JP2006035019A - Inorganic oxide, catalyst carrier for cleaning exhaust gas and catalyst for cleaning exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inorganic oxide in which grain growth of carried metals (rhodium, or the like) is sufficiently suppressed, a catalyst carrier for cleaning an exhaust gas comprising the same and a catalyst for cleaning the exhaust gas using the same. <P>SOLUTION: The granular inorganic oxide contains aluminum oxide; a metal oxide not forming a composite oxide with aluminum oxide; and an addition element comprising at least one of a rare-earth element and an alkaline earth element and contains a secondary particle formed by coagulation of a primary particle. In the inorganic oxide, at least a part of the secondary particle is formed by coagulation of a plurality of the first primary particles with a particle diameter of 100 nm or less containing aluminum oxide and the addition element and a plurality of second primary particles with a particle diameter of 100 nm or less containing the metal oxide and the addition element. At least a part of the first and second primary particles has a surface thickening area where a content ratio of the addition element is locally enhanced at the surface layer part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inorganic oxide, an exhaust purification catalyst carrier, and an exhaust purification catalyst.

  An exhaust gas purification catalyst used for purifying exhaust gas of an internal combustion engine or the like is required to have extremely high heat resistance in order to maintain high catalytic activity even when used at a high temperature for a long period of time.

As an exhaust purification catalyst, for example, a catalyst in which a metal having catalytic activity is supported on a carrier made of a particulate metal oxide is known. And in order to improve the heat resistance of such an exhaust purification catalyst, a zirconium oxide particle in which an oxide of a rare earth element is uniformly dissolved (Patent Document 1), an aluminum oxide and an oxide of a rare earth element are used. A catalyst using a combination (Patent Document 2) as a carrier has been proposed so far.
Japanese Patent No. 3498453 Japanese Patent No. 3275356

  However, the conventional catalyst as described above has high heat resistance as compared with the case where no rare earth element is used, but is not always sufficient. Therefore, the present inventors have studied in detail to further improve the heat resistance, and in the conventional catalyst, the heat resistance of the carrier supporting a metal having catalytic activity (hereinafter, sometimes referred to as “catalytic metal”). It became clear that sex was still lacking. The exhaust temperature of an automobile usually reaches a high temperature of about 600 to 1000 ° C. However, if the heat resistance of the carrier is insufficient, the sintering of the carrier proceeds under such a high temperature environment, thereby causing the growth of the supported metal grains. Will be promoted. When the metal grain growth is promoted, the specific surface area is reduced, and as a result, the catalytic activity is lowered.

  The present invention has been made in view of the above-described problems of the prior art, and includes an inorganic oxide in which grain growth of the supported metal is sufficiently suppressed, an exhaust purification catalyst carrier comprising the same, and a catalyst carrier for the same. An object of the present invention is to provide a used exhaust purification catalyst.

  In order to solve the above problems, the present invention contains aluminum oxide, a metal oxide that does not form a composite oxide of aluminum oxide, and an additive element composed of at least one of a rare earth element and an alkaline earth element. , A particulate inorganic oxide including secondary particles formed by agglomeration of primary particles, wherein at least a part of the secondary particles includes a plurality of second particles having a particle size of 100 nm or less containing aluminum oxide and an additive element. One primary particle and a plurality of second primary particles having a particle size of 100 nm or less containing the metal oxide and the additive element, and at least a part of the first and second primary particles are The surface layer portion has a surface enriched region in which the content ratio of the additive element is locally increased.

  The inorganic oxide of the present invention is a combination of aluminum oxide and a specific metal oxide other than this, and is mainly composed of a plurality of types of primary particles having a nanometer-scale size and different composition, and further includes a rare earth element, etc. In the surface layer portion of the primary particle, the additive element is contained in such a manner that the concentration is locally high, so that the grain growth of the supported catalyst metal is sufficiently suppressed even in a high temperature environment.

  In the inorganic oxide composed of the combination as described above, the aluminum oxide and the metal oxide do not form a composite oxide with each other, and therefore the first and second primary particles as described above exist separately. ing. And since these different types of primary particles are aggregated while interposing each other to form secondary particles, the mutual particles serve as a diffusion barrier, and sintering due to fusion of the primary particles is suppressed. Conceivable.

  Further, in the surface layer portion of the primary particles constituting the inorganic particles, a surface concentrated region in which the content ratio of the additive element is locally increased is formed. In other words, the region where the content of the additive element is increased is formed so as to cover the surface of the primary particles. However, this region does not necessarily need to completely cover the surface of the primary particles, and it is sufficient if it covers at least a part of the surface layer portion of the primary particles. Since the additive element as described above has basicity when it becomes an oxide, it is represented by Rh-OM (M is an additive element in the carrier) when rhodium (Rh) is supported. Create a bond. Accordingly, when a large amount of rare earth elements are present on the surface of the primary particles of the support, the supported rhodium particles are difficult to diffuse, and thereby the rhodium grain growth is effectively suppressed. The primary particles in the inorganic oxide contain the additive element not only in the surface layer portion but also in the inner layer portion (inner layer portion) rather than the surface concentrated region, but the content ratio of the rare earth element is not localized but the inner layer. If it is increased over the entire primary particles including the part, the interaction with the catalyst metal such as rhodium is strengthened, but the heat resistance of the support itself is lowered, so that the grain growth of the catalyst metal is not sufficiently suppressed.

  The present invention also includes particles containing secondary particles formed by agglomeration of primary particles, containing aluminum oxide, zirconium oxide, and an additive element composed of at least one of a rare earth element and an alkaline earth element. A plurality of first primary particles having a particle size of 100 nm or less containing aluminum oxide and an additive element, and a particle size containing zirconium oxide and an additive element. A plurality of second primary particles of 100 nm or less, and at least a part of the first and second primary particles has a surface concentration in which the content ratio of the additive element is locally increased in the surface layer portion thereof It has a region.

  Since zirconium oxide does not substantially form a composite oxide with aluminum oxide, the first and second primary particles as described above are formed in the inorganic oxide in which these oxides are combined. Therefore, the same effect as that of the above-described inorganic oxide can be obtained by this inorganic oxide.

  In the surface concentration region, it is preferable that 1 to 5% by mass of an additive element is present with respect to the total amount of the inorganic oxide when converted to the amount of the oxide. Thus, when an inorganic oxide is used as a catalyst carrier, a catalyst having excellent heat resistance and higher catalytic activity can be obtained.

  The present invention relates to a coprecipitate containing aluminum, a metal element that does not form a composite oxide with aluminum oxide when it becomes an oxide, and an additive element composed of at least one of a rare earth element and an alkaline earth element A coprecipitation step for obtaining a mixture, a first firing step for firing the coprecipitate to obtain a mixture of oxides, and adding an additive element comprising at least one of a rare earth element and an alkaline earth element to the mixture, Furthermore, it is obtained by a manufacturing method provided with the 2nd baking process of baking, It is a particulate inorganic oxide characterized by the above-mentioned.

  The present invention also provides a coprecipitation step for obtaining a coprecipitate containing aluminum, zirconium, and an additive element comprising at least one of a rare earth element and an alkaline earth element, and firing the coprecipitate to obtain an oxide. And a second baking step of attaching an additive element consisting of at least one of a rare earth element and an alkaline earth element to the mixture and further baking this. It is a particulate inorganic oxide characterized by the above.

  The primary particles of the inorganic oxide obtained by the production method combining such specific raw materials and steps mainly contain a portion derived from the coprecipitate as an additive element in the inner layer portion in the vicinity of the central portion thereof. In the surface layer part, the part adhering to the mixture after the first firing is mainly contained as an additive element. Thereby, this primary particle has the surface concentration area | region where the content rate of the additive element was locally raised in the surface layer part. Therefore, the inorganic oxide obtained by the above-described production method has a structure almost similar to that of the above-described inorganic oxide, and when used as a catalyst support, the supported catalyst metal is supported even in a high temperature environment. Grain growth is sufficiently suppressed.

  In said 2nd baking process, it is preferable to adhere | attach the quantity of an additional element which will be 1-5 mass% with respect to the whole quantity of the inorganic oxide obtained when converted into the quantity of an oxide. Thereby, when used as a catalyst carrier, a catalyst having excellent heat resistance and higher catalytic activity can be obtained.

  In the first firing step, the coprecipitate is heated to 600 to 1200 ° C. in an oxidizing atmosphere and fired. In the second firing step, the mixture to which the additive element is attached is heated to 500 to 900 ° C. and fired. It is preferable to do.

  As additive elements contained in the inorganic oxide of the present invention as described above, rare earth elements include yttrium, lanthanum, praseodymium, neodymium (neodymium), samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and It is preferably at least one element selected from the group consisting of lutetium, and the alkaline earth element is preferably at least one element selected from the group consisting of magnesium, calcium, strontium and barium. Among these, from the viewpoint of heat resistance, the additive element is preferably at least one selected from yttrium, lanthanum, praseodymium, neodymium, ytterbium, magnesium, calcium, and barium, and lanthanum or neodymium is particularly preferable.

  The exhaust gas purification catalyst carrier of the present invention is characterized by comprising the inorganic oxide of the present invention, and the exhaust gas purification catalyst of the present invention comprises the exhaust gas purification catalyst carrier and a carrier carried thereon. Rhodium. Furthermore, it is preferable that at least a part of rhodium in the catalyst is supported so as to be in contact with a region where the content ratio of the additive element is locally increased in the surface layer portion of the primary particles of the inorganic oxide. The exhaust purification catalyst of the present invention uses the inorganic oxide of the present invention as a carrier, so that the grain growth of the supported rhodium is sufficiently suppressed even in a high temperature environment.

  ADVANTAGE OF THE INVENTION According to this invention, the inorganic oxide by which the particle growth of the carry | supported metal is fully suppressed, the exhaust gas purification catalyst carrier which consists of this, and the exhaust gas purification catalyst using the same are provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

  The inorganic oxide of the present invention contains aluminum oxide, a metal oxide that does not form a composite oxide of aluminum oxide, and an additive element consisting of at least one of a rare earth element and an alkaline earth element, and the primary particles are It consists of a particulate mixture containing secondary particles formed by aggregation.

Aluminum oxide (Al ₂ O ₃ ) in the inorganic oxide may be amorphous (for example, activated alumina) or crystalline.

  A metal oxide that does not form a composite oxide with aluminum oxide is an oxide that does not form primary particles composed of composite oxides in a state where they are substantially uniformly dissolved or dispersed in each other in combination with aluminum oxide. In other words, when the metal oxide is calcined with a coprecipitate obtained by coprecipitation of hydroxide as a precursor and aluminum hydroxide, the metal oxide is separated from primary particles mainly composed of aluminum oxide. Form. Therefore, the inorganic oxide of the present invention includes first primary particles containing aluminum oxide as a main component and second primary particles containing a metal oxide other than aluminum oxide as a main component.

  Here, the first and second primary particles each further contain an additive element. Furthermore, the first primary particles may contain a small amount of the above metal oxide or the like in the surface layer portion, and the second primary particles may contain a small amount of aluminum oxide or the like in the surface layer portion. Good.

  At least some of the secondary particles in the inorganic oxide are formed by aggregation of a plurality of first primary particles having a particle size of 100 nm or less and a plurality of second primary particles having a particle size of 100 nm or less. ing. As a result, primary particles having different compositions serve as diffusion barriers, and sintering of the carrier in a high temperature environment is suppressed. In this way, it is possible to confirm that primary particles having different compositions are formed separately, and that these primary particles are aggregated to form secondary particles by an analysis method described later.

  80% or more of the primary particles in the inorganic oxide preferably have a particle size of 100 nm or less in order to increase the specific surface area and increase the catalytic activity. The ratio of primary particles having a particle size of 100 nm or less is more preferably 90% or more, and further preferably 95% or more. This particle diameter is the largest diameter that can be defined for one particle. Moreover, the average particle diameter of the primary particles in the entire particulate inorganic oxide is preferably 1 to 50 nm, and more preferably 3 to 40 nm.

  In addition, the primary particle size, each composition, and the aggregation state of the secondary particles are TEM (transmission electron microscope), SEM (scanning electron microscope), FE-STEM (field emission-scanning transmission electron microscope), EDX ( It can be confirmed by observing and analyzing the inorganic oxide by appropriately combining an energy dispersive X-ray detector), XPS (photoelectron spectrometer) and the like.

As a metal oxide that does not form a composite oxide with aluminum oxide, it is preferable to use at least one selected from the group consisting of zirconium oxide (ZrO ₂ ), silicon oxide (SiO ₂ ), and titanium oxide (TiO ₂ ). it can. Among these, zirconium oxide is particularly preferable. For example, when zirconium oxide is combined with rhodium as a catalyst metal, a catalyst having particularly excellent heat resistance and catalytic activity can be obtained.

  Rare earth elements and alkaline earth elements are usually contained in inorganic oxides as their oxides. Rare earth elements are yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium It is preferably at least one element selected from the group consisting of (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu), from yttrium, lanthanum, praseodymium, neodymium and ytterbium. More preferably, it is at least one element selected from the group consisting of: On the other hand, the alkaline earth element is preferably at least one element selected from the group consisting of magnesium (Mg), calcium (Ca), strontium (Sr) and barium (Ba), and includes magnesium, calcium and barium. More preferably, it is at least one element selected from the group consisting of: Among these, lanthanum or neodymium, which is a rare earth element, is more preferably used as an additive element from the viewpoint of heat resistance as a support. In this case, lanthanum and neodymium may be used in combination. Further, different additive elements may be contained in the inorganic oxide in a surface enrichment region described later and other regions.

  The additive element in the inorganic oxide exists in a state of solid solution, dispersion, or the like with respect to aluminum oxide or the metal oxide. In particular, in order to express the effect of the present invention by the additive element more remarkably, at least a part of the additive element is aluminum oxide or the above metal in the inner layer portion (portion other than the surface concentrated region) of the primary particles of the inorganic oxide. It is preferably dissolved in the oxide. In this case, it is more preferable that the aluminum oxide and the metal oxide both have the additive element dissolved.

  The content ratio of the additive element in the inorganic oxide is 1.5 to 5.5 based on the total amount of the additive element, aluminum in the aluminum oxide, and the metal element in the metal oxide, in terms of the amount of the oxide. It is preferably 6 mol%, more preferably 2.0 to 4.0 mol%, and even more preferably 2.5 to 3.8 mol%. When the ratio of the oxide of the additive element is less than 1.5 mol% or exceeds 5.6 mol%, the particle growth of the catalyst metal tends to be hardly suppressed in a high temperature environment. On the other hand, when the additive element exceeds 5.6 mol%, the interaction with the catalyst metal becomes excessively strong, and the catalytic activity tends to decrease.

  FIG. 1 is a schematic diagram showing an image when an inorganic oxide according to an embodiment of the present invention is observed by FE-STEM. The inorganic oxide in the image of FIG. 1 contains zirconium oxide as a metal oxide that does not form a composite oxide with aluminum oxide, and contains lanthanum as an additive element. In this image, the secondary particles 24, 25, 26, 27 and 28 are formed by agglomerating a plurality of types of primary particles having different compositions. As primary particles, primary particles 12 mainly made of aluminum oxide, primary particles 14 made mainly of zirconium oxide, primary particles 16 made mainly of aluminum oxide and lanthanum oxide, and primary particles 18 made mainly of zirconium oxide and lanthanum oxide, Is present. Primary particles made of a composite oxide in which aluminum oxide and zirconium oxide are substantially uniformly dissolved or dispersed in each other are not formed. In addition, the composition and distribution state of the oxide in each primary particle can be analyzed by EDX or the like.

  The secondary particles 22, 25, 27 and 28 are formed by agglomerating the primary particles 12, 14, 16 and 18, respectively. Further, secondary particles such as the secondary particles 24 composed of the primary particles 14 and 18 and the secondary particles 26 composed of the primary particles 12 and 16 may partially exist. When the secondary particles 24 and 26 are present, the metal elements contained in these secondary particles are preferably 30 mol% or less, and 15 mol% or less with respect to all metal elements present in the inorganic oxide. More preferably, it is 10 mol% or less.

  At least a part of the primary particles constituting the inorganic oxide has a surface concentration region in which the content ratio of the additive element is locally increased in the surface layer portion. Of the primary particles constituting the inorganic oxide, those containing lanthanum oxide preferably have substantially all of this surface enriched region, but to the extent that the effects of the present invention are not significantly impaired. Primary particles that do not have a surface concentrated region may be mixed. Note that an additive element may also be present in the surface layer of primary particles that do not contain lanthanum oxide as a main constituent.

  The additive element in the surface concentration region exists in the surface layer portion of the primary particles. The amount of the additive element present in the surface concentration region is preferably 1 to 5% by mass with respect to the total amount of the inorganic oxide. If this amount is not less than 1% by mass or exceeds 5% by mass, the effect of improving the heat resistance of the catalyst by the additive element tends to decrease.

  The additive elements present in the surface concentration region are eluted when they come into contact with an acidic solution such as an aqueous nitric acid solution. Therefore, the amount of the additive element present in the surface concentration region can be confirmed by quantifying the amount of the additive element eluted in the nitric acid aqueous solution when the inorganic oxide is brought into contact with the nitric acid aqueous solution. More specifically, for example, 0.1 g of inorganic oxide is added to 10 ml of 1N nitric acid aqueous solution, and this is stirred for 2 hours to elute the additive elements present in the surface concentration region. By quantifying the amount by chemical analysis, the amount of additive elements present can be confirmed.

  The inorganic oxide containing primary particles having such a surface-enriched region may be obtained by, for example, attaching the additive element to particles of a mixture composed of a plurality of types of oxides including the oxide of the additive element, and further firing it. Can be obtained by: In the primary particles of the inorganic oxide obtained by this method, most of the adhering additive elements are converted into oxides by firing, and are present in the primary particle surface layer portion to form a surface concentrated region.

  When an inorganic oxide containing primary particles having a surface-enriched region is obtained by the above method, the amount of the additive element adhering to the oxide mixture is obtained when converted to the mass of the oxide. It is preferable to set it as 1-5 mass% with respect to the whole quantity. Thereby, about 1-5 mass% of additional elements can exist in the surface layer part of the primary particle of the obtained inorganic oxide.

  In the primary particles of the inorganic oxide, the surface enrichment region as described above is formed in addition to the method by elution of the additive element as described above, for example, EDX (energy dispersive X-ray detector), This can be confirmed by analyzing the composition using a SIMS (secondary ion mass spectrometer) or the like and comparing the content ratio of the additive element between the primary particle surface layer part and the central part. Alternatively, instead of directly analyzing the composition of the primary particle center, the composition of the inorganic oxide is analyzed by ICP (high frequency plasma emission analyzer) or the like, and the content ratio of the additive element as the average value of the entire inorganic oxide is determined. And you may confirm that the content rate of the additional element in a surface layer part is higher than this.

  The inorganic oxide as described above includes, for example, aluminum, a metal element that does not form a composite oxide with aluminum oxide when it becomes an oxide, and an addition of at least one of a rare earth element and an alkaline earth element A coprecipitation step of obtaining a coprecipitate containing the element, a first firing step of firing the coprecipitate to obtain a mixture of oxides, and the mixture from at least one of a rare earth element and an alkaline earth element It can be suitably obtained by a manufacturing method comprising: a second baking step in which an additional element to be attached is attached and further fired.

  The coprecipitate is generated from a solution in which aluminum, the metal element, and the additive element are dissolved. When the content ratio of the additive element in this solution is converted to the amount of the oxide, it may be 0.20 to 4.0 mol% with respect to the total amount of the additive element, aluminum, and the metal element. Preferably, it is more preferable to set it as 0.5-3.8 mol%. When the additive element in the solution is less than 0.20 mol% or exceeds 4.0 mol%, the effect of suppressing the grain growth of the catalyst metal is lowered when the obtained inorganic oxide is used as a support. There is a tendency.

  As said solution, what melt | dissolved the salt of each metal element which comprises an inorganic oxide, etc. in water, alcohol, etc. is used suitably. Examples of the salt include sulfate, nitrate, hydrochloride, acetate, and the like.

  This solution is mixed with an alkaline solution so that the pH of the solution is adjusted to a range in which the hydroxide of each metal element is precipitated (preferably pH 9 or more). A sediment is formed. As the alkaline solution, an ammonia or ammonium carbonate solution is preferable because it can be easily removed by volatilization during firing.

  In the subsequent first firing step, the obtained coprecipitate is preferably centrifuged and washed, and then fired by heating to obtain a mixture of oxides. In the first firing step, the coprecipitate is fired by heating at 600 to 1200 ° C., preferably for 0.5 to 10 hours, in an oxidizing atmosphere such as an air atmosphere.

  Furthermore, in the second firing step, an additive element is attached to the oxide mixture, and further fired to obtain a particulate inorganic oxide. The adhesion can be performed by suspending a mixture of oxides in a solution in which a salt of an additive element (nitrate or the like) is dissolved and stirring the mixture. Moreover, in this 2nd baking process, it is good to heat and bake the mixture to which the additional element adhered at 500-900 degreeC, Preferably it is 0.5 to 10 hours in an acidic atmosphere.

  The exhaust purification catalyst carrier of the present invention is a carrier comprising at least the inorganic oxide described above. For example, one or more kinds of noble metals selected from the group consisting of rhodium, platinum and palladium can be suitably supported on the carrier as a catalyst metal.

  The exhaust purification catalyst of the present invention comprises the exhaust purification catalyst carrier of the present invention and rhodium supported on the catalyst support. By using the inorganic oxide of the present invention as a carrier, this catalyst can sufficiently suppress the grain growth of the supported rhodium even in a high temperature environment. Rhodium can be supported on a carrier by employing a conventionally known method such as an impregnation method.

  At least a portion of rhodium in the exhaust purification catalyst of the present invention is in contact with a region (surface enriched region) in which the content of the additive element is locally increased in the surface layer portion of the primary particles of the inorganic oxide. It is preferably supported. Thereby, the effect of suppressing the grain growth of rhodium by the additive element is more remarkably exhibited.

  The amount of rhodium supported is preferably 0.01 to 3% by mass, more preferably 0.05 to 2% by mass with respect to the mass of the carrier in order to develop sufficiently high catalytic activity. More preferably, it is 1-1 mass%.

  The form using the exhaust purification catalyst is not particularly limited, for example, by forming a layer made of the exhaust purification catalyst on the surface of a substrate such as a honeycomb-shaped monolith substrate, pellet substrate or foam substrate, This can be used by arranging it in an exhaust passage of an internal combustion engine or the like.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
<Preparation of catalyst>
A solution obtained by dissolving 1 mol of aluminum nitrate nonahydrate, 0.95 mol of zirconyl oxynitrate dihydrate and 0.05 mol of lanthanum nitrate hexahydrate in 1600 mL of ion-exchanged water, In addition to ammonia water containing 1.2 times the neutralization equivalent to the metal cation in the solution while stirring, the pH of the solution is adjusted to 9 or more to coprecipitate aluminum, zirconium and lanthanum hydroxides. Thus, a coprecipitate containing these was produced. Then, the coprecipitate was centrifuged and sufficiently washed, and then heated at 400 ° C. in the atmosphere for 5 hours to be pre-baked. Subsequently, the pre-baked solid material is heated in the atmosphere at 700 ° C. for 5 hours, and further heated at 900 ° C. for 5 hours to be fired (first baking), thereby producing aluminum oxide, zirconium oxide, and lanthanum oxide. A mixture of oxides containing was obtained. The composition ratio of the mixture was aluminum oxide / zirconium oxide / lanthanum oxide = 50/95 / 2.5 (molar ratio).

  Nitric acid in which 6.5 g of the obtained mixture was dissolved in 6.5 g of lanthanum nitrate hexahydrate (in terms of the amount of lanthanum oxide, the amount was 5% by mass with respect to the total amount of the obtained inorganic oxide). The suspension suspended in the aqueous lanthanum solution was stirred for 2 hours. Then, after the water was evaporated from the suspension, the solid matter remaining was heated in the atmosphere at 110 ° C. for 12 hours and then further heated in the atmosphere at 800 ° C. for 5 hours to be fired (second firing) to form particles. An inorganic oxide was obtained. The primary particles in the inorganic oxide are locally increased in content of lanthanum as an additive element in the surface layer portion by adding lanthanum as a post-addition element after forming the composite oxide. Moreover, when the obtained inorganic oxide was observed by TEM, a plurality of first primary particles having a particle size of 100 nm or less containing aluminum oxide and an additive element, and a particle size of 100 nm or less containing lanthanum oxide and an additive element were obtained. It was confirmed that a plurality of second primary particles aggregated while interposing each other to form secondary particles.

Using the obtained inorganic oxide as a carrier, this was added to a Rh (NO ₃ ) ₃ aqueous solution and stirred, and then the water was evaporated and the remaining solid was baked by heating at 500 ° C. in the atmosphere for 3 hours. Was shaped into a pellet having a length of 0.5 to 1 mm to obtain a catalyst having rhodium supported on a carrier. The amount of rhodium supported was about 0.5 g with respect to 100 g of the carrier.

<Durability (heat resistance) test of catalyst>
The obtained pellet-shaped catalyst was placed in an endurance test apparatus to form a catalyst layer, the gas catalyst layer inlet temperature was set to 1000 ° C., and the space velocity was set to 10,000 / hour, and the composition shown in Table 1 was obtained. An endurance test in which rich gas and lean gas were alternately passed through the catalyst layer for 5 minutes was performed for 25 hours. About the catalyst after an endurance test, rhodium dispersibility (ratio of rhodium atoms present on the particle surface in all rhodium atoms) was measured by a CO adsorption method. A large value of rhodium dispersibility corresponds to maintaining a large specific surface area and means that grain growth of rhodium particles is suppressed.

(Example 2)
The inorganic oxide and the catalyst were prepared and the catalyst durability test was performed in the same manner as in Example 1 except that the second baking temperature was 500 ° C.

Example 3
The inorganic oxide and catalyst were prepared and the durability test of the catalyst was performed in the same manner as in Example 1 except that the second baking temperature was 900 ° C.

Example 4
The mixture after the first calcination was replaced with lanthanum nitrate hexahydrate and suspended in an aqueous solution of neodymium nitrate in which 6.6 g of neodymium nitrate hexahydrate was dissolved. Inorganic oxide and catalyst preparation and catalyst durability test were performed.

(Example 5)
The mixture after the first firing was replaced with lanthanum nitrate hexahydrate and suspended in an aqueous solution of neodymium nitrate in which 6.6 g of neodymium nitrate hexahydrate was dissolved. Inorganic oxide and catalyst preparation and catalyst durability test were performed.

(Example 6)
The mixture after the first firing was replaced with lanthanum nitrate hexahydrate and suspended in an aqueous solution of neodymium nitrate in which 6.6 g of neodymium nitrate hexahydrate was dissolved. Inorganic oxide and catalyst preparation and catalyst durability test were performed.

(Example 7)
Using a solution obtained by dissolving 1 mol of aluminum nitrate nonahydrate, 0.95 mol of zirconyl oxynitrate dihydrate and 0.05 mol of neodymium nitrate hexahydrate in 1600 mL of ion-exchanged water An inorganic oxide and a catalyst were produced in the same manner as in Example 1 except that a coprecipitate was produced and the composition ratio of the mixture was aluminum oxide / zirconium oxide / neodymium oxide = 50/95 / 2.5 (molar ratio). And a durability test of the catalyst.

(Comparative Example 1)
In the same manner as in Example 1, except that aluminum nitrate was not used and the composition ratio of the mixture after the first firing was changed to zirconium oxide / lanthanum oxide = 95 / 2.5 (molar ratio), the inorganic oxide and the catalyst The preparation and the durability test of the catalyst were performed.

(Comparative Example 2)
Aluminum oxide particles obtained by obtaining a precipitate of aluminum hydroxide from an aqueous aluminum nitrate solution in the same manner as the procedure for obtaining the coprecipitate in Example 1, and firing this under the same conditions as in the first firing in Example 1. And the mixture after the first firing consisting of zirconium oxide and lanthanum oxide, obtained in the same manner as in Comparative Example 1, was composed of aluminum oxide / zirconium oxide / lanthanum oxide = 50/95 / 2.5 (molar ratio). An inorganic oxide was obtained by uniformly mixing with each other so as to obtain a ratio. When the obtained inorganic oxide was observed by TEM, secondary particles in which a plurality of primary particles made of aluminum oxide were aggregated and secondary particles in which a plurality of second primary particles containing lanthanum oxide and an additive element were aggregated were obtained. It was confirmed that each was formed.

(Comparative Example 3)
The mixture after the first calcination obtained in the same manner as in Example 1 is used as it is as a carrier, and rhodium is supported in the same manner as in Example 1 to prepare an inorganic oxide and a catalyst, and the durability test of the catalyst. went.

  As shown in Table 2, according to the catalysts of Examples 1 to 7 obtained by further attaching lanthanum or neodymium to a mixture containing lanthanum or neodymium, the rhodium dispersibility after the durability test in a high temperature environment is A sufficiently large value was shown. On the other hand, Comparative Example 1 containing no aluminum oxide, Comparative Example 2 in which aluminum oxide and zirconium oxide each constitute another secondary particle, and Comparative Example 3 in which no post-added element was adhered were durable. The rhodium dispersibility after the property test was low. Therefore, according to the present invention, it was confirmed that an inorganic oxide in which grain growth of the supported catalyst metal is sufficiently suppressed and an exhaust purification catalyst using the inorganic oxide can be obtained.

It is a schematic diagram which shows the FE-STEM image of the inorganic oxide which concerns on one Embodiment of this invention.

Explanation of symbols

  12, 14, 16, 18 ... primary particles, 22, 24, 25, 26, 27, 28 ... secondary particles.

Claims (13)

2. An aluminum oxide, a metal oxide that does not form a composite oxide of aluminum oxide, and an additive element composed of at least one of a rare earth element and an alkaline earth element, and formed by aggregation of primary particles. A particulate inorganic oxide containing secondary particles,
At least some of the secondary particles are
A plurality of first primary particles having a particle size of 100 nm or less containing the aluminum oxide and the additive element;
A plurality of second primary particles having a particle size of 100 nm or less containing the metal oxide and the additive element,
At least a part of the first and second primary particles is an inorganic oxide having a surface concentrated region in which the content of the additive element is locally increased in the surface layer portion. A particulate inorganic oxide containing secondary particles formed by agglomerating primary particles, containing aluminum oxide, zirconium oxide, and an additive element composed of at least one of a rare earth element and an alkaline earth element There,
At least some of the secondary particles are
A plurality of first primary particles having a particle size of 100 nm or less containing the aluminum oxide and the additive element;
A plurality of second primary particles having a particle size of 100 nm or less containing the zirconium oxide and the additive element,
At least a part of the first and second primary particles is an inorganic oxide having a surface concentrated region in which the content of the additive element is locally increased in the surface layer portion.   In the said surface concentration area | region, when converted into the quantity of an oxide, 1-5 mass% of the said additional element exists with respect to the whole quantity of the said inorganic oxide, The claim 1 or 2 Inorganic oxide. Coprecipitation to obtain a coprecipitate containing aluminum, a metal element that does not form a complex oxide with aluminum oxide when it becomes an oxide, and an additive element consisting of at least one of a rare earth element and an alkaline earth element Process,
A first firing step of firing the coprecipitate to obtain a mixture of oxides;
A particulate inorganic oxide obtained by a production method comprising: a second firing step in which an additive element composed of at least one of a rare earth element and an alkaline earth element is attached to the mixture, and further fired. A coprecipitation step of obtaining a coprecipitate containing aluminum, zirconium, and an additive element comprising at least one of a rare earth element and an alkaline earth element;
A first firing step of firing the coprecipitate to obtain a mixture of oxides;
A particulate inorganic oxide obtained by a production method comprising: a second firing step in which an additive element composed of at least one of a rare earth element and an alkaline earth element is attached to the mixture, and further fired.   In the second baking step, when added to the amount of oxide, the additive element is attached in such an amount that the amount is 1 to 5% by mass with respect to the total amount of the obtained inorganic oxide. 5. The inorganic oxide according to 5. In the first firing step, the coprecipitate is heated to 600 to 1200 ° C. in an oxidizing atmosphere and fired,
The inorganic oxide according to any one of claims 4 to 6, wherein in the second firing step, the mixture to which the additive element is attached is heated to 500 to 900 ° C and fired. The rare earth element is at least one element selected from the group consisting of yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium,
The inorganic oxide according to any one of claims 1 to 7, wherein the alkaline earth element is at least one element selected from the group consisting of magnesium, calcium, strontium, and barium.   The inorganic oxide according to any one of claims 1 to 7, wherein the additive element is at least one element selected from the group consisting of yttrium, lanthanum, praseodymium, neodymium, ytterbium, magnesium, calcium, and barium. .   The inorganic oxide according to any one of claims 1 to 7, wherein the additive element is lanthanum or neodymium.   An exhaust purification catalyst carrier comprising the inorganic oxide according to any one of claims 1 to 10.   An exhaust gas purification catalyst comprising the exhaust gas purification catalyst carrier according to claim 11 and rhodium supported thereon.   The exhaust according to claim 12, wherein at least a part of the rhodium is supported so as to be in contact with a region where the content ratio of the additive element is locally increased in a surface layer portion of a primary particle of the inorganic oxide. Purification catalyst.

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