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

Abstract

To provide a Rh-supported exhaust gas purification catalyst that exhibits excellent purification performance (particularly, transient purification performance and low-temperature purification performance) even after being exposed to high temperatures, and an oxide nanocomposite used as a catalyst carrier therefor. 【Solution】Containing Al2O3 at a content of 16 to 60% by mass, CeO2 at a content of 5 to 19% by mass, ZrO2 at a content of 21 to 62% by mass, La2O3 at a content of 1.4 to 4.9% by mass, and Y2O3 at 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)] being 0.12 to 0.33, At least a part of CeO2 and ZrO2 forming a solid solution, The solid solution after heat treatment at 1100°C for 5 hours in the atmosphere showing an X-ray diffraction pattern attributable to a cubic crystal Characterized by an oxide nanocomposite, and An exhaust gas purification catalyst characterized by containing the oxide nanocomposite and Rh supported on the oxide nanocomposite.

Description

Technical Field

[0001] The present invention relates to an oxide nanocomposite and an exhaust gas purification three-way catalyst containing the same, and more particularly to an oxide nanocomposite containing Al2O3, CeO2 and ZrO2 and an exhaust gas purification three-way catalyst containing the same.

Background Art

[0002] Conventionally, as a purification catalyst for exhaust gas of internal combustion engines such as automobile engines, a catalyst containing alumina, zirconia and ceria is known. As such an exhaust gas purification catalyst, for example, in Japanese Patent Application Laid-Open No. 2013-193042 (Patent Document 1), alumina, ceria and zirconia, and a first additive element oxide and a second additive element oxide composed of two kinds of 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, and in the composite oxide carrier, an exhaust gas purification catalyst in which alumina is contained in the range of 30 to 40% by mass and zirconia is contained in the range of 36 to 46% by mass is disclosed. Further, Japanese Patent Application Laid-Open No. 2018-8255 (Patent Document 2) discloses an exhaust gas purification catalyst including a catalyst carrier made of a composite metal oxide porous body containing alumina, ceria and zirconia and further containing lanthanum and yttrium, and a noble metal supported on the catalyst carrier.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in recent years, exhaust gas regulations have been strengthened under European Euro 7, U.S. Environmental Protection Agency (EPA) Tier 4, and Chinese 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] This invention has been made in view of the problems of the above-mentioned prior art, and aims to provide an 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. [Means for solving the problem]

[0006] The present inventors, through diligent research to achieve the above objectives, have discovered that in an exhaust gas purification catalyst in which Rh is supported on an oxide nanocomposite containing Al2O3, CeO2, ZrO2, La2O3, and Y2O3, by reducing the amount of CeO2 and increasing the amount of Al2O3 to the extent that the amount of ZrO2 does not decrease too much, and by keeping the content of Al2O3, CeO2, ZrO2, La2O3, and Y2O3, as well as the molar ratio of Ce to the total amount of Ce and Zr, within a specific range, an Rh-supported exhaust gas purification catalyst with excellent transient and low-temperature purification performance even after exposure to high temperatures can be obtained, thus completing the present invention.

[0007] In other words, the present invention provides the following embodiments. [1] Al2O3 is contained in an amount of 16 to 60% by mass. CeO2 is contained in a content of 5-19% by mass. ZrO2 is contained in an amount of 21-62% by mass. La2O3 is contained in an amount of 1.4 to 4.9% by mass, and It contains Y2O3 in an amount of 1.6 to 6.6% by mass. The molar ratio of Ce to the total amount of Zr [Ce / (Ce+Zr)] is between 0.12 and 0.33. At least a portion of CeO2 and ZrO2 forms a solid solution. An oxide nanocomposite exhibiting an X-ray diffraction pattern that attributes the solid solution to a cubic crystal structure after heat treatment at 1100°C for 5 hours in air. [2] The Al2O3 content is 20-55% by mass, The CeO2 content is 10-19% by mass. The ZrO2 content is 25-55% by mass. The La2O3 content is 2.0 to 4.9% by mass. The Y2O3 content is 1.8 to 4.9% by mass. The oxide nanocomposite described in [1], wherein the molar ratio [Ce / (Ce+Zr)] is 0.16 to 0.30. [3] The Al2O3 content is 28-52% by mass, The CeO2 content is 14-19% by mass. The ZrO2 content is 28-48% by mass. The La2O3 content is 2.8-4.9% by mass. The Y2O3 content is 1.8 to 4.0% by mass. The oxide nanocomposite described in [2], having a molar ratio [Ce / (Ce+Zr)] of 0.18 to 0.27. An exhaust gas purification catalyst comprising an oxide nanocomposite described in any one of [4][1] to [3] and Rh supported on the oxide nanocomposite. [5] BET specific surface area is 15m 2 The exhaust gas purification catalyst described in [4] is 1 / g or more.

[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. To exhibit excellent oxygen storage capacity in an exhaust gas purification catalyst, it is necessary to include a solid solution of CeO2 and ZrO2 (CZ solid solution). However, when a CZ solid solution is included in an exhaust gas purification catalyst supporting Rh, CeO2 shows a strong interaction with Rh, inhibiting the metallization of Rh and reducing the catalytic activity of Rh, especially at low temperatures. Therefore, 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 this invention, the amount of Al2O3 is increased to the extent that the amount of ZrO2 is not reduced too much, forming an oxide nanocomposite of Al2O3 and CZ solid solution. In this oxide nanocomposite, the surface concentration of Ce is reduced by increasing the amount of Al2O3, so it is presumed that the interaction between Rh and CeO2 is suppressed, inhibiting the metallation of Rh is suppressed, and the catalytic activity of Rh at low temperatures is improved. Furthermore, since the amount of Al2O3 is increased to the extent that the amount of ZrO2 is not reduced too much, a sufficient amount of CZ solid solution is formed, which is presumed to improve oxygen storage capacity and transient purification performance. Moreover, since the amount of Al2O3 is increased to the extent that the amount of ZrO2 is not reduced too much, that is, the amount of ZrO2 is appropriate, the heat resistance of the CZ solid solution is maintained, so it is presumed that it exhibits excellent transient purification performance and low-temperature purification performance even after exposure to high temperatures. [Effects of the Invention]

[0011] According to the present invention, it is 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, and an oxide nanocomposite used as a catalyst support therefor. [Brief explanation of the drawing]

[0012] [Figure 1]It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 1. [Figure 2] It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 2. [Figure 3] It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 3. [Figure 4] It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 4. [Figure 5] It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Example 5. [Figure 6] It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Comparative Example 1. [Figure 7] It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Comparative Example 2. [Figure 8] It is a graph showing the X-ray diffraction pattern near 2θ = 34.5° of the CZ solid solution after heat treatment of the oxide nanocomposite powder prepared in Comparative Example 3. [Figure 9] It is a graph showing the relationship between the oxygen storage capacity and the Al2O3 content of the exhaust gas purification catalyst after being exposed to high temperature. [Figure 10] It is a graph showing the relationship between the NOx purification performance and the Al2O3 content of the exhaust gas purification catalyst after being exposed to high temperature. [Figure 11] It is a graph showing the relationship between the specific surface area and the Al2O3 content of the exhaust gas purification catalyst after being exposed to high temperature. [Figure 12] It is a graph showing the relationship between the oxygen storage capacity and the CeO2 content of the exhaust gas purification catalyst after being exposed to high temperature. [Figure 13]This graph shows the relationship between the NOx purification performance of an exhaust gas purification catalyst after exposure to high temperatures and its CeO2 content. [Figure 14] This graph shows the relationship between the specific surface area and CeO2 content of an exhaust gas purification catalyst after exposure to high temperatures. [Figure 15] This graph shows the relationship between the oxygen storage capacity of an exhaust gas purification catalyst after exposure to high temperatures and its ZrO2 content. [Figure 16] This graph shows the relationship between the NOx purification performance of an exhaust gas purification catalyst after exposure to high temperatures and its ZrO2 content. [Figure 17] This graph shows the relationship between the specific surface area of ​​an exhaust gas purification catalyst after exposure to high temperatures and its ZrO2 content. [Figure 18] This graph shows the relationship between the oxygen storage capacity of an exhaust gas purification catalyst after exposure to high temperatures and its La2O3 content. [Figure 19] This graph shows the relationship between the NOx purification performance of an exhaust gas purification catalyst after exposure to high temperatures and its La2O3 content. [Figure 20] This graph shows the relationship between the specific surface area of ​​an exhaust gas purification catalyst after exposure to high temperatures and its La2O3 content. [Figure 21] This graph shows the relationship between the oxygen storage capacity of an exhaust gas purification catalyst after exposure to high temperatures and its Y2O3 content. [Figure 22] This graph shows the relationship between the NOx purification performance of an exhaust gas purification catalyst after exposure to high temperatures and its Y2O3 content. [Figure 23] This graph shows the relationship between the specific surface area of ​​an exhaust gas purification catalyst after exposure to high temperatures and its Y2O3 content. [Figure 24] This graph shows the relationship between the oxygen storage capacity of an exhaust gas purification catalyst after exposure to high temperatures and its molar ratio [Ce / (Ce+Zr)]. [Figure 25] This graph shows the relationship between the NOx purification performance of an exhaust gas purification catalyst after exposure to high temperatures and its molar ratio [Ce / (Ce+Zr)]. [Figure 26] This graph shows the relationship between the specific surface area and molar ratio [Ce / (Ce+Zr)] of an exhaust gas purification catalyst after exposure to high temperatures. [Figure 27] This graph shows the relationship between the oxygen storage capacity and specific surface area of ​​an exhaust gas purification catalyst after exposure to high temperatures. [Figure 28] This graph shows the relationship between the NOx purification performance and specific surface area of ​​an exhaust gas purification catalyst after exposure to high temperatures. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below with reference to its preferred embodiments.

[0014] [Oxide nanocomposites] The oxide nanocomposite of the present invention will now be described. The oxide nanocomposite of the present invention contains Al2O3, CeO2, ZrO2, La2O3, and Y2O3. There are no particular restrictions on Al2O3, CeO2, ZrO2, La2O3, and Y2O3, and conventionally known materials can be used.

[0015] The Al2O3 content is 16 to 60% by mass, preferably 20 to 55% by mass, more preferably 25 to 53% by mass, and even more preferably 28 to 52% by mass. If the Al2O3 content falls below the lower limit, the low-temperature purification performance of the resulting exhaust gas purification catalyst 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. On the other hand, if the Al2O3 content exceeds the upper 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.

[0016] The CeO2 content is 5 to 19% by mass, preferably 10 to 19% by mass, more preferably 13 to 19% by mass, and even more preferably 14 to 19% by mass, from the viewpoint of the oxygen storage capacity, transient purification performance, and low-temperature purification performance of the resulting exhaust gas purification catalyst after exposure to high temperatures.

[0017] The ZrO2 content is 21 to 62% by mass, preferably 25 to 55% by mass, more preferably 27 to 50% by mass, and even more preferably 28 to 48% by mass. If the ZrO2 content falls below the lower limit, the oxygen storage capacity of the resulting exhaust gas purification catalyst after high-temperature exposure tends to decrease, 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, if the ZrO2 content exceeds the upper limit, the purification performance 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] The La2O3 content is preferably 1.4 to 4.9% by mass, more 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 high-temperature exposure.

[0019] The Y2O3 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. If the Y2O3 content falls below the lower limit, the oxygen storage capacity of the resulting exhaust gas purification catalyst after high-temperature exposure tends to decrease, 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, if the Y2O3 content exceeds the upper limit, the purification performance 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 between 0.12 and 0.33, preferably between 0.16 and 0.30, more preferably between 0.17 and 0.28, and even more preferably between 0.18 and 0.27. When the molar ratio [Ce / (Ce+Zr)] falls below the lower limit, the low-temperature purification performance of the resulting exhaust gas purification catalyst 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. On the other hand, when 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 described above, at least a portion of CeO2 and ZrO2 forms a solid solution (CZ solid solution), and the CZ solid solution, after heat treatment in air at 1100°C for 5 hours, 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 can be manufactured by setting the content of Al2O3 and ZrO2 within the above-mentioned range (preferably, further, the content of CeO2, La2O3, and Y2O3 and the molar ratio [Ce / (Ce+Zr)] within the above-mentioned range). On the other hand, in oxide nanocomposites that do not satisfy the aforementioned 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, one method is to first prepare 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 so that the content of Al2O3, CeO2, ZrO2, La2O3, and Y2O3 in the resulting oxide nanocomposite and the molar ratio [Ce / (Ce+Zr)] are within a predetermined range, then mix 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 calcine 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, transient purification performance, and purification performance at low temperatures, the BET specific surface area after a heat resistance test in which rich gas [H2 (2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (remaining)] and lean gas [O2 (1 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (remaining)] are alternately flowed for 5 minutes while heating at 1050°C for 5 hours is 15 m². 2 It is preferable that it is 18m or more / g 2 It is more preferable that it be 20m or more per g. 2 It is even more preferable that the amount is 1 / g or more. Furthermore, an exhaust gas purification catalyst in which the BET specific surface area after the heat resistance test is within the above range can be manufactured by setting the content of Al2O3 and ZrO2 to at least within the above range (preferably, further, the content of CeO2, La2O3 and Y2O3 and the molar ratio [Ce / (Ce+Zr)] to within the above range).

[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. [Examples]

[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 neutralization 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 to determine the ratio of CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 17.6 / 46.6 / 2.9 / 2.8 / 30.1 (by mass).

[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 press-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, an Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 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, an Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 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, an Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 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, an Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 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, an Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 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, an Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 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, an Rh-supported pellet catalyst with a particle size of 0.5 to 1 mm was prepared. The composition of the oxide nanocomposite powder was CeO2 / ZrO2 / La2O3 / Y2O3 / Al2O3 = 13.9 / 20.0 / 3.6 / 1.7 / 60.8 (mass ratio).

[0041] <Heat resistance test> A heat resistance test was conducted by heating the pellet catalyst at 1050°C for 5 hours while alternately flowing rich gas [H2 (2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (remainder)] and lean gas [O2 (1 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (remainder)] at a flow rate of 500 ml / min for 5 minutes.

[0042] <Specific surface area measurement> The Rh-supported pellet catalyst, after the heat resistance test, was placed in a fully automatic specific surface area measuring device (Micro-Data Corporation, "MODEL-4232III") and pre-treated in air at 250°C for 20 minutes. Subsequently, a mixed gas of N2 (30%) / He (70%) was passed through it, 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 absorption / release capacity (OSC)> 0.5 g of the Rh-supported pellet catalyst after the heat resistance test was filled into a sample holder with an inner diameter of 11 mm and installed in a fixed-bed flow-type catalyst activity evaluation apparatus ("CATA-50000-SP7" manufactured by Best Measuring Instruments Co., Ltd.). CO gas [CO (2 vol%) + N2 (the rest)] and O2 gas [O2 (1 vol%) + N2 (the rest)] were alternately introduced into this pellet catalyst for 180 seconds at a temperature of 450 °C and a flow rate of 15 L / min. The amount of CO2 generated during the third introduction of CO gas was measured, and the oxygen storage capacity (OSC amount) was calculated. The results are shown in Table 1.

[0044] <Catalytic activity> 0.5 g of the Rh-supported pellet catalyst after the heat resistance test was filled into a sample holder with an inner diameter of 11 mm and installed in a fixed-bed flow-type catalyst activity evaluation apparatus ("CATA-50000-SP7" manufactured by Best Measuring Instruments Co., Ltd.). While introducing the stoichiometric gas [CO (0.65 vol%) + O2 (0.675 vol%) + C3H6 (0.3 vol%) + NO (0.2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (the rest)] at a flow rate of 15 L / min, the temperature of the pellet catalyst was raised 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 NO50 when the NO purification rate reached 50%.

[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 powders were placed in a horizontal sample type multi-purpose X-ray diffractometer (Ultima IV, Rigaku Corporation), 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 patterns were subjected to crystal structure analysis using powder XRD analysis software (JADE9, Lightstone Corporation), and the diffraction pattern around 2θ = 34.5° of the solid solution of CeO2 and ZrO2 (CZ solid solution) after the heat treatment was obtained. The results are shown in Figures 1 to 8. Furthermore, the peak positions in the X-ray diffraction pattern of the heat-treated CZ solid solution around 2θ = 34.5° are shown in Table 1.

[0046] As shown in Figures 1 to 5, the CZ solid solutions of oxide nanocomposite powders (Examples 1 to 5) containing Al2O3, CeO2, ZrO2, La2O3, and Y2O3 in predetermined amounts, with 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°, indicating that they belonged to a cubic crystal structure.

[0047] On the other hand, as shown in Figures 6 to 8, the CZ solid solutions after heat treatment of oxide nanocomposite powders (Comparative Examples 1 to 3) in which the content of at least Al2O3 and ZrO2 was not within the predetermined range showed two diffraction peaks in the X-ray diffraction pattern around 2θ = 34.5°, and were attributed to a tetragonal crystal structure.

[0048] [Table 1]

[0049] Based on the results shown in Table 1, the temperature T at which the oxygen absorption / desorption rate (OSC) and NO purification rate reached 50% was determined. NO50The BET specific surface area was plotted against the content and molar ratio [Ce / (Ce+Zr)] of Al2O3, CeO2, ZrO2, La2O3, and Y2O3. The results are shown in Figures 9 to 26. In addition, the oxygen absorption / desorption rate (OSC) and the temperature T at which 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, exhaust gas purification catalysts with Al2O3 and ZrO2 content within predetermined ranges exhibited excellent oxygen storage capacity after exposure to high temperatures (Examples 1-5). This is because, when the Al2O3 and ZrO2 content was within the predetermined range, as shown in Figures 1-5, the CZ solid solution after exposure to high temperatures had a single diffraction peak in the X-ray diffraction pattern around 2θ = 34.5° and was attributed to a cubic crystal structure, suggesting that the CZ solid solution had excellent heat resistance. On the other hand, when the Al2O3 content exceeded the predetermined range and the ZrO2 content fell below the predetermined range, the oxygen storage capacity after exposure to high temperatures decreased (Comparative Example 3). This is thought to be because, when the Al2O3 content becomes too high and the ZrO2 content becomes too low, the CZ solid solution exposed to high temperatures exhibits two diffraction peaks in the X-ray diffraction pattern around 2θ = 34.5°, as shown in Figure 8, and is attributed to a tetragonal crystal structure. Therefore, 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, exhaust gas purification catalysts with Al2O3 and ZrO2 content within predetermined ranges exhibited excellent NOx purification performance at low temperatures after exposure to high temperatures (Examples 1-5). This is thought to be because, when the Al2O3 and ZrO2 content is within the predetermined range, the specific surface area after exposure to high temperatures is large (Examples 1-5), as shown in Figures 11 and 17, and Rh sintering is suppressed. On the other hand, when the ZrO2 content exceeds the predetermined range and the Al2O3 content falls below the predetermined range, the NOx purification performance at low temperatures after exposure to high temperatures decreases (Comparative Examples 1-2). This is thought to be because, when the ZrO2 content is too high and the Al2O3 content is too low, the specific surface area after the heat resistance test is small (Comparative Examples 1-2), as shown in Figures 11 and 17, and Rh sintering occurs.

[0052] As shown in Figure 19, exhaust gas purification catalysts with a La2O3 content within a predetermined range were found to exhibit excellent NOx purification performance at low temperatures after exposure to high temperatures (Examples 1-5 and Comparative Example 3). On the other hand, when the La2O3 content fell below or exceeded the predetermined range, the NOx purification performance at low temperatures after exposure to high temperatures decreased (Comparative Examples 1-2).

[0053] As shown in Figure 21, exhaust gas purification catalysts with a Y2O3 content 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 Y2O3 content fell below the predetermined range, it was found that the oxygen storage capacity after exposure to high temperatures decreased (Comparative Example 3).

[0054] As shown in Figure 22, exhaust gas purification catalysts with a Y2O3 content 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 Y2O3 content exceeded the predetermined range, it was found that the NOx purification performance at low temperatures after exposure to high temperatures decreased (Comparative Examples 1-2).

[0055] As shown in Figure 23, exhaust gas purification catalysts with a Y2O3 content 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 Y2O3 content 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).

[0056] As shown in Figure 24, exhaust gas purification catalysts with a molar ratio [Ce / (Ce+Zr)] within a predetermined range were found to exhibit superior oxygen storage capacity after exposure to high temperatures (Examples 1-5). On the other hand, when the molar ratio [Ce / (Ce+Zr)] exceeded a predetermined range, 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 a 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 exhibit excellent oxygen storage capacity after exposure to high temperatures and NOx purification performance at low temperatures (Examples 1 to 5). On the other hand, it was found that when the specific surface area after exposure to high temperatures falls below a predetermined range, 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). [Industrial applicability]

[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 In a content of 16 to 60% by mass, CEO ２ In a content of 5 to 19% by mass, ZrO ２ In a content of 21 to 62% by mass, La ２ O ３ The content of 1.4 to 4.9% by mass, and Y ２ O ３ It contains in an amount of 1.6 to 6.6% by mass, The molar ratio of Ce to the total amount of Zr [Ce / (Ce+Zr)] is between 0.12 and 0.

33. CeO ２ and ZrO ２ at least a part of which forms a solid solution, The X-ray diffraction pattern of the solid solution after heat treatment at 1100°C for 5 hours in air indicates that it belongs to a cubic crystal structure. A characteristic oxide nanocomposite.

2. Al ２ O ３ The content is 20 to 55% by mass, CEO ２ The content is 10 to 19% by mass, ZrO ２ The content is 25 to 55% by mass, La ２ O ３ The content is 2.0 to 4.9% by mass, Y ２ O ３ The content is 1.8 to 4.9% by mass, The molar ratio [Ce / (Ce+Zr)] is between 0.16 and 0.

30. The oxide nanocomposite according to feature 1.

3. Al ２ O ３ The content is 28 to 52% by mass, CEO ２ The content is 14 to 19% by mass, ZrO ２ The content is 28 to 48% by mass, La ２ O ３ The content is 2.8 to 4.9% by mass, Y ２ O ３ The content is 1.8 to 4.0% by mass, The molar ratio [Ce / (Ce+Zr)] is between 0.18 and 0.

27. The oxide nanocomposite according to feature 2.

4. An exhaust gas purification catalyst characterized by containing 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, characterized in that it is 1 / g or more.

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