JP6044605B2 - Particulate filter with catalyst and method for producing the same - Google Patents

Description

  The present invention relates to a particulate filter with catalyst and a method for producing the same.

  The exhaust gas of diesel engines and lean-burn gasoline engines contains particulates (particulate particulate matter) mainly composed of carbon. Therefore, a filter is arranged in the exhaust gas passage to collect particulates, and when the collected amount increases, the particulates are burned and removed from the filter to regenerate the filters. It is. A catalyst is supported on the filter body in order to promote the combustion of the particulates.

  As the catalyst, a Pt / alumina catalyst in which Pt is supported on alumina is known. Patent Document 1 describes that after a particulate material having a predetermined particle size distribution is supported on a filter body, the particulate material is impregnated with a Pt solution to support Pt. Examples of the granular material include γ-alumina, ceria and the like, and it is described in the literature that the granular material may contain an alkaline earth metal in order to impart NOx absorption and reduction ability. ing.

JP 2005-152774 A

  Alkaline earth metals occlude NOx in the exhaust gas and produce nitrates. When this alkaline earth metal is supported on the filter body, the particulates are oxidized by the active oxygen released along with the decomposition of the nitrate formed by storing NOx, and this reaction promotes the burning of the particulates. it is conceivable that.

  The inventor mixed Pt-supported active alumina and an active oxygen release material (oxide that takes in oxygen in exhaust gas and releases the oxygen as active oxygen), coats the filter body, and then adds alkaline earth. The metal salt was made into an aqueous solution and impregnated in the coating layer to be supported. And when the combustion test of the particulate was done, the improvement of the particulate combustion performance was recognized by the use of alkaline earth metal, but the combustion improvement effect was low unexpectedly.

  The present inventor repeated experiments to investigate the cause of the fact that the effect of improving the combustion of particulates by alkaline earth metals is small unexpectedly. As a result, in the above alkaline earth metal loading method, the alkaline earth metal is supported on the active alumina and the active oxygen release material substantially evenly, but the alkaline earth metal supported on the active oxygen release material is particulate. It was recognized that it had a negative effect on the combustion of. That is, when the amount of the alkaline earth metal supported on the active oxygen release material increases, the active oxygen release amount of the active oxygen release material decreases, or the active sites on the surface of the active oxygen release material are covered. The metal was found to have a lower burning effect of particulates than expected.

  Accordingly, an object of the present invention is to prepare a catalyst so that an alkaline earth metal effectively works to promote combustion of particulates, suppress the amount of catalyst metal such as Pt, and reduce the cost of the catalyst. To do.

  In order to solve the above-mentioned problems, the present invention actively supports an alkaline earth metal on the binder of the catalyst.

The catalyst-attached particulate filter presented here is a particulate combustion catalyst provided on the exhaust gas passage wall of the filter body that collects particulates in the exhaust gas.
The catalyst includes active alumina, an active oxygen release material composed of one or more oxides that take in oxygen in exhaust gas and release the oxygen as active oxygen, a catalyst metal, an alkaline earth metal, Contains a finer binder than the activated alumina particles,
The alkaline earth metal is carried on each of the activated alumina and the binder,
The total amount of the alkaline earth metal supported on each of the activated alumina and the binder is 90% by mass or more of the total amount of the alkaline earth metal contained in the catalyst.

  In the above particulate filter with catalyst, the alkaline earth metal supported on each of the activated alumina and the binder traps NOx in the exhaust gas. At this time, the alkaline earth metal changes from carbonate to nitrate. When the filter is regenerated (at the time of particulate removal), the nitrate is decomposed as the exhaust gas temperature rises, and the active oxygen released by the decomposition of the nitrate and the active oxygen release material are released. Active oxygen serves as an oxidant to promote particulate combustion by the catalytic metal.

  Here, when the amount of alkaline earth metal in the catalyst increases, the amount of active oxygen released by the decomposition of nitrate increases accordingly, which is advantageous for promoting the combustion of particulates. However, as described above, when the amount of the alkaline earth metal supported by the active oxygen release material increases, the release of active oxygen is suppressed, which is disadvantageous for promoting the combustion of particulates. In the case of activated alumina, it does not release active oxygen. However, when the amount of alkaline earth metal supported increases, the catalytic metal supported on the activated alumina is covered with alkaline earth metal, and the catalytic activity is increased. Becomes lower.

  Therefore, in the present invention, 90% by mass or more of the total amount of the alkaline earth metal is divided and supported on the activated alumina and the binder. This makes it possible to increase the amount of alkaline earth metal in the entire catalyst by supporting the alkaline earth metal in the binder while suppressing the amount of alkaline earth metal supported on the activated alumina, thereby promoting the combustion of particulates. To be advantageous.

  As the binder, an alumina binder or a zirconia binder can be preferably used.

  In a preferred embodiment of the particulate filter with catalyst, the supported ratio of the alkaline earth metal to the activated alumina is 2% by mass or more and 7.8% by mass or less, and the supported ratio of the alkaline earth metal to the binder is 1. It is 1 mass% or more and 17.1 mass% or less. Thereby, an alkaline earth metal can be effectively used for promoting the combustion of particulates.

  In a preferred embodiment of the particulate filter with catalyst, the proportion of the amount of the alkaline earth metal supported on the activated alumina in the total amount of the alkaline earth metal supported on each of the activated alumina and the binder is 24% by mass. It is more than 95 mass%, It is characterized by the above-mentioned. Thereby, an alkaline earth metal can be effectively used for promoting the combustion of particulates. More preferably, the proportion is 48% by mass or more and 85% by mass or less.

  A preferred embodiment of the particulate filter with catalyst is characterized in that the active oxygen release material includes a Ce-containing composite oxide and a Ce-free Zr-based composite oxide. Here, the Ce-containing composite oxide is a Ce-free Zr-based composite oxide that absorbs oxygen in the exhaust gas and releases it as active oxygen by a reversible reaction involving Ce valence change. Has high ionic conductivity and releases oxygen by taking oxygen into the interior by oxygen exchange reaction.

Further, a method for producing a particulate filter with catalyst, in which a catalyst for particulate combustion is provided on an exhaust gas passage wall of a filter body that collects particulates in exhaust gas, presented here,
Active alumina, active oxygen release material composed of one or more oxides that take in oxygen in exhaust gas and release it as active oxygen, alkaline earth metal, catalyst metal, and finer particles than the above active alumina particles A process for preparing a binder,
A step of supporting the entire amount of the alkaline earth metal separately in the activated alumina and the binder;
Forming a slurry in which the activated alumina carrying the alkaline earth metal, the binder carrying the alkaline earth metal, and the active oxygen release material are mixed;
Coating the slurry on the filter body;
A step of supporting the catalytic metal on the active alumina and the active oxygen release material before forming the slurry, or supporting the catalyst metal on the coating layer after coating the slurry on the filter body. Features.

  As a result, a particulate filter with catalyst in which an alkaline earth metal is supported on each of the activated alumina and the binder is obtained. Further, since the total amount of the alkaline earth metal is supported in advance divided into activated alumina and the binder, even if a part of the alkaline earth metal is eluted in the slurry, 90% by mass or more of the total amount of the activated earth and Remain in the binder. Therefore, the desired particulate filter with catalyst can be obtained.

  According to the particulate filter with catalyst of the present invention, the catalyst contains activated alumina, an active oxygen release material, a catalytic metal, an alkaline earth metal, and a fine binder, and the total amount of the alkaline earth metal is the above. Since 90% by mass or more is supported on activated alumina and a binder, the combustion of particulates can be promoted by active oxygen released by the decomposition of nitrates composed of alkaline earth metals, and filter regeneration. This is advantageous for shortening the time required for the engine and for improving the fuel efficiency of the engine. In addition, the amount of catalyst metal used can be reduced, which is advantageous for cost reduction.

  According to the method for producing a particulate filter with a catalyst of the present invention, the entire amount of alkaline earth metal is loaded separately into activated alumina and a binder, the activated alumina carrying the alkaline earth metal, and the alkaline earth metal. Since the active oxygen release material is mixed to form a slurry and this slurry is coated on the filter body, 90% by mass or more of the total amount of the alkaline earth metal is dispersed in the active alumina and the binder. Thus, a supported particulate filter with catalyst can be obtained.

The figure which has arrange | positioned the filter with a catalyst in the exhaust-gas channel | path of an engine. The front view which shows the same filter typically. The longitudinal cross-sectional view which shows the same filter typically. The expanded sectional view which shows typically the exhaust-gas channel | path wall of the same filter. Sectional drawing which shows the structure of the catalyst of the filter typically. The figure which shows the pore distribution of La containing alumina and pure alumina. The graph which shows the carbon combustion performance of each reference catalyst. The graph which shows the relationship between the loading ratio of Sr with respect to activated alumina, and carbon combustion performance. The graph which shows the relationship between the loading ratio of Sr with respect to a binder, and carbon combustion performance. The graph which shows the relationship between the ratio of Sr carry | supported to the activated alumina in the total amount of Sr carried | supported by the activated alumina and the binder, and carbon combustion performance. The graph which shows the peak top temperature of the exothermic peak accompanying the carbon combustion of the activated alumina powder which carry | supported only Pt, and the activated alumina powder which carry | supported Pt and various alkaline-earth metals.

  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.

  As shown in FIG. 1, a particulate filter with catalyst (hereinafter simply referred to as “filter with catalyst”) 10 is disposed in an exhaust gas passage 11 of a diesel engine or the like, and particulates (hereinafter referred to as “PM” in exhaust gas). ")"). An oxidation catalyst (not shown) in which a catalyst metal such as Pt is supported on a support material made of an oxide or the like can be disposed in the exhaust gas passage 11 upstream of the filter 10 in the exhaust gas flow.

[Filter structure]
As schematically shown in FIGS. 2 and 3, the catalyst-equipped filter 10 has a honeycomb structure and includes a large number of exhaust gas passages 12 and 13 extending in parallel with each other. Exhaust gas inflow passages 12 whose downstream ends are closed by plugs 14 and exhaust gas outflow passages 13 whose upstream ends are closed by plugs 14 are alternately provided, and the exhaust gas inflow passages 12 and 13 They are separated by a thin partition wall 15. In FIG. 2, the hatched portion indicates the plug 14 at the upstream end of the exhaust gas outflow passage 13.

In the filter with catalyst 10, the filter body including the partition wall 15 is formed of an inorganic porous material such as cordierite, SiC, Si ₃ N ₄ , sialon, or AlTiO ₃ . The exhaust gas flowing into the exhaust gas inflow passage 12 flows out into the adjacent exhaust gas outflow passage 13 through the surrounding partition wall 15 as shown by an arrow in FIG. As shown in FIG. 4, the partition wall 15 has minute pores (exhaust gas passages) 16 communicating the exhaust gas inflow passage 12 and the exhaust gas outflow passage 13, and the exhaust gas passes through the pores 16. PM is trapped and deposited mainly in the exhaust gas inflow passage 12 and the walls of the pores 16.

  The wall surface forming the exhaust gas passage (exhaust gas inflow passage 12, exhaust gas outflow passage 13 and pore 16) of the filter body is coated with a catalyst 20. It is not always necessary to provide a catalyst on the wall surface on the exhaust gas outflow path 13 side.

[About catalyst]
Next, the configuration of the catalyst 20 will be described.

  As schematically shown in FIG. 5, the catalyst 20 includes a plurality of types of active alumina 21 and 22 and a plurality of types of active oxygen release materials 23 and 24 that take in oxygen in exhaust gas and release the oxygen as active oxygen. contains. This will be specifically described below.

  This embodiment has two types of activated aluminas 21 and 22, both of which are mainly γ-alumina, and one of them is pure alumina (first alumina) 21 containing no additive, The other is La-containing alumina (second alumina) 22 containing about 4% by mass of La as an additive. The pure alumina 21 and the La-containing alumina 22 carry Pt 25 and an alkaline earth metal 26 as catalyst metals, respectively.

The catalyst metal is not limited to Pt25, and other catalyst metals such as Pd may be used, or a plurality of types of catalyst metals may be supported. In the present embodiment, the catalyst 20, for containing the active alumina 21 and 22 carrying the PT25, the NO be oxidized to NO ₂ at high efficiency, which is advantageous in combustion promotion of PM. In this embodiment, not only the bulky La-containing alumina 22 but also pure alumina 21 is used as the activated alumina, so that the total bulk can be suppressed as compared with the case where only the La-containing alumina 22 is used. This is advantageous for preventing clogging of the exhaust gas passage of the filter with catalyst.

This embodiment has two types of active oxygen release materials 23 and 24. One active oxygen release material 23 is made of a Ce-containing composite oxide, and the other active oxygen release material 24 is made of a Ce-free Zr-based composite oxide. In the present embodiment, as one of the active oxygen release material 23, Rh-doped CeZrNd mixed oxide Rh forms a solid solution with (Rh-doped CeZrNdO _X) employed between crystal lattice or lattice of CeZrNd mixed oxide, the other active oxygen As the release material 24, a ZrNdPr composite oxide (ZrNdPrO _X ) is employed. The active oxygen releasing materials 23 and 24 also carry Pt25.

  As the active oxygen release material 24 made of a Ce-free Zr-based composite oxide, it is preferable to use a material having an average pore diameter of 20 nm or more and 60 nm or less. In the filter with catalyst 10, the gas space velocity per catalyst weight becomes very large. However, when the active oxygen release material 24 having a relatively large pore diameter is used, not only the exhaust gas contacts the surface but also the exhaust gas Active oxygen can be generated efficiently because it easily contacts the pores. As a result, it is advantageous for promoting combustion of PM.

  In the catalyst 20, the support materials (the activated aluminas 21 and 22 and the active oxygen release materials 23 and 24) are bonded to each other, and the alkaline earth metal 26 is also supported on the binder 27 that holds the catalyst 20 on the partition wall 15. Yes. The binder 27 is made of oxide particles finer than the particles of the activated aluminas 21 and 22.

  In a preferred embodiment, the total supported amount of the plurality of types of activated aluminas 21 and 22 is 4 g / L or more and 10 g / L or less, and the supported amount of the active oxygen release material 23 made of Ce-based composite oxide is 4 g / L or more and 10 g / L. Hereinafter, the supported amount of the active oxygen release material 24 made of Ce-free Zr-based composite oxide is 6 g / L or more and 15 g / L or less.

  When the above pure alumina and La-containing alumina are used as the plurality of activated aluminas 21 and 22, it is preferable that the mass ratio between them is pure alumina / La-containing alumina = 1/8 or more and 4/1 or less. The total supported amount of Pt25 with respect to the plural types of mixed activated aluminas 21 and 22 is preferably 0.3 g / L or more and 0.4 g / L or less. The amount of Pt supported on each of the active oxygen release materials 23 and 24 is preferably 0.07 g / L or more and 1.0 g / L or less. The amount of alkaline earth metal supported on the activated aluminas 21 and 22 and the binder 27 will be described later.

[Estimation of PM combustion promotion mechanism]
When the exhaust gas temperature rises, PM trapped in the filter main body is burned by the catalytic action of Pt 25 carried on the activated aluminas 21 and 22 and the activated oxygen release materials 23 and 24. Pt-supported alumina in which Pt is supported on activated aluminas 21 and 22 has a function of oxidizing NO in exhaust gas to NO ₂ , and this NO ₂ becomes an oxidant that burns PM. Is promoted.

  The active oxygen release materials 23 and 24 promote the combustion of PM by releasing active oxygen. Here, the Ce-free Zr-based composite oxide 24 takes in oxygen from the inside by an oxygen exchange reaction and releases active oxygen. Therefore, Pt supported on the Zr-containing composite oxide 24 is kept in a highly active oxidized state and has excellent PM combustion performance. On the other hand, the Ce-containing composite oxide 23 has a high oxygen storage / release capability, and even if oxygen at the combustion site is locally consumed with the combustion of PM, the Ce-containing composite oxide 23 quickly accelerates oxygen. PM combustion is maintained by being supplemented by.

The alkaline earth metal 26 supported on the activated aluminas 21 and 22 and the binder 27 is carbonate when not storing NOx, and stores NOx in the exhaust gas in the form of nitrate (for example, Sr). In this case, SrCO ₃ ← → Sr (NO ₃ ) ₂ ) or NOx is adsorbed. As the exhaust gas temperature rises, the nitrate is decomposed, and the active oxygen released by the decomposition of the nitrate promotes the combustion of the particulates.

  Moreover, the filter with a catalyst has the following characteristics by using a mixture of pure alumina 21 and La-containing alumina 22 as active alumina.

As shown in FIG. 6 showing the pore distribution measurement results of pure alumina 21 and La-containing alumina 22 (using SIMADZU, micrometrics TriStar 3000), the pore distribution of pure alumina 21 has a sharp peak near the pore diameter of 10 nm. On the other hand, the pore distribution of the La-containing alumina 22 has a broad peak extending from around 10 nm to a larger size, and many pores having a diameter exceeding 10 nm are included. In the example of FIG. 6, the average pore diameter of the pure alumina 21 is 10.07 nm, the average pore volume is 0.537 cm ³ / g, the average pore diameter of the La-containing alumina 22 is 13.15 nm, Its average pore volume is 0.822 cm ³ / g.

Thus, in the case of the pure alumina 21, since the pore diameter is smaller than that of the La-containing alumina 22, the amount of Pt 25 supported on the surface increases. As a result, according to the pure alumina 21, the exhaust gas easily comes into contact with the Pt 25 and a large amount of NO ₂ is generated, which is advantageous for promoting the combustion of PM. In addition, unlike the La-containing alumina 22 (basic), the pure alumina 21 is amphoteric and has an acid point, and therefore has a strong force for bonding Pt25. Therefore, even if Pt25 is exposed to high-temperature exhaust gas, it is difficult to aggregate, and good PM combustibility is maintained for a long time.

  On the other hand, the La-containing alumina 22 has a characteristic that the bulk specific gravity is smaller than that of the pure alumina 21, that is, it is bulky but has high heat resistance. Moreover, being bulky means that the gas diffusibility is good and the contact with the exhaust gas is good.

  Therefore, by mixing the pure alumina 21 and the La-containing alumina 22, the PM combustibility can be enhanced by the pure alumina 21 while ensuring the heat resistance and gas diffusibility of the catalyst by the La-containing alumina 22. In addition, the use of pure alumina 21 can suppress the bulkiness of the activated alumina as a whole. That is, it is possible to avoid an increase in the catalyst volume and, in turn, a reduction in the exhaust gas passage of the filter. Therefore, an increase in the back pressure of the engine due to the filter with the catalyst is suppressed, and filter clogging is less likely to occur and the frequency of filter regeneration processing is reduced, so that deterioration in fuel consumption can be avoided.

[Method of manufacturing filter with catalyst]
As activated alumina such as La-containing alumina and pure alumina, commercially available powders can be used. The Rh-doped CeZrNd composite oxide as the active oxygen release material 23 and the ZrNdPr composite oxide as the active oxygen release material 24 can be obtained by the following preparation methods.

-Preparation of Rh-doped CeZrNd composite oxide-
Dissolve cerium nitrate hexahydrate, zirconyl oxynitrate solution, neodymium nitrate hexahydrate, and rhodium nitrate solution in ion-exchanged water. A coprecipitate is obtained by mixing and neutralizing this nitrate solution with an 8-fold diluted solution of 28% by mass ammonia water. A dehydration operation in which the solution containing the coprecipitate is centrifuged to remove the supernatant and a water washing operation in which ion-exchanged water is added and stirred are repeated alternately as many times as necessary. The coprecipitate after the final dehydration is dried in the atmosphere at 150 ° C. for a whole day and then pulverized by a ball mill. Thereafter, the Rh-doped CeZrNd composite oxide particle material can be obtained by firing in the atmosphere at 500 ° C. for 2 hours.

-Preparation of ZrNdPr composite oxide-
Praseodymium nitrate hexahydrate, zirconyl oxynitrate solution and neodymium nitrate hexahydrate are dissolved in ion-exchanged water. A coprecipitate is obtained by mixing and neutralizing this nitrate solution with an 8-fold diluted solution of 28% by mass ammonia water. A dehydration operation in which the solution containing the coprecipitate is centrifuged to remove the supernatant and a water washing operation in which ion-exchanged water is added and stirred are repeated alternately as many times as necessary. The coprecipitate after the final dehydration is dried in the atmosphere at 150 ° C. for a whole day and then pulverized by a ball mill. Thereafter, the ZrNdPr composite oxide can be obtained by firing in the atmosphere at 500 ° C. for 2 hours.

-Pt support on active oxygen release material-
Rh-doped CeZrNd composite oxide and ZrNdPr composite oxide are mixed, and ion-exchanged water is added to this to form a slurry, which is sufficiently stirred with a stirrer or the like. While continuing this stirring, a predetermined amount of ethanolamine Pt (hexahydroxoplatinum (IV) acid ethanolamine solution) is dropped into the slurry and stirred sufficiently. Thereafter, stirring is continued while heating to completely evaporate moisture. After evaporation, the obtained dried product is pulverized and baked at 500 ° C. for 2 hours in the air. Thereby, a catalyst powder in which Pt is supported on each composite oxide particle material is obtained.

-Loading Pt and alkaline earth metal on activated alumina-
A plurality of types of activated alumina (pure alumina and La-containing alumina) are mixed, and ion exchange water is added to form a slurry, which is sufficiently stirred by a stirrer or the like. Subsequently, a predetermined amount of ethanolamine Pt is dropped into the slurry while stirring, and a predetermined amount of alkaline earth metal salt solution (alkaline earth metal acetate in ion-exchanged water is added to the slurry while stirring. The dissolved solution) is added dropwise and stirred thoroughly. Thereafter, stirring is continued while heating to completely evaporate water. After evaporation, the obtained dried product is pulverized and baked at 500 ° C. for 2 hours in the air. As a result, catalyst powders in which Pt and alkaline earth metal carbonate are supported on the respective active aluminas are obtained.

Here, ethanolamine Pt is a complex of ethanolamine and Pt, and compared with a Pt raw material (Pt-P salt) having a planar tetragonal molecular structure in which a nitro group and an amine group are coordinated around Pt. It has an octahedral molecular structure in which a hydroxyl group is coordinated around Pt. In addition, since ethanolamine (NH ₃ C ₂ H ₅ OH) is present around the Pt-hydroxyl group complex, the complex is large. Therefore, when ethanolamine Pt is used, most of the complex is supported on the surface of the active alumina or active oxygen release material without entering the pores. That is, many Pt can be arrange | positioned on the surface of those support materials. As a result, the contact rate between Pt and the exhaust gas can be increased, the oxidation efficiency of NO in the exhaust gas by Pt can be improved, and the amount of NO ₂ generated can be increased. As a result, PM combustion efficiency can be improved.

-Loading of alkaline earth metal on binder-
A binder (for example, alumina sol) is dissolved in ion-exchanged water, and after sufficiently stirring with a stirrer or the like, a predetermined amount of an alkaline earth metal salt (for example, an alkaline earth metal acetate) is dissolved. Thereafter, stirring is continued while heating to completely evaporate water. After evaporation, the obtained dried product is pulverized and baked at 500 ° C. for 2 hours in the air. Thereby, the alkaline earth metal carbonate is supported on the binder. This is pulverized by a ball mill so that the number average particle diameter is about 30 nm to 150 nm. And an alkaline earth metal carrying | support binder is obtained by adding ion-exchange water to this.

  The following method can also be adopted for supporting the alkaline earth metal on the binder. That is, after the alkaline earth metal salt is dissolved in ion-exchanged water containing a binder, the mixture is sufficiently stirred with a stirrer or the like, and then an aqueous ammonium solution is dropped so that the pH is 7 to 8 for the purpose of pH adjustment. Then, by stirring with a stirrer or the like, a precursor of an alkaline earth metal compound is deposited on the binder particles. After that, as in the previous loading method, moisture is completely evaporated, and the resulting dried product is pulverized and baked, and then pulverized to a predetermined average particle size by a ball mill, and ion exchange is performed on this. An alkaline earth metal-supported binder can be obtained by adding water.

-Coating of catalyst powder on filter body-
Active alumina catalyst powder (powder in which pure alumina and La-containing alumina are supported with Pt and alkaline earth metal) and active oxygen release material powder (Rh-doped CeZrNd composite oxide and ZrNdPr composite oxide are each supported with Pt) And a binder carrying an alkaline earth metal are mixed. Ion exchange water is added to the obtained mixed powder and mixed to form a slurry. And it grind | pulverizes until it becomes number average particle diameter 200nm or more and about 400nm or less (preferably about 300nm) with a ball mill, and coats this slurry on a filter main body. And after drying at 150 degreeC in air | atmosphere, baking for 2 hours is performed at 500 degreeC in air | atmosphere. Thereby, a filter with a catalyst is obtained.

[Reference example]
Each filter of Reference Example 1-5 was prepared using Sr as the alkaline earth metal and having a different amount of Sr supported on activated alumina as shown in Table 1. Table 2 shows the specifications of the used filter body, activated alumina, and activated oxygen release material.

  In Reference Example 1-3, a zirconia binder not supporting an alkaline earth metal was used as the binder, and the others were prepared by the same method as the above-described method for producing a filter with catalyst. Here, when a slurry in which the active alumina catalyst powder and the active oxygen release material are mixed is formed, a part of Sr is eluted from the active alumina into the slurry, and the active oxygen release material (Rh-doped CeZrNd composite oxide and ZrNdPr composite oxide). Small amount). The amount of Sr supported on the activated alumina and the amount of Sr supported on the active oxygen release material in Reference Example 1-3 in Table 1 was 90% by mass of the total amount of Sr previously supported on the activated alumina, remaining 8% of the total amount of Sr. Is a value calculated by assuming that the active oxygen releasing material is supported by the slurry.

  In Reference Example 4, the coating layer is impregnated with the Sr solution, so that Sr is supported on the active alumina and the active oxygen release material. The specific preparation method is as follows.

  That is, a plurality of types of activated alumina (pure alumina and La-containing alumina) are mixed, and ion-exchanged water is added to form a slurry, which is sufficiently stirred with a stirrer or the like. Subsequently, a predetermined amount of ethanolamine Pt is dropped into the slurry while stirring, and the mixture is sufficiently stirred. Thereafter, stirring is continued while heating to completely evaporate water. After evaporation, the obtained dried product is pulverized and baked at 500 ° C. for 2 hours in the air. As a result, catalyst powder in which Pt is supported on each activated alumina is obtained.

  A catalyst powder in which only Pt is supported on this active alumina (pure alumina and La-containing alumina) and the above-mentioned active oxygen release material powder (powder in which Pt is supported on each of the Rh-doped CeZrNd composite oxide and the ZrNdPr composite oxide) A zirconia binder solution and ion exchange water are added to the mixed powder and mixed to form a slurry. The slurry is coated on the filter body and dried at 150 ° C. in the atmosphere. Then, the coating layer of the filter body is impregnated with a predetermined amount of Sr solution (a solution of Sr acetate in ion-exchanged water) and baked in the atmosphere at 500 ° C. for 2 hours.

  In the case of Reference Example 4, since Sr is impregnated and supported on the active alumina and the active oxygen release material, the mass ratio of Sr to active alumina and the mass ratio of Sr to the active oxygen release material are the same.

  In Reference Example 5, only Pt is supported on active alumina, and the active alumina supporting Pt and the active oxygen releasing material supporting Pt are mixed and coated on the filter body.

[PM combustion performance evaluation of reference example]
Each filter of the reference example was aged at a temperature of 800 ° C. for 24 hours in the atmosphere, and then the PM combustion performance of each filter was examined.

  First, ion exchange water was added to carbon black corresponding to 5 g / L, and the carbon black was sufficiently dispersed by stirring using a stirrer. The inlet end of the aged filter was immersed in the obtained slurry, and suction was performed with an aspirator from the outlet end. Moisture that could not be removed by this suction was removed by air blow from the end face of the filter immersed in the slurry. And the filter was dried by hold | maintaining at the temperature of 150 degreeC for 2 hours.

Each of the obtained filters was attached to a fixed-bed model gas flow device, and the gas temperature at the filter inlet was increased from room temperature to 580 ° C. while N ₂ gas was allowed to flow through the filter. After the temperature stabilizes at 580 ° C., the gas composition is switched to “7.5% O ₂ +300 ppm NO + N ₂ (balance gas)” while maintaining the temperature, and the space velocity of the model gas is set to 40000 / h. Washed away. Then, by measuring the concentration of a model gas of CO and CO ₂ generated by the combustion of carbon was measured the time course of carbon combustion amount in the filter. Each time required until carbon burned 30%, 50% burned, 70% burned, and 90% burned was determined.

  The results are shown in FIG. It can be seen that Reference Example 1-4 containing Sr generally has better PM combustion performance than Reference Example 5 containing no Sr. When the reference example 1-3 is seen, the tendency for PM combustion performance to fall is seen as the load of Sr with respect to activated alumina increases. This is recognized as a result that the proportion of the active sites on the activated alumina covered with the Sr compound increased as the amount of Sr supported increased. Reference Example 1 and Reference Example 4 have the same Sr loading on activated alumina, but Reference Example 1 has better PM combustion performance. This is because, in Reference Example 4, a large amount of Sr is supported on the active oxygen release material, and therefore the active oxygen release performance is lowered by the Sr compound, and the active sites of the active oxygen release material are covered with Sr. It is recognized.

[Examples and Comparative Examples]
Based on the above reference examples, Sr is used as the alkaline earth metal, alumina binder is used as the binder, and the filters of Examples 1-8 and Comparative Examples 1 and 2 are prepared by the above-described method for manufacturing a filter with catalyst. did. Table 2 shows the specifications of the filter main body, activated alumina, and active oxygen releasing material used in the examples and comparative examples.

  Here, in Examples 1-8 and Comparative Examples 1 and 2, the total amount of Sr contained in the catalyst is the same at 0.58 g / L, but the amount of Sr supported on the binder is different as shown in Table 3. Comparative Example 1 is a case where a filter with catalyst was prepared by supporting the entire amount of Sr on a binder. Comparative Example 2 is a case where a filter with catalyst was prepared by supporting the entire amount of Sr on activated alumina. Example 1-8 is a case where a filter with a catalyst was prepared by supporting Sr separately in activated alumina and a binder.

[PM combustion performance evaluation of Examples and Comparative Examples]
Each filter of Example 1-8 and Comparative Examples 1 and 2 was aged at a temperature of 800 ° C. for 24 hours in the atmosphere, and then PM combustion performance of each filter (required until 90% of carbon burned) Time) was examined by the PM combustion performance evaluation method described above. The results are shown in FIGS. 8-10. In each graph of FIGS. 8-10, the leftmost plot is Comparative Example 1, the rightmost plot is Comparative Example 2, and the middle eight plots are Example 1-8 in order from the left.

  As is apparent from FIGS. 8-10, when Sr is dispersed and supported in activated alumina and a binder as in the example, the carbon combustion time tends to be shortened.

  In the case of Comparative Example 2 (wherein the total amount of Sr is supported on activated alumina), the active sites of activated alumina are covered with Sr, and the active sites are more effective than the effect of promoting carbon combustion by active oxygen released by the decomposition of Sr nitrate. It is recognized that the carbon combustion time is prolonged because the effect of lowering the carbon combustibility due to the reduction is increased.

  On the other hand, in the case of the example, by supporting a part of Sr on the binder, the ratio of the active sites of the activated alumina covered with Sr is reduced, and Pt supported on the activated alumina is effective for carbon combustion. In addition, it is recognized that the combustion of carbon was promoted by active oxygen released by the decomposition of Sr nitrate supported on the binder and activated alumina.

  However, when the supporting ratio of Sr with respect to the activated alumina decreases and the supporting ratio of Sr with respect to the binder increases, the carbon combustibility decreases. The Pt supported on the activated alumina promotes the storage of NOx in the exhaust gas into the Sr. However, the effect of promoting the storage of the NOx is hardly exerted on the Sr supported on the binder. As a result, it is recognized that as the amount of Sr with respect to the binder increases, the total amount of active oxygen released by the decomposition of nitrate that promotes the combustion of particulates decreases.

  As is clear from the description of the previous reference example, in the filter with catalyst, a small amount of Sr eluted from the activated alumina or the binder into the slurry is supported on the active oxygen release material.

  When Sr is dispersed and supported on activated alumina and a binder, according to FIG. 8, the supported ratio of Sr to activated alumina is preferably 2% by mass or more and 7.8% by mass or less, and 4% by mass or more and 7% by mass or less. It can be said that it is more preferable. Further, in the case of the dispersion loading, according to FIG. 9, the loading ratio of Sr to the binder is preferably 1.1% by mass or more and 17.1% by mass or less, and preferably 2.8% by mass or more and 11.4% by mass. It can be said that the following is more preferable. Further, in the case of the dispersion support, according to FIG. 10, the ratio of the amount of Sr supported on the activated alumina in the total amount of Sr supported on the activated alumina and the binder is set to be 24 mass% or more and 95 mass% or less. It can be said that 48 mass% or more and 85 mass% or less is still more preferable.

[Other alkaline earth metals]
An activated alumina powder sample carrying Pt and four activated alumina powder samples each carrying Pt and one alkaline earth metal carbonate were prepared. Each sample and 20 mg of carbon black were mixed (tight contact) for 1 minute only with the weight of the agate mortar. 5 mg of each mixed powder was weighed and placed in a DTA thermal analyzer using an alumina pan. A temperature increase test was performed at 10 ° C./min with an air flow of “20% O ₂ +500 ppm NO ₂ / N ₂ ” (total flow rate 100 cc / min). Commercial α-alumina powder was used as a reference in the DTA analysis. The peak top temperature of the exothermic peak accompanying carbon combustion was read.

  The results are shown in FIG. The sample carrying the alkaline earth metal has a lower DTA peak top temperature than the sample not carrying the alkaline earth metal, and it can be seen that the PM combustibility is improved by loading the alkaline earth metal. The DTA peak top temperature is lower in the order of Mg → Sr → Ca → Ba, and it can be seen that the PM combustion start temperature is lowest when Ba is supported.

  In the above embodiment, one kind of alkaline earth metal is supported on the activated alumina and the binder, but two or more kinds of alkaline earth metals may be supported.

10 Filter with catalyst 11 Exhaust gas passage 12 Exhaust gas inflow passage (exhaust gas passage of filter)
13 Exhaust gas outflow passage (filter exhaust gas passage)
14 Plug 15 Bulkhead (Exhaust gas passage wall)
16 pores (exhaust gas passage of the filter)
20 Catalyst 21 Pure alumina (activated alumina)
22 La-containing alumina (activated alumina)
23 Ce-free Zr-based composite oxide 24 Ce-containing composite oxide 25 Pt (platinum)
26 Alkaline earth metal 27 Binder

Claims (4)

A particulate filter with a catalyst in which a catalyst for particulate combustion is provided on an exhaust gas passage wall of a filter body that collects particulates in exhaust gas,
The catalyst includes active alumina, an active oxygen release material composed of one or more oxides that take in oxygen in exhaust gas and release the oxygen as active oxygen, a catalyst metal, and an alkaline earth metal. , Containing a finer binder than the activated alumina particles,
The alkaline earth metal is carried on each of the activated alumina and the binder,
The particulate filter with catalyst, wherein the total amount of the alkaline earth metal supported on each of the activated alumina and the binder is 90% by mass or more of the total amount of the alkaline earth metal contained in the catalyst. In claim 1,
The supporting ratio of the alkaline earth metal to the activated alumina is 2% by mass or more and 7.8% by mass or less,
A particulate filter with a catalyst, wherein a supporting ratio of the alkaline earth metal to the binder is 1.1% by mass or more and 17.1% by mass or less. In claim 1 or claim 2,
A ratio of the amount of the alkaline earth metal supported on the activated alumina to the total amount of the alkaline earth metal supported on each of the activated alumina and the binder is 24% by mass or more and 95% by mass or less. Particulate filter with catalyst. A method for producing a particulate filter with a catalyst, wherein a particulate combustion catalyst is provided on an exhaust gas passage wall of a filter body that collects particulates in exhaust gas,
Active alumina, active oxygen release material composed of one or more oxides that take in oxygen in exhaust gas and release it as active oxygen, alkaline earth metal, catalyst metal, and finer particles than the above active alumina particles A process for preparing a binder,
A step of supporting the entire amount of the alkaline earth metal separately in the activated alumina and the binder;
Forming a slurry in which the activated alumina carrying the alkaline earth metal, the binder carrying the alkaline earth metal, and the active oxygen release material are mixed;
Coating the slurry on the filter body;
A step of supporting the catalytic metal on the active alumina and the active oxygen release material before forming the slurry, or supporting the catalyst metal on the coating layer after coating the slurry on the filter body. A method for producing a particulate filter with a catalyst.