EP4301512A1

EP4301512A1 - Method for the hydrogenation of aromatic nitro compounds

Info

Publication number: EP4301512A1
Application number: EP22708545.3A
Authority: EP
Inventors: Bernd Pennemann; Lennart Sandbrink; Eberhard Zirngiebl; Thomas KAESE; Hans-Jürgen QUELLA; Paul Sprenger; Marc Williams; Daniel ULLRICH
Original assignee: Covestro Deutschland AG; Lanxess Deutschland GmbH
Current assignee: Covestro Deutschland AG; Lanxess Deutschland GmbH
Priority date: 2021-03-01
Filing date: 2022-02-28
Publication date: 2024-01-10
Also published as: US20240157343A1; KR20230154011A; WO2022184614A1; JP2024508014A

Abstract

The present invention relates (i) to a method for producing a doped copper-tetraammine-salt-based hydrogenation catalyst suitable for the hydrogenation of an aromatic nitro compound such that an aromatic amine is obtained, the hydrogenation catalyst comprising copper in metal form or in oxidic form and a doping metal selected from iron, cobalt, manganese, vanadium, zinc or a mixture of two or more thereof in metal form or in oxidic form on a carrier, the carrier comprising silicon dioxide shaped bodies and/or silicon carbide shaped bodies, (ii) to a doped copper-tetraammine-salt-based hydrogenation catalyst obtainable using the aforementioned method according to the invention, and (iii) to a method for producing an aromatic amine, comprising the hydrogenation of an aromatic nitro compound in the presence of a doped copper-tetraammine-salt-based hydrogenation catalyst comprising copper in metal form or in oxidic form and comprising a doping metal in metal form or in oxidic form on a carrier as hydrogenation catalyst, the carrier comprising silicon dioxide shaped bodies and/or silicon carbide shaped bodies, and the hydrogenation catalyst being, more particularly, the aforementioned hydrogenation catalyst according to the invention.

Description

The present invention relates to (i) a process for preparing a hydrogenation catalyst, namely a process for preparing a doped copper tetrammine salt-based hydrogenation catalyst suitable for hydrogenating an aromatic nitro compound to obtain an aromatic amine, the hydrogenation catalyst comprising copper in metallic or oxidic form and a doping metal selected from iron, cobalt, manganese, vanadium, zinc or a mixture of two or more of these in metallic or oxidic form on a carrier, the carrier comprising silicon dioxide shaped bodies and/or silicon carbide shaped bodies, (ii) a hydrogenation catalyst, namely a doped copper tetrammine salt-based hydrogenation catalyst obtainable by the aforementioned process according to the invention, and (iii) a process for preparing an aromatic amine, the process comprising the hydrogenation of an aromatic nit ro compound in the presence of a doped copper tetrammine salt-based hydrogenation catalyst comprising copper in metallic or oxidic form and a doping metal in metallic or oxidic form on a support as a hydrogenation catalyst, the support comprising silicon dioxide shaped bodies and/or silicon carbide shaped bodies, the hydrogenation catalyst in particular the aforementioned hydrogenation catalyst according to the invention. The hydrogenation of nitroaromatics to the corresponding aromatic amines with hydrogen has been known for a long time and is of great industrial importance. A representative example is the hydrogenation of nitrobenzene to aniline. Most of the aniline produced worldwide is used to manufacture the di- and polyamines of the diphenylmethane series (MDA), which in turn are intermediates for the manufacture of the important di- and polyisocyanates of the diphenylmethane series (MDI). The hydrogenation can be operated in the liquid or gas phase, under isothermal or adiabatic conditions. A combination of isothermal and adiabatic reaction conditions is also known. A number of catalysts have been described in the literature for this purpose. In particular, palladium and copper-based catalyst systems should be mentioned here. For example, the use of palladium-based catalysts on ceramic supports is known. The German patent application DE 2849002 A1 describes a process for the reduction of nitro compounds in the presence of palladium-containing three-component supported catalysts in cooled tubular reactors. In preferred embodiments, the catalyst contains 1 to 20 g of palladium, 1 to 20 g of vanadium and 1 to 20 g of lead per liter of α-Al ₂ O ₃ . Similar catalysts, albeit additionally doped with Mo, Re or W, have also been described in DE 19715746 A1. EP 1882681 A1 discloses that it is advantageous to additionally coat such three-component supported catalysts with a sulfur- or phosphorus-containing, preferably phosphorus-containing, compound (such as the To dope oxygen acids of phosphorus or their alkali metal salts such as in particular sodium dihydrogen phosphate, sodium or potassium phosphate or sodium hypophosphite). International publication WO 2013/030221 A1 describes the advantageous effects of potassium doping of the catalyst on the phenol content of the aniline formed. The use of copper-based catalysts for the hydrogenation of, in particular, nitrobenzene has long been known (see US Pat. No. 1,207,802 and US Pat. No. 3,136,818). The natural rock pumice was used as a carrier for the catalytically active material, which contains silicates and sodium as the main components. The use of silica-supported copper catalysts for the hydrogenation of nitrobenzene to aniline has also been known for a long time (e.g. GB 823,026 or US 2,891,094 from the 1950s). Both patents describe the use of copper ammine complexes as catalyst precursors. To produce the catalysts, a hydrogel is precipitated by acidifying a sodium silicate solution and, after filtration and washing, the copper-ammine complex is added to this hydrogel. The hydrogel treated in this way is filtered off, washed, dried and calcined in a reducing atmosphere. The treatment of the hydrogel with the copper-ammine complex is referred to as impregnation, but due to the finely divided nature of the carrier (which is present as a freshly precipitated hydrogel and therefore does not have any pores that can absorb copper particles), the process described corresponds more closely a simple deposition of copper particles on the hydrogel. A proven and frequently used method for producing hydrogenation catalysts is impregnation with metal salt solutions, in which the support used has pores which take up the metal salt solutions. For this purpose, the support is either moistened with the metal salt solution until its water absorption capacity is saturated (so-called “incipient wetness” method) or treated in supernatant solution. Impregnation processes are described, for example, in the patent applications WO 2010/130604 A2, EP 0696573 A1, DE 2311114, WO 95/32171 A1 and WO 2009/027135 A1 discussed below: The international patent application WO 2010/130604 A2 describes a process for preparing aromatic amines , In particular aniline, using copper-containing catalysts on SiO ₂ supports. In addition to copper, other hydrogenation-active metals such as potassium (K), sodium (Na), barium (Ba), chromium (Cr), molybdenum (Mo), palladium (Pd), zinc (Zn), tungsten (W), nickel (Ni) or cobalt (Co) can be used. The copper and such a further metal are applied to the carrier by joint impregnation. The method is particularly characterized in that the SiO ₂ was produced by wet grinding and subsequent spray drying. Wet milling within the meaning of this patent application is understood to mean the reduction in size of the silicon dioxide (SiO ₂ ) that has already formed into particles of a specific size/a specific diameter (Page 6, third paragraph). According to this document, SiO ₂ particles of any size/any diameter can be obtained by wet grinding. However, only silicon dioxide particles with a diameter in the order of micrometers, preferably in the range from 1 to 35 μm, in particular 2 to 30 μm, are specifically disclosed (page 6, last paragraph). Example 1 discloses the production of a carrier with particle sizes in the range from 10 to 300 μm (ie at most 0.3 mm). Such small catalyst diameters are also required for the process described, because the catalysts produced in this way are to be used as fluidized bed catalysts, which would not be practicable with macroscopically detectable shaped bodies with sizes in the millimeter range. Impregnation from supernatant solution is described for applying the catalytically active metals, for example using ammoniacal carbonate solutions. The international patent application WO 2020/207874 A1 also deals with catalysts for the hydrogenation of aromatic nitro compounds, the mean particle sizes of which are at most in the range of tenths of a millimeter (e.g. 114 μm in Example 2 and 118 μm in Example 3). Catalyst systems are described which contain a component A, in particular silicon carbide, and a component B1, in particular silicon dioxide, as support. Component A can also be fed to the reaction space, preferably a fluidized-bed reactor, separately from component B1 provided with the hydrogenation-active metals. Copper, in particular, is mentioned as the hydrogenation-active metal (B2). The catalyst can be doped with other metals (B3). These other metals B3 are preferably potassium (K), sodium (Na), barium (Ba), lead (Pb), zinc (Zn), vanadium (V), chromium (Cr), molybdenum (Mo), Tungsten (W) or Iron (Fe). The metals B2 and B3 are applied to the carrier B1 by joint impregnation. EP 0696573 A1 describes a process in which aromatic amines are prepared by hydrogenating the associated nitroaromatics in the gas phase over stationary catalysts. The catalysts contain hydrogenation-active metals on supports, which can be produced by impregnation. The hydrogenation catalyst used is, in particular, a catalyst containing palladium on α-Al ₂ O ₃ and containing 1 to 100 g of Pd per liter of α-Al ₂ O ₃ , which is preferably deposited in the form of a shell, and the catalyst can additionally contain vanadium and lead. Catalysts based on amine complexes are not described. The German patent application DE 2311114 deals with the improvement of copper chromite catalysts used for the hydrogenation of ketones, carboxylic acid esters and nitro compounds. For this purpose, a process for the production of a copper chromite catalyst applied to supports is proposed, which is characterized in particular in that basic ammonium copper(II) chromate in the pores of an inorganic oxidic support material by reacting precursors of basic ammonium reacting with one another here -Copper(II) chromates are formed and the carrier material is then used to convert the basic ammonium copper(II) chromate into copper chromite is heated to a temperature of about 250 to 500 °C for about 0.1 to 20 hours. According to this document, copper chromite is often represented as "xCuO,Cr ₂ O ₃ ". It is immediately apparent to those skilled in the art that this is merely a description of the stoichiometric ratios and does not provide any information about the actual structure of the catalyst. International patent application WO 95/32171 A1 deals with the preparation of alcohols by catalytic hydrogenation of the corresponding carbonyl compounds at elevated temperature and elevated pressure in the liquid phase. For this purpose, copper catalysts are described, which are obtained by impregnating SiO ₂ -containing carrier materials with various thermally "easily" (ie below 350 °C) decomposable copper salts such as copper nitrate, copper carbonate, copper formate, copper oxalate and their readily water-soluble, am(m )inic complexes are available. The international patent application WO 2009/027135 A1 also deals with the production of alcohols by hydrogenation of carbonyl compounds. The hydrogenation catalyst used consists of a support material and at least one hydrogenation-active metal, the support material being based on titanium dioxide, zirconium dioxide, aluminum oxide, silicon oxide or mixed oxides thereof and the hydrogenation-active metal being at least one element from the group copper, cobalt, nickel, chromium, and the support material also contains the element barium. The production of a copper-containing impregnation catalyst on aluminum oxide with an approximately 14% copper tetrammine carbonate solution is described as an example. The German patent application DE 3933661 A1 deals with a catalyst for the hydrogenation of acetophenone to methyl benzyl alcohol. The catalyst is prepared by impregnation, by which is meant in particular spraying, of a silica support with a solution of copper tetrammine carbonate and a solution of ammonium chromate or with a mixture thereof and subsequent drying. Spraying a support with a metal salt solution is a method that can represent an alternative to the soaking described above. Here, too, the metal salt solution to be used can be used “in excess” (according to the method of impregnation in supernatant solution explained above) or adjusted to the absorption capacity of the pores of the support (according to the “incipient wetness” method described above). The German patent application DE 102010029924 A1 deals with the regeneration of copper, chromium and/or nickel-containing hydrogenation catalysts, such as those used in the production of higher alcohols, in particular those with 8 to 13 carbon atoms, by catalytic hydroformylation (also referred to as an oxo reaction) of the olefins with one carbon atom poorer and subsequent hydrogenation of the aldehydes formed are used. British patent GB 825,602 deals with the dehydrogenation of alcohols to aldehydes and ketones, with reduced and small amounts of unreduced Copper oxide and "alkali metal oxides containing catalyst is used. The catalyst is prepared by heating a copper tetrammine complex followed by heating under hydrogen. The European patent application EP 3320969 A1 deals with chromium and nickel-free catalysts for the heterogeneous hydrogenation of oxo aldehydes. The catalysts only contain copper; however, it is necessary here for silicon dioxide to be used as the support material and for the content of Cu and SiO ₂ in the active catalyst to be set precisely within very narrow limits. In addition to being used as catalysts for a wide variety of reactions, copper compounds are also used in many other areas, for example as a fungicide (see, for example, US Pat. No. 3,900,504). The as yet unpublished international patent application with the application number PCT/EP2020/073991 describes a process for preparing an aromatic amine by hydrogenating an aromatic nitro compound, comprising the steps (I) providing a copper tetrammine salt-based impregnation catalyst, in particular an impregnation catalyst obtainable by the incipient wetness method , comprising a metal or metal oxide on a support as a hydrogenation catalyst, wherein at least metallic or oxidic copper (especially CuO) is present and the mole fraction of Cu, based on all metals present, is in the range from 0.75 to 1, and wherein the support contains silicon dioxide moldings or silicon carbide moldings; (II) optionally, activating the hydrogenation catalyst by treating it with hydrogen in the absence of the aromatic nitro compound; and (III) reacting the aromatic nitro compound with hydrogen in the presence of the optionally activated hydrogenation catalyst to give the aromatic amine. The use of doping metals selected from iron, cobalt, manganese, vanadium, zinc or a mixture of two or more of these is not disclosed. Catalyst alloys, for example the well-known Raney catalysts, are completely different from impregnated catalysts. WO 98/53910 A1 discloses a shaped, activated metal fixed bed catalyst with a pore volume of 0.05 to 1 ml / g and an outer, activated shell consisting of a sintered, finely divided catalyst alloy and optionally promoters, the catalyst alloy from the production of Alloy resulting metallurgical phase domains, whose largest phase by volume has a specific interface density of more than 0.5 microns ^-1 . In addition to the use of palladium-based or copper-based catalysts, the use of catalysts that contain both metals is also known. An example of this is described in British Patent GB 961,394. Catalysts for cleaning exhaust gas from motor vehicles are described there, which contain 0.5 to 25% copper and 0.01 to 3% palladium. Although the prior art catalysts described for the hydrogenation of nitroaromatics, in particular nitrobenzene, are in principle suitable for this purpose, there is still room for improvement in terms of selectivity and long-term stability. The focus here was on the copper-based catalysts, which are cheaper than the known palladium-based catalysts. Taking the above into account, the present invention provides the following: In a first aspect, the invention relates to a process for preparing a doped copper tetrammine salt-based hydrogenation catalyst suitable for hydrogenating an aromatic nitro compound to obtain an aromatic amine, the hydrogenation catalyst comprising copper in metallic or oxidic form and (at least) one dopant metal in metallic or oxidic form on a carrier, the carrier comprising silicon dioxide shaped bodies and/or (preferably or) silicon carbide shaped bodies (and in particular comprising no further support materials apart from silicon dioxide and/or silicon carbide), the method comprising the steps: (a) dissolving a metal salt selected from an iron salt, a cobalt salt, a manganese salt, a vanadium salt, a zinc salt or a mixture of two or more of the aforesaid metal salts in water or aqueous ammonia solution while obtaining lt an aqueous metal salt solution; (b) treating the support with the aqueous metal salt solution to obtain a first impregnated catalyst precursor; (c) drying the first impregnated catalyst precursor to obtain a first dried catalyst precursor; (d) calcining the first dried catalyst precursor to obtain a first calcined catalyst precursor, it being possible for steps (a) to (c) or (a) to (d) to be repeated several times (including with different metal salts); (e) dissolving a copper salt in aqueous ammonia to obtain an ammoniacal copper salt solution; (f) treating the first calcined catalyst precursor with the ammoniacal copper salt solution to obtain a second impregnated catalyst precursor; (g) forming the doped copper tetrammine salt-based hydrogenation catalyst by (1) drying the second impregnated catalyst precursor or (2) drying and calcining the second impregnated catalyst precursor, in which case steps (e) to (g)(1) or (e) to (g)(2) can also be repeated several times (including with different metal salts). Completely surprisingly, it was found that a two-stage impregnation process leads to more active catalysts than a one-stage impregnation process and that the order in which the metals are applied to the support – first the doping metal and then the copper – has a decisive influence on the quality of the catalyst. In a second aspect, the invention relates to a doped copper tetrammine salt-based hydrogenation catalyst obtainable by the aforementioned process according to the invention. In a third aspect, the invention relates to a method for preparing an aromatic amine by hydrogenating an aromatic nitro compound, comprising the steps: (I) providing a doped copper tetrammine salt-based hydrogenation catalyst according to the second aspect of the invention, ie providing a hydrogenation catalyst comprising copper in metallic or oxidic form Form and (at least) one doping metal in metallic or oxidic form on a support as a hydrogenation catalyst, the doped copper tetrammine salt-based hydrogenation catalyst being obtainable by applying the doping metal to the support, followed by applying the copper to the support containing the doping metal, the doping metal is selected from iron, cobalt, manganese, vanadium, zinc or a mixture of two or more thereof, and wherein the carrier comprises silicon dioxide shaped bodies and/or (preferably or) silicon carbide shaped bodies (and in particular no white other support materials in addition to silicon dioxide and/or silicon carbide); (II) optionally, activating the hydrogenation catalyst by treating it with hydrogen in the absence of the aromatic nitro compound; (III) Reacting the aromatic nitro compound with hydrogen in the presence of the optionally activated hydrogenation catalyst to give the aromatic amine. Formulations such as “a doping metal or, with reference thereto, “the doping metal” naturally also include the case in which several different doping metals are used, unless the context clearly indicates otherwise or something else is expressly stated; such a procedure therefore does not leave the scope of the present invention. The same applies to formulations such as “a metal”, “a metal oxide” and the like. In the terminology of the present invention, a doped copper tetrammine salt-based hydrogenation catalyst is understood to comprise a metal or metal oxide on a support, a catalyst which is obtained by treating, in particular by means of impregnation or spraying, a support containing the doping metal with an aqueous, in particular ammoniacal, solution of a Copper tetrammine salt (ie a salt containing the tetrammine complex of Cu(II), namely the cation [Cu(NH ₃ ) ₄ ] ²⁺ ), followed by drying and optional calcination (preferably in an oxygen-containing atmosphere) was obtained. The impregnation, the first preferred variant of the application of the copper tetrammine salt to the carrier containing the doping metal, is carried out by mixing it with the aqueous, in particular ammoniacal, solution of a copper tetrammine salt (by introducing the carrier containing the doping metal into or by pouring over the carrier containing the doping metal with the copper tetrammine salt solution). The type of carrier containing the doping metal and the amount of the aqueous, in particular ammoniacal, solution of the copper tetrammine salt are coordinated in such a way that either (= impregnation in supernatant solution) more copper tetrammine salt solution is present than the pores of the carrier containing the doping metal (see also the section below on shaped bodies) or (= incipient wetness method - preferred method) at most just as much (preferably a little less, in particular only 95% to 99% or even only 96% to 98% of the maximum Amount) copper tetrammine salt solution is present, as the pores of the support containing the doping metal can accommodate. The spraying, the second preferred variant of the application of the copper tetrammine salt to the carrier containing the doping metal, is carried out by spraying the carrier containing the doping metal with an aqueous, in particular ammoniacal, solution of the copper tetrammine salt by means of one or more nozzles which are aligned into the rotating drum . With this method, too, more copper tetrammine salt solution can be used than the pores of the support containing the doping metal can hold (corresponding to the impregnation in supernatant solution), or at most just as much (preferably a little less, in particular only 95% to 99% or even only 96% to 98% of the maximum amount) Copper tetrammine salt solution can be used, as the pores of the carrier containing the doping metal can absorb (corresponding to the incipient wetness method—also the preferred method here). The term incipient wetness method is also used below for spraying. The hydrogenation catalyst is therefore in particular one which can be obtained by the incipient wetness method mentioned (and was preferably actually prepared by this method). In other words, this means that in the production process for the hydrogenation catalyst, the support containing the doping metal is preferably treated with the aqueous, in particular ammoniacal, solution of a copper tetrammine salt in such a way that the maximum absorbency of the support containing the doping metal, determined by saturation with water, is not exceeded. The amount of the copper salt solution is preferably chosen so that it is in the range from 95% to 99%, particularly preferably in the range from 96% to 98%, of the maximum absorbency. Possibilities for determining the maximum absorbency of the carrier containing the doping metal, determined by means of saturation with water, are known in the technical field. For the purposes of the present invention, the method described in the section "Determination of the maximum absorbency of the carrier" at the beginning of the example part is decisive (this applies regardless of whether the carrier material to be treated is an already doped carrier or one not yet with Metals doped carrier is). In the terminology of the present invention, a carrier containing the doping metal refers to such a carrier which is obtained by treating, in particular by means of impregnation or spraying, the carrier with an aqueous solution of a salt of the doping metal, followed by drying and calcination (preferably in an oxygen-containing atmosphere) was received. With regard to the use of the incipient wetness method described for copper impregnation or spraying, the same also applies to the impregnation of the starting support with doping metal: Here too, the use of this method under the conditions described above is preferred. According to the invention, the carrier comprises silicon dioxide and/or silicon carbide shaped bodies, a shaped body in this context being understood to mean that the carrier is in the form of discrete (ie macroscopically detectable) particles with mean diameters in particular in the range from 1.0 mm to 15 mm , preferably in the range from 4.0 mm to 15 mm, particularly preferably 4.0 to 10 mm. Examples include, in particular, cylindrical shaped bodies and spherical shaped bodies, with the diameter of the base area being the diameter in the case of cylindrical shaped bodies and the length of the cylindrical shaped body is always greater than the diameter and in particular up to 2.0 times, preferably up to up to 1.8 times, particularly preferably up to 1.6 times the diameter. In the case of cylindrical moldings, the individual cylinders can also be combined to form aggregates comprising a plurality of cylinders, in particular to so-called trilobes (aggregates of three cylinders that are connected to each other along the longitudinal direction). In the case of such aggregates of cylinders, the diameter is the diameter of an imaginary circle enveloping the bases of the connected cylinders. In aggregates of this type, too, the length of the cylindrical moldings is always greater than the diameter and in particular up to 2.0 times, preferably up to 1.8 times, particularly preferably up to 1.6 times the diameter amounts to. The person skilled in the art is familiar with determining an average diameter in the aforementioned sense and can in principle be carried out using all methods known in the art for determining particle sizes in the mm range. In general, the result does not depend significantly on the type of method chosen. In case of doubt (i.e. should, contrary to expectations, different methods for particle size determination recognized in the professional world deliver significantly different results) the method described below is decisive for the purposes of the present invention: The shaped bodies of the carrier to be measured are mixed, and then a representative sample of 20 taken from moldings. The diameter defined above is now measured 3 times for each of the molded bodies removed using a caliper or a micrometer (also known as a micrometer). The mean value is formed from the three individual measurements and the mean value is again calculated from the 20 mean values obtained in this way. This last-mentioned mean value designates the mean diameter within the meaning of the present invention. A vernier caliper is used as a measuring device if the mean diameter is at least 4.0 mm. For average diameters below 4.0 mm, a micrometer (= micrometer) is used. In order to select the correct measuring device in a first step, it is usually sufficient to refer to the manufacturer's information on particle sizes. If a vernier caliper is selected on the basis of such information and the measurement reveals an average diameter of less than 4.0 mm (which may be the case with manufacturer information of or only slightly larger than 4.0 mm), the measurement is included to repeat with a micrometer. Suitable measuring devices can be analog or digital and are available from specialist dealers. Shaped bodies as described are different both from bulky structures (such as dust or hydrogels) and from monolithic structures. The silicon dioxide or silicon carbide shaped bodies contain pores into which the aqueous solution of the copper tetrammine salt penetrates. Silicon dioxide (SiO ₂ ), as used in the terminology of the present invention, is commonly referred to as silica in the English language literature. The mole fraction of Cu (= x(Cu)) related to all metals present refers to the metals as such, i.e ௌ௨ௗௌ௧௩ௗெ௧ . The mass fractions of the metals present on the catalyst are known from the point of manufacture; From this, the mole fraction of copper x(Cu) can be easily calculated. First of all, there follows a brief summary of various possible embodiments of the invention, the enumeration of embodiments not being to be regarded as exhaustive: In a first embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, in step (b) for the Treatment of 100 g of the carrier T such a volume of aqueous metal salt solution V _MS (100 g T) is used that the ratio of the numerical value of the volume V _MS (100 g T) given in milliliters to the numerical value of the maximum absorbency given in percent of the to be treated Carrier S _T maximum equal to 1.00: [ V _MS (100 g T) / ml] / [ S _T / %] ≤ 1.00, where the maximum absorbency of the carrier S _T is calculated from the ratio of the maximum mass to deionized water m _H2O , which can hold a sample P _T of the carrier, to the mass of the sample of the carrier m _PT , multiplied by 100%: S _T = [ m _H2O / _mPT ] × 100%. In a second embodiment of the process according to the invention for preparing a hydrogenation catalyst, which is a particular embodiment of the first embodiment, the following applies: 0.95≦[V _MS (100 g T)/ml]/[S _T /%]≦0.99. In a third embodiment of the process according to the invention for preparing a hydrogenation catalyst, which is a further particular embodiment of the first embodiment, the following applies: 0.96≦[V _MS (100 g T)/ml]/[S _T /%]≦0.98 . In a fourth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, in step (f) for the treatment of 100 g of the first calcined catalyst precursor KV1 such a volume of ammoniacal copper salt solution V _KS (100 g KV1) used that the ratio of the numerical value of the volume V _KS (100 g KV1), indicated in milliliters, to the numerical value of the maximum absorption capacity, indicated in percent, of the first calcined catalyst precursor S _KV1 to be treated is at most 1.00: [ V _KS (100 g KV1) / ml] / [ S _KV1 / %] ≤ 1.00, where the maximum absorbency of the first calcined catalyst precursor S _KV1 is calculated from the ratio of the maximum mass of deionized water m _H2O that a sample P _KV1 of the first calcined catalyst precursor can hold, to the mass of the sample of the first calcined catalyst precursor m _PKV1 , multiplied by 100%: S _KV1 = [m _H2O / m _PKV1 ] × 100%. In a fifth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which is a particular configuration of the fourth embodiment, the following applies: 0.95≦[V _KS (100 g KV1)/ml]/[S _KV1 /%]≦0.99. In a sixth embodiment of the process according to the invention for producing a hydrogenation catalyst, which is a further particular configuration of the fourth embodiment, the following applies: 0.96≦[V _KS (100 g KV1)/ml]/[S _KV1 /%]≦0.98 . In a seventh embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the metal salt comprises an iron salt, a zinc salt, a cobalt salt or a mixture of two or more of the aforementioned metal salts and consists in particular of one of the aforementioned. In an eighth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the metal salt comprises a metal nitrate or metal oxalate and is in particular a metal nitrate or metal oxalate. In a ninth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the metal salt comprises zinc(II) nitrate, iron(III) nitrate, cobalt(III) nitrate or a mixture of two or more of the aforementioned metal nitrates and consists in particular of one of the aforementioned. Of course, hydrates (eg Zn(NO ₃ ) ₂ .4H ₂ O) of the nitrates mentioned are also included. In a tenth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the dissolving in step (a) is carried out at temperatures in the range from 20.degree. C. to 25.degree. In an eleventh embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments the drying in step (c) is carried out at temperatures in the range from 80°C to 150°C, preferably from 100°C to 130°C. In a twelfth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the calcination in step (d) is carried out at temperatures in the range from 300° C. to 600° C., preferably from 400° C. to 500° C . In a thirteenth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the copper salt comprises basic copper carbonate (copper hydroxide carbonate, e.g. malachite, CuCO ₃ · Cu(OH) ₂ ; other copper hydroxide carbonates with other ratios of " CuCO ₃ " to "Cu(OH) ₂ " can also be used). In a fourteenth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, in step (e) an ammonium salt, in particular ammonium carbonate or ammonium acetate, is dissolved in the aqueous ammonia in addition to the copper salt. In a fifteenth embodiment of the method according to the invention for producing a hydrogenation catalyst, which can be combined with all other embodiments, the dissolving in step (e) is carried out at temperatures in the range from 0.0° C. to 25.0° C. (with excess ammonia, corresponding to pH 9.0 or greater) or in the range of 0.0°C to 10.0°C (at lower pH). In a sixteenth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the drying in step (g)(1) or step (g)(2) is carried out at temperatures in the range from 80° C. to 150 °C performed. In a seventeenth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the calcination in step (g)(2) is carried out at temperatures in the range from 300°C to 600°C. In an eighteenth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the ammoniacal copper salt solution has a pH (20° C.) in the range from 7.0 to 14.0, preferably 7.0 to 12 ,0 on. In a nineteenth embodiment of the process according to the invention for producing a hydrogenation catalyst, which can be combined with all other embodiments, a mass fraction of copper compounds, calculated as metallic Cu, in the doped copper tetrammine salt-based hydrogenation catalyst, based on its total mass, in the range from 8% to 25%. In a twentieth embodiment of the method according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, a mass fraction of metal compounds that are different from copper compounds, calculated as metals, in the doped copper tetrammine salt-based hydrogenation catalyst, based on its total mass, is in the range from 0.1% to 25%, preferably 1.0% to 20%. In a twenty-first embodiment of the process according to the invention for producing a hydrogenation catalyst, which can be combined with all other embodiments, a mole fraction of Cu, based on all metals present, in the doped copper tetrammine salt-based hydrogenation catalyst is in the range from 0.30 to 0.99, preferably 0. 45 to 0.95 set. In a twenty-second embodiment of the method according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the treatment in steps (b) and/or (f) comprises impregnating the support or the first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution. In a twenty-third embodiment of the method according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the treatment in steps (b) and/or (f) comprises spraying the support or the first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution. In a twenty-fourth embodiment of the process according to the invention for preparing a hydrogenation catalyst, which can be combined with all other embodiments, the silicon dioxide or silicon carbide shaped bodies are (i) spheres, (ii) cylinders or (iii) aggregates of several connected to one another along their longitudinal axis Cylinders and have an average diameter in the range of 1.0 mm to 15 mm, preferably 4.0 mm to 15 mm (determined with a caliper or a micrometer by measuring 20 shaped bodies three times and calculating the mean value - see the above description of the method for details). , particularly preferably 4.0 mm to 10 mm, with the mean diameter in the case of cylinders on the base of the cylinder and in the case of aggregates of several cylinders connected to one another along their longitudinal direction on a circle enveloping the bases of the connected cylinders relates. In the case of cylindrical shaped bodies, regardless of whether they are individual cylinders or aggregates of a plurality of cylinders, the length of the cylindrical shaped body is always greater than the diameter and is in particular up to 2.0 times, preferably up to 1.8 times, particularly preferably up to 1.6 times the diameter. In a first embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, step (II) is carried out, the treatment with hydrogen taking place at temperatures in the range from 180.degree. C. to 240.degree. In a second embodiment of the inventive process for preparing an aromatic amine, which can be combined with all other embodiments, step (III) becomes adiabatic at temperatures in the range of 160°C to 500°C or (preferably) 180°C to 400°C , or isothermally at temperatures ranging from 180°C to 550°C or (preferably) 190°C to 400°C. In a third embodiment of the inventive process for preparing an aromatic amine, which is combinable with all other embodiments, step (III) becomes adiabatic at a molar ratio of hydrogen to nitro groups in the range of 10 to 200, or isothermally at a molar ratio of hydrogen to nitro groups ranging from 3 to 100. In a fourth embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, the proportion by mass of copper compounds, calculated as metallic Cu, in the hydrogenation catalyst provided in (I), based on its total mass, is in the range of 8% up to 25%. In a fifth embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, a copper tetrammine carbonate-based hydrogenation catalyst is used as the hydrogenation catalyst. In a sixth embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, the hydrogenation catalyst used is a copper tetrammine carbonate-ammonium salt-based hydrogenation catalyst, in particular a copper tetrammine carbonate-ammonium carbonate-based hydrogenation catalyst or a copper tetrammine carbonate-ammonium acetate-based hydrogenation catalyst , used. In a seventh embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, the mass fraction of metal compounds that are different from copper compounds, calculated as metals, of the hydrogenation catalyst provided in (I), based on its total mass, is in the range 0.1% to 25%, preferably 1.0% to 20%. In an eighth embodiment of the method according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, the doping metal comprises iron, zinc, cobalt or a mixture of two or more of the aforementioned metals and consists in particular of one of the aforementioned. In a ninth embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, the mole fraction of Cu in the doped copper tetrammine salt-based hydrogenation catalyst, based on all the metals present, is in the range from 0.30 to 0.99, preferably 0 .45 to .95. In a tenth embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, step (I) comprises: (a) dissolving a metal salt selected from an iron salt, a cobalt salt, a manganese salt, a vanadium salt, a zinc salt or a mixture of two or more of the above metal salts in water or aqueous ammonia solution to obtain an aqueous metal salt solution; (b) treating the support with the aqueous metal salt solution to obtain a first impregnated catalyst precursor; (c) drying the first impregnated catalyst precursor to obtain a first dried catalyst precursor; (d) calcining the first dried catalyst precursor to obtain a first calcined catalyst precursor, steps (a) to (c) or (preferably) (a) to (d) also being repeated several times, in particular twice, (with the same or another metal salt ) can be traversed; (e) dissolving a copper salt in aqueous ammonia to obtain an ammoniacal copper salt solution; (f) treating the first calcined catalyst precursor with the ammoniacal copper salt solution to obtain a second impregnated catalyst precursor; (g) formation of the doped copper tetrammine salt-based hydrogenation catalyst by (1) drying the second impregnated catalyst precursor or (2) drying and calcining the second impregnated catalyst precursor, wherein steps (e) to (g)(1) or (preferably) (e) to (g)(2) can also be run through several times, in particular twice (with the same or a different copper salt). In an eleventh embodiment of the process according to the invention for preparing an aromatic amine, which is a particular embodiment of the tenth embodiment, in step (b) for the treatment of 100 g of the support T such a volume of aqueous metal salt solution V _MS (100 g T) uses that the ratio of the numerical value of the volume V _MS (100 g T) expressed in milliliters to the numerical value of the maximum absorbency expressed in percent of the carrier to be treated S _T is at most equal to 1.00: [V _MS (100 g T) / ml ] / [S _T / %] ≤ 1.00, where the maximum absorbency of the carrier S _T is calculated from the ratio of the maximum mass of deionized water m _H2O that a sample P _T of the carrier can absorb to the mass of the sample of the carrier m _PT , multiplied by 100%: S _T = [ m _H2O / m _PT ] × 100 %. In a twelfth embodiment of the process according to the invention for preparing an aromatic amine, which is a particular embodiment of the eleventh embodiment, the following applies: 0.95 ≤ [V _MS (100 g T) / ml] / [S _T / %] ≤ 0.99. In a thirteenth embodiment of the process according to the invention for preparing an aromatic amine, which is a further particular embodiment of the eleventh embodiment, the following applies: 0.96≦[V _MS (100 g T)/ml]/[S _T /%]≦0, 98 In a fourteenth embodiment of the process according to the invention for preparing an aromatic amine, which is a particular embodiment of the tenth to thirteenth embodiment, in step (f) for the treatment of 100 g of the first calcined catalyst precursor KV1 such a volume of ammoniacal copper salt solution V _KS ( 100 g KV1) used that the ratio of the numerical value of the volume V _KS (100 g T), given in milliliters, to the numerical value of the maximum absorption capacity, given in percent, of the first calcined catalyst precursor S _KV1 to be treated is at most equal to 1.00: [V _KS ( 100 g KV1) / ml] / [S _KV1 / %] ≤ 1.00, where the maximum absorbency of the first calcined catalyst precursor S _KV1 is calculated from the ratio of the maximum mass of deionized water m _H2O that a sample P _KV1 of the first can accommodate calcined catalyst precursor, to the mass of the sample first calcined catalyst precursor m _PKV1 , multiplied ert with 100%: S _KV1 = [m _H2O / m _PKV1 ] × 100%. In a fifteenth embodiment of the process according to the invention for preparing an aromatic amine, which is a particular embodiment of the fourteenth embodiment, the following applies: 0.95≦[V _KS (100 g KV1)/ml]/[S _KV1 /%]≦0.99 . In a sixteenth embodiment of the process according to the invention for preparing an aromatic amine, which is a further particular embodiment of the fourteenth embodiment, the following applies: 0.96≦[V _KS (100 g KV1)/ml]/[S _KV1 /%]≦0, 98 In a seventeenth embodiment of the process for preparing an aromatic amine according to the present invention, which is a particular aspect of the tenth to sixteenth embodiments, the metal salt comprises a metal nitrate or metal oxalate. In an eighteenth embodiment of the inventive method for preparing an aromatic amine, which is a particular aspect of the tenth to seventeenth embodiments, the metal salt comprises zinc(II) nitrate, iron(III) nitrate, Cobalt(III) nitrate or a mixture of two or more of the aforementioned metal nitrates and consists in particular of one of the aforementioned. In a nineteenth embodiment of the process for preparing an aromatic amine of the present invention, which is a particular aspect of the tenth to eighteenth embodiments, the dissolving in step (I)(a) is carried out at temperatures ranging from 20.0°C to 25°C . In a twentieth embodiment of the process for preparing an aromatic amine of the present invention, which is a particular aspect of the tenth to nineteenth embodiments, the drying in step (I)(c) is carried out at temperatures ranging from 80°C to 150°C. In a twenty-first embodiment of the process for preparing an aromatic amine according to the present invention, which is a particular aspect of the tenth to twentieth embodiments, the calcination in step (I)(d) is carried out at temperatures ranging from 300°C to 600°C. In a twenty-second embodiment of the process for producing an aromatic amine according to the present invention, which is a specific aspect of the tenth to twenty-first embodiments, the copper salt comprises basic copper carbonate (copper hydroxide carbonate, CuCO ₃ .Cu(OH) ₂ ). In a twenty-third embodiment of the process for preparing an aromatic amine according to the invention, which is a particular aspect of the tenth to twenty-second embodiments, in step (I)(e) in addition to the copper salt, an ammonium salt, in particular ammonium carbonate or ammonium acetate, is also added to the aqueous ammonia solved. In a twenty-fourth embodiment of the process of the present invention for preparing an aromatic amine, which is a particular aspect of the tenth to twenty-third embodiments, the dissolving in step (I)(e) is carried out at temperatures ranging from 0.0°C to 25.0°C C (with excess ammonia, corresponding to pH 9.0 or greater) or in the range from 0.0 °C to 10.0 °C (at a lower pH value). In a twenty-fifth embodiment of the process for preparing an aromatic amine according to the present invention, which is a particular aspect of the tenth to twenty-fourth embodiments, the drying in step (I)(g)(1) or step (I)(g)(2) carried out at temperatures ranging from 80 °C to 150 °C. In a twenty-sixth embodiment of the process of the present invention for preparing an aromatic amine, which is a particular aspect of the tenth to twenty-fifth embodiments, the calcination in step (I)(g)(2) is at temperatures ranging from 300°C to 600°C carried out. In a twenty-seventh embodiment of the inventive method for preparing an aromatic amine, which is a particular aspect of the tenth to twenty-sixth embodiment, the ammoniacal copper salt solution has a pH (20° C.) in the range from 7.0 to 14, preferably 7.0 up to 12.0. In a twenty-eighth embodiment of the process according to the invention for preparing an aromatic amine, which is a particular embodiment of the tenth to twenty-seventh embodiments, the treatment in steps (I)(b) and/or (I)(f) comprises impregnating the support or The first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution. In a twenty-ninth embodiment of the inventive method for preparing an aromatic amine, which is another particular aspect of the tenth to twenty-seventh embodiments, the treating in steps (I)(b) and/or (I)(f) comprises spraying the support or the first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution. In a thirtieth embodiment of the process according to the invention for preparing an aromatic amine, which can be combined with all other embodiments, the optionally activated hydrogenation catalyst in step (III) is arranged in a fixed catalyst bed. In a thirty-first embodiment of the process according to the invention for the preparation of an aromatic amine, which can be combined with all other embodiments, an aromatic nitro compound of the formula hydrogenated, in which R1 and R2 are independently hydrogen, methyl or ethyl, and R2 can also be NO ₂ . The embodiments briefly described above and further possible refinements of the invention are explained in more detail below. All of the embodiments and further configurations of the invention can be combined with one another as desired, unless the context clearly indicates the opposite to a person skilled in the art or something else is explicitly stated. PREPARING THE CATALYST FOR CARRYING OUT THE HYDROGEN The preparation of the hydrogenation catalyst according to the first aspect of the invention comprises the following steps: (a) Dissolving a metal salt selected from an iron salt, a cobalt salt, a manganese salt, a vanadium salt, a zinc salt or a mixture of two or more of the aforementioned metal salts in water or aqueous ammonia solution to obtain an aqueous metal salt solution; (b) treating the support with the aqueous metal salt solution to obtain a first impregnated catalyst precursor; (c) drying the first impregnated catalyst precursor to obtain a first dried catalyst precursor; (d) calcining the first dried catalyst precursor to obtain a first calcined catalyst precursor, steps (a) to (c) or (preferably) (a) to (d) also being repeated several times, in particular twice, (with the same or another metal salt ) can be traversed; (e) dissolving a copper salt in aqueous ammonia to obtain an ammoniacal copper salt solution; (f) treating the first calcined catalyst precursor with the ammoniacal copper salt solution to obtain a second impregnated catalyst precursor; (g) forming the doped copper tetrammine salt-based hydrogenation catalyst by (1) drying the second impregnated catalyst precursor or (2) drying and calcining the second impregnated catalyst precursor, wherein steps (e) to (g)(1) or (preferably) (e ) to (g)(2) can also be run through several times, in particular twice (with the same or a different copper salt). The treatment of the support or the first catalyst precursor with a solution of the doping metal or copper salt can be carried out by impregnation or spraying, as further already explained above. Treatment by soaking is preferred. Both techniques are well known per se in the technical field and therefore do not need to be explained in more detail here. Both when using impregnation and when using spraying, it is preferable to use the solution of the doping metal or copper salt in such a ratio to the support (T) or to the first calcined catalyst precursor (KV1) that the maximum absorbency S of the support ( S _T ) or the first calcined catalyst precursor (S _KV1 ) is not exceeded (so-called incipient wetness method), with the maximum absorbency of the carrier or the first calcined catalyst precursor being calculated from the ratio of the maximum mass of deionized water m _H2O , which can hold a sample of the support or the first calcined catalyst precursor, to the mass of the sample of the support (m _PT ) or the first calcined catalyst precursor (m _PKV1 ), multiplied by 100 %: S _T = [ m _H2O / m _PT ] × 100%. S _KV1 = [m _H2O / m _PKV1 ] × 100%. In the context of the present invention, the fact that the maximum absorbency S is not exceeded means that for the treatment of 100 g of the support T or 100 g of the first calcined catalyst precursor KV1, such a volume of aqueous metal salt solution V _MS (100 g T) or Copper salt solution V _KS (100 g KV1) is used that the ratio of the numerical value of the volume of the metal salt solution V _MS (100 g T) or the copper salt solution V _KS (100 g T) given in milliliters to the numerical value of the maximum absorbency given in percent of the support S _T to be treated or of the first calcined catalyst precursor S _KV1 to be treated is at most 1.00. It therefore preferably applies: [V _MS (100 g T) / ml] / [S _T /%] ≤ 1.00. Particularly preferably, 0.95≦[V _MS (100 g T)/ml]/[S _T /%]≦0.99 applies, very particularly preferably 0.96≦[V _MS (100 g T)/ml]/ [S _T /%] ≤ 0.98. Furthermore, the following preferably applies: [V _KS (100 g KV1)/ml]/[S _KV1 /%]≦1.00. Particularly preferably, 0.95≦[V _KS (100 g KV1)/ml]/[S _KV1 /%]≦0.99, very particularly preferably 0.96≦[V _KS (100 g KV1)/ml]/ [S _KV1 / %] ≤ 0.98. Irrespective of the type of treatment and the choice of proportions in the treatment step, it is preferred to use an iron salt, a zinc salt, a cobalt salt or a mixture of two or more of the aforementioned metal salts as the metal salt. Especially Metal nitrates or metal oxalates are preferably used. The metal salt is very particularly preferably zinc(II) nitrate, iron(III) nitrate, cobalt(III) nitrate or a mixture of two or more of the aforementioned metal nitrates. The dissolving of the metal salts in step (a) is not temperature critical and can occur at ambient temperature, e.g. B.20 °C to 25 °C can be carried out. When treating the support with the metal salt solution in step (b), it is possible to leave the wet support for a longer period of time before carrying out the next step (so-called "mauking"). However, this is not necessary. Temperatures in the range from 80° C. to 150° C. have proven suitable for the drying step (c). The calcination in step (d) is preferably carried out at temperatures ranging from 300°C to 600°C. Drying and calcination are preferably carried out in an oxygen-containing atmosphere, in particular air. However, calcination in an inert gas atmosphere (for example in a nitrogen atmosphere) is also conceivable. Basic copper carbonate (copper hydroxide carbonate, CuCO ₃ .Cu(OH) ₂ ) is preferably used as the copper salt. Irrespective of the exact type of copper salt, it has proven useful in step (e) to also dissolve an ammonium salt, such as in particular ammonium carbonate or ammonium acetate, in the aqueous ammonia in addition to the copper salt. Step (e) is preferably carried out at temperatures in the range from 0.0°C to 25.0°C (in particular with excess ammonia, corresponding to pH 9.0 or greater) or in the range from 0.0°C to 10.0°C (especially at lower pH). It is preferred that the ammoniacal copper salt solution has a pH (20°C) in the range of 7.0 to 14.0, preferably 7.0 to 12.0. When treating the first calcined catalyst precursor with the copper salt solution in step (f), it is possible to leave the wet first calcined catalyst precursor for a longer period of time before carrying out the next step (so-called "mauking"). However, this is not necessary. The drying according to step (g)(1) or step (g)(2) is preferably carried out at temperatures in the range from 80°C to 150°C. If a calcination is carried out in step (g)(2), this is preferably carried out at temperatures in the range from 300.degree. C. to 600.degree. Drying and calcination are preferably carried out in an oxygen-containing atmosphere, in particular air. However, calcination in an inert gas atmosphere (for example in a nitrogen atmosphere) is also conceivable. The process according to the invention is preferably carried out in such a way that a mass fraction of copper compounds, calculated as metallic Cu, in the doped copper tetrammine salt-based hydrogenation catalyst, based on its total mass, is in the range from 8% to 25%. A mass fraction of metal compounds that are different from copper compounds, calculated as metals, in the doped copper tetrammine salt-based hydrogenation catalyst, based on its total mass, is preferably in the range from 0.1% to 25%, preferably set at 1.0% to 20%. The mole fraction of Cu, based on all metals present, in the doped copper tetrammine salt-based hydrogenation catalyst is preferably set to a value in the range from 0.30 to 0.99, preferably 0.45 to 0.95. Accordingly, the mole fraction of all doping metals, based on all metals present, is preferably from 0.01 to 0.70, preferably from 0.05 to 0.55. The hydrogenation catalyst according to the second aspect of the invention can be obtained by using the above-described method for preparing a hydrogenation catalyst. CARRYING OUT THE HYDROGEN The process for preparing an aromatic amine by hydrogenating an aromatic nitro compound according to the third aspect of the invention comprises the following steps: (I) providing a doped copper tetrammine salt-based hydrogenation catalyst according to the second aspect of the invention, ie providing a hydrogenation catalyst comprising copper in metallic or oxidic form and (at least) one doping metal in metallic or oxidic form on a support as a hydrogenation catalyst, the hydrogenation catalyst being obtainable by applying the doping metal to the support, followed by applying the copper to the support containing the doping metal and in particular being obtainable by the process according to the invention for preparing a hydrogenation catalyst (ie the hydrogenation catalyst is in particular the hydrogenation catalyst according to the invention), the doping metal being selected from iron and cobalt , manganese, vanadium, zinc, or a mixture of two or more thereof, and wherein the support comprises silica shaped bodies and/or silicon carbide shaped bodies; (II) optionally, activating the hydrogenation catalyst by treating it with hydrogen in the absence of the aromatic nitro compound; (III) Reacting the aromatic nitro compound with hydrogen in the presence of the optionally activated hydrogenation catalyst to give the aromatic amine. The mass fraction of copper compounds, calculated as metallic Cu, of the hydrogenation catalyst provided in step (I), based on its total mass, is preferably in the range from 8% to 25%. The mass fraction of metal compounds (calculated as metal), which are different from copper compounds, of the hydrogenation catalyst provided in (I), based on its total mass, is preferably in the range from 0.1% to 25%, preferably 1.0% to 20% %. It is preferred that the mole fraction of Cu, based on all metals present, in the doped copper tetrammine salt-based hydrogenation catalyst is in the range from 0.30 to 0.99, preferably 0.45 to 0.95. Accordingly, the mole fraction of all metals other than copper is preferably from 0.01 to 0.70, preferably from 0.05 to 0.55. The doping metal is in particular iron, zinc, cobalt or a mixture of two or more of the aforementioned metals. The hydrogenation catalyst is in particular a copper tetrammine carbonate-based hydrogenation catalyst. Particular preference is given to using a copper tetrammine carbonate-ammonium salt-based hydrogenation catalyst, in particular a copper tetrammine carbonate-ammonium carbonate-based hydrogenation catalyst or a copper tetrammine carbonate-ammonium acetate-based hydrogenation catalyst, as the hydrogenation catalyst. For further details of the hydrogenation catalyst to be provided in step (I), reference can be made to the description of the process for preparing a hydrogenation catalyst according to the first aspect of the invention. It is preferred to carry out the activation according to step (II). Temperatures in the range from 180 °C to 240 °C have proven suitable for this step. The actual hydrogenation, step (III), can be carried out adiabatically (ie without cooling or heating) or isothermally (ie with cooling by dissipating the heat of reaction, for example by using a tube bundle reactor with a heat carrier flushing the tubes). With adiabatic reaction management, molar ratios of hydrogen to nitro groups in the range from 10 to 200 and temperatures in the range from 160° C. to 500° C. or (preferably) 180° C. to 400° C. have proven useful. When the reaction is carried out isothermally, molar ratios of hydrogen to nitro groups in the range from 3 to 100 and temperatures in the range from 180° C. to 550° C. or (preferably) 190° C. to 400° C. have proven useful. It is preferred to arrange the hydrogenation catalyst for carrying out step (III) in a fixed catalyst bed. The hydrogenation process according to the invention has proven particularly useful for hydrogenating aromatic nitro compounds of the following formula: in which R1 and R2, independently of one another, are hydrogen, methyl or ethyl, it also being possible for R2 to be NO ₂ . The invention is explained in more detail below with the aid of examples.

EXAMPLES General Methods Determining the Maximum Absorbency of the Backing The maximum absorbency is determined by weighing the shaped bodies before and after water absorption, as described below. For this purpose, the carrier material TM (either untreated carrier or carrier already treated with doping metal or copper) is weighed and left covered with deionized water (DI water) until no more air bubbles rise. The supernatant water is decanted and the moist moldings are dried externally by rolling on filter paper. The water absorption in grams, which corresponds to the maximum absorbency of the shaped body used, is obtained by weighing the shaped bodies dried externally in this way and subtracting the initial weight. In the case of multiple impregnations, the absorbency of the carrier material is determined before each impregnation. The maximum absorbency S is expressed as a percentage in the terminology of the present invention: S=[(mass of water absorbed)/(mass of substrate before water absorption)]×100%. For the purpose of calculating the amount of impregnating salt solution to be used, the volume of the metal salt solution V _MS or copper salt solution V _KS to be used for impregnation, whose numerical value in ml corresponds to the numerical value of the maximum absorbency S in %, is set as the impregnating volume which 100 g of the carrier material used can absorb maximum. In the following examples, an impregnation volume of metal salt solution V _MS (100 g DM) or copper salt solution V _KS (100 g DM) was used to saturate 100 g of the carrier material, which corresponded to 98% of the value for S determined in this way. This applies to all impregnation steps (i.e. both for the application of the doping metal and for the application of the copper and, in the case of multiple impregnations, for each individual impregnation step). Calculation examples: a) The absorptivity of SiO ₂ shaped bodies “SS69138” (3 mm extrudates) from Saint-Gobain Norpro (used as carrier in all tests) was determined to be 108.5%. In order to saturate 100 g of these shaped bodies up to the maximum absorbency S in the terminology of the present invention, 108.5 ml of saline solution would therefore be required. [108.5 ml×0.98=] 106.3 ml of impregnation solution per 100 g of moldings were actually used. b) The absorptivity of Zn-doped SiO ₂ shaped bodies was determined to be 88.8%. [88.8 ml×0.98=]87.0 ml copper tetrammine solution were therefore used for the copper impregnation of 100 g of the Zn-doped SiO ₂ molded body. General instructions for preparing the catalysts 21 catalysts were prepared. Details can be found in Table 1. Unless expressly stated otherwise in Table 1, the following conditions were met: 1. Impregnation of the carrier with doping metal Preparation of the impregnation solution (step (a)): The required amount of metal salt is dissolved in 75 ml of deionized water (DI water ) and filled up to the required volume of soaking solution with deionized water. Implementation of the impregnation (step (b)): 100 g of the SiO ₂ carrier are added to the aqueous metal salt solution while mixing with tumbling movements. After 10 minutes of movement, the liquid intake is complete. Carrying out the drying (step (c)): The impregnated carrier is dried in a warm-air dryer at 120° C. for 40 minutes. Carrying out the calcination (step (d)): the dried support impregnated with the doping metal is heated in a static oven at a rate of 3° C./min to 450° C. and this temperature is maintained for 4 h. After cooling to room temperature, steps (a) to (d) can be repeated. 2. Impregnation of the doped carrier with copper Preparation of the copper tetrammine salt solution (step (e)): masses used for a solution with a mass fraction of Cu of (10.0 ± 0.5)% at pH = 10.0 ±1, 0: · ammonium carbonate 316 g · basic copper carbonate 364 g · 25-30% ammonia 652 g · deionized water 668 g First, the ingredients are cooled in the refrigerator to below 5 °C. Water and ammonia are mixed in a sealable container. The solids are weighed together in a bowl, quickly added to the cooled ammonia solution and mixed with the lid closed (with a pressure equalization valve for safety reasons) until the salts have dissolved. A dark blue solution with a copper concentration of 10% by mass and a pH of 10 was obtained. The density of the solution at room temperature was determined to be 1.22 g/ml. Carrying out the impregnation (step (f)): The carrier material covered with one or more doping metals from step 1 is added to the required proportion of the copper tetrammine salt solution while mixing with tumbling movements. After 10 minutes of movement, the fluid intake was over. Carrying out the drying (step (g) (1)): The carrier material impregnated with copper tetrammine salt solution is dried in a hot-air dryer at 120° C. for 60 minutes. A color change from dark blue to green or black is observed. Carrying out the calcination (step (g)(2), optional): The dried support material is heated to 450° C. at a rate of 3° C./min and held at this temperature for 4 h. The black catalyst particles obtained are cooled to room temperature within about 8 hours. After cooling to room temperature, steps (e) through (g)(1) or (e) through (g)(2) can be repeated. The metal contents relate to the hydrogenation catalyst in the reduced state (after reduction with hydrogen). If there was only 1 or 2 soaks, the final calcination is identical to the calcination after the first (or second) soak. Max Absorbency = maximum absorbency; na = not applicable; according to = according to the invention. Hydrogenation Experiments The catalysts prepared as described above were used in the hydrogenation of nitrobenzene to aniline. For this purpose, the respective catalysts were transferred in the oxidized state to a fixed-bed reactor and nitrogen flowed through them until the remaining oxygen had been expelled. The temperature was adjusted to values in the range from 200°C to 240°C and activation started by metering in hydrogen. The exotherm caused by the reaction should be kept as low as possible. Nitrobenzene (NB) was dosed to the activated catalyst for the reaction, with the amount of nitrobenzene being successively increased and adjusted to the target load of 0.9 gNB ml _cat ^-1 h ^-1 . The molar hydrogen:nitrobenzene ratio was 10:1. The reaction was carried out polytropically, with a heat transfer medium dissipating the heat generated during the reaction. The hydrogenation was carried out in each case until breakthrough of nitrobenzene and thus incomplete conversion was observed. After completion of the reaction, the catalyst was flushed with nitrogen to remove the excess hydrogen. For reactivation, air was passed through the deactivated catalyst at 260° C. to 320° C. until the resulting exotherm had subsided. As a result, the catalyst was again in the oxidic state, after which a second run could be started following the same procedure. The results in terms of running times and aniline selectivities are summarized in Table 2. The catalysts were used and evaluated in at least two consecutive runs.

As can be seen, the use of doping elements has a significant impact on the

catalyst performance. In particular, the elements zinc and iron turned out to be suitable additives to stabilize the running time in the second run or to increase it in the first run, while magnesium proved to be unsuitable. In example K11, it was possible to produce a catalyst which was stable over three hydrogenation tests and had a long service life and selectivity, as can be seen from example H11. With the catalyst from Example K14, it was even possible to combine the positive influence of two doping elements (see the corresponding hydrogenation experiment H14).

Claims

Claims: 1. A process for preparing a doped copper tetrammine salt-based hydrogenation catalyst suitable for hydrogenating an aromatic nitro compound to obtain an aromatic amine, the hydrogenation catalyst comprising copper in metallic or oxidic form and a doping metal in metallic or oxidic form on a support, the support being silicon dioxide moldings and/or silicon carbide moldings, the method comprising the steps: (a) dissolving a metal salt selected from an iron salt, a cobalt salt, a manganese salt, a vanadium salt, a zinc salt or a mixture of two or more of the aforementioned metal salts in water or aqueous ammonia solution to obtain an aqueous metal salt solution; (b) treating the support with the aqueous metal salt solution to obtain a first impregnated catalyst precursor; (c) drying the first impregnated catalyst precursor to obtain a first dried catalyst precursor; (d) calcining the first dried catalyst precursor to obtain a first calcined catalyst precursor, it also being possible for steps (a) to (c) or (a) to (d) to be repeated several times; (e) dissolving a copper salt in aqueous ammonia to obtain an ammoniacal copper salt solution; (f) treating the first calcined catalyst precursor with the ammoniacal copper salt solution to obtain a second impregnated catalyst precursor; (g) forming the doped copper tetrammine salt-based hydrogenation catalyst by (1) drying the second impregnated catalyst precursor or (2) drying and calcining the second impregnated catalyst precursor, wherein steps (e) through (g)(1) or (e) through ( g)(2) can also be run through multiple times.

2. The method according to claim 1, in which in step (b) for the treatment of 100 g of the carrier T such a volume of aqueous metal salt solution V _MS (100 g T) is used that the ratio of the numerical value of the volume V indicated in milliliters _MS (100 g T) to the numerical value of the maximum absorbency expressed as a percentage of the carrier to be treated S _T is at most equal to 1.00: [V _MS (100 g T) / ml] / [S _T / %] ≤ 1.00, where the maximum absorbency of the carrier S _T is calculated from the ratio of the maximum mass of deionized water m _H2O that a sample P _T of the carrier can absorb to the mass of the sample of the carrier m _PT , multiplied by 100%: S _T = [ m _H2O / m _PT ] × 100%; and/or in which in step (f) for the treatment of 100 g of the first calcined catalyst precursor KV1 such a volume of ammoniacal copper salt solution V _KS (100 g KV1) is used that the ratio of the numerical value of the volume V _KS given in milliliters ( 100 g T) for the numerical value of the maximum absorption capacity, given in percent, of the first calcined catalyst precursor S _KV1 to be treated is at most equal to 1.00: [V _KS (100 g KV1) / ml] / [S _KV1 / %] ≤ 1.00, where the maximum suction capacity of the first calcined catalyst precursor S _KV1 is calculated from the ratio of the maximum mass of deionized water m _H2O that a sample P _KV1 of the first calcined catalyst precursor can absorb to the mass of the sample of the first calcined catalyst precursor m _PKV1 , multiplied by 100 %: S _KV1 = [m _H2O / m _PKV1 ] × 100%.

3. A method according to any one of the preceding claims, wherein the metal salt comprises a metal nitrate or metal oxalate; and/or wherein the copper salt comprises copper hydroxide carbonate.

4. The method according to any one of the preceding claims, wherein in step (e) in addition to the copper salt, an ammonium salt is also dissolved in the aqueous ammonia.

5. The method according to any one of the preceding claims, in which the treatment in steps (b) and/or (f) comprises impregnating the support or the first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution; or in which the treatment in steps (b) and/or (f) comprises spraying the support or the first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution.

6. The method according to any one of the preceding claims, in which the silicon dioxide or silicon carbide shaped bodies are (i) spheres, (ii) cylinders or (iii) aggregates of several cylinders connected to one another along their longitudinal axis and have an average diameter in the range of 1 .0 mm to 15 mm, whereby the average diameter in the case of cylinders refers to the base of the cylinder and in the case of aggregates of several cylinders connected to one another along their longitudinal direction to a circle enveloping the bases of the connected cylinders.

7. Doped copper tetrammine salt-based hydrogenation catalyst obtainable by a process according to any one of the preceding claims.

8. A process for producing an aromatic amine by hydrogenating an aromatic nitro compound, comprising the steps of: (I) providing a doped copper tetrammine salt-based hydrogenation catalyst according to claim 7; (II) optionally, activating the hydrogenation catalyst by treating it with hydrogen in the absence of the aromatic nitro compound; (III) Reacting the aromatic nitro compound with hydrogen in the presence of the optionally activated hydrogenation catalyst to give the aromatic amine.

9. The process as claimed in claim 8, in which a copper tetrammine carbonate-based hydrogenation catalyst is used as the hydrogenation catalyst.

10. The process as claimed in claim 9, in which a hydrogenation catalyst based on copper tetrammine carbonate and ammonium salt is used as the hydrogenation catalyst.

11. A method according to any one of claims 8 to 10, wherein step (I) comprises: (a) dissolving a metal salt selected from an iron salt, a cobalt salt, a manganese salt, a vanadium salt, a zinc salt or a mixture of two or more of the foregoing metal salts in water or aqueous ammonia solution to obtain an aqueous metal salt solution; (b) treating the support with the aqueous metal salt solution to obtain a first impregnated catalyst precursor; (c) drying the first impregnated catalyst precursor to obtain a first dried catalyst precursor; (d) calcining the first dried catalyst precursor to obtain a first calcined catalyst precursor, it also being possible for steps (a) to (c) or (a) to (d) to be repeated several times; (e) dissolving a copper salt in aqueous ammonia to obtain an ammoniacal copper salt solution; (f) treating the first calcined catalyst precursor with the ammoniacal copper salt solution to obtain a second impregnated catalyst precursor; (g) formation of the doped copper tetrammine salt-based hydrogenation catalyst by (1) drying the second impregnated catalyst precursor or (2) drying and calcining the second impregnated catalyst precursor, wherein steps (e) to (g)(1) or (e) to (g )(2) can also be run through multiple times.

12. The method according to claim 11, in which in step (b) for the treatment of 100 g of the carrier T such a volume of aqueous metal salt solution V _MS (100 g T) is used that the ratio of the numerical value of the volume V indicated in milliliters _MS (100 g T) to the numerical value of the maximum absorbency expressed as a percentage of the carrier to be treated S _T is at most equal to 1.00: [V _MS (100 g T) / ml] / [S _T / %] ≤ 1.00, where the maximum absorbency of the carrier S _T is calculated from the ratio of the maximum mass of deionized water m _H2O that a sample PT of the carrier can hold to the mass of the sample of the carrier m _PT , multiplied by 100%: S _T = [m _H2O / _mPT ] × 100%; and/or in which in step (f) for the treatment of 100 g of the first calcined catalyst precursor KV1 such a volume of ammoniacal copper salt solution V _KS (100 g KV1) is used that the ratio of the numerical value of the volume V _KS given in milliliters ( 100 g T) for the numerical value of the maximum absorption capacity, given in percent, of the first calcined catalyst precursor S _KV1 to be treated is at most equal to 1.00: [V _KS (100 g KV1) / ml] / [S _KV1 / %] ≤ 1.00, where the maximum suction capacity of the first calcined catalyst precursor S _KV1 is calculated from the ratio of the maximum mass of deionized water m _H2O that a sample P _KV1 of the first calcined catalyst precursor can absorb to the mass of the sample of the first calcined catalyst precursor m _PKV1 , multiplied by 100% : S _KV1 = [m _H2O / m _PKV1 ] × 100%.

13. The method according to claim 11 or 12, wherein the treatment in steps (b) and/or (f) comprises impregnating the support or the first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution; or in which the treatment in steps (b) and/or (f) comprises spraying the support or the first catalyst precursor with the metal salt solution or the ammoniacal copper salt solution.

14. A method according to any one of claims 8 to 13, wherein the metal salt comprises a metal nitrate or metal oxalate; and/or wherein the copper salt comprises copper hydroxide carbonate; and/or at which in step (I)(e), in addition to the copper salt, an ammonium salt is also dissolved in the aqueous ammonia.

15. The process as claimed in any of claims 8 to 14, in which the optionally activated hydrogenation catalyst in step (III) is arranged in a fixed catalyst bed.