JP6146436B2 - Exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to an exhaust gas purification catalyst.

  Conventionally, a three-way catalyst that simultaneously purifies HC, CO, and NOx in the vicinity of stoichiometry is known. For example, Pt, Pd, and Rh as catalyst metals are surfaces of support material particles such as oxygen storage / release materials containing Ce. The one supported on the surface is used. And the support material particle | grains with which the said catalyst metal was carry | supported are normally carry | supported by the cell wall of the honeycomb support | carrier via the fine particle material which has a binder function.

  As such a fine particle material, for example, a material obtained by doping the above oxygen storage / release material with Rh as a catalyst metal is pulverized (see, for example, Patent Document 1).

The catalyst described in Patent Document 1 includes an upper layer containing Rh and a lower layer containing Pd, the upper layer is a fine Rh-doped CeZr composite oxide having a catalytic function, and the lower layer is fine with ZrO ₂ having no catalytic function. It is contained as a particulate material. According to this, as the exhaust gas diffuses and flows in the catalyst layer, the fine particle material in the upper layer itself has the catalyst performance, so that the contact opportunity between the exhaust gas and the catalyst is increased and the purification performance. Is known to improve.

JP 2011-200187 A

  Here, although the said patent document 1 is based on this applicant, as a result of subsequent experiment and examination, in the transition period when exhaust gas temperature becomes high temperature gradually from low temperature, improvement of the purification performance of HC, CO, NOx is carried out. I found that there was room.

  Accordingly, it is an object of the present invention to obtain a higher purification performance of HC, CO, NOx in the transition period in which the exhaust gas temperature gradually increases from a low temperature as described above by improving the fine particle material. To do.

In order to solve the above problems, the present invention, the catalyst layer containing Rh, and so as to contain a fine particle of Rh-doped Z r double if oxide containing no Ce.

That is, the exhaust gas purifying catalyst disclosed herein is a catalyst provided with an Rh-containing catalyst layer containing Rh as a catalytic metal and a particulate material, and the particulate material has an average particle diameter D50 of Ce of 50 nm or less. characterized in that it is a free Rh-doped Z r double focus oxide.

  In general, a complex oxide containing Ce occludes oxygen in exhaust gas and releases it as active oxygen by a reaction reversibly proceeding with a valence change of Ce. For this reason, the oxygen release rate is high and fluctuations in the air-fuel ratio (A / F) can be effectively absorbed.

  However, for example, immediately after the exhaust gas atmosphere is switched from lean to rich, oxygen release by the Ce-containing composite oxide proceeds rapidly. Therefore, when the Ce-containing composite oxide is doped with Rh as a catalyst metal, Most of Rh tends to be in an oxidized state, which is disadvantageous for NOx purification, and cannot effectively purify NOx in the exhaust gas that starts to occur immediately after the atmosphere is switched.

According to the present invention, Z r double if oxide containing no Ce is capable of oxygen ion-exchange reaction, a composite oxide containing Ce and (occludes oxygen lean atmosphere active oxygen in the stoichiometric or rich atmosphere since the speed to release active oxygen as compared with a) a function of release is mild, by containing Ce-free Rh-doped Z r double coupling oxide as particles material, for example, a / F is from lean to rich In the process of switching and the exhaust gas temperature rising, Rh can maintain an appropriate oxidation state or reduction state and effectively purify the NOx.

Then, Ce by containing the non-containing Rh-doped Z r double coupling oxide as fine particles, because the diffusion path exhaust gas or oxygen diffuses moves is shortened, only the secondary particle surface portion formed by aggregation with each other In addition, the primary particles inside the secondary particles also work effectively to release active oxygen. In addition, since the particle material is doped with Rh as the catalyst metal, there are many opportunities for contact between the catalyst metal and the exhaust gas, so the entire catalyst layer works for exhaust gas purification without waste, and the catalyst purification performance is improved. improves.

  In a preferred embodiment, the particulate material contains a rare earth metal other than Ce in addition to Rh.

By containing a rare earth metal other than ce, Z r double focus oxide becomes to have a surface basicity to improve the adsorptivity of NOx. Therefore, such a Z r double coupling oxide, the Rh-doped as a catalyst metal, by miniaturized to nanoscale, the reaction site increases, thereby making it possible to lower temperature the reaction temperature. In addition, rare earth metals other than Ce are La, Y, Nd, Sc, etc., for example, More preferably, it is La, Y.

Thus, in a particularly preferred embodiment, the particles material is Rh-doped ZrLa Y double focus oxide. ZrLa Y double coupling oxide, since it has a surface basicity as described above, NOx effectively adsorb, can be purified, it is possible to lower the reaction temperature effectively.

In a preferred embodiment, the Rh-containing catalyst layer further includes an additional particle material, and the additional particle material is a Ce-containing Rh-doped Zr composite oxide having an average particle diameter D50 of 50 nm or less.

As described above, the Ce-containing composite oxide has an excellent oxygen storage / release capability, and even when A / F fluctuates, it can effectively release oxygen and absorb the fluctuation of A / F. In addition, while Rh is preferably in a reduced metal state for NOx purification, an oxidized state is preferred for HC and CO purification. Therefore, in addition to the particulate material, Ce has excellent oxygen storage / release capability as an additional particulate material. By including fine particles of the contained Rh-doped Zr composite oxide, Rh can further maintain an appropriate oxidation state or reduction state, and the catalyst performance can be effectively improved.

  In addition to Ce and Rh, the additional particulate material may further contain a rare earth metal other than Ce. The rare earth metal other than Ce is, for example, Nd, Y, La, Sc, etc., and particularly preferably Nd, Y.

Thus, in a particularly preferred embodiment, it said additional particle material is Rh-doped CeZrN d double focus oxide. Thereby, Rh can maintain a more appropriate oxidation state or reduction state, and the catalyst performance can be effectively improved.

In a preferred embodiment, the Rh-containing catalyst layer, than the particles material and / or additional particle material contains further a larger support particles material having an average particle size, the support particles material is activated alumina, CEZ r double focus oxide things, are at least one selected from the group of ZRL a double coupling oxide, the particle material and / or additional particle material is mixed so as to be interposed between the support particles material particles. Thereby, the said particle material and / or an additional particle material have a binder function between the particles of the said support particle material, and can combine these effectively .

In good preferable embodiment, the Rh-containing catalyst layer is formed on the surface of the Pd-containing catalyst layer provided in the exhaust gas passage on the wall. Thereby, HC, CO, NOx in the exhaust gas can be effectively purified.

The method for producing an exhaust gas purification catalyst disclosed herein is a method for producing an exhaust gas purification catalyst comprising an Rh-containing catalyst layer containing Rh as a catalyst metal and a particulate material, wherein the particulate material is the average particle size D50 less Ce-free Rh-doped Z r double coupling oxide 50 nm, the particles by the average particle diameter D50 is crushed containing non more Ce 150 nm Rh-doped Z r double focus oxide Preparing a material, preparing a slurry by suspending the particle material in a solvent, immersing the base material in the slurry, drying the base material, and supporting the particle material on the base material Features.

According to the present invention, by Rh as a catalytic metal is further refine the Ce-free Z r double coupling oxide as support particles material doped, and prepare particles material. Thereby, the exclusive material which has a binder function becomes unnecessary, or even when using together an exclusive material and the said particle | grain material, the quantity of the exclusive material can be decreased. Moreover, since the particulate material itself has a catalytic function, the purification performance of the catalyst can be effectively improved.

In a preferred embodiment, the Rh-containing catalyst layer further includes a Ce-containing Rh-doped Zr composite oxide having an average particle diameter D50 of 50 nm or less as an additional particle material, and a Ce-containing Rh-doped alloy having an average particle diameter D50 of 200 nm or more. The additional particle material is prepared by pulverizing the Zr composite oxide, and when the slurry is prepared, the slurry is prepared by suspending the additional particle material in a solvent in addition to the particle material. Thereby, even if A / F fluctuates, Rh can maintain an appropriate oxidation state or reduction state, and an exhaust gas purification catalyst having excellent catalytic performance can be provided.

The particulate material and / or the additional particulate material is preferably subjected to CO reduction heat treatment.

Usually, most of Rh is dissolved in the particulate material and the additional particulate material in an oxidized state. At this time, Rh in the oxidized state is contained in the solid solution in a form that spreads on the surface of the particle material, and the total surface area of Rh exposed from the particle material is small. On the other hand, when the reduction treatment is performed on the particulate material, the oxidized solid solution Rh is dissociated and metallized by oxygen, and the metal Rh is deposited on the surface of the particulate material and scattered throughout the surface of the particulate material. As a result, the surface area of Rh increases and the contact area with the exhaust gas increases, so that the active points increase, the exhaust gas can be purified efficiently, and the catalytic performance of the particulate material can be improved. .

As described above, according to the present invention, by containing Ce-free Rh-doped Z r double coupling oxide as particles material, for example, A / F is switched from lean to rich, the process of the exhaust gas temperature rises In this case, it is possible to effectively purify the NOx while maintaining an appropriate oxidation state or reduction state of Rh.

FIG. 1 is a schematic cross-sectional view showing an exhaust gas purifying catalyst according to an embodiment of the present invention. FIG. 2 is a graph showing the particle size distribution (frequency distribution) of the Ce-containing binder material and the catalyst material in the present embodiment. FIG. 3 is a graph showing the particle size distribution (frequency distribution) of the Ce-free binder material and the catalyst material in the present embodiment. FIG. 4 is a graph showing the particle size distribution (frequency distribution) of La—Al ₂ O _{3 in} the present embodiment. FIG. 5 is a graph showing the exhaust gas temperature (T50) at which the purification rate is 50% for each exhaust gas component in the exhaust gas purification catalysts of Examples and Comparative Examples.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or its application.

  FIG. 1 shows a basic configuration of an exhaust gas purification catalyst (three-way catalyst) suitable for purification of automobile exhaust gas according to this embodiment. In the figure, reference numeral 1 denotes a cell wall (exhaust gas passage wall) of a honeycomb carrier (base material), and a plurality of catalyst layers laminated on the cell wall 1, that is, a first catalyst layer (Pd-containing catalyst layer) 2. And a second catalyst layer (Rh-containing catalyst layer) 3 formed on the surface of the first catalyst layer 2.

[First catalyst layer]
As shown in FIG. 1, the first catalyst layer 2 contains activated alumina particles 4, Ce-containing oxide particles 6, and Ce-containing oxide particles 8. A catalyst metal 5 is supported on the particles 4 and 6. The binder particles 7 are interposed between these particles.

  The activated alumina particles 4 are excellent in heat resistance and durability, and have a large specific surface area and high dispersibility of the catalyst metal. By supporting the catalyst metal 5 on the activated alumina particles 4, the dispersibility of the catalyst metal is improved, the contact area with the exhaust gas is increased, and the catalyst performance is improved.

  The Ce-containing oxide particles 6 and 8 are oxygen storage / release materials, and store the oxygen in the exhaust gas and release it as active oxygen by a reaction reversibly proceeding with a valence change of Ce. The catalyst metal 5 is supported on the Ce-containing oxide particles 6 and is not supported on the Ce-containing oxide particles 8. The amount of catalyst metal can be adjusted by adjusting these content ratios. Further, different catalyst metals can be supported on the Ce-containing oxide particles 8.

  The catalyst metal 5 is at least one selected from the group consisting of Pt, Pd, and Rh, and is particularly preferably Pd. In this embodiment, Pd is supported as the catalyst metal 5.

  As the binder particles 7, for example, ZrYO fine particles having oxygen ion conductivity are preferably used. Accordingly, even when the exhaust gas atmosphere is lean or rich, the binder particles 7 having oxygen ion conductivity take in oxygen from the surroundings and release active oxygen. Can be planned.

[Second catalyst layer]
As shown in FIG. 1, the second catalyst layer 3, Rh-doped CEZ r double if oxide particles 9 and the active alumina particles (activated alumina) 10 and the ZRL a double focus oxide particles (ZRL a double focus oxide) 12 Containing. In addition, binder particles 13 are interposed between these particles.

Rh-doped CEZ r double if oxide particles 9, the particles of CEZ r double coupling oxide as support particles material, in which Rh as a catalytic metal is solid-solved. The activated alumina particles 10 improve the heat resistance and durability of the catalyst as described above. The ZRL a double focus oxide particles 12 as support particles material, Rh11 as a catalyst metal is supported.

CEZ r double focus oxides are oxygen storage materials, because it has excellent oxygen storage capacity based on a reversible reaction involving the valence change of Ce, the air-fuel ratio of the exhaust gas (A / F) is Even if it fluctuates, the CeZr composite oxide absorbs fluctuations in the air-fuel ratio by absorbing and releasing oxygen. By doping such CeZr composite oxide with Rh as a catalytic metal, the air-fuel ratio window in which Rh effectively works to purify HC, CO and NOx is expanded. CEZ r double coupling oxide, in addition to Ce, may further contain a rare earth metal other than Ce. The rare earth metal other than Ce is, for example, Nd, Y, La, Sc, etc., and particularly preferably Nd, Y.

ZRL a double focus oxide is obtained by incorporating a La to Z r double if oxide containing no Ce. Z r double coupling oxide, by further containing a rare earth metal other than Ce, it takes on the surface basicity to improve the adsorptivity of NOx. Therefore, such a Z r double coupling oxide, by supporting the Rh11 as the catalyst metal, it is possible to improve the purification performance of NOx. Incidentally, Rh may be configured to dope the Z r double focus oxide. Further, the rare earth metal other than Ce is, for example, Y, Nd, Sc or the like other than La of the present embodiment. In particular, ZrLa Y double if oxide containing La, and Y as the rare earth metal other than Ce are preferred.

  Here, the binder particles 13 are made of a mixture of Ce-containing binder particles (additional particle material) 13a and Ce-free binder particles (particle material) 13b.

Ce-containing binder particles 13a is one in which the Rh as a catalytic metal was supported or doped to the CEZ r double if oxides are oxygen storage materials. Ce-containing binder particles 13a may be, for example, by using the fine particles separately Rh-doped CEZ r double if oxides prepared, support particles material, or as a catalyst material catalyst metal is supported or doped support particles member You may use what was further refine | pulverized by grind | pulverizing what is contained in a catalyst layer. If the separately manufactured, regulation or Rh amount of catalyst metal contained in the binder particles, it is possible to adjust the structure of CEZ r double coupling oxide, effectively the entire catalyst catalyst performance can be improved . Moreover, when using what further refined | miniaturized the support particle material or the catalyst material, while being able to prepare a binder material easily, the effective catalyst performance can be provided to a catalyst. In this embodiment, Ce-containing binder particles 13a are those prepared by further pulverizing the Rh-doped CEZ r double if oxide particles 9.

Incidentally, CEZ r double if oxide used in the Ce-containing binder particles 13a also, in addition to Ce, may further contain a rare earth metal other than Ce. The rare earth metal other than Ce is, for example, Nd, Y, La, Sc, etc., and particularly preferably Nd, Y.

  Rh contained in the Ce-containing binder particles 13a may be carried or may be doped (solid solution). Preferably, it is doped. As a result, the oxygen storage / release ability of the Ce-containing binder particles 13a can be further increased, the aggregation of Rh can be suppressed, and the purification performance of the catalyst under A / F fluctuation can be improved.

Ce-free binder particles 13b is obtained a solid solution of Rh as the catalyst metal to Z r double if oxide containing no Ce. Also in the Ce-free binder particles 13b, fine particles produced separately may be used in the same manner as the Ce-containing binder particles 13a. This regulation and the amount of Rh contained in the binder particle by, Z r enables adjustment of structure of a double coupling oxide, can be effectively improve the overall catalyst catalyst performance. Further, as the Ce-free binder particles 13b, particles that are further pulverized and further refined from those contained in the catalyst layer as support particle materials or catalyst materials may be used. Thereby, while being able to prepare a binder material easily, the effective catalyst performance can be provided to a catalyst. In this embodiment, Ce-free binder particles 13b are those produced by separately making a Ce-free Rh-doped Z r double coupling oxide, finer.

Incidentally, Z r double if oxide used in the Ce-free binder particles 13b also preferably includes a rare earth metal other than Ce. As described above, the inclusion of rare earth metals other than Ce improves NOx adsorption. Moreover, by doping with Rh and miniaturizing to nanoscale, the reaction sites increase and the reaction temperature can be further lowered. In addition, rare earth metals other than Ce are La, Y, Nd, Sc, etc., for example, More preferably, it is La, Y.

Rh contained in the Ce-free binder particles 13b is doped (solid solution). Thereby, aggregation of Rh of Ce-free binder particles 13b can be suppressed, and Rh can be maintained in a metal state even in an oxygen-excess atmosphere.

The present embodiment is characterized in that the binder particles 13 include Ce-free binder particles 13b. Z r double if oxide containing no Ce is capable of oxygen ion-exchange reaction, the rate of release of active oxygen as compared with the composite oxides containing Ce are mild, Ce-free Rh as particle material by including the doped Z r double engagement oxides, for example a / F is switched from lean to rich, in the process of the exhaust gas temperature rises, Rh is kept moderate oxidation state or a reduced state, the NOx It can be effectively purified. Further, by making the binder particles 13 a mixture of the Ce-containing binder particles 13a and the Ce-free binder particles 13b, as described above, Rh can maintain a more appropriate oxidized state or reduced state, and the catalytic performance can be improved. It can be improved effectively.

  The mixing ratio of the Ce-containing binder particles 13a and the Ce-free binder particles 13b is the content of the Ce-free binder particles 13b with respect to the total content of the binder particles 13, and is preferably 30 to 90% as a mass ratio. More preferably, it is 50 to 85%, particularly preferably 60 to 80%.

  Further, the content of the binder particles 13 in the second catalyst layer 3 is preferably 3 to 25%, more preferably 5 to 20%, particularly preferably 7 to 15%, of the supported amount of the second catalyst layer 3. It is.

<Method for producing catalyst>
-Preparation of support particle material and catalyst material-
The support particle material and catalyst material contained in each catalyst layer can be prepared using a coprecipitation method. In the coprecipitation method, a basic solution is added to an acidic solution of a metal salt, preferably nitrate, contained in a composite oxide to obtain a hydroxide coprecipitate, and then the hydroxide is dried and pulverized. This is a method for preparing a desired composite oxide by firing.

  In addition, when doping a catalyst metal in complex oxide, it can carry out by making the said acidic solution contain the metal salt of a catalyst metal, and coprecipitating. When the catalyst metal is supported, it can be supported on the composite oxide obtained by the coprecipitation method using an evaporation to dryness method or the like.

  The support particle material and the catalyst material, particularly those doped with Rh, may be subjected to CO reduction heat treatment. As a result, the surface area of Rh increases and the contact area with the exhaust gas increases, so that the active points increase, the exhaust gas can be purified efficiently, and the catalytic performance of the particulate material can be improved. .

-Preparation of binder material-
Binder particles 7 contained in the first catalyst layer 2 may be, for example, Z r double focus oxide obtained by wet grinding.

The Ce-containing binder particles 13a contained in the second catalyst layer 3 are prepared by pulverizing the Ce-containing Rh-doped Zr composite oxide prepared by the coprecipitation method until a desired average particle diameter is obtained before or after firing. can do. The Ce-containing Rh-doped Zr composite oxide A having a large average particle size used as a support particle material or a catalyst material is prepared by firing and then pulverized to obtain a Ce-containing Rh-doped Zr having a small average particle size as binder particles. It is preferable to obtain the composite oxide B.

The Ce-free binder particles 13b can be prepared using a Ce-free Rh-doped Zr composite oxide in the same manner as the Ce-containing binder particles 13a. In this case as well, it is preferable that the Ce-free Rh-doped Zr composite oxide A having a large average particle size is prepared and then pulverized to obtain a Ce-free Rh-doped Zr composite oxide B having a small average particle size.

  The binder particles 13a and 13b are preferably subjected to CO reduction heat treatment. As a result, the surface area of Rh increases and the contact area with the exhaust gas increases, so that the active points increase, the exhaust gas can be purified efficiently, and the catalytic performance of the particulate material can be improved. .

-Supporting catalyst on honeycomb carrier-
First, a slurry is prepared by suspending the support particle material, catalyst material, and binder particles 7 contained in the first catalyst layer 2 in a solvent, and after immersing the honeycomb carrier in the slurry, By drying, the first catalyst layer 2 can be formed on the cell walls of the carrier. Next, a slurry is prepared by suspending the support particle material, the catalyst material, and the binder particles 13a and 13b contained in the second catalyst layer 3 in a solvent, and the first catalyst layer 2 is formed in the slurry. The second catalyst layer 3 can be formed on the surface of the first catalyst layer 2 provided on the cell wall by immersing the honeycomb support thus formed and then drying the support.

  In the catalyst thus formed, the binder particles 13a and 13b are mixed so as to be interposed between the support particle material and the catalyst material particles. Thereby, the said binder particle | grains 13a and 13b have a binder function between the particle | grains of the said support particle material and a catalyst material, and can combine these effectively.

<About particle size>
The support particle material and the catalyst material contained in the second catalyst layer 3 have a larger average particle diameter than the Ce-containing binder particles 13a and / or the Ce-free binder particles 13b. The average particle diameter is preferably 100 nm or more, more preferably 120 nm or more, and particularly preferably 150 nm or more.

The average particle diameter of the Ce-containing Rh-doped Zr composite oxide A is preferably 150 nm or more, more preferably 180 nm or more, and particularly preferably 200 nm or more.

  The average particle diameter of the Ce-containing binder particles 13a is preferably 80 nm or less, more preferably 50 nm or less, and particularly preferably 40 nm or less.

The average particle diameter of the Ce-free Rh-doped Zr composite oxide A is preferably 100 nm or more, more preferably 120 nm or more, and particularly preferably 150 nm or more.

  The average particle size of the Ce-free binder particles 13b is preferably 80 nm or less, more preferably 50 nm or less, and particularly preferably 40 nm or less.

  Next, specific examples will be described.

Example 1
[Carrier]
In the catalyst configuration shown in FIG. 1, the carrier 1 is a ceramic honeycomb carrier having a cell wall thickness of 3.5 mil (8.89 × 10 ⁻² mm) and 600 cells per square inch (645.16 mm ² ). (Capacity about 1 L) was used.

[First catalyst layer]
Table 1 shows the catalyst configuration of the first catalyst layer 2.

The first catalyst layer 2 is configured to contain a mixture of Pd-supported La—Al ₂ O ₃ , Pd-supported CeZrNdLaYO, non-catalyst-supported CeZrNdLaYO, and ZrY binder as binder particles 7 having oxygen ion conductivity. .

The Pd-supporting La—Al ₂ O ₃ of the first catalyst layer 2 is obtained by supporting Pd as the catalyst metal 5 on La—Al ₂ O ₃ as the activated alumina 4. Note that La—Al ₂ O ₃ is activated alumina containing 4% by mass of La ₂ O ₃ . Pd-supported CeZrNdLaYO is obtained by supporting Pd as the catalyst metal 5 on CeZrNdLaYO (a composite oxide containing Ce, Zr, Nd, La, and Y) as the Ce-containing oxide 6. CeZrNdLaYO without catalyst metal is contained as Ce-containing oxide particles 8. The ZrY binder uses a ZrY sol (ZrY composite oxide powder sol) obtained by wet-grinding ZrO ₂ containing 3 mol% of Y ₂ O ₃ as a binder. Evaporation to dryness was adopted for loading Pd.

  The first catalyst layer 2 has the same catalyst structure in Example 2 and Comparative Examples 1 and 2 described later.

[Second catalyst layer]
Next, Table 2 shows the catalyst configuration of the second catalyst layer.

The second catalyst layer 3, Rh-doped CEZ r Rh-doped CeZrNdLaYO as double focus oxide particles 9, _{La-Al 2} O 3 as the active alumina particles 10, Rh supported ZrLaYO, and Rh-doped as Ce-containing binder particles 13a A CeZrNdLaYO binder and Rh-doped ZrLaYO as Ce-free binder particles 13b were mixed and contained.

Rh as a catalytic metal is dissolved in Rh-doped CeZrNdLaYO. Further, Rh supported ZrLaYO is obtained by supporting Rh as the catalytic metal ZrLaYO as ZRL a double focus oxide particles 12.

[Preparation of catalyst material and binder material]
As La-Al ₂ O ₃ , a commercially available powder was used.

  Rh-doped CeZrNdLaYO was prepared as follows. That is, cerium nitrate hexahydrate, zirconium oxynitrate, neodymium nitrate hexahydrate, lanthanum nitrate, yttrium nitrate, and rhodium nitrate were dissolved in ion-exchanged water, and this nitrate solution was diluted 8 times with 28 mass% aqueous ammonia. Were mixed and neutralized to obtain a coprecipitate. The coprecipitate was washed with water by a centrifugal separation method, dried in air at a temperature of 150 ° C. for a whole day and night, pulverized, and then fired at a temperature of 500 ° C. in air for 2 hours. Next, Rh-doped CeZrNdLaYO powder A was obtained by heat treatment at 550 ° C. or higher and 800 ° C. or lower in a CO atmosphere.

  The Rh-doped CeZrNdLaYO binder was obtained by further pulverizing and refining the Rh-doped CeZrNdLaYO powder A. That is, ion-exchanged water was added to the Rh-doped CeZrNdLaYO powder A to obtain a slurry (solid content: 25% by mass), and this slurry was put into a ball mill and pulverized with 0.5 mm zirconia beads (about 3 hours). In this way, Rh-doped CeZrNdLaYO powder B having a reduced particle size was obtained.

The Rh-doped ZrLaYO binder was prepared by preparing a Rh-doped ZrLaYO powder having a large average particle size, and then further pulverizing and refining. That is, zirconium oxynitrate, yttrium nitrate, and rhodium nitrate were dissolved in ion exchange water. A coprecipitate was obtained by mixing and neutralizing this nitrate solution with an 8-fold diluted solution of 28% by mass ammonia water. This coprecipitate was further loaded with Rh and La ₂ O ₃ by evaporation to dryness using an aqueous rhodium nitrate solution and then an aqueous lanthanum nitrate solution, and then dried and pulverized in air at a temperature of 150 ° C. overnight. Thereafter, firing was performed in air at a temperature of 500 ° C. for 2 hours to obtain Rh-doped ZrLaYO powder. The Rh-doped ZrLaYO powder A was obtained by heat-treating the Rh-doped ZrLaYO powder at 550 ° C. or higher and 800 ° C. or lower in a CO atmosphere. Note that the amount of Rh added to the coprecipitate is 35% of the total amount of Rh. Ion exchange water was added to the Rh-doped ZrLaYO powder A to obtain a slurry (solid content: 25% by mass), and this slurry was put into a ball mill and pulverized with 0.5 mm zirconia beads (about 3 hours). As a result, Rh-doped ZrLaYO powder B having a reduced particle size was obtained as the Rh-doped ZrLaYO binder.

  Rh-supported ZrLaYO was obtained by dissolving zirconium oxynitrate, lanthanum nitrate, and yttrium nitrate in ion-exchanged water. A coprecipitate was obtained by mixing and neutralizing this nitrate solution with an 8-fold diluted solution of 28% by mass ammonia water. The coprecipitate is washed with water by a centrifugal separation method, dried in air at a temperature of 150 ° C. for a whole day and night, pulverized, and then fired in air at a temperature of 500 ° C. for 2 hours to obtain a ZrLaYO powder. Obtained. This ZrLaYO powder was loaded with Rh using an aqueous rhodium nitrate solution by evaporation to dryness, and then heat-treated at 550 ° C. or higher and 800 ° C. or lower in a CO atmosphere to obtain Rh-supported ZrLaYO powder.

[Average particle size of catalyst material and binder material]
The Rh-doped CeZrNdLaYO powders A and B have a particle size distribution (frequency distribution) as shown in FIG. 2, and the average particle diameter D50 is 250 nm and 40 nm, respectively.

  The Rh-doped ZrLaYO powders A and B have a particle size distribution (frequency distribution) as shown in FIG. 3, and the average particle size D50 is 190 nm and 30 nm, respectively.

The La—Al ₂ O ₃ has a particle size distribution (frequency distribution) as shown in FIG. 4 and an average particle size D50 of 1400 nm.

[Method of supporting catalyst material and binder material on honeycomb carrier]
The method for preparing the catalyst of Example 1 is as follows. First, the catalyst material of Table 1, a binder material, and ion-exchange water are mixed, a slurry is prepared, this is coated to a support | carrier, the 1st catalyst layer 2 is formed by drying and baking. Next, the catalyst material, binder material and ion-exchanged water shown in Table 2 are mixed to prepare a slurry, which is coated on the first catalyst layer 2 and dried and fired to form the second catalyst layer 3. To do.

-Example 2-
Table 3 shows the configuration of the second catalyst layer 3 of Example 2.

The second catalyst layer 3 differs from Example 1 in that the content of the Rh-supported ZrLaYO of Example 1 is reduced to Rh-doped ZrLaYO powder A and the content of La-Al ₂ O ₃ is increased.

-Comparative Example 1-
Table 4 shows the configuration of the second catalyst layer 3 of Comparative Example 1.

  The second catalyst layer 3 uses the Rh-supported CeZrNdLaYO instead of Rh-doped CeZrNdLaYO as the catalyst material, and uses only the Rh-doped CeZrNdLaYO binder of the Ce-containing binder particles 13a as the binder particles 13. Different from 1.

  Rh-supported CeZrNdLaYO was prepared by obtaining CeZrNdLaYO powder and then supporting Rh by evaporation to dryness using an aqueous rhodium nitrate solution in the same manner as the preparation method of Rh-doped CeZrNdLaYO powder A.

-Comparative Example 2-
Table 5 shows the configuration of the second catalyst layer 3 of Comparative Example 2.

  The second catalyst layer 3 is different from Example 1 in that only the Rh-doped CeZrNdLaYO binder of Ce-containing binder particles 13 a is used as the binder particles 13.

[Evaluation of exhaust gas purification performance]
The catalysts of Examples 1 and 2 and Comparative Examples 1 and 2 were subjected to bench aging treatment. This is because each catalyst is attached to the engine exhaust system, (1) A / F = 14 exhaust gas flows for 15 seconds → (2) A / F = 17 exhaust gas flows for 5 seconds → (3) A / F = 14.7 The exhaust gas flowing for 40 seconds is repeated for a total of 100 hours, and the engine is operated so that the catalyst inlet gas temperature is 930 ° C.

Thereafter, a core sample having a carrier capacity of about 25 mL (diameter 25.4 mm, length 50 mm) is cut out from each catalyst, and this is attached to a gas flow reactor, and a light-off temperature T50 (° C.) for purifying HC, CO and NOx. The exhaust gas purification rate C400 was measured. T50 (° C.) is the gas temperature at the catalyst inlet when the exhaust gas temperature flowing into the catalyst is gradually increased from room temperature and the purification rate reaches 50%. The exhaust gas purification rate C400 is the purification rate of each component of the gas when the model exhaust gas temperature at the catalyst inlet is 400 ° C. The model exhaust gas was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The space velocity SV is 60000 h ⁻¹ , and the heating rate is 30 ° C./min. The gas composition when A / F = 14.7, A / F = 13.8 and A / F = 15.6 is shown in Table 6, the measurement result of T50 is shown in Table 7, FIG. 5, and the measurement result of C400. Table 7 shows.

  Comparative Example 1 is a case where only conventional Ce-containing binder particles 13a are employed as the binder particles 13, and Comparative Example 2 is an Rh-doped CeZr composite that is an Rh-supported CeZr composite oxide material that is a catalyst material of Comparative Example 1. It is an oxide material.

On the other hand, Example 1 uses the binder particles 13 of Comparative Example 2 as a mixture of Ce-containing binder particles 13a and Ce-free binder particles 13b. In Example 2, as in Example 1, while using the above mixture as the binder particles 13, and a Rh-supporting Z r double if oxides contained as catalyst material Rh-doped Z r double focus oxide It is a thing.

  According to Table 7 and FIG. 5, the light-off temperature (T50) is lower in Examples 1 and 2 than in Comparative Examples 1 and 2 in any of HC, CO, and NOx. It can be seen that the performance is improved.

  The NOx light-off performance is improved by adding the Ce-free binder particles 13b having a gentle oxygen storage / release rate compared to the Ce-containing binder particles 13a, for example, to switch the exhaust gas atmosphere from lean to rich. This is because, in the process of increasing the exhaust gas temperature, Rh can maintain an appropriate oxidation state or reduction state, and can effectively purify NOx that starts to occur immediately after lean / rich switching. It is done.

  In addition, unpurified NOx can also be a poisoning element of the catalyst. As the purification of NOx proceeds as described above, the purification of HC and CO effectively proceeds, and the light-off performance is improved. It is thought that there is.

The present invention includes the Ce-free Rh-doped Z r double coupling oxide as particles material, for example, A / F is switched from lean to rich, in the process of the exhaust gas temperature rises, Rh is moderate oxidation Since the NOx can be effectively purified while maintaining the state or the reduced state, it is extremely useful.

1 Cell wall (exhaust gas passage wall)
2 First catalyst layer (Pd-containing catalyst layer)
3 Second catalyst layer (Rh-containing catalyst layer)
9 Rh-doped CEZ r double if oxide particles (Rh-doped CEZ r double if oxide)
10 Activated alumina particles (activated alumina)
11 Rh
12 ZRL a double focus oxide particles (ZRL a double focus oxide)
13 Binder particles 13a Ce-containing binder particles (additional particle material)
13b Ce-free binder particles (particle material)

Claims (10)

An exhaust gas purifying catalyst having an Rh-containing catalyst layer containing Rh as a catalytic metal and a particulate material,
The particles material, the exhaust gas purifying catalyst, wherein the average particle diameter D50 is less Ce-free Rh-doped Z r double focus oxide 50nm. In claim 1,
The particulate material contains a rare earth metal other than Ce in addition to Rh, and an exhaust gas purifying catalyst. In claim 1 or claim 2,
The particles material, Rh-doped ZrLa Y double focus oxide exhaust gas purifying catalyst, characterized in that. In any one of Claim 1 thru | or 3,
The Rh-containing catalyst layer further includes an additional particulate material,
The exhaust gas purifying catalyst, wherein the additional particulate material is a Ce-containing Rh-doped Zr composite oxide having an average particle diameter D50 of 50 nm or less. In claim 4,
It said additional particles material, Rh-doped CeZrN d double focus oxide exhaust gas purifying catalyst, characterized in that. In any one of Claims 1 thru | or 5,
The Rh-containing catalyst layer further contains a support particle material having an average particle size larger than that of the particle material and / or the additional particle material,
Said support particles material is activated alumina, CEZ r double engagement oxide is at least one selected from the group of ZRL a double coupling oxide,
The exhaust gas purifying catalyst, wherein the particulate material and / or the additional particulate material are mixed so as to be interposed between the particles of the support particulate material. In any one of Claims 1 thru | or 6 ,
The exhaust gas purifying catalyst, wherein the Rh-containing catalyst layer is formed on a surface of a Pd-containing catalyst layer provided on an exhaust gas passage wall. A method for producing an exhaust gas purifying catalyst comprising an Rh-containing catalyst layer containing Rh as a catalytic metal and a particulate material,
The particles material has an average particle diameter D50 is less Ce-free Rh-doped Z r double coupling oxide 50 nm,
To prepare the particles material by an average particle diameter D50 is crushed containing non more Ce 150 nm Rh-doped Z r double coupling oxide,
A slurry is prepared by suspending the particulate material in a solvent,
A method for producing an exhaust gas purifying catalyst, comprising: immersing a base material in the slurry; and drying the base material to support the particulate material on the base material. In claim 8 ,
The Rh-containing catalyst layer further includes a Ce-containing Rh-doped Zr composite oxide having an average particle diameter D50 of 50 nm or less as an additional particle material.
The additional particle material is produced by pulverizing a Ce-containing Rh-doped Zr composite oxide having an average particle diameter D50 of 200 nm or more,
A method for producing an exhaust gas purifying catalyst, wherein the slurry is prepared by suspending the additional particle material in a solvent in addition to the particle material when preparing the slurry. In claim 8 or claim 9,
The particulate material and / or the additional particulate material is subjected to CO reduction heat treatment.
A method for producing an exhaust gas purifying catalyst.

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