FI93085B - Supported catalyst, method for the manufacture thereof and application thereof - Google Patents

Abstract

A highly active and selective supported catalyst is obtained by treating an inorganic oxide carrier with a mixed metal cluster compound having the formula (I) Co2Ru2H2n(CO)13-a (I) where n is 0 or 1. The carrier catalyst is well suited to synthesis by the Fischer-Tropsch reaction and to hydrogenation of carbon monoxide.

Description

93085

Supported catalyst, its preparation method and use

The invention relates to a support catalyst prepared by treating a solid inorganic oxide support with a mixed metal cluster based on cobalt, ruthenium and carboxyl and reducing the treatment product thus obtained. The invention also relates to a process for preparing a support catalyst, wherein a) the solid inorganic oxide support is treated with a mixed metal cluster based on cobalt, ruthenium and carboxyl and b) the oxide support treated with the mixed metal cluster according to step a) is reduced.

The invention also relates to the use of a support catalyst of the above-mentioned type.

Metal clusters and their reaction products can be used in a wide variety of reactions. Typical reactions are mentioned in Muetterties, E.L., Krause, M.J., Angew. Chem. 95 (1983) 137. One important reaction is e.g. conversion of a gas mixture containing carbon monoxide and hydrogen (so-called synthesis gas) into hydrocarbons. This process is also commonly referred to as the Fischer-Tropsch reaction. Particularly active metals in this reaction are iron, ruthenium, cobalt and rhodium. When these metals are used as a reaction product, a mixture of numerous, mainly straight-chain, aliphatic and olefinic hydrocarbons is obtained.

. ·. Typically, the catalysts are prepared by a process in which a metal nitrate or other inorganic metal salt is absorbed from an aqueous solution onto a solid inorganic oxide support, which is usually SiO 2, Al 2 O 3 or another similar oxide material. The catalyst is then calcined and, to reduce metal oxides, the catalyst is typically treated in a stream of hydrogen at a temperature of about 350-500 ° C. It is typical of the catalysts prepared by this method that the metal particles formed on the surface of the support are relatively large in size, i.e. the dispersion of the metal is low. In addition, the reduction of metal oxides, especially cobalt oxides, is difficult and even after hydrotreating a significant part of the metal is in oxidized form. The degree of reduction and dispersion of the metal has been found to have a significant effect on the activity of the catalyst and the composition of the reaction product obtained with it.

Catalysts of the above type have also been prepared by a process in which the surface of a solid, inorganic oxide support is modified using organometallic carbonyl clusters or grapes as starting material. From these carriers and clusters, metal particles formed on the surface of the carrier are obtained, which are smaller in size than before, i.e. the dispersion of the metal is higher. The size distribution of the formed metal particles is also even. These catalysts work well, especially in the hydrogenation of carbon monoxide, whereby their activity and selectivity are better than those of catalysts prepared by impregnating a support with a metal salt.

Xiao, F-S., Fukuoka, A., Ichikawa, M., J. of Catalysis, 138 (1992) 206-222 investigates the behavior of SiO2-supported multinuclear mixed metal clusters in the hydrogenation of carbon monoxide. The following compounds were studied [HRu3 (CO) n] 'H3Ru3Co (CO) i2 RuCon (CO) 11 HRuCo3 (CO) 12 RuCl3 + CoCl2 Co4 (CO), 2 [HRu3 (CO) n]' + Co4 (CO) 12 Of these by far the most active was HRuCo3 (CO) 12. In this work, carbon monoxide was hydrogenated at 247 ° C at a pressure of 5 bar, with a flow rate of 40 ml / min and a synthesis gas composition of H 2: CO = 2: 1. * 3 93085

The main weakness of the support catalysts prepared from both metal salts and cluster compounds is the unfavorable hydrocarbon distribution of the reaction product and thus the insufficient yield of the desired hydrocarbon products. Particularly undesirable products are methane and carbon dioxide. In the above-mentioned cases, the product distribution has been found to substantially comply with the so-called Anderson-Schulz-Flory rule for all catalysts supported by ordinary solid inorganic oxides. According to this distribution, for example, the maximum achievable yield of c5-c, 2 hydrocarbons is only 48% by weight. In addition, the product distribution is wide and the reaction product contains hydrocarbons from methane to high molecular weight waxes, which reduces the value of the product and makes its recovery more difficult. The poor selectivity of the catalysts is the most significant factor limiting the competitiveness of this reaction.

In addition to the above-mentioned cluster starting materials, other mixed metal clusters are also known. From An-gew. Chem. Int. Ed. Engl. 20 (1981) No. 8, 679-678, and Chem. Ber. 118 (1985) 1133-1142 discloses a process for preparing a Ru2Co2 (CO) 13 cluster and from Organometallics, 19 83, 2, 184-185, a process for preparing a Ru2Co2H2 (CO) 12 cluster is known.

The object of the invention is to provide such a carrier! a catalyst capable of producing a high yield of the desired product. The invention also aims at the most selective catalyst possible, which, for example in the hydrogenation of carbon monoxide, produces the desired hydrocarbons without the formation of undesired products. In particular, the aim is to produce as many C2-C12 hydrocarbons as possible without generating larger amounts of methane or hydrocarbons heavier than C12.

These objects have now been achieved with a new support catalyst, which is mainly characterized by what is stated in the characterizing part of claim 1. Thus, it has been found that even larger amounts and a more selective product are obtained with a support catalyst prepared by treating a solid inorganic oxide support with a mixed metal cluster of formula (I).

Co2Ru2H2n (CO) 13.n (I) where n is 0 or 1. Thus, the most efficient and selective catalyst is obtained from mixed metal clusters with a cobalt to ruthenium content and ratio of 2: 2. This refutes the teaching of the above-mentioned Xiao article that activity and selectivity e.g. for hydrocarbons improves as the Co: Ru ratio increases.

According to a preferred embodiment, the support catalyst according to the invention is prepared from a mixed metal cluster of formula (II)

Co2Ru2H2 (CO) n (II) This cluster produces very little unwanted methane, while very much C2-C12 hydrocarbon is generated. Oxygenate, on the other hand, is generated very little. The cluster is thus preferred when as much C2-C12 hydrocarbon as possible but little oxygenate is desired.

According to another embodiment of the invention, the support catalyst is prepared from a mixed metal cluster of formula (III).

Co2Ru2 (CO) 13 (III) In addition to C2-C12 hydrocarbons, this bimetallic cluster also produces oxygenate, while less methane is generated than the corresponding catalysts according to the prior art.

When starting to prepare a support catalyst according to the invention, it is advantageous if the inorganic support is dried with heat and / or under reduced pressure. Suitable carriers are any solid inorganic oxide support, e.g. MgO, SiO 2, A103, 5,93085

SiO2-Al2O3 and zeolites. Preferred carriers are silica SiO 2, a derivative or a mixture thereof. In said oxides, the silicon element can also be replaced, for example, by germanium and aluminum, for example, by boron, chromium, iron or gadolinium. Other elements may also be included in the crystal structure.

The cobalt- and ruthenium-based support catalysts according to the invention can also be promoted by means of alkali or alkaline earth metals. This further emphasizes the selectivity of a good catalyst.

The preparation of the support catalyst according to the invention is started by treating the solid inorganic oxide support with a mixed metal cluster. This is preferably done by contacting the solid inorganic oxide support with the mixed metal cluster and the organic solvent dissolving the mixed metal cluster and then removing the organic solvent. After the inorganic oxide support is treated with a mixed metal cluster, it is reduced. The reduction is preferably carried out by heating the treatment product with hydrogen.

The weight ratio of cobalt to ruthenium metal in the catalyst according to the invention is important. The preferred weight ratio is 1: 3-1: 1.3, which corresponds to molar ratios of 1: 1.75-1: 0.75. The most preferred molar ratio is about 1: 1.

It has also been found in the invention that the preferred support catalyst contains about 0.6-3.0% by weight of cobalt and 1.0-5.0% by weight of ruthenium, respectively, with a total metal content of about 2.0-5.0% by weight. %.

: * The invention also relates to a process for the preparation of a support catalyst, in which a) a solid inorganic oxide support is treated with a mixed metal cluster of formula (I)

Co2Ru3H2n (CO) 13.n (I) 93085 6 wherein n is 0 or 1 and b) the oxide support treated with the mixed metal cluster according to step a) is reduced. Thus, a good catalyst is obtained by a process in which an inorganic oxide support is treated with a cobalt ruthenium carbonyl compound having 2 cobalt atoms and 2 ruthenium atoms in the molecule. The process thus uses a compound of formula (II) as a mixed metal cluster.

Co2Ru2H2 (CO) 12 (II) or formula (III)

Co2Ru2 (CO) 13 (III)

An inorganic support dried by heat and / or vacuum is used in the preparation of the support catalyst. The preferred treatment temperature is 100-300 ° C, preferably about 200 ° C, with a preferred treatment time of about 1-3, preferably about 2 hours. The inorganic oxide support can then be further cooled with an inert gas such as nitrogen or helium. The preferred inorganic support is, as mentioned above in connection with the product protection text, silica, SiO 2, a derivative thereof or a mixture thereof. It is preferred to treat the inorganic oxide support with a mixed metal cluster in a weight ratio of 1: 1 to 30: 1, preferably 5: 1 to 20: 1, and most preferably about 10: 1.

According to a preferred embodiment, the inorganic oxide support is treated in step a) by contacting it with a mixed metal cluster and an organic solvent dissolving the mixed metal cluster and removing the organic solvent. It is preferred to prepare in step a) first a dry mixture of an inorganic oxide support and an organic solvent, to which a mixed metal cluster is added under anhydrous conditions and mixed, after which the organic solvent is removed by evaporation.

. In step b) of the process according to the invention, it is advantageous to carry out the reduction of the inorganic oxide 7 93085 carrier supported by the mixed metal cluster by treating it with hydrogen gas. Such a reduction is preferably carried out by raising the temperature to about 250-500 ° C in a stream of hydrogen, after which the temperature is kept constant for a certain time. In one embodiment, the inorganic oxide support treated with the mixed metal cluster is treated with a stream of hydrogen of about 6 1 / h. At the same time, it is preferable to raise the temperature at a rate of about 3 ° C / min up to a temperature of about 450 ° C, after which the temperature should be kept constant for at least about 2 hours. Steps a) and b) of the process according to the invention should be carried out under the most inert conditions possible.

In addition to a novel support catalyst and a process for its preparation, the invention also relates to the use of such a support catalyst in the reactions catalyzed by it. Such reactions include, for example, isomerization of alkenes, reduction of carbon monoxide and ketones, hydrogenation of alkenes, hydroformylation of alkenes, hydrogenation of ketones, Fischer-Tropsch synthesis, hydrogenation of alkyl cyanides and isocyanides to nitric acid to hydrogen monoxide and hydrogen, preparation of methanol from carbon monoxide and hydrogen, polyalcohols hydrogenation of amides, hydrogenation of alkynes, cyclization of alkynes to arenas, aminomethylation, hydroxymethylation, and conversion, i.e. water-gas reaction. The most preferred reactions are Fischer-Tropsch synthesis and reduction of carbon monoxide with hydrogen, i.e. hydrogenation. In the hydrogenation of carbon monoxide, it is preferred to use a molar ratio of hydrogen to carbon monoxide of 1: 1 to 3.5: 1, most preferably 1.5: 1 to 2.5: 1. A temperature of 150 to 300 ° C, preferably about 200 to 300 ° C, can be used in the hydrogenation reaction.

The following are a few examples, the sole purpose of which is to illustrate the present invention.

Example 1

The catalyst was prepared according to the following procedure: 1.0 g of silica supported silica was dried in a double-necked flask equipped with taps at a pressure of less than 5 kPa at 200 ° C for 2 h. The silica was then cooled to 93085 in a nitrogen atmosphere. 10 ml of dried and nitrogen-dichloromethane were added on top of the support. About 100 mg of the cluster was added to a mixture of silica and dichloromethane in a stream of nitrogen. The mixture was stirred for 2 h. Evaporation of dichloromethane was performed at room temperature under reduced pressure to prevent the mixed metal grape from detaching from the support and sublimating into the vacuum line or flask walls. The product formed was transferred under anaerobic conditions (nitrogen stream) to a reactor tube made of acid-resistant steel. The product was heated in a stream of hydrogen (6 L / h) at a rate of 3 ° C / min, after which the temperature was kept constant for 2 h. The resulting catalyst, having a cobalt content of about 1.8% by weight and a ruthenium content of about 3.2% by weight, was cooled in a stream of hydrogen to an initial reaction temperature of 190 ° C.

Example 2

According to Example 1, Co 2 Ru 2 (CO), 3 / SiO 2,

Co2Ru2H2 (CO) 12 / SiO2, Co3RuH (CO) I2 / SiO2, Co3Rh (CO) | 2 / SiO2 and Co2Rh2 (CO) 12 / SiO2 catalysts. Table 1 summarizes the activities and selectivities obtained when the catalysts were subjected to CO hydrogenation reactions in a continuous fixed bed reactor. The catalysts according to the invention are marked with one asterisk.

Table 1.

Comparison of catalysts based on reaction experiments

Precursors GHSV S (%) S (%) S (%) S (%) / SiO 2 (1 / h) (C 1) (C 2 -C 5) (C 6 -C 12) Oxyg.

Co2Ru2 (CO), 3 * 3070 23 27 24 26

Co2Ru2H2 (CO) 12 * 3700 15 42 40 3

Co3RuH (C0) 12 * 2970 34 29 14 23

Co3Rh (C0) i2 * '2300 78 6 0 16

Co2Rh2 (CO) 12 ** 2000 61 12 1 26

The reaction conditions were: temperature 190-300 ° C, pressure 0.5-5 MPa, gas flow rate 1-30 nl / h and synthesis gas composition H 2: CO = 1: 1-2: 1. The most favorable reaction conditions were: pressure 9 93085 2.0 MPa, GHSV = 1000-4000 h'1 (GHSV = Synthesis gas flow rate / catalyst volume) and synthesis gas composition H2: CO = 2: 1. The reaction temperature was 233 ° C (active catalysts) or 290 ° C ** (weakly active catalysts). The GHSV value at which a 3% conversion is achieved has been used as a measure of activity in Table 1. The higher the GHSV value, the more active the catalyst is. Selectivities are reported at a conversion rate of 3%.

Figure 1 schematically shows different types of Rh-Rh-Co mixed metal clusters.

Figures 2-4 show the hydrocarbon and oxygenate distributions of the different samples.

Co3RuH (CO) 12 / SiO2 has been found to be the best catalyst in the literature. In our reaction experiments, its activity and selectivity are significantly weaker than the Co2Ru2H2 (CO) 12 / SiO2 and Co2Ru2 (CO) 13 / SiO2 catalysts of the invention. In particular, the undesired formation of methane is abundant with the Co3RuH (CO) 12 / SiO2 catalyst.

Based on the reaction experiments, it was realized that the molar ratio Co: Ru = 2: 2 in mixed metal grapes is the best in terms of activity and selectivity. When Co2Ru2 (CO), 3 and Co2Ru2H2 (CO) 12 are used as precursors, even better catalysts are obtained. Figure 1 shows further arguments why Co2Ru2 (CO) 13 and Co2Ru2H2 (CO) 12 are particularly preferred as catalyst precursors.

Figure 2 shows the product distribution obtained with Co2Ru2H2 (CO) 12 / SiO2 catalyst and Figure • *: 3 with Co2Ru2 (CO) 13 / SiO2 catalyst using a Schulz-Floor graph. The abscissa is the number of carbon atoms i in the product molecule and the ordinate is log [w (i) / i], where w (i) is the mass fraction of products containing i carbon atoms. For catalysts with a Schulz-Flory distribution, the graph is a linearly decreasing line with the exception of C2 hydrocarbons. For the catalysts of the invention, the graph is an almost horizontal curve up to C12 hydrocarbons running at a relatively high altitude. No heavier products are formed than this (significant advantage). Product distributions of this kind are usually obtained only with catalysts using a zeolite support. When using conventional carrier materials, this is very exceptional. In addition, from the Schulz-Flory graph, it can be seen that the amounts of oxygenates formed are very small and have a low carbon number. These catalysts produce only alcohols from oxygenates. No measurable amounts of other oxygenates are formed, which facilitates the separation of the products (azeotropes make it crucial to separate the mixture). In this sense, eo. the catalysts according to the invention differ decisively from the prior art catalyst, cf. Figure 4.

The mixed metal clusters used in the present invention are new types of compounds whose use as precursors of heterogeneous catalysts has been little studied. The catalysts according to the invention are prepared by impregnating a mixed metal cluster according to one of formulas (I) to (III), e.g. from an organic solvent, on a conventional catalyst support, such as silica, to give a highly active and selective catalyst for e.g. hydrogenation of carbon monoxide.

The mixed metal clusters used in the invention provide, under ideal conditions, a near-atomic dispersion on the surface of the support, whereby the catalyst is highly active in the hydrogenation of carbon monoxide. In addition, mixed clusters can achieve a dispersion homogeneous with respect to two metals and no single metal agglomerations usually occur. As a result, the electronic and physical interaction between these two metals on the support surface is so strong that the catalysts are more active and more selective than the corresponding catalysts prepared from two different precursors. This phenomenon is accentuated when the atomic ratio of the metals in the support catalyst is about 1: 1.

Claims (23)

93085 A bark catalyst comprising a genome of a fast organic organoxide with a blister metal cluster based on cobalt, ruthenium and carboxyl and a reduction of the organoal oxide, with the addition of a blank metal cluster (I) Co2 ) där n är 0 eller 1. A support catalyst prepared by treating a solid inorganic oxide support with a mixed metal cluster based on cobalt, ruthenium and carboxyl and reducing the inorganic oxide support thus treated, characterized in that said mixed metal cluster has the formula (I) n (i) n . 2. Bärarkatalysator enligt patentkrav 1, kännetecknad av at blandmetallklustret har formeln (II) Co2Ru2H2 (CO) 12 (II) Supported catalyst according to Claim 1, characterized in that the mixed metal cluster has the formula (II) Co 2 Ru 2 H 2 (CO) 12 (II) 3. Bärarkatalysator enligt patentkrav l, kännetecknad av att a bland metal metal cluster of formula (III): Co2Ru2 (CO) 13 (III) [93085 Supported catalyst according to Claim 1, characterized in that said mixed metal cluster has the formula (III) Co 2 Ru 2 (CO) 13 (III) 4. Bärarkatalysator enligt nägot av de föregäende patentkra-ven, kännetecknad av att den den organic bäraren torkats me-delst värme och / eller undertryck. Supported catalyst according to one of the preceding claims, characterized in that the inorganic support is dried by heat and / or under reduced pressure. 5. A bark catalyst comprising a patented compound, which comprises an organic oxide mixture with SiO 2, which is derivatized or bleached. Supported catalyst according to one of the preceding claims, characterized in that the inorganic oxide support is SiO 2, a derivative or a mixture thereof. 6. A catalyst according to the invention, which comprises the action of an organic oxide oxide-free genome on the contact of a bland metal cluster and an organic leachate, in which the leachate clusters are retained, and the leachate is organic. Supported catalyst according to one of the preceding claims, characterized in that the solid inorganic: oxide support is treated by contacting it with a mixed metal cluster and an organic solvent dissolving the mixed metal cluster and removing the organic solvent. 7. A catalyst according to the invention relates to a patent, which comprises the use of an organic oxide reducing agent for reducing the genome content. Supported catalyst according to one of the preceding claims, characterized in that the inorganic oxide support treated with the mixed metal cluster «93085" is reduced by heating it with hydrogen. 8. A catalyst according to the invention provides a mixture of cobalt and ruthenium in the range of 1: 3 to 1: 1.3 (molar ratio 1: 1.75 to 1: 0.75). Supported catalyst according to one of the preceding claims, characterized in that it contains cobalt and ruthenium in a weight ratio of 1: 3 to 1: 1.3 (molar ratio 1: 1.75 to 1: 0.75). 9. Bärarkatalysator enligt segot av de föregäende patent- I kraven, kännetecknad av att den denehehler 0,6 - 3,0 vikt-% kobolt. Supported catalyst according to one of the preceding claims, characterized in that it contains 0.6 to 3.0% by weight of cobalt. 10. The bark catalyst according to the invention comprises a mixture of 1.0 to 5.0% by weight of ruthenium. Support catalyst according to one of the preceding claims, characterized in that it contains 1.0 to 5.0% by weight of ruthenium. 11. A preferred form of a catalyst based on a catalyst, comprising: a) a fast organic oxide mixture based on a cobalt base, ruthenium and carboxyl, and b) a preferred compound (a) a mixture of oxide-free crystals based on cobalt, ruthenium and carboxyl; ό ϋ 8 b can be used as a blister metal pattern for the preparation of the formula (I) Co2Ru2H2n (CO) I3.n (I) from 0 to 1. A process for preparing a support catalyst, comprising a) treating a solid inorganic oxide support with a mixed metal cluster based on cobalt, ruthenium and carboxyl, and b) reducing the oxide support treated with a mixed metal cluster according to step a); COjRUjHjh (CO) 13.n (1) where n is 0 or 1. 12. A patent according to claim 11, which comprises a cluster of said metal clusters for the preparation of (II) Co2Ru2H2 (CO) 12 (II) Process according to Claim 11, characterized in that a compound of the formula (II) Co 2 Ru 2 H 2 (CO) 12 (II) 93085 is used as said mixed metal cluster. 13. A patent according to claim 11, comprising a cluster of said metal clusters for the preparation of the formula (III) Co2Ru2 (CO), j (III) Process according to Claim 11, characterized in that a compound of the formula (III) Co 2 Ru 2 (CO) 13 (III) is used as said mixed metal cluster. 14. A method according to claims 11-13, which comprises an organic oxide solution having a color of och / or undertryck, a temperature of 100-300 ° C and a pressure of less than about 5 kPa. Process according to one of Claims 11 to 13, characterized in that an inorganic oxide support which is dried under heat and / or under reduced pressure, for example at a temperature of 100 to 300 ° C and at a pressure of less than about 5 kPa, is used. 15. The invention is further described in claims 11-14, which discloses the addition of carbon dioxide, SiO2, which is derived or bleached from an organic oxide mixture. Process according to one of Claims 11 to 14, characterized in that silica, SiO 2, a derivative or a mixture thereof is used as the inorganic oxide support. 16. For example, a compound according to claims 11-15 is used, which comprises an organic oxide mixture having a weight of a metal cluster of 1: 1 to 30: 1, the ratio being 5: 1 to 20: 1. Process according to one of Claims 11 to 15, characterized in that the inorganic oxide support is treated with a mixed metal cluster in a weight ratio of 1: 1 to 30: 1, preferably 5: 1 to 20: 1. 17. An embodiment of the invention according to claims 11-16, which comprises the use of an organic oxide mixture and a) the use of a genome to contact a bland metal cluster and an organic leachate, in which the leachate is an organic leachate. 93085 Process according to one of Claims 11 to 16, characterized in that the inorganic oxide support is treated in step a) by contacting it with a mixed metal cluster and an organic solvent dissolving the mixed metal cluster and removing the organic solvent. • 18. A patent according to claim 17, which relates to a mixture of organic organics and organic feedstocks, is shown to be a mixture of organic bleaches and organic feedstocks. Process according to Claim 17, characterized in that in step a) a dry mixture of the inorganic oxide support and the organic solvent is first prepared, to which a mixed metal cluster is added under anhydrous conditions and mixed, after which the organic solvent is removed by evaporation. 19. An embodiment of the invention according to claims 11-18, the invention is described in b) reducing the use of an organic metal-containing organic oxide mixture. Process according to one of Claims 11 to 18, characterized in that in step b) the inorganic oxide support treated with the mixed metal cluster is reduced by means of hydrogen gas. 9ό085 20. A preferred embodiment according to claim 19, which comprises a b) reduction of the genome at a temperature of about 250-500 ° C and a constant temperature at a constant temperature of 1-3 h. Process according to Claim 19, characterized in that the reduction of step b) is carried out by raising the temperature to about 250 to 500 ° C in a stream of hydrogen, after which the temperature is kept constant for 1 to 3 hours. 21. An embodiment of a barrier catalyst according to claims 1-10 or frameworks for the preparation according to claims 11-20 for converting the synthesis to a column with / or hydrogenation of colmonoxide. Use of a support catalyst according to one of Claims 1 to 10 or prepared by a process according to one of Claims 11 to 20 for the conversion of synthesis gas into hydrocarbons and / or hydrogenation of carbon monoxide. Use according to Claim 21, characterized in that a hydrogen to carbon monoxide ratio of 1: 1 to 3.5: 1, preferably 1.5: 1 to 2.5: 1, is used for the hydrogenation of carbon monoxide. Use according to Claim 21, characterized in that a temperature of 150 to 300 ° C, preferably a temperature of 200 to 300 ° C, is used. 22. An invention according to claim 21, which comprises a range of 1: 1 to 3.5: 1, a ratio of 1.5: 1 to 2.5: 1, and preferably a mixture of hydrogen oxide and hydrogen oxide and hydrogen oxide. '; 23. An invention according to claim 21, which comprises a temperature of 150-300 ° C, at a temperature of 200-300 ° C, according to the invention. «• ·