DE1958952A1 - Catalyst manufacture - Google Patents

Description

2131

Dr. F. Initially. - Dr. B. Astmann Dr. R. Koenigsberger - Dipl. Phys. R. Holzbauer

Dr. F. Zumslein jun.

Patent attorneys

8 Mönchen 2, Bräuhaujstraße 4 / III

STAMICARBO ^ NV, HEERLEN (the Netherlands ) Manufacture of catalysts

The invention relates to a process for the production of a supported catalyst, wherein a catalytically active element either as a compound or in the elemental state from an aqueous solution of a preferably complex Connection of the catalytically active element to one suspended in the solution The carrier substance is precipitated by looking at the valence of the Ions of the element to be precipitated decreased with a reducing agent. Simultaneously the invention comprises catalyst systems prepared according to the process of Invention.

In the Dutch patent application 6705259 a method is described which is characterized in that on a finely dispersed carrier material Particles of one or more catalytically active elements are applied, by placing in an aqueous containing a salt of the catalytically active element Solution in which the vehicle has been suspended, a compound of the catalytically active element precipitates so slowly that the migration speed the connection to be precipitated to the carrier surface is sufficient to avoid the formation of precipitation nuclei in the solution, thereby reducing this Compound is deposited exclusively on the suspended carrier in insoluble form.

In the aforementioned patent application as well as in the Dutch patent application 0Α1323Φ the methodology for the production of the above-mentioned catalyst * Λ ayeteee nSh # r is included. It is noticed that it is possible to

009837/1017

- ο -

constant carrier mutually isolated, catalytically active particles to the size of 50 A or less by adjusting the hydroxyl ion concentration in the Solution increases slowly and homogeneously. In this context, “homogeneous” is understood to mean that the hydroxyl ion concentration is not a function of the location in the solution, not even if arbitrarily small volume units are taken into account; by "slowly" it is meant that the increase in the concentration of hydroxyl ions in the Solution per unit of time is less than the scope of the transport of the one to be precipitated Substance from the solution to the support surface. Because the catalytically active particles do not form agglomerates, the susceptibility to sintering at high treatment or application temperatures is much lower than with other methods' Catalysts; because the catalytically active particles are extremely small, it becomes one very large active surface per unit volume of catalyst obtained, which for many Large-scale applications can be attractive. ___ ^ _—— "

It is also possible - especially in the case of oxidation reactions - that the Selectivity of the catalyst system for certain reactions due to the dimensions the catalytically active particles is affected. There are various reasons for this. For example, the atoms in the corners and edges of the catalyst particles are more weakly bound, which means that their chemical reactivity can be greater; it can also sterically a larger number of reacting molecules are bound to atoms in corners and edges, whereby other reactions can occur. With an increase in Particle size from 30 to 50 Å, the fraction in the corners and decreases Surface atoms located at the edges are strong. As expected, they are catalytic effective particles with dimensions below 30 A also have a different selectivity for certain reactions show as particles with larger dimensions. It is very advantageous if the catalyst can be produced in such a way that either extremely small particles or particles over 50 Å applied to the carrier can be. If particles with dimensions over 50 Å are required, it is attractive that the mean particle size not be too far below 50 Å and the scatter in the particle size is as small as possible. In this way, a maximum specific surface area of the catalytically active substance is achieved obtain.

The method described in the aforementioned patent applications in which the precipitation in one by the solubility product of the hydroxyde or the Hydrated oxides conditioned pH range is enough for some, technically important catalyst systems. There are various reasons for this:

D09837 / 1867

1. There is no pH range where the solubility of the compound to be precipitated is sufficient is low. Examples are the elements molybdenum and osmium, which are readily soluble in a wide pH range, causing precipitation slow increase in pH is not quite possible.

2. It is also possible that the precipitated compound is not on the suspended one Carrier adheres. There are various reasons for this; the most important are:

a. The compound to be precipitated precipitates in a form that does not penetrate the surface of the carrier is bonded. This is the case when copper compounds are deposited on suspended silicon dioxide. When applied of the process described beat very large crystals more basic -Copper compounds down; basic copper salts do not adhere to the carrier.

b. The precipitation takes place at a pH value at which the adhesion of the precipitated Connection on the carrier material is poor. An example is ferric oxide, which precipitates at a pH below 2. In this pH range are both Silicon dioxide and ferric oxide particles are positively charged, as a result of which the ferric oxide is repelled from the silicon dioxide.

The object of the present invention is to provide a method with whose help makes the concentration of poorly soluble compounds more catalytically effective Elements in the solution in a form adhering firmly to the support surface can be increased homogeneously, in other ways than by gradually changing the Hydroxylxonenkonzentrati on.

The solution to the problem is based on the fact that a precipitation occurs in a for the precipitation and good adhesion desired and set in advance pH can take place if a known precipitation method is used becomes, in which one is aware of the difference in solubility between the various valences corresponding ions of the elements to be precipitated, possibly formed into complexes If this method of precipitation is used, the Procedure the relationship between the migration speed of the to be precipitated connection to the carrier surface and the speed with which this compound is formed in the solution, can be adjusted in such a way that the Concentration of the poorly soluble compound in the solution is responsible for the formation does not exceed the stable, isolated state of germs present in the solution.

According to the method of the invention to be described in more detail, therefore per se known precipitation methods applied in a special embodiment, The precipitation of copper, silver, molybdenum, tungsten and platinum should be mentioned as known

009837/1867

-A-

and osmium as an element or in the form of a compound with the help of reducing agents, such as hydrazine, hydroxylamine, formaldehyde, glucose, cane sugar or polyhydric alcohols .

It is essential for the method according to the invention that - if at set pH values and, in the presence of a suspended carrier, the valencies the ions of the element to be precipitated are changed - this homogeneously and slowly and ■ has to take place under control of the conditions, so that a precipitation is extreme fine particles is achieved. "Homogeneous" is understood here to mean that the concentration the ions of the old and new valence are not a function of the position in the solution, even if arbitrarily small volume units are taken into account will; by "slowly" it is meant that the increase in the concentration of the Ions from old to new valency per unit of time is less than the scope of the Transport of the compound to be precipitated from the solution to the carrier surface.

According to the invention, this is achieved in that, with such stirring, that the concentration of the ions of the old and the new valence is hardly any Function of the body in the solution can be the amount of each in the solution present reducing agent and the temperature, or the course of the temperature regulated over time in such a way that the pH is adjusted to one suitable for the combination of the carrier and the compound to be precipitated Value, the precipitation of a compound does not occur in the bulk of the solution itself, but slowly on the surface of the carrier substance suspended in the solution. All of the reducing agent can be added to the solution at the beginning of the precipitation; however, it may be advisable to use the reducing agent To be injected into the solution in an appropriate amount. “Injecting” is understood here to mean that the reducing agent and the solution (suspension) interact with one another be brought into contact without another phase being in the immediate vicinity.

This results in an extremely rapid distribution of the reducing agent in the stirred solution (suspension) is achieved without being affected by surface tension is made more difficult, so that the distribution of different valued ions among slower Change remains homogeneous. "Adjusted amount" here means that per unit of time To adjust the amount of reducing agent to be injected exactly to the reaction conditions which is necessary for maintaining a catalyst mass of the desired structure with small isolated, catalytically active particles on supports are. While maintaining the basic concept of the invention, these reaction conditions are different in an absolute sense for each element.

009837/1867

_ tr _

Although the method according to the invention is basically surprising is simple, for each intended application it requires:

1. a carrier suspended in the solution;

2. very good stirring of the solution;

3. a suitable choice of reducing agent;

4. Correct and very regular dosing of the reducing agent;

5. a programming of the temperature conditions; and

6. a very specific pH range of the solution.

According to the invention it is necessary that the amount of the volume unit and metal ions reduced to a certain extent per unit of time during the precipitation process Limits remain. This is achieved in that either the temperature or the amount of a fast reducing agent is regulated in such a way that the concentration of the reduced compound does not exceed 0.01 gmol per liter of suspension and increases every minute. It should be emphasized that the concentration of reduced compound affects both those already dissolved and those already on the carrier material down atoms. In order to avoid local oversaturation it is necessary that the concentration of the reduced compound does not exist in places Deviates from the mean concentration by more than 0.001 g mol per liter.

Examples in which the present process is reduced by reducing the Valence of the metal ions at set pH values can be used successfully can include copper, tungsten, molybdenum and precious metals such as silver.

If the precipitation takes place with a reducing agent already present in the solution under control of the temperature conditions, then many organic reducing agents, in particular aldehydes, monosaccharides such as aldoses and ketoses, bisaccharides such as maltose, lactose and dextrose or alcohols can be used, whereby the temperature to a value between 40 and 100 ⁰ C is set. Furthermore, compounds such as resorcinol, pyrogallol, gallotannic acid, formic acid, cyclohexanone, cyclopropanols and hydroquinone can be used as reducing agents. For example, copper, palladium and platinum can be treated excellently with a monosaccharide such as glucose. In the case of compounds that can be reduced very well, for example hexavalent osmium, the reduction can be carried out successfully with an alcohol. The desired exposure time is regulated by setting the temperature of the stirred solution (suspension). When using a mild reducing agent, for example Glucoee, this time can vary in the temperature range from 40 to 100 ° C. from almost unlimited to a duration of 10 minutes; at 50 ° C it is about 72 hours.

009837/1867

Will be strong reducing agents like hydrazine, or hydroxylamine compounds If these substances are used, they can best be used in appropriate quantities at temperatures be injected into the solution between 0 and 100 ° C. Examples of this process are copper, silver, tungsten, and molybdenum. Most of the time, however, you can choose between the action of an existing reducing agent under control the temperature conditions and. Injection of a reducing agent in adapted Lot.

For the adhesion of a precipitating metal ion or metal atom The rather universally applicable carrier silica is a pH range of 6 to 8 very suitable, above a pH value of 6 the ionization of the in the Silanol groups located on the surface of hydrated silica noticeable; it proceeds according to the reaction:

- Si - OH * • Si - O + H

I. I.

Positively charged ions or clusters of precipitating atoms are strongly bound on such a negatively charged silicon dioxide surface. Although the ionization of the surface silanol groups increases more and more with increasing pH values, an upper limit must also be taken into account for the pH values at which very useful catalysts are obtained, above a pH value of about 8 the silicon dioxide goes namely noticeably in solution. The intermediate dissolved silicon dioxide then precipitates with the catalytically active component and includes this to a greater or lesser extent. As a result, the part accessible to reaction participants is not very active. In the case of other common carriers such as Al _o 0_, TiO ₀ , ThO ₀ or clays, the surface charge fluctuates in an analogous way with the pH value of the solution. The invention is therefore not limited to the use of SiO ₀ as a carrier.

According to the invention of compounds of the catalytically active element assumed which are soluble in the stated pH range. In addition to simple salt compounds In many cases, water-soluble complex compounds, e.g. ethylenediamine, ethylenetetrarain, but especially tartrate and ammonia complexes can be used to be used. Thus, the copper in the divalent state forms a soluble complex with tartrate ions at a pH value above 6, preferably between 7 and 8.5. This complex formation is not possible in a monovalent state. As a result, when a cuprite tartrate complex is reduced at a pH value above 6, this beats the Cuprooxide down. A monosaccharide such as glucose can be used as the reducing agent are »at room temperature and a pH value above 6, preferably between 7 and

009837/1867

OO Ό 0

8.5 the reduction is not noticeable. When the suspension of the carrier in a Solution of cuprite tartrate and glucose is brought to temperatures above 40 C. the reduction, in the suspension. Excellent results are also achieved when a solution of a hydroxyl anionic salt such as hydroxylamine hydrochloride in a Suspension of the carrier in a cuprite tartrate solution at a pH above 6 and is injected at temperatures up to 100 C.

Auen precious metals, e.g. palladium, can be obtained by reducing a tartrate complex be precipitated. It is possible for the precipitation to take place at a pH value above 6, preferably about 7, and at a temperature up to 100 ° C through ^ to lead. At such a pH, the adhesion of the palladium to a silica support is poor very good. In contrast to copper ions, which are only monovalent Form, the palladium ion is reduced to the metal by glucose.

It can also be assumed from ammonia complexes, which are mentioned in the above pH range are soluble, which applies to a large number of metal ions. Such metal ions are e.g. those of silver, palladium, and platinum. By reducing Ammonia complexes of ions of these metals can precipitate the metal from the solution will. A specific example is the preparation of a platinum catalyst by reduction with a monosaccharide such as glucose at a pH greater than 8. The injection method can also be used successfully for the reduction of ammonia complexes to be used. One example is the production of a silver catalyst by injecting a hydrazine solution at a pH of about 8.

Another variant of the method according to the invention is reduction an oxyacid, whereby metal ions are converted into insoluble, possibly hydrated oxides implemented. An example of this is the oxyacid of hexavalent molybdenum, This compound forms in an alkaline medium with ammonium or alkali metal ions soluble salts of the oxyacid HJWoO .. the pH value of such a molybdate solution if only by a sufficiently high level, MoO “is knocked down Concentration is assumed. Because the solubility of Mo0 "is quite high is, a relatively large amount of molybdenum remains in the solution. If the pH value is lowered further, the solubility of the molybdenum increases sharply again. So it is difficult to precipitate molybdenum oxide on a support by changing the pH. In contrast to hexavalent molybdenum, the oxide of tetravalent molybdenum is poorly soluble in a wide pH range. The requirement for precipitation at a set pH value above 6 one can thus suffice by reducing the molybdenum. Injection of hydrazine into a suspension of the carrier in an M 'ybdatiösung leads to the desired precipitation. The extremely finely divided Molybdenum dioxide generally quickly becomes that of many in air catalytic process used molybdenum trioxide oxidized.

009837/1867

The invention is illustrated by means of some examples in which the operating conditions be specified in more detail, explained.

It should be expressly noted that the implementation of the inventive Procedure is not limited to the specifications of the examples given, neither with regard to the reducing agents used nor with regard to the elements mentioned or the carrier used.

Example I.

Manufacture of copper catalysts

^w . Example Ia

A solution of 38.0 g of Cu (NO ₃ ) .3 HO in 500 ml of water and a solution of 44.5 g of potassium sodium tartrate, 90 g of sodium hydrocarbonate and 22.5 g of sodium carbonate in 500 ml of water are combined. The resulting deep blue solution is made up to 1.5 liters, after which 10 g .Silicon dioxide "AEROSIL 220 V" (Fabr. Degussa, spe-

2 - 1

specific surface 200 mg) are suspended. Eventually this will be suspension 31.0 g of glucose were added.

The temperature is increased to 74 ° C. within about 6 hours, with the Suspension is stirred well. The suspension is kept at 74 ° C. for 20 hours, the pH increasing from 8.0 to 8.3. After all, it is meanwhile yellow colored suspension cooled to room temperature with stirring, it turns found that the suspension can be filtered very quickly. The filter residue is ocher yellow in color and contains a small amount of orange-colored substance, which deposited on the wall of the glass reaction vessel during precipitation Has. The filtrate shows a pale green color due to the yellow color of partially decomposed glucose and the blue color of a very small amount caused by non-reduced cuprite tartrate.

After drying the preparation at 120 ° C., the X-ray diffraction pattern shows the presence of cuprous oxide; the broadening of the reflections indicates the presence of particles of 110 S. Examination of the dried precipitate with an electron microscope shows that very few larger cuprous oxide particles (dimensions about 100 Å) are present. These strongly adhering particles come from the glass wall; this creates the broadening of the X-ray reflections. The remaining part of the preparation consists of the carrier, which is homogeneously covered with extremely fine cuprous oxide particles of about 20 Å.

009837/1867

Example Ib

Solutions of 38, Og Cu (N0 ") _o .3 H ₀ O in 500 ml of water and 44.5 g of potassium sodium tartrate, 90 g of sodium hydrogen carbonate and 22.5 g of sodium carbonate in 500 ml are put together. In the resulting deep blue solution, after dilution to 1.5 liters, 10 g of silicon dioxide "AEROSIL 200 V" (make Degussa, specific upper

2 ~ 1

area 200 mg) suspended. The pH of the suspension is 7.8. In the suspension is then stirred vigorously at a temperature of 35 C. a solution of 11.1 g of hydroxylamine hydrochloride in 500 ml within lj hours Water injected; the pH of the solution has previously been adjusted to 7.0 with sodium hydroxide been discontinued. During the injection, the color of the suspension changes from blue to green to yellow. After the injection is finished, there will be another half an hour stirred, after which the suspension is filtered. The precipitate can only be filtered slowly; it shows a yellow-red color.

The X-ray diffraction pattern obtained after drying the preparation at 120.degree indicates the presence of cuprous oxide and a little cupric oxide. The reflections of the cuprous oxide are widened; the line broadening indicates a dimension from 110 A. An examination with the electron microscope shows that the carrier is homogeneous with cuprous oxide particles with an average dimension of about 70 Å is covered.

Example II

Manufacture of palladium catalysts

5 g of palladium chloride are dissolved in 400 ml of water; the solution becomes cloudy due to hydrolysis of the palladium.
Then 11.9 g of potassium sodium tartrate are added and the mixture is boiled until a clear solution is obtained. The pH of the solution is 7. 2 g

2 -1 silicon dioxide "AEROSIL 200 V" (make Degussa, specific surface 200 mg) suspended, after which 6 g of glucose are added. The suspension is under intense Stirring heated to 90 C for 4 hours; the AEROSIL is colored black. The loaded AEROSIL, which precipitates quickly, is then quickly filtered off and washed out.

The X-ray diffraction pattern obtained after drying the preparation at 120 ° C. for 20 hours indicates the presence of metallic palladium. The broadening of the X-ray reflections results in an average particle size of about 60 X »

00 9837/1867

Example III

2.64 g of H ₀ PtCl-.6 H ₀ O are dissolved in 2 liters of water, in which 2 g

Δ Ο Δ

NH "and $ d 86 g NH ₁ NO ₁ , have been dissolved. The yellow precipitate formed as an intermediate is dissolved by heating at 70 ° C. for 16 hours. The pH of the resulting, clear, colorless solution is 8.5. After cooling the solution to room temperature, 2 g of glucose and 10 g of silicon dioxide "AEROSIL 200 V" (make Degus-

2 ~ 1
sa, specific surface area 200 mg) was added. The suspension is then

ο with intensive stirring for 150 hours at a constant temperature of 70 C.

L · heated. The brown-colored precipitate is then filtered off; no platinum can be detected in the filtrate. Finally, the filter residue is dried at 120 ° C. for 16 hours.

The X-ray diffraction pattern shows only a few, strongly broadened bands. Conclusions about the structure of the deposited platinum cannot be drawn from this will. The broadening of the reflections indicates the presence extremely fine particles of about 10 Å. This also results from the electron microscopic Examination in which extremely small particles can also be seen.

Example IV
Manufacture of a silver catalyst

3.14 gAgNO are dissolved in 2 liters of an ammonia solution; 10 g of "AEROSIL 380" (manufactured by Degussa, specific surface area 400 m ² g of "S") are suspended therein.

In this suspension are stirred vigorously within 40 minutes

3
At room temperature 2 cm of an 80% hydrazine solution was injected, the pH of the solution remaining within the limits 7.5 to 8.0. After the injection has ended, the precipitation proves to be complete. The precipitate is filtered and washed out. It turns out that there is no longer any silver present in the filtrate.

After drying the preparation at 120 ° C., the X-ray diffraction pattern shows the presence of metallic silver. From broadening the reflections the result is a particle size of 160 Å. An electron micrograph also shows that in addition to many small particles of around 100 Å, some larger particles of around 500 Å are present.

Injecting hydrazine at higher temperatures up to 100 C results to smaller dimensions of the silver particles and one to be filtered faster Precipitate.

009837/1867

Example V

3 g (MH.) Mo 0 .4 H ₀ O are dissolved in 150 ml of water; the pH of the solution, which was originally around 6, is adjusted to 8.7 with ammonia.

1 g of "AEROSIL 130 V" (make. Degussa, specific surface

2 - 1

175 mg) suspended. A solution of 3 g of hydrazine in 50 ml of water is neutralized with acetic acid until the pH of the solution is 8. The hydrazine solution is then first injected into the ammonium molybdate suspension with vigorous stirring and then the temperature of the suspension is slowly increased, likewise with vigorous stirring. At around 60 G, the AEROSIL quickly turns brown; at 100 ° C. a dark brown precipitate is obtained which precipitates quickly. The precipitate is quickly filtered off and dried at 120.degree. The X-ray diffraction pattern shows that a _{mixture consisting of MoO and MoO 0} has been deposited homogeneously on the surface of the carrier.

0098 3v7 / 1867

Claims (14)

PATENT CLAIMS Yl ΛVerfahren for the production of a supported catalyst, wherein a catalytically active element as a compound or in the elemental state from an aqueous one Solution of a preferably complex compound of the catalytically active element is deposited on a carrier substance suspended in the solution by determining the valence of the ions of the random element with the aid of a Reducing agent lowered, characterized in that one under such Stir that the concentration of the ions of the old and the new valence can hardly be a function of the place in the solution, the amount of each The reducing agent present in the solution and the temperature, or the course of the temperature over time is regulated in such a way that under setting the pH to one for the combination · the carrier and the random Compound suitable value, the precipitation of a compound not in bulk the solution itself takes place, but slowly on the surface of the carrier substance suspended in the solution. 2. The method according to claim 1, characterized in that either the temperature or the amount of a fast reducing agent is controlled in such a way that the concentration of the reduced compound does not exceed 0.01 gmol per liter Suspension and per minute increases and the concentration of reduced compound in places not more than 0.001 gmol per liter of the mean concentration Deviates. 3. The method according to claim 1 or 2, characterized in that organic reducing agents, in particular aldehydes, aldoses, ketoses and alcohols, are present in the solution at temperatures between 40 and 100 ^° C. 4. The method according to claim 1 or 2, characterized in that the reducing agent Hydrazine or hydroxylamine or compounds of these substances in adapted Quantities can be injected at temperatures between 0 and 100 C. 5. The method according to claims 1-3, characterized in that of a water-soluble Tartrate complex of the catalytically active element is assumed. 6. A method for producing a copper catalyst according to claims 1, 2, 3 and 5, characterized in that a tartrate complex of copper is assumed the pH of the solution is more than 6, preferably 7 to 8.5, a monosaccharide such as glucose is used as the reducing agent and the temperature is more than 40 C. 009837/1867 7. Process for the production of a copper catalyst according to claims 1, 2, 4 and 5, characterized in that a tartrate complex of copper is assumed, the pH of the solution is more than 6, preferably about 7, and a hydroxylamine salt is used as the reducing agent is injected and the temperature is up to 100 ° C. 8. A method for producing a platinum catalyst according to claims 1, 2, 3 and 5, characterized in that a Tftrtratkooplcx of palladium is assumed the pH of the solution is more than 6, preferably about 7, a monosaccharide such as glucose is present as a reducing agent and the temperature up to 100 C. 9. The method according to claims 1-4, characterized in that a water-soluble one Ammonia complex of the catalytically active element is raised » 10. A method for producing a platinum catalyst according to claims 1, 2, 3 and 9, characterized in that an Amaniakkoaplex of platinum is assumed the pH of the solution is more than 8, as a reducing agent a monosaccharide such as glucose is used and the temperature is around 70C. 11. A method for producing a silver catalyst according to claims 1, 2, 4 and 9, characterized in that starting from an ammonia complex of silver If the pH of the solution is about 8, the reducing agent is hydrazine ο is injected and the temperature is up to 100 C. 12. The method according to claims 1-4, characterized in that a water-soluble salt of an oxyacid of the catalytically active element is assumed. 13. A method for producing a molybdenum catalyst according to claims 1-4 and 12, characterized in that an oxyacid of molybdenum ((NH ₄ ) JKo 0 ^ .4 HO) is assumed, the pH of the solution is more than 6 , hydrazine is injected as a reducing agent and the temperature is at least 50 ° C. 14. Catalyst aassen, prepared according to the process according to one or more of the preceding claims and according to the examples of the invention. 0098 37/1807