JPH0478447A - Catalytic metal carrier and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title monolithic carrier having superior exfoliation resistance and especially fit for a catalytic converter for an automobile using a ternary catalyst for combustion by forming a metal oxide ceramic layer on the surface of heat resistant stainless steel and laminating an acicular ceramic layer on the metal oxide ceramic layer. CONSTITUTION:A metal oxide ceramic layer is formed on the surface of a heat resistant stainless steel sheet and an acicular ceramic layer is laminated on the metal oxide ceramic layer to obtain the title carrier supporting a catalyst for combustion on the acicular ceramic layer. This acicular ceramic layer is formed by applying a suspension of fine ceramic powder to the steel sheet with the metal oxide ceramic layer formed on the surface and carrying out firing at >=1,000 deg.C. Stainless steel contg. Cr, Al, etc., is used as the heat resistant stainless steel.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a metal catalyst carrier used to support a combustion catalyst, and more specifically, to a metal catalyst carrier used to support a combustion catalyst, and more specifically, to a method for imparting properties as a catalyst carrier to the surface of heat-resistant stainless steel. The present invention relates to a metal catalyst carrier. The aim is to develop a catalyst carrier in which acicular ceramic crystals (whiskers) are efficiently and easily densely formed on the surface of the steel sheet, forming a catalyst carrier layer with excellent peeling resistance. .

[Conventional technology] Conventionally, as a pollution control measure for automobiles, CO1HC in exhaust gas,
A three-way catalytic converter is inserted in the middle of the exhaust pipe to reduce NOx. One of these carriers is a monolith type metal carrier, which is made of 20Cr.
-5Aj2 series heat-resistant stainless steel is heat-treated at high temperature for a long period of time to form dense alumina whiskers on its surface. More specifically, the carrier on which the alumina whiskers have been formed is produced by heating the stainless steel foil with a thickness of 0.05 m for a long time of 16 hours at 950°C to precipitate and form alumina whiskers on the surface of the foil. This creates the necessary surface conditions for the material to function as a material. Stainless steel, which has a naturally high aluminum blond color, has excellent oxidation resistance, so heating in a high temperature range takes an extremely long time in order to densely generate the necessary and sufficient alumina whiskers, which increases industrial heat treatment costs. There is a big drawback.

(Problem to be Solved by the Invention) The problem to be solved by the present invention is to eliminate the above-mentioned drawbacks of the conventional metal catalyst carrier using this type of heat-resistant stainless steel.

[Means for Solving the Problem] This problem involves first forming a ceramic layer on the surface of the stainless steel plate through extremely short heat treatment, and then further forming acicular ceramic crystals (whiskers) on the formed ceramic layer. This problem can be solved by allowing it to precipitate.

(Function and structure of the invention) The basics of this invention are: (a) first forming a metal oxide ceramic layer on the surface of heat-resistant stainless steel;
(b) densely forming acicular ceramic crystals (whiskers), particularly preferably mullite whiskers, on the metal oxide layer; (c) forming (c) the above (a) and (
(b) Using the base material obtained by the treatment as a catalytic metal carrier, particularly as a monolith type metal carrier for a three-way catalytic converter for automobiles;
It is.

The present invention will be explained below in the order of steps (a) and (b) above.

(Step (a)) As the heat-resistant stainless steel used in this invention, a wide variety of stainless steels that have been known as so-called heat-resistant stainless steels can be used, and typical examples include chromium, aluminum, etc. Examples include stainless steels containing 20Cr-5Aj2 series, 6Cr-5A1. system, 12 Cr-1,53i-0
, 5Ti system, 25Cr-20N i system, etc.

A wide variety of ceramics can be used as the metal oxide ceramic layer formed on the steel plate, and a ceramic layer containing at least one of chromium and alumina as a main component is particularly preferred.

When forming this ceramic layer, 850
C. or higher, preferably 870.degree. C. or higher, for 4 hours or less, preferably 1 to 2 hours in the atmosphere to oxidize the surface, thereby forming a ceramic layer. for example,
When the stainless steel is a 2OCr-5A1 stainless steel mesh, this is directly subjected to the above heat treatment. That is, the aluminum contained in the stainless steel moves to the surface by the heat treatment and is oxidized over time to produce and grow alumina on the surface, forming a ceramic layer made of alumina. The thickness of this ceramic layer is usually 40 μm or less, preferably about 10 to 20 μm.

<Step (B)> This step is a step in which ceramic crystals are further formed in the shape of whiskers on the ceramic layer. The type of ceramic crystal whisker to be produced is not particularly limited, but preferably contains silica and alumina, or one of these as a main component, and mullite whiskers are particularly preferred. When producing this ceramic crystal whisker, select the ceramic raw material powder necessary to produce the desired ceramic crystal whisker, make it into a suspension or dispersion using an appropriate solvent, usually water, and add it to this liquid. Dip or coat the product after the step (a) above. Various materials containing silica and/or alumina are used as the ceramic powder, and typical examples include china clay, kaolin, various glasses, and various clay silicates. After coating or impregnation, it is fired at 1000° C. or higher for about 1 to 2 hours to form acicular ceramic crystal whiskers on the ceramic layer (a). At this time, glass may be generated along with whiskers, so in this case, the glass may be removed by treatment with hydrogen fluoride, for example. The ceramic crystal whiskers generated by this treatment are incompletely formed on the surface of the ceramic layer (A) above, and while they continue to grow, they combine with or become integrated with the ceramic layer (A) above, resulting in a dense surface. Needle-shaped ceramic crystals covered with whiskers. In this way, the above (a) and (
Since the material obtained by the process (b) is produced by compounding and resting a ceramic layer and acicular ceramic crystal whiskers on the surface of heat-resistant stainless steel,
It has extremely excellent peeling resistance, and its surface has a porous structure that is most suitable for anchoring the catalyst. It is strong and can withstand use over a wide temperature range. Moreover, it is a stable and durable material that does not rust even if it condenses or comes into contact with water while the car engine is not running. Therefore, it is extremely excellent as a catalyst carrier for automobiles.

〔Example〕

The present invention will be explained in more detail with reference to Examples below.

First, in the first embodiment, as shown in FIG. 1, a monolith type (1) catalyst metal carrier of the present invention is applied to a catalytic converter for an automobile. In this case the honeycomb structure (
The metal substrate constituting 2) is a ferrite-based 20Cr-5A/! with low thermal expansion. High-temperature oxidation-resistant stainless steel with a thickness of 0.05 ma was used. Then, as shown in FIG. 2, flat plates (3) and corrugated plates (4) were alternately combined and rolled into a cylindrical shape as shown in FIG. 3 to form a catalyst carrier material (5).

The carrier material (5) is fixed by welding or the like at necessary points.

It is desirable that the fixation is such that it can be sufficiently applied to changes including subsequent heat treatment and actual use. Examples of fixing means include brazing, welding, and soldering.

Next, the surface of the catalyst carrier material (5) is oxidized in the air at 870° C. or higher for 1 hour. At this time, 5% of A1 added to this ferritic high-temperature oxidation-resistant stainless steel moves to the surface at high temperature and becomes concentrated, and then mainly oxidizes over time to form and grow alumina crystals on the surface.

Conventionally, this process was continued for as long as 16 hours to generate the alumina crystals in the form of whiskers and to form a sufficient amount, that is, densely grown, to serve as a catalyst carrier, but in the present invention, this process was stopped after a short period of one hour or less. Cool. Thereafter, if necessary, this is washed with acid or alkali or the surface is activated. This dough (5) is dipped in an aqueous suspension of ceramic powder made of fine powder prepared separately to impregnate the dough (5), and then baked at 1000 to 1350°C for 1 hour to form the dough (5). On the surface of the glass, acicular mullite, a compound of silica and alumina, forms within the glass layer. Next, when the glass layer is removed with hydrogen fluoride, only the acicular mullite produced remains as shown in FIG. The produced acicular mullite (6) is incompletely produced on the surface of the carrier fabric (5),
Furthermore, by combining with the alumina whiskers that continue to grow,
Alternatively, they are entangled and strongly integrated 1 to form a metal carrier whose surface is covered with dense acicular mullite (6).

As explained above, this invention uses heat-resistant stainless steel as a substrate and has a composite layer of acicular mullite on its surface, so as mentioned above, it has various characteristics. However, it is an extremely stable and durable catalyst carrier suitable for use in automobiles.

In addition, in the present invention, at this time, the flat plate (3) and the corrugated plate (4)
The ceramic suspension that enters the gap (7) between the two generates acicular mullite to fill it, so the surface area of the catalyst is reduced because of the gas to be treated, which conventionally had difficulty flowing through the gap (7). The unused portion, which is thought to account for 2 to 5%, is eliminated, and filling allows all catalyst surfaces to work effectively, reducing the amount of catalyst used and essentially making the catalytic converter more compact. There is. Moreover, the acicular mullite joins the apexes of the flat plate and the corrugated plate firmly as if they were hardened with adhesive, resulting in a strong structure with high heat resistance.

Examples of stainless steel used in this invention are alumina,
! , 0. Although 20Cr-5Al stainless steel, which is mainly made of

Further, the ceramic needle crystals are not limited to mullite, which is a compound of silica and alumina, but may be other compounds or other compositions that produce ceramic whiskers in a lower temperature range. Further, although the method of elution with an aqueous hydrogen fluoride solution has been described to remove the formed glass layer, other acid treatment or alkali treatment may be used.

It is only necessary that other oxidized impurities liberated from the ceramics on the stainless steel plate can be removed at the same time as the elution treatment of the glass layer.

Increasing the surface area in this way reduces the amount of acicular mullite to be deposited and the cost of heat treatment, providing a lower cost metal carrier.

The present invention further includes the following equalization technical means. That is, the second embodiment is a cross honeycomb type catalyst metal carrier in which corrugated plates (30) and corrugated plates (31) are wound obliquely in a cylindrical shape as shown in FIG. 5, for example.

They intersect one another at a predetermined oblique angle and at an angle in the axial direction, and their contact points are joined to each other at points at the peaks of the waves of the corrugated sheets.

Therefore, it is not necessary to use some flat plates that were previously required, but
As shown in FIG. 6, a flat plate (32) may be used if necessary. In addition, FIG. 7 shows the one shown in FIG. 6 wound into a cylindrical shape.

According to this embodiment, joining means such as soldering, brazing, welding, etc. can be applied to the joining point between the corrugated sheet (30) and the corrugated sheet (31). However, acicular mullite on the surface generated by treatment as a catalyst metal carrier. Alternatively, when this contact is joined partly by a glass layer, the cost of the metal carrier of the invention is significantly reduced.

Conventionally, a honeycomb-shaped catalyst metal carrier formed into a cylindrical shape is composed of a large number of extremely small subdivided cells (passages) each having a cross-sectional area of 1 to 2a+rn'', and the gas to be treated passes straight through these cells. However, it is catalytically treated by a three-way catalyst supported on the cell wall.Therefore, in order to treat the gas passing through more completely, it must come into contact with the catalyst more, so it is necessary to subdivide the cell. However, this increases the resistance when gas passes through the converter, or leads to an increase in the size of the converter.Also, due to its structure, the tube in contact with the inlet of the converter The flow of exhaust gas and its processing heat are concentrated in the center of the shaped metal carrier.

Therefore, the burden of exhaust gas treatment is concentrated on the central part of the catalyst carrier, which not only has the risk of becoming significantly hotter than the surrounding area, leading to destruction of the metal carrier, but also has the disadvantage of degrading the catalyst performance.

Furthermore, since the cell is extremely segmented, it is extremely difficult for the catalyst present in the long joint between the flat plate and the corrugated plate constituting the cell and at least in the narrow gap in the immediate vicinity to come into contact with the gas passing through. In other words, the expensive catalyst that does not function as a catalyst accounts for 5 to 15% of the total surface area of the metal carrier.

However, according to this embodiment, the gas diffuses and flows;
At the same time, heat is dissipated and the life of the support and catalyst is extended.

Since the vertices of the diagonal corrugated sheets are joined at a point, the catalyst on the metal surface other than the joining point can come into contact with the exhaust gas, so the surface area of the metal, that is, the surface area of the catalyst has increased by 10 to 30%. Efficiency is increased and size can be reduced.

The joint area of the point joint is pressed by the strength of the winding of the corrugated sheet, and the joint area can be freely increased or decreased.

According to this embodiment, the exhaust gas entering from the inlet does not pass through a straight path as in the conventional case, but is prevented from going straight by diagonal passages, and mixes and diffuses inside the converter while repeatedly colliding with the catalyst wall, resulting in an almost uniform flow. Can undergo catalytic treatment.

In addition, by changing the oblique angle between the center and the outer periphery, heat can be diffused freely.

In this second embodiment, the oblique angle is typically 45°.
The length is preferably about 3 to 10 inches.

In particular, this invention includes making stainless steel itself into such an aspect as the second embodiment,
It is not necessary to necessarily apply the means (a) and (b) above, or only one of (a) and (b) may be applied.

In this invention, we have described the case where the catalyst is supported directly on the acicular ceramic crystals, but the invention is not limited to this, and the catalyst may be applied after applying a gamma alumina or other appropriate coating layer on the acicular ceramics. It may be supported.

〔Effect of the invention〕

This invention provides a new metal carrier for supporting a catalyst, and has great industrial application effects.

[Brief explanation of drawings]

Figure 1 shows an example of the monolith type catalytic converter of the present invention, Figure 2 is an explanatory diagram of a honeycomb-shaped metal carrier, Figure 3 is an explanatory diagram of a honeycomb-shaped metal carrier fabric, and Figure 4 is an illustration of a metal formed with acicular mullite. FIG. 2 is an explanatory diagram of a carrier. Also 5th~
FIG. 7 is an explanatory diagram showing an example of another catalyst carrier. ...Converter...Metal carrier...Flat plate...Corrugated plate...Dough 6...Whisker 7...Gap 30...Corrugated plate 31...Corrugated plate 32...Flat plate (hereinafter referred to as Figure 1 Figure 2

Claims (3)

[Claims] (1) A catalyst metal carrier characterized in that a metal oxide ceramic layer is formed on the surface of heat-resistant stainless steel, a needle-shaped ceramic layer is laminated on top of the metal oxide ceramic layer, and a combustion catalyst is supported on this layer. . (2) Claim (1) for a monolith type honeycomb metal carrier in a catalytic converter for automobile exhaust gas.
The catalyst metal carrier according to claim 1, wherein the base material according to claim 1 is used, and a combustion catalyst is supported on the base material. (3) A suspension of fine ceramic powder is applied or impregnated onto a heat-resistant stainless steel plate with a metal oxide ceramic layer formed on its surface, and then fired at 1000°C or higher,
A method for producing a catalytic metal carrier having acicular ceramics densely composited on its surface, characterized by producing acicular ceramics and removing glass that may be co-formed if necessary.