JP2009090235A - Catalyst material for purification of exhaust gas ingredient and particulate filter equipped with the catalyst material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the performance of purifying exhaust gas ingredients, including HCs, CO and particulates, and the heat resistance of the performance. <P>SOLUTION: A catalyst metal is supported by a support material in which primary particles of activated alumina and those of a composite oxide containing Ce, Zr and a rare earth metal R other than Ce are mixed to form secondary particles. The primary particles of the composite oxide contain CeO<SB>2</SB>at a ratio of 20-60 mol%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

    The present invention relates to an exhaust gas component purification catalyst material and a particulate filter with the catalyst material.

    In diesel engines that use light oil-based fuels and gasoline engines that burn leanly using gasoline-based fuels, in addition to HC (hydrocarbon), CO, and NOx (nitrogen oxides) Are known to contain particulates (particulate matter PM; suspended particulate matter containing carbon particles). Therefore, in order to suppress discharge of the particulates into the atmosphere, a filter for collecting the particulates is disposed in the exhaust gas passage of the engine. However, if the particulate accumulation amount of this filter increases, engine output and fuel consumption are reduced. Therefore, it is necessary to combust the accumulated particulate matter and remove it from the filter.

    In order to efficiently perform the combustion of the particulates (the particulates ignite at a relatively low temperature and complete the combustion in a short time), an alumina carrying a catalyst metal is disposed on the wall of the exhaust gas passage of the filter body. Formation of the catalyst layer containing is performed. This Pt-supported alumina is not only effective for purifying HC and CO, but also effective for burning particulates. In recent years, filter catalyst materials for burning particulates more efficiently have been developed.

    For example, Patent Document 1 describes that a catalyst material in which a catalytic metal such as Pt is supported on a composite oxide of a rare earth metal R selected from Pr, Nd, and La, Ce, and Zr is used for a filter. The content of R in the composite oxide is preferably 2 mol% or more and 11 mol% or less. Since such a complex oxide contains Ce, it has an oxygen storage / release capability, and oxygen released from the complex oxide promotes ignition and combustion of particulates.

    Patent Document 2 discloses a composite oxide ZrRO particle of R and Zr selected from Yb, Nd and Sc (R content is 18 mol% at the maximum), and a rare earth metal M and Ce selected from Sm and Gd. It is described that a catalyst material containing composite oxide CeMO particles and having a catalyst metal supported on the composite oxide particles is used for a filter. The ZrRO particles have oxygen ion conductivity and release active oxygen, but the oxygen release mechanism is different from that of CeZr-based composite oxide as disclosed in Patent Document 1.

    That is, the CeZr-based composite oxide has a high oxygen storage capacity and releases active oxygen due to a change in the valence of Ce ions. On the other hand, ZrRO particles have oxygen ion conductivity, so-called oxygen pumping function, and when there are a high oxygen concentration portion and a low oxygen concentration portion on the particle surface, the low oxygen oxygen concentration portion to the low oxygen concentration portion. Oxygen ions are transported to and released as active oxygen.

    Therefore, in the case of the above ZrRO particles, a small fire type that burns particulates can be formed on the surface, and when the fire type part is in an oxygen-deficient state, oxygen is transported from another part having a high oxygen concentration, and thus combustion continues. As a result, the combustion region easily spreads from the fire type.

    Patent Document 3 describes that a catalyst material containing ZrRO and alumina having oxygen ion conductivity as described above and having a catalyst noble metal supported thereon is used for the filter.

Patent Document 4 describes a method for producing an exhaust gas component purification catalyst material. That is, by adding ammonia water excessively to a mixed solution of an aqueous solution of Al nitrate and an aqueous solution of La nitrate, the first hydroxide containing Al and La is precipitated, and then mixing of an aqueous solution of Ce nitrate and an aqueous solution of Zr nitrate By adding a liquid, a second hydroxide containing Ce and Zr is deposited on the precipitate of the first hydroxide, and the resulting precipitate is filtered, dried and fired. . According to this production method, a catalyst material in which activated alumina particles containing La serve as a core and the entire surface is covered with a CeZr composite oxide as a shell material can be obtained.
JP 2006-326573 A JP 2007-54713 A JP 2007-83224 A JP 2007-98200 A

    The CeZr-based composite oxide particles having the above-described oxygen storage capacity and the Zr-based composite oxide particles having oxygen ion conductivity promote the oxidative purification of HC and CO, and also ignite particulates deposited on the filter. Although it promotes combustion, it has the following problems.

    That is, these composite oxide particles can be obtained by a coprecipitation method in which a basic solution is added to and mixed with an acidic solution containing metal ions such as Ce and Zr, and the resulting precipitate is dried and fired. In this case, primary particles of the composite oxide are formed by firing the precipitate, and the primary particles are further aggregated and grown into secondary particles. When such composite oxide secondary particles are exposed to high-temperature exhaust gas, they are further agglomerated and grain-grown and their surface area is reduced. As a result, the diffusion of the exhaust gas into the particles does not proceed smoothly, and the catalytic metal is buried or agglomerated inside the particles, thereby reducing the HC and CO purification performance and the particulate combustion performance.

    In addition, in the case of CeZr-based composite oxide particles having oxygen storage capacity, oxygen is stored / released mainly on the surface of the particle, and the inside of the particle hardly participates in storage / release of oxygen. When it becomes larger, the internal volume that is not used for oxygen storage / release increases, and the oxygen storage / release efficiency decreases accordingly.

    Also, in the case of Zr-based composite oxide particles having oxygen ion conductivity, when the particle size becomes large, the distance that oxygen ions conduct inside the particle from the particle surface portion having a high oxygen concentration to the particle surface portion having a low oxygen concentration. And the oxygen concentration gradient inside the particle is also reduced, so that the oxygen ion conductivity is lowered and the oxygen supplied from the inside of the particle is reduced.

    On the other hand, in the case of the catalyst material described in Patent Document 4, the particle size of the CeZr composite oxide particles serving as the shell material is relatively small, but the particle size of the activated alumina particles serving as the core material is also small (largely). Even about 0.05 μm). This is because when the precipitated particles of hydroxide containing Al and La become the precursor of activated alumina primary particles, the hydroxide containing Ce and Zr (CeZr composite) on the precipitated particles which are the primary particle precursors. This is because the aggregation of primary particles of activated alumina is hindered by the CeZr composite oxide because the oxide precursor) is deposited and covers the precipitated particles.

    As a result, the surface of the activated alumina particles is entirely covered with the CeZr composite oxide particles, and the catalyst metal is supported on the core of the activated alumina particles even if supported by the CeZr composite oxide. Is hardly carried. For this reason, the activated alumina particles are not effectively used as a support material for supporting the catalyst metal in a highly dispersed state, and high catalytic activity cannot be expected. Moreover, since the catalyst particles (the surfaces of the activated alumina particles covered with CeZr composite oxide) are in contact with each other with CeZr composite oxide having the same composition, when exposed to high-temperature exhaust gas, There is also a problem that the particles tend to aggregate and grow easily, leading to a decrease in their activity.

    Accordingly, the present invention relates to a catalyst material comprising a combination of activated alumina and CeZr-based composite oxide, and aims to improve the purification performance of exhaust gas components (HC, CO, particulates, etc.) and to improve its heat resistance. This is the issue.

    In the present invention, in order to solve the above problems, the activated alumina and the CeZr-based composite oxide are mixed with each other to form secondary particles.

That is, the present invention aggregates so that primary particles of activated alumina and primary particles of complex oxide containing rare earth metal R other than Ce, Zr, and Ce are mixed with each other to form secondary particles. Become
The primary particle of the composite oxide contains CeO _{2 at} a ratio of 20 mol% to 60 mol%, which is an exhaust gas component purification catalyst material.

    In this way, primary particles of activated alumina and primary particles of composite oxide are mixed to form secondary particles, so that when exposed to high temperature exhaust gas, activated alumina particles aggregate to form a particle. This is hindered by the composite oxide particles, and the composite alumina particles are prevented from agglomerating and growing to be activated by the activated alumina particles.

    Thus, the composite oxide particle is a primary particle and has a small particle size, and therefore has a large specific surface area, and therefore has a high oxygen storage / release efficiency. When this composite oxide particle is used in a three-way catalyst that repeats an oxygen-excess state (lean state) and an oxygen-deficient state (rich state), it is assumed that oxygen is occluded in the lean state and oxygen is released in the rich state. However, it has an “oxygen exchange reaction (oxygen substitution reaction)” that releases active oxygen from the inside of the particle while incorporating oxygen into the particle even in the lean state (Japanese Patent Application Laid-Open No. 2007-190460 by the present applicant). reference). Therefore, even in an oxygen-excess gas atmosphere, the composite oxide particles release active oxygen due to a change in the valence of Ce ions, which is advantageous for promoting the oxidation of HC and CO and promoting the combustion of particulates.

In addition, since the activated alumina particles are mixed with the composite oxide particles and exposed on the surfaces of the secondary particles, when the catalyst metal is supported on the catalyst material according to the present invention, the catalyst metal is Not only oxide particles but also activated alumina particles are supported. Therefore, the activated alumina particles having a large specific surface area effectively function as a support material for supporting the catalyst metal in a highly dispersed state. The catalyst metal supported on the activated alumina particles is used to oxidize HC and CO in the exhaust gas, and NO. Can be oxidized to NO ₂ . Moreover, the heat generated by the oxidation reaction of the exhaust gas component promotes the combustion of the particulates, and the NO ₂ becomes an oxidizing agent that efficiently burns the particulates. In addition, the catalytic metal effectively works to promote the occlusion / release of oxygen in the composite oxide particles, and the active oxygen released from the composite oxide particles causes oxidation of HC and CO by the catalyst metal, and combustion of particulates. Will be used efficiently.

The composite oxide particles preferably contain CeO _{2 at} a ratio of 20 mol% to 60 mol%. Thereby, high flammability of particulates can be obtained while securing HC purification and CO purification at low temperatures. A more preferable CeO ₂ ratio is 20 mol% or more and 45 mol% or less. This is advantageous in improving the HC purification performance and CO purification performance at low temperatures.

    As the rare earth metal R contained in the composite oxide particles, La, Nd, Pr, Sm, Gd, Y and the like can be adopted, and among them, at least one selected from Nd, La, Pr and Y is used. It is preferable to employ it in order to increase the combustibility of the particulates.

    The ratio of the composite oxide particles to the total amount of the activated alumina particles and the composite oxide particles is preferably 10% by mass or more and 75% by mass or less. It is possible to obtain high particulate combustibility while ensuring low temperature purification of HC and CO. A more preferable ratio of the composite oxide particles is 25% by mass or more and 50% by mass or less.

    When the exhaust gas component purification catalyst material is used in a particulate filter, a catalyst layer is formed on the exhaust gas passage wall surface of the filter body that collects particulates discharged from the engine, and the exhaust gas component purification catalyst is formed on the catalyst layer. The material may be included. Thereby, the particulates deposited on the filter body can be efficiently burned and removed while purifying HC and CO in the exhaust gas.

In that case, it is preferable to employ Pt as the catalyst metal. That is, when the supported Pt on activated alumina particles, be advantageous to the oxidation of NO to NO ₂ in the exhaust gas, the NO ₂ can be efficiently burn the particulates as an oxidizing agent.

As described above, according to the present invention, primary particles of activated alumina and primary particles of composite oxide containing rare earth metal R other than Ce, Zr, and Ce are mixed with each other to form secondary particles, Since the primary particles of the composite oxide contain CeO _{2 in} a proportion of 20 mol% or more and 60 mol% or less, the oxygen storage efficiency of the composite oxide particles is increased and the active alumina particles are highly dispersed in the catalyst metal. It effectively works as a support material supported on the metal, which is advantageous for promoting combustion of particulates and for promoting oxidative purification of HC and CO and improving heat resistance.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

In FIG. 1, reference numeral 1 denotes a particulate filter (hereinafter simply referred to as “filter”) disposed in an exhaust gas passage 11 of an 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 arranged on the upstream side of the filter 1, 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. Further, NO is oxidized to NO _2, the NO ₂ is to be supplied as an oxidizing agent for burning particulates to the filter 1.

    As schematically shown in FIGS. 2 and 3, 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. 2, the hatched portion indicates the plug 4 at the upstream end of the exhaust gas outflow passage 3.

In the filter 1, the filter body including the partition wall 5 is formed of an inorganic porous material such as cordierite, SiC, Si ₃ N ₄ , sialon, and the exhaust gas flowing into the exhaust gas inflow passage 2 is indicated by an arrow in FIG. As shown in Fig. 5, the gas flows out through the surrounding partition wall 5 into the adjacent exhaust gas outflow passage 3. That is, as shown in FIG. 4, the partition wall 5 has fine 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. The particulates are trapped and deposited mainly on the wall surfaces of the exhaust gas inflow passage 2 and the pores 6.

    A catalyst layer 7 is formed on the wall surface of the exhaust gas passage (exhaust gas inflow path 2, exhaust gas outflow path 3 and pore 6) of the filter body of the filter 1. It is not always necessary to form a catalyst layer on the wall surface of the exhaust gas outflow passage 3.

One feature of the present invention is that the catalyst layer 7 contains catalyst particles (catalyst material) schematically shown in FIG. That is, the catalyst particles include primary particles of activated alumina (particles with parallel oblique lines; Al ₂ O ₃ ) and primary particles of CeZr-based composite oxide containing rare earth metal R other than Ce, Zr, and Ce ( The white circle particles (CeZrRO) are mixed with each other to form secondary particles, and the primary particles of activated alumina (Al ₂ O ₃ ) and the primary particles of CeZr composite oxide (CeZrRO) are catalyzed. Pt (represented by black circles) is supported as a metal. The average particle diameter of primary particles of activated alumina is 1 nm to 100 nm, and the average particle diameter of primary particles of CeZr-based composite oxide is 5 nm to 100 nm.

<Preparation method of catalyst material>
The exhaust gas component purification catalyst material according to the present invention can be prepared by the following method.

-Preparation of activated alumina particle precursor-
An acidic solution containing Al ions and La ions is prepared. Aluminum nitrate nonahydrate can be used as the Al source, and lanthanum nitrate hexahydrate can be used as the La source. A predetermined amount of each of the Al source and La source and water are mixed to obtain a raw material solution (acidic).

    A basic solution is added to and mixed with the raw material solution to produce precipitated particles of composite hydroxides of Al and La, which are precursors of activated alumina primary particles. In this case, after stirring the raw material solution at room temperature for about 1 hour, an aqueous ammonia having a concentration of, for example, about 7% may be added thereto as a basic solution. Other basic solutions such as aqueous caustic soda can also be employed.

-Preparation of CeZr-based composite oxide particle precursor-
An acidic solution containing Ce ions, Zr ions, and ions of rare earth metal R other than Ce is prepared. Cerium (III) nitrate hexahydrate can be used as the Ce source, and zirconium oxynitrate dihydrate can be used as the Zr source. As the rare earth metal R source other than Ce, nitrates such as Nd, La, Pr, and Y can be employed. A predetermined amount of each of these Ce source, Zr source and R source and water are mixed to obtain a raw material solution (acidic).

    A basic solution is added to and mixed with the raw material solution to produce precipitated particles of Ce, Zr, and R composite hydroxides that are precursors of CeZr-based composite oxide primary particles. In this case, after stirring the raw material solution at room temperature for about 1 hour, an aqueous ammonia having a concentration of, for example, about 7% may be added thereto as a basic solution. Other basic solutions such as aqueous caustic soda can also be employed.

-Mixing of activated alumina particle precursor and CeZr composite oxide particle precursor-
The activated alumina particle precursor obtained in each of the above steps and the CeZr composite oxide particle precursor are mixed. That is, a solution containing the activated alumina particle precursor precipitate and a solution containing the CeZr-based composite oxide particle precursor precipitate are mixed. At that time, the pH of each solution is adjusted to be the same.

-Washing and dehydration-
The mixed solution containing the activated alumina particle precursor and the precipitate of the CeZr-based composite oxide particle precursor is centrifuged to remove the supernatant. The water washing and dehydration operation of adding ion-exchanged water to the precipitated dehydrated product from which the supernatant has been removed, stirring, and re-centrifuged (dehydrated) is repeated as many times as necessary. The excess basic solution is removed by the washing / dehydrating operation.

-Drying and firing-
The precipitate dehydrated product is dried, fired and pulverized. Drying can be performed, for example, by holding at a temperature of about 100 ° C. to 250 ° C. for a predetermined time in an air atmosphere. Moreover, baking can be performed by hold | maintaining at the temperature of about 400 to 600 degreeC for several hours, for example in an atmospheric condition. Thereby, the primary particles of activated alumina containing La and the primary particles of CeZr-based composite oxide containing Ce, Zr and rare earth metal R are agglomerated so as to form secondary particles. Support material powder is obtained.

-Catalytic metal support-
A catalyst metal solution containing catalyst metal ions is added to and mixed with the obtained support material powder, evaporated to dryness, and then pulverized. Thereby, the catalyst material which consists of a catalyst particle shown in FIG. 5 is obtained. As the catalytic metal solution, a noble metal solution such as a dinitrodiamine platinum nitric acid solution or a palladium nitrate aqueous solution can be employed. The support material powder may be impregnated with the catalyst metal solution, dried and fired.

[Suitable catalyst material]
Hereinafter, preferred compositions of the CeZr-based composite oxide particles and catalyst particles will be described based on a carbon combustion performance test and an exhaust gas (HC, CO) purification performance test using carbon as a particulate.

<About CeZr-based composite oxide particles>
-Preparation of test material-
Various composite oxide powders were prepared by changing the kind and blending ratio of the rare earth metal R in the CeZr composite oxide (CeZrRO). The molar ratio of CeO ₂ and ZrO ₂ was 1: 3. Each composite oxide powder is mixed with dinitrodiamineplatinum nitrate solution and ion-exchanged water, evaporated to dryness, dried sufficiently, and then fired at 500 ° C for 2 hours (in air) to support Pt. Each catalyst material was prepared. However, these catalyst materials do not contain activated alumina.

Each obtained catalyst material was mixed with a binder and ion-exchanged water to form a slurry, and a SiC filter carrier (filter body, capacity: 25 mL, cell wall thickness: 12 mil (304.8 × 10 ⁻³ mm), 300 cpsi ( After coating to 300 cells) per square inch (635.16 mm ² ), drying and firing for 2 hours at 500 ° C. in an air atmosphere, each test material (with catalyst) A particulate filter) was obtained. The amount of CeZr-based composite oxide powder supported per liter of filter was 50 g / L, and the amount of Pt supported was 0.5 g / L. Then, each sample material was subjected to a thermal aging treatment in which it was kept at a temperature of 800 ° C. for 24 hours in an air atmosphere.

    Next, 10 mL of ion-exchanged water was added to an amount of carbon (carbon black) equivalent to 10 g per liter of filter, and the carbon was sufficiently dispersed in water by stirring for 5 minutes using a stirrer. At the same time as immersing one end face of each specimen in this carbon dispersion, suction was performed from the other end face by an aspirator. Moisture that could not be removed by this suction was removed by air blowing from the one end face, and then the specimen was placed in a dryer and kept at a temperature of 150 ° C. for 2 hours for drying. Thereby, carbon was deposited on the exhaust gas passage wall surface of the test material filter.

-Carbon combustion performance test-
The test material was attached to the fixed bed simulated gas flow reactor, and the simulated exhaust gas (O ₂ ; 10%, NO; 300 ppm, H ₂ O; 10%, remaining N ₂ ) was passed through the test material at a space velocity of 80000 / h. The sample gas inlet gas temperature was increased at a rate of 15 ° C./min, and the carbon combustion rate when the temperature reached 590 ° C. was measured. In this case, the carbon burning rate was calculated by the following equation based on the amount of CO and CO ₂ generated by burning carbon.
Carbon burning rate (g / hr)
= {Gas flow rate (L / hr) x [(CO + CO ₂ ) concentration (ppm) / (1 x 10 ⁶ )]} x 12 (g / mol) /22.4 (L / mol)

    The results are shown in FIG. The horizontal axis of FIG. 6 shows the ratio (mol%) of the rare earth metal R oxide R—O in the CeZr-based composite oxide.

According to the figure, in the case of Pr, a relatively large carbon burning rate is obtained when the ratio of the oxide is a small amount of 0.3 mol% or more and 2 mol% or less, and other rare earth metals Nd, La and Y In this case, it can be seen that a relatively large carbon burning rate can be obtained when the ratio as an oxide is 1 mol% or more and 7 mol% or less or 6 mol% or less. In addition, among the four types of rare earth metals, it is most advantageous to adopt Nd for improving the carbon combustibility, and it is preferable to set the Nd ₂ O ₃ ratio to 4 mol%.

<Preferred composition of catalyst particles>
-Preparation of test material-
According to the above-mentioned method for preparing catalyst particles, the CeO ₂ ratio (mol% of CeO ₂ / CeZrRO) in the CeZr-based composite oxide primary particles, and the activated alumina particles (La ₂ O ₃ ratio: 5 mol%) and the CeZr-based composite oxidation Each catalyst material of the Example from which the ratio (henceforth "CeZrRO ratio") of this CeZr-type complex oxide particle which occupies for the total amount with a product particle differs was prepared. Nd was adopted as the rare earth metal R of the CeZr-based composite oxide particles, and the Nd ₂ O ₃ ratio was fixed at 4 mol%. Further, the evaporation to dryness method was adopted for supporting the catalyst metal Pt.

Further, as a comparative example catalyst material, CeZr-based composite oxide secondary particles (Nd ₂ O ₃ ratio; 4 mol%) having different CeO ₂ ratios were prepared by a coprecipitation method, which was also prepared by the coprecipitation method. It was physically mixed with the contained activated alumina secondary particles (La ₂ O ₃ ratio; 5 mol%) at an appropriate ratio to obtain a support material powder, and Pt was supported thereon by evaporation to dryness.

    By coating the catalyst materials of Examples and Comparative Examples on SiC filter carriers (capacity: 25 mL, cell wall thickness: 12 mil, cell number: 300 cpsi) according to the preparation method of the test material described above, each sample was prepared. A sample (particulate filter with catalyst) was obtained. The amount of catalyst material supported per liter of filter was 50 g / L, and the amount of Pt supported was 1.0 g / L. Subsequently, each sample material was subjected to a heat aging treatment in which it was kept at a temperature of 800 ° C. for 24 hours in an air atmosphere.

-Evaluation of carbon combustion performance-
For each sample material of the above Examples and Comparative Examples, carbon (carbon black) equivalent to 10 g per 1 L of filter was deposited on the wall surface of the exhaust gas passage, and then carbon combustion at a temperature of 590 ° C. was performed by the above-described carbon combustion performance test. The speed was measured. Table 1 shows the results of the examples and Table 2 shows the results of the comparative examples.

In the following, each of the examples and comparative examples in Tables 1 and 2 is a two-digit number in which the CeO ₂ ratio number (No) is placed at the tens place and the CeZrRO ratio number (No) is placed at the first place. (For example, an example in which the CeO ₂ ratio is 45 mol% (ratio number 3) and the CeZrRO ratio is 25% by mass (ratio number 2) is referred to as “Example 32”). This also applies to Tables 3 and 4 described later.

According to Table 1 and Table 2, the exception is when the CeO ₂ ratio is 10 mol% and 80 mol%. However, in the other CeO ₂ ratio and CeZrRO ratio, the carbon burning rate is higher in the example than in the comparative example. It is getting bigger. As a result, in the case of the example, the activated alumina and the CeZr-based composite oxide are mixed in the form of primary particles having a small particle size to form secondary particles. This is considered to be due to the higher performance and the higher heat resistance of the catalyst material. In particular, Example 32 (CeO ₂ ratio 45 mol%, CeZrRO ratio 25 mass%) shows good results.

Therefore, the carbon combustion rates of Examples 12, 22, 32, 42, and 52 and Comparative Examples 12, 22, 32, 42, and 52 in which the CeO ₂ ratio was changed while fixing the CeZrRO ratio to 25% by mass were graphed. (FIG. 7). Further, the carbon combustion rates of Examples 31 to 35 and Comparative Examples 31 to 35 in which the CeZrRO ratio was changed while fixing the CeO ₂ ratio to 45 mol% were graphed (FIG. 8). In the graph of FIG. 7, “25 mass%” described in the window portion indicating the type of characteristic line indicates the CeZrRO ratio, and is described in the window portion indicating the type of characteristic line in the graph of FIG. 8. “45 mol%” indicates the CeO ₂ ratio. This also applies to FIGS. 9 and 10 described later.

According to FIG. 7, when the CeO ₂ ratio is 20 mol% or more and 60 mol% or less, the carbon burning rate in the example is larger than that in the comparative example, and particularly in the case of 20 mol% or more and 45 mol% or less, the carbon burning rate of the example and the comparative example. It can be seen that there is a relatively large difference.

    According to FIG. 8, when the CeZrRO ratio is 10% by mass or more and 90% by mass or less, the example has a higher carbon combustion rate than the comparative example, and particularly when the CeZrRO ratio is 10% by mass or more and 75% by mass or less, It turns out that it is obtained.

-Evaluation of light-off characteristics of exhaust gas purification-
Unlike the case of the above-described carbon combustion performance test, the light-off characteristics regarding the purification of HC and CO in the exhaust gas were examined for each of the test materials of the above Examples and Comparative Examples without depositing carbon black. That is, each test material was set in a simulated gas flow reactor, and simulated exhaust gas (O ₂ ; 10%, H ₂ O; 10%, NO; 100 ppm, C ₃ H ₆ ; 200 ppm C, CO; 400 ppm, remaining N ₂ ) Was passed through the specimen at a space velocity of 50000 / h, and the specimen inlet gas temperature was increased at a rate of 15 ° C./min. Then, when the concentration of each component (HC, CO) of the gas detected downstream of the sample material becomes half of the concentration of each component (HC, CO) of the gas flowing into the sample material (that is, the purification rate is 50). The gas inlet gas temperature T50 (° C.) at the time when the sample gas was% was obtained. Table 3 shows the results of the examples and Table 4 shows the results of the comparative examples.

According to Tables 3 and 4, when the CeO ₂ ratio is 10 mol% and 80 mol%, and the CO of Example 41 is an exception, the Examples are compared with other CeO ₂ ratios and CeZrRO ratios. The light-off temperature is lower than the example. This result is also recognized because the example catalyst material has higher oxygen storage / release capability and higher heat resistance than the comparative example catalyst material.

FIG. 9 is a graph of the light-off temperature of Examples 12, 22, 32, 42, 52 and Comparative Examples 12, 22, 32, 42, 52 in which the CeO ₂ ratio was changed while the CeZrRO ratio was fixed at 25 mass%. FIG. 10 shows a graph of light-off temperatures of Examples 31 to 35 and Comparative Examples 31 to 35 in which the CeZrRO ratio was changed while fixing the CeO ₂ ratio to 45 mol%.

According to FIG. 9, for both HC and CO, when the CeO ₂ ratio is 20 mol% or more and 60 mol% or less, the example has a lower light-off temperature than the comparative example, and in particular, 20 mol% or more and 45 mol% or less. It can be seen that the light-off temperature decreases.

    According to FIG. 10, when the CeZrRO ratio is 10% by mass or more and 90% by mass or less, the example has a lower light-off temperature than the comparative example, and particularly when the CeZrRO ratio is 10% by mass or more and 75% by mass or less. I understand that

    In the above embodiment, the catalyst material according to the present invention is employed in the particulate filter. However, the catalyst material is intended to purify HC, CO and NOx, and does not aim to collect particulates. Can also be used.

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 a particulate filter typically. It is a longitudinal section showing a particulate filter typically. It is an expanded sectional view showing typically the wall which separates the exhaust-gas inflow path and exhaust-gas outflow path of a particulate filter. It is a figure which shows typically the catalyst particle which concerns on this invention. It is a graph which shows the relationship between the ratio of the rare earth metal R oxide in CeZr type complex oxide, and a carbon combustion rate. Is a graph showing the relationship between the CeO ₂ ratio and the carbon burning rates of Examples and Comparative Examples. It is a graph which shows the relationship between the CeZrRO ratio of an Example and a comparative example, and a carbon combustion rate. Is a graph showing the relationship between the CeO ₂ ratio and the light-off temperature of the examples and comparative examples. It is a graph which shows the relationship between the CeZrRO ratio of an Example and a comparative example, and light-off temperature.

Explanation of symbols

1 Particulate filter 2 Exhaust gas inflow passage (exhaust gas passage)
3 Exhaust gas outflow passage (exhaust gas passage)
4 Plug 5 Bulkhead 6 Pore passage (exhaust gas passage)
7 Catalyst layer

Claims (6)

The primary particles of activated alumina and the primary particles of the composite oxide containing rare earth metal R other than Ce, Zr, and Ce are mixed together to form secondary particles,
A catalyst material for exhaust gas component purification, wherein the primary particles of the composite oxide contain CeO _{2 in} a proportion of 20 mol% to 60 mol%. In claim 1,
A catalyst material for exhaust gas component purification, wherein a ratio of the composite oxide primary particles to a total amount of the activated alumina primary particles and the composite oxide primary particles is 10% by mass or more and 75% by mass or less. In claim 1 or claim 2,
A catalyst material for exhaust gas component purification, wherein the primary particles of the composite oxide contain CeO _{2 in} a proportion of 20 mol% to 45 mol%. In any one of Claim 1 thru | or 3,
The exhaust gas component purification catalyst material, wherein the rare earth metal R is at least one selected from Nd, La, Pr and Y. A particulate filter in which a catalyst layer is formed on an exhaust gas passage wall surface of a filter body that collects particulates discharged from an engine,
A particulate filter comprising the catalyst layer containing the exhaust gas component purification catalyst material according to any one of claims 1 to 4. In claim 5,
The particulate filter, wherein the exhaust gas component purification catalyst material has Pt supported on the secondary particles as a catalyst metal.

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