CA1083122A

CA1083122A - Process for applying a catalytically active coating on catalyst supports

Info

Publication number: CA1083122A
Application number: CA257,193A
Authority: CA
Inventors: Eduard Lakatos; Edgar Koberstein; Jorg Hensel; Alfred Bozon
Original assignee: Deutsche Gold und Silber Scheideanstalt
Current assignee: Evonik Operations GmbH
Priority date: 1975-07-16
Filing date: 1976-07-16
Publication date: 1980-08-05
Also published as: PL105832B1; JPS5211185A; DE2531770B2; DE2531770A1; IT1062756B; GB1538330A; DE2531770C3; CS251054B2; BE844186A; JPS608863B2; FR2317963B1; FR2317963A1

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides a process for applying a coating or film of catalytically active elements by means of solution on the external surface of a porous catalyst support i.e., a catalyst support having a large surface area, character-ized in that the catalyst support is impregnated with a solution of at least one of various complexing agents, precipitants and reducing agents in an organic liquid, without exceeding the saturation of the catalyst supports, the solution of catalytic-ally active elements is then added, the liquid is removed by heating and when required, the catalyst support thus treated is subjected to an aftertreatment which is treatment with a reduc-ing agent or tempering at elevated temperature. The process provides a catalyst of uniform quality without a high loss of active components.

Description

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The invention relates to a process for applying a coating or a film of catalytically active elements by means of solutions on the external surface of porous catalyst supports, ~ -i.e., catalyst supports having a large surface area.
Catalyst supports (also referred to as structural re-inforcers) are substances having a large surface area on which catalytically active substances are precipitated in thin films.
Since the catalytic reactions take place on the surfaces, the effect is thus increased and valuable catalytically active substance is saved. ~-It is known that, for the surface coating of porous pelleted catalyst supports, said supports are sprayed - if required while hot - with concentrated aqueous salt solutions of components in which ~ water is substantially deficient as compared with the absorbing power of the support, and subsequently calcined. If required, the coating is facilitated by evacuating `~ the catalyst support.
Another known process for applying catalytically active substances which is similar to the surface coating is the vapour-phase impregnation in which a hot butane flow charged withAlC13 is passed over the catalyst and the AlC13 is precipitated thereon.
Moreover, it is also known to dissolve platinum salts in methanol, acetone, methyl acetate or similar salts, to :
impregnate the catalyst support with this solution and to ignite it, whereby the platinum is reduced (British Patent 496 579 Baker & Company). According to yet another known process platinum salts are dissolved in high-boiling organic oils, for example, fish oil (boiling point above 250C). This solution is applied on the catalyst supports with a maximum depth of infil-tration of 1 mm. The oil is subsequently removed by heating while it ignites (British Patent 594 463 Baker & Company).

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The processes have the disadvantage that they must be carried out in a closed tank. A uniform supply of the catalyst support with the active substance is not assured, where-by catalysts of varying quality are obtained. The high loss of active components is a further disadvantage.
The present invention provides a process for the surface supply of catalyst supports which avoids the disadvan-tages mentioned hereinbefore.
According to the present invention there is provided ~ 10 a process for applying a coating or film of catalytically active - elements, by means of a solution, on the external surfaces of a porous catalyst support, i.e. a catalyst support having a large ` surface area which process is characterized in that the catalyst support is impregnated with a solution of complexing agents, precipitants and/or reducing agents in an organic liquid without exceeding the saturation of the catalyst support and that the solution of catalytically active elements is added, whereupon the liquid is removed by heating and, when required, the catalyst - thus treated is subjected to an after-treatment as hereinafter defined. ~
-i According to the process of the invention the organic -liquid is preferably an incombustible organic liquid, for example~ CC14. According to a preferred embodiment of the invention the catalyst support is impregnated with a solution ; of at leas~ one member selected from complexing agents, . . . :
precipitants and reducing agents in a combustible organic liquid without exceeding the saturation of the catalyst supports, ., .
whereupon catalytically active elements dissolved in an amount ~ of solvent which does not impair the combustibi]ity of the organic liquid are added, the liquid is then burned off and, -:
when required, the catalyst supports thus treated are subjected to an aftertreatment as hereinafter defined. If desired the . .

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catalyst support may be pretreated before said impregnation with said organic liquid.

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The process according to the invention can be carried out on a granulator or by means of a pellet-coating machine which can be heated if required. The burn~off time of the organic liquid can be controlled by means of the speed of rotation of the vessel. On burning off the organic liquid the catalysts can be treated with reducing agent for the after-treatment. For example, this can be done by treating the catalyst supports with a hydrogen flow for a lengthy period, for example, for 1/2 to 3 hours, at elevated temperature of up to 600C. Further reducing agents which can possibly be used are forming gas, formaldehyde, carbon monoxide, hydrazine, hydroxyl amine, glyoxal, sulphur dioxide, etc. The termination of the reduction stage can be determined by way of a separate activity test.
A possible modification of the aftertreatment can lie in that the catalyst supports are tempered at elevated tempera-ture, which can also be up to 600C.
Substances which have porous surfaces and are chemically and physically resistant, i.e., which, for example, are difficultly fusible, can be used as catalyst supports in the process according to the invention.

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Substances whiah satisfy these requirements can be of natural and/or synthetic origin. Aluminium oxides such as y-aluminium oxide or corundum, silica gel, kieselguhr, lime, barium sulphate, magnesium, carbon black, titanium dioxide, iron oxide, zinc oxide, silicon carbide, alumina, silicates, pumice, kaolin, asbestos, zeolites and/or magnesia can be ....
used for this purpose either individually or in mixture.
Depending on the intended use these substances can be produced in the form of pellets, rings, cylinders, cubes, chips, beads and also as pourable or monolithic catalyst supports.

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Corresponding to the catalyzing reaction catalyst supports having large surface areas of approximately 50 sg m per gram and catalyst supports having small surface areas of approximately 5 sq m per gram and correspondingly larger radii of pores or coarse-grained catalyst supports can be used.
In any structural reinforcer a synergetic interaction between reinforcer (catalyst support) and active substance (coating or film) must be expected, that is to say, the more intimate the mutual intermixing the greater will be said 10 interaction. Thus, the boundary between a structural reinforcer and a synthetic reinforcer can be fluid. Synergetic reinforcers or promoters impart to the active substance (principal component) of the catalyst an increased activity or a marked selectivity in the direction of one single reaction out of several thermo-dynamically possible reactions. With respect to their material ~; composition and with respect to the kind of their activity they present an extra ordinarily varied picture.
A large number of elements and compounds are used as principal components of catalysts and this includes elements of all the groups of the periodic system (with the exception of the noble gases). One substance can be active for several and very different processes. It is not possible to generally assign specific substances to specific reactions. For example, from the groups I, VI and VIII of the periodic system the elements ~
copper, silver, gold, chromium, tungsten, molybdenum, iron, ~ `
cobalt, manganese, nickel, rhodium, platinum, palladium, . . .
rhenium, ruthenium and iridium can be used. Other metals from the groups II, III, IV, V and VII of the periodic system, as for example, zinc, aluminium, tin, zirconium, titanium, vanadium, `
tantalum and magnesium, can also be used. Rare earths, for example, lanthanum, can also be used.
Depending on the intended use these catalytically . , ', : : . :'. ., :

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active elements can be used in the volume phase of the catalyst in the metallic, oxidic or sulphidic form as well as in the form of salts. Uses in which the catalysts obtained by means of the process according to the invention can be applied are chemical reactions in the liquid or gaseous phase, as for example, hydrogenations, dehydrogenations, oxidations, dehydra-tions, alkylations or cyclizations.
Depending on the kind and the special character of the reaction to be catalyzed, a structural reinforcer can be coated with the principal component and thus has scarcely a synergetic effect of the catalyst support, i.e., for metals mentioned hereinbefore, the catalytic action can still be influenced by the volume phase.
This kind of catalyst can be used in the production of monolithic waste-gas purification catalysts for internal .; : :.. ..
combustion engines. Further possibilites of combinations are obtained if the principal components are absorbed on a synergetic reinforcer, for example, r-AlO3, or if the synergetic reinforcer is absorbed on a structural one and if as the third ;~
layer the principal component is applied as a film or coating, for example, in the case of a globular catalyst. This would be conceivable, for example, in:the combination of ~-A12O3 ~
(structural reinforcer) and ~-A12O3 (synergetic reinforcer). -According to the invention, in the production of catalytically active coatings or films the catalyst supports can be impregnated with a combustible organic liquid. For this purpose alcohols, ketones, ethers and hydrocarbons can be ;
used either individually or in mixture. They can be, for example, n-butenyl ether, acetone, acetone oils, ethanol (spirit) ethyl acetate, ethyl-isoamyl ketone, ethyl butyrate, ethylene ;
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glycol-monoacetate (glycol monoacetate), ethylene glycol monoethyl ether (ethyl glycol), ethylene glycol-monoethyl ether --\ ~L083~2 acetate (ethyl ~lycol acetate), ethylene glycol-monobutyl ether (butyl glycol), ethylene glycol-monobutyrl ether acetate (butyl glycol acetate), ethylene glycol-monoisopropyl ether (isopropyl glycol) ethylene glycol-monomethyl ether (methyl glycol), ethyl-ene glycol-monomethyl ether acetate (methyl glycol acetate), ethylene glycol-monopropyl ether (propyl glycol) ethyl formate, ethyl hexanol, ethyl propionate, amyl acetate, amyl alcohol, amyl butyrate, amyl formate, benzene benzyl acetate, benzyl alcohol, n-butanol,`n-butyl acetate, n-butyl butyrate, 1,3-butylene-glycol-(3)-monomethyl ether (methoxybutanol), butylene glycol- :
(3)-monomethyl ether-1-acetate (supplied under the trademark Butoxyl*), n-butyl formate, n-butyl propionate, cyclohexane, ~:
. cyclohexanol, cyclohexanol acetate, cyclohexanone (Anon), cyclo- ~:~
hedanone, cymene, decahydro naphthalene (supplied under the trade-mark Dekalin*), diacetone alcohol, diethyl ether, diisobutyl ; . ~ .
ketone, dichloro ethane, dimethyl cyclohexanone, dimethyl forma-mide, dimethyl sulphoxide, dioxane (diethylene dioxide), furfurol, glycol carbonate, glycolic acid butyl ester (supplied under the ~
trademark GB ester), hexyl alcohol, Isanol* (a trademark), iso- - .
butanol, isobut~l acetate, isobutyl butyrate, isoheptyl acetate, .
isoheptyl alcohol, isohexyl acetate, isohexyl alcohol, isophorone, isopropanol, isopropyl acetate, pine oil, solvent naphtha, mesityl oxide, methanol, methyl acetate, methyl-ethyl ketone, methyl iso-butyl carbinol (2-methyl-4-pentanol), methyl-isobutyl ketone, -:
methyl cyclohexanol, methyl cyclohexanol acetate, methyl cyclo-hexanone (supplied under the trademark Methyl anon), methyl cyclo~
hexenone, methylene chloride, methyl formate, lactic acid ethyl ester.(ethyl acetate), lactic acid butyl ester (butyl acetate), monochloro benzene, nonanol, polyethylene glycol monoether, n-propanol, n-propyl acetate, propyl butyrate, propylene glycol ether, propylene glycol carbonate, n-propyl propionate, carbon disulphide, boiling-point benzines, Solvenon M (a trademark for . . .

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technical dimethyl acetate), turpentine, turpentine derivatives, mineral spirits, tetrachloroethane, tetrahydroEuran (tetramethyl-ene oxide), tetrahydronaphthalene (supplied under the trademark Tetralin*), tetramethyl sulphone, toluene, trichloroethylene, V.M.P. naphtha, root turpentine, chloroform.
Water, alcohols, ketones, ethers, aldehydes and aro-matic hydrocarbons, either individually or in mixture, can be used as solvents in which the catalytically active elements are dissolved. Moreover, the organic liquids mentioned hereinbefore can also be used. Depending on both the catalyst material and the catalytically active element the mixing proportions can vary -~ and must be determined empirically.
In order to avoid impairment of the combustibility of .
the organic liquid, the maximum amount of e.g. water added to e.g. methanol must be such that ignition of the methanol is still possible.
The catalytically active elements can be present in the ~ -solvent as free and complex ions. Thus, complex compounds can be ` formed by chelating agents, as for example, acetyl acetone or -additions, as for example, ammonia. The use of complex halides, as for example, H2 Pt C16 can be of particular interest.
Complexing agents, precipitants and/or reducing agents ~, : .
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Thus, the organic liquid can be mixed with hydrogen 1, sulphide, Urotropin, ammonia, ammonium polysulphide or ammonium ~1, . ... .
`~ chloride. Hydrogen sulphide and ammonium sulphide cause the metals to be fixed on the surface of the catalyst while ammonia and ammonium chloride cause the metallic salts to diffuse in ; more slowly due to a complexing action. Thus, soluble substances ~-which react the catalytically active elements to compounds having reduced solubility (fixing) ox to compounds having a reduced rate of diffusion (complexing) are added to the organic liquid.

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Phosphates, particularly pyrophosphates and metallic phosphates, citrates, acetates, oxalates, tartrates, - o - phenanthroline, thiocyanates, thiosulphates, thioureas, pyridine, quinoline and cyano groups can be further complexing agents. Halides, for example, chloro, hydraxo and amino complexes may also be used as complexing agents.
Olefin and olefin-like compounds, as for example, ethylene, propylene, butadien, cyclohexene or styrene, can also be used for the complexing action.
These complexes can be used in non-aqueous systems, for example, benzene, toluene, pyridine, acetone or diethyl ether.
If noble metals from the group of the platinun metals are used as catalytically active elements, then a reducing agent may be additionally added to the organic liquid. For example, hydrazine, hydroxyl amine, glyoxal, formaldehyde, carbon monoxide and sulphur dioxide can be used as these reducing agents.
The reducing aftertreatment stage can then be dispensed with.
If monolithic catalyst supports, i.e., catalyst supports -which consist of one piece and are used as such, are treated by means of the process according to the invention, then the ; monoIith is suitably mixed with an amount of water which is ; such that approximately 80% of the pores are filled. The remaining 20~ of the pores are filled with the salt-containing solvent.
The process according to the invention has the advantage that the catalytically active catalyst uniformly covers the surface of the catalyst support. Irrespective of the catalyst support size used the film formed is very thin since the catalytically active elements are retained on the surface of " : LV833L~2 the support by the diffusion of the ~iquid from the inside. The fact that the loss of metallic salts is avoided is a further advantage.
The process according to the invention is described and explained in greater detail by means of the example hereafter.
Example 1 . :
110 g of pellets of y-Al~O3 (supplied under the trade-mark Pechinery SCS 79 having a diameter of 2.8 to 4 mm) are rolled in a rotating enamelled reactor. A solution of 22 g of H2 Pt C1 :
- 10 and Rh C13 in 1 litre of water is poured over these pellets while they are rolled. After drying the pellets with a warm air flow they are treated with hydrogen for one hour at 500C.
Example 2 . : .
' 110 g of pellets of ~-A12O3 (supplied under the trade-mark Pechiney SCS 79 having a diameter of 2.8 to 4 mm) which are rolled in an enamelled rotary reactor are treated with methanol, .
whereupon 15 ml of a solution of 22 g of H2 Pt C16 and Rh C13 in 1 litre of water is added and intimately mixed with the impreg- ;
~, nated pellets. The methanol is then ignitedand completely burned, ; 20 whereupon the pellets are treated with hydrogen for one hour at ' 500C.
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Example 3 110 g of pellets of ~-A12O3 (supplied under the trade-mark Pechiney SCS 79 having a diameter of 2.8 to 4 mm) which are rolled in an enamelled rotaxy reactor are impregnated with cyclo-hexane, whereupon 15 ml of a solution of 22 g of H2 Pt C16 and Rh C13 in 1 litre of water are added and intimately mixed with the impregnated pellets.
~ The cyclohexane is then ignited and completely burned, s 30 whereupon the pellets are treated withhydrogen forone hourat 500C.
Exam~le 4 ~- `
110 g of pellets of ~-A12O3 (supplied under the trade-mark Pechiney SCS 79 _ g _ ~ .

having a diameter of 2.8 to 4 mm) are impregnated with a cold-saturated solution of Urotropin (a trademark for hexamethylene tetramine) in methanol while they are rolled in an enamelled rotary reactor. While rolling, 15 ml of a solution of 22 g of H2 Pt C16 and Rh C13 in 1 litre of water are then added and intimately mixed with the impregnated pellets. The mixture is ignited and completely burned~ The pellets are then treated with hydrogen for one hour at 500C.
Example 5 110 g of pellets of ~-A103 (supplied under the trade-mark Pechiney SCS 79 having a diameter of 2.8 to 4 mm) are impregnated with methanol while they are rolled in an enamelled rotary reactor, whereupon they are wetted with 15 ml of a cold-saturated solution of Urotropin (a trademark for hexamethylene tetramine) in methanol. 15 ml of a solution of 22 g of H2 Pt C16 and Rh C13 in 1 litre of water are then added and intimately mixed with the impregnated pellets. The mixture is ignited and com-; pletely burned. The pellets~are then treated with hydrogen for one hour at 500C.
Example 6 Pellets of ~-A12O3 are tempered for 2 hours at 800C
whereupon the specific surface area is 42 sq m per gram. 10 kg of the y-A12O3 pellets thus treated are impregnated with 9 litres of methanol in an enamelled reactor and in order to be homogenized they are rolled for 5 minutes. While the rolling i9 continued 500 ml of an aquéous solution containing 13.1 g of H2 Pt C16, 4.6 g of Rh C13 and 26.0 g of AlC13 6H2O are added. The pellets ;
are rolled for a further 5 minutes in order to be homogenized.
The alcohol is ignited and burned while the loose material is rolled. After extinguishing the flame, the pellets are rolled for a further 15 minutes and subsequently treated with a flow of H2 for 1/2 hour at 500C.

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33~ 2 The ~-A12O3 applied (supplied under the trademark Rhone-Progil SCS 279) have a screen frac-tion of 2.38 to 4 mm, the powder density being 0.7 to 0.72 kg per litre.
Example 7 A cylindrical monolithic support of the type EX 20 (a trademark of Corning Glass) having a diameter of 100 mm and a length of 150 mm was provided with a coating of active alumina corresponding to the laid-open German Patent Application No.
23 06 395.8, whereupon the supports had a specific surface area of 13 sq m per gram. -The activated support was dipped into methanol and the excess methanol was blown out of the ducts with compressed air and weighed. The support absorbed 113 g of methanol (wet weight).
The support was subsequently dried to 70% of its wet weight. The support was then dipped into an aqueous methanol solution (92% of methanol), which contained 23.8 g of Pd as PdC12, 57.4 g of Cu(NO3)2 3H2O, 47.6 g of CrO3 and 61.9 g of aluminium acetyl acetonate Al(C5H7O2)3 per litre. The methanol was burned off.
i The support was then calcined in air for 1/2 hour at 400C where-upon it was subjected to aftertreatment in a flow of H2 for 15 minutes at 200C.
Example 8 .
11 kg of ~-A12O3 pellets (supplied under the trademark ` SCS 79 by the firm of Pechiney, fraction 2.8 to 4 mm) were impreg-i nated with 6 litres of carbon tetrachloride (CCL4) in a rotary reactor as described in Example 1, whereupon 1000 litres of an aqueous methanol solution (40% by weight of methanol) which -;
contained 22 g of Pd as PdC12, were added, dried in a stream of . .
hot air (2aOC) and subsequently treated with a flow of hydrogen ~ 30 for one hour at 500C (40 litres per hour).
-~ Example 9 ~ A cylindrical monolithic support of the type AlSi Mag ;
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7.95 (a trademark of Am.La~a) having a diameter of 100 mm and a -length of 75 mm was provided with a coating of active alumina as described in Example 8. The support then had a specific surface area of 20 sq m per gram.
The support thus pretreated was dipped into acetone, whereupon the ducts were cleared by blowing with compressed air.
The support was then dried to approximately 65% of its initial acetone absorption (wet weight) and dipped into acetic acid ethyl ester, which contained 21.8 g of Pt as Pt C14 and 143.5 g of CrO3 per litre. The support was calcined in air for 1 hour at ~; 600C and further treated. The catalyst contained 0.5 g of Pt and 2.5 g of Cr2O3.

Example 10 1 kg of material extruded from active alumina (supplied under the trademark VHA 300T) (diameter = 3 mm, length 3 to 9 mm) was homogenized for 10 minutes and then impregnated with 0.75 litre of carbon tetrachloride (CC14) in vacuo (20 mm Hg), where-upon, while rolling, 100 ml of an aqueous methanol solution (95%
of CH30H), which contained 13.15 g of CrO3 were added and poured into a rotary vacuum evaporator and evaporated at an oil-bath temperature of 80C while rolling. The material was calcined in air~for 1/2 hour at 500C.
Example 11 11000 g of globular catalyst supports of the type "Pechiney SCS 250" (a trademark) (diameter of the pellets - 2.8 ~
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` to 4 mm) are saturated with B litres of an aqueous ammoniacal methanol solution (6.3% of NH3) in an enamelled reactor, where- ~ -upon 1000 ml of a methanol solution containing 22 g of Pt as H2 Pt Cl are added and further treated as described in Example 8.
Example 12 ~ . .
10 kg of a pelleted active aluminium oxide (supplied under the trademark ~A 300T) (size of the tablets 3 x 3 mm) were impregnated with , . , . : , : , , :. : .
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~3~22 8 litres of a formaldehyde-containing methanol solution (8.75% of CH2O) in an enamelled reactor while rolling, ~hereupon 1000 ml of an aqueous methanol solution (95% of methanol) containing 40 g of Pd as Pd-II-chloride were added and further treated as described in Example 1.
In order to determine the depth of infiltration of the catalytic active coating and thus the amount of noble metallic salts required, the cross section of a treated pellet is photographically enlarged 100 times. The width of the dark-colored edge is measured.

Example Width of Edge Reality Photo Example 1 3.5 to 4 cm 0.35 to 0.4 mm on the inside .~ the edge is not .
sharply defined :
` Example 2 2 to 2.5 cm 0.2 to 0.25 mm Example 3 3 cm 0.3 mm . Example 4 0.5 to 1 cm 0.05 to 0.1 mm, -:. . on the inside the edge is sharply ~ defined :
.~ 20 Example 5 0.5 to 1 cm 0.05 to 0.1 mm .
' Example 6 2 to 2.5 cm 0.2 to 0.25 mm ,"',''.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for applying a coating or film of catalytically active elements by means of solution on the exter-nal surface of a porous catalyst support having a large surface area, the improvement in which the catalyst support is impreg-nated with a solution of least one member selected from complex-ing agents, precipitants and reducing agents in an organic liquid without exceeding the saturation of the catalyst supports, the solution of catalytically active element is then added and the liquid is removed by heating and when required, the catalyst support thus treated is subjected to an aftertreatment with a reducing agent or tempering at elevated temperature.

2. A process according to claim 1, in which the organic liquid is a non-combustible organic liquid.

3. A process according to claim 1, in which the catalyst support is impregnated with a combustible organic liquid having at least one member selected from complexing agents, precipitants and reducing agents dissolved therein without exceeding the saturation of the catalyst supports, catalytically active elements dissolved in an amount of solvent which does not impair the combustibility of the organic liquid are then added, the organic liquid is burned off and when required the catalyst support thus treated is subjected to said aftertreatment with a reducing agent or tempering at elevated temperature.

4. A process as claimed in claim 1, 2 or 3 in which prior to said impregnation with said solution in said organic liquid the support is impregnated with an organic liquid.

5. A process according to claim 1, 2 or 3 in which the catalyst support is aftertreated with reducing agents.

6. A process according to claims 1, 2 or 3, wherein the catalyst support is aftertreated by being tempered at elevated temperature.