JP2010012397A - Catalytic material for cleaning exhaust gas, method for producing the same, and catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalytic material for cleaning exhaust gas, which has excellent cleaning performance and can keep the cleaning performance even when exposed to high-temperature exhaust gas and to provide a method for producing the catalytic material for cleaning exhaust gas, and a catalyst for cleaning exhaust gas, which has a catalyst layer containing the catalytic material for cleaning exhaust gas. <P>SOLUTION: The catalytic material 10 for cleaning exhaust gas contains alumina particles 13, Ce-Zr compound oxide particles 12 having oxygen storage/release capacity and Pd(s) 11. Only the Ce-Zr compound oxide particle 12 is doped fixedly with the Pd 11. The Ce-Zr compound oxide particles 12 are dispersed/deposited on the surface of the alumina particles 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst, a method for producing the same, and an exhaust gas purification catalyst having the catalyst material.

  The exhaust gas purifying catalyst for purifying exhaust gas exhausted from the engine includes oxygen storage and release capacity (Oxygen) represented by ceria, CeZr-based complex oxides including cerium (Ce) and zirconium (Zr). In many cases, an oxygen storage material having Storage Capacity (OSC) is contained. For example, a typical configuration of an exhaust gas purifying catalyst includes a catalyst-like noble metal supported catalyst layer containing alumina particles, oxygen storage material particles, and the like formed on a honeycomb carrier. Such an exhaust gas purifying catalyst oxidizes hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas, and also reduces nitrogen oxides (NOx) to water, carbon dioxide, And exhaust gas is purified by converting into nitrogen. At this time, the oxygen storage material contained in the exhaust gas purification catalyst functions to store oxygen in the exhaust gas and reduce NOx to nitrogen when the air-fuel ratio of the exhaust gas is lean. Further, when the air-fuel ratio of the exhaust gas is rich, it works to release the stored oxygen and oxidize HC and CO in the exhaust gas to water and carbon dioxide, respectively. Therefore, the oxygen storage material is useful for enhancing the purification performance of the exhaust gas purification catalyst.

  However, it is known that ceria material and CeZr-based composite oxide, which are oxygen storage materials, have lower heat resistance than alumina used as an exhaust gas purification catalyst material. That is, when the exhaust gas purifying catalyst containing an oxygen storage material is exposed to a high temperature exhaust gas for a long time, the crystal structure of the oxygen storage material changes or the oxygen storage material is sintered, thereby There is a problem that the specific surface area of the material tends to be small, and as a result, it is difficult to exert the effect of improving the purification performance of the exhaust gas by the oxygen storage material as described above.

In view of this, it has been studied to add a rare earth metal component other than cerium to the CeZr-based composite oxide or to form a composite with alumina that does not substantially dissolve in the CeZr-based composite oxide. As an example of such an exhaust gas purification catalyst, for example, in Patent Document 1 and Patent Document 2 below, a hydroxide is co-precipitated from an aqueous solution containing Al, Ce, Zr, Y, and La. A catalyst obtained by adding an aqueous solution containing a catalyst noble metal to a composite oxide obtained by firing a hydroxide and evaporating it to dryness is described. Patent Document 3 listed below describes a catalyst obtained by coprecipitation of a hydroxide from an aqueous solution containing Al, Ce, Zr, and a catalyst noble metal, and firing the hydroxide.
JP 2000-271480 A JP 2005-224792 A Japanese Patent Laid-Open No. 10-182155

  According to Patent Document 1 and Patent Document 2, it is disclosed that sintering and the like of CeZr composite oxide particles that are oxygen storage materials can be suppressed and the heat resistance of the catalyst can be increased. However, when such a catalyst is exposed to high-temperature exhaust gas, there is a problem that the catalyst noble metal is sintered. This is because the catalyst obtained by the methods described in Patent Document 1 and Patent Document 2 is a catalyst noble metal post-supported, that is, a catalyst noble metal on each surface of alumina particles and CeZr composite oxide particles. It is thought that this is because the is supported. With such a catalyst, it is considered that when exposed to high-temperature exhaust gas, the catalyst noble metal rolls on the surfaces of the alumina particles and the CeZr composite oxide particles, and the catalyst noble metal is sintered.

  Patent Document 3 discloses that the heat resistance of the catalyst can be increased. However, when palladium (Pd) is used as the catalyst noble metal, it is known that Pd dissolves in the alumina particles, and Pd that is dissolved in the alumina particles and embedded in the particles acts as a catalyst noble metal. There was a problem that could not be demonstrated at all.

  The present invention has been made in view of such circumstances, and an object of the present invention is to obtain an exhaust gas purifying catalyst material that is excellent in purifying performance and can maintain the purifying performance even when exposed to high-temperature exhaust gas. Another object of the present invention is to provide a method for producing the exhaust gas purification catalyst material and an exhaust gas purification catalyst provided with a catalyst layer containing the exhaust gas purification catalyst material.

  The exhaust gas purifying catalyst material according to the present invention is an exhaust gas purifying catalyst material containing alumina particles, CeZr-based composite oxide particles having oxygen storage / release capability, and Pd, The CeZr-based complex oxide particles are doped and fixed only, and the CeZr-based complex oxide particles are dispersed and supported on the surfaces of the alumina particles.

  According to such a configuration, CeZr-based composite oxide particles in which Pd is doped (solid solution) and fixed have higher oxygen storage / release performance than the case where Pd is supported on the surface by post-supporting. This is considered to be due to the fact that oxygen storage / release by the CeZr-based composite oxide particles is preferentially performed at the portion in contact with Pd. The CeZr-based composite oxide particles doped and fixed with Pd are considered to have Pd fixed so as to be partially exposed on the surface of the CeZr-based composite oxide particles. Pd and CeZr-based composite oxide particles It is considered that the oxygen storage / release performance is enhanced because of the large contact area with the. Thus, when the oxygen storage / release performance of the CeZr-based composite oxide particles is enhanced, the effect of improving the exhaust gas purification performance by the CeZr-based composite oxide particles having the oxygen storage / release capability is sufficiently exhibited.

  Further, CeZr-based composite oxide particles doped with Pd and fixed can suppress sintering of Pd and improve heat resistance even when exposed to high-temperature exhaust gas. This is considered to be because Pd is difficult to roll on the surface of the CeZr-based composite oxide particles because Pd is considered to be partially embedded in the CeZr-based composite oxide particles. Thus, if Pd which is a catalyst noble metal is difficult to roll, it is considered that sintering of Pd is suppressed even when exposed to high-temperature exhaust gas.

  As described above, an exhaust gas purification catalyst material that has excellent purification performance and can maintain the purification performance even when exposed to high-temperature exhaust gas can be obtained.

In the exhaust gas purification catalyst material, the CeZr-based composite oxide particles preferably contain 10% by mass to 90% by mass of ZrO ₂ with respect to the total mass of CeO ₂ and ZrO _2. 40 mass% or more and 85 mass% or less is more preferable, and it is further more preferable that 50 mass% or more and 80 mass% or less are contained.

  The method for producing an exhaust gas purifying catalyst material according to the present invention includes adding a basic solution to an acidic solution containing Ce, Zr, and Pd, thereby performing first hydroxylation containing Ce, Zr, and Pd. By adding a basic solution to a first coprecipitation step of co-precipitating an object to form a first dispersion in which the first hydroxide is dispersed, and an acidic solution containing Al, A second coprecipitation step of coprecipitating the second hydroxide contained to form a second dispersion in which the second hydroxide is dispersed, and mixing the first dispersion and the second dispersion And a firing step of drying and firing the mixture of the first dispersion and the second dispersion.

  According to such a configuration, the above-described exhaust gas purification catalyst material containing alumina particles, CeZr-based composite oxide particles having oxygen storage / release ability, and Pd, wherein the Pd is the CeZr It is possible to obtain an exhaust gas purifying catalyst material that is doped and fixed only in the system composite oxide particles and in which the CeZr system composite oxide particles are dispersed and supported on the surfaces of the alumina particles. That is, it is possible to obtain an exhaust gas purification catalyst material that is excellent in purification performance and that can maintain the purification performance even when exposed to high-temperature exhaust gas.

  An exhaust gas purification catalyst according to the present invention is an exhaust gas purification catalyst disposed in an exhaust passage of an engine, and includes a honeycomb-shaped carrier and a catalyst layer formed on a cell wall surface of the honeycomb-shaped carrier. And the catalyst layer contains the exhaust gas purifying catalyst material.

  According to such a configuration, since the exhaust gas purification catalyst material that has excellent purification performance and can maintain the purification performance even when exposed to high-temperature exhaust gas is provided, it has excellent purification performance and heat resistance. An exhaust gas purifying catalyst is obtained.

  In the exhaust gas purification catalyst, the catalyst layer includes at least two layers of a first catalyst layer containing the exhaust gas purification catalyst material and a second catalyst layer containing Rh-supported CeZr-based composite oxide particles. It is preferable that the first catalyst layer is present at a position closer to the cell wall than the second catalyst layer.

  According to such a configuration, the purification performance can be further improved by disposing the second catalyst layer containing the Rh-supported CeZr-based composite oxide particles on the exhaust gas passage side.

  The catalyst layer further includes a third catalyst layer containing Pd-supported CeZr-based composite oxide particles, and the third catalyst layer is located farther from the cell wall than the second catalyst layer. It is preferable to do.

  According to such a configuration, the third catalyst layer containing the Pd-supported CeZr-based composite oxide particles is further arranged on the exhaust gas passage side, so that the catalyst covered by P, Ca, Zn, etc. contained in the exhaust gas is covered. Can suppress poison.

  Moreover, it is preferable from the point of purification | cleaning performance that the said Pd carrying | support CeZr type complex oxide particle is doped with Pd to CeZr type complex oxide particle.

  ADVANTAGE OF THE INVENTION According to this invention, the catalyst material for exhaust gas purification which is excellent in purification performance and can maintain purification performance even if it exposes to high temperature exhaust gas can be provided. Further, a method for producing the exhaust gas purification catalyst material and an exhaust gas purification catalyst provided with a catalyst layer containing the exhaust gas purification catalyst material are provided.

  An exhaust gas purifying catalyst material according to an embodiment (first embodiment) of the present invention will be described.

  FIG. 1 is an enlarged cross-sectional view schematically showing an exhaust gas purifying catalyst material 10 according to the first embodiment. As shown in FIG. 1, the exhaust gas purifying catalyst material 10 according to the first embodiment contains alumina particles 13, CeZr-based composite oxide particles 12 having an oxygen storage / release capability, and Pd11, and the Pd11 Are doped and fixed on the CeZr-based composite oxide particles 12, and the CeZr-based composite oxide particles 12 are dispersed and supported on the surfaces of the alumina particles 13. It is considered that the Pd11 is fixed so that the CeZr-based composite oxide particles 12 doped and fixed with the Pd11 are partially exposed on the surface of the CeZr-based composite oxide particles 12. That is, in the exhaust gas purification catalyst material 10, CeZr-based composite oxide particles 12 fixed in a state where a part of the Pd 11 is embedded are dispersedly supported on the surfaces of the alumina particles 13. The Pd11 is not substantially supported on the alumina particles 13.

  The CeZr-based composite oxide particles 12 have higher oxygen storage / release performance than the case where the CeZr-based composite oxide particles 12 are supported on the surface by post-supporting Pd as will be described later. Thus, when the oxygen storage / release performance of the CeZr-based composite oxide particles is enhanced, the effect of improving the exhaust gas purification performance by the CeZr-based composite oxide particles having the oxygen storage / release capability is sufficiently exhibited.

  That is, it has been conventionally known that Pd11 is useful as an oxidation catalyst. In particular, when Pd11 is in an oxidized state, its oxidation catalyst function is enhanced. However, when the air-fuel ratio of the exhaust gas becomes rich, the oxygen concentration for oxidizing HC and CO in the exhaust gas decreases. Furthermore, Pd11 tends to be reduced to the metallic state. Therefore, the oxidation catalyst function of Pd11 tends to decrease. Therefore, when the oxygen storage / release performance of the CeZr-based composite oxide particles 12 is increased as described above, Pd11 is oxidized by the oxygen released from the CeZr-based composite oxide particles 12 even when the air-fuel ratio becomes rich. It becomes easier to maintain an oxidation state having a high catalytic function.

  Further, even when the CeZr-based composite oxide particles 12 are exposed to high-temperature exhaust gas, sintering of Pd11 is suppressed and heat resistance is improved. Further, in the exhaust gas purification catalyst material 10, the alumina particles 13 become steric hindrance, and sintering of the CeZr-based composite oxide particles 12 is also suppressed.

  As described above, the exhaust gas purification catalyst material 10 is excellent in purification performance and can maintain the purification performance even when exposed to high temperature exhaust gas.

  The improvement of the oxygen storage / release performance and the suppression of Pd sintering are considered as follows. FIG. 2 is an enlarged cross-sectional view showing the vicinity of the surface of the CeZr-based composite oxide particles 12, and also shows the CeZr-based composite oxide particles 12 on which Pd is post-supported. 2A shows the vicinity of the surface of the CeZr-based composite oxide particles 12 in the exhaust gas purifying catalyst material 10 according to the first embodiment, and FIG. 2B shows CeZr after supporting Pd. The surface vicinity of the system complex oxide particle 12 is shown.

  The oxygen storage / release performance of the CeZr-based composite oxide particles 12 is improved because the oxygen storage / release by the CeZr-based composite oxide particles 12 is preferentially performed at the portion 14 in contact with Pd. it is conceivable that. As shown in FIG. 2A, the CeZr-based composite oxide particles 12 are considered that Pd11 is partially embedded in the CeZr-based composite oxide particles 12, and Pd11 and CeZr-based composite oxide particles 12 Since the area of the portion 14 in contact with Pd is wider than when Pd is post-supported, it is considered that the oxygen storage / release performance is enhanced. On the other hand, as shown in FIG. 2B, the CeZr-based composite oxide particles 12 that post-support Pd11 have Pd11 supported on the surface of the CeZr-based composite oxide particles 12, and Pd11 and CeZr-based composite particles. Since the area of the portion 15 in contact with the oxide particles 12 is narrower than that in the above case, the oxygen occlusion / release ability is the same as when Pd11 is doped and fixed to the CeZr-based composite oxide particles 12. It is thought that it does not increase.

  In addition, Pd sintering is suppressed because Pd11 is considered to be partially embedded in CeZr-based composite oxide particles 12 as shown in FIG. 2 (a). This is probably because Pd11 hardly rolls on the surface of 12. If Pd11 is difficult to roll in this way, it is considered that sintering of Pd11 is suppressed even when exposed to high-temperature exhaust gas. On the other hand, the CeZr-based composite oxide particles 12 on which Pd11 is post-supported are supported on the surface of the CeZr-based composite oxide particles 12 as shown in FIG. When exposed to exhaust gas, it is considered that Pd11 rolls on the surface of CeZr-based composite oxide particles 12 and is easily sintered.

The alumina particles 13 can be used without particular limitation as long as they are particulate alumina having a plurality of pores. Specific examples include activated alumina particles having a BET specific surface area of 50 to 300 m ² / g and a pore volume of 0.5 to ² cm ³ / g.

  The CeZr-based composite oxide particles 12 can be used without particular limitation as long as they contain Ce and Zr and have oxygen storage / release ability. Specifically, for example, particles made of a CeZr-based composite oxide containing only Ce and Zr as a metal, or CeZr-based composite oxide containing Ce, Zr, and a rare earth metal or alkaline earth metal excluding Ce. And the like. The rare earth metal contained in the CeZr-based composite oxide particles is preferably a trivalent and stable metal, for example, scandium (Sc), yttrium (Y), lanthanum (La) excluding cerium (Ce). , Praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er) , Thulium (Tm), ytterbium (Yb), lutetium (Lu) and the like. Among these, at least one metal selected from La and Nd is preferable. Further, the alkaline earth metal contained in the CeZr-based composite oxide particles is at least one metal selected from magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). preferable.

In addition, the CeZr-based composite oxide particles 12 preferably contain 10 to 90% by mass of ZrO ₂ with respect to the total mass of CeO ₂ and ZrO _2, and are 40 to 85% by mass. % Or less is more preferable, and 50% by mass or more and 80% by mass or less is further preferable. Within such a range, higher purification performance can be maintained even after exposure to high-temperature exhaust gas, as will be shown in the examples described later. When the amount of ZrO ₂ is too small, the heat resistance of the CeZr-based composite oxide particles 12 tends to decrease. Further, when the amount of ZrO ₂ is too large, the amount of CeO ₂ becomes too small, the oxygen storage / release performance of the CeZr-based composite oxide particles 12 is lowered, and there is a tendency that high purification performance cannot be exhibited. The content ratio of the CeZr-based composite oxide particles 12 and the alumina particles 13 is preferably 5:95 to 70:30 by mass ratio.

  The Pd11 is a catalytic noble metal capable of oxidizing hydrocarbons (HC) and carbon monoxide (CO) and reducing nitrogen oxides (NOx). The supported amount of Pd11 is preferably 0.03 to 5% by mass with respect to the total mass of the CeZr-based composite oxide particles 12 and the alumina particles 13. Moreover, although said Pd11 may be a particulate form or a powder form, it is preferable that the particle diameter is 0.1-30 nm.

  The exhaust gas purifying catalyst material 10 may contain a precious metal other than Pd, such as platinum (Pt) and rhodium (Rh).

  Next, a method for manufacturing the exhaust gas purifying catalyst according to the first embodiment will be described. FIG. 3 is a process diagram showing the method for manufacturing the exhaust gas purifying catalyst material according to the first embodiment.

First, an acidic solution containing Ce, Zr and Pd is prepared (step A1). Specifically, for example, an aqueous solution of nitrate of each metal can be mixed and prepared. The content of each component of the acidic solution is an amount corresponding to the CeO ₂ content rate, ZrO ₂ content rate, and Pd loading amount of the CeZr-based composite oxide particles.

  Next, a coprecipitation step is performed in which a basic solution is added to and mixed with the acidic solution containing Ce, Zr and Pd (step A2). By doing so, the 1st hydroxide containing each structural metal (Ce, Zr, and Pd) contained in the said acidic solution is obtained as a complex oxide precursor. At this time, it is obtained in a state of a first dispersion in which the first hydroxide is dispersed. Specific examples of this step include an ammonia coprecipitation method in which excess ammonia water is added to and mixed with the acidic solution. Moreover, as said basic solution, sodium hydroxide aqueous solution etc. can be used other than ammonia water, for example. Step A1 and step A2 correspond to the first coprecipitation step.

  Moreover, an acidic solution containing Al is prepared (step A3). Specifically, for example, an aqueous solution of Al nitrate is prepared. Next, a coprecipitation step is performed in which a basic solution is added to and mixed with the acidic solution containing Al (step A4). By doing so, the 2nd hydroxide containing Al is obtained as a complex oxide precursor. At this time, it is obtained in a state of a second dispersion in which the second hydroxide is dispersed. Specific examples of this step include an ammonia coprecipitation method in which excess ammonia water is added to and mixed with the acidic solution. Moreover, as said basic solution, sodium hydroxide aqueous solution etc. can be used other than ammonia water, for example. Steps A3 and A4 correspond to the second coprecipitation step and are performed separately from the first coprecipitation step, but may be performed simultaneously.

  Then, the first dispersion and the second dispersion are mixed (step A5). Specifically, the dispersion containing the first hydroxide obtained in Step A2 and the dispersion containing the second hydroxide obtained in Step A4 are mixed with stirring.

  Next, the mixed hydroxide is precipitated and separated from the mixed dispersion, washed with water, and dried (step A6). Specifically, the liquid containing the mixed dispersion is left for a whole day and night, the cake obtained by removing the supernatant is applied to a centrifuge, and then washed with water. And the cake washed with water is heated and dried. The drying conditions at that time may be sufficiently dried at a temperature lower than the firing temperature, but are preferably 100 to 200 ° C. and about 1 to 20 hours, for example.

  Next, the baking process which bakes the obtained cake is performed (step A7). As firing conditions, for example, 400 to 600 ° C. and about 1 to 20 hours are preferable. Specifically, for example, the drying is performed by holding the dried cake in an air atmosphere at, for example, a temperature of 500 ° C. for 10 hours.

  The exhaust gas purifying catalyst material according to the first embodiment can be manufactured by the above manufacturing method. That is, the exhaust gas purifying catalyst material according to the first embodiment contains CeZr-based composite oxide particles manufactured in a state of containing Pd, that is, CeZr-based composite oxide particles doped with so-called Pd. By doing so, the exhaust gas purifying catalyst material according to the first embodiment can be manufactured. This is because when CeZr-based composite oxide particles are doped with Pd, Pd collects on the surface of the CeZr-based composite oxide particles due to the surface tension of the CeZr-based composite oxide particles and is fixed in a partially exposed state. This is considered to be because of this. On the other hand, CeZr-based composite oxide particles obtained by evaporating and drying Pd, that is, CeZr-based composite oxide particles after supporting Pd are hardly embedded in CeZr-based composite oxide particles, and Pd is CeZr. It is only supported on the surface of the system composite oxide particles.

  Further, the exhaust gas purifying catalyst according to the first embodiment can also be manufactured by using separately prepared aluminum hydroxide instead of the hydroxide obtained in the second coprecipitation step.

  Next, an exhaust gas purifying catalyst which is another embodiment (second embodiment) of the present invention will be described.

  FIG. 4 is a cross-sectional view schematically showing the catalytic converter 20 including the exhaust gas purifying catalyst according to the second embodiment. The catalytic converter 20 is disposed in an exhaust passage connected to the engine, and hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust gas are purified in the catalytic converter 20. It is configured to be discharged. This catalytic converter 20 is configured by incorporating a purification catalyst (exhaust gas purification catalyst) 22 in a heat-resistant container 21. Although not shown, the heat-resistant container 21 may be provided with a temperature sensor that detects the temperature of the purification catalyst 22.

  FIG. 5 is an enlarged sectional view showing a part of the purification catalyst 22. The purification catalyst 22 is configured by forming a catalyst layer 32 on the surface of a cell wall 31 of a substantially cylindrical honeycomb-shaped carrier having a large number of cells partitioned by partition walls, and exhaust gas flows from the upstream side to the downstream side. In order to purify harmful components (HC, CO, NOx) by diffusing into the catalyst layer 32 formed on the cell surface while passing through the cell and coming into contact with the catalyst noble metal contained in the catalyst layer 32 It has become.

  The purification catalyst 22 can use, for example, a cordierite ceramic carrier or a stainless steel metal carrier as the honeycomb carrier. Further, the catalyst layer 32 of the purification catalyst 22 only needs to contain the exhaust gas purification catalyst material, and may contain other materials. Other materials included in the catalyst layer 32 are those other than the exhaust gas purifying catalyst material as long as the effects of the present invention are not impaired, and those conventionally used as catalyst materials, for example, Examples thereof include alumina, nickel (Ni) for suppressing poisoning by the sulfur (S) component, and barium (Ba) for suppressing poisoning by the phosphorus (P) component.

  Further, the catalyst layer 32 only needs to contain the exhaust gas purification catalyst material, and other layers may be laminated on the layer containing the exhaust gas purification catalyst material. . Specifically, for example, at least two layers of a first catalyst layer containing the exhaust gas purification catalyst material and a second catalyst layer containing Rh-supported CeZr-based composite oxide particles are laminated. And the first catalyst layer is located closer to the cell wall than the second catalyst layer.

  As described above, the purification performance can be further improved by disposing the second catalyst layer containing the Rh-supported CeZr-based composite oxide particles on the exhaust gas passage side. Further, when Rh is contained as a catalyst noble metal in the layer containing the exhaust gas purifying catalyst material, Pd and Rh may be alloyed to reduce the catalytic activity. By laminating the second catalyst layer, alloying of Pd and Rh can be suppressed, and both the catalytic metals maintain a high catalytic activity, which is advantageous for purification of exhaust gas. Furthermore, the problem of thermal deterioration and poisoning of Pd contained in the first catalyst layer is reduced by arranging the second catalyst layer on the exhaust gas passage side.

  Examples of the Rh-supporting CeZr-based composite oxide particles include CeZr-based composite oxide particles that post-support Rh, and CeZr-based composite oxide particles doped with Rh.

  The catalyst layer 32 further includes a third catalyst layer containing Pd-supported CeZr-based composite oxide particles, and the third catalyst layer is located farther from the cell wall than the second catalyst layer. The thing which exists is mentioned.

  Thus, the purification performance can be further improved by further disposing the third catalyst layer containing the Pd-supported CeZr-based composite oxide particles on the exhaust gas passage side. Further, as in the case described above, alloying of Pd and Rh can be suppressed, and both the catalytic metals maintain a high catalytic activity, which is advantageous for purification of exhaust gas. Further, by disposing the third catalyst layer further on the exhaust gas passage side, problems of thermal deterioration and poisoning of Rh contained in the second catalyst layer and Pd contained in the first catalyst layer are reduced.

  Examples of the Pd-supported CeZr-based composite oxide particles contained in the third catalyst layer include CeZr-based composite oxide particles post-supported with Pd, CeZr-based composite oxide particles doped with Pd, and the like. CeZr-based composite oxide particles doped with Pd are preferred. The CeZr-based composite oxide particles doped with Pd are considered to be fixed so that Pd is partially exposed on the surface of the CeZr-based composite oxide particles, and CeZr contained in the exhaust gas purification catalyst material. It is the same as the system composite oxide particles.

  The catalyst layer 32 is prepared as follows, for example.

  First, the exhaust gas purification catalyst material, water, and a binder raw material are mixed to produce a slurry. Then, the honeycomb-like carrier is immersed in this slurry to coat the slurry. Then, excess slurry is removed by air blowing, followed by drying and baking. Further, as the binder raw material, for example, zirconyl nitrate, alumina sol or the like can be used, and the firing condition is preferably maintained at 450 to 550 ° C. in the atmosphere for about 1 to 3 hours. In addition, when forming a catalyst layer of multiple layers, it can produce by repeating said operation.

  Examples of the exhaust gas purifying catalyst material and the exhaust gas purifying catalyst which are embodiments of the present invention will be described below, but the present invention is not limited to the examples.

[Example A]
First, the oxygen storage / release capacity of the exhaust gas purification catalyst material was examined.

Example 1
The exhaust gas purifying catalyst material according to Example 1 was manufactured as follows according to the manufacturing process shown in FIG.

First, an aqueous solution of Ce, Zr and a nitrate of each metal of Pd which is a catalyst noble metal is mixed to prepare an acidic solution containing Ce, Zr and Pd (Step A1), an aqueous ammonia solution is added to the acidic solution, Mixed (step A2). By doing so, the dispersion liquid in which the hydroxide containing Ce, Zr and Pd was dispersed was obtained. Next, an aqueous solution of Al nitrate was prepared (step A3). An aqueous ammonia solution was added to the aqueous solution and mixed (step A4). By doing so, a dispersion in which Al hydroxide was dispersed was obtained. The amount of each component of the acidic solution is next CeZr-based mixed oxide CeO ₂ content of 60 wt% of the particles to be produced, is an amount which was adjusted to ZrO ₂ content of 40 wt%. Moreover, it is the quantity adjusted so that the mass ratio of an alumina and CeZr type complex oxide particle might be set to 80:20. Furthermore, the amount is adjusted so that the amount of Pd supported is 0.5% by mass with respect to the total mass of alumina and CeZr-based composite oxide particles.

  And the dispersion liquid in which the hydroxide containing Ce, Zr and Pd was dispersed and the dispersion liquid in which the hydroxide of Al was dispersed were mixed (step A5). The mixture was allowed to stand for a whole day and night, and the cake obtained by removing the supernatant was centrifuged and then washed with water. The cake washed with water was dried by heating at 150 ° C. for about 10 hours (step A6). Next, the obtained cake was baked by holding at a temperature of 500 ° C. for about 10 hours in an air atmosphere (step A7).

  Through the above steps, the exhaust gas purifying catalyst material according to Example 1 was obtained. That is, an exhaust gas purifying catalyst material in which CeZr-based composite oxide particles doped with Pd were dispersed and supported on alumina particles was obtained.

(Comparative Example 1)
The exhaust gas purifying catalyst material according to Comparative Example 1 was manufactured as follows according to the manufacturing process shown in FIG. FIG. 6 is a process diagram showing a method for manufacturing the exhaust gas purifying catalyst material according to Comparative Example 1.

  First, an aqueous solution of a nitrate of Ce, Zr and Al is mixed to prepare an acidic solution containing Ce, Zr and Al (step B1), and an aqueous ammonia solution which is a basic solution is added to the acidic solution. (Step B2). By doing so, the dispersion liquid in which the hydroxide containing Ce, Zr and Al was dispersed was obtained. And the dispersion liquid in which the hydroxide containing Ce, Zr and Al was dispersed was allowed to stand for a whole day and night, and the cake obtained by removing the supernatant was applied to a centrifuge, and then washed with water. The cake washed with water was heated at 150 ° C. for about 10 hours and dried (step B3). Next, the obtained cake was baked by holding at a temperature of 500 ° C. for about 10 hours in an air atmosphere (step B4).

  Next, an aqueous solution of Pd nitrate was prepared (step B5). Then, the aqueous solution was added to the fired product obtained in Step B4, mixed (Step B6), and evaporated to dryness (Step B7). The content of each metal was adjusted to be the same as that of the exhaust gas purifying catalyst material according to Example 1.

  Through the above steps, the exhaust gas purifying catalyst material according to Comparative Example 1 was obtained. That is, an exhaust gas purifying catalyst material containing CeZr-based composite oxide particles on which Pd was post-supported and alumina particles was obtained. Note that this corresponds to those described in Patent Document 1 and Patent Document 2.

(Comparative Example 2)
The exhaust gas purifying catalyst material according to Comparative Example 2 was manufactured as follows according to the manufacturing process shown in FIG. FIG. 7 is a process diagram showing a method for manufacturing an exhaust gas purifying catalyst material according to Comparative Example 2.

  First, an aqueous solution of nitrate of each metal of Ce, Zr, Al, and Pd is mixed to prepare an acidic solution containing Ce, Zr, Al, and Pd (step C1), and ammonia that is a basic solution is added to the acidic solution. Aqueous solution was added and mixed (step C2). By doing so, the dispersion liquid in which the hydroxide containing Ce, Zr, Al and Pd was dispersed was obtained. And the dispersion liquid in which the hydroxide containing Ce, Zr, Al and Pd was dispersed was allowed to stand for a whole day and night, and the cake obtained by removing the supernatant was applied to a centrifugal separator and then washed with water. The cake washed with water was heated at 150 ° C. for about 10 hours and dried (step C3). Next, the obtained cake was baked by holding at a temperature of 500 ° C. for about 10 hours in an air atmosphere (step C4). The content of each metal was adjusted to be the same as that of the exhaust gas purifying catalyst material according to Example 1.

  Through the above steps, the exhaust gas purifying catalyst material according to Comparative Example 2 was obtained. That is, an exhaust gas purifying catalyst material was obtained in which Ce and Zr oxides and / or CeZr-based composite oxides were dispersed in alumina particles, and Pd was dissolved in these oxides. Note that this corresponds to that described in Patent Document 3.

(Comparative Example 3)
The exhaust gas purifying catalyst material according to Comparative Example 3 was manufactured as follows according to the manufacturing process shown in FIG. FIG. 8 is a process diagram showing a method for producing an exhaust gas purifying catalyst material according to Comparative Example 3.

  First, an aqueous solution of a nitrate of each metal of Ce, Zr and Pd is mixed to prepare an acidic solution containing Ce, Zr and Pd (step D1), and an aqueous ammonia solution which is a basic solution is added to the acidic solution. (Step D2). By doing so, the dispersion liquid in which the hydroxide containing Ce, Zr and Pd was dispersed was obtained. And the dispersion liquid in which the hydroxide containing Ce, Zr and Pd was dispersed was allowed to stand for a whole day and night, and the cake obtained by removing the supernatant was applied to a centrifuge and then washed with water. The cake washed with water was heated at 150 ° C. for about 10 hours and dried (step D3). Next, the obtained cake was baked by holding at a temperature of 500 ° C. for about 10 hours in an air atmosphere (step D4).

  Next, the alumina powder was dispersed in water to prepare an aqueous dispersion (Step D5). Then, the aqueous dispersion and the fired product obtained in Step D4 were mixed (Step D6), dried and fired (Step D7). The content of each metal was adjusted to be the same as that of the exhaust gas purifying catalyst material according to Example 1.

  Through the above steps, the exhaust gas purifying catalyst material according to Comparative Example 3 was obtained. That is, an exhaust gas purifying catalyst material obtained by physically mixing CeZr-based composite oxide particles doped with Pd and alumina particles was obtained.

  The oxygen storage / release capacity of each exhaust gas purifying catalyst material according to Example 1 and Comparative Examples 1 to 3 was evaluated by using a temperature reduction method.

First, each obtained exhaust gas purifying catalyst material was subjected to an aging treatment at 1000 ° C. for 24 hours in a gas atmosphere of 2 vol% O ₂ , 10 vol% H ₂ O, and the balance N ₂ .

Each exhaust gas purifying catalyst material subjected to this aging treatment is allowed to adsorb oxygen to a saturated state, and then 1% by volume of CO and the remaining He gas are circulated from the room temperature at a heating rate of 10 ° C./second. The amount of CO ₂ produced when the temperature was raised to 600 ° C. was measured. The amount of released oxygen was calculated from the amount of CO ₂ produced. The result is shown in FIG. FIG. 9 is a graph showing the results of examining the oxygen storage / release ability of the exhaust gas purifying catalyst material, and the vertical axis represents the relative oxygen release amount when the oxygen release amount in Example 1 is 100. Show.

  As can be seen from FIG. 9, the exhaust gas purifying catalyst material according to Example 1 has a larger oxygen release amount than the exhaust gas purifying catalyst material according to Comparative Examples 1 to 3. From this, the storage and release of oxygen by the CeZr-based composite oxide particles is preferentially performed at the portion in contact with Pd, and the contact area between the CeZr-based composite oxide particles and Pd greatly contributes. I understand that. The exhaust gas purifying catalyst material according to Example 1 is considered to be fixed so that Pd is partially exposed on the surface of the CeZr-based composite oxide particles. It can be seen that the contact area is wide.

  Further, since the exhaust gas purifying catalyst material according to Comparative Example 1 supports Pd afterwards, it is supported not only on CeZr-based composite oxide particles but also on alumina particles. From this, the exhaust gas purifying catalyst material according to Comparative Example 1 has the same Pd content as the exhaust gas purifying catalyst material according to Example 1, but Pd is supported on the alumina particles. Therefore, it is considered that the amount of Pd supported on the CeZr-based composite oxide particles decreases and the oxygen release amount is inferior. The contact area between Pd and CeZr-based composite oxide particles is narrower than that of the exhaust gas purifying catalyst material according to Example 1. Also from this, it is considered that the exhaust gas purification catalyst material according to Comparative Example 1 is inferior in oxygen release amount to the exhaust gas purification catalyst material according to Example 1. Further, since the exhaust gas purifying catalyst material according to Comparative Example 1 has Pd supported thereon, the effect of suppressing sintering of Pd is lower than when Pd is doped and fixed. Seems to be causing sintering.

  In the exhaust gas purifying catalyst material according to Comparative Example 2, each oxide of Ce and Zr and / or CeZr-based composite oxide is dispersed in alumina particles, and Pd is dissolved in each of these oxides. . From this, the exhaust gas purifying catalyst material according to Comparative Example 2 has the same Pd content as that of the exhaust gas purifying catalyst material according to Example 1, but Pd is also dissolved in the alumina particles. Therefore, it is considered that the amount of Pd dissolved in the CeZr-based composite oxide particles decreases and the oxygen release amount is inferior. In addition, since Pd is dissolved in CeZr-based composite oxide particles, the contact area between Pd and CeZr-based composite oxide particles is wider than when Pd is post-supported. Therefore, it is considered that the oxygen release amount is improved as compared with the exhaust gas purifying catalyst material according to Comparative Example 1.

  In the exhaust gas purifying catalyst material according to Comparative Example 3, the alumina particles are less effective in suppressing sintering of the CeZr-based composite oxide particles than other exhaust gas purifying catalyst materials. It is considered that the composite oxide particles are sintered and have reduced oxygen storage / release capacity.

  Next, the case where the amount of alumina particles was changed was further examined.

(Example 2)
It was produced in the same manner as in Example 1 except that the mass ratio of alumina to CeZr-based composite oxide particles was adjusted to 65:35.

(Comparative Example 4)
It was produced in the same manner as Comparative Example 1 except that the mass ratio of alumina to CeZr-based composite oxide particles was adjusted to 65:35.

  The oxygen storage / release capacity of each exhaust gas purifying catalyst material according to Examples 1 and 2 and Comparative Examples 1 and 4 was evaluated using the same method as the temperature rising reduction method. The result is shown in FIG. In addition, FIG. 10 is also a graph which shows the result of having examined about the oxygen storage-and-release capability of the exhaust gas purification catalyst material similarly to FIG. However, since FIG. 10 differs from the case of FIG. 9 in the amount of CeZr-based composite oxide particles, the vertical axis of FIG. 10 shows the oxygen release amount per mole of Ce in Example 1 as 100. Relative oxygen release is shown.

  As can be seen from FIG. 10, Example 1 in which Pd is doped into CeZr-based composite oxide particles and the amount of CeZr-based composite oxide particles is small has the largest oxygen release amount per mole of Ce. Therefore, even if the amount of CeZr-based composite oxide particles is small, Pd is effectively supported on the CeZr-based composite oxide particles, and the contact area between Pd and CeZr-based composite oxide particles is wide. Recognize. Further, by comparing Comparative Example 1 and Comparative Example 4, even in the case where Pd is post-supported, in Comparative Example 4 where the amount of CeZr-based composite oxide particles is large, Pd is CeZr-based composite oxide particles. It can be seen that the oxygen storage / release ability of can be increased.

[Example B]
Next, the influence of the mass ratio of CeO ₂ and ZrO _{2 on} the purification performance of the exhaust gas purification catalyst according to the embodiment of the present invention was examined.

First, an exhaust gas purifying catalyst material was produced in the same manner as in Example 1 except that the mass ratio of alumina to CeZr-based composite oxide particles was adjusted to 65:35. At that time, a plurality of exhaust gas purifying catalyst materials were prepared by changing the mass ratio of CeO ₂ and ZrO ₂ .

Then, Rh-supported CeZr-based composite oxide particles in which Rh was post-supported on composite oxide particles having a mass ratio of CeO ₂ , ZrO _2, and Nd ₂ O ₃ of 10:80:10 were prepared.

  Next, the above-mentioned exhaust gas purification catalyst material is washed with a honeycomb material made of cordierite having a cell wall of 4 mil and a cell number of 400 cpsi (400 cells per square inch) together with zirconyl nitrate as a binder material. , Dried and fired. Further, the Rh-supported CeZr-based composite oxide particles were wash-coated with zirconyl nitrate as a binder material, dried and fired. By doing so, an exhaust gas purification catalyst was obtained. The amount of Pd supported was adjusted to 0.4 g / L, and the amount of Rh supported was adjusted to 0.1 g / L.

  Then, the purification performance of the obtained exhaust gas purification catalyst was evaluated by measuring the light-off temperature by the following method.

  First, the obtained exhaust gas purifying catalyst was housed in a catalyst case to produce a catalytic converter. This catalytic converter was connected to an engine with an engine displacement of 2 L via an upstream pipe, the catalyst temperature was heated to 900 ° C., and the exhaust gas was circulated for 60 hours to perform an aging treatment. The exhaust gas is in accordance with a cycle in which the exhaust gas with A / F = 14.7 is passed for 40 seconds, the exhaust gas with A / F = 13.5 is passed for 10 seconds, and the exhaust gas with A / F = 16 is passed for 10 seconds. Circulated.

  And after performing an aging process, it was once cooled. From this catalyst, a mini sample of φ25.4 mm × length 50 mm was extracted with a core drill. The purification performance of this mini sample was evaluated using model exhaust gas that simulates the exhaust gas of a gasoline engine. The exhaust gas at this time was prepared such that A / F = 14.7 and the perturbation was ± 0.9. The space velocity (SV) was 60,000 / h. While circulating this model exhaust gas, the temperature was raised at a rate of 30 ° C./min, and the model exhaust gas on the inlet side of the catalyst at the time when the HC, CO, and NOx concentrations immediately after the catalyst outlet became 50%. The temperature (light-off temperature T50) was measured. The result is shown in FIG. FIG. 11 is a graph showing the results of examining the influence of the composition of CeZr-based composite oxide particles on the purification performance of the exhaust gas purification catalyst. The light-off temperature T50 is an index for evaluating catalyst activity and exhaust gas purification performance. The lower the light-off temperature T50, the higher the catalyst activity and exhaust gas purification performance at low temperatures.

As can be seen from FIG. 11, the CeZr-based composite oxide particles are preferably composed of a composite oxide containing Ce and Zr. And it turns out that it is preferable that it is the following ranges as the content. It is preferably ZrO ₂ based on the total weight of CeO ₂ and ZrO ₂ is contained 10 to 90 mass%, more preferably be contained in an amount of 40 mass% or more and 85 mass% or less, 50 wt More preferably, the content is from 80% to 80% by mass.

[Example C]
Next, the influence of the layer structure on the purification performance of the exhaust gas purification catalyst according to the embodiment of the present invention was examined. The difference in layer structure is that the catalyst layer is composed of one layer containing the exhaust gas purification catalyst material, or the layer containing the exhaust gas purification catalyst material and other layers. investigated.

  As the catalyst layer, an exhaust gas purification catalyst consisting of one layer containing the exhaust gas purification catalyst material was produced, and its purification performance was evaluated.

(Example 1-1)
First, except that the mass ratio between alumina and CeZr-based composite oxide particles was adjusted to 50:50, and the mass ratio between CeO ₂ and ZrO ₂ was adjusted to 60:40. In the same manner as in No. 1, an exhaust gas purification catalyst material was produced.

  Next, the obtained exhaust gas purifying catalyst material is washed with a binder raw material zirconyl nitrate on a cordierite honeycomb carrier having 4 mil cell walls and 400 cpsi cells (400 cells per square inch). And dried and fired. By doing so, an exhaust gas purification catalyst was obtained. The amount of the exhaust gas purification catalyst material supported was adjusted to 80 g / L.

(Comparative Example 1-1)
First, Comparative Example except that the mass ratio of alumina and CeZr-based composite oxide particles was adjusted to be 50:50, and the mass ratio of CeO ₂ and ZrO ₂ was adjusted to be 60:40. In the same manner as in No. 1, an exhaust gas purification catalyst material was produced.

  Using the obtained exhaust gas purification catalyst material, an exhaust gas purification catalyst was produced in the same manner as in Example 1-1.

(Comparative Example 2-1)
First, Comparative Example except that the mass ratio of alumina and CeZr-based composite oxide particles was adjusted to be 50:50, and the mass ratio of CeO ₂ and ZrO ₂ was adjusted to be 60:40. In the same manner as in No. 2, an exhaust gas purification catalyst material was produced.

  Using the obtained exhaust gas purification catalyst material, an exhaust gas purification catalyst was produced in the same manner as in Example 1-1.

(Comparative Example 3-1)
First, Comparative Example except that the mass ratio of alumina and CeZr-based composite oxide particles was adjusted to be 50:50, and the mass ratio of CeO ₂ and ZrO ₂ was adjusted to be 60:40. In the same manner as in No. 3, an exhaust gas purification catalyst material was produced.

  Using the obtained exhaust gas purification catalyst material, an exhaust gas purification catalyst was produced in the same manner as in Example 1-1.

  The obtained exhaust gas purifying catalyst was subjected to the same aging treatment as in Example B, and evaluated by measuring the light-off temperature T50 by the same method as in Example B. The result is shown in FIG.

  As can be seen from FIG. 12, an exhaust gas purification catalyst produced using an exhaust gas purification catalyst material containing CeZr-based composite oxide particles doped with Pd having the highest oxygen storage / release capability (Example 1-1) However, the light-off temperatures T50 for HC, CO, and NOx are all lower than the exhaust gas purification catalysts (Comparative Example 1-1 to Comparative Example 3-1) produced using other exhaust gas purification catalyst materials. I understand that. From this, it can be seen that an exhaust gas purification catalyst having high purification performance can be obtained by using the exhaust gas purification catalyst material according to the present invention.

  Next, as the catalyst layer, two layers of a first catalyst layer containing an exhaust gas purification catalyst material and a second catalyst layer containing Rh-supported CeZr-based composite oxide particles are laminated, An exhaust gas purification catalyst in which the first catalyst layer is located closer to the cell wall than the second catalyst layer was produced, and the purification performance was evaluated.

(Example 1-2)
First, except that the mass ratio between alumina and CeZr-based composite oxide particles was adjusted to 40:60, and the mass ratio between CeO ₂ and ZrO ₂ was adjusted to 60:40. In the same manner as in No. 1, an exhaust gas purification catalyst material was produced.

Then, Rh-supported CeZr-based composite oxide particles in which Rh was post-supported on composite oxide particles having a mass ratio of CeO ₂ , ZrO _2, and Nd ₂ O ₃ of 10:80:10 were prepared.

  Next, the exhaust gas purification catalyst material is wash-coated with zirconyl nitrate as a binder raw material on a honeycomb carrier made of cordierite having a cell wall of 4 mil and a cell count of 400 cpsi (400 cells per square inch), Dried and fired. Further, the Rh post-supported catalyst material was wash-coated with zirconyl nitrate as a binder material, dried and fired. By doing so, an exhaust gas purification catalyst was obtained. The amount of the exhaust gas purifying catalyst material was adjusted to 60 g / L, and the amount of the post-Rh supported catalyst material was adjusted to 40 g / L.

(Comparative Example 1-2)
First, Comparative Example except that the mass ratio of alumina and CeZr-based composite oxide particles was adjusted to 40:60, and the mass ratio of CeO ₂ and ZrO ₂ was adjusted to 60:40. In the same manner as in No. 1, an exhaust gas purification catalyst material was produced. Exhaust gas purification catalyst was produced by the same method as in Example 1-2 except that the obtained exhaust gas purification catalyst material was used.

(Comparative Example 2-2)
First, Comparative Example except that the mass ratio of alumina and CeZr-based composite oxide particles was adjusted to 40:60, and the mass ratio of CeO ₂ and ZrO ₂ was adjusted to 60:40. In the same manner as in No. 2, an exhaust gas purification catalyst material was produced. Exhaust gas purification catalyst was produced by the same method as in Example 1-2 except that the obtained exhaust gas purification catalyst material was used.

(Comparative Example 3-2)
First, Comparative Example except that the mass ratio of alumina and CeZr-based composite oxide particles was adjusted to 40:60, and the mass ratio of CeO ₂ and ZrO ₂ was adjusted to 60:40. In the same manner as in No. 3, an exhaust gas purification catalyst material was produced. Exhaust gas purification catalyst was produced by the same method as in Example 1-2 except that the obtained exhaust gas purification catalyst material was used.

  The obtained exhaust gas purifying catalyst was subjected to the same aging treatment as in Example B, and evaluated by measuring the light-off temperature T50 by the same method as in Example B. The result is shown in FIG.

  As can be seen from FIG. 13, an exhaust gas purification catalyst produced using an exhaust gas purification catalyst material containing CeZr-based composite oxide particles doped with Pd having the highest oxygen storage / release capability (Example 1-2) However, the light-off temperatures T50 for HC, CO, and NOx are all lower than the exhaust gas purification catalysts (Comparative Example 1-2 to Comparative Example 3-2) manufactured using other exhaust gas purification catalyst materials. I understand that. From this, it can be seen that an exhaust gas purification catalyst having high purification performance can be obtained by using the exhaust gas purification catalyst material according to the present invention. Further, it was found that by providing the second catalyst layer containing Rh-supported CeZr-based composite oxide particles on the side where the exhaust gas circulates, the purification performance is higher than in the case of the single layer shown in FIG.

  Next, as a catalyst layer, a first catalyst layer (lower layer) containing an exhaust gas purification catalyst material, a second catalyst layer (middle layer) containing Rh-supported CeZr-based composite oxide particles, and a Pd-supported CeZr-based composite Three layers including a third catalyst layer (upper layer) containing oxide particles are laminated, and the first catalyst layer is present at a position closer to the cell wall than the second catalyst layer, An exhaust gas purification catalyst having three catalyst layers located farther from the cell wall than the second catalyst layer was produced, and the purification performance was evaluated.

  The exhaust gas purifying catalyst here was produced by the same method as in Example B so as to achieve the loading shown in Table 1.

In addition, each component in Table 1 is as follows. The Pd-doped CeZrNd composite oxide in the upper layer is obtained by doping a CeZrNd composite oxide having a mass ratio of CeO ₂ , ZrO _2, and Nd ₂ O ₃ of 35:55:10 so that Pd is 0.01% by mass. It is a thing. The Pd-doped CeZrY composite oxide-containing alumina in the upper layer is a CeZrY composite in which the mass ratio of CeO ₂ , ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ and Al ₂ O ₃ is 8: 25: 2: 1: 64. The oxide-containing alumina is doped with Pd at 0.01% by mass.

The Pd-supported CeZrNd composite oxide in the upper layer is dry-solid-supported so that the mass ratio of CeO ₂ , ZrO ₂ and Nd ₂ O ₃ is 35:55:10, and Pd is 0.01% by mass. (Post-supported). Pd-supported CeZrY composite oxide-containing alumina in the upper layer is CeZrY composite oxide having a mass ratio of CeO ₂ , ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ and Al ₂ O ₃ of 8: 25: 2: 1: 64. This is one in which Pd is dry-solid supported (post-supported) so as to be 0.01% by mass on the product-containing alumina.

In addition, the Rh-supported CeZrNd composite oxide in the middle layer has a supported amount shown in Table 1 in the CeZrNd composite oxide in which the mass ratio of CeO ₂ , ZrO ₂ and Nd ₂ O ₃ is 10:80:10. It is dry-supported (post-supported). The Rh-supported ZrLa composite oxide-containing alumina in the middle layer is a CeZrY composite oxide-containing alumina having a mass ratio of ZrO ₂ , La ₂ O ₃ and Al ₂ O ₃ of 30: 5: 65, and Rh is shown in Table 1. It is dry-solid supported (post-supported) so that The La-containing alumina in the middle layer is adjusted so that La ₂ O ₃ is contained by 5 mass% and Al ₂ O ₃ is contained by 95 mass%.

Further, the Pd-doped CeZr composite oxide-containing alumina in the lower layer is an exhaust gas purifying catalyst material according to the present invention, and the mass ratio of CeO ₂ , ZrO ₂ and Al ₂ O ₃ is 10:30:60. CeZr composite oxide-containing alumina is doped with Pd at 0.5 mass%. The Pd-supported La-containing alumina in the lower layer is such that the Lad-alumina adjusted to contain 5% by mass of La ₂ O _{3 and} 95% by mass of Al ₂ O ₃ so that Pd has a supported amount shown in Table 1. It is dry-supported (post-supported). The amount of Pd supported is adjusted so that the total amount of Pd contained in the exhaust gas purification catalyst is the same in all of Examples 1-3 to 1-7. Further, ZrO _{2 as} a binder contains zirconyl nitrate as a binder raw material so as to have a loading amount shown in Table 1 when an exhaust gas purification catalyst is produced.

  Then, the purification performance of the obtained exhaust gas purification catalyst was evaluated by measuring the light-off temperature by the following method.

  First, the obtained exhaust gas purifying catalyst was housed in a catalyst case to produce a catalytic converter. This catalytic converter was connected to an engine with an engine displacement of 2 L through an upstream pipe, the catalyst temperature was heated to 900 ° C., and the exhaust gas was allowed to flow for 100 hours to perform an aging treatment. The exhaust gas is in accordance with a cycle in which the exhaust gas with A / F = 14.7 is passed for 40 seconds, the exhaust gas with A / F = 13.5 is passed for 10 seconds, and the exhaust gas with A / F = 16 is passed for 10 seconds. Circulate. Further, engine oil was added to the exhaust gas at an addition amount of 0.5 mL / min from the intake manifold of the engine.

  And after performing an aging process, it was once cooled. From this catalyst, a mini sample of φ25.4 mm × length 50 mm was extracted with a core drill. The purification performance of this mini sample was evaluated using model exhaust gas that simulates the exhaust gas of a gasoline engine. The exhaust gas at this time was prepared so that A / F = 14.7 and the perturbation was ± 0.9. The space velocity (SV) was 60,000 / h. While circulating the model exhaust gas, the temperature was raised at a rate of 30 ° C./min, and the model exhaust gas on the inlet side of the catalyst at the time when the HC, CO and NOx concentrations immediately after the catalyst outlet became 50%. The temperature (light-off temperature T50) was measured. The result is shown in FIG.

  As can be seen from FIG. 14, when the catalyst layer is three layers (Example 1-4 to Example 1-7), the light-off temperature T50 is higher than when the catalyst layer is two layers (Example 1-3). It can be seen that the purification performance is further improved. In addition, in the case where the measurement is performed in a situation where oil is added to the exhaust gas and the poisoning of the exhaust gas purification catalyst is promoted, there are three catalyst layers (Examples 1-4 to Examples). 1-7) showed high purification performance. From this, by providing another catalyst layer in the upper layer, not only the purification performance is improved, but also the poisoning of the catalyst is suppressed.

It is an expanded sectional view showing typically exhaust gas purification catalyst material 10 concerning a 1st embodiment. FIG. 3 is a cross-sectional view showing the vicinity of the surface of the CeZr-based composite oxide particles 12 in an enlarged manner. It is process drawing which shows the manufacturing method of the exhaust gas purification catalyst material which concerns on 1st Embodiment. It is sectional drawing which shows typically the catalytic converter 20 provided with the exhaust gas purification catalyst which concerns on 2nd Embodiment. 3 is an enlarged cross-sectional view showing a part of the purification catalyst 22. FIG. 6 is a process diagram illustrating a method for producing an exhaust gas purifying catalyst material according to Comparative Example 1. FIG. 6 is a process diagram showing a method for manufacturing an exhaust gas purifying catalyst material according to Comparative Example 2. FIG. 6 is a process diagram illustrating a method for producing an exhaust gas purifying catalyst material according to Comparative Example 3. FIG. It is a graph which shows the result of having examined about the oxygen storage-and-release capability of the exhaust gas purification catalyst material. It is a graph which shows the result of having examined about the oxygen storage-and-release capability of the exhaust gas purification catalyst material. It is a graph which shows the result of having examined about the influence of the composition of CeZr system complex oxide particles to the purification performance of the catalyst for exhaust gas purification. It is a graph which shows the result of having examined about the purification performance of the catalyst for exhaust gas purification. It is a graph which shows the result of having examined about the purification performance of the catalyst for exhaust gas purification. It is a graph which shows the result of having examined about the purification performance of the catalyst for exhaust gas purification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exhaust gas purification catalyst material 12 CeZr system complex oxide particle 13 Alumina particle 20 Catalytic converter 21 Heat-resistant container 22 Purification catalyst 31 Cell wall 32 Catalyst layer

Claims (9)

An exhaust gas purifying catalyst material containing alumina particles, CeZr-based composite oxide particles having oxygen storage / release ability, and Pd,
The Pd is doped and fixed only to the CeZr-based composite oxide particles,
An exhaust gas purifying catalyst material, wherein the CeZr-based composite oxide particles are dispersed and supported on the surfaces of the alumina particles. _2. The exhaust gas purifying catalyst material according to claim 1, wherein the CeZr-based composite oxide particles contain 10 mass% or more and 90 mass% or less of ZrO ₂ with respect to the total mass of CeO ₂ and ZrO ₂ . _2. The exhaust gas purifying catalyst material according to claim 1, wherein the CeZr-based composite oxide particles contain 40 mass% or more and 85 mass% or less of ZrO ₂ with respect to the total mass of CeO ₂ and ZrO ₂ . _2. The exhaust gas purification catalyst material according to claim 1, wherein the CeZr-based composite oxide particles contain 50 mass% or more and 80 mass% or less of ZrO ₂ with respect to the total mass of CeO ₂ and ZrO ₂ . By adding a basic solution to an acidic solution containing Ce, Zr, and Pd, the first hydroxide containing Ce, Zr, and Pd is coprecipitated, and the first hydroxide is dispersed. A first coprecipitation step for forming the first dispersion liquid,
By adding a basic solution to the acidic solution containing Al, the second hydroxide containing Al is coprecipitated to form a second dispersion in which the second hydroxide is dispersed. 2 co-precipitation process,
A mixing step of mixing the first dispersion and the second dispersion;
A method for producing an exhaust gas purifying catalyst material, comprising: a firing step of drying and firing a mixture of the first dispersion and the second dispersion. An exhaust gas purifying catalyst disposed in an exhaust passage of an engine,
A honeycomb carrier;
A catalyst layer formed on the cell wall surface of the honeycomb-shaped carrier,
An exhaust gas purification catalyst, wherein the catalyst layer contains the exhaust gas purification catalyst material according to any one of claims 1 to 4. The catalyst layer is formed by laminating at least two layers of a first catalyst layer containing the exhaust gas purification catalyst material and a second catalyst layer containing Rh-supported CeZr-based composite oxide particles,
The exhaust gas purifying catalyst according to claim 6, wherein the first catalyst layer is located closer to the cell wall than the second catalyst layer. The catalyst layer is obtained by further laminating a third catalyst layer containing Pd-supported CeZr-based composite oxide particles,
The exhaust gas purifying catalyst according to claim 7, wherein the third catalyst layer is located farther from the cell wall than the second catalyst layer.   The exhaust gas purifying catalyst according to claim 8, wherein the Pd-supported CeZr-based composite oxide particles are fixed by doping Pd with CeZr-based composite oxide particles.

Images