EP3684505A1

EP3684505A1 - Synthesis of a movnbte shell catalyst for oxidative dehydrogenation of ethane to ethylene

Info

Publication number: EP3684505A1
Application number: EP18769672.9A
Authority: EP
Inventors: Gerhard Mestl; Klaus Wanninger; Silvia Neumann; Peter Schinke
Original assignee: Clariant International Ltd
Current assignee: Clariant International Ltd
Priority date: 2017-09-19
Filing date: 2018-09-13
Publication date: 2020-07-29
Also published as: US11059032B2; JP2021506561A; DE102017121709A1; US20200215516A1; JP7314122B2; WO2019057602A1; KR20200042921A; CN111132764A

Abstract

The invention relates to a shell catalyst, which has, in the outer shell, a mixed oxide material, comprising the elements molybdenum, vanadium, niobium and tellurium, characterised in that the shell catalyst has a BET surface area of > 30 m²/g. The catalyst according to the invention is produced by a method comprising the following steps: a) producing a mixture of starting compounds, which mixture contains molybdenum, vanadium, niobium and a tellurium-containing starting compound, in which tellurium is present in the oxidation state +4, as well as oxalic acid and at least one further oxo ligand; b) hydrothermally treating the mixture of starting compounds at a temperature of 100 to 300 °C to obtain a product suspension; c) separating and drying the mixed oxide material contained in the product suspension resulting from step b); d) optionally calcining the mixed oxide material obtained in step c) under inert gas at 300 to 450°C, e) creating a coating suspension that contains the mixed oxide material from step d) with the addition of organic and/or inorganic binders, f) coating an inert catalyst carrier with the coating suspension from step e) by spraying the coating suspension into a moved bed of the inert catalyst carrier, and optionally g) calcining the catalyst particles from step f) at a temperature of 80 to 400°C.

Description

Synthesis of a MoVN Te-shelled catalyst for the oxidative dehydrogenation of ethane to ethylene

The invention relates to a novel coated catalyst having an outer shell of a high surface area catalyst material containing molybdenum, vanadium, tellurium and niobium and the use of this catalyst for the oxidative dehydrogenation of ethane to ethene or the oxidation of propane to acrylic acid and a method for producing the catalyst.

MoVNbTe mixed oxides for the oxidation of propane to acrylic acid or for the oxidative dehydrogenation of ethane to ethene are state of the art. More than 200 patents and numerous scientific publications treat catalysts based on MoVNbTe mixed oxides. The promotion of these mixed oxides with other metals of the periodic table is known. The highest acrylic acid yields described above are 60% and those of ethene are about 80%.

The MoVNbTe base system based on four elements for a catalyst was first proposed by Mitsubishi for the ammoxidation of propane to acrylonitrile (1989, EP 318295 Al) and the oxidation to acrylic acid (1994, EP 608838 A2). JP H07-053414 (Mitsubishi) discloses a catalytic process for the production of ethylene by the oxidative hydrogenation of ethane at low temperature, with a high yield and with a high selectivity. This method of producing ethylene by contacting ethane with a molecular oxygen-containing gas in the presence of a catalyst composition at elevated temperature comprises that the catalyst composition contains a mixed metal oxide comprising as essential components molybdenum, vanadium, tellurium and oxygen and which shows a powder X-ray diffractogram having substantially the following relative peak intensities: 2Θ (+ - 0.4 °), rel. Int: 22.1 ° (100), 28.2 ° (400-3), 36.2 ° (80-3), 45.1 ° (40-3), 50 ° (50-3). MoVNbTe catalysts consist mainly of two orthorhombic phases called "Ml" and "M2" (T. Ushikubo, K. Oshima, A. Kayou, M. Hatano, Studies in Surface Science and Catalysis 112, (1997), 473). The Ml phase seems to play the essential role in the selective oxidation reactions.

According to P. De Santo et al. , Z. Kristallogr. 219 (2004) 152, the main phases M1 and M2 in MoVNbTe mixed oxides for the selective oxidation can be described, for example, with the following structural formulas:

Ml: MoiVo, i5Teo, i2Nbo, 128O3, 7 or M07, sVi, ₂ Teo, 937 bi028, 9

M2: * MoiV ₀ , 32Teo, 42 bo, o804,6 or M04, 31V1, ₃ eTei, siNbo, 33O19, si

The two main phases can also occur with a slightly different stoichiometry. Both vanadium and molybdenum are at the center of an octahedron of oxygen atoms and therefore partially interchangeable in structure so that the same structure, e.g. the Ml phase, even with a higher vanadium content is possible. A detailed investigation of these relationships can be found in P. Botella et al. , Solid State Science 7 (2005) 507-519. Specifically, the M2 phase is not active for the oxidative dehydrogenation of ethane (see J.S. Valente et al., ACS Catal.4 (2014), 1292-1301, p.1293, in particular). For the oxidative dehydrogenation of ethane, therefore, a catalyst which consists of a very pure Ml phase is desired. It is therefore attempted to produce these crystal phases cleanly and separately.

EP 529853 A2 discloses a catalyst suitable for preparing a nitrile from an alkane, the catalyst having the empirical formula MoVbTe _c XxO _n , wherein X is at least one of Nb, Ta, W, Ti, Al, Zr, Cr, Mn Fe, Ru, Co, Rh, Ni, Pd, Pt, Sb, Bi, B and Ce, b is 0.01 to 1.0, c is 0.01 to 1.0; x is 0.01 to 1.0 and n is a number that satisfies the total metal elements and that the catalyst has X - ray diffraction peaks at the following 2Θ angles in its X - ray diffraction pattern: diffraction angle at 2Θ (22.1 ° +/- 0 , 3 °, 28.2 ° +/- 0.3 °, 36.2 ° +/- 0.3 °, 45.2 ° +/- 0.3 °, 50.0 ° +/- 0,3 °)

JP H07-232071 discloses a catalytic process for producing a nitrile, at a relatively low temperature and in a high yield, by using an alkane as a raw material and a specific catalyst. The major component of the catalyst is a mixed metal oxide of molybdenum, vanadium, tellurium, oxygen, and X (X is one or more elements selected from the group of niobium, tantalum, etc.) wherein the ratio of the major components, i. excluding oxygen, expressed by the formulas I to IV: I) 0.25 <rMo <0.98, II) 0.003 <rV <0.50, III) 0.003 <rTe <0.50, IV) 0 <rX <0.5, (rMo, rV, rTe and rX are respectively the molar parts of molybdenum, vanadium, tellurium and X) and in the XRD, XRD bands of this mixed oxide at the different 29 angles 9.0 ° ± 0.3 °, 22.1 ° ± 0.3 °, 27.3 ° ± 0.3 °, 29.2 ° ± 0.3 ° and 35.4 ° ± 0.3 °. Thus, a nitrile may be prepared by reacting an alkane without the presence of a halogenated substance, e.g. is reacted with water, etc., in the reaction system at a low temperature with a high yield.

Other successful attempts to produce a pure Ml phase are based on dissolving the M2 phase out of the phase mixture. These experiments are e.g. in EP 1301457 A2, EP 1558569 A1 or WO 2009106474 A2.

AC Sanfiz et al. , Top. Catal. 50 (2008) 19-32 describe hydrothermal syntheses of MoVNbTe oxide. These syntheses are based exclusively on soluble compounds. As a soluble compound of tellurium usually telluric acid Te (OH) 6 is used. In the most common oxide tellurium compound TeÜ2, tellurium has the oxidation state +4. Unfortunately, tellurium dioxide (TeÜ2) is poorly soluble in water. In telluric acid, however, tellurium has the oxidation state +6. Tellurium must therefore be highly oxidized in the production of telluric acid. The common synthesis is carried out by oxidation of tellurium oxide with hydrogen peroxide, which involves safety problems on a large scale, because hydrogen peroxide can be found in Even disproportionate decomposition to water and oxygen. Therefore, telluric acid is difficult to produce in large quantities.

The Nb component used in the synthesis of MoVNbTe mixed oxides is usually ammonium niobium oxalate. By contrast, niobium oxide is sparingly soluble and is therefore only suitable to a limited extent as starting compound.

Watanabe (Applied Catal. A General, 194-195 (2000) 479-485) describes inter alia the hydrothermal synthesis from the less soluble precursors Mo0 ₃ , V ₂ 0 ₅ and Te0 ₂ . The hydrothermal synthesis gives a ammoxidation catalyst precursor which has twice the activity after calcination compared with a catalyst prepared by the known dry method. The mixed oxides produced by the solid-state reaction show rather low activity. It has been suggested that the higher activity of the catalyst prepared by the hydrothermal synthesis has to do mainly with the higher surface area.

WO 2013021034 A1 relates to a catalyst material for the oxidation and / or oxidative dehydrogenation of hydrocarbons, in particular for the selective oxidation of propane to acrylic acid, comprising a) molybdenum (Mo), b) vanadium (V), c) niobium (Nb), d ) Tellurium (Te), e) manganese (Mn) and cobalt (Co), in which the molar ratio of at least one element selected from manganese and cobalt to molybdenum ranges from 0.01 to 0.2, more preferably 0, 02 to 0.15 and more preferably from 0.03: 1 to 0.1: 1. Further, a catalyst for the oxidation and / or oxidative dehydrogenation of hydrocarbons, a use of the catalyst material or the catalyst, a process for the preparation of a catalyst material for the oxidation and / or oxidative dehydrogenation of hydrocarbons and a process for the selective oxidation of propane to acrylic acid is given.

WO 2008068332 A1 relates to novel, mesoporous mixed metal oxide catalysts and to a process for their preparation and to their use as catalysts for the oxidation of hydrocarbons or partially oxidized hydrocarbons. In particular, the disclosure relates to mesoporous mixed oxide catalysts containing at least two, preferably at least three different metal species, at least one of which belongs to the group of transition metals, to a process for preparing such a catalyst comprising a neutral templating route and a substantially oxygen-free atmosphere calcining step Temperature between 300 to 700 ° C and the use of such catalysts as oxidation catalysts for the production of oxidized hydrocarbons and in particular for the selective oxidation or ammoxidation of propane to acrylic acid and acrylonitrile A preferred catalyst comprises the elements Mo, V, Te and Nb.

WO 0232571 A1 describes a shell catalyst whose shell of active material is a multimetal oxide which contains the elements Mo, V and Te and or Sb and which is provided as a catalyst for the heterogeneously catalyzed gas phase oxidation of propane to acrylic acid.

The syntheses of the Ml phase described in the prior art have in common that after the reaction of the starting materials, the Ml phase forms only during a high-temperature treatment, typically above 500 ° C. under inert gas ("activation") The state of the art then usually has BET surface areas of 4 to 20 m ² / g.

MoVNbTe mixed oxide catalysts could be used as particle squeezed in large industrial reactors. For this purpose, special geometries of the particles prove to be particularly advantageous, for example, rings have a lower pressure loss than full, cylindrical tablets. The disadvantage here is that the pressed particles consist entirely of active material (solid catalysts) and correspondingly large amounts of the expensive elements niobium and tellurium must be used. There is therefore a need for coated catalysts which have active material only on the surface and consist of an inert carrier in the interior. However, a prerequisite for the preparation of such coated catalysts is a high activity of the active composition, so that with the, in comparison to the full catalyst, a smaller amount of active mass a comparable catalytic conversion is achieved.

The object of the present invention was to find a highly active coated catalyst based on this mixed oxide material, comprising the elements molybdenum, vanadium, tellurium and niobium ("MoVTeNb mixed oxide"), which has the Ml phase and the largest possible specific surface area The invention was also to provide a shell catalyst for the oxidation of alkanes, which has the highest possible activity using as low a mass of MoVTeNb mixed oxide.The latter is significant, because MoVNbTe mixed oxide is very particularly because of the rare metals Te and niobium very expensive.

The object is achieved by a shell catalyst comprising an inert support and a catalytically active outer shell comprising a mixed oxide material comprising the elements molybdenum, vanadium, niobium and tellurium (MoVNbTe mixed oxide), characterized in that the catalyst has a BET surface area of more than 30 m ² / g.

The coated catalyst of the invention is prepared by a process comprising the steps of: a) preparing a mixture of starting compounds containing molybdenum, vanadium, niobium and a tellurium-containing starting compound in which tellurium is in the +4 oxidation state, and oxalic acid and at least one further oxo ligands,

b) hydrothermal treatment of the mixture of starting compounds at a temperature of 100 to 300 ° C to obtain a product suspension,

c) separating and drying the mixed oxide material contained in the product suspension resulting from step b), d) optionally calcining the mixed oxide material obtained in step c) (MoVTeNb mixed oxide) under inert gas at 300 up to 450 ° C,

e) preparing a coating suspension containing the mixed oxide material from step d) with the addition of organic and / or inorganic binders,

f) coating an inert catalyst support with the coating suspension from step e) by spraying the coating suspension into a moving bed of the inert catalyst supports, and optionally

g) calcining the catalyst particles from step f) at a temperature of 80 to 400 ° C.

Step g) may optionally be carried out in the preparation of the catalyst or first in the reactor in which the catalytic reaction is carried out before use in the catalytic reaction.

The starting compounds are the molybdenum, vanadium, tellurium and niobium containing reactants of the hydrothermal synthesis (precursor compounds). These each contain one or more of the elements molybdenum, vanadium, tellurium or niobium.

The molybdenum-containing starting compound may be, for example, an ammonium heptamolybdate or molybdenum trioxide, the vanadium-containing starting compound may be, for example, an ammonium metavanadate, vanadyl sulfate or vanadium pentoxide, the niobium-containing starting compound may be, for example, ammonium niobium oxalate or niobium oxalate or niobium oxide. The tellurium-containing starting compound according to the invention is one in which tellurium is present in the oxidation state +4, ie as tellurium (IV) cation, as in tellurium dioxide or a compound of the formula M _x ^{n +} TeC> 3 (with n = 1 or 2 and x = 2 / n), where M is an alkali or alkaline earth metal ^¬ such as Na2TeC> 3rd More preferably, the tellurium-containing starting compound is tellurium dioxide, which may be in any degree of hydration.

The inert catalyst support can be made of aluminum oxide, silicon dioxide, zirconium oxide or mixed oxides of the elements, for example ceramics such as steatite, or consist of silicon carbide. The support molding is particularly preferably composed of inert oxides of very small specific BET surface area without internal porosity, such as steatite, alpha-alumina, quartz (silica), mullite or cordierite.

One aspect of the production process of the invention is that a synthesis of the Ml phase from the insoluble and inexpensive oxides, e.g. M0O3, V2O5, b2Üs and TeÜ2 and a combination of oxalic acid with at least one other oxo ligand succeeds. Other oxo ligands (i.e., besides oxalic acid) have been found to be particularly useful are dicarboxylic acids and diols, as well as organic compounds having two adjacent carbon atoms each having a hydroxy group. Particularly preferred as another oxo ligand is the use of a mixture of citric acid and glycol. The oxalic acid should preferably be in a mixture of the starting compounds in a Mo / oxalic acid ratio of 1: 0.01 to 1: 1, preferably 1: 0.08 to 1: 0.4, more preferably 1: 0.15 to 1: 0 , 25 present. The at least one further oxo ligand, or all other oxo ligands together, should preferably be more preferably in a mixture of the starting compounds in a Mo / oxo ligand ratio of 1: 0.01 to 1: 1, preferably 1: 0.025 to 1: 0.2 1: 0.05 to 1: 0.1.

If metal oxides in powder form are used as starting compounds, then the D50 value of the particular metal oxide used is less than 10 μm. If the metal oxide powders have too large particles, they must first be ground wet or dry until their Dso values are <10 pm.

Surprisingly, the synthesis according to the invention provides the Ml phase already after the hydrothermal synthesis and drying. Subsequent calcining under nitrogen at 300 to 400 ° C provides a catalyst having a surface area greater than 30 m ² / g.

Another advantage of the synthesis according to the invention of the Ml phase is the completely surprising, high efficiency of the reaction of Starting materials by hydrothermal synthesis. If the stoichiometry of the starting materials is in the range Mo / V / Nb / Te = 1: 0.22: 0.1: 0.1 to 1: 0.3: 0.17: 0.17, Mo, V, Nb and Te are almost completely converted to the Ml phase, leaving less than 100 ppm of all metals in the mother liquor.

The possible stoichiometry of the Ml phase is well known from the literature and can be described by the formula Mo _! V _a Nb _b Te _c O _x with a = 0.2 to 0.3, b = 0.05 to 0.2, c = 0.05 to 0.25 and x depending on the oxidation state of the metals (Mo, V , Nb and Te) a size that leads to charge balance.

The mixture of starting compounds for the hydrothermal synthesis is preferably present as an aqueous suspension and is subsequently treated hydrothermally. The term "hydrothermal" refers mainly to the reaction conditions for producing a catalyst ^¬ materials in the presence of water and under elevated temperature and / or elevated pressure, for example in an autoclave. In this case, bar of the pressure ranging from 5 to 30, preferably from 10 to 27 bar are exemplary pressure ranges are 11 to 20 bar.

The hydrothermal treatment (step b)) gives a product suspension which contains the MoVNbTe mixed oxide as a solid. In the process according to the invention, the separation of the solid from the suspension in step c), which is the MoVNbTe mixed oxide, can take place in one or more filtration steps, for example by filtering off the mother liquor. The drying may be carried out in one or more, preferably two, steps in flowing or static air. In this case, the first drying step is preferably at 60 ° C to 150 ° C (more preferably at 80 ° C to 120 ° C), a second drying step can be carried out at 200 to 400 ° C. In addition, step c) of the process according to the invention may comprise one or more washing, calcining (thermal treatment) and / or grinding steps include. The calcination can be carried out at 200 ° C to 450 ° C, preferably 300 ° C to 400 ° C in inert gas.

To prepare the coated catalyst, a coating suspension with the addition of a solvent, preferably water, is first prepared from the MoVNbTe mixed oxide. This coating suspension then contains organic and / or inorganic binders. Possible organic binders are e.g. Plastics or emulsions of plastics polyvinyl acetate, ethylene vinyl acetate, polyacrylates and other acrylate copolymers. Possible inorganic binders are e.g. Brine of silica, zirconia or titania.

This coating suspension is applied to the inert support to form the catalytically active outer shell. Preferably, this application is done by spraying. Particularly preferably, a coating is carried out by spraying the suspension into a moving bed of inert catalyst carrier body. Subsequently, the coated catalyst support bodies are dried and optionally calcined, with any existing organic binder being burned out. However, this treatment can also be carried out in the reactor in which the shell catalyst is used, before the actual commissioning.

The shell catalyst preferably has a catalytically active outer shell with a layer thickness of between 200 and 400 μm.

The coated catalyst according to the invention can be used as a catalyst for the oxidation and / or oxidative dehydrogenation ("ODH") of

Hydrocarbons, in particular for the oxidative dehydrogenation of ethane to ethylene are used.

Characterization methods: The following methods are used to determine the parameters of the catalysts according to the invention:

1. BET surface area:

The BET surface area of the shaped catalyst bodies was determined by the BET method according to DIN 66131; a publication of the BET method can also be found in J. Am. Chem. Soc. 60,309 (1938). The measurements were carried out on a TriStar from Micromeritics at 77K. Before the measurement, the sample was evacuated for 2 h at 523 K. The linear regression of the isotherms according to the BET method was in a

Pressure range of p / po = 0.01 - 0.3 (po = 730 Torr) performed.

2. N2 pore distribution

The pore size distribution of a catalyst powder was determined by nitrogen adsorption measurements on a: TriStar of

Micromeritics performed at 77K. Before the measurement, the sample was evacuated for 2 h at 523 K. There have been both ad and

Desorption isotherms determined and used for evaluation according to the Barrett-Joyner-Halenda method (BJH).

3. Hg pore volume

The pore distribution and the pore volume of the catalyst particles

(Tablets and coated rings as shell catalysts) was measured with a mercury porosimeter: Pascal 440 from Thermo Electron

Corporation determined according to DIN 66133. The sample was previously evacuated for 30 minutes at room temperature. Samples in the range 600-900 mg were measured and the pressure increased to 2000 bar.

Tablets are made entirely of porous material, so that the

Pore volume is always related to the entire measured tablet.

Coated catalysts have in their interior a carrier material which usually has almost no internal surface (BET). Surface ~ 0 m ² / g) and almost no pore volume (pore volume ~ 0 cm ³ / g).

Since here the mass of the inert carrier is weighed and codetermined for the measurement, the final values refer to the

complete coated catalyst, but not on the catalytically active outer shell. In order to relate the measured pore volume in cm ³ / g to the catalytically active outer shell, the determined pore volume must be divided by the (mass) proportion of the porous layer in the total mass.

Exemplary embodiments:

The invention is not limited by the following

Embodiments explained.

Comparative Example 1 describes a MoVTeNb catalyst which was activated according to the prior art at 600 ° C and was pressed into tablets by conventional methods with the addition of conventional Tablettier additives such as graphite and stearic acid.

Comparative Example 1

First, 68.25 g of TeÜ2 (Alfa Aesar) and 200 g of dist. H2O weighed together in the ZrÜ2 coated grinding container and in a

Planetary ball mill with 50 1 cm balls (ZrC> 2) for 1 h at 400 rpm

ground. Subsequently, the ground slurry 1 with 500 ml of dist. Transfer H2O to a 2 1 beaker. 56, 83 g b2Üs and 200 g dist. H2O were weighed together in the ZrO2 coated milling vessel and ground in the same ball mill under the same conditions as TeC> 2. Subsequently, this was ground

Slurry for 2 h with 500 ml of dist. Transfer H2O to a second 2 1 beaker. After 20 h, the mixture was heated to 80 ° C., 107.8 g of oxalic acid dihydrate were added to the B 2Üs suspension 2. It forms the

Slurry 3, which was stirred for about 1 h on a magnetic stirrer. In an autoclave (40 1) 6 1 dist. Submitted H2O and stirring heated to 80 ° C. After the water had reached the temperature, 61.58 g of citric acid, 19.9 g of ethylene glycol, 615.5 g of M0O3 (Sigma Aldrich D50 = 13.0 pm), 124.5 g of V2O5, the ground TE02 (slurry 1 ) and the ground Nb2Üs in oxalic acid

(Slurry 3) was added. 850 ml dist. H2O was used to transfer to the autoclave and rinse the vessels. The complete

The amount of water in the autoclave was 8.25 l (stirrer speed 90 rpm). After the autoclave was capped, it was allowed to stir for 5 min

Nitrogen superimposed under slight overpressure (4 bar). It was a hydrothermal synthesis in 40 1 autoclave at 190 ° C for

48 1 (heating time 3 h) performed. After the synthesis (suspension has less than 50 ° C) was filtered off under vacuum through a Blauband filter and the filter cake with 5 1 dist. Washed H2O. Thus, the precursor material PI was produced. PI was then dried at 80 ° C in a drying oven for 3 days. It became like that

Precursor material P2 produced. P2 was subsequently in a

Ground mill. It became the precursor material P3

manufactured .

Solid yield: 0.8 kg

P3 was then calcined under the following conditions: heating rate

5 ° C / min, 280 ° C / 4 h, air flow: 1 1 / min. It became so precursor material

P4 produced.

P4 was then activated under the following conditions: In one

Retort in the oven was activated at 650 ° C for 2 h, (heating rate 10 ° C / min) under N 2 (0.5 1 / min). It was thus produced the catalyst Kl. The catalyst Kl has a BET surface area of 9 m ² / g and an N 2 pore volume of 0.04 cm ³ / g.

This powder Kl was now used to prepare catalyst tablets K2. For this purpose, 473 g of the powder Kl was intimately mixed with 9.65 g of graphite, 54.96 g of stearic acid and 54.96 g of fine silica (Syloid C809). There was thus prepared the catalyst powder K3. The catalyst powder K3 was granulated twice (ie pressed and re-comminuted into a granulate with particles in the range of about 30-400 pm through a sieve, with a Powtec roller compactor). It was thus produced the catalyst granules K4. The

Catalyst granulate K4 was tabletted into rings (diameter 5.4 mm, height 5 mm, inside diameter 2.5 mm) in a tablet press (Rotab company) with a contact pressure of about 1 1 kN. It became so

Catalyst body K5 produced.

After tabletting, the shaped catalyst body K5 was heated at 350 ° C. in air in a Nabertherm circulating air oven at a slow heating rate

(<1 ° C / 10min) burned out the stearic acid. It became so

Comparative catalyst K6 prepared.

Comparative Example 2 describes a comparative catalyst wherein the catalyst powder was prepared by the process of the invention, but which was prepared in the same manner as Comparative Example 1

was tabletted.

Comparative Example 2:

First, 116.06 g of TeO ₂ (Alfa Aesar) in 1000 g of dist. H ₂ 0 slurried using a KPG stirrer and in a MicroCer ball mill

(Netsch) with 0.8 mm balls (Zr0 ₂ ) ground. Subsequently, the portion was distilled with 750 ml. H ₂ 0 transferred to a 3 beaker and stirred with a magnetic stirrer. 96.64 g of Nb ₂ Os and 183.35 g of oxalic acid dihydrate were distilled in 1000 g. Slurried H ₂ 0 using a KPG stirrer and ground in the same ball mill. Subsequently, the portion was distilled with 750 ml. H ₂ 0 transferred to a 3 1 beaker and stirred with a magnetic stirrer. After 20 h both were

1046, 7 g M0O3 (Sigma Aldrich, slightly larger particles) were suspended in 8.5 1 of water and also ground rapidly through this ball mill

(D50 = 12.7pm). This 8.5 1 MoO 3 suspension was placed in the autoclave (40 1) and heated to 80 ° C with stirring. After that

Water had reached the temperature was sequentially 14.61 g

Citric acid, 33.85 g of ethylene glycol, 211.61 g of V2O5, the ground Te2 and the ground Nb2's in oxalic acid were added. The complete

Water volume in the autoclave was 14 1 (speed of the stirrer 90 rpm). After the autoclave was sealed, was with 5 min

Nitrogen superimposed under slight overpressure (4 bar). It was a hydrothermal synthesis in 40 1 autoclave at 190 ° C / 48 h (heating time 3 h) performed. After the synthesis (ie, when the suspension has less than 50 ° C) was filtered off under vacuum over a blue ribbon filter and the filter cake with 5 1 dist. H ₂ O washed. It was then dried at 80 ° C in a drying oven for 3 days and

then ground in a hammer mill. The solids yield was 0.8 kg.

The solid was then activated: In a retort in the oven at 400 ° C / 2h, (heating rate 10 ° C / min) under N ₂ (0.5 1 / min)

kal ziert.

The activated solid has a BET surface area of 27 m ² / g and an N ₂ pore volume of 0.116 cm ³ / g.

This powder was used to prepare catalyst tablets. These tablets were prepared as described in Comparative Example 1.

Example 3 describes the catalyst according to the invention, wherein only 20 wt. -% - catalyst mass were coated on an inert carrier.

Example 1 : First, 116.06 g of Te02 (Alfa Aesar) in 250 g of dist. H2O

slurried and ground in a ball mill. Subsequently, the portion was distilled with 7500 ml. Transferred H2O into a beaker. 96.64 g M02O5 were distilled with 250 g. H2O slurried and ground in a ball mill. Subsequently, the portion with 500 ml of dist. Transferred H2O into a beaker. The next morning, the mixture was heated to 80 ° C, 183.35 g of oxalic acid dihydrate in the Nb2Üs suspension and stirred for about 1 h. 1046, 7 g M0O3 (Sigma Aldrich) were suspended in 8.5 1 of water and using A MicroCer ball mill is circulated for 4 h (D50 = 2.9 pm). This 8.5 1 MoO 3 suspension was introduced into the autoclave (40 l) and heated to 80 ° C. with stirring. After the water had reached the temperature, 14.61 g of citric acid, 33.85 g of ethylene glycol, 211.61 g of V2O5, the ground TEO2, and the milled b2Üs in oxalic acid were added sequentially. The total amount of water in the autoclave was 14 1 (speed of the stirrer 90 rpm). Subsequently, it was overlaid with nitrogen. It was a hydrothermal synthesis in 40 1 autoclave at 190 ° C / 48 h performed. After the synthesis was carried out under vacuum over a

Blue filter filtered off and the filter cake with 5 1 dist. Washed H2O. It was then stored at 80 ° C in a drying oven for 3 days

dried and then ground in a hammer mill (small IKA laboratory mill). The solids yield was 1.4 kg.

The resulting solid was then calcined: in a

Retort in the oven was calcined at 400 ° C / 2h, (heating rate 10 ° C / min) under N 2 (0.5 1 / min).

The activated solid has a BET surface area of 50 m ² / g and an N ² pore volume of 0.27 cm ³ / g.

This powder was now used to prepare a coating suspension. To this was added 181 g of the powder in 1047 g of water

and 39.93 g of Bindzil 2034DI silica sol, 4.52 g of Syloid C809 and 13.57 g of coconite were added. This suspension was Turrax stirrer homogenized (5 min / 6000 rpm). Subsequently, 54.30 g EP16 vinyl acetate adhesive from Wacker was added and the whole was then stirred for 1 h with a magnetic stirrer. Thereafter, 600 g steatite rings (4 mm diameter, 2 mm inner diameter, 4 mm height) were in a coating system of the company. Hüttlin with

Coating suspension coated. In this case, the bed of the rings with an air flow of 198 m ³ / h to 260 m ³ / h (70 ° C) was offset from below through oblique slots in a plate in a rotating motion. The coating suspension was sprayed into this rotating bed via nozzles (0.3 bar).

(Coating loss over the air flow: 14.5%, proportion of the porous layer (Silca + catalyst): 21.5%, proportion of the active material: 19.2%) After coating the catalyst support molding was at 320 ° C in air in a Furnace burned out of vinyl acetate glue.

Example 2 describes a catalytic activity assay in the oxidative dehydrogenation of ethane to ethylene at various

Temperatures.

Example 2:

The catalysts were tested in a test for the activity in the oxidative dehydrogenation of ethane.

In a tempered with a salt bath tube reactor (diameter

2.54 cm, length 1 m, isothermally heated zone 80 cm) were charged 380 to 420 ml (373 g tablets or 460 g coated rings).

Under a Stickstoffström was heated to 290 ° C. Then water vapor, air and then ethane were switched on until the following flow rates were reached: N2 = 48 nl / h; Water = 0.7 ml / min (liquid, water was evaporated); Air = 35.3 nl / h and ethane 13.7 nl / min. Thereafter, the salt bath temperature was increased in 2 ° C increments up to the temperatures listed in Table 1 (The unit [nl] corresponds to the standard liter, ie one liter at 1.0133 bar and 0 ° C). The input gas compositions and the starting gas compositions were analyzed. For this purpose, a partial flow was drawn off via heated pipes with a vacuum pump. This partial analysis stream was first drawn through a sample valve of a GC, through a gas cooler and then dried, through an NDIR analyzer (Rosemount). In the GC, an Rt U-BOND column having a temperature profile of 45 ° C to 190 ° C was analyzed in 8.4 minutes with a gas flow of 10 ml / min of ethane, ethene, acetic acid and water. The NDIR analyzer (Rosemount) contains NDIR cells for CO, CO2, ethane, ethene, and one

paramagnetic oxygen sensor.

By comparing the inlet and outlet Gaszusammenset tion the conversion of ethene was calculated, which is shown in Tab. 1.

From the results of Table 1 it can be seen that the catalyst of Comparative Example 2 is significantly more active than that

Comparative catalyst 1 according to the prior art at 330 ° C, because it reaches the same ethane conversion of 67% already at 302 ° C. The salt bath temperature for the catalyst according to Comparative Example 2 can not be adjusted to 330 ° C., because under these conditions an uncontrolled rise in the temperature of the exothermic reaction is observed ("runaway").

By contrast, the catalyst according to Example 3 according to the invention has only 20% of the active material in the same reactor volume and reaches an ethane conversion of 50% at 330 ° C. Table 1:

Table 1 compares the BET surface areas and pore volumes of the inventive catalyst of Example 3 with the other comparative examples.

Claims

claims

A coated catalyst comprising an inert carrier and a

catalytically active outer shell, which is a mixed oxide material,

comprising the elements molybdenum, vanadium, niobium and tellurium

characterized in that the shell catalyst has a BET surface area of more than 30 m ² / g.

2. coated catalyst according to claim 1, characterized in that the shell catalyst has a mercury pore volume of greater than 0.1 cmVg.

3. coated catalyst according to claim 1, characterized in that the shell catalyst in the shell based on the mass of the shell has a mercury pore volume of greater than 0.2 cm ³ / g.

4. coated catalyst according to one of the preceding claims, characterized in that the inert carrier is selected from the group consisting of silica, alumina, steatite, mullite and

Cordierite.

5. A process for preparing a coated catalyst according to any one of the preceding claims comprising the steps of: a) preparing a mixture of starting compounds containing molybdenum, vanadium, niobium and a tellurium-containing starting compound in which tellurium is in the +4 oxidation state, and oxalic acid and at least one other oxo ligand,

c) separating and drying the mixed oxide material contained in the product suspension resulting from step b), d) optionally calcining the product obtained in step c) Mixed oxide material under inert gas at 300 to 450 ° C., e) production of a coating suspension containing the mixed oxide material from step d) with the addition of organic and / or inorganic binders,

6. The method according to claim 5, characterized in that the tellurium-containing starting compound is tellurium dioxide or a compound of the formula M _x ^{n +} TeC> 3 with n = 1 or 2 and x = 2 / n, where M is an alkali or alkaline earth metal.

7. The method according to claim 5 or 6, characterized in that the mixture of starting compounds is present as an aqueous suspension.

8. The method according to any one of claims 5 to 7, characterized in that the mixture of starting compounds containing a dicarboxylic acid, a diol, or another compound having two hydroxy groups in adjacent position as further oxo ligands.

9. The method according to any one of claims 5 to 8, characterized indicates that the mixture of starting compounds contains molybdenum trioxide.

10. The method according to any one of claims 5 to 9, characterized

characterized in that the mixture of starting compounds

Vanadium pentoxide contains.

11. The method according to any one of claims 5 to 10 characterized

characterized in that the mixture of starting compounds

Contains citric acid as another oxo ligand.

12. The method according to any one of claims 5 to 11, characterized

characterized in that the mixture of starting compounds

Citric acid and glycol as further oxo ligands.

13. Use of a shell catalyst according to claim 1 to 4 as a catalyst for the oxidative dehydrogenation of ethane to ethene.

14. Use of a shell catalyst according to claim 1 to 4 as a catalyst for the oxidation of propane to acrylic acid.