EP2106292A2 - Method for producing catalysts and their use for the gas phase oxidation of olefins - Google Patents

Abstract

The invention relates to a method for producing catalysts on stable, high-purity molded bodies that are produced from pyrogenic metal oxides without the addition of binders, and to the use of said catalysts for the gas phase oxidation of olefins.

Description

Process for the preparation of catalysts and their use for the gas-phase oxidation of olefins

The invention relates to a process for the preparation of catalysts on stable, high-purity moldings of pyrogenic metal oxides without the addition of binders and their use in the gas phase oxidation of olefins.

Pyrogenically produced metal oxides are characterized by extreme fineness, high specific surface areas, defined, spherical primary particles with defined surface chemistry and by non-existent internal surfaces (pores). Furthermore, they are characterized by a very high chemical purity.

Against the background of the properties just outlined, e.g. Fumed silicas are increasingly of interest as supports for catalysts (D. Koth, H. Ferch, Chem. Ing. Techn. 52, 628 (1980)).

Due to the particular fineness of the pyrogenic metal oxides, however, the production of moldings, as used for example as a catalyst or catalyst support, made difficult from these pyrogenic metal oxides. The production of moldings from metal oxide powders is usually carried out by pressing or extrusion using binders and lubricants to obtain stable moldings. The binders and lubricants are inorganic and organic additives.

Inorganic additives, such as magnesium stearate, remain in the moldings produced in the form of inorganic compounds, such as magnesium oxide. Organic additives can also cause impurities, such as carbon, in the production process of the shaped bodies. The desired very high purity of the pyrogenic metal oxides used, such as pyrogenic SiO 2, is lost in the moldings produced thereby. In addition to the high purity and high surface area, it is another desired property to obtain catalysts with the lowest possible bulk density. As a result, on the one hand, the mass transport in the later catalyzed

Reaction are favorably influenced and on the other hand, a lower mass of support material is required to fill a specific reactor volume. Thus, the cost ratio of carrier material to reactor volume is better and the process more economical.

Low bulk densities can be achieved, for example, with catalyst molds which have at least one through-channel, for example rings.

Particularly suitable are annular body with the least possible wall thickness. However, low wall thicknesses lead to moldings in which the mechanical strengths are no longer sufficient for catalyst preparation and / or reactor filling and are therefore unsuitable as catalyst support materials.

As catalytically active components may inter alia palladium and / or its compounds and alkali compounds, and in addition gold and / or its compounds (System

Pd / alkali / Au) or cadmium and / or its compounds (system Pd / alkali / Cd) or barium and / or its compounds (system Pd / alkali / Ba) or palladium, alkali compounds and mixtures of gold and / or cadmium and / or barium.

Many possibilities have been described in the state of the art for producing catalysts on metal oxide moldings, with binders or other solidification steps being necessary for later strength, and the resulting surfaces of the catalyst supports requiring high bulk densities of the catalysts. EP 72390 describes the preparation of pressings from a mixture of fumed metal oxides, water, silica sol and a pressing aid. As auxiliary a polyfunctional alcohol (eg Glycerin) is claimed.

From EP 327722 it is known to add fumed silica with kaolin and / or graphite, sugar, starch, urea, wax in water. The production of the compacts can be done by using stamp presses, eccentric presses, extruders, concentric presses or compactors. According to EP 327815 the procedure is analogous, but used instead of fumed silica fumed silica / alumina mixed oxide.

EP 807615 includes a process for producing pressings consisting of fumed silica,

Methyl cellulose, microwax and polyethylene glycol and water. The compacts usually have contents of 50 to 90 wt .-% silica, 0.1 to 20 wt .-% of methyl cellulose and 0.1 to 15 wt .-% of microwax and 0.1 to 15 wt .-% polyethylene glycol on.

According to DE4142898, it is possible to produce stable moldings of fumed silica and aqueous-alcoholic ammonia solution. By contrast, a purely aqueous ammonia solution does not lead to success. Due to the high proportion of aqueous-alcoholic ammonia solution, the mixture to be formed is made strongly alkaline. The use of alcohol entails the risk of C contamination for the resulting catalyst carrier. According to DE4142902 stable moldings of fumed silica and ammonia solution or of fumed silica and alkali metal-containing silica sol can only be obtained if the moldings are subjected to a hydrothermal treatment. In the case of ammonia addition, the mixture is again made very alkaline. It is known that this excess of base (pH> 10) leads to the partial dissolution of SiO 2. US 4048096 describes the preparation of Pd / Au coated catalysts in which the noble metals occur in a layer thickness equal to or less than 0.5 mm from the outer surface of the carrier body. As a base for the transfer of the soluble noble metal compounds in the respective

Precious metal hydroxides are used alkali metal silicates, during which a pH of 6.5 - 9.5 is set for a period of 12 - 24 hours. As support materials of the VAM catalysts based thereon, supports having surface areas of 10 to 800 square meters per gram are used.

EP 807615 describes a process for producing fusions of fumed silica using silica with methylcellulose, microwax and

Polyethylene glycol is homogenized with the addition of water. After mixing, a drying is carried out at 80 to 150 ⁰ C. The possibly previously crushed powder is deformed into pressings, which are tempered for a period of 0.5 to 8 hours at temperatures of 400 to 1200 ⁰ C. The

Mixtures before compression of the masses usually have contents of 50 to 90% by weight of silicon dioxide, 0.1 to 20% by weight of methylcellulose and 0.1 to 15% by weight of microwax and 0.1 to 15% by weight. Polyethylene glycol on. The compacts listed in the examples have BET surface areas of 120 to 210 m ² / g at pore volumes of 0.71 to 0.97 ml / g. The claimed in the patent compacts having an outer diameter of 0.8 to 20 mm and a BET surface area of 30 to 400 m ² / g have a pore volume of 0.5 to 1.3 ml / g. The moldings having a bulk density of 350 to 750 g / l consist of at least 99.8 wt .-% silica (other ingredients <0.2 wt .-%) and reach at an abrasion <5 wt .-% mechanical stabilities of 10 to 250 Newtons. Based on these support materials, catalysts for the production of vinyl acetate monomer containing palladium, gold and alkali acetate are claimed. EP 997192 Bl describes palladium-supported catalysts (Pd / Au / alkali, Pd / Cd / alkali or Pd / Ba / alkali systems), which are based on moldings of pyrogenically prepared mixed oxides. The shaped bodies underlying the catalyst have an outer diameter of 0.8 to 25 mm, a BET surface area of 5 to 400 m ² / g and a pore volume of 0.2 to 1.8 ml / g and are composed of at least two from the group SiO ₂ , Al ₂ O 3, TiO 2 and ZrO 2 in any order but with the exception of SiO ₂ / Al ₂ O ₃ mixed oxides together, other constituents being <1% by weight. In addition, the described support materials have compressive strengths of 5 to 350 Newtons and bulk densities of 250 to 1500 g / l. Based on these support materials, catalysts are claimed, the palladium, gold and alkali compounds or palladium, cadmium and alkali compounds or palladium, barium and

Alkaline compounds included. The alkali compound in a preferred embodiment is potassium acetate. The catalyst is used to prepare unsaturated esters, e.g. Vinyl acetate monomer used in the gasase.

EP 464633 describes a catalyst having at least one passage channel with an inner diameter of the channel of at least one millimeter, the palladium and / or its compounds in an amount of 1 to 20 grams / liter and optionally gold and / or its compounds in an amount of 0, 1 to 10 grams / liter. At least 95% of the palladium, gold and / or compounds thereof extend in a range from the surface up to 0.5 mm below the surface of the support (coated catalyst). The catalyst is used to prepare unsaturated esters (e.g.

Vinyl acetate) by reaction of an olefin (e.g., ethene) with an organic carboxylic acid (e.g., acetic acid) and oxygen in the gas phase. Hydrazine hydrate is used as the reducing agent in the examples.

The documents cited in the prior art show that the

Production of stable moldings so far not without inorganic or organic additives, such as Extrusion aids, pore formers, sols or additional solidification steps is possible. Furthermore, the prior art catalysts show unfavorable bulk densities and low activities. The object of the invention is to improve the prior art and to provide catalysts with lower bulk densities based on pyrogenic metal oxides, such as pyrogenic SiO 2, which have the lowest possible contamination of metals, carbon and phosphorus, at the same time have a high strength and have improved selectivity and higher activity than known catalysts.

The invention relates to a process for the preparation of catalysts for the gas phase oxidation of olefins, comprising the steps:

(I) suspending at least one pyrogenically prepared metal oxide in a solvent,

(II) conversion of the metal oxide into an activated state by fine suspension by means of a dispersing device and / or wet milling,

(III) coagulation of the suspension into a pasty mass,

(IV) transfer of the coagulated suspension into a shaped body,

(V) drying the shaped body,

(VI) calcination of the resulting shaped body,

(VII) conversion of the molding into an active catalyst by applying one or more catalytically active compounds or one or more precursor compounds and / or one or more promoter compounds, which in a subsequent step can be converted into one or more catalytically active compounds.

The fumed metal oxide powders are replaced by a

Flame hydrolysis or flame oxidation from a metal oxide precursor in a blast gas flame. This initially produces approximately spherical primary particles which sinter together during the reaction to form aggregates. The aggregates can then agglomerate to form agglomerates. In contrast to the agglomerates, which are usually relatively easy to separate into the aggregates by the introduction of energy, the aggregates are, if at all, further decomposed only by intensive input of energy.

Silica (Si _x O y), alumina (Al _x O y), titanium oxide (Ti _x O y), zirconium oxide (Zr _x O y), cerium oxide (Ce _x O y) or mixtures of these metal oxides can be used as pyrogenic metal oxides. Preferably, silica is used, more preferably silica (SiO ₂ ) (WACKER ^HDK® T40).

To prepare the suspension, pyrogenically prepared metal oxide powder or mixtures of different metal oxide powders are introduced slowly into a solvent, preferably water, by means of stirring energy. To avoid premature gelation, this is preferably done within 5 to 90 minutes.

In order to activate the metal oxides used, these are converted into a high-energy state by grinding or with the aid of a dispersing device. This is preferably carried out in the presence of a solvent, preferably water, that dissipates the heat generated during processing. Organic solvents may also be used, but these involve the risk of carbon contamination of the later catalyst support. Particular preference is given to using water in a highly pure form (Fe <2 ppb), as can be obtained, for example, by processes known from the literature or commercially available is available. Preferably, specially purified water is used which has a resistance of> 18 Megaθhm * cm.

For the preparation of the activated, finely divided suspension, it has proven to be advantageous if the components are ground in an attrition mill, for example an annular gap mill. In the annular gap mill, a centrically mounted grinding cone rotates in a bell-shaped hollow cone. The material to be milled enters the bottom of the mill, is crushed in the annular gap between the grinding cone and the inner wall of the housing and occurs in the upper part of the mill, which is also called bell mill out. The suspension obtained can be collected in a container and recirculated back to the mill inlet. As an alternative to annular gap mills, it is also possible to use all other types of mill known to the person skilled in the art for wet grinding, for example a stationary or horizontal agitator ball mill. The solvent is preferably kept at room temperature in all sections during a circulation. In addition, an internal cooling circuit in the mill can be provided for eliminating possibly occurring temperature gradients.

The activation of the suspension can alternatively also be carried out with the aid of various dispersing apparatus, for example by means of a dissolver or planetary dissolver. In this case, the metal oxide powder is dispersed in water with the aid of a dissolver disk and redispersed at a peripheral speed of at least 8 m / s, preferably at least 12 m / s, for at least 25 min. To adjust the particle, aggregate and agglomerate size, the suspension is finely dispersed by means of a dissolver, ultrasonic disperser, planetary dissolver, high-energy mill or high-purity ball mill for at least 25 minutes. As an alternative to pre-suspending the metal oxide in the liquid and then activating the suspension in two separate steps, the addition of the solid (metal oxide and / or mixture of various metal oxides) to the solvent may also be effected during the activation step. Regardless of whether the solids input takes place beforehand or during the activation step, it is preferable to continue treatment for a period of 0.5 to 4 hours after solids have been added.

For the production of the activated metal oxide suspension by milling, grinding tools, for example, beads made of steel, glass, alumina, zirconium oxide, zirconium silicate, silicon carbide, silicon nitride or other materials known to those skilled in the art can be used. Preference is given to materials of zirconium silicate, zirconium oxide, silicon nitride, particularly preferably of silicon nitride. The Mahlperlendurchmesser be usually 0.8 to 2.0 millimeters.

In the preparation of the suspension as homogeneous a suspension should be generated. A homogeneous suspension according to the invention is present when the suspension is as agglomerate-free as possible. Agglomerates cause inhomogeneities in the later ceramic structure of the respective application, e.g. as a catalyst support. In order to ensure freedom from agglomeration, the suspensions can also be freed by sieving residual agglomerates at the end of the dispersion.

A low viscosity (e.g., <2 Pa s) and yield point is important for optimal homogenization of the suspension. These can be achieved by pH change. In the case of fumed silica this can be done by adding an acid.

The pH is maintained within a range of 2.0 to 4.0, preferably 2.5 to 3.5, both during the pre-suspension and during the activation step. This can be done by optional Addition of an acid or a base happen. As acid or base, it is possible to use all mineral or non-mineral acids or bases known to the person skilled in the art, which later leave no or only negligible impurities in the molding. As the acid is preferred

Hydrochloric acid or nitric acid is used and as the base ammonia, preferably an aqueous ammonia solution.

The solids content within the metal oxide suspension is preferably 5 and 40% by weight, preferably between 10 and 30% by weight and particularly preferably between 15 and 25% by weight. This is independent of whether the metal oxide suspension was prepared in two separate steps or the metal oxide powder was added only during the activation step.

In the coagulation step, the suspension with the activated metal oxide is converted from its homogeneous, stable, low-viscosity state by a pH change or by further addition of one or more metal oxides in a state in which the suspension coagulates and solidifies to a pasty mass , In the coagulated state one can speak of a viscoelastic solid, i. the memory module G 'is many times higher than the loss modulus G' '. The metal oxide added for the coagulation may also differ from the metal oxide added in the presuspension and / or the activation step.

If the coagulation is carried out to a pasty mass by stirring further, powdered metal oxide or mixtures of different metal oxides in the suspension, this can optionally also by additional addition of a base, for example, aqueous ammonia solution happen to facilitate the gelling process.

Until completion of the addition of further powdered metal oxide, by an optional addition of an acid, for example hydrochloric acid, the pH may be in a range of 2 to be held until 4. After the addition of the additional amount of solid has been completed, optionally by adding dropwise a base, for example, an aqueous ammonia solution, while stirring, the pH may be adjusted to within the range of 4 to 10, more preferably 5 to 8. By changing the pH and / or the addition of one or more metal oxides in this case changes the rheology. From a liquid suspension, a gel-forming substance is formed. The ratio of the amount of additionally added powdered metal oxide to the metal oxide present in the suspension is usually 1: 1 to 1 part of powdered metal oxide to 2 parts of metal oxide in suspension. During stirring, care must be taken to distribute the metal oxide as uniformly as possible in the initially introduced activated metal oxide suspension and to avoid inhomogeneities in the pasty mass. The mixing of the metal oxide powder into the suspension using high shear forces should be avoided, otherwise the plasticity of the mass suitable for the subsequent shaping step will be lost again and the mass will become too liquid. Prolonged waiting times (several hours to days) for a suspension that is too liquid can again achieve the suitable plastic properties required for the subsequent shaping step.

Alternatively, the coagulation step can also be generated only by a change in the pH. In this embodiment of the invention, no further metal oxide is added. The coagulation of the suspension occurs only by pH change by means of an acid or base. In the case of silica, the pH adjustment is preferably done by the aid of bases such as NaOH, KOH, NH ₃ or their aqueous solutions. These are slowly, preferably drop-shaped, added to the activated suspension to a final value in a range from 4 to 10, particularly preferably 5 to 8. NH _{3 is} particularly preferably used here. The suspension can be expanded by adding NH ₃ from its homogeneous, stable, low-viscosity region into one region be transferred, in which the suspension coagulates and solidifies.

Surprisingly, it was found that the suspension was preferably suitable for shaping especially after little addition of NH 3. A typical ratio of pyrogenic silica, which itself has a pH of 3.9 to 4.5, to 1% of NH ₃ solution is 45 to 1. Stable shaped bodies can arise when the suspension is at a pH of 5 , 6 to 6.9, preferably from 6.0 to 6.4. The pH of the resulting suspension is therefore just below the neutral pH of 7.0. After adjusting to the above pH, the suspension absorbs within a few minutes and forms a moldable mass with viscoelastic behavior.

Viscoelastic behavior means that in a rheological deformation experiment in oscillation, the storage modulus G 'is greater than the loss modulus G' '. The moduli G 'and G "can be determined according to the equation τ = γ (t) * (G' sin ωt + G" cosωt), where τ is the voltage response of the sample to the time change of the deformation γ (t) at a Maximum amplitude γo and the angular velocity ω is, ie γ (t) = γo * sinωt. The determination of the amounts of G 'and G' 'takes place in

Plateau area of the storage module G '. The storage modulus G 'in the context of the invention should be at least 10000 Pa, preferably at least 50,000 Pa, and the quotient G "/ G' should be less than 1, preferably less than 0.55 and most preferably less than 0.25. The respective module was using

Plate-plate geometry measured at a shear gap of 1.5 mm, or in another embodiment, 2 mm at a temperature of 23 ° C. The inventive use of the composition according to the invention is characterized by particular long-term stability of the viscoelastic behavior. This means that the storage module G 'after a storage period of 1 week at room temperature in a closed container has fallen to a maximum of 70% of the initial value, preferably a maximum of 90% of the initial value, the module using plate-plate geometry with a shear gap of 1.5 mm or, in another embodiment, 2.0 mm at a temperature of 23 ° C.

If the mixing of the masses is insufficient, inhomogeneities within the molding compound can undesirably influence the subsequent shaping step. This results in moldings with lower mechanical stability or masses that are absolutely unsuitable for shaping. The solids content of metal oxide in the molding composition is, for example, in the case of pyrogenic SiO 2 ~ based carrier materials 10 to 40 wt .-%.

If tableting is carried out later as shaping, it is expedient to choose a significantly higher solids content. If the metal oxide particles precipitated by the fumed metal oxide particles are mixed in, the solids content in the dispersion of 40% by weight can be increased up to 60% by weight, as in the precipitated silica, for example.

The shaping of the mass can be done for example by extrusion, tableting or pressing. Preferably, the shaped catalyst body is produced by extrusion. All devices known to those skilled in the art, such as extruders, screw extruders, tableting machines, extruders, ram extruders, are conceivable here. Preferably, a ram extruder is used, in the use of which no further or only slight shearing forces act on the shaping compound, which could lead to liquefaction of the mass or phase separation of the molding compound. The geometry of the shaped catalyst body results from the respectively selected shaping tool. Manufactures include geometries such as rings, pellets, cylinders, carriage wheels, balls, etc. The length of rings and pellets is defined using a cutter immediately after molding. The molding is dried by means of methods known to the person skilled in the art (drying oven, IR heating, microwave). The drying is carried out at temperatures between 25 ° C and 200 ⁰ C, preferably between 30 ⁰ C and 100 ⁰ C, more preferably between 40 ° C and 80 ° C. The drying time depends on the quantitative ratio of metal oxide to water, but is between 0.5 and 50 hours, preferably between 2 and 30 hours. The drying of the shaped catalyst body is very critical, since too fast drying (for example, too high temperatures or low humidity), the moisture still contained can not escape quickly enough from the material on the pores and thus the body can get cracks.

After drying the shaped catalyst bodies, they are subjected to calcination. Suitable calcining methods are all customary processes known to the person skilled in the art. Preference is given to calcining in an oven under an air atmosphere, wherein the oxygen content can be varied. The air can be mixed with another gas. For this purpose, various shielding gases come into question. Suitable protective gases are all protective gases known to those skilled in the art, particularly preferably nitrogen, argon or helium. The air can also be completely replaced by the inert gas. The calcination is carried out at temperatures between 500 ⁰ C and 1250 ° C, preferably between 700 ° C and HOO ⁰ C and more preferably between 850 ⁰ C and 1000 ⁰ C. The sintering time is between 0.5 and 20 hours, a typical sintering period is between 2 and 10 hours. The calcination can under

Normal pressure or under vacuum. By the process according to the invention can already be the same Strengths at lower calcination temperatures than usual in the art.

The calcining step reduces the surface area of the catalyst support, which is an important size for the catalytic process. However, since the support materials according to the invention, because of their excellent homogeneity, exhibit sufficient stability even without calcination or after calcination at low temperatures, they have, in addition to the higher purity, significantly higher levels

Carrier surfaces and pore volumes over the prior art.

The catalysts obtained from the process according to the invention are further distinguished by the fact that the

Shaped bodies without the usual addition of excipients / additives, such as extrusion aids, pore formers or sols are produced. By dispensing with auxiliaries, the high chemical purity of (for example pyrogenic) metal oxides can be maintained. The carrier form of the materials is not critical to the process of the invention. Whether the active components are added to the pasty mass before the shaping step and thus already present more or less finely dispersed on the carrier material after the shaping step or only after the final

Completion of the catalyst support in a subsequent process step, for. B. by impregnation, are applied, is also not critical to the invention.

Due to the high purity of the starting powder and the high-purity production process, a targeted doping of the high-purity metal oxide with another high-purity metal oxide is possible. An example is the preparation of acidic catalyst supports by doping pyrogenic SiO ₂ with pyrogenic Al ₂ O 3. By means of this doping, Lewis acid centers are created in the SiO 2. In this sense, high-purity mixed oxides can be produced from the high-purity oxides SiO 2, Al 2 O 3, ZrO 2 and TiO 2. The high purity of the undoped shaped bodies produced also permits doping with other inorganic dopants. One condition is that the sum of impurities, ie all elements except the metal oxides M _x O _y or mixtures of different metal oxides, for example when using silicon dioxide Si and O, is always less than 400 ppm, preferably less than 100 ppm, particularly preferably less than 20 ppm , The process according to the invention makes it possible to produce moldings with a total of impurities (all metals and also phosphorus and sulfur and carbon) of less than 10 ppm and ideally even less than 1 ppm. As dopants inorganic metal salts can be selected. These may be, for example, halides, oxides, nitrates, nitrites, silicates, carbonates, borates, aluminates, molybdates, tungstates, vanadates, niobates, tantalates, titanates or zirconates. In principle any cationic species is suitable as counterion to this anionic component. It is preferably a cation from the group of

Alkali or alkaline earth ions. Most preferably, an alkali cation is used.

The inventive use of finely divided oxides gives shaped catalyst bodies with very high surface areas. The achieved BET surface areas are between 30 m ² / g and 500 m ² / g, preferably between 150 m ² / g and 450 m ² / g and more preferably between 250 m ² / g and 400 m ² / g. The finely divided oxides furthermore bring about the production of a shaped body with a high pore volume which is between 0.5 ml / g and 1.3 ml / g, preferably between 0.7 ml / g and 1.25 ml / g and particularly preferably between 0, 9 ml / g and 1.2 ml / g.

By means of sintering, fine-pore shaped bodies can be formed from the finely divided metal oxides. The proportion of pores with a diameter between 10 nm and 20 nm is typically more than 60%, preferably more than 70% and most preferably more than 80%. The conversion of the shaped body into an active catalyst takes place by applying one or more catalytically active compounds or one or more precursor compounds and / or one or more promoter compounds, which can be converted into one or more catalytically active compounds in a subsequent step. In this case, all processes known to those skilled in the art which lead to catalysts for the gas phase oxidation of olefins can be used. By using the high-purity and high-surface carrier bodies according to the invention, thus far unachieved high surface areas and the finest possible distribution of the noble metal centers with associated higher catalyst activity are made possible.

The addition of one or more promoter compounds can also take place after the conversion of the shaped bodies into a catalyst in a separate step.

Alternatively to the application of one or more catalytically active compounds or one or more precursor compounds together with one or more promoter compounds in one step, the application of one or more promoter compounds separately in an upstream or downstream process step for the application of one or more catalytically active compounds or one or more Precursor compounds take place.

The finished catalysts have advantages in terms of activity (space-time yield), selectivity (lower side reaction: ethene combustion to carbon dioxide and lower ethyl acetate formation rate) and / or long-term stability due to the novel super-surface support materials based thereon.

As catalytic components for coating the shaped bodies, preference is given in the process according to the invention to an or several systems from the group containing Pd / Au / alkali compounds, Pd / Cd / alkali compounds and Pd / Ba / alkali compounds for use.

One or more of the abovementioned components are applied to the carrier by impregnation, spraying, vapor deposition, immersion or precipitation of the Pd and / or Au and / or Cd and / or Ba metal compounds. Optionally, these components can also be obtained by reducing the reducible metal compounds supported on the support, and / or by washing to remove any chloride content, by impregnation with alkali metal acetate or alkali compounds which convert wholly or partly to alkali metal acetate under the reaction conditions in the production of vinyl acetate monomer. be applied in a suitable order.

As alkali compounds potassium compounds, such as potassium acetate, are preferably used. All other components and / or promoters known to those skilled in the art for increasing the catalyst activity and / or catalyst selectivity are likewise possible.

In the following, the coating step of the process according to the invention will be described in more detail with reference to the preparation of supported catalysts using the example of the system Pd / alkali / Au.

Shaped bodies, in particular in the form of hollow cylinders (ring extrudates), are impregnated with a solution containing palladium and / or gold according to one embodiment of the invention. Simultaneously with the noble metal-containing solutions or in any desired sequence successively, the support materials used can be impregnated with a basic solution which may contain one or more basic compounds. The basic compound or compounds serve to convert the palladium compound and gold compound into their hydroxides. The application of various noble metal compounds can be carried out in succession in one step or in several steps. Between these steps, an intermediate drying and / or calcination and / or one or more reduction steps can take place.

As an alternative to the addition of a base after application of the noble metal-containing solution or solutions, the addition of base may also be carried out simultaneously with the noble metal-containing solution (s).

In a further embodiment, the shaped body can first be coated with one or more basic compounds before the addition of one or more noble metal-containing solutions takes place.

Between the application of one or more basic compounds and the application of the precious metals, an intermediate drying step may be carried out.

The compounds in the basic solution can consist of alkali metal hydroxides, alkali metal bicarbonates, alkali metal carbonates, alkali metal silicates or mixtures of these substances. Preference is given to using potassium hydroxide, sodium hydroxide and / or sodium metasilicate.

For the preparation of the noble metal-containing solution can be used as palladium salts, for example palladium chloride, Natriumbeziehungsweise potassium palladium chloride, palladium acetate or palladium nitrate. Suitable gold salts are gold (III) chloride and tetrachloroauric (III) acid. Preferably, potassium palladium chloride, sodium palladium chloride and / or tetrachloroauric acid can be used.

Impregnation of the catalyst support with the basic solution affects deposition of the noble metals on the catalyst support. The basic solution may be contacted with this solution either before, simultaneously with the noble metal solution, or after application of the noble metal salt (s) become. In successive impregnation of the catalyst support with the two solutions, an intermediate drying and / or a reduction and / or a calcination can be carried out after the first impregnation step.

The shell thickness can be influenced by the amount of basic compound applied to the support material relative to the desired amount of noble metals. The higher this ratio, the smaller the thickness of the shell being formed. The quantitative ratio of basic compound to the noble metal compounds required for a desired shell thickness may depend on the nature of the support material as well as the basic compound chosen and the noble metal compounds. The required ratio is suitably by a few

Preliminary tests determined. The resulting shell thickness can be determined in a simple manner by cutting the catalyst particles.

The minimum necessary amount of the basic compound or

Compounds result from the stoichiometrically calculated amount of hydroxide ions needed to convert the palladium and gold into the hydroxides. As a guideline, the basic compound should be applied for a shell thickness of up to 1.0 mm in a 1 to 10-fold stoichiometric excess.

Catalyst supports can be coated with the noble metal salts and the basic compounds according to the process of pore volume impregnation. Will with

Intermediate drying, one selects the volumes of the two solutions so that they each 90 to 100% of the

Capacity of the catalyst carrier correspond. If the intermediate drying is dispensed with, then the sum of the individual volumes of the two impregnating solutions of the above

Conditions, wherein the individual volumes in the ratio of 1: 9 to 9: 1 may stand to each other. Preference is given to a volume ratio of 3: 7 to 7: 3, in particular 1: 1, applied. The solvent used in both cases is preferably water. However, it is also possible to use suitable organic or aqueous-organic solvents.

The reaction of the noble metal salt solution with the basic solution to form insoluble noble metal compounds can be slow and, depending on the preparation method, is generally completed after 1 to 24 hours. Thereafter, the water-insoluble noble metal compounds are treated with reducing agents. A wet reduction, for example with aqueous hydrazine hydrate or formaldehyde, or a gas phase reduction, for example with hydrogen, ethene or forming gas, can be carried out. The reduction can be carried out at normal temperature or elevated temperature and at normal pressure or elevated pressure, if appropriate also with the addition of inert gases, such as nitrogen.

Before and / or after the reduction of the noble metal compounds, the chloride which may be present on the support can be removed by a thorough washing. The washing of the catalyst is carried out with water, more preferably with a basic aqueous solution (pH> 7), very particularly preferably with a solution having a pH of 8-12. After the washing, the catalyst preferably contains less than 500 ppm Chloride, more preferably less than 200 ppm chloride.

The catalyst precursor obtained after the reduction can be dried and finally impregnated with alkali metal acetates or alkali compounds, which under the reaction conditions in the production of vinyl acetate monomer are completely or partially converted to alkali metal acetates. Preferably, it can be impregnated with potassium acetate. In this case, the pore volume impregnation may again preferably be used. This means: The required amount of potassium acetate is in one

Solvent, preferably water, whose volume is about the absorption capacity of the submitted support material for the total solvent corresponds, dissolved. This volume is approximately equal to the total pore volume of the carrier material.

The finished catalyst can then be dried to a residual moisture of less than 5%. The

Drying may be carried out in air, optionally under nitrogen, as an inert gas.

In the following, the coating step of the inventive method based on the production of

Supported catalysts for the systems Pd / alkali / Ba and Pd / alkali / Cd described in more detail.

In the preparation of Pd / Alkali / Ba and Pd / Alkali / Cd catalysts, the metal salts may be applied by known methods such as impregnation, spraying, vapor deposition, dipping or precipitation. The detailed preparation of supported catalysts of the systems Pd / alkali / Cd or Pd / alkali / Ba on suitable support materials can be found in US Pat. No. 4,093,559 (Pd / Cd) and EP 565952 (Pd / Ba without

Ultraschallverstäubung) are taken (incorporated by reference).

For the synthesis of vinyl acetate monomer, it is expedient to use the catalyst with 0.1 to 5.0% by weight of palladium and 0.2 to 3.5% by weight of gold or 0.1 to 3.5% by weight of cadmium or from 0.1 to 3.5% by weight of barium and from 0.5 to 15% by weight of potassium, based in each case on the weight of the carrier used. The loadings can vary depending on the catalyst system used (Pd / Au system, Pd / Cd system or Pd / Ba system). In the case of catalyst supports having a bulk density of, for example, 500 g / l, the concentration data correspond to volume-related concentrations of 0.5 to 25 g / l palladium and 1.0 to 17.5 g / l gold or 0.5 to 17.5 g / l cadmium or 0.5 to 17.5 g / l barium and 2.5 to 75 g / l potassium.

The catalyst loadings are in detail: The palladium content of the Pd / alkali / Au catalysts is 0.2 to 3.5 wt .-%, preferably 0.3 to 3.0 wt .-%.

The gold content of the Pd / alkali / Au catalysts is 0.2 to 3.5 wt .-%, preferably 0.3 to 3.0 wt .-%. The potassium content of the Pd / alkali / Au catalysts is 0.5 to 15 wt .-%, preferably 1.0 to 12 wt .-%. The palladium content of the Pd / alkali / Cd or Pd / alkali / Ba catalysts is 0.1 to 5.0 wt .-%, preferably 0.2 to 4.5 wt .-%. The cadmium content of the Pd / alkali / Cd catalysts is 0.1 to 3.5 wt .-%, preferably 0.2 to 3.0 wt .-%. The barium content of the Pd / alkali / Ba catalysts is 0.1 to 3.5 wt .-%, preferably 0.2 to 3.0 wt .-%. The Ba content is preferably in the same range as the Cd content in Cd systems.

The potassium content of the Pd / alkali / Cd or Pd / alkali / Ba catalysts is 0.3 to 10 wt .-%, preferably 0.5 to 9 wt .-%.

To prepare the impregnation solutions, the appropriate amounts of the palladium and gold compounds in a volume of water, which corresponds to about 10 to 100% of the water absorption capacity of the submitted support material, can be solved. Likewise, it can be done in the preparation of the basic solution.

The moldings of the invention show, respectively, low pressure losses, low bulk densities, large outer surfaces per unit volume of a reaction vessel, good mass and heat transport and in particular compared to known hollow cylinders and other carrier forms, such as honeycomb carrier materials, a significantly increased fracture and Abrasion resistance.

Through the use of highly superficial carrier materials, the catalytically active noble metal centers can be used in the catalysts according to the invention with the same amount of noble metal be removed from each other (higher long-term stability for the same activity) or at higher distances higher noble metal loadings can be achieved (higher activity with the same long-term stability achievable). However, since too high a concentration of catalytically active metals (Pd / Au or Pd / Cd or Pd / Ba) leads to catalysts which reach high temperature maxima with correspondingly high formation of undesired by-products, the

Catalyst composition adapted to the carrier material and be balanced with the reactor geometry (heat dissipation).

The supported catalysts according to the invention can be used for the preparation of unsaturated esters of olefins, organic acids and oxygen in the gas phase. In particular, the supported catalysts of the invention can be used for the production of vinyl acetate monomer. For this purpose, ethene, acetic acid and molecular oxygen or air in the gas phase, optionally with the addition of inert gases, at temperatures of 100 and 250 ⁰ C and at normal or elevated pressure, for example 1 to 25 bar, reacted in the presence of the supported catalyst according to the invention , Typically, space velocities with respect to the gas phase of 1000 to 5000 standard liters of gas mixture per liter of catalyst and per hour are realized.

In the process for preparing vinyl acetate monomer, the catalyst is first slowly loaded with the reactants. During this start-up phase, the activity of the catalyst increases and usually reaches its final level only after days or weeks. The invention

Supported catalysts achieve a significantly improved product yield due to increased activity and / or improved selectivity.

The catalysts according to the invention can also be used for

Acetoxylation of olefins, such as propene, are used. The performance of the supported catalysts based on hollow cylinders (ring extrudates) according to the invention is explained in the following examples. In particular, ring extrudates based on pyrogenically prepared silicon dioxides are discussed here.

The stated bulk densities are determined by filling a tube with an inside diameter of 33 millimeters.

Activity and selectivity of the catalysts from the following Examples and Comparative Examples are measured over a period of up to 200 hours. The catalysts are tested in an oil tempered flow reactor (reactor length 1200 mm, inner diameter 19 mm) at an absolute pressure of 9.5 bar and a space velocity (GHSV) of 3500 Nm / (m * h) with the following gas composition: 60 vol. % Ethene, 19.5% by volume of carbon dioxide, 13% by volume of acetic acid and 7.5% by volume of oxygen. The catalysts are investigated in the temperature range from 130 to 180 ^° C., measured in the catalyst bed. The reaction products are analyzed at the outlet of the reactor by means of online gas chromatography. As a measure of catalyst activity, the space-time yield of the catalyst is determined in grams of vinyl acetate monomer per hour and liter of catalyst (g (VAM) / l _cat * h). Carbon dioxide, which is formed in particular by the combustion of ethene, is also determined and used to assess the catalyst selectivity.

In addition to the determination of the reaction products in the gas phase, the liquid reaction products are collected in a container maintained at 15 ° C and the condensate obtained is analyzed by gas chromatography to determine the liquid by-products (e.g., ethyl acetate). The formation rates of the liquid by-products are always given based on vinyl acetate monomer, e.g. Ethyl acetate formation rate in mg (ethyl acetate) / g (VAM).

The BET surface area is determined in accordance with DIN 66131 with nitrogen. The pore distribution is determined by means of mercury porosimetry. The pore volume is determined according to DIN 66134 (Langmuir, p / p _o = 0.9995). The strength is with the help of Zwick Z 010

Material testing machine with force transducer nominal force 1 kN, type II determined.

Examples:

Example 1: (Carrier Production by Milling and Additional Metal Oxide)

10 kilograms of fumed silica (WACKER HDK ^® T40) are stirred into 40 kilograms of deionized water, recirculated and stored for a period of 2 hours

Agitator ball mill with grinding beads of silicon nitride (diameter of the grinding beads 2.0 mm, degree of filling 70 vol .-%) milled. The angular velocity during the grinding step is 11 meters per second. After completion of the grinding process, 5 kilograms of powdered fumed silica (WACKER HDK ^®

T40) is stirred into the dispersion until a pasty, gel-like mass is formed. This mass is extruded in a ram extruder by a suitable tool to the desired shapes and optionally cut to the desired length of the molding. The resulting molded articles - in this case rings 5.5 mm long, 5.5 mm outside diameter and 2.5 mm bore - are dried for 24 hours at a temperature of 85 ° C and a humidity of 75 % and then calcined at 900 ⁰ C for a period of 8 hours. The invention

Ring carrier bodies have a surface area (BET surface area) of 290 m ² / g and a pore volume of 1.2 ml / g. The mechanical strength of the rings in the transverse direction is 10 N. The bulk density is 320 grams per liter.

Example 2: (carrier preparation by grinding and pH adjustment) 4 kilograms of fumed silica (WACKER HDK ^® T40) are stirred into 35 kilograms of deionized water. By adding hydrochloric acid, a pH of 2.8 is set and kept constant. With constant stirring, an additional 4.5 kilograms of pyrogenic silica (WACKER ^HDK® T40) are stirred in. After complete addition of the metal oxide powder is homogenized for a further 10 minutes before the suspension for a period of 45 minutes in a stirred ball mill with grinding beads of silicon nitride (diameter of the grinding beads 2.0 mm, degree of filling 70 vol .-%) under pH consistency at a pH of 2.8 by adding additional hydrochloric acid is ground. The angular velocity during the grinding step is 11 meters per second. After completion of the grinding, an aqueous ammonia solution is added to the suspension, with constant stirring, until a pH of 6.2 is obtained and at this point gelling of the mass takes place. The mass obtained is extruded in a ram extruder by a suitable tool to the desired shapes and optionally cut to the desired length of the molding. The resulting moldings - in this case rings with a

5.5 mm long, 5.5 mm outside diameter and 2.5 mm bore hole - dried for 24 hours at a temperature of 85 ° C and a humidity of 70% and then for a period of 2 hours Calcined 900 ⁰ C. The ring carrier bodies according to the invention have a surface area (BET surface area) of 260 m ² / g and a pore volume of 1.1 ml / g. The mechanical strength of the rings in the transverse direction is 10 N. The bulk density is 280 grams per liter.

Example 3: (carrier preparation without grinding and pH

Attitude)

In a 4 liter plastic cup 1155 g bidistilled. H ₂ O submitted. 345 g of fumed silica (WACKER HDK ^® T40) are stirred in at 1000 rpm using a plastic-coated dissolver disc. Subsequently, at 8000 rpm. Stirred for 30 minutes. The slip is placed in a planetary mixer with 2 plastic-coated beam stirrers transferred. At 100 rpm, 7.5 g of 1% (wt.%) Aqueous ammonia solution is added dropwise. After the addition is stirred for 10 min. Then the mixture is introduced into a ram extruder. In parallel, rheology and pH are measured from one sample: G '= 200000, G "= 25000, pH = 6.1.

The mass is extruded in a ram extruder by a suitable tool to the desired shapes and cut to the desired length of the molding. The resulting molded articles - in this case rings with a length of 6 mm, an outer diameter of 6 mm and a bore of 3 mm - are dried for 24 hours at a temperature of 85 ° C and a relative humidity of 70%. The ring carrier bodies according to the invention have a surface area (BET surface area) of 350 m ² / g and a pore volume of 1.1 ml / g. The mechanical strength of the rings is 17 N. The bulk density is 340 grams per liter. The moldings produced in this way have the following impurities (all data in ppm): Cu (0.03), Fe (2), Ti (0.05), Al (0.3), Ca (0.4), Mg ( 0.3), Na (0.3), K (0.2), Ni (0.5), Cr (0.03), P (0.06), C undetectable and S undetectable.

Example 4:

500 grams of a SiO 2 support material from Example 1 are impregnated with 600 milliliters of an aqueous solution containing 27.60

Grams of a 41.8% (wt%) solution of tetrachloroauric acid and 42.20 grams of a 20.8% (wt%) solution of tetrachloropalladic acid. After a period of 2 hours, the catalyst is dried in a next step in a vacuum at a temperature of 80 ⁰ C for a period of 5 hours. Subsequently, 236 milliliters of a 1 molar sodium carbonate solution are applied together with 364 milliliters of distilled water. After a period of 2 hours, the catalyst is dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. Subsequently, the catalyst is washed with an aqueous ammonia solution with a proportion of 0.25 wt .-% ammonia for a period of 45 hours. The catalyst is at a temperature reduced by 200 ° C for a period of 5 hours with forming gas (95% N2 / 5% H ₂ ). Subsequently, the catalyst with an acetic acid-containing potassium acetate solution is impregnated (71.65 grams of potassium acetate in 600 milliliters of acetic acid) and finally dried at a temperature of 8O ⁰ C for a period of 5 hours in vacuo. The finished catalyst has a concentration of 1.6% by weight of palladium (5.1 g / l), 2.1% by weight of gold (6.7 g / l) and 5.2% by weight of potassium ( 16.6 g / l). With this catalyst according to the invention can be in the test in the reactor under conditions described above, activities of 800 g (VAM) / l _Kat * h (156 g (VAM) / g _Pd * h) reach at ethene selectivities of 90.5%. The ethyl acetate formation rate is 0.35 grams of ethyl acetate per kilogram of vinyl acetate formed.

Example 5:

500 g of a SiO 2 support material from Example 1 are prepared analogously to Example 4, but the concentrations of the impregnating solutions are chosen so that the finished catalyst has a concentration of 2.0% by weight of palladium (6.4 g / l), 2, 0 wt .-% gold (6.4 g / l) and 6.5 wt .-% potassium (20.8 g / l).

With this catalyst according to the invention can be in the test in the reactor under the conditions described above, activities of 930 g (VAM) / l _Kat * h (145 g (VAM) / g _Pd * h) achieve ethene selectivities of 92.5%. The ethyl acetate formation rate is 0.35 grams of ethyl acetate per kilogram of vinyl acetate formed.

Example 6:

80 grams of a SiO 2 support material from Example 2 are impregnated with 88 milliliters of an aqueous solution containing 4.43

Grams of a 41.6% (wt%) solution of tetrachloroauric acid and 7.03 grams of a 20.0% (wt%) solution of tetrachloropalladic acid. After a period of 2 hours in a next step, the catalyst at a temperature of 8O ⁰ C for a period of 5 hours in

Vacuum dried. Subsequently, 37.8 milliliters of a 1 molar sodium carbonate solution are applied together with 50 milliliters of distilled water. After a duration of 2 Hours the catalyst is dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. Subsequently, the catalyst is washed with an aqueous ammonia solution in a proportion of 0.25 wt .-% ammonia for a period of 30 hours. The catalyst is reduced at a temperature of 200 ^° C. for 5 hours with forming gas (95% N ₂ /5% H ₂ ). Subsequently, the catalyst is impregnated with an acetic acid-containing potassium acetate solution (11.46 grams of potassium acetate in 88 milliliters of acetic acid) and finally dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. The finished catalyst has a concentration of 1.6% by weight of palladium (4.5 g / l), 2.1% by weight of gold (5.9 g / l) and 5.2% by weight of potassium ( 14.6 g / l). With this catalyst according to the invention can be in the test in the reactor under the conditions described above, activities of 750 g (VAM) / l _Kat * h (167 g (VAM) / g _Pd * h) reach at ethene selectivities of 90.5%. The ethyl acetate formation rate is 0.55 grams of ethyl acetate per kilogram of vinyl acetate formed.

Example 7:

80 grams of a SiO ₂ support material from Example 3 are impregnated with 88 milliliters of an aqueous solution containing 5.14 grams of a 41.6 percent (wt%) solution of tetrachloroauric acid and 8.47 grams of a 20.0 percent (Wt.%) Solution of tetrachloropalladic acid. After a period of 2 hours, the catalyst is dried in a next step in a vacuum at a temperature of 80 ⁰ C for a period of 5 hours. Subsequently, 44.5 milliliters of a 1 molar sodium carbonate solution are applied together with 43.5 milliliters of distilled water. After a duration of 2

Hours the catalyst is dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. Subsequently, the catalyst is washed with an aqueous ammonia solution in a proportion of 0.25 wt .-% ammonia for a period of 30 hours. The catalyst is reduced at a temperature of 200 ^° C. for 5 hours with forming gas (95% N ₂ /5% H ₂ ). Subsequently, the catalyst is impregnated with an acetic acid-containing potassium acetate solution (13.43 grams of potassium acetate in 88 milliliters of acetic acid) and finally dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. The finished catalyst has a concentration of 1.9% by weight of palladium (6.5 g / l), 2.4% by weight of gold (8.2 g / l) and 6.0% by weight of potassium ( 20.4 g / l).

With this catalyst according to the invention can be in the test in the reactor under the conditions described above, activities of 800 g (VAM) l _Kat * h (124 g (VAM) / g _Pd * h) reach at ethene selectivities of 90.2%. The ethyl acetate formation rate is 0.45 grams of ethyl acetate per kilogram of vinyl acetate formed.

Comparative Example 1

60 grams of spherical support materials with a

Bentonite-based diameter of 6 millimeters (KA-120, from Sud Chemie, bulk density 540 grams / liter) becomes 36

Milliliters of an aqueous solution containing 0.80 grams of gold chloride and 2.0 grams of palladium acetate. After a period of 2 hours, the catalyst is dried in a next step in a vacuum at a temperature of 80 ⁰ C for a period of 4 hours. Subsequently, 28.2

Milliliter of a 1 molar potassium carbonate solution was applied together with 8 milliliters of distilled water. After a period of 2 hours, the catalyst is dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. Subsequently, the catalyst with an aqueous

Washed ammonia solution with a proportion of 0.25 wt .-% ammonia for a period of 60 hours. The catalyst is reduced at a temperature of 200 ⁰ C for a period of 5 hours with forming gas (95% N2 / 5% H2). Subsequently, the catalyst is impregnated with an acetic acid-containing potassium acetate solution (3.30 grams of potassium acetate in 36 milliliters of acetic acid) and finally dried at a temperature of 8O ⁰ C for a period of 4 hours in vacuo. The finished catalyst has a concentration of 1.5% by weight of palladium (8.1 g / l), 0.7% by weight of gold (3.8 g / l) and 2.1% by weight of potassium ( 11.3 g / l).

With this catalyst, which is not according to the invention, it is possible to carry out the test in the reactor under the conditions described above Activities of 680 g (VAM) l _cat * h (84 g (VAM) / g _Pd * h) at ethene selectivities of 89.0%. The ethyl acetate formation rate is 1.90 grams of ethyl acetate per kilogram of vinyl acetate formed.

Example 8: (Pd / Cd system)

100 grams of a SiO 2 support material from Example 1 are impregnated with 120 milliliters of an acetic acid-containing solution containing 5.17 grams of cadmium acetate, 6.02 grams of potassium acetate, 8.74 grams of palladium acetate, and 1.33 grams of manganese acetate. After a period of 2 hours, the catalyst is dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. The finished catalyst has a concentration of 3.8% by weight of palladium (12.2 g / l), 2.0% by weight of cadmium (6.4 g / l), 2.2% by weight of potassium ( 7.0 g / l) and 0.25 wt% manganese (0.8 g / l).

With this catalyst according to the invention can be in the test in the reactor under the conditions described above activities of 900 g (VAM) l _Kat * h (74 g (VAM) / g _Pd * h) reach at ethene selectivities of 92.8%. The ethyl acetate formation rate is 0.70 grams of ethyl acetate per kilogram of vinyl acetate formed.

Comparative Example 2: (Pd / Cd system)

100 grams of spherical support materials with a diameter of 6 millimeters bentonite (KA-120, the company Süd Chemie, bulk density 540 grams / liter) are impregnated with 60 milliliters of an acetic acid-containing solution containing 4.55 grams of cadmium acetate, 5, Contains 34 grams of potassium acetate, 5.17 grams of palladium acetate and 0.36 grams of manganese acetate. After a period of 2 hours, the catalyst is dried at a temperature of 80 ° C for a period of 5 hours in vacuo. The finished catalyst has a concentration of 2.3 wt .-% palladium (12.4 g / l), 1.8 wt .-% cadmium (9.7 g / l), 2.0 wt .-% potassium ( 10.8 g / l) and 0.07 wt% manganese (0.4 g / l). With this catalyst, which is not according to the invention, in the test in the reactor under the conditions described above, activities of 560 g (VAM) 1 _cat * h (45 g (VAM) / g _Pd * h) can be achieved with ethene selectivities of 92.8%. The ethyl acetate Formation rate is 1.30 grams of ethyl acetate per kilogram of vinyl acetate formed.

Example 9: (carrier preparation without grinding and pH

Adjustment with the addition of a dopant)

In a 4 liter plastic cup 1155 g of bidistilled H ₂ O are submitted. A plastic-coated dissolver disk is used to stir 345 g of fumed silica (WACKER ^HDK® T40) at 1000 rpm. The mixture is then stirred at a peripheral speed of 14 m / s for 40 min. The slurry is transferred to a planetary mixer with 2 plastic-coated beam stirrers. At 100 rpm, 8.5 g of 1% NH ₃ solution is added dropwise. The pH of the resulting mass is pH = 6.4. Thereafter, 45 mg of Na ₂ SiO _{3 are} added. After the addition is stirred for a further 5 min. Then the mixture becomes one

Piston extruder introduced. In parallel, the rheology is measured from a sample: G '= 320000, G''= 35000. The mass is extruded in a ram extruder by a suitable tool to the desired shapes and cut to the desired length of the molding. The resulting molded articles - in this case rings with a length of 6 mm, a diameter of 6 mm - are dried for 24 hours at a temperature of 85 ⁰ C. Afterwards the

Shaped body still sintered at 850 ⁰ C. The moldings according to the invention have a surface area (BET surface area) of 205 m ² / g and a pore volume of 0.75 ml / g. The mechanical strength of the rings is 45 N. The bulk density is 370 grams per liter. The shaped bodies produced in this way have the following impurities (all data in ppm): Cu (0.03), Fe (4), Ti (0.05), Al (1.1), Ca (1.2), Mg ( 0.3), Na (49), K (4), Ni (0.5), Cr (0.3), P (0.06), C undetectable and S undetectable. Example 10:

500 grams of a SiO 2 support material from Example 9 are impregnated with 375 milliliters of an aqueous solution containing 27.60 grams of a 41.8% (wt%) solution of tetrachloroauric acid and 42.20 grams of a 20.8% ( % By weight) solution of

Contains tetrachloropalladic acid. After a period of 2 hours, the catalyst is dried in a next step in a vacuum at a temperature of 80 ⁰ C for a period of 5 hours. Subsequently, 236 milliliters of a 1 molar sodium carbonate solution are applied together with 139 milliliters of distilled water. After a period of 2 hours, the catalyst is dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. Subsequently, the catalyst is washed with an aqueous ammonia solution with a proportion of 0.25 wt .-% ammonia for a period of 45 hours. The catalyst is reduced at a temperature of 200 ° C for 5 hours with forming gas (95% N2 / 5% H ₂ ). Subsequently, the catalyst is impregnated with an acetic acid-containing potassium acetate solution (71.65 grams of potassium acetate in 375 milliliters of acetic acid) and finally dried at a temperature of 80 ⁰ C for a period of 5 hours in vacuo. The finished catalyst has a concentration of 2.0% by weight of palladium (7.4 g / l), 2.0% by weight of gold (7.4 g / l) and 6.5% by weight of potassium ( 24.1 g / l). With this catalyst according to the invention, in the test in the reactor under the conditions described above, activities of 870 g (VAM) / l _cat * h (118 g (VAM) / g _Pd * h) can be achieved at ethene selectivities of 92.4%. The ethyl acetate formation rate is 0.35 grams of ethyl acetate per kilogram of vinyl acetate formed. Table 1:

Claims

Claims:

1. A process for the preparation of catalysts for the gas phase oxidation of olefins, comprising the steps:

(I) suspending at least one pyrogenically prepared metal oxide in a solvent,

(II) conversion of the metal oxide into an activated

Condition by fine suspension by means of a dispersing device and / or wet grinding,

(III) coagulation of the suspension into a pasty mass,

(IV) transfer of the coagulated suspension into a shaped body,

(V) drying the shaped body,

(VI) calcination of the resulting shaped body,

(VII) conversion of the molding into an active catalyst by applying one or more catalytically active compounds or one or more precursor compounds and / or one or more promoter compounds, which can be converted in a subsequent step in one or more catalytically active compounds.

2. The method according to claim 1, characterized in that as pyrogenic metal oxide one or more compounds from the group containing S i _x O _y , Al _x O _y , Ti _x O _y , Zr _x O _y , Ce _x O _y are used.

3. The method according to claim 2, characterized in that SiO 2 is used as the fumed metal oxide.

4. The method according to claim 1 to 3, characterized in that water is used as the solvent.

5. The method according to claim 1 to 4, characterized in that the activation is carried out in an attrition mill, an annular gap mill or a stirred ball mill.

6. The method according to claim 1 to 5, characterized in that the activation takes place by means of one or more dispersing devices from the group comprising dissolver, ultrasonic disperser and planetary dissolver.

7. The method according to claim 1 to 6, characterized in that the Vorsuspendierung of the metal oxide is omitted in the solvent and the addition of the metal oxide to the solvent during the activation step takes place.

8. The method according to claim 1 to 7, characterized in that the suspension is activated for a time of 0.5 to 4 hours.

9. The method according to claim 1 to 8, characterized in that as grinding tools one or more auxiliaries from the group containing beads of steel, glass, alumina, zirconia, zirconium silicate,

Silicon carbide and silicon nitride can be used.

10. The method according to claim 1 to 9, characterized in that the pH during the Vorsuspendierung as well as during the activation step in a range of 2.0 to 4, 0.

11. The method according to claim 10, characterized in that the pH is regulated by means of hydrochloric acid, nitric acid, ammonia or their aqueous solutions.

12. The method according to claim 1 to 11, characterized in that the solids content in the activated metal oxide suspension is between 5 and 40 wt.%.

13. The method according to claim 1 to 12, characterized in that the coagulation of the suspension by one or more of the measures comprising changing the pH or further addition of one or more metal oxides, is performed.

14. The method according to claim 1 to 13, characterized in that the coagulation of the suspension containing the activated metal oxide, by adjusting the pH to a value in the range of 4 to 10 is performed.

15. The method according to claim 1 to 14, characterized in that the coagulation of the suspension containing the activated metal oxide is carried out by means of further addition of one or more metal oxides.

16. The method according to claim 13 to 15, characterized in that the adjustment of the pH and / or the addition of further metal oxide causes a change in the rheology of the activated suspension.

17. The method of claim 1 to 16, characterized in that the shaping step by one or more measures from the group consisting of extrusion, tableting and pressing takes place.

18. The method according to claim 1 to 17, characterized in that the shaped bodies have the form of rings, pellets, cylinders, carriage wheels or balls.

19. The method according to claim 1 to 18, characterized in that the resulting moldings are dried at temperatures between 25 ° C and 200 ⁰ C.

20. The method according to claim 1 to 19, characterized in that the calcination is carried out under air atmosphere, wherein the oxygen content can be optionally varied and the air is optionally mixed with another gas.

21. The method according to claim 1 to 20, characterized in that the calcination takes place at temperatures between 500 ⁰ C and 1250 ° C.

22. The method according to claim 1 to 21, characterized in that the resulting shaped catalyst bodies have a BET surface area between 30 m ² / g and 500 m ² / g.

23. The method according to claim 1 to 22, characterized in that the addition of one or more promoter compounds takes place after the conversion of the shaped body into a catalyst in a separate step.

24. The method according to claim 1 to 23, characterized in that alternatively to the application of one or more catalytically active compounds or one or more precursor compounds together with one or more promoter compounds in one step, the application of one or more promoter compounds separately in an upstream or downstream Process step for applying one or more catalytically active compounds or one or more precursor compounds takes place.

25. The method according to claim 1 to 24, characterized in that the shaped body with one or more of the systems from the group containing Pd / Au / alkali compounds, Pd / Cd / alkali compounds and Pd / Ba / alkali compounds are coated.

26. The method according to claim 25, characterized in that the above-mentioned components by one or more of the measures from the group containing watering, spraying, vapor deposition, dipping, precipitating the Pd and / or Au and / or Cd and / or Ba metal compounds are applied to the support, reducing the metal reducible compounds applied to the support, washing to remove any chloride levels present, impregnation with alkali metal acetate or alkali compounds, in appropriate order.

27. The method according to claim 26, characterized in that potassium compounds are used as alkali compounds.

28. The method according to claim 1 to 27, characterized in that the application of various noble metal compounds in one step or in several steps takes place successively and optionally between these steps one or more steps comprising from the group intermediate drying, calicination or reduction takes place.

29. The method according to claim 1 to 28, characterized in that before and / or after the reduction of

Precious metal compounds which may be removed on the support optionally present chloride by a thorough washing.

30. The method according to claim 29, characterized in that the washing of the catalyst is carried out by means of water or a basic aqueous solution having a pH> 7.

31. The method according to claim 1 to 28, characterized in that the catalyst obtained one or more Quantitative constituents based on the weight of the carrier used, from the group comprising 0.1 to 5.0% by weight of palladium, 0.2 to 3.5% by weight of gold, 0.1 to 3.5% by weight Cadmium, 0.1 to 3.5% by weight of barium, and 0.5 to 15% by weight of potassium.

32. The method according to claim 1 to 31, characterized in that the noble metal concentration is constant within the carrier body.

33. The method according to claim 1 to 32, characterized in that the noble metal concentration decreases from the accessible outer surface forth in the direction of the carrier interior.

34. The method of claim 1 to 33, characterized in that the sum of all impurities in the catalyst is less than 400 ppm.

35. A catalyst obtainable by the process according to one or more of claims 1 to 34.

36. A catalyst according to claim 35, characterized in that the shaped body has a sum of impurities (all other metals and carbon and phosphorus and sulfur) less than 400 ppm.

37. Use of the catalyst according to claim 35 to 36 as a catalyst in chemical reactions.

38. Use of the catalyst according to claim 35 to 36 as supported catalysts for the preparation of unsaturated esters of olefins and / or organic acids.

39. Use of the catalyst according to claim 35 to 36 as supported catalysts for the production of vinyl acetate monomer.

40. Use of the catalyst according to claim 35 to 36 for the acetoxylation of olefins.