DE3330621C2 - Process for the production of supported catalysts with metals or metal compounds as active components - Google Patents

Abstract

Supported catalysts with metal compounds as active components are produced by the deposition of metal carbonyls from the gas phase on carrier materials with a large surface area, in that the metal carbonyls are cleaved oxidatively on the carrier materials. Activated carbon is particularly suitable as a carrier material. A pretreatment of the carrier materials with promoters is advantageous. These supported catalysts are particularly suitable for the production of hydrocarbons by the Fischer-Tropsch process or for the methanation of gas mixtures containing hydrogen and carbon monoxide.

Description

several stages, whereby at first multinuclear clusters are formed, which with further CO elimination in metal crystallites skip [J. Catal. 50: 196-199 (1977); Organic Chemistry, Vol. 18 (1979) 5.1479; Engels, dissertation 1978, TH Aachen]. If this thermal decomposition is carried out on surfaces, metal films are formed. When a magnetic field is applied, these crystallites agglomerate to form metal hairs, so-called Whiskers (DE-PS 12 24 934).

It is also known to use supported catalysts with pure metal coating by thermal cleavage of Metal carbonyls to produce activated carrier materials with a large surface (US-PS 28 46 488 and 25 99 978). In the case of supported catalysts to be prepared according to US Pat. No. 2,846,488 or US Pat. No. 2,599,978, the reaction temperature must above the decomposition temperature of the carbonyls, and it must be in a reducing atmosphere be worked, d. i.e., with hydrogen gas to deposit the metal from the carbonyl. That requires elaborate safety measures, since the handling of hydrogen gas is difficult; moreover is accordingly they are very expensive.

The present invention is based on the object of a process for the production of supported catalysts to develop with metal compounds as the active component that has the disadvantages of the above Process according to the prior art does not have, so that no anions remain in the catalyst, a there is a uniform distribution of the active component, an application of higher contents of the active component takes place in one operation and no drying step, which has previously been carried out in addition, and which at the same time adversely affects the distribution of the active component is required, at comparatively low levels Temperatures can be applied opposite the thermal cracking in the gas phase under simultaneous Significant reduction in the safety risks associated with handling and cheaper production.

In the method of the generic type, this object is achieved according to the invention by the feature of the main claim dissolved, which makes it possible to use supported catalysts provided with metal compounds as the active component by the deposition of metal carbonyls from the gas phase on carrier materials with a large surface and to produce their oxidative cleavage.

It is a particular advantage of the process according to the invention that no drying step is required in the production process, and therefore there is no disadvantageous redistribution of the active component in the carrier. The original distribution of the active component therefore remains in the catalysts prepared according to the invention obtain. Since the active component is also present as a metal oxide, there is also no negative influence the anions present in the known processes.

Preferred metal carbonyls for the production of the supported catalysts according to the invention are listed, for example, in Table 1 below. ^case brings:

Table 1

metal Metal carbonyls
(with or without anion compound)
general formula name Chromium hexacarbonyl chrome Cr (CO) ₆ Iron pentacarbonyl
Diiron nonacarbonyl
Triiron dodecacarbonyl iron Fe (CO) ₅
Fe ₂ (CO) ₉
Fe ₃ (CO) ₁ , Diiridium octacarbonyl iridium Ir ₂ (CO) ₈ Dicobalt octacarbonyl
Tetracobalt dodecacarbonyl cobalt Co ₂ (CO) ₈
Co ₄ (CO) ₁₂ Dimanganese decacarbonyl manganese Mn ₂ (CO) I ₀ Molybdenum hexacarbonyl molybdenum Mo (CO) " Nickel tetracarbonyl nickel Ni (CO) ₄ Osmium pentacarbonyl
Diosmium nonacarbonyl osmium Os (CO) ₅
Os ₂ (CO) ₉ Dirhenium decacarbonyl rhenium Re ₂ (CO) I ₀ Dirhodium octacarbonyl Rhodium Rh ₂ (CO) ₈ Ruthenium pentacarbonyl
Diruthenium noncarbonyl
Triruthenium dodecacarbonyi Ruthenium Ru (CO) ₅
Ru ₂ (CO) ₉
Ru, (C0) _i2 Tungsten hexacarbonyl tungsten W (CO) ₈

In the production of the supported catalysts according to the invention, the support material is coated with an inert one Gas stream, for example nitrogen, brought into contact, the desired metal carbonyl or a Contains mixture of different metal carbonyls. This can be done in a fixed bed, moving bed or fluidized bed reactor take place. Since the metal carbonyl cleavage takes place in a metal oxide and in CO, the The amount of oxygen required for the reaction is added to the gas stream. The reaction temperature is here comparatively low, namely below the thermal decomposition temperature of the metal carbonyls. as As already stated, catalyst supports can preferably be the customary support materials with a large surface area Activated carbon. It is also possible to use the carrier materials with known promoters, preferably all water-soluble potassium compounds that are present on heat treatment in potassium oxide ι »pass over to pretreatment in a known manner and only then carry out the metal carbonyl cleavage. This has the advantage that the catalytic activity is increased.

Activated carbon is preferably used as the carrier material. What is surprising is that when activated carbon is used as the carrier material, the metal is not deposited on the outer surface as a metal film, but rather that the metal is deposited on the inner surface in the pores of the activated carbon. In this case, the desired amount of active component, for example iron, can be applied to the activated carbon as a carrier material in one operation in a wide concentration range from 0.1 to 80% by weight. Depending on the catalytically active metal oxides applied by the metal carbonyl cleavage, the supported catalysts prepared according to the invention have a wide field of application. They are preferably used in the preparation of hydrocarbons from carbon monoxide and hydrogen-containing gases or 2ii in the methanation of carbon monoxide and hydrogen-containing gases · - rwendet ^.

example 1

10 g of activated carbon (BET surface according to DIN 66131 = 1,000 mVg, microporous

- ^s volume, measured with benzene adsorption isotherm, of 40 cmV100g, macropore volume, measured with

Mercury porosimetry, of 41 cmV100g) from an inert gas stream with a flow rate of 15 NL / h flows through which, in addition to 0.6 volume- «iron pentacarbonyl, also contains 1.3 NL air / h. During the In the test series, an oxidative carbonyl cleavage took place at 50 ° C. According to the The respective residence time of the activated carbon in the gas stream were the catalysts No. 1 to 3 with different

- ¹ »iron content produced, as the following table 2 shows:

Table 2

Catalyst no. Test duration iron content
(h) (% by weight)

1 24 20.4 2 16 14.6 3 6th 5.8

In order to show the catalytic activity, the catalyst No. 2 was used for the production of hydrocarbons used after the Flscher-Tropsch synthesis.

Through a fixed bed reactor having a catalyst volume of 15 cm ³ of a gas mixture, consisting of 50 vol ¹ V. H ₂ and 50 vol .- * CO, at a temperature of 300 ⁰ C and a pressure of 1 bar at a space velocity of 540 NL χ 1 'χ h " ¹ headed.

It became a product gas with a composition of saturated gas that is typical for the Flscher-Tropsch synthesis and unsaturated hydrocarbons, as shown in Table 3 below:

Table 3

Product gas composition of catalyst # 2

-oxidative cleavage

C, 23.0

C ₂ 12.7

C ₂ = 8.4

C ₃ 6.5

C ₃ = 14.0

C ₄ 2.9

C ₄ ' 8.6

Ci. Cj. Ci, C '<denote added hydrocarbons C ^- : -. Ci -. Cj = dull unsaturated hydrocarbon Example 2

The activated charcoal of Example 1 was flowed through in a reactor by an Incri gas stream at a flow rate of 15 NL / h, to which 0.65 NL / h nitrogen tetracarbonyl and 2.25 NL / h air for oxidative cleavage at 60 ° C. were admixed. According to the Verwellzelt the activated carbon in the gas flow were the catalysts no. 4 and 5 were produced with different nickel contents, as the following table 4 shows:

Table 4 Test duration
(H) Ni content
(Wt .-%) Catalyst no. 17th
6th 72.7
37.5 4th
5

To test the activity, catalyst no. 5 was used for methanation.

_{A gas mixture consisting of 75% by volume of H 2} and 25% by volume of CO with a space velocity over the catalyst of 1.9 NL / h χ gcat was passed through a vertical, electrically heated tubular reactor filled with the catalyst. CO flows through. · '<>

The composition of the dried product gas corresponds almost to the calculated thermodynamic Equilibrium composition, as shown in Table 5 below

Table 5 Test result
Catalyst # 5
T = 510-530
Vol.% Thermodynamic ^
calculation
T = 5iof C P = 1 bar
Vol.% Product gas
composition 36.8 36.7 CIu 3.7 4.1 CO 9.0 9.4 CO ₂ 50.6 49.8 H ₂ Example 3

In a reactor, 50 g of molecular sieve 10 AU (pearl shape, approx. 2 mm) were from a nitrogen stream with a Flow rate of 15 NL / h flows through, the 0.56 NL / h Elsenpentacarbonyl and 3 NL / h air to oxidative cleavage at 50 ° C were admixed. After the molecular liver had been swollen for 24 hours in a gas stream, a catalyst with an iron content of 13% by weight was obtained. This catalyst is for that Fischer-Tropsch synthesis well suited.

Claims (1)

Claim: Process for the production of supported catalysts provided with metal compounds as active components by the deposition of metal carbonyls from the gas phase on support materials with a large Surface and its cleavage, characterized in that the metal carbonyls are cleaved by oxidation will. The invention relates to a method according to the preamble of the patent claim. For the production of supported catalysts with metal compounds or with pure metals are coated, it is known to first apply a porous support with solutions of metal salts or others To impregnate metal compounds, which are then converted into the catalytically active state in a post-treatment step. It is known, for example, to deposit the active component on the carrier from readily water-soluble and easily decomposable metal compounds. As easily decomposable anlons of the metals are referred to Hydroxides, nitrates, carbonates, oxalates, formates and chromates used (G. Horn In catalysts, tensides and mineral oil additives, Georg Thieme Verlag, Stuttgart 1978, pp. 7-22). The distribution of the active component on the carrier depends on the adsorption capacity of the carrier. 1st For example, if the rate of adsorption is greater than the rate of diffusion of the dissolved metal compound in the pores of the carrier, only the outer carrier zone is initially loaded. If the impregnation is stopped at this point in time, coated or layered catalysts are obtained. With a sufficiently long impregnation tent, on the other hand, an almost even distribution of the active component on and in the carrier is achieved «(R. Krabetz, W. D. Mross in Ullmanns Enzyklopadie der technischen Chemie, 4th edition, vol. 13, pp. 558-565). The level of the desired active component loading on the carrier can be determined by the concentration of the Soaking solution and the number of soaking processes can be set. As a rule, there are several soaking processes necessary. Complete impregnation of the carrier is only possible if the air has been removed from the pores beforehand the carrier has been removed. This can be done by evacuating the carrier, or by heating the soaking solution can also be done by previously gassing the carrier with a gas that is readily soluble in water. The impregnation of porous supports with liquid celts has so far been carried out by the immersion process, the SprühimprSgnierung or by the vacuum or vacuum-pressure method (DE-OS 27 32 553). In this case, coated or layered catalysts are produced by means of spray impregnation by the heated carrier is sprayed with the impregnation solution, for example in a rotating drum. The high of The loading and penetration depth of the active component can be adjusted by changing the spray speed, the drum temperature, the concentration of the impregnation solution or the speed of the drum rotation. The disadvantage of this process is that a uniform distribution of the active component in the catalyst grain cannot be achieved. Also in the dipping process there is the disadvantage that the impregnation is not deep enough into the pores of the support system ■ vi penetrates and thus no uniform impregnation can be achieved. In the vacuum process, the carrier is first evacuated until cavities and pores of the carrier are gas-free are. The method has the disadvantage that it can only be used with well-wetting impregnation solutions and long impregnation tents. In the vacuum-pressure process, the carrier is finally placed in a sieve-like basket with the 4> The pressure vessel filled with impregnation solution is immersed, whereupon the pressure vessel is evacuated. During this During the process, the carrier is completely saturated with the impregnation solution. Then the container put under pressure. The disadvantage of this process is the high outlay on equipment. In all known impregnation processes, the catalyst must then be dried, with one first fixation of the active component on the carrier takes place, while not adsorptively bound to the carrier > <i Active components inside the grain fail as soon as the saturation limit is exceeded. A steady one Distribution over the carrier is not achieved. JTMe evaporation begins on the surface of the carrier and then preferably continues in the wide pores. The liquid evaporating from narrow pores is initially supplemented by liquid from wide pores due to capillary attraction. At a slow drying process and with readily soluble active components, there is accordingly a preferred enrichment of the active components in the narrower pores and in the middle of the grain. The active component is thus difficult to access for the diffusion stream and the catalyst efficiency drops. It is finally known. To use metal carbonyls as homogeneous catalysts, for example in the Homologation [Chemiker Zeltung 106 (1982), p. 249]. Metal carbonyls are complex compounds. In which Carbon monoxide molecules are coordinated to a metal atom. They arise through the accumulation of CO Mi the transition metals of the periodic table of the elements or their compounds. It is also known. To soak aluminum oxide or silver oxide as a carrier with solutions of metal carbonyls in organic solvents. Here, the solvent and metal carbonyl are adsorbed by the carrier, whereupon the solvent has to be evaporated again. Another disadvantage here is that some of the metal carbonyls also evaporate. Therefore, with a Tränkgang only small amounts of Metallcarbo- '• ^s Nylen applied. In addition, some of the metal carbonyls applied are absorbed again during the drying step. However, if the catalytically active substance is not the metal carbonyl itself, but only the metal atoms, then a thermal aftertreatment takes place in which the CO groups are split off. This process runs in