JP2009078202A - Catalytic metal-deposited oxygen storage material, method for manufacturing the same and catalyst using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxygen storage material in which Pd is deposited on a Ce-Zr composite oxide and which has excellent oxygen releasability and high catalytic activity even after exposed to high-temperature gas though the deposited amount of Pd is vary small. <P>SOLUTION: A most of Pd particles 2 are deposited in recessed parts 4 on the surface of a primary particle 3 of a Ce-Zr compound oxide particle 1 or among primary particles. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

    The present invention relates to a catalyst metal-supported oxygen storage material, a method for producing the same, an engine exhaust gas purification catalyst using the same material, and a fuel cell CO selective oxidation catalyst.

    It is known to employ a catalyst in which Pt or Pd is supported on an oxygen storage material containing Ce as an engine exhaust gas purification catalyst or a fuel cell CO selective oxidation catalyst. In the case of an exhaust gas purification catalyst, a catalyst metal is supported on an oxygen storage material, so that the catalyst metal promotes the storage and release of oxygen in the exhaust gas into the oxygen storage material, and this oxygen storage and release. Thus, the catalytic metal becomes in an oxidation state suitable for the oxidation of HC and CO, and further, the reduction and purification of NOx easily proceeds along with the oxidation of HC and CO. In the case of a fuel cell CO selective oxidation catalyst (including a CO shift catalyst), the presence of the oxygen storage material makes the catalyst metal in an oxidation state suitable for the oxidation of CO in the reformed gas, and the CO concentration in the reformed gas. It becomes advantageous for reduction.

    By the way, since Pt and Pd are rare metals, it is required to reduce their use amount, and development of such a catalyst is being promoted.

    For example, Patent Document 1 discloses a noble metal-containing composite oxide for an exhaust gas purification catalyst composed of Zr, Ce, and a noble metal (Pt, Pd, or Rh). It is described that it is g or more and the noble metal content is 0.001 to 1%. Prior to this, the present applicant has developed a composite oxide for purifying exhaust gas whose metal components are Ce, Zr, Nd and Rh (see Patent Document 2).

    The composite oxide containing such a catalytic metal is obtained by coprecipitation of the metal component as a hydroxide by adding and mixing a basic solution to the mixed solution of the metal component, and dehydrating, drying and drying the resulting precipitate. It is obtained by firing. In this case, a small amount of noble metal contained in the composite oxide improves its oxygen storage / release ability and enhances the catalyst performance.

Further, Patent Document 3 relates to a catalyst in which iron oxide and a noble metal (Pt, Pd or Rh) are supported on a CeZr composite oxide, the amount of noble metal supported is 0.0004 to 1% by mass, and iron oxide is 100% by mass. It is described that the amount of noble metal is 0.005 to 15 parts by mass with respect to parts. This is recognized to improve the catalyst performance by loading a relatively large amount of iron oxide instead of reducing the amount of noble metal supported.
JP 2006-247635 A JP 2004-174490 A JP 2005-246177 A

    However, in the case of the noble metal-containing composite oxide, the noble metal is contained in the crystal, so that the oxygen storage / release ability is increased, but the noble metal is mainly in the composite oxide particle, so that the noble metal on the surface of the composite oxide particle. Much cannot be expected about the contact between the exhaust gas and the noble metal, and high catalytic activity cannot be expected.

    In the case of a catalyst using both iron oxide and noble metal, there is a problem of a decrease in activity due to sintering of iron oxide supported in a relatively large amount on the composite oxide, and the noble metal is involved in the sintering and the activity is large. There is concern about the decline.

    Therefore, the present invention relates to an oxygen storage material in which Pd is supported as a catalytic metal on a CeZr-based composite oxide, obtaining an excellent oxygen storage / release ability and high catalytic activity while keeping the amount of Pd supported in a trace amount, and An object is to maintain excellent oxygen storage / release ability and high catalytic activity even after being exposed to a high-temperature gas.

    In order to solve such problems, the present inventor can achieve excellent oxygen occlusion even if the amount of Pd is supported between the concave portion of the primary particle surface of the CeZr-based composite oxide or between the primary particles. -The present invention was completed by finding that the release ability and high catalytic activity were obtained and the heat resistance increased.

The invention according to claim 1 is a catalyst metal-supported oxygen storage material in which Pd is supported as a catalyst metal on CeZr-based composite oxide particles,
Most of the Pd is arranged in the concave portion of the surface of the primary particles constituting the CeZr-based composite oxide particles or between the primary particles.

    Here, “disposed between primary particles” means that Pd is sandwiched between primary particles or that Pd is disposed in pores that are voids between primary particles.

    The surface of the primary particles does not have many concave portions, and the Pd particles supported between the concave portions and the primary particles are limited to those having a very small particle size. That is, in the present invention, the fact that most (half or more) of Pd is disposed in the depressions on the surface of such primary particles or between the primary particles means that the amount of Pd of the catalyst metal-supported oxygen storage material itself is small. However, it means that the Pd is extremely fine particles and is supported in a highly dispersed state on the CeZr-based composite oxide particles. The small Pd particle size means that Pd works effectively with catalytic reactions such as oxygen storage / release and exhaust gas purification in combination with CeZr-based composite oxides.

    In addition, in the recesses on the surface of the primary particles or between the primary particles, other parts of the CeZr-based composite oxide particles (secondary particles formed by agglomeration of the primary particles), for example, parts that are not recessed on the surface of the primary particles. In comparison, the loaded state of Pd tends to be stable. That is, Pd is less likely to move and aggregate to cause sintering (grain growth). For this reason, when the said catalyst metal carrying | support oxygen storage material is exposed to high temperature exhaust gas, there is little fall of oxygen storage / release capability and catalyst activity.

    As described above, according to the present invention, an excellent oxygen storage / release capability and high catalytic activity can be obtained with a small amount of Pd supported, and the effect of high heat resistance can be obtained.

    The amount of Pd supported on the catalyst metal-supported oxygen storage material can be 0.05% by mass or less (Claim 2), and further 0.01% by mass or less (Claim 4).

The invention according to claim 3 is formed by agglomerating primary particles of CeZr-based composite oxide in which Pd is supported as a catalyst metal to form secondary particles,
The catalyst metal-supported oxygen storage material, wherein the supported amount of Pd is 0.05% by mass or less.

    The fact that primary particles supporting Pd are aggregated to form secondary particles means that most of Pd is arranged between primary particles of CeZr-based composite oxide, that is, voids between primary particles. It means that it is arranged in pores or sandwiched between primary particles.

    Therefore, as is clear from the description of the invention according to claim 1 described above, according to the present invention, excellent oxygen storage / release ability and high catalytic activity can be obtained with a small amount of Pd supported, and heat resistance is high. The effect is obtained.

    The amount of Pd supported can be 0.01% by mass or less.

The catalyst metal-supported oxygen storage material according to each of the above inventions can be obtained by an ammonia coprecipitation method, which will be described later. When the pore size distribution after holding at 1000 ° C. for 24 hours in an air atmosphere was examined, The peak was in the range of 50 nm to 70 nm, and the log differential pore volume at the peak pore diameter was 0.15 cm ³ / g or more (Claim 5). On the other hand, when a small amount of Pd was supported on the CeZr-based composite oxide particles by a known evaporation and drying method, the peak position of the pore size distribution was substantially the same as that of the oxygen storage material according to the present invention. Log differential pore volume was about 0.10 cm ³ / g, and the oxygen storage material according to the present invention had a larger pore volume.

    Although it is not certain how the peak characteristics of the pore size distribution affect the oxygen releasing ability, catalytic activity, and heat resistance, in the present invention, there are many micropores having a pore size of about 50 nm to 70 nm, It is recognized that the catalytic metal supported on the inner surface of such fine pores is increasing. For this reason, it can be said that the catalytic activity is high due to the good dispersibility of the catalyst metal and the diffusibility of the gas to be treated, and the sintering of the catalyst metal is less likely to occur.

Further, in the catalyst metal-supported oxygen storage material described above, the oxygen release amount at 100 ° C. or more and less than 200 ° C. was 2.0 × 10 ⁴ μmol / g or more as oxygen atoms (Claim 6). This is considered to contribute to enhancing the activity of the catalyst.

The invention according to claim 7 is a method for producing a catalyst metal-supported oxygen storage material in which Pd is supported as a catalyst metal on CeZr-based composite oxide particles,
Adding and mixing aqueous ammonia to an acidic solution containing Ce ions, Zr ions and Pd ions;
A step of dehydrating the obtained precipitate;
A step of obtaining the catalyst metal-supported oxygen storage material by calcining the obtained dehydrated product,
In the dehydration step, a part of the component relating to the Pd ions is removed together with the supernatant so that the amount of Pd supported on the catalyst metal-supported oxygen storage material is 0.05% by mass or less.

    According to this production method, Ce ions and Zr ions become Ce and Zr composite hydroxide particles by the addition of the ammonia water, and they aggregate and precipitate in units of several to several tens, but Pd is water. It does not precipitate as an oxide. Pd is considered to form a stable compound such as an ammine complex. Such Pd compounds adhere to the CeZr composite hydroxide particles and migrate to the precipitate side.

    In this case, most of the components related to the Pd ions (most of the charged Pd) are removed together with the supernatant liquid by the dehydration treatment, so that most of the Pd components remaining in the dehydrated product are the CeZr composite water. It is thought that it exists in the site | part which is hard to receive the influence of the said dehydration process like the recessed part of the oxide particle surface or between this composite hydroxide particle. The Ce and Zr composite hydroxide particles become CeZr-based composite oxide primary particles by subsequent firing, and further aggregate to form secondary particles. Moreover, the recessed part of the surface of each composite hydroxide particle turns into the surface recessed part of CeZr type complex oxide primary particle. Therefore, by firing the dehydrated product, Pd is in a state of being arranged in the surface recesses of the CeZr-based composite oxide primary particles and between the primary particles (including pores).

    In such a catalyst metal-supported oxygen storage material, primary particles supporting Pd are aggregated to form secondary particles. Therefore, the degree of dispersion of Pd is extremely high, and an excellent oxygen storage / release capability and a high catalyst. Activity is obtained. Moreover, since Pd is supported in the recesses on the surface of the primary particles or in the pores that are voids between the primary particles, or is sandwiched between the primary particles, the Pd is not affected by exposure to high-temperature gas. It is hard to produce a ring. That is, the effect that heat resistance is high is acquired.

    Therefore, by the production method according to the present invention, most of Pd is disposed between the concave portions on the surface of the primary particles constituting the CeZr-based composite oxide particles or between the primary particles, and the amount of Pd supported is 0.05% by mass or less. Is obtained, or the primary particles of CeZr-based composite oxide on which Pd is supported are aggregated so as to form secondary particles, and the supported amount of Pd is 0.05% by mass. The following catalyst metal-supported oxygen storage material is obtained.

    In the dehydration step, the resulting precipitate is centrifuged to remove the supernatant, the ion-exchanged water is added to the resulting mixture, and the mixture is stirred and re-centrifuged. be able to. By this water washing / dehydration operation, excess ammonia water is removed and a part of Pd contained in the precipitate is washed away. In this case, Pd remains in the portion where the surface of the CeZr composite hydroxide particles, which are the precursors of the primary particles, is not easily subjected to the washing power between the concave portions and the composite hydroxide particles.

    In the dehydration step, the amount of catalyst metal of the catalyst metal-supported oxygen storage material can be 0.01% by mass or less (claim 8).

    Further, the catalytic metal-supported oxygen storage material described above can be used as an engine exhaust gas purification catalyst or a fuel cell CO selective oxidation catalyst (claims 9 and 10).

    As described above, according to the present invention, most of Pd is disposed in or between the primary particles of the primary particle surface constituting the CeZr-based composite oxide particles, or Pd is supported. The primary particles of the CeZr-based composite oxide are aggregated to form secondary particles, and the amount of supported Pd is 0.05% by mass or less, so that the oxygen storage / release ability is excellent with a small amount of supported Pd. In addition, a high catalytic activity can be obtained, and the heat resistance is high.

Further, the peak of the pore size distribution after being kept at a temperature of 1000 ° C. for 24 hours in the air atmosphere is in the range of 50 nm to 70 nm, and the log differential pore volume at the peak pore size is 0.15 cm ³ / g or more. According to a certain catalyst metal-supported oxygen storage material, high catalytic activity can be obtained with a small amount of Pd and high heat resistance due to good dispersibility of the catalyst metal and good diffusibility of the gas to be treated. The effect is obtained.

Moreover, according to the catalyst metal-supported oxygen storage material in which the oxygen release amount at 100 ° C. or more and less than 200 ° C. is 2.0 × 10 ⁴ μmol / g or more as oxygen atoms, high catalytic activity is obtained with a small amount of Pd. Become advantageous.

    In addition, according to the production method of the present invention, ammonia water is added to and mixed with a solution containing Ce, Zr and Pd ions, and the resulting precipitate is dehydrated and calcined. Since the catalyst metal-supported oxygen storage material of 05% by mass or less is obtained, excellent oxygen storage / release ability and high catalytic activity can be obtained with a small amount of Pd supported, and the effect of high heat resistance can be obtained.

    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.

<Configuration of catalyst metal-supported oxygen storage material>
FIG. 1 is a view schematically showing a catalytic metal-supported oxygen storage material according to the present invention. In the figure, 1 is a CeZr-based composite oxide particle, and 2 is a Pd particle. The CeZr-based composite oxide particle 1 is a secondary particle obtained by aggregating a large number of primary particles 3. Most of the Pd particles 2 are arranged (supported) between the surface recesses 4 of the primary particles 3 and the primary particles, and a small amount of Pd particles 2 are present in other parts (parts where the surface of the primary particles 3 are not recessed). It is supported. The average particle size of the primary particles 3 is about 10 nm to 30 nm.

    In the figure, the Pd particles 2 carried on the surface recesses 4 of the primary particles 3 are represented by circles with crossed oblique lines, and the Pd particles 2 carried between the primary particles are represented by circles with one side oblique lines. The Pd particles 2 carried on the surface of the primary particles 3 that are not recessed are represented by black circles. As the Pd particles 2 supported between the primary particles, as shown in the figure, in addition to the Pd particles sandwiched between the primary particles, the Pd particles supported on the inner surfaces of the pores that are voids between the primary particles. The latter is not shown in the figure.

<Method for preparing catalyst metal-supported oxygen storage material>
The catalytic metal-supported oxygen storage material according to the present invention can be obtained by using a coprecipitation method using ammonia water as an alkaline solution.

-Preparation of raw material solution-
An acidic solution containing Ce ions, Zr ions and Pd ions is prepared. As the Ce source, cerium (III) nitrate hexahydrate can be used, as the Zr source, zirconium oxynitrate dihydrate, and as the Pd source, a palladium nitrate solution can be used. A predetermined amount of each of these Ce source, Zr source, and Pd source and water are mixed to obtain a raw material solution.

-Formation of precipitate-
Ammonia water is added to and mixed with the raw material solution to form a precipitate. That is, after stirring the raw material solution at room temperature for about 1 hour, the temperature is raised to about 80 ° C., and ammonia water (for example, having a concentration of about 7%) may be added thereto.

-Dehydration-
The resulting precipitate is centrifuged to remove the supernatant liquid to obtain a dehydrated cake (dehydrated product). After removing the supernatant, water washing / dehydration operation (hereinafter simply referred to as “water washing”) in which ion-exchanged water is added and stirred and then centrifuged again (dehydrated) can be repeated as many times as necessary. By the dehydration step, excess ammonia water is removed, and part of Pd contained in the precipitate is removed.

    In this dehydration step, part of the Pd is removed so that the amount of catalyst metal in the catalyst metal-supported oxygen storage material obtained through the subsequent firing step is 0.05% by mass or less.

-Drying and firing-
The obtained dehydrated cake is dried and then baked to obtain a catalyst metal-supported oxygen storage material in which Pd is supported on CeZr-based composite oxide particles. Drying can be performed by holding the cake at a temperature of about 100 ° C. to 250 ° C. for a predetermined time, and baking can be performed by holding the cake at a temperature of about 400 ° C. to 600 ° C. for several hours.

<Examination of Pd carrying position>
Regarding the catalytic metal-supported oxygen storage material according to the present invention, it was examined where Pd was supported on CeZr-based composite oxide particles.

-Examination of precipitate-
In the method for preparing the catalyst metal-supported oxygen storage material described above, a precipitate is formed when ammonia water is added. In this case, it is well known that Ce ions and Zr ions are precipitated as composite hydroxide particles (precursor of CeZr composite oxide primary particles). On the other hand, Pd ions do not precipitate as hydroxide even when ammonia water is added. That is, when aqueous ammonia was added to a solution containing Ce, Zr and Pd ions to produce a precipitate, and the supernatant was analyzed, Pd was detected. Therefore, it is considered that the Pd ion generates a stable Pd compound such as an ammine complex, and the Pd compound is dissolved in the solution.

    Moreover, 80% or more of the charged amount was contained in the supernatant liquid separated from the precipitate. Therefore, it is considered that a part of the Pd compound is attached to the composite hydroxide particles of Ce and Zr.

    Further, in the above preparation method, when the above washing was repeated, Pd was detected in each washing waste liquid. Therefore, it is considered that most of the Pd compound remaining on the precipitate side after the several water washings adheres to the composite hydroxide particles at a site on the precipitate that is difficult to be washed away.

    The place considered first as the site | part to which it is hard to flow is between the composite hydroxide particle | grains of Ce and Zr. The composite hydroxide particles are aggregated into several to several tens of units to form precipitated particles, but the Pd compound existing between such composite hydroxide particles is difficult to fall off from the precipitated particles by washing with water. it is conceivable that.

    Next, the possible locations will be examined. FIG. 2 is a TEM (transmission electron microscope) photograph of the Pd-supported CeZr-based composite oxide particles obtained by the above preparation method. In the photograph, the small mass protruding downward from the large mass shown in the upper part is the primary particle. Four spots with a diameter of about several nanometers appear whitish on the primary particle surface, which are concave portions. Such a surface depression is considered to have originated from a depressed portion on the surface of the composite hydroxide particle. Thus, it is considered that the Pd compound adhering to the recessed portion of such composite hydroxide particles is difficult to fall off by washing with water.

-TPO test of product by adding ammonia water-
Whether or not the precipitate formed by adhering the Pd compound to the Ce and Zr composite hydroxide particles is dried and fired, whether or not Pd is incorporated into the crystal of the CeZr-based composite oxide to obtain TPO (increase). It was examined by a (warm oxidation) test. This will be described below.

    A palladium nitrate solution was added to and mixed with the activated alumina powder, and ammonia water was added thereto and stirred, followed by heating to evaporate the liquid (evaporation to dryness). The obtained dried product was dried by maintaining at a temperature of 120 ° C. for 10 hours, and pulverized and sized to obtain a first test material. Hereinafter, this is referred to as “Pd-ammonia dry / alumina”.

    A second test material was prepared by performing the same operation as in the above “Pd-ammonia dry / alumina” except that the palladium nitrate solution was not added to the activated alumina powder. Hereinafter, this is referred to as “ammonia dry / alumina”.

    Aqueous ammonia is added to an aqueous solution of cerium (III) nitrate hexahydrate and stirred. The resulting precipitate is centrifuged to remove the supernatant, and then ion-exchanged water is added to this and stirred and centrifuged again. The washing operation of applying to a separator was repeated three times. The obtained cake was dried by keeping it at a temperature of 120 ° C. for 10 hours, and this was pulverized and sized to obtain a third test material. Hereinafter, this is referred to as “Ce-ammonia precipitation”.

    Instead of cerium (III) nitrate hexahydrate, zirconium oxynitrate dihydrate was employed, and the other operations were performed in the same manner as “Ce-ammonia precipitation” to obtain a fourth specimen. Hereinafter, this is referred to as “Zr-ammonia precipitation”.

For each of the above four types of test materials, while supplying a mixed gas of O ₂ and He (O ₂ ; 20%) at a flow rate of 100 cm ³ / min, from 30 ° C. to 600 ° C. at a rate of 20 ° C./min. The temperature was raised and the amount of generated H ₂ O was measured (mass number 18 (H ₂ O) was measured with a TPO mass spectrometer). The results are shown in FIG.

According to the figure, Ce hydroxide produced by “Ce-ammonia precipitation” and Zr hydroxide produced by “Zr-ammonia precipitation” started to decompose around 100 ° C. to generate H ₂ O. You can see that

    On the other hand, the decomposition temperature of the Pd compound produced by adding ammonia water to the Pd solution can be known from comparison between “Pd-ammonia dry / alumina” and “ammonia dry / alumina”. In this case, “ammonia dry / alumina” is a blank test for determining the decomposition temperature of the Pd compound. From this comparison, it can be seen that the decomposition temperature of the Pd compound is 150 ° C. to 350 ° C., and the decomposition does not start unless it is 150 ° C. or higher.

    From the above test results, when the precipitate formed by adhering the Pd compound to the Ce and Zr composite hydroxide particles was dried and fired, the Ce and Zr composite hydroxide was first thermally decomposed and CeZr-based composite oxidation. It can be said that the Pd compound is thermally decomposed after starting to form a product, and thus Pd is not taken into the crystal lattice of the CeZr-based composite oxide.

-Summary-
Therefore, when a precipitate formed by adhering a Pd compound to Ce and Zr composite hydroxide particles is dried and fired, the Pd compound is supported as a Pd oxide on CeZr composite oxide particles. It will be. Thus, as described above, it is considered that most of the Pd compound exists between the composite hydroxide particles and in the recessed portions of the particle surface.

    In this case, the composite hydroxide particles of Ce and Zr become primary particles of CeZr-based composite oxide particles, and the recessed portion of the surface of the composite hydroxide particles becomes a surface recess of the primary particles, and the composite hydroxide particles The space develops into pores of the composite oxide particles.

    Therefore, the obtained catalyst metal-supported oxygen storage material is a secondary particle formed by agglomerating primary particles of CeZr-based composite oxide in which fine Pd particles are supported, and most of Pd is CeZr-based composite oxide particles. It can be said that it is in a state of being arranged between the primary particles and the concave portions on the surface of the primary particles constituting the.

<Pore properties of catalyst metal-supported oxygen storage material>
-Preparation of test material-
Five types of coprecipitation type test materials (catalyst metal-supported oxygen storage materials) having different numbers of water washing (0 to 4 times) were prepared by the above-described preparation method.

    That is, a predetermined amount of each of cerium (III) nitrate hexahydrate, zirconium oxynitrate dihydrate and palladium nitrate solution was mixed with water to make a total of 400 mL, and this was stirred at room temperature for about 1 hour, then 80 The temperature was raised to 0 ° C., and 1200 mL of 7% aqueous ammonia was added and mixed. The resulting precipitate was centrifuged to remove the supernatant, and then the water washing operation of adding ion-exchanged water to this, stirring, and re-centrifuged was repeated the required number of times (0 to 4 times) to obtain The resulting cake was dried (held at a temperature of 200 ° C. for 10 hours) and fired (held at a temperature of 500 ° C. for 10 hours) to obtain five types of test materials.

The charged amount of cerium (III) nitrate hexahydrate and zirconium oxynitrate dihydrate was set to be CeO ₂ : ZrO ₂ = 75: 25 (mass ratio), and the charged amount of palladium nitrate was temporarily charged. When the total amount of Pd was supported on the CeZr-based composite oxide particles, the amount of Pd supported was set to an amount that would be 0.5% by mass of the oxygen storage material. The measured values (analyzed values) of the Pd amounts of the five types of test materials are as shown in Table 1. Here, the test material with the number of times of washing with water of 0 was only the supernatant was removed by centrifuging the precipitate, but the measured value of the Pd amount was 0.05% by mass. 90% by mass of Pd was separated and removed from the precipitate together with the supernatant.

    The pore distribution of each of the above five types of specimens (fresh product that had not been heat-treated after preparation) and heat-treated product (maintained at a temperature of 1000 ° C. for 24 hours in the air after preparation) was determined by Shimadzu Corporation. It investigated using the manufactured pore distribution measuring apparatus. The result of the fresh product is shown in FIG. 4, and the result of the heat-treated product is shown in FIG. In both figures and in FIG. 6 described later, the vertical axis indicates the log differential pore volume.

Looking at FIG. 4 (fresh product), the peak of the pore size distribution is in the range of 8 nm or more and 10 nm or less, and as the number of water washing increases, the pore volume at the peak pore size tends to increase. The log differential pore volume is 0.2 cm ³ / g or more when the number of washings is one or more. However, when the number of washings is 3 or more, the pore volume is not increased.

Looking at FIG. 5 (heat-treated product), the peak of the pore size distribution is shifted to a range of 50 nm to 70 nm, and as with the fresh product, the pore volume at the peak pore size increases as the number of water washing increases. However, when the number of washings is 3 or more, the pore volume is not increased. The log differential pore volume is 0.15 cm ³ / g or more when the number of washings is twice or more.

In addition, a comparative sample material in which 0.01 mass% of Pd was supported on a CeZr composite oxide (CeO ₂ : ZrO ₂ = 75: 25 (mass ratio)) by evaporation to dryness using a palladium nitrate solution was prepared. The pore distribution after the heat treatment was examined. The result is shown in FIG. 6 together with the result of the test material with the number of times of washing three times. When the evaporation to dryness method is employed, the peak of the pore size distribution is in the range of 50 nm to 70 nm as in the coprecipitation method, but the log differential pore volume at the peak pore size is 0.1 cm ³ / g. It is small and small.

    Tables 2 and 3 show the total pore volumes (cumulative pore volumes) having pore diameters of 10 nm or less and 100 nm or less in the fresh product and the heat-treated product, respectively.

    According to Tables 2 and 3, a tendency that the pore volume increases as the number of times of water washing increases in any of pore diameters of 10 nm or less and 100 nm or less (however, in the case of heat-treated products, the number of times of water washing is 4 times. The pore volume is smaller than 3 times.) This increasing tendency can be said to be a result of the water washing process promoting the formation of pores.

However, in the case of the heat-treated product, the pore volume is larger than that of the comparative example when the number of washings is one or more times (when the pore diameter is 10 nm or less, the total pore volume is 0.08 cm ³ / g or more, and when the pore size is 100 nm or less, The pore volume is 1.00 cm ³ / g or more), and the deterioration rate of the fresh product → heat-treated product is smaller in the example than in the comparative example.

<Oxygen releasing ability of catalytic metal-supported oxygen storage material>
Each example test material in Table 1, the above comparative sample material (Pd loading by evaporation to dryness; 0.01% by mass), and a comparative sample material (CeZr composite oxide (CeO ₂ : ZrO ₂₎ = 75: 25 (mass ratio)), Pd unsupported) for a total of 7 kinds of test materials, the oxygen release capacity after heat treatment (maintained at a temperature of 1000 ° C. for 24 hours in an air atmosphere) was increased using CO. It investigated by the temperature reduction method (CO-TPR).

That is, while supplying a mixed gas of O ₂ and N ₂ (O ₂ ; 20%) to each sample material 0.10 g at a flow rate of 100 mL / min, the temperature was raised and held at a temperature of 600 ° C. for 20 minutes. Then, a pretreatment (oxygen occlusion treatment) for cooling to room temperature was performed. Thereafter, while supplying 2% CO gas (remaining; N ₂ ) at a flow rate of 100 mL / min, the temperature was increased at a rate of 20 ° C./min, and changes due to the temperature of CO ₂ release were measured. The CO ₂ release amount corresponds to the oxygen release amount of the test material.

    The results are shown in FIG. The test materials of Examples and Comparative Examples (evaporation to dryness) supporting Pd have a larger oxygen release amount than the Comparative Samples without Pd. This indicates that Pd is involved in oxygen release in the low temperature region of the test material supporting Pd.

    In addition, all of the test materials in the examples, particularly in the four examples in which the amount of Pd supported is less than 0.01% by mass, the oxygen release amount in the low temperature range (220 ° C. or less) is the comparative test sample. It is more than the material (Pd loading 0.01% by mass). From this, it can be seen that when a small amount of Pd is supported on the CeZr-based composite oxide by the ammonia coprecipitation method as in the present invention, the oxygen releasing ability at a low temperature increases.

FIG. 8 is a graph obtained by dividing the oxygen release amount of the above seven kinds of test materials every 100 ° C. It can be seen that in the example specimen, the oxygen release amount is significantly higher than that in the comparative example specimen in the temperature range of 100 ° C. or higher and lower than 200 ° C. The oxygen release amount of the example test material in the temperature range of 100 ° C. or more and less than 200 ° C. is 2.0 × 10 ⁴ μmol / g or more as oxygen atoms.

    FIG. 9A and FIG. 9B are model diagrams of the oxygen release mechanism of the example test material and the comparative sample material (evaporation to dryness). In the case of the example test material (FIG. 9A), the Pd particles 2 supported on the CeZr-based composite oxide particles 1 are finer and higher than the comparative example test material (FIG. 9B). It is thought that it is carried in dispersion. That is, in the case of the example test material, there are many places where the Pd particles 2 are in contact with the CeZr-based composite oxide particles 1. For this reason, in the example test material, Pd mediates oxygen storage / release more efficiently than the comparative sample material, and it is considered that the amount of active oxygen released in the low temperature range is increased. It is done.

<Exhaust gas purification performance of catalytic metal-supported oxygen storage material>
5 types of test materials with different numbers of washing times (0 to 4 times) shown in Table 1, comparative sample materials (Pd loading by evaporation to dryness: 0.05 mass%), comparative sample materials (Pd loading by evaporation to dryness; 0.01% by mass) and comparative sample materials (no Pd supported), honeycomb catalysts for rig evaluation were prepared and their exhaust gas purification performance (light-off temperature T50 and high temperature) The purification performance C400) was evaluated. In addition, only the light-off temperature was measured about the comparative sample material (Pd carrying amount; 0.05 mass%).

That is, a slurry is prepared by combining a binder and water with each sample material, and the honeycomb carrier is dipped in this slurry and pulled up, the excess adhering slurry is removed, and dried and fired to obtain the above sample material. A honeycomb catalyst for rig evaluation in which the contained catalyst layer was formed on the cell wall surface was prepared. The firing condition of the slurry adhered to the honeycomb carrier was 500 ° C. × 2 hours (in the air). The loading amount of the test material per liter of honeycomb carrier was 80 g / L. A Zr binder was used as the binder, and the binder amount was 8.9 g / L. As the honeycomb carrier, a cell having a cell wall thickness of 4 mil (101.6 × 10 ⁻³ mm) and 400 cells per square inch (635.16 mm ² ) was employed.

    Thus, each honeycomb catalyst was subjected to heat aging (atmospheric atmosphere, 1000 ° C. × 24 hours), set in a model exhaust gas flow reactor, preconditioned, and then T50 and C400 were measured. Preconditioning is performed by increasing the gas temperature from room temperature at a rate of 30 ° C./minute while flowing model exhaust gas (see Table 4) with A / F = 14.7 through the catalyst at a space velocity of 120,000 / h. A temperature of 20 ° C. is allowed to flow for 20 minutes.

    The model exhaust gas for exhaust gas purification performance evaluation was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. Table 4 shows the gas composition when A / F = 14.7, A / F = 13.8 and A / F = 15.6. The space velocity SV was 60000 / h, and the temperature elevation rate was 30 ° C./min.

    T50 (° C.) indicates that the concentration of each component (HC, CO and NOx) of the gas detected downstream of the catalyst due to the rise of the model exhaust gas temperature is the concentration of each component (HC, CO and NOx) of the gas flowing into the catalyst. This is the catalyst inlet gas temperature at the time when it is halved (that is, when the purification rate is 50%) and represents the low-temperature purification performance of the catalyst. C400 (%) is the purification rate of each component (HC, CO and NOx) of the gas when the catalyst inlet gas temperature is 400 ° C., and represents the high temperature purification performance of the catalyst. The result of T50 is shown in FIG. 10, and the result of C400 is shown in FIG.

    Looking at T50 (FIG. 10) and C400 (FIG. 11), all of the five types of example catalysts with different numbers of water washings have better exhaust gas purification performance than the comparative example catalyst. Characteristically, the four example catalysts having a Pd loading of 0.01% by mass or less have a smaller Pd loading than the comparative catalyst (Pd loading by evaporation to dryness; 0.01% by mass). Nevertheless, T50 is as low as 40 ° C. or higher, and C400 is as high as about 10% or higher. Even when each of the Pd loadings of 0.05% by mass is compared with the comparative example, T50 is lower by 40 ° C. or more in the example.

    From this result, it is effective to drastically improve the exhaust gas purification performance while greatly reducing the amount of Pd supported while supporting a small amount of Pd on the CeZr-based composite oxide by the ammonia coprecipitation method as in the present invention. I understand. Further, when looking at the five types of sample materials, T50 increases and C400 tends to decrease as the amount of Pd supported decreases, but when the number of water washing increases, that is, Pd When the loading amount approaches zero, both the increasing tendency of T50 and the decreasing tendency of C400 are dull, and the exhaust gas purification performance is settled down. However, the exhaust gas purification performance is much better than the comparative example catalyst.

    This is because, when Pd is supported on the CeZr-based composite oxide by the ammonia coprecipitation method, a very small amount of Pd is difficult to sinter on the CeZr-based composite oxide particles (the concave portion of the primary particle surface, the primary This suggests that they are arranged in a highly dispersed state (between particles).

    In the above embodiment, the catalyst metal-supported oxygen storage material is used as an exhaust gas purification catalyst. However, when the catalyst metal-supported oxygen storage material according to the present invention is used as a fuel cell CO selective oxidation catalyst, a very small amount of Pd supported. With this, an excellent oxygen releasing ability and high catalytic activity can be obtained, which is advantageous for reducing the CO concentration of the reformed gas.

It is a perspective view which shows typically the catalyst metal carrying | support oxygen storage material which concerns on this invention. It is a TEM photograph of the catalyst metal carrying oxygen storage material concerning the present invention. It is a graph showing of H _{2 O} emissions by heating oxidation test various test materials. It is a graph which shows the pore distribution of five types of catalyst metal carrying | support oxygen storage materials (fresh goods) from which the frequency | count of water washing (Pd carrying amount) differs. It is a graph which shows the pore distribution of five types of catalyst metal carrying | support oxygen storage materials (heat treatment goods) from which the frequency | count of water washing (Pd carrying amount) differs. It is a graph which shows the pore distribution after the heat processing of each catalyst metal carrying | support oxygen storage material which concerns on this invention, and a comparative example. It is a graph which shows the oxygen release characteristic of various test materials. It is a graph which shows the oxygen release amount of various test materials. It is a model figure of the oxygen release mechanism of an Example and a comparative example. It is a graph which shows the light-off temperature of an Example catalyst and a comparative example catalyst. It is a graph which shows the exhaust gas high temperature purification rate of an Example catalyst and a comparative example catalyst.

Explanation of symbols

1 CeZr-based composite oxide particle 2 Pd particle 3 Primary particle 4 Surface recess

Claims (10)

A catalyst metal-supported oxygen storage material in which Pd is supported as a catalyst metal on CeZr-based composite oxide particles,
A catalytic metal-supported oxygen storage material, wherein most of the Pd is disposed in a concave portion of a surface of a primary particle constituting the CeZr-based composite oxide particle or between the primary particles. In claim 1,
A catalytic metal-supported oxygen storage material, wherein the supported amount of Pd is 0.05% by mass or less. The primary particles of CeZr-based composite oxide in which Pd is supported as a catalyst metal aggregate to form secondary particles,
A catalytic metal-supported oxygen storage material, wherein the supported amount of Pd is 0.05% by mass or less. In claim 1 or claim 3,
A catalytic metal-supported oxygen storage material, wherein the supported amount of Pd is 0.01% by mass or less. In any one of Claims 1 thru | or 4,
The peak of the pore size distribution after being kept at a temperature of 1000 ° C. for 24 hours in the air atmosphere is in the range of 50 nm to 70 nm and the log differential pore volume at the peak pore size is 0.15 cm ³ / g or more. A catalyst metal-supported oxygen storage material. In any one of Claims 1 thru | or 5,
A catalyst metal-supported oxygen storage material, wherein an oxygen release amount at 100 ° C. or more and less than 200 ° C. is 2.0 × 10 ⁴ μmol / g or more as oxygen atoms. A method for producing a catalyst metal-supported oxygen storage material in which Pd is supported as a catalyst metal on CeZr-based composite oxide particles,
Adding and mixing aqueous ammonia to an acidic solution containing Ce ions, Zr ions and Pd ions;
A step of dehydrating the obtained precipitate;
A step of obtaining the catalyst metal-supported oxygen storage material by calcining the obtained dehydrated product,
In the dehydration step, a part of the component relating to the Pd ions is removed together with the supernatant so that the amount of Pd supported on the catalyst metal-supported oxygen storage material is 0.05% by mass or less. A method for producing a supported oxygen storage material. In claim 7,
In the dehydration step, part of the component relating to the Pd ions is removed so that the amount of Pd supported on the catalyst metal-supported oxygen storage material is 0.01% by mass or less. Production method of occlusion material.     An engine exhaust gas purification catalyst containing the catalyst metal-supported oxygen storage material according to any one of claims 1 to 6.     A CO selective oxidation catalyst for a fuel cell, comprising the catalytic metal-supported oxygen storage material according to any one of claims 1 to 6.