JP7087557B2 - Catalytic material for purification of particulate and its manufacturing method - Google Patents

Description

The present invention relates to a catalyst material for purifying particulates and a method for producing the same.

Exhaust gas from diesel engines and lean-burn gasoline engines contains carbon-based particulates (fine-grained particulate matter). Therefore, a filter is placed in the exhaust gas passage to collect the particulate, and when the collected amount is large, the filter is regenerated by burning the particulate and removing it from the filter. It has been. A catalyst is supported on the filter body in order to promote the combustion of the particulate.

As a catalyst material used for such a catalyst, for example, a Zr-based composite oxide containing Zr and a rare earth element other than Ce is known (see, for example, Patent Document 1). The Zr-based composite oxide can efficiently burn the particulate by releasing active oxygen by an oxygen exchange reaction.

Japanese Unexamined Patent Publication No. 2009-101342

By the way, since Pr, which is a rare earth element, easily changes in valence, it is known that Pr oxide (Pr ₆ O ₁₁ ) has high oxygen release characteristics, and is expected as a catalyst material for particulate purification. can.

However, when the Pr oxide is independently supported on the filter, there is a problem that the catalytic performance is deteriorated due to sintering.

Therefore, it is an object of the present invention to provide a catalytic material for purifying particulates having higher particulate combustion performance by improving the sintering resistance of Pr.

In order to solve the above-mentioned problems, the catalytic material for purifying the particulate according to the first technique disclosed herein contains Pr and is a particulate for purifying the particulate contained in the exhaust gas of the internal combustion engine. A purifying catalyst material, a Pr-based composite oxide material containing Zr and a part of the Pr, a Pr - based composite oxide containing the rest of the Pr, and one or more rare earth elements other than Pr. When an oxide material is provided and X-ray diffraction measurement is performed, the peak derived from the Zr-based composite oxide material and the Pr-based composite oxide material are the (220) reflection peaks derived from the fluorite-shaped structure. The Pr-based composite oxide material is contained in the Zr-based composite oxide material in a state where the derived peaks are observed as separate peaks and the (220) reflection peak of Pr 6O 11 _{is not} observed. It is characterized by that.

When Pr oxide is used alone as a catalytic material for purifying particulates, the catalytic activity of Pr oxide is lowered by sintering. According to the present technique, by incorporating Pr as a composite oxide containing Pr and a metal element other than Pr in the catalytic material for purifying particulates, the sintering resistance of Pr can be improved. Further, the remaining amount of Pr contained in the catalyst material for purifying the particulate is doped into the Zr-based composite oxide material as a Pr-based composite oxide material containing Pr and one or more rare earth elements other than Pr. By doing so, it is possible to further improve the syntering resistance of Pr and provide a catalyst material for purifying the particulate with high particulate combustion performance.

Further , Pr contained in the particulate purification catalyst material does not form Pr ₆ O ₁₁ .

If Pr is contained in the catalytic purification catalyst material in a state where Pr ₆ O ₁₁ is formed, it may be deteriorated by sintering. According to this technique, by not containing Pr ₆ O ₁₁ in the catalyst material for purifying the particulate, the sintering resistance of the catalyst material for purifying the particulate can be improved, and the particulate purification having high particulate combustion performance can be improved. Can bring catalyst material.

The second technique is characterized in that, in the first technique, the rare earth element is Nd and / or Y.

According to this technology, by dissolving Nd and / or Y, which have a smaller ionic radius than Pr, as a rare earth element in a Pr-based composite oxide material, the stability of the Pr-based composite oxide material is improved and synter resistance is improved. Ringability is improved. As a result, it is possible to provide a catalyst material for purifying particulates having high particulate combustion performance.

The third technique is characterized in that, in the first or second technique , the Zr-based composite oxide material further contains Nd and / or Y.

According to the present technology, a composite oxide further containing Zr and Nd and / or Y, which are rare earth elements other than Ce as additional rare earth elements, has excellent PM combustion performance. Therefore, by including the Pr-based composite oxide material in such a Zr-based composite oxide material, the particulate combustion performance of the catalytic material for purifying the particulate can be further improved.

The method for producing a particulate purification catalyst material according to the fourth technique disclosed herein is a method for producing a particulate purification catalyst material according to any one of the first to third techniques, and at least . , A co-precipitation step of co-precipitating a Zr salt and a Pr salt to obtain a first co-sediment, and co-precipitation by adding a Pr salt and a salt containing a rare earth element to the first co-precipitate. It is characterized by including an addition step of obtaining a second co-precipitate, a drying step of drying the second co-precipitate, and a baking step of firing the dried second co-precipitate.

According to this technique, it is possible to obtain a catalyst material for particulate purification in which a Zr-based composite oxide material is doped with a Pr-based composite oxide material. This particulate purification catalyst material has excellent Pr sintering resistance and can have high particulate combustion performance, and is useful as a catalyst for purifying exhaust gas.

As described above, according to the present invention, by incorporating Pr as a composite oxide containing Pr and a metal element other than Pr in the catalytic material for purifying the particulate, the sintering resistance of Pr is improved. be able to. Further, at least a part of Pr contained in the catalyst material for purifying the particulate was doped into the Zr-based oxide material as a Pr-based composite oxide material containing Pr and one or more rare earth elements other than Pr. By setting the state, it is possible to further improve the syntering resistance of Pr and provide a catalyst material for purifying the particulate with high particulate combustion performance.

It is a figure which shows typically the structure of the catalyst material for particulate purification which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the manufacturing process of the catalyst material for particulate purification which concerns on one Embodiment of this invention. It is a graph which shows the influence on the internal oxygen release characteristic which contributes to a carbon combustion reaction by PrREOx. It is a graph which shows the X-ray diffraction measurement result about the catalyst material of Examples 1 to 3 and Comparative Examples 1 and 2. It is a graph which shows the X-ray diffraction measurement result about the catalyst material of Example 4 and Comparative Example 3. 3 is a graph showing oxygen release characteristics in vacuum for the catalyst materials of Example 3 and Comparative Example 1. 6 is a graph showing oxygen release characteristics in vacuum for the catalyst materials of Example 4 and Comparative Examples 3 and 4. 6 is a graph showing the amount of oxygen ( ¹⁶ O) released inside the catalyst for the catalyst materials of Examples 3 and 4 and Comparative Examples 1 and 3.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of preferred embodiments is merely exemplary and is not intended to limit the invention, its applications or its uses.

(Embodiment 1)
<Catalyst material for particulate purification>
The catalyst material 1 for purifying the particulate according to the first embodiment (hereinafter, may be referred to as “catalyst material 1”) is a particulate whose main component is carbon contained in the exhaust gas of an internal combustion engine (hereinafter, “catalyst material 1”). It is for purifying (referred to as PM).

The internal combustion engine may be any engine whose exhaust gas contains PM. In addition to lean-burn engines such as diesel engines and lean-burn gasoline engines of automobiles, PM emissions are relatively small, but direct injection of stoichiometric combustion or Examples include a port-injection gasoline engine.

As shown in FIG. 1, the catalyst material 1 has a structure in which a Zr-based oxide material 11 is doped as a Pr-based composite oxide material 12 containing rare earth elements other than Pr and Pr.

In the present specification, the "state in which the element is solid-dissolved" means that the added element is dissolved in the lattice to form a solid solution, and the XRD obtained by X-ray diffraction measurement (XRD) is obtained. A state in which the diffraction peak indicates a single layer. Further, the "state in which the element is doped" means that the element was added in the addition step S2 described later, and the XRD diffraction peak in this state is the coprecipitation obtained in the coprecipitation step S1. A peak can be given at a position different from the peak given by the deposit. Further, the "state in which the element is supported" means a state in which the element is added by the evaporation to dryness method after the firing step S5 described later. The "state containing an element" or the "state containing an element" means that the element is "solid solution", "doped" and / or "supported" in the catalyst material. It means that you are doing.

≪Zr-based oxide material≫
The Zr-based oxide material 11 is an oxide containing Zr. The Zr-based oxide material 11 may be a composite oxide containing one or more rare earth elements RE (additional rare earth elements) other than Ce in addition to Zr. Since the composite oxide containing rare earth elements other than Zr and Ce has excellent PM combustion performance, it can contribute to the improvement of the particulate combustion performance of the catalytic material 1 for purifying the particulate. The rare earth element other than Ce is specifically at least one selected from the group of Pr, Nd, Y, La, and Sc, and is preferably a ZrPrNd composite oxide containing Pr and Nd, and Pr. It is a ZrPrY composite oxide containing Y.

When Pr is contained in the Zr-based oxide material 11, Pr is not only contained in the catalyst material 1 as a Pr-based composite oxide material, but also Pr and one or more metal elements other than Pr. A Zr-based composite oxide containing Zr is also contained in the catalyst material 1.

≪Pr-based composite oxide material≫
The Pr-based composite oxide material 12 is doped with the Zr-based oxide material 11. By setting the Pr-based composite oxide material 12 containing Pr and a rare earth element in a state of being doped with a Zr-based oxide material, the sintering resistance of the Pr oxide can be improved. By doping the Zr-based oxide material 11 with the Pr-based composite oxide material 12, the sintering resistance of the Pr oxide is further improved, and the catalytic material for purifying the particulate with high particulate combustion performance. Can bring.

The Pr-based composite oxide material 12 is a composite oxide containing Pr and one or more rare earth elements other than Pr. The rare earth element other than Pr is preferably a trivalent rare earth element other than Ce from the viewpoint of stabilizing the composite oxide by introducing oxygen defects. In other words, the Pr-based composite oxide material 12 is preferably an oxide containing Pr and rare earth elements other than Ce and Pr. Composite oxides containing Pr and one or more rare earth elements other than Pr are known to have a fluorite-type structure based on the XRD diffraction pattern, and the introduction of oxygen defects stabilizes the fluorite-type structure. It is known to get. Therefore, it is desirable that the rare earth element other than Pr is a rare earth element other than Ce that can take only trivalent rather than Ce that can take trivalent and tetravalent. The rare earth element other than Pr is specifically at least one selected from the group of Nd, Y, La, and Sc, and is preferably Nd and / or Y. By containing Nd and / or Y having an ionic radius smaller than that of Pr, the stability of the Pr oxide is improved and the sintering resistance is improved.

<Manufacturing method of catalyst material for particulate purification>
As shown in FIG. 2, the manufacturing step of the catalyst material 1 includes a co-precipitation step S1, an addition step S2, a drying step S3, a crushing step S4, and a firing step S5.

≪Coprecipitation process≫
The coprecipitation step S1 is a step of coprecipitating a Zr salt and, if necessary, a rare earth element other than Ce under alkaline conditions to obtain a first coprecipitate.

Specifically, for example, an alkaline solution is added to an acidic solution of Zr and, if necessary, a nitrate of a rare earth element other than Ce to neutralize the mixture to obtain a first coprecipitate.

≪Addition process≫
In the addition step S2, a Pr salt and a salt containing a rare earth element other than Pr are added to the first coprecipitate obtained in the coprecipitation step S1, and a basic solution is further added to neutralize the first coprecipitate. , Pr composite oxide is a step of precipitating and precipitating, that is, further co-precipitating to obtain a second co-precipitate. The dehydration operation of centrifuging the second coprecipitate to remove the supernatant liquid and the water washing operation of adding ion-exchanged water and stirring the mixture are alternately repeated as many times as necessary. Then, a gel-like second coprecipitate is obtained.

≪Drying process≫
The drying step S3 is a step of drying the second coprecipitate obtained in the addition step S2. The drying method is not intended to be limited, but specifically, it can be dried by holding it in the air at about 100 ° C. to 180 ° C. for about 5 hours to 24 hours.

≪Crushing process≫
The crushing step S4 is a step of crushing the second coprecipitate dried in the drying step S3 to a desired size. In the crushing step S4, the second coprecipitate is crushed to a desired average particle size D50 by, for example, a ball mill or the like.

≪Baking process≫
The firing step S5 is a step of firing the second coprecipitate crushed in the crushing step S4. The calcination conditions are not intended to be limited, but specifically, calcination can be performed by holding the calcination in air at a temperature of 300 ° C. to 700 ° C. for about 1 hour to 4 hours.

In this way, the catalyst material 1 in which the Zr-based oxide material 11 is doped with the Pr-based composite oxide material 12 can be obtained. If it is not necessary to crush the second coprecipitate, the crushing step S4 can be omitted.

<Composition, shape, and size of catalyst material for particulate purification>
The catalyst material 1 prepared as described above has a composition composed of Zr oxide (ZrO ₂ ), Pr oxide (Pr ₂ O ₃ ) and rare earth element oxide (REOx).

The amount of the Zr oxide (ZrO ₂ ) component in the above composition of the catalyst material 1 is preferably 50 mol% or more and 80 mol% or less, more preferably 55 mol% or more and 75 mol% or less, from the viewpoint of improving the catalyst performance. Particularly preferably, it is 60 mol% or more and 70 mol% or less.

The amount of the component of Pr oxide (Pr ₂ O ₃ ) in the above composition of the catalyst material 1 is preferably 5 mol% or more and 45 mol% or less, and more preferably 10 mol% or more and 40 mol% from the viewpoint of improving the catalyst performance. Hereinafter, it is particularly preferably 15 mol% or more and 30 mol% or less.

The amount of the rare earth element oxide (REOx) component in the above composition of the catalyst material 1 is preferably 3 mol% or more and 35 mol% or less, more preferably 5 mol% or more and 30 mol% or less, from the viewpoint of improving the catalyst performance. Particularly preferably, it is 6 mol% or more and 25 mol% or less.

Of the Pr oxide (Pr ₂ O ₃ ) components contained in the catalyst material 1, the amount of the component as the Pr-based composite oxide material 12 (PrREOx) is the Pr oxide (Pr ₂ O 3) contained in the catalyst material 1. The ratio to the total amount of components in ₃ ) is preferably 0.1 or more and 0.7 or less, more preferably 0.12 or more and 0.6 or less, and particularly preferably 0.15 or more and 0.5 or less.

Of the rare earth element oxides (REOx) components contained in the catalyst material 1, the amount of the components as the Pr-based composite oxide material 12 (PrREOx) is the total amount of the rare earth element oxides (REOx) contained in the catalyst material 1. The ratio to the amount of the component is preferably 0.1 or more and 0.7 or less, more preferably 0.12 or more and 0.6 or less, and particularly preferably 0.15 or more and 0.5 or less.

The shape of the catalyst material 1 is not particularly limited, but may be, for example, a particulate powder from the viewpoint of increasing the contact area with the exhaust gas and improving the catalyst performance. The average particle size D50 of the powder is not particularly limited, but can be, for example, 10 nm or more and 5 mm or less. The aspect ratio obtained by dividing the maximum diameter of the powder particles by the minimum diameter is not particularly limited, but can be, for example, 1 or more and 20 or less.

<Characteristics of catalyst material for particulate purification>
Here, the catalyst material 1 can be said to be an oxide material containing Zr, Pr, and one or more rare earth elements other than Pr. In the catalyst material 1, Pr forms a composite oxide with a metal element other than Pr, and in particular, at least a part of Pr forms a composite oxide with a rare earth element other than Pr in the catalyst material 1. It exists in the state of being. And Pr is not contained as Pr oxide, particularly Pr ₆ O ₁₁ .

Such a catalyst material 1 has a fluorite-shaped structure. Then, when X-ray diffraction measurement (XRD) is performed, the peak derived from the Zr-based oxide material 11 and the peak derived from the Pr-based composite oxide material 12 are the (220) reflection peaks derived from the fluorite-shaped structure. _Are observed as separate peaks, and the (220) reflection peak of Pr oxide, especially Pr _6O11 , is not observed.

The fact that the peak derived from the Pr-based composite oxide material 12 is observed at a position different from the peak derived from the Zr-based oxide material 11 means that the Pr-based composite oxide material 12 is formed in the catalyst material 1. Is shown. Further, the fact that no peak derived from Pr oxide, particularly Pr ₆ O ₁₁ is observed indicates that Pr oxide, particularly Pr ₆ O ₁₁ , is not formed.

In the catalyst material 1, Pr forms a composite oxide with a metal element other than Pr, so that the sintering resistance of Pr is improved, so that the heat resistance is improved and PM due to the internal oxygen release performance is improved. Excellent combustion performance. Regarding the amount of internal oxygen released that contributes to the carbon combustion reaction measured by the method of evaluation experiment 1 described later, the amount of internal oxygen released from the catalyst material 1 is prepared by adding all the salts in the co-precipitation step without providing the addition step. It can be increased preferably 1.03 times or more, more preferably 1.03 times or more and 1.20 times or less, and particularly preferably 1.03 times to 1.10 times, as compared with the above-mentioned catalyst material.

Further, the catalyst material 1 can release oxygen in contact with PM in the exhaust gas due to the high oxygen release characteristics of the Pr-based composite oxide material 12. Then, oxygen vacancies may be formed in the Pr-based composite oxide material 12. Then, it is considered that the PM combustion performance of the Zr-based oxide material 11 can be effectively utilized through the formed oxygen vacancies. Therefore, it is considered that the catalyst material 1 can exhibit excellent oxygen release characteristics particularly in a reducing atmosphere as compared with the catalyst material prepared by adding all the salts in the co-precipitation step without providing the addition step.

<How to use the catalyst material for particulate purification>
The catalyst material 1 can be supported and used, for example, on a particulate filter for collecting PM arranged in an exhaust gas passage of an internal combustion engine. The method for supporting the catalyst material 1 on the particulate filter is not particularly limited, and a general method can be adopted. Specifically, for example, the catalyst material 1 can be supported as follows. That is, the catalyst material 1 is mixed with ion-exchanged water together with other catalyst materials, support materials, binder materials, and the like to prepare a slurry containing the catalyst material 1. Then, the slurry is sucked from the outlet side of the filter body having a honeycomb structure formed of an inorganic porous material such as cordierite, SiC, Si 3N ₄ , Sialon, and _{AlTiO 3 and} contained in the filter body. Let me. Then, after removing the excess slurry by air blow, the slurry is dried (150 ° C.) and calcined (held at 500 ° C. for 2 hours) in the air. As a result, the catalyst material 1 is supported on the filter body.

Other catalyst materials and support materials are not particularly limited, and specific examples thereof include activated alumina materials, CeZr-based composite oxide materials containing Zr and Ce, and the like.

Further, the catalyst material 1, the other catalyst material, and the support material may contain a catalyst metal such as Pt, Pd, and Rh.

When the catalyst metal is dissolved or doped in the catalyst material 1, it can be carried out by adding, for example, a nitrate of the catalyst metal to an acidic solution in the co-precipitation step S1 or the addition step S2, respectively. The same can be performed when the catalyst metal is dissolved or doped in another catalyst material or support material. Further, when the catalyst metal is supported, the catalyst metal can be supported on the catalyst material 1, another catalyst material, and the support material by using an evaporative drying method or the like.

The binder material is for improving the adhesion between the particles of the catalyst material 1, another catalyst material, the support material, and the wall surface of the filter body, and specific examples thereof include a zirconia binder and the like. Further, from the viewpoint of imparting catalytic performance to the binder material, a Zr-based composite oxide containing rare earth elements other than Zr and Ce, a powder of CeZr-based composite oxide containing Ce and Zr, and a catalyst for these powders. A fine particle powder obtained by pulverizing a powder containing a metal to an average particle size D50 of, for example, 150 nm or less, further to 80 nm or less may be used as a binder material.

As described above, by containing other components such as other catalyst materials, support materials, catalyst metals, binder materials, etc. in addition to the catalyst material 1, PM combustion performance can be improved or contained in the exhaust gas, for example. Purification performance of other purification components such as HC, CO, and NOx can be imparted.

(Other embodiments)
Hereinafter, other embodiments according to the present invention will be described. In the description of these embodiments, the same parts as those of the first embodiment are designated by the same reference numerals and detailed description thereof will be omitted.

The method of supporting the catalyst material 1 of the first embodiment on the particulate filter has a configuration in which only one catalyst layer is provided on the wall surface of the filter main body, but the catalyst material 1 and other catalyst materials, support materials, and catalyst metals are provided. , A plurality of additional catalyst layers including a binder material and the like may be laminated.

Next, a concrete example will be described.

<Catalyst material>
Table 1 shows the configurations of the catalyst materials of Examples 1 to 4 and Comparative Examples 1 to 4.

Hereinafter, a method for preparing each catalyst material of Examples 1 to 4 and Comparative Examples 1 to 4 will be described. In Table 1, the place where- (hyphen) is entered indicates that the corresponding salt has not been added. In addition, the shaded area indicates that the addition step is not provided.

<< Example 1 >>
ZrYPrOx as the catalyst material 1 by doping ZrYPrOx as the Zr-based oxide material 11 with _PrYOx as the Pr-based composite oxide material 12 (composition; 70 mol% ZrO _2-8 mol% _Y2O 3-22). Mol% Pr ₂ O ₃ ) was prepared.

After dissolving zirconium oxynitrate (Zr salt), yttrium nitrate (Y salt), and placeodium nitrate hexahydrate (Pr salt) in ion-exchanged water, add a 8-fold diluted solution of 28% by mass ammonia water to this nitrate solution. The first co-precipitate was obtained by mixing and neutralizing. (Coprecipitation process).

To this gel-like first co-precipitate, an aqueous solution obtained by dissolving placeodium nitrate hexahydrate and yttrium nitrate in ion-exchanged water is added, and an 8-fold diluted solution of 28% by mass ammonia water is further mixed. A second co-precipitate was obtained by neutralization. The dehydration operation of centrifuging the second coprecipitate to remove the supernatant liquid and the washing operation of adding ion-exchanged water and stirring the mixture are alternately repeated about three times, and finally the gel-like second coprecipitate is formed. The product was obtained (addition step).

Then, this gel-like second co-precipitate is dried in air at a temperature of 150 ° C. for a whole day and night (drying step), crushed by a ball mill (crushing step), and held at a temperature of 500 ° C. in air for 2 hours. The ZrYPrOx powder as the catalyst material 1 was obtained by performing the firing (firing step).

The addition ratios of the Zr salt, Pr salt, and Y salt added in each step are as shown in Table 1. That is, the Zr salt was added only in the co-precipitation step. The addition ratio (Pr salt amount in the co-precipitation step / Pr salt amount in the addition step) in the co-precipitation step and the addition step of the Pr salt was 0.85 / 0.15. Further, the addition ratio (the amount of Y salt in the co-precipitation step / the amount of Y salt in the addition step) in the co-precipitation step and the addition step of Y salt was 0.85 / 0.15.

<< Example 2 >>
The addition ratio (Pr salt amount in the co-precipitation step / Pr salt amount in the addition step) in the co-precipitation step and the addition step of the Pr salt was 0.75 / 0.25. Further, the addition ratio (the amount of Y salt in the co-precipitation step / the amount of Y salt in the addition step) in the co-precipitation step and the addition step of Y salt was 0.75 / 0.25.

Except for the above, ZrYPrOx as the catalyst material 1 was prepared in the same manner as in Example 1.

<< Example 3 >>
The addition ratio (Pr salt amount in the co-precipitation step / Pr salt amount in the addition step) in the co-precipitation step and the addition step of the Pr salt was 0.5 / 0.5. Further, the addition ratio (the amount of Y salt in the co-precipitation step / the amount of Y salt in the addition step) in the co-precipitation step and the addition step of Y salt was 0.5 / 0.5.

Except for the above, ZrYPrOx as the catalyst material 1 was prepared in the same manner as in Example 1.

<< Example 4 >>
ZrNdPrOx as the Zr-based oxide material 11 is doped with PrNdOx as the Pr-based composite oxide material 12, and _ZrNdPrOx as the catalyst material 1 (composition; 70 mol% ZrO _2-8 mol% Nd ₂ O 3-22). Mol% Pr ₂ O ₃ ) was prepared.

After dissolving zirconium oxynitrate, neodymium nitrate hexahydrate, and placeodium nitrate hexahydrate in ion-exchanged water, this nitrate solution is mixed with an 8-fold diluted solution of 28% by mass ammonia water to neutralize it. , The first co-deposit was obtained. (Coprecipitation process).

To this first co-precipitate, an aqueous solution obtained by dissolving placeodium nitrate hexahydrate and neodymium nitrate hexahydrate in ion-exchanged water is further added, and an 8-fold diluted solution of 28% by mass ammonia water is further mixed. The second co-precipitate was obtained by neutralizing. The dehydration operation of centrifuging the coprecipitate to remove the supernatant liquid and the washing operation of adding ion-exchanged water and stirring the coprecipitate are alternately repeated about 3 times, and finally the gel-like second coprecipitate is formed. Obtained (addition step).

Then, this gel-like second co-precipitate is dried in air at a temperature of 150 ° C. for a whole day and night (drying step), crushed by a ball mill (crushing step), and held at a temperature of 500 ° C. in air for 2 hours. The ZrNdPrOx powder as the catalyst material 1 was obtained by performing the firing (firing step).

The addition ratios of the Zr salt, Pr salt, and Nd salt added in each step are as shown in Table 1. That is, the Zr salt was added only in the co-precipitation step. The addition ratio (Pr salt amount in the co-precipitation step / Pr salt amount in the addition step) in the co-precipitation step and the addition step of the Pr salt was 0.5 / 0.5. Further, the addition ratio (the amount of Nd salt in the co-precipitation step / the amount of Nd salt in the addition step) in the co-precipitation step and the addition step of the Nd salt was 0.5 / 0.5.

<< Comparative Example 1 >>
ZrYPrOx powder as a catalyst material was obtained in the same manner as in Example 1 except that the addition step was not provided and all of the Zr salt, Pr salt, and Y salt were added in the co-precipitation step.

<< Comparative Example 2 >>
All Y salts were added in the co-precipitation step. Then, in the addition step, an aqueous solution of praseodymium nitrate hexahydrate was added. The addition ratio (Pr salt amount in the co-precipitation step / Pr salt amount in the addition step) in the co-precipitation step and the addition step of the Pr salt was 0.5 / 0.5.

Except for the above, ZrYPrOx powder as a catalyst material was obtained in the same manner as in Example 1.

<< Comparative Example 3 >>
ZrNdPrOx powder as a catalyst material was obtained in the same manner as in Example 4 except that the addition step was not provided and all of the Zr salt, Pr salt, and Nd salt were added in the co-precipitation step.

<< Comparative Example 4 >>
After dissolving zirconium oxynitrate and neodymium nitrate hexahydrate in ion-exchanged water, a co-precipitate was obtained by mixing this nitrate solution with an 8-fold diluted solution of 28% by mass ammonia water to neutralize it. .. The dehydration operation of centrifuging the coprecipitate to remove the supernatant liquid and the water washing operation of adding ion-exchanged water and stirring are alternately repeated about 3 times to finally obtain a gel-like coprecipitated product. (Coprecipitation process). The co-precipitation product is dried in air at a temperature of 150 ° C. for 24 hours (drying step) and then calcined in air at a temperature of 500 ° C. for 2 hours to obtain ZrNdOx powder (90 mol% ZrO ₂ ). -10 mol% Nd ₂ O ₃ ) was obtained (calcination step).

Then, Pr ₂ O ₃ was supported on ZrNdOx powder by an evaporation dry-solid method using an aqueous solution obtained by dissolving placeodium nitrate hexahydrate in ion-exchanged water. The amount of Pr ₂ O ₃ supported on the ZrNdOx powder was 20% by mass.

<Evaluation experiment>
The catalyst materials of Examples 1 to 4 and Comparative Examples 1 to 4 were aged to be kept at a temperature of 800 ° C. for 24 hours in an air atmosphere. After that, the characteristics of each catalyst were investigated by the following methods.

≪Evaluation experiment 1≫
As evaluation experiment 1, the influence on the internal oxygen release characteristics contributing to the carbon combustion reaction was investigated by the following method.

That is, 80 mg of each of the aged composite oxide powders and 20 mg of carbon black (manufactured by Sigma-Aldrich) were mixed for 1 minute using an agate mortar to prepare a sample powder. This sample powder was placed in a cylindrical quartz tube. Then, silica wool was inserted from both sides in the longitudinal direction of the quartz tube, and the sample powder was sandwiched between the silica wool. Next, the temperature of the sample powder was raised to 580 ° C. while flowing He gas through the quartz tube. Then, at the same temperature, the gas was switched from He gas to 3.5% ¹⁸ O ₂ containing He gas (flow rate; 100 cc / min). The concentration of CO ₂ (C ¹⁶ O ₂ , C ¹⁶ O ¹⁸ O) emitted by the carbon oxidation reaction was measured using a quadrupole mass analyzer (manufactured by Canon Anerva Technics Co., Ltd.) for 10 minutes after this gas switching. The amount of internal oxygen ( ¹⁶ O) released (mmol / g) used in the carbon oxidation reaction was determined. The results are shown in FIG.

The catalyst materials of Examples 1 to 3 and Comparative Examples 1 and 2 contain Y as a rare earth element RE. In FIG. 3, the catalyst material of Comparative Example 1 shown by C1 is obtained by adding all the salts in the co-precipitation step without providing the addition step, and the catalyst material of Comparative Example 2 (C2) is the Y salt in the addition step. Is not added and only the Pr salt is added. It can be seen that the amount of internal oxygen released in the catalyst material of Comparative Example 2 is lower than that of the catalyst material of Comparative Example 1, and the internal oxygen release capacity that contributes to the carbon combustion performance of the catalyst material is reduced. On the other hand, the catalyst materials of Examples 1 to 3 were prepared by adding Pr salt and Y salt in both the co-precipitation step and the addition step. It can be seen that in the catalyst materials of Examples 1 to 3, the amount of internal oxygen released is increased and the internal oxygen release capacity is improved as compared with the catalyst material of Comparative Example 1. Further, when the amount of internal oxygen released from the catalyst materials of Examples 1 to 3 is compared, the amount of internal oxygen released gradually increases as the amount of Pr salt and Y salt added in the addition step increases. It can be seen that the internal oxygen release capacity is improved.

The catalyst materials of Example 4 and Comparative Example 3 contain Nd as a rare earth element RE. In this case as well, it can be seen that the amount of internal oxygen released is increased in the catalyst material of Example 4 as compared with the catalyst material of Comparative Example 3, and the internal oxygen release capacity is improved.

The amounts of internal oxygen released from the catalyst materials of Comparative Examples 1, 1 and 2 and 3 are 24.6 mmol / g, 25.4 mmol / g, 25.45 mmol / g and 26.1 mmol / g, respectively, from FIG. Since it is g, the amount of internal oxygen released in the catalyst materials of Examples 1, 2 and 3 is 1.03 times, 1.035 times, and 1.06 times, respectively, as compared with the catalyst material of Comparative Example 1. It can be said that it is increasing.

Further, since the amounts of internal oxygen released from the catalyst materials of Comparative Examples 3 and 4 are 23.25 mmol / g and 24.6 mmol / g, respectively, from FIG. 3, the catalyst material of Comparative Example 3 is compared with the catalyst material of Example 3. It can be said that the amount of internal oxygen released from the catalyst material of No. 4 is increased 1.06 times.

Then, as compared with the catalyst materials of Comparative Examples 1 and 3 in which all the salts were added in the co-precipitation step without providing the addition step, Example 1 in which the Pr salt and the RE salt were partially added in the addition step by providing the addition step. It can be said that the amount of internal oxygen released increased 1.03 to 1.06 times with the catalyst materials of to 4.

≪Evaluation experiment 2≫
As evaluation experiment 2, X-ray diffraction measurement (XRD) was carried out for each of the aged composite oxide powders. From the (220) reflection peak position derived from the fluorite-type structure, the formation of ZrREPrOx and the formation of PrREOx, that is, the presence or absence of solid solution of RE (RE = Y, Nd) to PrOx were considered. The results are shown in FIG. 4 (RE = Y) and FIG. 5 (RE = Nd).

It is known that the Pr ₆ O ₁₁ (220) reflection peak appears at 2θ = 47 degrees (indicated by the alternate long and short dash line in FIGS. 4 and 5). It is known that when RE is dissolved in PrOx to form PrREOx, which is a composite oxide, the peak at 2θ = 47 degrees shifts to the right.

As shown in FIG. 4, in the catalyst material of Comparative Example 1 (C1) in which the addition step was not provided and all the salts were added in the co-precipitation step, the peak derived from ZrYPrOx at 2θ = 48.9 degrees (dashed line in FIG. 4). Indicated by.) Appears. And the peak derived from Pr ₆ O ₁₁ does not appear at 2θ = 47 degrees.

On the other hand, in the catalyst material of Comparative Example 2 (C2) in which the addition step was provided and only the Pr salt was added in the addition step, the peak derived from ZrYPrOx was shifted to the right, and 2θ = 47.6 degrees and 2θ = 47 degrees. A peak appears in.

The shift of the peak derived from ZrYPrOx to the right side is considered to indicate that the content of Pr in ZrYPrOx was reduced in the catalyst material of Comparative Example 2 (C2). The fact that peaks appeared at 2θ = 47.6 degrees and 2θ = 47 degrees means that Pr added in the addition step forms PrYOx (2θ = 47.6 degrees), which is a part of the composite oxide. At the same time, it is considered that the other part forms PrOx (2θ = 47 degrees), indicating that it is doped in ZrYPrOx.

Then, it was found that in the catalyst materials of Examples 1 to 3 (E1 to E3), the peaks derived from ZrYPrOx shift to the right side as compared with the catalyst materials of Comparative Example 1 (C1). Then, the peak near 2θ = 47.6 degrees observed with the catalyst material of Comparative Example 2 (C2) was observed, while the peak at 2θ = 47 degrees disappeared. This means that in the catalyst materials of Examples 1 to 3 (E1 to E3), Pr and Y added in the addition step form PrYOx which is a composite oxide and are doped in ZrYPrOx, and PrOx is It shows that it is not formed.

Further, as shown in FIG. 5, even in the catalyst material of RE = Nd, in the catalyst material of Comparative Example 3 (C3), a peak derived from ZrNdPrOx (indicated by a broken line in FIG. 5) is found at 2θ = 48.6 degrees. It appears, and it can be seen that no peak appears at 2θ = 47 degrees. In the catalyst material of Example 4 (E4), the peak derived from ZrNdPrOx was shifted to the right, a peak appeared in the vicinity of 2θ = 47.2 degrees, and a peak of 2θ = 47 degrees was not observed. The shift of the peak derived from ZrNdPrOx to the right indicates that the content of Nd and Pr in ZrNdPrOx is decreasing. The fact that a peak appeared at 2θ = 47.2 degrees and no peak at 2θ = 47 degrees was observed means that Pr and Nd added in the addition step formed PrNdOx, which is a composite oxide, in ZrNdPrOx. It is doped and is considered to indicate that PrOx is not formed.

≪Evaluation experiment 3≫
As evaluation experiment 3, the effect of lowering the temperature of oxygen release characteristics in vacuum was investigated by the following method.

That is, each of the aged composite oxide powders was compacted with a pressure of 25 tons, then pulverized, and 100 mg of each sized sample was weighed and inserted into a quartz tube. The sample was sandwiched between silica wool from both sides in the longitudinal direction of the quartz tube. As a pretreatment, the temperature was raised to 650 ° C. at 10 ° C./min while flowing a He gas containing 10% O ₂ (flow rate; 100 cc / min), and the sample was oxidized. After that, the temperature was lowered to 90 ° C. in the same gas atmosphere, and the temperature was maintained for 30 minutes. Then, the inside of the quartz tube was switched to a vacuum exhaust atmosphere, and the temperature was raised from 90 ° C. to 650 ° C. at 10 ° C./min. The amount of O ₂ desorbed from the powder during the temperature rise, that is, the amount of O ₂ released (mmol / s · g) was measured with a mass spectrometer (manufactured by Canon Anerva Technics Co., Ltd.). Then, the oxygen release characteristics in vacuum were investigated. The results are shown in FIGS. 6 and 7. It can be said that the catalyst material that releases more oxygen on the lower temperature side has better oxygen release characteristics.

As shown in FIG. 6, in the catalyst material of RE = Y, the catalyst material of Example 3 (E3) has a larger amount of _O2 emission on the low temperature side than the catalyst material of Comparative Example 1 (C1). It turns out.

As shown in FIG. 7, in the catalyst material of RE = Nd, the catalyst material of Example 4 (E4) has a larger amount of _O2 emission on the low temperature side than the catalyst material of Comparative Example 3 (C3). It turns out. Further, in the catalyst material of Comparative Example 4 (C4) in which Pr ₂ O ₃ is supported on ZrNdOx, the oxygen release characteristics are significantly different from those of the catalyst materials of Comparative Example 3 (C3) and Example 4 (E4), and the oxygen release characteristics are significantly different on the high temperature side. It can be seen that the amount of O ₂ released is large.

≪Evaluation experiment 4≫
As evaluation experiment 4, the influence on the oxygen exchange reaction characteristics characteristic of Zr-based oxides was investigated by the following method.

That is, each of the aged composite oxide powders was compacted with a pressure of 25 tons, then pulverized, and 100 mg of each sized sample was weighed and inserted into a quartz tube. The sample was sandwiched between silica wool from both sides in the longitudinal direction of the quartz tube. After raising the temperature of the sample to 580 ° C. while flowing He gas through the quartz tube, the He gas was switched from He gas to 3.5% ¹⁸ O ₂ containing He gas (flow rate; 100 cc / min) at the same temperature. Over 10 minutes from this switch, the concentrations of various O ₂ types ( ¹⁶ O ₂ , ¹⁶ O ¹⁸ O, ¹⁸ O ₂ ) produced by the ¹⁶ O in the sample and ¹⁸ O in the gas are measured by a quadrupole mass analyzer. Based on the amount of ¹⁶ O ₂ and ¹⁶ O ¹⁸ O released, the amount of lattice oxygen ( ¹⁶ O) released from the inside of the sample by the oxygen exchange reaction (mmol / g) was determined. The results are shown in FIG.

In the catalyst material of RE = Y, the amount of lattice oxygen ( ¹⁶ O) released in the catalyst material of Example 3 (E3) was lower than that of the catalyst material of Comparative Example 1 (C1). I understand.

Even in the catalyst material of RE = Nd, the amount of lattice oxygen ( ¹⁶ O) released in the catalyst material of Example 4 (E4) is lower than that of the catalyst material of Comparative Example 3 (C3). I understand.

These results are considered to be related to the fact that the proportions of Pr salt and RE salt added in the co-precipitation step are smaller in the catalyst materials of Examples 3 and 4 than in the catalyst materials of Comparative Examples 1 and 3. Be done.

As described above, in the catalyst materials of Examples 3 and 4, oxygen can be released in contact with carbon due to the high oxygen release characteristics of the Pr-based composite oxide material. Then, oxygen vacancies can be formed by extracting oxygen from the Pr-based composite oxide material. It is considered that the oxygen exchange reaction of the Zr-based oxide material is promoted through the formed oxygen vacancies.

INDUSTRIAL APPLICABILITY The present invention is extremely useful because it provides a catalyst material for purifying particulates having high particulate combustion performance.

1 Catalytic material for purification of particulate 11 Zr-based oxide material 12 Pr-based composite oxide material S1 Co-precipitation step S2 Addition step S3 Drying step S4 Crushing step S5 Firing step

Claims (4)

A catalyst material for purifying a particulate that contains Pr and is used to purify the particulate contained in the exhaust gas of an internal combustion engine .
A Zr-based composite oxide material containing Z r and a part of the Pr ,
A Pr-based composite oxide material containing the remainder of Pr and one or more rare earth elements other than Pr is provided .
When the X-ray diffraction measurement is performed, the peak derived from the Zr-based composite oxide material and the peak derived from the Pr-based composite oxide material are different as the (220) reflection peak derived from the fluorite-type structure. The Pr-based composite oxide material is contained in the Zr-based composite oxide material in a state where the (220) reflection peak of Pr 6O 11 is not observed while being observed as a _{peak .}
A catalyst material for purifying particulates, which is characterized by this. In claim 1 ,
The rare earth element is a catalyst material for purifying particulates, which is Nd and / or Y. In claim 1 or 2 ,
The Zr-based composite oxide material further contains Nd and / or Y.
A catalyst material for purifying particulates, which is characterized by this. The method for producing a catalytic purification catalyst material according to any one of claims 1 to 3 .
At least, a co-precipitation step of co-precipitating a Zr salt and a Pr salt to obtain a first co-precipitate,
An addition step of obtaining a second co-precipitate by adding a Pr salt and a salt containing a rare earth element to the first co-precipitate and co-precipitating the first co-precipitate.
The drying step of drying the second coprecipitate and
A method for producing a catalytic material for purifying a particulate, which comprises a firing step of firing the dried second coprecipitate.

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