JP2005193179A - Inorganic oxide powder, catalyst carrier and catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inorganic oxide powder having a sufficiently superior heat resistance, a precursor of the inorganic oxide powder capable of forming the inorganic oxide powder, a catalyst carrier using the above inorganic oxide powder and a catalyst using the catalyst carrier. <P>SOLUTION: The inorganic oxide powder of the present invention for solving the above problem comprises Al<SB>2</SB>O<SB>3</SB>, a metal oxide which does not form a complex oxide with Al<SB>2</SB>O<SB>3</SB>and a rare-earth element and/or a rare-earth oxide. Not less than 80% of primary particles of the metal oxide have a particle size of not more than 100 nm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inorganic oxide powder, a catalyst carrier using the inorganic oxide powder, and a catalyst including the catalyst carrier.

  In recent years, the presence of harmful gases that can exist in the environment surrounding humans and can affect the human body has been regarded as a problem. For example, aldehydes emitted from the building materials into the air Development of technology capable of reliably purifying NOx, CH and CO, which are harmful components in automobile exhaust gas, is desired.

  Under such circumstances, various catalysts for purifying harmful gases have been developed. For example, Patent Document 1 discloses an inexpensive and stable three-way catalyst system for treating exhaust gas from an internal combustion engine. A layered catalyst composite comprising a first layer and a second layer, intended for development, wherein the first layer comprises a first support, substantially only one platinum group metal component in the first layer. At least one first palladium component, a first oxygen storage component in intimate contact with the first palladium component, optionally a first zirconium component, optionally at least one first alkaline earth metal component, and Optionally, at least one first rare earth metal component selected from the group consisting of a lanthanum metal component and a neodymium metal component, wherein the first layer comprises at least one first alkaline earth metal component and At least 1 At least one second palladium component that requires a first rare earth metal component and wherein the second layer is a second support, substantially only one platinum group metal component within the second layer; Optionally a second zirconium component, optionally at least one second alkaline earth metal component, and optionally at least one second rare earth metal component selected from the group consisting of a lanthanum metal component and a neodymium metal component. Wherein the second layer requires at least one second alkaline earth metal component and at least one second rare earth metal component, the first and second supports being the same or different and alumina Activated silica selected from the group consisting of silica, silica-alumina, alumino-silicates, alumina-zirconia, alumina-chromia and alumina-ceria Layered catalyst composites are described a compound.

  Patent Document 2 intends to provide an exhaust gas purifying catalyst having improved low-temperature activity and purifying performance even after high-temperature endurance, and a method for producing the same, as compared with conventional catalysts. In the monolithic catalyst having the catalyst component-supporting layer, the catalyst component includes at least rhodium and zirconium oxide, and the zirconium oxide is at least selected from the group consisting of magnesium, calcium, strontium, barium, yttrium and lanthanum. An exhaust gas purifying catalyst containing one kind has been proposed. The zirconium oxide is prepared by dissolving or dispersing the water-soluble salt of at least one of the above and zirconium in water, and then adding aqueous ammonia or an aqueous solution of an ammonium compound to adjust the pH of the solution to a range of 6.0 to 10.0. It is disclosed that after being adjusted to become, after removing moisture, it is dried and then calcined.

Further, Patent Document 3 discloses a mixture of a Zr oxide and an oxide of a metal M that does not form a solid solution with the Zr oxide. The Zr oxide and the oxide of the metal M are uniformly distributed on the nm scale. Dispersed fine mixed oxide powders have been proposed. In this Patent Document 3, the fine mixed oxide powder has a large specific surface area and pore volume even after high temperature durability, and when noble metal is supported as a catalyst, grain growth of the noble metal is suppressed after high temperature durability. Is intended.
JP-T 9-500570 JP-A-9-141098 JP 2003-20227 A

  However, the present inventors have studied in detail the conventional catalysts including those described in Patent Documents 1 to 3, and all of these conventional catalysts have sufficient heat resistance. I found out that it is not. Further, when such a catalyst that does not have sufficient heat resistance, for example, the above-described conventional catalyst is used as an exhaust gas purification catalyst, the exhaust gas of automobiles is at a high temperature of about 600 to 1100 ° C., so that CO (carbon monoxide) of the catalyst And CH (hydrocarbon) oxidation activity and NOx (nitrogen oxide) reduction activity have decreased over time, and it has become clear that the catalyst does not have a sufficient function as an exhaust gas purification catalyst.

  As one of the factors affecting the heat resistance of such a catalyst, it is considered that the heat resistance of the inorganic oxide powder used for the catalyst carrier is insufficient. That is, when a catalyst obtained by supporting a metal on a support made of an inorganic oxide powder with insufficient heat resistance is used, sintering of the support occurs under a high temperature environment, and the supported metal Since the grain growth is promoted, it is presumed that the specific surface area and pore volume as a catalyst are reduced, and the catalytic activity is lowered.

  Accordingly, the present invention has been made in view of the above circumstances, and provides an inorganic oxide powder having sufficiently excellent heat resistance, a catalyst carrier using the inorganic oxide powder, and a catalyst using the catalyst carrier. The purpose is to do.

  As a result of intensive studies to achieve the above object, the present inventors have appropriately selected a combination of oxide materials constituting the inorganic oxide powder, and further, set the particle size of the primary particles in the inorganic oxide powder. As a result of the adjustment, it was found that the grain growth of the oxide is suppressed even under a high temperature environment, and the present invention has been completed.

Inorganic oxide powder of the present invention, Al ₂ O _3, containing a metal oxide forming no composite oxide of Al ₂ O _3, a rare earth element and / or rare earth oxides, 80% of the primary particles The above has a particle diameter of 100 nm or less. Here, “metal” of “metal oxide” includes Si, and therefore “metal oxide” includes SiO ₂ .

  The present inventors consider the following factors regarding the reason why such inorganic oxide powder has sufficiently excellent heat resistance. However, the factors are not limited to these.

Conventional inorganic oxide powder, for example as those described in Patent Document 1 contains an Al ₂ O _3, a metal oxide forming no composite oxide of Al ₂ O _3, such as ZrO ₂ Even if the primary particles of each oxide are poorly dispersible, the primary particles of any oxide are likely to be unevenly distributed, that is, the aggregates of the primary particles of the metal oxide are unevenly distributed. The aggregates composed of primary particles of Al ₂ O ₃ tend to be unevenly distributed. When such an inorganic oxide powder is placed in a high temperature environment, it is considered that primary particles of metal oxide that do not form a composite oxide with Al ₂ O ₃ are aggregated and / or bonded.

For example, the inorganic oxide powder described in Patent Document 2 is intended to improve high-temperature durability by adding a rare earth element such as yttrium to ZrO ₂ . However, all of the added elements have a property of forming a complex oxide by dissolving in ZrO ₂ under a high temperature environment. Therefore, such an inorganic oxide powder does not contain a barrier when the primary particles of the composite oxide obtained in a high temperature environment diffuse, and as a result, the primary particles are sintered together. It is presumed that the ring aggregates and / or bonds.

Furthermore, for example, in the inorganic oxide powder described in Patent Document 3, ZrO ₂ and Al ₂ O ₃ as a metal oxide not dissolved in ZrO ₂ are uniformly dispersed on a nanometer scale. Therefore, in such an inorganic oxide powder, the primary particles of the respective oxides serve as diffusion barriers, and the grain growth of these primary particles tends to be suppressed as compared with that in the above-described inorganic oxide powder. . However, even such inorganic oxide powders are placed in a high temperature environment for a relatively long time, or in a high temperature environment where the state of the atmospheric gas changes in a short time, such as in an automobile exhaust gas. If it is placed, the grain growth of the primary particles proceeds, so it was confirmed that it cannot be said to have sufficient heat resistance (see Comparative Example 3).

On the other hand, in the inorganic oxide powder of the present invention, metal oxide contained together with Al ₂ O ₃ is, because it has a property of not forming a composite oxide with its Al ₂ O _3, consisting of oxide composite There are almost no primary particles of oxide, and primary particles of each single oxide are present. Furthermore, since 80% or more of the primary particles have a particle diameter of 100 nm or less, the particles of the same type of primary particles (for example, primary particles of Al ₂ O ₃ ) are present in which primary particles of each type are interposed. Dispersed in a state where different kinds of primary particles (for example, metal oxide not forming a complex oxide with Al ₂ O ₃ ) are interposed between them. Therefore, even when this inorganic oxide powder is exposed to a high temperature environment, the primary particles of the same type of oxide are not relatively close to each other, and the primary particles of one single oxide are not mixed with the other single oxide. Therefore, it is presumed that the progress of aggregation of the primary particles of the single oxide accompanying the diffusion is sufficiently prevented. Therefore, it is presumed that the progress of grain growth of the primary particles of the single oxide is sufficiently suppressed.

In addition, the inorganic oxide powder of the present invention contains a rare earth oxide, so that the rare earth oxide is solid-solved in the metal oxide contained in Al ₂ O ₃ and / or together, thereby improving the crystallinity of the primary particles. In order to reduce the surface energy of the particles, it is considered that the aggregation due to the bonding between the primary particles is effectively inhibited.

From the same viewpoint, the inorganic oxide powder of the present invention comprises a Al ₂ O _3, and a metal oxide forming no composite oxide of Al ₂ O _3, a rare earth element and / or rare earth oxides, 80% or more of the primary particles of the metal oxide may have a particle size of 100 nm or less. In such an inorganic oxide powder, since the primary particles of the metal oxide have high dispersibility and exist between the primary particles of Al ₂ O ₃ , the particles of the primary particles are similar to the inorganic oxide described above. It is thought that the progress of growth is sufficiently suppressed.

  From the viewpoint of more effectively demonstrating the effects of the present invention, the rare earth oxide is more preferably contained in the inorganic oxide powder in an amount of 0.5 to 10 atomic% or more, and more preferably 1 to 5 atomic% or more. preferable.

When the inorganic oxide powder of the present invention is used by being contained in a catalyst carrier, it is preferable because the effect resulting from its sufficient heat resistance is exhibited. That is, since Al ₂ O ₃ has a high specific surface area among inorganic oxides, the metal can be supported in a highly dispersed state as compared with other inorganic oxides. Further, a metal oxide that does not form a composite oxide with Al ₂ O ₃ can suppress solid solution of the supported metal in the carrier, particularly when ZrO ₂ is used as the metal oxide. Furthermore, since the support has high heat resistance, even if it is used as a catalyst exposed to a high temperature environment, the decrease in specific surface area and pore volume is sufficiently suppressed, and the dispersibility of the supported metal such as Rh is sufficiently suppressed. It can be held. As a result, it is estimated that the catalyst provided with the carrier maintains the catalytic activity even when used under high temperature conditions.

  In the inorganic oxide powder of the present invention, the content ratio of Al to the metal constituting the metal oxide is preferably 1: 5 to 5: 1 on a molar basis. By containing each oxide in such a ratio, the primary particles of each oxide tend not to be adjacent to each other.

Further, the secondary particles formed by agglomerating the primary particles described above contain primary particles made of Al ₂ O _3, primary particles made of the metal oxide, and a rare earth element and / or rare earth oxide. It is preferable that the content ratio of Al to the metal constituting the metal oxide is 1: 4 to 4: 1 on a molar basis because aggregation and / or bonding between primary particles tends to be further suppressed. From such a viewpoint, it is even more preferable that the inorganic oxide powder of the present invention comprises the above-described secondary particles at 50 atomic% or more.

The _"Al 2 _{O 3} primary particles composed of" herein, in addition to the primary particles composed of only _Al 2 _{O 3,} the metal oxide near the surface of the primary particles of _Al 2 _{O 3} ( Primary particles in which (metal) is dissolved are also included. In addition to “primary particles composed of metal oxides”, in addition to primary particles composed only of metal oxides that do not form composite oxides with Al ₂ O ₃ , the surface of the primary particles of the metal oxides In addition, primary particles in which Al ₂ O ₃ (Al) is dissolved are also included. Furthermore, the rare earth element and / or rare earth oxide may be dissolved in the primary particles thereof.

Inorganic oxide powder of the present invention comprises a _Al 2 _{O 3,} and a metal oxide forming no composite oxide of _Al 2 _{O 3,} and rare earth elements and / or rare earth oxides, a, _Al 2 _{O 3} Among the primary particles made of the above and the primary particles made of the above metal oxide, the primary particles having a particle diameter determined based on FE-STEM and EDX in the analysis range of 1 μm square are 100 nm or less, and Al and the above metal oxide In the analysis range in which the content ratio of secondary particles to be included is 1 μm square so that the molar ratio of the metal constituting the product is within ± 20% of the molar ratio of Al to the metal in the raw material, It is characterized by being adjusted so that it may become 50 atomic% or more of the secondary particle which exists in the analysis range.

  Even when such inorganic oxide powder is exposed to a high temperature environment, the probability that primary particles of the same type of oxide are close to each other is relatively low, and the primary particle of one single oxide is the single oxide of the other. Therefore, it is considered that the progress of aggregation of the primary particles of the single oxide accompanying the diffusion is sufficiently prevented. Further, the presence of rare earth elements and / or rare earth oxides is considered to effectively suppress the bonding between primary particles. As a result, the inorganic oxide powder of the present invention is sufficiently excellent in heat resistance because the grain growth of primary particles is sufficiently suppressed even in a high temperature atmosphere.

From the same viewpoint, the inorganic oxide powder of the present invention comprises a Al ₂ O _3, and a metal oxide forming no composite oxide of Al ₂ O _3, and rare earth elements and / or rare earth oxides, the Among the primary particles made of Al ₂ O ₃ and the primary particles made of the metal oxide, the particle diameter determined based on FE-STEM and EDX in the analysis range of 1 μm square after the heat test is 100 nm or less. Secondary particle content ratio including primary particles so that the molar ratio of Al to the metal constituting the metal oxide is within ± 20% of the molar ratio of Al to the metal in the raw material However, in the analysis range of 1 μm square, it is preferable that the secondary particles existing in the analysis range be adjusted to 50 atomic% or more because the heat resistance is further improved.

  Here, the “endurance test” refers to a temperature of about 800 to 1100 ° C. in an exhaust gas atmosphere generated by burning an air-fuel mixture or a gas atmosphere having a gas composition simulating the exhaust gas. This is a test performed by exposing to 1 to 50 hours. This “endurance test” includes, for example, an exhaust gas atmosphere generated by burning a lean mixture (an air-fuel mixture whose air-fuel ratio is larger than the theoretical mixture ratio) or a gas atmosphere having a gas composition simulating the exhaust gas, 1000 ° C. in both the gas atmospheres of the exhaust gas atmosphere generated by burning the rich mixture (the fuel-excess mixture whose air-fuel ratio is smaller than the theoretical mixture ratio) or the gas atmosphere simulating the exhaust gas It is carried out by alternately exposing at a high temperature for about 5 hours. The “endurance test” is usually performed to evaluate the durability of the exhaust gas purification catalyst.

At least a portion of the rare earth oxide, Al 2 _{O 3,} or the Al ₂ O ₃ and the formed as a solid solution in the composite oxide of the metal oxide forming no preferred. Since rare earth oxides are relatively low in stability, they tend to exist in the form of solid solutions in the primary particles of any of the single oxides described above. However, the rare earth oxides are dissolved in the primary particles. By doing, it exists in the tendency which can suppress the coupling | bonding of primary particles further. From such a viewpoint and a viewpoint of further improving the catalytic activity when the inorganic oxide powder is used as a catalyst carrier, the rare earth element constituting the rare earth oxide is selected from the group consisting of La, Nd, Y, Pr and Tb. One or more selected elements are preferred. Note that the rare earth elements in this specification do not include radioactive elements (Pm and actinoids).

The inorganic oxide powder of the present invention described above is a coprecipitate that obtains a coprecipitation product of an Al compound, a metal compound that does not form a composite oxide of Al ₂ O ₃ when formed into an oxide, and a rare earth compound. If it forms through a process and the baking process which bakes a coprecipitation product in 600-1200 degreeC oxidizing atmosphere, it is preferable from a viewpoint of a heat resistant improvement.

As described above, the inorganic oxide powder of the present invention can be used as a catalyst carrier, and the catalyst carries one or more precious metals selected from the group consisting of Rh, Pt and Pd on the catalyst carrier. This is preferable. Since such a catalyst is often used at a relatively high temperature, the inorganic oxide powder of the present invention can be used more effectively as a carrier. Furthermore, when Rh is used as a supported metal, Rh is originally liable to be dissolved in the support, so that the effect of suppressing solid solution of metal oxides that do not form a complex oxide with Al ₂ O ₃ , particularly ZrO ₂ , is suppressed. Is more preferable, and the catalytic activity can be further improved.

  If this catalyst is used for exhaust gas purification, the inorganic oxide powder of the present invention can be used very effectively as a carrier. That is, the conventional catalyst for exhaust gas purification is easily deteriorated because the exposed atmosphere is very easy to change, and its activity is reduced in a relatively short period of time. However, by using the inorganic oxide powder of the present invention as a carrier, the exhaust gas purifying catalyst of the present invention tends to be further suppressed in deterioration and to maintain high activity.

  According to the present invention, it is possible to provide an inorganic oxide powder having sufficiently excellent heat resistance, and an inorganic oxide powder precursor capable of forming the inorganic oxide powder, and furthermore, sufficiently excellent heat resistance. By providing the catalyst carrier having the above and the catalyst carrier, a catalyst having sufficiently excellent activity can be provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as necessary.

Inorganic oxide powder of the present embodiment (hereinafter sometimes referred to as "oxide powder".) Is, Al ₂ O _3, metal oxide forming no composite oxide of Al ₂ O ₃ (hereinafter, sometimes " MOx)) and a rare earth oxide, and 80% or more of the primary particles in the inorganic oxide powder have a particle size of 100 nm or less. In the inorganic oxide powder, primary particles are aggregated to form secondary particles.

One The primary particles, Al ₂ O primary particles consisting of only _three, primary particles composed of MOx only primary particles with a rare earth oxide Al ₂ O ₃ principal components is formed as a solid solution, and, the main component MOx Primary particles formed by dissolving a rare earth oxide in a solid solution. However, an element other than oxygen (hereinafter also referred to as “M” in some cases) constituting the metal compound is slightly dissolved in the vicinity of the surface of the primary particles of Al ₂ O ₃ , or Al is a primary particle of MOx. Further, primary particles mainly composed of rare earth oxides may be formed.

Secondary particles of the above-described primary particles, as a main component _Al 2 _{O 3,} that is, a solid solution is the rare earth oxide _Al 2 _{O 3} of the primary particles and / or principal component _Al 2 _{O 3} Primary particles formed and / or primary particles in which M is partly dissolved in the vicinity of the surface of the primary particles, and those containing MOx as a main component, that is, MOx primary particles and / or main components Primary particles formed by solid solution of rare earth oxides in MOx and / or primary particles formed by solid solution of Al in the vicinity of the surface of the primary particles are formed by aggregation. Preferably there is. When the secondary particles are composed of such primary particles, the oxide powder tends to have sufficiently excellent heat resistance.

In the inorganic oxide powder of this embodiment, the property that MOx does not form a composite oxide with Al ₂ O ₃ (for example, the ionic radius of M ions (M ^{2x +} ) is significantly different from the ionic radius of Al ions (Al ³⁺ ). Therefore, it is difficult to replace M ions with Al ions, or the ion radius of M ions is too large to enter between lattices of Al ₂ O ₃ ). There are almost no primary particles of the product, and primary particles of each single oxide are present. Furthermore, since most primary particles have a particle diameter of 100 nm or less, they are dispersed in a state where primary particles of each other are interposed. Therefore, even if this inorganic oxide powder is exposed to a high temperature environment, the same kind of oxides are not relatively close to each other, so that it is presumed that the progress of primary particle growth tends to be suppressed.

In addition, since the inorganic oxide powder of the present embodiment contains a rare earth oxide, the rare earth oxide is dissolved in a metal oxide contained in Al ₂ O ₃ and / or together, and the crystallinity of primary particles is increased. In order to improve and reduce the surface energy of the particles, it is considered that the aggregation due to the bonding between these primary particles is effectively inhibited. From such a viewpoint, it is preferable that the oxide powder of the present embodiment contains primary particles formed by dissolving at least a part of the rare earth oxide in Al ₂ O ₃ and / or MOx.

Note that, among the secondary particles provided in the oxide powder of the present embodiment, even when only the primary particles of Al ₂ O ₃ are aggregated and formed, only the primary particles of MOx are aggregated and formed. There may be something that has been done. However, it is preferable that the above-described preferred secondary particles are provided in the inorganic oxide powder in an amount of 50 atomic% or more because it tends to have more excellent heat resistance.

As described above, in the inorganic oxide powder of this embodiment, 80% or more of the primary particles have a particle diameter of 100 nm or less. By making the primary particles so fine, in the oxide powder of this embodiment, and further in the secondary particles provided in the oxide powder, the primary particles of Al ₂ O _{3 and} the primary particles of MOx Can be uniformly dispersed in a state where they are intervened with each other. As a result, the primary particles of one single oxide serve as a diffusion barrier that prevents the diffusion and aggregation of the primary particles of the other single oxide, and therefore, the progress of primary particle growth is likely to be suppressed. It is done.

  Furthermore, since the mesopores of about 1 to 100 nm are formed between the primary particles by reducing the particle diameter of the primary particles, an oxide powder having a high specific surface area can be obtained. The “mesopore” means a pore having a diameter of 2 to 50 nm in IUPAC, but it may mean a pore of about 1 to 100 nm in terms of molecular adsorption characteristics. Such mesopores are measured by a known pore diameter measurement technique using a mercury porosimeter or the like.

  From the above viewpoint, the inorganic oxide powder of the present embodiment preferably contains 80% or more of primary particles having a particle diameter of 100 nm or less, more preferably 90% or more, and still more preferably 95% or more. From the same viewpoint, the average particle size of the entire inorganic oxide powder is preferably 1 to 50 nm, and more preferably 3 to 40 nm.

Al ₂ O ₃ contained in the inorganic oxide powder of the present embodiment may be amorphous (for example, activated alumina) or crystalline, but the inorganic oxide powder is used as a catalyst. When used as a carrier, it is preferable that the specific surface area is large and the heat resistance is relatively excellent from the viewpoint of further improving the catalytic activity.

The metal oxide (MOx) that does not form a composite oxide with Al ₂ O ₃ is a metal oxide in which M does not substitute or penetrate into the primary particles of Al ₂ O ₃ , in other words, a solid solution together with Al ₂ O _3. Is a metal oxide that does not form Such MOx is because it forms a separate primary particles and primary particles of Al ₂ O _3, it does not form primary particles of the complex oxide with Al ₂ O _3. However, as described above, M may be slightly dissolved in the vicinity of the surface of the primary particles of Al ₂ O ₃ , or Al may be slightly dissolved in the vicinity of the surface of the primary particles of MOx.

Examples of such MOx include ZrO ₂ , SiO _{2, and} TiO _2, and one of these can be used alone or two or more can be used in combination. Among these, when inorganic oxide powder is used as a catalyst carrier, ZrO ₂ is preferably employed from the viewpoint of suppressing solid solution of the supported metal in the carrier.

The rare earth oxide contained in the inorganic oxide powder of this embodiment is added in order to improve the heat resistance of the oxide powder. Since rare earth oxides are generally highly basic along with alkaline earth oxides and the like, when used as a catalyst carrier, they cause a solid phase reaction with the supported metal and inactivate the supported metal. However, even if a rare earth oxide is used in the inorganic oxide powder of this embodiment, the decrease in the activity of the metal-supported catalyst using this as a catalyst carrier is sufficiently suppressed. This is because the inorganic oxide powder contains a metal oxide such as ZrO ₂ that does not form a composite oxide with Al ₂ O ₃ , and the primary particles have a fine particle diameter of 100 nm or less. It is presumed that ZrO _{2 and the} like having a solid solution suppressing effect on the supported metal are uniformly dispersed throughout the oxide powder. Even when such an oxide powder is used as a catalyst support, the metal oxide uniformly dispersed throughout the oxide powder suppresses the solid-state reaction of the supported metal due to the basicity of the rare earth oxide. It is considered that the catalytic activity of is maintained.

Among the rare earth oxides, the rare earth elements constituting the rare earth oxide are La, Nd, and Y from the viewpoint of further improving the heat resistance and the catalytic activity when the oxide powder is used as a catalyst carrier. It is preferable that a rare earth oxide which is one or more elements selected from the group consisting of Pr and Tb is contained in the oxide powder, and it is more preferable that La ₂ O ₃ is contained in the oxide powder.

  The preferable rare earth oxides contained in the inorganic oxide powder of the present embodiment described above are the factors that improve the heat resistance of the oxide powder and the catalytic activity when the oxide powder is used as a catalyst carrier. Although not clarified, one of the factors that can be referred to is the standard electrode potential of the rare earth element constituting the rare earth oxide. Table 1 shows the standard electrode potentials of the main elements having rare earth elements and the oxidation number + IV or + III when forming a stable oxide in the atmosphere at room temperature (Source: Web Elements Periodic Table presented by 210th American Chemical) Society Meeting).

  This standard electrode potential also serves as one of the indexes for the cation reduction ease. When the cation forms an oxide, it is considered to be an index for the electron withdrawing from the metal supported on the oxide. That is, it is considered that as the standard electrode potential value of an element other than oxygen constituting the oxide increases, electrons are more easily attracted from the metal supported on the oxide, that is, the supported metal becomes cationic. When a metal is cationic, that is, has a low electron density, if the catalyst obtained by supporting the metal is exposed to a high-temperature oxidizing atmosphere, the metal becomes difficult to form a stable oxide, and the carrier oxide and the supported metal It is thought that the supported metal grows and the catalytic activity decreases because the interaction with the catalyst becomes insufficient.

  On the other hand, as apparent from Table 1 above, the rare earth elements (La, Nd, Y, Pr and Tb) constituting the preferred rare earth oxide contained in the inorganic oxide powder of the present embodiment are all other It shows a standard electrode potential smaller than that of a main element whose oxidation number is + IV or + III, such as rare earth elements or Al or Zr. As described above, a metal supported on a metal oxide having a small standard electrode potential has a strong tendency to become anionic, and easily forms a stable bond with oxygen in a high-temperature oxidizing atmosphere. Since the metal oxide formed in this way has sufficient interaction with the carrier oxide, it is considered that the above-described metal grain growth can be suppressed when exposed to a high-temperature oxidizing atmosphere.

The content ratio of Al ₂ O ₃ and MOx contained in the inorganic oxide powder of the present embodiment is preferably a molar ratio (atomic ratio) between Al and M of 1: 5 to 5: 1. When the oxide powder contains each oxide in such a ratio, the primary particles of each oxide tend not to be adjacent to each other, and when this oxide powder is used as a catalyst support, There is a tendency to keep the supported metal stable. From such a viewpoint, the content ratio of Al and M is more preferably 1: 4 to 4: 1 on a molar basis.

  The content ratio of the rare earth oxide is preferably 1: 191 to 1: 9 in terms of a molar ratio between the rare earth element and (Al + M). If the rare earth oxide is contained in an amount larger than this content ratio, the standard electrode potential as the whole carrier oxide tends to be small. Since the interaction between the supported metal and the support oxide becomes too strong, the supported metal tends to be in an oxide state and tends to be difficult to exist as a metal. Further, if the rare earth oxide is contained in less than this content ratio, the effects due to the addition of the rare earth oxide as described above tend not to be achieved. Therefore, the content ratio of the rare earth oxide is more preferably 1:99 to 1: 9 in terms of a molar ratio of the rare earth element to (Al + M).

  Even after the endurance test, this inorganic oxide powder tends to contain 80% or more of primary particles having a particle size of 100 nm or less, and thus can be said to be sufficiently excellent in heat resistance. In this case, the test object of the “endurance test” is inorganic oxide powder.

  The inorganic oxide powder of the present embodiment has been described above. The particle diameter of the primary particles and the content ratio of each oxide related to the inorganic oxide powder described above should be analyzed and measured using a conventionally known method. Examples of such methods include the following. The particle diameter of each primary particle can be examined using XRD (X-ray diffraction method), TEM (transmission electron microscopy), SEM (scanning electron microscopy) or the like. In addition, when employ | adopting SEM, it is preferable after performing metal vapor deposition to oxide powder normally.

  The specific surface area, average particle diameter, or pore distribution of the entire oxide powder can be measured using a BET method utilizing nitrogen adsorption, a CI (Cranston and Inkley) method, an air permeation method, or a mercury intrusion method. The content ratio of each oxide is EDX (energy dispersive X-ray detection method), WDX (wavelength dispersive X-ray detection method), EELS (electron energy loss spectroscopy) method, chemical analysis, atomic absorption analysis, XRF. (Fluorescence X-ray analysis method), EPMA (X-ray microanalyzer method) or MS (mass spectrometry) can be used for confirmation.

  Furthermore, by combining the above methods, information such as the primary particle size and the content of each oxide can be obtained efficiently. For example, by combining FE-STEM (Field Emission-Scanning Transmission Electron Microscopy) and EDX, information on secondary particles in the oxide powder can be obtained as follows.

  That is, first, all or a part of the inorganic oxide powder is collected as a sample, and is set on the sample stage so that the secondary particles do not overlap as much as possible in the analysis range (observation screen). Next, the location where the secondary particles exist and the particle size of the primary particles are observed and confirmed by FE-STEM. FIG. 1 schematically shows the state of secondary particles and primary particles in the field of view (analysis range) of this FE-STEM (for example, 1 μm square). What can be confirmed by FE-STEM is the shapes of the secondary particles 22, 24, 26, etc. and the primary particles 12, 14, 16, 18, etc., the dispersion state of the particles, and the particle diameter.

Then, the spot diameter of EDX is set to a relatively wide range of about 50 nm, for example, and the state of inclusion of each oxide in the secondary particles is examined. Thereby, it is possible to quickly confirm whether or not Al ₂ O _3, MOx, and the like are contained in all the secondary particles in the sample and confirm the content ratio of these oxides. That is, among the secondary particles shown in FIG. 1, the secondary particles 22, 25, 27, and 28 contain Al ₂ O ₃ , MOx, and a rare earth oxide, and the secondary particles 24 include Al ₂ O ₃ and Only the rare earth oxide is contained, and it can be confirmed that the secondary particles 26 contain MOx and rare earth oxide, and the content ratio of each oxide in each secondary particle.

  Thus, for example, based on FE-STEM and EDX in the analysis range of 1 μm square, the particle diameter of the primary particles and the type of oxide constituting the primary particles are determined.

Furthermore, the spot diameter of EDX is set to a relatively narrow range of about 0.5 nm and measured, and by measuring it at a plurality of analysis points for each secondary particle, each oxide in each secondary particle is measured. The dispersion state can also be confirmed. That is, it can be confirmed which primary particles 12, 14, 16, 18 and the like shown in FIG. Specifically, for example, _Al 2 _{O 3} primary particles 12 consisting of primary particles made of MOx 14, _Al 2 _{O 3} and the primary particles 16 made of rare earth oxide, as well as primary particles consisting MOx and rare earth oxide 18 Can be confirmed. Among the analysis points measured in this way, at an analysis point of 90% or more in one secondary particle, the content ratio (atomic ratio) of Al and M is the ratio of Al and M in the raw material of the inorganic oxide powder. It is preferable that the error is within ± 20% with respect to the molar ratio because Al ₂ O ₃ and MOx are very uniformly dispersed and tend to intervene with each other.

  By adjusting the production or selection of the inorganic oxide powder so that such secondary particles are 50 atomic% or more of the total secondary particles in the analysis range, the heat resistance is further improved. It tends to be an oxide powder. From such a viewpoint, it is more preferable that the analysis / measurement method as described above is performed on the inorganic oxide powder after the heat test.

  Note that it is actually very difficult to perform the above-described analysis and measurement for all of the inorganic oxide powders of the present embodiment. However, information obtained by arbitrarily sampling a part of the sample as a sample and analyzing / measuring the sample is highly likely to correspond to all of the inorganic oxide powders of the present embodiment. At this time, the amount of sample to be sampled varies depending on the amount of inorganic oxide powder and the type of information, but is preferably 0.01% by mass or more of the inorganic oxide powder from the viewpoint of improving reproducibility and repeatability. .

  Further, the analysis / measurement method described above can be applied to a catalyst or a catalyst carrier described later as needed.

  The inorganic oxide powder of the present embodiment is preferably used by being contained in a catalyst carrier. As described above, since the inorganic oxide powder of the present embodiment has a heat resistance sufficiently excellent by having the above-described configuration, even if it is employed as a support for a catalyst used in a high temperature environment, the specific surface area. In addition, it is considered that the decrease in pore volume is sufficiently suppressed and the dispersibility of the supported metal such as Rh can be sufficiently maintained. As a result, it is considered that the catalyst provided with the carrier maintains the catalytic activity even when used under high temperature conditions.

  If the primary particle having a particle size of 100 nm or less in the catalyst carrier is obtained after the endurance test, the catalyst activity and the catalyst life are improved by improving the heat resistance of the catalyst using the carrier. This is preferable. In this case, the test object of the “endurance test” is a catalyst carrier or a catalyst in which a metal is supported on the catalyst carrier.

In addition, Al ₂ O ₃ has a high specific surface area among inorganic oxides and can support the metal in a highly dispersed state, so that the initial activity of the catalyst tends to be increased. Furthermore, as described above, it is preferable to use ZrO ₂ as a metal oxide that does not form a composite oxide with Al ₂ O ₃ because solid solution of the supported metal in the carrier can be suppressed. Further, when the rare earth element constituting the rare earth oxide is at least one element selected from the group consisting of La, Nd, Y, Pr and Tb, from the viewpoint of improving the heat resistance of the catalyst and improving the catalytic activity. Preferably, La is more preferable.

An inorganic oxide powder using these Al ₂ O ₃ , ZrO ₂ and the rare earth oxide (an oxide composed of one or more elements selected from the group consisting of La, Nd, Y, Pr and Tb). In particular, it is particularly preferable that 80% or more of the primary particles have a particle size of 100 nm or less as the catalyst carrier because the activity of the catalyst tends to be synergistically improved.

  The catalyst of this embodiment is formed by supporting the above-described inorganic oxide powder as a carrier and supporting a metal thereon. Such a catalyst has sufficiently excellent heat resistance and weather resistance. That is, even if the atmosphere (reactive gas) to which the catalyst is exposed changes extremely, and the temperature of the atmosphere is high, sintering of the catalyst carrier hardly occurs and the grain growth of the supported metal is sufficiently suppressed. . As a result, in this catalyst, the decrease in the specific surface area is sufficiently suppressed, and the pores carrying the metal remain sufficiently. Therefore, even if the catalyst of this embodiment is used under such severe conditions, the decrease in activity is sufficiently suppressed.

As the supported metal, no catalyst deterioration due to grain growth or the like tends to occur even under severe conditions. Therefore, it is preferable to use a noble metal, and one or more kinds of noble metals selected from the group consisting of Rh, Pt and Pd are used. More preferably, Rh is more preferable. When Rh is used as a supported metal, it is easily dissolved in the support originally, so that it does not form a complex oxide with Al ₂ O _{3 in} the support, and ZrO has an effect of suppressing the dissolution of Rh in the support. _When it is supported on the carrier of this embodiment containing ₂ , it is also preferable from the viewpoint of suppressing deterioration of the catalyst and further improving the catalytic activity.

  The amount of metal supported is not particularly limited, and may be adjusted according to the use of the obtained catalyst, reaction gas conditions, and the like. For example, when Rh is employed as a supported metal and used as an exhaust gas purification catalyst, the amount of Rh supported is in the range of 0.01 to 3% by mass, and tends to exhibit a catalytic action effectively as an exhaust gas purification catalyst. Therefore, it is preferable. When the amount of Rh supported is less than the above lower limit value, sufficient catalytic activity tends not to be expressed, and when it exceeds the upper limit value, the performance tends to be saturated. From such a viewpoint, the loading amount of Rh is more preferably 0.05 to 2% by mass, and further preferably 0.1 to 1% by mass.

  The catalyst of the present embodiment is not particularly limited as its application, but when used as a low temperature oxidation catalyst capable of removing HC in a low temperature range, a NOx reduction catalyst, a methane oxidation catalyst, a hydrogen purification catalyst, or an exhaust gas purification three-way catalyst, it is effectively catalyzed. It is preferable because it has a tendency to exhibit high heat resistance and weather resistance, and from the same viewpoint, it is particularly preferable when used as an exhaust gas purification three-way catalyst. Although the exhaust gas purification three-way catalyst needs to fully exhibit its function at high temperature and in a harsh environment, the catalyst of this embodiment has sufficient heat resistance and weather resistance. Even under such an environment, a decrease in catalyst activity over time can be sufficiently suppressed, so that it can be said that the catalyst is sufficiently useful as an exhaust gas purification three-way catalyst.

The catalyst of this embodiment may use an alkali metal such as Li, Na, K, or Cs or an alkaline earth metal such as Ba, Be, Mg, Ca, or Sr as the NOx storage material. Such NOx storage material stores NOx in the reaction gas in the form of nitrate or nitrite, and is effectively used particularly when the catalyst of this embodiment is used as a three-way catalyst for a lean burn engine that is an exhaust gas purification catalyst. It is done. That is, by using the NOx occlusion material, NOx stored in these NOx occlusion materials under an oxygen-excess atmosphere is reduced to N ₂ and discharged under a reducing atmosphere, which is further useful as an exhaust gas purification catalyst. Become.

  The catalyst of the present embodiment is not particularly limited in its use shape, and a coating layer is formed from the inorganic oxide powder of the present embodiment on the surface of a substrate such as a honeycomb-shaped monolith substrate, pellet substrate or foam substrate. In addition, the coating layer may be configured to carry a metal such as Rh, Pt or Pd.

  Next, the inorganic oxide powder of this embodiment and a method for producing a catalyst using the same as a carrier will be described.

The manufacturing method of the inorganic oxide powder of this embodiment is not specifically limited, For example, it carries out as follows. First, a mixed solution in which a water-soluble compound of Al, a water-soluble compound of an element M other than oxygen constituting a metal oxide whose oxide does not form a solid solution with Al ₂ O _3, and a water-soluble compound of a rare earth element are dissolved Is used to precipitate (coprecipitate) a coprecipitation product, which is a precipitate composed of an Al ₂ O ₃ precursor, an MOx precursor, and a rare earth oxide precursor (coprecipitation step).

  As each of the above water-soluble compounds, a salt is generally used, and as the salt, sulfate, nitrate, hydrochloride, acetate, and the like can be used. Moreover, water and alcohol can be used as a solvent which melt | dissolves a salt uniformly. Further, for example, aluminum hydroxide, nitric acid and water may be mixed and used as a raw material for aluminum nitrate. And precipitation of each oxide precursor precipitates by adding an alkaline solution to this solution. As the alkaline solution, an aqueous solution or alcohol solution in which ammonia, ammonium carbonate, sodium hydroxide, potassium hydroxide, sodium carbonate, or the like is dissolved can be used.

  Among these alkaline solutions, an aqueous solution or an alcohol solution in which ammonia or ammonium carbonate that volatilizes during firing is dissolved is more preferable. In addition, since the precipitation reaction of each oxide precursor is accelerated | stimulated as the pH of an alkaline solution is 9 or more, it is more preferable. Note that the precursor of each oxide is a hydroxide, carbonate, nitrate, or the like of an element other than oxygen constituting each oxide.

When the conventional inorganic oxide powder is obtained by the coprecipitation method, various oxides constituting the inorganic oxide powder are likely to form a solid solution by coprecipitation of the precursor. However, in the manufacturing method of the inorganic oxide powder of the present embodiment, the inorganic oxide constituting the inorganic oxide powder obtained is, Al ₂ O _3, metal oxide forming no composite oxide with Al ₂ O ₃ Therefore, even if the coprecipitation method is used, it is difficult for those oxides to form a solid solution, and furthermore, since rare earth oxides that are thought to inhibit the bonding between the primary particles of these oxides are included, it is even more Al. ₂ O ₃ and Al ₂ O ₃ tend to suppress the formation of a solid solution with a metal oxide that does not form a composite oxide.

  Subsequently, each oxide precursor obtained by coprecipitation is centrifuged, washed thoroughly, and then evaporated to dryness (temporary calcination) (evaporation to dryness step), whereby the inorganic oxidation of this embodiment is performed. A product powder is obtained. This evaporating and drying step is preferably performed at 100 to 550 ° C. for about 1 to 6 hours in an oxidizing atmosphere such as an air atmosphere.

  In the manufacturing method of the inorganic oxide powder of this embodiment, after the above-mentioned evaporation to dryness step, it is further fired in an oxidizing atmosphere at 600 to 1200 ° C. (baking step), and the inorganic oxide powder of this embodiment Is preferable. The inorganic oxide powder obtained through this firing step tends to have excellent heat resistance.

  Since the inorganic oxide powder obtained by the manufacturing method of the present embodiment described above is subjected to an endurance test after the firing step, primary particle growth is suppressed, so primary particles having a particle diameter of 100 nm or less are used. It tends to contain 80% or more

  In addition, as for the inorganic oxide powder obtained by the said evaporation-drying process or the baking process, the particle diameter of a primary particle is about several nanometer normally.

  The catalyst production method of the present embodiment is performed using the catalyst carrier obtained by the above-described inorganic oxide powder production method as a raw material. That is, the catalyst production method of the present embodiment is carried out by supporting a metal, for example, a noble metal such as Rh, Pt or Pd, on the carrier by a conventionally known metal loading method such as an impregnation method. For example, a cordierite or metal monolith substrate is coated with the above-mentioned carrier supporting the noble metal, or the carrier is pre-supported on the monolith substrate and further supported with the noble metal, and a three-way catalyst for exhaust gas purification. Can be used as The catalyst formed by being supported on this carrier is excellent in heat resistance and also exhibits sulfur poisoning resistance and phosphorus poisoning resistance.

  Even after the endurance test, 80% or more of the primary particles tend to have a particle diameter of 100 nm or less in the catalyst obtained by such a production method.

  The coating method using the catalyst carrier can be performed, for example, by preparing a slurry containing the catalyst carrier and the binder component, and firing after wet coating. Examples of the binder component include alumina sol, zirconia sol, and silica sol.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment. For example, the inorganic oxide powder of the present embodiment can be used not only as a catalyst carrier, but also as an adsorbent or molecular sieve. In another embodiment of the inorganic oxide powder of the present invention, Al ₂ O ₃ , a metal oxide that does not form a composite oxide with Al ₂ O _3, and a rare earth element and / or rare earth oxide, Of these, at least 80% or more of the primary particles of the metal oxide that do not form a composite oxide with Al ₂ O ₃ may have a particle size of 100 nm or less. At this time, it is preferable to use ZrO ₂ as the metal oxide because the inorganic oxide powder is more excellent in heat resistance.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[Preparation of inorganic oxide powder]
(Example 1)
First, 500 mL of 1.6 mol / L aluminum nitrate aqueous solution, 520 mL of 1.46 mol / L zirconyl oxynitrate aqueous solution, and 25 mL of 1.63 mol / L yttrium nitrate aqueous solution were mixed to obtain a mixed solution. . Next, the precursor of Al ₂ O ₃ , ZrO ₂ and rare earth oxide is added by adding 356 mL of 25% aqueous ammonia (pH ≧ 9) and 500 mL of pure water while sufficiently stirring the mixed solution. It was obtained by coprecipitation of each hydroxide precipitate.

The obtained hydroxide precipitate was centrifuged, washed thoroughly, and then evaporated to dryness by maintaining at 400 ° C. for 5 hours in an air atmosphere. And the inorganic oxide powder of Example 1 was obtained by baking at 700 degreeC for 5 hours in air | atmosphere. The composition ratio of Al ₂ O ₃ / ZrO ₂ / Y ₂ O ₃ in this inorganic oxide powder was 1 / 1.9 / 0.05 in molar ratio.

(Example 2)
The inorganic oxide powder obtained in Example 1 was further baked at 1000 ° C. for 5 hours in the air atmosphere to obtain the inorganic oxide powder of Example 2.

(Example 3)
The inorganic oxide powder obtained in Example 1 was further baked at 1000 ° C. for 5 hours in a mixed gas atmosphere of 5% by volume of hydrogen and 95% by volume of nitrogen to obtain the inorganic oxide powder of Example 3. .

Example 4
Inorganic of Example 4 except that 25 mL of 1.63 mol / L lanthanum nitrate aqueous solution was used instead of 25 mL of 1.63 mol / L yttrium nitrate aqueous solution used in Example 1 An oxide powder was obtained. The composition ratio of Al ₂ O ₃ / ZrO ₂ / La ₂ O ₃ in this inorganic oxide powder was 1 / 1.9 / 0.05 on a molar basis.

(Example 5)
The inorganic oxide powder obtained in Example 4 was further baked at 1000 ° C. for 5 hours in the air atmosphere to obtain the inorganic oxide powder of Example 5.

(Example 6)
The inorganic oxide powder obtained in Example 4 was further baked at 1000 ° C. for 5 hours in a mixed gas atmosphere of 5% by volume of hydrogen and 95% by volume of nitrogen to obtain the inorganic oxide powder of Example 6. .

(Example 7)
Inorganic of Example 7 in the same manner as in Example 1 except that 25 mL of 1.63 mol / L yttrium nitrate aqueous solution was used instead of 25 mL of 1.63 mol / L yttrium nitrate aqueous solution used in Example 1. An oxide powder was obtained. The composition ratio of Al ₂ O ₃ / ZrO ₂ / Nd ₂ O _{3 in} the inorganic oxide powder was 1 / 1.9 / 0.05 on a molar basis.

(Example 8)
Inorganic of Example 8 except that 25 mL of 1.63 mol / L praseodymium nitrate aqueous solution was used instead of 25 mL of 1.63 mol / L yttrium nitrate aqueous solution used in Example 1. An oxide powder was obtained. The composition ratio of Al ₂ O ₃ / ZrO ₂ / Pr ₂ O _{3 in} the inorganic oxide powder was 1 / 1.9 / 0.05 on a molar basis.

Example 9
Inorganic of Example 9 except that 25 mL of 1.63 mol / L terbium nitrate aqueous solution was used instead of 25 mL of 1.63 mol / L yttrium nitrate aqueous solution used in Example 1 An oxide powder was obtained. The composition ratio of Al ₂ O ₃ / ZrO ₂ / Tb ₂ O _{3 in} the inorganic oxide powder was 1 / 1.9 / 0.05 on a molar basis.

(Example 10)
The inorganic oxide powder obtained in Example 7 was further baked at 1000 ° C. for 5 hours in a mixed gas atmosphere of 5% by volume of hydrogen and 95% by volume of nitrogen to obtain the inorganic oxide powder of Example 10. .

(Comparative Example 1)
An inorganic oxide powder of Comparative Example 1 was obtained in the same manner as Example 1 except that no aqueous yttrium nitrate solution was used.

(Comparative Example 2)
An inorganic oxide powder of Comparative Example 2 was obtained in the same manner as in Example 1 except that the aqueous aluminum nitrate solution was not used.

[Preparation of catalyst supporting noble metal]
(Example 11)
20 g of the inorganic oxide powder obtained in Example 1 was mixed with 100 mL of ion-exchanged water, and further 2 mL of 30 g / L aqueous rhodium nitrate (Rh (NO ₃ ) ₃ ) was mixed. This was evaporated to dryness, impregnated and supported with 0.3 g of Rh on 100 g of the inorganic oxide powder, and then calcined at 300 ° C. for 3 hours in an air atmosphere to obtain the Rh-supported catalyst of Example 11.

(Examples 12 to 20)
The Rh-supported catalysts of Examples 12 to 20 were treated in the same manner as Example 11 except that the inorganic oxide powders obtained in Examples 2 to 10 were used instead of the inorganic oxide powders obtained in Example 1. I got each.

(Comparative Examples 3 and 4)
The Rh-supported catalysts of Comparative Examples 3 and 4 were prepared in the same manner as in Example 1 except that the inorganic oxide powders obtained in Comparative Examples 1 and 2 were used instead of the inorganic oxide powders obtained in Example 1. I got each.

<Durability test>
The Rh-supported catalysts of Examples 11 to 20 and Comparative Examples 1 and 2 were compacted and pulverized to adjust the particle size to about 0.5 to 1 mm, thereby obtaining pellet-shaped Rh-supported catalysts.

  Next, 1.5 g of the obtained pellet-shaped Rh-supported catalyst was placed in a predetermined position of the durability test apparatus. Then, the model gas of the rich gas (exhaust gas generated by burning the rich mixture) having the composition shown in Table 2 is set with the gas catalyst layer inlet temperature of 1000 ° C. and the SV (space velocity) of 10,000 / hour. An endurance test was conducted for 5 hours, in which a model gas of lean gas (exhaust gas generated by burning a lean air-fuel mixture) was alternately passed through the catalyst layer for 5 minutes.

<Catalyst activity evaluation>
A steady model gas having a stoichiometric air-fuel ratio (stoichiometric) having the composition shown in Table 3 is applied to the catalyst layer in which the Rh-supported catalysts of Examples 11 to 20 and Comparative Examples 1 and 2 after the durability test is performed. SV = 400,000 / hour, and the gas catalyst layer inlet temperature was increased from 100 ° C. to 500 ° C. at a rate of temperature increase of 12 ° C./hour. And the catalyst layer inlet temperature (T50; ° C) of the gas when each component of NO, CO, and CH in the model gas was converted by 50% was confirmed. The catalyst layer inlet temperature results are shown in Table 4.

Regarding the catalysts of Examples 12, 14, and 17 after the durability test, the state of primary particles was observed by FE-STEM. As a result, for the primary particles mainly composed of ZrO ₂ , primary particles having a particle diameter of about 30 nm or less could be clearly confirmed in any of the catalysts of the examples. On the other hand, the primary particles mainly composed of Al ₂ O ₃ were not observed as clear crystals as the primary particles mainly composed of ZrO _2. However, in any of the examples, ZrO ₂ and Al ₂ O were not observed. It was possible to confirm that ₃ was intervening with each other. Although Rh could not be confirmed as a STEM image, from the analysis results of EDX, both the part mainly composed of ZrO ₂ and the part mainly composed of Al ₂ O ₃ were found in the catalyst of any example. It was confirmed that it was supported without any separation. In addition, from the result of EDX, the presence position of rare earth elements (rare earth oxides) is, in the case of Example 4, that is, La (La ₂ O ₃ ), primary particles mainly composed of Al ₂ O ₃ and ZrO ₂ . It became clear that it was dissolved in both primary particles as the main component. In the case of Examples 12 and 17, that is, Y (Y ₂ O ₃ ) and Nd (Nd ₂ O ₃ ), it is clear that the solid solution is dissolved only in the primary particles mainly composed of ZrO _2. It was.

It is a schematic diagram of the FE-STEM image of the inorganic oxide powder concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Inorganic oxide powder (sample), 12, 14, 16, 18 ... Primary particle, 22, 24, 25, 26, 27, 28 ... Secondary particle.

Claims (16)

Al ₂ O ₃ and
A metal oxide that does not form a composite oxide with Al ₂ O ₃ ;
A rare earth element and / or a rare earth oxide,
An inorganic oxide powder, wherein 80% or more of primary particles have a particle size of 100 nm or less. Al ₂ O ₃ and
A metal oxide that does not form a composite oxide with Al ₂ O ₃ ;
A rare earth element and / or a rare earth oxide,
An inorganic oxide powder, wherein 80% or more of the primary particles of the metal oxide have a particle size of 100 nm or less. The inorganic oxide powder according to claim 1 or 2, wherein the content ratio of Al to the metal constituting the metal oxide is 1: 5 to 5: 1 on a molar basis. A primary particle composed of Al ₂ O ₃ , a primary particle composed of the metal oxide, a rare earth element and / or a rare earth oxide, and the content ratio of Al and the metal constituting the metal oxide is molar. Secondary particles that are from 1: 7 to 7: 1 on a basis,
The inorganic oxide powder according to any one of claims 1 to 3, comprising: The inorganic oxide powder according to claim 4, wherein the secondary particles contain 50 atomic% or more. And Al ₂ O _3, containing a metal oxide forming no composite oxide of _Al 2 _{O 3,} and rare earth elements and / or rare earth oxides, and
Of the primary particles composed of Al ₂ O ₃ and the primary particles composed of the metal oxide, primary particles having a particle diameter determined based on FE-STEM and EDX in an analysis range of 1 μm square are 100 nm or less, The secondary particle content is 1 μm so that the molar ratio of Al to the metal constituting the metal oxide is within ± 20% of the molar ratio of Al to the metal in the raw material. An inorganic oxide powder characterized by being adjusted so as to be 50 atomic% or more of secondary particles existing in the analysis range in a four-way analysis range. And Al ₂ O _3, containing a metal oxide forming no composite oxide of _Al 2 _{O 3,} and rare earth elements and / or rare earth oxides, and
Of the primary particles made of Al ₂ O ₃ and the primary particles made of the metal oxide, the particle diameter determined based on FE-STEM and EDX in the analysis range of 1 μm square after the durability test is 100 nm or less. Secondary particle content ratio including primary particles such that the molar ratio of Al to the metal constituting the metal oxide is within ± 20% of the molar ratio of Al to the metal in the raw material Is adjusted to be 50 atomic% or more of secondary particles existing in the analysis range in the 1 μm square analysis range. At least a portion of the rare earth oxide, the Al 2 _{O 3,} or Al ₂ O ₃ and the metal oxide forming no composite oxide, claim, characterized in that a solid solution to 1-7 The inorganic oxide powder as described in any one of these. The inorganic oxide powder according to claim 1, wherein the metal oxide that does not form a composite oxide with Al ₂ O ₃ is ZrO ₂ . The rare earth element constituting the rare earth element and / or the rare earth oxide is one or more elements selected from the group consisting of La, Nd, Y, Pr, and Tb. The inorganic oxide powder according to claim 1. A coprecipitation step of obtaining a coprecipitation product of an Al compound, a metal compound that does not form a composite oxide of Al ₂ O ₃ when converted into an oxide, and a rare earth compound; The inorganic oxide powder according to any one of claims 1 to 10, wherein the inorganic oxide powder is formed through a baking step of baking in an oxidizing atmosphere at 1200 ° C. The inorganic oxide powder according to claim 1, wherein the inorganic oxide powder is used as a catalyst carrier. A catalyst carrier comprising the inorganic oxide powder according to any one of claims 1 to 12. A catalyst comprising at least one noble metal selected from the group consisting of Rh, Pt and Pd supported on the catalyst carrier according to claim 13. The catalyst according to claim 14, wherein the noble metal is Rh. The catalyst according to claim 14 or 15, which is used for exhaust gas purification.

Images