SE426786B - Method for production of a carried catalyst, which is effective for spontaneous decomposition of hydrazine - Google Patents

Abstract

The invention concerns a method for production of a catalyst, which is effective for spontaneous decomposition of hydrazine, during which a) into the pores of a carrier which has a pore volume of at least 0.1 cm<3>/g and a specific surface area expressed in m<2>/g that is equal to 195, Cp + 0.013 + 0.736 Vp, where Cp is the specific heat of the carrier at approximately 25 degrees C, expressed in cal/g, and Vp is the pore volume of the carrier, expressed in cm<3>/g, is introduced a solution of a salt containing iridium salts or mixtures of salts of iridium and ruthenium, which salt undergoes decomposition at a temperature in excess of 450 degrees C, wherein the solution contains said salt in a quantity of between around 0.02 and around 0.6 gram-atoms of metal per litre and has a pH of approximately 0.5 to approximately 4, b) the solution-containing carrier is dried to precipitate the salt in its pores, c) the carrier is then heated in order to break down the precipitated salt, d) the pores of the carrier are again impregnated with said salt solution, e) the carrier is again dried and the salt is caused to decompose, f) the impregnation of the carrier with the salt, the drying of the reimpregnated carrier and the breakdown of the precipitated salt are repeated at least seven times until the catalyst contains around 20 wt.percent to around 40 wt.percent of said metal, and g) the catalyst is heated in a hydrogen gas stream at a temperature between around 200 and around 500 degrees C to convert the products of decomposition of the precipitated salt into catalytically active metal. According to a preferred embodiment of the method, the carrier consists of beads of aluminium oxide and the beads are immersed in an ammonia solution of an iridium salt, after which the above-mentioned steps b)-g) are carried out.

Description

In the order of 1093 ° C, which often occurs with decomposition of hydrazine. It must have adequate physical strength to withstand the treatment of rocket applications and should be useful after about a year in space. These are essential requirements which are not at all met in the case of hydrazine decomposition catalysts prepared by conventional, prior art methods.

An important object of the present invention is to provide a catalyst which meets the above requirements in the decomposition of hydrazine and substituted hydrazines, which are collectively referred to below as hydrazines. Since hydrazi is a relatively stable chemical compound that can be stored in unventilated containers for long periods of time, a highly active catalyst is necessary for spontaneous ignition at the high flow rates thereof used in rocket engines. Furthermore, since the temperature reached by the decomposition of hydrazine is high relative to the temperature in normal catalytic processes, the catalyst must exhibit exceptional stability if it is to have the capacity for many restarts. The new catalysts meet these requirements and have a long effective life as spontaneous catalysts for decomposition of hydrazines, a spontaneous catalyst being one which initiates and maintains decomposition of hydrazines when they are introduced into the catalyst at the high speeds used. in rocket engines and in gas generation chambers. Further advantages of the new catalysts appear from the following description of the invention, in which certain suitable catalysts are illustrated by representative examples, which are not intended to limit the scope of the invention.

It has been found that a particular type of iridium metal catalyst, which is precipitated in a particular manner and in a critical, high concentration on a particular form of support, has a unique combination of properties which make it meet the above exact requirements of high activity and good stability required for an improved catalyst for decomposition of hydrazines. The new catalysts have as an important component a support, which has a specific surface area, SS, expressed in m2 / g, which is determined by the equation> SS__ l95 (Cp + 0.013 + 0.736Vp) where C is the specific heat for the support at approx. 2506, expressed in cal / g degree (ÛÖ), and VP is the pore volume, expressed in cm3 / g. The CEO should not be less than 0.1. With a support of this kind, not only will there be a proper pore volume for applying the required amount of catalytic metal required in the new catalysts without the pores being constrained to interfere with the contact of the hydrazines with the catalytic metal, but the there will also be a desirable average temperature increase of at least 20 ° C based on the amount of heat present when wetting the porous catalyst volume when the pores are filled with liquid hydrazine at the start time. With the new catalysts prepared with supports of this kind, a smooth, spontaneous decomposition of hydrazines is obtained even under unfavorable starting conditions. Iridium has excellent advantages as the catalytic metal in the new catalysts, not only when used as the sole catalytic metal, but also in its particularly effective combinations with ruthenium. In these combinations, it is desirable to use from about 30 to 80 atom ~% iridium in the mixture with ruthenium. In order for the catalyst to have the desired high activity for spontaneous! decomposition of hydrazines, it is necessary that iridium or a mixture of iridium and ruthenium be present in an amount of between 20% and about 40% by weight of the final catalyst. This metal must be properly dispersed on the surface of the support if the catalyst is to have the stability which allows the successful use of the new catalysts for many successive starts. The metal or metals must be precipitated as spaced apart particles at a sufficient distance from each other so that they do not sinter or fuse together at the high temperatures obtained by decomposition of hydrazines. Most desirably, the catalytic metal is uniformly distributed over the surface of the support as particles having a diameter of from about 10 to about 100 Å, which are spaced apart by an average distance of from about 20 Å to about 200 Å. most preferably, the catalytic metal is present as particles having an approximate diameter of 20 Å, and spaced apart by an approximate distance of 50 Å. the pore walls.

The required distribution of the catalytic metal cannot be obtained by conventional catalyst preparation methods. It is necessary to use special methods which avoid the more or less uniform, continuous coating of catalyst supports with metal, which would take place if known methods for the preparation of catalysts intended for decomposition of hydrazines were used. It is necessary to diffuse the required amount of the indicated metal or mixture of metals deep into the pores of the selected support, and then build up from the depth an increasing concentration of the metal or metals until the concentration is fairly substantial in the outer portion of the carrier, in particular the peripheral outer portion (skin portion), with a thickness of about 0.5 nn, of the carrier particles. The carrier, which is advantageously in the form of spheres or cylindrical pellets (spheres), although other shapes are suitable, should not contain so much metal in this "skin portion" that the metal unduly interferes with the penetration of the hydrazines to be decomposed. It is likely that the first part of the hydrazine deposition takes place in the skin portion of the sphere, whereby for example this outer portion may have a thickness of 0.1-1.5 nm. The penetrated net metal (or metals) probably serves two purposes: (l) it facilitates heat transfer through the ball and thus reduces the sudden heat shock on the insulated carrier; oth (2) continues to catalyze the reaction after smaller amounts of the outer surface, which to a greater extent contains metal, have been successively eroded away after successive ignitions.

A particularly advantageous process for the preparation of the new catalysts uses repeated impregnations of the support with dilute solutions of a salt of iridium with or without any ruthenium salt. During each impregnation, the metal-bearing ions are adsorbed on the surface of the support. If a concentrated solution is used, the metal ions clump together to high concentrations thereof and the resulting metal particles formed after decomposition and reduction are too large or are located too close to each other. If the impregnation with dilute solution is followed only by drying, seed crystals are left, which means that the next precipitation can be applied at the same seats, which is why the same difficulties arise as when using solutions with too high a concentration. Accordingly, it is necessary to apply a treatment which changes the metal ions before the next impregnation with the diluted solution. The treatment must also be one which prevents redissolution of salt which has precipitated during the next impregnation and which promotes precipitation at places on the carrier surface which have not previously been covered with solution. In this multiple type impregnation treatment, in order to obtain the best possible performance for the final catalyst, it is advantageous to degas the beads of support by evacuation during one or more of the previous impregnations, whereby better penetration of the saline solution is achieved.

Methods for achieving good metal distribution vary with the type of metal salt or salts used, the types of ions present and their distributions. These in turn are affected by the nature of the solvent, pH, salt concentration and the fact whether the salt solutions were "aged" before use or not. It is important that the conditions are set so that deep penetration of the beads is achieved at the beginning of said plurality of impregnations, and that in these early stages a heavy or strong outer coating should not be formed which counteracts this purpose.

In this multiple type impregnation method, it is advantageous to use for the impregnations a solution of a metal salt, which can decompose by heating at a temperature below about 45006, and to dissolve the precipitated salt in this way after application of heat.

Among the suitable salts of iridium and ruthenium which can be used in this way are, for example, H2IrCl6, H3IrCl6, HIrCl2 (OH) ¿, IrCl3-H2O, (NH4) 3IrCl6, (NH4) 2IrCl5 (H2O), [lr (NH3) 4Cl 2] Cl, [Ir (NH 3) 5 (H 2 O fl C 13, RuCl 3, H 3 RuCl 6, (NH 4) 3 RuCl 6 ° Ch íRU {NH 3) 4 Clé] Cl- Particularly advantageous results have been obtained with the chlorides.

Particularly suitable for the preparation of the preferred iridium catalysts are hexachloriridate (Hgl / strl), strongly acidic solutions of iridium trichloride, such as IrCl3-3HC or H3IrCl6, and iridium trichloride hydrate. Mixtures of ruthenium trichloride with any of these iridium salt solutions provide particularly advantageous impregnating agents for use in the preparation of catalysts having these two metals on the support.

Solutions of the selected metal salt or the selected metal salts in water only, or aqueous solutions or anhydrous alcoholic solutions, for example the water-miscible alcohols methanol, ethanol, isopropyl alcohol, tert-butyl alcohol, etc., are useful for the multiple type impregnations. As a general rule, the solutions will contain salts in an amount which gives from about 0.02 to about 1 gram atom of the required metal or metal mixture per liter; and preferably from about 0.1 to about 0.6 gram atoms per liter is suitable.

It has been found that iridium-containing catalysts, which have more satisfactory performance in the decomposition of hydrazines, are obtained if the alcohol or aqueous solutions are aged before they are used to impregnate the support. Not only are the solutions more homogeneous and therefore more suitable for uniform distribution of the catalyst metal in the support, but the metal ions are also often less strongly adsorbed from the aged solutions, so they can penetrate the support beads more gradually and precipitate more uniformly on the inner surface area. the balls. This is impaired in experiments carried out in order to adsorb aqueous IrCl3 solutions containing about 0.02 g iridium / ml and 0.15 M with respect to added HCl on an alumina support. A homogeneous solution was obtained after overnight storage.

Particles of the alumina support, having a surface area of 156 m2 / g, a pore volume of 0,343 ml per g, a specific heat at 20 ° C of 0,18 kcal / g OC and a size range of 0,15 - 0,075 mm were packed in a column, the inner diameter of which was 1 mm, to form a bed with a depth of 20.3 - 22.9 cm, over which the iridium chloride solution was poured. After passing the aged solution, the column of alumina was slightly light green along a distance of 27, 0 mm, blue to light green below the next 69.25 mm, and then light yellow below the next 6.35 mm. This shows a rather weak adsorption and verifies the observation that rapid penetration of spheres takes place with this type of saline solution. More concentrated acid resulted in further dispersal (or tail formation) of the ribbons and more dilute acid less dispersion. Catalytically, the best results were obtained with IrCl3 alone and with the dilute acid type solution. Absorption of Hzlrt10 from isopropyl alcohol solution on the same support showed similar results.

With a fresh solution very strong adsorption took place, the iridium being taken up mainly at the top of the column, where a dark ionic layer formed a 1.27 cm band.

With aged solutions, there was only a trace of the dark ionic layer at the beginning of the kelone and there was an extensive, light green band. Consequently, the aged, less strongly adsorbed ions were able to penetrate the aluminum oxide deeper. in catalyst production, this means that the metal precipitates more uniformly in the mwmma.

The mechanism by which the more advantageous catalysts are prepared through the use of aged solutions has not been fully established. In the case of the alcoholic solutions, it may be the case that a reduction of catalyst metal ions to such ionic species as Ir3 + takes place or that a slow formation of a complexion occurs. Whatever the explanation for the improvement, it is generally desirable that the impregnation solutions used be aged for at least about 24 hours prior to application to the selected catalyst support. Fresh solutions can be substantially precipitated in a thick coating on the peripheral surface of the balls and thus the desired, deep penetration can not be achieved by successive Wmæmæ fi nwr.

As already pointed out, the pH of the impregnation solution has an effect on the precipitation of the catalyst metal or metals on the surface of the support. With iridium salts, such as, for example, iridium trichloride hydrate, hexachloriridate and iridium tetrachloride, an acidic pH in the range of from about 0.5 to about 4 is desirable, with a pH of from about 2 to about 3 being more advantageous in solution.

There is some increase in the pH of the remaining aqueous hexachlorirate solutions after the first impregnation of the alumina beads. Thus, the hydrogen ion as well as the iridium-containing ionic species are adsorbed or reacted with the alumina. The equilibrium probably shifts to polymeric iridium material due to the decrease in hydrogen ion concentration. Successive thickening of the solutions has been observed after many impregnations. This again underlines the importance of deep penetration of the beads at an early stage following impregnation.

However, alkaline solutions can be used when amine complexes of the metals are used. Thus, there are advantages in using iridium chloropentamine solutions for the multiple type impregnation of the carrier, and in this case ammoniacal solutions having a pH in the range of from about 8 to about 10 are suitable.

According to a successful method of carrying out the impregnations, the selected catalyst support is immersed in the solution of the catalyst metal salt for a period of time of the order of about 10 minutes. to about 60 min. until proper penetration of the pores into the carrier has taken place. the excess solution is then removed by drainage within from about 1 min. to about 20 minutes, and the carrier is dried in a stream of hot air, preferably at a temperature of from about 120 ° C to about 150 ° C. The partially dried support particles are then successively heated to a temperature of from about 25006 to about 450 ° C to complete the drying and effect partial decomposition of the catalyst metal salt. Usually from about 10 to about 60 minutes. sufficient to perform this operation, after which the support is cooled and the same series of treatments is repeated until the required amount of catalyst salt has precipitated to obtain the required amount of catalyst metal after subsequent reduction, as described above. Usually at least seven separate impregnations are required, and in general it turns out to be more economical to use a single batch of impregnation solution, which is reused until it is completely taken up by the carrier. However, one can also continuously or intermittently add fresh catalyst metal salt solution to the solution applied to the support, or proceed in other ways which give the desired precipitation of catalyst metal, as described above.

For final reduction of the precipitated decomposition products of the starting metal salt or salts, hydrogen gas can be successfully used at a temperature of from about 25,000 to 6,000. More generally, it is preferable to start the reduction with hydrogen dilute with nitrogen at about 300 ° C and increase the temperature and hydrogen concentration in the gases until the reduction is completed by heating at about 550 ° C for about 30 minutes. with dilute hydrogen.

The following examples further illustrate suitable methods for preparing the new catalysts and show some of their advantages. ššål fl l The preparation of a catalyst comprising iridium on alumina by multiple impregnation of the support with an ammoniacal solution of IrCl3 was carried out as follows.

An ammoniacal solution containing 9.2 g Ir / 100 ml was prepared by dissolving 25.0 g iridium trichloride containing 54.6% Ir in 85 ml H 2 O by heating to 50 ° C, cooling, and adding 60 ml 3 N NH 4 OH. The alumina support had a surface area of 175 m2 / g, a pore volume of 0.34 cm 3 / g, and was in the form of cylindrical spheres with a diameter of 1.8 mm. The compressive strength of individual spheres, measured between flat plates, averaged 7.7 kg. 55 g of carrier were immersed for 10 min. in the above solution, drained for 5 minutes, pre-dried for 2-5 minutes. with a warm stream of air and then dried for 15 minutes. in a single layer in a l5, Z4 cm petri dish on a hot plate. In addition, the hot air stream from a 20 A heat gun was directed at the catalyst from a distance of 25.4 cm. The catalyst reached a temperature of approximately 380 ° C and acid vapors and ammonium chloride vapors evolved. The material was cooled and weighed.

The procedure described above was performed a total of 6 times to consume the entire solution. The beads were then heated in dry nitrogen to 300 ° C and reduced with a mixture of nitrogen and hydrogen (about 1: 10), which was passed over the catalyst at 30006 for 0.5 hours, during which time a very large amount of HC] is removed. The beads were cooled in nitrogen and then allowed to oxidize by exposure to air. the beads were then washed with 300 cm 3 portions of water. A small amount of aluminum chloride (probably oxychloride) was removed, but no ammonium chloride was detected. The washing step may be unnecessary and was performed in this case to remove any non-decomposed ammonium chloride (none was detected).

The balls were dried on the hot plate.

The beads were then treated for a second series with an immediately prepared ammoniacal solution of iridium trichloride, as already described. This series also required six treatments to absorb the entire solution. The reduction and washing were carried out as described above, and then the final catalyst was heated again to 300 ° C in nitrogen followed by heating under 0.5 h nz / ion via soo ° c an siutiigen under 0.5 h 1 'H2 via 550%.

This catalyst had an iridium content of 32% by weight. In hydrazine decomposition tests in a 2.3 kg traction generating reactor with a cylinder whose inner diameter was 2.66 cm and whose length was 8.9 cm, at an feed temperature of 3-5 ° C and an feed rate of 13.6 g hydrazine / sec., fairly good ignition was observed. The ignition delay at 10 starts with the reactor vessel at 2-4 ° C was initially less than 25 ms, and increased to 90 ms at the end of the series. Constant pressures of 13.0-13.5 kg / cm 2 (gauge) were noted and there were no gauges at start-up. The ammonia decomposition was 57-62% and the catalyst loss, in the form of fine material, was about 1% / min. at the ignition. EXAMPLE II The need to use more than seven impregnations in the preparation of the catalysts is illustrated by the following results, obtained with catalysts comprising iridium on alumina, prepared by the following method.

Catalysts are prepared by immersing alumina beads of the type described in Example I in separate acidic aqueous solutions of H 2 IrCl 6 for 1 hour. The beads were then drained, dried by a hot stream of air and then decomposed in air at 380 ° C for about 1 hour. The procedure described above was repeated 5 times for Catalyst A using a solution with an iridium concentration of 22 g Ir per 100 ml, and 20 times for Catalyst B, where the concentration of the impregnation solution was 6 g Ir per 100 ml. After the final impregnation and decomposition or decomposition, each catalyst was reduced in a hydrogen stream at 500-55000. The results obtained are shown in the following table, where the hydrazine decomposition test was carried out in the reactor described in Example I.

Catalyst Section 5 Number of impregnations 5 20 Iridium content in finished catalyst, weight% 32 ~ 33 Hydrogen chemisorption, micromol per g 100 370 Catalyst activity Fairly good Ignition delay, ms at 10 ignitions in case of hydrazine decay _ 127 _ 80 Catalyst loss rate,% /. 2.4 h 0.8 The large difference in hydrogen chemisorption, which was observed, shows the large difference in the atomization state of the precipitated metal. The smaller the size of the precipitated metal particles, the larger the area available for hydrogen chemisorption but also the catalytic activity in the decomposition of hydrazines.

The catalyst prepared by five impregnations had an iridium surface area which was only about 1/4 of the surface area of the catalyst prepared by impregnations, although the total iridium content was approximately the same. The average metal particle diameter was about 17 Å in the catalyst produced 9 vsossiz-s by 20 impregnations, which resulted in a substantially superior hydrazine decomposition.

EXAMPLE III The following data show the excellent results obtained with a catalyst prepared from an aqueous solution of hexachloridate, aged overnight before impregnation of the same alumina support as described in Example I.

The alumina had been fired in an oven at 70,000 for 1 hour. The impregnation solution contained 0.29 g / l Ir / liter. and showed a content of 0.3 N hydrochloric acid added.

A total of 20 consecutive impregnations and decompositions were performed, the impregnation times varying from 5 to 10 minutes. to 16 hours to obtain the desired metal salt penetration into the beads. The reduced catalyst contained 35% iridium metal.

In the traction generating reactor engine described in Example I, the ignition delay at 10 starts with the reactor at 2-400 was initially less than 40 msec, which increased to 80 msec at the end of the test series. Constant pressures amounting to 13.0 - 13.4 kp / cmz overpressure were measured and there was no overpressure at start-up. The catalyst loss in the form of very fine material was only 0.6% per minute. during ignition.

The usefulness of other iridium salt solutions as impregnating agents in the preparation of the new catalysts is shown by the following results obtained with catalysts prepared by the general method of Examples II and III using the same alumina support and 0.29 g solution Ir. / lit.

The number of successive impregnations varied from 17 to 20 and the precipitated salt was decomposed by heating after each impregnation. These catalysts contained 30-35% by weight of iridium on 1.8 mm bullets, which was used in a 45 cm 3 bed for decomposition of hydrazine with a feed rate for hydrazine of 13.6 g / s.

The initial temperatures were 2-4 ° C for both the hydrazine fed and the catalyst, and each ignition lasted 60 seconds.

Ignition Catalyst- Number of delay loss lnmn} §nuningslö§ning_ ignitions (ms) §_Eer min.

Irssls in aqueous 0.02 N HC! 6 25-30 1.0 H Irßl in isopropylalkane 7 zo-so 0.9 H IrCl5 in aqueous nêi io 20-45 "o, a .IrCl3i water l0 60-l25 0.8 H2lrCl6 in aqueous HQ] 10 20 -40 0.5 H9IrClR 1 aqueous Hßl l0 20-80 .05 l0 l5 20 25 30 35 40 EXAMPLE V _.

The results obtained with catalysts prepared with mixtures applied to the alumina support as tested for iridium metal and ruthenium metal Examples I in the same manner as in Examples II and III and as hydrazine decomposition as described in Example I , is the following. In all cases, the catalysts contained 25-32% ruthenium + iridium, and more than 10 impregnations were used in their preparation.

Ru / Ir Ignition- Catalyst- Atomic- Number of on- loss loss in impregnation solution holding ignitions (ms)% per min.C). , _, a) RuCl3 i l0 A H20 90 A IPA Ogzb) 13 89_] 17 0,6 H2IrCl5 i 0,15 N HCl (an) RuCl3 i l0% H20-90% IPA 0,3 8 20_] 45 1, IrCl3 in 0.3 N HCl (aq) RuCl3i 10% H20-90% IPA 0.2] 5 20_179 2.8 H2IrCl6 il, 5 N HCl (aq) RuCl3 in 10% H20-90% IPA 0.21 3 80 1.5 H2IrCl6 in 0.15 N HCl (aq) RuCl3 in 10% H20-90% IPA 0.21 2 125 1.9 H2IrCl6 in 0.15 N HCl (aq) a) Isopropyl alcohol b) Prepared from alumina with surface area 80 and finished catalyst washed with 0.1 N HCl. c) Weight loss plus fine material, which passed sieve with 1.68 mm mesh openings. gxsrlrsL _v_1_ m2 / g, pore volume 0.29 cm3 / g, A catalyst for decomposition of hydrazine which was particularly suitable for use in small control engines with only the low traction force (approximately 0.5 kg or less) required for size control, supplemented fine tuning and the like, where pericdically small amounts of hydrazine are to be decomposed, were prepared by impregnating granules of the alumina support according to Example d 3l m iridium according to the procedure described in this example with a size of 0.6-1.0 mm using a similar solution of ammoniacal irim impregnations, each of which lasted dium trichloride and using seven l5 min.

IN

Claims (7)

This catalyst ignited very well in a small reactor, in which 2.3 cm 2 of catalyst was used. At about 3 ° C, at least six 9 sec. ignitions using 8 ml of hydrazine per ignition and equally good results were obtained on re-ignition repeatedly after the catalyst was stored in the reactor for 6 weeks. While the use of alumina supports is carefully emphasized in the above examples, due to their superiority in the preparation of particularly active and stable catalysts, it will be appreciated that the invention is not limited thereto, as advantageous novel catalysts for decomposition of hydrazines can be prepared with other supports. , which has specific surface areas, which conform to the above formula and have the correct pore volume. These include, for example, zirconia, boron carbide, titanium nitride, zirconium nitride, boron nitride, zirconium carbide, carbon zirconium boride, calcium zirconate and similar substantially refractory carriers. Among the aluminas, the substantially stable forms derived from gels (such as gelatinous tree fi are particularly advantageous. The invention is also not limited to the decomposition of hydrazine but can be applied to the decomposition of substituted hydrazines, such as monomethylhydrazine, asymmetric dimethylhydrazine and the like. It is thus apparent that the invention has many advantages and has a wide application.The invention is not limited to the examples set forth for illustrative purposes, nor is it limited to any theory proposed in explaining the improvements achieved. 1. A process for the preparation of a catalyst which is effective for the spontaneous decomposition of hydrazine and which is capable of at least ten ignitions in 1 minute. each from cold starts with less than 50 msec. delay and no significant overpressure at the start, k net marked by the fact that in the pores of a carrier having a pore volume of at least 0.1 cm 3 / g and a specific surface area, expressed in m2 / g, equal to C + 0.013 + 0.736 Vp) where Cp is the specific heat of the support at about 25 ° C, expressed in cal./g, and VD is the pore volume of the support, expressed in cm 3 / g, a solution of a salt comprising iridium salts is introduced or mixtures of salts of iridium and ruthenium with a certain pH value, which salt undergoes decomposition at a temperature below 450 ° C, and which solution contains an amount of between about 0.02 and about 0.6 g atoms metal / lit., that the solvent-containing carrier is dried to precipitate the salt in the pores thereof, that the carrier is then heated to decompose the precipitated salt, that the pores of the carrier are re-impregnated with said saline solution, that the carrier is again dried and the salt is decomposed, that the impregnation of the carrier with the salt, the drying of the impregnated support and the decomposition of the precipitated salt are repeated at least seven times until the catalyst contains from about 20% by weight to about 40% by weight of said metal, and the catalyst is heated in a stream of hydrogen at a temperature vaoasiz-s 1 * between about 200 and 500 ° C to convert the decomposition products of the precipitated salt into catalytically active metal. A process according to claim 1, characterized in that the saline solution has a pH of from about 0.5 to about 4. 3. A process according to claim 1, characterized in that the solution comprises an amine complex of said salt and has an alkaline pH value. 4. A method according to claim 1, characterized in that the impregnations of the support are carried out with metal salt solution, which has aged at least 24 hours. before introducing the saline solution into the carrier. 2 The method of claim 1, characterized in that the support is an alumina having a surface area of about 100-300 m 2 / g, a pore volume of from about 0.3 to about 0.5 cm 3 / g, and a compressive strength of from about 4.5 to about 13.6 kg. 6. A method according to claim 3, characterized in that the metal on the support of alumina consists of iridium only. A method according to claim 3, characterized in that the metal on the alumina support is a mixture of from about 30 to 80 atomic% iridium and the remainder ruthenium. The invention relates to a process for the preparation of a catalyst which is effective for the spontaneous decomposition of hydrazine, in which (a) in the pores of a support having a pore volume of at least 0.1 cm 3 / g and a specific surface area expressed in M2 / g, which is equal to l95 (CP + 0,013 + 0,736 Vp) where Cp is the specific heat for the support at approximately 25 ° C, expressed in cal./g, and Vp is the pore volume for the carrier, expressed in cm 3 / g, is introduced into a solution of a salt comprising iridium salts or mixtures of salts of iridium and ruthenium, which salt undergoes decomposition at a temperature below 450 ° C, the solution containing said salt in an amount of between about 0, 02 and about 0.6 gatomer of metal) lit. and has a pH of from about 0.5 to about 4, (b) drying the solvent-containing carrier to precipitate the salt in the pores thereof, (c) subsequently heating the carrier to decompose the precipitated salt, (d) the pores of the support are re-impregnated with said saline solution, (e) the support is dried and the salt is decomposed, (f) the impregnation of the support with the salt, the drying of the re-impregnated support and the decomposition of the precipitated salt are repeated at least seven times until the catalyst contains from about 20% to about 40% by weight of said metal, and (g) heating the catalyst in a stream of hydrogen at a temperature between about 200 and about 500 ° C to convert the decomposition products of the precipitated salt to catalytically active metal. According to a preferred embodiment of the method, the support consists of balls of alumina and the balls are immersed in an annular solution of an iridium salt, after which the above-mentioned steps (b) - (g) are carried out.