DE2219425A1 - Process for reducing the amount of undesirable constituents in gases - Google Patents

Description

PATENT LAWYERS
DR.- IN QH FINCKE DIPL.-INQ. H. BOHR DIPL-ING. S. STAEGER

Fe r η r u fi * 26 60 60

Folder 22871 - Dr. Case MD 23784

8 MUNICH 5, Müllerstrasse 31

2 APR 0, 1972

Imperial Chemical Industries Ltd. London, UK

Process for reducing the amount of undesired constituents in gases

Priority: April 20, 1971 - Great Britain

The invention relates to the treatment of gases in order to to prevent the amount of gases in it that pollute the air.

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Exhaust gases often contain varying amounts of gaseous components which pose pollution problems when released into the atmosphere. For example, gases produced by the combustion of hydrocarbons * contain carbon monoxide, unburned hydrocarbons and nitrogen oxides. The pollution problems are particularly serious with the exhaust gases from internal combustion engines. Exhaust gases from nitric acid plants also contain nitrogen oxides. There is therefore a considerable need for reducing the content of pollutant gases in similar exhaust gases.

The legislation in the Ü3A has stipulated upper limit values for the permissible levels of hydrocarbons, carbon monoxide and nitrogen oxides in car exhaust gases. The catalytic treatment of exhaust gases has been around for many years
taken into consideration. However, the previous methods did not result in a catalytic treatment which reduced all impurities simultaneously to the desired low levels for a sufficiently long time.

In most previous processes for catalytic Treatment of automobile exhaust fumes, air is added to these gases. There are methods (see U.S. Patents 3370914, $ 34-93325, $ 3228746 and $ 354426 in which the exhaust fumes in absence secondary air, but these methods obviously have no general application found.

The catalysts are usually on refractories
Straps used. For exhaust gas treatment processes, at
where hot post-combustion (ie, oxidation) takes place, asbestos and metal fibers (see US Pat. Nos. 1875024 and 3495950) have been used.

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The invention now relates to a method for reducing the amount of colil monoscid; Hydrocarbons and nitrogen oxides in gases, which are carried out by contacting the gases under essentially n ± cb, t-oxide:? Ead6 & conditions with a fibrous catalyst consisting of a synthetic refractory fiber and a k & ta ™ lytic agent » which promotes one or more reactions by which at least one of the components mentioned is completely or partially destroyed.

The expression "essentially non-oxidizing conditions" means that the oxygen content in d @ n Gases is less than the equivalent of oxidizable materials - present in the gases * It is preferred that the oxygen content be less than half this equivalent is.

Preferably the catalytic agent is one which promotes more than one (and possibly all) of the sewn functions. In its simplest form, the process according to the invention consists in contacting the gases with a single fibrous catalyst. Gewünechtenfalla but can gases also in sswei or more steps or even contacted with a mixed fibrous catalyst "A multiple contact can for example be carried out by _t that is repeated with the same fibrous catalyst in contact talagt the gases or in that the gases consecutively with vwscnieaenta fibrous catalysts in contact or that the contact is carried out under different conditions (for example different temperatures or contact g® £ t <8 &). Combinations of these methods can also be used.

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The gases are contacted with the catalyst at a temperature sufficient to ensure effective catalyst function. For the decomposition of hydrocarbons and nitrogen oxides, the temperature is preferably above 40O ⁰ C, especially above 600 ⁰ and up to about 1000 ⁰ O. It is preferred that measures be taken to ensure that the fibrous catalyst reaches its active temperature as soon as it is in use as possible and maintained at this temperature during use. It is usually very useful to maintain the desired temperature by thermally isolating the catalyst container or by utilizing the sensible heat of exhaust gases, especially those produced by a combustion process. If desired, however, this heat can be modified by additionally heating or cooling the catalyst in its container. It is therefore particularly expedient to arrange the catalyst as close as possible to the combustion zone in which the gases are generated, preferably as close as possible to the exhaust gas outlet of an internal combustion engine. Alternatively, the catalyst can be heated by combustion using an auxiliary air supply which can be used when warming up, that is, when the engine and catalyst are below operating temperature. This auxiliary air supply is then switched off, for example by a known mechanism which automatically sets the carburettor to cold start, or by an equivalent mechanism.

Thus, this embodiment of the invention can be defined as a method for treating exhaust gases from internal combustion engines, which have a cold start phase and an operating phase, the cold start phase under oxidizing conditions with added air in the presence

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of the fibrous catalyst is carried out until the normal operating temperature of the catalytic converter has been reached, whereupon the operating phase is allowed to run off under non-oxidizing conditions is _described, then this embodiment can be operated to the invention in such a manner that the upstream feeding of the fiber catalyst air during the starting phase and in that then wipe during the operating phase "auführt the fibrous catalyst and the oxidation catalyst air. the starting phase may be as long as to extend" until the catalyst of the subsequent stage or stages has been heated to its operating temperature.

The amount of air that is supplied during the start-up phase must not be so large that it corresponds to the total oxidation requirement, only sufficient air must be available in order for an exothermic reaction to take place «It can be useful to preheat this air, in particular during the start phase *

The fibrous catalyst can be any catalytic agent • containj which is active for the respective reaction is. This active agent can also be distributed throughout the refractory fiber or it can be localized therein be concentrated «, for example, as a surface covering or in the surface zones of the fiber. The refractory Fiber can be inert or can also have some catalytic properties Have activity for the mentioned reactions «You can also have the catalytic« activity of the katalytlechen Improve by means of.

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Üe: c Fibrous catalysts can be associated with an inorganic fiber which can be used, for example, as an inert diluent or as a carrier or as a reinforcing material. Suitable fibers for this purpose are any of the refractory fibers used to make fibrous catalysts. They can be natural or artificial fibers such as asbestos, mineral wool and the like.

Particularly suitable fibrous catalysts are those which are derived from aluminum phosphate fibers, as described in more detail in British patent application 29862/69, carbon fibers or fibers made from the carbides of, for example Titanium, silicon, boron or zircon «Particularly suitable are fibrous catalysts, which are different from refractory inorganic derive fibrous oxides, such as fibers from Alumina, ZirconoxicL Titanium Dioxide or Silicon Dioxide. Fibers which contain the oxides mentioned physically or chemically in combination can also be used.

It is particularly preferred to use fibrous catalysts asu derived from refractory fibers made in accordance with British patent applications 22909/70, 4369/71 and 18259/71. The content of this Patent applications are intended to be included in the present description.

As set out in the above patent applications, particularly valuable fibrous catalysts consist of a catalyst material and an aluminum oxide and / or zirconium oxide fiber, which is produced by _; that a composition is processed into fibers,

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which has a viscosity of more than 1 poise and consists of ^: an aqueous solution of a salt of aluminum TO ^ / a & isr ^: zircon (as the case may be) and a water-soluble organic polymer, preferably partially hydrolyzed polyvinyl acetate, the fiber made dries and heats the fiber to decompose the organic polymer and the aluminum or zirconium salt to make a fiber composed of the oxides of the metals. The preferred salts of aluminum or zircon are the acetates, nitrates, sulfates or oxychlorides. The conversion of the composition into fibers is performed in conveniently effected by a blowing method in particular if _f Batten or felts of fibrous catalysts are desired *

Fibrous catalysts which are derived from aluminum oxide or zirconium oxide can advantageously contain various additives, which expediently thereby are incorporated into the fiber that they are incorporated into the composition to be processed into fibers. Examples of additives that can be incorporated are: ;

(a) Grain growth inhibitors such as Sale ©

of magnesium or calcium; Cb) phase change stabilizers ^ f such as e.g.

Salts of yttrium or the rare earths;

Calcium oxide for zirconium oxide;

(c) reinforcing particles such as colloidal silica; and

(d) Compounds that improve the fire resistance qualities of the fiber, such as acidic oxides (for example SiO ₂ , ^ O ^ «? 2 ^ 5 or ZrO ₂ in the case of aluminum oxide fibers»

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The average fiber diameter from which the fibrous catalysts for use according to the invention are made is preferably less than 20yCt · For example it is in the range from 0.5 to 5JU * The thermal conductivity of the material of the fiber is preferably less than 0.02 and is preferably in the range from 0.0001 to 0.01 calories per sec de · 0 per cm *. The surface area of the fibrous catalyst is preferably greater than 0.5 m / g. In particular, it is between 5 and 150 m / g.

The catalytic agents which can be used are, for example, especially if the process is carried out above 40O ⁰ C, metals of group VIII of the periodic table, or mixtures thereof, and in particular ruthenium, iridium, rhodium, nickel or cobalt. These metals can be in the form of elemental metal (in which case it is preferably in a finely divided form) or as a compound with suitable activity, such as an oxide. If desired, the metal can initially be in the form of a salt or another derivative, which is converted into the catalytic jora by treatment before use (for example by heating, oxidation or reduction) or under the conditions of use when treating the exhaust gases. If the active metal consists of cobalt, then the invention method is particularly suitable for the treatment of the exhaust gases from an internal combustion engine which is fed with a fuel which contains sulfur compounds. It has been found that while nickel is poisoned by sulfur in both hydrocarbon / vapor reforming reactions and nitrogen oxide removal reactions, cobalt is less poisoned in hydrocarbon / vapor reactions and much less poisoned in nitrogen removal reactions. So if the sulfur content of the gasoline fed to the engine

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considerably iat, such as 200 to 1000 Gew7 ~ ppm sulfur, the active metal is the Katalysetors the eraten stage preferably cobalt "However, since the required slope cobalt is greater, $ e is greater iatι the sulfur content of these AuafÜhrungsform the invention is extremely economical and effective at low concentrations of sulfate, for example up to 200 ppm by weight sulfur. Such a value can be supplied by the gasoline manufacturers without excessive price increase «

If a cobalt catalyst is used, then it advantageously consists essentially (over 70%) of cobalt oxide Co, 0 _{/ +} η since cobalt is less catalytically active than nickel.

In use of some catalysts, especially nickel, cobalt, copper or iron, and with the use of Temporatüren about 600 ⁰ C hydrocarbons are substantially removed by reaction with steam and residual oxygen, while nitrogen oxides eliminated by reduction, and · by such a reduction caused · Ammonia is cracked into nitrogen and hydrogen. The conditions of the temperature, the catalytic activity and the space velocity are preferably chosen so that at least 7056 of the nitrogen oxides are destroyed, but that at most 20% of them are converted into ammonia. Without the use of excessive temperature or a large volume of catalyst, more than 90% destruction is possible with less than 10% paint formation. The higher the temperature, the more effective these reactions are. The abetrom from the process can, if necessary, by oxidation using known processes or by further reaction via shifting into carbon monoxide or itethanation.

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catalyst can be rendered harmless. A carbon monoxide shift catalyst is a catalyst that promotes the reaction of carbon monoxide and steam, βο that carbon dioxide and hydrogen are formed. A Höthanization " katalysator is a catalyst that allows the reduction of carbon monoxide by hydrogen with the formation of methane promotes. For hydrocarbon removal and disposal It is necessary to ensure that a there is sufficient steam in the gases. *

Alternatively, the method can at a! Be executed temperature in the range of 400 to 600 ⁰ C, held the temperature at which an extended reaction of carbon monoxide with steam, nitrogen oxides are world continuously transferred in undecomposed ammonia and a partial reaction of hydrocarbons with steam takes place "However, If certain catalysts are used, in particular ruthenium, iridium or rhodium, little ammonia is formed at these temperatures. The effluent from such processes can be made harmless by oxidation, for example by contacting with a suitable catalyst, such as sB · ftiokelaalybdat «

in The fibrous catalyst can cause the shift reaction or JKftthanization reaction can be used · For the Shift reaction can change the temperature via a * "High temperature type" catalyst (for example Nickel zinc oxide / chromium oxide, cobalt molybdate or iron oxide / chromium oxide) 350 to 550 ° C or over a catalyst of the "litderteaperrairtype" (example of copper with a Oxide from ZiUt and / or Kangan, Ohroe, MaepieeiUB or Aluminum) 150 bend? 0Q ° 0. For the

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reaction (temperature 200 to 350 ⁰ C) is a nickel or Oobaltkatalyeator particular suitable. The Verschieteniafs «». and Kethanelierungskatalyaatoren can be used in the same way as the catalysts for higher. Temperatures are produced *

When a ffiedertemperaturvers ^ Mebungskatalysator is used, it can be voa sulfur protected by a guard bed _v consisting appropriately selected from zinc oxide, iron oxide or Cobaltoxld · If it is likely "that halogen in the exhaust gases exists," then a guard bed is bevorsugt, that contains a material that is more basic than zinc oxide. A catalyst consisting of a combination or mixture of high temperature and low temperature displacement catalysts is also very effective. Which shift level is used depends on the required composition of the outlet gases and also on the sulfur content of the gas. The high temperature type is preferred, why. the fuel used contains sulfur in an amount of more than 50 ppm by weight.

For the oxidation of Pahrseug exhaust gases after treatment By the process according to the invention, inlet temperatures of 200 to 600 ° C are suitable, but it can also Temperatures above 600 * 0 consecrated in which If only one seringa cooling is required, if at all * - Lich is · With continuous operation, the air should wipe the fibrous catalyst and the Oxidatlonsatufe in one ! Senge, be injected, eo that it is enough, that Oxidize carbon monoxide and the hydrocarbons and that also «ta, siSiger excess of, for example up to Jiu 2 vol% Torfaanden 1st With steady operating conditions, 2 to 3 vol% acidic

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Added substance. However, correspondingly more is added during a cold start or during transition, since more hydrocarbons · * substances and carbon monoxide are present.

Venn is concerned with the removal of hydrocarbons or Nitrogen oxides is followed by an oxidation, then the oxidation catalyst is preferably a noble metal from the group VIII of the periodic table (according to Sidgwick "The Chemical Elements and their Compounds, Oxford 1950); he points thereby either in particulate form or on a mechanical support such as lump refractory Material, deposited "It can also be in the form of fibers or a woven metal net" Appropriately the oxidation catalyst is an Oobalt catalyst of the kind used for the removal of hydrocarbons or nitrogen oxides, or an in appropriately funded cobalt catalyst, such as a copper / cobalt catalyst other materials, which can be used are copper chromite and also platinum group metals, especially palladium, alone or together with one or more basic metal promoters such as copper or copper oxides, preferably on a refractory support such as anhydrous alumina. The concentration of the platinum group metal is suitably in the range from 0.002 to 1.0%, calculated as metal

A very suitable oxidation catalyst contains the oxide of one or more basic Group VIII metals of the periodic table and an oxide of chromium or tungsten, preferably in an intimate mixture. This catalyst contains the two oxides preferably in an amount between half and twice as much as they are in the Ohromat

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or tungstates exist, expediently in approximately equi, atomic Relationships with regard to the metals.

The oxides are preferably formed by co-precipitation brought together (in particular the metal cation of the group VIII ait a chromate or tungstate) whereupon a Heating follows / around the chromate or tungstate in to decompose a lower oxide. The catalyst can Carrier materials, such as aluminum oxide / silicon dioxide or contain magnesium oxide «

The amount of catalytically active material in the fibrous catalyst depends on which reaction is to be catalyzed and which active material is to be used. However, it is generally in the range from 0 * 001 to 10% by weight. For example, platinum group metals show sufficient activity for the hydrocarbon / vapor reaction at lower concentrations (for example 0.01 to 1 wt.% As metal) than other metals of group VIII of the periodic table, such as. Nickel, of which about $ 2 to $ 10 (calculated as Mo) are necessary to achieve smooth activity. ♦ Preferred concentrations of platinum group metals, such as, for example, ruthenium, iridium or rhodium, are 0.001 to; 1 wt .-%, calculated as metal "Preferred concentrations of cobalt or nickel are expected 1 to 10 wt .-% ₉ as equivalent NiO. The proportion of the catalytically active Hatexal should of course be so low that the mechanical properties of the fiber are not impaired *

Katalyaatorförderer can with some designs incorporated into the fibrous catalyst, such as alkali or alkaline earth metal oxides (especially barium oxide

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for nickel), mineral oxides or transition metal oxides.

The catalytic agent can pass into the refractory fiber Coating or impregnation techniques or by Incorporation into the preliminary product from which the fiber is made, can be incorporated, as for example in British patent applications 22909/70 and .4369 / 7 * 1 is described *

Ss is useful, especially in the case of fibrous catalysts derived from alumina or • Derive zirconium oxide, which according to the British patent : registration 4369/71 or 18259/71 has been made, to disperse the catalytic agent in the composition which is processed into fibers. It's special expedient if the catalytic agent or its precursor are dissolved in the composition mentioned can * For example, water-soluble salts can be found in aqueous solutions of aluminum or zirconium compounds which are suitable for processing into fibers

The dispersion of the catalytic agent in the composition which is processed into fibers can also be carried out in are advantageously carried out in that one insoluble or partially soluble particulate catalytic agent mixes with the composition to be processed into fibers * Preferably the middle Particle size of particles dispersed in this way must be smaller than the mean diameter of the fiber produced. In particular, the particles should have a colloidal in size.

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There may be any desired amount of catalytic agent in the Composition to be processed in fibers dispergi ^? · * provided that the fiber produced is laser is still sufficiently firm and cohesive that it is can be used as a fibrous catalyst. It was found that up to about 5 wt% and in some Precipitates up to about 10 wt% catalytic agent appropriately sized can be incorporated into the fiber without seriously affecting the properties of the fiber be impaired

It is preferred that the catalytic agent with the Components of the composition to be processed into fibers are chemically compatible when the fiber is heated is, for example, to make a refractory metal oxide, then it is preferred that the cat & lytic Means at the heating temperature is stable «In the event of a precursor for a catalytic agent, it is often useful that d #? Catalyst from the above Pre-product is formed during the heating of the fiber «

The catalytic agent can also be incorporated into the fiber by soaking the fiber in a solution of the catalytic agent By means of or its precursor in a suitable solvent and by subsequent removal of said Solvent may be incorporated into the fiber. Water is a suitable solvent for many catalytic * Agents or their preliminary products, e.g. for metal salts * A fiber can be used before or after heating, which is heated to form a fiber with a different composition.

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The catalytic agent can also be used in a convenient manner a suitable shape on at least one. Part of the fiber surface can be deposited be effected «that you have a composition to be processed into fibers. the said surface or on the applying catalytic agents or both and removing the solvent from said composition.

In the case of embodiments in which no binder is used to ensure the adhesion of the catalytic! Smock on the To support the barrel surface, it is often possible to to bring about some chemical reaction between the catalytic agent and the fiber, thereby forming a bond arises in many embodiments of the invention however, it is desirable to have only the catalytic agent on the fiber surface in a sufficiently fine form ■ to be deposited so that the normal physical forces of attraction • come into effect. So it is expedient to separate the catalytic agent from a mist or a vapor, which the catalytic agent or a gate .. product contains the same. In a very useful manner, the catalytic agent or its precursor is on the Fiber surface deposited in that said Surface is treated with a dispersion which contains the catalytic agent or its precursor in a suitable liquid. A solution of the catalytic Kittels or its precursor in a volatile solvent is particularly useful. In cases in where the catalytic gown is dispersed in a liquid that does not dissolve it, it is preferred

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that the catalytic agent is in a fine form and that it is in particular a medium size of veniger than 0.5 / t

The fibrous catalyst can be treated, for example, to bring about desired changes in the catalytic agent " bring to. For example, it will be used in cases where a The product of a catalytic agent incorporated into the fiber or applied to the fiber may be necessary, the active catalytic agent by an appropriate one Process to develop «The processes normally used for this are chemical reactions to produce a other connection, reduction and heating «All these processes, especially heating« can be related to others desired heating stages can be combined, for example metal compounds or organic polymers in the composition to be processed into fibers. Treatments of the fibrous catalyst can also be carried out to give desired physical properties Changes in the catalytic. Achieve funds au; For example, changes in the surface or the crystal structure may be desired in order to achieve special catalytic effects to achieve. The treatment of the fibrous catalyst to remove undesirable substances such as e.g. Catalysts can be used in some designs to be useful. .

The fibrous catalyst can be in a container which has any convenient geometry and (any convenient Can have dimension, also can <fer container the fibrous catalyst contained in one or more zones * The packing of the fibrous catalyst in the container can be adjusted so that the resistance compared to the

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Gas flow (the pressure drop) is as low as desired * Sine packing density is in the range from 0.1 to 0 »3 g / cnr is preferred * It is possible to use the most varied Use container geometries because the fibrous catalyst is easily incorporated into any container shape can be.

The invention thus additionally relates to a reactor which is suitable for the process and has a chamber suitable for receiving the fibrous catalyst and which further has means by which a gas stream is in contact with the fibrous catalyst can be brought. The reactor can contain the catalyst in the form of loose or partially compacted fibers or included as easily interchangeable preformed fittings. In the latter case, the header / has at least one Termination of a size such that one catalyst unit can be easily inserted and removed «The shaped units are conveniently contained in cages made of a metal wire mesh or expanded metal.

It should be noted that the in the invention Process used catalyst can be present at least in the partially reduced state, and that then the gas treatment container be airtight and closed to air in order to achieve the best results should as soon as the gas flow has stopped. In particular this can be done through a check valve at the exit of the treatment system be effected, which closes the outlet elastically. To increase the slide-related To be sure, a second valve of this type can be provided just downstream of the catalytic converter which is to be protected be.

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The use of fibrous catalysts has numerous Advantages. Because of the small diameter of the fiber, the mass transfer velocities are sswisches, & ©, # Main gas phase and the active surface in comparison! > <& au particulate catalysts very high. This means that very highly active catalysts are used very effectively can be used, which means the use of large amounts of space possible is «This also means that the necessary to achieve a given conversion Catalyst weight is less than it is in conventional particulate catalysts of the Pail · In addition Fibrous catalysts have shorter warm-up times. A suitable area for I & umgesohwindigkelt is between 50,000 and 300,000 et * in certain cases it has been found »that about half to 1/5 the weight of a conventional catalyst for the same result is required when getting one fibrous catalyst used. Due to the strength of the fiber, which can be increased if the are felted "especially when a binder is used, the fibrous catalyst withstands for a long time Fibrations. This is important when the gases from one Ko Ibenverb rburn araotci »come as these gases in pulses "The catalytic converter knows more appropriately Be arranged in a reactor (such as «im Exhaust manifold or in an extension of the same) d®r is firmly connected to the engine cylinder block, despite the Vlbration of the cylinder block

The processes running according to the invention are in generally not strongly exothermic · As a result, self-heating of the catalyst takes place, which for reactions as is characteristic of oxidations, not instead · Due to its low heat capacity and its

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low cliermi see conductivity, the fibrous catalyst is therefore particularly suitable for processes that under essentially non-oxidising conditions expire"

The gases. Which by the inventive method and the devices according to the invention are treated, can be any gases that contain carbon monoxide, carbon * 'is hydrogen or nitrogen oxides contained be © * The treatment of _Abgaeen} generated by combustion, and zv & T particular by combustion of hydrocarbons, such as "B * 01, natural gas and different petroleum products including gasoline, is particularly useful. The source of these gases can be any burner or any combustion device that does not itself provide a sufficiently pure combustion gas. However, the invention is particularly suitable for cleaning the exhaust gases of internal combustion engines, and was particularly for cleaning the exhaust gases of engines with spark ignition.

The invention thus applies to exhaust gases, for example Applicable to piston engines, rotary piston engines and gas turbines ·. These engines know, for example, with town gas, natural gas, liquid petroleum gas or liquid hydrocarbons, such as s * B * Berlin, jet fuel or Diesel oil can be operated. Although maintaining temperatures in the higher range for the primary Level and by monitoring or refusing to use one If the copper-based low temperature shift catalyst can be used, fuels containing sulfur or halogen impurities are preferred, use a fuel that is less than 200 ppm by weight Contains sulfur and in veeentlierte no halogen. TJm keep the active life of the catalytic converter as long as possible »

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it is also preferred. Use gasoline with a low lead content, for example less than 0 ₉ 4 g _v preferably less than 0.01 g Fb per 398 1, i.e. that ^: the gasoline should be largely unleaded *

As for contact with the fibrous catalyst non-oxidizing Conditions are required, it is preferred to run the engines with a rich mixture, in order to generate an exhaust gas which inherently contains at least 1% carbon monoxide «door gasoline engines this means that the air / fuel weight ratio is preferably not more than 15 »0 and, for example, im Range from 13 to 15 is »

Thus, according to the invention, there is also a device for .the treatment of exhaust gases from internal combustion engines proposed the method according to the invention, which has the following parts: an insulated first reactor which can be built close to the internal combustion engine and is fed from the engine outlet or the engine outlets; a second reactor disposed downstream of the first reactor; and an air supply device with which alternatively, air can be introduced upstream of the isolated reactor or between the reactors.

The alternation of the air supply can be done by an automatic starter device, by measuring the temperature of the catalytic converter or can be controlled by a switching time · The combinations of these devices' with the above Devices represent further objects of the invention

represent.

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The device can have a branch line with which exhaust gas is returned to the engine inlet can. Such a branch provides a sufficient removal of nitrogen oxides in the pail an unusual high emission or in the case of structural reasons forced catalytic reactors with low Volume safe.

According to the invention, a motor is also used in combination with the device, which in particular has internally insulated outlet openings, and proposed with a reactor, which preferably has the shape of a modified Has exhaust manifold which can be inserted into the device and contains the fibrous catalyst. ' The gases from other burners, e.g. from the combustion of heating oil, can also be used more advantageously Wise treated, among other things, to reduce their impurity content. Another application of the invention is in the removal of nitrogen oxides from waste gases from saltpeter ' acid systems. In this case the addition of a burn * gas, like s »B. of a hydrocarbon, necessary " to ensure non-oxidized conditions · Im In general, the exhaust gases will contain all gases that are necessary for the desired reactions (e.g. Steam) and which are also necessary to maintain non-oxidizing conditions, but additional ones if necessary Quantities thereof are required, then they can be injected into the gas stream or into the catalyst zone or, preferably, into the gas stream upstream of the catalyst zone The devices according to the invention can be adapted accordingly

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The conditions of contact of the gases with the catalyst can be selected by a simple experiment, whereby © i the respective gases and the respective operating conditions: s © a to consider si * d. It doesn't have to be «the Eliminate contaminants completely, but the use of one or more of the devices described above makes it possible to reduce emissions from, for example Significantly reduce automobile emissions *

The invention is illustrated in more detail by the following examples.

example 1

A sample of polycrystalline zirconia fiber containing yttria and 7% nickel oxide was prepared from an aqueous precursor solution containing the mixed chlorides and acetates of the metals. The method described in British patent application 22909/70 was used. The fibers had a mean diameter of 2 / t and were at. 1000 ° 0 has been burned. The fibers were reduced in the form of a soft mat in a stream of Hg / JITg ^feei 650 ° 0 for 15 minutes, whereupon ^! they were black. X-ray diffraction showed the presence of tetragonal zirconium oxide, nickel metal and traces of nickel oxide. The surface measured by nitrogen adsorption was 7 m / g. Approximately 1 g of the material was packed in a reactor, with a bulk density of approximately 0.2 g / is selected car · a gas which simulated the exhaust gas from an internal combustion engine was passed therethrough at 73O ⁰ O with an hourly space velocity of approximately 100,000 st. The entry

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and exit gases had the following compositions: J.

ppm weight %

NO ^ - GO ^H 2 ° 2 entry 1781 200 2.8 3.0 1.0 exit 521 2.3 2.0 below 0.1

Despite the high space velocity and the low weight of the catalyst, about 70% dee Ν0 _{χ were} removed · At higher temperatures the conversion of Η0 _χ would be even more complete, and also less ammonia would then be formed

Example 2

A sample of polycrystalline zirconium oxide fibers in the cubic phase, which contained 10% aluminum oxide and 3% cobalt metal in the form of the oxide, was prepared from an aqueous precursor solution of the mixed chlorides and acetates of the metals according to the method of British patent application 22909/70. The green or unfired fibers were first heated ^{to 200 °} C. for 15 minutes and then to 1000 ^{° C. for 10 minutes.} Then they had a sky-blue color. The fibers were ^{reduced at 650 °} C. in a mixture of H ₂ ZN ₂ , a black, soft, flexible hat being obtained. The fibers ranged in diameter from 1 to

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The reduced mat was rolled up in a biscuit roll and 0.85 g of the reduced mat was introduced into the reactor * through which it was possible to drive in öimüiieriaö .. Attfcoabgas Mndur cage. all C ₃ ), 2.5% CO _4, 2.5% H ₅ , 0.9% O ₂ and 50 ppm nitrogen oxide, which the catalyst bed passed through at a rate of 300 l / h (tree speed about 70,000 st ") · the Eintrittskoaaentration to Stickoadden of 2350 ppm was ppiä reduced to $ 20 and were formed only 111 ppm lämoniak "the percentage of nitrogen oxides was 99% reduced Mm, although the Raumgesckwindigkeit was high and the weight of the fiber was small * After trying were removed the fibers.

It was found that oils practically did not change would have.

example 3

A fiber pad of Ziroonoxidfasern in the cubic phase with an average diameter of 6 / ^ vmrde in a methanolic solution of cobalt nitrate (.5 Gev. ~%) A * gedeicht and carefully drained "After firing at 500 ⁹ C had the Faaerkieaen 6 Weight% increased. A sample of these fibers was exposed in a tea reactor to a gas stream similar to that in Example 2, but containing 3991 ppm nitrogen oxides. Die! Temperature was 77ö ^e E # 40% of the nitrogen oxides in the exhaust gas were removed.

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Example 4

100 g of a fibrous catalyst "dei" consisted of stabilized zirconium oxide and contained JTic & al as a catalyst and barium as a promoter (5% NI and 1% Ba) * was produced in the form of long, uniform strips with randomly oriented fibers. The strips had a width of 5 ob * a® thickness of approximately 0.5 cm and a bulk density of up to 0.05 g cm ™ *.

The fiber strips were evenly wound onto a cylindrical former which was 10 cm thick and 20 cm long and from a 0.0? ca thick sheet-shaped heat-resistant Nickel alloy had been made «Bar Former was perforated with circular holes 0.2 cm in diameter, so that the open area was 40%. The fiber wrap was pressed together, so that a layer thickness of 0.5 cm was obtained, through another perforated sheet covered and welded in, so that a gate direction was created, which consisted of two concentric cylinders of a perforated metal, one 0.5 cm thick Layer of compressed fibers lay in between.

The device was installed in a thermally insulated container in the exhaust system of a 4-cylinder gasoline engine with a ^{capacity of 1600 cm x 5} , which was located in a diameter meter. The device was placed close behind the exhaust manifold in such a way that the exhaust gas flows from the exhaust manifold into the central area of the device, through the fibrous catalyst in the container and through the peat bed exhaust system. The system was locked, leaving no air at any point

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dsm hot or eiatret ^ n the £ & s «rige & catalyst could, Hab ^ ecd the engine was running «The engine was with els practically ble-i £ r $ i © a Esnsia operated *

Hit this Yorriöhtimg •• would the Ie table 1 Eesultaöe received ..

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!Table 1

Engine middle Catalyst- Pressure drop Exhaust gas analysis HO stroEi-
upwards HO current
down scütfinaig—
speed rpm Brake pressure
bar bed temperature case in
catalyst
bed mbar CO electricity,
upwards Ppm by weight Ppm by weight Wt% O co 00 500 400 cn
N) 2000 1.75 500 33 3.9 > «. 1200 450 O
cn 5000 2.7 620 82 3.9 • «j 1400 600 co 4000 5.4 735 300 4.1

Example 5

65 S of a fibrous catalyst on the Baal of alumina containing 0.1% ruthenium metal "were arranged in the same manner as in Example 4. the
The device was tested in a manner similar to that in Example 4, but with a 2! Motor in the Teatstand dynamometer. "

The results are given in Table 2 *

209852/0570

gabella 2

Engine
scliwindig-
speed
TJ / min middle
Brake encLruck
bar Catalyst-
bed temperature
° c Pressure drop
case in the 1st
catalyst
bed mbar Exhaust gas analysis HO current
upwards
Wt. Ppm I. HO current
down
Ppm by weight 3000 Z ₉ Z 600 303 CO electricity
upwards 500 200 I. 5000 2.2 620 298 5.0 1000 I.
300 3000 2.1 640 298 3.1 1400 550 LJ
CO
00 3000 2.1 650 300 1.5 1550 1100 cn
NJ
^^ 4000 3.0 740 610 0.8 1500 300 ^r 0579 3.0

6th
Manufacture , e in it fibrous en ffatal ^ aatpra

Zireonoxi & ~ and aluminum oxide fibers were produced as described in the "British patent application 22909/70" In this way various solutions of polymeric basic zirconium or odoriferous salts were produced "stabilizers, salts of catalytic metals and smaller quantities of organic polymers" such as high molecular weight polyvinyl alcohol, polyethylene oxide or polyvinylpyrrolidone collected on a wire Nets or current RIBBONS "These fibers were fired at 100 dried to 150 ° C and at temperatures up to 1000 ⁰ C to produce substantially shot free fibers with diameters in the range of 1 to 4yit in the form of soft flexible blankets.

A fiber catalyst based on zirconium oxide, wie.er used in experiments 1 to 29 (Table 4) was made from the following components:

1. Solution of basic zirconium acetate

Ex Magnesium Electron Limited 22% by weight

2. Solution of rare earth chlorides Powder made from rare earth oxides Solution of rare earth nitrates

as shown in Table 4

Yttria

Ex Thorium Limited

Polyethylene oxide powder molecular weight

Ex Union Carbide Corporation 300,000

2 0 9852/0579

4. Transitional metal chlorides of analytical purity Chloroplatinic acid huthenium chloride Ex British Drug Houses limited

The rare earth oxides and the chlorides made from them contained 60% tttrium oxide. Sufficient rare earth salts or oxides were dissolved in a small excess of hydrochloric acid and mixed with the zirconium acetate solution so that the rare earth oxide content was 7% by weight, based on the zirconium oxide content, so that the finished fired fibers had a tetragonal shape. · The solutions were mixed with a solution of polyethylene oxide in order to achieve an organic polymer content of 2 (Sew · -9 »« based on the zirconium oxide content * vaaä the solutions were evaporated until a viscosity of approximately 10 poise was obtained The salts of the catalytic elements were dissolved in the form of chlorides or nitrides either before or after evaporation, so that the desired concentration of latalyaator in the fibers was obtained, as shown in Table 4. Similar solutions were thereby prepared that zirconium carbonate, ex Ifagnesium Electron Limited, was dissolved directly in ELeesslg, whereby also di e other components were added as solids * They were lase dried at 100 to 150 ⁰ C, carbonated at 35O ° C and 15 aia to 1/2 st fired at 900 ⁰ C. Some samples were fired directly at 800'C and then at 900 ⁰ C. Fibrous catalysts containing cobalt or slckel were then reduced in a 1: 5 mixture of hydrogen and nitrogen at TOO ⁰ O to produce black fibers which contained some reduced metal and of which a considerable proportion of the sulfur (present in the original Zirconium acetate as sulphate impurity) in SOm of hydrogen sulphide ent

209852/0579

had been. The zirconium oxide fibers had a surface in

Range from 0.5 to 40 m / g before use. After several weeks of use at temperatures of up to 90O ⁰ C in synthetic exhaust gases, it generally fell to 0.5 to 20 m / g. The crystallite size of the tetragonal zirconium oxide, measured by X-ray diffraction, ranged from 200 to 600 pounds with the pore volume ranged from 0.01 to 0.06 cm ^ / g *

Alumina-based fiber catalysts were made from solutions of aluminum oxychloride with an AlCl ratio of approximately 2: 1. The oxychloride solution was made by dissolving aluminum metal in hydrochloric acid, which developed vase cloth. The resulting solution was mixed with catalytic salts so that the compositions shown in Table 4 were obtained, and sufficient polyvinyl alcohol or polyvinylpyrrolidone was also dissolved so that a polymer concentration of 6% by weight based on the alumina content was obtained. The solutions were adjusted to a viscosity of 20 poise and spun by the extrusion / air wax method to produce fibers having an average diameter of 3 / *. The fibers were briefly dried and placed in an oven containing a steam atmosphere at 350.degree. After 15 minutes at 35O ° C, the fibers were fired in air for 15 minutes at 900 ⁰ C, whereby strong flexible fibers were obtained · The surfaces of the alumina "· fibers were in the range of 5 to 150 m / g. After use, the surface areas ranged generally from 40 to 70 m / g. The pore volumes were 0.01 to 0 _# OE7 cer / g · X-ray diffraction showed that the fibers produced at 800 ⁰ C were largely amorphous, but that the alumina chart, "it traces of chi Alueiniumoxid slowly with time at 600 to SOO ⁰ C or rapidly developed at 900 ^° C,

209852/0579

so that an average crystal size in the range from 50 to 200 S.

Respiratory gases

The fibrous catalysts were tested using synthetic exhaust gas mixtures, toluene * »oxygen, nitrogen and steam containing the nitrogen oxide, carbon monoxide _f hydrogen, methane. The catalysts were tested with two gas compositions ₉ which corresponded to air / fuel ratios (L / B ratios) of 13 and 14. The two L / B ratios used are defined in Table 4. Changes in the feed rate around the desired nominal value were recorded continuously during an experiment ; and the observed ranges for the various gases are given in Table 3

209852/0579

2219Λ25

table 3

β 13

component at the - Bereicli .. 1000 ppm or / *) SO 3% 900-1200 ppm GO 1.2% 3-3.6% 700 ppm 1-2% S% 2 $ 0 ppm 5ÖD-75O ppii * V% 0.25% 200-500 ppm ° 2 i3% 0.2-0.45% H ₂ O Heat i0-i3 £ Best

Tfliit / B'i'eniiisiJöijr' — V'ei'liB.'l'fei'ii 1 * 14 component area SO
ÖO nominal concentration
Or /?) 1800-240Qppm
2.0-2.3%, % 2000 ppm 0.35-0.75% 0 * 7% 400r600 ppm * 600 ppm 20Ö-5D0 ppm 200 ppm
0.25% Best Best

* la tiles 2? ε1

-2098S7 / -Q579

contraption

The test device consisted of conventional integral flow reactors «Pie analysis was carried out primarily through Gas chromatography. The nitric oxide concentrations were measured by a chemiluminescence analyzer «except in cases where a non-dispersive infrared analyzer has been used. None of the instruments showed substantial sensitivity to ammonia under the analytical conditions. So there were no errors whatsoever the presence of ammonia ia gas flow.

Nitric oxide conversion

The percent NO conversion is defined by the following expression: percent HO conversion * (Πίθ]) | _{) eec} j _l iokt "'^ * stepped out) χ 100

charged where | _NÖ] is the concentration of NO in the gas stream *

Amnon lactic electivities

The selectivity of the catalyst for the production of ammonia is indicated when the results are available stood * It is defined as follows}

Ammonia selectivity: _m D ^ l _ausgetr eten * ¹⁰ °

^^ resigned

209852/0579

Bed pack

The fibers were either packed into the reactors in the form of a highly compressed cushion (indicated by * in Tate.LIe 4) * or they were slurried in water _T, where appropriate, diluent fibers were also used. In the latter case, the fibers were mixed together with water in a liquefier which was operated for 60 to 120 seconds "The slurry was then fed into the reactor and the water was sucked off to compact the cushion"

Construction speed

The gas hourly space velocity (SGRG) is defined as the volume of gas, measured at Standardtemparatur and prints obtained by a unit volume dea in bed existing fibrous catalyst in one hour through "goes * It is assumed _# that Verdünnungsfaeern and Faaerkatalysator have the same Packungedichte «

209ÖS2 / 0S79

6ASU / ZS86Q2

CTk

VJI

VX

Trial number

(vT α *;

χα ro α

"ο

(V) (V)

Composition of the fibrous catalyst (wt # - # catalytic agent, based on the. last named component

surface according to Qe ~

A VM ©

need

(■ Ve)

fV)

8 I. Weight of the catalytic fiber (g)

II Weight of the dilution fiber (g)

ο ο ο

VH Vp 1 *

O O

Bed density

σ »

SBB

ro

ο ¹ SGHG (et * " ¹ )

«* IS

NO "conversion

vn

Net CO conversion {%)

VJI

Hydrocarbon conversion (%)

si c ©

8 8

Reaction ^{temperature (0} C)

Vji

V *

_! k _i -i VJl VJ4 PYY

L / B ratio

I I

I I

ο *

Ammonia selectivity

Table 4 continued

c te OO he SJ

<v

eat

7th
ι 3% JIi / REC / ZrO ₂ 0.5 1.455 * - 0.17 35,000 77 3 38 645 13th "M" mm 8th 3% Μ / 1% BaZl ₀ O _x /
ZrO ₂ ^{2 3} 0.5 0.500 3.5 0.27 116 230 90 3 9 670 13th 39 478+ 9 3% ffi / 1% CuZEElJZ
ZrO ₂ 4.0 4,000 0.26 14 200 91 30th 50 550 14th 25 300 10 2% Cu0Z2% V ₂ O ₅ ZHEOZ 2.4 3 _? ooo - 0.29 21 600 90 5 - 650 13th - - 11 I.
2% CuZ2% WiZRENZ
ZrO ₂ 2.286 0.15 14 500 90 70 60 680 14th 84 530 12th 3% CuZHECZZrO ₂ 4.4 4,000 0.20 10 660 95 40 550 14th 65 500 13th 0.5% RuZHEOZZrO ₂ 8.8 4,000 - - 0.21 11 500 95 20th 30th 420 14th 2.5 495 14th 1% PdZHEOZZrO ₂ 6.8 4,000 _i - 0.23 12 500 90 19th 97 710 14th > 75 495 15th 0.01% EuZEEOZZrO ₂ 4.7 4,000 - 0.20 10 940 96 9 50 542 13th 6 - 16 * 3% NiZi # CuZO, 1%
EuZEEOZZrO ₂ 4.1
I. 4,000 - 0.24 ' 12 960 93 33 38 500 14th 3.8 490

ro co

ro cn

IO

U.N. U.N.

ΙΛ VD

U.N.

O O

CVJ τ-

U.N.

κν

KN

VO ΙΛ

Sn &

UN. U.N.

T "

KN

UN UN

KN

KN ν

CO

KN V

UN Q

CVI KN

<Γ »UN O

U) ν-

IS Cv KN KN

CVJ

O ^ he » ch co

$ 'ft

CVI KN

KN

KN CV

KN

8 a

• *> · ο ο ο

KN KN

O δ

R 8

ο ο CVJ

V * ·

KN

I 'I

CVI CM

VN O

Cu Cu Ri —Π5 co

Table 4 continued

26th 3% Ρβ / 1% <3τ / ΗΙΧ5 / ΖΟ ₂ 2.5 3,220 * - 0.13 10 170 90 53 - 760 13th 81 620 27 1.9 4.00 - 0.24 12,980 94 39 - 460 13th 90 500 28 3% Ρβ / 1% ffo / HEC /
ZrO ₂ 2.6 4.00 - 0 _f 20 10 950 95 19th - 550 13th 70 500 29 3% Pe / CaO / 5% AIpO- /
ZrO ₂ ² * 1.4 4.00 - 0.20 10 730 92 49 25th 700 13th 90 500 <3
ίΙ.50 0.5% RuZAlpO » 57.6 0.310 3.690 0.23 160,000 99 35 10 400 14th 6 515 * : ■ ³¹ 0.1% HeZAl ₂ O ₅ 60.0 0.200 3,800 0.30 140,000 95 20th - 600 14th 0.6 480 P / D Hl / AXpU jr - 0.500 3,500 0.35 149,000 90 4th 20th 650 13th ■ -. «. I.
0.1% BuZ3% OVAl ₂ O ₅ 0.120 3,900 0.35 616 790 65 17th 42 684 14th 5 715 ,
34 0.1% He / 3% HiZ
Al ₂ O, 0.120 5,900 0.23 403 060 60 0 64 690 14th 2,695 H 0.120 3,900 0.25 471 420 55 4th 59 700 14th "60 700

* «Fiber packed as a pillow

REO β rare earth chlorides

REBT * rare earth nitrates

REO * rare earth oxides

+ * HDIR eel analyzer used for NO analysis

209857 / Π579

Claims (11)

Claims 1. PROCEDURE / ?, sur reduction represents amount of carbon monoxide, hydrocarbons or nitrogen oxides in gases _t characterized ,, & TSS men * the gases under substantially non-oxidizing conditions with a catalyst contact f aserigen ie rt _t of the synthetic of a refractory Fiber and a catalytic ». There is a means that promotes one or more reactions «by which at least one of the components mentioned is partially or completely destroyed. 2. The method according to claim 1, characterized in that that the gases age the fibrous catalyst at a temperature ν <? η at least 400 ° 0. 3 · The method according to claim 2, characterized in that dft! the temperature is 600 to 1000 ⁰ G * 4 * Process for the treatment of exhaust gases from internal combustion engines with a cold start phase and a running phase, thereby characterized in that the running phase is carried out according to a method of the preceding claims and that the start phase, which is before the running phase, under oxidizing Be * conditions with the addition of air in the presence of the fibrous Catalyst runs until the operating temperature of the fibrous catalyst reaches 1st 5 «Method according to one of the preceding claims, characterized in that it is in combination with a subsequent oxidation stage and / or a further reaction via a carbon monoxide shift or Hethanielerungskatalysator is carried out 209857 / Π579 6. The method according to claim 4, characterized in> that it is carried out in combination with a subsequent oxidation stage, with an air supply upstream of the fibrous catalyst during the start-up phase takes place and with an air supply between the fibrous Catalyst and the oxidation catalyst takes place during the running phase. 7 · Method according to one of the preceding claims «characterized in that the synthetic refractory Fiber consists of an inorganic oxide 8 «Method according to claim 7, characterized in that that the inorganic oxide consists of one or more of the oxides aluminum oxide, zirconium oxide, titanium dioxide or silicon oxide consists· 9. The method according to claim 7 or 8, characterized in that the refractory fiber is produced in such a way as described in one of UK patent applications 22909/70, 4369/71 and 18259/71. 10 · Method according to one of the preceding claims, characterized in that the refractory fiber has a has an average diameter of less than 20.0 11. The method according to claim 10, characterized in that the refractory fiber has an average diameter in the range from 0.5 to 5/1 « 12. Method according to one of the preceding claims, characterized in that the surface of the fibrous catalyst is greater than 0.5 » ² / g. 209852/0579 2219A25 15- »method according to claim 12, characterized in that that the surface of the fibrous catalyst is 5 to 150 m / g amounts to* 14. Method according to one of the preceding claims, characterized in that the catalytic agent from a metal of group VIII of the periodic table or from a Mixture consists of two or more of the metals mentioned " 15 * The method according to claim 14, characterized in that that the fetal is made of ruthenium, iridium, rhodium, iron, nickel or cobalt. 16 »Method according to one of the preceding claims, characterized in that it is applied to the exhaust gases of an internal combustion engine, the fuel being 200 contains up to 1000 ppm by weight of sulfur and where the catalytically Smock on the fibrous cobalt catalyst. 17 · Method according to one of the preceding claims, characterized by the fact that the amount of catalytic Mean in the fibrous catalyst 0.001 to 10 wt. =% amounts to. 18, ' method according to claim 15 «characterized in that ruthenium, iridium or rhodium is present in the fibrous catalyst in a concentration of 0.001 to 1% by weight, calculated as metal» Method according to claim 15, characterized in that that nickel or cobalt in the fibrous catalyst in a concentration of 1 to 10 wt * - $, calculated as equivalent HiO, is present. 209852/0579 20 β Combine :! onsverfahren η according to any one of claims 5 "and 6 to 19, rückbesogea to claim 5 insofar as 3ie _g are characterized ₉ that the subsequent oxidation step is performed with a Oxi & ationskatalysator consisting of a platinum group metal and in a concentration from 0.002 to 1 ₉ 0 wt * - #, based on the refractory support, is present » 21a combination method according to one of claims 5 and 6 to 19, insofar as they refer back to claim 5, characterized in that the subsequent oxidation stage is carried out with an oxidizing catalyst, that of the oxides of one or more basic metals of group VIII of the periodic table and of an oxide of Chromium or Tungsten is made " 22 * method according to one of claims 1 to 19 «thereby marked "that the catalytic agent enters the refractory fiber by dispersing or dissolving the catalytic"! By means of or a preliminary product of the same in a composition that can be processed into fibers, from which the refractory fibers are made, incorporated will. 2J method according to claim 22, characterized in that that the catalytic agent in an aqueous solution of an aluminum or suitable for fiber production Zirconium compound is dispersed or dissolved. 24 “Seaktor for the implementation of the procedure according to one of the preceding claims, characterized in that that it has a chamber for receiving the fibrous catalyst as a preformed removable unit is suitable, and that he still has a device for contacting a gas stream with the fibrous catalyst owns. 209852/0579 Apparatus for treating the exhaust gases from an internal combustion engine by a method according to one of the claims 1 to 23i characterized in that they have the following skins has an isolated first reactor «the one in the HShe an internal combustion engine are arranged and with the Engine can be charged with exhaust gases; a second reactor, which is located downstream of the first reactor; and an air inlet device with which, alternatively, before the Isolated reactor or air can be introduced between the reactors. 26 «Device according to claim 25» characterized in that it has a branch line with which a return « Lead flow from exhaust gases returned to the engine inlet can be· . 27 _a internal combustion engine, characterized in that it is combined with a device according to claim 25 or 26. 28 »Combustion engine according to claim 27, characterized in that it has internally insulated exhaust gas openings having. 29 * catalyst unit, characterized in that it consists of a preformed hasse of a fibrous catalyst that is a synthetic refractory fiber and a catalytic agent, the unit being suitably shaped to be placed in a reactor after Claim 24 or in a device according to Claim 25 or 26 can be typed in 20985? / Π579 -48- 2219A25 50 »catalyst unit according to claim 29» thereby characterized in that it is located in a cage made of a metal net or an expanded metal 209857 / Π579