JPH10151357A - Catalyst production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry platinum and barium on two catalyst layers 2, 3 coated on a carrier 1 of an exhaust gas purifying catalyst and in contact with each other. Barium is prevented from being coated with barium or, conversely, barium is eluted into the platinum solution, and the dispersibility of platinum by barium is ensured, thereby improving the exhaust gas purification performance. SOLUTION: After two inner and outer catalyst layers 2 and 3 are coated on a carrier 1, both catalyst layers 2 and 3 are impregnated with a mixed solution of a barium solution and a platinum solution to carry barium and platinum. Then, platinum and barium are dispersed in the catalyst layers 2 and 3 in a state of being close to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a catalyst, and more particularly to a method for producing a catalyst suitable for purifying NOx in exhaust gas of an automobile engine.

[0002]

2. Description of the Related Art In recent years, attention has been paid to a lean-burn engine having a low fuel consumption rate as an automobile engine. In this engine, fuel is burned in an oxygen-excess atmosphere with a lean air-fuel ratio. A large amount of NOx is generated, and an exhaust gas purifying catalyst for purifying NOx is required.

As an example of this type of lean NOx catalyst, as disclosed in JP-A-7-108172, an inner catalyst layer in which barium-supported alumina is supported on a carrier, platinum And a catalyst layer coated with two catalyst layers, i.e., an outer catalyst layer on which rhodium-supported alumina is supported.

[0004] In addition, as disclosed in Japanese Patent Application Laid-Open No. 7-60117, this is not a lean NOx catalyst as described above, but after coating two inner and outer catalyst layers on a carrier,
It has been proposed that the carrier is immersed in a mixed solution of barium and platinum together with a catalyst layer, and the amount of barium carried is 2 to 8 g / L per liter of the carrier.

[0005]

According to the study of the present inventors, the inner catalyst layer of the two catalyst layers which are in contact with each other has a catalytic metal comprising a noble metal such as platinum as an active species. It was also found that when barium was carried together with the barium, the barium increased the dispersibility of the catalyst metal in the inner catalyst layer, and was effective for improving the NOx purification rate in exhaust gas.

[0006] In addition to the two catalyst layers that are in contact with each other, even when the catalyst layer is a single layer, when the catalyst layer carries barium together with a catalyst metal composed of a noble metal, for example, a catalyst carrying a catalyst metal is used. There is a method in which the layer is impregnated with a barium solution to support barium. However, according to the method, the catalyst metal particles are partially covered with barium of a barium solution to be impregnated later, and it becomes difficult to generate NOx which is easily absorbed by the catalyst metal. As a result, the catalyst metal after thermal aging Although there is a merit that sintering can be reduced, there is a problem that the initial NOx purification rate decreases.

On the other hand, when the catalyst layer is impregnated with a barium solution to carry barium, and then the catalyst layer is impregnated with a catalyst metal solution to carry the catalyst metal, the amount of barium carried on the catalyst layer is reduced. When the amount of barium is large, there is no problem. However, when the amount of barium carried is large, the barium component carried on the catalyst layer is eluted into the catalyst metal solution when the catalyst metal solution is impregnated. That is, barium carried on the catalyst layer acts as a stabilizer for the support material (particularly alumina) and a sintering inhibitor for platinum in the catalyst layer. At this time, barium enters the micropores of the porous support material. At the same time, it adheres firmly and partly to the surface of the crystal of the support material at the atomic ion level. After firing, it is a compound of barium and the metal component of the support material or a type of crystal structure that is resistant to heat. A hexanate having a property structure is formed. Therefore, when the supported amount of barium is small, all of the barium forms the above hexanate, so that barium hardly elutes in the catalyst metal solution to be impregnated next. However, when the supported amount of barium is large, the amount of barium that does not form hexanate with the metal component of the support material increases, and the barium elutes into the catalyst metal solution. As a result, there is a problem that the effect of dispersing the catalyst metal by barium in the catalyst layer cannot be expected well, and the purification performance of the catalyst becomes insufficient.

The present invention has been made in view of the above points, and an object of the present invention is to improve a method for carrying a metal such as barium and a catalyst metal such as platinum on the catalyst layer by improving the method. Prevents the catalyst metal supported on the catalyst layer from being coated with a metal such as barium, and conversely prevents the metal such as barium from the catalyst layer from being eluted into a solution of the catalyst metal. It is an object of the present invention to ensure the dispersibility of the metal and maintain the improvement of the purification performance of the catalyst.

[0009]

In order to achieve the above-mentioned object, the present invention utilizes the concept of the above-mentioned proposal, and applies a mixed solution of a catalyst metal and a metal such as barium to a catalyst layer of a carrier. Simultaneous impregnation was carried to carry both metals.

That is, according to the first aspect of the present invention, the catalyst layer coated on the carrier and supporting the catalyst metal is coated with the catalyst metal comprising at least one of an alkali metal, an alkaline earth metal and a rare earth metal. As a method for producing a catalyst in which 12% by weight or more of the layer is supported, first, a solution of a supported metal comprising at least one of the above alkali metals, alkaline earth metals or rare earth metals is mixed with a solution of the catalyst metal. I do. Next, the catalyst layer is impregnated with the mixed solution to support the supported metal and the catalyst metal. Examples of the alkali metal include sodium (Na) and the like, examples of the alkaline earth metal include strontium (Sr) and barium (Ba), and examples of the rare earth metal include lanthanum (La) and the like.

With this configuration, in a state where the catalyst layer is coated on the carrier, a solution of a supported metal comprising at least one of an alkali metal, an alkaline earth metal and a rare earth metal is applied to the catalyst layer. Since the mixed solution with the solution of the above is impregnated and the supported metal and the catalyst metal are supported, for example, when impregnating the solution of the supported metal after the impregnation of the solution of the catalyst metal, part of the catalyst metal is supported by the supported metal. The coating can be prevented, and the initial NOx purification rate can be increased. On the other hand, even when the amount of the supported metal is as large as 12% by weight or more of the catalyst layer, the supported metal is not impregnated with the catalyst metal solution, as in the case of impregnating the catalyst metal solution after the impregnation of the supported metal solution. Elution from the layer can be prevented, and the supported metal can be reliably supported on the catalyst layer and the catalyst metal can be highly dispersed in the catalyst layer. Therefore, it is possible to reliably improve the NOx purification performance of the catalyst.

In the second aspect of the present invention, the supported metal is supported on the catalyst layer of the catalyst in an amount of 12 to 26% by weight of the catalyst layer. In the invention of claim 3, it is assumed that the supported metal is supported by 19 to 23% by weight of the catalyst layer.
By doing so, it is possible to specify a desirable range of the amount of the supported metal on which the above-mentioned effect is effectively obtained.

According to the fourth aspect of the present invention, the support material of the catalyst layer of the catalyst is at least one of alumina and zeolite.
And a porous material consisting of This makes it easier for the supported metal to enter and adhere to the micropores of the support material of the catalyst layer, and the above-described effect is effective.

In the invention of claim 5, the weight ratio (catalyst metal / supported metal) between the catalyst metal and the supported metal in the catalyst layer of the catalyst is 1/10 to 1/20. In this case, the same effect as the above-described second aspect can be obtained.

According to a sixth aspect of the present invention, there is provided a method for manufacturing a catalyst comprising a catalyst layer coated on a carrier and supporting a catalyst metal, wherein the NOx absorbent is supported by 12% by weight or more of the catalyst layer. The solution of the material and the solution of the catalyst metal are mixed, and the catalyst layer is impregnated with the mixed solution to form NOx.
An absorbent and a catalyst metal are supported. According to this invention, the same operation and effect as those of the first invention can be obtained.

In the invention of claim 7, the catalyst metal is a noble metal and the supported metal is barium.

According to the eighth aspect of the present invention, a supported metal comprising at least one of an alkali metal, an alkaline earth metal or a rare earth metal is provided on the catalyst layer coated on the carrier and supporting the catalyst metal. As a method for producing a catalyst supported at 19.3% by weight, a solution of the supported metal and a solution of the catalyst metal are mixed, and the mixed metal solution is impregnated in a catalyst layer to support the supported metal and the catalyst metal. According to this invention, the same effect as that of the first invention can be obtained.

According to the ninth aspect of the present invention, at least two of the plurality of catalyst layers coated on the carrier are in contact with each other.
Platinum as a catalyst metal and 12 of the catalyst layer
As a method for producing a catalyst supporting barium of at least% by weight, a solution in which a barium solution and a platinum solution are mixed with the two catalyst layers after coating the two catalyst layers on a carrier, respectively. To support barium and platinum.

According to this configuration, in a state where the two catalyst layers are coated on the carrier, both catalyst layers are impregnated with a mixed solution of a barium solution and a platinum solution to support barium and platinum. The barium component can be prevented from being eluted from the inner catalyst layer with the coating of the outer catalyst layer as in the case of coating the slurry of the outer catalyst layer after coating the slurry containing the inner catalyst layer to form the inner catalyst layer. Can be reliably carried on the inner catalyst layer, and platinum and barium can be highly dispersed in a state where platinum and barium are brought close to the catalyst layer, so that the catalyst, in particular, the NOx purification performance can be further improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 2 shows the structure of an exhaust gas purifying catalyst C according to Embodiment 1 of the present invention, and the catalyst C is provided in an exhaust passage for discharging exhaust gas of a lean burn engine for a vehicle. The catalyst C is used to control HC in exhaust gas during stoichiometric air-fuel ratio combustion operation.
It purifies air pollutants such as CO and NOx, and also effectively purifies NOx during lean combustion operation. That is, this catalyst C is used for purifying lean NOx, and the oxygen concentration in the lean atmosphere is 4 to 5% to 20%, and the air-fuel ratio is used under the condition of A / F = 18 or more.

The catalyst C is made of, for example, a honeycomb-shaped carrier 1 made of cordierite which is a carrier material having excellent heat resistance.
On the support 1, an inner catalyst layer 2 (lower catalyst layer) on the side close to the surface of the support 1, and an outer catalyst layer 3 (upper catalyst layer) on the side further away from the surface of the support 1. ) Are coated.

In the inner catalyst layer 2, platinum (Pt) as a noble metal serving as a catalyst metal and barium Ba (supporting metal) as a NOx absorbent are supported using alumina as a porous material as a support material. I have. This inner catalyst layer 2
Rhodium (Rh) or palladium (Pd) may be added to platinum.

On the other hand, platinum and barium as noble metals are supported on the outer catalyst layer 3 by using zeolite as a porous material as a support material. The catalyst metal of the outer catalyst layer 3 may be both platinum and rhodium. Note that the impurity is set to 1% or less.

The amount of barium carried on each of the catalyst layers 2 and 3 is 12% by weight or more, specifically 12 to 26% by weight of the catalyst layers 2 and 3, and more preferably 19 to 26% by weight.
~ 23% by weight is good. The weight ratio of platinum (catalyst metal) to barium is preferably Pt / Ba = 1/10 to 1/20.

Although the barium is an alkali metal, sodium, lanthanum, strontium or the like may be used instead, or two or three of barium, sodium, lanthanum, strontium and the like may be used in combination. Is also good. In short, it is sufficient if at least one kind of metal among alkali metals, alkaline earth metals or rare earth metals, that is, a NOx absorbent.

The support material of the inner catalyst layer 2 is made of ceria or zeolite instead of alumina.
As the support material, alumina or ceria may be used instead of zeolite, or two or three of alumina, ceria and zeolite may be combined. The point is that the catalyst layers 2 and 3 only need to be made of a porous material having micropores.

In this embodiment, the outer catalyst layer 3 of the catalyst C
NOx and HC in the exhaust gas are activated by platinum as a noble metal carried on the NOx, NOx is reduced to NO2, and HC undergoes partial oxidation and cracking. In other words, they are in a state where they easily react energetically. At this time, the noble metal of the outer catalyst layer 3 is platinum, and the effect of promoting the NOx reduction reaction and the HC oxidation reaction of platinum is large.
The oxidation reaction of C can be promoted. When the noble metals of the outer catalyst layer 3 are platinum and rhodium, the rhodium enhances the effect of promoting the NOx reduction reaction.

Since platinum and barium are supported on the inner catalyst layer 2, the barium makes it easier for platinum to be dispersed in the inner catalyst layer 2, and under the dispersed platinum, NOx is removed from the outer catalyst layer. Platinum (and rhodium) in catalyst layer 3
It is decomposed and purified by reacting with NO2 and partially oxidized HC generated in the above. Therefore, the NOx purification rate of the engine can be improved. This effect is exhibited more favorably by making the noble metal component of the outer catalyst layer 3 richer than the noble metal component of the inner catalyst layer 2.

Next, a method for producing the catalyst C of Embodiment 1 will be described with reference to FIG. First, the inner catalyst layer 2 and then the outer catalyst layer 3 are formed on the support 1. In this case, the inner catalyst layer 2 is formed by an impregnation method, and the outer catalyst layer 3 uses a spray dry method.

That is, a slurry is prepared by mixing a binder and a powder, such as alumina, which does not carry a noble metal or slightly carries a noble metal. The slurry is wash-coated on the carrier 1 and dried and fired.

On the other hand, the O / C
(Overcoat) Generate powder. The spray drying method is a method also called a spray drying method, in which a slurry is prepared by mixing zeolite powder, a platinum solution as a complex, and water, and the slurry is sprayed in a heated atmosphere to be dried and calcined. / C powder.

Then, a slurry is prepared by mixing the O / C powder with a binder, and this slurry is wash-coated on the carrier 1 from above the inner catalyst layer 2 and dried and fired.

After the two catalyst layers 2 and 3 are coated on the carrier 1 in this manner, the catalyst layers 2 and 3 are impregnated with a mixed solution of platinum and barium to support platinum and barium. Thereafter, drying and baking are performed.

In this embodiment, two inner and outer catalyst layers 2,
3 are coated on the carrier 1 respectively.
Since platinum and barium are supported on both catalyst layers 2 and 3 by impregnation with a mixed solution of platinum and barium, even if barium is supported in a large amount of 12% by weight or more of each catalyst layer, for example, barium-containing The barium component is prevented from being eluted from the inner catalyst layer 2 with the coating of the outer catalyst layer 3 as in the case of coating the slurry of the outer catalyst layer 3 after forming the inner catalyst layer 2 by coating the slurry of As a result, barium can be reliably carried on the inner catalyst layer 2. In addition, since barium and platinum are supported on the catalyst layers 2 and 3 by impregnation of a solution obtained by mixing a barium solution and a platinum solution, the inner catalyst layer 2 is kept close to platinum and barium.
Therefore, it is possible to obtain the catalyst C in which the NOx purification performance is particularly surely improved.

The inner and outer catalyst layers 2 and 2
3 is different in the method of supporting the active species, so that both catalyst layers 2, 3
In the inner catalyst layer 2, the particle diameter of the platinum component is reduced, which is effective for NOx purification, and is particularly advantageous under circumstances where the composition of the exhaust gas changes. On the other hand, in the outer catalyst layer 3 formed by using the spray drying method, the particle system of the platinum component is large, and exhibits an effective effect for purifying HC, CO, and NOx in a steady state. That is, the temperature and atmosphere at which the catalyst C starts to be activated can have a certain range.

(Embodiment 2) FIG. 3 shows Embodiment 2 of the present invention.
(Note that the same parts as in FIG. 2 are denoted by the same reference numerals and detailed description thereof is omitted), and the catalyst layer on the carrier 1 is a single layer. is there.

In this embodiment, one catalyst layer 4 is coated on a honeycomb-shaped carrier 1 made of cordierite in the catalyst C, and the catalyst layer 4 has platinum (catalytic metal) as a noble metal and a NOx absorbent. (Supported metal) is supported with alumina as a support material.

The other structure of the catalyst C is the same as that of the first embodiment. That is, the supported amount of barium in the catalyst layer 4 is 12 to 26% by weight of the catalyst layer 4 (preferably 19 to 23% by weight). Further, as the supported metal of the catalyst layer 4, at least one metal selected from alkali metals, alkaline earth metals and rare earth metals can be used instead of barium. Further, zeolite may be used as the support material of the catalyst layer 4 instead of alumina, and a porous material made of at least one of alumina and zeolite may be used. The weight ratio of platinum (catalytic metal) to barium (supported metal) in the catalyst layer 4 is Pt / Ba = 1/10.
１ ／ 1/20 is desirable.

When the catalyst C of the second embodiment is manufactured, the catalyst layer 4 is coated on the carrier 1 and then the catalyst layer 4 is coated.
Is impregnated with a mixed solution of a barium solution and a platinum solution, whereby barium and platinum are supported on the catalyst layer 4.

Therefore, in this embodiment, when the catalyst layer 4 is impregnated with the barium solution after the impregnation of the platinum solution, part of the platinum is prevented from being covered with barium, and the initial NOx purification is performed. Rate can be increased. Further, even when the supported amount of barium is as large as 12% by weight or more of the catalyst layer 4, when the platinum layer is impregnated with the platinum solution after the impregnation of the catalyst layer 4 with the barium solution, the barium does 4 can be prevented from being eluted, and barium can be reliably supported on the catalyst layer 4 to highly disperse platinum. As a result, the NOx purification performance of the catalyst C can be reliably improved.

The present invention can be applied to a catalyst having three or more catalyst layers on the support 1.
Further, the present invention is not limited to a catalyst for purifying an exhaust gas of an automobile, and any catalyst having a plurality of layers and having a structure in which barium is carried on a layer on the side opposite to the surface may be SOx
It can also be applied to catalysts, denitration catalysts, cracking oil conversion catalysts, and the like. However, it is particularly excellent as a NOx purification catalyst.

[0042]

Next, a specific embodiment will be described.

About Two-Layer Coating (Example 1) Alumina, standard ceria, and alumina binder were prepared at a ratio of 46.5: 46.5: 7.0, respectively, to a total weight of 300 g, and this was mixed with ion-exchanged water. To prepare a slurry. Next, this slurry was applied to a honeycomb-structured carrier by its weight (420 g / L).
After wash coat to 37% by weight of
It was dried at a temperature of 50 ° C. and calcined at a temperature of 300 to 600 ° C. for 2 to 4 hours to form an inner catalyst layer.

On the other hand, a platinum dinitrodiamine solution and a rhodium nitrate solution
Spray-dry by spray-drying so that t: Rh = 75: 1 at a total of 2.67 g, then 200 to 60
Bake at 0 ° C for 1 to 24 hours and O / C (overcoat)
Got powder.

The O / C powder was mixed with an alumina binder at a ratio of 85:15, and ion-exchanged water was added to prepare a slurry. The slurry was adjusted to 5% by weight based on the weight of the carrier. After wash coating, the coating was dried at a temperature of 150 ° C. and calcined at a temperature of 300 to 600 ° C. for 1 to 4 hours to form an outer catalyst layer on the inner catalyst layer.

Finally, 2 g / L of platinum and 30 g / L of barium, which are the amounts supported by impregnation over the entire overcoat and base coat, are added to 1 L (liter) of the carrier starting from a dinitrodiamine solution and acetate. Impregnated as raw material, then dried at a temperature of 150 ° C. and 3
The sample of Example 1 was obtained by firing at a temperature of 00 to 600 ° C. for 1 to 4 hours.

(Example 2) In the structure of Example 1, the amount of platinum supported by impregnation over the entire overcoat and base coat (excluding that carried before the overcoat) was 2 g /. 1 g / L was used instead of L. Others are the same as the first embodiment.

(Example 3) In the structure of Example 1, the amount of barium supported by impregnation over the entire overcoat and base coat (excluding that carried before the overcoat) was 30 g / L. And 15 g / L. Others are the same as the first embodiment.

Example 4 In the structure of Example 1, the outer catalyst layer was changed from 5% by weight to 10% by weight, and the inner catalyst layer was changed from 37% by weight to 32% by weight. Others are the same as the first embodiment.

Comparative Example 1 In the process of Example 1, after forming the inner and outer catalyst layers respectively, instead of impregnating with a mixed solution of platinum and barium, first impregnate with a platinum solution, and then It was dried at a temperature of ° C. for 1 to 4 hours and impregnated with a barium solution without firing. Others are the same as the first embodiment.

(Comparative Example 2) In the process of Comparative Example 1, after forming the inner and outer catalyst layers,
The barium solution was impregnated and then the platinum solution without calcination. Others are the same as the first embodiment.

(Comparative Example 3) In the process of Example 1, after forming the inner catalyst layer, a mixed solution of platinum and barium was impregnated, and then the outer catalyst layer was formed. Others are the same as the first embodiment.

(Comparative Example 4) In the process of Example 1, after forming the inner catalyst layer, impregnated with a platinum solution, then calcined, formed the outer catalyst layer, and finally impregnated with a barium solution. Others are the same as the first embodiment.

(Comparative Example 5) In the process of Example 1, after forming the inner catalyst layer, a barium solution and then a platinum solution were respectively impregnated, and finally an outer catalyst layer was formed.
Others are the same as the first embodiment.

(Comparative Example 6) In the process of Example 1, after forming the inner catalyst layer, the barium solution was impregnated, then the outer catalyst layer was formed, and then the platinum solution was impregnated. Others are the same as the first embodiment.

The NOx purification rates of the catalyst samples of Examples 1 to 4 and Comparative Examples 1 to 6 were examined. As in Example 1, the amount of platinum supported by impregnation over the entire overcoat and basecoat per liter of carrier was 2 as in Example 1.
g / L in case A, case B in which the amount of platinum was 1 g / L as in Example 2, and case B in which the amount of barium was 15 g / L as in Example 3. C, the outer catalyst layer is 10% by weight as in Example 4,
The case where the inner catalyst layer was 32% by weight was set in each case D, and the evaluation was made for each case A to D. In the evaluation method, each sample was attached to a fixed bed flow type reaction evaluation apparatus, and the NOx purification rate was measured through simulated exhaust gas corresponding to A / F = 22, which was preheated by a heater. The composition of the simulated exhaust gas is as shown in Table 1. Table 2 shows the NOx purification rates of Examples 1 to 4 and Comparative Examples 1 to 6.

[0057]

[Table 1]

[0058]

[Table 2]

In Table 2, when comparison is made for each case, Examples 1 to 4 are all more NOx than Comparative Examples 1 to 6.
Purification rate is high. For this reason, when the inner and outer catalyst layers are respectively formed and then impregnated with a mixed solution of platinum and barium (Examples 1 to 4), the barium solution is impregnated after impregnation with the platinum solution (comparative example). In comparison with Example 1) or impregnating with a barium solution and then impregnating with a platinum solution (Comparative Example 2), coating of some platinum particles with barium and elution of a barium component into the platinum solution are eliminated, and platinum is added by barium. Is highly dispersed in the catalyst layer, and the NOx purification rate is improved.

When Comparative Examples 1 and 2 are compared, when the platinum and barium solutions are impregnated after the inner and outer catalyst layers are formed, the barium solution is impregnated first (Comparative Example 2). When barium elutes into the platinum solution during the subsequent impregnation of the platinum solution, barium does not elute when the platinum solution is impregnated first and the barium solution is impregnated later (Comparative Example 1). it is conceivable that.

Furthermore, the reason why the NOx purification rate in Comparative Example 4 is reduced is that when the inner catalyst layer is baked after being impregnated with a platinum solution, the calcination changes the platinum and then is impregnated with the barium solution. It is considered that it becomes difficult to approach barium.

Further, comparing Examples 1-4, even if the amount of platinum was 1 g / L, the amount of barium was 15 g / L.
It can be seen that even with L, even if the ratio of the inner and outer catalyst layers is further changed, for example, the amount of the inner catalyst layer is reduced and the amount of the outer catalyst layer is increased, a high NOx purification rate can be obtained.

One Layer Coating (Example 1) Alumina, standard ceria, and alumina binder were prepared at a ratio of 46.5: 46.5: 7.0, respectively, to a total weight of 300 g, and this was mixed with ion-exchanged water. To prepare a slurry. Next, this slurry was applied to a honeycomb-structured carrier by its weight (420 g / L).
After wash coat to 37% by weight of
The catalyst layer was dried at a temperature of 50 ° C. and calcined at a temperature of 300 to 600 ° C. for 2 to 4 hours to form a catalyst layer.

Next, with respect to 1 L (liter) of the above carrier, 2 g of platinum was used as an amount supported by impregnation over the entire catalyst layer.
/ L and 30 g / L of barium are impregnated with dinitrodiamine solution and acetate as starting materials.
Dry at a temperature of 0 ° C. and 1 at a temperature of 300-600 ° C.
The sample of Example 1 was obtained by firing for ４4 hours.

Example 2 In the same manner as in Example 1, the slurry was applied to a honeycomb-structured carrier at a weight (420 g /
After wash-coating to 42% by weight of L), it was dried and fired to form a catalyst layer. Of the 42% by weight of this catalyst layer, 37% by weight contained 4% of alumina, standard ceria and alumina binder as in Example 1.
The mixture was prepared in a ratio of 6.5: 46.5: 7.0, and the remaining 5% by weight was prepared by mixing platinum rhodium-supported MFI zeolite and a binder in a ratio of 85:15, respectively. Others are the same as those in Example 1. Therefore, the final loading amount of the catalytic metal is 2.3 g / L of platinum,
Rhodium is 0.004 g / L.

Comparative Example 1 In the process of Example 1, after the catalyst layer was formed, instead of impregnating with a mixed solution of platinum and barium, first, impregnated with a platinum solution and then at a temperature of 200 ° C. Dry for 1-4 hours and impregnate the barium solution without firing. Others are the same as the first embodiment.

(Comparative Example 2) In the process of Example 1, after forming the catalyst layer, contrary to Comparative Example 1, first, a barium solution was impregnated, and then a platinum solution was impregnated without firing. Others are the same as the first embodiment.

Comparative Example 3 In the process of Example 2, after the catalyst layer was formed, instead of impregnating with a mixed solution of platinum and barium, first, impregnated with a platinum solution, and then at a temperature of 200 ° C. Dry for 1-4 hours and impregnate the barium solution without firing. Others are the same as the second embodiment.

(Comparative Example 4) In the process of Example 2, after forming the catalyst layer, contrary to Comparative Example 3, first, a barium solution was impregnated, and then a platinum solution was impregnated without firing. Others are the same as the second embodiment.

Table 3 shows the NOx purification rates of Examples 1 and 2 and Comparative Examples 1 to 4. According to Table 3, it can be seen that both the NOx purification rates and HC light-off of Examples 1 and 2 are superior to Comparative Examples 1 to 4.

[0071]

[Table 3]

On the other hand, in Example 1 (in which a mixed solution of platinum and barium was simultaneously impregnated) and Comparative Example 2 (in which a platinum solution was impregnated after impregnation with a barium solution), the loading amount of barium was determined. FIG. 4 shows the change in the NOx purification rate when it is changed.

The abscissa of FIG. 4 represents the amount of barium carried per liter of the carrier (g / L), and the numerical value (%) in parentheses represents the weight ratio of the amount of barium carried in the catalyst layer. I have. That is, for example, the supported amount of barium is 2
When it is 0 g / L, the weight of the catalyst layer is 155.4 g (=
420 × 0.37), the weight ratio of the supported amount of barium to the catalyst layer is (20 / 155.4) × 100 =
12.87%. Similarly, when the supported amount of barium on the support is 30 g / L, the weight ratio of the supported amount of barium is 19.3%, and when the supported amount of barium on the support is 40 g / L, the weight ratio of the supported amount of barium is 40 g / L. The weight ratios are each converted to 25.7%.

When the amount of barium exceeds 40 g / L, the barium becomes vitrified with firing and becomes unsuitable for a catalyst. The amount of barium supported is 20 to 40 g with respect to the carrier.
/ L, the weight ratio of platinum (2 g / L) to barium is Pt / Ba = 1/10 to 1/20.

As is apparent from FIG. 4, the amount of barium supported is 12% by weight or more of the catalyst layer, specifically 12 to 2% by weight.
If it is 6% by weight (the optimum range is 19 to 23% by weight), impregnating the mixed solution of barium and platinum simultaneously impregnates the N solution with the platinum solution after impregnation with the barium solution.
The Ox purification rate was increased, confirming the effectiveness of the effects of the present invention.

[0076]

As described above, claims 1 and 2,
According to the invention of 3, 5, 6 or 8, a supported metal comprising at least one of an alkali metal, an alkaline earth metal or a rare earth metal is added to the catalyst layer coated on the carrier and supporting the catalyst metal. In the case of producing a catalyst in which 12% by weight or more of the layer is supported, the catalyst layer is impregnated with a mixed solution of the above-mentioned supported metal and the catalyst metal to support the supported metal and the catalyst metal, thereby impregnating the catalyst metal solution. When the solution of the supported metal is later impregnated, it is possible to prevent a part of the catalyst metal from being covered with the supported metal, and to reduce the initial NOx
While the purification rate can be increased, even when the amount of the supported metal is large, when the catalyst metal solution is impregnated after the impregnation of the supported metal solution, elution of the supported metal from the catalyst layer can be prevented,
Therefore, it is possible to reliably improve the NOx purification performance of the catalyst.

According to the fourth aspect of the present invention, since the support material of the catalyst layer is a porous material made of at least one of alumina and zeolite, the supported metal enters and adheres to the micropores of the support material of the catalyst layer. Easier to do,
The above effects are effective.

According to the ninth aspect of the present invention, of the plurality of catalyst layers coated on the carrier, at least two catalyst layers in contact with each other include platinum as a catalyst metal and 12% by weight or more of the catalyst layer. In the case of producing a catalyst carrying barium, two catalyst layers are respectively coated on a carrier, and then the two catalyst layers are impregnated with a mixed solution of a barium solution and a platinum solution to remove barium and platinum. By supporting the barium-containing slurry, the barium component can be prevented from being eluted from the inner catalyst layer when the slurry of the outer catalyst layer is coated after forming the inner catalyst layer by coating the slurry containing barium. Precious metals can be highly dispersed by reliable loading, and the exhaust gas purification performance of the catalyst can be improved.

[Brief description of the drawings]

FIG. 1 is a process chart showing a process for producing an exhaust gas purifying catalyst according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view illustrating a main part of an exhaust gas purifying catalyst according to Embodiment 1 of the present invention.

FIG. 3 is a diagram corresponding to FIG. 2, showing an exhaust gas purifying catalyst according to a second embodiment of the present invention.

FIG. 4 is a graph showing characteristics of changes in NOx purification rates when barium and platinum are simultaneously impregnated while changing the barium carrying amount, and when platinum is impregnated after barium impregnation.

[Explanation of symbols]

 C Exhaust gas purification catalyst 1 Carrier 2 Inner catalyst layer 3 Outer catalyst layer 4 Catalyst layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B01J 29/74 ZAB B01D 53/36 102H 102B (72) Inventor Kazu Kitagawa 360 Mukohara-cho, Takada-gun, Hiroshima Prefecture Tokyo Filter Co., Ltd. Hiroshima Co., Ltd. Inside the plant (72) Inventor Tadashi Tokuyama 360 Mukohara-cho, Takada-gun, Hiroshima Prefecture Inside the Hiroshima Plant of Tokyo Roki Co., Ltd. (72) Inventor Takahiro Kurokawa 3-1 Shinchi, Funaka-cho, Aki-gun, Hiroshima Mazda Corporation (72) Inventor Hideharu Iwakuni 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Akihide Takami 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Makoto Kyogoku Hiroshima 3-1, Shinchi, Fuchu-cho, Aki-gun Mazda Co., Ltd. (72) Inventor Kenji Okamoto 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Keiji Yamada 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Motor Corporation

Claims (9)

[Claims] 1. A catalyst layer coated on a carrier and supporting a catalyst metal, wherein a supported metal comprising at least one of an alkali metal, an alkaline earth metal and a rare earth metal is supported in an amount of 12% by weight or more of the catalyst layer. A method for producing a catalyst, comprising: mixing a solution of the supported metal and a solution of the catalyst metal; and impregnating the catalyst layer with the mixed solution to support the supported metal and the catalyst metal. Method for producing catalyst. 2. The method for producing a catalyst according to claim 1, wherein the supported metal is supported on the catalyst layer of the catalyst in an amount of 12 to 26% by weight of the catalyst layer. 3. The method for producing a catalyst according to claim 1, wherein 19 to 23% by weight of the supported metal is supported on the catalyst layer of the catalyst. 4. The method for producing a catalyst according to claim 1, wherein the support material for the catalyst layer of the catalyst is a porous material made of at least one of alumina and zeolite. 5. The method for producing a catalyst according to claim 1, wherein the weight ratio between the catalyst metal and the supported metal in the catalyst layer of the catalyst is 1/10 to 1/20. 6. A method for producing a catalyst, comprising a catalyst layer coated on a carrier and supporting a catalyst metal, wherein a NOx absorbent is supported in an amount of 12% by weight or more of the catalyst layer. And a solution of the catalyst metal, and a catalyst layer is impregnated with the mixed solution to support the NOx absorbent and the catalyst metal. 7. The method for producing a catalyst according to claim 1, wherein the catalytic metal is a noble metal, and the supported metal is barium. 8. A catalyst layer coated on a carrier and supporting a catalyst metal, wherein the supported metal comprising at least one of an alkali metal, an alkaline earth metal and a rare earth metal is 19.3% by weight of the catalyst layer. A method for producing a supported catalyst, comprising mixing a solution of the supported metal and a solution of the catalyst metal, and impregnating the catalyst layer with the mixed solution to support the supported metal and the catalyst metal. Of producing a catalyst. 9. At least two catalyst layers in contact with each other among a plurality of catalyst layers coated on a carrier carry platinum as a catalyst metal and barium at 12% by weight or more of the catalyst layer. A method for producing a catalyst comprising: coating a carrier with each of the two catalyst layers; and impregnating the two catalyst layers with a solution obtained by mixing a barium solution and a platinum solution to form barium and platinum. A method for producing a catalyst, comprising: