JP5332131B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly durable catalyst for exhaust gas purification which can be applied for purification treatment of exhaust gas discharged from internal combustion engines. <P>SOLUTION: This catalyst for exhaust gas purification comprises a noble metal 1, a perovskite composite oxide 2, and a heat resistant oxide 3. The noble metal 1 is supported on the composite oxide 2. The catalyst comprises a unit 4 comprising the composite oxides 2, on which the noble metal 1 is supported, separated from each other by the heat resistant oxide 3. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an exhaust gas purification catalyst applied to a purification process of exhaust gas discharged from an internal combustion engine and a method for manufacturing the same.

In order to remove harmful substances such as hydrocarbon compounds (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) contained in the exhaust gas discharged from the internal combustion engine, alumina (Al ₂ O ₃₎ Exhaust gas purification catalysts in which noble metal particles having catalytic activity such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on a metal oxide carrier such as) are widely used.

  The exhaust gas regulations in recent years are becoming stricter, and in order to satisfy these regulations, it is necessary to use many precious metals. However, mass use of precious metals is not desirable from the viewpoint of depletion of earth resources. One of the causes of the increase in the amount of noble metal in the conventional exhaust gas purification catalyst is to ensure durability. Therefore, if durability can be secured, the amount of noble metal can be significantly reduced. Further, since the exhaust gas purifying catalyst comes into contact with the high temperature exhaust gas discharged from the internal combustion engine, it is required to have excellent durability with little deterioration in the catalyst performance even when used at a high temperature for a long time.

  In order to improve the durability of the exhaust gas purifying catalyst, it is considered important to properly arrange the noble metal and the oxide carrier supporting the noble metal. However, it is difficult to design these arrangements. For example, when a noble metal is supported on a support by an impregnation method, the noble metal and the support are brought into contact with each other by adjusting the pH or salt of the solution. It wasn't perfect to see. In addition, the noble metal particle diameter is ideally 2 nm or more when considering the durability improvement of the noble metal and 5 nm or less when considering the catalytic activity, but the noble metal particle diameter is ideally 1 nm or less in the conventional impregnation method. It was difficult to adjust to a certain particle size range.

Further, an exhaust gas purification catalyst has been proposed in which a perovskite complex oxide containing a noble metal is supported on θ-alumina and / or α-alumina (Patent Document 1).
JP 2004-243305 A

  However, in the exhaust gas purification catalyst in which the perovskite-type composite oxide containing a noble metal is supported on θ-alumina and / or α-alumina, the perovskite-type composite oxide is produced in the manufacturing process when manufactured by, for example, the alkoxide method. Since the gelation rates of various elements constituting the complex oxide are different, a uniform noble metal-containing perovskite complex oxide is not formed. As a result, the noble metal (for example, Pd) not contained in the perovskite structure is not stably supported, and gradually aggregates and deteriorates due to the high temperature in the environment where the exhaust gas purification catalyst is used.

  The exhaust gas purifying catalyst of the present invention in which the arrangement of the noble metal and the oxide carrier supporting the noble metal is appropriately composed of a noble metal, a complex oxide containing a rare earth element, and a heat-resistant oxide, The gist is that the complex oxides supported by the complex oxide and supported by the noble metal include units having a structure separated by the heat-resistant oxide.

  The exhaust gas purifying catalyst of the present invention comprises a noble metal, a composite oxide having a perovskite structure, and a heat-resistant oxide. The gist is that the oxides include units having a structure separated by the heat-resistant oxide.

  Furthermore, the method for producing a gas purification catalyst of the present invention comprises an exhaust gas catalyst comprising a unit having a structure in which a noble metal is supported on a composite oxide and the composite oxides on which the noble metal is supported are separated from each other by a heat-resistant oxide. A method of manufacturing, comprising colloiding a composite oxide carrying a noble metal and dispersing it in a solution, forming a precursor of a heat-resistant oxide around the colloidal particles in the solution, and then firing it. Is the gist.

  According to the exhaust gas purifying catalyst of the present invention, a structure in which a noble metal is supported on a composite oxide and the composite oxide supporting the noble metal is separated by a heat-resistant oxide, the catalytic activity is improved and the exhaust gas purification is improved in durability. A catalyst is obtained.

  Hereinafter, embodiments of the exhaust gas purifying catalyst of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram of an exhaust gas purification catalyst according to an embodiment of the present invention. The exhaust gas purifying catalyst shown in the figure has noble metal 1 particles having catalytic activity. This noble metal is, for example, Pt, Pd, or Rh. The noble metal 1 particles are supported on the composite oxide 2. This composite oxide 2 contains a rare earth element, such as La, and has a perovskite structure. A refractory oxide 3 is formed around the composite oxide 2 supporting one noble metal particle. The heat-resistant oxide 3 separates each unit 4 of the single or plural composite oxides 2 carrying one or plural noble metal particles.

  The noble metal 1 supported on the composite oxide 2 having a perovskite structure is more stable than the case where it exists on the heat-resistant oxide 3. That is, the composite oxide 2 can function as an anchor material that suppresses the movement of the noble metal 1. Therefore, the exhaust gas purifying catalyst according to the present invention has a structure in which the independent units 4 of the respective complex oxides 2 are accommodated in the heat-resistant oxide 3 and dispersed in a form separated from each other. The movement of the noble metal 1 particles on the object 2 to the heat-resistant oxide 3 can be suppressed, and as a result, the aggregation of the noble metal 1 particles can be suppressed. In addition, since the independent units 4 of each composite oxide 2 are separated by the heat-resistant oxide 3, the units 4 are prevented from contacting and aggregating. Thereby, aggregation of 1 noble metal 1 particle | grains carry | supported by the complex oxide 2 can be suppressed.

About each unit 4, it is desirable that the amount of noble metal contained in this unit is a unit of 8 × 10 ⁻²⁰ mol or less. The effect of the present invention that the exhaust gas purifying catalyst is excellent in durability is particularly great when the number of atoms of the noble metal 1 in the unit 4 is 8 × 10 ⁻²⁰ mol or less. If the total number of noble metal 1 atoms in the unit 4 is 8 × 10 ⁻²⁰ or less, the particle diameter of the noble metal 1 particles after aggregation is aggregated even if the noble metal 1 particles aggregate in the unit 4. Is about 10 nm or less, and the catalyst activity does not decrease. This will be described with reference to the drawings.

FIG. 2 is a diagram schematically showing the shape of the exhaust gas purification catalyst according to the present invention in an initial state (FIG. 2A) and after use at a high temperature for a long time (FIG. 2B). . As can be seen from a comparison between FIG. 2A and FIG. 2B, in the exhaust gas purification catalyst according to the present invention, even if the units 4 are separated by the heat-resistant oxide 3, one unit 4 The plurality of noble metal particles 1 contained therein can be aggregated into 4 unit units after use at a high temperature for a long time to become enlarged noble metal particles 11. However, with respect to platinum or palladium as the noble metal 1, when the number of atoms in the unit 4 is 8 × 10 ⁻²⁰ mol or less, the noble metal particles in the unit 4 are aggregated even if they are aggregated into one. The enlarged noble metal particles 11 have a particle size of about 10 nm or less. If the particle diameter after aggregation is about 10 nm or less, the exposed area of the noble metal particles 11 is sufficiently large, and sufficient catalytic activity can be obtained.

  The size of the unit 4 is not particularly limited, but a sufficient effect can be obtained at 2 μm or less. More desirably, it is 50 nm or less. If the size of the unit 4 can be reduced, the number of atoms of the noble metal 1 contained in the unit 4 can also be limited. As a result, when the noble metal in the unit 4 is aggregated and deteriorated into one noble metal particle 11 as described above. This is because even if the aggregated noble metal particles 11 have a particle diameter of several nanometers, sufficient catalytic activity can be obtained.

  As a means for limiting the number of atoms of the noble metal 1 contained in the unit 4, it is conceivable to reduce the amount of the noble metal 1 supported on the composite oxide 2 in addition to reducing the size of the unit 4. However, when the amount of the noble metal 1 supported on the composite oxide 2 is reduced, the exhaust gas purification performance is lowered in accordance with the decrease in the amount of the noble metal 1, so that the precious metal 1 is used in order to ensure the necessary exhaust gas purification performance. It is necessary to increase the amount of coating when the honeycomb substrate is coated, which is not a practical means.

The composite oxide 2 is preferably a composite oxide having a perovskite structure represented by the chemical formula ABO ₃ as a basic structure. In this case, the heat-resistant oxide 3 contains an element at the A site of the composite oxide 2. It is preferable to do. The perovskite structure is a complex oxide generally represented by the chemical formula of ABO ₃ , and the element of the A portion of this chemical formula forms the basic skeleton of the perovskite structure.

Since the composite oxide 2 having a perovskite structure can function as an anchor material for the noble metal 1, it is suitable as a carrier for supporting the noble metal 1. Representative compounds of composite oxides 2 of this perovskite _{structure, BaTiO 3, LaFeO 3, LaMnO} 3, but LaCoO _3, and the like, in the exhaust gas HC, CO, to a reactive or catalytic noble metal 1 and NO _X In view of the above action, a LaMn-based perovskite complex oxide is preferable.

  On the other hand, when a general catalyst-supporting oxide such as alumina is placed in contact with the perovskite structure composite oxide 2 as the heat-resistant oxide 3, for example, the perovskite structure composite oxide Since the element at the A site easily dissolves in the heat-resistant oxide 3, the element at the A site diffuses from the complex oxide 2 to the heat-resistant oxide 3 and dissolves in a high temperature environment. There was a risk that the perovskite structure of No. 2 would easily collapse.

FIG. 3 shows the shape of the exhaust gas purifying catalyst when LaMnO ₃ is applied to the composite oxide 2 and alumina is applied to the heat-resistant oxide 5, respectively, in the initial state (FIG. 3 (a)) and used at a high temperature for a long time. It is a figure typically shown later (the same figure (b)). As can be seen from the comparison between FIG. 3A and FIG. 3B, the composite oxide 2 collapses and the MnAl ₂ O ₄ particles 22 after use at a high temperature for a long time (FIG. 3B). May be formed, and the alumina of the heat-resistant oxide 5 may become La-alumina 23 and spherical α-alumina 25 in some cases. If the composite oxide 2 having a perovskite structure collapses in this way, the noble metal 1 aggregates and enlarges, and the durability expected in the present invention cannot be expected.

  Therefore, for example, the heat-resistant oxide 3 containing alumina as a main component and the element of the A site of the composite oxide 2 having a perovskite structure can be used in advance. If the refractory oxide 3 contains the element at the A site of the composite oxide 2 having a perovskite structure, the element at the A site is converted from the complex oxide 2 to the refractory oxide even after using the catalyst at a high temperature for a long time. 3 is prevented from diffusing and moving to solid solution 3, and the collapse of the composite oxide 2 having a perovskite structure can be suppressed. As a result, the structure of the exhaust gas purifying catalyst according to the present invention can be maintained.

In the composite oxide 2 having a perovskite structure, the A site and the B site in the chemical formula of ABO ₃ may be composed of two or more different elements. For example, La _0.8 Ba _0.2 Mn _0.5 Fe _0.4 O3 may be used, and in this case, the heat-resistant oxide 3 containing the element at the A site contains La and Ba.

The composite oxide 2 may have a perovskite structure having an ABO ₃ type stoichiometric composition, but the A site of the perovskite structure represented by the chemical formula ABO ₃ is less than the stoichiometric amount. It is more preferable that the oxide has a perovskite structure. The composite oxide 2 having a perovskite structure having a stoichiometric composition tends to collapse the perovskite structure under a repeated environment of an oxidation-reduction atmosphere. The cause is not necessarily clear, but it is presumed that the perovskite structure itself is easily oxidized or reduced. And the ease of maintenance of the structure improves by making the A site which makes the basic skeleton of this perovskite structure slightly smaller than the stoichiometric ratio (A: B = 1/1). The details of this are unknown, but the lack of a part of the A-site atoms that form the basic skeleton of the perovskite structure allows the perovskite itself to maintain its oxygen retention balance, improving resistance to oxidation-reduction atmosphere fluctuations. I guess that.

In addition, the composite oxide 2 can have a structure including the component of the heat-resistant oxide 3 at the B site of the perovskite structure represented by the chemical formula ABO ₃ . When the composite oxide contains the component of the heat-resistant oxide 3 at the B site of the perovskite structure, the atoms of the B site of the composite oxide 2 of the perovskite structure react with the heat-resistant oxide 3 to form a constituent element Can be prevented from being denatured. Therefore, even after a long period of use, the change in physical properties accompanying the reaction between the composite oxide 2 having the perovskite structure and the heat-resistant oxide 3 can be suppressed, and as a result, the unit of the present invention having excellent characteristics can be maintained for a long time. can do.

  That is, in the present invention, in order to suppress the collapse of the composite oxide 2 having the perovskite structure, the heat-resistant oxide 3 previously contains the element at the A site of the composite oxide 2 having the perovskite structure as described above. In addition to the use of, a compound containing the component of the heat-resistant oxide 3 at the B site of the composite oxide 2 having a perovskite structure as described above can be used. In addition, the combined structure, that is, the composite oxide 2 contains a component of the heat-resistant oxide 3 at the B site, and the heat-resistant oxide 3 contains the element at the A site of the composite oxide 2 having the perovskite structure. It can also be a structure.

As an example of the composite oxide 2 having a perovskite structure represented by the chemical formula ABO ₃ and containing a component of the heat-resistant oxide 3 at the B site, the B site is at least one of Al and Zr. Some have seed components. Since the heat-resistant oxide 3 is a material for the purpose of suppressing aggregation of the composite oxide 2, it is desirable to have heat resistance. Specifically, materials such as Al ₂ O ₃ and ZrO ₂ are particularly desirable as the material having heat resistance. This is because Al ₂ O ₃ and ZrO ₂ have high resistance to fluctuations in the oxidizing / reducing atmosphere as an exhaust gas purification catalyst, can maintain a high surface area, and are excellent in heat resistance. Since the function of the heat-resistant oxide 3 in the present invention is the same as the function required for the base material component in the conventional exhaust gas purification catalyst, the above Al ₂ O ₃ and ZrO ₂ are desirable materials, and have particularly high heat resistance. It is desirable to have Al ₂ O ₃ . Therefore, it is preferable that the B site of the composite oxide 2 having a perovskite structure has at least one component of Al and Zr.

Note that the B site of the composite oxide 2 having a perovskite structure represented by the chemical formula ABO ₃ is not limited to the case of being composed of one kind of element, like the A site. The B site may be composed of two or more components in order to stabilize the perovskite structure.

  The composite oxide 2 in the exhaust gas purification catalyst of the present invention more preferably has an average particle size of the composite oxide 2 larger than the average pore size of the heat-resistant oxide 3. The smaller the composite oxide 2 is, the smaller the concentration of the noble metal supported is, and the aggregation of the noble metal 1 can be suppressed. The larger the pore diameter of the heat-resistant oxide 3 is, the better the gas (exhaust gas) diffusibility is. If it is smaller than the pores of the heat-resistant oxide 3, the composite oxide 2 escapes from the pores of the heat-resistant oxide 3 and aggregates. The phenomenon that the composite oxide 2 escapes from the pores of the heat-resistant oxide 3 is effectively suppressed by making the average particle diameter of the composite oxide 2 larger than the average pore diameter of the heat-resistant oxide 3. Can do.

  Next, it is more preferable that the heat-resistant oxide 3 has a mesopore diameter of 10 nm or less. As an example, alumina having a mesopore diameter of 10 nm or less can be suitably used for the heat-resistant oxide 3. When the pores of the heat-resistant oxide 3 are blocked, the exhaust gas to be reacted no longer reaches the catalytic noble metal 1, and even if the fine particle state of the noble metal 1 can be maintained, sufficient catalytic activity cannot be obtained. . On the other hand, if the pore diameter exceeds 10 nm, the unit 4 surrounded by the heat-resistant oxide 3 may move from the pores and aggregate. The pore diameter can be measured as an average value by a gas adsorption method or the like.

  As described above, in the exhaust gas purifying catalyst according to the present invention, the A-site element forming the basic skeleton of the perovskite structure of the composite oxide 2 can be contained in the heat-resistant oxide 3. Is effective in improving the heat resistance of the heat-resistant oxide 3, and can maintain pores having an average pore diameter of 10 nm or less. Although the details are unknown as the reason for showing this effect, the A-site atom stays at the grain boundary between the primary particles of the heat-resistant oxide 3, lowering the adhesion between the particles, and as a result, pore clogging hardly occurs. It is presumed that

  The noble metal 1 is preferably at least one selected from Pt, Pd and Rh. The effect of the present invention is particularly effective when it contains at least one kind of noble metal selected from Pt, Pd and Rh. As the complex oxide supporting the noble metal 1, an appropriate complex oxide according to the type of the noble metal 1 can be selected. Further, when a plurality of types of noble metals are used as the noble metal 1, different types of noble metals may be arranged in combination with appropriate composite oxides 2 in units separated by the same heat-resistant oxide 3. In addition, powders of different types of exhaust gas purification catalysts may coexist. An exhaust gas purifying catalyst using a plurality of types of precious metals can be realized by separately preparing colloidal particles of composite oxides supporting various precious metals according to the manufacturing method described below, and performing a mixing process or the like.

  Next, the manufacturing method of the exhaust gas purification catalyst of the present invention will be described. When producing an exhaust gas purifying catalyst according to the present invention, a composite oxide supporting a noble metal is colloided and dispersed in a solution, and then a precursor of a heat resistant oxide is formed around the colloidal particles in the solution. And a subsequent baking step.

  The structure of the exhaust gas purifying catalyst according to the present invention is prepared in advance by preparing a composite oxide supporting a noble metal, preparing fine colloidal particles from the composite oxide powder supporting the noble metal, and then heat resistance. It is obtained by forming an oxide precursor (mainly hydroxide) around the colloidal particles. In addition, the size of the unit can be controlled by changing the size of the colloidal particles when preparing the colloidal particles. The size of the colloidal particles can be changed, for example, depending on the degree of crushing of the composite oxide powder supporting the noble metal.

  The above-described method for producing an exhaust gas purification catalyst of the present invention makes it possible to form a heat-resistant oxide between colloidal particles by colloidalizing a composite oxide supporting a noble metal, and fine noble metal-supported composite oxidation. It is possible to arrange the object in a state of being isolated in the heat-resistant oxide. Also, by forming colloidal particles of a complex oxide carrying a noble metal in advance, it becomes possible to obtain a stable catalyst without the noble metal being carried on a heat-resistant oxide in which the noble metal is easy to move.

  In the method for producing an exhaust gas purification catalyst of the present invention, steps other than the steps described above can be performed according to a conventional method.

  The exhaust gas purification catalyst according to the present invention has been described above with reference to the drawings. However, the exhaust gas purification catalyst of the present invention is not limited to the description of the specification and the description of the drawings, and does not depart from the spirit of the present invention. Needless to say, many variations are possible.

  For comparison with the exhaust gas purifying catalyst according to the present invention, FIG. 4 shows an initial example of a conventional example in which the noble metal 1 is supported on the perovskite type composite oxide 2 but the heat-resistant oxide 3 is not formed. It is a figure shown typically in a state (the figure (a)) and after use for a long time at high temperature (the figure (b)). As can be seen from the comparison between FIG. 4A and FIG. 4B, in the exhaust gas purifying catalyst of the conventional example, the composite oxide 2 is used after being used at a high temperature for a long time (FIG. 4B). As a result, the noble metal 1 is significantly aggregated and enlarged. This enlarged noble metal has a reduced exhaust gas purification performance. By comparison with FIG. 4, the effect of the exhaust gas purification catalyst according to the present invention shown in FIG. 1 is obvious.

[Example 1]
i) Preparation of noble metal-supported composite oxide La nitrate, Mn nitrate, and Fe nitrate are poured into ion-exchanged water so that the molar ratio of each element is 1: 0.8: 0.2, and they are thoroughly stirred and dissolved. Then, it was dripped at the tetramethylammonium hydroxide (TMAH) solution. The obtained gel was left to stand overnight and aged, washed, dried at 120 ° C. overnight, pulverized, calcined in an air stream at 400 ° C. for 1 hour, and then at 800 ° C. for 2 hours to obtain a composite oxide. Got.

  The obtained composite oxide was impregnated and supported with a dinitrodiamine Pt nitric acid aqueous solution so that the Pt supporting concentration was 0.6 wt%, dried at 120 ° C. overnight, and then at 400 ° C. for 1 hour in an air stream. The noble metal-supported composite oxide of Example 1 was obtained.

ii) Colloidalization of the noble metal-supported composite oxide The powder of the noble metal-supported composite oxide obtained above is charged into ion-exchanged water, and the polymer is protected twice as much as the charged powder while irradiating with ultrasonic waves. A material (polyvinylpyrrolidone) was charged and dissolved to obtain a 10 wt% colloidal aqueous solution as a solid content. At this time, the average particle diameter of the colloidal particles measured by TEM was 200 nm.

iii) Inclusion of noble metal-supported composite oxide colloid particles with heat-resistant oxide In hexylene glycol (HEG), a predetermined amount of aluminum isopropoxide (AIP) as a raw material for heat-resistant oxide and lanthanum isopropoxide ( LIP) was added, and the mixture was stirred at 120 ° C. and then cooled to 80 ° C., and the obtained colloid aqueous solution was added dropwise to cause gelation.

  The obtained gel was dried under reduced pressure on a rotary evaporator at 150 ° C. for 5 hours and then calcined in an air stream at 400 ° C. for 1 hour to obtain 50 g of catalyst powder of Example 1. Note that the precious metal loading concentration is 0.6% to 0.3% because of the amount of lanthanum alumina oxide equivalent to the solid content of the colloid.

iv) Application to honeycomb substrate After stirring and mixing 45 g of the catalyst powder of Example 1 obtained in the above iii), 6.7 g of boehmite, 10 g of 10% acetic acid aqueous solution and 130 g of ion-exchanged water, the mixture was added to the magnetic pot. The mixture was pulverized with 5 mmφ alumina balls (slurry diameter 2.5 μm).

  Then, the obtained slurry was applied to a cordierite honeycomb substrate (400 cpsi, 6 mil, 0.12 L), excess slurry was removed with an air stream, dried with an air stream of 150 ° C., and then at 400 ° C. After firing for 1 hour, a catalyst honeycomb body coated with 100 g of catalyst powder per liter of honeycomb carrier was obtained.

[Example 2]
A catalyst honeycomb of Example 2 was obtained in the same manner as in Example 1 except that the starting material of the composite oxide of Example 1 was La nitrate and Ni nitrate at a ratio of 1: 1 and the noble metal salt was an aqueous Pd nitrate solution. It was.

[Example 3]
The starting materials of the composite oxide of Example 1 are La nitrate, Sr nitrate, Mn nitrate and Fe nitrate in a ratio of 0.8: 0.2: 0.8: 0.2, respectively, and the noble metal salt is an aqueous Pd nitrate solution. A catalyst honeycomb body of Example 3 was obtained in the same manner as Example 1 except that predetermined amounts of AIP, LIP, and strontium isopropoxide (SrIP) were added as raw materials for the heat-resistant oxide.

[Example 4]
The starting materials for the composite oxide of Example 1 are La nitrate, Sr nitrate, Co nitrate and Fe nitrate in a ratio of 0.8: 0.18: 0.8: 0.2, respectively, and the noble metal salt is an aqueous Pd nitrate solution. The noble metal support concentration is 1.6 wt%, and predetermined amounts of AIP, LIP, and strontium isopropoxide (SrIP) are introduced as raw materials for the heat-resistant oxide. In step iii, the noble metal support composite oxide and the clathrate are added. The composition of (heat-resistant oxide) was changed, and the amount of noble metal in the catalyst was adjusted to be equal to obtain the catalyst honeycomb of Example 4.

[Example 5]
The starting material of the composite oxide of Example 1 is an oxide having an average particle diameter of 250 nm with La nitrate, Ca nitrate, Co nitrate, and Fe nitrate in a ratio of 0.8: 0.2: 0.8: 0.2, respectively. A colloidal solution was obtained. Further, a noble metal salt was made into an aqueous Pd nitrate solution, and predetermined amounts of AIP, LIP, and Ca isopropoxide (CaIP) were added as heat-resistant oxide raw materials. The composition of the oxide and the clathrate (heat-resistant oxide) was changed, and the amount of noble metal in the catalyst was adjusted to be equal to obtain the catalyst honeycomb of Example 5.

[Example 6]
The starting materials for the composite oxide of Example 1 were La nitrate, Ca nitrate, Co nitrate, and Fe nitrate in a ratio of 0.8: 0.2: 0.8: 0.2, respectively, and the noble metal salt was an aqueous Rh nitrate solution. A catalyst honeycomb of Example 6 was obtained in the same manner except that predetermined amounts of AIP, LIP, and Ca isopropoxide (CaIP) were added as raw materials for the heat-resistant oxide.

[Example 7]
The starting materials of the composite oxide of Example 1 are La nitrate, Ca nitrate, Co nitrate, and Ni nitrate in a ratio of 0.8: 0.2: 0.8: 0.2, respectively, and the noble metal salt is an aqueous Rh nitrate solution. A catalyst honeycomb of Example 7 was obtained in the same manner except that predetermined amounts of AIP, LIP, and Ca isopropoxide (CaIP) were added as raw materials for the heat-resistant oxide.

[Comparative Example 1]
Nitrogen La, Mn nitrate, and Fe nitrate were added to ion-exchanged water so that the molar ratio of each element was 1: 0.8: 0.2, and after stirring and dissolving well, tetramethylammonium hydroxide ( The resulting gel was dropped into the TMAH) solution, left to stand overnight and aged, washed, dried at 120 ° C. overnight, pulverized, and then in an air stream at 400 ° C. for 1 hour, and then at 800 ° C. for 2 hours. Firing was performed to obtain a composite oxide.

  The obtained composite oxide was impregnated and supported with a dinitrodiamine Pt nitric acid aqueous solution so that the Pt supporting concentration was 0.6 wt%, dried at 120 ° C. overnight, and then at 400 ° C. for 1 hour in an air stream. To obtain a noble metal-supported composite oxide.

  22.5 g of this noble metal-supported composite oxide as catalyst powder, 22.5 g of γ-alumina, 6.7 g of boehmite, 10 g of 10% acetic acid aqueous solution and 130 g of ion-exchanged water were stirred and mixed, and then charged into a magnetic pot. Vibration grinding (slurry diameter 2.5 μm) was performed with 5 mmφ alumina balls.

  Then, the obtained slurry was applied to a cordierite honeycomb substrate (400 cpsi, 6 mil, 0.12 L), excess slurry was removed with an air stream, dried with an air stream of 150 ° C., and then at 400 ° C. After firing for 1 hour, a catalyst honeycomb body coated with 100 g of catalyst powder per liter of honeycomb carrier was obtained.

[Comparative Example 2]
A catalyst honeycomb of Comparative Example 2 was obtained in the same manner except that the starting material of the composite oxide of Comparative Example 1 was La nitrate, Ni nitrate was 1: 1, and the noble metal salt was an aqueous Pd nitrate solution.

Durability tests were performed on Examples 1 to 7 and Comparative Examples 1 and 2 described above. In this test, an exhaust gas purification catalyst of each sample was attached to an exhaust system of an engine with a displacement of 3500 cc, and after performing an endurance test for operating the engine at an inlet temperature of 900 ° C. for 30 hours, the exhaust gas purification catalyst was passed through a simulated exhaust gas flow. The exhaust gas having the composition shown in Table 1 below was circulated and the NOx purification rate (ηNOx)% at 400 ° C. of each exhaust gas purification catalyst was calculated from the NOx concentration at the inlet side and the outlet side at 400 ° C. . The results of this durability test are shown in Table 2.

〔Test results〕
As is apparent from Table 2, Examples 1 to 7 according to the present invention are superior in NOx to the comparative example in which the heat-resistant oxide is not formed around the perovskite complex oxide supporting the noble metal. It can be seen that this is an exhaust gas purification catalyst exhibiting a purification rate and excellent in durability.

[ Reference Example 8]
Reference Example 8 is an example in which the composite oxide includes a component of a heat resistant oxide.

i) Preparation of noble metal-supported composite oxide Nitrogen La and Al nitrate are poured into ion-exchanged water so that the molar ratio of elements is 1: 1, and after stirring and dissolving well, tetramethylammonium hydroxide (TMAH) ) Added dropwise to the solution. The resulting gel was left to stand overnight and aged, washed, dried at 120 ° C. overnight, pulverized, calcined in an air stream at 400 ° C. for 1 hour, and then at 850 ° C. for 3 hours to obtain a composite oxide. Got.

The obtained composite oxide was impregnated and supported with a dinitrodiamine Pt nitric acid aqueous solution so that the Pt supporting concentration was 0.6 wt%, dried at 120 ° C. overnight, and then at 400 ° C. for 1 hour in an air stream. And the noble metal-supported composite oxide of Reference Example 8 was obtained.

ii) Colloidalization of the noble metal-supported composite oxide The powder of the noble metal-supported composite oxide obtained in i) above is charged into ion-exchanged water, and irradiated with ultrasonic waves. A molecular protective material (polyvinyl pyrrolidone) was charged and dissolved to obtain a 10 wt% colloidal aqueous solution as a solid content. At this time, the average particle diameter of the colloidal particles measured by TEM was 200 nm.

iii) Inclusion of noble metal-supported composite oxide colloidal particles with heat-resistant oxide Into hexylene glycol (HEG), a predetermined amount of aluminum isopropoxide (AIP) is added as a heat-resistant oxide raw material and heated to 120 ° C. After stirring, the mixture was cooled to 80 ° C., and the colloidal solution obtained in the above ii) was dropped to cause gelation.

The obtained gel was dried under reduced pressure on a rotary evaporator at 150 ° C. for 5 hours and then calcined in an air stream at 550 ° C. for 1 hour to obtain 50 g of catalyst powder of Reference Example 8. Note that the precious metal loading concentration is 0.6% to 0.3% because of the amount of alumina oxide equivalent to the solid content of the colloid.

iv) Application to honeycomb substrate The catalyst powder, boehmite, 10% aqueous acetic acid solution and ion-exchanged water obtained in Reference Example 8 obtained in the above iii) were stirred and mixed, and then charged into a magnetic pot, and vibrationally pulverized together with 5 mmφ alumina balls. (Slurry diameter 2.5 μm).

  Thereafter, the obtained slurry was applied to a cordierite honeycomb carrier (400 cpsi, 6 mil, 0.12 L), excess slurry was removed with an air stream, dried with an air stream of 150 ° C., and then at 400 ° C. After firing for 1 hour, a catalyst honeycomb body coated with 100 g of catalyst powder per liter of honeycomb carrier was obtained.

[ Reference Example 9]
Starting nitric acid La composite oxide of Example 8, 1 nitrate Al: a 1 ratio, a noble metal salt and Pd nitrate solution, except that the noble metal support concentration and 1.6 wt% in the same manner in Reference Example 9 The catalyst honeycomb was obtained.

[ Reference Example 10]
The starting material of the composite oxide of Reference Example 8 is La nitrate, Sr nitrate, and Al nitrate in a ratio of 0.6: 0.4: 1, the noble metal salt is an aqueous Pd nitrate solution, and the noble metal loading concentration is 1.6 wt%. A catalyst honeycomb of Reference Example 10 was obtained in the same manner except that.

[ Reference Example 11]
The starting material of the complex oxide of Reference Example 8 is La nitrate and Zr nitrate in a ratio of 1: 1, the noble metal salt is an aqueous Pd nitrate solution, the noble metal loading concentration is 1.6 wt%, was charged with a predetermined amount of zirconium isopropoxide, in step iii, changing the composition of the noble metal loaded composite oxide inclusion material (heat-resistant oxide), was prepared as the noble metal amount in the catalyst is equal, reference example Eleven catalyst honeycombs were obtained.

[Comparative Example 3]
Nitric acid La and Al nitrate were each added to ion-exchanged water so as to have an element molar ratio of 1: 1, thoroughly stirred and dissolved, and then dropped into a tetramethylammonium hydroxide (TMAH) solution. The gel was allowed to stand overnight and aged, then washed, dried at 120 ° C. overnight, pulverized, and calcined in an air stream at 400 ° C. for 1 hour and then at 850 ° C. for 3 hours to obtain a composite oxide. .

  The obtained composite oxide was impregnated and supported with a dinitrodiamine Pt nitric acid aqueous solution so that the Pt supporting concentration was 0.6 wt%, dried at 120 ° C. overnight, and then at 400 ° C. for 1 hour in an air stream. This was used as the catalyst powder of Comparative Example 3 by firing with a noble metal-supported composite oxide.

  The obtained catalyst powder, boehmite, 10% acetic acid aqueous solution and ion-exchanged water of Comparative Example 3 were stirred and mixed, and then charged into a magnetic pot, and vibrationally pulverized (slurry diameter 2.5 μm) with 5 mmφ alumina balls.

  Thereafter, the obtained slurry was applied to a cordierite honeycomb carrier (400 cpsi, 6 mil, 0.12 L), excess slurry was removed with an air stream, dried with an air stream of 150 ° C., and then at 400 ° C. After firing for 1 hour, a catalyst honeycomb body coated with 100 g of catalyst powder per liter of honeycomb carrier was obtained.

[Comparative Example 4]
Comparative Example 4 was similarly performed except that the starting material of the composite oxide of Comparative Example 4 was La nitrate and Al nitrate in a ratio of 1: 1, the noble metal salt was an aqueous Pd nitrate solution, and the noble metal loading concentration was 1.6 wt%. The catalyst honeycomb was obtained.

Durability tests were performed on Reference Examples 8 to 11 and Comparative Examples 3 and 4 described above. This test is the same as the test performed for Examples 1 to 7 and Comparative Examples 1 and 2. The results of this durability test are shown in Table 3.

〔Test results〕
As is clear from Table 3, Reference Examples 8 to 11 according to the present invention are compared with Comparative Examples 3 and 4 in which the heat-resistant oxide is not formed around the perovskite complex oxide supporting the noble metal, It can be seen that the exhaust gas purification catalyst has an excellent NOx purification rate and excellent durability.

It is a schematic diagram of the exhaust gas purification catalyst which becomes one Embodiment of this invention. It is a figure which shows typically the time-dependent change of the shape of the exhaust gas purification catalyst which concerns on this invention. It is a figure which shows typically the time-dependent change of the shape of the exhaust gas purification catalyst which concerns on this invention. It is a figure which shows typically the time-dependent change of the shape of the conventional exhaust gas purification catalyst.

Explanation of symbols

1 Precious metal 2 Composite oxide 3 Heat-resistant oxide 4 Unit

Claims (7)

Consists of noble metals, complex oxides containing rare earth elements, and heat-resistant oxides,
The noble metal, wherein is supported on the composite oxide, and a noble metal to each other supported composite oxide, saw including a unit of said separated by refractory oxide structure,
The amount of noble metal contained in the unit is 8 × 10 ⁻²⁰ mol or less,
The composite oxide is a composite oxide having a perovskite structure represented by the chemical formula ABO ₃ as a basic structure, and the heat-resistant oxide contains lanthanum, an element of the A site of the composite oxide. Exhaust gas purification catalyst. 2. The exhaust gas purification according to claim 1 , wherein the composite oxide is an oxide having an A site deficient perovskite structure in which the A site of the perovskite structure represented by the chemical formula ABO ₃ is less than the stoichiometric amount. catalyst. The composite oxide, the B site of the perovskite structure represented by the chemical formula ABO _3, the exhaust gas purifying catalyst according to claim 1 or 2, characterized in that it comprises a component of the heat-resistant oxide. The composite oxide, the B site of the perovskite structure represented by the chemical formula ABO _3, according to any one of claims 1-3, characterized in that it comprises at least one component of the Al and Zr Exhaust gas purification catalyst. The exhaust gas purification catalyst according to any one of claims 1 to 4 , wherein an average particle diameter of the composite oxide is larger than an average pore diameter of the heat-resistant oxide. The exhaust gas purification catalyst according to any one of claims 1 to 5 , wherein the heat-resistant oxide has a mesopore diameter of 10 nm or less. The exhaust gas purification catalyst according to any one of claims 1 to 6 , wherein the noble metal is at least one selected from Pt, Pd, and Rh.

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