particularly limited, but a normal wet coating method such as a wash coating method or a dip coating method can be used. In addition, after the application, a process such as removal of an excess coating liquid more than an amount necessary for obtaining a desired film thickness may be performed using compressed air or the like.

  At the time of application, the porous support may be in a dry state, but the porous support is immersed in a solvent, and the air in the pores of the porous support is replaced with a solvent in advance. Those are preferred. The reason for this is that air remaining in the pores of the porous support is released as bubbles from the porous support during or after the coating process, and the porous film is not partially formed. This is because there is an effect that a uniform porous film can be obtained.

In addition to the dispersant, the coating film contains the above-described polymer, surfactant, preservative, stabilizer, antifoaming agent, leveling agent, and the like as necessary. In addition, heat treatment is performed to form a microporous structure in the coating film.
The heat treatment temperature is preferably 200 ° C. or higher and 2000 ° C. or lower, more preferably 300 ° C. or higher and 1500 ° C. or lower.
The heat treatment time is preferably 0.25 hours or more and 10 hours or less, more preferably 0.5 hours or more and 5 hours or less.
The atmosphere during this heat treatment is not particularly limited, and may be any of an oxidizing atmosphere such as air, an inert atmosphere such as nitrogen, argon, neon, or xenon, or a reducing atmosphere such as hydrogen or carbon monoxide. Can be done.
An exhaust gas purification filter can be manufactured as described above.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

"Example 1"
(Preparation of paint)
90 g of cerium oxide (CeO ₂ ) fine particles having an average primary particle size of 5 nm, 9 g of a polycarboxylic acid-based dispersant, and 201 g of water were mixed with a ball mill for 2 hours to obtain a CeO ₂ dispersion A having a solid content of 30% by mass.
To 167 g of this CeO ₂ dispersion A, 67 g of an aqueous solution containing 15% by mass of methyl cellulose A (2% aqueous solution viscosity at 25 ° C.) and 16 g of water were added and stirred for 1 hour using a magnetic stirrer. A coating material A of Example 1 in which CeO ₂ fine particles were dispersed was obtained.

(Production of exhaust gas purification filter)
The surface of the partition walls of the honeycomb structure was repeatedly subjected to dip coating three times after the SiC honeycomb structure (DPF, average pore diameter: 10 μm, average porosity: 42%) was immersed in the coating material A three times. to form a coating film composed of CeO ₂ fine particles. The honeycomb structure was previously immersed in pure water, and the pores were filled and held with water.
Next, the honeycomb structure after dip coating was dried at 150 ° C. for 1 hour, and further heat-treated in the atmosphere at 500 ° C. for 2 hours to form a CeO ₂ porous film on the partition wall surface of the honeycomb structure. An exhaust gas purification filter of Example 1 was obtained.

(Evaluation of exhaust gas purification filter)
About the obtained exhaust gas purification filter, the average pore diameter, average porosity, and film thickness of the porous membrane were measured by the following methods, and the collection efficiency test, the pressure loss test, and the combustion test were conducted by the following methods.

(1) The average pore diameter and average porosity of the porous membrane The average pore diameter and average porosity of the porous membrane formed on the partition wall surface of the exhaust gas purification filter were measured using a mercury porosimeter AutoPoreIV 9505 (manufactured by Shimadzu Corporation). Measured by mercury intrusion method. Since the measurement result is a combination of the porous film and the SiC honeycomb structure (porous support), the same results were obtained using the SiC honeycomb structure in which the porous film of Comparative Example 1 was not formed. The measured value of the average pore diameter and the average porosity thus obtained was used as a reference value. Further, from the weight of the porous membrane and the measured value of the SiC honeycomb structure including the porous membrane, the porous membrane The average pore diameter and average porosity were calculated.

(2) Thickness of the porous membrane By rupturing the partition wall of the exhaust gas purification filter and observing the partition section with a field emission scanning electron microscope (FE-SEM) S-4000 (manufactured by Hitachi Instrument Service Co., Ltd.), The film thickness of the porous film was measured.

(3) Collection efficiency test The collection efficiency of the particulate matter in the exhaust gas purification filter in a state where the particulate matter is not deposited on the exhaust gas purification filter was measured.
Here, the exhaust gas purification filter is attached to a standard particle generator that generates particulate matter by the combustion of propane, and the particle concentration at the inflow and outflow of the exhaust gas purification filter is measured using SMPS (Scanning Mobility Particle Sizer). The particle concentration ratio was defined as the collection efficiency of the exhaust gas purification filter.

(4) Pressure loss test A flow rate of 100 L / min. Then, dry air was flowed in, passed through the partition wall of the exhaust gas purification filter and passed through the discharge port, and the pressure loss at this time was measured.
The obtained result was calculated as a relative value based on the pressure loss of the SiC honeycomb structure in which the porous film of Comparative Example 1 was not formed.

(5) Combustion test The exhaust gas purification filter was attached to a diesel engine having a displacement of 2.2 L, and operated at an engine speed of 1500 rpm, and particulate matter was deposited in the exhaust gas purification filter.
Next, the exhaust gas purification filter on which the particulate matter is deposited is heated to 600 ° C. in a nitrogen atmosphere, and then oxygen is introduced so that a nitrogen-oxygen mixed atmosphere containing 4% by volume of oxygen is introduced. Burned. The time from when oxygen was introduced until the particulate matter was burned off by combustion and its mass reached 10% of the amount deposited was measured and used as an indicator of particulate matter flammability.
Relative values of the measurement time were calculated using the value obtained with the SiC honeycomb structure in which the porous film of Comparative Example 1 was not formed as a reference (100).

  The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 2"
A CeO ₂ dispersion B having a solid content of 30% by mass was obtained in the same manner as in Example 1 except that CeO ₂ fine particles having an average primary particle diameter of 20 nm were used as oxide fine particles containing cerium.
Using this CeO ₂ dispersion B, paint B of Example 2 in which CeO ₂ fine particles were dispersed in water was obtained in the same manner as in Example 1.
Using this paint B, an exhaust gas purification filter of Example 2 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

The surface and cross section of the porous membrane of the exhaust gas purification filter of Example 2 were observed with a field emission scanning electron microscope S-4000 (manufactured by Hitachi Instrument Service Co., Ltd.). A field emission scanning electron microscope image of the surface of the porous film is shown in FIG. 3, and a field emission scanning electron microscope image of the cross section of the partition including the porous film is shown in FIG. For comparison, FIG. 5 shows a field emission scanning electron microscope image of the surface of a SiC honeycomb structure which is a porous support.
According to these field emission scanning electron microscopic images, a porous membrane made of CeO ₂ fine particles on the surface of a SiC honeycomb structure (porous support) and having fine pores as compared with the SiC honeycomb structure. Further, it was found that the CeO ₂ fine particles did not substantially penetrate into the pores of the SiC honeycomb structure.

"Example 3"
A CeO ₂ dispersion C having a solid content of 30% by mass was obtained in the same manner as in Example 1 except that CeO ₂ fine particles having an average primary particle diameter of 50 nm were used as oxide fine particles containing cerium.
Using this CeO ₂ dispersion C, paint C of Example 3 in which CeO ₂ fine particles were dispersed in water was obtained in the same manner as in Example 1.
Using this paint C, an exhaust gas purification filter of Example 3 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

Example 4
A CeO ₂ dispersion D having a solid content of 30% by mass was obtained in the same manner as in Example 1 except that CeO ₂ fine particles having an average primary particle diameter of 300 nm were used as oxide fine particles containing cerium.
Using this CeO ₂ dispersion D, paint D of Example 4 in which CeO ₂ fine particles were dispersed in water was obtained in the same manner as in Example 1.
Using this coating material D, an exhaust gas purification filter of Example 4 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 5"
18 g of CeO ₂ fine particles having an average primary particle diameter of 20 nm, 72 g of CeO ₂ fine particles having an average primary particle diameter of 300 nm, 9 g of a polycarboxylic acid-based dispersant, and 201 g of water are mixed for 2 hours by a ball mill, and CeO ₂ dispersion having a solid content of 30% by mass is dispersed. Liquid E was obtained.
Using this CeO ₂ dispersion E, paint E of Example 5 in which CeO ₂ fine particles were dispersed in water was obtained in the same manner as in Example 1.
Using this paint E, an exhaust gas purification filter of Example 5 was obtained in the same manner as in Example 1 except that the heat treatment temperature was 1200 ° C. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 6"
The same paint B as that prepared in Example 2 was used as the paint, and the dip coat was pulled up after the SiC honeycomb structure (DPF, average pore diameter: 10 μm, average porosity: 42%) was immersed in this paint B Was repeated 6 times to form a coating film made of CeO ₂ fine particles on the surface of the partition walls of the honeycomb structure.
Next, the honeycomb structure after dip coating was dried at 150 ° C. for 1 hour, and further heat-treated in the atmosphere at 500 ° C. for 2 hours to obtain an exhaust gas purification filter of Example 6. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 7"
The same paint B as that prepared in Example 2 was used as the paint, and the dip coat was pulled up after the SiC honeycomb structure (DPF, average pore diameter: 10 μm, average porosity: 42%) was immersed in this paint B Was repeated four times to form a coating film made of CeO ₂ fine particles on the surface of the partition walls of the honeycomb structure.
Next, the honeycomb structure after dip coating was dried at 150 ° C. for 1 hour, and further heat-treated in the atmosphere at 500 ° C. for 2 hours.
The dip coating 4 times, drying at 150 ° C. for 1 hour, and heat treatment at 500 ° C. for 2 hours were repeated once more to obtain an exhaust gas purification filter of Example 7. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 8"
Except for using the same paint B as that prepared in Example 2 as the paint and using a cordierite honeycomb structure (DPF, average pore diameter: 20 μm, average porosity: 60%) as the honeycomb structure, In the same manner as in Example 1, an exhaust gas purification filter of Example 8 was obtained. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 9"
The same coating material B as that prepared in Example 2 was used as the coating material, and an aluminum titanate honeycomb structure (DPF, average pore diameter: 10 μm, average porosity: 40%) was used as the honeycomb structure. In the same manner as in Example 1, an exhaust gas purification filter of Example 9 was obtained. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 10"
As the oxide fine particles containing cerium, composite oxide (Ce _0.5 Zr _0.5 O ₂ ) fine particles having an average primary particle diameter of 20 nm and a composition ratio of cerium and zirconium of 1: 1 were used. A Ce _0.5 Zr _0.5 O ₂ dispersion F having a solid content of 30% by mass was obtained in the same manner as in Example 1.
Here, what is indicated as Ce _0.5 Zr _0.5 O ₂ is an oxide having a composition ratio of cerium and zirconium of 1: 1 as a whole, and cerium and zirconium are 1: 1. In addition to CeZrO ₄ , which is a complex oxide that is completely solid-solved at a composition ratio of 1, a composite oxide having a different composition ratio of cerium and zirconium and cerium oxide alone are included.
Using this Ce _0.5 Zr _0.5 O ₂ dispersion F, paint F of Example 10 in which Ce _0.5 Zr _0.5 O ₂ fine particles were dispersed in water was obtained in the same manner as in Example 1. It was.

Using this paint F, an exhaust gas purification filter of Example 10 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 11"
As oxide fine particles containing cerium, composite oxide (Ce _0.7 Zr _0.3 O ₂ ) fine particles having an average primary particle diameter of 20 nm and a composition ratio of cerium and zirconium of 7: 3 were used. A Ce _0.7 Zr _0.3 O ₂ dispersion G having a solid content of 30% by mass was obtained in the same manner as in Example 1.
Here, what is indicated as Ce _0.7 Zr _0.3 O ₂ is an oxide having a cerium / zirconium composition ratio of 7: 3 as a whole, and cerium / zirconium is 7: 3. In addition to Ce ₇ Zr ₃ O ₂₀ , which is a complex oxide that is completely solid-solved at a composition ratio of 1, composite oxides having different composition ratios of cerium and zirconium and cerium oxide alone are included.
Using this Ce _0.7 Zr _0.3 O ₂ dispersion G, paint G of Example 11 in which Ce _0.7 Zr _0.3 O ₂ fine particles were dispersed in water was obtained in the same manner as in Example 1. It was.

Using this paint G, an exhaust gas purification filter of Example 11 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 12"
As oxide fine particles containing cerium, composite oxide (Ce _0.2 Zr _0.8 O ₂ ) fine particles having an average primary particle diameter of 20 nm and a composition ratio of cerium and zirconium of 2: 8 were used. A Ce _0.2 Zr _0.8 O ₂ dispersion H having a solid content of 30% by mass was obtained in the same manner as in Example 1.
Here, what is indicated as Ce _0.2 Zr _0.8 O ₂ is an oxide having a composition ratio of cerium and zirconium of 2: 8 as the whole fine particles, and cerium and zirconium are in a ratio of 2: 8. In addition to CeZr ₄ O ₁₀ which is a complex oxide completely dissolved in the composition ratio, complex oxides having different composition ratios of cerium and zirconium and cerium oxide alone are included.
Using this Ce _0.2 Zr _0.8 O ₂ dispersion H, paint H of Example 12 in which Ce _0.2 Zr _0.8 O ₂ fine particles were dispersed in water was obtained in the same manner as in Example 1. It was.

Using this paint H, an exhaust gas purification filter of Example 12 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 13"
Other than using oxide fine particles containing cerium, composite oxide (Ce _0.9 La _0.1 O _2-x ) fine particles having an average primary particle diameter of 20 nm and a composition ratio of cerium and lanthanum of 9: 1. Obtained a Ce _0.9 La _0.1 O _2-x dispersion I having a solid content of 30% by mass in the same manner as in Example 1.
In addition, what is indicated as Ce _0.9 La _0.1 O _2-x here is an oxide having a composition ratio of cerium and lanthanum of 9: 1 as a whole as a whole, and in the cerium oxide crystal It includes not only complex oxides in which lanthanum oxide is dissolved, but also complex oxides in which the composition ratio of cerium and lanthanum is not 9: 1 and cerium oxide alone.
Using this Ce _0.9 La _0.1 O _2-x dispersion I, in the same manner as in Example 1, Ce _0.9 La _0.1 O _2-x fine particles dispersed in water were used. Paint I was obtained.

Using this paint I, an exhaust gas purification filter of Example 13 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 14"
Other than using oxide fine particles containing cerium, composite oxide (Ce _0.9 Pr _0.1 O _2-x ) fine particles having an average primary particle diameter of 20 nm and a composition ratio of cerium and praseodymium of 9: 1. Obtained a Ce _0.9 Pr _0.1 O _2-x dispersion J having a solid content of 30% by mass in the same manner as in Example 1.
In addition, what is indicated as Ce _0.9 Pr _0.1 O _2-x here is an oxide having a composition ratio of cerium and praseodymium of 9: 1 as a whole of the fine particles, and in the cerium oxide crystal It includes not only a complex oxide in which praseodymium oxide is dissolved, but also a complex oxide in which the composition ratio of cerium and praseodymium is not 9: 1 or cerium oxide alone.
Using this Ce _0.9 Pr _0.1 O _2-x dispersion liquid J, in the same manner as in Example 1, Ce _0.9 Pr _0.1 O _2-x fine particles were dispersed in water. Paint J was obtained.

Using this paint J, an exhaust gas purification filter of Example 14 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

"Example 15"
Other than using oxide fine particles containing cerium, composite oxide (Ce _0.9 Y _0.1 O _2-x ) fine particles having an average primary particle diameter of 20 nm and a composition ratio of cerium and yttrium of 9: 1. Obtained a Ce _0.9 Y _0.1 O _2-x dispersion K having a solid content of 30% by mass in the same manner as in Example 1.
In addition, what is indicated as Ce _0.9 Y _0.1 O _2-x here is an oxide having a composition ratio of cerium and yttrium of 9: 1 as a whole of the fine particles, and in the cerium oxide crystal It includes not only complex oxides in which yttrium oxide is dissolved, but also complex oxides in which the composition ratio of cerium and yttrium is not 9: 1 and cerium oxide alone.
Using this Ce _0.9 Y _0.1 O _2-x dispersion liquid K, in the same manner as in Example 1, Ce _0.9 Y _0.1 O _2-x fine particles were dispersed in water. A paint K was obtained.

Using this paint K, an exhaust gas purification filter of Example 15 was obtained in the same manner as Example 1. The obtained exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

“Comparative Example 1”
As a honeycomb structure not provided with a porous membrane, the same SiC honeycomb structure as the SiC honeycomb structure (DPF, average pore diameter: 10 μm, average porosity: 42%) used in Example 1 was used. The exhaust gas purification filter of Comparative Example 1 was obtained.
This exhaust gas purification filter was evaluated in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

“Comparative Example 2”
(Preparation of paint)
90 g of CeO ₂ fine particles having an average primary particle diameter of 5 nm, 9 g of a polycarboxylic acid-based dispersant, and 201 g of water were dispersed by a sand grinder for 4 hours to obtain a CeO ₂ dispersion L having a solid content of 30% by mass.
To this 167 g of CeO ₂ dispersion liquid, 67 g of an aqueous solution containing 15% by mass of methylcellulose A (2% aqueous solution viscosity at 25 ° C.) and 16 g of water were added and stirred for 1 hour using a magnetic stirrer. A paint L of Comparative Example 2 in which CeO ₂ fine particles were dispersed was obtained.

(Production of exhaust gas purification filter)
The surface of the partition walls of the honeycomb structure was repeatedly subjected to dip coating three times after the SiC honeycomb structure (DPF, average pore diameter: 10 μm, average porosity: 42%) was immersed in the paint L to form a coating film composed of CeO ₂ fine particles. The honeycomb structure was previously immersed in pure water, and the pores were filled and held with water.
Next, the honeycomb structure after dip coating was dried at 150 ° C. for 1 hour, and further heat-treated in the atmosphere at 500 ° C. for 2 hours to obtain an exhaust gas purification filter of Comparative Example 2.

(Evaluation of exhaust gas purification filter)
With respect to the obtained exhaust gas purification filter, the partition wall surface of the honeycomb structure was observed with a field emission scanning electron microscope S-4000 (manufactured by Hitachi Keiki Service Co., Ltd.), and a porous film was not formed on the partition wall surface. First, the applied CeO ₂ fine particles were dispersed throughout the partition including the pores.
Further, the exhaust gas purification filter was evaluated by performing a collection efficiency test, a pressure loss test, and a combustion test in the same manner as in Example 1.
The production conditions for the exhaust gas purification filter are shown in Table 1, and the evaluation results of the obtained exhaust gas purification filter are shown in Table 2.

According to these evaluation results, the exhaust gas purification filters of Examples 1 to 15 are superior in the collection efficiency of the particulate matter as compared with the honeycomb structure in which the porous film of Comparative Example 1 is not provided. It was found that the increase in pressure loss was slight, the combustion time of the particulate matter was shortened, and an exhaust gas purification filter having good characteristics was obtained.
However, the exhaust gas purification filter of Example 7 had a somewhat higher pressure loss than the exhaust gas purification filters of other examples, and the combustion time of the particulate matter was not so shortened. This is considered to be because the film thickness of the porous film is slightly too thick, and the film thickness of the porous film is more preferably 40 μm or less.

On the other hand, since the exhaust gas purification filter of Comparative Example 1 is a conventional filter without a porous membrane, the particulate matter collection efficiency is lower than that of the exhaust gas purification filters of Examples 1 to 15, and the particulate matter The burning time of the substance was also long.
In the exhaust gas purification filter of Comparative Example 2, the porous film was not formed, because the secondary particle diameter of the CeO ₂ fine particles was too small, so that the CeO ₂ fine particles spread over the entire partition including the pores. As a result, it was considered that the porous film could not be formed.

In the exhaust gas purification filter of Comparative Example 2, since the porous film was not formed, the collection efficiency was hardly improved. Moreover, the burning time of the particulate matter is rather increased, and the effect of supporting CeO ₂ fine particles having an oxidation catalyst effect is not obtained. This is because the particulate matter is deposited on the partition wall surface, but most of the CeO ₂ fine particles are present in the pores and do not come into contact with the particulate matter, so that the catalytic effect of the CeO ₂ fine particles was not expressed. it is conceivable that.

It is a partially broken perspective view showing DPF which is an exhaust gas purification filter of one embodiment of the present invention. It is sectional drawing which shows the partition structure of DPF which is an exhaust gas purification filter of one Embodiment of this invention. It is a field emission type scanning electron microscope image which shows the surface of the porous membrane of the exhaust gas purification filter of Example 2 of this invention. It is a field emission scanning electron microscope image which shows the partition cross section containing the porous membrane of the exhaust gas purification filter of Example 2 of this invention. It is a field emission type scanning electron microscope image which shows the surface of a SiC honeycomb structure.

Explanation of symbols

10 DPF
DESCRIPTION OF SYMBOLS 11 Filter base | substrate 12 Gas flow path 12A Inflow cell 12B Outflow cell 13 Porous membrane 14 Partition 30 Particulate matter (alpha), (gamma) End face G Exhaust gas C Purified gas

Claims (5)

A filter base made of a porous body, an inflow gas passage provided on the inflow side of the exhaust gas containing particulate matter of the filter base and having an open inflow end, and the outflow side of the exhaust gas of the filter base An outflow side gas passage having an open end on the outflow side, and a partition wall disposed between the inflow side gas passage and the outflow side gas passage to purify the exhaust gas by passing therethrough. Exhaust gas purification filter,
The average pore diameter of the partition walls is 5 μm or more and 50 μm or less,
An exhaust gas purification filter comprising a porous film containing an oxide containing cerium having an average pore diameter of 0.05 μm or more and 5 μm or less on at least an inner wall surface of the inflow side gas flow path. The oxide containing cerium is
Cerium oxide alone,
Or a composite oxide of cerium with one or more elements selected from the group consisting of zirconium, yttrium, and rare earth elements,
Or a mixture of a complex oxide of cerium and one or more elements selected from the group consisting of zirconium, yttrium, and rare earth elements, and cerium oxide alone,
The exhaust gas purification filter according to claim 1, wherein   The exhaust gas purification filter according to claim 1 or 2, wherein an average porosity of the porous membrane is 35% or more and 90% or less.   4. The exhaust gas purification filter according to claim 1, wherein an average film thickness of the porous membrane is 40 μm or less.   The porous film is formed by applying a solution containing oxide fine particles to the filter substrate to form a coating film, and then heat-treating the coating film. The exhaust gas purification filter as described.

Images