Device for the catalytic purfication of flowing gases, especially exhaust gases of internal combustion engines

BACKGROUND OF THE INVENTION The present invention relates to an apparatus for the catalytic treatment of exhaust gases, in particular from exhaust gases of internal combustion engines. Such an apparatus has a housing arranged in the flow path of a stream of gases to be purified, comprising a gas-permeable carrier made of heat-resistant fibrous material in the form of a textile surface onto which a catalytically active agent is applied.

Catalysts commonly used in the cleaning of exhaust gases from vehicle engines, especially Otto engines, include a ceramic monolithic insert, usually an extruded hollow body, which is coated with catalytic agent, particularly platinum, on the surfaces associated with the exhaust gas. These ceramic inserts are very susceptible to mechanical damage and are usually housed in a metal housing requiring elastic support, which is inherently problematic. In order to provide a sufficiently large surface area, prior to the application of the catalytic agent, these hollow ceramic bodies are provided with a special so-called "washing layer" which, however, rapidly ages at temperatures above 800 ° C. It is due to this thermal sensitivity that such catalysts cannot be located directly in the engine area. Arranging at a relatively greater distance from the engine, however, with the relatively large weight of the ceramic body, has the disadvantage that it takes a relatively long time to warm the ceramic body to operating temperature after a cold start. In the meantime, however, the catalyst is only of limited effectiveness during the warm-up period. Because the exhaust gases pass through the ceramic body cells in a substantially laminar flow, throughput is thus inherently limited.

A solution is also known from Australian patent application AU-61 419, which uses a filter to purify the exhaust gases, especially combustion engines.

In this filter, the fibers are made of heat-resistant polycrystalline material having a crystal size between 50 and 500 Angstroms. Polycrystalline alumina or zirconium oxide were used for such fibrous materials. In general, metal oxides which are heat resistant up to 900 ° C can be used for this purpose.

In order to reduce the temperature, the fibers can be coated with a catalytic material, in particular silver, bismuth, lead, uranium, cobalt or the like, to reduce the temperature to burn fine particulate matter from the exhaust stream. To remove unwanted gaseous components, such as carbon monoxides or hydrocarbons from the flue gas, the zirconia fibers are coated with finely divided platinum in the filter of the above document.

In the filters, the fibrous material is arranged as a loose set, paper, fabric, foil, cardboard or felt, which may include the use of filter elements in which a paper (or corrugated) or yarn or felt made of such fibrous material is freely wound in a gas-permeable filter. It is noted, however, that loose fiber filter bodies are problematic because unbound fibers become free over time.

Furthermore, in the case of paper, felt, fabric or similar fibers processed into linear textile surface shapes, the flow resistance is too high or there is a risk that the filter will disintegrate relatively quickly. The surface area of ​​the bonded fibers has very little free surface, and the free fiber surfaces are increasingly reduced during operation. It is for these reasons that catalytic filters of this type have so far been unable to gain any economic significance for themselves.

It is an object of the present invention to overcome the above disadvantages, that is, to provide an improved catalytic flue gas cleaning device (catalyst) which is mainly used for internal combustion engines and which is mechanically insensitive to the improved solutions with improved efficiency.

To accomplish this object, we started with a device of the type described in the introduction, which was further developed in accordance with the present invention by using knitted-crocheted fabric as a carrier for the catalytically effective material.

According to a further feature of the invention, the fibrous material preferably comprises ceramic microfibers having a diameter of 3 micrometers or more. It is particularly advantageous to use polycrystalline mullite fibers (refractory aluminum silicate fibers) as microfibres, but other heat resistant fibers may also be considered. Thus, for example, in certain applications, the fibrous material may contain or consist entirely of carbon fibers. The fiber surface preferably has a surface area of ​​0.2-0.4 m²/ g or greater, but this is not to limit the surface area of ​​the usable fibers.

Thus, the fibers of the proposed knit-knit fabric are the carrier of the catalytically active material which, in our experience, provides excellent contact with the flowing gases along their fiber surfaces, and at the same time forms an excellent flow technique. A further advantage of such a carrier is that it is capable of volume changes while being insensitive to vibrations and pulsations of the gas stream. The fibers coated with the catalytic material in the knitted and crocheted fabrics can be pre-scaled to a predetermined extent and properly secured, i.e. secured. In spite of this, the fiber surfaces are largely free, with limited displacement relative to one another, thereby reducing and dampening bias. The highly exposed fiber surface has been shown to provide near-maximal catalytic efficiency.

The structure of the knit-knit fabric forms a multiple pore system in which resilient elements are formed. Thus, even when flue gas travels in a laminar flow in all flow regions, a high degree of surface contact and thus an efficient catalytic process takes place. Within the knit-loop fabric, the flow paths are widely branched, with the result that the fibers carrying the catalytically active substance come into contact with the flue gas streams over a large area.

Because of its particular structure, the knitwear fabric of the present invention provides excellent mixing of the exhaust gas.

EN 213 976 Β since it may initially contain partial currents of different concentrations or temperatures. This provides a special advantage, especially for larger internal combustion engines and the so-called "Lambda 1" technique. It is also noted that the proposed knitted-knit fabric has very good noise insulation properties and, moreover, also filters particulate matter such as soot particles in the flue gas.

By the good bonding of the fibers to the knit-knit fabric, as mentioned above, it is possible to keep any tear-off fibers in the knit-knit fabric from being anchored, so that no further degradation of the fabric can occur. Therefore, even short filament yarns can be used to make knit-knit fabrics.

It is further preferred that the knitted-knit fabric be made of at least two fibers of different materials, one or more of which may have the same or different catalytic activity. Alternatively, the knitted-knit fabric may be provided with at least one metal fiber, which provides improved form-retention for the knitted-knit fabric. It is also advantageous to incorporate carbon fiber with an increased surface area (activated carbon fiber) into the knit-knit fabric, thereby allowing, for example, the temporary adsorption of the unsaturated hydrocarbons produced during the cold start phase and the subsequent desorption of the adsorbed materials during the next operating period. ).

For the above purpose, the knit-knit fabric may also include electrically conductive fibers which may be connected to an electrical power source by means of suitable connecting units. This allows direct heating of the knitted and crocheted fabric. However, this internal heating can be used not only for desorption of adsorbed materials, but also, in particular, for rapid heating of the knit-knitted fabric of the catalytically active material to the operating temperature during the cold start phase. The electrically conductive fibers may be in the form of carbon or metal fibers, such as metal wires, and the like.

The carbon fibers may be provided with an electrically insulating coating on their surface, such as a silicon oxide coating. To do this, SiC is first applied to the fibers, which are then converted to SiCE by heat treatment. This silicon dioxide coating also provides protection against oxidation.

In a knitted or crocheted fabric, the fibrous material may generally be man-made fibers or filaments. Yarn bundles of endless filaments in a knitted fabric essentially have only one beginning and end, and thus have little damage surface. In contrast, stacked fibers provide a larger surface area and better filtering effect with their fiber ends protruding from the bundles. A mixture of the two types of yarn may also be used, which has the additional benefit of being better adapted to the conditions of use. It is also possible to design a knit-crocheted fabric in the form of a yarn.

In each case, the fibers preferably have a rough surface. According to our experimental experience, the surface quality of the fibers is influenced by approx. It can be increased by 20 factors.

The yarn used for the knit-knit fabric may be slightly twisted, in which case practical experience has shown that the yarn is 25.4 mm long. The use of textured yarn is often advantageous.

When the flow of gas is passed through these knitted and crocheted fabrics, there is almost no resistance flow along the "large pores" defined by the mesh structure. The knit-knit fabric is inserted into the housing so that the flow is substantially in the plane of the knit-knit fabric. Alternatively, the knit fabric may be compacted to close the "large pores". However, this usually increases the resulting flow resistance, which increases the pressure drop in the knit-knit fabric.

In knitted and crocheted fabrics, the loop loops remain curved even under strong local tension, which means that the fibers are never fully stretched, unlike the stresses in the fabric. As a result, the biasing of the fibers remains limited so that the fibers in the wire bundle remain slack relative to one another and thus have large free, effective surfaces.

In some cases, it may be expedient to tension the crochet-knit fabric to a predetermined amount of tension towards the loop posts and / or loop rows to vary the bias.

In the housing carrying the stream of gas to be cleaned through the catalytically active knit-loop fabric, the knit-loop fabric can be arranged to fill the catalyst space using a variety of assembly techniques. For example, a knit-knit fabric can be partially wound or folded, and even optionally at least partially pleated or folded. It has also been found advantageous for the knitted and crocheted fabric to be circular. The circular hose thus formed can then itself be wound or pleated, folded or otherwise arranged. Alternatively, this knitted hose can be wound like wire and wound in this form to a mandrel in a spiral fashion, optionally in multiple layers.

When using certain fibrous materials, such as ceramic fibers, the ceramic fibers are coated with a catalytically effective material and such knitted-and-knit fabric is resistant to high temperatures. A catalyst made from such a knit loop fabric can be located immediately downstream of the exhaust valves of the internal combustion engine. The knit-crocheted fabric provides the fibers with such an anchorage in the loop that it can withstand the strong pulsating effect of the exhaust gases in this area. However, the pressure drop in such a knit-knit fabric can be so small that it does not substantially affect the operation of the internal combustion engine.

The knit-crochet fabric can also be arranged in a properly assembled condition in the exhaust pipe elbow of the internal combustion engine so that it or

The exhaust manifold also forms part of the catalytic converter housing. In cases where the internal combustion engine is provided with a turbocharger or a pressure wave charger, the catalyst of the present invention may also be provided prior to this.

The catalytically active substance may be applied to the finished knitted or crocheted fabric, or to the yarn before it is made. Moreover, optionally, the catalytically active material may be applied to the fibrous material prior to processing into the yarn.

The invention will be described in more detail with reference to the accompanying drawing, in which some exemplary embodiments of the present invention are illustrated. In the drawing:

Figure 1 is a schematic side view of a first exemplary embodiment of a device according to the invention which can be mounted in the exhaust pipe of an internal combustion engine;

Figure 2 shows a variant of the apparatus of Figure 1;

Figure 3 is a detail view of a knit-loop knitted fabric used for the equipment of Figures 1 and 2 in a prespective view showing the different gas flow directions;

Figure 4 is a top view of a detail of a knitted fabric used in the solution of Figure 1, illustrating the various elongation conditions;

Figure 5 illustrates a slightly twisted yarn of the knit-knit fabric of Figure 3 on a relatively larger scale;

Figure 6 shows a highly twisted version of the yarn of Figure 5;

Figure 7 illustrates the flow conditions of a single yarn of the knit-knit fabric of Figure 3;

Figure 8 is a cross-sectional view showing the flow conditions of the knit-knit fabric of Figure 3;

Figure 9 is a schematic perspective view showing a rolled up version of the knit-knit fabric of Figure 3;

Figure 10 is a schematic perspective view of a pleated arrangement of the knit-knit fabric of Figure 3;

- underneath. Figure 3B shows a knit-knit fabric of Figure 3 in a folded configuration;

Figure 12 shows a knitted-knit fabric of Figure 3 in the form of a circular hose which is partially wound;

Fig. 13 is a schematic sectional view showing an arrangement in which a plurality of coil rings of Fig. 12 are arranged side by side;

Figure 14 is a schematic perspective view of a knit-knit version of the knit-knit fabric of Figure 3, which is formed as a partially pleated fabric hose;

Figure 15 is a schematic sectional view of the circular pleated hose of Figure 14 showing flow conditions;

Fig. 16 is a perspective view of a knit-knit fabric of Fig. 3 in a folded configuration at least once;

Figure 17 is a schematic sectional view of the folded version of Figure 16 showing the flow conditions;

18-21. 3 to 5 show three views of the device according to the invention, which are formed directly as catalysts in the exhaust manifold of the internal combustion engine;

Figure 22 shows a further variant of the knitted-knit fabric of Figure 3;

Figure 23 illustrates a fiber system of a knit-knit fabric of Figure 22, with electrical connections also shown;

Figures 24 and 25 are schematic side views of two further embodiments of the apparatus of Figure 1 employing a knit-crochet fabric of Figures 22 and 23.

Figures 1 and 2 show two embodiments of the inventive catalyst device which can be used for internal combustion engines. Each of these preferably has a cylindrical or oval housing 1 in cross-section, which is made of sheet metal and has funnels 2 and 3 on its two ends. The inlet funnel is connected to the inlet manifold 4 and the outlet funnel 3 to the exhaust manifold outlet 5. The housing 1 can be arranged in the exhaust system of an internal combustion engine (not shown) so that, during operation, the interior of the housing 1 reaches the stream of exhaust gases to be cleaned, evenly distributed in the direction of arrow 6.

In the simplest embodiment of Fig. 1, a gas permeable catalyst body 8 is provided between two perforated sheets 7 which completely fills the interior of the housing 1. 2, however, cylindrical catalyst units 10, each of which has a candle-like housing 11, are connected to the perforated plate 9 formed in the housing 1 in the manner shown. The housing 11 has a sealed configuration on its bottom plate 12, but the slate portion is made of a perforated plate 13. Each hub-like housing 11 is provided with a gas-permeable cylindrical catalyst body 8a on which, during operation, the flue gases flow substantially radially from the inside to the outside.

HU 213,976 Β

The catalyst bodies 8 and 8a have a gas-permeable carrier material according to the invention which comprises a knit-loop fabric comprising a catalytically active fibrous material, and the catalyst bodies 8 and 8a have a configurable shape.

The details of the knit-knit fabric are shown in FIG. Figures 3 and 4 show that this is a left / right knit fabric, however, it is noted that other single or multi-layer knitting patterns may be used, depending on the intended use. This knit-knit fabric 14 may, for example, be made with double-mesh loops, but may optionally include different loop shapes.

It can be seen from detail "a" and "b" of Figure 4 that the same knit-knit fabric 14 is unstretched on part "a" but stretched in the direction of the loops on part "b". In the latter case the loop of the loops remains. Contrary to the fabric conditions, the fibers are never completely stretched here. Appropriate confinement avoids over-stretching the knit fabric and therefore the fibers in the fiber bundle are displaceable relative to one another so that their catalytically active surfaces are substantially completely accessible to the flue gas flowing through the catalyst bodies 8 and 8a respectively.

Knitted-knit fabric 14 is made up of yarns 15, which may be composed of synthetic fibers (Figure 5) or endless fibers or a mixture of the two types of fiber. Basically, the yarn 15 may be single or multi-filament, and in some cases may be so-called "core-spun" yarn.

In general, it is desirable to twist the yarns 15 slightly to expose as much fiber as possible. This can be clearly seen from Figures 5 and 6, which show lightly twisted yarns (Figure 5) and heavily twisted yarns (Figure 6). As shown in Figure 5, the slightly twisted yarn 15 has a structure that allows the flue gases to flow through it. The stronger the twisting of the yarn 15, the greater the resistance of the flue gas flow. According to our experimental results good results can be obtained if the yarn 15 is approx. has a twist. It is also advantageous if the yarn 15 is of textured design.

The fiber material used to make the yarn 15 must be heat resistant to the extent that it can withstand operating flue gas temperatures over a long period of operation.

In our experience, this temperature range should be between 200 ° C and 800 ° C. In view of the larger surface area, it is preferable to use microfibres, which means fiber diameters of 3 micrometers or more.

The material from which the fibers are made is usually ceramic, however, depending on the temperature range, other organic or inorganic materials may be used. All metal oxides are suitable for this purpose. When pure carbon fibers are used, they offer a number of advantages, such as electrical conductivity. The surface of the fibers may be increased by appropriate measures. so e.g. fibers with a coarser surface are preferred over plain fibers. In our experience, the surface shape of the fibers can be increased by 20 factors. Activated carbon fibers having substantially enlarged surfaces can be incorporated in carbon fiber applications, thereby utilizing them as an absorption material during the cold start phase of the internal combustion engine.

In general, knitted or crocheted fabrics 14 may comprise different yarns or fibers 15 made of different materials. Thus, they can perform different functions in single or multi-threaded applications. For example, at least one metal fiber may comprise a knitted-knit fabric 14, which gives the catalyst body 8 and 8a a certain shape, which may be of significant significance depending on the chosen assembly method of the catalyst body 8 and 8a and the operating conditions.

The structure of the catalyst bodies 8 and 8a made of knitted-knit fabrics 14 may be different as described in the examples below. However, first of all, it is emphasized that the flue gas stream must pass through the knit-knit fabric 14 such that no resistance paths are formed along the entire length of the fabric at the large pores due to the loop structure. In particular, if the flue gas to be cleaned in the catalyst body 8 and 8a is not forced to flow through a plurality of stacked fabric layers and thereby follow branched flow channels, it is usually necessary to ensure that the gas stream flows through the knit-knitted fabric 14. as shown by arrows 16 and 17 in FIG. Flow through perpendicular to the plane of the fabric, indicated by arrows 18, is less convenient than a single layer fabric arrangement as shown in FIG. Figure 4a. Here, it can be seen that in the knit-knit fabric 14, the "large pores" formed between the individual loops and the arches would be too large for a transverse flow.

The conditions of gas flow in the film plane are well illustrated in Figure 8. Here, it is ensured that the flue gas stream 19 encounters a flow resistance at each fiber 20, which is then passed through a relatively large surface, as shown in FIG.

Examples of assembly technologies that can be used to make catalyst bodies 8 and 8a that fill the catalyst space are shown in Figures 9-17. FIGS. However, the solutions disclosed herein are exemplary embodiments only, and may be combined with each other or may be complemented by other forms of assembly.

In the embodiment of Fig. 9, the knit-knit fabric 14 is wound into a simple coil 21, which may further form the catalyst body 8 of the catalyst of Fig. 1. For the reasons already detailed above, it is desirable to ensure that the flue gas is axially flushed through the coil 21 of knit-knit fabric 14, indicated by an arrow 22 in FIG. Transverse flow (ie, flow perpendicular to the centerline) is possible but less desirable.

In the embodiment of Figure 10, the knitted-knit fabric 14 is pleated, that is to say, in a continuous manner.

The HU 213 976 Β is designed as a stack of 23. Here again, 22 arrows indicate the most favorable flow direction. In the arrow flow 22, the gas streams to be cleaned pass through the plane of the fabric 14. In principle, transverse flow is also possible, as indicated by arrow 24, but this is less advantageous.

All. The knit-knit fabric 14 is folded together. This fold can be single or multi-layered, and can be folded in the direction of the loops or loops. Folds are also possible in which at least one fold in the direction of the loop rows and at least one subsequent fold in the transverse direction thereof. Here again, 22 arrows indicate the most favorable flow direction. Transverse flow in the direction of arrow 24 is also possible; above.

12-17. 1 to 4, a knit-knit fabric 14 is formed as a circular hose 140. This hose 140 allows for the simplest hollow shape that is appropriate for a variety of applications. A very simple embodiment, for example, is that the hose 140 is preferably tucked in several layers in a stocking-like manner to the housing 11 of Figure 2, or is inserted into the housing 11 in cylindrical form.

The embodiment of Fig. 12 provides a greater effective fiber surface for the gas flow through. In this case, the hose 140 is wound into a ring (torus) 25. Referring now to FIG. 13, the hollow cylindrical housing 26 is filled with such rings 25 and forms the catalyst body 8a. The direction of gas flow is indicated by an arrow 27 transverse to the plane of the rings 25.

Figures 14 and 15 show a further exemplary embodiment in which the hose 140 made of circular knitted fabric 14 is pleated at the location designated by reference numeral 28. Thereby a cylindrical shape is formed, the walls of which consist of the overlapping layers of the leaf-folded fabric 14. This shape can be inserted into, or loaded onto, the housing 26 or the candle-like housing 11 (FIG. 2). An additional advantage of this embodiment is that the arrow-shaped radial flow through the layers of the pleated portion 28 occurs substantially in the plane of the knit-knit fabric 14.

In a further embodiment of Figures 16 and 17, the hose 140 is folded one or more times about its longitudinal axis. The folded shape 29 can then, for example, be helically wound, as shown in FIG. 17, or inserted into the housing 26 or even tucked in or inserted into the candle-like housing 11 of FIG. In this embodiment, the flow is essentially in the plane of the knit-knit fabric 14 as indicated by the arrow 27.

Catalyst bodies 8 and 8a assembled as described above may be circular or non-circular cylindrical surfaces or any other hollow shape. The catalyst bodies 8a thus formed, in particular candle-like catalyst bodies 8a, can be coupled in parallel as shown in FIG. 2, but may also optionally be connected in series. In this way, the effective flow area can be significantly increased, and at the same time, little pressure loss is achieved.

Although, in the exemplary embodiments of Figures 1 and 2, the catalyst bodies 8 and 8a are housed in a housing 1, the housing of the knit-knitted fabric 14 forming the catalyst body may in some cases be omitted. Examples of such embodiments are shown in Figures 18-21. FIGS. In this case, the catalytically active knit-loop fabric 14 is disposed directly in the exhaust elbow 30 of the internal combustion engine 31.

In the embodiment of Figure 18, the knit-knit fabric 14 is wound, as shown in Figure 14, in a roll 21 which is directly disposed in the exhaust manifold 30, thereby constituting the "housing" of the catalyst. Alternatively, the coil 21 is disposed in another part of the exhaust pipe by using the tube wall as a catalyst housing. The direction of flow is indicated by arrows 32.

The arrangement of Figs. 19 and 20 differs from the embodiment of Fig. 18 in that the exhaust manifold 30 is provided with a full-length rectangular housing 33 which includes, for example, the knurl according to Figs. pleated or folded version of knitted fabric in the form of 23 piles. Here, the direction of the exhaust gas flow is also indicated by 32 arrows.

In a further embodiment of Figure 21, the exhaust manifold 30 is provided with a gas-permeable housing 34 extending along its entire length, for example pleated as shown in Figures 14 or 15 or as shown in Figures 16 and 17. FIG. 5a includes a roller assembly 35, which, for the whole arrangement, is substantially a "filter candle" located in the exhaust manifold 30 and substantially flowing radially through the wall of the exhaust gas to be cleaned, as indicated by arrows 32.

Platinum may be used as the catalytically active substance if the exhaust gases of the internal combustion engine are to be purged of unburnt hydrocarbons and carbon monoxides. Conversely, if other contaminants are to be converted in the exhaust stream or for applications where the combustion temperature is to be reduced, for example for soot particles, other catalytically active materials may be used which are applied to the fiber surfaces to be cleaned. Examples of such materials are: Pt, Pd, Bv, Rh, etc.

When platinum is used as the catalytically active substance, the fibers may be coated with platinum in various ways. The coating can be made from a gas phase (so-called CVD process, i.e. chemical vapor deposition). Another technology may be wet impregnation. In this process, the knitted-knit fabric 14 is impregnated with a dilute solution of platinum salt, then the impregnated fabric is dried and finally the salt is converted to platinum by heat treatment.

Depending on the reaction conditions for thermal decomposition of the salt, there are three variants of platinum: physically sorbed oxygen (Mohr-platinum) or non-sorbed oxygen-rich non-crystalline surfaces (platinum sponge) and crystallized but poor surface-platinum metal (platinum) .

HU 213,976 Β

First EXAMPLE

The knitted-knit fabric 14 of FIG. 3 was made from a yarn with half a strand of 25.4 mm. This yarn is made of polycrystalline mullite, ie refractory aluminum silicate fibers, 0.2 to 4.0 m²/ g surface (the second value is interpreted as leaching). The fibers have a diameter of approx. It was 10 micrometers, so it was outside the health-damaging range. Optionally, fibers having a diameter of 5 micrometers and a correspondingly larger surface area may be used.

The knitted-knit fabric 14 was then immersed in a dilute solution of platinum salt (wet impregnation) and then converted to a platinum sponge (chelated needles) at a temperature of about 800 ° C. The coating amount is approx. It was 1% by weight, but this value can be reduced to mass relays.

Subsequently, the platinum-coated knitted-knit fabric 14 was wound into a roll 21 as shown in Figure 9, and the gas stream to be cleaned was axially flowed through it. The roll 21 is placed in a stainless steel housing 1 in the arrangement shown in Fig. 1.

Second EXAMPLE

The knitted-knit fabric 14 was made here of carbon microfibres having a density of about 10 to about 10 cm. 0.5-1.0 g / cm³ was worth. The fibers were endless monofilaments with a fiber diameter of 6.5 micrometers. 3000 bundles of monofilaments were used. The flow rate relative to normal operating conditions was 85 mm / s. The experiments were performed with carbon monoxide enriched air.

Already approx. At 230 ° C, carbon monoxide was completely converted to carbon dioxide at a spatial velocity of 10,000 l / h (spatial velocity: m³ volume of gas flowing through the catalyst per hour, in cubic meters).

Instead of the platinum catalyst, an optional rhodium catalyst or a Pt / Rh (platinum / rhodium) catalyst may be used.

Third EXAMPLE

The carbon fibers mentioned in Example 2 were first coated with SiC (CVD). The fibers were then wet impregnated with a Pt / Pd mixture, and then ca. The catalytic coating was formed by calcination at 800 ° C.

The knitted-knit fabric 14 thus prepared was formed into a roll 21 corresponding to the first example, through which propane gas was passed axially.

At a space velocity of about 10,000 l / h, the catalytic conversion of propane began, ca. At a starting temperature of 210 ° C and then for approx. At 330 ° C, 100% propanate conversion was found.

If carbon fibers are used as a carrier for the catalytically active material, this has the additional advantage that the catalyst bodies 8 and 8a can be heated directly from the inside, since the carbon fibers are electrically conductive. A further possibility for internal heating is that the knitted-knit fabric 14 is formed of two types of yarn, for example, one made of catalytically active material and made of ceramic fiber 15, and electrically conductive yarn 36. An example of this is shown in Figure 22, where it can be clearly seen that in applications where the internal heating of knitted-knit fabric 14 is not required, the auxiliary yarn 36 may be made of non-conductive material, which may be chosen This additional yarn 36 imparts to the knit-knit fabric 14 a feature suitable for the purpose.

It is also possible to use weft yarns which are made of electrically conductive material for internal heating purposes, but otherwise have other desired properties. Such properties to be achieved include, for example, improved form strength, greater strength, or a particular expansion property of the fabric, which is different from the transverse direction in the loops.

The electrically conductive filaments may be connected to a power source not specifically described as shown in FIG. To this end, the filaments 36 are to be soldered to the contact sheets 39 and 40, preferably after pre-coating the filaments. The contact sheets 39 and 40 are substantially transverse to the bonding direction. Thus, clear resistance conditions are created and a steady current flow through the yarn lengths formed by the loops 21 can be ensured.

A similar arrangement is, of course, obtained when the fabric of Fig. 22 is formed as shown in Fig. 23 into a double fiber. In Figure 23, only the yarn system made of 36 yarns is shown for clarity.

In order to eliminate short circuits between the individual layers in the case of a multilayer catalytic body in a knitted-and-knit fabric 14 including electrically conductive fibers, relatively simple steps have to be taken, which are illustrated in two examples in Figures 24 and 25.

Fig. 24 shows a catalyst similar to that of Fig. 1, the catalyst body 8 of which is made of a pleated design of knitted-knit fabric 14, for example of Figs. 14 or 15. An insulating layer 42 is provided between the layers 41 of the folded fabric 14, which may be made of mica, for example, and extend from each end to the catalyst body 8.

In another embodiment of Figure 25, an insulating fabric 45 is provided adjacent to the folded knit fabric 14, which is made of, for example, ceramic or fiberglass. The fabrics 14 and 45 are folded parallel to each other as shown.

The electrical internal heating of the catalyst bodies 8 and 8a rapidly heats the catalyst to operating temperature, as noted above. Furthermore, the proposed solution is capable of additional desorption, for which the use of a dual-fiber fabric seems preferable, in which one of the fiber systems may consist of activated carbon fibers having a particularly large surface area and thus a high degree of absorption.