Catalytic converter and method for producing the same

A catalytic converter includes a metal carrier body, an adhesion-promoting intermediate layer in the form of an oxide film applied to the carrier body and a catalytically active layer applied to the intermediate layer. A method for producing a catalytic converter includes heating a metal carrier body in an oxidizing atmosphere to form an adhesion-promoting intermediate layer in the form of an oxide film on the carrier body and applying a catalytically active layer to the intermediate layer.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The invention relates to a catalytic converter and a method for producing 
the same. 
Typical catalytic converters of the kind which are used, for instance, to 
reduce the nitrogen oxides in flue gas, usually include a metal carrier 
body, an adhesion-promoting intermediate layer, and a catalytically active 
layer applied to the intermediate layer. In the manufacture of catalytic 
converters, a fundamental problem which arises is that of establishing 
good adhesion of the catalytically active layer to the metal carrier body. 
Particularly for producing plate-type catalytic converters, methods for 
solving that problem are known in which an adhesion-promoting intermediate 
layer is produced on an expanded metal carrier body (U.S. Pat. Nos. 
4,370,262; 4,285,838 and 4,455,281) by spraying on liquid aluminum 
(aluminum flame spraying). However, producing a catalytic converter with 
that method requires that a very large amount of energy be expended to 
liquefy the aluminum. Moreover, liquid aluminum, which drops through voids 
in the carrier body during the spraying process, is no longer directly 
reusable, because some of it is oxidized. Both of those situations make 
such a method relatively expensive. 
Published European Application No. 0 387 394 A1 also discloses a method in 
which the carrier body of the catalytic converter is produced by sintering 
from multiple-ply fabrics and/or from knitted goods and/or from fibrous 
material. A disadvantage of that method is that fabrics and knitted goods 
are complicated and expensive to produce, while conversely fibrous 
materials can be produced only in a relatively poorly defined form. 
It is accordingly an object of the invention to provide a catalytic 
converter and a method for producing the same, which overcome the 
hereinafore-mentioned disadvantages of the heretofore-known devices and 
methods of this general type, with which a catalytic converter, in 
particular a plate-type catalytic converter, can be produced economically 
and in which good adhesion of the catalytically active layer to the metal 
carrier body is achieved at the same time. 
SUMMARY OF THE INVENTION 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, a catalytic converter, comprising a metal 
carrier body; an adhesion-promoting intermediate layer in the form of an 
oxide film applied to the carrier body; and a catalytically active layer 
applied to the intermediate layer. 
On one hand, oxide films can adhere adequately firmly to the substrate 
material, and on the other hand they produce adequate surface roughness 
for the adhesion of the catalytically active material. 
With the objects of the invention in view, there is also provided a method 
for producing a catalytic converter, in particular a plate-type catalytic 
converter, which comprises heating a metal carrier body in an oxidizing 
atmosphere to form an adhesion-promoting intermediate layer in the form of 
an oxide film on the carrier body; and applying a catalytically active 
layer to the intermediate layer. 
As a result, the surface of the carrier body is oxidized and is given a 
roughness and a porosity that promote the adhesion of the catalytically 
active layer to the carrier body. 
In accordance with another mode of the invention, the catalytic material 
can be applied in the form of a paste-like composition, onto an 
adhesion-promoting intermediate layer that is produced in this way, by 
being rolled onto the intermediate layer and then calcined. 
In accordance with a further feature of the invention, the intermediate 
layer contains a chlorine compound of the carrier body. As a result, 
chlorine and chlorine-oxygen compounds of the carrier body also contribute 
to improving the adhesion promotion. 
In accordance with an added mode of the invention, the intermediate layer 
contains particles sintered onto the carrier body. Depending on the 
particle size, the particles can contribute to a considerable extent to 
the macroscopic or microscopic roughening of the carrier body surface. 
In accordance with an additional mode of the invention, an oil film is 
applied to the carrier body before the heating is finished. This is done 
in order to accelerate and homogenize the oxidation process at the surface 
of the metal carrier body, and as a precondition for a further feature of 
the invention. Preferably, the cutting oil applied to the expanded metal 
for the expanding process can be left on the carrier body, for example. In 
the oxidation process the cutting oil, although itself a reducing agent, 
leads to an additional spot-wise importation of heat to the carrier body 
surface and therefore, given an adequate supply of oxidizing agent, it 
leads to thickening of the oxide film. 
In accordance with yet another mode of the invention, a mechanical mixture 
of particles adhering to the oil film is applied to the carrier body, 
after the oil film is applied and before the heating. As a result, a 
partially oxidized and relatively greatly roughened layer forms on the 
carrier body. Its properties of adhesion with respect to the catalytic 
material can be adapted to this material by means of a suitable selection 
of the particles. The term mechanical mixture of particles is understood 
to mean particles of metal and/or glass and/or ceramic, in particular 
particles of silver-tin-oxide AgSnO.sub.2 and a material X.sub.5 
CrNi.sub.18,9 (material No. 1.4306). 
In accordance with yet a further mode of the invention, the mechanical 
mixture of particles is made into a slurry in oil and applied with it to 
the carrier body in the form of a suspension before the heating. This kind 
of procedure has the same advantages already discussed above. These 
advantages apply equally to a further alternative procedure for applying 
the particles to the carrier body, in which a mechanical mixture of 
oil-saturated particles is calendered onto the carrier body in the form of 
a paste-like composition prior to the sintering. 
In accordance with yet an added mode of the invention, an oil with a 
chlorine content of at least 1% is used, in order to further speed up the 
oxidation of the carrier body surface. As a result, not only oxygen 
compounds of the carrier body material but also chlorine compounds of the 
carrier body material are formed on the surface of the carrier body. They 
contribute to eroding the surface of the carrier body and therefore to 
improving the adhesion promotion of the intermediate layer. 
In accordance with yet an additional mode of the invention, if no particles 
have been applied, then the heating is carried out at a temperature of 
200.degree. to 600.degree. C. and over a period of time lasting at least 5 
hours. This forms a homogeneous oxide film that adheres very well to the 
carrier body and serves as an adhesion-promoting intermediate layer for 
the catalytically active material. 
In accordance with a concomitant mode of the invention, if a mechanical 
mixture of particles is applied to the carrier body before the carrier 
body is heated, then the heating is performed at a temperature of from 
700.degree. to 1000.degree. C., over a period of time lasting several 
minutes. As a result, on one hand the applied particles are sintered onto 
the carrier body, but on the other hand an oxidized film is also formed on 
the surface of the carrier body, which also adheres firmly to the 
non-oxidized material of the carrier body according to this procedure. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
catalytic converter and a method for producing the same, it is 
nevertheless not intended to be limited to the details shown, since 
various modifications and structural changes may be made therein without 
departing from the spirit of the invention and within the scope and range 
of equivalents of the claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the figures of the drawing in detail and first, 
particularly, to FIG. 1 thereof, it is seen that in order to produce a 
plate-type catalytic converter 2, a stainless steel mesh, which is also 
known as an expanded metal made of stainless steel, is used as a carrier 
body 4 in an exemplary embodiment. In order to carry out the mesh making 
or expansion process, a cutting oil that has a chlorine content of 2% was 
applied to the carrier body. It was left on the expanded metal. 
In the exemplary embodiment, relatively fine particles 6 of 
silver-tin-oxide AgSnO.sub.2 were atomized onto the carrier body 4 
moistened with cutting oil. These particles for the most part adhere 
adhesively to the cutting oil on the surface of the carrier body 4. Next, 
the carrier body 4, on which the cutting oil and the particles 6 adhering 
to it were located, were heated to a temperature of 900.degree. C. over a 
period of five minutes. In the process, on one hand the particles 6 
located on the carrier body 4 were sintered onto the carrier body 4. On 
the other hand, the chlorine contained in the cutting oil dictates 
relatively major erosion of a surface film 8 of the carrier body 4, on 
which compounds of the carrier body 4 that preferentially contain oxygen, 
chlorine, and chlorine-oxygen were formed as a result. Both situations 
together result in both macroscopic and microscopic roughening of the 
surface 8 of the carrier body 4. This creates a very good basis for 
adhesion for a catalytically active layer 10 applied to it on the carrier 
body 4, so that the surface film 8 is in the form of an adhesion-promoting 
intermediate layer. The catalytically active material 10 in the exemplary 
embodiment was applied to the intermediate layer in the form of a 
paste-like composition. The catalytic converter blank was then dried and 
calcined. 
Alternatively, in a further exemplary embodiment seen in FIG. 2, a further 
plate-type catalytic converter 12 was produced with an adhesion-promoting 
intermediate layer 14 without particles being sintered on, and was placed 
onto a metal mesh or expanded metal carrier body 16. In this case the 
cutting oil, which has a chlorine content of 2% and was applied to the 
carrier body 16, was left on the carrier body 16. In this case the carrier 
body 16 was heated to a temperature of 450.degree. C. and kept at this 
temperature for a period five hours. In the process, besides the formation 
of oxygen compounds, chlorine and oxygen-chlorine compounds of the carrier 
body 16 also form, which predominantly change into oxygen compounds of the 
carrier body 16 because of the relatively long holding time. The surface 
film 14 of the carrier body 16 that is oxidized in this way offers a very 
good basis for adhesion for a catalytically active layer 18. This layer 18 
was applied in the form of a paste-like composition to the roughened 
carrier body 16, then dried, and then hardened on the carrier body 16 by 
calcination. 
FIG. 3 is a flow chart which once again explicitly shows the sequence of 
method steps for producing a plate-type catalytic converter in accordance 
with FIGS. 1 and 2. 
Beginning with the carrier body 4, 16, which is formed of expanded metal 
made of stainless steel, the first step is an application 20 of a 
chlorine-containing cutting oil, followed by an expansion process 22. This 
can be followed by an application 24 of the particles 6. The carrier body 
4, while still moistened by cutting oil, expanded, and provided with 
particles 6 that adhesively stick to the cutting oil, then arrives at a 
heating step 26. In the present case, a temperature of approximately 
900.degree. C. is employed over a period of approximately 5 minutes. This 
is followed by an application 28 of the catalytically active layer 10, 18 
onto the carrier body 4, which now has a microscopically and 
macroscopically roughened surface layer 8. Finally, the catalytic 
converter blank which is then available is also subjected to calcination 
30, as a result of which the plate-type catalytic converter 2 of FIG. 1 is 
obtained as a finished product. 
The plate-type catalytic converter 12 of FIG. 2 is obtained if the 
application 24 of the particles 6 is omitted. The heating 26 is then 
carried out at a temperature of approximately 450.degree. C. over a period 
of approximately five hours. The roughened surface layer 8 then has 
chlorine and/or oxygen and/or chlorine-oxygen compounds of the carrier 
body 16, as a result of which the roughening is originally brought about. 
All of the other method steps 20, 22, 28, 30, as described above, may be 
retained.