WO2019020793A1

WO2019020793A1 - Process for producing a shaped catalyst body comprising silver applied to an alumina support

Info

Publication number: WO2019020793A1
Application number: PCT/EP2018/070423
Authority: WO
Inventors: Joseph John ZAKZESKI; Marco Bosch; Thomas Metzger; Christian Bartosch; Juergen Zuehlke; Andreas Lehr; Tobias GOEBEL; Marc Wagner; Andrey Karpov
Original assignee: Basf Se
Priority date: 2017-07-28
Filing date: 2018-07-27
Publication date: 2019-01-31

Abstract

The present invention is directed to a process for producing a shaped catalyst body comprising silver applied to an alumina support, which comprises providing an alumina support, with a defined pore structure and then applying a defined amount of an impregnation solution comprising silver to the alumina support. Furthermore, the present invention is directed to a shaped catalyst body comprising silver applied to an alumina support obtained or obtainable according to the process of the present invention and its use as catalyst for preparing ethylene oxide by gas-phase oxidation of ethylene by means of oxygen.

Description

PROCESS FOR PRODUCING A SHAPED CATALYST BODY COMPRISING SILVER APPLIED TO AN ALUMINA SUPPORT

The present invention is directed to a process for producing a shaped catalyst body comprising silver applied to an alumina support, which comprises providing an alumina support, with a de- fined pore structure and then applying a defined amount of an impregnation solution comprising silver to the alumina support. Furthermore, the present invention is directed to a shaped catalyst body comprising silver applied to an alumina support obtained or obtainable according to the process of the present invention and its use as catalyst for preparing ethylene oxide by gas- phase oxidation of ethylene by means of oxygen.

Ethylene oxide is an important basic chemical and frequently prepared on an industrial scale by direct oxidation of ethylene with oxygen in the presence of silver-containing catalysts. These catalysts usually comprise metallic silver and further elements, which have been deposited on a support material by means of a suitable process. As support, it is in principle possible to use various porous materials such as activated carbon, titanium dioxide, zirconium dioxide or silicon dioxide or ceramic compositions or mixtures of these materials. In general, alpha-aluminum oxide is used as support. It is in principle possible to use alpha-aluminum with a wide-range of physical properties as support material. Typically, supports with relatively low surface area, for example below 10 m²/g, and either a mono-modal or bi-modai pore distribution are preferred. For example, US 7560577 B2 and US 7977274 B2 discloses the use of a support with a two log differential pore volume distribution peaks in a pore diameter range of 0.01 - 100 μπι and 1 -20 μπι, respectively, and at least one peak in a pore diameter range of 0.01 - 1 .0 μπι and 0.1 - 5 pm, respectively, measured by mercury porosimetry. It is thought that the smaller pores of size e.g. 0.1 μηι repress sequential oxidation of ethylene oxide caused by retention of the gaseous product during the production of ethylene oxide, whereas pores of diameter e.g. 10 μπι or smaller give strength to the carrier. Apart from silver as active component, these catalysts often comprise promoters for improving the catalytic properties (WO 2007/122090 A1 , WO

2010/123856 A1 ). Examples of promoters are alkali metal compounds and/or alkaline earth metal compounds. Some documents teach the use of transition metals such as cobalt (EP 0 480 538 A1 ), tungsten or molybdenum. A particularly preferred promoter for influencing the activity and selectivity of catalysts is rhenium. In industry, preference is given to using catalysts comprising rhenium and/or other transition metal promoters in combination with alkali metal compounds and/or alkaline earth metal compounds because of their high selectivity. Selectivity is, for example in the case of the oxidation of ethylene, the molar percentage of ethylene which reacts to form ethylene oxide. The activity of the catalyst is usually characterized by the ethylene oxide concentration at the reactor outlet under otherwise constant conditions, for example temperature, pressure, gas throughput, amount of catalyst, etc. The higher the ethylene oxide concentration in the reactor output stream, the higher the activity of the catalyst. The lower the temperature required for achieving a predetermined ethylene oxide concentration, the higher the activity.

The direct oxidation of ethylene to ethylene oxide using supported silver catalysts is described, for example, in DE-A-2300512, DE-A 2521906, EP-A-0014457, DE-A-2454972, EP-A-0172565, EP-A-0357293, EP-A-0266015, EP-A-001 1356, EP-A-0085237, DE-A-2560684 and DE-A- 2753359.

EP 1 613 428 B1 describes the production of ethylene oxide from ethylene using a catalyst con- taining rhenium in an amount of at most 1 .5 mmol/kg with respect to the total weight of the catalyst or 0.0015 mmol/m² with respect to the BET surface area of the support. EP 2 152 41 1 A2 describes the use of promoters and co-promoters consisting of sulfur, phosphorus, boron, or mixtures thereof, tungsten, molybdenum, chromium, such that the quantity of the co-promoter deposited on the support is at most 3.8 mmol/kg relative to the weight of the support. EP 0 764 464 B1 describes the pretreating of a porous carrier with a solution of lithium and cesium and then heat-treating the carrier and thereafter impregnating with a silver and cesium compound.

EP 0 425 020 describes the use of two or more impregnations to achieve a desired silver concentration preferably 30 to 60 percent by weight, in which the promoters may be dosed either in both or only during the last impregnation.

It was an object of the present invention to provide novel catalysts for the epoxidation of al- kenes, which display advantageous activities and/or selectivities and a process for the preparation thereof.

This object according to the present invention is solved by a process for producing a shaped catalyst body comprising silver applied to an alumina support or a pretreated alumina support, which comprises an impregnation step which comprises

(a) providing an alumina support or a pretreated alumina support, wherein the alumina support or the pretreated alumina support, preferably the alpha-alumina support, has a total pore volume (V_totai) of 0.1 mL/g to 1.2 mL/g and at least two log differential pore volume distribution peaks in a pore diameter range of 0.01 to 100 μηη and at least one of the peaks is present in a pore diameter range of 0.1 to 5 μηη in the pore size distribution as measured by mercury porosimetry and the second peak is present in a pore diameter range of 6 to 100 μηη, and

wherein the pores of the alumina support or the pretreated alumina support with a pore diameter in the range of from 0.1 to 5 μηη form a volume (V1 ) mL/g of the alumina support or the pretreated alumina support wherein V1 is in the range of

0.1 (Vtotai) tO 0.9(Vtotal);

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support or the pretreated alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support or the pretreated alumina support.

According to the present invention, the process for producing a shaped catalyst body comprise an impregnation step which is carried out in controlled manner in order to predominantly fill the pores with a pore diameter in the range of for example 0.1 to 5 μηη. The impregnation solution can be applied to an alumina support or a pretreated alumina support according to the present invention. In the context of the present invention, if not specified otherwise, an alumina support is to be understood as an support which has not previously been impregnated with active com- ponents, i.e. a support which is free of silver and promotor metals. In the context of the present invention, a pretreated alumina support for example is a support which has already been impregnated with silver and/or promotor metals. In case a pretreated alumina support is impregnated according to the present invention, the volume of the pores with a pore diameter in the range of from 0.1 to 5 μηη might be smaller than the volume of the pores with a pore diameter in the range of from 0.1 to 5 μηη of the respective untreated alumina support.

According to the present invention, the process for producing a shaped catalyst body can comprise one or more impregnation steps, for example two or three impregnation steps. Each of the impregnation steps can comprise steps (a) and (b) as defined above.

According to one embodiment of the present invention, an alumina support is impregnated. According to a further embodiment, the present invention is therefore directed to a process for producing a shaped catalyst body comprising silver applied to an alumina support, which comprises an impregnation step which comprises providing an alumina support, wherein the alumina support, preferably the alpha- alumina support, has a total pore volume (V_totai) of 0.1 mL/g to 1.2 ml_/g and at least two log differential pore volume distribution peaks in a pore diameter range of 0.01 to 100 μηη and at least one of the peaks is present in a pore diameter range of 0.1 to 5 μηη in the pore size distribution as measured by mercury porosimetry and the second peak is present in a pore diameter range of 6 to 100 μηη, and

wherein the pores of the alumina support with a pore diameter in the range of from 0.1 to 5 μηη form a volume (V1 ) mL/g of the alumina support wherein V1 is in the range of

0.1 (Vtotai) tO 0.9 (Vtotai)! applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support.

According to a further aspect the present invention is also directed to a shaped catalyst body obtainable or obtained by a process for producing a shaped catalyst body comprising silver applied to an alumina support as disclosed above.

It was surprisingly found that when using the process of the present invention, impregnating the support with only sufficient silver-containing solution to fill the smallest pores during one or more impregnation steps, advantageous properties of the catalyst are obtained. More specifically, dosing only sufficient silver-containing solution to fill only the small pores with silver-containing solution has a favorable effect on the silver distribution in the catalyst, which leads to a relatively low silver-containing catalyst with exceptional activity comparable to high silver-containing catalysts. Thus a catalyst with relatively low silver content, produced as described in this invention, has surprisingly similar or better activity than a catalyst with higher silver content. The process according to the present invention comprises steps (a) and (b). According to step (a), an alumina support is provided, wherein the alumina support, preferably the alpha-alumina support, has a total pore volume (V_totai) of 0.1 ml_/g to 1 .2 mL/g and at least two log differential pore volume distribution peaks in a pore diameter range of 0.01 to 100 μηη and at least one of the peaks is present in a pore diameter range of 0.1 to 5 μηη in the pore size distribution as measured by mercury porosimetry and the second peak is present in a pore diameter range of 6 to 100 μηη, and wherein the pores of the alumina support with a pore diameter in the range of from 0.1 to 5 μηη form a volume (V1 ) mL/g of the alumina support wherein V1 is in the range of 0.1 (Vtotai) to 0.9 (Vtotai), preferably 0.2(V_totai) to 0.85(V_totai), more preferably 0.4(V_totai) to 0.8 (V_totai), more preferably 0.5(V_totai) to 0.7 (V_totai).

According to step (b), a volume (VA₉-IS) of an impregnation solution comprising silver is applied to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support. Preferably, the impregnation solution is applied under vacuum to allow for a defined impregnation step. Therefore, according to a further em- bodiment, the present invention is also directed to the process for producing a shaped catalyst body comprising silver applied to an alumina support as disclosed above, wherein the impregnation solution is applied under vacuum, wherein the applied vacuum is preferably below 200 mbar, more preferably below 100 mbar. Preferably, the volume (VA₉-IS) is in the range of 0.6(V1 ) to 1 .08(V1 ) mL/g, more preferable in the range of 0.7(V1 ) to 1.05(V1 ) mL/g, more preferable in the range of 0.8(V1 ) to 1.0(V1 ) mL/g.

Supports suitable for the purposes of the invention can be produced by processes known from the prior art. Examples are the processes described in US 2009/0198076 A1 , WO 2006/133187, WO 03/072244, US 2005/0096219 A1 and EP 0 496 386 B2.

Examples of suitable support materials are aluminum oxide, silicon dioxide, silicon carbide, titanium dioxide, zirconium dioxide and mixtures thereof, with aluminum oxide being preferred.

The term aluminum oxide as used here comprises all conceivable structures such as alpha-, gamma- or theta-aiuminum oxide. In a preferred embodiment, the support is an alpha-aluminum oxide support. The present invention accordingly also provides a process for producing a shaped catalyst body or a catalyst body or catalyst respectively in which the support is an alpha-aluminum oxide. In a further preferred embodiment, the alpha-aluminum oxide has a purity of at least 75%, preferably a purity of at least 80%, more preferably a purity of at least 85%, more preferably a purity of at least 90%, more preferably a purity of at least 98%, more preferably a purity of at least 98.5% and particularly preferably a purity of at least 99%. The term alpha-aluminum oxide ac- cordingly also comprises alpha-aluminum oxides which comprise further constituents, for example elements selected from the group consisting of zirconium, alkali metals, alkaline earth metals, silicon, zinc, gallium, hafnium, boron, fluorine, copper, nickel, manganese, iron, cerium, titanium, chromium and compounds of these elements and also mixtures of two or more of these elements and/or compounds thereof.

In general, a catalyst support suitable for the purposes of the present invention can be produced by mixing the aluminum oxide with water or another suitable liquid and also a burnout material or a pore former and at least one binder. Suitable pore formers are, for example, cellulose and cellulose derivatives such as methylcellulose, ethylcelluiose, carboxymethyl cellulose or polyole- fins such as polyethylene and polypropylene or natural burnout materials such as ground walnut shells. The pore formers are selected so that they are completely burnt out of the aluminum oxide to form the finished alpha-aluminum oxide support at the furnace temperatures selected for the calcination. Suitable binders or extrusion aids are described, for example, in EP 35 0 496 386 B2. Mention may be made by way of example of aluminum oxide gels with nitric acid or acetic acid, cellulose, e.g. methylcellulose, ethylcelluiose or carboxyethylcellulose or methyl stearate or ethyl stearate, polyolefin oxides, waxes and similar substances. The paste formed by mixing can be brought to the desired shape by extrusion. To assist the extrusion process, it is possible to use extrusion aids.

The shaped body obtained as described above is, after shaping, usually optionally dried and calcined to give the aluminum oxide support. Calcination is usually carried out at temperatures in the range from 1200 C to 1600 C. It is usual to wash the aluminum oxide support after calcination in order to remove soluble constituents.

The alpha-aluminum oxide can comprise the further constituents in any suitable form, for example as elements and/or in the form of one or more compounds. If the alpha-aluminum oxide comprises one or more constituents in the form of a compound, it comprises these as, for example, oxide or mixed oxide. Supports which are suitable for the purposes of the invention therefore also include alpha-aluminum oxides comprising at least one further constituent selected from the group consisting of silicon dioxide, sodium oxide, potassium oxide, calcium oxide and magnesium oxide, nickel oxide, gallium oxide, hafnium oxide, copper -oxide, iron oxide and mixtures thereof. As regards the amount of the further constituents, the totality of the further constituents is preferably in the range of less than 25% by weight, more preferably less than 20% by weight, more preferably less than 15% by weight, more preferably less than 10 % by weight, more preferably less than 5% by weight, more preferably less than 2% by weight, more preferably less than 1 .5% by weight and particularly preferably less than 1 % by weight, based on the total weight of the support. If the support comprises, for example, sodium or potassium, it preferably comprises from 10 to 1500 ppm of sodium or potassium, more preferably from 10 to 1000 ppm of sodium or potassium, more preferably from 10 to 500 ppm of sodium or potassium based on the total weight of the support and calculated as element. If the support comprises, for example, calcium, it preferably comprises from 1 0 to 2000 ppm of calcium, more preferably from 1 0 to 1 000 ppm of calcium, based on the total weight of the support and calculated as element. If the support comprises, for example, magnesium, it preferably comprises from 1 0 to 1 000 ppm of magnesium, more preferably from 1 0 to 500 ppm of magnesium based on the total weight of the support and calculated as element.

If the support comprises, for example, silicon, it preferably comprises this in an amount in the range from 1 0 to 1 0000 ppm, more preferably in an amount of from 50 to 5000 ppm, more preferably in an amount of from 75 to 1 000 ppm, based on the total weight of the support and calculated as element. If the support comprises, for example, zirconium, it preferably comprises this in an amount in the range from 1 0 to 1 0000 ppm, more preferably in an amount of from 1 00 to 7500 ppm, more preferably in an amount of from 500 to 5000 ppm, based on the total weight of the support and calculated as element.

Particular preference is given to an alpha-aluminum oxide which has a purity of at least 98% by weight and comprises from 75 to 1 000 ppm of silicon, from 1 0 to 500 ppm of sodium, from 1 0 to 500 ppm of potassium, from 1 0 to 1 000 ppm of calcium, from 1 0 to 500 ppm of magnesium, and optionally from 500 to 5000 ppm of zirconium, in each case calculated as element and based on the total weight of the support.

The support used for the catalyst of the invention preferably has a BET surface area, determined in accordance with the method described in the standard ISO 9277, of from 0.3 to 3.0 m²/g, more preferably in the range from 0.5 to 2.6 m²/g, more preferably in the range from 0.6 to 2.3 m²/g.

According to a further embodiment, the present invention is also directed to the process for producing a shaped catalyst body comprising silver applied to an alumina support as disclosed above, wherein the alumina support has a BET surface area in the range from 0.3 to 3.0 m²/g.

According to the present invention, the alumina support has a total pore volume (V_totai) of 0.1 mL/g to 1 .2 mL/g, preferably from 0.2 to 1 .0 mL/g, more preferably from 0.4 to 0.8 mL/g and at least two log differential pore volume distribution peaks in a pore diameter range of 0.01 to 1 00 μηη and at least one of the peaks is present in a pore diameter range of 0.1 to 5 μηη in the pore size distribution as measured by mercury porosimetry and the second peak is present in a pore diameter range of 6 to 1 00 μηη. The pores of the alumina support with a pore diameter in the range of from 0.1 to 5 μηη form a volume (V1 ) mL/g of the alumina support wherein V1 is in the range of 0.1 (Vtotai) to 0.9 (Vtotai), preferably 0.2(V_totai) to 0.85(V_totai), more preferably 0.4(V_totai) to 0.8(Vtotai), more preferably 0.5(V_totai) to 0.7 (Vtotai).

The supports more preferably have a bimodal pore size distribution having peak maxima in the range from 0.1 to 5 μπι and from 6 to 1 00 μιη, preferably in the range from 0.2 to 2 μιη and from 8 to 80 μηΊ, more preferably in the range from 0.3 to 1 .5 μπι and from 10 to 70 μπι. The pore diameters are determined by Hg porosimetry (as described in the standard DIN 66133:1993- 06). The geometric shape of the support can vary in wide ranges, but the support should advantageously be in the form of particles which allow unhindered diffusion of the reaction gases to a very large part of the outer surface area coated with the catalytically active silver particles and optionally further promoters and internal surface area of the support. The selected geometric shape of the support should ensure a very small pressure drop over the entire reactor length. In a preferred embodiment, the support is used as shaped bodies, for example as extrudate, hollow extrudate, star extrudate, sphere, ring or hollow ring. The support is preferably a shaped body having the geometry of a hollow body. Particular preference is given to cylinders having the following geometries (external diameter x length x internal diameter, in each case reported in mm): 5x5x1 .8, 6x6x2, 7x7x2.5, 7x7.5x2.5, 7.7x7x2.5, 7.5x7.5x2.5, 7x7x3, 7x7.5x3.0, 7.5x7x3.0, 7.5x7.5x3.0, 8x8x2.8, 8x8.5x2.8, 8.5x8x2.8, 8.5x8.5x2.8, 8x8x3, 8x8.5x3, 8.5x8x3, 8.5x8.5x3, 8x8x3.3, 8x8.5x3.3, 8.5x8x3.3, 8.5x8.5x3.3, 8.5x9x3, 9x8.5x3, 9x9x3, 9x9.5x3, 9.5x9x3, 9x9.5x3.5, 9.5x9x3.5. Each length indicated is subject to tolerances in the region of ± 0.5 mm. According to the invention, it is also possible for the catalyst to be used in the form of crushed catalyst material obtained from one or more of the shaped bodies mentioned.

The water absorption of the support is, for example, in the range from 0.1 mL/g to 1 .2 mL/g, preferably in the range from 0.2 mL/g to 1.0 mL/g, more preferably from 0.4 to 0.8 mL/g determined by vacuum cold-water uptake. According to step (b) of the process, the support is impregnated with a solution comprising silver. The catalyst obtained thus comprises silver as active metal. The impregnation solution can comprise silver in a suitable amount, for example suitable that the catalyst obtained comprises silver in an amount of, for example, from 1 to 50% by weight, preferably from 5 to 40% by weight, more preferably 10 to 35% by weight, based on the total weight of the catalyst and cal- culated as element.

The silver is preferably deposited on the support in the form of a silver compound, which can be a salt or a silver complex. The silver compound is preferably applied as a solution, in particular as a solution in water. In order to obtain the silver compound in soluble form, a complexing agent such as ethanolamine, EDTA, 1 ,3- or 1 ,2-propanediamine, ethylenediamine and/or oxalic acid, an alkali metal and/or ammonium oxalate can also be added in an appropriate way to the silver compound, for example silver (I) oxide or silver (I) oxalate and this complexing agent can also simultaneously act as reducing agent. Further examples of suitable silver complexes are disclosed in US2015/0174554. Silver is particularly preferably applied in the form of a silver- amine compound, particularly preferably a silver-ethylenediamine compound. The support is then impregnated with the resulting silver complex solution according to step (b) to yield a silver containing support. Furthermore, during the impregnation step or in a separate impregnation step, one or more promoters can be applied to the support and thus the catalyst of the invention can comprise one or more further elements as promoters. For the purposes of the present invention, a promoter is a constituent of the catalyst by means of which an improvement in one or more catalytic proper- ties, e.g. selectivity, activity, conversion, yield and/or operating life, compared to a catalyst which does not comprise the constituent is achieved. Preference is given to compounds which under the reaction conditions are chemically stable and do not catalyze any undesirable reactions. Promoters are usually used in a total amount of from 10 to 10000 ppm and each in an amount of from 5 to 2000 ppm, more preferably each in an amount of from 10 to 1500 ppm and particularly preferably each in an amount of from 50 to 1500 ppm, based on the total weight of the catalyst and calculated as sum of the elements. Promoters are preferably applied in the form of compounds to the support, for example in the form of complexes or in the form of salts, for example in the form of halides, fluorides, bromides or chlorides, or in the form of carbox- ylates, nitrates, sulfates or sulfides, phosphates, cyanides, hydroxides, carbonates, oxides, oxa- lates or as salts of heteropolyacids, for example in the form of salts of heteropolyacids of rhenium.

According to a further embodiment, the present invention is also directed to the process for producing a shaped catalyst body comprising silver applied to an alumina support as disclosed above, wherein the impregnation solution comprises at least one promoter selected from the group consisting of elements of groups IA, VI B, VI IB and VIA, preferably selected from the group consisting of tungsten, cesium, lithium and sulfur.

According to the present invention, rhenium is preferred as a promoter. More preferably, rheni- urn is used in combination with one or more additional promoters.

The catalyst of the invention preferably comprises rhenium as a promoter. According to a further embodiment, the present invention therefore is also directed to the process for producing a shaped catalyst body comprising silver applied to an alumina support as disclosed above, wherein the impregnation solution comprises rhenium.

The impregnation solution can comprise rhenium in a suitable amount, for example suitable that the catalyst obtained comprises rhenium in an amount of, for example from 10 to 2000 ppm, more preferably in an amount of from 50 to 1500 ppm, more preferably in an amount of from 100 to 1000 ppm, based on the total weight of the catalyst and calculated as element. Rhenium is preferably applied as a compound, for example as halide, oxyhalide, oxide, rhenate, per- rhenate or as acid. Examples of suitable rhenium compounds are ammonium perrhenate, rhe- nium(lll) chloride, rhenium(V) chloride, rhenium(V) fluoride, rhenium(VI) oxide and rhenium(VII) oxide. For the purposes of the invention, rhenium is particularly preferably applied as ammoni- urn perrhenate to the support. The catalyst of the invention comprises cesium as a promoter.

The impregnation solution and thus the catalyst can comprise cesium in an amount of from 10 to 2000 ppm, preferably in an amount of from 100 to 1500 ppm, based on the total weight of the catalyst and calculated as element. Cesium Is preferably applied as cesium compound to the support. Here, any suitable cesium compound can in principle be used. Cesium is preferably applied in the form of cesium hydroxide. The impregnation solution and thus the catalyst of the invention preferably comprises lithium as a promoter. The catalyst can comprise lithium in an amount of from 10 to 600 ppm, preferably in an amount of from 50 to 500 ppm, based on the total weight of the catalyst and calculated as element. Lithium is preferably applied as lithium compound to the support. Here, any suitable lithium compound can in principle be used. Lithium is preferably applied in the form of lithium nitrate.

The impregnation solution and thus the catalyst of the invention can comprise sulphur as a promoter. The catalyst can comprise sulfur in an amount of from 5 to 300 ppm, in particular in an amount of from 5 to 150 ppm, based on the total weight of the catalyst and calculated as element. Sulfur is preferably applied as sulfur compound to the support. Here, any suitable sulfur compound can in principle be used. Sulfur is preferably applied in the form of ammonium sulfate.

The impregnation solution and thus the catalyst of the invention preferably comprises tungsten as a promoter. The catalyst can comprise tungsten in an amount of from 10 to 600 ppm, more preferably in an amount of from 50 to 500 ppm, based on the total weight of the catalyst and calculated as element. According to the invention tungsten has to be applied as a compound, for example as halide, hydroxide, oxalate, oxide, tungstate or as acid, that has a sulphur content of 20 ppm or less, preferably of 10 ppm or less, more preferably of 5 ppm or less, even more preferably of 1 ppm or less. Examples of suitable tungsten compounds are tungsten oxides like tungsten(VI) oxide, tungstic acid, sodium polytungstate, ammonium paratungstate and any other heteropolyacid of tungsten. For the purposes of the invention, tungsten is particularly preferably applied as tungstic acid to the support. In a particularly preferred embodiment, the catalyst of the invention comprises silver in an amount of from 10 to 35% by weight, rhenium in an amount of from 150 to 850 ppm, cesium in an amount of from 100 to 1500 ppm, lithium in an amount of from 50 to 500 ppm, tungsten in an amount of from 50 to 500 ppm and sulfur in an amount of from 5 to 150 ppm. In another embodiment the impregnation solution and the catalyst obtained comprises silver, rhenium, cesium, lithium, tungsten and sulfur and also at least one further promoter, for example five, four, three or two further promoters or one further promoter. All promoters known in the prior art are conceivable as at least one further promoter. The at least one further promoter is preferably selected from the group consisting of sodium, potassium, rubidium, beryllium, mag- nesium, calcium, strontium, barium, manganese, molybdenum, cadmium, chromium, tin and mixtures of two or more thereof. The catalyst particularly preferably comprises at least one further promoter selected from the group consisting of chromium, manganese, molybdenum, tin and mixtures of two or more thereof. Silver and the promoter metals may be applied together in the impregnation according to step (b). According to the present invention it is also possible, that the process comprises additional impregnation steps and the promoter metals are applied to the support separately.

The promoters, more preferably the promoter compounds, are preferably dissolved in a suitable solvent, preferably in water, before application. The silver-containing support is then preferably impregnated with the resulting solution comprising one or more of the promoters. As regards the solution comprising one or more of the promoters, this can be produced in any suitable way.

For example, the promoters can be dissolved separately in one solution each and the resulting solutions comprising in each case one promoter can subsequently be used for the impregnation. It is likewise possible to dissolve two or more promoters together in a solution and subsequently use the resulting solution for the impregnation. In addition, it is possible to combine the resulting solutions comprising at least one promoter before impregnation and apply the resulting solution comprising all promoters to the support. If, for example, at least tungsten, cesium, lithium, sulfur and rhenium are used as promoters, in a particularly preferred embodiment at least one solution comprising cesium, a further solution comprising tungsten, a further solution comprising lithium and sulfur, a further solution comprising rhenium are produced. The solutions are either applied to the silver-containing support in separate impregnation steps or are combined to form one solution before application and only then used for impregnation. The solutions are preferably applied together, more preferably together with the mixture comprising silver as sil- ver-amine compound, preferably as silver-ethylenediamine compound, to the support. It is also possible in the context of the present invention that silver or any of the promoters are applied in two or more impregnation steps. After a first impregnation step, the impregnated support is calcined and then a second impregnation solution is applied, and the impregnated material is calcined again.

In case silver is applied in two or more impregnation steps, each impregnation solution can comprise silver in a suitable amount. Preferably the sum of the amount of silver applied in the individual steps is suitable that the catalyst obtained comprises silver in an amount of, for example, from 1 to 40% by weight, preferably from 5 to 40% by weight, more preferably 10 to 35% based on the total weight of the catalyst and calculated as element.

In case promoters are applied in two or more impregnation steps, each impregnation solution can comprise a promoter or a combination of promoters in a suitable amount. If impregnation solution comprises rhenium, preferably the sum of the amount of rhenium applied in the individual steps is suitable that the catalyst obtained comprises rhenium in an amount of, for example from 10 to 2000 ppm, more preferably in an amount of from 50 to 1500 ppm, more preferably in an amount of from 100 to 1000 ppm, based on the total weight of the catalyst and calculated as element.

If impregnation solution comprises cesium, preferably the sum of the amount of cesium applied in the individual steps is suitable that the catalyst obtained comprises cesium in an amount of, for example from 10 to 2000 ppm, more preferably in an amount of from 100 to 1500 ppm, based on the total weight of the catalyst and calculated as element.

If impregnation solution comprises lithium, preferably the sum of the amount of lithium applied in the individual steps is suitable that the catalyst obtained comprises lithium in an amount of, for example from 10 to 600 ppm, more preferably in an amount of from 50 to 500 ppm, based on the total weight of the catalyst and calculated as element.

If impregnation solution comprises sulphur, preferably the sum of the amount of sulphur applied in the individual steps is suitable that the catalyst obtained comprises sulphur in an amount of, for example from 5 to 300 ppm, more preferably in an amount of from 5 to 150 ppm, based on the total weight of the catalyst and calculated as element.

If impregnation solution comprises tungsten, preferably the sum of the amount of tungsten ap- plied in the individual steps is suitable that the catalyst obtained comprises tungsten in an amount of, for example from 10 to 600 ppm, more preferably in an amount of from 50 to 500 ppm, based on the total weight of the catalyst and calculated as element.

The application of the respective compounds can in principle be carried out by any suitable methods, for example by impregnation of the support. The application is preferably effected by vacuum impregnation at room temperature. In vacuum impregnation, the support is preferably firstly treated at a pressure in the range of not more than 500 mbar, more preferably at a pressure of not more than 250 mbar and particularly preferably at a pressure of not more than 80 mbar, more preferably not more than 50 mbar, and preferably at a temperature in the range from 2 C to 50 C, more preferably at a temperature in the range from 5 C to 30 C and particularly preferably at room temperature. The vacuum treatment is, for example, carried out for a time of at least 1 minute, preferably at least 5 minutes, more preferably for a time in the range from 5 minutes to 120 minutes, in particular in the range from 10 minutes to 45 minutes, particularly preferably in the range from 15 minutes to 30 minutes. After the vacuum treatment, the at least one solution, for example the mixture comprising silver, cesium, and rhenium or at least one solution comprising at least one further promoter, preferably the mixture comprising silver, cesium and rhenium and at least one further promoter, is applied to the support in a quantity limited to fill only the small pores of the support. The solution is preferably dripped on or sprayed on, preferably sprayed on.

Application is in this case preferably effected by means of a nozzle. After the application, the support is preferably evacuated further. The evacuation is preferably carried out at a pressure in the range of not more than 500 mbar, more preferably at a pressure of not more than 250 mbar and particularly preferably at a pressure of not more than 50 mbar, and preferably at a temperature in the range of from 2 C to 50 C, more preferably at a temperature in the range of from 5 C to 30 C, and particularly preferably at room temperature. The vacuum treatment is carried out, for example, for a time of at least 1 minute, preferably at least 5 minutes, more preferably for a time in the range from 5 minutes to 120 minutes, in particular in the range from 10 minutes to 45 minutes, particularly preferably in the range from 10 minutes to 20 minutes.

According to the present invention, the impregnation solution comprising silver is applied to the alumina support in an amount (VA₉-IS), wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support.

The application of silver and optionally one or more promoter such as rhenium, cesium, lithium, tungsten and sulfur and optionally further promoters to a support can be conducted such that only sufficient solution to fill the small pores of a bi- or multi-modal support are filled. This filling is accomplished by the stronger capillary force of the small pores relative to the large pores in the carrier.

The application of silver, rhenium, cesium, lithium, tungsten and sulfur and optionally further promoters to a support can be followed by at least one after-treatment step, for example one, two or more drying steps. Drying is usually carried out at temperatures in the range of from 2 to 200 C. The after-treatment step is drying by means of vacuum treatment, for example, as described above.

The silver-containing support material is preferably calcined after the application of silver and optionally rhenium, cesium, lithium, tungsten and sulfur and further promoters, optionally after a drying step.

According to a further embodiment, the present invention is also directed to the process for producing a shaped catalyst body comprising silver applied to an alumina support as disclosed above, wherein the process further comprises

(c) calcining the impregnated alumina support obtained according to (b).

Calcination is preferably carried out at temperatures in the range of from 150 to 750 C, prefera- bly in the range of from 200 to 500 C, more preferably in the range of from 220 to 350 C, more preferably in the range of from 250 to less than 300 C and particularly preferably in the range of from 270 to 295 C, with the calcination time generally being at least 5 minutes or^■ more, for example in the range of from 5 minutes to 24 hours or in the range of from 10 minutes to 12 hours. The calcination time is particularly preferably in the range of from 5 minutes to 3 hours. The calcination can be carried out at a constant temperature. Furthermore, embodiments in which the temperature is altered continuously or discontinuously during the calcination time are comprised. The calcination can be carried out under any gas atmosphere suitable for this purpose, for example in an inert gas or a mixture of inert gas and from 10 ppm to 21 % by volume of oxygen. Inert gases which may be mentioned are, for example, nitrogen, argon, carbon dioxide, helium and mixtures of the abovementioned inert gases. If the calcination is carried out in an inert gas, nitrogen is particularly preferred. In an alternative preferred embodiment, air and/or lean air are/is used. Furthermore, the calcination is preferably carried out in a muffle furnace, convection oven, in a rotary furnace and/or a belt calcination oven. In a preferred embodiment of the present invention, the support material impregnated with silver, rhenium, cesium, lithium, tungsten and sulfur obtained by the above-described process, which has a temperature To, is calcined in a multistage process. This process comprises at least the following steps:

(c1 ) heating the impregnated support material from the temperature To to a temperature Ti at a heating rate of at least 30 K/min, preferably in the range from 30 to 80 K/min, more preferably in the range from 40 to 75 K/min;

(c2) holding the support material which has been heated to the temperature Ti at a temperature T2, where T2 is preferably in the range from 0.95 Ti to 1 .1 Ti ;

(c3) cooling the support material which has been held at the temperature T2 to a temperature T3, where T3 is not more than 60 C.

Should the impregnated support material be obtained at a temperature of greater than To in the impregnation, in particular in the particularly preferred one-step impregnation, it is, according to the invention, firstly cooled to the temperature To. Temperatures To in the range up to 35 C, for example in the range up to 30 C are conceivable in principle. The temperature To is preferably in the range from 5 to 20 C, more preferably in the range from 10 to 15 C. In preferred embodiments, the temperature To is, according to the invention, such that the impregnated support material obtained does not have to be subjected to predrying before it is heated according to the invention at a heating rate of at least 30 K/min in step (c1 ). The present invention thus prefera- bly provides a process in which the support material impregnated with silver, optionally rhenium, cesium, lithium, tungsten and sulfur and optionally further promoters obtained by the above- described process is not subjected to a temperature which is greater than 35 C, preferably greater than 30 C, more preferably greater than 25 C and more preferably greater than 20 C, before being heated at a heating rate of at least 30 K/min. In step (c1 ) of the calcination process according to the invention, the impregnated support material which has been provided at the temperature To is heated at a heating rate of at least K/min. Heating rates of up to 150 K/min, for example up to 100 K/min or 80 K/min, are conceivable. The heating rate in step (c1 ) is preferably in the range from 30 to 80 K/min, more preferably in the range from 40 to 75 K/min.

In step (c1 ) of the calcination process according to the invention, the support material is heated from the temperature To to the temperature Ti . According to the invention, heating is carried out to temperatures Ti which are suitable for calcination of the impregnated support material. Here, temperatures Ti of up to 350 C, for example up to 340 C or up to 330 C or up to 320°C or up to 310 C or up to 300 C, are conceivable in principle. Preferred minimum temperatures Ti are in the region of 250 C. Accordingly, temperatures Ti in the range from 250 to 310 C or in the range from 250 to 300 C are conceivable. However, it has been found, according to the invention, that it is possible to set calcination temperatures of less than 300 C. The present invention therefore provides the process as described above in which the temperature Ti is less than 300 C, preferably less than or equal to 299 C. According to the invention, the temperature Ti is preferably in the range from 250 to 295 C, more preferably in the range from 260 to 295 C, more preferably in the range from 270 to 295 C, more preferably in the range from 270 to 290 C, for example in the range from 270 to 285 C, from 275 to 290 C, or from 275 to 285 C. As concerns the way in which the heating rate according to the invention is achieved, there are in principle no restrictions. Preference is given to the support material present at the temperature To being brought into contact with a gas during heating, with further preference being given to heating the support material by means of this gas and the gas thus having a temperature which allows the support material to be heated to the temperature Ti.

As regards the chemical composition of the gas which is brought into contact with the support material in order to heat the support material, there are in principle no restrictions. It is thus conceivable for the gas to comprise oxygen, with mention being able to be made by way of example of oxygen contents of the gas of up to 100% by volume or up to 25% by volume. The use of air, for example, is also conceivable. Lower contents of oxygen are also conceivable, with, for example, mixtures of nitrogen and air, e.g. lean air, being conceivable. Mention may be made of oxygen contents of the gas of up to 20% by volume or up to 15% by volume or up to 10% by volume or up to 5% by volume or up to 1 % by volume. For the purposes of the present invention, particular preference is given to using an inert gas or a mixture of two or more inert gases, with the oxygen content preferably being less than 10 ppm, more preferably in the range from 5 to 9 ppm, as gas for heating. As inert gases, mention may be made by way of example of nitrogen, carbon dioxide, argon and/or helium. For the purposes of the present invention, nitrogen is particularly preferably used as inert gas. The present invention accordingly provides the process as described above in which heating in step (c1 ) is carried out by bringing the support material into contact with an inert gas h . The present invention preferably provides the process as described above in which heating in step (c1 ) is carried out by bringing the support material into contact with an inert gas which comprises less than 10 ppm, preferably from 5 to 9 ppm, of oxygen. The present invention more preferably provides the process as described above in which heating in step (c1 ) is carried out by bringing the support material into contact with an inert gas h , where the inert gas is nitrogen and the inert gas comprises less than 10 ppm, preferably from 5 to 9 ppm, of oxygen. The expression "inert gas h comprising less than 10 ppm, preferably from 5 to 9 ppm, of oxygen" refers here to a gas mixture comprising the inert gas h and oxygen, where the oxygen content of less than 10 ppm or from 5 to 9 ppm relates to the oxygen content of the gas mixture and the inert gas can be a mixture of 2 or more inert gases. For the purposes of the present invention, the gas which is brought into contact with the support material during heating in step (c1 ) is very particularly preferably technical-grade nitrogen, preferably obtained from fractionation of air, which typically comprises nitrogen in an amount of from 99.995 to 99.9999, oxygen in an amount of from 6 to 8 ppm and traces of noble gases. The temperature of the gas which is brought into contact with the support material during heating is in principle selected so that the heating rates according to the invention can be made possible and the support material can be brought to the temperature Ti . The gas with which the support material is brought into contact during heating in step (c1 ) preferably has a temperature in the range from Ti to 1 .1 Ti , more preferably in the range from Ti to 1 .07 Ti , more preferably in the range from Ti to 1 .05 Ti .

The contacting of the support material with the gas in step (c1 ) can in principle be carried out in any desired way as long as it is ensured that the heating rate according to the invention is achieved for the support material, in this regard, particular preference is given to bringing the support material into contact with a stream of the gas, preferably a stream of the inert gas , i.e. passing the gas through the support material. Here, the volume flow of the gas is basically selected so that the heating rate according to the invention is achieved. In particular, the volume flow of the gas is selected so that the heating rate according to the invention is achieved by the combination of the temperature and the volume flow of the gas which is brought into contact with the support material. The volume flow is particularly preferably in the range from 2500 to 5000 m³/h, in particular in the range from 3200 to 4500 m³/h. In a preferred embodiment, the present invention provides the process as described above in which an inert gas , preferably nitrogen, is passed through the support material to be heated up in step (c1 ), where h preferably comprises less than 10 ppm, more preferably from 5 to 9 ppm, of oxygen, preferably has a temperature in the range from Ti to 1 .1 Ti and h preferably flows through the support material at a volume flow in the range from 2500 to 5000 m³/h, more preferably from 3200 to 4500 m^'Vh. During heating of the support material as per step (c1 ), the heating rate can be constant or can vary, as long as it is ensured that the overall heating rate calculated from the temperature difference (T1-T0) divided by the total time required for heating is at least 30 K/min, preferably in the range from 30 to 80 K/min, more preferably in the range from 30 to 75 K/min, more preferably in the range from 30 to 70 K/min. The heating rate during the total heating operation is preferably at least 30 K/min, more preferably in the range from 30 to 80 K min, more preferably in the range from 30 to 75 K/min, more preferably in the range from 30 to 70 K/min. Ranges which are possible according to the invention for the heating rate are, for example, from 35 to 80 K/min or from 40 to 75 K/min or from 40 to 70 K/min or from 45 to 70 K/min or from 50 to 70 K/min or from 55 to 70 K/min or from 60 to 70 K/min or from 65 to 70 K/min. In step (c2) of the calcination process according to the invention, the support material which has been heated to the temperature Ti is, after heating, preferably directly after heating, maintained at a temperature T2 which is suitable for the purposes of the calcination according to the invention. Preference is here given to temperatures T2 in the region of the temperature Ti . Particular preference is given to temperatures T2 in the range from 0.95 to 1.1 Ti , for example in the range from 0.95 to 1.05 Ti, from 0.96 to 1 .04 Ti , from 0.97 to 1.03 Ti , from 0.98 to 1 .02 Ti or from 0.99 to 1.01 Ti . The temperature T2 is preferably selected so as to be less than 300 C, preferably less than or equal to 299 C. Holding of the support material at the temperature T2 also comprises embodiments in which the value of T2 is not constant during the hold time but instead varies within the above-described limits. The present invention thus also comprises, inter alia, embodiments in which the holding is carried out at two or more different temperatures which are within the above-described limits T2. The time for which the support material is held at the temperature T2 is in principle not subject to any restrictions. For the purposes of the present invention, preference is given to the support being held at the temperature T2 for a time in the range from 1 to 15 minutes, preferably from 2 to 10 minutes, more preferably from 3 to 5 minutes, in step (c2). As regards the way in which the holding according to the invention in step (c2) is achieved, there are in principle no restrictions. During holding at the temperature T2, the support material is preferably brought into contact with a gas which is at a temperature which allows the support material to be maintained at the temperature T2. As regards the chemical composition of the gas which is brought into contact with the support material in order to hold the support material at the temperature T2, there are in principle no restrictions. It is thus conceivable, for instance, for the gas to comprise oxygen, with, for example, oxygen contents of the gas of up to 100% by volume or up to 25% by volume being possible. The use of air, for example, is also conceivable. Lower contents of oxygen are also con- ceivable, with, for example, mixtures of nitrogen and air, e.g. lean air, being conceivable. Mention may be made of oxygen contents of the gas of up to 20% by volume or up to 15% by volume or up to 10% by volume or up to 5% by volume or up to 1 % by volume. For the purposes of the present invention, particular preference is given to using an inert gas or a mixture of two or more inert gases, in which the oxygen content is preferably less than 10 ppm, more preferably in the range from 5 to 9 ppm, as gas for holding at the temperature T2. As inert gases, mention may be made by way of example of nitrogen, carbon dioxide, argon and helium. Particular preference is given to using nitrogen as inert gas for the purposes of the present invention.

The present invention accordingly provides the process as described above in which the holding as per step (c2) is carried out by bringing the support material into contact with an inert gas . The present invention preferably provides the process as described above in which the holding in step (c2) is carried out by bringing the support material into contact with an inert gas comprising less than 10 ppm, preferably from 5 to 9 ppm, of oxygen. The present invention more preferably provides the process as described above in which the holding in step (c2) is carried out by bringing the support material into contact with an inert gas , where the inert gas is nitrogen and the inert gas comprises less than 10 ppm, preferably from 5 to 9 ppm, of oxygen. The expression "inert gas comprising less than 10 ppm, preferably from 5 to 9 ppm, of oxygen" refers here to a gas mixture comprising the inert gas band oxygen, where the oxygen content of less than 10 ppm or from 5 to 9 ppm relates to the oxygen content of the gas mixture and the inert gas can be a mixture of 2 or more inert gases.

For the purposes of the present invention, the gas with which the support material is brought into contact during the holding in step (c2) is very particularly preferably technical-grade nitro- gen, preferably obtained from fractionation of air, which typically comprises nitrogen in amounts of from 99.995 to 99.9999% by volume, oxygen in amounts of from 6 to 8 ppm and traces of noble gases. The temperature of the gas with which the support material is brought into contact during holding in step (c2) is basically selected so that the hold temperature according to the invention can be made possible. The gas with which the support material is brought into contact during holding in step (c2) preferably has a temperature in the range from T2 to 1 .1 T2, more preferably in the range from T2 to 1 .07 T2, more preferably in the range from T2 to 1 .05 T2, for example in the range from T2 to 1 .04 T2 or in the range from T2 to 1 .03 T2 or in the range from T2 to 1 .02 T2 or in the range from T2 to 1 .01 T2.

The contacting of the support material with the gas in step (c2) can in principle be carried out in any desired way as long as it is ensured that the holding according to the invention of the sup- port material at the temperature T2 is achieved. In this regard, particular preference is given to the support material being brought into contact with a stream of the gas, preferably with a stream of the inert gas b, i.e. the gas being passed through the support material. Here, the volume flow of the gas is basically selected so that the holding according to the invention of the support material at the temperature T2 is achieved. In particular, the volume flow of the gas is selected so that the holding according to the invention of the support at the temperature T2 is achieved by the combination of the temperature and the volume flow of the gas which is brought into contact with the support material. The volume flow is particularly preferably in the range from 1000 to 3000 m³/h, more preferably from 1500 to 2000 m³/h. In a preferred embodiment, the present invention provides the process as described above in which an inert gas , preferably nitrogen, is passed through the support material to be held at the temperature T2 in step (c2), where I2 preferably comprises less than 10 ppm, more preferably from 5 to 9 ppm, of oxygen, b preferably has a temperature in the range from T2 to 1 .05 T2 and b preferably flows through the support at a volume flow in the range from 1000 to 3000 m³/h, more preferably from 1500 to 2000 m³/h. It is preferred, but not necessary, that the inert gas is used as inert gas for the purposes of the present invention, with, as described above, the volume flow of being able to be different from the volume flow of h and/or the temperature of being able to be different from the temperature of h. In step (c3) of the calcination process according to the invention, the support material which has been held at the temperature T2 is cooled after holding, preferably directly after holding, to a temperature T3. As regards the value of T.j, there are in principle no particular restrictions. For the purposes of the present invention, temperatures T3 of not more than 60 C are preferred. As regards the way in which the cooling according to the invention in step (c3) is achieved, there are in principle no restrictions. During cooling to the temperature T3, the support material is preferably brought into contact with a gas which has a temperature which allows the support material to be cooled to the temperature T3. As regards the chemical composition of the gas which is brought into contact with the support material in order to cool the support material to the temperature T3, there are in principle no restrictions. It is thus conceivable, for instance, for an inert gas as is used, for example, in steps (c1 ) or (c2) to be used as gas. For the purposes of the present invention, particular preference is given to using a gas having an oxygen content of at least 5% by volume, preferably at least 10% by volume, more preferably at least 15% by volume, more preferably at least 20% by volume, as gas for cooling to the temperature T3. In particular, air is used according to the invention for effecting cooling in step (c3). In the process of the invention, the support material is preferably cooled at a cooling rate in the range from 30 to 80 K/min, preferably in the range from 40 to 60 K/min, more preferably in the range from 45 to 55 K/min, in step (c3).

The calcined and cooled support material obtained in this way can either be used as catalyst immediately after step (c3) or it can be stored in a suitable way.

As regards the apparatus used for the above-described calcination process, there are essentially no restrictions as long as it is ensured that the heating according to the invention in step (c1 ), preferably also the holding according to the invention in step (c2), preferably also the cooling according to the invention in step (c3) can be carried out as described above. According to the invention, preference is given to embodiments in which at least the heating in step (c1 ), preferably the heating in step (c1 ) and holding in step (c2) and also the cooling in step (c3), is/are carried out continuously. With particular preference the process of the invention is carried out in a belt calciner in respect of step (c1 ), preferably at least in respect of steps (c1 ) and (c2). As regards the time at which the promoters are applied, they can also be applied after the above-described calcination. As well, it is possible to apply the promoters together with the silver compound to the support. The silver-containing support is then preferably impregnated again with a silver complex solution, more preferable with one or more promoters, to yield a second silver-containing support. The second silver-containing support material is preferably calcined after the application of silver, optionally after a drying step. Calcination is preferably carried out at temperatures in the range of from 150 to 750 C, preferably in the range of from 200 to 500 C, more preferably in the range of from 220 to 350 C, more preferably in the range of from 250 to less than 300 C and particularly preferably in the range of from 270 to 295 C, with the calcination time generally being at least 5 minutes or more, for example in the range of from 5 minutes to 24 hours or in the range of from 10 minutes to 12 hours. The calcination time is particularly preferably in the range of from 5 minutes to 3 hours. The calcination can be carried out at a constant temperature. Furthermore, embodiments in which the temperature is altered continuously or discontinuously during the calcination time are comprised. Accordingly, the invention comprises embodiments in which the at least one further promoter, that is to say, for example, five different further promoters, four different further promoters, three different further promoters, two different further promoters or one further promoter are applied to the support and the support which has been treated in this way is only subsequently calcined as described above to give a catalyst according to the invention.

With respect to the preferred embodiments, reference is made to the disclosure above. Thus, according to a further embodiment, the present invention is also directed to the shaped catalyst body as disclosed above, wherein the shaped catalyst body comprises silver in an amount of from 1 to 50% by weight, based on the total weight of the shaped catalyst body and calculated as element, preferably silver in an amount of from 5 to 40% by weight, based on the total weight of the shaped catalyst body and calculated as element, more preferable silver in an amount of from 10 to 35% by weight, based on the total weight of the shaped catalyst body and calculated as element.

According to a further embodiment, the present invention is also directed to the shaped catalyst body as disclosed above, wherein the shaped catalyst body comprises rhenium, preferably in an amount of from 100 to 1500 ppm by weight, based on the total weight of the shaped catalyst body and calculated as element per m² surface area of the support.

According to a further embodiment, the present invention is also directed to the shaped catalyst body as disclosed above, wherein the catalyst comprises at least one promoter selected from the group consisting of elements of groups IA, VI B, VI IB and VIA, preferably selected from the group consisting of tungsten, cesium, lithium and sulfur.

The catalyst according to the present invention can advantageously be used as a catalyst in the epoxidation of ethylene. Thus, according to a further aspect the present invention is also di- rected to a process for preparing ethylene oxide by gas-phase oxidation of ethylene by means of oxygen in the presence of a shaped catalyst body as disclosed above.

According to a further aspect the present invention is also directed to the use of a shaped catalyst body as disclosed above as catalyst for preparing ethylene oxide by gas-phase oxidation of ethylene by means of oxygen.

The present invention further provides a process for preparing ethylene oxide from ethylene, which comprises oxidation of ethylene in the presence of a catalyst for the epoxidation of al- kenes, comprising silver, rhenium, cesium, lithium, tungsten and sulfur on a support. According to the invention, the epoxidation can be carried out by all processes known to those skilled in the art. Here, it is possible to use all reactors which can be used in the ethylene oxide production processes of the prior art, for example externally cooled shell-and-tube reactors (cf.

Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A-10, pp. 1 17-135, 123-125, VCH-Verlagsgesellschaft, Weinheim 1987), or reactors having a loose catalyst bed and cooling tubes, for example the reactors described in DE-A 3414717, EP 0082609 and EP-A 0339748.

The epoxidation is preferably carried out in at least one tube reactor, preferably in a shell-and tube reactor. The catalyst of the invention can be used either alone or together with other catalysts in a combined or structured catalyst bed.

The preparation of ethylene oxide from ethylene and oxygen can, according to the invention, be carried out under conventional reaction conditions as are described, for example, in DE 25 21 906 A1 , EP 0 014 457 A2, DE 2 300 512 A1 , EP 0 172 565 A2, DE 24 54 972 A1 , EP 0 357 293 A1 , EP 0 266 015 A1 , EP 0 085 237 A1 , EP 0 082 609 A1 and EP 0 339 748 A2. Inert gases such as nitrogen or gases such as water vapor and methane which are inert under the reaction conditions and optionally reaction moderators, for example hydrocarbons or organo halides such as ethyl chloride, vinyl chloride or 1 ,2-dichloroethane, can additionally be mixed into the reaction gas comprising ethylene and molecular oxygen. The oxygen content of the reaction gas is advantageously in a range in which no explosive gas mixtures are present. A suitable composition of the reaction gas for preparing ethylene oxide can comprise, for example, an amount of ethylene in the range from 10 to 80% by volume, preferably from 20 to 60% by volume, more preferably from 25 to 50% by volume and particularly preferably in the range from 30 to 40% by volume, based on the total volume of the reaction gas. The oxygen content of the reaction gas is advantageously in the range of not more than 10% by volume, preferably not more than 9% by volume, more preferably not more than 8% by volume and very particularly preferably not more than 7% by volume, based on the total volume of the reaction gas. The reaction gas preferably comprises a chlorine-comprising reaction moderator such as ethyl chloride, methyl chloride, vinyl chloride or dichloro ethane in an amount of from 0 to 100 ppm, preferably in an amount of from 0.1 to 25 ppm. The remainder of the reaction gas generally comprises hydrocarbons such as methane or other inert gases such as nitrogen. In addition, the reaction gas can also comprise other materials such as water vapor, carbon dioxide or noble gases. The above-described constituents of the reaction mixture can optionally comprise small amounts of impurities. Ethylene can, for example, be used in any purity which is suitable for the epoxidation according to the invention. Suitable purities include, but are not limited to, polymer- grade ethylene, which typically has a purity of at least 99%, and chemical-grade ethylene, which has a lower purity of typically below 95%. The impurities typically comprise mainly ethane, pro- pane and/or propene.

The epoxidation is usually carried out at elevated temperature. Preference is given to temperatures in the range from 150 to 350 C, more preferably in the range from 180 to 300 C, more preferably in the range from 190 to 280 C and particularly preferably in the range from 200 to 280 C. The present invention accordingly also provides a process as described above in which the oxidation takes place at a temperature in the range from 180 to 300 C, preferably in the range from 200 to 280 C. The oxidation is preferably carried out at pressures in the range from 5 bar to 30 bar. The oxidation is more preferably carried out at a pressure in the range from 5 bar to 25 bar, preferably at a pressure in the range from 10 bar to 20 bar and in particular in the range from 14 bar to 20 bar. The present invention accordingly also provides a process as described above in which the oxidation is carried out at a pressure in the range from 14 bar to 20 bar. The oxidation is preferably carried out in a continuous process. If the reaction is carried out continuously, use is made of a GHSV (gas hourly space velocity) which is, as a function of the type of reactor selected, for example of the size/cross-sectional area of the reactor, the shape and size of the catalyst, pref- erably in the range from 800 to 10000/h, preferably in the range from 2000 to 6000/h, more preferably in the range from 2500 to 5000/h, where the figures are based on the volume of the catalyst.

The preparation of ethylene oxide from ethylene and oxygen can advantageously be carried out in a circulation process. Here, the reaction mixture is circulated through the reactor with the newly formed ethylene oxide and the by-products formed in the reaction being removed from the product gas stream after each pass and the product stream being, after being supplemented with the required amounts of ethylene, oxygen and reaction moderators, fed into the reactor again. The separation of the ethylene oxide from the product gas stream and its work-up can be carried out by the conventional methods of the prior art (cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A-10, pages 1 17 to 135, 123 to 125, VCH-Verlagsgesellschaft, Weinheim 1987).

The present invention is further illustrated by the following embodiments and combinations of embodiments as indicated by the respective dependencies and back-references. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The process of any one of embodiments 1 to 4", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The process of any one of embodiments 1 , 2, 3, and 4".

A process for producing a shaped catalyst body comprising silver applied to an alumina support or a pretreated alumina support, which comprises an impregnation step which comprises

0.1 (Vtotal) tO 0.9(Vtotal);

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support or the pretreated alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) ml_/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support or the pretreated alumina support.

A process for producing a shaped catalyst body comprising silver applied to an alumina support, which comprises an impregnation step which comprises

(a) providing an alumina support, wherein the alumina support, preferably the alpha- alumina support, has a total pore volume (V_totai) of 0.1 mL/g to 1 .2 mL/g and at least two log differential pore volume distribution peaks in a pore diameter range of 0.01 to 100 μηη and at least one of the peaks is present in a pore diameter range of 0.1 to 5 μηη in the pore size distribution as measured by mercury porosimetry and the second peak is present in a pore diameter range of 6 to 100 μηη, and wherein the pores of the alumina support with a pore diameter in the range of from 0.1 to 5 μηη form a volume (V1 ) mL/g of the alumina support wherein V1 is in the range of 0.1 (V_totai) to 0.9(V_totai);

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support.

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support;

(c) calcining the impregnated alumina support obtained according to (b). The process according to any of embodiments 1 to 3, wherein the impregnation solution is applied under vacuum.

(a) providing an alumina support, wherein the alumina support, preferably the alpha- alumina support, has a total pore volume (V_totai) of 0.1 mL/g to 1.2 mL/g and at least two log differential pore volume distribution peaks in a pore diameter range of 0.01 to 100 μηη and at least one of the peaks is present in a pore diameter range of 0.1 to 5 μηη in the pore size distribution as measured by mercury porosimetry and the second peak is present in a pore diameter range of 6 to 100 μηη, and wherein the pores of the alumina support with a pore diameter in the range of from 0.1 to 5 μηη form a volume (V1 ) mL/g of the alumina support wherein V1 is in the range of 0.1 (V_totai) to 0.9(V_totai);

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support, wherein the impregnation solution is applied under vacuum

(c) calcining the impregnated alumina support obtained according to (b). wherein the impregnation solution is applied under vacuum. The process according to any of embodiments 1 to 6, wherein the alumina support has a BET surface area in the range from 0.3 to 3.0 m²/g.

The process according to any of embodiments 1 to 7, wherein the impregnation solution comprises rhenium.

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support, wherein the impregnation solution comprises rhenium. A process for producing a shaped catalyst body comprising silver applied to an alumina support, which comprises an impregnation step which comprises

(c) calcining the impregnated alumina support obtained according to (b), wherein the impregnation solution comprises rhenium.

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1 .1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support, wherein the impregnation solution is applied under vacuum and wherein the impregnation solution comprises rhenium.

(c) calcining the impregnated alumina support obtained according to (b). wherein the impregnation solution is applied under vacuum and wherein the impregna- tion solution comprises rhenium. The process according to any of embodiments 1 to 12, wherein the impregnation solution comprises at least one promoter selected from the group consisting of elements of groups IA, VI B, VI IB and VIA, preferably selected from the group consisting of tungsten, cesium, lithium and sulfur. The process according to any of embodiments 1 to 13, wherein the process further comprises

(c) calcining the impregnated alumina support obtained according to (b).

The process according to any of embodiments 1 to 14, wherein the process comprises two or more impregnation steps.

A shaped catalyst body obtainable or obtained by a process according to any of embodiments 1 to 15.

A shaped catalyst body obtainable or obtained by a process for producing a shaped catalyst body comprising silver applied to an alumina support, which comprises an impregnation step which comprises

(c) calcining the impregnated alumina support obtained according to (b), wherein the impregnation solution comprises rhenium. The shaped catalyst body according to embodiment 1 6 or 17, wherein the shaped catalyst body comprises silver in an amount of from 1 to 50% by weight, based on the total weight of the shaped catalyst body and calculated as element, preferably silver in an amount of from 5 to 40% by weight, based on the total weight of the shaped catalyst body and calculated as element, more preferable silver in an amount of from 10 to 35% by weight, based on the total weight of the shaped catalyst body and calculated as element.

19. The shaped catalyst body according to any of embodiments 16 to 18, wherein the

shaped catalyst body comprises rhenium, preferably in an amount of from 10 to 2000 ppm by weight, based on the total weight of the shaped catalyst body and calculated as element per m² surface area of the support.

20. The shaped catalyst body according to any of embodiments 16 to 19, wherein the catalyst comprises at least one promoter selected from the group consisting of elements of groups IA, VIB, VIIB and VIA, preferably selected from the group consisting of tungsten, cesium, lithium and sulfur.

21 . A process for preparing ethylene oxide by gas-phase oxidation of ethylene by means of oxygen in the presence of a shaped catalyst body according to any of embodiments 16 to 20. 22. The use of a shaped catalyst body according to any of embodiments 16 to 20 as catalyst for preparing ethylene oxide by gas-phase oxidation of ethylene by means of oxygen.

The present invention is illustrated below with the aid of examples.

Examples

1 . General method for producing catalysts according to the invention 1 .1 . Production of the silver complex solution

550 g of silver nitrate were completely dissolved in 1.5 I of water under constant stirring and the solution was warmed to 40 C. 402 g of KOH (47.8%) was mixed with 1.29 I water. A separate solution of 216.3 g oxalic acid was added to the KOH solution, which was then warmed to 40 C.

The potassium oxalate solution was then added to the silver nitrate solution within 45 min (volume flow rate ca. 33 ml/min) with the aid of a dosing pump and the solution was stirred for approximately 1 h at 40 C. The precipitated silver oxalate was then filtered and the ob- tained filter cake was washed with 1 I water portions until the filter cake was free of potassium and nitrate (ca. 10 I total). The water was removed from the filter cake by flowing air through the filter apparatus and the water content of the filter cake was measured. Typically a cake of 620 g with a water content of 20.8% was obtained. Ethylenediamine (306 g) was cooled in an ice bath to ca. 10 C and 245 g water was added in small portions. At the end of the water addition, 484.7 g of the (still damp) silver oxalate was added to the ethylenediamine/water mixture within 30 minutes. The mixture was stirred at room temperature overnight and any undissolved material removed via centrifu- gation. The silver content was determined refractometrically and the density was measured.

The obtained solution contained 28.83 weight % silver and had a density of 1.528 g/ml. Produced catalysts Comparative Example 1 Impregnation of the support with silver complex solution

173 g of the support material (according to Table 1 ) with V_totai of 173 g ^χ 0.4297 ml/g = 74 ml and V1 of 173 g ^χ 0.2290 ml/g = 39.6 ml were placed in a rotary evaporator and under of vacuum pressure of 80 mbar evacuated for approximately 10 min. 1 16.3 g of the silver solution described in step 1 .1 . corresponding to a volume VA_Q-IS of about 76 ml was added drop-wise to the support under vacuum within 15 minutes and then left to rotate additional 15 minutes. Both, small and large pores were filled with impregnation solution. Thereafter, the impregnated support was left for 1 h at room temperature and normal pressure and every 15 minutes lightly mixed. Calcination of the impregnated support

The impregnated support was calcined for 12 minutes at 290 C under 8.3 m³/h flowing nitrogen in a calcination oven (Company HORO, Type 129 ALV-SP, Fabrication number 53270) to yield a silver-containing support. Production of the silver and promoter solution

To 93.02 g of the silver complex solution according to step 1 .1 . were added 1.53 g of a solution made from dissolving 28.44 g lithium nitrate (FMC, 99.3%) and 0.87 g ammonium sulfate (Merck, 99.4%) in 72.43 g water and then 2.29 g of a solution consisting of 9,40 g cesium hydroxide in water (HC Starck, 48%) and 2.72 g tungstic acid (HC Starck, 99.99% containing either 0, 4, or 23 ppm sulfur) in 88.26 g water. Finally, 2.19 g of a solution made from dissolving 5.91 g ammonium perrhenate (Engelhard, 99.4%) in 94.01 g water were added. The combined solution was stirred for 5 minutes. The quantity of impregnation solution corresponded to a volume VA₉-IS of about 66.9 ml. Impregnation of the support with silver and promoter solutions 202.7 g of the support material according to step 2.1 .2. with V_totai of 202.7 g ^χ 0.33 ml/g = 66.9 ml were placed in a rotary evaporator and under of vacuum pressure of 80 mbar evacuated for approximately 10 min. The silver and promoter solution described in step 2.1 .3. was added drop-wise to the support under vacuum within 15 minutes and then left to rotate additional 15 minutes. Both, small and large pores were filled with impregnation solution. Thereafter, the impregnated support was left for 1 h at room temperature and normal pressure and every 15 minutes lightly mixed.

2.1 .5. Calcination of the impregnated support

The impregnated support was calcined for 10 minutes at 290 C under 8.3 m³/h flowing nitrogen in a calcination oven (Company HORO, Type 129 ALV-SP, Fabrication number 53270). 2.2. Example 1

2.2.1 . Impregnation of the support with silver and promoter solution

1 73 g of the support material (according to Table 1 ) with Vtotai of 1 73 g ^χ 0.4297 ml/g = 74 ml and V1 of 1 73 g ^χ 0.2290 ml/g = 39.6 ml were placed in a rotary evaporator and under of vacuum pressure of 80 mbar evacuated for approximately 10 min.

To 50.60 g of the silver complex solution according to step 1 .1 were added 0.685 g of a solution made from dissolving 28.44 g lithium nitrate (FMC, 99.3%) and 0.87 g ammonium sulfate (Merck, 99.4%) in 72.43 g water and then 1 .028 g of a solution consisting of 9.40 g cesium hydroxide in water (HC Starck, 48%) and 2.72 g tungstic acid (HC Starck, 99.99% containing either 0, 4, or 23 ppm sulfur) in 88.26 g water. Finally, 0.979 g of a solution made from dissolving 5.91 g ammonium perrhenate (Engelhard, 99.4%) in 94.01 g water were added.

The quantity of impregnation solution corresponded to a volume VA₉-IS of about 35.8 ml that was sufficient only to fill the small pores of the catalyst support (VA_S-IS = 0.9V1 ). The combined solution was stirred for 5 minutes.

The silver and promoter solution was added drop-wise to the support under vacuum within 1 5 minutes and then left to rotate additional 1 5 minutes. Thereafter, the impregnated support was left for 1 hat room temperature and normal pressure and every 15 minutes lightly mixed.

2.2.2. Calcination of the impregnated support The impregnated support was calcined for 10 minutes at 290 C under 8.3 m³/h flowing nitrogen in a calcination oven (Company HORO, Type 129 ALV-SP, Fabrication number 53270) to yield a silver-containing support. 2.2.3. Impregnation of the support with silver and promoter solutions

188 g of the silver-containing support material according to step 2.2.2. were placed in a rotary evaporator and under of vacuum pressure of 80 mbar evacuated for approximately 10 min. To 50.60 g of the silver complex solution according to step 1.1 . were added 0.685 g of a solution made from dissolving 28, .44 g lithium nitrate (FMC, 99.3%) and 0.87 g ammonium sulfate (Merck, 99.4%) in 72.43 g water and then 1.028 g of a solution consisting of 9.40 g cesium hydroxide in water (HC Starck, 48%) and 2.72 g tungstic acid (HC Starck, 99.99% containing either 0, 4, or 23 ppm sulfur) in 88.26 g water. Finally, 0.979 g of a solution made from dissolving 5.91 g ammonium perrhenate (Engelhard, 99.4%) in 94.01 g water were added.

The combined solution was stirred for 5 minutes.

The silver and promoter solution was added drop-wise to the support under vacuum within 15 minutes and then left to rotate additional 15 minutes. Thereafter, the impregnated support was left for 1 h at room temperature and normal pressure and every 15 minutes lightly mixed.

2.2.4. Calcination of the impregnated support

The impregnated support was calcined for 10 minutes at 290 C under 8.3 m³/h flowing nitrogen in a calcination oven (Company HORO, Type 129 ALV-SP, Fabrication number 53270). 3.1 . Epoxidation

The epoxidation reaction was conducted in a vertically-placed test reactor constructed from stainless steel with an inner-diameter of 6 mm and a length of 2.2 m. The reactor was heated using hot oil contained in a heating mantel at a specified temperature. The re- actor was filled to a height of 212 mm with inert steatite balls (1 .0 -1 .6 mm), then packed to a height of 1 100 mm with split catalyst (particle size 0.5- 0.9 mm) and then again packed with an additional 707 mm inert steatite balls (1.0- 1.6 mm). The inlet gas was introduced to the top of the reactor. The inlet gas consisted of 35 vol% ethylene, 7 vol% oxygen, 1 vol%C02, with methane used as a balance and ethylene chloride (EC) used as a moderator. The reactions were conducted at a pressure of 15 bar and a GHSV of 4750 r¹ at a workrate of 250 kg EO/m³ catalyst h. The reaction temperature was adjusted such that an ethylene oxide concentration of 2.7% was obtained in the outlet gas stream. In the course of operating the reactor, the EC moderation was varied between 1 .9 and 2.6 ppm to maximize catalyst performance with regard to selectivity and activity.

Results of the catalyst test are shown in Table 2. The results show that the catalyst of Example 1 has a significantly improved activity (that is, lower operating temperature) relative to comparative Example 1 , despite significantly reduced silver content. Moreover, the selectivity is also improved relative to comparative Example 1.

Table 1 : Support material characteristics

Table 2: Test reaction results

Cited Literature

DE 23 00 512 A1

DE 24 54 972 A1

DE 25 21 906 A1

DE 27 53 359 A1

DE 34 14 717 A1

DE 25 60 684 A1

EP 0 014 457 A2

EP 0 082 609 A1

EP 0 085 237 A1

EP O 172 565 A2

EP 0 266 015 A1

EP 0 339 748 A2

EP 0 357 293 A1

EP 0 425 020 A2

EP 0 480 538 A2

EP 0 496 386 B2

EP 0 764 464 B1

EP 1 613 428 B1

EP 2 152 41 1 A2

EP O 01 1 356 A1

Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A-10, pp. 1 17-135, 123-125, VCH-Verlagsgesellschaft, Weinheim 1987

US 2005/0096219 A1

US 2009/0198076 A1

US 7560577 B2

US 7977274 B2

WO 03/072244 A1

WO 2006/133187 A1

WO 2007/122090 A1

WO 2010/123856 A1

Claims

1 . A process for producing a shaped catalyst body comprising silver applied to an alumina support or a pretreated alumina support, which comprises an impregnation step which comprises

(a) providing an alumina support or a pretreated alumina support, wherein the alumina support or the pretreated alumina support, preferably the alpha-alumina support, has a total pore volume (V_totai) of 0.1 mL/g to 1 .2 mL/g and at least two log differential pore volume distribution peaks in a pore diameter range of 0.01 to 100 μηη and at least one of the peaks is present in a pore diameter range of 0.1 to 5 μηη in the pore size distribution as measured by mercury porosimetry and the second peak is present in a pore diameter range of 6 to 100 μηη, and

0.1 (Vtotai) tO 0.9 (Vtotai)!

2. A process according to claim 1 , which comprises an impregnation step which comprises

(b) applying a volume of an impregnation solution comprising silver (VA₉-IS) to the alumina support wherein VA₉-IS is in the range of 0.5(V1 ) to 1.1 (V1 ) mL/g and VA₉-IS is less than 0.95(V_totai) ml/g of the alumina support.

3. The process according to claim 1 or 2, wherein the impregnation solution is applied under vacuum.

4. The process according to any of claims 1 to 3, wherein the alumina support has a BET surface area in the range from 0.3 to 3.0 m²/g.

5. The process according to any of claims 1 to 4, wherein the impregnation solution comprises rhenium.

6. The process according to any of claims 1 to 5, wherein the impregnation solution com- prises at least one promoter selected from the group consisting of elements of groups IA,

VIB, VI IB and VIA, preferably selected from the group consisting of tungsten, cesium, lithium and sulfur.

7. The process according to any of claims 1 to 6, wherein the process further comprises

(c) calcining the impregnated alumina support obtained according to (b).

8. The process according to any of claims 1 to 7, wherein the process comprises two or more impregnation steps.

9. A shaped catalyst body obtainable or obtained by a process according to any of claims 1 to 8.

The shaped catalyst body according to claim 9, wherein the shaped catalyst body comprises silver in an amount of from 1 to 50% by weight, based on the total weight of the shaped catalyst body and calculated as element, preferably silver in an amount of from 5 to 40% by weight, based on the total weight of the shaped catalyst body and calculated as element, more preferable silver in an amount of from 10 to 35% by weight, based on the total weight of the shaped catalyst body and calculated as element.

The shaped catalyst body according to any of claims 9 or 10, wherein the shaped catalyst body comprises rhenium, preferably in an amount of from 10 to 2000 ppm by weight, based on the total weight of the shaped catalyst body and calculated as element per m² surface area of the support.

The shaped catalyst body according to any of claims 9 to 1 1 , wherein the catalyst comprises at least one promoter selected from the group consisting of elements of groups IA, VIB, VI IB and VIA, preferably selected from the group consisting of tungsten, cesium, lithium and sulfur.

A process for preparing ethylene oxide by gas-phase oxidation of ethylene by means of oxygen in the presence of a shaped catalyst body according to any of claims 9 to 12.

The use of a shaped catalyst body according to any of claims 9 to 12 as catalyst for preparing ethylene oxide by gas-phase oxidation of ethylene by means of oxygen.