JPH02253853A - Method for depositing catalyst metal - Google Patents

Abstract

PURPOSE:To decrease the contact area of two kinds of catalyst metals and to enhance the performance of the catalysts to clean exhaust gases by nonuniformly depositing the 1st catalyst metal and the 2nd catalyst metal on a catalyst carrier layer formed with interference fringe by UV rays. CONSTITUTION:The 1st interference fringes by UV rays are formed on the surface of the catalyst carrier layer on a catalyst carrier base material in the presence of the gaseous 1st catalyst metal compd. The 1st catalyst metal compd. is decomposed mainly in the bright part of the 1st interference fringes to deposit the 1st catalyst metal on the catalyst carrier layer. The 2nd interference fringes shifted in the bright and dark phases from the 1st interference fringes are formed by UV rays on the surface of the catalyst carrier layer in the presence of the gaseous 2nd catalyst metal compd. The 2nd catalyst metal compd. is decomposed mainly in the bright part of the 2nd interference fringes to deposit the 2nd catalyst metal. The catalyst for cleaning exhaust gases is thus produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for supporting a catalyst metal on a catalyst support layer. The supporting method of the present invention is used when manufacturing a catalyst for purifying automobile exhaust gas.

[Prior Art] When manufacturing a catalyst for purifying automobile exhaust gas, a catalyst support layer made of activated alumina or the like is formed on the surface of a carrier base material,
Catalytic metals such as platinum, rhodium, and palladium are supported on the catalyst support layer to form a catalyst. Here, in order to support the catalyst metal on the catalyst support layer, a general method is to impregnate the catalyst support layer with a solution of the catalyst metal compound, and then to carry it by drying and firing. When a plurality of catalyst metals are supported, this impregnation, drying, and calcination are repeated to support them.

[Problem to be Solved by the Invention J] In the conventional catalytic metal supporting method described above, when a plurality of types of catalytic metals are supported, each catalytic metal is uniformly supported. When the particles are supported in this way, there are some effects, but there are also some disadvantages. For example, if palladium particles and rhodium particles are supported adjacent to each other, a palladium-rhodium alloy may be formed.

Then, since palladium is more easily oxidized than rhodium, rhodium becomes coated with palladium oxide, resulting in a problem in that the catalytic performance of rhodium deteriorates.

It is also known that this phenomenon similarly occurs in the palladium-platinum system. In order to prevent such problems, JP-A-60-114341 discloses a catalyst in which at least one of neodymium and samarium is made to coexist with palladium and rhodium.

The present invention was made in view of these circumstances, and
By deliberately supporting multiple catalyst metals unevenly,
The purpose is to prevent the above problems.

[! Il! Means for Solving the Problems] The present inventors attempted to solve the above-mentioned problems by non-uniformly supporting a plurality of catalyst metals, and conducted extensive research into a method for supporting them. From the knowledge that bright and dark interference fringes are formed due to the interference effect of light, and the light intensity differs greatly between bright and dark areas, and that metal compounds are easily decomposed by ultraviolet rays, it was thought that the interference fringes of ultraviolet rays could be used. This completes the present invention.

That is, the method for supporting a catalyst metal of the present invention is a method of supporting a catalyst metal on the surface of a catalyst support layer of a catalyst support base material having a catalyst support layer, the method comprising: supporting the catalyst in the presence of a gaseous first catalyst metal compound; a first step of forming first interference fringes with ultraviolet rays on the layer surface and decomposing the first catalyst metal compound mainly in the bright portions of the first interference fringes to support the first catalyst metal on the catalyst support layer; In the presence of the second catalytic metal compound, a second interference fringe is formed on the surface of the catalyst supporting layer by ultraviolet rays, in which the light and dark phases of the first interference fringe are shifted. It is characterized by comprising a second step of decomposing and supporting a second catalyst metal.

Although there are no particular restrictions on the catalyst carrier base material, a flat shape is preferable for forming interference fringes, and it is desirable to use a metal plate of a metal catalyst formed by winding a metal plate. A catalyst supporting layer is formed on the surface of this catalyst carrier base material. The catalyst support layer can be formed from activated alumina such as γ-alumina as in the conventional case.

The first step is a step of supporting the first catalyst metal on the catalyst supporting layer, and is carried out using interference fringes of ultraviolet light. That is,
First interference fringes of ultraviolet light are formed on the surface of the catalyst support layer in the presence of the gaseous first catalyst metal compound. As a result, the first catalytic metal compound is mainly decomposed in the bright part of the first interference pattern,
The first catalyst metal is supported on the catalyst support layer in that portion. Here, as the ultraviolet rays, it is preferable to use laser light that is coherent and has high coherence. Examples of such laser light include argon laser and ximer laser. In addition, interference fringes can be easily formed using ultraviolet rays by simultaneously irradiating two ultraviolet rays with different optical path lengths.

In the second step, second interference fringes in which the bright and dark phases of the first interference fringes are shifted are formed on the surface of the catalyst support layer in the presence of the second catalytic metal compound. As a result, the second catalyst metal is supported mainly on the bright portions of the second interference fringes. Here, the phase of the interference fringes can be easily shifted by changing the difference in optical path length of the two ultraviolet rays. Note that the degree to which the phase is shifted can be changed in various ways depending on the situation. For example, when the reactivity between the first catalyst metal and the second catalyst metal is large, the phase is set to 1.
Shift it about 80 degrees. In addition, if another catalyst metal is to be supported on the surface, the temperature can be set to about 120 degrees.

The first catalytic metal and the second catalytic metal are preferably ones that would cause problems if they exist adjacent to each other, but are not particularly limited. For example, when palladium is used as the first catalyst metal, one or both of platinum and rhodium can be selected as the second catalyst metal. Further, as the first catalytic metal compound or the second catalytic metal compound,
It is preferable to use a material that vaporizes at a relatively low temperature by heating to become a gas, such as Pd(C3Hs) 2 (bisallyl palladium (It)), Pt(C2H+) (PP
h3) 2(η-ethylenebistriphenylphosphine platinum), Rh(Ctl2CH2)2(C#H
s) (bis η-ethylene η-cyclopentagenyl rhodium), etc. are used.

Note that it is desirable to wash the catalyst support layer after the first step and immediately after the second step. The dark part of the interference fringe contains the first
This is because the catalytic metal compound or the second catalytic metal compound is attached. This can be easily removed, for example, by washing with hot water. Further, in order to prevent impurities from adhering to the catalyst supporting layer, the first step and the second step are desirably carried out under an inert gas atmosphere or under vacuum.

[Operations and Effects of the Invention] In the catalytic metal supporting method of the present invention, first interference fringes are formed by ultraviolet rays on the surface of the catalyst supporting layer in the presence of a gaseous first catalytic metal compound. Here, the intensity of the ultraviolet rays is high in the bright parts of the first interference fringe, and the intensity of the ultraviolet rays is low in the dark parts. Therefore, the first catalytic metal compound decomposes mainly in the bright portion of the first interference pattern due to the photochemical reactivity of the ultraviolet rays, becomes the first catalytic metal, and is bonded to the catalyst support layer. Therefore, after the first step, the first catalyst metal is supported on the surface of the catalyst support layer in a striped manner.

Next, second interference fringes are formed by ultraviolet rays in the presence of a gaseous second catalyst metal compound on the surface of the catalyst support layer on which the first catalyst metal is supported. Here, since the phase of the second interference fringes is out of phase with the phase of the first interference fringes, the bright portion of the second interference fringes on the catalyst support layer is out of phase with the portion where the first catalyst metal is supported. Then, the second interference pattern mainly occurs in the bright part of the second interference fringe.
The catalytic metal compound is decomposed and the second catalytic metal is supported.

Therefore, in the catalyst support layer in the second step, the first catalyst metal is supported in a striped manner, and the second catalyst metal is supported on the portions where the first catalyst metal is not supported. That is, the contact area between the first catalytic metal and the second catalytic metal is extremely small compared to the prior art, and mutually adverse effects are prevented.

The first catalytic metal and the second catalytic metal can exhibit their respective catalytic performance to the maximum, and the resulting catalyst has extremely excellent purification performance.

That is, according to the method for supporting catalytic metals of the present invention, it is possible to easily and stably support the respective catalytic metals so that they are not uniform and do not come into contact with each other.

[Example] Hereinafter, the present invention will be explained more specifically using one example and two comparative examples.

(Example) A ferritic high heat-resistant stainless steel containing 15% by weight of aluminum was rolled to a thickness of 50 μm and a width of 10C.
m, a flat plate and a corrugated plate with a length of 9000 m are formed. On the surface of this flat plate and corrugated plate, 1 part by weight of alumina powder,
0 parts by weight of alumina silua with an alumina content of 10% by weight,
A slurry consisting of 15 parts by weight of aluminum nitrate aqueous solution with a concentration of 40% by weight and 30 parts by weight of water was sprayed at 150 parts by weight.
After drying at 1 hour at 700° C., the mixture was further calcined at 700° C. for 1 hour to form a catalyst supporting layer having a weight ratio of 10% on the flat plate and the corrugated plate, respectively.

(1) First step Next, as shown in Figure 1, the flat plate 1 and the corrugated plate 2 with the catalyst support layer are placed in a quartz container 3, and nitrogen gas is flowed through the container 3 to remove air and moisture. remove. After the pressure is further reduced to remove nitrogen gas, ultraviolet rays with a wavelength of 340 nm are irradiated from two optical paths, optical path A and optical path B, using an argon laser.

Here, the ultraviolet light emitted from the laser source 4 is divided into light reflected by the half mirror 5 and light passing through the half mirror 5. The light reflected by the half mirror 5 passes through the optical path A and is irradiated through the beam expander 6. On the other hand, the light that has passed through the half mirror 5 is reflected by the mirror 7, passes through the optical path B, and is irradiated from the beam expander 8. Therefore, there is a difference in optical path length between the optical path A and the optical path B by the distance between the half mirror 5 and the mirror 7, and the ultraviolet rays irradiated from the beam expander 6 and the beam expander 8 are 1. Forms interference fringes.

Incidentally, the difference in optical path length was 200 mm, and the interval between adjacent bright parts of the first interference fringe was about 8.5 μm.

Container 3, flat plate 1 and corrugated plate 2 are heated to 150°C using infrared rays.
The container 3 is kept warm and the first interference fringes are formed.
Pd (C3Hs) was heated to 150°C and vaporized in
) Fill with 1.3 g of steam from Step 2 to support palladium. After holding for 3 minutes, the flat plate 1 and the corrugated plate 2 were washed with hot water and dried at 150° C. for 1 hour.

(2) Second step Next, in the same manner as shown in FIG. 2, except that the configuration of the optical path B was changed, a second Forms interference fringes. In this optical path B, the light that has passed through the half mirror 5 passes through the mirror 9 and the mirror 1.
0 and travels parallel to the light of optical path A, roughly reaching the aquarium 1.
1 and is irradiated from the beam expander 8.

The phase of the second interference fringes thus formed is shifted by 180 degrees compared to the first interference fringes, and the brightness and darkness are reversed from those of the first interference fringes.

Then, using infrared rays, the container 3, the flat plate 1, and the corrugated plate 2 are
Insulated at 50°C, Pt(C2H4)(PPh 3 )2
After filling with 1.6 g of steam and holding it for 3 minutes to support platinum, it was washed with hot water and dried in the same manner as in the first step.

In addition, Rh(C1l 2
It was filled with 0.3Q worth of vapor of CM 2) 2 (C7HS), and rhodium was similarly supported.

(3) Catalysis As shown in Fig. 3, the flat plate 1 and the corrugated plate 2 carrying the catalyst are stacked and rolled into a roll to a thickness of 5 mm.
It was inserted into a metal cylinder 12 with a diameter of 122 mm to form a metal exhaust gas purifying contact 113.

The obtained exhaust gas purifying catalyst 1Q contained palladium at a concentration of 0.470. Platinum is 0.53CJ, rhodium is 0.11
0 was carried.

(Comparative Example 1) In the apparatus shown in FIG. 1, Pd(C3Hs) 2 and Pt(C2
H+)(PPh3)2 and Rh(CI2
A sample for exhaust gas purification was prepared in the same manner as in Example except that the vapor of CH2) 2 (C#Is) was sequentially supplied, and after each compound was adsorbed, it was calcined at 300°C for 1 hour to support each catalyst metal. A catalyst was formed. The amount of each catalyst metal supported in the exhaust gas purifying catalyst was adjusted to be the same as in the example.

(Comparative Example 2) Using the same flat plate and corrugated plate as in Example, they were immersed in a palladium nitrate aqueous solution, a dinitrodiammine platinum aqueous solution and a rhodium nitrate aqueous solution in order, and after drying, they were fired at 300°C for 1 hour to support each catalyst metal. Ta.

Then, an exhaust gas purifying catalyst was formed in the same manner as in the example. The amount of each catalyst metal supported in the exhaust gas purifying catalyst was adjusted to be the same as in the example.

(Evaluation) The catalytic performance of three types of exhaust gas purification catalysts formed in Examples and Comparative Examples was evaluated. Catalyst performance: Large gas temperature near 50℃ Space velocity (SV): 76000-/hr Air fuel consumption (A/
F): 14.6 (Stoichiometric) Endurance time: Durability test was conducted under the conditions of 200 hours, Large gas temperature: 300℃, 320℃ Space velocity (SV): 60000/hr Air fuel consumption (A/F): 14. HC, CO and N under conditions of 6.

The purification rate of × was measured. The results are shown in Table 1.

Table 1 From Table 1, the exhaust gas purifying catalyst in which the catalytic metal was supported by the supporting method of the example shows superior purification performance compared to the comparative example. This is because in the examples, palladium is supported on a different part from platinum and rhodium, so palladium is prevented from alloying with platinum or rhodium, and palladium, platinum, and rhodium exhibit their original catalytic activity. It is presumed that this is the case.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a method of forming the first P interference fringes by irradiating ultraviolet rays in an example, and FIG.
FIG. 7 is an explanatory diagram showing a method of forming second interference fringes whose phase is shifted by 180 degrees from the interference fringes. FIG. 3 is an explanatory diagram showing the structure of the exhaust gas purifying catalyst formed in the example. 1...Flat plate 2...Corrugated plate 3...Container 4
... Laser source 5 ... Half mirror 6, 8.
・・Beam expander 7.9.10・Mirror 11・Aquarium 12・
...Metal tube 13... Patent applicant for exhaust gas purification catalyst Hiroshi Okawa, Patent attorney, Toyota Motor Corporation representative

Claims (1)

[Claims] (1) A method for supporting a catalyst metal on the surface of a catalyst support layer of a catalyst support base material having a catalyst support layer, the method comprising:
In the presence of the catalyst metal compound, first interference fringes are formed by ultraviolet rays on the surface of the catalyst support layer, and the first catalyst metal compound is decomposed mainly in the bright part of the first interference fringes, so that the first interference fringes are formed on the catalyst support layer. a first step of supporting a catalytic metal, and forming second interference fringes in which the bright and dark phases of the first interference fringes are shifted by ultraviolet rays on the surface of the catalyst supporting layer in the presence of a gaseous second catalytic metal compound; A method for supporting a catalytic metal, comprising a second step of decomposing the second catalytic metal compound in the bright portion of the second interference pattern to support the second catalytic metal.