A composite oxide containing Ce and Zr, and a catalytic composition and catalyst for exhaust gas purification using the composite oxide.

Abstract

To provide a CeO2-ZrO2-based composite oxide with improved OSC, and an exhaust gas purification catalyst composition and an exhaust gas purification catalyst using the composite oxide.SOLUTION: Provided is a composite oxide containing Ce and Zr that has a value of SB / SA of 4.2 or more, which ratio is between the area SA of a peak observed between 1100 cm-1 and 1110 cm-1 and the area SB of a peak observed between 1030 cm-1 and 1100 cm-1, when methanol is adsorbed on the composite oxide in the absence of precious metal elements and the infrared absorption spectrum is measured. Also provided are an exhaust gas purification catalyst composition and an exhaust gas purification catalyst using the composite oxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a composite oxide containing Ce and Zr, and to a catalytic composition for exhaust gas purification and a catalytic catalyst for exhaust gas purification using the composite oxide. [Background technology]

[0002] Exhaust gases emitted from internal combustion engines of automobiles, motorcycles, and other vehicles contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Three-way catalysts are used as exhaust gas purification catalysts to purify and neutralize these harmful components. These catalysts have catalytic activity that oxidizes HC and CO into water and carbon dioxide, and reduces NOx into nitrogen. These three-way catalysts typically contain precious metal elements such as Pt, Pd, and Rh. Pt and Pd are primarily involved in the oxidation and purification of HC and CO, while Rh is primarily involved in the reduction and purification of NOx.

[0003] To mitigate fluctuations in the oxygen concentration of exhaust gas and efficiently purify harmful components such as HC, CO, and NOx, materials with oxygen storage capacity (i.e., the ability to absorb oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low), such as composite oxides containing Ce and Zr (Ce-Zr composite oxides), are used as constituent materials of the three-way catalyst. Hereinafter, oxygen storage capacity will be referred to as "OSC". OSC is an abbreviation for Oxygen Storage Capacity.

[0004] Patent Document 1 describes a method for producing a CeO2-ZrO2-based composite oxide by mixing cerium chloride, zirconium oxychloride, praseodymium chloride, and water, then adding ammonium peroxodisulfate to obtain a slurry containing sulfates, adding ammonia water to the obtained slurry to obtain a slurry containing hydroxides, filtering and washing the obtained slurry to obtain a cake, and then calcining the obtained cake. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-047425 [Overview of the project] [Problems that the invention aims to solve]

[0006] The CeO2-ZrO2 composite oxide obtained by the method described in Patent Document 1 has insufficient OSC (Optical Scaling), therefore, there is a need for a CeO2-ZrO2 composite oxide with improved OSC.

[0007] Therefore, the present invention aims to provide a CeO2-ZrO2-based composite oxide with improved OSC, as well as a catalytic composition for exhaust gas purification and an exhaust gas purification catalyst using the composite oxide. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides the following composite oxide, exhaust gas purification catalyst composition, and exhaust gas purification catalyst. [1] When methanol is adsorbed onto a composite oxide containing Ce and Zr, which does not have a supported noble metal element, and the infrared absorption spectrum is measured, 1100 cm⁻¹ -1 More than 1110cm -1 The area S of the peak observed within the following range A 1030cm -1 More than 1100cm -1 Area S of peaks observed in the range less than B S is the ratio of B / S A A composite oxide in which the value of is 4.2 or higher. A catalyst composition for exhaust gas purification comprising the composite oxide described in [2][1] and a catalytically active component. [3] An exhaust gas purification catalyst comprising a base material and a catalyst layer provided on the base material, wherein the catalyst layer is composed of the exhaust gas purification catalyst composition described in [2]. [Effects of the Invention]

[0009] According to the present invention, a CeO2-ZrO2-based composite oxide with improved OSC, and a catalytic composition for exhaust gas purification and a catalytic catalyst for exhaust gas purification using the composite oxide are provided. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a partial end view showing an exhaust gas purification catalyst according to the first embodiment of the present invention, arranged in the exhaust passage of an internal combustion engine. [Figure 2] Figure 2 is an end view of line AA in Figure 1. [Figure 3] Figure 3 is an enlarged view of the region indicated by the symbol R in Figure 2. [Figure 4] Figure 4 is an end view of line BB in Figure 1. [Figure 5] Figure 5 is an end view (corresponding to Figure 4) of an exhaust gas purification catalyst according to a second embodiment of the present invention. [Figure 6] Figure 6 is a schematic diagram of a hydrothermal synthesis apparatus suitable for producing the composite oxide of the present invention. [Modes for carrying out the invention]

[0011] <<Composite Oxides>> The composite oxides of the present invention will be described below. Unless otherwise specified, "mass%" in the description of the composite oxides of the present invention refers to the mass of the composite oxide.

[0012] The composite oxide of the present invention is a composite oxide containing Ce and Zr (CeO2-ZrO2-based composite oxide).

[0013] The form of the composite oxide of the present invention is, for example, particulate.

[0014] Ce primarily contributes to improving OSC, while Zr primarily contributes to improving heat resistance.

[0015] From the viewpoint of more effectively improving OSC, the amount of Ce in the composite oxide of the present invention, in terms of CeO2, is preferably 5.0% by mass or more and 90% by mass or less, more preferably 10% by mass or more and 80% by mass or less, and even more preferably 10% by mass or more and 70% by mass or less.

[0016] From the viewpoint of more effectively improving heat resistance, the amount of Zr in the composite oxide of the present invention, in terms of ZrO2 equivalent, is preferably 5.0% by mass or more and 90% by mass or less, more preferably 10% by mass or more and 80% by mass or less, and even more preferably 20% by mass or more and 80% by mass or less.

[0017] From the viewpoint of more effectively improving OSC and heat resistance, the total amount of Ce (calculated as CeO2) and Zr (calculated as ZrO2) in the composite oxide of the present invention is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The upper limit is 100% by mass.

[0018] From the viewpoint of balancing OSC and heat resistance, the mass ratio of Zr (in ZrO2 equivalent) to Ce (in CeO2 equivalent) in the composite oxide of the present invention is preferably 0.5 to 10.0, more preferably 0.8 to 8.0, and even more preferably 1.0 to 5.0.

[0019] The composite oxide of the present invention may contain one or more metal elements other than Ce and Zr (hereinafter referred to as "other metal elements").

[0020] Other metallic elements can be selected from, for example, rare earth elements other than Ce, alkaline earth metal elements, etc., but from the viewpoint of forming stable composite oxides with zirconium oxide (ZrO2), it is preferable to select from rare earth elements other than Ce.

[0021] Rare earth elements other than Ce can be selected from, for example, Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. From the viewpoint of easy industrial availability, it is preferable to select from Y, Pr, La, and Nd, and more preferably to select from Pr, La, and Nd.

[0022] When the composite oxide of the present invention contains rare earth elements other than Ce, from the viewpoint of more effectively realizing the improvement of OSC and heat resistance, the amount of the oxide of rare earth elements other than Ce in the composite oxide of the present invention is preferably 1.0% by mass or more and 40% by mass or less, more preferably 1.0% by mass or more and 30% by mass or less, and even more preferably 1.0% by mass or more and 20% by mass or less. The "amount of the oxide of rare earth elements other than Ce" means the amount of the oxide of one kind of rare earth element other than Ce when the composite oxide contains one kind of rare earth element other than Ce, and means the total amount of the oxides of two or more kinds of rare earth elements other than Ce when the composite oxide contains two or more kinds of rare earth elements other than Ce. The "oxide of rare earth elements other than Ce" means sesquioxide (Ln2O3 [where Ln represents a rare earth element]) except for Pr and Tb. The oxide of Pr is Pr6O 11 , and the oxide of Tb means Tb4O7.

[0023] In one embodiment, the composite oxide of the present invention contains one, two, or three kinds of rare earth elements selected from Pr, La, and Nd. When the composite oxide of the present invention contains Pr, from the viewpoint of more effectively realizing the improvement of OSC and heat resistance, Pr6O of Pr in the composite oxide of the present invention 11The converted amount is preferably 1.0% by mass or more and 40% by mass or less, more preferably 1.0% by mass or more and 30% by mass or less, and even more preferably 1.0% by mass or more and 20% by mass or less. When the composite oxide of the present invention contains La, from the viewpoint of more effectively achieving improved OSC and improved heat resistance, the La2O3 equivalent amount of La in the composite oxide of the present invention is preferably 1.0% by mass or more and 40% by mass or less, more preferably 1.0% by mass or more and 30% by mass or less, and even more preferably 1.0% by mass or more and 20% by mass or less. When the composite oxide of the present invention contains Nd, from the viewpoint of more effectively achieving improved OSC and improved heat resistance, the Nd2O3 equivalent amount of Nd in the composite oxide of the present invention is preferably 1.0% by mass or more and 40% by mass or less, more preferably 1.0% by mass or more and 30% by mass or less, and even more preferably 1.0% by mass or more and 20% by mass or less.

[0024] Alkaline earth metal elements can be selected from, for example, Mg, Ca, Sr, Ba, Ra, etc., but from the viewpoint of improving purification performance and OSC performance, it is preferable to select from Sr and Ba.

[0025] When the composite oxide of the present invention contains alkaline earth metal elements, from the viewpoint of improving purification performance and OSC performance, the oxide equivalent amount of alkaline earth metal elements in the composite oxide of the present invention is preferably 1.0% by mass or more and 20% by mass or less. "Oxide equivalent amount of alkaline earth metal elements" means the oxide equivalent amount of one alkaline earth metal element if the composite oxide contains one type of alkaline earth metal element, and the sum of the oxide equivalent amounts of two or more alkaline earth metal elements if the composite oxide contains two or more types of alkaline earth metal elements. Mg oxide means MgO, Ca oxide means CaO, Sr oxide means SrO, Ba oxide means BaO, and Ra oxide means RaO.

[0026] When the composite oxide of the present invention contains rare earth elements other than Ce and alkaline earth metal elements, from the viewpoint of improving purification performance and OSC performance, the total amount of oxide equivalent of rare earth elements other than Ce and the oxide equivalent of alkaline earth metal elements is preferably 2.0% by mass or more and 60% by mass or less, more preferably 2.0% by mass or more and 50% by mass or less, and even more preferably 2.0% by mass or more and 40% by mass or less.

[0027] The oxide-equivalent amount of metal elements contained in the composite oxide of the present invention can be calculated, for example, by measuring the amount of metal elements in the molten material obtained by dissolving the composite oxide of the present invention by alkali melting or the like using a conventional method such as inductively coupled plasma atomic emission spectroscopy (ICP-AES), and then calculating from the measured amount of metal elements.

[0028] In the composite oxide of the present invention, Ce may form a solid solution phase with Zr and O, or form a single phase that is either crystalline or amorphous (for example, a CeO2 phase), or form both a solid solution phase and a single phase, but it is preferable that at least a portion of Ce forms a solid solution phase.

[0029] In the composite oxide of the present invention, Zr may form a solid solution phase with Ce and O, or it may form a single phase that is either crystalline or amorphous (for example, a ZrO2 phase), or it may form both a solid solution phase and a single phase, but it is preferable that at least a portion of Zr forms a solid solution phase.

[0030] In the composite oxide of the present invention, metal elements other than Ce and Zr (for example, rare earth elements other than Ce, alkaline earth metal elements, etc.) may form a solid solution phase together with Ce, Zr and O, or they may form individual phases that are crystalline or amorphous (for example, oxide phases of rare earth elements other than Ce, oxide phases of alkaline earth metal elements, etc.), or they may form both solid solution phases and individual phases, but it is preferable that at least a portion of the metal elements other than Ce and Zr form a solid solution phase.

[0031] The formation of the solid solution phase can be confirmed by conventional methods such as X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX).

[0032] When methanol was adsorbed onto the composite oxide of the present invention, which does not support any precious metal elements, and the infrared absorption spectrum was measured, 1100 cm⁻¹ was observed. -1 More than 1110cm -1 The area S of the peak observed within the following range A 1030cm -1 More than 1100cm -1 Area S of peaks observed in the range less than B S is the ratio of B / S A The value of is preferably 4.2 or higher, more preferably 4.3 or higher, and even more preferably 4.4 or higher. B / S A The upper limit of the value is not particularly limited, but is usually 10.0, preferably 8.0, more preferably 7.5, even more preferably 6.5, and even more preferably 6.0. Each of these upper limits may be combined with any of the lower limits mentioned above.

[0033] According to the first or second method described later, the solid solubility on the surface of the composite oxide can be increased, thereby improving the OSC of the composite oxide, i.e., S B / S A A composite oxide can be manufactured in which the value of is 4.2 or higher.

[0034] S B / S A A value of 4.2 or higher indicates that the composite oxide of the present invention has excellent OSC. The reason for this is presumed to be as follows.

[0035] In composite oxides containing Ce and Zr, there are sites where Ce is coordination-unsaturated (hereinafter referred to as "coordination-unsaturated sites") and sites where Ce is coordination-saturated (hereinafter referred to as "coordination-saturated sites").

[0036] When methanol is adsorbed onto a composite oxide containing Ce and Zr, the methanol adsorption mode for Ce differs depending on the coordination state of Ce in the composite oxide. Furthermore, when the infrared absorption spectrum of the composite oxide after methanol adsorption is measured, multiple peaks are observed that reflect the differences in methanol adsorption modes.

[0037] Examples of methanol adsorption modes include Type I, Type II, and Type II'.

[0038] [ka]

[0039] Methanol adsorption to coordination-saturated sites is considered to be Type I, while adsorption to coordination-unsaturated sites is considered to be Type II and Type II'. The peak corresponding to Type I is at 1100 cm⁻¹. -1 More than 1110cm -1 The following range is thought to be observed, with peaks corresponding to Type II and Type II' being at 1030 cm. -1 More than 1100cm -1 It is thought that these peaks are observed in the range of less than . Note that the peak corresponding to Type II' is usually observed at lower wavenumbers than the peak corresponding to Type II.

[0040] Based on the above, 1100cm -1 More than 1110cm -1 The area S of the peak observed within the following range A This reflects the proportion of coordination saturation sites, 1030 cm -1 More than 1100cm -1 Area S of peaks observed in the range less than B This is thought to reflect the proportion of coordination-unsaturated sites. Coordination-unsaturated sites have a higher OSC than coordination-saturated sites, so S B / S A A value of 4.2 or higher indicates that there is a large amount of Ce with high OSC in the composite oxide, that is, the composite oxide has excellent OSC.

[0041] The following describes the method for measuring the infrared absorption spectrum of the composite oxide of the present invention.

[0042] The infrared absorption spectrum is measured after methanol is adsorbed onto a composite oxide that does not contain any supported noble metal elements. The measurement can be performed, for example, using a disc-shaped sample obtained by compression molding a composite oxide that does not contain any supported noble metal elements.

[0043] The composite oxide may be pre-treated before adsorbing methanol onto it. Pre-treatment can be performed, for example, by heating a container holding the composite oxide while evacuating it, then oxidizing the composite oxide by contacting it with oxygen, and then evacuating it again. The temperature of the composite oxide when contacting it with oxygen is preferably 400°C to 800°C, more preferably 500°C to 700°C. Pre-treatment is preferably carried out according to the method described in the examples.

[0044] The temperature of the composite oxide when methanol is adsorbed is preferably between room temperature (30°C) and 300°C, more preferably between room temperature (30°C) and 100°C. Within this temperature range, it is preferable to contact methanol vapor with the composite oxide to adsorb methanol onto the composite oxide. The pressure of the methanol vapor contacted with the composite oxide is preferably between 100 Pa and 2500 Pa, more preferably between 600 Pa and 1500 Pa. The contact time of methanol vapor with the composite oxide is preferably between 1 minute and 60 minutes, more preferably between 20 minutes and 40 minutes. Adsorption of methanol onto the composite oxide is preferably carried out according to the method described in the examples.

[0045] The temperature used when measuring the infrared absorption spectrum is preferably between room temperature (30°C) and 600°C, more preferably between room temperature (30°C) and 200°C. The infrared absorption spectrum is preferably measured according to the method described in the examples.

[0046] After measuring the infrared absorption spectrum, peak separation is performed on the obtained spectrum. Peak separation can be performed using commercially available peak separation software (for example, OMNIC from Thermo Scientific).

[0047] A certain wavenumber range (for example, 1100 cm) -1 More than 1110cm -1 Within the following range, 1030cm -1 More than 1100cm -1 With respect to ranges such as less than a certain frequency, "a peak observed in that wavenumber range" means a peak that has its peak in that wavenumber range in the spectrum after peak separation. It is sufficient that the peak's peak is located within that wavenumber range; the tail of the peak may extend outside that wavenumber range.

[0048] A certain wavenumber range (for example, 1100 cm) -1 More than 1110cm -1 Within the following range, 1030cm -1 More than 1100cm -1 With respect to ranges such as less than a certain wavenumber, "the area of ​​the peak observed in that wavenumber range" means the area of ​​the region enclosed by the peak having its peak in that wavenumber range and the baseline in the spectrum after peak separation. If the peak's peak is located within that wavenumber range, but the tail of the peak extends outside that wavenumber range, the area of ​​the portion outside that wavenumber range is also included in "the area of ​​the region enclosed by the peak having its peak in that wavenumber range and the baseline."

[0049] A certain wavenumber range (for example, 1100 cm) -1 More than 1110cm -1 Within the following range, 1030cm -1 More than 1100cm -1With respect to ranges less than a certain value, etc., "the area of ​​the peaks observed in the wavenumber range" means the area of ​​the single peak observed in the wavenumber range in the spectrum after peak separation, or the sum of the areas of the two or more peaks observed. Furthermore, even if two or more peaks are observed in the wavenumber range in the spectrum after peak separation and these two or more peaks have overlapping portions, the area of ​​the overlapping portion is not subtracted from the sum of the areas of the two or more peaks.

[0050] In the spectrum after peak separation, 1100 cm⁻¹ -1 More than 1110cm -1 Within the following range, one peak is usually observed. Therefore, area S A This is typically the area of ​​the single peak in question. This single peak is considered to be a peak corresponding to Type I. Area S A The value is typically 2.0 au cm. -1 The above is 20.0aucm -1 Preferably 5.0 au cm -1 The above is 15.0aucm -1 More preferably 5.9 au cm -1 The above is 13.0 au cm. -1 The following applies:

[0051] In the spectrum after peak separation, 1030 cm⁻¹ -1 More than 1100cm -1 Within the range less than , three peaks are usually observed. Therefore, area S B This is usually the sum of the areas of the three peaks. These three peaks are typically 1080 cm². -1 More than 1100cm -1 The first peak is located below 1050cm -1 More than 1080cm -1 It consists of a second peak located below a certain wavenumber and a third peak located at a lower wavenumber than the second peak. The first and second peaks are considered to correspond to Type II peaks, and the third peak is considered to correspond to Type II'. Area SB The value is typically 25.0 au cm. -1 The above is 95.0 au cm. -1 Preferably 25.0 au cm -1 The above is 85.0 au cm. -1 More preferably 25.0 au cm -1 The above is 55.0 au cm. -1 The following applies:

[0052] From the viewpoint of more effectively improving OSC, the crystallite size of the composite oxide of the present invention is preferably 60 Å or less, more preferably 55 Å or less, and even more preferably 52 Å or less. The lower limit of the crystallite size of the composite oxide of the present invention is not particularly limited, but is usually 10 Å, preferably 20 Å, more preferably 30 Å, and even more preferably 40 Å. Each of these lower limits may be combined with any of the upper limits above. The crystallite size of the composite oxide is preferably measured according to the method described in the examples.

[0053] According to the first or second method described later, a composite oxide having a crystallite size of 60 Å or less can be produced.

[0054] D 90 When the ratio decreases, the specific surface area of ​​the composite oxide increases, improving the exhaust gas purification performance of the exhaust gas purification catalyst composition and exhaust gas purification catalyst using the composite oxide. From the viewpoint of more effectively achieving improved exhaust gas purification performance, the D of the composite oxide of the present invention 90 The thickness is preferably 30 μm or less, more preferably 20 μm or less. 90 The lower limit is not particularly limited, but is usually 5 μm, preferably 10 μm. Each of these lower limits may be combined with any of the upper limits mentioned above. 90 This refers to the particle size at which the cumulative volume accounts for 90% in the volume-based particle size distribution obtained by the laser diffraction-scattering particle size distribution measurement method. The laser diffraction-scattering particle size distribution measurement method is preferably performed according to the conditions described in the examples.

[0055] According to the first or second method described later, D 90It is possible to produce composite oxides with a particle size of 30 μm or less.

[0056] As the specific surface area of ​​the composite oxide increases, the exhaust gas purification performance of the exhaust gas purification catalyst composition and the exhaust gas purification catalyst using the composite oxide improves. From the viewpoint of more effectively achieving improved exhaust gas purification performance, the specific surface area of ​​the composite oxide of the present invention is preferably 80 m². 2 / g or more, comfortably 100m 2 / g or more, more preferably 150m 2 The amount is 1 / g or more. The upper limit of the specific surface area is preferably 350 m². 2 / g, preferably 300m 2 / g, more comfortably 250m 2 The values ​​are / g. These upper limits may be combined with any of the lower limits mentioned above. Specific surface area measurement is preferably performed according to the conditions described in the examples.

[0057] According to the first or second method described later, the specific surface area is 150 m². 2 It is possible to produce composite oxides with a concentration of 1 / g or more.

[0058] ≪Method for producing complex oxides≫ The method for producing the composite oxide of the present invention will be described below.

[0059] <Method 1> The composite oxide of the present invention can be produced by a first method comprising steps (a), (b), and (c). Steps (a) to (c) are described below.

[0060] Process (a) Step (a) is a step in which a slurry is obtained from a raw material liquid containing cerium salt and zirconium salt by coprecipitation.

[0061] The cerium salt contained in the raw material liquid may be a water-soluble salt or a sparingly water-soluble salt, but a water-soluble salt is preferred. Water-soluble cerium salts can be selected from, for example, cerium chloride, cerium nitrate, cerium(III) sulfate, cerium acetate, etc., but from the viewpoint of productivity on an industrial scale, selection from cerium chloride and cerium nitrate is preferred. Sparingly water-soluble cerium salts can be selected from, for example, cerium hydroxide, cerium oxide, cerium carbonate, etc. The raw material liquid may contain one type of cerium salt or two or more types. The amount of cerium salt in the raw material liquid is appropriately adjusted so that the amount of Ce in the final product, the composite oxide, in terms of CeO2, falls within a desired range.

[0062] The zirconium salt contained in the raw material solution may be a water-soluble salt or a sparingly water-soluble salt, but a water-soluble salt is preferred. Water-soluble zirconium salts can be selected from, for example, zirconium oxychloride, zirconium chloride, zirconium oxynitrate, zirconium nitrate, zirconium oxyacetate, etc., but from the viewpoint of productivity on an industrial scale, selection from zirconium oxychloride, zirconium chloride, and zirconium oxynitrate is preferred. Sparingly water-soluble zirconium salts can be selected from, for example, zirconium hydroxide, basic zirconium sulfate, zirconium oxide, basic zirconium carbonate, etc. The raw material solution may contain one type of zirconium salt or two or more types. The amount of zirconium salt in the raw material solution is appropriately adjusted so that the amount of Zr in the final composite oxide (equivalent to ZrO2) falls within a desired range.

[0063] The raw material liquid may contain one or more metal salts other than cerium salts and zirconium salts (hereinafter referred to as "other metal salts"), depending on the composition of the final product, the composite oxide. Examples of other metal salts include rare earth metal salts other than cerium salts, alkaline earth metal salts, etc. Other metal salts may be water-soluble salts or sparingly water-soluble salts, but water-soluble salts are preferred. Water-soluble salts can be selected from, for example, chlorides, nitrates, sulfates, acetates, etc., but from the viewpoint of productivity on an industrial scale, it is preferable to select from chlorides (e.g., lanthanum chloride, neodymium chloride, praseodymium chloride, etc.) and nitrates (e.g., lanthanum nitrate, neodymium nitrate, praseodymium nitrate, etc.). Sparingly water-soluble salts can be selected from, for example, hydroxides, oxides, carbonates, etc. The type and amount of other metal salts in the raw material liquid are appropriately adjusted so that the oxide equivalent amount of other metal elements in the final product, the composite oxide, is within a desired range.

[0064] The raw material solution contains a solvent. The solvent is usually water (for example, pure water such as deionized water). The raw material solution may also contain one or more solvents other than water. Examples of solvents other than water include organic solvents such as alcohols. The total amount of one or more organic solvents in the raw material solution is usually 20 vol% or less, preferably 10 vol% or less, based on the volume of the raw material solution. The lower limit is zero.

[0065] The coprecipitation method can be carried out according to conventional methods. In the coprecipitation method, a precipitate (coprecipitation) containing Ce, Zr, and optionally one or more other metal elements (for example, one or more metal elements selected from rare earth elements other than Ce and alkaline earth metal elements) can be formed by adding a precipitant to the raw material liquid, or by adding the raw material liquid to the precipitant liquid. The slurry obtained by the coprecipitation method contains the precipitate (coprecipitation) and a solvent. The solvent in the slurry originates from the solvent in the raw material liquid. The precipitate (coprecipitation) contains sparingly water-soluble cerium salts, sparingly water-soluble zirconium salts, and optionally other sparingly water-soluble metal salts.

[0066] The precipitating agent is not particularly limited as long as it can precipitate metal ions contained in the raw material solution (for example, cerium ions produced by the ionization of cerium salts, zirconium ions produced by the ionization of zirconium salts, and other metal ions produced by the ionization of other metal salts, etc.) as sparingly water-soluble salts, and can be appropriately selected from known precipitating agents.

[0067] In one embodiment, a first precipitating agent selected from an aqueous solution containing sulfate ions and a compound that can dissolve in water to produce sulfate ions, and a second precipitating agent selected from an aqueous solution containing hydroxide ions and a compound that can dissolve in water to produce hydroxide ions are used. The amounts of the first and second precipitating agents used can be appropriately adjusted considering the amount of metal ions in the raw material solution, etc., so that a sufficient amount of precipitate (co-precipitate) is deposited.

[0068] Compounds that can dissolve in water to produce sulfate ions can be selected from, for example, ammonium sulfate, sulfuric acid, alkali metal sulfates (e.g., sodium sulfate, potassium sulfate, etc.), cerium(III) sulfate, rare earth metal sulfates, etc. However, from the viewpoint of improving the uniformity of the solid solution phase formed by cerium, zirconium, and oxygen (e.g., a solid solution phase of cerium oxide and zirconium oxide) and from the viewpoint of ease of availability, it is preferable to select from ammonium sulfate, sulfuric acid, and alkali metal sulfates. An aqueous solution containing sulfate ions can be obtained, for example, by dissolving a compound that can dissolve in water to produce sulfate ions in water (e.g., pure water such as deionized water).

[0069] Compounds that can dissolve in water to produce hydroxide ions can be selected from alkalis such as ammonia, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide, but from the viewpoint of ease of industrial availability, it is preferable to select from sodium hydroxide, potassium hydroxide, and ammonia. An aqueous solution containing hydroxide ions can be obtained, for example, by dissolving a compound that can dissolve in water to produce hydroxide ions in water (for example, pure water such as deionized water).

[0070] The first precipitating agent precipitates zirconium ions in the raw material solution as basic zirconium sulfate. Therefore, by adding the first precipitating agent to the raw material solution, or by adding the raw material solution to the first additive, a precipitate (co-precipitate) containing basic zirconium sulfate is formed. After the formation of the precipitate (co-precipitate) containing basic zirconium sulfate, by adding the second precipitating agent to the raw material solution, a precipitate (co-precipitate) containing cerium hydroxide, zirconium hydroxide, and optionally hydroxides of other metal elements (e.g., lanthanum hydroxide, neodymium hydroxide, praseodymium hydroxide, etc.) is formed, and a slurry containing this precipitate (co-precipitate) is obtained. The pH of the obtained slurry is usually 9.0 to 14.0, preferably 10.0 to 14.0. The basic zirconium sulfate formed by the first precipitating agent is converted to zirconium hydroxide by the second precipitating agent.

[0071] In another embodiment, the second precipitant is used alone. The amount of the second precipitant used can be appropriately adjusted, taking into account the amount of metal ions in the raw material solution, etc., so that a sufficient amount of precipitate (coprecipitate) is formed.

[0072] The second precipitating agent precipitates metal ions (e.g., cerium ions, zirconium ions, and other metal ions) in the raw material solution as hydroxides (e.g., cerium hydroxide, zirconium hydroxide, and hydroxides of other metal elements). Therefore, by adding the second precipitating agent to the raw material solution, or by adding the raw material solution to the second additive, a precipitate (coprecipitate) containing cerium hydroxide, zirconium hydroxide, and optionally hydroxides of other metal elements (e.g., lanthanum hydroxide, neodymium hydroxide, praseodymium hydroxide, etc.) is formed, and a slurry containing the precipitate (coprecipitate) is obtained. The pH of the obtained slurry is usually 9.0 to 14.0, preferably 10.0 to 14.0.

[0073] The slurry obtained by the coprecipitation method is preferably washed with a washing solution before being subjected to step (b). Water (for example, pure water such as deionized water) is preferably used as the washing solution.

[0074] In one embodiment, the slurry obtained by coprecipitation is filtered, the resulting cake is filtered and washed with a washing solution, water (for example, pure water such as deionized water) is added to the washed cake to obtain a slurry, and the obtained slurry is subjected to step (b).

[0075] Process (b) Step (b) is a step in which the slurry obtained in step (a) is subjected to hydrothermal treatment.

[0076] From the viewpoint of increasing the solid solubility on the surface of the composite oxide and improving the OSC of the composite oxide, the hydrothermal treatment temperature is preferably 100°C to 200°C, more preferably 120°C to 180°C, and even more preferably 150°C to 180°C. The hydrothermal treatment time is preferably 1 hour to 30 hours, more preferably 6 hours to 20 hours, and even more preferably 8 hours to 15 hours.

[0077] Hydrothermal treatment is preferably carried out under subcritical conditions (i.e., using subcritical water), while it is not preferable to carry it out under supercritical conditions (i.e., using supercritical water). Supercritical conditions are those with a temperature of 374°C or higher and a pressure of 22.1 MPa or higher, while subcritical conditions are those with a temperature of 270°C or higher and a pressure of 20 MPa or higher, which do not meet the supercritical conditions. Under subcritical conditions, the precursor hydroxide dissolves, resulting in a more uniform mixture of Ce and Zr, and fine particles with high solid solubility are obtained. On the other hand, under supercritical conditions, the hydrothermal reaction of the hydroxide proceeds, and the oxide precipitates rapidly, so fine particles with high solid solubility cannot be obtained.

[0078] Process (c) Step (c) is a step in which the slurry that has been hydrothermally treated in step (b) is calcined.

[0079] Before firing, the hydrothermally treated slurry may be dried. The drying temperature is usually between 50°C and 200°C, preferably between 80°C and 150°C. The drying time is usually between 1 hour and 30 hours, preferably between 5 hours and 15 hours.

[0080] Firing is usually carried out in an atmospheric environment. The firing temperature is usually between 500°C and 1000°C, preferably between 500°C and 800°C. The firing time is usually between 1 hour and 12 hours, preferably between 1 hour and 8 hours.

[0081] The fired product obtained by firing may be pulverized as needed. The pulverization can be carried out dry or wet using, for example, a mortar and pestle, hammer mill, ball mill, bead mill, jet mill, roller mill, etc.

[0082] According to the first method, the composite oxide of the present invention can be obtained as a calcined product or a pulverized product thereof.

[0083] <Second Method> The composite oxide of the present invention can be produced by a second method comprising steps (a) and (d). Steps (a) and (d) will be described below.

[0084] Process (a) Step (a) is a step in which a slurry is obtained from a raw material liquid containing cerium salt and zirconium salt by coprecipitation.

[0085] The explanation for process (a) is as described above.

[0086] Process (d) Step (d) is a step in which hydrothermal synthesis is performed using the slurry obtained in step (a).

[0087] Hydrothermal synthesis can be carried out using the hydrothermal synthesis apparatus 101 shown in Figure 6. The hydrothermal synthesis apparatus 101 is a continuous synthesis apparatus.

[0088] As shown in Figure 6, the hydrothermal synthesis apparatus 101 comprises a water tank 102, a raw material supply tank 103, a mixing unit 108, and a reactor 110.

[0089] The water tank 102 stores water for hydrothermal synthesis. The water stored in the water tank 102 is drawn up by the drive of the pump 104 and supplied to the mixing unit 108 through the water supply passage 105. A heating means 109 is interposed between the pump 104 and the mixing unit 108 in the water supply passage 105.

[0090] The slurry obtained in process (a) is stored in the raw material supply tank 103. The slurry stored in the raw material supply tank 103 is drawn up by the drive of the pump 106 and supplied to the mixing section 108 through the raw material supply passage 107.

[0091] The water supply channel 105 and the raw material supply channel 107 are connected to each other at the mixing section 108.

[0092] A reactor 110 is located downstream of the mixing section 108. The mixing section 108 and the reactor 110 are connected by a reaction liquid supply passage 111. The products generated by the reaction in the reactor 110 are introduced into a cooler 113 through a product discharge passage 112. The cooler 113 may have a water-cooling jacket (not shown). Downstream of the cooler 113, a pressure regulating valve 114 and a recovery tank 115 are arranged in that order.

[0093] Hydrothermal synthesis using the hydrothermal synthesis apparatus 101 can be performed as follows: Pump 104 is started to supply water (e.g., pure water such as deionized water) stored in the water tank 102 to the water supply channel 105. The supplied water is then guided to the heating means 109 under pressurized conditions by pump 104. The water is heated in the heating means 109 and becomes high temperature and high pressure. In parallel with this operation, pump 106 is started to supply slurry stored in the raw material supply tank 103 to the raw material supply channel 107. The supplied slurry is pressurized by pump 106. At this point, the slurry is not heated.

[0094] Water under high temperature and pressure and a slurry under room temperature and pressure are mixed in the mixing section 108. The reaction solution obtained by mixing the water and slurry is led to the reactor 110 through the reaction solution supply passage 111. The reactor 110 is equipped with a heating means (not shown), and the reaction solution is heated as needed. The reaction solution may be at the same temperature in the mixing section 108 and the reactor 110, or it may be at different temperatures. Heating of the reaction solution by the heating means attached to the reactor 10 may be performed so that the temperature of the reaction solution in the mixing section 108 and the reactor 110 is the same, or it may be performed so that the temperature of the reaction solution in the mixing section 108 and the reactor 110 is different. The reaction solution is subjected to hydrothermal synthesis in the mixing section 108 and the subsequent reactor 110. In the hydrothermal synthesis apparatus 101 of this embodiment, the temperature of the reaction solution is controlled in the mixing section 108 and the reactor 110, respectively, to hydrothermally synthesize the target complex oxide.

[0095] From the viewpoint of increasing the solid solubility on the surface of the composite oxide and improving the OSC of the composite oxide, the temperature of the reaction solution in the mixing section 108 is preferably 110°C to 400°C, more preferably 120°C to 350°C, and even more preferably 130°C to 300°C.

[0096] From the viewpoint of increasing the solid solubility on the surface of the composite oxide and improving the OSC of the composite oxide, the temperature of the reaction solution in the reactor 110 is preferably 110°C to 600°C, more preferably 150°C to 500°C, and even more preferably 200°C to 450°C.

[0097] From the viewpoint of increasing the solid solubility on the surface of the composite oxide and improving the OSC of the composite oxide, the pressure for hydrothermal synthesis in the mixing section 108 and the reactor 110 is preferably 20 MPa or higher, more preferably 22.1 MPa or higher. The upper limit of the pressure is not particularly limited, but is preferably 40 MPa, more preferably 35 MPa, and even more preferably 30 MPa. Each of these upper limits may be combined with any of the lower limits mentioned above.

[0098] The temperature of the hydrothermal synthesis can be controlled by heating means 109 and / or heating means (not shown) attached to reactor 110. The pressure of the hydrothermal synthesis can be controlled by adjusting the pressure of pumps 104 and 106 and / or the valve opening of pressure regulating valve 114. In the hydrothermal synthesis apparatus 1, the flow path between pumps 104 and 106 and pressure regulating valve 114 is substantially a closed space, so the pressure in the flow path is the same.

[0099] Hydrothermal synthesis in the mixing section 108 and reactor 110 is preferably carried out under subcritical conditions (i.e., using subcritical water), while it is undesirable to carry it out under supercritical conditions (i.e., using supercritical water). The significance of supercritical and subcritical conditions is as described above. Under subcritical conditions, the precursor hydroxide dissolves, resulting in a more uniform mixture of Ce and Zr, and fine particles with high solid solubility are obtained. On the other hand, under supercritical conditions, the hydrothermal reaction of the hydroxide proceeds, and the oxide precipitates rapidly, so fine particles with high solid solubility cannot be obtained.

[0100] The desired composite oxide is formed by hydrothermal synthesis in the mixing section 108 and the reactor 110. The formed composite oxide is cooled in the cooler 113 located downstream of the reactor 110, and then recovered in the recovery tank 115.

[0101] The complex oxide is usually recovered in the form of a complex oxide-containing slurry. The recovered complex oxide-containing slurry may be filtered, dried, and sieved as needed. The drying temperature is usually 50°C to 200°C, preferably 80°C to 150°C. The drying time is usually 1 hour to 30 hours, preferably 1 hour to 15 hours.

[0102] The composite oxide of the present invention can be obtained as a hydrothermal product by a method comprising steps (a) and (d).

[0103] <<Catalyst composition for exhaust gas purification>> The exhaust gas purification catalyst composition of the present invention will be described below. In the description of the exhaust gas purification catalyst composition of the present invention, "mass%" refers to the mass of the exhaust gas purification catalyst composition of the present invention, unless otherwise specified.

[0104] The exhaust gas purification catalyst composition of the present invention comprises the composite oxide of the present invention and a catalytically active component.

[0105] The composite oxide of the present invention has excellent OSC (Oxygen Circulation Control), which mitigates fluctuations in oxygen concentration in exhaust gas and expands the operating window of the catalytic active component. Therefore, the exhaust gas purification catalyst composition of the present invention has excellent exhaust gas purification ability.

[0106] The form of the exhaust gas purification catalyst composition of the present invention may be, for example, a powder, a molded body, or a layered structure.

[0107] The description of the composite oxide of the present invention is as described above.

[0108] The catalytically active component preferably contains one or more noble metal elements. The noble metal elements can be selected from, for example, Au, Ag, Pt, Pd, Rh, Ir, Ru, Os, etc., but from the viewpoint of improving exhaust gas purification performance, it is preferable to select from Pt, Pd, and Rh.

[0109] The noble metal element is included in the exhaust gas purification catalyst composition of the present invention in a form that can function as a catalytic active component, such as a metal, an alloy containing the noble metal element, or a compound containing the noble metal element (e.g., an oxide of the noble metal element). From the viewpoint of improving exhaust gas purification performance, the catalytic active component is preferably in particulate form.

[0110] From the viewpoint of balancing exhaust gas purification performance and cost, the amount of noble metal elements in the exhaust gas purification catalyst composition of the present invention is preferably 0.1% by mass or more and 40% by mass or less, more preferably 0.1% by mass or more and 30% by mass or less, and even more preferably 0.1% by mass or more and 20% by mass or less. The "amount of noble metal elements" refers to the metal equivalent amount of one noble metal element if the catalyst composition contains one noble metal element, and to the total metal equivalent amounts of two or more noble metal elements if the catalyst composition contains two or more noble metal elements.

[0111] The amount of noble metal elements in the exhaust gas purification catalyst composition of the present invention can be measured by conventional methods such as inductively coupled plasma atomic emission spectroscopy (ICP-OES), X-ray fluorescence spectroscopy (XRF), and scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX).

[0112] From the viewpoint of improving exhaust gas purification performance, it is preferable that at least a portion of the catalytically active component is supported on the composite oxide of the present invention. "Supported" means a state in which the catalytically active component is physically or chemically adsorbed or retained on the outer surface or inner surface of the pores of the composite oxide of the present invention. The fact that at least a portion of the catalytically active component is supported on the composite oxide of the present invention can be confirmed, for example, by analyzing a sample obtained from the exhaust gas purification catalyst composition of the present invention using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) and observing that at least a portion of the catalytically active component and the composite oxide of the present invention are present in the same region.

[0113] The exhaust gas purification catalyst composition of the present invention may contain one or more inorganic oxides other than the composite oxide of the present invention (hereinafter referred to as "other inorganic oxides"). The other inorganic oxides are, for example, particulate. From the viewpoint of improving the support of the catalytic active component, the other inorganic oxides are preferably porous. The inorganic oxides may or may not have oxygen storage capacity (OSC).

[0114] Inorganic oxides used as carriers are distinct from inorganic oxides used as binders (e.g., inorganic oxide binders such as alumina binder, zirconia binder, titania binder, and silica binder). Inorganic oxides used as binders originate from sols used as raw materials (e.g., inorganic oxide sols such as alumina sol, zirconia sol, titania sol, and silica sol).

[0115] Other inorganic oxides can be selected from, for example, alumina (Al2O3), modified alumina, zirconia (ZrO2), silica (SiO2), titania (TiO2), rare earth metal oxides, zeolites (aluminosilicates), and oxides based on MgO, ZnO, SnO2, etc. Oxides of rare earth elements (Ln) refer to sesquioxides (Ln2O3), excluding oxides of Ce, Pr, and Tb, with Ce oxide being CeO2 and Pr oxide being Pr6O 11 The oxide of Tb is Tb4O7.

[0116] Modified alumina contains one or more elements other than Al and O. Modified alumina may be an oxide obtained by modifying the surface of alumina with elements other than Al and O, or an oxide obtained by solid-solving elements other than Al and O in alumina. Elements other than Al and O can be selected from, for example, B, Si, Zr, Cr, rare earth elements, alkaline earth metal elements, etc. Examples of modified alumina include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, and alumina-lantana.

[0117] At least a portion of the catalytically active component may be supported on other inorganic oxides. The meaning and method of confirming "supported" are as described above.

[0118] The exhaust gas purification catalyst composition of the present invention may contain stabilizers, binders, etc. Examples of binders include inorganic oxide binders such as alumina binder, zirconia binder, titania binder, and silica binder. Inorganic oxide binders are derived from inorganic oxide sols such as alumina sol, zirconia sol, titania sol, and silica sol. Examples of stabilizers include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements.

[0119] The exhaust gas purification catalyst composition of the present invention can be produced, for example, by mixing a noble metal salt-containing solution, the composite oxide of the present invention, and optionally other components (e.g., other inorganic oxides, binders, stabilizers, etc.), then drying and calcining the mixture. The calcined product may be pulverized as needed. Examples of noble metal salts include nitrates, ammine complex salts, and chlorides. The solvent for the noble metal salt-containing solution is, for example, water (e.g., pure water such as deionized water). The noble metal salt-containing solution may also contain organic solvents such as alcohol. The drying temperature is, for example, 50°C to 120°C, and the drying time is, for example, 0.5 hours to 12 hours. The calcination temperature is, for example, 300°C to 600°C, and the calcination time is, for example, 0.5 hours to 6 hours. Calcination can be carried out, for example, under an atmospheric environment.

[0120] ≪Exhaust gas purification catalyst≫ The exhaust gas purification catalyst of the present invention will be described below.

[0121] The exhaust gas purification catalyst of the present invention comprises a substrate and a catalyst layer of the present invention provided on the substrate. The exhaust gas purification catalyst of the present invention may also include a catalyst layer other than the catalyst layer of the present invention at one or more positions selected from below, above, downstream, and upstream of the catalyst layer of the present invention.

[0122] <Base material> The substrate can be appropriately selected from substrates commonly used as substrates for exhaust gas purification catalysts. Examples of substrates include wall-flow type substrates and flow-through type substrates.

[0123] The materials constituting the base material can be selected as appropriate. Examples of materials constituting the base material include ceramic materials and metallic materials, but ceramic materials are preferred. Examples of ceramic materials include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; and oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of metallic materials include alloys such as stainless steel.

[0124] <Catalyst layer> The catalyst layer of the present invention is composed of the exhaust gas purification catalyst composition of the present invention. That is, the catalyst layer of the present invention includes the composite oxide of the present invention and a catalytically active component. The description of the exhaust gas purification catalyst composition of the present invention is as described above. As described above, it is preferable that at least a portion of the catalytically active component is supported on the composite oxide of the present invention.

[0125] From the viewpoint of balancing exhaust gas purification performance and cost, the mass of the catalyst layer of the present invention per unit volume of the substrate (mass after drying and calcination) is preferably 50 g / L or more and 500 g / L or less, more preferably 70 g / L or more and 400 g / L or less, and even more preferably 90 g / L or more and 300 g / L or less. The mass of the catalyst layer of the present invention per unit volume of the substrate is calculated by the formula: Mass of the catalyst layer of the present invention / Volume of the substrate. Note that the volume of the substrate refers to the apparent volume of the substrate. For example, if the substrate is cylindrical with an outer diameter of 2r, the volume of the substrate is given by the formula: Volume of substrate = π × r 2 It is expressed as × (length of the base material).

[0126] <First Embodiment> The exhaust gas purification catalyst 1A according to the first embodiment of the present invention will be described below with reference to Figures 1 to 4.

[0127] As shown in Figure 1, the exhaust gas purification catalyst 1A is located in the exhaust passage within the exhaust pipe P of the internal combustion engine. The internal combustion engine is, for example, a gasoline engine. The exhaust gas discharged from the internal combustion engine flows through the exhaust passage within the exhaust pipe P from one end to the other and is purified by the exhaust gas purification catalyst 1A installed in the exhaust pipe P. In the drawing, the direction of exhaust gas flow is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas inlet side," and the downstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas outlet side."

[0128] In the exhaust passage within the exhaust pipe P, other exhaust gas purification catalysts may be arranged along with the exhaust gas purification catalyst 1A. For example, the exhaust gas purification catalyst 1A may be arranged on the upstream side of the exhaust passage within the exhaust pipe P, and other exhaust gas purification catalysts may be arranged on the downstream side of the exhaust passage within the exhaust pipe P. Examples of other exhaust gas purification catalysts include the exhaust gas purification catalyst 1B, which will be described later.

[0129] As shown in Figures 2-4, the exhaust gas purification catalyst 1A comprises a base material 10 and a catalyst layer 20 provided on the base material 10.

[0130] The above description regarding the base material also applies to base material 10.

[0131] The catalyst layer 20 is composed of the exhaust gas purification catalyst composition of the present invention. That is, the catalyst layer 20 contains the composite oxide and catalytically active components of the present invention. The above description of the catalyst layer of the present invention also applies to the catalyst layer 20.

[0132] As shown in Figures 2-4, the base material 10 has a cylindrical portion 11 that defines the outer shape of the base material 10, a partition wall portion 12 provided inside the cylindrical portion 11, and cells 13 separated by the partition wall portion 12.

[0133] As shown in Figure 2, the shape of the cylindrical portion 11 is cylindrical, but it may also be an elliptical cylinder, a polygonal cylinder, or other shapes.

[0134] As shown in Figures 2-4, a partition wall 12 exists between adjacent cells 13, and adjacent cells 13 are separated by the partition wall 12. The partition wall 12 is preferably porous. The thickness of the partition wall 12 is, for example, 20 μm or more and 1500 μm or less.

[0135] As shown in Figure 4, cell 13 extends in the exhaust gas flow direction X and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0136] As shown in Figure 4, both the exhaust gas inlet and exhaust gas outlet ends of cell 13 are open. Therefore, exhaust gas entering from the exhaust gas inlet end (opening) of cell 13 flows out from the exhaust gas outlet end (opening) of cell 13. This type of configuration is called a flow-through type.

[0137] As shown in Figures 2 and 3, the plan view shape of the exhaust gas inlet end (opening) of cell 13 and the plan view shape of the exhaust gas outlet end (opening) of cell 13 are rectangular, but other shapes such as hexagons or octagons may also be used.

[0138] The cell density per square inch of the substrate 10 is, for example, between 200 and 1000 cells. The cell density per square inch of the substrate 10 is the total number of cells 13 per square inch in a cross-section obtained by cutting the substrate 10 with a plane perpendicular to the exhaust gas flow direction X.

[0139] As shown in Figure 4, the catalyst layer 20 is provided on the partition wall portion 12 of the substrate 10.

[0140] As shown in Figure 4, the catalyst layer 20 extends along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12 to the exhaust gas outlet end of the partition wall 12. The catalyst layer 20 may extend along the exhaust gas flow direction X from the exhaust gas inlet end of the partition wall 12 so as not to reach the exhaust gas outlet end of the partition wall 12, or it may extend along the direction opposite to the exhaust gas flow direction X from the exhaust gas outlet end of the partition wall 12 so as not to reach the exhaust gas inlet end of the partition wall 12.

[0141] The exhaust gas purification catalyst 1A can be manufactured by forming a catalyst layer 20 on the partition wall portion 12 of the base material 10. For example, a slurry can be prepared by mixing a noble metal salt-containing solution, the composite oxide of the present invention, and other components as needed (e.g., other inorganic oxides, binders, stabilizers, etc.), applying the slurry to the partition wall portion 12 of the base material 10, drying it, and firing it to form the catalyst layer 20 on the partition wall portion 12 of the base material 10. The above description regarding the noble metal salt, the solvent of the noble metal salt-containing solution, drying conditions, firing conditions, etc., also applies to the exhaust gas purification catalyst 1A.

[0142] <Second Embodiment> Hereinafter, the exhaust gas purification catalyst 1B according to the second embodiment of the present invention will be described with reference to Figure 5. In the exhaust gas purification catalyst 1B, the same components as those in the exhaust gas purification catalyst 1A are indicated by the same reference numerals as those in the exhaust gas purification catalyst 1A. Unless otherwise stated below, the above description of the exhaust gas purification catalyst 1A also applies to the exhaust gas purification catalyst 1B.

[0143] As shown in Figure 5, the exhaust gas purification catalyst 1B is The base material 10 is provided with a first sealing portion 14 that seals the exhaust gas outlet end of some of the cells 13, and a second sealing portion 15 that seals the exhaust gas inlet end of the remaining cells 13. This results in the base material 10 having inlet-side cells 13a, where the exhaust gas inlet end is open and the exhaust gas outlet end is sealed by the first sealing portion 14, and outlet-side cells 13b, where the exhaust gas inlet end is sealed by the second sealing portion 15 and the exhaust gas outlet end is open. A catalyst layer 20a is provided on the inlet side cell 13a side of the partition wall portion 12 of the base material 10, and a catalyst layer 20b is provided on the outlet side cell 13b side of the partition wall portion 12 of the base material 10. Therefore, it differs from exhaust gas purification catalyst 1A.

[0144] As shown in Figure 5, multiple (e.g., four) outlet cells 13b are arranged adjacent to one inlet cell 13a, and the inlet cell 13a and the outlet cells 13b adjacent to it are separated by a porous partition 12.

[0145] As shown in Figure 5, the catalyst layer 20a extends from the exhaust gas inlet end of the partition wall 12 along the exhaust gas flow direction X. In this embodiment, the catalyst layer 20a does not reach the exhaust gas outlet end of the partition wall 12, but it may reach the exhaust gas outlet end of the partition wall 12.

[0146] As shown in Figure 5, the catalyst layer 20b extends from the exhaust gas outlet end of the partition wall 12 along a direction opposite to the exhaust gas flow direction X. In this embodiment, the catalyst layer 20b does not reach the exhaust gas inlet end of the partition wall 12, but it may reach the exhaust gas inlet end of the partition wall 12.

[0147] At least one of the catalyst layers 20a and 20b is the catalyst layer of the present invention, and the above description relating to the catalyst layer of the present invention applies. The compositions of the catalyst layers 20a and 20b may be the same or different.

[0148] In the exhaust gas purification catalyst 1B, exhaust gas flows in from the exhaust gas inlet end (opening) of the inlet cell 13a, passes through the porous partition wall 12, and flows out from the exhaust gas outlet end (opening) of the outlet cell 13b. This type of configuration is called a wall-flow type.

[0149] In the exhaust gas purification catalyst 1B, when exhaust gas flowing in from the exhaust gas inlet end (opening) of the inlet cell 13a passes through the porous partition wall 12, particulate matter (PM) in the exhaust gas is collected in the pores of the partition wall 12. Therefore, the exhaust gas purification catalyst 1B is useful as a gasoline particulate filter for gasoline engines or a diesel particulate filter for diesel engines.

[0150] The exhaust gas purification catalyst 1B can be manufactured by the following method: The exhaust gas inlet end of the base material 10 is immersed in a slurry for forming the catalyst layer 20a, the slurry is sucked from the opposite side and dried to form a precursor layer of the catalyst layer 20a. The exhaust gas outlet end of the base material 10 is immersed in a slurry for forming the catalyst layer 20b, the slurry is sucked from the opposite side and dried to form a precursor layer of the catalyst layer 20b. After forming the precursor layers of the catalyst layer 20a and the catalyst layer 20b, the catalyst layers 20a and 20b are formed by firing, and the exhaust gas purification catalyst 1B is manufactured. The manufacturing conditions for the exhaust gas purification catalyst 1B are the same as those for the exhaust gas purification catalyst 1A. [Examples]

[0151] [Example 1] 35.6g of zirconium oxynitrate aqueous solution (equivalent to 20g of Zr in ZrO2), 41.2g of cerium nitrate aqueous solution (equivalent to 16g of Ce in CeO2), 3.8g of lanthanum nitrate aqueous solution (equivalent to 0.8g of La in La2O3), 8.1g of neodymium nitrate aqueous solution (equivalent to 1.6g of Nd in Nd2O3), 7.1g of praseodymium nitrate aqueous solution (equivalent to Pr in Pr6O 111.6g of the raw material was dissolved in 370mL of deionized water and mixed uniformly in a 1L beaker to obtain the raw material solution. The raw material solution was added to 200g of 11wt% ammonia aqueous solution over 80 minutes to neutralize it, and a coprecipitation (precipitate) was generated from the raw material solution by coprecipitation to obtain a slurry. The slurry was filtered, and the resulting cake was filtered and washed with deionized water. Deionized water was added to the cake so that the solid content was 3.3%, and the raw material slurry was obtained. The raw material slurry was hydrothermally treated at 150°C for 12 hours. The slurry after hydrothermal treatment was collected, and the collected slurry was dried overnight at 120°C and calcined in a muffle oven at 700°C for 3 hours. After calcination, the calcined material was crushed with a hand mixer (Force Mill FM-1 manufactured by Osaka Chemical Co., Ltd.) and sieved with a 100 mesh. A composite oxide powder was produced by the above process.

[0152] [Example 2] A composite oxide powder was prepared in the same manner as in Example 1, except that the temperature of the hydrothermal treatment was changed to 180°C.

[0153] [Example 3] A raw material slurry was obtained in the same manner as in Example 1. Hydrothermal synthesis was performed using the raw material slurry. Hydrothermal synthesis was carried out using the hydrothermal synthesis apparatus 101 shown in Figure 6. The temperature of the mixing section 108 was set to 150°C, the temperature of the reactor 110 was set to 350°C, and the pressure of the reactor 110 was set to 25 MPa. After filtering the composite oxide-containing slurry recovered in the recovery tank 115, it was dried overnight at 120°C and sieved with a 100-mesh sieve. A composite oxide powder was prepared by the above process.

[0154] [Example 4] A composite oxide powder was prepared in the same manner as in Example 3, except that the temperature of the mixing section 8 was set to 250°C.

[0155] [Example 5] A composite oxide powder was prepared in the same manner as in Example 3, except that the raw material slurry was obtained by the following method.

[0156] 106.2g of zirconium chloride aqueous solution (equivalent to 20g of ZrO2), 74.6g of cerium chloride aqueous solution (equivalent to 16g of CeO2), 3.3g of lanthanum chloride aqueous solution (equivalent to 0.8g of LaO2), 6.8g of neodymium chloride aqueous solution (equivalent to 1.6g of NdO2), 9.1g of praseodymium chloride aqueous solution (equivalent to PrO2) 11 (Converted amount: 1.6g) was dissolved in 275mL of deionized water and mixed uniformly in a 1L beaker to obtain the raw material solution. 40g of 25wt% ammonium sulfate aqueous solution was added to the raw material solution over 40 minutes, followed by the addition of 200g of 25% sodium hydroxide aqueous solution over 80 minutes to neutralize the mixture. A coprecipitation (precipitate) was generated from the raw material solution by coprecipitation, and a slurry was obtained. The slurry was filtered, and the resulting cake was filtered and washed with deionized water. Deionized water was added to the cake until the solid content was 3.3%, and the raw material slurry was obtained.

[0157] [Example 6] A composite oxide powder was prepared in the same manner as in Example 5, except that the temperature of the mixing section 8 was set to 250°C.

[0158] [Comparative Example 1] 97.9g of zirconium oxychloride aqueous solution (equivalent to 20g of ZrO2), 74.6g of cerium chloride aqueous solution (equivalent to 16g of CeO2), 3.3g of lanthanum chloride aqueous solution (equivalent to 0.8g of LaO2), 6.8g of neodymium chloride aqueous solution (equivalent to 1.6g of NdO2), 9.1g of praseodymium chloride aqueous solution (equivalent to PrO2) 11 1.6g of the raw material was dissolved in 330mL of deionized water and mixed uniformly in a 1L beaker to obtain the raw material solution. 200g of 24wt% sodium hydroxide aqueous solution was added to the raw material solution over 80 minutes to neutralize it, and a coprecipitation (precipitate) was generated from the raw material solution by coprecipitation to obtain a slurry. The slurry was filtered, and the resulting cake was filtered and washed with deionized water. The cake was dried overnight at 90°C and then baked in a muffle oven at 700°C for 3 hours. After baking, the baked material was crushed with a hand mixer (Force Mill FM-1, manufactured by Osaka Chemical Co., Ltd.) and sieved through a 100-mesh sieve. A composite oxide powder was prepared by the above process.

[0159] <Infrared absorption spectrum after methanol adsorption (MeOH-IR)> Regarding each of the composite oxide powders obtained in the examples and comparative examples, infrared absorption spectra were measured by the following method.

[0160] Approximately 80 mg of the composite oxide powder (the composite oxide powder without supporting a noble metal element) was molded at a pressure of 30 MPa / cm 2 to obtain a sample disk. This was set in an in-situ IR cell and pretreated by the following procedures (a) to (d). (a) Under vacuum evacuation conditions (1×10 -2 Pa or less), the temperature was raised from room temperature (30 °C) to 600 °C at a heating rate of 10 °C / min, and then vacuum evacuation (1×10 -2 Pa or less) was performed at 600 °C for 30 minutes. (b) Oxidation treatment was performed at 600 °C for 1 hour while flowing O2 at a pressure of 3.99×10 4 Pa (300 Torr). (c) While maintaining the temperature of the composite oxide at 600 °C, vacuum evacuation treatment (1×10 -2 Pa or less) was performed for 2 hours. (d) It was cooled to room temperature.

[0161] The sample disk pretreated by the above procedures was brought into contact with methanol vapor at a pressure of 1.33×10 3 Pa (10 Torr) for 5 minutes at room temperature (30 °C) to adsorb methanol. Then, after evacuation at room temperature, the infrared absorption spectrum was measured at room temperature. For the measurement, Nicolet 6700 FT-IR manufactured by Thermo Scientific was used.

[0162] Regarding the obtained spectrum, peak separation was performed using peak separation software (OMNIC manufactured by Thermo Scientific).

[0163] In the spectrum after peak separation, at 1100 cm -1 or higher and 1110 cm -1Within the following range, one peak (corresponding to Type I) was observed. The area of ​​this single peak was calculated to be 1100 cm². -1 More than 1110cm -1 The area S of the peak observed within the following range A (Unit: au cm) -1 ) was used. Note that "au" is an abbreviation for arbitrary unit.

[0164] In the spectrum after peak separation, 1030 cm⁻¹ -1 More than 1100cm -1 Within the range below 1080 cm, there are three peaks, namely 1080 cm. -1 More than 1100cm -1 The first peak is located below 1050cm. -1 More than 1080cm -1 A second peak located below a certain wavenumber, and a third peak located at a lower wavenumber than the second peak, were observed. The first and second peaks were designated as Type II peaks, and the third peak as Type II' peak. The first peak corresponds to the crystal plane {100}, and the second peak corresponds to the crystal plane {110}. The areas of the first, second, and third peaks were calculated, and the sum of the areas of these three peaks was calculated to be 1030 cm². -1 More than 1100cm -1 Area S of peaks observed in the range less than B (Unit: au cm) -1 )

[0165] The obtained S A and S B Based on S B / S A The value of was calculated. The results are shown in Table 1.

[0166] <crystallite size> The crystallite size was measured for each of the composite oxide powders obtained in the examples and comparative examples using the following method. The results are shown in Table 1.

[0167] X-ray diffraction (XRD) was performed using a composite oxide and a commercially available powder X-ray diffractometer (MiniFlex600, Rigaku Corporation) under the following conditions: X-ray source: CuKα, operating axis: 2θ / θ, measurement method: continuous, counting unit: cps, start angle: 5°, end angle: 90°, sampling width: 0.02°, scan speed: 10° / min, voltage: 40kV, current: 150mA. From the obtained XRD patterns, the diffraction peaks originating from the composite oxide that were located at 2θ = 28~30° were identified. Using analysis software (PDXL version 2, Rigaku Corporation), Scherrer's equation was applied to the identified peaks to automatically calculate the crystallite size. The crystallite size obtained from the peaks at 2θ = 28~30° was selected as the crystallite size of the composite oxide.

[0168] <D 90 > For each of the composite oxide powders obtained in the examples and comparative examples, D is performed by the following method. 90 Measurements were taken. The results are shown in Table 1.

[0169] Using an automated sample feeder for laser diffraction particle size distribution analyzers ("Microtorac SDC" manufactured by Nikkiso Co., Ltd.), powder samples were placed in an aqueous solvent. After irradiating with 40W ultrasound at a flow rate of 40% for 360 seconds, the volume-based particle size distribution was measured using a Nikkiso Co., Ltd. laser diffraction particle size distribution analyzer "Microtorac MT3300II". From the volume-based particle size distribution, the particle size (μm) at which the cumulative volume reached 90% was measured. The measurement was performed twice, and the average value of the particle size (μm) at which the cumulative volume reached 90% was calculated as D. 90 The measurement was performed in (μm). The measurement conditions were: particle refractive index 1.5, particle shape spherical, solvent refractive index 1.3, set zero 30 seconds, and measurement time 30 seconds.

[0170] <Specific surface area> The specific surface area of ​​each of the composite oxide powders obtained in the examples and comparative examples was measured using the following method. The results are shown in Table 1.

[0171] The specific surface area was measured according to the "(3.5) Single-point method" in "6.1 Quantitative Method" of JIS R1626:1996 "Method for Measuring Specific Surface Area of ​​Fine Ceramic Powder by Gas Adsorption BET Method". Nitrogen, an adsorption gas, was used as the gas, and a single measurement was performed within the equilibrium relative pressure range of 0.05 to 0.35. The measuring device used was the "BELSORP-miniX" manufactured by Microtrac-Bel.

[0172] <osc> The OSC was measured for each of the composite oxide powders obtained in the examples and comparative examples using the following method. The results are shown in Table 1.

[0173] OSC measurements were performed using the BP-1 gas adsorption meter manufactured by Hemmi Slide Rule Co., Ltd. For the OSC measurements, the composite oxide was pre-treated by heating it to 600°C under a 5%-H2 / Ar flow and maintaining that temperature for 30 minutes. Then, while maintaining the temperature at 600°C, O2 gas was injected in 10 pulses. The total amount of OSC per unit mass of the composite oxide powder at 600°C (mL / g) was determined from the total amount of O2 gas consumed using an infrared gas concentration meter (Shimadzu Corporation, CGT-7000).

[0174] [Table 1]

[0175] As shown in Table 1, S B / S A The composite oxide powders (Examples 1-6) whose value is 4.2 or higher are S B / S A Compared to the composite oxide powder (Comparative Example 1) with a value of less than 4.2, it had improved OSC. [Explanation of Symbols]

[0176] 1A, 1B... Catalysts for exhaust gas purification 10...Base material 11. Cylindrical part 12...Bulkhead part 13...cell 20,20a,20b...Catalyst layer 101...Hydrothermal synthesis equipment 102... Aquarium 103...Raw material supply tank 104... Pump 105...Water supply channel 106... pump 107...Raw material supply route 108...Mixing section 109...Heating means 110... Reactor 111... Reaction liquid supply channel 112...product discharge path 113...Cooler 114. Pressure regulating valve 115... Recovery tank< / osc>

Claims

1. A composite oxide containing Ce, Zr, and one or more rare earth elements other than Ce, One or more rare earth elements other than Ce are selected from Pr, La, and Nd. When methanol was adsorbed onto a composite oxide without supporting noble metal elements and the infrared absorption spectrum was measured, the value was 1100 cm⁻¹. －１ 1110cm or more －１ The area S of the peak observed within the following range Ａ 1030cm －１ More than 1100cm －１ Area S of peaks observed in the range less than Ｂ S is the ratio of Ｂ / S Ａ The value is between 4.2 and 6.5, A composite oxide having a specific surface area of ​​150 m² / g or more.

2. The composite oxide according to Claim 1, wherein the value of S B / S A is 4.4 or more.

3. The composite oxide according to claim 1 or 2, wherein the value of S B / S A is 6.0 or less.

4. The composite oxide according to any one of claims 1 to 3, wherein the crystallite size of the composite oxide is 60 Å or less.

5. The composite oxide according to claim 4, wherein the crystallite size of the composite oxide is 52 Å or less.

6. D of the composite oxide ９０ The composite oxide according to any one of claims 1 to 5, wherein ９０ is 30 μm or less.

7. A catalyst composition for exhaust gas purification comprising a composite oxide according to any one of claims 1 to 6 and a catalytically active component.

8. The exhaust gas purification catalyst composition according to claim 7, wherein the catalytic active component contains a noble metal element.

9. The exhaust gas purification catalyst composition according to claim 7 or 8, wherein at least a portion of the catalytically active component is supported on the composite oxide.

10. An exhaust gas purification catalyst comprising a base material and a catalyst layer provided on the base material, A catalyst for exhaust gas purification, wherein the catalyst layer is composed of the exhaust gas purification catalyst composition described in any one of claims 7 to 9.

11. The following steps (a) and (d): (a) A step of obtaining a slurry by coprecipitation from a raw material liquid containing a cerium salt, a zirconium salt, and one or more rare earth metal salts other than a cerium salt; (d) A step in which hydrothermal synthesis is performed using the slurry obtained in step (a) to obtain a complex oxide as a hydrothermal product. A method for producing a composite oxide according to any one of claims 1 to 6, comprising: One or more rare earth metal salts other than cerium salts are selected from praseodymium salts, lanthanum salts, and neodymium salts. A manufacturing method in which hydrothermal synthesis is carried out under subcritical conditions, where "subcritical conditions" means conditions where the temperature is 270°C or higher and the pressure is 20 MPa or higher, but not meeting the supercritical conditions, and "supercritical conditions" means conditions where the temperature is 374°C or higher and the pressure is 22.1 MPa or higher.

12. The manufacturing method according to claim 11, wherein in the coprecipitation method, by adding a precipitant to the raw material liquid or by adding the raw material liquid to the precipitant, a precipitate is formed containing Ce, Zr, and one or more rare earth elements other than Ce, wherein one or more rare earth elements other than Ce are selected from Pr, La, and Nd.

13. The manufacturing method according to claim 12, wherein the precipitating agent is selected from an aqueous solution containing hydroxide ions and a compound that can dissolve in water to produce hydroxide ions.

Images