JP5023950B2 - Exhaust gas component purification catalyst material and particulate filter 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 particulate, 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, those of a Ce type composite oxide and those of a Zr type composite oxide are mixed to form secondary particles. <P>COPYRIGHT: (C)2009,JPO&amp;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 the Ce-based composite oxide as disclosed in Patent Document 1.

    That is, the Ce-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 Ce-based composite oxide particles having the above-described oxygen storage ability and the Zr-based composite oxide particles having oxygen ion conductivity promote the oxidative purification of HC , and also ignite / burn the particulates deposited on the filter. However, there are 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. By thereof will not proceed smoothly diffusion of exhaust gas into the particle inside, more catalyst metal embedded therein particles or agglomerated, purification performance of the H C, and the particulate combustion performance decreases.

    In the case of Ce-based composite oxide particles having oxygen storage capacity, oxygen is stored and released mainly on the surface of the particle, and the inside of the particle hardly participates in storage and 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 as the shell material is relatively small, but the particle size of the active alumina particles 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, an object of the present invention is to obtain a high particulate combustibility while improving the HC purifying property at a low temperature .

    In order to solve the above-mentioned problem, the present invention forms secondary particles by mixing activated alumina, a composite oxide having oxygen storage ability, and a composite oxide having oxygen ion conductivity with each other in primary particles. I tried to do it.

That is, the present invention includes primary particles of activated alumina, primary particles of a Zr-based composite oxide containing rare earth metals M other than Zr, Nd, and Ce, and rare earth metals R other than Ce, Zr, and Ce. the primary particles of the Ce-based composite oxide is, Ri Na aggregate to form secondary particles mixed with each other,
The mass ratio of the primary particles of the active alumina, the primary particles of the Zr-based composite oxide, and the primary particles of the Ce-based composite oxide is indicated by points A (15:10:75) and B (15:15: 75:10) and C (75:15:10).
The primary particles of the Ce-based composite oxide contain at least one selected from Nd, La and Pr as the rare earth metal R, and contain CeO ₂ in a proportion of 20 mol% to 45 mol%,
The primary particle of the Zr-based composite oxide is an exhaust gas component purification catalyst material characterized by containing ZrO ₂ in a proportion of 55 mol% to 75 mol% .

    In this way, the primary particles of activated alumina, the primary particles of the Zr-based composite oxide, and the primary particles of the Ce-based composite oxide are mixed to form secondary particles, and thus exposed to high-temperature exhaust gas. When the activated alumina particles are agglomerated with each other, the Zr-based composite oxide particles and the Ce-based composite oxide particles are prevented from agglomerating, and the Zr-based composite oxide particles are agglomerated to grow particles, or Ce. Aggregation of the system composite oxide particles and particle growth are also hindered by other composite oxide particles or activated alumina particles, respectively.

Thus, the Ce-based composite oxide particles are primary particles and have a small particle size, and therefore have a large specific surface area, so that the oxygen storage / release efficiency is high. 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). Accordingly, 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 promoting the combustion of particulates.

On the other hand, Zr-based composite oxide particles, because the particle diameter is small, the oxygen ion amount of oxygen concentration the oxygen concentration from the high surface portion is supplied to a lower surface portion increases a primary particle, the oxidation of H C It is advantageous for promoting and promoting combustion of particulates.

    In addition, since the activated alumina particles and the composite oxide particles are mixed with each other and exposed on the surface of the secondary particles, when the catalyst metal is supported on the catalyst material according to the present invention, the catalyst metal is The active alumina particles and both composite oxide particles are supported on each.

Accordingly, the activated alumina particles having a large specific surface area effectively work as a support material for supporting the catalyst metal (for example, Pt) in a highly dispersed state, and oxidation of HC in the exhaust gas is performed using the catalyst metal supported on the activated alumina particles. In addition, oxidation of NO to NO ₂ can be achieved. 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 oxygen ion conduction in the Zr-based composite oxide particles and the oxygen storage / release in the Ce-based composite oxide particles, and active oxygen released from these composite oxide particles. Is efficiently used for the oxidation of HC by the catalyst metal and the combustion of particulates.

The mass ratio of the primary particles of the activated alumina, the primary particles of the Zr-based composite oxide, and the primary particles of the Ce-based composite oxide is indicated by points A (15:10:75) and B (15:15) in the triangular chart shown in FIG. 75:10) and C (75:15:10) area by the near area enclosed by the lines connecting the. Thereby, it is possible to obtain a high particulate combustibility while improving the HC purifying property at a low temperature.

    The numerical value “33” of the center point (33:33:33) in the triangular chart of FIG. 1 is strictly “33 + 1/3”, but is expressed as “33” for convenience. This also applies to FIGS. 9 to 11 described later.

As the rare earth metal R contained in the Ce-based 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 and Pr is used. It is preferable to contain. Also, the Ce-based composite oxide particles, you in a proportion of CeO ₂ below 20 mol% or more 45 mol%. Thereby, it is possible to obtain a high particulate combustibility while improving the HC purifying property at a low temperature.

The primary particles of the Zr-based composite oxide, you containing ZrO ₂ in a proportion of less 55 mol% or more 75 mol%. Thereby, it is possible to obtain a high particulate combustibility while improving the HC purifying property at a low temperature.

In addition to Nd , La, Pr, Sm, Gd, Y and the like can be adopted as the rare earth metal contained in the Zr-based composite oxide particles. Among these, at least one selected from La and Pr And Nd are preferable in terms of enhancing the combustibility of the particulates.

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 main body can be efficiently burned and removed while purifying HC in the exhaust gas.

Moreover, it is preferable to employ Pt as the catalyst metal of the exhaust gas component purification catalyst material. Accordingly, since it is possible to carry the Pt active alumina particles, Hakare oxidation of NO to NO ₂ in the exhaust gas, the NO ₂ can be efficiently burn the particulates as an oxidizing agent.

According to the present invention as described above, Ri and primary particles of the primary particles and the Ce-based composite oxide primary particles and Zr-based composite oxide of the active alumina greens to form a mixed each other by secondary particles together, active The mass ratio of the primary particles of alumina, the primary particles of the Zr-based composite oxide, and the primary particles of the Ce-based composite oxide is indicated by points A (15:10:75) and B (15:75: 10) and C (75:15:10) in a range surrounded by a straight line, the Ce-based composite oxide primary particles contain at least one kind selected from Nd, La and Pr as the rare earth metal R, Since CeO ₂ is contained in a proportion of 20 mol% or more and 45 mol% or less, and the primary particles of the Zr-based composite oxide contain ZrO ₂ in a proportion of 55 to 75 mol% , the oxygen ions of the Zr-based composite oxide particles With higher conductivity , Oxygen storage efficiency of Ce-based mixed oxide particles is increased, also works effectively as a support material in which the active alumina particles support the catalyst metal in a highly dispersed, therefore, while improving the HC purification at low temperatures, High particulate combustibility can be obtained, and heat resistance can be improved.

    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. 2, reference numeral 1 denotes a particulate filter (hereinafter simply referred to as “filter”) disposed in the exhaust gas passage 11 of the 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 FIG. 3 and FIG. 4, the filter 1 has a honeycomb structure and includes a large number of exhaust gas passages 2 and 3 extending in parallel to 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. 3, 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 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. 5, 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 active alumina (white circle particles; Al ₂ O ₃ ) and primary particles of Zr-based composite oxide containing rare earth metal M other than Zr, Nd, and Ce (crossing parallel particles). The slanted particles; ZrNdMO) and the primary particles of Ce-based composite oxide containing rare earth metal R other than Ce, Zr, and Ce (parallel-shaded particles; CeZrRO) are mixed with each other. Agglomerated so as to form secondary particles, and the catalyst is added to each of primary particles of activated alumina (Al ₂ O ₃ ), primary particles of Zr-based composite oxide (ZrNdMO), and primary particles of Ce-based composite oxide (CeZrRO). Pt (represented by black circles) is supported as a metal. The average particle size of primary particles of activated alumina is 1 nm to 100 nm, the average particle size of primary particles of Zr-based composite oxide is 5 nm to 50 nm, and the average particle size of primary particles of Ce-based composite oxide is 5 nm to 100 nm.

In the figure, the Zr-based composite oxide particles are represented by “ZrNdMO”, which contains Zr, Nd, and rare earth metal M other than Ce and Nd as an example of the Zr-based composite oxide particles. Ru der shows the composite oxide particles.

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

    A basic solution is added to and mixed with the raw material solution to produce precipitated particles of Zr, Nd, and M composite hydroxides, which are precursors of Zr-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.

-Preparation of Ce-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, which are precursors of Ce-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 three kinds of particle precursors-
The activated alumina particle precursor, Zr-based composite oxide particle precursor, and Ce-based composite oxide particle precursor obtained in each of the above steps are mixed. That is, the solution containing the precipitate of the activated alumina particle precursor, the solution containing the precipitate of the Ce-based composite oxide particle precursor, and the solution containing the precipitate of the Zr-based composite oxide particle precursor are mixed. To do. At that time, the pH of each solution is adjusted to be the same.

-Washing and dehydration-
The mixed solution containing the three kinds of particle precursor precipitates 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 support material powder formed by agglomerating the primary particles of the activated alumina, the primary particles of the Zr-based composite oxide, and the primary particles of the Ce-based composite oxide to be mixed with each other to form secondary particles. can get.

-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. 6 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.

[About suitable catalyst materials]
Hereinafter, the preferred composition of the Ce-based composite oxide particles, the Zr-based composite oxide particles, and the catalyst particles are based on the carbon combustion performance test and the exhaust gas (HC, CO) purification performance test using carbon as a particulate. explain.

<About Ce-based composite oxide particles>
-Preparation of test material-
Various composite oxide powders were prepared by changing the kind and blending ratio of rare earth metal R in Ce-based 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 supported amount of Ce-based composite oxide powder per liter of filter was 50 g / L, and the supported amount of Pt 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. 7 shows the ratio (mol%) of the oxide R—O of the rare earth metal R in the Ce-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%.

<About Zr-based complex oxide particles>
-Preparation of test material-
In order to formulate a preferred composition of the Zr-based composite oxide, various composite oxide powders that employ La, Pr, and Y as the rare earth metal M and have different blending ratios of Nd ₂ O ₃ and M oxides Prepared. 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, which was coated on a SiC filter carrier (capacity: 25 mL, cell wall thickness: 16 mil, number of cells: 178 cpsi), dried, and then in an air atmosphere Each sample material (particulate filter with a catalyst) was obtained by carrying out baking for 2 hours at a temperature of 500 ° C.

    In the same manner as in the case of the Ce-based composite oxide described above, the test material has a Zr-based composite oxide powder loading of 50 g / L, a Pt loading of 0.5 g / L, and an atmospheric atmosphere. The sample was subjected to heat aging treatment at a temperature of 800 ° C. for 24 hours. Further, 10 g / L of carbon was deposited on the wall of the exhaust gas passage of the test material filter.

    Thus, the carbon combustion rate at 590 ° C. was measured and the amount of CO generated was determined by the above-described carbon combustion performance test. The results are shown in Table 1.

    Specimens 5, 12, and 21 combining La, Pr, or Y and Nd have a higher carbon burning rate than specimens 3 and 4 that do not contain Nd, so Nd is essential. Can be said to be preferable. However, in the case where only Nd is used as the rare earth metal as in the test materials 1 and 2, the carbon combustion rate does not increase even if the amount of Nd increases, so La, Pr or Y and Nd can be combined. It can be said that it is preferable.

    In cases where the ratio of rare earth metal M is small (samples 7, 14, 22 or specimens 8, 15, 23), when La, Pr or Y is compared, it is better to use La as the rare earth metal M for carbon combustion. It can be said that it is advantageous in increasing the speed. On the other hand, in the case where the ratio of the rare earth metal M is large (the specimens 6 and 13, or the specimens 11, 20, and 25), when La, Pr, or Y is compared, it is better to use Pr as the rare earth metal M. It can be said that it is advantageous in increasing the burning rate.

    Although there are exceptions, basically, increasing the ratio of the total amount of both Nd and M oxides increases the carbon burning rate. However, as can be seen from the test materials 16 to 20, when the total amount is increased to increase the carbon combustion rate, the amount of CO generated due to incomplete combustion of carbon tends to increase. Therefore, in order to increase the combustibility of the particulates, it is preferable to increase the ratio of the total amount. However, in order to suppress an increase in the amount of CO generated, the ratio of the total amount is less than 45 mol%, and further less than 40 mol%. It is preferable to make it.

    On the other hand, when the ratio of the total amount exceeds 20 mol%, a large carbon burning rate can be obtained. Therefore, it is preferable to increase the ratio of the total amount to more than 20 mol% in order to improve the combustibility of the particulates. be able to. In particular, it is preferable to increase the ratio of Nd or Pr so that the ratio of the total amount is greater than 20 mol%.

FIG. 8 shows a case where a SiC filter carrier having a cell wall thickness and a cell number different from those of the previous case is coated with a Zr-based composite oxide (not including activated alumina) using Pr or La as the rare earth metal M. About the sample, the result of having measured the carbon burning rate in 590 degreeC on the same conditions as the previous is shown. However, it can be seen from Table 1 that the Nd ₂ O ₃ ratio is 6 mol% or more and 18 mol% or less, and good results are shown. Therefore, the Nd ₂ O ₃ ratio was fixed to 12 mol%. The filter body has a capacity of 25 mL, a cell wall thickness of 12 mil, and a cell count of 300 cpsi. As in the previous case, the loading amount of the Zr-based composite oxide powder per 1 L of filter is 50 g / L, the loading amount of Pt is 0.5 g / L, and each test material is 800 ° C. in the air atmosphere. A thermal aging treatment was carried out at a temperature for 24 hours.

According to the figure, it is preferable to employ Pr as the rare earth metal M and to make the Pr ₂ O ₃ ratio 6 mol% or more in order to increase the carbon combustion rate.

<ZrO ₂ ratio of Zr-based composite oxide, CeO ₂ ratio of Ce-based composite oxide>
-Preparation of test material-
By the above-described method for preparing catalyst particles, primary particles of activated alumina (Al ₂ O ₃ ), primary particles of Zr-based composite oxide (ZrNdMO), and primary particles of Ce-based composite oxide (CeZrRO) are converted into Al ₂ O _3. : ZrNdMO: CeZrRO = 66: 22: 12, and the ratio of ZrO ₂ in the Zr-based composite oxide particles (ZrO ₂ / mol% of ZrNdMO) and CeO ₂ in the Ce-based composite oxide particles The catalyst materials of Examples and Reference Examples having different ratios (mol% of CeO ₂ / CeZrRO) were prepared. Pr was adopted as the rare earth metal M of the Zr-based composite oxide particles, and the Pr ₂ O ₃ ratio was fixed at 12 mol%. Nd was employed as the rare earth metal R of the Ce-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.

Moreover, as a comparative example catalyst material, secondary particles of activated alumina, secondary particles of Zr-based composite oxides having different ZrO ₂ ratios (Pr ₂ O ₃ ratio; 12 mol%), and CeO ₂ ratios are different. Several kinds of Ce-based composite oxide secondary particles (Nd ₂ O ₃ ratio; 4 mol%) were prepared by coprecipitation, respectively. The activated alumina secondary particles, Zr-based composite oxide secondary particles, and Ce The secondary particles of the system composite oxide are physically mixed in the same mass ratio of “66:22:12” as in the examples and reference examples , so that the ZrO ₂ ratio in the Zr system composite oxide particles and the Ce system composite are Various support material powders having different CeO ₂ ratios in the oxide particles were used, and Pt was supported on these powders by evaporation to dryness.

By coating the catalyst materials of Examples , Reference Examples and Comparative Examples on SiC filter carriers (capacity: 25 mL, cell wall thickness: 12 mil, cell number: 300 cpsi) by the preparation method of the test material described above. Each sample material (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-
About each sample material of the said Example , a reference example, and a comparative example, after depositing carbon (carbon black) equivalent to 10g per 1L of filter on an exhaust gas passage wall surface, by the above-mentioned carbon combustion performance test, at a temperature of 590C The carbon burning rate was measured. Table 2 shows the results of Examples and Reference Examples , and Table 3 shows the results of Comparative Examples.

According to Table 2 and Table 3, Example and ZrO ₂ ratio is in CeO ₂ ratio of less 20 mol% or more 45 mol% is Ru der less 55 mol% or more 75 mol%, the carbon burning than approximately Comparative Examples although exceptions The speed is increasing. This result shows that, in the case of the example, the Ce-based composite oxide and the Zr-based composite oxide are mixed in the state of primary particles having a small particle size to form secondary particles. This is probably because the oxygen storage / release capability and the oxygen ion conductivity of the Zr-based composite oxide are high, and the heat resistance of the catalyst material is high. In particular, an example with a CeO ₂ ratio of 20 mol% and a ZrO ₂ ratio of 55 mol% shows good results.

-Evaluation of light-off characteristics of exhaust gas purification-
Unlike the case of the above-described carbon combustion performance test, carbon black is deposited on each of the above-described sample materials of the examples , reference examples, and comparative examples (same sample materials as those obtained in Tables 2 and 3). The light-off characteristics relating to the purification of HC and CO in the exhaust gas were investigated. 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 allowed to flow through the specimen at a space velocity of 50000 / h, and the specimen inlet gas temperature was increased at a rate of 15 ° C./minute. 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 4 shows the results of Examples and Reference Examples , and Table 5 shows the results of Comparative Examples.

Table 4 and according to Table 5, the light-off temperature for purification of HC than all and ZrO ₂ ratio is in CeO ₂ ratio of less 20 mol% or more 45 mol% is Example Ru der less 55 mol% or more 75 mol% Comparative Example Is low. This result is also considered to be due to the fact that the example catalyst material has higher oxygen storage / release properties and oxygen ion conductivity and higher heat resistance than the comparative example catalyst material.

<Mixing ratio of activated alumina, Zr composite oxide and Ce composite oxide>
-Preparation of test material-
Therefore, the ZrO ₂ ratio of the Zr-based composite oxide is fixed to 55 mol%, the CeO ₂ ratio of the Ce-based composite oxide is fixed to 20 mol%, and the active alumina, the Zr-based composite oxide, and the Ce-based composite oxide The test materials of Examples (primary particle mixing) and Comparative Examples (secondary particle mixing) having different mixing ratios (mass ratio of Al ₂ O ₃ : ZrNdMO: CeZrRO) were prepared by the method described above.

-Evaluation of carbon combustion performance-
After performing the above-mentioned thermal aging treatment and carbon deposition treatment on each sample material of the example and the comparative example, the carbon combustion rate at a temperature of 590 ° C. was measured by the above-described carbon combustion performance test. The filter carrier of each test material, the loading amount of the catalyst material and the loading amount of Pt are also the same as those in Tables 2 to 5. The results are shown in Table 6 and FIG.

According to Table 6 and FIG. 9, the carbon burning speed of the example is higher than that of the comparative example at any mixing ratio. The carbon burning rate of _example, Al ₂ O 3: ZrNdMO: ratio CeZrRO the largest when it is (66:22:12), and go to the periphery of the triangular diagram shown in FIG. 1, i.e., Al ₂ When the point C (75:15:10) where the O ₃ ratio is large, the point B (15:75:10) where the ZrNdMO ratio is large, and the point A (15:10:75) where the CeZrRO ratio is large, There is a tendency to become smaller. In addition, the carbon combustion rate difference between the example and the comparative example also tends to decrease as it goes to the periphery of the triangular chart (FIG. 1).

-Evaluation of light-off characteristics of exhaust gas purification-
After performing the above-mentioned heat aging treatment on each sample material of the example and the comparative example, the light-off temperature relating to the purification of HC and CO was measured by the above-described light-off performance evaluation test. The light-off temperature for HC purification is shown in Table 7 and FIG. 10, and the light-off temperature for CO purification is shown in Table 7 and FIG.

    According to Tables 7 and 8 and FIGS. 10 and 11, the light-off temperature is lower in the example than in the comparative example at any mixing ratio. Further, the light-off temperature of the example is an exception at the point A (15:10:75) where the CeZrRO ratio is large, but basically, the light-off temperature tends to become higher when going to the periphery of the triangular chart (FIG. 1). It can be seen. In addition, the light-off temperature difference between the example and the comparative example also tends to decrease as it goes to the periphery of the triangular chart (FIG. 1).

-Summary of mixing ratio-
From the evaluation results of the above carbon combustion performance and light-off performance, in the present invention, the mass ratio of the activated alumina particles, the Zr-based composite oxide particles, and the Ce-based composite oxide particles is shown in the triangle chart shown in FIG. While it is within the range surrounded by the straight line connecting A (15:10:75), B (15:75:10) and C (75:15:10), while improving the HC purification and CO purification at low temperatures It can be said that the combustibility of the particulates can be enhanced.

    More preferably, the above three mass ratios are surrounded by straight lines connecting points A (15:10:75), C (75:15:10) and D (22:66:12) in the triangular chart shown in FIG. It is within the range.

    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.

Activated alumina _{(Al 2} O 3), a triangular diagram showing the mass ratio of Zr-based composite oxide (ZrNdMO) and Ce-based composite oxide (CeZrRO). 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 Ce type complex oxide, and a carbon combustion rate. It is a graph which shows the relationship between the ratio of the rare earth metal M oxide in Zr system complex oxide, and a carbon combustion rate. It is a graph which shows the relationship between the mixing ratio of the activated alumina of Example and a comparative example, Zr type complex oxide, and Ce type complex oxide, and a carbon combustion rate. It is a graph which shows the relationship between the mixing ratio of the active alumina of an Example and a comparative example, Zr type complex oxide, and Ce type complex oxide, and the light-off temperature of HC purification | cleaning. It is a graph which shows the relationship between the mixing ratio of the activated alumina of an Example and a comparative example, Zr type complex oxide, and Ce type complex oxide, and the light-off temperature of CO purification | cleaning.

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 (3)

Primary particles of activated alumina, primary particles of Zr-based composite oxide containing rare earth metal M other than Zr, Nd, and Ce , and Ce-based composite oxide containing rare earth metal R other than Ce, Zr, and Ce the primary particles of, Ri Na aggregate to form secondary particles mixed with each other,
The mass ratio of the primary particles of the active alumina, the primary particles of the Zr-based composite oxide, and the primary particles of the Ce-based composite oxide is indicated by points A (15:10:75) and B (15:15: 75:10) and C (75:15:10).
The primary particles of the Ce-based composite oxide contain at least one selected from Nd, La and Pr as the rare earth metal R, and contain CeO ₂ in a proportion of 20 mol% to 45 mol%,
The exhaust gas component purification catalyst material , wherein the primary particles of the Zr-based composite oxide contain ZrO ₂ in a proportion of 55 mol% to 75 mol% . 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 claim 1 . In claim 2 ,
The particulate filter, wherein the exhaust gas component purification catalyst material comprises Pt supported as a catalyst metal on the secondary particles.

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