DE1272896B - Process for the production of carrier catalysts - Google Patents

Description

Method of manufacture The invention relates to a method of Production of supported catalysts from supported catalysts.

The known supported aluminum oxide catalysts show at higher Temperatures caused a sharp decrease in their activity is that the aluminum oxide sinters and the available surface area accordingly decreased. Show when used to detoxify automobile exhaust gases These catalyst supports also lack strength by being exposed to the action The shock partially disintegrates into a fine powder, which in turn is catalytic Activity impaired. A third disadvantage of the known supported aluminum oxide catalysts is that you have to use them in the form of a loose layer, whatever the type the catalyst chamber has special requirements.

The invention is based on the object of catalysts with aluminum oxide supports to produce which do not have the above-mentioned disadvantages.

This is achieved according to the invention in that a molded body consists of Aluminum particles with a dimension of at least 0.18 mm in one dimension, at least 13 #t in the second dimension and 13 #t to 5 mm in the third dimension or a honeycomb-shaped body made of aluminum foil in the presence of oxides of alkali or alkaline earth metals, oxides of vanadium, chromium, molybdenum, tungsten, copper, silver, Zinc, antimony or bismuth or of the raw materials that make up such oxides form, or of alkali hydroxides as a flux in amounts of at least 0.02 percent by weight of aluminum, optionally in the presence of heat-resistant fillers in Amounts up to 48 percent by weight, based on the total amount of aluminum and flux, is fired at temperatures of 400 to 1500 ° C in the presence of oxygen until at least 10% of the aluminum is oxidized, at least 111/0 of the aluminum is still in an oxidation state corresponding to a valence below 3 and the product contains at least 30 weight percent alumina, followed by the Carrier is acted upon with a catalytically active component in the form of Oxides or mixed oxides of iron, cobalt, nickel, vanadium, chromium, manganese, Copper, zinc, molybdenum, silver, tin, barium, cerium, tungsten, lead and / or Bismuth c) in the form of metallic ruthenium, platinum, palladium, rhodium, osmium and / or iridium is present on the carrier.

The aluminum particles to be used as starting material preferably have a dimension of less than 3.2 mm in at least one dimension.

The in this process before the application of the catalytic Catalyst carriers produced by active components are porous, heat-resistant bodies, which consist of a framework of dense, crystalline cells with wall thicknesses of 7.6 P to 5 mm, diameters of 13 g, to 5 mm and an aluminum oxide content of at least 30 weight percent and at least 1 weight percent aluminum in one an oxidation state corresponding to a valence below 3, the cell wall material of a-aluminum oxide, compounds or solid solutions of aluminum oxide and at least another oxide or solid solutions of at least one oxide in the aluminum oxide compounds, optionally in a mixture with heat-resistant fillers.

If a honeycomb-shaped body is used as an aluminum foil as the starting material the resulting catalyst carrier also has a honeycomb structure.

If the originally obtained, from a framework denser, more crystalline Cells existing body is crushed to form a present in the form of individual particles To obtain a catalyst carrier, the wall thickness as well as the chemical and physical The structure of the material that originally formed the cell walls can still be recognized.

According to the preferred embodiment of the invention, the aluminum particles are initially mixed with metal oxides or metal oxide formers, which act as fluxes and optionally simultaneously as fillers, and preferably also with inorganic fillers, to form a type of unfired ceramic body which, after the volatile constituents have been driven off, has a porosity of at least 200 /. has, whereupon the aluminum is oxidized by burning the ceramic body at at least 400 ° C until a weight increase of at least 110 /, of the aluminum contained in the starting mixture has occurred. This gives a framework structure containing aluminum oxide. The unfired body can contain 0 to 8 parts of a particulate refractory filler per part of aluminum. In order to achieve the greatest catalytic activity, the content of heat-resistant filler in the unfired body should be less than 33%.

The catalyst support can also be prepared by moving from one another separate aluminum particles are oxidized, so that the catalyst support is in the form of individual particles accrues. The aluminum particles can e.g. B. before oxidation with a powdery, heat-resistant substance that will be mixed with the aluminum or when burning Aluminum oxide does not react. The alumina particles can then e.g. B. by Classifying are separated.

The surprising catalytic activity of those prepared according to the invention Supported catalysts are likely to be based on the incomplete oxidation of the aluminum, the black to dark gray color of the catalyst carrier after firing can be seen (pure aluminum oxide is known to be white). This color can, however be covered by any other elements present (e.g. chrome), but is always darker than a completely fired sample, otherwise the same composition. It is believed that the paint is based on aluminum and possibly sub-oxides finely divided metallic aluminum is due.

In the process according to the invention one can use pure aluminum or from aluminum alloys, in which aluminum is the main component forms. The metal is preferably used in a clean, grease and oil-free condition. The aluminum particles should have the dimensions given above. At work with aluminum balls, these must have a diameter between 0.18 and 5 mm. When working with fibers in the form of cylindrical rods, these must have a diameter between 13 #t and 5 mm and a length of at least 0.18 mm. The length can also range from short staple to continuous thread form. The aluminum but can also be in the form of ordered structures, e.g. $. as a honeycomb body or mesh fabric, can be applied.

Suitable flux for the production of Kataly satorträger are the oxides of alkali metals, alkaline earth metals, vanadium, chromium, molybdenum, tungsten, Copper, silver, zinc, antimony and bismuth, compounds that make up when burning form such oxides, as well as the hydroxides of the alkali metals. The oxides and hydroxides the alkali metals, magnesium, strontium and barium are preferred.

Suitable oxide formers are, for. B. organic salts such as acetates or Benzoates, and inorganic salts, such as the bisulfates, bisulfites, bromates, nitrates, Silicates, sulfates, sulfites and thiosulfates of the metals mentioned. More suitable Fluxes are trialkyltin oxide and lead silicate (PbSi03).

In addition, the unfired starting moldings can be heat-resistant Contain fillers in amounts up to about 48% / a. Such fillers are e.g. B. the carbides of aluminum, boron, hafnium, niobium, silicon, tantalum, thorium, titanium, Tungsten, vanadium and zirconium, the nitrides of aluminum, boron, hafnium, niobium, Tantalum, thorium, titanium, uranium, vanadium and zirconium, the borides of chromium, hafnium, Molybdenum, niobium, tantalum, titanium, tungsten, vanadium and zirconium as well as the oxides of Aluminum, beryllium, cerium, hafnium, lanthanum, magnesium, uranium and yttrium that stabilized Oxide of zirconium and, if not quite so cheap, silicon dioxide. Mixtures too these heat-resistant compounds can be used. These connections can be present as such in the catalyst support, or they can be formed with formation of spinels, mullite, etc. react or form a solid solution.

In some embodiments of the invention, particularly for education of alumina-containing linings "or coatings on steel, are considered to be heat-resistant Fillers silica or silicic acid compounds used, such as. B. sound, Kaolin, brick dust or minerals containing magnesium and silicon such as asbestos, Talc, steatite, soapstone, fosterite and vermiculite.

Certain clays can already contain enough alkali oxide to act as a flux at the same time. However, it has been shown that in one Clay may contain (or be added to) about 3.0 percent by weight of alkali oxide must if it is to act as a flux at around 1000 ° C.

The minimum amount of aluminum in the starting material that can be used as a catalyst carrier obtained with the mentioned framework structure depends on the size distribution of the metal particles and the nature of the refractory filler. If the output material z. B, Mg0 or contains another reactive oxide and aluminum particles with a mean Diameter of 0.38 mm can be used, the minimum aluminum content can be added to the Time at which the reaction temperature for the formation of a compound with Aluminum oxide (such as spinel) can be achieved to be about 11 percent by weight. at Aluminum .. oxide, silicon carbide or other heat-resistant, non-reactive Fillers, on the other hand, must have at least about 20 weight percent aluminum particles use the same size. In both cases, larger amounts of aluminum, e.g. B. 14 or 25 percent by weight, required when larger particles, e.g. B. with a Diameter of 1.3 mm.

Before heating the shaped metal aggregate particles in an oxidizing The surfaces of the aggregate particles are in intimate contact with an atmosphere Brought flux, which is supplied dry, in solution, as a gas or as a melt can be. The flux can e.g. B. dusted or sprayed onto the metal or the metal in a solution or melt of the flux or in the powdery Flux can be immersed. A concentrated aqueous solution or slurry allows comfortable work. Often the application of pressure and / or vacuum beneficial to the even and complete distribution of the flux over to lighten the particle surfaces. Furthermore, when working with diluted Solutions, the addition of a thickening agent such as sodium carboxymethyl cellulose is advantageous be. You can use the flux with the heat-resistant filler mix and add the metal moldings to the mixture. Certain heat resistant Fillers can also serve as flux at the same time (e.g. Mg0). In some Cases, as with certain minerals, the refractory filler can do that too Contains flux.

It may be advantageous to use smaller amounts of water, ethyl alcohol, Ethylene glycol, acetone, solutions of carboxymethyl cellulose, rubber, gum arabic, Add polyvinyl alcohol, natural resins or glue to increase the strength of the unfired Increase molded body. A self-binding additive such as Sorel cement can also be used can be used for this purpose. Preferably, a material is used which is among the Burning conditions burns out. Usually about 0.1 to 2 percent by weight of binder is sufficient.

If a metal oxide former is used as the flux, its Amount calculated on the basis of the resulting metal oxide. The amount of metal oxide or hydroxides can be 0.02 to 20 weight percent or more based on weight of aluminum. A range of about 0.2 to 5% is preferred. Higher Flux concentrations are only considered if the flux also acts as a heat-resistant filler. Otherwise they would have the melting point and reduce the high temperature strength of the catalyst support too much.

The required porosity (at least 20% after removal of the volatile substances) can be reached in a number of ways, e.g. B. by compressing of the unfired molded body up to a certain degree of compression or through Addition of substances that volatilize or burn out at the firing temperature. The molded body is then dried.

The dried, raw molding is in an oxidizing atmosphere, such as air, oxygen or mixtures of oxygen and inert gases, to one temperature of at least about 400 ° C, but below the ignition temperature of the metal the applied oxygen concentration. Set up the exact firing conditions depending on the raw porosity of the molding, the amount of metal, the amount and type of Flux and the temperature and are preferably chosen so that no spontaneous and rapid ignition or reduction of the non-aluminum components occurs. in the in general, oxidation should at least initially be relatively lower Temperature can be carried out until a stress-absorbing oxide film is formed which has the shape of the aggregate obtained during molding during the subsequent further oxidation preserved at higher temperatures. With very small amounts of alkali oxide or hydroxide, such as 0.1 to 3 percent by weight, you can, for. B. Temperatures of about 650 to 800 ° C Leave on for about 1 / a to 48 hours. Less active fluxes, such as MgO in Amounts from 0.1 to 10 percent by weight require 1 to 72 hours at temperatures from 1000 to 1350 ° C or above.

The aluminum oxidation in the finished catalyst support is 10 up to 99 ° / o completely. Products with a metallic aluminum content of no more than 10% is preferred. In the production of ordered structures, like honeycomb bodies, tiny pills, or linings on metal, these can be Oxidation can be carried out in a single firing. When the catalyst carrier to be used in particulate form, the mixture is preferably first Aluminum and flux in the form of thin, porous shaped bodies (e.g. a plate from 6 to 13 mm thickness) up to an aluminum conversion rate of 50 to 900/0 fired, then to the desired particle size (e.g. from 0.84 mm to about 5 mm) crushed and finally burned to the desired degree of conversion.

The above working method can also be used to form firm, well-adhering, heat-resistant coatings can be applied to various substrates. Such coatings or linings are in reaction tubes and especially in manifolds and silencers of motor vehicle exhaust pipes of particular value.

A firm, adherent coating of x-aluminum oxide was applied to steel obtained by dipping the steel in molten aluminum, the cold aluminum coating coated with sodium silicate and oxidized the aluminum by heating in the air became. An excellent alumina coating was obtained by mixing of aluminum fibers and sodium silicate pressed onto the inner surface of a steel pipe and burned on it.

You can also have a partially fired liner made from 40 percent by weight Aluminum particles and 60 percent by weight binding clay with the required content of flux in a precisely fitting steel exhaust manifold. The from The heat generated by the exhaust gases then secures the liner with it the steel.

The catalytically active components can provide such linings or added after firing.

The above operation provides a heat-resistant body with a dense, coherent, one-piece, aluminum oxide-containing framework. The with each other communicating walls that make up the scaffolding form cells or Pores. The mean cell or pore size depends on the initial size of the Metal particles. These particles are partially or completely in the oxide converted into the form of a shell or wall that covers that of the original metal particle surrounding cavity left behind. The wall or shell therefore forms a cell that corresponds in size and shape to the original metal particle. The cells can be empty or contain some non-oxidized aluminum. These pores are from to distinguish the pores that are in the refractory body outside the framework structure are contained and result from the volatilization of volatile substances or in the raw body were present.

The pores in the framework (excluding the micropores with sizes under 13 #t) have a mean diameter, measured in one through the body laid cutting plane, between about 13 i. and 5 mm. The pore size is preferably about 0.05 to 1 mm. These pores have the nature of closed cells. the Pore walls have a minimum thickness of about 7.6 p, and are at least this Width practically homogeneous, i.e. i.e., the wall is practically free for the minimum thickness of inclusions of non-framework material or voids of more than about 2.5 p. Diameter. In general are the aluminum particles in the original material so far apart that between the metal resulting cavities can form a wall of the specified minimum thickness. However, if several metal particles are so close together in the starting material, that there is no wall of at least 7.6 t thickness between the cavities that are created can form is the wall surrounding the cavity combination in question as the wall to watch.

The maximum thickness of a pore wall in the framework is roughly equal to the diameter the enclosed pore. The walls of two adjacent pores can, however, be trained meet a double wall thickness. The walls can also be given in a Plan section appear thicker; but since the structure is three-dimensional, can the thickness of a wall is best measured using one perpendicular to the main axis of the cell determine the cut fed.

The crystal grains in the framework wall have a "density function" between about 0.5 and 1.0.

The continuity of the framework structure can be demonstrated by treating the refractory material with chemicals which are inert to the framework phase but which dissolve or destroy all other phases. Then what remains is namely a one-piece structure made of the entire framework material. A simpler way of determining this is to look at the scaffolding on enlarged photographs of slices taken through the body. In order to obtain a faithful reproduction of the structure, the sections chosen for the examination should lie well in the body, e.g. B. at a depth of at least about 20 "/, of each outer dimension of the body. The framework structure can then be recognized by the fact that the dense, coherent phase extends over the entire section considered and at least about 190 /, the area of the solid material of the sectional view If the amount of aluminum used is at the lower limit of the specified range, the dense framework structure may appear somewhat discontinuous in a plane section. In such cases, successive parallel sections obtained by cutting or polishing the body are examined to determine the continuity of the framework structure .

The chemical constitution of the framework can be determined by conventional Determine analysis or quantitative X-ray analysis.

Another characteristic of the catalysts produced according to the invention is the "perfection factor" of the catalyst carrier. To determine this size an X-ray diagram of a sample of the compound to be examined (grain sizes below 0.074 mm) with a recording diffractometer at a scanning speed of 2 O = 1/8 ° per minute, time constant of 8 and recording sheet speed of 21 / z cm per minute, with the recorder on a record is set to the full scale width at 100 counting pulses per second.

To obtain a baseline, one draws on the graphical representation the intensity towards 2 0 is a straight line from the intensity value at 2 0 = 94.00 ° that at 2 0 = 96.50 °. You construct and then measure the height by the maximum Peak intensity perpendicular to the baseline and draws a parallel to the baseline the height bisecting the straight line. The length of this straight line between the intensity values the curve gives the width of the diffraction maximum at half the maximum intensity (E).

Part of the original sample is kept in oxygen for 3 hours at 1425 ° C afterburning, which creates the characteristic black or dark gray color of the Catalyst carrier turns into a white or very light color. Then how above, the width of the diffraction maximum at half the maximum intensity of the afterburned Sample determined (G). The perfection factor (F) is then equal to E / G. Preferred catalyst supports have a perfection factor of at least 1.5 or even 3 or 4.

With the post-fired sample, two partially resolved curves are obtained above the baseline (CuK "and CuKa2), this method comparing the width of the higher maximum (CuKtt i) with the broadened, combined (unresolved) maximum of the original sample The »density function« is a measure of the density of the framework structure: Density function = mean value of part of the circumference that is in contact with other grains , Total circumference of the grain under consideration The density function is determined for each grain by examining a photomicrograph of a polished section of the sample and averaging the results. Most of the products in the form obtained during their manufacture show no visible grain boundaries after etching at 750x magnification. In this case, the density function value approaches an upper limit value of 1.0. With prolonged heating, e.g. B. 100 hours at 1600 ° C, grain growth can occur and an average grain size of about 8 #t can be achieved. Further growth of the grain is limited by the thickness of the framework and the density function value approaches the lower limit of 0.5.

The cell or pore size is determined according to the technique of linear analysis the microstructure according to W. D. K i n g e r y, "Introduction to Ceramics", p. 412 to 417, determined. The individual cells can be used depending on the shape of the starting material used aluminum and the compression of the unfired green body diameter have between 1 and 5000 #L. The main part of the total porosity results however, from the larger cells with a diameter of 50 to 5000 p ,.

The catalyst support is with the catalytically active component applied according to the usual known methods.

For some purposes you can use the catalytically active component in the Bring in the catalyst by adding it to the raw mixture before firing. So chromium oxide, nickel oxide, tungsten trioxide or sodium molybdate can be used as part of the Use heat-resistant filler or as a flux. Since this is a significant Part of the catalytically active component built into the framework structure of the support is, this procedure is less favorable than the post-treatment of the finished fired Catalyst carrier. The catalyst support can also be small amounts on promoters or stabilizers, such as silicon dioxide, titanium oxide, zirconium oxide or thorium oxide.

The catalysts produced according to the invention are suitable for the detoxification of motor vehicle exhaust gases and also for many other oxidation-reduction reactions. EXAMPLE 1 Various catalyst supports are produced as follows: 1. Aluminum fibers (99.995 % Al) with a diameter of 0.1 mm are lightly pressed into a 7.6 15.2 cm mold and a sodium silicate solution (40 ° Bi) is poured over it. The nonwoven is pressed in the mold at 7 to 21 kg / cm 2 pressure, the excess sodium silicate is removed, the wet block is dried overnight in a vacuum at 180 ° C. and heated in air according to the following schedule: 20 hours at 600 ° C. , then 15 hours at 600 ° C, then 5 hours at 650 ° C, then 5 hours at 700 ° C and finally 15 hours at 850 ° C. The increase in weight of the block shows that 640/0 of the aluminum has been oxidized to aluminum oxide. The fired block is broken up with a hammer and the particles are classified using sieves of 4.76 mm and 2.38 mm mesh size. The classified particles are fired in air at 900 ° C. for 12 hours.

The afterburned particles are dark gray, have a low apparent appearance Dense and are very pressure resistant. Microscopic examination at low magnification shows a framework structure made of a fused dark gray substance, which has open pores. There are white or light gray sections here and there. The X-ray analysis shows that the product consists essentially of a-aluminum oxide in addition to some metallic aluminum, the perfection factor of the product (carrier 1) is 2.1.

The above procedure is carried out using tempered turnings made of an aluminum alloy (main impurities 3.910 / 0 copper, 1.50% manganese and 1.97% nickel) repeated to obtain a similar product (carrier 2) will.

By repeating the procedure of FIG. 1 using tempered Turning chips made of an aluminum alloy with a magnesium content of 10% another carrier (3) made.

For comparison with the carriers 1 to 3, a carrier 4 is used in the form of straight, 3.2 # 3.2 mm cylinders with an apparent density of 2.2 Commercial alpha alumina (purity 99.49%). The four carriers have similar ones specific surface areas of <1 ms / g, determined by nitrogen adsorption B r u n a u e r and E m e t t (cf. HAdvances in Catalysis ”, vol. I. p. 65 bis 89, Academic Press, New York, 1948).

The particulate catalyst supports are 10 minutes in an aqueous Immersed solution containing 1 mole of manganese nitrate and 1 mole of chromium trioxide per liter, and then placed wet in a glass tube through which gaseous ammonia is passed. 5 minutes after the appearance of ammonia in the exhaust gas, the passage of ammonia is stopped interrupted and the particles are removed from the tube and heated to 400 ° C for 2 hours heated. This impregnation process is repeated once more.

A is used as the reaction device for evaluating the catalysts vertical tube made of stainless steel with a clear width of 21 / s cm, one sealed, removable cap on the head and a horizontal outlet near the head. The lower end of the tube contains a baffle that connects to a preheater coil made of stainless steel (6.4 mm pipe inside diameter) is connected to a sieve. A small tube is provided in the middle of the reaction tube above the sieve, which is equipped with thermocouples at certain intervals. The pipe is with a Magnesia insulation that contains electric radiators.

The reaction device is filled with the classified catalyst up to a height of 21.6 cm, a sieve is placed on top and heated to 450.degree. The test gas, which is also heated to 450 ° C, is fed at 251 / min. passed through the reaction device. The temperature rise in the catalyst layer is observed and the activity index is calculated for each gas as follows: K for CO = 1.42, for C2H4 = 1.26 and for C @ Ha .--- 2.64; d means the length of the catalyst layer in centimeters over which a temperature rise of 22 ° C (for CO) or 19 ° C (for CZH4 or C2He) occurs. This distance is determined by interpolation between the thermocouples. The determinations are reproducible to ± 501.

The gases used are diluted with 1200 parts of air and 25,000 parts of nitrogen to 150 parts of carbon monoxide or to 9.5 parts of ethylene or ethane. Such gas mixtures are typical of the combustible components in motor vehicle exhaust gases. The results are as follows: Table I. Catalyst support activity index Ver with manganese for the oxidation of search no. chromite applied to CO I C2H4 I C2H8 a 4 no 5 to 10 5 to 10 5 to 10 b 1 no 20 15 18 c 1 yes> 284 164 172 d 2 yes> 284 158 176 e 3 yes> 284 165 170 f 4 yes 284 126 138 g 1 yes 181 74 72 h 2 yes 164 77 59 i 3 yes 160 57 59 y 4 yes <5 <5 <5 The catalyst supports in experiments a to f are heated to 450 ° C. for 3 hours before the test, and the supports in experiments g to j are heated to 1000 ° C. for 31/2 hours.

A comparison of a and b shows that the is not catalytically active Catalyst support containing metal components as an oxidation catalyst for α-aluminum oxide of trade (a) is substantially superior. The higher temperature rise per layer height unit shows that there is greater oxidation.

A comparison of c to f shows that the inventively produced, finished catalyst is superior to the control sample (f). This superiority is with g, h and i even more pronounced in comparison with j. This shows that the invention produced catalyst in its heat resistance compared to conventional catalysts is far superior.

Example 2 Five pieces of a 10.2-10.2-5.1 cm section a 0.05 mm thick honeycomb material made of aluminum foil (with open hexagonal cells 5.1 cm in length and with a spacing of the opposing cell walls of about 3.2 mm) are oxidized as follows and then treated with manganese chromite: The honeycomb material is cleaned with dilute aqueous hydrochloric acid, ih. 'a solution of equals Parts by weight of sodium silicate (40 ° B6), 1% aqueous sodium alginate and aluminum powder (Grain size <0.044 mm) immersed, the excess covering material with compressed air blown out of the honeycomb material and the cover dried for 16 hours at 100 ° C.

The dry, coated molding is heated in air to 600 ° C. for 16 hours, to 720 ° C. for 7 hours, then from 720 to 1200 ° C. over the course of 3 hours and finally held at 1200 ° C. for 12 hours. The product is dark gray and has a perfection factor of 2; 7. The fired honeycomb material is treated with manganese chromite according to Example 1 and in the process shown in FIG. 1 device shown checked. The inlet 3 is connected to the exhaust of a motor vehicle engine cylinder, while auxiliary air is supplied through line 4. The course of the reaction is followed on two thermocouples, which are arranged directly in front of the honeycomb material sections a and e. In addition, the exhaust gas from the outlet 5 is analyzed with a flame ionization hydrocarbon analyzer. The following results are obtained, with tests b and d showing an improvement over a and c, respectively: Table Il attempt a I b I c 1 d Motor operation, km / h .............. 48 48 80 80 Auxiliary air, percent by weight 0 10 0 10 Hydrocarbon concentration tration, ppm. . . . . . . . . . 790 465 560 325 Reduction of coal hydrogen- concentration, ° / ....... - 35 - 36 Exhaust temperature, ° C at the entrance to the tion device ...... 660 665 810 810 in the reaction device ........... 671 793 826 865 If the reaction device is replaced by a simple steel pipe, the addition of 10% auxiliary air reduces the hydrocarbon content of the exhaust gases by only 5 to 7%.

If you run the engine in different conditions for 27 hours the results are equivalent to those given above. When the reaction device is taken apart after the tests, leave the honeycomb material sections detect no physical deterioration.

Example 3 This example shows the preparation of the catalysts using catalytically active components as flux.

Various mixtures of metallic aluminum and flux are made here, burns, grinds to grain sizes from 2.38 to 4.76 mm and caleined at 400 ° C. The activity index is determined according to example l. The working conditions and results are summarized in Table III.

In experiments a, b and c, aluminum wool is used as the starting material, while experiment d is carried out with aluminum cylinders 2.03 mm in diameter and 3.2 mm in length. Table -III attempt a I b I cd Flux Connection ............: ................: ..... Cr203 Ni203 W03 Na2Mo04 % of total .............................. 15 41 14 15 Firing temperature, ° C. . . . . . . . . . . ... . . . . . . . . . . 1000 1000 850 850 Conversion, ° / o ... .......................... 50 40 60 Activity index for the oxidation of CO ................... <..................: ...>284>284>284> 284 CZH4 .............-... ..................... 208 174 252 72 CZHs .............: .......................... 202 149 343 70 Example 4 A block of the aluminum honeycomb material described in Example 12 is oxidized in the manner described there. The fired molding (250 parts) is immersed in a solution containing 5 parts by weight of platinum in the form of platinum hydrochloric acid in 500 parts by weight of water at 50 ° C., the block is removed after 15 minutes and reduced with hydrogen at 75 ° C. and a water vapor saturation level of 60 0/0, where the block is also at 75'C. The catalyst obtained in this way, in which the aluminum is oxidized to less than 100%, is suitable for catalytic reactions.

One of the main uses of the catalytic converter is in automotive exhaust gas treatment, but you can use the catalyst generally for oxidation and reduction reactions use. It is particularly suitable for the partial oxidation of hydrocarbons to carbon monoxide, hydrogen and carbon dioxide.

The following example illustrates the effectiveness of the same catalyst for the reduction of nitrogen oxide. Example 5 Above that described in Example 4 The catalyst is a mixture of 6.21 percent by volume of oxygen in a glass vessel, 0.266 percent by volume NO, 0.98 percent by volume ammonia and 92.5 percent by volume nitrogen at a speed of 50.81 / hour. passed, the temperature in the reaction zone is kept at 214 ° C. The escaping gas contains 0.0274 percent by volume of nitrogen oxide. So 900/0 of the nitrogen oxide has been removed from the gas mixture. Of the 0.2386 Percentage by volume of NO that has disappeared from the gas is based on analytical determination 30% has been reduced to nitrogen and 70% to N20. It has also proven to be a reduction product of the NO water formed. Example 6 The procedure is as in Example 14, but using of 2½ parts by weight of platinum in the form of platinum hydrochloric acid and 21/2 Parts by weight of palladium in the form of palladium chloride.

This catalytic converter is suitable for the oxidation of exhaust gases from internal combustion engines and generally for catalytic oxidation. This catalyst is particularly favorable for reactions at very high temperatures, such as the partial combustion of hydrocarbons. Example ? 1 part by volume of aluminum particles (0.84 to 2 mm grain size), which contain 1.0% NaOH are coated, and 10 parts by volume of aluminum oxide particles with grain sizes below 0.15 mm are mixed thoroughly and poured into an aluminum oxide pan. Of the The crucible with its loose contents is made according to the firing schedule in Example 2 Air heated. After cooling, the aluminum oxide powder from the mixture is through sieved out a sieve with a mesh size of 0.15 mm. Those retained on the sieve Particles have the approximate shape of hollow spheres, their cavities in terms of size correspond to the original metal particles. The beads consist of a-aluminum oxide, are black and contain 2 to 5 in their dense wall in finely divided form 0/0 metallic aluminum. The beads then turn into a powder with grain sizes shredded below 74 #t.

40 parts by weight of this powder are in a solution of 100 parts by weight Chromic anhydride and 29 parts by weight of nickel in the form of nickel nitrate in 1000 Parts by weight of water at 45 ° C are slurried and the slurry becomes slow mixed with concentrated ammonium carbonate solution until complete precipitation. The precipitate is filtered off and calcined at 400 ° C. for 1 hour.

The calcined powder becomes a uniform paste with water kneaded, dried for 12 hours at 150 ° C, then powdered to grain sizes below 2 mm, mixed with 10/0 graphite and placed in the tablet press to form cylinders (3.2 - 3.2 mm) is pressed. The tablets are finally left in the air at 500 ° C for 3 hours heated.

These catalyst tablets are suitable for the removal of combustible Components and nitrogen oxide from the exhaust gases of internal combustion engines and also for oxidations, such as the synthesis of formaldehyde by partial oxidation of Methane. Example 8 Aluminum foil particles (0.13-0.25, 4.83 mm) are impregnated with 10/0 Alcoholic caustic soda, drains and dries. The coated film will mixed with a 2% aqueous solution of sodium carboxymethyl cellulose, the Mixture formed into a stick and the stick dried. The dried stick will Fired, ground and post-fired according to Example 1.

The aluminum oxide granulate (250 parts; grain size 2.38 to 4.76 mm), which contains at least 10/0 incompletely oxidized aluminum is 10 minutes into a slurry of 117 parts by weight ammonium metavanadate, 25 parts by weight Titanium dioxide and 32 parts by weight of copper in the form of copper nitrate in 500 parts by weight Submerged in water at 90 ° C, allowed the soaked granules to drain and then 10 Calcined at 300 ° C for minutes.

The catalyst obtained in this way is generally suitable for oxidation reactions, but especially for the conversion of sulfur dioxide into sulfur trioxide and for the oxidation of the combustible components in the exhaust gas of internal combustion engines. Example 9 250 parts by weight of the carrier 1 of Example 1, in which the Aluminum is only partially oxidized to the trivalent state, 15 minutes in a solution of 30 parts by weight of cobalt, 27.5 parts by weight of manganese and 4 parts by weight Magnesium oxide (in each case in the form of nitrates) in 500 parts by weight of water at 90 ° C, lets the impregnated mass drain off and calcined for 1 hour at 500 ° C, whereby a Cobalt manganate catalyst is obtained.

This catalyst is suitable for the oxidation of ethylene to ethylene oxide, from sulfur dioxide to sulfur trioxide, from naphthalene to phthalic anhydride, from Methanol to formaldehyde and especially to oxidize the combustible components in exhaust gases from internal combustion engines. The catalyst is also particularly suitable for high temperature reactions, such as those involving hydrocarbons partially to synthesis gases are oxidized, the hydrogen, carbon dioxide and carbon monoxide.

Claims (1)

Claim: A process for the production of supported catalysts, characterized in that a shaped body made of aluminum particles with a dimension of at least 0.18 mm in one dimension, at least 13 p in the second dimension and 13 to 5 mm in the third dimension or a honeycomb body made of aluminum foil in the presence of oxides of alkali or alkaline earth metals, oxides of vanadium, chromium, molybdenum, tungsten, copper, silver, zinc, antimony or bismuth or of starting materials from which such oxides are formed, or of alkahydroxides as a flux in Amounts of at least 0.02 percent by weight of the aluminum, optionally in the presence of heat-resistant fillers in amounts up to 48 percent by weight, based on the total amount of aluminum and flux, is fired at temperatures of 400 to 1500 ° C in the presence of oxygen, up to at least 10 ° / o of the aluminum are oxidized, at least 1 % of the aluminum is still in a valency below 3 Prechenden oxidation state is present and the product contains at least 30 percent by weight of aluminum oxide, whereupon the carrier is acted upon with a catalytically active component in the form of oxides or mixed oxides of iron, cobalt, nickel, vanadium, chromium, manganese, copper, zinc, molybdenum, silver , Tin, barium, cerium, tungsten, lead and / or bismuth or in the form of metallic ruthenium, platinum, palladium, rhodium, osmium and / or iridium is present on the carrier.