JP2013141649A - Catalyst-equipped particulate filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently advance the combustion of PM (Particulate matter) accumulated on a particulate filter.SOLUTION: A catalyst layer 7 of the exhaust gas passage wall of the filter contains: Zr-Nd complex oxide wherein NdOcontent is 5 mol.% or above and 30 mol.% or below; Zr-Nd-Pr complex oxide wherein PrOcontent is 10 mol.% or above and 35 mol.% or below; and a catalyst metal. The mixing ratio between Zr-Nd complex oxide and Zr-Nd-Pr complex oxide is, by mass, 70:30 to 10:90.

Description

  The present invention relates to a particulate filter with a catalyst provided with a catalyst that collects particulates discharged from an engine and burns and removes the collected particulates.

  A filter for collecting particulates (PM: Particulate matter) in exhaust gas is provided in an exhaust gas passage of an automobile equipped with a lean combustion engine such as a diesel engine. When the amount of PM deposited on the filter increases, the filter is clogged. Therefore, the PM accumulation amount is estimated based on the pressure difference of the pressure sensors provided before and after the filter, and when the accumulation amount reaches a predetermined value, engine fuel injection control (fuel increase, post-injection, etc.) Thus, the temperature of the exhaust gas reaching the filter is raised, and PM is burned and removed. In order to promote the combustion of PM, a catalyst is generally carried on the exhaust gas passage wall of the filter.

  For example, in Patent Document 1, a catalyst material in which a catalyst metal is supported on a composite oxide containing Zr, Nd, and a rare earth metal R other than Ce and Nd is provided on an exhaust gas passage wall of a filter. Have been described. Further, when Pr is employed as the rare earth metal R, the composite oxide is advantageous for maintaining oxygen ion conductivity even after being exposed to a high-temperature atmosphere, having excellent oxygen storage / release performance, and combustion of PM. This is described in the same document.

JP 2008-221204 A

  By the way, in the conventional particulate filter with catalyst, when the amount of PM deposited on the surface of the catalyst layer is small, the PM is combusted and removed relatively efficiently. However, when the amount of PM deposited is large, it takes time for the PM to be removed by combustion. This tendency is seen. The reason is as follows according to findings based on experiments and research by the present inventors.

  That is, the graph of FIG. 1 schematically shows a change with time of the PM remaining ratio when PM deposited on the catalyst layer burns. Initially, the combustion of PM proceeds rapidly, but after passing through the rapid combustion region (for example, the first combustion period until the PM remaining ratio becomes 100% to 50%), the PM combustion becomes slow (PM remaining) It shifts to the combustion late stage until the ratio becomes 50% to 0%. This point will be described in detail below.

  As shown in the photograph of FIG. 2, at the beginning of combustion, PM is in contact with the catalyst layer supported on the surface of the filter. For this reason, for example, when the catalyst layer contains Ce-based oxide particles or Zr-based oxide particles, as schematically shown in FIG. 3, active internal oxygen released from these oxide particles is generated in the catalyst layer. It is supplied in a highly active state to the contacting PM. As a result, the PM on the catalyst layer surface burns rapidly.

  However, as described above, the PM on the surface of the catalyst layer is burned and removed. As a result, a gap of about several tens of μm is partially formed between the catalyst layer and the PM deposit layer as shown in the photograph of FIG. Therefore, as schematically shown in FIG. 5, the active oxygen released from the inside of the oxide particles maintains the activity for a very short time, but the activity decreases while passing through the gap. It becomes the same normal oxygen as the oxygen in it. As a result, the combustion of PM becomes slow. Of course, as shown in the upper left and lower left of FIG. 5, the oxygen in the exhaust gas also contributes to the combustion of PM, but the combustion is slower than the combustion by the active oxygen described above.

  On the other hand, it is conceivable that the catalyst layer is formed in a porous structure having large internal voids so that PM can easily enter the catalyst layer. According to this, PM is dispersed and deposited not only on the surface of the catalyst layer but also inside the catalyst layer, so that most of the PM comes into contact with the catalyst and is easily combusted. However, since the catalyst layer becomes bulky as a result of forming a large internal space, there is a problem that the communication hole in the exhaust gas passage wall of the filter is likely to be blocked and the flow resistance of the exhaust gas passing through the filter is increased. In addition, there is a problem that the manufacturing cost increases due to the formation of such a catalyst layer.

  Therefore, the present invention allows the combustion to proceed efficiently in both the rapid combustion region and the slow combustion region of PM deposited on the filter.

  In order to solve the above problems, the present invention combines a ZrNd composite oxide having a predetermined composition range and a ZrNdPr composite oxide having a predetermined composition range.

That is, in the invention according to claim 1, the catalyst layer containing the ZrNd composite oxide, the ZrNdPr composite oxide, and the catalyst metal is provided on the exhaust gas passage wall of the filter that collects the particulates in the exhaust gas. In particulate filter with catalyst,
The content of Nd ₂ O ₃ in the ZrNd composite oxide is 5 mol% or more and 30 mol% or less, and the content of Pr ₂ O ₃ in the ZrNdPr composite oxide is 10 mol% or more and 35 mol% or less. And the mixing ratio of the ZrNd composite oxide and the ZrNdPr composite oxide is in the range of 70:30 to 10:90 by mass ratio.

  According to the experiment and research by the present inventor, both the ZrNd composite oxide and the ZrNdPr composite oxide have high oxygen ion conductivity, and oxygen is taken into the inside by an oxygen exchange reaction to release active oxygen. In particular, the ZrNdPr composite oxide has excellent oxygen exchange reaction characteristics in an oxygen-rich atmosphere and releases a large amount of active oxygen. On the other hand, the ZrNd composite oxide, compared with the ZrNdPr composite oxide, has a small amount of active oxygen released by itself, but PM combustion using active oxygen, in particular, PM is in contact with the oxide surface. It excels in combustion in a state where

  Although the specific mechanism is not clear, PM combustion in the particulate filter with a catalyst of the present invention is considered as follows.

  Since the ZrNd composite oxide and the ZrNdPr composite oxide are mixed and as a result, both are in partial contact, the ZrNdPr composite oxide having a large oxygen release amount is likely to be an oxygen supply source for the ZrNd composite oxide. That is, oxygen released from the ZrNdPr composite oxide is taken into the ZrNd composite oxide. Alternatively, oxygen released from the ZrNdPr composite oxide is supplied by spilling over the particle surface of the ZrNd composite oxide. As a result, under conditions where PM is in contact with the catalyst (rapid combustion region), combustion of PM by active oxygen proceeds efficiently on the surface of the ZrNd composite oxide particles.

  On the other hand, in the above-described slow combustion region in which a gap is partially generated between the PM deposition layer and the catalyst layer, the contact between PM and the ZrNd composite oxide is reduced. However, although it is small, at the contact interface, PM proceeds on the particle surface of the ZrNd composite oxide due to the above-described effect that the ZrNdPr composite oxide becomes an oxygen supply source. Furthermore, the ZrNdPr composite oxide has the ability to supply active oxygen to PM, which is relatively poor in contact with the oxide surface, with respect to the ZrNd composite oxide. Continuous PM combustion from the rapid combustion zone is ensured.

Here, when the ZrNd composite oxide has a Nd ₂ O ₃ content of 5 mol% or more and 30 mol% or less, the ZrNdPr composite oxide has a Pr ₂ O ₃ content of 10 mol% or more and 35 mol% or less. When it is, PM is burned efficiently. As described above, when the ZrNdPr composite oxide serves as an oxygen supply source for the ZrNd composite oxide, the mixing ratio of the ZrNd composite oxide and the ZrNdPr composite oxide is in the range of 70:30 to 10:90 by mass ratio. In this case, PM combustion proceeds efficiently.

  As the catalyst metal, it is preferable to employ a noble metal, and it is particularly preferable to employ Pt.

The invention according to claim 2 is a particulate filter with catalyst, wherein a catalyst layer is provided on an exhaust gas passage wall of a filter that collects particulates in exhaust gas.
The catalyst layer contains a ZrNdPr composite oxide carrying a catalyst metal and provided on the exhaust gas passage wall, and a ZrNd composite oxide carrying a catalyst metal and provided on the lower layer. With an upper layer,
The content of Nd ₂ O ₃ in the ZrNd composite oxide is 5 mol% or more and 30 mol% or less, and the content of Pr ₂ O ₃ in the ZrNdPr composite oxide is 10 mol% or more and 35 mol% or less. It is characterized by being.

In the case of the present invention, since the ZrNd composite oxide supporting the catalyst metal is contained in the upper layer, PM in the exhaust gas is likely to be deposited on the filter in contact with the ZrNd composite oxide. As described above, oxygen released from the ZrNd composite oxide is highly reactive with PM in contact with the ZrNd composite oxide. Therefore, according to the layer configuration of the present invention, efficient combustion of PM is achieved. To be advantageous. Also in this case, the lower ZrNdPr composite oxide becomes an oxygen supply source for the upper ZrNd composite oxide, and active oxygen having high reactivity with PM is actively released from the ZrNd composite oxide. When the ZrNd composite oxide has a Nd ₂ O ₃ content of 5 mol% or more and 30 mol% or less, the ZrNdPr composite oxide has a Pr ₂ O ₃ content of 10 mol% or more and 35 mol% or less. At a certain time, since PM combustibility is good, PM combustion proceeds efficiently.

  As the catalyst metal, it is preferable to employ a noble metal, and it is particularly preferable to employ Pt.

According to the first aspect of the present invention, the exhaust gas passage wall of the filter has a ZrNd composite oxide having a Nd ₂ O ₃ content of 5 mol% or more and 30 mol% or less, and a Pr ₂ O ₃ content of 10 mol%. A catalyst layer containing a ZrNdPr composite oxide of 35 mol% or less and a catalyst metal is provided, and the mixing ratio of the ZrNd composite oxide and the ZrNdPr composite oxide is in the range of 70:30 to 10:90 by mass ratio. Therefore, according to the invention according to claim 2, the catalyst layer of the exhaust gas passage wall includes a lower layer and an upper layer, and in the lower layer, the ZrNdPr content of Pr ₂ O ₃ is 10 mol% or more and 35 mol% or less. catalytic metal is supported on composite oxide, because the catalytic metal ZrNd composite oxide Nd ₂ O ₃ content is less than 5 mol% to 30 mol% in the top layer is supported, ZrNd composite oxide and ZrN Pr mixed oxide and the combustion of the PM I coupled with the effect that proceeds efficiently obtained.

It is a graph which shows typically a time-dependent change of PM residual ratio when PM deposited on the catalyst layer burns. It is a microscope picture which shows the state (state in the rapid combustion area of FIG. 1) where PM deposit layer is contacting the catalyst layer. It is a schematic diagram which shows the combustion mechanism of PM in a rapid combustion area. It is a microscope picture which shows the state (state in the slow combustion area of FIG. 1) where the clearance gap was made between the catalyst layer and the soot deposition layer. It is a schematic diagram which shows the combustion mechanism of PM in a slow combustion area. It is a figure which shows the state which has arrange | positioned the particulate filter in the exhaust gas path of an engine. It is a front view which shows the same filter typically. It is a longitudinal cross-sectional view which shows the same filter typically. It is an expanded sectional view showing typically the exhaust gas passage wall of the filter. It is a perspective view which shows the instrument for carbon deposition. Is a graph showing the relationship between the _Nd 2 _{O 3} content of ZrNd composite oxide and the carbon burning rate. It is a graph showing the relationship between the _Pr 2 _{O 3} content of ZrNdPr composite oxide and the carbon burning rate. It is a graph which shows the relationship between the mixing rate of ZrNd complex oxide and ZrNdPr complex oxide, and a carbon combustion rate.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.

<Particulate filter structure>
FIG. 6 shows a particulate filter (hereinafter simply referred to as “filter”) 1 arranged in the exhaust gas passage 11 of the diesel engine. In the exhaust gas passage 11 on the upstream side of the exhaust gas flow from the filter 1, an oxidation catalyst (not shown) in which a catalytic metal typified by Pt, Pd or the like is supported on a support material such as activated alumina can be disposed. When such an oxidation catalyst is disposed on the upstream side of the filter 1, the HC and CO in the exhaust gas are oxidized by the oxidation catalyst, and the temperature of the exhaust gas flowing into the filter 1 is increased by the oxidation combustion heat to heat the filter 1. This is advantageous for PM removal by combustion. Further, NO is oxidized to NO ₂ by the oxidation catalyst, and the NO ₂ is supplied to the filter 1 as an oxidant for burning PM.

  As schematically shown in FIGS. 7 and 8, the filter 1 has a honeycomb structure and includes a large number of exhaust gas passages 2 and 3 extending in parallel with each other. That is, in the filter 1, the exhaust gas inflow passage 2 whose downstream end is closed by the plug 4 and the exhaust gas outflow passage 3 whose upstream end is closed by the plug 4 are alternately provided. Is separated by a thin partition wall 5. In FIG. 7, hatched portions indicate the plugs 4 at the upstream end of the exhaust gas outflow passage 3.

In the filter 1, the filter body including the partition walls 5 is formed of an inorganic porous material such as cordierite, SiC, Si ₃ N ₄ , or sialon. The exhaust gas flowing into the exhaust gas inflow passage 2 flows out into the adjacent exhaust gas outflow passage 3 through the surrounding partition walls 5 as indicated by arrows in FIG. That is, as shown in FIG. 9, the partition wall 5 has minute pores (exhaust gas passages) 6 that connect the exhaust gas inflow passage 2 and the exhaust gas outflow passage 3, and the exhaust gas passes through the pores 6. PM is trapped and accumulated mainly in the exhaust gas inflow passage 2 and the wall portions of the pores 6.

  A catalyst layer 7 is formed on the wall surface forming the exhaust gas passage (exhaust gas inflow passage 2, exhaust gas outflow passage 3 and pore 6) of the filter body. It is not always necessary to form a catalyst layer on the wall surface on the exhaust gas outflow passage 3 side.

<Embodiment 1>
In the first embodiment, the catalyst layer 7 of FIG. 9 includes a ZrNd composite oxide having an Nd ₂ O ₃ content of 5 mol% to 30 mol%, and a Pr ₂ O ₃ content of 10 mol% to 35 mol%. The ZrNdPr composite oxide and the catalytic metal are contained, and the mixing ratio of the ZrNd composite oxide and the ZrNdPr composite oxide is in the range of 70:30 to 10:90 by mass ratio.

  The catalyst layer 7 can be formed by the following method. That is, the ZrNd composite oxide powder and the ZrNdPr composite oxide powder are mixed uniformly. When adopting Pt as the catalyst metal, a solution obtained by diluting a dinitrodiamine platinum nitrate solution with ion-exchanged water so as to have a predetermined Pt carrying amount is added to the mixture, followed by evaporation to dryness. The dried product is dried at 150 ° C. in the air, pulverized, and calcined at 500 ° C. for 2 hours in the air to obtain a catalyst powder. The slurry containing the catalyst powder and binder is milled and then coated on the filter, followed by drying and firing. Thus, the catalyst layer 7 is formed. In the catalyst layer 7, the ZrNd composite oxide particles supporting the catalyst metal and the ZrNdPr composite oxide particles supporting the catalyst metal are mixed.

  The ZrNd composite oxide powder can be prepared by a coprecipitation method. That is, by co-precipitation by neutralization by mixing an 8-fold diluted solution of 28% by mass ammonia water as a basic solution into a nitric acid solution obtained by mixing a zirconyl oxynitrate solution, neodymium nitrate hexahydrate and ion-exchanged water. Get things. The solution containing this coprecipitate is centrifuged to remove the supernatant (dehydration), and ion-exchanged water is further added and stirred (water washing). Remove basic solution. The coprecipitate after the final dehydration is dried at 150 ° C. in the air, pulverized, and fired at 500 ° C. for 2 hours in the air. Thereby, ZrNd composite oxide powder can be obtained. A ZrNdPr composite oxide powder can also be obtained from a nitric acid solution containing a zirconyl oxynitrate solution, neodymium nitrate hexahydrate, and praseodymium nitrate by the coprecipitation method described above.

  Hereinafter, the present embodiment will be specifically described based on examples.

[Test 1: Formulation of preferred Nd ₂ O ₃ content of ZrNd composite oxide]
-Test sample preparation-
A plurality of ZrNd composite oxides having different Nd ₂ O ₃ contents were prepared, and Pt was supported at 2.4% by mass in each. A sample filter (particulate filter with catalyst) was obtained by coating the obtained catalyst powder on a filter. As the filter, a SiC honeycomb filter having a cell wall thickness of 16 mil (4.064 × 10 ⁻¹ mm) and 178 cells per square inch (645.16 mm ² ) (capacity 11.3 mL (diameter 17 mm × diameter) The coating amount of the catalyst powder per 1 L of the filter was 20.5 g / L (of which the Pt amount was about 0.5 g / L), and at the upstream and downstream ends of the sample filter. Was plugged with the stopper 4 shown in FIGS.

-Measurement of carbon burning rate-
In order to see the PM combustion performance of the sample filter, carbon (carbon black) was deposited on each sample filter after aging, and the carbon combustion rate was measured. Aging is a heat treatment in which the sample filter is kept at a temperature of 800 ° C. in the atmosphere for 24 hours.

  FIG. 10 shows an instrument for carbon deposition. In the figure, 11 is a container for containing carbon powder, to which an air supply pipe 12 and a carbon powder pressure feed pipe 13 are connected. Carbon powder is put into the container 11, a sample filter 14 is fitted to the tip of the pressure feeding pipe 13, and air is blown into the container 11 from the air supply pipe 12. As a result, the carbon powder rolls up and diffuses in the container 11 and flows along with the air through the pressure feed tube 13 and accumulates on the sample filter 14.

  The carbon powder to be used is pulverized so that there is no portion aggregated by ultrasonic treatment. In addition, the container 11 is charged with carbon powder in an amount of 7 g / L deposited per 1 L of the sample filter. That is, the amount of slip (the amount of carbon that slips through without being deposited on the sample filter 14) is grasped in advance, and the container 11 contains carbon powder in an amount that is the sum of the amount deposited (7 g / L) and the amount of slip. Put in. The air may be blown at SV = 12000 / h for 3 minutes.

Each of the obtained sample filters was attached to a simulated gas flow reactor, and the gas temperature was raised while flowing N ₂ gas. After the filter inlet temperature was stabilized at 580 ° C., the simulated exhaust gas was switched from N ₂ gas to simulated exhaust gas (O ₂ ; 7.5%, remaining N ₂ ), and flowed at a space velocity of 40000 / h. Then, the CO and CO ₂ gas concentrations produced by carbon combustion are measured in real time at the filter outlet, and from these concentrations, the carbon combustion rate (unit time) is determined at predetermined intervals using the following formula. Per PM combustion amount) was calculated.

Carbon burning rate (g / h)
= {Gas flow rate (L / h) x [(CO + CO ₂ ) concentration (ppm) / (1 x 10 ⁶ )]} x 12 (g / mol) /22.4 (L / mol)

  The time-dependent change in the integrated value of the carbon combustion amount is obtained based on the carbon combustion rate for each predetermined time, and the time required for the carbon combustion rate to reach from 0% to 90% and the integrated value of the carbon combustion amount during that time are calculated. The combustion rate (PM combustion amount per minute (1 mg / min-L) in the filter 1 L) was determined. The results are shown in Table 1 and FIG.

The carbon burning rate increases as the Nd ₂ O ₃ content increases, reaches a maximum at 15 mol%, and then decreases. This is because, in the ZrNd composite oxide, as the ratio of trivalent Nd to tetravalent Zr increases, oxygen defects increase and oxygen ion conductivity increases. If oxygen defects increase excessively, the oxygen defects are reversed. This is thought to be due to hindering the movement of oxygen ions. From Table 1 and FIG. 11, it can be seen that when the Nd ₂ O ₃ content in the ZrNd composite oxide is 5 mol% or more and 30 mol% or less, the carbon burning rate becomes larger than ZrO ₂ . A more preferable Nd ₂ O ₃ content is 10 mol% or more and 25 mol% or less.

[Test 2: Formulation of preferred Pr ₂ O ₃ content of ZrNdPr composite oxide]
A plurality of ZrNdPr composite oxides having different Pr ₂ O ₃ contents (Nd ₂ O ₃ contents were all 15 mol%) were prepared, and Pt was supported on each so as to be 2.4 mass%. A sample filter (particulate filter with catalyst) was obtained by coating the obtained catalyst powder on the same filter as in Test 1. As in Test 1, the coating amount of the catalyst powder was 20.5 g / L (of which the Pt amount was about 0.5 g / L), and the upstream and downstream ends of the sample filter were sealed. Then, carbon was deposited on each sample filter after aging by the same method as in Test 1, and the carbon burning rate was measured. The results are shown in Table 2 and FIG.

In the case of the ZrNdPr composite oxide, the carbon burning rate increases as the Pr ₂ O ₃ content increases, reaches a maximum at 20 mol%, and then tends to decrease. From Table 2 and FIG. 12, when the Pr ₂ O ₃ content in the ZrNdPr composite oxide is 5 mol% or more and 40 mol% or less, the Nd ₂ O ₃ content is more carbon than the 15 mol% ZrNd composite oxide. It can be seen that the speed increases. A suitable Pr ₂ O ₃ content is 10 mol% or more and 35 mol% or less.

[Test 3: Formulation of suitable mixing ratio of ZrNd composite oxide and ZrNdPr composite oxide]
Based on the results of Test 1 and Test 2, _Nd 2 _{O 3} and ZrNd composite oxide powder content of 15 mol%, _Nd 2 _{O 3} content of 15 mol%, _Pr 2 _{O 3} content of 20 mol% of ZrNdPr composite An oxide powder was prepared. A plurality of mixed powders having different mixing ratios of the ZrNd composite oxide and the ZrNdPr composite oxide were prepared, and Pt was supported on each so as to be 2.4% by mass. A sample filter (particulate filter with catalyst) was obtained by coating the obtained catalyst powder on the same filter as in Test 1.

  As in Test 1, the coating amount of the catalyst powder was 20.5 g / L (of which the Pt amount was about 0.5 g / L), and the upstream and downstream ends of the sample filter were sealed. Then, carbon was deposited on each sample filter after aging by the same method as in Test 1, and the carbon burning rate was measured. The results are shown in Table 3 and FIG. 13 together with the results of the case of the ZrNd composite oxide alone in Test 1 and the case of the ZrNdPr composite oxide alone in Test 2.

  The carbon burning rate is maximum when the mixing ratio of the ZrNd composite oxide and the ZrNdPr composite oxide is 30:70. It can be seen that when the mixing ratio is in the range of 70:30 to 10:90, the carbon burning rate is higher than in the case of the ZrNd composite oxide alone and the ZrNdPr composite oxide alone. This is considered to be a result of the active release of active oxygen from the ZrNd composite oxide using the ZrNdPr composite oxide as an oxygen supply source. A more preferred mixing ratio is in the range of 50:50 to 10:90.

<Embodiment 2>
In the second embodiment, the catalyst layer 7 in FIG. 9 includes a lower layer and an upper layer, and the lower layer contains a ZrNdPr composite oxide having a Pr ₂ O ₃ content of 10 to 35 mol% supporting a catalyst metal, Is characterized in that it contains a ZrNd composite oxide having a Nd ₂ O ₃ content of 5 to 30% by mole supporting a catalyst metal.

  The catalyst layer 7 can be formed by the following method. That is, when adopting Pt as a catalyst metal, a solution obtained by diluting a dinitrodiamine platinum nitrate solution with ion-exchanged water so as to have a predetermined Pt loading amount is added to each of the ZrNd composite oxide powder and the ZrNdPr composite oxide powder, and evaporated. Dry to dryness. The dried product is dried at 150 ° C. in the air, pulverized, and calcined at 500 ° C. for 2 hours in the air to obtain a Pt-supported ZrNd composite oxide powder and a Pt-supported ZrNdPr composite oxide powder. Thus, first, the filter is coated with the slurry containing the Pt-supported ZrNdPr composite oxide powder and the binder, dried and fired, and then the slurry containing the Pt-supported ZrNd composite oxide powder and the binder is coated, dried and The catalyst layer 7 is formed by baking.

  Hereinafter, the present embodiment will be specifically described based on examples.

Based on the results of Test 1 and Test 2, _Nd 2 _{O 3} and ZrNd composite oxide powder content of 15 mol%, _Nd 2 _{O 3} content of 15 mol%, _Pr 2 _{O 3} content of 20 mol% of ZrNdPr composite An oxide powder was prepared. Pt was supported on each of these composite oxide powders at 2.4% by mass to obtain Pt-supported ZrNd composite oxide powder and Pt-supported ZrNdPr composite oxide powder.

  First, a filter was coated with Pt-supported ZrNdPr composite oxide powder together with a binder, dried and fired to form a lower layer. Next, the Pt-supported ZrNd composite oxide powder was coated on a filter together with a binder, dried and fired to form an upper layer. This obtained the sample filter (particulate filter with a catalyst) which concerns on an Example. The coating amount of each of the lower layer and the upper layer is 10.25 g / L (of which the Pt amount is about 0.25 g / L). Sealing was applied to the upstream and downstream ends of the sample filter. Then, carbon was deposited on the sample filter after aging by the same method as in Test 1, and the carbon burning rate was measured.

  As a comparative example, the upper layer and the lower layer were reversed from the examples, that is, a sample filter in which the upper layer contained a Pt-supported ZrNdPr composite oxide and the lower layer contained a Pt-supported ZrNd composite oxide was prepared. The carbon burning rate was measured under the same conditions and method. The coating amount of each of the lower layer and the upper layer is 10.25 g / L (of which the Pt amount is about 0.25 g / L).

  The results of Examples and Comparative Examples are shown in the case of the ZrNd composite oxide alone in Test 1, the case of the ZrNdPr composite oxide alone in Test 2, and the Pt-supported ZrNd composite oxide / Pt-supported ZrNdPr composite oxide in Test 3. It shows in Table 4 together with the result of a mixing case (mixing ratio 50:50).

  The sample combustion filter (ZN upper layer + ZNP lower layer) of the example has the highest carbon burning rate. In the comparative example in which the upper layer and the lower layer are opposite to those of the example, the carbon burning rate is lower than that of the mixing case (ZN + ZNP mixing). In the case of the example (ZN upper layer + ZNP lower layer), carbon was deposited in contact with the upper ZrNd composite oxide, and as a result, oxygen released from the ZrNd composite oxide was considered to have worked effectively on carbon combustion. .

  The present invention can be applied not only to a diesel engine but also to a filter that collects particulates in exhaust gas of a lean burn gasoline engine.

1 Filter 2 Exhaust gas inflow passage (exhaust gas passage)
3 Exhaust gas outflow passage (exhaust gas passage)
5 Bulkhead 6 Fine pore (exhaust gas passage)
7 Catalyst layer

Claims (2)

In the particulate filter with catalyst, in which the catalyst layer containing ZrNd composite oxide, ZrNdPr composite oxide, and catalytic metal is provided on the exhaust gas passage wall of the filter that collects particulates in the exhaust gas,
The content of Nd ₂ O ₃ in the ZrNd composite oxide is 5 mol% or more and 30 mol% or less, and the content of Pr ₂ O ₃ in the ZrNdPr composite oxide is 10 mol% or more and 35 mol% or less. A catalytic particulate filter, wherein a mixing ratio of the ZrNd composite oxide and the ZrNdPr composite oxide is in a range of 70:30 to 10:90 by mass ratio. In the particulate filter with catalyst, in which the catalyst layer is provided on the exhaust gas passage wall of the filter that collects particulates in the exhaust gas,
The catalyst layer contains a ZrNdPr composite oxide carrying a catalyst metal and provided on the exhaust gas passage wall, and a ZrNd composite oxide carrying a catalyst metal and provided on the lower layer. With an upper layer,
The content of Nd ₂ O ₃ in the ZrNd composite oxide is 5 mol% or more and 30 mol% or less, and the content of Pr ₂ O ₃ in the ZrNdPr composite oxide is 10 mol% or more and 35 mol% or less. Particulate filter with catalyst characterized by being.