JP2022150376A - oxygen storage material - Google Patents

Abstract

The present invention provides an oxygen storage material that can reduce pressure loss and is applicable to three-way catalysts (TWCs) suitable for use as filter substrates in exhaust gas purification filters (GPFs). The oxygen storage material contains core-shell nanoparticles that are made of a core containing zirconia and a shell containing ceria. [Selected Figure] None

Description

The present invention relates to oxygen storage materials.

Conventionally, among gasoline engines installed in automobiles, etc., direct-injection gasoline engines with excellent combustion efficiency emit a large amount of particulate matter such as soot PM (particulate matter), so exhaust that traps particulate matter in the exhaust passage. There is a technique of providing a purification filter (Gasoline Particulate Filter) (GPF).

In addition, a three-way catalyst (TWC) that purifies CO, HC and NOx contained in exhaust gas is provided in an exhaust passage of a gasoline engine while being carried on a honeycomb support. In recent years, in particular, a plurality of three-way catalysts (TWC) are often arranged in series in an exhaust passage in order to meet the required catalytic purification performance. If an attempt is made to carry a three-way catalyst (TWC) on the filter base material of an exhaust purification filter (GPF), it becomes difficult to achieve both pressure loss and exhaust purification performance.

Therefore, in addition to these three-way catalysts (TWC), newly providing an exhaust purification filter (GPF) in the exhaust passage is not preferable from the viewpoint of pressure loss and cost. Therefore, a technology has been proposed in which a three-way catalyst (TWC) is supported on an exhaust purification filter (GPF) to provide the exhaust purification filter (GPF) with a three-way purification function in addition to the particulate matter trapping performance (for example, See Patent Document 1).

From another point of view, development of a three-way catalyst (TWC) suitable for a filter base material of an exhaust purification filter (GPF) is desired. For example, in the technique described in Patent Literature 2, when a three-way catalyst (TWC) containing Rh as a catalyst metal is used, the NOx purification performance may be greatly reduced. For example, a three-way catalyst (TWC) having a two-layer structure of an Rh layer and a Pd layer is known as a three-way catalyst (TWC) having an excellent three-way purification function. Carrying a two-layer three-way catalyst (TWC) causes a large pressure loss. Therefore, it is conceivable that the filter substrate supports a three-way catalyst (TWC) having a single-layer structure obtained by mixing Rh and Pd. However, in this case, since there is no effective support material for both, the deterioration of Pd and the oxidation deterioration of Rh occur in different conditions. There is a problem that the NOx purification performance cannot be achieved.

Although Patent Document 3 describes that the pressure loss can be solved by adjusting the wall thickness of the honeycomb base material, a three-way catalyst (TWC) suitable for the filter base material of the exhaust purification filter (GPF) is used. If it can be provided, the manufacturing process can be simplified.

On the other hand, as an exhaust gas purifying catalyst, Patent Document 4 discloses a particulate oxidation catalyst using at least one of cerium oxide and zirconium oxide as a carrier. From US Pat. Nos. 5,300,000 and 5,000,000, it is generally stated that cerium-zirconium composite oxides as oxygen storage materials preferably have a high cerium content, such as about 50 mol %.

JP 2017-082745 A WO2011/015615 WO2017/061458 JP-A-10-151348 JP-A-2000-169148 JP-A-10-212122

The present invention is intended to solve the above problems, and can reduce pressure loss and can be applied to a three-way catalyst (TWC) suitable for a filter base material of an exhaust purification filter (GPF). The object is to provide an oxygen storage material.

As a result of diligent efforts, the present inventors have found that core-shell nanoparticles composed of a core containing zirconia and a shell containing ceria can reduce pressure loss and are suitable for filter substrates of exhaust gas purification filters (GPF). It was found that it is an oxygen storage material that can be applied to a three-way catalyst (TWC). That is, the present invention includes the following configurations.

Section 1. An oxygen storage material containing core-shell nanoparticles consisting of a core containing zirconia and a shell containing ceria.

Section 2. Composition formula:
(CeO ₂ ) _x (ZrO ₂ ) _1−x
[In the formula, x represents 0.05 to 0.50. ]
Item 2. The oxygen storage material according to item 1, represented by

Item 3. Item 3. The oxygen storage material according to Item 1 or 2, wherein x is 0.10 to 0.30.

Section 4. 4. The oxygen storage material according to any one of Items 1 to 3, which has a specific surface area of 5 to 40 m ² /g.

Item 5. An exhaust gas purification catalyst containing the oxygen storage material according to any one of Items 1 to 4.

Item 6. Item 6. An exhaust gas purification catalyst according to Item 5, wherein at least one noble metal selected from the group consisting of platinum, palladium and rhodium is supported on the oxygen storage material.

Item 7. Item 7. The exhaust gas purification catalyst according to item 6, wherein the supported amount of the noble metal is 0.00001 to 2 parts by mass with respect to 100 parts by mass of the oxygen storage material.

Item 8. A particulate matter purification catalyst containing the oxygen storage material according to any one of Items 1 to 4.

Item 9. Item 9. The particulate matter purification catalyst according to Item 8, wherein silver is supported on the oxygen storage material.

Item 10. Item 10. The particulate matter purification catalyst according to Item 9, wherein the supported amount of silver is 0.2 to 5.0 parts by mass with respect to 100 parts by mass of the oxygen storage material.

Item 11. Item 11. The particulate matter purification catalyst according to Item 9 or 10, wherein the supported amount of silver is 0.5 to 1.0 parts by mass with respect to 100 parts by mass of the oxygen storage material.

Item 12. The oxygen storage material according to any one of Items 1 to 4, the exhaust gas purification catalyst according to any one of Items 5 to 7, or the particulate matter purification catalyst according to any one of Items 8 to 11. an exhaust purification filter.

According to the present invention, it is possible to provide an oxygen storage material that can reduce pressure loss and is applicable to a three-way catalyst (TWC) that is suitable for a filter base material of an exhaust gas purification filter (GPF).

As used herein, "contain" is a concept that includes both "comprise," "consist essentially of," and "consist of."

Further, in this specification, when a numerical range is indicated by "A to B", it means from A to B.

The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be made without departing from the scope of the invention.

1. Oxygen Storage Material The oxygen storage material of the present invention contains core-shell nanoparticles consisting of a core containing zirconia and a shell containing ceria. As a result, the pressure loss can be reduced, and it can be applied to a three-way catalyst (TWC) suitable for the filter base material of an exhaust gas purification filter (GPF).

The actual method of controlling the purification performance of an autocatalyst varies somewhat with each type of engine design, but is characterized by limiting the air-fuel ratio (A/F), which varies with engine operating conditions, within a constant narrow range. An oxygen sensor maintains the A/F, creating optimal combustion conditions and reaction conditions for purifying exhaust gas. However, a trace amount of harmful gas contained in the exhaust gas is actually purified by being adsorbed on the catalytic precious metal or co-catalyst oxide on the carrier and causing a catalytic reaction thereon. In the course of these series of reaction processes, the reaction conditions, especially the gas composition, must be maintained in a fairly microscopic space. It is not possible to sufficiently exhibit the performance of the purification catalyst only with this. Therefore, the catalyst layer itself is required to have a function of controlling the A/F value in a microscopic space. Such a function is achieved by a function called oxygen storage capacity (OSC) of autocatalysts, and the oxygen storage material of the present invention has such an oxygen storage capacity.

In particular, the oxygen storage material of the present invention has a particulate matter combustion activity at a low temperature by being composed of a core containing zirconia and a shell containing ceria, and is excellent in oxygen storage. have the ability In addition, even when exposed to high-temperature exhaust gas, the solid-solution reaction between zirconia and ceria is suppressed. A ring can be suppressed.

In core-shell nanoparticles, the core contains zirconia. Zirconia has high heat resistance and can improve the heat resistance of core-shell nanoparticles. In the present invention, the content of zirconia in the core is not particularly limited, but from the viewpoint of heat resistance, oxygen storage capacity, pressure loss, etc., it is preferably 50 to 100% by mass, with the total amount of the core being 100% by mass. , more preferably 70 to 100% by mass, more preferably 90 to 100% by mass.

Although the crystal structure of zirconia is not particularly limited, it is preferably monoclinic or tetragonal from the viewpoints of heat resistance, oxygen storage capacity, pressure loss, and the like.

In the core-shell nanoparticles, the core contains, in addition to zirconia, other metal oxides to an extent that does not impair the effects of the present invention, for example, 0 to 50% by mass, particularly 0%, based on the total amount of the core being 100% by mass. ~30% by mass, and even 0~10% by mass are not excluded. Such other metal oxides include, for example, alumina, silica, titania, and the like.

In core-shell nanoparticles, the shell contains ceria. Ceria has a strong affinity with noble metals and can suppress sintering of the noble metals carried thereon at high temperatures. In the present invention, the content of ceria in the shell is not particularly limited, but from the viewpoint of heat resistance, oxygen storage capacity, pressure loss, etc., it is preferably 50 to 100% by mass when the total amount of the shell is 100% by mass. , more preferably 70 to 100% by mass, more preferably 90 to 100% by mass.

The crystal structure of ceria is not particularly limited, but a cubic crystal is preferable from the viewpoints of heat resistance, oxygen storage capacity, pressure loss, and the like.

In the core-shell nanoparticles, the shell contains other metal oxides in addition to ceria to an extent that does not impair the effects of the present invention, for example, 0 to 50% by mass, particularly 0%, where the total amount of the shell is 100% by mass. ~30% by mass, and even 0~10% by mass are not excluded. Examples of such other metal oxides include lanthanum oxide, yttria, neodymium oxide, and praseodymium oxide.

The core-shell nanoparticles preferably include a shell containing ceria in an amount sufficient to uniformly coat the surface of the core containing zirconia, preferably at the nano level. Although not particularly limited, core-shell nanoparticles generally contain 0.50 to 0.95 mol (0.70 to 0.90 mol), preferably 0.05 to 0.50 mol (0.10 to 0.30 mol) of a shell containing ceria.

Therefore, when the core is composed of zirconia and the shell is composed of ceria, the core-shell nanoparticles have the composition formula:
(CeO ₂ ) _x (ZrO ₂ ) _1−x
[In the formula, x represents 0.05 to 0.50 (especially 0.10 to 0.30). ]
It is preferable to have a composition represented by

The oxygen storage material of the present invention as described above preferably has a specific surface area of 5 to 40 m ² /g, more preferably 10 to 35 m ² /g, from the viewpoint of heat resistance, oxygen storage capacity, pressure loss and the like. The specific surface area of the oxygen storage material of the present invention is measured by a nitrogen adsorption method.

Core-shell nanoparticles can be produced by any method known to those skilled in the art.

For example, core-shell nanoparticles can be produced by conventional so-called impregnation, evaporation, drying, etc., that is, by mixing a powder containing zirconia and a solution containing a metal salt as a source of ceria, followed by drying and firing. It can be manufactured by Alternatively, a powder containing zirconia is added to a solution containing a metal salt as a source of ceria, and a basic substance or the like is further added to this to convert the metal salt into a hydroxide or the like around the core containing zirconia. and then drying and firing at a temperature and time sufficient to oxidize the hydroxide or the like to form a ceria-containing shell. Furthermore, a solution obtained by dissolving a cerium salt such as (NH ₄ ) ₂ Ce(NO ₃ ) ₆ in water and dissolving a surfactant such as a carboxylate or an organic protective agent is mixed, and this mixed solution is It can also be produced by adding ZrO ₂ powder to and mixing the liquid, neutralizing it with ammonia water or the like, heat-treating it, and then drying and calcining it.

2. Exhaust gas purifying catalyst The exhaust gas purifying catalyst of the present invention contains the above oxygen storage material of the present invention.

In the exhaust gas purifying catalyst of the present invention, at least one noble metal selected from the group consisting of platinum, palladium and rhodium can be further supported on the oxygen storage material of the present invention.

As a result, not only has particulate matter (particulate matter) combustion activity at low temperatures, but also the three-way catalyst activity for purifying CO, HC and NOx contained in the exhaust can be dramatically improved. .

For this reason, the exhaust gas purifying catalyst of the present invention is carried on the filter base material of an exhaust gas purifying filter (GPF) to trap particulate matter such as soot-like PM (particulate matter) while reducing CO contained in the exhaust gas. HC and NOx can also be purified.

When the exhaust gas purifying catalyst of the present invention is supported on the filter base material of an exhaust gas purifying filter (GPF), it captures particulate matter such as soot-like PM (particulate matter) while removing CO and HC contained in the exhaust gas. And NOx can also be purified, so the thickness of the catalyst layer of the exhaust gas purification catalyst of the present invention can be reduced. Specifically, the thickness of the catalyst layer can be 0.001 to 10 μm, particularly 0.01 to 1 μm.

When at least one noble metal selected from the group consisting of platinum, palladium and rhodium is further supported on the oxygen storage material of the present invention described above, the noble metal can be supported by any method known to those skilled in the art. can.

From the viewpoint of heat resistance, oxygen storage capacity, particulate matter combustion activity, three-way catalytic activity, pressure loss, etc., these noble metals are used in an amount of 0.00001 to 2 parts by mass per 100 parts by mass of the oxygen storage material of the present invention. is preferred, 0.0001 to 1 part by mass is more preferred, and 0.001 to 0.5 part by mass is even more preferred.

For example, these noble metals can be supported by using a compound containing the above noble metal as a cation as a noble metal source, immersing the oxygen storage material of the present invention in a solution of this compound at a predetermined concentration, and then drying and calcining it, or Using the above noble metal complex as the noble metal source, the oxygen storage material of the present invention is immersed in a solution of this complex at a predetermined concentration, and then dried and fired to support the noble metal.

The baking and drying of the oxygen storage material of the present invention immersed in the solution containing these noble metal compounds or complexes can be carried out at a temperature and time sufficient to support the noble metal on the oxygen storage material of the present invention. . For example, drying can be carried out at a temperature of 70-250° C. for 6-48 hours and calcination can be carried out at a temperature of 500-800° C. for 1-5 hours.

3. Particulate Matter Purification Catalyst The particulate matter purification catalyst of the present invention contains the oxygen storage material of the present invention described above.

In the particulate matter purification catalyst of the present invention, silver can be further supported on the oxygen storage material of the present invention described above.

Thereby, it is possible to have particulate matter (particulate matter) combustion activity at a lower temperature.

For this reason, the particulate matter purification catalyst of the present invention can be supported on the filter base material of an exhaust gas purification filter (GPF) to trap particulate matter such as soot-like PM (particulate matter).

When the particulate matter purification catalyst of the present invention is supported on the filter base material of an exhaust purification filter (GPF), the combustion activity of particulate matter such as soot-like PM (particulate matter) is further improved. The catalyst layer thickness of the particulate matter purification catalyst of the present invention can be reduced. Specifically, the thickness of the catalyst layer can be 0.001 to 10 μm, particularly 0.01 to 1 μm.

When silver is further supported on the oxygen storage material of the present invention described above, silver can be supported by any method known to those skilled in the art.

Silver is preferably 0.2 to 5.0 parts by mass with respect to 100 parts by mass of the oxygen storage material of the present invention, from the viewpoint of heat resistance, oxygen storage capacity, particulate matter combustion activity, pressure loss, etc. 3 to 3.0 parts by mass is more preferable, and 0.5 to 1.0 parts by mass is even more preferable.

For example, to support silver, a compound containing silver as a cation is used as the silver source, the oxygen storage material of the present invention is immersed in a solution of this compound at a predetermined concentration, and then dried and fired, or the silver source is A silver complex is used as the oxygen storage material, and the oxygen storage material of the present invention is immersed in a solution of this complex at a predetermined concentration, followed by drying, firing, and the like, whereby silver can be supported.

Calcination and drying of the oxygen storage material of the present invention immersed in a solution containing a silver compound or complex can be performed at a temperature and time sufficient to load silver onto the oxygen storage material of the present invention. For example, drying can be carried out at a temperature of 70-250° C. for 6-48 hours and calcination can be carried out at a temperature of 500-800° C. for 1-5 hours.

Examples are given below to further describe the present invention, but the present invention is not limited to the examples.

Example 1: Synthesis of zirconia-ceria core-shell particles (Ce:Zr=5:95)
A sample consisting of zirconia-ceria core-shell type particles with Ce:Zr=5:95 (molar ratio) was prepared as follows.

A solution of (NH ₄ ) ₂ Ce(NO ₃ ) ₆ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 60 mL of H ₂ O and C ₁₇ H ₃₃ COOK (manufactured by Kanto Chemical Co., Ltd.) as an organic protective agent ) was mixed, and ZrO ₂ powder (TZ-0 manufactured by Toso Co., Ltd.) was added to the mixed solution so that Ce:Zr = 5:95 (molar ratio) and mixed. While stirring the mixed liquid, 10 mL of 25% by mass ammonia water (NH ₄ OH: manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added for neutralization reaction to obtain a precipitate. A precipitate deposited in the liquid was filtered, washed and dried. Further, this sample was heat-treated in the atmosphere at 600° C. for 60 minutes to obtain zirconia-ceria core-shell type particles (Invention Sample 1). As a result, ceria particles having an average particle diameter of 10 nm or less were supported on the zirconia particle surfaces.

The crystal structure of zirconia and ceria constituting the core-shell was examined using a powder X-ray diffractometer (MiniFlexII, Rigaku Co., Ltd.), and zirconia was monoclinic and ceria was cubic. The particle size was calculated by applying Scherrer's formula to the result of the X-ray diffraction pattern. Further, the crystal structure was the same in Examples 2 to 6 below.

Example 2: Synthesis of zirconia-ceria core-shell particles (Ce:Zr=10:90)
Ceria-supported zirconia particles were obtained in the same manner as in Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=10:90 (molar ratio). Furthermore, a sample obtained by heat-treating the ceria-supporting zirconia particles at 600° C. for 60 minutes in the air (sample 2 of the present invention) and a sample obtained by heat-treating the ceria-supporting zirconia particles at 1000° C. for 3 hours in the air after the heat treatment at 600° C. and got As a result, ceria particles having an average particle diameter of 10 nm or less were supported on the zirconia particle surfaces.

Example 3: Synthesis of zirconia-ceria core-shell particles (Ce:Zr=20:80)
Ceria-supported zirconia particles were obtained in the same manner as in Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=20:80 (molar ratio). Further, a sample obtained by heat-treating the ceria-supporting zirconia particles at 600° C. for 60 minutes in the air (sample 3 of the present invention) and a sample obtained by heat-treating the ceria-supporting zirconia particles at 1000° C. for 3 hours in the air after heat treatment at 600° C. and got As a result, ceria particles having an average particle diameter of 10 nm or less were supported on the zirconia particle surfaces.

Example 4: Synthesis of zirconia-ceria core-shell particles (Ce:Zr=30:70)
Ceria-supported zirconia particles were obtained in the same manner as in Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=30:70 (molar ratio). Furthermore, a sample obtained by heat-treating the ceria-supporting zirconia particles at 600°C for 60 minutes in the air (Sample 4 of the present invention) and a sample obtained by heat-treating the ceria-supporting zirconia particles at 1000°C for 3 hours in the air after heat treatment at 600°C. and got As a result, ceria particles having an average particle diameter of 10 nm or less were supported on the zirconia particle surfaces.

Example 5: Synthesis of zirconia-ceria core-shell particles (Ce:Zr=40:60)
Ceria-supported zirconia particles were obtained in the same manner as in Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=30:70 (molar ratio). Further, a sample obtained by heat-treating the ceria-supporting zirconia particles at 600° C. for 60 minutes in the air (sample 5 of the present invention) and a sample obtained by heat-treating the ceria-supporting zirconia particles at 1000° C. for 3 hours in the air after heat treatment at 600° C. and got As a result, ceria particles having an average particle diameter of 10 nm or less were supported on the zirconia particle surfaces.

Example 6: Synthesis of zirconia-ceria core-shell particles (Ce:Zr=50:50)
Ceria-supported zirconia particles were obtained in the same manner as in Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=50:50 (molar ratio). Further, a sample obtained by heat-treating the ceria-supporting zirconia particles at 600° C. for 60 minutes in the air (sample 6 of the present invention) and a sample obtained by heat-treating the ceria-supporting zirconia particles at 1000° C. for 3 hours in the air after the heat treatment at 600° C. and got As a result, ceria particles having an average particle diameter of 10 nm or less were supported on the zirconia particle surfaces.

Test Example 1: Specific Surface Area When the specific surface areas of the present invention samples 1 to 6 obtained in Examples 1 to 6 were measured by a nitrogen adsorption method, the present invention sample 1: 12.0 m ² /g, respectively. , Inventive sample 2: 13.1 m ² /g, Inventive sample 3: 16.5 m ² /g, Inventive sample 4: 28.5 m ² /g, Inventive sample 5: 33.1 m ² /g, this Inventive sample 6: 34.9 m ² /g.

Comparative Example 1: Synthesis of Ceria-Zirconia Uniform Solid Solution Particles (Ce:Zr=5:95)
Zirconyl nitrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and (NH ₄ ) ₂ Ce(NO ₃ ) ₆ (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) at a ratio of Ce:Zr = 5:95 (molar ratio) ), distilled water was added to make 1 liter, and the mixture was stirred with a stirrer and dissolved. After dissolution, an aqueous ammonia solution obtained by further diluting 25% by mass ammonia water (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) by 3 times was added and stirred for 1 hour to form a precipitate. After stirring was stopped and the precipitate was aged for 24 hours, it was suction-filtered, washed with 3 liters of distilled water, and dried. Drying was performed in an electric furnace at 120° C. for 24 hours. After drying, a heat treatment was performed at 600° C. for 3 hours each to obtain a comparative sample 1. When the phase was examined by XRD, it was a tetragonal or cubic fluorite crystal phase.

Comparative Example 2: Synthesis of Ceria-Zirconia Uniform Solid Solution Particles (Ce:Zr=10:90)
Ceria-zirconia homogeneous solid solution particles were obtained as Comparative Sample 2 in the same manner as in Comparative Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=10:90 (molar ratio). When the phase was examined by XRD, it was a tetragonal or cubic fluorite crystal phase.

Comparative Example 3: Synthesis of Ceria-Zirconia Uniform Solid Solution Particles (Ce:Zr=20:80)
Ceria-zirconia uniform solid solution particles were obtained as Comparative Sample 3 in the same manner as in Comparative Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=20:80 (molar ratio). When the phase was examined by XRD, it was a tetragonal or cubic fluorite crystal phase.

Comparative Example 4: Synthesis of Ceria-Zirconia Uniform Solid Solution Particles (Ce:Zr=30:70)
Ceria-zirconia uniform solid solution particles were obtained as Comparative Sample 4 in the same manner as in Comparative Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=30:70 (molar ratio). When the phase was examined by XRD, it was a tetragonal or cubic fluorite crystal phase.

Comparative Example 5: Synthesis of Ceria-Zirconia Uniform Solid Solution Particles (Ce:Zr=40:60)
Ceria-zirconia uniform solid solution particles were obtained as Comparative Sample 5 in the same manner as in Comparative Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=40:60 (molar ratio). When the phase was examined by XRD, it was a tetragonal or cubic fluorite crystal phase.

Comparative Example 6: Synthesis of Ceria-Zirconia Uniform Solid Solution Particles (Ce:Zr=50:50)
Ceria-zirconia uniform solid solution particles were obtained as Comparative Sample 6 in the same manner as in Comparative Example 1, except that the amounts of raw materials used were adjusted so that Ce:Zr=50:50 (molar ratio). When the phase was examined by XRD, it was a tetragonal or cubic fluorite crystal phase.

When the specific surface areas of Comparative Samples 1 to 6 obtained in Comparative Examples 1 to 6 were measured, the values were as high as 52.5 to 85.0 m ² /g, indicating that the particles after firing were in a bulky state. Further, even when the comparative samples 1 to 6 obtained were pulverized, the specific surface area was high and bulky.

Test Example 2: Comparative investigation of the performance of Examples 1 to 6 and Comparative Examples 1 to 6 by temperature programmed reduction test Soot-like particulates on the inventive samples of Examples 1 to 6 and the comparative samples of Comparative Examples 1 to 6. Evaluation of the matter (PM) combustion reaction was performed using a thermogravimetry (TG) apparatus (Thermo plus EVO2 differential type differential thermobalance TG8120, Rigaku Corporation). In this experiment, carbon black (Printex V (Orion Engineered Carbons); hereinafter referred to as PM) used in PM combustion studies was used as PM. PM and catalyst (each sample of Examples 1 to 5 or Comparative Examples 1 to 5) are respectively pulverized in an alumina mortar, then 0.1 g of catalyst and 0.005 g of pulverized PM are weighed and mixed in an agate mortar. prepared a mixed sample of catalyst and PM used for PM combustion evaluation. 15 mg of a mixed sample of PM and catalyst was placed on an alumina pan, and the temperature was raised from room temperature to 800° C. by circulating 5% by volume oxygen (Ar diluted) gas at a gas flow rate of 30 mL/min. At this time, the temperature increase rate was 5° C./min, and the PM combustion reaction of each catalyst was evaluated at a temperature (T50) at which the measured weight loss was 50%.

Table 1 shows the results. The samples of the present invention have a T50 of 373 to 408° C., whereas the samples of the comparative examples have a T50 higher than that. The samples of the present invention become active at lower temperatures, demonstrating that they are superior to the comparative samples in terms of oxygen storage capacity and particulate matter purification performance (PM combustion activity).

Example 7: Synthesis of silver-supported zirconia-ceria core-shell type particles (silver-supported amount: 0.2% by mass)
A sample in which 0.2% by mass of silver was supported on zirconia-ceria core-shell type particles of Ce:Zr=10:90 (molar ratio) was prepared as follows.

A solution of (NH ₄ ) ₂ Ce(NO ₃ ) ₆ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 60 mL of H ₂ O and C ₁₇ H ₃₃ COOK (manufactured by Kanto Chemical Co., Ltd.) as an organic protective agent ) was mixed, and ZrO ₂ powder (TZ-0 manufactured by Toso Corporation) was added to the mixed solution so that Ce:Zr = 10:90 (molar ratio) and mixed. While stirring the mixed liquid, 10 mL of 25% by mass ammonia water (NH ₄ OH: manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added for neutralization reaction to obtain a precipitate. A precipitate deposited in the liquid was filtered, washed and dried. Further, the obtained particles were heat-treated in air at 600° C. for 60 minutes and then heat-treated in air at 800° C. for 3 hours to obtain zirconia-ceria core-shell type particles.

Silver (Ag) was supported on the obtained zirconia-ceria core-shell type particles by an impregnation method to produce silver-supported zirconia-ceria core-shell type particles. A silver nitrate standard aqueous solution (AgNO ₃ aq (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.)) was added to the obtained zirconia-ceria core-shell type particles, stirred for 15 minutes, then dried at 90°C for 24 hours, and dried in air at 600°C. for 3 hours to obtain silver-supported zirconia-ceria core-shell type particles. The concentration of the silver nitrate standard aqueous solution was adjusted so that the supported amount was 0.2 parts by mass with respect to 100 parts by mass of the zirconia-ceria core-shell type particles.

Example 8: Synthesis of silver-supported zirconia-ceria core-shell type particles (silver-supported amount: 0.5% by mass)
A silver-supported zirconia-ceria core-shell type was prepared in the same manner as in Example 7, except that the concentration of the nitric acid standard aqueous solution was adjusted so that the supported amount was 0.5 parts by mass with respect to 100 parts by mass of the zirconia-ceria core-shell type particles. Particles were obtained.

Example 9: Synthesis of silver-supported zirconia-ceria core-shell type particles (silver-supported amount: 0.8% by mass)
Silver-supported zirconia-ceria core-shell type particles were prepared in the same manner as in Example 7, except that the concentration of the nitric acid standard aqueous solution was adjusted so that the supported amount was 0.8 parts by mass with respect to 100 parts by mass of the zirconia-ceria core-shell type particles. Particles were obtained.

Example 10: Synthesis of silver-supported zirconia-ceria core-shell type particles (silver-supported amount: 0.9% by mass)
A silver-supported zirconia-ceria core-shell type was prepared in the same manner as in Example 7 except that the concentration of the nitric acid standard aqueous solution was adjusted so that the supported amount was 0.9 parts by mass with respect to 100 parts by mass of the zirconia-ceria core-shell type particles. Particles were obtained.

Example 11: Synthesis of silver-supported zirconia-ceria core-shell type particles (silver-supported amount: 3.1% by mass)
A silver-supported zirconia-ceria core-shell type was prepared in the same manner as in Example 7 except that the concentration of the nitric acid standard aqueous solution was adjusted so that the supported amount was 3.1 parts by mass with respect to 100 parts by mass of the zirconia-ceria core-shell type particles. Particles were obtained.

Test Example 3: Comparative investigation of the performance of Examples 7 to 11 by temperature-programmed reduction test For the silver-supported zirconia-ceria core-shell particles of Examples 7 to 11, evaluation of particulate matter (PM) combustion reaction was performed by thermogravimetric analysis. (TG: Thermogravimetry) apparatus (Thermo plus EVO2 differential type differential thermal balance TG8120, Rigaku Corporation). In this experiment, carbon black (Printex V (Orion Engineered Carbons); hereinafter referred to as PM) used in PM combustion studies was used as PM. PM and catalyst (each sample of Examples 7 to 11) are each pulverized in an alumina mortar, and then 0.1 g of catalyst and 0.005 g of pulverized PM are weighed and mixed in an agate mortar to evaluate PM combustion. A mixed sample of catalyst and PM was prepared. 15 mg of a mixed sample of PM and catalyst was placed on an alumina pan, and the temperature was raised from room temperature to 800° C. by circulating 5% by volume oxygen (Ar diluted) gas at a gas flow rate of 30 mL/min. At this time, the temperature increase rate was 5° C./min, and the PM combustion reaction of each catalyst was evaluated at a temperature (T50) at which the measured weight loss was 50%.

Table 2 shows the results. For comparison, Table 2 also shows the results of Example 2 in which no silver is supported. In either case, the PM burning activity did not decrease due to silver loading. Also, when a small amount of silver (for example, 0.3 to 3.0% by mass, particularly 0.5 to 1.0% by mass) was supported, the PM combustion activity was dramatically improved.

Example 12: Synthesis of platinum-supported zirconia-ceria core-shell particles (platinum supported amount: 0.2% by mass)
A sample in which 0.2% by mass of platinum was supported on zirconia-ceria core-shell type particles of Ce:Zr=10:90 (molar ratio) was prepared as follows.

A solution of (NH ₄ ) ₂ Ce(NO ₃ ) ₆ (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 60 mL of H ₂ O and C ₁₇ H ₃₃ COOK (manufactured by Kanto Chemical Co., Ltd.) as an organic protective agent ) was mixed, and ZrO ₂ powder (TZ-0 manufactured by Toso Corporation) was added to the mixed solution so that Ce:Zr = 10:90 (molar ratio) and mixed. While stirring the mixed liquid, 10 mL of 25% by mass ammonia water (NH ₄ OH: manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added for neutralization reaction to obtain a precipitate. A precipitate deposited in the liquid was filtered, washed and dried. Further, the obtained particles were heat-treated in air at 600° C. for 60 minutes and then heat-treated in air at 800° C. for 3 hours to obtain zirconia-ceria core-shell type particles.

Platinum (Pt) was supported on the obtained zirconia-ceria core-shell type particles by an impregnation method to produce platinum-supported zirconia-ceria core-shell type particles. A dinitrodiammineplatinum (II) nitric acid solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was added to the resulting zirconia-ceria core-shell particles, stirred for 15 minutes, then dried at 90°C for 24 hours, and dried at 600°C for 3 hours in air. After sintering for several hours, platinum-supported zirconia-ceria core-shell type particles were obtained. The concentration of the dinitrodiammineplatinum (II) nitric acid solution was adjusted so that the supported amount was 0.2 parts by mass with respect to 100 parts by mass of the zirconia-ceria core-shell type particles.

Comparative Example 7: Synthesis of palladium-supported ceria particles (palladium-supported amount: 0.2% by mass)
Palladium-supported ceria particles were obtained in the same manner as in Example 12, except that ceria particles were used instead of the zirconia-ceria core-shell type particles.

Example 13: Synthesis of palladium-supported zirconia-ceria core-shell particles (palladium-supported amount: 0.2% by mass)
Instead of dinitrodiammineplatinum (II) nitric acid solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), dinitrodiamminepalladium (II) nitric acid solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) is used, and the amount supported is zirconia-ceria core-shell type. Palladium-supported zirconia-ceria core-shell particles were obtained in the same manner as in Example 12, except that the concentration of the dinitrodiammine palladium (II) nitric acid solution was adjusted to 0.2 parts by mass with respect to 100 parts by mass of the particles. .

Comparative Example 8: Synthesis of palladium-supported ceria particles (palladium-supported amount: 0.2% by mass)
Ceria particles were used instead of zirconia-ceria core-shell particles, and dinitrodiammineplatinum (II) nitric acid solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was replaced with dinitrodiammine palladium (II) nitric acid solution (Tanaka Kikinzoku Kogyo Co., Ltd.). )), and the concentration of the dinitrodiammine palladium (II) nitric acid solution is adjusted so that the supported amount is 0.2 parts by mass with respect to 100 parts by mass of ceria particles. Palladium-supported ceria particles were obtained.

Example 14: Synthesis of rhodium-supported zirconia-ceria core-shell particles (rhodium-supported amount: 0.2% by mass)
An aqueous solution of rhodium nitrate (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was used instead of the dinitrodiammineplatinum (II) nitric acid solution (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.), and the supported amount was 100 parts by mass of the zirconia-ceria core-shell type particles. Rhodium-supported zirconia-ceria core-shell particles were obtained in the same manner as in Example 12, except that the concentration of the rhodium nitrate aqueous solution was adjusted to 0.2 parts by mass.

Comparative Example 9: Synthesis of rhodium-supported ceria particles (palladium-supported amount: 0.2% by mass)
Ceria particles were used instead of zirconia-ceria core-shell type particles, and rhodium nitrate aqueous solution (Tanaka Kikinzoku Kogyo Co., Ltd.) was used instead of dinitrodiammine platinum (II) nitric acid solution (Tanaka Kikinzoku Kogyo Co., Ltd.). Then, rhodium-supported ceria particles were obtained in the same manner as in Example 12, except that the concentration of the rhodium nitrate aqueous solution was adjusted so that the supported amount was 0.2 parts by mass with respect to 100 parts by mass of the ceria particles.

Test Example 4: Comparative investigation of three-way catalyst activity of Examples 12-14 and Comparative Examples 7-9 The three-way catalyst activity measurement of the samples of Examples 12-14 and Comparative Examples 7-9 was used to perform a performance evaluation test. 100 mg (0.1 g) of the samples of Examples 12 to 14 and Comparative Examples 7 to 9 were weighed and set in a straight reaction tube, and mixed gas (C ₃ H ₆ : 0 0.04% by volume, NO: 0.1% by volume, CO: 0.3% by volume, _O2 : 0.33% by volume, H2: 0.1% by volume, _H2O : 2.0% by volume, _N2 : remainder) was flowed at a flow rate of 500 mL/min, the gas composition after passing through the samples of Examples 12 to 14 and Comparative Examples 7 to 9 was measured, and a catalyst performance test was performed. In the temperature rising process, the temperature was raised from room temperature to 700 ° C. at 10 ° C./min, held for 30 minutes, then gradually lowered and air-cooled to room temperature, and then raised to 700 ° C. at 4 ° C./min. , NO and C ₃ H ₆ purification rates were used to evaluate the three-way catalyst activity. The space velocity converted to volume is 120000/hour.

The temperature at which 50% by volume of CO, NO and C ₃ H ₆ were purified (50% by volume purification temperature T50) was measured and summarized in Table 3.

The oxygen storage material of the present invention exhibits PM burning activity at low temperatures, and is excellent in purification, especially when added with a low loading of silver. At the same time, since it has good three-way activity even with low-load catalysts of platinum, palladium, and rhodium, it can be used as a carrier that exhibits both three-way catalyst (TWC) performance and PM combustion activity suitable for exhaust gas purification filters (GPF) at the same time. It turns out to be useful.

As a three-way catalyst, even without a multi-layer coating, each precious metal is promoted to exhibit higher activity than conventional carriers, simplifying the process of manufacturing a catalytic converter. Moreover, since these high activities are exhibited even with a low specific surface area, the thickness of the honeycomb coat layer can be reduced. It becomes a support material and a catalyst that can greatly suppress pressure drop reduction.

In order to reduce the pressure loss of the exhaust purification filter (GPF), the thickness of the conventional catalyst layer is several tens of μm, and the thinnest part is several μm. It is necessary to secure a sufficient gas passage.

When a three-way catalyst (TWC catalyst) is supported, a certain amount of thickness is required in order to exhibit activity in the carrier coating layer of aggregated particles with a high specific surface area and high porosity as in the past, and this problem could not be solved. .

On the other hand, in the present invention, the specific surface area is small and the particles are easy to become independent, and even when Pd or the like is supported, the activity is high. It has the advantage of being thin. That is, according to the present invention, it is clear that a thin coating layer on an exhaust purification filter (GPF) substrate can achieve three-way catalyst (TWC) activity and PM purification activity. The three-way catalyst (TWC) activity and PM purification activity were sufficiently expressed even in the catalyst having a layer of 100 nm formed on the substrate. Furthermore, even for the same coated layer carrier, it is possible to sort the carrier by adding Rh and Pd, which are particularly excellent in three-way catalyst (TWC) activity, and Ag, etc., which improves PM purification activity. maintained good purification performance.

Due to the core-shell structure of this material, the core-shell nanoparticles of the present invention worked effectively not only for three-way catalyst (TWC) activity but also for PM purification. In other words, the material of the present invention is effective as a catalytic material that does not cause problems such as clogging or narrowing of pores due to the coat layer at the wall inlet or inside of the exhaust gas purification filter (GPF) substrate. Thus, provision of a three-way catalyst (TWC) according to the present invention is useful for optimal utilization of the exhaust gas purification filter (GPF) substrate and maintenance of its purification activity, and further simplifies the manufacturing process. There is an advantage that

Claims (12)

An oxygen storage material containing core-shell nanoparticles consisting of a core containing zirconia and a shell containing ceria. Composition formula:
(CeO ₂ ) _x (ZrO ₂ ) _1−x
[In the formula, x represents 0.05 to 0.50. ]
The oxygen storage material according to claim 1, represented by: Oxygen storage material according to claim 1 or 2, wherein x is between 0.10 and 0.30. Oxygen storage material according to any one of claims 1 to 3, having a specific surface area of 5 to 40 m ² /g. An exhaust gas purification catalyst containing the oxygen storage material according to any one of claims 1 to 4. 6. The exhaust gas purifying catalyst according to claim 5, wherein at least one precious metal selected from the group consisting of platinum, palladium and rhodium is supported on said oxygen storage material. 7. The exhaust gas purification catalyst according to claim 6, wherein the supported amount of said noble metal is 0.00001 to 2 parts by mass with respect to 100 parts by mass of said oxygen storage material. A particulate matter purification catalyst containing the oxygen storage material according to any one of claims 1 to 4. 9. The particulate matter purification catalyst according to claim 8, wherein silver is supported on said oxygen storage material. 10. The particulate matter purification catalyst according to claim 9, wherein the supported amount of silver is 0.2 to 5.0 parts by mass with respect to 100 parts by mass of the oxygen storage material. 11. The particulate matter purification catalyst according to claim 9, wherein the supported amount of silver is 0.5 to 1.0 parts by mass with respect to 100 parts by mass of the oxygen storage material. The oxygen storage material according to any one of claims 1 to 4, the exhaust gas purification catalyst according to any one of claims 5 to 7, or the particulate form according to any one of claims 8 to 11. An exhaust purification filter comprising a material purification catalyst.