JPH01218636A - Catalyst and its manufacturing method - Google Patents

Abstract

PURPOSE:To provide a catalyst excellent in resistance to oxidation and corrosion, by providing a catalyst-supporting metal honeycomb structure formed by building up flat and corrugated metal plates in alternate layer and diffusion bonding together the contacts between these two plates. CONSTITUTION:A laminate is formed by building up flat metal plates 2 and corrugated metal plates 3 of 20Cr-6Al ferrite stainless steel in alternate layer. Said flat metal plates 2 and said corrugated metal plates 3 are heated at a high temperature (e.g., 850-1400 deg.C) in a nonoxidizing environment with these plates retained in a contact point 21, at which the flat and corrugated metal plates 2 and 3 are diffusion bonded to form a metal honeycomb structure 1, on whose surface a layer of inorganic powder such as alumina is attached and heated at a temperature of 600-700 deg.C to fixedly form a porous catalyst support 4 thereon and a catalytic component (e.g., Pt) is then deposited on this porous catalyst support 4, resulting in the formation of a catalyst excellent in resistance to oxidation and corrosion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalyst used for purifying exhaust gas from internal combustion engines, etc., and a method for manufacturing the same.

[Prior art]

Catalysts used for exhaust gas purification and the like usually consist of a catalyst component that exhibits a catalytic function and a porous carrier that supports the catalyst component.

Therefore, as the structure of the porous carrier, a honeycomb structure has been frequently used in order to obtain a large surface area. Furthermore, in recent years, it has been proposed that the honeycomb structure is made of metal, a porous carrier such as alumina powder is formed thereon, and a catalyst component is supported on the porous carrier. This is because metal has high thermal conductivity, so the temperature of the carrier and catalyst layer rises quickly. Therefore.

In particular, when this is used for exhaust gas purification, the temperature of this catalyst layer rises to almost the same temperature as the exhaust gas even in the early stages of operation of the internal combustion engine, making it possible to perform exhaust gas purification from the early stages of operation.

As described above, a catalyst using a metal honeycomb structure has excellent functions, but since it is used in exhaust gas, it is required to have oxidation resistance and corrosion resistance at high temperatures.

As such a metal honeycomb structure, one made of a metal containing AN (aluminum), for example, Fe (iron)-15Cr (chromium)-5Al steel, has been proposed. This item consists of 3 thin flat plates and corrugated plates made of the above materials stacked alternately.

Alternatively, the two rolls are stacked one on top of the other and the contacting portions of the two rolls are joined with brazing material.

In addition, to form a porous carrier on the honeycomb structure, the metal honeycomb structure is heated in an oxidizing atmosphere to form a coating of aluminum oxide on its surface, and a layer of aluminum oxide for the porous carrier is formed on the coating. This is done by applying powder (Japanese Patent Publication No. 48-23138).

The honeycomb structure is made by alternately laminating flat plates and corrugated plates, as illustrated in FIGS. 1 and 2.

The porous carrier and the catalyst components are supported on the surface of the porous carrier and the catalyst components are fixed to each other.Exhaust gas and the like flow into the gap between the two plates.

[Problem to be solved]

However, since conventional honeycomb structures use brazing material to join the flat plate and the corrugated plate as described above, they have poor corrosion resistance. That is.

Conventionally, for the above-mentioned joining, a plating sheet coated with a material for brazing was interposed between the flat plate and the corrugated plate, and the two were joined together by heating.

However, the honeycomb structure made by such brazing.

While using the catalyst prepared in this manner, the brazed portion is likely to corrode. For example, corrosion occurs at 1000°C 12O hours. This is considered to be because the exhaust gas is a high temperature gas containing water vapor.

Corrosion of the brazed portion causes the bond between the flat plate and the corrugated plate to separate, making it impossible to use the catalyst itself.

Furthermore, conventionally, as described above, the surface of the honeycomb structure is oxidized when supporting the porous carrier on the honeycomb structure. That is, it is necessary to heat the honeycomb structure in an oxidizing atmosphere prior to supporting the porous carrier. Furthermore, since such an oxidation process involves a high-temperature oxidizing atmosphere, the equipment needs to be oxidation-resistant.

In view of these problems, the present invention was made as a result of intensive research into joining a flat plate and a corrugated plate without using brazing and supporting a porous carrier without using an oxidation process. .

The present invention aims to provide a catalyst that has excellent oxidation resistance and corrosion resistance during use, and a method for producing the same.

(Means for Solving the Problems) The catalyst according to the present invention is a catalyst comprising a metal honeycomb structure, a porous carrier fixedly formed on the surface of the metal honeycomb structure, and a catalyst component supported on the carrier. The catalyst is characterized in that it is formed by alternately laminating flat metal plates and corrugated metal plates, and the contact portions of the flat plates and the corrugated plates are diffusion bonded to each other (first invention).

In the present invention, the metal plates constituting the metal honeycomb structure as the skeleton of the catalyst are both flat plates and corrugated plates made of metals that have excellent oxidation resistance and heat resistance at high temperatures. Such metals include ferritic or austenitic stainless steel. Also.

There are nickel-based and cobalt-based metals. Further, the thickness of the flat plate and the corrugated plate is preferably 0.03 to 1.0 mm from the viewpoint of workability, weight reduction of the honeycomb structure, and formation of a large number of cells.

What is also important in the present invention is that the contact portions of the flat plate and the corrugated plate are firmly bonded to each other by diffusion bonding. Regarding this point.

To explain with reference to FIG. 3, the flat plate 2 and the corrugated plate 3 are denoted by 21
They are diffusion bonded to each other at the portion shown by (the contact portion of the drawing board). Such diffusion bonding.

This method mainly utilizes atomic diffusion and creep deformation to bond the contact surfaces. This joining means will be described in the second invention described later. In addition.

In the figure, reference numeral 4 indicates a porous carrier provided on the honeycomb structure, and 5 indicates a catalyst component supported on the porous carrier.

Further, the honeycomb structure related to the present invention has the following characteristics:
As shown in the figure, flat plates and corrugated plates are stacked alternately to form a laminate, or as shown in Fig. 2, long flat plates and long corrugated plates are overlapped and rolled into a laminate. There is.

Next, polyγ1. 4 bodies of mass 7U are formed (
(See Figure 3). The porous carrier is a layer for supporting a catalyst component, and is composed of a porous fired body of ceramic powder as -1'. Such porous carriers include alumina, silica, alumina-silica, titania,
It is preferable to use one or more of zirconia and cordierite. These powders themselves are porous.

It is a carrier with a large surface area necessary for catalysts, excellent heat resistance, and excellent durability.

In addition, the catalyst components supported on the porous carrier include catalyst usage purpose 1, for example, exhaust from internal combustion engines, diesel particulates (unburned carbon particulates) in diesel engine exhaust, exhaust from nitric acid factories, etc. Use one that is compatible with the purification of various types of exhaust such as flue gas. for example,
For exhaust purification of internal combustion engines, the catalyst components include platinum (pt), palladium (Pd), and rhodium (
It is preferable to use one or more of Rh) and ruthenium (Ru).

Next, as a method for producing the above catalyst, a laminate is made by alternately stacking flat metal plates and corrugated metal plates.

The laminate is heated to a high temperature in a non-oxidizing atmosphere while the contact portion between the flat plate and the corrugated sheet is held in contact, and the contact portion between the flat plate and the corrugated sheet is diffusion bonded to form a metal honeycomb structure. Tonashi 9 A catalyst characterized in that an inorganic powder layer is then attached to the surface of the metal honeycomb structure, heated to firmly form a porous carrier, and then a catalyst component is supported on the porous carrier. There is a manufacturing method (second invention).

In this method, first, flat metal plates and corrugated plates are alternately laminated to form a laminate, and the laminate is kept in contact with the flat metal plates and the corrugated plates in a non-oxidizing atmosphere. C,
: Come and heat it up. Due to this.

The contact area between the flat plate and the corrugated plate is bonded by diffusion bonding.
Create a honeycomb structure consisting of:

In the above, the surfaces of the flat plate and the corrugated plate should be as clean and smooth as possible in order to perform diffusion bonding. In particular, a thin plate produced by cold rolling has excellent cleanliness and smoothness on one surface, and excellent diffusion bonding properties. Note that the surfaces of the flat plates and corrugated plates are preferably subjected to degreasing treatment before being laminated. The purpose of the dirt is to clean the surface.

The non-oxidizing atmosphere during the heating may be in a vacuum or in a gas such as nitrogen, hydrogen, or an inert gas.

The heating temperature is preferably 850 to 1400°C. If the temperature is lower than 850° C., the atomic diffusion rate and creep deformation of both metal plates will be insufficient, resulting in insufficient bonding. On the other hand 14
If the temperature exceeds 00'C, the shape of the laminate may be deformed. Further, the heating time is preferably 30 minutes to 8 hours. If the time is less than 30 minutes, it is difficult to obtain sufficient strength against tension.

Even if it exceeds 8 hours, it is difficult to obtain more strength.

Further, during the above heating, the contact portions of the three stroke plates are brought into sufficient contact to ensure sufficient diffusion bonding between the flat plate and the corrugated plate.

In addition, in the case of a laminate in which a flat plate and a corrugated plate are rolled into a roll as shown in Fig. 2, the corrugated plate is deformed by this rolling. It's in close contact.

Also, in the above, the material of the drawing board and its thickness.

The state of the diffusion bonding formed by the heating is the same as that described for the honeycomb structure. Further, the cross-sectional passage of the honeycomb structure may be arbitrary, such as hexagonal, quadrangular, or triangular.

Next, inorganic powder is attached to the honeycomb structure and heated to form a porous carrier on the surfaces of the flat plate and corrugated plate. As such powder, one or more of alumina, silica, alumina-silica, titania, zirconia, and cordierite are used. Moreover, it is preferable that the average particle size of this powder is 5 to 20 μm. Further, the adhesion is carried out by mixing the powder with a glue such as carboxymethyl cellulose (CMC) and water to form a slurry, and immersing the honeycomb structure in the slurry. During this dipping, dipping and drying can be repeated to increase the amount of the powder adhered.

Then, the honeycomb structure to which the powder is attached is heated to 600 to 700'C to burn the powder and fix it on the honeycomb structure. 600'C
If it is less than that, it will take a long time for firing and fixing.

On the other hand, if the temperature exceeds 700°C, there will be little effect commensurate with that temperature.

Through the above steps, a porous carrier is formed on the honeycomb structure.

Next, a catalyst component is supported on the porous carrier on the honeycomb structure to form a catalyst. Here.

As described above, a catalyst component is used depending on the intended use of the catalyst. As a method for supporting a catalyst component on a porous carrier, there is a dipping method. for example,
In the case of supporting Pt-Rh, the honeycomb structure provided with the above porous carrier is immersed in an aqueous solution of these chlorides (platinum chloride, rhodium chloride), dinitrate compounds (platinum nitrate, rhodium nitrate), etc. , the aqueous solution is adsorbed into a porous carrier.

Dry and heat to obtain Pt and Rh.

[Operations and Effects] In the catalyst according to the present invention, the metal honeycomb structure serving as the skeleton joins the contact portion between the flat plate and the corrugated plate by diffusion bonding. Therefore, the catalyst has excellent oxidation resistance and corrosion resistance against high temperature gases containing oxygen such as exhaust gas from internal combustion engines. Also.

It also has excellent mechanical strength. This effect is achieved by directly bonding the drawing boards due to the above-mentioned diffusion bonding.

This is because an adhesive layer such as a brazing material is not interposed between the drawing boards as in the conventional art.

Thus, the catalyst includes a porous carrier on the surface of the metal honeycomb structure described in item 1, and a catalyst component supported on the porous carrier. Therefore, when the catalyst is used for purifying engine exhaust gas, the heat of the exhaust gas is quickly transferred to the metal honeycomb structure that is the skeleton of the catalyst.

The entire catalyst quickly reaches the exhaust temperature, allowing purification to occur from the beginning of engine operation.

Therefore, according to the present invention, it is possible to provide a catalyst that has excellent oxidation resistance, corrosion resistance, and low-temperature activity.

Further, according to the manufacturing method related to the second invention.

A catalyst having excellent performance as described above can be produced. In the two methods, a flat plate and a corrugated plate are diffusion bonded in a non-oxidizing atmosphere, and then inorganic powder is attached to the surface and fired to form a porous carrier. Therefore, the two methods do not require an oxidation heating step to form an oxide film on the flat plates and corrugated plates of the honeycomb structure, as in the prior art.

Therefore, in addition to the above-mentioned effects, the method of the present invention also has the effect of simplifying the catalyst manufacturing process.

〔Example〕

1st Embodiment 20Cr-6Al steel, which is a ferritic stainless steel, was used as the metal material for the flat plate and the corrugated plate. One drawing plate was stacked on top of the other to form a laminate, which was heated in a non-oxidizing atmosphere as shown in Fig. 1. A metal honeycomb structure 1 was manufactured. Next, a porous carrier made of alumina powder was formed on the surface thereof, and Pt-Rh was supported on the porous carrier to produce a catalyst according to the present invention.

That is, as a material, the above 20C formed by cold rolling
A thin plate made of r-6Aff steel and having a thickness of 0104 mm and a width of 130 mm was prepared. Then, the thin plate was formed into a corrugated shape with a pitch of 2.45 mm using a corrugated roll to obtain a corrugated plate. Next, the thin flat plate and the corrugated plate were subjected to a degreasing treatment, and then the flat plate and the corrugated plate were alternately stacked in two boxes to produce a laminate. Then, in these laminates, a load was applied from above to restrain the whole so that the contact parts of the flat plate and the corrugated plate were in contact with each other.1.Then, the laminate was heated at 1100'C for 2 hours in a nitrogen gas atmosphere. The drawing board was diffusion bonded.

The honeycomb structure 1 manufactured as described above is made by vertically stacking flat plates 2 and corrugated plates 3 alternately in a box 10, as shown in FIGS. 1 and 3.

The contact portions 21 of both plates 2 and 3 are diffusion bonded. Note that the reference numeral 4.5 shown in the figure represents a porous carrier and a catalyst component that will be formed in the next step.

Next, the honeycomb structure 1 is prepared with an average particle size of 5 to 20 μm.
The alumina powder was immersed in a slurry liquid consisting of α-alumina powder, a small amount of CMC, and water, and dried three times, thereby depositing the alumina powder on the flat plate and the corrugated plate. Further, this product was heated to 650° C. for 2 hours to fix the powder onto the flat plate and the corrugated plate and to sinter it to form a porous carrier.

Next, the honeycomb structure with the porous carrier formed therein is immersed in a chloroplatinic acid solution and a rhodium chloride solution, and then immersed in one solution and dried, then immersed in the other solution and dried, and this operation is repeated twice. First, it was heated to 200°C to support Pt-Rh as a catalyst component on the porous carrier. In the obtained catalyst, as shown in FIGS. 1 and 3, the flat plate 2 and the corrugated plate 3 are diffusion bonded at the contact portion 21, and the flat plate 2
A porous carrier 4 of alumina powder is formed on the surface of the corrugated plate 3, and Pt- as a catalyst component is contained in the porous carrier 4.
It carries Rh.

The catalyst thus produced could be satisfactorily used as an engine exhaust purification catalyst.

Next, the oxidation resistance of the above catalyst was evaluated. In this evaluation, the oxidation resistance of the catalyst was measured after heating at 1100° C. for a predetermined period of time in the atmosphere. For comparison, when making the honeycomb structure without using the diffusion bonding described above, a plating sheet of Ni-based brazing material was interposed between the flat plate and the corrugated plate, and the two were bonded together by heating. A brazed honeycomb structure was prepared, and a porous carrier and a catalyst component were formed and supported thereon in the same manner as above, and the catalyst was also measured. The material, thickness, etc. of both the plates are the same as in this embodiment.

As a result, the catalyst according to the present invention did not show any trouble even after being heated for 500 hours under the above conditions.

It had excellent oxidation and corrosion resistance. In contrast, oxidative corrosion was observed in the comparative catalyst described above after 30 hours of heating.

25Cr-7Ajl, which is ferritic stainless steel, is used as the metal material for the flat plate and corrugated plate in the second embodiment! Using m, roll a long flat plate and a long corrugated sheet overlapping each other.

This was placed in an outer cylinder and heated in a non-oxidizing atmosphere to produce a roll-shaped metal honeycomb structure 11 as shown in FIG.

That is, a thin plate of the metal described above with a thickness of 0.05 mm and a width of 130 mm was prepared, and this was made into a corrugated plate with a pitch of 4 mm in the same manner as in the first embodiment. Next, the corrugated plate and the thin plate (flat plate) were stacked and rolled (see Figure 2), and the resulting laminate was inserted into a cylindrical outer cylinder and heated under the same conditions as in the first example. 2
The drawing board was diffusion bonded. Note that the surface of the drawing board was degreased prior to double winding.

As shown in FIG. 2, the honeycomb structure 11 obtained as described above is made by rolling a flat plate 25 and a corrugated plate 35 into an outer cylinder 6.
The contact portions 26 of the two plates 25 and 35 disposed inside the plate were bonded together by diffusion bonding and were firmly connected.

Next, in the same manner as in the first example, a porous carrier made of alumina powder was formed on the honeycomb structure 11, and then Pt--Pd was supported thereon. Palladium chloride was used to support Pd. The rest is the same as the first embodiment.

The catalyst obtained in this way could be fully used as a catalyst for purifying engine exhaust gas.

Next, the above catalyst was subjected to the same oxidation resistance evaluation test as in the first example. As a result, like the catalyst of the first example, this catalyst did not cause any trouble even after heating for 500 hours, and exhibited excellent oxidation resistance and corrosion resistance.

[Brief explanation of the drawing]

FIGS. 1 and 2 are perspective views of metal honeycomb structures according to the first and second embodiments, and FIG. 3 is a diagram for explaining the joining state of the flat plate and the corrugated plate and the state of the catalyst. be. 1.11. ,,metal honeycomb structure. 2,25. ,, flat plate. 21.26. ,,contact part. 3.35. ,, corrugated plate. 401. Porous carrier. 513. Catalyst component. 691. Outer cylinder.

Claims (3)

[Claims] (1) A catalyst consisting of a metal honeycomb structure, a porous carrier fixedly formed on the surface of the metal honeycomb structure, and a catalyst component supported on the carrier, wherein the honeycomb structure is composed of alternating layers of metal flat plates and corrugated plates. A catalyst characterized in that the flat plate and the corrugated plate are in contact with each other by diffusion bonding. (2) A laminate is made by alternately stacking metal flat plates and corrugated plates, and the laminate is heated at high temperature in a non-oxidizing atmosphere by keeping the contact parts of the flat plate and the corrugated plate in contact with each other. Heat to diffusion bond the contact area between the flat plate and the corrugated plate to form a metal honeycomb structure, then attach an inorganic powder layer to the surface of the metal honeycomb structure, and heat to fix the porous carrier. A method for producing a catalyst, which comprises subsequently supporting a catalyst component on the porous carrier. (3) The method for producing a catalyst according to claim 1, wherein the laminate is heated at a temperature of 850 to 1400°C.