JP6076936B2 - Exhaust purification filter - Google Patents

Description

  The present invention relates to an exhaust purification filter. Specifically, the present invention relates to an exhaust gas purification filter that captures and purifies particulate matter in exhaust gas discharged from an internal combustion engine.

  In an internal combustion engine mounted on an automobile or the like, in particular, a compression ignition type internal combustion engine, it is known that a large amount of particulate matter is contained in the exhaust gas discharged. This particulate matter (Particulate Matter, hereinafter referred to as “PM”) is harmful to the human body and is an emission-regulated substance. Therefore, a DPF (Diesel Particulate Filter) as an exhaust gas purification filter that captures PM is usually provided in the exhaust passage of the internal combustion engine.

  In the DPF, trapped PM gradually accumulates. Then, a differential pressure is generated between the upstream side and the downstream side of the DPF, leading to a decrease in output and a deterioration in fuel consumption. For this reason, the DPF generally carries a catalyst for burning and removing the deposited PM when PM is accumulated to some extent.

  As said catalyst, the Ag type catalyst which shows the especially outstanding purification | cleaning activity with respect to PM is known. As an Ag-based catalyst, for example, a catalyst in which Ag is supported on a Ce-containing oxide containing Ce has been proposed (see, for example, Patent Documents 1 to 3). According to these catalysts, it is said that PM can be removed by combustion at a low temperature.

Japanese Patent No. 5092281 Japanese Patent No. 4678596 JP 2011-143352 A

  By the way, since an Ag-based catalyst burns PM by releasing active oxygen, the contact property between Ag and PM has a characteristic that greatly affects the PM purification performance. Therefore, in the conventional catalyst, the PM purification performance is improved by increasing the content of Ag in the catalyst. However, when the Ag content is increased, in reality, Ag aggregates and the coverage of Ag with respect to the Ce-containing oxide is lowered, and the contact property between Ag and PM is lowered. Can not. Further, when the content of Ag is increased, sintering due to excessive Ag occurs, resulting in a decrease in PM purification performance and an increase in cost.

  This invention is made | formed in view of the above, The objective is to provide the exhaust gas purification filter which can improve PM purification performance, suppressing cost.

In order to achieve the above object, the present invention provides an exhaust purification filter that is provided in an exhaust passage of an internal combustion engine and captures and purifies particulate matter in the exhaust of the internal combustion engine, comprising a porous filter substrate, A catalyst which is supported on the filter base material and oxidizes and purifies the particulate matter, and the catalyst includes a Ce-containing oxide containing Ce, and Ag supported on the Ce-containing oxide, has a content of said Ag in said catalyst is more than 50 wt%, the specific surface area of the Ce-containing oxide ^is 0.5m ² /g~105.6m 2 / g, the Ce A surface concentration of Ag on the contained oxide is 25.1% to 67.7% in terms of element.

In the present invention, a catalyst for oxidizing and purifying particulate matter is formed by an Ag-based catalyst in which Ag is supported on a Ce-containing oxide. Further, the content of Ag in the catalyst was 50 wt% or less, the specific surface area of Ce-containing oxide by setting low as 0.5m ² /g~105.6m ² / g, on the Ce-containing oxide The surface concentration of Ag is set to 25.1% to 67.7% in terms of element.
According to the present invention, by reducing the specific surface area of the Ce-containing oxide, the surface concentration of Ag on the Ce-containing oxide can be increased without changing the Ag content in the catalyst. That is, by reducing the specific surface area of the Ce-containing oxide, it is possible to suppress the burying of Ag in the pores of the Ce-containing oxide, so that a large amount of Ag can be exposed on the surface of the Ce-containing oxide. Therefore, according to the present invention, the contact between Ag and PM is improved, so that the PM purification performance can be improved.
Moreover, in the conventional catalyst, Ag particles aggregated by increasing the Ag content slide down into the pores from the surface of the Ce-containing oxide, and become larger aggregates and unevenly distributed in the pores. The contact property between Ag and PM is lowered, and the PM purification performance is lowered. On the other hand, according to the present invention, Ag purification can be suppressed by reducing the specific surface area of the Ce-containing oxide, so that the PM purification performance can be improved.
Furthermore, according to the present invention, since there is no need to increase the Ag content as in the prior art, the occurrence of sintering due to excessive Ag can be suppressed, the PM purification performance can be improved, and the cost can be suppressed.

The specific surface area of the Ce-containing oxide is preferably 13.0 m ² / g or more, and the surface concentration of the Ag on the Ce-containing oxide is preferably 45.7% or less in terms of element.

In this invention, the specific surface area of the Ce-containing oxide is set to 13.0 m ² / g or more, and the surface concentration of Ag on the Ce-containing oxide is set to 45.7% or less in terms of element.
An exhaust purification filter is required to have high CO / HC purification performance in addition to high PM purification performance. If the specific surface area of the Ce-containing oxide is too low, the oxygen release function (OSC) of the Ce-containing oxide is lost. As a result, the CO / HC purification performance decreases. On the other hand, according to the present invention, the lower limit value of the specific surface area of the Ce-containing oxide is 13.0 m ² / g, thereby improving the PM purification performance while avoiding the deterioration of the CO / HC purification performance. it can.

The specific surface area of the Ce-containing oxide ^is 13.0m ² /g~65.0m 2 / g, the surface concentration of the Ag on the Ce-containing oxide 29.6% to 45 in terms of an element. 7% is preferable.

In this invention, the specific surface area of Ce containing oxide and ^{13.0m 2 /g~65.0m 2 / g, 29.6} % ~45.7% of the surface concentration of Ag on Ce-containing oxide in terms of element And According to the present invention, the above-described effects are more remarkably exhibited.

  The Ag content in the catalyst is preferably 30% by mass to 45% by mass.

  In this invention, the content of Ag in the catalyst is 30% by mass to 45% by mass. According to the present invention, the above-described effects are more remarkably exhibited.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification filter which can improve PM purification performance can be provided, suppressing cost.

It is a figure for demonstrating the relationship between the specific surface area of Ce containing oxide, and Ag surface concentration, (a) is a schematic diagram which shows the presence position of Ag when changing the specific surface area of Ce containing oxide. It is a figure which shows Ag surface concentration when (b) is (a). It is a figure which shows the relationship between the specific surface area of Ag content and Ce containing oxide, and PM purification performance. It is a figure which shows the relationship between the calcination temperature of Ce containing oxide, and a specific surface area. It is a figure which shows the relationship between the calcination temperature of Ce containing oxide, and Ag surface concentration. It is a figure which shows the relationship between reaction time and PM purification rate. It is a figure which shows T90 of each Example and a comparative example. It is a figure which shows the relationship between Ag surface concentration and T90. It is a figure which shows the CO purification rate of Example 2, 4, and 5. FIG. It is a figure which shows the relationship between Ag content in the catalyst of Examples 6-10 and the comparative example 2, and Ag surface concentration. It is a figure which shows the relationship between Ag content and T90 in the catalyst of Examples 6-10. It is a figure which shows the relationship between the specific surface area of Ce containing oxide in the catalyst of Examples 11-13, and T90.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
The exhaust purification filter according to the first embodiment of the present invention is provided in an exhaust passage of an internal combustion engine such as a diesel engine, for example, and captures and purifies PM in the exhaust of the internal combustion engine. The exhaust purification filter according to the present embodiment includes a DPF as a filter base material, and an Ag-based catalyst supported on the DPF.

  The DPF of the present embodiment has a three-dimensional network structure and is formed from a porous material such as silicon carbide or cordierite. Further, any form such as foam metal or foam ceramic having PM collecting ability, a nonwoven fabric in which metals and ceramic fibers are superimposed, a wall flow type filter, or the like can be used. Among these, a wall flow type honeycomb structure filter is preferably used from the viewpoint of PM collection efficiency and contact between the catalyst and PM.

  In the DPF of this embodiment, the cell shape is preferably any one of 4 to 8 octagons from the viewpoint of increasing the contact area between the catalyst and the PM. From the same viewpoint, the number of cells is preferably 200 to 400 cells per square inch. When the number of cells is less than 200 cells, a sufficient contact area between the catalyst and PM cannot be ensured. When the number exceeds 400 cells, PM is clogged in the cells, leading to an increase in pressure loss.

  The catalyst layer of this embodiment is composed of an Ag-based catalyst containing Ag as a catalytic metal that is an active species. An Ag-based catalyst is currently the most effective catalyst for burning PM, and can burn PM at a lower temperature than other noble metal-based catalysts such as Pt. For example, if the contact property with the PM is good, the PM can be ignited from 200 ° C. or less, and the combustion of the PM can be completed at 400 ° C.

Here, the PM combustion mechanism of the Ag-based catalyst will be described.
In the Ag-based catalyst, Ag in the vicinity of the surface exists as Ag ₂ O in an oxidizing atmosphere and as Ag metal in a reducing atmosphere. Ag ₂ O has the smallest oxygen desorption energy and is the most effective compound for PM combustion.
When oxygen is supplied from a Ce-containing oxide having an oxygen releasing ability, which will be described later, to Ag metal near the surface, Ag metal is converted to Ag ₂ O which is an active species. And although this Ag ₂ O returns to the Ag metal by reacting with PM, as a result of immediately supplying oxygen from the Ce-containing oxide to the Ag metal, the Ag near the surface is always in the state of Ag ₂ O. Exists. In this way, the Ag-based catalyst efficiently removes PM at a low temperature by the action of the active species Ag ₂ O existing near the surface. Therefore, the Ag-based catalyst has a characteristic that the contact property between Ag and PM greatly affects the PM purification performance.

In the Ag-based catalyst of the present embodiment, a Ce-containing oxide containing Ce is used as a catalyst carrier that supports Ag. Ce-containing oxides are known to have oxygen releasing ability. As the Ce-containing oxide, CeO ₂ , CeZrO ₂ , and CePrLaSiO ₂ are preferably used. Thereby, the stability of the Ag ₂ O is ensured by oxygen released from the Ce-containing oxide having oxygen releasing ability.

As the Ce-containing oxide, at least one selected from the group consisting of perovskite type, spinel type, rutile type, delafossite type, magnetoplumbite type, ilmenite type, and fluorite type can be used. Among these, a fluorite-type complex oxide is preferably used from the viewpoint of oxygen releasing ability.
In addition, the composite oxide contains at least two kinds selected from the group consisting of alkaline earth metal elements, transition metal elements, Group 12 elements, and Group 13 elements as constituent elements. What absorbs and discharge | releases oxygen by changing a number is preferable.
In addition, since the composite oxide has an oxygen releasing ability, it is preferable that at least one element having a polyvalence is included. Specifically, Zr, V, Cr, Mn, Fe, Co, Cu, Nb, Ta, Mo, W, Ce, Pr, Sm, Eu, Tb, Yb, Pt, Pd, Rh, Ir, Ru, etc. It is preferable that at least one transition metal element is contained. Oxygen release is a phenomenon in which oxygen in the lattice of the composite oxide is desorbed in order to maintain a charge balance in accordance with a change in the valence of the elements constituting the composite oxide. For this reason, Ce, Zr, Pr, La, and Y are particularly preferable among the above transition metal elements from the viewpoint of oxygen releasing ability in combination with Ag.

  Further, the Ag-based catalyst of the present embodiment may be one in which at least one noble metal selected from the group consisting of Ru, Pd, and Pt is co-supported on the catalyst carrier together with Ag.

Ag-based catalyst according to the present embodiment has a specific surface area of the Ce-containing oxide is characterized by a 0.5m ² /g~105.6m ² / g. When the specific surface area of the Ce-containing oxide is within this range, the Ag surface concentration described later can be increased without increasing the Ag content. Preferably, the lower limit is 13.0m ² / g, a specific surface area of more preferred Ce-containing oxide ^is 13.0m ² /g~65.0m 2 / g.

The “specific surface area” in the present embodiment means the surface area (m ² / g) per unit mass of the Ce-containing oxide, and is calculated by the BET method. Specifically, the specific surface area is calculated by adsorbing gas particles such as nitrogen to solid particles and using the BET equation from the relationship between the pressure and the adsorption amount at that time.

  The Ag-based catalyst according to the present embodiment is characterized in that the surface concentration of Ag on the Ce-containing oxide is 25.1% to 67.7% in terms of element. When the surface concentration of Ag on the Ce-containing oxide is within this range, the contact between Ag and PM can be improved, and the PM purification performance can be improved. Preferably, the upper limit is 45.7%, and the more preferable surface concentration of Ag on the Ce-containing oxide is 29.6% to 45.7% in terms of element.

  The “Ag surface concentration” in the present embodiment means an element equivalent surface concentration (atm%) of Ag supported on the Ce-containing oxide, and is measured by XPS (X-ray photoelectron spectroscopy) measurement. For example, it is measured by elemental analysis using an XPS apparatus “Quantera SXM” manufactured by PHI.

As a method of adjusting the specific surface area of the Ce-containing oxide within the above range, changing the firing conditions of the Ce-containing oxide can be mentioned. For example, the firing time of the Ce-containing oxide and 2 hours, the calcination temperature is be in the range of 800 ° C. to 1300 ° C., a specific surface area of Ce-containing oxide 0.5m ² /g~105.6m ² / g. Thereby, the surface concentration of Ag on the Ce-containing oxide can be set to 25.1% to 67.7%.

Here, FIG. 1 is a diagram for explaining the relationship between the specific surface area of the Ce-containing oxide and the Ag surface concentration. Specifically, (a) is a schematic diagram showing the presence position of Ag when the specific surface area of the Ce-containing oxide is changed, and (b) shows the Ag surface concentration at (a). FIG. More specifically, FIG. 1 shows Ag-based catalysts of Comparative Example 1 and Example 3 described later.
As shown in FIG. 1A, for example, when the specific surface area of the Ce-containing oxide is lowered while the Ag content is kept constant at 30% by mass, the burying of Ag in the pores of the Ce-containing oxide is suppressed. It can be seen that a large amount of Ag is exposed on the surface of the Ce-containing oxide. That is, as is clear from FIG. 1B, when the specific surface area of the Ce-containing oxide is lowered, the Ag surface concentration is increased. Thereby, as a result of the increase in the number of contacts PM that come into contact with Ag, PM purification performance is improved.

  In the Ag-based catalyst according to this embodiment, the content of Ag in the Ag-based catalyst is 50% by mass or less. When the content of Ag in the Ag-based catalyst is within this range, the above-described effects can be obtained by setting the specific surface area of the Ce-containing oxide within the above-described range. The content of Ag in the Ag-based catalyst is more preferably 30% by mass to 45% by mass.

  Here, FIG. 2 is a diagram showing the relationship between the Ag content and the specific surface area of the Ce-containing oxide and the PM purification performance. As shown in FIG. 2, it can be seen that the PM purification performance is maximized when the specific surface area of the Ce-containing oxide is low when the Ag content is low. In addition, when the specific surface area of the Ce-containing oxide is low, it can be seen that when the Ag content is increased, the region where Ag not supported on the Ce-containing oxide is present increases as compared with the case where the specific surface area is high. . This is because when the Ag content is increased when the specific surface area of the Ce-containing oxide is low, a large amount of Ag that cannot be supported is generated. Therefore, as described above, in this embodiment, the Ag content in the Ag-based catalyst is set to a small range of 50% by mass or less.

In the exhaust purification filter according to the present embodiment, a fine foaming method using citric acid or the like is preferably employed in addition to the dipping method.
In the dipping method, for example, a slurry containing a predetermined amount of a constituent material of an Ag-based catalyst is prepared by wet pulverization or the like. After the DPF is immersed in the prepared slurry, the DPF is pulled up and fired at a predetermined temperature condition. Thus, an Ag-based catalyst can be supported on the DPF.
In the fine foaming method, an organic acid such as citric acid is added to the slurry produced as described above to foam and disperse the catalyst particles during firing. Thereby, the catalyst particles are dispersed and supported on the entire DPF, and the Ag-based catalyst can be uniformly supported on the surface of the DPF.

According to this embodiment, the following effects are produced.
In the present embodiment, the catalyst for oxidizing and purifying PM is formed of an Ag-based catalyst in which Ag is supported on a Ce-containing oxide. Further, the content of Ag in the Ag-based catalyst and 50 mass% or less, the specific surface area of Ce-containing oxide by setting low as 0.5m ² /g~105.6m ² / g, Ce-containing oxide The surface concentration of the above Ag was 25.1% to 67.7% in terms of element.
According to this embodiment, by reducing the specific surface area of the Ce-containing oxide, it is possible to increase the surface concentration of Ag on the Ce-containing oxide while keeping the Ag content in the catalyst unchanged. That is, by reducing the specific surface area of the Ce-containing oxide, it is possible to suppress the burying of Ag in the pores of the Ce-containing oxide, so that a large amount of Ag can be exposed on the surface of the Ce-containing oxide. Therefore, according to this embodiment, since the contact property between Ag and PM is improved, the PM purification performance can be improved.

Moreover, in the conventional catalyst, Ag particles aggregated by increasing the Ag content slide down into the pores from the surface of the Ce-containing oxide, and become larger aggregates and unevenly distributed in the pores. The contact property between Ag and PM is lowered, and the PM purification performance is lowered. On the other hand, according to this embodiment, since the aggregation of Ag can be suppressed by reducing the specific surface area of the Ce-containing oxide, the PM purification performance can be improved.
Furthermore, according to the present embodiment, since it is not necessary to increase the Ag content as in the prior art, generation of sintering due to excessive Ag can be suppressed, PM purification performance can be improved, and cost can be suppressed.

In the present embodiment, preferably, the specific surface area of the Ce-containing oxide is set to 13.0 m ² / g or more, and the surface concentration of Ag on the Ce-containing oxide is set to 45.7% or less in terms of element.
An exhaust purification filter is required to have high CO / HC purification performance in addition to high PM purification performance. If the specific surface area of the Ce-containing oxide is too low, the oxygen release function (OSC) of the Ce-containing oxide is lost. As a result, the CO / HC purification performance decreases. On the other hand, according to the present embodiment, by setting the lower limit value of the specific surface area of the Ce-containing oxide to 13.0 m ² / g, the PM purification performance is improved while avoiding the deterioration of the CO / HC purification performance. it can.

In this embodiment also, more preferably, the specific surface area of the Ce-containing oxide and 13.0m ² /g~65.0m ² / g, the surface concentration of Ag on Ce-containing oxide in terms of element 29.6 % To 45.7%. Thereby, the above-mentioned effect is exhibited more remarkably.

  In the present embodiment, more preferably, the content of Ag in the catalyst is 30% by mass to 45% by mass. Thereby, the above-mentioned effect is more remarkably exhibited.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

  Next, examples of the present invention will be described, but the present invention is not limited to these examples.

[Examples 1 to 5, Comparative Example 1]
Ce _84.9 La _5.1 Pr _5.0 Si _5.0 O ₂ as the Ce-containing oxide is 10. so that the Ag content in the catalyst is 30% by mass with respect to the target production amount of 15 g. 20 g, 7.09 g of nitric acid Ag, and 2.99 g of a 5% Pd nitric acid aqueous solution were weighed, and an appropriate amount of distilled water was mixed to obtain a solution A. Next, the solution A was evaporated to dryness with an evaporator to obtain a catalyst B carrying Ag, and then the catalyst B was dried at 200 ° C. and then calcined at 700 ° C. for 2 hours to prepare an Ag-based catalyst.

  The Ce-containing oxide used was fired at 800 ° C. in Example 1 and was fired at 1100 ° C. in Example 2. Moreover, what was baked at 1150 degreeC was used in Example 3, what was baked at 1200 degreeC was used in Example 4, and what was baked at 1300 degreeC was used in Example 5. The firing time of the Ce-containing oxide was 2 hours in all cases. In the comparative example, a firing temperature of 0 ° C., that is, an unfired one was used.

[Specific surface area]
The specific surface area of the Ce-containing oxide used in each example and comparative example was measured. Specifically, the Ce-containing oxide used in each example and comparative example was calculated using the BET equation from the relationship between the pressure and the amount of adsorption when nitrogen was adsorbed. The results are shown in Table 1.

[Ag surface concentration]
The Ag surface concentration was measured for the catalysts prepared in each Example and Comparative Example. Specifically, the element-converted Ag surface concentration (atm%) supported on the Ce-containing oxide was measured using an XPS apparatus “Quantera SXM” manufactured by PHI. The results are shown in Table 1.

  Here, FIG. 3 is a diagram showing the relationship between the firing temperature of the Ce-containing oxide and the specific surface area. As shown in FIG. 3, it was found that the specific surface area of the Ce-containing oxide rapidly decreases when the firing temperature is 800 ° C. (Example 1) or higher. This was thought to be due to sintering caused by an increase in the firing temperature.

  FIG. 4 is a diagram showing the relationship between the firing temperature of the Ce-containing oxide and the Ag surface concentration. As shown in FIG. 4, it was found that the Ag surface concentration rapidly increased when the firing temperature was 800 ° C. (Example 1) or higher. This was considered because Ag buried in the pores decreased as the specific surface area of the Ce-containing oxide decreased as shown in FIG.

[PM purification performance]
(Preparation of exhaust purification filter)
The catalyst powder prepared in each Example and Comparative Example, distilled water, and SiO ₂ sol were placed in a container with 10 mm Al ₂ O ₃ balls, and wet pulverized for about 1 hour. Then, after adding 4 times amount citric acid with respect to the amount of powder, the powder slurry was obtained by performing wet grinding again for about 1 hour. Next, the obtained slurry was impregnated with a Si—SiC filter (15 cc) as DPF, air-blown, and dried at 200 ° C. for 2 hours.
The above operation was repeated, and after confirming that a predetermined loading amount was obtained, each exhaust gas purification filter was prepared by firing at 700 ° C. for 2 hours and sealing.

(PM deposition)
Each exhaust purification filter prepared as described above was dried at 200 ° C. for 5 hours, the weight A was measured, and PM discharged from the actual engine was deposited. Then, after making it dry at 200 degreeC for 5 hours, the weight B was measured. The PM deposition amount was calculated by the following formula (1).
[Equation 1]

PM deposition amount (g / L) = (B−A) / 15 × 1000 (1)

(T90 measurement)
An NOx storage catalyst is installed in front of each exhaust purification filter after PM deposition, and after raising the temperature to 600 ° C. in a nitrogen atmosphere, exhaust model gas (O ₂ = 4%, NO = 250 ppm, N ₂ balance gas) Was introduced so that SV = 100,000 / hour, and PM was burned and removed. At this time, the CO and CO ₂ emissions accompanying PM combustion were measured, and the PM purification rate with respect to the reaction time was obtained from the integrated value.
Here, FIG. 5 is a diagram showing the relationship between the reaction time and the PM purification rate. As shown in FIG. 5, the reaction time until the PM purification rate reaches 90% is defined as T90, which is used as an index of PM purification performance. That is, the smaller the T90, the higher the PM purification performance, and the larger the T90, the lower the PM purification performance.

FIG. 6 is a diagram illustrating T90 of each example and comparative example.
As shown in FIG. 6, all of Examples 1 to 5 were found to have small T90 and high PM purification performance as compared with the comparative example. From this result, the specific surface area of the Ce-containing oxide as 0.5m ² /g~105.6m ² / g, increasing the Ag surface concentration on the Ce-containing oxide 25.1% ～67.7% Thus, it was confirmed that the PM purification performance can be improved.

Moreover, when a calcination temperature exceeded 1200 degreeC (Example 4), it turned out that there is no big change in T90 and the further improvement of PM purification performance is not recognized. This is because when the firing temperature exceeds 1200 ° C., the surface concentration of Ag is excessively increased, the oxygen supply ability from the Ce-containing oxide is decreased, and the specific surface area is excessively decreased so that Ag is added to the Ce-containing oxide. It is thought that this is because it cannot be supported. From this result, the lower limit value of the specific surface area of the Ce-containing oxide is preferably 13.0 m ² / g, and the upper limit value of the Ag surface concentration on the Ce-containing oxide is preferably 45.7. confirmed.

Moreover, it turned out that T90 is small and it has high PM purification performance in the range whose baking temperature is 1100 degreeC (Example 2)-1200 degreeC (Example 4). Among these, when the firing temperature was 1100 ° C. (Example 2), it was found that T90 was the smallest and the highest PM purification performance was obtained. From this result, the lower limit value of the specific surface area of the Ce-containing oxide is preferably 13.0 m ² / g, and the Ag surface concentration on the Ce-containing oxide is 29.6% to 45.7%. It was confirmed that is more preferable.

  FIG. 7 is a diagram showing the relationship between the Ag surface concentration and T90 created based on the results of the examples and comparative examples. Also from FIG. 7, according to this example, it was confirmed that the PM purification performance higher than that of the comparative example was obtained, and the usefulness of limiting the numerical value of the Ag surface concentration defined in the present invention was confirmed.

[CO purification performance]
For each of the exhaust purification filters of Examples 2, 4, and 5, the exhaust model gas (CO = 0.11%, O ₂ = 10%, N ₂ balance gas) was flowed at 15 L / min (SV = 60,000 / hour). Introduced to be. At this time, the temperature was raised from room temperature to 450 ° C. at 10 ° C./min. By measuring the CO content in the discharged gas with a gas chromatograph, the CO purification rate% was calculated.

FIG. 8 is a graph showing the CO purification rates of Examples 2, 4, and 5.
As shown in FIG. 8, when the firing temperature is 1100 ° C. (Example 2) and 1200 ° C. (Example 4), the CO purification rate is almost the same, but the firing temperature is 1300 ° C. (Example 5). ), It was found that the CO purification rate was significantly reduced. This was thought to be because the specific surface area was extremely small at 1 m ² / g or less when the firing temperature reached 1300 ° C., and the oxidation performance (OSC performance) of the Ce-containing oxide was lost.
Therefore, from this result, in order to achieve both PM purification performance and CO purification performance, the lower limit value of the specific surface area of the Ce-containing oxide is set to 13.0 m ² by setting the upper limit value of the Ce-containing oxide to 1200 ° C. It was confirmed that the upper limit of the Ag surface concentration on the Ce-containing oxide is preferably 45.7. In this regard, the same can be said for the HC purification rate as for the CO purification rate.

[Examples 6 to 10, Comparative Example 2]
Ce _84.9 La _5.1 Pr _5.0 Si _5.0 O ₂ as the Ce-containing oxide, Ag nitrate, so that the Ag content in the catalyst is a predetermined mass% with respect to the target production amount. A predetermined amount of each 5% aqueous solution of Pd nitrate was weighed, and an appropriate amount of distilled water was mixed to obtain a solution A. Next, the solution A was evaporated to dryness with an evaporator to obtain a catalyst B carrying Ag, and then the catalyst B was dried at 200 ° C. and then calcined at 700 ° C. for 2 hours to prepare an Ag-based catalyst.

As the Ce-containing oxide, one having a specific surface area of 50 m ² / g measured by the same measurement method as in the above example was used. Further, the Ag content in the catalyst of Example 6 is 30% by mass, the Ag content in the catalyst of Example 7 is 35% by mass, the Ag content in the catalyst of Example 8 is 40% by mass, The Ag content in the catalyst of Example 9 was 45% by mass, the Ag content in the catalyst of Example 10 was 50% by mass, and the Ag content in the catalyst of Comparative Example 2 was 60% by mass.

For the catalysts of Examples 6 to 10 and Comparative Example 2, the Ag surface concentration was measured by the same measurement method as in the above Examples. Further, the PM purification performance of the catalysts of Examples 6 to 10 was evaluated by the same measurement method as in the above Examples. However, as aging conditions, hydrothermal aging (O ₂ = 10%, H ₂ O = 6%, N ₂ balance gas) was performed at 750 ° C. for 21 hours.

FIG. 9 is a graph showing the relationship between the Ag content and the Ag surface concentration in the catalysts of Examples 6 to 10 and Comparative Example 2. As shown in FIG. 9, when the specific surface area of the Ce content oxide is constant (50 m ² / g), the Ag content increases to 50% by mass after the Ag surface concentration increases as the Ag content increases. It has been found that the Ag surface concentration decreases when the amount exceeds.
Moreover, FIG. 10 is a figure which shows the relationship between Ag content and T90 in the catalyst of Examples 6-10. As shown in FIG. 10, when the specific surface area of the Ce content oxide is constant (50 m ² / g), when the Ag content exceeds 45 mass%, T90 starts to deteriorate, and when the Ag content exceeds 50 mass%. It turned out that T90 deteriorates significantly.
This is because, when the specific surface area of the Ce-containing oxide is constant at 50 m ² / g, when the Ag content exceeds 50% by mass, the embedding of Ag in the Ce-containing oxide is given priority. Was also considered to decrease when the Ag content exceeded 50 mass%. From this result, it was confirmed that the Ag content is preferably 30% by mass to 45% by mass.

[Examples 11 to 13]
Ce _84.9 La _5.1 Pr _5.0 Si _5.0 O ₂ as the Ce-containing oxide, Ag nitrate, so that the Ag content in the catalyst is 40% by mass with respect to the target production amount. A predetermined amount of each 5% aqueous solution of Pd nitrate was weighed, and an appropriate amount of distilled water was mixed to obtain a solution A. Next, the solution A was evaporated to dryness with an evaporator to obtain a catalyst B carrying Ag, and then the catalyst B was dried at 200 ° C. and then calcined at 700 ° C. for 2 hours to prepare an Ag-based catalyst.

In Example 11, a Ce-containing oxide having a specific surface area of 35 m ² / g measured by the same measurement method as in the above example was used. In Example 12, a Ce-containing oxide having a specific surface area of 50 m ² / g measured by the same measurement method as in the above example was used. In Example 13, as the Ce-containing oxide, one having a specific surface area of 65 m ² / g measured by the same measurement method as in the above example was used.

About the catalyst of Examples 11-13, PM purification performance was evaluated with the measuring method similar to the said Example. However, as aging conditions, hydrothermal aging (O ₂ = 10%, H ₂ O = 6%, N ₂ balance gas) was performed at 750 ° C. for 21 hours.

FIG. 11 is a diagram showing the relationship between the specific surface area of the Ce-containing oxide and T90 in the catalysts of Examples 11 to 13. As shown in FIG. 11, under the constant Ag content of 40% by mass, the T90 is almost constant even if the specific surface area of the Ce content oxide changes in the range of 35 to 65 m ² / g. I understood. From this result, when the Ag content is 50% by mass or less, the upper limit of the specific surface area of the Ce content oxide is preferably 65 m ² / g, and together with the results of the above examples, the ratio of the Ce content oxide surface ^area, it was confirmed preferably in the range of 13.0m ² / g~65m 2 / g.

Claims (4)

An exhaust purification filter that is provided in an exhaust passage of an internal combustion engine and captures and purifies particulate matter in the exhaust of the internal combustion engine,
A porous filter substrate;
A catalyst that is supported on the filter substrate and oxidizes and purifies the particulate matter,
The catalyst has a Ce-containing oxide containing Ce, and Ag supported on the Ce-containing oxide,
The content of Ag in the catalyst is 50% by mass or less,
The specific surface area of the Ce-containing oxide ^is 0.5m ² /g~105.6m 2 / g,
The exhaust gas purification filter according to claim 1, wherein the surface concentration of Ag on the Ce-containing oxide is 25.1% to 67.7% in terms of element. The Ce-containing oxide has a specific surface area of 13.0 m ² / g or more,
2. The exhaust gas purification filter according to claim 1, wherein a surface concentration of Ag on the Ce-containing oxide is 45.7% or less in terms of element. The specific surface area of the Ce-containing oxide ^is 13.0m ² /g~65.0m 2 / g,
3. The exhaust gas purification filter according to claim 1, wherein the surface concentration of Ag on the Ce-containing oxide is 29.6% to 45.7% in terms of element.   4. The exhaust gas purification filter according to claim 1, wherein a content of the Ag in the catalyst is 30% by mass to 45% by mass.

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