JP2017094312A - Complex oxide carrier particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a complex oxide carrier particle which can suppress the emission of oxygen while maintaining the adsorption of NOx.SOLUTION: A complex oxide carrier particle has ceria and yttria, wherein the ratio of the mass of yttria to the total mass of ceria and yttria is 17 mass% or more and 28 mass% or less, and the ratio of the mass of ceria to the mass of the complex oxide carrier particle is 40 mass% or more and 65 mass% or less.SELECTED DRAWING: Figure 5

Description

  The present invention relates to composite oxide support particles.

  In exhaust gas discharged from internal combustion engines for automobiles, for example, gasoline engines or diesel engines, carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), etc. Contains ingredients.

  For this reason, in general, an exhaust gas purification device for decomposing and removing these components is provided in the internal combustion engine, and these components are almost decomposed by the exhaust gas purification catalyst installed in the exhaust gas purification device. ing. As an example of such an exhaust gas purification catalyst, a NOx storage reduction catalyst is known.

The NOx storage reduction catalyst is a catalyst that oxidizes NO in exhaust gas to NO ₂ in a lean atmosphere and stores it in the form of nitrate, and reduces NO ₂ to nitrogen (N ₂ ) in a stoichiometric atmosphere and a rich atmosphere. The catalyst skillfully utilizes changes in exhaust gas components in a lean atmosphere, stoichiometric atmosphere, and rich atmosphere.

In this NOx occlusion reduction catalyst, there is a possibility that the NOx purification rate is lowered under conditions of a high temperature, for example, a high temperature of 400 ° C. or higher. This is considered to be due to the thermal decomposition of the nitrate occurring in such a high temperature region, whereby NO ₂ is discharged outside without being reduced.

  As one of means for solving this problem, a Di-Air (Diesel NOx Aftertreatment by Adsorbed Intermediate Reductants) system is known.

The Di-Air system is a system that is applied to a catalyst, particularly a NOx occlusion reduction catalyst, and alternately creates a lean atmosphere and a rich atmosphere at a predetermined cycle, particularly a short cycle. In this system, NO ₂ active species generated instantaneously in a lean atmosphere and hydrocarbon radical species generated in a rich atmosphere are reacted to generate a reducing intermediate (for example, an organic isocyanate compound) and the like. This is a system that achieves a high NOx purification rate by reacting this reducing intermediate or the like with another NO ₂ active species and reducing it to N ₂ . This Di-Air system can achieve a high NOx purification rate in a high temperature region.

  Therefore, it is expected that the NOx storage reduction catalyst and the Di-Air system using the NOx storage reduction catalyst achieve a high NOx purification rate. However, there is still room for improvement regarding NOx storage reduction.

  The exhaust gas purifying catalyst of Patent Document 1 includes a support base, a NOx storage layer formed on the surface of the support base, and a NOx purification layer formed on the surface of the NOx storage layer, and The NOx storage layer contains a NOx adsorbent. In Patent Document 1, ceria is described as an example of the NOx adsorbent, and further, in a temperature range of 200 ° C. or less where it is difficult to purify NOx, the ceria adsorbs NOx and purifies the NOx in a high temperature region. There is also a description.

JP 2009-226349 A

  In the exhaust gas purifying catalyst of Patent Document 1, ceria is used as the NOx adsorbent. However, ceria has an oxygen storage capacity (OSC), which may release oxygen excessively.

  Accordingly, an object of the present invention is to provide composite oxide carrier particles that can suppress the release of oxygen while maintaining NOx adsorption.

  The present inventors have found that the above problem can be solved by the following means.

<1> Composite oxide carrier particles containing ceria and yttria,
The ratio of the mass of the yttria to the total mass of the ceria and the yttria is 17% by mass or more and 28% by mass or less,
The ratio of the mass of the ceria to the mass of the composite oxide support particles is 40% by mass or more and 65% by mass or less.
Composite oxide carrier particles.

  According to the present invention, it is possible to provide composite oxide carrier particles that can suppress the release of oxygen while maintaining NOx adsorption.

FIG. 1 is a schematic view showing an embodiment of an exhaust gas purification catalyst including the composite oxide support particles of the present invention. FIG. 2 is a diagram showing X-ray diffraction patterns of the powder carriers of Example 1 and Comparative Example 1. FIG. 3 shows Y ₂ O ₃ / (Y ₂ O ₃ + CeO ₂ ) (mass ratio) and O ₂ with respect to the exhaust gas purifying catalysts containing the composite oxide support particles of Examples 1 and 2 and Comparative Example 1, respectively. It is a figure which shows the relationship with the reaction amount (mg / g). FIG. 4 shows the relationship between CeO ₂ (mass%) and O ₂ reaction amount (mg / g) with respect to the exhaust gas purification catalysts including the composite oxide support particles of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. It is a figure which shows a relationship. FIG. 5 shows the NOx purification rate (%) for the exhaust gas purification catalysts containing the composite oxide support particles of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. FIG. 6 shows the relationship between CeO ₂ (% by mass) and NOx purification rate (%) for exhaust gas purification catalysts containing the composite oxide support particles of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. FIG.

  Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist of the present invention.

  In the present invention, the “composite oxide carrier particle” means a material in which at least two kinds of metal oxides are at least partially solid solution. Thus, for example, composite oxide support particles containing ceria and yttria are ceria and yttria at least partially solid solution, in particular ceria and yttria are at least partially oxides of a single crystal structure. Is formed together. That is, for example, “a composite oxide carrier particle containing ceria and yttria” has not only a portion in which ceria and yttria are solid-solved but also a portion in which ceria and yttria are present alone. May be.

《Features of Ceria》
Ceria (also referred to as CeO ₂ ) generally has an OSC (Oxygen Storage Capacity) characteristic that occludes oxygen in a lean atmosphere and releases oxygen in a rich atmosphere. It can be suitably applied.

Although not limited by any principle, it is thought that the reason that ceria develops OSC characteristics is that ceria causes a structural change between a cubic crystal (CeO ₂ type) and a hexagonal crystal (Ce ₂ O ₃ type).

Further, ceria has the characteristic of easily adsorbing NO ₂ in addition to the above OSC characteristics. Therefore, ceria performs oxygen storage and NO ₂ adsorption in a lean atmosphere, and releases oxygen and NO ₂ in a rich atmosphere. The reason why ceria easily adsorbs NO ₂ is thought to be because ceria is more basic than alumina (also referred to as Al ₂ O ₃ ).

Adsorption effect of NO ₂ in the ceria, because it can hold more NOx in a lean atmosphere, an advantageous effect in the NOx storage reduction catalyst. On the other hand, the OSC characteristic of ceria is a disadvantageous effect in the NOx storage reduction catalyst because oxygen released in a rich atmosphere consumes a reducing agent.

The present inventors have studied the means for maintaining the NO ₂ adsorption ability while suppressing the OSC characteristics of the above-mentioned ceria, and have found the following composite oxide support particles.

<Composite oxide carrier particles>
In the composite oxide carrier particles of the present invention containing ceria and yttria, the ratio of the mass of yttria to the total mass of ceria and yttria is 17% by mass to 28% by mass, and the mass of the complex oxide carrier particles The ratio of the mass of the ceria with respect to is 40 mass% or more and 65 mass% or less.

<Description of Composite Oxide Support Particles of the Present Invention>
As described above, the reason why ceria exhibits OSC characteristics is considered to be a structural change between cubic and hexagonal crystals. In this regard, the composite oxide support particles containing ceria and yttria are not limited by any principle, but yttria suppresses the structural change of ceria, which is thought to suppress the OSC characteristics of ceria. It is done.

  Moreover, when the ratio of the mass of yttria to the total mass of ceria and yttria is too small in the composite oxide support particles, the suppression of structural change of ceria by yttria may be insufficient. Therefore, the ratio of the mass of yttria to the total mass of ceria and yttria in the composite oxide support particles may be 17 mass% or more, 18 mass% or more, 19 mass% or more, or 20 mass% or more.

Furthermore, when the ratio of the mass of yttria to the total mass of ceria and yttria in the composite oxide support particles is too large, the adsorption effect of ceria NO ₂ may be suppressed. Therefore, the ratio of the mass of yttria to the total mass of ceria and yttria in the composite oxide support particles may be 28 mass% or less, 27 mass% or less, 26 mass% or less, or 25 mass% or less.

When the ratio of the mass of ceria to the mass of the composite oxide support particles is sufficiently large, the adsorption effect of ceria NO ₂ can be improved. Therefore, the ratio of the mass of ceria to the mass of the composite oxide support particles may be 40% by mass or more, or 45% by mass or more.

  Furthermore, when the ratio of the mass of ceria to the mass of the composite oxide support particles is sufficiently small, the ceria particles can be prevented from sintering with other ceria particles and other metal oxides. . Therefore, the ratio of the mass of ceria to the mass of the composite oxide support particles may be 65% by mass or less, 60% by mass or less, or 55% by mass or less.

Examples of components other than ceria and yttria in the composite oxide support particles include silica (SiO ₂ ), magnesium oxide (MgO), zirconia (ZrO ₂ ), ceria (CeO ₂ ), and alumina (Al ₂ O ₃ ). , Titania (TiO ₂ ), and solid solutions thereof. Among these, it is preferable that alumina is contained from the viewpoint of the diffusion barrier and the specific surface area.

  The composite oxide carrier particles of the present invention having the above-described configuration can suppress the release of oxygen while maintaining NOx adsorption.

  With reference to FIG. 1, the composite oxide carrier particles of the present invention will be described. FIG. 1 is a schematic view showing an embodiment of an exhaust gas purification catalyst including the composite oxide support particles of the present invention. In FIG. 1, exhaust gas purification in which a base material 110, a NOx storage layer 120 formed on the surface of the base material 110, and a NOx purification layer 130 formed on the surface of the NOx storage layer 120 are laminated in this order. A catalyst 100 is shown. In this exhaust gas purification catalyst 100, NOx and the like are adsorbed in the NOx purification layer 130 and NOx is occluded in the NOx storage layer 120. The NOx purification layer 130 includes composite oxide support particles containing ceria and yttria, and yttria suppresses the OSC characteristics of ceria.

<Application example of composite oxide support particles>
The composite oxide support particles of the present invention are not particularly limited, but may be applied to, for example, a NOx storage reduction catalyst or a NOx storage reduction catalyst used in a Di-Air system.

(NOx storage reduction catalyst)
The NOx occlusion reduction catalyst may be composed of, for example, a catalyst metal, a carrier, a NOx occlusion material, and a base material.

  The catalyst metal is not particularly limited, and at least one base metal, oxide thereof, and composite oxide thereof; at least one noble metal, oxide thereof, and composite oxide thereof; and combinations thereof Can be mentioned.

  Examples of the carrier include silica, magnesium oxide, zirconia, ceria, alumina, titania, and solid solutions thereof, and combinations thereof in addition to the composite oxide carrier particles of the present invention.

  The NOx storage material is not particularly limited, but may be a basic material. Examples of NOx storage materials include alkali metals and salts thereof, such as potassium (K) and potassium acetate; alkaline earth metals and salts thereof, such as barium (Ba) and barium acetate; and combinations thereof Can do.

  The substrate is not particularly limited, and may be, for example, a cordierite honeycomb or a cordierite monolith.

(Catalyst used in the Di-Air system)
The catalyst used in the Di-Air system may be, for example, the above NOx storage reduction catalyst.

  Regarding the composite oxide carrier particles of the present invention, the following method for producing the composite oxide carrier particles can be referred to.

<< Production Method of Composite Oxide Support Particles >>
Examples of methods for producing composite oxide support particles containing ceria and yttria include citric acid complex method, complex polymerization method, impregnation method, coprecipitation method, uniform precipitation method, reverse homogeneous precipitation method, micelle method, And the reverse micelle method. A coprecipitation method will be described as one embodiment of a method for producing such composite oxide carrier particles.

<Coprecipitation method>
The method for producing composite oxide support particles containing ceria and yttria includes the following steps:
Preparing a mixed solution containing a cerium salt, a yttrium salt, and a solvent;
Adding a neutralizing agent to the mixed solution to precipitate a precursor of the composite oxide carrier particles, thereby preparing a precursor slurry; and drying and / or calcining the precursor slurry and thereby oxidizing the composite A step of producing the product carrier particles.

(Mixed solution preparation process)
Examples of cerium salts include inorganic salts such as sulfates, nitrates, chlorides, and phosphates; organic acid salts such as acetates and oxalates; and combinations thereof. .

  For examples of yttrium salts, reference may be made to the description of the examples of cerium salts above.

  The molar ratio of cerium and yttrium in the mixed solution is not particularly limited as long as the ratio of the mass of yttria to the total mass of ceria and yttria in the composite oxide support particles of the present invention can be achieved. In this case, these molar ratios may be determined in consideration of the scale of reduction of cerium and yttrium, for example, the redox potential and the easiness of solid solution of ceria and yttria.

  Although it does not specifically limit as an example of a solvent, Alcohol, such as methanol, ethanol, isopropanol, and water can be mentioned.

  The mixed solution may contain a dispersing agent such as sodium pyrrolidonecarboxylate (PAA-Na) or polyvinylpyrrolidone (PVP).

(Precursor slurry preparation process)
Examples of the neutralizing agent include inorganic basic compounds such as ammonia (NH ₃ ), sodium carbonate (Na ₂ CO ₃ ), sodium hydroxide (NaOH), potassium hydroxide (KOH) and the like. Moreover, as a neutralizing agent, the organic basic compound of a pyridine and a (poly) ethylenediamine compound can be mentioned, for example, A (poly) ethylenediamine compound can be mentioned suitably.

As examples of suitable neutralizing agents, (poly) ethylenediamine compounds include those having 1 to 10 ethylene units, particularly those having 1 to 6 ethylene units. Specifically, preferred polyethylene diamine compounds include ethylene diamine (EDA: H ₂ NCH ₂ CH ₂ NH ₂ ), diethylene triamine (DETA: H ₂ NCH ₂ CH ₂ NHCH ₂ CH ₂ NH ₂ ), triethylene tetramine (TETA: _{H 2 NCH 2 CH 2 NHCH 2} CH 2 NHCH 2 CH 2 NH 2), tetraethylene pentamine _{[TEPA: H 2 N (CH} 2 CH 2 NH) 3 CH 2 CH 2 NH 2)], pentaethylene hexamine [PEHA _{: H 2 N (CH 2 CH} 2 NH) 4 H 2 CH 2 NH 2], mention may be made in particular of ethylenediamine (DDA).

  In the step of adding a neutralizer and precipitating the precursor of the composite oxide, it is preferable to adjust the pH of the aqueous solution to a range of 7-9.

(Composite oxide carrier particle production process)
Drying and firing can be performed under any conditions that can obtain composite oxide support particles. For example, drying can be performed in air at a temperature of 50 ° C. or higher and 200 ° C. or lower, and baking is performed at a temperature of 300 ° C. or higher and 600 ° C. or higher, less than 800 ° C., and 700 ° C. or lower. It can be performed for 1 to 10 hours, or 2 to 8 hours.

(Other processes)
In addition, the method for producing composite oxide support particles optionally includes a catalyst metal supporting step, a substrate supporting step, and a NOx storage material supporting step.

  The order of these steps is not particularly limited. An example of a combination of these steps is to impregnate and support a solution containing the composite oxide support particles by adding a salt of the catalyst metal; a solution containing the composite oxide support particles on which the catalyst metal is supported Or, a base material, for example, cordierite honeycomb, is immersed in the slurry to perform a wash coat; an impregnation support is performed by immersing the cordierite honeycomb in a solution containing NOx storage material, for example, barium. Can do. These steps may optionally include an operation of drying and / or firing and an operation of adding a binder such as a binder.

  Note that the reaction vessel for carrying out these methods is not particularly limited, and a batch-type reaction apparatus or a continuous-type reaction apparatus can be used.

  Furthermore, the mass ratio of ceria, yttria, and alumina in the composite oxide support particles can be measured by inductively coupled plasma (ICP) emission spectroscopy.

<Others>
Regarding the method for producing the composite oxide support particles, the description of the composite oxide support particles of the present invention can be referred to.

  The present invention will be described in more detail with reference to the following examples, but it goes without saying that the scope of the present invention is not limited by these examples.

Example 1
<Process for preparing mixed solution>
A mixed solution containing cerium nitrate, yttrium nitrate, aluminum nitrate, and pure water as a solvent was prepared. For the mixed solution, the molar ratio of cerium, yttrium, and aluminum was adjusted to achieve a mass ratio of ceria, yttria, and alumina of the target composite oxide support particles, that is, 50:10:40.

<Precursor slurry preparation process>
An aqueous ammonia solution as a neutralizing agent was added to the mixed solution to precipitate a precursor of the composite oxide carrier particles, thereby preparing a precursor slurry.

<Composite oxide carrier particle production process>
The precursor slurry was dried and fired, thereby producing composite oxide support particles containing ceria, yttria, and alumina. The mass ratio of ceria, yttria, and alumina in the composite oxide support particles was 50:10:40. Regarding the calculation of these mass ratios, the composite oxide support particles were subjected to quantitative analysis by inductively coupled plasma (ICP) analysis, and the mass ratios were calculated thereby.

<< Example 2 and Comparative Examples 1-3 >>
In the step of preparing the mixed solution of Example 1, the molar ratio of cerium, yttrium, and aluminum is the mass ratio of ceria, yttria, and alumina of the composite oxide support particles of the targets of Example 2 and Comparative Examples 1-3. The composite oxide support particles of Example 2 and Comparative Examples 1 to 3 were produced in the same manner as the composite oxide support particles of Example 1, except that the adjustment was performed to achieve the above. The mass ratio of ceria, yttria, and alumina in the target composite oxide support particles in each example is shown below:
Example 2 50:20:30;
Comparative Example 1 50: 0: 50;
Comparative Example 2 35: 7: 58;
Comparative Example 3 70:10:20.

  Table 1 below shows the ratio of yttria mass to ceria (% by mass), yttria (% by mass), and alumina (% by mass) and the total mass of ceria and yttria for the composite oxide support particles of each example. ing.

<Evaluation>
<Evaluation of X-ray diffraction analysis>
X-ray diffraction analysis was performed on the composite oxide carrier particles of Example 1 and Comparative Example 1. The results are shown in FIG.

In FIG. 2, the approximately 28.5 ° line represents the CeO ₂ peak, the approximately 28.7 ° line represents the Ce ₂ Y ₂ O ₇ peak, and the approximately 29.0 ° line represents the Y ₂ O line. ₃ peaks are shown. 2 that the X-ray diffraction peak of the composite oxide support particle of Comparative Example 1 corresponds to the CeO ₂ peak. On the other hand, FIG. 2 shows that the peak of the X-ray diffraction of the composite oxide support particle of Example 1 appears in the vicinity of the peak of Ce ₂ Y ₂ O ₇ .

  Further, FIG. 2 shows that the X-ray diffraction peak of the composite oxide particles of Example 1 is broader than that of Comparative Example 1. This indicates that yttria is at least partially dissolved in ceria.

<Evaluation of oxygen reaction amount>
Catalyst metal-supported composite oxide support particles in which Pt and Pd as catalyst metals were supported on the composite oxide support particles of Examples 1 and 2 and Comparative Examples 1 to 3 (the following catalyst metal support step C-1 and Table 1) 2), the amount of oxygen reaction was measured. In addition, the exhaust gas purification catalyst obtained by the following processes A-1, A-2, B, C-1, and C-2 is used in the evaluation of the exhaust gas purification ability in the following Di-Air system.

(NOx storage layer: catalyst metal supporting step A-1)
The solution containing ceria was impregnated and supported by adding a Pt salt as a catalyst metal, and further dried and calcined. Further, an Rh salt as a catalyst metal was added to a solution containing zirconia to carry out impregnation and further dried and fired. Further, a Pd salt as a catalyst metal was added to a solution containing zirconia to carry out impregnation, and this was dried and fired.

(NOx occlusion layer: base material carrying step A-2)
The above Pt-carrying ceria, Rh-carrying zirconia, Pd-carrying zirconia, and a binder are mixed to prepare a slurry. Baked.

(NOx storage layer: NOx storage material carrying process B)
The cordierite monolith passed through the substrate supporting step A was immersed in a solution containing barium acetate as a NOx storage material to carry out impregnation, and this was dried and fired.

(NOx purification layer: catalyst metal supporting step C-1)
The solution containing the composite oxide support particles was impregnated and supported by adding a Pt salt and a Pd salt as catalyst metals, and then dried and calcined.

(NOx purification layer: base material carrying step C-2)
A slurry is prepared by mixing the above Pt and Pd-supported composite oxide carrier particles and a binder, and in this slurry, cordierite monolith that has undergone the NOx storage material supporting step B is dipped to perform a wash coat, This was dried and fired. Thus, an exhaust gas purification catalyst was obtained.

  In this exhaust gas purification catalyst, cordierite monolith as a base material, NOx occlusion layer formed on the surface of this cordierite monolith, and NOx purification layer formed on the surface of this NOx occlusion layer, They are stacked in this order. Table 2 below shows the structure of the base material, the structure of the NOx occlusion layer, and the structure of the NOx purification layer.

  In Table 2, “composite oxide support particles” correspond to the composite oxide support particles of each of the above examples. In Table 2, for example, the description of “ceria (Pt)” means Pt-supported ceria, and the corresponding description of “170 g (1 g)” means that the amount of ceria is 170 g, and this ceria This means that the amount of Pt supported on 1 g is 1 g.

(Measurement of oxygen reaction amount)
The catalyst metal-supporting composite oxide carrier particles produced in the catalyst metal-supporting step C-1 were formed into 2 mm square pellets at a press pressure of 1 ton / cm ² . This pellet was baked in an electric furnace at 700 ° C. for 33 hours, thereby performing an endurance test.

  After the endurance test, the catalyst metal-supported composite oxide support particles were placed in a flow-through tubular reactor, and a model gas was passed through the reactor to measure the oxygen reaction amount.

The model gas was composed of lean gas and rich gas. The temperature of the model gas was 430 ° C., the flow rate of the gas was 15 L / min, and the lean gas and the rich gas were switched every 2 minutes under these conditions. Thereby, the amount of O ₂ reacted with CO was calculated from the generated CO ₂ . The composition of lean gas and rich gas is shown in Table 3 below, and the results are shown in FIGS.

FIG. 3 shows Y ₂ O ₃ / (Y ₂ O ₃ + CeO ₂ ) (mass ratio) and O ₂ with respect to the exhaust gas purifying catalysts containing the composite oxide support particles of Examples 1 and 2 and Comparative Example 1, respectively. It is a figure which shows the relationship with the reaction amount (mg / g).

3 that the O ₂ reaction amount of the catalyst metal-supported composite oxide support particles of Examples 1 and 2 is lower than that of Comparative Example 1 with respect to the O ₂ reaction amount. That is, the content of ceria in the composite oxide support particles is the same in each composite oxide support particle (for example, the content of ceria in the composite oxide support particles of Examples 1 and 2 and Comparative Example 1 is It is understood that the higher the yttria content, the lower the O ₂ reaction amount. This is presumably because yttria suppressed the structural change of ceria, thereby suppressing the expression of OSC characteristics of ceria.

FIG. 4 shows the relationship between ceria (mass%) and O ₂ reaction amount (mg / g) with respect to the exhaust gas purification catalysts containing the composite oxide support particles of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. FIG.

FIG. 4 shows that the catalyst metal-supported composite oxide support particles of Comparative Example 2, Examples 1 and 2 and Comparative Example 3 are aligned on a straight line (dotted line). This is because the ceria and yttria mass ratios in these examples are approximately the same at 5: 1, 5: 1, 5: 2, and 7: 1, respectively, thereby having a predetermined mass ratio. This is probably because an approximate proportional relationship exists with respect to the amount of ceria containing yttria and the amount of O ₂ reaction.

From the straight line (dotted line) in FIG. 4, the O ₂ reaction amount of the catalyst metal-supported composite oxide carrier particles of Comparative Example 1 containing 50% by mass of ceria is about 50 (mg / g). When attention is paid to this, the ratio of ceria is increased while suppressing the O ₂ reaction amount to 50 (mg / g) or less under the condition that at least ceria is in the range between 50 mass% and 65 mass%. It is understood that NOx adsorption can be promoted.

<Evaluation of exhaust gas purifying ability in Di-Air system>
The composite oxide carrier particles of Examples 1 and 2 and Comparative Examples 1 to 3 were prepared by the method for preparing an exhaust gas purification catalyst composed of the steps A-1, A-2, B, C-1 and C-2. Exhaust gas purification catalysts (1.3 L) containing each of the above were prepared, and the exhaust gas purification performance was evaluated by a Di-Air system to which these exhaust gas purification catalysts were applied.

Specifically, the conditions for such evaluation are shown in the following (1) to (3), and the results are shown in the following Table 4 and FIGS. 5 and 6:
(1) The exhaust gas purification catalyst containing the composite oxide support particles of each example is baked in an electric furnace at 700 ° C. for 33 hours, thereby carrying out a durability test.
(2) A test apparatus having a configuration including a diesel engine, a fuel supply valve for supplying fuel, and an exhaust gas purification catalyst that has undergone the above-described durability test is prepared.
(3) With respect to such a test apparatus, the rotational speed of the diesel engine is set to 2000 rpm, and the torque thereof is set to 40 Nm; the addition of fuel from the fuel supply valve, the fuel consumption deterioration rate 2%, and the predetermined lean time and Perform in a rich time cycle.

  FIG. 5 shows the NOx purification rate (%) for the exhaust gas purification catalysts containing the composite oxide support particles of Examples 1 and 2 and Comparative Examples 1 to 3, respectively.

From Table 5 and FIG. 5, it can be seen that the NOx purification rates of the exhaust gas purification catalysts of Examples 1 and 2 are higher than the NOx purification rates of the exhaust gas purification catalysts of Comparative Examples 1 to 3. This is probably because yttria suppressed the structural change of ceria, thereby suppressing the expression of OSC characteristics of ceria, while maintaining the NO ₂ adsorption capacity of ceria.

  FIG. 6 is a diagram showing the relationship between ceria (mass%) and NOx purification rate (%) for exhaust gas purification catalysts containing the composite oxide support particles of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. It is.

  The curve (dotted line) in FIG. 6 is substantially the same in the ratio of the mass of ceria to the mass of yttria 5: 1, 5: 1, 5: 2, and 7: 1, as described in FIG. These are approximate curves for Comparative Example 2, Examples 1 and 2, and Comparative Example 3, respectively.

  From the curve of FIG. 6, when focusing on the NOx purification rate of the exhaust gas purification catalyst of Comparative Example 1 containing 50% by mass of ceria being 32%, at least ceria is 40% by mass and 65% by mass. It is understood that the NOx purification rate can be improved to 32% or more under the condition in the range between%.

  Although the preferred embodiment of the present invention has been described in detail, it is possible to change the manufacturer, grade, quality, etc. of the apparatus, equipment, chemicals, etc. used in the present invention without departing from the scope of the claims. Those skilled in the art understand that.

DESCRIPTION OF SYMBOLS 100 Exhaust gas purification catalyst 110 Base material 120 NOx occlusion layer 130 NOx purification layer

Claims (1)

A composite oxide carrier particle containing ceria and yttria,
The ratio of the mass of the yttria to the total mass of the ceria and the yttria is 17% by mass or more and 28% by mass or less,
The ratio of the mass of the ceria to the mass of the composite oxide support particles is 40% by mass or more and 65% by mass or less.
Composite oxide carrier particles.

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