MXPA98010156A - Procedure for the preparation of a catalyst - Google Patents

Abstract

The present invention relates to a process for the preparation of a catalyst, having a coating for the preparation of a catalyst, having a catalyst, having a catalytically active coating constituted by finely divided materials of large surface area and catalytically active components on an inert support body. A powder mixture of the finely divided materials provided is impregnated with a solution of precursor compounds of the catalytically active components. By a suitable combination of the finely divided materials in the precursor compounds and a convenient execution of the impregnation, a highly dispersed precipitation and the absorption of the catalytically active components on the finely divided materials are guaranteed. An aqueous coating dispersion is then prepared using the impregnated powder mixture, the support body being coated therewith, after which the coating is dried and calcined.

Description

PROCEDURE FOR THE PREPARATION OF A CATALYST Field of Invention The present invention relates to a process for the preparation of a catalyst, which has a catalytically active coating constituted by finely divided materials of large surface and catalytically active components on an inert body, which consists in the application of the catalytically active components on the finely divided materials, the development of a coating dispersion of these materials and the support coating with them.

Background of the Invention This type of process provides catalysts, which are used in many fields of chemical engineering. These are so-called carrier catalysts, in which the catalytically active components are applied in REF .: 28997 highly dispersed form on carrier materials, in order to guarantee a high catalytic activity of the catalyst with the smallest possible quantities of active components. For this purpose, carrier materials are used which have a large specific surface for the incorporation of the catalytically active components, these being generally cases of metal oxides stable at finely divided temperature, that is to say in powder form.

In the case of catalysts for automobile exhaust gases, the carrier materials are applied in the form of a coating on catalytically inert support bodies. Suitable support bodies for the purification of exhaust gases of automobiles are so-called ceramic or metal honeycomb bodies, which are crossed by parallel channels of circulation for the exhaust gas. For the coating of the honeycomb bodies with the carrier materials, the carrier materials are generally dispersed in water and are commonly homogenized by a grinding process. By means of grinding, the average grain size of the carrier material is brought to a value between 1 and 10 μ.

The walls of the circulation channels cover by simple or multiple immersion of the alveolar bodies in this coating dispersion with subsequent drying or calcination. The finished coating is designated as a dispersion coating.

In the case of this process, the catalytically active components can be incorporated at different times on the specific surface of the carrier materials. It is known, for example, to precipitate the catalytically active components on the carrier materials, just after the coating of the honeycomb bodies with the dispersion coating by immersion of the coated honeycombs in an aqueous solution of soluble precursors of the catalytically active components. An alternative to this is the possibility of incorporating the catalytically active components on the powdered carrier materials in a work step interspersed prior to the preparation of the dispersion coating.

The present invention deals with this second possibility of precipitation of the catalytically active components. In order to achieve a high catalytic activity, the type of precipitation must guarantee deposition in the form of the finest possible dispersion of the components on the specific surface of the carrier materials. In addition, the type of precipitation must also lead to high temperature stability and aging of the finished catalyst, ie, that the particles of the catalytically active components must be well fixed on the surface of the carrier materials, in order to avoid agglutination of the adjoining particles in case of temperature loading of the catalyst.

For the precipitation of the catalytically active components on the powdered carrier materials, various processes have been disclosed, among which may be mentioned, for example, impregnation with an excess of impregnation solution. In this case, an aqueous solution of catalytically active components is added to the powder carrier material, the volume of which can be substantially greater than the water absorption capacity of the carrier material. This results in a mass of grass consistency, which is dehydrated for example in an oven at an elevated temperature of 80-150 ° C, then calcined at even higher temperatures to fix the catalytically active components. Dehydration can produce chromatographic effects, which can cause an irregular distribution of the catalytically active components on the carrier material.

In the case of so-called pore volume impregnation, an amount of solvent is used to dissolve the catalytically active components, which corresponds to approximately 70-100% of the absorption capacity of the carrier material for that solvent. Normally it is water in these cases. This solution is distributed as homogeneously as possible, for example, by spraying on a carrier material that is stirred in a container. After the distribution of the entire solution on the carrier material it remains this regardless of the content of elusive water. The impregnated material is then dried and calcined at elevated temperatures so that the catalytically active components are fixed on the carrier material. With the impregnation of pore volume, chromate effects can be largely avoided, obtaining better results regularly, than with the procedure described above of impregnation with an excess of solvent.

It is a disadvantage in these known processes of impregnation of materials with catalytically active components that the catalytically active components after the impregnation process on the carrier materials must be fixed by means of drying and calcination treatments on the carrier materials with consumptions. of large amounts of energy to avoid that these in the inevitable redispersion of the carrier material for the preparation of the coating dispersion are detached again from the carrier material.

Description of the invention.

It is an object of the present invention to provide a process for the preparation of a catalyst which guarantees a highly dispersed distribution of the catalytically active components on the carrier materials, largely eliminating the expensive drying and calcination steps. As highly dispersed, crystallite sizes of the catalytically active components of less than 10 nm, preferably between 2 and 7 nm are considered.

This purpose is achieved according to the present invention by a process for the preparation of a catalyst having a catalytically active coating on an inert support body constituted by finely divided materials of large surface area and catalytically active components on an inert support body, which consists of the application of the catalytically active components on the finely divided materials, the preparation of a coating dispersion of these materials and the coating of the support body with them. The process is characterized in that it includes the following process steps: a) Impregnate a powder mixture of the finely divided materials provided with a solution of precursor compounds of catalytically active components according to the pore volume impregnation process, in which the compounds precursors are absorbed in at least one of the materials, prepare an aqueous coating dispersion using the impregnated powder mixture, c) coat the inert support body with the dispersion thus obtained, and d) dry and calcinate the coating.

Within the context of this invention, it is understood by highly surface materials, materials whose specific surfaces (measured according to DIN 66132) are more than 10 m2 / g. For the purification of exhaust gases of automobiles, the noble metals of the platinum group of the periodic system of elements are preferred as catalytically active components, among which are ruthenium, rhodium, palladium, osmium, iridium and platinum. .

The absorption of the precursor compounds in the carrier materials depends both on the surface conditions of the carrier materials and the precursor compounds and on the pH value of the impregnating solution. It is known, for example, that the nitrates of the metals of the platinum group are strongly absorbed on aluminum oxide, whereas chlorides in acidic conditions analogously do it on the contrary only weakly. This is used for the preparation of catalysts in pellets, in order to influence the distribution of the al active elements in the pellets. By using nitrates, for example, a marked bark profile is obtained, whereas in the case of the use of chlorides, an almost uniform penetration of the entire pellet with the active components is possible.

It has become evident that neither a very strong absorption nor a very weak absorption leads to an optimal arrangement of the catalytically active noble metals on the powdered materials, in the case of a very pronounced absorption, the dust particles of the carrier materials. they are only insufficiently penetrated by the precursor compounds.The precursor compounds are deposited only on the outer part of the specific surface of the powder particle.The high concentration resulting in that area for this reason leads to the development of a crystallite size of the metals catalytically active noble elements In the case of weak absorption, the precursor compounds remain mobile for a long time, resulting in the drying of the impregnated carrier materials, chromatically induced effects with a very irregular distribution of catalytically noble metals assets on different portions of the materi When impregnated, the crystallite sizes of the noble metals for this reason a very broad spectrum. Together with small crystallites, a considerable portion of noble metals with cpstalite sizes of more than 10 nm also coexist.

It has now been discovered that for a suitable combination of the carrier materials with the noble metal precursor compounds it is possible to obtain a uniform and highly dispersed deposition of the noble metals. This is, for example, in the case when at least one of the finely divided materials has an isoelectric point between 6 and 10 and when ammonium salts of the metals of the platinum group are used as precursor compounds. This combination of properties leads to a homogenous impregnation of the powder particle of the corresponding material and to a good absorption. Absorption is based essentially on an electrostatic interaction between the positive surface charges of the carrier material and the negatively charged anions.

After the impregnation, the precursor compounds are thermally fixed on the carrier materials. For this purpose, the impregnated powder material is first dried at temperatures of up to 180 ° C, then calcined at temperatures above 300 ° C. In the calcination, the precursor compounds are decomposed. According to the chosen temperature and the type of precursor compound, a mixture of different oxidation grades of the noble materials is formed in this step, which do not redissolve in the subsequent preparation of the coating dispersion.

In a particularly advantageous variant of the process according to the present invention, the thermal fixation of the precursor compounds is dispensed with, rather the direct dispersion of the coating is directly processed with the powder material still wet from the impregnation process directly. watery By adjusting the pH value of this dispersion to a value that is 1 to 3 units below said isoelectric point, preferably between 4 and 8, the precursor compounds are prevented from redissolving. This process can save a considerable energy cost for thermal fixation of the precursor compounds and configure the entire catalyst manufacturing process very efficiently.

To carry out the pore volume impregnation, for example, the mixture of the chosen carrier materials is uniformly stirred in a container, while the solution of the precursor compounds is sprayed by means of a nozzle onto the powder material. Here, according to the present invention, the volume of solvent used is limited to a maximum of 90% of the absorption capacity of the powder mixture. By means of the minimum amount of solvent it is prevented that the precursor compounds that have been absorbed can be desorbed or agglutinated forming larger critalites. The smaller the volume of solvent chosen, with more security, unwanted desorption is prevented. The volume of solvent is however limited downward by the requirement that the amount of precursor compounds necessary for the loading of desired carrier materials must be dissolved in the volume employed. This can lead to different lower limits for the volume of solvent depending on the solubility of the precursor compounds. Regularly volumes below 40% are no longer usable. Especially advantageous for the process according to the present invention are solvent volumes comprised between 50 and 70% of the absorption capacity of the powder mixture.

If a solvent volume of 90% of the absorption capacity is not sufficient due to the low solubility of the precursor compound, to incorporate the desired amount of the ally active ca component in an impregnation process on a carrier material, then it must be repeated several times the impregnation with a quantity of solvent with the respective intermediate dryings.

The impregnation process must guarantee, in spite of the reduced volumes of solvent, that all parts of the powder mixture come into uniform contact with the impregnation solution. For this purpose, the powder material is removed in a container, by spraying the solution of impregnation with a constant volume stream on the surface of the powder material. Volume flow rates of 560 ml of solution per kilogram of powder and per minute (50 ml / (Kg'min)) have proved effective. Above 200 ml / (Kg'min) the powder material can not be impregnated with sufficient uniformity. Substantially long impregnation times are made below 5 ml / (Kg'min).

The powder material thus impregnated is still completely slippery, which essentially facilitates its subsequent processing, being dispersed in water and optionally organic additives either after thermal fixing or directly without additional treatment, for the preparation of a coating dispersion for the bodies of inert support.

After the coating of the inert support body with the dispersion thus obtained, it is dried at elevated temperatures of from 80 to approximately 180 ° C and then it is calcined at temperatures of more than 300 ° C.

Suitable carrier materials with an isoelectric point of between 6 and 10 are for example aluminum oxide, cerium oxide, zirconium oxide, titanium oxide, silicon oxide or mixed oxides thereof. The anionic noble metal salts suitable for the purposes of the present invention are for example methanohydroxide methanoaminaminoplat ino (IV), ethanolaminoplat hexahydroxide (IV) and hexachloroplatinic acid (IV) or mixtures thereof. Especially preferred are the anionic salts of the platinum group metals complexed with mtZ anolamine or ethanolamine.

Frequently, a finished catalyst having certain catalytically active components deposited only on certain carrier materials is required for a desired catalytic effect in order to avoid harmful interactions between catalytically active components and carrier materials. In such cases, the different carrier materials of a catalyst must be impregnated separately with the corresponding noble metals, and a common coating dispersion is then prepared with these materials. Thus, it is known, for example, that for the preparation of catalysts for diesel engines using zeolites it must be taken into account that the zeolite can not be coated with metals of the platinum group, since this can produce coking on the surface of the zeolite. Therefore, the other catalyst carrier materials for diesel engines with the platinum group metals had to be separately impregnated before they could be combined with the zeolite portion in a common coating dispersion.

Unexpectedly it has been found that according to the process of the present invention such separation is not necessary, because the anionic salts of noble metals are only absorbed in a very small portion by the zeolites.

It has been found that the desired interaction between carrier material and noble metal salt can also be achieved in the case of carrier materials with an isoelectric point comprised between 2 and 7, when cationic noble metal salts are used. Also in this variant of the method according to the present invention, a thermal fixation can optionally be carried out or dispensed with. If thermal fixation is omitted, the pH value of the coating dispersion must be adjusted so that it is 1 to 5 units above said isoelectric point, preferably between 7 and 9, in order to avoid desorption of the precursor compounds.

Table 1 shows different carrier materials with their isoelectric points. For the respective isoelectric points, pH ranges were indicated, since the isoelectric points of a given carrier oxide have different values according to the manufacturing process and therefore the isoelectric points vary within a certain pH zone. Thus titanium oxide which has been sulphonated is more acidic than pure titanium oxide and therefore has a lower isoelectric point.

The isoelectric points of Table 1 were measured according to the elective method of sound and amplitude with the ESA 8000 apparatus from Matee Applied Sciences MA, USA. A description of the measurement method is found in J. Winkler's article "Potential zeta of pigments and fillers" in EJC, 1-2 / 97, pages 38-42.

Table 1: Carrier materials Table 2 contains some ammonium and cationic platinum compounds, which are suitable for the process in combination with the carrier materials of Table 1. The platinum complexes of Table 2 are indicated as being representative of analogous complexes of other materials from the group of platinum.

Table 2: Platinum precursor compounds Anionic platinum complex Cationic platinum complex Hexahydroxide Platinum Nitrate Methylethanolaminoplatinum (IV) (MEA) 2Pt (OH) 6 Hexahydrc-Nitrate of tetraaminoplatm ethanolaminoplane IV) (ID (EA) 2Pt (OH) 6 [Pt (NH3) 4_ (N03) 2 Acid hexachloropla unique Hydroxide of (IV) tetraaminoplatin (II H2PtCl6 [Pt (NH3) 4] (0H) 2 Using the method according to the present invention, the preparation of some catalysts is described in the following examples. For them the following raw materials were used Aluminum silicate with 5% by weight of silicon dioxide, stabilized oxide of a luminance specific substance: 153 m / g Titanium dioxide surface area: 95 m2 / g Zircon dioxide or specific surface area: 96 m2 / g DAY Zeolite Y of sodium salt with a molar ratio of sodium dioxide / aluminum oxide of approximately 200. Methoxide hydroxide 1 aminoplatine ethanol (IV) Acetone hydroxide (IV) Platinum nitrate Acid hexachloroplasty eo (IV): H2PtCld Support body: alveolar body of open cells of cordierit with 2.5 cm in diameter and 7.6 cm in length; cell density: 62 cm ", wall thickness of the circulation channels: 0.2 mm Example of comparison Cl 1 Kg of a powdered mixture of aluminum silicate and zeolite DAY was placed in a weight ratio of 84:16 in a dragee machine. The mixture had a water absorption capacity of 1220 ml / kg. it was sprayed by constantly stirring with 833 ml, which corresponds to 68.3% of the water absorption capacity of the powder mixture, of an aqueous solution of tet raaminopla tino nitrate (II) with a volumetric flow rate of 56 ml ( Kg'min). the dust that was still elusive was dried for a period of 12 hours at 150 ° C in a studio, then calcined for a period of 4 hours at 300 ° C in air for platinum fixation. The powder thus obtained contained 0.95% by weight of platinum, based on its total weight.

Analysis of the powder with a transmission electron microscope resulted in a mean platinum crystallite size of 10 nm. Using this powder an aqueous coating dispersion was prepared. The coating dispersion had a pH value of 6. A first body was coated by immersion in this dispersion with 140 g of dry material per liter of honeycomb volume. The coating was dried at 120 ° C in air and calcined at 300 ° C for 4 hours in air.

Comparison example C2: Another kilogram of powder mix of aluminum silicate and zeolite DAY was impregnated in a manner analogous to that described in the Comparison Example Cl. The impregnated powder was, however, not thermally treated, but was immediately processed further by preparing an aqueous coating solution, which had a pH of about 6. The analyzes of the aqueous phases of the coating dispersion showed a high content of platinum. A second honeycomb body was coated by immersion in this dispersion. The dried and calcined alveolar body contained 140 g / 1 of support material and only 0.56 g / 1 of platinum.

Example 1 : Another kilogram of powdered mixture of aluminum iliac and DAY zeolite was impregnated with platinum in the same manner as that described in Comparison Example Cl. Instead of taminamine (II) nitrate, however, an aqueous solution was used. Monoe tanolaminopla tino (IV) hydroxide for impregnation. As in comparison Example Cl, the still slippery powder was dried for a period of 12 hours at 150 ° C in an oven and then calcined for a period of 4 hours at 300 ° C in air for fixing the platinum powder. The powder thus prepared contained 0.95% by weight of platinum, based on its total weight.

The analysis of the platinum activated powder resulted in a very uniform distribution of the platinum crystallites on the aluminum silicate. The average size of the crystallites was 5 nm. Although the zeolite had been impregnated with the aluminum silicate only slightly, no platinum crystallite was found on the zeolite particles.

The platinum activated powder was dispersed in water and homogenized by grinding in a ball mill. The solids concentration of the finished coating dispersion was 35% by weight, the pH value of the coating dispersion being 6.5. Analysis of the aqueous phase of the coating dispersion did not provide evidence of a detachment of the platinum particles from the aluminum silicate.

A third alveolar body was coated by immersion in this dispersion with 140 g of dry material per liter of alveolar body volume. The coating was dried at 120 ° C in air and calcined at 300 ° C for 4 hours in air.

The finished catalyst contained 1.34 g of platinum per liter of catalyst volume.

Example 2 A fourth honeycomb body was coated with the coating dispersion of Example 1. After calcining the coating the catalyst was reduced over a period of 2 hours in a forming gas stream (95% by volume of N2; % by volume of H2). The catalyst contained the same amount of coating as in the case of Example 1.

Example 3 Another kilogram of aluminum silicate mixture was prepared _ > / zeolite DAY and impregnated with platinum in the same manner as described in Example 1. The impregnated powder was not thermally treated however, being immediately used to prepare an aqueous coating dispersion. The dispersion had a pH value of 6.5. Analysis of the aqueous phase of the coating dispersion showed no evidence of detached platinum particles (see in this regard Example 8).

With this dispersion a fifth alveolar body was coated, which was dried, calcined and reduced. The coating amounts were identical to those of Example 1.

Example 4: Another kilogram of aluminum silicate / zeolite DAY mixture was prepared and impregnated with platinum in a manner analogous to that described in Example 3. As the platinum precursor substance, anolaminoplast hydroxide (IV) was used. The impregnated powder was not thermally treated as described in Example 3, but was immediately used to prepare an aqueous coating dispersion. The dispersion had a pH value of 6.5.

The analysis of the aqueous phase of the coating dispersion also showed no evidence of detached platinum particles.

With this dispersion a sixth alveolar body was coated, which was dried, calcined and reduced. The coating amounts were identical to those of Example 1.

Example 5: Another kilogram of aluminum silicate mixture / zeo 1 i ta DAY was prepared and impregnated with platinum in a manner analogous to that described in Example 3. Platinum nitrate was used as the platinum precursor substance. The impregnated powder was not thermally treated as described in Example 3, but was immediately used to prepare an aqueous coating dispersion. The dispersion was brought to a pH value of 5.8 by nitric acid. The analysis of the aqueous phase of the coating dispersion also showed no evidence of detached platinum particles.

With this dispersion a seventh alveolar body was coated, which was dried, calcined and reduced. The coating amounts were identical to those of Example 1.

Example 6 A master kilog of titamo / zeolite DAY mixture was prepared and impregnated with platinum in a manner analogous to that described in Example 3. The powder mixture had a water absorption capacity of 920 ml / kg. the volume of the impregnation solution was 506 ml, that is, 55% of the water absorption capacity of the powder mixture. Platinum metal hydroxide (IV) was used as the precursor substance of platinum. The impregnated powder was not thermally treated as described in Example 3, but was immediately used to prepare an aqueous coating dispersion. The dispersion was brought to a pH value of 5.0 by nitric acid. The analysis of the aqueous phase of the coating dispersion also showed no evidence of detached platinum particles.

Example 7 One kilogram of zirconium oxide / zeolite DAY mixture was prepared and impregnated with platinum analogously to that described in Example 3. The powder mixture had a water absorption capacity of 875 ml / kg. the volume of the impregnation solution was 534 ml, ie 61% of the water absorption capacity of the powder mixture. The precursor was not thermally treated as described in Example 3, but was immediately used to prepare an aqueous coating dispersion. The dispersion was brought to a pH value of 5.0 by nitric acid. The analysis of the aqueous phase of the coating dispersion also showed no evidence of detached platinum particles.

As the preceding examples and comparison examples demonstrate, it can only be ensured by the correct combination of materials that the deposited noble metal components adhere firmly without thermal fixation on the materials being transferred to the aqueous phase in the preparation of the dispersion, causing loss of noble metals.

Example 8: The carrier oxides impregnated with platinum according to Example 1-4 were used in the preparation of coating dispersions with different pH values (4, 7 and 10), in order to verify the possible detachment of the platinum components of the carrier oxides by the action of the aqueous phase of the coating dispersions. The measurement of the platinum content in the aqueous phase was carried out in each case after 2 and 24 hours, as well as after 7 days. These periods of time will be designated below as the time of permanence.

To carry out the measurement, the corresponding coating dispersion was filtered and the aqueous phase was analyzed by means of ICP-MS ("plasma coupled plasma - mass spectacle try") to determine the platinum content. The platinum content of the carrier oxide was determined by the difference between the amount of platinum used and the amount of platinum determined by analysis of the solution. The results are detailed in Table 3.

Table 3 contains in the second column the platinum content of the carrier oxides prior to the preparation of the coating dispersion. In all cases it amounted to 95% in volume. Columns 5 and 7 contain the platinum concentrations of the aqueous phase measured with different pH values and with different dwell times in% by weight based on the platinum content of the respective carrier oxide. Columns 8 and 10 show the remaining platinum contents in the carrier oxide deduced by calculating the above.

In Examples 1 and 2, the platinum components were thermally fixed to the carrier oxides, not showing within the limits of the measuring accuracy any release of platinum by the action of the aqueous phase of the coating dispersion. In Examples 3 and 4 were not thermally fixed platinum components on the carrier oxides. From Table 3 it is concluded that also in this case correctly selecting the pH value of the coating dispersion (values below 7) only negligible platinum losses are observed. In the event of an incorrect adjustment of the pH value (pH = 10) of the coating dispersion, massive platinum detachments of up to 30% by weight take place.

Table 3: Platinum content of the aqueous phase of the coating dispersions or of the carrier oxides as a function of the pH value and the residence time according to Example 8.

Application example Al The catalytic activity of the exhaust gas purification catalysts of the preceding examples was measured in a synthesis plant. With this installation it is possible to simulate almost all the gaseous components existing in the real exhaust gases of an Otto or Diesel engine. The chosen test conditions and composition of the model gas are listed in Table 4. As the hydrocarbon component, n-hexadecane, commonly called cetane, is used, which is known as a reference substance for the determination of the ignitability of fuels. diesel. This long chain aliphatic compound is also found in the real diesel exhaust gas.

Table 4: Test conditions and composition of the model gas for the determination of the conversion rates of harmful gases CO, HC, NOx and SO2 in the synthesis facility For the measurement of the gaseous components contained in the exhaust gas, the measuring equipment indicated in Table 5 was used.

Table 5: Classification of the measuring equipment for the determination of the concentration of exhaust gases in the synthesis gas test facility.

In the synthesis gas installation, the conversion of carbon monoxide and hydrocarbons in constant operation with exhaust gas temperatures of 140 ° C was measured. The measurement was carried out both on the fresh catalyst and also on the aged catalyst (oven aging: 16 hours at 750 ° C in air + 10% by volume of water + 20 ppm of SO2).

In order to determine the initial temperature, the exhaust gas was heated starting at 75 ° C with a heating rate of 15 ° C / min. The determination of the conversion of the nitrogen oxides was carried out at that temperature of the exhaust gases TN0x, max. to which the emission of the nitrogen oxides presents a maximum. These temperatures are indicated in Tables 6 and 7 following the respective measurement values in parentheses.

The calculation of conversion rates is made using the following formula X = Conversion rate [%] N? = Concentration of the noxious substance before the catalyst [vppm] NA = Concentration of the noxious substance after the catalyst [vppm] The results of the measurements are summarized in Table 6 for the fresh catalysts and in Table 7 for the aged catalysts.

Table 6: Conversion of harmful substances by means of the catalysts of examples 1 to 7 and of comparison C1 and C2 in fresh state Table 7: Conversion of harmful substances by catalysts of selected examples after oven aging (16 hours, 750 ° C, air + 10% by volume of water + 20 ppm of SO2) It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (13)

Claims

1. A process for the preparation of a catalyst having a catalytically active coating constituted by finely divided materials of large surface and catalytically active components on an inert support body, consisting of the application of the catalytically active components on the finely divided materials, the preparation of a coating dispersion of these materials and the coating of the support body with them, characterized in that the process consists of the following process steps: a) impregnating a powder mixture of finely divided materials with a solution of compounds precursors of catalytically active components according to the pore volume impregnation process, in which the precursor compounds are absorbed into at least one of the materials, b) preparing an aqueous coating dispersion using the impregnated powder mixture, c) coating the body po of inert support with the dispersion thus obtained, d) dry and calcine the coating.

2. The process according to claim 1, characterized in that at least one of the finely divided materials has an isoelectric point between 6 and 10 and that is treated in the case of the precursor compounds of the catalytically active components of anionic salts of the metals of the platinum group of the periodic system of the elements, which are thermally fixed on the carrier materials after impregnation.

3. The process according to claim 1, characterized in that at least one of the finely divided materials has an isoelectric point between 6 and 10 and is treated in the case of the precursor compounds of the catalytically active components of anionic complexes of metals of the platinum group of the periodic system of the elements, the impregnated carrier materials being employed without thermal fixation of the precursor compounds in the preparation of an aqueous coating dispersion with a pH value that is 1 to 3 units below said point isoelectric, preferably between 4 and 8.

4. The process according to claim 2 or 3, characterized in that the volume of the solvent in the pore volume impregnation is selected between 40 and 90%, preferably 50 to 70%, of the water absorption capacity of the powder mix

5. The process according to claim 4, characterized in that the finely divided materials provided consist of at least one material from the group consisting of aluminum oxide, cerium oxide, zirconium oxide, titanium oxide or mixed oxides of these materials with each other or with silicon oxide.

6. The process according to claim 5, characterized in that as anionic complexes of metals of the platinum group, chlorides or anionic salts complexed with alkanolamines or mixtures thereof are used.

7. The process according to claim 6, characterized in that a zeolite with a molar ratio of silicon dioxide / aluminum oxide of more than 50 is used as a finely divided additional material.

8. The process according to claim 7, characterized in that the finished coating on the support body is reduced to temperatures of 300CC in a gaseous stream containing hydrogen.

9. The process according to claim 1, characterized in that at least one of the finely divided materials has an isoelectric point between 2 and 7 and is treated in the case of the precursor compounds of the catalytically active components of cationic complexes of the metals of the platinum group of the periodic system of the elements which are thermally fixed on the carrier materials after impregnation.

10. The method according to claim 1, characterized in that at least one of the finely divided materials has an isoelectric point between 2 and 7 and is treated in the case of the precursor compounds of the catalytically active components of cationic complexes of metals of the platinum group of the periodic system of the elements, the impregnated carrier materials being employed without thermal fixation of the precursor compounds in the preparation of an aqueous coating dispersion with a pH value that is in 1 to 5 units above said isoelectric point, preferably between 7 and 10. and 9.

11. The process according to claim 9 or 10 characterized in that the volume of the solvent in the pore volume impregnation is selected between 40 to 90%, preferably 50 to 70%, of the water absorption capacity of the mixture powdered.

12. The process according to claim 11, characterized in that the finely divided materials provided consist of at least one material from the group consisting of titanium oxide, cerium oxide, zirconium oxide, silicon oxide or mixed oxides of the same.

13. The process according to claim 12, characterized in that tera-aminic complexes, nitrates or mixtures thereof are used as cationic complexes of metals of the platinum group.