EP2271424A2

EP2271424A2 - Shell catalyst containing a multi-metal oxide containing a molybdenum

Info

Publication number: EP2271424A2
Application number: EP09730114A
Authority: EP
Inventors: Alexander Czaja; Martin Kraus
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2008-04-09
Filing date: 2009-04-08
Publication date: 2011-01-12
Also published as: WO2009124974A2; CN101990459A; US20110034326A1; CA2719532A1; US8461074B2; JP2011516256A; WO2009124974A3; TW200948474A

Abstract

The invention relates to a shell catalyst comprising: (a) a support body, (b) a first layer containing a molybdenum oxide or a precursor compound forming molybdenum oxide, (c) a second layer containing a multi-metal oxide containing a molybdenum and at least one other metal. Preferably, the molybdenum oxide of the first layer is MoO3 and the multi-metal oxide of the second layer is a multi-metal oxide represented by general formula (Il): Mo12BiaCrbX1 cFedX2 eX3 fOy.

Description

Shell catalysts containing a molybdenum-containing multimetal

description

The present invention relates to coated catalysts comprising a catalytically active, molybdenum-containing multimetal.

Processes for the production of coated catalysts of the aforementioned type are known, for example from WO 95/11081, WO 2004/108267, WO 2004/108284, US-A 2006/0205978, EP-A 714700 and DE-A 102005010645. The active Mass is a molybdenum-containing multimetal. The term multimetal oxide expresses the fact that the active mass in addition to molybdenum and oxygen still contains at least one other chemical element.

Catalysts of the aforementioned type are suitable, for example, for the catalysis of the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid.

It is known from DE-A 10350822 and DE-A 102004025445 that the heterogeneously catalyzed gas phase partial oxidation of acrolein to acrylic acid can be operated essentially continuously over a longer period of time on one and the same fixed catalyst bed. However, the activity of the fixed catalyst bed deteriorates during operation.

In order to be able to operate the fixed catalyst bed, the replacement of which is comparatively complicated and costly, as long as possible, attempts are made in the prior art to counteract the aging process of the fixed catalyst bed in various ways.

EP-A 990636 and EP-A 1106598 suggest that the reduction in the activity of the fixed catalyst bed is largely compensated for by the fact that the temperature of the fixed catalyst bed is gradually increased in the course of the operating time under otherwise largely constant operating conditions in order to reduce the acrolein conversion once Passage of the reaction gas mixture through the fixed catalyst bed substantially maintain. A disadvantage of this procedure is that as the temperature of the fixed catalyst bed increases, the aging process accelerates progressively. Finally, the catalyst bed must be completely replaced.

DE-A 102004025445 proposes the long-term operation of the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid, the deactivation of the catalyst. Counteract catalyst fixed bed by the fact that the working pressure in the gas phase is increasingly increased with increasing service life of the fixed catalyst bed. A disadvantage of this procedure is that with increasing working pressure in the heterogeneously catalyzed partial gas phase oxidation increased compression powers are required gene.

EP-A 614872 recommends prolonging the service life of the fixed catalyst bed by interrupting the partial oxidation process after several years of operation of the fixed catalyst bed and passing a regeneration gas mixture of oxygen, water vapor and inert gas through the catalyst catalyst bed at elevated temperature, followed by partial oxidation continues.

The above-described prior art methods for extending the service life of the fixed catalyst bed have in common that they do not preventively counteract the deactivation of the fixed catalyst bed, but rather try to counteract the consequences of deactivation which has already taken place.

EP-A 0 630 879 describes a process for the catalytic oxidation of propene, isobutene or tert-butanol over a multimetal oxide catalyst comprising molybdenum, bismuth and iron, in the presence of a molybdenum oxide which is essentially catalytically inactive. The presence of the molybdenum oxide inhibits the deactivation of the multimetal oxide catalyst. The molybdenum oxide can be present in the form of separate molybdenum oxide particles, optionally on a support, in admixture with particles of the multimetal oxide catalyst. It is also possible to prepare a mixture of pulverulent molybdenum oxide and pulverulent multimetal oxide catalyst and to extrude the mixture into shaped catalyst bodies or to apply it to a support.

German patent application DE 10 2007 010 422 describes a deactivation of shell catalysts for the heterogeneously catalyzed partial gas phase oxidation of acrolein to acrylic acid, the active composition of which is a finely divided multi-element oxide containing Mo and V applied to a support body. that the catalytically active material from the Mo and V-containing multimetal oxide, an oxide of molybdenum or a compound fertilize the molybdenum, from which forms an oxide of molybdenum admixed. The shell catalyst is coated with a mixture of molybdenum oxide or the precursor compound and the multimetal oxide. The object of the invention is to provide catalysts based on molybdenum-containing multi-metal oxides which have improved deactivation behavior.

The problem is solved by a shell catalyst, comprising

(a) a carrier,

(b) a first layer containing molybdenum oxide or a precursor compound forming molybdenum oxide, (c) a second layer containing a molybdenum and at least one further metal-containing catalytically active multimetal oxide.

The object is further achieved by a process for the preparation of the coated catalysts according to the invention, in which applying a first layer of a molybdenum oxide or a precursor compound which forms molybdenum oxide on a carrier body by means of a binder, optionally drying the coated with the first layer carrier body and calcined, and applied to the first layer by means of a binder, a second layer of a molybdenum-containing multimetal, and drying and calcining the coated with the first and second layer carrier body.

The object is further achieved by the use of the coated catalysts according to the invention in processes for the catalytical gas-phase oxidation of organic compounds.

The first layer may comprise a molybdenum oxide or a precursor compound which forms molybdenum oxide. The precursor compound is a compound of molybdenum from which an oxide of molybdenum forms under the action of elevated temperature and in the presence of molecular oxygen. The action of the elevated temperature and of the molecular oxygen can take place following the application of the precursor compound to the surface of the carrier body. For this purpose, a thermal treatment z. B. under an oxygen or air atmosphere.

Examples of suitable precursor compounds other than an oxide of molybdenum include ammonium molybdate [(NH ₄ J ₂ MoO ₄ ] and ammonium polymolybdate such as ammonium heptamolybdate tetrahydrate [(NH ₄ J ₆ Mo ₇ O ₂₄ • 4 H ₂ O]. Another example is molybdenum oxide hydrate (MoO ₃ · xH ₂ O), but molybdenum hydroxides are also suitable precursor compounds of this type. The conversion of the precursor compound into an oxide of molybdenum by the action of heat and oxygen can also be carried out only during the use of the catalyst in the catalytic gas phase oxidation.

However, the first layer preferably already contains an oxide of molybdenum. This is understood as meaning a substance which consists of ≥98% by weight, preferably ≥99% by weight and more preferably ≥99.9% by weight and more, only of Mo and O. Particularly preferred molybdenum oxide is molybdenum trioxide (MoO ₃ ).

Additional suitable molybdenum oxides are, for example Mo ₁₈ O _52, Mo ₈ O ₂₃ and Mo ₄ O ₁₁ (see, e.g., Surface ^Sc;.. Ence 292 (1993) 261-6, or J. Solid State Chem 124 (1996) 104th ).

In general, the specific surface area 0 _{M of} a suitable molybdenum oxide is ≦ 10 ² m ² / g, preferably ≦ 5 m ² / g and particularly preferably ≦ 2 m ² / g. In general, however, the specific surface area 0 _{M will} be ≥ 0.01 m ² / g, frequently ≥ 0.05 m ² / g and in many cases 0.1 m ² / g. The specific surface area is understood to mean the BET surface area (determined by gas adsorption (N ₂ ) according to Brunauer-Emmet-Teller (BET)). The above statements regarding O _M apply in particular when the finely divided molybdenum oxide is MoO ₃ . The advantageousness of a low value for O _M is due to the fact that a molybdenum oxide with a low value for O _M is largely inert in the context of an oxidative alkane dehydrogenation.

Particle diameter distributions and particle diameters d _x taken from them (eg d ₁₀ , or d ₅₀ , or d ₉₀ ) refer to determinations according to ISO 13320 with the Malvern Mastersizer S laser diffraction spectrometer (Malvern Instruments, Worcestshire WR 14 1AT, United Kingdom). The particle diameter d _x indicated as the measurement result is defined such that X% of the total particle volume consists of particles with this or a smaller diameter.

For the preparation of the catalysts according to the invention, precursor compounds or molybdenum oxides, in particular MoO _3, are generally used for which 0.1 μm ≦ d ₅₀ ≦ 800 μm, preferably 0.5 μm ≦ d ₅₀ ≦ 600 μm, particularly preferably 0.75 μm ≦ d ₅₀ ≤400 μm, and most preferably 1 μm ≤ d ₅₀ ≤ 200 μm. In principle, the grain size of the precursor compound or the molybdenum oxide (eg MoO ₃ ) is adapted to the desired thickness D _{A of} the first layer on the surface of the carrier body. In general, d is ₅₀ ≤ D _A, preferably ≤0,75 • D _A, particularly preferably ≤ 0.5 • D _A and very particularly preferably ≤ 0.3 • D _A. Normalerwei- However, d _{50 will} be ≥ 0.001 • D _A , or> 0.01 • D _A , often ≥ 0.05 • D _A and often> 0.1 • D _A.

In principle, a suitable molybdenum oxide (eg MoO ₃ ) can be produced from a precursor compound containing another Mo. For this purpose, z. B. of ammonium heptamolybdate tetrahydrate [(NH ₄ ) _B Mo ₇ O ₂₄ • 4 H ₂ O] are assumed. By z. B. 3 hours of thermal treatment at 350 ⁰ C in likewise a temperature of 350 ⁰ C having air flow this is converted into MoO ₃ . The grain size of the MoO ₃ can be adjusted as required by appropriate grinding and sieving. Similarly, the specific surface area of the MoO ₃ can be adjusted as desired. With increasing duration of the thermal treatment and / or increase in the temperature of the thermal treatment (after MoO _{3 has been formed} under inert gas or under a molecular oxygen-containing gas atmosphere, eg air), the specific surface area decreases.

After the formation of MoO ₃ at 350 ⁰ C is usually a A to 8 hours of thermal treatment at 550 to 650 ⁰ C in a corresponding temperature having air flow sufficient to the specific surface O _M of MoO ₃ to a value of ≤ 2 m ² / g.

However, it is also possible to use commercial molybdenum oxides. For example, for the process according to the invention MoO ₃ is suitable for the Climax Molybdenum Marketing Corporation (Phoenix, USA), which has a Mo content of 66.60% by weight and a specific surface O _M of 3.7 m ² / g (trade name : "Pure Mooney Oxide Crystalline POC").

In general, the aforementioned MoO ₃ additionally has the following foreign constituent specification: Na ≦ 8 ppm by weight, K <29 ppm by weight, Fe ≦ 4 ppm by weight, Pb ≦ 1 ppm by weight, Al ≦ 4% by weight ppm, Cr ≤ 2 ppm by weight, Ca ≤ 2 ppm by weight, Cu ≤ 2 ppm by weight, Mg ≤ 5 ppm by weight, Ni ≤ 2 ppm by weight, Si ≤ 5% by weight. ppm, Sn ≦ 1 ppm by weight, and Ti ≦ 2 ppm by weight.

However, MoO ₃ from Climax Molybdenum Marketing Corporation of the "POS" type of trade can also be used according to the invention Alternatively, MoO _{3 from} the company HC Starck, D-38615 Goslar can be used for the process according to the invention as commercial MoO ₃ (trade name: "Molybdenum Trioxide I"). This has a specific surface O _M of 1 m ² / g. The Mo content of this MoO ₃ is 66.6 wt .-%. This has the following foreign component specification: NH ₄ ≦ 0.01% by weight, Al <10 ppm by weight, Ca <5 ppm by weight, Co ≦ 10 ppm by weight, Cr <5 Ppm by weight, Cu ≦ 5 ppm by weight, Fe ≦ 10 ppm by weight, K ≦ 80 ppm by weight, Mg ≦ 5 ppm by weight Mn <10 ppm by weight, Na <20% by weight. ppm, Ni ≦ 5 wt ppm, P <10 wt ppm, Pb <10 wt ppm, Si <10 wt ppm, Sn <10 wt ppm, Ti ≤ 5 wt ppm, V <10 wt ppm, Zn ≤ 10 wt ppm, and Zr ≤ 10 wt ppm.

However, it is also possible to use "Molybdenum Trioxide" of the "II" types from HC Starck, Incidentally, MoO _{3 from} the following manufacturers can also be used:

- Metal-Tech.-Ltd. (Israel), purity> 98% by weight, O _M = 1.1 m ² / g; Guill Chemical (Texas, USA), 65.76 wt.% Mo, O _M = 1.2 m ² / g;

Nanjing Chemical Industries (China), 66.6 wt% Mo, O _M = 0.8 m ² / g;

Kankal Exports (India), purity> 99% by weight, O _M = 1.7 m ² / g;

- Taiyo Koko Co., Ltd. (Japan), purity ≥ 99.7 wt%, O _M = 1.6 m ² / g;

- Anhui Chizhou Huangshanling Lead and Zinc Mine (China), purity ≥ 99.7 wt .-%, 66.5 wt .-% Mo, O _M = 0.3 m ² / g;

- CCI MoIy BV (Netherlands), purity> 99.5 wt .-%,> 66 wt .-% Mo, O _M = 2.5 m ² / g.

The catalytically active, molybdenum-containing multimetal oxide may be, for example, a Mo and V-containing multimetal oxide of the general formula (I),

Mθ ₁₂ V _a X ¹ _b X ² _c X ³ dX ⁴ eX ⁵ fX ⁶ g ON (I),

in which the variables have the following meaning: X ¹ = W, Nb, Ta, Cr and / or Ce,

X ² = Cu, Ni, Co, Fe, Mn and / or Zn,

X ³ = Sb and / or Bi,

X ⁴ = one or more alkali metals (Li, Na, K, Rb, Cs) and / or H,

X ⁵ = one or more alkaline earth metals (Mg, Ca, Sr, Ba), X ⁶ = Si, Al, Ti and / or Zr, a = 1 to 6, b = 0.2 to 4, c = 0 to 18, preferably 0.5 to 18, d = 0 to 40, e = 0 to 2, f = 0 to 4, g = 0 to 40 and n = a number determined by the valency and frequency of the elements other than oxygen in I. becomes. Such molybdenum and vanadium-containing multimetal oxides are known as catalysts for the selective gas phase oxidation of propene to acrolein.

The catalytically active molybdenum-containing multimetal oxide is preferably a multimetal oxide of the general formula II

Mo ₁₂ Bi _a Cr _b X ¹ _c Fe _d X ² _e X ³ _f O _y (II)

With

X ¹ = Co and / or Ni,

X ² = Si and / or Al,

X ³ = Li, Na, K, Cs and / or Rb, 0.2 ≤ a ≤ 1,

0 ≤ b ≤ 2

2 <c <10,

0.5 <d <10,

0 <e <10, 0 <f <0.5 and y = a number determined on the assumption of charge neutrality by the valency and frequency of the elements other than oxygen in Il.

Preference is given to those shell catalysts whose catalytically active oxide material has only Co as X ¹ . Preferred X ² is Si and X ³ is preferably K, Na and / or Cs, more preferably X ³ = K.

The stoichiometric coefficient a is preferably 0.4 ≦ a ≦ 1, more preferably 0.4 ≦ a <0.95. The stoichiometric coefficient b is preferably in the range 0.1 ≦ b ≦ 2, and particularly preferably in the range 0.1 ≦ b ≦ 1. The stoichiometric coefficient c is preferably in the range 4 ≦ c ≦ 8, and particularly preferably in the range 6 ≦ The value for the variable d is advantageously in the range 1 ≤ d ≤ 5 and with particular advantage in the range 2 ≤ d ≤ 4. The stoichiometric coefficient f is expediently> 0. Preferably, 0.01 ≤ f ≤ 0 , 5 and more preferably 0.05 ≤ f ≤ 0.2.

The value for the stoichiometric coefficient of the oxygen y results from the valence and frequency of the cations under the assumption of charge neutrality. Coated catalysts according to the invention with catalytically active oxide whose molar ratio of Co / Ni is at least 2: 1, preferably at least 3: 1 and more preferably at least 4: 1. The best is only Co.

Such molybdenum-containing multimetal oxides are not only suitable for the selective gas phase oxidation of propene to acrolein, but also for the partial gas phase oxidation of other alkenes, alkanes, alkanones or alkanols to alpha, beta-unsaturated aldehydes and / or carboxylic acids. Examples include the preparation of methacrolein and methacrylic acid from isobutene, isobutane, tert-butanol or tert-butyl methyl ether.

Preferred gas phase oxidations for which the coated catalysts according to the invention are used are oxidative dehydrogenations of alkenes to 1,3-dienes, in particular of 1-butene and / or 2-butene to 1,3-butadiene.

According to the invention to be used in finely divided Mo multimetal oxides containing are obtainable in principle that one of the starting compounds of the elemental constituents of the catalytically active oxide material produces an intimate dry mixture and treating the intimate dry blend at a temperature of 150 to 350 ⁰ C thermally.

To prepare such and other suitable finely divided multimetal oxide masses, starting from known starting compounds of the elemental constituents of the desired multimetal oxide composition in the respective stoichiometric ratio is started, and from these produces a very intimate, preferably finely divided dry mixture, which then undergoes thermal treatment is subjected. In this case, the sources can either already be oxides, or those compounds which can be converted into oxides by heating in the presence of oxygen. In addition to the oxides, therefore, suitable starting compounds are, in particular, halides, nitrates, formates, oxalates, acetates, carbonates or hydroxides.

Suitable starting compounds of Mo are also its oxo compounds (lybdate) or derived from these acids.

Suitable starting compounds of Bi, Fe and Co are in particular their nitrates.

The intimate mixing of the starting compounds can in principle be carried out in dry or in the form of aqueous solutions or suspensions. Preferably, the intimate mixing takes place in the form of aqueous solutions or aqueous suspensions. Particularly intimate dry mixtures are obtained in the described mixing process when starting exclusively from sources and starting compounds present in dissolved form. The solvent used is preferably water. Subsequently, the aqueous mass (solution or suspension) is dried and the resulting intimate dry mixture optionally directly thermally treated. Preferably, the drying process is carried out by spray drying (the outlet temperatures are generally 100 to 150 ⁰ C) and immediately after the completion of the aqueous solution or suspension.

If the resulting powder for immediate further processing often proves to be too finely divided, it is expediently kneaded with the addition of water. In many cases, the addition of a lower organic carboxylic acid (eg acetic acid) proves advantageous during kneading. Typical additional amounts are from 5 to 10 wt .-%, based on the powder mass. The resulting plasticine is then suitably shaped into strands, these are thermally treated as already described and then ground to a finely divided powder.

Support materials suitable for shell-type catalysts obtainable according to the invention are e.g. porous or preferably non-porous aluminum oxides, silicon dioxide, zirconium oxide, silicon carbide or silicates such as magnesium or aluminum silicate (for example C 220 steatite from CeramTec). The materials of the carrier bodies are chemically inert.

The carrier bodies may be regularly or irregularly shaped, with regularly shaped carrier bodies having a distinct surface roughness, e.g. B. balls, cylinders or hollow cylinder with chippings, are preferred. Their longest extent is usually 1 to 10 mm.

The support materials may be porous or non-porous. The carrier material is preferably non-porous (total volume of the pores based on the volume of the carrier body preferably ≦ 1% by volume). An increased surface roughness of the carrier body usually requires an increased adhesive strength of the applied shell of the first and second layers.

Preferably, the surface roughness R _{z of} the carrier body is in the range of 30 to 100 μm, preferably 50 to 70 μm (determined according to DIN 4768 Part 1 with a "Hommel tester for DIN-ISO surface measurement quantities" from Hommelwerke). Surface-roughened carrier bodies from CeramTec made of steatite C 220 are particularly preferred.

Particularly suitable according to the invention is the use of substantially nonporous, surface-rough, spherical supports made of steatite (eg steatite of the C 220 type from CeramTec) whose diameter is 1 to 8 mm, preferably 2 to 6 mm, particularly preferably 2 to 3 or 4 to 5 mm. However, it is also suitable to use cylinders as support bodies whose length is 2 to 10 mm and whose outer diameter is 4 to 10 mm. In addition, in the case of rings as a carrier body, the wall thickness is usually 1 to 4 mm. Preferably to be used annular support body have a length of 2 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. Particularly suitable are rings of geometry 7 mm x 3 mm x 4 mm (outer diameter x length x inner diameter) as a carrier body.

The shell thickness D _{A of} the applied on the support body first layer of molybdenum oxide or the precursor compound is usually at 5 to 1000 microns. Preferred are 10 to 500 microns, more preferably 20 to 250 microns and most preferably 30 to 150 microns.

The shell thickness D _{8 of} the second layer of a molybdenum-containing multimetal oxide material applied to the first layer is generally from 5 to 1000 μm. Preferred are 10 to 500 microns, more preferably 20 to 250 microns and most preferably 30 to 150 microns.

The grain size (fineness) of the Mo-containing finely divided multimetal oxide is adjusted in the same way as the grain size of the molybdenum oxide or the precursor compound to the desired shell thickness D _B. All statements made with regard to the longitudinal expansion d _{L of} the molybdenum oxide or of the precursor compound therefore apply correspondingly to the longitudinal expansion d _{L of} the finely divided Mo-containing multimetal oxide.

The mass ratio of the second layer of multimetal oxide to the first layer of molybdenum oxide in the final calcined catalyst is generally from 100: 1 to 1: 1, preferably from 50: 1 to 5: 1.

The application of the finely divided masses (molybdenum oxide or precursor compound or molybdenum-containing multimetal oxide) to the surface of the carrier body can in accordance with the methods described in the prior art, for example as described in US-A 2006/0205978 and EP-A 0 714 700.

In general, the finely divided masses are applied to the surface of the carrier body or to the surface of the first layer by means of a liquid binder. As a liquid binder z. As water, an organic solvent or a solution of an organic substance (eg., An organic solvent) in water or in an organic solvent into consideration.

Examples which may be mentioned as organic binders mono- or polyhydric organic alcohols such. As ethylene glycol, 1, 4-butanediol, 1, 6-hexanediol or glycerol, mono- or polyvalent organic carboxylic acids such as propionic acid, oxalic acid, malonic acid, glutaric acid or maleic acid, amino alcohols such as ethanolamine or diethanolamine and mono- or polyhydric organic amides such formamide. As in water, in an organic liquid or in a mixture of water and an organic liquid soluble organic binder promoters are, for. As monosaccharides and oligosaccharides such as glucose, fructose, sucrose and lactose suitable.

The liquid binder used is particularly advantageously a solution consisting of 20 to 98% by weight of water and 2 to 80% by weight of an organic compound. Preferably, the organic content of the aforementioned liquid binders is 2 to 50 and more preferably 5 to 20 wt .-%.

Preferably, generally are those organic binders or binder components whose boiling point or sublimation temperature at atmospheric pressure (1 atm) ≥ 100 ⁰ C, preferably ≥ 150 ⁰ C. At very low atmospheric pressure, the boiling point or sublimation point of such organic binders or binder constituents is at the same time below the highest calcination temperature used in the preparation of the finely divided multimetal oxide containing the Mo moieties. Ub SHORT- is this highest calcination temperature at ≤ 600 ⁰ C, often at ≤ 500 ⁰ C or at <400 ⁰ C, sometimes even at <300 ⁰ C.

Particularly preferred liquid binders are solutions which consist of 20 to 98% by weight of water and 2 to 80% by weight of glycerol. The proportion of glycerol in these aqueous solutions is preferably 2 to 50% by weight and more preferably 5 to 20% by weight.

The application of the molybdenum oxide or the precursor compound and the Mo-containing finely divided multimetal oxide can be carried out in such a way that the finely divided ge substance disperses dispersed in the liquid binder and sprayed the resulting suspension to moving and optionally hot carrier body, as described in DE-A 1642921, DE-A 2106796 and DE-A 2626887.

After completion of spraying, as described in DE-A 2909670, by passing hot air, the moisture content of the resulting coated catalysts can be reduced.

After application of the first layer of molybdenum oxide or the precursor compound, the coated carrier body can be dried and calcined. Subsequently, in the same manner, the second layer of Mo-containing multimetal oxide is applied to the first layer, dried and calcined. However, it is also possible to apply the second layer directly to the first layer in the manner described above without drying and calcining beforehand, and drying and calcining first the carrier body coated with first and second layers. Preferably, after application of the first layer, the coated carrier body is dried.

Preferably, however, the carrier body is first moistened with the liquid binder, and subsequently the finely divided mass (molybdenum oxide or precursor compound) is applied to the surface of the carrier body moistened with the binder by rolling the moistened carrier body in the finely divided mass. To achieve the desired layer thickness, the method described above is preferably repeated several times, i. H. the base-coated carrier body is moistened again and then coated by contact with dry finely divided mass.

After application of the first layer of molybdenum oxide or the precursor compound, the coated carrier body can be dried and calcined. Subsequently, the second layer of multimetal oxide is applied in the same manner, and dried the first and second layer coated carrier body and calcined.

In general, the coated carrier body is calcined at a temperature of 150 to 600 ⁰ C, preferably from 270 to 500 ⁰ C. The calcination time is generally 2 to 24 hours, preferably 5 to 20 hours. The calcination is carried out in an oxygen-containing atmosphere, preferably air and / or lean air. In one embodiment of the invention, the calcination is carried out according to a temperature program in which a total of 2 to 10 h at temperatures between 150 and 350 ⁰ C, preferably calcined 200 to 300 ⁰ C and then calcined at temperatures between 350 and 550 ⁰ C, preferably 400 to 500 ⁰ C calcined. For a calcination of the first layer before applying the second layer, a calcining temperature of about 300 ⁰ C is sufficient, wherein after application of the second layer is preferably calcined at at least 400 ⁰ C.

The molybdenum oxide, the molybdenum oxide-forming precursor compound and the catalytically active molybdenum-containing multimetal oxide composition may each contain a pore-forming agent. This may be contained in the finely divided masses or added to the liquid binder. Suitable pore formers are, for example, malonic acid, melamine, nonylphenol ethoxylate, stearic acid, glucose, starch, fumaric acid and succinic acid. Preference is given to stearic acid, nonylphenol ethoxylate and melamine. Pore formers are generally present in amounts of from 1 to 40% by weight, preferably from 1 to 20% by weight, in the masses applied to the carrier body, these details being based on the sum of all components of the respective layer (molybdenum oxide or precursor compound, Pore-forming agent, binder or multimetal oxide, pore-forming agent, binder).

For carrying out the process according to the invention on an industrial scale, it is advisable to use the process disclosed in DE-A 2909671, but preferably using the binders recommended in EP-A 714700. In other words, the carrier bodies to be coated are filled into a preferably inclined (the angle of inclination is generally 30 to 90 °) rotating rotary container (eg turntable or coating pan). The rotating rotary container guides the in particular spherical, cylindrical or hollow-cylindrical carrier bodies under two metering devices arranged at a certain distance one after the other. The first of the two metering devices is expediently a nozzle, through which the carrier bodies rolling in the rotating turntable are sprayed with the liquid binder to be used and moistened in a controlled manner. The second metering device is located outside of the atomizing cone of the sprayed liquid binder and serves to supply the finely divided mass, for example via a vibrating trough. The controlled moistened carrier balls take up the supplied active mass powder, which compacts by the rolling movement on the outer surface of the cylindrical or spherical carrier body to form a coherent shell.

If necessary, the support body coated in this way in the course of the subsequent revolution, in turn, passes through the spray nozzle, is moisturized in a controlled manner in order to receive a further layer of finely divided mass in the course of the further movement can, etc. An intermediate drying is usually not required. The removal of the liquid binder used in the invention may, partially or completely, by final heat, for. B. by the action of hot gases such as N ₂ or air done.

A particular advantage of the above-described embodiment of the method according to the invention is that shell catalysts with shells consisting of two or more different masses can be produced in one operation. Remarkably, the method according to the invention in this case brings about both a fully satisfactory adhesion of the successive layers to one another, as well as the base layer on the surface of the carrier body. This also applies in the case of annular carrier bodies.

The present invention also provides for the use of the shell catalysts according to the invention in processes for the catalytic gas-phase oxidation of organic compounds, for example from propene to acrolein, from acrolein to acrylic acid, from isobutene or tert-butanol to methacrolein or methacrylic acid, or in processes for oxidative Dehydrogenation of olefins to serve. Of the uses described above, the use of the coated catalysts in processes for the oxidative dehydrogenation of olefins to dienes, especially 1-butene and / or 2-butene to butadiene, is particularly preferred.

The invention is further illustrated by the following examples.

Examples

Example 1 Preparation of precursor mass A of stoichiometry

Mθi2Cθ7Fe3Ko, o ₈ Bio, 6Cro, 5

Solution A:

In a 10 l stainless steel pot 3200 g of water were submitted. With stirring by means of an anchor stirrer, 4.9 g of a KOH solution (32 wt.% KOH) was added to the initially charged water. The solution was heated to 60 ⁰ C. Now, 1066 g of an ammonium heptamolybdate solution ((NH ₄ ) ₆ Mo ₇ O ₂₄ * 4H ₂ O, 54% by weight Mo) were added in portions over a period of 10 minutes. The suspension obtained was stirred for a further 10 minutes. Solution B:

In a 5 liter stainless steel pot 1663 g of a cobalt were (II) nitrate solution introduced (12.4 wt .-% Co) and with stirring (anchor stirrer) was heated to 60 ⁰ C. Now, 616 g of a Fe (III) nitrate solution (13.6% by weight of Fe) was added portionwise while maintaining the temperature over a period of 10 minutes. The resulting solution was stirred for 10 min. Now, 575 g of a bismuth nitrate solution (10.9 wt% Bi) was added while maintaining the temperature. After stirring for a further 10 minutes, 102 g of chromium (III) nitrate were added in portions and the resulting dark red solution was stirred for a further 10 minutes.

Precipitation:

While maintaining the 60 ⁰ C, the solution B was pumped to solution A by means of a hose pump within 15 min. During the addition and then by means of an intensive mixer (Ultra-Turrax) was stirred. After completion of the addition, stirring was continued for a further 5 minutes.

Spray drying:

The suspension obtained was spray-dried in a spray tower from NIRO (spray head No. FO A1, rotational speed 25,000 rpm) over a period of 1.5 h. The original temperature was kept at 60 ⁰ C. The gas inlet temperature of the spray tower was 300 ⁰ C, the gas outlet temperature 110 ⁰ C. The obtained powder had a particle size (d90) of less than 40 microns.

calcination:

The resulting powder was calcined batchwise (500 g) in a covered porcelain dish in a convection oven (500 Nl / h) at 460 ^° C.

After completion of calcination and cooling, 296 g of light brown powder (precursor A) were obtained.

Comparative example

Preparation of a Comparative Shell Catalyst VS1 49.5 g of the precursor material A were applied to 424 g of carrier body (steatite balls with 2-3 mm diameter with chippings). For this purpose, the carrier was placed in a coating drum (2 l internal volume, angle of inclination of the center axis of the drum against the horizontal = 30 °). The drum was rotated (25 rpm). About 32 ml of liquid binder (mixture glycerol: water 10: 1) were sprayed onto the support over a spray nozzle operated with compressed air for about 30 minutes (spray air 500 NUh). The nozzle was installed in such a way that the spray cone wetted the carried in the drum carrier body in the upper half of the rolling distance. The finely powdered precursor composition A was introduced into the drum via a powder screw, with the point of powder addition being within the unrolling section but below the spray cone. The powder addition was metered so that a uniform distribution of the powder on the surface was formed. After completion of the coating, the resulting coated catalyst from precursor material A and the support body was dried in a drying oven at 120 ^° C. for 2 hours.

The shell catalyst was then calcined at 455 ° C. in a convection oven from Heraeus, DE (type K, 750/2 S, internal volume 55 l).

Example 2 Preparation of a Double-shell Schalk Catalyst According to the Invention (1st Layer: MoO ₃ with Nonylphenol Ethoxylate as

Pore former, 2nd layer: precursor material A with melamine as pore former)

24.7 g MoO ₃ were applied according to the procedure in VS1 on 400 g carrier body (steatite balls with 2-3 mm diameter with chippings). Contrary to the method described under VS1, the pore former (2.47 g nonylphenol ethoxylate, BASF Lutensol AP6) had to be dissolved in the binder (15 ml in total) and was not mixed with the molybdenum oxide powder because it was a liquid product. The product obtained was S2a.

In a second step, the coated catalyst S2 was prepared:

49.5 g of precursor A were mixed with 4.95 g of melamine. The resulting powder was applied to 424 g of S2a according to the procedure of VS1. Consumption and procedure were identical to VS 1.

The resulting double-shelled catalyst was S2. Example 3 Preparation of a double-shelled shell catalyst according to the invention (1st layer: MoO _3, 2nd layer: A Voriäufermasse with pore formers melamine)

24.71 g MoO ₃ were applied according to the procedure in VS1 on 400 g carrier body (steatite balls with 2-3 mm diameter with chippings). The consumption of binder was 10 ml, the application time was 15 min. Deviating from VS1 was calcined only for 120 min at 300 ⁰ C. The product obtained was S3a.

In a second step, the shell catalyst S3 was prepared:

49.5 g of precursor A were intimately mixed with 4.95 g of melamine. The resulting powder was applied to 424 g of S3a according to the procedure of VS1. The consumption of binder was 31 ml, the application time was 43 min. The obtained double-shelled catalyst was S3.

Example 4 Production of a Double-shell Coated Catalyst According to the Invention (1st Layer: MoO ₃ , 2nd Layer: Precursor Mass A)

24.71 g MoO ₃ were applied according to the procedure in VS1 to 400 g carrier body (steatite beads with 2-3 mm diameter, with a grit layer). The consumption of binder was 13 ml, the application time was 24 min. Deviating from VS1 was calcined only for 120 min at 300 ⁰ C. The product obtained was S4a. In a second step, the coated catalyst S4 was prepared as follows: 49.5 g precursor A was applied to 425 g S4a according to the procedure at VS1. The consumption of binder was 31 ml, the application time was 36 min. The resulting double-shelled catalyst was S4.

Claims

claims

1. coated catalyst, comprising

(a) a carrier,

(b) a first layer containing a molybdenum oxide or a precursor compound forming molybdenum oxide,

(c) a second layer containing a molybdenum and at least one further metal-containing multimetal oxide.

2. A coated catalyst as claimed in claim 1, characterized in that the molybdenum oxide of the first layer of MoO _3.

3. coated catalyst according to claim 1 or 2, characterized in that the molybdenum-containing multimetal of the second layer, a multimetal of the general formula II

Mo ₁₂ Bi _a Cr _b X ¹ _c Fe _d X ² _e X ³ _f O _y (II)

With

X ¹ = Co and / or Ni,

X ² = Si and / or Al,

X ³ = Li ₁ Na, K, Cs and / or Rb, 0.2 <a ≤ 1,

0 ≤ b ≤ 2

2 <c <10,

0.5 <d ≤ 10,

O ≤ e ≤ 10, 0 ≤ f ≤ 0.5 and y = a number which, given the charge neutrality by the

Valence and frequency of elements other than oxygen in Il is determined.

4. A process for the preparation of a coated catalyst according to any one of claims 1 to 3, wherein applying to the carrier body by means of a binder, a first layer of the molybdenum oxide or the precursor compound which forms molybdenum oxide, given the coated with the first layer carrier body optionally dried and calcined, and applied to the obtained first layer by means of a binder, a second layer of the molybdenum-containing multimetal, and dried and calcined the coated with the first and second layer carrier body.

5. Use of the coated catalyst according to any one of claims 1 to 3 in a process for the catalytic gas phase oxidation of organic compounds.

6. Use according to claim 5 in a process for the oxidative dehydrogenation of 1-butene and / or 2-butene to butadiene.