NO853818L - FINE PARTICLES WITH A METAL OR METAL SURFACE COATING, SPECIFICALLY A CATALYTIC ACTIVE MATERIAL, AND PROCEDURE FOR PRODUCING THEM. - Google Patents

Description

In connection with, for example, the refining of petroleum, many catalytically active materials are used, for example oxides and sulphides of Fe, Co, Mo, Ni, W etc., which are very insoluble and even metals such as Pt, Pd etc. These catalytically active materials are most often deposited on a catalyst support in order to obtain a suitable form for the catalytic process and to save on the often very expensive catalytic materials. In all catalytic methods, one tends to strive at the same time for the catalytically active materials to present as large a surface as possible against the material to be treated.

A problem in this connection is that the catalytically active materials easily form colloidal solutions and precipitates which are difficult to handle, e.g. due to having to work with highly diluted solutions. Such colloidal solutions and their preparation were studied in detail by The Svedberg and Zsigmundy about 50 years ago. As far as is known, no actual development of the then proposed technique has been presented in the literature.

Another problem with the use of the catalytically active materials is that the current application technique leads to unnecessary wastage of the materials, i.e. it is difficult to keep the weight of materials low in relation to the size of the available catalytically active surface. The large weight of valuable material means that a lot of work has been done to recover the materials, even if the recovery methods are often very difficult.

Similar difficulties can arise when one wants to use other metals or metal compounds for different purposes, for example for adsorption purposes, when one wants to utilize the ability of the metal or metal compound to adsorb other materials. In these cases too, the metal or metal compounds can be so valuable that a great deal of work has to be done to recover the same after it has been used for the adsorption in question.

In the Swedish patent documents S-B-345 393 and SE-B-408 375, a method is specified for providing a large surface area of catalytically active material on the surface of carrier particles, whereby the catalytically active material is precipitated on carrier particles which may have the form of a suspension of synthetic or natural minerals. As an example of suspended carrier material, "AEROSIL" is mentioned, which is a highly porous spray-dried silicon dioxide and which, when used, is suspended in a suitable liquid. By regulating the hydroxyl ion concentration and causing it to increase at a low rate of no more than 0.1 pH units during the addition of the two components which will react with each other and form a coating on the suspended particles, the precipitation of the catalytically active material on the surface of the carrier particles take the form of fine particles with a diameter of 10-50 Å. A relatively thick coating of the catalytically active material is therefore obtained on the carrier particles, which are themselves made up of aggregate particles. However, these known methods have disadvantages, partly for example limitations with regard to the achievable degree of dispersion for the catalytically active material, partly for example a relatively large consumption of catalytically active material. Similar methods for the production of supported catalysts are described in the German patent documents DE-B2-1 963 952 and DE-B2-1 963 827.

An object of the present invention is to provide extremely fine particles with a surface coating of a metal or a sparingly soluble metal compound, especially a catalytically active material. Another object of the invention is to provide a new method for producing fine catalytically active particles. Yet another object of the invention is to provide particles which are coated with a metal or a metal compound, and with a low content of metal or metal compound material present on the surface of the particles in relation to the mass of the particles. Another object of the invention is to provide a method for depositing and/or precipitating thin coatings of insoluble or poorly soluble materials on surfaces of fine particles. A further object of the invention is to provide a catalyst mass with a coating of solid solar particles, which in turn has a surface coating of a metal or a sparingly soluble metal compound, especially a catalytically active material. Another object of the invention is to provide a catalyst mass which has its catalytically active material concentrated on the surface of the catalyst particles so that only a small part of the catalyst particles will need to be dissolved when recovering the catalytically active material from a used catalyst mass. A further object of the invention is to produce a catalyst mass with such a low content of catalytically active material that the losses of catalytic material are minimal when the used catalyst mass is wasted.

The above purposes and other purposes of the invention will be apparent from the subsequent description of the invention and some advantageous embodiments thereof.

The present invention is based on the idea of depositing from a solution, preferably but not necessarily a water solution, a metal, a metal compound or a precursor for the metal or the metal compound on monodisperse solid solar particles in the suspension, such as sols of, for example, silicon dioxide or aluminum oxide . With this technique, one can first produce monodisperse sols with a very well-defined particle size, whereby well-known techniques are used for the production of sols.

According to the invention, a liquid-bored monodisperse sol is first prepared from carrier particles with a specific surface accessible to the liquid of at least 100 m o/g and then a soluble metal compound is dissolved in this sol, which then precipitates as a metal or poorly soluble metal compound on the carrier particles. By using a monodisperse sol, a maximally large particle surface will be available for receiving the precipitated material, which is the case if aggregate particles are used as carrier particles. When depositing a sparingly soluble compound on the solar particles, the sparingly soluble compound's components are therefore added in such a way that the precipitation occurs on the surface of the solar particles. This can happen because the components, under vigorous stirring of the sun, can be added simultaneously at different places or added in sequence, so that one component is attracted to the particle surface before or in connection with the reaction with the other component, or so that the newly formed compound is preferentially attracted by the solar particles without larger aggregates of the insoluble compound having time to form. By "larger aggregates" is meant here so-called oligomeric or more polymeric aggregates. The addition of the components must take place under conditions which favor colloidal stability. The electrolyte content in the solution must therefore not reach a content that destabilises, coagulates the solar particles, i.e. not exceed a critical content which depends on the specific surface of the solar particles and the valence of the electrolyte. The pH value is also of great importance for the stability of the sun, and one must therefore work at a pH that counteracts destabilization of the sun in question. The same considerations must be made when it comes to temperature.

In a method for practicing the invention, one can thus dissolve a soluble compound of the sparingly soluble metal compound's one component (anion or cation part) in a very low concentration in a fluid-drilled sol of carrier particles, after which the sparingly soluble metal compound's other component is added at a feed rate which allows preferential adsorption or attraction of the precipitated sparingly soluble compound onto the solar particles instead of exceeding the compound's solubility limit in the liquid phase of the sun and thus crystal nucleation of the sparingly soluble metal compound therein. However, the reason for the observed effect is not completely clear, and it may be due to an adsorption or attraction in accordance with what has been stated, or due to the fact that the low concentrations produce such a slow formation of crystal seeds that the individual crystal seeds have a shorter distance to the surface of the solar particles than to each other, so that they are attracted to the surface of the solar particles rather than to each other.

A surface coating of metal on the solar particles can also be provided by the metal first being precipitated on the solar particles as a reducible sparingly soluble metal compound, which is then reduced to metal. Alternatively, a soluble compound of the desired metal can be dissolved in the sun in order for it to adsorb or attract the compound's metal-containing ion or molecule, whereupon these ions or molecules are directly reduced to metal.

The characteristics of the invention are stated in the patent claims.

In one embodiment of the invention, a soluble compound of the desired metal or metal compound (i.e. a precursor for the ultimately desired catalytically active material) is thus dissolved in the monodisperse sol, whereby the soluble compound is added in such an amount that essentially all metal ions or -molecules in the solution have the possibility of being adsorbed towards or attracted to the surface of the solar particles by surface chemical forces, such as surface charge, van der Waals forces, dispersion forces etc. After this, a very slow addition of a material occurs which precipitates the desired catalytically active material or a precursors for this directly on the surface of the solar particles by reaction with the ions or molecules adsorbed or attracted to it.

The production of the coated solar particles can take place in several stages, i.e. if the particles from the beginning do not have a surface chemical nature suitable for the deposition with regard to the final catalytically active material or other desired material, one can similarly build up several layers in order to reverse the original solar particles' surface charges from minus to plus and vice versa. The same technique can be used if one wishes to deposit a mixture of catalytically active materials on the particles, for example a mixture of cobalt oxide and molybdenum oxide or a mixture of cobalt sulphide and molybdenum sulphide.

In the invention, the solar particles will thus serve as carriers for the catalytically active material or materials. In order for a coating of the surface of the solar particles to be possible without a separate precipitation of the catalytically active material occurring

in the sun's liquid phase (water phase), it is required 1) that the carrier particles (solar particles) are monodisperse and have a large available specific surface, so that the carrier surface per unit volume of the sun is large, and 2) that the precipitation of the desired material (or its precursor) occurs so slowly that the formed material has enough time to diffuse to the carrier surface and is deposited on it without exceeding the material's solubility limit in the sun's liquid phase and self-formation of crystal germ in this.

When carrying out the invention, it is easiest to use water as the liquid medium in which the coating of the surface of the solar particles is carried out. However, other liquid media can be used provided that the materials in question are soluble in the liquid media and can be precipitated from these using the technique described here.

As materials for coating or deposition, one must generally use materials which precipitate as very poorly soluble compounds and which do not readily crystallize. If the compounds have a tendency to crystallization, they must not undergo so-called Ostwald ripening, since such ripening involves crystal grain growth at the expense of the formation of new crystal seeds on adjacent surface particles of the carrier particles. The best materials for coating or deposition are considered to be those which have the most difficulty in independently forming nuclei when supersaturated solutions of the materials are formed. This is most often the case with compounds which are highly insoluble and which crystallize very slowly, for example barium sulphate, cobalt sulphide, etc. Carried out experiments indicate that the best conditions for a good coating of the carrier particles to be obtained (i.e. so that the surface of the carrier particles is no longer in contact with the solution), exists if the deposited material is amorphous or only exhibits very weak X-ray diffraction lines and is therefore microcrystalline in height. Materials of this kind are

1. siO2' for example from Si(OH)4

Aluminum oxide, for example Al (OE) .j • SI^O

Aluminum silicates

ZrO2/for example from ZrOC^

A1(P0)4, for example from Al<3+>andP043-

2. Most insoluble hydroxides and oxide hydrides of polyvalent metals.

3. Insoluble metal sulphides and metal selenides.

4. Silicates and carbonates of multivalent metals.

5. Metals, for example precious metals such as Pd and Pt.

The carrier present as a sol must have a very low solubility in the liquid phase used, usually and preferably water, or at least have a very low dissolution rate in the liquid phase.

In order for a sol to be used in the invention, the sol's particles must be monodisperse and have a large specific surface, calculated on the available surface, because particles that are large and have a spongy structure do indeed have a large internal surface, but this surface does not always need be available for the solution from which the coating is precipitated or deposited. The required size of the available surface is determined by various factors, of which the surface chemistry of the surface is one of the most important. The available surface to the solution must be at least 100 m 2 /g for practical production rates to be achieved, and a practical range is 100-1000 m /g. When it comes to silicic acid sols as carriers for the deposited catalytically active materials or other materials, one can advantageously use sols with a specific surface of 300-700 m 2 /g, which corresponds to a particle size of approx.

4-9 nm.

As mentioned above, it is not necessary that the original solar particles have a surface charge of the polarity necessary for the deposition of the ultimately desired catalytically active material or other material. Thus, silicic acid sols (which have a negative surface charge) can first be modified with a polyaluminium compound, for example from basic aluminum chloride, to obtain a positive surface charge, if such is necessary for the deposition or precipitation of the desired catalytically active material or its precursor. In certain cases, the polarity can also be affected by the pH of the liquid medium; in the case of, for example, a silicic acid sol, it applies that the surface of the sol is approximately neutral at pH 2-3 and that the negative charge increases with increasing pH. Thus, depending on the system, pH can be used as an aid to adjust the surface charge. As a further means of increasing a silicic acid particle's negative charge, aluminum can be allowed to react with the surface of the silicic acid particles to form negative SiAl^ sites. Such modified silicic acid retains a significant negative charge even at acidic pH, which is in contrast to unmodified silicic acid sols. Regardless of whether the adsorption or attraction is achieved through the surface charge or through another mechanical mechanism, it is however necessary to ensure that the carrier particles have or are first imparted with an ability to adsorb or attract one or more of the components of the desired coating (for example by ensuring that the surface of the carrier particles has an appropriate surface charge), so that through a slow controlled precipitation rate, the precipitation to the surface of the solar particles can be controlled.

Another condition for the carrier, i.e. the solar particles, is that

they have a slow dissolution rate or are insoluble under the deposition or precipitation conditions, according to which it would otherwise be difficult to deposit or precipitate other materials on the surface of the particles.

The conditions for the deposition must be such that the carrier material's solar particles (or modified particles) have a sufficiently large total surface area for surface chemistry to adsorb or attract essentially all ions or molecules present in the solution which are to be included in the subsequently precipitated or deposited material. The other ions or molecules that are to combine with the ions or molecules adsorbed or attracted to the solar particles must then be added at such a low speed that the chemical compound(s) to be precipitated or deposited have enough time to diffuse to the surface of the particles and be deposited on this without exceeding the solubility limit and self-formation of crystal seeds in the solution occurring.

As an extreme example of an insufficiently large carrier surface, one can consider some glass spheres under stirring in water. If a dilute solution of barium acetate and a solution of sodium sulfate are added with stirring, a mist of fine barium sulfate crystals is formed, and no coating of barium sulfate is formed on the glass sphere. If, on the other hand, a corresponding amount of silicon dioxide or aluminum silicate is used in the form of solar particles with a specific surface area of a few hundred square meters per gram, 'and if the pH is about 9, the solution remains clear on a very slow addition of sodium sulphate and barium acetate, and some barium sulphate does not fall out as a separate precipitate. A control experiment without silicic acid sol will show that a precipitate of barium sulphate forms quickly and sediments quickly.

The rate at which a coating can build up on the solar particles without new free crystal nuclei forming in the solution,

depends on the crystallinity of the coating and varies over a very wide range depending on which materials are combined to form the coating.

The invention is also applicable in connection with catalysts of the type where the surface of the solar particles comprises a catalytically active metal, for example Pt or Pd. One way to provide such catalytically active surfaces is to reduce a metal compound together with the sol, so that the metal is precipitated directly on the surface of the particles. Another way is to first precipitate an insoluble compound of the metal on the surface of the solar particles and then transfer this compound to a catalytically active form of the metal.

The liquid-borne sol of surface-coated particles can be used for various purposes, for example for the production of a

adsorbent or a catalyst in spray drying.

When used for the production of a catalyst, one can very advantageously coat the surface of a catalyst carrier with said surface-coated solid solar particles. This gives an advantageous increase in the activity of the obtained catalyst mass, in that the available specific surface of active catalytic material is thereby increased 2-3 times compared to if the surface coating of active material is deposited directly on the surface of the catalyst carrier instead of on the surface of the solar particles.

In the following, the invention will be explained in more detail by means of some design examples, which, however, must not be considered to be limiting for the invention. In these examples, monodisperse sols are used.

EXAMPLE 1

Comparative example without sun

By adding NaOH to 50 ml of water in a beaker, the pH is adjusted to 9.7. 150 g of an aqueous solution containing 0.256 g of CoCl2.6H20 and 160 g of an aqueous solution containing 0.272 g of Na2S.9H20 are added dropwise and simultaneously to the beaker at a rate corresponding to 10 g of solution every 27 minutes. The temperature of the solutions is kept at 25°C. A black precipitate of CoS forms immediately upon the addition of the first drops of the sulphide and chloride solutions.

EXAMPLE 2

CoS on silica sol

To 50 ml silicic acid sol which contains 4.85% SiO and has

a specific surface of 392 m 2 /g (equivalent to a particle size of approx. 7 nm) and pH 9.7, 160 g of water solution containing 0.256 g of CoCl2.6H20, and 160 g of water solution containing 0.2 72 g of Na2S.9H20, dropwise and at the same time with vigorous stirring, whereby the addition takes place at a rate corresponding to 10 g of solution every 27 minutes. The solutions are kept at a temperature of 25°C. The sol solution gradually turns brown-black during the addition of the two solutions, but no separate precipitation of CoS occurs. During ultracentrifugation of the solar solution, black colored solar particles are sedimented and a clear supernatant is produced. CoS is found in the sediment, which corresponds to added amounts of sulphide and cobalt.

EXAMPLE 3

CoS on aluminum modified sol

To 50 ml silicic acid sol containing 4.85% SiO~ and has

a specific surface of 392 m 2 /g (equivalent to a particle size of approx. 7 nm) and pH 9.7, and whose surface has been modified with sodium aluminate so that 25% of the atoms in the surface are made up of aluminum atoms, is partly 160 g of an aqueous solution containing 0.256 g CoCl2.6H20, and partly 160 g of an aqueous solution containing 0.272 g Na2S.9H20, dropwise. and at the same time under vigorous stirring, whereby the rate of addition corresponds to 10 g of solution every 27 minutes. The solutions are kept at a temperature of 25°C. The sol solution gradually turns black during the addition of the solutions, but no precipitation of CoS occurs. During ultracentrifugation of the solar solution, black colored solar particles will sediment and a clear supernatant will result. CoS is found in the sediment corresponding to the added amount of sulphide and cobalt.

EXAMPLE 4

CoS on silica sol

Different particle size in the sun

To 50 ml silicic acid sol which contains 3.94% SiO„ and has

a specific surface of 110 m 2 /g (equivalent to a particle size of approx. 25 nm) and pH 9.7, and if the surface is modified with sodium aluminate so that 25% of the surface's atoms consist of aluminum atoms, 160 g of a water solution containing 0.256 g CoCl2.6H20, and partly 160 g water solution containing 0.272 g Na2S.9H20, dropwise and simultaneously at a rate corresponding to 10 g solution every 27 minutes. The solution's temperature is kept at 25°. The sol solution gradually turns black-brown during the addition of the two solutions, but no precipitation of CoS occurs. During ultracentrifugation of the sol solution, black-brown sol particles will sediment and a clear supernatant will result. CoS is found in the sediment corresponding to the added amount of sulphide and cobalt.

EXAMPLE 5

CoS on silica sol

Effect of content of added solutions

40 g of an aqueous solution containing 0.256 g CoCl2.6H20 and 40 g of an aqueous solution containing 0.272 gNa2S.9H20 are added to the same sol as in example 3. The addition takes place dropwise and at the same time with vigorous stirring, whereby the addition takes place at a rate corresponding to 10 g of solution every 27 minutes. The temperature of the solutions is kept at 25°C. During the addition of the solutions, the surface of the solar particles is gradually coated with black cobalt sulphide. No separate cobalt sulphide precipitation occurs.

EXAMPLE 6

Nickel sulphide on aluminium-modified silica sol

Example 3 is repeated with the exception that together with the sodium sulphide solution, 160 g of a water solution containing 0.256 g of NiCl2.6H20 is added. The solar solution gradually turns black during the addition of the two solutions, but no elimination of nickel sulphide occurs. When the solar solution is ultracentrifuged, black colored solar particles settle and a clear supernatant solution is formed. NiS is found in the sediment corresponding to the added amount of sulphide and nickel.

EXAMPLE 7

Molybdenum sulfide on aluminum modified silica sol

To 100 g of silicic acid sol containing 11.5% SiO„ and has

a specific surface of 4 76 m 2 /g (corresponds to a particle size of approx. 6 nm) and pH 10, and whose surface is modified with sodium aluminate, so that 25% of the atoms in the surface are aluminum atoms, is placed dropwise and under strong stirring 45 g of a 0.2 molar Na2S.9H20 solution. The pH is then lowered to 4.3-4.4 by adding a 0.5 molar HCl solution with vigorous stirring. Then 12.8 g of a 5% ammonium molybdate top solution, (NH4 ) ^Mo^O^ , are added. 4H.>0, to the sol solution with vigorous stirring. This keeps the pH constant at pH 4.3-4.4. The experiment is carried out at room temperature. The sol solution is gradually colored black-grey by the addition of the ammonium molybdate solution, but no precipitation of molybdenum sulphide occurs. During ultracentrifugation, a black-grey sediment settles, in which added molybdenum and sulphide can be found quantitatively. If the experiment is repeated without the presence of aluminium-modified silica sol, a black-grey precipitate of molybdenum sulphide falls out in the reaction vessel.

EXAMPLE 8

Barium sulfate on aluminum modified silica sol

To 100 ml silicic acid sol, which contains 12.2% SiO„ and has

a specific surface of 4 70 m 2/g (corresponding to a particle size of approx. 6 nm) and pH 9.7, 20 g of a water solution containing 0.0956% by weight of barium nitrate and 20 g of a water solution containing 0.1% by weight of sodium sulphate, dropwise and at the same time with vigorous stirring, whereby the rate of addition corresponds to 10 g of solution every 27 minutes. The temperature of the solutions is kept at 25°C. The sol solution remains clear during the addition of the barium nitrate and sodium sulfate solutions, and no formation of barium sulfate can be observed. During ultracentrifugation of the solar solution, the solar particles sediment and a clear supernatant solution is formed. In the sediment, barium sulphate is found corresponding to the added amount of sulphate and barium.

EXAMPLE 9

Cobalt and molybdenum oxide hydroxides on modified

silicic acid sol

0.2 g of Co(NO^)2•6H2° is dissolved in 100 g of silicic acid sol whose surface of the sol particles is modified with sodium aluminate so that 25% of the atoms in the surface are aluminum atoms. The sol contains 3.9% SiO2 and has a specific surface area of 110 m 2/g (corresponding to a particle size of approx. 25 nm). A solution of 0.2 g (NH^)gMo^024.4 H20 in 100 ml of water is prepared and placed dropwise under vigorous stirring at room temperature into the sun. Using ammonium hydroxide, the pH is adjusted to 10.5. The solution is allowed to stand under stirring for 1 hour at room temperature. After centrifugation, the sample consists of a faint pink precipitate and a colorless clear overlying phase. Added amounts of molybdenum and cobalt are found quantitatively in the precipitate. If the experiment is carried out without the presence of silicic acid sol, a blue-coloured precipitate occurs when the pH is adjusted to 10.5 using ammonium hydroxide.

EXAMPLE 10

Cobalt and molybdenum sulfides on modified silica sol

Example 9 is repeated, but the precipitate produced is dried.

The dried precipitate is then treated with hydrogen sulphide by

a temperature in the range 300-500°C, whereby the oxides are converted into cobalt sulphide and molybdenum sulphide.

EXAMPLE 11

Platinum on silicic acid sol

A first solution is prepared by adding 2 ml of hydrazine hydrate while stirring to a silicic acid sol which contains 3.94% SiO2 and has a specific surface of 110 m o/g. 4.5 ml of a F^PtClg solution containing 30 g Pt/liter and acidified with Hel so that it is 5.8 molar with respect to HCl is diluted with 20.5 ml of water, whereby a second solution is obtained .

At a feed rate of 0.37 ml/min, the second solution is added dropwise to the first solution while stirring. When adding the second solution to the first solution, an ammonium hydroxide solution is also added dropwise,

so that the pH never falls below 4.3. The resulting solution is slowly heated to 50°C. On reduction to metallic platinum, the solution is colored black, but no separate precipitation of platinum occurs. If the reduction is carried out in the absence of silicic acid sol, a black precipitate is formed. After reduction in the presence of sunlight, the sample is centrifuged. This results in a black precipitate and a clear colorless overlying phase. Added quantity of platinum is found quantitatively in the precipitate.

EXAMPLE 12

Platinum on aluminum silicate sol

Example 11 is repeated, but as the first solution a solution of 2 ml of hydrazine hydrate in 25 g of silica sol is used instead, the surface of which is modified with sodium aluminate, so that 25% of the atoms are aluminum atoms, whereby this silica sol contains 3.87% SiO 2 and has a specific surface on. 110 m 2/g (corresponding to a particle size of approx. 22 nm). Upon centrifugation, a black-brown precipitate and a clear, colorless overlying phase are formed. Added quantity of platinum is found quantitatively in the precipitate.

EXAMPLE 13

Molybdenum sulfide on surface modified silica sol

50 g of silicic acid sol containing 4.5 g of solar particles and 4 5.5 g of water is weighed into a beaker, and whose surface of the silicic acid particles has been modified with sodium aluminate, so that 25% of the atoms in the surface are aluminum atoms. The sun has a specific surface area of 110 m<2>/g and contains 3.87% SiO2 and 0.07% Al203.

A first solution of 0.18 g of (NH4)gMo7024.4H20 in 39.83 g of deionized water and a second solution of 1.0 g of Na2S.9H20 in 39 g of deionized water are formed. These two solutions are dripped simultaneously at a drip rate of 3.7 g every 10 minutes into the silicic acid sol. Stirring takes place throughout the addition process, and the pH is kept constant at 4.3 by adjusting with 0.5 molar HC1 solution. The weighed amount of Na^S is 5 times greater than the amount of molybdenum salt to obtain a 1/10 mono-layer of MoS2 on the surface of the solar particles. The experiment is carried out at room temperature. The solar solution is gradually colored black-grey by the addition of the ammonium molybdate solution, but no separate precipitation of molybdenum sulphide occurs. On ultracentrifugation, a black-grey sediment settles at the bottom , in which can quantitatively detect added molybdenum and sulphide.If the experiment is repeated without the presence of aluminium-modified silicic acid sol, a black-gray precipitate of molybdenum sulphide falls out in the reaction vessel.

In all of the design examples, it is found by electron microscopy of coated solar particles that the insoluble salt is indeed precipitated on the surfaces of the particles.

Claims (10)

1. Solid particles of colloidal size and with a specific surface area of at least 100 m 2 /g and with a surface coating of metal or a sparingly soluble metal compound, especially a catalytically active material, or aggregates of such particles. 2. Particles or aggregates of such particles according to claim 1, characterized in that the solid particles are particles of silicic acid sol, modified silicic acid sol, aluminum oxide sol or aluminum silicate sol. 3. Particles or aggregates of particles according to claim 1 or 2, characterized in that the surface coating on the particles consists of silver metal, gold metal, ruthenium metal, platinum metal, palladium metal, cobalt sulphide, nickel sulphide, molybdenum sulphide + cobalt sulphide, molybdenum sulphide + nickel sulphide, tungsten sulphide + cobalt sulphide or tungsten sulphide + nickel sulphide . 4. Process for producing fine particles with a surface coating of metal or poorly soluble metal compound, characterized in that a liquid-borne monodisperse sol of carrier particles with a specific surface accessible to the liquid of at least 100 m 2 /g is formed, and that a soluble metal compound is dissolved in this sol and from this is precipitated as a metal or poorly soluble metal compound on the surface of the carrier particles. 5. Method according to claim 4, characterized in that the soluble metal compound that dissolves in the sun is made up of one component of a poorly soluble metal compound (anion part or cation part) and is added to the sun in a deficit in relation to the ability of the carrier particles for surface chemical adsorption or attraction of the dissolved component at the prevailing conditions, and that the complementary component of the sparingly soluble metal compound is supplied at such a low supply rate that the sparingly soluble metal compound precipitated by the supply has enough time to diffuse to the surface of the carrier particles and is deposited on this without exceeding the solubility limit of the sparingly soluble metal compound in the liquid phase of the sun and self-formation of crystal nuclei of the sparingly soluble metal compound therein, and that if a surface coating of the metal on the carrier particles is desired, the metal is first precipitated as a reducible sparingly soluble metal compound, which is then reduced to metal, eve ntual after previous drying of the solar particles. 6. Method according to claim 4, characterized in that the soluble compound of the metal is dissolved in the liquid-borne sol by solid carrier particles which have the ability for surface chemical adsorption or attraction of the dissolved metal compound or petal-containing ion or molecule, whereby the soluble metal compound is added in deficit in relation to the ability of the carrier particles for said surface chemical adsorption or attraction at the prevailing conditions, and that the metal-containing ions or molecules are then reduced to metal. 7. Method according to claim 4 or 5, characterized in that a mixture of sparingly soluble metal compounds is deposited as a surface coating on the solar particles by successively adding the metals in the form of soluble compounds with alternately positively and negatively charged metal-containing ions or molecules and in that the sparingly soluble metal compounds' complementary component is then added. 8. Use of a liquid-borne sol of solid particles with a specific surface area of at least 100 m 2 /g and with a surface coating of a catalytically active metal or sparingly soluble metal compound or a precursor of this metal or metal compound for the production of a catalyst by injection molding rking or for the production of a catalyst mass by coating the surface of a catalyst carrier with said surface-coated solid solar particles. 9. Use according to claim 8, in which the solar particles are coated with a surface coating of silver metal, gold metal, ruthenium metal, platinum metal, palladium metal, cobalt sulphide, nickel sulphide, molybdenum sulphide + cobalt sulphide, molybdenum sulphide + nickel sulphide, tungsten sulphide + cobalt sulphide or tungsten sulphide + nickel sulphide. 10. Use according to claim 8 or 9, in which the surface-coated solid particles are particles of silicic acid sol, modified silicic acid sol, aluminum oxide sol or aluminum silicate sol.