Oxide nanocomposite and three-way catalyst for exhaust purification containing same

Abstract

The present invention provides: an oxide nanocomposite having an Al2O3 content between 16% and 60% by mass, a CeO2 content between 5% and 19% by mass, a ZrO2 content between 21% and 62% by mass, an La2O3 content between 1.4% and 4.9% by mass, and a Y2O3 content between 1.6% and 6.6% by mass, wherein the molar ratio [Ce / (Ce + Zr)] of Ce to the total amount of Ce and Zr is between 0.12 and 0.33, at least part of the CeO2 and the ZrO2 form a solid solution, and the oxide nanocomposite exhibits an X-ray diffraction pattern in which the solid solution belongs to a cubic crystal after heat treatment is performed at 1100°C for 5 hours in air; and a catalyst for exhaust gas purification containing the oxide nanocomposite and Rh supported on the oxide nanocomposite.

Description

Oxide nanocomposites and exhaust gas purification three-way catalysts containing them

[0001] The present invention relates to oxide nanocomposites and exhaust gas purification three-way catalysts containing them, and more specifically, Al ２ O ３ , CEO ２ and ZrO ２ This invention relates to oxide nanocomposites containing the same and exhaust gas purification three-way catalysts containing the same.

[0002] Conventionally, catalysts containing alumina, zirconia, and ceria have been known as exhaust gas purification catalysts for internal combustion engines such as automobile engines. As such an exhaust gas purification catalyst, for example, Japanese Patent Application Publication No. 2013-193042 (Patent Document 1) discloses an exhaust gas purification catalyst comprising a composite oxide carrier consisting of alumina, ceria, and zirconia, a first additive element oxide and a second additive element oxide consisting of two elements selected from the group consisting of rare earth elements other than cerium or alkaline earth elements, and a noble metal catalyst supported on the composite oxide carrier, wherein the composite oxide carrier contains alumina in the range of 30 to 40% by mass and zirconia in the range of 36 to 46% by mass. Furthermore, Japanese Patent Publication No. 2018-8255 (Patent Document 2) discloses an exhaust gas purification catalyst comprising a catalyst support made of a composite metal oxide porous material containing alumina, ceria, and zirconia, and further containing lanthanum and yttrium, and a noble metal supported on the catalyst support.

[0003] Japanese Patent Publication No. 2013-193042 Japanese Patent Publication No. 2018-8255

[0004] However, in recent years, exhaust gas regulations have been strengthened under European Euro 7, the US Environmental Protection Agency (EPA) Tier 4, and China's CN7. To meet these requirements, there is a demand for exhaust gas purification catalysts that exhibit excellent purification performance even after exposure to high temperatures, particularly exhaust gas purification catalysts that support Rh, which is necessary for NOx purification.

[0005] The present invention has been made in view of the problems of the above prior art, and an object thereof is to provide a Rh-supported exhaust gas purification catalyst having excellent purification performance (particularly, transient purification performance and low-temperature purification performance) even after being exposed to high temperature, and an oxide nanocomposite used as a catalyst carrier therefor.

[0006] As a result of intensive studies to achieve the above object, the present inventors have found that in an exhaust gas purification catalyst in which Rh is supported on an oxide nanocomposite containing Al ２ O ３ and CeO ２ and ZrO ２ and La ２ O ３ and Y ２ O ３ when the amount of CeO ２ is reduced and the amount of Al ２ is increased so that the amount of ZrO ２ O ３ does not decrease too much, and the contents of Al ２ O ３ 、CeO ２ 、ZrO ２ 、La ２ O ３ and Y ２ O ３ and the molar ratio of Ce to the total amount of Ce and Zr are within specific ranges, an Rh-supported exhaust gas purification catalyst having excellent transient purification performance and low-temperature purification performance even after being exposed to high temperature can be obtained, and the present invention has been completed.

[0007] That is, the present invention provides the following aspects. [1] Al ２ O ３ is contained in an amount of 16 to 60% by mass, CeO ２ is contained in an amount of 5 to 19% by mass, ZrO ２ is contained in an amount of 21 to 62% by mass, La ２ O ３ is contained in an amount of 1.4 to 4.9% by mass, and Y ２ O ３ is contained in an amount of 1.6 to 6.6% by mass, the molar ratio of Ce to the total amount of Ce and Zr [Ce / (Ce + Zr)] is 0.12 to 0.33, and CeO ２ and ZrO２ [2] Al ２ O ３ The content is 20-55% by mass, and CeO ２ The content is 10 to 19% by mass, and ZrO ２ The content is 25 to 55% by mass, and La ２ O ３ The content is 2.0 to 4.9% by mass, Y ２ O ３ The oxide nanocomposite described in [1], wherein the content of is 1.8 to 4.9% by mass and the molar ratio [Ce / (Ce+Zr)] is 0.16 to 0.30. [3] Al ２ O ３ The content is 28-52% by mass, and CeO ２ The content is 14-19% by mass, and ZrO ２ The content is 28-48% by mass, and La ２ O ３ The content is 2.8 to 4.9% by mass, Y ２ O ３ The oxide nanocomposite according to [2], wherein the content of is 1.8 to 4.0 mass%, and the molar ratio [Ce / (Ce+Zr)] is 0.18 to 0.27. [4] An exhaust gas purification catalyst containing the oxide nanocomposite according to any one of [1] to [3] and Rh supported on the oxide nanocomposite. [5] BET specific surface area is 15 m ２ The exhaust gas purification catalyst described in [4] is greater than or equal to / g.

[0008] Although the reason why the exhaust gas purification catalyst of the present invention exhibits excellent transient and low-temperature purification performance even after exposure to high temperatures is not entirely clear, the inventors speculate as follows.

[0009] In exhaust gas purification catalysts supporting Rh, it is important to have excellent oxygen storage capacity (OSC) to mitigate the decrease in purification performance due to fluctuations in the exhaust gas atmosphere in order to improve transient purification performance. In order to exhibit excellent oxygen storage capacity in exhaust gas purification catalysts, CeO ２ and ZrO ２ It is necessary to include a solid solution (CZ solid solution) with . However, if a CZ solid solution is included in an exhaust gas purification catalyst supported with Rh, CeO ２ Because it exhibits a strong interaction with Rh, the metallization of Rh is inhibited, and the catalytic activity of Rh, especially at low temperatures, decreases. For this reason, from the viewpoint of Rh's catalytic activity at low temperatures, a low CZ solid solution content is preferable, but if the CZ solid solution content is low, oxygen storage capacity does not improve, and transient purification performance does not improve either.

[0010] Therefore, in the present invention, ZrO ２ Al ２ O ３ Increase the amount of Al ２ O ３ Al forms an oxide nanocomposite with a CZ solid solution. In this oxide nanocomposite, Al ２ O ３ By increasing the amount of Ce, the surface concentration of Rh and CeO ２ It is presumed that the interaction with is suppressed, inhibiting the metallation of Rh is suppressed, and the catalytic activity of Rh at low temperatures is improved. Also, Al ２ O ３ Increased amount of ZrO ２ Since the amount is not reduced too much, a sufficient CZ solid solution is formed, which is presumed to improve oxygen storage capacity and transient purification performance. Furthermore, ZrO ２ Al ２ O ３ The amount is being increased, that is, ZrO ２ Because the amount is appropriate and the heat resistance of the CZ solid solution is maintained, it is presumed to exhibit excellent transient and low-temperature purification performance even after exposure to high temperatures.

[0011] According to the present invention, it is possible to obtain a Rh-supported exhaust gas purification catalyst and an oxide nanocomposite used as a catalyst support therefor, which exhibits excellent purification performance (particularly transient purification performance and low-temperature purification performance) even after exposure to high temperatures.

[0012] This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 1. This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 2. This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 3. This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 4. This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 5. This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Comparative Example 1. This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Comparative Example 2. This graph shows the X-ray diffraction pattern around 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Comparative Example 3. The oxygen storage capacity of the exhaust gas purification catalyst and Al after exposure to high temperature. ２ O ３ This graph shows the relationship between the NOx purification performance of the exhaust gas purification catalyst after exposure to high temperatures and Al ２ O ３ This graph shows the relationship between the specific surface area of ​​the exhaust gas purification catalyst after exposure to high temperatures and Al. ２ O ３ This graph shows the relationship with the content. It shows the relationship between the oxygen storage capacity of the exhaust gas purification catalyst after exposure to high temperatures and CeO2. ２ This graph shows the relationship between the content and the NOx purification performance of the exhaust gas purification catalyst after exposure to high temperatures. ２ This graph shows the relationship between the specific surface area of ​​the exhaust gas purification catalyst after exposure to high temperatures and CeO2. ２It is a graph showing the relationship with the content. Oxygen storage capacity of the exhaust gas purification catalyst after being exposed to high temperature and ZrO ２ It is a graph showing the relationship with the content. NOx purification performance of the exhaust gas purification catalyst after being exposed to high temperature and ZrO ２ It is a graph showing the relationship with the content. Specific surface area of the exhaust gas purification catalyst after being exposed to high temperature and ZrO ２ It is a graph showing the relationship with the content. Oxygen storage capacity of the exhaust gas purification catalyst after being exposed to high temperature and La ２ O ３ It is a graph showing the relationship with the content. NOx purification performance of the exhaust gas purification catalyst after being exposed to high temperature and La ２ O ３ It is a graph showing the relationship with the content. Specific surface area of the exhaust gas purification catalyst after being exposed to high temperature and La ２ O ３ It is a graph showing the relationship with the content. Oxygen storage capacity of the exhaust gas purification catalyst after being exposed to high temperature and Y ２ O ３ It is a graph showing the relationship with the content. NOx purification performance of the exhaust gas purification catalyst after being exposed to high temperature and Y ２ O ３ It is a graph showing the relationship with the content. Specific surface area of the exhaust gas purification catalyst after being exposed to high temperature and Y ２ O ３ It is a graph showing the relationship with the content. A graph showing the relationship between the oxygen storage capacity of the exhaust gas purification catalyst after being exposed to high temperature and the molar ratio [Ce / (Ce + Zr)]. A graph showing the relationship between the NOx purification performance of the exhaust gas purification catalyst after being exposed to high temperature and the molar ratio [Ce / (Ce + Zr)]. A graph showing the relationship between the specific surface area of the exhaust gas purification catalyst after being exposed to high temperature and the molar ratio [Ce / (Ce + Zr)]. A graph showing the relationship between the oxygen storage capacity of the exhaust gas purification catalyst after being exposed to high temperature and the specific surface area. A graph showing the relationship between the NOx purification performance of the exhaust gas purification catalyst after being exposed to high temperature and the specific surface area.

[0013] Hereinafter, the present invention will be described in detail according to its preferred embodiments.

[0014] [Oxide nanocomposite] The oxide nanocomposite of the present invention will be described. The oxide nanocomposite of the present invention is Al ２ O３ and CeO ２ and ZrO ２ and La ２ O ３ and Y ２ O ３ and contains. Al ２ O ３ CeO ２ ZrO ２ La ２ O ３ and Y ２ O ３ There is no particular limitation as, and those conventionally known can be used.

[0015] Al ２ O ３ The content of is 16 to 60% by mass, preferably 20 to 55% by mass, more preferably 25 to 53% by mass, and still more preferably 28 to 52% by mass. Al ２ O ３ When the content of Al is less than the above lower limit, the purification performance at low temperature after high-temperature exposure of the obtained exhaust gas purification catalyst tends to decrease, and the specific surface area of the obtained exhaust gas purification catalyst after high-temperature exposure also tends to decrease. On the other hand, when the content of Al ２ O ３ exceeds the above upper limit, the oxygen storage capacity of the obtained exhaust gas purification catalyst after high-temperature exposure decreases, and the transient purification performance after high-temperature exposure tends to decrease.

[0016] CeO ２ The content of is 5 to 19% by mass from the viewpoints of the oxygen storage capacity, transient purification performance, and purification performance at low temperature of the obtained exhaust gas purification catalyst after high-temperature exposure, preferably 10 to 19% by mass, more preferably 13 to 19% by mass, and still more preferably 14 to 19% by mass.

[0017] ZrO ２ The content of is 21 to 62% by mass, preferably 25 to 55% by mass, more preferably 27 to 50% by mass, and still more preferably 28 to 48% by mass. ZrO ２When the content of ZrO falls below the aforementioned lower limit, the oxygen storage capacity of the resulting exhaust gas purification catalyst after high-temperature exposure decreases, and the transient purification performance after high-temperature exposure tends to decrease. Furthermore, the specific surface area of ​​the resulting exhaust gas purification catalyst after high-temperature exposure also tends to decrease. On the other hand, ZrO ２ When the content of exceeds the aforementioned upper limit, the purification performance of the resulting exhaust gas purification catalyst at low temperatures after high-temperature exposure tends to decrease, and the specific surface area of ​​the resulting exhaust gas purification catalyst after high-temperature exposure also tends to decrease.

[0018] La ２ O ３ The content of is 1.4 to 4.9% by mass, preferably 2.0 to 4.9% by mass, more preferably 2.5 to 4.9% by mass, and even more preferably 2.8 to 4.9% by mass, from the viewpoint of the purification performance of the resulting exhaust gas purification catalyst at low temperatures after exposure to high temperatures.

[0019] Y ２ O ３ The content is 1.6 to 6.6% by mass, preferably 1.8 to 4.9% by mass, more preferably 1.8 to 4.5% by mass, and even more preferably 1.8 to 4.0% by mass. ２ O ３ When the content of falls below the aforementioned lower limit, the oxygen storage capacity of the resulting exhaust gas purification catalyst after high-temperature exposure decreases, and the transient purification performance after high-temperature exposure tends to decrease. Furthermore, the specific surface area of ​​the resulting exhaust gas purification catalyst after high-temperature exposure also tends to decrease. On the other hand, Y ２ O ３ When the content of exceeds the aforementioned upper limit, the purification performance of the resulting exhaust gas purification catalyst at low temperatures after high-temperature exposure tends to decrease, and the specific surface area of ​​the resulting exhaust gas purification catalyst after high-temperature exposure also tends to decrease.

[0020] The molar ratio of Ce to the total amount of Ce and Zr [Ce / (Ce+Zr)] is 0.12 to 0.33, preferably 0.16 to 0.30, more preferably 0.17 to 0.28, and even more preferably 0.18 to 0.27. If the molar ratio [Ce / (Ce+Zr)] falls below the lower limit, the purification performance at low temperatures after high-temperature exposure of the resulting exhaust gas purification catalyst tends to decrease, and the specific surface area of ​​the resulting exhaust gas purification catalyst after high-temperature exposure also tends to decrease. On the other hand, if the molar ratio [Ce / (Ce+Zr)] exceeds the upper limit, the oxygen storage capacity of the resulting exhaust gas purification catalyst after high-temperature exposure tends to decrease, the transient purification performance after high-temperature exposure tends to decrease, and the specific surface area of ​​the resulting exhaust gas purification catalyst after high-temperature exposure also tends to decrease.

[0021] In the oxide nanocomposite, CeO ２ and ZrO ２ At least a portion of the material forms a solid solution (CZ solid solution), and the CZ solid solution, after heat treatment at 1100°C for 5 hours in air, exhibits a diffraction pattern that attributes it to a cubic crystal structure. This assignment is determined by the presence of a single diffraction peak in the X-ray diffraction pattern of the CZ solid solution around 2θ = 34.5°. The oxide nanocomposite in which the heat-treated CZ solid solution is attributed to a cubic crystal structure exhibits excellent heat resistance. The oxide nanocomposite in which the heat-treated CZ solid solution is attributed to a cubic crystal structure contains at least Al ２ O ３ and ZrO ２ The content of is within the above range (preferably, further, CeO ２ La ２ O ３ and Y ２ O ３It can be manufactured by setting the content and molar ratio [Ce / (Ce+Zr)] within the range described above. On the other hand, in oxide nanocomposites that do not satisfy the above conditions, two diffraction peaks are observed in the X-ray diffraction pattern of the CZ solid solution around 2θ = 34.5° after the heat treatment, and such CZ solid solutions are attributed to a tetragonal crystal structure. Generally, when a CZ solid solution with insufficient heat resistance is exposed to high temperatures, the symmetry of the crystal structure decreases, and a phase transition from cubic to tetragonal (or monoclinic) occurs. In other words, oxide nanocomposites in which the CZ solid solution is attributed to a tetragonal crystal structure after the heat treatment have lower heat resistance than oxide nanocomposites in which the CZ solid solution is attributed to a cubic crystal structure.

[0022] There are no particular limitations on the method for producing the oxide nanocomposite of the present invention, but for example, first, a raw material solution containing a salt of Al, a salt of Ce, a salt of Zr, a salt of La, and a salt of Y is used to produce the Al in the resulting oxide nanocomposite. ２ O ３ , CEO ２ , ZrO ２ La ２ O ３ and Y ２ O ３ One method involves preparing a raw material solution such that the content and molar ratio [Ce / (Ce+Zr)] are within a predetermined range, then mixing this raw material solution with a neutralizing solution containing a basic compound to prepare hydroxides (oxide precursors) of Al, Ce, Ze, La, and Y, and finally calcining the obtained oxide precursors.

[0023] Examples of salts of Al, Ce, Zr, La, and Y include acetates, nitrates, and chlorides. Examples of basic compounds include hydroxides of alkali metals such as Na and K, and ammonia, but ammonia is preferred from the viewpoint that the resulting oxide nanocomposite does not contain any metals other than Al, Ce, Zr, La, and Y.

[0024] There are no particular restrictions on the firing temperature, but 500 to 1100°C is preferred, and 700 to 1000°C is more preferred. Similarly, there are no particular restrictions on the firing time, but 1 to 10 hours is preferred, and 2 to 7 hours is more preferred.

[0025] [Exhaust Gas Purification Catalyst] Next, the exhaust gas purification catalyst of the present invention will be described. The exhaust gas purification catalyst of the present invention contains the oxide nanocomposite of the present invention and Rh supported on the oxide nanocomposite.

[0026] In the exhaust gas purification catalyst, there are no particular restrictions on the amount of Rh supported, but from the viewpoint of exhaust gas purification performance, 0.01 to 1.0% by mass is preferred, and 0.05 to 0.5% by mass is more preferred, relative to the entire exhaust gas purification catalyst.

[0027] In the exhaust gas purification catalyst, from the viewpoint of oxygen storage capacity after high-temperature exposure of the obtained exhaust gas purification catalyst, transient purification performance and purification performance at low temperatures, rich gas [H ２ (2vol%)+CO ２ (10vol%)+H ２ O (3 vol%) + N ２ (Remaining) and lean gas [O ２ (1vol%)+CO ２ (10vol%)+H ２ O (3 vol%) + N ２ The BET specific surface area after a heat resistance test, in which the remaining material and the other material are alternately passed through for 5 minutes while heated at 1050°C for 5 hours, is 15 m². ２ It is preferable that it be 18m or more per gram. ２ It is more preferable that it be 20 m or more per g. ２ It is even more preferable that the amount is 1 / g or more. Furthermore, an exhaust gas purification catalyst whose BET specific surface area after the heat resistance test is within the above range contains at least Al ２ O ３ and ZrO ２ The content of is within the above range (preferably, further, CeO ２ La ２ O ３ and Y ２ O ３ It can be manufactured by setting the content and the molar ratio [Ce / (Ce+Zr)] within the range described above.

[0028] There are no particular restrictions on the method of supporting Rh. Examples include immersing the oxide nanocomposite in a solution containing a salt of Rh to impregnate the oxide nanocomposite with Rh, followed by drying and calcination (impregnation method); or adsorbing a solution containing a salt of Rh onto the oxide nanocomposite, followed by drying and calcination (adsorption method).

[0029] There are no particular restrictions on the firing temperature, but from the viewpoint of decomposing the Rh salt, 300 to 700°C is preferred, and 400 to 600°C is more preferred. Similarly, there are no particular restrictions on the firing time, but from the viewpoint of sufficient decomposition of the Rh salt, 1 hour or more is preferred, and 2 hours or more is more preferred.

[0030] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0031] (Example 1) First, 90.42 g of a 28% by mass cerium nitrate solution and 371.136 g of an 18% by mass zirconium nitrate solution were mixed. To the resulting mixed solution, an aqueous solution prepared by dissolving 11.09 g of lanthanum nitrate hexahydrate and 13.48 g of yttrium nitrate tetrahydrate in 100 g of deionized water, an aqueous solution prepared by dissolving 318.11 g of aluminum nitrate in 100 g of deionized water, and 199.5 g of hydrogen peroxide solution were added in order to prepare the raw material solution. In addition, a neutralizing solution was prepared by adding 347.29 g of ammonia water at a concentration of 25% by mass to 800 g of deionized water.

[0032] Next, the raw material solution was added to the neutralization solution while stirring with a propeller stirrer and homogenizer to prepare an oxide precursor (hydroxide). This oxide precursor was dried in a degreasing furnace at 150°C for 7 hours, and then calcined at 400°C for 5 hours to obtain calcined powder. This calcined powder was pulverized to a particle size of 75 μm or less using a pulverizer ("Wonder Blender WB-1" manufactured by Osaka Chemical Co., Ltd.), and then calcined in air at 900°C for 5 hours to obtain oxide nanocomposite powder. The composition of this oxide nanocomposite powder was calculated from the amount of raw materials used, and it was found to be CeO ２ / ZrO ２ / La ２ O ３ / Y ２O ３ / Al ２ O ３ The ratios were 17.6 / 46.6 / 2.9 / 2.8 / 30.1 (mass ratio).

[0033] Next, the obtained oxide nanocomposite powder was impregnated with an aqueous rhodium nitrate solution and then calcined in air at 500°C for 3 hours to obtain an Rh-supported catalyst powder in which 0.15% by mass of Rh was supported on the oxide nanocomposite. This Rh-supported catalyst powder was pressure-molded at a pressure of 98.1 MPa for 1 minute using a hydrostatic press (CL10-55-40 manufactured by Nikkiso Co., Ltd.), and then pulverized to obtain Rh-supported pellet catalysts with a particle size of 0.5 to 1 mm.

[0034] (Example 2) An oxide nanocomposite powder was prepared in the same manner as in Example 1, except that the amount of cerium nitrate solution was changed to 40.00 g, the amount of zirconium nitrate solution to 156.22 g, the amount of lanthanum nitrate hexahydrate to 8.19 g, the amount of yttrium nitrate tetrahydrate to 5.43 g, the amount of aluminum nitrate to 270.20 g, and the amount of aqueous ammonia to 234.48 g. Furthermore, a Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO ２ / ZrO ２ / La ２ O ３ / Y ２ O ３ / Al ２ O ３ The ratios were 14.0 / 35.2 / 3.9 / 2.0 / 45.0 (mass ratio).

[0035] (Example 3) An oxide nanocomposite powder was prepared in the same manner as in Example 1, except that the amount of cerium nitrate solution was changed to 50.00 g, the amount of zirconium nitrate solution to 171.11 g, the amount of lanthanum nitrate hexahydrate to 12.77 g, the amount of yttrium nitrate tetrahydrate to 12.89 g, the amount of aluminum nitrate to 349.76 g, and the amount of aqueous ammonia to 300.37 g. Furthermore, a Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO ２ / ZrO ２ / La ２ O３ / Y ２ O ３ / Al ２ O ３ The ratios were 14.0 / 30.8 / 4.8 / 3.8 / 46.6 (mass ratio).

[0036] (Example 4) An oxide nanocomposite powder was prepared in the same manner as in Example 1, except that the amount of cerium nitrate solution was changed to 40.00 g, the amount of zirconium nitrate solution to 136.89 g, the amount of lanthanum nitrate hexahydrate to 10.43 g, the amount of yttrium nitrate tetrahydrate to 5.16 g, the amount of aluminum nitrate to 290.62 g, and the amount of aqueous ammonia to 244.04 g. Furthermore, a Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO ２ / ZrO ２ / La ２ O ３ / Y ２ O ３ / Al ２ O ３ The ratios were 14.0 / 30.8 / 4.9 / 1.9 / 48.4 (mass ratio).

[0037] (Example 5) An oxide nanocomposite powder was prepared in the same manner as in Example 1, except that the amount of cerium nitrate solution was changed to 40.00 g, the amount of zirconium nitrate solution to 136.89 g, the amount of lanthanum nitrate hexahydrate to 7.02 g, the amount of yttrium nitrate tetrahydrate to 5.16 g, the amount of aluminum nitrate to 300.22 g, and the amount of aqueous ammonia to 248.27 g. Furthermore, a Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO ２ / ZrO ２ / La ２ O ３ / Y ２ O ３ / Al ２ O ３ The ratios were 14.0 / 30.8 / 3.3 / 1.9 / 50.0 (mass ratio).

[0038] (Comparative Example 1) An oxide nanocomposite powder was prepared in the same manner as in Example 1, except that the amount of cerium nitrate solution was changed to 74.77 g, the amount of zirconium nitrate solution to 641.33 g, the amount of lanthanum nitrate hexahydrate to 23.58 g, the amount of yttrium nitrate tetrahydrate to 29.44 g, the amount of aluminum nitrate to 153.21 g, and the amount of aqueous ammonia to 315.10 g. Furthermore, a Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO ２ / ZrO ２ / La ２ O ３ / Y ２ O ３ / Al ２ O ３ The ratios were 12.0 / 66.0 / 5.0 / 5.0 / 11.9 (mass ratio).

[0039] (Comparative Example 2) An oxide nanocomposite powder was prepared in the same manner as in Example 1, except that the amount of cerium nitrate solution was changed to 40.00 g, the amount of zirconium nitrate solution to 280.00 g, the amount of lanthanum nitrate hexahydrate to 2.77 g, the amount of yttrium nitrate tetrahydrate to 18.18 g, the amount of aluminum nitrate to 90.07 g, and the amount of aqueous ammonia to 153.74 g. Furthermore, a Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO ２ / ZrO ２ / La ２ O ３ / Y ２ O ３ / Al ２ O ３ The ratios were 14.0 / 63.0 / 1.3 / 6.7 / 15.0 (mass ratio).

[0040] (Comparative Example 3) An oxide nanocomposite powder was prepared in the same manner as in Example 1, except that the amount of cerium nitrate solution was changed to 54.06 g, the amount of zirconium nitrate solution to 120.27 g, the amount of lanthanum nitrate hexahydrate to 10.39 g, the amount of yttrium nitrate tetrahydrate to 6.13 g, the amount of aluminum nitrate to 486.17 g, and the amount of aqueous ammonia to 377.32 g. Furthermore, a Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO ２ / ZrO ２ / La ２ O ３ / Y ２ O ３ / Al ２ O ３ The ratios were 13.9 / 20.0 / 3.6 / 1.7 / 60.8 (mass ratio).

[0041] <Heat Resistance Test> 2.0 g of the Rh-supported pellet catalyst obtained in the examples and comparative examples was packed into a quartz reaction tube with an inner diameter of 7 mm and mounted in a tubular endurance furnace. A rich gas [H] was introduced at a flow rate of 500 ml / min. ２ (2vol%)+CO ２ (10vol%)+H ２ O (3 vol%) + N ２ (Remaining) and lean gas [O ２ (1vol%)+CO ２ (10vol%)+H ２ O (3 vol%) + N ２ A heat resistance test was conducted by heating the pellet catalyst at 1050°C for 5 hours while alternately circulating the remaining material for 5 minutes.

[0042] <Specific Surface Area Measurement> After the heat resistance test, the Rh-supported pellet catalyst was placed in a fully automatic specific surface area measuring device (Micro-Data Co., Ltd. "MODEL-4232III") and pre-treated in air at 250°C for 20 minutes. After that, N ２ A mixed gas of (30%) / He(70%) was passed through the catalyst, and the amount of nitrogen adsorbed at liquid nitrogen temperature (-196°C) was measured. The BET specific surface area of ​​the pellet catalyst was then determined from the obtained nitrogen adsorbed amount using the BET single-point method. The results are shown in Table 1.

[0043] <Oxygen Saturation / Release Performance (OSC)> 0.5 g of Rh-supported pellet catalyst, after heat resistance testing, was packed into a sample holder with an inner diameter of 11 mm and mounted in a fixed-bed flow-type catalyst activity evaluation apparatus (CATA-50000-SP7, manufactured by Best Measuring Instruments Co., Ltd.). This pellet catalyst was subjected to CO gas [CO(2 vol%) + N] at a temperature of 450°C and a flow rate of 15 L / min. ２ (Remaining) and O ２ gas [O ２ (1 vol%) + N ２ (Remaining) ) and were introduced alternately for 180 seconds. CO generated during the third introduction of CO gas. ２ The amount of oxygen produced was measured, and the amount of oxygen absorbed and released (OSC) was calculated. The results are shown in Table 1.

[0044] <Catalyst Activity> 0.5 g of Rh-supported pellet catalyst, after heat resistance testing, was packed into a sample holder with an inner diameter of 11 mm and mounted on a fixed-bed flow-type catalyst activity evaluation apparatus (CATA-50000-SP7, manufactured by Best Measuring Instruments Co., Ltd.). Stoichiometric gas [CO (0.65 vol%) + O ２ (0.675vol%)+C ３ H ６ (0.3vol%) + NO (0.2vol%) + CO ２ (10vol%)+H ２ O (3 vol%) + N ２ While introducing the remaining solution at a flow rate of 15 L / min, the pellet catalyst was heated from 100°C to 500°C, and the NO concentration at each temperature was measured to determine the NO purification rate. Table 1 shows the temperature T at which the NO purification rate reached 50%. ＮＯ５０ This indicates.

[0045] <X-ray Diffraction (XRD) Measurement> The oxide nanocomposite powders prepared in the examples and comparative examples were heat-treated in air at 1100°C for 5 hours. The heat-treated oxide nanocomposite powder was set in a horizontal sample type multi-purpose X-ray diffractometer (Rigaku Corporation "Ultima IV"), and the X-ray diffraction pattern in the range of 2θ = 10° to 80° was measured using CuKα rays as the X-ray source under the conditions of voltage 40kV, current 40mA, scan speed 10° / min, and sampling width 0.05°. The obtained X-ray diffraction pattern was subjected to crystal structure analysis using powder XRD analysis software (Lightstone Corporation "JADE9"), and the CeO2 after the heat treatment was analyzed. ２ and ZrO ２ The diffraction pattern of the solid solution (CZ solid solution) around 2θ = 34.5° was obtained. The results are shown in Figures 1 to 8. Furthermore, Table 1 shows the peak positions in the X-ray diffraction pattern of the CZ solid solution after heat treatment around 2θ = 34.5°.

[0046] As shown in Figures 1 to 5, Al ２ O ３ , CEO ２ , ZrO ２ La ２ O ３ and Y ２ O ３ The CZ solid solutions of the oxide nanocomposite powders (Examples 1-5) containing a predetermined amount of [Ce / (Ce+Zr)] and having a molar ratio [Ce / (Ce+Zr)] within a predetermined range, after heat treatment, showed only one diffraction peak in the X-ray diffraction pattern around 2θ = 34.5°, and were attributed to a cubic crystal structure.

[0047] On the other hand, as shown in Figures 6 to 8, at least Al ２ O ３ and ZrO ２ The CZ solid solutions of oxide nanocomposite powders (Comparative Examples 1-3) whose content was not within the predetermined range, after the heat treatment, showed two diffraction peaks in the X-ray diffraction pattern around 2θ = 34.5°, and were attributed to a tetragonal crystal structure.

[0048]

[0049] Based on the results shown in Table 1, the temperature T when the oxygen absorption / release rate (OSC) and NO purification rate reached 50% ＮＯ５０ And the BET specific surface area, Al ２ O ３ , CEO ２ , ZrO ２ La ２ O ３ and Y ２ O ３ The content and molar ratio [Ce / (Ce+Zr)] were plotted against each other. These results are shown in Figures 9 to 26. In addition, the oxygen absorption / release rate (OSC amount) and the temperature T when the NO purification rate reached 50% were plotted. ＮＯ５０ The values ​​were plotted against the BET specific surface area. The results are shown in Figures 27 and 28.

[0050] As shown in Figures 9 and 15, Al ２ O ３ and ZrO ２ It was found that exhaust gas purification catalysts with a content within a predetermined range exhibited excellent oxygen storage capacity after exposure to high temperatures (Examples 1-5). This is because Al ２ O ３ and ZrO ２ When the content of is within a predetermined range, as shown in Figures 1 to 5, the CZ solid solution after exposure to high temperature has one diffraction peak in the X-ray diffraction pattern around 2θ = 34.5° and is attributed to a cubic crystal, which suggests that the CZ solid solution had excellent heat resistance. On the other hand, Al ２ O ３ If the content exceeds a predetermined range, ２ It was found that when the content of falls below a predetermined range, the oxygen storage capacity decreases after exposure to high temperatures (Comparative Example 3). This is because Al ２ O ３ The content of ZrO becomes too high, ２ When the content of becomes too low, as shown in Figure 8, the CZ solid solution after exposure to high temperature exhibits two diffraction peaks in the X-ray diffraction pattern around 2θ = 34.5° and is attributed to a tetragonal crystal structure. This suggests that the heat resistance of the CZ solid solution of Comparative Example 3 is lower than that of Examples 1 to 5.

[0051] As shown in Figures 10 and 16, Al ２ O３ and ZrO ２ It was found that exhaust gas purification catalysts with a content within a predetermined range exhibited excellent NOx purification performance at low temperatures after exposure to high temperatures (Examples 1-5). This is because Al ２ O ３ and ZrO ２ When the content of is within a predetermined range, the specific surface area after exposure to high temperature is large (Examples 1-5), as shown in Figures 11 and 17, which is thought to be because Rh sintering is suppressed. On the other hand, ZrO ２ If the content exceeds a predetermined range, ２ O ３ It was found that when the content of ZrO falls below a predetermined range, the NOx purification performance at low temperatures after exposure to high temperatures decreases (Comparative Examples 1-2). ２ The content of Al becomes too high, ２ O ３ When the content of Rh becomes too low, the specific surface area after the heat resistance test is small (Comparative Examples 1-2), as shown in Figures 11 and 17, which is thought to be due to Rh sintering.

[0052] As shown in Figure 19, La ２ O ３ It was found that exhaust gas purification catalysts with a content within a predetermined range exhibited excellent NOx purification performance at low temperatures after exposure to high temperatures (Examples 1-5 and Comparative Example 3). On the other hand, La ２ O ３ It was found that when the content of [the substance] falls below a predetermined range, or exceeds a predetermined range, the NOx purification performance at low temperatures after exposure to high temperatures decreases (Comparative Examples 1-2).

[0053] As shown in Figure 21, Y ２ O ３ It was found that exhaust gas purification catalysts with a content within a predetermined range exhibited excellent oxygen storage capacity after exposure to high temperatures (Examples 1-5). On the other hand, Y ２ O ３ It was found that when the content of falls below a predetermined range, the oxygen storage capacity decreases after exposure to high temperatures (Comparative Example 3).

[0054] As shown in Figure 22, Y ２ O ３It was found that exhaust gas purification catalysts with a content within a predetermined range exhibited excellent NOx purification performance at low temperatures after exposure to high temperatures (Examples 1-5). On the other hand, Y ２ O ３ It was found that when the content of exceeds a predetermined range, the NOx purification performance at low temperatures after exposure to high temperatures decreases (Comparative Examples 1-2).

[0055] As shown in Figure 23, Y ２ O ３ It was found that exhaust gas purification catalysts with a content within a predetermined range have a large specific surface area after exposure to high temperatures (Examples 1-5). On the other hand, Y ２ O ３ It was found that when the content of [substance] falls below a predetermined range, or exceeds a predetermined range, the specific surface area after exposure to high temperature is small (Comparative Examples 1 and 3).

[0056] As shown in Figure 24, exhaust gas purification catalysts with a molar ratio [Ce / (Ce+Zr)] within a predetermined range were found to have excellent oxygen storage capacity after exposure to high temperatures (Examples 1-5). On the other hand, when the molar ratio [Ce / (Ce+Zr)] exceeded the predetermined range, it was found that the oxygen storage capacity after exposure to high temperatures decreased (Comparative Example 3).

[0057] As shown in Figure 25, exhaust gas purification catalysts with a molar ratio [Ce / (Ce+Zr)] within a predetermined range were found to exhibit excellent NOx purification performance at low temperatures after exposure to high temperatures (Examples 1-5). On the other hand, when the molar ratio [Ce / (Ce+Zr)] fell below the predetermined range, it was found that the NOx purification performance at low temperatures after exposure to high temperatures decreased (Comparative Examples 1-2).

[0058] As shown in Figure 26, exhaust gas purification catalysts with a molar ratio [Ce / (Ce+Zr)] within a predetermined range were found to have a large specific surface area after exposure to high temperatures (Examples 1-5). On the other hand, when the molar ratio [Ce / (Ce+Zr)] fell below or exceeded the predetermined range, the specific surface area after exposure to high temperatures was found to be small (Comparative Examples 1 and 3).

[0059] As shown in Figures 27 to 28, exhaust gas purification catalysts whose specific surface area after exposure to high temperatures is within a predetermined range were found to have excellent oxygen storage capacity after exposure to high temperatures and NOx purification performance at low temperatures (Examples 1 to 5). On the other hand, when the specific surface area after exposure to high temperatures falls below a predetermined range, it was found that at least one of the oxygen storage capacity after exposure to high temperatures and NOx purification performance at low temperatures decreases (Comparative Examples 1 and 3).

[0060] As described above, the present invention makes it possible to obtain an Rh-supported exhaust gas purification catalyst that exhibits excellent purification performance (particularly transient purification performance and low-temperature purification performance) even after exposure to high temperatures. Therefore, the exhaust gas purification catalyst of the present invention is useful as a catalyst for removing harmful components such as hydrocarbons (HC) and nitrogen oxides (NOx) contained in exhaust gas from internal combustion engines such as automobile engines, as it exhibits excellent purification performance even after exposure to high temperatures and at low temperatures such as during the startup of internal combustion engines such as automobile engines.

Claims

1. Al ２ O ３ is contained in a content of 16 to 60% by mass, CeO ２ is contained in a content of 5 to 19% by mass, ZrO ２ is contained in a content of 21 to 62% by mass, La ２ O ３ is contained in a content of 1.4 to 4.9% by mass, and Y ２ O ３ is contained in a content of 1.6 to 6.6% by mass, the molar ratio of Ce to the total amount of Ce and Zr [Ce / (Ce + Zr)] is 0.12 to 0.33, at least a part of CeO ２ and ZrO ２ forms a solid solution, and the solid solution after heat treatment at 1100 °C for 5 hours in the atmosphere shows an X-ray diffraction pattern attributed to cubic crystals, an oxide nanocomposite.

2. Al ２ O ３ The content is 20-55% by mass, and CeO ２ The content is 10 to 19% by mass, and ZrO ２ The content is 25 to 55% by mass, and La ２ O ３ The content is 2.0 to 4.9% by mass, Y ２ O ３ The oxide nanocomposite according to claim 1, wherein the content of is 1.8 to 4.9% by mass, and the molar ratio [Ce / (Ce+Zr)] is 0.16 to 0.

30.

3. Al ２ O ３ The content is 28-52% by mass, and CeO ２ The content is 14-19% by mass, and ZrO ２ The content is 28-48% by mass, and La ２ O ３ The content is 2.8 to 4.9% by mass, Y ２ O ３ The oxide nanocomposite according to claim 2, wherein the content of is 1.8 to 4.0% by mass, and the molar ratio [Ce / (Ce+Zr)] is 0.18 to 0.

27.

4. An exhaust gas purification catalyst comprising an oxide nanocomposite according to any one of claims 1 to 3 and Rh supported on the oxide nanocomposite.

5. BET specific surface area is 15 m² ２ The exhaust gas purification catalyst according to claim 4, wherein the amount is 1 / g or more.

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