JP2006181484A - Catalyst, exhaust gas cleaning catalyst and method for preparing the catalyst - Google Patents

Catalyst, exhaust gas cleaning catalyst and method for preparing the catalyst Download PDF

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JP2006181484A
JP2006181484A JP2004378105A JP2004378105A JP2006181484A JP 2006181484 A JP2006181484 A JP 2006181484A JP 2004378105 A JP2004378105 A JP 2004378105A JP 2004378105 A JP2004378105 A JP 2004378105A JP 2006181484 A JP2006181484 A JP 2006181484A
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step
catalyst
alumina
noble metal
nm
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Makoto Aoyama
Toshifumi Fukushige
Toshiharu Miyamura
Masaki Nakamura
Katsuo Suga
雅紀 中村
利春 宮村
敏文 福重
克雄 菅
誠 青山
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Nissan Motor Co Ltd
日産自動車株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent durable catalyst which is for cleaning exhaust gas, in particular, cleaning the exhaust gas exhausted from an internal engine. <P>SOLUTION: The catalyst has alumina with a size of 30-1,000 nm and a noble metal carried by the alumina with a carrying concentration of 0.001-0.3 wt%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a catalyst, an exhaust gas purification catalyst, and a catalyst manufacturing method, and more particularly to an exhaust gas purification catalyst for purifying exhaust gas discharged from an internal combustion engine.

Automobile emission regulations are expanding worldwide. Therefore, noble metal particles such as platinum (Pt), palladium (Pd), rhodium (Rh) are supported on a carrier such as alumina (Al 2 O 3 ) which is a porous oxide, and further coated on a refractory inorganic carrier or the like. The developed catalysts are being developed and used for the purpose of fuel reforming catalysts and automobile exhaust gas purification catalysts. And since the amount of catalyst used per vehicle is increasing in response to the tightening of exhaust gas regulations, the amount of precious metals used per vehicle is also increased, which increases the cost of the vehicle. There is. In addition, there is a problem of resource depletion because noble metals are used as a catalyst in the fuel cell technology, which is attracting attention as a means for solving the recent energy resource problem and the global warming problem associated with carbon dioxide emissions. For this reason, it is necessary to reduce the amount of noble metal used for the catalyst.

  Since the catalytic activity of the noble metal is a catalytic reaction in which the reaction proceeds on the surface of the noble metal, it is almost proportional to the surface area of the noble metal. Therefore, in order to obtain the maximum catalytic activity from a small amount of noble metal, precious metal particles with a small particle size and a high specific surface area are produced, and uniformly dispersed on a support such as a porous body while maintaining the particle size. It is desirable to make it. However, in the case of fine particles having a noble metal particle size of 1 [nm] or less, the surface reactivity of the noble metal particles is high, and the noble metal particles have a large surface energy and are very unstable. For this reason, the noble metal particles tend to aggregate and sinter together. In particular, Pt agglomerates when heated, so even if dispersed and supported on the support, Pt agglomerates to increase the particle size and reduce the catalytic activity. Since a catalyst for an automobile is usually exposed to a high temperature exceeding 800 to 900 [° C.] and sometimes exceeding 1000 [° C.], it is difficult to maintain the catalyst activity in a fine particle state. For this reason, agglomeration of noble metal particles is the greatest difficulty in establishing an exhaust gas purification catalyst with a small amount of noble metal.

  In order to prevent aggregation of the noble metal particles, it is conceivable to reduce the surface energy of the noble metal particles. However, in order to suppress the surface energy, it is necessary to make the particle size of the noble metal particles large particles such as 50 [nm], 100 [nm], and in this case, there is a problem that the catalyst activity itself is lost.

Therefore, for example, precious metal is supported on the first carrier particles having an average particle diameter of 1 to 100 [nm], and then the second carrier particles having an average particle size equal to or larger than and / or less than the first carrier particles are mixed. By doing so, an exhaust gas purification catalyst that suppresses aggregation of noble metal particles has been proposed (see Patent Document 1).
JP-A-10-249198

  However, if the noble metal support concentration is an amount that can be coated on the refractory inorganic support, the diameter of the noble metal particles after durability becomes too large, and the activity is greatly reduced. On the contrary, if the noble metal support concentration is set to an amount that causes a small decrease in catalyst performance, coating on the refractory inorganic support becomes impossible.

  The present invention has been made in order to solve the above-mentioned problems. The catalyst according to the first invention includes alumina having a particle size of 30 to 1000 [nm], and a supported concentration of 0.001 to 0 on the alumina. And 3 [wt%] supported noble metal.

  Further, the method for producing a catalyst according to the second invention includes an alumina fine powder production step for producing an alumina fine powder having a particle size of 30 to 1000 [nm], a dispersion step for dispersing the alumina fine powder in water, A supporting step for supporting the noble metal salt on the alumina fine powder after the dispersion step, a mixing step for mixing the second carrier in the same amount or more with the alumina fine powder after the supporting step, and 100 to 150 [° C. after the mixing step. And a firing step of firing at a temperature of less than 500 [° C.] after the drying step.

  Further, the exhaust gas purification catalyst according to the third invention is an exhaust gas purification catalyst having a refractory inorganic carrier coated with the catalyst according to the first invention, and the catalyst per 1 [L] of the refractory inorganic carrier capacity. The gist is that the coating amount is 600 [g] or less.

  According to the first invention, in this catalyst, even when all the precious metals on the alumina are aggregated, only the amount of which the particle size is 10 nm or less is supported on the alumina. Even if all the above precious metals are aggregated, the catalyst performance is not significantly reduced. For this reason, even if it reduces the usage-amount of a noble metal, the catalyst activity ability at the time of catalyst preparation is maintained, and the catalyst which can be coated to a refractory inorganic support | carrier is obtained.

  According to the second invention, it is possible to uniformly disperse and carry only the amount of which the particle size is 10 [nm] or less even when the noble metal on the alumina aggregates.

  According to the third aspect of the invention, an exhaust gas purification catalyst that is durable and that maintains the catalytic activity can be obtained.

  Hereinafter, the details of the catalyst, the exhaust gas purifying catalyst, and the method for producing the catalyst according to the embodiment of the present invention will be described with reference to FIGS.

(catalyst)
The catalyst according to the embodiment of the present invention will be described. As shown in FIG. 1A, the catalyst 1 according to the present embodiment has an alumina 2 having a particle size of 30 to 1000 [nm], and a supported concentration of 0.001 to 0.3 [weight] on the alumina 2. %] And a noble metal 3 supported on the substrate. This catalyst 1 supports only the amount that the particle size is 10 nm or less even when all the noble metals 3 on the alumina 2 are aggregated. Even if the particles are aggregated, the catalyst performance is not significantly reduced. For this reason, even if it reduces the usage-amount of a noble metal, the catalyst activity ability at the time of catalyst preparation is maintained, and the catalyst which can be coated to a refractory inorganic support | carrier is obtained.

  In this catalyst 1, when all the noble metals 3 supported on the alumina 2 are aggregated into one particle due to thermal durability, as shown in FIG. 1B, the catalyst 11 after thermal durability is configured. The particle size of the noble metal 13 supported on the alumina 12 is 10 [nm] or less. When the particle size of the noble metal supported on the alumina is 10 nm or less, the balance between the surface energy of the noble metal and the catalytic activity is maintained, and even when heated, the noble metal hardly aggregates and maintains durability. be able to. For this reason, in the catalyst according to the present embodiment, even after the heat endurance, the catalytic activity is not significantly reduced as compared with the time of catalyst preparation. Note that when the particle size of the noble metal is smaller than 5 [nm], the melting point is remarkably lowered, and the noble metal is melted and easily aggregates. On the other hand, the smaller the particle size of the noble metal, the higher the conversion rate and the higher the function as a catalyst. However, when the particle size is large, the catalytic activity of the noble metal decreases. For this reason, when considering the balance between the aggregation of the noble metal and the catalytic activity, the particle diameter of the noble metal after thermal endurance should be 10 [nm] or less, preferably 3 [nm] to 8 [nm], particularly preferably. Is 2 [nm] to 5 [nm].

Here, as an example, FIG. 2 shows the relationship between the surface area of the noble metal supported on alumina and the NO x conversion rate when the concentration of the noble metal supported on alumina is 0.3 [%] and 3 [%]. FIG. 2A shows the NO X conversion rate at the time of catalyst preparation, that is, when the supported concentration of the noble metal before heat endurance is 3 [%]. Here, the particle size of the noble metal is 1.5 [nm]. FIG. 2B shows the NO X conversion rate when the concentration of the noble metal supported on alumina before thermal endurance is 0.3 [%]. Here, the particle size of the noble metal is 1.5 [nm]. C in FIG. 2 shows the NO x conversion rate after the catalyst shown in FIGS. 2A and 2B is subjected to heat durability of 400 [° C.]. As shown in FIG. 2C, the catalyst shown in FIG. 2A has a high performance in which the NO X conversion rate before heat endurance is 90 [%] or more, but after heat endurance, it is also up to 60 [%] or less. Decreases. As a cause of this, it is conceivable that the catalyst shown in FIG. 2A has a noble metal particle size that increases from 1.5 [nm] to 60 [nm] due to thermal durability, and the surface area of the noble metal decreases. In the catalyst shown in FIG. 2B in which the noble metal loading concentration is 1/10 of the catalyst shown in FIG. 2A with respect to the catalyst shown in FIG. 2A, the NO X conversion rate before heat endurance is about 70 [%]. The subsequent NO X conversion is about 50%, and the performance is not lowered as much as the catalyst shown in FIG. In the catalyst shown in FIG. 2B, the noble metal support concentration is 1/10, and the particle size after heat endurance is suppressed from about 1.5 [nm] to about 5 [nm]. It is not considered. Thus, with this catalyst, it is possible to obtain a catalyst having excellent durability with a small amount of noble metal.

  In addition, the catalyst according to the present embodiment preferably has a noble metal particle size of 10 [nm] or less after the produced catalyst is further calcined at 700 [° C.] for 3 [hours]. In this case, even after calcination, the catalyst performance is not significantly lowered, and a catalyst having excellent durability can be obtained. A noble metal particle size larger than 10 [nm] is not preferable because the catalytic activity of the noble metal decreases.

The reason for this number will be explained with an example. Even if Pt particles on alumina with a specific surface area of 200 [m 2 / g] are aggregated, the particle size becomes 5 [nm]. When the noble metal support concentration is 0.05 [wt%], the catalyst amount is 100 [ In the case of g], 0.05 [g] of Pt is present in the catalyst. In this case, the number of moles of Pt is 2.6 × 10 −4 [mol]. Since about 6000 Pt atoms are present in the Pt particles having a particle size of 5 [nm], Pt particles having a particle size of 5 [nm] are 2.6 × in the catalyst amount of 100 [g]. There are 10-4 . When the Pt particles are uniformly dispersed in alumina, the area occupied by the Pt particles having a particle size of 5 [nm] is Pt atoms contained in the alumina surface area 200 × catalyst amount 100 / particle size 5 [nm]. From a number of about 6000, it becomes approximately 77000 [nm 2 ]. Assuming that one sphere has this area, the diameter of the sphere is calculated from 77000 = 4πr 2, and the particle diameter of alumina is about 500 [nm].

  The noble metal is preferably at least one kind of noble metal selected from the group of Pt (platinum), Pd (palladium), and Rh (rhodium), and a mixture of two or more kinds of noble metals, for example, Pt and Rh. Then, it may be supported on alumina.

Alumina is further selected from the group of Ce (cerium), La (lanthanum), Zr (zirconium), Co (cobalt), Mn (manganese), Fe (iron), Ni (nickel), and Mg (magnesium). It is preferable to have at least one element selected from the above, and two or more elements may be mixed and used. In order to reduce the amount of noble metal used, a method of assisting the catalytic activity of the noble metal with a transition element or the like is also effective. Among transition elements, elements such as Co, Mn, Fe, and Ni, other rare earth elements such as Ce and La, and elements such as Zr and Mg are particularly effective as elements that assist the catalytic activity of noble metals. Although these transition elements have low catalytic activity when the transition group element alone is used, the catalytic activity of the transition element is improved by allowing the transition element to coexist with the noble metal. It becomes possible. Ce, La, and Zr contribute to the activation of O 2 effective for the catalytic reaction, and Mg has an effect of suppressing HC poisoning. In addition, these elements also have the effect of increasing the heat resistance of the support alumina.

Further, the catalyst is at least one second selected from the group consisting of alumina (Al 2 O 3 ), titania (TiO 2 ), ceria (CeO 2 ), zirconia (ZrO 2 ), and ceria-zirconia composite oxide. It is preferable to have a carrier, and two or more kinds of second carriers may be mixed and used. In the catalyst according to the embodiment of the present invention, one noble metal particle exists on one alumina particle after heat endurance. However, when heated to a higher temperature, the alumina as the carrier may sinter and further agglomerate. Therefore, when the catalyst has the second carrier as a buffer material that suppresses the sintering of alumina, the contact between the aluminas supporting the noble metal as the first carrier is suppressed, and the aggregation of the noble metals due to the sintering of the aluminas. Can be suppressed.

  Thus, in the catalyst according to the present embodiment, alumina having a particle size of 30 to 1000 [nm], noble metal supported on alumina at a supported concentration of 0.001 to 0.3 [wt%], In this case, only the amount of noble metal having a particle size of 10 nm or less is supported even if all the noble metals on the alumina are aggregated. However, the catalyst performance is not significantly reduced. For this reason, even if it reduces the usage-amount of a noble metal, the catalyst activity ability at the time of catalyst preparation is maintained, and the catalyst which can be coated to a refractory inorganic support | carrier is obtained.

(Catalyst production method)
Next, an embodiment of a method for producing a catalyst according to an embodiment of the present invention will be described. This catalyst production method includes an alumina fine powder production step for producing an alumina fine powder having a particle size of 30 to 1000 [nm], a dispersion step for dispersing the alumina fine powder in water, and an alumina fine powder after the dispersion step. A supporting step for supporting the noble metal salt on the substrate, a mixing step for mixing the second carrier in the same amount or more with the fine alumina powder after the supporting step, and drying for drying at a temperature of 100 to 150 [° C.] after the mixing step. And a baking step of baking at a temperature lower than 500 [° C.] after the drying step.

  In the method for producing a catalyst according to the embodiment of the present invention, since there is a step of pulverizing alumina into a fine powder before the dispersion step of dispersing alumina in water, the alumina becomes a uniform fine powder. For this reason, a noble metal can be uniformly supported on each alumina fine powder. In addition, since the second carrier having the same amount or more as the fine alumina powder is mixed after the noble metal is supported on the alumina, the contact probability of the alumina as the first carrier is reduced, and the precious metal is sintered by the sintering of the alumina. Aggregation can be suppressed.

  FIG. 3 is a diagram for explaining a schematic process of the method for producing a catalyst according to the embodiment of the present invention. First, alumina is pulverized by a ball mill to produce alumina fine powder having a particle size of 30 to 1000 [nm] (alumina fine powder production step), and then the alumina fine powder is dispersed in water (step 20: dispersion step). Here, a general high specific surface area alumina can be used as the alumina. Next, an aqueous noble metal salt solution is put into water in which fine alumina powder is dispersed and mixed. Through this step, the noble metal salt is supported on the alumina fine powder (step 21: supporting step). As the water-soluble noble metal salt, dinitrodiamine Pt, tetraammine Pt, nitric acid Pd, nitric acid Rh and the like can be used. Next, the second carrier is further added so that the weight ratio with the fine alumina powder is 1: 1, and further mixed (step 22: mixing step). And a liquid mixture is dried at the temperature of 100-150 [degreeC] (process 23: drying process). In this drying process, it is only necessary to remove moisture. For this reason, the temperature required for drying is at least 100 [° C.] or higher. However, if the temperature is too high, drying proceeds rapidly, and the noble metal supported in the alumina pores may be deposited on the surface of the alumina. Therefore, the drying step is preferably performed at 150 [° C.] or less. Furthermore, after the drying step, firing is performed at a temperature of less than 500 [° C.] (step 24: firing step). Since the noble metal supported on the alumina is in a salt state, it is necessary to remove the anions by firing so that the noble metal is in a metal state. In order to fly anions by firing, a temperature of about 450 to 500 [° C.] is required. However, when the temperature reaches 500 [° C.] or higher, aggregation of noble metals begins. For this reason, in a baking process, it is preferable that a baking temperature shall be less than 500 [degreeC]. In addition, when a calcination temperature is 400 [degrees C] or less, since it is not enough to fix a noble metal on an alumina, it is more preferable that a calcination temperature is 450-500 [degrees C].

  In addition, it is preferable that an alumina fine powder preparation process is a process which wet-grinds the alumina fine powder with a particle size of 20-30 [micrometer] in a ball mill. By wet pulverizing alumina in a ball mill, it becomes possible to maintain a dispersed state of the fine alumina powder pulverized to a particle size of 30 to 1000 [nm], and it becomes possible to disperse and carry a precious metal on the fine alumina powder. .

  Further, after the firing step (step 24), a high temperature firing step (step 25) in which firing is performed at a temperature of 500 to 700 [° C.] for 3 hours. By this high-temperature firing step, the particle size of the noble metal supported on alumina can be controlled to 2 to 5 [nm] in advance. And the initial rate of aggregation of a noble metal can be reduced by making the particle size of a noble metal into 2-5 nm beforehand. For this reason, the further aggregation of a noble metal can be suppressed.

  Further, before the supporting step (step 21) of supporting the noble metal salt on the alumina fine powder, palladium is added to the alumina fine powder so that the weight ratio of palladium supported on the catalyst and the noble metal is 1:50 to 1:10. There may also be a palladium supporting step for supporting, and a precipitation step of depositing a noble metal on the palladium supported on the alumina fine powder by adding a reducing agent after adding the noble metal salt aqueous solution to the alumina fine powder.

  FIG. 4 is a diagram illustrating a schematic process of a method for producing a catalyst according to another embodiment of the present invention. First, alumina is pulverized by a ball mill to produce fine alumina powder having a particle size of 30 to 1000 [nm] (alumina fine powder production step), and then the fine alumina powder is dispersed in water (step 30: dispersion step). Here, a general high specific surface area alumina can be used as the alumina. Next, an aqueous palladium salt solution is introduced into the water in which the fine alumina powder is dispersed, and the fine palladium powder is supported on the alumina so that the weight ratio of palladium supported on the alumina and the noble metal is 1:50 to 1:10. (Step 31: Palladium loading step). Next, an aqueous noble metal salt solution is put into water in which fine palladium-supported alumina powder is dispersed and mixed (step 32). As the water-soluble noble metal salt, dinitrodiamine Pt, tetraammine Pt, nitric acid Pd, nitric acid Rh and the like can be used. Next, a reducing agent is added to the mixed solution to precipitate a noble metal salt on palladium supported on the alumina fine powder (step 33: precipitation step). Here, as the reducing agent, hydrazine, sodium borohydride, or the like can be used. Next, the second carrier is further added and mixed with the fine alumina powder so that the weight ratio is 1: 1 (step 34: mixing step). And a liquid mixture is dried at the temperature of 100-150 [degreeC] (process 35: drying process). Further, after the drying step, firing is performed at a temperature lower than 500 [° C.] (step 36: firing step). In addition, it is preferable that an alumina fine powder preparation process is a process which wet-grinds the alumina fine powder with a particle size of 20-30 [micrometer] in a ball mill. Further, after the baking step (step 36), a high temperature baking step of baking at a temperature of 500 to 700 [° C.] for 3 [hours] may be added.

  In the method for producing a catalyst according to another embodiment of the present invention, palladium is supported on alumina in advance, and by using this as a nucleus, it is possible to selectively deposit a noble metal to be subsequently supported on palladium. It becomes. And since the particle size of a noble metal when a noble metal precipitates on palladium will be 2-5 [nm], a catalyst with high catalyst performance is obtained. Further, by precipitating a noble metal on palladium, palladium exhibits an effect as an anchor for the noble metal. For this reason, aggregation of a noble metal can be prevented. When the weight ratio of palladium to noble metal is smaller than 1:50, palladium does not function as a noble metal nucleus. On the other hand, when the weight ratio of palladium to noble metal is larger than 1:10, the particle size of the noble metal becomes large, which is not preferable because the catalyst performance is lowered.

  As another method for producing the catalyst according to the embodiment of the present invention, there is a method for producing a catalyst using a reverse micelle method. The reverse micelle method is a method of mixing an aqueous solution containing a surfactant and a noble metal element as a catalytic active component in an organic solvent, and collecting the aqueous solution containing the noble metal element and the like inside the organic solvent. In this method, the retained reverse micelle is formed, and the noble metal is formed into fine particles by precipitating the noble metal inside the reverse micelle by precipitation or reduction. The diameter of the reverse micelle is generally determined by the ratio of the surfactant and water, and can be controlled to a predetermined size. And since the final product cannot exceed the size of the reverse micelle, it becomes possible to produce fine particles having a size smaller than the size of the reverse micelle with good controllability, and the particle size of the noble metal is preferably 1 to 10 [nm], preferably The size can be controlled to 3 [nm] to 8 [nm], particularly preferably 2 [nm] to 5 [nm]. Furthermore, the size of the entire catalyst can be controlled.

  FIG. 5 is a diagram illustrating a schematic process of a method for producing a catalyst according to still another embodiment of the present invention. First, a surfactant and water are mixed in an organic solvent to prepare a mixed solution (step 40: mixed solution preparation step). Here, cyclohexane, cycloheptane, octanol, isooctane, n-hexane, n-decane, benzene, toluene, xylene, or the like can be used as the organic solvent. Moreover, you may use these 2 or more types of mixed solutions. As the surfactant, polyethylene glycol-p-nonylphenyl ether, pentaethylene glycol dodecyl ether, or the like can be used. An aluminum salt aqueous solution is added to this mixed solution and stirred to form reverse micelles containing an aluminum salt and water inside (step 41: aluminum salt-containing step). As the aluminum salt, acetate, nitrate, aluminum alkoxide and the like can be used. Next, a noble metal salt aqueous solution is mixed in the mixed solution, and the noble metal salt is contained in the reverse micelle. Then, a reducing agent is added to the mixed solution, and the noble metal salt contained in the reverse micelle is reduced and metallized to obtain a solution containing the noble metal metal and the aluminum salt in the reverse micelle (step 42: precipitation). Process). As the reducing agent, hydrazine, sodium borohydride and the like can be used. Moreover, you may use these 2 or more types of mixed solutions.

  Next, in another container, a mixed solution is prepared by mixing a surfactant and water in an organic solvent as in step 40 (step 43: mixed solution preparation step). Next, as in step 41, an aqueous aluminum salt solution is added to this mixed solution and stirred to form reverse micelles containing the aluminum salt and water therein (step 44: aluminum salt-containing step). The mixed solution obtained here is added to the solution obtained in step 42 and mixed (step 45). And alcohol is added and stirred in the mixed solution of the organic solvent containing this reverse micelle, and a reverse micelle is collapsed (process 46). By the collapse of the reverse micelle, a precipitate containing fine particles of a noble metal / alumina composite and aluminum salt fine particles is obtained. For example, methanol or ethanol can be used as the alcohol. Next, the obtained precipitate is filtered with a membrane filter and then washed with alcohol and water to remove impurities such as a surfactant contained in the precipitate (step 47). Further, it is dried for a whole day and night at 120 [° C.] (step 48). After drying, the target catalyst can be obtained by calcining in an air stream at 400 [° C.] for 1 [hour] (step 49).

  In yet another method for producing a catalyst according to an embodiment of the present invention, it is possible to obtain a catalyst in which a precious metal is uniformly dispersed in alumina by precipitating the precious metal and alumina simultaneously in reverse micelles. In the reverse micelle, the noble metal precipitates in a state of being clad with alumina. For this reason, when the catalyst obtained by calcining the precipitate obtained after collapsing the reverse micelles is obtained, it becomes easy to obtain a state in which a part of the noble metal is supported in alumina in a state where it is buried in alumina. For this reason, since alumina acts as a noble metal anchor, aggregation of the noble metal can be suppressed. Moreover, since the state at the time of catalyst preparation can be maintained even after heating, a catalyst having excellent durability can be obtained.

  In addition, a reverse micelle solution containing reverse micelles containing aluminum salt is prepared in a separate container, and this reverse micelle is disrupted by mixing this reverse micelle solution with a reverse micelle solution containing a reverse micelle containing noble metal and alumina. Thus, when the precipitate is formed, it is possible to dispose another alumina as the second carrier on the surface of the composite fine particles of the noble metal and the alumina. For this reason, in the catalyst according to the embodiment of the present invention, one noble metal particle is present on one alumina particle, and further, the second carrier is alumina as a buffer material that suppresses sintering of alumina. As a result, contact between the aluminas, which are the first carriers on which the noble metals are supported, is suppressed, and aggregation of the noble metals due to the sintering of the aluminas can be suppressed. Furthermore, since the catalyst is manufactured by the reverse micelle method, the particle sizes of alumina and noble metal can be controlled, and the size of the entire catalyst can be controlled. The alumina added later as the second carrier is not limited to alumina, but may be titania, ceria, zirconia, ceria-zirconia composite oxide, or the like.

  Further, if necessary, the alumina may further include at least one element selected from the group consisting of Ce, La, Zr, Co, Mn, Fe, Ni, and Mg. In addition to the method of adding the above element by impregnation after preparing the catalyst, the method of adding this element into the catalyst includes the method of precipitating the above element in the same manner as the precious metal and alumina when preparing reverse micelles. It may be used. Further, after the baking step (step 49), a high temperature baking step of baking at a temperature of 500 to 700 [° C.] for 3 [hours] may be added.

  Thus, according to the method for producing a catalyst of the present invention, alumina having a particle size of 30 to 1000 [nm], and a noble metal supported on alumina at a loading concentration of 0.001 to 0.3 [wt%]. Thus, it is possible to obtain a highly durable catalyst that maintains its catalytic performance even when the amount of noble metal is reduced.

(Exhaust gas purification catalyst)
Next, an embodiment of the exhaust gas purification catalyst according to the present invention will be described. The exhaust gas purifying catalyst according to the present embodiment is an exhaust gas purifying catalyst having the above-described catalyst and a refractory inorganic carrier coated with the catalyst, and the catalyst per 1 [L] of the refractory inorganic carrier capacity. The coat amount is 600 [g] or less. In the conventional exhaust gas purifying catalyst, when the coating amount of the catalyst per 1 [L] of the refractory inorganic carrier is 600 [g] or less, sufficient catalytic activity cannot be obtained. The amount of noble metal used was reduced in the case of a catalyst having an alumina having an A of 30 to 1000 [nm] and a noble metal supported on alumina at a supported concentration of 0.001 to 0.3 [wt%]. Even in this case, sufficient catalytic activity can be obtained.

  Hereinafter, the catalyst according to the embodiment of the present invention, the exhaust gas purifying catalyst, and the method for producing the catalyst will be described more specifically with reference to Examples 1 to 27 and Comparative Examples 1 to 6, but the scope of the present invention Is not limited to these examples. These examples are for examining the effectiveness of the catalyst according to the present invention, the exhaust gas purifying catalyst and the catalyst manufacturing method, and show examples of the catalyst adjusted with different materials and the exhaust gas purifying catalyst. is there.

<Preparation of sample>
(Example 1) Pt (0.1%) / Al 2 O 3 + Al 2 O 3
In Example 1, the alumina was wet pulverized, and then Pt was supported on the alumina as a noble metal, and then mixed with alumina as the second support (method of FIG. 3).

First, 180 [g] of alumina and 1610 [g] of water were put into a magnetic ball mill and pulverized for 7 [hour] to make the average particle size of alumina 0.4 [μm] (step 20: alumina fine powder production step) And dispersion step). The balls used were zirconia balls and the ball diameter was 1 [mm]. Ten minutes later, 2.3 [g] of 8 [%] dinitrodiamine Pt aqueous solution was added and mixed (step 21: loading step). Next, 180 [g] of alumina and 1610 [g] of water were put into another magnetic ball mill and pulverized for 7 [hour] to prepare alumina fine powder having an average particle size of 0.4 [μm] (second carrier). ). The balls used were zirconia balls and the ball diameter was 1 [mm]. The second carrier and the alumina fine powder obtained in step 21 are weighed so that the weight ratio is 1: 1 and mixed for 2 [hours] (step 22: mixing step), and then dried at 120 [° C.]. It was dried for one day by a machine (step 23: drying step). Thereafter, firing was performed at 400 [° C.] to obtain a mixed powder of Pt (0.1 [%]) / Al 2 O 3 and Al 2 O 3 (step 24: firing step). The obtained catalyst had a Pt particle size of 0.5 [nm] determined by the CO gas adsorption method. Next, the catalyst was calcined at 700 [° C.] for 3 [hour] (step 25: high-temperature calcining step). The Pt particle size determined by the CO gas adsorption method after firing was 9.6 [nm].

(Example 2) Pt (0.1%) / Al 2 O 3 + TiO 2
In Example 2, the same treatment was performed except that Al 2 O 3 of the second carrier in Example 1 was changed to TiO 2 . The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Further, the Pt particle size determined by the CO gas adsorption method after firing was 9.2 [nm].

(Example 3) Pt (0.1%) / Al 2 O 3 + CeO 2
In Example 3, the same treatment was performed except that Al 2 O 3 of the second support in Example 1 was changed to CeO 2 . The Pt particle size at the time of catalyst preparation was 0.5 [nm]. The Pt particle size determined by the CO gas adsorption method after firing was 9.6 [nm].

(Example 4) Pt (0.1%) / Al 2 O 3 + ZrO 2
In Example 4, the same treatment was performed except that Al 2 O 3 of the second support in Example 1 was changed to ZrO 2 . The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Further, the Pt particle size determined by the CO gas adsorption method after firing was 9.6 [nm].

(Example 5) Pt (0.1%) / Al 2 O 3 + Ce-Zr composite In Example 5, the second support Al 2 O 3 of Example 1 was replaced with a CeO 2 : ZrO 2 weight ratio of 3: 1. The same treatment was conducted except that the composite oxide was changed. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Further, the Pt particle size determined by the CO gas adsorption method after firing was 9.3 [nm].

(Example 6) Pd (0.1%) / Al 2 O 3 + Al 2 O 3
In Example 6, the same treatment was performed except that the dinitrodiamine Pt aqueous solution was changed to a Pd nitrate aqueous solution in Step 21 of Example 1. The Pd particle size at the time of catalyst preparation was 0.5 [nm]. Further, Pd particle size determined by CO gas adsorption method after firing was 9.0 [nm] (Example 7) Rh (0.1%) / Al 2 O 3 + Al 2 O 3
In Example 7, it processed similarly except having changed the dinitrodiamine Pt aqueous solution into the nitric acid Rh aqueous solution in the process 21 of Example 1. FIG. The Rh particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Rh particle size obtained by the CO gas adsorption method after firing was 9.1 [nm] (Example 8) Pt (0.1%) / Ce (10%)-Al 2 O 3 + Al 2 O 3
In Example 8, the treatment was performed in the same manner as in Example 1 except that the alumina was changed to Ce (10% by metal weight ratio) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.5 [nm].

(Example 9) Pt (0.1%) / Zr (5%) - Al 2 O 3 + Al 2 O 3
In Example 9, the same treatment as in Example 1 was performed except that alumina was changed to Zr (metal weight ratio: 5 [%]) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.4 [nm].

(Example 10) Pt (0.1%) / La (5%) - Al 2 O 3 + Al 2 O 3
In Example 10, the same treatment as in Example 1 was performed except that alumina was replaced with La (a metal weight ratio of 5 [%]) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.2 [nm].

(Example 11) Pt (0.1%) / Ce (10%), Zr (5%), La (5%) - Al 2 O 3 + Al 2 O 3
In Example 11, the treatment was performed in the same manner as in Example 1 except that alumina was changed to Ce (metal weight ratio: 10 [%]), Zr (5 [%]), La (5 [%]) supported alumina. did. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.1 [nm].

(Example 12) Pt (0.1%) / Mg (3%) - Al 2 O 3 + Al 2 O 3
In Example 12, the same treatment as in Example 1 was carried out except that alumina was replaced with Mg (a metal weight ratio of 3 [%]) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.8 [nm].

(Example 13) Pt (0.1%) / Fe (5%) - Al 2 O 3 + Al 2 O 3
In Example 13, the same treatment as in Example 1 was performed except that alumina was changed to Fe (metal weight ratio: 5 [%]) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.8 [nm].

(Example 14) Pt (0.1%) / Ni (5%) - Al 2 O 3 + Al 2 O 3
In Example 14, the same treatment as in Example 1 was performed except that alumina was replaced with Ni (metal weight ratio: 5 [%]) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.8 [nm].

(Example 15) Pt (0.1%) / Co (5%) - Al 2 O 3 + Al 2 O 3
In Example 15, the same treatment as in Example 1 was performed except that alumina was changed to Co (aluminum weight ratio: 5%) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.8 [nm].

(Example 16) Pt (0.1%) / Mn (5%) - Al 2 O 3 + Al 2 O 3
In Example 16, treatment was performed in the same manner as in Example 1 except that alumina was changed to Mn (5% metal weight ratio) supported alumina. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.8 [nm].

(Example 17) Pt (0.1%) / Ce (10%), Zr (5%), La (5%), Co (5%) - Al 2 O 3 + Al 2 O 3
In Example 17, alumina was changed to Ce (10 [%] by weight of metal), Zr (5 [%]), La (5 [%]), and Co (5 [%]) supported alumina. Except for this, the same processing as in Example 1 was performed. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.5 [nm].

(Example 18) Pd (0.1%) / Ce (10%), Zr (5%), La (5%) - Al 2 O 3 + Al 2 O 3
In Example 18, the alumina was changed to Ce (10% by metal weight ratio), Zr (5%), La (5%), and Co (5%) supported alumina, The same treatment as in Example 1 was performed except that the dinitrodiamine Pt aqueous solution was changed to a Pd nitrate aqueous solution in Step 21. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 8.8 [nm].

(Example 19) Rh (0.1%) / Zr (5%) - Al 2 O 3 + Al 2 O 3
In Example 19, the treatment was performed in the same manner as in Example 1 except that the alumina was changed to Zr (metal weight ratio: 5 [%]) supported alumina, and the dinitrodiamine Pt aqueous solution was changed to the Rh nitrate aqueous solution in Step 21. The Pt particle size at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pt particle size after firing was 9.2 [nm].

(Example 20) Pt (0.1%) / Al 2 O 3 + Al 2 O 3 + 500 ° C. × 3 hours firing In Example 20, after the firing step of Step 24 of Example 1, 3 at 500 ° C. [Time] Calcination (Step 25: High-temperature calcination step) The Pt particle size at the time of catalyst preparation was 2.0 [nm]. Moreover, the Pt particle size after firing was 9.0 [nm].

(Example 21) Pt (0.1%) / Al 2 O 3 + Al 2 O 3 + 600 ° C. × 3 hours firing
In Example 21, after the calcination step of Step 24 of Example 1, calcination was performed at 600 [° C.] for 3 [hours] (Step 25: high temperature calcination step). The Pt particle size at the time of catalyst preparation was 3.5 [nm]. Met. Moreover, the Pt particle size after firing was 8.8 [nm].

(Example 22) Pt (0.1%) / Al 2 O 3 + Al 2 O 3 + 700 ° C. × 3 hours firing
In Example 22, after the calcination step of Step 24 of Example 1, calcination was performed at 700 [° C.] for 3 [hour] (Step 25: high-temperature calcination step). The Pt particle size at the time of catalyst preparation was 4.8 [nm]. Met. Moreover, the Pt particle size after firing was 8.7 [nm].

(Example 23) Pt (0.05%) / Al 2 O 3 + Al 2 O 3
In Example 23, alumina was wet pulverized, Pt was supported on alumina as a noble metal, and then alumina was mixed as a second support (method of FIG. 3).

First, 180 [g] of alumina and 1610 [g] of water were put into a magnetic ball mill and pulverized for 3 [hours] to make the average particle diameter of alumina 0.7 [μm] (step 20: alumina fine powder preparation step) And dispersion step). The balls used were zirconia balls and the ball diameter was 1 [mm]. Ten minutes later, 1.3 [g] of 8 [%] dinitrodiamine Pt aqueous solution was added and mixed (step 21: loading step). Next, alumina 180 [g] and water 1610 [g] were put into another magnetic ball mill, and pulverized for 3 [hours] to prepare alumina fine powder having an average particle size of 0.7 [μm] (second carrier). ). The balls used were zirconia balls and the ball diameter was 1 [mm]. The second carrier and the alumina fine powder obtained in step 21 are weighed so that the weight ratio is 1: 1 and mixed for 2 [hours] (step 22: mixing step), and then dried at 120 [° C.]. It was dried for one day by a machine (step 23: drying step). Thereafter, firing was performed at 400 [° C.] to obtain a mixed powder of Pt (0.05 [%]) / Al 2 O 3 and Al 2 O 3 (step 24: firing step). The obtained catalyst had a Pt particle size of 0.4 [nm] determined by the CO gas adsorption method. Next, the catalyst was calcined at 700 [° C.] for 3 [hour] (step 25: high-temperature calcining step). The Pt particle size determined by the CO gas adsorption method after firing was 9.1 [nm].

(Example 24) Pt (0.3%) / Al 2 O 3 + Al 2 O 3
In Example 24, alumina having an average particle size of 200 [nm] was dispersed in water (solid content 10 [%]), and 8 [%] dinitrodiamine Pt aqueous solution 6.8 [g] was added to this solution and mixed. (Step 21). The powder obtained in step 21 and alumina having an average particle size of 200 [nm] dispersed in water (solid content: 10 [%]) were weighed to a weight ratio of 1: 1 and mixed for 2 [hours]. (Step 22). Then, it dried for one day and night with 120 degreeC dryer (process 23). Next, baking was performed at 400 [° C.] to obtain a mixed powder of Pt (0.3%) / Al 2 O 3 and Al 2 O 3 (step 24: baking step). The Pt particle size determined by the CO gas adsorption method at the time of catalyst preparation was 0.8 [nm]. The Pt particle size determined by the CO gas adsorption method after firing was 9.7 [nm].

(Example 25) Pt (0.1%), Pd (0.01%) / Al 2 O 3 + Al 2 O 3
In Example 25, Pd was supported on alumina, and then a noble metal was supported on alumina, and then alumina was mixed as a second support (the method of FIG. 4).

First, 180 [g] of alumina and 1610 [g] of water were put into a magnetic ball mill and pulverized for 7 [hour] to make the average particle diameter of alumina 0.4 [μm] (step 30: dispersion step). Next, 8% Pd nitrate was supported on alumina so that the supported concentration was 0.01% (step 31: palladium loading step). A zirconia ball was used as the Pd-carrying ball, and the ball diameter was 1 [mm]. Then, after 10 minutes, 2.3 [g] of 8 [%] dinitrodiamine Pt aqueous solution was added and mixed (step 32). Next, 0.107 [g] NaBH 4 was added, and the mixture was further stirred for 2 [hours] (step 33: precipitation step). Next, 180 [g] of alumina and 1610 [g] of water were put into another magnetic ball mill, and pulverized for 7 [hour] to make the average particle diameter of alumina 0.4 [μm]. The balls used were zirconia balls and the ball diameter was 1 [mm]. The alumina powder obtained here and the powder obtained in step 33 are weighed out to have a weight ratio of 1: 1, and further mixed for 2 [hour] (step 34: mixing step), and 120 [° C.]. And dried for a whole day and night (step 35: drying step). Then, it baked at 400 [° C.] for 1 [hour] to obtain a mixed powder of Pt (0.1 [%]) / Al 2 O 3 + Al 2 O 3 (step 36: baking step). The Pt particle size determined by the CO gas adsorption method at the time of catalyst preparation was 2.4 [nm]. In addition, the Pt particle size determined by the CO gas adsorption method after firing was 8.0 [nm].

(Example 26) Pt (0.3%) / Al 2 O 3
In Example 26, adjustment was performed by the reverse micelle method (the method of FIG. 5).

First, cyclohexane 5 [L] and polyethylene glycol-p-nonylphenyl ether 330 [g] were mixed to prepare a mixed solution (surfactant / solvent ratio = 0.15 [mol / L]) (step 40: Mixed solution preparation step). Next, Al 36.79 [g] nitrate and 38.08 [mL] water were added to the prepared mixed solution (water / surfactant ratio = 4), and this was stirred for 2 [hours] and placed in a reverse micelle. A mixed solution of an organic solvent containing Al ions was prepared (step 41: aluminum salt-containing step). After the stirring, 0.178 [g] of 8 [%] dinitrodiamine Pt aqueous solution was added to the mixed solution. After stirring, NaBH 4 0.0083 [g] was added as a reducing agent, and further stirred for 2 [hours] to obtain a solution containing Pt metal and Al nitrate in reverse micelles (NaBH 4 / (Pt + Al nitrate). ) Weight ratio =?) (Step 42: precipitation step).

  In another container, cyclohexane 5 [L] and polyethylene glycol-p-nonylphenyl ether 330 [g] were mixed to prepare a mixed solution (surfactant / solvent ratio = 0.15 [mol / L]) (process) 43: Mixed solution preparation step). Next, Al nitrate (36.79 [g]) and water (38.08 [mL]) were added to the prepared mixed solution (water / surfactant ratio = 4), and the mixture was stirred for 2 [hours]. Reverse micelles containing salt and water were formed (step 44: aluminum salt-containing step). After stirring, the mixture was mixed with the mixed solution obtained in Step 42 and stirred (Step 45). After stirring, 500 [mL] of methanol was added to the mixed solution and further stirred for 2 [hour] to disrupt the reverse micelles (step 46), and then the solution was filtered through a membrane filter. Thereafter, the precipitate obtained by filtration was washed with ethanol and water (step 17), and then the precipitate was dried at 120 [° C.] overnight (step 48) and calcined at 400 [° C.] for 1 [hour]. To obtain a powder (step 49). The Pt particle size of the obtained powder was 2.2 [nm]. Moreover, the Pt particle size after firing was 8.2 [nm].

(Example 27) Exhaust gas purification catalyst 52.9 [g] of the catalyst obtained in Example 17, 10.5 [g] of the catalyst obtained in Example 19, 5.4 [g] of alumina, 6.2 of alumina sol 6.2 [g], water 69 [g], and nitric acid 6 [g] were charged into a magnetic ball mill, mixed and pulverized to obtain a catalyst slurry. After the obtained catalyst slurry was attached to a cordierite monolith support (0.119 [L], 400 [cell]), excess slurry in the cell was removed by air flow and dried at 120 [° C.] Firing was carried out at 400 [° C.] for 1 [hour] to obtain an exhaust gas purification catalyst having a coating layer of 400.0 [g / L]. The amount of Pt in the obtained exhaust gas purification catalyst was 0.14 [g / L], and the amount of Rh was 0.028 [g / L].

(Comparative Example 1) Pt (0.1%) / Al 2 O 3 + Al 2 O 3
In Comparative Example 1, a catalyst was prepared using an impregnation method. First, 2.3 [g] of 8 [%] dinitrodiamine Pt aqueous solution was added to alumina having a specific surface area of 200 [m 2 / g] and mixed. Next, the same amount of alumina was measured, further mixed, stirred for 2 [hours], and then dried for a whole day and night in a dryer at 120 [° C]. Next, it was fired at 400 [° C.] for 1 [hour] to obtain a mixed powder of Pt (0.1%) / Al 2 O 3 + Al 2 O 3 . The Pt particle size determined by the CO gas adsorption method at the time of catalyst preparation was 0.6 [nm]. Moreover, the Pt particle size after firing was 20.4 [nm].

Comparative Example 2 Pd (0.1%) / Al 2 O 3 + Al 2 O 3
In Comparative Example 2, a catalyst was prepared using an impregnation method. The difference from Comparative Example 1 is that the dinitrodiamine Pt aqueous solution was changed to a Pd nitrate aqueous solution. The Pd particle size determined by the CO gas adsorption method at the time of catalyst preparation was 0.5 [nm]. Moreover, the Pd particle size after firing was 22.6 [nm].

Comparative Example 3 Rh (0.1%) / Al 2 O 3 + Al 2 O 3
In Comparative Example 3, a catalyst was prepared using an impregnation method. The difference from Comparative Example 1 is that the dinitrodiamine Pt aqueous solution was changed to an aqueous Rh nitrate solution. The Rh particle size determined by the CO gas adsorption method at the time of catalyst preparation was 0.5 [nm]. Moreover, the Rh particle size after firing was 19.3 [nm].

(Comparative Example 4) Pt (0.1%) / Ce (10%), Zr (5%), La (5%) - Al 2 O 3 + Al 2 O 3
In Comparative Example 4, a catalyst was produced using an impregnation method. The difference from Comparative Example 1 is that the alumina supporting Pt is changed to Ce (10% by metal weight ratio), Zr (5%), La (5%) support alumina. It is a point. The Rh particle size determined by the CO gas adsorption method at the time of catalyst preparation was 0.6 [nm]. The Rh particle size after firing was 18.4 [nm].

(Comparative Example 5) Rh (0.1%) / Zr (5%) - Al 2 O 3 + Al 2 O 3
In Comparative Example 5, a catalyst was prepared using an impregnation method. The difference from Comparative Example 1 is that the dinitrodiamine Pt aqueous solution was changed to a Rh nitric acid aqueous solution, and the alumina supporting Rh was changed to Zr (5% by metal weight ratio) supported alumina. The Rh particle size determined by the CO gas adsorption method at the time of catalyst preparation was 0.5 [nm]. Moreover, the Rh particle size after firing was 18.1 [nm].

(Comparative Example 6) Exhaust gas purification catalyst 52.9 [g] of the catalyst obtained in Comparative Example 4, 10.5 [g] of the catalyst obtained in Comparative Example 5, 5.4 [g] of alumina, 6.2 of alumina sol [g], water 69 [g], and nitric acid 6 [g] were charged into a magnetic ball mill, mixed and pulverized to obtain a catalyst slurry. The obtained catalyst slurry was attached to a cordierite monolith support (0.119 [L], 400 [cell]), excess slurry in the cell was removed with an air stream, and dried at 120 ° C., and then 400 [ Baked at [° C.] for 1 [hour] to obtain an exhaust gas purification catalyst having a coat layer of 400.0 [g / L]. The amount of Pt in the obtained exhaust gas purification catalyst was 0.14 [g / L], and the amount of Rh was 0.028 [g / L].

  Here, the sample obtained by the sample preparation was evaluated by the following method.

<Durability test>
In the durability test of the catalyst powder, when the noble metal was Pt (Examples 1 to 5, 8 to 17, 20 to 26, Comparative Examples 1 and 4), the noble metal was Pd and Rh. (Examples 6, 7, 18, 19 and Comparative Examples 2, 3, and 5) were performed by firing at 700 [° C.] for 3 hours in a reducing atmosphere. When a cordierite monolith support is coated with a catalyst (Example 27, Comparative Example 6), it is calcined at 700 [° C.] for 3 [hours] while changing the oxygen atmosphere and the reducing atmosphere every minute. It went by.

<Evaluation method of conversion>
Using the model gas shown in Table 1, the 50 [%] conversion temperature when the temperature was raised from room temperature to 400 [° C.] at 10 [° C./min] was determined. The measurement conditions for the 50 [%] conversion temperature were a stoichiometric composition in which the oxygen amount and the reducing agent amount were equal, and the reaction gas flow rate was 40 [L / min].

<Measurement method of CO adsorption amount>
For the measurement of the CO adsorption amount, a metal dispersion measuring device BEL-METAL-3 manufactured by Nippon Bell Co., Ltd. was used, and the measurement was performed according to the following procedure. The sample was heated to 400 [° C.] at 10 [° C./min] in a He 100 [%] gas stream, and then oxidized for 15 minutes in a 400 [° C.] and O 2100 [%] gas stream. Processed. Then, purging was performed for 5 minutes with He100 [%] gas, and reduction treatment was performed for 15 minutes in a 400 [° C.], H240 [%] / He balance gas stream. Next, the temperature was lowered to 50 [° C.] in a He 100 [%] gas stream. Then, CO10 [%] / He balance gas was introduced in a pulse manner to determine the CO adsorption amount.

In the above-mentioned Examples 1 to 26 and Comparative Examples 1 to 5, the noble metal species, the supporting concentration, the first carrier, the second carrier, the firing temperature, the precious metal particle diameter before durability, and the precious metal particle diameter after durability are reduced. Tables 2 to 4 show 50 [%] conversion rate temperatures [° C.] after endurance in Example 27 and Comparative Example 6 in Table 5 below.

  From Table 2, when the supported concentration of Pt is 0.1 [%], the catalyst obtained in Comparative Example 1 and Comparative Example 4 has a small particle size before durability, but is 30 times or more after durability. became. On the other hand, in any of Examples 1 to 5, 8 to 17, and 20 to 26, the noble metal particle size after durability was 20 times or less, and it was found that the durability was higher than that of the comparative example. Also, from Tables 3 and 4, it was found that even when Pd or Rh was used as the noble metal, the same effect as that obtained with Pt was obtained. In addition, from the results of Table 5, the catalyst obtained in Example 27 had a significantly lower 50 [%] conversion temperature than the comparative example, and a catalyst capable of exhibiting exhaust gas purification performance at a lower temperature was obtained. I understood.

(A) It is explanatory drawing which shows the state at the time of preparation of the catalyst which concerns on embodiment of this invention. (B) It is explanatory drawing which shows the state after durability of the catalyst which concerns on embodiment of this invention. Is an explanatory view showing the relationship between the surface area and the NO X conversion rate of the noble metal. It is process drawing explaining the manufacturing method of the catalyst which concerns on embodiment of this invention. It is process drawing explaining another manufacturing method of the catalyst which concerns on embodiment of this invention. It is process drawing explaining another manufacturing method of the catalyst which concerns on embodiment of this invention.

Explanation of symbols

1 Catalyst 2 Alumina 3 Precious metal

Claims (11)

  1. Alumina having a particle size of 30 to 1000 [nm];
    A noble metal supported at a supported concentration of 0.001 to 0.3 [wt%] on the alumina;
    The catalyst characterized by having.
  2.   2. The catalyst according to claim 1, wherein the catalyst has a noble metal particle size of 10 nm or less after calcining the catalyst at 700 ° C. for 3 hours.
  3.   The catalyst according to claim 1 or 2, wherein the noble metal is at least one kind of noble metal selected from the group consisting of Pt, Pd, and Rh.
  4.   4. The alumina according to claim 1, further comprising at least one element selected from the group consisting of Ce, La, Zr, Co, Mn, Fe, Ni, and Mg. The catalyst described in the item.
  5.   Furthermore, it has at least 1 or more types of 2nd support | carrier chosen from the group of an alumina, a titania, a ceria, a zirconia, and a ceria-zirconia complex oxide, The Claim 1 thru | or 4 characterized by the above-mentioned. Catalyst.
  6. An alumina fine powder production step of producing an alumina fine powder having a particle size of 30 to 1000 [nm];
    A dispersion step of dispersing the alumina fine powder in water;
    A supporting step of supporting a noble metal salt on the alumina fine powder after the dispersing step;
    After the supporting step, a mixing step of further mixing the second carrier with the same amount or more as the alumina fine powder;
    A drying step of drying at a temperature of 100 to 150 [° C.] after the mixing step;
    A firing step of firing at a temperature of less than 500 [° C.] after the drying step;
    A method for producing a catalyst, comprising:
  7. An alumina fine powder production step of producing an alumina fine powder having a particle size of 30 to 1000 [nm];
    A dispersion step of dispersing the alumina fine powder in water;
    A palladium supporting step of supporting palladium on the alumina fine powder so that the weight ratio of palladium supported on the catalyst and the noble metal is 1:50 to 1:10;
    Adding a noble metal salt aqueous solution and a reducing agent after the palladium supporting step, and depositing a noble metal salt on palladium supported on the alumina fine powder;
    After the precipitation step, a mixing step of further mixing the same amount or more of the second carrier with the alumina fine powder,
    A drying step of drying at a temperature of 100 to 150 [° C.] after the mixing step;
    A firing step of firing at a temperature of less than 500 [° C.] after the drying step;
    A method for producing a catalyst, comprising:
  8.   The method for producing a catalyst according to claim 6 or 7, wherein the alumina fine powder preparation step is a step of wet-pulverizing an alumina fine powder having a particle size of 20 to 30 [μm] in a ball mill.
  9.   The catalyst according to any one of claims 6 to 8, further comprising a high-temperature calcining step of calcining at a temperature of 500 to 700 [° C] for 3 [hours] after the calcining step. Production method.
  10. A mixed solution preparation step of preparing a mixed solution by mixing a surfactant and water in an organic solvent;
    An aluminum salt-containing step of adding an aqueous aluminum salt solution to the mixed solution to form reverse micelles containing the aluminum salt inside;
    Furthermore, a precipitation step of mixing a noble metal salt aqueous solution in the mixed solution and precipitating a noble metal in the reverse micelles;
    A method for producing a catalyst, comprising:
  11. A catalyst according to any one of claims 1 to 5;
    An exhaust gas purification catalyst having a refractory inorganic carrier coated with the catalyst,
    The exhaust gas purifying catalyst, wherein a coating amount of the catalyst per 1 [L] of the refractory inorganic carrier capacity is 600 [g] or less.
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