SE408137B - CATALYST INCLUDING AN ELEGANT METAL SUBSTRATE MADE OF A HEAT AND OXIDATION RESISTANT IRON ALLOY - Google Patents

Abstract

Catalysts and catalytic structures are provided comprising a substrate, an intermediate oxide layer and a catalytic layer. For example, the catalyst may comprise: (a) a metal substrate made from a heat and oxidation resistant alloy of iron including chromium (3-40) wt. %, aluminum (trace - 10) wt. %, cobalt (0 - 5.0) wt. %, nickel (trace 72) wt. % and carbon (0 - 0.5) wt. %, balance essentially iron, the metal substrate being extended on an assembly of at least two juxtaposed sheets made from the alloy with at least one sheet shaped so that when contacted with an adjacent sheet channels are formed therebetween for the passage of gaseous reactants through the substrate; (b) an aluminum oxide film on the surface of the extended metal substrate, the film being formed by oxidizing the surface of the metal substrate; (c) a high surface area aluminum coating disposed over the aluminum oxide film and keyed to the substrate through the film; and (d) a catalytic layer comprising at least one metal selected from the group consisting of ruthenium, rhodium, palladium, iridium, platinum, silver, gold, and alloys of at least one of such metals with at least one additional element comprising a base metal selected from the group consisting of aluminum, magnesium, chromium, molybdenum, tungsten, manganese, iron, rhenium, cobalt, titanium, vanadium, copper, zinc, cadmium, indium, thorium, bismuth, tin, lead, antimony, a lanthanide or an actinide, the base metal being present in an amount from a trace to 25 wt. % on the high surface area alumina coating. Such catalysts have been found to be useful for a wide variety of catalytic reactions, e.g. the catalytic oxidation of ammonia in the manufacture of nitric acid and the catalytic oxidation of organic compounds.

Description

'? cl | 13242 ~ 4 whereby the nitrogen oxides are reacted with a gaseous reducing fuel. It is essential that the catalyst used be very active, exhibit the least possible gas flow resistance and achieve reaction catalysis at low initial reaction or initial temperature. However, the catalyst itself must be sufficiently high, for example 750-80,000 temperature stability. An object of the invention is to provide improved catalysts and catalyst devices, for such processes, which can replace those currently used.

Control of air pollutants by catalytic combustion poses major problems with respect to the type of catalyst used. In addition to the requirement that the catalyst be active at low temperatures, it must be stable under both oxidizing and reducing conditions. Furthermore, when the catalyst is packed in a reactor, it must cause a very low pressure drop across the bed and must be abrasion resistant, be able to withstand thermal and mechanical stresses and not be blocked by dust particles.

Such a catalyst comprises an elongate metal substrate, made of a heat and oxidation resistant iron alloy, on which metal substrate is applied a coating and a catalytic layer, consisting of an alloy containing at least one metal, selected from the group consisting of ruthenium, rhodium, palladium, iridium, platinum, silver and gold. The iron alloy consists of 3-40% by weight of chromium, 1-10% by weight of aluminum, trace-5% by weight of cobalt, trace-72% by weight of nickel, trace-0.5% by weight of carbon and the remainder iron. The coating, which contains acid, consists of alumina, phosphates or nitrates.

Preferably, a maximum of 10% by weight and preferably not more than 3 or 5% by weight of the iron alloy consists of one or more of the additive elements silicon, manganese, zirconium, copper, tungsten, vanadium, molybdenum, cerium, niobium, tantalum and titanium. A special catalyst according to the invention consists of an elongate metal substrate, containing 3-NO% by weight of chromium, 1-10% by weight of aluminum, trace amounts up to 3% by weight of one or more of the mentioned additional elements and in addition to impurities in the iron residues, the second catalytic layer comprising a metal selected from the group consisting of ruthenium, rhodium, palladium, iridium, platinum, silver, gold, an alloy containing at least one of these metals and alloys containing at least 10 % by weight of one of the metals mentioned. According to the invention there is further provided a catalyst, consisting of an elongate metal substrate of a heat-resistant alloy, having a total nickel and / or chromium content, exceeding 20% by weight, which heat-resistant alloy has relatively high mechanical strength and thermal conductivity. a first layer of the elongate metal substrate, comprising an adhesive coating containing oxygen and a second layer applied to the first layer, comprising a metal selected from the group consisting of ruthenium, rhodium, palladium, iridium, platinum, silver, gold, an alloy containing at least one of these metals and alloys containing at least 10% by weight of one of these metals.

The second catalytic layer comprises one or more of the platinum group metals mentioned above, or an alloy containing at least one of these platinum group metals, applied to the oxide coating or film and precipitation may take place in such a form that catalytic activity is obtained or it may be made catalytic. active by subsequent treatment. Catalytic bodies according to the invention are extremely robust and active under specified reaction conditions.

It has further been found that in certain reaction environments, for example when purifying combustion gases from cars, a metal substrate will cause the catalyst to reach operating temperature much faster and thereby become significantly more efficient than conventional catalysts, for example those which are constructed on ceramic substrates.

In the following, the term "elongate metal substrate" refers to a metal substrate which has been mechanically deformed in such a way that, in comparison with an ordinary undeformed substrate, it has a considerably increased surface area. This increased surface area can be achieved, for example, by corrugating or folding in a molding machine and then winding a flat foil and a corrugated foil together to form a tube with a helical cross-section.

In a preferred embodiment of the invention, the metallic substrates used in the catalyst body are first shrunk, corrugated, folded, punched and / or perforated in such a way that a much increased surface area is obtained. Such a surface area is normally considerably larger than that obtained with honeycomb-type ceramic bodies or when granular catalyst material is supported within the same given volume. An example of a metallic substrate according to the invention, consisting of a roll of a corrugated sheet of a heat-resistant alloy with a spacer of a non-corrugated sheet of such an alloy is shown in the attached figure. Alternatively, two corrugated sheets or sheets can be used with the corrugations parallel to each other or forming an angle with each other. A coated substrate is then obtained with a good adhesive oxide layer which is porous and absorbent and has a large surface area and which acts as a support for the second catalytically active layer containing one or more of the platinum group metals described herein. defined.

The heat-resistant alloys for the metal substrate preferably consist of alloys with a minimum amount of nickel plus chromium of 20% by weight. Typical alloys which can thus be used for the elongate metal substrate are stainless steels with a high nickel and chromium content and commercial products of the type "INCONEL 60W'0dh" INCONEL 601 ".

Preferably, a metal substrate is provided with a first, highly adhesive oxide coating in a two-step process. In the first step, the metallic substrate is thermally oxidized to form a thin first oxide layer, which acts as a bonding layer. Preferably, the heat oxidation is performed by keeping the preformed metal substrate at 1000-1200 ° C in air or cracked ammonia vapor for one hour. The higher temperature '1413242-4 is required for very oxidation-resistant alloys, such as Kanthal, for example, and the humid hydrogen atmosphere is preferred in connection with alloys with a high nickel content.

The adhesive, oxygen-containing film or oxide film can be provided by any of a variety of known methods, including chemical treatment. The film must be of sufficient thickness to provide adequate absorption capacity to retain the catalytically active alloy comprising one or more of the platinum group metals. The film preferably has a thickness of 0.1-0.025 mm.

When aluminum is present in the alloy used for the elongate metal substrate, the oxide film can be obtained by surface treating the substrate with a solution of an alkaline carbonate, usually a sodium carbonate chromate solution. The film can be produced by anode oxidation of the metal surface, the metal forming the anode in an electrolytic solution. When anodizing aluminum-containing surfaces, 15% sulfuric acid solution is usually used as the electrolyte, but other acidic electrolytes, such as, for example, chromic acid, oxalic acid, phosphoric acid and in some cases boric acid can be used. The oxide film of the invention is applied at any location and does not include the relatively thin natural oxide film which in some cases appears on metal surfaces exposed to the atmosphere.

One way of forming an alumina layer on such alloys, which do not contain enough aluminum to form alumina layers themselves during oxidation, is to use the process known as "CALORISIHG". This includes evaporation of an aluminum coating, accompanied by anodizing or heating in an oxygen-containing gas. Other coatings, such as chromate, phosphate, silicon or silicate or zirconium, can all be precipitated by known methods. The large number of different methods available for producing a thin coating of a catalytically active, heat-resistant metal oxide with a large surface area, containing one or more of the high-strength metal oxides which are particularly good with respect to aging and which are inert as well as the platinum group metals at high temperatures and under oxidizing and reducing conditions, are well known in the art and need not be further discussed here.

A preferred adhesive oxide coating on the metal substrate is alumina. a_vu1z242-4 A method of precipitating aqueous alumina is described in U.S. Pat. No. 2 NO6 H2O. Any suitable aluminum composition, such as, for example, alkali metal aluminates and aluminum salts, can be used as the starting material.

Either acidic or basic precipitants are used depending on the nature of the starting material. Suitable acidic precipitants are ammonium chloride, ammonium sulphate, ammonium nitrate, hydrochloric acid, nitric acid, etc. Suitable basic precipitants are ammonium hydroxide, sodium hydroxide, hexamethylenetetramine, etc. In a method of precipitating the aqueous alumina from an alkali metal aluminum and alkali metal hydroxide directly on the elongate metal substrate. If the aluminate solution is kept at a temperature of 60-85 ° C, a film or coating of alpha alumina trihydrate (Gibbsite) precipitates. Upon subsequent heating to 15 DEG-180 DEG C., the trihydrate is converted to monohydrate and subsequent heating to 5 DEG C. causes the monohydrate to be converted to gamma alumina without losing the very large surface area coating which is produced. The large surface area is obtained by the formation of hexagonal crystal aggregates with an approximate size of 8x8x20 microns. Micropores with a size of NOA diameter are present in the hexagonal crystal aggregates, but do not appear to play a role in the catalytic activity of the body. The large surface area is illustrated (Example 12) by the resistance to lead and phosphorus poisoning after precipitation of the catalytic metal.

The heat and oxidation resistant alloys that form the metal substrate of the invention include alloys of iron, chromium and aluminum, with cobalt, nickel and carbon being preferably present. The ranges in which each element may be present in the alloys, excluding trace elements and impurities, are as follows: _ 1% by weight Cr '_ - 3 - 30 A1 1' - io C Û ~ 0,5 A Co 0 ~ _5, Preferred ranges for the mentioned elements are: 7410242-'4 7% by weight Cr 13 - 24 Al _ 3.5 - 6.5 C 0 - 0.1 Co 0.2 - 0 , 8 Ni 0 - 5.0 Fe Rest Typical amounts of trace elements, which may be present in the alloy to improve the strength, oxidation and heat resistance ~ sen are: weight percentage si 0.2 ~ 0.9 Mn 0.2 - 0.7 zr 0.01 - 0.20 Cu 0.01 - 0.15 Nb 0.01 ~ 0.3 Ta 0.8 - 1.2 Ti 0.0 - 1.2 Co 0.01 - 1.0 Ca 0, 01 - 0.5 C 0.01 - 0.1 Specific heat and oxidation resistant alloys suitable for use in the invention are set forth in the following examples.

Exemgel 1 "KANTHAL D" (A commercial product, manufactured by the Swedish company Kanthal): 7% by weight C 0.09 Cr 22.60 Co 2.0 Al 0.5 Fe _ Rest Exemgel 2 "MEGAPYR" (Registered trademark , manufactured by Telcon Metals Ltd, England): Cr - 30 Fe 65 A1 5 .7u13242-4 8 Example gel 3 Stainless steel 316, an austenitic stainless steel standard: _ weight percentage C 0.08 cr ~ 10.00 Ni 10, 00 Ti 0 I 0, H0 Fe. Residue Example H The following alloys are manufactured by the Swedish company Kanthal: weight percentage cr 10 - 00 A1 1 - 9 Fe 51 - 00,0 Ta “0,1 - 5 co 0,01 - 1 Above can Ta be partially replaced with Ti and Ce can partially replaced by Approx.

In addition, the following substances may be included to improve the mechanical strength and oxidation resistance of the alloys: weight percentage Mn 0 - 2 Si 0 - 2 C 0 ~ 0,5 Co O - S Nb 0 - 2 Mo 0 - 1, 5 Th 0 - 0, 2 Zr 0.01 - 1 and P and S may be present as impurities.

Examples in this range are as follows: I. weight percentage CP 20 - 30 A1 3.5 - 0 Ta 2.5 ce 5 0.15 Fe Residue 741321424: 9 II. - weight percent Cr 20 - 30 _ Al Å 3.5 - 6 (or Al 2.5) Take 0.1 Ce 0.1 Co 0.1 - 5 Fe Residue III. ï weight percent Cr 3.5 - H Al 5 - 9 Nb 1.5 Zr 0.15 Ta 0.1 - 5 Fe Residue IV. weight percentage Cr 10 - 15 Al 3 - 5.5 Mo Th 0.1 Ta 0.1 - s ce 0.01 - 1 'Fe Rest Exemgel 5 "IMMACULATE S" (Registered trademark). The alloy is sold by Firth Vickers Ltd, England. weight percent Cr 23.0 Ni _21.0 C 0.1 Fe _ Residual Q Example gel 6 "INCONEL 600" (Registered trademark). A product marketed by Henry Wiggin Ltd, England. weight percentage Ni not less than 72.00 C not more than 0,15 Mn not more than 1,00 ', 741324241 weight percentage Fe 8,00 S not more than 0,015 Si not more than 0,50 Cu not more than 0,50 cr 15.50 "INCONEL 601" weight percent Reach '0 4 60.50 Cr 23.00 Fe lU, l0 A1 1.35' Mn not more than 0.50 Cu not more than 0.25 Si not more than 0.25 not more than 0,50 S not more than 0,007 Exemgel 7 "INCONLEY 800", a product marketed by Henry Wiggin Ltd, England. weight percentage Ni 32.50 C not more than 0.10 Mn not more than 1.50 S not more than 0.15 Cu not more than 0.75 cr not more than 1.00 Fe Rest Exemgel 8 "BRIGHTRAY S", a product marketed by Henry wiggin Ltd, England. weight percentage cr 20.0 Fe 1.0 Si not more than 1.0 Mn not more than 0.4 C not more than 0.1 Ni Residue Stainless Cr Ni C Mn Si Fe Stainless England.

Cr Ni C Mn Si Fe Stainless Cr Ni C Mn Si Ti Fe “APMCO Cr Al Ti Si C Fe i 7lß132l42 ~ 4 ll Exemgel 9 steel 309. weight percentage 22 - 20 12 - 15 not more than 0.2 not more than 2, No more than 1.0 Residue Exemgel 10 steel 310, marketed by British Steel Corporation, weight percentage - 26 (preferably 25) - 22 "20 not more than 0.25" 0.1 not more than 2.0 "1.8 not more than 2,0 "1,5 Rest Rest Exemgel ll Steel 321. weight percentage 17 - 19 U - 12 0,8 not more than 2,0 not more than 1,0 not more than 0, u Rest Exemgel 12 l8SR" , marketed by Armco Corporation, England, weight percent 18 2 0.0 1 _ 0.05 Pest Generally, the Fe-Cr-Al system contains very few ferric steels, which contain less than 12-12.5 weight percent chromium and The aluminum content of alloys which are satisfactory according to the invention is hardly outside the range of 1-6% by weight.

The metal substrate according to the invention is deformed so that it has a large surface area for the vapor phase reactants whose reaction is to be catalyzed. This can be achieved, for example, by first producing the alloy in thin sheet form by rolling, a subsequent corrugation by means of grooved rollers, coil winding of the corrugated sheet into a round screen body, the openings of which correspond to the groove depths in the corrugated sheet. The two sheets can be wound at the same time, one sheet being corrugated and the other flat or corrugated to another shape in comparison with the first-mentioned sheet or the corrugations on the two sheets can be equal and furthermore the corrugations in the respective sheets can form an angle with each other. When a flat and a corrugated strip sheet are used, the leading edges of the sheets are spot welded to each other and strips of a certain length are fed into a device which rolls the strips between three rolls, so that a spirally wound substantially annular body according to the accompanying figure is obtained. .

Elongated metal substrates according to the invention have one and a half to three times greater ratio between surface and volume, than ceramic substrates of honeycomb type. For the normal ceramic substrate, the ratio is 19.7-23.0 cm2 / cma. Examples are commercial products of the type EX 20 (Corning), which has a ratio of 18.9 cm2 / cm3 and Grace 400 which has a ratio of 25.6.

This ratio is the highest reached so far and should be compared with 36.2 for a 0.076 mm thick sheet of Kanthal D and 65.7 cm2 / cm3 for a 0.051 mm thick sheet of Kanthal D.

Preferably, sheets or foils having a thickness between 0.038 and 0.114 mm and preferably a thickness of 0.051 mm are used, which are corrugated and assembled to form a body of about 62 cells per cm 2, calculated on the cross-sectional area. A preferred range is 31-124 cells per cm 2. Suitable area / volume ratios are 39.1 H cm 2 / cm with 62 cells per cm 2 and 65.7 cm 2 / cm with 12 H cells per cm 2.

An alternative way of designing the body or module is to spot weld the two strips or foils on a stainless steel pipe with an outer diameter of, for example, 6.35 mm, which facilitates the winding and formation of the body.

According to another method, the two strips are spot-welded, which are to be wound up along the leading edges at the same time and then wound up in a hollow, cone-shaped shape. after which, with the aid of friction rollers and sliding means in the cone, the strip is wound up and pressed into a sleeve or a casing in one and the same operation.

When a sleeve or casing is not used, it is desirable to weld successive corrugations on the module by applying one or more radially extending welding strands to the ends of the body. Other ways of securing the successive winding turns or at least the outermost winding turns are by nailing or welding to prevent the spiral from being wound up. After shaping the bodies into finished units, they are preferably cleaned before the adhesive layer containing the oxygen or coating is applied, and this cleaning is preferably carried out by means of a steam degreasing technique with a halogen containing a solvent such as trichlorethylene, after which rinsing in acetone takes place and then drying. Example 13 Gibbsite was precipitated on Kanthal D thermally oxidized modules of the type shown in the accompanying figure by contact with sodium aluminate solution, which contained excess aluminum and caustic soda and had a temperature of 80 ° C. After heating, the thin metal film was found to consist of virtually pure gamma alumina.

The metal coating was metallized with a 7% Rh / Pt alloy using prior art to provide a metal coating of 1 g / dm 3 thickness, based on the entire catalyst body.

Such a device has been found to better tolerate poisoning in metal-coated ceramic and non-metal-coated metallic substrates.

This is illustrated by results obtained from simulated lead and phosphorus tests on catalyst devices with metal and ceramic substrates: a. Simulated lead poisoning tests The exhaust gas contained: Hydrocarbons 1000 ppm co 2,596 NOX 1000 ppm Pb 0.5 g / hour ~ Residual N2 Metal coating: 2 gamma-alumina Metallised with: 7,5% 'Rh / Pt in 14132u2-4 p 5 9 1 14 Subsïräï U fl dermeïäll- Metal conversion Hydrocarbon conversion, working capacity V g / cm g / dm 1 hour 3 hours 7 hours Kanfhal D 0,193 1,059 79% ss% 's2% Kanthal D 0,090 1,059 7U% 63% 156% Kanrhal D o, ous 0 1,059 67% ue% 36% Keramiskt _> I Ex 20 0, l22 1,059 56-75% 40- 54% 27-39% (Corning) b. Simulated experiments with phosphorus Sub-metal coating: gamma-alumina Metallized with: 7.5% Rh / Pt Substrate Sub-metal- Metal conversion Hydrogen conversion, coating capacity cm gl g / dm l hour 3 hours 7 hours Edge Hall D 0.153 1.059 98% 97.5% 97% Edge Hall D 0.110 1.059 96.5% 95.0% 93% Ceramic Ex 20 0.12 2,059 85% 76,5% 59% (Corníng) Instead of lead, the exhaust gases contained 1000 ppm lead in the form of 1% tributylphosphate toluene in air at the rate leo ooo h'l, A submetallic coating in the range 5-30% by weight of the monolithic monolithic substrate is preferred. A suitable Al2O3 coating on Kanthal D and 62 cells per cm2 is 10% by weight.

The surface area of the alumina is 50-500 m2 per gram of alumina. The aluminate method described above for precipitating alumina gives a surface area between 120 and 160 m2 per gram of alumina.

Another suitable method of precipitating an adhesive alumina layer on the metallic substrate is to use a slurry of preactivated Gibbsite (alumina trihydrate) and an alumina monohydrate having a ratio of solids 74132424; substances and liquid between 25 and 50% and a pH below 7, which slurry is used to impregnate the preformed metal substrate, which is dipped. The exact concentration of slurry used is determined by experiment and should be sufficient to provide an alumina coating of the required thickness. The substrate is then allowed to dry in hot air and then heated for two hours at a temperature of H50 ° C to form chi and gamma alumina, which forms an adhesive coating with a thickness of up to 0.05l mm on the metallic substrate. . Crystal aggregates with a diameter of 3-7 microns are formed and have micropores of approximately the same size, ie a diameter of about H0 angstroms.

An additional, alternative way to provide a coating of an adhesive alumina layer on the metal substrate is to use an alpha-aluminum monohydrate slurry. After heating to 450 ° C, gamma alumina is formed with a surface area between 180 and 300 m2 per gram. Gamma alumina is added to alpha alumina nonohydrate in the slurry step and before heating to give a thixotropic mixture.

Crystals or crystal aggregates with a diameter of 20-100 angstroms are formed. The micropore diameters are still at H0 steam current.

Suitable alumina trihydrates (Gibbsite) are "FRF 80", marketed by British Aluminum Chemicals Ltd, and "C 333", marketed by Aluminum Corp. of America. Suitable alumina monohydrates (Boehmite) are "Sol-Gel Alumina", supplied by the United Kingdom Atomic Energy Authority. "Dispal M" supplied by Conooo and "Condea F" supplied by Condea Group are also suitable. Gibbsite is added to "Sol-Gel Alumina" (which is a microcrystalline Boehmite) in the slurrying step to form a thixotropic mixture. .

In addition, one or more of the oxides titanium oxide, zirconia, hafnium oxide and thorium oxide may be present in the alumina to provide further stabilization of the intermediate oxide layer, as described in our British Patent Applications Nos. 28 283/71 and 28 Slß / 71. If desired, rare earth oxides, alkaline earth metal oxides and alkali metal oxides can be used.

Many of the aluminum-containing metal substrates of the invention have the property of oxidizing "inwardly". This means that a factor which contributes to the advantageous properties obtained according to the invention is that the elongate metal substrate as such, which forms part of the catalyst body, has a tendency to oxidize under very strong oxidation conditions. in such a way that the first layer of adhesive oxide film has no tendency to grow over or cover the outer layer of the alloy containing platinum group metal, silver or gold.

Impregnation or precipitation of platinum group metal alloy, silver and gold alloy and optionally a base metal on the first, oxygen-containing, adhesive layer can be accomplished by methods known per se for precipitating catalytically active metals on metal coatings or other supports, i.e. if a strong metal oxide with a high surface area constitutes the adhesive, oxygen-containing layer, the support or substrate can be dipped in a solution of an inorganic or several inorganic salts of platinum group metals, for example platinum, rhodium and nickel. In that case, chloroplatinic acid, rhodium trichloride and nickel chloride were used.

Preferably, the outermost layer consists of catalytic metal of platinum group metals or alloys of platinum group metals, alloyed together or with base metals. Particularly preferred combinations are 7.5% Rh / Pt for catalysts used for car exhaust, 10% Rh / Pt for oxidation of ammonium and -50% Rh / Pt for NOX treatment, ie reduction of nitrogen oxides with a gaseous reducing fuel in nitric acid gas .

Particularly preferred alloys of platinum, rhodium and a base metal, which according to the invention are suitable for the outer catalytic metal alloy layer, are alloys containing: weight percent m1 1 - so Base metal 0.01 - 25 Pt Residue, the base metal being selected from the group consisting of Al, Mg, ~ Cr, Mo, W, Mn, Fe, Co, Ni, Ti, V, Th, U, Cu, Ag, Zn, Cd, Hg, In, Tl, Bi, Sn, Pb, the lanthanides and actinides. This combination is useful for oxidation and reducing reactions and also for steam reforming of naphtha and naphtha distillates.

However, the above-mentioned base metals are also useful together with other platinum group metal alloys and also in catalysts according to the invention, in which the outermost catalytic metal layer contains silver or gold. Ruthenium is suitable for the decomposition of NOX in connection with the purification of car exhaust gases.

Example 14 A 76 mm wide piece of Kanthal D with a thickness of 0.076 mm had 50,000 corrugations formed by the method described above and was wound in a spiral shape. The body was oxidized for one hour at 120 ° C to form an alumina layer which adhered to the substrate. Thereafter, a 7.5% percent rhodium-platinum alloy was precipitated on the alumina and the catalyst body was subjected to oxidation tests in car exhaust gases with a space velocity of 80,000 h_l. The hydrocarbon conversion was initially 73% and after 100 hours 66%. The initial temperature was 265 ° C and after 100 hours a2o ° c.

Example 15 A corrugated spiral body as above, made of a 1 mm wide piece of stainless steel 321 was calorized to form an aluminum coating, which was then oxidized for one hour at a temperature of 100 ° C and the thickness of the coating was 0.88 g / dm 3 and of 7.5% rhodium-platinum, which was applied to the oxide-coated substrate. When using a space velocity of zuo ooo h "1 The hydrocarbon conversion was initially 72%, after 24 hours the following results were obtained: 77%, the initial temperature was 23000 and after QU hours 29000.

Example 16 A 25 mm wide piece of 316 stainless steel was calorized and oxidized for 1 hour at 1200 ° C with the same amount of rhodium-platinum alloy and space velocity as in Example 14, giving the following results: The hydrocarbon conversion was 76% from the beginning, the initial temperature was l95 ° C and after 24 hours the temperature was 290 ° C.

Example 17 I A 0.051 mm thick stainless steel foil 310SS and an equally thick foil of Kanthal D were used to make two cylindrical bodies with a length of 76 mm and a diameter of 51 mm and with 22 H cells per cm 2. An alumina coating with a very large surface area was precipitated on both by the aluminate method described above and 1.1 g per dm 3 of platinum was applied to the alumina layer by a technique known per se.

Both units were then tested on an engine, which was powered by low-lead fuel in accordance with the specifications set by the Environmental Protection Agency of the United States.

Hydrocarbon conversion Carbon monoxide conversion Kanfhal D 9 9 (100 hours) gÜ ° 8 ° 99 ”2 ° 3 OSS 0 U (200 hours) 79 ° uü 9Û ° 3 fi Example 18 This example compares a ceramic monolith with a Kanthal D body, both of which have a strong coating of FRF 80 / Sol-Gel alumina and a catalytic layer of 100% platinum and also includes a Kanthal D body with a strong coating of hydrolytic alumina (the aluminate method) and with a catalytic layer of 100% platinum .

Aluminum- Dimensions Effective Effective coating cm area cm volume cm Ceramic FRF MUS0l ~ l0,2xl5,2 71.6 1088 body Gel Al203 Edge Hall D "" 69.3 1060 Edge Hall D HWmolyti§ <_ "73.5 1090 alumina ~ Results Results refers to a car engine under different operating conditions.

I Hydrocarbon conversion Carbon monoxide conversion Û h 100 h 200 h 300 h 0 h 100 h 200 h 300 h Ceramic + FRF 80 / Sol- 92.9 76.5 77.0 75.1 96.1 89.7 9H .6 98.2 Gel Kanthal D 0 + FRF 80 / Sol- 87.8 71.8 75.3 63.0 88.5 90.5 79.5 80.0 Gel Kanthal D _ * hYd ”° lYtiSk 92 3 79.3 80, 2 75.0 g9s, u 87.6 91.1 90.0 alumina 7413242-ë 19 These results show that the metal substrates are completely comparable with ceramic substrates from both a functional and a stability point of view.

Claims (8)

1. 'llr132lr2-lo 20 2. A catalyst comprising an elongate metal substrate made of a heat and oxidation resistant iron alloy, to which metal substrate is applied a coating and a catalytic layer, consisting of an alloy containing at least one metal selected from the group consisting of ruthenium , rhodium, palladium, iridium, platinum, silver and gold, characterized in that the iron alloy consists of 3. -H0% by weight of chromium, 1-10% by weight of aluminum, trace - 5% by weight of cobalt, trace - 72% by weight of nickel, trace - 0.5% by weight of carbon and the rest iron and that the coating consists of alumina, phosphates or nitrates. Catalyst according to Claim 1, characterized in that the catalytic layer contains, in addition to the metals mentioned, the addition of bismuth, antimony, aluminum, magnesium, chromium, tungsten, manganese, iron, rhenium, cobalt, titanium, vanadium, copper, , cadmium, indium, thorium, tin, lead, a lanthanide or an actinide. Catalyst according to claim 1, characterized in that said additive amounts to a maximum of 25% by weight. Catalyst according to claim 1, characterized in that the iron alloy consists of 13-24% by weight of chromium, 3, 5. -6.5% by weight of aluminum, 0.2-0.8% by weight of cobalt, trace - 5% by weight of nickel, trace - 0.1% by weight of carbon and the remainder iron. Catalyst according to Claim 1, characterized in that the catalytic layer consists of 7.5% by weight of Rh / Pt alloy. Catalyst according to Claim 1, characterized in that the catalytic layer consists of 10% by weight of Rh / Pt alloy. _ _ vß1z2 # 2-4 21 Catalyst according to Claim 1, characterized in that the catalytic layer consists of 20-50% by weight of Rh / Pt alloy. Catalyst according to any one of claims 1 to 7, characterized in that the substrate consists of a plurality of thin foils applied to each other and of which at least every other V is corrugated. Catalyst according to claim 8, characterized in that Catalyst according to Claim 8 or 9, characterized in that the foils have a thickness of 0.03. 8. -0, 11H mm. ll. Catalyst according to Claim 9, characterized in that the cells formed by the corrugations have a size corresponding to 31-12% of cells / cm 2 measured perpendicular to the corrugations. PROMISED PUBLICATIONS: Sweden patent application 10 617/74, 400 713 (B01J 37/00) US 3,410,651 (423-213), 3,437,605 (252-463)