Indian Patents. 270249:METHOD FOR THE PRODUCTION OF A NANOCRYSTALLINE MOLYBDENUM MIXED OXIDE

Title of Invention	METHOD FOR THE PRODUCTION OF A NANOCRYSTALLINE MOLYBDENUM MIXED OXIDE
Abstract	The invention relates to a method for the production of a nanocrystalline molybdenum mixed oxide, the use of the molybdenum mixed oxide as catalyst for chemical conversions, in particular for a conversion of acrolein to acrylic acid as well as a catalyst which contains the molybdenum mixed oxide.

Full Text	The invention relates to a method for the production of a nanocrystalline molybdenum mixed oxide, the use of the molybdenum mixed oxide as catalyst for chemical conversions as well as a catalyst which contains the molybdenum mixed oxide. Until now, molybdenum mixed oxides have been obtained in the state of the art by precipitation methods, sol-gel methods or solid-state reactions. Molybdenum mixed oxides are used in the state of the art as catalyst for chemical conversions. Conversions of alkyl compounds or alkene compounds to acrolein or derivatives thereof as well as a conversion of acrolein to acrylic acid may be named here as examples. The molybdenum mixed oxide catalysts according to the state of the art often do not display a sufficient activity in these reactions. WO 2008/028681 and WO 2008/006565 Al disclose a method for the production of nanocrystalline metal oxides or mixed metal oxides. There is no indication in these documents that special nanocrystalline molybdenum mixed oxides which are particularly well-suited as catalyst in particular for the conversion of acrolein to acrylic acid can be produced with the method. A crystalline molybdenum mixed oxide can be obtained only with difficulty via conventional methods. Thus, G.A. Zenkovets et al., "The structural genesis of a complex (MoVW) 5O14 oxide during thermal treatments and its redox behaviour at elevated temperatures", Materials Chemistry and Physics, 103 (2007), 295-304, disclose that an mixed oxide obtained via spray drying has an amorphous structure. This mixed oxide is present in the form of large aggregates approximately 5 um in size. A partially nanocrystalline structure forms inside the aggregates due to subsequent calcining. A pure crystalline phase with crystallites more than 1000 nm in size forms only after prolonged thermal treatment at approximately 440°C. The production of a nanocrystalline molybdenum mixed oxide can thus be accomplished only with difficulty. It is clear from 0. Ovsiter et al., "Molybdenum oxide based partial oxidation catalyst Part 3", Journal of Molecular Catalysis A: Chemical 185 (2002), 291-303, that a molybdenum mixed oxide does not display well-crystallized particles after thermal treatment. A crystalline phase, however, was able to be observed during a conversion of acrolein to acrylic acid, i.e. a crystallization first takes place during the oxidation reaction. Such a catalyst thus has a sufficient activity only after a prolonged reaction period. A disadvantage of the molybdenum mixed oxides described in the state of the art is thus that a uniform particle size of the molybdenum mixed oxides cannot be obtained and a control of the crystallization, in particular with regard to the crystallite size, is not possible. The BET surface area of the molybdenum mixed oxides described in the state of the art is likewise mostly too small. A small particle size with as large as possible a BET surface area is desired, in particular for catalytic uses. The object of the present invention was thus the provision of a nanocrystalline molybdenum mixed oxide which, in catalytic conversions, in particular in a conversion of acrolein to acrylic acid, has an increased activity and selectivity. The object is achieved by a method for the production of a nanocrystalline molybdenum mixed oxide, comprising the steps of a) the introduction of a solution, suspension or slurry which contains a molybdenum starting compound and at least one further metal-containing starting compound, selected from a tungsten- containing and/or vanadium-containing starting compound, into a reaction chamber by means of a carrier fluid, b) a thermal treatment of the solution, suspension or slurry which contains the molybdenum starting compound and the at least one further metal- containing starting compound in a treatment zone by means of a pulsating flow at a temperature of from 200 to 500°C, c) the formation of nanocrystalline molybdenum mixed oxide, d) the discharge of the nanocrystalline molybdenum mixed oxide obtained in steps b) and c) from the reactor. It was surprisingly found that a uniform particle size of the molybdenum mixed oxides can be obtained by the method according to the invention and a control of the crystallization, in particular with regard to the crystallite size, is achieved. The BET surface area was likewise able to be increased compared with the molybdenum mixed oxides known in the state of the art. The molybdenum mixed oxide obtained according to the invention is characterized by a crystallite size in the range of from 5 nm to 450 nm. The catalytic activity of a catalyst containing the molybdenum mixed oxide obtained according to the invention, in particular in the case of a conversion of acrolein to acrylic acid, was able to be increased by roughly IS compared with known conventional catalysts. By the term "mixed oxide" is meant within the meaning of the invention a mixed oxide that comprises two or more metals and constitutes a single chemical compound that can be expressed with a formula. This is to be distinguished accordingly from a pure (physical) mixture of several metal oxides. Preferably a molybdate, particularly preferably ammonium heptamolybdate tetrahydrate, is used as molybdenum starting compound. However, it is clear to a person skilled in the art in this field that other molybdates and molybdenum compounds known in the state of the art can also be used. In order to obtain a mixed oxide, at least one further metal- containing starting compound should be used. Tungstates and/or vanadates are preferred further compounds according to the present invention. The further starting compound ammonium metatungstate and/or ammonium metavanadate is particularly preferred. A combination of the two last named is most preferred. The molybdenum starting compound and the at least one further metal-containing starting compounds are preferably used together as solution, suspension or slurry. It is most preferred if the starting compounds are present in solution, in particular in aqueous solution. If necessary, the solution can be heated in order to achieve a complete dissolution of the starting compounds, in particular in the case of poorly soluble starting compounds. The solution of the starting compounds is advantageously heated to > 50°C. In a particularly preferred embodiment, a solution of ammonium metatungstate, ammonium heptamolybdate tetrahydrate and ammonium metavanadate is used in the method according to the invention. Prior to or during the introduction into the reaction chamber, a solution, suspension or slurry which contains at least one additional metal salt can be added to the solution, suspension or slurry which contains the molybdenum starting compound and the at least one further metal-containing starting compound. The at least one metal salt is preferably a copper salt or an iron salt or a combination of a copper and an iron salt. The addition of a solution, suspension or slurry containing metal salt to the solution, suspension or slurry which contains the molybdenum starting compound and the at least one further metal-containing starting compound brings about a doping of the resulting molybdenum mixed oxide with the corresponding metal. Any fine adjustments•for the respective desired catalytic function of the molybdenum mixed oxide can thereby be achieved. In a particularly preferred embodiment, a solution of ammonium metatungstate, ammonium heptamolybdate tetrahydrate and ammonium metavanadate, to which a copper-salt solution is added, is used in the method according to the invention. The copper salt is preferably copper sulphate or copper acetate. In a further particularly preferred embodiment, a solution of ammonium metatungstate, ammonium heptamolybdate tetrahydrate and ammonium metavanadate, to which a copper-salt and iron- salt solution is added, is used in the method according to the invention. The copper salt is preferably copper sulphate or copper acetate and the iron salt is preferably iron nitrate. It was surprisingly found that the method can be carried out at relatively low temperatures of from 200 to 500°C, particularly preferably from 250 to 450°C, particularly preferably from 300 to 400°C. Hitherto, preferred temperatures of more than 700°C, indeed up to 1400°C, were known in the state of the art. Quite particularly surprisingly, it was also found that the crystallization process of the molybdenum mixed oxide can be controlled in a targeted manner by the method according to the invention, in particular the size of the crystallites and the pore-size distribution of the corresponding molybdenum mixed oxides. This can further be advantageously influenced by the residence time in the flame or by the reactor temperature. The nanocrystalline molybdenum mixed oxide particles that form are prevented from agglomerating by the pulsating thermal treatment. Typically, the nanocrystalline particles are immediately transferred by the stream of hot gas into a colder zone, where some of the molybdenum mixed oxide crystallites are obtained with diameters of even less than 2 0 nm. In the case of the thus-obtainable molybdenum mixed oxide crystallites, this leads to clearly increased BET surface areas of > 1 m2/g, particularly preferably 2 to 10 m2/g and particularly preferably 3 to 7 m2/g. The BET surface area is determined using the Brunauer, Emmett and Teller method according to DIN 66132. In the method according to the invention, suspensions can be calcined within a very short period, typically within a few milliseconds, at comparatively lower temperatures than are usual with methods of the state of the art, without additional filtration and/or drying steps or without the addition of additional solvents. The molybdenum mixed oxide nanocrystallites that form have significantly increased BET surface areas and thus represent a molybdenum mixed oxide catalyst with increased reactivity, improved rate of conversion and improved selectivity, in particular with regard to a conversion of acrolein to acrylic acid. The nearly identical residence time of every molybdenum mixed oxide particle in the homogeneous temperature field created by the method results in an extremely homogeneous end product with narrow monomodal particle distribution. A device for carrying out the method according to the invention in the production of such monomodal nanocrystalline metal oxide powders is known for example from DE 101 09 892 Al. Unlike the device described there and the method disclosed there, the present method does not, however, require an upstream evaporation step in which the starting material, i.e. the molybdenum starting compound, is heated to an evaporation temperature. The molybdenum starting compound and the further starting compounds from which the molybdenum mixed oxides according to the invention are produced are inserted directly via a carrier fluid, in particular a carrier gas, preferably an inert carrier gas, such as for example nitrogen, etc., into so-called reaction chambers, i.e. into the combustion chamber. Attached exhaust side to the reaction chamber is a resonance tube with a flow cross-section which is clearly reduced compared with the reaction chamber. The floor of the combustion chamber is equipped with several valves for the entry of the combustion air into the combustion chamber. The aerodynamic valves are fluidically and acoustically matched with the combustion chamber and the resonance tube geometry such that the pressure waves, created in the combustion chamber, of the homogeneous "flameless" temperature field spread pulsating predominantly in the resonance tube. A so- called Helmholtz resonator forms with pulsating flow with a pulsation frequency of between 10 and 150 Hz, preferably 30 to 110 Hz. Material is typically fed into the reaction chamber either with an injector or with a suitable two-component nozzle or in a Schenk dispenser. Preferably, the molybdenum starting compound is introduced into the reaction chamber in atomized form, with the result that a fine distribution in the region of the treatment zones is guaranteed. After the thermal treatment, the nanocrystalline molybdenum mixed oxides that form are immediately transferred into a colder zone of the reaction chamber, if possible by means of the carrier fluid, with the result that they can be separated and discharged in the colder zone. The yield of the method according to the invention is almost 100%, as all of the product that forms can be discharged from the reactor. Typically, the method is carried out at a pressure of between 15 and 40 bar. A subject of the invention is furthermore the nanocrystalline molybdenum mixed oxide that can be obtained by the method according to the invention. It was found that the thus- obtainable nanocrystalline molybdenum oxide preferably has a crystallite size in the range of from 5 nm to 450 nm, preferably of from 10 nm to 400 nm, quite particularly preferably 15 to 250 nm, which, as already stated above, can preferably be set by the pulsation of the thermal treatment. The particle size can be determined by XRD or TEM. Furthermore, molybdenum oxide particles which have a BET surface area of preferably > 1 nr/g, particularly preferably 2 to 10 nr/g and particularly preferably 3 to 7 nr/g are obtained by the method according to the invention. The molybdenum mixed oxide obtained according to the invention is exceptionally suitable for use as catalyst, for example in the catalytic conversion of acrolein to acrylic acid. Acrylic acid or propenoic acid belongs to the unsaturated carboxylic acids. Acrylic acid is a colourless chemical compound, with a pungent, vinegary odour, that can be mixed with water and is liquid at room temperature. Acrylic acid has a strong corrosive action and is flammable. Large-scale industrial production usually takes place by a two-stage oxidation of propylene with the aid of catalysts. In the first stage, propylene is converted with air to propenal (acrolein). The oxidation of propenal to acrylic acid takes place in the second stage. Its main use is polymerization to superabsorbent polymers (use e.g. in nappies), acrylate esters (which are in turn used for the production of polymers) and as comonomers in the production of polymer dispersions. The water-soluble polymerisates of acrylic acid are used as finishes and thickeners as well as coatings for solid dosage forms and as ointment bases. Polyacrylic acid ethyl ester has proved its worth as copolymerization partner for the production of weather-proof elastomers. A subject of the invention is thus also a catalyst which contains the molybdenum mixed oxide according to the invention. The catalyst can be a supported or an unsupported catalyst (bulk catalyst, extruded catalyst). In an embodiment of the present invention, the molybdenum mixed oxide can be processed together with a suitable binder to an extrudate (tablets, shaped bodies, honeycomb bodies and the like). Any binder that is familiar to a person skilled in the art and appears suitable, in particular silicate materials, aluminium oxide, zirconium compounds, titanium oxide, as well as their mixtures, and materials such as e.g. cement, clay, silica/alumina, can be used as binders. Preferred binders are, among others, pseudoboehmite as well as siliceous binders such as colloidal silicon oxide or silica sol. In preferred developments of the invention, the molybdenum mixed oxide can furthermore be processed together with other components, preferably with a binder, particularly preferably with an organic binder, for example organic glues, polymers, resins or waxes, to a washcoat which can be applied to a metallic or ceramic support. Optionally, additional impregnating steps or calcining steps can take place. Preferably, the molybdenum mixed oxide obtained according to the invention is present as coating on a support. A preferred support material is steatite, steatite spheres are particularly preferred. The coating is preferably carried out in a fluidized bed coating device known per se to a person skilled in the art. A subject of the invention is also a method for the conversion of acrolein to acrylic acid, wherein an above- defined catalyst is used. In the method, acrolein, preferably with oxygen, steam and nitrogen, is passed at 200 to 400°C over a bed of the catalyst according to the invention. An improvement with regard to acrolein conversion rate, acrylic acid selectivity and acrylic acid yield is apparent in the method according to the invention compared with a method which has been carried out with a catalyst according to the state of the art. The invention is described in more detail with reference to the following embodiment examples and the figures, which are not to be regarded as limitative. The device used corresponds largely to the device described in DE 101 09 892 Al, with the difference that the device used for carrying out the method according to the invention had no preliminary evaporator stage. There are shown in: Figure 1 the XRD spectrum of the molybdenum mixed oxide according to the invention obtained in Example 6 Figure 2 the XRD spectrum of the doped mixed oxide according to the invention obtained in Example 7 Embodiment examples: General The essential advantages of the preparation with the aid of the pulsation reactor are the reduction of the overall preparation time, the small outlay (only the reactor is needed) and the fact that there is no drying and treatment of the product. The desired BET surface areas, particle sizes and also the crystallinity of the material can be varied in one step by the pulsation reactor. The following methods were varied for the preparation of the mixed oxides: Example 1: MoWV variant 1 Two solutions were produced for the production. For solution 1, 18 1 dist. H20 was placed in a steel drum and heated. 487.8 g ammonium metatungstate was added and dissolved. Once 70°C had been reached, 3300 g ammonium heptamolybdate tetrahydrate and 546.6 g ammonium metavandadate were added. Once the components had dissolved completely, 113.4 g antimony trioxide was added and the mixture stirred for 1 hour at 95°C. The solution was cooled to room temperature. Solution 2 was produced by dissolving 466.8 g copper sulphate in 2880 ml dist. H20 at room temperature. The two solutions were mixed at room temperature and stirred for approx. 1 h. A suspension formed. The solution was atomized in the pulsation reactor as follows: after a heating-up period, conditional on the equipment, of several hours, the suspension was sprayed at different reactor temperatures (380, 360, 400°C). Air was used as carrier gas. The BET surface areas of the obtained molybdenum mixed oxide were between 1 and 4 irr/g. Example 2: MoWV variant 2 For the production, 11820 ml distilled H20 was introduced. 3150.12 g ammonium heptamolybdate tetraydrate was added to this and dissolved. Continuous stirring was carried out during the whole production process. 822.24 g ammonium metatungstate was then added and dissolved. After subsequent heating to approx. 80°C, 585.6 g ammonium metavanadate was then added and the mixture heated further to 100°C. This temperature was maintained for 5 hours, then the solution was cooled to room temperature. 444 g ammonium acetate was then added, also at room temperature. Half of the 5 kg batch was doped with iron and copper. For this, 1.86 g copper acetate and 4.14 g iron nitrate were dissolved in 120 ml dist. H20 in each case and then added to the solution. The solution was heated for 12 h under reflux. A clear, orange-red solution formed. This solution was atomized doped and undoped into the pulsation reactor at 380°C using air as carrier gas. A grey powder with BET surface areas of 3-4 mz/g formed. Example 3: MOWV variant 3 11820 ml dist. H20 was placed in a drum. 3150.12 g ammonium heptamolybdate tetrahydrate was added to this, then heated and left until it had completely dissolved. 822.24 g ammonium metatungstate was then added and dissolved. The mixture was then heated to approx. 80°C, then 585.6 g ammonium metavanadate was added and the mixture heated further to 100°C. This temperature was maintained for 5 hours and then cooled to room temperature. After cooling to room temperature, 444 g ammonium acetate was added. Continuous stirring was carried out during the whole production process. Doping: The batch was doped with iron and copper. For this, 3.72 g copper acetate and 8.28 g iron nitrate were dissolved in 240 ml dist. H20 in each case and then added to the solution. Atomization + results: The solution was atomized in normal air in the pulsation reactor. Solution with doping: Temperature: 380°C Colour of the powder: grey/black BET: 3.2 XRD: Displays main peak at 22 Crystallite size: 210 A Composition: W 14.7% Theoretical: 9.3 V 6.6% 6.2- Mo 45.9% 46.9- Fe Cu 0.15% 3.1 Powder from the filter bags Temperature: 380°C Powder: grey/black BET: 3.3 XRD: Displays main peak at 22 Crystallite size: 201 A Composition: W 14.6% V 6.7% Mo 4 6.9% Fe 240 ppm Cu 2.2% Example 4: MbWV variant 4 Solution 1: 18 litres dist. H20 was placed in a steel drum and heated. 487.8 g ammonium metatungstate was added and dissolved. Once the temperature had reached approx. 70°C, 3300 g ammonium heptamolybdate tetraydrate and 546.6 g ammonium metavandadate were added. Once the components had dissolved completely, 113.4 g antimony trioxide was added and the mixture stirred for 1 hour at 95°C. The mixture was then cooled to room temperature. Continuous stirring was carried out during the whole production process. Solution 2: 466.8 g copper sulphate was dissolved in 2880 ml dist. H2O at room temperature. After cooling solution 1, the two solutions were mixed and stirred for 1 hour. A black solution with fine white particles formed. Atomization + results: All atomizations were carried out with normal air in the pulsation reactor. Powder from the drum Temperature: 380°C Powder: grey/black BET: 1. 0 m2/g XRD: Displays main peak at 22 Crystallite size: 207 A Composition W 9.1% Theoretical: 9.3- V 6.0% 6.2 Mo 45.8% 46.9 Sb 1.8% ' 2.5 Cu 2.2% 3.1 Powder from the filter bags Temperature: 380°C Powder: grey/black BET: 1.5 XRD: Displays main peak at 22 Crystallite size: 197 A Composition: W 9.2% Theoretical: 9.3% V 6.1% 6.2% Mo 46.5% 46.9 Sb 1.8% 2.5: Cu 2.2% 3.1 Exazsple 5 (coznparlson example) Example 5 was carried out according to US 6,124,499: 127 g copper(II) acetate monohydrate (Cu content 32.3 wt.- ) was dissolved in 2700 g water (solution I). 860 g ammonium heptamolybdate tetrahydrate (81.3 wt.-% M0O3) , 143 g ammonium metavanadate (72.2 wt.-% V2O5) and 126 g ammonium paratungstate heptahydrate (89.3 wt.-% WO3) were dissolved in succession in 5500 g water at 95°C (solution II). Solution I was then stirred all at once into solution II and the aqueous mixture spray-dried at an outlet temperature of 110°C. The obtained spray product was kneaded with 0.15 kg water per kg powder. The kneaded matter was calcined in a convection oven in an oxygen/nitrogen mixture. The oxygen content was set such that the 0: starting concentration was 1.5 vol.-* at the oven outlet. The kneaded material was first heated to 300°C at a rate of 10°C/min and then kept at 300°C for 6 h. The mixture was then heated to 400°C at a heating rate of 10°C/min and kept at 400°C for 1 h. The catalyst had the composition Mo12V3W2.2Cu1.6Ok. The calcined active material was ground down to 0.1 urn to 50 Vim. Powder: grey/black BET: 1.0 m2/g XRD: Displays main peak at 22 Crystallite size: > 960 A Example 6 (according to the Invention) Solution 1: 18 litres dist. H20 was placed in a steel drum and heated. 487.8 g ammonium metatungstate was added and dissolved. When the temperature had reached approx. 70°C,"3300 g ammonium heptamolybdate tetrahydrate and 546.6 g ammonium metavandadate were added. Once the components had dissolved completely, 113.4 g antimony trioxide was added and the mixture stirred for 1 h at 95°C. The mixture was then allowed to cool. Continuous stirring was carried out during the whole production process. Solution 2: 466.8 g copper sulphate was dissolved in 2880 ml dist. HjO at room temperature. After cooling solution 1, the two solutions were mixed and stirred for 1 hour. A black solution with"fine white particles formed. After atomization of the solution/suspension at 380°C in the pulsation reactor, a powder with the following characteristics was obtained: Powder: grey/black BET: 5-7 m2/g XRD (see Figure 1): Displays main peak at 22 Crystallite size: 207 A Example 7 (according to the invention) 11820 ml dist. H20 was placed in a vessel. 3150.12 g ammonium heptamolybdate tetrahydrate was added to this vessel, then the heating was started and continued until everything had completely dissolved. 822.24 g ammonium metatungstate was then added and the mixture was left until everything had dissolved. The mixture was then heated to approx. 80°C, then 585.6 g ammonium metavanadate was added and the mixture heated further to 100°C. This temperature was maintained for 5 hours, followed by cooling to room temperature. After cooling to room temperature, 444 g ammonium acetate was added. Continuous stirring was carried out during the whole production process. Doping: The batch was doped with iron and copper. For this, 3.72 g copper acetate and 8.28 g iron nitrate were dissolved in 240 ml dist. H20 in each case and then added to the solution. After atomization of the solution at 380CC in the pulsation reactor, a powder with the following characteristics was obtained: Colour of the powder: BET: XRD (see Figure 2): Crystallite size: grey/black 6 Displays main peak at 22 210 A Example 8 (production of coated catalysts) A fluidized bed coating device was used to carry out the coating. The steatite spheres were coated with the various mixed oxide active materials from Examples 5 to 7 under the following conditions: 22.22 g of the powder was weighed into a measuring cylinder, made into a slurry with 500 ml dist. H20. The resulting suspension was stirred intensively. 8.89 g binder was then added and the mixture stirred for 1 h on a magnetic stirrer. The "coating" of the produced suspension took place on a weighed-in sample of 80 g steatite spheres of (2-4 mm) , wherein the active material charge was 20% (50 g powder per 200 g steatite spheres) . The catalyst was then dried in air at 110°C. Example 9 (determination of the catalytic performance data of the catalysts) 21 g catalyst (i.e. the above-described coated steatite spheres), diluted with 350 g steatite spheres with a diameter of 4.5 mm to avoid hotspots, was poured into a 120-cm long reaction tube with an internal diameter of 24.8 mm to a length of 105 cm. The reaction tube was in a liquid salt bath which was able to be heated to temperatures of up to 500°C. In the catalyst bed there was a 3 mm protective tube with an integrated thermocouple via which the catalyst temperature over the complete catalyst combination was able to be displayed. To determine the catalytic performance data, acrolein was put into the gas phase by means of a saturator. An air-inert gas mixture was passed through the saturator in such a way and the thermostat temperature of the saturator set such that an acrolein content of 5 vol.-% in the feed gas resulted. The reactor feed consisted of a mixture of 7 vol.-% 0, 10 vol.-- steam and the remainder N;. The acrolein charge was 150 Nl/lh at most. The acrolein conversion rate and the acrylic acid selectivity were determined at an average catalyst temperature of 250°C. The results of the tests with the catalysts which contain the active material according to the examples named in the table are listed in Table 1. The ascertained results demonstrate an improvement of the catalysts according to the invention with regard to acrolein conversion rate, acrylic acid selectivity and acrylic acid yield compared with a catalyst according to the state of the art. WE CLAIM 1. Method for the production of a nanocrystalline molybdenum mixed oxide, comprising the steps of a) the introduction of a solution, suspension or slurry which contains a molybdenum starting compound and at least one further metal-containing starting compound, selected from a tungsten- containing and/or vanadium-containing starting compound, into a reaction chamber by means of a carrier fluid, b) a thermal treatment of the solution, suspension or slurry which contains the molybdenum starting compound and the at least one further metal- containing starting compound in a treatment zone by means of a pulsating flow at a temperature of from 200 to 500°C, c) the formation of nanocrystalline molybdenum mixed oxide, d) the discharge of the nanocrystalline molybdenum mixed oxide obtained in steps b) and c) from the reactor. 2. Method according to claim 1, characterized in that the molybdenum starting compound is ammonium heptamolybdate tetrahydrate. 3. Method according to claim 1 or 2, characterized in that the at least one further metal-containing starting compound is ammonium metatungstate and/or ammonium metavanadate. 4. Method according to one of claims 1 to 3, characterized in that the carrier fluid is a gas. 5. Method according to one of claims 1 to 4, characterized in that, prior to or during the introduction into the reaction chamber, a solution, suspension or slurry of a metal salt is added to the solution, suspension or slurry which contains the molybdenum starting compound and the at least one further metal-containing starting compound. 6. Method according to claim 4, characterized in that the metal salt is a copper and/or iron salt. 7. Nanocrystalline molybdenum mixed oxide that can be obtained by a method according to one of claims 1 to 6. 8. Nanocrystalline molybdenum mixed oxide according to claim 7, characterized in that its crystallite size lies in the range of from 10 nm to 450 nm. 9. Nanocrystalline molybdenum mixed oxide according to claim 7 or 8, characterized in that it has a BET surface area of from 1 to 10 m2/g. 10. Nanocrystalline molybdenum mixed oxide according to one of claims 7 to 9, characterized in that the molybdenum mixed oxide is doped. 11. Nanocrystalline molybdenum mixed oxide according to one of claims 7 to 10, characterized in that the molybdenum mixed oxide is doped with Cu and/or Fe. 12. Use of a nanocrystalline molybdenum mixed oxide according to one of claims 7 to 9 as catalyst for chemical conversions. 13. Use according to claim 12 for the conversion of acrolein to acrylic acid. 14. Catalyst, containing the nanocrystalline molybdenum mixed oxide according to one of claims 7 to 11. 15. Catalyst according to claim 14, characterized in that the molybdenum mixed oxide is present as coating on a support. 16. Catalyst according to claim 14 or 15, characterized in that the catalyst comprises a binder. 17. Method for the conversion of acrolein to acrylic acid, wherein a catalyst according to one of claims 14 to 16 is used. The invention relates to a method for the production of a nanocrystalline molybdenum mixed oxide, the use of the molybdenum mixed oxide as catalyst for chemical conversions, in particular for a conversion of acrolein to acrylic acid as well as a catalyst which contains the molybdenum mixed oxide.

Full Text

The invention relates to a method for the production of a
nanocrystalline molybdenum mixed oxide, the use of the
molybdenum mixed oxide as catalyst for chemical conversions
as well as a catalyst which contains the molybdenum mixed
oxide.
Until now, molybdenum mixed oxides have been obtained in the
state of the art by precipitation methods, sol-gel methods or
solid-state reactions.
Molybdenum mixed oxides are used in the state of the art as
catalyst for chemical conversions. Conversions of alkyl
compounds or alkene compounds to acrolein or derivatives
thereof as well as a conversion of acrolein to acrylic acid
may be named here as examples. The molybdenum mixed oxide
catalysts according to the state of the art often do not
display a sufficient activity in these reactions.
WO 2008/028681 and WO 2008/006565 Al disclose a method for
the production of nanocrystalline metal oxides or mixed metal
oxides. There is no indication in these documents that
special nanocrystalline molybdenum mixed oxides which are
particularly well-suited as catalyst in particular for the
conversion of acrolein to acrylic acid can be produced with
the method.
A crystalline molybdenum mixed oxide can be obtained only
with difficulty via conventional methods. Thus, G.A.
Zenkovets et al., "The structural genesis of a complex
(MoVW) 5O14 oxide during thermal treatments and its redox
behaviour at elevated temperatures", Materials Chemistry and

Physics, 103 (2007), 295-304, disclose that an
mixed oxide obtained via spray drying has an amorphous
structure. This mixed oxide is present in the form of large
aggregates approximately 5 um in size. A partially
nanocrystalline structure forms inside the aggregates due to
subsequent calcining. A pure crystalline phase with
crystallites more than 1000 nm in size forms only after
prolonged thermal treatment at approximately 440°C. The
production of a nanocrystalline molybdenum mixed oxide can
thus be accomplished only with difficulty.
It is clear from 0. Ovsiter et al., "Molybdenum oxide based
partial oxidation catalyst Part 3", Journal of Molecular
Catalysis A: Chemical 185 (2002), 291-303, that a molybdenum
mixed oxide does not display well-crystallized particles
after thermal treatment. A crystalline phase, however, was
able to be observed during a conversion of acrolein to
acrylic acid, i.e. a crystallization first takes place during
the oxidation reaction. Such a catalyst thus has a sufficient
activity only after a prolonged reaction period.
A disadvantage of the molybdenum mixed oxides described in
the state of the art is thus that a uniform particle size of
the molybdenum mixed oxides cannot be obtained and a control
of the crystallization, in particular with regard to the
crystallite size, is not possible. The BET surface area of
the molybdenum mixed oxides described in the state of the art
is likewise mostly too small. A small particle size with as
large as possible a BET surface area is desired, in
particular for catalytic uses.
The object of the present invention was thus the provision of
a nanocrystalline molybdenum mixed oxide which, in catalytic
conversions, in particular in a conversion of acrolein to
acrylic acid, has an increased activity and selectivity.

The object is achieved by a method for the production of a
nanocrystalline molybdenum mixed oxide, comprising the steps
of
a) the introduction of a solution, suspension or
slurry which contains a molybdenum starting
compound and at least one further metal-containing
starting compound, selected from a tungsten-
containing and/or vanadium-containing starting
compound, into a reaction chamber by means of a
carrier fluid,
b) a thermal treatment of the solution, suspension or
slurry which contains the molybdenum starting
compound and the at least one further metal-
containing starting compound in a treatment zone by
means of a pulsating flow at a temperature of from
200 to 500°C,
c) the formation of nanocrystalline molybdenum mixed
oxide,
d) the discharge of the nanocrystalline molybdenum
mixed oxide obtained in steps b) and c) from the
reactor.
It was surprisingly found that a uniform particle size of the
molybdenum mixed oxides can be obtained by the method
according to the invention and a control of the
crystallization, in particular with regard to the crystallite
size, is achieved. The BET surface area was likewise able to
be increased compared with the molybdenum mixed oxides known
in the state of the art.
The molybdenum mixed oxide obtained according to the
invention is characterized by a crystallite size in the range
of from 5 nm to 450 nm.

The catalytic activity of a catalyst containing the
molybdenum mixed oxide obtained according to the invention,
in particular in the case of a conversion of acrolein to
acrylic acid, was able to be increased by roughly IS compared
with known conventional catalysts.
By the term "mixed oxide" is meant within the meaning of the
invention a mixed oxide that comprises two or more metals and
constitutes a single chemical compound that can be expressed
with a formula. This is to be distinguished accordingly from
a pure (physical) mixture of several metal oxides.
Preferably a molybdate, particularly preferably ammonium
heptamolybdate tetrahydrate, is used as molybdenum starting
compound. However, it is clear to a person skilled in the art
in this field that other molybdates and molybdenum compounds
known in the state of the art can also be used.
In order to obtain a mixed oxide, at least one further metal-
containing starting compound should be used. Tungstates
and/or vanadates are preferred further compounds according to
the present invention. The further starting compound ammonium
metatungstate and/or ammonium metavanadate is particularly
preferred. A combination of the two last named is most
preferred.
The molybdenum starting compound and the at least one further
metal-containing starting compounds are preferably used
together as solution, suspension or slurry. It is most
preferred if the starting compounds are present in solution,
in particular in aqueous solution. If necessary, the solution
can be heated in order to achieve a complete dissolution of
the starting compounds, in particular in the case of poorly
soluble starting compounds. The solution of the starting
compounds is advantageously heated to > 50°C.
In a particularly preferred embodiment, a solution of
ammonium metatungstate, ammonium heptamolybdate tetrahydrate
and ammonium metavanadate is used in the method according to
the invention.
Prior to or during the introduction into the reaction
chamber, a solution, suspension or slurry which contains at
least one additional metal salt can be added to the solution,
suspension or slurry which contains the molybdenum starting
compound and the at least one further metal-containing
starting compound. The at least one metal salt is preferably
a copper salt or an iron salt or a combination of a copper
and an iron salt.
The addition of a solution, suspension or slurry containing
metal salt to the solution, suspension or slurry which
contains the molybdenum starting compound and the at least
one further metal-containing starting compound brings about a
doping of the resulting molybdenum mixed oxide with the
corresponding metal. Any fine adjustments•for the respective
desired catalytic function of the molybdenum mixed oxide can
thereby be achieved.
In a particularly preferred embodiment, a solution of
ammonium metatungstate, ammonium heptamolybdate tetrahydrate
and ammonium metavanadate, to which a copper-salt solution is
added, is used in the method according to the invention. The
copper salt is preferably copper sulphate or copper acetate.
In a further particularly preferred embodiment, a solution of
ammonium metatungstate, ammonium heptamolybdate tetrahydrate
and ammonium metavanadate, to which a copper-salt and iron-

salt solution is added, is used in the method according to
the invention. The copper salt is preferably copper sulphate
or copper acetate and the iron salt is preferably iron
nitrate.
It was surprisingly found that the method can be carried out
at relatively low temperatures of from 200 to 500°C,
particularly preferably from 250 to 450°C, particularly
preferably from 300 to 400°C. Hitherto, preferred
temperatures of more than 700°C, indeed up to 1400°C, were
known in the state of the art. Quite particularly
surprisingly, it was also found that the crystallization
process of the molybdenum mixed oxide can be controlled in a
targeted manner by the method according to the invention, in
particular the size of the crystallites and the pore-size
distribution of the corresponding molybdenum mixed oxides.
This can further be advantageously influenced by the
residence time in the flame or by the reactor temperature.
The nanocrystalline molybdenum mixed oxide particles that
form are prevented from agglomerating by the pulsating
thermal treatment. Typically, the nanocrystalline particles
are immediately transferred by the stream of hot gas into a
colder zone, where some of the molybdenum mixed oxide
crystallites are obtained with diameters of even less than
2 0 nm.
In the case of the thus-obtainable molybdenum mixed oxide
crystallites, this leads to clearly increased BET surface
areas of > 1 m2/g, particularly preferably 2 to 10 m2/g and
particularly preferably 3 to 7 m2/g. The BET surface area is
determined using the Brunauer, Emmett and Teller method
according to DIN 66132.
In the method according to the invention, suspensions can be
calcined within a very short period, typically within a few

milliseconds, at comparatively lower temperatures than are
usual with methods of the state of the art, without
additional filtration and/or drying steps or without the
addition of additional solvents. The molybdenum mixed oxide
nanocrystallites that form have significantly increased BET
surface areas and thus represent a molybdenum mixed oxide
catalyst with increased reactivity, improved rate of
conversion and improved selectivity, in particular with
regard to a conversion of acrolein to acrylic acid.
The nearly identical residence time of every molybdenum mixed
oxide particle in the homogeneous temperature field created
by the method results in an extremely homogeneous end product
with narrow monomodal particle distribution. A device for
carrying out the method according to the invention in the
production of such monomodal nanocrystalline metal oxide
powders is known for example from DE 101 09 892 Al. Unlike
the device described there and the method disclosed there,
the present method does not, however, require an upstream
evaporation step in which the starting material, i.e. the
molybdenum starting compound, is heated to an evaporation
temperature.
The molybdenum starting compound and the further starting
compounds from which the molybdenum mixed oxides according to
the invention are produced are inserted directly via a
carrier fluid, in particular a carrier gas, preferably an
inert carrier gas, such as for example nitrogen, etc., into
so-called reaction chambers, i.e. into the combustion
chamber. Attached exhaust side to the reaction chamber is a
resonance tube with a flow cross-section which is clearly
reduced compared with the reaction chamber. The floor of the
combustion chamber is equipped with several valves for the
entry of the combustion air into the combustion chamber. The
aerodynamic valves are fluidically and acoustically matched

with the combustion chamber and the resonance tube geometry
such that the pressure waves, created in the combustion
chamber, of the homogeneous "flameless" temperature field
spread pulsating predominantly in the resonance tube. A so-
called Helmholtz resonator forms with pulsating flow with a
pulsation frequency of between 10 and 150 Hz, preferably 30
to 110 Hz.
Material is typically fed into the reaction chamber either
with an injector or with a suitable two-component nozzle or
in a Schenk dispenser.
Preferably, the molybdenum starting compound is introduced
into the reaction chamber in atomized form, with the result
that a fine distribution in the region of the treatment zones
is guaranteed.
After the thermal treatment, the nanocrystalline molybdenum
mixed oxides that form are immediately transferred into a
colder zone of the reaction chamber, if possible by means of
the carrier fluid, with the result that they can be separated
and discharged in the colder zone. The yield of the method
according to the invention is almost 100%, as all of the
product that forms can be discharged from the reactor.
Typically, the method is carried out at a pressure of between
15 and 40 bar.
A subject of the invention is furthermore the nanocrystalline
molybdenum mixed oxide that can be obtained by the method
according to the invention. It was found that the thus-
obtainable nanocrystalline molybdenum oxide preferably has a
crystallite size in the range of from 5 nm to 450 nm,
preferably of from 10 nm to 400 nm, quite particularly
preferably 15 to 250 nm, which, as already stated above, can

preferably be set by the pulsation of the thermal treatment.
The particle size can be determined by XRD or TEM.
Furthermore, molybdenum oxide particles which have a BET
surface area of preferably > 1 nr/g, particularly preferably
2 to 10 nr/g and particularly preferably 3 to 7 nr/g are
obtained by the method according to the invention.
The molybdenum mixed oxide obtained according to the
invention is exceptionally suitable for use as catalyst, for
example in the catalytic conversion of acrolein to acrylic
acid.
Acrylic acid or propenoic acid belongs to the unsaturated
carboxylic acids. Acrylic acid is a colourless chemical
compound, with a pungent, vinegary odour, that can be mixed
with water and is liquid at room temperature. Acrylic acid
has a strong corrosive action and is flammable. Large-scale
industrial production usually takes place by a two-stage
oxidation of propylene with the aid of catalysts. In the
first stage, propylene is converted with air to propenal
(acrolein). The oxidation of propenal to acrylic acid takes
place in the second stage. Its main use is polymerization to
superabsorbent polymers (use e.g. in nappies), acrylate
esters (which are in turn used for the production of
polymers) and as comonomers in the production of polymer
dispersions. The water-soluble polymerisates of acrylic acid
are used as finishes and thickeners as well as coatings for
solid dosage forms and as ointment bases. Polyacrylic acid
ethyl ester has proved its worth as copolymerization partner
for the production of weather-proof elastomers.
A subject of the invention is thus also a catalyst which
contains the molybdenum mixed oxide according to the

invention. The catalyst can be a supported or an unsupported
catalyst (bulk catalyst, extruded catalyst).
In an embodiment of the present invention, the molybdenum
mixed oxide can be processed together with a suitable binder
to an extrudate (tablets, shaped bodies, honeycomb bodies and
the like). Any binder that is familiar to a person skilled in
the art and appears suitable, in particular silicate
materials, aluminium oxide, zirconium compounds, titanium
oxide, as well as their mixtures, and materials such as e.g.
cement, clay, silica/alumina, can be used as binders.
Preferred binders are, among others, pseudoboehmite as well
as siliceous binders such as colloidal silicon oxide or
silica sol.
In preferred developments of the invention, the molybdenum
mixed oxide can furthermore be processed together with other
components, preferably with a binder, particularly preferably
with an organic binder, for example organic glues, polymers,
resins or waxes, to a washcoat which can be applied to a
metallic or ceramic support. Optionally, additional
impregnating steps or calcining steps can take place.
Preferably, the molybdenum mixed oxide obtained according to
the invention is present as coating on a support. A preferred
support material is steatite, steatite spheres are
particularly preferred. The coating is preferably carried out
in a fluidized bed coating device known per se to a person
skilled in the art.
A subject of the invention is also a method for the
conversion of acrolein to acrylic acid, wherein an above-
defined catalyst is used.
In the method, acrolein, preferably with oxygen, steam and
nitrogen, is passed at 200 to 400°C over a bed of the

catalyst according to the invention. An improvement with
regard to acrolein conversion rate, acrylic acid selectivity
and acrylic acid yield is apparent in the method according to
the invention compared with a method which has been carried
out with a catalyst according to the state of the art.
The invention is described in more detail with reference to
the following embodiment examples and the figures, which are
not to be regarded as limitative. The device used corresponds
largely to the device described in DE 101 09 892 Al, with the
difference that the device used for carrying out the method
according to the invention had no preliminary evaporator
stage.
There are shown in:
Figure 1 the XRD spectrum of the molybdenum mixed oxide
according to the invention obtained in Example 6
Figure 2 the XRD spectrum of the doped mixed oxide
according to the invention obtained in Example 7
Embodiment examples:
General
The essential advantages of the preparation with the aid of
the pulsation reactor are the reduction of the overall
preparation time, the small outlay (only the reactor is
needed) and the fact that there is no drying and treatment of
the product. The desired BET surface areas, particle sizes
and also the crystallinity of the material can be varied in
one step by the pulsation reactor.
The following methods were varied for the preparation of the
mixed oxides:
Example 1: MoWV variant 1
Two solutions were produced for the production.
For solution 1, 18 1 dist. H20 was placed in a steel drum and
heated. 487.8 g ammonium metatungstate was added and
dissolved. Once 70°C had been reached, 3300 g ammonium
heptamolybdate tetrahydrate and 546.6 g ammonium
metavandadate were added. Once the components had dissolved
completely, 113.4 g antimony trioxide was added and the
mixture stirred for 1 hour at 95°C. The solution was cooled
to room temperature.
Solution 2 was produced by dissolving 466.8 g copper sulphate
in 2880 ml dist. H20 at room temperature. The two solutions
were mixed at room temperature and stirred for approx. 1 h. A
suspension formed.
The solution was atomized in the pulsation reactor as
follows: after a heating-up period, conditional on the

equipment, of several hours, the suspension was sprayed at
different reactor temperatures (380, 360, 400°C).
Air was used as carrier gas. The BET surface areas of the
obtained molybdenum mixed oxide were between 1 and 4 irr/g.
Example 2: MoWV variant 2
For the production, 11820 ml distilled H20 was introduced.
3150.12 g ammonium heptamolybdate tetraydrate was added to
this and dissolved. Continuous stirring was carried out
during the whole production process.
822.24 g ammonium metatungstate was then added and dissolved.
After subsequent heating to approx. 80°C, 585.6 g ammonium
metavanadate was then added and the mixture heated further to
100°C. This temperature was maintained for 5 hours, then the
solution was cooled to room temperature.
444 g ammonium acetate was then added, also at room
temperature.
Half of the 5 kg batch was doped with iron and copper.
For this, 1.86 g copper acetate and 4.14 g iron nitrate were
dissolved in 120 ml dist. H20 in each case and then added to
the solution.
The solution was heated for 12 h under reflux. A clear,
orange-red solution formed.
This solution was atomized doped and undoped into the
pulsation reactor at 380°C using air as carrier gas. A grey
powder with BET surface areas of 3-4 mz/g formed.
Example 3: MOWV variant 3
11820 ml dist. H20 was placed in a drum. 3150.12 g ammonium
heptamolybdate tetrahydrate was added to this, then heated
and left until it had completely dissolved.
822.24 g ammonium metatungstate was then added and dissolved.
The mixture was then heated to approx. 80°C, then 585.6 g
ammonium metavanadate was added and the mixture heated
further to 100°C. This temperature was maintained for 5 hours
and then cooled to room temperature.
After cooling to room temperature, 444 g ammonium acetate was
added. Continuous stirring was carried out during the whole
production process.
Doping:
The batch was doped with iron and copper. For this, 3.72 g
copper acetate and 8.28 g iron nitrate were dissolved in 240
ml dist. H20 in each case and then added to the solution.
Atomization + results:
The solution was atomized in normal air in the pulsation
reactor.
Solution with doping:
Temperature: 380°C
Colour of the powder: grey/black
BET: 3.2
XRD: Displays main peak at 22
Crystallite size: 210 A
Composition: W 14.7% Theoretical: 9.3

V 6.6% 6.2-
Mo 45.9% 46.9-
Fe Cu 0.15% 3.1
Powder from the filter bags
Temperature: 380°C
Powder: grey/black
BET: 3.3
XRD: Displays main peak at 22
Crystallite size: 201 A
Composition: W 14.6%
V 6.7%
Mo 4 6.9%
Fe 240 ppm
Cu 2.2%
Example 4: MbWV variant 4
Solution 1: 18 litres dist. H20 was placed in a steel drum
and heated. 487.8 g ammonium metatungstate was added and
dissolved. Once the temperature had reached approx. 70°C,
3300 g ammonium heptamolybdate tetraydrate and 546.6 g
ammonium metavandadate were added. Once the components had
dissolved completely, 113.4 g antimony trioxide was added and
the mixture stirred for 1 hour at 95°C. The mixture was then
cooled to room temperature. Continuous stirring was carried
out during the whole production process.
Solution 2: 466.8 g copper sulphate was dissolved in 2880 ml
dist. H2O at room temperature. After cooling solution 1, the
two solutions were mixed and stirred for 1 hour. A black
solution with fine white particles formed.
Atomization + results:
All atomizations were carried out with normal air in the
pulsation reactor.
Powder from the drum
Temperature: 380°C
Powder: grey/black
BET: 1. 0 m2/g
XRD: Displays main peak at 22
Crystallite size: 207 A
Composition W 9.1% Theoretical: 9.3-
V 6.0% 6.2
Mo 45.8% 46.9
Sb 1.8% ' 2.5
Cu 2.2% 3.1
Powder from the filter bags
Temperature: 380°C
Powder: grey/black
BET: 1.5
XRD: Displays main peak at 22
Crystallite size: 197 A
Composition: W 9.2% Theoretical: 9.3%
V 6.1% 6.2%
Mo 46.5% 46.9
Sb 1.8% 2.5:
Cu 2.2% 3.1
Exazsple 5 (coznparlson example)
Example 5 was carried out according to US 6,124,499:
127 g copper(II) acetate monohydrate (Cu content 32.3 wt.- )
was dissolved in 2700 g water (solution I). 860 g ammonium

heptamolybdate tetrahydrate (81.3 wt.-% M0O3) , 143 g ammonium
metavanadate (72.2 wt.-% V2O5) and 126 g ammonium
paratungstate heptahydrate (89.3 wt.-% WO3) were dissolved in
succession in 5500 g water at 95°C (solution II). Solution I
was then stirred all at once into solution II and the aqueous
mixture spray-dried at an outlet temperature of 110°C. The
obtained spray product was kneaded with 0.15 kg water per kg
powder.
The kneaded matter was calcined in a convection oven in an
oxygen/nitrogen mixture. The oxygen content was set such that
the 0: starting concentration was 1.5 vol.-* at the oven
outlet. The kneaded material was first heated to 300°C at a
rate of 10°C/min and then kept at 300°C for 6 h. The mixture
was then heated to 400°C at a heating rate of 10°C/min and
kept at 400°C for 1 h. The catalyst had the composition
Mo12V3W2.2Cu1.6Ok.
The calcined active material was ground down to 0.1 urn to 50
Vim.
Powder: grey/black
BET: 1.0 m2/g
XRD: Displays main peak at 22
Crystallite size: > 960 A
Example 6 (according to the Invention)
Solution 1:
18 litres dist. H20 was placed in a steel drum and heated.
487.8 g ammonium metatungstate was added and dissolved. When
the temperature had reached approx. 70°C,"3300 g ammonium
heptamolybdate tetrahydrate and 546.6 g ammonium
metavandadate were added. Once the components had dissolved
completely, 113.4 g antimony trioxide was added and the
mixture stirred for 1 h at 95°C. The mixture was then allowed
to cool. Continuous stirring was carried out during the whole
production process.
Solution 2:
466.8 g copper sulphate was dissolved in 2880 ml dist. HjO at
room temperature.
After cooling solution 1, the two solutions were mixed and
stirred for 1 hour. A black solution with"fine white
particles formed.
After atomization of the solution/suspension at 380°C in the
pulsation reactor, a powder with the following
characteristics was obtained:
Powder: grey/black
BET: 5-7 m2/g
XRD (see Figure 1): Displays main peak at 22
Crystallite size: 207 A
Example 7 (according to the invention)
11820 ml dist. H20 was placed in a vessel. 3150.12 g ammonium
heptamolybdate tetrahydrate was added to this vessel, then
the heating was started and continued until everything had
completely dissolved.
822.24 g ammonium metatungstate was then added and the
mixture was left until everything had dissolved. The mixture
was then heated to approx. 80°C, then 585.6 g ammonium
metavanadate was added and the mixture heated further to
100°C. This temperature was maintained for 5 hours, followed
by cooling to room temperature.
After cooling to room temperature, 444 g ammonium acetate was
added. Continuous stirring was carried out during the whole
production process.
Doping:
The batch was doped with iron and copper. For this, 3.72 g
copper acetate and 8.28 g iron nitrate were dissolved in 240
ml dist. H20 in each case and then added to the solution.
After atomization of the solution at 380CC in the pulsation
reactor, a powder with the following characteristics was
obtained:
Colour of the powder:
BET:
XRD (see Figure 2):
Crystallite size:
grey/black
6
Displays main peak at 22
210 A
Example 8 (production of coated catalysts)

A fluidized bed coating device was used to carry out the
coating.
The steatite spheres were coated with the various mixed oxide
active materials from Examples 5 to 7 under the following
conditions:
22.22 g of the powder was weighed into a measuring cylinder,
made into a slurry with 500 ml dist. H20. The resulting
suspension was stirred intensively. 8.89 g binder was then
added and the mixture stirred for 1 h on a magnetic stirrer.
The "coating" of the produced suspension took place on a
weighed-in sample of 80 g steatite spheres of (2-4 mm) ,
wherein the active material charge was 20% (50 g powder per
200 g steatite spheres) . The catalyst was then dried in air
at 110°C.
Example 9 (determination of the catalytic performance data of
the catalysts)
21 g catalyst (i.e. the above-described coated steatite
spheres), diluted with 350 g steatite spheres with a diameter
of 4.5 mm to avoid hotspots, was poured into a 120-cm long
reaction tube with an internal diameter of 24.8 mm to a
length of 105 cm. The reaction tube was in a liquid salt bath
which was able to be heated to temperatures of up to 500°C.
In the catalyst bed there was a 3 mm protective tube with an
integrated thermocouple via which the catalyst temperature
over the complete catalyst combination was able to be
displayed.
To determine the catalytic performance data, acrolein was put
into the gas phase by means of a saturator. An air-inert gas
mixture was passed through the saturator in such a way and

the thermostat temperature of the saturator set such that an
acrolein content of 5 vol.-% in the feed gas resulted. The
reactor feed consisted of a mixture of 7 vol.-% 0, 10 vol.--
steam and the remainder N;. The acrolein charge was 150 Nl/lh
at most.
The acrolein conversion rate and the acrylic acid selectivity
were determined at an average catalyst temperature of 250°C.
The results of the tests with the catalysts which contain the
active material according to the examples named in the table
are listed in Table 1.
The ascertained results demonstrate an improvement of the
catalysts according to the invention with regard to acrolein
conversion rate, acrylic acid selectivity and acrylic acid
yield compared with a catalyst according to the state of the
art.
WE CLAIM
1. Method for the production of a nanocrystalline
molybdenum mixed oxide, comprising the steps of
a) the introduction of a solution, suspension or
slurry which contains a molybdenum starting
compound and at least one further metal-containing
starting compound, selected from a tungsten-
containing and/or vanadium-containing starting
compound, into a reaction chamber by means of a
carrier fluid,
b) a thermal treatment of the solution, suspension or
slurry which contains the molybdenum starting
compound and the at least one further metal-
containing starting compound in a treatment zone by
means of a pulsating flow at a temperature of from
200 to 500°C,
c) the formation of nanocrystalline molybdenum mixed
oxide,
d) the discharge of the nanocrystalline molybdenum
mixed oxide obtained in steps b) and c) from the
reactor.
2. Method according to claim 1, characterized in that the
molybdenum starting compound is ammonium heptamolybdate
tetrahydrate.
3. Method according to claim 1 or 2, characterized in that
the at least one further metal-containing starting
compound is ammonium metatungstate and/or ammonium
metavanadate.
4. Method according to one of claims 1 to 3, characterized
in that the carrier fluid is a gas.

5. Method according to one of claims 1 to 4, characterized
in that, prior to or during the introduction into the
reaction chamber, a solution, suspension or slurry of a
metal salt is added to the solution, suspension or
slurry which contains the molybdenum starting compound
and the at least one further metal-containing starting
compound.
6. Method according to claim 4, characterized in that the
metal salt is a copper and/or iron salt.
7. Nanocrystalline molybdenum mixed oxide that can be
obtained by a method according to one of claims 1 to 6.
8. Nanocrystalline molybdenum mixed oxide according to
claim 7, characterized in that its crystallite size lies
in the range of from 10 nm to 450 nm.
9. Nanocrystalline molybdenum mixed oxide according to
claim 7 or 8, characterized in that it has a BET surface
area of from 1 to 10 m2/g.
10. Nanocrystalline molybdenum mixed oxide according to one
of claims 7 to 9, characterized in that the molybdenum
mixed oxide is doped.
11. Nanocrystalline molybdenum mixed oxide according to one
of claims 7 to 10, characterized in that the molybdenum
mixed oxide is doped with Cu and/or Fe.
12. Use of a nanocrystalline molybdenum mixed oxide
according to one of claims 7 to 9 as catalyst for
chemical conversions.
13. Use according to claim 12 for the conversion of acrolein
to acrylic acid.
14. Catalyst, containing the nanocrystalline molybdenum
mixed oxide according to one of claims 7 to 11.
15. Catalyst according to claim 14, characterized in that
the molybdenum mixed oxide is present as coating on a
support.
16. Catalyst according to claim 14 or 15, characterized in
that the catalyst comprises a binder.
17. Method for the conversion of acrolein to acrylic acid,
wherein a catalyst according to one of claims 14 to 16
is used.

The invention relates to a method for the production of a
nanocrystalline molybdenum mixed oxide, the use of the
molybdenum mixed oxide as catalyst for chemical conversions, in
particular for a conversion of acrolein to acrylic acid as well
as a catalyst which contains the molybdenum mixed oxide.

Documents:

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Patent Number

270249

Indian Patent Application Number

3499/KOLNP/2010

PG Journal Number

50/2015

Publication Date

11-Dec-2015

Grant Date

04-Dec-2015

Date of Filing

22-Sep-2010

Name of Patentee

SUD-CHEMIE IP GMBH & CO KG

Applicant Address

LENBACHPLATZ 6, 80333 MUNICH, GERMANY

Inventors:

#	Inventor's Name	Inventor's Address
1	MESTL, GERHARD	EBERESCHENSTR. 71, 80935 MÜNCHEN, GERMANY
2	WÖLK, HANS-JÖRG	AM SALZSTADEL 7, 83022 ROSENHEIM, GERMANY
3	HAGEMEYER, ALFRED	FLURSTR. 7, 83043 BAD AIBLING, GERMANY
4	NEUMANN SILVIA	DAHLIENWEG 15, 83109 BROßKAROLINENFELD, GERMANY

PCT International Classification Number

C01G 39/00

PCT International Application Number

PCT/EP2009/002476

PCT International Filing date

2009-04-03

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10 2008 017 311.8	2008-04-04	Germany